Cardiac monoamine oxidase-A inhibition protects against catecholamine-induced ventricular arrhythmias via enhanced diastolic calcium control.

AIMS: A mechanistic link between depression and risk of arrhythmias could be attributed to altered catecholamine metabolism in the heart. Monoamine oxidase-A (MAO-A), a key enzyme involved in catecholamine metabolism and longstanding antidepressant target, is highly expressed in the myocardium. The present study aimed to elucidate the functional significance and underlying mechanisms of cardiac MAO-A in arrhythmogenesis. METHODS AND RESULTS: Analysis of the TriNetX database revealed that depressed patients treated with MAO inhibitors had a lower risk of arrhythmias compared with those treated with selective serotonin reuptake inhibitors. This effect was phenocopied in mice with cardiomyocyte-specific MAO-A deficiency (cMAO-Adef), which showed a significant reduction in both incidence and duration of catecholamine stress-induced ventricular tachycardia compared with wild-type mice. Additionally, cMAO-Adef cardiomyocytes exhibited altered Ca2+ handling under catecholamine stimulation, with increased diastolic Ca2+ reuptake, reduced diastolic Ca2+ leak, and diminished systolic Ca2+ release. Mechanistically, cMAO-Adef hearts had reduced catecholamine levels under sympathetic stress, along with reduced levels of reactive oxygen species and protein carbonylation, leading to decreased oxidation of Type II PKA and CaMKII. These changes potentiated phospholamban (PLB) phosphorylation, thereby enhancing diastolic Ca2+ reuptake, while reducing ryanodine receptor 2 (RyR2) phosphorylation to decrease diastolic Ca2+ leak. Consequently, cMAO-Adef hearts exhibited lower diastolic Ca2+ levels and fewer arrhythmogenic Ca2+ waves during sympathetic overstimulation. CONCLUSION: Cardiac MAO-A inhibition exerts an anti-arrhythmic effect by enhancing diastolic Ca2+ handling under catecholamine stress.

TECRL deficiency results in aberrant mitochondrial function in cardiomyocytes.

Sudden cardiac death (SCD) caused by ventricular arrhythmias is the leading cause of mortality of cardiovascular disease. Mutation in TECRL, an endoplasmic reticulum protein, was first reported in catecholaminergic polymorphic ventricular tachycardia during which a patient succumbed to SCD. Using loss- and gain-of-function approaches, we investigated the role of TECRL in murine and human cardiomyocytes. Tecrl (knockout, KO) mouse shows significantly aggravated cardiac dysfunction, evidenced by the decrease of ejection fraction and fractional shortening. Mechanistically, TECRL deficiency impairs mitochondrial respiration, which is characterized by reduced adenosine triphosphate production, increased fatty acid synthase (FAS) and reactive oxygen species production, along with decreased MFN2, p-AKT (Ser473), and NRF2 expressions. Overexpression of TECRL induces mitochondrial respiration, in PI3K/AKT dependent manner. TECRL regulates mitochondrial function mainly through PI3K/AKT signaling and the mitochondrial fusion protein MFN2. Apoptosis inducing factor (AIF) and cytochrome C (Cyc) is released from the mitochondria into the cytoplasm after siTECRL infection, as demonstrated by immunofluorescent staining and western blotting. Herein, we propose a previously unrecognized TECRL mechanism in regulating CPVT and may provide possible support for therapeutic target in CPVT.

Epoxylipids and soluble epoxide hydrolase in heart diseases.

Cardiovascular and heart diseases are leading causes of morbidity and mortality. Coronary artery endothelial and vascular dysfunction, inflammation, and mitochondrial dysfunction contribute to progression of heart diseases such as arrhythmias, congestive heart failure, and heart attacks. Classes of fatty acid epoxylipids and their enzymatic regulation by soluble epoxide hydrolase (sEH) have been implicated in coronary artery dysfunction, inflammation, and mitochondrial dysfunction in heart diseases. Likewise, genetic and pharmacological manipulations of epoxylipids have been demonstrated to have therapeutic benefits for heart diseases. Increasing epoxylipids reduce cardiac hypertrophy and fibrosis and improve cardiac function. Beneficial actions for epoxylipids have been demonstrated in cardiac ischemia reperfusion injury, electrical conductance abnormalities and arrhythmias, and ventricular tachycardia. This review discusses past and recent findings on the contribution of epoxylipids in heart diseases and the potential for their manipulation to treat heart attacks, arrhythmias, ventricular tachycardia, and heart failure.

