Previous studies have revealed that, at the initial step of carcinogenesis, transformed cells are often eliminated from epithelia via cell competition with the surrounding normal cells. In this study, we performed cell competition-based high-throughput screening for chemical compounds using cultured epithelial cells and confocal microscopy. PLX4720 was identified as a hit compound that promoted apical extrusion of RasV12-transformed cells surrounded by normal epithelial cells. Knockdown/knockout of ZAK, a target of PLX4720, substantially enhanced the apical elimination of RasV12 cells in vitro and in vivo. ZAK negatively modulated the accumulation or activation of multiple cell competition regulators. Moreover, PLX4720 treatment promoted apical elimination of RasV12-transformed cells in vivo and suppressed the formation of potentially precancerous tumors. This is the first report demonstrating that a cell competition-promoting chemical drug facilitates apical elimination of transformed cells in vivo, providing a new dimension in cancer preventive medicine.

Plasma aldosterone concentration increases in proportion to the severity of heart failure, even during treatment with renin-angiotensin system inhibitors. This study investigated alternative regulatory mechanisms of aldosterone production that are significant in heart failure. Dahl salt-sensitive rats on a high-salt diet, a rat model of heart failure with cardio-renal syndrome, had high plasma aldosterone levels and elevated β3-adrenergic receptor expression in hypoxic zona glomerulosa cells. In H295R cells (a human adrenocortical cell line), hypoxia-induced β3-adrenergic receptor expression. Hypoxia-mediated β3-adrenergic receptor expression augmented aldosterone production by facilitating hydrolysis of lipid droplets though ERK-mediated phosphorylation of hormone-sensitive lipase, also known as cholesteryl ester hydrolase. Hypoxia also accelerated the synthesis of cholesterol esters by acyl-CoA:cholesterol acyltransferase, thereby increasing the cholesterol ester content in lipid droplets. Thus, hypoxia enhanced aldosterone production by zona glomerulosa cells via promotion of the accumulation and hydrolysis of cholesterol ester in lipid droplets. In conclusion, hypoxic zona glomerulosa cells with heart failure show enhanced aldosterone production via increased catecholamine responsiveness and activation of cholesterol trafficking, irrespective of the renin-angiotensin system.

Stromal cell-derived factor-2 (SDF-2) is reportedly involved in multiple endoplasmic reticulum (ER) functions, including the misfolded protein catabolic process, protein glycosylation, and ER protein quality control. However, the precise molecular and cellular functions of SDF-2 remain unknown. Previously, we discovered that SDF-2 mediates acquired resistance to oxaliplatin in human gastric cancer cells. In this study, we have generated SDF-2-specific monoclonal antibodies (mAbs), using the rat medial iliac lymph node method, as a tool to explore novel mechanisms of oxaliplatin resistance. The antibodies detected endogenous human SDF-2 in immunoblotting analyses. In addition, immunoprecipitation analyses revealed the availability of these antibodies for human SDF-2. Thus, these mAbs will be available to elucidate molecular and cellular functions of SDF-2 in cancer cells.

Macrophages are major components of tuberculosis (TB) granulomas and are responsible for host defenses against the intracellular pathogen, Mycobacterium tuberculosis. We herein showed the strong expression of hypoxia-inducible factor-1α (HIF-1α) in TB granulomas and more rapid death of HIF-1α-conditional knockout mice than wild-type (WT) mice after M. tuberculosis infection. Although interferon-γ (IFN-γ) is a critical host-protective cytokine against intracellular pathogens, HIF-1-deficient macrophages permitted M. tuberculosis growth even after activation with IFN-γ. These results prompted us to investigate the role of HIF-1α in host defenses against infection. We found that the expression of lactate dehydrogenase-A (LDH-A) was controlled by HIF-1α in M. tuberculosis-infected macrophages IFN-γ independently. LDH-A is an enzyme that converts pyruvate to lactate and we found that the intracellular level of pyruvate in HIF-1α-deficient bone marrow-derived macrophages (BMDMs) was significantly higher than in WT BMDMs. Intracellular bacillus replication was enhanced by an increase in intracellular pyruvate concentrations, which were decreased by LDH-A. Mycobacteria in phagosomes took up exogenous pyruvate more efficiently than glucose, and used it as the feasible carbon source for intracellular growth. These results demonstrate that HIF-1α prevents the hijacking of pyruvate in macrophages, making it a fundamental host-protective mechanism against M. tuberculosis.

Fatty acid (FA) oxidation is impaired and glycolysis is promoted in the damaged heart. However, the factor(s) in the early stages of myocardial metabolic impairment remain(s) unclear. C57B6 mice were subcutaneously administered monocrotaline (MCT) in doses of 0.3 mg/g body weight twice a week for 3 or 6 weeks. Right and left ventricles at 3 and 6 weeks after administration were subjected to capillary electrophoresis-mass spectrometry metabolomic analysis. We also examined mRNA and protein levels of key metabolic molecules. Although no evidence of PH and right ventricular failure was found in the MCT-administered mice by echocardiographic and histological analyzes, the expression levels of stress markers such as TNFα and IL-6 were increased in right and left ventricles even at 3 weeks, suggesting that there was myocardial damage. Metabolites in the tricarboxylic acid (TCA) cycle were decreased and those in glycolysis were increased at 6 weeks. The expression levels of FA oxidation-related factors were decreased at 6 weeks. The phosphorylation level of pyruvate dehydrogenase (PDH) was significantly decreased at 3 weeks. FA oxidation and the TCA cycle were down-regulated, whereas glycolysis was partially up-regulated by MCT-induced myocardial damage. PDH activation preceded these alterations, suggesting that PDH activation is one of the earliest events to compensate for a subtle metabolic impairment from myocardial damage.

The ductus arteriosus, an essential embryonic blood vessel between the pulmonary artery and the descending aorta, constricts after birth or hatching and eventually closes to terminate embryonic circulation. Chicken embryos have two long ductus arteriosi, which anatomically differ from mammal ductus arteriosus. Each long ductus arteriosus is divided into two parts: the pulmonary artery-sided and descending aorta-sided ductus arteriosi. Although the pulmonary artery-sided and descending aorta-sided ductus arteriosi have distinct functional characteristics, such as oxygen responsiveness, the difference in their transcriptional profiles has not been investigated. We performed a DNA microarray analysis (GSE 120116 at NCBI GEO) with pooled tissues from the chicken pulmonary artery-sided ductus arteriosus, descending aorta-sided ductus arteriosus, and aorta at the internal pipping stage. Although several known ductus arteriosus-dominant genes such as tfap2b were highly expressed in the pulmonary artery-sided ductus arteriosus, we newly found genes that were dominantly expressed in the chicken pulmonary artery-sided ductus arteriosus. Interestingly, cluster analysis showed that the expression pattern of the pulmonary artery-sided ductus arteriosus was closer to that of the descending aorta-sided ductus arteriosus than that of the aorta, whereas the morphology of the descending aorta-sided ductus arteriosus was closer to that of the aorta than that of the pulmonary artery-sided ductus arteriosus. Subsequent pathway analysis with DAVID bioinformatics resources revealed that the pulmonary artery-sided ductus arteriosus showed enhanced expression of the genes involved in melanogenesis and tyrosine metabolism compared with the descending aorta-sided ductus arteriosus, suggesting that tyrosinase and the related genes play an important role in the proper differentiation of neural crest-derived cells during vascular remodeling in the ductus arteriosus. In conclusion, the transcription profiles of the chicken ductus arteriosus provide new insights for investigating the mechanism of ductus arteriosus closure.

Adaptive responses to hypoxia regulate hepatic lipid metabolism, but their consequences in nonalcoholic fatty liver disease (NAFLD) are largely unknown. Here, we show that hypoxia inducible factor-1 (HIF-1), a key determinant of hypoxic adaptations, prevents excessive hepatic lipid accumulation in the progression of NAFLD. When exposed to a choline-deficient diet (CDD) for 4 weeks, the loss of hepatic Hif-1α gene accelerated liver steatosis with enhanced triglyceride accumulation in the liver compared to wild-type (WT) livers. Expression of genes involved in peroxisomal fatty acid oxidation was suppressed significantly in CDD-treated WT livers, whereas this reduction was further enhanced in Hif-1α-deficient livers. A lack of induction and nuclear accumulation of lipin1, a key regulator of the PPARα/PGC-1α pathway, could be attributed to impaired peroxisomal β-oxidation in Hif-1α-deficient livers. The lipin1-mediated binding of PPARα to the acyl CoA oxidase promoter was markedly reduced in Hif-1α-deficient mice exposed to a CDD. Moreover, forced Lipin1 expression restored the aberrant lipid accumulation caused by Hif-1α deletion in cells incubated in a choline-deficient medium. These results strongly suggest that HIF-1 plays a crucial role in the regulation of peroxisomal lipid metabolism by activating the expression and nuclear accumulation of lipin1 in NAFLD.

Under chronic or severe liver injury, liver progenitor cells (LPCs) of biliary origin are known to expand and contribute to the regeneration of hepatocytes and cholangiocytes. This regeneration process is called ductular reaction (DR), which is accompanied by dynamic remodeling of biliary tissue. Although the DR shows apparently distinct mode of biliary extension depending on the type of liver injury, the key regulatory mechanism remains poorly understood. Here, we show that Lutheran (Lu)/Basal cell adhesion molecule (BCAM) regulates the morphogenesis of DR depending on liver disease models. Lu+ and Lu- biliary cells isolated from injured liver exhibit opposite phenotypes in cell motility and duct formation capacities in vitro. By overexpression of Lu, Lu- biliary cells acquire the phenotype of Lu+ biliary cells. Lu-deficient mice showed severe defects in DR. Our findings reveal a critical role of Lu in the control of phenotypic heterogeneity of DR in distinct liver disease models.

BACKGROUND: Aging is known to be associated with increased risk of lipid disorders related to the development of type 2 diabetes. Recent evidence revealed that change of lipid molecule species in blood is associated with the risk of type 2 diabetes. However, changes in lipid molecular species induced by aging are still unknown. We assessed the effects of age on the serum levels of lipid molecular species as determined by lipidomics analysis. METHODS: Serum samples were collected from ten elderly men (71.7 ± 0.5 years old) and women (70.2 ± 1.0 years old), ten young men (23.9 ± 0.4 years old), and women (23.9 ± 0.7 years old). Serum levels of lipid molecular species were determined by liquid chromatography mass spectrometry-based lipidomics analysis. RESULTS: Our mass spectrometry analysis revealed increases in the levels of multiple triacylglycerol molecular species in the serum of elderly men and women. Moreover, serum levels of total ester-linked phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were increased by aging. In contrast, serum levels of specific ether-linked PC and PE molecular species were lower in elderly individuals than in young individuals. CONCLUSIONS: Our finding indicates that specific lipid molecular species, such as ether- and ester- linked phospholipids, may be selectively altered by aging.

The mitochondria-associated ER membrane (MAM) is a specialized subdomain of ER that physically connects with mitochondria. Although disruption of inter-organellar crosstalk via the MAM impairs cellular homeostasis, its pathological significance in insulin resistance in type 2 diabetes mellitus remains unclear. Here, we reveal the importance of reduced MAM formation in the induction of fatty acid-evoked insulin resistance in hepatocytes. Palmitic acid (PA) repressed insulin-stimulated Akt phosphorylation in HepG2 cells within 12h. Treatment with an inhibitor of the ER stress response failed to restore PA-mediated suppression of Akt activation. Mitochondrial reactive oxygen species (ROS) production did not increase in PA-treated cells. Even short-term exposure (3h) to PA reduced the calcium flux from ER to mitochondria, followed by a significant decrease in MAM contact area, suggesting that PA suppressed the functional interaction between ER and mitochondria. Forced expression of mitofusin-2, a critical component of the MAM, partially restored MAM contact area and ameliorated the PA-elicited suppression of insulin sensitivity with Ser473 phosphorylation of Akt selectively improved. These results suggest that loss of proximity between ER and mitochondria, but not perturbation of homeostasis in the two organelles individually, plays crucial roles in PA-evoked Akt inactivation in hepatic insulin resistance.

