CaMKII-mediated phosphorylation of RyR2 plays a crucial role in aberrant Ca2+ release as an arrhythmogenic substrate in cardiac troponin T-related familial hypertrophic cardiomyopathy

Current perspectives of sudden cardiac death management in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder characterized by left ventricular hypertrophy. Sudden cardiac death (SCD) is a rare but the most catastrophic complication in patients with HCM. Implantable cardioverter-defibrillators (ICDs) are widely recognized as effective preventive measures for SCD. Individualized risk stratification and early intervention in HCM can significantly improve patient prognosis. In this study, we review the latest findings regarding pathogenesis, risk stratification, and prevention of SCD in HCM patients, highlighting the clinic practice of cardiovascular magnetic resonance imaging for SCD management.

Enhanced myofilament calcium sensitivity aggravates abnormal calcium handling and diastolic dysfunction in patient-specific induced pluripotent stem cell-derived cardiomyocytes with MYH7 mutation

Hypertrophic cardiomyopathy (HCM), the most common inherited heart disease, is frequently caused by mutations in the β-cardiac myosin heavy chain gene (MYH7). Abnormal calcium handling and diastolic dysfunction are archetypical features of HCM caused by MYH7 gene mutations. However, the mechanism of how MYH7 mutations leads to these features remains unclear, which inhibits the development of effective therapies. Initially, cardiomyocytes were generated from induced pluripotent stem cells from an eight-year-old girl diagnosed with HCM carrying a MYH7(C.1063 G>A) heterozygous mutation(mutant-iPSC-CMs) and mutation-corrected isogenic iPSCs(control-iPSC-CMs) in the present study. Next, we compared phenotype of mutant-iPSC-CMs to that of control-iPSC-CMs, by assessing their morphology, hypertrophy-related genes expression, calcium handling, diastolic function and myofilament calcium sensitivity at days 15 and 40 respectively. Finally, to better understand increased myofilament Ca2+ sensitivity as a central mechanism of central pathogenicity in HCM, inhibition of calcium sensitivity with mavacamten can improveed cardiomyocyte hypertrophy. Mutant-iPSC-CMs exhibited enlarged areas, increased sarcomere disarray, enhanced expression of hypertrophy-related genes proteins, abnormal calcium handling, diastolic dysfunction and increased myofilament calcium sensitivity at day 40, but only significant increase in calcium sensitivity and mild diastolic dysfunction at day 15. Increased calcium sensitivity by levosimendan aggravates cardiomyocyte hypertrophy phenotypes such as expression of hypertrophy-related genes, abnormal calcium handling and diastolic dysfunction, while inhibition of calcium sensitivity significantly improves cardiomyocyte hypertrophy phenotypes in mutant-iPSC-CMs, suggesting increased myofilament calcium sensitivity is the primary mechanisms for MYH7 mutations pathogenesis. Our studies have uncovered a pathogenic mechanism of HCM caused by MYH7 gene mutations through which enhanced myofilament calcium sensitivity aggravates abnormal calcium handling and diastolic dysfunction. Correction of the myofilament calcium sensitivity was found to be an effective method for treating the development of HCM phenotype in vitro.

Chai-Hu-San-Shen Capsule Ameliorates Ventricular Arrhythmia Through Inhibition of the CaMKII/FKBP12.6/RyR2/Ca2+ Signaling Pathway in Rats with Myocardial Ischemia

