Mitofusin 2 inhibits angiotensin II-induced myocardial hypertrophy

Omega-3 Fatty Acids Modify Drp1 Expression and Activate the PINK1-Dependent Mitophagy Pathway in the Kidney and Heart of Adenine-Induced Uremic Rats

Mitochondrial homeostasis is controlled by biogenesis, dynamics, and mitophagy. Mitochondrial dysfunction plays a central role in cardiovascular and renal disease and omega-3 fatty acids (FAs) are beneficial for cardiovascular disease. We investigated whether omega-3 fatty acids (FAs) regulate mitochondrial biogenesis, dynamics, and mitophagy in the kidney and heart of adenine-induced uremic rats. Eighteen male Sprague Dawley rats were divided into normal control, adenine control, and adenine with omega-3 FA groups. Using Western blot analysis, the kidney and heart expression of mitochondrial homeostasis-related molecules, including peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), dynamin-related protein 1 (Drp1), and phosphatase and tensin homolog-induced putative kinase 1 (PINK1) were investigated. Compared to normal, serum creatinine and heart weight/body weight in adenine control were increased and slightly improved in the omega-3 FA group. Compared to the normal controls, the expression of PGC-1α and PINK1 in the kidney and heart of the adenine group was downregulated, which was reversed after omega-3 FA supplementation. Drp1 was upregulated in the kidney but downregulated in the heart in the adenine group. Drp1 expression in the heart recovered in the omega-3 FA group. Mitochondrial DNA (mtDNA) was decreased in the kidney and heart of the adenine control group but the mtDNA of the heart was recovered in the omega-3 FA group. Drp1, which is related to mitochondrial fission, may function oppositely in the uremic kidney and heart. Omega-3 FAs may be beneficial for mitochondrial homeostasis by activating mitochondrial biogenesis and PINK1-dependent mitophagy in the kidney and heart of uremic rats.

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.

3D Mitochondrial Structure in Aging Human Skeletal Muscle: Insights into MFN-2 Mediated Changes

Age-related atrophy of skeletal muscle, is characterized by loss of mass, strength, endurance, and oxidative capacity during aging. Notably, bioenergetics and protein turnover studies have shown that mitochondria mediate this decline in function. Although exercise has been the only therapy to mitigate sarcopenia, the mechanisms that govern how exercise serves to promote healthy muscle aging are unclear. Mitochondrial aging is associated with decreased mitochondrial capacity, so we sought to investigate how aging affects mitochondrial structure and potential age-related regulators. Specifically, the three-dimensional (3D) mitochondrial structure associated with morphological changes in skeletal muscle during aging requires further elucidation. We hypothesized that aging causes structural remodeling of mitochondrial 3D architecture representative of dysfunction, and this effect is mitigated by exercise. We used serial block-face scanning electron microscopy to image human skeletal tissue samples, followed by manual contour tracing using Amira software for 3D reconstruction and subsequent analysis of mitochondria. We then applied a rigorous in vitro and in vivo exercise regimen during aging. Across 5 human cohorts, we correlate differences in magnetic resonance imaging, mitochondria 3D structure, exercise parameters, and plasma immune markers between young (under 50 years) and old (over 50 years) individuals. We found that mitochondria we less spherical and more complex, indicating age-related declines in contact site capacity. Additionally, aged samples showed a larger volume phenotype in both female and male humans, indicating potential mitochondrial swelling. Concomitantly, muscle area, exercise capacity, and mitochondrial dynamic proteins showed age-related losses. Exercise stimulation restored mitofusin 2 (MFN2), one such of these mitochondrial dynamic proteins, which we show is required for the integrity of mitochondrial structure. Furthermore, we show that this pathway is evolutionarily conserved as Marf, the MFN2 ortholog in Drosophila, knockdown alters mitochondrial morphology and leads to the downregulation of genes regulating mitochondrial processes. Our results define age-related structural changes in mitochondria and further suggest that exercise may mitigate age-related structural decline through modulation of mitofusin 2.

Effect of diminazene on cardiac hypertrophy through mitophagy in rat models with hyperthyroidism induced by levothyroxine

Hyperthyroidism is associated with the alteration in molecular pathways involved in the regulation of mitochondrial mass and apoptosis, which contribute to the development of cardiac hypertrophy. Diminazene (DIZE) is an animal anti-infection drug that has shown promising effects on improving cardiovascular disease. The aim of the present study was to investigate the therapeutic effect of DIZE on cardiac hypertrophy and the signaling pathways involved in this process in the hyperthyroid rat model. Twenty male Wistar rats were equally divided into four groups: control, hyperthyroid, DIZE, and hyperthyroid + DIZE. After 28 days of treatment, serum thyroxine (T4) and thyroid stimulating hormone (TSH) level, cardiac hypertrophy indices, cardiac damage markers, cardiac malondialdehyde (MDA), and superoxide dismutase (SOD) level, the mRNA expression level of mitochondrial and apoptotic genes were evaluated. Hyperthyroidism significantly decreased the cardiac expression level of SIRT1/PGC1α and its downstream involved in the regulation of mitochondrial biogenesis, mitophagy, and antioxidant enzyme activities including TFAM, PINK1/MFN2, Drp1, and Nrf2, respectively, as well as stimulated mitochondrial-dependent apoptosis by reducing Bcl-2 expression and increasing Bax expression. Treatment with DIZE significantly reversed the downregulation of SIRT1, PGC1α, PINK1, MFN2, Drp1, and Nrf2 but did not significantly change the TFAM expression. Moreover, DIZE suppressed apoptosis by normalizing the cardiac expression levels of Bax and Bcl-2. DIZE is effective in attenuating hyperthyroidism-induced cardiac hypertrophy by modulating the mitophagy-related pathway, suppressing apoptosis and oxidative stress.

