Cyclophilin D modulates mitochondrial acetylome

Coordinated metabolic responses to cyclophilin D deletion in the developing heart

In the embryonic heart, the activation of the mitochondrial electron transport chain (ETC) coincides with the closure of the cyclophilin D (CypD) regulated mitochondrial permeability transition pore (mPTP). However, it remains to be established whether the absence of CypD has a regulatory effect on mitochondria during cardiac development. Using a variety of assays to analyze cardiac tissue from wildtype and CypD knockout mice from embryonic day (E)9.5 to adult, we found that mitochondrial structure, function, and metabolism show distinct transitions. Deletion of CypD altered the timing of these transitions as the mPTP was closed at all ages, leading to coupled ETC activity in the early embryo, decreased citrate synthase activity, and an altered metabolome particularly after birth. Our results suggest that manipulating CypD activity may control myocyte proliferation and differentiation and could be a tool to increase ATP production and cardiac function in immature hearts.

T-2 toxin induces mitochondrial dysfunction in chondrocytes via the p53-cyclophilin D pathway

Kashin-Beck disease is an endemic joint disease characterized by deep chondrocyte necrosis, and T-2 toxin exposure has been confirmed its etiology. This study investigated mechanism of T-2 toxin inducing mitochondrial dysfunction of chondrocytes through p53-cyclophilin D (CypD) pathway. The p53 signaling pathway was significantly enriched in T-2 toxin response genes from GeneCards. We demonstrated the upregulation of the p53 protein and p53-CypD complex in rat articular cartilage and ATDC5 cells induced by T-2 toxin. Transmission electron microscopy showed the damaged mitochondrial structure of ATDC5 cells induced by T-2 toxin. Furthermore, it can lead to overopening of the mitochondrial permeability transition pore (mPTP), decreased mitochondrial membrane potential, and increased reactive oxygen species generation in ATDC5 cells. Pifithrin-α, the p53 inhibitor, alleviated the increased p53-CypD complex and mitochondrial dysfunction of chondrocytes induced by T-2 toxin, suggesting that p53 played an important role in T-2 toxin-induced mitochondrial dysfunction. Mechanistically, T-2 toxin can activate the p53 protein, which can be transferred to the mitochondrial membrane and form a complex with CypD. The increased binding of p53 and CypD mediated the excessive opening of mPTP, changed mitochondrial membrane permeability, and ultimately induced mitochondrial dysfunction and apoptosis of chondrocytes.

Prophylactic supplement with melatonin prevented the brain injury after cardiac arrest in rats

Prophylactic pharmacotherapy for health care in patients with high risk of cardiac arrest (CA) is an elusive and less explored strategy. Melatonin has possibilities used as a daily nutraceutical to trigger the cellular adaptation. We sought to find the effects of long-term daily prophylactic supplement with melatonin on the victim of CA. Rats were divided into sham, CA, and melatonin + CA (Mel + CA) groups. The rats in the Mel + CA group received daily IP injection of melatonin 100 mg/kg for 14 days. CA was induced by 8 min asphyxia and followed by manual cardiopulmonary resuscitation. The endpoint was 24 h after resuscitation. Survival, neurological outcome, and hippocampal mitochondrial integrity, dynamics and function were assessed. Survival was significantly higher in the Mel + CA group than the CA group (81 vs. 42%, P = 0.04). Compared to the CA group, neurological damage in the CA1 region and the level of cytochrome c, cleaved caspase-3 and caspase-9 in the Mel + CA group were decreased (P < 0.05). Mitochondrial function and integrity were protected in the Mel + CA group compared to the CA group, according to the results of mitochondrial swelling, ΔΨm, ROS production, oxygen consumption rate, and respiratory control rate (P < 0.05). Melatonin increased SIRT3 and downregulated acetylated CypD. The mitochondrial dynamics and autophagy were improved in the Mel + CA group (P < 0.05). Long-term daily prophylactic supplement with melatonin buy the time from brain injury after CA.

Cyclophilin D in Mitochondrial Dysfunction: A Key Player in Neurodegeneration?

Mitochondrial dysfunction plays a pivotal role in numerous complex diseases. Understanding the molecular mechanisms by which the "powerhouse of the cell" turns into the "factory of death" is an exciting yet challenging task that can unveil new therapeutic targets. The mitochondrial matrix protein CyPD is a peptidylprolyl cis-trans isomerase involved in the regulation of the permeability transition pore (mPTP). The mPTP is a multi-conductance channel in the inner mitochondrial membrane whose dysregulated opening can ultimately lead to cell death and whose involvement in pathology has been extensively documented over the past few decades. Moreover, several mPTP-independent CyPD interactions have been identified, indicating that CyPD could be involved in the fine regulation of several biochemical pathways. To further enrich the picture, CyPD undergoes several post-translational modifications that regulate both its activity and interaction with its clients. Here, we will dissect what is currently known about CyPD and critically review the most recent literature about its involvement in neurodegenerative disorders, focusing on Alzheimer's Disease and Parkinson's Disease, supporting the notion that CyPD could serve as a promising therapeutic target for the treatment of such conditions. Notably, significant efforts have been made to develop CyPD-specific inhibitors, which hold promise for the treatment of such complex disorders.

Post-translational modifications and protein quality control of mitochondrial channels and transporters

Mitochondria play a critical role in energy metabolism and signal transduction, which is tightly regulated by proteins, metabolites, and ion fluxes. Metabolites and ion homeostasis are mainly mediated by channels and transporters present on mitochondrial membranes. Mitochondria comprise two distinct compartments, the outer mitochondrial membrane (OMM) and the inner mitochondrial membrane (IMM), which have differing permeabilities to ions and metabolites. The OMM is semipermeable due to the presence of non-selective molecular pores, while the IMM is highly selective and impermeable due to the presence of specialized channels and transporters which regulate ion and metabolite fluxes. These channels and transporters are modulated by various post-translational modifications (PTMs), including phosphorylation, oxidative modifications, ions, and metabolites binding, glycosylation, acetylation, and others. Additionally, the mitochondrial protein quality control (MPQC) system plays a crucial role in ensuring efficient molecular flux through the mitochondrial membranes by selectively removing mistargeted or defective proteins. Inefficient functioning of the transporters and channels in mitochondria can disrupt cellular homeostasis, leading to the onset of various pathological conditions. In this review, we provide a comprehensive overview of the current understanding of mitochondrial channels and transporters in terms of their functions, PTMs, and quality control mechanisms.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

Microplitis bicoloratus Bracovirus Promotes Cyclophilin D-Acetylation at Lysine 125 That Correlates with Apoptosis during Insect Immunosuppression

Cyclophilin D (CypD) is regulated during the innate immune response of insects. However, the mechanism by which CypD is activated under innate immunosuppression is not understood. Microplitis bicoloratus bracovirus (MbBV), a symbiotic virus in the parasitoid wasp, Microplitis bicoloratus, suppresses innate immunity in parasitized Spodoptera litura. Here, we demonstrate that MbBV promotes the CypD acetylation of S. litura, resulting in an immunosuppressive phenotype characterized by increased apoptosis of hemocytes and MbBV-infected cells. Under MbBV infection, the inhibition of CypD acetylation significantly rescued the apoptotic cells induced by MbBV, and the point-mutant fusion proteins of CypDK125R-V5 were deacetylated. The CypD-V5 fusion proteins were acetylated in MbBV-infected cells. Deacetylation of CypDK125R-V5 can also suppress the MbBV-induced increase in apoptosis. These results indicate that CypD is involved in the MbBV-suppressed innate immune response via the CypD-acetylation pathway and S. litura CypD is acetylated on K125.

