Adipsin in NASH

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Project Abstract The obesity pandemic brings with it multiple attendant metabolic comorbidities, including Non-Alcoholic Fatty Liver Disease (NAFLD). NAFLD is now the leading cause for chronic liver disease, with prevalence approaching 30% in certain populations, but may in fact be considered a “pre-disease” state for Non-Alcoholic Steatohepatitis (NASH) and associated liver fibrosis. NASH has no approved pharmacotherapy, and is thus the fastest-growing reason for liver transplantation. As the prevalence of obesity-related NASH continues to rise, and available livers for transplantation remain limiting, this unmet need grows more urgent. Intercellular crosstalk between lipid-laden hepatocytes and non-parenchymal cells (NPCs), including hepatic stellate cells (HSC), determine obesity-induced liver pathology. To determine signals that mediate hepatocyte- NPC crosstalk, we performed transcriptomic analysis in hepatocytes isolated from mice fed a NASH-provoking diet. When compared to normal chow-fed mice, we found significantly increased expression of Cfd (Complement factor d), which encodes Adipsin, a secreted protein thought uniquely produced in adipocytes that mediates complement factor C3 cleavage. We first confirmed these data in three other dietary NASH mouse models, as well as in liver biopsies from patients with NASH, all of which revealed increased liver (but not adipose) Adipsin in NASH. These robust correlations prompted us to test potential of Adipsin to mediate NASH phenotypes. First, as Adipsin cleaves complement factor C3 to two bioactive species – C3a, which binds C3aR1 on target cells, and C3b that drives alternative complement pathway activation – we analyzed C3 knockout mice fed NASH diet, which showed lower fibrosis than controls. Next, we transduced NASH diet-fed wildtype mice with a viral vector encoding shRNA to Cfd, which phenocopied lower fibrosis seen in C3 knockout animals, in both prevention and treatment strategies. Consistently, application of recombinant C3a increased HSC activity in vitro. These results suggest that aberrant liver Adipsin plays a pathogenic role in NASH, which we will test in Aim 1 of this application, including studies to test whether Adipsin-derived C3a acts directly on HSC C3aR1 to drive liver fibrosis. In Aim 2, we study mechanistic determinants of aberrant liver Adipsin in NASH. Preliminary data revealed a striking induction of the master adipogenic factor PPARγ2 in mouse and human NASH. These data prompt the hypothesis that a PPARγ2-mediated adipogenic reprogramming of hepatocytes in NASH is necessary and sufficient to drive Cfd expression in the obese liver. Achieving the goals of this application will identify mechanistic determinants of aberrant Adipsin expression and resultant liver pathology, and potentially lead to development of Adipsin or C3aR1 inhibitors for NASH-induced fibrosis.