蛋白磷酸酶2A催化亚基下调参与人tau蛋白所致线粒体分裂融合和功能失衡

Down-regulation of Protein Phosphatase 2A Catalytic Subunit Involved in Mitochondria Fission/fusion Dynamics Imbalance and Functional Impairment Induced by Human tau

目的探讨蛋白磷酸酶2A催化亚基(PP2Ac)下调是否参与人tau蛋白积聚引起的线粒体分裂融合动态及功能失衡的机制。方法大鼠原代海马神经元转染mito-dsRed质粒和人tau40质粒48 h后,共聚焦显微镜观测线粒体分布,免疫印迹检测线粒体分裂融合蛋白、PP2Ac及PP2A调节亚基b(PP2Ab)表达水平;大鼠原代海马神经元和野生型HEK293细胞(293wt)共转染siPP2Ac-EGFP质粒和mito-dsRed质粒48 h后,检测线粒体形态和分布;293wt细胞共转染siPP2Ac质粒和mito-Dendra2质粒40 h后,实时观测线粒体分裂融合动态;293wt细胞沉默PP2Ac表达后,检测线粒体分裂融合蛋白水平及细胞膜电位和细胞活力;稳定表达人tau的HEK293细胞(293htau)共转染PP2Ac-EGFP质粒和mito-dsRed质粒48 h后,分析线粒体分布和形态及功能。结果大鼠原代海马神经元表达人tau蛋白引起突起线粒体分布下降并伴有PP2Ac水平显著下降(t=4.814,P=0.0086)。下调PP2Ac表达引起大鼠原代海马神经元和HEK293细胞线粒体变长并异常分布于细胞核周围;引起293wt细胞线粒体融合明显加速(t=2.857,P=0.0074);使293wt细胞融合蛋白线粒体融合蛋白(MFN)1(t=6.768,P=0.0025)、MFN2(t=3.121,P=0.0035)和视神经萎缩蛋白1水平显著升高(t=3.775,P=0.0199),动力样蛋白1和Fis1水平不变;使HEK293细胞线粒体相对膜电位(t=2.300,P=0.0270)和细胞活力(t=6.249,P<0.0001)显著降低。上调PP2Ac表达可减轻293htau细胞线粒体形态和分布及功能异常。结论PP2Ac表达下调参与了人tau蛋白引起的大鼠原代海马神经元和HEK293细胞线粒体形态分布异常及细胞活力下降。

Objective To explore whether the downregulation of protein phosphatase 2A catalytic subunit(PP2Ac)involved in the pathogenesis of mitochondria fission/fusion dynamics and functional imbalance induced by human tau accumulation.Methods After cotransfection with mito-dsRed plasmids and pIRES-eGFP-tau40 plasmids 48 hours,the rat primary hippocampal neurons were observed with a laser scanning confocal microscope for their changes in shape and distribution of mitochondria.The expressions of mitochondria fission/fusion protein and PP2Ac and PP2Ab were detected by Western blotting.Furthermore,the shape and distribution of mitochondria of rat primary hippocampal neuron and wild type 293wt cells were assayed 48 hours after co-transfection with siPP2Ac-EGFP plasmids and mito-DsRed plasmids,and the fission/fusion dynamics of 293wt cells was captured with live cell time-lapse imaging after co-transfection with siPP2Ac plasmids and mito-Dendra2 plasmids.After transfection with siPP2Ac plasmids,the relative level of mitochondria fission/fusion protein of 293wt cells was assayed by Western blotting,and mitochondria membrane potential was detected by JC-1 staining,and the cellular viability was measured by CCK8 assay.Finally,the shape and distribution and membrane potential of mitochondria of HEK293 cells with stable transfection of htau40(293htau)were detected after co-transfection with PP2Ac and mito-dsRed plasmids.Results Human tau40 expression decreased distribution of mitochondria and significantly lowered PP2Ac level in primary hippocampal neuron(t=4.814,P=0.0086).Down-regulation of PP2Ac caused mitochondria elongation and perinuclear accumulation in primary hippocampal neuron and 293wt cells;in addition,down-regulation of PP2Ac in 293wt cells significantly increased mitochondria fusion rate(t=2.857,P=0.0074)and the levels of mitochondria fusion protein mitofusin(MFN)1(t=6.768,P=0.0025),MFN2(t=3.121,P=0.0035),and optic atrophy 1(t=3.775,P=0.0199);however,the levels of dynamin-like protein-1 and Fis1 remained unchanged.The down-regulation of PP2Ac in 293wt cells led to the significant decrease in mitochondria membrane potential(t=2.300,P=0.0270)and cell viability(t=6.249,P<0.0001).Finally,up-regulation of PP2Ac attenuated the abnormalities in the shape,distribution and function of mitochondria in the 293htau cells.Conclusion Down-regulation of PP2Ac is involved in the abnormal shape and distribution of mitochondria and its dysfunction induced by human tau40 in rat primary hippocampal neurons and HEK293 cells.