Human cardiomyocyte calcium handling and transverse tubules in mid-stage of post-myocardial-infarction heart failure

L-Carnitine improves mechanical responses of cardiomyocytes and restores Ca2+ homeostasis during aging

L-Carnitine (β-hydroxy-γ-trimethylaminobutyric acid, LC) is a crucial molecule for the mitochondrial oxidation of fatty acids. It facilitates the transport of long-chain fatty acids into the mitochondrial matrix. The reduction in LC levels during the aging process has been linked to numerous cardiovascular disorders, including contractility dysfunction, and disrupted intracellular Ca2+ homeostasis. The aim of this study was to examine the effects of long-term (7 months) LC administration on cardiomyocyte contraction and intracellular Ca2+ transients ([Ca2+]i) in aging rats. Male albino Wistar rats were randomly assigned to either the control or LC-treated groups. LC (50 mg/kg body weight/day) was dissolved in distilled water and orally administered for a period of 7 months. The control group received distilled water alone. Subsequently, ventricular single cardiomyocytes were isolated, and the contractility and Ca2+ transients were recorded in aging (18 months) rats. This study demonstrates, for the first time, a novel inotropic effect of long-term LC treatment on rat ventricular cardiomyocyte contraction. LC increased cardiomyocyte cell shortening and resting sarcomere length. Furthermore, LC supplementation led to a reduction in resting [Ca2+]i level and an increase in the amplitude of [Ca2+]i transients, indicative of enhanced contraction. Consistent with these results, decay time of Ca2+ transients also decreased significantly in the LC-treated group. The long-term administration of LC may help restore the Ca2+ homeostasis altered during aging and could be used as a cardioprotective medication in cases where myocyte contractility is diminished.

RyR2-targeting therapy prevents left ventricular remodeling and ventricular tachycardia in post-infarction heart failure

BACKGROUND

Dantrolene binds to the Leu⁶⁰¹-Cys⁶²⁰ region of the N-terminal domain of cardiac ryanodine receptor (RyR2), which corresponds to the Leu⁵⁹⁰-Cys⁶⁰⁹ region of the skeletal ryanodine receptor, and suppresses diastolic Ca²⁺ leakage through RyR2.

OBJECTIVE

We investigated whether the chronic administration of dantrolene prevented left ventricular (LV) remodeling and ventricular tachycardia (VT) after myocardial infarction (MI) by the same mechanism with the mutation V3599K of RyR2, which indicated that the inhibition of diastolic Ca²⁺ leakage occurred by enhancing the binding affinity of calmodulin (CaM) to RyR2.

METHODS AND RESULTS

A left anterior descending coronary artery ligation MI model was developed in mice. Wild-type (WT) were divided into four groups: sham-operated mice (WT-Sham), sham-operated mice treated with dantrolene (WT-Sham-DAN), MI mice (WT-MI), and MI mice treated with dantrolene (WT-MI-DAN). Homozygous V3599K RyR2 knock-in (KI) mice were divided into two groups: sham-operated mice (KI-Sham) and MI mice (KI-MI). The mice were followed for 12 weeks. Survival was significantly higher in the WT-MI-DAN (73%) and KI-MI groups (70%) than the WT-MI group (40%). Echocardiography, pathological tissue, and epinephrine-induced VT studies showed that LV remodeling and VT were prevented in the WT-MI-DAN and KI-MI groups compared to the WT-MI group. An increase in diastolic Ca²⁺ spark frequency and a decrease in the binding affinity of CaM to the RyR2 were observed at 12 weeks after MI in the WT-MI group, although significant improvements in these values were observed in the WT-MI-DAN and KI-MI groups.

CONCLUSIONS

Pharmacological or genetic stabilization of RyR2 tetrameric structure improves survival after MI by suppressing LV remodeling and proarrhythmia.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Efficacy of the New Inotropic Agent Istaroxime in Acute Heart Failure

Current therapeutic strategies for acute heart failure (AHF) are based on traditional inotropic agents that are often associated with untoward effects; therefore, finding new effective approaches with a safer profile is dramatically needed. Istaroxime is a novel compound, chemically unrelated to cardiac glycosides, that is currently being studied for the treatment of AHF. Its effects are essentially related to its inotropic and lusitropic positive properties exerted through a dual mechanism of action: activation of the sarcoplasmic reticulum Ca2+ ATPase isoform 2a (SERCA2a) and inhibition of the Na+/K+-ATPase (NKA) activity. The advantages of istaroxime over the available inotropic agents include its lower arrhythmogenic action combined with its capability of increasing systolic blood pressure without augmenting heart rate. However, it has a limited half-life (1 hour) and is associated with adverse effects including pain at the injection site and gastrointestinal issues. Herein, we describe the main mechanism of action of istaroxime and we present a systematic overview of both clinical and preclinical trials testing this drug, underlining the latest insights regarding its adoption in clinical practice for AHF.

