Melatonin preserves the transient mitochondrial permeability transition for protection during mitochondrial Ca(2+) stress in astrocyte

Drp1 and neuroinflammation: Deciphering the interplay between mitochondrial dynamics imbalance and inflammation in neurodegenerative diseases

Neuroinflammation and mitochondrial dysfunction are closely intertwined with the pathophysiology of neurological disorders. Recent studies have elucidated profound alterations in mitochondrial dynamics across a spectrum of neurological disorders. Dynamin-related protein 1 (DRP1) emerges as a pivotal regulator of mitochondrial fission, with its dysregulation disrupting mitochondrial homeostasis and fueling neuroinflammation, thereby exacerbating disease severity. In addition to its role in mitochondrial dynamics, DRP1 plays a crucial role in modulating inflammation-related pathways. This review synthesizes important functions of DRP1 in the central nervous system (CNS) and the impact of epigenetic modification on the progression of neurodegenerative diseases. The intricate interplay between neuroinflammation and DRP1 in microglia and astrocytes, central contributors to neuroinflammation, is expounded upon. Furthermore, the use of DRP1 inhibitors to influence the activation of microglia and astrocytes, as well as their involvement in processes such as mitophagy, mitochondrial oxidative stress, and calcium ion transport in CNS-mediated neuroinflammation, is scrutinized. The modulation of microglia to astrocyte crosstalk by DRP1 and its role in inflammatory neurodegeneration is also highlighted. Overall, targeting DRP1 presents a promising avenue for ameliorating neuroinflammation and enhancing the therapeutic management of neurological disorders.

Cyclophilin D in Mitochondrial Dysfunction: A Key Player in Neurodegeneration?

Mitochondrial dysfunction plays a pivotal role in numerous complex diseases. Understanding the molecular mechanisms by which the "powerhouse of the cell" turns into the "factory of death" is an exciting yet challenging task that can unveil new therapeutic targets. The mitochondrial matrix protein CyPD is a peptidylprolyl cis-trans isomerase involved in the regulation of the permeability transition pore (mPTP). The mPTP is a multi-conductance channel in the inner mitochondrial membrane whose dysregulated opening can ultimately lead to cell death and whose involvement in pathology has been extensively documented over the past few decades. Moreover, several mPTP-independent CyPD interactions have been identified, indicating that CyPD could be involved in the fine regulation of several biochemical pathways. To further enrich the picture, CyPD undergoes several post-translational modifications that regulate both its activity and interaction with its clients. Here, we will dissect what is currently known about CyPD and critically review the most recent literature about its involvement in neurodegenerative disorders, focusing on Alzheimer's Disease and Parkinson's Disease, supporting the notion that CyPD could serve as a promising therapeutic target for the treatment of such conditions. Notably, significant efforts have been made to develop CyPD-specific inhibitors, which hold promise for the treatment of such complex disorders.

Aging-Related Ovarian Failure and Infertility: Melatonin to the Rescue

Aging has a major detrimental effect on the optimal function of the ovary with changes in this organ preceding the age-related deterioration in other tissues, with the middle-aged shutdown leading to infertility. Reduced fertility and consequent inability to conceive by women in present-day societies who choose to have children later in life leads to increased frustration. Melatonin is known to have anti-aging properties related to its antioxidant and anti-inflammatory actions. Its higher follicular fluid levels relative to blood concentrations and its likely synthesis in the oocyte, granulosa, and luteal cells suggest that it is optimally positioned to interfere with age-associated deterioration of the ovary. Additionally, the end of the female reproductive span coincides with a significant reduction in endogenous melatonin levels. Thus, the aims are to review the literature indicating melatonin production in mitochondria of oocytes, granulosa cells, and luteal cells, identify the multiple processes underlying changes in the ovary, especially late in the cessation of the reproductive life span, summarize the physiological and molecular actions of melatonin in the maintenance of normal ovaries and in the aging ovaries, and integrate the acquired information into an explanation for considering melatonin in the treatment of age-related infertility. Use of supplemental melatonin may help preserve fertility later in life and alleviate frustration in women delaying childbearing age, reduce the necessity of in vitro fertilization–embryo transfer (IVF-ET) procedures, and help solve the progressively increasing problem of non-aging-related infertility in women throughout their reproductive life span. While additional research is needed to fully understand the effects of melatonin supplementation on potentially enhancing fertility, studies published to date suggest it may be a promising option for those struggling with infertility.

Melatonin promoted osteogenesis of human periodontal ligament cells by regulating mitochondrial functions through the translocase of the outer mitochondrial membrane 20

BACKGROUND AND OBJECTIVE

Melatonin plays an important role in various beneficial functions, including promoting differentiation. However, effects on osteogenic differentiation, especially in human periodontal cells (hPDLCs), still remain inconclusive. Mitochondria are highly dynamic organelles that play an important role in various biological processes in cells, including energy metabolism and oxidative stress reaction. Furthermore, the translocase of the outer mitochondrial membrane 20 (TOM20) is responsible for recognizing and transporting precursor proteins. Thus, the objective of this study was to evaluate the functionality of melatonin on osteogenesis in human periodontal cells and to explore the involved mechanism of mitochondria.

METHODS

The hPDLCs were extracted and identified by flow cytometry and multilineage differentiation. We divided hPDLCs into control group, osteogenic induction group, and osteogenesis with melatonin treatment group (100, 10, and 1 μM). Then we used a specific siRNA to achieve interference of TOM20. Alizarin red and Alkaline phosphatase staining and activity assays were performed to evaluate osteogenic differentiation. Osteogenesis-related genes and proteins were measured by qPCR and western blot. Mitochondrial functions were tested using ATP, NAD+/NADH, JC-1, and Seahorse Mito Stress Test kits. Finally, TOM20 and mitochondrial dynamics-related molecules expression were also assessed by qPCR and western blot.

RESULTS

Our results showed that melatonin-treated hPDLCs had higher calcification and ALP activity as well as upregulated OCN and Runx2 expression at mRNA and protein levels, which was the most obvious in 1 μM melatonin-treated group. Meanwhile, melatonin supplement elevated intracellular ATP production and mitochondrial membrane potential by increasing mitochondrial oxidative metabolism, hence causing a lower NAD⁺ /NADH ratio. In addition, we also found that melatonin treatment raised TOM20 level and osteogenesis and mitochondrial functions were both suppressed after knocking down TOM20.

