Hepatocyte-specific C-C motif chemokine ligand 9 signaling promotes liver fibrosis progression in mice

Background and Aims: Liver fibrosis involves the activation of hepatic stellate cells (HSCs) and persistent inflammatory responses. Ccl9, a CC chemokine implicated in inflammation, has an undefined role in liver homeostasis. Our study investigates this murine homolog of human CCL15 to elucidate its role in the development of liver fibrosis. Approach and Results: We investigated the expression of Ccl9 and its upstream regulatory elements in liver fibrosis using mouse models induced by carbon tetrachloride (CCl 4 ), bile-duct ligation, and a high-fat, methionine- and choline-deficient diet. A significant increase in Ccl9 expression was observed in fibrotic liver tissues, predominantly in damaged hepatocytes, with Myc identified as a key driver of this upregulation. The role of Ccl9 was further elucidated through hepatocyte-specific knockout mice, neutralizing antibodies, and in vitro analyses of hepatic stellate cells (HSCs) and macrophages. Targeted deletion of Ccl9 in hepatocytes mitigated liver fibrosis and injury across multiple models, characterized by reduced inflammation and decreased monocyte/macrophage and neutrophil infiltration. Additionally, neutralizing Ccl9 in CCl 4 -induced models reduced both fibrosis and liver damage. Mechanistically, Ccl9 modulated macrophage infiltration, promoted M1 polarization, and regulated inflammatory cytokine responses through the Ccr1 receptor in models of hepatic injury induced by CCl 4 and bile-duct ligation. Furthermore, Ccl9 directly activated HSCs by recruiting Myh9 via Ccr1, thereby enhancing the Wnt signaling pathway through Myh9-mediated Gsk3β ubiquitination. Conclusions: Ccl9 is a significant contributor to liver fibrosis, influencing macrophage behavior and directly activating HSCs. Targeting Ccl9 offers a potential therapeutic approach for treating liver fibrosis.