Inhibition of mitochondrial permeability transition by deletion of the ANT family and CypD

Determination of ADP/ATP translocase isoform ratios in malignancy and cellular senescence

Cellular senescence has recently been recognized as a significant contributor to the poor prognosis of glioblastoma, one of the most aggressive brain tumors. Consequently, effectively eliminating senescent glioblastoma cells could benefit patients. Human ADP/ATP translocases (ANTs) play a role in oxidative phosphorylation in both normal and tumor cells. Previous research has shown that the sensitivity of senescent cells to mitochondria-targeted senolytics depends on the level of ANT2. Here, we systematically mapped the transcript and protein levels of ANT isoforms in various types of senescence and glioblastoma tumorigenesis. We employed bioinformatics analysis, targeted mass spectrometry, RT-PCR, immunoblotting, and assessment of cellular energy state to elucidate how individual ANT isoforms are expressed during the development of senescence in noncancerous and glioblastoma cells. We observed a consistent elevation of ANT1 protein levels across all tested senescence types, while ANT2 and ANT3 exhibited variable changes. Alterations in ANT protein isoform levels correlated with shifts in the cellular oxygen consumption rate. Our findings suggest that ANT isoforms are mutually interchangeable for oxidative phosphorylation and manipulating individual ANT isoforms could have potential for senolytic therapy.

Cryo-EM structure of the brine shrimp mitochondrial ATP synthase suggests an inactivation mechanism for the ATP synthase leak channel

Mammalian mitochondria undergo Ca2+-induced and cyclosporinA (CsA)-regulated permeability transition (mPT) by activating the mitochondrial permeability transition pore (mPTP) situated in mitochondrial inner membranes. Ca2+-induced prolonged openings of mPTP under certain pathological conditions result in mitochondrial swelling and rupture of the outer membrane, leading to mitochondrial dysfunction and cell death. While the exact molecular composition and structure of mPTP remain unknown, mammalian ATP synthase was reported to form voltage and Ca2+-activated leak channels involved in mPT. Unlike in mammals, mitochondria of the crustacean Artemia franciscana have the ability to accumulate large amounts of Ca2+ without undergoing the mPT. Here, we performed structural and functional analysis of A. franciscana ATP synthase to study the molecular mechanism of mPTP inhibition in this organism. We found that the channel formed by the A. franciscana ATP synthase dwells predominantly in its inactive state and is insensitive to Ca2+, in contrast to porcine heart ATP synthase. Single-particle cryo-electron microscopy (cryo-EM) analysis revealed distinct structural features in A. franciscana ATP synthase compared with mammals. The stronger density of the e-subunit C-terminal region and its enhanced interaction with the c-ring were found in A. franciscana ATP synthase. These data suggest an inactivation mechanism of the ATP synthase leak channel and its possible contribution to the lack of mPT in this organism.

Adenine Nucleotide Translocase 1 Promotes Functional Integrity of Mitochondria via Activating DDIT3-CytC Pathway and Intensifying Actin Filament Structures

Adenine nucleotide translocase 1 (ANT1), involved in exchanging ATP and ADP across the mitochondrial inner membrane, is downregulated in mouse brains with Parkinsonian variations. To further explore the role of ANT1 in neuronal cells, an intensive investigation was conducted by introducing overexpressed ANT1 and ANT1 mutant at Asn177 into neuroblastoma SH-SY5Y cells treated with MPP+. Consequently, ANT1 was found to be involved in maintaining mitochondrial functions by attenuating ROS levels and ameliorating a long-lasting mPTPs opening and aberrant mitochondrial membrane potential (△Ψm) induced by MPP+. RNA-Seq analysis revealed that the processes including respiration, mitochondrial transporting, mitochondrial organization and apoptosis were highly facilitated in response to ANT1 supplement under MPP+ treatment. Additionally, ANT1 enrichment promoted a clearance of the damaged cells via activating the DDIT3-CytC-related pathway and resulted in an intensified structure of actin microfilaments. However, ANT1 mutant served as a causative factor, since it led to mitochondrial dysfunction via promoting a long-lasting mPTPs opening, inactivating DDIT3-CytC-related pathway and strongly impairing actin microfilaments. These observations are helpful to improve the understanding of the role of ANT1 in regulating mitochondrial functions in neuronal cells and to explore a potential therapeutic implication of ANT1 for Parkinson's disease as a promising target.

Exploring genetic associations and drug targets for mitochondrial proteins and schizophrenia risk

Numerous observational studies have highlighted associations between mitochondrial dysfunction and schizophrenia (SCZ), yet the causal relationship remains elusive. This study aims to elucidate the causal link between mitochondria-associated proteins and SCZ. We used summary data from a genome-wide association study (GWAS) of 66 mitochondria-associated proteins in 3,301 individuals from Europe, as well as a GWAS on the large, multi-ethnic ancestry of SCZ, involving 76,755 cases and 243,649 controls. We conducted bidirectional two-sample Mendelian randomization (MR) analyses, with inverse variance weighting (IVW) as the primary method. To account for multi-directionality and ensure robustness, we included MR-Egger, weighted median (WM), weighted mode, and simple mode methods as supplementary sensitivity analyses. Moreover, we explored the GWAS catalog and the Drug-Gene Interaction Database (DGIdb) to identify and evaluate potential therapeutic targets. MR analysis revealed significant genetically determined causal associations between ETHE1 (OR: 1.06), SOD (OR: 0.97), CALU3 (OR: 1.03), and C1QBP (OR: 1.05) and SCZ. According to the reverse MR analysis, a causal relationship was shown between SCZ and CA5A (OR: 1.09), DLD (OR: 1. 08), AIF1 (OR: 0.93), SerRS (OR: 0.93) and MULA of NFKB1 (OR: 0.77). After conducting the gene-drug analysis, HRG, F12, GPLD1, C1R, BCHE, CFH, PON1, and CA5A were identified as promising therapeutic targets. This present study reveals a significant causal relationship between mitochondria-associated proteins and SCZ, offering valuable insights into the disease's pathogenicity and identifying potential therapeutic targets for drug development.

Adenine nucleotide translocator and ATP synthase cooperate in mediating the mitochondrial permeability transition

The permeability transition (PT) is a permeability increase of the mitochondrial inner membrane causing mitochondrial swelling in response to matrix Ca2+. The PT is mediated by regulated channel(s), the PT pore(s) (PTP), which can be generated by at least two components, adenine nucleotide translocator (ANT) and ATP synthase. Whether these provide independent permeation pathways remains to be established. Here, we assessed the contribution of ANT to the PT based on the effects of the selective ANT inhibitors atractylate (ATR) and bongkrekate (BKA), which trigger and inhibit channel formation by ANT, respectively. BKA partially inhibited Ca2+-dependent PT and did not prevent the inducing effect of phenylarsine oxide, which was still present in mouse embryonic fibroblasts deleted for all ANT isoforms. The contribution of ANT to the PT emerged at pH 6.5 (a condition that inhibits ATP synthase channel opening) in the presence of ATR, which triggered mitochondrial swelling and elicited currents in patch-clamped mitoplasts. Unexpectedly, ANT-dependent PT at pH 6.5 could also be stimulated by benzodiazepine-423 [a selective ligand of the oligomycin sensitivity conferral protein (OSCP) subunit of ATP synthase], suggesting that the ANT channel is regulated by the peripheral stalk of ATP synthase. In keeping with docking simulations, ANT could be co-immunoprecipitated with ATP synthase subunits c and g, and oligomycin (which binds adjacent c subunits) decreased the association of ANT with subunit c. These results reveal a close cooperation between ANT and ATP synthase in the PT and open new perspectives in the study of this process. KEY POINTS: We have assessed the relative role of adenine nucleotide translocator (ANT) and ATP synthase in generating the mitochondrial permeability transition (PT). At pH 7.4, bongkrekate had little effect on Ca2+-dependent PT, and did not prevent the inducing effect of phenylarsine oxide, which was still present in mouse embryonic fibroblasts deleted for all ANT isoforms. The contribution of ANT emerged at pH 6.5 (which inhibits ATP synthase channel opening) in the presence of atractylate, which triggered mitochondrial swelling and elicited currents in patch-clamped mitoplasts. Benzodiazepine-423, a selective ligand of the oligomycin sensitivity conferral protein subunit of ATP synthase, stimulated ANT-dependent PT at pH 6.5, suggesting that the ANT channel is regulated by the peripheral stalk of ATP synthase. ANT could be co-immunoprecipitated with ATP synthase subunits c and g; oligomycin, which binds adjacent c subunits, decreased the association with subunit c, in keeping with docking simulations.

