95 MONOCYTE CHEMOATTRACTANT PROTEIN-1 (MCP-1) IS REQUIRED FOR THE DEVELOPMENT OF INFLAMMATION, OXIDATIVE DAMAGE AND FIBROSIS IN MURINE STEATOHEPATITIS

Abstract

as treatments for steatohepatitis. The mechanisms implicated remain poorly understood. Activation of PPARg induces expression of adiponectin, an anti-inflammatory and insulin-sensitising adipocytokine. Upon binding to specific receptors on liver cells, adiponectin activates the AMP-activated protein kinase (AMPK), stimulates b-oxidation and represses hepatic de novo lipogenesis. Also, adiponectin, through PPARa, activates fat oxidation and inhibits inflammatory reaction. Here we tested the hypothesis that the beneficial effect of PGZ on steatohepatitis results from reduced hepatic fat accumulation due to adiponectin-dependent stimulation of AMPK and PPARa. Methods: Mice lacking adiponectin (adipo−/−), the AMPK catalytic subunit alpha1 (AMPKa1−/−) and their respective littermates were fed a methionine and choline (MCD) deficient diet, supplemented or not with pioglitazone 0.01%. Histopathology, hepatic lipid content, serum adiponectin levels were assessed. In liver tissues, we evaluated AMPK (total, a1, a2) activities, proteins and mRNA levels, PPARa mRNA and the expression of downstream targets of AMPK or PPARa. Results: In wt mice, PGZ reduces the severity of MCD diet-induced steatohepatitis, while it increased circulating levels of adiponectin. By contrast, in adiponectin−/− mice, PGZ did not alter the severity of steatohepatitis. AMPKa1−/− mice and their littermates were genetically less sensitive to dietary steatohepatitis than C57 mice. In AMPKa1−/− mice fed the MCD diet, PGZ did not reduce the severity of steatohepatitis, although it significantly increased serum adiponectin levels. In wt mice, PGZ almost completely repressed the expression and activation of SREBP1c, a key transcription factor for de novo lipogenesis and downstream target of AMPK. This effect of PGZ was lacking in adiponectin−/− and in AMPKa1−/− mice. In the strains analysed, PGZ did not alter the expression of PPARa or of its downstream targets implicated in the regulation of lipid oxidation. In conclusion, we showed that the preventive effect of PGZ on MCD-induced steatohepatitis is dependent on the up-regulation of adiponectin. While the adiponectin-PPARa-boxidation axis does not appear to be implicated, our data strongly suggest that adiponectin produces its effect by controlling the expression and activity of SREBP-1c via the activation of the AMPK complex.