Epac-Rap1-activated mesenchymal stem cells improve cardiac function in rat model of myocardial infarction.

INTRODUCTION: Rap1, a member of Ras superfamily of small GTP-binding proteins, is involved in cardiovascular biology in numerous ways. It is an evolutionary conserved regulator of adhesion, polarity, differentiation and growth.

AIMS: Our aim was to analyze Rap1-activated rat bone marrow mesenchymal stem cells (MSCs) for their potential role in adhesion and cardiac differentiation.

METHODS: Myocardial infarction (MI) was produced in Sprague Dawley (SD) rats through occlusion of the left anterior descending coronary artery. MSCs were treated with 8-pCPT-2'-O-Me-cAMP (CPT) to activate Rap1. Normal (untreated) and CPT-treated MSCs were transplanted through intramyocardial injection in respective groups. Cardiac function was assessed by echocardiography at 2 and 4 weeks after cell transplantation. Histological analysis was performed to observe changes at tissue level.

RESULTS: Homing of CPT-treated MSCs was significantly (***P<.001) higher as compared to normal MSCs in the infarcted hearts. This may be due to increase in the gene expression of some of the cell adhesion molecules as evident by qRT-PCR analysis. Significant (***P<.001) improvement in the restoration of heart function in terms of left ventricular diastolic and systolic internal diameters (LVIDd, LVIDs), % ejection fraction, % fraction shortening and end-systolic and end-diastolic volumes were observed in CPT-treated MSCs as compared to the MI model. Histological analyses showed significant (***P<.001) reduction in scar formation in the CPT-treated group. Differentiation of treated MSCs into functional cardiomyocytes was evident through immunohistochemical staining. LV wall thickness was also preserved significantly (***P<.001). Blood vessel formation was more pronounced in CPT-treated group although both cell therapy groups showed significant increase as compared to MI model.

CONCLUSION: Our findings showed that pharmacological activation of Epac-Rap1 improves cardiac function through better survival, adhesion and differentiation of transplanted cells. Transplantation of these MSCs in the infarct area restored functional myocardium.