Role of SIRT3 in mitochondrial biology and its therapeutic implications in neurodegenerative disorders

Sirtuin 3 (SIRT3), a mitochondrial deacetylase expressed preferentially in high-metabolic-demand tissues including the brain, requires NAD⁺ as a cofactor for catalytic activity. It regulates various processes such as energy homeostasis, redox balance, mitochondrial quality control, mitochondrial unfolded protein response (UPRmt), biogenesis, dynamics and mitophagy by altering protein acetylation status. Reduced SIRT3 expression or activity causes hyperacetylation of hundreds of mitochondrial proteins, which has been linked with neurological abnormalities, neuro-excitotoxicity and neuronal cell death. A body of evidence has suggested, SIRT3 activation as a potential therapeutic modality for age-related brain abnormalities and neurodegenerative disorders.

SZC-6, a small-molecule activator of SIRT3, attenuates cardiac hypertrophy in mice

Sirtuin3 (SIRT3), a class III histone deacetylase, is implicated in various cardiovascular diseases as a novel therapeutic target. SIRT3 has been proven to be cardioprotective in a model of Ang II-induced cardiac hypertrophy. However, a few small-molecule compounds targeting deacetylases could activate SIRT3. In this study, we generated a novel SIRT3 activator, 3-(2-bromo-4-hydroxyphenyl)-7-hydroxy-2H-chromen-2-one (SZC-6), through structural optimization of the first SIRT3 agonist C12. We demonstrated that SZC-6 directly bound to SIRT3 with Kd value of 15 μM, and increased SIRT3 deacetylation activity with EC50 value of 23.2 ± 3.3 µM. In neonatal rat cardiomyocytes (NRCMs), pretreatment with SZC-6 (10, 20, 40 µM) dose-dependently attenuated isoproterenol (ISO)-induced hypertrophic responses. Administration of SZC-6 (20, 40 and 60 mg·kg-1·d-1, s.c.) for 2 weeks starting from one week prior ISO treatment dose-dependently reversed ISO-induced impairment of diastolic and systolic cardiac function in wild-type mice, but not in SIRT3 knockdown mice. We showed that SZC-6 (10, 20, 40 µM) dose-dependently inhibited cardiac fibroblast proliferation and differentiation into myofibroblasts, which was abolished in SIRT3-knockdown mice. We further revealed that activation of SIRT3 by SZC-6 increased ATP production and rate of mitochondrial oxygen consumption, and reduced ROS, improving mitochondrial function in ISO-treated NRCMs. We also found that SZC-6 dose-dependently enhanced LKB1 phosphorylation, thereby promoting AMPK activation to inhibit Drp1-dependent mitochondrial fragmentation. Taken together, these results demonstrate that SZC-6 is a novel SIRT3 agonist with potential value in the treatment of cardiac hypertrophy partly through activation of the LKB1-AMPK pathway.

Anastrozole-mediated modulation of mitochondrial activity by inhibition of mitochondrial permeability transition pore opening: an initial perspective

The mitochondrial permeability transition pore (mtPTP) plays a vital role in altering the structure and function of mitochondria. Cyclophilin D (CypD) is a mitochondrial protein that regulates mtPTP function and a known drug target for therapeutic studies involving mitochondria. While the effect of aromatase inhibition on the mtPTP has been studied previously, the effect of anastrozole on the mtPTP has not been completely elucidated. The role of anastrozole in modulating the mtPTP was evaluated by docking, molecular dynamics and network-guided studies using human CypD data. The peripheral blood mononuclear cells (PBMCs) of patients with mitochondrial disorders and healthy controls were treated with anastrozole and evaluated for mitochondrial permeability transition pore (mtPTP) function and apoptosis using a flow cytometer. Spectrophotometry was employed for estimating total ATP levels. The anastrozole-CypD complex is more stable than cyclosporin A (CsA)-CypD. Anastrozole performed better than cyclosporine in inhibiting mtPTP. Additional effects included inducing mitochondrial membrane depolarization and a reduction in mitochondrial swelling and superoxide generation, intrinsic caspase-3 activity and cellular apoptosis, along with an increase in ATP levels. Anastrozole may serve as a potential therapeutic agent for mitochondrial disorders and ameliorate the clinical phenotype by regulating the activity of mtPTP. However, further studies are required to substantiate our preliminary findings.Communicated by Ramaswamy H. Sarma.

Microplitis bicoloratus parasitism promotes cyclophilin D-p53 interaction to induce apoptosis of hemocytes in Spodoptera litura

Microplitis bicoloratus parasitism can induce apoptosis of hemocytes in the M. bicolortus host, Spodoptera litura. However, it is unclear how M. bicolortus parasitism regulates host signaling pathways to induce apoptosis. Expression of cyclophilin D (CypD) and p53 was significantly upregulated in S. litura hemocytes at 6 days postparasitization. In the parasitized hemocytes, there was mitochondrial membrane potential (△Ψ_m ) loss, cytochrome c (Cyt C) release from mitochondria, and caspase-3 activation. These occurred while hemocytes were undergoing upregulation of CypD and p53. Parasitism also promoted the interaction between CypD and p53. CypD silencing could rescue the apoptotic phenotypes induced by parasitism, but had no effect on apoptosis in unparasitized S. litura. These findings suggest that the CypD-p53 pathway may be an important component of the parasitism-induced immunosuppressive response and establish a basis for further studies of parasitoid/host interactions.

The mitochondrial permeability transition: Recent progress and open questions

Major progress has been made in defining the basis of the mitochondrial permeability transition, a Ca²⁺ -dependent permeability increase of the inner membrane that has puzzled mitochondrial research for almost 70 years. Initially considered an artefact of limited biological interest by most, over the years the permeability transition has raised to the status of regulator of mitochondrial ion homeostasis and of druggable effector mechanism of cell death. The permeability transition is mediated by opening of channel(s) modulated by matrix cyclophilin D, the permeability transition pore(s) (PTP). The field has received new impulse (a) from the hypothesis that the PTP may originate from a Ca²⁺ -dependent conformational change of F-ATP synthase and (b) from the reevaluation of the long-standing hypothesis that it originates from the adenine nucleotide translocator (ANT). Here, we provide a synthetic account of the structure of ANT and F-ATP synthase to discuss potential and controversial mechanisms through which they may form high-conductance channels; and review some intriguing findings from the wealth of early studies of PTP modulation that still await an explanation. We hope that this review will stimulate new experiments addressing the many outstanding problems, and thus contribute to the eventual solution of the puzzle of the permeability transition.

Cyclophilin D regulation of the mitochondrial permeability transition pore

The opening of the mitochondrial permeability transition pore (PTP) has been proposed to play a critical role in activating cell death in many settings, including cardiac ischemia and reperfusion. Although the identity of pore forming unit of the PTP is still debated, it is generally agreed that cyclophilin D (CyPD) is a regulator of the PTP. This manuscript will focus on understanding how CyPD might regulate the PTP and how understanding CyPD might give insight about the identify and regulation of the PTP.

