Schulte J S, Fehrmann E, Tekook M A, Kranick D, Fels B, Li N, Wehrens X H T, Heinick A, Seidl M D, Schmitz W, Müller F U
Institute of Pharmacology and Toxicology, University of Münster, Domagkstr. 12, 48149, Münster, Germany.
Department of Molecular Physiology and Biophysics, Medicine (Cardiology), and Pediatrics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA.
Basic Res Cardiol. 2016 Mar;111(2):15. doi: 10.1007/s00395-016-0532-y. Epub 2016 Jan 27.
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 Ca(2+) releases was increased in TG accompanied by an enhanced transduction rate of sub-threshold Ca(2+) waves into these supra-threshold events. As a likely cause we discovered enhanced NCX-mediated Ca(2+) transport and NCX1 protein level in TG. An increase in I NCX and decrease in I to 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.
慢性β-肾上腺素能刺激被认为是心力衰竭进展中的关键步骤，而心力衰竭与心律失常的高风险相关。依赖cAMP的转录因子cAMP反应元件结合蛋白（CREB）和cAMP反应元件调节剂（CREM）介导对β-肾上腺素能刺激的转录调控，并且在β-肾上腺素能受体刺激后诱导产生CREM阻遏物亚型。在此，我们通过分析转基因表达CREM阻遏物亚型CREM-IbΔC-X（TG）的小鼠心室心肌细胞（VCM）中的致心律失常改变，来研究CREM阻遏物是否促成心脏中的致心律失常重塑。进行膜片钳分析、钙成像、免疫印迹和实时定量RT-PCR以研究TG VCM与野生型对照相比的促心律失常改变。TG中显示自发性超阈值瞬态样Ca(2+)释放的VCM百分比增加，同时亚阈值Ca(2+)波向这些超阈值事件的转导速率增强。作为可能的原因，我们发现TG中NCX介导的Ca(2+)转运增强以及NCX1蛋白水平升高。I NCX增加、I to及其辅助通道亚基KChIP2减少与动作电位延长以及显示早期后去极化的TG VCM比例增加有关。最后，TG小鼠的室性期前收缩增加，强调了我们研究结果在体内的相关性。小鼠VCM中CREM-IbΔC-X的转基因表达导致明显的致心律失常改变。由于CREM阻遏物可由慢性β-肾上腺素能刺激诱导产生，我们的结果表明，CRE依赖性转录的抑制促成了慢性心脏病中致心律失常底物的形成。
