Department of Physiology, Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin;
Am J Physiol Heart Circ Physiol. 2014 Feb 15;306(4):H475-84. doi: 10.1152/ajpheart.00001.2013. Epub 2013 Nov 27.
Amyloid-β (Aβ) has long been implicated as a causative protein in Alzheimer's disease. Cellular Aβ accumulation is toxic and causes mitochondrial dysfunction, which precedes clinical symptoms of Alzheimer's disease pathology. In the present study, we explored the possible use of epoxyeicosatrienoic acids (EETs), epoxide metabolites of arachidonic acid, as therapeutic target against Aβ-induced mitochondrial impairment using cultured neonatal hippocampal astrocytes. Inhibition of endogenous EET production by a selective epoxygenase inhibitor, MS-PPOH, caused a greater reduction in mitochondrial membrane potential in the presence of Aβ (1, 10 μM) exposure versus absence of Aβ. MS-PPOH preincubation also aggravated Aβ-induced mitochondrial fragmentation. Preincubation of the cells with either 14,15- or 11,12-EET prevented this mitochondrial depolarization and fragmentation. EET pretreatment also further improved the reduction observed in mitochondrial oxygen consumption in the presence of Aβ. Preincubation of the cells with EETs significantly improved cellular respiration under basal condition and in the presence of the protonophore, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP). The uncoupling of ATP synthase from the electron transfer chain that occurred in Aβ-treated cells was also prevented by preincubation with EETs. Lastly, cellular reactive oxygen species production, a hallmark of Aβ toxicity, also showed significant reduction in the presence of EETs. We have previously shown that Aβ reduces EET synthesis in rat brain homogenates and cultured hippocampal astrocytes and neurons (Sarkar P, Narayanan J, Harder DR. Differential effect of amyloid beta on the cytochrome P450 epoxygenase activity in rat brain. Neuroscience 194: 241-249, 2011). We conclude that reduction of endogenous EETs may be one of the mechanisms through which Aβ inflicts toxicity and thus supplementing the cells with exogenous EETs improves mitochondrial dynamics and prevents metabolic impairment.
淀粉样蛋白-β(Aβ)长期以来一直被认为是阿尔茨海默病的致病蛋白。细胞内 Aβ 的积累是有毒的,并导致线粒体功能障碍,这先于阿尔茨海默病病理的临床症状。在本研究中,我们使用培养的新生海马星形胶质细胞探索了环氧二十碳三烯酸(EETs),即花生四烯酸的环氧化物代谢物作为针对 Aβ 诱导的线粒体损伤的治疗靶点的可能性。用选择性环氧合酶抑制剂 MS-PPOH 抑制内源性 EET 产生,在存在 Aβ(1、10 μM)暴露时,比不存在 Aβ时,线粒体膜电位的降低更大。MS-PPOH 预孵育也加重了 Aβ 诱导的线粒体碎片化。用 14,15-EET 或 11,12-EET 预处理细胞可防止这种线粒体去极化和碎片化。EET 预处理还进一步改善了存在 Aβ时观察到的线粒体耗氧量的减少。用 EET 预处理细胞可显著改善基础条件下和质子载体羰基氰化物 4-(三氟甲氧基)苯腙(FCCP)存在下的细胞呼吸。EET 预处理还防止了 Aβ 处理细胞中线粒体 ATP 合酶与电子传递链解偶联的发生。最后,Aβ 毒性的一个标志是细胞内活性氧物质的产生,也在存在 EET 的情况下显著减少。我们之前已经表明,Aβ 减少了大鼠脑匀浆和培养的海马星形胶质细胞和神经元中的 EET 合成(Sarkar P,Narayanan J,Harder DR。淀粉样蛋白-β对大鼠脑细胞色素 P450 环氧合酶活性的差异影响。神经科学 194:241-249,2011)。我们得出结论,内源性 EET 的减少可能是 Aβ 造成毒性的机制之一,因此用外源性 EET 补充细胞可改善线粒体动力学并防止代谢损伤。