Mitochondrial division/mitophagy inhibitor (Mdivi) ameliorates pressure overload induced heart failure

Autophagy and Mitophagy in Cardiovascular Disease

Autophagy contributes to the maintenance of intracellular homeostasis in most cells of cardiovascular origin, including cardiomyocytes, endothelial cells, and arterial smooth muscle cells. Mitophagy is an autophagic response that specifically targets damaged, and hence potentially cytotoxic, mitochondria. As these organelles occupy a critical position in the bioenergetics of the cardiovascular system, mitophagy is particularly important for cardiovascular homeostasis in health and disease. Consistent with this notion, genetic defects in autophagy or mitophagy have been shown to exacerbate the propensity of laboratory animals to spontaneously develop cardiodegenerative disorders. Moreover, pharmacological or genetic maneuvers that alter the autophagic or mitophagic flux have been shown to influence disease outcome in rodent models of several cardiovascular conditions, such as myocardial infarction, various types of cardiomyopathy, and atherosclerosis. In this review, we discuss the intimate connection between autophagy, mitophagy, and cardiovascular disorders.

The pharmacological regulation of cellular mitophagy

Small molecules are pharmacological tools of considerable value for dissecting complex biological processes and identifying potential therapeutic interventions. Recently, the cellular quality-control process of mitophagy has attracted considerable research interest; however, the limited availability of suitable chemical probes has restricted our understanding of the molecular mechanisms involved. Current approaches to initiate mitophagy include acute dissipation of the mitochondrial membrane potential (ΔΨ_m) by mitochondrial uncouplers (for example, FCCP/CCCP) and the use of antimycin A and oligomycin to impair respiration. Both approaches impair mitochondrial homeostasis and therefore limit the scope for dissection of subtle, bioenergy-related regulatory phenomena. Recently, novel mitophagy activators acting independently of the respiration collapse have been reported, offering new opportunities to understand the process and potential for therapeutic exploitation. We have summarized the current status of mitophagy modulators and analyzed the available chemical tools, commenting on their advantages, limitations and current applications.

Role of the calcium sensing receptor in cardiomyocyte apoptosis via mitochondrial dynamics in compensatory hypertrophied myocardium of spontaneously hypertensive rat

Calcium sensing receptor (CaSR) mediates pathological cardiac hypertrophy. Mitochondria maintain their function through fission and fusion and disruption of mitochondrial dynamic is linked to various cardiac diseases. This study examined how inhibition of CaSR by the inhibitor Calhex₂₃₁ affected the mitochondrial dynamics in a hypertensive model in rats. Spontaneously hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats were used in this study. Cardiac function and blood pressure was evaluated at the end of the study. SHRs showed increases in the ratio of heart weight to body weight and the levels of CaSR; all of these increases were suppressed by Calhex₂₃₁. Additionally, Calhex₂₃₁ treatment of SHRs changed the expression of proteins involved in mitochondrial dynamics. Our results demonstrated that CaSR activation induced cardiomyocyte apoptosis through the mitochondrial dynamics mediated apoptotic pathway in hypertensive hearts.

Dynamin-related protein-1 as potential therapeutic target in various diseases

Mitochondria can interchange morphology due to their dynamic nature. It can exist in either fragmented disconnected arrangement or elongated interconnected mitochondrial networks due to fission and fusion, respectively. The recent studies have revealed the remarkable and unexpected insights into the physiological impact and molecular regulation of mitochondrial morphology. The balance between fission and fusion governs the faith of the cell. The active targeting of DRP 1 to the outer mitochondrial membrane (OMM) is done by non-GTPase receptor proteins such as mitochondrial fission factor, mitochondrial fission protein 1 and mitochondrial elongation factor 1. The active targeting of DRP 1 to OMM leads to the fission of mitochondria. However, the imbalance of DRP 1-dependent mitochondrial fission and modulation of equilibrium of fission and fusion has been documented to be involved in several cardiovascular and neurodegenerative disorders. In this review, we are focusing on the active participation of DRP 1 in various diseases and also the factors responsible for the activation of DRP 1 for its action.

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.

Sarcoplasmic reticulum-mitochondria communication in cardiovascular pathophysiology

Repetitive, calcium-mediated contractile activity renders cardiomyocytes critically dependent on a sustained energy supply and adequate calcium buffering, both of which are provided by mitochondria. Moreover, in vascular smooth muscle cells, mitochondrial metabolism modulates cell growth and proliferation, whereas cytosolic calcium levels regulate the arterial vascular tone. Physical and functional communication between mitochondria and sarco/endoplasmic reticulum and balanced mitochondrial dynamics seem to have a critical role for optimal calcium transfer to mitochondria, which is crucial in calcium homeostasis and mitochondrial metabolism in both types of muscle cells. Moreover, mitochondrial dysfunction has been associated with myocardial damage and dysregulation of vascular smooth muscle proliferation. Therefore, sarco/endoplasmic reticulum-mitochondria coupling and mitochondrial dynamics are now viewed as relevant factors in the pathogenesis of cardiac and vascular diseases, including coronary artery disease, heart failure, and pulmonary arterial hypertension. In this Review, we summarize the evidence related to the role of sarco/endoplasmic reticulum-mitochondria communication in cardiac and vascular muscle physiology, with a focus on how perturbations contribute to the pathogenesis of cardiovascular disorders.

Ischemia-induced Drp1 and Fis1-mediated mitochondrial fission and right ventricular dysfunction in pulmonary hypertension

Right ventricular (RV) function determines prognosis in pulmonary arterial hypertension (PAH). We hypothesize that ischemia causes RV dysfunction in PAH by triggering dynamin-related protein 1 (Drp1)-mediated mitochondrial fission. RV function was compared in control rats (n = 50) versus rats with monocrotaline-induced PAH (MCT-PAH; n = 60) both in vivo (echocardiography) and ex vivo (RV Langendorff). Mitochondrial membrane potential and morphology and RV function were assessed before or after 2 cycles of ischemia-reperfusion injury challenge (RV-IR). The effects of Mdivi-1 (25 μM), a Drp1 GTPase inhibitor, and P110 (1 μM), a peptide inhibitor of Drp1-Fis1 interaction, were studied. We found that MCT caused RV hypertrophy, RV vascular rarefaction, and RV dysfunction. Prior to IR, the mitochondria in MCT-PAH RV were depolarized and swollen with increased Drp1 content and reduced aconitase activity. RV-IR increased RV end diastolic pressure (RVEDP) and mitochondrial Drp1 expression in both control and MCT-PAH RVs. IR depolarized mitochondria in control RV but did not exacerbate the basally depolarized MCT-PAH RV mitochondria. During RV IR mdivi-1 and P110 reduced Drp1 translocation to mitochondria, improved mitochondrial structure and function, and reduced RVEDP. In conclusion, RV ischemia occurs in PAH and causes Drp1-Fis1-mediated fission leading to diastolic dysfunction. Inhibition of mitochondrial fission preserves RV function in RV-IR.

