Growth Factor-Induced Mobilization of Cardiac Progenitor Cells Reduces the Risk of Arrhythmias, in a Rat Model of Chronic Myocardial Infarction

Heart repair by stem cell treatment may involve life-threatening arrhythmias. Cardiac progenitor cells (CPCs) appear best suited for reconstituting lost myocardium without posing arrhythmic risks, being commissioned towards cardiac phenotype. In this study we tested the hypothesis that mobilization of CPCs through locally delivered Hepatocyte Growth Factor and Insulin-Like Growth Factor-1 to heal chronic myocardial infarction (MI), lowers the proneness to arrhythmias. We used 133 adult male Wistar rats either with one-month old MI and treated with growth factors (GFs, n = 60) or vehicle (V, n = 55), or sham operated (n = 18). In selected groups of animals, prior to and two weeks after GF/V delivery, we evaluated stress-induced ventricular arrhythmias by telemetry-ECG, cardiac mechanics by echocardiography, and ventricular excitability, conduction velocity and refractoriness by epicardial multiple-lead recording. Invasive hemodynamic measurements were performed before sacrifice and eventually the hearts were subjected to anatomical, morphometric, immunohistochemical, and molecular biology analyses. When compared with untreated MI, GFs decreased stress-induced arrhythmias and concurrently prolonged the effective refractory period (ERP) without affecting neither the duration of ventricular repolarization, as suggested by measurements of QTc interval and mRNA levels for K-channel α-subunits Kv4.2 and Kv4.3, nor the dispersion of refractoriness. Further, markers of cardiomyocyte reactive hypertrophy, including mRNA levels for K-channel α-subunit Kv1.4 and β-subunit KChIP2, interstitial fibrosis and negative structural remodeling were significantly reduced in peri-infarcted/remote ventricular myocardium. Finally, analyses of BrdU incorporation and distribution of connexin43 and N-cadherin indicated that cytokines generated new vessels and electromechanically-connected myocytes and abolished the correlation of infarct size with deterioration of mechanical function. In conclusion, local injection of GFs ameliorates electromechanical competence in chronic MI. Reduced arrhythmogenesis is attributable to prolongation of ERP resulting from improved intercellular coupling via increased expression of connexin43, and attenuation of unfavorable remodeling.

干细胞治疗用于心脏修复时，可能引发危及生命的心律失常。心脏祖细胞（Cardiac Progenitor Cells, CPCs）似乎最适合用于重构受损心肌，且不会带来心律失常风险，因其定向分化为心肌表型。
本研究旨在验证下述假说：通过局部递送肝细胞生长因子（Hepatocyte Growth Factor, HGF）与胰岛素样生长因子-1（Insulin-Like Growth Factor-1, IGF-1）来动员心脏祖细胞以治疗慢性心肌梗死（Myocardial Infarction, MI），可降低心律失常易感性。
本研究共纳入133只成年雄性Wistar大鼠，分为三组：其一为1月龄心肌梗死造模后给予生长因子（Growth Factors, GFs，n=60）治疗组，其二为同造模后给予赋形剂（Vehicle, V，n=55）对照组，其三为假手术组（n=18）。
在选定的大鼠亚组中，我们分别于生长因子/赋形剂给药前及给药后两周，通过遥测心电图评估应激诱导的室性心律失常，利用超声心动图检测心脏力学功能，并通过心外膜多导联记录评估心室兴奋性、传导速度与不应期。
在处死大鼠前进行有创血流动力学检测，随后对心脏样本开展解剖学、形态计量学、免疫组织化学及分子生物学分析。
与未接受治疗的心肌梗死组相比，生长因子治疗可降低应激诱导的心律失常发生率，同时延长有效不应期（Effective Refractory Period, ERP）；根据QTc间期以及钾离子通道α亚基Kv4.2、Kv4.3的mRNA水平检测结果，该治疗并未影响心室复极时长与不应期离散度。
此外，梗死周边区/远隔区心室心肌中，心肌细胞反应性肥大的相关标志物（包括钾离子通道α亚基Kv1.4与β亚基KChIP2的mRNA水平）、间质纤维化以及不良结构重构均显著降低。
最后，通过对溴脱氧尿嘧啶核苷（Bromodeoxyuridine, BrdU）掺入情况以及连接蛋白43（Connexin43, Cx43）与N-钙粘蛋白（N-cadherin）分布的分析显示，生长因子可促进新生血管生成与肌细胞电机械耦连，并消除了梗死面积与机械功能恶化之间的相关性。
综上，局部注射生长因子可改善慢性心肌梗死大鼠的电机械功能。致心律失常作用降低的原因在于：连接蛋白43表达上调增强了细胞间耦连，从而延长了有效不应期，同时不良结构重构得到缓解。