Down-regulation of mitofusin-2 expression in cardiac hypertrophy in vitro and in vivo

Harnessing exercise to combat chronic diseases: the role of Drp1-Mediated mitochondrial fission

Enhanced Drp1 activity mediates excessive mitochondrial fission, contributing to the onset and progression of various chronic diseases, including neurodegenerative, cardiovascular, and metabolic disorders. Studies indicate that exercise mitigates mitochondrial dysfunction by modulating Drp1-related signaling targets, thereby inhibiting Drp1 activity and reducing excessive mitochondrial fission. This, in turn, enhances mitochondrial function and cellular metabolism. This review synthesizes the current understanding of Drp1 structure and activation mechanisms, and analyzes the effects of exercise interventions on Drp1-mediated mitochondrial fission in different disease models to improve common chronic conditions. This research deepens our insight into the specific mechanisms of Drp1-induced excessive mitochondrial fission in chronic disease pathogenesis, offering new theoretical support and practical guidance for exercise as a non-pharmacological intervention strategy.

17-beta estradiol prevents cardiac myocyte hypertrophy by regulating mitochondrial E3 ubiquitin ligase 1

Cardiac hypertrophy is a cellular process characterized by the increased size of cardiomyocytes in response to a high workload or stress. 17-beta estradiol (E2) has cardioprotective and anti-hypertrophic effects by maintaining mitochondrial network and function. MUL1 is a mitochondrial ubiquitin ligase directly involved in the control of mitochondrial fission and mitophagy. Studies from our group and others have previously shown that cardiomyocyte hypertrophy is associated with mitochondrial fission and dysfunction. These findings led us to study in vitro whether E2 regulates MUL1 to prevent cardiac hypertrophy, mitochondrial fission, and dysfunction induced by the catecholamine norepinephrine (NE). Our results showed that NE induces hypertrophy in cultured rat cardiomyocytes. Pre-treatment with E2 (10-100 nM) prevented the NE-dependent increases in cell perimeter and the hypertrophic stress markers ANP and BNP at both the protein and mRNA levels. NE induced the fragmentation of the mitochondrial network and reduced ATP levels, effects that were both prevented by E2. In silico analysis suggested a putative binding site for estrogen receptors on the MUL1 gene promoter. In accordance with this finding, E2 prevented increases in MUL1 mRNA and protein levels induced by NE. Our data also showed that a siRNA MUL1 knockdown counteracted NE-induced cardiomyocyte hypertrophy and mitochondrial dysfunction, mirroring the protective effect triggered by E2. In contrast, a MUL1 adenovirus did not prevent the E2 protection from cardiomyocyte hypertrophy. Further, in vivo analysis in a transgenic mouse model overexpressing MUL1 revealed that only young male mice overexpressed the protein. Consequently, they exhibited increased levels of the hypertrophic marker ANP, an elevated heart weight, and larger cardiomyocyte size. Therefore, our data demonstrate that 17-beta estradiol prevents cardiac myocyte hypertrophy by regulating MUL1.

Diminazine protects against cardiac aging through the improvement of mitophagy and apoptosis in aging rats induced by D-galactose

BACKGROUND

Mitochondrial dysfunction is a main feature of the aged heart. However, there is still no effective treatment against cardiac aging. Diminazine (DIZE) is an anti-infective agent for animals. It is effective against cardiac disorders. The present study aimed to investigate the effects of DIZE on age-related cardiac dysfunction.

METHODS AND RESULTS

Wistar rats were randomly divided into four groups, with eight rats per group: control rats (CONT), control rats treated with DIZE (CONT + DIZE), aged rats induced by D-galactose (D-GAL), aged rats treated with DIZE (D-GAL + DIZE). Rats received intraperitoneal (IP) injection of D-GAL at 150 mg/kg daily for 8 weeks to induce aging. The aging animals in the D-GAL + DIZE group were treated with subcutaneous injection of DIZE at 15 mg/kg daily for 8 weeks. Heart tissues were harvested to assay molecular parameters. Our results exhibited cardiac hypertrophy and a significant increase in the expression of cardiac BCL2-associated X (Bax) along with a significant decrease in the expression of cardiac Mitofusin 2 (Mfn2), Phosphatase, and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), Dynamin-related protein 1 (Drp1), and B-cell lymphoma 2 (Bcl2) in the aged rats compared with the control animals. DIZE treatment improved cardiac hypertrophy and the expression of genes.

CONCLUSIONS

Overall, DIZE treatment significantly reversed the downregulation of PINK1, Mfn2, and Drp1. Moreover, DIZE significantly inhibited apoptosis though improving the gene expression of Bax and Bcl-2 in the heart. DIZE is effective in reducing cardiac hypertrophy induced aging through regulating mitochondrial dynamics, mitophagy and apoptosis.

Mitochondrial Reactive Oxygen Species Dysregulation in Heart Failure with Preserved Ejection Fraction: A Fraction of the Whole

Heart failure with preserved ejection fraction (HFpEF) is a multifarious syndrome, accounting for over half of heart failure (HF) patients receiving clinical treatment. The prevalence of HFpEF is rapidly increasing in the coming decades as the global population ages. It is becoming clearer that HFpEF has a lot of different causes, which makes it challenging to find effective treatments. Currently, there are no proven treatments for people with deteriorating HF or HFpEF. Although the pathophysiologic foundations of HFpEF are complex, excessive reactive oxygen species (ROS) generation and increased oxidative stress caused by mitochondrial dysfunction seem to play a critical role in the pathogenesis of HFpEF. Emerging evidence from animal models and human myocardial tissues from failed hearts shows that mitochondrial aberrations cause a marked increase in mitochondrial ROS (mtROS) production and oxidative stress. Furthermore, studies have reported that common HF medications like beta blockers, angiotensin receptor blockers, angiotensin-converting enzyme inhibitors, and mineralocorticoid receptor antagonists indirectly reduce the production of mtROS. Despite the harmful effects of ROS on cardiac remodeling, maintaining mitochondrial homeostasis and cardiac functions requires small amounts of ROS. In this review, we will provide an overview and discussion of the recent findings on mtROS production, its threshold for imbalance, and the subsequent dysfunction that leads to related cardiac and systemic phenotypes in the context of HFpEF. We will also focus on newly discovered cellular and molecular mechanisms underlying ROS dysregulation, current therapeutic options, and future perspectives for treating HFpEF by targeting mtROS and the associated signal molecules.

SIRT1 Ameliorates Lamin A/C Deficiency-Induced Cardiac Dysfunction by Promoting Mitochondrial Bioenergetics

Dilated cardiomyopathy (DCM) is associated with high mortality despite advanced therapies. The LMNA gene encodes lamin A/C and is the second most frequently mutated gene associated with DCM, for which therapeutic options are limited. Here we generated Lmna -/- mice and found they exhibited cardiac dysfunction at the age of 1 month but not at 2 weeks. Proteomics showed down-regulation of mitochondrial function-related pathways in Lmna -/- hearts. Moreover, early injured mitochondria with decreased cristae density and sirtuin 1 (SIRT1) down-regulation were observed in 2-week-old Lmna -/- hearts. Adenoviral overexpression of SIRT1 in lamin A/C knockdown neonatal rat ventricular myocytes improved mitochondrial oxidative respiration capacity. Adeno-associated virus-mediated SIRT1 overexpression alleviated mitochondrial injury, cardiac systolic dysfunction, ventricular dilation, and fibrosis, and prolonged lifespan in Lmna -/- mice. Mechanistically, LMNA maintains mitochondrial bioenergetics through the SIRT1-PARKIN axis. Our results suggest that targeting the SIRT1 signaling pathway is expected to be a novel therapeutic strategy for LMNA mutation-associated DCM.

