Interdependence of Parkin-Mediated Mitophagy and Mitochondrial Fission in Adult Mouse Hearts

The Ubiquitin Ligase RBX2/SAG Regulates Mitochondrial Ubiquitination and Mitophagy

Clearance of damaged mitochondria via mitophagy is crucial for cellular homeostasis. While the role of ubiquitin (Ub) ligase PARKIN in mitophagy has been extensively studied, increasing evidence suggests the existence of PARKIN-independent mitophagy in highly metabolically active organs such as the heart. Here, we identify a crucial role for Cullin-RING Ub ligase 5 (CRL5) in basal mitochondrial turnover in cardiomyocytes. CRL5 is a multi-subunit Ub ligase comprised by the catalytic RING box protein RBX2 (also known as SAG), scaffold protein Cullin 5 (CUL5), and a substrate-recognizing receptor. Analysis of the mitochondrial outer membrane-interacting proteome uncovered a robust association of CRLs with mitochondria. Subcellular fractionation, immunostaining, and immunogold electron microscopy established that RBX2 and Cul5, two core components of CRL5, localizes to mitochondria. Depletion of RBX2 inhibited mitochondrial ubiquitination and turnover, impaired mitochondrial membrane potential and respiration, and increased cell death in cardiomyocytes. In vivo , deletion of the Rbx2 gene in adult mouse hearts suppressed mitophagic activity, provoked accumulation of damaged mitochondria in the myocardium, and disrupted myocardial metabolism, leading to rapid development of dilated cardiomyopathy and heart failure. Similarly, ablation of RBX2 in the developing heart resulted in dilated cardiomyopathy and heart failure. Notably, the action of RBX2 in mitochondria is not dependent on PARKIN, and PARKIN gene deletion had no impact on the onset and progression of cardiomyopathy in RBX2-deficient hearts. Furthermore, RBX2 controls the stability of PINK1 in mitochondria. Proteomics and biochemical analyses further revealed a global impact of RBX2 deficiency on the mitochondrial proteome and identified several mitochondrial proteins as its putative substrates. These findings identify RBX2-CRL5 as a mitochondrial Ub ligase that controls mitophagy under physiological conditions in a PARKIN-independent, PINK1-dependent manner, thereby regulating cardiac homeostasis.

Mitophagy modulation for the treatment of cardiovascular diseases

BACKGROUND

Defects of mitophagy, the selective form of autophagy for mitochondria, are commonly observed in several cardiovascular diseases and represent the main cause of mitochondrial dysfunction. For this reason, mitophagy has emerged as a novel and potential therapeutic target.

METHODS

In this review, we discuss current evidence about the biological significance of mitophagy in relevant preclinical models of cardiac and vascular diseases, such as heart failure, ischemia/reperfusion injury, metabolic cardiomyopathy and atherosclerosis.

RESULTS

Multiple studies have shown that cardiac and vascular mitophagy is an adaptive mechanism in response to stress, contributing to cardiovascular homeostasis. Mitophagy defects lead to cell death, ultimately impairing cardiac and vascular function, whereas restoration of mitophagy by specific compounds delays disease progression.

CONCLUSIONS

Despite previous efforts, the molecular mechanisms underlying mitophagy activation in response to stress are not fully characterized. A comprehensive understanding of different forms of mitophagy active in the cardiovascular system is extremely important for the development of new drugs targeting this process. Human studies evaluating mitophagy abnormalities in patients at high cardiovascular risk also represent a future challenge.

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

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

ULP-2 SUMO protease regulates UPRmt and mitochondrial homeostasis in Caenorhabditis elegans

Mitochondria are the powerhouses of cells, responsible for energy production and regulation of cellular homeostasis. When mitochondrial function is impaired, a stress response termed mitochondrial unfolded protein response (UPRmt) is initiated to restore mitochondrial function. Since mitochondria and UPRmt are implicated in many diseases, it is important to understand UPRmt regulation. In this study, we show that the SUMO protease ULP-2 has a key role in regulating mitochondrial function and UPRmt. Specifically, down-regulation of ulp-2 suppresses UPRmt and reduces mitochondrial membrane potential without significantly affecting cellular ROS. Mitochondrial networks are expanded in ulp-2 null mutants with larger mitochondrial area and increased branching. Moreover, the amount of mitochondrial DNA is increased in ulp-2 mutants. Downregulation of ULP-2 also leads to alterations in expression levels of mitochondrial genes involved in protein import and mtDNA replication, however, mitophagy remains unaltered. In summary, this study demonstrates that ULP-2 is required for mitochondrial homeostasis and the UPRmt.

Mitochondrial dynamics and mitochondrial autophagy: Molecular structure, orchestrating mechanism and related disorders

Mitochondrial dynamics and autophagy play essential roles in normal cellular physiological activities, while abnormal mitochondrial dynamics and mitochondrial autophagy can cause cancer and related disorders. Abnormal mitochondrial dynamics usually occur in parallel with mitochondrial autophagy. Both have been reported to have a synergistic effect and can therefore complement or inhibit each other. Progress has been made in understanding the classical mitochondrial PINK1/Parkin pathway and mitochondrial dynamical abnormalities. Still, the mechanisms and regulatory pathways underlying the interaction between mitophagy and mitochondrial dynamics remain unexplored. Like other existing reviews, we review the molecular structure of proteins involved in mitochondrial dynamics and mitochondrial autophagy, and how their abnormalities can lead to the development of related diseases. We will also review the individual or synergistic effects of abnormal mitochondrial dynamics and mitophagy leading to cellular proliferation, differentiation and invasion. In addition, we explore the mechanisms underlying mitochondrial dynamics and mitochondrial autophagy to contribute to targeted and precise regulation of mitochondrial function. Through the study of abnormal mitochondrial dynamics and mitochondrial autophagy regulation mechanisms, as well as the role of early disease development, effective targets for mitochondrial function regulation can be proposed to enable accurate diagnosis and treatment of the associated disorders.

Cellular Senescence, Mitochondrial Dysfunction, and Their Link to Cardiovascular Disease

Cardiovascular diseases (CVDs), a group of disorders affecting the heart or blood vessels, are the primary cause of death worldwide, with an immense impact on patient quality of life and disability. According to the World Health Organization, CVD takes an estimated 17.9 million lives each year, where more than four out of five CVD deaths are due to heart attacks and strokes. In the decades to come, an increased prevalence of age-related CVD, such as atherosclerosis, coronary artery stenosis, myocardial infarction (MI), valvular heart disease, and heart failure (HF) will contribute to an even greater health and economic burden as the global average life expectancy increases and consequently the world's population continues to age. Considering this, it is important to focus our research efforts on understanding the fundamental mechanisms underlying CVD. In this review, we focus on cellular senescence and mitochondrial dysfunction, which have long been established to contribute to CVD. We also assess the recent advances in targeting mitochondrial dysfunction including energy starvation and oxidative stress, mitochondria dynamics imbalance, cell apoptosis, mitophagy, and senescence with a focus on therapies that influence both and therefore perhaps represent strategies with the most clinical potential, range, and utility.

