Physiological role of mitochondrial Ca2+ transport

Aristolochic acid I induced mitochondrial Ca2+ accumulation triggers the production of MitoROS and activates Src/FAK pathway in hepatocellular carcinoma cells

Aristolochic acid I (AAI) is one of the nephrotoxic and carcinogenic compounds in Aristolochic acids (AAs). Recent studies have reported its promoting effect on hepatocellular carcinoma. However, the underlying mechanisms of AAI for the development of HCC is still unclear. Here, we found that AAI exposure caused alterations in mitochondrial function, which featured with increased ATP level and mitochondrial membrane potential, accumulation of mitochondrial Ca2+ and mitochondrial ROS (MitoROS) in Hepa1-6 and HepG2 cells. The restriction of mitochondrial Ca2+ uptake alleviated these effects. Our results showed that increased MitoROS was associated with AAI-induced migration and invasion in HCC cells. MitoROS/Src/FAK pathway was involved in the AAI-induced migration and invasion of HCC cells. In summary, our study showed that AAI affected mitochondrial metabolism of HCC cells by promoting the accumulation of mitochondrial Ca2+. These effects resulted in the activation of the MitoROS/SRC/FAK pathway in AAI-treated HCC cells, which in turn induced cell migration and invasion.

So close, yet so far away: the relationship between MAM and cardiac disease

Mitochondria-associated membrane (MAM) serve as crucial contact sites between mitochondria and the endoplasmic reticulum (ER). Recent research has highlighted the significance of MAM, which serve as a platform for various protein molecules, in processes such as calcium signaling, ATP production, mitochondrial structure and function, and autophagy. Cardiac diseases caused by any reason can lead to changes in myocardial structure and function, significantly impacting human health. Notably, MAM exhibits various regulatory effects to maintain cellular balance in several cardiac diseases conditions, such as obesity, diabetes mellitus, and cardiotoxicity. MAM proteins independently or interact with their counterparts, forming essential tethers between the ER and mitochondria in cardiomyocytes. This review provides an overview of key MAM regulators, detailing their structure and functions. Additionally, it explores the connection between MAM and various cardiac injuries, suggesting that precise genetic, pharmacological, and physical regulation of MAM may be a promising strategy for preventing and treating heart failure.

Disruption of mitochondrial and lysosomal functions by human CACNA1C variants expressed in HEK 293 and CHO cells

Objective

To investigate the pathogenesis of three novel de novo CACNA1C variants (p.E411D, p.V622G, and p.A272V) in causing neurodevelopmental disorders and arrhythmia.

Methods

Several molecular experiments were carried out on transfected human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells to explore the effects of p.E411D, p.V622G, and p.A272V variants on electrophysiology, mitochondrial and lysosomal functions. Electrophysiological studies, RT-qPCR, western blot, apoptosis assay, mito-tracker fluorescence intensity, lyso-tracker fluorescence intensity, mitochondrial calcium concentration test, and cell viability assay were performed. Besides, reactive oxygen species (ROS) levels, ATP levels, mitochondrial copy numbers, mitochondrial complex I, II, and cytochrome c functions were measured.

Results

The p.E411D variant was found in a patient with attention deficit-hyperactive disorder (ADHD), and moderate intellectual disability (ID). This mutant demonstrated reduced calcium current density, mRNA, and protein expression, and it was localized in the nucleus, cytoplasm, lysosome, and mitochondria. It exhibited an accelerated apoptosis rate, impaired autophagy, and mitophagy. It also demonstrated compromised mitochondrial cytochrome c oxidase, complex I, and II enzymes, abnormal mitochondrial copy numbers, low ATP levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, and elevated mitochondrial calcium ions. The p.V622G variant was identified in a patient who presented with West syndrome and moderate global developmental delay. The p.A272V variant was found in a patient who presented with epilepsy and mild ID. Both mutants (p.V622G and p.A272V) exhibited reduced calcium current densities, decreased mRNA and protein expressions, and they were localized in the nucleus, cytoplasm, lysosome, and mitochondria. They exhibited accelerated apoptosis and proliferation rates, impaired autophagy, and mitophagy. They also exhibited abnormal mitochondrial cytochrome c oxidase, complex I and II enzymes, abnormal mitochondrial copy numbers, low ATP, high ROS levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, as well as elevated mitochondrial calcium ions.

Conclusion

The p.E411D, p.V622G and p.A272V mutations of human CACNA1C reduce the expression level of CACNA1C proteins, and impair mitochondrial and lysosomal functions. These effects induced by CACNA1C variants may contribute to the pathogenesis of CACNA1C-related disorders.

Molecular and biochemical regulation of skeletal muscle metabolism

Skeletal muscle hypertrophy is a culmination of catabolic and anabolic processes that are interwoven into major metabolic pathways, and as such modulation of skeletal muscle metabolism may have implications on animal growth efficiency. Muscle is composed of a heterogeneous population of muscle fibers that can be classified by metabolism (oxidative or glycolytic) and contractile speed (slow or fast). Although slow fibers (type I) rely heavily on oxidative metabolism, presumably to fuel long or continuous bouts of work, fast fibers (type IIa, IIx, and IIb) vary in their metabolic capability and can range from having a high oxidative capacity to a high glycolytic capacity. The plasticity of muscle permits continuous adaptations to changing intrinsic and extrinsic stimuli that can shift the classification of muscle fibers, which has implications on fiber size, nutrient utilization, and protein turnover rate. The purpose of this paper is to summarize the major metabolic pathways in skeletal muscle and the associated regulatory pathways.

Mitochondrial Calcium-Triggered Oxidative Stress and Developmental Defects in Dopaminergic Neurons Differentiated from Deciduous Teeth-Derived Dental Pulp Stem Cells with MFF Insufficiency

Mitochondrial fission factor (MFF) is an adapter that targets dynamin-related protein 1 from the cytosol to the mitochondria for fission. Loss-of-function MFF mutations cause encephalopathy due to defective mitochondrial and peroxisomal fission 2 (EMPF2). To elucidate the molecular mechanisms that were involved, we analyzed the functional effects of MFF depletion in deciduous teeth-derived dental pulp stem cells differentiating into dopaminergic neurons (DNs). When treated with MFF-targeting small interfering RNA, DNs showed impaired neurite outgrowth and reduced mitochondrial signals in neurites harboring elongated mitochondria. MFF silencing also caused mitochondrial Ca²⁺ accumulation through accelerated Ca²⁺ influx from the endoplasmic reticulum (ER) via the inositol 1,4,5-trisphosphate receptor. Mitochondrial Ca²⁺ overload led DNs to produce excessive reactive oxygen species (ROS), and downregulated peroxisome proliferator-activated receptor-gamma co-activator-1 alpha (PGC-1α). MFF was co-immunoprecipitated with voltage-dependent anion channel 1, an essential component of the ER-mitochondrial Ca²⁺ transport system. Folic acid supplementation normalized ROS levels, PGC-1α mediated mitochondrial biogenesis, and neurite outgrowth in MFF depleted DNs, without affecting their mitochondrial morphology or Ca²⁺ levels. We propose that MFF negatively regulates the mitochondrial Ca²⁺ influx from the ER. MFF-insufficiency recapitulated the EMPF2 neuropathology with increased oxidative stress and suppressed mitochondrial biogenesis. ROS and mitochondrial biogenesis might be potential therapeutic targets for EMPF2.

