Epigenetic regulation of hepatic stellate cell activation

Gene Expression Profiles During Hepatic Stellate Cell Activation in Culture and In Vivo

DNMT1 controls LncRNA H19/ERK signal pathway in hepatic stellate cell activation and fibrosis

Keywords: : liver fibrosismyofibroblastshepatic stellate cellsinactivation into a quiescent-like phenotyperegression of liver fibrosis

Transforming growth factor-β (TGF-β) is considered to be a major factor contributing to liver fibrosis. We have previously shown that nuclear translocation of YB-1 antagonizes the TGF-β/Smad3 signaling in regulating collagen gene expression. More recently, we have demonstrated that the novel small compound HSc025 promotes nuclear translocation of YB-1, resulting in the improvement of skin and pulmonary fibrosis. Here, we presented evidence as to the mechanism by which HSc025 stimulates nuclear translocation of YB-1 and the pharmacological effects of HSc025 on a murine model of hepatic fibrosis. A proteomics approach and binding assays using HSc025-immobilized resin showed that HSc025 binds to the amino acid sequence within the C-tail region of YB-1. In addition, immunoprecipitation experiments and glutathione S-transferase pulldown assays identified poly(A)-binding protein (PABP) as one of the cytoplasmic anchor proteins of YB-1. HSc025 directly binds to YB-1 and interrupts its interaction with PABP, resulting in accelerated nuclear translocation of YB-1. Transfection of cells with PABP siRNA promoted nuclear translocation of YB-1 and subsequently inhibited basal and TGF-β-stimulated collagen gene expression. Moreover, HSc025 significantly suppressed collagen gene expression in cultured activated hepatic stellate cells. Oral administration of HSc025 to mice with carbon tetrachloride-induced hepatic fibrosis improved liver injury as well as the degree of hepatic fibrosis. Altogether, the results provide a novel insight into therapy for organ fibrosis using YB-1 modulators.

Hepatic stellate cells (HSCs), vitamin A-storing liver pericytes, undergo myofibroblastic trans-differentiation or "activation" to participate in liver wound healing. This cellular process involves loss of regulation by adipogenic transcription factors such as peroxisome proliferator-activated receptor γ (PPARγ). Necdin, a melanoma antigen family protein, promotes neuronal and myogenic differentiation while inhibiting adipogenesis. The present study demonstrates that necdin is selectively expressed in HSCs among different liver cell types and induced during their activation in vitro and in vivo. Silencing of necdin with adenovirally expressed shRNA, reverses activated HSCs to quiescent cells in a manner dependent on PPARγ and suppressed canonical Wnt signaling. Promoter analysis, site-directed mutagenesis, and chromatin immunoprecipitation demonstrate that Wnt10b, a canonical Wnt induced in activated HSCs, is a direct target of necdin. Necdin silencing abrogates three epigenetic signatures implicated in repression of PPARγ: increased MeCP2 (methyl CpG binding protein 2) and HP-1α co-repressor recruitments to Pparγ promoter and enhanced H3K27 dimethylation at the exon 5 locus, again in a manner dependent on suppressed canonical Wnt. These epigenetic effects are reproduced by antagonism of canonical Wnt signaling with Dikkopf-1. Our results demonstrate a novel necdin-Wnt pathway, which serves to mediate antiadipogenic HSC trans-differentiation via epigenetic repression of PPARγ.

ObjectiveAlthough glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor-β superfamily, its function in liver fibrosis has rarely been studied. Here, we investigated the role...

Chronic liver diseases (CLD) represent a worldwide health problem. While CLDs may have diverse etiologies, a common pathogenic denominator is the presence of liver fibrosis. Cirrhosis, the end-stage of CLD, is characterized by extensive fibrosis and is markedly associated with the development of hepatocellular carcinoma. The most important event in hepatic fibrogenesis is the activation of hepatic stellate cells (HSC) following liver injury. Activated HSCs acquire a myofibroblast-like phenotype becoming proliferative, fibrogenic, and contractile cells. While transient activation of HSCs is part of the physiological mechanisms of tissue repair, protracted activation of a wound healing reaction leads to organ fibrosis. The phenotypic changes of activated HSCs involve epigenetic mechanisms mediated by non-coding RNAs (ncRNA) as well as by changes in DNA methylation and histone modifications. During CLD these epigenetic mechanisms become deregulated, with alterations in the expression and activity of epigenetic modulators. Here we provide an overview of the epigenetic alterations involved in fibrogenic HSCs transdifferentiation with particular focus on histones acetylation changes. We also discuss recent studies supporting the promising therapeutic potential of histone deacetylase inhibitors in liver fibrosis.

