Visualization of melatonin’s multiple mitochondrial levels of protection against mitochondrial Ca²⁺‐mediated permeability transition and beyond in rat brain astrocytes

Abstract

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.

Melatonin Prevents Chemical-Induced Haemopoietic Cell Death

“…These findings are in agreement with our previous works reporting that MEL prevented UVB cell death by stabilizing the mitochondrial membrane potential and by inhibiting cytochrome c release [6,35]. Many of the beneficial effects of MEL administration may depend on its action on mitochondria [46–48] where high concentrations of MEL were found. In fact, there is evidence that mitochondria may have the capacity to synthesize and metabolize MEL [49,50].…”

Functional Recovery of Human Cells Harbouring the Mitochondrial DNA Mutation MERRF <b><i>A8344G</i></b> via Peptide-Mediated Mitochondrial Delivery

“…In the present study, we not only demonstrated the co-localization of delivered mitochondria and endogenous mitochondria in host cells but also showed that the overloading of [Ca 2+ ]m with or without inducing oxidative stress was dramatically reduced in both types of treated cells. These findings suggest that steric hindrance resulting from the translocation of foreign mitochondria interfered with the endogenous MFN2-ER connection and led to a reduction in the excessive uptake of [Ca 2+ ]m, which in turn triggered mitochondrial permeability transition pore opening and cell death [28]. Recently, an ER-mitochondrial disorder was considered to be involved in the pathogenesis of Alzheimer's disease [29,30], although it remains unidentified in other neurodegenerative diseases.…”

Melatonin, a Full Service Anti-Cancer Agent: Inhibition of Initiation, Progression and Metastasis

“…Considering the higher concentration of the free radical scavenger melatonin in mitochondria relative to some other subcellular organelles [65], melatonin’s ability to detoxify ROS in both the intermembrane space and matrix is certainly feasible and has been documented [115]. Judging from the greater efficacy in protecting mitochondria from damage when compared to synthetically-produced, mitochondria-targeted antioxidants [116,117], melatonin itself has been classified as a mitochondria-targeted antioxidant [73,81,118] and may also have a transporter to aid in its transfer into the cell and possibly into the mitochondrial matrix [119,120], which permits it to concentrate in this organelle [65,73,81].…”