Prenatal hormone stress triggers embryonic cardiac hypertrophy outcome by ubiquitin-dependent degradation of mitochondrial mitofusin 2

Prenatal stress has been extensively documented as a contributing factor to adverse cardiac development and function in fetuses and infants. The release of glucocorticoids (GCs), identified as a significant stressor, may be a potential factor inducing cardiac hypertrophy. However, the underlying mechanism remains largely unknown. Herein, we discovered that corticosterone (CORT) overload induced cardiac hypertrophy in embryonic chicks and fetal mice in vivo, as well as enlarged cardiomyocytes in vitro. The impaired mitochondria dynamics were observed in CORT-exposed cardiomyocytes, accompanied by dysfunction in oxidative phosphorylation and ATP production. This phenomenon was found to be linked to decreased mitochondrial fusion protein mitofusin 2 (MFN2). Subsequently, we found that CORT facilitated the ubiquitin-proteasome-system-dependent degradation of MFN2 with an enhanced binding of appoptosin to MFN2, serving as the underlying cause. Collectively, our findings provide a comprehensive understanding of the mechanisms by which exposure to stress hormones induces cardiac hypertrophy in fetuses.

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.

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.

Cardiac lipid metabolism, mitochondrial function, and heart failure

A fine balance between uptake, storage, and the use of high energy fuels, like lipids, is crucial in the homeostasis of different metabolic tissues. Nowhere is this balance more important and more precarious than in the heart. This highly energy-demanding muscle normally oxidizes almost all the available substrates to generate energy, with fatty acids being the preferred source under physiological conditions. In patients with cardiomyopathies and heart failure, changes in the main energetic substrate are observed; these hearts often prefer to utilize glucose rather than oxidizing fatty acids. An imbalance between uptake and oxidation of fatty acid can result in cellular lipid accumulation and cytotoxicity. In this review, we will focus on the sources and uptake pathways used to direct fatty acids to cardiomyocytes. We will then discuss the intracellular machinery used to either store or oxidize these lipids and explain how disruptions in homeostasis can lead to mitochondrial dysfunction and heart failure. Moreover, we will also discuss the role of cholesterol accumulation in cardiomyocytes. Our discussion will attempt to weave in vitro experiments and in vivo data from mice and humans and use several human diseases to illustrate metabolism gone haywire as a cause of or accomplice to cardiac dysfunction.

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.

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.

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.

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 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.

Gallic acid protects against isoproterenol-induced cardiotoxicity in rats

BACKGROUND

Gallic acid (GA) is a polyphenolic agent with interesting pharmacological impacts on the cardiovascular system.

OBJECTIVE

The present study purposed to study the protective effects of GA at 25 and 50 mg/kg against isoproterenol (ISO)-induced cardiac damage in ischemia/reperfusion (I/R) in rats.

METHODS

Male Wistar rats were randomly assigned into six groups: Control, Control treated with GA at 25 mg/kg (GA25), Control treated with GA at 50 mg/kg (GA50), Hypertrophic rats induced by ISO (ISO), Hypertrophic rats treated with GA at 25 mg/kg (ISO+GA25), and Hypertrophic rats treated with GA at 50 mg/kg (ISO+GA50). Heart isolation was performed to induce a cardiac I/R injury model. Cardiac hemodynamic parameters were recorded. Serum Lactate Dehydrogenase (LDH) and Creatine Kinase-MB (CK-MB) and cardiac Superoxide dismutases (SOD) levels were evaluated. The gene expression of Sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) was assessed.

RESULTS

We found that GA at 50 mg/kg was significantly increased cardiac function at post I/R period in ISO-induced hypertrophic hearts. Moreover, it suppressed cardiac hypertrophy, the serum LDH and CK-MB levels in ISO injected rats. Administration of GA at 50 mg/kg was significantly increased SOD level and SERCA2a gene expression in the hypertrophic hearts.

CONCLUSION

GA at 50 mg/kg could improve cardiac performance possibly by increasing antioxidant defense enzymes, reducing cell damage, and enhancing SERCA2a gene expression in hypertrophic heart induced by ISO in I/R injury conditions.

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.