Non-energy mechanism of phosphocreatine on the protection of cell survival

If mitochondrial energy availability or oxidative metabolism is altered, patients will suffer from insufficient energy supply Phosphocreatine (PCr) not only acts as an energy carrier, but also acts as an antioxidant and defensive agent to maintain the integrity and stability of the membrane, to maintain ATP homeostasis through regulating mitochondrial respiration. Meanwhile, PCr can enhance calcium balance and reduce morphological pathological changes, ultimately, PCr helps to reduce apoptosis. On the other aspect, the activities of ATP synthase and MitCK play a crucial role in the maintenance of cellular energy metabolic function. It is interesting to note, PCr not only rises the activities of ATP synthase as well as MitCK, but also promotes these two enzymatic reactions. Additionally, PCr can also inhibit mitochondrial permeability transition in a concentration-dependent manner, prevent ROS and CytC from spilling into the cytoplasm, thereby inhibit the release of proapoptotic factors caspase-3 and caspase-9, and eventually, effectively prevent LPS-induced apoptosis of cells. Understandably, PCr prevents the apoptosis caused by abnormal mitochondrial energy metabolism and has a protective role in a non-energy manner. Moreover, recent studies have shown that PCr protects cell survival through PI3K/Akt/eNOS, MAPK pathway, and inhibition of Ang II-induced NF-κB activation. Furthermore, PCr antagonizes oxidative stress through the activation of PI3K/Akt/GSK3b intracellular pathway, PI3K/AKT-PGC1α signaling pathway, while through the promotion of SIRT3 expression to maintain normal cell metabolism. Interestingly, PCr results in delaying the time to enter pathological metabolism through the delayed activation of AMPK pathway, which is different from previous studies, now we propose the hypothesis that the "miRNA-JAK2/STAT3 -CypD pathway" may take part in protecting cells from apoptosis, PCr may be further be involved in the dynamic relationship between CypD and STAT3. Furthermore, we believe that PCr and CypD would be the central link to maintain cell survival and maintain cell stability and mitochondrial repair under the mitochondrial dysfunction caused by oxidative stress. This review provides the modern progress knowledge and views on the molecular mechanism and molecular targets of PCr in a non-energy way.

Mitochondrial Permeability Transition: A Pore Intertwines Brain Aging and Alzheimer's Disease

Advanced age is the greatest risk factor for aging-related brain disorders including Alzheimer's disease (AD). However, the detailed mechanisms that mechanistically link aging and AD remain elusive. In recent years, a mitochondrial hypothesis of brain aging and AD has been accentuated. Mitochondrial permeability transition pore (mPTP) is a mitochondrial response to intramitochondrial and intracellular stresses. mPTP overactivation has been implicated in mitochondrial dysfunction in aging and AD brains. This review summarizes the up-to-date progress in the study of mPTP in aging and AD and attempts to establish a link between brain aging and AD from a perspective of mPTP-mediated mitochondrial dysfunction.

A systematic review of post-translational modifications in the mitochondrial permeability transition pore complex associated with cardiac diseases

The mitochondrial permeability transition pore (mPTP) opening is involved in the pathophysiology of multiple cardiac diseases, such as ischemia/reperfusion injury and heart failure. A growing number of evidence provided by proteomic screening techniques has demonstrated the role of post-translational modifications (PTMs) in several key components of the pore in response to changes in the extra/intracellular environment and bioenergetic demand. This could lead to a fine, complex regulatory mechanism that, under pathological conditions, can shift the state of mitochondrial functions and, thus, the cell's fate. Understanding the complex relationship between these PTMs is still under investigation and can provide new, promising therapeutic targets and treatment approaches. This review, using a systematic review of the literature, presents the current knowledge on PTMs of the mPTP and their role in health and cardiac disease.

Cyclophilin D: An Integrator of Mitochondrial Function

Cyclophilin D (CypD) is a mitochondrial peptidyl-prolyl cis-trans isomerase, well-known for regulating the mitochondrial permeability transition pore (PTP), a nonspecific large conductance pore whose opening leads to cell death and has been implicated in ischemia/reperfusion injury in multiple organs, in neurodegenerative disorders, and in muscular dystrophies. While the main target of CypD is a matter of ongoing research, inhibiting CypD protects in models of those diseases making it an interesting therapeutic target. The present review focuses on post-translational modifications of CypD that have been identified by recent studies, which can alter the regulation of the PTP and contribute to understanding the mechanisms of action of CypD.

Cardiac metabolism as a driver and therapeutic target of myocardial infarction

Reducing infarct size during a cardiac ischaemic‐reperfusion episode is still of paramount importance, because the extension of myocardial necrosis is an important risk factor for developing heart failure. Cardiac ischaemia‐reperfusion injury (IRI) is in principle a metabolic pathology as it is caused by abruptly halted metabolism during the ischaemic episode and exacerbated by sudden restart of specific metabolic pathways at reperfusion. It should therefore not come as a surprise that therapy directed at metabolic pathways can modulate IRI. Here, we summarize the current knowledge of important metabolic pathways as therapeutic targets to combat cardiac IRI. Activating metabolic pathways such as glycolysis (eg AMPK activators), glucose oxidation (activating pyruvate dehydrogenase complex), ketone oxidation (increasing ketone plasma levels), hexosamine biosynthesis pathway (O‐GlcNAcylation; administration of glucosamine/glutamine) and deacetylation (activating sirtuins 1 or 3; administration of NAD⁺‐boosting compounds) all seem to hold promise to reduce acute IRI. In contrast, some metabolic pathways may offer protection through diminished activity. These pathways comprise the malate‐aspartate shuttle (in need of novel specific reversible inhibitors), mitochondrial oxygen consumption, fatty acid oxidation (CD36 inhibitors, malonyl‐CoA decarboxylase inhibitors) and mitochondrial succinate metabolism (malonate). Additionally, protecting the cristae structure of the mitochondria during IR, by maintaining the association of hexokinase II or creatine kinase with mitochondria, or inhibiting destabilization of F_OF₁‐ATPase dimers, prevents mitochondrial damage and thereby reduces cardiac IRI. Currently, the most promising and druggable metabolic therapy against cardiac IRI seems to be the singular or combined targeting of glycolysis, O‐GlcNAcylation and metabolism of ketones, fatty acids and succinate.

Regulation of metabolism by mitochondrial enzyme acetylation in cardiac ischemia-reperfusion injury

Ischemia reperfusion injury (I/R injury) contributes significantly to morbidity and mortality following myocardial infarction (MI). Although rapid reperfusion of the ischemic myocardium was established decades ago as a highly beneficial therapy for MI, significant cell death still occurs after the onset of reperfusion. Mitochondrial dysfunction is closely associated with I/R injury, resulting in the uncontrolled production of reactive oxygen species (ROS). Considerable efforts have gone into understanding the metabolic perturbations elicited by I/R injury. Recent work has identified the critical role of reversible protein acetylation in maintaining normal mitochondrial biologic function and energy metabolism both in the normal heart and during I/R injury. Several studies have shown that modification of class I HDAC and/or Sirtuin (Sirt) activity is cardioprotective in the setting of I/R injury. A better understanding of the role of these metabolic pathways in reperfusion injury and their regulation by reversible protein acetylation presents a promising way forward in improving the treatment of cardiac reperfusion injury. Here we briefly review some of what is known about how acetylation regulates mitochondrial metabolism and how it relates to I/R injury.

Multiple mitochondrial thioesterases have distinct tissue and substrate specificity and CoA regulation, suggesting unique functional roles

Acyl-CoA thioesterases (Acots) hydrolyze fatty acyl-CoA esters. Acots in the mitochondrial matrix are poised to mitigate β-oxidation overload and maintain CoA availability. Several Acots associate with mitochondria, but whether they all localize to the matrix, are redundant, or have different roles is unresolved. Here, we compared the suborganellar localization, activity, expression, and regulation among mitochondrial Acots (Acot2, -7, -9, and -13) in mitochondria from multiple mouse tissues and from a model of Acot2 depletion. Acot7, -9, and -13 localized to the matrix, joining Acot2 that was previously shown to localize there. Mitochondria from heart, skeletal muscle, brown adipose tissue, and kidney robustly expressed Acot2, -9, and -13; Acot9 levels were substantially higher in brown adipose tissue and kidney mitochondria, as was activity for C4:0-CoA, a unique Acot9 substrate. In all tissues, Acot2 accounted for about half of the thioesterase activity for C14:0-CoA and C16:0-CoA. In contrast, liver mitochondria from fed and fasted mice expressed little Acot activity, which was confined to long-chain CoAs and due mainly to Acot7 and Acot13 activities. Matrix Acots occupied different functional niches, based on substrate specificity (Acot9 versus Acot2 and -13) and strong CoA inhibition (Acot7, -9, and -13, but not Acot2). Interpreted in the context of β-oxidation, CoA inhibition would prevent Acot-mediated suppression of β-oxidation, while providing a release valve when CoA is limiting. In contrast, CoA-insensitive Acot2 could provide a constitutive siphon for long-chain fatty acyl-CoAs. These results reveal how the family of matrix Acots can mitigate β-oxidation overload and prevent CoA limitation.

