Mitochondrial fission and autophagy in the normal and diseased heart

Deletion of Sigmar1 leads to increased arterial stiffness and altered mitochondrial respiration resulting in vascular dysfunction

Sigmar1 is a ubiquitously expressed, multifunctional protein known for its cardioprotective roles in cardiovascular diseases. While accumulating evidence indicate a critical role of Sigmar1 in cardiac biology, its physiological function in the vasculature remains unknown. In this study, we characterized the expression of Sigmar1 in the vascular wall and assessed its physiological function in the vascular system using global Sigmar1 knockout (Sigmar1-/-) mice. We determined the expression of Sigmar1 in the vascular tissue using immunostaining and biochemical experiments in both human and mouse blood vessels. Deletion of Sigmar1 globally in mice (Sigmar1-/-) led to blood vessel wall reorganizations characterized by nuclei disarray of vascular smooth muscle cells, altered organizations of elastic lamina, and higher collagen fibers deposition in and around the arteries compared to wildtype littermate controls (Wt). Vascular function was assessed in mice using non-invasive time-transit method of aortic stiffness measurement and flow-mediated dilation (FMD) of the left femoral artery. Sigmar1-/- mice showed a notable increase in arterial stiffness in the abdominal aorta and failed to increase the vessel diameter in response to reactive-hyperemia compared to Wt. This was consistent with reduced plasma and tissue nitric-oxide bioavailability (NOx) and decreased phosphorylation of endothelial nitric oxide synthase (eNOS) in the aorta of Sigmar1-/- mice. Ultrastructural analysis by transmission electron microscopy (TEM) of aorta sections showed accumulation of elongated shaped mitochondria in both vascular smooth muscle and endothelial cells of Sigmar1-/- mice. In accordance, decreased mitochondrial respirometry parameters were found in ex-vivo aortic rings from Sigmar1 deficient mice compared to Wt controls. These data indicate a potential role of Sigmar1 in maintaining vascular homeostasis.

Mzb1 Attenuates Atherosclerotic Plaque Vulnerability in ApoE-/- Mice by Alleviating Apoptosis and Modulating Mitochondrial Function

In this study, we investigated the protective role of Mzb1 in atherosclerotic plaque vulnerability. To explore the impact of Mzb1, we analyzed Mzb1 expression, assessed apoptosis, and evaluated mitochondrial function in atherosclerosis (AS) mouse models and human vascular smooth muscle cells (HVSMCs). We observed a significant decrease in Mzb1 expression in AS mouse models and ox-LDL-treated HVSMCs. Downregulation of Mzb1 increased ox-LDL-induced apoptosis and cholesterol levels of HVSMCs, while Mzb1 overexpression alleviated these effect. Mzb1 was found to enhance mitochondrial function, as evidenced by restored ATP synthesis, mitochondrial membrane potential, and reduced mtROS production. Moreover, Mzb1 overexpression attenuated atherosclerotic plaque vulnerability in ApoE-/- mice. Our findings suggest that Mzb1 overexpression regulates the AMPK/SIRT1 signaling pathway, leading to the attenuation of atherosclerotic plaque vulnerability. This study provides compelling evidence for the protective effect of Mzb1 on atherosclerotic plaques by alleviating apoptosis and modulating mitochondrial function in ApoE-/- mice.

GPR84-mediated signal transduction affects metabolic function by promoting brown adipocyte activity

The G protein-coupled receptor 84 (GPR84), a medium-chain fatty acid receptor, has garnered attention because of its potential involvement in a range of metabolic conditions. However, the precise mechanisms underlying this effect remain elusive. Our study has shed light on the pivotal role of GPR84, revealing its robust expression and functional significance within brown adipose tissue (BAT). Mice lacking GPR84 exhibited increased lipid accumulation in BAT, rendering them more susceptible to cold exposure and displaying reduced BAT activity compared with their WT counterparts. Our in vitro experiments with primary brown adipocytes from GPR84-KO mice revealed diminished expression of thermogenic genes and reduced O2 consumption. Furthermore, the application of the GPR84 agonist 6-n-octylaminouracil (6-OAU) counteracted these effects, effectively reinstating the brown adipocyte activity. These compelling in vivo and in vitro findings converge to highlight mitochondrial dysfunction as the primary cause of BAT anomalies in GPR84-KO mice. The activation of GPR84 induced an increase in intracellular Ca2+ levels, which intricately influenced mitochondrial respiration. By modulating mitochondrial Ca2+ levels and respiration, GPR84 acts as a potent molecule involved in BAT activity. These findings suggest that GPR84 is a potential therapeutic target for invigorating BAT and ameliorating metabolic disorders.

The Role of Mitochondria in Phytochemically Mediated Disease Amelioration

Mitochondrial dysfunction may cause cell death, which has recently emerged as a cancer prevention and treatment strategy mediated by chemotherapy drugs or phytochemicals. However, most existing drugs cannot target cancerous cells and may adversely affect normal cells via side effects. Mounting studies have revealed that phytochemicals such as resveratrol could ameliorate various diseases with dysfunctional or damaged mitochondria. For instance, resveratrol can regulate mitophagy, inhibit oxidative stress and preserve membrane potential, induce mitochondrial biogenesis, balance mitochondrial fusion and fission, and enhance the functionality of the electron transport chain. However, there are only a few studies suggesting that phytochemicals could potentially protect against the cytotoxicity of some current cancer drugs, especially those that damage mitochondria. Besides, COVID-19 and long COVID have also been reported to be correlated to mitochondrial dysfunction. Curcumin has been reported bringing a positive impact on COVID-19 and long COVID. Therefore, in this study, the benefits of resveratrol and curcumin to be applied for cancer treatment/prevention and disease amelioration were reviewed. Besides, this review also provides some perspectives on phytochemicals to be considered as a treatment adjuvant for COVID-19 and long COVID by targeting mitochondrial rescue. Hopefully, this review can provide new insight into disease treatment with phytochemicals targeting mitochondria.

gp130 Activates Mitochondrial Dynamics for Hepatocyte Survival in a Model of Steatohepatitis

Obesity is the main cause of metabolic complications. Fatty liver infiltration is a companion of obesity. NAFLD is associated with impaired energy metabolism with an excess of nutrients. Mitochondrial dynamics are important for the regulation of energy balance, which regulates mitochondrial function, apoptosis, and mitophagy. The aim of this study was to investigate the effect of gp130 on the components of mitochondrial dynamics in a cellular model of steatohepatitis. Addition of IL-6/gp130 contributed to an increase in the percentage of live cells and a decrease in the percentage of dead and apoptotic cells. Addition of IL-6/gp130 increased the expression of NF-kB1 gene and mitochondrial dynamics markers (MFN2 and TFAM) in HepG2 with tBHP/Oleic. Addition of IL-6 or gp130 reduced the expression of cytoprotector genes (HSF1 and HSP70) in HepG2 cell cultures with tBHP/Oleic. Increased mitochondrial dynamics gene activity protected against HepG2 cell death in the steatohepatitis model. Trans-signaling resulted in increased TFAM and MAPLC3B, and decreased DNM1L gene expression in HepG2 with tBHP/Oleic.

