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Mitochondrial calcium (Ca2+) signals play a central role in cardiac homeostasis and disease. In the healthy heart, mitochondrial Ca2+ levels modulate the rate of oxidative metabolism to match the rate of adenosine triphosphate consumption in the cytosol. During ischemia/reperfusion (I/R) injury, pathologically high levels of Ca2+ in the mitochondrial matrix trigger the opening of the mitochondrial permeability transition pore, which releases solutes and small proteins from the matrix, causing mitochondrial swelling and ultimately leading to cell death. Pharmacological and genetic approaches to tune mitochondrial Ca2+ handling by regulating the activity of the main Ca2+ influx and efflux pathways, i.e., the mitochondrial Ca2+ uniporter and sodium/Ca2+ exchanger, represent promising therapeutic strategies to protect the heart from I/R injury. [ABSTRACT FROM AUTHOR]

Diphenyleneiodonium (DPI) has been widely used as an inhibitor of NADPH oxidase (Nox) to discover its function in cardiac myocytes under various stimuli. However, the effects of DPI itself on Ca2+ signaling and contraction in cardiac myocytes under control conditions have not been understood. We investigated the effects of DPI on contraction and Ca2+ signaling and their underlying mechanisms using video edge detection, confocal imaging, and whole-cell patch clamp technique in isolated rat cardiac myocytes. Application of DPI suppressed cell shortenings in a concentration-dependent manner (IC50 of -0.17 µM) with a maximal inhibition of ~70% at ~100 µM. DPI decreased the magnitude of Ca2+ transient and sarcoplasmic reticulum Ca2+ content by 20%-30% at 3 µM that is usually used to remove the Nox activity, with no effect on fractional release. There was no significant change in the half-decay time of Ca2+ transients by DPI. The L-type Ca2+ current (ICa) was decreased concentration-dependently by DPI (IC50 of -40.3 µM) with -13.1%-inhibition at 3 µM. The frequency of Ca2+ sparks was reduced by 3 µM DPI (by ~25%), which was resistant to a brief removal of external Ca2+ and Na+. Mitochondrial superoxide level was reduced by DPI at 3-100 µM. Our data suggest that DPI may suppress L-type Ca2+ channel and RyR, thereby attenuating Ca2+-induced Ca2+ release and contractility in cardiac myocytes, and that such DPI effects may be related to mitochondrial metabolic suppression. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Investigación e Innovación en Ciencias de la Salud (RIICS) is the property of Fundacion Universitaria Maria Cano and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cardiovascular diseases are a leading cause of morbidity and mortality world-wide. While many factors like smoking, hypertension, diabetes, dyslipidaemia, a sedentary lifestyle, and genetic factors can predispose to cardiovascular diseases, the natural process of aging is by itself a major determinant of the risk. Cardiac aging is marked by a conglomerate of cellular and molecular changes, exacerbated by age-driven decline in cardiac regeneration capacity. Although the phenotypes of cardiac aging are well characterised, the underlying molecular mechanisms are far less explored. Recent advances unequivocally link cardiovascular aging to the dysregulation of critical signalling pathways in cardiac fibroblasts, which compromises the critical role of these cells in maintaining the structural and functional integrity of the myocardium. Clearly, the identification of cardiac fibroblast-specific factors and mechanisms that regulate cardiac fibroblast function in the senescent myocardium is of immense importance. In this regard, recent studies show that Discoidin domain receptor 2 (DDR2), a collagen-activated receptor tyrosine kinase predominantly located in cardiac fibroblasts, has an obligate role in cardiac fibroblast function and cardiovascular fibrosis. Incisive studies on the molecular basis of cardiovascular aging and dysregulated fibroblast function in the senescent heart would pave the way for effective strategies to mitigate cardiovascular diseases in a rapidly growing elderly population. [ABSTRACT FROM AUTHOR]

The heart is a dynamic organ that beats >2.5 billion times in the average lifetime. Humankind's fascination for its complex yet elegant physiology can be traced as far back as the ancient Egyptians, who first documented the association between abnormalities in the peripheral pulse and the heart. To operate on the heart, modern day cardiac surgery requires a non-beating (arrested) heart for surgeons to correct pathological lesions. Arrest is achieved with a 'cardioplegic' solution; usually this involves increasing the extracellular potassium to a concentration that depolarizes the membrane potential and thereby prevents the voltage-induced sodium spike of the action potential. In this article, we discuss the basic physiological, electrophysiological and haemodynamic concepts of the heart and how we cause arrest to perform open heart surgery. [ABSTRACT FROM AUTHOR]

Aims The mitochondrial dynamics protein Mitofusin 2 (MFN2) coordinates critical cellular processes including mitochondrial bioenergetics, quality control, and cell viability. The NF-κB kinase IKKβ suppresses mitochondrial injury in doxorubicin cardiomyopathy, but the underlying mechanism is undefined. Methods and results Herein, we identify a novel signalling axis that functionally connects IKKβ and doxorubicin cardiomyopathy to a mechanism that impinges upon the proteasomal stabilization of MFN2. In contrast to vehicle-treated cells, MFN2 was highly ubiquitinated and rapidly degraded by the proteasomal-regulated pathway in cardiac myocytes treated with doxorubicin. The loss of MFN2 activity resulted in mitochondrial perturbations, including increased reactive oxygen species (ROS) production, impaired respiration, and necrotic cell death. Interestingly, doxorubicin-induced degradation of MFN2 and mitochondrial-regulated cell death were contingent upon IKKβ kinase activity. Notably, immunoprecipitation and proximity ligation assays revealed that IKKβ interacted with MFN2 suggesting that MFN2 may be a phosphorylation target of IKKβ. To explore this possibility, mass spectrometry analysis identified a novel MFN2 phospho-acceptor site at serine 53 that was phosphorylated by wild-type IKKβ but not by a kinase-inactive mutant IKKβK–M. Based on these findings, we reasoned that IKKβ-mediated phosphorylation of serine 53 may influence MFN2 protein stability. Consistent with this view, an IKKβ-phosphomimetic MFN2 (MFN2S53D) was resistant to proteasomal degradation induced by doxorubicin whereas wild-type MFN2 and IKKβ-phosphorylation defective MFN2 mutant (MFNS53A) were readily degraded in cardiac myocytes treated with doxorubicin. Concordantly, gain of function of IKKβ or MFN2S53D suppressed doxorubicin-induced mitochondrial injury and cell death. Conclusions The findings of this study reveal a novel survival pathway for IKKβ that is mutually dependent upon and obligatory linked to the phosphorylation and stabilization of the mitochondrial dynamics protein MFN2. [ABSTRACT FROM AUTHOR]

