Search

Mitochondrial fission is a key trigger of cardiac ischemia-reperfusion injuries (IR). Exercise training is an efficient cardioprotective strategy, but its impact on mitochondrial fragmentation during IR remains unknown. Using isolated rat hearts, we found that exercise training limited the activation of dynamin-like protein 1 and limited mitochondrial fragmentation during IR. These results support the hypothesis that exercise training contributes to cardioprotection through its capacity to modulate the mitochondrial fragmentation during IR., (© 2024 Dubois et al.)

Although a mechanism accounting for hyperthermic death at critical temperatures remains elusive, the mitochondria of crucial active excitable tissues (i.e. heart and brain) may well be key to this process. Mitochondria produce ∼90% of the ATP required by cells to maintain cellular integrity and function. They also integrate into biosynthetic pathways that support metabolism as a whole, allow communication within the cell, and regulate cellular health and death pathways. We have previously shown that cardiac and brain mitochondria demonstrate decreases in the efficiency of, and absolute capacity for ATP synthesis as temperatures rise, until ultimately there is too little ATP to support cellular demands, and organ failure follows. Importantly, substantial decreases in ATP synthesis occur at temperatures immediately below the temperature of heart failure, and this suggests a causal role of mitochondria in hyperthermic death. However, what causes mitochondria to fail? Here, we consider the answers to this question. Mitochondrial dysfunction at high temperature has classically been attributed to elevated leak respiration suspected to result from increased movement of protons (H+) through the inner mitochondrial membrane (IMM), thereby bypassing the ATP synthases. In this Commentary, we introduce some alternative explanations for elevated leak respiration. We first consider respiratory complex I and then propose that a loss of IMM structure occurs as temperatures rise. The loss of the cristae folds of the IMM may affect the efficiency of H+ transport, increasing H+ conductance either through the IMM or into the bulk water phases of mitochondria. In either case, O2 consumption increases while ATP synthesis decreases., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Background: Due to the shortage of donor organs, an increasing number of transplant organs are harvested after circulatory arrest (donation after circulatory death [DCD]). Using a translational porcine model of DCD, this study developed and evaluated a protocol based on cardioprotection by multidrug postconditioning to optimize resuscitation of DCD hearts during ex situ heart perfusion (ESHP)., Methods: Hearts of female pigs (45.0 ± 4.5 kg) were procured following a clinically identical DCD protocol, consisting of the termination of ventilator support and confirmation of circulatory arrest, followed by a 15-min standoff period. DCD hearts were randomly allocated to ESHP (38.4°C) in the absence (untreated, N = 5) or presence (treated, N = 5) of a postconditioning treatment added to the perfusate, consisting of Intralipid (1%), sevoflurane (2% v/v), and remifentanil (3 nM). All hearts were perfused with blood and Krebs-Henseleit solution (1:1) for 60 min in Langendorff mode and for an additional 300 min in working mode for a total perfusion time of 6 h. Oxidative capacity and detailed left ventricular mechanical function under an increasing workload (left atrial pressure, 6 to 12 mmHg) were assessed hourly. Left ventricular tissue was snap-frozen at the end of ESHP and used for molecular analyses., Results: Left ventricular inotropy (LVdP/dtmax) did not decline over time in treated DCD hearts and was significantly higher at the end of the protocol as compared with untreated DCD hearts (ΔLVdP/dtmax = 440 mmHg/s; P = 0.009). Treated DCD hearts exhibited persistently higher left ventricular stroke work index during the 6-h period of ESHP, whereas untreated DCD hearts displayed a significant decline (change in left ventricular stroke work index = -3.10 ml · mmHg/g; P(time within untreated group) < 0.001). Treated DCD hearts displayed higher metabolic activity as measured by oxygen consumption (ΔO2 = 3.11 ml O2 · min-1 · 100 g-1; P = 0.004) and released lower amounts of cell-free mitochondrial DNA into the perfusate, a marker of potential graft dysfunction. Treated hearts also used fatty acids from Intralipid as an energy source, whereas untreated DCD hearts showed glyceroneogenesis with triglyceride accumulation and depletion of tricarboxylic acid cycle intermediates; reduced mitochondrial complex I, II, and III activities with accumulation of mitochondrial NADH, and signs of ultrastructural damage., Conclusions: A translationally relevant protective ESHP protocol consisting of treatment with Intralipid, sevoflurane, and remifentanil markedly accelerated functional recovery and improved viability of DCD hearts., (Copyright © 2024 American Society of Anesthesiologists. All Rights Reserved.)

Myocardial dysfunction is associated with an imbalance in mitochondrial fusion/fission dynamics in patients with diabetes. However, effective strategies to regulate mitochondrial dynamics in the diabetic heart are still lacking. Nicotinamide riboside (NR) supplementation ameliorated mitochondrial dysfunction and oxidative stress in both cardiovascular and aging-related diseases. This study investigated whether NR protects against diabetes-induced cardiac dysfunction by regulating mitochondrial fusion/fission and further explored the underlying mechanisms. Here, we showed an evident decrease in NAD + (nicotinamide adenine dinucleotide) levels and mitochondrial fragmentation in the hearts of leptin receptor-deficient diabetic (db/db) mouse models. NR supplementation significantly increased NAD + content in the diabetic hearts and promoted mitochondrial fusion by elevating Mfn2 level. Furthermore, NR-induced mitochondrial fusion suppressed mitochondrial H 2 O 2 and O 2 • - production and reduced cardiomyocyte apoptosis in both db/db mice hearts and neonatal primary cardiomyocytes. Mechanistically, chromatin immunoprecipitation (ChIP) and luciferase reporter assay analyses revealed that PGC1α and PPARα interdependently regulated Mfn2 transcription by binding to its promoter region. NR treatment elevated NAD + levels and activated SIRT1, resulting in the deacetylation of PGC1α and promoting the transcription of Mfn2. These findings suggested the promotion of mitochondrial fusion via oral supplementation of NR as a potential strategy for delaying cardiac complications in patients with diabetes., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Analysis of the function, structure, and intracellular organization of mitochondria is important for elucidating energy metabolism and intracellular energy transfer. In addition, basic and clinically oriented studies that investigate organ/tissue/cell dysfunction in various human diseases, including myopathies, cardiac/brain ischemia-reperfusion injuries, neurodegenerative diseases, cancer, and aging, require precise estimation of mitochondrial function. It should be noted that the main metabolic and functional characteristics of mitochondria obtained in situ (in permeabilized cells and tissue samples) and in vitro (in isolated organelles) are quite different, thereby compromising interpretations of experimental and clinical data. These differences are explained by the existence of the mitochondrial network, which possesses multiple interactions between the cytoplasm and other subcellular organelles. Metabolic and functional crosstalk between mitochondria and extra-mitochondrial cellular environments plays a crucial role in the regulation of mitochondrial metabolism and physiology. Therefore, it is important to analyze mitochondria in vivo or in situ without their isolation from the natural cellular environment. This review summarizes previous studies and discusses existing approaches and methods for the analysis of mitochondrial function, structure, and intracellular organization in situ.

Chronic magnesium (Mg) deficiency induces and exacerbates various cardiovascular diseases. We previously investigated the mechanisms underlying decline in cardiac function caused by chronic Mg deficiency and the effectiveness of Mg supplementation on this decline using the Langendorff-perfused isolated mouse heart model. Herein, we used the Langendorff-perfused isolated rat heart model to demonstrate the chronic Mg-deficient rats (Mg-deficient group) had lower the heart rate (HR) and left ventricular pressure (LVDP) than rats with normal Mg levels (normal group). Furthermore, decline in cardiac function due to hypoxia/reoxygenation injury was significantly greater in the Mg-deficient group than in the normal group. Experiments on mitochondrial permeability transition pore (mPTP) using isolated mitochondria revealed that mitochondrial membrane was fragile in the Mg-deficient group, implying that cardiac function decline through hypoxia/reoxygenation injury is associated with mitochondrial function. Mg supplementation for chronic Mg-deficient rats not only improved hypomagnesemia but also almost completely restored cardiac and mitochondrial functions. Therefore, proactive Mg supplementation in pathological conditions induced by Mg deficiency or for those at risk of developing hypomagnesemia may suppress the development and exacerbation of certain disease states., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2021 The Authors. Production and hosting by Elsevier B.V. All rights reserved.)

