Mitochondrial permeability transition dictates mitochondrial maturation upon switch in cellular identity of hematopoietic precursors.

The mitochondrial permeability transition pore (mPTP) is a supramolecular channel that regulates exchange of solutes across cristae membranes, with executive roles in mitochondrial function and cell death. The contribution of the mPTP to normal physiology remains debated, although evidence implicates the mPTP in mitochondrial inner membrane remodeling in differentiating progenitor cells. Here, we demonstrate that strict control over mPTP conductance shapes metabolic machinery as cells transit toward hematopoietic identity. Cells undergoing the endothelial-to-hematopoietic transition (EHT) tightly control chief regulatory elements of the mPTP. During EHT, maturing arterial endothelium restricts mPTP activity just prior to hematopoietic commitment. After transition in cellular identity, mPTP conductance is restored. In utero treatment with NIM811, a molecule that blocks sensitization of the mPTP to opening by Cyclophilin D (CypD), amplifies oxidative phosphorylation (OXPHOS) in hematopoietic precursors and increases hematopoiesis in the embryo. Additionally, differentiating pluripotent stem cells (PSCs) acquire greater organization of mitochondrial cristae and hematopoietic activity following knockdown of the CypD gene, Ppif. Conversely, knockdown of Opa1, a GTPase critical for proper cristae architecture, induces cristae irregularity and impairs hematopoiesis. These data elucidate a mechanism that regulates mitochondrial maturation in hematopoietic precursors and underscore a role for the mPTP in the acquisition of hematopoietic fate.

Dynamic interaction of REEP5-MFN1/2 enables mitochondrial hitchhiking on tubular ER.

Mitochondrial functions can be regulated by membrane contact sites with the endoplasmic reticulum (ER). These mitochondria-ER contact sites (MERCs) are functionally heterogeneous and maintained by various tethers. Here, we found that REEP5, an ER tubule-shaping protein, interacts with Mitofusins 1/2 to mediate mitochondrial distribution throughout the cytosol by a new transport mechanism, mitochondrial "hitchhiking" with tubular ER on microtubules. REEP5 depletion led to reduced tethering and increased perinuclear localization of mitochondria. Conversely, increasing REEP5 expression facilitated mitochondrial distribution throughout the cytoplasm. Rapamycin-induced irreversible REEP5-MFN1/2 interaction led to mitochondrial hyperfusion, implying that the dynamic release of mitochondria from tethering is necessary for normal mitochondrial distribution and dynamics. Functionally, disruption of MFN2-REEP5 interaction dynamics by forced dimerization or silencing REEP5 modulated the production of mitochondrial reactive oxygen species (ROS). Overall, our results indicate that dynamic REEP5-MFN1/2 interaction mediates cytosolic distribution and connectivity of the mitochondrial network by "hitchhiking" and this process regulates mitochondrial ROS, which is vital for multiple physiological functions.

Mitochondrial-derived compartments remove surplus proteins from the outer mitochondrial membrane.

The outer mitochondrial membrane (OMM) creates a boundary that imports most of the mitochondrial proteome while removing extraneous or damaged proteins. How the OMM senses aberrant proteins and remodels to maintain OMM integrity remains unresolved. Previously, we identified a mitochondrial remodeling mechanism called the mitochondrial-derived compartment (MDC) that removes a subset of the mitochondrial proteome. Here, we show that MDCs specifically sequester proteins localized only at the OMM, providing an explanation for how select mitochondrial proteins are incorporated into MDCs. Remarkably, selective sorting into MDCs also occurs within the OMM, as subunits of the translocase of the outer membrane (TOM) complex are excluded from MDCs unless assembly of the TOM complex is impaired. Considering that overloading the OMM with mitochondrial membrane proteins or mistargeted tail-anchored membrane proteins induces MDCs to form and sequester these proteins, we propose that one functional role of MDCs is to create an OMM-enriched trap that segregates and sequesters excess proteins from the mitochondrial surface.

MICU1 and MICU2 control mitochondrial calcium signaling in the mammalian heart.

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.

BRG1 promotes liver cancer cell proliferation and metastasis by enhancing mitochondrial function and ATP5A1 synthesis through TOMM40.