KEY MESSAGES

Right ventricular ischemia reperfusion (RV-IR) causes RV diastolic dysfunction. IR-induced mitochondrial fission causes RV diastolic dysfunction. In RV-IR Drp1 translocates to mitochondria, binds Fis1 and causes fission and injury. A baseline RV mitochondriopathy in MCT PAH resembles IR-induced mitochondrial injury. Drp1 inhibitors (Mdivi-1 and P110) preserve RV diastolic function post RV-IR.

Calcineurin signaling in the heart: The importance of time and place

The calcium-activated protein phosphatase, calcineurin, lies at the intersection of protein phosphorylation and calcium signaling cascades, where it provides an essential nodal point for coordination between these two fundamental modes of intracellular communication. In excitatory cells, such as neurons and cardiomyocytes, that experience rapid and frequent changes in cytoplasmic calcium, calcineurin protein levels are exceptionally high, suggesting that these cells require high levels of calcineurin activity. Yet, it is widely recognized that excessive activation of calcineurin in the heart contributes to pathological hypertrophic remodeling and the progression to failure. How does a calcium activated enzyme function in the calcium-rich environment of the continuously contracting heart without pathological consequences? This review will discuss the wide range of calcineurin substrates relevant to cardiovascular health and the mechanisms calcineurin uses to find and act on appropriate substrates in the appropriate location while potentially avoiding others. Fundamental differences in calcineurin signaling in neonatal verses adult cardiomyocytes will be addressed as well as the importance of maintaining heterogeneity in calcineurin activity across the myocardium. Finally, we will discuss how circadian oscillations in calcineurin activity may facilitate integration with other essential but conflicting processes, allowing a healthy heart to reap the benefits of calcineurin signaling while avoiding the detrimental consequences of sustained calcineurin activity that can culminate in heart failure.

Inhibition of Drp1 attenuates mitochondrial damage and myocardial injury in Coxsackievirus B3 induced myocarditis

Viral myocarditis (VMC) is closely related to apoptosis, oxidative stress, innate immunity, and energy metabolism, which are all linked to mitochondrial dysfunction. A close nexus between mitochondrial dynamics and cardiovascular disease with mitochondrial dysfunction has been deeply researched, but there is still no relevant report in viral myocarditis. In this study, we aimed to explore the role of Dynamin-related protein 1 (Drp1)-linked mitochondrial fission in VMC. Mice were inoculated with the Coxsackievirus B3 (CVB3) and treated with mdivi1 (a Drp1 inhibitor). Protein expression of Drp1 was increased in mitochondria while decreased in cytoplasm and accompanied by excessive mitochondrial fission in VMC mice. In addition, midivi1 treatment attenuate inflammatory cells infiltration in myocardium of the mice, serum Cardiac troponin I (CTnI) and Creatine kinase-MB (CK-MB) level. Mdivi1 also could improved the survival rate of mice and mitochondrial dysfunction reflected as the up-regulated mitochondrial marker enzymatic activities of succinate dehydrogenase (SDH), cytochrome c oxidase (COX) and mitochondrial membrane potential (MMP). At the same time, mdivi1 rescued the body weight loss, myocardial injury and apoptosis of cardiomyocyte. Furthermore, decease in LVEDs and increase in EF and FS were detected by echocardiogram, which indicated the improved myocardial function. Thus, Drp1-linked excessive mitochondrial fission contributed to VMC and midivi1 may be a potential therapeutic approach.

Mitochondrial contribution to lipofuscin formation

Mitochondria have been in the focus of oxidative stress and aging research for decades due to their permanent production of ROS during the oxidative phosphorylation. The hypothesis exists that mitochondria are involved in the formation of lipofuscin, an autofluorescent protein aggregate that accumulates progressively over time in lysosomes of post-mitotic and senescent cells. To investigate the influence and involvement of mitochondria in lipofuscinogenesis, we analyzed lipofuscin amounts as well as the mitochondrial function in young and senescent cells. In addition we used an aging model and Lon protease deficient HeLa cells to investigate the influence of mitochondrial degradation processes on lipofuscin formation.

We were able to show that mitophagy is impaired in senescent cells resulting in an increased mitochondrial mass and superoxide formation. In addition, the inhibition of mitochondrial fission leads to increased lipofuscin formation.

Moreover, we observed that Lon protease downregulation is linked to a higher lipofuscinogenesis whereas the application of the mitochondrial-targeted antioxidant mitoTEMPO is able to prevent the accumulation of this protein aggregate.

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.

Coordinated Upregulation of Mitochondrial Biogenesis and Autophagy in Breast Cancer Cells: The Role of Dynamin Related Protein-1 and Implication for Breast Cancer Treatment

Overactive mitochondrial fission was shown to promote cell transformation and tumor growth. It remains elusive how mitochondrial quality is regulated in such conditions. Here, we show that upregulation of mitochondrial fission protein, dynamin related protein-1 (Drp1), was accompanied with increased mitochondrial biogenesis markers (PGC1α, NRF1, and Tfam) in breast cancer cells. However, mitochondrial number was reduced, which was associated with lower mitochondrial oxidative capacity in breast cancer cells. This contrast might be owing to enhanced mitochondrial turnover through autophagy, because an increased population of autophagic vacuoles engulfing mitochondria was observed in the cancer cells. Consistently, BNIP3 (a mitochondrial autophagy marker) and autophagic flux were significantly upregulated, indicative of augmented mitochondrial autophagy (mitophagy). The upregulation of Drp1 and BNIP3 was also observed in vivo (human breast carcinomas). Importantly, inhibition of Drp1 significantly suppressed mitochondrial autophagy, metabolic reprogramming, and cancer cell viability. Together, this study reveals coordinated increase of mitochondrial biogenesis and mitophagy in which Drp1 plays a central role regulating breast cancer cell metabolism and survival. Given the emerging evidence of PGC1α contributing to tumor growth, it will be of critical importance to target both mitochondrial biogenesis and mitophagy for effective cancer therapeutics.

Resveratrol Ameliorates Pressure Overload-induced Cardiac Dysfunction and Attenuates Autophagy in Rats

Pressure overload has an important role in heart failure, inducing excessive autophagy in cardiac myocytes that is considered to be pathogenic. Resveratrol has been reported to improve cardiac dysfunction induced by pressure overload, but it has been unclear whether resveratrol ameliorates cardiac dysfunction by regulating autophagy. In this study, heart failure was induced in rats by constriction of the abdominal aorta. Four weeks after surgery, the rats with heart failure were randomized to treatment with resveratrol (8 mg · kg(-1) · d(-1) by intraperitoneal injection) for 28 days or to intraperitoneal injection of the vehicle (propylene glycol) alone. Echocardiography was performed to assess cardiac function. Expression of brain natriuretic peptide messenger RNA in the left ventricle was detected by real-time polymerase chain reaction, whereas expression of proteins associated with autophagy (beclin-1 and lamp-1) was detected by western blotting and immunohistochemistry. Furthermore, autophagic vacuoles were detected in the heart by transmission electron microscopy, and the myocardial ATP content was measured by the bioluminescence method. Treatment with resveratrol significantly improved cardiac dysfunction and reduced brain natriuretic peptide expression in rats with heart failure. Resveratrol down-regulated beclin-1 and lamp-1 expression and also inhibited the formation of autophagic vacuoles in failing hearts. Furthermore, resveratrol restored the myocardial ATP level and reduced phosphorylation of AMP-activated protein kinase at Thr172. These results suggest that resveratrol may inhibit autophagy through inactivation of AMP-activated protein kinase and restoration of ATP in heart failure induced by pressure overload. Accordingly, resveratrol may be beneficial for patients with hypertensive heart disease.