A key metabolic integrator, coenzyme A, modulates the activity of peroxiredoxin 5 via covalent modification

Peroxiredoxins (Prdxs) are antioxidant enzymes that catalyse the breakdown of peroxides and regulate redox activity in the cell. Peroxiredoxin 5 (Prdx5) is a unique member of Prdxs, which displays a wider subcellular distribution and substrate specificity and exhibits a different catalytic mechanism when compared to other members of the family. Here, the role of a key metabolic integrator coenzyme A (CoA) in modulating the activity of Prdx5 was investigated. We report for the first time a novel mode of Prdx5 regulation mediated via covalent and reversible attachment of CoA (CoAlation) in cellular response to oxidative and metabolic stress. The site of CoAlation in endogenous Prdx5 was mapped by mass spectrometry to peroxidatic cysteine 48. By employing an in vitro CoAlation assay, we showed that Prdx5 peroxidase activity is inhibited by covalent interaction with CoA in a dithiothreitol-sensitive manner. Collectively, these results reveal that human Prdx5 is a substrate for CoAlation in vitro and in vivo, and provide new insight into metabolic control of redox status in mammalian cells.

Mitochondrial NAD+/NADH Redox State and Diabetic Cardiomyopathy

Significance: Diabetic cardiomyopathy (DCM) is a frequent complication occurring even in well-controlled asymptomatic diabetic patients, and it may advance to heart failure (HF). Recent Advances: The diabetic heart is characterized by a state of "metabolic rigidity" involving enhanced rates of fatty acid uptake and mitochondrial oxidation as the predominant energy source, and it exhibits mitochondrial electron transport chain defects. These alterations promote redox state changes evidenced by a decreased NAD⁺/NADH ratio associated with an increase in acetyl-CoA/CoA ratio. NAD⁺ is a co-substrate for deacetylases, sirtuins, and a critical molecule in metabolism and redox signaling; whereas acetyl-CoA promotes protein lysine acetylation, affecting mitochondrial integrity and causing epigenetic changes. Critical Issues: DCM lacks specific therapies with treatment only in later disease stages using standard, palliative HF interventions. Traditional therapy targeting neurohormonal signaling and hemodynamics failed to improve mortality rates. Though mitochondrial redox state changes occur in the heart with obesity and diabetes, how the mitochondrial NAD⁺/NADH redox couple connects the remodeled energy metabolism with mitochondrial and cytosolic antioxidant defense and nuclear epigenetic changes remains to be determined. Mitochondrial therapies targeting the mitochondrial NAD⁺/NADH redox ratio may alleviate cardiac dysfunction. Future Directions: Specific therapies must be supported by an optimal understanding of changes in mitochondrial redox state and how it influences other cellular compartments; this field has begun to surface as a therapeutic target for the diabetic heart. We propose an approach based on an alternate mitochondrial electron transport that normalizes the mitochondrial redox state and improves cardiac function in diabetes.

Cyclophilin D deficiency attenuates mitochondrial F1Fo ATP synthase dysfunction via OSCP in Alzheimer's disease

Mitochondrial dysfunction is pivotal in inducing synaptic injury and neuronal stress in Alzheimer's disease (AD). Mitochondrial F1Fo ATP synthase deregulation is a hallmark mitochondrial defect leading to oxidative phosphorylation (OXPHOS) failure in this neurological disorder. Oligomycin sensitivity conferring protein (OSCP) is a crucial F1Fo ATP synthase subunit. Decreased OSCP levels and OSCP interaction with amyloid β (Aβ) constitute key aspects of F1Fo ATP synthase pathology in AD-related conditions. However, the detailed mechanisms promoting such AD-related OSCP changes have not been fully resolved. Here, we have found increased physical interaction of OSCP with Cyclophilin D (CypD) in AD cases as well as in an AD animal model (5xFAD mice). Genetic depletion of CypD mitigates OSCP loss via ubiquitin-dependent OSCP degradation in 5xFAD mice. Moreover, the ablation of CypD also attenuates OSCP/Aβ interaction in AD mice. The relieved OSCP changes by CypD depletion in 5xFAD mice are along with preserved F1Fo ATP synthase function, restored mitochondrial bioenergetics as well as improved mouse cognition. The simplest interpretation of our results is that CypD is a critical mediator that promotes OSCP deficits in AD-related conditions. Therefore, to block the deleterious impact of CypD on OSCP has the potential to be a promising therapeutic strategy to correct mitochondrial dysfunction for AD therapy.

Cyclophilin D, Somehow a Master Regulator of Mitochondrial Function

Cyclophilin D (CyPD) is an important mitochondrial chaperone protein whose mechanism of action remains a mystery. It is well known for regulating mitochondrial function and coupling of the electron transport chain and ATP synthesis by controlling the mitochondrial permeability transition pore (PTP), but more recent evidence suggests that it may regulate electron transport chain activity. Given its identification as a peptidyl-prolyl, cis-trans isomerase (PPIase), CyPD, is thought to be involved in mitochondrial protein folding, but very few reports demonstrate the presence of this activity. By contrast, CyPD may also perform a scaffolding function, as it binds to a number of important proteins in the mitochondrial matrix and inner mitochondrial membrane. From a clinical perspective, inhibiting CyPD to inhibit PTP opening protects against ischemia⁻reperfusion injury, making modulation of CyPD activity a potentially important therapeutic goal, but the lack of knowledge about the mechanisms of CyPD's actions remains problematic for such therapies. Thus, the important yet enigmatic nature of CyPD somehow makes it a master regulator, yet a troublemaker, for mitochondrial function.

SIRT3 a Major Player in Attenuation of Hepatic Ischemia-Reperfusion Injury by Reducing ROS via Its Downstream Mediators: SOD2, CYP-D, and HIF-1α

Reactive oxygen species (ROS) production in hepatic ischemia-reperfusion injury (IRI) is a complex process where multiple cellular and molecular pathways are involved. Few of those molecular pathways are under the direct influence of SIRT3 and its downstream mediators. SIRT3 plays a major role in the mechanism of IRI, and its activation has been shown to attenuate the deleterious effect of ROS during IRI via SOD2-, CYP-D-, and HIF-1α-mediated pathways. The objective of this review is to analyze the current knowledge on SIRT3 and its downstream mediators: SOD2, CYP-D, and HIF-1α, and their role in IRI. For the references of this review article, we have searched the bibliographic databases of PubMed, Web of Science databases, MEDLINE, and EMBASE with the headings "SIRT3," "SOD2," "CYP-D," "HIF-1α," and "liver IRI." Priority was given to recent experimental articles that provide information on ROS modulation by these proteins. All the recent advancement demonstrates that activation of SIRT3 can suppress ROS production during IRI through various pathways and few of those are via SOD2, CYP-D, and HIF-1α. This effect can improve the quality of the remnant liver following resection as well as a transplanted liver. More research is warranted to disclose its role in IRI attenuation via this pathway.

