Mitophagy and Mitochondrial Quality Control Mechanisms in the Heart

Enhanced Parkin-mediated mitophagy mitigates adverse left ventricular remodelling after myocardial infarction: role of PR-364

BACKGROUND AND AIMS

Almost 30% of survivors of myocardial infarction (MI) develop heart failure (HF), in part due to damage caused by the accumulation of dysfunctional mitochondria. Organelle quality control through Parkin-mediated mitochondrial autophagy (mitophagy) is known to play a role in mediating protection against HF damage post-ischaemic injury and remodelling of the subsequent deteriorated myocardium.

METHODS

This study has shown that a single i.p. dose (2 h post-MI) of the selective small molecule Parkin activator PR-364 reduced mortality, preserved cardiac ejection fraction, and mitigated the progression of HF. To reveal the mechanism of PR-364, a multi-omic strategy was deployed in combination with classical functional assays using in vivo MI and in vitro cardiomyocyte models.

RESULTS

In vitro cell data indicated that Parkin activation by PR-364 increased mitophagy and mitochondrial biogenesis, enhanced adenosine triphosphate production via improved citric acid cycle, altered accumulation of calcium localization to the mitochondria, and initiated translational reprogramming with increased expression of mitochondrial translational proteins. In mice, PR-364 administered post-MI resulted in widespread proteome changes, indicating an up-regulation of mitochondrial metabolism and mitochondrial translation in the surviving myocardium.

CONCLUSIONS

This study demonstrates the therapeutic potential of targeting Parkin-mediated mitophagy using PR-364 to protect surviving cardiac tissue post-MI from progression to HF.

Zbp1 gene: a modulator of multiple aging hallmarks as potential therapeutic target for age-related diseases

The Zbp1 gene has recently emerged as a potential therapeutic target for age-related diseases. Multiple studies have reported that Zbp1 plays a key role in regulating several aging hallmarks, including cellular senescence, chronic inflammation, DNA damage response, and mitochondrial dysfunction. Regarding cellular senescence, Zbp1 appears to regulate the onset and progression of senescence by controlling the expression of key markers such as p16INK4a and p21CIP1/WAF1. Similarly, evidence suggests that Zbp1 plays a role in regulating inflammation by promoting the production of pro-inflammatory cytokines, such as IL-6 and IL-1β, through activation of the NLRP3 inflammasome. Furthermore, Zbp1 seems to be involved in the DNA damage response, coordinating the cellular response to DNA damage by regulating the expression of genes such as p53 and ATM. Additionally, Zbp1 appears to regulate mitochondrial function, which is crucial for energy production and cellular homeostasis. Given the involvement of Zbp1 in multiple aging hallmarks, targeting this gene represents a potential strategy to prevent or treat age-related diseases. For example, inhibiting Zbp1 activity could be a promising approach to reduce cellular senescence and chronic inflammation, two critical hallmarks of aging associated with various age-related diseases. Similarly, modulating Zbp1 expression or activity could also improve DNA damage response and mitochondrial function, thus delaying or preventing the development of age-related diseases. Overall, the Zbp1 gene appears to be a promising therapeutic target for age-related diseases. In the current review, we have discussed the molecular mechanisms underlying the involvement of Zbp1 in aging hallmarks and proposed to develop effective strategies to target this gene for therapeutic purposes.

Control of mitochondrial integrity influences oocyte quality during reproductive aging

Reduced quality in oocytes from women of advanced maternal age (AMA) is associated with dysfunctional mitochondria. The objective of this study was to investigate the mechanisms controlling mitochondrial quality during maternal aging in mouse and human oocytes. We first evaluated the expression of proteins involved in the mitochondrial unfolded protein response (UPRmt) and mitophagy in in vivo matured metaphase II (MII) oocytes collected from young and aged mice. Expression of UPRmt proteins, HSPD1 and LONP1, and mitophagy proteins, total-PRKN and phosphorylated-PRKN, was significantly decreased in aged compared to young oocytes. Treatment of aged oocytes during in vitro maturation with the mitochondrially targeted antioxidant mitoquinone (MQ) specifically restored total-PRKN and phosphorylated-PRKN expression to levels seen in young oocytes. We next investigated whether maturing young oocytes under a high-oxygen environment would mimic the effects observed in oocytes from aged females. Phosphorylated-PRKN expression in oxidatively stressed young oocytes was reduced compared to that in oocytes matured under normal oxygen levels, and the mitochondrial DNA (mtDNA) copy number was increased. Treating oxidatively challenged young oocytes with MQ restored the phosphorylated-PRKN expression and mtDNA copy numbers. Treatment of oxidatively challenged oocytes with MQ also increased the co-localization of mitochondria and lysosomes, suggesting increased mitophagy. These data correlated with the developmental potential of the oocytes, as blastocyst development and hatching of oxidatively stressed oocytes were reduced, while treatment with MQ resulted in a significant increase in blastocyst development and hatching, and in the percentage of inner cell mass. Consistent with our results in mice, MII oocytes from women of AMA exhibited a significant decrease in phosphorylated-PKRN and total-PRKN compared to those of young women. Our findings suggest that the protein machinery to control the health of the mitochondria via UPRmt and mitophagy may be compromised in oocytes from aged females, which may result in inefficient clearance of dysfunctional mitochondria and reduced oocyte quality.

Linolenic acid ameliorates sarcopenia in C. elegans by promoting mitophagy and fighting oxidative stress

Sarcopenia is a syndrome of age-related loss of muscle mass and strength that seriously affects human health, and there are currently no effective drugs to treat the disease. Linolenic acid as a common n-3 polyunsaturated fatty acid (n-3 PUFA) is known to have many beneficial functions. Some studies have found that n-3 PUFA might have the potential to improve sarcopenia. In this study, Caenorhabditis elegans (C. elegans) was used as a model animal to investigate the effects of linolenic acid on C. elegans muscles. The results showed that 50 μg mL-1 linolenic acid significantly improved sarcopenia by repairing mitochondrial function by promoting mitophagy and fighting oxidative stress (p < 0.05). This included the increase of the expression of the mitophagy gene pink-1 and DAF-16/FOXO transcription factors, respectively, by linolenic acid. This study could provide some evidence for the application of n-3 PUFA in improving sarcopenia.