Fenofibrate reduces cardiac remodeling by mitochondrial dynamics preservation in a renovascular model of cardiac hypertrophy

Fenofibrate, a PPAR-α agonist clinically used to lower serum lipid levels, reduces cardiac remodeling and improves cardiac function. However, its mechanism of action is not completely elucidated. In this study we examined the effect of fenofibrate on mitochondria in a rat model of renovascular hypertension, focusing on mediators controlling mitochondrial dynamics and autophagy. Rats with two-kidney one-clip (2K1C) hypertension were treated with fenofibrate 150 mg/kg/day (2K1C-FFB) or vehicle (2K1C-VEH) for 8 weeks. Systolic blood pressure and cardiac functional were in-vivo assessed, while cardiomyocyte size and protein expression of mediators of cardiac hypertrophy and mitochondrial dynamics were ex-vivo examined by histological and Western blot analyses. Fenofibrate treatment counteracted the development of hypertension and the increase of left ventricular mass, relative wall thickness and cross-sectional area of cardiomyocytes. Furthermore, fenofibrate re-balanced the expression Mfn2, Drp1 and Parkin, regulators of fusion, fission, mitophagy respectively. Regarding autophagy, the LC3-II/LC3-I ratio was increased in 2K1C-VEH and 2K1C-FFB, whereas the autophagy was increased only in 2K1C-FFB. In cultured H9C2 cardiomyoblasts, fenofibrate reversed the Ang II-induced mRNA up-regulation of hypertrophy markers Nppa and Myh7, accumulation of reactive oxygen species and depolarization of the mitochondrial membrane exerting protection mediated by up-regulation of the Uncoupling protein 2. Our results indicate that fenofibrate acts directly on cardiomyocytes and counteracts the pressure overload-induced cardiac maladaptive remodeling. This study reveals a so far hidden mechanism involving mitochondrial dynamics in the beneficial effects of fenofibrate, support its repurposing for the treatment of cardiac hypertrophy and provide new potential targets for its pharmacological function.

Mitochondria and NLRP3 inflammasome in cardiac hypertrophy

Cardiac hypertrophy is the main adaptive response of the heart to chronic loads; however, prolonged or excessive hypertrophy promotes myocardial interstitial fibrosis, systolic dysfunction, and cardiomyocyte death, especially aseptic inflammation mediated by NLRP3 inflammasome, which can aggravate ventricular remodeling and myocardial damage, which is an important mechanism for the progression of heart failure. Various cardiac overloads can cause mitochondrial damage. In recent years, the mitochondria have been demonstrated to be involved in the inflammatory response during the development of cardiac hypertrophy in vitro and in vivo. As the NLRP3 inflammasome and mitochondria are regulators of inflammation and cardiac hypertrophy, we explored the potential functions of the NLRP3 inflammasome and mitochondrial dysfunction in cardiac hypertrophy. In particular, we proposed that the induction of mitochondrial dysfunction in cardiomyocytes may promote NLRP3-dependent inflammation during myocardial hypertrophy. Further in-depth studies could prompt valuable discoveries regarding the underlying molecular mechanisms of cardiac hypertrophy, reveal novel anti-inflammatory therapies for cardiac hypertrophy, and provide more desirable therapeutic outcomes for patients with cardiac hypertrophy.

Mitochondrial regulation of diabetic endothelial dysfunction: Pathophysiological links

Micro- and macrovascular complications frequently occur in patients with diabetes, with endothelial dysfunction playing a key role in the development and progression of the complications. For the early diagnosis and optimal treatment of vascular complications associated with diabetes, it is imperative to comprehend the cellular and molecular mechanisms governing the function of diabetic endothelial cells. Mitochondria function as crucial sensors of environmental and cellular stress regulating endothelial cell viability, structural integrity and function. Impaired mitochondrial quality control mechanisms and mitochondrial dysfunction are the main features of endothelial damage. Hence, targeted mitochondrial therapy is considered promising novel therapeutic options in vascular complications of diabetes. In this review, we focus on the mitochondrial functions in the vascular endothelial cells and the pathophysiological role of mitochondria in diabetic endothelial dysfunction, aiming to provide a reference for related drug development and clinical diagnosis and treatment.

A review for the correlation between optic atrophy 1-dependent mitochondrial fusion and cardiovascular disorders

Mitochondrial dynamics homeostasis is sustained by continuous and balanced fission and fusion, which are determinants of morphology, abundance, biogenesis and mitophagy of mitochondria. Optic atrophy 1 (OPA1), as the only inner mitochondrial membrane fusion protein, plays a key role in stabilizing mitochondrial dynamics. The disturbance of mitochondrial dynamics contributes to the pathophysiological progress of cardiovascular disorders, which are the main cause of death worldwide in recent decades and result in tremendous social burden. In this review, we describe the latest findings regarding OPA1 and its role in mitochondrial fusion. We summarize the post-translational modifications (PTMs) for OPA1 and its regulatory role in mitochondrial dynamics. Then the diverse cell fates caused by OPA1 expression during cardiovascular disorders are discussed. Moreover, cardiovascular disorders (such as heart failure, myocardial ischemia/reperfusion injury, cardiomyopathy and cardiac hypertrophy) relevant to OPA1-dependent mitochondrial dynamics imbalance have been detailed. Finally, we highlight the potential that targeting OPA1 to impact mitochondrial fusion may be used as a novel strategy against cardiovascular disorders.

Therapeutic effects of the combination of moderate-intensity endurance training and MitoQ supplementation in rats with isoproterenol-induced myocardial injury: The role of mitochondrial fusion, fission, and mitophagy

INTRODUCTION

Mitochondrial dysfunction causes myocardial disease. This study investigated the effects of MitoQ alone and in combination with moderate-intensity endurance training (EX) on cardiac function and content and mRNA expression of several proteins involved in mitochondrial quality control in isoproterenol (ISO)-induced heart injuries METHODS: Seven groups of CTL, ISO, ISO-EX, ISO-MitoQ-125, ISO-MitoQ-250, ISO-EX+MitoQ-125, and ISO-EX+MitoQ-250 were assigned. Rats were trained on a treadmill, and the MitoQ groups received MitoQ in drinking water for 8 weeks, starting one week after the induction of heart injury. Arterial pressure and cardiac function indices, mRNA expression, protein content, oxidant and antioxidant markers, fibrosis, and histopathological changes were assessed by physiograph, Real-Time PCR, immunofluorescence, calorimetry, Masson's trichrome, and H&E staining, respectively.

RESULTS

The impacts of MitoQ-125, EX+MitoQ-125, and EX+MitoQ-250 on arterial pressure and left ventricular systolic pressure were higher than MitoQ-250 or EX alone. ± dp/dt max were higher in ISO-EX+MitoQ-125 and ISO-EX+MitoQ-250 than ISO-MitoQ-125 and ISO-MitoQ-250 groups, respectively. Histopathological scores and fibrosis decreased in ISO-EX, ISO-MitoQ-125, ISO-EX+MitoQ-125, and ISO-EX+MitoQ-250 groups. The restoration of MFN2, PINK-1, and FIS-1 changes was higher in ISO-EX+MitoQ-125 and ISO-EX+MitoQ-250 than ISO-EX, ISO-MitoQ-125 and ISO-MitoQ-250 groups. The expression of MFN2 and PINK-1 was lower in ISO-MitoQ-125 and ISO-EX+MitoQ-125 than ISO and CTL groups. The expression of FIS-1 in ISO-EX and ISO-EX+MitoQ-250 increased compared to CTL and ISO groups. MDA decreased in ISO-MitoQ-125 and ISO-EX+MitoQ-125 groups.

CONCLUSION

Exercise and MitoQ combination have additive effects on cardiac function by modulating cardiac mitochondria quality. This study provided a possible therapy to treat heart injuries.

Current Advances of Mitochondrial Dysfunction and Cardiovascular Disease and Promising Therapeutic Strategies

Mitochondria are cellular power stations and essential organelles for maintaining cellular homeostasis. Dysfunctional mitochondria have emerged as a key factor in the occurrence and development of cardiovascular disease. This review focuses on advances in the relationship between mitochondrial dysfunction and cardiovascular diseases such as atherosclerosis, heart failure, myocardial ischemia reperfusion injury, and pulmonary arterial hypertension. The clinical value and challenges of mitochondria-targeted strategies, including mitochondria-targeted antioxidants, mitochondrial quality control modulators, mitochondrial function protectors, mitochondrial biogenesis promoters, and recently developed mitochondrial transplants, are also discussed.