CONCLUSION

We found that melatonin promoted osteogenesis of hPDLCs and 1 μM melatonin had the most remarkable effect. Melatonin treatment can reinforce mitochondrial functions by upregulating TOM20.

Melatonin Protects Mitochondrial Function and Inhibits Oxidative Damage against the Decline of Human Oocytes Development Caused by Prolonged Cryopreservation

Melatonin (MT) can improve the effect of cryopreservation on oocytes by suppressing oxidative stress and maintaining the permeability of the oolemma. In this study, MT was firstly applied to human oocytes' cryopreservation to explore the effect of prolonged cryopreservation on developmental competence and its role. Collected in vitro-matured human oocytes were cryopreserved in MT-containing or MT-free medium for 0 and 6 months; after warming, viable oocytes were assessed for developmental viability, intracellular protein expression, mitochondrial function, and oxidation-antioxidant system. Meanwhile, fresh oocytes were set as the control. The results showed that with the extension of cryopreservation time, the developmental competence of oocytes gradually declined, accompanied by the down-regulation of most mitochondrial function-related proteins, the reduction in ATP and GSH production, the increase in ROS accumulation, and the aggravation of the imbalance of ROS/GSH in oocytes. However, the participation of MT seemed to effectively mitigate these negative effects. Therefore, we speculate that melatonin may maintain normal ATP production and ROS/GSH balance in cryopreserved oocytes by protecting mitochondrial function and inhibiting oxidative damage, thereby effectively maintaining the developmental competence of human oocytes in prolonged cryopreservation.

Redox Biology of Melatonin: Discriminating Between Circadian and Noncircadian Functions

Melatonin has not only to be seen as a regulator of circadian clocks. In addition to its chronobiotic functions, it displays other actions, especially in cell protection. This includes antioxidant, anti-inflammatory, and mitochondria-protecting effects. Although protection is also modulated by the circadian system, the respective actions of melatonin can be distinguished and differ with regard to dose requirements in therapeutic settings. It is the aim of this article to outline these differences in terms of function, signaling, and dosage. Focus has been placed on both the nexus and the dissecting properties between circadian and noncircadian mechanisms. This has to consider details beyond the classic view of melatonin's role, such as widespread synthesis in extrapineal tissues, formation in mitochondria, effects on the mitochondrial permeability transition pore, and secondary signaling, for example, via upregulation of sirtuins and by regulating noncoding RNAs, especially microRNAs. The relevance of these findings, the differences and connections between circadian and noncircadian functions of melatonin shed light on the regulation of inflammation, including macrophage/microglia polarization, damage-associated molecular patterns, avoidance of cytokine storms, and mitochondrial functions, with numerous consequences to antioxidative protection, that is, aspects of high actuality with regard to deadly viral and bacterial diseases. Antioxid. Redox Signal. 37, 704-725.

FDA approved L-type channel blocker Nifedipine reduces cell death in hypoxic A549 cells through modulation of mitochondrial calcium and superoxide generation

As hypoxia is a major driver for the pathophysiology of COVID-19, it is crucial to characterize the hypoxic response at the cellular and molecular levels. In order to augment drug repurposing with the identification of appropriate molecular targets, investigations on therapeutics preventing hypoxic cell damage is required. In this work, we propose a hypoxia model based on alveolar lung epithelial cells line using chemical inducer, CoCl₂ that can be used for testing calcium channel blockers (CCBs). Since recent studies suggested that CCBs may reduce the infectivity of SARS-Cov-2, we specifically select FDA approved calcium channel blocker, nifedipine for the study. First, we examined hypoxia-induced cell morphology and found a significant increase in cytosolic calcium levels, mitochondrial calcium overload as well as ROS production in hypoxic A549 cells. Secondly, we demonstrate the protective behaviour of nifedipine for cells that are already subjected to hypoxia through measurement of cell viability as well as 4D imaging of cellular morphology and nuclear condensation. Thirdly, we show that the protective effect of nifedipine is achieved through the reduction of cytosolic calcium, mitochondrial calcium, and ROS generation. Overall, we outline a framework for quantitative analysis of mitochondrial calcium and ROS using 3D imaging in laser scanning confocal microscopy and the open-source image analysis platform ImageJ. The proposed pipeline was used to visualize mitochondrial calcium and ROS level in individual cells that provide an understanding of molecular targets. Our findings suggest that the therapeutic value of nifedipine may potentially be evaluated in the context of COVID-19 therapeutic trials.

Melatonin as an Antioxidant and Immunomodulator in Atopic Dermatitis-A New Look on an Old Story: A Review

Atopic dermatitis (AD) is common inflammatory dermatosis, typically with chronic and recurrent course, which significantly reduces the quality of life. Sleep disturbances are considered to be remarkably burdensome ailments in patients with AD, and are routinely included during assessment of disease severity. Therefore, endogenous substances engaged in the control of circadian rhythms might be important in pathogenesis of AD and, possibly, be used as biomarkers of disease severity or even in development of novel therapies. Melatonin (MT), the indoleamine produced by pineal gland (but also by multiple other tissues, including skin), plays a pivotal role in maintaining the sleep/wake homeostasis. Additionally, it possesses strong antioxidant and anti-inflammatory properties, which might directly link chronic skin inflammation and sleep abnormalities characteristic of AD. The objective of this work is to systematically present and summarize the results of studies (both experimental and clinical) that investigated the role of MT in the AD, with a focus on the antioxidant and immunomodulatory effects of MT.

