No abstract

Background Spontaneous calcium release evoking delayed after-depolarization is believed to cause CPVT, a lethal human arrhythmia provoked by exercise or emotional stress. Beta-adrenergic blockers are the drug of choice, but fail to achieve complete arrhythmia control in some patients. These individuals often require flecainide, device implantation and/or sympathetic denervation. Objective To optimize the arrhythmia therapy by pharmacological inhibition of the sympathetic nervous system in the CASQ2Δ/Δ mouse model of CPVT2. Methods A heart telemetry device was implanted for continuous ECG recording at rest and during provocation testing. Calcium transients and abnormal calcium release were studied in cardiomyocytes isolated from adult mice. Adrenergic receptor expression was determined by western blotting and confocal microscopy. Results Adult CASQ2Δ/Δ mice suffer from complex ventricular arrhythmia at rest and ventricular tachycardia during treadmill exercise and after epinephrine injection. Beta adrenergic blockers, propranolol and metoprolol attenuated arrhythmia at rest but not after stress. Reserpine had no efficacy in controlling arrhythmia. Agents with alpha blocking activity, phentolamine or labetalol, abolished both exercise and epinephrine-induced arrhythmia. To the contrary, injection of alpha adrenergic agonist phenylephrine reproducibly provoked VT. Isolated cardiomyocytes from CASQ2Δ/Δ mice had delayed calcium release waves upon exposure to sympathetic agonists which was abolished by phentolamine. Hearts of calsequestrin mutant mice expressed more alpha adreno-receptor1 compared to controls (p<0.05). Conclusions We identified a contribution of alpha adrenergic pathway to pathogenesis of catecholamine-induced arrhythmia. Alpha blockade emerges an effective therapy in the murine model of CPVT2 and should be tried in humans resistant to beta blockers.

The limited regenerative capacity of the injured myocardium leads to remodeling and often heart failure. Novel therapeutic approaches are essential. Induced pluripotent stem cells (iPSC) differentiated into cardiomyocytes are a potential future therapeutics. We hypothesized that organ-specific reprogramed fibroblasts may serve an advantageous source for future cardiomyocytes. Moreover, exosomes secreted from those cells may have a beneficial effect on cardiac differentiation and/or function. We compared RNA from different sources of human iPSC using chip gene expression. Protein expression was evaluated as well as exosome micro-RNA levels and their impact on embryoid bodies (EBs) differentiation. Statistical analysis identified 51 genes that were altered (p ≤ 0.05), and confirmed in the protein level, cardiac fibroblasts-iPSCs (CF-iPSCs) vs. dermal fibroblasts-iPSCs (DF-iPSCs). Several miRs were altered especially miR22, a key regulator of cardiac hypertrophy and remodeling. Lower expression of miR22 in CF-iPSCs vs. DF-iPSCs was observed. EBs treated with these exosomes exhibited more beating EBs p = 0.05. vs. control. We identify CF-iPSC and its exosomes as a potential source for cardiac recovery induction. The decrease in miR22 level points out that our CF-iPSC-exosomes are naïve of congestive heart cell memory, making them a potential biological source for future therapy for the injured heart.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a lethal ventricular arrhythmia evoked by physical or emotional stress. Recessively inherited CPVT is caused by either missense or null-allele mutations in the cardiac calsequestrin (CASQ2) gene. It was suggested that defects in CASQ2 cause protein deficiency and impair Ca(2+) uptake to the sarcoplasmic reticulum and Ca(2+)-dependent inhibition of ryanodine channels, leading to diastolic Ca(2+) leak, after-depolarizations, and arrhythmia. To examine the effect of exercise training on left ventricular remodeling and arrhythmia, CASQ2 knockout (KO) mice and wild-type controls underwent echocardiography and heart rhythm telemetry before and after 6 wk of training by treadmill exercise. qRT-PCR and Western blotting were used to measure gene and protein expression. Left ventricular fractional shortening was impaired in KO (33 ± 5 vs. 51 ± 7% in controls, P < 0.05) and improved after training (43 ± 12 and 51 ± 9% in KO and control mice, respectively, P = nonsignificant). The exercise tolerance was low in KO mice (16 ± 1 vs. 29 ± 2 min in controls, P < 0.01), but improved in trained animals (26 ± 2 vs. 30 ± 3 min, P = nonsignificant). The hearts of KO mice had a higher basal expression of the brain natriuretic peptide gene. After training, the expression of natriuretic peptide genes markedly decreased, with no difference between KO and controls. Exercise training was not associated with a change in ventricular tachycardia prevalence, but appeared to reduce arrhythmia load, as manifested by a decrease in ventricular beats during stress. We conclude that, in KO mice, which recapitulate the phenotype of human CPVT2, exercise training is well tolerated and could offer a strategy for heart conditioning against stress-induced arrhythmia.