Mitochondrial Ca2+ transport regulates many neuronal functions including synaptic transmission, ATP production, gene expression and neuronal survival. The mitochondrial Ca2+ uniporter (MCU) is the core molecular component of the mitochondrial Ca2+ uptake complex in the inner mitochondrial membrane. MCUb is a paralog of MCU that negatively regulates mitochondrial Ca2+ uptake in the heart and the cells of the immune system. However, the function of MCUb in the brain is largely unknown. Here, we report that MCUb knockout (KO) led to enhanced mitochondrial Ca2+ uptake in cortical neurons. By simultaneously monitoring changes in cytosolic and mitochondrial Ca2+ concentrations, [Ca2+]cyt and [Ca2+]mt, respectively, we also found that MCUb KO reduced the [Ca2+]cyt threshold required to induce mitochondrial uptake in cortical neurons during electrical stimulation. Exposure of cortical neurons to toxic concentrations of glutamate led to a collapse of mitochondrial membrane potential (ΔΨmt) and [Ca2+]cyt deregulation, and MCUb deletion accelerated the development of both events. Furthermore, using the middle cerebral artery occlusion (MCAO) as a model of transient ischemic stroke in mice, we found that MCUb KO significantly increased MCAO-induced brain damage in male, but not female mice. These results suggest that MCUb regulates neuronal Ca2+ dynamics and excitotoxicity and reveal a sex-dependent role of MCUb in controlling resistance to brain damage following ischemic stroke.

Mitochondria represent a fundamental structure for cellular homeostasis, controlling multiple conditions regarding energetic functions and cellular survival. To maintain these organelles functioning in ideal conditions, their membranes count with ion channels for different inorganic ions, which must be balanced to offer the proper function for both the organelle and the cell. However, studies have shown that other health conditions impair the activities of mitochondrial ion channels, including cancer. In this sense, the altered activities of potassium, calcium, and calcium-activated potassium channels are mainly linked with cancer development and cellular homeostasis alteration, demonstrating their role as pharmacological targets. With that in mind, scientists have found significant mitochondrial and cellular responses related to apoptosis and reduction of cellular survival from cells with modulated ion channels, indicating the potential of this possible therapy in carcinogenic contexts. Nonetheless, few studies still evaluate mitochondrial ion channel modulation as a treatment against cancer. Hence, more research must be conducted on this subject.

In most eukaryotes, the mitochondrial calcium uniporter (MCU) mediates Ca2+ influx into the mitochondrial matrix through a process regulated by MICUs and the EMRE. In Dictyostelium discoideum, a model organism for amoebozoans that lack an EMRE, the MCU complex consists solely of the MCU and MICU. Most likely, therefore, the mechanism by which DdMICU regulates the DdMCU differs from the extensively studied metazoan MCU-EMRE-MICU system. Here, we report the crystal structure of Ca2+-bound DdMICU at 2.5 Å resolution. Unlike human MICUs, which contain two Ca2+-binding EF-hand motifs, DdMICU possesses three EF-hand motifs, each with a submicromolar Ca2+ binding affinity. The overall structure of DdMICU is comparable to that of human MICUs, and their well-conserved dimer interface interactions are similar. In addition to the face-to-face dimer observed in human MICUs, DdMICU forms a head-to-head dimer with multimeric states that equilibrate between tetrameric and dimeric forms, depending on the solution ionic strength. Moreover, the C-helix of DdMICU plays a critical role in membrane binding. These findings provide a molecular basis for the unique mechanism regulating Ca2+ uptake by MICUs in an EMRE-free system and offer insight into the evolution and functional diversity of the MCU complex in non-metazoan organisms.

Voltage-gated calcium channels are emerging regulators of cellular homeostasis, but their molecular interplay with mitochondrial bioenergetics in chondrocytes remains poorly characterized. This study elucidates how the T-type calcium channel CaV3.3 governs mitochondrial calcium-redox coupling through structural interactions with MICU1, the regulatory subunit of the mitochondrial calcium uniporter (MCU) complex. The absence of the CaV3.3 precipitated mitochondrial ultrastructural disorganization characterized, coupled with MICU1 downregulation and consequent loss of MCU gating fidelity. Through integrated transcriptomic-proteomic profiling and live-cell imaging, we demonstrate that CaV3.3 deficiency induces pathological mitochondrial calcium influx, triggering Reactive oxygen species (ROS) overproduction and bioenergetic collapse, these metabolic derangements activated intrinsic apoptosis. Notably, lentiviral overexpression of MICU1 in CaV3.3 knockout cells restored the mitochondrial calcium set point and inhibited ROS burst, while rescued cell proliferation and inhibited apoptosis execution. Our findings establish CaV3.3 as a redox rheostat coordinating MICU1-mediated mitochondrial calcium buffering, with direct implications for cartilage matrix maintenance and osteoarthritis therapy targeting calcium-handling macromolecules.

Mitochondrial dysfunction fuels vascular inflammation and atherosclerosis. Mitochondrial calcium uptake 1 (MICU1) maintains mitochondrial Ca2+ homeostasis. However, the role of MICU1 in vascular inflammation and atherosclerosis remains unknown. Here, we report that endothelial MICU1 prevents vascular inflammation and atherosclerosis by maintaining mitochondrial homeostasis. We observed that vascular inflammation was aggravated in endothelial cell-specific Micu1 knockout mice (Micu1ECKO) and attenuated in endothelial cell-specific Micu1 transgenic mice (Micu1ECTg). Furthermore, hypercholesterolemic Micu1ECKO mice also showed accelerated development of atherosclerosis, while Micu1ECTg mice were protected against atherosclerosis. Mechanistically, MICU1 depletion increased mitochondrial Ca2+ influx, thereby decreasing the expression of the mitochondrial deacetylase sirtuin 3 (SIRT3) and the ensuing deacetylation of superoxide dismutase 2 (SOD2), leading to the burst of mitochondrial reactive oxygen species (mROS). Of clinical relevance, we observed decreased MICU1 expression in the endothelial layer covering human atherosclerotic plaques and in human aortic endothelial cells exposed to serum from patients with coronary artery diseases (CAD). Two-sample Wald ratio Mendelian randomization further revealed that increased expression of MICU1 was associated with decreased risk of CAD and coronary artery bypass grafting (CABG). Our findings support MICU1 as an endogenous endothelial resilience factor that protects against vascular inflammation and atherosclerosis by maintaining mitochondrial Ca2+ homeostasis.

