Identification and functionality of proteomes secreted by rat cardiac stem cells and neonatal cardiomyocytes.

In the heart, the proteomes secreted by both cardiac stem cells (CSCs) and cardiac myocytes could act synergistically, but the identification and functionality of the proteins comprising the individual secretomes have not yet been described. In this study, we have identified proteins present in the media obtained from cultured rat CSCs and from cultured neonatal rat ventricular myocytes (NRVMs) and compared them with proteins identified in the media alone. Briefly, 83 unique proteins were identified after analysis by RPLC and MS. In total 49 and 23% were NRVM-specific or CSC-specific proteins, respectively, and 63% of total 83 proteins were integral plasma membrane and/or known secreted proteins. Fifteen proteins met our criteria for paracrine/autocrine factors: (i) robust protein identification, (ii) cell specific and (iii) known to be secreted. Most of these proteins have not been previously linked to stem cells. NRVM-specific proteins atrial natriuretic factor (ANP) and connective tissue growth factor, and CSC-specific protein interleukin-1 receptor-like 1 (ST2) were found to affect rat CSC proliferation. These findings suggest that relative concentration of each protein may be crucial for cellular intertalk and for the final outcome of cardiac cell therapy.