Robustness of the Krebs Cycle under Physiological Conditions and in Cancer: New Clues for Evaluating Metabolism-Modifying Drug Therapies

The Krebs cycle in cells that contain mitochondria is necessary for both energy production and anabolic processes. In given cell/condition, the Krebs cycle is dynamic but remains at a steady state. In this article, we first aimed at comparing the properties of a closed cycle versus the same metabolism in a linear array. The main finding is that, unlike a linear metabolism, the closed cycle can reach a steady state (SS) regardless of the nature and magnitude of the disturbance. When the cycle is modeled with input and output reactions, the “open” cycle is robust and reaches a steady state but with exceptions that lead to sustained accumulation of intermediate metabolites, i.e., conditions at which no SS can be achieved. The modeling of the cycle in cancer, trying to obtain marked reductions in flux, shows that these reductions are limited and therefore the Warburg effect is moderate at most. In general, our results of modeling the cycle in different conditions and looking for the achievement, or not, of SS, suggest that the cycle may have a regulation, not yet discovered, to go from an open cycle to a closed one. Said regulation could allow for reaching the steady state, thus avoiding the unwanted effects derived from the aberrant accumulation of metabolites in the mitochondria. The information in this paper might be useful to evaluate metabolism-modifying medicines.

Mitochondrial Calcium: Effects of Its Imbalance in Disease

Calcium is used in many cellular processes and is maintained within the cell as free calcium at low concentrations (approximately 100 nM), compared with extracellular (millimolar) concentrations, to avoid adverse effects such as phosphate precipitation. For this reason, cells have adapted buffering strategies by compartmentalizing calcium into mitochondria and the endoplasmic reticulum (ER). In mitochondria, the calcium concentration is in the millimolar range, as it is in the ER. Mitochondria actively contribute to buffering cellular calcium, but if matrix calcium increases beyond physiological demands, it can promote the opening of the mitochondrial permeability transition pore (mPTP) and, consequently, trigger apoptotic or necrotic cell death. The pathophysiological implications of mPTP opening in ischemia-reperfusion, liver, muscle, and lysosomal storage diseases, as well as those affecting the central nervous system, for example, Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS) have been reported. In this review, we present an updated overview of the main cellular mechanisms of mitochondrial calcium regulation. We specially focus on neurodegenerative diseases related to imbalances in calcium homeostasis and summarize some proposed therapies studied to attenuate these diseases.

Carrier-free multifunctional nanomedicine for intraperitoneal disseminated ovarian cancer therapy

Background

Ovarian cancer is the most lethal gynecological cancer which is characterized by extensive peritoneal implantation metastasis and malignant ascites. Despite advances in diagnosis and treatment in recent years, the five-year survival rate is only 25–30%. Therefore, developing multifunctional nanomedicine with abilities of promoting apoptosis and inhibiting migration on tumor cells would be a promising strategy to improve the antitumor effect.

Methods and results

In this study, we developed a novel ACaT nanomedicine composed of alendronate, calcium ions and cyclin-dependent kinase 7 (CDK7) inhibitor THZ1. With the average size of 164 nm and zeta potential of 12.4 mV, the spherical ACaT nanoparticles were selectively internalized by tumor cells and effectively accumulated in the tumor site. Results of RNA-sequencing and in vitro experiments showed that ACaT promoted tumor cell apoptosis and inhibited tumor cell migration by arresting the cell cycle, increasing ROS and affecting calcium homeostasis. Weekly intraperitoneally administered of ACaT for 8 cycles significantly inhibited the growth of tumor and prolonged the survival of intraperitoneal xenograft mice.

Conclusion

In summary, this study presents a new self-assembly nanomedicine with favorable tumor targeting, antitumor activity and good biocompatibility, providing a novel therapeutic strategy for advanced ovarian cancer.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01300-4.

Sigma-1 Receptor Activation Suppresses Microglia M1 Polarization via Regulating Endoplasmic Reticulum-Mitochondria Contact and Mitochondrial Functions in Stress-Induced Hypertension Rats

Exposure to stress plays a detrimental role in the pathogenesis of hypertension via neuroinflammation pathways. Microglial neuroinflammation in the rostral ventrolateral medulla (RVLM) exacerbates stress-induced hypertension (SIH) by increasing sympathetic hyperactivity. Mitochondria of microglia are the regulators of innate immune response. Sigma-1R (σ-1R) localizes to the mitochondria-associated membranes (MAMs) and regulates endoplasmic reticulum (ER) and mitochondria communication, in part through its chaperone activity. The present study aims to investigate the protective role of σ-1R on microglial-mediated neuroinflammation. Stress-induced hypertension (SIH) was induced in rats using electric foot shocks and intermittent noise. Arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were measured to evaluate the sympathetic nervous system (SNS) activities. SKF10047 (100 µM), an agonist of σ-1R, was administrated to rats, then σ-1R localization and MAM alterations were detected by immuno-electron microscopy. Mitochondrial calcium homeostasis was examined in primary microglia and/or BV-2 microglia cells. The effect of SKF10047 treatment on the mitochondrial respiratory function of cultured microglia was measured using a Seahorse Extracellular Flux Analyzer. Confocal microscopic images were performed to indicate mitochondrial dynamics. Stress reduces σ-1R's localization at the MAMs, leading to decreased ER-mitochondria contact and IP3R-GRP75-VDAC calcium transport complexes expression in the RVLM of rats. SKF10047 promotes the length and coverage of MAMs in the prorenin-treated microglia. Prorenin treatment increases mitoROS levels, and inhibits Ca2+ signalling between the two organelles, therefore negatively affects ATP production in BV2 cells, and these effects are reversed by SKF10047 treatment. We found mitochondrial hyperfusion and microglial M1 polarization in prorenin-treated microglia. SKF10047 suppresses microglial M1 polarization and RVLM neuroinflammation, subsequently ameliorates sympathetic hyperactivity in stress-induced hypertensive rats. Sigma-1 receptor activation suppresses microglia M1 polarization and neuroinflammation via regulating endoplasmic reticulum-mitochondria contact and mitochondrial functions in stress-induced hypertension rats.

The interplay between mitochondria and store-operated Ca2+ entry: Emerging insights into cardiac diseases

Store‐operated Ca²⁺ entry (SOCE) machinery, including Orai channels, TRPCs, and STIM1, is key to cellular calcium homeostasis. The following characteristics of mitochondria are involved in the physiological and pathological regulation of cells: mitochondria mediate calcium uptake through calcium uniporters; mitochondria are regulated by mitochondrial dynamic related proteins (OPA1, MFN1/2, and DRP1) and form mitochondrial networks through continuous fission and fusion; mitochondria supply NADH to the electron transport chain through the Krebs cycle to produce ATP; under stress, mitochondria will produce excessive reactive oxygen species to regulate mitochondria‐endoplasmic reticulum interactions and the related signalling pathways. Both SOCE and mitochondria play critical roles in mediating cardiac hypertrophy, diabetic cardiomyopathy, and cardiac ischaemia‐reperfusion injury. All the mitochondrial characteristics mentioned above are determinants of SOCE activity, and vice versa. Ca²⁺ signalling dictates the reciprocal regulation between mitochondria and SOCE under the specific pathological conditions of cardiomyocytes. The coupling of mitochondria and SOCE is essential for various pathophysiological processes in the heart. Herein, we review the research focussing on the reciprocal regulation between mitochondria and SOCE and provide potential interplay patterns in cardiac diseases.

Oxidative Stress, Mitochondrial Dysfunction, and Neuroprotection of Polyphenols with Respect to Resveratrol in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease and is characterized by dopaminergic neuronal loss. The exact pathogenesis of PD is complex and not yet completely understood, but research has established the critical role mitochondrial dysfunction plays in the development of PD. As the main producer of cytosolic reactive oxygen species (ROS), mitochondria are particularly susceptible to oxidative stress once an imbalance between ROS generation and the organelle’s antioxidative system occurs. An overabundance of ROS in the mitochondria can lead to mitochondrial dysfunction and further vicious cycles. Once enough damage accumulates, the cell may undergo mitochondria-dependent apoptosis or necrosis, resulting in the neuronal loss of PD. Polyphenols are a group of natural compounds that have been shown to offer protection against various diseases, including PD. Among these, the plant-derived polyphenol, resveratrol, exhibits neuroprotective effects through its antioxidative capabilities and provides mitochondria protection. Resveratrol also modulates crucial genes involved in antioxidative enzymes regulation, mitochondrial dynamics, and cellular survival. Additionally, resveratrol offers neuroprotective effects by upregulating mitophagy through multiple pathways, including SIRT-1 and AMPK/ERK pathways. This compound may provide potential neuroprotective effects, and more clinical research is needed to establish the efficacy of resveratrol in clinical settings.

