Mitochondria and heart disease

Comparative Analysis of Mitochondria Surrounding the Intercalated Discs in Heart Diseases-An Ultrastructural Pilot Study

BACKGROUND

Mitochondria play a crucial role in adapting to fluctuating energy demands, particularly in various heart diseases. This study investigates mitochondrial morphology near intercalated discs in left ventricular (LV) heart tissues, comparing samples from patients with sinus rhythm (SR), atrial fibrillation (AF), dilated cardiomyopathy (DCM), and ischemic cardiomyopathy (ICM).

METHODS

Transmission electron microscopy was used to analyze mitochondria within 0-3.5 μm and 3.5-7 μm of intercalated discs in 9 SR, 10 AF, 9 DCM, and 8 ICM patient samples. Parameters included mean size in µm2 and elongation, count, percental mitochondrial area in the measuring frame, and a conglomeration score.

RESULTS

AF patients exhibited higher counts of small mitochondria in the LV myocardium, resembling SR. DCM and ICM groups had fewer, larger, and often hydropic mitochondria. Accumulation rates and percental mitochondrial area were similar across groups. Significant positive correlations existed between other defects/size and hydropic mitochondria and between count/area and conglomeration score, while negative correlations between count and size/other defects and between hydropic mitochondria and count could be seen as well.

CONCLUSION

Mitochondrial parameters in the LV myocardium of AF patients were similar to those of SR patients, while DCM and ICM displayed distinct changes, including a decrease in number, an increase in size, and compromised mitochondrial morphology. Further research is needed to fully elucidate the pathophysiological role of mitochondrial morphology in different heart diseases, providing deeper insights into potential therapeutic targets and interventions.

Identification of necroptosis-related diagnostic biomarkers in coronary heart disease

Background

The implication of necroptosis in cardiovascular disease was already recognized. However, the molecular mechanism of necroptosis has not been extensively studied in coronary heart disease (CHD).

Methods

The differentially expressed genes (DEGs) between CHD and control samples were acquired in the GSE20681 dataset downloaded from the GEO database. Key necroptosis-related DEGs were captured and ascertained by bioinformatics analysis techniques, including weighted gene co-expression network analysis (WGCNA) and two machine learning algorithms, while single-gene gene set enrichment analysis (GSEA) revealed their molecular mechanisms. The diagnostic biomarkers were selected via receiver operating characteristic (ROC) analysis. Moreover, an analysis of immune elements infiltration degree was carried out. Authentication of pivotal gene expression at the mRNA level was investigated in vitro utilizing quantitative real-time PCR (qRT-PCR).

Results

A total of 94 DE-NRGs were recognized here, among which, FAM166B, NEFL, POLDIP3, PRSS37, and ZNF594 were authenticated as necroptosis-related biomarkers, and the linear regression model based on them presented an acceptable ability to different sample types. Following regulatory analysis, the ascertained biomarkers were markedly abundant in functions pertinent to blood circulation, calcium ion homeostasis, and the MAPK/cAMP/Ras signaling pathway. Single-sample GSEA exhibited that APC co-stimulation and CCR were more abundant, and aDCs and B cells were relatively scarce in CHD patients. Consistent findings from bioinformatics and qRT-PCR analyses confirmed the upregulation of NEFL and the downregulation of FAM166B, POLDIP3, and PRSS37 in CHD.

Conclusion

Our current investigation identified 5 necroptosis-related genes that could be diagnostic markers for CHD and brought a novel comprehension of the latent molecular mechanisms of necroptosis in CHD.

GRAF1 Acts as a Downstream Mediator of Parkin to Regulate Mitophagy in Cardiomyocytes

Cardiomyocytes rely on proper mitochondrial homeostasis to maintain contractility and achieve optimal cardiac performance. Mitochondrial homeostasis is controlled by mitochondrial fission, fusion, and mitochondrial autophagy (mitophagy). Mitophagy plays a particularly important role in promoting the degradation of dysfunctional mitochondria in terminally differentiated cells. However, the precise mechanisms by which this is achieved in cardiomyocytes remain opaque. Our study identifies GRAF1 as an important mediator in PINK1-Parkin pathway-dependent mitophagy. Depletion of GRAF1 (Arhgap26) in cardiomyocytes results in actin remodeling defects, suboptimal mitochondria clustering, and clearance. Mechanistically, GRAF1 promotes Parkin-LC3 complex formation and directs autophagosomes to damaged mitochondria. Herein, we found that these functions are regulated, at least in part, by the direct binding of GRAF1 to phosphoinositides (PI(3)P, PI(4)P, and PI(5)P) on autophagosomes. In addition, PINK1-dependent phosphorylation of Parkin promotes Parkin-GRAF1-LC3 complex formation, and PINK1-dependent phosphorylation of GRAF1 (on S668 and S671) facilitates the clustering and clearance of mitochondria. Herein, we developed new phosphor-specific antibodies to these sites and showed that these post-translational modifications are differentially modified in human hypertrophic cardiomyopathy and dilated cardiomyopathy. Furthermore, our metabolic studies using serum collected from isoproterenol-treated WT and GRAF1CKO mice revealed defects in mitophagy-dependent cardiomyocyte fuel flexibility that have widespread impacts on systemic metabolism. In summary, our study reveals that GRAF1 co-regulates actin and membrane dynamics to promote cardiomyocyte mitophagy and that dysregulation of GRAF1 post-translational modifications may underlie cardiac disease pathogenesis.

Physiological indices and liver gene expression related to glucose supply in Brandt's vole (Lasiopodomys brandtii) exhibit species- and oxygen concentration-specific responses to hypoxia

Brandt's vole (Lasiopodomys brandtii) is a species with hypoxia tolerance, and glucose serves as the primary energy substrate under hypoxia. However, the glucose supply in Brandt's voles under hypoxia has not been studied. This study aimed to investigate characteristics in physiological indices and liver gene expression associated with glucose supply in Brandt's voles under hypoxia. Serum glucose of Brandt's voles remained stable under 10% O2, increased under 7.5% O2, and decreased under 5% O2. Serum lactate increased under 10% O2, decreased under 7.5% O2, increased at 6 h and decreased at 12 h under 5% O2. Liver glycogen increased under 10% O2, remained constant under 7.5% O2, and reduced under 5% O2. Pepck and G6pase expression associated with gluconeogenesis decreased under 10% O2, while Pepck expression decreased and G6pase expression increased under 7.5% and 5% O2. Regarding genes related to glycogen metabolism, Gys expression decreased at all oxygen concentrations, Phk expression increased under 5% O2, and Gp expression increased under 7.5% and 5% O2. The alterations in glucose, lactate, liver glycogen, and gene expression related to glycogenolysis in Kunming mice (Mus musculus, control species) are similar to discovery of Brandt's voles under 7.5% O2, but gene expression involved in gluconeogenesis and glycogen synthesis increased. The findings suggest that Brandt's voles are more tolerant to hypoxia than Kunming mice, and their physiological indices and liver gene expression related to glucose supply exhibit species- and oxygen concentration-specific responses to hypoxia. This research offers novel insights for studying hypoxia tolerance of Brandt's voles.

Changes in gene expression and enzyme activity related to glucose metabolism in the livers of Brandt's voles (Lasiopodomys brandtii) exposed to hypoxia

Brandt's vole (Lasiopodomys brandtii) is a hypoxia-tolerant species, and the metabolic characteristics of hypoxia-tolerant species have become a focus of recent research. However, insights into the anaerobic and aerobic metabolism of the livers of Brandt's voles under hypoxia remain limited. In this study, Brandt's voles and hypoxia-intolerant Kunming mice (Mus musculus, control species) were exposed to hypoxia conditions (Brandt's voles, 10% and 7.5% O₂; Kunming mice, 10% O₂) for 24 h, and changes in gene expression and enzyme activity related to anaerobic and aerobic metabolism in the livers were evaluated. Phosphofructokinase 1 (PFK1), phosphofructokinase 2 (PFK2), pyruvate kinase muscle (PKM), hexokinase 2 (HK2), and lactate dehydrogenase (LDH) related to anaerobic metabolism in the livers of Brandt's voles were increased under 7.5% O₂. Regarding gene expression and enzyme activity for aerobic metabolism in Brandt's voles under 7.5% and 10% O₂, pyruvate dehydrogenase kinase 1 (PDK1) expression was up-regulated, and succinate dehydrogenase (SDH) activity was decreased. In the livers of Kunming mice, gene expression related to anaerobic and aerobic metabolism was increased at the late stage of 10% O₂, and SDH activity was enhanced at 6 h and reduced at 18 h. In addition, PFK1,PKM, PDK1 expression and SDH activity in Brandt's voles were significantly correlated with HIF-1a expression. PFK1, PKM, LDHand PDK1 expression in Kunming mice were significantly correlated with HIF-1a expression. These findings indicate that the livers of Brandt's voles have a certain tolerance to hypoxia, and metabolic changes play important roles in hypoxia tolerance.

