Cardiac expression of the CREM repressor isoform CREM-IbΔC-X in mice leads to arrhythmogenic alterations in ventricular cardiomyocytes

Abstract

Chronic β-adrenergic stimulation is regarded as a pivotal step in the progression of heart failure which is associated with a high risk for arrhythmia. The cAMP-dependent transcription factors cAMP-responsive element binding protein (CREB) and cAMP-responsive element modulator (CREM) mediate transcriptional regulation in response to β-adrenergic stimulation and CREM repressor isoforms are induced after stimulation of the β-adrenoceptor. Here, we investigate whether CREM repressors contribute to the arrhythmogenic remodeling in the heart by analyzing arrhythmogenic alterations in ventricular cardiomyocytes (VCMs) from mice with transgenic expression of the CREM repressor isoform CREM-IbΔC-X (TG). Patch clamp analyses, calcium imaging, immunoblotting and real-time quantitative RT-PCR were conducted to study proarrhythmic alterations in TG VCMs vs. wild-type controls. The percentage of VCMs displaying spontaneous supra-threshold transient-like Ca2+ releases was increased in TG accompanied by an enhanced transduction rate of sub-threshold Ca2+ waves into these supra-threshold events. As a likely cause we discovered enhanced NCX-mediated Ca2+ transport and NCX1 protein level in TG. An increase in INCX and decrease in Ito and its accessory channel subunit KChIP2 was associated with action potential prolongation and an increased proportion of TG VCMs showing early afterdepolarizations. Finally, ventricular extrasystoles were augmented in TG mice underlining the in vivo relevance of our findings. Transgenic expression of CREM-IbΔC-X in mouse VCMs leads to distinct arrhythmogenic alterations. Since CREM repressors are inducible by chronic β-adrenergic stimulation our results suggest that the inhibition of CRE-dependent transcription contributes to the formation of an arrhythmogenic substrate in chronic heart disease.Electronic supplementary materialThe online version of this article (doi:10.1007/s00395-016-0532-y) contains supplementary material, which is available to authorized users.

The role of spatial organization of Ca2+ release sites in the generation of arrhythmogenic diastolic Ca2+ release in myocytes from failing hearts

“…Although various mechanisms can underlie disrupted Ca 2+ homeostasis in HF [39, 51, 52], dysfunction of RyR2s has consistently been reported in both animal models of HF and in human HF [8, 52], It was shown that in HF, RyR2s become abnormally active, or ‘leaky’, owing to an accumulation of posttranslational modifications due to phosphorylation and oxidation [8, 10, 11, 45, 48, 52]. This dysregulated RyR2 activity has the potential to decrease systolic contraction while giving rise to diastolic Ca 2+ waves (DCWs) and delayed after-depolarizations, precursors of triggered arrhythmias.…”

Increased sarcoplasmic/endoplasmic reticulum calcium ATPase 2a activity underlies the mechanism of the positive inotropic effect of ivabradine

“…The Ca 2+ transient is composed of a fast rising phase and a decay phase. The decay phase contains two components which are composed of a fast component, dominated by SERCA2a, and a slow component mainly associated with a combination of the Na + /Ca 2+ exchanger (NCX) and sarcolemmal Ca 2+ ‐ATPase (PMCA) (Choi & Eisner, ; Maczewski & Mackiewicz, ; Schulte et al., ). Isolation of the two components for the decay phase was analysed by two exponential equations following the theory and method of plasma concentration–time curve fitting for intravenous administration of a drug in human.…”

“…The rate constants of the decay phase of the caffeine‐evoked Ca 2+ transient in control solution and Na + , Ca 2+ ‐free solution were used to analyse the functions of mixed NCX plus PMCA and PMCA alone. The detailed methods were previously described (Choi & Eisner, ; Maczewski & Mackiewicz, ; Schulte et al., ). Briefly, following attaining a steady Ca 2+ transient triggered by field stimulation (5 V, 100 ms), caffeine (20 m m ) in control or in Na + , Ca 2+ ‐free solution was perfused to myocytes when the fluorescence intensity reached the steady diastolic level.…”

“…The amplitude, resting membrane potential and action potential durations at 50% and 90% repolarization levels (APD 50 and APD 90, respectively) were measured. (NCX) and sarcolemmal Ca 2+ -ATPase (PMCA) (Choi & Eisner, 1999;Maczewski & Mackiewicz, 2008;Schulte et al, 2016). Isolation of the two components for the decay phase was analysed by two exponential equations following the theory and method of plasma concentrationtime curve fitting for intravenous administration of a drug in human.…”

“…The rate constants of the decay phase of the caffeineevoked Ca 2+ transient in control solution and Na + , Ca 2+ -free solution were used to analyse the functions of mixed NCX plus PMCA and PMCA alone. The detailed methods were previously described(Choi & Eisner, 1999;Maczewski & Mackiewicz, 2008;Schulte et al, 2016).…”