Chronic fatigue syndrome (CFS) is a persistent and unexplained pathological state characterized by exertional and severely debilitating fatigue, with/without infectious or neuropsychiatric symptoms, lasting at least 6 consecutive months. Its pathogenesis remains incompletely understood. Here, we performed comprehensive metabolomic analyses of 133 plasma samples obtained from CFS patients and healthy controls to establish an objective diagnosis of CFS. CFS patients exhibited significant differences in intermediate metabolite concentrations in the tricarboxylic acid (TCA) and urea cycles. The combination of ornithine/citrulline and pyruvate/isocitrate ratios discriminated CFS patients from healthy controls, yielding area under the receiver operating characteristic curve values of 0.801 (95% confidential interval [CI]: 0.711-0.890, P < 0.0001) and 0.750 (95% CI: 0.584-0.916, P = 0.0069) for training (n = 93) and validation (n = 40) datasets, respectively. These findings provide compelling evidence that a clinical diagnostic tool could be developed for CFS based on the ratios of metabolites in plasma.

Proinflammatory cytokine production in macrophages involves multiple regulatory mechanisms, which are affected by environmental and intrinsic stress. In particular, accumulating evidence has suggested epigenetic control of macrophage differentiation and function mainly in vitro. SET domain, bifurcated 1 (Setdb1, also known as Eset) is a histone 3 lysine 9 (H3K9)-specific methyltransferase and is essential for early development of embryos. Here we demonstrate that Setdb1 in macrophages potently suppresses Toll-like receptor 4 (TLR4)-mediated expression of proinflammatory cytokines including interleukin-6 through its methyltransferase activity. As a molecular mechanism, Setdb1-deficiency decreases the basal H3K9 methylation levels and augments TLR4-mediated NF-κB recruitment on the proximal promoter region of interleukin-6, thereby accelerating interleukin-6 promoter activity. Moreover, macrophage-specific Setdb1-knockout mice exhibit higher serum interleukin-6 concentrations in response to lipopolysaccharide challenge and are more susceptible to endotoxin shock than wildtype mice. This study provides evidence that the H3K9 methyltransferase Setdb1 is a novel epigenetic regulator of proinflammatory cytokine expression in macrophages in vitro and in vivo. Our data will shed insight into the better understanding of how the immune system reacts to a variety of conditions.

Sarcolipin (SLN) is a small proteolipid and a regulator of sarco(endo)plasmic reticulum Ca(2+)-ATPase. In heart tissue, SLN is exclusively expressed in the atrium. Previously, we inserted Cre recombinase into the endogenous SLN locus by homologous recombination and succeeded in generating SLN-Cre knockin (Sln(Cre/+)) mice. This Sln(Cre/+) mouse can be used to generate an atrium-specific gene-targeting mutant, and it is based on the Cre-loxP system. In the present study, we used adult Sln(Cre/+) mice atria and analyzed the effects of heterozygous SLN deletion by Cre knockin before use as the gene targeting mouse. Both SLN mRNA and protein levels were decreased in Sln(Cre/+) mouse atria, but there were no morphological, physiological, or molecular biological abnormalities. The properties of contractility and Ca(2+) handling were similar to wild-type (WT) mice, and expression levels of several stress markers and sarcoplasmic reticulum-related protein levels were not different between Sln(Cre/+) and WT mice. Moreover, there was no significant difference in sarco(endo)plasmic reticulum Ca(2+)-ATPase activity between the two groups. We showed that Sln(Cre/+) mice were not significantly different from WT mice in all aspects that were examined. The present study provides basic characteristics of Sln(Cre/+) mice and possibly information on the usefulness of Sln(Cre/+) mice as an atrium-specific gene-targeting model.

BACKGROUND: Hepatic fibrosis progresses with right heart failure, and becomes cardiac cirrhosis in a severe case. Although its causal factor still remains unclear. Here we evaluated the progression of hepatic fibrosis using a pulmonary artery banding (PAB)-induced right heart failure model and investigated whether cardiac output (CO) is responsible for the progression of hepatic fibrosis. METHODS AND RESULTS: Five-week-old Sprague-Dawley rats divided into the PAB and sham-operated control groups. After 4 weeks from operation, we measured CO by echocardiography, and hepatic fibrosis ratio by pathological examination using a color analyzer. In the PAB group, CO was significantly lower by 48% than that in the control group (78.2±27.6 and 150.1±31.2 ml/min, P<0.01). Hepatic fibrosis ratio and serum hyaluronic acid, an index of hepatic fibrosis, were significantly increased in the PAB group than those in the control group (7.8±1.7 and 1.0±0.2%, P<0.01, 76.2±27.5 and 32.7±7.5 ng/ml, P<0.01). Notably, the degree of hepatic fibrosis significantly correlated a decrease in CO. Immunohistological analysis revealed that hepatic stellate cells were markedly activated in hypoxic areas, and HIF-1α positive hepatic cells were increased in the PAB group. Furthermore, by real-time PCR analyses, transcripts of profibrotic and fibrotic factors (TGF-β1, CTGF, procollargen I, procollargen III, MMP 2, MMP 9, TIMP 1, TIMP 2) were significantly increased in the PAB group. In addition, western blot analyses revealed that the protein level of HIF-1α was significantly increased in the PAB group than that in the control group (2.31±0.84 and 1.0±0.18 arbitrary units, P<0.05). CONCLUSIONS: Our study demonstrated that low CO and tissue hypoxia were responsible for hepatic fibrosis in right failure heart model rats.

In the present study, prior to the establishment of a method for the clinical diagnosis of chronic fatigue in humans, we validated the utility of plasma metabolomic analysis in a rat model of fatigue using capillary electrophoresis-mass spectrometry (CE-MS). In order to obtain a fatigued animal group, rats were placed in a cage filled with water to a height of 2.2 cm for 5 days. A food-restricted group, in which rats were limited to 10 g/d of food (around 50% of the control group), was also assessed. The food-restricted group exhibited weight reduction similar to that of the fatigued group. CE-MS measurements were performed to evaluate the profile of food intake-dependent metabolic changes, as well as the profile in fatigue loading, resulting in the identification of 48 metabolites in plasma. Multivariate analyses using hierarchical clustering and principal component analysis revealed that the plasma metabolome in the fatigued group showed clear differences from those in the control and food-restricted groups. In the fatigued group, we found distinctive changes in metabolites related to branched-chain amino acid metabolism, urea cycle, and proline metabolism. Specifically, the fatigued group exhibited significant increases in valine, leucine, isoleucine, and 2-oxoisopentanoate, and significant decreases in citrulline and hydroxyproline compared with the control and food-restricted groups. Plasma levels of total nitric oxide were increased in the fatigued group, indicating systemic oxidative stress. Further, plasma metabolites involved in the citrate cycle, such as cis-aconitate and isocitrate, were reduced in the fatigued group. The levels of ATP were significantly decreased in the liver and skeletal muscle, indicative of a deterioration in energy metabolism in these organs. Thus, this comprehensive metabolic analysis furthered our understanding of the pathophysiology of fatigue, and identified potential diagnostic biomarkers based on fatigue pathophysiology.

The liver is a central organ that metabolizes excessive nutrients for storage in the form of glycogen and lipids and supplies energy-producing substrates to the peripheral tissues to maintain their function, even under starved conditions. These processes require a considerable amount of oxygen, which causes a steep oxygen gradient throughout the hepatic lobules. Alcohol consumption and/or excessive food intake can alter the hepatic metabolic balance drastically, which can precipitate fatty liver disease, a major cause of chronic liver diseases worldwide, ranging from simple steatosis, through steatohepatitis and hepatic fibrosis, to liver cirrhosis. Altered hepatic metabolism and tissue remodeling in fatty liver disease further disrupt hepatic oxygen homeostasis, resulting in severe liver hypoxia. As master regulators of adaptive responses to hypoxic stress, hypoxia-inducible factors (HIFs) modulate various cellular and organ functions, including erythropoiesis, angiogenesis, metabolic demand, and cell survival, by activating their target genes during fetal development and also in many disease conditions such as cancer, heart failure, and diabetes. In the past decade, it has become clear that HIFs serve as key factors in the regulation of lipid metabolism and fatty liver formation. This review discusses the molecular mechanisms by which hypoxia and HIFs regulate lipid metabolism in the development and progression of fatty liver disease. (C) 2014 Baishideng Publishing Group Inc. All rights reserved.

Background: Patent ductus arteriosus (PDA) is one of the most common congenital cardiovascular defects in children. The Brown-Norway (BN) inbred rat presents a higher frequency of PDA. A previous study reported that 2 different quantitative trait loci on chromosomes 8 and 9 were significantly linked to PDA in this strain. Nevertheless, the genetic or molecular mechanisms underlying PDA phenotypes in BN rats have not been fully investigated yet.
Methods and Results: It was found that the elastic fibers were abundant in the subendothelial area but scarce in the media even in the closed ductus arteriosus (DA) of full-term BN neonates. DNA microarray analysis identified 52 upregulated genes (fold difference &gt;2.5) and 23 downregulated genes (fold difference &lt;0.4) when compared with those of F344 control neonates. Among these genes, 8 (Tbx20, Scn3b, Stac, Sphkap, Trpm8, Rup2, Slc37a2, and RGD1561216) are located in chromosomes 8 and 9. Interestingly, it was also suggested that the significant decrease in the expression levels of the PGE(2)-specfic receptor, EP4, plays a critical role in elastogenesis in the DA.
Conclusions: BN rats exhibited dysregulation of elastogenesis in the DA. DNA microarray analysis identified the candidate genes including EP4 involved in the DNA phenotype. Further investigation of these newly identified genes will hopefully clarify the molecular mechanisms underlying the irregular formation of elastic fibers in PDA.

Postoperative adhesion often causes serious adverse effects such as bowl obstruction, chronic abdominal pain, pelvic pain, and infertility. We previously reported that a poly-L-lactic acid (PLLA) nanosheet can efficiently seal a surgical incision without scarring. In this report, we examined whether the PLLA nanosheet can form an effective anti-adhesion barrier in partial hepatectomy accompanied by severe hemorrhaging in rats. To evaluate the anti-adhesive property of the nanosheet, the liver wound surface was covered with TachoComb((R)), a well-known hemostat material used in clinical procedures, and then with the PLLA nanosheet. Dressing the wound surface with TachoComb((R)) alone caused severe adhesion with omentum and/or residual parts of the liver. By contrast, combinational usage of TachoComb((R)) and the PLLA nanosheet significantly reduced such adhesion, presumably by inhibiting the permeation of oozing blood cells and the infiltration of fibroblastic cells. Moreover, the nanosheet displayed low permeability against serum proteins as well as cells in vitro, supporting the notion that the PLLA nanosheet has anti-adhesive properties in vivo. These results strongly suggested that the PLLA nanosheet is a promising material for reducing unwanted postoperative adhesion. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 101B: 1251-1258, 2013.

Energy of the cardiac muscle largely depends on fatty acid oxidation. It is known that the atrium and ventricle have chamber-specific functions, structures, gene expressions, and pathologies. The left ventricle works as a high-pressure chamber to pump blood toward the body, and its muscle wall is thicker than those of the other chambers, suggesting that energy utilization in each of the chambers should be different. However, a chamber-specific pattern of metabolism remains incompletely understood. Recently, innovative techniques have enabled the comprehensive analysis of metabolites. Therefore, we aimed to clarify differences in metabolic patterns among the chambers. Male C57BL6 mice at 6 wk old were subject to a comprehensive measurement of metabolites in the atria and ventricles by capillary electrophoresis and mass spectrometry. We found that overall metabolic profiles, including nucleotides and amino acids, were similar between the right and left ventricles. On the other hand, the atria exhibited a distinct metabolic pattern from those of the ventricles. Importantly, the high-energy phosphate pool (the total concentration of ATP, ADP, and AMP) was higher in both ventricles. In addition, the levels of lactate, acetyl CoA, and tricarboxylic acid cycle contents were higher in the ventricles. Accordingly, the activities and/or expression levels of key enzymes were higher in the ventricles to produce more energy. The present study provides a basis for understanding the chamber-specific metabolism underlining pathophysiology in the heart.