Cellular and mitochondrial calcium communication in obstructive lung disorders

Calcium (Ca²⁺) signalling is well known to dictate cellular functioning and fate. In recent years, the accumulation of Ca²⁺ in the mitochondria has emerged as an important factor in Chronic Respiratory Diseases (CRD) such as Asthma and Chronic Obstructive Pulmonary Disease (COPD). Various reports underline an aberrant increase in the intracellular Ca²⁺, leading to mitochondrial ROS generation, and further activation of the apoptotic pathway in these diseases. Mitochondria contribute to Ca²⁺ buffering which in turn regulates mitochondrial metabolism and ATP production. Disruption of this Ca²⁺ balance leads to impaired cellular processes like apoptosis or necrosis and thus contributes to the pathophysiology of airway diseases. This review highlights the key role of cytoplasmic and mitochondrial Ca²⁺ signalling in regulating CRD, such as asthma and COPD. A better understanding of the dysregulation of mitochondrial Ca²⁺ homeostasis in these diseases could provide cues for the development of advanced therapeutic interventions in these diseases.

Molecular machinery regulating mitochondrial calcium levels: The nuts and bolts of mitochondrial calcium dynamics

Mitochondria play vital role in regulating the cellular energetics and metabolism. Further, it is a signaling hub for cell survival and apoptotic pathways. One of the key determinants that calibrate both cellular energetics and survival functions is mitochondrial calcium (Ca2+) dynamics. Mitochondrial Ca2+ regulates three Ca2+-sensitive dehydrogenase enzymes involved in tricarboxylic acid cycle (TCA) cycle thereby directly controlling ATP synthesis. On the other hand, excessive Ca2+ concentration within the mitochondrial matrix elevates mitochondrial reactive oxygen species (mROS) levels and causes mitochondrial membrane depolarization. This leads to opening of the mitochondrial permeability transition pore (mPTP) and release of cytochrome c into cytosol eventually triggering apoptosis. Therefore, it is critical for cell to maintain mitochondrial Ca2+ concentration. Since cells can neither synthesize nor metabolize Ca2+, it is the dynamic interplay of Ca2+ handling proteins involved in mitochondrial Ca2+ influx and efflux that take the center stage. In this review we would discuss the key molecular machinery regulating mitochondrial Ca2+ concentration. We would focus on the channel complex involved in bringing Ca2+ into mitochondrial matrix i.e. Mitochondrial Ca2+ Uniporter (MCU) and its key regulators Mitochondrial Ca2+ Uptake proteins (MICU1, 2 and 3), MCU regulatory subunit b (MCUb), Essential MCU Regulator (EMRE) and Mitochondrial Ca2+ Uniporter Regulator 1 (MCUR1). Further, we would deliberate on major mitochondrial Ca2+ efflux proteins i.e. Mitochondrial Na+/Ca2+/Li+ exchanger (NCLX) and Leucine zipper EF hand-containing transmembrane1 (Letm1). Moreover, we would highlight the physiological functions of these proteins and discuss their relevance in human pathophysiology. Finally, we would highlight key outstanding questions in the field.

Hematopoietic Stem Cell Metabolism during Development and Aging

Cellular metabolism in hematopoietic stem cells (HSCs) is an area of intense research interest, but the metabolic requirements of HSCs and their adaptations to their niches during development have remained largely unaddressed. Distinctive from other tissue stem cells, HSCs transition through multiple hematopoietic sites during development. This transition requires drastic metabolic shifts, insinuating the capacity of HSCs to meet the physiological demand of hematopoiesis. In this review, we highlight how mitochondrial metabolism determines HSC fate, and especially focus on the links between mitochondria, endoplasmic reticulum (ER), and lysosomes in HSC metabolism.

Mitochondrial calcium in command of juggling myriads of cellular functions

The puzzling traits related to the evolutionary aspect of mitochondria, still positions the mitochondrion at the center of the research. The theory of endosymbiosis popularized by Lynn Margulis in 1967 gained prominence wherein the mitochondrion is believed to have emerged as a prokaryote and later integrated into the eukaryotic system. This semi-autonomous organelle has bagged two responsible but perilous cellular functions: a) energy metabolism, and b) calcium buffering, though both are interdependent. While most of the mitochondrial functions are saliently regulated by calcium ions, the calcium buffering role of mitochondria decides the cellular fate. Though calcium overload in few mitochondria makes them dysfunctional at the early stage of cellular stress, this doesn't lead to sudden cell death due to critical checkpoints like mitophagy, mitochondrial fusion, etc. Thus, mitochondrion juggles with multiple crucial cellular functions with its calcium buffering skill.

A Novel Biomarker Driving Poor-Prognosis Liver Cancer: Overexpression of the Mitochondrial Calcium Gatekeepers

Several studies have indicated the biological role of mitochondrial Ca²⁺ uptake in cancer pathophysiology; however, its implications in predicting the prognosis of hepatocellular carcinoma (HCC) are not yet fully understood. Here, we collected tumor specimens and adjacent normal liver tissues from 354 confirmed HCC patients and analyzed the levels of cyclic adenosine monophosphate (cAMP) responsive element binding protein 1 (CREB), mitochondrial calcium uniporter (MCU), mitochondrial calcium uptake 1 and 2 (MICU1, MICU2) using bioinformatics, qRT-PCR, and immunohistochemistry (IHC), and their relationship with clinicopathological characteristics and prognosis. HCC patients with low CREB/MICU1 and high MCU/MICU2 expression exhibited poor survival rate and prognosis in overall survival (OS) and disease-free survival (DFS) analyses. Low CREB/MICU1 and low MICU1 alone indicated poor prognosis in stage I/II and III/IV patients, respectively. In the poor differentiation/undifferentiation group, low expression of MICU1 indicated poor clinical outcomes. Low CREB/MICU1 expression suggested poor outcomes in patients with or without hepatitis B virus (HBV) infection and poor prognosis in the HCV infection group. In the non- hepatitis C virus (HCV) infection group, low MCU1 indicated a poor prognosis. Multivariate analysis demonstrated that CREB and MICU1 expression showed prognostic significance. This study demonstrates the prognostic significance of CREB, MCU, MICU1, and MICU2, in predicting HCC outcomes. Low CREB/MICU1 and high MCU/MICU2 in HCC tissues are associated with poor prognosis, thus offering a novel perspective in the clinical management for HCC patients.