Mitochondrial Dysfunction: The Hidden Player in the Pathogenesis of Atherosclerosis?

Atherosclerosis is a multifactorial inflammatory pathology that involves metabolic processes. Improvements in therapy have drastically reduced the prognosis of cardiovascular disease. Nevertheless, a significant residual risk is still relevant, and is related to unmet therapeutic targets. Endothelial dysfunction and lipid infiltration are the primary causes of atherosclerotic plaque progression. In this contest, mitochondrial dysfunction can affect arterial wall cells, in particular macrophages, smooth muscle cells, lymphocytes, and endothelial cells, causing an increase in reactive oxygen species (ROS), leading to oxidative stress, chronic inflammation, and intracellular lipid deposition. The detection and characterization of mitochondrial DNA (mtDNA) is crucial for assessing mitochondrial defects and should be considered the goal for new future therapeutic interventions. In this review, we will focus on a new idea, based on the analysis of data from many research groups, namely the link between mitochondrial impairment and endothelial dysfunction and, in particular, its effect on atherosclerosis and aging. Therefore, we discuss known and novel mitochondria-targeting therapies in the contest of atherosclerosis.

The world's first (and probably last) autophagy video game

Macroautophagy/autophagy is the process by which portions of the cytoplasm are sequestered within a transient compartment and delivered to the degradative organelle of the cell, the vacuole or lysosome. Autophagy is a fundamental cytoprotective mechanism, and defects in this process are associated with many diseases. For example, the inability to degrade certain cargo such as mitochondria may lead to neurodegenerative disorders such as Parkinson disease. Autophagic cargo can be many different things including organelles, but also proteins and protein aggregates, nucleic acids, and lipids. Much of our understanding of autophagy comes from studies in baker's yeast, Saccharomyces cerevisiae. In that organism, autophagy begins at the phagophore assembly site (PAS), which nucleates the initial sequestering compartment, referred to as a phagophore. With the help of autophagy-related (Atg) proteins and lipid addition, the phagophore membrane expands to enclose damaged or superfluous cytoplasmic components, eventually closing into a completed double-membrane vesicle called the autophagosome. The autophagosome is delivered to the degradative organelle where it fuses, releasing the encapsulated cargo into the interior of the organelle where it is broken down into macromolecular building blocks. The resulting building blocks are released back into the cytosol for reuse. Video games are modern expressions of art incorporating illustration, animation, and mechanistic design. While often underappreciated as a scientific art form, video games can beautifully express scientific topics in a way that is both intuitive and engaging, especially to a younger audience.

VH-4-A Bioactive Peptide from Soybean and Exercise Training Constrict Hypertension in Rats through Activating Cell Survival and AMPKα1, Sirt1, PGC1α, and FoX3α

Hypertension is a chronic disease related to age, which affects tens of millions of people around the world. It is an important risk factor that causes myocardial infarction, heart failure, stroke, and kidney damage. Bioactive peptide VHVV (VH-4) from soybean has shown several biological activities. Physical exercise is a cornerstone of non-pharmacologic treatment for hypertension and has established itself as an effective and complementary strategy for managing hypertension. The present study evaluates the efficacy of VH-4 supplement and swimming exercise training in preventing hypertension in spontaneously hypertensive rats (SHR). SHR animals were treated with VH-4 (25 mg/kg by intraperitoneal administration) and swimming exercise (1 h daily) for eight weeks, and the hemodynamic parameters, histology, and cell survival pathway protein expression were examined. In SHR rats, increased heart weight, blood pressure, and histological aberrations were observed. Cell survival protein p-PI3K and p-AKT and antiapoptosis proteins Bcl2 and Bcl-XL expression decreased in SHR animals. SIRT1 and FOXO3 were decreased in hypertensive rats. Both bioactive peptide VH-4 treatment and swimming exercise training in hypertensive rats increased the cell survival proteins p-PI3K and p-AKT and AMPKα1, Sirt1, PGC1α, and FoX3α proteins. Soy peptide VH-4, along with exercise, acts synergistically and prevents hypertension by activating cell survival and AMPKα1, Sirt1, PGC1α, and FoX3α proteins.

Therapeutic potential and recent advances on targeting mitochondrial dynamics in cardiac hypertrophy: A concise review

Pathological cardiac hypertrophy begins as an adaptive response to increased workload; however, sustained hemodynamic stress will lead it to maladaptation and eventually cardiac failure. Mitochondria, being the powerhouse of the cells, can regulate cardiac hypertrophy in both adaptive and maladaptive phases; they are dynamic organelles that can adjust their number, size, and shape through a process called mitochondrial dynamics. Recently, several studies indicate that promoting mitochondrial fusion along with preventing mitochondrial fission could improve cardiac function during cardiac hypertrophy and avert its progression toward heart failure. However, some studies also indicate that either hyperfusion or hypo-fission could induce apoptosis and cardiac dysfunction. In this review, we summarize the recent knowledge regarding the effects of mitochondrial dynamics on the development and progression of cardiac hypertrophy with particular emphasis on the regulatory role of mitochondrial dynamics proteins through the genetic, epigenetic, and post-translational mechanisms, followed by discussing the novel therapeutic strategies targeting mitochondrial dynamic pathways.

Cardiac Aging: From Basic Research to Therapeutics

With research progress on longevity, we have gradually recognized that cardiac aging causes changes in heart structure and function, including progressive myocardial remodeling, left ventricular hypertrophy, and decreases in systolic and diastolic function. Elucidating the regulatory mechanisms of cardiac aging is a great challenge for biologists and physicians worldwide. In this review, we discuss several key molecular mechanisms of cardiac aging and possible prevention and treatment methods developed in recent years. Insights into the process and mechanism of cardiac aging are necessary to protect against age-related diseases, extend lifespan, and reduce the increasing burden of cardiovascular disease in elderly individuals. We believe that research on cardiac aging is entering a new era of unique significance for the progress of clinical medicine and social welfare.

