Effects Of Tea Polyphenols On Growth Performance,Carbohydrate Metabolism And Liver Transcriptome In Grass Carps(Ctenopharyngodon Idellus)

The aim for the present study was to investigate the effects of tea polyphenols(TPs)on the growth performance,carbohydrate(CHO)metabolism and liver transcriptome in grass carp(Ctenopharyngodon idellus).A basal diet supplemented with TPs at 0(control),250,500,1000,2000 and 4000 mg/kg were fed to grass carp for 8 weeks.Results showed that the feeding rate(FR)of grass carp was not different among dietary treatment(P>0.05),while TPs increased the feed conversion efficiency(FCE)at different levels,and 500 mg/kg TPs increased FCE significantly and resulted in the higher specific growth rate(SGR)significantly(P<0.05).TPs had no significant effect on the contents of body moisture,crude protein,crude fat and ash(P>0.05).With the increase of TPs,pyruvate kinase(PK)activity changed irregularly,which was significantly higher than that of the control group at 250 mg/kg and 500 mg/kg(P<0.05).The activities of lactate dehydrogenase(LDH),malate dehydrogenase(MDH)and succinate dehydrogenase(SDH)increased first and then decreased with the increasing TPs,and significantly increased in the range of 250 mg/kg to 1000 mg/kg(P<0.05).TPs had no significant effect on the insulin(INS)concentrations(P>0.05),while reduced the contents of glycogen significantly in muscle and liver(P<0.05),and the contents were similar among different TPs groups(P>0.05).RNA-seq analysis was performed on grass carp liver for the control group and 500 mg/kg TPs group,and 1209 up-regulated genes and 714 down-regulated genes were identified(qvalue<0.05,|log2Foldchange|>1).GO enrichment and KEGG enrichment analysis were performed on the screened differential genes(qvalue<0.001,|log2Foldchange|>1).Among the top 30 GO terms with significant enrichment(qvalue<0.05),a large number of differentially expressed genes were found in the cell process,metabolic process,single-organism process,organelle,cell,catalytic activity and binding.Among the top 20 KEGG pathways with significant enrichment(qvalue<0.05),the primary classification of 12 pathways was metabolism,including CHO metabolism,lipid metabolism and amino acid metabolism.Metabolic pathways were enriched for the largest number of differential genes,and the two pathways of starch and sucrose metabolism and galactose metabolism had the highest enrichment rates.There were 8 pathways related to CHO metabolism in the significantly enriched KEGG pathways(qvalue<0.05),including the insulin signaling pathway,starch and sucrose metabolism,glycolysis and pentose phosphate pathway.In the above pathways,the expressions of glycogen phosphorylase(PYG)and sucrose-isomaltose(SI)genes were up-regulated,while glucose-6-phosphatase(G6PC)was down-regulated,which promoted glycogen catabolism.The expressions of glucose kinase(GK),pyruvate kinase(PK),6-phosphofructose kinase(PFK),glucose-6-phosphodehydrogenase(G6PD)and fructose diphosphoaldoa(ALDOA)were up-regulated to promote glucose catabolism.By qRT-PCR analysis,the differences in the expressions of CHO metabolism-related genes were consistent with the results of RNA-seq.Results indicated that an appropriate TPs could change the expressions of CHO metabolism-related genes in grass carp liver,and increase the activity of carbohydrate-related metabolic enzymes,and enhance the decomposition and utilization of glycogen,and increase the utilization rate of carbohydrate,thereby improving feed conversion efficiency and promoting grass carp growth.The appropriate range of TPs was 250 mg/kg to 1000 mg/kg,and the most appropriate level in this study was 500 mg/kg.