Junctional adhesion molecule A expressed on human CD34+ cells promotes adhesion on vascular wall and differentiation into endothelial progenitor cells.

Objective: To investigate the role of junctional adhesion molecule A (JAM-A) on adhesion and differentiation of human CD34(+) cells into endothelial progenitor cells.
Methods and Results: Tissue healing and vascular regeneration is a multistep process requiring firm adhesion of circulating progenitor cells to the vascular wall and their further differentiation into endothelial cells. The role of JAM-A in platelet-mediated adhesion of progenitor cells was investigated by adhesion assays in vitro and with the help of intravital fluorescence microscopy in mice. Preincubation of human CD34(+) progenitor cells with soluble JAM-A-Fc (sJAM-A-Fc) resulted in significantly decreased adhesion over immobilized platelets or inflammatory endothelium under high shear stress in vitro and after carotid ligation in vivo or ischemia/reperfusion injury in the microcirculation of mice. Human CD34(+) cells express JAM-A, as defined by flow cytometry and Western blot analysis. JAM-A mediates differentiation of CD34(+) cells to endothelial progenitor cells and facilitates CD34(+) cell-induced reendothelialization in vitro. Pretreatment of human CD34(+) cells with sJAM-A-Fc resulted in increased neointima formation 3 weeks after endothelial denudation in the carotid arteries of nonobese diabetic/severe combined immunodeficient mice.
Conclusions: These results indicate that the expression of JAM-A on CD34(+) cells mediates adhesion to the vascular wall after injury and differentiation into endothelial progenitor cells, a mechanism potentially involved in vascular regeneration. Human CD34(+) cells express JAM-A, mediating their interaction with platelets and endothelial cells. Specifically, JAM-A expressed on human CD34(+) progenitor cells regulates their adhesion over immobilized platelets or inflammatory endothelium under high shear stress in vitro and after carotid ligation in vivo or ischemia/reperfusion injury in the microcirculation of mice. Moreover, it mediates differentiation of CD34(+) cells to endothelial progenitor cells and facilitates reendothelialization.