Ventricular arrhythmia is one of the main causes of sudden cardiac death, especially after myocardial ischemia. Previous studies have shown that Chai-Hu-San-Shen capsule (CHSSC) can reduce the incidence of ventricular arrhythmias following myocardial ischemia, however, the mechanisms of it are unclear. In present study, we explored the mechanism of CHSSC ameliorates ventricular arrhythmia following myocardial ischemia via inhibiting the CaMKII/FKBP12.6/RyR2/Ca²⁺ signaling pathway. In vivo, a myocardial ischemia rat model was established and treated with CHSSC to evaluate the therapeutic effect of CHSSC. In vitro, we established an ischemia model in H9C2 cells and treated with CHSSC, KN-93, or H-89. Then, intracellular Ca²⁺ content, the expression of RyR2, and the interaction between FKBP12.6 and RyR2 were detected. The results showed that CHSSC could delay the occurrence of ventricular arrhythmias and shorten the duration of ventricular arrhythmias. After myocardial ischemia, the intracellular Ca²⁺ content was increased, and CHSSC treatment mitigated this increase, down-regulated the levels of p-CaMKII, CaMKII, p-RyR2, and RyR2, and up-regulated the levels of p-RyR2 (Ser2808) and p-RyR2 (Ser2814). Co-immunoprecipitation showed an interaction between FKBP12.6 and RyR2, and CHSSC up-regulated the content of the FKBP12.6-RyR2 complex in ischemic cells. In conclusion, our study showed that CaMKII activation led to hyperphosphorylation of RyR2 (Ser2814) and RyR2 (Ser2808) during cardiomyocyte ischemia, which resulted in dissociation of the FKBP12.6-RyR2 complex, and increased intracellular Ca²⁺ content, which may contribute to the development of ventricular arrhythmias. CHSSC may reduce the incidence of ventricular arrhythmias following myocardial ischemia through inhibition of the CaMKII/RyR2/FKBP12.6/Ca²⁺ signaling pathway.

Ventricular arrhythmia and sudden cardiac death in hypertrophic cardiomyopathy: From bench to bedside

Patients with hypertrophic cardiomyopathy (HCM) mostly experience minimal symptoms throughout their lifetime, and some individuals have an increased risk of ventricular arrhythmias and sudden cardiac death (SCD). How to identify patients with a higher risk of ventricular arrythmias and SCD is the priority in HCM research. The American College of Cardiology/American Heart Association (ACC/AHA) and the European Society of Cardiology (ESC) both recommend the use of risk algorithms to identify patients at high risk of ventricular arrhythmias, to be selected for implantation of implantable cardioverters/defibrillators (ICDs) for primary prevention of SCD, although major discrepancies exist. The present SCD risk scoring systems cannot accurately identify early-stage HCM patients with modest structural remodeling and mild disease manifestations. Unfortunately, SCD events could occur in young asymptomatic HCM patients and even as initial symptoms, prompting the determination of new risk factors for SCD. This review summarizes the studies based on patients' surgical specimens, transgenic animals, and patient-derived induced pluripotent stem cells (hiPSCs) to explore the possible molecular mechanism of ventricular arrhythmia and SCD. Ion channel remodeling, Ca2+ homeostasis abnormalities, and increased myofilament Ca2+ sensitivity may contribute to changes in action potential duration (APD), reentry circuit formation, and trigger activities, such as early aferdepolarization (EAD) or delayed afterdepolarization (DAD), leading to ventricular arrhythmia in HCM. Besides the ICD implantation, novel drugs represented by the late sodium current channel inhibitor and myosin inhibitor also shed light on the prevention of HCM-related arrhythmias. The ideal prevention strategy of SCD in early-stage HCM patients needs to be combined with gene screening, hiPSC-CM testing, machine learning, and advanced ECG studies, thus achieving individualized SCD prevention.

Enhanced NCLX-dependent mitochondrial Ca2+ efflux attenuates pathological remodeling in heart failure

Mitochondrial calcium (_mCa²⁺) uptake couples changes in cardiomyocyte energetic demand to mitochondrial ATP production. However, excessive _mCa²⁺ uptake triggers permeability transition and necrosis. Despite these established roles during acute stress, the involvement of _mCa²⁺ signaling in cardiac adaptations to chronic stress remains poorly defined. Changes in NCLX expression are reported in heart failure (HF) patients and models of cardiac hypertrophy. Therefore, we hypothesized that altered _mCa²⁺ homeostasis contributes to the hypertrophic remodeling of the myocardium that occurs upon a sustained increase in cardiac workload. The impact of _mCa²⁺ flux on cardiac function and remodeling was examined by subjecting mice with cardiomyocyte-specific overexpression (OE) of the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX), the primary mediator of _mCa²⁺ efflux, to several well-established models of hypertrophic and non-ischemic HF. Cardiomyocyte NCLX-OE preserved contractile function, prevented hypertrophy and fibrosis, and attenuated maladaptive gene programs in mice subjected to chronic pressure overload. Hypertrophy was attenuated in NCLX-OE mice, prior to any decline in cardiac contractility. NCLX-OE similarly attenuated deleterious cardiac remodeling in mice subjected to chronic neurohormonal stimulation. However, cardiomyocyte NCLX-OE unexpectedly reduced overall survival in mice subjected to severe neurohormonal stress with angiotensin II + phenylephrine. Adenoviral NCLX expression limited _mCa²⁺ accumulation, oxidative metabolism, and de novo protein synthesis during hypertrophic stimulation of cardiomyocytes in vitro. Our findings provide genetic evidence for the contribution of _mCa²⁺ to early pathological remodeling in non-ischemic heart disease, but also highlight a deleterious consequence of increasing _mCa²⁺ efflux when the heart is subjected to extreme, sustained neurohormonal stress.