Divergent Effects of Cyclophilin-D Inhibition on the Female Rat Heart: Acute Versus Chronic Post-Myocardial Infarction

BACKGROUND/AIMS

The mitochondrial permeability transition pore opening plays a critical role in the pathogenesis of myocardial infarction. Inhibition of cyclophilin-D (CyP-D), a key regulator of the mitochondrial permeability transition pore, has been shown to exert cardioprotective effects against ischemia-reperfusion injury on various animal models, mostly in males. However, failure of recent clinical trials requires a detailed elucidation of the cardioprotective efficacy of CyP-D inhibition. The aim of this study was to examine whether cardioprotective effects of sanglifehrin A, a potent inhibitor of CyP-D, on post-infarcted hearts depends on reperfusion.

METHODS

Acute or chronic myocardial infarction was induced by coronary artery ligation with/without subsequent reperfusion for 2 and 28 days in female Sprague-Dawley rats. Cardiac function was estimated by echocardiography. Oxygen consumption rates, ROS production, permeability transition pore opening, protein carbonylation and respiratory supercomplexes were analyzed in isolated cardiac mitochondria.

RESULTS

Sanglifehrin A significantly improved cardiac function of reperfused hearts at 2 days but failed to protect after 28 days. No protection was observed in non-reperfused post-infarcted hearts. The respiratory control index of mitochondria was significantly reduced in reperfused infarcted hearts at 2-days with no effect at 28-days post-infarction on reperfused and non-reperfused hearts. Likewise, only a minor increase in reactive oxygen species production was observed at 2-days in non-reperfused post-infarcted hearts.

CONCLUSION

This study demonstrates that CyP-D inhibition exerts cardioprotective effects in reperfused but not in non-reperfused infarcted hearts of female rats, and the effects are observed only during acute post-infarction injury.

Cyclophilin D regulates neuronal activity-induced filopodiagenesis by fine-tuning dendritic mitochondrial calcium dynamics

Recent studies have highlighted the role of mitochondria in dendritic protrusion growth and plasticity. However, the detailed mechanisms that mitochondria regulate dendritic filopodia morphogenesis remain elusive. Cyclophilin D (CypD, gene name: Ppif) controls the opening of mitochondrial permeability transition pore. Although the pathological relevance of CypD has been intensively investigated, little is known about its physiological function in neurons. Here, we have found that genetic depletion of or pharmaceutical inhibition of CypD blunts the outgrowth of dendritic filopodia in response to KCl-stimulated neuronal depolarization. Further cell biological studies suggest that such inhibitory effect of CypD loss-of-function is closely associated with compromised flexibility of dendritic mitochondrial calcium regulation during neuronal depolarization, as well as the resultant changes in intradendritic calcium homeostasis, calcium signaling activation, dendritic mitochondrial motility and redistribution. Interestingly, loss of CypD attenuates oxidative stress-induced mitochondrial calcium perturbations and dendritic protrusion injury. Therefore, our study has revealed the physiological function of CypD in dendritic plasticity by acting as a fine-tuner of mitochondrial calcium homeostasis. Moreover, CypD plays distinct roles in neuronal physiology and pathology. Cover Image for this issue: doi: 10.1111/jnc.14189.

Mitochondria and aging: A role for the mitochondrial transition pore?

The cellular mechanisms responsible for aging are poorly understood. Aging is considered as a degenerative process induced by the accumulation of cellular lesions leading progressively to organ dysfunction and death. The free radical theory of aging has long been considered the most relevant to explain the mechanisms of aging. As the mitochondrion is an important source of reactive oxygen species (ROS), this organelle is regarded as a key intracellular player in this process and a large amount of data supports the role of mitochondrial ROS production during aging. Thus, mitochondrial ROS, oxidative damage, aging, and aging-dependent diseases are strongly connected. However, other features of mitochondrial physiology and dysfunction have been recently implicated in the development of the aging process. Here, we examine the potential role of the mitochondrial permeability transition pore (mPTP) in normal aging and in aging-associated diseases.

The Role of SIRT3 in the Brain Under Physiological and Pathological Conditions

Sirtuin enzymes are a family of highly seven conserved protein deacetylases, namely SIRT1 through SIRT7, whose enzymatic activities require the cofactor nicotinamide adenine dinucleotide (NAD⁺). Sirtuins reside in different compartments within cells, and their activities have been shown to regulate a number of cellular pathways involved in but not limited to stress management, apoptosis and inflammatory responses. Given the importance of mitochondrial functional state in neurodegenerative conditions, the mitochondrial SIRT3 sirtuin, which is the primary deacetylase within mitochondria, has garnered considerable recent attention. It is now clear that SIRT3 plays a major role in regulating a host of mitochondrial molecular cascades that can contribute to both normal and pathophysiological processes. However, most of the currently available knowledge on SIRT3 stems from studies in non-neuronal cells, and the consequences of the interactions between SIRT3 and its targets in the CNS are only beginning to be elucidated. In this review, we will summarize current advances relating to SIRT3, and explore how its known functions could influence brain physiology.

The unique histidine in OSCP subunit of F-ATP synthase mediates inhibition of the permeability transition pore by acidic pH

The permeability transition pore (PTP) is a Ca2+-dependent mitochondrial channel whose opening causes a permeability increase in the inner membrane to ions and solutes. The most potent inhibitors are matrix protons, with channel block at pH 6.5. Inhibition is reversible, mediated by histidyl residue(s), and prevented by their carbethoxylation by diethylpyrocarbonate (DPC), but their assignment is unsolved. We show that PTP inhibition by H+ is mediated by the highly conserved histidyl residue (H112 in the human mature protein) of oligomycin sensitivity conferral protein (OSCP) subunit of mitochondrial F1FO (F)-ATP synthase, which we also show to undergo carbethoxylation after reaction of mitochondria with DPC. Mitochondrial PTP-dependent swelling cannot be inhibited by acidic pH in H112Q and H112Y OSCP mutants, and the corresponding megachannels (the electrophysiological counterpart of the PTP) are insensitive to inhibition by acidic pH in patch-clamp recordings of mitoplasts. Cells harboring the H112Q and H112Y mutations are sensitized to anoxic cell death at acidic pH. These results demonstrate that PTP channel formation and its inhibition by H+ are mediated by the F-ATP synthase.

HDAC1 localizes to the mitochondria of cardiac myocytes and contributes to early cardiac reperfusion injury

RATIONALE

Recent evidence indicates that histone deacetylase enzymes (HDACs) contribute to ischemia reperfusion (I/R) injury, and pan-HDAC inhibitors have been shown to be cardioprotective when administered either before an ischemic insult or during reperfusion. We have shown previously that selective inhibition of class I HDACs provides superior cardioprotection when compared to pan-HDAC inhibition in a pretreatment model, but selective class I HDAC inhibition has not been tested during reperfusion, and specific targets of class I HDACs in I/R injury have not been identified.

OBJECTIVE

We hypothesized that selective inhibition of class I HDACs with the drug MS-275 (entinostat) during reperfusion would improve recovery from I/R injury in the first hour of reperfusion.

METHODS AND RESULTS

Hearts from male Sprague-Dawley rats were subjected to ex vivo I/R injury±MS-275 class I HDAC inhibition during reperfusion alone. MS-275 significantly attenuated I/R injury, as indicated by improved LV function and tissue viability at the end of reperfusion. Unexpectedly, we observed that HDAC1 is present in the mitochondria of cardiac myocytes, but not fibroblasts or endothelial cells. We then designed mitochondria-restricted and mitochondria-excluded HDAC inhibitors, and tested both in our ex vivo I/R model. The selective inhibition of mitochondrial HDAC1 attenuated I/R injury to the same extent as MS-275, whereas the mitochondrial-excluded inhibitor did not. Further assays demonstrated that these effects are attributable to a decrease in SDHA activity and subsequent metabolic ROS production in reperfusion.

