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HNF4a regulates hepatic peroxisomal biogenesis and fatty acid elongation during the thermogenic response

ABSTRACT: We observed gene expression changes in livers of cold exposed mice along with changes in global genome occupancy for the transcription factor HNF4a, RNA polymerase II and the histone marker H3K27Ac, suggesting a hepatic transcriptional response to cold xposure.

ORGANISM(S): Mus musculus

PROVIDER: GSE213460 | GEO | 2023/04/14

REPOSITORIES: GEO

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Project description:To study the role of hepatic nuclear factor _ alpha (HNF4a_ in hepatogenesis, we used loxP-Cre technology to eliminate it from developing mouse livers. A comparison of control and experimental livers revealed that hepatocytes lacking HNF4a_failed to fully differentiate. Specifically, HNF4a null liver cells failed to express genes that are markers of mature hepatocytes including Gys2, Pck1, and G6pc. These cells also failed to form normal cellular junctions, which are critical for establishment of the hepatic epithelium [Parviz et al. (2003) Nat.Genet. 34, 292-96]. Because HNF4a functions as a transcription factor, we hypothesized that it regulates liver development by controlling the expression of genes whose products are essential in executing cellular differentiation and morphogenesis. To identify these genes, we compared expression profiles between HNF4a null and wild type E18.5 fetal livers using Affymetrix gene arrays. We identified 564 genes whose expression was decreased by at least 2.5-fold and 34 genes whose expression was increased by at least 2.5-fold when HNF4a was eliminated from hepatocytes. These represent genes involved in diverse molecular pathways, reflecting the pleiotropic phenotype of HNF4a null livers. Our goal was to use the information from the gene arrays to define the mechanisms through which HNF4a controls the generation of the hepatic epithelium. We identified 27 genes from our list of downregulated genes with either defined or predicted roles in cellular junctions and/or adhesion. Most striking was that loss of HNF4a altered the expression of genes encoding proteins involved in virtually all types of cellular junctions including tight junctions (Cldn1, Cldn-2, Cldn-12, Ocln, F11r/Jam1, Cxadr, Crb3), adherens junctions (Cdh1), desmosomes (Dsc2, Pkp2, Krt2-8), and gap junctions (Gjb1, Gjb2). Using immunoblotting and immunohistochemistry, we found that the expression of proteins representing each of these junction types was reduced or absent. Analysis of these genes for the presence of putative HNF4a binding sites revealed that 25 of 27 contain such sites. We have used chromatin immunoprecipitation to confirm that HNF4a occupies several of these sites in vivo, including Cdh1, Cldn1, and F11r/Jam1. From these data, we conclude that HNF4_ is a central mediator of the fully differentiated hepatocyte gene expression program and that it orchestrates the expression of cell junction and adhesion proteins required for establishing the hepatic epithelium. Experiment Overall Design: comparison of three hnf4 null livers to three control.

Project description:Intermittent fasting (IF) increases lifespan, decreases metabolic disease phenotypes, and cancer risk in model organisms, but the mechanisms mediating these effects are not fully characterized. In particular, the altered transcriptional programming has yet to be defined in key fasting responsive tissues such as liver from animals undergoing intermittent fasting. In this study, we employed every-other-day-fasting (EODF) in mice and high-resolution proteome analysis of liver and blood plasma as a screening tool to identify key regulated pathways with comparison to ad libitum fed animals. We observed many changes in the liver proteome abundance profile that were distinct from those observed after a single bout of fasting. Key among these were the induction by EODF of de novo lipogenesis (DNL) and cholesterol biosynthesis pathway enzymes, which were mirrored by related metabolite changes such as increased triacylglycerides and HMG-CoA in EODF liver of fed mice. Paradoxically, we also observed the up-regulation of mitochondrial proteins associated with fatty-acid beta oxidation including ACOT2, which is known to accelerate this pathway in vivo. The most surprising observation was the EODF-mediated 16-fold down-regulation of alpha-1-antitrypsin (SERPINA1E) in liver, which is an abundant plasma protein made exclusively in this tissue. Plasma proteome analysis confirmed a 3-fold decrease in SERPINA1E after 2 weeks of EODF among other significant changes such as increased levels of APOA4, a finding in common with previous human EODF intervention studies. We determined that in liver the SREBP1c and HNF4A transcription factors were playing a major role in the up-regulation of lipid/cholesterol synthesis and down-regulation of AAT, respectively. Further characterization of HNF4A function suggested a global inhibition of its ability to bind promoters of target genes in livers from EODF animals, which we hypothesize is mediated by either increased linoleic acid binding, or post translational modifications of HNF4A protein in EODF animal liver tissue. Together these data provide a comprehensive Omics resource highlighting the key changes observed during the intermittent fasting response in a model animal.

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HNF4a regulates hepatic peroxisomal biogenesis and fatty acid elongation during the thermogenic response

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