Objective Hypoxia-inducible factor is a hypoxia-responsive transcriptional factor that controls the expression of proteins contributing to homeostatic responses to hypoxia. Spatial heterogeneity of tissue oxygenation has been postulated as a determinant of structure and function of hepatic lobules, although its molecular mechanisms remain unknown. This study aimed to examine the role of HIF-1 expressed in hepatocytes in regulation of hepatic microcirculation.
Methods We have generated mice harboring a floxed HIF-1 alpha allele, and employed the albumin-Cre transgenic line to inactivate the gene site-specifically in hepatocytes.
Results Intravital observation of the hepatic microcirculation revealed extension of hepatic lobules in HIF-1 alpha-deficient mice. Measurement of microvascular diameter, velocity, and local oxygen tension by laser-assisted phosphorimetry showed that the oxygen consumption in the lobules of HIF-1 alpha-deficient mice was greater than that in those of control mice. Isolated hepatocytes from HIF-1 alpha-deficient mice also stimulated oxygen consumptions with increased contents of mtDNA. Overexpression of HIF-1 alpha decreased the expression of PGC-1 alpha mRNA, whereas the knockdown of the HIF-1 alpha gene increased it, suggesting that HIF-1 regulates cellular respiration through mitochondrial biogenesis.
Conclusions Our results suggest that constitutive expression of HIF-1 alpha in hepatocytes acts as a determinant of hepatic lobular structure and oxygen consumption by changing mitochondrial contents.

Defining the metabolic programs that underlie stem cell maintenance will be essential for developing strategies to manipulate stem cell capacity. Mammalian hematopoietic stem cells (HSCs) maintain cell cycle quiescence in a hypoxic microenvironrnent. It has been proposed that HSCs exhibit a distinct metabolic phenotype under these conditions. Here we directly investigated this idea using metabolomic analysis and found that HSCs generate adenosine-5'-triphosphate by anaerobic glycolysis through a pyruvate dehydrogenase kinase (Pdk)-dependent mechanism. Elevated Pdk expression leads to active suppression of the influx of glycolytic metabolites into mitochondria. Pdk overexpression in glycolysis-defective HSCs restored glycolysis, cell cycle quiescence, and stem cell capacity, while loss of both Pdk2 and Pdk4 attenuated HSC quiescence, glycolysis, and transplantation capacity. Moreover, treatment of HSCs with a Pdk mimetic promoted their survival and transplantation capacity. Thus, glycolytic metabolic status governed by Pdk acts as a cell cycle checkpoint that modulates HSC quiescence and function.

Recently, biomaterials have been widely used in a variety of medical applications. We previously reported that a poly-l-lactic acid (PLLA) nanosheet shows anti-adhesive properties and constitutes a useful biomaterial for preventing unwanted wound adhesion in surgical operations. In this article, we examine whether the PLLA nanosheet can be specifically modified with biomacromolecules on one surface only. Such an approach would endow each side of the nanosheet with discrete functions, that is anti-adhesive and pro-healing properties. We fabricated two distinct PLLA nanosheets: (i) collagen cast on the surface of a PLLA nanosheet (Col-Cast-PLLA) and (ii) collagen spin-coated on the nanosheet (Col-Spin-PLLA). In the Col-Spin-PLLA nanosheet, the collagen layer had a thickness of 5-10 nm on the PLLA surface and displayed increased hydrophilicity compared to both PLLA and Col-Cast-PLLA nanosheets. In addition, atomic force microscopy showed disorganized collagen fibril formation on the PLLA layer when covered using the spin-coating method, while apparent bundle formations of collagen were formed in the Col-Cast-PLLA nanosheet. The Col-Spin-PLLA nanosheet provided a microenvironment for cells to adhere and spread. By contrast, the Col-Cast-PLLA nanosheet displayed reduced cell adhesion compared to the Col-Spin-PLLA nanosheet. Consistent with these findings, immunocytochemical analysis clearly showed fine networks of actin filaments in cells cultured on the Col-Spin-PLLA, but not the Col-Cast-PLLA nanosheet. Therefore, the Col-Spin-PLLA nanosheet was shown to be more suitable for acting as a scaffold. In conclusion, we have succeeded in developing a heterofunctional nanosheet comprising a collagen modified side, which has the ability to rapidly adhere cells, and an unmodified side, which acts as an adhesion barrier, by using a spin-coating technique.

HIF-1 is active in hypoxia, such as inflamed mucosa, and HIF-1 in epithelium has been reported to control inflamed mucosa in IBD models. Although T cells play an important role for pathogenesis of IBD, the function of HIF-1 in T cells remains to be elucidated. We aimed to clarify the function of HIF-1 in T cells in IBD with focus on the balance between Treg and Teff. Double immunohistochemistry of colonic mucosa in IBD patients showed that HIF-1 was expressed in T cells infiltrating the inflamed mucosa, suggesting that HIF-1 in T cells is involved in the pathogenesis. DSS administration to T cell-specific HIF-1 alpha KO mice showed more severe colonic inflammation than control mice with the up-regulation of Th1 and Th17. Hypoxic stimulation in vitro increased Treg activation in WT T cells but not in HIF-1-deleted T cells. In contrast, hypoxic stimulation increased Th17 activation, and the degree was higher in HIF-1-deleted cells than in control cells. These results show that hypoxia controls intestinal inflammation by regulating cytokine balance in a HIF-1-dependent manner, suggesting that strengthening HIF-1 induction in T cells at the sites of inflammation might be a therapeutic strategy for IBD regulation. J. Leukoc. Biol. 91: 901-909; 2012.

Over the course of evolution, aerobic organisms have developed sophisticated systems for responding to alterations in oxygen concentration, as oxygen acts as a final electron acceptor in oxidative phosphorylation for energy production. Hypoxia-inducible factor (HIF) plays a central role in the adaptive regulation of energy metabolism, by triggering a switch from mitochondrial oxidative phosphorylation to anaerobic glycolysis in hypoxic conditions. HIF also reduces oxygen consumption in mitochondria by inhibiting conversion of pyruvate to acetyl CoA, suppressing mitochondrial biogenesis and activating autophagy of mitochondria concomitantly with reduction in reactive oxygen species production. In addition, metabolic reprogramming in response to hypoxia through HIF activation is not limited to the regulation of carbohydrate metabolism; it occurs in lipid metabolism as well. Recent studies using in vivo gene-targeting technique have revealed unexpected, but novel functions of HIF in energy metabolism in a context- and cell type-specific manner, and shed light on the possibility of pharmaceutical targeting HIF as a new therapy against many diseases, including cancer, diabetes, and fatty liver.

Interactions between astrocytes and endothelial cells (ECs) are crucial for retinal vascular formation. Astrocytes induce migration and proliferation of ECs via their production of vascular endothelial growth factor (VEGF) and, conversely, ECs induce maturation of astrocytes possibly by the secretion of leukemia inhibitory factor (LIF). Together with the maturation of astrocytes, this finalizes angiogenesis. Thus far, the mechanisms triggering LIF production in ECs are unclear. Here we show that apelin, a ligand for the endothelial receptor APJ, induces maturation of astrocytes mediated by the production of LIF from ECs. APJ (Aplnr)-and Apln-deficient mice show delayed angiogenesis; however, aberrant overgrowth of endothelial networks with immature astrocyte overgrowth was induced. When ECs were stimulated with apelin, LIF expression was upregulated and intraocular injection of LIF into APJ-deficient mice suppressed EC and astrocyte overgrowth. These data suggest an involvement of apelin/APJ in the maturation process of retinal angiogenesis.

Naive CD4(+) T cells are activated by antigen-presenting cells (APCs) and differentiate into distinct types of helper T (T-h) cells in the lymph node or spleen. Oxygen (O-2) tension is generally low in these secondary lymphoid tissues compared with the bloodstream or atmosphere. However, the effect of changes in O-2 concentration on the differentiation of T-h cells remains unclear. Here, we established a novel model of T-h-cell differentiation, which mimics physiological O-2 conditions. We primed naive CD4(+) T cells under 5% O-2, which has been observed in the lymph node or spleen and reoxygenated under normoxia that mimicked the O-2 concentration in blood. In this model, the differentiation of T(h)17 cells, but not T(h)1 or iTreg cells, was enhanced. Under the condition of 5% O-2, mammalian target of rapamycin complex 1 (mTORC1) was activated and led to the stabilization of hypoxia-inducible factor 1 alpha (HIF-1 alpha) in T(h)17 cells. The activation of mTORC1 and the acceleration of T(h)17-cell differentiation, which occurred when cells were primed under 5% O-2, were not observed in the absence of HIF-1 alpha but were accelerated in the absence of von Hippel-Lindau tumor suppressor protein (vHL), a factor critical for HIF-1 alpha degradation. Thus, a positive feedback loop between HIF-1 alpha and mTORC1 induced by hypoxia followed by reoxygenation accelerates T(h)17-cell differentiation.

The vascular and nervous systems display a high degree of cross-talk and depend on each other functionally. In the vascularization of the central nervous system, astrocytes have been thought to sense tissue oxygen levels in hypoxia-inducible factors (HIFs)-dependent manner and control the vascular growth into the hypoxic area by secreting VEGF. However, recent genetic evidences demonstrate that not only astrocyte HIFs but also astrocyte VEGF expression is dispensable for developmental angiogenesis of the retina. This study demonstrates that hypoxia-inducible factor 1 alpha subunit (HIF-1 alpha), a key transcription factor involved in cellular responses to hypoxia, is most abundantly expressed in the neuroretina, especially retinal progenitor cells (RPCs). A neuroretina-specific knockout of HIF-1 alpha (alpha Cre(+)Hif1 alpha(flox/flox)) showed impaired vascular development characterized by decreased tip cell filopodia and reduced vessel branching. The astrocyte network was hypoplastic in alpha Cre(+)Hif1 alpha(flox/flox) mice. Mechanistically, platelet-derived growth factor A (PDGF-A), a mitogen for astrocytes, was downregulated in the neuroretina of alpha Cre(+)Hif1 alpha(flox/flox) mice. Supplementing PDGF-A restored reduced astrocytic and vascular density in alpha Cre(+)Hif1 alpha(flox/flox) mice. Our data demonstrates that the neuroretina but not astrocytes acts as a primary oxygen sensor which ultimately controls the retinal vascular development by regulating an angiogenic astrocyte template. (C) 2011 Elsevier Inc. All rights reserved.

Hematopoietic stem cells (HSCs) are sustained in a specific microenvironment known as the stem cell niche. Mammalian HSCs are kept quiescent in the endosteal niche, a hypoxic zone of the bone marrow (BM). In this study, we show that normal HSCs maintain intracellular hypoxia and stabilize hypoxia-inducible factor-1 alpha (HIF-1 alpha) protein. In HIF-1 alpha-deficient mice, the HSCs lost their cell cycle quiescence and HSC numbers decreased during various stress settings including bone marrow transplantation, myelosuppression, or aging, in a p16(Ink4a)/p19(Arf)-dependent manner. Overstabilization of HIF-1 alpha by biallelic loss of an E3 ubiquitin ligase for HIF-1 alpha (VHL) induced cell cycle quiescence in HSCs and their progenitors but resulted in an impairment in transplantation capacity. In contrast, monoallelic loss of VHL induced cell cycle quiescence and improved BM engraftment during bone marrow transplantation. These data indicate that HSCs maintain cell cycle quiescence through the precise regulation of HIF-1 alpha levels.

