New therapeutic targets in cardiology: arrhythmias and Ca2+/calmodulin-dependent kinase II (CaMKII)

Mechanisms of torsades de pointes: an update

Torsades de Pointes (TdP) refers to a polymorphic ventricular tachycardia (VT) with undulating QRS axis that occurs in long QT syndrome (LQTS), although the term has been used to describe polymorphic ventricular tachyarrhythmias in which QT intervals are not prolonged, such as short-coupled variant of TdP currently known as short-coupled ventricular fibrillation (VF) and Brugada syndrome. Extensive works on LQTS-related TdP over more than 50 years since it was first recognized by Dessertennes who coined the French term meaning "twisting of the points", have led to current understanding of the electrophysiological mechanism that TdP is initiated by triggered activity due to early afterdepolarization (EAD) and maintained by reentry within a substrate of inhomogeneous repolarization. While a recently emerging notion that steep voltage gradients rather than EADs are crucial to generate premature ventricular contractions provides additions to the initiation mode, the research to elucidate the maintenance mechanism hasn't made much progress. The reentrant activity that produces the specific form of VT is not well characterized. We have conducted optical mapping in a rabbit model of electrical storm by electrical remodeling (QT prolongation) due to chronic complete atrioventricular block and demonstrated that a tissue-island with prolonged refractoriness due to enhanced late Na+ current (INa-L) contributes to the generation of drifting rotors in a unique manner, which may explain the ECG characteristic of TdP. Moreover, we have proposed that the neural Na+ channel NaV1.8-mediated INa-L may be a new player to form the substrate for TdP. Here we discuss TdP mechanisms by comparing the findings in electrical storm rabbits with recently published studies by others in simulation models and human and animal models of LQTS.

Quercetin alleviates zearalenone-induced apoptosis and necroptosis of porcine renal epithelial cells by inhibiting CaSR/CaMKII signaling pathway

Zearalenone (ZEA) is a mycotoxin that is highly contaminated in feed and can cause severe toxic effects on the kidneys and other organs of animals. Quercetin (QUE) is a plant-derived flavonoid with a variety of detoxification properties, but the mechanism by which QUE detoxifies the toxic effects induced by ZEA has not yet been fully elucidated. We treated porcine kidney cells (PK15) with 80 μM ZEA and/or 30 μM QUE. The results showed that ROS and MDA levels were increased, antioxidant system levels were down-regulated, anti-apoptotic factor expression levels were decreased, and apoptotic and necroptosis-related factors were up-regulated after ZAE exposure. In addition, the results of Ca2+ staining, mitochondrial membrane potential, and mitochondrial dynamics-related indicators showed that ZEA induced Ca2+ overload in PK15 cells and increased mitochondrial Ca2+ uptake (MCU expression increased). The accumulated ROS and free Ca2+ further aggravate mitochondrial damage and eventually lead to mitochondrial pathway apoptosis and necroptosis. Nevertheless, QUE targets CaSR to inhibit the CaSR/CaMKII pathway and regulate calcium homeostasis, thereby alleviating apoptosis and necroptosis mediated by mitochondrial dynamic disorder and dysfunction. The present study demonstrated the mechanism by which ZEA induces apoptosis and necroptosis in PK15 and the protective role of QUE in this process.

Calmodulin Mutations in Human Disease

Calcium ions (Ca²⁺) are the basis of a unique and potent array of cellular responses. Calmodulin (CaM) is a small but vital protein that is able to rapidly transmit information about changes in Ca²⁺ concentrations to its regulatory targets. CaM plays a critical role in cellular Ca²⁺ signaling, and interacts with a myriad of target proteins. Ca²⁺-dependent modulation by CaM is a major component of a diverse array of processes, ranging from gene expression in neurons to the shaping of the cardiac action potential in heart cells. Furthermore, the protein sequence of CaM is highly evolutionarily conserved, and identical CaM proteins are encoded by three independent genes (CALM1-3) in humans. Mutations within any of these three genes may lead to severe cardiac deficits including severe long QT syndrome (LQTS) and/or catecholaminergic polymorphic ventricular tachycardia (CPVT). Research into disease-associated CaM variants has identified several proteins modulated by CaM that are likely to underlie the pathogenesis of these calmodulinopathies, including the cardiac L-type Ca²⁺ channel (LTCC) Ca_V1.2, and the sarcoplasmic reticulum Ca²⁺ release channel, ryanodine receptor 2 (RyR2). Here, we review the research that has been done to identify calmodulinopathic CaM mutations and evaluate the mechanisms underlying their role in disease.

CaMKII, 'jack of all trades' in inflammation during cardiac ischemia/reperfusion injury

Myocardial infarction and revascularization cause cardiac ischemia/reperfusion (I/R) injury featuring cardiomyocyte death and inflammation. The Ca2+/calmodulin dependent protein kinase II (CaMKII) family are serine/ threonine protein kinases that are involved in I/R injury. CaMKII exists in four different isoforms, α, β, γ, and δ. In the heart, CaMKII-δ is the predominant isoform，with multiple splicing variants, such as δB, δC and δ9. During I/R, elevated intracellular Ca2+ concentrations and reactive oxygen species activate CaMKII. In this review, we summarized the regulation and function of CaMKII in multiple cell types including cardiomyocytes, endothelial cells, and macrophages during I/R. We conclude that CaMKII mediates inflammation in the microenvironment of the myocardium, resulting in cell dysfunction, elevated inflammation, and cell death. However, different CaMKII-δ variants exhibit distinct or even opposite functions. Therefore, reagents/approaches that selectively target specific CaMKII isoforms and variants are needed for evaluating and counteracting the exact role of CaMKII in I/R injury and developing effective treatments against I/R injury.

Gene expression patterns and related pathways in the hearts of rhesus monkeys subjected to prolonged myocardial ischemia

After myocardial infarction (MI) occurs, progressive pathological cardiac remodeling results in heart dysfunction and even heart failure during the following months or years. The present study explored the molecular mechanisms underlying the late phase of MI at the global transcript level. A rhesus monkey model of myocardial ischemia induced by left anterior descending (LAD) artery ligation was established, and the heart tissue was collected eight weeks after ligation for transcriptome analysis by DNA microarray technology. Differentially expressed genes in the core infarcted area and remote infarcted area of the ischemic heart were detected with significance analysis of microarray (SAM), and related pathways were detected by Gene Ontology (GO)/pathway analysis. We found that compared to the sham condition, prolonged ischemia increased the levels of 941 transcripts, decreased the levels of 380 transcripts in the core infarcted area, and decreased the levels of 8 transcripts in the remote area in monkey heart tissue. Loss of coordination between the expression of genes, including natriuretic peptide A (NPPA), NPPB, and corin (Corin, serine peptidase), may aggravate cardiac remodeling. Furthermore, imbalance in the enriched significantly changed pathways, including fibrosis-related pathways, cardioprotective pathways, and the cardiac systolic pathway, likely also plays a key role in regulating the development of heart remodeling.

Calcium Signalling in Heart and Vessels: Role of Calmodulin and Downstream Calmodulin-Dependent Protein Kinases

Cardiovascular disease is the major cause of death worldwide. The success of medication and other preventive measures introduced in the last century have not yet halted the epidemic of cardiovascular disease. Although the molecular mechanisms of the pathophysiology of the heart and vessels have been extensively studied, the burden of ischemic cardiovascular conditions has risen to become a top cause of morbidity and mortality. Calcium has important functions in the cardiovascular system. Calcium is involved in the mechanism of excitation-contraction coupling that regulates numerous events, ranging from the production of action potentials to the contraction of cardiomyocytes and vascular smooth muscle cells. Both in the heart and vessels, the rise of intracellular calcium is sensed by calmodulin, a protein that regulates and activates downstream kinases involved in regulating calcium signalling. Among them is the calcium calmodulin kinase family, which is involved in the regulation of cardiac functions. In this review, we present the current literature regarding the role of calcium/calmodulin pathways in the heart and vessels with the aim to summarize our mechanistic understanding of this process and to open novel avenues for research.