Cognitive impairment caused by compromised hepatic ketogenesis is prevented by endurance exercise

Extensive research has demonstrated endurance exercise to be neuroprotective. Whether these neuroprotective benefits are mediated, in part, by hepatic ketone production remains unclear. To investigate the role of hepatic ketone production on brain health during exercise, healthy 6-month-old female rats underwent viral knockdown of the rate-limiting enzyme in the liver that catalyses the first reaction in ketogenesis: 3-hydroxymethylglutaryl-CoA synthase 2 (HMGCS2). Rats were then subjected to either a bout of acute exercise or 4 weeks of chronic treadmill running (5 days/week) and cognitive behavioural testing. Acute exercise elevated ketone plasma concentration 1 h following exercise. Hepatic HMGCS2 knockdown, verified by protein expression, reduced ketone plasma concentration 1 h after acute exercise and 48 h after chronic exercise. Proteomic analysis and enrichment of the frontal cortex revealed hepatic HMGCS2 knockdown reduced markers of mitochondrial function 1 h after acute exercise. HMGCS2 knockdown significantly reduced state 3 complex I + II respiration in isolated mitochondria from the frontal cortex after chronic exercise. Spatial memory and protein markers of synaptic plasticity were significantly reduced by HMGCS2 knockdown. These deficiencies were prevented by chronic endurance exercise training. In summary, these are the first data to propose that hepatic ketogenesis is required to maintain cognition and mitochondrial function, irrespective of training status, and that endurance exercise can overcome neuropathology caused by insufficient hepatic ketogenesis. These results establish a mechanistic link between liver and brain health that enhance our understanding of how peripheral tissue metabolism influences brain health. KEY POINTS: Decades of literature demonstrate endurance exercise to be neuroprotective. Whether neuroprotective benefits are mediated, in part, by hepatic ketone production remains unclear. This study provides the first set of data that suggest hepatic ketogenesis is required to maintain cognition, synaptic plasticity and mitochondrial function. These data indicate endurance exercise can protect against cognitive decline caused by compromised hepatic ketogenesis. These results establish a mechanistic link between liver and brain function, prompting further investigation of how hepatic metabolism influences brain health.

Mechanisms of postischemic cardiac death and protection following myocardial injury

Acute myocardial infarction (MI) is a leading cause of death worldwide. Although with current treatment, acute mortality from MI is low, the damage and remodeling associated with MI are responsible for subsequent heart failure. Reducing cell death associated with acute MI would decrease the mortality associated with heart failure. Despite considerable study, the precise mechanism by which ischemia and reperfusion (I/R) trigger cell death is still not fully understood. In this Review, we summarize the changes that occur during I/R injury, with emphasis on those that might initiate cell death, such as calcium overload and oxidative stress. We review cell-death pathways and pathway crosstalk and discuss cardioprotective approaches in order to provide insight into mechanisms that could be targeted with therapeutic interventions. Finally, we review cardioprotective clinical trials, with a focus on possible reasons why they were not successful. Cardioprotection has largely focused on inhibiting a single cell-death pathway or one death-trigger mechanism (calcium or ROS). In treatment of other diseases, such as cancer, the benefit of targeting multiple pathways with a "drug cocktail" approach has been demonstrated. Given the crosstalk between cell-death pathways, targeting multiple cardiac death mechanisms should be considered.

Modulation of mitochondrial permeability transition pores in reperfusion injury: Mechanisms and therapeutic approaches

Ischemia/reperfusion injury is attracting continuous interest in science for two reasons: because it affects several clinical conditions and because it has been identified, albeit in broad terms, the molecular entity becoming activated by the reperfusion damage paradoxes. Indeed, calcium, oxygen-dependent oxidative stress and pH would activate conformational changes in the mitochondrial cristae embedded F1/FO ATP synthase, allowing the formation of pores in the inner mitochondrial membrane thus increasing its permeability. This is a key determinant for mitochondrial stress, cell death and tissue dysfunction. Targeting each of these factors has never contributed to improved clinical outcome of the patients affected by reperfusion damage; now, the focus on the PTP opening could represent the closest target to solve this pathway made by extensive cell death when the tissues become revascularized. In this review, we summarized last knowledge about the structure, the modulation and the therapeutic targeting of the PTP, focusing on ATP synthase and cardiac ischemia/reperfusion.

Mitochondrial dysfunction in pancreatic acinar cells: mechanisms and therapeutic strategies in acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disease of the pancreas and a complex process involving multiple factors, with mitochondrial damage playing a crucial role. Mitochondrial dysfunction is now considered a key driver in the development of AP. This dysfunction often presents as increased oxidative stress, altered membrane potential and permeability, and mitochondrial DNA damage and mutations. Under stress conditions, mitochondrial dynamics and mitochondrial ROS production increase, leading to decreased mitochondrial membrane potential, imbalanced calcium homeostasis, and activation of the mitochondrial permeability transition pore. The release of mitochondrial DNA (mtDNA), recognized as damage-associated molecular patterns, can activate the cGAS-STING1 and NF-κB pathway and induce pro-inflammatory factor expression. Additionally, mtDNA can activate inflammasomes, leading to interleukin release and subsequent tissue damage and inflammation. This review summarizes the relationship between mitochondria and AP and explores mitochondrial protective strategies in the diagnosis and treatment of this disease. Future research on the treatment of acute pancreatitis can benefit from exploring promising avenues such as antioxidants, mitochondrial inhibitors, and new therapies that target mitochondrial dysfunction.

The adenine nucleotide translocase family underlies cardiac ischemia-reperfusion injury through the mitochondrial permeability pore independently of cyclophilin D

The mitochondrial permeability transition pore (mPTP) is implicated in cardiac ischemia-reperfusion (I/R) injury. During I/R, elevated mitochondrial Ca2+ triggers mPTP opening, leading to necrotic cell death. Although nonessential regulators of this pore are characterized, the molecular identity of the pore-forming component remains elusive. Two of these genetically verified regulators are cyclophilin D (CypD) and the adenine nucleotide translocase (ANT) family. We investigated the ANT/CypD relationship in mPTP dynamics and I/R injury. Despite lacking all ANT isoforms, Ca2+-dependent mPTP opening persisted in cardiac mitochondria but was desensitized. This desensitization conferred resistance to I/R injury in ANT-deficient mice. CypD is hypothesized to trigger mPTP opening through isomerization of ANTs at proline-62. To test this, we generated mice that expressed a P62A mutated version of ANT1. These mice showed similar mPTP dynamics and I/R sensitivity as the wild type, indicating that P62 is dispensable for CypD regulation. Together, these data indicate that the ANT family contributes to mPTP opening independently of CypD.

Proteomic insights of interaction between ichthyotoxic dinoflagellate Karenia mikimotoi and algicidal bacteria Maribacter dokdonensis

Omics technology has been employed in recent research on algicidal bacteria, but previous transcriptomic studies mainly focused on bacteria or algae, neglecting their interaction. This study explores interactions between algicidal bacterium Maribacter dokdonesis P4 and target alga Karenia mikimotoi KMHK using proteomics. Proteomics responses of KMHK after co-culture with P4 in separate compartments of the transwell for 8 and 24 h were evaluated using tandem mass tags (TMT) proteomics, and changes of P4 proteomics were also assessed. Results indicated that essential metabolic processes of KMHK were disrupted after 8 h co-culture with P4. Disturbance of oxidative phosphorylation in mitochondria and electron transport chain in chloroplast raised oxidative stress, leading to endoplasmic reticulum stress and cytoskeleton collapse, and eventual death of KMHK cells. Iron complex outer-membrane receptor protein in P4 was upregulated after co-culture with KMHK for 24 h, suggesting P4 might secrete ferric siderophores, a potential algicidal substance.