Integrin-Linked Kinase Activation Prevents Ventricular Arrhythmias Induced by Ischemia/Reperfusion Via Inhibition of Connexin 43 Remodeling.

Ischemia reperfusion (I/R)-induced arrhythmia is a serious complication in patients with cardiac infarction. Remodeling of connexin (Cx) 43, manifested as phosphorylation, contributes significantly to arrhythmogenesis. Integrin-linked kinase (ILK) attenuated ventricular remodeling and improved cardiac function in rats after myocardial infarction. We hypothesized that ILK, through Cx43 phosphorylation, would be protective against I/R-induced ventricular arrhythmias. Our study showed that I/R-induced ventricular arrhythmias were attenuated by an ILK agonist LPTP and worsened by the ILK inhibitor Cpd22. I/R disrupted Cx43 distribution, but it was partially normalized in the presence of LPTP. Compared with I/R, the phosphorylation of Akt was increased significantly after pretreatment with LPTP. The increase in phosphorylated Akt was physiologically significant because, in the presence of the Akt inhibitor MK2206, the protective effects of LPTP were blocked. This indicated that ILK activation prevented I/R-induced-ventricular arrhythmia, an effect potentially related to inhibition of Cx43 remodeling via Akt activation.

MICAL1 constrains cardiac stress responses and protects against disease by oxidizing CaMKII.

Oxidant stress can contribute to health and disease. Here we show that invertebrates and vertebrates share a common stereospecific redox pathway that protects against pathological responses to stress, at the cost of reduced physiological performance, by constraining Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity. MICAL1, a methionine monooxygenase thought to exclusively target actin, and MSRB, a methionine reductase, control the stereospecific redox status of M308, a highly conserved residue in the calmodulin-binding (CaM-binding) domain of CaMKII. Oxidized or mutant M308 (M308V) decreased CaM binding and CaMKII activity, while absence of MICAL1 in mice caused cardiac arrhythmias and premature death due to CaMKII hyperactivation. Mimicking the effects of M308 oxidation decreased fight-or-flight responses in mice, strikingly impaired heart function in Drosophila melanogaster, and caused disease protection in human induced pluripotent stem cell-derived cardiomyocytes with catecholaminergic polymorphic ventricular tachycardia, a CaMKII-sensitive genetic arrhythmia syndrome. Our studies identify a stereospecific redox pathway that regulates cardiac physiological and pathological responses to stress across species.

Novel variants in TECRL cause recessive inherited CPVT type 3 with severe and variable clinical symptoms.

INTRODUCTION: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by adrenergically stimulated ventricular tachycardia. The most common form of CPVT is due to autosomal dominant variants in the cardiac ryanodine-receptor gene (RYR2). However, trans-2,3-enoyl-CoA reductase-like (TECRL) was recently suggested to be a novel candidate gene for life-threatening inherited arrhythmias. Patients previously reported with pathogenic changes in TECRL showed a special mixed phenotype of CPVT and long-QT-syndrome (LQTS) termed CPVT type 3 (CPVT3), an autosomal recessive disorder. METHODS AND RESULTS: We implemented TECRL into our NGS panel diagnostics for CPVT and LQTS in April 2017. By December 2018, 631 index patients with suspected CPVT or LQTS had been referred to our laboratory for genetic testing. Molecular analysis identified four Caucasian families carrying novel variants in TECRL. One patient was homozygous for Gln139* resulting in a premature stop codon and loss-of-function of the TECRL protein. Another patient was homozygous for Pro290His, probably leading to an altered folding of the 3-oxo-5-alpha steroid 4-dehydrogenase domain of the TECRL protein. The LOF-variant Ser309* and the missense-variant Val298Ala have been shown to be compound heterozygous in another individual. NGS-based copy number variation analysis and quantitative PCR revealed a quadruplication of TECRL in the last individual, which is likely to be a homozygous duplication. CONCLUSION: The data from our patient collective indicate that CPVT3 occurs much more frequently than previously expected. Variants in TECRL may be causative in up to 5% of all CPVT cases. According to these findings, the default analysis of this gene is recommended if CPVT is suspected.

