Mitochondrial Calcium Uniporter Complex Research Articles

The MCU and MCUb amino-terminal domains tightly interact: mechanisms for low conductance assembly of the mitochondrial calcium uniporter complex

The mitochondrial calcium (Ca2+) uniporter (MCU) complex is regulated via integration of the MCU dominant negative beta subunit (MCUb), a low conductance paralog of the main MCU pore forming protein. The MCU amino (N)-terminal domain (NTD) also modulates channel function through cation binding to the MCU regulating acidic patch (MRAP). MCU and MCUb have high sequence similarities, yet the structural and functional roles of MCUb-NTD remain unknown. Here, we report that MCUb-NTD exhibits α-helix/β-sheet structure with a high thermal stability, dependent on protein concentration. Remarkably, MCU- and MCUb-NTDs heteromerically interact with ∼nM affinity, increasing secondary structure and stability and structurally perturbing MRAP. Further, we demonstrate MCU and MCUb co-localization is suppressed upon NTD deletion concomitant with increased mitochondrial Ca2+ uptake. Collectively, our data show that MCU:MCUb NTD tight interactions are promoted by enhanced regular structure and stability, augmenting MCU:MCUb co-localization, lowering mitochondrial Ca2+ uptake and implicating an MRAP-sensing mechanism.

Mitochondrial calcium function is altered by lithium in hippocampal cell culture and triple transgenic for Alzheimer’s disease

AbstractBackgroundCalcium (Ca2+) regulate many functions in neuronal and glial cells. The Mitochondrial Calcium Uniporter (Mcu) complex is thought to be the primary pathway for Ca2+ entry into mitochondria. The Mcu protein has an important role in regulating mitochondrial Ca2+ homeostasis. Dysregulation of mitochondrial Ca2+ homeostasis has been implicated in various pathological conditions, such as Alzheimer disease. AD pathology is characterized by the progressive accumulation of amyloid β‐peptide and neurofibrillary tangles. In AD patients a significant increase in an oxidative damage and decrease in energy metabolism resulting in a mitochondrial calcium disbalance. Lithium has been used for decades to treat neurodegenerative diseases, as it has an action on several intracellular organelles, including mitochondria. The lithium regulates calcium channels, decreases oxidative stress and increases autophagic processes. Therefore, we aim to analyze whether chronic treatment with lithium in primary cultures of hippocampal neurons and in the hippocampus of triple transgenic animals for Alzheimer’s disease (3xtgAD).MethodThe cultures were treated for 7 days (dose of 0.02; 0.2 and 2mM) and 3xtgAD for 8 months (doses of 1mM and 2mM). The hippocampus were analysed by proteomic and transcriptomics.ResultOur results showed that lithium increases Mcu and Micu 3 proteins, showing that lithium has an effect on the modulation of mitochondrial calcium channels that should be explored.ConclusionMitochondrial calcium is an important mechanism for understanding neurodegenerative diseases and lithium can reverse Alzheimer’s disease‐related dysfunction.

Negative modulation of mitochondrial calcium uniporter complex protects neurons against ferroptosis

Ferroptosis is an iron- and reactive oxygen species (ROS)-dependent form of regulated cell death, that has been implicated in Alzheimer’s disease and Parkinson’s disease. Inhibition of cystine/glutamate antiporter could lead to mitochondrial fragmentation, mitochondrial calcium ([Ca2+]m) overload, increased mitochondrial ROS production, disruption of the mitochondrial membrane potential (ΔΨm), and ferroptotic cell death. The observation that mitochondrial dysfunction is a characteristic of ferroptosis makes preservation of mitochondrial function a potential therapeutic option for diseases associated with ferroptotic cell death. Mitochondrial calcium levels are controlled via the mitochondrial calcium uniporter (MCU), the main entry point of Ca2+ into the mitochondrial matrix. Therefore, we have hypothesized that negative modulation of MCU complex may confer protection against ferroptosis. Here we evaluated whether the known negative modulators of MCU complex, ruthenium red (RR), its derivative Ru265, mitoxantrone (MX), and MCU-i4 can prevent mitochondrial dysfunction and ferroptotic cell death. These compounds mediated protection in HT22 cells, in human dopaminergic neurons and mouse primary cortical neurons against ferroptotic cell death. Depletion of MICU1, a [Ca2+]m gatekeeper, demonstrated that MICU is protective against ferroptosis. Taken together, our results reveal that negative modulation of MCU complex represents a therapeutic option to prevent degenerative conditions, in which ferroptosis is central to the progression of these pathologies.