RhoA signaling increases mitophagy and protects cardiomyocytes against ischemia by stabilizing PINK1 protein and recruiting Parkin to mitochondria

Mitophagy, a mitochondria-specific form of autophagy, removes dysfunctional mitochondria and is hence an essential process contributing to mitochondrial quality control. PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin are critical molecules involved in stress-induced mitophagy, but the intracellular signaling mechanisms by which this pathway is regulated are unclear. We tested the hypothesis that signaling through RhoA, a small GTPase, induces mitophagy via modulation of the PINK1/Parkin pathway as a protective mechanism against ischemic stress. We demonstrate that expression of constitutively active RhoA as well as sphingosine-1-phosphate induced activation of endogenous RhoA in cardiomyocytes result in an accumulation of PINK1 at mitochondria. This is accompanied by translocation of Parkin to mitochondria and ubiquitination of mitochondrial proteins leading to recognition of mitochondria by autophagosomes and their lysosomal degradation. Expression of RhoA in cardiomyocytes confers protection against ischemia, and this cardioprotection is attenuated by siRNA-mediated PINK1 knockdown. In vivo myocardial infarction elicits increases in mitochondrial PINK1, Parkin, and ubiquitinated mitochondrial proteins. AAV9-mediated RhoA expression potentiates these responses and a concurrent decrease in infarct size is observed. Interestingly, induction of mitochondrial PINK1 accumulation in response to RhoA signaling is neither mediated through its transcriptional upregulation nor dependent on depolarization of the mitochondrial membrane, the canonical mechanism for PINK1 accumulation. Instead, our results reveal that RhoA signaling inhibits PINK1 cleavage, thereby stabilizing PINK1 protein at mitochondria. We further show that active RhoA localizes at mitochondria and interacts with PINK1, and that the mitochondrial localization of RhoA is regulated by its downstream effector protein kinase D. These findings demonstrate that RhoA activation engages a unique mechanism to regulate PINK1 accumulation, induce mitophagy and protect against ischemic stress, and implicates regulation of RhoA signaling as a potential strategy to enhance mitophagy and confer protection under stress conditions.

Banxia-Houpu decoction diminishes iron toxicity damage in heart induced by chronic intermittent hypoxia

CONTEXT

Obstructive sleep apnoea (OSA) causes chronic intermittent hypoxia (CIH), which results in mitochondrial dysfunction and generates reactive oxygen species (ROS) in the heart. Excessive free iron could accelerate oxidative damage, which may be involved in this process. Banxia-Houpu decoction (BHD) was reported to improve the apnoea hypopnoea index in OSA patients, but the specific mechanism was still unclear.

OBJECTIVE

To investigate whether BHD could reduce CIH-induced heart damage by regulating iron metabolism and mitochondrial function.

MATERIALS AND METHODS

C57BL/6N mice were randomly divided into control, CIH and BHD groups. Mice were exposed to CIH (21 - 5% O2, 20 times/h, 8 h/d) and administered BHD (3.51, 7.01 and 14.02 g/kg, intragastrically) for 21 d. Cardiac and mitochondrial function, iron levels, apoptosis and mitophagy were determined.

RESULTS

BHD (7.01 g/kg) significantly improved cardiac dysfunction, pathological change and mitochondrial structure induced by CIH. BHD increased the Bcl-2/Bax ratio (1.4-fold) and inhibited caspase 3 cleavage in CIH mice (0.45-fold). BHD activated mitophagy by upregulating Parkin (1.94-fold) and PINK1 (1.26-fold), inhibiting the PI3K-AKT-mTOR pathway. BHD suppressed ROS generation by decreasing NOX2 (0.59-fold) and 4-HNE (0.83-fold). BHD reduced the total iron in myocardial cells (0.72-fold) and mitochondrial iron by downregulating Mfrn2 (0.81-fold) and MtFt (0.78-fold) proteins, and upregulating ABCB8 protein (1.33-fold). Rosmarinic acid, the main component of Perilla Leaf in BHD, was able to react with Fe2+ and Fe3+ in vitro.

DISCUSSION AND CONCLUSIONS

These findings encourage the use of BHD to resist cardiovascular injury and provide the theoretical basis for clinical treatment in OSA patients.

Exercise training differently improve cardiac function and regulate myocardial mitophagy in ischemic and pressure-overloaded heart failure mice

NEW FINDINGS

What is the central question of this study? The cardioprotective effects of different aerobic exercises on chronic heart failure with different etiologies and whether mitophagy is involved remain elusive. What is the main finding and its importance? Moderate-intensity continuous training may be the "optimum" modality for improving cardiac structure and function in ischemic heart failure, while both moderate-intensity continuous training and high-intensity interval training were suitable for pressure-overloaded heart failure. Various mitophagy pathways especially PRKN-dependent pathways participated in the protective effects of exercise on heart failure.

