Dietary nano-Se supplementation regulates lipid deposition, protein synthesis and muscle fibre formation in grass carp fed with high-fat diet.

The current study aims to confirm the positive effects of dietary nano-Se on nutrients deposition and muscle fibre formation in grass carp fed with high-fat diet (HFD) before overwintering and to reveal its possible molecular mechanism. The lipid deposition, protein synthesis and muscle fibre formation in grass carp fed with regular diet (RD), HFD or HFD supplemented with nano-Se (0·3 or 0·6 mg/kg) for 60 d were tested. Results show that nano-Se significantly reduced lipid content, dripping loss and fibre diameter (P < 0·05), but increased protein content, post-mortem pH24 h and muscle fibre density (P < 0·05) in muscle of grass carp fed with HFD. Notably, dietary nano-Se decreased lipid deposition in the muscle by regulating amp-activated protein kinase activity and increased protein synthesis and fibre formation in muscle by activating target of rapamycin and myogenic determining factors pathways. In summary, dietary nano-Se can regulate the nutrients deposition and muscle fibre formation in grass carp fed with HFD, which exhibit potential benefit for improving flesh quality of grass carp fed with HFD.

Dietary nano-selenium alleviated intestinal damage of juvenile grass carp (Ctenopharyngodon idella) induced by high-fat diet: Insight from intestinal morphology, tight junction, inflammation, anti-oxidization and intestinal microbiota.

In recent years, high-fat diet (HFD) has been widely applied in aquaculture, which reduces the intestinal health of cultured fish. The current study evaluated the protective effects of nano-selenium (nano-Se) on intestinal health of juvenile grass carp (Ctenopharyngodon idella) fed with HFD. A total of 135 experimental fish were fed with a regular diet (Con), a HFD (HFD) and a HFD containing nano-Se at 0.6 mg/kg (HSe) for 10 weeks. The results showed that dietary nano-Se significantly improved the survival rate and feed efficiency which were reduced by HFD in juvenile grass carp (P < 0.05). Also, nano-Se (0.6 mg/kg) supplement alleviated intestinal damage caused by the HFD, thus maintaining the integrity of the intestine. Moreover, it significantly up-regulated the expression of genes related to tight junction (ZO-1, c laudin-3 and o ccludin), anti-oxidization (GPx4a andGPx4b), and the protein of ZO-1 in the intestine of juvenile grass carp, which were depressed by the HFD (P < 0.05). Furthermore, nano-Se supplementation significantly suppressed the expressions of genes related to the inflammation, including inflammatory cytokines (IL-8, IL-1ß, IFN-γ, TNF-α and IL-6), signaling molecules (TLR4, p38 MAPK and NF-κB p65), and protein expression of NF-κB p65 and TNF-α in the intestine of juvenile grass carp which were induced by the HFD (P < 0.05). Besides, dietary nano-Se normalized the intestinal microbiota imbalance of juvenile grass carp caused by the HFD through increasing the abundance of the beneficial bacteria, e.g., Fusobacteria. Finally, dietary nano-Se increased the production of short chain fatty acids (SCFA) in the intestine, especially for butyric acid and caproic acid, which were negatively related to the increase of intestinal permeability and inflammation. In summary, supply of nano-Se (0.6 mg/kg) in HFD could effectively alleviate intestinal injury of juvenile grass carp by improving intestinal barrier function and reducing intestinal inflammation and oxidative stress. These positive effects may be due to the regulation of nano-Se on intestinal microbiota and the subsequently increased beneficial SCFA levels.

Molecular characterization and tissue distribution of nine selenoprotein genes in grass carp Ctenopharyngodon idella and their mRNA expressions in response to high-fat diet and high-fat diet supplemented with selenium.

Our previous study has found that selenium (Se) can alleviate lipid accumulation caused by high-fat diet (HFD) in fish. This study aims to explore the selenoproteins (SePs) in grass carp Ctenopharyngodon idella by characterizing cDNAs of nine SeP genes (SELENOF, SELENOM, SELENOS, SELENOP1, SELENOP2, SELENOE, SELENOL, SELENOU1a and SELENOU1b) and measuring their transcriptional activity in response to HFD and HFD supplemented with 0.3 mg/Kg and 0.6 mg/Kg of Se (HSe 0.3 and HSe 0.6). Firstly, the nine SeP genes in grass carp encoded proteins with conserved functional protein regions in fish and other vertebrates. Secondly, the nine SeP genes except SELENOS showed high expression levels in the hepatopancreas, but in the adipose tissue, only SELENOS, SELENOE and SELENOU1b showed high expression levels. Further, HFD significantly up-regulated the expressions of SELENOF and SELENOS in the hepatopancreas and SELENOM in the adipose tissue of grass carp (P < 0.05), but significantly down-regulated the expressions of SELENOU1b in the hepatopancreas, SELENOP2, SELENOE, SELENOL and SELENOU1a in the adipose tissue and SELENOM in the muscle of grass carp (P < 0.05). In addition, for the hepatopancreas, the expressions of SELENOS in the HSe 0.3 group and SELENOF, SELENOM and SELENOP2 in the HSe 0.6 group significantly decreased compared with the HFD group (P < 0.05). For the adipose tissue, the expressions of SELENOF, SELENOP2, SELENOL, SELENOU1a and SELENOU1b in the HSe 0.3 group and SELENOP2, SELENOE, SELENOU1a and SELENOU1b in the HSe 0.6 group significantly increased compared with the HFD group (P < 0.05). In summary, the transcriptional activities of the nine SeP genes were regulated by the HFD and HFD supplemented with Se, indicating the potential role of these genes in the Se regulated lipid metabolism processes in grass carp, which is worthy of in-depth study.