Essential role of suppressor of cytokine signaling 1 (SOCS1) in hepatocytes and macrophages in the regulation of liver fibrosis

The hepatic fibrogenic response is a protective mechanism activated by hepatocyte damage and is resolved upon elimination of the cause. However, persistent injuries cause liver fibrosis (LF) to evolve into cirrhosis, which promotes the development of hepatocellular carcinoma (HCC). Development of efficient treatments for LF requires better understanding the underlying molecular pathogenic mechanisms. The loss of suppressor of cytokine signaling 1 (SOCS1) expression promotes LF and HCC in human and mice, but the underlying mechanisms remain unclear. SOCS1 is a key regulator of immune cell activation. To investigate the anti-fibrogenic functions of SOCS1 in hepatocytes and macrophages, we generated mice lacking SOCS1 in hepatocytes (Socs1fl/flAlbCre) or macrophages (Socs1fl/flLysMCre) and evaluated hepatic fibrogenic response to carbon tetrachloride (CCl4). Socs1fl/flAlbCre and Socs1fl/flLysMCre mice showed severe LF characterized by increased collagen deposition, hydroxyproline content, myofibroblast accumulation along with elevated expression of Acta2 and Col1a1 genes. CCl4 treatment triggered significant damage to hepatocytes in Socs1fl/flAlbCre mice but not in Socs1fl/flLysMCre mice. In both mice CCl4 treatment reduced the expression of Mmp2 and increased the expression of Timp1. SOCS1 deficiency in hepatocytes or macrophages did not affect Il6, Tnfa or Tgfb, but diminished Infg and augmented Pdgfb expression. Both Socs1fl/flAlbCre and Socs1fl/flLysMCre livers showed increased mononuclear cell infiltration accompanied by elevated Ccl2 expression. Our findings show that SOCS1 exerts non-redundant functions in hepatocytes and macrophages to regulate the hepatic fibrogenic response possibly through limiting hepatocyte damage and the inflammatory response of macrophages, and support the idea of exploiting SOCS1 in LF treatment.