Effects And Molecular Mechanism Of Saccharina Japonica On Liver Health Of Black Sea Bream,Acanthopagrus Schlegelii

Excess hepatic lipid accumulation is the main liver disease in rearing fish.Black seabream Acanthopagrus schlegelii tends to accumulate excess fat in the liver,which can damage the liver and reduce production.Saccharina japonica(SJ)plays a key role in maintaining the liver health in animals with reducing hepatic lipid accumulation,improving antioxidant and enhancing immunity etc.The aim of this study was to investigate the effects and molecular mechanism of SJ and its extraction on the liver health of black seabream,which provides a reference for the development of compound feed for maintaining liver health of black sea bream,and also provide a theoretical basis for the study of liver health of other fish.The main contents and results in this study were as follows:1.Effects of dietary Saccharina japonica on growth,fillets quality and liver health of black seabreamThe aim of this study was to investigate the effects of seven levels(0%,0.1%,0.2%,1.2%,2.5%,5% and 10%)of dietary SJ on the growth,fillets quality and liver health of black seabream.The best growth performance was achieved in SJ2.5%group with significantly higher FBW and WGR,and lower FC compared with SJ0%group,whereas SJ10% inhibited the growth(P<0.05).The contents of PUFA and total iodine in dorsal muscle were significantly increased(P<0.05),and there were no significant effects on the moisture,protein,lipid and ash of whole body and dorsal muscle,and fillet edible quality and textural with the increasing dietary SJ(P>0.05).However,the protease activity in foregut was inhibited by SJ supplemented(P<0.05).Meanwhile,dietary SJ also reduced serum TG,TC,AST and ALT,and the number and diameter of vacuole in the liver(P<0.05).In conclusion,appropriate dietary SJ could promote the growth,reduce plasm lipid and hepatic vacuole,maintain liver health,and increase the PUFA and total iodine contents in dorsal muscle.2.5% was the optimum supplemental level of SJ in black seabream diets.2.Integrative analysis of transcriptomics and metabolomics profiling on liver health of black seabream fed Saccharina japonica supplementation diets.This study aimed to explore the mechanism of the effects of dietary SJ on liver health of black seabream by transcriptomics and metabolomics analysis on SJ0%,SJ2.5% and SJ10% groups.The transcriptomics analysis showed that differentially expressed genes(DEGs)in the top 20 significant enrichment KEGG pathways related to lipid metabolism were as follows: DEGs in the pathway of primary bile acid biosynthesis were down-regulated between SJ2.5% and SJ0% group;DEGs in pathways of steroid biosynthesis and biosynthesis of unsaturated fatty acids were down-regulated between SJ10% and SJ0% group;DEGs in pathways of linoleic acid metabolism,arachidonic acid metabolism,alpha-linolenic acid metabolism,fatty acid metabolism,biosynthesis of unsaturated fatty acids were down-regulated between SJ10% and SJ2.5% group.Besides,DEGs in the pathway of regulation of autophagy were up-regulated in SJ2.5% and SJ10% groups compared with SJ0% group.The metabolomics analysis showed that differentially expressed metabolites(DEMs)involved in lipid metabolism were the most metabolites compared with other types of metabolism through the enrichment analysis of KEGG pathway.Both DEGs and DEMs co-enriched in KEGG pathway showed that the significant enriched pathways related to lipid metabolism were primary bile acid biosynthesis,glycerophospholipid metabolism,biosynthesis of unsaturated fatty acids and fatty acid biosynthesis in SJ2.5% and SJ10% groups compared with SJ0% group.However,there were no pathways co-enriched between SJ10% and SJ2.5% group.In conclusion,2.5% and10% SJ supplementation diets may reduce hepatic lipid accumulation through promoting autophagy,and inhibiting the synthesis of lipids and bile acids in black seabream.In addition,primary bile acid biosynthesis pathway could be the key pathway by which dietary SJ affected liver health of black seabream.3.Effects of dietary aqueous and ethanol extraction of Saccharina japonica on growth,antioxidant and liver health of black seabreamThe aim of the present study was to evaluate the effects of different levels of aqueous extraction(ASJ1,0.83g/kg;ASJ2,3.32g/kg)and ethanol extraction(ESJ1,0.99g/kg;ESJ2,3.96g/kg)of SJ supplementation diets on the growth,antioxidant and liver health of black seabream.FBW and WGR were significantly increased,whereas the serum TC,TG,LDL-C and ALT,and hepatic TC and TG were significantly decreased in ASJ2 and ESJ2 groups compared with CTRL group(base diet,0g/kg)(P<0.05).The relative area of lipid droplets and vacuoles in liver were significantly decreased,and serum CAT activity were significantly increased,and serum MDA content was significantly decreased(P<0.05),and the activities of digestive enzymes in foregut were not significantly affected(P>0.05)with the increasing level of dietary ASJ and ESJ.In conclusion,0.83 and 3.32g/kg of ASJ supplementation,and 0.99 and3.96g/kg of ESJ supplementation diets promoted growth,reduced serum and hepatic lipids,and sustained the liver health in black seabream,which eliminated the inhibition of growth by SJ supplementation in diets directly.4.Integrative analysis of transcriptomics and metabolomics profiling on liver health of black seabream fed ASJ and ESJ supplementation dietsThis study aimed to explore the mechanism of the effects of dietary ASJ1 and ESJ1 on liver health of black seabream by transcriptomics and metabolomics analysis on CTRL,ASJ1 and ESJ1 groups.The transcriptomics analysis showed that differentially expressed genes(DEGs)in the top 20 significant enrichment KEGG pathways related to lipid metabolism were as follows: DEGs in the pathway of primary bile acid biosynthesis,fatty acid biosynthesis,and belonging the type of amino acid metabolism were down-regulated,whereas those in the pathway of regulation of autophagy were up-regulated between ASJ1 and CTRL group;DEGs in fatty acid biosynthesis were down-regulated,whereas those in regulation of autophagy were up-regulated between ESJ1 and CTRL group;DEGs in the pathway of regulation of autophagy were down-regulated,whereas those in the pathway of primary bile acid biosynthesis,and belonging the type of amino acid metabolism were up-regulated between ESJ1 and ASJ1.The enrichment analysis of KEGG pathway in metabolomics showed that differentially expressed metabolites(DEMs)involved in lipid metabolism were the most metabolites in ASJ1 and ESJ1 groups compared with CTRL group,whereas DEMs involved in global and overview maps were the most metabolites between ESJ1 and ASJ1 group.Both DEGs and DEMs co-enriched in KEGG pathway showed that the significant enriched pathways related to lipid metabolism were primary bile acid biosynthesis,glycerophospholipid metabolism,biosynthesis of unsaturated fatty acids,fatty acid biosynthesis,sphingolipid metabolism,arachidonic acid metabolism and drug metabolism-cytochrome P450.In conclusion,0.83 g/kg ASJ and 0.99 g/kg ESJ supplementation diets may reduce hepatic lipid accumulation through promoting autophagy,and inhibiting the synthesis of lipids and bile acids in black seabream.Meanwhile,ASJ may be more effective in promoting autophagy and inhibiting bile acids synthesis compared with ESJ.In addition,the pathway of primary bile acid biosynthesis pathway and glycerophospholipid metabolism could be the key pathway by which dietary ASJ and ESJ affected liver health of black seabream,respectively.