Mitochondrial dysfunction at the crossroad of cardiovascular diseases and cancer

A large body of evidence indicates the existence of a complex pathophysiological relationship between cardiovascular diseases and cancer. Mitochondria are crucial organelles whose optimal activity is determined by quality control systems, which regulate critical cellular events, ranging from intermediary metabolism and calcium signaling to mitochondrial dynamics, cell death and mitophagy. Emerging data indicate that impaired mitochondrial quality control drives myocardial dysfunction occurring in several heart diseases, including cardiac hypertrophy, myocardial infarction, ischaemia/reperfusion damage and metabolic cardiomyopathies. On the other hand, diverse human cancers also dysregulate mitochondrial quality control to promote their initiation and progression, suggesting that modulating mitochondrial homeostasis may represent a promising therapeutic strategy both in cardiology and oncology. In this review, first we briefly introduce the physiological mechanisms underlying the mitochondrial quality control system, and then summarize the current understanding about the impact of dysregulated mitochondrial functions in cardiovascular diseases and cancer. We also discuss key mitochondrial mechanisms underlying the increased risk of cardiovascular complications secondary to the main current anticancer strategies, highlighting the potential of strategies aimed at alleviating mitochondrial impairment-related cardiac dysfunction and tumorigenesis. It is hoped that this summary can provide novel insights into precision medicine approaches to reduce cardiovascular and cancer morbidities and mortalities.

MFN2 deficiency promotes cardiac response to hypobaric hypoxia by reprogramming cardiomyocyte metabolism

AIM

Under hypobaric hypoxia (HH), the heart triggers various defense mechanisms including metabolic remodeling against lack of oxygen. Mitofusin 2 (MFN2), located at the mitochondrial outer membrane, is closely involved in the regulation of mitochondrial fusion and cell metabolism. To date, however, the role of MFN2 in cardiac response to HH has not been explored.

METHODS

Loss- and gain-of-function approaches were used to investigate the role of MFN2 in cardiac response to HH. In vitro, the function of MFN2 in the contraction of primary neonatal rat cardiomyocytes under hypoxia was examined. Non-targeted metabolomics and mitochondrial respiration analyses, as well as functional experiments were performed to explore underlying molecular mechanisms.

RESULTS

Our data demonstrated that, following 4 weeks of HH, cardiac-specific MFN2 knockout (MFN2 cKO) mice exhibited significantly better cardiac function than control mice. Moreover, restoring the expression of MFN2 clearly inhibited the cardiac response to HH in MFN2 cKO mice. Importantly, MFN2 knockout significantly improved cardiac metabolic reprogramming during HH, resulting in reduced capacity for fatty acid oxidation (FAO) and oxidative phosphorylation, and increased glycolysis and ATP production. In vitro data showed that down-regulation of MFN2 promoted cardiomyocyte contractility under hypoxia. Interestingly, increased FAO through palmitate treatment decreased contractility of cardiomyocyte with MFN2 knockdown under hypoxia. Furthermore, treatment with mdivi-1, an inhibitor of mitochondrial fission, disrupted HH-induced metabolic reprogramming and subsequently promoted cardiac dysfunction in MFN2-knockout hearts.

CONCLUSION

Our findings provide the first evidence that down-regulation of MFN2 preserves cardiac function in chronic HH by promoting cardiac metabolic reprogramming.

MFN2-mediated mitochondrial fusion facilitates acute hypobaric hypoxia-induced cardiac dysfunction by increasing glucose catabolism and ROS production

BACKGROUND

Rapid ascent to high-altitude environment which is characterized by acute hypobaric hypoxia (HH) may increase the risk of cardiac dysfunction. However, the potential regulatory mechanisms and prevention strategies for acute HH-induced cardiac dysfunction have not been fully clarified. Mitofusin 2 (MFN2) is highly expressed in the heart and is involved in the regulation of mitochondrial fusion and cell metabolism. To date, however, the significance of MFN2 in the heart under acute HH has not been investigated.

METHODS AND RESULTS

Our study revealed that MFN2 upregulation in hearts of mice during acute HH led to cardiac dysfunction. In vitro experiments showed that the decrease in oxygen concentration induced upregulation of MFN2, impairing cardiomyocyte contractility and increasing the risk of QT prolongation. Additionally, acute HH-induced MFN2 upregulation promoted glucose catabolism and led to excessive mitochondrial reactive oxygen species (ROS) production in cardiomyocytes, ultimately resulting in decreased mitochondrial function. Furthermore, co-immunoprecipitation (co-IP) and mass spectrometry analyses indicated that MFN2 interacted with the NADH-ubiquinone oxidoreductase 23 kDa subunit (NDUFS8). Specifically, acute HH-induced MFN2 upregulation increased NDUFS8-dependent complex I activity.

CONCLUSIONS

Taken together, our studies provide the first direct evidence that MFN2 upregulation exacerbates acute HH-induced cardiac dysfunction by increasing glucose catabolism and ROS production.

GENERAL SIGNIFICANCE

Our studies indicate that MFN2 may be a promising therapeutic target for cardiac dysfunction under acute HH.

Single-cell transcriptional profiling of hearts during cardiac hypertrophy reveals the role of MAMs in cardiomyocyte subtype switching

Pathological cardiac hypertrophy is the main predecessor of heart failure. Its pathology is sophisticated, and its progression is associated with multiple cellular processes. To explore new therapeutic approaches, more precise examination of cardiomyocyte subtypes and involved biological processes is required in response to hypertrophic stimuli. Mitochondria and the endoplasmic reticulum (ER) are two crucial organelles associated with the progression of cardiac hypertrophy and are connected through junctions known as mitochondria-associated endoplasmic reticulum membranes (MAMs). Although MAM genes are altered in cardiac hypertrophy, the importance of MAMs in cardiac hypertrophy and the expression pattern of MAMs in certain cardiac cell types require a comprehensive analysis. In this study, we analyzed the temporal expression of MAM proteins in the process of cardiac hypertrophy and observed that MAM-related proteins preferentially accumulated in cardiomyocytes at the initial stage of cardiac hypertrophy and underwent a gradual decline, which was synchronized with the proportion of two cardiomyocyte subtypes (CM2 and CM3). Meanwhile, these subtypes went through a functional switch during cardiac hypertrophy. Trajectory analysis suggested that there was a differentiation trajectory of cardiomyocyte subtypes from high to low MAM protein expression. Distinct regulon modules across different cardiomyocyte cell types were revealed by transcriptional regulatory network analysis. Furthermore, scWGCNA revealed that MAM-related genes were clustered into a module that correlated with diabetic cardiomyopathy. Altogether, we identified cardiomyocyte subtype transformation and the potential critical transcription factors involved, which may serve as therapeutic targets in combating cardiac hypertrophy.

Mitochondrion: A bridge linking aging and degenerative diseases

Aging is a natural process, characterized by progressive loss of physiological integrity, impaired function, and increased vulnerability to death. For centuries, people have been trying hard to understand the process of aging and find effective ways to delay it. However, limited breakthroughs have been made in anti-aging area. Since the hallmarks of aging were summarized in 2013, increasing studies focus on the role of mitochondrial dysfunction in aging and aging-related degenerative diseases, such as neurodegenerative diseases, osteoarthritis, metabolic diseases, and cardiovascular diseases. Accumulating evidence indicates that restoring mitochondrial function and biogenesis exerts beneficial effects in extending lifespan and promoting healthy aging. In this paper, we provide an overview of mitochondrial changes during aging and summarize the advanced studies in mitochondrial therapies for the treatment of degenerative diseases. Current challenges and future perspectives are proposed to provide novel and promising directions for future research.