In early neonates, the fetal circulatory system undergoes dramatic transition to the adult circulatory system. Normally, embryonic connecting vessels, such as the ductus arteriosus and the foramen ovale, close and regress. In the neonatal retina, hyaloid vessels maintaining blood flow in the embryonic retina regress, and retinal vessels take over to form the adult-type circulatory system. This process is regulated by a programmed cell death switch mediated by macrophages via Wnt and angiopoietin 2 pathways. In this study, we seek other mechanisms that regulate this process, and focus on the dramatic change in oxygen environment at the point of birth. The von Hippel-Lindau tumor suppressor protein (pVHL) is a substrate recognition component of an E3-ubiquitin ligase that rapidly destabilizes hypoxia-inducible factor alpha s (HIF-alpha s) under normoxic, but not hypoxic, conditions. To examine the role of oxygen-sensing mechanisms in retinal circulatory system transition, we generated retina-specific conditional-knockout mice for VHL (Vhl(alpha-CreKO) mice). These mice exhibit arrested transition from the fetal to the adult circulatory system, persistence of hyaloid vessels and poorly formed retinal vessels. These defects are suppressed by intraocular injection of FLT1-Fc protein [a vascular endothelial growth factor (VEGF) receptor-1 (FLT1)/Fc chimeric protein that can bind VEGF and inhibit its activity], or by inactivating the HIF-1 alpha gene. Our results suggest that not only macrophages but also tissue oxygen-sensing mechanisms regulate the transition from the fetal to the adult circulatory system in the retina.

Nonalcoholic fatty liver disease (NAFLD) is a common disease of chronic liver diseases. Peroxisome proliferator-activated receptor alpha (PPAR alpha) has been implicated to play important roles in the development of the disease. Beyond its effects on lipid metabolisms, PPAR alpha activation in the vascular system has emerged as an attractive therapeutic potential for NAFLD, although its actions in the microcirculatory system are not fully understood. In this study, we investigated the effects of fenofibrate, a PPAR alpha synthetic agonist, on hepatic microcirculation in a high-fat diet (HFD)-induced fatty liver in mice. In vivo imaging analysis revealed the adverse effects of HFD on hepatic vasculature with narrowing of hepatic sinusoids and hepatic microcirculatory perfusion. Oxygen tension was significantly decreased in portal venules, while NADH autofluorescence in hepatocytes was greatly elevated. Fenofibrate treatment remarkably improved microvascular patency, tissue oxygenation and redox states in the affected liver. These results suggest beneficial roles of PPAR alpha activated by fenofibrate on the regulation of both lipid metabolisms and microvascular environments of oxygen metabolism in HFD-induced fatty liver.

Coordinated recovery of hepatic glucose metabolism is prerequisite for normal liver regeneration. To examine roles of hypoxia inducible factor-1 alpha (HIF-1 alpha) for hepatic glucose homeostasis during the reparative process, we inactivated the gene in hepatocytes in vivo. Following partial hepatectomy (PH), recovery of residual liver weight was initially retarded in the mutant mice by down-regulation of hepatocyte proliferation, but occurred comparably between the mutant and control mice at 72 h after PH. At this time point, the mutant mice showed lowered blood glucose levels with enhanced accumulation of glycogen in the liver. The mutant mice exhibited impairment of hepatic gluconeogenesis as assessed by alanine tolerance test. This appeared to result from reduced expression of PGK-1 and PEPCK since 3-PG, PEP and malate were accumulated to greater extents in the regenerated liver. In conclusion, these findings provide evidence for roles of HIF-1 alpha in the regulation of gluconeogenesis under liver regeneration. (C) 2009 Elsevier Inc. All rights reserved.

Carbon monoxide (CO) is a stress-inducible gas generated by heme oxygenase (HO) eliciting adaptive responses against toxicants; however, mechanisms for its reception remain unknown. Serendipitous observation in metabolome analysis in CO-overproducing livers suggested roles of cystathionine beta-synthase (CBS) that rate-limits transsulfuration pathway and H2S generation, for the gas-responsive receptor. Studies using recombinant CBS indicated that CO binds to the prosthetic heme, stabilizing 6-coordinated CO-Fe(II)-histidine complex to block the activity, whereas nitric oxide (NO) forms 5-coordinated structure without inhibiting it. The CO-overproducing livers down-regulated H2S to stimulate HCO3--dependent choleresis: these responses were attenuated by blocking HO or by donating H2S. Livers of heterozygous CBS knockout mice neither down-regulated H2S nor exhibited the choleresis while overproducing CO. In the mouse model of estradiol-induced cholestasis, CO overproduction by inducing HO-1 significantly improved the bile output through stimulating HCO3- excretion; such a choleretic response did not occur in the knockout mice. Conclusion: Results collected from metabolome analyses suggested that CBS serves as a CO-sensitive modulator of H2S to support biliary excretion, shedding light on a putative role of the enzyme for stress-elicited adaptive response against bile-dependent detoxification processes. (HEPATOLOGY 2009;49:141-150.)

This study aimed to examine if T-state stabilization of hemoglobin in erythrocytes could protect against postischemic organ injury. Human erythrocytes containing three different states of Hb allostery were prepared: control Hb (hRBC), CO-Hb that is stabilized under R-state with the 6-coodinated prosthetic heme (CO-hRBC), and alpha-NO-deoxyHb stabilized under T-state (alpha-NO-hRBC). To prepare alpha-NO-RBC, deoxygenated RBC was treated with FK409, a thiol-free NO donor, at its half molar concentration to that of Hb; this procedure resulted in the 5-coordinated NO binding on the alpha-subunit heme, as judged by electron spin resonance spectrometry. Rats were subject to 20 min systemic hemorrhage to maintain mean arterial pressure at 40 mm Hg, and reperfused with one of hRBCs. This protocol for ischemia, followed by 60 min reperfusion with physiological saline, caused modest metabolic acidosis and cholestasis. Administration of hRBC or CO-hRBC significantly attenuated cholestasis and improved acidosis. Rats treated with alpha-NO-hRBC exhibited greater recovery of metabolic acidosis and bile excretion than those treated with hRBC or CO-hRBC, displaying the best outcome of local oxygen utilization in hepatic lobules. Half-life time of alpha-NO-RBC administered in vivo was approximately 60 min. These results suggest that T-state Hb stabilization by NO serves as a stratagem to treat postischemic organ dysfunction.

Although the brain generates NO and carbon monoxide ( CO), it is unknown how these gases and their enzyme systems interact with each other to regulate cerebrovascular function. We examined whether CO produced by heme oxygenase (HO) modulates generation and action of constitutive NO in the rat pial microcirculation. Immunohistochemical analyses indicated that HO-2 occurred in neurons and arachnoid trabecular cells, where NO synthase 1 (NOS1) was detectable, and also in vascular endothelium-expressing NOS3, suggesting colocalization of CO- and NO-generating sites. Intravital microscopy using a closed cranial window preparation revealed that blockade of the HO activity by zinc protoporphyrin IX significantly dilates arterioles. This vasodilatation depended on local NOS activities and was abolished by CO supplementation, suggesting that the gas derived from HO-2 tonically regulates NO-mediated vasodilatory response. Bioimaging of NO by laser-confocal microfluorography of diaminofluorescein indicated detectable amounts of NO at the microvascular wall, the subdural mesothelial cells, and arachnoid trabecular cells, which express NOS in and around the pial microvasculature. On CO inhibition by the HO inhibitor, regional NO formation was augmented in these cells. Such a pattern of accelerated NO formation depended on NOS activities and was again attenuated by the local CO supplementation. Studies using cultured porcine aortic endothelial cells suggested that the inhibitory action of CO on NOS could result from the photo-reversible gas binding to the prosthetic heme. Collectively, CO derived from HO-2 appears to serve as a tonic vasoregulator antagonizing NO-mediated vasodilatation in the rat cerebral microcirculation.

Carbon monoxide (CO) generated through the reaction of heme oxygenase (HO) has attracted great interest in regulation of hepatobiliary homeostasis. The gas generated by HO-2 in the hepatic parenchyma can modestly activate soluble guanylate cyclase (sGC) expressed in hepatic stellate cells in a paracrine manner and thereby constitutively relax sinusoids. Kupffer cells express HO-1, the inducible isozyme, even under normal unstimulated conditions and constitutes approximately 30% of the total HO activity in this organ. Upon exposure to a variety of stressors such as cytokines, endotoxin, hypoxia and oxidative stress, the liver induces HO-1 and overproduces CO. The stress-inducible CO has been shown to guarantee ample blood supply during detoxification of heme and thus to play a protective role in the liver. However, molecular mechanisms by which CO serves as a protectant for hepatocytes, the cells expressing little sGC, remain to be solved. Previous observation suggested that CO modulates intracellular calcium mobilization through inhibiting cytochrome P-450 activities and thereby maintain stroke volume of bile canalicular contraction in cultured hepatocytes. CO also stimulates mrp2-dependent excretion of bilirubin-IX alpha and helps heme catabolism. Although a direct molecular target responsible for the latter event remains unknown, such properties of CO could support xenobiotic metabolism through its actions on sinusoidal hemodynamics and hepatobiliary systems.

This study aimed to examine distribution of cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), the hydrogen sulfide (H2S)-generating enzymes, and metabolomic alterations in sulfur-containing amino acids in rat testes exposed to stressors. Immunohistochemistry revealed distinct distribution of the two enzymes: CBS occurred mainly in Leydig cells and was also detectable in Sertoli cells and germ cells, whereas CSE was evident in Sertoli cells and immature germ cells involving spermatogonia. The amounts of CSE and CBS in testes did not alter in response to administration of cadmium chloride, an antispermatogenic stressor leading to apoptosis. Metabolome analyses assisted by liquid chromatography equipped with mass spectrometry revealed marked alterations in sulfur-containing amino acid metabolism: amounts of methionine and cysteine were significantly elevated concurrently with a decrease in the ratio between S-adenosylhomocysteine and S-adenosylmethionine, suggesting expansion of the remethylation cycle and acceleration of methyl donation. Despite a marked increase in cysteine, amounts of H,S were unchanged, leading to a remarkable decline of the H2S/cysteine ratio in the cadmium-treated rats. Under such circumstances, oxidized glutathione (GSSG) was significantly reduced, whereas reduced glutathione (GSH) was well maintained, and the GSH/GSSG ratio was consequently elevated. These results collectively showed that cadmium induces metabolomic remodeling of sulfur-containing amino acids even when the protein expression of CBS or CSE is not evident. Although detailed mechanisms for such a remodeling event remain unknown, our study suggests that metabolomic analyses serve as a powerful tool to pinpoint a critical enzymatic reaction that regulates metabolic systems as a whole.

Cystathionine gamma-lyase (CSE) is an enzyme catalyzing cystathionine and cysteine to yield cysteine and hydrogen sulfide (H 2 S), respectively. This study aimed to examine if H,S generated from the enzyme could serve as an endogenous regulator of hepatobiliary function. Gas chromatographic analyses indicated that, among rat organs herein examined, liver constituted one of the greatest components of H,S generation in the body, at 100 mu mol/g of tissue, comparable to that in kidney and 1.5-fold greater than that in brain, where roles of the gas in the regulation of neurotransmission were reported previously. At least half of the gas amount in the liver appeared to be derived from CSE, because blockade of the enzyme by propargylglycine suppressed it by 50%. Immunohistochemistry revealed that CSE occurs not only in hepatocytes, but also in bile duct. In livers in vivo, as well as in those perfused ex vivo, treatment with the CSE inhibitor induced choleresis by stimulating the basal excretion of bicarbonate in bile samples. Transportal supplementation of NaHS at 30 mu mol/L, but not that of N-acetylcysteine as a cysteine donor, abolished these changes elicited by the CSE inhibitor in the perfused liver. The changes elicited by the CSE blockade did not coincide with alterations in hepatic vascular resistance, showing little involvement of vasodilatory effects of the gas in these events, if any. These results first provided evidence that H,S generated through CSE modulates biliary bicarbonate excretion and is thus a determinant of bile salt-independent bile formation in the rat liver.

Cells in a low oxygen, or hypoxic, microenvironment must have the ability to sense oxygen levels in the nucleus in order to maintain oxygen homeostasis by gene regulation. Hypoxia inducible factor-1 (HIF-1) serves as a molecular bridge between the sensation and utilization of oxygen, and thus functions as a key player in oxygen homeostasis. HIF-1 is a heterodimeric transcription factor and is composed of two subunits, the oxygen-sensitive HIF-1alpha and constitutively expressed HIF-1beta. HIF-1 regulates the expression of a broad range of genes that facilitate acclimation to low oxygen conditions by changes in protein levels in circulation, metabolism, and proliferation. Appropriate temporal and spatial activation of HIF-1 is crucial not only in developmental and physiological processes, characterized by programmed cellular proliferation, but also in pathophysiological conditions such as tumorigenesis, which exhibit unregulated cellular proliferation. However, many contradictory reports as to the role of HIF-1 in the regulation of cellular proliferation have been put forward in recent years. In this review, our first aim is to summarize the current knowledge of oxygen-dependent HIF-1 activation mechanisms based on its structure. Then we will describe the proposed mechanisms through which HIF-1 regulates cellular proliferation of different cell types, including tumor cells as well as non-transformed, nonimmortalized cells under normoxic and hypoxic conditions.