MicroRNA-17-5p Promotes Cardiac Hypertrophy by Targeting Mfn2 to Inhibit Autophagy

Pathological cardiac hypertrophy is the leading cause of heart failure, and miRNAs have been recognized as key factors in cardiac hypertrophy. This study aimed to elucidate whether miR-17-5p affects cardiac hypertrophy by targeting the mitochondrial fusion protein mitofusin 2 (Mfn2)-mediated phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway and regulating autophagy. miR-17-5p expression was shown to be upregulated both in vivo and in vitro. In addition, a miR-17-5p inhibitor significantly reversed AngII-induced cell hypertrophy in neonatal rat left ventricle myocytes (NRVMs). In contrast to miR-17-5p expression, Mfn2 expression was inhibited in rat hearts at 4 weeks after transverse aortic constriction (TAC) and in an Ang II-induced cell hypertrophy model. We examined miR-17-5p targeting of Mfn2 by dual luciferase reporter and Western blot assays. In addition, we also verified the relationship between Mfn2 and the PI3K/AKT/mTOR pathway. Mfn2 overexpression attenuated miR-17-5p-induced cell hypertrophy, and in rat myocardial tissue, miR-17-5p induced autophagy inhibition. In summary, the results of the present study demonstrated that miR-17-5p inhibits Mfn2 expression, activates the PI3K/AKT/mTOR pathway and suppresses autophagy to promote cardiac hypertrophy.

Long non-coding RNAs in cardiac hypertrophy

Cardiac hypertrophy (CH) is generally considered adaptive responses that may occur after myocardial infarction, pressure overload, volume overload, inflammatory heart muscle disease, or idiopathic dilated cardiomyopathy, whereas long-term stimulation eventually leads to heart failure (HF). However, the current molecular mechanisms involved in CH are unclear. Recently, increasing evidences reveal that long non-coding RNAs (lncRNAs) play vital roles in CH. Different lncRNAs can promote or inhibit the pathological process of CH by different mechanisms, while the regulation of lncRNAs expression can improve CH. Thus, CH-related lncRNAs may become a novel field of research on CH.

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.

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.

The Expression of microRNA in Adult Rat Heart with Isoproterenol-Induced Cardiac Hypertrophy

Cardiac hypertrophy is a common pathological condition and an independent risk factor that triggers cardiovascular morbidity. As an important epigenetic regulator, miRNA is widely involved in many biological processes. In this study, miRNAs expressed in rat hearts that underwent isoprenaline-induced cardiac hypertrophy were identified using high-throughput sequencing, and functional verification of typical miRNAs was performed using rat primary cardiomyocytes. A total of 623 miRNAs were identified, of which 33 were specifically expressed in cardiac hypertrophy rats. The enriched pathways of target genes of differentially expressed miRNAs included the FoxO signaling pathway, dopaminergic synapse, Wnt signaling pathway, MAPK (mitogen-activated protein kinase) signaling pathway, and Hippo signaling pathway. Subsequently, miR-144 was the most differentially expressed miRNA and was subsequently selected for in vitro validation. Inhibition of miR-144 expression in primary myocardial cells caused up-regulation of cardiac hypertrophy markers atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The dual luciferase reporter system showed that ANP may be a target gene of miR-144. Long non-coding RNA myocardial infarction associated transcript (LncMIAT) is closely related to heart disease, and here, we were the first to discover that LncMIAT may act as an miR-144 sponge in isoproterenol-induced cardiac hypertrophy. Taken together, these results enriched the understanding of miRNA in regulating cardiac hypertrophy and provided a reference for preventing and treating cardiac hypertrophy.

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.

Targeting mitochondria for cardiovascular disorders: therapeutic potential and obstacles

A large body of evidence indicates that mitochondrial dysfunction has a major role in the pathogenesis of multiple cardiovascular disorders. Over the past 2 decades, extraordinary efforts have been focused on the development of agents that specifically target mitochondria for the treatment of cardiovascular disease. Despite such an intensive wave of investigation, no drugs specifically conceived to modulate mitochondrial functions are currently available for the clinical management of cardiovascular disease. In this Review, we discuss the therapeutic potential of targeting mitochondria in patients with cardiovascular disease, examine the obstacles that have restrained the development of mitochondria-targeting agents thus far, and identify strategies that might empower the full clinical potential of this approach.

Expression Profile of microRNAs in Hypertrophic Cardiomyopathy and Effects of microRNA-20 in Inducing Cardiomyocyte Hypertrophy Through Regulating Gene MFN2

