Mitochondrial Ca2+ concentrations in live cells: quantification methods and discrepancies

Bioelectronic tools for understanding the universal language of electrical signaling across species and kingdoms

Modern bioelectronic tools are rapidly advancing to detect electric potentials within networks of electrogenic cells, such as cardiomyocytes, neurons, and pancreatic beta cells. However, it is becoming evident that electrical signaling is not limited to the animal kingdom but may be a universal form of cell-cell communication. In this review, we discuss the existing evidence of, and tools used to collect, subcellular, single-cell and network-level electrical signals across kingdoms, including bacteria, plants, fungi, and even viruses. We discuss how cellular networks employ altered electrical "circuitry" and intercellular mechanisms across kingdoms, and we assess the functionality and scalability of cutting-edge nanobioelectronics to collect electrical signatures regardless of cell size, shape, or function. Researchers today aim to design micro- and nano-topographic structures which harness mechanosensitive membrane and cytoskeletal pathways that enable tight electrical coupling to subcellular compartments within high-throughput recording systems. Finally, we identify gaps in current knowledge of inter-species and inter-kingdom electrical signaling and propose critical milestones needed to create a central theory of electrical signaling across kingdoms. Our discussion demonstrates the need for high resolution, high throughput tools which can probe multiple, diverse cell types at once in their native or experimentally-modeled environments. These advancements will not only reveal the underlying biophysical laws governing the universal language of electrical communication, but can enable bidirectional electrical communication and manipulation of biological systems.

Mitochondrial Calcium Regulation of Cardiac Metabolism in Health and Disease

Oxidative phosphorylation is regulated by mitochondrial calcium (Ca2+) in health and disease. In physiological states, Ca2+ enters via the mitochondrial Ca2+ uniporter and rapidly enhances NADH and ATP production. However, maintaining Ca2+ homeostasis is critical: insufficient Ca2+ impairs stress adaptation, and Ca2+ overload can trigger cell death. In this review, we delve into recent insights further defining the relationship between mitochondrial Ca2+ dynamics and oxidative phosphorylation. Our focus is on how such regulation affects cardiac function in health and disease, including heart failure, ischemia-reperfusion, arrhythmias, catecholaminergic polymorphic ventricular tachycardia, mitochondrial cardiomyopathies, Barth syndrome, and Friedreich's ataxia. Several themes emerge from recent data. First, mitochondrial Ca2+ regulation is critical for fuel substrate selection, metabolite import, and matching of ATP supply to demand. Second, mitochondrial Ca2+ regulates both the production and response to reactive oxygen species (ROS), and the balance between its pro- and antioxidant effects is key to how it contributes to physiological and pathological states. Third, Ca2+ exerts localized effects on the electron transport chain (ETC), not through traditional allosteric mechanisms but rather indirectly. These effects hinge on specific transporters, such as the uniporter or the Na+/Ca2+ exchanger, and may not be noticeable acutely, contributing differently to phenotypes depending on whether Ca2+ transporters are acutely or chronically modified. Perturbations in these novel relationships during disease states may either serve as compensatory mechanisms or exacerbate impairments in oxidative phosphorylation. Consequently, targeting mitochondrial Ca2+ holds promise as a therapeutic strategy for a variety of cardiac diseases characterized by contractile failure or arrhythmias.

Vacancy-Rich Bismuth-Based Nanosheets for Mitochondrial Destruction via CO Poisoning, Ca2+ Dyshomeostasis, and Oxidative Damage