Inhibitory effects of zinc chloride (ZnCl2), n-acetyl-L-cysteine (NAC), and calcium/calmodulin dependent protein kinase II inhibitor (KN93) on Cd2+-induced abnormal cell morphology and membrane permeability

Cadmium (Cd) could reduce abnormal cell morphology and membrane permeability, however, there are few studies on the detoxification of Cd-reduced cell membrane toxicity. In the present study, we firstly studied the effects of zinc chloride (ZnCl₂), n-acetyl-L-cysteine (NAC), and calcium/calmodulin dependent protein kinase II inhibitor (KN93) on cell membrane permeability, respectively; then, we studied the inhibitory effects of ZnCl₂, NAC, and KN93 on Cd²⁺-induced abnormal cell membrane permeability by scanning electrochemical microscopy (SECM) scanning imaging, transverse scanning curve and DPV technology. Our results showed that 10 μmol·L^-1 ZnCl₂, 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could significantly improve the activity of MCF-7 cells, while did not destroy the cell morphology and membrane permeability. 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could significantly inhibit the effects of Cd²⁺ on the morphology and membrane permeability of MCF-7 cells (p < 0.01). 10 μmol·L^-1 ZnCl₂ could significantly inhibit the effect of Cd on the membrane permeability of MCF-7 cells, however, it cannot completely eliminate the morphological changes of MCF-7 cells caused by Cd²⁺. The results of cell activity experiment showed that 10 μmol·L^-1 ZnCl₂, 0.5 mmol·L^-1 NAC and 5 μmol·L^-1 KN93 could inhibit the effect of Cd²⁺ on the activity of MCF-7 cells. By comparing the inhibitory effects of ZnCl₂, NAC and KN93 on Cd²⁺- induced cytotoxicity, 5 μmol·L^-1 KN93 had the robust effect on the maintenance of MCF-7 cell morphology and cell membrane integrity. Our research provided evidence on Zn supplement, NAC as antioxidant drugs, and KN93 as special inhibitor for the detoxification of Cd²⁺-reduced abnormal cell morphology and membrane permeability.

CaMKII inhibition protects against hyperthyroid arrhythmias and adverse myocardial remodeling

Hyperthyroidism can potentiate arrhythmias and cardiac hypertrophy, whereas Ca²⁺/calmodulin-dependent kinase II (CaMKII) promotes maladaptive myocardial remodeling. However, it remains unclear whether CaMKII contributes to the progression of hyperthyroid heart disease (HHD). This study demonstrated that CaMKII inhibition can relieve adverse myocardial remodeling and reduce sinus tachycardia, isoproterenol-induced atrial fibrillation, and ventricular arrhythmias in hyperthyroid mice with preserved heart function. Hyperthyroid cardiac hypertrophy was promoted by CaMKII upregulation-induced HDAC4/MEF2a activation. Briefly, CaMKII inhibition benefits HHD management greatly in mice by preventing arrhythmias and maladaptive remodeling.

Effects of Sacubitril/Valsartan on the Expression of CaMKII/Cav1.2 in Atrial Fibrillation Stimulation Rabbit Model

Background and Objective. Atrial fibrillation (AF) is linked to high morbidity and death rates throughout the world due to limited therapeutic options and thus presents a major challenge to the developed and developing countries. In this study, we aim to investigate the influence of sacubitril/valsartan (sac/val) treatment on the calmodulin-dependent protein kinase II (CaMKII)/Cav1.2 expression in AF models. Methods. Overall, 18 rabbits were randomly divided into control, pacing (600 beats/min), and pacing+sac/val groups. The rabbits in the pacing+sac/val cohort received oral sac/val (10 mg/kg twice daily) across the 21-day investigation period. After three weeks, the atrial effective refractory period (AERP) and AF induction rate were compared. HL-1 cultures were exposed to fast pacing (24 h) with and without LBQ657 (active sacubitril form)/valsartan. Western blots were used for detecting Cav1.2 and CaMKII expression within atrial muscles of the rabbits and HL-1 cultures of AF model. Results. In comparison to the sham cohort, the AF induction rate was markedly increased together with AERP reduction within pacing cohort. Such changes were markedly rescued through sac/val treatment in pacing+sac/val cohort. The proteomic expression profiles of CaMKII and Cav1.2 showed that the CaMKII expression was markedly upregulated, while Cav1.2 expression was downregulated in the pacing cohort. Importantly, these effects were absent in pacing+sac/val cohort. Conclusion. Results of this study show that sac/val treatment regulates the expression of CaMKII/Cav1.2 and could alter this pathway in atrial rapid electrical stimulation models. Therefore, this investigation could contribute to a novel strategy in AF therapeutics in clinical settings.

Stachydrine hydrochloride ameliorates cardiac hypertrophy through CaMKII/HDAC4/MEF2C signal pathway

Stachydrine hydrochloride (Sta), an activated alkaloid, is isolated from traditional Chinese medicine Yimucao. In previous studies, the cardioprotective effects of Sta were found in our laboratory. However, the underling mechanisms of Sta is not fully elucidated. The aim of this study was to provide a detailed account of the anti-hypertrophic effects of Sta on transcriptional regulation. In vivo, C57BL/6J mice were subjected to transverse aortic constriction (TAC) and were orally treated with Sta. Morphological assessments, echocardiographic parameters, histological analyses and immunofluorescence were used to evaluate cardiac hypertrophy. In vitro, cardiomyocytes were stimulated by phenylephrine (PE), and cell surface and hypertrophy markers were tested by immunofluorescence and real-time polymerase chain reaction (RT-PCR). Moreover, western blotting, RT-PCR and luciferase reporter genes were used to assess the expression of proteins, mRNA and the activity of the CaMKII/HDAC4/MEF2C signal pathway in vivo and in vitro. We found that Sta blocked cardiac hypertrophy induced by pressure overload. We also demonstrated that Sta inhibited nuclear export or promoted nuclear import of HDAC4 through regulation of p-CaMKII, and it further improved the repression of MEF2C. Taken together, our findings demonstrated that Sta ameliorates cardiac hypertrophy through CaMKII/HDAC4/MEF2C signal pathway.

Hydrogen sulfide-induced post-translational modification as a potential drug target

Hydrogen sulfide (H₂S) is one of the three known gas signal transducers, and since its potential physiological role was reported, the literature on H₂S has been increasing. H₂S is involved in processes such as vasodilation, neurotransmission, angiogenesis, inflammation, and the prevention of ischemia-reperfusion injury, and its mechanism remains to be further studied. At present, the role of post-translational processing of proteins has been considered as a possible mechanism for the involvement of H₂S in a variety of physiological processes. Current studies have shown that H₂S is involved in S-sulfhydration, phosphorylation, and S-nitrosylation of proteins, etc. This paper focuses on the effects of protein modification involving H₂S on physiological and pathological processes, looking forward to providing guidance for subsequent research.

Ellagic Acid Prevents Myocardial Infarction-induced Left Ventricular Diastolic Dysfunction in Ovariectomized Rats

Estrogen deficiency is associated with increased oxidative stress, which can contribute to left ventricular diastolic dysfunction (LVDD). We hypothesized that oral treatment with ellagic acid (EA), a potent and natural antioxidant compound, can improve MI-induced LVDD in ovariectomized rats, by reducing the formation of reactive oxygen species (ROS). Ovariectomized rats MI-induced LVDD followed by treatment with vehicle (DD) or EA (DD+EA) for 4 weeks. Non-LVDD-induced rats treated with vehicle (S) or EA (S+EA) were used as controls. Left ventricular systolic pressure: LVSP; left ventricular end-diastolic pressure: LVEDP; maximum rate of pressure rise: +dP/dt and fall: -dP/dt) were evaluated in all animals after treatment. Left ventricle superoxide anion formation was quantified in situ by fluorescence. Phospho-CAMKII, SOD2, catalase and gp91-phox abundances were evaluated by Western blot analyses. SOD and catalase activities were measured by spectrophotometry. The results showed that the LVEDP was significantly increased in both DD and DD+EA groups compared to S and S+EA. However, LVEDP in the DD+EA group was significantly decreased compared to DD, indicating an EA-mediated effect. In the DD group, superoxide production and gp91-phox protein abundance were increased while SOD2 abundance was decreased when compared to the S and S+EA groups. An increase in SOD activity was also observed in the DD+EA group. EA treatment reduced CaMKII phosphorylation in the DD+EA group compared to the DD. We concluded that EA treatment attenuated diastolic dysfunction in our experimental model, via reduction of ROS and CaMKII activity, indicating EA as a promising natural therapeutic option for cardiac dysfunction.

Rotors anchored by refractory islands drive torsades de pointes in an experimental model of electrical storm

BACKGROUND

Electrical storm (ES) is a life-threatening emergency in patients at high risk of ventricular tachycardia/ventricular fibrillation (VF), but the pathophysiology and molecular basis are poorly understood.

OBJECTIVE

The purpose of this study was to explore the electrophysiological substrate for experimental ES.

METHODS

A model was created by inducing chronic complete atrioventricular block in defibrillator-implanted rabbits, which recapitulates QT prolongation, torsades des pointes (TdP), and VF episodes.