Myocardial hypertrophy is an important cause of heart failure and sudden death. Studies have shown that Mitofusin-2 (MFN2) is downregulated in myocardial hypertrophy, but the upstream regulation mechanism underlying its downexpression in cardiomyocytes is still unclear. This study aims to identify the expression profile of microRNAs (miRNAs) in hypertrophic cardiomyopathy (HCM) and explore the function of miRNA-20 in inducing cardiomyocyte hypertrophy through regulating MFN2. Through miRNA + mRNA microarray analysis, 1451 miRNAs were identified, 367 miRNAs expressed differently between groups. Meanwhile, a number of 24,718 mRNAs were identified, among which 5850 mRNAs were upregulated and 3005 mRNAs were downregulated in HCM group compared with the control group. Expression of hsa-miRNA-20a-5p was 2.26 times higher in the HCM group compared with the control group and 7 target gene prediction programs predicted MFN2 as a target of miRNA-20. In vitro model of hypertrophic cardiomyocytes displayed high expression level of miRNA-20, atrial natriuretic peptide (ANP) mRNA, and protein, accompanying low expression level of Mfn2 mRNA and protein, which meant miRNA-20 played a role in cardiomyocyte hypertrophy and might interact with MFN2 to function. Thereafter, overexpression of miRNA-20 led to cell hypertrophy accompanied with lowly expressed Mfn2 mRNA and protein. When transfected with miRNA-20 inhibitors, the expression of miRNA-20 and ANP gene was attenuated and MFN2 was the other way around. The cell surface area of Ang II group and mimic group was significantly larger compared with the control group, and in the inhibitor+Ang II group, the area was significantly decreased compared with the Ang II group. Dual-luciferase assays showed that miRNA-20 bound to 3' untranslated region of MFN2 and inhibited its expression. In conclusion, hypertrophic myocardium and normal myocardium have different miRNA expression profiles and the effect of miRNA-20 reducing the expression of MFN2 plays a role in promoting cardiomyocyte hypertrophy.

Inhibition of Mitofusin-2 Promotes Cardiac Fibroblast Activation via the PERK/ATF4 Pathway and Reactive Oxygen Species

Mitofusin-2 (Mfn2) is a key outer mitochondrial membrane protein, which maintains normal mitochondrial dynamics and function. However, its role in cardiac fibroblast activation remains poorly understood. In the present study, a rat model of transverse aortic constriction (TAC) was established to observe the cardiac fibroblast activation in vivo. TGF-β1 treatment for 24 hours was used to induce cardiac fibroblast activation in vitro. As a result, the expression of Mfn2 decreased in the hypertrophic heart tissues and cardiac fibroblasts treated with TGF-β1. siMfn2 and adenovirus were applied to mediate Mfn2 gene silencing and overexpression in cardiac fibroblasts to elucidate the relationship between Mfn2 and cardiac fibroblast activation, as well as the possible underlying mechanisms. Knockdown of Mfn2 further promoted TGF-β1-induced cardiac fibroblast activation, while forced expression of Mfn2 attenuated this pathological reaction. The PERK/ATF4 pathway, one of the branches of endoplasmic reticulum (ER) stress, was identified to be involved in this process. Knockdown and overexpression of Mfn2 lead to aggravation or alleviation of the PERK/ATF4 pathway. Blocking this pathway by silencing ATF4 with siATF4 attenuated the pathological process. During the activation of cardiac fibroblasts, knockdown of Mfn2 also increased the production of reactive oxygen species (ROS), while ROS scavenger N-acetyl-l-cysteine (NAC) could attenuate the effect caused by knockdown of Mfn2. Our data suggested that inhibition of Mfn2 could promote cardiac fibroblast activation by activating the PERK/ATF4 signaling pathway and increasing the generation of ROS.

Single Nucleotide Polymorphisms (SNPs) Genotyping Reveals that Mfn2 Polymorphisms are Associated with Thoracic Aortic Dissection in Han Chinese Population

BACKGROUND Many studies have shown that hypertension may contribute to thoracic aortic dissection (TAD). Among the factors that modulate hypertension are endoplasmic reticulum stress and vascular smooth muscle cell proliferation which are in turn modulated by mitofusion-2 (Mfn2). Specifically, we determined, in the Han Chinese population, whether single nucleotide polymorphisms (SNPs) of Mfn2 influenced the occurrence of TAD. MATERIAL AND METHODS Six tagging SNPs of Mfn2 (rs2236057, rs3766741, rs2236058, rs17037564, rs2295281, and rs2336384) were genotyped using a TaqMan assay in 200 TAD patients and 451 health individuals from the Han Chinese population. RESULTS Logistic regression analysis indicated CC genotype of rs2295281 was highly linked to an increased risk of TAD (TT+CT versus CC, OR=0.540, 95% CI [0.320-0.911], P=0.021), implying that TT genotype and CT genotype of rs2295281 have a lower risk for TAD. Logistic regression analysis also indicated that rs2236058 was highly linked to the risk of TAD based on recessive genetic model, which indicated that the GG genotype was a protective factor against TAD (GG versus (CG+CC), OR=0.545, 95% CI [0.351-0.845], P=0.007). CG genotype and CC genotype of rs2236058 had a higher risk for TAD. In addition, rs2236058 was linked to the risk of TAD in the recessive genetic and homozygous models in the normotensive subgroup (GG versus (CG+CC), OR=0.298, 95% CI [0.112-0.792], P=0.015; GG versus CC, OR=0.528, 95% CI [0.302-0.925], P=0.026) but not in the hypertension subgroup. CONCLUSIONS Our findings showed that the occurrence of TAD in a Han Chinese population was influenced by Mfn2 polymorphisms.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Antiarrhythmic effect linked to melatonin cardiorenal protection involves AT1 reduction and Hsp70-VDR increase

