小胶质细胞TAK1在小鼠抑郁样行为中的作用机制

Role of microglial TAK1 in depressive-like behaviour in mice

Key words:  抑郁  小胶质细胞  神经炎症  海马  TAK1基因； 小鼠

Key words:  depression  microglia  neuroinflammation  hippocampus  TAK1 gene  mouse

Abstract:

目的 探讨小胶质细胞转化生长因子β活化激酶1(transforming growth factor beta kinase 1, TAK1)在小鼠抑郁样行为中的作用。 方法 使用Cre/LoxP系统构建小胶质细胞特异性敲除TAK1基因小鼠模型；通过慢性束缚应激建立抑郁模型。将CX3CR1cre+/-、TAK1flox/flox(cKO)小鼠和同窝TAK1flox/flox(f/f)雄性小鼠随机分为对照组(control group, CON组)、慢性束缚模应激组(chronic restraint stress group, CRS组)，每组8只。造模21 d后，进行行为学测试。使用RT-qPCR测量海马区IL-1β、IL-6、TNF-α的mRNA水平来评估炎症水平；通过免疫荧光试验观察海马区小胶质细胞的激活情况；通过Western印迹法检测p-ERK1/2、ERK1/2蛋白的表达水平。 结果 cKO小鼠小胶质细胞中TAK1 mRNA的水平较f/f小鼠明显下降（P<0.001）。CRS组中cKO小鼠与f/f小鼠相比，在旷场中心区域停留的时间明显增加（P<0.01），在悬尾实验和强迫游泳中不动的时间明显减少（均P<0.05）；小鼠海马区TNF-α、IL-6 mRNA水平明显减少（P<0.01，P<0.05），IL-1β mRNA水平差异没有统计学意义（P＞0.05）；小鼠海马区CA1区Iba1阳性细胞数量显著减少（P<0.05）；小鼠海马区的ERK1/2磷酸化水平显著升高（P<0.05）。 结论 小胶质细胞特异性敲除TAK1可有效改善CRS诱导的小鼠抑郁样行为，降低海马区炎症水平，抑制小胶质细胞的激活，这可能是通过促进ERK1/2磷酸化途径来实现的。

Abstract:

Objective To investigate the role of microglial transforming growth factor beta kinase 1(TAK1) in depressive-like behavior in mice. Methods Microglia-specific knockout TAK1 mice were constructed by using the Cre/LoxP system. Chronic bound-mode stress was used to establish a depression model, CX3CR1cre+/-; TAK1flox/flox(cKO) mice and TAK1flox/flox(f/f) male mice from the same litter were randomly divided into control(CON) group, and chronic restraint stress(CRS) group with 6 mice in each group.Behavioral tests were performed 21 days after modelling. Real-time quantitative polymerase chain reaction(RT-qPCR) was used to measure mRNA levels of IL-6 and TNF-α in the hippocampus to assess inflammation. Activation of microglia in the hippocampus was observed by immunofluorescence. The expression levels of p-ERK1/2 and ERK1/2 proteins were detected by Western blotting. Results The level of TAK1 mRNA in microglia of cKO mice was significantly decreased(P<0.001) when compared with that in f/f mice. cKO mice in the CRS group spent significantly more time in the central area in the open field test(P<0.01) and significantly less time of immobility in the tail suspension test and forced swimming test when compared with those in f/f mice(both P<0.05). In the CRS group, TNF-α and IL-6 mRNA levels in the hippocampal region of the cKO mice were both significantly lower than those of the f/f mice(both P<0.05), while the difference in IL-1β mRNA level was not statistically significant(P>0.05). The number of Iba1-positive cells in cKO mice in the hippocampal region was significantly decreased when compared with that in f/f mice in the CRS group(P<0.05). cKO mice in the CRS group had significantly higher ERK1/2 phosphorylation levels in the hippocampus than those in the f/f mice(P<0.05). Conclusion It’s indicated that microglia-specific knockdown of TAK1 effectively ameliorates CRS-induced depressive-like behaviors, reduces inflammation levels in the hippocampal region of mice, and inhibites microglia activation, which may be achieved by promoting ERK1/2 phosphorylation.