Rhein alleviates myocardial ischemic injury by inhibiting mitochondrial division, activating mitochondrial autophagy and suppressing myocardial cell apoptosis through the Drp1/Pink1/Parkin pathway

BACKGROUND

Rhein, which has antioxidant and anti-inflammatory response properties, is a beneficial treatment for different pathologies. However, the mechanism by which rhein protects against myocardial ischemic injury is poorly understood.

METHODS AND RESULTS

To establish an acute myocardial infarction (AMI) rat model, we performed left anterior descending (LAD) ligation. Sprague‒Dawley rats were randomly divided into four groups: sham, AMI, AMI + rhein (AMI + R), and AMI + mitochondrial fission inhibitor (AMI + M). The extent of myocardial injury was evaluated by TTC staining, serum myocardial injury markers, and HE and Masson staining. Cardiac mitochondria ultrastructure was visualized by transmission electron microscopy. TUNEL assay and flow cytometry analysis were used to estimate cell apoptosis. Protein expression levels were measured by Western blotting. In vitro, the efficacy of rhein was assessed in H9c2 cells under hypoxic condition. Our results revealed that rats with AMI exhibited increased infarct size and indicators of myocardial damage, along with activation of Drp1-dependent mitochondrial fission, decreased mitophagy and increased apoptosis rates. However, pretreatment with rhein significantly reversed these effects and demonstrated similar efficacy to Mdivi-1. Furthermore, rhein pretreatment protected against myocardial ischemic injury by inhibiting mitochondrial fission, as evidenced by decreased Drp1 expression. It also enhanced mitophagy, as indicated by increased expression of Beclin1, Pink1 and Parkin, an increased LC3-II/LC3-I ratio and increased formation of autolysosomes. Additionally, rhein pretreatment mitigated apoptosis in AMI. These results were also confirmed in vitro in H9c2 cells.

CONCLUSION

Our results demonstrate that rhein pretreatment exerts cardioprotective effects against myocardial ischemic injury via the Drp1/Pink1/Parkin pathway.

Effect of vitamin D on cardiac hypertrophy in D-galactose-induced aging model through cardiac mitophagy

BACKGROUND

Cardiac apoptosis plays a key role in increased morbidity associated with aging-induced-cardiac disorder. Mitochondria play an important role in cardiac apoptosis, and dynamin-related protein 1 (Drp1), as a main mediator of mitochondrial fission, can trigger the mitophagy process to sustain the mitochondrial quality. The present study was done to determine the effect of vitamin D (VitD) treatment on cardiac hypertrophy through mitophagy regulation in aged animals induced by D-galactose (D-GAL).

METHODS AND RESULTS

Male Wistar rats were randomly divided into four groups: control, D-GAL (aging group), D-GAL co-injected with VitD (D-GAL ± VitD), and D-GAL plus ethanol (D-GAL ± Ethanol). Aging was induced by an intraperitoneal (i.p.) administration of D-GAL at 150 mg/kg daily for eight weeks and also VitD (400 IU/kg) or ethanol was injected (i.p.) into aging rats. Then, the levels of cardiac mitophagy and cardiac apoptosis were determined by measuring the expression of tensin homologue (PTEN)-induced putative kinase 1 (PINK1), Drp1, Bcl2-Associated X (Bax), and B-cell lymphoma 2 (Bcl2) genes. Aging in rats was associated with a reduction in mitophagy and also an increase in apoptosis of the heart through down-regulation of Drp1, PINK1, and Bcl2 genes and also up-regulation of Bax. However, VitD improved cardiac hypertrophy through cardiac mitophagy in D-GAL-induced aging rats.

CONCLUSION

VitD can inhibit cardiac hypertrophy by an increase in mitophagy and a decrease in apoptosis in the aging heart. The illustration of the suggested mechanism underlying of Vitamin D in cardiac hypertrophy induced by aging.

The role of mitochondrial dynamics in disease

Mitochondria are multifaceted and dynamic organelles regulating various important cellular processes from signal transduction to determining cell fate. As dynamic properties of mitochondria, fusion and fission accompanied with mitophagy, undergo constant changes in number and morphology to sustain mitochondrial homeostasis in response to cell context changes. Thus, the dysregulation of mitochondrial dynamics and mitophagy is unsurprisingly related with various diseases, but the unclear underlying mechanism hinders their clinical application. In this review, we summarize the recent developments in the molecular mechanism of mitochondrial dynamics and mitophagy, particularly the different roles of key components in mitochondrial dynamics in different context. We also summarize the roles of mitochondrial dynamics and target treatment in diseases related to the cardiovascular system, nervous system, respiratory system, and tumor cell metabolism demanding high-energy. In these diseases, it is common that excessive mitochondrial fission is dominant and accompanied by impaired fusion and mitophagy. But there have been many conflicting findings about them recently, which are specifically highlighted in this view. We look forward that these findings will help broaden our understanding of the roles of the mitochondrial dynamics in diseases and will be beneficial to the discovery of novel selective therapeutic targets.

Critical roles of parkin and PINK1 in coxsackievirus B3-induced viral myocarditis

Viral myocarditis is an inflammatory disease of the myocardium, often leads to cardiac dysfunction and death. PARKIN (PRKN) and PINK1, well known as Parkinson's disease-associated genes, have been reported to be involved in innate immunity and mitochondrial damage control. Therefore, we investigated the role of parkin and PINK1 in coxsackievirus B3 (CVB3)-induced viral myocarditis because the etiology of myocarditis is related to abnormal immune response to viral infection and mitochondrial damage. After viral infection, the survival was significantly lower and myocardial damage was more severe in parkin knockout (KO) and PINK1 KO mice compared to wild-type (WT) mice. Parkin KO and PINK1 KO showed defective immune cell recruitment and impaired production of antiviral cytokines such as interferon-gamma, allowing increased viral replication. In addition, parkin KO and PINK1 KO mice were more susceptible to CVB3-induced mitochondrial damage than WT mice, resulting in susceptibility to viral-induced cardiac damage. Finally, using publicly available RNA-seq data, we found that pathogenic mutants of the PRKN gene are more common in patients with dilated cardiomyopathy and myocarditis than in controls or the general population. This study will help elucidate the molecular mechanism of CVB3-induced viral myocarditis.

p53 contributes to cardiovascular diseases via mitochondria dysfunction: A new paradigm

Cardiovascular diseases (CVDs) are leading causes of global mortality; however, their underlying mechanisms remain unclear. The tumor suppressor factor p53 has been extensively studied for its role in cancer and is also known to play an important role in regulating CVDs. Abnormal p53 expression levels and modifications contribute to the occurrence and development of CVDs. Additionally, mounting evidence underscores the critical involvement of mitochondrial dysfunction in CVDs. Notably, studies indicate that p53 abnormalities directly correlate with mitochondrial dysfunction and may even interact with each other. Encouragingly, small molecule inhibitors targeting p53 have exhibited remarkable effects in animal models of CVDs. Moreover, therapeutic strategies aimed at mitochondrial-related molecules and mitochondrial replacement therapy have demonstrated their advantageous potential. Therefore, targeting p53 or mitochondria holds immense promise as a pioneering therapeutic approach for combating CVDs. In this comprehensive review, we delve into the mechanisms how p53 influences mitochondrial dysfunction, including energy metabolism, mitochondrial oxidative stress, mitochondria-induced apoptosis, mitochondrial autophagy, and mitochondrial dynamics, in various CVDs. Furthermore, we summarize and discuss the potential significance of targeting p53 or mitochondria in the treatment of CVDs.