Mitochondrial scenario: roles of mitochondrial dynamics in acute myocardial ischemia/reperfusion injury

The main therapeutic strategy currently used for acute myocardial infarction (AMI) is to open occluded coronary arteries, a process defined as blood reperfusion. However, blood reperfusion will increase cardiac mortality, tissue damage and cardiac dysfunction in patients with AMI, which is mechanically defined as "ischemia/reperfusion (I/R) injury". It is currently believed that mitochondrial dynamics plays a key role in myocardial I/R, especially excessive mitochondrial fission, which is the main cause of cardiac dysfunction. Therefore, in the process of I/R injury, effective drug intervention and correct treatment strategies can be used to regulate mitochondrial dynamic balance to combat ischemia-reperfusion injury, which can play a huge role in improving the prognosis of patients. This review summarized the effects of mitochondrial fission and mitochondrial fusion balance on myocardial and mitochondrial functional changes during myocardial I/R injury. Finally, combined with the previous injury mechanisms, this review also briefly described some drug intervention that may be beneficial to clinical practice to improve the postoperative quality of life of patients with AMI.

ER membranes associated with mitochondria: Possible therapeutic targets in heart-associated diseases

Cardiovascular system cell biology is tightly regulated and mitochondria play a relevant role in maintaining heart function. In recent decades, associations between such organelles and the sarco/endoplasmic reticulum (SR) have been raised great interest. Formally identified as mitochondria-associated SR membranes (MAMs), these structures regulate different cellular functions, including calcium management, lipid metabolism, autophagy, oxidative stress, and management of unfolded proteins. In this review, we highlight MAMs' alterations mainly in cardiomyocytes, linked with cardiovascular diseases, such as cardiac ischemia-reperfusion, heart failure, and dilated cardiomyopathy. We also describe proteins that are part of the MAMs' machinery, as the FUN14 domain containing 1 (FUNDC1), the sigma 1 receptor (Sig-1R) and others, which might be new molecular targets to preserve the function and structure of the heart in such diseases. Understanding the machinery of MAMs and its function demands our attention, as such knowledge might contribute to strengthen the role of these relative novel structures in heart diseases.

Stress-Induced Cyclin C Translocation Regulates Cardiac Mitochondrial Dynamics

Background Nuclear-to-mitochondrial communication regulating gene expression and mitochondrial function is a critical process following cardiac ischemic injury. In this study, we determined that cyclin C, a component of the Mediator complex, regulates cardiac and mitochondrial function in part by modifying mitochondrial fission. We tested the hypothesis that cyclin C functions as a transcriptional cofactor in the nucleus and a signaling molecule stimulating mitochondrial fission in response to stimuli such as cardiac ischemia. Methods and Results We utilized gain- and loss-of-function mouse models in which the CCNC (cyclin C) gene was constitutively expressed (transgenic, CycC cTg) or deleted (knockout, CycC cKO) in cardiomyocytes. The knockout and transgenic mice exhibited decreased cardiac function and altered mitochondria morphology. The hearts of knockout mice had enlarged mitochondria with increased length and area, whereas mitochondria from the hearts of transgenic mice were significantly smaller, demonstrating a role for cyclin C in regulating mitochondrial dynamics in vivo. Hearts from knockout mice displayed altered gene transcription and metabolic function, suggesting that cyclin C is essential for maintaining normal cardiac function. In vitro and in vivo studies revealed that cyclin C translocates to the cytoplasm, enhancing mitochondria fission following stress. We demonstrated that cyclin C interacts with Cdk1 (cyclin-dependent kinase 1) in vivo following ischemia/reperfusion injury and that, consequently, pretreatment with a Cdk1 inhibitor results in reduced mitochondrial fission. This finding suggests a potential therapeutic target to regulate mitochondrial dynamics in response to stress. Conclusions Our study revealed that cyclin C acts as a nuclear-to-mitochondrial signaling factor that regulates both cardiac hypertrophic gene expression and mitochondrial fission. This finding provides new insights into the regulation of cardiac energy metabolism following acute ischemic injury.

Unlocking the Secrets of Mitochondria in the Cardiovascular System: Path to a Cure in Heart Failure—A Report from the 2018 National Heart, Lung, and Blood Institute Workshop

Mitochondria have emerged as a central factor in the pathogenesis and progression of heart failure, and other cardiovascular diseases, as well, but no therapies are available to treat mitochondrial dysfunction. The National Heart, Lung, and Blood Institute convened a group of leading experts in heart failure, cardiovascular diseases, and mitochondria research in August 2018. These experts reviewed the current state of science and identified key gaps and opportunities in basic, translational, and clinical research focusing on the potential of mitochondria-based therapeutic strategies in heart failure. The workshop provided short- and long-term recommendations for moving the field toward clinical strategies for the prevention and treatment of heart failure and cardiovascular diseases by using mitochondria-based approaches.

The impact of exercise on mitochondrial dynamics and the role of Drp1 in exercise performance and training adaptations in skeletal muscle

OBJECTIVE

Mitochondria are organelles primarily responsible for energy production, and recent evidence indicates that alterations in size, shape, location, and quantity occur in response to fluctuations in energy supply and demand. We tested the impact of acute and chronic exercise on mitochondrial dynamics signaling and determined the impact of the mitochondrial fission regulator Dynamin related protein (Drp)1 on exercise performance and muscle adaptations to training.

METHODS

Wildtype and muscle-specific Drp1 heterozygote (mDrp1+/-) mice, as well as dysglycemic (DG) and healthy normoglycemic men (control) performed acute and chronic exercise. The Hybrid Mouse Diversity Panel, including 100 murine strains of recombinant inbred mice, was used to identify muscle Dnm1L (encodes Drp1)-gene relationships.

RESULTS

Endurance exercise impacted all aspects of the mitochondrial life cycle, i.e. fission-fusion, biogenesis, and mitophagy. Dnm1L gene expression and Drp1Ser616 phosphorylation were markedly increased by acute exercise and declined to baseline during post-exercise recovery. Dnm1L expression was strongly associated with transcripts known to regulate mitochondrial metabolism and adaptations to exercise. Exercise increased the expression of DNM1L in skeletal muscle of healthy control and DG subjects, despite a 15% ↓(P = 0.01) in muscle DNM1L expression in DG at baseline. To interrogate the role of Dnm1L further, we exercise trained male mDrp1+/- mice and found that Drp1 deficiency reduced muscle endurance and running performance, and altered muscle adaptations in response to exercise training.

CONCLUSION

Our findings highlight the importance of mitochondrial dynamics, specifically Drp1 signaling, in the regulation of exercise performance and adaptations to endurance exercise training.

Global phosphoproteomic analysis reveals ARMC10 as an AMPK substrate that regulates mitochondrial dynamics

AMP-activated protein kinase (AMPK) is a key regulator of cellular energy homeostasis. Although AMPK has been studied extensively in cellular processes, understanding of its substrates and downstream functional network, and their contributions to cell fate and disease development, remains incomplete. To elucidate the AMPK-dependent signaling pathways, we performed global quantitative phosphoproteomic analysis using wild-type and AMPKα1/α2-double knockout cells and discovered 160 AMPK-dependent phosphorylation sites. Further analysis using an AMPK consensus phosphorylation motif indicated that 32 of these sites are likely direct AMPK phosphorylation sites. We validated one uncharacterized protein, ARMC10, and demonstrated that the S45 site of ARMC10 can be phosphorylated by AMPK both in vitro and in vivo. Moreover, ARMC10 overexpression was sufficient to promote mitochondrial fission, whereas ARMC10 knockout prevented AMPK-mediated mitochondrial fission. These results demonstrate that ARMC10 is an effector of AMPK that participates in dynamic regulation of mitochondrial fission and fusion.