Mitochondrial dysfunction is a feature of type I and type II diabetes, but there is a lack of consistency between reports and links to disease development. We aimed to investigate if mitochondrial structure-function remodelling occurs in the early stages of diabetes by employing a mouse model (GENA348) of Maturity Onset Diabetes in the Young, exhibiting hyperglycemia, but not hyperinsulinemia, with mild left ventricular dysfunction. Employing 3-D electron microscopy (SBF-SEM) we determined that compared to wild-type, WT, the GENA348 subsarcolemma mitochondria (SSM) are ~ 2-fold larger, consistent with up-regulation of fusion proteins Mfn1, Mfn2 and Opa1. Further, in comparison, GENA348 mitochondria are more irregular in shape, have more tubular projections with SSM projections being longer and wider. Mitochondrial density is also increased in the GENA348 myocardium consistent with up-regulation of PGC1-α and stalled mitophagy (down-regulation of PINK1, Parkin and Miro1). GENA348 mitochondria have more irregular cristae arrangements but cristae dimensions and density are similar to WT. GENA348 Complex activity (I, II, IV, V) activity is decreased but the OCR is increased, potentially linked to a shift towards fatty acid oxidation due to impaired glycolysis. These novel data reveal that dysregulated mitochondrial morphology, dynamics and function develop in the early stages of diabetes., (© 2022. The Author(s).)

Aim: We aimed to investigate the association of SIRT4 gene polymorphisms with the susceptibility and prognosis of dilated cardiomyopathy (DCM) in a Chinese population. Materials & methods: A total of 369 controls and 373 DCM patients were enrolled. Three tag single-nucleotide polymorphisms (rs2261612, rs2522138 and rs16950058) on SIRT4 were evaluated. Results: G carriers of rs2261612 were associated with the susceptibility of DCM in codominant, dominant and overdominant genetic models (all p < 0.01). Furthermore, the AG/GG and AG genotype of rs2261612 in dominant and overdominant models correlated with poor prognosis of DCM, independent of left ventricular ejection fraction and cardiac resynchronization therapy (p < 0.001). Conclusion: SIRT4 polymorphisms were associated with the susceptibility and prognosis of DCM in a Chinese population.

During cardiac reperfusion after myocardial infarction, the heart is subjected to cascading cycles of ischaemia reperfusion injury (IRI). Patients presenting with this injury succumb to myocardial dysfunction resulting in myocardial cell death, which contributes to morbidity and mortality. New targeted therapies are required if the myocardium is to be protected from this injury and improve patient outcomes. Extensive research into the role of mitochondria during ischaemia and reperfusion has unveiled one of the most important sites contributing towards this injury; specifically, the opening of the mitochondrial permeability transition pore. The opening of this pore occurs during reperfusion and results in mitochondria swelling and dysfunction, promoting apoptotic cell death. Activation of mitochondrial ATP-sensitive potassium channels (mitoK ATP ) channels, uncoupling proteins, and inhibition of glycogen synthase kinase-3β (GSK3β) phosphorylation have been identified to delay mitochondrial permeability transition pore opening and reduce reactive oxygen species formation, thereby decreasing infarct size. Statins have recently been identified to provide a direct cardioprotective effect on these specific mitochondrial components, all of which reduce the severity of myocardial IRI, promoting the ability of statins to be a considerate preconditioning agent. This review will outline what has currently been shown in regard to statins cardioprotective effects on mitochondria during myocardial IRI., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Sigmar1 is a widely expressed molecular chaperone protein in mammalian cell systems. Accumulating research demonstrated the cardioprotective roles of pharmacologic Sigmar1 activation by ligands in preclinical rodent models of cardiac injury. Extensive biochemical and immuno-electron microscopic research demonstrated Sigmar1's sub-cellular localization largely depends on cell and organ types. Despite comprehensive studies, Sigmar1's direct molecular role in cardiomyocytes remains elusive. In the present study, we determined Sigmar1's subcellular localization, transmembrane topology, and function using complementary microscopy, biochemical, and functional assays in cardiomyocytes. Quantum dots in transmission electron microscopy showed Sigmar1 labeled quantum dots on the mitochondrial membranes, lysosomes, and sarcoplasmic reticulum-mitochondrial interface. Subcellular fractionation of heart cell lysates confirmed Sigmar1's localization in purified mitochondria fraction and lysosome fraction. Immunocytochemistry confirmed Sigmar1 colocalization with mitochondrial proteins in isolated adult mouse cardiomyocytes. Sigmar1's mitochondrial localization was further confirmed by Sigmar1 colocalization with Mito-Tracker in isolated mouse heart mitochondria. A series of biochemical experiments, including alkaline extraction and proteinase K treatment of purified heart mitochondria, demonstrated Sigmar1 as an integral mitochondrial membrane protein. Sigmar1's structural requirement for mitochondrial localization was determined by expressing FLAG-tagged Sigmar1 fragments in cells. Full-length Sigmar1 and Sigmar1's C terminal-deletion fragments were able to localize to the mitochondrial membrane, whereas N-terminal deletion fragment was unable to incorporate into the mitochondria. Finally, functional assays using extracellular flux analyzer and high-resolution respirometry showed Sigmar1 siRNA knockdown significantly altered mitochondrial respiration in cardiomyocytes. Overall, we found that Sigmar1 localizes to mitochondrial membranes and is indispensable for maintaining mitochondrial respiratory homeostasis in cardiomyocytes., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Abuse of the potent psychostimulant cocaine is widely established to have cardiovascular consequences. The cardiotoxicity of cocaine is mainly associated with oxidative stress and mitochondrial dysfunction. Mitochondrial dynamics and biogenesis, as well as the mitochondrial unfolded protein response (UPR mt ), guarantee cardiac mitochondrial homeostasis. Collectively, these mechanisms act to protect against stress, injury, and the detrimental effects of chemicals on mitochondria. In this study, we examined the effects of cocaine on cardiac mitochondrial dynamics, biogenesis, and UPR mt in vivo. Rats administered cocaine via the tail vein at a dose of 20 mg/kg/day for 7 days showed no structural changes in the myocardium, but electron microscopy revealed a significant increase in the number of cardiac mitochondria. Correspondingly, the expressions of the mitochondrial fission gene and mitochondrial biogenesis were increased after cocaine administration. Significant increase in the expression and nuclear translocation of activating transcription factor 5, the major active regulator of UPR mt , were observed after cocaine administration. Accordingly, our findings show that before any structural changes are observable in the myocardium, cocaine alters mitochondrial dynamics, elevates mitochondrial biogenesis, and induces the activation of UPR mt . These alterations might reflect cardiac mitochondrial compensation to protect against the cardiotoxicity of cocaine., (© 2021. The Author(s).)