RESULTS

Optical mapping revealed island-like regions with action potential duration (APD) prolongation in the left ventricle, leading to increased spatial APD dispersion, in rabbits with ES (defined as ≥3 VF episodes/24 h). The maximum APD and its dispersion correlated with the total number of VF episodes in vivo. TdP was initiated by an ectopic beat that failed to enter the island and formed a reentrant wave and perpetuated by rotors whose centers swirled in the periphery of the island. Epinephrine exacerbated the island by prolonging APD and enhancing APD dispersion, which was less evident after late Na⁺ current blockade with 10 μM ranolazine. Nonsustained ventricular tachycardia in a non-ES rabbit heart with homogeneous APD prolongation resulted from multiple foci with an electrocardiographic morphology different from TdP driven by drifting rotors in ES rabbit hearts. The neuronal Na⁺-channel subunit Na_V1.8 was upregulated in ES rabbit left ventricular tissues and expressed within the myocardium corresponding to the island location in optically mapped ES rabbit hearts. The Na_V1.8 blocker A-803467 (10 mg/kg, intravenously) attenuated QT prolongation and suppressed epinephrine-evoked TdP.

CONCLUSION

A tissue island with enhanced refractoriness contributes to the generation of drifting rotors that underlies ES in this model. Na_V1.8-mediated late Na⁺ current merits further investigation as a contributor to the substrate for ES.

COMP (Cartilage Oligomeric Matrix Protein), a Novel PIEZO1 Regulator That Controls Blood Pressure

BACKGROUND

Vascular endothelial cells are critical for maintaining blood pressure (BP) by releasing biologically active molecules, such as nitric oxide. A non-endothelial cell resident matricellular protein, COMP (cartilage oligomeric matrix protein), plays a pivotal role in maintaining cardiovascular homeostasis, but little is known about its regulatory effect on BP.

METHODS

Mice were infused with AngII (angiotensin II; 450 ng/kg per minute) for 3 days via an osmotic minipump, and BP was monitored by a tail-cuff system. Second-order mesenteric arteries were isolated from mice for microvascular tension measurement. Nitric oxide was detected by an electron paramagnetic resonance technique. Small-interfering RNA transfection, co-immunoprecipitation, bioluminescence resonance energy transfer assays, and patch-clamp electrophysiology experiments were used for further detailed mechanism investigation.

RESULTS

COMP^-/- mice displayed elevated BP and impaired acetylcholine-induced endothelium-dependent relaxation compared with wild-type mice with or without AngII. Inhibition of eNOS (endothelial nitric oxide synthase) abolished the difference in endothelium-dependent relaxation between wild-type and COMP^-/- mice. Furthermore, COMP directly interacted with the C-terminus of Piezo1 via its C-terminus and activated the endogenous Piezo1 currents, which induced intracellular Ca²⁺ influx, Ca²⁺/calmodulin-dependent protein kinase type II and eNOS activation, and nitric oxide production. The Piezo1 activator, Yoda1, reduced the difference in endothelium-dependent relaxation and BP in wild-type and COMP^-/- mice. Moreover, COMP overexpression increased eNOS activation and improved endothelium-dependent relaxation and BP.

CONCLUSIONS

Our study demonstrated that COMP is a novel Piezo1 regulator that plays a protective role in BP regulation by increasing cellular Ca²⁺ influx, eNOS activity, and nitric oxide production.

Relevance of mitochondrial oxidative stress to arrhythmias: Innovative concepts to target treatments

Cardiac arrhythmia occurs frequently worldwide, and in severe cases can be fatal. Mitochondria are the power plants of cardiomyocytes. In recent studies, mitochondria under certain stimuli produced excessive reactive oxygen species (ROS), which affect the normal function of cardiomyocytes through ion channels and related proteins. Mitochondrial oxidative stress (MOS) plays a key role in diseases with multifactorial etiopathogenesis, such as arrhythmia; MOS can lead to arrhythmias such as atrial fibrillation and ventricular tachycardia. This review discusses the mechanisms of arrhythmias caused by MOS, particularly of ROS produced by mitochondria. MOS can cause arrhythmias by affecting the activities of Ca²⁺-related proteins, the mitochondrial permeability transition pore protein, connexin 43, hyperpolarization-activated cyclic nucleotide-gated potassium channel 4, and ion channels. Based on these mechanisms, we discuss possible new treatments for arrhythmia. Targeted treatments focusing on mitochondria may reduce the progression of arrhythmias, as well as the occurrence of severe arrhythmias, and may be effective for personalized disease prevention.

Late sodium current and calcium homeostasis in arrhythmogenesis

The cardiac late sodium current (INa,late) is the small sustained component of the sodium current active during the plateau phase of the action potential. Several studies demonstrated that augmentation of the current can lead to cardiac arrhythmias; therefore, INa,late is considered as a promising antiarrhythmic target. Fundamentally, enlarged INa,late increases Na+ influx into the cell, which, in turn, is converted to elevated intracellular Ca2+ concentration through the Na+/Ca2+ exchanger. The excessive Ca2+ load is known to be proarrhythmic. This review describes the behavior of the voltage-gated Na+ channels generating INa,late in health and disease and aims to discuss the physiology and pathophysiology of Na+ and Ca2+ homeostasis in context with the enhanced INa,late demonstrating also the currently accessible antiarrhythmic choices.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

CaMKII in Regulation of Cell Death During Myocardial Reperfusion Injury

Cardiovascular disease is the leading cause of death worldwide. In spite of the mature managements of myocardial infarction (MI), post-MI reperfusion (I/R) injury results in high morbidity and mortality. Cardiomyocyte Ca²⁺ overload is a major factor of I/R injury, initiating a cascade of events contributing to cardiomyocyte death and myocardial dysfunction. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a critical role in cardiomyocyte death response to I/R injury, whose activation is a key feature of myocardial I/R in causing intracellular mitochondrial swelling, endoplasmic reticulum (ER) Ca²⁺ leakage, abnormal myofilament contraction, and other adverse reactions. CaMKII is a multifunctional serine/threonine protein kinase, and CaMKIIδ, the dominant subtype in heart, has been widely studied in the activation, location, and related pathways of cardiomyocytes death, which has been considered as a potential targets for pharmacological inhibition. In this review, we summarize a brief overview of CaMKII with various posttranslational modifications and its properties in myocardial I/R injury. We focus on the molecular mechanism of CaMKII involved in regulation of cell death induced by myocardial I/R including necroptosis and pyroptosis of cardiomyocyte. Finally, we highlight that targeting CaMKII modifications and cell death involved pathways may provide new insights to understand the conversion of cardiomyocyte fate in the setting of myocardial I/R injury.

Stress-driven cardiac calcium mishandling via a kinase-to-kinase crosstalk

Calcium homeostasis in the cardiomyocyte is critical to the regulation of normal cardiac function. Abnormal calcium dynamics such as altered uptake by the sarcoplasmic reticulum (SR) Ca²⁺-ATPase and increased diastolic SR calcium leak are involved in the development of maladaptive cardiac remodeling under pathological conditions. Ca²⁺/calmodulin-dependent protein kinase II-δ (CaMKIIδ) is a well-recognized key molecule in calcium dysregulation in cardiomyocytes. Elevated cellular stress is known as a common feature during pathological remodeling, and c-jun N-terminal kinase (JNK) is an important stress kinase that is activated in response to intrinsic and extrinsic stress stimuli. Our lab recently identified specific actions of JNK isoform 2 (JNK2) in CaMKIIδ expression, activation, and CaMKIIδ-dependent SR Ca²⁺ mishandling in the stressed heart. This review focuses on the current understanding of cardiac SR calcium handling under physiological and pathological conditions as well as the newly identified contribution of the stress kinase JNK2 in CaMKIIδ-dependent SR Ca²⁺ abnormal mishandling. The new findings identifying dual roles of JNK2 in CaMKIIδ expression and activation are also discussed in this review.

Mitochondrial Dysfunction Increases Arrhythmic Triggers and Substrates; Potential Anti-arrhythmic Pharmacological Targets

Incidence of cardiac arrhythmias increases significantly with age. In order to effectively stratify arrhythmic risk in the aging population it is crucial to elucidate the relevant underlying molecular mechanisms. The changes underlying age-related electrophysiological disruption appear to be closely associated with mitochondrial dysfunction. Thus, the present review examines the mechanisms by which age-related mitochondrial dysfunction promotes arrhythmic triggers and substrate. Namely, via alterations in plasmalemmal ionic currents (both sodium and potassium), gap junctions, cellular Ca²⁺ homeostasis, and cardiac fibrosis. Stratification of patients' mitochondrial function status permits application of appropriate anti-arrhythmic therapies. Here, we discuss novel potential anti-arrhythmic pharmacological interventions that specifically target upstream mitochondrial function and hence ameliorates the need for therapies targeting downstream changes which have constituted traditional antiarrhythmic therapy.

