Mitochondrial quality control in diabetic cardiomyopathy: from molecular mechanisms to therapeutic strategies

In diabetic cardiomyopathy (DCM), a major diabetic complication, the myocardium is structurally and functionally altered without evidence of coronary artery disease, hypertension or valvular disease. Although numerous anti-diabetic drugs have been applied clinically, specific medicines to prevent DCM progression are unavailable, so the prognosis of DCM remains poor. Mitochondrial ATP production maintains the energetic requirements of cardiomyocytes, whereas mitochondrial dysfunction can induce or aggravate DCM by promoting oxidative stress, dysregulated calcium homeostasis, metabolic reprogramming, abnormal intracellular signaling and mitochondrial apoptosis in cardiomyocytes. In response to mitochondrial dysfunction, the mitochondrial quality control (MQC) system (including mitochondrial fission, fusion, and mitophagy) is activated to repair damaged mitochondria. Physiological mitochondrial fission fragments the network to isolate damaged mitochondria. Mitophagy then allows dysfunctional mitochondria to be engulfed by autophagosomes and degraded in lysosomes. However, abnormal MQC results in excessive mitochondrial fission, impaired mitochondrial fusion and delayed mitophagy, causing fragmented mitochondria to accumulate in cardiomyocytes. In this review, we summarize the molecular mechanisms of MQC and discuss how pathological MQC contributes to DCM development. We then present promising therapeutic approaches to improve MQC and prevent DCM progression.     

氧化应激研究进展及其在缺血性心肌病发病中的作用

缺血性心肌病(ischemic cardiomyopathy,ICM)是指由于长期心肌缺血导致心肌局限性或弥漫性纤维化,从而产生心脏收缩和(或)舒张功能受损,引起心脏扩大或僵硬、充血性心力衰竭、心律失常等一系列临床表现的临床综合症。大量研究表明,ICM的发病机制与氧化应激密切相关。研究和开发新的抗氧化药物,将为缺血性心肌病的防治提供新的方向和途径。     

Melatonin therapy for diabetic cardiomyopathy: A mechanism involving Syk-mitochondrial complex I-SERCA pathway

Melatonin and its metabolites have been demonstrated to modulate the glucose, dyslipidemia and other metabolic disorders. This study aimed to explore a novel mechanism responsible for diabetic cardiomyopathy development, and also validated whether melatonin played a protective role in repairing damaged heart in the diabetes setting. Our data demonstrated that spleen tyrosine kinase (Syk) was activated by chronic high-glucose stimulus and contributed to the development of diabetic cardiomyopathy. However, genetic ablation of Syk or supplementation of melatonin to inhibit Syk activation improved diabetic myocardial function, reduced cardiac fibrosis and preserved cardiomyocytes viability. Mechanistically, activated Syk repressed the expression and activity of mitochondrial complex I (COX-1), unfortunately evoking mitochondrial and/or cellular ROS overproduction. Subsequently, excessive superoxide facilitated SERCA peroxidation which failed to re-uptake the cytoplasmic calcium back into endoplasmic reticulum (ER), leading to cellular calcium overload. Finally, activated oxidative stress and calcium overload collectively promoted the high-glucose-induced cardiomyocytes death via caspase-9-related mitochondrial apoptosis and caspase-12-involved ER apoptosis, respectively. Interestingly, inhibition of Syk via Syk genetic ablation or melatonin administration blocked Syk/COX-1/SERCA signalling pathways, and thus abolished mitochondrial- and ER-mediated cardiomyocyte death in the setting of diabetes. Based on these results, we suggest a novel pathway by which high-glucose stimulus induces diabetic cardiomyopathy is possibly through an activation of Syk/COX-1/SERCA axis which could be abrogated by melatonin treatment.     

