Human adenovirus 36 decreases fatty acid oxidation and increases de novo lipogenesis in primary cultured human skeletal muscle cells by promoting Cidec/FSP27 expression.

It has been well documented that human adenovirus type 36 (Ad-36) is associated with obesity. However, the underlying molecular mechanism of Ad-36 inducing obesity remains unknown. We sought to investigate the effect of Ad-36 infection on Cidec, AMPK pathway and lipid metabolism in primary cultured human skeletal muscle cells. Cidec/fat-specific protein 27 (FSP27), fatty acid oxidation, AMPK signaling and the abundance of proteins involved in lipid synthesis were determined in muscle cells infected with various doses (1.9-7.6 MOI) of Ad-36 and non-lipogenic adenovirus type 2 (Ad-2) as a negative control as well as an uninfected control. Cidec/FSP27 siRNA transfection was performed in Ad-36-infected muscle cells. Our data show that Ad-36 significantly reduced fatty acid oxidation in a dose-dependent manner (all P values are <0.01), but Ad-2 did not affect fatty acid oxidation. Ad-36 substantially increased Cidec/FSP27, ACC, sterol regulatory element-binding protein 1c (SREBP-1c), SREBP-2 and 3-hydroxy-3-methylglutaryl-CoA reductase protein abundance, but significantly reduced AMPK activity, mitochondrial mass and uncoupling protein 3 (UCP3) abundance in comparison with control cells (all P values are <0.01). Oil Red O staining revealed that there was substantial fat accumulation in the Ad-36-infected muscle cells. Furthermore, Cidec/FSP27 siRNA transfection significantly reduced FSP27 expression and partially restored AMPK signaling, increased UCP3 and decreased SERBP 1c and perilipin proteins in Ad-36-infected muscle cells. Interestingly, neither Ad-36 nor Ad-2 affected peroxisome proliferator-activated receptor γ protein expression in muscle cells. This study suggests that Ad-36 induced lipid droplets in the cultured skeletal muscle cells and this process may be mediated by promoting Cidec/FSP27 expression.