We developed a 96-well plate assay which allows fast, reproducible, and high-throughput generation of 3D cardiac rings around a deformable optically transparent hydrogel (polyethylene glycol [PEG]) pillar of known stiffness. Human induced pluripotent stem cell-derived cardiomyocytes, mixed with normal human adult dermal fibroblasts in an optimized 3:1 ratio, self-organized to form ring-shaped cardiac constructs. Immunostaining showed that the fibroblasts form a basal layer in contact with the glass, stabilizing the muscular fiber above. Tissues started contracting around the pillar at D1 and their fractional shortening increased until D7, reaching a plateau at 25±1%, that was maintained up to 14 days. The average stress, calculated from the compaction of the central pillar during contractions, was 1.4±0.4 mN/mm2. The cardiac constructs recapitulated expected inotropic responses to calcium and various drugs (isoproterenol, verapamil) as well as the arrhythmogenic effects of dofetilide. This versatile high-throughput assay allows multiple in situ mechanical and structural readouts.

BackgroundAltered kinase localization is gaining appreciation as a mechanism of cardiovascular disease. Previous work suggests GSK-3β (glycogen synthase kinase 3β) localizes to and regulates contractile function of the myofilament. We aimed to discover GSK-3β's in vivo role in regulating myofilament function, the mechanisms involved, and the translational relevance.MethodsInducible cardiomyocyte-specific GSK-3β knockout mice and left ventricular myocardium from nonfailing and failing human hearts were studied.ResultsSkinned cardiomyocytes from knockout mice failed to exhibit calcium sensitization with stretch indicating a loss of length-dependent activation (LDA), the mechanism underlying the Frank-Starling Law. Titin acts as a length sensor for LDA, and knockout mice had decreased titin stiffness compared with control mice, explaining the lack of LDA. Knockout mice exhibited no changes in titin isoforms, titin phosphorylation, or other thin filament phosphorylation sites known to affect passive tension or LDA. Mass spectrometry identified several z-disc proteins as myofilament phospho-substrates of GSK-3β. Agreeing with the localization of its targets, GSK-3β that is phosphorylated at Y216 binds to the z-disc. We showed pY216 was necessary and sufficient for z-disc binding using adenoviruses for wild-type, Y216F, and Y216E GSK-3β in neonatal rat ventricular cardiomyocytes. One of GSK-3β's z-disc targets, abLIM-1 (actin-binding LIM protein 1), binds to the z-disc domains of titin that are important for maintaining passive tension. Genetic knockdown of abLIM-1 via siRNA in human engineered heart tissues resulted in enhancement of LDA, indicating abLIM-1 may act as a negative regulator that is modulated by GSK-3β. Last, GSK-3β myofilament localization was reduced in left ventricular myocardium from failing human hearts, which correlated with depressed LDA.ConclusionsWe identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA. Importantly, z-disc GSK-3β levels were reduced in patients with heart failure, indicating z-disc localized GSK-3β is a possible therapeutic target to restore the Frank-Starling mechanism in patients with heart failure.

Cardiac excitation-contraction coupling (ECC) depends on Ca2+ release from intracellular stores via ryanodine receptors (RyRs) triggered by L-type Ca2+ channels (LCCs). Uncertain numbers of RyRs and LCCs form 'couplons' whose activation produces Ca2+ sparks, which summate to form a cell-wide Ca2+ transient that switches on contraction. Voltage (V m) changes during the action potential (AP) and stochasticity in channel gating should create variability in Ca2+ spark timing, but Ca2+ transient wavefronts have remarkable uniformity. To examine how this is achieved, we measured the V m -dependence of evoked Ca2+ spark probability (P spark) and latency over a wide voltage range in rat ventricular cells. With depolarising steps, Ca2+ spark latency showed a U-shaped V m -dependence, while repolarising steps from 50 mV produced Ca2+ spark latencies that increased monotonically with V m. A computer model based on reported channel gating and geometry reproduced our experimental data and revealed a likely RyR:LCC stoichiometry of ∼ 5:1 for the Ca2+ spark initiating complex (IC). Using the experimental AP waveform, the model revealed a high coupling fidelity (P cpl ∼ 0.5) between each LCC opening and IC activation. The presence of ∼ 4 ICs per couplon reduced Ca2+ spark latency and increased P spark to match experimental data. Variability in AP release timing is less than that seen with voltage steps because the AP overshoot and later repolarization decrease P spark due to effects on LCC flux and LCC deactivation respectively. This work provides a framework for explaining the V m - and time-dependence of P spark , and indicates how ion channel dispersion in disease can contribute to dyssynchrony in Ca 2 + release. [Display omitted] • Evoked Ca2+ spark latency was measured in rat cardiomyocytes using voltage clamp. • The latency was highly voltage dependent and different for action potentials and steps. • Computer simulations of experiments were used to analyse the origin of Ca2+ latency. • 4 initiating complexes of 3–8 RyRs per LCC could explain Ca2+ transient latency. • During an action potential, 50% of LCC openings could trigger a Ca2+ spark. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases are a leading cause of morbidity and mortality world-wide. While many factors like smoking, hypertension, diabetes, dyslipidaemia, a sedentary lifestyle, and genetic factors can predispose to cardiovascular diseases, the natural process of aging is by itself a major determinant of the risk. Cardiac aging is marked by a conglomerate of cellular and molecular changes, exacerbated by age-driven decline in cardiac regeneration capacity. Although the phenotypes of cardiac aging are well characterised, the underlying molecular mechanisms are far less explored. Recent advances unequivocally link cardiovascular aging to the dysregulation of critical signalling pathways in cardiac fibroblasts, which compromises the critical role of these cells in maintaining the structural and functional integrity of the myocardium. Clearly, the identification of cardiac fibroblast-specific factors and mechanisms that regulate cardiac fibroblast function in the senescent myocardium is of immense importance. In this regard, recent studies show that Discoidin domain receptor 2 (DDR2), a collagen-activated receptor tyrosine kinase predominantly located in cardiac fibroblasts, has an obligate role in cardiac fibroblast function and cardiovascular fibrosis. Incisive studies on the molecular basis of cardiovascular aging and dysregulated fibroblast function in the senescent heart would pave the way for effective strategies to mitigate cardiovascular diseases in a rapidly growing elderly population.