AMPK is regulates cellular energy and has been extensively studied, although our knowledge of downstream substrates is incomplete. Here, Chen et al. perform global quantitative analysis for AMPK-dependent sites and validate one hit, ARMC10, as a direct AMPK effector of mitochondrial dynamics.

Honokiol, an activator of Sirtuin-3 (SIRT3) preserves mitochondria and protects the heart from doxorubicin-induced cardiomyopathy in mice

Doxorubicin is the chemotherapeutic drug of choice for a wide variety of cancers, and cardiotoxicity is one of the major side effects of doxorubicin treatment. One of the main cellular targets of doxorubicin in the heart is mitochondria. Mitochondrial sirtuin, SIRT3 has been shown to protect against doxorubicin-induced cardiotoxicity. We have recently identified honokiol (HKL) as an activator of SIRT3, which protects the heart from developing pressure overload hypertrophy. Here, we show that HKL-mediated activation of SIRT3 also protects the heart from doxorubicin-induced cardiac damage without compromising the tumor killing potential of doxorubicin. Doxorubicin-induced cardiotoxicity is associated with increased ROS production and consequent fragmentation of mitochondria and cell death. HKL-mediated activation of SIRT3 prevented Doxorubicin induced ROS production, mitochondrial damage and cell death in rat neonatal cardiomyocytes. HKL also promoted mitochondrial fusion. We also show that treatment with HKL blocked doxorubicin-induced cardiac toxicity in mice. This was associated with reduced mitochondrial DNA damage and improved mitochondrial function. Furthermore, treatments of mice, bearing prostrate tumor-xenografts, with HKL and doxorubicin showed inhibition of tumor growth with significantly reduced cardiac toxicity. Our results suggest that HKL-mediated activation of SIRT3 protects the heart from doxorubicin-induced cardiotoxicity and represents a potentially novel adjunct for chemotherapy treatments.

Dysregulated autophagy in restrictive cardiomyopathy due to Pro209Leu mutation in BAG3

Myofibrillary myopathies (MFM) are hereditary myopathies histologically characterized by degeneration of myofibrils and aggregation of proteins in striated muscle. Cardiomyopathy is common in MFM but the pathophysiological mechanisms are not well understood. The BAG3-Pro209Leu mutation is associated with early onset MFM and severe restrictive cardiomyopathy (RCM), often necessitating heart transplantation during childhood. We report on a young male patient with a BAG3-Pro209Leu mutation who underwent heart transplantation at eight years of age. Detailed morphological analyses of the explanted heart tissue showed intracytoplasmic inclusions, aggregation of BAG3 and desmin, disintegration of myofibers and Z-disk alterations. The presence of undegraded autophagosomes, seen by electron microscopy, as well as increased levels of p62, LC3-I and WIPI1, detected by immunohistochemistry and western blot analyses, indicated a dysregulation of autophagy. Parkin and PINK1, proteins involved in mitophagy, were slightly increased whereas mitochondrial OXPHOS activities were not altered. These findings indicate that altered autophagy plays a role in the pathogenesis and rapid progression of RCM in MFM caused by the BAG3-Pro209Leu mutation, which could have implications for future therapeutic strategies.

Mechanisms driving the ageing heart

Cardiovascular disease (CVD) is the leading cause of death globally. One of the main risk factors for CVD is age, however the biological processes that occur in the heart during ageing are poorly understood. It is therefore important to understand the fundamental mechanisms driving heart ageing to enable the development of preventions and treatments targeting these processes. Cellular senescence is often described as the irreversible cell-cycle arrest which occurs in somatic cells. Emerging evidence suggests that cellular senescence plays a key role in heart ageing, however the cell-types involved and the underlying mechanisms are not yet elucidated. In this review we discuss the current understanding of how mechanisms known to contribute to senescence impact on heart ageing and CVD. Finally, we evaluate recent data suggesting that targeting senescent cells may be a viable therapy to counteract the ageing of the heart.

Roles of mitochondrial dynamics modulators in cardiac ischaemia/reperfusion injury

The current therapeutic strategy for the management of acute myocardial infarction (AMI) is to return blood flow into the occluded coronary artery of the heart, a process defined as reperfusion. However, reperfusion itself can increase mortality rates in AMI patients because of cardiac tissue damage and dysfunction, which is termed ‘ischaemia/reperfusion (I/R) injury’. Mitochondria play an important role in myocardial I/R injury as disturbance of mitochondrial dynamics, especially excessive mitochondrial fission, is a predominant cause of cardiac dysfunction. Therefore, pharmacological intervention and therapeutic strategies which modulate the mitochondrial dynamics balance during I/R injury could exert great beneficial effects to the I/R heart. This review comprehensively summarizes and discusses the effects of mitochondrial fission inhibitors as well as mitochondrial fusion promoters on cardiac and mitochondrial function during myocardial I/R injury. The comparison of the effects of both compounds given at different time‐points during the course of I/R injury (i.e. prior to ischaemia, during ischaemia and at the reperfusion period) are also summarized and discussed. Finally, this review also details important information which may contribute to clinical practices using these drugs to improve the quality of life in AMI patients.

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.

SUMO-Modified FADD Recruits Cytosolic Drp1 and Caspase-10 to Mitochondria for Regulated Necrosis

Fas-associated protein with death domain (FADD) plays a key role in extrinsic apoptosis. Here, we show that FADD is SUMOylated as an essential step during intrinsic necrosis. FADD was modified at multiple lysine residues (K120/125/149) by small ubiquitin-related modifier 2 (SUMO2) during necrosis caused by calcium ionophore A23187 and by ischemic damage. SUMOylated FADD bound to dynamin-related protein 1 (Drp1) in cells both in vitro and in ischemic tissue damage cores, thus promoting Drp1 recruitment by mitochondrial fission factor (Mff) to accomplish mitochondrial fragmentation. Mitochondrial-fragmentation-associated necrosis was blocked by FADD or Drp1 deficiency and SUMO-defective FADD expression. Interestingly, caspase-10, but not caspase-8, formed a ternary protein complex with SUMO-FADD/Drp1 on the mitochondria upon exposure to A23187 and potentiated Drp1 oligomerization for necrosis. Moreover, the caspase-10 L285F and A414V mutants, found in autoimmune lymphoproliferative syndrome and non-Hodgkin lymphoma, respectively, regulated this necrosis. Our study reveals an essential role of SUMOylated FADD in Drp1- and caspase-10-dependent necrosis, providing insights into the mechanism of regulated necrosis by calcium overload and ischemic injury.