Real-ambient particulate matter exposure-induced FGFR1 methylation contributes to cardiac dysfunction via lipid metabolism disruption

Particulate matter (PM)-induced cardiometabolic disorder contributes to the progression of cardiac diseases, but its epigenetic mechanisms are largely unknown. This study used bioinformatic analysis, in vivo and in vitro multiple models to investigate the role of PM-induced cardiac fibroblast growth factor 1 (FGFR1) methylation and its impact on cardiomyocyte lipid metabolic disruption. Bioinformatic analysis revealed that FGFR1 was associated with cardiac pathologies, mitochondrial function and metabolism, supporting the possibility that FGFR1 may play regulatory roles in PM-induced cardiac functional impairment and lipid metabolism disorders. Individually ventilated cage (IVC)-based real-ambient PM exposure system mouse models were used to expose C57/BL6 mice for six and fifteen weeks. The results showed that PM induced cardiac lipid metabolism disorder, DNA nucleotide methyltransferases (DNMTs) alterations and FGFR1 expression declines in mouse heart. Lipidomics analysis revealed that carnitines, phosphoglycerides and lysophosphoglycerides were most significantly affected by PM exposure. At the cellular level, AC16 cells treated with FGFR1 inhibitor (PD173074) led to impaired mitochondrial and metabolic functions in cardiomyocytes. Inhibition of DNA methylation in cells by 5-AZA partially restored the FGFR1 expression, ameliorated cardiomyocyte injury and mitochondrial functions. These changes involved alterations in AMP-activated protein kinase (AMPK)-peroxisome proliferator activated receptors gamma, coactivator 1 alpha (PGC1α) pathways. Bisulfite sequencing PCR (BSP) and DNA methylation specific PCR (MSP) confirmed that PM exposure induced FGFR1 gene promoter region methylation. These results suggested that, by inducing FGFR1 methylation, PM exposure would affect cardiac injury and deranged lipid metabolism. Overexpression of FGFR1 in mouse heart using adeno-associated virus 9 (AAV9) effectively alleviated PM-induced cardiac impairment and metabolic disorder. Our findings identified that FGFR1 methylation might be one of the potential indicators for PM-induced cardiac mitochondrial and metabolic dysfunction, providing novel insights into underlying PM-related cardiotoxic mechanisms.

Mitochondrial miRNA as epigenomic signatures: Visualizing aging-associated heart diseases through a new lens

Aging bears many hard knocks, but heart disorders earn a particular allusion, being the most widespread. Cardiovascular diseases (CVDs) are becoming the biggest concern to mankind due to sundry health conditions directly or indirectly related to heart-linked abnormalities. Scientists know that mitochondria play a critical role in the pathophysiology of cardiac diseases. Both environment and genetics play an essential role in modulating and controlling mitochondrial functions. Even a minor abnormality may prove detrimental to heart function. Advanced age combined with an unhealthy lifestyle can cause most cardiomyocytes to be replaced by fibrotic tissue which upsets the conducting system and leads to arrhythmias. An aging heart encounters far more heart-associated comorbidities than a young heart. Many state-of-the-art technologies and procedures are already being used to prevent and treat heart attacks worldwide. However, it remains a mystery when this heart bomb would explode because it lacks an alarm. This calls for a novel and effective strategy for timely diagnosis and a sure-fire treatment. This review article provides a comprehensive overture of prospective potentials of mitochondrial miRNAs that predict complicated and interconnected pathways concerning heart ailments and signature compilations of relevant miRNAs as biomarkers to plot the role of miRNAs in epigenomics. This article suggests that analysis of DNA methylation patterns in age-associated heart diseases may determine age-impelled biomarkers of heart disease.

Cadmium induced cardiac toxicology in developing Japanese quail (Coturnix japonica): Histopathological damages, oxidative stress and myocardial muscle fiber formation disorder

The anthropogenic-induced cadmium (Cd) pollution poses great threats to human health and wildlife survival. Birds also suffer from Cd contamination and Cd exerts negative impacts on multiple organs in birds. However, its toxic effects on cardiac organ of birds are still unclear. In this study, one-week old male Japanese quails were exposed to 15, 30, 60 and 75 mg/kg Cd for 5 weeks when birds in control group reached sex maturity. The results showed that Cd could cause microstructural damages including congestion and myocardial fiberolysis. Ultrastructural analysis also showed myocardial muscle fiber disarrangement and rupture as well as mitochondrial swelling, vacuolation and membrane lysis in Cd concentration groups. Moreover, Cd induced oxidative stress in the heart by decreasing antioxidant enzyme activities of catalase (CAT), glutathione peroxidase (GPX), total antioxidant capacity (T-AOC), superoxide dismutase (SOD) while increasing oxidative biomarkers such as malondialdehyde (MDA), inducible nitric oxide synthase (iNOS), and content of nitric oxide (NO). In addition, mRNA expression levels of genes involved in muscle fiber formation signaling pathway such as Follistatin (FST), paired box 3 (PAX3), myogenic differentiation 1 (MYoD1) and SRY-box transcription factor 6 (SOX6), were down-regulated by Cd exposure. Furthermore, PI3K/Akt/mTOR signaling pathway were disrupted by Cd exposure implying energy supply deficiency in the heart. We concluded that Cd caused cardiac dysfunction by inducing heart underdevelopment, histopathological injury, oxidative stress and myocardial muscle fiber formation disruption.

Mitochondrion as a Target of Astaxanthin Therapy in Heart Failure

Mitochondria are considered to be important organelles in the cell and play a key role in the physiological function of the heart, as well as in the pathogenesis and development of various heart diseases. Under certain pathological conditions, such as cardiovascular diseases, stroke, traumatic brain injury, neurodegenerative diseases, muscular dystrophy, etc., mitochondrial permeability transition pore (mPTP) is formed and opened, which can lead to dysfunction of mitochondria and subsequently to cell death. This review summarizes the results of studies carried out by our group of the effect of astaxanthin (AST) on the functional state of rat heart mitochondria upon direct addition of AST to isolated mitochondria and upon chronic administration of AST under conditions of mPTP opening. It was shown that AST exerted a protective effect under all conditions. In addition, AST treatment was found to prevent isoproterenol-induced oxidative damage to mitochondria and increase mitochondrial efficiency. AST, a ketocarotenoid, may be a potential mitochondrial target in therapy for pathological conditions associated with oxidative damage and mitochondrial dysfunction, and may be a potential mitochondrial target in therapy for pathological conditions.

Melatonin as a Potential Multitherapeutic Agent

Melatonin (N-acetyl-5-methoxytryptamine, MEL) is a hormone produced by the pineal gland that was discovered many years ago. The physiological roles of this hormone in the body are varied. The beneficial effects of MEL administration may be related to its influence on mitochondrial physiology. Mitochondrial dysfunction is considered an important factor in various physiological and pathological processes, such as the development of neurodegenerative and cardiovascular diseases, diabetes, various forms of liver disease, skeletal muscle disorders, and aging. Mitochondrial dysfunction induces an increase in the permeability of the inner membrane, which leads to the formation of a permeability transition pore (mPTP) in the mitochondria. The long-term administration of MEL has been shown to improve the functional state of mitochondria and inhibit the opening of the mPTP during aging. It is known that MEL is able to suppress the initiation, progression, angiogenesis, and metastasis of cancer as well as the sensitization of malignant cells to conventional chemotherapy and radiation therapy. This review summarizes the studies carried out by our group on the combined effect of MEL with chemotherapeutic agents (retinoic acid, cytarabine, and navitoclax) on the HL-60 cells used as a model of acute promyelocytic leukemia. Data on the effects of MEL on oxidative stress, aging, and heart failure are also reported.

Isoproterenol-Induced Permeability Transition Pore-Related Dysfunction of Heart Mitochondria Is Attenuated by Astaxanthin

Mitochondria are key organelles of the cell because their main function is the capture of energy-rich substrates from the cytoplasm and oxidative cleavage with the generation of carbon dioxide and water, processes that are coupled with the synthesis of ATP. Mitochondria are subject to oxidative stress through the formation of the mitochondrial permeability transition pore (mPTP). Various antioxidants are used to reduce damage caused by oxidative stress and to improve the protection of the antioxidant system. Astaxanthin (AST) is considered to be a dietary antioxidant, which is able to reduce oxidative stress and enhance the antioxidant defense system. In the present investigation, the effect of AST on the functional state of rat heart mitochondria impaired by isoproterenol (ISO) under mPTP functioning was examined. It was found that AST raised mitochondrial respiration, the Ca²⁺ retention capacity (CRC), and the rate of TPP⁺ influx in rat heart mitochondria (RHM) isolated from ISO-injected rats. However, the level of reactive oxygen species (ROS) production increased. In addition, the concentrations of cardiolipin (CL), Mn-SOD2, and the proteins regulating mPTP rose after the injection of ISO in RHM pretreated with AST. Based on the data obtained, we suggest that AST has a protective effect in rat heart mitochondria.