Novel insights into the involvement of mitochondrial fission/fusion in heart failure: From molecular mechanisms to targeted therapies

Mitochondria are dynamic organelles that alter their morphology through fission (fragmentation) and fusion (elongation). These morphological changes correlate highly with mitochondrial functional adaptations to stressors, such as hypoxia, pressure overload, and inflammation, and are important in the setting of heart failure. Pathological mitochondrial remodeling, characterized by increased fission and reduced fusion, is associated with impaired mitochondrial respiration, increased mitochondrial oxidative stress, abnormal cytoplasmic calcium handling, and increased cardiomyocyte apoptosis. Considering the impact of the mitochondrial morphology on mitochondrial behavior and cardiomyocyte performance, altered mitochondrial dynamics could be expected to induce or exacerbate the pathogenesis and progression of heart failure. However, whether alterations in mitochondrial fission and fusion accelerate or retard the progression of heart failure has been the subject of intense debate. In this review, we first describe the physiological processes and regulatory mechanisms of mitochondrial fission and fusion. Then, we extensively discuss the pathological contributions of mitochondrial fission and fusion to heart failure. Lastly, we examine potential therapeutic approaches targeting mitochondrial fission/fusion to treat patients with heart failure.

Mitochondria-associated endoplasmic reticulum membranes (MAMs): Possible therapeutic targets in heart failure

Mitochondria-associated endoplasmic reticulum membranes (MAMs) are formed by physical connections of the endoplasmic reticulum and mitochondria. Over the past decades, great breakthroughs have been made in the study of ER-mitochondria communications. It has been identified that MAM compartments are pivotal in regulating neurological function. Accumulating studies indicated that MAMs participate in the development of cardiovascular diseases. However, the specific role of MAMs in heart failure remains to be fully understood. In this article, we first summarize the structural and functional properties of MAM and MAM-associated proteins. We then focus on the roles of MAMs in myocardial infarction, cardiomyopathy and heart failure, and discuss the involvement of MAMs in disease progression and treatment. Elucidating these issues may provide important insights into therapeutic intervention of heart failure.

Mitochondrial dynamics in vascular remodeling and target-organ damage

Vascular remodeling is the pathological basis for the development of many cardiovascular diseases. The mechanisms underlying endothelial cell dysfunction, smooth muscle cell phenotypic switching, fibroblast activation, and inflammatory macrophage differentiation during vascular remodeling remain elusive. Mitochondria are highly dynamic organelles. Recent studies showed that mitochondrial fusion and fission play crucial roles in vascular remodeling and that the delicate balance of fusion-fission may be more important than individual processes. In addition, vascular remodeling may also lead to target-organ damage by interfering with the blood supply to major body organs such as the heart, brain, and kidney. The protective effect of mitochondrial dynamics modulators on target-organs has been demonstrated in numerous studies, but whether they can be used for the treatment of related cardiovascular diseases needs to be verified in future clinical studies. Herein, we summarize recent advances regarding mitochondrial dynamics in multiple cells involved in vascular remodeling and associated target-organ damage.

Targeting mitochondrial impairment for the treatment of cardiovascular diseases: From hypertension to ischemia-reperfusion injury, searching for new pharmacological targets

Mitochondria and mitochondrial proteins represent a group of promising pharmacological target candidates in the search of new molecular targets and drugs to counteract the onset of hypertension and more in general cardiovascular diseases (CVDs). Indeed, several mitochondrial pathways result impaired in CVDs, showing ATP depletion and ROS production as common traits of cardiac tissue degeneration. Thus, targeting mitochondrial dysfunction in cardiomyocytes can represent a successful strategy to prevent heart failure. In this context, the identification of new pharmacological targets among mitochondrial proteins paves the way for the design of new selective drugs. Thanks to the advances in omics approaches, to a greater availability of mitochondrial crystallized protein structures and to the development of new computational approaches for protein 3D-modelling and drug design, it is now possible to investigate in detail impaired mitochondrial pathways in CVDs. Furthermore, it is possible to design new powerful drugs able to hit the selected pharmacological targets in a highly selective way to rescue mitochondrial dysfunction and prevent cardiac tissue degeneration. The role of mitochondrial dysfunction in the onset of CVDs appears increasingly evident, as reflected by the impairment of proteins involved in lipid peroxidation, mitochondrial dynamics, respiratory chain complexes, and membrane polarization maintenance in CVD patients. Conversely, little is known about proteins responsible for the cross-talk between mitochondria and cytoplasm in cardiomyocytes. Mitochondrial transporters of the SLC25A family, in particular, are responsible for the translocation of nucleotides (e.g., ATP), amino acids (e.g., aspartate, glutamate, ornithine), organic acids (e.g. malate and 2-oxoglutarate), and other cofactors (e.g., inorganic phosphate, NAD⁺, FAD, carnitine, CoA derivatives) between the mitochondrial and cytosolic compartments. Thus, mitochondrial transporters play a key role in the mitochondria-cytosol cross-talk by leading metabolic pathways such as the malate/aspartate shuttle, the carnitine shuttle, the ATP export from mitochondria, and the regulation of permeability transition pore opening. Since all these pathways are crucial for maintaining healthy cardiomyocytes, mitochondrial carriers emerge as an interesting class of new possible pharmacological targets for CVD treatments.

Modified Linggui Zhugan Decoction protects against ventricular remodeling through ameliorating mitochondrial damage in post-myocardial infarction rats

Introduction

Modified Linggui Zhugan Decoction (MLZD) is a Traditional Chinese Medicine prescription developed from Linggui Zhugan Decoction (LZD) that has been used for the clinical treatment of ischemic cardiovascular diseases. However, the cardioprotective mechanism of MLZD against post-myocardial infarction (MI) ventricular remodeling remains unclear.

Methods

We explored the effects of MLZD on ventricular remodeling and their underlying mechanisms, respectively, in SD rats with MI models and in H9c2 cardiomyocytes with oxygen-glucose deprivation (OGD) models. The cardiac structure and function of rats were measured by echocardiography, HE staining, and Masson staining. Apoptosis, inflammation, mitochondrial structure and function, and sirtuin 3 (SIRT3) expression were additionally examined.

Results

MLZD treatment significantly ameliorated cardiac structure and function, and thus reversed ventricular remodeling, compared with the control. Further research showed that MLZD ameliorated mitochondrial structural disruption, protected against mitochondrial dynamics disorder, restored impaired mitochondrial function, inhibited inflammation, and thus inhibited apoptosis. Moreover, the decreased expression level of SIRT3 was enhanced after MLZD treatment. The protective effects of MLZD on SIRT3 and mitochondria, nevertheless, were blocked by 3-TYP, a selective inhibitor of SIRT3.

Discussion

These findings together revealed that MLZD could improve the ventricular remodeling of MI rats by ameliorating mitochondrial damage and its associated apoptosis, which might exert protective effects by targeting SIRT3.

Role of cardiac mitofusins in cardiac conduction following simulated ischemia-reperfusion

Mitochondrial dysfunction induced by acute cardiac ischemia-reperfusion (IR), may increase susceptibility to arrhythmias by perturbing energetics, oxidative stress production and calcium homeostasis. Although changes in mitochondrial morphology are known to impact on mitochondrial function, their role in cardiac arrhythmogenesis is not known. To assess action potential duration (APD) in cardiomyocytes from the Mitofusins-1/2 (Mfn1/Mfn2)-double-knockout (Mfn-DKO) compared to wild-type (WT) mice, optical-electrophysiology was conducted. To measure conduction velocity (CV) in atrial and ventricular tissue from the Mfn-DKO and WT mice, at both baseline and following simulated acute IR, multi-electrode array (MEA) was employed. Intracellular localization of connexin-43 (Cx43) at baseline was evaluated by immunohistochemistry, while Cx-43 phosphorylation was assessed by Western-blotting. Mfn-DKO cardiomyocytes demonstrated an increased APD. At baseline, CV was significantly lower in the left ventricle of the Mfn-DKO mice. CV decreased with simulated-ischemia and returned to baseline levels during simulated-reperfusion in WT but not in atria of Mfn-DKO mice. Mfn-DKO hearts displayed increased Cx43 lateralization, although phosphorylation of Cx43 at Ser-368 did not differ. In summary, Mfn-DKO mice have increased APD and reduced CV at baseline and impaired alterations in CV following cardiac IR. These findings were associated with increased Cx43 lateralization, suggesting that the mitofusins may impact on post-MI cardiac-arrhythmogenesis.