Activation of hepatic stellate cells (HSCs) is a prominent driver of liver fibrosis. This study was designed to investigate the effect of exosomes derived from natural killer (NK) cells on HSC activation and liver fibrosis. The exosomes were isolated from NK-92MI cells (NK-Exo) and identified by transmission electron microscopy, nanoparticle tracking analysis, and western blot. Then NK-Exo was administered into TGF-β1-treated LX-2 cells (human HSC line) and mice with CCl4-induced liver fibrosis. LX-2 cell proliferation was determined by CCK-8 assay. The levels of α-SMA and CoL1A1 were measured by qRT-PCR and western blot to evaluate HSC activation. Serum levels of AST and ALT were measured. Hematoxylin-eosin, Masson staining, and Sirius Red staining were performed to assess the pathological changes and collagen deposition. Cell supernatant derived from NK-92MI cells inhibited TGF-β1-induced HSC proliferation and activation in LX-2 cells, and this effect was counteracted by the exosome inhibitor GW4869. Further assays confirmed that NK-Exo treatment significantly inhibited TGF-β1-induced HSC proliferation and activation. Moreover, NK-Exo administration alleviated CCl4-induced liver fibrosis in mice. NK-Exo inhibited TGF-β1-induced HSC activation and CCl4-induced liver fibrosis.

MicroRNA (miRNA)-mediated gene regulation contributes to liver pathophysiology, including hepatic stellate cell (HSC) activation and fibrosis progression. Here, we investigated the role of miR-942 in human liver fibrosis. The expression of miR-942, HSC activation markers, transforming growth factor-beta pseudoreceptor BMP and activin membrane-bound inhibitor (BAMBI), as well as collagen deposition, were investigated in 100 liver specimens from patients with varying degree of hepatitis B virus (HBV)-related fibrosis. Human primary HSCs and the immortalized cell line (LX2 cells) were used for functional studies. We found that miR-942 expression was upregulated in activated HSCs and correlated inversely with BAMBI expression in liver fibrosis progression. Transforming growth factor beta (TGF-β) and lipopolyssacharide (LPS), two major drivers of liver fibrosis and inflammation, induce miR-942 expression in HSCs via Smad2/3 respective NF-κB/p50 binding to the miR-942 promoter. Mechanistically, the induced miR-942 degrades BAMBI mRNA in HSCs, thereby sensitizing the cells for fibrogenic TGF-β signaling and also partly mediates LPS-induced proinflammatory HSC fate. In conclusion, the TGF-β and LPS-induced miR-942 mediates HSC activation through downregulation of BAMBI in human liver fibrosis. Our study provides new insights on the molecular mechanism of HSC activation and fibrosis.

Vitamin A-coupled liposome system targeting free cholesterol accumulation in hepatic stellate cells offers a beneficial therapeutic strategy for liver fibrosis.

Liver fibrosis is the common outcome of almost all cases of chronic liver disease. The hallmark of liver fibrosis is the activation of hepatic stellate cells (HSCs). microRNA‑34a (miR‑34a), which regulates a plethora of target proteins involved in the cell cycle, apoptosis, differentiation and cellular development, is found to be upregulated in both activated HSCs and liver fibrosis, while it is consistently downregulated in numerous cancer types. In the present study, the possible mechanisms underlying the role of miR‑34a and miR‑34c in the activation of the HSCs was investigated. Through bioinformatics analysis and a luciferase reporter assay, five genes were identified to be the target genes of miR‑34a and miR‑34c. Of these, peroxisome proliferator‑activated receptor γ (PPARγ) was selected for further investigation. Mutation luciferase reporter assay confirmed the direct interaction of PPARγ and miR‑34a and miR‑34c. Western blot analysis and quantitative polymerase chain reaction demonstrated that the expression of PPARγ was negatively correlated with the expression of miR‑34a and miR‑34c during the activation of HSCs. In activated human HSCs, inhibitors of miR‑34a and miR‑34c upregulated the expression of PPARγ and downregulated the expression of α‑smooth muscle actin. These data suggested that the miR‑34 family may be involved the process of liver fibrosis by targeting PPARγ.

