Department Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, CT 06511, USA.
Department Anesthesiology and Center for Shock, Trauma and Anesthesiology Research, University of Maryland School of Medicine, 685 W. Baltimore Street, Baltimore, MD 21201, USA.
Cell Death Differ. 2017 Nov;24(11):1963-1974. doi: 10.1038/cdd.2017.123. Epub 2017 Aug 4.
ABT-737 is a pharmacological inhibitor of the anti-apoptotic activity of B-cell lymphoma-extra large (Bcl-xL) protein; it promotes apoptosis of cancer cells by occupying the BH3-binding pocket. We have shown previously that ABT-737 lowers cell metabolic efficiency by inhibiting ATP synthase activity. However, we also found that ABT-737 protects rodent brain from ischemic injury in vivo by inhibiting formation of the pro-apoptotic, cleaved form of Bcl-xL, ΔN-Bcl-xL. We now report that a high concentration of ABT-737 (1 μM), or a more selective Bcl-xL inhibitor WEHI-539 (5 μM) enhances glutamate-induced neurotoxicity while a low concentration of ABT-737 (10 nM) or WEHI-539 (10 nM) is neuroprotective. High ABT-737 markedly increased ΔN-Bcl-xL formation, aggravated glutamate-induced death and resulted in the loss of mitochondrial membrane potential and decline in ATP production. Although the usual cause of death by ABT-737 is thought to be related to activation of Bax at the outer mitochondrial membrane due to sequestration of Bcl-xL, we now find that low ABT-737 not only prevents Bax activation, but it also inhibits the decline in mitochondrial potential produced by glutamate toxicity or by direct application of ΔN-Bcl-xL to mitochondria. Loss of mitochondrial inner membrane potential is also prevented by cyclosporine A, implicating the mitochondrial permeability transition pore in death aggravated by ΔN-Bcl-xL. In keeping with this, we find that glutamate/ΔN-Bcl-xL-induced neuronal death is attenuated by depletion of the ATP synthase c-subunit. C-subunit depletion prevented depolarization of mitochondrial membranes in ΔN-Bcl-xL expressing cells and substantially prevented the morphological change in neurites associated with glutamate/ΔN-Bcl-xL insult. Our findings suggest that low ABT-737 or WEHI-539 promotes survival during glutamate toxicity by preventing the effect of ΔN-Bcl-xL on mitochondrial inner membrane depolarization, highlighting ΔN-Bcl-xL as an important therapeutic target in injured brain.
ABT-737 是 B 细胞淋巴瘤-extra large（Bcl-xL）蛋白抗凋亡活性的药理学抑制剂；它通过占据 BH3 结合口袋促进癌细胞凋亡。我们之前已经表明，ABT-737 通过抑制 ATP 合酶活性降低细胞代谢效率。然而，我们还发现 ABT-737 通过抑制促凋亡的、切割形式的 Bcl-xL（ΔN-Bcl-xL）的形成来保护体内啮齿动物大脑免受缺血性损伤。我们现在报告说，高浓度的 ABT-737（1μM）或更选择性的 Bcl-xL 抑制剂 WEHI-539（5μM）增强谷氨酸诱导的神经毒性，而低浓度的 ABT-737（10nM）或 WEHI-539（10nM）则具有神经保护作用。高浓度的 ABT-737 显著增加 ΔN-Bcl-xL 的形成，加重谷氨酸诱导的死亡，并导致线粒体膜电位丧失和 ATP 产生减少。尽管 ABT-737 通常被认为是由于 Bcl-xL 的隔离导致 Bax 在线粒体外膜上的激活而导致死亡，但我们现在发现低浓度的 ABT-737 不仅可以防止 Bax 的激活，而且可以抑制谷氨酸毒性或直接应用 ΔN-Bcl-xL 至线粒体引起的线粒体电位下降。环孢菌素 A 也可防止线粒体内膜电位的丧失，这表明线粒体通透性转换孔在 ΔN-Bcl-xL 加重的死亡中起作用。与此一致的是，我们发现谷氨酸/ΔN-Bcl-xL 诱导的神经元死亡通过耗尽 ATP 合酶 c 亚基而减弱。C 亚基耗尽可防止在表达 ΔN-Bcl-xL 的细胞中线粒体膜的去极化，并大大防止与谷氨酸/ΔN-Bcl-xL 损伤相关的神经突的形态变化。我们的研究结果表明，低浓度的 ABT-737 或 WEHI-539 通过防止 ΔN-Bcl-xL 对线粒体内膜去极化的影响来促进谷氨酸毒性期间的存活，凸显了 ΔN-Bcl-xL 作为受损大脑中的重要治疗靶点。
