Effects Of Different Selenium Sources On Intestinal Epithelial Tight Junction Barrier Function In Oxidative Stressed Broilers

Oxidative stress can cause a 40-50% reduction in production performance and more than20% increase in mortality in yellow-finned broilers,causing serious economic losses in poultry farming.The disruption of the intestinal epithelial tight junction(TJ)barrier caused by oxidative stress is the main reason for the reduced performance of broiler chickens.In this project,we propose to investigate the effects of sodium selenite(SS)and selenomethionine(Se-Met)on oxidative stress-induced TJ barrier function,TJ protein expression,inflammatory response and The effects of selenomethionine(Se-Met)on oxidative stress-induced TJ barrier function,TJ protein expression,inflammatory response and myosin light chain kinase(MLCK)-myosin light chain(MLC)pathway activation in intestinal epithelial cells were investigated to reveal the effects of different selenium sources on the repair of oxidative stress-induced intestinal epithelial TJ barrier damage and its mechanism.1.Effects of different selenium sources on the production performance and oxidative damage,permeability and inflammatory response of intestinal mucosa in broiler chickens under oxidative stress720 1-day-old Lingnan yellow meat chicks were randomly divided into 4 experimental groups(6 replicates per group,30 chickens per replicate)as groups Ⅰ,Ⅱ,Ⅲ and Ⅳ,respectively.Group I was fed the basal diet(fluoride content: 23 mg/kg;selenium content: 0.04 mg/kg);group II was supplemented with 800 mg fluoride/kg of sodium fluoride;groups III and IV were supplemented with 0.15 mg selenium/kg of SS or Se-Met on top of the diet of group II.The experiment lasted for 56 days.The experiment lasted for 56 days.At the end of the experiment,two males of similar body weight were selected from each replicate and slaughter experiments were performed,and intestinal samples were taken for analysis.The results showed that.(1)Compared with the group I,the levels of reactive oxygen species(ROS),malondialdehyde(MDA),8-hydroxy-2 deoxyguanosine(8-OHd G)and protein carbonyl(PC)in the duodenal and jejunal mucosa of group II were significantly higher.protein carbonyl(PC)levels were significantly increased(P < 0.05).The levels of ROS,MDA,8-OHd G and PC in duodenal and jejunal mucosa were significantly lower(P < 0.05)in groups III and IV(except for PC in duodenal mucosa in group III)than in group II,and reached a significant difference(P <0.05)in groups III and IV(except for MDA in jejunal mucosa).It indicates that HF can cause oxidative stress in the intestinal mucosa of broiler chickens,resulting in oxidative damage of intestinal mucosa,and the addition of selenium can alleviate the oxidative damage of intestinal mucosa induced by HF,and the alleviating effect of Se-Met is better than that of SS.(2)The levels of serum diamine oxidase(DAO),D-lactic acid(D-LA)and endotoxin in group II were significantly higher(P < 0.05)than those in group I.Serum DAO,D-LA and endotoxin levels were significantly lower(P < 0.05)in groups III and IV compared to group II(except for endotoxin in group III),and the best effect was observed in group IV.It indicates that oxidative stress can lead to increased intestinal mucosal permeability in broiler chickens,and the addition of selenium is beneficial to reducing intestinal mucosal permeability,and the effect of Se-Met is better than that of SS.(3)The intestinal mucosal interferon-γ(IFN-γ),tumor necrosis factor-α(TNF-α),interleukin-6(IL-6)and interleukin-1β(IL-1β)in duodenum and jejunum of group Ⅱ.interleukin-1β,IL-1β)levels were significantly higher(P < 0.05)in group I.The levels of TNF-αand IL-1β in duodenal and jejunal mucosa were significantly lower(P < 0.05)in group III compared with group II,and the levels of IFN-γ,TNF-α,IL-6 and IL-1β in duodenal and jejunal mucosa were significantly lower(P < 0.05)in group IV.IFN-γ,TNF-α and IL-1β in duodenal intestinal mucosa and IFN-γ,TNF-α and IL-6 in jejunum intestinal mucosa reached significant levels of difference(P < 0.05)in group IV and group III.It indicates that oxidative stress can lead to elevated levels of pro-inflammatory factors in the intestinal mucosa of broiler chickens,and the addition of selenium can alleviate the oxidative stress-induced inflammatory response in the intestinal mucosa,and the alleviating effect of Se-Met was better than that of SS.