Physiological roles of the mitochondrial permeability transition pore

High-dose vitamin C promotes mitochondrial biogenesis in HCT116 colorectal cancer cells by regulating the AMPK/PGC-1α signaling pathway

BACKGROUND

Mitochondrial dysfunction is closely associated with cancer development. Colorectal cancer (CRC) cells often exhibit altered energy metabolism, characterized by increased glycolysis and reduced oxidative phosphorylation. Enhancing mitochondrial biogenesis and function may represent a promising therapeutic approach. High-dose vitamin C has demonstrated anti-tumor properties and the ability to reverse the Warburg effect, but its role in regulating mitochondrial biogenesis and function remains unclear.

METHODS

We evaluated the altered mitochondrial functional status of HCT116 colorectal cancer cells compared to FHC colorectal epithelial cells, assessed the effects of high-dose vitamin C on mitochondrial biogenesis and function in HCT116 cells, and explored the underlying regulatory mechanisms.

RESULTS

HCT116 cells exhibited mitochondrial dysfunction compared to FHC cells, including decreased expression of electron transport chain complexes III and IV, reduced TFAM levels, and lower mtDNA content. Vitamin C treatment significantly enhanced mitochondrial biogenesis and function, as reflected by increased AMPK phosphorylation, upregulation of PGC-1α, SOD2, NRF2, TFAM, MT-CYB, and MTCO1, elevated mtDNA content, restored membrane potential, enhanced oxidative phosphorylation, and reduced glycolytic activity. Furthermore, vitamin C markedly suppressed HCT116 cell viability and clonogenic capacity, while these effects were substantially diminished by cotreatment with Compound C.

CONCLUSION

This study demonstrates that high-dose vitamin C ameliorates mitochondrial dysfunction and promotes mitochondrial biogenesis and function in colorectal cancer cells through activation of the AMPK-PGC-1α signaling pathway, thereby suppressing tumor cell proliferation. These findings suggest that vitamin C may serve as a promising therapeutic agent for targeting mitochondrial metabolism in colorectal cancer.

Cryo-EM structure of the brine shrimp mitochondrial ATP synthase suggests an inactivation mechanism for the ATP synthase leak channel

Mammalian mitochondria undergo Ca2+-induced and cyclosporinA (CsA)-regulated permeability transition (mPT) by activating the mitochondrial permeability transition pore (mPTP) situated in mitochondrial inner membranes. Ca2+-induced prolonged openings of mPTP under certain pathological conditions result in mitochondrial swelling and rupture of the outer membrane, leading to mitochondrial dysfunction and cell death. While the exact molecular composition and structure of mPTP remain unknown, mammalian ATP synthase was reported to form voltage and Ca2+-activated leak channels involved in mPT. Unlike in mammals, mitochondria of the crustacean Artemia franciscana have the ability to accumulate large amounts of Ca2+ without undergoing the mPT. Here, we performed structural and functional analysis of A. franciscana ATP synthase to study the molecular mechanism of mPTP inhibition in this organism. We found that the channel formed by the A. franciscana ATP synthase dwells predominantly in its inactive state and is insensitive to Ca2+, in contrast to porcine heart ATP synthase. Single-particle cryo-electron microscopy (cryo-EM) analysis revealed distinct structural features in A. franciscana ATP synthase compared with mammals. The stronger density of the e-subunit C-terminal region and its enhanced interaction with the c-ring were found in A. franciscana ATP synthase. These data suggest an inactivation mechanism of the ATP synthase leak channel and its possible contribution to the lack of mPT in this organism.

Point of No Return-What Is the Threshold of Mitochondria With Permeability Transition in Cells to Trigger Cell Death

Programmed cell death (apoptosis) is essential part of the process of tissue regeneration that also plays role in the mechanism of pathology. The phenomenon of fast and transient permeability of mitochondrial membranes by various triggers, known as permeability transition pore (mPTP) leads to the release of proapoptotic proteins and acts as an initial step in initiation of apoptosis. However, a role for mPTP was also suggested for physiology and it is unclear if there is a threshold in number of mitochondria with mPTP which induces cell death and how this mechanism is regulated in different tissues. Using simultaneous measurements of mitochondrial membrane potential and a fluorescent marker for caspase-3 activation we studied the number of mitochondria with calcium-induced mPTP opening necessary for induction of apoptosis in rat primary cortical neurons, astrocytes, fibroblasts, and cancer (BT-474) cells. The induction of apoptosis was correlated with 80%-90% mitochondrial signal loss in neural cells but only 35% in fibroblasts, and in BT-474 cancer cells over 90% of mitochondria opens mPTP before apoptosis becomes obvious. The number of mitochondria with mPTP which induce cell death did not correlate with total expression levels of proapoptotic proteins but was consistent with the Bax/Bcl-2 ratio in these cells. Calcium-induced mPTP opening increased levels of necrosis which was higher in fibroblasts compared to neurons, astrocytes and BT-474 cells. Thus, different tissues require specific numbers of mitochondria with PTP opening to induce apoptosis and it correlates to the proapoptotic/antiapoptotic proteins expression ratio in them.

Spop deficiency impairs adipogenesis and promotes thermogenic capacity in mice

As the adaptor protein that determines substrate specificity of the Cul3-SPOP-Rbx1 E3 ligase complex, SPOP is involved in numerous biological processes. However, its physiological connections with adipogenesis and thermogenesis remain poorly understood. In the current study, we report that the conditional knockout of Spop in mice results in substantial changes in protein expression, including the upregulation of a critical factor associated with thermogenesis, UCP1. Loss of SPOP also led to defects in body weight gain. In addition, conditional knockout mice exhibited resistance to high-fat-diet-induced obesity. Proteomics analysis found that proteins upregulated in the knockout mice are primarily enriched for functions in glycolysis/gluconeogenesis, oxidative phosphorylation, and thermogenesis. Furthermore, Spop knockout mice were more resilient during cold tolerance assay compared with the wild-type controls. Finally, the knockout of SPOP efficiently impaired adipogenesis in primary preadipocytes and the expression of associated genes. Collectively, these findings demonstrate the critical roles of SPOP in regulating adipogenesis and thermogenic capacity in mice.

Brain development and bioenergetic changes

Bioenergetics describe the biochemical processes responsible for energy supply in organisms. When these changes become dysregulated in brain development, multiple neurodevelopmental diseases can occur, implicating bioenergetics as key regulators of neural development. Historically, the discovery of disease processes affecting individual stages of brain development has revealed critical roles that bioenergetics play in generating the nervous system. Bioenergetic-dependent neurodevelopmental disorders include neural tube closure defects, microcephaly, intellectual disability, autism spectrum disorders, epilepsy, mTORopathies, and oncogenic processes. Developmental timing and cell-type specificity of these changes determine the long-term effects of bioenergetic disease mechanisms on brain form and function. Here, we discuss key metabolic regulators of neural progenitor specification, neuronal differentiation (neurogenesis), and gliogenesis. In general, transitions between glycolysis and oxidative phosphorylation are regulated in early brain development and in oncogenesis, and reactive oxygen species (ROS) and mitochondrial maturity play key roles later in differentiation. We also discuss how bioenergetics interface with the developmental regulation of other key neural elements, including the cerebrospinal fluid brain environment. While questions remain about the interplay between bioenergetics and brain development, this review integrates the current state of known key intersections between these processes in health and disease.

Mechanism and treatment of intracerebral hemorrhage focus on mitochondrial permeability transition pore

Intracerebral hemorrhage (ICH) is the second most common subtype of stroke, characterized by high mortality and a poor prognosis. Despite various treatment methods, there has been limited improvement in the prognosis of ICH over the past decades. Therefore, it is imperative to identify a feasible treatment strategy for ICH. Mitochondria are organelles present in most eukaryotic cells and serve as the primary sites for aerobic respiration and energy production. Under unfavorable cellular conditions, mitochondria can induce changes in permeability through the opening of the mitochondrial permeability transition pore (mPTP), ultimately leading to mitochondrial dysfunction and contributing to various diseases. Recent studies have demonstrated that mPTP plays a role in the pathological processes associated with several neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, Huntington's disease, ischemic stroke and ischemia-reperfusion injury, among others. However, there is limited research on mPTP involvement specifically in ICH. Therefore, this study comprehensively examines the pathological processes associated with mPTP in terms of oxidative stress, apoptosis, necrosis, autophagy, ferroptosis, and other related mechanisms to elucidate the potential mechanism underlying mPTP involvement in ICH. This research aims to provide novel insights for the treatment of secondary injury after ICH.