The Role of Mitochondrial Permeability Transition in Bone Metabolism, Bone Healing, and Bone Diseases

Bone is a dynamic organ with an active metabolism and high sensitivity to mitochondrial dysfunction. The mitochondrial permeability transition pore (mPTP) is a low-selectivity channel situated in the inner mitochondrial membrane (IMM), permitting the exchange of molecules of up to 1.5 kDa in and out of the IMM. Recent studies have highlighted the critical role of the mPTP in bone tissue, but there is currently a lack of reviews concerning this topic. This review discusses the structure and function of the mPTP and its impact on bone-related cells and bone-related pathological states. The mPTP activity is reduced during the osteogenic differentiation of mesenchymal stem cells (MSCs), while its desensitisation may underlie the mechanism of enhanced resistance to apoptosis in neoplastic osteoblastic cells. mPTP over-opening triggers mitochondrial swelling, regulated cell death, and inflammatory response. In particular, mPTP over-opening is involved in dexamethasone-induced osteoblast dysfunction and bisphosphonate-induced osteoclast apoptosis. In vivo, the mPTP plays a significant role in maintaining bone homeostasis, with many bone disorders linked to its excessive opening. Genetic deletion or pharmacological inhibition of the over-opening of mPTP has shown potential in enhancing bone injury recovery and alleviating bone diseases. Here, we review the findings on the relationship of the mPTP and bone at both the cellular and disease levels, highlighting novel avenues for pharmacological approaches targeting mitochondrial function to promote bone healing and manage bone-related disorders.

Maintained mitochondrial integrity without oxygen in the anoxia-tolerant crucian carp

Very few vertebrates survive without oxygen (anoxia) for more than a few minutes. Crucian carp (Carassius carassius) are one example, surviving months of anoxia at low temperatures, and we hypothesised that they maintain mitochondrial membrane potential and function. Isolated crucian carp cardiomyocytes indeed maintained mitochondrial membrane potential after blocking complex IV of the electron transport system with cyanide, while those of anoxia-intolerant trout depolarised. When complexes I-III were inhibited, crucian carp mitochondria depolarised, indicating that these complexes need to function during anoxia. Mitochondrial membrane potential depended on reversal of ATP synthase in chemical anoxia, as blocking with cyanide combined with oligomycin to inhibit ATP synthase led to depolarisation. ATP synthase activity was reduced in the heart after 1 week of anoxia in crucian carp, together with a downregulation of ATP synthase subunit gene expression. However, the morphology of cardiac mitochondria was not affected by 1 week of anoxia, even with a large increase in mitofusin 2 mRNA expression. Cardiac citrate synthase activity was not affected by anoxia, while cytochrome c oxidase activity was increased. We show how mitochondria respond to anoxia. A mechanistic understanding of how mitochondrial function can be maintained in anoxia may provide new perspectives to reduce mitochondrial damage in anoxia-sensitive organisms.

Role of Mitochondrial Iron Uptake in Acetaminophen Hepatotoxicity

Overdose of acetaminophen (APAP) produces fulminant hepatic necrosis. The underlying mechanism of APAP hepatotoxicity involves mitochondrial dysfunction, including mitochondrial oxidant stress and the onset of mitochondrial permeability transition (MPT). Reactive oxygen species (ROS) play an important role in APAP-induced hepatotoxicity, and iron is a critical catalyst for ROS formation. This review summarizes the role of mitochondrial ROS formation in APAP hepatotoxicity and further focuses on the role of iron. Normally, hepatocytes take up Fe3+-transferrin bound to transferrin receptors via endocytosis. Concentrated into lysosomes, the controlled release of iron is required for the mitochondrial biosynthesis of heme and non-heme iron-sulfur clusters. After APAP overdose, the toxic metabolite, NAPQI, damages lysosomes, causing excess iron release and the mitochondrial uptake of Fe2+ by the mitochondrial calcium uniporter (MCU). NAPQI also inhibits mitochondrial respiration to promote ROS formation, including H2O2, with which Fe2+ reacts to form highly reactive •OH through the Fenton reaction. •OH, in turn, causes lipid peroxidation, the formation of toxic aldehydes, induction of the MPT, and ultimately, cell death. Fe2+ also facilitates protein nitration. Targeting pathways of mitochondrial iron movement and consequent iron-dependent mitochondrial ROS formation is a promising strategy to intervene against APAP hepatotoxicity in a clinical setting.

Mitochondrial Calcium Regulation of Cardiac Metabolism in Health and Disease

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

Aging and physiological barriers: mechanisms of barrier integrity changes and implications for age-related diseases

The phenomenon of compartmentalization is one of the key traits of life. Biological membranes and histohematic barriers protect the internal environment of the cell and organism from endogenous and exogenous impacts. It is known that the integrity of these barriers decreases with age due to the loss of homeostasis, including age-related gene expression profile changes and the abnormal folding/assembly, crosslinking, and cleavage of barrier-forming macromolecules in addition to morphological changes in cells and tissues. The critical molecular and cellular mechanisms involved in physiological barrier integrity maintenance and aging-associated changes in their functioning are reviewed on different levels: molecular, organelle, cellular, tissue (histohematic, epithelial, and endothelial barriers), and organ one (skin). Biogerontology, which studies physiological barriers in the aspect of age, is still in its infancy; data are being accumulated, but there is no talk of the synthesis of complex theories yet. This paper mainly presents the mechanisms that will become targets of anti-aging therapy only in the future, possibly: pharmacological, cellular, and gene therapies, including potential geroprotectors, hormetins, senomorphic drugs, and senolytics.

Exploring the multifaceted role of adenosine nucleotide translocase 2 in cellular and disease processes: A comprehensive review

Adenosine nucleotide translocases (ANTs) are a family of proteins abundant in the inner mitochondrial membrane, primarily responsible for shuttling ADP and ATP across the mitochondrial membrane. Additionally, ANTs are key players in balancing mitochondrial energy metabolism and regulating cell death. ANT2 isoform, highly expressed in undifferentiated and proliferating cells, is implicated in the development and drug resistance of various tumors. We conduct a detailed analysis of the potential mechanisms by which ANT2 may influence tumorigenesis and drug resistance. Notably, the significance of ANT2 extends beyond oncology, with roles in non-tumor cell processes including blood cell development, gastrointestinal motility, airway hydration, nonalcoholic fatty liver disease, obesity, chronic kidney disease, and myocardial development, making it a promising therapeutic target for multiple pathologies. To better understand the molecular mechanisms of ANT2, this review summarizes the structural properties, expression patterns, and basic functions of the ANT2 protein. In particular, we review and analyze the controversy surrounding ANT2, focusing on its role in transporting ADP/ATP across the inner mitochondrial membrane, its involvement in the composition of the mitochondrial permeability transition pore, and its participation in apoptosis.

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.

Decoding mitochondria's role in immunity and cancer therapy

The functions of mitochondria, including energy production and biomolecule synthesis, have been known for a long time. Given the rising incidence of cancer, the role of mitochondria in cancer has become increasingly popular. Activated by components released by mitochondria, various pathways interact with each other to induce immune responses to protect organisms from attack. However, mitochondria play dual roles in the progression of cancer. Abnormalities in proteins, which are the elementary structures of mitochondria, are closely linked with oncogenesis. Both the aberrant accumulation of intermediates and mutations in enzymes result in the generation and progression of cancer. Therefore, targeting mitochondria to treat cancer may be a new strategy. Several drugs aimed at inhibiting mutated enzymes and accumulated intermediates have been tested clinically. Here, we discuss the current understanding of mitochondria in cancer and the interactions between mitochondrial functions, immune responses, and oncogenesis. Furthermore, we discuss mitochondria as hopeful targets for cancer therapy, providing insights into the progression of future therapeutic strategies.

