| Nutritional fatty liver is a common problem in cultured fish,which slows down the growth rate of fish and reduces the ability to disease resistance and stress resistance,seriously affecting the healthy development of the fish breeding industry.Therefore,the mitigation of fatty liver in fish through nutritional interventions is urgently needed to be studied.According to the results of previous studies,mitochondrial damage and endoplasmic reticulum stress(ER stress)lead to fat deposition.Therefore,modulating the function of the ER or mitochondria in fish hepatocytes may alleviate fatty liver in fish.Based on this,this study aimed to investigate the effects of natural substances on fat deposition,ER stress,and mitochondrial damage in fish.The relevant research content and results are as follows:(1)The effect of quercetin on the growth and fat deposition in Lateolabrax maculatus.The L.maculatus was used as the research object,to investigate the effects of quercetin on growth,fat deposition,and ER stress.The diets containing 11% fat(NFD)and 17% fat(HFD)were prepared,and quercetin(QUE)was added to the high-fat diets at the levels of 0.5 g/kg and1.0 g/kg,respectively,i.e.QUE0.5 and QUE1.0.The four diets were fed to L.maculatus for 8weeks,then the samples were collected and analyzed.The results showed that ingestion of HFD significantly reduced the growth performance,feed utilization,and protein efficiency of fish.And the addition of QUE to HFD could improve growth performance,feed utilization,and protein efficiency.The HFD group significantly increased serum and liver TAG and T-CHO levels,increased total fat levels in the liver,and significantly increased abdominal lipid rates,while QUE supplementation in the HFD significantly reduced fat deposition in fish.In addition,HFD caused damage to the ER and mitochondria of liver cells under the transmission electron microscope,and QUE could alleviate the damage of liver cells.Further analysis of ER stressrelated genes showed that HFD significantly up-regulated the expression of grp78,chop,perk,atf6 and ire1,while QUE significantly down-regulated the expression of ER stress-related genes.These results indicated that QUE could alleviate ER stress in the liver of L.maculatus.The mechanism of QUE in reducing fat deposition may be related to its regulation of ER stress.(2)Regulatory effects of quercetin on fat deposition and endoplasmic reticulum stress in zebrafish hepatocytes.To further study the mechanism of QUE in relieving fat deposition,this study used Zebrafish liver cell line for in vitro tests.Control group(normal medium),FA group(normal medium with 0.40 m M fatty acids)and FA+QUE group(FA medium supplemented with 30 μM QUE)were set up.Cells were collected and analyzed after 24 h of culture.The results showed that FA group significantly increased the content of TAG in the cells,and Bodipy staining showed a large number of lipid droplets in the cells,which indicated that FA caused excessive deposition of cellular fat.QUE decreased the content of triglyceride and the number of lipid droplets in cells.In addition,FA significantly up-regulated the expression of ER stress-related genes grp78,chop,perk,ire1,xbp1 in ZFL cells,and caused the high expression of ER stressrelated proteins GRP78 and CHOP.While QUE alleviates ER stress.In ZFL,QUE also has a role in reducing fat deposition and alleviating ER stress.Based on the above results,it is speculated that: the mechanism of QUE to reduce fat deposition may be related to its regulation of ER stress.Conduct further research,the FA group,FA+QUE group,and FA+QUE+TM group(Tunicamycin,ER stress activator pretreatment)were set up.The results showed that the content of TAG in cells of the FA+QUE+TM group was significantly increased,and the number of lipid droplets in cells was significantly increased by Bodipy staining.Namely,the effect of QUE in reducing fat deposition disappeared after pretreatment with tunicamycin.This part of the study further confirmed that QUE to alleviate fat deposition depends on the regulation of ER stress.(3)The combined effect of quercetin and hydroxytyrosol on liver fat deposition in Lateolabrax maculatus.ER stress and mitochondrial damage are common phenomena in the development of the fatty liver.Mitochondria and ER are closely linked and talk to each other.Is there a synergistic effect between the alleviation of ER stress and mitochondrial damage in the prevention and treatment of fatty liver in fish? Based on this,this part of the study is carried out.L.maculatus was used as the research object.Set the six groups as control group(NFD),high-fat diet group(HFD),quercetin group(HFD+QUE),hydroxytyrosol group(HFD+HT),high-fat compatibility group(HFD+QUE+HT),control compatibility group(NFD+QUE+HT).L.maculatus was fed with 6 kinds of diets for 8 weeks,collect samples and conducted analysis.The result showed that the addition of QUE and HT to a high-fat diet significantly improve the growth performance,protein efficiency,and feed coefficient of L.maculatus,and the effect was better than that of adding QUE and HT separately.The results of oil red O staining showed that the number of lipid droplets in the liver was significantly reduced in the HFD+QUE+HT.The compatibility group down-regulated the expression of ER stress-related genes,improved the ultrastructure of ER,and enhanced the coupling between mitochondria and ER.At the same time,the compatibility group significantly improved the function of liver mitochondria.The results showed that the combination of QUE and HT was better than their single addition.In summary,QUE alleviated liver fat accumulation and improved growth performance of L.maculatus.Further studies showed that QUE exerted similar effects on cultured cells in vitro to that of the living body of L.maculatus,and the effects of QUE disappeared after tunicamycin pretreatment.Results from cellular tests suggest that QUE alleviates fat deposition dependent on the modulation of ER stress.QUE and HT have synergistic effect,their compatibility is better than the single addition,and improve the coupling of mitochondria and ER. |