The interplay between neuroinflammatory pathways and Parkinson's disease

Parkinson's disease, a progressive neurodegenerative disorder predominantly affecting elderly, is marked by the gradual degeneration of the nigrostriatal dopaminergic pathway, culminating in neuronal loss within the substantia nigra pars compacta (SNpc) and dopamine depletion. At the molecular level, neuronal loss in the SNpc has been attributed to factors including neuroinflammation, impaired protein homeostasis, as well as mitochondrial dysfunction and the resulting oxidative stress. This review focuses on the interplay between neuroinflammatory pathways and Parkinson's disease, drawing insights from current literature.

The mitochondria in schizophrenia with 22q11.2 deletion syndrome: From pathogenesis to therapeutic promise of targeted natural drugs

Schizophrenia is a complex multi-factor neurological disorder that caused an array of severe indelible consequences to the individuals and society. Additionally, anti-schizophrenic drugs are unsuitable for treating negative symptoms and have more significant side effects and drug resistance. For better treatment and prevention, we consider exploring the pathogenesis of schizophrenia from other perspectives. A growing body of evidence of 22q11.2 deletion syndrome (22q11DS) suggested that the occurrence and progression of schizophrenia are related to mitochondrial dysfunction. So combing through the literature of 22q11DS published from 2000 to 2023, this paper reviews the mechanism of schizophrenia based on mitochondrial dysfunction, and it focuses on the natural drugs targeting mitochondria to enhance mitochondrial function, which are potential to improve the current treatment of schizophrenia.

Mitochondrial dysfunction and neurological disorders: A narrative review and treatment overview

Mitochondria play a vital role in the nervous system, as they are responsible for generating energy in the form of ATP and regulating cellular processes such as calcium (Ca2+) signaling and apoptosis. However, mitochondrial dysfunction can lead to oxidative stress (OS), inflammation, and cell death, which have been implicated in the pathogenesis of various neurological disorders. In this article, we review the main functions of mitochondria in the nervous system and explore the mechanisms related to mitochondrial dysfunction. We discuss the role of mitochondrial dysfunction in the development and progression of some neurological disorders including Parkinson's disease (PD), multiple sclerosis (MS), Alzheimer's disease (AD), depression, and epilepsy. Finally, we provide an overview of various current treatment strategies that target mitochondrial dysfunction, including pharmacological treatments, phototherapy, gene therapy, and mitotherapy. This review emphasizes the importance of understanding the role of mitochondria in the nervous system and highlights the potential for mitochondrial-targeted therapies in the treatment of neurological disorders. Furthermore, it highlights some limitations and challenges encountered by the current therapeutic strategies and puts them in future perspective.

Is Intrinsic Cardioprotection a Laboratory Phenomenon or a Clinically Relevant Tool to Salvage the Failing Heart?

Cardiovascular diseases, especially ischemic heart disease, as a leading cause of heart failure (HF) and mortality, will not reduce over the coming decades despite the progress in pharmacotherapy, interventional cardiology, and surgery. Although patients surviving acute myocardial infarction live longer, alteration of heart function will later lead to HF. Its rising incidence represents a danger, especially among the elderly, with data showing more unfavorable results among females than among males. Experiments revealed an infarct-sparing effect of ischemic "preconditioning" (IPC) as the most robust form of innate cardioprotection based on the heart's adaptation to moderate stress, increasing its resistance to severe insults. However, translation to clinical practice is limited by technical requirements and limited time. Novel forms of adaptive interventions, such as "remote" IPC, have already been applied in patients, albeit with different effectiveness. Cardiac ischemic tolerance can also be increased by other noninvasive approaches, such as adaptation to hypoxia- or exercise-induced preconditioning. Although their molecular mechanisms are not yet fully understood, some noninvasive modalities appear to be promising novel strategies for fighting HF through targeting its numerous mechanisms. In this review, we will discuss the molecular mechanisms of heart injury and repair, as well as interventions that have potential to be used in the treatment of patients.

Mitochondrial DNA and the STING pathway are required for hepatic stellate cell activation

BACKGROUND AND AIMS

TGF-β induces multiple structural and functional changes in quiescent HSCs, including an increase in proliferation, mitochondrial mass, and matrix deposition. HSC transdifferentiation requires significant bioenergetic capacity, and it is not known how TGF-β-mediated transcriptional upregulation is coordinated with the bioenergetic capacity of HSCs.

APPROACH AND RESULTS

Mitochondria are key bioenergetic organelles, and here, we report that TGF-β induces release of mitochondrial DNA (mtDNA) from healthy HSCs through voltage-dependent anion channels (VDACs), with the formation of an mtDNA-CAP on the external mitochondrial membrane. This stimulates organization of cytosolic cyclic GMP-AMP synthase (cGAS) onto the mtDNA-CAP and subsequent activation of the cGAS-STING-IRF3 pathway. TGF-β is unable to induce conversion of HSCs from a quiescent to a transdifferentiated phenotype in the absence of mtDNA, VDAC, or stimulator of interferon genes (STING). Transdifferentiation by TGF-β is blocked by a STING inhibitor, which also reduces liver fibrosis prophylactically and therapeutically.

CONCLUSIONS

We have identified a pathway that requires the presence of functional mitochondria for TGF-β to mediate HSC transcriptional regulation and transdifferentiation and therefore provides a key link between bioenergetic capacity of HSCs and signals for transcriptional upregulation of genes of anabolic pathways.

Identity, structure, and function of the mitochondrial permeability transition pore: controversies, consensus, recent advances, and future directions

The mitochondrial permeability transition (mPT) describes a Ca2+-dependent and cyclophilin D (CypD)-facilitated increase of inner mitochondrial membrane permeability that allows diffusion of molecules up to 1.5 kDa in size. It is mediated by a non-selective channel, the mitochondrial permeability transition pore (mPTP). Sustained mPTP opening causes mitochondrial swelling, which ruptures the outer mitochondrial membrane leading to subsequent apoptotic and necrotic cell death, and is implicated in a range of pathologies. However, transient mPTP opening at various sub-conductance states may contribute several physiological roles such as alterations in mitochondrial bioenergetics and rapid Ca2+ efflux. Since its discovery decades ago, intensive efforts have been made to identify the exact pore-forming structure of the mPT. Both the adenine nucleotide translocase (ANT) and, more recently, the mitochondrial F1FO (F)-ATP synthase dimers, monomers or c-subunit ring alone have been implicated. Here we share the insights of several key investigators with different perspectives who have pioneered mPT research. We critically assess proposed models for the molecular identity of the mPTP and the mechanisms underlying its opposing roles in the life and death of cells. We provide in-depth insights into current controversies, seeking to achieve a degree of consensus that will stimulate future innovative research into the nature and role of the mPTP.