Mitochondria are core regulators of tumor cell homeostasis, and their damage has become an arresting therapeutic modality against cancer. Despite the development of many mitochondrial-targeted pharmaceutical agents, the exploration of more powerful and multifunctional medications is still underway. Herein, oxygen vacancy-rich BiO2-x wrapped with CaCO3 (named BiO2-x@CaCO3/PEG, BCP) is developed for full-fledged attack on mitochondrial function. After endocytosis of BCP by tumor cells, the CaCO3 shell can be decomposed in the acidic lysosomal compartment, leading to immediate Ca2+ release and CO2 production in the cytoplasm. Near-infrared irradiation enhances the adsorption of CO2 onto BiO2-x defects, which enables highly efficient photocatalysis of CO2-to-CO. Meanwhile, such BiO2-x nanosheets possess catalase-, peroxidase- and oxidase-like catalytic activities under acidic pH conditions, allowing hypoxia relief and the accumulation of diverse reactive oxygen species (ROS) in the tumor microenvironment. Ca2+ overload-induced ion dyshomeostasis, CO-mediated respiratory chain poisoning, ROS-triggered oxidative stress aggravation, and cytosolic hyperoxia can cause severe mitochondrial disorders, which further lead to type I cell death in carcinoma. Not only does BCP cause irreversible apoptosis, but immunogenic cell death is simultaneously triggered to activate antitumor immunity for metastasis inhibition. Collectively, this platform promises high benefits in malignant tumor therapy and may expand the medical applications of bismuth-based nanoagents.

Latest assessment methods for mitochondrial homeostasis in cognitive diseases

Mitochondria play an essential role in neural function, such as supporting normal energy metabolism, regulating reactive oxygen species, buffering physiological calcium loads, and maintaining the balance of morphology, subcellular distribution, and overall health through mitochondrial dynamics. Given the recent technological advances in the assessment of mitochondrial structure and functions, mitochondrial dysfunction has been regarded as the early and key pathophysiological mechanism of cognitive disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, mild cognitive impairment, and postoperative cognitive dysfunction. This review will focus on the recent advances in mitochondrial medicine and research methodology in the field of cognitive sciences, from the perspectives of energy metabolism, oxidative stress, calcium homeostasis, and mitochondrial dynamics (including fission-fusion, transport, and mitophagy).

Calcium-based biomaterials: Unveiling features and expanding applications in osteosarcoma treatment

Calcium, an indispensable element in bone tissues, plays a crucial role in various cellular processes involved in cancer progression. Its ubiquitous yet spatially distinct distribution in the body presents an opportunity to target calcium homeostasis as a novel strategies for cancer treatment, with specific advantages in osteosarcoma therapy. In this comprehensive review, we retrospect the calcium biology intersected with cancer progression, highlight the unveiling features of calcium-based biomaterials in regulating both bone homeostasis and cancer development. We also provide an overview of recent breakthroughs in cancer therapy that leverage calcium biomaterials, showcasing their potential to serve as versatile, customizable platforms for osteosarcoma treatment and as reservoirs for supporting bone reconstruction.

Beyond the TCA cycle: new insights into mitochondrial calcium regulation of oxidative phosphorylation

While mitochondria oxidative phosphorylation is broadly regulated, the impact of mitochondrial Ca2+ on substrate flux under both physiological and pathological conditions is increasingly being recognized. Under physiologic conditions, mitochondrial Ca2+ enters through the mitochondrial Ca2+ uniporter and boosts ATP production. However, maintaining Ca2+ homeostasis is crucial as too little Ca2+ inhibits adaptation to stress and Ca2+ overload can trigger cell death. In this review, we discuss new insights obtained over the past several years expanding the relationship between mitochondrial Ca2+ and oxidative phosphorylation, with most data obtained from heart, liver, or skeletal muscle. Two new themes are emerging. First, beyond boosting ATP synthesis, Ca2+ appears to be a critical determinant of fuel substrate choice between glucose and fatty acids. Second, Ca2+ exerts local effects on the electron transport chain indirectly, not via traditional allosteric mechanisms. These depend critically on the transporters involved, such as the uniporter or the Na+-Ca2+ exchanger. Alteration of these new relationships during disease can be either compensatory or harmful and suggest that targeting mitochondrial Ca2+ may be of therapeutic benefit during diseases featuring impairments in oxidative phosphorylation.