ABSTRACT

The cardioprotective effects of different aerobic exercises on chronic heart failure with different etiologies and whether mitophagy is involved remain elusive. In the current research, left anterior descending ligation and transverse aortic constriction surgeries were used to establish mice models of heart failure, followed by 8 weeks of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT). The results showed that MICT significantly improved ejection fraction (P < 0.05) and fractional shortening (P < 0.05), mitigated left ventricular end-systolic dimension (P < 0.01), brain natriuretic peptide (P < 0.0001), and fibrosis (P < 0.0001), while HIIT only decreased brain natriuretic peptide (P < 0.0001) and fibrosis (P < 0.0001) for ischemic heart failure. Both MICT and HIIT significantly increased ejection fraction (P < 0.0001) and fractional shortening (MICT: P < 0.001, HIIT: P < 0.0001), reduced left ventricular end-diastolic and end-systolic dimension, brain natriuretic peptide (P < 0.0001), and fibrosis (MICT: P < 0.01, HIIT: P < 0.0001), even HIIT was better in reducing brain natriuretic peptide on pressure-overloaded heart failure. Myocardial autophagy and mitophagy were compromised in heart failure, exercises improved myocardial autophagic flux and mitophagy inconsistently in heart failure with different etiologies. Significant correlations were found between multiple mitophagy pathways and cardioprotection of exercises. Collectively, MICT may be the "optimum" modality for ischemic heart failure, both MICT and HIIT (especially HIIT) were suitable for pressure-overloaded heart failure. Exercises differently improved myocardial autophagy/mitophagy and multiple mitophagy-related pathways were closely implicated in cardioprotection of exercises for chronic heart failure. This article is protected by copyright. All rights reserved.

Early-onset dietary restriction maintains mitochondrial health, autophagy and ER function in the left ventricle during aging

Dietary restriction (DR) exerts healthy benefits, including heart functions. However, the cardioprotective role of DR is till controversial among researchers due to the variation of DR conditions. The present study focuses on the protective effect of early-onset DR on cardiac injury using mitochondrial structure and expression of protein associated with mitochondrial homeostasis, autophagy and endoplasmic reticulum (ER) function as measures.

METHODS

Two-month-old mice were fed with a breeding diet ad libitum (AL) or DR (60% of AL) for 3 (Young) or 20 (Aged) months.

RESULTS

Body weight increased with aging, whereas DR treatment kept body weight consistent. DR mice exhibited a higher relative heart weight than AL mice. DR mice displayed lower plasma glucose levels, compared with AL groups. Furthermore, Aged-AL, but not Aged-DR mice, had increased collagen content and morphological distortions in the left ventricle (LV). Aged-DR mice had a higher ATP and lower TBARS in the LV than Aged-AL mice. Mitochondrial morphology was detected by electron microscopy; Aged-AL mice had increased abnormal morphology of mitochondria. Treatment with DR reduced abnormal mitochondrial accumulation. Aging elevated the protein expressions of mitochondrial functions and ER-induced apoptosis. Aging downregulated autophagy-related proteins and chaperones in the heart. Dietary restriction reversed those protein expressions.

CONCLUSIONS

The present study demonstrated a beneficial effect of early onset DR on cardiac aging. The age-dependent mitochondrial dysfunction and protein quality control dysregulation was significantly reversed by long-term DR, demonstrating a concordance with the beneficial effect in the heart.

Exercise: a molecular tool to boost muscle growth and mitochondrial performance in heart failure?

Impaired exercise capacity is the key symptom of heart failure (HF) and is associated with reduced quality of life and higher mortality rates. Unfortunately, current therapies, although generally lifesaving, have only small or marginal effects on exercise capacity. Specific strategies to alleviate exercise intolerance may improve quality of life, while possibly improving prognosis as well. There is overwhelming evidence that physical exercise improves performance in cardiac and skeletal muscles in health and disease. Unravelling the mechanistic underpinnings of exercise‐induced improvements in muscle function could provide targets that will allow us to boost exercise performance in HF. With the current review we discuss: (i) recently discovered signalling pathways that govern physiological muscle growth as well as mitochondrial quality control mechanisms that underlie metabolic adaptations to exercise; (ii) the mechanistic underpinnings of exercise intolerance in HF and the benefits of exercise in HF patients on molecular, functional and prognostic levels; and (iii) potential molecular therapeutics to improve exercise performance in HF. We propose that novel molecular therapies to boost adaptive muscle growth and mitochondrial quality control in HF should always be combined with some form of exercise training.

Muscle-specific programmed cell death 5 deletion attenuates cardiac aging

Programmed cell death 5 (PDCD5) is a tumor suppressor gene that regulates the cell cycle, apoptosis and immune responses. However, the physiological function of Pdcd5 in cardiac aging remains unknown. We find that Pdcd5 mRNA and protein levels were significantly increased in the heart of mice with age. Therefore, we hypothesize that Pdcd5 regulates cardiac aging. To test the hypothesis, we generated muscle-specific Pdcd5-deficient mice. Mature adult Pdcd5-deficient mice had normal cardiac morphology and function. In naturally aged mice, Pdcd5 deficiency alleviated age-related cardiac phenotypes including reduced fibrosis and suppressed cardiomyocyte hypertrophy. Moreover, muscle-specific Pdcd5 deficiency attenuated cellular senescence in the heart as demonstrated by decreased number of senescence-associated β-galactosidase-positive cells, diminished p53, p21 and p16 expression, and reduced the senescence-associated secretory phenotype. Apoptotic cell death was reduced by Pdcd5 deficiency in the heart as revealed by terminal deoxynucleotidyl transferase dUTP nick end labeling assay, which was coincident with diminished Bcl-2-associated X protein, and enhanced B-cell lymphoma 2 and X-linked inhibitor of apoptosis protein expression. Mitochondrial quality in cardiomyocytes was improved by Pdcd5 deficiency through increased Parkin-mediated mitophagy. In addition, Pdcd5 deficiency alleviated doxorubicin-induced premature cellular senescence and cardiac aging. Furthermore, Pdcd5 protein abundance was significantly correlated with p53 protein abundance, and Pdcd5 interacted with p53 in the heart. Taken together, our results reveal that Pdcd5 deficiency attenuates cardiac aging by reducing cellular senescence and apoptosis, and increasing Parkin-mediated mitophagy, likely through p53. Pdcd5 is a novel regulator of cardiac aging and a potential therapeutic target.