Gene Therapy for Catecholaminergic Polymorphic Ventricular Tachycardia by Inhibition of Ca2+/Calmodulin-Dependent Kinase II.

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited cardiac arrhythmia characterized by adrenergically triggered arrhythmias, is inadequately treated by current standard of care. Ca2+/calmodulin-dependent protein kinase II (CaMKII), an adrenergically activated kinase that contributes to arrhythmogenesis in heart disease models, is a candidate therapeutic target in CPVT. However, translation of CaMKII inhibition has been limited by the need for selective CaMKII inhibition in cardiomyocytes. Here, we tested the hypothesis that CaMKII inhibition with a cardiomyocyte-targeted gene therapy strategy would suppress arrhythmia in CPVT mouse models. METHODS: We developed AAV9-GFP-AIP, an adeno-associated viral vector in which a potent CaMKII inhibitory peptide, autocamtide-2-related inhibitory peptide [AIP], is fused to green fluorescent protein (GFP) and expressed from a cardiomyocyte selective promoter. The vector was delivered systemically. Arrhythmia burden was evaluated with invasive electrophysiology testing in adult mice. AIP was also tested on induced pluripotent stem cells derived from patients with CPVT with different disease-causing mutations to determine the effectiveness of our proposed therapy on human induced pluripotent stem cell-derived cardiomyocytes and different pathogenic genotypes. RESULTS: AAV9-GFP-AIP was robustly expressed in the heart without significant expression in extracardiac tissues, including the brain. Administration of AAV9-GFP-AIP to neonatal mice with a known CPVT mutation (RYR2R176Q/+) effectively suppressed ventricular arrhythmias induced by either ß-adrenergic stimulation or programmed ventricular pacing, without significant proarrhythmic effect. Intravascular delivery of AAV9-GFP-AIP to adolescent mice transduced ≈50% of cardiomyocytes and was effective in suppressing arrhythmia in CPVT mice. Induced pluripotent stem cell-derived cardiomyocytes derived from 2 different patients with CPVT with different pathogenic mutations demonstrated increased frequency of abnormal calcium release events, which was suppressed by a cell-permeable form of AIP. CONCLUSIONS: This proof-of-concept study showed that AAV-mediated delivery of a CaMKII peptide inhibitor to the heart was effective in suppressing arrhythmias in a murine model of CPVT. CaMKII inhibition also reversed the arrhythmia phenotype in human CPVT induced pluripotent stem cell-derived cardiomyocyte models with different pathogenic mutations.

Exercise training prevents ventricular tachycardia in CPVT1 due to reduced CaMKII-dependent arrhythmogenic Ca2+ release.

AIMS: Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is caused by mutations in the cardiac ryanodine receptor (RyR2) that lead to disrupted Ca(2+) handling in cardiomyocytes and ventricular tachycardia. The aim of this study was to test whether exercise training could reduce the propensity for arrhythmias in mice with the CPVT1-causative missense mutation Ryr2-R2474S by restoring normal Ca(2+) handling. METHODS AND RESULTS: Ryr2-R2474S mice (RyR-RS) performed a 2 week interval treadmill exercise training protocol. Each exercise session comprised five 8 min intervals at 80-90% of the running speed at maximal oxygen uptake (VO2max) and 2 min active rest periods at 60%. VO2max increased by 10 ± 2% in exercise trained RyR-RS (ET), while no changes were found in sedentary controls (SED). RyR-RS ET showed fewer episodes of ventricular tachycardia compared with RyR-RS SED, coinciding with fewer Ca(2+) sparks and waves, less diastolic Ca(2+) leak from the sarcoplasmic reticulum, and lower phosphorylation levels at RyR2 sites associated with Ca(2) (+)-calmodulin-dependent kinase type II (CaMKII) compared with RyR-RS SED. The CaMKII inhibitor autocamtide-2-related inhibitory peptide and also the antioxidant N-acetyl-l-cysteine reduced Ca(2+) wave frequency in RyR-RS equally to exercise training. Protein analysis as well as functional data indicated a mechanism depending on reduced levels of oxidized CaMKII after exercise training. Two weeks of detraining reversed the beneficial effects of the interval treadmill exercise training protocol in RyR-RS ET. CONCLUSION: Long-term effects of interval treadmill exercise training reduce ventricular tachycardia episodes in mice with a CPVT1-causative Ryr2 mutation through lower CaMKII-dependent phosphorylation of RyR2.

