Abstract 3420: Potential of Human Mesenchymal Stem Cells to Differentiate into Cardiomyocytes Depends on Donor Age and Donor Tissue
Treatment of damaged myocardium using autologous adult stem cells is under intense investigation as this may regenerate lost myocardium, thereby improving cardiac function. Initial cardiac cell therapy trials using various adult stem cell types have shown beneficial effects. However in contrast to earlier animal studies no true, quantitative reconstitution of myocardium has been observed. We hypothesized that the cardiomyogenic potential of stem cells depends on donor age and cell source. We used an in vitro differentiation protocol that employs co-culture of enhanced green fluorescent protein-labeled human mesenchymal stem cells (hMSCs) with neonatal rat cardiomyocytes (nrCMCs) for 13 days, without additional chemical or mutagenic stimulation. hMSCs were either derived from adult patients, or from human fetal tissue (gestational age 18 –22 weeks) or post natally collected umbilical cord blood. Differentiation of hMSCs was assessed by the presence of a properly developed sarcomere using immunological labeling for cardiac troponin I, myosin heavy chain and actinin. Functionality of newly differentiated cardiomyocytes was assessed by the presence of a functional calcium transient in conjunction with myocyte contraction. Mesenchymal stem cells isolated from clinically relevant sources (bone marrow, fat, and synovium) of adult patients are unable to adopt a cardiomyocyte phenotype upon co-incubation with nrCMCs. In contrast, MSCs from fetal donor material all give rise to functional cardiomyocytes, although with varying efficiency (umbilical cord blood: 6.8%±3.0, bone marrow: 0.4%±1.4, liver: 1.8%±0.8, lung: 1.4%±1.3, amnion: 9.3%±5.0 [mean±SD, n=3]). Using short hairpin RNA-mediated knockdown of connexin 43 (Cx43) gene expression, we found that sarcomeric development (organization) depends on the presence of Cx43 in the differentiating stem cells. Both donor age and the tissue source of human MSCs critically influence their cardiomyogenic differentiation potential. These results suggest that these non-embryonic, fetal cells may potentially be clinically useful for cardiac cell therapy.