Hepatocellular carcinoma (HCC) is one of the most lethal malignant tumors worldwide. Brahma-related gene 1 (BRG1), as a catalytic ATPase, is a major regulator of gene expression and is known to mutate and overexpress in HCC. The purpose of this study was to investigate the mechanism of action of BRG1 in HCC cells. In our study, BRG1 was silenced or overexpressed in human HCC cell lines. Transwell and wound healing assays were used to analyze cell invasiveness and migration. Mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (mPTP) detection were used to evaluate mitochondrial function in HCC cells. Colony formation and cell apoptosis assays were used to evaluate the effect of BRG1/TOMM40/ATP5A1 on HCC cell proliferation and apoptosis/death. Immunocytochemistry (ICC), immunofluorescence (IF) staining and western blot analysis were used to determine the effect of BRG1 on TOMM40, ATP5A1 pathway in HCC cells. As a result, knockdown of BRG1 significantly inhibited cell proliferation and invasion, promoted apoptosis in HCC cells, whereas BRG1 overexpression reversed the above effects. Overexpression of BRG1 can up-regulate MMP level, inhibit mPTP opening and activate TOMM40, ATP5A1 expression. Our results suggest that BRG1, as an oncogene, promotes HCC progression by regulating TOMM40 affecting mitochondrial function and ATP5A1 synthesis. Targeting BRG1 may represent a new and effective way to prevent HCC development.

Bongkrekic acid alleviates airway inflammation via breaking the mPTP/mtDAMPs/RAGE feedback loop in a steroid-insensitive asthma model.

Mitochondrial dysfunction is critical in the pathogenesis of asthma. Mitochondrial permeability transition pore (mPTP) regulates the release of mitochondrial damage-associated molecular patterns (mtDAMPs) to maintain mitochondrial homeostasis. Bongkrekic acid (BKA) is a highly selective inhibitor of mPTP opening, participates the progression of various diseases. This research investigated the exact roles of BKA and mPTP in the pathogenesis of asthma and elucidated its underlying mechanisms. In the present study, cytochrome c, one of the mtDAMPs, levels were elevated in asthmatic patients, and associated to airway inflammation and airway obstruction. BKA, the inhibitor of mPTP markedly reversed TDI-induced airway hyperresponsiveness, airway inflammation, and mitochondrial dysfunction. Pretreatment with mitochondrial precipitation, to simulate the release of mtDAMPs, further increased TDI-induced airway inflammation and the expression of RAGE in mice. Administration of the inhibitor of RAGE, FPS-ZM1, alleviated the airway inflammation, the abnormal open of mPTP and mitochondrial dysfunction induced by mtDAMPs and TDI. Furthermore, stimulation with different mtDAMPs activated RAGE signaling in human bronchial epithelial cells. Accordingly, our study indicated that mPTP was important and BKA was efficient in alleviating inflammation in TDI-induced asthma. A positive feedback loop involving mPTP, mtDAMPs and RAGE was present in TDI-induced asthma, indicating that mPTP might serve as a potential therapeutic target for asthma.

Metal Uptake by Mitochondrial Carrier Family Proteins Using Lactococcus lactis.

Metal ion homeostasis in mitochondria is essential to maintaining proper cellular physiology. However, the ability of metals to bind off target or form complexes with multiple metabolites presents major challenges to understanding the mechanisms that govern this homeostasis. Adding further to the complexity, some of the major mitochondrial transporters have shown substrate promiscuity. In many cases, mitochondrial metals are found in the matrix compartment that is surrounded by the impermeable inner membrane. Four major classes of transporters facilitate the movement of solute across the inner membrane. These are mitochondrial carrier family, ATP-binding cassette transporters, mitochondrial pyruvate carriers, and sideroflexins. For iron, the matrix is the site of iron-sulfur clusters and heme synthesis and therefore transport must occur in a coordinated fashion with the cellular needs for these critical cofactors. Iron could be transported in numerous forms as it has been shown to form complexes with abundant metabolites such as citrate, nucleotides, or glutathione. Here, we describe assays to study iron (or any metal) transport by mitochondrial carrier family proteins expressed in Lactococcus lactis using a nisin-controlled expression system.

Metabolic gene function discovery platform GeneMAP identifies SLC25A48 as necessary for mitochondrial choline import.