A classical cellular response to hypoxia is a cessation of growth. Hypoxia-induced growth arrest differs in different cell types but is likely an essential aspect of the response to wounding and injury. An important component of the hypoxic response is the activation of the hypoxia-inducible factor I (HIF-1) transcription factor. Although this transcription factor is essential for adaptation to low oxygen levels, the mechanisms through which it influences cell cycle arrest, including the degree to which it cooperates with the tumor suppressor protein p53, remain poorly understood. To determine broadly relevant aspects of HIF-1 function in primary cell growth arrest, we examined two different primary differentiated cell types which contained a deletable allele of the oxygen-sensitive component of HIF-1, the HIF-1alpha gene product. The two cell types were murine embryonic fibroblasts and splenic B lymphocytes; to determine how the function of HIF-1alpha influenced p53, we also created double-knockout (HIF-1alpha null, p53 null) strains and cells. In both cell types, loss of HIF-1alpha abolished hypoxia-induced growth arrest and did this in a p53-independent fashion. Surprisingly, in all cases, cells lacking both p53 and HIF-1alpha genes have completely lost the ability to alter the cell cycle in response to hypoxia. In addition, we have found that the loss of HIF-1alpha causes an increased progression into S phase during hypoxia, rather than a growth arrest. We show that hypoxia causes a HIF-1alpha-dependent increase in the expression of the cyclin-dependent kinase inhibitors p21 and p27; we also find that hypophosphorylation of retinoblastoma protein in hypoxia is HIF-1alpha dependent. These data demonstrate that the transcription factor HIF-1 is a major regulator of cell cycle arrest in primary cells during hypoxia.

A classical cellular response to hypoxia is a cessation of growth. Hypoxia-induced growth arrest differs in different cell types but is likely an essential aspect of the response to wounding and injury. An important component of the hypoxic response is the activation of the hypoxia-inducible factor I (HIF-1) transcription factor. Although this transcription factor is essential for adaptation to low oxygen levels, the mechanisms through which it influences cell cycle arrest, including the degree to which it cooperates with the tumor suppressor protein p53, remain poorly understood. To determine broadly relevant aspects of HIF-1 function in primary cell growth arrest, we examined two different primary differentiated cell types which contained a deletable allele of the oxygen-sensitive component of HIF-1, the HIF-1alpha gene product. The two cell types were murine embryonic fibroblasts and splenic B lymphocytes; to determine how the function of HIF-1alpha influenced p53, we also created double-knockout (HIF-1alpha null, p53 null) strains and cells. In both cell types, loss of HIF-1alpha abolished hypoxia-induced growth arrest and did this in a p53-independent fashion. Surprisingly, in all cases, cells lacking both p53 and HIF-1alpha genes have completely lost the ability to alter the cell cycle in response to hypoxia. In addition, we have found that the loss of HIF-1alpha causes an increased progression into S phase during hypoxia, rather than a growth arrest. We show that hypoxia causes a HIF-1alpha-dependent increase in the expression of the cyclin-dependent kinase inhibitors p21 and p27; we also find that hypophosphorylation of retinoblastoma protein in hypoxia is HIF-1alpha dependent. These data demonstrate that the transcription factor HIF-1 is a major regulator of cell cycle arrest in primary cells during hypoxia.

This study examined the role of bilirubin in heme oxygenase (HO)-1-mediated amelioration of mast cell (MC)-elicited inflammatory responses. Pretreatment of rats with an intraperitoneal injection of hemin, an inducer of HO-1, evolved a marked induction of the enzyme in MCs. Intravital videomicroscopy revealed that hemin pretreatment attenuated compound 48/80-elicited degranulation of MCs and resultant leukocyte adhesion in venules. Superfusion with biliverdin or bilirubin, but not with carbon monoxide (CO), another product of the HO reaction, mimicked suppressive actions of the HO-1 induction on both the cell degranulation and leukocyte adhesion elicited by the stimulus, suggesting a requirement of the enzyme reaction to generate bilirubin in the inhibitory mechanisms. Such MC-desensitizing actions of bilirubin were observed in primary-cultured MCs and reproduced irrespective of the choice of stimuli, such as compound 48/80, calcium ionophore, and anti-IgE serum. Furthermore, MC-stabilizing effects of HO-1 were reproduced by the gene transfection of the enzyme into mastocytoma cell line RBL2H3. These results suggest that bilirubin generated through HO-1 serves as an anti-inflammatory substance that desensitizes MCs and ameliorates leukocyte recruitment.

This study examined the role of bilirubin in heme oxygenase (HO)-1-mediated amelioration of mast cell (MC)-elicited inflammatory responses. Pretreatment of rats with an intraperitoneal injection of hemin, an inducer of HO-1, evolved a marked induction of the enzyme in MCs. Intravital videomicroscopy revealed that hemin pretreatment attenuated compound 48/80-elicited degranulation of MCs and resultant leukocyte adhesion in venules. Superfusion with biliverdin or bilirubin, but not with carbon monoxide (CO), another product of the HO reaction, mimicked suppressive actions of the HO-1 induction on both the cell degranulation and leukocyte adhesion elicited by the stimulus, suggesting a requirement of the enzyme reaction to generate bilirubin in the inhibitory mechanisms. Such MC-desensitizing actions of bilirubin were observed in primary-cultured MCs and reproduced irrespective of the choice of stimuli, such as compound 48/80, calcium ionophore, and anti-IgE serum. Furthermore, MC-stabilizing effects of HO-1 were reproduced by the gene transfection of the enzyme into mastocytoma cell line RBL2H3. These results suggest that bilirubin generated through HO-1 serves as an anti-inflammatory substance that desensitizes MCs and ameliorates leukocyte recruitment.

Carbon monoxide (CO) is synthesized in vivo by heme oxygenase. Although for many years CO had been regarded as potentially toxic waste, recent studies have indicated that it is a signaling molecule with important physiological functions. Nitric oxide (NO), another diatomic diffusible gas, is regarded as an established signaling molecule. Structural similarities between CO and NO have led many investigators to draw analogies between the two gaseous mediators. Whereas the NO signaling system has been Well defined as to its receptor molecule, soluble guanylate cyclase, the CO system has been conceived to require further tuning with respect to identifying its receptor molecules and its downstream effectors. Furthermore, there has been little quantitative information to argue for a physiological role of CO in vivo. This review, therefore, focuses on recent developments on both physiologic and pathophysiologic roles of CO in the model of isolated perfused liver of rats where endogenous production of CO is actually estimated. This model has revealed that CO acts as an endogenous vasorelaxant in the liver and that effects of CO are at least in part cyclic GMP-dependent. It has also provided answers to many questions of hepatobiliary functions that had not been resolved because of the complexity introduced by the interplay between NO and CO.

Heme oxygenase (HO)-1 is a stress-inducible enzyme protecting cells against oxidative stress, and mechanisms have been considered to depend exclusively on its enzyme activity. This study aimed to examine if the protein lacking catalytic activities could also display such resistance against oxidative stress. Stable transfectants of rat wild type HO-1 cDNA (HO-1-U937) and those of its H25A mutant gene (mHO-1-U937) were established using human monoblastic lymphoma cell U937. HO-1-U937 and mHO-1-U937 used in the study exhibited similar levels of the protein expression, while only the former increased enzyme activities. HO-1- and mHO-1 U937 cells became more and less sensitive to H2O2 than mock transfectants, respectively; such distinct susceptibility between the cells was ascribable to differences in the capacity to scavenge H2O2 through catalase and to execute iron-mediated oxidant propagation. On the other hand, both cell lines exhibited greater resistance to tertbutyl hydroperoxide than mock transfectants. The resistance of HO-1-U937 to hydroperoxides appeared to result from antioxidant properties of bilirubin, an HO-derived product, while that of mHO-1-U937 was ascribable to increased contents of catalase and glutathione. These results provided evidence that gene transfection of the activity-lacking mutant HO-1 protects cells against oxidative stress through multiple mechanisms involving up-regulation of catalase and glutathione contents.

Stress-induced downregulation of spermatogenesis remains poorly understood. This study examined the induction of heme oxygenase-1 (HO-1), a carbon monoxide-generating inducible enzyme, in modulation of spermatogenesis. Rats were exposed to cadmium chloride (CdCl2), a stressor causing oligo-zoospermia, and HO-1-induction was monitored by following HO isozyme expression. CdCl2-treated testes increased HO-1 activity and suppressed microsomal cytochromes P450, which are required for steroidogenesis. CdCl2-elicited HO-1 occurred mostly in Leydig cells and coincided with CO generation, as judged by bilirubin-IXalpha immunoreactivity. Under these circumstances, germ cells in peripheral regions of seminiferous tubules exhibited apoptosis; laser flow cytometry revealed that these apoptotic cells involve diploid and tetraploid germ cells, suggesting involvement of spermatogonia and primary spermatocytes in CdCl2-elicited apoptosis. Pretreatmentwith zinc protoporphyrin-IX, an HO inhibitor, but not copper protoporphyrin-IX, which does not block the enzyme, attenuated the CdCl2-induced apoptosis. Such antiapoptotic effects of zinc protoporphyrin-IX were repressed by supplementation of dichloromethane, a CO donor. Upon CdCl2-treatment, both Sertoli cells and the germ cells upregulated Fas ligand; this event was also suppressed by zinc protoporphyrin-IX and restored by dichloromethane. Thus, Leydig cells appear to use HO-1-derived CO to trigger apoptosis of premeiotic germ cells and thereby modulate spermatogenesis under conditions of stress.

The majority of molecular oxygen (O2) consumed in the body is used as a substrate of cytochrome c oxidase to maintain oxidative phospholylation for ATP synthesis. Rest of the O2 is used for oxidative biosynthesis including synthesis of vasoactive substances such as prostaglandins and secondary gaseous mediators such as nitric oxide (NO) and carbon monoxide (CO). Thus, O2 is not only used for maintenance of energy supply but also for regulating blood supply into tissues. Nitrous oxide (N2O), laughing gas for anesthesia, is generated endogenously through NO reductase in bacteria and fungi, and has recently been shown to modulate N-methyl-D-aspartic acid (NMDA) receptor function. A number of other biologically active gases could participate in regulation of cell and tissue functions. Carbon dioxide (CO2) is generated mainly through the Krebs cycle as a result of glucose oxidation and serves as a potent vasodilator, and hydrogen sulfide (H2S) synthesized through degradation of cysteine has recently been postulated to be a neuromodulater, although their receptor proteins for signaling have not been verified as a discernible molecular entity. Easy penetration allow these gases to access the inner space of receptor proteins and to execute their biological actions. These gases are generated and consumed in anaerobic bacteria through varied reactions distinct from those in mammals. This review summarizes recent information on mechanisms for gas generation and reception in biological systems.

This study was designed to determine changes in expression of heme oxygenase (HO)-1, the stress-inducible and carbon monoxide-producing enzyme, in normotensive and portal hypertensive human livers. GTS-1, a monoclonal antibody against rat HO-1 cross-reacted with the human HO-1 and blocked its enzyme activity, allowing us to-examine the activity and localization of HO-1. in controls, approximately 50% of the total HO activity was from HO-1 as judged by the sensitivity to GTS-1, while the rest of activity was from other isozymes such as HO-2. HO-1 was expressed mainly in a subpopulation of Kupffer cells, and the expression in hepatic stellate cells, sinusoidal endothelial cells, and hepatocytes was little, if any The HO-1 expression exhibited quite different pictures in the livers of portal hypertensive diseases. In cirrhotic livers, which undergo portal hypertension through increases in intrasinusoidal resistance and regenerative changes in the parenchyma, HO-1 occurred in a majority of Kupffer cells and was also observed in hepatocytes. Consequently, the total HO-1 activities became significantly greater in these tissues than those from normal individuals: By contrast, livers of idiopathic portal hypertension that are characterized by an increase in presinusoidal resistance displayed a significant decrease in the HO-1 expression in Kupffer cells, and its hepatocellular expression was not detectable. Although factors involved in altered HO-1 expression in these cells remain unknown, the results suggest that Kupffer cells could alter their expression of HO-1 in response to local hemodynamic changes associated with chronic portal hypertension in humans.