The Functions of Mitochondrial 2',3'-Cyclic Nucleotide-3'-Phosphodiesterase and Prospects for Its Future

2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNPase) is a myelin-associated enzyme that catalyzes the phosphodiester hydrolysis of 2’,3’-cyclic nucleotides to 2’-nucleotides. However, its presence is also found in unmyelinated cells and other cellular structures. Understanding of its specific physiological functions, particularly in unmyelinated cells, is still incomplete. This review concentrates on the role of mitochondrial CNPase (mtCNPase), independent of myelin. mtCNPase is able to regulate the functioning of the mitochondrial permeability transition pore (mPTP), and thus is involved in the mechanisms of cell death, both apoptosis and necrosis. Its participation in the development of various diseases and pathological conditions, such as aging, heart disease and alcohol dependence, is also reviewed. As such, mtCNPase can be considered as a potential target for the development of therapeutic strategies in the treatment of mitochondria-related diseases.

Vanillic Acid Alleviates Acute Myocardial Hypoxia/Reoxygenation Injury by Inhibiting Oxidative Stress

Oxidative stress is an important factor of myocardial hypoxia/reoxygenation (H/R) injury. Our research focuses on how to reduce the cardiac toxicity caused by oxidative stress through natural plant extracts. Vanillic acid (VA) is a phenolic compound found in edible plants and rich in the roots of Angelica sinensis. Experimental studies have provided evidence for this compound's effectiveness in cardiovascular diseases; however, its mechanism is still unclear. In this study, molecular mechanisms related to the protective effects of VA were investigated in H9c2 cells in the context of H/R injury. The results showed that pretreatment with VA significantly increased cell viability and decreased the percentage of apoptotic cells, as well as lactate dehydrogenase and creatine phosphokinase activity, in the supernatant, accompanied by reduced levels of reactive oxygen species and reduced caspase-3 activity. VA pretreatment also restored mitochondrial membrane potentials. Moreover, preincubation with VA significantly attenuated mitochondrial permeability transition pore activity. VA administration upregulated adenosine monophosphate-activated protein kinase α2 (AMPKα2) protein expression, and interestingly, pretreatment with AMPKα2-siRNA lentivirus effectively attenuated the cardioprotective effects of VA in response to H/R injury.

Astaxanthin Prevents Mitochondrial Impairment Induced by Isoproterenol in Isolated Rat Heart Mitochondria

Mitochondria are considered to be a power station of the cell. It is known that they play a major role in both normal and pathological heart function. Alterations in mitochondrial bioenergetics are one of the main causes of the origin and progression of heart failure since they have an inhibitory effect on the activity of respiratory complexes in the inner mitochondrial membrane. Astaxanthin (AST) is a xanthophyll carotenoid of mainly marine origin. It has both lipophilic and hydrophilic properties and may prevent mitochondrial dysfunction by permeating the cell membrane and co-localizing within mitochondria. The carotenoid suppresses oxidative stress-induced mitochondrial dysfunction and the development of diseases. In the present study, it was found that the preliminary oral administration of AST upregulated the activity of respiratory chain complexes and ATP synthase and the level of their main subunits, thereby improving the respiration of rat heart mitochondria (RHM) in the heart injured by isoproterenol (ISO). AST decreased the level of cyclophilin D (CyP-D) and increased the level of adenine nucleotide translocase (ANT) in this condition. It was concluded that AST could be considered as a potential mitochondrial-targeted agent in the therapy of pathological conditions associated with oxidative damage and mitochondrial dysfunction. AST, as a dietary supplement, has a potential in the prevention of cardiovascular diseases.

Astaxanthin Inhibits Mitochondrial Permeability Transition Pore Opening in Rat Heart Mitochondria

The mitochondrion is the main organelle of oxidative stress in cells. Increased permeability of the inner mitochondrial membrane is a key phenomenon in cell death. Changes in membrane permeability result from the opening of the mitochondrial permeability transition pore (mPTP), a large-conductance channel that forms after the overload of mitochondria with Ca²⁺ or in response to oxidative stress. The ketocarotenoid astaxanthin (AST) is a potent antioxidant that is capable of maintaining the integrity of mitochondria by preventing oxidative stress. In the present work, the effect of AST on the functioning of mPTP was studied. It was found that AST was able to inhibit the opening of mPTP, slowing down the swelling of mitochondria by both direct addition to mitochondria and administration. AST treatment changed the level of mPTP regulatory proteins in isolated rat heart mitochondria. Consequently, AST can protect mitochondria from changes in the induced permeability of the inner membrane. AST inhibited serine/threonine protein kinase B (Akt)/cAMP-responsive element-binding protein (CREB) signaling pathways in mitochondria, which led to the prevention of mPTP opening. Since AST improves the resistance of rat heart mitochondria to Ca²⁺-dependent stress, it can be assumed that after further studies, this antioxidant will be considered an effective tool for improving the functioning of the heart muscle in general under normal and medical conditions.

A critical appraisal of the tafazzin knockdown mouse model of Barth syndrome: what have we learned about pathogenesis and potential treatments?

Pediatric heart failure remains poorly understood, distinct in many aspects from adult heart failure. Limited data point to roles of altered mitochondrial functioning and, in particular, changes in mitochondrial lipids, especially cardiolipin. Barth syndrome is a mitochondrial disorder caused by tafazzin mutations that lead to abnormal cardiolipin profiles. Patients are afflicted by cardiomyopathy, skeletal myopathy, neutropenia, and growth delay. A mouse model of Barth syndrome was developed a decade ago, which relies on a doxycycline-inducible short hairpin RNA to knock down expression of tafazzin mRNA (TAZKD). Our objective was to review published data from the TAZKD mouse to determine its contributions to our pathogenetic understanding of, and potential treatment strategies for, Barth syndrome. In regard to the clinical syndrome, the reported physiological, biochemical, and ultrastructural abnormalities of the mouse model mirror those in Barth patients. Using this model, the peroxisome proliferator-activated receptor pan-agonist bezafibrate has been suggested as potential therapy because it ameliorated the cardiomyopathy in TAZKD mice, while increasing mitochondrial biogenesis. A clinical trial is now underway to test bezafibrate in Barth syndrome patients. Thus the TAZKD mouse model of Barth syndrome has led to important insights into disease pathogenesis and therapeutic targets, which can potentially translate to pediatric heart failure.

The Role of Mitochondria in the Mechanisms of Cardiac Ischemia-Reperfusion Injury

Mitochondria play a critical role in maintaining cellular function by ATP production. They are also a source of reactive oxygen species (ROS) and proapoptotic factors. The role of mitochondria has been established in many aspects of cell physiology/pathophysiology, including cell signaling. Mitochondria may deteriorate under various pathological conditions, including ischemia-reperfusion (IR) injury. Mitochondrial injury can be one of the main causes for cardiac and other tissue injuries by energy stress and overproduction of toxic reactive oxygen species, leading to oxidative stress, elevated calcium and apoptotic and necrotic cell death. However, the interplay among these processes in normal and pathological conditions is still poorly understood. Mitochondria play a critical role in cardiac IR injury, where they are directly involved in several pathophysiological mechanisms. We also discuss the role of mitochondria in the context of mitochondrial dynamics, specializations and heterogeneity. Also, we wanted to stress the existence of morphologically and functionally different mitochondrial subpopulations in the heart that may have different sensitivities to diseases and IR injury. Therefore, various cardioprotective interventions that modulate mitochondrial stability, dynamics and turnover, including various pharmacologic agents, specific mitochondrial antioxidants and uncouplers, and ischemic preconditioning can be considered as the main strategies to protect mitochondrial and cardiovascular function and thus enhance longevity.

