Abstract 3903: IGF-1, Angiotensin II and Human Cardiac Progenitor Cell Function
The objective of this work was to characterize the molecular properties of functionally competent c-kit-positive human cardiac progenitor cells (hCPCs) which are critical for their clinical implementation. A fundamental issue to be resolved concerns the identification of hCPCs which retain the ability to divide and differentiate possessing therapeutic potential. Two growth factor receptor systems were identified in hCPCs by Q-RT-PCR and immunocytochemistry. hCPCs express the components of the renin-angiotensin system (RAS) including renin, angiotensinogen, ACE, AT1 and AT2 receptors and synthesize Ang II. Similarly, hCPCs possess IGF-1 receptors (IGF-1R) and form IGF-1. Based on the hypothesis that the IGF-1-IGF-1R axis is a determinant of cell youth, hCPCs were sorted by FACS to obtain IGF-1R-positive and IGF-1R-negative hCPCs. The growth behavior of these hCPC classes was evaluated by population doubling time (PDT), which characterizes the growth kinetics of the cell population, and BrdU incorporation, which detects the fraction of cycling cells. IGF-1R-positive hCPCs had a ~2-fold shorter PDT and a ~1.6-fold higher level of BrdU labeling than IGF-1R-negative hCPCs. Apoptosis determined by FACS after labeling with Annexin V and PI was ~2-fold higher in IGF-1R-negative than IGF-1R-positive hCPCs. Replicative senescence was assessed by measuring telomere length and p16INK4a. Telomere length distribution in IGF-1R-negative hCPCs was shifted to the left towards shorter telomeres. Additionally, p16INK4a was detected in nearly twice IGF-1R-negative hCPCs than IGF-1R-positive cells. Also, telomerase activity was significantly higher in IGF-1R-positive hCPCs. Finally, the low proliferation rate of IGF-1R-negative hCPCs was accompanied by upregulation of AT1R and higher susceptibility to Ang II-induced apoptosis. Thus, in comparison with IGF-1R-negative hCPCs, IGF-1R-positive hCPCs have a greater rate of cell division, a lower degree of apoptosis, longer telomeres, enhanced telomerase activity and a smaller fraction of senescent cells. In conclusion, IGF-1R expression is critical for the preservation of the proliferative capacity of hCPCs and can be employed to sort functionally competent hCPCs from the pool of senescent cells.