| Metabolic liver disease is a complex dynamic process involving a series of metabolic disorders,but there is currently no systematic study on the metabolic features and regulation mechanisms in fish.In this study,the main cause for metabolic liver disease and the possible regulatory mechanisms were investigated,to provide a foundation for the widespread use of artificial diets.Experimment 1: The phenotype and metabolic characteristics of metabolic liver disease caused by artificial diets and the involved regulation function of MAPKBy comparing the fish fed with chilled fish(CF)and artificial diets(AD),the main phenotype and metabolic characteristics of metabolic liver disease caused by AD and the involved regulation function of MAPK were explored.The results showed that fish fed AD had decreased FBW but increased VSI,HSI and HL.The fish in CF group showed normal hepatocytes while the hepatocytes in AD group were vacuolated,fibrotic,and glycogen accumulated.Besides,the fish fed with AD had higher hepatic inflammation and apoptosis.Liver damage caused by AD was associated with glucose and lipid metabolism disorder and Cholestasis.Dietary AD significantly induced the activation of ERK1/2、JNK1/2 and inhibition of p38α,indicating that MAPK participated in the regulation of metabolic liver disease induced by AD.Experiment 2: Effects of bile acid supplementation in a high carbohydrate inclusion diet on growth and metabolic liver disease and the involved regulation function of MAPKThree experimental diets were prepared with bile acid levels at 0(B0),300(the highest recommended dose,ADI = 5.20 mg/kg w/d,B300)and 1500(pharmaceutical dose,ADI = 25.8 mg/kg w/d,B1500)mg/kg in a basal diet with 25.6% carbohydrate(18.7% starch),to explore the effects of bile acid supplementation on high carbohydrate-induced metabolic liver disease and the involved regulation function of MAPK.The results showed that dietary 300,1500 mg/kg bile acid significantly improved the growth performance of largemouth bass.300 mg/kg bile acid supplementation improved glucose and lipid metabolism and significantly attenuated liver fibrosis,but the inflammation and apoptosis responses in the liver were significantly enhanced.Dietary 1500 mg/kg bile acid significantly reduced HSI,HL and the hepatic inflammation and apoptosis,and the metabolic liver disease caused by high carbohydrate was alleviated and fundamental cured.1500mg/kg bile acid had no significant effect on hepatic protein expression level of JNK,but significantly activated ERK1/2 and p38α,suggesting that ERK1/2 activation may be involved in the bile acid-mediated alleviation of metabolic liver disease and p38α phosphorylation was the key point for the regulation of metabolic liver disease in largemouth bass.Experiment 3: p38α/NFκB/TNFα signal pathway was involved in the development of metabolic liver disease of largemouth bass.The protein expression level of p65NFκB and the co-localization of p38α/p65NFκB were analysized to explore the potential regulation mechanism of p38α phosphorylation in metabolic liver disease and the verification was conducted in primary hepatocytes of largemouth bass.Compared with the CF group,p65NFκB was significantly activated in the liver of the fish in AD group,while dietary 1500mg/kg bile acid significantly inhibited the phosphorylation of p65NFκB,suggesting p65NFκB was involved in the regulation of metabolic liver disease.Besides,immunofluorescence staining showed that that p38α activation inhibited the expression of p65NFκB,indicationg that p38α may participate in the development of metabolic liver disease by regulating p65NFκB.In the primary hepatocytes of largemouth bass,it was found that p65NFκB was significantly activated when p38α was inhibited by BIRB796,and the protein expression level of activated TNFα was significantly increased,indicating that p38α-p65NFκB-TNFα played an important role in regulating metabolic liver disease caused by high carbohydrate inclusion in largemouth bass. |