A coronary artery disease-associated tRNAThr mutation altered mitochondrial function, apoptosis and angiogenesis

The tissue specificity of mitochondrial tRNA mutations remains largely elusive. In this study, we demonstrated the deleterious effects of tRNAThr 15927G>A mutation that contributed to pathogenesis of coronary artery disease. The m.15927G>A mutation abolished the highly conserved base-pairing (28C-42G) of anticodon stem of tRNAThr. Using molecular dynamics simulations, we showed that the m.15927G>A mutation caused unstable tRNAThr structure, supported by decreased melting temperature and slower electrophoretic mobility of mutated tRNA. Using cybrids constructed by transferring mitochondria from a Chinese family carrying the m.15927G>A mutation and a control into mitochondrial DNA (mtDNA)-less human umbilical vein endothelial cells, we demonstrated that the m.15927G>A mutation caused significantly decreased efficiency in aminoacylation and steady-state levels of tRNAThr. The aberrant tRNAThr metabolism yielded variable decreases in mtDNA-encoded polypeptides, respiratory deficiency, diminished membrane potential and increased the production of reactive oxygen species. The m.15927G>A mutation promoted the apoptosis, evidenced by elevated release of cytochrome c into cytosol and increased levels of apoptosis-activated proteins: caspases 3, 7, 9 and PARP. Moreover, the lower wound healing cells and perturbed tube formation were observed in mutant cybrids, indicating altered angiogenesis. Our findings provide new insights into the pathophysiology of coronary artery disease, which is manifested by tRNAThr mutation-induced alterations.

Dynamics of Dynamin-Related Protein 1 in Alzheimer's Disease and Other Neurodegenerative Diseases

The purpose of this article is to highlight the role of dynamin-related protein 1 (Drp1) in abnormal mitochondrial dynamics, mitochondrial fragmentation, autophagy/mitophagy, and neuronal damage in Alzheimer's disease (AD) and other neurological diseases, including Parkinson's, Huntington's, amyotrophic lateral sclerosis, multiple sclerosis, diabetes, and obesity. Dynamin-related protein 1 is one of the evolutionarily highly conserved large family of GTPase proteins. Drp1 is critical for mitochondrial division, size, shape, and distribution throughout the neuron, from cell body to axons, dendrites, and nerve terminals. Several decades of intense research from several groups revealed that Drp1 is enriched at neuronal terminals and involved in synapse formation and synaptic sprouting. Different phosphorylated forms of Drp1 acts as both increased fragmentation and/or increased fusion of mitochondria. Increased levels of Drp1 were found in diseased states and caused excessive fragmentation of mitochondria, leading to mitochondrial dysfunction and neuronal damage. In the last two decades, several Drp1 inhibitors have been developed, including Mdivi-1, Dynasore, P110, and DDQ and their beneficial effects tested using cell cultures and mouse models of neurodegenerative diseases. Recent research using genetic crossing studies revealed that a partial reduction of Drp1 is protective against mutant protein(s)-induced mitochondrial and synaptic toxicities. Based on findings from cell cultures, mouse models and postmortem brains of AD and other neurodegenerative disease, we cautiously conclude that reduced Drp1 is a promising therapeutic target for AD and other neurological diseases.

Amyloid Beta and Phosphorylated Tau-Induced Defective Autophagy and Mitophagy in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by memory loss and multiple cognitive impairments. Several decades of intense research have revealed that multiple cellular changes are implicated in the development and progression of AD, including mitochondrial damage, synaptic dysfunction, amyloid beta (Aβ) formation and accumulation, hyperphosphorylated tau (P-Tau) formation and accumulation, deregulated microRNAs, synaptic damage, and neuronal loss in patients with AD. Among these, mitochondrial dysfunction and synaptic damage are early events in the disease process. Recent research also revealed that Aβ and P-Tau-induced defective autophagy and mitophagy are prominent events in AD pathogenesis. Age-dependent increased levels of Aβ and P-Tau reduced levels of several autophagy and mitophagy proteins. In addition, abnormal interactions between (1) Aβ and mitochondrial fission protein Drp1; (2) P-Tau and Drp1; and (3) Aβ and PINK1/parkin lead to an inability to clear damaged mitochondria and other cellular debris from neurons. These events occur selectively in affected AD neurons. The purpose of our article is to highlight recent developments of a Aβ and P-Tau-induced defective autophagy and mitophagy in AD. This article also summarizes several aspects of mitochondrial dysfunction, including abnormal mitochondrial dynamics (increased fission and reduced fusion), defective mitochondrial biogenesis, reduced ATP, increased free radicals and lipid peroxidation, and decreased cytochrome c oxidase (COX) activity and calcium dyshomeostasis in AD pathogenesis. Our article also discusses how reduced levels of Drp1, Aβ, and P-Tau can enhance the clearance of damaged mitochondria and other cellular debris by autophagy and mitophagy mechanisms.

Nutritional Preconditioning of Apigenin Alleviates Myocardial Ischemia/Reperfusion Injury via the Mitochondrial Pathway Mediated by Notch1/Hes1

Apigenin (Api), a natural flavone found in high amounts in several herbs, has shown potent cardioprotective effects in clinical studies, although the underlying mechanisms are not clear. We hypothesized that Api protects the myocardium from simulated ischemia/reperfusion (SI/R) injury via nutritional preconditioning (NPC). Rats fed with Api-containing food showed improvement in cardiac functions; lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) activities; infarct size; apoptosis rates; malondialdehyde (MDA) levels; caspase-3, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) activities; and ferric reducing antioxidant power (FRAP) compared to those fed standard chow following SI/R injury. In addition, Api pretreatment significantly improved the viability, decreased the LDH activity and intracellular reactive oxygen species (ROS) generation, alleviated the loss of mitochondrial membrane potential (MMP), prevented the opening of the mitochondrial permeability transition pore (mPTP), and decreased the caspase-3 activity, cytochrome c (Cyt C) release, and apoptosis induced by SI/R in primary cardiomyocytes. Mechanistically, Api upregulated Hes1 expression and was functionally neutralized by the Notch1 γ-secretase inhibitor GSI, as well as the mPTP opener atractyloside (Atr). Taken together, Api protected the myocardium against SI/R injury via the mitochondrial pathway mediated by the Notch1/Hes1 signaling pathway.

Calcium in the Pathophysiology of Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is commonly associated with heart failure. A bidirectional relationship exists between the two-AF exacerbates heart failure causing a significant increase in heart failure symptoms, admissions to hospital and cardiovascular death, while pathological remodeling of the atria as a result of heart failure increases the risk of AF. A comprehensive understanding of the pathophysiology of AF is essential if we are to break this vicious circle. In this review, the latest evidence will be presented showing a fundamental role for calcium in both the induction and maintenance of AF. After outlining atrial electrophysiology and calcium handling, the role of calcium-dependent afterdepolarizations and atrial repolarization alternans in triggering AF will be considered. The atrial response to rapid stimulation will be discussed, including the short-term protection from calcium overload in the form of calcium signaling silencing and the eventual progression to diastolic calcium leak causing afterdepolarizations and the development of an electrical substrate that perpetuates AF. The role of calcium in the bidirectional relationship between heart failure and AF will then be covered. The effects of heart failure on atrial calcium handling that promote AF will be reviewed, including effects on both atrial myocytes and the pulmonary veins, before the aspects of AF which exacerbate heart failure are discussed. Finally, the limitations of human and animal studies will be explored allowing contextualization of what are sometimes discordant results.

Co-exposure of silica nanoparticles and methylmercury induced cardiac toxicity in vitro and in vivo

The released nanoparticles into environment can potentially interact with pre-existing pollution, maybe causing higher toxicity. As such, assessment of their joint toxic effects is necessary. This study was to investigate the co-exposure cardiac toxicity of silica nanoparticles (SiNPs) and methylmercury (MeHg). Factorial design was used to determine the potential joint action type. In vitro study, human cardiomyocytes (AC16) were exposed to SiNPs and MeHg alone or the combination. Higher toxicity was observed on cell viability, cell membrane damage in co-exposure compared with single exposure and control. The co-exposure enhanced the ROS, MDA generation and reduced the activity of SOD and GSH-Px. In addition, the co-exposure induced much higher cellular apoptotic rate in AC16. In vivo study, after SD rats exposed to SiNPs and MeHg and their mixture by intratracheal instillation for 30days, pathological changes (myocardial interstitial edema) of heart were occurred in co-exposure compared with single exposure and control. Moreover obvious ultra-structural changes, including myofibril disorder, myocardial gap expansion, and mitochondrial damage were observed in co-exposure group. The activity of myocardial enzymes, including CK-MB, ANP, BNP and cTnT, were significantly elevated in co-exposure group of rat serum. Meanwhile, the cardiac injury-linked proteins expression showed an increase in SERCA2 and decreased levels of cTnT, ANP and BNP in co-exposure group. Factorial design analysis demonstrated that additive and synergistic interactions were responsible for the co-exposure cardiac toxicity in vitro and vivo. In summary, our results showed severe cardiac toxicity induced by co-exposure of SiNPs and MeHg in both cardiomycytes and heart. It will help to clarify the potential cardiovascular toxicity in regards to combined exposure pollutions.