Susceptibility Modules and Genes in Hypertrophic Cardiomyopathy by WGCNA and ceRNA Network Analysis

Background: We attempted to identify a regulatory competing endogenous RNA (ceRNA) network and a hub gene of Hypertrophic Cardiomyopathy (HCM). Methods: Microarray datasets of HCM tissue were obtained from NCBI Gene Expression Omnibus (GEO) database. The R package "limma" was used to identify differentially expressed genes. Online search databases were utilized to match the relation among differentially expressed long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and mRNAs. Weighted correlation network analysis (WGCNA) was used to identify the correlations between key modules and HCM. STRING database was applied to construct PPI networks. Gene Set Enrichment Analysis (GSEA) was used to perform functional annotations and verified the hub genes. Results: A total of 269 DE-lncRNAs, 63 DE-miRNAs and 879 DE-mRNAs were identified in myocardial tissues from microarray datasets GSE130036, GSE36946 and GSE36961, respectively. According to online databases, we found 1 upregulated miRNA hsa-miR-184 that was targeted by 2 downregulated lncRNAs (SNHG9, AC010980.2), potentially targeted 2 downregulated mRNAs (LRRC8A, SLC7A5). 3 downregulated miRNAs (hsa-miR-17-5p, hsa-miR-876-3p, hsa-miR-139-5p) that were targeted by 9 upregulated lncRNAs, potentially targeted 21 upregulated mRNAs. Black and blue modules significantly related to HCM were identified by WGCNA. Hub gene IGFBP5 regulated by hsa-miR-17-5p, AC007389.5, AC104667.1, and AC002511.2 was identified. GSEA indicated that IGFBP5 might involve in the synthesis of myosin complex, participate in kinesin binding, motor activity and function via the regulation of actin cytoskeleton. Conclusion: The results provide a potential molecular regulatory mechanism for the diagnosis and treatment of HCM. IGFBP5 might play an important role in the progression of HCM.

Magnesium Ions Moderate Calcium-Induced Calcium Release in Cardiac Calcium Release Sites by Binding to Ryanodine Receptor Activation and Inhibition Sites

Ryanodine receptor channels at calcium release sites of cardiac myocytes operate on the principle of calcium-induced calcium release. In vitro experiments revealed competition of Ca2+ and Mg2+ in the activation of ryanodine receptors (RyRs) as well as inhibition of RyRs by Mg2+. The impact of RyR modulation by Mg2+ on calcium release is not well understood due to the technical limitations of in situ experiments. We turned instead to an in silico model of a calcium release site (CRS), based on a homotetrameric model of RyR gating with kinetic parameters determined from in vitro measurements. We inspected changes in the activity of the CRS model in response to a random opening of one of 20 realistically distributed RyRs, arising from Ca2+/Mg2+ interactions at RyR channels. Calcium release events (CREs) were simulated at a range of Mg2+-binding parameters at near-physiological Mg2+ and ATP concentrations. Facilitation of Mg2+ binding to the RyR activation site inhibited the formation of sparks and slowed down their activation. Impeding Mg-binding to the RyR activation site enhanced spark formation and speeded up their activation. Varying Mg2+ binding to the RyR inhibition site also dramatically affected calcium release events. Facilitation of Mg2+ binding to the RyR inhibition site reduced the amplitude, relative occurrence, and the time-to-end of sparks, and vice versa. The characteristics of CREs correlated dose-dependently with the effective coupling strength between RyRs, defined as a function of RyR vicinity, single-channel calcium current, and Mg-binding parameters of the RyR channels. These findings postulate the role of Mg2+ in calcium release as a negative modulator of the coupling strength among RyRs in a CRS, translating to damping of the positive feedback of the calcium-induced calcium-release mechanism.