Mitochondrial remodeling: Rearranging, recycling, and reprogramming

Mitochondria are highly dynamic and responsive organelles that respond to environmental cues with fission and fusion. They undergo mitophagy and biogenesis, and are subject to extensive post-translational modifications. Calcium plays an important role in regulating mitochondrial functions. Mitochondria play a central role in metabolism of glucose, fatty acids, and amino acids, and generate ATP with effects on redox poise, oxidative stress, pH, and other metabolites including acetyl-CoA and NAD(+) which in turn have effects on chromatin remodeling. The complex interplay of mitochondria, cytosolic factors, and the nucleus ensure a well-coordinated response to environmental stresses.

Resuscitation of a dead cardiomyocyte

Although cardiac resuscitation can revive the whole body, the mechanisms are unclear. To this end, we propose that reviving a dead/dysfunctional cardiomyocyte will shed light on resuscitation mechanisms and pave the way to treat cardiac myopathies. The degradation of the myocyte cytoskeleton by the proteasome system which involves calpains, ubiquitin, caspases and matrix metalloproteases is the main focus of this review. The activation of calpains beyond the calpastatin-mediated inhibition due to extensive calcium harbor can lead to titin degradation, damage to the sarcomere and contractile dysfunction. The ubiquitin proteasome system can disturb the protein homeostasis within the cell and generate a dysfunctional myocyte. The matrix metalloproteases disrupt the collagen/elastin ratio and connexins to generate arrhythmias. The concept of cardiac resuscitation stems from protecting the myocyte cytoskeleton and keeping the protein homeostasis intact through management of the degradation machinery. In this regard, proteasome inhibitors for the degradation machinery have an elegant space. Recently exosomes have been identified potentially, as carriers of microRNAs or proteins that can modify the target cells. Exosomes loaded with the inhibitor "cargo" which comprises microRNAs, siRNAs or proteins to inhibit the degradation machinery can be a method of choice for cardiac resuscitation-a process difficult to execute.

Lipocalin-2 inhibits autophagy and induces insulin resistance in H9c2 cells

Lipocalin-2 (Lcn2; also known as neutrophil gelatinase associated lipocalin, NGAL) levels are increased in obesity and diabetes and associate with insulin resistance. Correlations exist between Lcn2 levels and various forms or stages of heart failure. Insulin resistance and autophagy both play well-established roles in cardiomyopathy. However, little is known about the impact of Lcn2 on insulin signaling in cardiomyocytes. In this study, we treated H9c2 cells with recombinant Lcn2 for 1 h followed by dose- and time-dependent insulin treatment and found that Lcn2 attenuated insulin signaling assessed via phosphorylation of Akt and p70S6K. We used multiple assays to demonstrate that Lcn2 reduced autophagic flux. First, Lcn2 reduced pULK1 S555, increased pULK1 S757 and reduced LC3-II levels determined by Western blotting. We validated the use of DQ-BSA to assess autolysosomal protein degradation and this together with MagicRed cathepsin B assay indicated that Lcn2 reduced lysosomal degradative activity. Furthermore, we generated H9c2 cells stably expressing tandem fluorescent RFP/GFP-LC3 and this approach verified that Lcn2 decreased autophagic flux. We also created an autophagy-deficient H9c2 cell model by overexpressing a dominant-negative Atg5 mutant and found that reduced autophagy levels also induced insulin resistance. Adding rapamycin after Lcn2 could stimulate autophagy and recover insulin sensitivity. In conclusion, our study indicated that acute Lcn2 treatment caused insulin resistance and use of gain and loss of function approaches elucidated a causative link between autophagy inhibition and regulation of insulin sensitivity by Lcn2.

Research progress of cardioprotective agents for prevention of anthracycline cardiotoxicity

Anthracyclines, including doxorubicin, epirubicin, daunorubicin and aclarubicin, are widely used as chemotherapeutic agents in the treatment of hematologic and solid tumor, including acute leukemia, lymphoma, breast cancer, gastric cancer, soft tissue sarcomas and ovarian cancer. In the cancer treatment, anthracyclines also can be combined with other chemotherapies and molecular-targeted drugs. The combination of anthracyclines with other therapies is usually the first-line treatment. Anthracyclines are effective and potent agents with a broad antitumor spectrum, but may cause adverse reactions, including hair loss, myelotoxicity, as well as cardiotoxicity. We used hematopoietic stimulating factors to control the myelotoxicity, such as G-CSF, EPO and TPO. However, the cardiotoxicity is the most serious side effect of anthracyclines. Clinical research and practical observations indicated that the cardiotoxicity of anthracyclines is commonly progressive and irreversible. Especially to those patients who have the first time use of anthracyclines, the damage is common. Therefore, early detection and prevention of anthracyclines induced cardiotoxicity are particularly important and has already aroused more attention in clinic. By literature review, we reviewed the research progress of cardioprotective agents for prevention of anthracycline cardiotoxicity.

Autophagy in cardiac metabolic control: Novel mechanisms for cardiovascular disorders

As an extensively studied quality control system, autophagy is responsible for clearance of dysfunctional organelles and damaged marcomolecules in cells. In addition to its biological recycling function, autophagy plays a significant role in the pathogenesis of metabolic syndromes such as obesity and diabetes. In particular, metabolic disorders contribute to cardiovascular disease development. As energy required to maintain cardiac cells functional is immense, disturbances in the balance between anabolic and catabolic metabolism possibly contribute to cardiovascular disorders. Therefore, an urgent need to expand our knowledge on the role of autophagy on the metabolic regulation of hearts emerges. In this review, the potential relationship between autophagic activity and cardiac metabolism is explored and we also discuss how dysregulated autophagy leads to severe cardiac disorders from the perspective of metabolic control.