Despite the efficacy of bortezomib (BTZ)-based chemotherapy in treating multiple myeloma (MM) patients, chemoresistance occurs frequently over time, particularly in individuals exhibiting an initial positive response to BTZ therapy. In this study, we established BTZ-resistant MM cells and identified that suppressed expression of the hepatoma-derived growth factor (HDGF)-related protein-2 (HRP2) was a key determinant of chemoresistance in MM cells. Manipulating HRP2 expression remodeled the chemosensitivity of MM cells in vitro and in vivo. Clinically, lower expression of HRP2 predicted a shorter survival rate in MM patients receiving BTZ-based regimens. Mechanistically, HRP2 depletion resulted in elevated acetylation modifications of histone 3 at lysine 27 (H3K27Ac), and enhanced chromatin accessibility as well as transcriptional elongation of mitochondrial calcium uptake 1(MICU1) gene, thus promoting the expression of MICU1 gene and alleviating calcium (Ca2+) overload and excessive reactive oxygen species (ROS) induced mitochondria damage and apoptosis in MM cells. Thereby, MICU1 suppression improved BTZ sensitivity in vitro and relieved tumor burden in a mouse model of MM. Similarly, elevated MICU1 expression was observed in the B220+CD19+ B cells from HRP2-knockout mice and significantly correlated with poor prognosis in the clinic. Thus, our study elucidates the previously unrecognized epigenetic role of HRP2 in regulating calcium homeostasis of MM cells, providing new theoretical insights into the mechanisms underlying the development of drug resistance in multiple myeloma.

Cells utilize protein disaggregases to avoid abnormal protein aggregation that causes many diseases. Among these, caseinolytic peptidase B protein homolog (CLPB) is localized in the mitochondrial intermembrane space and linked to human disease. Upon CLPB loss, MICU1 and MICU2, regulators of the mitochondrial calcium uniporter complex (mtCU), and OPA1, a main mediator of mitochondrial fusion, become insoluble but the functional outcome remains unclear. In this work we demonstrate that CLPB is required to maintain mitochondrial calcium signalling and fusion dynamics. CLPB loss results in altered mtCU composition, interfering with mitochondrial calcium uptake independently of cytosolic calcium and mitochondrial membrane potential. Additionally, OPA1 decreases, and aggregation occurs, accompanied by mitochondrial fragmentation. Disease-associated mutations in the CLPB gene present in skin fibroblasts from patients also display mitochondrial calcium and structural changes. Thus, mtCU and fusion activity are dependent on CLPB, and their impairments might contribute to the disease caused by CLPB variants.

The mitochondrial Ca2+ uniporter is the Ca2+ channel responsible for mitochondrial Ca2+ uptake. It plays crucial physiological roles in regulating oxidative phosphorylation, intracellular Ca2+ signaling, and cell death. The uniporter contains the pore-forming MCU subunit, the auxiliary EMRE protein, and the regulatory MICU1 subunit, which blocks the MCU pore under resting cellular Ca2+ concentrations. It has been known for decades that spermine, a biological polyamine ubiquitously present in animal cells, can enhance mitochondrial Ca2+ uptake, but the underlying mechanisms remain incompletely understood. In this study, we demonstrate that spermine exerts both potentiation and inhibitory effects on the uniporter. At physiological concentrations, spermine binds to membranes and disrupts MCU-MICU1 interactions, thereby opening the uniporter to import more Ca2+. However, at millimolar concentrations, spermine also inhibits the uniporter by targeting the pore-forming region in a MICU1-independent manner. These findings provide molecular insights into how cells can use spermine to control the critical processes of mitochondrial Ca2+ signaling and homeostasis.

Calcium signaling plays a pivotal role in diverse cellular processes through precise spatiotemporal regulation and interaction with effector proteins across distinct subcellular compartments. Mitochondria, in particular, act as central hubs for calcium buffering, orchestrating energy production, redox balance and apoptotic signaling, among others. While controlled mitochondrial calcium uptake supports ATP synthesis and metabolic regulation, excessive accumulation can trigger oxidative stress, mitochondrial membrane permeabilization, and cell death. Emerging findings underscore the intricate interplay between calcium homeostasis and mitophagy, a selective type of autophagy for mitochondria elimination. Although the literature is still emerging, this review delves into the bidirectional relationship between calcium signaling and mitophagy pathways, providing compelling mechanistic insights. Furthermore, we discuss how disruptions in calcium homeostasis impair mitophagy, contributing to mitochondrial dysfunction and the pathogenesis of common neurodegenerative diseases.

