| Backgrounds: Bone marrow mesenchymal stem cells (MSCs) transplantation has been reported to improve cardiac pump function after acute myocardial infarction (MI). However, poor homing, engraftment and survival of donor cells in damaged heart tissue compromise the efficacy of cell therapy. Moreover, concern that intramyocardial delivery of cells could cause potentially life-threatening ventricular arrhythmias has been repeatedly raised. Connexin 43 (Cx43), low expressed in MSCs and increased progressively under cardiac micro-environments, was involved in regulating cell growth and integrating with host tissue.Objectives: to investigate the role of Cx43 in cell survival and therapeutic effects of intramyocardial bone marrow MSCs injection in rats with AMI, to assess the electrophysiological and arrhythmogenic effects and provide efficacy and safety evidences for MSCs therapy in AMI .Methods: We genetically modified male MSCs with plasmids with full-length cDNA or a siRNA sequence of rat Cx43 and evaluated Cx43 protein expression and sustained time by Western blots and immunofluorescence. Four days after intracardiac injection into a female rat left anterior descending (LAD) ligation model, cell survival and engraftment were identified by GFP immunofluorescence. Two weeks after transplantation, cardiac function, effective refractory period(ERP), ventricular arrhythmias (VAs)inducibility and ventricular fibrillation threshold (VFT) were assessed by echocardiography and programmed electrical stimulation(PES), respectively. Epicardial monophasic action potential (MAP) recordings were obtained from the infarcted zone, infarcted border zone(IBZ) and none infarcted zone(NIZ) of left ventricular epicardium. Action potential duration (APD) and activation time (AT) were calculated. Cell survival was quantitative detected Sry-1 in host heart by Real-time PCR. Histological analysis was used to observe infarct size, collagen deposition and distribution, blood vessel density and maturity, Cx43 distribution in heart tissue. Quantitative analysis of Cx43, collagen I and Kv4.2 (transient outward Potassium Current) were determined by immunoblots.Results:1. MSCs were negative for haemopoietic markers CD34,CD14 and CD45 and positive for CD29, CD44, and CD105. MSCs cultured in differentiation medium led to Oil red-O-positive or Alizarin Red positive. Part of 5-azacytidine treated MSCs expressed cardiac marker troponin T, myosin light chain 2a and Cx43. Cx43 protein expression increased significantly in MSCs-Cx43 but decreased greatly in MSCs-SiCx43 compared with MSCs-vector and wild MSCs after 2 days transfection. The regulating effects could be sustained for one weeks.2. Cx43 overexpressed in MSCs resulted in about three fold cell survival compared with MSCs-vector transfected MSCs. There were significantly reduced infarct size, increased blood vessel density and maturity, and markedly improved left ventricular ejection fraction (LVEF) and shortening fraction (LVSF) compared with control MSCs treated animals. Furthermore, cardiac fibrosis was attenuated mostly in MSCs-Cx43 group, although the difference between MSCs groups have not reach statistical significance.3. MSCs injection led to significantly reduced VFT,inducibility of VAs, prolonged APD and shortened AT in IBZ compared with PBS group. MSCs improve protein expression of Kv4.2 and Cx43 in left ventricular tissue. Moreover, Cx43 distribution in the IBZ was significantly improved by MSCs injection. However, Cx43 regulation in MSCs has no significant further effects on these electrophysiological parameters.Conclusions:1. Cx43 in MSCs could be regulated by plasmids vector mediated gene modification.2. Cx43 promotes engraftment and survival of injected MSCs in infarcted tissue,which further reduce infarcted size and fibrosis, improve angiogenesis and preserve heart function.3. MSCs injection decreases inducibility of VAs and focal dispersion of APD, increase VFT and conductive velocity. Moreover, MSCs transplantation improve protein expression and distribution of Kv4.2 and Cx43 in infarcted border zone of the hearts. However, Cx43 overexpression has no further electrophysiological benefits.
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