Dystrophic cardiomyopathy arises from mutations in the dystrophin gene. Dystrophin forms part of the dystrophin glycoprotein complex and is postulated to act as a membrane stabilizer, protecting the sarcolemma from contraction-induced damage. Duchenne muscular dystrophy (DMD) is the most severe dystrophinopathy, caused by a total absence of dystrophin. Patients with DMD present with progressive skeletal muscle weakness and, because of treatment advances, a cardiac component of the disease (i.e., dystrophic cardiomyopathy) has been unmasked later in disease progression. The role that myofilaments play in dystrophic cardiomyopathy is largely unknown and, as such, this study aimed to address cardiac myofilament function in a mouse model of muscular dystrophy. To assess the effects of DMD on myofilament function, isolated permeabilized cardiomyocytes of wild-type (WT) littermates and Dmdmdx-4cv mice were attached between a force transducer and motor and subjected to contractile assays. Maximal tension and rates of force development (indexed by the rate constant, ktr) were similar between WT and Dmdmdx-4cv cardiac myocyte preparations. Interestingly, Dmdmdx-4cv cardiac myocytes exhibited greater sarcomere length dependence of peak power output compared to WT myocyte preparations. These results suggest dystrophin mitigates length dependence of activation and, in the absence of dystrophin, augmented sarcomere length dependence of myocyte contractility may accelerate ventricular myocyte contraction-induced damage and contribute to dystrophic cardiomyopathy. Next, we assessed if mavacamten, a small molecule modulator of thick filament activation, would mitigate contractile properties observed in Dmdmdx-4cv permeabilized cardiac myocyte preparations. Mavacamten decreased maximal tension and ktr in both WT and Dmdmdx-4cv cardiac myocytes, while also normalizing the length dependence of peak power between WT and Dmdmdx-4cv cardiac myocyte preparations. These results highlight potential benefits of mavacamten (i.e., reduced contractility while maintaining exquisite sarcomere length dependence of power output) as a treatment for dystrophic cardiomyopathy associated with DMD. [ABSTRACT FROM AUTHOR]

Background: Right ventricular (RV) contractile dysfunction commonly occurs and worsens outcomes in patients with heart failure with reduced ejection fraction and pulmonary hypertension (HFrEF-PH). However, such dysfunction often goes undetected by standard clinical RV indices, raising concerns that they may not reflect aspects of underlying myocyte dysfunction. We thus sought to characterize RV myocyte contractile depression in HFrEF-PH, identify those components reflected by clinical RV indices, and uncover underlying biophysical mechanisms. Methods: Resting, calcium-, and load-dependent mechanics were prospectively studied in permeabilized RV cardiomyocytes isolated from explanted hearts from 23 patients with HFrEF-PH undergoing cardiac transplantation and 9 organ donor controls. Results: Unsupervised machine learning using myocyte mechanical data with the highest variance yielded 2 HFrEF-PH subgroups that in turn mapped to patients with decompensated or compensated clinical RV function. This correspondence was driven by reduced calcium-activated isometric tension in decompensated clinical RV function, whereas surprisingly, many other major myocyte contractile measures including peak power and myocyte active stiffness were similarly depressed in both groups. Similar results were obtained when subgroups were first defined by clinical indices, and then myocyte mechanical properties in each group compared. To test the role of thick filament defects, myofibrillar structure was assessed by x-ray diffraction of muscle fibers. This revealed more myosin heads associated with the thick filament backbone in decompensated clinical RV function, but not compensated clinical RV function, as compared with controls. This corresponded to reduced myosin ATP turnover in decompensated clinical RV function myocytes, indicating less myosin in a crossbridge-ready disordered-relaxed (DRX) state. Altering DRX proportion (%DRX) affected peak calcium-activated tension in the patient groups differently, depending on their basal %DRX, highlighting potential roles for precision-guided therapeutics. Last, increasing myocyte preload (sarcomere length) increased %DRX 1.5-fold in controls but only 1.2-fold in both HFrEF-PH groups, revealing a novel mechanism for reduced myocyte active stiffness and by extension Frank-Starling reserve in human heart failure. Conclusions: Although there are many RV myocyte contractile deficits in HFrEF-PH, commonly used clinical indices only detect reduced isometric calcium-stimulated force, which is related to deficits in basal and recruitable %DRX myosin. Our results support use of therapies to increase %DRX and enhance length-dependent recruitment of DRX myosin heads in such patients. [ABSTRACT FROM AUTHOR]

Human induced pluripotent stem cells (hiPSC) offer an unprecedented opportunity to generate model systems that facilitate a mechanistic understanding of human disease. Current differentiation protocols are capable of generating cardiac myocytes (hiPSC-CM) and sympathetic neurons (hiPSC-SN). However, the ability of hiPSC-derived neurocardiac co-culture systems to replicate the human phenotype in disease modelling is still in its infancy. Here, we adapted current methods for efficient and replicable induction of hiPSC-CM and hiPSC-SN. Expression of cell-type-specific proteins were confirmed by flow cytometry and immunofluorescence staining. The utility of healthy hiPSC-CM was tested with pressor agents to develop a model of cardiac hypertrophy. Treatment with angiotensin II (AngII) resulted in: (i) cell and nuclear enlargement, (ii) enhanced fetal gene expression, and (iii) FRET-activated cAMP responses to adrenergic stimulation. AngII or KCl increased intracellular calcium transients in hiPSC-SN. Immunostaining in neurocardiac co-cultures demonstrated anatomical innervation to myocytes, where myocyte cytosolic cAMP responses were enhanced by forskolin compared with monocultures. In conclusion, human iPSC-derived cardiac myocytes and sympathetic neurons replicated many features of the anatomy and (patho)physiology of these cells, where co-culture preparations behaved in a manner that mimicked key physiological responses seen in other mammalian systems. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'. [ABSTRACT FROM AUTHOR]

