Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan.
J Pineal Res. 2010 Jan;48(1):20-38. doi: 10.1111/j.1600-079X.2009.00721.x. Epub 2009 Nov 17.
Melatonin protects cells against various types of oxidative stress-induced apoptosis due primarily to its ability to effectively scavenge pathological and disease condition-augmented generation of mitochondrial reactive oxygen species (mROS). Once produced, mROS indiscriminately damage mitochondrial components and more importantly they crucially activate directly the mitochondrial permeability transition (MPT), one of the critical mechanisms for initiating post mitochondrial apoptotic signaling. Whether or not melatonin targets directly the MPT, however, remains inconclusive, particularly during oxidative stress. This study, thus, investigated this possibility of an 'oxidation free Ca(2+) stress' in the presence of vitamin E after ionomycin exposure as a sole Ca(2+)-mediated MPT in order to exclude melatonin's primary antioxidative effects as well as Ca(2+)-mediated oxidative stress. The studies were carried out using cultured rat brain astrocytes RBA-1. With the application of laser scanning multiple fluorescence imaging microscopy, we visualized for the first time multiple mitochondrial protective effects provided by melatonin during Ca(2+) stress. First, melatonin, due to its primary antioxidative actions, completely prevented mCa(2+)-induced mROS formation during ionomycin exposure. Secondly, when melatonin(')s antioxidative effects were prevented due to the addition of vitamin E, melatonin significantly prevented mCa(2+)-mediated MPT and apoptosis suggesting its direct targeting of the MPT. Surprisingly, in the presence of cyclosporin A, a MPT inhibitor, melatonin reduced further mCa(2+)-mediated apoptosis during ionomycin exposure also suggesting its targeting beyond the MPT. As astrocytes are actively involve in regulating synaptic transmission and neurovascular coupling in the CNS, these multiple mitochondrial layers of protection provided by melatonin against mCa(2+)-and/or mROS-mediated apoptosis in astrocytes may be crucial for future therapeutic prevention and treatment of astrocyte-mediated neurodegenerative diseases in the CNS.
褪黑素主要通过有效清除病理性和疾病增强的线粒体活性氧物种 (mROS) 的产生，从而保护细胞免受各种类型的氧化应激诱导的细胞凋亡。一旦产生，mROS 会无差别地破坏线粒体成分，更重要的是，它们会直接激活线粒体通透性转换（MPT），这是启动线粒体后细胞凋亡信号的关键机制之一。然而，褪黑素是否直接靶向 MPT，尤其是在氧化应激期间，仍然没有定论。因此，本研究在单独使用离子霉素作为唯一的 Ca2+ 介导的 MPT 后，研究了维生素 E 存在下的“无氧化 Ca2+ 应激”的这种可能性，以排除褪黑素的主要抗氧化作用以及 Ca2+ 介导的氧化应激。研究使用培养的大鼠脑星形胶质细胞 RBA-1 进行。通过激光扫描多荧光成像显微镜的应用，我们首次可视化了褪黑素在 Ca2+ 应激期间提供的多种线粒体保护作用。首先，由于其主要的抗氧化作用，褪黑素完全阻止了离子霉素暴露期间 mCa2+ 诱导的 mROS 形成。其次，当由于添加维生素 E 而阻止了褪黑素的抗氧化作用时，褪黑素显著阻止了 mCa2+ 介导的 MPT 和细胞凋亡，表明其直接靶向 MPT。令人惊讶的是，在环孢菌素 A（一种 MPT 抑制剂）存在的情况下，褪黑素在离子霉素暴露期间进一步降低了 mCa2+ 介导的细胞凋亡，这也表明其作用超越了 MPT。由于星形胶质细胞积极参与调节中枢神经系统中的突触传递和神经血管耦联，因此，褪黑素对 mCa2+ 和/或 mROS 介导的星形胶质细胞凋亡的这些多种线粒体保护作用对于未来预防和治疗星形胶质细胞介导的中枢神经系统神经退行性疾病可能至关重要。