GRKs and Epac1 Interaction in Cardiac Remodeling and Heart Failure

β-adrenergic receptors (β-ARs) play a major role in the physiological regulation of cardiac function through signaling routes tightly controlled by G protein-coupled receptor kinases (GRKs). Although the acute stimulation of β-ARs and the subsequent production of cyclic AMP (cAMP) have beneficial effects on cardiac function, chronic stimulation of β-ARs as observed under sympathetic overdrive promotes the development of pathological cardiac remodeling and heart failure (HF), a leading cause of mortality worldwide. This is accompanied by an alteration in cAMP compartmentalization and the activation of the exchange protein directly activated by cAMP 1 (Epac1) signaling. Among downstream signals of β-ARs, compelling evidence indicates that GRK2, GRK5, and Epac1 represent attractive therapeutic targets for cardiac disease. Here, we summarize the pathophysiological roles of GRK2, GRK5, and Epac1 in the heart. We focus on their signalosome and describe how under pathological settings, these proteins can cross-talk and are part of scaffolded nodal signaling systems that contribute to a decreased cardiac function and HF development.

MD1 Depletion Predisposes to Ventricular Arrhythmias in the Setting of Myocardial Infarction

BACKGROUND

Myeloid differentiation protein 1 (MD1) is expressed in the human heart and is a negative regulator of Toll-like receptor 4 (TLR4) signalling. MD1 exerts anti-arrhythmic effects.

AIM

The aim of this study was to determine the role of MD1 in myocardial infarction (MI)-related ventricular arrhythmias (VAs).

METHOD

Myocardial infarction was induced by surgical ligation of the left anterior coronary artery in MD1 knockout (KO) mice and their wild-type littermates. Myocardial infarction-induced vulnerability to VAs and its underlying mechanisms were evaluated.

RESULTS

Myeloid differentiation protein 1 was downregulated in the MI mice. Myeloid differentiation protein 1 deficiency decreased post-MI left ventricular (LV) function and increased the infarct size. The MI mice exhibited prolonged action potential duration (APD), enhanced APD alternans thresholds, and a higher incidence of VAs. Myocardial infarction-induced LV fibrosis and inflammation decreased the expression levels of Kv4.2, Kv4.3, Kv1.5, and Kv2.1, increased Cav1.2 expression, and disturbed Ca²⁺ handling protein expression. These MI-induced adverse effects were further exacerbated in KO mice. Mechanistically, MD1 deletion markedly enhanced the activation of the TLR4/calmodulin-dependent protein kinase II (CaMKII) signalling pathway in post-MI mice.

CONCLUSIONS

Myeloid differentiation protein 1 deletion increases the vulnerability to VAs in post-MI mice. This is mainly caused by the aggravated maladaptive LV fibrosis and inflammation and interference with the expressions of ion channels and Ca²⁺ handling proteins, which is related to enhanced activation of the TLR4/CaMKII signalling pathway.

An Overview of the Role of Calcium/Calmodulin-Dependent Protein Kinase in Cardiorenal Syndrome

Calcium/calmodulin-dependent protein kinases (CaMKs) are key regulators of calcium signaling in health and disease. CaMKII is the most abundant isoform in the heart; although classically described as a regulator of excitation–contraction coupling, recent studies show that it can also mediate inflammation in cardiovascular diseases (CVDs). Among CVDs, cardiorenal syndrome (CRS) represents a pressing issue to be addressed, considering the growing incidence of kidney diseases worldwide. In this review, we aimed to discuss the role of CaMK as an inflammatory mediator in heart and kidney interaction by conducting an extensive literature review using the database PubMed. Here, we summarize the role and regulating mechanisms of CaMKII present in several quality studies, providing a better understanding for future investigations of CamKII in CVDs. Surprisingly, despite the obvious importance of CaMKII in the heart, very little is known about CaMKII in CRS. In conclusion, more studies are necessary to further understand the role of CaMKII in CRS.

Genetic Etiology Shared by Multiple Sclerosis and Ischemic Stroke

Although dramatic progress has been achieved in the understanding and treatment of multiple sclerosis (MS) and ischemic stroke (IS), more precise and instructive support is required for further research. Recent large-scale genome-wide association studies (GWASs) have already revealed risk variants for IS and MS, but the common genetic etiology between MS and IS remains an unresolved issue. This research was designed to overlapping genes between MS and IS and unmask their transcriptional features. We designed a three-section analysis process. Firstly, we computed gene-based analyses of MS GWAS and IS GWAS data sets by VGEAS2. Secondly, overlapping genes of significance were identified in a meta-analysis using the Fisher’s procedure. Finally, we performed gene expression analyses to confirm transcriptional changes. We identified 24 shared genes with Bonferroni correction (P_combined < 2.31E-04), and five (FOXP1, CAMK2G, CLEC2D, LBH, and SLC2A4RG) had significant expression differences in MS and IS gene expression omnibus data sets. These meaningful shared genes between IS and MS shed light on the underlying genetic etiologies shared by the diseases. Our results provide a basis for in-depth genomic studies of associations between MS and IS.

Regulation of cardiovascular calcium channel activity by post-translational modifications or interacting proteins

Voltage-gated calcium channels are the major pathway for Ca²⁺ influx to initiate the contraction of smooth and cardiac muscles. Alterations of calcium channel function have been implicated in multiple cardiovascular diseases, such as hypertension, atrial fibrillation, and long QT syndrome. Post-translational modifications do expand cardiovascular calcium channel structure and function to affect processes such as channel trafficking or polyubiquitination by two E3 ubiquitin ligases, Ret finger protein 2 (Rfp2) or murine double minute 2 protein (Mdm2). Additionally, biophysical property such as Ca²⁺-dependent inactivation (CDI) could be altered through binding of calmodulin, or channel activity could be modulated via S-nitrosylation by nitric oxide and phosphorylation by protein kinases or by interacting protein partners, such as galectin-1 and Rem. Understanding how cardiovascular calcium channel function is post-translationally remodeled under distinctive disease conditions will provide better information about calcium channel-related disease mechanisms and improve the development of more selective therapeutic agents for cardiovascular diseases.

The effect of Sirt1 deficiency on Ca2+ and Na+ regulation in mouse ventricular myocytes

This study addressed the hypothesis that cardiac Sirtuin 1 (Sirt1) deficiency alters cardiomyocyte Ca²⁺ and Na⁺ regulation, leading to cardiac dysfunction and arrhythmogenesis. We used mice with cardiac‐specific Sirt1 knockout (Sirt1^−/−). Sirt1^flox/flox mice were served as control. Sirt1^−/− mice showed impaired cardiac ejection fraction with increased ventricular spontaneous activity and burst firing compared with those in control mice. The arrhythmic events were suppressed by KN93 and ranolazine. Reduction in Ca²⁺ transient amplitudes and sarcoplasmic reticulum (SR) Ca²⁺ stores, and increased SR Ca²⁺ leak were shown in the Sirt1^−/− mice. Electrophysiological measurements were performed using patch‐clamp method. While L‐type Ca²⁺ current (I_{Ca, L}) was smaller in Sirt1^−/− myocytes, reverse‐mode Na⁺/Ca²⁺ exchanger (NCX) current was larger compared with those in control myocytes. Late Na⁺ current (I_{Na, L}) was enhanced in the Sirt1^−/− mice, alongside with elevated cytosolic Na⁺ level. Increased cytosolic and mitochondrial reactive oxygen species (ROS) were shown in Sirt1^−/− mice. Sirt1^−/− cardiomyocytes showed down‐regulation of L‐type Ca²⁺ channel α1c subunit (Cav1.2) and sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a), but up‐regulation of Ca²⁺/calmodulin‐dependent protein kinase II and NCX. In conclusions, these findings suggest that deficiency of Sirt1 impairs the regulation of intracellular Ca²⁺ and Na⁺ in cardiomyocytes, thereby provoking cardiac dysfunction and arrhythmogenesis.

Brain-Heart Axis and Biomarkers of Cardiac Damage and Dysfunction after Stroke: A Systematic Review and Meta-Analysis

BACKGROUND

Cardiac complications after a stroke are the second leading cause of death worldwide, affecting the treatment and outcomes of stroke patients. Cardiac biomarkers such as cardiac troponin (cTn), brain natriuretic peptide (BNP), and N-terminal pro-brain natriuretic peptide (NT-proBNP) have been frequently reported in patients undergoing a stroke. The aim of the present study is to meta-analyze the relationship between changes in such cardiac biomarkers and stroke and to present a systematic review of the previous literature, so as to explore the brain-heart axis.