Preserving optimal mitochondrial function is critical in the heart, which is the most ATP-avid organ in the body. Recently, we showed that global deficiency of the nuclear receptor RORα in the "staggerer" mouse exacerbates angiotensin II-induced cardiac hypertrophy and compromises cardiomyocyte mitochondrial function. However, the mechanisms underlying these observations have not been defined previously. Here, we used pharmacological and genetic gain- and loss-of-function tools to demonstrate that RORα regulates cardiomyocyte mitophagy to preserve mitochondrial abundance and function. We found that cardiomyocyte mitochondria in staggerer mice with lack of functional RORα were less numerous and exhibited fewer mitophagy events than those in WT controls. The hearts of our novel cardiomyocyte-specific RORα KO mouse line demonstrated impaired contractile function, enhanced oxidative stress, increased apoptosis, and reduced autophagic flux relative to Cre(-) littermates. We found that cardiomyocyte mitochondria in "staggerer" mice with lack of functional RORα were upregulated by hypoxia, a classical inducer of mitophagy. The loss of RORα blunted mitophagy and broadly compromised mitochondrial function in normoxic and hypoxic conditions in vivo and in vitro. We also show that RORα is a direct transcriptional regulator of the mitophagy mediator caveolin-3 in cardiomyocytes and that enhanced expression of RORα increases caveolin-3 abundance and enhances mitophagy. Finally, knockdown of RORα impairs cardiomyocyte mitophagy, compromises mitochondrial function, and induces apoptosis, but these defects could be rescued by caveolin-3 overexpression. Collectively, these findings reveal a novel role for RORα in regulating mitophagy through caveolin-3 and expand our currently limited understanding of the mechanisms underlying RORα-mediated cardioprotection., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia., (© 2021. The Author(s).)

Women with preeclampsia (PE) have a greater risk of developing hypertension, cardiovascular disease (CVD), and renal disease later in life. Angiotensin II type I receptor agonistic autoantibodies (AT1-AAs) are elevated in women with PE during pregnancy and up to 2-year postpartum (PP), and in the reduced uterine perfusion pressure (RUPP) rat model of PE. Blockade of AT1-AA with a specific 7 amino acid peptide binding sequence ('n7AAc') improves pathophysiology observed in RUPP rats; however, the long-term effects of AT1-AA inhibition in PP is unknown. Pregnant Sprague Dawley rats were divided into three groups: normal pregnant (NP) (n = 16), RUPP (n = 15), and RUPP + 'n7AAc' (n = 16). Gestational day 14, RUPP surgery was performed and 'n7AAc' (144 μg/day) administered via osmotic minipump. At 10-week PP, mean arterial pressure (MAP), renal glomerular filtration rate (GFR) and cardiac functions, and cardiac mitochondria function were assessed. MAP was elevated PP in RUPP vs. NP (126 ± 4 vs. 116 ± 3 mmHg, p < 0.05), but was normalized in in RUPP + 'n7AAc' (109 ± 3 mmHg) vs. RUPP (p < 0.05). PP heart size was reduced by RUPP + 'n7AAc' vs. RUPP rats (p < 0.05). Complex IV protein abundance and enzymatic activity, along with glutamate/malate-driven respiration (complexes I, III, and IV), were reduced in the heart of RUPP vs. NP rats which was prevented with 'n7AAc'. AT1-AA inhibition during pregnancy not only improves blood pressure and pathophysiology of PE in rats during pregnancy, but also long-term changes in blood pressure, cardiac hypertrophy, and cardiac mitochondrial function PP., (© 2021. The Author(s).)

Abstract: Mitochondria is often considered as the common nexus of cardiac and cerebral dysfunction after cardiac arrest. Here, our goal was to determine whether the time course of cardiac and cerebral mitochondrial dysfunction is similar after shockable versus non-shockable cardiac arrest in rabbits. Anesthetized rabbits were submitted to 10 min of no-flow by ventricular fibrillation (VF group) or asphyxia (non-shockable group). They were euthanized at the end of the no-flow period or 30 min, 120 min, or 24 h after resuscitation for in vitro evaluation of oxygen consumption and calcium retention capacity. In the brain (cortex and hippocampus), moderate mitochondrial dysfunction was evidenced at the end of the no-flow period after both causes of cardiac arrest versus baseline. It partly recovered at 30 and 120 min after cardiac arrest, with lower calcium retention capacity and higher substrate-dependant oxygen consumption after VF versus non-shockable cardiac arrest. However, after 24 h of follow-up, mitochondrial dysfunction dramatically increased after both VF and non-shockable cardiac arrest, despite greater neurological dysfunction after the latter one. In the heart, mitochondrial dysfunction was also maximal after 24 h following resuscitation, with no significant difference among the causes of the cardiac arrest. During the earlier timing of evaluation, calcium retention capacity and ADP-dependant oxygen consumption were lower and higher, respectively, after non-shockable cardiac arrest versus VF. In conclusion, the kinetics of cardiac and cerebral mitochondrial dysfunction suggests that mitochondrial function does not play a major role in the early phase of the post-resuscitation process but is only involved in the longer pathophysiological events., Competing Interests: The authors report no conflicts of interest., (Copyright © 2021 by the Shock Society.)

The adult mammalian heart cannot regenerate after myocardial injury because most cardiomyocytes lack the ability to proliferate. In contrast, cardiomyocytes of vertebrates such as zebrafish and urodele amphibians, but also those of fetal and early neonatal mammals, maintain the ability to proliferate and therefore support regeneration of injured tissue and recovery of cardiac function. Whether evolutionarily conserved regulatory mechanisms of cardiomyocyte proliferation exist and, if so, whether they are modifiable to allow cardiac regeneration in adult mammals are questions of great scientific and medical interest. Environmental hypoxia, hypoxia-induced cellular signaling, and mitochondrial metabolism have recently emerged as key regulators of the cardiomyocyte cell cycle and cardiac regeneration in vertebrates. In this review, we address the cardiac regenerative capacity of several model animals and discuss potential strategies related to hypoxia and mitochondrial metabolism for induction of therapeutic heart regeneration., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Purpose: Cardioprotective effect of carbon monoxide, a gasotransmitter against myocardial ischemia-reperfusion injury (I/R), is well established in preclinical studies with male rats. However, its ischemic tolerance in post-menopausal animals has not been examined due to functional perturbations at the cellular level., Methods: The protective role of carbon monoxide releasing molecule-2 (CORM-2) on myocardial I/R was studied in female Wistar rats using the Langendorff apparatus. The animals were randomly divided into normal and ovariectomized (Ovx) female rats and were maintained 2 months post-surgery. Each group was further divided into 4 subgroups (n = 6/subgroup): normal, I/R, CORM-2-control (20 μmol/L), and CORM-2-I/R. The cardiac injury was estimated via myocardial infarct size, lactate dehydrogenase, and creatine kinase levels in coronary effluent and cardiac hemodynamic indices. Mitochondrial functional activity was assessed by measuring mitochondrial electron transport chain enzyme activities, swelling behavior, mitochondrial membrane potential, and oxidative stress., Results: Hemodynamic indices were significantly lower in ovariectomized rat hearts than in normal rat hearts. Sixty minutes of reperfusion of ischemic heart exhibited deteriorated cardiac physiological recovery in both ovariectomized and normal groups, where prominent decline was observed in ovariectomized rat. However, preconditioning the isolated heart with CORM-2 improved hemodynamics parameters significantly in both ovariectomized and normal rat hearts challenged with I/R, but with a limited degree of protection in ovariectomized rat hearts. The protective effect of CORM-2 was further confirmed via a reduction in cardiac injury, preservation of mitochondrial enzymes, and reduction in oxidative stress in all groups., Conclusion: CORM-2 administration significantly attenuated myocardial I/R injury in ovariectomized rat hearts by attenuating I/R-associated mitochondrial perturbations and reducing oxidative stress., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Mitochondrial transplantation is emerging as a novel cellular biotherapy to alleviate mitochondrial damage and dysfunction. Mitochondria play a crucial role in establishing cellular homeostasis and providing cell with the energy necessary to accomplish its function. Owing to its endosymbiotic origin, mitochondria share many features with their bacterial ancestors. Unlike the nuclear DNA, which is packaged into nucleosomes and protected from adverse environmental effects, mitochondrial DNA are more prone to harsh environmental effects, in particular that of the reactive oxygen species. Mitochondrial damage and dysfunction are implicated in many diseases ranging from metabolic diseases to cardiovascular and neurodegenerative diseases, among others. While it was once thought that transplantation of mitochondria would not be possible due to their semiautonomous nature and reliance on the nucleus, recent advances have shown that it is possible to transplant viable functional intact mitochondria from autologous, allogenic, and xenogeneic sources into different cell types. Moreover, current research suggests that the transplantation could positively modulate bioenergetics and improve disease outcome. Mitochondrial transplantation techniques and consequences of transplantation in cardiomyocytes are the theme of this review. We outline the different mitochondrial isolation and transfer techniques. Finally, we detail the consequences of mitochondrial transplantation in the cardiovascular system, more specifically in the context of cardiomyopathies and ischemia.