Activation of Ca2+ channels in Ca2+ stores in organelles and the plasma membrane generates cytoplasmic calcium ([Ca2+]c) signals that control almost every aspect of cell function, including metabolism, vesicle fusion and contraction. Mitochondria have a high capacity for Ca2+ uptake and chelation, alongside efficient Ca2+ release mechanisms. Still, mitochondria do not store Ca2+ in a prolonged manner under physiological conditions and lack the capacity to generate global [Ca2+]c signals. However, mitochondria take up Ca2+ at high local [Ca2+]c signals that originate from neighbouring organelles, and also during sustained global elevations of [Ca2+]c. Accumulated Ca2+ in the mitochondria stimulates oxidative metabolism and upon return to the cytoplasm, can produce spatially confined rises in [Ca2+]c to exert control over processes that are sensitive to Ca2+. Thus, the mitochondrial handling of [Ca2+]c is of physiological relevance. Furthermore, dysregulation of mitochondrial Ca2+ handling can contribute to debilitating diseases. We discuss the mechanisms and relevance of mitochondria in local and global calcium signals.

Cardiac ischemia followed by reperfusion results in cardiac cell death, which has been attributed to an increase of mitochondrial Ca2+ concentration, resulting in activation of the mitochondrial permeability transition pore (PTP). Evaluating this hypothesis requires understanding of the mechanisms responsible for control of mitochondrial Ca2+ in physiological conditions and how they are altered during both ischemia and reperfusion. Ca2+ influx is thought to occur through the mitochondrial Ca2+ uniporter (MCU). However, with deletion of the MCU, an increase in mitochondrial Ca2+ still occurs, suggesting an alternative Ca2+ influx mechanism during ischemia. There is less certainty about the mechanisms responsible for Ca2+ efflux, with contributions from both Ca2+/H+ exchange and a Na+-dependent Ca2+ efflux pathway. The molecular details of both mechanisms are not fully resolved. We discuss this and the contributions of both pathways to the accumulation of mitochondrial Ca2+ during ischemia and reperfusion. We further discuss the role of mitochondrial Ca2+ in activation of the PTP.

The key role of calcium in various physiological and pathological processes includes its involvement in various forms of regulated cell death (RCD). The concept of 'calcicoptosis' has been introduced as a calcium-induced phenomenon associated with oxidative stress and cellular damage. However, its definition remains controversial within the research community, with some considering it a general form of calcium overload stress, while others view it as a tumor-specific calcium-induced cell death. This review examines 'calcicoptosis' in the context of established RCD mechanisms such as apoptosis, necroptosis, ferroptosis, and others. It further analyzes the intricate relationship between calcium dysregulation and oxidative stress, emphasizing that while calcium overload often triggers cell death, it may not represent an entirely new type of RCD but rather an extension of known pathways. The purpose of this paper is to discuss the implications of this perspective for cancer therapy focusing on calcium-based nanoparticles. By investigating the connections between calcium dynamics and cell death pathways, this review contributes to the advancement of our understanding of calcicoptosis and its possible therapeutic uses.

The field of ferroptosis research has grown exponentially since this form of cell death was first identified over a decade ago. Ferroptosis, an iron- and ROS-dependent type of cell death, is controlled by various metabolic pathways, including but not limited to redox and calcium (Ca2+) homeostasis, iron fluxes, mitochondrial function and lipid metabolism. Importantly, therapy-resistant tumors are particularly susceptible to ferroptotic cell death, rendering ferroptosis a promising therapeutic strategy against numerous malignancies. Calcium signals are important regulators of both cancer progression and cell death, with recent studies indicating their involvement in ferroptosis. Cells undergoing ferroptosis are characterized by plasma membrane rupture and the formation of nanopores, which facilitate influx of ions such as Ca2+ into the affected cells. Furthermore, mitochondrial Ca²⁺ levels have been implicated in directly influencing the cellular response to ferroptosis. Despite the remarkable progress made in the field, our understanding of the contribution of Ca2+ signals to ferroptosis remains limited. Here, we summarize key connections between Ca²⁺ signaling and ferroptosis in cancer pathobiology and discuss their potential therapeutic significance.

Metabolic adaptations in response to changes in energy supply and demand are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating TCA cycle activation, mitochondrial fatty acid oxidation, and cellular calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial pathways has remained unexplored. Here, we investigate metabolic consequences of uniporter loss- and gain-of-function using uniporter knockout cells and the liver cancer fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. Our results reveal that branched-chain amino acid (BCAA) catabolism and the urea cycle are uniporter-regulated metabolic pathways. Reduced uniporter function boosts expression of BCAA catabolism genes, and the urea cycle enzyme ornithine transcarbamylase (OTC). In contrast, high uniporter activity in FLC suppresses their expression. This suppression is mediated by reduced expression of the transcription factor KLF15, a master regulator of liver metabolism. Thus, uniporter responsive calcium signaling plays a central role in FLC-associated metabolic changes, including hyperammonemia. Our study identifies an important role for mitochondrial calcium signaling in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism in FLC.

High-altitude cardiac injury is a prevalent form of tissue damage resulting from hypobaric hypoxia (HH). MICU1 is a critical modulator of mitochondrial calcium uptake, with significant implications for the regulation of mitochondrial redox homeostasis. This study sought to examine the impact of MICU1 and elucidate the underlying mechanism in myocardial exposed to HH.

Loss-and gain-of-function approaches were used to investigate the role of MICU1 in cardiac response to HH. In vitro, the function of MICU1 in the primary neonatal rat cardiomyocytes under hypoxia was examined.

We observed that MICU1 was downregulated in hearts exposed to HH, contributing to myocardial apoptosis. In vitro experiments demonstrated that MICU1 knockdown exacerbated hypoxic cardiomyocyte injury, as evidenced by an increase in apoptotic cells and a decrease in mitochondrial membrane potential. Conversely, overexpression of MICU1 in mice significantly mitigated myocardial injury, leading to enhanced cardiac function and reduced myocardial hypertrophy and fibrosis in hypobaric hypoxic mice, consistent with the in vitro findings. Further investigations revealed that overexpression of MICU1 inhibited apoptosis by augmenting mitochondrial Ca2+ uptake and subsequently enhancing the activity of tricarboxylic acid cycle (TCA) related enzymes. Lastly, our results suggest that hypoxia-induced downregulation of MICU1 is mediated by the reduction of MAZ expression in primary neonatal rat cardiomyocytes.