Mitoregulin supports mitochondrial membrane integrity and protects against cardiac ischemia-reperfusion injury

We and others discovered a highly-conserved mitochondrial transmembrane microprotein, named Mitoregulin (Mtln), that supports lipid metabolism. We reported that Mtln strongly binds cardiolipin (CL), increases mitochondrial respiration and Ca 2+ retention capacities, and reduces reactive oxygen species (ROS). Here we extend our observation of Mtln-CL binding and examine Mtln influence on cristae structure and mitochondrial membrane integrity during stress. We demonstrate that mitochondria from constitutive- and inducible Mtln-knockout (KO) mice are susceptible to membrane freeze-damage and that this can be rescued by acute Mtln re-expression. In mitochondrial-simulated lipid monolayers, we show that synthetic Mtln decreases lipid packing and monolayer elasticity. Lipidomics revealed that Mtln-KO heart tissues show broad decreases in 22:6-containing lipids and increased cardiolipin damage/remodeling. Lastly, we demonstrate that Mtln-KO mice suffer worse myocardial ischemia-reperfusion injury, hinting at a translationally-relevant role for Mtln in cardioprotection. Our work supports a model in which Mtln binds cardiolipin and stabilizes mitochondrial membranes to broadly influence diverse mitochondrial functions, including lipid metabolism, while also protecting against stress.

Monitoring mitochondrial calcium in cardiomyocytes during coverslip hypoxia using a fluorescent lifetime indicator

An increase in mitochondrial calcium via the mitochondrial calcium uniporter (MCU) has been implicated in initiating cell death in the heart during ischemia-reperfusion (I/R) injury. Measurement of calcium during I/R has been challenging due to the pH sensitivity of indicators coupled with the fall in pH during I/R. The development of a pH-insensitive indicator, mitochondrial localized Turquoise Calcium fluorescence Lifetime Sensor (mito-TqFLITS), allows for quantifying mitochondrial calcium during I/R via fluorescent lifetime imaging. Mitochondrial calcium was monitored using mito-TqFLITS, in neonatal mouse ventricular myocytes (NMVM) isolated from germline MCU-KO mice and MCUfl/fl treated with CRE-recombinase to acutely knockout MCU. To simulate ischemia, a coverslip was placed on a monolayer of NMVMs to prevent access to oxygen and nutrients. Reperfusion was induced by removing the coverslip. Mitochondrial calcium increases threefold during coverslip hypoxia in MCU-WT. There is a significant increase in mitochondrial calcium during coverslip hypoxia in germline MCU-KO, but it is significantly lower than in MCU-WT. We also found that compared to WT, acute MCU-KO resulted in no difference in mitochondrial calcium during coverslip hypoxia and reoxygenation. To determine the role of mitochondrial calcium uptake via MCU in initiating cell death, we used propidium iodide to measure cell death. We found a significant increase in cell death in both the germline MCU-KO and acute MCU-KO, but this was similar to their respective WTs. These data demonstrate the utility of mito-TqFLITS to monitor mitochondrial calcium during simulated I/R and further show that germline loss of MCU attenuates the rise in mitochondrial calcium during ischemia but does not reduce cell death.

Molecular mechanisms of naringenin modulation of mitochondrial permeability transition acting on F1FO-ATPase and counteracting saline load-induced injury in SHRSP cerebral endothelial cells

Naringenin (NRG) was characterized for its ability to counteract mitochondrial dysfunction which is linked to cardiovascular diseases. The F1FO-ATPase can act as a molecular target of NRG. The interaction of NRG with this enzyme can avoid the energy transmission mechanism of ATP hydrolysis, especially in the presence of Ca2+ cation used as cofactor. Indeed, NRG was a selective inhibitor of the hydrophilic F1 domain displaying a binding site overlapped with quercetin in the inside surface of an annulus made by the three α and the three β subunits arranged alternatively in a hexamer. The kinetic constant of inhibition suggested that NRG preferred the enzyme activated by Ca2+ rather than the F1FO-ATPase activated by the natural cofactor Mg2+. From the inhibition type mechanism of NRG stemmed the possibility to speculate that NRG can prevent the activation of F1FO-ATPase by Ca2+. The event correlated to the protective role in the mitochondrial permeability transition pore opening by NRG as well as to the reduction of ROS production probably linked to the NRG chemical structure with antioxidant action. Moreover, in primary cerebral endothelial cells (ECs) obtained from stroke prone spontaneously hypertensive rats NRG had a protective effect on salt-induced injury by restoring cell viability and endothelial cell tube formation while also rescuing complex I activity.

The mitochondrial stress-induced protein carboxyl-terminal alanine and threonine tailing (msiCAT-tailing) promotes glioblastoma tumorigenesis by modulating mitochondrial functions

The rapid and sustained proliferation in cancer cells requires accelerated protein synthesis. Accelerated protein synthesis and disordered cell metabolism in cancer cells greatly increase the risk of translation errors. ribosome-associated quality control (RQC) is a recently discovered mechanism for resolving ribosome collisions caused by frequent translation stalls. The role of the RQC pathway in cancer initiation and progression remains controversial and confusing. In this study, we investigated the pathogenic role of mitochondrial stress-induced protein carboxyl-terminal terminal alanine and threonine tailing (msiCAT-tailing) in glioblastoma (GBM), which is a specific RQC response to translational arrest on the outer mitochondrial membrane. We found that msiCAT-tailed mitochondrial proteins frequently exist in glioblastoma stem cells (GSCs). Ectopically expressed msiCAT-tailed mitochondrial ATP synthase F1 subunit alpha (ATP5α) protein increases the mitochondrial membrane potential and blocks mitochondrial permeability transition pore (MPTP) formation/opening. These changes in mitochondrial properties confer resistance to staurosporine (STS)-induced apoptosis in GBM cells. Therefore, msiCAT-tailing can promote cell survival and migration, while genetic and pharmacological inhibition of msiCAT-tailing can prevent the overgrowth of GBM cells.

Highlights

The RQC pathway is disturbed in glioblastoma (GBM) cellsmsiCAT-tailing on ATP5α elevates mitochondrial membrane potential and inhibits MPTP openingmsiCAT-tailing on ATP5α inhibits drug-induced apoptosis in GBM cellsInhibition of msiCAT-tailing impedes overall growth of GBM cells.

Neurotoxic β-amyloid oligomers cause mitochondrial dysfunction-the trigger for PANoptosis in neurons

As the global population ages, the incidence of elderly patients with dementia, represented by Alzheimer's disease (AD), will continue to increase. Previous studies have suggested that β-amyloid protein (Aβ) deposition is a key factor leading to AD. However, the clinical efficacy of treating AD with anti-Aβ protein antibodies is not satisfactory, suggesting that Aβ amyloidosis may be a pathological change rather than a key factor leading to AD. Identification of the causes of AD and development of corresponding prevention and treatment strategies is an important goal of current research. Following the discovery of soluble oligomeric forms of Aβ (AβO) in 1998, scientists began to focus on the neurotoxicity of AβOs. As an endogenous neurotoxin, the active growth of AβOs can lead to neuronal death, which is believed to occur before plaque formation, suggesting that AβOs are the key factors leading to AD. PANoptosis, a newly proposed concept of cell death that includes known modes of pyroptosis, apoptosis, and necroptosis, is a form of cell death regulated by the PANoptosome complex. Neuronal survival depends on proper mitochondrial function. Under conditions of AβO interference, mitochondrial dysfunction occurs, releasing lethal contents as potential upstream effectors of the PANoptosome. Considering the critical role of neurons in cognitive function and the development of AD as well as the regulatory role of mitochondrial function in neuronal survival, investigation of the potential mechanisms leading to neuronal PANoptosis is crucial. This review describes the disruption of neuronal mitochondrial function by AβOs and elucidates how AβOs may activate neuronal PANoptosis by causing mitochondrial dysfunction during the development of AD, providing guidance for the development of targeted neuronal treatment strategies.

Inhibition of the mPTP and Lipid Peroxidation Is Additively Protective Against I/R Injury

BACKGROUND

During myocardial ischemia/reperfusion (I/R) injury, high levels of matrix Ca2+ and reactive oxygen species (ROS) induce the opening of the mitochondrial permeability transition pore (mPTP), which causes mitochondrial dysfunction and ultimately necrotic death. However, the mechanisms of how these triggers individually or cooperatively open the pore have yet to be determined.