Left ventricular remodeling due to pressure overload is associated with poor prognosis. Sacubitril/valsartan is the first-in-class Angiotensin Receptor Neprilysin Inhibitor and has been demonstrated to have superior beneficial effects in the settings of heart failure. The aim of this study was to determine whether sacubitril/valsartan has cardioprotective effect in the early intervention of pressure overloaded hearts and whether it is superior to valsartan alone. We induced persistent left ventricular pressure overload in rats by ascending aortic constriction surgery and orally administrated sacubitril/valsartan, valsartan, or vehicle one week post operation for 10 weeks. We also determined the effects of sacubitril/valsartan over valsartan on adult ventricular myocytes and fibroblasts that were isolated from healthy rats and treated in culture. We found that early intervention with sacubitril/valsartan is superior to valsartan in reducing pressure overload-induced ventricular fibrosis and in reducing angiotensin II-induced adult ventricular fibroblast activation. While neither sacubitril/valsartan nor valsartan changes cardiac hypertrophy development, early intervention with sacubitril/valsartan protects ventricular myocytes from mitochondrial dysfunction and is superior to valsartan in reducing mitochondrial oxidative stress in response to persistent left ventricular pressure overload. In conclusion, our findings demonstrate that sacubitril/valsartan has a superior cardioprotective effect over valsartan in the early intervention of pressure overloaded hearts, which is independent of the reduction of left ventricular afterload. Our study provides evidence in support of potential benefits of the use of sacubitril/valsartan in patients with resistant hypertension or in patients with severe aortic stenosis., (© 2021. The Author(s).)

Background: Cardiovascular diseases are the leading cause of death globally, and they are causing enormous socio-economic burden to the developed and developing countries. Allyl Methyl Sulfide (AMS) is a novel cardioprotective metabolite identified in the serum of rats after raw garlic administration. The present study explored the cardioprotective effect of AMS on thoracic aortic constriction (TAC)-induced cardiac hypertrophy and heart failure model in rats., Methods: Thoracic aortic constriction (TAC) by titanium ligating clips resulted in the development of pressure overload-induced cardiac hypertrophy and heart failure model. Four weeks prior to TAC and for 8 weeks after TAC, Sprague Dawley (SD) rats were administered with AMS (25 and 50 mg/kg/day) or Enalapril (10 mg/kg/day)., Results: We have observed AMS (25 and 50 mg/kg/day) intervention significantly improved structural and functional parameters of the heart. mRNA expression of fetal genes i.e., atrial natriuretic peptide (ANP), alpha skeletal actin (α-SA) and beta myosin heavy chain (β-MHC) were reduced in AMS treated TAC hearts along with decrease in perivascular and interstitial fibrosis. AMS attenuated lipid peroxidation and improved protein expression of endogenous antioxidant enzymes i.e., catalase and manganese superoxide dismutase (MnSOD) along with electron transport chain (ETC) complex activity. AMS increased mitochondrial fusion proteins i.e., mitofusin 1 (MFN1), mitofusin 2 (MFN2) and optic atrophy protein (OPA1), and reduced fission protein i.e., dynamin-related protein 1 (DRP1). Preliminary study suggests that AMS intervention upregulated genes involved in mitochondrial bioenergetics in normal rats. Further, in-vitro studies suggest that AMS reduced mitochondrial reactive oxygen species (ROS), preserved mitochondrial membrane potential and oxygen consumption rate (OCR) in isoproterenol-treated cardiomyoblast., Conclusion: This study demonstrated that AMS protected cardiac remodelling, LV dysfunction and fibrosis in pressure overload-induced cardiac hypertrophy and heart failure model by improving endogenous antioxidants and mitochondrial function., (Copyright © 2021 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)

This review provides a comprehensive overview of the past 25+ years of research into the development of left ventricular assist device (LVAD) to improve clinical outcomes in patients with severe end-stage heart failure and basic insights gained into the biology of heart failure gleaned from studies of hearts and myocardium of patients undergoing LVAD support. Clinical aspects of contemporary LVAD therapy, including evolving device technology, overall mortality, and complications, are reviewed. We explain the hemodynamic effects of LVAD support and how these lead to ventricular unloading. This includes a detailed review of the structural, cellular, and molecular aspects of LVAD-associated reverse remodeling. Synergisms between LVAD support and medical therapies for heart failure related to reverse remodeling, remission, and recovery are discussed within the context of both clinical outcomes and fundamental effects on myocardial biology. The incidence, clinical implications and factors most likely to be associated with improved ventricular function and remission of the heart failure are reviewed. Finally, we discuss recognized impediments to achieving myocardial recovery in the vast majority of LVAD-supported hearts and their implications for future research aimed at improving the overall rates of recovery.

Mitochondria share attributes of vesicular transport with their bacterial ancestors given their ability to form mitochondrial-derived vesicles (MDVs). MDVs are involved in mitochondrial quality control and their formation is enhanced with stress and may, therefore, play a potential role in mitochondrial-cellular communication. However, MDV proteomic cargo has remained mostly undefined. In this study, we strategically used an in vitro MDV budding/reconstitution assay on cardiac mitochondria, followed by graded oxidative stress, to identify and characterize the MDV proteome. Our results confirmed previously identified cardiac MDV markers, while also revealing a complete map of the MDV proteome, paving the way to a better understanding of the role of MDVs. The oxidative stress vulnerability of proteins directed the cargo loading of MDVs, which was enhanced by antimycin A (Ant-A). Among OXPHOS complexes, complexes III and V were found to be Ant-A-sensitive. Proteins from metabolic pathways such as the TCA cycle and fatty acid metabolism, along with Fe-S cluster, antioxidant response proteins, and autophagy were also found to be Ant-A sensitive. Intriguingly, proteins containing hyper-reactive cysteine residues, metabolic redox switches, including professional redox enzymes and those that mediate iron metabolism, were found to be components of MDV cargo with Ant-A sensitivity. Last, we revealed a possible contribution of MDVs to the formation of extracellular vesicles, which may indicate mitochondrial stress. In conclusion, our study provides an MDV proteomics signature that delineates MDV cargo selectivity and hints at the potential for MDVs and their novel protein cargo to serve as vital biomarkers during mitochondrial stress and related pathologies., (© 2020 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Aims: Diabetic cardiomyopathy represents the main cause of death among diabetic people. Despite this evidence, the molecular mechanisms triggered by impaired glucose and lipid metabolism inducing heart damage remain unclear. The aim of our study was to investigate the effect of altered metabolism on the early stages of cardiac injury in experimental diabetes., Methods: For this purpose, rats were fed a normocaloric diet (NPD) or a high fat diet (HFD) for up to 12 weeks. After the fourth week, streptozocin (35 mg/kg) was administered in a subgroup of both NPD and HFD rats to induce diabetes. Cardiac function was analysed by echocardiography. Matrix metalloproteinases (MMPs) activity and intracellular localization were assessed through zymography and immunofluorescence, whereas apoptotic and oxidative markers by immunohistochemistry and western blot., Results: Hyperglycaemia or hyperlipidaemia reduced ejection fraction and fractional shortening as compared with control. Unexpectedly, cardiac dysfunction was less marked in diabetic rats fed a hyperlipidaemic diet, suggesting an adaptive response of the myocardium to hyperglycaemia-induced injury. This response was characterized by the inhibition of N-terminal truncated-MMP-2 translocation from endoplasmic reticulum into mitochondria and by superoxide anion overproduction observed in cardiomyocytes under hyperglycaemia., Conclusion: Overall, these findings suggest novel therapeutic targets aimed to counteract mitochondrial dysfunction in the onset of diabetic cardiomyopathy., (Copyright © 2020 Italian Federation of Cardiology - I.F.C. All rights reserved.)