Lethal ventricular arrhythmias increase in patients with chronic kidney disease that suffer an acute coronary event. Chronic kidney disease induces myocardial remodeling, oxidative stress, and arrhythmogenesis. A manifestation of the relationship between kidney and heart is the concomitant reduction in vitamin D receptor (VDR) and the increase in angiotensin II receptor type 1 (AT₁ ). Melatonin has renal and cardiac protective actions. One potential mechanism is the increase in the heat shock protein 70 (Hsp70)-an antioxidant factor. We aim to determine the mechanisms involved in melatonin (Mel) prevention of kidney damage and arrhythmogenic heart remodeling. Unilateral ureteral-obstruction (UUO) and sham-operated rats were treated with either melatonin (4 mg/kg/day) or vehicle for 15 days. Hearts and kidneys from obstructed rats showed a reduction in VDR and Hsp70. Associated with AT₁ up-regulation in the kidneys and the heart of UUO rats also increased oxidative stress, fibrosis, apoptosis, mitochondrial edema, and dilated crests. Melatonin prevented these changes and ventricular fibrillation during reperfusion. The action potential lengthened and hyperpolarized in melatonin-treated rats throughout the experiment. We conclude that melatonin prevents renal damage and arrhythmogenic myocardial remodeling during unilateral ureteral obstruction due to a decrease in oxidative stress/fibrosis/apoptosis associated with AT₁ reduction and Hsp70-VDR increase.

Emerging Role of mTOR Signaling-Related miRNAs in Cardiovascular Diseases

Mechanistic/mammalian target of rapamycin (mTOR), an atypical serine/threonine kinase of the phosphoinositide 3-kinase- (PI3K-) related kinase family, elicits a vital role in diverse cellular processes, including cellular growth, proliferation, survival, protein synthesis, autophagy, and metabolism. In the cardiovascular system, the mTOR signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of both physiological and pathological processes. MicroRNAs (miRs), a class of short noncoding RNA, are an emerging intricate posttranscriptional modulator of critical gene expression for the development and maintenance of homeostasis across a wide array of tissues, including the cardiovascular system. Over the last decade, numerous studies have revealed an interplay between miRNAs and the mTOR signaling circuit in the different cardiovascular pathophysiology, like myocardial infarction, hypertrophy, fibrosis, heart failure, arrhythmia, inflammation, and atherosclerosis. In this review, we provide a comprehensive state of the current knowledge regarding the mechanisms of interactions between the mTOR signaling pathway and miRs. We have also highlighted the latest advances on mTOR-targeted therapy in clinical trials and the new perspective therapeutic strategies with mTOR-targeting miRs in cardiovascular diseases.

The lncRNA Plscr4 Controls Cardiac Hypertrophy by Regulating miR-214

Cardiac hypertrophy accompanied by maladaptive cardiac remodeling is the uppermost risk factor for the development of heart failure. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) have various biological functions, and their vital role in the regulation of cardiac hypertrophy still needs to be explored. In this study, we demonstrated that lncRNA Plscr4 was upregulated in hypertrophic mice hearts and in angiotensin II (Ang II)–treated cardiomyocytes. Next, we observed that overexpression of Plscr4 attenuated Ang II-induced cardiomyocyte hypertrophy. Conversely, the inhibition of Plscr4 gave rise to cardiomyocyte hypertrophy. Furthermore, overexpression of Plscr4 attenuated TAC (transverse aortic constriction)-induced cardiac hypertrophy. Finally, we demonstrated that Plscr4 acted as an endogenous sponge of miR-214 and forced expression of Plscr4 downregulated miR-214 expression to promote Mfn2 and attenuate hypertrophy. In contrast, knockdown of Plscr4 upregulated miR-214 to induce cardiomyocyte hypertrophy. Additionally, luciferase assay showed that miR-214 was the direct target of Plscr4, and overexpression of miR-214 counteracted the anti-hypertrophy effect of Plscr4. Collectively, these findings identify Plscr4 as a negative regulator of cardiac hypertrophy in vivo and in vitro due to its regulation of the miR-214-Mfn2 axis, suggesting that Plscr4 might act as a therapeutic target for the treatment of cardiac hypertrophy and heart failure.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Mitochondrial-Shaping Proteins in Cardiac Health and Disease - the Long and the Short of It!

Mitochondrial health is critically dependent on the ability of mitochondria to undergo changes in mitochondrial morphology, a process which is regulated by mitochondrial shaping proteins. Mitochondria undergo fission to generate fragmented discrete organelles, a process which is mediated by the mitochondrial fission proteins (Drp1, hFIS1, Mff and MiD49/51), and is required for cell division, and to remove damaged mitochondria by mitophagy. Mitochondria undergo fusion to form elongated interconnected networks, a process which is orchestrated by the mitochondrial fusion proteins (Mfn1, Mfn2 and OPA1), and which enables the replenishment of damaged mitochondrial DNA. In the adult heart, mitochondria are relatively static, are constrained in their movement, and are characteristically arranged into 3 distinct subpopulations based on their locality and function (subsarcolemmal, myofibrillar, and perinuclear). Although the mitochondria are arranged differently, emerging data supports a role for the mitochondrial shaping proteins in cardiac health and disease. Interestingly, in the adult heart, it appears that the pleiotropic effects of the mitochondrial fusion proteins, Mfn2 (endoplasmic reticulum-tethering, mitophagy) and OPA1 (cristae remodeling, regulation of apoptosis, and energy production) may play more important roles than their pro-fusion effects. In this review article, we provide an overview of the mitochondrial fusion and fission proteins in the adult heart, and highlight their roles as novel therapeutic targets for treating cardiac disease.