METHODS

We searched four online databases pertinent to the literature, including PubMed, Embase, the Cochrane Library, and the Web of Science. Then, we performed a meta-analysis to investigate changes in cTn, BNP, and NT-proBNP associated with different types of stroke.

RESULTS AND CONCLUSIONS

A significant increase in cTnI concentration was found in patients exhibiting a brain hemorrhage. BNP increased in cases of brain infarction, while the NT-proBNP concentration was significantly elevated in patients suffering an acute ischemic stroke and brain hemorrhage, indicating cardiac damage and dysfunction after a stroke. Our analysis suggests that several potential mechanisms may be involved in the brain-heart axis. Finally, clinicians should pay careful attention to monitoring cardiac function in the treatment of cerebrovascular diseases in order to provide a timely and more accurate treatment.

Mechanisms underlying direct actions of hyperlipidemia on myocardium: an updated review

Hyperlipidemia is a common metabolic disorder and one of risk factors for cardiovascular disease. Clinical studies have shown that hyperlipidemia increases the risk of non-ischemic heart failure, while decreasing serum lipids can reverse heart dysfunction. Apart from indirectly affecting the function of the heart by promoting the development of atherosclerosis, hyperlipidemia also affects the systolic function and cardiac electrophysiological response of the heart directly, which may be related to gradual accumulation of cardiac lipids and consequent systemic oxidative stress, proinflammatory state and mitochondrial dysfunction. However, the mechanism underlying direct effects of hyperlipidemia on the heart are not fully understood. In this review, we provide an updated summary of recent experimental and clinical studies that focus on elucidating the mechanisms of the action of hyperlipidemia on cardiac function, the relationship between heart failure and serum lipids, and protective effects of lipid-lowering drugs on the heart. The exciting progress in this field supports the prospect of guiding early protection of the heart to benefit the patients with chronic hyperlipidemia and familial hyperlipidemia.

The cardiac CaMKII-Nav1.5 relationship: From physiology to pathology

The SCN5A gene encodes Nav1.5, which, as the cardiac voltage-gated Na+ channel's pore-forming α subunit, is crucial for the initiation and propagation of atrial and ventricular action potentials. The arrhythmogenic propensity of inherited SCN5A mutations implicates the Na+ channel in determining cardiomyocyte excitability under normal conditions. Cytosolic kinases have long been known to alter the kinetic profile of Nav1.5 inactivation via phosphorylation of specific residues. Recent substantiation of both the role of calmodulin-dependent kinase II (CaMKII) in modulating the properties of the Nav1.5 inactivation gate and the significant rise in oxidation-dependent autonomous CaMKII activity in structural heart disease has raised the possibility of a novel pathway for acquired arrhythmias - the CaMKII-Nav1.5 relationship. The aim of this review is to: (1) outline the relationship's translation from physiological adaptation to pathological vicious circle; and (2) discuss the relative merits of each of its components as pharmacological targets.

Mitochondrial Dysfunction as Substrate for Arrhythmogenic Cardiomyopathy: A Search for New Disease Mechanisms

Arrhythmogenic cardiomyopathy (ACM) is a familial heart disease, associated with ventricular arrhythmias, fibrofatty replacement of the myocardial mass and an increased risk of sudden cardiac death (SCD). Malignant ventricular arrhythmias and SCD largely occur in the pre-clinical phase of the disease, before overt structural changes occur. To prevent or interfere with ACM disease progression, more insight in mechanisms related to electrical instability are needed. Currently, numerous studies are focused on the link between cardiac arrhythmias and metabolic disease. In line with that, a potential role of mitochondrial dysfunction in ACM pathology is unclear and mitochondrial biology in the ACM heart remains understudied. In this review, we explore mitochondrial dysfunction in relation to arrhythmogenesis, and postulate a link to typical hallmarks of ACM. Mitochondrial dysfunction depletes adenosine triphosphate (ATP) production and increases levels of reactive oxygen species in the heart. Both metabolic changes affect cardiac ion channel gating, electrical conduction, intracellular calcium handling, and fibrosis formation; all well-known aspects of ACM pathophysiology. ATP-mediated structural remodeling, apoptosis, and mitochondria-related alterations have already been shown in models of PKP2 dysfunction. Yet, the limited amount of experimental evidence in ACM models makes it difficult to determine whether mitochondrial dysfunction indeed precedes and/or accompanies ACM pathogenesis. Nevertheless, current experimental ACM models can be very useful in unraveling ACM-related mitochondrial biology and in testing potential therapeutic interventions.

CaMKII Activity in the Inflammatory Response of Cardiac Diseases

Inflammation is a physiological process by which the body responds to external insults and stress conditions, and it is characterized by the production of pro-inflammatory mediators such as cytokines. The acute inflammatory response is solved by removing the threat. Conversely, a chronic inflammatory state is established due to a prolonged inflammatory response and may lead to tissue damage. Based on the evidence of a reciprocal regulation between inflammation process and calcium unbalance, here we described the involvement of a calcium sensor in cardiac diseases with inflammatory drift. Indeed, the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is activated in several diseases with an inflammatory component, such as myocardial infarction, ischemia/reperfusion injury, pressure overload/hypertrophy, and arrhythmic syndromes, in which it actively regulates pro-inflammatory signaling, among which includes nuclear factor kappa-B (NF-κB), thus contributing to pathological cardiac remodeling. Thus, CaMKII may represent a key target to modulate the severity of the inflammatory-driven degeneration.

Loss of MD1 increases vulnerability to ventricular arrhythmia in diet-induced obesity mice via enhanced activation of the TLR4/MyD88/CaMKII signaling pathway

BACKGROUND AND AIM

Obesity is an important risk factor for ventricular arrhythmia (VA), and myeloid differentiation protein 1 (MD1) has been reported to decrease in obese hearts. Nevertheless, underlying mechanisms linking MD1 and VA have not been fully studied. This study aims to investigate the regulatory role of MD1 in VA caused by diet-induced obesity.

METHODS AND RESULTS

MD1 knock-out (KO) and wild type (WT) mice from experimental groups were fed with a high-fat diet (HFD) since the age of six weeks for 20 weeks. The body weight gain, fast glucose and serum lipid levels were measured and recorded. In addition, pathological analysis, echocardiography, electrocardiography, langendorff-perfused heart and molecular analysis were performed to detect HFD-induced vulnerability to VA and its underlying mechanisms. After a 20-week HFD feeding, the mice showed an increase in body weight, glycemic, lipid levels, QTc interval, LVEDd, LVEDs and LVFS. HFD feeding also increased vulnerability to VA, as shown by the prolonged action potential duration (APD), enhanced APD alternans threshold and greater incidence of VA. Moreover, HFD feeding caused LV hypertrophy and fibrosis, and decreased the protein expressions of Kv4.2, Kv4.3, Kv1.5, Kv2.1 and Cav1.2 channels. At last, the above-mentioned HFD-induced adverse effects were further exacerbated in KO mice compared with WT mice. Mechanistically, MD1 deletion markedly enhanced the activation of TLR4/MyD88/CaMKII signaling pathway in HFD-fed mice.

CONCLUSION

MD1 deficiency increased HFD-induced vulnerability to VA. This is mainly caused by the aggravated maladaptive LV hypertrophy, fibrosis and decreased protein expressions of ion channels, which are induced by the enhanced activation of the TLR4/MyD88/CaMKII signaling pathway.

Transcriptional regulation of stress kinase JNK2 in pro-arrhythmic CaMKIIδ expression in the aged atrium

Aims

c-jun N-terminal kinase (JNK) is a critical stress response kinase that activates in a wide range of physiological and pathological cellular processes. We recently discovered a pivotal role of JNK in the development of atrial arrhythmias in the aged heart, while cardiac CaMKIIδ, another pro-arrhythmic molecule, was also known to enhance atrial arrhythmogenicity. Here, we aimed to reveal a regulatory role of the stress kinase JNK2 isoform on CaMKIIδ expression.