The mitochondrial permeability transition pore: an evolving concept critical for cell life and death

In this review, we summarize current knowledge of perhaps one of the most intriguing phenomena in cell biology: the mitochondrial permeability transition pore (mPTP). This phenomenon, which was initially observed as a sudden loss of inner mitochondrial membrane impermeability caused by excessive calcium, has been studied for almost 50 years, and still no definitive answer has been provided regarding its mechanisms. From its initial consideration as an in vitro artifact to the current notion that the mPTP is a phenomenon with physiological and pathological implications, a long road has been travelled. We here summarize the role of mitochondria in cytosolic calcium control and the evolving concepts regarding the mitochondrial permeability transition (mPT) and the mPTP. We show how the evolving mPTP models and mechanisms, which involve many proposed mitochondrial protein components, have arisen from methodological advances and more complex biological models. We describe how scientific progress and methodological advances have allowed milestone discoveries on mPTP regulation and composition and its recognition as a valid target for drug development and a critical component of mitochondrial biology.

Melatonin as a Potential Multitherapeutic Agent

Melatonin (N-acetyl-5-methoxytryptamine, MEL) is a hormone produced by the pineal gland that was discovered many years ago. The physiological roles of this hormone in the body are varied. The beneficial effects of MEL administration may be related to its influence on mitochondrial physiology. Mitochondrial dysfunction is considered an important factor in various physiological and pathological processes, such as the development of neurodegenerative and cardiovascular diseases, diabetes, various forms of liver disease, skeletal muscle disorders, and aging. Mitochondrial dysfunction induces an increase in the permeability of the inner membrane, which leads to the formation of a permeability transition pore (mPTP) in the mitochondria. The long-term administration of MEL has been shown to improve the functional state of mitochondria and inhibit the opening of the mPTP during aging. It is known that MEL is able to suppress the initiation, progression, angiogenesis, and metastasis of cancer as well as the sensitization of malignant cells to conventional chemotherapy and radiation therapy. This review summarizes the studies carried out by our group on the combined effect of MEL with chemotherapeutic agents (retinoic acid, cytarabine, and navitoclax) on the HL-60 cells used as a model of acute promyelocytic leukemia. Data on the effects of MEL on oxidative stress, aging, and heart failure are also reported.

Divergent Importance of Chronobiological Considerations in High- and Low-dose Melatonin Therapies

Melatonin has been used preclinically and clinically for different purposes. Some applications are related to readjustment of circadian oscillators, others use doses that exceed the saturation of melatonin receptors MT1 and MT2 and are unsuitable for chronobiological purposes. Conditions are outlined for appropriately applying melatonin as a chronobiotic or for protective actions at elevated levels. Circadian readjustments require doses in the lower mg range, according to receptor affinities. However, this needs consideration of the phase response curve, which contains a silent zone, a delay part, a transition point and an advance part. Notably, the dim light melatonin onset (DLMO) is found in the silent zone. In this specific phase, melatonin can induce sleep onset, but does not shift the circadian master clock. Although sleep onset is also under circadian control, sleep and circadian susceptibility are dissociated at this point. Other limits of soporific effects concern dose, duration of action and poor individual responses. The use of high melatonin doses, up to several hundred mg, for purposes of antioxidative and anti-inflammatory protection, especially in sepsis and viral diseases, have to be seen in the context of melatonin's tissue levels, its formation in mitochondria, and detoxification of free radicals.

The Mitochondrial Permeability Transition: Nexus of Aging, Disease and Longevity

The activity of the mitochondrial permeability transition pore, mPTP, a highly regulated multi-component mega-channel, is enhanced in aging and in aging-driven degenerative diseases. mPTP activity accelerates aging by releasing large amounts of cell-damaging reactive oxygen species, Ca²⁺ and NAD⁺. The various pathways that control the channel activity, directly or indirectly, can therefore either inhibit or accelerate aging or retard or enhance the progression of aging-driven degenerative diseases and determine lifespan and healthspan. Autophagy, a catabolic process that removes and digests damaged proteins and organelles, protects the cell against aging and disease. However, the protective effect of autophagy depends on mTORC2/SKG1 inhibition of mPTP. Autophagy is inhibited in aging cells. Mitophagy, a specialized form of autophagy, which retards aging by removing mitochondrial fragments with activated mPTP, is also inhibited in aging cells, and this inhibition leads to increased mPTP activation, which is a major contributor to neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. The increased activity of mPTP in aging turns autophagy/mitophagy into a destructive process leading to cell aging and death. Several drugs and lifestyle modifications that enhance healthspan and lifespan enhance autophagy and inhibit the activation of mPTP. Therefore, elucidating the intricate connections between pathways that activate and inhibit mPTP, in the context of aging and degenerative diseases, could enhance the discovery of new drugs and lifestyle modifications that slow aging and degenerative disease.

Relationships between Mitochondrial Dysfunction and Neurotransmission Failure in Alzheimer's Disease

Besides extracellular deposition of amyloid beta and formation of phosphorylated tau in the brains of patients with Alzheimer's disease (AD), the pathogenesis of AD is also thought to involve mitochondrial dysfunctions and altered neurotransmission systems. However, none of these components can describe the diverse cognitive, behavioural, and psychiatric symptoms of AD without the pathologies interacting with one another. The purpose of this review is to understand the relationships between mitochondrial and neurotransmission dysfunctions in terms of (1) how mitochondrial alterations affect cholinergic and monoaminergic systems via disruption of energy metabolism, oxidative stress, and apoptosis; and (2) how different neurotransmission systems drive mitochondrial dysfunction via increasing amyloid beta internalisation, oxidative stress, disruption of mitochondrial permeabilisation, and mitochondrial trafficking. All these interactions are separately discussed in terms of neurotransmission systems. The association of mitochondrial dysfunctions with alterations in dopamine, norepinephrine, and histamine is the prospective goal in this research field. By unfolding the complex interactions surrounding mitochondrial dysfunction in AD, we can better develop potential treatments to delay, prevent, or cure this devastating disease.

Targeting Mitochondrial Dysfunction for Bipolar Disorder

People with bipolar disorder (BD) all too often have suboptimal long-term outcomes with existing treatment options. They experience relapsing episodes of depression and mania and also have interepisodic mood and anxiety symptoms. We need to have a better understanding of the pathophysiology of BD if we are to make progress in improving these outcomes. This chapter will focus on the critical role of mitochondria in human functioning, oxidative stress, and the biological mechanisms of mitochondria in BD. Additionally, this chapter will present the evidence that, at least for some people, BD is a product of mitochondrial dysregulation. We review the modulators of mitochondria, the connection between current BD medication treatments and mitochondria, and additional medications that have theoretical potential to treat BD.