Inducible NO synthase is constitutively expressed in porcine myocardium and its level decreases along with tachycardia-induced heart failure.

BACKGROUND: The adverse effects of oxidative stress and the presence of proinflammatory factors in the heart have been widely demonstrated mainly on rodent models. However, larger clinical trials focusing on inflammation or oxidative stress in heart failure (HF) have not been carried out. This may be due to differences in the anatomy and physiology of the cardiovascular system between small rodents and large mammals. Thus, we investigated myocardial inflammatory factors, such as inducible NO synthase (iNOS) and oxidative stress indices in female pigs with chronic tachycardia-induced cardiomyopathy. METHODS: Homogenous female siblings of Large White breed swine (n=15) underwent continuous right ventricular (RV) pacing at 170bpm, whereas five sham-operated subjects served as controls. In the course of RV pacing, animals developed a clinical picture of HF and were euthanized at subsequent stages of the disease: mild, moderate and severe HF. Left ventricle (LV) sections were examined with electron microscopy. The relative expression of iNOS in LV was determined by quantitative PCR. The protein level of iNOS was determined by Western blotting and immunohistochemistry. The level of the S-nitrosylated (S-NO) protein in LV was determined after S-NO moieties were substituted by biotin, followed by a colorimetrical detection with streptavidin. Malondialdehyde (MDA), a marker of lipid peroxidation, was evaluated in the LV and serum using thiobarbituric acid. The aconitase activity (based on measurement of the concomitant formation of NADPH from NADP(+)), a marker of oxidative stress, was analyzed in mitochondrial and cytosolic LV fractions. The concentration of interleukin-1ß (IL-1ß) was measured in LV homogenates using enzyme-linked immunosorbent assay. RESULTS: RV pacing resulted in an impairment of LV systolic function, LV dilatation and neurohormonal activation. The electron microscopy revealed abnormalities within the cardiomyocytes of failing hearts, i.e. swollen mitochondria and myofibril derangement. iNOS was expressed in the control LV myocardium. The development of HF was accompanied by a decrease in iNOS mRNA (P<.05), which was also reflected at a protein level, and a decrease in the protein S-nitrosylation (P<.05). Both iNOS mRNA and S-NO relative moiety levels were inversely related to the dilatation of the LV (P<.05). There was no difference in the concentration of MDA in the LV and serum. Similarly, no differences in the concentration of IL-1ß LV were found between diseased and healthy animals. Aconitase activity was decreased only in the LV mitochondrial fraction of pigs with severe HF. CONCLUSIONS: iNOS was shown to be constitutively expressed within porcine LV. Its level decreases during the progression of systolic nonischemic HF in the pig model. Thus, it can be assumed that an up-regulation of proinflammatory factors is not involved in porcine tachycardia-induced cardiomyopathy and that the impact of oxidative stress may be restricted to the mitochondria in this HF model.

Role of NADPH oxidase and xanthine oxidase in mediating inducible VT/VF and triggered activity in a canine model of myocardial ischemia.

