Pham Ted D, Pham Phi Q, Li Jinfeng, Letai Anthony G, Wallace Douglas C, Burke Peter J
Department of Biomedical Engineering, University of California, Irvine, CA, USA.
Department of Chemical Engineering and Materials Science, University of California, Irvine, CA, USA.
Sci Rep. 2016 Oct 27;6:35907. doi: 10.1038/srep35907.
The intrinsic apoptotic pathway and the resultant mitochondrial outer membrane permeabilization (MOMP) via BAK and BAX oligomerization, cytochrome c (cytc) release, and caspase activation are well studied, but their effect on cytosolic pH is poorly understood. Using isolated mitochondria, we show that MOMP results in acidification of the surrounding medium. BAK conformational changes associated with MOMP activate the OMA1 protease to cleave OPA1 resulting in remodeling of the cristae and release of the highly concentrated protons within the cristae invaginations. This was revealed by utilizing a nanomaterial graphene as an optically clear and ultrasensitive pH sensor that can measure ionic changes induced by tethered mitochondria. With this platform, we have found that activation of mitochondrial apoptosis is accompanied by a gradual drop in extra-mitochondrial pH and a decline in membrane potential, both of which can be rescued by adding exogenous cytc. These findings have importance for potential pharmacological manipulation of apoptosis, in the treatment of cancer.
细胞内凋亡途径以及通过BAK和BAX寡聚化、细胞色素c（cytc）释放和半胱天冬酶激活所导致的线粒体外膜通透性改变（MOMP）已得到充分研究，但其对细胞质pH值的影响却知之甚少。我们利用分离的线粒体表明，MOMP会导致周围培养基酸化。与MOMP相关的BAK构象变化会激活OMA1蛋白酶，从而切割OPA1，导致嵴重塑并释放嵴内陷中高度浓缩的质子。这是通过利用纳米材料石墨烯作为光学透明且超灵敏的pH传感器来揭示的，该传感器可以测量由附着的线粒体引起的离子变化。通过这个平台，我们发现线粒体凋亡的激活伴随着线粒体外pH值的逐渐下降和膜电位的降低，而添加外源性cytc可以挽救这两者。这些发现对于癌症治疗中凋亡的潜在药理学操纵具有重要意义。