Mouse cytohesin-1 (CTH-1) is a guanine nucleotide exchange factor, specific for ADP ribosylation factors. The CTH-1 gene promoter was characterized by deletion mapping and mutational analysis. The region between -101 and -38 relative to the transcription start site showed the essential promoter activity when transfected into both NIH3T3 and COS7 cells. The nucleotides of the core promoter region contain three tandem GC boxes, which can offer potential binding sites for the ubiquitous transcription factor Sp-l family. Mutational analysis revealed that these tandem GC boxes are indispensable for activation of the gene transcription. (C) 2000 Elsevier Science B.V. All rights reserved.

The structural organization and 5'-flanking region of the mouse V1a and V1b vasopressin receptor genes were determined. The mouse Via receptor gene was located within an 8-kb XbaI fragment, and the mouse V1b receptor gene was located within a 14-kb EcoRV fragment. Both genes were comprised of two coding exons that were separated by a 2.3-kb and a 8.0-kb intron, respectively, located before the respective seventh transmembrane domain of the receptor sequence. The availability of these genes would allow us to study the functional role of V1a and V1b receptors by disrupting the gene in mice.

This study aimed to examine whether livers overexpressing heme oxygenase (HO)-1 could alter the vascular resistance through the vasorelaxing action of carbon monoxide (CO). The relationship among HO-1 expression, CO generation, and the vascular resistance was assessed in perfused rat Livers pretreated with hemin, an inducer of HO-1. At 18 h after the hemin treatment, Livers displayed marked increases in HO-1 expression in hepatocytes and venous CO flux and a reduction of the basal resistance. The reduction of the resistance in hemin-treated livers was canceled by administration of oxyhemoglobin, a reagent trapping both CO and nitric oxide (NO), but not by methemoglobin, which captures NO but not CO. Liposome-encapsulated oxyhemoglobin, which cannot access the space of Disse, did not cause vasoconstriction. Furthermore, these livers became less sensitive to endothelin-1, a vasoconstrictive peptide, than the untreated controls through mechanisms involving CO. On the other hand, at 12 or 24 h after the treatment when the HO-1 induction was not accompanied by CO overproduction, neither a decrease in the basal resistance nor vascular hyporeactivity to endothelin-1 was observed. These results suggest that CO overproduced in the extrasinusoidal compartment is a determinant of the HO-1-mediated vasorelaxation in the liver.

1 We pharmacologically studied the alpha(1)-adrenoceptor (AR) subtype(s) involved in receptor-mediated signalling in a novel vascular smooth muscle cell line cloned from p53 knockout mice, P53LMAC01 (AC01) cells.
2 Radioligand binding studies with [I-125]-HEAT showed the existence of a homogeneous population of binding site with an affinity (K-d value) of 0.4 nhl and a maximum number of binding sites (B-max) of 100 fmol mg(-1) protein. Catecholamines competed for [I-125]-HEAT binding stereospecifically and with the characteristic alpha(1)-AR potency series.
3 Displacement curves for BMY-7378 and KMD-3213 best fitted a one-site model with a pK(1) value (-log(10) (equilibrium inhibition constant)) of 6.06 and 7.07, respectively.
4 Reverse transcription-polymerase chain reaction (RT-PCR) assay detected alpha(1B)- and alpha(1D)-AR, but not alpha(1A)-AR transcript.
5 Chlorethylclonidine (CEC) treatment nearly abolished (-)noradrenaline (NA) (10 mu M)-induced inositol[1,4,5]trisphosphate (IP3) production, and BMY-7378 inhibited the response with a K-i value of 0.3 nM, which value was similar to that obtained in the cells expressing alpha(1D)-AR. In both AC01 cells and cells expressing alpha(1D)-AR, BMY-7378 protected alpha(1)-ARs from CEC alkylation while it had little protective effect on CEC alkylation and NA-induced IP3 production in cells expressing alpha(1B)-AR
6 The results indicate that AC01 cells contain predominantly alpha(1B)-ARs and a small population of alpha(1D)-ARs; however, phosphoinositide (PI)/Ca2+ signalling is mainly mediated through the minor population of alpha(1D)-ARs, rather than the alpha(1B)-ARs.

Although discontinuous total parenteral nutrition (d-TPN) has recently been favored for clinical use over continuous total parenteral nutrition (c-TPN) to ameliorate liver dysfunction, mechanisms for the protection against postoperative liver dysfunction remain unknown. This study aimed to examine differences in mitochondrial function in d-TPN-and c-TPN-pretreated livers during ischemia-reperfusion. Rat livers pretreated with d-TPN or c-TPN were perfused with Krebs-Ringer buffer and were exposed to 25% low-flow hypoxia followed by reperfusion, Intrahepatic mitochondrial membrane potential (Delta Psi) and cell viability were assessed by dual-color digital microfluorography using rhodamine 123 (Rh123) and propidium iodide (PI), respectively. In response to hypoxia, livers pretreated with c-TPN, d-TPN, and an ordinary chow diet exhibited a significant Delta Psi reduction among the entire lobules, Upon reperfusion, the regional Delta Psi values further decreased in the c-TPN liver, whereas those in the d-TPN-treated or chow-treated livers displayed a rapid recovery toward the control levels. The severity of cell injury did not differ among the groups, showing that the reperfusion-induced Delta Psi drop in the c-TPN-pretreated liver is not a consequence of cell injury. Differences in the Delta Psi drop among the groups appear to occur irrespective of those in the glycogen storage, because the livers undergoing d-TPN display a marked Delta Psi recovery even when reperfused at the end of a fasted state. These results indicate that c-TPN, but not d-TPN, jeopardizes mitochondrial re-energization and suggest that a circadian pattern of the TPN serves as a potentially beneficial strategy to reduce the risk of postischemic mitochondrial dysfunction in the liver.

This study aimed to examine the mechanism(s) by which carbon monoxide (CO), a product of heme oxygenase reaction, controls the contractility of bile canaliculus (BC) in hepatocytes, When BCs associated with the couplet cells in cultured rat hepatocyte suspension were observed using time-lapse video microscopy, they exhibited periodical contractions with a most-probable interval of 6 minutes under our experimental conditions. The addition of 1 mu mol/L zinc protoporphyrin IX (ZnPP), a potent inhibitor of heme oxygenase, to the culture medium elicited a 40% shortening of the interval time together with an increase in intracellular calcium concentrations, while the same concentration of iron protoporphyrin IX did not induce such changes. The production of CO, which was 0.5 nmol/h/10(8) cells in the absence of ZnPP, diminished to less than 0.1 nmol/h/10(8) cells upon application of ZnPP, The ZnPP-elicited increases in both contractile frequency and intracellular calcium concentrations were attenuated by the addition of 1 mu mol/L CO or 50 mu mol/L 1,2-bis(2-aminophenoxy) ethane-tetraacetate, a calcium chelator. Clotrimazole or metyrapone, inhibitors of cytochrome P450-dependent monooxygenase activities, also attenuated the ZnPP-induced elevation of the contractile frequency. On the other hand, intracellular cyclic guanosine monophosphate (cGMP) contents were not altered significantly by the application of ZnPP or by CO. These results indicate that CO generated by heme oxygenase controls the BC function by changing intracellular calcium concentrations presumably through a mechanism involving the cytochrome P450 reaction.

Carbon monoxide (CO) derived from heme oxygenase has recently been shown to play a role in controlling hepatobiliary function, but intrahepatic distribution of the enzyme is unknown. We examined distribution of two kinds of the heme oxygenase isoforms (HO-1 and HO-2) in rat liver immunohistochemically suing monoclonal antibodies. The results showed that distribution of the two isoforms had distinct topographic patterns: HO-1, an inducible isoform, was observed only in Kupffer cells, while HO-2, a constitutive form, distributed to parenchymal cells, but not to Kupffer cells. Both isoforms were undetectable in hepatic stellate cells and sinusoidal endothelial cells. Of the two isoforms, HO-2 in the parenchymal cell rather than HO-1 in the Kupffer cell, appears to play a major role in regulation of microvascular tone. In the perfused liver, administration of HbO(2), a CO-trapping reagent that can diffuse across the fenestrated endothelium into the space of Disse, elicited a marked sinusoidal constriction, while administration of a liposome-encapsulated Hb that cannot enter the space had no effect on the microvascular tone. These results suggest that CO evolved by HO-2 in the parenchymal cells, and released to the extrasinusoidal space, served as the physiological relaxant for hepatic sinusoids.

Ito cells are microvascular pericytes occurring specifically in the liver. They are characterized by abundant fat droplets and constitute a major storage pool of vitamin A in the liver. These cells encircle the outer surface of microvascular walls and constitute a well-organized meshwork of intercellular connection by using their unique neuron-like dendritic structure. Ito cells have thus been considered to be a putative machinery controlling sinusoidal blood flow. Carbon monoxide (CO) generated by the heme oxygenase reaction serves as an endogenous relaxing factor that actively relaxes hepatic sinusoids. Although such a GO-dependent vasorelaxing mechanism seems to involve cyclic guanosine monophosphate- (cGMP-) dependent relaxation of Ito cells, it is still unknown whether Ito cells can exhibit cell relaxation in response to CO through unidentified cGMP-independent mechanisms. This chapter provides an overview of mechanisms for GO-dependent Ito cell relaxation in vivo and in vitro.

Nitric oxide (NO) has recently attracted great interest as a mediator of cell and organ functions. During pregnancy, larger amounts of NO are known to be produced in systemic circulation on the maternal side than those in nonpregnant females. Placental trophoblastic cells (PTCs), which are major constituents of placenta and are in direct contact with maternal blood, can produce NO via the reaction of endothelial form of NO synthase during pregnancy. Endogenously produced NO in placenta can relax vascular tone, inhibit platelet aggregations, and attenuate adherent reactions of leukocytes and platelets. By contrast, the decrease of NO generation in the placenta is correlated with impairment of uteroplacental perfusion, which elicits severe perinatal complications such as preeclampsia (PE) and intrauterine growth retardation (IUGR). Although the mechanisms through which endogenous NO modulates a variety of cellular functions in the placenta have not been revealed yet, our results provide new insight into molecular mechanisms of endogenous NO in PTCs, suggesting that alterations in placental NO formation may not only play a role in the physiological changes of advancing gestation but may also contribute to the pathophysiology of PE and IUGR.

Nitric oxide (NO) has been shown to inhibit platelet adhesion and aggregation, but there are no reports on its interaction with the coagulation system. We investigated the effect of the L-arginine analogues, N-nitro-L-arginine (LNA), N-G-nitro-L-arginine methyl ester (L-NAME), and NG-monomethyl-L arginine (L-NMMA), competitive inhibitors of NO production, on endothelial-surface heparan sulfate. Addition of LNA to porcine aortic endothelial cells reduced I-125-labeled antithrombin III binding to the cell surface heparan sulfate in a dose-and time-dependent fashion. Significant inhibition was observed with 1 mM LNA, and the maximal suppression (-50% of control) occurred at 10 mM LNA after 12 h, L-NAME (1 mM) and L-NMMA (1 mM) also significantly inhibited the antithrombin III binding. The iron chelator desferrioxamine significantly prevented the reduction of antithrombin III binding to LNA-treated cells. We further investigated the effect of L-NAME on intracellular oxidative stress of endothelial cells using a hydroperoxide-sensitive fluorochrome, carboxy-dichloro-dihydrofluorescein diacetate bisacetoxymethyl ester probe, and revealed that inhibition of NO synthesis by L-NAME led to a marked increase in intracellular oxidative stress. These results demonstrated that the prolonged inhibition of NO synthesis in porcine aortic endothelial cells decreases the expression of anticoagulant heparan sulfate on endothelial cells through the increase in intracellular oxidative stress, perhaps comprising another mechanism by which NO affects the coagulation system in the vasculature. (C) 1997 Elsevier Science Ireland Ltd.