METHODS

Here, we use a combination of isolated mitochondrial assays and in vivo I/R surgery in mice. We challenged isolated liver and heart mitochondria with Ca2+, ROS, and Fe2+ to induce mitochondrial swelling. Using inhibitors of the mPTP (cyclosporine A or ADP) lipid peroxidation (ferrostatin-1, MitoQ), we determined how the triggers elicit mitochondrial damage. Additionally, we used the combination of inhibitors during I/R injury in mice to determine if dual inhibition of these pathways is additivity protective.

RESULTS

In the absence of Ca2+, we determined that ROS fails to trigger mPTP opening. Instead, high levels of ROS induce mitochondrial dysfunction and rupture independently of the mPTP through lipid peroxidation. As expected, Ca2+ in the absence of ROS induces mPTP-dependent mitochondrial swelling. Subtoxic levels of ROS and Ca2+ synergize to induce mPTP opening. Furthermore, this synergistic form of Ca2+- and ROS-induced mPTP opening persists in the absence of CypD (cyclophilin D), suggesting the existence of a CypD-independent mechanism for ROS sensitization of the mPTP. These ex vivo findings suggest that mitochondrial dysfunction may be achieved by multiple means during I/R injury. We determined that dual inhibition of the mPTP and lipid peroxidation is significantly more protective against I/R injury than individually targeting either pathway alone.

CONCLUSIONS

In the present study, we have investigated the relationship between Ca2+ and ROS, and how they individually or synergistically induce mitochondrial swelling. Our findings suggest that Ca2+ mediates mitochondrial damage through the opening of the mPTP, although ROS mediates its damaging effects through lipid peroxidation. However, subtoxic levels both Ca2+ and ROS can induce mPTP-mediated mitochondrial damage. Targeting both of these triggers to preserve mitochondria viability unveils a highly effective therapeutic approach for mitigating I/R injury.

Nano-flow cytometry unveils mitochondrial permeability transition process and multi-pathway cell death induction for cancer therapy

Mitochondrial permeability transition (mPT)-mediated mitochondrial dysfunction plays a pivotal role in various human diseases. However, the intricate details of its mechanisms and the sequence of events remain elusive, primarily due to the interference caused by Bax/Bak-induced mitochondrial outer membrane permeabilization (MOMP). To address these, we have developed a methodology that utilizes nano-flow cytometry (nFCM) to quantitatively analyze the opening of mitochondrial permeability transition pore (mPTP), dissipation of mitochondrial membrane potential ( Δ Ψm), release of cytochrome c (Cyt c), and other molecular alternations of isolated mitochondria in response to mPT induction at the single-mitochondrion level. It was identified that betulinic acid (BetA) and antimycin A can directly induce mitochondrial dysfunction through mPT-mediated mechanisms, while cisplatin and staurosporine cannot. In addition, the nFCM analysis also revealed that BetA primarily induces mPTP opening through a reduction in Bcl-2 and Bcl-xL protein levels, along with an elevation in ROS content. Employing dose and time-dependent strategies of BetA, for the first time, we experimentally verified the sequential occurrence of mPTP opening and Δ Ψm depolarization prior to the release of Cyt c during mPT-mediated mitochondrial dysfunction. Notably, our study uncovers a simultaneous release of cell-death-associated factors, including Cyt c, AIF, PNPT1, and mtDNA during mPT, implying the initiation of multiple cell death pathways. Intriguingly, BetA induces caspase-independent cell death, even in the absence of Bax/Bak, thereby overcoming drug resistance. The presented findings offer new insights into mPT-mediated mitochondrial dysfunction using nFCM, emphasizing the potential for targeting such dysfunction in innovative cancer therapies and interventions.

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

1,2,4-Triazole benzamide derivative TPB against Gaeumannomyces graminis var. tritici as a novel dual-target fungicide inhibiting ergosterol synthesis and adenine nucleotide transferase function

BACKGROUND

Isopropyl 4-(2-chloro-6-(1H-1,2,4-triazol-1-yl)benzamido)benzoate (TPB) was a 1,2,4-triazole benzoyl arylamine derivative with excellent antifungal activity, especially against Gaeumannomyces graminis var. tritici (Ggt). Its mechanism of action was investigated by transmission electron microscopy (TEM) observation, assays of sterol composition, cell membrane permeability, intracellular ATP and mitochondrial membrane potential, and mPTP permeability, ROS measurement, RNA sequencing (RNA-seq) analysis.

RESULTS

TPB interfered with ergosterol synthesis, reducing ergosterol content, increasing toxic intermediates, and finally causing biomembrane disruption such as increasing cell membrane permeability and content leakage, and destruction of organelle membranes such as coarse endoplasmic reticulum and vacuole. Moreover, TPB destroyed the function of adenine nucleotide transferase (ANT), leading to ATP transport obstruction in mitochondria, inhibiting mPTP opening, inducing intracellular ROS accumulation and mitochondrial membrane potential loss, finally resulting in mitochondrial damage including mitochondria swelled, mitochondrial membrane dissolved, and cristae destroyed and reduced. RNA-seq analyses showed that TPB increased the expression of ERG11, ERG24, ERG6, ERG5, ERG3 and ERG2 genes in ergosterol synthesis pathway, interfered with the expression of genes (NDUFS5, ATPeV0E, NCA2 and Pam17) related to mitochondrial structure, and inhibited the expression of genes (WrbA and GST) related to anti-oxidative stress.

CONCLUSIONS

TPB exhibited excellent antifungal activity against Ggt by inhibiting ergosterol synthesis and destroying ANT function. So, TPB was a novel compound with dual-target mechanism of action and can be considered a promising novel fungicide for the control of wheat Take-all. The results provided new guides for the structural design of active compounds and powerful tools for pathogen resistance management. © 2023 Society of Chemical Industry.

MCU-independent Ca2+ uptake mediates mitochondrial Ca2+ overload and necrotic cell death in a mouse model of Duchenne muscular dystrophy

Mitochondrial Ca2+ overload can mediate mitochondria-dependent cell death, a major contributor to several human diseases. Indeed, Duchenne muscular dystrophy (MD) is driven by dysfunctional Ca2+ influx across the sarcolemma that causes mitochondrial Ca2+ overload, organelle rupture, and muscle necrosis. The mitochondrial Ca2+ uniporter (MCU) complex is the primary characterized mechanism for acute mitochondrial Ca2+ uptake. One strategy for preventing mitochondrial Ca2+ overload is deletion of the Mcu gene, the pore forming subunit of the MCU-complex. Conversely, enhanced MCU-complex Ca2+ uptake is achieved by deleting the inhibitory Mcub gene. Here we show that myofiber-specific Mcu deletion was not protective in a mouse model of Duchenne MD. Specifically, Mcu gene deletion did not reduce muscle histopathology, did not improve muscle function, and did not prevent mitochondrial Ca2+ overload. Moreover, myofiber specific Mcub gene deletion did not augment Duchenne MD muscle pathology. Interestingly, we observed MCU-independent Ca2+ uptake in dystrophic mitochondria that was sufficient to drive mitochondrial permeability transition pore (MPTP) activation and skeletal muscle necrosis, and this same type of activity was observed in heart, liver, and brain mitochondria. These results demonstrate that mitochondria possess an uncharacterized MCU-independent Ca2+ uptake mechanism that is sufficient to drive MPTP-dependent necrosis in MD in vivo.