Cyclosporine A (CsA) prevents synaptic impairment caused by truncated tau by caspase-3

During Alzheimer's (AD), tau protein suffers from abnormal post-translational modifications, including cleaving by caspase-3. These tau forms affect synaptic plasticity contributing to the cognitive decline observed in the early stages of AD. In addition, caspase-3 cleaved tau (TauC3) impairs mitochondrial dynamics and organelles transport, which are both relevant processes for synapse. We recently showed that the absence of tau expression reverts age-associated cognitive and mitochondrial failure by blocking the mitochondrial permeability transition pore (mPTP). mPTP is a mitochondrial complex involved in calcium regulation and apoptosis. Therefore, we studied the effects of TauC3 against the dendritic spine and synaptic vesicle formation and the possible role of mPTP in these alterations. We used mature hippocampal mice neurons to express a reporter protein (GFP, mCherry), coupled to full-length human tau protein (GFP-T4, mCherry-T4), and coupled to human tau protein cleaved at D421 by caspase-3 (GFP-T4C3, mCherry-T4C3) and synaptic elements were evaluated. Treatment with cyclosporine A (CsA), an immunosuppressive drug with inhibitory activity on mPTP, prevented ROS increase and mitochondrial depolarization induced by TauC3 in hippocampal neurons. These results were corroborated with immortalized cortical neurons in which ROS increase and ATP loss induced by this tau form were prevented by CsA. Interestingly, TauC3 expression significantly reduced dendritic spine density (filopodia type) and synaptic vesicle number in hippocampal neurons. Also, neurons transfected with TauC3 showed a significant accumulation of synaptophysin protein in their soma. More importantly, all these synaptic alterations were prevented by CsA, suggesting an mPTP role in these negative changes derived from TauC3 expression.

1,3,8-Triazaspiro[4.5]decane Derivatives Inhibit Permeability Transition Pores through a FO-ATP Synthase c Subunit Glu119-Independent Mechanism That Prevents Oligomycin A-Related Side Effects

Permeability transition pore (PTP) molecular composition and activity modulation have been a matter of research for several years, especially due to their importance in ischemia reperfusion injury (IRI). Notably, c subunit of ATP synthase (Csub) has been identified as one of the PTP-forming proteins and as a target for cardioprotection. Oligomycin A is a well-known Csub interactor that has been chemically modified in-depth for proposed new pharmacological approaches against cardiac reperfusion injury. Indeed, by taking advantage of its scaffold and through focused chemical improvements, innovative Csub-dependent PTP inhibitors (1,3,8-Triazaspiro[4.5]decane) have been synthetized in the past. Interestingly, four critical amino acids have been found to be involved in Oligomycin A-Csub binding in yeast. However, their position on the human sequence is unknown, as is their function in PTP inhibition. The aims of this study are to (i) identify for the first time the topologically equivalent residues in the human Csub sequence; (ii) provide their in vitro validation in Oligomycin A-mediated PTP inhibition and (iii) understand their relevance in the binding of 1,3,8-Triazaspiro[4.5]decane small molecules, as Oligomycin A derivatives, in order to provide insights into Csub interactions. Notably, in this study we demonstrated that 1,3,8-Triazaspiro[4.5]decane derivatives inhibit permeability transition pores through a FO-ATP synthase c subunit Glu119-independent mechanism that prevents Oligomycin A-related side effects.

Common Mechanisms Underlying α-Synuclein-Induced Mitochondrial Dysfunction in Parkinson's Disease

Parkinson's disease (PD) is the most common neurological movement disorder characterized by the selective and irreversible loss of dopaminergic neurons in substantia nigra pars compacta resulting in dopamine deficiency in the striatum. While most cases are sporadic or environmental, about 10% of patients have a positive family history with a genetic cause. The misfolding and aggregation of α-synuclein (α-syn) as a casual factor in the pathogenesis of PD has been supported by a great deal of literature. Extensive studies of mechanisms underpinning degeneration of the dopaminergic neurons induced by α-syn dysfunction suggest a complex process that involves multiple pathways, including mitochondrial dysfunction and increased oxidative stress, impaired calcium homeostasis through membrane permeabilization, synaptic dysfunction, impairment of quality control systems, disruption of microtubule dynamics and axonal transport, endoplasmic reticulum/Golgi dysfunction, nucleus malfunction, and microglia activation leading to neuroinflammation. Among them mitochondrial dysfunction has been considered as the most primary target of α-syn-induced toxicity, leading to neuronal cell death in both sporadic and familial forms of PD. Despite reviewing many aspects of PD pathogenesis related to mitochondrial dysfunction, a systemic study on how α-syn malfunction/aggregation damages mitochondrial functionality and leads to neurodegeneration is missing in the literature. In this review, we give a detailed molecular overview of the proposed mechanisms by which α-syn, directly or indirectly, contributes to mitochondrial dysfunction. This may provide valuable insights for development of new therapeutic approaches in relation to PD. Antioxidant-based therapy as a potential strategy to protect mitochondria against oxidative damage, its challenges, and recent developments in the field are discussed.

High oxygen-modified packaging (HiOx-MAP) mediates HIF-1α regulation of tenderness changes during postmortem aging of yak meat

In the present study, we studied the effect of high oxygen-modified packaging (HiOx-MAP) on yak meat tenderness and the underlying mechanism. HiOx-MAP significantly increased the myofibril fragmentation index (MFI) of yak meat. In addition, western blotting showed that the expression of hypoxia-inducible factor (HIF-1α) and ryanodine receptors (RyR) in the HiOx-MAP group was reduced. HiOx-MAP increased the activity of sarcoplasmic reticulum calcium-ATPase (SERCA). The energy disperse spectroscopy (EDS) mapping showed gradually reduced calcium distribution in the treated endoplasmic reticulum. Furthermore, HiOx-MAP treatment increased the caspase-3 activity and the apoptosis rate. The activity of calmodulin protein (CaMKKβ) and AMP-activated protein kinase (AMPK) was down-regulated leading to apoptosis. These results indicated that HiOx-MAP promoted apoptosis during postmortem aging to improve the tenderization of meat.

The Role of Mitochondria-Targeting miRNAs in Intracerebral Hemorrhage

Non-traumatic intracerebral hemorrhage (ICH) is the most common type of hemorrhagic stroke, most often occurring between the ages of 45 and 60. Arterial hypertension (AH) is most often the cause of ICH, followed by atherosclerosis, blood diseases, inflammatory changes in cerebral vessels, intoxication and vitamin deficiencies. Cerebral hemorrhage can occur by diapedesis or as a result of a ruptured vessel. AH is difficult to treat, requires surgery and can lead to disability or death. One of the important directions in the study of the pathogenesis of ICH is mitochondrial dysfunction and its regulation. The key role of mitochondrial dysfunction in AH and atherosclerosis, as well as in the development of brain damage after hemorrhage, has been acknowledged. MicroRNAs (miRNAs) are a class of non-coding RNAs (about 18-22 nucleotides) that regulate a variety of biological processes including cell differentiation, proliferation, apoptosis, etc., primarily through gene repression. There is growing evidence to support dysregulated miRNAs in various cardiovascular diseases, including ICH. Further, the realization of miRNAs within mitochondrial compartment has challenged the traditional knowledge of signaling pathways involved in the regulatory network of cardiovascular diseases. However, the role of miRNAs in mitochondrial dysfunction for ICH is still under-appreciated, with comparatively much lesser studies and investigations reported, than those in other cardiovascular diseases. In this review, we summarize the up-to-date findings on the published role miRNAs in mitochondrial function for ICH, and the potential use of miRNAs in clinical settings, such as potential therapeutic targets and non-invasive diagnostic/prognostic biomarker tools.

Isolated Mitochondrial Preparations and In organello Assays: A Powerful and Relevant Ex vivo Tool for Assessment of Brain (Patho)physiology

Mitochondria regulate multiple aspects of neuronal development, physiology, plasticity, and pathology through their regulatory roles in bioenergetic, calcium, redox, and cell survival/death signalling. While several reviews have addressed these different aspects, a comprehensive discussion focussing on the relevance of isolated brain mitochondria and their utilities in neuroscience research has been lacking. This is relevant because the employment of isolated mitochondria rather than their in situ functional evaluation, offers definitive evidence of organelle-specificity, negating the interference from extra mitochondrial cellular factors/signals. This mini-review was designed primarily to explore the commonly employed in organello analytical assays for the assessment of mitochondrial physiology and its dysfunction, with a particular focus on neuroscience research. The authors briefly discuss the methodologies for biochemical isolation of mitochondria, their quality assessment, and cryopreservation. Further, the review attempts to accumulate the key biochemical protocols for in organello assessment of a multitude of mitochondrial functions critical for neurophysiology, including assays for bioenergetic activity, calcium and redox homeostasis, and mitochondrial protein translation. The purpose of this review is not to examine each and every method or study related to the functional assessment of isolated brain mitochondria, but rather to assemble the commonly used protocols of in organello mitochondrial research in a single publication. The hope is that this review will provide a suitable platform aiding neuroscientists to choose and apply the required protocols and tools to address their particular mechanistic, diagnostic, or therapeutic question dealing within the confines of the research area of mitochondrial patho-physiology in the neuronal perspective.