Mitochondrial calcium and reactive oxygen species in cardiovascular disease

Cardiomyocytes are one of the most mitochondria-rich cell types in the body, with ∼30-40% of the cell volume being composed of mitochondria. Mitochondria are well established as the primary site of adenosine triphosphate (ATP) generation in a beating cardiomyocyte, generating up to 90% of its ATP. Mitochondria have many functions in the cell, which could contribute to susceptibility to and development of cardiovascular disease (CVD). Mitochondria are key players in cell metabolism, ATP production, reactive oxygen species (ROS) production, and cell death. Mitochondrial calcium (Ca2+) plays a critical role in many of these pathways, and thus the dynamics of mitochondrial Ca2+ are important in regulating mitochondrial processes. Alterations in these varied and in many cases interrelated functions play an important role in CVD. This review will focus on the interrelationship of mitochondrial energetics, Ca2+, and ROS and their roles in CVD. Recent insights into the regulation and dysregulation of these pathways have led to some novel therapeutic approaches.

The human MRS2 magnesium-binding domain is a regulatory feedback switch for channel activity

Mitochondrial RNA splicing 2 (MRS2) forms a magnesium (Mg2+) entry protein channel in mitochondria. Whereas MRS2 contains two transmembrane domains constituting a pore on the inner mitochondrial membrane, most of the protein resides within the matrix. Yet, the precise structural and functional role of this obtrusive amino terminal domain (NTD) in human MRS2 is unknown. Here, we show that the MRS2 NTD self-associates into a homodimer, contrasting the pentameric assembly of CorA, an orthologous bacterial channel. Mg2+ and calcium suppress lower and higher order oligomerization of MRS2 NTD, whereas cobalt has no effect on the NTD but disassembles full-length MRS2. Mutating-pinpointed residues-mediating Mg2+ binding to the NTD not only selectively decreases Mg2+-binding affinity ∼sevenfold but also abrogates Mg2+ binding-induced secondary, tertiary, and quaternary structure changes. Disruption of NTD Mg2+ binding strikingly potentiates mitochondrial Mg2+ uptake in WT and Mrs2 knockout cells. Our work exposes a mechanism for human MRS2 autoregulation by negative feedback from the NTD and identifies a novel gain of function mutant with broad applicability to future Mg2+ signaling research.

Mitochondrial responses to intracellular Ca2+ release following infrared stimulation

Many studies of Ca2+ effects on mitochondrial respiration in intact cells have used electrical and/or chemical stimulation to elevate intracellular [Ca2+], and have reported increases in [NADH] and increased ADP/ATP ratios as dominant controllers of respiration. This study tested a different form of stimulation: brief temperature increases produced by pulses of infrared light (IR, 1,863 nm, 8-10°C for ∼5 s). Fluorescence imaging techniques applied to single PC-12 cells in low µM extracellular [Ca2+] revealed IR stimulation-induced increases in both cytosolic (fluo5F) and mitochondrial (rhod2) [Ca2+]. IR stimulation increased O2 consumption (porphyrin fluorescence), and produced an alkaline shift in mitochondrial matrix pH (Snarf1), indicating activation of the electron transport chain (ETC). The increase in O2 consumption persisted in oligomycin, and began during a decrease in NADH, suggesting that the initial increase in ETC activity was not driven by increased ATP synthase activity or an increased fuel supply to ETC complex I. Imaging with two potentiometric dyes [tetramethyl rhodamine methyl ester (TMRM) and R123] indicated a depolarizing shift in ΔΨm that persisted in high [K+] medium. High-resolution fluorescence imaging disclosed large, reversible mitochondrial depolarizations that were inhibited by cyclosporin A (CSA), consistent with the opening of transient mitochondrial permeability transition pores. IR stimulation also produced a Ca2+-dependent increase in superoxide production (MitoSox) that was not inhibited by CSA, indicating that the increase in superoxide did not require transition pore opening. Thus, the intracellular Ca2+ release that follows pulses of infrared light offers new insights into Ca2+-dependent processes controlling respiration and reactive oxygen species in intact cells.NEW & NOTEWORTHY Pulses of infrared light (IR) provide a novel method for rapidly transferring Ca2+ from the endoplasmic reticulum to mitochondria in intact cells. In PC12 cells the resulting ETC activation was not driven by increased ATP synthase activity or NADH. IR stimulation produced a Ca2+-dependent, reversible depolarization of ΔΨm that was partially blocked by cyclosporin A, and a Ca2+-dependent increase in superoxide that did not require transition pore opening.