Dual inhibition of MAPK and PI3K/AKT pathways enhances maturation of human iPSC-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide great opportunities for mechanistic dissection of human cardiac pathophysiology; however, hiPSC-CMs remain immature relative to the adult heart. To identify novel signaling pathways driving the maturation process during heart development, we analyzed published transcriptional and epigenetic datasets from hiPSC-CMs and prenatal and postnatal human hearts. These analyses revealed that several components of the MAPK and PI3K-AKT pathways are downregulated in the postnatal heart. Here, we show that dual inhibition of these pathways for only 5 days significantly enhances the maturation of day 30 hiPSC-CMs in many domains: hypertrophy, multinucleation, metabolism, T-tubule density, calcium handling, and electrophysiology, many equivalent to day 60 hiPSC-CMs. These data indicate that the MAPK/PI3K/AKT pathways are involved in cardiomyocyte maturation and provide proof of concept for the manipulation of key signaling pathways for optimal hiPSC-CM maturation, a critical aspect of faithful in vitro modeling of cardiac pathologies and subsequent drug discovery.

The Mutual Relationship among Cardiovascular Diseases and COVID-19: Focus on Micronutrients Imbalance

Micronutrients are ions and vitamins humbly required by the human body. They play a main role in several physiological mechanisms and their imbalance is strongly associated with potentially-fatal complications. Micronutrient imbalance is associated with many cardiovascular diseases, such as arrythmias, heart failure, and ischemic heart disease. It has been also observed in coronavirus disease 2019 (COVID-19), particularly in most severe patients. The relationship between cardiovascular diseases and COVID-19 is mutual: the latter triggers cardiovascular disease onset and worsening while patients with previous cardiovascular disease may develop a more severe form of COVID-19. In addition to the well-known pathophysiological mechanisms binding COVID-19 and cardiovascular diseases together, increasing importance is being given to the impact of micronutrient alterations, often present during COVID-19 and able to affect the balance responsible for a good functioning of the cardiovascular system. In particular, hypokalemia, hypomagnesemia, hyponatremia, and hypocalcemia are strongly associated with worse outcome, while vitamin A and D deficiency are associated with thromboembolic events in COVID-19. Thus, considering how frequent the cardiovascular involvement is in patients with COVID-19, and how it majorly affects their prognosis, this manuscript provides a comprehensive review on the role of micronutrient imbalance in the interconnection between COVID-19 and cardiovascular diseases.

Mechanisms for the development of heart failure and improvement of cardiac function by angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, are well-known for the treatments of cardiovascular diseases, such as heart failure, hypertension and acute coronary syndrome. Several of these inhibitors including captopril, enalapril, ramipril, zofenopril and imidapril attenuate vasoconstriction, cardiac hypertrophy and adverse cardiac remodeling, improve clinical outcomes in patients with cardiac dysfunction and decrease mortality. Extensive experimental and clinical research over the past 35 years has revealed that the beneficial effects of ACE inhibitors in heart failure are associated with full or partial prevention of adverse cardiac remodeling. Since cardiac function is mainly determined by coordinated activities of different subcellular organelles, including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils, for regulating the intracellular concentration of Ca2+ and myocardial metabolism, there is ample evidence to suggest that adverse cardiac remodelling and cardiac dysfunction in the failing heart are the consequence of subcellular defects. In fact, the improvement of cardiac function by different ACE inhibitors has been demonstrated to be related to the attenuation of abnormalities in subcellular organelles for Ca2+-handling, metabolic alterations, signal transduction defects and gene expression changes in failing cardiomyocytes. Various ACE inhibitors have also been shown to delay the progression of heart failure by reducing the formation of angiotensin II, the development of oxidative stress, the level of inflammatory cytokines and the occurrence of subcellular defects. These observations support the view that ACE inhibitors improve cardiac function in the failing heart by multiple mechanisms including the reduction of oxidative stress, myocardial inflammation and Ca2+-handling abnormalities in cardiomyocytes.

Cenário Disfuncional dos Principais Componentes Responsáveis pelo Equilíbrio do Trânsito de Cálcio Miocárdico na Insuficiência Cardíaca Induzida por Estenose Aórtica

Fundamento

O remodelamento cardíaco patológico se caracteriza por disfunção diastólica e sistólica, levando à insuficiência cardíaca. Neste contexto, o cenário disfuncional do trânsito de cálcio miocárdico (Ca²⁺) tem sido pouco estudado. Um modelo experimental de estenose aórtica tem sido extensamente utilizado para aprimorar os conhecimentos sobre os principais mecanismos do remodelamento patológico cardíaco.

Objetivo

Entender o processo disfuncional dos principais componentes responsáveis pelo equilíbrio do cálcio miocárdico e sua influência sobre a função cardíaca na insuficiência cardíaca induzida pela estenose aórtica.