Role of Mitochondrial Dynamics in Heart Diseases

Mitochondrial dynamics, including fission and fusion processes, are essential for heart health. Mitochondria, the powerhouses of cells, maintain their integrity through continuous cycles of biogenesis, fission, fusion, and degradation. Mitochondria are relatively immobile in the adult heart, but their morphological changes due to mitochondrial morphology factors are critical for cellular functions such as energy production, organelle integrity, and stress response. Mitochondrial fusion proteins, particularly Mfn1/2 and Opa1, play multiple roles beyond their pro-fusion effects, such as endoplasmic reticulum tethering, mitophagy, cristae remodeling, and apoptosis regulation. On the other hand, the fission process, regulated by proteins such as Drp1, Fis1, Mff and MiD49/51, is essential to eliminate damaged mitochondria via mitophagy and to ensure proper cell division. In the cardiac system, dysregulation of mitochondrial dynamics has been shown to cause cardiac hypertrophy, heart failure, ischemia/reperfusion injury, and various cardiac diseases, including metabolic and inherited cardiomyopathies. In addition, mitochondrial dysfunction associated with oxidative stress has been implicated in atherosclerosis, hypertension and pulmonary hypertension. Therefore, understanding and regulating mitochondrial dynamics is a promising therapeutic tool in cardiac diseases. This review summarizes the role of mitochondrial morphology in heart diseases for each mitochondrial morphology regulatory gene, and their potential as therapeutic targets to heart diseases.

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.

The mitophagy pathway and its implications in human diseases

Mitochondria are dynamic organelles with multiple functions. They participate in necrotic cell death and programmed apoptotic, and are crucial for cell metabolism and survival. Mitophagy serves as a cytoprotective mechanism to remove superfluous or dysfunctional mitochondria and maintain mitochondrial fine-tuning numbers to balance intracellular homeostasis. Growing evidences show that mitophagy, as an acute tissue stress response, plays an important role in maintaining the health of the mitochondrial network. Since the timely removal of abnormal mitochondria is essential for cell survival, cells have evolved a variety of mitophagy pathways to ensure that mitophagy can be activated in time under various environments. A better understanding of the mechanism of mitophagy in various diseases is crucial for the treatment of diseases and therapeutic target design. In this review, we summarize the molecular mechanisms of mitophagy-mediated mitochondrial elimination, how mitophagy maintains mitochondrial homeostasis at the system levels and organ, and what alterations in mitophagy are related to the development of diseases, including neurological, cardiovascular, pulmonary, hepatic, renal disease, etc., in recent advances. Finally, we summarize the potential clinical applications and outline the conditions for mitophagy regulators to enter clinical trials. Research advances in signaling transduction of mitophagy will have an important role in developing new therapeutic strategies for precision medicine.

The immunoproteasome subunit β2i ameliorates myocardial ischemia/reperfusion injury by regulating Parkin-Mfn1/2-mediated mitochondrial fusion

Mitochondrial dynamics are critical for maintaining mitochondrial morphology and function during cardiac ischemia and reperfusion (I/R). The immunoproteasome complex is an inducible isoform of the proteasome that plays a key role in modulating inflammation and some cardiovascular diseases, but the importance of immunoproteasome catalytic subunit β2i (also known as LMP10 or MECL1) in regulating mitochondrial dynamics and cardiac I/R injury is largely unknown. Here, using β2i-knockout (KO) mice and rAAV9-β2i-injected mice, we discovered that β2i expression and its trypsin-like activity were significantly attenuated in the mouse I/R myocardium and in patients with myocardial infarction (MI). Moreover, β2i-KO mice exhibited greatly enhanced I/R-mediated cardiac dysfunction, infarct size, myocyte apoptosis and oxidative stress accompanied by excessive mitochondrial fission due to Mfn1/2 and Drp1 imbalance. Conversely, cardiac overexpression of β2i in mice injected with recombinant adeno-associated virus 9 (rAAV9)-β2i ameliorated cardiac I/R injury. Mechanistically, I/R injury reduced β2i expression and activity, which increased the expression of the E3 ligase Parkin protein and promoted the degradation of mitofusin 1/2 (Mfn1/2), leading to excessive mitochondrial fission. In conclusion, our data suggest for the first time that β2i exerts a protective role against cardiac I/R injury and that increasing β2i expression may be a new therapeutic option for cardiac ischemic disease in clinical practice. Graphical abstract showing how the immunoproteasome subunit β2i ameliorates myocardial I/R injury by regulating Parkin-Mfn1/2-mediated mitochondrial fusion.

Mitochondrial Dysfunction in the Cardio-Renal Axis

Cardiovascular disease (CVD) frequently complicates chronic kidney disease (CKD). The risk of all-cause mortality increases from 20% to 500% in patients who suffer both conditions; this is referred to as the so-called cardio-renal syndrome (CRS). Preclinical studies have described the key role of mitochondrial dysfunction in cardiovascular and renal diseases, suggesting that maintaining mitochondrial homeostasis is a promising therapeutic strategy for CRS. In this review, we explore the malfunction of mitochondrial homeostasis (mitochondrial biogenesis, dynamics, oxidative stress, and mitophagy) and how it contributes to the development and progression of the main vascular pathologies that could be affected by kidney injury and vice versa, and how this knowledge may guide the development of novel therapeutic strategies in CRS.

Delivery of mitochondria confers cardioprotection through mitochondria replenishment and metabolic compliance

Mitochondrial dysfunction is a hallmark of heart failure. Mitochondrial transplantation has been demonstrated to be able to restore heart function, but its mechanism of action remains unresolved. Using an in-house optimized mitochondrial isolation method, we tested efficacy of mitochondria transplantation in two different heart failure models. First, using a doxorubicin-induced heart failure model, we demonstrate that mitochondrial transplantation before doxorubicin challenge protects cardiac function in vivo and prevents myocardial apoptosis, but contraction improvement relies on the metabolic compatibility between transplanted mitochondria and treated cardiomyocytes. Second, using a mutation-driven dilated cardiomyopathic human induced pluripotent stem cell-derived cardiomyocyte model, we demonstrate that mitochondrial transplantation preferentially boosts contraction in the ventricular myocytes. Last, using single-cell RNA-seq, we show that mitochondria transplantation boosts contractility in dystrophic cardiomyocytes with few transcriptomic alterations. Together, we provide evidence that mitochondria transplantation confers myocardial protection and may serve as a potential therapeutic option for heart failure.