NOX2 and NOX4 control mitochondrial function in chronic myeloid leukaemia

Cancer cells are characterised by an elevated metabolic plasticity and enhanced production of reactive oxygen species (ROS), two features acknowledged as hallmarks in cancer, with a high translational potential to the therapeutic setting. These aspects, that have been traditionally studied separately, are in fact intimately intermingled. As part of their transforming activity, some oncogenes stimulate rewiring of metabolic processes, whilst simultaneously promoting increased production of intracellular ROS. In this scenario the latest discoveries suggest the relevance of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) to connect ROS production and metabolic control. Here we have analysed the relevance of NOX2 and NOX4 in the regulation of metabolism in chronic myeloid leukaemia (CML), a neoplasia driven by the expression of the breakpoint cluster region-Abelson fusion oncogene (BCR-ABL). Silencing of NOX2 enhances glycolysis and oxidative phosphorylation rates, together with an enhanced production of mitochondrial ROS and a decrease in mitochondrial DNA copy number, which reflects mitochondrial dysfunction. NOX4 expression was upregulated upon NOX2 silencing, and this was required to alter mitochondrial function. Our results support the relevance of NOX2 to regulate metabolism-related signalling pathways downstream of BCR-ABL. Overall we show that NOX2, through the regulation of NOX4 expression, controls metabolism and mitochondrial function in CML cells. This notion was confirmed by transcriptomic analyses, that strongly relate both NOX isoforms with metabolism regulation in CML.

Environmental Chemical Exposures and Mitochondrial Dysfunction: a Review of Recent Literature

PURPOSE OF REVIEW

Mitochondria play various roles that are important for cell function and survival; therefore, significant mitochondrial dysfunction may have chronic consequences that extend beyond the cell. Mitochondria are already susceptible to damage, which may be exacerbated by environmental exposures. Therefore, the aim of this review is to summarize the recent literature (2012-2022) looking at the effects of six ubiquitous classes of compounds on mitochondrial dysfunction in human populations.

RECENT FINDINGS

The literature suggests that there are a number of biomarkers that are commonly used to identify mitochondrial dysfunction, each with certain advantages and limitations. Classes of environmental toxicants such as polycyclic aromatic hydrocarbons, air pollutants, heavy metals, endocrine-disrupting compounds, pesticides, and nanomaterials can damage the mitochondria in varied ways, with changes in mtDNA copy number and measures of oxidative damage the most commonly measured in human populations. Other significant biomarkers include changes in mitochondrial membrane potential, calcium levels, and ATP levels. This review identifies the biomarkers that are commonly used to characterize mitochondrial dysfunction but suggests that emerging mitochondrial biomarkers, such as cell-free mitochondria and blood cardiolipin levels, may provide greater insight into the impacts of exposures on mitochondrial function. This review identifies that the mtDNA copy number and measures of oxidative damage are commonly used to characterize mitochondrial dysfunction, but suggests using novel approaches in addition to well-characterized ones to create standardized protocols. We identified a dearth of studies on mitochondrial dysfunction in human populations exposed to metals, endocrine-disrupting chemicals, pesticides, and nanoparticles as a gap in knowledge that needs attention.

Single-cell RNA sequencing reveals the role of immune-related autophagy in spinal cord injury in rats

Spinal cord injury refers to damage to the spinal cord due to trauma, disease, or degeneration; and the number of new cases is increasing yearly. Significant cellular changes are known to occur in the area of spinal cord injury. However, changes in cellular composition, trajectory of cell development, and intercellular communication in the injured area remain unclear. Here, we used single-cell RNA sequencing to evaluate almost all the cell types that constitute the site of spinal cord injury in rats. In addition to mapping the cells of the injured area, we screened the expression of immune autophagy-related factors in cells and identified signaling pathways by the measuring the expression of the receptor−ligand pairs to regulate specific cell interactions during autophagy after spinal cord injury. Our data set is a valuable resource that provides new insights into the pathobiology of spinal cord injury and other traumatic diseases of the central nervous system.

A controversial issue: Can mitochondria modulate cytosolic calcium and contraction of skeletal muscle fibers?

