Abstract 5375: Mutations of c-kit Receptor are Coupled with Impaired Growth and Enhanced Death of Cardiac Progenitor Cells
The W/Wv mouse has a mutated non-functional c-kit receptor representing a model of genetically induced partial ablation of the stem cell pool. Since c-kit-positive cardiac progenitor cells (CPCs) modulate cardiac homeostasis, defects in c-kit signaling may affect growth and death of CPCs favoring their premature aging. Thus, CPCs were isolated from W/WV and WT mice and cultured. At baseline, there was no significant difference in the fraction of dividing CPCs in W/WV and WT. However, after stimulation with IGF-1 and SCF, the fraction of BrdU-labeled CPCs was nearly 50% lower in W/WV. The attenuated growth response of W/WV CPCs was accompanied by a 4-fold higher level of apoptosis. To determine whether these alterations in CPC behavior were dictated by changes in gene expression, the transcriptional profile of WT and W/WV mouse heart was determined by Affimetrix microarray. In comparison with WT, 300 genes were upregulated and 150 were downregulated in W/WV. Among these differentially expressed genes, we elected to study 5 genes implicated in cell division, death and aging. Consistent with the negative effects of c-kit mutations on CPC survival, the expression of the anti-apoptotic gene Bre was 2.2-fold lower in W/WV CPCs. Two growth-promoting genes Taf1 and Id2 were tested. Taf1 phosphorylates p53 at Thr-55 resulting in Mdm2-mediated p53 degradation and cell cycle progression. Id2 binds to the retinoblastoma protein (Rb) abolishing its growth-suppressive activity. The expression of Taf1 and Id2 in W/WV CPCs was, respectively, 2.6 and 3.2-fold lower than in WT CPCs. Nearly 70% and 30% CPCs expressed phospho-p53 at Thr-55 in W/WV and WT CPCs, respectively, indicating that p53 degradation is more efficient in WT than W/WV CPCs. Finally, the expression of the mitotic spindle checkpoint proteins Bub1 and Cdc42GAP was, respectively, 2.3 and 3.8-fold lower in W/WV CPCs than WT CPCs. Downregulation of these two genes is coupled with precocious cellular senescence. In conclusion, mutations of the c-kit receptor impair CPC division and survival promoting cellular aging. With time, these defects in CPC function alter cardiac homeostasis and myocyte turnover, leading to a reduction in myocyte number, cellular hypertrophy and the development of a premature aging myopathy.