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder with patients exhibiting bone fragility and muscle weakness. The synergistic biochemical and biomechanical relationship between bone and muscle is a critical potential therapeutic target, such that muscle weakness should not be ignored. Previous studies demonstrated mitochondrial dysfunction in the skeletal muscle of oim/oim mice, which model a severe human type III OI. Here, we further characterize this mitochondrial dysfunction and evaluate several parameters of whole body and skeletal muscle metabolism. We demonstrate reduced mitochondrial respiration in female gastrocnemius muscle, but not in liver or heart mitochondria, suggesting that mitochondrial dysfunction is not global in the oim/oim mouse. Myosin heavy chain fiber type distributions were altered in the oim/oim soleus muscle with a decrease (-33 to 50%) in type I myofibers and an increase (+31%) in type IIa myofibers relative to their wildtype (WT) littermates. Additionally, altered body composition and increased energy expenditure were observed oim/oim mice relative to WT littermates. These results suggest that skeletal muscle mitochondrial dysfunction is linked to whole body metabolic alterations and to skeletal muscle weakness in the oim/oim mouse., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Primary graft dysfunction is an important cause of morbidity and mortality after cardiac transplantation. Donor brain stem death (BSD) is a significant contributor to donor heart dysfunction and primary graft dysfunction. There remain substantial gaps in the mechanistic understanding of peritransplant cardiac dysfunction. One of these gaps is cardiac metabolism and metabolic function. The healthy heart is an "omnivore," capable of utilizing multiple sources of nutrients to fuel its enormous energetic demand. When this fails, metabolic inflexibility leads to myocardial dysfunction. Data have hinted at metabolic disturbance in the BSD donor and subsequent heart transplantation; however, there is limited evidence demonstrating specific metabolic or mitochondrial dysfunction. This review will examine the literature surrounding cardiometabolic and mitochondrial function in the BSD donor, organ preservation, and subsequent cardiac transplantation. A more comprehensive understanding of this subject may then help to identify important cardioprotective strategies to improve the number and quality of donor hearts., Competing Interests: Outside of the submitted work, Professor Fraser provides consultancy services to Fisher and Paykel Healthcare, BiVACOR, De Motu Cordis Pty Limited, and the Quantum Medical Innovation Fund. Professor Fraser and his research group have received grant funding from the National Health and Medical Research Council, The Prince Charles Hospital Foundation, the Queensland Government (Department of Health, Metro North Hospital and Health Service. Additionally, Prof. Fraser and his research group work with Fisher and Paykel healthcare, Mallinckrodt Pharmaceuticals, CSL, BiVACOR, De Motu Cordis Pty Limited, Australian Red Cross Blood service. This has no direct impact on the contents of the manuscript. The other authors declare no conflicts of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

There is evidence demonstrating that heart failure (HF) occurs in 1-2% of the global population and is often accompanied by comorbidities which contribute to increasing the prevalence of the disease, the rate of hospitalization and the mortality. Although recent advances in both pharmacological and non-pharmacological approaches have led to a significant improvement in clinical outcomes in patients affected by HF, residual unmet needs remain, mostly related to the occurrence of poorly defined strategies in the early stages of myocardial dysfunction. Nutritional support in patients developing HF and nutraceutical supplementation have recently been shown to possibly contribute to protection of the failing myocardium, although their place in the treatment of HF requires further assessment, in order to find better therapeutic solutions. In this context, the Optimal Nutraceutical Supplementation in Heart Failure (ONUS-HF) working group aimed to assess the optimal nutraceutical approach to HF in the early phases of the disease, in order to counteract selected pathways that are imbalanced in the failing myocardium. In particular, we reviewed several of the most relevant pathophysiological and molecular changes occurring during the early stages of myocardial dysfunction. These include mitochondrial and sarcoplasmic reticulum stress, insufficient nitric oxide (NO) release, impaired cardiac stem cell mobilization and an imbalanced regulation of metalloproteinases. Moreover, we reviewed the potential of the nutraceutical supplementation of several natural products, such as coenzyme Q10 (CoQ10), a grape seed extract, Olea Europea L.-related antioxidants, a sodium-glucose cotransporter (SGLT2) inhibitor-rich apple extract and a bergamot polyphenolic fraction, in addition to their support in cardiomyocyte protection, in HF. Such an approach should contribute to optimising the use of nutraceuticals in HF, and the effect needs to be confirmed by means of more targeted clinical trials exploring the efficacy and safety of these compounds.

Mitochondria have a remarkable ability to uptake and store massive amounts of calcium. However, the consequences of massive calcium accumulation remain enigmatic. In the present study, we analyzed a series of time-course experiments to identify the sequence of events that occur in a population of guinea pig cardiac mitochondria exposed to excessive calcium overload that cause mitochondrial permeability transition (MPT). By analyzing coincident structural and functional data, we determined that excessive calcium overload is associated with large calcium phosphate granules and inner membrane fragmentation, which explains the extent of mitochondrial dysfunction. This data also reveals a novel mechanism for cyclosporin A, an inhibitor of MPT, in which it preserves cristae despite the presence of massive calcium phosphate granules in the matrix. Overall, these findings establish a mechanism of calcium-induced mitochondrial dysfunction and the impact of calcium regulation on mitochondrial structure and function.