Métodos

Ratos Wistar de 21 dias de idade foram distribuídos em dois grupos: controle (placebo; n=28) e estenose aórtica (EaO; n=18). A função cardíaca foi analisada com o ecocardiograma, músculo papilar isolado e cardiomiócitos isolados. No ensaio do músculo papilar, SERCA2a e a atividade do canal de Ca²⁺ do tipo L foram avaliados. O ensaio de cardiomiócitos isolados avaliou o trânsito de cálcio. A expressão proteica da proteínas do trânsito de cálcio foi analisada com o western blot. Os resultados foram estatisticamente significativos quando p <0,05.

Resultados

Os músculos papilares e cardiomiócitos dos corações no grupo EaO demonstraram falhas mecânicas. Os ratos com EaO apresentaram menor tempo de pico do Ca²⁺, menor sensibilidade das miofibrilas do Ca²⁺, prejuízos nos processos de entrada e recaptura de cálcio pelo retículo sarcoplasmático, bem como disfunção no canal de cálcio do tipo L (CCTL). Além disso, os animais com EaO apresentaram maior expressão de SERCA2a, CCTL e trocador de Na⁺/Ca²⁺.

Conclusão

Insuficiência cardíaca sistólica e diastólica devido à estenose aórtica supravalvular acarretou comprometimento da entrada de Ca²⁺ celular e inibição da recaptura de cálcio pelo retículo sarcoplasmático devido à disfunção no CCTL e SERCA2a, assim como mudanças no trânsito de cálcio e na expressão das principais proteínas responsáveis pela homeostase de Ca²⁺ celular.

Phospholamban antisense oligonucleotides improve cardiac function in murine cardiomyopathy

Heart failure (HF) is a major cause of morbidity and mortality worldwide, highlighting an urgent need for novel treatment options, despite recent improvements. Aberrant Ca2+ handling is a key feature of HF pathophysiology. Restoring the Ca2+ regulating machinery is an attractive therapeutic strategy supported by genetic and pharmacological proof of concept studies. Here, we study antisense oligonucleotides (ASOs) as a therapeutic modality, interfering with the PLN/SERCA2a interaction by targeting Pln mRNA for downregulation in the heart of murine HF models. Mice harboring the PLN R14del pathogenic variant recapitulate the human dilated cardiomyopathy (DCM) phenotype; subcutaneous administration of PLN-ASO prevents PLN protein aggregation, cardiac dysfunction, and leads to a 3-fold increase in survival rate. In another genetic DCM mouse model, unrelated to PLN (Cspr3/Mlp-/-), PLN-ASO also reverses the HF phenotype. Finally, in rats with myocardial infarction, PLN-ASO treatment prevents progression of left ventricular dilatation and improves left ventricular contractility. Thus, our data establish that antisense inhibition of PLN is an effective strategy in preclinical models of genetic cardiomyopathy as well as ischemia driven HF.

Etiology-Dependent Impairment of Diastolic Cardiomyocyte Calcium Homeostasis in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Whereas heart failure with reduced ejection fraction (HFrEF) is associated with ventricular dilation and markedly reduced systolic function, heart failure with preserved ejection fraction (HFpEF) patients exhibit concentric hypertrophy and diastolic dysfunction. Impaired cardiomyocyte Ca²⁺ homeostasis in HFrEF has been linked to disruption of membrane invaginations called t-tubules, but it is unknown if such changes occur in HFpEF.

OBJECTIVES

This study examined whether distinct cardiomyocyte phenotypes underlie the heart failure entities of HFrEF and HFpEF.

METHODS

T-tubule structure was investigated in left ventricular biopsies obtained from HFrEF and HFpEF patients, whereas cardiomyocyte Ca²⁺ homeostasis was studied in rat models of these conditions.

RESULTS

HFpEF patients exhibited increased t-tubule density in comparison with control subjects. Super-resolution imaging revealed that higher t-tubule density resulted from both tubule dilation and proliferation. In contrast, t-tubule density was reduced in patients with HFrEF. Augmented collagen deposition within t-tubules was observed in HFrEF but not HFpEF hearts. A causative link between mechanical stress and t-tubule disruption was supported by markedly elevated ventricular wall stress in HFrEF patients. In HFrEF rats, t-tubule loss was linked to impaired systolic Ca²⁺ homeostasis, although diastolic Ca²⁺ removal was also reduced. In contrast, Ca²⁺ transient magnitude and release kinetics were largely maintained in HFpEF rats. However, diastolic Ca²⁺ impairments, including reduced sarco/endoplasmic reticulum Ca²⁺-ATPase activity, were specifically observed in diabetic HFpEF but not in ischemic or hypertensive models.

CONCLUSIONS

Although t-tubule disruption and impaired cardiomyocyte Ca²⁺ release are hallmarks of HFrEF, such changes are not prominent in HFpEF. Impaired diastolic Ca²⁺ homeostasis occurs in both conditions, but in HFpEF, this mechanism for diastolic dysfunction is etiology-dependent.