Mitochondrial Permeability Transition in Stem Cells, Development, and Disease

The mitochondrial permeability transition (mPT) is a process that permits rapid exchange of small molecules across the inner mitochondrial membrane (IMM) and thus plays a vital role in mitochondrial function and cellular signaling. Formation of the pore that mediates this flux is well-documented in injury and disease but its regulation has also emerged as critical to the fate of stem cells during embryonic development. The precise molecular composition of the mPTP has been enigmatic, with far more genetic studies eliminating molecular candidates than confirming them. Rigorous studies in the recent decade have implicated central involvement of the F₁F_o ATP synthase, or complex V of the electron transport chain, and continue to confirm a regulatory role for Cyclophilin D (CypD), encoded by Ppif, in modulating the sensitivity of the pore to opening. A host of endogenous molecules have been shown to trigger flux characteristic of mPT, including positive regulators such as calcium ions, reactive oxygen species, inorganic phosphate, and fatty acids. Conductance of the pore has been described as low or high, and reversibility of pore opening appears to correspond with the relative abundance of negative regulators of mPT such as adenine nucleotides, hydrogen ion, and divalent cations that compete for calcium-binding sites in the mPTP. Current models suggest that distinct pores could be responsible for differing reversibility and conductance depending upon cellular context. Indeed, irreversible propagation of mPT inevitably leads to collapse of transmembrane potential, arrest of ATP synthesis, mitochondrial swelling, and cell death. Future studies should clarify ambiguities in mPTP structure and reveal new roles for mPT in dictating specialized cellular functions beyond cell survival that are tied to mitochondrial fitness including stem cell self-renewal and fate. The focus of this review is to describe contemporary models of the mPTP and highlight how pore activity impacts stem cells and development.

Folium Ginkgo extract and tetramethylpyrazine sodium chloride injection (Xingxiong injection) protects against focal cerebral ischaemia/reperfusion injury via activating the Akt/Nrf2 pathway and inhibiting NLRP3 inflammasome activation

CONTEXT

Folium Ginkgo extract and tetramethylpyrazine sodium chloride injection (Xingxiong injection) is a compound preparation commonly used for treating cerebral ischaemia/reperfusion injury in ischaemic stroke in China. However, its potential mechanisms on ischaemic stroke remain unknown.

OBJECTIVE

This study explores the potential mechanisms of Xingxiong injection in vivo or in vitro.

MATERIALS AND METHODS

Sprague-Dawley (SD) rats were randomly assigned to five groups: the sham (normal saline), the model (normal saline) and the Xingxiong injection groups (12.5, 25 or 50 mL/kg). The rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) followed by reperfusion for 14 d. Xingxiong injection was administered via intraperitoneal (i.p.) injection immediately after ischaemia induction for 14 d. Afterwards, rats were sacrificed at 14 d induced by administration of Xingxiong injection.

RESULTS

Xingxiong injection significantly reduces infarct volume (23%) and neurological deficit scores (93%) compared with the MCAO/R group. Additionally, Xingxiong injection inhibits the loss in mitochondrial membrane potential (43%) and reduces caspase-3 level (44%), decreases NOX (41%), protein carbonyl (29%), 4-HNE (40%) and 8-OhdG (41%) levels, inhibits the expression of inflammatory factors, such as TNF-α (26%), IL-1β (34%), IL-6 (39%), MCP-1 (36%), CD11a (41%) and ICAM-1 (43%). Moreover, Xingxiong injection can increase p-Akt/Akt (35%) and Nrf2 (47%) protein expression and inhibit NLRP3 (42%) protein expression.

CONCLUSIONS

Xingxiong injection prevents cerebral ischaemia/reperfusion injury via activating the Akt/Nrf2 pathway and inhibiting NLRP3 inflammasome. These findings provide experimental evidence for clinical use of drugs in the treatment of ischaemic stroke.

The use of fibroblasts as a valuable strategy for studying mitochondrial impairment in neurological disorders

Neurological disorders (NDs) are characterized by progressive neuronal dysfunction leading to synaptic failure, cognitive impairment, and motor injury. Among these diseases, Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) have raised a significant research interest. These disorders present common neuropathological signs, including neuronal dysfunction, protein accumulation, oxidative damage, and mitochondrial abnormalities. In this context, mitochondrial impairment is characterized by a deficiency in ATP production, excessive production of reactive oxygen species, calcium dysregulation, mitochondrial transport failure, and mitochondrial dynamics deficiencies. These defects in mitochondrial health could compromise the synaptic process, leading to early cognitive dysfunction observed in these NDs. Interestingly, skin fibroblasts from AD, PD, HD, and ALS patients have been suggested as a useful strategy to investigate and detect early mitochondrial abnormalities in these NDs. In this context, fibroblasts are considered a viable model for studying neurodegenerative changes due to their metabolic and biochemical relationships with neurons. Also, studies of our group and others have shown impairment of mitochondrial bioenergetics in fibroblasts from patients diagnosed with sporadic and genetic forms of AD, PD, HD, and ALS. Interestingly, these mitochondrial abnormalities have been observed in the brain tissues of patients suffering from the same pathologies. Therefore, fibroblasts represent a novel strategy to study the genesis and progression of mitochondrial dysfunction in AD, PD, HD, and ALS. This review discusses recent evidence that proposes fibroblasts as a potential target to study mitochondrial bioenergetics impairment in neurological disorders and consequently to search for new biomarkers of neurodegeneration.

Curcumin Improves Cardiopulmonary Resuscitation Outcomes by Modulating Mitochondrial Metabolism and Apoptosis in a Rat Model of Cardiac Arrest

Background

Curcumin, a diarylheptanoid chemical compound extracted from curcuma longa, exerts a variety of biological and pharmacological effects in numerous pathological conditions, including ischemia/reperfusion (I/R) injury. In this study, we investigated its role in post-resuscitation myocardial dysfunction in a rat model of cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) by targeting on mitochondrial metabolism and apoptosis.

Methods

Animals were randomized into three groups: sham, control and curcumin, with fifteen rats in each group. Ventricular fibrillation (VF) was induced in the rats of the control and curcumin groups. The rats in the two groups were untreated for 8 min, followed by CPR for 8 min. Placebo (saline) or curcumin was administered by intraperitoneal injection, respectively, 5 min after successful resuscitation. Myocardial function was measured at baseline and post-resuscitation for 6 h consecutively. Ten rats in each group were closely observed for an additional 66 h to analyze the survival status, and the remaining five were sacrificed for the measurement of mitochondrial parameters and cell apoptosis.

Results

Compared with the control group, myocardial function was significantly enhanced in the curcumin group, contributing to a better survival status. Curcumin treatment mitigated the depletion of superoxide dismutase (SOD) and the production of malondialdehyde (MDA). The structural damage of mitochondria was also alleviated, with improved conditions of mPTP and ΔΨm. Curcumin boosted the production of ATP and attenuated myocardial apoptosis. Cytochrome C, caspase-3 and its cleavage were suppressed by curcumin. Proteins closely related to the functional performance of mitochondria, including uncoupling protein 2 (UCP2) and uncoupling protein 3 (UCP3) were downregulated, while mitochondrial transcription factor A (mtTFA) was upregulated.

Conclusion

Curcumin improves the outcomes of CPR via alleviating myocardial dysfunction induced by I/R injury. It exhibits anti-oxidation properties. Moreover, it is capable of ameliorating mitochondrial structure and energy metabolism, as well as inhibiting the mitochondrial apoptosis pathway. UCP2, UCP3, and mtTFA might also be involved in curcumin mediated protective effects on mitochondria.

