Complex I and II are required for normal mitochondrial Ca2+ homeostasis

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.

Mitochondrial division inhibitor (mdivi-1) induces extracellular matrix (ECM)-detachment of viable breast cancer cells by a DRP1-independent mechanism

Increasing evidence supports the hypothesis that cancer progression is under mitochondrial control. Mitochondrial fission plays a pivotal role in the maintenance of cancer cell homeostasis. The inhibition of DRP1, the main regulator of mitochondrial fission, with the mitochondrial division inhibitor (mdivi-1) had been associated with cancer cell sensitivity to chemotherapeutics and decrease proliferation. Here, using breast cancer cells we find that mdivi-1 induces the detachment of the cells, leading to a bulk of floating cells that conserved their viability. Despite a decrease in their proliferative and clonogenic capabilities, these floating cells maintain the capacity to re-adhere upon re-seeding and retain their migratory and invasive potential. Interestingly, the cell detachment induced by mdivi-1 is independent of DRP1 but relies on inhibition of mitochondrial complex I. Furthermore, mdivi-1 induces cell detachment rely on glucose and the pentose phosphate pathway. Our data evidence a novel DRP1-independent effect of mdivi-1 in the attachment of cancer cells. The generation of floating viable cells restricts the use of mdivi-1 as a therapeutic agent and demonstrates that mdivi-1 effect on cancer cells are more complex than anticipated.

Transcriptome analysis of porcine oocytes during postovulatory aging

Decreased oocyte quality is a significant contributor to the decline in female fertility that accompanies aging in mammals. Oocytes rely on mRNA stores to support their survival and integrity during the protracted period of transcriptional dormancy as they await ovulation. However, the changes in mRNA levels and interactions that occur during porcine oocyte maturation and aging remain unclear. In this study, the mRNA expression profiles of porcine oocytes during the GV, MII, and aging (24 h after the MII stage) stages were explored by transcriptome sequencing to identify the key genes and pathways that affect oocyte maturation and postovulatory aging. The results showed that 10,929 genes were coexpressed in porcine oocytes during the GV stage, MII stage, and aging stage. In addition, 3037 genes were expressed only in the GV stage, 535 genes were expressed only in the MII stage, and 120 genes were expressed only in the aging stage. The correlation index between the GV and MII stages (0.535) was markedly lower than that between the MII and aging stages (0.942). A total of 3237 genes, which included 1408 upregulated and 1829 downregulated genes, were differentially expressed during porcine oocyte postovulatory aging (aging stage vs. MII stage). Key functional genes, including ATP2A1, ATP2A3, ATP2B2, NDUFS1, NDUFA2, NDUFAF3, SREBF1, CYP11A1, CYP3A29, GPx4, CCP110, STMN1, SPC25, Sirt2, SYCP3, Fascin1/2, PFN1, Cofilin, Tmod3, FLNA, LRKK2, CHEK1/2, DDB1/2, DDIT4L, and TONSL, and key molecular pathways, such as the calcium signaling pathway, MAPK signaling pathway, TGF-β signaling pathway, PI3K/Akt signaling pathway, FoxO signaling pathway, gap junctions, and thermogenesis, were found in abundance during porcine postovulatory aging. These genes are mainly involved in the regulation of many biological processes, such as oxidative stress, calcium homeostasis, mitochondrial function, and lipid peroxidation, during porcine oocyte postovulatory aging. These results contribute to a more in-depth understanding of the biological changes, key regulatory genes and related biological pathways that are involved in oocyte aging and provide a theoretical basis for improving the efficiency of porcine embryo production in vitro and in vivo.

Revitalizing Ancient Mitochondria with Nano-Strategies: Mitochondria-Remedying Nanodrugs Concentrate on Disease Control

Mitochondria, widely known as the energy factories of eukaryotic cells, have a myriad of vital functions across diverse cellular processes. Dysfunctions within mitochondria serve as catalysts for various diseases, prompting widespread cellular demise. Mounting research on remedying damaged mitochondria indicates that mitochondria constitute a valuable target for therapeutic intervention against diseases. But the less clinical practice and lower recovery rate imply the limitation of traditional drugs, which need a further breakthrough. Nanotechnology has approached favorable regiospecific biodistribution and high efficacy by capitalizing on excellent nanomaterials and targeting drug delivery. Mitochondria-remedying nanodrugs have achieved ideal therapeutic effects. This review elucidates the significance of mitochondria in various cells and organs, while also compiling mortality data for related diseases. Correspondingly, nanodrug-mediate therapeutic strategies and applicable mitochondria-remedying nanodrugs in disease are detailed, with a full understanding of the roles of mitochondria dysfunction and the advantages of nanodrugs. In addition, the future challenges and directions are widely discussed. In conclusion, this review provides comprehensive insights into the design and development of mitochondria-remedying nanodrugs, aiming to help scientists who desire to extend their research fields and engage in this interdisciplinary subject.