The mitochondrial ubiquitin ligase plays an anti‐apoptotic role in cardiomyocytes by regulating mitochondrial fission

Apoptosis plays a critical role in the development of myocardial infarction. Cardiomyocytes are enriched with mitochondria and excessive mitochondrial fission can trigger cellular apoptosis. Recently, the mitochondrial ubiquitin ligase (MITOL), localized in the mitochondrial outer membrane, was reported to play an important role in the regulation of mitochondrial dynamics and apoptosis. However, the underlying mechanism of its action remains uncertain. The present study was aimed at uncovering the role of MITOL in the regulation of cardiomyocyte apoptosis. Our results showed that MITOL expression was up‐regulated in cardiomyocytes in response to apoptotic stimulation. Mitochondrial ubiquitin ligase overexpression blocked dynamin‐related protein 1 accumulation in the mitochondria, and attenuated the mitochondrial fission induced by hydrogen peroxide. Conversely, MITOL knockdown sensitized cardiomyocytes to undergo mitochondrial fission, resulting in subsequent apoptosis. These findings suggest that MITOL plays a protective role against apoptosis in cardiomyocytes, and may serve as a potential therapeutic target for apoptosis‐related cardiac diseases.     

Echinacoside reverses myocardial remodeling and improves heart function via regulating SIRT1/FOXO3a/MnSOD axis in HF rats induced by isoproterenol

Myocardial remodelling is important pathological basis of HF, mitochondrial oxidative stress is a promoter to myocardial hypertrophy, fibrosis and apoptosis. ECH is the major active component of a traditional Chinese medicine Cistanches Herba, plenty of studies indicate it possesses a strong antioxidant capacity in nerve cells and tumour, it inhibits mitochondrial oxidative stress, protects mitochondrial function, but the specific mechanism is unclear. SIRT1/FOXO3a/MnSOD is an important antioxidant axis, study finds that ECH binds covalently to SIRT1 as a ligand and up-regulates the expression of SIRT1 in brain cells. We hypothesizes that ECH may reverse myocardial remodelling and improve heart function of HF via regulating SIRT1/FOXO3a/MnSOD signalling axis and inhibit mitochondrial oxidative stress in cardiomyocytes. Here, we firstly induce cellular model of oxidative stress by ISO with AC-16 cells and pre-treat with ECH, the level of mitochondrial ROS, mtDNA oxidative injury, MMP, carbonylated protein, lipid peroxidation, intracellular ROS and apoptosis are detected, confirm the effect of ECH in mitochondrial oxidative stress and function in vitro. Then, we establish a HF rat model induced by ISO and pre-treat with ECH. Indexes of heart function, myocardial remodelling, mitochondrial oxidative stress and function, expression of SIRT1/FOXO3a/MnSOD signalling axis are measured, the data indicate that ECH improves heart function, inhibits myocardial hypertrophy, fibrosis and apoptosis, increases the expression of SIRT1/FOXO3a/MnSOD signalling axis, reduces the mitochondrial oxidative damages, protects mitochondrial function. We conclude that ECH reverses myocardial remodelling and improves cardiac function via up-regulating SIRT1/FOXO3a/MnSOD axis and inhibiting mitochondrial oxidative stress in HF rats.     

Mitochondrial quality control in stroke: From the mechanisms to therapeutic potentials

Mitochondrial damage is a critical contributor to stroke‐induced injury, and mitochondrial quality control (MQC) is the cornerstone of restoring mitochondrial homeostasis and plays an indispensable role in alleviating pathological process of stroke. Mitochondria quality control promotes neuronal survival via various adaptive responses for preserving mitochondria structure, morphology, quantity and function. The processes of mitochondrial fission and fusion allow for damaged mitochondria to be segregated and facilitate the equilibration of mitochondrial components such as DNA, proteins and metabolites. The process of mitophagy is responsible for the degradation and recycling of damaged mitochondria. This review aims to offer a synopsis of the molecular mechanisms involved in MQC for recapitulating our current understanding of the complex role that MQC plays in the progression of stroke. Speculating on the prospect that targeted manipulation of MQC mechanisms may be exploited for the rationale design of novel therapeutic interventions in the ischaemic stroke and haemorrhagic stroke. In the review, we highlight the potential of MQC as therapeutic targets for stroke treatment and provide valuable insights for clinical strategies.     