CONCLUSIONS

We demonstrate for the first time that HDAC1 is present within the mitochondria of cardiac myocytes, and mitochondrial HDAC1 contributes significantly to I/R injury within the first hour of reperfusion.

Mitochondrial cyclophilin D ablation is associated with the activation of Akt/p70S6K pathway in the mouse kidney

The mitochondrial matrix protein cyclophilin D (CypD) is an essential component of the mitochondrial permeability transition pore (MPTP). Here we characterized the effects of CypD ablation on bioenergetics in the kidney. CypD loss triggers a metabolic shift in Ppif-/- male and female mouse kidneys towards glycolysis and Krebs cycle activity. The shift is accompanied by increased glucose consumption and a transcriptional upregulation of effectors of glucose metabolism in the kidney. These included activation of Akt, AMPK (only in males) and p70S6K kinases. Gender specific differences between the Ppif-/- male and female mouse kidneys were observed including activation of pro-surviving ERK1/2 kinase and inhibited expression of pro-apoptotic and pro-fibrotic JNK and TGFβ1 proteins in Ppif-/- females. They also showed the highest expression of phosphorylated-ERK1/2 and Akt S473 proteins of all four investigated animal groups. Furthermore, Ppif-/- females showed higher lactate concentrations and ATP/ADP-ratios in the kidney than males. These metabolic and transcriptional modifications could provide an additional level of protection to Ppif-/- females. In summary, loss of mitochondrial CypD results in a shift in bioenergetics and in activation of glucose-metabolism regulating Akt/AMPK/p70S6 kinase pathways that is expected to affect the capability of Ppif-/- mice kidneys to react to stimuli and injury.

Mitochondrial permeability transition in cardiac ischemia-reperfusion: whether cyclophilin D is a viable target for cardioprotection?

Growing number of studies provide strong evidence that the mitochondrial permeability transition pore (PTP), a non-selective channel in the inner mitochondrial membrane, is involved in the pathogenesis of cardiac ischemia-reperfusion and can be targeted to attenuate reperfusion-induced damage to the myocardium. The molecular identity of the PTP remains unknown and cyclophilin D is the only protein commonly accepted as a major regulator of the PTP opening. Therefore, cyclophilin D is an attractive target for pharmacological or genetic therapies to reduce ischemia-reperfusion injury in various animal models and humans. Most animal studies demonstrated cardioprotective effects of PTP inhibition; however, a recent large clinical trial conducted by international groups demonstrated that cyclosporine A, a cyclophilin D inhibitor, failed to protect the heart in patients with myocardial infarction. These studies, among others, raise the question of whether cyclophilin D, which plays an important physiological role in the regulation of cell metabolism and mitochondrial bioenergetics, is a viable target for cardioprotection. This review discusses previous studies to provide comprehensive information on the physiological role of cyclophilin D as well as PTP opening in the cell that can be taken into consideration for the development of new PTP inhibitors.

Proteomics Research in Cardiovascular Medicine and Biomarker Discovery

Proteomics is a systems physiology discipline to address the large-scale characterization of protein species within a biological system, be it a cell, a tissue, a body biofluid, an organism, or a cohort population. Building on advances from chemical analytical platforms (e.g., mass spectrometry and other technologies), proteomics approaches have contributed powerful applications in cardiovascular biomedicine, most notably in: 1) the discovery of circulating protein biomarkers of heart diseases from plasma samples; and 2) the identification of disease mechanisms and potential therapeutic targets in cardiovascular tissues, in both preclinical models and translational studies. Contemporary proteomics investigations offer powerful means to simultaneously examine tens of thousands of proteins in various samples, and understand their molecular phenotypes in health and disease. This concise review introduces study design considerations, example applications and use cases, as well as interpretation and analysis of proteomics data in cardiovascular biomedicine.

Stress-induced dynamic regulation of mitochondrial STAT3 and its association with cyclophilin D reduce mitochondrial ROS production

Signal transducer and activator of transcription 3 (STAT3) is associated with various physiological and pathological functions, mainly as a transcription factor that translocates to the nucleus upon tyrosine phosphorylation induced by cytokine stimulation. In addition, a small pool of STAT3 resides in the mitochondria, where it serves as a sensor for various metabolic stressors including reactive oxygen species (ROS). Mitochondrially localized STAT3 largely exerts its effects through direct or indirect regulation of the activity of the electron transport chain (ETC). It has been assumed that the amounts of STAT3 in the mitochondria are static. We showed that various stimuli, including oxidative stress and cytokines, triggered a signaling cascade that resulted in a rapid loss of mitochondrially localized STAT3. Recovery of the mitochondrial pool of STAT3 over time depended on phosphorylation of Ser727 in STAT3 and new protein synthesis. Under these conditions, mitochondrially localized STAT3 also became competent to bind to cyclophilin D (CypD). Binding of STAT3 to CypD was mediated by the amino terminus of STAT3, which was also important for reducing mitochondrial ROS production after oxidative stress. These results outline a role for mitochondrially localized STAT3 in sensing and responding to external stimuli.

Methylene blue decreases mitochondrial lysine acetylation in the diabetic heart

Diabetic cardiomyopathy is preceded by mitochondrial alterations, and progresses to heart failure. We studied whether treatment with methylene blue (MB), a compound that was reported to serve as an alternate electron carrier within the mitochondrial electron transport chain (ETC), improves mitochondrial metabolism and cardiac function in type 1 diabetes. MB was administered at 10 mg/kg/day to control and diabetic rats. Both echocardiography and hemodynamic studies were performed to assess cardiac function. Mitochondrial studies comprised the measurement of oxidative phosphorylation and specific activities of fatty acid oxidation enzymes. Proteomic studies were employed to compare the level of lysine acetylation on cardiac mitochondrial proteins between the experimental groups. We found that MB facilitates NADH oxidation, increases NAD⁺, and the activity of deacetylase Sirtuin 3, and reduces protein lysine acetylation in diabetic cardiac mitochondria. We identified that lysine acetylation on 83 sites in 34 proteins is lower in the MB-treated diabetic group compared to the same sites in the untreated diabetic group. These changes occur across critical mitochondrial metabolic pathways including fatty acid transport and oxidation, amino acid metabolism, tricarboxylic acid cycle, ETC, transport, and regulatory proteins. While the MB treatment has no effect on the activities of acyl-CoA dehydrogenases, it decreases 3-hydroxyacyl-CoA dehydrogenase activity and long-chain fatty acid oxidation, and improves cardiac function. Providing an alternative route for mitochondrial electron transport is a novel therapeutic approach to decrease lysine acetylation, alleviate cardiac metabolic inflexibility, and improve cardiac function in diabetes.

Traditional and novel tools to probe the mitochondrial metabolism in health and disease

Mitochondrial metabolism links energy production to other essential cellular processes such as signaling, cellular differentiation, and apoptosis. In addition to producing adenosine triphosphate (ATP) as an energy source, mitochondria are responsible for the synthesis of a myriad of important metabolites and cofactors such as tetrahydrofolate, α-ketoacids, steroids, aminolevulinic acid, biotin, lipoic acid, acetyl-CoA, iron-sulfur clusters, heme, and ubiquinone. Furthermore, mitochondria and their metabolism have been implicated in aging and several human diseases, including inherited mitochondrial disorders, cardiac dysfunction, heart failure, neurodegenerative diseases, diabetes, and cancer. Therefore, there is great interest in understanding mitochondrial metabolism and the complex relationship it has with other cellular processes. A large number of studies on mitochondrial metabolism have been conducted in the last 50 years, taking a broad range of approaches. In this review, we summarize and discuss the most commonly used tools that have been used to study different aspects of the metabolism of mitochondria: ranging from dyes that monitor changes in the mitochondrial membrane potential and pharmacological tools to study respiration or ATP synthesis, to more modern tools such as genetically encoded biosensors and trans-omic approaches enabled by recent advances in mass spectrometry, computation, and other technologies. These tools have allowed the large number of studies that have shaped our current understanding of mitochondrial metabolism. WIREs Syst Biol Med 2017, 9:e1373. doi: 10.1002/wsbm.1373 For further resources related to this article, please visit the WIREs website.