Our results suggest that MICU1 plays an important role in myocardial protection subjected to HH, suggesting that enhancing the expression or activity of MICU1 may be a potential pharmacological target to ameliorate myocardial injury at high altitude.

Mitochondrial Calcium Uptake 1 (MICU1) is an important component of mitochondrial calcium channel regulator. Mutations in MICU1 result in a rare syndrome of myopathy with extrapyramidal features. Here we report a rare case of MICU1 related myopathy from India. A 23 years old male presented with 10 years history of proximal muscle weakness with exertional myalgia and fatigue. Examination showed facial dysmorphism with facial weakness and mildly reduced visual acuity. Limb girdle pattern of weakness with hypoactive tendon reflexes were noted without extrapyramidal signs. He had elevated serum creatine level of 1542 IU/L. Muscle MRI had novel findings of selective fatty infiltration of hamstrings, medial gastrocnemius and soleus. Muscle biopsy showed myopathic with secondary neurogenic changes along with few COX deficient fibres. Genetic analysis showed compound heterozygous pathogenic variants in MICU1 gene at intron 9 (c.1072-1 G > C) - splice site variant and exon 5 (c.513T > A) - stop gained variant, both resulting in loss of function of the protein. The variants were segregating in unaffected parents in heterozygous state with variant c.1072-1 G > C in the unaffected father and variant c.513T > A (p. Tyr171*) in the unaffected mother confirming the diagnosis. This report highlights the phenotype of limb girdle weakness with facial dysmorphism and optic atrophy expanding the spectrum of MICU1 related syndrome with novel MRI muscle and histopathological findings.

The mitochondrial calcium uniporter channel (MCUC) mediates mitochondrial calcium entry, regulating energy metabolism and cell death. Although several MCUC components have been identified, the molecular basis of mitochondrial calcium signaling networks and their remodeling upon changes in uniporter activity have not been assessed. Here, we map the MCUC interactome under resting conditions and upon chronic loss or gain of mitochondrial calcium uptake. We identify 89 high-confidence interactors that link MCUC to several mitochondrial complexes and pathways, half of which are associated with human disease. As a proof-of-concept, we validate the mitochondrial intermembrane space protein EFHD1 as a binding partner of the MCUC subunits MCU, EMRE, and MCUB. We further show a MICU1-dependent inhibitory effect of EFHD1 on calcium uptake. Next, we systematically survey compensatory mechanisms and functional consequences of mitochondrial calcium dyshomeostasis by analyzing the MCU interactome upon EMRE, MCUB, MICU1, or MICU2 knockdown. While silencing EMRE reduces MCU interconnectivity, MCUB loss-of-function leads to a wider interaction network. Our study provides a comprehensive and high-confidence resource to gain insights into players and mechanisms regulating mitochondrial calcium signaling and their relevance in human diseases.

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.

Hepatic Ca2+ signaling has been identified as a crucial key factor in driving gluconeogenesis. The involvement of mitochondria in hormone-induced Ca2+ signaling and their contribution to metabolic activity remain, however, poorly understood. Moreover, the molecular mechanism governing the mitochondrial Ca2+ efflux signaling remains unresolved. This study investigates the role of the Na+/Ca2+ exchanger, NCLX, in modulating hepatic mitochondrial Ca2+ efflux, and examines its physiological significance in hormonal hepatic Ca2+ signaling, gluconeogenesis, and mitochondrial bioenergetics.

Primary mouse hepatocytes from both an AAV-mediated conditional hepatic-specific and a total mitochondrial Na+/Ca2+ exchanger, NCLX, knockout (KO) mouse models were employed for fluorescent monitoring of purinergic and glucagon/vasopressin-dependent mitochondrial and cytosolic hepatic Ca2+ responses in cultured hepatocytes. Isolated liver mitochondria and permeabilized primary hepatocytes were used to analyze the ion-dependence of Ca2+ efflux. Utilizing the conditional hepatic-specific NCLX KO model, the rate of gluconeogenesis was assessed by first monitoring glucose levels in fasted mice, and subsequently subjecting the mice to a pyruvate tolerance test while monitoring their blood glucose. Additionally, cultured primary hepatocytes from both genotypes were assessed in vitro for glucagon-dependent glucose production and cellular bioenergetics through glucose oxidase assay and Seahorse respirometry, respectively.

Analysis of Ca2+ responses in isolated liver mitochondria and cultured primary hepatocytes from NCLX KO versus WT mice showed that NCLX serves as the principal mechanism for mitochondrial calcium extrusion in hepatocytes. We then determined the role of NCLX in glucagon and vasopressin-induced Ca2+ oscillations. Consistent with previous studies, glucagon and vasopressin triggered Ca2+ oscillations in WT hepatocytes, however, the deletion of NCLX resulted in selective elimination of mitochondrial, but not cytosolic, Ca2+ oscillations, underscoring NCLX's pivotal role in mitochondrial Ca2+ regulation. Subsequent in vivo investigation for hepatic NCLX role in gluconeogenesis revealed that, as opposed to WT mice which maintained normoglycemic blood glucose levels when fasted, conditional hepatic-specific NCLX KO mice exhibited a faster drop in glucose levels, becoming hypoglycemic. Furthermore, KO mice showed deficient conversion of pyruvate to glucose when challenged under fasting conditions. Concurrent in vitro assessments showed impaired glucagon-dependent glucose production and compromised bioenergetics in KO hepatocytes, thereby underscoring NCLX's significant contribution to hepatic glucose metabolism.