Mitochondria are characterized by a high capacity to accumulate calcium thanks to the electrochemical gradient created by the extrusion of protons in the respiratory chain. Thereby calcium can enter crossing the inner mitochondrial membrane via MCU complex, a high-capacity, low-affinity transport mechanism. Calcium uptake serves numerous purposes, among them the regulation of three dehydrogenases of the citric cycle, apoptosis via permeability transition, and, in some cell types, modulation of cytosolic calcium transients. This Review is focused on mitochondrial calcium uptake in skeletal muscle fibers and aims to reanalyze its functional impact. In particular, we ask whether mitochondrial calcium uptake is relevant for the control of cytosolic calcium transients and therefore of contractile performance. Recent data suggest that this may be the case, at least in particular conditions, as modified expression of MCU complex subunits or of proteins involved in mitochondrial dynamics and ablation of the main cytosolic calcium buffer, parvalbumin.

Assessment of mitochondrial dysfunction and implications in cardiovascular disorders

Mitochondria play a pivotal role in cellular function, not only acting as the powerhouse of the cell, but also regulating ATP synthesis, reactive oxygen species (ROS) production, intracellular Ca²⁺ cycling, and apoptosis. During the past decade, extensive progress has been made in the technology to assess mitochondrial functions and accumulating evidences have shown that mitochondrial dysfunction is a key pathophysiological mechanism for many diseases including cardiovascular disorders, such as ischemic heart disease, cardiomyopathy, hypertension, atherosclerosis, and hemorrhagic shock. The advances in methodology have been accelerating our understanding of mitochondrial molecular structure and function, biogenesis and ROS and energy production, which facilitates new drug target identification and therapeutic strategy development for mitochondrial dysfunction-related disorders. This review will focus on the assessment of methodologies currently used for mitochondrial research and discuss their advantages, limitations and the implications of mitochondrial dysfunction in cardiovascular disorders.

Structural basis for the calmodulin-mediated activation of eukaryotic elongation factor 2 kinase

Translation is a tightly regulated process that ensures optimal protein quality and enables adaptation to energy/nutrient availability. The α-kinase eukaryotic elongation factor 2 kinase (eEF-2K), a key regulator of translation, specifically phosphorylates the guanosine triphosphatase eEF-2, thereby reducing its affinity for the ribosome and suppressing the elongation phase of protein synthesis. eEF-2K activation requires calmodulin binding and autophosphorylation at the primary stimulatory site, T348. Biochemical studies predict a calmodulin-mediated activation mechanism for eEF-2K distinct from other calmodulin-dependent kinases. Here, we resolve the atomic details of this mechanism through a 2.3-Å crystal structure of the heterodimeric complex of calmodulin and the functional core of eEF-2K (eEF-2KTR). This structure, which represents the activated T348-phosphorylated state of eEF-2KTR, highlights an intimate association of the kinase with the calmodulin C-lobe, creating an "activation spine" that connects its amino-terminal calmodulin-targeting motif to its active site through a conserved regulatory element.

The Functional Characterization of GCaMP3.0 Variants Specifically Targeted to Subcellular Domains

Calcium (Ca²⁺) ions play a pivotal role in physiology and cellular signaling. The intracellular Ca²⁺ concentration ([Ca²⁺]_i) is about three orders of magnitude lower than the extracellular concentration, resulting in a steep transmembrane concentration gradient. Thus, the spatial and the temporal dynamics of [Ca²⁺]_i are ideally suited to modulate Ca²⁺-mediated cellular responses to external signals. A variety of highly sophisticated methods have been developed to gain insight into cellular Ca²⁺ dynamics. In addition to electrophysiological measurements and the application of synthetic dyes that change their fluorescent properties upon interaction with Ca²⁺, the introduction and the ongoing development of genetically encoded Ca²⁺ indicators (GECI) opened a new era to study Ca²⁺-driven processes in living cells and organisms. Here, we have focused on one well-established GECI, i.e., GCaMP3.0. We have systematically modified the protein with sequence motifs, allowing localization of the sensor in the nucleus, in the mitochondrial matrix, at the mitochondrial outer membrane, and at the plasma membrane. The individual variants and a cytosolic version of GCaMP3.0 were overexpressed and purified from E. coli cells to study their biophysical properties in solution. All versions were examined to monitor Ca²⁺ signaling in stably transfected cell lines and in primary cortical neurons transduced with recombinant Adeno-associated viruses (rAAV). In this comparative study, we provide evidence for a robust approach to reliably trace Ca²⁺ signals at the (sub)-cellular level with pronounced temporal resolution.