Hypertrophic cardiomyopathy is characterized by alterations of the mitochondrial calcium uniporter complex proteins: insights from patients with aortic valve stenosis versus hypertrophic obstructive cardiomyopathy

Hypertrophic cardiomyopathy is characterized by alterations of the mitochondrial calcium uniporter complex proteins: insights from patients with aortic valve stenosis versus hypertrophic obstructive cardiomyopathy

Regulation of mitochondrial calcium uniporter expression and calcium-dependent cell signalling by lncRNA Tug1 in cardiomyocytes.

Cardiomyocyte calcium homeostasis is a tightly regulated process. The mitochondrial calcium uniporter (MCU) complex can buffer elevated cytosolic Ca2+ levels and consists of pore-forming proteins including MCU, and various regulatory proteins such as mitochondrial calcium uptake proteins 1 and 2 (MICU1/2). The stoichiometry of these proteins influences the sensitivity to Ca2+ and activity of the complex. However, the factors that regulate their gene expression remain incompletely understood. Long non-coding RNAs (lncRNAs) regulate gene expression through various mechanisms, and we recently found that the lncRNA Tug1 increased the expression of Mcu and associated genes. To further explore this, we performed antisense LNA knockdown of Tug1 (Tug1 KD) in H9c2 rat cardiomyocytes. Tug1 KD increased MCU protein expression, yet pyruvate dehydrogenase dephosphorylation, which is indicative of mitochondrial Ca2+ uptake, was not enhanced. However, RNA-seq revealed that Tug1 KD increased Mcu along with differential expression of >1000 genes including many related to Ca2+ regulation pathways in the heart. To understand the effect of this on Ca2+ signalling, we measured phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its downstream target cAMP Response Element-Binding protein (CREB), a transcription factor known to drive Mcu gene expression. In response a Ca2+ stimulus, the increase in CAMKII and CREB phosphorylation was attenuated by Tug1 KD. Inhibition of CaMKII, but not CREB, partially prevented the Tug1 KD-mediated increase in Mcu. Together, these data suggest that Tug1 modulates MCU expression via a mechanism involving CAMKII and regulates cardiomyocyte Ca2+ signalling which could have important implications for cardiac function.

Modulation of oxidized low-density lipoprotein-affected macrophage efferocytosis by mitochondrial calcium uniporter in a murine model

ObjectiveEfferocytosis dysfunction contributes to the progression and rupture of atherosclerotic plaques. Efferocytosis is crucially modulated by intracytoplasmic Ca2+, and mitochondrial calcium uniporter (MCU) complex proteins serve as key channels for regulating Ca2+ concentration. Therefore, it was speculated that MCU may affect the development of atherosclerosis (AS) by regulating efferocytosis. In the present study, we aimed to investigate whether MCU could affect foam cell formation by regulating efferocytosis. MethodsWe stimulated primary macrophages (Møs) using oxidized low-density lipoprotein (ox-LDL) to mimic the atherosclerotic microenvironment and treated them with Ru360, an MCU-specific inhibitor, and UNC1062, an inhibitor of efferocytosis. Additionally, we conducted double staining to determine the Mø efferocytosis rate. We measured the expression of MCU complexes and efferocytosis-associated proteins using western blotting (WB) and real-time quantitative polymerase chain reaction (RT-qPCR), respectively. In addition, we separately detected the Ca2+ level in the cytoplasm and mitochondria (MT) using Fluo-4 AM and Rhod-2 methods. We separately determined the reactive oxygen species (ROS) level in cytoplasm and MT using dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probing method and Mito-SOXTM superoxide indicator staining. Additionally, we conducted the enzyme-linked immunosorbent assay (ELISA) to detect the production of interleukin-6 (IL-6), interleukin-18 (IL-18), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α). Oil Red O staining was performed to measure cytoplasmic lipid levels. ResultsRu360 attenuated ox-LDL-induced efferocytosis dysfunction, and attenuated the upregulation of MCU and MCUR1 induced by ox-LDL, and meanwhile attenuated the downregulation of MCUb induced by ox-LDL. Ru360 attenuated the decrease of intracytoplasmic Ca2+ concentration induced by ox- LDL, Ru360 also attenuated the ROS production induced by ox- LDL, attenuated the release of IL-6, IL-18, IL-1β, and TNF-α induced by ox- LDL, and attenuated the increase of intracytoplasmic lipid content induced by ox-LDL. UNC1062 attenuated the effects of Ru360 in reducing inflammatory cytokines and intracytoplasmic lipid content. ConclusionsIn this study, we found that MCU inhibition modulated intracytoplasmic Ca2+ concentration, improved impaired Mø efferocytosis, and reduced ROS generation. Macrophage efferocytosis removed apoptotic cells and prevented the release of inflammatory factor and foam cell formation, and this can be a potential new therapeutic target for alleviating atherosclerosis.