Respiratory Complex I dysfunction in cancer: from a maze of cellular adaptive responses to potential therapeutic strategies

Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cell survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a protumorigenic hit, genetic ablation or pharmacological inhibition of respiratory complex I causing a severe impairment is associated with a low-proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here, we highlight the current knowledge on molecular responses activated by complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with complex I impairment, thus providing new synergistic strategies for mitochondrial-based anticancer therapy.

Genetic impairment of succinate metabolism disrupts bioenergetic sensing in adrenal neuroendocrine cancer

Metabolic dysfunction mutations can impair energy sensing and cause cancer. Loss of function of the mitochondrial tricarboxylic acid (TCA) cycle enzyme subunit succinate dehydrogenase B (SDHB) results in various forms of cancer typified by pheochromocytoma (PC). Here we delineate a signaling cascade where the loss of SDHB induces the Warburg effect, triggers dysregulation of [Ca²⁺]_i, and aberrantly activates calpain and protein kinase Cdk5, through conversion of its cofactor from p35 to p25. Consequently, aberrant Cdk5 initiates a phospho-signaling cascade where GSK3 inhibition inactivates energy sensing by AMP kinase through dephosphorylation of the AMP kinase γ subunit, PRKAG2. Overexpression of p25-GFP in mouse adrenal chromaffin cells also elicits this phosphorylation signaling and causes PC. A potent Cdk5 inhibitor, MRT3-007, reverses this phospho-cascade, invoking a senescence-like phenotype. This therapeutic approach halted tumor progression in vivo. Thus, we reveal an important mechanistic feature of metabolic sensing and demonstrate that its dysregulation underlies tumor progression in PC and likely other cancers.

Chronic di(2-ethylhexyl) phthalate exposure leads to dopaminergic neuron degeneration through mitochondrial dysfunction in C. elegans

The plasticizer di(2-ethylhexyl) phthalate (DEHP) is frequently detected in the environment due to the abundance of its use. These levels might be hazardous to human health and ecosystems. Phthalates have been associated with neurological disorders, yet whether chronic DEHP exposure plays a role in Parkinson's disease (PD) or its underlying mechanisms is unknown. We investigated the effects of chronic DEHP exposure less than an environmentally-relevant dose on PD hallmarks, using Caenorhabditis elegans as a model. We show that developmental stage and exposure timing influence DEHP-induced dopaminergic neuron degeneration. In addition, in response to chronic DEHP exposure at 5 mg/L, mitochondrial fragmentation became significantly elevated, reactive oxygen species (ROS) levels increased, and ATP levels decreased, suggesting that mitochondrial dysfunction occurs. Furthermore, the data show that mitochondrial complex I (nuo-1 and gas-1) and complex II (mev-1) are involved in DEHP-induced dopaminergic neuron toxicity. These results suggest that chronic exposure to DEHP at levels less than an environmentally-relevant dose causes dopaminergic neuron degeneration through mitochondrial dysfunction involving mitochondrial complex I and II. Considering the high level of genetic conservation between C. elegans and mammals, chronic DEHP exposure might elevate the risk of developing PD in humans.

Mitochondrial calcium uniporter stabilization preserves energetic homeostasis during Complex I impairment

Calcium entering mitochondria potently stimulates ATP synthesis. Increases in calcium preserve energy synthesis in cardiomyopathies caused by mitochondrial dysfunction, and occur due to enhanced activity of the mitochondrial calcium uniporter channel. The signaling mechanism that mediates this compensatory increase remains unknown. Here, we find that increases in the uniporter are due to impairment in Complex I of the electron transport chain. In normal physiology, Complex I promotes uniporter degradation via an interaction with the uniporter pore-forming subunit, a process we term Complex I-induced protein turnover. When Complex I dysfunction ensues, contact with the uniporter is inhibited, preventing degradation, and leading to a build-up in functional channels. Preventing uniporter activity leads to early demise in Complex I-deficient animals. Conversely, enhancing uniporter stability rescues survival and function in Complex I deficiency. Taken together, our data identify a fundamental pathway producing compensatory increases in calcium influx during Complex I impairment.

