γ-氨基丁酸对高脂膳食小鼠免疫功能的影响

The effect of GABA on immune function of mice fed with high fat diet

目的探讨γ-氨基丁酸(GABA)对高脂膳食小鼠免疫功能的影响及其机制。方法 30只雄性C57BL/6小鼠被随机分为正常组(正常饲料),高脂组(高脂饲料),GABA干预组(高脂饲料,饮用水中加入2 mg/ml的GABA)饲喂20周后,测定小鼠体质量和胸腺、脾脏脏器指数,流式检测小鼠外周血中CD4+细胞、CD8+细胞和CD4+CD25+CD127-/low调节性T细胞(regulatory T cell,Treg)的比例,分选出外周血Treg并测其活性氧(reactive oxygen species,ROS)、线粒体膜电位水平及基因Nrf2、GSK-3βmRNA表达水平。结果高脂膳食小鼠胸腺、脾脏脏器指数、CD4+/CD8+比值、Treg比例的显著下降显示其免疫功能受到损伤。Treg中的ROS水平显著上升,线粒体膜电位下降。Nrf2 mRNA表达水平显著下调,GSK-3βmRNA表达水平显著上调,并且基因的表达水平与Treg的ROS水平和线粒体膜电位水平显著相关。通过添加GABA能够有效改善高脂膳食诱导的机体免疫功能损伤,并可能通过GSK-3β、Nrf2基因的作用来减少过量ROS导致的调节性T细胞线粒体膜电位降低。结论长期高脂膳食可导致免疫功能损伤,GABA能够改善免疫功能并通过清除自由基来减少调节性T细胞凋亡。

To explore the protecting effect of GABA on acquired immunity of mice fed with high fat diet （HFD）, male C57BL/6 mice were randomly assigned to three groups with 10 in each group. The control group was fed with normal diet, while the two experiment groups were fed with high fat diet, in which GABA group was provided additionally with water containing 2 mg/ml GABA for 20 weeks. The final body weight, thymus index and spleen index were estimated; the frequency of CD4＋ lymphocytes, CD8＋ lymphocytes and CD4＋/CD8＋ in peripheral blood were examined by flow cytometry. The peripheral blood Tregs was evaluated and separated for further analysis of Nrf2 and GSK-3β mRNA expression by means of RT-PCR. Also, ROS and mitochondrial membrane potential （MMP） of Tregs were measured. The data indicated HFD induced significant decrease of thymus index, spleen index, CD4＋/CD8＋ ratio and regulatory T cells percentages in peripheral blood, demonstrating the immune imbalance status in HFD group mice. Tregs ROS level was significantly increased but the MMP was significantly decreased in HFD group when compared with the control group; Treg Nrf2 mRNA expression was significantly decreased but the GSK-3β mRNA expression was significantly increased in HFD group. GABA could improve the immune imbalance and prevent the excess ROS-indueed MMP decrease via modulating the mRNA expression of Nrf2 and GSK-3β. In conclusion, GABA can prevent the immune imbalance and protect the Treg from ROS induced apoptosis in mice fed with HFD.