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Chromatin architecture as a checkpoint for NASH-associated liver injury

ABSTRACT: Nonalcoholic steatohepatitis (NASH) is a progressive liver disease that is characterized by liver injury, inflammation and fibrosis. NASH pathogenesis is linked to reprogramming of chromatin landscape in the liver that predisposes hepatocytes to stress-induced tissue injury. However, the molecular nature of the putative checkpoint that maintains chromatin architecture and preserves hepatocyte health remains elusive. Here we show that heterogeneous nuclear ribonucleoprotein U (hnRNPU), a nuclear matrix protein that governs chromatin architecture and gene transcription, is a critical factor that couples chromatin disruption to NASH pathogenesis. RNA-seq and ChIP-seq studies revealed an extensive overlap between hnRNPU occupancy and altered gene expression during NASH. Hepatocyte-specific inactivation of hnRNPU disrupted liver chromatin accessibility, activated the molecular signature of NASH and sensitized mice to diet-induced NASH pathogenesis. Mechanistically, hnRNPU deficiency stimulated the expression of a truncated isoform of TrkB that promotes inflammatory signaling in hepatocytes and stress-induced cell death. These findings illustrate a novel mechanism through which disruptions of chromatin architecture drive the emergence of disease-specific signaling patterns that promote liver injury and exacerbate NASH pathogenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE131336 | GEO | 2019/09/10

REPOSITORIES: GEO

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Project description:The mechanisms underlying the progression of non-alcoholic steatohepatitis (NASH) are not completely elucidated. In this study we have integrated gene expression profiling of liver biopsies of NASH patients with translational studies in a mouse model of steatohepatitis and with pharmacological interventions in isolated hepatocytes to identify a novel mechanism implicated in the pathogenesis of NASH. By using high-density oligonucleotide microarray analysis we identified a significant enrichment of known genes involved in the multi-step catalysis of long chain polyunsaturated fatty acids, including delta-5 and 6 desaturases. A combined inhibitor of delta-5 and delta-6 desaturases significantly reduced intracellular lipid accumulation and inflammatory gene expression in isolated hepatocytes. Gas chromatography analysis revealed impaired delta-5 desaturase activity toward the omega-3 pathway in livers from mice with high-fat diet (HFD)-induced NASH. Consistently, restoration of omega-3 index in transgenic fat-1 mice expressing an omega-3 desaturase, which allows the endogenous conversion of omega-6 into omega-3 fatty acids, produced a significant reduction in hepatic insulin resistance, hepatic steatosis, macrophage infiltration and necroinflammatory liver injury, accompanied by attenuated expression of genes involved in inflammation, fatty acid uptake and lipogenesis. These results were comparable to those obtained in a group of mice receiving a HFD supplemented with EPA/DHA. Of interest, hepatocytes from fat-1 mice or supplemented with EPA exhibited synergistic anti-steatotic and anti-inflammatory actions with the delta-5/ delta-6 inhibitor. Conclusion: These findings indicate that both endogenous and exogenous restoration of the hepatic balance between omega-6 and omega-3 fatty acids and/or modulation of desaturase activities exert preventive actions in NASH. The complete database comprised the expression measurements of 18185 genes for liver sample groups: 8 non-alcoholic steatohepatitis (NASH ) and 7 control samples. This dataset is part of the TransQST collection.

Project description:Background: Senescent hepatocytes accumulate in parallel with fibrosis progression during NASH. The mechanisms that enable progressive expansion of nonreplicating cell populations and the significance of that process in determining NASH outcomes are unclear. Many types of senescing cells upregulate the THBD-PAR-1 signaling axis to remain viable. Vorapaxar, an FDA-approved PAR-1 inhibitor, blocks the activity of that pathway. We used vorapaxar to determine if and how THBD-PAR1 signaling promotes fibrosis progression in NASH. Methods: We evaluated the THBD-PAR1 pathway in liver biopsies from NAFLD patient cohorts with a spectrum of liver fibrosis. Chow fed mice were treated with viral vectors to over-express p16 specifically in hepatocytes and induce replicative senescence. Effects on the THBD-PAR-1 axis and regenerative capacity were assessed; the transcriptome of p16 over-expressing hepatocytes was characterized and we examined how conditioned medium from senescent but viable (dubbed ‘undead’) hepatocytes reprograms hepatic stellate cells. A genetically obese mouse model of NASH with little liver fibrosis, and a diet-induced mouse model of NASH with advanced fibrosis were treated with vorapaxar to determine effects on hepatocyte senescence and liver damage. Results: Inducing senescence up-regulates the THBD-PAR1 signaling axis in hepatocytes and induces their expression of fibrogenic factors, including hedgehog ligands. Hepatocyte THBD-PAR1 signaling increases in NAFLD and supports sustained hepatocyte senescence that limits effective liver regeneration and promotes maladaptive repair. Inhibiting PAR-1 signaling with vorapaxar interrupts this process, reduces the burden of ‘undead’ senescent cells, and safely improves NASH and fibrosis despite ongoing lipotoxic stress Conclusion: The THBD-PAR1 signaling axis is a novel therapeutic target for NASH because blocking this pathway prevents accumulation of senescing but viable hepatocytes that generate factors that promote maladaptive liver repair.

Project description:We previously showed that severe liver diseases are characterized by expansion of liver progenitor cells (LPC), which correlates with disease severity. However, the origin and role of LPC in liver physiology and in the hepatic response to injury remains a contentious topic. We have now used genetic lineage tracing of Hnf1Î²-expressing biliary duct cells to assess their contribution to LPC expansion and hepatocyte generation during normal liver homeostasis, and following different types of liver injury. We found that ductular reaction cells in human cirrhotic livers express HNF1Î². However, HNF1Î² expression was not present in newly generated EpCAM-positive hepatocytes. Using a tamoxifen-inducible Hnf1Î²CreER/R26RYFP/LacZ mouse, we show that there is no contribution of the biliary epithelium to hepatocyte turnover during liver homeostasis in healthy mice. Moreover, after loss of liver mass, Hnf1Î²+ LPC did not contribute to hepatocyte regeneration. We also assessed the contribution of Hnf1Î²+ cells following acute and repeated liver injury. All animal models showed expansion of LPC, as assessed by immunostaining and gene expression profile of sorted YFP-positive cells. A contribution of Hnf1Î²+ LPC to hepatocyte generation was not detected in animal models of liver injury with preserved hepatocyte regenerative potential such as acute acetaminophen, carbon tetrachloride injury, or chronic diethoxycarbonyl-1,4-dihydro-collidin (DDC)-diet. However, in mice fed with choline-deficient ethionine-supplemented (CDE)-diet, which causes profound hepatocyte damage and arrest, a small number of hepatocytes were derived from Hnf1Î²+ cells. Conclusion: Hnf1Î²+ cells do not participate in hepatocyte turnover in the healthy liver or during liver regeneration after partial hepatectomy. After liver injury, LPC arise from the biliary duct epithelium, which gives rise to a limited number of hepatocytes only when hepatocyte regeneration is compromised. Transcriptomic profile using MoGeneST-2.0 chip from 3 samples of YFP+ CDE, 3 samples of YFP+ DDC, 2 samples of YFP+ UTR and 3 samples YFP-

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Chromatin architecture as a checkpoint for NASH-associated liver injury

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