The study findings demonstrate that NCLX acts as the primary Ca2+ efflux mechanism in hepatocytes. NCLX is indispensable for regulating hormone-induced mitochondrial Ca2+ oscillations, mitochondrial metabolism, and sustenance of hepatic gluconeogenesis.

Activating Ca2+-sensitive enzymes of oxidative metabolism while preventing calcium overload that leads to mitochondrial and cellular injury requires dynamic control of mitochondrial Ca2+ uptake. This is ensured by the mitochondrial calcium uptake (MICU)1/2 proteins that gate the pore of the mitochondrial calcium uniporter (mtCU). MICU1 is relatively sparse in the heart, and recent studies claimed the mammalian heart lacks MICU1 gating of mtCU. However, genetic models have not been tested. We find that MICU1 is present in a complex with MCU in nonfailing human hearts. Furthermore, using murine genetic models and pharmacology, we show that MICU1 and MICU2 control cardiac mitochondrial Ca2+ influx, and that MICU1 deletion alters cardiomyocyte mitochondrial calcium signaling and energy metabolism. MICU1 loss causes substantial compensatory changes in the mtCU composition and abundance, increased turnover of essential MCU regulator (EMRE) early on and, later, of MCU, that limit mitochondrial Ca2+ uptake and allow cell survival. Thus, both the primary consequences of MICU1 loss and the ensuing robust compensation highlight MICU1's relevance in the beating heart.

Synaptic plasticity is believed to underlie the cellular and molecular basis of memory formation. Mitochondria are one of the main organelles involved in metabolism and energy maintenance as plastic organelles that change morphologically and functionally in response to cellular needs and regulate synaptic function and plasticity through multiple mechanisms, including ATP generation, calcium homeostasis, and biogenesis. An increased neuronal activity enhances synaptic efficiency, during which mitochondria's spatial distribution and morphology change significantly. These organelles build up in the pre-and postsynaptic zones to produce ATP, which is necessary for several synaptic processes like neurotransmitter release and recycling. Mitochondria also regulate calcium homeostasis by buffering intracellular calcium, which ensures proper synaptic activity. Furthermore, mitochondria in the presynaptic terminal have distinct morphological properties compared to dendritic or postsynaptic mitochondria. This specialization enables precise control of synaptic activity and plasticity. Mitochondrial dysfunction has been linked to synaptic failure in many neurodegenerative disorders, like Alzheimer's disease (AD). In AD, malfunctioning mitochondria cause delays in synaptic vesicle release and recycling, ionic gradient imbalances, and mostly synaptic failure. This review emphasizes mitochondrial plasticity's contribution to synaptic function. It also explores the profound effect of mitochondrial malfunction on neurodegenerative disorders, focusing on AD, and provides an overview of how they sustain cellular health under normal conditions and how their malfunction contributes to neurodegenerative diseases, highlighting their potential as a therapeutic target for such conditions.

Type 2 diabetes (T2D) is a frequent comorbidity encountered in patients with severe aortic stenosis (AS), leading to an adverse left ventricular (LV) remodeling and dysfunction. Metabolic alterations have been suggested as contributors of the deleterious effect of T2D on LV remodeling and function in patients with severe AS, but so far, the underlying mechanisms remain unclear. Mitochondria play a central role in the regulation of cardiac energy metabolism.

We aimed to explore the mitochondrial alterations associated with the deleterious effect of T2D on LV remodeling and function in patients with AS, preserved ejection fraction, and no additional heart disease.

We combined an in-depth clinical, biological and echocardiography phenotype of patients with severe AS, with (n = 34) or without (n = 50) T2D, referred for a valve replacement, with transcriptomic and histological analyses of an intra-operative myocardial LV biopsy.

T2D patients had similar AS severity but displayed worse cardiac remodeling, systolic and diastolic function than non-diabetics. RNAseq analysis identified 1029 significantly differentially expressed genes. Functional enrichment analysis revealed several T2D-specific upregulated pathways despite comorbidity adjustment, gathering regulation of inflammation, extracellular matrix organization, endothelial function/angiogenesis, and adaptation to cardiac hypertrophy. Downregulated gene sets independently associated with T2D were related to mitochondrial respiratory chain organization/function and mitochondrial organization. Generation of causal networks suggested a reduced Ca2+ signaling up to the mitochondria, with the measured gene remodeling of the mitochondrial Ca2+ uniporter in favor of enhanced uptake. Histological analyses supported a greater cardiomyocyte hypertrophy and a decreased proximity between the mitochondrial VDAC porin and the reticular IP3-receptor in T2D.

Our data support a crucial role for mitochondrial Ca2+ signaling in T2D-induced cardiac dysfunction in severe AS patients, from a structural reticulum-mitochondria Ca2+ uncoupling to a mitochondrial gene remodeling. Thus, our findings open a new therapeutic avenue to be tested in animal models and further human cardiac biopsies in order to propose new treatments for T2D patients suffering from AS.

URL: https://www.

gov ; Unique Identifier: NCT01862237.

Calcium (Ca2+) signalling acts a pleiotropic message within the cell that is decoded by the mitochondria through a sophisticated ion channel known as the Mitochondrial Ca2+ Uniporter (MCU) complex. Under physiological conditions, mitochondrial Ca2+ signalling is crucial for coordinating cell activation with energy production. Conversely, in pathological scenarios, it can determine the fine balance between cell survival and death. Over the last decade, significant progress has been made in understanding the molecular bases of mitochondrial Ca2+ signalling. This began with the elucidation of the MCU channel components and extended to the elucidation of the mechanisms that regulate its activity. Additionally, increasing evidence suggests molecular mechanisms allowing tissue-specific modulation of the MCU complex, tailoring channel activity to the specific needs of different tissues or cell types. This review aims to explore the latest evidence elucidating the regulation of the MCU complex, the molecular factors controlling the tissue-specific properties of the channel, and the physiological and pathological implications of mitochondrial Ca2+ signalling in different tissues.