氧化应激研究进展及其在缺血性心肌病发病中的作用

缺血性心肌病（ischemic cardiomyopathy,ICM）是指由于长期心肌缺血导致心肌局限性或弥漫性纤维化,从而产生心脏收缩和（或）舒张功能受损,引起心脏扩大或僵硬、充血性心力衰竭、心律失常等一系列临床表现的临床综合症。大量研究表明,ICM的发病机制与氧化应激密切相关。研究和开发新的抗氧化药物,将为缺血性心肌病的防治提供新的方向和途径。     

急性心肌梗死患者心肌顿抑发病机制探讨

心肌顿抑也称缺血后心肌功能障碍,为持续数小时、数天、甚至数周的心肌细胞可逆性损伤。可见于急性冠脉综合症早期再灌注、心脏移植、心脏瓣膜置换等心脏外科大手术术后,应激性心肌病、心脏骤停、心肺复苏、主动脉狭窄、高血压性心脏病、房颤转复。心肌梗死后发生心肌顿抑是导致心梗死亡、心衰再住院的重要病因,但目前其发病机制尚不明确。有关心肌顿抑的研究已经由器官细胞水平,深入到分子基因水平。具体而言,心肌顿抑的发病机制包括：缺血再灌注导致的心肌细胞直接损伤、心肌细胞兴奋收缩脱偶联、线粒体及内质网损伤、血管内皮细胞功能障碍及微循环痉挛、能量代谢障碍、氧自由基损伤、钙超载理论、炎性介质释放理论、心肌顿抑的基因组学机制等。目前,广为接受的是氧自由基理论和钙超载理论。前者认为心肌梗死时,心肌组织氧自由基产生增多,清除障碍,导致心肌细胞结构受伤和功能障碍;后者认为心肌梗死时,心肌细胞酸中毒,细胞膜通透性增加,钙内流增多,同时,钙库重吸收钙障碍,导致钙超载,引起心肌细胞破坏、肌钙蛋白溶解,导致心功能障碍。阐明心肌顿抑发病机制,指导心梗治疗,有助于完善救治策略,改善预后。     

MCU Up‐regulation contributes to myocardial ischemia‐reperfusion Injury through calpain/OPA‐1–mediated mitochondrial fusion/mitophagy Inhibition

Mitochondrial dynamic disorder is involved in myocardial ischemia/reperfusion (I/R) injury. To explore the effect of mitochondrial calcium uniporter (MCU) on mitochondrial dynamic imbalance under I/R and its related signal pathways, a mouse myocardial I/R model and hypoxia/reoxygenation model of mouse cardiomyocytes were established. The expression of MCU during I/R increased and related to myocardial injury, enhancement of mitochondrial fission, inhibition of mitochondrial fusion and mitophagy. Suppressing MCU functions by Ru360 during I/R could reduce myocardial infarction area and cardiomyocyte apoptosis, alleviate mitochondrial fission and restore mitochondrial fusion and mitophagy. However, spermine administration, which could enhance MCU function, deteriorated the above‐mentioned myocardial cell injury and mitochondrial dynamic imbalanced. In addition, up‐regulation of MCU promoted the expression and activation of calpain‐1/2 and down‐regulated the expression of Optic atrophy type 1 (OPA1). Meantime, in transgenic mice (overexpression calpastatin, the endogenous inhibitor of calpain) I/R model and OPA1 knock‐down cultured cell. In I/R models of transgenic mice over‐expressing calpastatin, which is the endogenous inhibitor of calpain, and in H/R models with siOPA1 transfection, inhibition of calpains could enhance mitochondrial fusion and mitophagy, and inhibit excessive mitochondrion fission and apoptosis through OPA1. Therefore, we conclude that during I/R, MCU up‐regulation induces calpain activation, which down‐regulates OPA1, consequently leading to mitochondrial dynamic imbalance.     