Vagal nerve stimulation improves mitochondrial dynamics via an M3 receptor/CaMKKβ/AMPK pathway in isoproterenol-induced myocardial ischaemia

Mitochondrial dynamics-fission and fusion-are associated with ischaemic heart disease (IHD). This study explored the protective effect of vagal nerve stimulation (VNS) against isoproterenol (ISO)-induced myocardial ischaemia in a rat model and tested whether VNS plays a role in preventing disorders of mitochondrial dynamics and function. Isoproterenol not only caused cardiac injury but also increased the expression of mitochondrial fission proteins [dynamin-related peptide1 (Drp1) and mitochondrial fission protein1 (Fis-1)) and decreased the expression of fusion proteins (optic atrophy-1 (OPA1) and mitofusins1/2 (Mfn1/2)], thereby disrupting mitochondrial dynamics and leading to increase in mitochondrial fragments. Interestingly, VNS restored mitochondrial dynamics through regulation of Drp1, Fis-1, OPA1 and Mfn1/2; enhanced ATP content and mitochondrial membrane potential; reduced mitochondrial permeability transition pore (MPTP) opening; and improved mitochondrial ultrastructure and size. Furthermore, VNS reduced the size of the myocardial infarction and ameliorated cardiomyocyte apoptosis and cardiac dysfunction induced by ISO. Moreover, VNS activated AMP-activated protein kinase (AMPK), which was accompanied by phosphorylation of Ca2+ /calmodulin-dependent protein kinase kinase β (CaMKKβ) during myocardial ischaemia. Treatment with subtype-3 of muscarinic acetylcholine receptor (M3 R) antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide or AMPK inhibitor Compound C abolished the protective effects of VNS on mitochondrial dynamics and function, suggesting that M3 R/CaMKKβ/AMPK signalling are involved in mediating beneficial effects of VNS. This study demonstrates that VNS modulates mitochondrial dynamics and improves mitochondrial function, possibly through the M3 R/CaMKKβ/AMPK pathway, to attenuate ISO-induced cardiac damage in rats. Targeting mitochondrial dynamics may provide a novel therapeutic strategy in IHD.

Role of cell death in the progression of heart failure

All multicellular organisms develop during evolution the highly regulated and interconnected pathways of cell death. This complex network contributes to the pathogenesis of various cardiovascular disorders including ischemia/reperfusion injury, myocardial infarction, heart failure, dysrhythmias and atherosclerosis. Chronic cardiac remodeling response and transition to overt HF have been associated with modestly increased apoptosis, although the actual burden of chronic cell loss attributable to apoptosis is not clear. Central mediators of cardiomyocyte survival and death are the mitochondrial organelles. Based on its morphological characteristics, cell death can be classified into three major types: apoptosis, necrosis and autophagy. Recently, a new pathway of regulated necrosis, necroptosis, has also been reported in the failing heart. The mitochondrial (intrinsic) and the death-receptor-mediated (extrinsic) converge at mitochondria inducing release of mitochondrial apoptogens to initiate the caspase cascade and eventually degradation of the doomed cardiomyocyte. Activation of death receptors can initiate not only extrinsic apoptotic pathway, but also necrosis. On the other hand, autophagy, which is characterized by the massive formation of lysosomal-derived vesicles, containing degenerating cytoplasmic contents, is primarily a survival response to nutrient deprivation, and a selective form of autophagy, mitophagy, is also a protective mechanism that allows to eliminate damaged mitochondria and thereby to attenuate mitochondria-mediated apoptosis and necrosis in the myocardium. Further insight into the molecular mechanisms underlying cell death will increase the efficiency and repertoire of therapeutic interventions available in cardiovascular disease.

Peroxisome proliferator-activated receptors (PPARs) as therapeutic target in neurodegenerative disorders

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and they serve to be a promising therapeutic target for several neurodegenerative disorders, which includes Parkinson disease, Alzheimer's disease, Huntington disease and Amyotrophic Lateral Sclerosis. PPARs play an important role in the downregulation of mitochondrial dysfunction, proteasomal dysfunction, oxidative stress, and neuroinflammation, which are the major causes of the pathogenesis of neurodegenerative disorders. In this review, we discuss about the role of PPARs as therapeutic targets in neurodegenerative disorders. Several experimental approaches suggest potential application of PPAR agonist as well as antagonist in the treatment of neurodegenerative disorders. Several epidemiological studies found that the regular usage of PPAR activating non-steroidal anti-inflammatory drugs is effective in decreasing the progression of neurodegenerative diseases including PD and AD. We also reviewed the neuroprotective effects of PPAR agonists and associated mechanism of action in several neurodegenerative disorders both in vitro as well as in vivo animal models.

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.

Apelin Gene Therapy Increases Autophagy via Activation of Sirtuin 3 in Diabetic Heart

Heart failure is the leading cause of death in diabetic patients. Recently we showed that apelin gene therapy attenuates heart failure following myocardial infarction. This study further explored the potential mechanisms by which apelin may reduce cardiac injury in Postmyocardial infarction (MI)) model of diabetes. Wild type and Sirt3 knockout (Sirt3 KO) mice were induced into diabetes by intra-peritoneal (i.p.) Streptozotocin (STZ). STZ mice were then subjected to MI followed by immediate intramyocardial injection with Adenovirus-apelin (Ad-apelin). Ad-apelin treatment resulted in over expression of apelin in the ischemic hearts of STZ mice. Apelin over expression led to a significant increase in Sirt3 expression. Apelin over expression significantly reduced gp91^phox expression. This was accompanied by a significant reduction of reactive oxygen species formation. Ad-apelin treatment also dramatically reduced NF-κb-p65 expression in WT-STZ mice. Over expression of apelin further enhanced autophagy markers (LC3-II and beclin-1) expression in post-MI heart. Most intriguingly, knockout of Sirt3 in STZ mice abolished these beneficial effects of apelin treatment. In vitro, knockout of Sirt3 in EPCs significantly enhanced high glucose-induced ROS formation. Conversely, treatment of Sirt3 KO-EPCs with NADPH oxidase inhibitor led to two fold increase in LC3-II levels. Our studies demonstrate that apelin increases autophagy via up regulation of Sirt3 and suppression of ROS-NF-κb pathway in diabetic heart.