Therapeutic potential of targeting mitochondrial dynamics in cancer

In the past mitochondria were considered as the "powerhouse" of cell, since they generate more than 90% of ATP in aerobic conditions through the oxidative phosphorylation. However, based on the current knowledge, mitochondria play several other cellular functions, including participation in calcium homeostasis, generation of free radicals and oxidative species, triggering/regulation of apoptosis, among others. Additionally, previous discoveries recognized mitochondria as highly dynamic structures, which undergo morphological alterations resulting in long or short fragments inside the living cells. This highly regulated process was referred as mitochondrial dynamics and involves mitochondrial fusion and fission. Thus, the number of mitochondria and the morphology of mitochondrial networks depend on the mitochondrial dynamics, biogenesis, and mitophagy. In each cell, there is a delicate balance between fusion and fission to allow the maintenance of appropriate mitochondrial functions. It has been proposed that the fusion and fission dynamics process controls cell cycle, metabolism, and survival, being implicated in a wide range of physiological and pathological conditions. Mitochondrial fusion is mediated by dynamin-like proteins, including mitofusin 1 (MFN1), mitofusin 2 (MFN2), and optic atrophy 1 protein (OPA1). Conversely, mitochondrial fission results in a large number of small fragments, which is mediated mainly by dynamin-related protein 1 (DRP1). Interestingly, there is growing evidence proposing that tumor cells modify the mitochondrial dynamics rheostat in order to gain proliferative and survival advantages. Increased mitochondrial fission has been reported in several types of human cancer cells (melanoma, ovarian, breast, lung, thyroid, glioblastoma, and others) and some studies have reported a possible direct correlation between increased mitochondrial fusion and chemoresistance of tumor cells. Here, the current knowledge about alterations of mitochondrial dynamics in cancer will be reviewed and its potential as a target for adjuvant cancer chemotherapy will be discussed.

Cytosolic Ca2+ oversees the MASs production of pyruvate for the mitochondrial market

It is generally accepted that mitochondrial Ca²⁺ controls the pace of mitochondrial bioenergetics and thus ATP production. Szibor et al. challenge this paradigm, proposing that the balance between ATP consumption and production depends on mitochondrial pyruvate supply via the malate-aspartate shuttle (MAS) and is controlled by cytosolic Ca²⁺.

Mitochondrial dysfunction plays a key role in the development of neurodegenerative diseases in diabetes

Mitochondria have an essential function in cell survival due to their role in bioenergetics, reactive oxygen species generation, calcium buffering, and other metabolic activities. Mitochondrial dysfunctions are commonly found in neurodegenerative diseases (NDs), and diabetes is a risk factor for NDs. However, the role of mitochondria in diabetic neurodegeneration is still unclear. In the present study, we review the latest evidence on the role of mitochondrial dysfunctions in the development of diabetes-related NDs and the underlying molecular mechanisms. Hypoglycemic agents, especially metformin, have been proven to have neuroprotective effects in the treatment of diabetes, in which mitochondria could act as one of the underlying mechanisms. Other hypoglycemic agents, including thiazolidinediones (TZDs), dipeptidyl peptidase 4 (DPP-4) inhibitors, and glucagon-like peptide 1 (GLP-1) receptor agonists, have gained more attention because of their beneficial effects on NDs, presumably by improving mitochondrial function. Our review highlights the notion that mitochondria could be a promising therapeutic target in the treatment of NDs in patients with diabetes.

Reactive oxygen species in reproduction: harmful, essential or both?

The process of embryonic development is crucial and radically influences preimplantation embryo competence. It involves oocyte maturation, fertilization, cell division and blastulation and is characterized by different key phases that have major influences on embryo quality. Each stage of the process of preimplantation embryonic development is led by important signalling pathways that include very many regulatory molecules, such as primary and secondary messengers. Many studies, both in vivo and in vitro, have shown the importance of the contribution of reactive oxygen species (ROS) as important second messengers in embryo development. ROS may originate from embryo metabolism and/or oocyte/embryo surroundings, and their effect on embryonic development is highly variable, depending on the needs of the embryo at each stage of development and on their environment (in vivo or under in vitro culture conditions). Other studies have also shown the deleterious effects of ROS in embryo development, when cellular tissue production overwhelms antioxidant production, leading to oxidative stress. This stress is known to be the cause of many cellular alterations, such as protein, lipid, and DNA damage. Considering that the same ROS level can have a deleterious effect on the fertilizing oocyte or embryo at certain stages, and a positive effect at another stage of the development process, further studies need to be carried out to determine the rate of ROS that benefits the embryo and from what rate it starts to be harmful, this measured at each key phase of embryonic development.

Mitochondrial Calcium Regulation of Redox Signaling in Cancer

Calcium (Ca²⁺) uptake into the mitochondria shapes cellular Ca²⁺ signals and acts as a key effector for ATP generation. In addition, mitochondria-derived reactive oxygen species (mROS), produced as a consequence of ATP synthesis at the electron transport chain (ETC), modulate cellular signaling pathways that contribute to many cellular processes. Cancer cells modulate mitochondrial Ca²⁺ ([Ca²⁺]m) homeostasis by altering the expression and function of mitochondrial Ca²⁺ channels and transporters required for the uptake and extrusion of mitochondrial Ca²⁺. Regulated elevations in [Ca²⁺]m are required for the activity of several mitochondrial enzymes, and this in turn regulates metabolic flux, mitochondrial ETC function and mROS generation. Alterations in both [Ca²⁺]m and mROS are hallmarks of many tumors, and elevated mROS is a known driver of pro-tumorigenic redox signaling, resulting in the activation of pathways implicated in cellular proliferation, metabolic alterations and stress-adaptations. In this review, we highlight recent studies that demonstrate the interplay between [Ca²⁺]m and mROS signaling in cancer.

Imaging Mitochondrial Functions: from Fluorescent Dyes to Genetically-Encoded Sensors

Mitochondria are multifunctional organelles that are crucial to cell homeostasis. They constitute the major site of energy production for the cell, they are key players in signalling pathways using secondary messengers such as calcium, and they are involved in cell death and redox balance paradigms. Mitochondria quickly adapt their dynamics and biogenesis rates to meet the varying energy demands of the cells, both in normal and in pathological conditions. Therefore, understanding simultaneous changes in mitochondrial functions is crucial in developing mitochondria-based therapy options for complex pathological conditions such as cancer, neurological disorders, and metabolic syndromes. To this end, fluorescence microscopy coupled to live imaging represents a promising strategy to track these changes in real time. In this review, we will first describe the commonly available tools to follow three key mitochondrial functions using fluorescence microscopy: Calcium signalling, mitochondrial dynamics, and mitophagy. Then, we will focus on how the development of genetically-encoded fluorescent sensors became a milestone for the understanding of these mitochondrial functions. In particular, we will show how these tools allowed researchers to address several biochemical activities in living cells, and with high spatiotemporal resolution. With the ultimate goal of tracking multiple mitochondrial functions simultaneously, we will conclude by presenting future perspectives for the development of novel genetically-encoded fluorescent biosensors.

Dichotomous role of the human mitochondrial Na+/Ca2+/Li+ exchanger NCLX in colorectal cancer growth and metastasis

Despite the established role of mitochondria in cancer, the mechanisms by which mitochondrial Ca²⁺ (mtCa²⁺) regulates tumorigenesis remain incompletely understood. The crucial role of mtCa²⁺ in tumorigenesis is highlighted by altered expression of proteins mediating mtCa²⁺ uptake and extrusion in cancer. Here, we demonstrate decreased expression of the mitochondrial Na⁺/Ca²⁺/Li⁺ exchanger NCLX (SLC8B1) in human colorectal tumors and its association with advanced-stage disease in patients. Downregulation of NCLX causes mtCa²⁺ overload, mitochondrial depolarization, decreased expression of cell-cycle genes and reduced tumor size in xenograft and spontaneous colorectal cancer mouse models. Concomitantly, NCLX downregulation drives metastatic spread, chemoresistance, and expression of epithelial-to-mesenchymal, hypoxia, and stem cell pathways. Mechanistically, mtCa²⁺ overload leads to increased mitochondrial reactive oxygen species, which activate HIF1α signaling supporting metastasis of NCLX-null tumor cells. Thus, loss of NCLX is a novel driver of metastasis, indicating that regulation of mtCa²⁺ is a novel therapeutic approach in metastatic colorectal cancer.