BACKGROUND: Ventricular tachycardia or fibrillation (VT/VF) of focal origin due to triggered activity (TA) from delayed afterdepolarizations (DADs) is reproducibly inducible after anterior coronary artery occlusion. Both VT/VF and TA can be blocked by reducing reactive oxygen species (ROS). We tested the hypothesis that inhibition of NADPH oxidase and xanthine oxidase would block VT/VF. METHODS: 69 dogs received apocynin (APO), 4 mg/kg intraveneously (IV), oxypurinol (OXY), 4 mg/kg IV, or both APO and OXY (BOTH) agents, or saline 3 h after coronary occlusion. Endocardium from ischemic sites (3-D mapping) was sampled for Rac1 (GTP-binding protein in membrane NADPH oxidase) activation or standard microelectrode techniques. Results (mean±SE, * p<0.05): VT/VF originating from ischemic zones was blocked by APO in 6/10 *, OXY in 4/9 *, BOTH in 5/8 * or saline in 1/27; 11/16 VT/VFs blocked were focal. In isolated myocardium, TA was blocked by APO (10(-6) M) or OXY (10(-8) M). Rac1 levels in ischemic endocardium were decreased by APO or OXY. CONCLUSION: APO and OXY suppressed focal VT/VF due to DADs, but the combination of the drugs was not more effective than either alone. Both drugs inhibited ischemic Rac1 with inhibition by OXY suggesting ROS-induced ROS. The inability to totally prevent VT/VF suggests that other mechanisms also contribute to ischemic VT.

Pak1 is required to maintain ventricular Ca²âº homeostasis and electrophysiological stability through SERCA2a regulation in mice.

BACKGROUND: Impaired sarcoplasmic reticular Ca(2+) uptake resulting from decreased sarcoplasmic reticulum Ca(2+)-ATPase type 2a (SERCA2a) expression or activity is a characteristic of heart failure with its associated ventricular arrhythmias. Recent attempts at gene therapy of these conditions explored strategies enhancing SERCA2a expression and the activity as novel approaches to heart failure management. We here explore the role of Pak1 in maintaining ventricular Ca(2+) homeostasis and electrophysiological stability under both normal physiological and acute and chronic ß-adrenergic stress conditions. METHODS AND RESULTS: Mice with a cardiomyocyte-specific Pak1 deletion (Pak1(cko)), but not controls (Pak1(f/f)), showed high incidences of ventricular arrhythmias and electrophysiological instability during either acute ß-adrenergic or chronic ß-adrenergic stress leading to hypertrophy, induced by isoproterenol. Isolated Pak1(cko) ventricular myocytes correspondingly showed aberrant cellular Ca(2+) homeostasis. Pak1(cko) hearts showed an associated impairment of SERCA2a function and downregulation of SERCA2a mRNA and protein expression. Further explorations of the mechanisms underlying the altered transcriptional regulation demonstrated that exposure to control Ad-shC2 virus infection increased SERCA2a protein and mRNA levels after phenylephrine stress in cultured neonatal rat cardiomyocytes. This was abolished by the Pak1-knockdown in Ad-shPak1-infected neonatal rat cardiomyocytes and increased by constitutive overexpression of active Pak1 (Ad-CAPak1). We then implicated activation of serum response factor, a transcriptional factor well known for its vital role in the regulation of cardiogenesis genes in the Pak1-dependent regulation of SERCA2a. CONCLUSIONS: These findings indicate that Pak1 is required to maintain ventricular Ca(2+) homeostasis and electrophysiological stability and implicate Pak1 as a novel regulator of cardiac SERCA2a through a transcriptional mechanism.

CaMKII inhibition rectifies arrhythmic phenotype in a patient-specific model of catecholaminergic polymorphic ventricular tachycardia.

