Abstract 15359: Alterations in Ephrin A1/EphA2 Signaling Causes Defects in the Migration of Senescent Human Cardiac Stem Cells
The male human heart loses 64x10^6 myocytes per year indicating that the formation of new cells derived from the differentiation of human cardiac stem cells (hCSCs) is not sufficient to counteract the increase in myocyte death with aging. In this study, we raised the possibility that defective migration of hCSCs to sites of tissue damage contributes to myocardial aging and ventricular dysfunction. In an experimental model of acute infarct, guidance of hCSCs was found to be controlled by the EphA2 receptor tyrosine kinase. Activation of EphA2-positive hCSCs with ephrin A1 promoted the mobilization of hCSCs to the ischemic region enhancing myocardial regeneration. To study the effects of aging on hCSC migration, we have employed two models of cellular senescence: replicative senescence of serially-passaged hCSCs and stress-induced senescence of hCSCs exposed to doxorubicin. To validate our strategies, several parameters were evaluated. In both cases, hCSCs showed a flattened morphology and displayed nuclear swelling. In old cells, p53 was phosphorylated at Ser 15 and was localized to the nucleus. With respect to young cells, the fraction of cycling Ki67-positive hCSCs decreased 3-fold. Additionally, a 4-fold increase in the expression of the senescence-associated marker p16INK4a was documented by Western blotting and immunocytochemistry. Senescent hCSCs were sessile and did not migrate in response to hepatocyte-growth-factor (HGF) and ephrin A1. Although the expression of EphA2 and c-Met did not differ in young and old hCSCs, ephrin A1-induced EphA2 phosphorylation and internalization were markedly attenuated in senescent hCSCs. Defective internalization of the ephrin A1-EphA2 complex led to a reduced phosphorylation of Src and a significant decrease of cell binding to the immobilized ephrin A1 ligand. In senescent hCSCs, the insufficient activation of Src precluded changes in caveolin-1 redistribution from pre-existing cell-matrix adhesions, a process required for cell motile responses. Collectively, our data indicate that ephrinA1-EphA2 signaling is impaired in senescent hCSCs, negatively affecting their motile properties and possibly contributing to the aging cardiac phenotype.
- © 2011 by American Heart Association, Inc.