Supplementation with optimized multivitamin premix relieves liver steatosis by inhibiting CD36 palmitoylation and regulating intestinal microorganisms in largemouth bass (Micropterus salmoides)

In this study, optimized multivitamin premix (OVP) was added to three kinds of different protein quality feeds (by decreasing dietary protein levels from 50% to 45% and replacing marine fish meal with terrestrial proteins) to investigate the effects of OVP on dietary protein quality-induced fatty liver in largemouth bass. Lysine (Lys) and methionine (Met) were supplied to ensure a consistent level of these two limiting amino acids. The results showed that decreased dietary protein quality did not affect the FBW and SGR of largemouth bass (P>0.05), but improved protein efficiency (P<0.05). However, decreased dietary protein quality impaired fish health and induced the occurrence of liver steatosis, manifested by fat accumulation, lipid metabolism disturbance, apoptosis, ER stress, and gut microbiome changes. Meanwhile, supplementation with OVP significantly reduced the FCR (P<0.05) and promoted dietary utilization in high- and low-protein-quality feed treatments. Supplementation with OVP reduced the contents of lipids, TC and TG, downregulated the mRNA expression of proinflammatory cytokines (nf-kb, tnf-α and il15), upregulated the mRNA expression of anti-inflammatory cytokines (il10 and tgf-β) in the liver, and reduced the relative abundance of intestinal flora related to liver steatosis (P<0.05). Furthermore, in the middle- and low-protein-quality feed treatments, supplementation with OVP alleviated ER stress and reduced ER stress-induced apoptosis through the hsp90/p38-mediated pathway. Finally, we found that supplementation with OVP could affect dhhc4 and dhhc5-mediated pathway to inhibit CD36 palmitoylation and facilitate CD36 mitochondrial localization, and alleviating the crosstalk between CD36 and the ER stress to prevent decreased dietary protein quality-induced hepatic steatosis.