UCP2 protect the heart from myocardial ischemia/reperfusion injury via induction of mitochondrial autophagy

Uncoupling protein 2 (UCP2), located in the mitochondrial inner membrane, is a predominant isoform of UCP that expressed in the heart and other tissues of human and rodent tissues. Nevertheless, its functional role during myocardial ischemia/reperfusion (I/R) is not entirely understood. Ischemic preconditioning (IPC) remarkably improved postischemic functional recovery followed by reduced lactate dehydrogenase (LDH) release with simultaneous upregulation of UCP2 in perfused myocardium. We then investigated the role of UCP2 in IPC-afforded cardioprotective effects on myocardial I/R injury with adenovirus-mediated in vivo UCP2 overexpression (AdUCP2) and knockdown (AdshUCP2). IPC-induced protective effects were mimicked by UCP2 overexpression, while which were abolished with silencing UCP2. Mechanistically, UCP2 overexpression significantly reinforced I/R-induced mitochondrial autophagy (mitophagy), as measured by biochemical hallmarks of mitochondrial autophagy. Moreover, primary cardiomyocytes infected with AdUCP2 increased simulated ischemia/reperfusion (sI/R)-induced mitophagy and therefore reversed impaired mitochondrial function. Finally, suppression of mitophagy with mdivi-1 in cultured cardiomyocytes abolished UCP2-afforded protective effect on sI/R-induced mitochondrial dysfunction and cell death. Our data identify a critical role for UCP2 against myocardial I/R injury through preventing the mitochondrial dysfunction through reinforcing mitophagy. Our findings reveal novel mechanisms of UCP2 in the cardioprotective effects during myocardial I/R.     

Disruption of mitochondrial quality control genes promotes caspase-resistant cell survival following apoptotic stimuli

In cells undergoing cell-intrinsic apoptosis, mitochondrial outer membrane permeabilization (MOMP) typically marks an irreversible step in the cell death process. However, in some cases, a subpopulation of treated cells can exhibit a sublethal response, termed “minority MOMP.” In this phenomenon, the affected cells survive, despite a low level of caspase activation and subsequent limited activation of the endonuclease caspase-activated DNase (DNA fragmentation factor subunit beta). Consequently, these cells can experience DNA damage, increasing the probability of oncogenesis. However, little is known about the minority MOMP response. To discover genes that affect the MOMP response in individual cells, we conducted an imaging-based phenotypic siRNA screen. We identified multiple candidate genes whose downregulation increased the heterogeneity of MOMP within single cells, among which were genes related to mitochondrial dynamics and mitophagy that participate in the mitochondrial quality control (MQC) system. Furthermore, to test the hypothesis that functional MQC is important for reducing the frequency of minority MOMP, we developed an assay to measure the clonogenic survival of caspase-engaged cells. We found that cells deficient in various MQC genes were indeed prone to aberrant post-MOMP survival. Our data highlight the important role of proteins involved in mitochondrial dynamics and mitophagy in preventing apoptotic dysregulation and oncogenesis.     