Cardiovascular proteomics in the era of big data: experimental and computational advances

Proteomics plays an increasingly important role in our quest to understand cardiovascular biology. Fueled by analytical and computational advances in the past decade, proteomics applications can now go beyond merely inventorying protein species, and address sophisticated questions on cardiac physiology. The advent of massive mass spectrometry datasets has in turn led to increasing intersection between proteomics and big data science. Here we review new frontiers in technological developments and their applications to cardiovascular medicine. The impact of big data science on cardiovascular proteomics investigations and translation to medicine is highlighted.

Lysine acetylation in mitochondria: From inventory to function

Cellular signaling pathways are regulated in a highly dynamic fashion in order to quickly adapt to distinct environmental conditions. Acetylation of lysine residues represents a central process that orchestrates cellular metabolism and signaling. In mitochondria, acetylation seems to be the most prevalent post-translational modification, presumably linked to the compartmentation and high turnover of acetyl-CoA in this organelle. Similarly, the elevated pH and the higher concentration of metabolites in mitochondria seem to favor non-enzymatic lysine modifications, as well as other acylations. Hence, elucidating the mechanisms for metabolic control of protein acetylation is crucial for our understanding of cellular processes. Recent advances in mass spectrometry-based proteomics have considerably increased our knowledge of the regulatory scope of acetylation. Here, we review the current knowledge and functional impact of mitochondrial protein acetylation across species. We first cover the experimental approaches to identify and analyze lysine acetylation on a global scale, we then explore both commonalities and specific differences of plant and animal acetylomes and the evolutionary conservation of protein acetylation, as well as its particular impact on metabolism and diseases. Important future directions and technical challenges are discussed, and it is pointed out that the transfer of knowledge between species and diseases, both in technology and biology, is of particular importance for further advancements in this field.

Cyclophilin D regulates mitochondrial flashes and metabolism in cardiac myocytes

Cyclophilin D (CyP-D) is the mitochondrial-specific member of the evolutionally conserved cyclophilin family, and plays an important role in the regulation of mitochondrial permeability transition (MPT) under stress. Recently we have demonstrated that respiratory mitochondria undergo mitochondrial flash ("mitoflash") activity which is coupled with transient MPT under physiological conditions. However, whether and how CyP-D regulates mitoflashes remain incompletely understood. By using both loss- and gain-of-function approaches in isolated cardiomyocytes, beating hearts, and skeletal muscles in living mice, we revisited the role of CyP-D in the regulation of mitoflashes. Overexpression of CyP-D increased, and knockout of it halved, cardiac mitoflash frequency, while mitoflash amplitude and kinetics remained unaffected. However, CyP-D ablation did not alter mitoflash frequency, with mitoflash amplitude increased, in gastrocnemius muscles. This disparity was accompanied by 4-fold higher CyP-D expression in mouse cardiac than skeletal muscles. The mitochondrial maximal respiration rate and reserved capacity were reduced in CyP-D-null cardiomyocytes. These data indicate that CyP-D is a significant regulator of mitoflash ignition and mitochondrial metabolism in heart. In addition, tissue-specific CyP-D expression may partly explain the differential regulation of mitoflashes in the two types of striated muscles.

Post-Translational Modifications of Cardiac Mitochondrial Proteins in Cardiovascular Disease: Not Lost in Translation

Protein post-translational modifications (PTMs) are crucial in regulating cellular biology by playing key roles in processes such as the rapid on and off switching of signaling network and the regulation of enzymatic activities without affecting gene expressions. PTMs lead to conformational changes in the tertiary structure of protein and resultant regulation of protein function such as activation, inhibition, or signaling roles. PTMs such as phosphorylation, acetylation, and S-nitrosylation of specific sites in proteins have key roles in regulation of mitochondrial functions, thereby contributing to the progression to heart failure. Despite the extensive study of PTMs in mitochondrial proteins much remains unclear. Further research is yet to be undertaken to elucidate how changes in the proteins may lead to cardiovascular and metabolic disease progression in particular. We aimed to summarize the various types of PTMs that occur in mitochondrial proteins, which might be associated with heart failure. This study will increase the understanding of cardiovascular diseases through PTM.

Characterization of the cardiac succinylome and its role in ischemia-reperfusion injury

Succinylation refers to modification of lysine residues with succinyl groups donated by succinyl-CoA. Sirtuin5 (Sirt5) is a mitochondrial NAD(+)-dependent deacylase that catalyzes the removal of succinyl groups from proteins. Sirt5 and protein succinylation are conserved across species, suggesting functional importance of the modification. Sirt5 loss impacts liver metabolism but the role of succinylation in the heart has not been explored. We combined affinity enrichment with proteomics and mass spectrometry to analyze total succinylated lysine content of mitochondria isolated from WT and Sirt5(-/-) mouse hearts. We identified 887 succinylated lysine residues in 184 proteins. 44 peptides (5 proteins) occurred uniquely in WT samples, 289 (46 proteins) in Sirt5(-/-) samples, and 554 (133 proteins) were common to both groups. The 46 unique proteins in Sirt5(-/-) heart participate in metabolic processes such as fatty acid β-oxidation (Eci2) and branched chain amino acid catabolism, and include respiratory chain proteins (Ndufa7, 12, 13, Dhsa). We performed label-free analysis of the peptides common to WT and Sirt5(-/-) hearts. 16 peptides from 9 proteins were significantly increased in Sirt5(-/-) by at least 30%. The adenine nucleotide transporter 1 showed the highest increase in succinylation in Sirt5(-/-) (108.4 fold). The data indicate that succinylation is widespread in the heart and enriched in metabolic pathways. We examined whether the loss of Sirt5 would impact ischemia-reperfusion (I/R) injury and we found an increase in infarct size in Sirt5(-/-) hearts compared to WT littermates (68.5(+)/-1.1% Sirt5(-/-) vs 39.6(+)/(-) 6.8% WT) following 20min of ischemia and 90-min reperfusion. We further demonstrate that I/R injury in Sirt5(-/-) heart is restored to WT levels by pretreatment with dimethyl malonate, a competitive inhibitor of succinate dehydrogenase (SDH), implicating alteration in SDH activity as causative of the injury.

Cyclosporine A Treatment Inhibits Abcc6-Dependent Cardiac Necrosis and Calcification following Coxsackievirus B3 Infection in Mice

Coxsackievirus type B3 (CVB3) is a cardiotropic enterovirus. Infection causes cardiomyocyte necrosis and myocardial inflammation. The damaged tissue that results is replaced with fibrotic or calcified tissue, which can lead to permanently altered cardiac function. The extent of pathogenesis among individuals exposed to CVB3 is dictated by a combination of host genetics, viral virulence, and the environment. Here, we aimed to identify genes that modulate cardiopathology following CVB3 infection. 129S1 mice infected with CVB3 developed increased cardiac pathology compared to 129X1 substrain mice despite no difference in viral burden. Linkage analysis identified a major locus on chromosome 7 (LOD: 8.307, P<0.0001) that controlled the severity of cardiac calcification and necrosis following infection. Sub-phenotyping and genetic complementation assays identified Abcc6 as the underlying gene. Microarray expression profiling identified genotype-dependent regulation of genes associated with mitochondria. Electron microscopy examination showed elevated deposition of hydroxyapatite-like material in the mitochondrial matrices of infected Abcc6 knockout (Abcc6-/-) mice but not in wildtype littermates. Cyclosporine A (CsA) inhibits mitochondrial permeability transition pore opening by inhibiting cyclophilin D (CypD). Treatment of Abcc6 -/- mice with CsA reduced cardiac necrosis and calcification by more than half. Furthermore, CsA had no effect on the CVB3-induced phenotype of doubly deficient CypD-/-Abcc6-/- mice. Altogether, our work demonstrates that mutations in Abcc6 render mice more susceptible to cardiac calcification following CVB3 infection. Moreover, we implicate CypD in the control of cardiac necrosis and calcification in Abcc6-deficient mice, whereby CypD inhibition is required for cardioprotection.