Repolarization instability and arrhythmia by IKr block in single human-induced pluripotent stem cell-derived cardiomyocytes and 2D monolayers

Aims

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have proven valuable for studies in drug discovery and safety, although limitations regarding their structural and electrophysiological characteristics persist. In this study, we investigated the electrophysiological properties of Pluricyte^® CMs, a commercially available hiPSC-CMs line with a ventricular phenotype, and assessed arrhythmia incidence by I_Kr block at the single-cell and 2D monolayer level.

Methods and results

Action potentials were measured at different pacing frequencies, using dynamic clamp. Through voltage-clamp experiments, we determined the properties of I_Na, I_Kr, and I_CaL. Intracellular Ca²⁺ measurements included Ca²⁺-transients at baseline and during caffeine perfusion. Effects of I_Kr block were assessed in single hiPSC-CMs and 2D monolayers (multi-electrode arrays). Action-potential duration (APD) and its rate dependence in Pluricyte^® CMs were comparable to those reported for native human CMs. I_Na, I_Kr, and I_CaL revealed amplitudes, kinetics, and voltage dependence of activation/inactivation similar to other hiPSC-CM lines and, to some extent, to native CMs. Near-physiological Ca²⁺-induced Ca²⁺ release, response to caffeine and excitation–contraction coupling gain characterized the cellular Ca²⁺-handling. Dofetilide prolonged the APD and field-potential duration, and induced early afterdepolarizations. Beat-to-beat variability of repolarization duration increased significantly before the first arrhythmic events in single Pluricyte^® CMs and 2D monolayers, and predicted pending arrhythmias better than action-potential prolongation.

Conclusion

Taking their ion-current characteristics and Ca²⁺ handling into account, Pluricyte^® CMs are suitable for in vitro studies on action potentials and field potentials. Beat-to-beat variability of repolarization duration proved useful to evaluate the dynamics of repolarization instability and demonstrated its significance as proarrhythmic marker in hiPSC-CMs during I_Kr block.

Abnormal Coagulation Function of Patients With COVID-19 Is Significantly Related to Hypocalcemia and Severe Inflammation

This study aimed to detect, analyze, and correlate the clinical characteristics, blood coagulation functions, blood calcium levels, and inflammatory factors in patients with mild and severe COVID-19 infections. The enrolled COVID-19 infected patients were from Wuhan Jin Yin-tan Hospital (17 cases, Wuhan, China), Suzhou Infectious Disease Hospital (87 cases, Suzhou, China), and Xuzhou Infectious Disease Hospital (14 cases, Xuzhou, China). After admission, basic information was collected; X-ray and chest CT images were obtained; and data from routine blood tests, liver and kidney function, myocardial enzymes, electrolytes, blood coagulation function, (erythrocyte sedimentation rate) ESR, C-reactive protein (CRP), IL-6, procalcitonin (PCT), calcitonin, and other laboratory tests were obtained. The patients were grouped according to the clinical classification method based on the pneumonia diagnosis and treatment plan for new coronavirus infection (trial version 7) in China. The measurements from mild (56 cases) and severe cases (51 cases) were compared and analyzed. Most COVID-19 patients presented with fever. Chest X-ray and CT images showed multiple patchy and ground glass opacities in the lungs of COVID 19 infected patients, especially in patients with severe cases. Compared with patients with mild infection, patients with severe infection were older (p = 0.023) and had a significant increase in AST and BUN. The levels of CK, LDH, CK-MB, proBNP, and Myo in patients with severe COVID-19 infection were also increased significantly compared to those in patients with mild cases. Patients with severe COVID-19 infections presented coagulation dysfunction and increased D-dimer and fibrin degradation product (FDP) levels. Severe COVID-19 patients had low serum calcium ion (Ca²⁺) concentrations and high calcitonin and PCT levels and exhibited serious systemic inflammation. Ca²⁺ in COVID-19 patients was significantly negatively correlated with PCT, calcitonin, D-dimer, PFDP, ESR, CRP and IL-6. D-dimer in COVID-19 patients was a significantly positively correlated with CRP and IL-6. In conclusion, patients with severe COVID-19 infection presented significant metabolic dysfunction and abnormal blood coagulation, a sharp increase in inflammatory factors and calcitonin and procalcitonin levels, and a significant decrease in Ca²⁺. Decreased Ca²⁺ and coagulation dysfunction in COVID-19 patients were significantly correlated with each other and with inflammatory factors.

Chronic Alcohol Intake Exacerbates Cardiac Dysfunction After Myocardial Infarction

AIMS

Alcohol intake is a risk factor for cardiovascular diseases. This study was designed to investigate whether chronic alcohol intake affects myocardial infarction (MI)-induced cardiac remodeling and heart failure.