IL-22 Protects against Biliary Ischemia-Reperfusion Injury after Liver Transplantation via Activating STAT3 and Reducing Apoptosis and Oxidative Stress Levels In Vitro and In Vivo

Biliary complications are currently one of the leading causes of liver failure and patient death after liver transplantation and need to be solved urgently. Biliary ischemia-reperfusion injury (IRI) is one of the important causes of biliary complications. IL-22 has a protective effect on liver injury and hepatitis diseases, and its safety and efficacy in the treatment of hepatitis have also been proved in human clinical experiments. Furthermore, multiple studies have confirmed that IL-22 promotes the proliferation and repair of epithelial cells in various organs. Still, its function in the bile duct after transplantation has not been explored. This study was aimed at investigating the effects of IL-22 on cholangiocyte IRI in vitro and in vivo and exploring its underlying mechanisms. We simulated the hypoxia process of bile duct epithelial cells through in vitro experiments to investigate the protective function and molecular mechanism of IL-22 on bile duct epithelial cells. Subsequently, the function and mechanism of IL-22 in the biliary IRI model of autologous orthotopic liver transplantation in rats were assessed. This study confirmed that IL-22 could promote cholangiocyte proliferation, decrease the apoptosis rate of cholangiocytes and tissues, decrease MDA levels, and increase SOD levels by activating STAT3. In addition, IL-22 can also reduce the level of mitochondrial membrane depolarization, protect mitochondria, reduce ROS production, and play a role in protecting bile ducts. These findings provide evidence for IL-22 as a novel and effective treatment for biliary IRI after liver transplantation.

Mitochondrial Dysfunction and Redox Homeostasis Impairment as Pathomechanisms of Brain Damage in Ethylmalonic Encephalopathy: Insights from Animal and Human Studies

Ethylmalonic encephalopathy (EE) is a severe intoxication disorder caused by mutations in the ETHE1 gene that encodes a mitochondrial sulfur dioxygenase involved in the catabolism of hydrogen sulfide. It is biochemically characterized by tissue accumulation of hydrogen sulfide and its by-product thiosulfate, as well as of ethylmalonic acid due to hydrogen sulfide-induced inhibition of short-chain acyl-CoA dehydrogenase. Patients usually present with early onset severe brain damage associated to encephalopathy, chronic hemorrhagic diarrhea and vascular lesions with petechial purpura and orthostatic acrocyanosis whose pathophysiology is poorly known. Current treatment aims to reduce hydrogen sulfide accumulation, but does not significantly prevent encephalopathy and most fatalities. In this review, we will summarize the present knowledge obtained from human and animal studies showing that disruption of mitochondrial and redox homeostasis may represent relevant pathomechanisms of tissue damage in EE. Mounting evidence show that hydrogen sulfide and ethylmalonic acid markedly disturb critical mitochondrial functions and induce oxidative stress. Novel therapeutic strategies using promising candidate drugs for this devastating disease are also discussed.

The Use of Panax Ginseng to Reduce the Cardiotoxicity of Doxorubicin and Study its Effect on Modulating Oxidative Stress, Inflammatory, and Apoptosis Pathways

BACKGROUND: Doxorubicin (DOX) is a broad-spectrum anti-cancer drug that is used to treat a variety of cancers, including blood cancers such as leukemia and solid tissue cancers. However, its use some time limited because of its cardiotoxicity. OBJECTIVE: The objective of the study was to determine the cardioprotective effect of ginseng in the case of cardiotoxicity caused by doxorubicin therapy. Methods: Thirty experimental animals (male Sprague Wistar rats) were used in this research and they were separated into three groups: Rats in Group I (n# = 10) were given distilled water plus normal saline, rats in Group II (n# = 10) were given distilled water plus doxorubicin, and rats in Group III (n# = 10) were given Panax ginseng plus doxorubicin. Serum concentration, malondialdehyde (MDA), glutathione reductase (GSH), lipid peroxidase (LPO), TNF (ng/L), cardiac troponin (ng/L), brain natriuretic peptide BNP(g/L), and caspase-3 (pmol/L) levels were measured in all groups. RESULTS: Doxorubicin caused substantial cardiotoxicity as a result of a significant increase in the elevation of cTnI to 40.09 ± 6.67 (ng/L). In addition, MDA, LPO, TNF-α, and caspase-3 levels were increased in doxorubicin group compared to the control group p < 0.05. Panax ginseng reduced cardiac troponin (cTnI) However, its effect on reduction of BNP levels insignificantly compared to the doxorubicin group p = 0.06. Panax ginseng reduced LPO and MDA and raised the antioxidant potential biomarker GSH significantly compared to the doxorubicin group p < 0.05. Panax ginseng significantly reduced inflammatory (TNF-α) and apoptotic (caspase-3) biomarkers when compared to the doxorubicin group. CONCLUSIONS: According to the findings of this study, Panax ginseng suppresses reactive oxygen species and inflammatory and apoptotic pathways in experimental rats, thereby preventing doxorubicin-induced cardiovascular events.

Uncovering the molecular mechanisms of Ilex pubescens against myocardial ischemia-reperfusion injury using network pharmacology analysis and experimental pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Ilex pubescens (I. pubescens), has been widely used to treat cardiovascular disease (CVD) in South China. Several studies have revealed aspect of its phytochemistry and pharmacological activities in cardiovascular diseases, but its active compounds and mechanisms of action are still unclear. The aim of this study was to search for the active compounds and the pharmacological mechanisms of I. pubescens for myocardial ischemia-reperfusion injury (MI/RI) by an integrative pharmacology-based investigation.

MATERIALS AND METHODS

The main targets of compounds in I. pubescens were predicted using the TargetNet webserver (http://targetnet.scbdd.com). The network between compounds and predicted targets related to MI/RI and compounds was constructed. Functional enrichment analysis was performed to investigate the specific functions and pathways involved in the candidate I. pubescens targets acting on MI/RI, which were further validated by in vitro and in vivo experiments.

RESULTS

A total of 191 targets were predicted for 64 chemical compounds in I. pubescens. Following Venn's analysis, we found that 38 candidate targets of I. pubescens were associated with protective effects against MI/RI. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these targets were related to estrogen signaling pathway. Importantly, the cardioprotective effects of I. pubescens and its active compounds were evaluated and the regulatory effects on key targets of heat shock protein 90 alpha family class A member 1 (HSP90AA1) and Estrogen receptor 1 (ESRα) in estrogen signaling pathway were validated in vitro and in vivo.

CONCLUSION

Our discoveries revealed that I. pubescens ameliorated MI/RI by regulating HSP90AA1 and ESRα in estrogen signaling pathway.

Quercetin Improves Mitochondrial Function and Inflammation in H2O2-Induced Oxidative Stress Damage in the Gastric Mucosal Epithelial Cell by Regulating the PI3K/AKT Signaling Pathway

Functional dyspepsia (FD) is one of the most common functional gastrointestinal disorders, the therapeutic strategy of which it is limited due to its complex pathogenesis. Oxidative stress-induced damage in gastric mucosal epithelial cells is related to the pathogenesis and development of FD. Quercetin (Que) is one of the active ingredients of Zhishi that showed antioxidant, antiapoptotic, and anti-inflammatory effects. The aim of this study is to investigate the effect of Que on oxidative stress-induced gastric mucosal epithelial cells damage and its underlying molecular mechanism. The gastric mucosal epithelial cell line GES-1 was treated with 200 μM of H₂O₂ to construct an oxidative stress-induced damage model. The H₂O₂ cells were then administrated with different concentrations of Que. The results indicated that high concentration of Que (100 μM) showed cytotoxicity in H₂O₂-induced GES-1 cells. However, appropriate concentration of Que (25 and 50 μM) alleviated the oxidative stress damage induced by H₂O₂, as demonstrated by the increase of proliferation, decrease of ROS generation, apoptosis, inflammation, and alleviation of mitochondrial function and cell barrier. In addition, Que increased the activation of phosphorylation of PI3K and AKT decreased by H₂O₂. To investigate whether Que alleviated the oxidative stress damage in GES-1 cells by the PI3K/AKT signaling pathway, the GES-1 cells were treated with Que (25 μM) combined with and without LY294002, the PI3K inhibitor. The results showed that LY294002 suppressed the alleviation effect on Que in H₂O₂-induced GES-1 cells. In conclusion, the current study demonstrates that Que alleviates oxidative stress damage in GES-1 cells by improving mitochondrial function and mucosal barrier and suppressing inflammation through regulating the PI3K/AKT signaling pathway, indicating the potential therapeutic effects of Que on FD.