Methods and results

Activated JNK2 leads to increased CaMKIIδ protein expression in aged human and mouse atria, evidenced from the reversal of CaMKIIδ up-regulation in JNK2 inhibitor treated wild-type aged mice. This JNK2 action in CaMKIIδ expression was further confirmed in HL-1 myocytes co-infected with AdMKK7D-JNK2, but not when co-infected with AdMKK7D-JNK1. JNK2-specific inhibition (either by a JNK2 inhibitor or overexpression of inactivated dominant-negative JNK2 (JNK2dn) completely attenuated JNK activator anisomycin-induced CaMKIIδ up-regulation in HL-1 myocytes, whereas overexpression of JNK1dn did not. Moreover, up-regulated CaMKIIδ mRNA along with substantially increased phosphorylation of JNK downstream transcription factor c-jun [but not activating transcription factor2 (ATF2)] were exhibited in both aged atria (humans and mice) and transiently JNK activated HL-1 myocytes. Cross-linked chromatin-immunoprecipitation assays (XChIP) revealed that both c-jun and ATF2 were bound to the CaMKIIδ promoter, but significantly increased binding of c-jun only occurred in the presence of anisomycin and JNK inhibition alleviated this anisomycin-elevated c-jun binding. Mutated CaMKII consensus c-jun binding sites impaired its promoter activity. Enhanced transcriptional activity of CaMKIIδ by anisomycin was also completely reversed to the baseline by either JNK2 siRNA or c-jun siRNA knockdown.

Conclusion

JNK2 activation up-regulates CaMKIIδ expression in the aged atrium. This JNK2 regulation in CaMKIIδ expression occurs at the transcription level through the JNK downstream transcription factor c-jun. The discovery of this novel molecular mechanism of JNK2-regulated CaMKII expression sheds new light on possible anti-arrhythmia drug development.

Effects of icariin on long noncoding RNA and mRNA expression profile in the aortas of apoE-deficient mice

Objective: The beneficial effects of icariin (ICA) in ameliorating atherosclerosis (AS) are well known, but the underlying protective mechanism has not been fully elucidated. The present study aimed to investigate altered long noncosing RNA (lncRNA) and mRNA expression profiles in ApoE^−/− mice after ICA treatment.

Method: The atherosclerotic plaque area was evaluated on high-fat diet (HFD)-induced ApoE^−/− mice treated with either ICA or vehicle. LncRNA and mRNA integrated microarrays was performed on aortic tissues. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were utilized to explore the significant function and pathway of the differentially expressed (DE) mRNAs, global signal transduction network were constructed to select key mRNAs, and lncRNA–mRNA co-expression network was built to find out the interactions between lncRNA and mRNA. Quantitative real-time PCR (qPCR) was used to further validate the expressions of selected lncRNAs and mRNAs.

Results: Administration of ICA significantly reduced plaque size after 12 weeks (P<0.05). A total of 1512 DE lncRNAs and 2059 DE mRNAs were identified. The mRNAs: protein kinase C, β (Prkcb), Cyp2c65, Mapk10, Calmodulin 5 (Calm5), Calmodulin-like 3 (Calml3) and Camk4 were selected as hub mRNAs, the correlated lncRNAs in co-expression network were identified as important regulatory lncRNAs. The identified target pairs such as lncRNA-NONMMUT000659/Prkcb may play critical roles in AS development mediated by ICA.

Conclusion: Taken together, our study highlights a panel of DE lncRNAs and mRNAs that could explain the molecular mechanism of ICA’s anti-atherosclerotic effects. The work lays a foundation for subsequent genes functional researches, which could contribute to provide new therapeutic targets for AS.

Atrial Infarction-Induced Spontaneous Focal Discharges and Atrial Fibrillation in Sheep: Role of Dantrolene-Sensitive Aberrant Ryanodine Receptor Calcium Release

BACKGROUND

The mechanisms underlying spontaneous atrial fibrillation (AF) associated with atrial ischemia/infarction are incompletely elucidated. Here, we investigate the mechanisms underlying spontaneous AF in an ovine model of left atrial myocardial infarction (LAMI).

METHODS AND RESULTS

LAMI was created by ligating the atrial branch of the left anterior descending coronary artery. ECG loop recorders were implanted to monitor AF episodes. In 7 sheep, dantrolene-a ryanodine receptor blocker-was administered in vivo during the 8-day observation period (LAMI-D, 2.5 mg/kg, IV, BID). LAMI animals experienced numerous spontaneous AF episodes during the 8-day monitoring period that were suppressed by dantrolene (LAMI, 26.1±5.1; sham, 4.3±1.1; LAMI-D, 2.8±0.8; mean±SEM episodes per sheep, P<0.01). Optical mapping showed spontaneous focal discharges (SFDs) originating from the ischemic/normal-zone border. SFDs were calcium driven, rate dependent, and enhanced by isoproterenol (0.03 µmol/L, from 210±87 to 3816±1450, SFDs per sheep) but suppressed by dantrolene (to 55.8±32.8, SFDs per sheep, mean±SEM). SFDs initiated AF-maintaining reentrant rotors anchored by marked conduction delays at the ischemic/normal-zone border. NOS1 (NO synthase-1) protein expression decreased in ischemic zone myocytes, whereas NADPH (nicotinamide adenine dinucleotide phosphate, reduced form) oxidase and xanthine oxidase enzyme activities and reactive oxygen species (DCF [6-carboxy-2',7'-dichlorodihydrofluorescein diacetate]-fluorescence) increased. CaM (calmodulin) aberrantly increased [³H]ryanodine binding to cardiac RyR2 (ryanodine receptors) in the ischemic zone. Dantrolene restored the physiological binding of CaM to RyR2.

CONCLUSIONS

Atrial ischemia causes spontaneous AF episodes in sheep, caused by SFDs that initiate reentry. Nitroso-redox imbalance in the ischemic zone is associated with intense reactive oxygen species production and altered RyR2 responses to CaM. Dantrolene administration normalizes the CaM response, prevents LAMI-related SFDs, and AF initiation. These findings provide novel insights into the mechanisms underlying ischemia-related atrial arrhythmias.

Ca2+/Calmodulin-Dependent Protein Kinase II Regulation by Inhibitor 1 of Protein Phosphatase 1 Protects Against Myocardial Ischemia-Reperfusion Injury

Ca²⁺/calmodulin-dependent protein kinase IIδ (CaMKIIδ) plays a vital role in cardiovascular system. However, the potential protective role of inhibitor 1 of protein phosphatase 1 (I1PP1), which can regulate CaMKII, on myocardial ischemia-reperfusion (I/R) injury remains unknown. In the present study, expression of CaMKIIδ variants was detected by quantitative real-time polymerase chain reaction. I1PP1 was overexpressed by pericardial injection of recombinant adenovirus. Two weeks later, rats were subjected to left anterior descending ligation for 30 minutes followed by reperfusion. Myocardial infarct size was assessed by Evans blue/triphenyl tetrazolium chloride staining. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activity as well as myocardial pathological structure were detected. CaMKII activity was evaluated by phosphorylation of phospholamban (PLB) and oxidation of CaMKII. Expression of dynamin-related protein 1 (DRP1) and optic atrophy 1 (OPA1) in the mitochondria was measured by Western blot. We found that CaMKIIδA and CaMKIIδB expression decreased, while the expression of CaMKIIδC increased after myocardial I/R. Moreover, after 30-minute ischemia followed by 6 hours of reperfusion, I1PP1 overexpression reduced myocardial infarct size, decreased serum CK and LDH activity, ameliorated myocardial pathological structure, inhibited PLB phosphorylation at Thr17, suppressed CaMKII oxidation, elevated CaMKIIδA and CaMKIIδB variants but reduced CaMKIIδC variants, attenuated myocardial oxidative stress, improved myocardial mitochondrial ultrastructure, increased mitochondrial number and mitochondrial DNA copy number, and decreased DRP1 but increased OPA1 protein expression from the mitochondria in rats. Thus, I1PP1 regulated CaMKII, protected mitochondrial function, reduced oxidative stress, and attenuated myocardial I/R injury.

Unique mechanistic insights into the beneficial effects of angiotensin-(1-7) on the prevention of cardiac fibrosis: A metabolomic analysis of primary cardiac fibroblasts

BACKGROUND

Cell metabolic pathways are highly conserved among species and change rapidly in response to drug stimulation. Therefore, we explore the effects of angiotensin-(1-7) in a primary cell model of cardiac fibrosis established in angiotensin II-stimulated cardiac fibroblasts via metabolomics analysis and further clarify the potential protective mechanism of angiotensin-(1-7).