Conundrum of pathogenesis of diabetic cardiomyopathy: role of vascular endothelial dysfunction, reactive oxygen species, and mitochondria

Diabetic cardiomyopathy and heart failure have been recognized as the leading causes of mortality among diabetics. Diabetic cardiomyopathy has been characterized primarily by the manifestation of left ventricular dysfunction that is independent of coronary artery disease and hypertension among the patients affected by diabetes mellitus. A complex array of contributing factors including the hypertrophy of left ventricle, alterations of metabolism, microvascular pathology, insulin resistance, fibrosis, apoptotic cell death, and oxidative stress have been implicated in the pathogenesis of diabetic cardiomyopathy. Nevertheless, the exact mechanisms underlying the pathogenesis of diabetic cardiomyopathy are yet to be established. The critical involvement of multifarious factors including the vascular endothelial dysfunction, microangiopathy, reactive oxygen species (ROS), oxidative stress, mitochondrial dysfunction has been identified in the mechanism of pathogenesis of diabetic cardiomyopathy. Although it is difficult to establish how each factor contributes to disease, the involvement of ROS and mitochondrial dysfunction are emerging as front-runners in the mechanism of pathogenesis of diabetic cardiomyopathy. This review highlights the role of vascular endothelial dysfunction, ROS, oxidative stress, and mitochondriopathy in the pathogenesis of diabetic cardiomyopathy. Furthermore, the review emphasizes that the puzzle has to be solved to firmly establish the mitochondrial and/or ROS mechanism(s) by identifying their most critical molecular players involved at both spatial and temporal levels in diabetic cardiomyopathy as targets for specific and effective pharmacological/therapeutic interventions.     

Angiopoietin-1 protects heart against ischemia/reperfusion injury through VE-cadherin dephosphorylation and myocardiac integrin-β1/ERK/caspase-9 phosphorylation cascade

Early reperfusion after myocardial ischemia that is essential for tissue salvage also causes myocardial and vascular injury. Cardioprotection during reperfusion therapy is an essential aspect of treating myocardial infarction. Angiopoietin-1 is an endothelial-specific angiogenic factor. The potential effects of angiopoietin-1 on cardiomyocytes and vascular cells undergoing reperfusion have not been investigated. We propose a protective mechanism whereby angiopoietin-1 increases the integrity of the endothelial lining and exerts a direct survival effect on cardiomyocytes under myocardial ischemia followed by reperfusion. First, we found that angiopoietin-1 prevents vascular leakage through regulating vascular endothelial (VE)-cadherin phosphorylation. The membrane expression of VE-cadherin was markedly decreased on hypoxia/reoxygenation but was restored by angiopoietin-1 treatment. Interestingly, these effects were mediated by the facilitated binding between SH2 domain-containing tyrosine phosphatase (SHP2) or receptor protein tyrosine phosphatase μ (PTPμ) and VE-cadherin, leading to dephosphorylation of VE-cadherin. siRNA against SHP2 or PTPμ abolished the effect of angiopoietin-1 on VE-cadherin dephosphorylation and thereby decreased levels of membrane-localized VE-cadherin. Second, we found that angiopoietin-1 prevented cardiomyocyte death, although cardiomyocytes lack the angiopoietin-1 receptor Tie2. Angiopoietin-1 increased cardiomyocyte survival through integrin-β1-mediated extracellular signal-regulated kinase (ERK) phosphorylation, which inhibited caspase-9 through phosphorylation at Thr12? and subsequently reduced active caspase-3. Neutralizing antibody against integrin-β1 blocked these protective effects. In a mouse myocardial ischemia/reperfusion model, angiopoietin-1 enhanced cardiac function and reduction in left ventricular-end systolic dimension (LV-ESD) and left ventricular-end diastolic dimension (LV-EDD) with an increase in ejection fraction (EF) and fractional shortening (FS). Our findings suggest the novel cardioprotective mechanisms of angiopoietin-1 that are achieved by reducing both vascular leakage and cardiomyocyte death after ischemia/reperfusion injury.     