Alginate oligosaccharide alleviates D-galactose-induced cardiac ageing via regulating myocardial mitochondria function and integrity in mice

Ageing is a crucial risk factor for the development of age‐related cardiovascular diseases. Therefore, the molecular mechanisms of ageing and novel anti‐ageing interventions need to be deeply studied. Alginate oligosaccharide (AOS) possesses high pharmacological activities and beneficial effects. Our study was undertaken to investigate whether AOS could be used as an anti‐ageing drug to alleviate cardiac ageing. D‐galactose (D‐gal)‐induced C57BL/6J ageing mice were established by subcutaneous injection of D‐gal (200 mg·kg^‐1·d^‐1) for 8 weeks. AOS (50, 100 and 150 mg·kg^‐1·d^‐1) were administrated intragastrically for the last 4 weeks. As a result, AOS prevented cardiac dysfunction in D‐gal‐induced ageing mice, including partially preserved ejection fraction (EF%) and fractional shortening (FS%). AOS inhibited D‐gal‐induced up‐regulation of natriuretic peptides A (ANP), brain natriuretic peptide (BNP) and ageing markers p53 and p21 in a dose‐dependent manner. To further explore the potential mechanisms contributing to the anti‐ageing protective effect of AOS, the age‐related mitochondrial compromise was analysed. Our data indicated that AOS alleviated D‐gal‐induced cardiac ageing by improving mitochondrial biogenesis, maintaining the mitochondrial integrity and enhancing the efficient removal of impaired mitochondria. AOS also decreased the ROS production and oxidative stress status, which, in turn, further inhibiting cardiac mitochondria from being destroyed. Together, these results demonstrate that AOS may be an effective therapeutic agent to alleviate cardiac ageing.

Translational Proteomics Analysis of Anthracycline-Induced Cardiotoxicity From Cardiac Microtissues to Human Heart Biopsies

Anthracyclines, including doxorubicin, idarubicin, and epirubicin, are common antitumor drugs as well as well-known cardiotoxic agents. This study analyzed the proteomics alteration in cardiac tissues caused by these 3 anthracyclines analogs. The in vitro human cardiac microtissues were exposed to drugs in 2 weeks; the proteomic data were measured at 7 time points. The heart biopsy data were collected from heart failure patients, in which some patients underwent anthracycline treatment. The anthracyclines-affected proteins were separately identified in the in vitro and in vivo dataset using the WGCNA method. These proteins engage in different cellular pathways including translation, metabolism, mitochondrial function, muscle contraction, and signaling pathways. From proteins detected in 2 datasets, a protein-protein network was established with 4 hub proteins, and 7 weighted proteins from both cardiac microtissue and human biopsies data. These 11 proteins, which involve in mitochondrial functions and the NF-κB signaling pathway, could provide insights into the anthracycline toxic mechanism. Some of them, such as HSPA5, BAG3, and SH3BGRL, are cardiac therapy targets or cardiotoxicity biomarkers. Other proteins, such as ATP5F1B and EEF1D, showed similar responses in both the in vitro and in vivo data. This suggests that the in vitro outcomes could link to clinical phenomena in proteomic analysis.

Tributyltin Alters Calcium Levels, Mitochondrial Dynamics, and Activates Calpains Within Dorsal Root Ganglion Neurons

Tributyltin (TBT) remains a global health concern. The primary route of human exposure to TBT is either through ingestion or skin absorption, but TBT's effects on the peripheral nervous system have still not been investigated. Therefore, we exposed in vitro sensory dorsal root ganglion (DRG) neurons to TBT at a concentration of 50-200 nM, which is similar to the observed concentrations of TBT in human blood samples. We observed that TBT causes extensive axon degeneration and neuronal death in the DRG neurons. Furthermore, we discovered that TBT causes an increase in both cytosolic and mitochondrial calcium levels, disrupts mitochondrial dynamics, decreases neuronal ATP levels, and leads to the activation of calpains. Additional experiments demonstrated that inhibition of calpain activation prevented TBT-induced fragmentation of neuronal cytoskeletal proteins and neuronal cell death. Thus, we conclude that calpain activation is the key executioner of TBT-induced peripheral neurodegeneration.

Mitophagy in Human Diseases

Mitophagy is a selective autophagic process, essential for cellular homeostasis, that eliminates dysfunctional mitochondria. Activated by inner membrane depolarization, it plays an important role during development and is fundamental in highly differentiated post-mitotic cells that are highly dependent on aerobic metabolism, such as neurons, muscle cells, and hepatocytes. Both defective and excessive mitophagy have been proposed to contribute to age-related neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, metabolic diseases, vascular complications of diabetes, myocardial injury, muscle dystrophy, and liver disease, among others. Pharmacological or dietary interventions that restore mitophagy homeostasis and facilitate the elimination of irreversibly damaged mitochondria, thus, could serve as potential therapies in several chronic diseases. However, despite extraordinary advances in this field, mainly derived from in vitro and preclinical animal models, human applications based on the regulation of mitochondrial quality in patients have not yet been approved. In this review, we summarize the key selective mitochondrial autophagy pathways and their role in prevalent chronic human diseases and highlight the potential use of specific interventions.

