The Effect Of Dietary Vitamin E On Growth Performance,Intestinal Health,Body Health,Gill Health And Flesh Quality As Well As The Related Molecule Mechanisms In The Intestine,Head Kidney,Spleen,Skin,Gill And Muscle Of Young Grass Carp(Ctenopharyngodon Idel

The aim of this study was to investigate the effect of dietary vitamin E on growth performance,intestinal health,body health,gill health and flesh quality and the potential mechanisms of these effects in the intestine,head kidney,spleen,skin,gill and muscle of young grass carp(Ctenopharyngodon idella).A total of 540 grass carp(266.39±0.33 g)were fed diets containing graded levels of vitamin E at 4.93(basal diet),45.07,90.62,135.54,180.29 and 225.36 mg/kg diet for 10 weeks to investigate the effect of dietary vitamin E on growth performance and flesh quality of young grass carp.Subsequently,an exposure test was conducted by infecting fish with Aeromonas hydrophila and Flavobacterium colummare to investigate the effect of dietary vitamin E on intestinal health,body health and gill health and the potential mechanisms in the head kidney,spleen,skin and gill of young grass carp.The results of the present study showed that optimal vitamin E supplementation increased the percentage weight gain(PWG),specific growth rate(SGR),feed intake(FI)and feed efficiency(FE)of young grass carp(P<0.05).Meanwhile,the results from the Aeromonas hydrophila and F.colunmare infection trail showed that optimal vitamin E supplementation significantly decreased enteritis morbidity,skin lesion morbidity and gill rot morbidity(P<0.05),enhanced the disease resistance of fish intestine,head kidney,spleen,skin and gill.First,the optimal vitamin E supplementation significantly decreased the contents of reactive oxygen species(ROS),malondialdehyde(MDA)and protein carbonyl(PC)(P<0.05),significantly increased the activities of copper/zinc superoxide dismutase(CuZnSOD)(except for the proximal intestine),manganese superoxide dismutase(MnSOD),glutathione peroxidase(GPx),glutathione S-transferases(GST)and glutathione reductase(GR)(P<0.05),significantly up-regulated the mRNA levels of those antioxidant enzymes and signalling molecule NF-E2-related factor 2(Nrf2)and down-regulated the mRNA levels of signalling molecule Keapla(except for the gill)and Keaplb in the intestine,head kidney,skin and gill of young grass carp(P<0.05);meanwhile,optimal dietary vitamin E significantly up-regulated the relative mRNA levels of myeloid cell leukemia-1(Mcl-1)and B cell lymphoma-2 protein(Bcl-2),down-regulated the relative mRNA levels of caspase-3,caspase-7,caspase-8(except for the gill),caspase-9,Bcl-2 associated X protein(Bax)(except for the head kidney and spleen),apoptotic protease activating facter-1(Apaf-1),Fas ligand(FasL)(except for the middle intestine,distal intestine and gill),c-Jun N-terminal kinase(JNK)and p38 mitogen-activated protein kinase(p38 MAPK)in the intestine,head kidney,spleen,skin and gill of fish(P<0.05);furthermore,optimal dietary vitamin E significantly up-regulated the relative mRNA levels of tight junction proteins occludin,zonula occludens-1,claudin-3(except for the distal intestine),claudin-b,claudin-c(except for the distal intestine),down-regulated the relative mRNA levels of myosin light chain kinase(MLCK)in the intestine,head kidney,spleen,skin and gill of fish(P<0.05),indicating that vitamin E enhanced the structural integrity of intestine,head kidney,spleen,skin and gill.In addition,optimal vitamin E supplementation significantly enhanced lysozyme and acid phosphatase activities.complement component 3 and complement component 4 contents and up-regulated the mRNA levels of antimicrobial peptides(liver-expressed antimicrobial peptide-2A,liver-expressed antimicrobial peptide-2B.hepcidin.?-defensin)in the intestine,head kidney.spleen,skin and gill of grass carp(P<0.05).meanwhile.optimal dietary vitamin E supplementation significantly up-regulated the mRNA levels of anti-inflammatory cytokines IL-10 and TGF?1 and the signalling molecules inhibitory protein KBa(I?B?),the target of rapamycin(TOR)and ribosome protein S6 kinase 1(S6K1)(P<0.05)and significantly down-regulated the mRNA levels of pro-inflammatory cytokines TNFa(except for the proximal intestine),IFN?2,IL-1?,IL-6 and IL-8 and signalling molecules NF-?B p65,I?B kinase ?(IKK?),IKK?,IKK?(except for the gill)and eIF4E-binding protein 1(4E-BP1)(except for the kidney)(P<0.05)in the intestine,head kidney,spleen,skin and gill of fish,indicating that vitamin E enhanced the immune barrier of fish intestine,head kidney,spleen,skin and gill.Study in the flesh quality of young grass carp indicated that optimal dietary vitamin E supplementation increased muscle protein and lipid contents and decreased muscle moisture content(P<0.05).The potential mechanism of the effect of vitamin E on muscle protein content may related to the up-regulated gene expression of TOR,S6K1,CK2a and CK2b in the muscle of young grass carp.Meanwhile,optimal dietary vitamin E supplementation increased flavor amino acid Glu,Ala and Gly and essential amino acid Lys,Leu,Ile,Thr and His and polyunsaturated fatty acids contents in the muscle of young grass carp(P.<0.05).In addition,optimal dietary vitamin E supplementation improved muscle shear force,hydroxyproline content and pH value,decreased muscle cathepsin B and cathepsin L activities,lactate content and cooking loss,increased GSH content and CuZnSOD?MnSOD?CAT?GPx?GR and GST activities,up-regulated the mRNA levels of those antioxidant enzymes and signalling molecule NF-E2-related factor 2(Nrf2)and down-regulated the mRNA levels of signalling molecule Keapla and Keaplb in the muscle of young grass carp(P<0.05).In conclusion,optimal dietary vitamin E supplementation increased the growth performance,improved flesh quality,and enhanced the disease resistance of fish intestine,head kidney,spleen,skin and gill.The enhanced disease resistance of fish intestine,head kidney,spleen,skin and gill was related to the improved intestine,head kidney,spleen,skin and gill structural integrity and immune barrier function.First,optimal vitamin E supplementation enhanced the structural integrity of intestine,head kidney,spleen,skin and gill by improving intestine,head kidney,spleen,skin and gill antioxidant capacity to decrease oxidative damage,which may be due to up-regulate antioxidant enzyme gene transcriptions through regulating Nrf2 signalling in fish,and depressing apoptosis through JNK/p38 MAPK signaling in the intestine,head kidney,spleen,skin and gill of fish.Meanwhile,optimal dietary vitamin E supplementation improved TJ barrier function through up-regulating the relative mRNA levels of tight junction proteins via MLCK signaling in the intestine,head kidney,spleen,skin and gill of fish.In addtion,optimal dietary vitamin E supplementation enhanced the immune barrier of fish intestine,head kidney,spleen,skin and gill via improving the bactericidal ability and regulating the gene transcriptions of inflammatory cytokine through NF-?B and TOR signaling to alleviate intestine,head kidney,spleen,skin and gill inflammation.The improved flesh quality was probably related to the enhanced nutrient contents and antioxidant ability of muscle by optimal dietary vitamin E supplementation.The optimal vitamin E levels of young grass carp(266.39-1026.63g)based on percent weight gain,the protection of gill against enteritis morbidity,skin lesion morbidity,gill rot morbidity and muscle hydroxyproline content were estimated to 116.2,127.0,130.9,139.6 and 115.2 mg/kg diet,respectively.