Abstract 13292: Alterations in the EphA2 Endocytic Pathway Interfere With the Motility of Old Human Cardiac Stem Cells
Experimental evidence indicates that the migratory capacity of cardiac stem cells (CSCs) declines with age, but the molecular bases of this alteration are unknown. We have shown that human CSCs (hCSCs) express the cell guidance receptor EphA2. EphA2 stimulation with ephrin A1 ligand promoted cell movement in young but not in old hCSCs, both in vitro and in the infarcted myocardium. However, defects in EphA2 signaling may occur with age, impairing the motility of old hCSCs. Since EphA2 level did not differ in young and old hCSCs, we studied whether old cells are characterized by deficiencies in EphA2 function. Upon binding to ephrin A1, EphA2 underwent efficient endocytosis and accumulated in the perinuclear region of young hCSCs. This was accompanied by a time dependent increase in EphA2 colocalization with early endosomes and a progressive enlargement of EphA2-carrying vesicles: bigger EphA2 endosomes >3 μm2, were detected in the perinuclear region and smaller EphA2 vesicles <2 μm2, were observed at the cell periphery. In response to ephrin A1, caveolin 1, but not clathrin, colocalized with EphA2 in early endosomes in young hCSCs. Phospho-caveolin 1 content was increased in endocytic vesicles containing the activated EphA2 receptor and its target Src. The formation of this signaling endosome was required to initiate cell motility. The endocytic process of EphA2 was altered in old hCSCs. Internalized EphA2 was mostly restricted to the cell periphery and was frequently associated with late endosomes, possibly targeting EphA2 for degradation. Endocytic vesicles carrying ephrin A1/EphA2 did not undergo maturation in old hCSCs. Moreover, attenuated EphA2 autophosphorylation in response to ephrin A1 was coupled with decreased formation of signaling endosomes with Src and caveolin 1 effectors, and with a loss of caveolin 1 polarized pattern at the lateral cell membrane. Importantly, defects in EphA2 signaling and cell migration, similar to those present in old hCSCs, were found in young cells exposed to a blocker of endocytosis or to a Src inhibitor. Our results demonstrate that EphA2 function is maintained in endosomes of young hCSCs. Impaired EphA2 activation and endocytosis in old cells negatively impacted on the EphA2 downstream pathway and hCSC motility.
- Stem cell biology
- Receptor-mediated signaling
- Regenerative medicine stem cells
- Progenitor cell
- Oxidative stress
- © 2013 by American Heart Association, Inc.