Mitochondrial functions and melatonin: a tour of the reproductive cancers

Cancers of the reproductive organs have a strong association with mitochondrial defects, and a deeper understanding of the role of this organelle in preneoplastic-neoplastic changes is important to determine the appropriate therapeutic intervention. Mitochondria are involved in events during cancer development, including metabolic and oxidative status, acquisition of metastatic potential, resistance to chemotherapy, apoptosis, and others. Because of their origin from melatonin-producing bacteria, mitochondria are speculated to produce melatonin and its derivatives at high levels; in addition, exogenously administered melatonin accumulates in the mitochondria against a concentration gradient. Melatonin is transported into tumor cell by GLUT/SLC2A and/or by the PEPT1/2 transporters, and plays beneficial roles in mitochondrial homeostasis, such as influencing oxidative phosphorylation and electron flux, ATP synthesis, bioenergetics, calcium influx, and mitochondrial permeability transition pore. Moreover, melatonin promotes mitochondrial homeostasis by regulating nuclear DNA and mtDNA transcriptional activities. This review focuses on the main functions of melatonin on mitochondrial processes, and reviews from a mechanistic standpoint, how mitochondrial crosstalk evolved in ovarian, endometrial, cervical, breast, and prostate cancers relative to melatonin's known actions. We put emphasis on signaling pathways whereby melatonin interferes within cancer-cell mitochondria after its administration. Depending on subtype and intratumor metabolic heterogeneity, melatonin seems to be helpful in promoting apoptosis, anti-proliferation, pro-oxidation, metabolic shifting, inhibiting neovasculogenesis and controlling inflammation, and restoration of chemosensitivity. This results in attenuation of development, progression, and metastatic potential of reproductive cancers, in addition to lowering the risk of recurrence and improving the life quality of patients.

Melatonin plays critical role in mesenchymal stem cell-based regenerative medicine in vitro and in vivo

Although stem cells have emerged as promising sources for regenerative medicine, there are many potential safety hazards for their clinical application, including tumorigenicity, an availability shortage, senescence, and sensitivity to toxic environments. Mesenchymal stem cells (MSCs) have various advantages compared to other stem cells, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); thus, MSCs have been intensely investigated in recent studies. However, they are placed in a harsh environment after isolation and transplantation, and the adverse microenvironment substantially reduces the viability and therapeutic effects of MSCs. Intriguingly, melatonin (MT), which is primarily secreted by the pineal organ, has been found to influence the fate of MSCs during various physiological and pathological processes. In this review, we will focus on the recent progress made regarding the influence of MT on stem cell biology and its implications for regenerative medicine. In addition, several biomaterials have been proven to significantly improve the protective effects of MT on MSCs by controlling the release of MT. Collectively, MT will be a promising agent for enhancing MSC activities and the regenerative capacity via the regulation of reactive oxygen species (ROS) generation and the release of immune factors in regenerative medicine.

Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3-OHM and AFMK in RBA1 astrocytes

Cyclic 3-hydroxymelatonin (C3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria-targeted protection beyond as a mitochondrial antioxidant during ionomycin-induced mitochondrial Ca²⁺ (mCa²⁺ ) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time-lapse digital imaging microscopy, this study investigated whether C3-OHM and AFMK also provide mitochondrial levels of protection during ionomycin-induced mCa²⁺ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3-OHM and AFMK prevented specifically mCa²⁺ -mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS-mediated depolarization of mitochondrial membrane potential (△Ψ_m ) and permanent lethal opening of the MPT (p-MPT). The antioxidative effects of AFMK, however, were less potent than that of C3-OHM. Whether C3-OHM and AFMK targeted directly the MPT was investigated under a condition of "oxidation free-Ca²⁺ stress" using a classic antioxidant vitamin E to remove mCa²⁺ -mediated mROS stress and the potential antioxidative effects of C3-OHM and AFMK. Intriguingly, two compounds still effectively postponed "oxidation free-Ca²⁺ stress"-mediated depolarization of △Ψ_m and p-MPT. Measurements using a MPT pore-specific indicator Calcein further identified that C3-OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t-MPT), a critical mechanism to reduce overloaded mROS and mCa²⁺ . These multiple layers of mitochondrial protection provided by C3-OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS- and mCa²⁺ -mediated MPT-associated apoptotic stresses and may provide therapeutic benefits against astrocyte-mediated neurodegeneration in the CNS.

The role of melatonin, a multitasking molecule, in retarding the processes of ageing

Biological ageing is generally accompanied by a gradual loss of cellular functions and physiological integrity of organ systems, the consequential enhancement of vulnerability, senescence and finally death. Mechanisms which underlie ageing are primarily attributed to an array of diverse but related factors including free radical-induced damage, dysfunction of mitochondria, disruption of circadian rhythms, inflammaging, genomic instability, telomere attrition, loss of proteostasis, deregulated sensing of nutrients, epigenetic alterations, altered intercellular communication, and decreased capacity for tissue repair. Melatonin, a prime regulator of human chronobiological and endocrine physiology, is highly reputed as an antioxidant, immunomodulatory, antiproliferative, oncostatic, and endocrine-modulatory molecule. Interestingly, several recent reports support melatonin as an anti-ageing agent whose multifaceted functions may lessen the consequences of ageing. This review depicts four categories of melatonin's protective effects on ageing-induced molecular and structural alterations. We also summarize recent findings related to the function of melatonin during ageing in various tissues and organs.

