0128 : Sca-1 positive cells, but not c-kit positive cells, differentiate into mature cardiomyocytes after brain natriuretic peptide treatment

The Brain Natriuretic Peptide (BNP) is a cardiac hormone, which promotes the recovery of cardiac function and the preservation of cardiac tissue in animal models of heart diseases. Its cardiac protective role in animals was attributed to fibrosis inhibition, as well as to reduction of cardiomyocyte apoptosis and hypertrophy. Recently, we demonstrated that BNP induces heart regeneration via the stimulation of cardiac precursor cell (CPC) proliferation and differentiation into mature cardiomyocytes. The aim of our study was to identify which CPC’s subset is able to respond to BNP stimulation. Cardiac precursor cells identified as being Sca-1 + Nkx2.5 + or c-kit + Nkx2.5 + cells, expressed in neonatal and adult hearts BNP’s receptors (NPR-A and NPR-B), showing their ability to be activated by BNP treatment. Cell sorting experiments based on the expression of Sca-1 or c-kit were performed on nonmyocyte cells isolated from neonatal wild-type hearts. Sca-1 + and c-kit + cells were cultured up to 3 weeks with or without BNP in differentiating medium. Sca-1 positive cells, which contained few c-kit + cells, responded clearly to BNP stimulation by upregulating mRNA levels of genes coding for Nkx2.5, Mlc-2v, c-kit, Sca-1, beta and alpha MHC. Furthermore, higher number of Troponin I + cells was detected in BNP treated cells compared to untreated cells, suggesting that Sca-1 + cells differentiated after BNP stimulation into mature cardiomyocytes. BNP treatment of c-kit + cells didn’t induce the upregulation of mRNA coding for cardiomyocyte specific genes. However, we determined that c-kit positive cells spontaneously differentiated into mature cardiomyocytes during the 3 weeks of cell culture without BNP stimulation. To determine which receptor is involved, Sca-1 + cells, isolated from neonatal hearts of NPR-A or NPR-B deficient mice, were treated with BNP. The effects of BNP on wild type and NPR-A KO cells did not differ substantially. However, Sca-1 + cells isolated from NPR-B deficient hearts couldn’t respond anymore to BNP stimulation. Thus, BNP specifically stimulates via NPR-B Sca-1 + cell differentiation into cardiomyocytes. c-kit + cells display clearly a cardiogenic potential which is BNP independent.