Ginsenoside Rg1 Protects against Cardiac Remodeling in Heart Failure via SIRT1/PINK1/Parkin-Mediated Mitophagy

Adverse cardiac remodeling may lead to the development and progression of heart failure, which is lack of effective clinical treatment. Ginsenoside Rg1 (GRg1), a primary ingredient of Panax ginseng, protects against diverse cardiovascular disease, but its effects on cardiac remodeling remain unclear. Thus, we investigated the protective effect and mechanism of GRg1 on cardiac remodeling after myocardial infarction. GRg1 significantly ameliorated cardiac remodeling in mice with left anterior descending coronary artery ligation, reflected by reduced left ventricular dilation and decreased cardiac fibrosis, accompanied by improved cardiac function. Mechanistically, GRg1 considerably increased mitophagosomes formation, ameliorated cardiac mitochondria damage, and enhanced SIRT1/PINK1/Parkin-mediated mitophagy during cardiac remodeling. Consistently, GRg1 increased cell viability and attenuated apoptosis and fibrotic responses in H₂ O₂ -treated H9c2 cells by promoting the SIRT1/PINK1/Parkin axis. Furthermore, SIRT1-specific inhibitor (EX527) or the use of small interfering RNA against Parkin abolished the protective effect of GRg1 in vitro. These findings reveal a novel mechanism of GRg1 alleviating cardiac remodeling via enhancing SIRT1/PINK1/Parkin-mediated mitophagy.

Mitofusin 2 mutation drives cell proliferation in Charcot-Marie-Tooth 2A fibroblasts

Dominant mutations in ubiquitously expressed mitofusin 2 gene (MFN2) cause Charcot-Marie-Tooth type 2A (CMT2A; OMIM 609260), an inherited sensory-motor neuropathy that affects peripheral nerve axons. Mitofusin 2 protein has been found to take part in mitochondrial fusion, mitochondria-endoplasmic reticulum tethering, mitochondrial trafficking along axons, mitochondrial quality control and various types of cancer, in which MFN2 has been indicated as a tumor suppressor gene. Discordant data on the mitochondrial altered phenotypes in patient-derived fibroblasts harboring MFN2 mutations and in animal models have been reported. We addressed some of these issues by focusing on mitochondria behavior during autophagy and mitophagy in fibroblasts derived from a CMT2AMFN2 patient with an MFN2650G > T/C217F mutation in the GTPase domain. This study investigated mitochondrial dynamics, respiratory capacity and autophagy/mitophagy, to tackle the multifaceted MFN2 contribution to CMT2A pathogenesis. We found that MFN2 mutated fibroblasts showed impairment of mitochondrial morphology, bioenergetics capacity, and impairment of the early stages of autophagy, but not mitophagy. Unexpectedly, transcriptomic analysis of mutated fibroblasts highlighted marked differentially expressed pathways related to cell population proliferation and extracellular matrix organization. We consistently found the activation of mTORC2/AKT signaling and accelerated proliferation in the CMT2AMFN2 fibroblasts. In conclusion, our evidence indicates that MFN2 mutation can positively drive cell proliferation in CMT2AMFN2 fibroblasts.

The dynamic interplay between cardiac mitochondrial health and myocardial structural remodeling in metabolic heart disease, aging, and heart failure

This review provides a holistic perspective on the bi-directional relationship between cardiac mitochondrial dysfunction and myocardial structural remodeling in the context of metabolic heart disease, natural cardiac aging, and heart failure. First, a review of the physiologic and molecular drivers of cardiac mitochondrial dysfunction across a range of increasingly prevalent conditions such as metabolic syndrome and cardiac aging is presented, followed by a general review of the mechanisms of mitochondrial quality control (QC) in the heart. Several important mechanisms by which cardiac mitochondrial dysfunction triggers or contributes to structural remodeling of the heart are discussed: accumulated metabolic byproducts, oxidative damage, impaired mitochondrial QC, and mitochondrial-mediated cell death identified as substantial mechanistic contributors to cardiac structural remodeling such as hypertrophy and myocardial fibrosis. Subsequently, the less studied but nevertheless important reverse relationship is explored: the mechanisms by which cardiac structural remodeling feeds back to further alter mitochondrial bioenergetic function. We then provide a condensed pathogenesis of several increasingly important clinical conditions in which these relationships are central: diabetic cardiomyopathy, age-associated declines in cardiac function, and the progression to heart failure, with or without preserved ejection fraction. Finally, we identify promising therapeutic opportunities targeting mitochondrial function in these conditions.

Perspectives on mitochondrial relevance in cardiac ischemia/reperfusion injury

Cardiovascular disease is the most common cause of death worldwide and in particular, ischemic heart disease holds the most considerable position. Even if it has been deeply studied, myocardial ischemia-reperfusion injury (IRI) is still a side-effect of the clinical treatment for several heart diseases: ischemia process itself leads to temporary damage to heart tissue and obviously the recovery of blood flow is promptly required even if it worsens the ischemic injury. There is no doubt that mitochondria play a key role in pathogenesis of IRI: dysfunctions of these important organelles alter cell homeostasis and survival. It has been demonstrated that during IRI the system of mitochondrial quality control undergoes alterations with the disruption of the complex balance between the processes of mitochondrial fusion, fission, biogenesis and mitophagy. The fundamental role of mitochondria is carried out thanks to the finely regulated connection to other organelles such as plasma membrane, endoplasmic reticulum and nucleus, therefore impairments of these inter-organelle communications exacerbate IRI. This review pointed to enhance the importance of the mitochondrial network in the pathogenesis of IRI with the aim to focus on potential mitochondria-targeting therapies as new approach to control heart tissue damage after ischemia and reperfusion process.

Cell Biology of Parkin: Clues to the Development of New Therapeutics for Parkinson's Disease

Parkinson's disease is the second most prevalent neurodegenerative disease and contributes significantly to morbidity globally. Currently, no disease-modifying therapies exist to combat this disorder. Insights from the molecular and cellular pathobiology of the disease seems to indicate promising therapeutic targets. The parkin protein has been extensively studied for its role in autosomal recessive Parkinson's disease and, more recently, its role in sporadic Parkinson's disease. Parkin is an E3 ubiquitin ligase that plays a prominent role in mitochondrial quality control, mitochondrial-dependent cell death pathways, and other diverse functions. Understanding the numerous roles of parkin has introduced many new possibilities for therapeutic modalities in treating both autosomal recessive Parkinson's disease and sporadic Parkinson's disease. In this article, we review parkin biology with an emphasis on mitochondrial-related functions and propose novel, potentially disease-modifying therapeutic approaches for treating this debilitating condition.