(4)Compared with the group I,group II significantly(P < 0.05)reduced the average daily gain(ADG)and increased the feed to gain(F/G)ratio of broiler chickens at each growth stage.Group II significantly reduced(P < 0.05)the average daily feed intake(ADFI)of broilers from 1to 21 days of age compared to group I.Group IV and group III significantly(P < 0.05)increased ADG and decreased F/G at all growth stages compared to group II.Group IV significantly(P <0.05)increased ADG and decreased F/G at 22-56 and 1-56 days of age compared to group III.This indicates that oxidative stress can reduce broiler growth performance,and the addition of selenium antagonized the growth inhibition caused by oxidative stress.The growth inhibition caused by oxidative stress was antagonized by the addition of selenium,and the antagonistic effect of Se-Met was better than that of SS.2.The role of the MLCK-MLC pathway in the regulation of intestinal epithelial tight junction barrier in broiler chickens under oxidative stress by different selenium sourcesBased on the above experiments,we further investigated whether different selenium sources achieve the repairing effect on the oxidative stress-induced disruption of intestinal epithelial TJ barrier function in broiler chickens by affecting the MLCK-MLC pathway.The experimental design and grouping and sampling were as above.The results showed that.(1)Compared with group I,group II significantly increased(P < 0.05)the relative expression of MLCK and MLC m RNA in the duodenal and jejunal intestinal mucosa.Groups IV and III were significantly lower(P < 0.05)than group II.The relative expression levels of MLCK and MLC m RNA in duodenal and jejunal intestinal mucosa were significantly reduced in group IV than group II,and the best effect was observed in group IV.It indicates that oxidative stress can increase the expression of MLCK and MLC m RNA in broiler intestinal mucosa,and the addition of selenium can inhibit the effect of oxidative stress,and the inhibitory effect of Se-Met is better than that of SS.(2)The m RNA and protein expression levels of closure protein-1(Claudin-1),Occludin and closure small ring protein-1(Zonula occluden-1,ZO-1)in the duodenal and jejunal intestinal mucosa of group Ⅱ were significantly lower(P < 0.05)than those of group Ⅰ.Compared with group II,group III significantly increased(P < 0.05)the relative expression of Claudin-1 and ZO-1 m RNA in duodenal and jejunal intestinal mucosa and Occludin m RNA in jejunal intestinal mucosa;group IV significantly increased(P < 0.05)the relative expression of Claudin-1,Occludin and ZO-1 m RNA and protein expression levels.The levels of Claudin-1,Occludin and ZO-1 m RNA and protein expression in duodenal and jejunal mucosa in group IV and group III reached a significant level of difference(P < 0.05).It indicates that oxidative stress decreased intestinal mucosal TJ protein gene expression,and the addition of selenium inhibited the oxidative stress-induced decrease in TJ protein gene expression levels,and the effect of Se-Met was superior to that of SS.(3)Compared with the group I,the TJ structure between intestinal epithelial cells of the duodenum and jejunum in group II was disrupted and the gap between intestinal epithelial cells was enlarged;the TJ between intestinal epithelial cells in group IV was normally distributed and was close to the level of group I;while the effect of SS in alleviating the disorder of TJ structure between intestinal epithelial cells was inferior to that of Se-Met.and the effect of Se-Met was better than that of SS.In summary,oxidative stress can lead to the destruction of the intestinal epithelial TJ barrier,which in turn causes an increase in intestinal mucosal permeability,resulting in an increase in serum endotoxin levels,inducing an intestinal inflammatory response,and ultimately reducing the performance of broiler chickens;while the addition of SS and Se-Met to the diet increased the expression of intestinal mucosal TJ protein genes by reducing the expression levels of MLCK and MLC m RNA in the intestinal mucosa.The results of this study can provide a theoretical basis for the development of Se-Met and its protective effect on the intestinal mucosal barrier.At the same time,the results of this study are also useful for the pathogenesis and prevention of oxidative stress-induced oviductitis,pneumonia and tracheitis in chickens,because TJ exists not only between intestinal epithelial cells,but also between oviductal mucosal epithelial cells,alveolar epithelial cells and tracheal epithelial cells.