Genetic basis and molecular biology of cardiac arrhythmias in cardiomyopathies

Cardiac arrhythmias are common, often the first, and sometimes the life-threatening manifestations of hereditary cardiomyopathies. Pathogenic variants in several genes known to cause hereditary cardiac arrhythmias have also been identified in the sporadic cases and small families with cardiomyopathies. These findings suggest a shared genetic aetiology of a subset of hereditary cardiomyopathies and cardiac arrhythmias. The concept of a shared genetic aetiology is in accord with the complex and exquisite interplays that exist between the ion currents and cardiac mechanical function. However, neither the causal role of cardiac arrhythmias genes in cardiomyopathies is well established nor the causal role of cardiomyopathy genes in arrhythmias. On the contrary, secondary changes in ion currents, such as post-translational modifications, are common and contributors to the pathogenesis of arrhythmias in cardiomyopathies through altering biophysical and functional properties of the ion channels. Moreover, structural changes, such as cardiac hypertrophy, dilatation, and fibrosis provide a pro-arrhythmic substrate in hereditary cardiomyopathies. Genetic basis and molecular biology of cardiac arrhythmias in hereditary cardiomyopathies are discussed.

Shared Molecular Mechanisms of Hypertrophic Cardiomyopathy and Its Clinical Presentations: Automated Molecular Mechanisms Extraction Approach

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease with a prevalence of 1 in 500 people and varying clinical presentations. Although there is much research on HCM, underlying molecular mechanisms are poorly understood, and research on the molecular mechanisms of its specific clinical presentations is scarce. Our aim was to explore the molecular mechanisms shared by HCM and its clinical presentations through the automated extraction of molecular mechanisms. Molecular mechanisms were congregated by a query of the INDRA database, which aggregates knowledge from pathway databases and combines it with molecular mechanisms extracted from abstracts and open-access full articles by multiple machine-reading systems. The molecular mechanisms were extracted from 230,072 articles on HCM and 19 HCM clinical presentations, and their intersections were found. Shared molecular mechanisms of HCM and its clinical presentations were represented as networks; the most important elements in the intersections’ networks were found, centrality scores for each element of each network calculated, networks with reduced level of noise generated, and cooperatively working elements detected in each intersection network. The identified shared molecular mechanisms represent possible mechanisms underlying different HCM clinical presentations. Applied methodology produced results consistent with the information in the scientific literature.

CaMKII inhibition has dual effects on spontaneous Ca2+ release and Ca2+ alternans in ventricular cardiomyocytes from mice with a gain-of-function RyR2 mutation

In conditions with abnormally increased activity of the cardiac ryanodine receptor (RyR2), Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) can contribute to a further destabilization of RyR2 that results in triggered arrhythmias. Therefore, inhibition of CaMKII in such conditions has been suggested as a strategy to suppress RyR2 activity and arrhythmias. However, suppression of RyR2 activity can lead to the development of arrhythmogenic Ca²⁺ alternans. The aim of this study was to test whether the suppression of RyR2 activity caused by inhibition of CaMKII increases propensity for Ca²⁺ alternans. We studied spontaneous Ca²⁺ release events and Ca²⁺ alternans in isolated left ventricular cardiomyocytes from mice carrying the gain-of-function RyR2 mutation RyR2-R2474S and from wild-type mice. CaMKII inhibition by KN-93 effectively decreased the frequency of spontaneous Ca²⁺ release events in RyR2-R2474S cardiomyocytes exposed to the β-adrenoceptor agonist isoprenaline. However, KN-93-treated RyR2-R2474S cardiomyocytes also showed increased propensity for Ca²⁺ alternans and increased Ca²⁺ alternans ratio compared with both an inactive analog of KN-93 and with vehicle-treated controls. This increased propensity for Ca²⁺ alternans was explained by prolongation of Ca²⁺ release refractoriness. Importantly, the increased propensity for Ca²⁺ alternans in KN-93-treated RyR2-R2474S cardiomyocytes did not surpass that of wild type. In conclusion, inhibition of CaMKII efficiently reduces spontaneous Ca²⁺ release but promotes Ca²⁺ alternans in RyR2-R2474S cardiomyocytes with a gain-of-function RyR2 mutation. The dominant effect in RyR2-R2474S is to reduce spontaneous Ca²⁺ release, which supports this intervention as a therapeutic strategy in this specific condition. However, future studies on CaMKII inhibition in conditions with increased propensity for Ca²⁺ alternans should include investigation of both phenomena.NEW & NOTEWORTHY Genetically increased RyR2 activity promotes arrhythmogenic Ca²⁺ release. Inhibition of CaMKII suppresses RyR2 activity and arrhythmogenic Ca²⁺ release. Suppression of RyR2 activity prolongs refractoriness of Ca²⁺ release. Prolonged refractoriness of Ca²⁺ release leads to arrhythmogenic Ca²⁺ alternans. CaMKII inhibition promotes Ca²⁺ alternans by prolonging Ca²⁺ release refractoriness.

