Gα12 overexpression induced by miR16 dysregulation contributes to liver fibrosis by promoting autophagy in hepatic stellate cells

Background & aims: Hepatic stellate cells (HSCs) play a role in liver fibrosis. Guanine nucleotide-binding α-subunit12 (Gα ₁₂ ) converges signals from G protein-coupled receptors whose ligand levels are elevated in the environment during liver fibrosis; however, information is lacking on the effect of Gα ₁₂ on HSC trans-differentiation. This study investigated whether Gα ₁₂ is overexpressed in HSCs and, if so, its effect on liver fibrosis and the molecular basis. Methods: Gα ₁₂ expression was assessed by immunostaining, and immunoblot analyses of mouse fibrotic liver tissues and primary HSCs. The role of Gα ₁₂ for liver fibrosis was estimated using toxicant injury mouse model with Gα ₁₂ gene knockout and/or HSC-specific Gα ₁₂ delivery using lentiviral vectors, and primary HSCs and LX-2 cells with microRNA (miR) inhibitor, overexpression vectors, or adenoviruses. miR-16, Gα ₁₂ , and LC3 were examined in fibrosis patient samples. Results: Gα ₁₂ was overexpressed in activated HSCs and fibrotic liver, and was colocalized with desmin. In a CCl ₄ -induced fibrosis mouse model, Gα ₁₂ ablation prevented increases in fibrosis and liver injury. This effect was attenuated by HSC-specific lentiviral delivery of Gα ₁₂ . Moreover, Gα ₁₂ activation promoted autophagy accompanying JNK-dependent ATG12-5 conjugation. In addition, we found that miR-16 was a direct inhibitor of de novo synthesis of Gα ₁₂ . Modulations of miR-16 altered autophagy in HSCs. In a fibrosis animal model or patients with severe fibrosis, miR-16 levels were lower than their corresponding controls. Consistently, cirrhotic patient liver tissues showed Gα ₁₂ and LC3 up-regulation in desmin-positive areas. Conclusions: MiR-16 dysregulation in HSCs causes Gα ₁₂ overexpression, which activates HSCs by facilitating autophagy through ATG12-5 formation, implying that Gα ₁₂ and the regulatory molecules may serve targets in the amelioration of liver fibrosis. Lay Summary: Gα ₁₂ is up-regulated in activated HSCs as a consequence of dysregulation of a specific microRNA abundant in HSCs, facilitating the progression of liver fibrosis. This event is mediated by JNK-dependent ATG12-5 formation and promotion of autophagy. We suggest that Gα ₁₂ and associated regulators may serve as new targets in HSCs for treatment of liver fibrosis.