Organisms maintain metabolic homeostasis through the combined functions of small-molecule transporters and enzymes. While many metabolic components have been well established, a substantial number remains without identified physiological substrates. To bridge this gap, we have leveraged large-scale plasma metabolome genome-wide association studies (GWAS) to develop a multiomic Gene-Metabolite Association Prediction (GeneMAP) discovery platform. GeneMAP can generate accurate predictions and even pinpoint genes that are distant from the variants implicated by GWAS. In particular, our analysis identified solute carrier family 25 member 48 (SLC25A48) as a genetic determinant of plasma choline levels. Mechanistically, SLC25A48 loss strongly impairs mitochondrial choline import and synthesis of its downstream metabolite betaine. Integrative rare variant and polygenic score analyses in UK Biobank provide strong evidence that the SLC25A48 causal effects on human disease may in part be mediated by the effects of choline. Altogether, our study provides a discovery platform for metabolic gene function and proposes SLC25A48 as a mitochondrial choline transporter.

Enniatins A1 and B1 Modulate Calcium Flux through Alternative Pathways beyond Mitochondria.

Enniatins (ENNs) A1 and B1, previously considered ionophores, are emerging mycotoxins with effects on Ca2+ homeostasis. However, their exact mechanism of action remains unclear. This study investigated how these toxins affect Ca2+ flux in SH-SY5Y cells. ENN A1 induced Ca2+ influx through store-operated channels (SOC). The mitochondrial uncoupler FCCP reduced this influx, suggesting that the mitochondrial status influences the toxin effect. Conversely, ENN B1 did not affect SOC but acted on another Ca2+ channel, as shown when nickel, which directly blocks the Ca2+ channel pore, is added. Mitochondrial function also influenced the effects of ENN B1, as treatment with FCCP reduced toxin-induced Ca2+ depletion and uptake. In addition, both ENNs altered mitochondrial function by producing the opening of the mitochondrial permeability transition pore. This study describes for the first time that ENN A1 and B1 are not Ca2+ ionophores and suggests a different mechanism of action for each toxin.

MTCH2 in Metabolic Diseases, Neurodegenerative Diseases, Cancers, Embryonic Development and Reproduction.

Mitochondrial carrier homolog 2 (MTCH2) is a member of the solute carrier 25 family, located on the outer mitochondrial membrane. MTCH2 was first identified in 2000. The development in MTCH2 research is rapidly increasing. The most well-known role of MTCH2 is linking to the pro-apoptosis BID to facilitate mitochondrial apoptosis. Genetic variants in MTCH2 have been investigated for their association with metabolic and neurodegenerative diseases, however, no intervention or therapeutic suggestions were provided. Recent studies revealed the physiological and pathological function of MTCH2 in metabolic diseases, neurodegenerative diseases, cancers, embryonic development and reproduction via regulating mitochondrial apoptosis, metabolic shift between glycolysis and oxidative phosphorylation, mitochondrial fusion/fission, epithelial-mesenchymal transition, etc. This review endeavors to assess a total of 131 published articles to summarise the structure and physiological/pathological role of MTCH2, which has not previously been conducted. This review concludes that MTCH2 plays a crucial role in metabolic diseases, neurodegenerative diseases, cancers, embryonic development and reproduction, and the predominant molecular mechanism is regulation of mitochondrial function. This review gives a comprehensive state of current knowledgement on MTCH2, which will promote the therapeutic research of MTCH2.

Aerobic exercise-induced HIF-1α upregulation in heart failure: exploring potential impacts on MCT1 and MPC1 regulation.