Mitochondrial calcium exchange in physiology and disease

The uptake of calcium into and extrusion of calcium from the mitochondrial matrix is a fundamental biological process that has critical effects on cellular metabolism, signaling, and survival. Disruption of mitochondrial calcium (mCa2+) cycling is implicated in numerous acquired diseases such as heart failure, stroke, neurodegeneration, diabetes, and cancer and is genetically linked to several inherited neuromuscular disorders. Understanding the mechanisms responsible for mCa2+ exchange therefore holds great promise for the treatment of these diseases. The past decade has seen the genetic identification of many of the key proteins that mediate mitochondrial calcium uptake and efflux. Here, we present an overview of the phenomenon of mCa2+ transport and a comprehensive examination of the molecular machinery that mediates calcium flux across the inner mitochondrial membrane: the mitochondrial uniporter complex (consisting of MCU, EMRE, MICU1, MICU2, MICU3, MCUB, and MCUR1), NCLX, LETM1, the mitochondrial ryanodine receptor, and the mitochondrial permeability transition pore. We then consider the physiological implications of mCa2+ flux and evaluate how alterations in mCa2+ homeostasis contribute to human disease. This review concludes by highlighting opportunities and challenges for therapeutic intervention in pathologies characterized by aberrant mCa2+ handling and by summarizing critical unanswered questions regarding the biology of mCa2+ flux.

Imaging mitochondrial calcium dynamics in the central nervous system

Mitochondrial calcium handling is a particularly active research area in the neuroscience field, as it plays key roles in the regulation of several functions of the central nervous system, such as synaptic transmission and plasticity, astrocyte calcium signaling, neuronal activity… In the last few decades, a panel of techniques have been developed to measure mitochondrial calcium dynamics, relying mostly on photonic microscopy, and including synthetic sensors, hybrid sensors and genetically encoded calcium sensors. The goal of this review is to endow the reader with a deep knowledge of the historical and latest tools to monitor mitochondrial calcium events in the brain, as well as a comprehensive overview of the current state of the art in brain mitochondrial calcium signaling. We will discuss the main calcium probes used in the field, their mitochondrial targeting strategies, their key properties and major drawbacks. In addition, we will detail the main roles of mitochondrial calcium handling in neuronal tissues through an extended report of the recent studies using mitochondrial targeted calcium sensors in neuronal and astroglial cells, in vitro and in vivo.

Lipids modulate the BH3-independent membrane targeting and activation of BAX and Bcl-xL

Regulation of apoptosis is tightly linked with the targeting of numerous Bcl-2 proteins to the mitochondrial outer membrane (MOM), where their activation or inhibition dictates cell death or survival. According to the traditional view of apoptotic regulation, BH3-effector proteins are indispensable for the cytosol-to-MOM targeting and activation of proapoptotic and antiapoptotic members of the Bcl-2 protein family. This view is challenged by recent studies showing that these processes can occur in cells lacking BH3 effectors by as yet to be determined mechanism(s). Here, we exploit a model membrane system that recapitulates key features of MOM to demonstrate that the proapoptotic Bcl-2 protein BAX and antiapoptotic Bcl-xL have an inherent ability to interact with membranes in the absence of BH3 effectors, but only in the presence of cellular concentrations of Mg²⁺/Ca²⁺ Under these conditions, BAX and Bcl-xL are selectively targeted to membranes, refolded, and activated in the presence of anionic lipids especially the mitochondrial-specific lipid cardiolipin. These results provide a mechanistic explanation for the mitochondrial targeting and activation of Bcl-2 proteins in cells lacking BH3 effectors. At cytosolic Mg²⁺ levels, the BH3-independent activation of BAX could provide localized amplification of apoptotic signaling at regions enriched in cardiolipin (e.g., contact sites between MOM and mitochondrial inner membrane). Increases in MOM cardiolipin, as well as cytosolic [Ca²⁺] during apoptosis could further contribute to its MOM targeting and activity. Meanwhile, the BH3-independent targeting and activation of Bcl-xL to the MOM is expected to counter the action of proapoptotic BAX, thereby preventing premature commitment to apoptosis.