Calcium signalling in T cells

Calcium (Ca²⁺) signalling is of paramount importance to immunity. Regulated increases in cytosolic and organellar Ca²⁺ concentrations in lymphocytes control complex and crucial effector functions such as metabolism, proliferation, differentiation, antibody and cytokine secretion and cytotoxicity. Altered Ca²⁺ regulation in lymphocytes leads to various autoimmune, inflammatory and immunodeficiency syndromes. Several types of plasma membrane and organellar Ca²⁺-permeable channels are functional in T cells. They contribute highly localized spatial and temporal Ca²⁺ microdomains that are required for achieving functional specificity. While the mechanistic details of these Ca²⁺ microdomains are only beginning to emerge, it is evident that through crosstalk, synergy and feedback mechanisms, they fine-tune T cell signalling to match complex immune responses. In this article, we review the expression and function of various Ca²⁺-permeable channels in the plasma membrane, endoplasmic reticulum, mitochondria and endolysosomes of T cells and their role in shaping immunity and the pathogenesis of immune-mediated diseases.

Effects of egg yolk and soybean lecithin on sperm quality determined by computer-assisted sperm analysis and confocal laser scanning microscope in chilled canine sperm

The reduction of spermatozoa survival time is a major problem of canine chilled sperm for artificial insemination. The aim of the study was to improve the quality of canine chilled sperm during storage time. We therefore, evaluated the effects of eight treatments with different levels of soybean lecithin concentration (1, 3 and 5%) and egg yolk (20%) in Tris-citric-fructose or Tris-citric-fructose-mineral salts extender on chilled canine sperm quality during 10 days of storage. The sperm motility was analysed by computer-assisted sperm analysis (CASA), whereas plasma membrane integrity, acrosome membrane integrity and mitochondrial membrane potential parameters were determined using a fluorescent staining combination of propidium iodide (PI), Hoechst 33342 (H342), fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA) and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1) by confocal laser scanning microscope. The results showed that egg yolk was found to be better than soybean lecithin in Tris-citric-fructose or Tris-citric-fructose-mineral salts extender for maintaining the quality of chilled canine sperm within 10 days of storage (P < 0.05). Although egg yolk in Tris-citric-fructose extender could maintain the motility better than other extenders, egg yolk in Tris-citric-fructose-mineral salts extender was the highest in intact plasma membrane, intact acrosome membrane and high mitochondrial membrane potential (P < 0.05). In contrast, the sperm quality of soybean lecithin in Tris-citric-fructose-mineral salts extender was lower than that of soybean lecithin in Tris-citric-fructose extender, and soybean lecithin 1% was greater than soybean lecithin 3% and 5% in plasma membrane integrity, acrosome membrane integrity and mitochondrial membrane potential (P < 0.05). In conclusion, soybean lecithin cannot replace egg yolk in Tris-citric-fructose or Tris-citric-fructose-mineral salts extenders, and egg yolk in Tris-citric-fructose-mineral salts extender is superior to other extenders in chilling canine sperm.

Arginase II activity regulates cytosolic Ca2+ level in a p32-dependent manner that contributes to Ca2+-dependent vasoconstriction in native low-density lipoprotein-stimulated vascular smooth muscle cells

Although arginase II (ArgII) is abundant in mitochondria, Ca²⁺-accumulating organelles, the relationship between ArgII activity and Ca²⁺ translocation into mitochondria and the regulation of cytosolic Ca²⁺ signaling are completely unknown. We investigated the effects of ArgII activity on mitochondrial Ca²⁺ uptake through mitochondrial p32 protein (p32m) and on CaMKII-dependent vascular smooth muscle cell (VSMC) contraction. Native low-density lipoprotein stimulation induced an increase in [Ca²⁺]m as measured by CoCl₂-quenched calcein-AM fluorescence, which was prevented by Arg inhibition in hAoSMCs and reduced in mAoSMCs from ArgII^−/− mice. Conversely, [Ca²⁺]c analyzed with Fluo-4 AM was increased by Arg inhibition and ArgII gene knockout. The increased [Ca²⁺]c resulted in CaMKII and MLC 20 phosphorylation, which was associated with enhanced vasoconstriction activity to phenylephrine (PE) in the vascular tension assay. Cy5-tagged siRNA against mitochondrial p32 mRNA (sip32m) abolished mitochondrial Ca²⁺ uptake and induced activation of CaMKII. Spermine, a polyamine, induced mitochondrial Ca²⁺ uptake and dephosphorylation of CaMKII and was completely inhibited by sip32m incubation. In mAoSMCs from ApoE-null mice fed a high-cholesterol diet (ApoE^−/− +HCD), Arg activity was increased, and spermine concentration was higher than that of wild-type mice. Furthermore, [Ca²⁺]m and p32m levels were elevated, and CaMKII phosphorylation was reduced in mAoSMCs from ApoE^−/− +HCD. In vascular tension experiments, an attenuated response to vasoconstrictors in de-endothelialized aorta from ApoE^−/− +HCD was recovered by incubation of sip32m. ArgII activity-dependent production of spermine augments Ca²⁺ transition from the cytosol to the mitochondria in a p32m-dependent manner and regulates CaMKII-dependent constriction in VSMCs.

Researchers have illuminated how a protein, arginase II (ArgII), is involved in development of vascular diseases such as atherosclerosis, or narrowing of the arteries by plaque deposits. Blood vessel diameter is regulated by layers of muscle; the balance between constriction and relaxation is critical for blood flow and vascular health. Increased ArgII is known to be a factor in arterial disease; however, the details of regulation, and how they relate to plaque deposition, remain poorly understood. Sungwoo Ryoo at Kangwon National University, Chuncheon, South Korea and co-workers investigated how ArgII levels affect arterial constriction and relaxation in mice. Decreasing ArgII restored the muscle cells’ contraction response by preventing excessive calcium accumulation in the cellular powerhouse, mitochondria. These results may aid in developing treatments for one of the leading causes of death worldwide.

Calcium, mitochondria and cell metabolism: A functional triangle in bioenergetics

The versatility of mitochondrial metabolism and its fine adjustments to specific physiological or pathological conditions regulate fundamental cell pathways, ranging from proliferation to apoptosis. In particular, Ca²⁺ signalling has emerged as a key player exploited by mitochondria to tune their activity according with cell demand. The functional interaction between mitochondria and endoplasmic reticulum (ER) deeply impacts on the correct mitochondrial Ca²⁺ signal, thus modulating cell bioenergetics and functionality. Indeed, Ca²⁺ released by the ER is taken up by mitochondria where, both in the intermembrane space and in the matrix, it regulates the activity of transporters, enzymes and proteins involved in organelles' metabolism. In this review, we will briefly summarize Ca²⁺-dependent mechanisms involved in the regulation of mitochondrial activity. Moreover, we will discuss some recent reports, in which alterations in mitochondrial Ca²⁺ signalling have been associated with specific pathological conditions, such as neurodegeneration and cancer.

Mitochondrial Ca2+ signaling

Mitochondrial Ca²⁺ regulation is crucial for bioenergetics and cellular signaling. The mechanisms controlling mitochondrial calcium homeostasis have been recently unraveled with the discovery of mitochondrial inner membrane proteins that regulate mitochondrial Ca²⁺ uptake and extrusion. Mitochondrial Ca²⁺ uptake depends on a large complex of proteins centered around the Ca²⁺ channel protein, mitochondrial Ca²⁺ uniporter (MCU) in close interactions with several regulatory subunits (MCUb, EMRE, MICU1, MICU2). Mitochondrial Ca²⁺ extrusion is mainly mediated by the mitochondrial Na⁺/Ca²⁺/Li⁺ exchanger (NCLX). Here, we review the major players of mitochondrial Ca²⁺ homeostasis and their physiological functions.