Effect of Melatonin on Rat Heart Mitochondria in Acute Heart Failure in Aged Rats

Excessive generation of reactive oxygen species (ROS) in mitochondria and the opening of the nonselective mitochondrial permeability transition pore are important factors that promote cardiac pathologies and dysfunction. The hormone melatonin (MEL) is known to improve the functional state of mitochondria via an antioxidant effect. Here, the effect of MEL administration on heart mitochondria from aged rats with acute cardiac failure caused by isoprenaline hydrochloride (ISO) was studied. A histological analysis revealed that chronic intake of MEL diminished the age-dependent changes in the structure of muscle fibers of the left ventricle, muscle fiber swelling, and injury zones characteristic of acute cardiac failure caused by ISO. In acute heart failure, the respiratory control index (RCI) and the Ca²⁺ retention capacity in isolated rat heart mitochondria (RHM) were reduced by 30% and 40%, respectively, and mitochondrial swelling increased by 34%. MEL administration abolished the effect of ISO. MEL partially prevented ISO-induced changes at the subunit level of respiratory complexes III and V and drastically decreased the expression of complex I subunit NDUFB8 both in control RHM and in RHM treated with ISO, which led to the inhibition of ROS production. MEL prevents the mitochondrial dysfunction associated with heart failure caused by ISO. It was shown that the level of 2′,3′-cyclicnucleotide-3′-phosphodiasterase (CNPase), which is capable of protecting cells in aging, increased in acute heart failure. MEL also retained the CNPase content in RHM both in control experiments and after ISO-induced heart damage. We concluded that an increase in the CNPase level promotes cardioprotection.

Mitochondrial responses to anoxia exposure in red eared sliders (Trachemys scripta)

When deprived oxygen, mitochondria from most vertebrates transform from the main site of ATP production to the dominant site of cellular ATP use due to the reverse functioning of the F1FO-ATPase (complex V). The anoxia-tolerant freshwater turtle Trachemys scripta however, has previously been shown to inhibit complex V activity in heart and brain in response to anoxia exposure, but the regulatory mechanism is unknown. To gain insight into the putative regulatory mechanisms underlying the anoxia-induced inhibition of complex V in T. scripta, we examined the effects of two weeks anoxia exposure at 4 °C on the mitochondrial proteome and candidate mechanisms that have been shown to regulate complex V in other organisms. In T. scripta, we confirmed that anoxia exposure resulted in a >80% inhibition of complex V in heart, brain and liver. Incubation of mitochondria with the nitric oxide donor, s-nitrosoglutathione, did not affect complex V activity despite showing the expected inhibition in mice. Proteomics analysis showed anoxia-induced decreases in three peripheral stalk subunits of complex V, possibly pointing to a unique site of regulation. Proteomics analysis also revealed differential expression of numerous enzymes involved with the electron transport system, the tricarboxylic acid cycle, as well as lipid and amino acid metabolism in response to anoxia exposure.

Tri-allelic heteroplasmies, DNA-RNA differences and their polynucleotide tract associations in the mitochondrial genome

The human mitochondrial genome has been extensively studied for its function and disease associations. Utilizing five types of high-throughput sequencing data on ten breast cancer patients (total N=50), we examined several aspects of the mitochondrial genome that have not been thoroughly studied, including the occurrence of tri-allelic heteroplasmy, the difference between DNA and RNA, and the variants association with polynucleotide tracts. We validated four previously reported and identified 23 additional tri-allelic positions. Furthermore, we detected 18 single nucleotide and seven InDel differences between DNA and RNA. Previous studies have suggested that some of these differences are caused by post transcriptional methylation. The rest can be accredited to RNA editing, polyadenylation or sequencing errors. Most importantly, we found that the tri-allelic positions, and differences between DNA and RNA, are strongly associated with polynucleotide tracts in the mitochondrial genome, suggesting DNA instability or difficulty sequencing around the polynucleotide tract regions.

Protective Effects of Isorhamnetin on Cardiomyocytes Against Anoxia/Reoxygenation-induced Injury Is Mediated by SIRT1

It has been reported that apoptosis plays a very important role on anoxia/reoxygenation (A/R)-induced injury, and human silent information regulator type 1 (SIRT1) can inhibit the apoptosis of cardiomyocytes. It has been proved that isorhamnetin (IsoRN), 3'-O-methyl-quecetin, can protect the cardiomyocytes, but the mechanism is still not clear. The aim of the study was to explore whether the protective effects of IsoRN on the cardiomyocytes against the A/R-induced injury are mediated by SIRT1. The effects of IsoRN on cardioprotection against A/R injury in neonatal rat cardiomyocytes were monitored by cell viability, the levels of mitochondrial membrane potential (Δψm), apoptosis, and intracellular reactive oxygen species (ROS), the levels of lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and mitochondrial permeability transition pores (mPTP). The effects on protein expression were measured by western blot assay. The results showed that IsoRN can reduce A/R-induced injury by decreasing the level of lactate dehydrogenase and creatine phosphokinase release from the cardiomyocytes, increasing cell viability and expression of SIRT1, reducing the generation of reactive oxygen species, inhibiting opening of mitochondrial permeability transition pores and loss of Δψm and activation of caspase-3, and decreasing the release of cytochrome c, and reducing apoptosis. In addition, sirtinol, a SIRT1 inhibitor, drastically reduced the protective effects of IsoRN on cardioprotective effects in cardiomocytes. In conclusion, we firstly demonstrated that SIRT1 may be involved in the protective effects of IsoRN on cardiomocytes against the A/R-induced injury.

Novel Roles of Epoxyeicosanoids in Regulating Cardiac Mitochondria

Maintenance of a healthy pool of mitochondria is important for the function and survival of terminally differentiated cells such as cardiomyocytes. Epoxyeicosatrienoic acids (EETs) are epoxy lipids derived from metabolism of arachidonic acid by cytochrome P450 epoxygenases. We have previously shown that EETs trigger a protective response limiting mitochondrial dysfunction and reducing cellular death. The aim of this study was to investigate whether EET-mediated effects influence mitochondrial quality in HL-1 cardiac cells during starvation. HL-1 cells were subjected to serum- and amino acid free conditions for 24h. We employed a dual-acting synthetic analog UA-8 (13-(3-propylureido)tridec-8-enoic acid), possessing both EET-mimetic and soluble epoxide hydrolase (sEH) inhibitory properties, or 14,15-EET as model EET molecules. We demonstrated that EET-mediated events significantly improved mitochondrial function as assessed by preservation of the ADP/ATP ratio and oxidative respiratory capacity. Starvation induced mitochondrial hyperfusion observed in control cells was attenuated by UA-8. However, EET-mediated events did not affect the expression of mitochondrial dynamic proteins Fis1, DRP-1 or Mfn2. Rather we observed increased levels of OPA-1 oligomers and increased mitochondrial cristae density, which correlated with the preserved mitochondrial function. Increased DNA binding activity of pCREB and Nrf1/2 and increased SIRT1 activity together with elevated mitochondrial proteins suggest EET-mediated events led to preserved mitobiogenesis. Thus, we provide new evidence for EET-mediated events that preserve a healthier pool of mitochondria in cardiac cells following starvation-induced stress.

Emotional triggering of cardiac dysfunction: the present and future

Mental stress and emotional arousal can act as triggers of acute myocardial infarction and other adverse cardiovascular outcomes. Experimental research examining mechanisms of the adverse interplay between mind and heart has led to the discovery of mental stress-induced cardiac dysfunction or myocardial ischemia (MSIMI). Evidence about the prevalence, clinical significance, and mechanistic bases of MSIMI outlines a wide range of central and peripheral bio-pathologic processes that are associated with emotions and behaviors. MSIMI is recognized as an integrated and intermediate biomarker underpinning the negative mind-heart interplay. Particularly, MSIMI research paves the way toward investigations aiming more specifically at recognizing the susceptibilities of individuals who are prone to respond adversely to the psycho-social-environmental stress. This article reviews recent literature on MSIMI research following the comprehensive review of Strike and Steptoe Eur Heart J 24:690-703, 2003. Further, this article outlines the main steps in the identification of the specific bio-pathologic manifestations of the cardiovascular system to emotional stress. Finally, a speculative description is provided of future directions in better searching for areas that may be critical targets in resolving adverse mind-heart interplays.

Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation

Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can lead to the development of the substrate that promotes atrial fibrillation (AF) and its progression. However, the link between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were not significantly different for age, sex, major comorbidities, and medications. The overall functional activity of the electron transport chain (ETC), NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared with non-AF patients. This was predominantly due to a selective reduction in complex I (0.06 ± 0.007 vs. 0.09 ± 0.006 nmol·min(-1)·citrate synthase activity(-1), P = 0.02) and II (0.11 ± 0.012 vs. 0.16 ± 0.012 nmol·min(-1)·citrate synthase activity(-1), P = 0.003) functional activity in AF patients. Conversely, complex V activity was significantly increased in AF patients (0.21 ± 0.027 vs. 0.12 ± 0.01 nmol·min(-1)·citrate synthase activity(-1), P = 0.005). In addition, AF patients exhibited a higher oxidative stress with increased production of mitochondrial superoxide (73 ± 17 vs. 11 ± 2 arbitrary units, P = 0.03) and 4-hydroxynonenal level (77.64 ± 30.2 vs. 9.83 ± 2.83 ng·mg(-1) protein, P = 0.048). Our findings suggest that AF is associated with selective downregulation of ETC activity and increased oxidative stress that can contribute to the progression of the substrate for AF.

Ex Vivo Treatment with a Polyphenol-Enriched Cocoa Extract Ameliorates Myocardial Infarct and Postischemic Mitochondrial Injury in Normotensive and Hypertensive Rats

Our objective was to determine the effects of a polyphenol-enriched cocoa extract (PCE) on myocardial postischemic alterations in normotensive (Wistar rats, W) and spontaneously hypertensive rats (SHR). Isolated hearts were submitted to 110 min of perfusion or 20 min stabilization, 30 min global ischemia, and 60 min reperfusion (R). Other hearts were treated with PCE at the onset of R. Infarct size, the reduced glutathione (GSH), and the expression of phospho-Akt, P-GSK-3β, and P-eNOS were assessed. In isolated mitochondria, the Ca(2+)-mediated response of mitochondrial permeability transition pore (mPTP), membrane potential (Δψm), and superoxide production were determined. PCE decreased infarct size, partly preserved GSH, increased the P-Akt, P-GSK-3β, and P-eNOS contents, improved mPTP response to Ca(2+), decreased the superoxide production, and restored Δψm. These data show that PCE decreases the cardiac postischemic damage in W rats and SHR and suggest that Akt/GSK-3β/eNOS dependent pathways are involved.

Carnosic Acid Affords Mitochondrial Protection in Chlorpyrifos-Treated Sh-Sy5y Cells

Carnosic acid (CA; C20H28O4) is a phenolic diterpene found in rosemary (Rosmarinus officinalis L.) and exhibits protective properties, e.g., antioxidant, anti-inflammatory, antitumor, and antimicrobial activities. In this context, CA has been viewed as a neuroprotective agent due to its ability in rescuing neuronal cells from pro-oxidant and pro-apoptotic challenges. In the present work, we found that CA pretreatment at 1 µM for 12 h suppressed the mitochondria-related pro-oxidant and mitochondria-dependent pro-apoptotic effects of chlorpyrifos (CPF) in human neuroblastoma SH-SY5Y cells. CA prevented mitochondrial membrane potential disruption and decreased the levels of oxidative stress markers in mitochondrial membranes obtained from cells exposed to CPF. CA also inhibited cytochrome c release and activation of the caspases-9 and -3, as well as decreased DNA fragmentation, in CPF-treated cells. CA upregulated the content of glutathione (GSH) in mitochondria by a mechanism involving the activation of the phosphoinositide-3-kinase (PI3K)/Akt/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, since inhibition of PI3K/Akt or silencing of Nrf2 using siRNA strategy abolished the protection exerted by CA in SH-SY5Y cells. Therefore, CA protected mitochondria of SH-SY5Y cells through the activation of the PI3K/Akt/Nrf2 axis, causing upregulation of the mitochondrial GSH content and consequent antioxidant and anti-apoptotic effects.

Mitochondria single nucleotide variation across six blood cell types

It has been shown that heteroplasmic mitochondrial DNA variants can be tissue specific. However, whether mitochondrial DNA variants are specific by blood cell types has not been investigated. Motivated by this question and using mitochondria sequences extracted from RNAseq data from six distinct blood cell types (neutrophil, monocyte, myeloid dendritic, natural killer, T and B), we thoroughly compared SNPs and heteroplasmies among these cell types. Each cell type from each subject was sequenced at four time points used as biological replicates. We found that mitochondria content is low in neutrophil compared to the other five blood cell types. Subsequent analysis on the other five blood cell types showed that at the SNP level, there was no discrepancy. At the heteroplasmy level, we observed good concordances among all blood cell types. However, the allele frequencies of the heteroplasmy differed between blood cell types for certain heteroplasmic sites. Furthermore, we identified five tri-allelic sites (1610, 2617, 8303, 12146, 13710) that are likely caused by RNA editing. Three out of these five sites are located at the ninth position of tRNA genes, and are likely resulting from post-transcriptional methylation.

Myofibroblast secretome and its auto-/paracrine signaling

Myofibroblasts (myoFb) are phenotypically transformed, contractile fibroblast-like cells expressing α-smooth muscle actin microfilaments. They are integral to collagen fibrillogenesis with scar tissue formation at sites of repair irrespective of the etiologic origins of injury or tissue involved. MyoFb can persist long after healing is complete, where their ongoing turnover of collagen accounts for a progressive structural remodeling of an organ (a.k.a. fibrosis, sclerosis or cirrhosis). Such persistent metabolic activity is derived from a secretome consisting of requisite components in the de novo generation of angiotensin (Ang) II. Autocrine and paracrine signaling induced by tissue AngII is expressed via AT1 receptor ligand binding to respectively promote: i) regulation of myoFb collagen synthesis via the fibrogenic cytokine TGF-β1-Smad pathway; and ii) dedifferentiation and protein degradation of atrophic myocytes immobilized and ensnared by fibrillar collagen at sites of scarring. Several cardioprotective strategies in the prevention of fibrosis and involving myofibroblasts are considered. They include: inducing myoFb apoptosis through inactivation of antiapoptotic proteins; AT1 receptor antagonist to interfere with auto-/paracrine myoFb signaling or to induce counterregulatory expression of ACE2; and attacking the AngII-AT1R-TGF-β1-Smad pathway by antibody or the use of triplex-forming oligonucleotides.

SERCA2a upregulation ameliorates cellular alternans induced by metabolic inhibition

Cardiac alternans has been associated with the incidence of ventricular tachyarrhythmias and sudden cardiac death. The aim of this study was to investigate the effect of impaired mitochondrial function in the genesis of cellular alternans and to examine whether modulating the sarcoplasmic reticulum (SR) Ca(2+)ameliorates the level of alternans. Cardiomyocytes isolated from control and doxycyline-induced sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a (SERCA2a)-upregulated mice were loaded with two different Ca(2+)indicators to selectively measure mitochondrial and cytosolic Ca(2+)using a custom-made fluorescence photometry system. The degree of alternans was defined as the alternans ratio (AR) [1 - (small Ca(2+)intensity)/(large Ca(2+)intensity)]. Blocking of complex I and II, cytochrome-coxidase, F0F1synthase, α-ketoglutarate dehydrogenase of the electron transport chain, increased alternans in both control and SERCA2a mice (P< 0.01). Changes in AR in SERCA2a-upregulated mice were significantly less pronounced than those observed in control in seven of nine tested conditions (P< 0.04).N-acetyl-l-cysteine (NAC), rescued alternans in myocytes that were previously exposed to an oxidizing agent (P< 0.001). CGP, an antagonist of the mitochondrial Na(+)-Ca(2+)exchanger, had the most severe effect on AR. Exposure to cyclosporin A, a blocker of the mitochondrial permeability transition pore reduced CGP-induced alternans (P< 0.0001). The major findings of this study are that impairment of mitochondrial Ca(2+)cycling and energy production leads to a higher amplitude of alternans in both control and SERCA2a-upregulated mice, but changes in SERCA2a-upregulated mice are less severe, indicating that SERCA2a mice are more capable of sustaining electrical stability during stress. This suggests a relationship between sarcoplasmic Ca(2+)content and mitochondrial dysfunction during alternans, which may potentially help to understand changes in Ca(2+)signaling in myocytes from diseased hearts, leading to new therapeutic targets.

Chronic heart failure: Ca(2+), catabolism, and catastrophic cell death

Robust successes have been achieved in recent years in conquering the acutely lethal manifestations of heart disease. Many patients who previously would have died now survive to enjoy happy and productive lives. Nevertheless, the devastating impact of heart disease continues unabated, as the spectrum of disease has evolved with new manifestations. In light of this ever-evolving challenge, insights that culminate in novel therapeutic targets are urgently needed. Here, we review fundamental mechanisms of heart failure, both with reduced (HFrEF) and preserved (HFpEF) ejection fraction. We discuss pathways that regulate cardiomyocyte remodeling and turnover, focusing on Ca(2+) signaling, autophagy, and apoptosis. In particular, we highlight recent insights pointing to novel connections among these events. We also explore mechanisms whereby potential therapeutic approaches targeting these processes may improve morbidity and mortality in the devastating syndrome of heart failure.