Calcium (Ca2+) uptake by mitochondria occurs via the mitochondrial Ca2+ uniporter. Mitochondrial Ca2+ uniporter exists as a complex, regulated by 3 MICU (mitochondrial Ca2+ uptake) proteins localized in the intermembrane space: MICU1, MICU2, and MICU3. Although MICU3 is present in the heart, its role is largely unknown.

We used CRISPR-Cas9 to generate a mouse with global deletion of MICU3 and an adeno-associated virus (AAV9) to overexpress MICU3 in wild-type mice. We examined the role of MICU3 in regulating mitochondrial calcium ([Ca2+]m) in ex vivo hearts using an optical method following adrenergic stimulation in perfused hearts loaded with a Ca2+-sensitive fluorophore. Additionally, we studied how deletion and overexpression of MICU3, respectively, impact cardiac function in vivo by echocardiography and the molecular composition of the mitochondrial Ca2+ uniporter complex via Western blot, immunoprecipitation, and Blue native-PAGE analysis. Finally, we measured MICU3 expression in failing human hearts.

MICU3 knock out hearts and cardiomyocytes exhibited a significantly smaller increase in [Ca2+]m than wild-type hearts following acute isoproterenol infusion. In contrast, heart with overexpression of MICU3 exhibited an enhanced increase in [Ca2+]m compared with control hearts. Echocardiography analysis showed no significant difference in cardiac function in knock out MICU3 mice relative to wild-type mice at baseline. However, mice with overexpression of MICU3 exhibited significantly reduced ejection fraction and fractional shortening compared with control mice. We observed a significant increase in the ratio of heart weight to tibia length in hearts with overexpression of MICU3 compared with controls, consistent with hypertrophy. We also found a significant decrease in MICU3 protein and expression in failing human hearts.

Our results indicate that increased and decreased expression of MICU3 enhances and reduces, respectively, the uptake of [Ca2+]m in the heart. We conclude that MICU3 plays an important role in regulating [Ca2+]m physiologically, and overexpression of MICU3 is sufficient to induce cardiac hypertrophy, making MICU3 a possible therapeutic target.

The discovery of MICU1 as gatekeeper of mitochondrial calcium (mCa2+) entry has transformed our understanding of mCa2+ flux. Recent studies revealed an additional role of MICU1 as a Ca2+ sensor at MICOS (mitochondrial contact site and cristae organizing system). MICU1's presence at MICOS suggests its involvement in coordinating Ca2+ signaling and mitochondrial ultrastructure. Besides its role in Ca2+ regulation, MICU1 influences cellular signaling pathways including transcription, epigenetic regulation, metabolism, and cell death, thereby affecting human health. Here, we summarize recent findings on MICU1's canonical and noncanonical functions, and its relevance to human health and diseases.

The mitochondrial calcium (mCa2+) uniporter channel (mtCU) resides at the inner mitochondrial membrane and is required for Ca2+ to enter the mitochondrial matrix. The mtCU is essential for cellular function, as mCa2+ regulates metabolism, bioenergetics, signaling pathways and cell death. mCa2+ uptake is primarily regulated by the MICU family (MICU1, MICU2, MICU3), EF-hand-containing Ca2+-sensing proteins, which respond to cytosolic Ca2+ concentrations to modulate mtCU activity. Considering that mitochondrial function and Ca2+ signaling are ubiquitously disrupted in cardiovascular disease, mtCU function has been a hot area of investigation for the last decade. Here we provide an in-depth review of MICU-mediated regulation of mtCU structure and function, as well as potential mtCU-independent functions of these proteins. We detail their role in cardiac physiology and cardiovascular disease by highlighting the phenotypes of different mutant animal models, with an emphasis on therapeutic potential and targets of interest in this pathway.

Mitochondrial Ca2+ uptake is essential in regulating bioenergetics, cell death, and cytosolic Ca2+ transients. Mitochondrial Calcium Uniporter (MCU) mediates the mitochondrial Ca2+ uptake. Though MCU regulation by MICUs is unequivocally established, there needs to be more knowledge of whether divalent cations regulate MCU. Here, we set out to understand the mitochondrial matrix Mg2+-dependent regulation of MCU activity. We showed that decreased matrix [Mg2+] is associated with increased MCU activity and significantly prompted mitochondrial permeability transition pore opening. Our findings support the critical role of mMg2+ in regulating MCU activity.

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease associated with cardiomyopathy. DMD cardiomyopathy is characterized by abnormal intracellular Ca2+ homeostasis and mitochondrial dysfunction. We used dystrophin and utrophin double-knockout (mdx:utrn-/-) mice in a sarcolipin (SLN) heterozygous-knockout (sln+/-) background to examine the effect of SLN reduction on mitochondrial function in the dystrophic myocardium. Germline reduction of SLN expression in mdx:utrn-/- mice improved cardiac sarco/endoplasmic reticulum (SR) Ca2+ cycling, reduced cardiac fibrosis, and improved cardiac function. At the cellular level, reducing SLN expression prevented mitochondrial Ca2+ overload, reduced mitochondrial membrane potential loss, and improved mitochondrial function. Transmission electron microscopy of myocardial tissues and proteomic analysis of mitochondria-associated membranes showed that reducing SLN expression improved mitochondrial structure and SR-mitochondria interactions in dystrophic cardiomyocytes. These findings indicate that SLN upregulation plays a substantial role in the pathogenesis of cardiomyopathy and that reducing SLN expression has clinical implications in the treatment of DMD cardiomyopathy.

