Nano-Zn Increased Zn Accumulation and Triglyceride Content by Up-Regulating Lipogenesis in Freshwater Teleost, Yellow Catfish Pelteobagrus fulvidraco

The present study was conducted to explore the mechanism of nano-Zn absorption and its influence on lipid metabolism in the intestine of yellow catfish Pelteobagrus fulvidraco. Compared to ZnSO4, dietary nano-Zn addition increased the triglyceride (TG) content, enzymatic activities of malic enzyme (ME) and fatty acid synthase (FAS), and up-regulated mRNA levels of 6pgd, fas, acca, dgat1, ppar gamma, and fatp4. Using primary intestinal epithelial cells of yellow catfish, compared to the ZnSO4 group, nano-Zn incubation increased the contents of TG and free fatty acids (FFA), the activities of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6GPD), ME, and FAS, up-regulated mRNA levels of lipogenic genes (6pgd, g6pd, fas, dgat1, and ppar gamma), genes of lipid transport (fatp4 and ifabp), and Zn transport genes (znt5, znt7, mt, and mtf1), and increased the protein expression of fatty acid transport protein 4 (FATP4) and peroxisome proliferator activated receptor gamma (PPAR gamma). Further studies found that nano-Zn absorption was via the clathrin-dependent endocytic mechanism. PPAR gamma mediated the nano-Zn-induced increase in TG, and nano-Zn increased Zn accumulation and induced TG accumulation by activating the PPAR gamma pathway and up-regulating lipogenesis.