Role of defective calcium regulation in cardiorespiratory dysfunction in Huntington's disease

Huntington’s disease (HD) is a progressive, autosomal dominant neurodegenerative disorder affecting striatal neurons beginning in young adults with loss of muscle coordination and cognitive decline. Less appreciated is the fact that patients with HD also exhibit cardiac and respiratory dysfunction, including pulmonary insufficiency and cardiac arrhythmias. The underlying mechanism for these symptoms is poorly understood. In the present study we provide insight into the cause of cardiorespiratory dysfunction in HD and identify a potentially novel therapeutic target. We now show that intracellular calcium (Ca²⁺) leak via posttranslationally modified ryanodine receptor/intracellular calcium release (RyR) channels plays an important role in HD pathology. RyR channels were oxidized, PKA phosphorylated, and leaky in brain, heart, and diaphragm both in patients with HD and in a murine model of HD (Q175). HD mice (Q175) with endoplasmic reticulum Ca²⁺ leak exhibited cognitive dysfunction, decreased parasympathetic tone associated with cardiac arrhythmias, and reduced diaphragmatic contractile function resulting in impaired respiratory function. Defects in cognitive, motor, and respiratory functions were ameliorated by treatment with a novel Rycal small-molecule drug (S107) that fixes leaky RyR. Thus, leaky RyRs likely play a role in neuronal, cardiac, and diaphragmatic pathophysiology in HD, and RyRs are a potential novel therapeutic target.

This study explores the role of ryanodine receptor calcium channels in the brain, the heart, and the diaphragm and central versus peripheral pathophysiological mechanisms in Huntington’s disease.

Cardiac dopamine D1 receptor triggers ventricular arrhythmia in chronic heart failure

Pathophysiological roles of cardiac dopamine system remain unknown. Here, we show the role of dopamine D1 receptor (D1R)-expressing cardiomyocytes (CMs) in triggering heart failure-associated ventricular arrhythmia. Comprehensive single-cell resolution analysis identifies the presence of D1R-expressing CMs in both heart failure model mice and in heart failure patients with sustained ventricular tachycardia. Overexpression of D1R in CMs disturbs normal calcium handling while CM-specific deletion of D1R ameliorates heart failure-associated ventricular arrhythmia. Thus, cardiac D1R has the potential to become a therapeutic target for preventing heart failure-associated ventricular arrhythmia.

Isogenic models of hypertrophic cardiomyopathy unveil differential phenotypes and mechanism-driven therapeutics

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a prevalent and complex cardiovascular condition. Despite being strongly associated with genetic alterations, wide variation of disease penetrance, expressivity and hallmarks of progression complicate treatment. We aimed to characterize different human isogenic cellular models of HCM bearing patient-relevant mutations to clarify genetic causation and disease mechanisms, hence facilitating the development of effective therapeutics.