METHODS AND RESULTS

After exposing cardiac fibroblasts to angiotensin II and/or angiotensin-(1-7), 172 metabolites in these cells were quantified and identified by gas chromatography-mass spectrometry. The data were subsequently analyzed by orthogonal partial least squares discriminant analysis to shortlist biochemically significant metabolites associated with the antifibrotic action of angiotensin-(1-7). Seven significant metabolites were identified: 10,13-dimethyltetradecanoic acid, arachidonic acid, aspartic acid, docosahexaenoic acid (DHA), glutathione, palmitelaidic acid, and pyroglutamic acid. By metabolic network analysis, we found that these metabolites were involved in six metabolic pathways, including arachidonic acid metabolism, leukotriene metabolism, and the γ-glutamyl cycle. Since these metabolic pathways are related to calcium balance and oxidative stress, we further verified that angiotensin-(1-7) suppressed the abnormal extracellular calcium influx and excessive accumulation of intracellular reactive oxygen species (ROS) in angiotensin II-stimulated cardiac fibroblasts. Furthermore, we found that angiotensin-(1-7) suppressed the abnormal calcium- and ROS-dependent activation of calcium/calmodulin-dependent protein kinase II delta (CaMKIIδ), the increased expression of CaMKIIδ-related proteins (NADPH oxidase 4 (Nox4), cellular communication network factor 2 (CTGF), and p-ERK1/2), and excessive collagen deposition in vitro and in vivo.

CONCLUSIONS

Angiotensin-(1-7) can ameliorate the angiotensin II-stimulated metabolic perturbations associated with cardiac fibroblast activation. These metabolic changes indicate that modulation of calcium- and ROS-dependent activation of CaMKIIδ mediates the activity of angiotensin-(1-7) against cardiac fibrosis. Moreover, pyroglutamic acid and arachidonic acid may be potential biomarkers for monitoring the antifibrotic action of angiotensin-(1-7).

Increased oxidative stress and CaMKII activity contribute to electro-mechanical defects in cardiomyocytes from a murine model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative genetic disorder. Although described as a brain pathology, there is evidence suggesting that defects in other systems can contribute to disease progression. In line with this, cardiovascular defects are a major cause of death in HD. To date, relatively little is known about the peripheral abnormalities associated with the disease. Here, we applied a range of assays to evaluate cardiac electro-mechanical properties in vivo, using a previously characterized mouse model of HD (BACHD), and in vitro, using cardiomyocytes isolated from the same mice. We observed conduction disturbances including QT interval prolongation in BACHD mice, indicative of cardiac dysfunction. Cardiomyocytes from these mice demonstrated cellular electro-mechanical abnormalities, including a prolonged action potential, arrhythmic contractions, and relaxation disturbances. Cellular arrhythmia was accompanied by an increase in calcium waves and increased Ca²⁺ /calmodulin-dependent protein kinase II activity, suggesting that disruption of calcium homeostasis plays a key part. We also described structural abnormalities in the mitochondria of BACHD-derived cardiomyocytes, indicative of oxidative stress. Consistent with this, imbalances in superoxide dismutase and glutathione peroxidase activities were detected. Our data provide an in vivo demonstration of cardiac abnormalities in HD together with new insights into the cellular mechanistic basis, providing a possible explanation for the higher cardiovascular risk in HD.

alpha1A-adrenoceptor is involved in norepinephrine-induced proliferation of pulmonary artery smooth muscle cells via CaMKII signaling

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature characterized by excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). Some studies have demonstrated the sympathetic nervous system is activated in PAH and norepinephrine (NE) released is closely linked with its activation. However, the subtypes of adrenoreceptor (AR) and the downstream molecular cascades which are involved in the proliferation of PASMCs are still unclear. In this study, adult male Wistar rats were exposed to chronic hypoxia and PASMCs were cultured in hypoxic condition. Significant upregulation of α_1A -AR was identified by Western blot analysis or immunofluorescence in all of the pulmonary arteries, lung tissues, and cell hypoxic models. Western blot analysis, flow cytometry, and immunofluorescence were applied to detect the roles of α_1A -AR in NE mediated proliferation of PASMCs. We revealed 5-methylurapidil (5-MU) reversed NE-induced upregulation of PCNA, CyclinA and CyclinE, more cells from G₀ /G₁ phase to G₂ /M+S phase, enhancement of the microtubule formation. In addition, we found calcium/calmodulin(CaM)-dependent protein kinase type II (CaMKII) pathway was involved in α_1A -AR-mediated cell proliferation. [Ca²⁺ ]_i measurements showed that an increase of [Ca²⁺ ]_i caused by NE or/and hypoxia could be blocked by 5-MU in PASMCs. Western blot analysis results demonstrated the augmentation of CaMKII phosphorylation level was caused by hypoxia or NE in pulmonary arteries, lung tissues, and PASMCs. KN62 attenuated NE-induced proliferation of PASMCs under normoxia and hypoxia. In conclusion, those results suggested NE which stimulated α_1A -AR-mediated the proliferation of PASMCs, which may be via the CaMKII pathway, and it could be used as a novel treatment strategy in PAH.

Sudden unexpected death in the young - Value of massive parallel sequencing in postmortem genetic analyses

Cases of sudden cardiac death (SCD) in young and apparently healthy individuals represent a devastating event in affected families. Hereditary arrhythmia syndromes, which include primary electrical heart disorders as well as cardiomyopathies, are known to contribute to a significant number of these sudden death cases. We performed postmortem genetic analyses in young sudden death cases (aged <45years) by means of a defined gene panel using massive parallel sequencing (MPS). The data were evaluated bioinformatically and detected sequence variants were assessed using common databases and applying in silico prediction tools. In this study, we identified variants with likely pathogenic effect in 6 of 9 sudden unexpected death (SUD) cases. Due to the detection of numerous unknown and unclassified variants, interpretation of the results proved to be challenging. However, by means of an appropriate evaluation of the findings, MPS represents an important tool to support the forensic investigation and implies great progress for relatives of young SCD victims facilitating adequate risk stratification and genetic counseling.

Linagliptin improved myocardial function recovery in rat hearts after a prolonged hypothermic preservation

AIMS

To determine whether linagliptin, a dipeptidyl peptidase 4 inhibitor, can promote the recovery of cardiac function after hypothermic preservation.

MAIN METHODS

Rat hearts were preserved in cold Celsior solution with or without linagliptin for 9 h. Cardiac function was evaluated at 60 min of reperfusion after hypothermic preservation. Cardiac mitochondrial morphology was observed using transmission electron microscope. The expression of dynamin-related protein 1 (Drp1), NADPH oxidase 2 (NOX2), calmodulin-dependent protein kinase II (CaMKII) were detected using Western blot.

KEY FINDINGS

Compared with Celsior group, supplement of Celsior solution with linagliptin (0.25-0.75 nM) could significantly prevent hypothermic preservation-induced cardiac dysfunction. The expression of NOX2 protein, ROS level and MDA content in cardium were increased after hypothermic preservation, which was inhibited by linagliptin. Although the mitofusin1, 2, optic atrophy type 1, and total Drp1 expression in myocardium did not change, the level of p-Drp1 S616 and mitochondrial Drp1 were enhanced after hypothermic preservation. Linagliptin supplement could inhibit the hypothermic preservation-induced increase in p-Drp1 S616 and mitochondrial Drp1 protein, and mitigate the mitochondrial fragmentation. Level of p-CaMKII protein enhanced after hypothermic preservation, which could be prevented by linagliptin or a NOX2 inhibitor Phox-I2. Both Phox-I2 and a CaMKII inhibitor KN-93 could reduce the hypothermic preservation-induced increase in p-Drp1 S616 and mitochondrial Drp1 protein.

SIGNIFICANCE

Supplement Celsior solution with linagliptin could improve cardiac function recovery in 9-h hypothermic preserved rat hearts. The cardioprotective effect of linagliptin might be due to the inhibition of Drp1 phosphorylation and mitochondrial translocation by preventing NOX2-mediated CaMKII activation.

Amelioration of mitochondrial dysfunction in heart failure through S-sulfhydration of Ca2+/calmodulin-dependent protein kinase II

Aims

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a critical role in the development of heart failure and in the induction of myocardial mitochondrial injury. Recent evidence has shown that hydrogen sulfide (H₂S), produced by the enzyme cystathionine γ-lyase (CSE), improves the cardiac function in heart failure. However, the cellular mechanisms for this remain largely unknown. The present study was conducted to determine the functional role of H₂S in protecting against mitochondrial dysfunction in heart failure through the inhibition of CaMKII using wild type and CSE knockout mouse models.