METHODS

Eight-week-old male C57BL/6 mice were randomly divided into four groups: Sham group (Sham), MI plus drinking water group (MI + Vehicle), and MI plus daily alcohol intake for 6 weeks with or without gavage of additional alcohol every 3 days (MI + Alcohol and MI + Alcohol + G). The MI were induced by permanent left anterior descending (LAD) coronary artery ligation surgery before vehicle or alcohol treatment. The blood alcohol concentration (BAC), cardiac function, release of cardiac enzymes, pathological changes and mitochondrial function were measured.

RESULTS

As expected, supplementation of alcohol in drinking water significantly increased random BAC in mice. Long-term exposure to alcohol further reduced body weight, ejection fraction and fractional shortening in comparison with the MI + Vehicle group. Histopathological data showed that alcohol increased fibrosis in infarct zone, which was well correlated with the functional decline. Also, as compared to the MI + Vehicle group, the adenosine diphosphate-supported respiratory function of freshly isolated cardiac mitochondria was inhibited in the MI + Alcohol + G group. Besides, upon MI-induced cardiac damage, we did not observe further changes in heart weight, cardiomyocyte enlargement in remote zone, exercise capacity, lung edema and the release of cardiac enzyme after chronic alcohol intake.

CONCLUSIONS

Our study demonstrated that chronic daily alcohol exposure exacerbated MI-induced cardiac dysfunction, which is related to promoted myocardial fibrosis and inhibited mitochondrial function.

Disruption of transverse-tubular network reduces energy efficiency in cardiac muscle contraction

AIM

Altered organization of the transverse-tubular network is an early pathological event occurring even prior to the onset of heart failure. Such t-tubular remodelling disturbs the synchrony and signalling between membranous and intracellular ion channels, exchangers, receptors and ATPases essential in the dynamics of excitation-contraction coupling, leading to ionic abnormality and mechanical dysfunction in heart disease progression. In this study, we investigated whether a disrupted t-tubular network has a direct effect on cardiac mechano-energetics. Our aim was to understand the fundamental link between t-tubular remodelling and impaired energy metabolism, both of which are characteristics of heart failure. We thus studied healthy tissue preparations in which cellular processes are not altered by any disease event.

METHODS

We exploited the "formamide-detubulation" technique to acutely disrupt the t-tubular network in rat left-ventricular trabeculae. We assessed the energy utilization by cellular Ca²⁺ cycling and by crossbridge cycling, and quantified the change of energy efficiency following detubulation. For these measurements, trabeculae were mounted in a microcalorimeter where force and heat output were simultaneously measured.

RESULTS

Following structural disorganization from detubulation, muscle heat output associated with Ca²⁺ cycling was reduced, indicating impaired intracellular Ca²⁺ homeostasis. This led to reduced force production and heat output by crossbridge cycling. The reduction in force-length work was not paralleled by proportionate reduction in the heat output and, as such, energy efficiency was reduced.

CONCLUSIONS

These results reveal the direct energetic consequences of disrupted t-tubular network, linking the energy disturbance and the t-tubular remodelling typically observed in heart failure.

T-tubule remodeling in human hypertrophic cardiomyopathy

The highly organized transverse T-tubule membrane system represents the ultrastructural substrate for excitation–contraction coupling in ventricular myocytes. While the architecture and function of T-tubules have been well described in animal models, there is limited morpho-functional data on T-tubules in human myocardium. Hypertrophic cardiomyopathy (HCM) is a primary disease of the heart muscle, characterized by different clinical presentations at the various stages of its progression. Most HCM patients, indeed, show a compensated hypertrophic disease (“non-failing hypertrophic phase”), with preserved left ventricular function, and only a small subset of individuals evolves into heart failure (“end stage HCM”). In terms of T-tubule remodeling, the “end-stage” disease does not differ from other forms of heart failure. In this review we aim to recapitulate the main structural features of T-tubules during the “non-failing hypertrophic stage” of human HCM by revisiting data obtained from human myectomy samples. Moreover, by comparing pathological changes observed in myectomy samples with those introduced by acute (experimentally induced) detubulation, we discuss the role of T-tubular disruption as a part of the complex excitation–contraction coupling remodeling process that occurs during disease progression. Lastly, we highlight how T-tubule morpho-functional changes may be related to patient genotype and we discuss the possibility of a primitive remodeling of the T-tubule system in rare HCM forms associated with genes coding for proteins implicated in T-tubule structural integrity, formation and maintenance.

Myocardial Dysfunction in Cirrhotic Cardiomyopathy is Associated with Alterations of Phospholamban Phosphorylation and IL-6 Levels

BACKGROUND

Decreased cardiac contractility has been observed in cirrhosis, but the mechanisms that initiate and maintain cardiac dysfunction are not entirely understood.

