Angiopoietin-like protein 6 protects against methionine-choline deficient diet induced liver fibrosis by suppressing hepatic stellate cells activation via TGF-β1/Smad3 pathway.

Liver fibrosis, characterized by excessive extracellular matrix deposition, is a critical stage in chronic liver disease progression. Angiopoietin-like protein 6 (ANGPTL6), a hepatocyte-secreted protein involved in metabolism, has an unclear role in fibrosis. This study investigated ANGPTL6's function in hepatic fibrosis, focusing on its suppression of hepatic stellate cells (HSCs) activation via the transforming growth factor-beta 1/Smad3 (TGF-β1/Smad3) pathway. Mouse models of metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis were established using a methionine-choline deficient diet (MCD). Adeno-associated virus serotype 8 (AAV8) was used to overexpress ANGPTL6 in vivo, with TGF-beta receptor 2 (TGFBR2) co-overexpression for rescue studies. In human HSCs (LX-2 cells), gain- and loss-of-function experiments were performed. Fibrosis was assessed via histology, immunohistochemistry, western blot, and quantitative real-time polymerase chain reaction (qRT-PCR). ANGPTL6 was downregulated in fibrotic livers. Consistently, its overexpression attenuated MCD-induced liver damage, reducing serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, inflammation, and fibrosis markers. TGFBR2 co-expression reversed this protection, restoring TGF-β1/Smad3 activation. In LX-2 cells, ANGPTL6 suppressed TGF-β1-induced HSCs activation, an effect eliminated by TGFBR2 plasmid transfection but enhanced by TGFBR2 inhibition. These findings identify ANGPTL6 as an endogenous suppressor of HSCs activation through TGF-β1/Smad3 inhibition, highlighting its therapeutic potential for fibrotic liver diseases like MASH.