Caveolin-1 influences mitochondrial plasticity and function in hepatic stellate cell activation

Caveolin-1 (Cav-1) is an integral membrane protein present in all organelles, responsible for regulating and integrating multiple signals as a platform. Mitochondria are extremely adaptable to external cues in chronic liver diseases, and expression of Cav-1 may affect mitochondrial flexibility in hepatic stellate cells (HSCs) activation. We previously demonstrated that exogenous expression of Cav-1 was sufficient to increase some classical markers of activation in HSCs. Here, we aimed to evaluate the influence of exogenous expression and knockdown of Cav-1 on regulating the mitochondrial plasticity, metabolism, endoplasmic reticulum (ER)-mitochondria distance, and lysosomal activity in HSCs. To characterize the mitochondrial, lysosomal morphology, and ER-mitochondria distance, we perform transmission electron microscope analysis. We accessed mitochondria and lysosomal networks and functions through a confocal microscope and flow cytometry. The expression of mitochondrial machinery fusion/fission genes was examined by real-time polymerase chain reaction. Total and mitochondrial cholesterol content was measured using Amplex Red. To define energy metabolism, we used the Oroboros system in the cells. We report that GRX cells with exogenous expression or knockdown of Cav-1 changed mitochondrial morphometric parameters, OXPHOS metabolism, ER-mitochondria distance, lysosomal activity, and may change the activation state of HSC. This study highlights that Cav-1 may modulate mitochondrial function and structural reorganization in HSC activation, being a potential candidate marker for chronic liver diseases and a molecular target for therapeutic intervention.

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.

Mechanistic and therapeutic role of Drp1 in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, has emerged as the most common form of dementia in the elderly. Two major pathological hallmarks have been identified for AD: extracellular amyloid plaques and intracellular neurofibrillary tangles (NFT). Recently, dynamin-related protein 1 (Drp1) was recognized to contribute significantly towards the pathogenesis of AD. Drp1 is primarily located in the cytosol, from where it translocates to the mitochondrial outer membrane and drives the mitochondrial fission via GTP hydrolysis. Drp1 interacts with Aβ and phosphorylated tau, leading to excessive mitochondrial fragmentation, which in turn results in synaptic dysfunction, neuronal damage and cognitive decline. Several studies suggest an increase in the level of Drp1 in the post-mortem brain specimen collected from the AD patients and murine models of AD. Interestingly, heterozygous deletion of Drp1 in the transgenic murine model of AD ameliorates the mitochondrial dysfunction, improving learning and memory. The current review article discusses the possible mechanistic pathways by which Drp1 can influence the pathogenesis of AD. Besides, it will describe various inhibitors for Drp1 and their potential role as therapeutics for AD in the future.

SUMOylation targeting mitophagy in cardiovascular diseases

Small ubiquitin-like modifier (SUMO) plays a key regulatory role in cardiovascular diseases, such as cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. As a multifunctional posttranslational modification molecule in eukaryotic cells, SUMOylation is essentially associated with the regulation of mitochondrial dynamics, especially mitophagy, which is involved in the progression and development of cardiovascular diseases. SUMOylation targeting mitochondrial-associated proteins is admittedly considered to regulate mitophagy activation and mitochondrial functions and dynamics, including mitochondrial fusion and fission. SUMOylation triggers mitochondrial fusion to promote mitochondrial dysfunction by modifying Fis1, OPA1, MFN1/2, and DRP1. The interaction between SUMO and DRP1 induces SUMOylation and inhibits lysosomal degradation of DRP1, which is further involved in the regulation of mitochondrial fission. Both SUMOylation and deSUMOylation contribute to the initiation and activation of mitophagy by regulating the conjugation of MFN1/2 SERCA2a, HIF1α, and PINK1. SUMOylation mediated by the SUMO molecule has attracted much attention due to its dual roles in the development of cardiovascular diseases. In this review, we systemically summarize the current understanding underlying the expression, regulation, and structure of SUMO molecules; explore the biochemical functions of SUMOylation in the initiation and activation of mitophagy; discuss the biological roles and mechanisms of SUMOylation in cardiovascular diseases; and further provide a wider explanation of SUMOylation and deSUMOylation research to provide a possible therapeutic strategy for cardiovascular diseases. Considering the precise functions and exact mechanisms of SUMOylation in mitochondrial dysfunction and mitophagy will provide evidence for future experimental research and may serve as an effective approach in the development of novel therapeutic strategies for cardiovascular diseases. Regulation and effect of SUMOylation in cardiovascular diseases via mitophagy. SUMOylation is involved in multiple cardiovascular diseases, including cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. Since it is expressed in multiple cells associated with cardiovascular disease, SUMOylation can be regulated by numerous ligases, including the SENP family proteins PIAS1, PIASy/4, UBC9, and MAPL. SUMOylation regulates the activation and degradation of PINK1, SERCA2a, PPARγ, ERK5, and DRP1 to mediate mitochondrial dynamics, especially mitophagy activation. Mitophagy activation regulated by SUMOylation further promotes or inhibits ventricular diastolic dysfunction, perfusion injury, ventricular remodelling and ventricular noncompaction, which contribute to the development of cardiovascular diseases.

Ischemic Preconditioning and Postconditioning Protect the Heart by Preserving the Mitochondrial Network

Background

Mitochondria fuse to form elongated networks which are more tolerable to stress and injury. Ischemic pre- and postconditioning (IPC and IPost, respectively) are established cardioprotective strategies in the preclinical setting. Whether IPC and IPost modulates mitochondrial morphology is unknown. We hypothesize that the protective effects of IPC and IPost may be conferred via preservation of mitochondrial network.

Methods

IPC and IPost were applied to the H9c2 rat myoblast cells, isolated adult primary murine cardiomyocytes, and the Langendorff-isolated perfused rat hearts. The effects of IPC and IPost on cardiac cell death following ischemia-reperfusion injury (IRI), mitochondrial morphology, and gene expression of mitochondrial-shaping proteins were investigated.

Results

IPC and IPost successfully reduced cardiac cell death and myocardial infarct size. IPC and IPost maintained the mitochondrial network in both H9c2 and isolated adult primary murine cardiomyocytes. 2D-length measurement of the 3 mitochondrial subpopulations showed that IPC and IPost significantly increased the length of interfibrillar mitochondria (IFM). Gene expression of the pro-fusion protein, Mfn1, was significantly increased by IPC, while the pro-fission protein, Drp1, was significantly reduced by IPost in the H9c2 cells. In the primary cardiomyocytes, gene expression of both Mfn1 and Mfn2 were significantly upregulated by IPC and IPost, while Drp1 was significantly downregulated by IPost. In the Langendorff-isolated perfused heart, gene expression of Drp1 was significantly downregulated by both IPC and IPost.

