皮质醇(COR)介导的氨氮抑制团头鲂免疫功能

Cortisol(COR)mediates ammonia nitrogen to inhibit the immune function of Megalobrama amblycephala

高浓度氨氮始终被视为水产养殖中最具危害的环境因子,严重影响鱼类的免疫抗性,导致死亡率升高,因此氨氮对鱼类免疫功能影响的机理亟需阐明。高浓度氨氮引发鱼类应激反应,导致肾间组织中皮质醇(COR)分泌激增以及免疫指标的下降。高浓度COR通常抑制机体免疫功能。为了阐明COR在氨氮抑制鱼类免疫功能中的作用,本实验设置对照、氨氮暴露、COR注射、米非司酮(RU486)注射以及RU486注射+氨氮暴露5个处理组,处理团头鲂(Megalobrama amblycephala)幼鱼[(2.63±0.33)g]48 h。结果显示,氨氮暴露与注射COR对团头鲂作用效果类似,均导致团头鲂血清COR含量显著升高,表明急性氨氮暴露和注射COR均能导致团头鲂应激反应。氨氮暴露与注射COR均显著抑制了团头鲂血清溶菌酶和补体C3水平以及头肾免疫相关基因(tnf-α、il-1β、il-6、tlr1、tlr2、tlr3、tlr4、tlr5、myd88、traf6、nf-κb1和nf-κb2)表达水平。此外,RU486可以有效地阻断氨氮对免疫指标的抑制作用,表明急性氨氮暴露可通过COR/TLR/MyD88信号通路抑制团头鲂免疫功能。综上所述,COR介导了氨氮抑制团头鲂免疫功能,为开发降应激措施来管理与预防氨氮胁迫以及培育抗氨氮鱼类新品种提供了科学依据。

In water,ammonia nitrogen,a harmful environmental factor in aquaculture,exists in two chemi-cal forms(the unionized NH_(3)and ionized NH_(4)^(+)).The unionized NH_(3)is considered more toxic to fish than NH_(4)^(+)since unionized NH_(3)can easily diffuse across the epithelial membranes of aquatic animals and lead to higher concentrations of ammonia in plasma and tissue.Under intensive fish farming conditions,massive organic wastes such as unconsumed feed and feces make ambient ammonia concentration easier to get to a high level.Addition-ally,the a much higher level(>20 mg/L)at times due to ineffective or nonexistent sewage treatment or other reasons.In fish,the immunosuppressive effects of ammonia have been proven to contribute to disease out-breaks.Therefore,it is urgently necessary to clarify the mechanism of ammonia nitrogen’s effect on immunity.Under ammonia nitrogen exposure,the cortisol secretion of the head-kidney increases,and the immune re-sponse is down-regulated.Generally,high cortisol levels(COR)often inhibit immune function.Consequently,we hypothesize that ammonia exposure might affect fish immunity by increasing COR levels.The aim of this study to clarify the effects of COR on the immune function of fish exposed to ammonia nitrogen.The juvenile Megalobrama amblycephala[(2.63±0.33)g]were randomly assigned to five different treatment groups(am-monia nitrogen group,COR group,Mifepristone(RU486:a glucocorticoid receptor blocker)group,RU486+ammonia nitrogen group and control group)for 48 h.The contents of serum COR,immune parameters,and mRNA expression of TLR(Toll-like receptors)pathway-related molecules were determined.Our present results showed that the contents of serum COR increased significantly in ammonia nitrogen and COR groups compared with the control group,indicating that stresses were caused by ammonia nitrogen and COR.Similar-ly,the significantly decreased serum lysozyme and C3 levels were detected in ammonia nitrogen and COR groups.The significantly down-regulation expression of tnf-α,il-1β,il-6 and the genes of TLR/MyD88 sig-naling pathway(trl1,tlr2,tlr3,tlr4,tlr5,myd88,traf6,nf-κb1 and nf-κb2)were detected in ammonia nitro-gen and COR groups.In addition,the significant effects of ammonia nitrogen on immunity were eliminated by RU486,which indicated that the immune function of Megalobrama amblycephala was inhibited by acute ammonia exposure through COR/TLR/MyD88 signaling pathways.In conclusion,the immune function of M.amblycepha-la was inhibited by acute ammonia nitrogen exposure through increasing COR secretion.These results provided a scientific basis for managing and preventing the effects of ammonia nitrogen through breeding new varieties and developing stress-reducing measures.