SK channel activation is neuroprotective in conditions of enhanced ER-mitochondrial coupling

Alterations in the strength and interface area of contact sites between the endoplasmic reticulum (ER) and mitochondria contribute to calcium (Ca²⁺) dysregulation and neuronal cell death, and have been implicated in the pathology of several neurodegenerative diseases. Weakening this physical linkage may reduce Ca²⁺ uptake into mitochondria, while fortifying these organelle contact sites may promote mitochondrial Ca²⁺ overload and cell death. Small conductance Ca²⁺-activated K⁺ (SK) channels regulate mitochondrial respiration, and their activation attenuates mitochondrial damage in paradigms of oxidative stress. In the present study, we enhanced ER–mitochondrial coupling and investigated the impact of SK channels on survival of neuronal HT22 cells in conditions of oxidative stress. Using genetically encoded linkers, we show that mitochondrial respiration and the vulnerability of neuronal cells to oxidative stress was inversely linked to the strength of ER–mitochondrial contact points and the increase in mitochondrial Ca²⁺ uptake. Pharmacological activation of SK channels provided protection against glutamate-induced cell death and also in conditions of increased ER–mitochondrial coupling. Together, this study revealed that SK channel activation provided persistent neuroprotection in the paradigm of glutamate-induced oxytosis even in conditions where an increase in ER–mitochondrial coupling potentiated mitochondrial Ca²⁺ influx and impaired mitochondrial bioenergetics.

MCU-dependent mitochondrial Ca2+ inhibits NAD+/SIRT3/SOD2 pathway to promote ROS production and metastasis of HCC cells

Mitochondrial Ca²⁺ signaling, which is strongly dependent on the mitochondrial Ca²⁺ uniporter (MCU) complex, has a series of key roles in physiopathological processes, including energy metabolism, reactive oxygen species (ROS) production and cell apoptosis. However, a mechanistic understanding of how the mitochondrial Ca²⁺ signaling is remodeled and its functional roles remains greatly limited in cancers, especially in hepatocellular carcinoma. Here we demonstrated that the MCU complex was dysregulated in hepatocellular carcinoma (HCC) cells and significantly correlated with metastasis and poor prognosis of HCC patients. Upregulation of MCU clearly enhanced the Ca²⁺ uptake into mitochondria, which significantly promoted ROS production by downregulating nicotinamide adenine dinucleotide⁺ (NAD⁺)/reduced form of nicotinamide adenine dinucleotid (NADH) ratio and the NAD⁺-dependent deacetylase activity of sirtuin 3 to inhibit superoxide dismutase 2 (SOD2) activity. Moreover, our data indicated that the MCU-dependent mitochondrial Ca²⁺ uptake promotes matrix metalloproteinase-2 activity and cell motility by ROS-activated c-Jun N-terminal kinase pathway, and thus contributed to the increased ability of invasion and migration in vitro and intrahepatic and distal lung metastasis in vivo of HCC cells. In addition, treatment with the mitochondrial Ca²⁺-buffering protein parvalbumin significantly suppressed ROS production and the ability of HCC metastasis. Our study uncovers a mechanism that links the remodeling of mitochondrial Ca²⁺ homeostasis to ROS production, and provides evidence supporting a metastasis-promoting role for the MCU-dependent mitochondrial Ca²⁺ uptake in HCC. Our findings suggest that the mitochondrial Ca²⁺ uptake machinery may potentially be a novel therapeutic target for HCC metastasis.

Cyclophilin D over-expression increases mitochondrial complex III activity and accelerates supercomplex formation

Cyclophilin D (CyPD), a mitochondrial matrix protein, has been widely studied for its role in mitochondrial-mediated cell death. Unexpectedly, we previously discovered that overexpression of CyPD in a stable cell line, increased mitochondrial membrane potentials and enhanced cell survival under conditions of oxidative stress. Here, we investigated the underlying mechanisms responsible for these findings. Spectrophotometric measurements in isolated mitochondria revealed that overexpression of CyPD in HEK293 cells increased respiratory chain activity, but only for Complex III (CIII). Acute treatment of mitochondria with the immumosupressant cyclosporine A did not affect CIII activity. Expression levels of the CIII subunits cytochrome b and Rieske-FeS were elevated in HEK293 cells overexpressing CyPD. However, CIII activity was still significantly higher compared to control mitochondria, even when normalized by protein expression. Blue native gel electrophoresis and Western blot assays revealed a molecular interaction of CyPD with CIII and increased levels of supercomplexes in mitochondrial protein extracts. Radiolabeled protein synthesis in mitochondria showed that CIII assembly and formation of supercomplexes containing CIII were significantly faster when CyPD was overexpressed. Taken together, these data indicate that CyPD regulates mitochondrial metabolism, and likely cell survival, by promoting more efficient electrons flow through the respiratory chain via increased supercomplex formation.

Electron Transport Chain Remodeling by GSK3 during Oogenesis Connects Nutrient State to Reproduction

Reproduction is heavily influenced by nutrition and metabolic state. Many common reproductive disorders in humans are associated with diabetes and metabolic syndrome. We characterized the metabolic mechanisms that support oogenesis and found that mitochondria in mature Drosophila oocytes enter a low-activity state of respiratory quiescence by remodeling the electron transport chain (ETC). This shift in mitochondrial function leads to extensive glycogen accumulation late in oogenesis and is required for the developmental competence of the oocyte. Decreased insulin signaling initiates ETC remodeling and mitochondrial respiratory quiescence through glycogen synthase kinase 3 (GSK3). Intriguingly, we observed similar ETC remodeling and glycogen uptake in maturing Xenopus oocytes, suggesting that these processes are evolutionarily conserved aspects of oocyte development. Our studies reveal an important link between metabolism and oocyte maturation.

Transport of Calcium Ions into Mitochondria

To uptake calcium ions of mitochondria is of significant functional connotation for cells, because calcium ions in mitochondria are involved in energy production, regulatory signals transfer, and mitochondrial permeability transition pore opening and even programmed cell death of apoptosis, further playing more roles in plant productivity and quality. Cytoplasmic calcium ions access into outer mitochondrial membrane (OMM) from voltage dependent anion-selective channel (VDAC) and were absorbed into inner mitochondrial membrane (IMM) by mitochondrial calcium uniporter (MCU), rapid mitochondrial calcium uptake (RaM) or mitochondrial ryanodine receptor (mRyR). Although both mitochondria and the mechanisms of calcium transport have been extensively studied, but there are still long-standing or even new challenges. Here we review the history and recent discoveries of the mitochondria calcium ions channel complex involved calcium assimilation, and discuss the role of calcium ions into mitochondria.

Oocyte activation and latent HIV-1 reactivation: AMPK as a common mechanism of action linking the beginnings of life and the potential eradication of HIV-1