Distinct changes of myocyte autophagy during myocardial hypertrophy and heart failure: association with oxidative stress

NEW FINDINGS

What is the central question of this study? We investigated the changes of myocyte autophagy during the stages of myocardial hypertrophy and failure and the relationship between autophagy and oxidative stress. What is the main findings and its importance? Myocyte autophagy is reduced during myocardial hypertrophy and increased during heart failure. Reduced autophagy is correlated with myocyte hypertrophy, and increased autophagy is correlated with myocyte apoptosis. The distinct alterations are associated with oxidative stress. Hydrogen peroxide causes distinct, concentration-dependent changes in autophagy in cultured cardiomyocytes. Oxidative stress may mediate the distinct alterations of myocyte autophagy during cardiac hypertrophy and failure. Myocyte autophagy occurs at basal levels in the heart in normal conditions and increases in heart failure. However, the changes of myocyte autophagy during the stages of myocardial hypertrophy and failure are not fully understood. Little is known about the relationship among myocyte autophagy, hypertrophy, apoptosis and oxidative stress. In the present study, we first examined the changes of myocyte autophagy in mice with chronic pressure overload and the relationships between myocyte autophagy and hypertrophy, apoptosis and oxidative stress. Second, we determined the direct role of hydrogen peroxide on autophagy in cultured cardiomyocytes. Eight-week-old male C57BL/6J mice underwent transverse aortic constriction (TAC) or sham operation. In TAC mice, left ventricular wall thickness was increased at 1 week and increased further at 9 weeks. Left ventricular end-diastolic dimension showed no change at 1 week, but increased at 9 weeks in association with systolic dysfunction. Myocyte autophagy was decreased at 1 week after TAC, and the decrease was correlated with increased myocyte size. Myocyte autophagy was increased at 9 weeks after TAC, and the increase was correlated with increased myocyte apoptosis. The alterations in autophagy after TAC were associated with myocardial oxidative stress. Hydrogen peroxide caused distinct, concentration-dependent changes in autophagy in cultured cardiomyocytes. In conclusion, myocyte autophagy was decreased during myocardial hypertrophy and increased during heart failure. The distinct changes were associated with myocyte hypertrophy, apoptosis and oxidative stress. These findings suggest that oxidative stress may mediate the distinct alterations of myocyte autophagy during myocardial hypertrophy and heart failure.

Mitochondrial quality control in the diabetic heart

Diabetes is a well-known risk factor for heart failure. Diabetic heart damage is closely related to mitochondrial dysfunction and increased ROS generation. However, clinical trials have shown no effects of antioxidant therapies on heart failure in diabetic patients, suggesting that simply antagonizing existing ROS by antioxidants is not sufficient to reduce diabetic cardiac injury. A potentially more effective treatment strategy may be to enhance the overall capacity of mitochondrial quality control to maintain a pool of healthy mitochondria that are needed for supporting cardiac contractile function in diabetic patients. Mitochondrial quality is controlled by a number of coordinated mechanisms including mitochondrial fission and fusion, mitophagy and biogenesis. The mitochondrial damage consistently observed in the diabetic hearts indicates a failure of the mitochondrial quality control mechanisms. Recent studies have demonstrated a crucial role for each of these mechanisms in cardiac homeostasis and have begun to interrogate the relative contribution of insufficient mitochondrial quality control to diabetic cardiac injury. In this review, we will present currently available literature that links diabetic heart disease to the dysregulation of major mitochondrial quality control mechanisms. We will discuss the functional roles of these mechanisms in the pathogenesis of diabetic heart disease and their potentials for targeted therapeutical manipulation.

Mitochondrial fission - a drug target for cytoprotection or cytodestruction?

Mitochondria are morphologically dynamic organelles constantly undergoing processes of fission and fusion that maintain integrity and bioenergetics of the organelle: these processes are vital for cell survival. Disruption in the balance of mitochondrial fusion and fission is thought to play a role in several pathological conditions including ischemic heart disease. Proteins involved in regulating the processes of mitochondrial fusion and fission are therefore potential targets for pharmacological therapies. Mdivi‐1 is a small molecule inhibitor of the mitochondrial fission protein Drp1. Inhibiting mitochondrial fission with Mdivi‐1 has proven cytoprotective benefits in several cell types involved in a wide array of cardiovascular injury models. On the other hand, Mdivi‐1 can also exert antiproliferative and cytotoxic effects, particularly in hyperproliferative cells. In this review, we discuss these divergent effects of Mdivi‐1 on cell survival, as well as the potential and limitations of Mdivi‐1 as a therapeutic agent.

Regulation of mitochondrial morphology by positive feedback interaction between PKCδ and Drp1 in vascular smooth muscle cell

Dynamin-related protein-1 (Drp1) plays a critical role in mitochondrial fission which allows cell proliferation and Mdivi-1, a specific small molecule Drp1 inhibitor, is revealed to attenuate proliferation. However, few molecular mechanisms-related to Drp1 under stimulus for restenosis or atherosclerosis have been investigated in vascular smooth muscle cells (vSMCs). Therefore, we hypothesized that Drp1 inhibition can prevent vascular restenosis and investigated its regulatory mechanism. Angiotensin II (Ang II) or hydrogen peroxide (H2 O2 )-induced proliferation and migration in SMCs were attenuated by down-regulation of Drp1 Ser 616 phosphorylation, which was demonstrated by in vitro assays for migration and proliferation. Excessive amounts of ROS production and changes in mitochondrial membrane potential were prevented by Drp1 inhibition under Ang II and H2 O2 . Under the Ang II stimulation, activated Drp1 interacted with PKCδ and then activated MEK1/2-ERK1/2 signaling cascade and MMP2, but not MMP9. Furthermore, in ex vivo aortic ring assay, inhibition of the Drp1 had significant anti-proliferative and -migration effects for vSMCs. A formation of vascular neointima in response to a rat carotid artery balloon injury was prevented by Drp1 inhibition, which shows a beneficial effect of Drp1 regulation in the pathologic vascular condition. Drp1-mediated SMC proliferation and migration can be prevented by mitochondrial division inhibitor (Mdivi-1) in in vitro, ex vivo and in vivo, and these results suggest the possibility that Drp1 can be a new therapeutic target for restenosis or atherosclerosis.

Mitochondrial dynamics, mitophagy and cardiovascular disease

Cardiac hypertrophy is often initiated as an adaptive response to haemodynamic stress or myocardial injury, and allows the heart to meet an increased demand for oxygen. Although initially beneficial, hypertrophy can ultimately contribute to the progression of cardiac disease, leading to an increase in interstitial fibrosis and a decrease in ventricular function. Metabolic changes have emerged as key mechanisms involved in the development and progression of pathological remodelling. As the myocardium is a highly oxidative tissue, mitochondria play a central role in maintaining optimal performance of the heart. 'Mitochondrial dynamics', the processes of mitochondrial fusion, fission, biogenesis and mitophagy that determine mitochondrial morphology, quality and abundance have recently been implicated in cardiovascular disease. Studies link mitochondrial dynamics to the balance between energy demand and nutrient supply, suggesting that changes in mitochondrial morphology may act as a mechanism for bioenergetic adaptation during cardiac pathological remodelling. Another critical function of mitochondrial dynamics is the removal of damaged and dysfunctional mitochondria through mitophagy, which is dependent on the fission/fusion cycle. In this article, we discuss the latest findings regarding the impact of mitochondrial dynamics and mitophagy on the development and progression of cardiovascular pathologies, including diabetic cardiomyopathy, atherosclerosis, damage from ischaemia-reperfusion, cardiac hypertrophy and decompensated heart failure. We will address the ability of mitochondrial fusion and fission to impact all cell types within the myocardium, including cardiac myocytes, cardiac fibroblasts and vascular smooth muscle cells. Finally, we will discuss how these findings can be applied to improve the treatment and prevention of cardiovascular diseases.