AIM OF THE STUDY

We test the hypothesis that cirrhotic cardiomyopathy is related to deterioration of myocardial contractility due to alterations in calcium-handling proteins expression. In addition, we evaluated whether cardiac pro-inflammatory cytokine levels are associated with this process.

METHODS

Cirrhosis was induced by thioacetamide (TAA, 100 mg/kg/i.p., twice weekly for eight weeks). The myocardial performance was evaluated in isolated left ventricle papillary muscles under basal conditions and after inotropic challenge. The cardiac calcium handling protein expression was detected by Western blotting. Cardiac TNF-α and IL-6 levels were measured by ELISA.

RESULTS

Thioacetamide induced liver cirrhosis, which was associated with cirrhotic cardiomyopathy characterized by in vivo left ventricular diastolic and systolic dysfunction as well as cardiac hypertrophy. In vitro baseline myocardial contractility was lower in cirrhosis. Also, myocardial responsiveness to post-rest contraction stimulus was declined. Protein expression for RYR2, SERCA2, NCX, pPBL Ser¹⁶ and L-type calcium channel was quantitatively unchanged; however, pPBL Thr¹⁷ was significantly lower while IL-6 was higher.

CONCLUSIONS

Our study demonstrates that cirrhotic cardiomyopathy is associated with decreased cardiac contractility with alteration of phospholamban phosphorylation in association with higher cardiac pro-inflammatory IL-6 levels. These findings provided molecular and functional insights about the effects of liver cirrhosis on cardiac function.

Adrenergic supersensitivity and impaired neural control of cardiac electrophysiology following regional cardiac sympathetic nerve loss

Myocardial infarction (MI) can result in sympathetic nerve loss in the infarct region. However, the contribution of hypo-innervation to electrophysiological remodeling, independent from MI-induced ischemia and fibrosis, has not been comprehensively investigated. We present a novel mouse model of regional cardiac sympathetic hypo-innervation utilizing a targeted-toxin (dopamine beta-hydroxylase antibody conjugated to saporin, DBH-Sap), and measure resulting electrophysiological and Ca²⁺ handling dynamics. Five days post-surgery, sympathetic nerve density was reduced in the anterior left ventricular epicardium of DBH-Sap hearts compared to control. In Langendorff-perfused hearts, there were no differences in mean action potential duration (APD₈₀) between groups; however, isoproterenol (ISO) significantly shortened APD₈₀ in DBH-Sap but not control hearts, resulting in a significant increase in APD₈₀ dispersion in the DBH-Sap group. ISO also produced spontaneous diastolic Ca²⁺ elevation in DBH-Sap but not control hearts. In innervated hearts, sympathetic nerve stimulation (SNS) increased heart rate to a lesser degree in DBH-Sap hearts compared to control. Additionally, SNS produced APD₈₀ prolongation in the apex of control but not DBH-Sap hearts. These results suggest that hypo-innervated hearts have regional super-sensitivity to circulating adrenergic stimulation (ISO), while having blunted responses to SNS, providing important insight into the mechanisms of arrhythmogenesis following sympathetic nerve loss.

Non-coding RNAs: emerging players in cardiomyocyte proliferation and cardiac regeneration

Soon after birth, the regenerative capacity of the mammalian heart is lost, cardiomyocytes withdraw from the cell cycle and demonstrate a minimal proliferation rate. Despite improved treatment and reperfusion strategies, the uncompensated cardiomyocyte loss during injury and disease results in cardiac remodeling and subsequent heart failure. The promising field of regenerative medicine aims to restore both the structure and function of damaged tissue through modulation of cellular processes and regulatory mechanisms involved in cardiac cell cycle arrest to boost cardiomyocyte proliferation. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) are functional RNA molecules with no protein-coding function that have been reported to engage in cardiac regeneration and repair. In this review, we summarize the current understanding of both the biological functions and molecular mechanisms of ncRNAs involved in cardiomyocyte proliferation. Furthermore, we discuss their impact on the structure and contractile function of the heart in health and disease and their application for therapeutic interventions.

In-silico human electro-mechanical ventricular modelling and simulation for drug-induced pro-arrhythmia and inotropic risk assessment

Human-based computational modelling and simulation are powerful tools to accelerate the mechanistic understanding of cardiac patho-physiology, and to develop and evaluate therapeutic interventions. The aim of this study is to calibrate and evaluate human ventricular electro-mechanical models for investigations on the effect of the electro-mechanical coupling and pharmacological action on human ventricular electrophysiology, calcium dynamics, and active contraction. The most recent models of human ventricular electrophysiology, excitation-contraction coupling, and active contraction were integrated, and the coupled models were calibrated using human experimental data. Simulations were then conducted using the coupled models to quantify the effects of electro-mechanical coupling and drug exposure on electrophysiology and force generation in virtual human ventricular cardiomyocytes and tissue. The resulting calibrated human electro-mechanical models yielded active tension, action potential, and calcium transient metrics that are in agreement with experiments for endocardial, epicardial, and mid-myocardial human samples. Simulation results correctly predicted the inotropic response of different multichannel action reference compounds and demonstrated that the electro-mechanical coupling improves the robustness of repolarisation under drug exposure compared to electrophysiology-only models. They also generated additional evidence to explain the partial mismatch between in-silico and in-vitro experiments on drug-induced electrophysiology changes. The human calibrated and evaluated modelling and simulation framework constructed in this study opens new avenues for future investigations into the complex interplay between the electrical and mechanical cardiac substrates, its modulation by pharmacological action, and its translation to tissue and organ models of cardiac patho-physiology.