Mitochondrial dynamics: Orchestrating the journey to advanced age

Aging is a degenerative process that unfortunately is an inevitable part of life and risk factor for cardiovascular disease including heart failure. Among the several theories purported to explain the effects of age on cardiac dysfunction, the mitochondrion has emerged a central regulator of this process. Hence, it is not surprising that abnormalities in mitochondrial quality control including biogenesis and turnover have such detrimental effects on cardiac function. In fact mitochondria serve as a conduit for biological signals for apoptosis, necrosis and autophagy respectively. The removal of damaged mitochondria by autophagy/mitophagy is essential for mitochondrial quality control and cardiac homeostasis. Defects in mitochondrial dynamism fission/fusion events have been linked to cardiac senescence and heart failure. In this review we discuss the impact of aging on mitochondrial dynamics and senescence on cardiovascular health. This article is part of a Special Issue entitled: CV Aging.

20 years of leptin: Role of leptin in cardiomyocyte physiology and physiopathology

Since the discovery of leptin in 1994 by Zhang et al., there have been a number of reports showing its implication in the development of a wide range of cardiovascular diseases. However, there exists some controversy about how leptin can induce or preserve cardiovascular function, as different authors have found contradictory results about leptin beneficial or detrimental effects in leptin deficient/resistant murine models and in wild type tissue and cardiomyocytes. Here, we will focus on the main discoveries about the leptin functions at cardiac level within the last two decades, focusing on its role in cardiac metabolism, remodeling and contractile function.

Mitochondria-targeted therapies for acute kidney injury

Acute kidney injury (AKI) is a serious clinical condition with no effective treatment. Tubular cells are key targets in AKI. Tubular cells and, specifically, proximal tubular cells are extremely rich in mitochondria and mitochondrial changes had long been known to be a feature of AKI. However, only recent advances in understanding the molecules involved in mitochondria biogenesis and dynamics and the availability of mitochondria-targeted drugs has allowed the exploration of the specific role of mitochondria in AKI. We now review the morphological and functional mitochondrial changes during AKI, as well as changes in the expression of mitochondrial genes and proteins. Finally, we summarise the current status of novel therapeutic strategies specifically targeting mitochondria such as mitochondrial permeability transition pore (MPTP) opening inhibitors (cyclosporine A (CsA)), quinone analogues (MitoQ, SkQ1 and SkQR1), superoxide dismutase (SOD) mimetics (Mito-CP), Szeto-Schiller (SS) peptides (Bendavia) and mitochondrial division inhibitors (mdivi-1). MitoQ, SkQ1, SkQR1, Mito-CP, Bendavia and mdivi-1 have improved the course of diverse experimental models of AKI. Evidence for a beneficial effect of CsA on human cardiac ischaemia-reperfusion injury derives from a clinical trial; however, CsA is nephrotoxic. MitoQ and Bendavia have been shown to be safe for humans. Ongoing clinical trials are testing the efficacy of Bendavia in AKI prevention following renal artery percutaneous transluminal angioplasty.

Autophagy and oxidative stress in cardiovascular diseases

Autophagy is a highly conserved degradation process by which intracellular components, including soluble macromolecules (e.g. nucleic acids, proteins, carbohydrates, and lipids) and dysfunctional organelles (e.g. mitochondria, ribosomes, peroxisomes, and endoplasmic reticulum) are degraded by the lysosome. Autophagy is orchestrated by the autophagy related protein (Atg) composed protein complexes to form autophagosomes, which fuse with lysosomes to generate autolysosomes where the contents are degraded to provide energy for cell survival in response to environmental and cellular stress. Autophagy is an important player in cardiovascular disease development such as atherosclerosis, cardiac ischemia/reperfusion, cardiomyopathy, heart failure and hypertension. Autophagy in particular contributes to cardiac ischemia, hypertension and diabetes by interaction with reactive oxygen species generated in endoplasmic reticulum and mitochondria. This review highlights the dual role of autophagy in cardiovascular disease development. Full recognition of autophagy as an adaptive or maladaptive response would provide potential new strategies for cardiovascular disease prevention and management. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Mitochondria in heart failure: the emerging role of mitochondrial dynamics

Over the past decade, mitochondria have emerged as critical integrators of energy production, generation of reactive oxygen species (ROS), multiple cell death, and signaling pathways in the constantly beating heart. Clarification of the molecular mechanisms, underlying mitochondrial ROS generation and ROS-induced cell death pathways, associated with cardiovascular diseases, by itself remains an important aim; more recently, mitochondrial dynamics has emerged as an important active mechanism to maintain normal mitochondria number and morphology, both are necessary to preserve cardiomyocytes integrity. The two opposing processes, division (fission) and fusion, determine the cell type-specific mitochondrial morphology, the intracellular distribution and activity. The tightly controlled balance between fusion and fission is of particular importance in the high energy demanding cells, such as cardiomyocytes, skeletal muscles, and neuronal cells. A shift toward fission will lead to mitochondrial fragmentation, observed in quiescent cells, while a shift toward fusion will result in the formation of large mitochondrial networks, found in metabolically active cardiomyocytes. Defects in mitochondrial dynamics have been associated with various human disorders, including heart failure, ischemia reperfusion injury, diabetes, and aging. Despite significant progress in our understanding of the molecular mechanisms of mitochondrial function in the heart, further focused research is needed to translate this knowledge into the development of new therapies for various ailments.

Oxidative stress and autophagy in cardiovascular homeostasis

SIGNIFICANCE

Autophagy is an evolutionarily ancient process of intracellular protein and organelle recycling required to maintain cellular homeostasis in the face of a wide variety of stresses. Dysregulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) leads to oxidative damage. Both autophagy and ROS/RNS serve pathological or adaptive roles within cardiomyocytes, depending on the context.

RECENT ADVANCES

ROS/RNS and autophagy communicate with each other via both transcriptional and post-translational events. This cross talk, in turn, regulates the structural integrity of cardiomyocytes, promotes proteostasis, and reduces inflammation, events critical to disease pathogenesis.

CRITICAL ISSUES

Dysregulation of either autophagy or redox state has been implicated in many cardiovascular diseases. Cardiomyocytes are rich in mitochondria, which make them particularly sensitive to oxidative damage. Maintenance of mitochondrial homeostasis and elimination of defective mitochondria are each critical to the maintenance of redox homeostasis.

FUTURE DIRECTIONS

The complex interplay between autophagy and oxidative stress underlies a wide range of physiological and pathological events and its elucidation holds promise of potential clinical applicability.

The dual role of autophagy in chondrocyte responses in the pathogenesis of articular cartilage degeneration in osteoarthritis

The present study aimed to analyze the responses to autophagy in osteoarthritis (OA) and aging chondrocytes in order to elucidate the role of autophagy in the pathogenesis of OA. We used multiple assays to confirm that autophagic activity was downregulated in chondrocytes of aged articular cartilage. Surprisingly, we found that the expression of autophagy-related proteins was not decreased in the tissues of patients with OA. We also observed that rapamycin-induced autophagy prevented the accumulation of subdiploid cells in young chondrocytes, while it induced cell death by autophagy in OA chondrocytes. Our results demonstrate that autophagic activity decreases with aging, and may be responsible for the cytoprotective effects in young cartilage. However, we found that autophagic activity in patients with OA was higher than in the aging group, and reported autophagic cell death in OA chondrocytes. These results suggest that autophagy plays both a cytoprotective and death-promoting role in the pathogenesis of OA.