This study aimed to investigate whether carbon monoxide (CO), a product of heme oxygenase that degrades protoheme IX serves as an endogenous modulator for biliary transport. To that end, effects of zinc protoporphyrin IX (ZnPP), a heme oxygenase inhibitor, on the biliary transport were tested in perfused rat liver. Perfusion of 1 mu M ZnPP abolished detectable levels of CO in the venous perfusate and increased bile acid-dependent bile output accompanying an increased secretion of bile salts. The ZnPP-induced choleresis coincided with a reduction of tissue guanosine 3',5'-cyclic monophosphate (cGMP) levels and a decrease in vascular conductance. On administration of 2.5 mu M CO, ZnPP-elicited choleresis, decreases in vascular conductance, and cGMP levels were all attenuated. Treatment with 1 mu M 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) partly attenuated the ZnPP-induced choleresis in concert with repression of vascular conductance. Furthermore, treatment of the liver with methylene blue, a guanylate cyclase inhibitor, evoked a choleresis similar to that induced by ZnPP. Thus endogenous CO suppression stimulates the biliary transport in part through a cGMP-dependent mechanism.

Intracellular hydroperoxide generation in cultured human placental trophoblastic cells (HPTCs) was quantitatively monitored in the presence or absence of an NO synthase inhibitor, N-G-nitro-L-arginine methyl ester (L-NAME, 1 mM), by digital microfluorography with use of carboxydichlorofluorescein, a hydroperoxide-sensitive fluorogenic probe. In the absence of L-NAME, HPTCs displayed a time-dependent gradual elevation of the fluorescence, suggesting the ability to produce oxidants spontaneously. In the presence of L-NAME, however, the fluorescent response in these cells increased further; the oxidative impact elicited by L-NAME treatment for 30 min was equivalent to that induced by application of 230 mu M tert-butyl hydroperoxide for 5 min. This oxidative process was completely blocked by rotenone, a reagent that interferes with electron entry into complex I of the mitochondrial respiratory chain. On the other hand, antimycin A, which blocks mitochondria at the distal site of the ubiquinone pool, potentiated the L-NAME-induced oxidative change. These findings suggest that constitutive levels of nitric oxide production contribute to regulation of mitochondrion-derived intracellular oxidant generation in HPTCs.

Heme oxygenase is a heme-oxidizing enzyme which generates biliverdin and carbon monoxide (CO). The present study was designed to elucidate whether CO endogenously produced by this enzyme serves as an active vasorelaxant in the hepatic microcirculation. Microvasculature of the isolated perfused rat liver was visualized by dual-color digital microfluorography to alternately monitor sinusoidal lining and fat-storing Ito cells. In the control liver, the CO flux in the venous effluent ranged at 0.7 nmol/min per gram of liver, Administration of a heme oxygenase inhibitor zinc protoporphyrin IX (1 mu M) eliminated the baseline CO generation, and the vascular resistance exhibited a 30% elevation concurrent with discrete patterns of constriction in sinusoids and reduction of the sinusoidal perfusion velocity, The major sites of the constriction corresponded to local sinusoidal segments colocalized with Ito cells which were identified by imaging their vitamin A autofluorescence, The increase in the vascular resistance and sinusoidal constriction were attenuated significantly by adding CO (1 mu M) or a cGMP analogue 8-bromo-cGMP (1 mu M) in the perfusate, From these findings, we propose that CO can function as an endogenous modulator of hepatic sinusoidal perfusion through a relaxing mechanism involving Ito cells.

Carbon monoxide (CO) generated by heme oxygenase has recently been considered a neural messenger in brain. This observation prompted us to investigate whether CO participates in vascular regulation in the liver, another organ with high levels of heme oxygenase activity. In isolated perfused rat liver, submicromolar levels of CO were detectable in the effluent and were able to be suppressed by the administration of Zn protoporphyrin IX (1 mu M), a potent inhibitor of heme oxygenase. Furthermore, zinc protoporphyrin IX (1 mu M) promoted an increase in the perfusion pressure under the constant flow conditions. These changes were reversed by adding CO (2 mu M) or a cGMP analogue 8-bromo-cGMP (1 mu M) in the perfusate. The present findings indicate that CO can function as an endogenous modulator of vascular perfusion in the liver. (C) 1994 Academic Press, Inc.

高分子超薄膜(ナノシート)は高い柔軟性と密着性を持ち、医用高分子を素材とすることで、新規な創傷被覆材として機能することが期待される。これまで研究代表者らは肺気胸モデル、胃切開モデルに対して術後の組織癒着の無い有用な創傷被覆材であることを実証してきた。本研究ではナノシートを機能化し、熱傷治療や消化管穿孔治療に向けた構造制御を行い、また、in vivo 試験による創傷被覆材としての有用性を実証した。

本研究課題は将来の臨床応用に繋がるより高い虚血耐性能を有する肝細胞の開発を目指し、低酸素環境への肝実質細胞の機能的適応変化に対する分子メカニズムを解明することを目的としてきた。この目的遂行のために、我々はCre-loxpシステムに基づいた遺伝子ターゲティングを行うことで肝細胞特異的に生体内低酸素感受性転写制御因子であるhypoxia inducible factor-1(HIF-1)の機能を欠失させたマウスを確立した。このマウスは肝臓においてサザンブロット解析上約60%以上の割合でHIF-1α遺伝子欠損が認められるにもかかわらず、全身性にHIF-1α遺伝子を欠失させた場合と異なり胎生致死に至らず正常に発生・成長することが確認された。肝湿重量変化は対照群と比較して特に有意な差は認められず、また組織学的な検討では肝小葉構築形成には異常が認められないものの、HIF-1α欠損マウス肝臓において終末肝静脈と終末門脈との血管距離が約50μm延長していることが明らかになった。一方、低酸素刺激によりHIF-1を介して発現誘導が認められる解糖系酵素群の肝小葉内発現パターンに関して特にHIF-1α欠損肝臓で変化が認められないことが免疫組織学的検討により明らかになった。以上の結果より、HIF-1発現は肝臓の発達において基本肝小葉構築形成には必須でないものの肝微小血管構築形成を規定する因子として重要な役割を演じている可能性があると考えられた。さらにHIF-1α欠損肝臓における部分肝切除術後の肝再生過程が対照群と比較して遅延することを見出し、この現象がG1期およびS期サイクリンなどの細胞周期関連蛋白質発現減少を伴った細胞増殖応答低下によるものであることを明らかにしてきた。本研究期間ではHIF-1が肝臓内基本構造および機能発現において重要な役割を演じていることを明らかにすることが出来たが、今後更に詳細な分子メカニズムの解明を行っていく必要があると考えている。

ヘムを一酸化炭素(CO)、鉄およびビリベルジンに分解するヘムオキシゲナーゼ(HO)は多彩な生物活性を有していることが知られているが、HOアイソザイム固有の生理活性の発現とその調節機構、COにより制御される標的分子の検索、さらに生体内で産生される他のガス分子との相互作用について未だその全貌が解明されていない。本研究課題では、HOアイソザイム発現とCOなどの反応生成物を介した生物作用発現との関係を明確に議論できる実験系を確立し、本酵素活性の生体制御における病態生理学的意義について解析することを目的としてきた。この目的遂行のために、既に報告のあるHO遺伝子欠損で認められる繁殖不全を回避できるOre-LoxPシステムに基づいた新しいコンディショナルノックアウトマウスの作成に着手し、現在までに目的とした相同組換えを起こしたES細胞を用いてキメラマウスの作成に至っている。次に、COにより特異的に作動する新規細胞内レセプタの検索を行うために、COにより惹起される細胞内代謝変動をCE-MSを用いて解析した。その結果、アセトアミノフェン投与による肝臓内CO産生増加に伴い、肝臓内メチオニンの増加とS-アデノシルメチオニンおよびシステインからグルタチオンやタウリンに至る代謝経路の抑制が認められた。この結果より、メチオニンからシステイン合成に至る含硫アミノ酸代謝経路に存在するcystathionine β-synthase(CBS)がCOの新しい細胞内標的分子であることが明らかになってきた。また、CBS精製蛋白を用いてCOによる酵素活性阻害様式を解析した結果、数mMのCOによりCBS活性阻害が認められるがこれはヘムの2つの軸配位子のうちシステイン残基がCOと置換することで生じることが明らかになった。さらに我々はCOと別の内因性ガス状メディエータである一酸化窒素(NO)と生体内における相互作用について解析した結果、網膜組織内において両者の既知標的分子である可溶性グアニル酸シクラーゼ(sGC)活性を局所で産生されるCOとNOが協調して制御しており、このCOによるsGCの活性制御は局所のNO濃度に強く依存していることが明らかになった。本研究期間でHO-CO系を介した新たな生物活性を見出すことが出来たが、今後我々が取り組んでいる新規遺伝子改変動物の利用により更なるHOの生物学的意義の解明を行う必要があると考えている。

肥満は糖尿病や動脈硬化など健康寿命の延伸を妨げる重篤な疾患の共通した基盤病態である。本研究では、肥満の形成・進展における低酸素の病態生理学的意義を明らかにすることを目指し、ショウジョウバエを用いた遺伝的スクリーニングによる新しい低酸素ストレス関連因子の同定とその機能解析に取り組んだ。その結果、脂肪組織において、低酸素ストレス応答の中心分子HIFの恒常的な活性化により惹起された脂肪蓄積抑制にかかわる遺伝子の同定に成功した。また、3T3-L1細胞を用いた解析から、この遺伝子のマウスオロソログの発現抑制が脂肪蓄積を抑制することも見出した。

本研究では、脂肪組織において異常な脂肪蓄積が認められる肥満病態に対する低酸素を標的とした新規治療法の開発を目指して、細胞内の脂肪蓄積に対する低酸素ストレス応答を介した新しい制御機構の解明に取り組んだ。その結果、低酸素ストレス応答の中心分子のHIFの恒常的な活性化が脂肪細胞における脂質蓄積を抑制することを見出した。また、この応答が細胞自律的であること、転写共役因子として機能する分子との相互作用が関与している可能性が明らかになった。さらに、リピドーム解析結果からHIFが量的制御のみならず、脂質の質的制御にも関与している可能性が示された。

本研究では、非アルコール性脂肪性肝疾患NAFLDの発症や進展過程における低酸素に対する肝細胞のストレス応答の新しい生物作用を明らかにすることを目指した。その結果、低酸素応答の中心分子HIF-1が、コリン欠乏食誘導性NAFLDの肝脂肪蓄積に対する内因性防御因子として機能することを見出した。また、HIF-1による脂肪蓄積防御機構に、転写共役因子として機能するlipin1の発現亢進を介したペルオキシゾーム内脂肪酸のb酸化制御が関与していることを明らかにした。さらに、リピドーム解析結果から、HIF-1の機能欠損により、肝臓内に超長鎖脂肪酸を含む中性脂肪が異常に蓄積することを見出した。

好気的生物は酸素利用が限られた環境に曝されると、劇的な代謝リモデリングを誘起しエネルギー産生を維持することで生体機能の恒常性を保つ。この代謝リモデリングの制御にかかわる中心的な分子が低酸素誘導性転写制御因子HIFである。本研究では、糖質にならび生体内の重要なエネルギー源である脂質の代謝制御における、HIFによる新しい調節機構の探索とその機能解明を目指した。この目的遂行のために、新たな遺伝学的なin vivoスクリーニング系を確立し、その結果としてHIFが脂肪組織における脂肪細胞および細胞内脂肪滴のサイズの制御にかかわることを見出した。

