Abnormalities In Excitation-contraction Coupling Research Articles

A perspective on Notch signalling in progression and arrhythmogenesis in familial hypertrophic and dilated cardiomyopathies.

In this perspective, we discussed emerging data indicating a role for Notch signalling in inherited disorders of the heart failure with focus on hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) linked to variants of genes encoding mutant proteins of the sarcomere. We recently reported an upregulation of elements in the Notch signalling cascade in cardiomyocytes derived from human inducible pluripotent stem cells expressing a TNNT2 variant encoding cardiac troponin T (cTnT-I79N+/-), which induces hypertrophy, remodelling, abnormalities in excitation-contraction coupling and electrical instabilities (Shafaattalab S et al. 2021 Front. Cell Dev. Biol. 9, 787581. (doi:10.3389/fcell.2021.787581)). Our search of the literature revealed the novelty of this finding and stimulated us to discuss potential connections between the Notch signalling pathway and familial cardiomyopathies. Our considerations focused on the potential role of these interactions in arrhythmias, microvascular ischaemia, and fibrosis. This finding underscored a need to consider the role of Notch signalling in familial cardiomyopathies which are trigged by sarcomere mutations engaging mechano-signalling pathways for which there is evidence of a role for Notch signalling with crosstalk with Hippo signalling. Our discussion included a role for both cardiac myocytes and non-cardiac myocytes in progression of HCM and DCM. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Loss of dysferlin or myoferlin results in differential defects in excitation\u2013contraction coupling in mouse skeletal muscle

Muscular dystrophies are disorders characterized by progressive muscle loss and weakness that are both genotypically and phenotypically heterogenous. Progression of muscle disease arises from impaired regeneration, plasma membrane instability, defective membrane repair, and calcium mishandling. The ferlin protein family, including dysferlin and myoferlin, are calcium-binding, membrane-associated proteins that regulate membrane fusion, trafficking, and tubule formation. Mice lacking dysferlin (Dysf), myoferlin (Myof), and both dysferlin and myoferlin (Fer) on an isogenic inbred 129 background were previously demonstrated that loss of both dysferlin and myoferlin resulted in more severe muscle disease than loss of either gene alone. Furthermore, Fer mice had disordered triad organization with visibly malformed transverse tubules and sarcoplasmic reticulum, suggesting distinct roles of dysferlin and myoferlin. To assess the physiological role of disorganized triads, we now assessed excitation contraction (EC) coupling in these models. We identified differential abnormalities in EC coupling and ryanodine receptor disruption in flexor digitorum brevis myofibers isolated from ferlin mutant mice. We found that loss of dysferlin alone preserved sensitivity for EC coupling and was associated with larger ryanodine receptor clusters compared to wildtype myofibers. Loss of myoferlin alone or together with a loss of dysferlin reduced sensitivity for EC coupling, and produced disorganized and smaller ryanodine receptor cluster size compared to wildtype myofibers. These data reveal impaired EC coupling in Myof and Fer myofibers and slightly potentiated EC coupling in Dysf myofibers. Despite high homology, dysferlin and myoferlin have differential roles in regulating sarcotubular formation and maintenance resulting in unique impairments in calcium handling properties.

1430CRISPR/Cas9-mediated correction of Troponin I R186Q mutation rescues myofibrillar disarray and excitation-contraction coupling abnormalities in IPSC model from hypertrophic cardiomyopathy patient

1430CRISPR/Cas9-mediated correction of Troponin I R186Q mutation rescues myofibrillar disarray and excitation-contraction coupling abnormalities in IPSC model from hypertrophic cardiomyopathy patient

Meet the First Authors.

Meet the First Authors.

Post-Myocardial Infarction Exercise Training Reverses Cardiac Excitation-Contraction Coupling Abnormalities by Activating Cytoplasmic CaMKII