Conclusion

IPC and IPost-mediated upregulation of pro-fusion proteins (Mfn1 and Mfn2) and downregulation of pro-fission (Drp1) promote maintenance of the interconnected mitochondrial network, ultimately conferring cardioprotection against IRI.

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.

TBC1D15-Drp1 interaction-mediated mitochondrial homeostasis confers cardioprotection against myocardial ischemia/reperfusion injury

OBJECTIVE

Mitochondria are essential for myocardial ischemia/reperfusion (I/R) injury. TBC domain family member 15 (TBC1D15) participates in the regulation of mitochondrial homeostasis although its role remains elusive in I/R injury.

METHODS AND MATERIALS

This study examined the role of TBC1D15 in mitochondrial homeostasis under myocardial I/R injury using inducible cardiac-specific TBC1D15 knockin (TBC1D15^CKI) and knockout (TBC1D15^CKO) mice.

RESULTS

TBC1D15 mRNA/protein levels were downregulated in human ischemic cardiomyopathy samples, mouse I/R hearts and neonatal mouse cardiomyocytes with H/R injury, consistent with scRNA sequencing finding from patients with coronary heart disease. Cardiac-specific knockin of TBC1D15 attenuated whereas cardiac-specific knockout of TBC1D15 overtly aggravated I/R-induced cardiomyocyte apoptosis and cardiac dysfunction. TBC1D15^CKI mice exhibited reduced mitochondrial damage and mitochondrial fragmentation following myocardial I/R injury, while TBC1D15^CKO mice displayed opposite results. TBC1D15 preserved mitochondrial function evidenced by safeguarding MMP and oxygen consumption capacity, antagonizing ROS accumulation and cytochrome C release, which were nullified by TBC1D15 knockdown. Time-lapse confocal microscopy revealed that TBC1D15 activated asymmetrical mitochondrial fission through promoting mitochondria-lysosome contacts untethering in NMCMs under H/R injury, whereas overexpression of TBC1D15 mutants (R400K and ∆231-240) failed to regulate asymmetrical fission and knockdown of TBC1D15 slowed down asymmetrical fission. Moreover, TBC1D15-offered benefits were mitigated by knockdown of Fis1 and Drp1. Mechanistically, TBC1D15 recruited Drp1 to mitochondria-lysosome contact sites via direct interaction with Drp1 through its C terminus (574-624) domain. Interfering with interaction between TBC1D15 and Drp1 abrogated asymmetrical mitochondrial fission and mitochondrial function. Cardiac phenotypes of TBC1D15^CKO mice upon I/R injury were rescued by adenovirus-mediated overexpression of wild-type but not mutants (R400K, ∆231-240 and ∆574-624) TBC1D15.

CONCLUSIONS

TBC1D15 ameliorated I/R injury through a novel modality to preserve mitochondrial homeostasis where mitochondria-lysosome contacts (through the TBC1D15/Fis1/RAB7 cascade) regulate asymmetrical mitochondrial fission (TBC1D15/Drp1 interaction), suggesting promises of targeting TBC1D15 in the management of myocardial I/R injury.

Mitochondrial quality control in cardiac ischemia/reperfusion injury: new insights into mechanisms and implications

The current effective method for the treatment of myocardial infarction is timely restoration of the blood supply to the ischemic area of the heart. Although reperfusion is essential for reestablishing oxygen and nutrient supplies, it often leads to additional myocardial damage, creating an important clinical dilemma. Reports from long-term studies have confirmed that mitochondrial damage is the critical mechanism in cardiac ischemia/reperfusion (I/R) injury. Mitochondria are dynamic and possess a quality control system that targets mitochondrial quantity and quality by modifying mitochondrial fusion, fission, mitophagy, and biogenesis and protein homeostasis to maintain a healthy mitochondrial network. The system of mitochondrial quality control involves complex molecular machinery that is highly interconnected and associated with pathological changes such as oxidative stress, calcium overload, and endoplasmic reticulum (ER) stress. Because of the critical role of the mitochondrial quality control systems, many reports have suggested that defects in this system are among the molecular mechanisms underlying myocardial reperfusion injury. In this review, we briefly summarize the important role of the mitochondrial quality control in cardiomyocyte function and focus on the current understanding of the regulatory mechanisms and molecular pathways involved in mitochondrial quality control in cardiac I/R damage.

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.

Energy Metabolism on Mitochondrial Maturation and Its Effects on Cardiomyocyte Cell Fate

Alterations in energy metabolism play a major role in the lineage of cardiomyocytes, such as the dramatic changes that occur in the transition from neonate to newborn. As cardiomyocytes mature, they shift from a primarily glycolytic state to a mitochondrial oxidative metabolic state. Metabolic intermediates and metabolites may have epigenetic and transcriptional roles in controlling cell fate by increasing mitochondrial biogenesis. In the maturing cardiomyocyte, such as in the postnatal heart, fatty acid oxidation increases in conjunction with increased mitochondrial biogenesis driven by the transcriptional coregulator PGC1-α. PGC1-α is necessary for mitochondrial biogenesis in the heart at birth, with deficiencies leading to postnatal cardiomyopathy. While stem cell therapy as a treatment for heart failure requires further investigation, studies suggest that adult stem cells may secrete cardioprotective factors which may regulate cardiomyocyte differentiation and survival. This review will discuss how metabolism influences mitochondrial biogenesis and how mitochondrial biogenesis influences cell fate, particularly in the context of the developing cardiomyocyte. The implications of energy metabolism on stem cell differentiation into cardiomyocytes and how this may be utilized as a therapy against heart failure and cardiovascular disease will also be discussed.

Neurohormonal Connections with Mitochondria in Cardiomyopathy and Other Diseases

Neurohormonal signaling and mitochondrial dynamism are seemingly distinct processes that are almost ubiquitous among multicellular organisms. Both of these processes are regulated by GTPases, and disturbances in either can provoke disease. Here, inconspicuous pathophysiological connectivity between neurohormonal signaling and mitochondrial dynamism is reviewed in the context of cardiac and neurological syndromes. For both processes, greater understanding of basic mechanisms has evoked a reversal of conventional pathophysiological concepts. Thus, neurohormonal systems induced in, and previously thought to be critical for, cardiac functioning in heart failure are now pharmaceutically interrupted as modern standard of care. And, mitochondrial abnormalities in neuropathies that were originally attributed to an imbalance between mitochondrial fusion and fission are increasingly recognized as an interruption of axonal mitochondrial transport. The data are presented in a historical context to provided insight into how scientific thought has evolved and to foster an appreciation for how seemingly different areas of investigation can converge. Finally, some theoretical notions are presented to explain how different molecular and functional defects can evoke tissue-specific disease.

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.