Mitochondrial Dynamics and Heart Failure

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

Mas receptor mediates cardioprotection of angiotensin-(1-7) against Angiotensin II-induced cardiomyocyte autophagy and cardiac remodelling through inhibition of oxidative stress

Angiotensin II (Ang II) plays an important role in the onset and development of cardiac remodelling associated with changes of autophagy. Angiotensin1-7 [Ang-(1-7)] is a newly established bioactive peptide of renin-angiotensin system, which has been shown to counteract the deleterious effects of Ang II. However, the precise impact of Ang-(1-7) on Ang II-induced cardiomyocyte autophagy remained essentially elusive. The aim of the present study was to examine if Ang-(1-7) inhibits Ang II-induced autophagy and the underlying mechanism involved. Cultured neonatal rat cardiomyocytes were exposed to Ang II for 48 hrs while mice were infused with Ang II for 4 weeks to induce models of cardiac hypertrophy in vitro and in vivo. LC3b-II and p62, markers of autophagy, expression were significantly elevated in cardiomyocytes, suggesting the presence of autophagy accompanying cardiac hypertrophy in response to Ang II treatment. Besides, Ang II induced oxidative stress, manifesting as an increase in malondialdehyde production and a decrease in superoxide dismutase activity. Ang-(1-7) significantly retarded hypertrophy, autophagy and oxidative stress in the heart. Furthermore, a role of Mas receptor in Ang-(1-7)-mediated action was assessed using A779 peptide, a selective Mas receptor antagonist. The beneficial responses of Ang-(1-7) on cardiac remodelling, autophagy and oxidative stress were mitigated by A779. Taken together, these result indicated that Mas receptor mediates cardioprotection of angiotensin-(1-7) against Ang II-induced cardiomyocyte autophagy and cardiac remodelling through inhibition of oxidative stress.

MKK3 deletion improves mitochondrial quality

Sepsis, a severe response to infection, leads to excessive inflammation and is the major cause of mortality in intensive care units. Mitochondria have been shown to influence the outcome of septic injury. We have previously shown that MAP kinase kinase 3 (MKK3)(-/-) mice are resistant to septic injury and MKK3(-/-) macrophages have improved mitochondrial function. In this study we examined processes that lead to improved mitochondrial quality in MKK3(-/-) mouse embryonic fibroblasts (MEFs) and specifically the role of mitophagy in mitochondrial health. MKK3(-/-) MEFs had lower inflammatory cytokine release and oxidant production after lipopolysaccharide (LPS) stimulation, confirming our earlier observations. MKK3(-/-) MEFs had better mitochondrial function as measured by mitochondrial membrane potential (MMP) and ATP, even after LPS treatment. We observed higher mitophagy in MKK3(-/-) MEFs compared to wild type (WT). Transmission electron microscopy studies showed longer and larger mitochondria in MKK3(-/-) MEFs, indicative of healthier mitochondria. We performed a SILAC (stable isotope labeling by/with amino acids in cell culture) study to assess differences in mitochondrial proteome between WT and MKK3(-/-) MEFs and observed increased expression of tricarboxylic acid (TCA) cycle enzymes and respiratory complex subunits. Further, inhibition of mitophagy by Mdivi1 led to loss in MMP and increased cytokine secretion after LPS treatment in MKK3(-/-) MEFs. In conclusion, this study demonstrates that MKK3 influences mitochondrial quality by affecting the expression of mitochondrial proteins, including TCA cycle enzymes, and mitophagy, which consequently regulates the inflammatory response. Based on our results, MKK3 could be a potential therapeutic target for inflammatory diseases like sepsis.

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.

High-density lipoprotein inhibits mechanical stress-induced cardiomyocyte autophagy and cardiac hypertrophy through angiotensin II type 1 receptor-mediated PI3K/Akt pathway

Mechanical stress triggers cardiac hypertrophy and autophagy through an angiotensin II (Ang II) type 1 (AT1) receptor-dependent mechanism. Low level of high density lipoprotein (HDL) is an independent risk factor for cardiac hypertrophy. This study was designed to evaluate the effect of HDL on mechanical stress-induced cardiac hypertrophy and autophagy. A 48-hr mechanical stretch and a 4-week transverse aortic constriction were employed to induce cardiomyocyte hypertrophy in vitro and in vivo, respectively, prior to the assessment of myocardial autophagy using LC3b-II and beclin-1. Our results indicated that HDL significantly reduced mechanical stretch-induced rise in autophagy as demonstrated by LC3b-II and beclin-1. In addition, mechanical stress up-regulated AT1 receptor expression in both cultured cardiomyocytes and in mouse hearts, whereas HDL significantly suppressed the AT1 receptor. Furthermore, the role of Akt phosphorylation in HDL-mediated action was assessed using MK-2206, a selective inhibitor for Akt phosphorylation. Our data further revealed that MK-2206 mitigated HDL-induced beneficial responses on cardiac remodelling and autophagy. Taken together, our data revealed that HDL inhibited mechanical stress-induced cardiac hypertrophy and autophagy through downregulation of AT1 receptor, and HDL ameliorated cardiac hypertrophy and autophagy via Akt-dependent mechanism.

Hyperhomocysteinemia associated skeletal muscle weakness involves mitochondrial dysfunction and epigenetic modifications

HHcy has been implicated in elderly frailty, but the underlying mechanisms are poorly understood. Using C57 and CBS+/- mice and C2C12 cell line, we investigated mechanisms behind HHcy induced skeletal muscle weakness and fatigability. Possible alterations in metabolic capacity (levels of LDH, CS, MM-CK and COX-IV), in structural proteins (levels of dystrophin) and in mitochondrial function (ATP production) were examined. An exercise regimen was employed to reverse HHcy induced changes. CBS+/- mice exhibited more fatigability, and generated less contraction force. No significant changes in muscle morphology were observed. However, there is a corresponding reduction in large muscle fiber number in CBS+/- mice. Excess fatigability was not due to changes in key enzymes involved in metabolism, but was due to reduced ATP levels. A marginal reduction in dystrophin levels along with a decrease in mitochondrial transcription factor A (mtTFA) were observed. There was also an increase in the mir-31, and mir-494 quantities that were implicated in dystrophin and mtTFA regulation respectively. The molecular changes elevated during HHcy, with the exception of dystrophin levels, were reversed after exercise. In addition, the amount of NRF-1, one of the transcriptional regulators of mtTFA, was significantly decreased. Furthermore, there was enhancement in mir-494 levels and a concomitant decline in mtTFA protein quantity in homocysteine treated cells. These changes in C2C12 cells were also accompanied by an increase in DNMT3a and DNMT3b proteins and global DNA methylation levels. Together, these results suggest that HHcy plays a causal role in enhanced fatigability through mitochondrial dysfunction which involves epigenetic changes.

