饲料中花生四烯酸水平对凡纳滨对虾免疫相关基因表达及抗菌能力的影响

摘要

为了评估饲料中花生四烯酸(arachidonic acid,ARA)水平对凡纳滨对虾免疫相关基因表达及抗菌能力的影响,分别以鱼油和混合植物油为脂肪源,设计了2个系列共9组不同ARA含量的等氮等能,且具备相同饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)、多不饱和脂肪酸(PUFA)和n-3/n-6比例的实验饲料,投喂对虾6周后,检测各组对虾在急性感染溶藻弧菌0、24、36和42 h时鳃组织中Toll受体、IMD(immune deficiency)和溶菌酶mRNA表达量,并统计感染后96 h内对虾的死亡情况.结果表明:①对虾摄食以鱼油为脂肪源的饲料[饲料DHA(22:6n-3)和EPA(20:5n-3)含量分别为5.85和3.83 mg/g饲料],其鳃组织中Toll受体、IMD和溶菌酶mRNA表达量均随饲料中ARA含量的升高呈现先升高后下降的变化;0.56(B组)和0.87 mg ARA/g饲料组(C组)对虾溶菌酶mRNA表达量显著高于0.44(A组)、1.02(D组)和0.28 mg ARA/g饲料组(E组)(P＜0.05);对虾摄食以植物混合油为脂肪源的饲料(DHA和EPA含量分别为3.28和1.87 mg/g饲料),其鳃组织中Toll受体、IMD和溶菌酶mRNA表达量随饲料中ARA含量的升高而升高;1.44 mg ARA/g饲料组(Ⅰ组)对虾Toll受体mRNA表达量显著高于0.19 mg ARA/g饲料组(F组)(P＜0.05).②人工急性感染溶藻弧菌后,各组对虾鳃组织中Toll受体、IMD和溶菌酶mRNA的表达量随感染进程均出现显著变化.摄食以鱼油为脂肪源的饲料时,对虾鳃组织中Toll受体、IMD和溶菌酶mRNA表达量峰值均出现在0.56 mg ARA/g饲料组(B组),且峰值分别出现在感染后24、42和24 h.摄食以混合植物油为脂肪源的饲料时,对虾鳃组织中Toll受体、IMD和溶菌酶mRNA表达量峰值均出现在1.44 mg ARA/g饲料组(Ⅰ组),且峰值分别出现在感染后24、42和36h.③各实验组对虾急性感染溶藻弧菌后96 h累积死亡率无显著差异.本研究表明,饲料ARA水平影响凡纳滨对虾免疫相关基因(Toll受体、IMD和溶菌酶)的表达,且ARA调控免疫基因表达的效果受饲料EPA和DHA水平的影响.%In order to assess the effect of dietary arachidonic acid on the immune-related genes expression and Vibrio-resistance in white shrimp Litopenaeus vannamei,two series of isonitrogenous and isoenergetic experimental diets based on either fish oil or blended vegetable oil,both with the equivalents of saturated fatty acids(SFA),mono-unsaturated fatty acids (MUFA),poly-unsaturated fatty acids (PUFA),and n-3/n-6 ratios,were fed to the white shrimp respectively for six weeks.Then the mRNA expression levels of Toll receptor,IMD and lysozyme in gills of all shrimp before and after Vibrio alginolyticus challenge(24,36 and 42 h),and Vibrio-resistance of all the shrimp were investigated.The results showed that:① The mRNA expressions of Toll receptor,IMD and lysozyme in gills of the shrimp fed diets based on fish oil (containing 5.85 mg DHA/g diet and 3.83 EPA mg/g diet),first increased,then decreased along with the increasing dietary ARA level.Compared to the other treatments,the shrimp in treatments of 0.56 mg ARA/g diet (B group) and 0.87mg ARA/g diet (C group)displayed significant higher lysozyme mRNA expression levels(P＜0.05).The mRNA expressions of Toll receptor,IMD and lysozyme in gills of the shrimp fed diets based on vegetable oil (containing 3.28 mg DHA/g diet and 1.87 mg EPA/g diet),increased along with the dietary ARA level.The Toll receptor mRNA expression level in treatment Ⅰ(1.44 mg ARA/g diet) was significantly higher than F group(0.19 mg ARA/g diet)(P＜0.05).② The mRNA expressions of Toll receptor,IMD and lysozyme in gills of all shrimp changed significantly when the shrimp experienced Vibrio challenge.For the shrimp fed diets based on fish oil,the peak of mRNA expressions of Toll receptor,IMD and lysozyme appeared at 24,42 and 24 h respectively.The maximum expressions of all the three genes appeared in B treatment(0.56 mgARA/g diet).For the shrimp fed diets based on vegetable oil,the peak of mRNA expressions of Toll receptor,IMD and lysozyme appeared at 24,42 and 36 h respectively.For the shrimp fed diets based on vegetable oil,the maximum expressions of all the three genes appeared in Ⅰ treatment (1.44 mg ARA/g diet).③ There was no significant difference in cumulative mortality among the different ARA treatments when the shrimp were challenged with V.alginolyticus for 96 h.It is therefore suggested that dietary ARA level could regulate the expressions of these immune-related genes of the white shrimp,and ARA's regulation on immune related genes could be affected by dietary DHA and EPA levels.