The Mitochondrial Calcium Uniporter (MCU): Molecular Identity and Role in Human Diseases.

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.

Abstract P3205: Differential Adaptation To Mitochondrial Ca 2+ Overload In The Left And Right Ventricles

Mitochondrial Ca 2+ (mtCa 2+ ) overload has emerged as a potential contributor to heart failure (HF), possibly through inducing oxidative stress. In HF, right ventricular (RV) function is predictive of mortality, and the RV is more vulnerable to oxidative stress than the left ventricle (LV). Therefore, how the response to mtCa 2+ overload might differ in the RV and LV is critical; however, ventricle-specific mtCa 2+ handling is still poorly understood. We sought to induce cardiac mtCa 2+ overload via genetic manipulation of the mitochondrial calcium uniporter complex (mtCU) formed by the MCU pore and several regulatory subunits. mtCU stoichiometry shapes mtCa 2+ kinetics: loss of mitochondrial calcium uptake 1 (MICU1) induces mtCa 2+ overload, and reduced essential MCU regulator (EMRE) to MCU ratio decreases mtCa 2+ uptake rate. Hypothesizing that mtCa 2+ overload differentially affects LV and RV function, we generated tamoxifen (Tmx)-inducible cardiac-specific Micu1 knockout mice ( Micu1 cKO ) . After confirming that MICU1 loss at 1 week post-Tmx resulted in mtCa 2+ overload in both ventricles, we explored how the LV and RV responses diverge. In Micu1 cKO mice, LV function assessed by echocardiography declined at 4 weeks post-Tmx but recovered partially by 6 weeks. However, impaired RV function at 4 weeks post-Tmx persisted at 6 weeks and longer, without evidence of pulmonary hypertension. Interestingly, at 7-9 weeks post-Tmx, mtCa 2+ levels and oxidative stress remained elevated in the RV but returned to control levels in the LV. Concurrently, EMRE protein levels and mtCa 2+ uptake rate were reduced only in the LV, suggesting that the LV has greater capacity to adapt to mtCa 2+ overload via downregulation of EMRE. We further traced this LV-specific adaptive response to increased maturation of the mAAA-proteases that degrade EMRE. In summary, mtCa 2+ overload induced by MICU1 deletion results in greater oxidative stress and functional impairment over time in the RV than the LV due to absence of compensatory EMRE reduction in the RV.

Reduced mitochondrial calcium uptake in macrophages is a major driver of inflammaging

Mitochondrial dysfunction is linked to age-associated inflammation or inflammaging, but underlying mechanisms are not understood. Analyses of 700 human blood transcriptomes revealed clear signs of age-associated low-grade inflammation. Among changes in mitochondrial components, we found that the expression of mitochondrial calcium uniporter (MCU) and its regulatory subunit MICU1, genes central to mitochondrial Ca2+ (mCa2+) signaling, correlated inversely with age. Indeed, mCa2+ uptake capacity of mouse macrophages decreased significantly with age. We show that in both human and mouse macrophages, reduced mCa2+ uptake amplifies cytosolic Ca2+ oscillations and potentiates downstream nuclear factor kappa B activation, which is central to inflammation. Our findings pinpoint the mitochondrial calcium uniporter complex as a keystone molecular apparatus that links age-related changes in mitochondrial physiology to systemic macrophage-mediated age-associated inflammation. The findings raise the exciting possibility that restoring mCa2+ uptake capacity in tissue-resident macrophages may decrease inflammaging of specific organs and alleviate age-associated conditions such as neurodegenerative and cardiometabolic diseases.