Role of mitochondrial fission and fusion in cardiomyocyte contractility

BACKGROUND

Mitochondria constitute 30% of cell volume and are engaged in two dynamic processes called fission and fusion, regulated by Drp-1 (dynamin related protein) and mitofusin 2 (Mfn2). Previously, we showed that Drp-1 inhibition attenuates cardiovascular dysfunction following pressure overload in aortic banding model and myocardial infarction. As dynamic organelles, mitochondria are capable of changing their morphology in response to stress. However, whether such changes can alter their function and in turn cellular function is unknown. Further, a direct role of fission and fusion in cardiomyocyte contractility has not yet been studied. In this study, we hypothesize that disrupted fission and fusion balance by increased Drp-1 and decreased Mfn2 expression in cardiomyocytes affects their contractility through alterations in the calcium and potassium concentrations.

METHODS

To verify this, we used freshly isolated ventricular myocytes from wild type mouse and transfected them with either siRNA to Drp-1 or Mfn2. Myocyte contractility studies were performed by IonOptix using a myopacer. Intracellular calcium and potassium measurements were done using flow cytometry. Immunocytochemistry (ICC) was done to evaluate live cell mitochondria and its membrane potential. Protein expression was done by western blot and immunocytochemistry.

RESULTS

We found that silencing mitochondrial fission increased the myocyte contractility, while fusion inhibition decreased contractility with simultaneous changes in calcium and potassium. Also, we observed that increase in fission prompted decrease in Serca-2a and increase in cytochrome c leakage leading to mitophagy.

CONCLUSION

Our results suggested that regulating mitochondrial fission and fusion have direct effects on overall cardiomyocyte contractility and thus function.

New therapeutics to modulate mitochondrial dynamics and mitophagy in cardiac diseases

The processes that control the number and shape of the mitochondria (mitochondrial dynamics) and the removal of damaged mitochondria (mitophagy) have been the subject of intense research. Recent work indicates that these processes may contribute to the pathology associated with cardiac diseases. This review describes some of the key proteins that regulate these processes and their potential as therapeutic targets for cardiac diseases.

Mitoconfusion: noncanonical functioning of dynamism factors in static mitochondria of the heart

Mitochondrial fitness is central to heart health. In many cell types, mitochondria are dynamic, interconnected filamentous networks. By comparison, mitochondria of healthy postmitotic adult cardiomyocytes are shortened, round, hypodynamic organelles. Mitochondrial networks are absent in cardiomyocytes; fission, fusion, and organelle mobility are not normally observed. Nevertheless, mitochondrial fission factor Drp1 and fusion factors Mfn1, Mfn2, and Opa1 are abundant and indispensable in adult hearts. Here, we review recent insights into roles for mitochondrial dynamics factors not strictly related to morphometric remodeling, advancing the argument that fission and fusion of cardiomyocyte mitochondria support surveillance, sequestration, and mitophagic removal of damaged organelles.

Molecular mechanisms mediating mitochondrial dynamics and mitophagy and their functional roles in the cardiovascular system

Mitochondria are essential organelles that produce the cellular energy source, ATP. Dysfunctional mitochondria are involved in the pathophysiology of heart disease, which is associated with reduced levels of ATP and excessive production of reactive oxygen species. Mitochondria are dynamic organelles that change their morphology through fission and fusion in order to maintain their function. Fusion connects neighboring depolarized mitochondria and mixes their contents to maintain membrane potential. In contrast, fission segregates damaged mitochondria from intact ones, where the damaged part of mitochondria is subjected to mitophagy whereas the intact part to fusion. It is generally believed that mitochondrial fusion is beneficial for the heart, especially under stress conditions, because it consolidates the mitochondria's ability to supply energy. However, both excessive fusion and insufficient fission disrupt the mitochondrial quality control mechanism and potentiate cell death. In this review, we discuss the role of mitochondrial dynamics and mitophagy in the heart and the cardiomyocytes therein, with a focus on their roles in cardiovascular disease. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".

The combination of thioxodihydroquinazolinones and platinum drugs reverses platinum resistance in tumor cells by inducing mitochondrial apoptosis independent of Bax and Bak

The effective management of tumors resistant to platinum drugs-based anticancer therapies is a critical challenge in current clinical practices. The proapoptotic Bcl-2 family proteins Bax and Bak are essential for cisplatin-induced apoptosis. Unfortunately, Bax and its related upstream endogenous apoptotic signaling pathways are often dysregulated in cancer cells. Strategies that are able to bypass Bax- and Bak-dependent apoptotic pathways will thus provide opportunities to overcome platinum drug resistance. We have identified the thioxodihydroquinazolinone mdivi-1 as a member of a novel class of small molecules that are able to induce Bax- and Bak-independent mitochondrial outer membrane permeabilization when combined with cisplatin, thereby efficiently triggering apoptosis in platinum-resistant tumor cells. In the present structure activity relationship (SAR) study of a computationally selected library of mdivi-1 related small molecules, we established a pharmacophore model that can lead to the enhancement of platinum drug efficacy and Bax/Bak-independent mitochondrial apoptosis. Specifically, we found that a thiourea function is necessary but not sufficient for the synergism of this class of thioxodihydroquinazolinones with cisplatin. We were also able to identify more potent mdivi-1 analogs through this SAR study, which will guide future designs with the goal to develop novel combination regimens for the treatment of platinum- and multidrug-resistant tumors.

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.

Lycopene protects against apoptosis in hypoxia/reoxygenation‑induced H9C2 myocardioblast cells through increased autophagy

Lycopene (Ly), the most common type of antioxidant in the majority of diet types, provides tolerance to ischemia/reperfusion injury. However, the underlying mechanism of the protective effects observed following Ly administration remains poorly investigated. The aim of the current study was to investigate whether Ly prevents damage to hypoxia/reoxygenation (HR)‑induced H9C2 myocardioblasts in an autophagy‑dependent manner. The levels of autophagic markers were detected using western blotting, the level of apoptosis was detected using western blotting and flow cytometry. The activation of autophagy was impaired via knockdown of the expression of 'microtubule‑associated protein 1‑light chain 3β (MAP1LC3B)' and 'Beclin 1'. After 16 h hypoxia, followed by 2 h reoxygenation, the expression levels of the microtubule‑associated protein 1A/1B‑light chain 3 (LC3) and Βeclin 1 autophagic biomarkers, and cell viability were reduced, whereas the percentage of apoptotic cells, and the expression levels of the Bax/B‑cell lymphoma 2 (Bcl‑2) and active caspase‑3 apoptotic biomarkers were increased. Pre‑incubation of the cells with different Ly concentrations reversed the HR‑induced inhibition of autophagy and cell viability, and the HR‑induced elevation in apoptotic levels. The induction of autophagy was accompanied by reduced apoptosis, and decreased expression levels of Bax/Bcl‑2 and active caspase‑3. In addition, the impairment of autophagy by silencing the expression of MAP1LC3B and Beclin 1 accelerated HR‑induced H9C2 cell apoptosis and the Ly‑mediated protective effects disappeared. Furthermore, Bax/Bcl‑2 and active caspase‑3 expression levels were increased. Moreover, Ly‑induced autophagy was associated with increased adenosine monophosphate kinase (AMPK) phosphorylation. Suppressed AMPK phosphorylation using compound C terminates Ly‑mediated cytoprotective effects. Ly treatment improves cell viability and reduces apoptosis as a result of the activation of the adaptive autophagic response on HR‑induced H9C2 myocardioblasts. AMPK phosphorylation may be involved in the progression.