METHODS

We directly compared the p.β-MHC-R453C and p.ACTC1-E99K HCM-associated mutations in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and their healthy isogenic counterparts, generated using CRISPR/Cas9 genome editing technology. By harnessing several state-of-the-art HCM phenotyping techniques, these mutations were investigated to identify similarities and differences in disease progression and hypertrophic signaling pathways, towards establishing potential targets for pharmacological treatment. CRISPR/Cas9 knock-in of the genetically-encoded calcium indicator R-GECO1.0 to the AAVS1 locus into these disease models resulted in calcium reporter lines.

RESULTS

Confocal line scan analysis identified calcium transient arrhythmias and intracellular calcium overload in both models. The use of optogenetics and 2D/3D contractility assays revealed opposing phenotypes in the two mutations. Gene expression analysis highlighted upregulation of CALM1, CASQ2 and CAMK2D, and downregulation of IRF8 in p.β-MHC-R453C mutants, whereas the opposite changes were detected in p.ACTC1-E99K mutants. Contrasting profiles of nuclear translocation of NFATc1 and MEF2 between the two HCM models suggest differential hypertrophic signaling pathway activation. Calcium transient abnormalities were rescued with combination of dantrolene and ranolazine, whilst mavacamten reduced the hyper-contractile phenotype of p.ACTC1-E99K hiPSC-CMs.

CONCLUSIONS

Our data show that hypercontractility and molecular signaling within HCM are not uniform between different gene mutations, suggesting that a 'one-size fits all' treatment underestimates the complexity of the disease. Understanding where the similarities (arrhythmogenesis, bioenergetics) and differences (contractility, molecular profile) lie will allow development of therapeutics that are directed towards common mechanisms or tailored to each disease variant, hence providing effective patient-specific therapy.

Genetic variants of uncertain significance: How to match scientific rigour and standard of proof in sudden cardiac death?

In many SCD cases, in particular in pediatric age, autopsy can be completely negative and then a post-mortem genetic testing (molecular autopsy) is indicated. In NGS era finding new/rare variants is extremely frequent and, when only variants of unknown significance are found, molecular autopsy fails to find a cause of death. We describe the emblematic case of the sudden death of a 7-year-old girl. We performed a full-body micro-CT analysis, an accurate autopsy, a serum tryptase test and toxicological tests. Since the only macroscopic abnormality we found was a myocardial bridging (length: 1,1 cm, thickness: 0,5 cm) of the left anterior descending coronary artery, a molecular autopsy has been performed. NGS analysis on victim DNA detected rare variants in DPP6, MYH7, SCN2B and NOTCH1 and segregation analysis was then achieved. On the basis of ACMG/AMP (clinical) guidelines, all the found variants were classified as of unknown significance. In other words, both the macroscopic and genetic anomalies we found were of uncertain significance and then the autopsy failed to find the cause of the death. Our case raises three main discussion points: (a) economical, ethical and legal limitations of genetic investigation; (b) risk that genetic testing does not succeed in finding a certain cause of the death; (c) absence of specific guidelines to face the problem of VUS in forensic cases.

Ablation of phospholamban rescues reperfusion arrhythmias but exacerbates myocardium infarction in hearts with Ca2+/calmodulin kinase II constitutive phosphorylation of ryanodine receptors

AIMS

Abnormal Ca2+ release from the sarcoplasmic reticulum (SR), associated with Ca2+-calmodulin kinase II (CaMKII)-dependent phosphorylation of RyR2 at Ser2814, has consistently been linked to arrhythmogenesis and ischaemia/reperfusion (I/R)-induced cell death. In contrast, the role played by SR Ca2+ uptake under these stress conditions remains controversial. We tested the hypothesis that an increase in SR Ca2+ uptake is able to attenuate reperfusion arrhythmias and cardiac injury elicited by increased RyR2-Ser2814 phosphorylation.