Schisandrin B Antagonizes Cardiotoxicity Induced by Pirarubicin by Inhibiting Mitochondrial Permeability Transition Pore (mPTP) Opening and Decreasing Cardiomyocyte Apoptosis

Objective: Pirarubicin (THP), one of the anthracycline anticancer drugs, is widely used in the treatment of various cancers, but its cardiotoxicity cannot be ignored. Schisandrin B (SchB) has the ability to upregulate cellular antioxidant defense mechanism and promote mitochondrial function and antioxidant status. However, it has not been reported whether it can resist THP-induced cardiotoxicity. The aim of this study was to investigate the effect of SchB on THP cardiotoxicity and its mechanism. Methods: The rat model of cardiotoxicity induced by THP was established, and SchB treatment was performed at the same time. The changes of ECG, cardiac coefficient, and echocardiogram were observed. The changes of myocardial tissue morphology were observed by H&E staining. Apoptosis was detected by TUNEL. The levels of LDH, BNP, CK-MB, cTnT, SOD, and MDA in serum were measured to observe the heart damage and oxidative stress state of rats. The expression of cleaved-caspase 9, pro/cleaved-caspase 3, Bcl-2/Bax, and cytosol and mitochondrial Cyt C and Bax was evaluated by western blot. H9c2 cardiomyocytes were cocultured with THP, SchB, and mPTP inhibitor CsA to detect the production of ROS and verify the above signaling pathways. The opening of mPTP and mitochondrial swelling were detected by mPTP kit and purified mitochondrial swelling kit. Results: After 8 weeks, a series of cardiotoxicity manifestations were observed in THP rats. These adverse effects can be effectively alleviated by SchB treatment. Further studies showed that SchB had strong antioxidant and antiapoptotic abilities in THP cardiotoxicity. Conclusion: SchB has an obvious protective effect on THP-induced cardiotoxicity. The mechanism may be closely related to the protection of mitochondrial function, inhibition of mPTP opening, and alleviation of oxidative stress and apoptosis of cardiomyocytes.

Quercetin Protects H9c2 Cardiomyocytes against Oxygen-Glucose Deprivation/Reoxygenation-Induced Oxidative Stress and Mitochondrial Apoptosis by Regulating the ERK1/2/DRP1 Signaling Pathway

Reperfusion of blood flow during ischemic myocardium resuscitation induces ischemia/reperfusion (I/R) injury. Oxidative stress has been identified as a major cause in this process. Quercetin (QCT) is a member of the flavonoid family that exerts antioxidant effects. The aim of this study was to investigate the preventive effects of QCT on I/R injury and its underlying mechanism. To this end, H9c2 cardiomyocytes were treated with different concentrations of QCT (10, 20, and 40 μM) and subsequently subjected to oxygen-glucose deprivation/reperfusion (OGD/R) administration. The results indicated that OGD/R-induced oxidative stress, apoptosis, and mitochondrial dysfunction in H9c2 cardiomyocytes were aggravated following 40 μM QCT treatment and alleviated following the administration of 10 and 20 μM QCT prior to OGD/R treatment. In addition, OGD/R treatment inactivated ERK1/2 signaling activation. The effect was mitigated using 10 and 20 μM QCT prior to OGD/R treatment. In conclusion, these results suggested that low concentrations of QCT might alleviate I/R injury by suppressing oxidative stress and improving mitochondrial function through the regulation of ERK1/2-DRP1 signaling, providing a potential candidate for I/R injury prevention.

A rohitukine derivative IIIM-290 induces p53 dependent mitochondrial apoptosis in acute lymphoblastic leukemia cells

Rohitukine, a chromone alkaloid extracted from Dysoxylum binectariferum, has a propitious anticancer activity. Our previous study shows that a new Rohitukine derivative IIIM-290 restricts the growth of pancreatic cancer in vivo and in vitro. In the present findings, we report the mechanism of cell death induced by IIIM-290 in MOLT-4 cells (acute lymphoblastic leukemia) and its anticancer potential against various murine leukemic tumor models in vivo. We found that IIIM-290 induced apoptosis through upregulation of different apoptotic proteins like PUMA, BAX, cytochrome c, cleaved (active) caspase-3, and cleaved PARP in MOLT-4 cells. Moreover, IIIM-290 abated mitochondrial membrane potential, elevated calcium levels, reactive oxygen species, and arrested growth of MOLT-4 cells in the synthesis (S) phase of the cell cycle. Interestingly, the elevation in proapoptotic markers was p53 dependent-the silencing of p53 abrogated apoptosis (programmed cell death) triggered by IIIM-290 in MOLT-4 cells. Furthermore, IIIM-290 significantly enhanced the survival of animals with P388 and L1210 leukemia. Thus, our results put IIIM-290 as a potential candidate for the anticancer lead.

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.

Mitochondrial Permeability Transition: A Pore Intertwines Brain Aging and Alzheimer's Disease

Advanced age is the greatest risk factor for aging-related brain disorders including Alzheimer's disease (AD). However, the detailed mechanisms that mechanistically link aging and AD remain elusive. In recent years, a mitochondrial hypothesis of brain aging and AD has been accentuated. Mitochondrial permeability transition pore (mPTP) is a mitochondrial response to intramitochondrial and intracellular stresses. mPTP overactivation has been implicated in mitochondrial dysfunction in aging and AD brains. This review summarizes the up-to-date progress in the study of mPTP in aging and AD and attempts to establish a link between brain aging and AD from a perspective of mPTP-mediated mitochondrial dysfunction.

Interaction of Agaric Acid with the Adenine Nucleotide Translocase Induces Mitochondrial Oxidative Stress

Mitochondrial permeability transition is characterized by the opening of a transmembranal pore that switches membrane permeability from specific to nonspecific. This structure allows the free traffic of ions, metabolites, and water across the mitochondrial inner membrane. The opening of the permeability transition pore is triggered by oxidative stress along with calcium overload. In this work, we explored if oxidative stress is a consequence, rather than an effector of the pore opening, by evaluating the interaction of agaric acid with the adenine nucleotide translocase, a structural component of the permeability transition pore. We found that agaric acid induces transition pore opening, increases the generation of oxygen-derived reactive species, augments the oxidation of unsaturated fatty acids in the membrane, and promotes the detachment of cytochrome c from the inner membrane. The effect of agaric acid was inhibited by the antioxidant tamoxifen in association with decreased binding of the thiol reagent eosin-3 maleimide to the adenine nucleotide translocase. We conclude that agaric acid promotes the opening of the pore, increasing ROS production that exerts oxidative modification of critical thiols in the adenine nucleotide translocase.

Inter-spike mitochondrial Ca2+ release enhances high frequency synaptic transmission

KEY POINTS

Presynaptic mitochondria not only absorb but also release Ca²⁺ during high frequency stimulation (HFS) when presynaptic [Ca²⁺ ] is kept low (<500 nm) by high cytosolic Ca²⁺ buffer or strong plasma membrane calcium clearance mechanisms under physiological external [Ca²⁺ ]. Mitochondrial Ca²⁺ release (MCR) does not alter the global presynaptic Ca²⁺ transients. MCR during HFS enhances short-term facilitation and steady state excitatory postsynaptic currents by increasing vesicular release probability. The intra-train MCR may provide residual calcium at interspike intervals, and thus support high frequency neurotransmission at central glutamatergic synapses.