The mitochondrial dynamism-mitophagy-cell death interactome: multiple roles performed by members of a mitochondrial molecular ensemble

Mitochondrial research is experiencing a renaissance, in part, because of the recognition that these endosymbiotic descendants of primordial protobacteria seem to be pursuing their own biological agendas. Not only is mitochondrial metabolism required to produce most of the biochemical energy that supports their eukaryotic hosts (us) but mitochondria can actively (through apoptosis and programmed necrosis) or passively (through reactive oxygen species toxicity) drive cellular dysfunction or demise. The cellular mitochondrial collective autoregulates its population through biogenic renewal and mitophagic culling; mitochondrial fission and fusion, 2 components of mitochondrial dynamism, are increasingly recognized as playing central roles as orchestrators of these processes. Mitochondrial dynamism is rare in striated muscle cells, so cardiac-specific genetic manipulation of mitochondrial fission and fusion factors has proven useful for revealing noncanonical functions of mitochondrial dynamics proteins. Here, we review newly described functions of mitochondrial fusion/fission proteins in cardiac mitochondrial quality control, cell death, calcium signaling, and cardiac development. A mechanistic conceptual paradigm is proposed in which cell death and selective organelle culling are not distinct processes, but are components of a unified and integrated quality control mechanism that exerts different effects when invoked to different degrees, depending on pathophysiological context. This offers a plausible explanation for seemingly paradoxical expression of mitochondrial dynamics and death factors in cardiomyocytes wherein mitochondrial morphometric remodeling does not normally occur and the ability to recover from cell suicide is severely limited.

Mitophagy-dependent necroptosis contributes to the pathogenesis of COPD

The pathogenesis of chronic obstructive pulmonary disease (COPD) remains unclear, but involves loss of alveolar surface area (emphysema) and airway inflammation (bronchitis) as the consequence of cigarette smoke (CS) exposure. Previously, we demonstrated that autophagy proteins promote lung epithelial cell death, airway dysfunction, and emphysema in response to CS; however, the underlying mechanisms have yet to be elucidated. Here, using cultured pulmonary epithelial cells and murine models, we demonstrated that CS causes mitochondrial dysfunction that is associated with a reduction of mitochondrial membrane potential. CS induced mitophagy, the autophagy-dependent elimination of mitochondria, through stabilization of the mitophagy regulator PINK1. CS caused cell death, which was reduced by administration of necrosis or necroptosis inhibitors. Genetic deficiency of PINK1 and the mitochondrial division/mitophagy inhibitor Mdivi-1 protected against CS-induced cell death and mitochondrial dysfunction in vitro and reduced the phosphorylation of MLKL, a substrate for RIP3 in the necroptosis pathway. Moreover, Pink1(-/-) mice were protected against mitochondrial dysfunction, airspace enlargement, and mucociliary clearance (MCC) disruption during CS exposure. Mdivi-1 treatment also ameliorated CS-induced MCC disruption in CS-exposed mice. In human COPD, lung epithelial cells displayed increased expression of PINK1 and RIP3. These findings implicate mitophagy-dependent necroptosis in lung emphysematous changes in response to CS exposure, suggesting that this pathway is a therapeutic target for COPD.

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.

Cardiac CD47 drives left ventricular heart failure through Ca2+-CaMKII-regulated induction of HDAC3

Background

Left ventricular heart failure (LVHF) remains progressive and fatal and is a formidable health problem because ever‐larger numbers of people are diagnosed with this disease. Therapeutics, while relieving symptoms and extending life in some cases, cannot resolve this process and transplant remains the option of last resort for many. Our team has described a widely expressed cell surface receptor (CD47) that is activated by its high‐affinity secreted ligand, thrombospondin 1 (TSP1), in acute injury and chronic disease; however, a role for activated CD47 in LVHF has not previously been proposed.

Methods and Results

In experimental LVHF TSP1‐CD47 signaling is increased concurrent with up‐regulation of cardiac histone deacetylase 3 (HDAC3). Mice mutated to lack CD47 displayed protection from transverse aortic constriction (TAC)‐driven LVHF with enhanced cardiac function, decreased cellular hypertrophy and fibrosis, decreased maladaptive autophagy, and decreased expression of HDAC3. In cell culture, treatment of cardiac myocyte CD47 with a TSP1‐derived peptide, which binds and activates CD47, increased HDAC3 expression and myocyte hypertrophy in a Ca²⁺/calmodulin protein kinase II (CaMKII)‐dependent manner. Conversely, antibody blocking of CD47 activation, or pharmacologic inhibition of CaMKII, suppressed HDAC3 expression, decreased myocyte hypertrophy, and mitigated established LVHF. Downstream gene suppression of HDAC3 mimicked the protective effects of CD47 blockade and decreased hypertrophy in myocytes and mitigated LVHF in animals.

Conclusions

These data identify a proximate role for the TSP1‐CD47 axis in promoting LVHF by CaKMII‐mediated up‐regulation of HDAC3 and suggest novel therapeutic opportunities.

Dexamethasone-induced autophagy mediates muscle atrophy through mitochondrial clearance

Glucocorticoids, such as dexamethasone, enhance protein breakdown via ubiquitin-proteasome system. However, the role of autophagy in organelle and protein turnover in the glucocorticoid-dependent atrophy program remains unknown. Here, we show that dexamethasone stimulates an early activation of autophagy in L6 myotubes depending on protein kinase, AMPK, and glucocorticoid receptor activity. Dexamethasone increases expression of several autophagy genes, including ATG5, LC3, BECN1, and SQSTM1 and triggers AMPK-dependent mitochondrial fragmentation associated with increased DNM1L protein levels. This process is required for mitophagy induced by dexamethasone. Inhibition of mitochondrial fragmentation by Mdivi-1 results in disrupted dexamethasone-induced autophagy/mitophagy. Furthermore, Mdivi-1 increases the expression of genes associated with the atrophy program, suggesting that mitophagy may serve as part of the quality control process in dexamethasone-treated L6 myotubes. Collectively, these data suggest a novel role for dexamethasone-induced autophagy/mitophagy in the regulation of the muscle atrophy program.

Cardiomyocyte autophagy: metabolic profit and loss

Cardiovascular disease remains the leading cause of morbidity and mortality worldwide, even despite recent scientific and technological advances and comprehensive preventive strategies. The cardiac myocyte is a voracious consumer of energy, and alterations in metabolic substrate availability and consumption are hallmark features of these disorders. Autophagy, an evolutionarily ancient response to metabolic insufficiency, has been implicated in the pathogenesis of a wide range of heart pathologies. However, the precise role of autophagy in these contexts remains obscure owing to its multifarious actions. Here, we review recently derived insights regarding the role of autophagy in cardiac hypertrophy and heart failure, highlighting its effects on metabolism.

