Conjugated Linoleic Acid Reduces Lipid Accumulation via Down-regulation Expression of Lipogenic Genes and Up-regulation of Apoptotic Genes in Grass Carp ( Ctenopharyngodon idella ) Adipocyte In Vitro

The relationship between conjugated linoleic acid (CLA) and lipogenesis has been extensively studied in mammals and some cell lines, but it is relatively rare in fish, and the potential mechanism of action of CLA reducing fat mass remains unclear. The established primary culture model for studying lipogenesis in grass carp ( Ctenopharyngodon idella ) preadipocytes was used in the present study, and the objective was to explore the effects of CLA on intracellular lipid and TG content, fatty acid composition, and mRNA levels of adipogenesis transcription factors, lipase, and apoptosis genes in grass carp adipocytes in vitro. The results showed that CLA reduced the size of adipocyte and lipid droplet and decreased the content of intracellular lipid and TG, which was accompanied by a significant down-regulation of mRNA abundance in transcriptional regulators including peroxisome proliferator-activated receptor (PPAR) γ , CCAAT/enhancer-binding protein (C/EBP) α , sterol regulatory element-binding protein (SREBP) 1c , lipase genes including fatty acid synthase (FAS) , acetyl-CoA carboxylase (ACC) , lipoprotein lipase (LPL) . Meanwhile, it decreased the content of saturated fatty acids (SFAs) and n − 6 polyunsaturated fatty acid (n-6 PUFA) and increased the content of monounsaturated fatty acid (MUFA) and n − 3 polyunsaturated fatty acid (n-3 PUFA) in primary grass carp adipocyte. In addition, CLA induced adipocyte apoptosis through downregulated anti-apoptotic gene B‐cell CLL/lymphoma 2 ( Bcl-2 ) mRNA level and up-regulated pro-apoptotic genes tumor necrosis factor-α (TNF-α) , Bcl-2-associated X protein (Bax) , Caspase-3 , and Caspase-9 mRNA level in a dose-dependent manner. These findings suggest that CLA can act on grass carp adipocytes through various pathways, including decreasing adipocyte size, altering fatty acid composition, inhibiting adipocyte differentiation, promoting adipocyte apoptosis, and ultimately decreasing lipid accumulation.