ABSTRACT

Emerging evidence indicates that mitochondrial Ca²⁺ buffering contributes to local regulation of synaptic transmission. It is unknown, however, whether mitochondrial Ca²⁺ release (MCR) occurs during high frequency synaptic transmission. Confirming the previous notion that 2 μm tetraphenylphosphonium (TPP⁺ ) is a specific inhibitor of the mitochondrial Na⁺ /Ca²⁺ exchanger (mNCX), we studied the role of MCR via mNCX in short-term plasticity during high frequency stimulation (HFS) at the calyx of Held synapse of the rat. TPP⁺ reduced short-term facilitation (STF) and steady state excitatory postsynaptic currents during HFS at mature calyx synapses under physiological extracellular [Ca²⁺ ] ([Ca²⁺ ]_o  = 1.2 mm), but not at immature calyx or at 2 mm [Ca²⁺ ]_o . The inhibitory effects of TPP⁺ were stronger at synapses with morphologically complex calyces harbouring many swellings and at 32°C than at simple calyx synapses and at room temperature. These effects of TPP⁺ on STF were well correlated with those on the presynaptic mitochondrial [Ca²⁺ ] build-up during HFS. Mitochondrial [Ca²⁺ ] during HFS was increased by TPP⁺ at mature calyces under 1.2 mm [Ca²⁺ ]_o , and further enhanced at 32°C, but not under 2 mm [Ca²⁺ ]_o or at immature calyces. The close correlation of the effects of TPP⁺ on mitochondrial [Ca²⁺ ] with those on STF suggests that mNCX contributes to STF at the calyx of Held synapses. The intra-train MCR enhanced vesicular release probability without altering global presynaptic [Ca²⁺ ]. Our results suggest that MCR during HFS elevates local [Ca²⁺ ] near synaptic sites at interspike intervals to enhance STF and to support stable synaptic transmission under physiological [Ca²⁺ ]_o .

Regulation of Cell Death by Mitochondrial Transport Systems of Calcium and Bcl-2 Proteins

Mitochondria represent the fundamental system for cellular energy metabolism, by not only supplying energy in the form of ATP, but also by affecting physiology and cell death via the regulation of calcium homeostasis and the activity of Bcl-2 proteins. A lot of research has recently been devoted to understanding the interplay between Bcl-2 proteins, the regulation of these interactions within the cell, and how these interactions lead to the changes in calcium homeostasis. However, the role of Bcl-2 proteins in the mediation of mitochondrial calcium homeostasis, and therefore the induction of cell death pathways, remain underestimated and are still not well understood. In this review, we first summarize our knowledge about calcium transport systems in mitochondria, which, when miss-regulated, can induce necrosis. We continue by reviewing and analyzing the functions of Bcl-2 proteins in apoptosis. Finally, we link these two regulatory mechanisms together, exploring the interactions between the mitochondrial Ca2+ transport systems and Bcl-2 proteins, both capable of inducing cell death, with the potential to determine the cell death pathway-either the apoptotic or the necrotic one.

A systematic review of post-translational modifications in the mitochondrial permeability transition pore complex associated with cardiac diseases

The mitochondrial permeability transition pore (mPTP) opening is involved in the pathophysiology of multiple cardiac diseases, such as ischemia/reperfusion injury and heart failure. A growing number of evidence provided by proteomic screening techniques has demonstrated the role of post-translational modifications (PTMs) in several key components of the pore in response to changes in the extra/intracellular environment and bioenergetic demand. This could lead to a fine, complex regulatory mechanism that, under pathological conditions, can shift the state of mitochondrial functions and, thus, the cell's fate. Understanding the complex relationship between these PTMs is still under investigation and can provide new, promising therapeutic targets and treatment approaches. This review, using a systematic review of the literature, presents the current knowledge on PTMs of the mPTP and their role in health and cardiac disease.

Impaired flickering of the permeability transition pore causes SPG7 spastic paraplegia

Background

Mutations of the mitochondrial protein paraplegin cause hereditary spastic paraplegia type 7 (SPG7), a so-far untreatable degenerative disease of the upper motoneuron with still undefined pathomechanism.

The intermittent mitochondrial permeability transition pore (mPTP) opening, called flickering, is an essential process that operates to maintain mitochondrial homeostasis by reducing intra-matrix Ca²⁺ and reactive oxygen species (ROS) concentration, and is critical for efficient synaptic function.

Methods

We use a fluorescence-based approach to measure mPTP flickering in living cells and biochemical and molecular biology techniques to dissect the pathogenic mechanism of SPG7. In the SPG7 animal model we evaluate the potential improvement of the motor defect, neuroinflammation and neurodegeneration by means of an mPTP inducer, the benzodiazepine Bz-423.

Findings

We demonstrate that paraplegin is required for efficient transient opening of the mPTP, that is impaired in both SPG7 patients-derived fibroblasts and primary neurons from Spg7^−/− mice. We show that dysregulation of mPTP opening at the pre-synaptic terminal impairs neurotransmitter release leading to ineffective synaptic transmission. Lack of paraplegin impairs mPTP flickering by a mechanism involving increased expression and activity of sirtuin3, which promotes deacetylation of cyclophilin D, thus hampering mPTP opening. Pharmacological treatment with Bz-423, which bypasses the activity of CypD, normalizes synaptic transmission and rescues the motor impairment of the SPG7 mouse model.

Interpretation

mPTP targeting opens a new avenue for the potential therapy of this form of spastic paraplegia.

Funding

Telethon Foundation grant (TGMGCSBX16TT); Dept. of Defense, US Army, grant W81XWH-18–1–0001

Cyclophilin D counterbalances mitochondrial calcium uniporter-mediated brain mitochondrial calcium uptake

Mitochondria play an essential role in maintaining intraneuronal calcium homeostasis. Mitochondrial calcium uniporter (MCU) is a determined major brain mitochondrial calcium entry pathway. Activated MCU-mediated mitochondrial calcium overloading has been linked with brain mitochondrial pathology in disease conditions. Cyclophilin D (CypD)-mediated mitochondrial permeability transition (mPT) favors mitochondrial calcium efflux. The physiological function of CypD-mediated mPT has received increasing recognition. However, the regulatory role of CypD-mediated mPT in brain mitochondrial calcium dynamics in response to mitochondrial calcium accumulation via MCU has not been comprehensively studied. Here, by adopting purified brain mitochondria, we have determined an effect of CypD and CypD-mediated mPT against mitochondrial calcium overloading. In addition, blockade of CypD pharmaceutically or genetically blunts brain mitochondrial MCU's sensitivity to its inhibitor. Therefore, our findings suggest that CypD-mediated mPT is a mitochondrial compensatory response to MCU-mediated excess mitochondrial calcium accumulation. Moreover, CypD may potentially modulate MCU function in calcium-stressed mitochondria.

Mitochondria as a promising target for developing novel agents for treating Alzheimer's disease

The mitochondria-targeting drugs can be conventionally divided into the following groups: those compensating for the energy deficit involved in neurodegeneration, including stimulants of mitochondrial bioenergetics and activators of mitochondrial biogenesis; and neuroprotectors, that are compounds increasing the resistance of mitochondria to opening of mitochondrial permeability transition (MPT) pores. Although compensating for the energy deficit and inhibition of MPT are obvious targets for drugs used in the very early stages of Alzheimer-like pathology, but their use as the monotherapy for patients with severe symptoms is unlikely to be sufficiently effective. It would be optimal to combine targets that would provide the cognitive-stimulating, the neuroprotective effects and the ability to affect specific disease-forming mechanisms. In the design of such drugs, assessment of their potential mitochondrial-targeted effects is of particular importance. The possibility of targeted drug design for simultaneous action on mitochondrial and neurotransmitter's receptors targets is, in particularly, based on the known interplay of various cellular pathways and the presence of common structural components. Of particular interest is directed search for multitarget drugs that would act simultaneously on mitochondrial calcium-dependent functions, the targets (receptors, enzymes, etc.) facilitating neurotransmission, and the molecular targets related to the action of so-called disease-modifying factors, in particular, the formation and overcoming of the toxicity of β-amyloid or hyperphosphorylated tau protein. The examples of such approaches realized on the level of preclinical and clinical trials are presented below.

