IL-17Inhibits Apoptosis Of Hepatocytes And Involves In Liver Injury And Repairment

【Background】 Hepatic fibrosis is a reversible wound-healing response after liver injury.The major causes of hepatic fibrosis are chronic viral hepatitis, alcoholic liver disease andnon-alcoholic fatty liver disease (NAFLD). These diseases cause the accumulation ofECM, which further leads to the liver cirrhosis. These decades, liver cirrhosis draws moreand more attention for the great damage to our health. Lots of studies had showen thatcytokines such as TGF-β1、TNF-、PDGF and kupffer cells and hepatic stellate cells areinvolved in liver fibrosis, however, the pathogenesis of liver fibrosis are not fullyexplained in these studies. Recently, some researches showed that IL-17exacerbatedpulmonary fibrosis. Meanwhile, IL-17linked with various hepatic diseases and the levelsof IL-17proved to have a positive correlation with the degree of hepatic damage in thesehepatic diseases, such as alcoholic liver disease, primary biliary cirrhosis, viral hepatitis(especially HBV) and NAFLD. Our group found that the level of serum IL-17inCCl4-injected mouse had a dynamic change during the process of fibrogenesis andrecovery. Injection of extrinsic recombinant mouse IL-17accelerated the liver injury,while anti-mouse IL-17antibody injection could ameliorate the injury. However, the levelof IL-17in liver is still unknowen. Some researches proved that IL-17could directlyactivate hepatic stellate cells and stimulate kupffer cells to secret TGF-β1which in turnaggravate liver fibrosis. The mechanisms of how IL-17affects hepatocytes remaincontroversial. Some scientsts hold the view that IL-17can reduce the apoptosis ofhepatocytes which induced by IFN-γ, while some scientists agreed that IL-17does notplay a role in hepatocytes. In our study, we adopted CCl4-induced liver injury model in vivo and CCl4-induced hepatocytes injury in vitro, in order to find out the exactmechanism between IL-17and hepatic fibrosis/corrihosis.【Objectives】Firstly, we aimed to investigate the changes of IL-17level and IL-17Rexpression of mouse liver after CCl4-induced injury. Secondly, we clarified the underlyingmechanism of apotosis through IL-17and the potential pathway. Thirdly, we clarified theeffect of IL-17on kupffer cells and hepatic stellate cells.【Methods】(1) Histology and serum changes proved mice liver fibrosis model was wellestablished after8-week CCl4treatment.(2) We found that the expression of IL-17in liver increased gradually.(3) According to flow cytometry and TUNEL assay, we found about10%-15%normalhepatocytes may apotosis when cultuted in vitro, and CCl4treatment significantlyincreased the proportion of apotosis cell. Besides, apoptosis of both normal hepatocytesand CCl4-induced injured hepatocytes was ameliorated by IL-17treatment.(4) Using BrdU and Ki-67, we found the proliferation of hepatocytes was not affectedby IL-17.(5)The expression of TGF-β1showed no statistical significance confirmed by ELISA.(6)The expression of IL-17R, measured by flow cytometry showed IL-17R,significantly increased in CCl4-induced injured hepatocytes than normal hepatocytes.(7) Using Western blot techonology, we found IL-17concentration significantlyincreased the expression of Bcl-2, meanwhile decreased the expression of cleavedCaspase-3.(8) Compared with control group, the expression of TGF-β1and TNF-were decreasedafter kupffer cells were co-cultured with hepatocytes which pretreated with IL-17.(9) The expression of-SMA, TGF-β1, MMP3, Collagen-1and TIMP1were decreasedafter hepatic stellate cells were co-cultured with hepatocytes which pretreated with IL-17.【Conclusion】This study confirmed the expression of IL-17in liver significantlyincreased induced by CCl4. IL-17could inhibit cell apotosis through increasing Bcl-2anddecreasing cleaved Caspase-3. Besides, the kupffer cells and hepatic stellate cells areaffected by hepatocytes which pretreated with IL-17. IL-17inhibits apoptosis of hepatocytes and involves in liver injury and repairmen.