BACKGROUND: The terminal stage of ischemic heart disease develops into heart failure (HF), which is characterized by hypoxia and metabolic disturbances in cardiomyocytes. The hypoxic failing heart triggers hypoxia-inducible factor-1α (HIF-1α) actions in the cells sensitized to hypoxia and induces metabolic adaptation by accumulating HIF-1α. Furthermore, soluble monocarboxylic acid transporter protein 1 (MCT1) and mitochondrial pyruvate carrier 1 (MPC1), as key nodes of metabolic adaptation, affect metabolic homeostasis in the failing rat heart. Aerobic exercise training has been reported to retard the progression of HF due to enhancing HIF-1α levels as well as MCT1 expressions, whereas the effects of exercise on MCT1 and MPC1 in HF (hypoxia) remain elusive. This research aimed to investigate the action of exercise associated with MCT1 and MPC1 on HF under hypoxia. METHODS: The experimental rat models are composed of four study groups: sham stented (SHAM), HF sedentary (HF), HF short-term exercise trained (HF-E1), HF long-term exercise trained (HF-E2). HF was initiated via left anterior descending coronary artery ligation, the effects of exercise on the progression of HF were analyzed by ventricular ultrasound (ejection fraction, fractional shortening) and histological staining. The regulatory effects of HIF-1α on cell growth, MCT1 and MPC1 protein expression in hypoxic H9c2 cells were evaluated by HIF-1α activatort/inhibitor treatment and plasmid transfection. RESULTS: Our results indicate the presence of severe pathological remodelling (as evidenced by deep myocardial fibrosis, increased infarct size and abnormal hypertrophy of the myocardium, etc.) and reduced cardiac function in the failing hearts of rats in the HF group compared to the SHAM group. Treadmill exercise training ameliorated myocardial infarction (MI)-induced cardiac pathological remodelling and enhanced cardiac function in HF exercise group rats, and significantly increased the expression of HIF-1α (p < 0.05), MCT1 (p < 0.01) and MPC1 (p < 0.05) proteins compared to HF group rats. Moreover, pharmacological inhibition of HIF-1α in hypoxic H9c2 cells dramatically downregulated MCT1 and MPC1 protein expression. This phenomenon is consistent with knockdown of HIF-1α at the gene level. CONCLUSION: The findings propose that long-term aerobic exercise training, as a non- pharmacological treatment, is efficient enough to debilitate the disease process, improve the pathological phenotype, and reinstate cardiac function in HF rats. This benefit is most likely due to activation of myocardial HIF-1α and upregulation of MCT1 and MPC1.

Mechanism of human PINK1 activation at the TOM complex in a reconstituted system.

Loss-of-function mutations in PTEN-induced kinase 1 (PINK1) are a frequent cause of early-onset Parkinson's disease (PD). Stabilization of PINK1 at the translocase of outer membrane (TOM) complex of damaged mitochondria is critical for its activation. The mechanism of how PINK1 is activated in the TOM complex is unclear. Here, we report that co-expression of human PINK1 and all seven TOM subunits in Saccharomyces cerevisiae is sufficient for PINK1 activation. We use this reconstitution system to systematically assess the role of each TOM subunit toward PINK1 activation. We unambiguously demonstrate that the TOM20 and TOM70 receptor subunits are required for optimal PINK1 activation and map their sites of interaction with PINK1 using AlphaFold structural modeling and mutagenesis. We also demonstrate an essential role of the pore-containing subunit TOM40 and its structurally associated subunits TOM7 and TOM22 for PINK1 activation. These findings will aid in the development of small-molecule activators of PINK1 as a therapeutic strategy for PD.

Icariin improves oxidative stress injury during ischemic stroke via inhibiting mPTP opening.

BACKGROUND: Ischemic stroke presents a significant threat to human health due to its high disability rate and mortality. Currently, the clinical treatment drug, rt-PA, has a narrow therapeutic window and carries a high risk of bleeding. There is an urgent need to find new effective therapeutic drugs for ischemic stroke. Icariin (ICA), a key ingredient in the traditional Chinese medicine Epimedium, undergoes metabolism in vivo to produce Icaritin (ICT). While ICA has been reported to inhibit neuronal apoptosis after cerebral ischemia-reperfusion (I/R), yet its underlying mechanism remains unclear. METHODS: PC-12 cells were treated with 200 µM H2O2 for 8 h to establish a vitro model of oxidative damage. After administration of ICT, cell viability was detected by Thiazolyl blue tetrazolium Bromide (MTT) assay, reactive oxygen species (ROS) and apoptosis level, mPTP status and mitochondrial membrane potential (MMP) were detected by flow cytometry and immunofluorescence. Apoptosis and mitochondrial permeability transition pore (mPTP) related proteins were assessed by Western blotting. Middle cerebral artery occlusion (MCAO) model was used to establish I/R injury in vivo. After the treatment of ICA, the neurological function was scored by ZeaLonga socres; the infarct volume was observed by 2,3,5-Triphenyltetrazolium chloride (TTC) staining; HE and Nissl staining were used to detect the pathological state of the ischemic cortex; the expression changes of mPTP and apoptosis related proteins were detected by Western blotting. RESULTS: In vitro: ICT effectively improved H2O2-induced oxidative injury through decreasing the ROS level, inhibiting mPTP opening and apoptosis. In addition, the protective effects of ICT were not enhanced when it was co-treated with mPTP inhibitor Cyclosporin A (CsA), but reversed when combined with mPTP activator Lonidamine (LND). In vivo: Rats after MCAO shown cortical infarct volume of 32-40%, severe neurological impairment, while mPTP opening and apoptosis were obviously increased. Those damage caused was improved by the administration of ICA and CsA. CONCLUSIONS: ICA improves cerebral ischemia-reperfusion injury by inhibiting mPTP opening, making it a potential candidate drug for the treatment of ischemic stroke.

