PGC-1α inhibits M2 macrophage polarization and alleviates liver fibrosis following hepatic ischemia reperfusion injury.

Oxidative stress can induce inflammation, promoting macrophage polarization and liver fibrosis following hepatic ischemia-reperfusion (I/R). Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) has anti-oxidant and anti-inflammatory activity. However, how PGC-1α regulates macrophage polarization following hepatic I/R remains largely unknown. Male C57BL/6 wild-type mice were pre-treated with vehicle or trichostatin A (TSA) for 2 days and subjected to surgical induction of I/R. Liver injury and fibrosis in individual mice were examined longitudinally and the expression levels of IL-6, STAT3, M2-type macrophage markers, Collagen I and α-SMA in the liver of mice were analyzed by immunohistochemistry, RT-qPCR and Western blot. The potential interaction of PGC-1α with phosphorylated NF-kBp65 was determined by immunoprecipitation. The impacts of PGC-1α deficiency in hepatocytes on their IL-6 production and macrophage polarization were tested in a Transwell co-culture system. Moreover, the M2-type macrophage polarization and liver fibrosis were examined in hepatocyte-specific PGC-1α knockout mice and AAV8-mediated PGC-1α over-expressing mice following liver I/R. The down-regulated PGC-1α expression by I/R was negatively correlated with IL-6 levels in the liver of I/R mice and PGC-1α deficiency enhanced IL-6 expression, STAT3 activation and M2-type macrophage polarization in the I/R mice, which were abrogated by TSA treatment. In addition, PGC-1α directly interacted with phosphorylated NF-kBp65 in I/R livers. Hepatocyte-specific PGC-1α deficiency increased IL-6 production and promoted macrophage polarization toward M2 type when co-culture. More importantly, administration with AAV8-PGC-1α rescued the I/R-induced liver fibrosis by inhibiting the IL-6/JAK2/STAT3 signaling and M2-type macrophage polarization in the liver. These results suggest that PGC-1α may alleviate the I/R-induced liver fibrosis by attenuating the IL-6/JAK2/STAT3 signaling to limit M2-type macrophage polarization. PGC-1α may be a therapeutic target for the treatment of liver fibrosis.

LncRNA Airn maintains LSEC differentiation to alleviate liver fibrosis via the KLF2-eNOS-sGC pathway.

BACKGROUND: Long noncoding RNAs (lncRNAs) have emerged as important regulators in a variety of human diseases. The dysregulation of liver sinusoidal endothelial cell (LSEC) phenotype is a critical early event in the fibrotic process. However, the biological function of lncRNAs in LSEC still remains unclear. METHODS: The expression level of lncRNA Airn was evaluated in both human fibrotic livers and serums, as well as mouse fibrotic livers. Gain- and loss-of-function experiments were performed to detect the effect of Airn on LSEC differentiation and hepatic stellate cell (HSC) activation in liver fibrosis. Furthermore, RIP, RNA pull-down-immunoblotting, and ChIP experiments were performed to explore the underlying mechanisms of Airn. RESULTS: We have identified Airn was significantly upregulated in liver tissues and LSEC of carbon tetrachloride (CCl4)-induced liver fibrosis mouse model. Moreover, the expression of AIRN in fibrotic human liver tissues and serums was remarkably increased compared with healthy controls. In vivo studies showed that Airn deficiency aggravated CCl4- and bile duct ligation (BDL)-induced liver fibrosis, while Airn over-expression by AAV8 alleviated CCl4-induced liver fibrosis. Furthermore, we revealed that Airn maintained LSEC differentiation in vivo and in vitro. Additionally, Airn inhibited HSC activation indirectly by regulating LSEC differentiation and promoted hepatocyte (HC) proliferation by increasing paracrine secretion of Wnt2a and HGF from LSEC. Mechanistically, Airn interacted with EZH2 to maintain LSEC differentiation through KLF2-eNOS-sGC pathway, thereby maintaining HSC quiescence and promoting HC proliferation. CONCLUSIONS: Our work identified that Airn is beneficial to liver fibrosis by maintaining LSEC differentiation and might be a serum biomarker for liver fibrogenesis.

Transcriptional factor ATF3 promotes liver fibrosis via activating hepatic stellate cells.

