Endogenous production of n−3 polyunsaturated fatty acids protects mice from carbon tetrachloride‐induced liver fibrosis by regulating mTOR and Bcl‐2/Bax signalling pathways

New Findings What is the central question of this study? What is the protective benefit of n−3 polyunsaturated fatty acids (PUFAs) on liver fibrosis and what are the relevant signalling pathways in a transgenic mouse model overexpressing the mfat‐1 enzyme? What is the main finding and its importance? n−3 PUFA elevation strongly prevented carbon tetrachloride (CCl4)‐induced hepatic damage and inhibited the activation of hepatic stellate cells. n−3 PUFAs suppressed CCl4‐induced activation of mTOR, elevated Bcl‐2 expression, and reduced Bax level, suggesting that n−3 PUFAs can render strong protective effects against liver fibrosis and point to the potential of mfat‐1 gene therapy as a treatment modality. Liver fibrosis is a reversible wound healing response with excessive accumulation of extracellular matrix proteins. It is a globally prevalent disease with ultimately severe pathological consequences. However, very few current clinical therapeutic options are available. Nutritional addition of n−3 polyunsaturated fatty acids (PUFAs) can delay and lessen the development of liver fibrosis. Herein, this study examined the protective benefit of n−3 PUFAs on liver fibrosis and the relevant signalling pathways using a transgenic mouse model overexpressing the mfat‐1 enzyme that converts n−6 to n−3 PUFAs. Male C57BL/6 wild‐type and mfat‐1 transgenic mice were administered carbon tetrachloride (CCl4) or control corn oil by intraperitoneal injection. Blood alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were subsequently measured. CCl4‐induced hepatic damage and fibrosis were assessed using haematoxylin–eosin and Masson's trichrome staining. Western blot assays were used to detect and quantify fibrosis‐related proteins and mechanistic target of rapamycin (mTOR) and B‐cell lymphoma 2 (Bcl‐2)/Bcl‐2‐associated X protein (Bax) signalling components. The direct effect of docosahexaenoic acid (DHA) on primary hepatic stellate cells (HSCs) was also investigated in a co‐culture experiment. n−3 PUFAs, as a result of mfat‐1 activity, had a strong protective effect on liver fibrosis. The elevation of ALT and AST induced by CCl4 was significantly lessened in the mfat‐1 mice. Histological determination revealed the protective effects of n−3 PUFAs on liver inflammation and collagen deposition. Co‐incubation with DHA reduced the expression of profibrogenic factors in the primary HSCs. Moreover, mfat‐1 transgenic mice showed significant reduction of protei