Increased Tim-3 expression alleviates liver injury by regulating macrophage activation in MCD-induced NASH mice

As an immune checkpoint,Tim-3 plays roles in the regulation of both adaptive and innate immune cells including macrophages and is greatly involved in chronic liver diseases.However,the precise roles of Tim-3 in nonalcoholic steatohepatitis(NASH)remain unstated.In the current study,we analyzed Tim-3 expression on different subpopulations of liver macrophages and further investigated the potential roles of Tim-3 on hepatic macrophages in methionine and choline-deficient diet(MCD)-induced NASH mice.The results of flow cytometry demonstrated the significantly increased expression of Tim-3 on all detected liver macrophage subsets in MCD mice,including F4/80^(+)CD11b^(+),F4/80^(+)CD68^(+),and F4/80^(+)CD169^(+)macrophages.Remarkably,Tim-3 knockout(KO)significantly accelerated MCD-induced liver steatosis,displaying higher serum ALT,larger hepatic vacuolation,more liver lipid deposition,and more severe liver fibrosis.Moreover,compared with wild-type C57BL/6 mice,Tim-3 KO MCD mice demonstrated an enhanced expression of NOX2,NLRP3,and caspase-1 p20 together with increased generation of IL-1βand IL-18 in livers.In vitro studies demonstrated that Tim-3 negatively regulated the production of reactive oxygen species(ROS)and related downstream pro-inflammatory cytokine secretion of IL-1βand IL-18 in macrophages.Exogenous administration of N-Acetyl-L-cysteine(NAC),a small molecular inhibitor of ROS,remarkably suppressed caspase-1 p20 expression and IL-1βand IL-18 production in livers of Tim-3 KO mice,thus significantly reducing the severity of steatohepatitis induced by MCD.In conclusion,Tim-3 is a promising protector in MCD-induced steatohepatitis by controlling ROS and the associated pro-inflammatory cytokine production in macrophages.