METHODS AND RESULTS

We used WT mice, which have been previously shown to exhibit a transient increase in RyR2-Ser2814 phosphorylation at the onset of reperfusion; mice with constitutive pseudo-phosphorylation of RyR2 at Ser2814 (S2814D) to exacerbate CaMKII-dependent reperfusion arrhythmias and cardiac damage, and phospholamban (PLN)-deficient-S2814D knock-in (SDKO) mice resulting from crossbreeding S2814D with phospholamban knockout deficient (PLNKO) mice. At baseline, S2814D and SDKO mice had structurally normal hearts. Moreover none of the strains were arrhythmic before ischaemia. Upon cardiac I/R, WT, and S2814D hearts exhibited abundant arrhythmias that were prevented by PLN ablation. In contrast, PLN ablation increased infarct size compared with WT and S2814D hearts. Mechanistically, the enhanced SR Ca2+ sequestration evoked by PLN ablation in SDKO hearts prevented arrhythmogenic events upon reperfusion by fragmenting SR Ca2+ waves into non-propagated and non-arrhythmogenic events (mini-waves). Conversely, the increase in SR Ca2+ sequestration did not reduce but rather exacerbated I/R-induced SR Ca2+ leak, as well as mitochondrial alterations, which were greatly avoided by inhibition of RyR2. These results indicate that the increase in SR Ca2+ uptake is ineffective in preventing the enhanced SR Ca2+ leak of PLN ablated myocytes from either entering into nearby mitochondria and/or activating additional CaMKII pathways, contributing to cardiac damage.

CONCLUSION

Our results demonstrate that increasing SR Ca2+ uptake by PLN ablation can prevent the arrhythmic events triggered by CaMKII-dependent phosphorylation of RyR2-induced SR Ca2+ leak. These findings underscore the benefits of increasing SERCA2a activity in the face of SR Ca2+ triggered arrhythmias. However, enhanced SERCA2a cannot prevent but rather exacerbates I/R cardiac injury.

Transcriptomic analyses of the biological effects of black carbon exposure to A549 cells

Ambient black carbon (BC) is found to be associated with increased risk of diverse pulmonary diseases, including acute respiratory inflammation and decreased lung function. Freshly emitted BC (FBC) can be transformed into oxidized BC (OBC) through the photochemical oxidization in the air. How this oxidization process influences the toxicity of BC particles is unclear. Previous studies found FBC and OBC could induce oxidative stress and inflammation. This study aimed to further compare the regulating pathways and tried to reveal the crucial target genes caused by FBC and OBC in A549 cells based on transcriptomic data. A total of 47,000 genes in A549 cells after treated with FBC and OBC were examined using Affymetrix Human U133 plus 2.0 chips. Gene ontology (GO) classification (functional enrichment of differentially expressed genes) and Kyoto encyclopedia of genes and genomes (KEGG) classification (pathway enrichment of differentially expressed genes) were conducted and crucial genes were screened. The results showed that top 50 GO terms of FBC and OBC were not completely consistent. The Go term of cation channel was only identified in OBC group, probably caused by the characteristic that zeta potential of OBC is negative, while, that of FBC is positive. In addition transient receptor potential melastatin 7 (trpm7) gene was suggested to be closely related to this process caused by OBC. There are 47 identical pathways in FBC and OBC group among the top 50 KEGG. The inconsistent pathways are mostly related to inflammation with different up-regulation or down-regulation trends of crucial genes. The KEGG results suggested that FBC and OBC both cause inflammatory responses, but through different regulating pathways. In conclusion, OBC and FBC could induce similar toxic endpoints in A549 cells, but the underline regulating processes are not exactly the same.

Evaluation of cardiac hypertrophy in the setting of sudden cardiac death

Ventricular hypertrophy is a common pathological finding at autopsy that can act as a substrate for arrhythmogenesis. Pathologists grapple with the significance of ventricular hypertrophy when assessing the sudden and unexpected deaths of young people and what it could mean for surviving family members. The pathological spectrum of left ventricular hypertrophy (LVH) is reviewed herein. This article is oriented to the practicing autopsy pathologist to help make sense of various patterns of increased heart muscle, particularly those that are not clearly cardiomyopathic, yet present in the setting of sudden cardiac death. The article also reviews factors influencing arrhythmogenesis as well as genetic mutations most commonly associated with ventricular hypertrophy, especially those associated with hypertrophic cardiomyopathy (HCM).

