Abstract
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, pparγ, 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 pparγ), 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 (PPARγ). Further studies found that nano-Zn absorption was via the clathrin-dependent endocytic mechanism. PPARγ mediated the nano-Zn-induced increase in TG, and nano-Zn increased Zn accumulation and induced TG accumulation by activating the PPARγ pathway and up-regulating lipogenesis.
Highlights
Zinc (Zn) is an essential nutrient required in animals for many important biological processes, including growth, development, and nutrient metabolism [1]
Survival, feed intake (FI), and intestinal somatic index (ISI) showed no significant differences between the two groups (Supplementary Table S2)
Intestinal Zn content and mtf-1 mRNA expression were higher in the nano-Zn group than in the ZnSO4 group (Figure 1A,B). mRNA levels of zip4, znt1, znt5, znt7, and mt showed no significant differences between the two groups
Summary
Zinc (Zn) is an essential nutrient required in animals for many important biological processes, including growth, development, and nutrient metabolism [1]. Zn uptake and the regulation of homeostasis are achieved through many key proteins and genes [3]. These proteins consist of metal-response transcription factor-1 (MTF-1), metallothionein (MT), and transmembrane transporters (ZIP and ZnT families) [4]. MTF-1 is the only Zn-sensing transcription factor in vertebrates and regulates the transcription of many genes involved in Zn metabolism [3]. The regulation of dietary Zn absorption in the intestine is believed to be important in Zn homeostasis and has been studied in rodent models, but not in fish. The molecular mechanism for Zn uptake and homeostatic regulation remains unknown in fish
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