Severity of cardiovascular disease increases markedly in elderly patients. In addition, many therapeutic strategies that decrease cardiac injury in adult patients are invalid in elderly patients. Thus, it is a challenge to protect the aged heart in the context of underlying chronic or acute cardiac diseases including ischemia-reperfusion injury. The cause(s) of this age-related increased damage remain unknown. Aging impairs the function of the mitochondrial electron transport chain (ETC), leading to decreased energy production and increased oxidative stress due to generation of reactive oxygen species (ROS). Additionally, ROS-induced oxidative stress can increase cardiac injury during ischemia-reperfusion by potentiating mitochondrial permeability transition pore (MPTP) opening. Aging leads to increased endoplasmic reticulum (ER) stress, which contributes to mitochondrial dysfunction, including reduced function of the ETC. The activation of both cytosolic and mitochondrial calcium-activated proteases termed calpains leads to mitochondrial dysfunction and decreased ETC function. Intriguingly, mitochondrial ROS generation also induces ER stress, highlighting the dynamic interaction between mitochondria and ER. Here, we discuss the role of ER stress in sensitizing and potentiating mitochondrial dysfunction in response to ischemia-reperfusion, and the promising potential therapeutic benefit of inhibition of ER stress and / or calpains to attenuate cardiac injury in elderly patients., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Aims: Voluntary exercise training has cardioprotective effects in humans, but the underlying mechanism is unknown. This research was done to estimate the effect of voluntary exercise training to attenuate middle-aged maturity-induced cardiac apoptosis., Materials and Methods: The study was designed to divide 64 male mice randomly into four groups, consisting of a 9-month sedentary pre-middle-aged group (9M), 15-month sedentary middle-aged group (15M), and two exercise groups using a voluntary wheel running respectively (9M+EX, 15M+EX). After 3 months, the condition of cardiac apoptosis in different groups was measured by HE dying, TUNEL and DAPI staining, and Western Blot analysis., Key Findings: TUNEL-positive cells were increased in 15M group compared with 9M group, while decreased in 9M+EX and 15M+EX groups compared with their control groups respectively. Protein levels of AIF, Endo G, TNF-α, TNFR1, TRAF2, TRADD, Fas, FasL, FADD, activated caspase 8, 3, 9, Bax/Bcl2, Bak/BclxL, and tBid were decreased in 9M+EX and 15M+EX groups compared with their control groups respectively. The protein levels of pBad/Bad, 14-3-3, IGF1, IGFR1, pPI3K/PI3K, and pAKT/AKT were more activated in the 9M+EX and 15M+EX groups than those in their control groups respectively. Significant differences were found between 9M group and 15M group for the protein levels of TRAF2, FADD, Bax/Bcl2, tBid and pAKT/AKT., Significance: Voluntary exercise training as an important lifestyle modification may prevent cardiac widely dispersed apoptosis and enhance cardiac survival at middle-aged maturity., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Maintaining energy balance over a wide range of temperatures is critical for an active pelagic fish species such as the mahi-mahi (Coryphaena hippurus), which can experience rapid changes in temperature during vertical migrations. Due to the profound effect of temperature on mitochondrial function, this study was designed to investigate the effects of temperature on mitochondrial respiration in permeabilized heart and red skeletal muscle (RM) fibres isolated from mahi-mahi. As RM is thought to be more anatomically isolated from rapid ambient temperature changes compared to the myocardium, it was hypothesized that heart mitochondria would be more tolerant of temperature changes through a greater ability to match respiratory capacity to an increase in temperature and to maintain coupling, when compared to RM mitochondria. Results show that heart fibres were more temperature sensitive and increased respiration rate with temperature increases to a greater degree than RM. Respiratory coupling ratios at the three assay temperatures (20, 26, and 30 °C), revealed that heart mitochondria were less coupled at a lower temperature (26 °C) compared to RM mitochondria (30 °C). In response to an in vitro acute temperature challenge, both tissues showed irreversible effects, where both heart and RM increased uncoupling whether the assay temperature was acutely changed from 20 to 30 °C or 30 to 20 °C. The findings from this study indicate that mahi-mahi heart mitochondria were more temperature sensitive compared to those from RM.

Ex vivo multicellular preparations are essential tools to study tissue physiology. Among them, the recent methodological and technological developments in living myocardial slices (LMS) are attracting increasing interest by the cardiac research field. Despite this, this research model remains poorly perceived and utilized by most research laboratories. Here, we provide a practical guide on how to use LMS to interrogate multiple aspects of cardiac function, structure and biochemistry. We discuss issues that should be considered to conduct successful experiments, including experimental design, sample preparation, data collection and analysis. We describe how laboratory setups can be adapted to accommodate and interrogate this multicellular research model. These adaptations can often be achieved at a reasonable cost with off-the-shelf components and operated reliably using well-established protocols and freely available software, which is essential to broaden the utilization of this method. We will also highlight how current measurements can be improved to further enhance data quality and reliability to ensure inter-laboratory reproducibility. Finally, we summarize the most promising biomedical applications and envision how living myocardial slices can lead to further breakthroughs.

As the powerhouse of the cells, mitochondria play a very important role in ensuring that cells continue to function. Mitochondrial dysfunction is one of the main factors contributing to the development of cardiomyopathy in diabetes mellitus. In early development of diabetic cardiomyopathy (DCM), patients present with myocardial fibrosis, dysfunctional remodeling and diastolic dysfunction, which later develop into systolic dysfunction and eventually heart failure. Cardiac mitochondrial dysfunction has been implicated in the development and progression of DCM. Thus, it is important to develop novel therapeutics in order to prevent the progression of DCM, especially by targeting mitochondrial dysfunction. To date, a number of studies have reported the potential of phenolic acids in exerting the cardioprotective effect by combating mitochondrial dysfunction, implicating its potential to be adopted in DCM therapies. Therefore, the aim of this review is to provide a concise overview of mitochondrial dysfunction in the development of DCM and the potential role of phenolic acids in combating cardiac mitochondrial dysfunction. Such information can be used for future development of phenolic acids as means of treating DCM by alleviating the cardiac mitochondrial dysfunction.

Advancing age is a major risk factor for developing heart disease, and the biological processes contributing to aging are currently under intense investigation. Autophagy is an important cellular quality control mechanism that is reduced in tissues with age but the molecular mechanisms underlying the age-associated defects in autophagy remain poorly characterized. Here, we have investigated how the autophagic process is altered in aged mouse hearts. We report that autophagic activity is reduced in aged hearts due to a reduction in autophagosome formation. Gene expression profile analysis to evaluate changes in autophagy regulators uncovered a reduction in Atg9b transcript and protein levels. Atg9 proteins are critical in delivering membrane to the growing autophagosome, and siRNA knockdown of Atg9b in cells confirmed a reduction in autophagosome formation. Autophagy is also the main pathway involved in eliminating dysfunctional mitochondria via a process known as mitophagy. The E3 ubiquitin ligase Parkin plays a key role in labeling mitochondria for mitophagy. We also found increased levels of Parkin-positive mitochondria in the aged hearts, an indication that they have been labeled for mitophagy. In contrast, Nrf1, a major transcriptional regulator of mitochondrial biogenesis, was significantly reduced in aged hearts. Additionally, our data showed reduced Drp1-mediated mitochondrial fission and formation of enlarged mitochondria in the aged heart. Overall, our findings suggest that cardiac aging is associated with reduced autophagosome number, decreased mitochondrial turnover, and formation of megamitochondria., (© 2020 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Background: Electroacupuncture is well known for its advantageous neuroanalgesic and therapeutic effects on myocardial ischemia-reperfusion injury. The purpose of the present research was to verify whether electroacupuncture can alleviate bupivacaine-induced myocardial injury., Methods: Specific pathogen-free Wistar rats were used to establish the bupivacaine-induced myocardial injury model. Western blot, PCR, transmission electron microscope and enzyme-linked immunosorbent (ELISA) methods were used to evaluate bupivacaine-induced structure injury and dysfunction of the mitochondria as well as the alleviating effects of lipid emulsion, acupoint injection, and electroacupuncture pre-treatment of the oxidase stress response., Results: Bupivacaine caused structural damage, degradation, and swelling of mitochondria. Furthermore, it reduced adenosine triphosphate (ATP) synthesis and impaired energy metabolism in the mitochondria. Structural and functional impairment of the mitochondria was alleviated via lipid emulsion injection, acupoint injection, and electroacupuncture pre-treatment. Electroacupuncture pre-treatment of PC6 yielded a greater alleviating effect than others approaches. Following electroacupuncture pre-treatment of PC6 point, the number of mitochondria increased; apoptosis was reduced, enzymatic activity of cytochrome C oxidase (COX) and superoxide dismutase and expression of uncoupling protein 2, voltage-dependent anion channel 1, and Bcl 2 were upregulated and SLC25A6, MDA levels were downregulated. Additionally, our findings indicated that electroacupuncture pre-treatment of PC6 point exerted an effect on the mitochondria via the mitochondrial-transcription-factor-A/nuclear-respiratory-factor-1/proliferator-activated-receptor-gamma-coactivator-1 pathway., Conclusion: The present study revealed that electroacupuncture pre-treatment of PC6 could effectively alleviate bupivacaine-induced myocardial mitochondrial damage, thereby providing a theoretical basis for clinical studies and applications of this treatment method.