Keap-NRF2 signaling contributes to the Notch1 protected heart against ischemic reperfusion injury via regulating mitochondrial ROS generation and bioenergetics

Myocardial ischemia/reperfusion (I/R) injury is recognized as the leading cause of death worldwide. However, the molecular mechanisms involved in this process are still not fully understood. We previously reported that the combined action of Notch1 and Keap1-NRF2 signaling pathway can significantly increase the activity of cardiomyocytes, inhibit the apoptosis of cardiomyocytes, reduce the formation of reactive oxygen species, and improve the antioxidant activity in neonate rat myocardial cells. However, the regulatory mechanism of Notch1 signaling pathway on the NRF2 signaling pathway and its actual role on I/R injury are still unclear. Herein, we found that Keap-NRF2 signaling is activated by Notch1 in RBP-Jκ dependent manner, thus protects the heart against I/R injury via inhibiting the mitochondrial ROS generation and improves the mitochondrial bioenergetics in vitro and in vivo. These results suggest that Keap-NRF2 signaling might become a promising therapeutic strategy for treating myocardial I/R injury.     

MKP1 overexpression reduces TNF-α-induced cardiac injury via suppressing mitochondrial fragmentation and inhibiting the JNK–MIEF1 pathways

Mitochondrial stress has been acknowledged as the pathogenesis for tumor necrosis factor-α (TNF-α)-induced septic cardiomyopathy. Recently, MAP kinase phosphatase 1 (MKP1) downregulation and mitochondrial fragmentation modulate the mitochondrial stress via multiple molecular mechanisms. Thereby, the goal of our current work is to figure out the functional role of mitochondrial fragmentation in TNF-α-induced septic cardiomyopathy. Our results exhibited that MKP1 expression was significantly repressed in hearts treated by TNF-α. Overexpression of MKP1 sustained cardiac function and attenuated cardiomyocytes death in TNF-α-treated hearts. At the molecular levels, decreased MKP1 induced mitochondrial stress, as indicated by mitochondrial calcium overloading, mitochondrial oxidative stress, mitochondrial antioxidant downregulation, mitochondrial membrane potential reduction, mitochondrial bioenergetics suppression, mitochondrial proapoptotic factors liberation, and caspase-9 apoptotic pathway activation. To the end, we illustrated that MKP1-modulated mitochondrial stress via mitochondrial fragmentation; reactivation of mitochondrial fragmentation abolished the protective effect of MKP1 overexpression on mitochondrial function. Further, MKP1 affected mitochondrial division in a mechanism through the JNK–MIEF1 axis. Blockade of JNK pathway abolished the regulatory actions of MKP1 on mitochondrial division. Altogether, our results identify MKP1 as a novel cardioprotective factor in TNF-α-related septic cardiomyopathy via affecting mitochondrial division by the way of JNK–MIEF1 signaling pathway. Therefore, MKP1 expression, mitochondrial fragmentation modification, and JNK–MIEF1 pathway modulation may be considered as potential therapeutic targets for the treatment of cardiac injury induced by sepsis.     

Endothelial protection from reperfusion injury by ischemic preconditioning and diazoxide involves a SOD-like anti-O2- mechanism.

Cardiac ischemia/reperfusion leads to coronary endothelial dysfunction, mediated by superoxide anion (O2-), but not hydroxyl radical (*OH). Ischemic preconditioning and mitochondrial ATP-dependent potassium channel opener (diazoxide) protect endothelium in the mechanism involving attenuation of O2- burst at reperfusion. We hypothesize that the endothelial protection involves upregulation of myocardial anty-O2- defense. Langendorff-perfused guinea-pig hearts were subjected to global ischemia/reperfusion (IR) or were preconditioned prior to IR with three cycles of ischemia/reperfusion (IPC) or infusion/washout of 0.5 microM diazoxide. Coronary flow responses to acetylcholine were measures of endothelium-dependent vascular function. Myocardial outflow of O2- and of *OH during reperfusion and myocardial activities of superoxide dismutase (SOD) and catalase were measured. IR impaired acetylcholine response and augmented cardiac O2- and *OH outflow. IPC, diazoxide, and SOD (150 IU/ml) attenuated O2- outflow, increased *OH outflow and protected endothelium. There were no differences in Cu/Zn-SOD, Mn-SOD and catalase activities between sham-perfused and IR hearts and only catalase activity was increased in the IPC hearts. We speculate that: (i) IPC and diazoxide endothelial protection involves activation of some SOD-like anti-O2- mechanism resulting in attenuation of O2- burst and increase in *OH burst, (ii) improved SOD activity might have not been detected because it was confined to a small, although functionally important, enzyme fraction, like that bound to the endothelial glycocalyx.     