Background: Many studies have found that viral infections affect different tissues, including the inner ear. Coronavirus disease 2019 (COVID-19), a viral infection, is a significant health problem worldwide. Prestin is a motor protein with important functions both in the outer hair cells of the inner ear and in cardiac tissue. In addition, prestin is promising as an early biomarker in the detection of ototoxicity. To determine the severity of infection in COVID-19 patients and to determine whether other tissues are affected by the infection, lactate dehydrogenase (LDH), C-reactive protein (CRP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase MB (CK-MB), biochemical markers such as ferritin and D-dimer are used. This study aimed to compare prestin levels in patients with COVID-19 and healthy volunteers. Methods: In blood samples taken from 45 patients diagnosed with COVID-19 and 40 healthy volunteers, prestin levels were determined with the kit that used an enzyme-linked immunosorbent assay method and was commercially available. At the same time, LDH, CRP, ALT, AST, CK-MB, ferritin, and D-dimer levels were also detected in both patients and healthy control groups and correlations with prestin levels were examined. Results: The main result of our study is that serum prestin levels in COVID-19 patients are significantly higher than in healthy controls (p < 0.001). In addition, a statistically significant strong positive correlation was found between prestin-LDL (r = 0.537, p = 0.001), prestin-CRP (r = 0.654, p = 0.001), and prestin-D-dimer (r = 0.659, p = 0.001). Conclusion: The levels of prestin, a motor protein in inner ear outer hair cells and cardiac myocytes, were found to be higher in COVID-19 patients than in healthy volunteers. It also showed a positive correlation with CRP and D-dimer. This may be associated with systemic dysfunction. [ABSTRACT FROM AUTHOR]

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia due to inadequate insulin secretion, resistance, or both. The cardiovascular complications of DM are the leading cause of morbidity and mortality in diabetic patients. There are three major types of pathophysiologic cardiac remodeling including coronary artery atherosclerosis, cardiac autonomic neuropathy, and DM cardiomyopathy in patients with DM. DM cardiomyopathy is a distinct cardiomyopathy characterized by myocardial dysfunction in the absence of coronary artery disease, hypertension, and valvular heart disease. Cardiac fibrosis, defined as the excessive deposition of extracellular matrix (ECM) proteins, is a hallmark of DM cardiomyopathy. The pathophysiology of cardiac fibrosis in DM cardiomyopathy is complex and involves multiple cellular and molecular mechanisms. Cardiac fibrosis contributes to the development of heart failure with preserved ejection fraction (HFpEF), which increases mortality and the incidence of hospitalizations. As medical technology advances, the severity of cardiac fibrosis in DM cardiomyopathy can be evaluated by non-invasive imaging modalities such as echocardiography, heart computed tomography (CT), cardiac magnetic resonance imaging (MRI), and nuclear imaging. In this review article, we will discuss the pathophysiology of cardiac fibrosis in DM cardiomyopathy, non-invasive imaging modalities to evaluate the severity of cardiac fibrosis, and therapeutic strategies for DM cardiomyopathy. [ABSTRACT FROM AUTHOR]

Most cardiomyocytes (CMs) in the adult mammalian heart are either binucleated or contain a single polyploid nucleus. Recent studies have shown that polyploidy in CMs plays an important role as an adaptive response to physiological demands and environmental stress and correlates with poor cardiac regenerative ability after injury. However, knowledge about the functional properties of polyploid CMs is limited. In this study, we generated tetraploid pluripotent stem cells (PSCs) by fusion of murine embryonic stem cells (ESCs) and somatic cells isolated from bone marrow or spleen and performed a comparative analysis of the electrophysiological properties of tetraploid fusion-derived PSCs and diploid ESC-derived CMs. Fusion-derived PSCs exhibited characteristics of genuine ESCs and contained a near-tetraploid genome. Ploidy features and marker expression were also retained during the differentiation of fusion-derived cells. Fusion-derived PSCs gave rise to CMs, which were similar to their diploid ESC counterparts in terms of their expression of typical cardiospecific markers, sarcomeric organization, action potential parameters, response to pharmacologic stimulation with various drugs, and expression of functional ion channels. These results suggest that the state of ploidy does not significantly affect the structural and electrophysiological properties of murine PSC-derived CMs. These results extend our knowledge of the functional properties of polyploid CMs and contribute to a better understanding of their biological role in the adult heart. [ABSTRACT FROM AUTHOR]

Copyright of Herz is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dystrophic cardiomyopathy arises from mutations in the dystrophin gene. Dystrophin forms part of the dystrophin glycoprotein complex and is postulated to act as a membrane stabilizer, protecting the sarcolemma from contraction-induced damage. Duchenne muscular dystrophy (DMD) is the most severe dystrophinopathy, caused by a total absence of dystrophin. Patients with DMD present with progressive skeletal muscle weakness and, because of treatment advances, a cardiac component of the disease (i.e., dystrophic cardiomyopathy) has been unmasked later in disease progression. The role that myofilaments play in dystrophic cardiomyopathy is largely unknown and, as such, this study aimed to address cardiac myofilament function in a mouse model of muscular dystrophy. To assess the effects of DMD on myofilament function, isolated permeabilized cardiomyocytes of wild-type (WT) littermates and Dmdmdx-4cv mice were attached between a force transducer and motor and subjected to contractile assays. Maximal tension and rates of force development (indexed by the rate constant, ktr) were similar between WT and Dmdmdx-4cv cardiac myocyte preparations. Interestingly, Dmdmdx-4cv cardiac myocytes exhibited greater sarcomere length dependence of peak power output compared to WT myocyte preparations. These results suggest dystrophin mitigates length dependence of activation and, in the absence of dystrophin, augmented sarcomere length dependence of myocyte contractility may accelerate ventricular myocyte contraction-induced damage and contribute to dystrophic cardiomyopathy. Next, we assessed if mavacamten, a small molecule modulator of thick filament activation, would mitigate contractile properties observed in Dmdmdx-4cv permeabilized cardiac myocyte preparations. Mavacamten decreased maximal tension and ktr in both WT and Dmdmdx-4cv cardiac myocytes, while also normalizing the length dependence of peak power between WT and Dmdmdx-4cv cardiac myocyte preparations. These results highlight potential benefits of mavacamten (i.e., reduced contractility while maintaining exquisite sarcomere length dependence of power output) as a treatment for dystrophic cardiomyopathy associated with DMD.

RationaleGq signaling in cardiac myocytes is classically considered toxic. Targeting Gq directly to test this is problematic, because cardiac myocytes have many Gq-coupled receptors.ObjectiveTest whether Gq coupling is required for the cardioprotective effects of an alpha-1A-AR (adrenergic receptor) agonist.Methods and resultsIn recombinant cells, a mouse alpha-1A-AR with a 6-residue substitution in the third intracellular loop does not couple to Gq signaling. Here we studied a knockin mouse with this alpha-1A-AR mutation. Heart alpha-1A receptor levels and antagonist affinity in the knockin were identical to wild-type. In wild-type cardiac myocytes, the selective alpha-1A agonist A61603-stimulated phosphoinositide-phospholipase C and myocyte contraction. In myocytes with the alpha-1A knockin, both A61603 effects were absent, indicating that Gq coupling was absent. Surprisingly, A61603 activation of cardioprotective ERK (extracellular signal-regulated kinase) was markedly impaired in the KI mutant myocytes, and A61603 did not protect mutant myocytes from doxorubicin toxicity in vitro. Similarly, mice with the α1A KI mutation had increased mortality after transverse aortic constriction, and A61603 did not rescue cardiac function in mice with the Gq coupling-defective alpha-1A receptor.ConclusionsGq coupling is required for cardioprotection by an alpha-1A-AR agonist. Gq signaling can be adaptive.