ATP synthase c-subunit ring as the channel of mitochondrial permeability transition: Regulator of metabolism in development and degeneration

The mitochondrial permeability transition pore (mPTP) or mitochondrial megachannel is arguably one of the most mysterious phenomena in biology today. mPTP has been at the center of ongoing extensive scientific research for the last several decades. In this review we will discuss recent advances in the field that enhance our understanding of the molecular composition of mPTP, its regulatory mechanisms and its pathophysiological role. We will describe our recent findings on the role of ATP synthase c-subunit ring as a central player in mitochondrial permeability transition and as an important metabolic regulator during development and in degenerative diseases.

Mitochondrial light switches: optogenetic approaches to control metabolism

Developing new technologies to study metabolism is increasingly important as metabolic disease prevalence increases. Mitochondria control cellular metabolism and dynamic changes in mitochondrial function are associated with metabolic abnormalities in cardiovascular disease, cancer, and obesity. However, a lack of precise and reversible methods to control mitochondrial function has prevented moving from association to causation. Recent advances in optogenetics have addressed this challenge, and mitochondrial function can now be precisely controlled in vivo using light. A class of genetically encoded, light-activated membrane channels and pumps has addressed mechanistic questions that promise to provide new insights into how cellular metabolism downstream of mitochondrial function contributes to disease. Here, we highlight emerging reagents-mitochondria-targeted light-activated cation channels or proton pumps-to decrease or increase mitochondrial activity upon light exposure, a technique we refer to as mitochondrial light switches, or mt^SWITCH . The mt^SWITCH technique is broadly applicable, as energy availability and metabolic signaling are conserved aspects of cellular function and health. Here, we outline the use of these tools in diverse cellular models of disease. We review the molecular details of each optogenetic tool, summarize the results obtained with each, and outline best practices for using optogenetic approaches to control mitochondrial function and downstream metabolism.

A mitochondrial journey through acetaminophen hepatotoxicity

Acetaminophen (APAP) overdose is the leading cause of acute liver failure in the United States and APAP-induced hepatotoxicity is initiated by formation of a reactive metabolite which depletes hepatic glutathione and forms protein adducts. Studies over the years have established the critical role of c-Jun N terminal kinase (JNK) and its mitochondrial translocation, as well as mitochondrial oxidant stress and subsequent induction of the mitochondrial permeability transition in APAP pathophysiology. However, it is now evident that mitochondrial responses to APAP overdose are more nuanced than appreciated earlier, with multiple levels of control, for example, to dose of APAP. In addition, mitochondrial dynamics, as well as the organelle's importance in recovery and regeneration after APAP-induced liver injury is also being recognized, which are exciting new areas with significant therapeutic potential. Thus, this review examines the temporal course of hepatocyte mitochondrial responses to an APAP overdose with an emphasis on mechanistic response to various trigger checkpoints such as NAPQI-mitochondrial protein adduct formation and activated JNK translocation. Mitochondrial dynamics, the organelle's role in recovery after APAP and emerging areas of research which promise to provide further insight into modulation of APAP pathophysiology by these fascinating organelles will also be discussed.

Targeted antioxidants as therapeutics for treatment of pneumonia in the elderly

Community acquired pneumonia is a leading cause of mortality in the United States. Along with predisposing comorbid health status, age is an independent risk factor for determining the outcome of pneumonia. Research over the last few decades has contributed to better understanding the underlying immunodysregulation and imbalanced redox homeostasis tied to this aged population group that increases susceptibility to a wide range of pathologies. Major approaches include targeting oxidative stress by reducing ROS generation at its main sources of production which includes the mitochondrion. Mitochondria-targeted antioxidants have a number of molecular strategies that include targeting the biophysical properties of mitochondria, mitochondrial localization of catalytic enzymes, and mitigating mitochondrial membrane potential. Results of several antioxidant studies both in vitro and in vivo have demonstrated promising potential as a therapeutic in the treatment of pneumonia in the elderly. More human studies will need to be conducted to evaluate its efficacy in this clinical setting.

Targeting putative components of the mitochondrial permeability transition pore for novel therapeutics

Few discoveries have influenced drug discovery programs more than the finding that mitochondrial membranes undergo swings in permeability in response to cellular perturbations. The conductor of these permeability changes is the aptly named mitochondrial permeability transition pore which, although not yet precisely defined, is comprised of several integral proteins that differentially act to regulate the flux of ions, proteins and metabolic byproducts during the course of cellular physiological functions but also pathophysiological insults. Pursuit of the pore's exact identity remains a topic of keen interest, but decades of research have unearthed provocative functions for the integral proteins leading to their evaluation to develop novel therapeutics for a wide range of clinical indications. Chief amongst these targeted, integral proteins have been the Voltage Dependent Anion Channel (VDAC) and the F₁F_O ATP synthase. Research associated with the roles and ligands of VDAC has been extensive and we will expand upon 3 examples of ligand:VDAC interactions for consideration of drug discovery projects: Tubulin:VDAC1, Hexokinase I/II:VDAC1 and olesoxime:VDAC1. The discoveries that cyclosporine blocks mitochondrial permeability transition via binding to cyclophilin D, and that cyclophilin D is an important component of F₁F_O ATP synthase, has heightened interest in the F₁F_O ATP synthase as a focal point for drug discovery, and we will discuss 2 plausible campaigns associated with disease indications. To date no drug has emerged from prospective targeting these integral proteins; however, continued exploration such as the approaches suggested in this Commentary will increase the likelihood of providing important therapeutics for severely unmet medical needs.

Inefficient thermogenic mitochondrial respiration due to futile proton leak in a mouse model of fragile X syndrome

Fragile X syndrome (FXS) is the leading known inherited intellectual disability and the most common genetic cause of autism. The full mutation results in transcriptional silencing of the Fmr1 gene and loss of fragile X mental retardation protein (FMRP) expression. Defects in neuroenergetic capacity are known to cause a variety of neurodevelopmental disorders. Thus, we explored the integrity of forebrain mitochondria in Fmr1 knockout mice during the peak of synaptogenesis. We found inefficient thermogenic respiration due to futile proton leak in Fmr1 KO mitochondria caused by coenzyme Q (CoQ) deficiency and an open cyclosporine-sensitive channel. Repletion of mitochondrial CoQ within the Fmr1 KO forebrain closed the channel, blocked the pathological proton leak, restored rates of protein synthesis during synaptogenesis, and normalized the key phenotypic features later in life. The findings demonstrate that FMRP deficiency results in inefficient oxidative phosphorylation during the neurodevelopment and suggest that dysfunctional mitochondria may contribute to the FXS phenotype.

Low abundance of NDUFV2 and NDUFS4 subunits of the hydrophilic complex I domain and VDAC1 predicts mammalian longevity

Mitochondrial reactive oxygen species (ROS) production, specifically at complex I (Cx I), has been widely suggested to be one of the determinants of species longevity. The present study follows a comparative approach to analyse complex I in heart tissue from 8 mammalian species with a longevity ranging from 3.5 to 46 years. Gene expression and protein content of selected Cx I subunits were analysed using droplet digital PCR (ddPCR) and western blot, respectively. Our results demonstrate: 1) the existence of species-specific differences in gene expression and protein content of Cx I in relation to longevity; 2) the achievement of a longevity phenotype is associated with low protein abundance of subunits NDUFV2 and NDUFS4 from the matrix hydrophilic domain of Cx I; and 3) long-lived mammals show also lower levels of VDAC (voltage-dependent anion channel) amount. These differences could be associated with the lower mitochondrial ROS production and slower aging rate of long-lived animals and, unexpectedly, with a low content of the mitochondrial permeability transition pore in these species.

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There are species-specific differences in gene expression and protein content of Cx I.

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The achievement of a longevity phenotype is associated with low protein abundance of subunits NDUFV2 and NDUFS4 from the matrix hydrophilic domain of Cx I.

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Long-lived mammals show also lower levels of VDAC (voltage-dependent anion channel) amount.

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These differences can be causally associated with the aging rate of long-lived animals.