Role of telomere dysfunction in cardiac failure in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), the most common inherited muscular dystrophy of childhood, leads to death due to cardiorespiratory failure. Paradoxically, mdx mice with the same genetic deficiency of dystrophin exhibit minimal cardiac dysfunction, impeding the development of therapies. We postulated that the difference between mdx and DMD might result from differences in telomere lengths in mice and humans. We show here that, like DMD patients, mice that lack dystrophin and have shortened telomeres (mdx/mTR(KO)) develop severe functional cardiac deficits including ventricular dilation, contractile and conductance dysfunction, and accelerated mortality. These cardiac defects are accompanied by telomere erosion, mitochondrial fragmentation and increased oxidative stress. Treatment with antioxidants significantly retards the onset of cardiac dysfunction and death of mdx/mTR(KO) mice. In corroboration, all four of the DMD patients analysed had 45% shorter telomeres in their cardiomyocytes relative to age- and sex-matched controls. We propose that the demands of contraction in the absence of dystrophin coupled with increased oxidative stress conspire to accelerate telomere erosion culminating in cardiac failure and death. These findings provide strong support for a link between telomere length and dystrophin deficiency in the etiology of dilated cardiomyopathy in DMD and suggest preventive interventions.

Mitochondrial hyperfusion during oxidative stress is coupled to a dysregulation in calcium handling within a C2C12 cell model

Atrial Fibrillation is the most common sustained cardiac arrhythmia worldwide harming millions of people every year. Atrial Fibrillation (AF) abruptly induces rapid conduction between atrial myocytes which is associated with oxidative stress and abnormal calcium handling. Unfortunately this new equilibrium promotes perpetuation of the arrhythmia. Recently, in addition to being the major source of oxidative stress within cells, mitochondria have been observed to fuse, forming mitochondrial networks and attach to intracellular calcium stores in response to cellular stress. We sought to identify a potential role for rapid stimulation, oxidative stress and mitochondrial hyperfusion in acute changes to myocyte calcium handling. In addition we hoped to link altered calcium handling to increased sarcoplasmic reticulum (SR)-mitochondrial contacts, the so-called mitochondrial associated membrane (MAM). We selected the C2C12 murine myotube model as it has previously been successfully used to investigate mitochondrial dynamics and has a myofibrillar system similar to atrial myocytes. We observed that rapid stimulation of C2C12 cells resulted in mitochondrial hyperfusion and increased mitochondrial colocalisation with calcium stores. Inhibition of mitochondrial fission by transfection of mutant DRP1K38E resulted in similar effects on mitochondrial fusion, SR colocalisation and altered calcium handling. Interestingly the effects of 'forced fusion' were reversed by co-incubation with the reducing agent N-Acetyl cysteine (NAC). Subsequently we demonstrated that oxidative stress resulted in similar reversible increases in mitochondrial fusion, SR-colocalisation and altered calcium handling. Finally, we believe we have identified that myocyte calcium handling is reliant on baseline levels of reactive oxygen species as co-incubation with NAC both reversed and retarded myocyte response to caffeine induced calcium release and re-uptake. Based on these results we conclude that the coordinate regulation of mitochondrial fusion and MAM contacts may form a point source for stress-induced arrhythmogenesis. We believe that the MAM merits further investigation as a therapeutic target in AF-induced remodelling.

Mitochondrial accumulation under oxidative stress is due to defects in autophagy

Mitochondrial dynamics maintains normal mitochondrial function by degrading damaged mitochondria and generating newborn mitochondria. The accumulation of damaged mitochondria influences the intracellular environment by promoting mitochondrial dysfunction, and thus initiating a vicious cycle. Oxidative stress induces mitochondrial malfunction, which is involved in many cardiovascular diseases. However, the mechanism of mitochondrial accumulation in cardiac myoblasts remains unclear. We observed mitochondrial dysfunction and an increase in mitochondrial mass under the oxidative conditions produced by tert-butyl hydroperoxide (tBHP) in cardiac myoblast H9c2 cells. However, in contrast to the increase in mitochondrial mass, mitochondrial DNA (mtDNA) decreased, suggesting that enhanced mitochondrial biogenesis may be not the primary cause of the mitochondrial accumulation. Therefore, we investigated changes in a number of proteins involved in autophagy. Beclin1, Atg12-Atg5 conjugate, Atg7 contents decreased but LC3-II accumulated in tBHP-treated H9c2 cells. Moreover, the capacity for acid hydrolysis decreased in H9c2 cells. We also demonstrated a decrease in DJ-1 protein under the oxidative conditions that deregulate mitochondrial dynamics. These results reveal that autophagy became defective under oxidative stress. We therefore suggest that defects in autophagy mediate mitochondrial accumulation under these conditions.

Mitochondria, myocardial remodeling, and cardiovascular disease

The process of muscle remodeling lies at the core of most cardiovascular diseases. Cardiac adaptation to pressure or volume overload is associated with a complex molecular change in cardiomyocytes which leads to anatomic remodeling of the heart muscle. Although adaptive at its beginnings, the sustained cardiac hypertrophic remodeling almost unavoidably ends in progressive muscle dysfunction, heart failure and ultimately death. One of the features of cardiac remodeling is a progressive impairment in mitochondrial function. The heart has the highest oxygen uptake in the human body and accordingly it has a large number of mitochondria, which form a complex network under constant remodeling in order to sustain the high metabolic rate of cardiac cells and serve as Ca(2+) buffers acting together with the endoplasmic reticulum (ER). However, this high dependence on mitochondrial metabolism has its costs: when oxygen supply is threatened, high leak of electrons from the electron transport chain leads to oxidative stress and mitochondrial failure. These three aspects of mitochondrial function (Reactive oxygen species signaling, Ca(2+) handling and mitochondrial dynamics) are critical for normal muscle homeostasis. In this article, we will review the latest evidence linking mitochondrial morphology and function with the process of myocardial remodeling and cardiovascular disease.