Activation of FMS-like tyrosine kinase 3 protects against isoprenaline-induced cardiac hypertrophy by improving autophagy and mitochondrial dynamics

FMS-like receptor tyrosine kinase 3 (Flt3) expression was reported to increase in the heart in response to pathological stress, but the role of Flt3 activation and its underlying mechanisms remain poorly elucidated. This study was designed to investigate the role of Flt3 activation in sympathetic hyperactivity-induced cardiac hypertrophy and its mechanisms through autophagy and mitochondrial dynamics. In vivo, cardiac hypertrophy was established by subcutaneous injection of isoprenaline (6 mg/kg·day) in C57BL/6 mice for 7 consecutive days. The Flt3-ligand intervention was launched 2 h prior to isoprenaline each day. In vitro, experiments of cardiomyocyte hypertrophy, autophagy, and mitochondrial dynamics were performed in neonatal rat cardiomyocytes (NRCMs). Our results revealed that the expression level of Flt3 protein was significantly increased in the hypertrophic myocardium provoked by isoprenaline administration. Flt3-ligand intervention alleviated isoprenaline-induced cardiac oxidative stress, hypertrophy, fibrosis, and contractile dysfunction. Isoprenaline stimulation impaired autophagic flux in hypertrophic mouse hearts, supported by the accumulation of LC3II and P62 proteins, while Flt3-ligand restored the impairment of autophagic flux. Flt3 activation normalized the imbalance of mitochondrial fission and fusion in the hearts of mice evoked by isoprenaline as evidenced by the neutralization of elevated mitochondrial fission markers and reduced mitochondrial fusion markers. In NRCMs, Flt3-ligand treatment attenuated isoprenaline-stimulated hypertrophy, which was abolished by a Flt3-specific blocker AC220. Activating Flt3 reversed isoprenaline-induced autophagosome accumulation and impairment of autophagic flux probably by enhancing SIRT1 expression and consequently TFEB nuclear translocation. Flt3 activation improved the imbalance of mitochondrial dynamics induced by isoprenaline in NRCMs through the SIRT1/P53 pathway. Activation of Flt3 mitigated ISO-stimulated hypertrophy probably involves the restoration of autophagic flux and balance of mitochondrial dynamics. Therefore, activation of Flt3 attenuates isoprenaline-induced cardiac hypertrophy in vivo and in vitro, the potential mechanism probably attributes to SIRT1/TFEB-mediated autophagy promotion and SIRT1/P53-mediated mitochondrial dynamics balance. These findings suggest that activation of Flt3 may be a novel target for protection against cardiac remodeling and heart failure during sympathetic hyperactivity.

The role of mitochondrial fission in cardiovascular health and disease

Mitochondria are organelles involved in the regulation of various important cellular processes, ranging from ATP generation to immune activation. A healthy mitochondrial network is essential for cardiovascular function and adaptation to pathological stressors. Mitochondria undergo fission or fusion in response to various environmental cues, and these dynamic changes are vital for mitochondrial function and health. In particular, mitochondrial fission is closely coordinated with the cell cycle and is linked to changes in mitochondrial respiration and membrane permeability. Another key function of fission is the segregation of damaged mitochondrial components for degradation by mitochondrial autophagy (mitophagy). Mitochondrial fission is induced by the large GTPase dynamin-related protein 1 (DRP1) and is subject to sophisticated regulation. Activation requires various post-translational modifications of DRP1, actin polymerization and the involvement of other organelles such as the endoplasmic reticulum, Golgi apparatus and lysosomes. A decrease in mitochondrial fusion can also shift the balance towards mitochondrial fission. Although mitochondrial fission is necessary for cellular homeostasis, this process is often aberrantly activated in cardiovascular disease. Indeed, strong evidence exists that abnormal mitochondrial fission directly contributes to disease development. In this Review, we compare the physiological and pathophysiological roles of mitochondrial fission and discuss the therapeutic potential of preventing excessive mitochondrial fission in the heart and vasculature.

Mitochondrial dynamics involves molecular and mechanical events in motility, fusion and fission

Mitochondria are cell organelles that play pivotal roles in maintaining cell survival, cellular metabolic homeostasis, and cell death. Mitochondria are highly dynamic entities which undergo fusion and fission, and have been shown to be very motile in vivo in neurons and in vitro in multiple cell lines. Fusion and fission are essential for maintaining mitochondrial homeostasis through control of morphology, content exchange, inheritance of mitochondria, maintenance of mitochondrial DNA, and removal of damaged mitochondria by autophagy. Mitochondrial motility occurs through mechanical and molecular mechanisms which translocate mitochondria to sites of high energy demand. Motility also plays an important role in intracellular signaling. Here, we review key features that mediate mitochondrial dynamics and explore methods to advance the study of mitochondrial motility as well as mitochondrial dynamics-related diseases and mitochondrial-targeted therapeutics.

Mitophagy: A Potential Target for Pressure Overload-Induced Cardiac Remodelling

The pathological mechanisms underlying cardiac remodelling and cardiac dysfunction caused by pressure overload are poorly understood. Mitochondrial damage and functional dysfunction, including mitochondrial bioenergetic disorder, oxidative stress, and mtDNA damage, contribute to heart injury caused by pressure overload. Mitophagy, an important regulator of mitochondrial homeostasis and function, is triggered by mitochondrial damage and participates in the pathological process of cardiovascular diseases. Recent studies indicate that mitophagy plays a critical role in the pressure overload model, but evidence on the causal relationship between mitophagy abnormality and pressure overload-induced heart injury is inconclusive. This review summarises the mechanism, role, and regulation of mitophagy in the pressure overload model. It also pays special attention to active compounds that may regulate mitophagy in pressure overload, which provide clues for possible clinical applications.

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Epidemiological studies indicate that pre-menopausal women are more protected against the development of CVDs compared to men of the same age. This effect is attributed to the action/effects of sex steroid hormones on the cardiovascular system. In this context, estrogen modulates cardiovascular function in physiological and pathological conditions, being one of the main physiological cardioprotective agents. Here we describe the common pathways and mechanisms by which estrogens modulate the retrograde and anterograde communication between the nucleus and mitochondria, highlighting the role of genomic and non-genomic pathways mediated by estrogen receptors. Additionally, we discuss the presumable role of bromodomain-containing protein 4 (BRD4) in enhancing mitochondrial biogenesis and function in different CVD models and how this protein could act as a master regulator of estrogen protective activity. Altogether, this review focuses on estrogenic control in gene expression and molecular pathways, how this activity governs nucleus-mitochondria communication, and its projection for a future generation of strategies in CVDs treatment.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

Mitochondrial Dynamics and Mitophagy in Cardiometabolic Disease

Mitochondria play a key role in cellular metabolism. Mitochondrial dynamics (fusion and fission) and mitophagy, are critical to mitochondrial function. Fusion allows organelles to share metabolites, proteins, and mitochondrial DNA, promoting complementarity between damaged mitochondria. Fission increases the number of mitochondria to ensure that they are passed on to their offspring during mitosis. Mitophagy is a process of selective removal of excess or damaged mitochondria that helps improve energy metabolism. Cardiometabolic disease is characterized by mitochondrial dysfunction, high production of reactive oxygen species, increased inflammatory response, and low levels of ATP. Cardiometabolic disease is closely related to mitochondrial dynamics and mitophagy. This paper reviewed the mechanisms of mitochondrial dynamics and mitophagy (focus on MFN1, MFN2, OPA1, DRP1, and PINK1 proteins) and their roles in diabetic cardiomyopathy, myocardial infarction, cardiac hypertrophy, heart failure, atherosclerosis, and obesity.

