Docosahexaenoic acid induces PPARγ-dependent preadipocytes apoptosis in grass carp Ctenopharyngodon idella

Our previous study showed that docosahexaenoic acid (DHA) plays an important role in decreasing lipid accumulation by inducing apoptosis of the adipocytes in grass carp. However, the mechanism involved remains unclear. DHA has been reported as the natural ligand of PPARγ. The present study aimed to assess whether PPARγ mediates the pro-apoptotic effects by DHA. Adipocytes of grass carp were cultured until 2 days post-confluence and were treated with DHA at various concentrations-0, 25, 50, 100, 200, and 400 μmol/L for 24 h and at 200 μmol/L for various time periods (0, 12, 24, and 48 h, respectively). Besides, the adipocytes were exposed to 200 μM DHA and PPARγ antagonist or inhibitor of certain key enzymes of apoptosis, following which the expression levels of key genes of the cell apoptotic and mitochondrial apoptotic pathways were detected. We found that DHA induced apoptosis of grass carp adipocytes in a time- and dose-dependent manner (P < 0.05). In addition, DHA treatment significantly increased the protein and gene expression levels of PPARγ (P < 0.05), but the PPARγ antagonist significantly abolished this effect and the DHA pro-apoptotic effect (P < 0.05). Moreover, treatment with caspase 9 inhibitor significantly attenuated the DHA-induced preadipocytes apoptosis effects, while treatment with caspase 8 inhibitor showed no influence. These observations suggest that the DHA-induced apoptosis in adipocytes might be mediated by PPARγ and via the intrinsic apoptotic pathway in grass carp.