Post-translational modifications of the cardiac proteome in diabetes and heart failure

Cardiovascular complications are the leading cause of death in diabetic patients. Decades of research has focused on altered gene expression, altered cellular signaling, and altered metabolism. This work has led to better understanding of disease progression and treatments aimed at reversing or stopping this deadly process. However, one of the pieces needed to complete the puzzle and bridge the gap between altered gene expression and changes in signaling/metabolism is the proteome and its host of modifications. Defining the mechanisms of regulation includes examining protein levels, localization, and activity of the functional component of cellular machinery. Excess or misutilization of nutrients in obesity and diabetes may lead to PTMs contributing to cardiovascular disease progression. PTMs link regulation of metabolic changes in the healthy and diseased heart with regulation of gene expression itself (e.g. epigenetics), protein enzymatic activity (e.g. mitochondrial oxidative capacity), and function (e.g. contractile machinery). Although a number of PTMs are involved in each of these pathways, we will highlight the role of the serine and threonine O‐linked addition of β‐N‐acetyl‐glucosamine or O‐GlcNAcylation. This nexus of nutrient supply, utilization, and storage allows for the modification and translation of mitochondrial function to many other aspects of the cell.

Mitochondrion as a Target for Heart Failure Therapy- Role of Protein Lysine Acetylation

Heart failure is a leading cause of death worldwide. Despite medical advances, the dismal prognosis of heart failure has not been improved. The heart is a high energy-demanding organ. Impairments of cardiac energy metabolism and mitochondrial function are intricately linked to cardiac dysfunction. Mitochondrial dysfunction contributes to impaired myocardial energetics and increased oxidative stress in heart failure, and the opening of mitochondrial permeability transition pore triggers cell death and myocardial remodeling. Therefore, there has been growing interest in targeting mitochondria and metabolism for heart failure therapy. Recent developments suggest that mitochondrial protein lysine acetylation modulates the sensitivity of the heart to stress and hence the propensity to heart failure. This article reviews the role of mitochondrial dysfunction in heart failure, with a special emphasis on the regulation of the nicotinamide adenine dinucleotide (NAD(+)/NADH) ratio and sirtuin-dependent lysine acetylation by mitochondrial function. Strategies for targeting NAD(+)-sensitive mechanisms in order to intervene in protein lysine acetylation and, thereby, improve stress tolerance, are described, and their usefulness in heart failure therapy is discussed.

Mitochondrial complex I defect and increased fatty acid oxidation enhance protein lysine acetylation in the diabetic heart

AIMS

Cardiomyopathy is a major complication of diabetes. Our study was aimed to identify the sites of mitochondrial dysfunction and delineate its consequences on mitochondrial metabolism in a model of type 1 diabetes.

METHODS AND RESULTS

Diabetes was induced by streptozotocin injection to male Lewis rats. We found a decrease in mitochondrial biogenesis pathway and electron transport chain complex assembly that targets Complex I. Oxidation of Complex II and long-chain fatty acid substrates support the electron leak and superoxide production. Mitochondrial defects do not limit fatty acid oxidation as the heart's preferred energy source indicating that the diabetic heart has a significant reserve in Complex I- and II-supported ATP production. Both mitochondrial fatty acid oxidation and Complex I defect are responsible for increased protein lysine acetylation despite an unchanged amount of the NAD(+)-dependent mitochondrial deacetylase sirt3. We quantitatively analysed mitochondrial lysine acetylation post-translational modifications and identified that the extent of lysine acetylation on 54 sites in 22 mitochondrial proteins is higher in diabetes compared with the same sites in the control. The increased lysine acetylation of the mitochondrial trifunctional protein subunit α may be responsible for the increased fatty acid oxidation in the diabetic heart.

CONCLUSION

We identified the specific defective sites in the electron transport chain responsible for the decreased mitochondrial oxidative phosphorylation in the diabetic heart. Mitochondrial protein lysine acetylation is the common consequence of both increased fatty acid oxidation and mitochondrial Complex I defect, and may be responsible for the metabolic inflexibility of the diabetic heart.

Acetyl-L-carnitine increases mitochondrial protein acetylation in the aged rat heart

Previously we showed that in vivo treatment of elderly Fisher 344 rats with acetylcarnitine abolished the age-associated defect in respiratory chain complex III in interfibrillar mitochondria and improved the functional recovery of the ischemic/reperfused heart. Herein, we explored mitochondrial protein acetylation as a possible mechanism for acetylcarnitine's effect. In vivo treatment of elderly rats with acetylcarnitine restored cardiac acetylcarnitine content and increased mitochondrial protein lysine acetylation and increased the number of lysine-acetylated proteins in cardiac subsarcolemmal and interfibrillar mitochondria. Enzymes of the tricarboxylic acid cycle, mitochondrial β-oxidation, and ATP synthase of the respiratory chain showed the greatest acetylation. Acetylation of isocitrate dehydrogenase, long-chain acyl-CoA dehydrogenase, complex V, and aspartate aminotransferase was accompanied by decreased catalytic activity. Several proteins were found to be acetylated only after treatment with acetylcarnitine, suggesting that exogenous acetylcarnitine served as the acetyl-donor. Two-dimensional fluorescence difference gel electrophoresis analysis revealed that acetylcarnitine treatment also induced changes in mitochondrial protein amount; a two-fold or greater increase/decrease in abundance was observed for thirty one proteins. Collectively, our data provide evidence for the first time that in the aged rat heart in vivo administration of acetylcarnitine provides acetyl groups for protein acetylation and affects the amount of mitochondrial proteins.

Cyclophilin D and myocardial ischemia-reperfusion injury: a fresh perspective

Reperfusion is characterized by a deregulation of ion homeostasis and generation of reactive oxygen species that enhance the ischemia-related tissue damage culminating in cell death. The mitochondrial permeability transition pore (mPTP) has been established as an important mediator of ischemia-reperfusion (IR)-induced necrotic cell death. Although a handful of proteins have been proposed to contribute in mPTP induction, cyclophilin D (CypD) remains its only bona fide regulatory component. In this review we summarize existing knowledge on the involvement of CypD in mPTP formation in general and its relevance to cardiac IR injury in specific. Moreover, we provide insights of recent advancements on additional functions of CypD depending on its interaction partners and post-translational modifications. Finally we emphasize the therapeutic strategies targeting CypD in myocardial IR injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

The mitochondrial permeability transition pore: molecular nature and role as a target in cardioprotection

The mitochondrial permeability transition (PT) - an abrupt increase permeability of the inner membrane to solutes - is a causative event in ischemia-reperfusion injury of the heart, and the focus of intense research in cardioprotection. The PT is due to opening of the PT pore (PTP), a high conductance channel that is critically regulated by a variety of pathophysiological effectors. Very recent work indicates that the PTP forms from the F-ATP synthase, which would switch from an energy-conserving to an energy-dissipating device. This review provides an update on the current debate on how this transition is achieved, and on the PTP as a target for therapeutic intervention. This article is part of a Special Issue entitled "Mitochondria: from basic mitochondrial biology to cardiovascular disease".