Abstract 2043: Bone Marrow Mesenchymal Stem Cells Acquire a Cardiogenic Phenotype via Transdifferentiation and Cell Fusion with Cardiomyocytes
Objective: After a myocardial infarction, implanted bone marrow mesenchymal stem cells (BMSCs) can regenerate the heart by enhancing regional perfusion, preventing ventricular dilatation and improving function. However, few reports demonstrate whether the BMSCs transdifferentiate or fuse. This study identified the optimal conditions for BMSCs to obtain the cardiogenic phenotype, either by transdifferentiation or cell fusion.
Method: In vitro: BMSCs derived from transgenic rats expressing green fluorescent protein (GFP-BMSCs) were co-cultured with neonatal rat cardiomyocytes in various ratios for 7 days. Fluorescent staining and flow cytometry with cardiac specific markers confirmed the cardiogenic phenotype of the BMSCs; current clamp recordings of membrane potential confirmed their functional activity. To identify cell fusion, cardiomyocytes pre-labeled with DiI were co-cultured with GFP-BMSCs in different ratios for 7 days, and stained for Troponin I. In vivo: Irradiated mice were reconstituted with bone marrow from GFP mice, and sacrificed 7 days after LAD ligation. Heart tissue was collected for immunohistochemical Troponin I staining.
Results: In vitro: After co-culture, 3–13% of GFP-BMSCs were positive for α-sarcomeric actinin, Troponin I, and MEF-2C. An increase in GFP and cardiac marker double positive cells was correlated with the number of co-cultured cardiomyocytes. Some GFP-BMSCs contracted synchronously with the cardiomy-ocytes, and the action potential properties of the cardiogenic phenotype GFP-BMSCs were similar to those of neonatal cardiomyocytes. In the cell fusion assay, 2– 6% of GFP-BMSCs were positive for both Troponin I and DiI; the rest were positive only for Troponin I. In vivo: More triple-positive BMSCs were seen in the heart tissue of the LAD ligation group than in that of the reconstituted control group.
Conclusion: In co-culture with cardiomyocytes, BMSCs acquire a functional cardiogenic phenotype positively correlated with the number of co-cultured cardiomyocytes. Both transdifferentiation and cell fusion are responsible for the myogenic characteristics of BMSCs. Further, BMSCs can migrate and home to damaged myocardium, and acquire a cardiogenic phenotype after a myocardial infarction.