Tributyltin (TBT) is an organotin environmental pollutant widely used as an agricultural and wood biocide and in antifouling paints. Countries began restricting TBT use in the 2000s, but their use continues in some agroindustrial processes. We studied the acute effect of TBT on cardiac function by analyzing myocardial contractility and Ca2+ handling. Cardiac contractility was evaluated in isolated papillary muscle and whole heart upon TBT exposure. Isolated ventricular myocytes were used to measure calcium (Ca2+) transients, sarcoplasmic reticulum (SR) Ca2+ content and SR Ca2+ leak (as Ca2+ sparks). Reactive oxygen species (ROS), as superoxide anion (O2•-) was detected at intracellular and mitochondrial myocardium. TBT depressed cardiac contractility and relaxation in papillary muscle and intact whole heart. TBT increased cytosolic, mitochondrial ROS production and decreased mitochondrial membrane potential. In isolated cardiomyocytes TBT decreased both Ca2+ transients and SR Ca2+ content and increased diastolic SR Ca2+ leak. Decay of twitch and caffeine-induced Ca2+ transients were slowed by the presence of TBT. Dantrolene prevented and Tiron limited the reduction in SR Ca2+ content and transients. The environmental contaminant TBT causes cardiotoxicity within minutes, and may be considered hazardous to the mammalian heart. TBT acutely induced a negative inotropic effect in isolated papillary muscle and whole heart, increased arrhythmogenic SR Ca2+ leak leading to reduced SR Ca2+ content and reduced Ca2+ transients. TBT-induced myocardial ROS production, may destabilize the SR Ca2+ release channel RyR2 and reduce SR Ca2+ pump activity as key factors in the TBT-induced negative inotropic and lusitropic effects.

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) are at the center of new cell-based therapies for cardiac disease, but may also serve as a useful in vitro model for cardiac cell development. An intriguing feature of hESC-CMs is that although they express contractile proteins and have sarcomeres, they do not develop transverse-tubules (T-tubules) with adult-like Ca2+ release units (CRUs). We tested the hypothesis that expression of the protein BIN1 in hESC-CMs promotes T-tubules formation, facilitates CaV 1.2 channel clustering along the tubules, and results in the development of stable CRUs. Using electrophysiology, [Ca2+ ]i imaging, and super resolution microscopy, we found that BIN1 expression induced T-tubule development in hESC-CMs, while increasing differentiation toward a more ventricular-like phenotype. Voltage-gated CaV 1.2 channels clustered along the surface sarcolemma and T-tubules of hESC-CM. The length and width of the T-tubules as well as the expression and size of CaV 1.2 clusters grew, as BIN1 expression increased and cells matured. BIN1 expression increased CaV 1.2 channel activity and the probability of coupled gating within channel clusters. Interestingly, BIN1 clusters also served as sites for sarcoplasmic reticulum (SR) anchoring and stabilization. Accordingly, BIN1-expressing cells had more CaV 1.2-ryanodine receptor junctions than control cells. This was associated with larger [Ca2+ ]i transients during excitation-contraction coupling. Our data support the view that BIN1 is a key regulator of T-tubule formation and CaV 1.2 channel delivery. By studying the role of BIN1 during the differentiation of hESC-CMs, we show that BIN1 is also important for CaV 1.2 channel clustering, junctional SR organization, and the establishment of excitation-contraction coupling. Stem Cells 2019;37:54-64.

Estrogen acting through estrogen receptor β (ERβ) has been shown to oppose the stimulation of cardiac myocytes and cardiac fibroblasts that results in cardiac hypertrophy and fibrosis. Previous work has implicated signal transduction from ERβ as being important to the function of estrogen in this regard. Here we address whether membrane ERβ is sufficient to oppose key mechanisms by which angiotensin II (AngII) stimulates cardiac cell pathology. To do this we first defined essential structural elements within ERβ that are necessary for membrane or nuclear localization in cells. We previously determined that cysteine 418 is the site of palmitoylation of ERβ that is required and sufficient for cell membrane localization in mice and is the same site in humans. Here we determined in Chinese hamster ovarian (CHO) cells, and mouse and rat myocytes and cardiac fibroblasts, the effect on multiple aspects of signal transduction by expressing wild-type (WT) or a C418A-mutant ERβ. To test the importance of the nuclear receptor, we determined a 4–amino acid deletion in the E domain of ERβ that strongly blocked nuclear localization. Using these tools, we expressed WT and mutant ERβ constructs into cardiomyocytes and cardiac fibroblasts from ERβ-deleted mice. We determined the ability of estrogen to mitigate cell pathology stimulated by AngII and whether the membrane ERβ is necessary and sufficient. [ABSTRACT FROM AUTHOR]

The cytochrome P450 reductase (POR) transfers electrons to all microsomal cytochrome P450 enzymes (CYP450) thereby driving their activity. In the vascular system, the POR/CYP450 system has been linked to the production of epoxyeicosatrienoic acids (EETs) but also to the generation of reactive oxygen species. In cardiac myocytes (CMs), EETs have been shown to modulate the cardiac function and have cardioprotective effects. The functional importance of the endothelial POR/CYP450 system in the heart is unclear and was studied here using endothelial cell-specific, inducible knockout mice of POR (ecPOR-/-). RNA sequencing of murine cardiac cells revealed a cell type-specific expression of different CYP450 homologues. Cardiac endothelial cells mainly expressed members of the CYP2 family which produces EETs, and of the CYP4 family that generates omega fatty acids. Tamoxifen-induced endothelial deletion of POR in mice led to cardiac remodelling under basal conditions, as shown by an increase in heart weight to body weight ratio and an increased CM area as compared to control animals. Endothelial deletion of POR was associated with a significant increase in endothelial genes linked to protein synthesis with no changes in genes of the oxidative stress response. CM of ecPOR-/- mice exhibited attenuated expression of genes linked to mitochondrial function and an increase in genes related to cardiac myocyte contractility. In a model of pressure overload (transverse aortic constriction, TAC with O-rings), ecPOR-/- mice exhibited an accelerated reduction in cardiac output (CO) and stroke volume (SV) as compared to control mice. These results suggest that loss of endothelial POR along with a reduction in EETs leads to an increase in vascular stiffness and loss in cardioprotection, resulting in cardiac remodelling. [ABSTRACT FROM AUTHOR]