Mitochondrial DNA deletion in human myocardium

Mutation of myocardial mitochondrial DNA was investigated in human left ventricles obtained at autopsy using the polymerase chain reaction (PCR). Seventeen autopsy cases were examined, including patients with diabetes mellitus, myocardial infarction, cardiomyopathy, cancer, and other diseases. Two cases of diabetes mellitus, 2 of myocardial infarction, and 1 of pulmonary fibrosis showed a 7.4 kb deletion of myocardial mitochondrial DNA. Primer shift PCR confirmed that an amplified DNA fragment had not been obtained by misannealing of the primers. It is unclear how much these findings are related to the severity or prognosis of the various diseases, but they indicate that mutation of myocardial mitochondrial DNA can occur in other diseases besides cardiomyopathy, although the influence of aging could not be excluded.     

Nitric oxide signaling during myocardial angiogenesis

Ischemic heart disease develops as a consequence of coronary atherosclerotic lesion formation. Coronary collateral vessels and microvascular angiogenesis develop as an adaptive response to myocardial ischemia, which ameliorates the function of the damaged heart. Angiogenesis, the formation of new blood vessels from pre-existing vascular bed, is of paramount importance in the maintenance of vascular integrity both in the repair process of damaged tissue and in the formation of collateral vessels in response to tissue ischemia. Angiogenesis is modulated by a multitude of cytokines/chemokines and growth factors. In this regard, angiogenesis cannot be viewed as a single process. It is likely that different mediators are involved in different phases of angiogenesis. Vascular endothelial cells (ECs) produce nitric oxide (NO), an endothelium-derived labile molecule, which maintains vascular homeostasis and thereby prevents vascular atherosclerotic changes. In patients with ischemic heart disease, the release of endothelium-derived NO is decreased, which plays an important role in the atherosclerotic disease progression. In recent years, endothelium-derived NO has been shown to modulate angiogenesis in vitro and in vivo. In this review, we summarize recent progress in the field of the NO-mediated regulation of postnatal angiogenesis, particularly in response to myocardial ischemia.     

Resistance of Dynamin-related Protein 1 Oligomers to Disassembly Impairs Mitophagy,Resulting in Myocardial Inflammation and Heart Failure

We have reported previously that a missense mutation in the mitochondrial fission gene Dynamin-related protein 1 (Drp1) underlies the Python mouse model of monogenic dilated cardiomyopathy. The aim of this study was to investigate the consequences of the C452F mutation on Drp1 protein function and to define the cellular sequelae leading to heart failure in the Python monogenic dilated cardiomyopathy model. We found that the C452F mutation increased Drp1 GTPase activity. The mutation also conferred resistance to oligomer disassembly by guanine nucleotides and high ionic strength solutions. In a mouse embryonic fibroblast model, Drp1 C452F cells exhibited abnormal mitochondrial morphology and defective mitophagy. Mitochondria in C452F mouse embryonic fibroblasts were depolarized and had reduced calcium uptake with impaired ATP production by oxidative phosphorylation. In the Python heart, we found a corresponding progressive decline in oxidative phosphorylation with age and activation of sterile inflammation. As a corollary, enhancing autophagy by exposure to a prolonged low-protein diet improved cardiac function in Python mice. In conclusion, failure of Drp1 disassembly impairs mitophagy, leading to a downstream cascade of mitochondrial depolarization, aberrant calcium handling, impaired ATP synthesis, and activation of sterile myocardial inflammation, resulting in heart failure.