細胞競合とは、増殖が速い生存細胞群(勝ち組)が、増殖が遅く細胞死によって排除される死細胞群（負け組）に競合し、細胞死、細胞の増殖と周期、分化などが統合的に制御されることにより、一定の大きさと機能をもつ器官が形成される現象である。これまでに細胞競合制御因子として、癌遺伝子c-MycのショウジョウバエホモログdMycが報告されているが、その分子機構は不明である。研究分担者である松田は、ショウジョウバエの翅原基、及び培養細胞株を用いて、dMycにより制御される細胞競合モデルを確立し、予備的解析より死細胞-生存細胞間の細胞運命決定に、それぞれの細胞群における1)エネルギー代謝変化、2)分泌因子が関わることを見いだした。本研究では、分子生物学的・生化学的解析、及びメタボローム解析により、競合する死細胞と生存細胞それぞれの細胞特性変化とエネルギー代謝ステータスとの関係の網羅的分析、及び新規細胞競合制御因子の同定と機能解析を行うことより、細胞競合の分子機構の解明を目指した。　ショウジョウバエ培養細胞株S2を用いたin vitro細胞競合モデル系において、勝ち組細胞と負け組細胞におけるエネルギー代謝ステータス解析系の構築を行った。勝ち組となる高dMyc細胞(メタロチオネインプロモーターの下流にdMycを連結させたベクターの導入により、CuSO4処理によりdMycを発現誘導できる安定発現細胞株; pMT-dMyc/S2細胞)と、負け組となる低dMyc細胞（アクチンプロモーターベクターの導入により核移行シグナル付きGFPを恒常的に発現する野生型細胞株; pAc5.1-GFP/S2細胞）を共培養する技術を応用し、3通りの方法（(i)直接共培養系、(ii)間接共培養系、及び(iii) 単培養系における直接共培養上清アッセイ系）により、dMycにより制御される細胞競合のモデルを作製した。それぞれのモデルにおいて、細胞死の初期マーカーである活性型カスパーゼ-3抗体による免疫染色、及び細胞増殖解析による細胞特性評価系をセットアップした。(iii) の単培養系における直接共培養上清アッセイ系を用いて、定量的PCR解析により、競合する勝ち組細胞（生細胞）と負け組細胞（死細胞）における糖代謝関連因子について、解析を行った。その結果、勝ち組となる細胞群（生細胞群）において、グルコーストランスポーターGLUT-1、及びGLUT-3の顕著な発現上昇（10&#12316;15倍）がみられ、一方、負け組となる細胞群（死細胞群）においても、GLUT-1、及びGLUT-3の上昇（2&#12316;3倍）がみられることが明らかとなった。さらに、勝ち組、及び負け組の両細胞群において、RNA干渉法によるGLUT-1、及びGLUT-3の機能抑制を行ったところ、勝ち組（生細胞）、あるいは負け組（死細胞）としてのそれぞれの特性が失われ、細胞競合が認められなくなることが明らかとなった。これらの結果は、両細胞群の代謝ステータスの変化が、細胞競合が生じるために必要であることを示唆している。　現在、(iii) の単培養系における直接共培養上清アッセイ系を用いて、勝ち組となる細胞群（生細胞群）、及び負け組となる細胞群（死細胞群）における代謝ステータスの詳細について明らかにするため、メタボローム解析を行うための準備を進めている。

肝実質細胞に脂質が蓄積した状態は脂肪肝と総称され、肥満、糖尿病、アルコール過剰摂取などの生活習慣に起因する肝疾患の最もありふれた初期病態である。これまで脂肪肝は可逆性の良性肝疾患と捉えられてきたが、しかし近年、慢性化した脂肪肝の一部が脂肪性肝炎、肝硬変、さらには肝細胞がんへと進展することが明らかになり、これらの疾患に対する効果的な治療法や予防法の開発のために脂肪肝発症に係わる分子メカニズムの解明が急務となっている。 これまで我々は、脂肪肝の発症過程で生じる低酸素環境が病態の形成および進展に係わっていると仮説を立て、病態モデルマウスを作成してその検証に取り組んできた。その成果として、生体内における低酸素応答の中心分子であるhypoxia inducible factor-1 (HIF-1)が、アルコール性脂肪肝の進展に対して抑制的に働く防御因子であることを明らかにしてきた。本研究では、HIF-1による肝脂肪蓄積抑制機構に係わる分子メカニズムの解明に取り組んだ。まず、HIF-1欠損マウス(HIFKO)で認められた脂肪蓄積増強機構に、脂肪酸合成系の活性化が関与している可能性を考え、定量的RT-PCR法を用いて遺伝子発現解析を行った。その結果、解析した脂肪酸合成に係わる全ての遺伝子が、エタノール混餌食4週間投与によりコントロールマウスと比較して増加していることが明らかになった。また、エタノール混餌食を2週間投与したHIFKOマウスからの肝臓を同様に解析したところ、脂質代謝の中心的な転写制御因子であるsterol regulatory element binding protein (SREBP)1cおよび下流の標的遺伝子のacetyl CoA carboxylase (ACC)以外の遺伝子は、エタノール混餌食2週間投与時より減少していることが明らかになった。一方、SREBP1cとACCの遺伝子発現は、エタノール混餌食投与により時間依存性に増加し、4週間の投与によりHIFKOマウスとコントロールマウスの間でさらに発現量の差が著明になることが明らかになった。次に、SREBP1cの制御にアディポネクチンが関与している可能性を考え、血清中アディポネクチン濃度の測定を行った。その結果、コントロールマウスでは食餌投与後2週間に一過性の上昇が認められ、4週間でも投与前より増加していることが明らかになった。一方、HIFKOマウスもコントロールマウスと同様な反応を示し、両者間で差が認められなかった。以上の結果より、エタノール性脂肪肝形成において、肝臓内HIF-1がSREBP1cとACCの遺伝子発現抑制による脂肪酸合成低下を介して病態防御的に機能することが示された。

肝臓は生体内で脂肪組織に次いで生理的条件下で脂肪を蓄積する能力を有する臓器である。一方、脂質の過剰摂取、ウイルス性肝炎、糖尿病やアルコール摂取は病的な過剰の脂質沈着を肝臓に引き起こし、所謂‘脂肪肝’と呼ばれる病態になる。これまで脂肪肝は可逆性の良性疾患として捉えられてきたが、近年脂肪肝の遷延は脂肪性肝炎、肝線維症や肝硬変などのさらに進行した病態へと高率に進展することが明らかになってきた。肝移植以外に進行性肝疾患に対する効果的な治療法がない現状では、脂肪肝発症・進展を如何に食い止めるかが緊急の課題となっている。低酸素は循環障害などに起因する絶対的な酸素供給の低下のみならず、酸素供給を上回る酸素消費の増加によっても生じる病態である。脂肪肝では、脂肪蓄積による物理的な肝微小循環傷害と代償性脂質代謝亢進に伴うミトコンドリア酸素消費の増加により肝臓が低酸素状態に陥ることから、低酸素への適応が肝脂肪肝蓄積に係わっていると考えられる。そこで、本研究では肝脂肪蓄積に低酸素により誘導される転写制御因子Hypoxia inducible factor-1(HIF-1)が重要な制御因子として機能しているのではないかと仮説を立て、脂肪肝におけるHIF-1の時空間的局在と病態生理学的意義について、エタノール性脂肪肝モデルを用いて解析を行った。その結果、マウスに5%エタノール混餌食4週間投与を行うと、肝小葉内中心静脈領域がpimonidazoleで強く染色され低酸素に陥っていることが明らかになった。また、この低酸素領域に一致して、核内にHIF-1発現の亢進が認められる肝細胞が局在することが分かった。さらに、HIF-1発現亢進に一致し、HIF-1標的遺伝子のVEGFやPGKの遺伝子発現も増加しており、このことはエタノール投与による脂肪肝発症過程で肝臓が低酸素に陥り、その結果HIF-1の転写活性化が生じることを示唆している。一方、肝臓特異的HIF-1alpha遺伝子マウスは、野生型と比較してエタノール応答性脂肪蓄積が増悪することが、oil red O染色、肝臓および血清脂質量の生化学的解析より明らかになった。このことは、低酸素で活性化される転写制御因子HIF-1がエタノール誘導性肝脂肪蓄積に対する抑制因子として機能していることを示唆している。今後、さらにHIF-1による脂肪肝制御機構について詳細に解析を進める予定である。

本研究課題では、次の2つの研究プロジェクトを同時に進めてきた。1）低酸素感知・応答機構の生物学的機能の解析昨年度に引き続き、糖尿病下における肝臓内の糖関連酵素発現リモデリングにおける低酸素感受性転写制御因子であるhypoxia inducible factor-1(HIF-1)の生物作用について検討を行った。これまで高糖質・脂質食の短期投与では、HIF-1依存性のグルコキナーゼ発現制御を介して肝臓における糖の取り込みを促進することでHIF-1が血糖降下作用を有することを明らかにしてきたが、今年度は25週間の長期投与を行うことで全身性および肝臓におけるインスリン抵抗性の発症に対するHIF-1の生物作用について検討を進めた。糖負荷試験およびインスリン負荷試験の結果、HIF-1欠損マウスでは肝臓のみならず骨格筋や脂肪組織におけるインスリン抵抗性が増強することが明らかになり、HIF-1が糖尿病抑制因子として機能することが明らかになった。現在、その分子メカニズムについて解析を進めている。2）新規低酸素感知蛋白質の検索HIF-1alphaの特定のプロリン残基が酸素濃度依存的に水酸化されることが低酸素応答の制御に重要であることが明らかにされて以来、この反応機構を触媒するalpha-KG/Fe(II)依存性酸素添加酵素群の中に新規低酸素感知蛋白質が存在する可能性が高まってきている。本研究課題では、プロリン水酸化をターゲットとした酸素センサータンパク質の検索を目的として、プロリン水酸化を特異的に認識する単クローン抗体の作成に取り組んだ。ペプチド抗原を用いたELISAの結果、これまでに少なくとも2種類の候補抗体を得ることができた。現在これらの抗体がHIF-1alphaに代表されるnativeなプロリン水酸化タンパク質を認識できるか否かについて検討を重ねている。この確認が得られた後には、この抗体で免疫沈降されるタンパク質の同定を質量分析により明らかにしていく予定である。

　本研究課題では、糖尿病下における肝臓内の糖関連酵素発現リモデリングにおける生体内低酸素感受性転写制御因子であるhypoxia inducible factor-1(HIF-1)の生物作用について、肝臓特異的にHIF-1活性を欠失させた遺伝子改変マウス(HIFKO)を用いて検討を行った。その結果、通常食摂取したHIFKOマウスは、空腹時血糖(FBS)、経口糖負荷試験(OGTT)およびインスリン負荷試験(ITT)で、コントロールマウスと同等の血糖変化を示し、また主要な肝臓内糖関連酵素の発現量とその発現分布には大きな変化が認められなかった。一方、高糖質・脂質食(HFSD)を5週間摂取させた場合、コントロールマウスと比較してFBSおよびITTでは有意な変化は認められなかったが、OGTTでは投与後1時間まで有意な血糖上昇が認められた。OGTT時の初期インスリン分泌能は両群間において全く変化なかったが、後期インスリン分泌はHIFKOマウスにおいて上昇傾向が認められた。一方、単位面積当たりの膵臓のラ氏島数および&#61538;細胞陽性率には、両群間において大きな変化は認められなかった。これらの結果は、HIFKOマウスにおいて認められた血糖クリアランス能の低下は、膵臓のインスリン分泌能の低下および骨格筋・脂肪組織などの末梢臓器におけるインスリン感受性の低下がプライマリーな原因ではなく、肝臓自身の糖処理能力の減少によるものであると考えられた。そこで、HFSD食5週間投与後の肝臓における主要な糖関連酵素発現を、遺伝子およびタンパク質レベルで詳細に解析を行った。その結果、低酸素に応答してHIF-1依存性に発現変化する代表的な解糖系酵素phosphoglycerate kinaseやpyruvate kinaseの発現は、HFSD投与によりHIFKOおよびコントロールマウスにおいてほんの僅かであるが上昇するものの、両群間において差は認められなかった。しかし、肝細胞へのグルコース取り込みを制御するglucokinase発現については、コントロールマウスでは5倍程度誘導が認められたものの、HIFKOマウスではこのような誘導が完全に抑制されていたことが明らかになった。以上の結果より、HIF-1は糖尿病発症初期に誘導され、肝臓におけるグルコース取り込みを制御することで、血糖降下作用を有していることが明らかになった。