Potential role of the cAMP/PKA/CREB signalling pathway in hypoxic preconditioning and effect on propofol‑induced neurotoxicity in the hippocampus of neonatal rats

Hypoxic preconditioning (HPC) is neuroprotective against ischaemic brain injury; however, the roles of potential anti‑apoptotic signals in this process have not been assessed. To elucidate the molecular mechanisms involved in HPC‑induced neuroprotection, the effects of HPC on the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element‑binding protein (CREB) signalling pathway and apoptosis in Sprague‑Dawley pups (postnatal day 7) treated with propofol were investigated. Western blot and histological analyses demonstrated that HPC exerts multiple effects on the hippocampus, including the upregulation of cAMP and phosphorylation of CREB. These effects were partially blocked by intracerebroventricular injection of the protein kinase antagonist H89 (5 µmol/5 µl). Notably, the level of cleaved caspase‑3 was significantly downregulated by treatment with the cAMP agonist Sp‑cAMP (20 nmol/5 µl). The results indicate that propofol increased the level of cleaved caspase‑3 and Bax by suppressing the activity of cAMP‑dependent proteins and Bcl‑2; thus, HPC prevents propofol from triggering apoptosis via the cAMP/PKA/CREB signalling pathway.

Ca2+/Calmodulin-dependent kinase II delta B is essential for cardiomyocyte hypertrophy and complement gene expression after LPS and HSP60 stimulation in vitro

Inflammation plays an important role in the development of cardiovascular diseases (CVDs), suggesting that the immune system is a target of therapeutic interventions used for treating CVDs. This study evaluated mechanisms underlying inflammatory response and cardiomyocyte hypertrophy associated with bacterial lipopolysaccharide (LPS)- or heat shock protein 60 (HSP60)-induced Toll-like receptor (TLR) stimulation and the effect of a small interfering RNA (siRNA) against Ca²⁺/calmodulin-dependent kinase II delta B (CaMKIIδB) on these outcomes. Our results showed that treatment with HSP60 or LPS (TLR agonists) induced cardiomyocyte hypertrophy and complement system C3 and factor B gene expression. In vitro silencing of CaMKIIδB prevented complement gene transcription and cardiomyocyte hypertrophy associated with TLR 2/4 activation but did not prevent the increase in interleukin-6 and tumor necrosis factor-alfa gene expression in primary cultured cardiomyocytes. Moreover, CaMKIIδB silencing attenuated nuclear factor-kappa B expression. These findings supported the hypothesis that CaMKIIδB acts as a link between inflammation and cardiac hypertrophy. Furthermore, the present study is the first to show that extracellular HSP60 activated complement gene expression through CaMKIIδB. Our results indicated that a stress stimulus induced by LPS or HSP60 treatment promoted cardiomyocyte hypertrophy and initiated an inflammatory response through the complement system. However, CaMKIIδB silencing prevented the cardiomyocyte hypertrophy independent of inflammatory response induced by LPS or HSP60 treatment.

Role of circular RNAs in cardiovascular diseases

IMPACT STATEMENT

Circular RNAs are important regulators of multiple biological processes such as organogenesis and oncogenesis. Although the bulk of concerning studies focused on revealing their diversified roles in various types of cancers, reports began to accumulate in cardiovascular field these days. We summarize circular RNAs implicated in cardiovascular diseases, aiming to highlight the advances in the knowledge of such diseases and their potential of being promising target for diagnosis and therapy.

Isogenic Pairs of hiPSC-CMs with Hypertrophic Cardiomyopathy/LVNC-Associated ACTC1 E99K Mutation Unveil Differential Functional Deficits

Hypertrophic cardiomyopathy (HCM) is a primary disorder of contractility in heart muscle. To gain mechanistic insight and guide pharmacological rescue, this study models HCM using isogenic pairs of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the E99K-ACTC1 cardiac actin mutation. In both 3D engineered heart tissues and 2D monolayers, arrhythmogenesis was evident in all E99K-ACTC1 hiPSC-CMs. Aberrant phenotypes were most common in hiPSC-CMs produced from the heterozygote father. Unexpectedly, pathological phenotypes were less evident in E99K-expressing hiPSC-CMs from the two sons. Mechanistic insight from Ca2+ handling expression studies prompted pharmacological rescue experiments, wherein dual dantroline/ranolazine treatment was most effective. Our data are consistent with E99K mutant protein being a central cause of HCM but the three-way interaction between the primary genetic lesion, background (epi)genetics, and donor patient age may influence the pathogenic phenotype. This illustrates the value of isogenic hiPSC-CMs in genotype-phenotype correlations.