The essential function of CARD9 in diet-induced inflammation and metabolic disorders in mice.

Inflammation and metabolic disorder are common pathophysiological conditions, which play a vital role in the development of obesity and type 2 diabetes. The purpose of this study was to explore the effects of caspase recruitment domain (CARD) 9 in the high fat diet (HFD)-treated mice and attempt to find a molecular therapeutic target for obesity development and treatment. Sixteen male CARD9-/- and corresponding male WT mice were fed with normal diet or high fat diet, respectively, for 12 weeks. Glucose tolerance, insulin resistance, oxygen consumption and heat production of the mice were detected. The CARD9/MAPK pathway-related gene and protein were determined in insulin-responsive organs using Western blotting and quantitative PCR. The results showed that HFD-induced insulin resistance and impairment of glucose tolerance were more severe in WT mice than that in the CARD9-/- mice. CARD9 absence significantly modified O2 consumption, CO2 production and heat production. CARD9-/- mice displayed the lower expression of p38 MAPK, JNK and ERK when compared to the WT mice in both HFD- and ND-treated groups. HFD induced the increase of p38 MAPK, JNK and ERK in WT mice but not in the CARD9-/- mice. The results indicated that CARD9 absence could be a vital protective factor in diet-induced obesity via the CARD9/MAPK pathway, which may provide new insights into the development of gene knockout to improving diet-induced obesity and metabolism disorder.