Reduced Protein Import via TIM23 SORT Drives Disease Pathology in TIMM50-Associated Mitochondrial Disease.

TIMM50 is a core subunit of the TIM23 complex, the mitochondrial inner membrane translocase responsible for the import of pre-sequence-containing precursors into the mitochondrial matrix and inner membrane. Here we describe a mitochondrial disease patient who is homozygous for a novel variant in TIMM50 and establish the first proteomic map of mitochondrial disease associated with TIMM50 dysfunction. We demonstrate that TIMM50 pathogenic variants reduce the levels and activity of endogenous TIM23 complex, which significantly impacts the mitochondrial proteome, resulting in a combined oxidative phosphorylation (OXPHOS) defect and changes to mitochondrial ultrastructure. Using proteomic data sets from TIMM50 patient fibroblasts and a TIMM50 HEK293 cell model of disease, we reveal that laterally released substrates imported via the TIM23SORT complex pathway are most sensitive to loss of TIMM50. Proteins involved in OXPHOS and mitochondrial ultrastructure are enriched in the TIM23SORT substrate pool, providing a biochemical mechanism for the specific defects in TIMM50-associated mitochondrial disease patients. These results highlight the power of using proteomics to elucidate molecular mechanisms of disease and uncovering novel features of fundamental biology, with the implication that human TIMM50 may have a more pronounced role in lateral insertion than previously understood.

DYRK1A signalling synchronizes the mitochondrial import pathways for metabolic rewiring.

Mitochondria require an extensive proteome to maintain a variety of metabolic reactions, and changes in cellular demand depend on rapid adaptation of the mitochondrial protein composition. The TOM complex, the organellar entry gate for mitochondrial precursors in the outer membrane, is a target for cytosolic kinases to modulate protein influx. DYRK1A phosphorylation of the carrier import receptor TOM70 at Ser91 enables its efficient docking and thus transfer of precursor proteins to the TOM complex. Here, we probe TOM70 phosphorylation in molecular detail and find that TOM70 is not a CK2 target nor import receptor for MIC19 as previously suggested. Instead, we identify TOM20 as a MIC19 import receptor and show off-target inhibition of the DYRK1A-TOM70 axis with the clinically used CK2 inhibitor CX4945 which activates TOM20-dependent import pathways. Taken together, modulation of DYRK1A signalling adapts the central mitochondrial protein entry gate via synchronization of TOM70- and TOM20-dependent import pathways for metabolic rewiring. Thus, DYRK1A emerges as a cytosolic surveillance kinase to regulate and fine-tune mitochondrial protein biogenesis.

Sex-dependent phosphorylation of Argonaute 2 reduces the mitochondrial translocation of miR-181c and induces cardioprotection in females.

Obesity-induced cardiac dysfunction is growing at an alarming rate, showing a dramatic increase in global prevalence. Mitochondrial translocation of miR-181c in cardiomyocytes results in excessive reactive oxygen species (ROS) production during obesity. ROS causes Sp1, a transcription factor for MICU1, to be degraded via post-translational modification. The subsequent decrease in MICU1 expression causes mitochondrial Ca2+ accumulation, ultimately leading to a propensity for heart failure. Herein, we hypothesized that phosphorylation of Argonaute 2 (AGO2) at Ser 387 (in human) or Ser 388 (in mouse) inhibits the translocation of miR-181c into the mitochondria by increasing the cytoplasmic stability of the RNA-induced silencing complex (RISC). Initially, estrogen offers cardioprotection in pre-menopausal females against the consequences of mitochondrial miR-181c upregulation by driving the phosphorylation of AGO2. Neonatal mouse ventricular myocytes (NMVM) treated with insulin showed an increase in pAGO2 levels and a decrease in mitochondrial miR-181c expression by increasing the binding affinity of AGO2-GW182 in the RISC. Thus, insulin treatment prevented excessive ROS production and mitochondrial Ca2+ accumulation. In human cardiomyocytes, we overexpressed miR-181c to mimic pathological conditions, such as obesity/diabetes. Treatment with estradiol (E2) for 48 h significantly lowered miR-181c entry into the mitochondria through increased pAGO2 levels. E2 treatment also normalized Sp1 degradation and MICU1 transcription that normally occurs in response to miR-181c overexpression. We then investigated these findings using an in vivo model, with age-matched male, female and ovariectomized (OVX) female mice. Consistent with the E2 treatment, we show that female hearts express higher levels of pAGO2 and thus, exhibit higher association of AGO2-GW182 in cytoplasmic RISC. This results in lower expression of mitochondrial miR-181c in female hearts compared to male or OVX groups. Further, female hearts had fewer consequences of mitochondrial miR-181c expression, such as lower Sp1 degradation and significantly decreased MICU1 transcriptional regulation. Taken together, this study highlights a potential therapeutic target for conditions such as obesity and diabetes, where miR-181c is upregulated. NEW AND NOTEWORTHY: In this study, we show that the phosphorylation of Argonaute 2 (AGO2) stabilizes the RNA-induced silencing complex in the cytoplasm, preventing miR-181c entry into the mitochondria. Furthermore, we demonstrate that treatment with estradiol can inhibit the translocation of miR-181c into the mitochondria by phosphorylating AGO2. This ultimately eliminates the downstream consequences of miR-181c overexpression by mitigating excessive reactive oxygen species production and calcium entry into the mitochondria.