Mitochondrial dysfunction induces radioresistance in colorectal cancer by activating [Ca2+]m-PDP1-PDH-histone acetylation retrograde signaling

Mitochondrial retrograde signaling (mito-RTG) triggered by mitochondrial dysfunction plays a potential role in regulating tumor metabolic reprogramming and cellular sensitivity to radiation. Our previous studies showed phos-pyruvate dehydrogenase (p-PDH) and PDK1, which involved in aerobic glycolysis, were positively correlated with radioresistance, but how they initiate and work in the mito-RTG pathway is still unknown. Our further genomics analysis revealed that complex I components were widely downregulated in mitochondrial dysfunction model. In the present study, high expression of p-PDH was found in the complex I deficient cells and induced radioresistance. Mechanistically, complex I defects led to a decreased PDH both in cytoplasm and nucleus through [Ca2+]m-PDP1-PDH axis, and decreased PDH in nucleus promote DNA damage repair (DDR) response via reducing histone acetylation. Meanwhile, NDUFS1 (an important component of the complex I) overexpression could enhance the complex I activity, reverse glycolysis and resensitize cancer cells to radiation in vivo and in vitro. Furthermore, low NDUFS1 and PDH expression were validated to be correlated with poor tumor regression grading (TRG) in local advanced colorectal cancer (CRC) patients underwent neoadjuvant radiotherapy. Here, we propose that the [Ca2+]m-PDP1-PDH-histone acetylation retrograde signaling activated by mitochondrial complex I defects contribute to cancer cell radioresistance, which provides new insight in the understanding of the mito-RTG. For the first time, we reveal that NDUFS1 could be served as a promising predictor of radiosensitivity and modification of complex I function may improve clinical benefits of radiotherapy in CRC.

The ER-mitochondria Ca2+ signaling in cancer progression: Fueling the monster

Cancer is a leading cause of death worldwide. All major tumor suppressors and oncogenes are now recognized to have fundamental connections with metabolic pathways. A hallmark feature of cancer cells is a reprogramming of their metabolism even when nutrients are available. Increasing evidence indicates that most cancer cells rely on mitochondrial metabolism to sustain their energetic and biosynthetic demands. Mitochondria are functionally and physically coupled to the endoplasmic reticulum (ER), the major calcium (Ca²⁺) storage organelle in mammalian cells, through special domains known as mitochondria-ER contact sites (MERCS). In this domain, the release of Ca²⁺ from the ER is mainly regulated by inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs), a family of Ca²⁺ release channels activated by the ligand IP3. IP3R mediated Ca²⁺ release is transferred to mitochondria through the mitochondrial Ca²⁺ uniporter (MCU). Once in the mitochondrial matrix, Ca²⁺ activates several proteins that stimulate mitochondrial performance. The role of IP3R and MCU in cancer, as well as the other proteins that enable the Ca²⁺ communication between these two organelles is just beginning to be understood. Here, we describe the function of the main players of the ER mitochondrial Ca²⁺ communication and discuss how this particular signal may contribute to the rise and development of cancer traits.

Heterokaryotic state of a point mutation (H249Y) in SDHB protein drives the evolution of thifluzamide resistance in Rhizoctonia solani

BACKGROUND

Sheath blight, caused by Rhizoctonia solani, can be effectively controlled by application of the succinate dehydrogenase inhibitor thifluzamide. Although the risk of resistance to thifluzamide in R. solani had been reported, the thifluzamide-resistance mechanism and the evolution of thifluzamide-resistance in R. solani have not been investigated in detail.

RESULTS

No differences were found between the sequences of proteins SDHA, SDHC, and SDHD in thifluzamide-sensitive isolates and thifluzamide-resistant mutants, but a single point mutation H249Y was found in SDHB. Two different types of thifluzamide-resistant R. solani mutants were characterized: homokaryotic, carrying only the resistance allele; and heterokaryotic, retaining the wild-type allele in addition to the resistance allele. The resistance level differed according to the nuclear composition at codon 249 in the sdhB gene. Molecular docking results suggested that the point mutation (H249Y) might significantly alter the affinity of thifluzamide and SDHB protein. Heterokaryotic mutants were able to evolve into a homokaryon when repeatedly cultured on agar media or rice plants in the presence of thifluzamide, but thifluzamide treatment had no effect on the genotypes of homokaryotic mutants or sensitive isolates.