Ataxia Telangiectasia Mutated Protein Kinase: A Potential Master Puppeteer of Oxidative Stress-Induced Metabolic Recycling

Ataxia Telangiectasia Mutated protein kinase (ATM) has recently come to the fore as a regulatory protein fulfilling many roles in the fine balancing act of metabolic homeostasis. Best known for its role as a transducer of DNA damage repair, the activity of ATM in the cytosol is enjoying increasing attention, where it plays a central role in general cellular recycling (macroautophagy) as well as the targeted clearance (selective autophagy) of damaged mitochondria and peroxisomes in response to oxidative stress, independently of the DNA damage response. The importance of ATM activation by oxidative stress has also recently been highlighted in the clearance of protein aggregates, where the expression of a functional ATM construct that cannot be activated by oxidative stress resulted in widespread accumulation of protein aggregates. This review will discuss the role of ATM in general autophagy, mitophagy, and pexophagy as well as aggrephagy and crosstalk between oxidative stress as an activator of ATM and its potential role as a master regulator of these processes.

Mitophagy receptor FUNDC1 is regulated by PGC-1α/NRF1 to fine tune mitochondrial homeostasis

Mitophagy is an essential cellular autophagic process that selectively removes superfluous and damaged mitochondria, and it is coordinated with mitochondrial biogenesis to fine tune the quantity and quality of mitochondria. Coordination between these two opposing processes to maintain the functional mitochondrial network is of paramount importance for normal cellular and organismal metabolism. However, the underlying mechanism is not completely understood. Here we report that PGC-1α and nuclear respiratory factor 1 (NRF1), master regulators of mitochondrial biogenesis and metabolic adaptation, also transcriptionally upregulate the gene encoding FUNDC1, a previously characterized mitophagy receptor, in response to cold stress in brown fat tissue. NRF1 binds to the classic consensus site in the promoter of Fundc1 to upregulate its expression and to enhance mitophagy through its interaction with LC3. Specific knockout of Fundc1 in BAT results in reduced mitochondrial turnover and accumulation of functionally compromised mitochondria, leading to impaired adaptive thermogenesis. Our results demonstrate that FUNDC1-dependent mitophagy is directly coupled with mitochondrial biogenesis through the PGC-1α/NRF1 pathway, which dictates mitochondrial quantity, quality, and turnover and contributes to adaptive thermogenesis.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

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

Mitochondria as a therapeutic target for cardiac ischemia‑reperfusion injury (Review)

Acute myocardial infarction is the leading cause of cardiovascular-related mortality and chronic heart failure worldwide. As regards treatment, the reperfusion of ischemic tissue generates irreversible damage to the myocardium, which is termed 'cardiac ischemia-reperfusion (IR) injury'. Due to the large number of mitochondria in cardiomyocytes, an increasing number of studies have focused on the roles of mitochondria in IR injury. The primary causes of IR injury are reduced oxidative phosphorylation during hypoxia and the increased production of reactive oxygen species (ROS), together with the insufficient elimination of these oxidative species following reperfusion. IR injury includes the oxidation of DNA, incorrect modifications of proteins, the disruption of the mitochondrial membrane and respiratory chain, the loss of mitochondrial membrane potential (∆Ψm), Ca²⁺ over-load, mitochondrial permeability transition pore formation, swelling of the mitochondria, and ultimately, cardiomyocyte necrosis. The present review article discusses the molecular mechanisms of IR injury, and summarizes the metabolic and dynamic changes occurring in the mitochondria in response to IR stress. The mitochondria are strongly recommended as a target for the development of therapeutic agents; however, the appropriate use of agents remains a challenge.

Rejection-associated Mitochondrial Impairment After Heart Transplantation

Background.

Mitochondrial dysfunction is associated with poor allograft prognosis. Mitochondrial-related gene expression (GE) in endomyocardial biopsies (EMBs) could be useful as a nonimmune functional marker of rejection. We hypothesize that acute cardiac allograft rejection is associated with decreased mitochondrial-related GE in EMBs.

Methods.

We collected 64 routines or clinically indicated EMB from 47 patients after heart transplant. The EMBs were subjected to mRNA sequencing. We conducted weighted gene coexpression network analysis to construct module-derived eigengenes. The modules were assessed by gene ontology enrichment and hub gene analysis. Modules were correlated with the EMBs following the International Society of Heart and Lung Transplantation histology-based criteria and a classification based on GE alone; we also correlated with clinical parameters.

Results.

The modules enriched with mitochondria-related and immune-response genes showed the strongest correlation to the clinical traits. Compared with the no-rejection samples, rejection samples had a decreased activity of mitochondrial-related genes and an increased activity of immune-response genes. Biologic processes and hub genes in the mitochondria-related modules were primarily involved with energy generation, substrate metabolism, and regulation of oxidative stress. Compared with International Society of Heart and Lung Transplantation criteria, GE-based classification had stronger correlation to the weighted gene coexpression network analysis–derived functional modules. The brain natriuretic peptide level, ImmuKnow, and Allomap scores had negative relationships with the expression of mitochondria-related modules and positive relationships with immune-response modules.

Conclusions.

During acute cardiac allograft rejection, there was a decreased activity of mitochondrial-related genes, related to an increased activity of immune-response genes, and depressed allograft function manifested by brain natriuretic peptide elevation. This suggests a rejection-associated mitochondrial impairment.

Targeting ER stress and calpain activation to reverse age-dependent mitochondrial damage in the heart

Severity of cardiovascular disease increases markedly in elderly patients. In addition, many therapeutic strategies that decrease cardiac injury in adult patients are invalid in elderly patients. Thus, it is a challenge to protect the aged heart in the context of underlying chronic or acute cardiac diseases including ischemia-reperfusion injury. The cause(s) of this age-related increased damage remain unknown. Aging impairs the function of the mitochondrial electron transport chain (ETC), leading to decreased energy production and increased oxidative stress due to generation of reactive oxygen species (ROS). Additionally, ROS-induced oxidative stress can increase cardiac injury during ischemia-reperfusion by potentiating mitochondrial permeability transition pore (MPTP) opening. Aging leads to increased endoplasmic reticulum (ER) stress, which contributes to mitochondrial dysfunction, including reduced function of the ETC. The activation of both cytosolic and mitochondrial calcium-activated proteases termed calpains leads to mitochondrial dysfunction and decreased ETC function. Intriguingly, mitochondrial ROS generation also induces ER stress, highlighting the dynamic interaction between mitochondria and ER. Here, we discuss the role of ER stress in sensitizing and potentiating mitochondrial dysfunction in response to ischemia-reperfusion, and the promising potential therapeutic benefit of inhibition of ER stress and / or calpains to attenuate cardiac injury in elderly patients.