Novel putative pharmacological therapies to protect the right ventricle in pulmonary hypertension: a review of current literature

Pulmonary hypertension (PH) is defined by elevated mean pulmonary artery pressure following the pathological remodelling of small pulmonary arteries. An increase in right ventricular (RV) afterload results in RV hypertrophy and RV failure. The pathophysiology of PH, and RV remodelling in particular, is not well understood, thus explaining, at least in part, why current PH therapies have a limited effect. Existing therapies mostly target the pulmonary circulation. Because the remodelled RV fails to support normal cardiac function, patients eventually succumb from RV failure. Developing novel therapies that directly target the function of the RV may therefore benefit patients with PH. In the past decade, several promising studies have investigated novel cardioprotective strategies in experimental models of PH. This review aims to comprehensively discuss and highlight these novel experimental approaches to confer, in the long-term, greater health benefit in patients with PH.

Mitochondrial Dynamics as a Therapeutic Target for Treating Cardiac Diseases

Mitochondria are dynamic in nature and are able to shift their morphology between elongated interconnected mitochondrial networks and a fragmented disconnected arrangement by the processes of mitochondrial fusion and fission, respectively. Changes in mitochondrial morphology are regulated by the mitochondrial fusion proteins - mitofusins 1 and 2 (Mfn1 and 2), and optic atrophy 1 (Opa1) as well as the mitochondrial fission proteins - dynamin-related peptide 1 (Drp1) and fission protein 1 (Fis1). Despite having a unique spatial arrangement, cardiac mitochondria have been implicated in a variety of disorders including ischemia-reperfusion injury (IRI), heart failure, diabetes, and pulmonary hypertension. In this chapter, we review the influence of mitochondrial dynamics in these cardiac disorders as well as their potential as therapeutic targets in tackling cardiovascular disease.

Melatonin prevents adverse myocardial infarction remodeling via Notch1/Mfn2 pathway

Mitochondrial dysfunction is linked with myocardial infarction (MI), a disorder in which Notch1 has attracted increasing attention. However, the involvement of Notch1 in mitochondrial impairment after an MI is poorly understood, as is the role of mitochondrial fusion-associated protein 2 (Mfn2). Moreover, whether melatonin potentiates the Notch1/Mfn2 pathway in post-MI cardiac damage remains unclear. In our study, small interfering RNAs against Notch1 or Mfn2 and Jagged1 peptide were delivered via intramyocardial injection. At 3 days after these treatments, MI was induced by ligation of the anterior descending branch. We found that this ablation of Notch1 or Mfn2 aggravated post-MI injury, including worsened mitochondrial damage and increased generation of reactive oxygen species (ROS). In contrast, Jagged1 improved mitochondrial structure and function, decreased ROS production and attenuated post-MI injury. Interestingly, though Mfn2 expression was mildly regulated by Notch1 signaling in myocardium, Mfn2 deficiency nearly eliminated the cardioprotection by Jagged1, as evidenced by suppressed cardiac function, aggravated myocardial fibrosis, increased cell apoptosis, worsened mitochondrial impairment and enhanced oxidative stress. These observations revealed that Mfn2 plays an indispensable role in protection against MI-induced injury by Notch1. The mechanism might involve disrupting a damaging cycle of mitochondrial damage and ROS generation. Furthermore, melatonin activated Notch1 signaling and increased Mfn2 expression were reversed by luzindole, a nonselective antagonist of the melatonin receptor. Notably, melatonin attenuated post-MI injury in normal mice, but not in mice deficient in Notch1 or Mfn2. These results demonstrate that melatonin attenuates post-MI injury via the Notch1/Mfn2 pathway in a receptor-dependent manner.

Candesartan cilexetil attenuated cardiac remodeling by improving expression and function of mitofusin 2 in SHR

BACKGROUND

Left ventricular hypotrophy (LVH) is very common in hypertensives even after antihypertensive treatment. Mitofusin 2 (Mfn2) is a critical negative regulator of vascular smooth muscle cell (VSMC) hypertrophy by regulating mitochondrial fusion, ras/raf/MEK signal pathway, et al. The purpose of this study was to investigate whether candesartan attenuated cardiac remodeling by improving expression and function of mitofusin 2 in SHR.