Lyssavirus M protein degrades neuronal microtubules by reprogramming mitochondrial metabolism

Infection with neurotropic viruses may result in changes in host behavior, which are closely associated with degenerative changes in neurons. The lyssavirus genus comprises highly neurotropic viruses, including the rabies virus (RABV), which has been shown to induce degenerative changes in neurons, marked by the self-destruction of axons. The underlying mechanism by which the RABV degrades neuronal cytoskeletal proteins remains incomplete. In this study, we show that infection with RABV or overexpression of its M protein can disrupt mitochondrial metabolism by binding to Slc25a4. This leads to a reduction in NAD+ production and a subsequent influx of Ca2+ from the endoplasmic reticulum and mitochondria into the cytoplasm of neuronal cell lines, activating Ca2+-dependent proteinase calpains that degrade α-tubulin. We further screened the M proteins of different lyssaviruses and discovered that the M protein of the dog-derived RABV strain (DRV) does not degrade α-tubulin. Sequence analysis of the DRV M protein and that of the lab-attenuated RABV strain CVS revealed that the 57th amino acid is vital for M-induced microtubule degradation. We generated a recombinant RABV with a mutation at the 57th amino acid position in its M protein and showed that this mutation reduces α-tubulin degradation in vitro and axonal degeneration in vivo. This study elucidates the mechanism by which lyssavirus induces neuron degeneration.IMPORTANCEPrevious studies have suggested that RABV (rabies virus, the representative of lyssavirus) infection induces structural abnormalities in neurons. But there are few articles on the mechanism of lyssavirus' effect on neurons, and the mechanism of how RABV infection induces neurological dysfunction remains incomplete. The M protein of lyssavirus can downregulate cellular ATP levels by interacting with Slc25a4, and this decrease in ATP leads to a decrease in the level of NAD+ in the cytosol, which results in the release of Ca2+ from the intracellular calcium pool, the endoplasmic reticulum, and mitochondria. The presence of large amounts of Ca2+ in the cytoplasm activates Ca2+-dependent proteases and degrades microtubule proteins. The amino acid 57 of M protein is the key site determining its disruption of mitochondrial metabolism and subsequent neuron degeneration.

So close, yet so far away: the relationship between MAM and cardiac disease

Mitochondria-associated membrane (MAM) serve as crucial contact sites between mitochondria and the endoplasmic reticulum (ER). Recent research has highlighted the significance of MAM, which serve as a platform for various protein molecules, in processes such as calcium signaling, ATP production, mitochondrial structure and function, and autophagy. Cardiac diseases caused by any reason can lead to changes in myocardial structure and function, significantly impacting human health. Notably, MAM exhibits various regulatory effects to maintain cellular balance in several cardiac diseases conditions, such as obesity, diabetes mellitus, and cardiotoxicity. MAM proteins independently or interact with their counterparts, forming essential tethers between the ER and mitochondria in cardiomyocytes. This review provides an overview of key MAM regulators, detailing their structure and functions. Additionally, it explores the connection between MAM and various cardiac injuries, suggesting that precise genetic, pharmacological, and physical regulation of MAM may be a promising strategy for preventing and treating heart failure.

Unveiling OSCP as the potential therapeutic target for mitochondrial dysfunction-related diseases

Mitochondria are important organelles in cells responsible for energy production and regulation. Mitochondrial dysfunction has been implicated in the pathogenesis of many diseases. Oligomycin sensitivity-conferring protein (OSCP), a component of the inner mitochondrial membrane, has been studied for a long time. OSCP is a component of the F1Fo-ATP synthase in mitochondria and is closely related to the regulation of the mitochondrial permeability transition pore (mPTP). Studies have shown that OSCP plays an important role in cardiovascular disease, neurological disorders, and tumor development. This review summarizes the localization, structure, function, and regulatory mechanisms of OSCP and outlines its role in cardiovascular disease, neurological disease, and tumor development. In addition, this article reviews the research on the interaction between OSCP and mPTP. Finally, the article suggests future research directions, including further exploration of the mechanism of action of OSCP, the interaction between OSCP and other proteins and signaling pathways, and the development of new treatment strategies for mitochondrial dysfunction. In conclusion, in-depth research on OSCP will help to elucidate its importance in cell function and disease and provide new ideas for the treatment and prevention of related diseases.

Mtfp1 ablation enhances mitochondrial respiration and protects against hepatic steatosis

Hepatic steatosis is the result of imbalanced nutrient delivery and metabolism in the liver and is the first hallmark of Metabolic dysfunction-associated steatotic liver disease (MASLD). MASLD is the most common chronic liver disease and involves the accumulation of excess lipids in hepatocytes, inflammation, and cancer. Mitochondria play central roles in liver metabolism yet the specific mitochondrial functions causally linked to MASLD remain unclear. Here, we identify Mitochondrial Fission Process 1 protein (MTFP1) as a key regulator of mitochondrial and metabolic activity in the liver. Deletion of Mtfp1 in hepatocytes is physiologically benign in mice yet leads to the upregulation of oxidative phosphorylation (OXPHOS) activity and mitochondrial respiration, independently of mitochondrial biogenesis. Consequently, liver-specific knockout mice are protected against high fat diet-induced steatosis and metabolic dysregulation. Additionally, Mtfp1 deletion inhibits mitochondrial permeability transition pore opening in hepatocytes, conferring protection against apoptotic liver damage in vivo and ex vivo. Our work uncovers additional functions of MTFP1 in the liver, positioning this gene as an unexpected regulator of OXPHOS and a therapeutic candidate for MASLD.

The mitochondrial ATP synthase is a negative regulator of the mitochondrial permeability transition pore

The mitochondrial permeability transition pore (mPTP) is a channel in the inner mitochondrial membrane whose sustained opening in response to elevated mitochondrial matrix Ca2+ concentrations triggers necrotic cell death. The molecular identity of mPTP is unknown. One proposed candidate is the mitochondrial ATP synthase, whose canonical function is to generate most ATP in multicellular organisms. Here, we present mitochondrial, cellular, and in vivo evidence that, rather than serving as mPTP, the mitochondrial ATP synthase inhibits this pore. Our studies confirm previous work showing persistence of mPTP in HAP1 cell lines lacking an assembled mitochondrial ATP synthase. Unexpectedly, however, we observe that Ca2+-induced pore opening is markedly sensitized by loss of the mitochondrial ATP synthase. Further, mPTP opening in cells lacking the mitochondrial ATP synthase is desensitized by pharmacological inhibition and genetic depletion of the mitochondrial cis-trans prolyl isomerase cyclophilin D as in wild-type cells, indicating that cyclophilin D can modulate mPTP through substrates other than subunits in the assembled mitochondrial ATP synthase. Mitoplast patch clamping studies showed that mPTP channel conductance was unaffected by loss of the mitochondrial ATP synthase but still blocked by cyclophilin D inhibition. Cardiac mitochondria from mice whose heart muscle cells we engineered deficient in the mitochondrial ATP synthase also demonstrate sensitization of Ca2+-induced mPTP opening and desensitization by cyclophilin D inhibition. Further, these mice exhibit strikingly larger myocardial infarctions when challenged with ischemia/reperfusion in vivo. We conclude that the mitochondrial ATP synthase does not function as mPTP and instead negatively regulates this pore.

Palmitoylation-dependent regulation of cardiomyocyte Rac1 signaling activity and minor effects on cardiac hypertrophy

S-palmitoylation is a reversible lipid modification catalyzed by 23 S-acyltransferases with a conserved zinc finger aspartate-histidine-histidine-cysteine (zDHHC) domain that facilitates targeting of proteins to specific intracellular membranes. Here we performed a gain-of-function screen in the mouse and identified the Golgi-localized enzymes zDHHC3 and zDHHC7 as regulators of cardiac hypertrophy. Cardiomyocyte-specific transgenic mice overexpressing zDHHC3 show cardiac disease, and S-acyl proteomics identified the small GTPase Rac1 as a novel substrate of zDHHC3. Notably, cardiomyopathy and congestive heart failure in zDHHC3 transgenic mice is preceded by enhanced Rac1 S-palmitoylation, membrane localization, activity, downstream hypertrophic signaling, and concomitant induction of all Rho family small GTPases whereas mice overexpressing an enzymatically dead zDHHC3 mutant show no discernible effect. However, loss of Rac1 or other identified zDHHC3 targets Gαq/11 or galectin-1 does not diminish zDHHC3-induced cardiomyopathy, suggesting multiple effectors and pathways promoting decompensation with sustained zDHHC3 activity. Genetic deletion of Zdhhc3 in combination with Zdhhc7 reduces cardiac hypertrophy during the early response to pressure overload stimulation but not over longer time periods. Indeed, cardiac hypertrophy in response to 2 weeks of angiotensin-II infusion is not diminished by Zdhhc3/7 deletion, again suggesting other S-acyltransferases or signaling mechanisms compensate to promote hypertrophic signaling. Taken together, these data indicate that the activity of zDHHC3 and zDHHC7 at the cardiomyocyte Golgi promote Rac1 signaling and maladaptive cardiac remodeling, but redundant signaling effectors compensate to maintain cardiac hypertrophy with sustained pathological stimulation in the absence of zDHHC3/7.