Calcium Signaling in Cardiomyocyte Function

Rhythmic increases in intracellular Ca²⁺ concentration underlie the contractile function of the heart. These heart muscle-wide changes in intracellular Ca²⁺ are induced and coordinated by electrical depolarization of the cardiomyocyte sarcolemma by the action potential. Originating at the sinoatrial node, conduction of this electrical signal throughout the heart ensures synchronization of individual myocytes into an effective cardiac pump. Ca²⁺ signaling pathways also regulate gene expression and cardiomyocyte growth during development and in pathology. These fundamental roles of Ca²⁺ in the heart are illustrated by the prevalence of altered Ca²⁺ homeostasis in cardiovascular diseases. Indeed, heart failure (an inability of the heart to support hemodynamic needs), rhythmic disturbances, and inappropriate cardiac growth all share an involvement of altered Ca²⁺ handling. The prevalence of these pathologies, contributing to a third of all deaths in the developed world as well as to substantial morbidity makes understanding the mechanisms of Ca²⁺ handling and dysregulation in cardiomyocytes of great importance.

microRNA-451a prevents activation of matrix metalloproteinases 2 and 9 in human cardiomyocytes during pathological stress stimulation

Matrix metalloproteinases (MMP) are important for cardiac remodeling. Recently, microRNA (miR)-451a has been found to inhibit the expression of both MMP-2 and MMP-9 in human malignancies, but its role in cardiomyocytes has not been explored. We hypothesized that miR-451a modulates MMP-2 and MMP-9 levels in human cardiomyocytes. The role of miR-451a on regulation of MMP-2 and MMP-9 was evaluated in two separate pathological models using Cor.4U human inducible pluripotent stem cell-derived cardiomyocytes (hiPS-CMs): 1) endothelin-1 (ET-1), and 2) 48-h hypoxia (1% O₂). Both models were transfected with synthetic miR-451a mimics or scramble control. Expression of both mRNA and miR was determined by quantitative real-time polymerase chain reaction and protein activity by (MMP-2/9) activity assay. Bioinformatic analyses were performed using Targetscan 7.1 and STRING 10.5. hiPS-CMs stimulated by hypoxia increased both MMP-2 and MMP-9 expression levels compared with normoxia (P < 0.05), whereas ET-1 stimulation only increased the MMP-9 level compared with vehicle controls (P < 0.05). miR-451a mimics prevented the increase of MMP-2 and MMP-9 expression in both models. Protein activity of MMP-2 and MMP-9 was confirmed to be lower following treatment with miR-451a mimic compared with scramble-controls. Six of 28 predicted gene transcripts of miR-451a were linked to MMP-2 and MMP-9; Macrophage migration inhibitory factor (MIF) was the only predicted target of miR-451a that was increased by ET-1 and hypoxia and reduced following miR-451a mimic transfection. miR-451a prevent the increase of MMP-2 and MMP-9 in human cardiomyocytes during pathological stress. The modulation by miR-451a on MMP-2 and MMP-9 is caused by MIF.

Cardiomyocyte damage control in heart failure and the role of the sarcolemma

The cardiomyocyte plasma membrane, termed the sarcolemma, is fundamental for regulating a myriad of cellular processes. For example, the structural integrity of the cardiomyocyte sarcolemma is essential for mediating cardiac contraction by forming microdomains such as the t-tubular network, caveolae and the intercalated disc. Significantly, remodelling of these sarcolemma microdomains is a key feature in the development and progression of heart failure (HF). However, despite extensive characterisation of the associated molecular and ultrastructural events there is a lack of clarity surrounding the mechanisms driving adverse morphological rearrangements. The sarcolemma also provides protection, and is the cell's first line of defence, against external stresses such as oxygen and nutrient deprivation, inflammation and oxidative stress with a loss of sarcolemma viability shown to be a key step in cell death via necrosis. Significantly, cumulative cell death is also a feature of HF, and is linked to disease progression and loss of cardiac function. Herein, we will review the link between structural and molecular remodelling of the sarcolemma associated with the progression of HF, specifically considering the evidence for: (i) Whether intrinsic, evolutionary conserved, plasma membrane injury-repair mechanisms are in operation in the heart, and (ii) if deficits in key 'wound-healing' proteins (annexins, dysferlin, EHD2 and MG53) may play a yet to be fully appreciated role in triggering sarcolemma microdomain remodelling and/or necrosis. Cardiomyocytes are terminally differentiated with very limited regenerative capability and therefore preserving cell viability and cardiac function is crucially important. This review presents a novel perspective on sarcolemma remodelling by considering whether targeting proteins that regulate sarcolemma injury-repair may hold promise for developing new strategies to attenuate HF progression.

