Abstract 19364: C-Kit + Cardiac Progenitor Cells are Important in Cardiomyocytes Generation i n vivo in Response to Sfrp2

Abstract

Introduction: Resident c-Kit + cardiac progenitor cells (CPCs) differentiation into cardiomyocytes in vivo is controversial. Using lineage tracing and gene ablation techniques we documented that the Wnt signaling modulator Sfrp2 substantially increased differentiation of c-Kit + CPCs into cardiomyocytes in post-MI heart and restored cardiac function. Methods: c-Kit-CreERT2/mTeG mice were used where the c-Kit promoter drives expression of a tamoxifen (TX)-inducible Cre. Upon TX treatment Cre-mediated recombination drives expression of eGFP exclusively in c-Kit cells. Mice were crossed with a Diphtheria toxin receptor (DT) strain to selectively ablate heart c-Kit cells. Mice were subjected to myocardial infarction. 2 days later, mice were injected with Sfrp2 (0.5 μg) or saline at the infarct border zone. Heart tissue was analyzed 2 months post-MI for eGFP expression and various markers by microscopy. Results: c-Kit-CreERT2/mTeG model was tested. eGFP expression had no effect on in vitro c-Kit CPC differentiation or proliferation. In TX treated mice, >90% of c-Kit+ cells were eGFP+. No eGFP+ c-Kit+ cells were seen in vehicle-only mice (N=6, p<0.001). c-Kit negative cells, such as cardiomyocytes, endothelial cells, and smooth muscle cells, did not express eGFP following TX treatment. In sham animals, eGFP was localized to small c-Kit+ cells. In the vehicle MI group eGFP+ cardiomyocytes were rare (0.08% in infarct border zone. N=8, P=0.005). In contrast, the number of eGFP+ cardiomyocytes was significantly higher in the Sfrp2 treated group (15% in infarct border zone, N=10, P=0.0002). Co-localization of eGFP with blood vessels (0.77%, N=10) was infrequent. Induction of c-Kit CPC differentiation into cardiomyocytes by Sfrp2 was associated with lower fibrosis (15%, N=10, P=0.01), higher LV mass (58mg, N=10, P=0.01) and increased ejection fraction (16%, N=10, P=0.02). DT treatment ablated c-Kit cells (>95% N=4, P=0.01). Sfrp2 induction of c-Kit differentiation to cardiomyocytes and functional improvements were completely ablated by DT. Conclusion: Using c-Kit lineage-tracing and genetic ablation we have identified that these cells are important in cardiomyocyte generation in vivo in response to Sfrp2 and improves cardiac function following MI.