The cytochrome P450 reductase (POR) transfers electrons to all microsomal cytochrome P450 enzymes (CYP450) thereby driving their activity. In the vascular system, the POR/CYP450 system has been linked to the production of epoxyeicosatrienoic acids (EETs) but also to the generation of reactive oxygen species. In cardiac myocytes (CMs), EETs have been shown to modulate the cardiac function and have cardioprotective effects. The functional importance of the endothelial POR/CYP450 system in the heart is unclear and was studied here using endothelial cell-specific, inducible knockout mice of POR (ecPOR−/−). RNA sequencing of murine cardiac cells revealed a cell type-specific expression of different CYP450 homologues. Cardiac endothelial cells mainly expressed members of the CYP2 family which produces EETs, and of the CYP4 family that generates omega fatty acids. Tamoxifen-induced endothelial deletion of POR in mice led to cardiac remodelling under basal conditions, as shown by an increase in heart weight to body weight ratio and an increased CM area as compared to control animals. Endothelial deletion of POR was associated with a significant increase in endothelial genes linked to protein synthesis with no changes in genes of the oxidative stress response. CM of ecPOR−/− mice exhibited attenuated expression of genes linked to mitochondrial function and an increase in genes related to cardiac myocyte contractility. In a model of pressure overload (transverse aortic constriction, TAC with O-rings), ecPOR−/− mice exhibited an accelerated reduction in cardiac output (CO) and stroke volume (SV) as compared to control mice. These results suggest that loss of endothelial POR along with a reduction in EETs leads to an increase in vascular stiffness and loss in cardioprotection, resulting in cardiac remodelling.

Simultaneous myofibril and mitochondrial development is crucial for the cardiac differentiation of pluripotent stem cells (PSCs). Specifically, mitochondrial energy metabolism (MEM) development in cardiomyocytes is essential for the beating function. Although previous studies have reported that MEM is correlated with cardiac differentiation, the process and timing of MEM regulation for cardiac differentiation remain poorly understood. Here, we performed transcriptome analysis of cells at specific stages of cardiac differentiation from mouse embryonic stem cells (mESCs) and human induced PSCs (hiPSCs). We selected MEM genes strongly upregulated at cardiac lineage commitment and in a time-dependent manner during cardiac maturation and identified the protein-protein interaction networks. Notably, MEM proteins were found to interact closely with cardiac maturation-related proteins rather than with cardiac lineage commitment-related proteins. Furthermore, MEM proteins were found to primarily interact with cardiac muscle contractile proteins rather than with cardiac transcription factors. We identified several candidate MEM regulatory genes involved in cardiac lineage commitment (Cck, Bdnf, Fabp4, Cebpα, and Cdkn2a in mESC-derived cells, and CCK and NOS3 in hiPSC-derived cells) and cardiac maturation (Ppargc1α, Pgam2, Cox6a2, and Fabp3 in mESC-derived cells, and PGAM2 and SLC25A4 in hiPSC-derived cells). Therefore, our findings show the importance of MEM in cardiac maturation. [ABSTRACT FROM AUTHOR]

Background: Mesenchymal stem cells (MSC) possess specific properties that make them good candidates for cell therapy, especially in organs like the heart with limited regeneration capacity. Generating cardiac myocytes in vitro is an important step toward restoring lost function in cardiovascular diseases. Objective: In this study, we investigated the potential of a human cardiomyocytes-conditioned medium to induce cardiogenic differentiation (indicated by GATA4 expression) of rat bone marrow MSCs. Methods: Rat bone marrow MSCs were extracted and cultured. They were characterized based on morphology, adipogenic and cardiogenic differentiation potential, and expression of mesenchymal markers. MSCs were exposed to the conditioned medium (case group) or normal saline for 1, 3, and 7 days. The growth curve, population doubling time, and GATA4 expression were compared between the groups. Results: MSCs of the case group showed accelerated growth with a lower population doubling time. GATA4 expression as a specific cardiac marker was significantly higher in the case group compared with the controls on day 1. By days 3 and 7, GATA4 expression remained higher, albeit the difference with the control group became less. Conclusions: Our findings demonstrated that possible cardiac myocyte-derived factors instigate the proliferation and cardiogenic differentiation of MSCs. This study provides a novel bone marrow MSC model for investigating early cardiomyocyte generation, which can open new avenues in the treatment of heart diseases. [ABSTRACT FROM AUTHOR]

Fibrosis is implicated in nearly all forms of cardiomyopathy and significantly influences disease severity and outcomes. The primary cell responsible for fibrosis is the cardiac fibroblast, which remains understudied relative to cardiomyocytes in the context of cardiomyopathy. The development of induced pluripotent stem cell-derived cardiac fibroblasts (iPSC-CFs) allows for the modeling of patient-specific disease characteristics and provides a scalable source of fibroblasts. iPSC-CFs are invaluable for understanding molecular pathways that affect disease progression and outcomes. This review explores various aspects of cardiomyopathy, with a focus on dilated cardiomyopathy (DCM), that can be modeled using iPSC-CFs and their application in drug discovery, given the current lack of approved therapies for cardiac fibrosis. We examine how iPSC-CFs can be utilized to study heart development, fibroblast heterogeneity, and activation, with the ultimate goal of developing better therapies for patients with cardiomyopathies. Significance Statement Here, we explore how iPSC-CFs can be used to study the fibrotic component of DCM. Most research has focused on cardiomyocytes, despite the significant contribution of fibroblasts to disease outcomes. iPSC-CFs serve as a valuable tool to elucidate molecular pathways leading to fibrosis, and paracrine interactions with cardiomyocytes, which are not fully understood. Gaining insights into these events could aid in the development of new therapies and enable the use of patient-derived iPSC-CFs for precision medicine, ultimately improving patient outcomes., (Copyright © 2024 American Society for Pharmacology and Experimental Therapeutics.)