Astragaloside IV protects cardiomyocytes from anoxia/reoxygenation injury by upregulating the expression of Hes1 protein

Astragaloside IV (ASI), a traditional Chinese medicine, is a main active ingredient of Astragalus membranaceus. Many clinical studies have found that ASI protects cardiomyocytes in cardiovascular diseases, but the underlying mechanisms remain obscure. The aim of this study was to investigate the molecular mechanisms responsible for the protective effects of ASI in cardiomyocytes from anoxia/reoxygenation (A/R) injury. According to the previous studies, we hypothesized that the cardioprotective effects of ASI against A/R injury might be associated with Notch1/Hes1 signaling pathway. In this study, neonatal rat primary cardiomyocytes were preconditioned with ASI prior to A/R injury. Our results showed that ASI effectively increased the cell viability, decreased the content of MDA, decreased the activities of CPK and LDH, increased the activities of GSH-Px and SOD, and reduced the reactive oxygen species (ROS) generation and the loss of mitochondrial membrane potential (Δψm). ASI inhibited the mitochondrial permeability transition pore (mPTP) opening and activation of caspase-3, and finally decreased the cell apoptosis in cardiomyocytes. Furthermore, ASI upregulated Hes1 protein expression. However, pretreatment with DAPT, a Notch1 inhibitor, effectively attenuated the cardioprotective effects of ASI against A/R injury, except MDA, SOD, GSH-Px, and the ROS generation. Taken together, we demonstrated that ASI could protect against A/R injury via the Notch1/Hes1 signaling pathway.

Mitochondrial Dynamics and Heart Failure

Mitochondrial dynamics, fission and fusion, were first identified in yeast with investigation in heart cells beginning only in the last 5 to 7 years. In the ensuing time, it has become evident that these processes are not only required for healthy mitochondria, but also, that derangement of these processes contributes to disease. The fission and fusion proteins have a number of functions beyond the mitochondrial dynamics. Many of these functions are related to their membrane activities, such as apoptosis. However, other functions involve other areas of the mitochondria, such as OPA1's role in maintaining cristae structure and preventing cytochrome c leak, and its essential (at least a 10 kDa fragment of OPA1) role in mtDNA replication. In heart disease, changes in expression of these important proteins can have detrimental effects on mitochondrial and cellular function.

The expression characteristics of mt-ND2 gene in chicken

Subunit 2 of NADH dehydrogenase (ND2) is encoded by the mt-ND2 gene and plays a critical role in controlling the production of the mitochondrial reactive oxygen species. Our study focused on exploring the mt-ND2 tissue expression patterns and the effects of energy restriction and dietary fat (linseed oil, corn oil, sesame oil or lard) level (2.5% and 5%) on its expression in chicken. The results showed that mt-ND2 gene was expressed in the 15 tissues of hybrid chickens with the highest level in heart and lowest level in pancreas tissue; 30% energy restriction did not significantly affect mt-ND2 mRNA level in chicken liver tissue. Both the mt-ND2 mRNA levels in chicken pectoralis (p < 0.05) and hepatic tissues (p < 0.05) at 42 d-old were affected by the type of dietary fats in 5% level, while not in abdominal fat tissues. The expression of mt-ND2 in hepatic tissues was down-regulated with chicken age (p < 0.01). The interactive effect of dietary fat types with chicken age (p < 0.05) was significant on mt-ND2 mRNA level. The study demonstrated that mt-ND2 gene was extensively expressed in tissues, and the expression was affected by dietary fat types and chicken age.

Mitochondrial flash as a novel biomarker of mitochondrial respiration in the heart

Mitochondrial respiration through electron transport chain (ETC) activity generates ATP and reactive oxygen species in eukaryotic cells. The modulation of mitochondrial respiration in vivo or under physiological conditions remains elusive largely due to the lack of appropriate approach to monitor ETC activity in a real-time manner. Here, we show that ETC-coupled mitochondrial flash is a novel biomarker for monitoring mitochondrial respiration under pathophysiological conditions in cultured adult cardiac myocyte and perfused beating heart. Through real-time confocal imaging, we follow the frequency of a transient bursting fluorescent signal, named mitochondrial flash, from individual mitochondria within intact cells expressing a mitochondrial matrix-targeted probe, mt-cpYFP (mitochondrial-circularly permuted yellow fluorescent protein). This mt-cpYFP recorded mitochondrial flash has been shown to be composed of a major superoxide signal with a minor alkalization signal within the mitochondrial matrix. Through manipulating physiological substrates for mitochondrial respiration, we find a close coupling between flash frequency and the ETC electron flow, as measured by oxygen consumption rate in cardiac myocyte. Stimulating electron flow under physiological conditions increases flash frequency. On the other hand, partially block or slowdown electron flow by inhibiting the F0F1 ATPase, which represents a pathological condition, transiently increases then decreases flash frequency. Limiting electron entrance at complex I by knocking out Ndufs4, an assembling subunit of complex I, suppresses mitochondrial flash activity. These results suggest that mitochondrial electron flow can be monitored by real-time imaging of mitochondrial flash. The mitochondrial flash frequency could be used as a novel biomarker for mitochondrial respiration under physiological and pathological conditions.

Kaempferol protects cardiomyocytes against anoxia/reoxygenation injury via mitochondrial pathway mediated by SIRT1

Mitochondria-mediated apoptosis is a critical mechanism of anoxia/ reoxygenation (A/R)-induced injury in cardiomyocytes. Kaempferol (Kae) is a natural polyphenol and a type of flavonoid, which has been demonstrated to protect myocardium against ischemia/reperfusion (I/R) injury. However, the mechanism is still not fully elucidated. We hypothesize that Kae may improve the mitochondrial function during I/R injury via a potential signal pathway. In this study, an in vitro I/R model was replicated on neonatal rat primary cardiomyocytes by A/R treatment. Cell viability was monitored by the 3-(4,5-dimethylthiazol- 2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) assay. The levels of intracellular reactive oxygen species, mitochondrial membrane potential (Δψm) and apoptosis were determined by flow cytometry. Protein expression was detected by Western Blotting. mPTP opening and the activity of caspase-3 were measured by colorimetric method. The results showed that Kae effectively enhanced the cell viability and decreased the LDH release in cardiomyocytes subjected to A/R injury. Kae reduced the A/R-induced reactive oxygen species generation, the loss of Δψm, and the release of cytochrome c from mitochondria into cytosol. Kae inhibited the A/R-stimulated mPTP opening and activation of caspase-3, and ultimate decrease in cardiomyocytes apoptosis. Furthermore, we found Kae up-regulated Human Silent Information Regulator Type 1 (SIRT1) expression, indicating SIRT1 signal pathway likely involved the cardioprotection of Kae. Sirtinol, a SIRT1 inhibitor, abolished the protective effect of Kae in cardiomyocytes subjected to A/R. Additionally, Kae significantly increased the expression of Bcl-2. Thus, we firstly demonstrate that Kae protects cardiomyocytes against A/R injury through mitochondrial pathway mediated by SIRT1.

Platelet mitochondrial DNA methylation: a potential new marker of cardiovascular disease

Background

Platelets are critical in the etiology of cardiovascular disease (CVD), and the mitochondria in these cells serve as an energy source for platelet function. Epigenetic factors, especially DNA methylation, have been employed as markers of CVD. Unlike nuclear DNA methylation, mitochondrial DNA (mtDNA) methylation has not been widely studied, in part, due to debate about its existence and role. In this study, we examined platelet mtDNA methylation in relation to CVD.

Results

We measured mtDNA methylation in platelets by bisulfite-PCR pyrosequencing and examined associations of CVD with methylation in mitochondrial genes; cytochrome c oxidase (MT-CO1, MT-CO2, and MT-CO3); tRNA leucine 1 (MT-TL1); ATP synthase (MT-ATP6 and MT-ATP8); and NADH dehydrogenase (MT-MD5). We report that CVD patients have significantly higher mtDNA methylation than healthy controls in MT-CO1 (18.53%, P < 0.0001), MT-CO2 (3.33%, P = 0.0001), MT-CO3 (0.92%, P < 0.0001), and MT-TL1 (1.67%, P = 0.0001), which are involved in ATP synthesis. Platelet mtDNA methylation was not related with age, BMI, and race in this study.

Conclusions

Our results suggest that platelet mtDNA methylation, which could serve as non-invasive and easy-to-obtain markers, may be implicated in the etiology of CVD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0078-0) contains supplementary material, which is available to authorized users.