TRAF2, an Innate Immune Sensor, Reciprocally Regulates Mitophagy and Inflammation to Maintain Cardiac Myocyte Homeostasis

Mitochondria are essential for cardiac myocyte function, but damaged mitochondria trigger cardiac myocyte death. Although mitophagy, a lysosomal degradative pathway to remove damaged mitochondria, is robustly active in cardiac myocytes in the unstressed heart, its mechanisms and physiological role remain poorly defined. We discovered a critical role for TRAF2, an innate immunity effector protein with E3 ubiquitin ligase activity, in facilitating physiological cardiac myocyte mitophagy in the adult heart, to prevent inflammation and cell death, and maintain myocardial homeostasis.

The strange case of Drp1 in autophagy: Jekyll and Hyde?

There is a debate regarding the function of Drp1, a GTPase involved in mitochondrial fission, during the elimination of mitochondria by autophagy. A number of experiments indicate that Drp1 is needed to eliminate mitochondria during mitophagy, either by reducing the mitochondrial size or by providing a noncanonical mitophagy function. Yet, other convincing experimental results support the conclusion that Drp1 is not necessary. Here, we review the possible functions for Drp1 in mitophagy and autophagy, depending on tissues, organisms and stresses, and discuss these apparent discrepancies. In this regard, it appears that the reduction of mitochondria size is often required for mitophagy but not always in a Drp1-dependent manner. Finally, we speculate on Drp1-independent mitochondrial fission mechanism that may take place during mitophagy and on noncanonical roles, which Drp1 may play such as modulating organelle contact sites dynamic during the autophagosome formation.

Role of Mitophagy in Coronary Heart Disease: Targeting the Mitochondrial Dysfunction and Inflammatory Regulation

Coronary heart disease (CHD) is one of the main causes of death worldwide. In the past few decades, several in-depth research on the pathological mechanisms and effective treatment methods for CHD have been conducted. At present, the intervention of a variety of therapeutic drugs and treatment technologies have greatly reduced the burden on global public health. However, severe arrhythmia and myocardial fibrosis accompanying CHD in the later stages need to be addressed urgently. Mitochondria are important structural components for energy production and the main sites for aerobic respiration in cells. Mitochondria are involved in arrhythmia, myocardial fibrosis, and acute CHD and play a crucial role in regulating myocardial ischemia/hypoxia. Mitochondrial dysfunction or mitophagy disorders (including receptor-dependent mitophagy and receptor-independent mitophagy) play an important role in the pathogenesis of CHD, especially mitophagy. Mitophagy acts as a “mediator” in the inflammatory damage of cardiomyocytes or vascular endothelial cells and can clear mitochondria or organelles damaged by inflammation under normal conditions. We reviewed experimental advances providing evidence that mitochondrial homeostasis or mitochondrial quality control are important in the pathological mechanism of CHD. Further, we reviewed and summarized relevant regulatory drugs that target mitochondrial function and quality control.

The SUMO protease SENP3 regulates mitochondrial autophagy mediated by Fis1

Mitochondria are unavoidably subject to organellar stress resulting from exposure to a range of reactive molecular species. Consequently, cells operate a poorly understood quality control programme of mitophagy to facilitate elimination of dysfunctional mitochondria. Here, we used a model stressor, deferiprone (DFP), to investigate the molecular basis for stress-induced mitophagy. We show that mitochondrial fission 1 protein (Fis1) is required for DFP-induced mitophagy and that Fis1 is SUMOylated at K149, an amino acid residue critical for Fis1 mitochondrial localization. We find that DFP treatment leads to the stabilization of the SUMO protease SENP3, which is mediated by downregulation of the E3 ubiquitin (Ub) ligase CHIP. SENP3 is responsible for Fis1 deSUMOylation and depletion of SENP3 abolishes DFP-induced mitophagy. Furthermore, preventing Fis1 SUMOylation by conservative K149R mutation enhances Fis1 mitochondrial localization. Critically, expressing a Fis1 K149R mutant restores DFP-induced mitophagy in SENP3-depleted cells. Thus, we propose a model in which SENP3-mediated deSUMOylation facilitates Fis1 mitochondrial localization to underpin stress-induced mitophagy.

Mitochondria in Pathological Cardiac Remodeling

Adverse cardiac remodeling is often precipitated by chronic stress or injury inflicted upon the heart during the progression of cardiovascular diseases. Mitochondria play an important role in the cardiomyocyte response to stress by serving as a signaling hub for changes in cellular energetics, redox balance, contractile function, and cell death. Cardiac remodeling involves alterations to mitochondrial form and function that are either compensatory to maintain contractility or maladaptive, which promotes heart failure progression. In this mini-review, we focus on three mitochondrial processes that contribution to cardiac remodeling: Ca²⁺ signaling, mitochondrial dynamics, and mitochondrial metabolism.

Mitophagy Regulation Following Myocardial Infarction

Mitophagy, which mediates the selective elimination of dysfunctional mitochondria, is essential for cardiac homeostasis. Mitophagy is regulated mainly by PTEN-induced putative kinase protein-1 (PINK1)/parkin pathway but also by FUN14 domain-containing 1 (FUNDC1) or Bcl2 interacting protein 3 (BNIP3) and BNIP3-like (BNIP3L/NIX) pathways. Several studies have shown that dysregulated mitophagy is involved in cardiac dysfunction induced by aging, aortic stenosis, myocardial infarction or diabetes. The cardioprotective role of mitophagy is well described, whereas excessive mitophagy could contribute to cell death and cardiac dysfunction. In this review, we summarize the mechanisms involved in the regulation of cardiac mitophagy and its role in physiological condition. We focused on cardiac mitophagy during and following myocardial infarction by highlighting the role and the regulation of PI NK1/parkin-; FUNDC1-; BNIP3- and BNIP3L/NIX-induced mitophagy during ischemia and reperfusion.

New Insights Into the Role of Mitochondria Quality Control in Ischemic Heart Disease

IHD is a significant cause of mortality and morbidity worldwide. In the acute phase, it's demonstrated as myocardial infarction and ischemia-reperfusion injury, while in the chronic stage, the ischemic heart is mainly characterised by adverse myocardial remodelling. Although interventions such as thrombolysis and percutaneous coronary intervention could reduce the death risk of these patients, the underlying cellular and molecular mechanisms need more exploration. Mitochondria are crucial to maintain the physiological function of the heart. During IHD, mitochondrial dysfunction results in the pathogenesis of ischemic heart disease. Ischemia drives mitochondrial damage not only due to energy deprivation, but also to other aspects such as mitochondrial dynamics, mitochondria-related inflammation, etc. Given the critical roles of mitochondrial quality control in the pathological process of ischemic heart disease, in this review, we will summarise the efforts in targeting mitochondria (such as mitophagy, mtROS, and mitochondria-related inflammation) on IHD. In addition, we will briefly revisit the emerging therapeutic targets in this field.