The excessive accumulation of extracellular matrix (ECM) is a key feature of liver fibrosis and the activated hepatic stellate cells (HSCs) are the major producer of ECM proteins. However, the precise mechanisms and target molecules that are involved in liver fibrosis remain unclear. In this study, we reported that activating transcription factor 3 (ATF3) was over-expressed in mice and human fibrotic livers, in activated HSCs and injured hepatocytes (HCs). Both in vivo and in vitro study have revealed that silencing ATF3 reduced the expression of pro-fibrotic genes and inhibited the activation of HSCs, thus alleviating the extent of liver fibrosis, indicating a potential protective role of ATF3 knockdown. However, ATF3 was not involved in either the apoptosis or proliferation of HCs. In addition, our data illustrated that increased nuclear localization of ATF3 promoted the transcription of fibrogenic genes and lnc-SCARNA10, which functioned as a novel positive regulator of TGF-ß signaling in liver fibrogenesis by recruiting SMAD3 to the promoter of these genes. Interestingly, further study also demonstrated that lnc-SCARNA10 promoted the expression of ATF3 in a TGF-ß/SMAD3-dependent manner, revealing a TGF-ß/ATF3/lnc-SCARNA10 axis that contributed to liver fibrosis by activating HSCs. Taken together, our data provide a molecular mechanism implicating induced ATF3 in liver fibrosis, suggesting that ATF3 may represent a useful target in the development of therapeutic strategies for liver fibrosis.

LncRNA Meg8 suppresses activation of hepatic stellate cells and epithelial-mesenchymal transition of hepatocytes via the Notch pathway.

Long non-coding RNAs (lncRNAs) play an important role in various physiological and pathological processes. However, the biological role of lncRNA Meg8 in liver fibrosis is largely unknown. In this study, we found that Meg8 was over-expressed in activated hepatic stellate cells (HSCs), injured hepatocytes (HCs) and fibrotic livers. Furthermore, we revealed that Meg8 suppressed the expression of the pro-fibrogenic and proliferation genes in activated HSCs. In addition, silencing Meg8 significantly inhibited the expression of the epithelial markers, while noticeably promoted the expression of the mesenchymal markers in primary HCs and AML12 cells. Mechanistically, we demonstrated that Meg8 suppressed HSCs activation and epithelial-mesenchymal transition (EMT) of HCs through inhibiting the Notch pathway. In conclusion, our findings indicate that Meg8 may serve as a novel protective molecule and a potential therapeutic target of liver fibrosis.

The hepatocyte-specifically expressed lnc-HSER alleviates hepatic fibrosis by inhibiting hepatocyte apoptosis and epithelial-mesenchymal transition.

Liver fibrosis leading to cirrhosis is one of the major health burdens worldwide with currently limited therapeutic options available. Long noncoding RNAs (lncRNAs) play important roles in various biological and pathological processes in a cell- or tissue-specific manner. However, there is still an important gap in the understanding of the role of hepatocyte-specific lncRNAs in liver fibrosis. Methods: The expressions of lnc-Hser in human and mice fibrotic livers as well as primary hepatocytes (HCs) of mice developing liver fibrosis were determined by real-time RT-PCR. The roles and mechanisms of lnc-Hser in HCs and liver fibrosis were determined in vitro and in vivo. Results: In this study, we have identified a hepatocyte-specifically expressed lnc-Hser, which was reduced in human and mice fibrotic livers as well as primary HCs of mice developing liver fibrosis. We have shown that silencing lnc-Hser aggravated liver fibrosis both in vitro and in vivo through inducing the epithelial-mesenchymal transition (EMT) and the apoptosis of HCs. In addition, knockdown of lnc-Hser promoted hepatic stellate cells (HSCs) activation through the signals derived from injured HCs. Mechanistically, we have revealed that lnc-Hser inhibited HCs apoptosis via the C5AR1-Hippo-YAP pathway and suppressed HCs EMT via the Notch signaling. Conclusions: Our work has identified a hepatocyte-specific lnc-HSER that regulates liver fibrosis, providing a proof that this molecule is a novel biomarker for damaged HCs and a potential target for anti-fibrotic therapy.