Endoplasmic reticulum stress-mediated mitochondrial dysfunction in aged hearts

Aging impairs the mitochondrial electron transport chain (ETC), especially in interfibrillar mitochondria (IFM). Mitochondria are in close contact with the endoplasmic reticulum (ER). Induction of ER stress leads to ETC injury in adult heart mitochondria. We asked if ER stress contributes to the mitochondrial dysfunction during aging. Subsarcolemmal mitochondria (SSM) and IFM were isolated from 3, 18, and 24 mo. C57Bl/6 mouse hearts. ER stress progressively increased with age, especially in 24 mo. mice that manifest mitochondrial dysfunction. OXPHOS was decreased in 24 mo. IFM oxidizing complex I and complex IV substrates. Proteomic analysis showed that the content of multiple complex I subunits was decreased in IFM from 24 mo. hearts, but remained unchanged in in 18 mo. IFM without a decrease in OXPHOS. Feeding 24 mo. old mice with 4-phenylbutyrate (4-PBA) for two weeks attenuated the ER stress and improved mitochondrial function. These results indicate that ER stress contributes to the mitochondrial dysfunction in aged hearts. Attenuation of ER stress is a potential approach to improve mitochondrial function in aged hearts.

Overexpression of PGC-1α influences the mitochondrial unfolded protein response (mtUPR) induced by MPP+ in human SH-SY5Y neuroblastoma cells

Parkinson’s disease (PD) is a common dyskinesia disease, the mitochondrial unfolded protein response (mtUPR) may be directly or indirectly involved in the occurrence and development of PD, although the exact mechanism is unclear. We established a dopaminergic neuronal-like cell model of PD, by overexpression of PGC-1α to detect evaluate the expression of proteases and molecular chaperones of involved in the mtUPR, as well as the expression of PGC-1α and LRPPRC, illustrated the distribution of LRPPRC. Remarkably, the mtUPR activation reached maximal at 24 h after MPP⁺ treatment in SH-SY5Y cells, which the protein and transcription levels of the proteases and molecular chaperones reached maximal. The proteases and molecular chaperones were significantly increased when overexpressed PGC-1α, which indicated that PGC-1α overexpression activated the mtUPR, and PGC-1α had a protective effect on SH-SY5Y cells. The expression levels of PGC-1α and LRPPRC were significantly improved in the PGC-1α overexpression groups. LRPPRC was markedly reduced in the nucleus, suggesting that PGC-1α overexpression may play a protective role to the mitochondria through LRPPRC. Our finding indicates that overexpression of PGC-1α may activate mtUPR, reducing the oxidative stress injury induced by MPP⁺ through LRPPRC signaling, thus maintain mitochondrial homeostasis.

A Mitochondrial Approach to Cardiovascular Risk and Disease

BACKGROUND

Cardiovascular diseases (CVDs) are a leading risk factor for mortality worldwide and the number of CVDs victims is predicted to rise through 2030. While several external parameters (genetic, behavioral, environmental and physiological) contribute to cardiovascular morbidity and mortality; intrinsic metabolic and functional determinants such as insulin resistance, hyperglycemia, inflammation, high blood pressure and dyslipidemia are considered to be dominant factors.

METHODS

Pubmed searches were performed using different keywords related with mitochondria and cardiovascular disease and risk. In vitro, animal and human results were extracted from the hits obtained.

RESULTS

High cardiac energy demand is sustained by mitochondrial ATP production, and abnormal mitochondrial function has been associated with several lifestyle- and aging-related pathologies in the developed world such as diabetes, non-alcoholic fatty liver disease (NAFLD) and kidney diseases, that in turn can lead to cardiac injury. In order to delay cardiac mitochondrial dysfunction in the context of cardiovascular risk, regular physical activity has been shown to improve mitochondrial parameters and myocardial tolerance to ischemia-reperfusion (IR). Furthermore, pharmacological interventions can prevent the risk of CVDs. Therapeutic agents that can target mitochondria, decreasing ROS production and improve its function have been intensively researched. One example is the mitochondria-targeted antioxidant MitoQ10, which already showed beneficial effects in hypertensive rat models. Carvedilol or antidiabetic drugs also showed protective effects by preventing cardiac mitochondrial oxidative damage.

CONCLUSION

This review highlights the role of mitochondrial dysfunction in CVDs, also show-casing several approaches that act by improving mitochondrial function in the heart, contributing to decrease some of the risk factors associated with CVDs.

Sirtuin1 Role in the Melatonin Protective Effects Against Obesity-Related Heart Injury

Obesity is a worldwide epidemic disease that induces important structural and functional changes to the heart and predisposes a patient to devastating cardiac complications. Sirtuin1 (SIRT1) has been found to have roles in regulating cardiac function, but whether it can help in cardioprotection is not clear. The aim of the present study was to determine whether melatonin, by modulating SIRT1 and in turn mitochondria signaling, may alleviate obesity-induced cardiac injuries. We investigated 10 lean control mice and 10 leptin-deficient obese mice (ob/ob) orally supplemented with melatonin for 8 weeks, as well as equal numbers of age-matched lean and ob/ob mice that did not receive melatonin. Hearts were evaluated using multiple parameters, including biometric values, morphology, SIRT1 activity and expression of markers of mitochondria biogenesis, oxidative stress, and inflammation. We observed that ob/ob mice experienced significant heart hypertrophy, infiltration by inflammatory cells, reduced SIRT1 activity, altered mitochondrial signaling and oxidative balance, and overexpression of inflammatory markers. Notably, melatonin supplementation in ob/ob mice reverted these obesogenic heart alterations. Melatonin prevented heart remodeling caused by obesity through SIRT1 activation, which, together with mitochondrial pathways, reduced oxidative stress and inflammation.