Melatonin and the electron transport chain

Melatonin protects the electron transport chain (ETC) in multiple ways. It reduces levels of ·NO by downregulating inducible and inhibiting neuronal nitric oxide synthases (iNOS, nNOS), thereby preventing excessive levels of peroxynitrite. Both ·NO and peroxynitrite-derived free radicals, such as ·NO2, hydroxyl (·OH) and carbonate radicals (CO3·-) cause blockades or bottlenecks in the ETC, by ·NO binding to irons, protein nitrosation, nitration and oxidation, changes that lead to electron overflow or even backflow and, thus, increased formation of superoxide anions (O2·-). Melatonin improves the intramitochondrial antioxidative defense by enhancing reduced glutathione levels and inducing glutathione peroxidase and Mn-superoxide dismutase (Mn-SOD) in the matrix and Cu,Zn-SOD in the intermembrane space. An additional action concerns the inhibition of cardiolipin peroxidation. This oxidative change in the membrane does not only initiate apoptosis or mitophagy, as usually considered, but also seems to occur at low rate, e.g., in aging, and impairs the structural integrity of Complexes III and IV. Moreover, elevated levels of melatonin inhibit the opening of the mitochondrial permeability transition pore and shorten its duration. Additionally, high-affinity binding sites in mitochondria have been described. The assumption of direct binding to the amphipathic ramp of Complex I would require further substantiation. The mitochondrial presence of the melatonin receptor MT1 offers the possibility that melatonin acts via an inhibitory G protein, soluble adenylyl cyclase, decreased cAMP and lowered protein kinase A activity, a signaling pathway shown to reduce Complex I activity in the case of a mitochondrial cannabinoid receptor.

Alpha-synuclein, epigenetics, mitochondria, metabolism, calcium traffic, & circadian dysfunction in Parkinson's disease. An integrated strategy for management

The motor deficits which characterise the sporadic form of Parkinson's disease arise from age-related loss of a subset of dopamine neurons in the substantia nigra. Although motor symptoms respond to dopamine replacement therapies, the underlying disease process remains. This review details some features of the progressive molecular pathology and proposes deployment of a combination of nutrients: R-lipoic acid, acetyl-l-carnitine, ubiquinol, melatonin (or receptor agonists) and vitamin D3, with the collective potential to slow progression of these features. The main nutrient targets include impaired mitochondria and the associated oxidative/nitrosative stress, calcium stress and impaired gene transcription induced by pathogenic forms of alpha- synuclein. Benefits may be achieved via nutrient influence on epigenetic signaling pathways governing transcription factors for mitochondrial biogenesis, antioxidant defences and the autophagy-lysosomal pathway, via regulation of the metabolic energy sensor AMP activated protein kinase (AMPK) and the mammalian target of rapamycin mTOR. Nutrients also benefit expression of the transcription factor for neuronal survival (NR4A2), trophic factors GDNF and BDNF, and age-related calcium signals. In addition a number of non-motor related dysfunctions in circadian control, clock genes and associated metabolic, endocrine and sleep-wake activity are briefly addressed, as are late-stage complications in respect of cognitive decline and osteoporosis. Analysis of the network of nutrient effects reveals how beneficial synergies may counter the accumulation and promote clearance of pathogenic alpha-synuclein.

Mitochondrial Ca2+ and regulation of the permeability transition pore

The mitochondrial permeability transition pore was originally described in the 1970's as a Ca2+ activated pore and has since been attributed to the pathogenesis of many diseases. Here we evaluate how each of the current models of the pore complex fit to what is known about how Ca2+ regulates the pore, and any insight that provides into the molecular identity of the pore complex. We also discuss the central role of Ca2+ in modulating the pore's open probability by directly regulating processes, such as ATP/ADP balance through the tricarboxylic acid cycle, electron transport chain, and mitochondrial membrane potential. We review how Ca2+ influences second messengers such as reactive oxygen/nitrogen species production and polyphosphate formation. We discuss the evidence for how Ca2+ regulates post-translational modification of cyclophilin D including phosphorylation by glycogen synthase kinase 3 beta, deacetylation by sirtuins, and oxidation/ nitrosylation of key residues. Lastly we introduce a novel view into how Ca2+ activated proteolysis through calpains in the mitochondria may be a driver of sustained pore opening during pathologies such as ischemia reperfusion injury.

2',3'-Cyclic nucleotide 3'-phosphodiesterase as a messenger of protection of the mitochondrial function during melatonin treatment in aging

The process of aging is considered to be tightly related to mitochondrial dysfunction. One of the causes of aging is an increased sensitivity to the induction of mitochondrial permeability transition pore (mPTP) opening in the inner membrane of mitochondria. Melatonin, a natural antioxidant, is a hormone produced by the pineal gland. The role of melatonin whose level decreases with aging is well understood. In the present study, we demonstrated that long-term treatment of aged rats with melatonin improved the functional state of mitochondria; thus, the Ca²⁺ capacity was enhanced and mitochondrial swelling was deaccelerated in mitochondria. Melatonin prevented mPTP and impaired the release of cytochrome c and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) from mitochondria of both young and aged rats. Our data suggest that melatonin retains СNPase inside mitochondria, thereby providing the protection of the protein against deleterious effects of 2',3'-cAMP in aging.

Melatonin prevents the dynamin-related protein 1-dependent mitochondrial fission and oxidative insult in the cortical neurons after 1-methyl-4-phenylpyridinium treatment

Mitochondrial dysfunction and oxidative stress are involved in the pathogenesis of Parkinson's disease (PD). Mitochondrial morphology is dynamic and precisely regulated by the mitochondrial fission and fusion machinery. Aberrant mitochondrial fragmentation controlled by the mitochondrial fission protein, dynamin-related protein 1 (Drp1), may result in cell death. Our previous results showed that melatonin protected neurons by inhibiting oxidative stress in a 1-methyl-4-phenylpyridinium (MPP(+) )-induced PD model. However, the effect of melatonin on mitochondrial dynamics remains uncharacterized. Herein, we investigated the effect of melatonin and the role of Drp1 on MPP(+) -induced mitochondrial fission in rat primary cortical neurons. We found that MPP(+) induced a rapid increase in the ratio of GSSG:total glutathione (a marker of oxidative stress) and mitochondrial fragmentation, Drp1 upregulation within 4 hours, and finally resulted in neuron loss 48 hours after the treatment. Neurons overexpressing wild-type Drp1 promoted mitochondrial and nuclear fragmentation; however, neurons overexpressing dominant-negative Drp1(K38A) or cotreated with melatonin exhibited significantly reduced MPP(+) -induced mitochondrial fragmentation and neuron death. Moreover, melatonin cotreatment prevented an MPP(+) -induced high ratio of GSSG and mitochondrial Drp1 upregulation. The prevention of mitochondrial fission by melatonin was not found in neurons transfected with wild-type Drp1. These results provide a new insight that the neuroprotective effect of melatonin against MPP(+) toxicity is mediated by inhibiting the oxidative stress and Drp1-mediated mitochondrial fragmentation.