MCUb is an inducible regulator of calcium-dependent mitochondrial metabolism and substrate utilization in muscle

Mitochondria use the electron transport chain to generate high-energy phosphate from oxidative phosphorylation, a process also regulated by the mitochondrial Ca2+ uniporter (MCU) and Ca2+ levels. Here, we show that MCUb, an inhibitor of MCU-mediated Ca2+ influx, is induced by caloric restriction, where it increases mitochondrial fatty acid utilization. To mimic the fasted state with reduced mitochondrial Ca2+ influx, we generated genetically altered mice with skeletal muscle-specific MCUb expression that showed greater fatty acid usage, less fat accumulation, and lower body weight. In contrast, mice lacking Mcub in skeletal muscle showed increased pyruvate dehydrogenase activity, increased muscle malonyl coenzyme A (CoA), reduced fatty acid utilization, glucose intolerance, and increased adiposity. Mechanistically, pyruvate dehydrogenase kinase 4 (PDK4) overexpression in muscle of Mcub-deleted mice abolished altered substrate preference. Thus, MCUb is an inducible control point in regulating skeletal muscle mitochondrial Ca2+ levels and substrate utilization that impacts total metabolic balance.

Adenine nucleotide carrier protein dysfunction in human disease

Adenine nucleotide translocase (ANT) is the prototypical member of the mitochondrial carrier protein family, primarily involved in ADP/ATP exchange across the inner mitochondrial membrane. Several carrier proteins evolutionarily related to ANT, including SLC25A24 and SLC25A25, are believed to promote the exchange of cytosolic ATP-Mg2+ with phosphate in the mitochondrial matrix. They allow a net accumulation of adenine nucleotides inside mitochondria, which is essential for mitochondrial biogenesis and cell growth. In the last two decades, mutations in the heart/muscle isoform 1 of ANT (ANT1) and the ATP-Mg2+ transporters have been found to cause a wide spectrum of human diseases by a recessive or dominant mechanism. Although loss-of-function recessive mutations cause a defect in oxidative phosphorylation and an increase in oxidative stress which drives the pathology, it is unclear how the dominant missense mutations in these proteins cause human diseases. In this review, we focus on how yeast was productively used as a model system for the understanding of these dominant diseases. We also describe the relationship between the structure and function of ANT and how this may relate to various pathologies. Particularly, mutations in Aac2, the yeast homolog of ANT, were recently found to clog the mitochondrial protein import pathway. This leads to mitochondrial precursor overaccumulation stress (mPOS), characterized by the toxic accumulation of unimported mitochondrial proteins in the cytosol. We anticipate that in coming years, yeast will continue to serve as a useful model system for the mechanistic understanding of mitochondrial protein import clogging and related pathologies in humans.

CypD induced ROS output promotes intracranial aneurysm formation and rupture by 8-OHdG/NLRP3/MMP9 pathway

Reactive Oxygen Species (ROS) are widely accepted as a pernicious factor in the progression of intracranial aneurysm (IA), which is eminently related to cell apoptosis and extracellular matrix degradation, but the mechanism remains to be elucidated. Recent evidence has identified that enhancement of Cyclophilin D (CypD) under stress conditions plays a critical role in ROS output, thus accelerating vascular destruction. However, no study has confirmed whether cypD is a detrimental mediator of cell apoptosis and extracellular matrix degradation in the setting of IA development. Our data indicated that endogenous cypD mRNA was significantly upregulated in human IA lesions and mouse IA wall, accompanied by higher level of ROS, MMPs and cell apoptosis. CypD-/- remarkably reversed vascular smooth muscle cells (VSMCs) apoptosis and elastic fiber degradation, and significantly decreased the incidence of aneurysm and ruptured aneurysm, together with the downregulation of ROS, 8-OHdG, NLRP3 and MMP9 in vivo and vitro. Furthermore, we demonstrated that blockade of cypD with CsA inhibited the above processes, thus preventing IA formation and rupture, these effects were highly dependent on ROS output. Mechanistically, we found that cypD directly interacts with ATP5B to promote ROS release in VSMCs, and 8-OHdG directly bind to NLRP3, which interacted with MMP9 to increased MMP9 level and activity in vivo and vitro. Our data expound an unexpected role of cypD in IA pathogenesis and an undescribed 8-OHdG/NLRP3/MMP9 pathway involved in accelerating VSMCs apoptosis and elastic fiber degradation. Repressing ROS output by CypD inhibition may be a promising therapeutic strategy for prevention IA development.

BAK contributes critically to necrosis and infarct generation during reperfused myocardial infarction

At least seven cell death programs are activated during myocardial infarction (MI), but which are most important in causing heart damage is not understood. Two of these programs are mitochondrial-dependent necrosis and apoptosis. The canonical function of the pro-cell death BCL-2 family proteins BAX and BAK is to mediate permeabilization of the outer mitochondrial membrane during apoptosis allowing apoptogen release. BAX has also been shown to sensitize cells to mitochondrial-dependent necrosis, although the underlying mechanisms remain ill-defined. Genetic deletion of Bax or both Bax and Bak in mice reduces infarct size following reperfused myocardial infarction (MI/R), but the contribution of BAK itself to cardiomyocyte apoptosis and necrosis and infarction has not been investigated. In this study, we use Bak-deficient mice and isolated adult cardiomyocytes to delineate the role of BAK in the pathogenesis of infarct generation and post-infarct remodeling during MI/R and non-reperfused MI. Generalized homozygous deletion of Bak reduced infarct size ∼50% in MI/R in vivo, which was attributable primarily to decreases in necrosis. Protection from necrosis was also observed in BAK-deficient isolated cardiomyocytes suggesting that the cardioprotection from BAK loss in vivo is at least partially cardiomyocyte-autonomous. Interestingly, heterozygous Bak deletion, in which the heart still retains ∼28% of wild type BAK levels, reduced infarct size to a similar extent as complete BAK absence. In contrast to MI/R, homozygous Bak deletion did not attenuate acute infarct size or long-term scar size, post-infarct remodeling, cardiac dysfunction, or mortality in non-reperfused MI. We conclude that BAK contributes significantly to cardiomyocyte necrosis and infarct generation during MI/R, while its absence does not appear to impact the pathogenesis of non-reperfused MI. These observations suggest BAK may be a therapeutic target for MI/R and that even partial pharmacological antagonism may provide benefit.

Mitochondrial Interaction with Serotonin in Neurobiology and Its Implication in Alzheimer's Disease

Alzheimer's disease (AD) is a lethal neurodegenerative disorder characterized by severe brain pathologies and progressive cognitive decline. While the exact cause of this disease remains unknown, emerging evidence suggests that dysregulation of neurotransmitters contributes to the development of AD pathology and symptoms. Serotonin, a critical neurotransmitter in the brain, plays a pivotal role in regulating various brain processes and is implicated in neurological and psychiatric disorders, including AD. Recent studies have shed light on the interplay between mitochondrial function and serotonin regulation in brain physiology. In AD, there is a deficiency of serotonin, along with impairments in mitochondrial function, particularly in serotoninergic neurons. Additionally, altered activity of mitochondrial enzymes, such as monoamine oxidase, may contribute to serotonin dysregulation in AD. Understanding the intricate relationship between mitochondria and serotonin provides valuable insights into the underlying mechanisms of AD and identifies potential therapeutic targets to restore serotonin homeostasis and alleviate AD symptoms. This review summarizes the recent advancements in unraveling the connection between brain mitochondria and serotonin, emphasizing their significance in AD pathogenesis and underscoring the importance of further research in this area. Elucidating the role of mitochondria in serotonin dysfunction will promote the development of therapeutic strategies for the treatment and prevention of this neurodegenerative disorder.