Decrease of Cardiac Parkin Protein in Obese Mice

Mitophagy plays a major role in heart physiology. Impairment of Parkin-dependent mitophagy in heart is known to be deleterious. Obesity is a known cardiovascular risk factor. Impaired autophagy has been reported in models of obesity or hyperlipidemia/hypercholesterolemia; however less is known regarding obesity and mitophagy. The aim of this study was to evaluate the regulation of Parkin expression in hearts of mice fed a high fat diet. Interestingly, we found a significant decrease in Parkin protein in hearts of HFD mice compared those fed a low-fat diet. This was associated with mitochondrial dysfunction in the context of ischemia/reperfusion (I/R). This downregulation was not associated with a decrease in Parkin mRNA expression. We did not detect any change in the degradation rate of Parkin and only a slight decrease in its translation. The reduction of Parkin protein abundance in HFD hearts remains a mystery and will need further studies. However, Parkin depletion in the setting of obesity may contribute to cardiovascular risk.

Spermidine alleviates cardiac aging by improving mitochondrial biogenesis and function

Polyamines have been shown to delay cellular and organismal aging and to provide cardiovascular protection in humans. Because age-related cardiovascular dysfunction is often accompanied by impaired mitochondrial biogenesis and function, we explored the ability of spermidine (SPD), a major mammalian polyamine, to attenuate cardiac aging through activation of mitochondrial biogenesis. Cardiac polyamine levels were reduced in aged (24-month-old) rats. Six-week SPD supplementation restored cardiac polyamine content, preserved myocardial ultrastructure, and inhibited mitochondrial dysfunction. Immunoblotting showed that ornithine decarboxylase (ODC) and SPD/spermine N1-acetyltransferase (SSAT) were downregulated and upregulated, respectively, in the myocardium of older rats. These changes were paralleled by age-dependent downregulation of components of the sirtuin-1/peroxisome proliferator-activated receptor gamma coactivator alpha (SIRT1/PGC-1α) signaling pathway, an important regulator of mitochondrial biogenesis. SPD administration increased SIRT1, PGC-1α, nuclear respiratory factors 1 and 2 (NRF1, NRF2), and mitochondrial transcription factor A (TFAM) expression; decreased ROS production; and improved OXPHOS performance in senescent (H₂O₂-treated) cardiomyocytes. Inhibition of polyamine biosynthesis or SIRT1 activity abolished these effects. PGC-1α knockdown experiments confirmed that SPD activated mitochondrial biogenesis through SIRT1-mediated deacetylation of PGC-1α. These data provide new insight into the antiaging effects of SPD, and suggest potential applicability to protect against deterioration of cardiac function with aging.

miR-218 Inhibits Mitochondrial Clearance by Targeting PRKN E3 Ubiquitin Ligase

The selective elimination of dysfunctional mitochondria through mitophagy is crucial for preserving mitochondrial quality and cellular homeostasis. The most described mitophagy pathway is regulated by a positive ubiquitylation feedback loop in which the PINK1 (PTEN induced kinase 1) kinase phosphorylates both ubiquitin and the E3 ubiquitin ligase PRKN (Parkin RBR E3 ubiquitin ligase), also known as PARKIN. This event recruits PRKN to the mitochondria, thus amplifying ubiquitylation signal. Here we report that miR-218 targets PRKN and negatively regulates PINK1/PRKN-mediated mitophagy. Overexpression of miR-218 reduces PRKN mRNA levels, thus also reducing protein content and deregulating the E3 ubiquitin ligase action. In fact, following miR-218 overexpression, mitochondria result less ubiquitylated and the autophagy machinery fails to proceed with correct mitochondrial clearance. Since mitophagy defects are associated with various human diseases, these results qualify miR-218 as a promising therapeutic target for human diseases.

Mitochondrial Dysfunction in Cardiac Surgery

Mitochondria are key to the cellular response to energetic demand, but are also vital to reactive oxygen species signaling, calcium hemostasis, and regulation of cell death. Cardiac surgical patients with diabetes, heart failure, advanced age, or cardiomyopathies may have underlying mitochondrial dysfunction or be more sensitive to perioperative mitochondrial injury. Mitochondrial dysfunction, due to ischemia/reperfusion injury and an increased systemic inflammatory response due to exposure to cardiopulmonary bypass and surgical tissue trauma, impacts myocardial contractility and predisposes to arrhythmias. Strategies for perioperative mitochondrial protection and recovery include both well-established cardioprotective protocols and targeted therapies that remain under investigation.

Inhibition of the ubiquitous calpains protects complex I activity and enables improved mitophagy in the heart following ischemia-reperfusion