Estrogen-related receptor α (ERRα) and ERRγ are essential coordinators of cardiac metabolism and function

Almost all cellular functions are powered by a continuous energy supply derived from cellular metabolism. However, it is little understood how cellular energy production is coordinated with diverse energy-consuming cellular functions. Here, using the cardiac muscle system, we demonstrate that nuclear receptors estrogen-related receptor α (ERRα) and ERRγ are essential transcriptional coordinators of cardiac energy production and consumption. On the one hand, ERRα and ERRγ together are vital for intact cardiomyocyte metabolism by directly controlling expression of genes important for mitochondrial functions and dynamics. On the other hand, ERRα and ERRγ influence major cardiomyocyte energy consumption functions through direct transcriptional regulation of key contraction, calcium homeostasis, and conduction genes. Mice lacking both ERRα and cardiac ERRγ develop severe bradycardia, lethal cardiomyopathy, and heart failure featuring metabolic, contractile, and conduction dysfunctions. These results illustrate that the ERR transcriptional pathway is essential to couple cellular energy metabolism with energy consumption processes in order to maintain normal cardiac function.

Long-term oral resveratrol intake provides nutritional preconditioning against myocardial ischemia/reperfusion injury: involvement of VDAC1 downregulation

SCOPE

This study elucidates the effects of long-term nutritional preconditioning by resveratrol on ischemia/reperfusion (I/R) injury and its underlying mechanisms.

METHODS AND RESULTS

Mice were treated with resveratrol at 2.0 mg/kg/day by gastric gavages for 6 wk. Then hearts were isolated and subjected to I/R injury in a Langendorff apparatus. Resveratrol significantly improved left ventricular pressure, ±dp/dtmax, and coronary flow; decreased the lactate dehydrogenase and creatine phosphokinase activities; and reduced the infarction size. Additionally, long-term oral resveratrol intake prevented mitochondrial permeability transition pore opening and subsequently inhibited mitochondria-mediated apoptosis, as demonstrated by decrease of cytochrome c release, inactivation of caspase-3, and reduction of terminal deoxynucleotidyl transferase mediated nick end labeling positive cells. Furthermore, resveratrol inhibited the upregulation of voltage-dependent anion channel 1 (VDAC1) expression induced by I/R injury. Local left-ventricle overexpression of VDAC1 by adenovirus diminished the protective effect of resveratrol against I/R injury, indicating that VDAC1 plays an important role in resveratrol-mediated cardioprotection.

CONCLUSION

Our data revealed that long-term oral intake of resveratrol sets nutritional preconditioning to cope with myocardial I/R injury. Strikingly, we found that resveratrol downregulates VDAC1, leading to prevention of mitochondrial permeability transition pore opening and cardiomyocyte apoptosis.

Impact of caloric restriction on myocardial ischaemia/reperfusion injury and new therapeutic options to mimic its effects

Caloric restriction (CR) is the most reliable intervention to extend lifespan and prevent age-related disorders in various species from yeast to rodents. Short- and long-term CR confers cardio protection against ischaemia/reperfusion injury in young and even in aged rodents. A few human trials suggest that CR has the potential to mediate improvement of cardiac or vascular function and induce retardation of cardiac senescence also in humans. The underlying mechanisms are diverse and have not yet been clearly defined. Among the known mediators for the benefits of CR are NO, the AMP-activated PK, sirtuins and adiponectin. Mitochondria, which play a central role in such complex processes within the cell as apoptosis, ATP-production or oxidative stress, are centrally involved in many aspects of CR-induced protection against ischaemic injury. Here, we discuss the relevant literature regarding the protection against myocardial ischaemia/reperfusion injury conferred by CR. Furthermore, we will discuss drug targets to mimic CR and the possible role of calorie restriction in preserving cardiovascular function in humans.

Regulation of metabolism in individual mitochondria during excitation-contraction coupling

The heart is an excitable organ that undergoes spontaneous force generation and relaxation cycles driven by excitation-contraction (EC) coupling. A fraction of the oscillating cytosolic Ca(2+) during each heartbeat is taken up by mitochondria to stimulate mitochondrial metabolism, the major source of energy in the heart. Whether the mitochondrial metabolism is regulated individually during EC coupling and whether this heterogeneous regulation bears any physiological or pathological relevance have not been studied. Here, we developed a novel approach to determine the regulation of individual mitochondrial metabolism during cardiac EC coupling. Through monitoring superoxide flashes, which are stochastic and bursting superoxide production events arising from increased metabolism in individual mitochondria, we found that EC coupling stimulated the metabolism in individual mitochondria as indicated by significantly increased superoxide flash activity during electrical stimulation of the cultured intact myocytes or perfused heart. Mechanistically, cytosolic calcium transients promoted individual mitochondria to take up calcium via mitochondrial calcium uniporter, which subsequently triggered transient opening of the permeability transition pore and stimulated metabolism and bursting superoxide flash in that mitochondrion. The bursting superoxide, in turn, promoted local calcium release. In the early stage of heart failure, EC coupling regulation of superoxide flashes was compromised. This study highlights the heterogeneity in the regulation of cardiac mitochondrial metabolism, which may contribute to local redox signaling.

Roles of Calcium Regulating MicroRNAs in Cardiac Ischemia-Reperfusion Injury

Cardiac Ca2+ cycling and signaling are closely associated with cardiac function. Changes in cellular Ca2+ homeostasis may lead to aberrant cardiac rhythm and may play a critical role in the pathogenesis of cardiac diseases, due to their exacerbation of heart failure. MicroRNAs (miRNAs) play a key role in the regulation of gene expression at the post-transcriptional level and participate in regulating diverse biological processes. The emerging evidence indicates that the expression profiles of miRNAs vary among human diseases, including cardiovascular diseases. Cardiac Ca2+-handling and signaling proteins are also regulated by miRNAs. Given the relationship between cardiac Ca2+ homeostasis and signaling and miRNA, Ca2+-related miRNAs may serve as therapeutic targets during the treatment of heart failure. In this review, we summarize the knowledge currently available regarding the role of Ca2+ in cardiac function, as well as changes in Ca2+ cycling and homeostasis and the handling of these processes by miRNAs during cardiac ischemia-reperfusion injury.

A dynamic interface between vacuoles and mitochondria in yeast

Cellular life depends on continuous transport of lipids and small molecules between mitochondria and the endomembrane system. Recently, endoplasmic reticulum-mitochondrial encounter structure (ERMES) was identified as an important yet nonessential contact for such transport. Using a high-content screen in yeast, we found a contact site, marked by Vam6/Vps39, between vacuoles (the yeast lysosomal compartment) and mitochondria, named vCLAMP (vacuole and mitochondria patch). vCLAMP is enriched with ion and amino-acid transporters and has a role in lipid relay between the endomembrane system and mitochondria. Critically, we show that mitochondria are dependent on having one of two contact sites, ERMES or vCLAMP. The absence of one causes expansion of the other, and elimination of both is lethal. Identification of vCLAMP adds to our ability to understand the complexity of interorganellar crosstalk.

Adrenergic signaling regulates mitochondrial Ca2+ uptake through Pyk2-dependent tyrosine phosphorylation of the mitochondrial Ca2+ uniporter

AIMS

Mitochondrial Ca2+ homeostasis is crucial for balancing cell survival and death. The recent discovery of the molecular identity of the mitochondrial Ca2+ uniporter pore (MCU) opens new possibilities for applying genetic approaches to study mitochondrial Ca2+ regulation in various cell types, including cardiac myocytes. Basal tyrosine phosphorylation of MCU was reported from mass spectroscopy of human and mouse tissues, but the signaling pathways that regulate mitochondrial Ca2+ entry through posttranslational modifications of MCU are completely unknown. Therefore, we investigated α1-adrenergic-mediated signal transduction of MCU posttranslational modification and function in cardiac cells.

RESULTS

α1-adrenoceptor (α1-AR) signaling translocated activated proline-rich tyrosine kinase 2 (Pyk2) from the cytosol to mitochondrial matrix and accelerates mitochondrial Ca2+ uptake via Pyk2-dependent MCU phosphorylation and tetrametric MCU channel pore formation. Moreover, we found that α1-AR stimulation increases reactive oxygen species production at mitochondria, mitochondrial permeability transition pore activity, and initiates apoptotic signaling via Pyk2-dependent MCU activation and mitochondrial Ca2+ overload.

INNOVATION

Our data indicate that inhibition of α1-AR-Pyk2-MCU signaling represents a potential novel therapeutic target to limit or prevent mitochondrial Ca2+ overload, oxidative stress, mitochondrial injury, and myocardial death during pathophysiological conditions, where chronic adrenergic stimulation is present.

CONCLUSION

The α1-AR-Pyk2-dependent tyrosine phosphorylation of the MCU regulates mitochondrial Ca2+ entry and apoptosis in cardiac cells.