Current Understanding of the Pivotal Role of Mitochondrial Dynamics in Cardiovascular Diseases and Senescence

The heart is dependent on ATP production in mitochondria, which is closely associated with cardiovascular disease because of the oxidative stress produced by mitochondria. Mitochondria are highly dynamic organelles that constantly change their morphology to elongated (fusion) or small and spherical (fission). These mitochondrial dynamics are regulated by various small GTPases, Drp1, Fis1, Mitofusin, and Opa1. Mitochondrial fission and fusion are essential to maintain a balance between mitochondrial biogenesis and mitochondrial turnover. Recent studies have demonstrated that mitochondrial dynamics play a crucial role in the development of cardiovascular diseases and senescence. Disruptions in mitochondrial dynamics affect mitochondrial dysfunction and cardiomyocyte survival leading to cardiac ischemia/reperfusion injury, cardiomyopathy, and heart failure. Mitochondrial dynamics and reactive oxygen species production have been associated with endothelial dysfunction, which in turn causes the development of atherosclerosis, hypertension, and even pulmonary hypertension, including pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. Here, we review the association between cardiovascular diseases and mitochondrial dynamics, which may represent a potential therapeutic target.

Sirtuin 3: Emerging therapeutic target for cardiovascular diseases

Acetylation is one of the most important methods of modification that lead to a change in the function of proteins. In humans, metabolic enzymes commonly undergo acetylation, which regulates the activities of metabolic enzymes and metabolic pathways. Sirtuin 3 (SIRT3) is a prominent deacetylase that participates in mitochondrial metabolism, redox balance, and mitochondrial dynamics by regulating mitochondrial protein acetylation, thereby protecting mitochondria from damage. Normal mitochondrial function is essential for maintaining the metabolism and function of the heart. Therefore, mitochondrial dysfunction caused by SIRT3 consumption and defects leads to the development of a variety of cardiovascular diseases. A comprehensive understanding of the role of SIRT3 in cardiovascular disease is critical for developing new therapeutic strategies. Herein, we summarize the function of SIRT3 in mitochondria, the complex mechanisms mediating cardiovascular diseases, and the potential value of SIRT3 small-molecule agonists in future clinical treatments.

Role of GTPase-Dependent Mitochondrial Dynamins in Heart Diseases

Heart function maintenance requires a large amount of energy, which is supplied by the mitochondria. In addition to providing energy to cardiomyocytes, mitochondria also play an important role in maintaining cell function and homeostasis. Although adult cardiomyocyte mitochondria appear as independent, low-static organelles, morphological changes have been observed in cardiomyocyte mitochondria under stress or pathological conditions. Indeed, cardiac mitochondrial fission and fusion are involved in the occurrence and development of heart diseases. As mitochondrial fission and fusion are primarily regulated by mitochondrial dynamins in a GTPase-dependent manner, GTPase-dependent mitochondrial fusion (MFN1, MFN2, and OPA1) and fission (DRP1) proteins, which are abundant in the adult heart, can also be regulated in heart diseases. In fact, these dynamic proteins have been shown to play important roles in specific diseases, including ischemia-reperfusion injury, heart failure, and metabolic cardiomyopathy. This article reviews the role of GTPase-dependent mitochondrial fusion and fission protein-mediated mitochondrial dynamics in the occurrence and development of heart diseases.

Therapeutic potential and recent advances on targeting mitochondrial dynamics in cardiac hypertrophy: A concise review

Pathological cardiac hypertrophy begins as an adaptive response to increased workload; however, sustained hemodynamic stress will lead it to maladaptation and eventually cardiac failure. Mitochondria, being the powerhouse of the cells, can regulate cardiac hypertrophy in both adaptive and maladaptive phases; they are dynamic organelles that can adjust their number, size, and shape through a process called mitochondrial dynamics. Recently, several studies indicate that promoting mitochondrial fusion along with preventing mitochondrial fission could improve cardiac function during cardiac hypertrophy and avert its progression toward heart failure. However, some studies also indicate that either hyperfusion or hypo-fission could induce apoptosis and cardiac dysfunction. In this review, we summarize the recent knowledge regarding the effects of mitochondrial dynamics on the development and progression of cardiac hypertrophy with particular emphasis on the regulatory role of mitochondrial dynamics proteins through the genetic, epigenetic, and post-translational mechanisms, followed by discussing the novel therapeutic strategies targeting mitochondrial dynamic pathways.

Aerobic exercise ameliorates cardiac hypertrophy by regulating mitochondrial quality control and endoplasmic reticulum stress through M2 AChR

Aerobic exercise increases M2 AChR, which thus improves cardiac function in cardiovascular disease (CVD) rats. This study aimed to determine whether aerobic exercise could ameliorate pressure overload-induced heart hypertrophy through M2 AChR, and to elucidate the underlying mechanisms of action. Mice were used to establish the myocardial hypertrophy model by transverse aortic constriction (TAC), and subjected to 2, 4, and 8 weeks of moderate-intensity aerobic exercise and choline intervention (14 mg/kg/day). Our results showed that 4 and 8 weeks of exercise and choline intervention reduced excessive mitochondrial fission and autophagy of myocardial mitochondria, thereby improving the ultrastructure and function of mitochondria after TAC. Moreover, 8-week exercise and choline intervention have enhanced parasympathetic function and promoted the expression of M2 AChR. In addition, 8-week exercise and choline intervention also inhibited the protein expression of myocardial MFN2, PERK/eIF2α/ATF4, and NLRP3/caspase-1/IL-1β signaling pathways, thereby effectively reducing mitochondrial fusion, endoplasmic reticulum stress, and inflammation. Taken together, these data suggest that pressure overload led to cardiac hypertrophy, cardiac dysfunction, and decreased parasympathetic function in cardiac tissues. Aerobic exercise attenuated cardiac dysfunction by modulating the expression of proteins involved in mitochondrial quality control, and induced endoplasmic reticulum stress and inflammation, thereby reducing cardiac hypertrophy and improving cardiac function in impaired heart tissues following TAC, which was likely mediated by M2 AChR activation.

Mitochondrial function, dynamics and quality control in the pathophysiology of HFpEF

Heart failure (HF) is one of the leading causes of hospitalization for the adult population and a major cause of mortality worldwide. The HF syndrome is characterized by the heart's inability to supply the cardiac output required to meet the body's metabolic requirements or only at the expense of elevated filling pressures. HF without overt impairment of left ventricular ejection fraction (LVEF) was initially labeled as "diastolic HF" until recognizing the coexistence of both systolic and diastolic abnormalities in most cases. Acknowledging these findings, the preferred nomenclature is HF with preserved EF (HFpEF). This syndrome primarily affects the elderly population and is associated with a heterogeneous overlapping of comorbidities that makes its diagnosis challenging. Despite extensive research, there is still no evidence-based therapy for HFpEF, reinforcing the need for a thorough understanding of the pathophysiology underlying its onset and progression. The role of mitochondrial dysfunction in developing the pathophysiological changes that accompany HFpEF onset and progression (low-grade systemic inflammation, oxidative stress, endothelial dysfunction, and myocardial remodeling) has just begun to be acknowledged. This review summarizes our current understanding of the participation of the mitochondrial network in the pathogenesis of HFpEF, with particular emphasis on the signaling pathways involved, which may provide future therapeutic targets.

Mitochondrial dynamics imbalance and mitochondrial dysfunction contribute to the molecular cardiotoxic effects of lenvatinib

Lenvatinib is a tyrosine kinase inhibitor (TKI) approved for the treatment of resistant differentiated thyroid cancer, advanced renal cell carcinoma, unresectable hepatocellular carcinoma, and endometrial carcinoma. Although it is successful in cancer treatment, it can cause life-threatening side effects such as cardiotoxicity. The molecular mechanism of cardiotoxicity caused by lenvatinib is not fully known. In this study, the molecular mechanism of lenvatinib's cardiotoxicity was investigated focusing on mitochondrial toxicity in the H9c2 cardiomyoblastic cell line. Lenvatinib inhibited cell viability at 48 and 72 h exposure with three selected concentrations (1.25 μM, 5 μM and 10 μM); and inhibited intracellular ATP after 72 h exposure compared to the control group. Mitochondrial membrane potential was decreased after 48 h and did not show significant changes after 72 h exposure. Evaluated with real-time PCR, mitochondrial dynamics (Mfn1, Mfn2, OPA1, DRP1, Fis1) expression levels after lenvatinib treatment significantly changed. Lenvatinib triggered the tendency from fusion to fission in mitochondria after 48 h exposure, and increased both fusion and fission after 72 h. The mtDNA ratio increased after 48 h and decreased after 72 h. ASK1, JNK and AMPKα2 increased. UCP2 showed downregulation, SOD2 level showed upregulation and Cat levels decreased after drug treatment. Nrf1 and Nrf2 also changed concentration-dependently. Protein carbonyl levels increased significantly after lenvatinib treatments indicating oxidative stress. The protein levels of the electron transport chain complexes, LONP1, UCP2, and P21 showed significant differences after lenvatinib treatment. The outcome of our study is expected to be a contribution to the understanding of the molecular mechanisms of TKI-induced cardiotoxicity.