Activation of calpain 1 (CPN1) and calpain 2 (CPN2) contributes to cardiac injury during ischemia (ISC) and reperfusion (REP). Complex I activity is decreased in heart mitochondria following ISC-REP. CPN1 and CPN2 are ubiquitous calpains that exist in both cytosol (cs)-CPN1 and 2 and mitochondria (mit)-CPN1 and 2. Recent work shows that the complex I subunit (NDUFS7) is a potential substrate of the mit-CPN1. We asked whether ISC-REP led to decreased complex I activity via proteolysis of the NDUFS7 subunit via activation of mit-CPN1 and -2. Activation of cs-CPN1 and -2 decreases mitophagy in hepatocytes following ISC-REP. We asked whether activation of cs-CPN1 and -2 impaired mitophagy in the heart following ISC-REP. Buffer-perfused rat hearts underwent 25 min of global ISC and 30 min of REP. MDL-28170 (MDL; 10 µM) was used to inhibit CPN1 and -2. Cytosol, subsarcolemmal mitochondria (SSM), and interfibrillar mitochondria (IFM) were isolated at the end of heart perfusion. Cardiac ISC-REP led to decreased complex I activity with a decrease in the content of NDUFS7 in both SSM and IFM. ISC-REP also resulted in a decrease in cytosolic beclin-1 content, a key component of the autophagy pathway required to form autophagosomes. MDL treatment protected the contents of cytosolic beclin-1 and mitochondrial NDUFS7 in hearts following ISC-REP. These results support that activation of both cytosolic and mitochondrial calpains impairs mitochondria during cardiac ISC-REP. Mitochondria-localized calpains impair complex I via cleavage of a key subunit. Activation of cytosolic calpains contributes to mitochondrial dysfunction by impairing removal of the impaired mitochondria through depletion of a key component of the mitophagy process.

Pathogenesis of cardiac ischemia reperfusion injury is associated with CK2α-disturbed mitochondrial homeostasis via suppression of FUNDC1-related mitophagy

Disturbed mitochondrial homeostasis contributes to the pathogenesis of cardiac ischemia reperfusion (IR) injury, although the underlying mechanism remains elusive. Here, we demonstrated that casein kinase 2α (CK2α) was upregulated following acute cardiac IR injury. Increased CK2α was shown to be instrumental to mitochondrial damage, cardiomyocyte death, infarction area expansion and cardiac dysfunction, whereas cardiac-specific CK2α knockout (CK2α^CKO) mice were protected against IR injury and mitochondrial damage. Functional assay indicated that CK2α enhanced the phosphorylation (inactivation) of FUN14 domain containing 1 (FUNDC1) via post-transcriptional modification at Ser13, thus effectively inhibiting mitophagy. Defective mitophagy failed to remove damaged mitochondria induced by IR injury, resulting in mitochondrial genome collapse, electron transport chain complex (ETC) inhibition, mitochondrial biogenesis arrest, cardiolipin oxidation, oxidative stress, mPTP opening, mitochondrial debris accumulation and eventually mitochondrial apoptosis. In contrast, loss of CK2α reversed the FUNDC1-mediated mitophagy, providing a survival advantage to myocardial tissue following IR stress. Interestingly, mice deficient in both CK2α and FUNDC1 failed to show protection against IR injury and mitochondrial damage through a mechanism possible attributed to lack of mitophagy. Taken together, our results confirmed that CK2α serves as a negative regulator of mitochondrial homeostasis via suppression of FUNDC1-required mitophagy, favoring the development of cardiac IR injury.

Fisetin Confers Cardioprotection against Myocardial Ischemia Reperfusion Injury by Suppressing Mitochondrial Oxidative Stress and Mitochondrial Dysfunction and Inhibiting Glycogen Synthase Kinase 3β Activity

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide. Timely reperfusion is considered an optimal treatment for AMI. Paradoxically, the procedure of reperfusion can itself cause myocardial tissue injury. Therefore, a strategy to minimize the reperfusion-induced myocardial tissue injury is vital for salvaging the healthy myocardium. Herein, we investigated the cardioprotective effects of fisetin, a natural flavonoid, against ischemia/reperfusion (I/R) injury (IRI) using a Langendorff isolated heart perfusion system. I/R produced significant myocardial tissue injury, which was characterized by elevated levels of lactate dehydrogenase and creatine kinase in the perfusate and decreased indices of hemodynamic parameters. Furthermore, I/R resulted in elevated oxidative stress, uncoupling of the mitochondrial electron transport chain, increased mitochondrial swelling, a decrease of the mitochondrial membrane potential, and induction of apoptosis. Moreover, IRI was associated with a loss of the mitochondrial structure and decreased mitochondrial biogenesis. However, when the animals were pretreated with fisetin, it significantly attenuated the I/R-induced myocardial tissue injury, blunted the oxidative stress, and restored the structure and function of mitochondria. Mechanistically, the fisetin effects were found to be mediated via inhibition of glycogen synthase kinase 3β (GSK3β), which was confirmed by a biochemical assay and molecular docking studies.

Mitochondria and Sex-Specific Cardiac Function

The focus of this chapter is the gender differences in mitochondria in cardiovascular disease. There is broad evidence suggesting that some of the gender differences in cardiovascular outcome may be partially related to differences in mitochondrial biology (Ventura-Clapier R, Moulin M, Piquereau J, Lemaire C, Mericskay M, Veksler V, Garnier A, Clin Sci (Lond) 131(9):803-822, 2017)). Mitochondrial disorders are causally affected by mutations in either nuclear or mitochondrial genes involved in the synthesis of respiratory chain subunits or in their posttranslational control. This can be due to mutations of the mtDNA which are transmitted by the mother or mutations in the nuclear DNA. Because natural selection on mitochondria operates only in females, mutations may have had more deleterious effects in males than in females (Ventura-Clapier R, Moulin M, Piquereau J, Lemaire C, Mericskay M, Veksler V, Garnier A, Clin Sci (Lond) 131(9):803-822, 2017; Camara AK, Lesnefsky EJ, Stowe DF. Antioxid Redox Signal 13(3):279-347, 2010). As mitochondrial mutations can affect all tissues, they are responsible for a large panel of pathologies including neuromuscular disorders, encephalopathies, metabolic disorders, cardiomyopathies, neuropathies, renal dysfunction, etc. Many of these pathologies present sex/gender specificity. Thus, alleviating or preventing mitochondrial dysfunction will contribute to mitigating the severity or progression of the development of diseases. Here, we present evidence for the involvement of mitochondria in the sex specificity of cardiovascular disorders.