Molecular Signaling to Preserve Mitochondrial Integrity against Ischemic Stress in the Heart: Rescue or Remove Mitochondria in Danger

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide, and ischemic heart disease is the most common cause of heart failure (HF). The heart is a high-energy demanding organ, and myocardial energy reserves are limited. Mitochondria are the powerhouses of the cell, but under stress conditions, they become damaged, release necrotic and apoptotic factors, and contribute to cell death. Loss of cardiomyocytes plays a significant role in ischemic heart disease. In response to stress, protective signaling pathways are activated to limit mitochondrial deterioration and protect the heart. To prevent mitochondrial death pathways, damaged mitochondria are removed by mitochondrial autophagy (mitophagy). Mitochondrial quality control mediated by mitophagy is functionally linked to mitochondrial dynamics. This review provides a current understanding of the signaling mechanisms by which the integrity of mitochondria is preserved in the heart against ischemic stress.

Decreased dynamin-related protein 1-related mitophagy induces myocardial apoptosis in the aging heart

An increase in cardiomyocyte apoptosis is the main contributor to the observed high morbidity of cardiac disease during aging. Mitochondria play important roles in cardiac apoptosis, and dynamin-related protein 1 (Drp1) is the critical factor that participates in mitochondrial fission and induces mitophagy to maintain mitochondria quality. However, whether Drp1 is involved in the increase of apoptosis in aging heart remains unclear. The purpose of this study was to determine whether Drp1 participates in inducing the apoptosis through regulating mitophagy in aging myocardium. To explore the effect of mitophagy and apoptosis in aging heart, we detected the expression of COX IV and the co-localization of COX IV and LC3 II, which reflect mitophagy, and measured adenosine triphosphate and reactive oxygen species contents, which reflect mitochondrial injury. Cell apoptosis was detected by measuring the activity of caspase-3 and the expression of cleaved caspase-3 and further confirmed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. The results showed an increase in apoptosis and a decrease in mitophagy in aging cardiomyocytes, and apoptosis was ameliorated after the induction of mitophagy by carbonyl cyanide m-chlorophenyl hydrazone (a mitophagy activator) in D-galactose (D-gal)-induced senescence H9c2 cells. To clarify the role of Drp1 in apoptosis, we knocked down Drp1 by transfecting si-Drp1, or overexpressed Drp1 in senescent cells, and then detected mitophagy, mitochondrial injury, and apoptosis. The data showed that downregulated Drp1 induces mitochondrial damage and apoptosis. In addition, to explore the regulatory relationship between Drp1 and phosphatase and tensin homologue (PTEN)-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy, we detected the expressions of PINK1 and Parkin after the overexpression of Drp1 in the D-gal group cells and found that Drp1-mediated mitophagy inhibited the PINK1/Parkin pathway in senescent cells. Our results demonstrated that insufficient Drp1 induces cardiomyocyte apoptosis by inhibiting mitophagy, and Drp1 affects the PINK1/Parkin pathway of mitophagy in the aging heart.

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.

Selective Autophagy in Hyperglycemia-Induced Microvascular and Macrovascular Diseases

Dysregulation of autophagy is an important underlying cause in the onset and progression of many metabolic diseases, including diabetes. Studies in animal models and humans show that impairment in the removal and the recycling of organelles, in particular, contributes to cellular damage, functional failure, and the onset of metabolic diseases. Interestingly, in certain contexts, inhibition of autophagy can be protective. While the inability to upregulate autophagy can play a critical role in the development of diseases, excessive autophagy can also be detrimental, making autophagy an intricately regulated process, the altering of which can adversely affect organismal health. Autophagy is indispensable for maintaining normal cardiac and vascular structure and function. Patients with diabetes are at a higher risk of developing and dying from vascular complications. Autophagy dysregulation is associated with the development of heart failure, many forms of cardiomyopathy, atherosclerosis, myocardial infarction, and microvascular complications in diabetic patients. Here, we review the recent findings on selective autophagy in hyperglycemia and diabetes-associated microvascular and macrovascular complications.

RAB7 activity is required for the regulation of mitophagy in oocyte meiosis and oocyte quality control during ovarian aging

There is increasing evidence that mitophagy, a specialized form of autophagy to degrade and clear long-lived or damaged mitochondria, is impaired in aging and age-related disease. Previous study has demonstrated the obesity-exposed oocytes accumulate and transmit damaged mitochondria due to an inability to activate mitophagy. However, it remains unknown whether mitophagy functions in oocyte and what's the regulatory mechanism in oocyte aging. In the study, when fully grown oocytes were treated with CCCP, an uncoupling agent to induce mitophagy, we found the activation of the PRKN-mediated mitophagy pathway accompanied the blockage of meiosis at metaphase I stage. Our result then demonstrated its association with the decreased activity of RAB7 and all the observed defects in CCCP treated oocytes could be effectively rescued by microinjection of mRNA encoding active RAB7^Q67L or treatment with the RAB7 activator ML098. Further study indicated PRKN protein level as a rate-limiting factor to facilitate degradation of RAB7 and its GEF (guanine nucleotide exchange factor) complex CCZ1-MON1 through the ubiquitin-proteasome system. In GV oocytes collected during ovarian aging, we found the age-related increase of PINK1 and PRKN proteins and a significant decrease of RAB7 which resulted in defects of mitophagosome formation and the accumulation of damaged mitochondria. The age-related retardation of female fertility was improved after in vivo treatment of ML098. Thus, RAB7 activity is required to maintain the balance between mitophagy and chromosome stability and RAB7 activator is a good candidate to ameliorate age-related deterioration of oocyte quality.Abbreviations: ATG9: autophagy related 9A; ATP: adenosine triphosphate; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CCZ1: CCZ1 vacuolar protein trafficking and biogenesis associated; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GAPs: GTPase-activating proteins; GEF: guanine nucleotide exchange factor; GV: germinal vesicle; GVBD: germinal vesicle breakdown; LAMP1: lysosomal-associated membrane protein 1; MI: metaphase I stage of meiosis; MII: metaphase II stage of meiosis; Mito: MitoTracker; mtDNA: mitochondrial DNA; MON1: MON1 homolog, secretory trafficking associated; OPTN: optineurin; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RAB7: RAB7, member RAS oncogene family; ROS: reactive oxygen species; TEM: transmission electron microscopy; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; TUBB: tubulin, beta; UB: ubiquitin.

The role of autophagy in cardiovascular pathology

Macroautophagy/autophagy is a conserved catabolic recycling pathway in which cytoplasmic components are sequestered, degraded, and recycled to survive various stress conditions. Autophagy dysregulation has been observed and linked with the development and progression of several pathologies, including cardiovascular diseases, the leading cause of death in the developed world. In this review, we aim to provide a broad understanding of the different molecular factors that govern autophagy regulation and how these mechanisms are involved in the development of specific cardiovascular pathologies, including ischemic and reperfusion injury, myocardial infarction, cardiac hypertrophy, cardiac remodeling, and heart failure.