Melatonin not only restores but also prevents the inhibition of the intestinal Ca(2+) absorption caused by glutathione depleting drugs

We have previously demonstrated that melatonin (MEL) blocks the inhibition of the intestinal Ca(2+) absorption caused by menadione (MEN). The purpose of this study were to determine whether MEL not only restores but also prevents the intestinal Ca(2+) absorption inhibited either by MEN or BSO, two drugs that deplete glutathione (GSH) in different ways, and to analyze the mechanisms by which MEN and MEL alter the movement of Ca(2+) across the duodenum. To know this, chicks were divided into four groups: 1) controls, 2) MEN treated, 3) MEL treated, and 4) treated sequentially with MEN and MEL or with MEN and MEL at the same time. In a set of experiments, chicks treated with BSO or sequentially with BSO and MEL or with BSO and MEL at the same time were used. MEL not only restored but also prevented the inhibition of the chick intestinal Ca(2+) absorption produced by either MEN or BSO. MEN altered the protein expression of molecules involved in the transcellular as well as in the paracellular pathway of the intestinal Ca(2+) absorption. MEL restored partially both pathways through normalization of the O2(-) levels. The nitrergic system was not altered by any treatment. In conclusion, MEL prevents or restores the inhibition of the intestinal Ca(2+) absorption caused by different GSH depleting drugs. It might become one drug for the treatment of intestinal Ca(2+) absorption under oxidant conditions having the advantage of low or null side effects.

Heat stress induced apoptosis is triggered by transcription-independent p53, Ca(2+) dyshomeostasis and the subsequent Bax mitochondrial translocation

In this study, We demonstrated that Bax mitochondrial translocation plays a vital role in the initiation of the mitochondrial signaling pathway upon activation by heat stress. In addition, both p53 mitochondrial translocation and Ca²⁺ signal mediated MPTP opening activate Bax mitochondrial translocation. Employing pifithrin-α (a p53 mitochondrial translocation inhibitor) and CsA (a permeability transition pore (MPTP) inhibitor), we found that heat stress induced Bax mitochondrial translocation was significantly inhibited in cells pretreated with both PFT and CsA. Furthermore, we demonstrated that generation of reactive oxygen species (ROS) is a critical mediator in heat stress induced apoptosis and that the antioxidant MnTBAP significantly decreased heat stress induced p53 mitochondrial translocation and Ca²⁺ signal mediated MPTP opening, as well as the subsequent Bax mitochondrial translocation and activation of the caspase cascade. Taken together, our results indicate that heat stress induces apoptosis through the mitochondrial pathway with ROS dependent mitochondrial p53 translocation and Ca²⁺ dyshomeostasis, and the ensuing intro Bax mitochondrial translocation as the upstream events involved in triggering the apoptotic process observed upon cellular exposure to heat stress.

Melatonin: a well-documented antioxidant with conditional pro-oxidant actions

Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.

Melatonin Therapy in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is a major health problem and a growing recognition exists that efforts to prevent it must be undertaken by both governmental and non-governmental organizations. In this context, the pineal product, melatonin, has a promising significance because of its chronobiotic/cytoprotective properties potentially useful for a number of aspects of AD. One of the features of advancing age is the gradual decrease in circulating melatonin levels. A limited number of therapeutic trials have indicated that melatonin has a therapeutic value as a neuroprotective drug in the treatment of AD and minimal cognitive impairment (which may evolve to AD). Both in vitro and in vivo, melatonin prevented the neurodegeneration seen in experimental models of AD. For these effects to occur, doses of melatonin about two orders of magnitude higher than those required to affect sleep and circadian rhythmicity are needed. More recently, attention has been focused on the development of potent melatonin analogs with prolonged effects, which were employed in clinical trials in sleep-disturbed or depressed patients in doses considerably higher than those employed for melatonin. In view that the relative potencies of the analogs are higher than that of the natural compound, clinical trials employing melatonin in the range of 50-100 mg/day are urgently needed to assess its therapeutic validity in neurodegenerative disorders such as AD.

Hypoxic preconditioning-induced mitochondrial protection is not disrupted in a cell model of mtDNA T8993G mutation-induced F1F0-ATP synthase defect: the role of mitochondrial permeability transition

Transient opening of the mitochondrial permeability transition pore plays a crucial role in hypoxic preconditioning-induced protection. Recently, the cyclophilin-D component of the mitochondrial permeability transition pore has been shown to interact with and regulate the F1F0-ATP synthase. However, the precise role of the F1F0-ATP synthase and the interaction between cyclophilin-D and F1F0-ATP synthase in the mitochondrial permeability transition pore and hypoxic preconditioning remain uncertain. Here we found that a 1-h hypoxic preconditioning delayed apoptosis and improved cell survival after stimulation with various apoptotic inducers including H2O2, ionomycin, and arachidonic acid in mitochondrial DNA T8993G mutation (NARP) osteosarcoma 143B cybrids, an F1F0-ATP synthase defect cell model. This hypoxic preconditioning protected NARP cybrid cells against focal laser irradiation-induced oxidative stress by suppressing reactive oxygen species formation and preventing the depletion of cardiolipin. Furthermore, the protective functions of transient opening of the mitochondrial permeability transition pore in both NARP cybrids and wild-type 143B cells can be augmented by hypoxic preconditioning. Disruption of the interaction between cyclophilin-D and F1F0-ATP synthase by cyclosporin A attenuated the mitochondrial protection induced by hypoxic preconditioning in both NARP cybrids and wild-type 143B cells. Our results demonstrate that the interaction between cyclophilin-D and F1F0-ATP synthase is important in the hypoxic preconditioning-induced cell protection. This finding improves our understanding of the mechanism of mitochondrial permeability transition pore opening in cells in response to hypoxic preconditioning, and will be helpful in further developing new pharmacological agents targeting hypoxia-reoxygenation injury and mitochondria-mediated cell death.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Melatonin improved rat cardiac mitochondria and survival rate in septic heart injury