Background: Matrine, an alkaloid derived from the dried roots of Sophora flavescens Aiton, has been utilized for the treatment of liver diseases, but its potential hepatotoxicity raises concerns. However, the precise condition and mechanism of action of matrine on the liver remain inconclusive. Therefore, the objective of this systematic review and meta-analysis is to comprehensively evaluate both the hepatoprotective and hepatotoxic effects of matrine and provide therapeutic guidance based on the findings. Methods: The meta-analysis systematically searched relevant preclinical literature up to May 2023 from eight databases, including PubMed, Web of Science, Cochrane Library, Embase, China National Knowledge Infrastructure, WanFang Med Online, China Science and Technology Journal Database, and China Biomedical Literature Service System. The CAMARADES system assessed the quality and bias of the evidence. Statistical analysis was conducted using STATA, which included the use of 3D maps and radar charts to display the effects of matrine dosage and frequency on hepatoprotection and hepatotoxicity. Results: After a thorough screening, 24 studies involving 657 rodents were selected for inclusion. The results demonstrate that matrine has bidirectional effects on ALT and AST levels, and it also regulates SOD, MDA, serum TG, serum TC, IL-6, TNF-α, and CAT levels. Based on our comprehensive three-dimensional analysis, the optimal bidirectional effective dosage of matrine ranges from 10 to 69.1 mg/kg. However, at a dose of 20-30 mg/kg/d for 0.02-0.86 weeks, it demonstrated high liver protection and low toxicity. The molecular docking analysis revealed the interaction between MT and SERCA as well as SREBP-SCAP complexes. Matrine could alter Ca2+ homeostasis in liver injury via multiple pathways, including the SREBP1c/SCAP, Notch/RBP-J/HES1, IκK/NF-κB, and Cul3/Rbx1/Keap1/Nrf2. Conclusion: Matrine has bidirectional effects on the liver at doses ranging from 10 to 69.1 mg/kg by influencing Ca2+ homeostasis in the cytoplasm, endoplasmic reticulum, Golgi apparatus, and mitochondria. Systematic review registration: https://inplasy.com/, identifier INPLASY202340114.

Calcium signal propagation from endoplasmic reticulum (ER) to mitochondria regulates a multitude of mitochondrial and cell functions, including oxidative ATP production and cell fate decisions. Ca2+ transfer is optimal at the ER-mitochondrial contacts, where inositol 1,4,5-trisphosphate (IP3) receptors (IP3R) can locally expose the mitochondrial Ca2+ uniporter (mtCU) to high [Ca2+] nanodomains. The Ca2+ loading state of the ER (Ca2 + ER) can vary broadly in physiological and pathological scenarios, however, the correlation between Ca2 + ER and the local Ca2+ transfer is unclear. Here, we studied IP3-induced Ca2+ transfer to mitochondria at different Ca2 + ER in intact and permeabilized RBL-2H3 cells via fluorescence measurements of cytoplasmic [Ca2+] ([Ca2+]c) and mitochondrial matrix [Ca2+] ([Ca2+]m). Preincubation of intact cells in high versus low extracellular [Ca2+] caused disproportionally greater increase in [Ca2+]m than [Ca2+]c responses to IP3-mobilizing agonist. Increasing Ca2 + ER by small Ca2+ boluses in suspensions of permeabilized cells supralinearly enhanced the mitochondrial Ca2+ uptake from IP3-induced Ca2+ release. The IP3-induced local [Ca2+] spikes exposing the mitochondrial surface measured using a genetically targeted sensor appeared to linearly correlate with Ca2 + ER, indicating that amplification happened in the mitochondria. Indeed, overexpression of an EF-hand deficient mutant of the mtCU gatekeeper MICU1 reduced the cooperativity of mitochondrial Ca2+ uptake. Interestingly, the IP3-induced [Ca2+]m signal plateaued at high Ca2 + ER, indicating activation of a matrix Ca2+ binding/chelating species. Mitochondria thus seem to maintain a "working [Ca2+]m range" via a low-affinity and high-capacity buffer species, and the ER loading steeply enhances the IP3R-linked [Ca2+]m signals in this working range.

Ca2+ ions serve as pleiotropic second messengers in the cell, regulating several cellular processes. Mitochondria play a fundamental role in Ca2+ homeostasis since mitochondrial Ca2+ (mitCa2+) is a key regulator of oxidative metabolism and cell death. MitCa2+ uptake is mediated by the mitochondrial Ca2+ uniporter complex (MCUc) localized in the inner mitochondrial membrane (IMM). MitCa2+ uptake stimulates the activity of three key enzymes of the Krebs cycle, thereby modulating ATP production and promoting oxidative metabolism. As Paracelsus stated, "Dosis sola facit venenum,"in pathological conditions, mitCa2+ overload triggers the opening of the mitochondrial permeability transition pore (mPTP), enabling the release of apoptotic factors and ultimately leading to cell death. Excessive mitCa2+ accumulation is also associated with a pathological increase of reactive oxygen species (ROS). In this article, we review the precise regulation and the effectors of mitCa2+ in physiopathological processes.

Calcium (Ca2+) ions act as a second messenger, regulating several cell functions. Mitochondria are critical organelles for the regulation of intracellular Ca2+. Mitochondrial calcium (mtCa2+) uptake is ensured by the presence in the inner mitochondrial membrane (IMM) of the mitochondrial calcium uniporter (MCU) complex, a macromolecular structure composed of pore-forming and regulatory subunits. MtCa2+ uptake plays a crucial role in the regulation of oxidative metabolism and cell death. A lot of evidence demonstrates that the dysregulation of mtCa2+ homeostasis can have serious pathological outcomes. In this review, we briefly discuss the molecular structure and the function of the MCU complex and then we focus our attention on human diseases in which a dysfunction in mtCa2+ has been shown.