CONCLUSION

This study showed that H249Y in SDHB protein could cause thifluzamide resistance in R. solani. Fungicide application could promote heterokaryotic mutants to evolve into a homokaryon. © 2020 Society of Chemical Industry.

Inhibition of InsP3R with Xestospongin B Reduces Mitochondrial Respiration and Induces Selective Cell Death in T Cell Acute Lymphoblastic Leukemia Cells

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy whose chemoresistance and relapse persist as a problem despite significant advances in its chemotherapeutic treatments. Mitochondrial metabolism has emerged as an interesting therapeutic target given its essential role in maintaining bioenergetic and metabolic homeostasis. T-ALL cells are characterized by high levels of mitochondrial respiration, making them suitable for this type of intervention. Mitochondrial function is sustained by a constitutive transfer of calcium from the endoplasmic reticulum to mitochondria through the inositol 1,4,5-trisphosphate receptor (InsP3R), making T-ALL cells vulnerable to its inhibition. Here, we determine the bioenergetic profile of the T-ALL cell lines CCRF-CEM and Jurkat and evaluate their sensitivity to InsP3R inhibition with the specific inhibitor, Xestospongin B (XeB). Our results show that T-ALL cell lines exhibit higher mitochondrial respiration than non-malignant cells, which is blunted by the inhibition of the InsP3R. Prolonged treatment with XeB causes T-ALL cell death without affecting the normal counterpart. Moreover, the combination of XeB and glucocorticoids significantly enhanced cell death in the CCRF-CEM cells. The inhibition of InsP3R with XeB rises as a potential therapeutic alternative for the treatment of T-ALL.

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.

Mitochondrial functional and structural impairment is involved in the antitumor activity of δ-tocotrienol in prostate cancer cells

The therapeutic options for castration-resistant prostate cancer (CRPC) are still limited. Natural bioactive compounds were shown to possess pro-death properties in different tumors. We previously reported that δ-tocotrienol (δ-TT) induces apoptosis, paraptosis and autophagy in CRPC cells. Here, we investigated whether δ-TT might exert its activity by impairing mitochondrial functions. We demonstrated that, in PC3 and DU145 cells, δ-TT impairs mitochondrial respiration and structural dynamics. In both cell lines, δ-TT triggers mitochondrial Ca²⁺ and ROS overload. In PC3 cells, both Ca²⁺ and ROS mediate the δ-TT-related anticancer activities (decrease of cell viability, apoptosis, paraptosis, autophagy and mitophagy). As expected, in autophagy-defective DU145 cells, Ca²⁺ overload was involved in δ-TT-induced pro-death effects but not in autophagy and mitophagy. In this cell line, we also demonstrated that ROS overload is not involved in the anticancer activities of δ-TT, supporting a low susceptibility of these cells to ROS-related oxidative stress. Taken together, these data demonstrate that, in CRPC cells, δ-TT triggers cell death by inducing mitochondrial functional and structural impairments, providing novel mechanistic insights in its antitumor activity.

The Two-Way Relationship Between Calcium and Metabolism in Cancer

Calcium ion (Ca²⁺) signaling is critical to many physiological processes, and its kinetics and subcellular localization are tightly regulated in all cell types. All Ca²⁺ flux perturbations impact cell function and may contribute to various diseases, including cancer. Several modulators of Ca²⁺ signaling are attractive pharmacological targets due to their accessibility at the plasma membrane. Despite this, the number of specific inhibitors is still limited, and to date there are no anticancer drugs in the clinic that target Ca²⁺ signaling. Ca²⁺ dynamics are impacted, in part, by modifications of cellular metabolic pathways. Conversely, it is well established that Ca²⁺ regulates cellular bioenergetics by allosterically activating key metabolic enzymes and metabolite shuttles or indirectly by modulating signaling cascades. A coordinated interplay between Ca²⁺ and metabolism is essential in maintaining cellular homeostasis. In this review, we provide a snapshot of the reciprocal interaction between Ca²⁺ and metabolism and discuss the potential consequences of this interplay in cancer cells. We highlight the contribution of Ca²⁺ to the metabolic reprogramming observed in cancer. We also describe how the metabolic adaptation of cancer cells influences this crosstalk to regulate protumorigenic signaling pathways. We suggest that the dual targeting of these processes might provide unprecedented opportunities for anticancer strategies. Interestingly, promising evidence for the synergistic effects of antimetabolites and Ca²⁺-modulating agents is emerging.

