Interleukin‐22 alleviates alcohol‐associated hepatic fibrosis, inhibits autophagy, and suppresses the PI3K/AKT/mTOR pathway in mice

Background Alcohol‐associated hepatic fibrosis is a widespread liver disease with no effective treatment. Recent studies have indicated that interleukin‐22 (IL‐22) can ameliorate alcohol‐associated liver disease. However, the mechanism underlying the role of IL‐22 in alcohol‐associated hepatic fibrosis remains unclear. Therefore, we investigated the effect of IL‐22 in a mouse model of alcohol‐associated hepatic fibrosis and its underlying mechanisms. Methods Alcohol‐associated hepatic fibrosis was induced by feeding male C57BL/6J mice with a Lieber‐DeCarli liquid diet containing 4% ethyl alcohol for 8 weeks and injecting them with 5% tetrachloromethane (CCl4) intraperitoneally for the last 4 weeks. During the last 4 weeks, IL‐22 was also administered. We investigated the role of IL‐22 in autophagy and the PI3K/AKT/mTOR signaling pathway using a 3‐methyladenine intraperitoneal injection in the mice treated with IL‐22. The effects of IL‐22 on alcohol‐associated hepatic fibrosis, autophagy‐related gene expression, and PI3K/AKT/mTOR activity were assessed using histopathology, biochemical analysis, transmission electron microscopy, quantitative real‐time PCR, immunohistochemistry, and western blotting. Results Mice treated with ethanol and CCl4 displayed distinct liver injuries, including hepatocyte necrosis, inflammatory cell infiltration, and hepatic fibrosis, which were substantially attenuated by IL‐22 treatment. In addition, we found that IL‐22 regulated the expression of autophagy‐related genes and inhibited the PI3K/AKT/mTOR pathway, as evidenced by the reduction in p‐PI3K, p‐AKT, and p‐mTOR expression after IL‐22 treatment. Conclusions IL‐22 exerts a marked protective effect against alcohol‐associated hepatic fibrosis. Its effect may be partly related to the alteration of autophagy‐related gene expression and inhibition of the PI3K/AKT/mTOR pathway in the liver. Mice fed with Lieber‐DeCarli liquid diet including 4% ethanol and injected intraperitoneally with 5% CCl4 displayed more distinct collagen fiber accumulation than control mice. Autophagy and the PI3K/AKT/mTOR pathway were activated in the liver. We demonstrated that IL‐22 alleviated hepatic fibrosis in ethanol plus CCl4‐induced mice. Our results indicated that the anti‐fibrotic effect of IL‐22 might be related to inhibition of autophagy and the PI3K/AKT/mTOR pathway. Our study provides new insights into the molecular mechanisms of IL‐22 in alcohol‐associated hepatic fibrosis.