Induced pluripotent stem cells (iPSC) offer a unique opportunity for developmental studies, disease modeling and regenerative medicine approaches in humans. The aim of our study was to create an in vitro 'patient-specific cell-based system' that could facilitate the screening of new therapeutic molecules for the treatment of catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited form of fatal arrhythmia. Here, we report the development of a cardiac model of CPVT through the generation of iPSC from a CPVT patient carrying a heterozygous mutation in the cardiac ryanodine receptor gene (RyR2) and their subsequent differentiation into cardiomyocytes (CMs). Whole-cell patch-clamp and intracellular electrical recordings of spontaneously beating cells revealed the presence of delayed afterdepolarizations (DADs) in CPVT-CMs, both in resting conditions and after ß-adrenergic stimulation, resembling the cardiac phenotype of the patients. Furthermore, treatment with KN-93 (2-[N-(2-hydroxyethyl)]-N-(4methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine), an antiarrhythmic drug that inhibits Ca(2+)/calmodulin-dependent serine-threonine protein kinase II (CaMKII), drastically reduced the presence of DADs in CVPT-CMs, rescuing the arrhythmic phenotype induced by catecholaminergic stress. In addition, intracellular calcium transient measurements on 3D beating clusters by fast resolution optical mapping showed that CPVT clusters developed multiple calcium transients, whereas in the wild-type clusters, only single initiations were detected. Such instability is aggravated in the presence of isoproterenol and is attenuated by KN-93. As seen in our RyR2 knock-in CPVT mice, the antiarrhythmic effect of KN-93 is confirmed in these human iPSC-derived cardiac cells, supporting the role of this in vitro system for drug screening and optimization of clinical treatment strategies.

Antagonism of endogenous nociceptin/orphanin FQ inhibits infarction-associated ventricular arrhythmias via PKC-dependent mechanism in rats.

BACKGROUND AND PURPOSE: Evidence indicates nociceptin/orphanin FQ (N/OFQ) may participate in the pathology of cardiac arrhythmias associated with myocardial infarction. But the role of N/OFQ in the arrhythmogenesis in acute myocardial infarction is unclear. The aim of this study was to investigate the effects of endogenous N/OFQ on infarction-associated arrhythmias. EXPERIMENTAL APPROACH: The expression of N/OFQ, PKC activity and ventricular arrhythmias in presence and absence of UFP-101, a specific antagonist of N/OFQ receptor, were examined following permanent coronary artery occlusion in anaesthetized rats. The effect of N/OFQ on action potential duration was examined in isolated rat cardiomyocytes. KEY RESULTS: It was observed that N/OFQ was increased by 41% in the myocardium after coronary artery occlusion (P < 0.01 vs. control). Pretreatment with UFP-101 (10(-7) mol·kg(-1) , i.v.) reduced the incidence of ventricular ectopic beats by 70% and ventricular tachycardia by 51% respectively (all P < 0.05 vs. control). Meanwhile, PKC activity was elevated in the rats treated with UFP-101 (by 35%, P < 0.05 vs. control). A selective PKC inhibitor, calphostin C, completely abolished the anti-arrhythmic effects of UFP-101 (P < 0.01). N/OFQ (at 10(-11) , 10(-9) and 1 × 10(-7) mol·L(-1) ) shortened the action potential duration by 3% (P > 0.05), 10% (P < 0.05) and 22% (P < 0.01), respectively, via N/OFQ receptor. CONCLUSIONS AND IMPLICATIONS: Antagonism of endogenous N/OFQ produces anti-arrhythmic effects on ventricular arrhythmias in acute myocardial infarction, possibly via modulating PKC activity and action potential of myocytes.

Phosphoinositide 3-kinase γ protects against catecholamine-induced ventricular arrhythmia through protein kinase A-mediated regulation of distinct phosphodiesterases.

BACKGROUND: Phosphoinositide 3-kinase γ (PI3Kγ) signaling engaged by ß-adrenergic receptors is pivotal in the regulation of myocardial contractility and remodeling. However, the role of PI3Kγ in catecholamine-induced arrhythmia is currently unknown. METHODS AND RESULTS: Mice lacking PI3Kγ (PI3Kγ(-/-)) showed runs of premature ventricular contractions on adrenergic stimulation that could be rescued by a selective ß(2)-adrenergic receptor blocker and developed sustained ventricular tachycardia after transverse aortic constriction. Consistently, fluorescence resonance energy transfer probes revealed abnormal cAMP accumulation after ß(2)-adrenergic receptor activation in PI3Kγ(-/-) cardiomyocytes that depended on the loss of the scaffold but not of the catalytic activity of PI3Kγ. Downstream from ß-adrenergic receptors, PI3Kγ was found to participate in multiprotein complexes linking protein kinase A to the activation of phosphodiesterase (PDE) 3A, PDE4A, and PDE4B but not of PDE4D. These PI3Kγ-regulated PDEs lowered cAMP and limited protein kinase A-mediated phosphorylation of L-type calcium channel (Ca(v)1.2) and phospholamban. In PI3Kγ(-/-) cardiomyocytes, Ca(v)1.2 and phospholamban were hyperphosphorylated, leading to increased Ca(2+) spark occurrence and amplitude on adrenergic stimulation. Furthermore, PI3Kγ(-/-) cardiomyocytes showed spontaneous Ca(2+) release events and developed arrhythmic calcium transients. CONCLUSIONS: PI3Kγ coordinates the coincident signaling of the major cardiac PDE3 and PDE4 isoforms, thus orchestrating a feedback loop that prevents calcium-dependent ventricular arrhythmia.