Mitochondrial Fusion Protein Mfn2 and Its Role in Heart Failure

Mitofusin 2 (Mfn2) is a transmembrane GTPase located on the mitochondrial outer membrane that contributes to mitochondrial network regulation. It is an essential multifunctional protein that participates in various biological processes under physical and pathological conditions, including mitochondrial fusion, reticulum-mitochondria contacts, mitochondrial quality control, and apoptosis. Mfn2 dysfunctions have been found to contribute to cardiovascular diseases, such as ischemia-reperfusion injury, heart failure, and dilated cardiomyopathy. Here, this review mainly focuses on what is known about the structure and function of Mfn2 and its crucial role in heart failure.

Mitochondria-associated membrane-modulated Ca2+ transfer: A potential treatment target in cardiac ischemia reperfusion injury and heart failure

Effective Ca²⁺ dependent mitochondrial energy supply is imperative for proper cardiac contractile activity, while disruption of Ca²⁺ homeostasis participates in the pathogenesis of multiple human diseases. This phenomenon is particularly prominent in cardiac ischemia and reperfusion (I/R) and heart failure, both of which require strict clinical intervention. The interface between endoplasmic reticula (ER) and mitochondria, designated the mitochondria-associated membrane (MAM), is now regarded as a crucial mediator of Ca²⁺ transportation. Thus, interventions targeting this physical and functional coupling between mitochondria and the ER are highly desirable. Increasing evidence supports the notion that restoration, and maintenance, of the physiological contact between these two organelles can improve mitochondrial function, while inhibiting cell death, thereby sufficiently ameliorating I/R injury and heart failure development. A better understanding regarding the underlying mechanism of MAM-mediated transport will pave the way for identification of novel treatment approaches for heart disease. Therefore, in this review, we summarize the crucial functions and potential mechanisms of MAMs in the pathogenesis of I/R and heart failure.

Novel Insights into the Molecular Features and Regulatory Mechanisms of Mitochondrial Dynamic Disorder in the Pathogenesis of Cardiovascular Disease

Mitochondria maintain mitochondrial homeostasis through continuous fusion and fission, that is, mitochondrial dynamics, which is precisely mediated by mitochondrial fission and fusion proteins, including dynamin-related protein 1 (Drp1), mitofusin 1 and 2 (Mfn1/2), and optic atrophy 1 (OPA1). When the mitochondrial fission and fusion of cardiomyocytes are out of balance, they will cause their own morphology and function disorders, which damage the structure and function of the heart, are involved in the occurrence and progression of cardiovascular disease such as ischemia-reperfusion injury (IRI), septic cardiomyopathy, and diabetic cardiomyopathy. In this paper, we focus on the latest findings regarding the molecular features and regulatory mechanisms of mitochondrial dynamic disorder in cardiovascular pathologies. Finally, we will address how these findings can be applied to improve the treatment of cardiovascular disease.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

Mitochondria are one of the most important organelles in cardiomyocytes. Mitochondrial homeostasis is necessary for the maintenance of normal heart function. Mitochondria perform four major biological processes in cardiomyocytes: mitochondrial dynamics, metabolic regulation, Ca2+ handling, and redox generation. Additionally, the cardiovascular system is quite sensitive in responding to changes in mechanical stress from internal and external environments. Several mechanotransduction pathways are involved in regulating the physiological and pathophysiological status of cardiomyocytes. Typically, the extracellular matrix generates a stress-loading gradient, which can be sensed by sensors located in cellular membranes, including biophysical and biochemical sensors. In subsequent stages, stress stimulation would regulate the transcription of mitochondrial related genes through intracellular transduction pathways. Emerging evidence reveals that mechanotransduction pathways have greatly impacted the regulation of mitochondrial homeostasis. Excessive mechanical stress loading contributes to impairing mitochondrial function, leading to cardiac disorder. Therefore, the concept of restoring mitochondrial function by shutting down the excessive mechanotransduction pathways is a promising therapeutic strategy for cardiovascular diseases. Recently, viral and non-viral protocols have shown potentials in application of gene therapy. This review examines the biological process of mechanotransduction pathways in regulating mitochondrial function in response to mechanical stress during the development of cardiomyopathy and heart failure. We also summarize gene therapy delivery protocols to explore treatments based on mechanical stress-induced mitochondrial dysfunction, to provide new integrative insights into cardiovascular diseases.

Mitochondrial architecture in cardiac myocytes depends on cell shape and matrix rigidity

Contraction of cardiac myocytes depends on energy generated by the mitochondria. During cardiac development and disease, the structure and function of the mitochondrial network in cardiac myocytes is known to remodel in concert with many other factors, including changes in nutrient availability, hemodynamic load, extracellular matrix (ECM) rigidity, cell shape, and maturation of other intracellular structures. However, the independent role of each of these factors on mitochondrial network architecture is poorly understood. In this study, we tested the hypothesis that cell aspect ratio (AR) and ECM rigidity regulate the architecture of the mitochondrial network in cardiac myocytes. To do this, we spin-coated glass coverslips with a soft, moderate, or stiff polymer. Next, we microcontact printed cell-sized rectangles of fibronectin with AR matching cardiac myocytes at various developmental or disease states onto the polymer surface. We then cultured neonatal rat ventricular myocytes on the patterned surfaces and used confocal microscopy and image processing techniques to quantify sarcomeric α-actinin volume, nucleus volume, and mitochondrial volume, surface area, and size distribution. On some substrates, α-actinin volume increased with cell AR but was not affected by ECM rigidity. Nucleus volume was mostly uniform across all conditions. In contrast, mitochondrial volume increased with cell AR on all substrates. Furthermore, mitochondrial surface area to volume ratio decreased as AR increased on all substrates. Large mitochondria were also more prevalent in cardiac myocytes with higher AR. For select AR, mitochondria were also smaller as ECM rigidity increased. Collectively, these results suggest that mitochondrial architecture in cardiac myocytes is strongly influenced by cell shape and moderately influenced by ECM rigidity. These data have important implications for understanding the factors that impact metabolic performance during heart development and disease.

Mitochondrial Dynamics in Adult Cardiomyocytes and Heart Diseases

Mitochondria are the powerhouse organelles of cells; they participate in ATP generation, calcium homeostasis, oxidative stress response, and apoptosis. Thus, maintenance of mitochondrial function is critical for cellular functions. As highly dynamic organelles, the function of mitochondria is dynamically regulated by their fusion and fission in many cell types, which regulate mitochondrial morphology, number, distribution, metabolism, and biogenesis in cells. Mature rod-shaped cardiomyocytes contain thousands of end-to-end contacted spheroid mitochondria. The movement of mitochondria in these cells is limited, which hinders the impetus for research into mitochondrial dynamics in adult cardiomyocytes. In this review, we discuss the most recent progress in mitochondrial dynamics in mature (adult) cardiomyocytes and the relationship thereof with heart diseases.

