Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.
Methamphetamine (METH), a psychostimulant with highly neurotoxic effects, has been known to induce neuronal apoptosis in part through an endoplasmic reticulum (ER) stress pathway. Melatonin is an endogenous antioxidant compound that exerts protective effects against several neurodegenerative conditions, including METH-induced neurotoxicity, via various mechanisms. However, the role of melatonin in ER stress is still relatively unclear. In the present study, we investigated ER stress and neuronal apoptosis following METH treatment and the role of melatonin in METH-mediated ER stress-induced cell death in the SH-SY5Y neuroblastoma cell line. We found that METH caused the overexpression of ER stress-related genes, including C/EBP homologous protein and spliced X-box binding protein 1, in dose- and time-dependent manners. Moreover, METH time-dependently activated caspase-12 and -3, leading to cellular apoptosis. Furthermore, we demonstrated that pretreatment with melatonin attenuated the overexpression of ER stress-related genes and the cleavages of caspase-12 and -3 caused by METH exposure. Flow cytometry revealed that METH-mediated neuronal apoptosis was also prevented by melatonin. These findings suggest the protective effects of melatonin against ER stress and apoptosis caused by METH and other harmful agents.
Methamphetamine use disorder is characterized by recurrent binge episodes. Humans addicted to methamphetamine experience various degrees of cognitive deficits and show evidence of neurodegenerative processes in the brain. Binge injections of METH to rodents also cause significant toxic changes in the brain. In addition, this pattern of METH injections can alter gene expression in the dorsal striatum. Gene expression is regulated, in part, by histone deacetylation. We thus tested the possibility that METH toxic doses might cause changes in the mRNA levels of histone deacetylases (HDACs). We found that METH did produce significant decreases in the mRNA expression of HDAC8, which is a class I HDAC. METH also decreased expression of HDAC6, HDAC9, and HDAC10 that are class II HDACs. The expression of the class IV HDAC, HDAC11, was also suppressed by METH. The expression of Sirt2, Sirt5, and Sirt6 that are members of class III HDACs was also downregulated by METH injections. Our findings implicate changes in HDAC expression may be an early indicator of impending METH-induced neurotoxicity in the striatum. This idea is consistent with the accumulated evidence that some HDACs are involved in neurodegenerative processes in the brain.
Background:: Melatonin, a neurohormone secreted from the pineal gland, circulates throughout the body and then mediates several physiological functions. The pharmacological effects of melatonin can be mediated through its direct antioxidant activity and receptor-dependent signaling. Objective: This article will mainly review receptor-dependent signaling. Human melatonin receptors include melatonin receptor type 1 (MT1) and melatonin receptor type 2 (MT2), which are widely distributed throughout the brain. Result: Several lines of evidence have revealed the involvement of the melatonergic system in different neurodegenerative diseases. Alzheimer’s disease pathology negatively affects the melatonergic system. Melatonin effectively inhibits β-amyloid (Aβ) synthesis and fibril formation. These effects are reversed by pharmacological melatonin receptor blockade. Reductions in MT1 and MT2 expression in the amygdala and substantia nigra pars compacta have been reported in Parkinson’s disease patients. The protective roles of melatonin against ischemic insults via its receptors have also been demonstrated. Melatonin has been reported to enhance neurogenesis through MT2 activation in cerebral ischemic/reperfusion mice. The neurogenic effects of melatonin on mesenchymal stem cells are particularly mediated through MT2. Conclusion: Understanding the roles of melatonin receptors in neuroprotection against diseases may lead to the development of specific analogues with specificity and potency greater than those of the original compound. These successfully developed compounds may serve as candidate preventive and disease-modifying agents in the future.
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