METHODS

Nine weeks old spontaneously hypertensive rats (SHR) were selected and treated with candesartan for eight weeks. Then, heart tissues were investigated for signs of cardiac remodeling, mitochondrial structure and membrane potential, mitochondrial enzyme activities, hydrogen peroxide, mRNA and protein expression of Mfn2/ras/raf/MEK signaling pathway in heart tissues.

RESULTS

The results showed that cardiac remodeling was obviously in SHR group: cardiac cell alignment was irregular; cardiac fibers became thick, irregular and enlarged; cell density was reduced in SHR compared to WKY. After candesartan treatment, histopathological structure improved significantly which were consistent with mitochondrial morphology, mitochondrial membrane potential, mitochondrial enzyme activities, hydrogen peroxide, Mfn2/ras/raf/MEK gene and protein expression in cardiac tissues. What's more, although blood pressure was well controlled in a normal range, cardiac remodeling wasn't avoided. In general, candesartan obviously repressed cardiac hypertrophy and cardiac remodeling significantly compared to SHR untreated group, but didn't reverse it.

CONCLUSIONS

Mfn2 is negatively associated with cardiac remodeling. Candesartan treatment can improve mitochondrial structure and function and regulate Mfn2/ras/raf/MEK signaling pathway. Mfn2 may be used a potential marker for cardiac remodeling and a novel therapeutic target for target organ damage protection.

Mitochondrial fusion and fission proteins as novel therapeutic targets for treating cardiovascular disease

The past decade has witnessed a number of exciting developments in the field of mitochondrial dynamics - a phenomenon in which changes in mitochondrial shape and movement impact on cellular physiology and pathology. By undergoing fusion and fission, mitochondria are able to change their morphology between elongated interconnected networks and discrete fragmented structures, respectively. The cardiac mitochondria, in particular, have garnered much interest due to their unique spatial arrangement in the adult cardiomyocyte, and the multiple roles they play in cell death and survival. In this article, we review the role of the mitochondrial fusion and fission proteins as novel therapeutic targets for treating cardiovascular disease.

Mitochondrial fusion and fission proteins: novel therapeutic targets for combating cardiovascular disease

Mitochondria are no longer considered to be solely the static powerhouses of the cell. While they are undoubtedly essential to sustaining life and meeting the energy requirements of the cell through oxidative phosphorylation, they are now regarded as highly dynamic organelles with multiple functions, playing key roles in cell survival and death. In this review, we discuss the emerging role of mitochondrial fusion and fission proteins, as novel therapeutic targets for treating a wide range of cardiovascular diseases.

Overexpression of mitofusin 2 inhibits reactive astrogliosis proliferation in vitro

Astrocytes become activated in response to central nervous system (CNS) injury, and excessive astrogliosis is considered an impediment to axonal regeneration by forming glial scar. Mitofusin 2 (Mfn2), a key protein in mitochondrial network, has been reported to negatively regulate cell proliferation. The present study aimed to explore whether reactive astrogliosis could be suppressed by Mfn2 overexpression. Scratch injury and starvation-serum stimulation models in cultured astrocytes were combined to address this issue. In scratch model, reactive proliferation status of damaged astrocytes was implicated by migration of high ratio of EdU(+) cells into lesion region and significantly increased expression of GFAP and PCNA. At meantime, Mfn2 expression was found to exert a down-regulated trend both in gen and protein levels. Pretreatment of cells with adenoviral vector encoding Mfn2 gene increased Mfn2 expression and subsequently attenuated injury-induced astrocytes hyperplasia, activation-relevant protein synthesis, cellular proliferation, eventually delayed wound healing process. Furthermore, Mfn2 overexpression markedly inhibited astrocytes proliferation induced by serum stimulation, by arresting the transition of cell cycle from G1 to S phase. Together, these in vitro results demonstrated that reactive astrogliosis can be effectively suppressed by up-regulation of Mfn2, which might contribute to a promising therapeutic intervention in CNS disease characterized by glia-related damage.

Mitochondrial fission is required for cardiomyocyte hypertrophy mediated by a Ca2+-calcineurin signaling pathway

Cardiomyocyte hypertrophy has been associated with diminished mitochondrial metabolism. Mitochondria are crucial organelles for the production of ATP, and their morphology and function are regulated by the dynamic processes of fusion and fission. The relationship between mitochondrial dynamics and cardiomyocyte hypertrophy is still poorly understood. Here, we show that treatment of cultured neonatal rat cardiomyocytes with the hypertrophic agonist norepinephrine promotes mitochondrial fission (characterized by a decrease in mitochondrial mean volume and an increase in the relative number of mitochondria per cell) and a decrease in mitochondrial function. We demonstrate that norepinephrine acts through α1-adrenergic receptors to increase cytoplasmic Ca(2+), activating calcineurin and promoting migration of the fission protein Drp1 (encoded by Dnml1) to mitochondria. Dominant-negative Drp1 (K38A) not only prevented mitochondrial fission, it also blocked hypertrophic growth of cardiomyocytes in response to norepinephrine. Remarkably, an antisense adenovirus against the fusion protein Mfn2 (AsMfn2) was sufficient to increase mitochondrial fission and stimulate a hypertrophic response without agonist treatment. Collectively, these results demonstrate the importance of mitochondrial dynamics in the development of cardiomyocyte hypertrophy and metabolic remodeling.