Inverse Regulation of SGK1 and the Mitochondrial Calcium Uniporter Complex in Aortic Smooth Muscle Cells from Mice and Humans with Obesity and Type 2 Diabetes

Background: Individuals with a body mass index (BMI) of ≥30 who are affected with obesity have an increased risk of developing type 2 diabetes (T2D) which exacerbates vascular disease and cardiovascular adverse events such as strokes and heart attacks. However, the molecular mechanisms that underlie obesity- and T2D-induced vascular disease are not fully understood. We have shown that serum and glucocorticoid-inducible kinase 1 (SGK1) is up-regulated in vascular smooth muscle cells (VSMC) of mice fed a high fat to induce obesity and hyperglycemia, a main symptom of T2D. Moreover, knocking out SGK1 in VSMC protects against vascular damage by abolishing the mitochondrial dysfunction that typically accompanies obesity and T2D. Vascular protection correlated with elevated levels of the mitochondrial calcium uniporter complex suggesting that our newly discovered SGK1/MCU pathway plays a role in obesity-associated T2D vascular disease development in humans. MCU is a multimeric complex that regulates Ca2+ influx into the mitochondrial matrix and is tightly controlled by different regulatory subunits with varying functions but its regulation in VSMC exposed to obesity and T2D is unknown. Thus, we tested the hypothesis that obesity and T2D exacerbates VSMC dysfunction via a mechanism that involves SGK1-dependent negative regulation of the MCU complex. Methods: We examined regulation of SGK1 and the MCU complex in aortic VSMC from lean and human subjects with obesity and lean and high fat diet-induced obese wildtype (VSMCWT) and VSMC-SGK1 knockout (VSMCKO) mice. To this end, western blot analysis was performed on VSMC total protein extracts from individuals with BMI = 23.5 ± 0.25 (Lean) and BMI = 37.6 ± 7.2 (Obese) with or without T2D and mice fed a 10 kcal% low fat or 45 kcal% high fat diet for eight weeks. Data was analyzed by 2-Way Analysis of Variance. Results: VSMCWT from obese mice showed reduced levels of MCU and its gatekeeping regulatory subunits, MICU1 and MICU2 compared to lean VSMCWT mice. Knocking out SGK1 in VSMC abolished obesity-related downregulation of MCU and its gatekeeper subunits. As observed in obese mice, SGK1 protein was enriched in VSMC from individuals with obesity. Interestingly, T2D potentiated up-regulation of SGK1 independent of BMI classification. In addition, VSMC from persons affected with obesity showed decreased levels of the MICU2 gatekeeping subunit and this decrease was exaggerated in VSMC from obese individuals with T2D. Conclusions: These findings show that obesity enhances SGK1 abundance in VSMC which may promote negative regulation of the MCU complex and that T2D may exacerbate these effects in the vasculature of humans and rodents. Furthermore, the SGK1/MCU novel pathway may play a permissive role in obesity-related VSMC dysfunction and consequent vascular disease. NIH RCMI G12 Grant: 5G12MD007602 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Evidence supporting the MICU1 occlusion mechanism and against the potentiation model in the mitochondrial calcium uniporter complex