Expanded bioinformatic analysis of Oximouse dataset reveals key putative processes involved in brain aging and cognitive decline

The theory that aging is driven by the damage produced by reactive oxygen species (ROS) derived from oxidative metabolism dominated geroscience studies during the second half of the 20th century. However, increasing evidence that ROS also plays a key role in the physiological regulation of numerous processes through the reversible oxidation of cysteine residues in proteins, has challenged this notion. Currently, the scope of redox signaling has reached proteomic dimensions through mass spectrometry techniques. Here, we perform a comprehensive bioinformatics analysis of cysteine oxidation changes during mouse brain aging, using the quantitative data provided in the Oximouse dataset. Interestingly, our unbiased analysis identified hundreds of putative cysteine redox switches covering several pathways previously associated with aging. These include the ubiquitin-proteasome pathway and one-carbon metabolism (folate cycle, methionine cycle, transsulfuration and polyamine pathways). Surprisingly, cysteine oxidation changes are enriched in synaptic proteins in a highly asymmetric distribution: while postsynaptic proteins tend to increase cysteine oxidation with age, the opposite occurs for presynaptic proteins. Additionally, cysteine oxidation changes during aging are associated with proteins involved in the regulation of the mitochondrial transition pore opening and synaptic calcium homeostasis. Our analysis reinforces the concept that brain aging is associated with selective changes in the oxidation state of key proteins, rather than an overall trend toward increased oxidation. Also, we provide a prioritized list of specific cysteine residues with putative impact in aging processes for future experimental validation.

Integrated Analysis of Cross-Links and Dead-End Peptides for Enhanced Interpretation of Quantitative XL-MS

Chemical cross-linking with mass spectrometry provides low-resolution structural information on proteins in cells and tissues. Combined with quantitation, it can identify changes in the interactome between samples, for example, control and drug-treated cells or young and old mice. A difference can originate from protein conformational changes that alter the solvent-accessible distance separating the cross-linked residues. Alternatively, a difference can result from conformational changes localized to the cross-linked residues, for example, altering the solvent exposure or reactivity of those residues or post-translational modifications of the cross-linked peptides. In this manner, cross-linking is sensitive to a variety of protein conformational features. Dead-end peptides are cross-links attached only at one end to a protein with the other terminus being hydrolyzed. As a result, changes in their abundance reflect only conformational changes localized to the attached residue. For this reason, analyzing both quantified cross-links and their corresponding dead-end peptides can help elucidate the likely conformational changes giving rise to observed differences in cross-link abundance. We describe analysis of dead-end peptides in the XLinkDB public cross-link database and, with quantified mitochondrial data isolated from failing heart versus healthy mice, show how a comparison of abundance ratios between cross-links and their corresponding dead-end peptides can be leveraged to reveal possible conformational explanations.

Resting membrane state as an interplay of electrogenic transporters with various pumps

In this study, a new idea that electrogenic transporters determine cell resting state is presented. The previous assumption was that pumps, especially the sodium one, determine it. The latter meets difficulties, because it violates the law of conservation of energy; also a significant deficit of pump activity is reported. The amount of energy carried by a single ATP molecule reflects the potential of the inner mitochondrial membrane, which is about -200 mV. If pumps enforce a resting membrane potential that is more than twice smaller, then the majority of energy stored in ATP would be dissipated by each pump turning. However, this problem could be solved if control is transferred from pumps to something else, e.g., electrogenic transporters. Then pumps would transfer the energy to the ionic gradient without losses, while the cell surface membrane potential would be associated with the reversal potential of some electrogenic transporters. A minimal scheme of this type would include a sodium-calcium exchanger as well as sodium and calcium pumps. However, note that calcium channels and pumps are positioned along both intracellular organelles and the surface membrane. Therefore, the above-mentioned scheme would involve them as well as possible intercellular communications. Such schemes where various kinds of pumps are assumed to work in parallel may explain, to a great extent, the slow turning rate of the individual members. Interaction of pumps and transporters positioned at distant biological membranes with various forms of energy transfer between them may thus result in hypoxic/reperfusion injury, different kinds of muscle fatigue, and nerve-glia interactions.

Antimicrobial mitochondrial reactive oxygen species induction by lung epithelial immunometabolic modulation

Pneumonia is a worldwide threat, making discovery of novel means to combat lower respiratory tract infection an urgent need. Manipulating the lungs' intrinsic host defenses by therapeutic delivery of certain pathogen-associated molecular patterns protects mice against pneumonia in a reactive oxygen species (ROS)-dependent manner. Here we show that antimicrobial ROS are induced from lung epithelial cells by interactions of CpG oligodeoxynucleotides (ODN) with mitochondrial voltage-dependent anion channel 1 (VDAC1). The ODN-VDAC1 interaction alters cellular ATP/ADP/AMP localization, increases delivery of electrons to the electron transport chain (ETC), increases mitochondrial membrane potential (ΔΨm), differentially modulates ETC complex activities and consequently results in leak of electrons from ETC complex III and superoxide formation. The ODN-induced mitochondrial ROS yield protective antibacterial effects. Together, these studies identify a therapeutic metabolic manipulation strategy to broadly protect against pneumonia without reliance on antibiotics.

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

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

Abscisic Acid and Its Receptors LANCL1 and LANCL2 Control Cardiomyocyte Mitochondrial Function, Expression of Contractile, Cytoskeletal and Ion Channel Proteins and Cell Proliferation via ERRα

The cross-kingdom stress hormone abscisic acid (ABA) and its mammalian receptors LANCL1 and LANCL2 regulate the response of cardiomyocytes to hypoxia by activating NO generation. The overexpression of LANCL1/2 increases transcription, phosphorylation and the activity of eNOS and improves cell vitality after hypoxia/reoxygenation via the AMPK/PGC-1α axis. Here, we investigated whether the ABA/LANCL system also affects the mitochondrial oxidative metabolism and structural proteins. Mitochondrial function, cell cycle and the expression of cytoskeletal, contractile and ion channel proteins were studied in H9c2 rat cardiomyoblasts overexpressing or silenced by LANCL1 and LANCL2, with or without ABA. Overexpression of LANCL1/2 significantly increased, while silencing conversely reduced the mitochondrial number, OXPHOS complex I, proton gradient, glucose and palmitate-dependent respiration, transcription of uncoupling proteins, expression of proteins involved in cytoskeletal, contractile and electrical functions. These effects, and LANCL1/2-dependent NO generation, are mediated by transcription factor ERRα, upstream of the AMPK/PGC1-α axis and transcriptionally controlled by the LANCL1/2-ABA system. The ABA-LANCL1/2 hormone-receptor system controls fundamental aspects of cardiomyocyte physiology via an ERRα/AMPK/PGC-1α signaling axis and ABA-mediated targeting of this axis could improve cardiac function and resilience to hypoxic and dysmetabolic conditions.

ANT-dependent MPTP underlies necrotic myofiber death in muscular dystrophy

Mitochondrial permeability transition pore (MPTP) formation contributes to ischemia-reperfusion injury in the heart and several degenerative diseases, including muscular dystrophy (MD). MD is a family of genetic disorders characterized by progressive muscle necrosis and premature death. It has been proposed that the MPTP has two molecular components, the adenine nucleotide translocase (ANT) family of proteins and an unknown component that requires the chaperone cyclophilin D (CypD) to activate. This model was examined in vivo by deleting the gene encoding ANT1 (Slc25a4) or CypD (Ppif) in a δ-sarcoglycan (Sgcd) gene-deleted mouse model of MD, revealing that dystrophic mice lacking Slc25a4 were partially protected from cell death and MD pathology. Dystrophic mice lacking both Slc25a4 and Ppif together were almost completely protected from necrotic cell death and MD disease. This study provides direct evidence that ANT1 and CypD are required MPTP components governing in vivo cell death, suggesting a previously unrecognized therapeutic approach in MD and other necrotic diseases.