Background The postmitotic state of adult cardiomyocytes, maintained by the cell cycle repressor Rbl2 (retinoblastoma‐like 2), is associated with considerable resistance to apoptosis. However, whether Rbl2 regulates cardiomyocyte apoptosis remains unknown. Methods and Results Here, we show that ablation of Rbl2 increased cardiomyocyte apoptosis following acute myocardial ischemia/reperfusion injury, leading to diminished cardiac function and exaggerated ventricular remodeling in the long term. Mechanistically, ischemia/reperfusion induced expression of the proapoptotic protein BCL2 interacting protein 3 (Bnip3), which was augmented by deletion of Rbl2. Because the Bnip3 promoter contains an adenoviral early region 2 binding factor (E2F)‐binding site, we further showed that loss of Rbl2 upregulated the transcriptional activator E2F1 but downregulated the transcriptional repressor E2F4. In cultured cardiomyocytes, treatment with H2O2 markedly increased the levels of E2F1 and Bnip3, resulting in mitochondrial depolarization and apoptosis. Depletion of Rbl2 significantly augmented H2O2‐induced mitochondrial damage and apoptosis in vitro. Conclusions Rbl2 deficiency enhanced E2F1‐mediated Bnip3 expression, resulting in aggravated cardiomyocyte apoptosis and ischemia/reperfusion injury. Our results uncover a novel antiapoptotic role for Rbl2 in cardiomyocytes, suggesting that the cell cycle machinery may directly regulate apoptosis in postmitotic cardiomyocytes. These findings may be exploited to develop new strategies to limit ischemia/reperfusion injury in the treatment of acute myocardial infarction.

Hypoxia exerts broad effects on cardiomyocyte function and viability, ranging from altered metabolism and mitochondrial physiology to apoptotic or necrotic cell death. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a key regulator of cardiomyocyte metabolism and mitochondrial function and is down-regulated in hypoxia; however, the underlying mechanism is incompletely resolved. Using primary rat cardiomyocytes coupled with electrophoretic mobility shift and luciferase assays, we report that hypoxia impaired mitochondrial energetics and resulted in an increase in nuclear localization of the Nuclear Factor-κB (NF-κB) p65 subunit, and the association of p65 with the PGC-1α proximal promoter. Tumor necrosis factor α (TNFα), an activator of NF-κB signaling, similarly reduced PGC-1α expression and p65 binding to the PGC-1α promoter in a dose-dependent manner, and TNFα-mediated down-regulation of PGC-1α expression could be reversed by the NF-κB inhibitor parthenolide. RNA-seq analysis revealed that cardiomyocytes isolated from p65 knockout mice exhibited alterations in genes associated with chromatin remodeling. Decreased PGC-1α promoter transactivation by p65 could be partially reversed by the histone deacetylase inhibitor trichostatin A. These results implicate NF-κB signaling, and specifically p65, as a potent inhibitor of PGC-1α expression in cardiac myocyte hypoxia. [ABSTRACT FROM AUTHOR]

Recent studies have shown that protein arginine methyltransferase 1 (PRMT1) is highly expressed in the human heart, and loss of PRMT1 contributes to cardiac remodeling in the heart failure. However, the functional importance of PRMT1 in cardiac ion channels remains uncertain. The slow activating delayed rectifier K+ (IKs) channel is a cardiac K+ channel composed of KCNQ1 and KCNE1 subunits and is a new therapeutic target for treating lethal arrhythmias in many cardiac pathologies, especially heart failure. Here, we demonstrate that PRMT1 is a critical regulator of the IKs channel and cardiac rhythm. In the guinea pig ventricular myocytes, treatment with furamidine, a PRMT1‐specific inhibitor, prolonged the action potential duration (APD). We further show that this APD prolongation was attributable to IKs reduction. In HEK293T cells expressing human KCNQ1 and KCNE1, inhibiting PRMT1 via furamidine reduced IKs and concurrently decreased the arginine methylation of KCNQ1, a pore‐forming α‐subunit. Evidence presented here indicates that furamidine decreased IKs mainly by lowering the affinity of IKs channels for the membrane phospholipid, phosphatidylinositol 4,5‐bisphosphate (PIP2), which is crucial for pore opening. Finally, applying exogenous PIP2 to cardiomyocytes prevented the furamidine‐induced IKs reduction and APD prolongation. Taken together, these results indicate that PRMT1 positively regulated IKs activity through channel–PIP2 interaction, thereby restricting excessive cardiac action potential. [ABSTRACT FROM AUTHOR]

The sodium/potassium ATPase (NKA) is essential for establishing the normal intracellular [Na+] and [K+] and transmembrane gradients that are essential for many cellular functions, including cardiac electrophysiology and contractility. Different NKA isoforms exhibit differential expression levels, cellular localization, and function in different tissues and species. Prior work has indicated that the NKA-α1 isoform is quantitatively predominant in cardiac myocytes, but that the α2 isoform is preferentially concentrated in the transverse tubules (TT), possibly at junctions with the sarcoplasmic reticulum (SR) where α2 may preferentially modulate cardiac contractility. Here we measured subcellular localization of NKA-α1 and α2 using super-resolution microscopy (STED and STORM) and isoform-selective antibodies in mouse ventricular myocytes. We confirm the preferential localization of NKA-α2 in TT vs. surface sarcolemma, but also show that α2 is relatively excluded from longitudinal TT elements. In contrast NKA-α1 is relatively uniformly expressed in all three sarcolemmal regions. We also tested the hypothesis that NKA-α2 (vs. α1) is preferentially concentrated at SR junctional sites near ryanodine receptors (RyR2). The results refute this hypothesis, in that NKA-α1 and α2 were equally close to RyR2 at the TT, with no preferential NKA isoform localization near RyR2. We conclude that in contrast to relatively uniform NKA-α1 distribution, NKA-α2 is preferentially concentrated in the truly transverse (and not longitudinal) TT elements. However, NKA-α2 does not preferentially cluster at RyR2 junctions, so the TT NKA-α2 concentration may suffice for preferential effects of NKA-α2 inhibition on cardiac contractility.