The pathogenesis of septic myocardial depression is complicated. Mitochondrial dysfunction has been suggested to be one of the main reasons for the reduced cardiac function. As melatonin is an antioxidant with the potential to scavenge radicals in mitochondria, we therefore employed a sepsis model, that is, cecal ligation and double puncture (CLP) in rats, to study the melatonin effects on: (i), myocardial mitochondrial function; (ii), heart systolic function; and (iii), prognosis of septic rats. We demonstrate that melatonin treatment (30 mg/kg, 3, 6, 12, 18, 24 hr after CLP) (i) improved myocardial cytochrome c oxidase (CcOX) activity and blood lactate level, (ii) attenuated heart dysfunction with a higher left ventricular ejection fraction (EF), and (iii) promoted 48-h survival of the rats compared to CLP animals with no melatonin treatment. In conclusion, our results show that rat myocardial mitochondrial CcOX activity was depressed during severe sepsis accompanied by myocardial depression characterized by the decline of EF. In septic rats, melatonin increased the CcOX activity, improved heart systolic function, and lowered mortality rate. The clinical use of melatonin in septic myocardial depression should be tested in the future.

Melatonin enhances antioxidative enzyme gene expression (CAT, GPx, SOD), prevents their UVR-induced depletion, and protects against the formation of DNA damage (8-hydroxy-2'-deoxyguanosine) in ex vivo human skin

UV radiation (UVR) induces serious structural and functional alterations in human skin leading to skin aging and carcinogenesis. Reactive oxygen species are key players in UVR-mediated photodamage and induce the DNA-base-oxidized, intermediate 8-hydroxy-2'-deoxyguanosine (8-OHdG). Herein, we report the protective action of melatonin against UVR-induced 8-OHdG formation and depletion of antioxidative enzymes using ex vivo human full-thickness skin exposed to UVR in a dose (0, 100, 300 mJ/cm(2))- and time-dependent manner (0, 24, 48 hr post-UVR). Dynamics of depletion of antioxidative enzymes including catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), or 8-OHdG formation were studied by real-time PCR and immunofluorescence/immunohistochemical staining. UVR-treated skin revealed significant and immediate (0 hr 300 mJ/cm(2)) reduction of gene expression, and this effect intensified within 24 hr post-UVR. Simultaneous increase in 8-OHdG-positive keratinocytes occurred already after 0 hr post-UVR reaching 71% and 99% up-regulation at 100 and 300 mJ/cm(2), respectively (P < 0.001). Preincubation with melatonin (10(-3) M) led to 32% and 29% significant reductions in 8-OHdG-positive cells and the prevention of antioxidative enzyme gene and protein suppression. Thus, melatonin was shown to play a crucial role as a potent antioxidant and DNA protectant against UVR-induced oxidative damage in human skin.

Mitochondria and chloroplasts as the original sites of melatonin synthesis: a hypothesis related to melatonin's primary function and evolution in eukaryotes

Mitochondria and chloroplasts are major sources of free radical generation in living organisms. Because of this, these organelles require strong protection from free radicals and associated oxidative stress. Melatonin is a potent free radical scavenger and antioxidant. It meets the criteria as a mitochondrial and chloroplast antioxidant. Evidence has emerged to show that both mitochondria and chloroplasts may have the capacity to synthesize and metabolize melatonin. The activity of arylalkylamine N-acetyltransferase (AANAT), the reported rate-limiting enzyme in melatonin synthesis, has been identified in mitochondria, and high levels of melatonin have also been found in this organelle. From an evolutionary point of view, the precursor of mitochondria probably is the purple nonsulfur bacterium, particularly, Rhodospirillum rubrum, and chloroplasts are probably the descendents of cyanobacteria. These bacterial species were endosymbionts of host proto-eukaryotes and gradually transformed into cellular organelles, that is, mitochondria and chloroplasts, respectively, thereby giving rise to eukaryotic cells. Of special importance, both purple nonsulfur bacteria (R. rubrum) and cyanobacteria synthesize melatonin. The enzyme activities required for melatonin synthesis have also been detected in these primitive species. It is our hypothesis that mitochondria and chloroplasts are the original sites of melatonin synthesis in the early stage of endosymbiotic organisms; this synthetic capacity was carried into host eukaryotes by the above-mentioned bacteria. Moreover, their melatonin biosynthetic capacities have been preserved during evolution. In most, if not in all cells, mitochondria and chloroplasts may continue to be the primary sites of melatonin generation. Melatonin production in other cellular compartments may have derived from mitochondria and chloroplasts. On the basis of this hypothesis, it is also possible to explain why plants typically have higher melatonin levels than do animals. In plants, both chloroplasts and mitochondria likely synthesize melatonin, while animal cells contain only mitochondria. The high levels of melatonin produced by mitochondria and chloroplasts are used to protect these important cellular organelles against oxidative stress and preserve their physiological functions. The superior beneficial effects of melatonin in both mitochondria and chloroplasts have been frequently reported.

Melatonin prevents ultraviolet radiation-induced alterations in plasma membrane potential and intracellular pH in human keratinocytes

Melatonin exhibits protective effects against ultraviolet radiation (UVR) via modulation of proinflammatory mediators and its free radical scavenging capacity. To date, several reports presented protective mechanisms of this agent against UVR-induced alterations in mitochondria and nuclei. This investigation evaluates the potent preventing action of melatonin regarding early-stage UVR-mediated perturbations in plasma membrane potential (mbΔψ) and intracellular (cytosolic) pH (pH i) analyzed by flow cytometry. Experiments were carried out in a dose- and time-dependent manner using human keratinocytes [HaCaT and normal human epidermal keratinocytes (NHEK)]. First investigations, which used viability/cytotoxicity assays, showed the gradual mortality with increasing UVR doses and cultivation time. Pre-incubation with melatonin (10(-3) m) prior to UVR exposure reduced lactate dehydrogenase release by 30% (HaCaT) and 28% (NHEK) at the dose of 50 mJ/cm(2) after 48 hr (P < 0.001). Furthermore, UVR caused hyperpolarization of mbΔψ immediately (0 hr) after irradiation (25 or 50 mJ/cm(2)). At the dose of 50 mJ/cm(2), cells cultivated for 48 hr manifested a marked increase in mbΔψ by 112% (HaCaT) and 123% (NHEK). The presence of melatonin significantly protected the cells by 12% (HaCaT) and 14% (NHEK) (P < 0.001). Simultaneously, 50 mJ/cm(2) induced dramatic acidification reaching after 24 hr the level of 6.40 (without melatonin), 6.56 (with melatonin) for HaCaT and 6.11 (without melatonin), 6.43 (with melatonin) for NHEK. The results presented provide information about the protective mechanisms of melatonin itself on one hand and, combined with data reported so far, confirm the potent antiapoptotic action of melatonin.