Calcific aortic stenosis is a disorder that impacts the physiology of heart valves. Fibrocalcific events progress in conjunction with thickening of the valve leaflets. Over the years, these events promote stenosis and obstruction of blood flow. Known and common risk factors are congenital defects, aging and metabolic syndromes linked to high plasma levels of lipoproteins. Inflammation and oxidative stress are the main molecular mediators of the evolution of aortic stenosis in patients and these mediators regulate both the degradation and remodeling processes. Mitochondrial dysfunction and dysregulation of autophagy also contribute to the disease. A better understanding of these cellular impairments might help to develop new ways to treat patients since, at the moment, there is no effective medical treatment to diminish neither the advancement of valve stenosis nor the left ventricular function impairments, and the current approaches are surgical treatment or transcatheter aortic valve replacement with prosthesis.

The mitochondrial permeability transition, an established mechanism for heart diseases, is a long-standing mystery of mitochondrial biology and a prime drug target for cardioprotection. Several hypotheses about its molecular nature have been put forward over the years, and the prevailing view is that permeabilization of the inner mitochondrial membrane follows opening of a high-conductance channel, the permeability transition pore, which is also called mitochondrial megachannel or multiconductance channel. The permeability transition strictly requires matrix Ca 2+ and is favored by the matrix protein cyclophilin D, which mediates the inhibitory effects of cyclosporin A. Here we provide a review of the field, with specific emphasis on the possible role of the adenine nucleotide translocator and of the F-ATP synthase in channel formation, and on currently available small molecule inhibitors. While the possible mechanisms through which the adenine nucleotide translocator and the F-ATP synthase might form high-conductance channels remain unknown, reconstitution experiments and site-directed mutagenesis combined to electrophysiology have provided important clues. The hypothesis that more than one protein may act as a permeability transition pore provides a reasonable explanation for current controversies in the field, and holds great promise for the solution of the mystery of the permeability transition., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The uptake of Ca 2+ into mitochondria is thought to be an important signal communicating the need for increased energy production. However, dysregulated uptake leading to mitochondrial Ca 2+ overload can trigger opening of the mitochondrial permeability transition pore and potentially cell death. Thus mitochondrial Ca 2+ entry is regulated via the activity of a Ca 2+ -selective channel known as the mitochondrial calcium uniporter. The last decade has seen enormous momentum in the discovery of the molecular identities of the multiple proteins comprising the uniporter. Increasing numbers of studies in cultured cells and animal models have provided insight into how disruption of uniporter proteins affects mitochondrial Ca 2+ regulation and impacts tissue function and physiology. This review aims to summarize some of these recent findings, particularly in the context of the heart., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

(1) Background: There are no successive treatments for heart failure with preserved ejection fraction (HFpEF) because of complex interactions between environmental, histological, and genetic risk factors. The objective of the study is to investigate changes in cardiomyocytes and molecular networks associated with HFpEF. (2) Methods: Dahl salt-sensitive (DSS) rats developed HFpEF when fed with a high-salt (HS) diet for 7 weeks, which was confirmed by in vivo and ex vivo measurements. Shotgun proteomics, microarray, Western blot, and quantitative RT-PCR analyses were further carried out to investigate cellular and molecular mechanisms. (3) Results: Rats with HFpEF showed diastolic dysfunction, impaired systolic function, and prolonged repolarization of myocytes, owing to an increase in cell size and apoptosis of myocytes. Heatmap of multi-omics further showed significant differences between rats with HFpEF and controls. Gene Set Enrichment Analysis (GSEA) of multi-omics revealed genetic risk factors involved in cardiac muscle contraction, proteasome, B cell receptor signaling, and p53 signaling pathway. Gene Ontology (GO) analysis of multi-omics showed the inflammatory response and mitochondrial fission as top biological processes that may deteriorate myocyte stiffening. GO analysis of protein-to-protein network indicated cytoskeleton protein, cell fraction, enzyme binding, and ATP binding as the top enriched molecular functions. Western blot validated upregulated Mff and Itga9 and downregulated Map1lc3a in the HS group, which likely contributed to accumulation of aberrant mitochondria to increase ROS and elevation of myocyte stiffness, and subsequent contractile dysfunction and myocardial apoptosis. (4) Conclusions: Multi-omics analysis revealed multiple pathways associated with HFpEF. This study shows insight into molecular mechanisms for the development of HFpEF and may provide potential targets for the treatment of HFpEF., Competing Interests: The authors declare no conflict of interest.

Mesalazine is widely used in the management of inflammatory bowel disease. Previous studies reported that mesalazine-induced cardiotoxicity is a rare, potentially fatal complication. Mitochondria play an important role in myocardial tissue homeostasis. Deterioration in mitochondrial function will eventually lead to cardiomyocyte death and consequently cardiovascular dysfunction. The aim of the current study was to investigate the effects of mesalazine on rat heart mitochondria. Rat heart mitochondria were isolated by mechanical lysis and differential centrifugation. Parameters of mitochondrial toxicity including succinate dehydrogenase (SDH) activity, reactive oxygen species (ROS) formation, mitochondrial membrane potential (MMP) collapse, mitochondrial swelling, and cytochrome c release were evaluated. Results revealed that mesalazine induced a concentration- and time-dependent rise in mitochondrial ROS formation, inhibition of SDH, MMP collapse, mitochondrial swelling, and cytochrome c release in rat heart mitochondria. These results indicate that the cardiotoxic effects of mesalazine are most likely associated with mitochondrial dysfunction and ROS formation, which finally ends in cytochrome c release signaling and induction of apoptosis.

"Mitochondrial transplantation" refers to a procedure for introducing isolated mitochondria into a damaged area of a heart or other organ. A considerable amount of data has been accumulated on the therapeutic effects of "mitochondrial transplantation" in animals with ischemic heart damage. In 2017, the first attempts were made to apply this procedure in a clinic. The authors of the method suggest that exogenous mitochondria penetrate into cardiomyocytes, retaining functional activity, and compensate for impaired energy output of endogenous mitochondria. This hypothesis contradicts the well-known fact of loss of mitochondrial functions in the presence of high concentrations of Ca2+, which are characteristic of the extracellular medium. This review critically considers the possible mechanisms of the therapeutic effect of "mitochondrial transplantation".

Purpose: To determine the actions of isoespintanol (Isoesp) on post-ischemic myocardial and mitochondrial alterations., Methods: Hearts removed from Wistar rats were perfused by 20 min. After this period, the coronary flow was interrupted by half an hour and re-established during 1 h. In the treated group, Isoesp was administered at the beginning of reperfusion. To assess the participation of ε isoform of protein kinase C (PKCε), protein kinase B (PKB/Akt), and nitric oxide synthase (NOS), hearts were treated with Isoesp plus the respective inhibitors (chelerythrine, wortmannin, and N-nitro-L-arginine methyl ester). Cell death was determined by triphenyl tetrazolium chloride staining technique. Post-ischemic recovery of contractility, oxidative stress, and content of phosphorylated forms of PKCε, Akt, and eNOS were also examined. Mitochondrial state was assessed through the measurement of calcium-mediated response, calcium retention capacity, and mitochondrial potential., Results: Isoesp limited cell death, decreased post-ischemic dysfunction and oxidative stress, improved mitochondrial state, and increased the expression of PKCε, Akt, and eNOS phosphorylated. All these beneficial effects achieved by Isoesp were annulled by the inhibitors., Conclusion: These findings suggest that activation of Akt/eNOS and PKCε signaling pathways are involved in the development of Isoesp-induced cardiac and mitochondria tolerance to ischemia-reperfusion.

