Effects Of Dietary Vitamin A On Growth Performance,Intestinal Health,Body Health,Gill Health And Muscle Quality As Well As The Potential Mechanisms In Young Grass Carp

The present study was for the first time to investigate the effects of dietary vitamin A on fish growth performance, intestinal health, body health, gill health and muscle quality as well as the potential mechanisms in young grass carp (Ctenopharyngodon idella). At the beginning of the experiment,540 young grass carp (262.02±0.45 g) were selected and divided into six treatments, then fed graded levels of vitamin A for 10 weeks to investigate the effects of vitamin A on the fish growth performance and the muscle quality. After the feeding trial, a challenge test was conducted by injection 15 fish with Aeromonas hydrophila for 14 days to explore the fish intestinal and body structural integrity and immune function as well as the potential mechanisms. Meanwhile, another 15 fish were selected for the infection of Myxococcus piscicola to investigate the gill structural integrity and immune function as well as the potential mechanisms.The results showed that optimal vitamin A diet remarkably increased percentage weight gain (PWG), specific growth rate (SGR). feed intake (FI) and feed efficiency (FE) of the fish and decreased the ability of fish defensing against enteritis, skin lesion and gill rot disease after challenged test. Further study showed that the improvement of enteritis, skin lesion and gill rot disease resistance are closely related to the maintenance of the intestine, organize and gill structure integrity:(1) optimum vitamin A up-regulating NF-E2-related factor 2 (Nrf2) mRNA levels and down-regulating kelch-like-ECH-associated protein (Keapla) (Keaplb included in skin and gill) mRNA levels in the intestine, body and gill, up-regulating copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase(MnSOD) (not including intestine), catalase (CAT), glutathione peroxidase 1a (GPx1a) (not including spleen and gill), GPx4a, GPx4b (not including PI, MI and gill), glutathione S-transferases r (GSTr) (not including head kidney) and glutathione reductase (GR) mRNA levels in the intestine, body and gill, up-regulating GSTp1 and GSTo1 in the MI and DI as well as GPx1b mRNA level in the skin, increased the corresponding antioxidant enzymes activity, thus, enhanced the ability of scavenging free radicals and decreased the reactive oxygen species (ROS) content, decreased the lipid peroxidation and protein oxidative damage. Meanwhile, optimal vitamin A up-regulated the target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1) mRNA levels and down-regulated the eIF4E-binding protein (4E-BP1) and Fas ligand (FasL) mRNA levels, down-regulated caspase-8-mediated death receptor pathway, and down-regulated pro-apoptotic protein apoptotic protease activating factor-1 (Apaf-1) (apart from skin) as well as B-cell lymphoma protein 2 associated X protein (Bax) while up-regulated the anti-apoptotic protein B-cell lymphoma-2 (Bcl-2) mRNA level, and down-regulated the caspase-9/caspase-3-mediated mitochondria-dependent pathway, decreased the cell apoptosis in the intestine, body and gill, thus, maintained the intestine, body and gill cell structure integrity; (2) optimum vitamin A down-regulated the molecule myosin light-chain kinase (MLCK) mRNA levels in the intestine, organize and gill, and up-regulated the mRNA levels of zonula occludens-1 (ZO-1), occludin, claudin-b, claudin-c, claudin-12 and claudin-15a (apart from gill), and up-regulated claudin-3 mRNA levels in the intestine and gill, up-regulated claudin-7 mRNA levels in the MI, DI and gill as well as claudin-11 in the DI, thus maintain the structural integrity between cells. Besides, optimum vitamin A diet enhanced fish enteritis, skin lesion and gill rot disease resistance are also partly owning to the enhanced fish intestine, organize and gill immunity:(1) optimum vitamin A diet increased innate immune-related factors complement 3 (C3) and C4 contents, lysozyme (LA) and acid phosphatase (ACP) activities, up-regulated mRNA levels of ?-defensin-1, hepcidin as well as liver expressed antimicrobial peptide 2A/2B (LEAP-2A/2B) (apart from PI and MI) in the intestine, organize and gill, improved the intestine, organize and gill immunity; (2) optimum vitamin A down-regulated pro-inflammatory signaling molecules I?B kinase ? (IKKP), IKKy (rather than IKKa), nuclear factor-KB p65 (NF-?B p65) (apart from the PI), NF-?B P52 (apart from intestine and gill) and c-Rel (only in intestine) while up-regulated inhibitor of ?B? (I?B?) mRNA levles, down-regulated proinflammatory cytokine tumor necrosis factor ? (TNF-?) (apart from spleen), interferon y2(IFN-y2) (apart from spleen), interleukin-1?(IL-1?), IL-6 (apart from the PI and gill), IL-8, IL-12p35 (only in intestine), IL-15 (only in intestine) and IL-17D (only in MI and DI) mRNA levels, and down-regulated fish p38mitogen-activated protein kinases (p38MAPK) mRNA levels in the MI and DI as well as up-regulated TOR and S6K1 mRNA levels in the organize and gill, leading to the up-regulated anti-inflammatory cytokines IL-10 (apart from the PI and skin), IL-11, IL-4/13A (only in intestine). IL-4/13B (only in intestine), transforming growth factor ?1/?2 (TGF-?1/?2) (apart from the PI), decresed the inflammatory response and improved the fish intestine, organize and gill immune function. Besides, optimum vitamin A improved the protein quality, fat quality, collagen content, water holding capacity, PH and the hardness of the fish muscle, up-regulated the mRNA levles of Nrf2 and down-regulated the mRNA levies of Keapla, leading to the up-reguation of CuZnSOD, MnSOD, CAT, GPx1a, GPx1b. GPx4a, GPx4b and GSTr, increased the corresponding antioxidant enzyme activity and decreased the ROS content as well as lipid peroxidation protein oxidative damage, suggested that optimum vitamin A improved the fish muscle quality and which might be partly attributed to the enhance of antioxidant ability in the fish muscle.Taken together, current study firstly demonstrated that optimum vitamin A increased fish growth performance and improved enteritis, skin lesion and gill rot disease resistance, which were closely related to the enhanced intestine, organize and gill structural integrity and immune function:(1) vitamin A might be through up-regulating Nrf2 signaling to increased the antioxidant enzyme (sunch as CuZnSOD) gene expressions, and up-regulated the anti-apoptotic protein Bcl-2 as well as down-regulated the main pro-apoptotic protein gene expressions, inhibited the intestinal cell apoptosis, maintained the cell structure integrity; (2) might be through down-regulated MLCK signaling-to regulating the tight junction protein gene expression, thus to maintain the structural integrity between cells; (3) improved the main antibacterial components activity and contents, up-regulating the antimicrobial peptide gene expression, and up-regulated the main anti-inflammatory cytokines and down-regulated the main pro-inflammatory cytokines as well as the related signaling molecules (sunch as NF-?B p65) gene expression, decreased the fish inflammatory response and improved the fish intestine, organize and gill immune function. Meanwhile, optimum vitamin A improved the fish muscle quality through the increase of the nutritional value, water holding capacity and so on, which might be partly attributed to the enhance of antioxidant ability in the fish muscle. Based on percentage of weight gain, protecting fish against the enteritis morbidity. ACP activity in the head kidney, C3 content in the spleen, protecting fish against the protein carbonyl (PC) in the gill, and the shear force of muscle, the optimum vitamin A levels for young grass carp (262-997g) were estimated to be 1929,2048,2016,2281,2054 and 2093 IU/kg diet, respectively.