DOT1L Suppresses Hepatic Stellate Cell Activation and Liver Fibrosis via an EDN1-Dependent Pathway

Background & Aims: Liver fibrosis, a consequence of chronic liver injury, can progress to cirrhosis and hepatocellular carcinoma, with hepatic stellate cell (HSC) activation being a central driver. The histone methyltransferase DOT1L, which catalyzes H3K79 methylation, has context-dependent roles in organ fibrosis, but its function in the liver remains unexplored. Given the significant downregulation of DOT1L observed in fibrotic livers, this study aims to investigate its specific role in HSC biology and liver fibrogenesis. Methods: Using both gain-of-function and loss-of-function approaches in vitro and HSC-specific DOT1L knockout mice (DOT1L ^f/f ; Lrat-cre) in vivo, we assessed the functional impact of DOT1L on HSC activation and liver fibrosis. Molecular mechanisms were also explored through pharmacological interventions. Results: DOT1L expression was significantly downregulated during HSC activation and in fibrotic livers. Knockdown of DOT1L promoted, while its overexpression suppressed, the expression of fibrogenic genes in HSCs. HSC-specific ablation of DOT1L spontaneously induced liver fibrosis in mice without external injury and exacerbated CCl ₄ -induced fibrogenesis. Mechanistically, DOT1L deficiency led to upregulation of Endothelin-1 (EDN1), and the ensuing fibrotic response was ameliorated by the endothelin receptor antagonist Bosentan. Conclusions: Our findings demonstrate a protective role for DOT1L in restraining HSC activation and liver fibrosis through suppression of EDN1 signaling. These results position DOT1L as a key epigenetic regulator in liver fibrogenesis.