Results

Treatment with S-propyl-L-cysteine (SPRC) or sodium hydrosulfide (NaHS), modulators of blood H₂S levels, attenuated the development of heart failure in animals, reduced lipid peroxidation, and preserved mitochondrial function. The inhibition CaMKII phosphorylation by SPRC and NaHS as demonstrated using both in vivo and in vitro models corresponded with the cardioprotective effects of these compounds. Interestingly, CaMKII activity was found to be elevated in CSE knockout (CSE^-/-) mice as compared to wild type animals and the phosphorylation status of CaMKII appeared to relate to the severity of heart failure. Importantly, in wild type mice SPRC was found to promote S-sulfhydration of CaMKII leading to reduced activity of this protein, however, in CSE^-/- mice S-sulfhydration was abolished following SPRC treatment.

Innovation and conclusions

A novel mechanism depicting a role of S-sulfhydration in the regulation of CaMKII is presented. SPRC mediated S-sulfhydration of CaMKII was found to inhibit CAMKII activity and to preserve cardiovascular homeostasis.

Caveolae-Specific CaMKII Signaling in the Regulation of Voltage-Dependent Calcium Channel and Cardiac Hypertrophy

Cardiac hypertrophy is a major risk for the progression of heart failure; however, the underlying molecular mechanisms contributing to this process remain elusive. The caveolae microdomain plays pivotal roles in various cellular processes such as lipid homeostasis, signal transduction, and endocytosis, and also serves as a signaling platform. Although the caveolae microdomain has been postulated to have a major contribution to the development of cardiac pathologies, including cardiac hypertrophy, recent evidence has placed this role into question. Lack of direct evidence and appropriate methods for determining activation of caveolae-specific signaling has thus far limited the ability to obtain a definite answer to the question. In this review, we focus on the potential physiological and pathological roles of the multifunctional kinase Ca²⁺/calmodulin-dependent kinase II and voltage-dependent L-type calcium channel in the caveolae, toward gaining a better understanding of the contribution of caveolae-based signaling in cardiac hypertrophy.

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

AIMS

Cardiac Troponin T (TnT) mutation-linked familial hypertrophic cardiomyopathy (FHC) is known to cause sudden cardiac death at a young age. Here, we investigated the role of the Ca²⁺ release channel of the cardiac sarcoplasmic reticulum (SR), ryanodine receptor (RyR2), in the pathogenic mechanism of lethal arrhythmia in FHC-related TnT-mutated transgenic mice (TG; TnT-delta160E).

METHODS AND RESULTS

In TG cardiomyocytes, the Ca²⁺ spark frequency (SpF) was much higher than that in non-TG cardiomyocytes. These differences were more pronounced in the presence of isoproterenol (ISO; 10 nM). This increase in SpF was largely reversed by a CaMKII inhibitor (KN-93), but not by a protein kinase A inhibitor (H89). CaMKII phosphorylation at Ser2814 in RyR2 was increased significantly in TG. Spontaneous Ca²⁺ transients (sCaTs) after cessation of a 1-5 Hz pacing, frequently observed in ISO-treated TG cardiomyocytes, were also attenuated by KN-93, but not by H89. The RyR2 stabilizer dantrolene attenuated Ca²⁺ sparks and sCaTs in ISO-treated TG cardiomyocytes, indicating that the mutation-linked aberrant Ca²⁺ release is mediated by destabilized RyR2.

CONCLUSIONS

In FHC-linked TnT-mutated hearts, RyR2 is susceptible to CaMKII-mediated phosphorylation, presumably because of a mutation-linked increase in diastolic [Ca²⁺]_i, causing aberrant Ca²⁺ release leading to lethal arrhythmia.

Stress Signaling JNK2 Crosstalk With CaMKII Underlies Enhanced Atrial Arrhythmogenesis

RATIONALE

Atrial fibrillation (AF) is the most common arrhythmia, and advanced age is an inevitable and predominant AF risk factor. However, the mechanisms that couple aging and AF propensity remain unclear, making targeted therapeutic interventions unattainable.

OBJECTIVE

To explore the functional role of an important stress response JNK (c-Jun N-terminal kinase) in sarcoplasmic reticulum Ca²⁺ handling and consequently Ca²⁺-mediated atrial arrhythmias.

METHODS AND RESULTS

We used a series of cutting-edge electrophysiological and molecular techniques, exploited the power of transgenic mouse models to detail the molecular mechanism, and verified its clinical applicability in parallel studies on donor human hearts. We discovered that significantly increased activity of the stress response kinase JNK2 (JNK isoform 2) in the aged atria is involved in arrhythmic remodeling. The JNK-driven atrial proarrhythmic mechanism is supported by a pathway linking JNK, CaMKII (Ca²⁺/calmodulin-dependent kinase II), and sarcoplasmic reticulum Ca²⁺ release RyR2 (ryanodine receptor) channels. JNK2 activates CaMKII, a critical proarrhythmic molecule in cardiac muscle. In turn, activated CaMKII upregulates diastolic sarcoplasmic reticulum Ca²⁺ leak mediated by RyR2 channels. This leads to aberrant intracellular Ca²⁺ waves and enhanced AF propensity. In contrast, this mechanism is absent in young atria. In JNK challenged animal models, this is eliminated by JNK2 ablation or CaMKII inhibition.

CONCLUSIONS

We have identified JNK2-driven CaMKII activation as a novel mode of kinase crosstalk and a causal factor in atrial arrhythmic remodeling, making JNK2 a compelling new therapeutic target for AF prevention and treatment.

CAMKIIγ suppresses an efferocytosis pathway in macrophages and promotes atherosclerotic plaque necrosis

Atherosclerosis is the underlying etiology of cardiovascular disease, the leading cause of death worldwide. Atherosclerosis is a heterogeneous disease in which only a small fraction of lesions lead to heart attack, stroke, or sudden cardiac death. A distinct type of plaque containing large necrotic cores with thin fibrous caps often precipitates these acute events. Here, we show that Ca2+/calmodulin-dependent protein kinase γ (CaMKIIγ) in macrophages plays a major role in the development of necrotic, thin-capped plaques. Macrophages in necrotic and symptomatic atherosclerotic plaques in humans as well as advanced atherosclerotic lesions in mice demonstrated activation of CaMKII. Western diet-fed LDL receptor-deficient (Ldlr-/-) mice with myeloid-specific deletion of CaMKII had smaller necrotic cores with concomitantly thicker collagen caps. These lesions demonstrated evidence of enhanced efferocytosis, which was associated with increased expression of the macrophage efferocytosis receptor MerTK. Mechanistic studies revealed that CaMKIIγ-deficient macrophages and atherosclerotic lesions lacking myeloid CaMKIIγ had increased expression of the transcription factor ATF6. We determined that ATF6 induces liver X receptor-α (LXRα), an Mertk-inducing transcription factor, and that increased MerTK expression and efferocytosis in CaMKIIγ-deficient macrophages is dependent on LXRα. These findings identify a macrophage CaMKIIγ/ATF6/LXRα/MerTK pathway as a key factor in the development of necrotic atherosclerotic plaques.

CaMKII Activation Promotes Cardiac Electrical Remodeling and Increases the Susceptibility to Arrhythmia Induction in High-fat Diet-Fed Mice With Hyperlipidemia Conditions

BACKGROUND

Obesity/hyperlipidemia is closely related to both atrial and ventricular arrhythmias. CaMKII, a multifunctional serine/threonine kinase, has been involved in cardiac arrhythmias of different etiologies. However, its role in obesity/hyperlipidemia-related cardiac arrhythmia is unexplored. The aim of this was to determine the involvement of CaMKII in the process.

METHODS

Adult male APOE mice were fed a high-fat diet (HFD), administrated with KN93 (10 mg·kg·2d), a specific inhibitor of CaMKII. Serum lipid and glucose profile, cardiac function, and surface electrocardiogram were determined. Electrophysiological study and epicardial activation mapping were performed in Langendorff-perfused heart. Expression of cardiac ion channels, gap junction proteins, Ca handling proteins, and CaMKII were evaluated, coupled with histological analysis.

RESULTS

A hyperlipidemia condition was induced by HFD in the APOE mice, which was associated with increased expression and activity of CaMKII in the hearts. In Langendorff-perfused hearts, HFD-induced heart showed increased arrhythmia inducibility, prolonged action potential duration, and decreased action potential duration alternans thresholds, coupled with slow ventricular conduction, connexin-43 upregulation, and interstitial fibrosis. Downregulation of ion channels including Cav1.2 and Kv4.2/Kv4.3 and disturbed Ca handling proteins were also observed in HFD-induced heart. Interestingly, all these alterations were significantly inhibited by KN93 treatment.

CONCLUSION

Our results demonstrated an adverse effect of metabolic components on cardiac electrophysiology and implicated an important role of CaMKII underlying this process.