Normal liver reveals only low expression of the facilitative glucose transporter (GLUT) 1. Recently, we have shown that GLUT1 expression is increased in hepatocellular carcinoma (HCC), where GLUT1 acts as a tumor promotor. Hyperglycemia is one of the factors known to induce and promote hepatic fibrogenesis, and the activation of hepatic stellate cells (HSCs) is the key event of hepatic fibrosis. Furthermore, these cells form and transduce the HCC stroma. The aim of this study was to assess the expression and functional role of GLUT1 in hepatic fibrosis. Methods and Results: Hepatic GLUT1 expression was significantly increased in different murine models of hepatic fibrosis, namely chronic TAA or CCl4-application, bile-duct-ligation and dietary models of non-alcoholic steatohepatitis (NASH). Also in cirrhotic human livers and human NASH GLUT1 expression was increased. Interestingly, hepatic GLUT1 expression revealed a significant correlation with collagen I and alpha-sma levels indicating activated HSCs as cellular source of GLUT1, which was confirmed by immunohistochemical analysis. In line with this, we found that GLUT1 expression increased during in vitro activation of primary murine and human HSCs. To gain insight in the functional role of GLUT1 in activated HSCs we inhibited GLUT1 expression with siRNA or the specific GLUT1 inhibitor WZB117 and found that GLUT1 suppression impaired glucose uptake and lactate secretion of HSCs indicative for reduced anaerobic glycolysis. Functional analysis demonstrated that reduced GLUT1 expression led to lower apoptosis resistance of HSCs. Transgenic GLUT1 knockdown mice subjected to TAA induced liver fibrosis model revealed less pronounced liver damage than WT animals confirmed by hepatic sirius red staining and alpha-sma protein expression. In line with this, treatment with GLUT1 inhibitor WZB117 in combination with the NASH inducing MCD diet resulted in less hepatic alpha-sma and collagen I expression than animals treated with vehicle. Conclusions: Increased GLUT1 expression during HSC activation functionally affects HSCs, and herewith, likely promotes the development and progression of hepatic fibrosis. Therefore and based on its known role as tumor-promotor, GLUT1 appears as attractive novel target to inhibit the progression of chronic liver disease. Corresponding author: Czech, Barbara E-Mail:barbara.czech@ukr.de

The activation of hepatic stellate cells (HSCs) from a quiescent state is a cause of liver fibrosis and a therapeutic target. HSCs are resident mesenchymal cells located in the space of Disse, exhibiting specialized morphological characteristics such as a stellate shape, large lipid droplets, and direct adhesions to hepatocytes via microprojections called HSC spines. Morphological alterations in HSCs play a crucial role in initiating their activation. However, the mechanisms regulating these changes remain unexplored. In this study, we analyzed the morphological alterations associated with HSC activation in vivo using carbon tetrachloride treatment and identified the key factors regulating these changes in vitro. Following carbon tetrachloride treatment, HSCs exhibited shortened cell processes and HSC spines, adopting an oval shape. Subsequently, the HSCs underwent further morphological changes into two activated forms: flattened and complex shapes. In vitro, activation of cell division cycle 42 (Cdc42) maintained the morphological characteristics of quiescent HSCs. Cdc42 activation in HSC cell lines inhibited the expression of markers associated with activated HSCs. Cdc42 inhibitor treatment in vivo prevented quiescent HSCs from maintaining their morphological characteristics and hindered activated HSCs from reverting to the quiescent state. In addition, HSCs around fibrotic areas in the human liver exhibited morphological alterations indicative of early activation. These findings demonstrate that Cdc42 is a crucial regulator of morphological and molecular alterations associated with HSC activation, identifying it as a novel target for the development of therapeutic agents against liver fibrosis.NEW & NOTEWORTHY The activation of hepatic stellate cells from a quiescent state is a cause and a therapeutic target for liver fibrosis. Morphological alterations in the hepatic stellate cells play a critical role in initiating their activation. However, the mechanisms that regulate these alterations remain unexplored. Our results indicate that cell division cycle 42 is a crucial regulator of hepatic stellate cell activation and a novel target for the development of therapeutic agents against liver fibrosis.

Aryl Hydrocarbon Receptor Signaling Prevents Activation of Hepatic Stellate Cells and Liver Fibrogenesis in Mice

BackgroundRecent studies have shown that microRNA-29 (miR-29) is significantly decreased in liver fibrosis and that its downregulation influences the activation of hepatic stellate cells (HSCs). In addition, inhibition of the activity of histone deacetylases 4 (HDAC4) has been shown to strongly reduce HSC activation in the context of liver fibrosis.ObjectivesIn this study, we examined whether miR-29a was involved in the regulation of HDAC4 and modulation of the profibrogenic phenotype in HSCs.MethodsWe employed miR-29a transgenic mice (miR-29aTg mice) and wild-type littermates to clarify the role of miR-29a in cholestatic liver fibrosis, using the bile duct-ligation (BDL) mouse model. Primary HSCs from both mice were treated with a miR-29a mimic and antisense inhibitor in order to analyze changes in profibrogenic gene expression and HSC activation using real-time quantitative RT-PCR, immunofluorescence staining, western blotting, and cell proliferation and migration assays.ResultsAfter BDL, overexpression of miR-29a decreased collagen-1α1, HDAC4 and activated HSC markers of glial fibrillary acidic protein expression in miR-29aTg mice compared to wild-type littermates. Overexpression of miR-29a and HDAC4 RNA-interference decreased the expression of fibrotic genes, HDAC4 signaling, and HSC migration and proliferation. In contrast, knockdown of miR-29a with an antisense inhibitor increased HDAC4 function, restored HSC migration, and accelerated HSC proliferation.ConclusionsOur results indicate that miR-29a ameliorates cholestatic liver fibrosis after BDL, at least partially, by modulating the profibrogenic phenotype of HSCs through inhibition of HDAC4 function.