Mitochondria-Associated Endoplasmic Reticulum Membranes in Cardiovascular Diseases

The endoplasmic reticulum (ER) and mitochondria are physically connected to form dedicated structural domains known as mitochondria-associated ER membranes (MAMs), which participate in fundamental biological processes, including lipid and calcium (Ca²⁺) homeostasis, mitochondrial dynamics and other related cellular behaviors such as autophagy, ER stress, inflammation and apoptosis. Many studies have proved the importance of MAMs in maintaining the normal function of both organelles, and the abnormal amount, structure or function of MAMs is related to the occurrence of cardiovascular diseases. Here, we review the knowledge regarding the components of MAMs according to their different functions and the specific roles of MAMs in cardiovascular physiology and pathophysiology, focusing on some highly prevalent cardiovascular diseases, including ischemia-reperfusion, diabetic cardiomyopathy, heart failure, pulmonary arterial hypertension and systemic vascular diseases. Finally, we summarize the possible mechanisms of MAM in cardiovascular diseases and put forward some obstacles in the understanding of MAM function we may encounter.

Extended regorafenib treatment can be linked with mitochondrial damage leading to cardiotoxicity

Regorafenib (RGF) has a great success in the treatment of colorectal cancer, gastrointestinal stromal tumours and hepatocellular carcinoma by inhibiting angiogenic, stromal and oncogenic kinases. However, RGF can induce life-threatening cardiotoxicity including hypertension and cardiac ischemia/infarction. The molecular mechanism of the adverse effects has not been elucidated. Mitochondrial dysfunction is one of the major causes of cardiac diseases since cardiac cells highly need ATP for their contractility. Therefore, we aimed to investigate molecular mechanisms of RGF-induced cardiac adverse effects using H9c2 cell model by focusing on mitochondria. Cells were treated with 0-20 μM RGF for 48 and 72 h. According to our results, RGF inhibited cell proliferation and decreased the ATP content of the cells depending on the exposure time and concentration. Loss of mitochondrial membrane potential was also observed at high dose. Mitochondrial fusion/fission genes and antioxidant SOD2 (superoxide dismutase) gene expression levels increased at high doses in both treatments. Mitochondrial DNA content decreased as exposure time and concentration increased. Also, protein expression levels of mitochondrial complex I and V have reduced and stress protein HSP70 level has increased following RGF treatment. Structural abnormalities in mitochondria was seen with transmission electron microscopy at the applied higher doses. Our findings suggest that RGF-induced cardiotoxicity may be associated with mitochondrial damage in cardiac cells.

Mitochondrial dysfunction in cardiovascular disease: Current status of translational research/clinical and therapeutic implications

Mitochondria provide energy to the cell during aerobic respiration by supplying ~95% of the adenosine triphosphate (ATP) molecules via oxidative phosphorylation. These organelles have various other functions, all carried out by numerous proteins, with the majority of them being encoded by nuclear DNA (nDNA). Mitochondria occupy ~1/3 of the volume of myocardial cells in adults, and function at levels of high-efficiency to promptly meet the energy requirements of the myocardial contractile units. Mitochondria have their own DNA (mtDNA), which contains 37 genes and is maternally inherited. Over the last several years, a variety of functions of these organelles have been discovered and this has led to a growing interest in their involvement in various diseases, including cardiovascular (CV) diseases. Mitochondrial dysfunction relates to the status where mitochondria cannot meet the demands of a cell for ATP and there is an enhanced formation of reactive-oxygen species. This dysfunction may occur as a result of mtDNA and/or nDNA mutations, but also as a response to aging and various disease and environmental stresses, leading to the development of cardiomyopathies and other CV diseases. Designing mitochondria-targeted therapeutic strategies aiming to maintain or restore mitochondrial function has been a great challenge as a result of variable responses according to the etiology of the disorder. There have been several preclinical data on such therapies, but clinical studies are scarce. A major challenge relates to the techniques needed to eclectically deliver the therapeutic agents to cardiac tissues and to damaged mitochondria for successful clinical outcomes. All these issues and progress made over the last several years are herein reviewed.

Targeting mitochondrial fusion and fission proteins for cardioprotection

New treatments are needed to protect the myocardium against the detrimental effects of acute ischaemia/reperfusion (IR) injury following an acute myocardial infarction (AMI), in order to limit myocardial infarct (MI) size, preserve cardiac function and prevent the onset of heart failure (HF). Given the critical role of mitochondria in energy production for cardiac contractile function, prevention of mitochondrial dysfunction during acute myocardial IRI may provide novel cardioprotective strategies. In this regard, the mitochondrial fusion and fissions proteins, which regulate changes in mitochondrial morphology, are known to impact on mitochondrial quality control by modulating mitochondrial biogenesis, mitophagy and the mitochondrial unfolded protein response. In this article, we review how targeting these inter-related processes may provide novel treatment targets and new therapeutic strategies for reducing MI size, preventing the onset of HF following AMI.

Role of Mitophagy in Cardiovascular Disease

Cardiovascular disease is the leading cause of mortality worldwide, and mitochondrial dysfunction is the primary contributor to these disorders. Recent studies have elaborated on selective autophagy-mitophagy, which eliminates damaged and dysfunctional mitochondria, stabilizes mitochondrial structure and function, and maintains cell survival and growth. Numerous recent studies have reported that mitophagy plays an important role in the pathogenesis of various cardiovascular diseases. This review summarizes the mechanisms underlying mitophagy and advancements in studies on the role of mitophagy in cardiovascular disease.

MicroRNA-20b Promotes Cardiac Hypertrophy by the Inhibition of Mitofusin 2-Mediated Inter-organelle Ca2+ Cross-Talk

MicroRNA (miRNA) and mitofusin-2 (Mfn2) are important in the development of cardiac hypertrophy, but the target relationship and mechanism associated with Ca²⁺ handling between SR and mitochondria under hypertrophic condition is not established. Mfn2 expression, Mfn2-mediated interorganelle Ca²⁺ cross-talk, and target regulation by miRNA-20b (miR-20b) were evaluated using animal/cellular hypertrophic models with state-of-the-art techniques. The results demonstrated that Mfn2 was downregulated and miR-20b was upregulated upon the target binding profile under hypertrophic condition. Our data showed that miR-20b induced cardiac hypertrophy that was reversed by recombinant adeno-associated virus vector 9 (rAAV9)-anti-miR-20b or miR-20b antisense inhibitor (AMO-20b). The deleterious action of miR-20b on Mfn2 expression/function and mitochondrial ATP synthesis was observed and reversed by rAAV9-anti-miR-20b or AMO-20b. The targeted regulation of miR-20b on Mfn2 was confirmed by luciferase reporter and miRNA-masking. Importantly, the facts that mitochondrial calcium uniporter (MCU) activation by Spermine increased the cytosolic Ca²⁺ into mitochondria, manifested as enhanced histamine-mediated Ca²⁺ release from mitochondrial, suggesting that Ca²⁺ reuptake/buffering capability of mitochondria to cytosolic Ca²⁺ is injured by miR-20b-mediated Mfn2 signaling, by which leads cytosolic Ca²⁺ overload and cardiac hypertrophy through Ca²⁺ signaling pathway. In conclusion, pro-hypertonic miR-20b plays crucial roles in cardiac hypertrophy through downregulation of Mfn2 and cytosolic Ca²⁺ overload by weakening the buffering capability of mitochondria.

Cellular Aging Characteristics and Their Association with Age-Related Disorders

Different molecular signaling pathways, biological processes, and intercellular communication mechanisms control longevity and are affected during cellular senescence. Recent data have suggested that organelle communication, as well as genomic and metabolic dysfunctions, contribute to this phenomenon. Oxidative stress plays a critical role by inducing structural modifications to biological molecules while affecting their function and catabolism and eventually contributing to the onset of age-related dysfunctions. In this scenario, proteins are not adequately degraded and accumulate in the cell cytoplasm as toxic aggregates, increasing cell senescence progression. In particular, carbonylation, defined as a chemical reaction that covalently and irreversibly modifies proteins with carbonyl groups, is considered to be a significant indicator of protein oxidative stress and aging. Here, we emphasize the role and dysregulation of the molecular pathways controlling cell metabolism and proteostasis, the complexity of the mechanisms that occur during aging, and their association with various age-related disorders. The last segment of the review details current knowledge on protein carbonylation as a biomarker of cellular senescence in the development of diagnostics and therapeutics for age-related dysfunctions.