Abstract 3544: Intracellular Calcium Mobilization Enhances the Regenerative Potential of Human Cardiac Progenitor Cells
The human heart possesses a pool of cardiac progenitor cells (CPCs) that have the properties of stem cells in vitro and in vivo. The aim of this study was to determine whether mobilization of intracellular calcium in human CPCs enhanced their ability to repair the infarcted myocardium in immunosuppressed mice. Initial experiments documented that ATP and histamine promoted transient increases in cytosolic calcium in CPCs which were inhibited by IP3 receptor blockers. Based on these results, EGFP-labeled human CPCs were pretreated with ATP or histamine for 30 minutes prior to their delivery to the acutely infarcted mouse heart. Engraftment, growth and differentiation of EGFP-positive cells within the necrotic myocardium was measured 2 and 8 days after coronary occlusion and CPC implantation. BrdU was also administered so that the halogenated nucleotide and EGFP were employed to evaluate the accumulation of newly formed structures within the damaged heart. Control infarcted mice received non-stimulated CPCs. Of the 60,000 CPCs injected in each heart, an average of 7,000 EGFP-positive cells were found in control infarcts while 17,000 and 22,000 EGFP-positive cells were detected in infarcted hearts in which CPCs were pretreated with ATP and histamine, respectively. The fraction of dying CPCs was higher in controls than in the other two groups. Conversely, replication of EGFP-labeled cells measured by BrdU was 10-fold higher in animals injected with activated CPCs than in controls. At 2 days, BrdU-EGFP positive cells expressed connexin 43 and N-cadherin indicating their active engraftment in the host myocardium. Importantly, the number of EGFP-positive cells committed to the myocyte lineage was more than 3-fold larger in hearts treated with preconditioned cells, as indicated by expression of Nkx2.5. At 8 days, the number of myocytes expressing EGFP and specific contractile proteins was dramatically increased in animals treated with human CPCs exposed to ATP or histamine. The high degree of myocardial regeneration led by activated CPCs was coupled with a significant improvement in ventricular hemodynamics. In conclusion, induction of calcium oscillation in progenitor cells has a critical impact on the recovery of structure and function of the infarcted heart.