Pathological role of serum- and glucocorticoid-regulated kinase 1 in adverse ventricular remodeling.

BACKGROUND: Heart failure is a growing cause of morbidity and mortality. Cardiac phosphatidylinositol 3-kinase signaling promotes cardiomyocyte survival and function, but it is paradoxically activated in heart failure, suggesting that chronic activation of this pathway may become maladaptive. Here, we investigated the downstream phosphatidylinositol 3-kinase effector, serum- and glucocorticoid-regulated kinase-1 (SGK1), in heart failure and its complications. METHODS AND RESULTS: We found that cardiac SGK1 is activated in human and murine heart failure. We investigated the role of SGK1 in the heart by using cardiac-specific expression of constitutively active or dominant-negative SGK1. Cardiac-specific activation of SGK1 in mice increased mortality, cardiac dysfunction, and ventricular arrhythmias. The proarrhythmic effects of SGK1 were linked to biochemical and functional changes in the cardiac sodium channel and could be reversed by treatment with ranolazine, a blocker of the late sodium current. Conversely, cardiac-specific inhibition of SGK1 protected mice after hemodynamic stress from fibrosis, heart failure, and sodium channel alterations. CONCLUSIONS: SGK1 appears both necessary and sufficient for key features of adverse ventricular remodeling and may provide a novel therapeutic target in cardiac disease.

Intercalated disc abnormalities, reduced Na(+) current density, and conduction slowing in desmoglein-2 mutant mice prior to cardiomyopathic changes.

AIMS: Mutations in genes encoding desmosomal proteins have been implicated in the pathogenesis of arrhythmogenic right ventricular cardiomyopathy (ARVC). However, the consequences of these mutations in early disease stages are unknown. We investigated whether mutation-induced intercalated disc remodelling impacts on electrophysiological properties before the onset of cell death and replacement fibrosis. METHODS AND RESULTS: Transgenic mice with cardiac overexpression of mutant Desmoglein2 (Dsg2) Dsg2-N271S (Tg-NS/L) were studied before and after the onset of cell death and replacement fibrosis. Mice with cardiac overexpression of wild-type Dsg2 and wild-type mice served as controls. Assessment by electron microscopy established that intercellular space widening at the desmosomes/adherens junctions occurred in Tg-NS/L mice before the onset of necrosis and fibrosis. At this stage, epicardial mapping in Langendorff-perfused hearts demonstrated prolonged ventricular activation time, reduced longitudinal and transversal conduction velocities, and increased arrhythmia inducibility. A reduced action potential (AP) upstroke velocity due to a lower Na(+) current density was also observed at this stage of the disease. Furthermore, co-immunoprecipitation demonstrated an in vivo interaction between Dsg2 and the Na(+) channel protein Na(V)1.5. CONCLUSION: Intercellular space widening at the level of the intercalated disc (desmosomes/adherens junctions) and a concomitant reduction in AP upstroke velocity as a consequence of lower Na(+) current density lead to slowed conduction and increased arrhythmia susceptibility at disease stages preceding the onset of necrosis and replacement fibrosis. The demonstration of an in vivo interaction between Dsg2 and Na(V)1.5 provides a molecular pathway for the observed electrical disturbances during the early ARVC stages.

