Abstract
BACKGROUND: Activation of hepatic stellate cells (HSCs) is a key event in the initiation of liver fibrosis. CD4 T cells can modulate positively or negatively this process. Briefly, Th1 cells despite their pro-inflammatory properties have anti-fibrogenic properties in contrast to Th2 cells. We and others have demonstrated that IL-17A produced by Th17 cells has pro-fibrogenic properties as it promotes activation of HSCs via different mechanisms. Th17 cells also produce IL-22, an enigmatic cytokine with proinflammatory and hepatoprotective properties. In addition, IL-10 produced by regulatory T cells (Treg) negatively modulates activation of HSCs. AIMS: We hypothesized that liver fibrosis progression results from an alteration in the Th17/Treg ratio leading to an imbalance in the pro-fibrotic cytokine profile within the liver. METHODS: We examined ex vivo the frequency of Th17 and Treg populations and the cytokine profile of intrahepatic lymphocytes isolated from liver biopsy samples (n=32). We validated these cytokines profiles using in vivo model of fibrosis in transgenic mice and primary human HSCs. RESULTS: We observed increased Th17/Treg ratio in advanced (F4, Metavir) as compared to moderate or non-fibrosis (F0-F2). Furthermore, we observed a bias towards Th17/Th9 cytokine profile in fibrotic livers with viral-hepatitis, whereas the cytokine profile was Th17/Th2 in non-viral hepatitis. All biopsies exhibited a 5-fold increase in IL-22 in fibrotic livers (p=0.0082) irrespective of aetiology. In vivo, lack of IL-22 signaling protects against thioacetamide-induced fibrosis. IL-22RA1 Knockout mice have reduced collagen deposition measured by picro-sirius red staining (p=0.0009) and pro-fibrotic genes expression (ACTA2, LOXL2, TIMP-I, TGFb1, COL1A1) in comparison to wild-type littermates. In vitro stimulation of primary human HSCs with IL-22 sensitized them to suboptimal doses of TGF-b. RNA-seq analysis demonstrated activation of p38 in HSCs in response to IL-22 and chemical inhibition of p38 suppressed the pro-fibrogenic effect of IL-22. CONCLUSIONS: Our results suggest a dysregulated Th17/Treg ratio in advanced fibrosis coupled with distinct cytokine profile dependant on the aetiology of liver disease. Finally, we have identified IL-22 as a common factor in advanced liver fibrosis acting through sensitization of HSCs to TGF-b in a p38-dependent manner. FUNDING AGENCIES: CIHR