Ceramide synthase 5 mediates lipid-induced autophagy and hypertrophy in cardiomyocytes

Diabetic cardiomyopathy (DbCM), which consists of cardiac hypertrophy and failure in the absence of traditional risk factors, is a major contributor to increased heart failure risk in type 2 diabetes patients. In rodent models of DbCM, cardiac hypertrophy and dysfunction have been shown to depend upon saturated fatty acid (SFA) oversupply and de novo sphingolipid synthesis. However, it is not known whether these effects are mediated by bulk SFAs and sphingolipids or by individual lipid species. In this report, we demonstrate that a diet high in SFA induced cardiac hypertrophy, left ventricular systolic and diastolic dysfunction, and autophagy in mice. Furthermore, treatment with the SFA myristate, but not palmitate, induced hypertrophy and autophagy in adult primary cardiomyocytes. De novo sphingolipid synthesis was required for induction of all pathological features observed both in vitro and in vivo, and autophagy was required for induction of hypertrophy in vitro. Finally, we implicated a specific ceramide N-acyl chain length in this process and demonstrated a requirement for (dihydro)ceramide synthase 5 in cardiomyocyte autophagy and myristate-mediated hypertrophy. Thus, this report reveals a requirement for a specific sphingolipid metabolic route and dietary SFAs in the molecular pathogenesis of lipotoxic cardiomyopathy and hypertrophy.

Mitochondria as a therapeutic target in heart failure

Heart failure is a pressing public health problem with no curative treatment currently available. The existing therapies provide symptomatic relief, but are unable to reverse molecular changes that occur in cardiomyocytes. The mechanisms of heart failure are complex and multiple, but mitochondrial dysfunction appears to be a critical factor in the development of this disease. Thus, it is important to focus research efforts on targeting mitochondrial dysfunction in the failing heart to revive the myocardium and its contractile function. This review highlights the 3 promising areas for the development of heart failure therapies, including mitochondrial biogenesis, mitochondrial oxidative stress, and mitochondrial iron handling. Moreover, the translational potential of compounds targeting these pathways is discussed.

Targets, trafficking, and timing of cardiac autophagy

Heart failure is the major case of death in developed countries, and its prevalence is growing worldwide. Autophagy is a fundamental cellular mechanism through which intracellular components can be removed, recycled and repaired. Studies in humans and animal models demonstrate a marked increase in cardiac autophagic activity under a wide range of disease states and in response to diverse stimuli. Recently, autophagy has been widely promoted as a potential therapeutic target for the treatment of cardiovascular disease and heart failure. An important challenge to achieving this goal is the dual nature of cardiac autophagy, sometimes acting to help preserve cardiac function, other times appearing to promote cardiac decline. Numerous control points regulating autophagic activity and cargo selection provide a diversity of opportunities for drug targeting. In addition there is an innate circadian rhythm to the systemic regulation of autophagy that is often overlooked but provides potential opportunities to target and optimize pharmacological intervention.

Caloric restriction ameliorates angiotensin II-induced mitochondrial remodeling and cardiac hypertrophy

Angiotensin II-induced cardiac damage is associated with oxidative stress-dependent mitochondrial dysfunction. Caloric restriction (CR), a dietary regimen that increases mitochondrial activity and cellular stress resistance, could provide protection. We tested that hypothesis in double transgenic rats harboring human renin and angiotensinogen genes (dTGRs). CR (60% of energy intake for 4 weeks) decreased mortality in dTGRs. CR ameliorated angiotensin II-induced cardiomyocyte hypertrophy, vascular inflammation, cardiac damage and fibrosis, cardiomyocyte apoptosis, and cardiac atrial natriuretic peptide mRNA overexpression. The effects were blood pressure independent and were linked to increased endoplasmic reticulum stress, autophagy, serum adiponectin level, and 5' AMP-activated protein kinase phosphorylation. CR decreased cardiac p38 phosphorylation, nitrotyrosine expression, and serum insulin-like growth factor 1 levels. Mitochondria from dTGR hearts showed clustered mitochondrial patterns, decreased numbers, and volume fractions but increased trans-sectional areas. All of these effects were reduced in CR dTGRs. Mitochondrial proteomic profiling identified 43 dTGR proteins and 42 Sprague-Dawley proteins, of which 29 proteins were in common in response to CR. We identified 7 proteins in CR dTGRs that were not found in control dTGRs. In contrast, 6 mitochondrial proteins were identified from dTGRs that were not detected in any other group. Gene ontology annotations with the Panther protein classification system revealed downregulation of cytoskeletal proteins and enzyme modulators and upregulation of oxidoreductase activity in dTGRs. CR provides powerful, blood pressure-independent, protection against angiotensin II-induced mitochondrial remodeling and cardiac hypertrophy. The findings support the notion of modulating cardiac bioenergetics to ameliorate angiotensin II-induced cardiovascular complications.

Measuring mitochondrial function in intact cardiac myocytes

Mitochondria are involved in cellular functions that go beyond the traditional role of these organelles as the power plants of the cell. Mitochondria have been implicated in several human diseases, including cardiac dysfunction, and play a role in the aging process. Many aspects of our knowledge of mitochondria stem from studies performed on the isolated organelle. Their relative inaccessibility imposes experimental difficulties to study mitochondria in their natural environment-the cytosol of intact cells-and has hampered a comprehensive understanding of the plethora of mitochondrial functions. Here we review currently available methods to study mitochondrial function in intact cardiomyocytes. These methods primarily use different flavors of fluorescent dyes and genetically encoded fluorescent proteins in conjunction with high-resolution imaging techniques. We review methods to study mitochondrial morphology, mitochondrial membrane potential, Ca(2+) and Na(+) signaling, mitochondrial pH regulation, redox state and ROS production, NO signaling, oxygen consumption, ATP generation and the activity of the mitochondrial permeability transition pore. Where appropriate we complement this review on intact myocytes with seminal studies that were performed on isolated mitochondria, permeabilized cells, and in whole hearts.

[Mitochondrial dynamics: a potential new therapeutic target for heart failure]

Mitochondria are dynamic organelles able to vary their morphology between elongated interconnected mitochondrial networks and fragmented disconnected arrays, through events of mitochondrial fusion and fission, respectively. These events allow the transmission of signaling messengers and exchange of metabolites within the cell. They have also been implicated in a variety of biological processes including embryonic development, metabolism, apoptosis, and autophagy. Although the majority of these studies have been confined to noncardiac cells, emerging evidence suggests that changes in mitochondrial morphology could participate in cardiac development, the response to ischemia-reperfusion injury, heart failure, and diabetes mellitus. In this article, we review how the mitochondrial dynamics are altered in different cardiac pathologies, with special emphasis on heart failure, and how this knowledge may provide new therapeutic targets for treating cardiovascular diseases.

The complex interplay between mitochondrial dynamics and cardiac metabolism

Mitochondria are highly dynamic organelles, capable of undergoing constant fission and fusion events, forming networks. These dynamic events allow the transmission of chemical and physical messengers and the exchange of metabolites within the cell. In this article we review the signaling mechanisms controlling mitochondrial fission and fusion, and its relationship with cell bioenergetics, especially in the heart. Furthermore we also discuss how defects in mitochondrial dynamics might be involved in the pathogenesis of metabolic cardiac diseases.