Abstract 855: Circulating Mesoangioblasts Differentiate Into Cardiac Myocytes And Improve Function After Acute Myocardial Infarction

Mesoangioblasts (MAB) are vessel-associated cells identified during embryonic development. In contrast to hemangioblasts, MAB express mesenchymal (CD73) and endothelial marker, but lack the hematopoietic marker CD45. We recently identified circulating MAB in children. Children-derived MAB showed vigorous proliferation capacity and high telomerase activity. However, the potential of cardiac differentiation in these cells was not elucidated. Therefore, we tested the capacity of children-derived MAB to aquire a cardiomyogenic phenotype. MAB expressed several cardiac transcription factors such as Nkx2.5, GATA4 and MEF2C and the stem cell markers c-kit and islet-1. In order to assess cardiac differentiation capacity, we performed co-culture assays with neonatal rat cardiomyocytes (CM). Immunochemical analysis revealed that MAB expressed cardiac α-sarcomeric actinin 6 days after co-culture. Moreover, human troponin T (TnT) was expressed as demonstrated by human specific RT-PCR. To confirm these data, we examined TnT expression in MAB isolated of a 2 years old patient with a known mutation of TnT. Sequences of the cloned RT-PCR products were identical to human TnT except for the known mutation providing genetic proof of concept for cardiac differentiation. In order to exclude fusion between MAB and CM as a mechanism, we used paraformaldehyde-fixed CM as scaffold. In this assay, human TnT also was detected, indicating that differentiation is sufficient to induce cardiac marker gene expression. Next, we tested the effect of MAB to improve cardiac function. MAB were injected intramuscularly in nude mice after myocardial infarction. Functional analysis using Millar catheter 2 weeks after infarction demonstrated that cell therapy lowered filling pressure and preserved diastolic function when compared to the PBS injected group (LVEDP: −20.3%, tau: −20.6%, vs PBS injected heart). Furthermore, left ventricular volume was also decreased (LVEDV/weight −27.3%). In summary, children-derived MAB express cardiac-specific genes after co-culture with CM and improved cardiac function in vivo. Given that MAB can be easily isolated and expanded from peripheral blood, these cells might be suitable to augment cardiac repair in children with heart failure.