VDACs: An Outlook on Biochemical Regulation and Function in Animal and Plant Systems

The voltage-dependent anion channels (VDACs) are the most abundant proteins present on the outer mitochondrial membrane. They serve a myriad of functions ranging from energy and metabolite exchange to highly debatable roles in apoptosis. Their role in molecular transport puts them on the center stage as communicators between cytoplasmic and mitochondrial signaling events. Beyond their general role as interchangeable pores, members of this family may exhibit specific functions. Even after nearly five decades of their discovery, their role in plant systems is still a new and rapidly emerging field. The information on biochemical regulation of VDACs is limited. Various interacting proteins and post-translational modifications (PTMs) modulate VDAC functions, amongst these, phosphorylation is quite noticeable. In this review, we have tried to give a glimpse of the recent advancements in the biochemical/interactional regulation of plant VDACs. We also cover a critical analysis on the importance of PTMs in the functional regulation of VDACs. Besides, the review also encompasses numerous studies which can identify VDACs as a connecting link between Ca2+ and reactive oxygen species signaling in special reference to the plant systems.

Post-Translational Modification of Cysteines: A Key Determinant of Endoplasmic Reticulum-Mitochondria Contacts (MERCs)

Cells must adjust their redox state to an ever-changing environment that could otherwise result in compromised homeostasis. An obvious way to adapt to changing redox conditions depends on cysteine post-translational modifications (PTMs) to adapt conformation, localization, interactions and catalytic activation of proteins. Such PTMs should occur preferentially in the proximity of oxidative stress sources. A particular concentration of these sources is found near membranes where the endoplasmic reticulum (ER) and the mitochondria interact on domains called MERCs (Mitochondria-Endoplasmic Reticulum Contacts). Here, fine inter-organelle communication controls metabolic homeostasis. MERCs achieve this goal through fluxes of Ca²⁺ ions and inter-organellar lipid exchange. Reactive oxygen species (ROS) that cause PTMs of mitochondria-associated membrane (MAM) proteins determine these intertwined MERC functions. Chronic changes of the pattern of these PTMs not only control physiological processes such as the circadian clock but could also lead to or worsen many human disorders such as cancer and neurodegenerative diseases.

Decreased Mitochondrial Function, Biogenesis, and Degradation in Peripheral Blood Mononuclear Cells from Amyotrophic Lateral Sclerosis Patients as a Potential Tool for Biomarker Research

Amyotrophic lateral sclerosis (ALS) is a multifactorial and progressive neurodegenerative disease of unknown etiology. Due to ALS’s unpredictable onset and progression rate, the search for biomarkers that allow the detection and tracking of its development and therapeutic efficacy would be of significant medical value. Considering that alterations of energy supply are one of ALS’s main hallmarks and that a correlation has been established between gene expression in human brain tissue and peripheral blood mononuclear cells (PBMCs), the present work investigates whether changes in mitochondrial function could be used to monitor ALS. To achieve this goal, PBMCs from ALS patients and control subjects were used; blood sampling is a quite non-invasive method and is cost-effective. Different parameters were evaluated, namely cytosolic calcium levels, mitochondrial membrane potential, oxidative stress, and metabolic compounds levels, as well as mitochondrial dynamics and degradation. Altogether, we observed lower mitochondrial calcium uptake/retention, mitochondria depolarization, and redox homeostasis deregulation, in addition to a decrease in critical metabolic genes, a diminishment in mitochondrial biogenesis, and an augmentation in mitochondrial fission and autophagy-related gene expression. All of these changes can contribute to the decreased ATP and pyruvate levels observed in ALS PBMCs. Our data indicate that PBMCs from ALS patients show a significant mitochondrial dysfunction, resembling several findings from ALS’ neural cells/models, which could be exploited as a powerful tool in ALS research. Our findings can also guide future studies on new pharmacological interventions for ALS since assessments of brain samples are challenging and represent a relevant limited strategy.