Background: Dilated cardiomyopathy with ataxia syndrome (DCMA) is an understudied autosomal recessive disease caused by loss-of-function mutations in the poorly characterized gene DNAJC19. Clinically, DCMA is commonly associated with heart failure and early death in affected children through an unknown mechanism. DCMA has been linked to Barth syndrome, a rare but well-studied disorder caused by deficient maturation of cardiolipin (CL), a key mitochondrial membrane phospholipid., Methods: Peripheral blood mononuclear cells from 2 children with DCMA and severe cardiac dysfunction were reprogrammed into induced pluripotent stem cells (iPSCs). Patient and control iPSCs were differentiated into beating cardiomyocytes (iPSC-CMs) using a metabolic selection strategy. Mitochondrial structure and CL content before and after incubation with the mitochondrially targeted peptide SS-31 were quantified., Results: Patient iPSCs carry the causative DNAJC19 mutation (rs137854888) found in the Hutterite population, and the iPSC-CMs demonstrated highly fragmented and abnormally shaped mitochondria associated with an imbalanced isoform ratio of the mitochondrial protein OPA1, an important regulator of mitochondrial fusion. These abnormalities were reversible by incubation with SS-31 for 24 hours. Differentiation of iPSCs into iPSC-CMs increased the number of CL species observed, but consistent, significant differences in CL content were not seen between patients and control., Conclusions: We describe a unique and novel cellular model that provides insight into the mitochondrial abnormalities present in DCMA and identifies SS-31 as a potential therapeutic for this devastating disease., (Copyright © 2019 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

New Findings: What is the topic for this review? This review summarizes recent discoveries in mitochondrial development and morphology studied with electron microscopy. What advances does it highlight? Although mitochondria are generally considered to be isolated from each other, this review highlights recently discovered evidence for the presence of intermitochondrial communication structures in cardiac and skeletal muscle, in animal models and humans. Within striated muscles, the means of intermitochondrial exchange and the reaction of mitochondria to external stimuli are uniquely dependent on the tissue, and we clearly differentiate between nanotunnels, the active protrusion of cardiac mitochondria, and the connecting ducts of skeletal muscle derived from fusion-fission and elongation events., Abstract: This review focuses on recent discoveries in skeletal and cardiac muscles indicating that mitochondria behave as an interactive cohort with inter-organelle communication and specific reactions to stress signals. Our new finding is that intermitochondrial communications in cardiac and skeletal muscles rely on two distinct methods. In cardiac muscle, mitochondria are discrete entities and are fairly well immobilized in a structural context. The organelles have developed a unique method of communication, via nanotunnels, which allow temporary connection from one mitochondrion to another over distances of up to several micrometres, without overall movement of the individual organelles and loss of their identity. Skeletal muscle mitochondria, in contrast, are dynamic. Through fusion, fission and elongation, they form connections that include constrictions and connecting ducts (distinct from nanotunnels) and lose individual identity in the formation of extensive networks. Connecting elements in skeletal muscle are distinct from nanotunnels in cardiac muscle., (© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.)

Electron microscopic study of cardiomyocytes taken from healthy Wistar and OXYS rats and naked mole rats ( Heterocephalus glaber ) revealed mitochondria in nuclei that lacked part of the nuclear envelope. The direct interaction of mitochondria with nucleoplasm is shown. The statistical analysis of the occurrence of mitochondria in cardiomyocyte nuclei showed that the percentage of nuclei with mitochondria was roughly around 1%, and did not show age and species dependency. Confocal microscopy of normal rat cardiac myocytes revealed a branched mitochondrial network in the vicinity of nuclei with an organization different than that of interfibrillar mitochondria. This mitochondrial network was energetically functional because it carried the membrane potential that responded by oscillatory mode after photodynamic challenge. We suggest that the presence of functional mitochondria in the nucleus is not only a consequence of certain pathologies but rather represents a normal biological phenomenon involved in mitochondrial/nuclear interactions.

Diabetic cardiomyopathy (DCM) is a major cause of morbidity and mortality in diabetic patients. Reactive oxygen species (ROS) produced by oxidative stress play an important role in the development of DCM. DCM involves abnormal energy metabolism, thereby reducing energy production. Exercise has been reported to be effective in protecting the heart against ROS accumulation during the development of DCM. We hypothesize that the AMPK/PGC-1α axis may play a crucial role in exercise-induced bioenergetic metabolism and aerobic respiration on oxidative stress parameters in the development of diabetic cardiomyopathy. Using a streptozotocin/high-fat diet mouse to generate a diabetic model, our aim was to evaluate the effects of exercise on the cardiac function, mitochondrial oxidative capacity, mitochondrial function, and cardiac expression of PGC-1α. Mice fed a high-fat diet were given MO-siPGC-1α or treated with AMPK inhibitor. Mitochondrial structure and effects of switching between the Warburg effect and aerobic respiration were analysed. Exercise improved blood pressure and systolic dysfunction in diabetic mouse hearts. The beneficial effects of exercise were also observed in a mitochondrial function study, as reflected by an enhanced oxidative phosphorylation level, increased membrane potential, and decreased ROS level and oxygen consumption. On the other hand, depletion of PGC-1α attenuated the effects of exercise on the enhancement of mitochondrial function. In addition, PGC-1α may be responsible for reversing the Warburg effect to aerobic respiration, thus enhancing mitochondrial metabolism and energy homoeostasis. In this study, we demonstrate the protective effects of exercise on shifting energy metabolism from fatty acid oxidation to glucose oxidation in an established diabetic stage. These data suggest that exercise is effective at ameliorating diabetic cardiomyopathy by improving mitochondrial function and reducing metabolic disturbances.

Autophagy is a cellular housekeeping and quality control mechanism that is essential for homeostasis and survival. By virtue of this role, any perturbations to the flow of this process in cardiac or vascular cells can elicit harmful effects on the cardiovascular system, and subsequently affect whole organismal health. In this chapter, we summarize the preclinical evidence supporting the role of autophagy in sustaining cardiovascular health during homeostasis and disease. Furthermore, we discuss how autophagy activation by dietary, genetic and pharmaceutical interventions can be exploited to counteract common cardiovascular disorders, including atherosclerosis, coronary artery disease, diabetic cardiomyopathy, arrhythmia, chemotherapy-induced cardiotoxicity and heart failure., (© 2020 Elsevier Inc. All rights reserved.)

Purpose: Previous studies implicate that the mitochondrial injury may play an important role in the development of post-resuscitation myocardial dysfunction, however few of them are available regarding the ultrastructural alterations of myocardial mitochondria, mitochondrial energy producing and utilization ability in the stage of arrest time (no-low) and resuscitation time (low-flow). This study aimed to observe the dynamic changes of myocardial mitochondrial function and metabolic disorders during cardiac arrest (CA) and following cardiopulmonary resuscitation (CPR)., Methods: A total of 30 healthy male Sprague-Dawley rats were randomized into three groups: 1) VF/CPR: Ventricular fibrillation (VF) was electrically induced, and 5 min of CPR was performed after 10 min of untreated VF; 2) Untreated VF: VF was induced and untreated for 15 min; and 3) Sham: Rats were identically prepared without VF/CPR. Amplitude spectrum area (AMSA) at VF 5, 10 and 15 min were calculated from ECG signals. The rats' hearts were quickly removed at the predetermined time of 15 min after beginning the procedure to gather measurements of myocardial mitochondrial function, high-energy phosphate stores, lactate, mitochondrial ultrastructure, and myocardial glycogen., Results: The mitochondrial respiratory control ratios significantly decreased after CA compared to sham group. CPR significantly increased respiratory control ratios compared with untreated VF animals. A significant decrease of myocardial glycogen was observed after CA, and a more rapid depletion of myocardial glycogen was observed in CPR animals. CPR significantly reduced the tissue lactate. The mitochondrial ultrastructure abnormalities in CPR animals were less severe than untreated VF animals. AMSA decayed during untreated VF; however, it was significantly greater in CPR group than the untreated VF group. In addition, AMSA was clearly positively correlated with ATP, but negatively correlated with myocardial glycogen., Conclusion: Impairment of myocardial mitochondrial function and the incapability of utilizing glycogen were observed after CA. Furthermore, optimal CPR might, in part, preserved mitochondrial function and enhanced utilization of myocardial glycogen., (Copyright © 2019. Published by Elsevier Inc.)