Most cardiomyocytes (CMs) in the adult mammalian heart are either binucleated or contain a single polyploid nucleus. Recent studies have shown that polyploidy in CMs plays an important role as an adaptive response to physiological demands and environmental stress and correlates with poor cardiac regenerative ability after injury. However, knowledge about the functional properties of polyploid CMs is limited. In this study, we generated tetraploid pluripotent stem cells (PSCs) by fusion of murine embryonic stem cells (ESCs) and somatic cells isolated from bone marrow or spleen and performed a comparative analysis of the electrophysiological properties of tetraploid fusion-derived PSCs and diploid ESC-derived CMs. Fusion-derived PSCs exhibited characteristics of genuine ESCs and contained a near-tetraploid genome. Ploidy features and marker expression were also retained during the differentiation of fusion-derived cells. Fusion-derived PSCs gave rise to CMs, which were similar to their diploid ESC counterparts in terms of their expression of typical cardiospecific markers, sarcomeric organization, action potential parameters, response to pharmacologic stimulation with various drugs, and expression of functional ion channels. These results suggest that the state of ploidy does not significantly affect the structural and electrophysiological properties of murine PSC-derived CMs. These results extend our knowledge of the functional properties of polyploid CMs and contribute to a better understanding of their biological role in the adult heart.

Regulation of intracellular pH (pHi) in cardiomyocytes is crucial for cardiac function; however, currently known mechanisms for direct or indirect extrusion of acid from cardiomyocytes seem insufficient for energetically efficient extrusion of the massive H+ loads generated under in vivo conditions. In cardiomyocytes, voltage‐sensitive H+ channel activity mediated by the HVCN1 proton channel would be a highly efficient means of disposing of H+, while avoiding Na+ loading, as occurs during direct acid extrusion via Na+/H+ exchange or indirect acid extrusion via Na+–HCO3− cotransport. PCR and immunoblotting demonstrated expression of HVCN1 mRNA and protein in canine heart. Patch clamp analysis of canine ventricular myocytes revealed a voltage‐gated H+ current that was highly H+‐selective. The current was blocked by external Zn2+ and the HVCN1 blocker 5‐chloro‐2‐guanidinobenzimidazole. Both the gating and Zn2+ blockade of the current were strongly influenced by the pH gradient across the membrane. All characteristics of the observed current were consistent with the known hallmarks of HVCN1‐mediated H+ current. Inhibition of HVCN1 and the NHE1 Na+/H+ exchanger, singly and in combination, showed that either mechanism is largely sufficient to maintain pHi in beating cardiomyocytes, but that inhibition of both activities causes rapid acidification. These results show that HVCN1 is expressed in canine ventricular myocytes and provides a major H+ extrusion activity, with a capacity similar to that of NHE1. In the beating heart in vivo, this activity would allow Na+‐independent extrusion of H+ during each action potential and, when functionally coupled with anion transport mechanisms, could facilitate transport‐mediated CO2 disposal. Key points: Intracellular pH (pHi) regulation is crucial for cardiac function, as acidification depresses contractility and causes arrhythmias. H+ ions are generated in cardiomyocytes from metabolic processes and particularly from CO2 hydration, which has been shown to facilitate CO2 venting from mitochondria.Currently, the NHE1 Na+/H+ exchanger is viewed as the dominant H+ extrusion mechanism in cardiac muscle.We show that the HVCN1 voltage‐gated proton channel is present and functional in canine ventricular myocytes, and that HVCN1 and NHE1 both contribute to pHi regulation.HVCN1 provides an energetically efficient mechanism of H+ extrusion that would not cause Na+ loading, which can cause pathology, and that could contribute to transport‐mediated CO2 disposal.These results provide a major advance in our understanding of pHi regulation in cardiac muscle. [ABSTRACT FROM AUTHOR]

Pulmonary atresia with ventricular septal defect (PA/VSD) is a rare congenital heart disease (CHD) characterized by a lack of luminal continuity and blood flow from either the right ventricle or the pulmonary artery, together with VSDs. The prevalence of PA/VSD is about 0.2% of live births and approximately 2% of CHDs. PA/VSD is similar to tetralogy of Fallot (TOF) in terms of structural and pathological characteristics. The pathogenesis of these two CHDs remains incompletely understood. It was previously reported that N‐myc downstream‐regulated gene (NDRG)4 is required for myocyte proliferation during early cardiac development. In the present study, we enrolled 80 unrelated patients with PA/VSD or TOF and identified a probably damaging variant p.T256M of NDRG4. The p.T256M variant impaired the proliferation ability of human cardiac myocytes (hCM). Furthermore, the p.T256M variant resulted in G1 and G2 arrest of hCM, followed by an increase in p27 and caspase‐9 expression. Our results provide evidence that the p.T256M variant in NDRG4 is a pathogenic variant associated with impaired hCM proliferation and cell‐cycle arrest and likely contributes towards the pathogenesis of PA/VSD and TOF.

Heart failure (HF) refers to a progressive pathological condition when cardiac muscles fail to pump adequate blood supply (cardiac output) to meet the metabolic demand of the body. Among various cellular and molecular mechanisms identified for the onset and progression of HF, autophagy dysregulation is increasingly getting recognized. Autophagy is a natural cellular process that is observed in almost all eukaryotic cells. Autophagy removes damaged/long-lived organelles, protein aggregates, and unwanted cellular compomemts via forming autophagosomes then fusing with lysosomes. Although mild-to-moderate induction of autophagy is deemed cytoprotective and adaptive, excessive or unchecked induction of autophagy can be detrimental and maladaptive. Both adaptive and maladaptive autophagy play a vital role in the pathophysiology of HF. In the current review, we provide an overview of autophagy regulation in HF and possible strategies targeting autophagy for the management of HF.

RationaleMitochondria produce ATP, especially critical for survival of highly aerobic cells, such as cardiac myocytes. Conversely, opening of mitochondrial high-conductance and long-lasting permeability transition pores (mPTP) causes respiratory uncoupling, mitochondrial injury, and cell death. However, low conductance and transient mPTP openings (tPTP) might limit mitochondrial Ca(2+) load and be cardioprotective, but direct evidence for tPTP in cells is limited.ObjectiveTo directly characterize tPTP occurrence during sarcoplasmic reticulum Ca(2+) release in adult cardiac myocytes.Methods and resultsHere, we measured tPTP directly as transient drops in mitochondrial [Ca(2+)] ([Ca(2+)]mito) and membrane potential (ΔΨm) in adult cardiac myocytes during cyclic sarcoplasmic reticulum Ca release, by simultaneous live imaging of 500 to 1000 individual mitochondria. The frequency of tPTPs rose at higher [Ca(2+)]mito, [Ca(2+)]i, with 1 μmol/L peroxide exposure and in myocyte from failing hearts. The tPTPs were suppressed by preventing mitochondrial Ca(2+) influx, by mPTP inhibitor cyclosporine A, sanglifehrin, and in cyclophilin D knockout mice. These tPTP events were 57±5 s in duration, but were rare (occurring in