Long-term Aβ exposure augments mCa2+-independent mROS-mediated depletion of cardiolipin for the shift of a lethal transient mitochondrial permeability transition to its permanent mode in NARP cybrids: a protective targeting of melatonin

Mitochondrial dysfunction is a hallmark of amyloid β-peptide (Aβ)-induced neurodegeneration of Alzheimer's disease (AD). This study investigated whether mtDNA T8993G mutation-induced complex V inhibition, clinically associated with neurological muscle weakness, ataxia, and retinitis pigmentosa (NARP), is a potential risk factor for AD and the pathological link for long-term exposure of Aβ-induced mitochondrial toxicity and apoptosis in NARP cybrids. Using noninvasive fluorescence probe-coupled laser scanning imaging microscopy and NARP cybrids harboring 98% mutant genes along with its parental 143B osteosarcoma cells, we demonstrated that Aβ-augmented mitochondrial Ca(2+) (mCa(2+))-independent mitochondrial reactive oxygen species (mROS) formation for a cardiolipin (CL, a major mitochondrial protective phospholipid)-dependent lethal modulation of the mitochondrial permeability transition (MPT). Aβ augmented not only the amount but also the propagation rate of mROS-induced mROS formation to significantly depolarize mitochondrial membrane potential (∆Ψ(m)) and reduce mCa(2+) stress. Aβ-augmented mROS oxidized and depleted CL, thereby enhances mitochondrial fission and movement retardation, which promoted the NARP-augmented lethal transient-MPT (t-MPT) to switch to its irreversible mode of permanent-MPT (p-MPT). Interestingly, melatonin, a multiple mitochondrial protector, markedly reduced Aβ-augmented mROS formation and therefore significantly reduced mROS-mediated depolarization of ∆Ψ(m), fission of mitochondria and retardation of mitochondrial movement to stabilize CL and hence the MPT. In the presence of melatonin, Aβ-promoted p-MPT was reversed to a protective t-MPT, which preserved ∆Ψ(m) and lowered elevated mCa(2+) to sublethal levels for an enhanced mCa(2+)-dependent O(2) consumption. Thus, melatonin may potentially rescue AD patients associated with NARP symptoms.

mtDNA T8993G mutation-induced mitochondrial complex V inhibition augments cardiolipin-dependent alterations in mitochondrial dynamics during oxidative, Ca(2+), and lipid insults in NARP cybrids: a potential therapeutic target for melatonin

Mitochondrial dynamics including morphological fission and mitochondrial movement are essential to normal mitochondrial and cellular physiology. This study investigated how mtDNA T8993G (NARP)-induced inhibition of mitochondrial complex V altered mitochondrial dynamics in association with a protective mitochondrial phospholipid, cardiolipin (CL), as a potential therapeutic target. NARP cybrids harboring 98% of mtDNA T8993G genes and its parental osteosarcoma 143B cells were studied for comparison, and protection provided by melatonin, a potent mitochondrial protector, was explored. We demonstrate for the first time that NARP mutation significantly enhances apoptotic death as a result of three distinct lethal mitochondrial apoptotic insults including oxidative, Ca(2+), and lipid stress. In addition, NARP significantly augmented pathological depletion of CL. NARP-augmented depletion of CL results in enhanced retardation of mitochondrial movement and fission and later swelling of mitochondria during all insults. These results suggest that CL is a common and crucial pathological target for mitochondrial apoptotic insults. Furthermore, CL possibly plays a central role in regulating mitochondrial dynamics that are associated with NARP-augmented mitochondrial pathologies. Intriguingly, melatonin, by differentially preserving CL during various stresses (oxidation > Ca(2+) > lipid), rescues differentially CL-altered mitochondrial dynamics and cell death (oxidation > Ca(2+) > lipid). Thus, melatonin, in addition to being a mitochondrial antioxidant to antagonize mitochondrial oxidative stress, a mitochondrial permeability transition modulator to antagonize mitochondrial Ca(2+) stress, may stabilize directly CL to prevent its oxidization and/or depletion and, therefore, exerts great potential in rescuing CL-dependent mitochondrial dynamics-associated mitochondrial pathologies for treatment of NARP-induced pathologies and diseases.

Melatonin protects against rotenone-induced cell injury via inhibition of Omi and Bax-mediated autophagy in Hela cells

Parkinson's disease is the second most common neurodegenerative disease, and environmental toxins such as rotenone play an important role in causing degeneration of dopaminergic neurons. Melatonin, a major secretory product of pineal, is recently reported to protect against rotenone-induced cell death in animal models. Yet, the mechanism involved in this protection needs to be elucidated. Here, we report that rotenone treatment (0-100 μM) decreased cell survival of Hela cells in a dose-dependent manner. At concentrations ranging from 0.1 to 100 μM, rotenone induced a dose-dependent increase in the expression of microtubule-associated protein 1 light chain 3 (LC3)-II, a protein associated with the autophagosomal membrane. Knockdown of Bax or Omi using shRNA inhibited 1 μM rotenone-induced autophagy. To determine whether melatonin would protect cells against rotenone-induced cell death and autophagy, we pretreated Hela cells with 250 μM melatonin for 24 hr in the presence of rotenone. Melatonin inhibited Bax expression and the release of the omi/HtrA2 into the cytoplasm induced by 1 μM rotenone. Melatonin 250 μM treatment also suppressed cell death induced by 0.1-100 μM rotenone and protected against the formation of LC3-II in cells exposed to 1 μM rotenone. This work demonstrates a novel role for melatonin as a neuroprotective agent against rotenone.