In all mammalian species studied to date, the initiation of oocyte activation is orchestrated through alterations in intracellular calcium (Ca(2+)) signaling. Upon sperm binding to the oocyte plasma membrane, a sperm-associated phospholipase C (PLC) isoform, PLC zeta (PLCζ), is released into the oocyte cytoplasm. PLCζ hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), which activates protein kinase C (PKC), and inositol 1,4,5-trisphosphate (IP3), which induces the release of Ca(2+) from endoplasmic reticulum (ER) Ca(2+) stores. Subsequent Ca(2+) oscillations are generated that drive oocyte activation to completion. Ca(2+) ionophores such as ionomycin have been successfully used to induce artificial human oocyte activation, facilitating fertilization during intra-cytoplasmic sperm injection (ICSI) procedures. Early studies have also demonstrated that the PKC activator phorbol 12-myristate 13-acetate (PMA) acts synergistically with Ca(2+) ionophores to induce parthenogenetic activation of mouse oocytes. Interestingly, the Ca(2+)-induced signaling cascade characterizing sperm or chemically-induced oocyte activation, i.e. the "shock and live" approach, bears a striking resemblance to the reactivation of latently infected HIV-1 viral reservoirs via the so called "shock and kill" approach, a method currently being pursued to eradicate HIV-1 from infected individuals. PMA and ionomycin combined, used as positive controls in HIV-1 latency reversal studies, have been shown to be extremely efficient in reactivating latent HIV-1 in CD4(+) memory T cells by inducing T cell activation. Similar to oocyte activation, T cell activation by PMA and ionomycin induces an increase in intracellular Ca(2+) concentrations and activation of DAG, PKC, and downstream Ca(2+)-dependent signaling pathways necessary for proviral transcription. Interestingly, AMPK, a master regulator of cell metabolism that is activated thorough the induction of cellular stress (e.g. increase in Ca(2+) concentration, reactive oxygen species generation, increase in AMP/ATP ratio) is essential for oocyte maturation, T cell activation, and mitochondrial function. In addition to the AMPK kinase LKB1, CaMKK2, a Ca(2+)/calmodulin-dependent kinase that also activates AMPK, is present in and activated on T cell activation and is also present in mouse oocytes and persists until the zygote and two-cell stages. It is our hypothesis that AMPK activation represents a central node linking T cell activation-induced latent HIV-1 reactivation and both physiological and artificial oocyte activation. We further propose the novel observation that various compounds that have been shown to reactivate latent HIV-1 (e.g. PMA, ionomycin, metformin, bryostatin, resveratrol, etc.) or activate oocytes (PMA, ionomycin, ethanol, puromycin, etc.) either alone or in combination likely do so via stress-induced activation of AMPK.

Identification of EFHD1 as a novel Ca(2+) sensor for mitoflash activation

Mitochondrial flashes (mitoflashes) represent stochastic and discrete mitochondrial events that each comprises a burst of superoxide production accompanied by transient depolarization and matrix alkalinization in a respiratory mitochondrion. While mitochondrial Ca(2+) is shown to be an important regulator of mitoflash activity, little is known about its specific mechanism of action. Here we sought to determine possible molecular players that mediate the Ca(2+) regulation of mitoflashes by screening mitochondrial proteins containing the Ca(2+)-binding motifs. In silico analysis and targeted siRNA screening identified four mitoflash activators (MICU1, EFHD1, SLC25A23, SLC25A25) and one mitoflash inhibitor (LETM1) in terms of their ability to modulate mitoflash response to hyperosmotic stress. In particular, overexpression or down-regulation of EFHD1 enhanced or depressed mitoflash activation, respectively, under various conditions of mitochondrial Ca(2+) elevations. Yet, it did not alter mitochondrial Ca(2+) handling, mitochondrial respiration, or ROS-induced mitoflash production. Further, disruption of the two EF-hand motifs of EFHD1 abolished its potentiating effect on the mitoflash responses. These results indicate that EFHD1 functions as a novel mitochondrial Ca(2+) sensor underlying Ca(2+)-dependent activation of mitoflashes.

Calcium and ROS: A mutual interplay

Calcium is an important second messenger involved in intra- and extracellular signaling cascades and plays an essential role in cell life and death decisions. The Ca²⁺ signaling network works in many different ways to regulate cellular processes that function over a wide dynamic range due to the action of buffers, pumps and exchangers on the plasma membrane as well as in internal stores. Calcium signaling pathways interact with other cellular signaling systems such as reactive oxygen species (ROS). Although initially considered to be potentially detrimental byproducts of aerobic metabolism, it is now clear that ROS generated in sub-toxic levels by different intracellular systems act as signaling molecules involved in various cellular processes including growth and cell death. Increasing evidence suggests a mutual interplay between calcium and ROS signaling systems which seems to have important implications for fine tuning cellular signaling networks. However, dysfunction in either of the systems might affect the other system thus potentiating harmful effects which might contribute to the pathogenesis of various disorders.

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Calcium and ROS act as signaling molecules inside the cell and their pathways can interact.

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The mutual interplay of calcium and ROS is required for the fine tuning of signaling.

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Failure in the interplay results in dysfunction and pathologies.

Malleable mitochondrion of Trypanosoma brucei

The importance of mitochondria for a typical aerobic eukaryotic cell is undeniable, as the list of necessary mitochondrial processes is steadily growing. Here, we summarize the current knowledge of mitochondrial biology of an early-branching parasitic protist, Trypanosoma brucei, a causative agent of serious human and cattle diseases. We present a comprehensive survey of its mitochondrial pathways including kinetoplast DNA replication and maintenance, gene expression, protein and metabolite import, major metabolic pathways, Fe-S cluster synthesis, ion homeostasis, organellar dynamics, and other processes. As we describe in this chapter, the single mitochondrion of T. brucei is everything but simple and as such rivals mitochondria of multicellular organisms.

The mitochondrial Ca(2+) uniporter complex

Calcium influx into the mitochondrial matrix plays important roles in the regulation of cell death pathways, bioenergetics and cytoplasmic Ca(2+) signals. During the last few years, several molecular components of the inner membrane mitochondrial Ca(2+) uniporter, the dominant pathway for Ca(2+) influx into the mitochondrial matrix, have been identified. The uniporter is now recognized as a complex of proteins that include a Ca(2+) pore forming component and accessory proteins that are either required for its channel activity or regulate it under various conditions. This review summarizes recent discoveries about the molecular basis of the uniporter complex. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease."

Effect of holding equine oocytes in meiosis inhibitor-free medium before in vitro maturation and of holding temperature on meiotic suppression and mitochondrial energy/redox potential

BACKGROUND

Evaluation of mitochondrial function offers an alternative to evaluate embryo development for assessment of oocyte viability, but little information is available on the relationship between mitochondrial and chromatin status in equine oocytes. We evaluated these parameters in immature equine oocytes either fixed immediately (IMM) or held overnight in an Earle's/Hank's' M199-based medium in the absence of meiotic inhibitors (EH treatment), and in mature oocytes. We hypothesized that EH holding may affect mitochondrial function and that holding temperature may affect the efficiency of meiotic suppression.

METHODS

Experiment 1 - Equine oocytes processed immediately or held in EH at uncontrolled temperature (22 to 27°C) were evaluated for initial chromatin configuration, in vitro maturation (IVM) rates and mitochondrial energy/redox potential. Experiment 2 - We then investigated the effect of holding temperature (25°C, 30°C, 38°C) on initial chromatin status of held oocytes, and subsequently repeated mitochondrial energy/redox assessment of oocytes held at 25°C vs. immediately-evaluated controls.

RESULTS

EH holding at uncontrolled temperature was associated with advancement of germinal vesicle (GV) chromatin condensation and with meiotic resumption, as well as a lower maturation rate after IVM. Holding did not have a significant effect on mitochondrial distribution within chromatin configurations. Independent of treatment, oocytes having condensed chromatin had a significantly higher proportion of perinuclear/pericortical mitochondrial distribution than did other GV configurations. Holding did not detrimentally affect oocyte energy/redox parameters in viable GV-stage oocytes. There were no significant differences in chromatin configuration between oocytes held at 25°C and controls, whereas holding at higher temperature was associated with meiosis resumption and loss of oocytes having the condensed chromatin GV configuration. Holding at 25°C was not associated with progression of mitochondrial distribution pattern and there were no significant differences in oocyte energy/redox parameters between these oocytes and controls.

CONCLUSIONS

Mitochondrial distribution in equine GV-stage oocytes is correlated with chromatin configuration within the GV. Progression of chromatin configuration and mitochondrial status during holding are dependent on temperature. EH holding at 25°C maintains meiotic arrest, viability and mitochondrial potential of equine oocytes. This is the first report on the effects of EH treatment on oocyte mitochondrial energy/redox potential.