A looming role of mitochondrial calcium in dictating the lung epithelial integrity and pathophysiology of lung diseases

With the increasing appreciation of mitochondria in modulating cellular homeostasis, various disease biology researchers have started exploring the detailed role of mitochondria in multiple diseases beyond neuronal and muscular diseases. In this context, emerging shreds of evidence in lung biology indicated the meticulous role of lung epithelia in provoking a plethora of lung diseases in contrast to earlier beliefs. As lung epithelia are ceaselessly exposed to the environment, they need to have multiple protective mechanisms to maintain the integrity of lung structure and function. As ciliated airway epithelium and type 2 alveolar epithelia require intense energy for executing their key functions like ciliary beating and surfactant production, it is no surprise that defects in mitochondrial function in these cells could perturb lung homeostasis and engage in the pathophysiology of lung diseases. On one hand, intracellular calcium plays the central role in executing key functions of lung epithelia, and on the other hand maintenance of intracellular calcium needs the buffering role of mitochondria. Thus, the regulation of mitochondrial calcium in lung epithelia seems to be critical in lung homeostasis and could be decisive in the pathogenesis of various lung diseases.

Perfluorooctane sulfonate acute exposure stimulates insulin secretion via GPR40 pathway

Perfluoroalkyl substances (PFASs) are widely used synthetic chemicals, showing environmental/biological persistence and adverse effects on ecosystem and human health. Several epidemiological and animal studies have revealed that PFASs levels are associated with elevated serum insulin level; however, the effect of PFASs on insulin secretion and the underlying mechanism are not clear. In this study, the effect of a most concerned PFAS, perfluorooctane sulfonate (PFOS) on insulin secretion in Beta-TC-6 pancreatic cells was studied. The results showed that PFOS acute exposure stimulated insulin secretion and elevated intracellular calcium concentration ([Ca²⁺]_i). The PFOS-stimulated [Ca²⁺]_i elevation was resulted from both extra- and intra-cellular sources. PFOS acute exposure decreased ATP content and ATP/ADP ratio, indicating the mitochondrial function was damaged under PFOS acute exposure. The PFOS-stimulated insulin secretion was inhibited by GW1100, a G Protein-coupled Receptor 40 (GPR40) specific inhibitor, but not affected by GW9662, a specific antagonist to the peroxisome proliferator-activated receptor gamma (PPARγ). The observation of RNA silencing further demonstrated that the PFOS-stimulated insulin secretion is, at least partially, via GPR40. By using specific inhibitors, we found that the GPR40 downstream pathways, phospholipase C (PLC) and L-type Ca²⁺ channels (LTCC) were involved in PFOS-stimulated [Ca²⁺]_i elevation and insulin secretion.

Is Mitochondrial Dysfunction a Common Root of Noncommunicable Chronic Diseases?

Mitochondrial damage is implicated as a major contributing factor for a number of noncommunicable chronic diseases such as cardiovascular diseases, cancer, obesity, and insulin resistance/type 2 diabetes. Here, we discuss the role of mitochondria in maintaining cellular and whole-organism homeostasis, the mechanisms that promote mitochondrial dysfunction, and the role of this phenomenon in noncommunicable chronic diseases. We also review the state of the art regarding the preclinical evidence associated with the regulation of mitochondrial function and the development of current mitochondria-targeted therapeutics to treat noncommunicable chronic diseases. Finally, we give an integrated vision of how mitochondrial damage is implicated in these metabolic diseases.

Cellular mechanisms of complex I-associated pathology

Mitochondria control vitally important functions in cells, including energy production, cell signalling and regulation of cell death. Considering this, any alteration in mitochondrial metabolism would lead to cellular dysfunction and the development of a disease. A large proportion of disorders associated with mitochondria are induced by mutations or chemical inhibition of the mitochondrial complex I - the entry point to the electron transport chain. Subunits of the enzyme NADH: ubiquinone oxidoreductase, are encoded by both nuclear and mitochondrial DNA and mutations in these genes lead to cardio and muscular pathologies and diseases of the central nervous system. Despite such a clear involvement of complex I deficiency in numerous disorders, the molecular and cellular mechanisms leading to the development of pathology are not very clear. In this review, we summarise how lack of activity of complex I could differentially change mitochondrial and cellular functions and how these changes could lead to a pathology, following discrete routes.