Human mitochondrial carriers of the SLC25 family function as monomers exchanging substrates with a ping-pong kinetic mechanism.

Members of the SLC25 mitochondrial carrier family link cytosolic and mitochondrial metabolism and support cellular maintenance and growth by transporting compounds across the mitochondrial inner membrane. Their monomeric or dimeric state and kinetic mechanism have been a matter of long-standing debate. It is believed by some that they exist as homodimers and transport substrates with a sequential kinetic mechanism, forming a ternary complex where both exchanged substrates are bound simultaneously. Some studies, in contrast, have provided evidence indicating that the mitochondrial ADP/ATP carrier (SLC25A4) functions as a monomer, has a single substrate binding site, and operates with a ping-pong kinetic mechanism, whereby ADP is imported before ATP is exported. Here we reanalyze the oligomeric state and kinetic properties of the human mitochondrial citrate carrier (SLC25A1), dicarboxylate carrier (SLC25A10), oxoglutarate carrier (SLC25A11), and aspartate/glutamate carrier (SLC25A13), all previously reported to be dimers with a sequential kinetic mechanism. We demonstrate that they are monomers, except for dimeric SLC25A13, and operate with a ping-pong kinetic mechanism in which the substrate import and export steps occur consecutively. These observations are consistent with a common transport mechanism, based on a functional monomer, in which a single central substrate-binding site is alternately accessible.

Mitochondrial calcium in cardiac ischemia/reperfusion injury and cardioprotection.

Mitochondrial calcium (Ca2+) signals play a central role in cardiac homeostasis and disease. In the healthy heart, mitochondrial Ca2+ levels modulate the rate of oxidative metabolism to match the rate of adenosine triphosphate consumption in the cytosol. During ischemia/reperfusion (I/R) injury, pathologically high levels of Ca2+ in the mitochondrial matrix trigger the opening of the mitochondrial permeability transition pore, which releases solutes and small proteins from the matrix, causing mitochondrial swelling and ultimately leading to cell death. Pharmacological and genetic approaches to tune mitochondrial Ca2+ handling by regulating the activity of the main Ca2+ influx and efflux pathways, i.e., the mitochondrial Ca2+ uniporter and sodium/Ca2+ exchanger, represent promising therapeutic strategies to protect the heart from I/R injury.

Nuclear receptor Nur77 and Yin-Yang 1 synergistically increase mitochondrial abundance and activity in macrophages.

Mitochondrial biogenesis requires precise regulation of both mitochondrial-encoded and nuclear-encoded genes. Nuclear receptor Nur77 is known to regulate mitochondrial metabolism in macrophages and skeletal muscle. Here, we compared genome-wide Nur77 binding site and target gene expression in these two cell types, which revealed conserved regulation of mitochondrial genes and enrichment of motifs for the transcription factor Yin-Yang 1 (YY1). We show that Nur77 and YY1 interact, that YY1 increases Nur77 activity, and that their binding sites are co-enriched at mitochondrial ribosomal protein gene loci in macrophages. Nur77 and YY1 co-expression synergistically increases Mrpl1 expression as well as mitochondrial abundance and activity in macrophages but not skeletal muscle. As such, we identify a macrophage-specific Nur77-YY1 interaction that enhances mitochondrial metabolism.