Oxidative stress, mitochondrial damage and neurodegenerative diseases

Oxidative stress and mitochondrial damage have been implicated in the pathogenesis of several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Oxidative stress is characterized by the overproduction of reactive oxygen species, which can induce mitochondrial DNA mutations, damage the mitochondrial respiratory chain, alter membrane permeability, and influence Ca²⁺ homeostasis and mitochondrial defense systems. All these changes are implicated in the development of these neurodegenerative diseases, mediating or amplifying neuronal dysfunction and triggering neurodegeneration. This paper summarizes the contribution of oxidative stress and mitochondrial damage to the onset of neurodegenerative eases and discusses strategies to modify mitochondrial dysfunction that may be attractive therapeutic interventions for the treatment of various neurodegenerative diseases.

Advanced glycation end products: role in pathology of diabetic cardiomyopathy

Increasing evidence demonstrates that advanced glycation end products (AGEs) play a pivotal role in the development and progression of diabetic heart failure, although there are numerous other factors that mediate the disease response. AGEs are generated intra- and extracellularly as a result of chronic hyperglycemia. Then, following the interaction with receptors for advanced glycation end products (RAGEs), a series of events leading to vascular and myocardial damage are elicited and sustained, which include oxidative stress, increased inflammation, and enhanced extracellular matrix accumulation resulting in diastolic and systolic dysfunction. Whereas targeting glycemic control and treating additional risk factors, such as obesity, dyslipidemia, and hypertension, are mandatory to reduce chronic complications and prolong life expectancy in diabetic patients, drug therapy tailored to reducing the deleterious effects of the AGE-RAGE interactions is being actively investigated and showing signs of promise in treating diabetic cardiomyopathy and associated heart failure. This review shall discuss the formation of AGEs in diabetic heart tissue, potential targets of glycation in the myocardium, and underlying mechanisms that lead to diabetic cardiomyopathy and heart failure along with the use of AGE inhibitors and breakers in mitigating myocardial injury.

Exocytosis of serotonin from the neuronal soma is sustained by a serotonin and calcium-dependent feedback loop

The soma of many neurons releases large amounts of transmitter molecules through an exocytosis process that continues for hundreds of seconds after the end of the triggering stimulus. Transmitters released in this way modulate the activity of neurons, glia and blood vessels over vast volumes of the nervous system. Here we studied how somatic exocytosis is maintained for such long periods in the absence of electrical stimulation and transmembrane Ca(2+) entry. Somatic exocytosis of serotonin from dense core vesicles could be triggered by a train of 10 action potentials at 20 Hz in Retzius neurons of the leech. However, the same number of action potentials produced at 1 Hz failed to evoke any exocytosis. The 20-Hz train evoked exocytosis through a sequence of intracellular Ca(2+) transients, with each transient having a different origin, timing and intracellular distribution. Upon electrical stimulation, transmembrane Ca(2+) entry through L-type channels activated Ca(2+)-induced Ca(2+) release. A resulting fast Ca(2+) transient evoked an early exocytosis of serotonin from sparse vesicles resting close to the plasma membrane. This Ca(2+) transient also triggered the transport of distant clusters of vesicles toward the plasma membrane. Upon exocytosis, the released serotonin activated autoreceptors coupled to phospholipase C, which in turn produced an intracellular Ca(2+) increase in the submembrane shell. This localized Ca(2+) increase evoked new exocytosis as the vesicles in the clusters arrived gradually at the plasma membrane. In this way, the extracellular serotonin elevated the intracellular Ca(2+) and this Ca(2+) evoked more exocytosis. The resulting positive feedback loop maintained exocytosis for the following hundreds of seconds until the last vesicles in the clusters fused. Since somatic exocytosis displays similar kinetics in neurons releasing different types of transmitters, the data presented here contributes to understand the cellular basis of paracrine neurotransmission.

MICU1 motifs define mitochondrial calcium uniporter binding and activity

Resting mitochondrial matrix Ca(2+) is maintained through a mitochondrial calcium uptake 1 (MICU1)-established threshold inhibition of mitochondrial calcium uniporter (MCU) activity. It is not known how MICU1 interacts with MCU to establish this Ca(2+) threshold for mitochondrial Ca(2+) uptake and MCU activity. Here, we show that MICU1 localizes to the mitochondrial matrix side of the inner mitochondrial membrane and MICU1/MCU binding is determined by a MICU1 N-terminal polybasic domain and two interacting coiled-coil domains of MCU. Further investigation reveals that MICU1 forms homo-oligomers, and this oligomerization is independent of the polybasic region. However, the polybasic region confers MICU1 oligomeric binding to MCU and controls mitochondrial Ca(2+) current (IMCU). Moreover, MICU1 EF hands regulate MCU channel activity, but do not determine MCU binding. Loss of MICU1 promotes MCU activation leading to oxidative burden and a halt to cell migration. These studies establish a molecular mechanism for MICU1 control of MCU-mediated mitochondrial Ca(2+) accumulation, and dysregulation of this mechanism probably enhances vascular dysfunction.

A combined metabonomic and proteomic approach identifies frontal cortex changes in a chronic phencyclidine rat model in relation to human schizophrenia brain pathology

Current schizophrenia (SCZ) treatments fail to treat the broad range of manifestations associated with this devastating disorder. Thus, new translational models that reproduce the core pathological features are urgently needed to facilitate novel drug discovery efforts. Here, we report findings from the first comprehensive label-free liquid-mass spectrometry proteomic- and proton nuclear magnetic resonance-based metabonomic profiling of the rat frontal cortex after chronic phencyclidine (PCP) intervention, which induces SCZ-like symptoms. The findings were compared with results from a proteomic profiling of post-mortem prefrontal cortex from SCZ patients and with relevant findings in the literature. Through this approach, we identified proteomic alterations in glutamate-mediated Ca(2+) signaling (Ca(2+)/calmodulin-dependent protein kinase II, PPP3CA, and VISL1), mitochondrial function (GOT2 and PKLR), and cytoskeletal remodeling (ARP3). Metabonomic profiling revealed changes in the levels of glutamate, glutamine, glycine, pyruvate, and the Ca(2+) regulator taurine. Effects on similar pathways were also identified in the prefrontal cortex tissue from human SCZ subjects. The discovery of similar but not identical proteomic and metabonomic alterations in the chronic PCP rat model and human brain indicates that this model recapitulates only some of the molecular alterations of the disease. This knowledge may be helpful in understanding mechanisms underlying psychosis, which, in turn, can facilitate improved therapy and drug discovery for SCZ and other psychiatric diseases. Most importantly, these molecular findings suggest that the combined use of multiple models may be required for more effective translation to studies of human SCZ.

Targeting microglial K(ATP) channels to treat neurodegenerative diseases: a mitochondrial issue

Neurodegeneration is a complex process involving different cell types and neurotransmitters. A common characteristic of neurodegenerative disorders is the occurrence of a neuroinflammatory reaction in which cellular processes involving glial cells, mainly microglia and astrocytes, are activated in response to neuronal death. Microglia do not constitute a unique cell population but rather present a range of phenotypes closely related to the evolution of neurodegeneration. In a dynamic equilibrium with the lesion microenvironment, microglia phenotypes cover from a proinflammatory activation state to a neurotrophic one directly involved in cell repair and extracellular matrix remodeling. At each moment, the microglial phenotype is likely to depend on the diversity of signals from the environment and of its response capacity. As a consequence, microglia present a high energy demand, for which the mitochondria activity determines the microglia participation in the neurodegenerative process. As such, modulation of microglia activity by controlling microglia mitochondrial activity constitutes an innovative approach to interfere in the neurodegenerative process. In this review, we discuss the mitochondrial K_ATP channel as a new target to control microglia activity, avoid its toxic phenotype, and facilitate a positive disease outcome.