Dysregulation of Mfn2 and Drp-1 proteins in heart failure

Therapeutic approaches for cardiac regenerative mechanisms have been explored over the past decade to target various cardiovascular diseases (CVD). Structural and functional aberrations of mitochondria have been observed in CVD. The significance of mitochondrial maturation and function in cardiomyocytes is distinguished by their attribution to embryonic stem cell differentiation into adult cardiomyocytes. An abnormal fission process has been implicated in heart failure, and treatment with mitochondrial division inhibitor 1 (Mdivi-1), a specific inhibitor of dynamin related protein-1 (Drp-1), has been shown to improve cardiac function. We recently observed that the ratio of mitofusin 2 (Mfn2; a fusion protein) and Drp-1 (a fission protein) was decreased during heart failure, suggesting increased mitophagy. Treatment with Mdivi-1 improved cardiac function by normalizing this ratio. Aberrant mitophagy and enhanced oxidative stress in the mitochondria contribute to abnormal activation of MMP-9, leading to degradation of the important gap junction protein connexin-43 (Cx-43) in the ventricular myocardium. Reduced Cx-43 levels were associated with increased fibrosis and ventricular dysfunction in heart failure. Treatment with Mdivi-1 restored MMP-9 and Cx-43 expression towards normal. In this review, we discuss mitochondrial dynamics, its relation to MMP-9 and Cx-43, and the therapeutic role of fission inhibition in heart failure.

A novel 5'-uncoding region -1248 A>G variation of mitofusin-2 gene is associated with hypertension in Chinese

PURPOSE

Mitofusin2 gene (Mfn2, also named Hyperplasia suppressive gene, HSG) is very important in the origin and development of hypertension. However, the mechanism of Mfn2/HSG expression regulation was not uncovered. This study was designed to explore the association of a novel 5'-uncoding region (UCR) -1248 A>G variation of HSG/Mfn2 gene and hypertension.

MATERIALS AND METHODS

472 healthy, normotensive subjects [normotension (NT) group], 454 prehypertensive subjects [prehypertension (PH) group] and 978 hypertensive patients [essential hypertension (EH) group] were screened for an association study between 5'-UCR -1248 A>G of Mfn2/HSG and hypertension by polymerase chain reaction and DNA sequencing after venous blood was drawn and DNA was extracted.

RESULTS

When comparing the A and G frequency in EH, PH and NT groups, in total, NT group significantly had higher A frequency than in PH group [odds ratio (OR)=1.605, confidence interval (CI) 95%=1.063-2.242, p=0.025] and EH group (OR=5.395, CI 95%=3.783-7.695, p<0.01). When subgrouped by gender, A frequency in NT group was still significantly higher than in EH group (male: OR= 4.264, CI 95%=2.780-6.543, p<0.01; female: OR=8.897, CI 95%=4.686-16.891, p<0.01), but not from PH group, either in male group or in female group. Ordinal Logistic Regression analysis showed that A>G variation was significantly related with blood pressure level (B=-1.271, Wald=40.914, CI 95%=-1.660 - -0.881, p<0.01).

CONCLUSION

5'-UCR -1248 A>G variation of Mfn2/HSG gene was a novel variation and may be associated with hypertension in Chinese.

Early protective effect of mitofusion 2 overexpression in STZ-induced diabetic rat kidney

Diabetic nephropathy (DN) is a serious complication of diabetes with a poorly defined etiology and limited treatment options. Early intervention is key to preventing the progression of DN. Mitofusin 2 (Mfn2) regulates mitochondrial morphology and signaling, and is involved in the pathogenesis of numerous diseases. Furthermore, Mfn2 is also closely associated with the development of diabetes, but its functional roles in the diabetic kidney remain unknown. This study investigated the effect of Mfn2 at an early stage of DN. Mfn2 was overexpressed by adenovirus-mediated gene transfer in streptozotocin-induced diabetic rats. Clinical parameters (proteinuria, albumin/creatinine ratio), pathological changes, ultra-microstructural changes in nephrons, expression of collagen IV and phosph-p38, ROS production, mitochondrial function, and apoptosis were evaluated and compared with diabetic rats expressing control levels of Mfn2. Endogenous Mfn2 expression decreased with time in DN. Compared to the blank transfection control group, overexpression of Mfn2 decreased kidney weight relative to body weight, reduced proteinuria and ACR, and improved pathological changes typical of the diabetic kidney, like enlargement of glomeruli, accumulation of ECM, and thickening of the basement membrane. In addition, Mfn2 overexpression inhibited activation of p38, and the accumulation of ROS; prevented mitochondrial dysfunction; and reduced the synthesis of collagen IV, but did not affect apoptosis of kidney cells. This study demonstrates that Mfn2 overexpression can attenuate pathological changes in the kidneys of diabetic rats. Further studies are needed to clarify the underlying mechanism of this protective function. Mfn2 might be a potential therapeutic target for the treatment of early stage DN.