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.

Mitochondrial mitophagy in mesenteric artery remodeling in hyperhomocysteinemia

Although high levels of homocysteine also termed as hyperhomocysteinemia (HHcy) has been associated with inflammatory bowel disease and mesenteric artery occlusion, the mitochondrial mechanisms behind endothelial dysfunction that lead to mesenteric artery remodeling are largely unknown. We hypothesize that in HHcy there is increased mitochondrial fission due to altered Mfn‐2/Drp‐1 ratio, which leads to endothelial dysfunction and collagen deposition in the mesenteric artery inducing vascular remodeling. To test this hypothesis, we used four groups of mice: (i) WT (C57BL/6J); (ii) mice with HHcy (CBS+/−); (iii) oxidative stress resistant mice (C3H) and (iv) mice with HHcy and oxidative stress resistance (CBS+/−/C3H). For mitochondrial dynamics, we studied the expression of Mfn‐2 which is a mitochondrial fusion protein and Drp‐1 which is a mitochondrial fission protein by western blots, real‐time PCR and immunohistochemistry. We also examined oxidative stress markers, endothelial cell, and gap junction proteins that play an important role in endothelial dysfunction. Our data showed increase in oxidative stress, mitochondrial fission (Drp‐1), and collagen deposition in CBS+/− compared to WT and C3H mice. We also observed significant down regulation of Mfn‐2 (mitochondrial fusion marker), CD31, eNOS and connexin 40 (gap junction protein) in CBS+/− mice as compared to WT and C3H mice. In conclusion, our data suggested that HHcy increased mitochondrial fission (i.e., decreased Mfn‐2/Drp‐1 ratio, causing mitophagy) that leads to endothelial cell damage and collagen deposition in the mesenteric artery. This is a novel report on the role of mitochondrial dynamics alteration defining mesenteric artery remodeling.

e00283

This article is a novel report on the role of mitochondrial dynamics in mesenteric artery remodeling during hyperhomocysteinemia. The study can contribute significantly toward understanding the mesenteric mitochondrial mechanisms underpinning inflammatory bowel disease – a major clinical concern.

Anti-Parstatin Promotes Angiogenesis and Ameliorates Left Ventricular Dysfunction during Pressure Overload

Parstatin, a novel protease activated receptor-1 (PAR-1) derived peptide is a potent inhibitor of angiogenesis. We and others have reported that imbalance between angiogenic growth factors and anti-angiogenic factors results in transition from compensatory cardiac hypertrophy to heart failure in a pressure overload condition. Though cardio protective role of parstatin was shown previously in ischemic cardiac injury, its role in pressure overload cardiac injury is yet to unveil. We hypothesize that supplementing anti-parstatin antibody during pressure overload condition augments angiogenesis and ameliorate left ventricular dysfunction and heart failure. To verify this, we created ascending aortic banding in mice to mimic pressure overload condition and then treated mice with anti-parstatin antibody. Left ventricular function was assessed by echocardiography and pressure-volume loop study. Angiogenic growth factors and anti-angiogenic factors along with MMP-2,-9 were evaluated by western blot and immunohistochemistry.

RESULTS

our results showed an improved left ventricular function in anti-parstatin treated aortic banding hearts compared to their corresponding wild type controls. Expression of angiogenic growth factor, VEGF, MMP-2 and CD31 expression was increased in treated aortic banding hearts compared to their corresponding wild type controls. Our results suggest that treating pressure overload mice with anti-parstatin antibody augments angiogenesis and ameliorates left ventricular dysfunction.

Hyperhomocysteinemia attenuates angiogenesis through reduction of HIF-1α and PGC-1α levels in muscle fibers during hindlimb ischemia

Hyperhomocysteinemia (HHcy) is associated with elderly frailty, skeletal muscle injury and malfunction, reduced vascular integrity and function, and mortality. Although HHcy has been implicated in the impairment of angiogenesis after hindlimb ischemia in murine models, the underlying mechanisms are still unclear. We hypothesized that HHcy compromises skeletal muscle perfusion, collateral formation, and arteriogenesis by diminishing postischemic vasculogenic responses in muscle fibers. To test this hypothesis, we created femoral artery ligation in wild-type and heterozygous cystathionine β-synthase (CBS(+/-)) mice (a model for HHcy) and assessed tissue perfusion, collateral vessel formation, and skeletal muscle function using laser-Doppler perfusion imaging, barium angiography, and fatigue tests. In addition, we assessed postischemic levels of VEGF and levels of its muscle-specific regulators: hypoxia-inducible factor (HIF)-1α and peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α. The observations indicated dysregulation of VEGF, HIF-1α, and PGC-1α levels in ischemic skeletal muscles of CBS(+/-) mice. Concomitant with the reduced ischemic angiogenic responses, we also observed diminished leptin expression and attenuated Akt signaling in ischemic muscle fibers of CBS(+/-) mice. Moreover, there was enhanced atrogene, ubiquitin ligases that conjugate proteins for degradation during muscle atrophy, transcription, and reduced muscle function after ischemia in CBS(+/-) mice. These results suggest that HHcy adversely affects muscle-specific ischemic responses and contributes to muscle frailty.

Fluvoxamine rescues mitochondrial Ca2+ transport and ATP production through σ(1)-receptor in hypertrophic cardiomyocytes

AIMS

We previously reported that fluvoxamine, a selective serotonin reuptake inhibitor with high affinity for the σ1-receptor (σ1R), ameliorates cardiac hypertrophy and dysfunction via σ1R stimulation. Although σ1R on non-cardiomyocytes interacts with the IP3 receptor (IP3R) to promote mitochondrial Ca(2+) transport, little is known about its physiological and pathological relevance in cardiomyocytes.

MAIN METHODS

Here we performed Ca(2+) imaging and measured ATP production to define the role of σ1Rs in regulating sarcoplasmic reticulum (SR)-mitochondrial Ca(2+) transport in neonatal rat ventricular cardiomyocytes treated with angiotensin II to promote hypertrophy.

KEY FINDING

These cardiomyocytes exhibited imbalances in expression levels of σ1R and IP3R and impairments in both phenylephrine-induced mitochondrial Ca(2+) mobilization from the SR and ATP production. Interestingly, σ1R stimulation with fluvoxamine rescued impaired mitochondrial Ca(2+) mobilization and ATP production, an effect abolished by treatment of cells with the σ1R antagonist, NE-100. Under physiological conditions, fluvoxamine stimulation of σ1Rs suppressed intracellular Ca(2+) mobilization through IP3Rs and ryanodine receptors (RyRs). In vivo, chronic administration of fluvoxamine to TAC mice also rescued impaired ATP production.

SIGNIFICANCE

These results suggest that σ1R stimulation with fluvoxamine promotes SR-mitochondrial Ca(2+) transport and mitochondrial ATP production, whereas σ1R stimulation suppresses intracellular Ca(2+) overload through IP3Rs and RyRs. These mechanisms likely underlie in part the anti-hypertrophic and cardioprotective action of the σ1R agonists including fluvoxamine.