Identification of time‑series differentially expressed genes and pathways associated with heart failure post‑myocardial infarction using integrated bioinformatics analysis

Heart failure (HF) secondary to acute myocardial infarction (AMI) is a public health concern. The current study aimed to investigate differentially expressed genes (DEGs) and their possible function in HF post-myocardial infarction. The GSE59867 dataset included microarray data from peripheral blood samples obtained from HF and non-HF patients following AMI at 4 time points (admission, discharge, and 1 and 6 months post-AMI). Time-series DEGs were analyzed using R Bioconductor. Functional enrichment analysis was performed, followed by analysis of protein-protein interactions (PPIs). A total of 108 DEGs on admission, 32 DEGs on discharge, 41 DEGs at 1 month post-AMI and 19 DEGs at 6 months post-AMI were identified. Among these DEGs, 4 genes were downregulated at all the 4 time points. These included fatty acid desaturase 2, leucine rich repeat neuronal protein 3, G-protein coupled receptor 15 and adenylate kinase 5. Functional enrichment analysis revealed that these DEGs were mainly enriched in ‘inflammatory response’, ‘immune response’, ‘toll-like receptor signaling pathway’ and ‘NF-κβ signaling pathway’. Furthermore, PPI network analysis revealed that C-X-C motif chemokine ligand 8 and interleukin 1β were hub genes. The current study identified candidate DEGs and pathways that may serve important roles in the development of HF following AMI. The results obtained in the current study may guide the development of novel therapeutic agents for HF following AMI.

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca²⁺ transport protein complexes including plasmalemmal L-type Ca²⁺ channels (LTCC), Na⁺-Ca²⁺ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca²⁺-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca²⁺ release channels. Here we provide an overview of changes in Ca²⁺ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca²⁺ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca²⁺ transport protein complexes including plasmalemmal L-type Ca²⁺ channels (LTCC), Na⁺-Ca²⁺ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca²⁺-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca²⁺ release channels. Here we provide an overview of changes in Ca²⁺ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca²⁺ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca²⁺ transport protein complexes including plasmalemmal L-type Ca²⁺ channels (LTCC), Na⁺-Ca²⁺ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca²⁺-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca²⁺ release channels. Here we provide an overview of changes in Ca²⁺ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca²⁺ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.

Human cardiomyocyte calcium handling and transverse tubules in mid-stage of post-myocardial-infarction heart failure

AIMS

Cellular processes in the heart rely mainly on studies from experimental animal models or explanted hearts from patients with terminal end-stage heart failure (HF). To address this limitation, we provide data on excitation contraction coupling, cardiomyocyte contraction and relaxation, and Ca²⁺ handling in post-myocardial-infarction (MI) patients at mid-stage of HF.

METHODS AND RESULTS

Nine MI patients and eight control patients without MI (non-MI) were included. Biopsies were taken from the left ventricular myocardium and processed for further measurements with epifluorescence and confocal microscopy. Cardiomyocyte function was progressively impaired in MI cardiomyocytes compared with non-MI cardiomyocytes when increasing electrical stimulation towards frequencies that simulate heart rates during physical activity (2 Hz); at 3 Hz, we observed almost total breakdown of function in MI. Concurrently, we observed impaired Ca²⁺ handling with more spontaneous Ca²⁺ release events, increased diastolic Ca²⁺ , lower Ca²⁺ amplitude, and prolonged time to diastolic Ca²⁺ removal in MI (P < 0.01). Significantly reduced transverse-tubule density (-35%, P < 0.01) and sarcoplasmic reticulum Ca²⁺ adenosine triphosphatase 2a (SERCA2a) function (-26%, P < 0.01) in MI cardiomyocytes may explain the findings. Reduced protein phosphorylation of phospholamban (PLB) serine-16 and threonine-17 in MI provides further mechanisms to the reduced function.

CONCLUSIONS

Depressed cardiomyocyte contraction and relaxation were associated with impaired intracellular Ca²⁺ handling due to impaired SERCA2a activity caused by a combination of alteration in the PLB/SERCA2a ratio and chronic dephosphorylation of PLB as well as loss of transverse tubules, which disrupts normal intracellular Ca²⁺ homeostasis and handling. This is the first study that presents these mechanisms from viable and intact cardiomyocytes isolated from the left ventricle of human hearts at mid-stage of post-MI HF.