Post-myocardial infarction (MI) heart failure (HF) leads to abnormal excitation-contraction-coupling (ECC) causing cardiac dysfunctions attributable to hyper-activation of CaMKII. In contrast, exercise improves ECC in post-MI HF, but whether this is through CaMKII remains unknown. Our purpose was to test whether exercise reverses ECC dysfunction in post-MI HF through modulation of CaMKII. Permanent coronary artery ligation leading to HF was induced in Wistar rats. Four weeks after, regular treadmill running started (MI-TRN, n=14). Sham-operated (SHAM, n=12) and sedentary MI-HF (MI-SED, n=16) served as controls. MI-HF reduced exercise capacity 16% (p<0.01); exercise normalised this. Contractile function of twitch-stimulated cardiomyocytes was assessed using edge-detection and Fura-2 fluorescence microscopy with and without the CaMK inhibitor AIP (5uM). MI reduced contraction 40% (p<0.01) and increased contraction-relaxation times. This was explained by reduced Ca2+ transient amplitude and increased Ca2+ rise-decay times. Exercise corrected contraction and contraction-relaxation times, and improved Ca2+ handling. AIP abolished the exercise-induced improvement in contraction and Ca2+ transient amplitude (both p<0.01) and impaired relaxation and Ca2+ transient decay times (p<0.01) more in MI-TRN than MI-SED. Spontaneous Ca2+ waves and sparks were linescan confocal imaged in Fluo-3-loaded cardiomyocytes at normal (1.8mM) and high (5mM) extracellular Ca2+. MI increased wave frequency 65% and amplitude 21% (p<0.01); this was more pronounced at high Ca2+ and reversed by exercise. MI and AIP had no effect on sparks but they were elevated by exercise (p<0.01). AIP had no effect on Ca2+ wave frequency in MI-SED but increased frequency and amplitude in MI-TRN (p<0.05). In conclusion, CaMKII modulated exercise-induced improvements in cardiomyocyte function following MI-HF. In particular, exercise improved sarcoplasmic reticulum (SR) Ca2+-uptake and SR-loading by activating CaMKII, whereas Ca2+ release parameters were less affected. This suggests that exercise activated cytoplasmic, but not dyadic CaMKII.

Myocardial insulin resistance, metabolic stress and autophagy in diabetes

Clinical studies in humans strongly support a link between insulin resistance and non-ischaemic heart failure. The occurrence of a specific insulin-resistant cardiomyopathy, independent of vascular abnormalities, is now recognized. The progression of cardiac pathology linked with insulin resistance is poorly understood. Cardiac insulin resistance is characterized by reduced availability of sarcolemmal Glut-4 transporters and consequent lower glucose uptake. A shift away from glycolysis towards fatty acid oxidation for ATP supply is apparent and is associated with myocardial oxidative stress. Reliance of cardiomyocyte excitation-contraction coupling on glycolytically derived ATP supply potentially renders cardiac function vulnerable to the metabolic remodelling adaptations observed in diabetes development. Findings from Glut-4-knockout mice demonstrate that cardiomyocytes with extreme glucose uptake deficiency exhibit cardiac hypertrophy and marked excitation-contraction coupling abnormalities characterized by reduced sarcolemmal Ca(2+) influx and sarcoplasmic reticulum Ca(2+) uptake. The 'milder' phenotype fructose-fed mouse model of type 2 diabetes does not show evidence of cardiac hypertrophy, but cardiomyocyte loss linked with autophagic activation is evident. Fructose feeding induces a marked reduction in intracellular Ca(2+) availability with myofilament adaptation to preserve contractile function in this setting. The cardiac metabolic adaptations of two load-independent models of diabetes, namely the Glut-4-deficient mouse and the fructose-fed mouse are contrasted. The role of autophagy in diabetic cardiopathology is evaluated and anomalies of type 1 versus type 2 diabetic autophagic responses are highlighted.

Postoperative atrial fibrillation: mechanism, prevention, and future perspective

Postoperative atrial fibrillation (POAF) is the most common complication after cardiac surgery, despite improvements in anesthesia, surgical techniques, and medical therapies. Although beta-blockers have been proven to be effective, the incidence of POAF is around 20 % even with these agents. The mechanism of POAF is not fully elucidated and no optimal strategy has been established for POAF. There are two important elements of "structural" and "electrical" remodelling of the atrium in the mechanism of POAF. A patient's age and preoperative left atrial fibrosis can predict POAF associated with structural remodelling. Although inflammation and oxidative stress during cardiac surgery may be the underlying mechanisms for electrical remodelling causing POAF, there are no reliable clinical parameters for their detection. Nonetheless, postoperative P-wave dispersion and electromechanical delay, which reflects excitation-contraction coupling abnormalities, could be new parameters for POAF. In conclusion, despite the importance of prevention of POAF, there are only a few parameters for predicting POAF. It is therefore necessary to consider both disease-mediated structural remodeling before surgery and electrical remodeling caused by cardiac surgery.

