Background:In obesity, enlarged adipocytes become hypoxic, which inhibits adipocyte differentiation. Results: Hypoxia induces the expression of Wnt1 and Wnt10b in both human and mouse adipogenic cells in a hypoxiainducible factor (HIF)-2␣-dependent manner. Conclusion: Hypoxia enhances the secretion of Wnt ligands, which trigger Wnt signaling in the neighboring cells. Significance: Wnt10b is a novel HIF-2␣-specific target gene and a paracrine factor in hypoxia.
Hypoxia increases both active and repressive histone methylation levels via decreased activity of histone demethylases. However, how such increases coordinately regulate induction or repression of hypoxia-responsive genes is largely unknown. Here, we profiled active and repressive histone tri-methylations (H3K4me3, H3K9me3, and H3K27me3) and analyzed gene expression profiles in human adipocyte-derived stem cells under hypoxia. We identified differentially expressed genes (DEGs) and differentially methylated genes (DMGs) by hypoxia and clustered the DEGs and DMGs into four major groups. We found that each group of DEGs was predominantly associated with alterations in only one type among the three histone tri-methylations. Moreover, the four groups of DEGs were associated with different TFs and localization patterns of their predominant types of H3K4me3, H3K9me3 and H3K27me3. Our results suggest that the association of altered gene expression with prominent single-type histone tri-methylations characterized by different localization patterns and with different sets of TFs contributes to regulation of particular sets of genes, which can serve as a model for coordinated epigenetic regulation of gene expression under hypoxia.
Black tea has been reported to have anti-obesity effects in both rodents and humans. Gallic acid, an active component of black tea, decomposes quickly into pyrogallol in high-temperature solutions. This study introduced a new, aqueous ethanol extraction of black tea, which resulted in extracts with higher concentrations of gallic acid than conventional black tea extracts prepared by hot-water extraction or hot-ethanol extraction. We confirmed that, compared with the hot-water extract of black tea, the cold-ethanol extract of black tea (CE-BTE) had greater effects on reducing body weight and body fat, improving fatty liver, regulating blood glucose, and reducing blood cholesterol in the high-fat diet-induced obese mouse model. Nonetheless, although CE-BTE significantly reduced fat content, it did not reduce peroxisome proliferator-activated receptor (PPARγ) protein in epididymal fat tissue of HFD mice. We also showed that CE-BTE did not inhibit the function of PPARγ protein to drive adipogenesis of mouse 3T3-L1 preadipocytes. Considering that PPARγ is a master transcription factor not only for adipocyte differentiation, but also for adipose tissue function, such as glucose and lipid metabolism and insulin sensitivity, these results suggest that CE-BTE reduced fat mass and body weight without dampening fat cell homeostasis and insulin sensitivity.
Adipogenesis is a process which induces or represses many genes in a way to drive irreversible changes of cell phenotypes; lipid accumulation, round cell-shape, secreting many adipokines. As a master transcription factor (TF), PPARγ2 induces several target genes to orchestrate these adipogenic changes. Thus induction of Pparg2 gene is tightly regulated by many adipogenic and also anti-adipogenic factors. Four hours after the treatment of adipogenic hormones, more than fifteen TFs including glucocorticoid receptor (GR), C/EBPβ and AP-1 cooperatively bind the promoter of Pparg2 gene covering 400 bps, termed “hotspot”. In this study, we show that TEA domain family transcription factor (TEAD)4 reinforces occupancy of both GR and C/EBPβ on the hotspot of Pparg2 during early adipogenesis. Our findings that TEAD4 requires GR for its expression and for the ability to bind its own promoter and the hotspot region of Pparg2 gene indicate that GR is a common component of two positive circuits, which regulates the expression of both Tead4 and Pparg2. Wnt3a disrupts these mutually related positive circuits by limiting the nuclear location of GR in a β-catenin dependent manner. The antagonistic effects of β-catenin extend to cytoskeletal remodeling during the early phase of adipogenesis. GR is necessary for the rearrangements of both cytoskeleton and chromatin of Pparg2, whereas Wnt3a inhibits both processes in a β-catenin-dependent manner. Our results suggest that hotspot formation during early adipogenesis is related to cytoskeletal remodeling, which is regulated by the antagonistic action of GR and β-catenin, and that Wnt3a reinforces β-catenin function.
Activation of Raf reduces the repressive histone mark H3K27me3 at the INK4a locus by inducing the H3K27me3 demethylase JMJD3. During hypoxia, the catalyitc activity of JMJD3 is reduced due to the limited availability of O 2 as a substrate. In our study, we found that hypoxia prevented Raf-induced JMJD3 from demethylating H3K27me3 at the INK4a locus. Nonetheless, hypoxia did not prevent Raf signaling from inducing INK4a mRNA. Interestingly, we found that hypoxia strongly enhanced the active histone mark H3K4me3 at the INK4a locus by inhibiting the H3K4me3 demethylases JARID1A and JARID1B. Therefore, this study demonstrates that the O 2 concentration in the microenvironment differentially affects the repressive methylation on K27 and the activating methylation on K4 at the INK4a locus by inhibiting the H3K27me3 and H3K4me3 demethylases.
Retinal neovascularization in retinopathy of prematurity (ROP) is the most common cause of blindness for children. Despite evidence that hypoxia inducible factor (HIF)-1α -VEGF axis is associated with the pathogenesis of ROP, the inhibitors of HIF-1α have not been established as a therapeutic target in the control of ROP pathophysiology. We investigated the hypothesis that degradation of HIF-1α as a master regulator of angiogenesis in hypoxic condition, using β-lapachone, would confer protection against hypoxia-induced retinopathy without affecting physiological vascular development in mice with oxygen-induced retinopathy (OIR), an animal model of ROP. The effects of β-lapachone were examined after intraocular injection in mice with OIR. Intraocular administration of β-lapachone resulted in significant reduction in hypoxia-induced retinal neovascularization without retinal toxicity or perturbation of developmental retinal angiogenesis. Our results demonstrate that HIF-1α–mediated VEGF expression in OIR is associated with pathological neovascularization, not physiological angiogenesis. Thus, strategies blocking HIF-1α in the developing eye in the pathological hypoxia could serve as a novel therapeutic target for ROP.
Liver cells experience hypoxic stress when drug-metabolizing enzymes excessively consume O2 for hydroxylation. Hypoxic stress changes the transcription of several genes by activating a heterodimeric transcription factor called hypoxia-inducible factor-1α/β (HIF-1α/β). We found that hypoxic stress (0.1% O2) decreased the expression of cytochrome P450 7A1 (CYP7A1), a rate-limiting enzyme involved in bile acid biosynthesis. Chenodeoxycholic acid (CDCA), a major component of bile acids, represses CYP7A1 by activating a transcriptional repressor named small heterodimer partner (SHP). We observed that hypoxia decreased the levels of both CDCA and SHP, suggesting that hypoxia repressed CYP7A1 without inducing SHP. The finding that overexpression of HIF-1α increased the activity of the CYP7A1 promoter suggested that hypoxia decreased the expression of CYP7A1 in a HIF-1-independent manner. Thus, the results of this study suggested that hypoxia decreased the activity of CYP7A1 by limiting its substrate O2, and by decreasing the transcription of CYP7A1. [BMB Reports 2016; 49(3): 173-178]
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