A CB2 Agonist Alleviates Liver Fibrosis by Downregulating the ERK1/2 Signalling Pathway in Mouse Hepatic Fibrosis Model

Abstract Cannabinoid type 2 (CB2) receptors have been reported to display potent anti-fibrogenic properties in mice with carbon tetrachloride (CCL4)-induced hepatic fibrosis.However, the mechanism by which CB2 receptors inhibit fibrogenesis remains unclear. We aimed to study the effects of CB2 receptors in a mouse CCL4-induced hepatic fibrosis model. Hepatic fibrosis was induced by CCL4 administration in wild-type (WT) and CB2−/− mice. WT mice received vehicle, CCL4, AM1241 (CB2 receptor agonist) or AM1241 plus AM630 (CB2 receptor antagonist), with the AM1241 and AM1241 plus AM630 treatments injected intraperitoneally on each day of the 16-week CCL4 treatment. Real-time PCR and immunohistochemical staining were used to analyse α-smooth muscle actin (α-SMA) and profibrogenic marker (TGF-β1) expression and extracellular matrix (ECM) deposition (collagen-Ⅰ). HSC apoptosis were performed by TUNEL staining. Extracellular signal-regulated kinase (ERK1/2), cAMP response element-binding protein (CREB), Bcl-2, Bax and cleaved caspase-3 levels were characterized in mouse hepatic tissues via western blotting. Hepatic fibrosis was enhanced in CB2−/− mice compared to that in WT mice, and this phenomenon was alleviated in AM1241-treated WT mice. Moreover, the CB2 receptor agonist AM1241 decreased α-SMA, TGF-β1 and collagen-Ⅰ mRNA and protein expression and inhibited ERK1/2-CREB-Bcl-2 signalling pathway activity. Combined AM1241 and AM630 administration reversed the effects of AM1241. AM1241 inhibited hepatic stellate cell (HSC) activation, downregulated profibrogenic marker expression, decreased ECM deposition and alleviated fibrosis in WT mice. These effects were mediated at least in part by the induction of HSC apoptosis through ERK1/2-CREB-Bcl-2 downregulation. Thus, CB2 agonists are potential therapeutic agents for managing liver fibrosis.