The mitochondrial calcium uniporter is a Ca2+ channel that imports cytoplasmic Ca2+ into the mitochondrial matrix to regulate cell bioenergetics, intracellular Ca2+ signaling, and apoptosis. The uniporter contains the pore-forming MCU subunit, an auxiliary EMRE protein, and the regulatory MICU1/MICU2 subunits. Structural and biochemical studies have suggested that MICU1 gates MCU by blocking/unblocking the pore. However, mitoplast patch-clamp experiments argue that MICU1 does not block, but instead potentiates MCU via allosteric mechanisms. Here, we address this direct clash of the proposed MICU1 function. Supporting the MICU1-occlusion mechanism, patch-clamp demonstrates that purified MICU1 strongly suppresses MCU Ca2+ currents, and this inhibition is abolished by mutating the MCU-interacting K126 residue. Moreover, a membrane-depolarization assay shows that MICU1 prevents MCU-mediated Na+ flux into intact mitochondria under Ca2+-free conditions. Examining the observations underlying the potentiation model, we found that MICU1 occlusion was not detected in mitoplasts not because MICU1 cannot block, but because MICU1 dissociates from the uniporter complex. Furthermore, MICU1 depletion reduces uniporter transport not because MICU1 can potentiate MCU, but because EMRE is down-regulated. These results firmly establish the molecular mechanisms underlying the physiologically crucial process of uniporter regulation by MICU1.

The mitochondrial calcium uniporter complex–A play in five acts

Mitochondrial Ca2+ (mitCa2+) uptake controls both intraorganellar and cytosolic functions. Within the organelle, [Ca2+] increases regulate the activity of tricarboxylic acid (TCA) cycle enzymes, thus sustaining oxidative metabolism and ATP production. Reactive oxygen species (ROS) are also generated as side products of oxygen consumption. At the same time, mitochondria act as buffers of cytosolic Ca2+ (cytCa2+) increases, thus regulating Ca2+-dependent cellular processes. In pathological conditions, mitCa2+ overload triggers the opening of the mitochondrial permeability transition pore (mPTP) and the release of apoptotic cofactors. MitCa2+ uptake occurs in response of local [Ca2+] increases in sites of proximity between the endoplasmic reticulum (ER) and the mitochondria and is mediated by the mitochondrial Ca2+ uniporter (MCU), a highly selective channel of the inner mitochondrial membrane (IMM). Both channel and regulatory subunits form the MCU complex (MCUC). Cryogenic electron microscopy (Cryo-EM) and crystal structures revealed the correct assembly of MCUC and the function of critical residues for the regulation of Ca2+ conductance.

Layer-specific mitochondrial diversity across hippocampal CA2 dendrites.

CA2 is an understudied subregion of the hippocampus that is critical for social memory. Previous studies identified multiple components of the mitochondrial calcium uniporter (MCU) complex as selectively enriched in CA2. The MCU complex regulates calcium entry into mitochondria, which in turn regulates mitochondrial transport and localization to active synapses. We found that MCU is strikingly enriched in CA2 distal apical dendrites, precisely where CA2 neurons receive entorhinal cortical input carrying social information. Furthermore, MCU-enriched mitochondria in CA2 distal dendrites are larger compared to mitochondria in CA2 proximal apical dendrites and neighboring CA1 apical dendrites, which was confirmed in CA2 with genetically labeled mitochondria and electron microscopy. MCU overexpression in neighboring CA1 led to a preferential localization of MCU in the proximal dendrites of CA1 compared to the distal dendrites, an effect not seen in CA2. Our findings demonstrate that mitochondria are molecularly and structurally diverse across hippocampal cell types and circuits, and suggest that MCU can be differentially localized within dendrites, possibly to meet local energy demands.

Acquired disorders of mitochondrial metabolism and dynamics in pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is an orphan disease of the cardiopulmonary unit that reflects an obstructive pulmonary vasculopathy and presents with hypertrophy, inflammation, fibrosis, and ultimately failure of the right ventricle (RVF). Despite treatment using pulmonary hypertension (PH)-targeted therapies, persistent functional impairment reduces the quality of life for people with PAH and death from RVF occurs in approximately 40% of patients within 5 years of diagnosis. PH-targeted therapeutics are primarily vasodilators and none, alone or in combination, are curative. This highlights a need to therapeutically explore molecular targets in other pathways that are involved in the pathogenesis of PAH. Several candidate pathways in PAH involve acquired mitochondrial dysfunction. These mitochondrial disorders include: 1) a shift in metabolism related to increased expression of pyruvate dehydrogenase kinase and pyruvate kinase, which together increase uncoupled glycolysis (Warburg metabolism); 2) disruption of oxygen-sensing related to increased expression of hypoxia-inducible factor 1α, resulting in a state of pseudohypoxia; 3) altered mitochondrial calcium homeostasis related to impaired function of the mitochondrial calcium uniporter complex, which elevates cytosolic calcium and reduces intramitochondrial calcium; and 4) abnormal mitochondrial dynamics related to increased expression of dynamin-related protein 1 and its binding partners, such as mitochondrial dynamics proteins of 49kDa and 51kDa, and depressed expression of mitofusin 2, resulting in increased mitotic fission. These acquired mitochondrial abnormalities increase proliferation and impair apoptosis in most pulmonary vascular cells (including endothelial cells, smooth muscle cells and fibroblasts). In the RV, Warburg metabolism and induction of glutaminolysis impairs bioenergetics and promotes hypokinesis, hypertrophy, and fibrosis. This review will explore our current knowledge of the causes and consequences of disordered mitochondrial function in PAH.