Review Article: Phospholemman: A Novel Cardiac Stress Protein

Phospholemman (PLM), a member of the FXYD family of regulators of ion transport, is a major sarcolemmal substrate for protein kinases A and C in cardiac and skeletal muscle. In the heart, PLM co-localizes and co-immunoprecipitates with Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and L-type Ca(2+) channel. Functionally, when phosphorylated at serine(68), PLM stimulates Na(+)-K(+)-ATPase but inhibits Na(+)/Ca(2+) exchanger in cardiac myocytes. In heterologous expression systems, PLM modulates the gating of cardiac L-type Ca(2+) channel. Therefore, PLM occupies a key modulatory role in intracellular Na(+) and Ca(2+) homeostasis and is intimately involved in regulation of excitation-contraction (EC) coupling. Genetic ablation of PLM results in a slight increase in baseline cardiac contractility and prolongation of action potential duration. When hearts are subjected to catecholamine stress, PLM minimizes the risks of arrhythmogenesis by reducing Na(+) overload and simultaneously preserves inotropy by inhibiting Na(+)/Ca(2+) exchanger. In heart failure, both expression and phosphorylation state of PLM are altered and may partly account for abnormalities in EC coupling. The unique role of PLM in regulation of Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and potentially L-type Ca(2+) channel in the heart, together with the changes in its expression and phosphorylation in heart failure, make PLM a rational and novel target for development of drugs in our armamentarium against heart failure. Clin Trans Sci 2010; Volume 3: 189-196.

Transgenic expression of replication-restricted enteroviral genomes in heart muscle induces defective excitation-contraction coupling and dilated cardiomyopathy.

Numerous studies have implicated Coxsackievirus in acute and chronic heart failure. Although enteroviral nucleic acids have been detected in selected patients with dilated cardiomyopathy, the significance of such persistent nucleic acids is unknown. To investigate the mechanisms by which restricted viral replication with low level expression of Coxsackieviral proteins may be able to induce cardiomyopathy, we generated transgenic mice which express a replication-restricted full-length Coxsackievirus B3 (CVB3) cDNA mutant (CVB3DeltaVP0) in the heart driven by the cardiac myocyte-specific myosin light chain-2v (MLC-2v) promoter. CVB3DeltaVP0 was generated by mutating infectious CVB3 cDNA at the VP4/VP2 autocatalytic cleavage site from Asn-Ser to Lys-Ala. Cardiac-specific expression of this cDNA leads to synthesis of positive- and negative-strand viral RNA in the heart without formation of infectious viral progeny. Histopathologic analysis of transgenic hearts revealed typical morphologic features of myocardial interstitial fibrosis and in some cases degeneration of myocytes, thus resembling dilated cardiomyopathy in humans. There was also an increase in ventricular atrial natriuretic factor mRNA levels, demonstrating activation of the embryonic program of gene expression typical of ventricular hypertrophy and failure. Echocardiographic analysis demonstrated the presence of left ventricular dilation and decreased systolic function in the transgenic mice compared with wild-type littermates, evidenced by increased ventricular end-diastolic and end-systolic dimensions and decreased fractional shortening. Analysis of isolated myocytes from transgenic mice demonstrate that there is defective excitation-contraction coupling and a decrease in the magnitude of isolated cell shortening. These data demonstrate that restricted replication of enteroviral genomes in the heart can induce dilated cardiomyopathy with excitation-contraction coupling abnormalities similar to pressure overload models of dilated cardiomyopathy.

Deficient cellular cyclic AMP may causeboth cardiac and skeletal muscle dysfunction in heart failure

Deficient myocardial cyclic AMP concentrations contribute to abnormal Ca 2+ handling and systolic and diastolic dysfunction in chronic heart failure (CHF). We tested the hypothesis that decreased cyclic AMP in skeletal muscle of animals with failure may contribute to the weakness and easy fatiguability also common in patients with CHF. We compared intracellular Ca 2+ signaling and contractility in skeletal muscle preparations from rats 6 weeks after myocardial infarction-induced CHF versus sham-operated controls. Bundles of 100 to 200 cells were dissected from the extensor digitorum longus (EDL) muscle of control and CHF rats. Muscles from CHF rats exhibited depressed tension development compared with control muscles during twitches. Treatment with 2mM dibutyryl cyclic AMP returned tension and Ca 2+ towards normal levels. There was no evidence of cellular atrophy in the CHF rats. In conclusion, EDL skeletal muscle from rats with CHF had intrinsic abnormalities in excitation-contraction coupling that could be reversed with cyclic AMP supplementation as previously reported for the heart. This suggests that deficient cyclic AMP levels may contribute to both cardiac and skeletal muscle dysfunction in CHF.