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Liver fibrosis, resulting from chronic and persistent injury to the liver, is a worldwide health problem. Advanced liver fibrosis results in cirrhosis, liver failure and even hepatocellular cancer (HCC), often eventually requiring liver transplantation, poses a huge health burden on the global community. However, the specific pathogenesis of liver fibrosis remains not fully understood. Numerous basic and clinical studies have provided evidence that epigenetic modifications, especially DNA methylation, might contribute to the activation of hepatic stellate cells (HSCs), the pivotal cell type responsible for the fibrous scar in liver. Here, reduced representation bisulfite sequencing (RRBS) and bisulfite pyrosequencing PCR (BSP) analysis identified hypermethylation status of Septin9 (Sept9) gene in liver fibrogenesis. Sept9 protein was dramatically decreased in livers of CCl4-treated mice and immortalized HSC-T6 cells exposed to TGF-β1. Nevertheless, the suppression of Sept9 could be blocked by DNMT3a-siRNA and DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (5-azadC). Overexpressed Sept9 attenuated TGF-β1-induced expression of myofibroblast markers α-SMA and Col1a1, accompanied by up-regulation of cell apoptosis-related proteins. Conversely, RNAi-mediated silencing of Sept9 enhanced accumulation of extracellular matrix. These observations suggested that Sept9 contributed to alleviate liver fibrosis might partially through promoting activated HSCs apoptosis and this anti-fibrogenesis effect might be blocked by DNMT-3a mediated methylation of Sept9. Therefore, pharmacological agents that inhibit Sept9 methylation and increase its expression could be considered as valuable treatments for liver fibrosis.

Recently, circular RNAs (circRNAs) have been frequently reported to be involved in hepatocellular carcinoma (HCC) development and progression. However, the role of circRNAs in hepatic fibrosis (HF) is still unclear. Our previous highthroughput screen revealed changes in many circRNAs in mice with carbon tetrachloride (CCl 4 )-induced HF. For instance, the expression of circPSD3, a circRNA derived from the Pleckstrin and Sec7 domain-containing 3 (PSD3) gene, was considerably downregulated in primary hepatic stellate cells (HSCs) and liver tissues of mice with CCl 4 -induced HF compared to those in the vehicle group. In vivo overexpression of circPSD3 using AAV8-circPSD3 arrested the deterioration of CCl 4 -induced HF as indicated by reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) content, liver hydroxyproline level, collagen deposition, and pro-fibrogenic gene and pro-inflammatory cytokine levels. Moreover, in vitro loss-of-function and gain-of-function analyses suggested that circPSD3 inhibited the activation and proliferation of HSCs. Mechanistically, circPSD3 served as a sponge for miR-92b-3p, subsequently promoting the expression of Smad7. In conclusion, our present findings reveal a novel mechanism by which circPSD3 alleviates hepatic fibrogenesis by targeting the miR-92b-3p/Smad7 axis, and they also indicate that circPSD3 may serve as a potential biomarker for HF.