Molecular and cellular mechanisms underlying tissue-specific MICU-dimer assembly in the mitochondrial calcium uniporter complex.

The mitochondria calcium uniporter is a multi-subunit Ca2+ channel that mediates mitochondrial Ca2+ uptake. It regulates multiple physiological processes including oxidative phosphorylation, intracellular Ca2+ signaling, and apoptosis. The uniporter is activated by Ca2+—It remains closed at resting cellular [Ca2+] and becomes open when stimulated by intracellular Ca2+ signals. Previous work suggests that in non-neuronal cells, such Ca2+ activation is exclusively mediated by a MICU1-2 heterodimer. Here, we find that kidney and skeletal muscle uniporters also complex with a MICU1-1 homodimer. Kinetic analyses show that the uniporter is more readily activated by Ca2+ when complexed with MICU1-1 (K0.5=0.6 µM) than MICU1-2 (K0.5=1.2 µM). Thus, tissues can create specific mitochondrial Ca2+ uptake properties by varying the population of MICU1-1 and MICU1-2. Here, we demonstrate two findings to establish the mechanisms by which cells control the relative abundance of these MICU dimers. Firstly, MICU1 has a >50-fold tendency to dimerize with MICU1 than MICU2; Secondly, mitochondria import MICU2 faster than MICU1 to maintain an excess of MICU2 monomers while the MICU1 monomer is depleted. In several types of cells, due to this MICU2 excess in mitochondria, an imported MICU1 monomer can only encounter MICU2 to form MICU1-2 heterodimers. Other types of cells can produce MICU1-1 by importing MICU1 slightly faster so MICU1 could form homodimers due to its higher tendency to homodimerize. Contradicting previous studies, we show that a conserved MICU intersubunit disulfide is not required for the MICUs to regulate uniporter transport. Instead, this disulfide functions to protect properly assembled MICU dimers from proteolytic degradation by YME1L1. These results shed light on the molecular and cellular mechanisms by which different types of cells can produce unique mitochondrial Ca2+ uptake properties to fulfill their unique physiological functions.

Mitochondrial sodium/calcium exchanger NCLX regulates glycolysis in astrocytes, impacting on cognitive performance.

Intracellular Ca2+ concentrations are strictly controlled by plasma membrane transporters, the endoplasmic reticulum, and mitochondria, in which Ca2+ uptake is mediated by the mitochondrial calcium uniporter complex (MCUc), while efflux occurs mainly through the mitochondrial Na+ /Ca2+ exchanger (NCLX). RNAseq database repository searches led us to identify the Nclx transcript as highly enriched in astrocytes when compared with neurons. To assess the role of NCLX in mouse primary culture astrocytes, we inhibited its function both pharmacologically or genetically. This resulted in re-shaping of cytosolic Ca2+ signaling and a metabolic shift that increased glycolytic flux and lactate secretion in a Ca2+ -dependent manner. Interestingly, in vivo genetic deletion of NCLX in hippocampal astrocytes improved cognitive performance in behavioral tasks, whereas hippocampal neuron-specific deletion of NCLX impaired cognitive performance. These results unveil a role for NCLX as a novel modulator of astrocytic glucose metabolism, impacting on cognition.

Identification and Validation of a Mitochondria Calcium Uptake-Related Gene Signature for Predicting Prognosis in COAD.