Circulating matrix metalloproteinases in adolescents with hypertrophic cardiomyopathy and ventricular arrhythmia.

BACKGROUND: Myocardial fibrosis is a hallmark of hypertrophic cardiomyopathy (HCM) and a risk factor for ventricular arrhythmia. Fibrosis can be reflected in circulating matrix remodeling protein concentrations. We explored differences in circulating markers of extracellular matrix turnover between young HCM patients with versus without history of serious arrhythmia. METHODS AND RESULTS: Using multiplexed and single ELISA, matrix metalloproteinases (MMPs) 1, 2, 3, and 9; tissue inhibitor of metalloproteinases (TIMPs) 1, 2, and 4; and collagen I carboxyterminal peptide (CICP) were measured in plasma from 45 young HCM patients (80% male patients; median age, 17 years [interquartile range, 15-20]). Participants were grouped into serious ventricular arrhythmia history (VA) versus no ventricular arrhythmia history (NoVA). Differences in MMPs between groups were examined nonparametrically. Relationships between MMPs and ventricular arrhythmia were assessed with linear regression, adjusted for interventricular septal thickness, family history of sudden death, abnormal exercise blood pressure, and implantable cardioverter-defibrillator (ICD). In post hoc sensitivity analysis, age was substituted for ICD. The 14 VA patients were older than 31 NoVA patients (median, 19 versus 17 years; P=0.03). All 14 VA and 12 NoVA patients had an ICD. MMP3 concentration was significantly higher in the VA group (VA median, 12.9 µg/mL [interquartile range, 5.7-16.7 µg/mL] versus NoVA, 5.8 µg/mL [interquartile range, 3.7-10.0 µg/mL]; P=0.01). On multivariable analysis, VA was independently associated with increasing MMP3 (standardized ß, 0.37; P=0.01). Post hoc adjustment for age attenuated this association. CONCLUSIONS: Circulating MMP3 may be a marker of ventricular arrhythmia in adolescent patients with HCM. Because of our role as pediatric providers, we cannot exclude age-related confounding.

Tachyarrythmias with elevated cardiac enzymes in Münchausen syndrome.

We report the case of a woman with Münchausen syndrome who surreptitiously injected epinephrine causing recurrent ventricular tachyarrhythmias accompanied by dramatically high plasma levels of epinephrine and normal norepinephrine levels.

Diminished cardiac fibrosis in heart failure is associated with altered ventricular arrhythmia phenotype.

OBJECTIVES: We sought to define the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium. BACKGROUND: Multiple cellular events that occur during pathological remodeling of the failing ventricle are implicated in the genesis of ventricular tachycardia (VT), including interstitial fibrosis. Recent studies suggest that ventricular fibrosis is reversible, and current anti-remodeling therapies attenuate ventricular fibrosis. However, the role of interstitial fibrosis in the proarrhythmic phenotype of failing ventricular myocardium is currently not well defined. METHODS: Class II histone deacetylases (HDACs) have been implicated in promoting collagen biosynthesis. As these enzymes are inhibited by protein kinase D1 (PKD1), we studied mice with cardiomyocyte-specific transgenic over-expression of a constitutively active mutant of PKD1 (caPKD). caPKD mice were compared with animals in which cardiomyopathy was induced by severe thoracic aortic banding (sTAB). Hearts were analyzed by echocardiographic and electrocardiographic means. Interstitial fibrosis was assessed by histology and quantified biochemically. Ventricular arrhythmias were induced by closed-chest, intracardiac pacing. RESULTS: Similar degrees of hypertrophic growth, systolic dysfunction and mortality were observed in the two models. In sTAB mice, robust ventricular fibrosis was readily detected, but myocardial collagen content was significantly reduced in caPKD mice. As expected, VT was readily inducible by programmed stimulation in sTAB mice and VT was less inducible in caPKD mice. Surprisingly, episodes of VT manifested longer cycle lengths and longer duration in caPKD mice. CONCLUSION: Attenuated ventricular fibrosis is associated with reduced VT inducibility, increased VT duration, and significantly longer arrhythmia cycle length.