Cellular homeostasis requires the use of multiple environmental sensors that can respond to a variety of endogenous and exogenous compounds. The aryl hydrocarbon receptor (AHR) is classically known as a transcription factor that induces genes that encode drug metabolizing enzymes when bound to toxicants such as 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD). The receptor has a growing number of putative endogenous ligands, such as tryptophan, cholesterol, and heme metabolites. Many of these compounds are also linked to the translocator protein (TSPO), an outer mitochondrial membrane protein. Given a portion of the cellular pool of the AHR has also been localized to mitochondria and the overlap in putative ligands, we tested the hypothesis that crosstalk exists between the two proteins. CRISPR/Cas9 was used to create knockouts for AHR and TSPO in a mouse lung epithelial cell line (MLE-12). WT, AHR-/-, and TSPO-/- cells were then exposed to AHR ligand (TCDD), TSPO ligand (PK11195), or both and RNA-seq was performed. More mitochondrial-related genes were altered by loss of both AHR and TSPO than would have been expected just by chance. Some of the genes altered included those that encode for components of the electron transport system and the mitochondrial calcium uniporter. Both proteins altered the activity of the other as AHR loss caused the increase of TSPO at both the mRNA and protein level and loss of TSPO significantly increased the expression of classic AHR battery genes after TCDD treatment. This research provides evidence that AHR and TSPO participate in similar pathways that contribute to mitochondrial homeostasis.

African trypanosomes are dixenous eukaryotic parasites that impose a significant human and veterinary disease burden on sub-Saharan Africa. Diversity between species and life-cycle stages is concomitant with distinct host and tissue tropisms within this group. Here, the spatial proteomes of two African trypanosome species, Trypanosoma brucei and Trypanosoma congolense, are mapped across two life-stages. The four resulting datasets provide evidence of expression of approximately 5500 proteins per cell-type. Over 2500 proteins per cell-type are classified to specific subcellular compartments, providing four comprehensive spatial proteomes. Comparative analysis reveals key routes of parasitic adaptation to different biological niches and provides insight into the molecular basis for diversity within and between these pathogen species.

Calcium (Ca2+) uptake by mitochondria is essential in regulating bioenergetics, cell death, and cytosolic Ca2+ transients. Mitochondrial Calcium Uniporter (MCU) mediates the mitochondrial Ca2+ uptake. MCU is a heterooligomeric complex with a pore-forming component and accessory proteins required for channel activity. Though MCU regulation by MICUs is unequivocally established, there needs to be more knowledge of whether divalent cations regulate MCU. Here we set out to understand the mitochondrial matrix Mg2+-dependent regulation of MCU activity. We showed Mrs2 as the authentic mammalian mitochondrial Mg2+ channel using the planar lipid bilayer recordings. Using a liver-specific Mrs2 KO mouse model, we showed that decreased matrix [Mg2+] is associated with increased MCU activity and matrix Ca2+ overload. The disruption of Mg2+dependent MCU regulation significantly prompted mitochondrial permeability transition pore opening-mediated cell death during tissue IR injury. Our findings support a critical role for mMg2+ in regulating MCU activity and attenuating mCa2+ overload.

The neurovascular unit (NVU) is composed of vascular cells, glia, and neurons that form the basic component of the blood brain barrier. This intricate structure rapidly adjusts cerebral blood flow to match the metabolic needs of brain activity. However, the NVU is exquisitely sensitive to damage and displays limited repair after a stroke. To effectively treat stroke, it is therefore considered crucial to both protect and repair the NVU. Mitochondrial calcium (Ca2+) uptake supports NVU function by buffering Ca2+ and stimulating energy production. However, excessive mitochondrial Ca2+ uptake causes toxic mitochondrial Ca2+ overloading that triggers numerous cell death pathways which destroy the NVU. Mitochondrial damage is one of the earliest pathological events in stroke. Drugs that preserve mitochondrial integrity and function should therefore confer profound NVU protection by blocking the initiation of numerous injury events. We have shown that mitochondrial Ca2+ uptake and efflux in the brain are mediated by the mitochondrial Ca2+ uniporter complex (MCUcx) and sodium/Ca2+/lithium exchanger (NCLX), respectively. Moreover, our recent pharmacological studies have demonstrated that MCUcx inhibition and NCLX activation suppress ischemic and excitotoxic neuronal cell death by blocking mitochondrial Ca2+ overloading. These findings suggest that combining MCUcx inhibition with NCLX activation should markedly protect the NVU. In terms of promoting NVU repair, nuclear hormone receptor activation is a promising approach. Retinoid X receptor (RXR) and thyroid hormone receptor (TR) agonists activate complementary transcriptional programs that stimulate mitochondrial biogenesis, suppress inflammation, and enhance the production of new vascular cells, glia, and neurons. RXR and TR agonism should thus further improve the clinical benefits of MCUcx inhibition and NCLX activation by increasing NVU repair. However, drugs that either inhibit the MCUcx, or stimulate the NCLX, or activate the RXR or TR, suffer from adverse effects caused by undesired actions on healthy tissues. To overcome this problem, we describe the use of nanoparticle drug formulations that preferentially target metabolically compromised and damaged NVUs after an ischemic or hemorrhagic stroke. These nanoparticle-based approaches have the potential to improve clinical safety and efficacy by maximizing drug delivery to diseased NVUs and minimizing drug exposure in healthy brain and peripheral tissues.