Background: Mitochondrial calcium uniporter (MCU) complex has been reported to be associated with the tumor occurrence and development in varieties of malignancies. However, the role of MCU complex in colon adenocarcinoma (COAD) remains unclear. Therefore, we constructed a risk score signature based on the MCU complex members to predict the prognosis and response to immunotherapy for patients with COAD. Methods: The MCU complex-associated risk signature (MCUrisk) was constructed based on the expressions of MCU, MCUb, MCUR1, SMDT1, MICU1, MICU2, and MICU3 in COAD. The immune score, stromal score, tumor purity and estimate score were calculated by the ESTIMATE algorithm. We systematically evaluated the relationship among the MCUrisk, mutation signature, immune cell infiltration, and immune checkpoint molecules. The response to immunotherapy was quantified by the Tumor Immune Dysfunction and Exclusion (TIDE). Results: Our results showed that high score of MCUrisk was a worse factor for overall survival (OS) in COAD, and MCUrisk score was significantly higher in advanced COAD. The mutation landscape was different between the MCUrisk-high and MCUrisk-low groups, and the mutation rate of TP53 was remarkably higher in MCUrisk-high group, which strongly suggested TP53 mutation might be associated with mitochondrial calcium dyshomeostasis in COAD. Furthermore, MCUrisk score was negatively correlated with tumor mutation burden (TMB), and combining risk score and TMB as a novel index was better than TMB alone in predicting the prognosis for COAD patients. The compositions of Tregs and M0/M2 macrophages were significantly increased in MCUrisk-high group, whereas CD4+ T cells was significantly decreased in MCUrisk-high group. Consistently, the immune score was lower in MCUrisk-high group. The expression levels of immune checkpoint molecules were negatively correlated with the MCUrisk score, including CD58 and CD226. Furthermore, a lower MCUrisk score indicated better response to immunotherapy, and combining risk score and immune score was a novel indicator to precisely predict the response to immuotherapy for COAD patients. Conclusion: Altogether, a novel MCUrisk signature was constructed based on the mitochondrial calcium uptake-associated genes, and a lower MCUrisk score may predict better OS outcome and better response to immunotherapy in COAD.

Selective and reversible disruption of mitochondrial inner membrane protein complexes by lipophilic cations

Triphenylphosphonium (TPP) derivatives are commonly used to target chemical into mitochondria. We show that alkyl-TPP cause reversible, dose- and hydrophobicity-dependent alterations of mitochondrial morphology and function and a selective decrease of mitochondrial inner membrane proteins including subunits of the respiratory chain complexes, as well as components of the mitochondrial calcium uniporter complex. The treatment with alkyl-TPP resulted in the cleavage of the pro-fusion and cristae organisation regulator Optic atrophy-1. The structural and functional effects of alkyl-TPP were found to be reversible and not merely due to loss of membrane potential. A similar effect was observed with the mitochondria-targeted antioxidant MitoQ.

Mechanisms and significance of tissue-specific MICU regulation of the mitochondrial calcium uniporter complex

Mitochondrial Ca2+ uptake, mediated by the mitochondrial Ca2+ uniporter, regulates oxidative phosphorylation, apoptosis, and intracellular Ca2+ signaling. Previous studies suggest that non-neuronal uniporters are exclusively regulated by a MICU1-MICU2 heterodimer. Here, we show that skeletal-muscle and kidney uniporters also complex with a MICU1-MICU1 homodimer and that human/mouse cardiac uniporters are largely devoid of MICUs. Cells employ protein-importation machineries to fine-tune the relative abundance of MICU1 homo- and heterodimers and utilize a conserved MICU intersubunit disulfide to protect properly assembled dimers from proteolysis by YME1L1. Using the MICU1 homodimer or removing MICU1 allows mitochondria to more readily take up Ca2+ so that cells can produce more ATP in response to intracellular Ca2+ transients. However, the trade-off is elevated ROS, impaired basal metabolism, and higher susceptibility to death. These results provide mechanistic insights into how tissues can manipulate mitochondrial Ca2+ uptake properties to support their unique physiological functions.

Differentiation-Induced Rearrangement of the Mitochondrial Calcium Uniporter Complex Regulates T-Cell-Mediated Immunity

Differentiation-Induced Rearrangement of the Mitochondrial Calcium Uniporter Complex Regulates T-Cell-Mediated Immunity