Estrogen Receptor α Expression in Both Endothelium and Hematopoietic Cells Is Required for the Accelerative Effect of Estradiol on Reendothelialization

OBJECTIVE: E2 accelerates reendothelialization through estrogen receptor alpha (ERalpha), and we now aimed at defining the precise local and systemic cellular actors of this process. METHODS AND RESULTS: The respective roles of endothelial and hematopoietic targets of E2 were investigated in a mouse carotid injury model, using confocal microscopy, to follow endothelium repair. Grafting ERalpha(-/-) mice with ERalpha(+/+) bone marrow (BM) was not sufficient to restore the accelerative effect of E2 on reendothelialization, demonstrating the necessary role of extrahematopoietic ERalpha. Using an endothelial-specific inactivation of ERalpha (Cre-Lox system), we showed that endothelial ERalpha plays a pivotal role in this E2 action. Conversely, in ERalpha(+/+) grafted with ERalpha(-/-) BM, the E2 regenerative effect was abolished, demonstrating that ERalpha-expressing hematopoietic cells are also needed. As eNOS expression in BM was required for this action, both endothelial progenitor cells and platelets could be the hematopoietic targets that participate to this beneficial E2 effect. CONCLUSIONS: We demonstrate that endothelial ERalpha plays a pivotal role in E2-mediated reendothelialization. However, endothelial targeting alone is not sufficient becuase the concomitant stimulation of a subpopulation of BM ERalpha is necessary. This cooperation should be taken into account in strategies aimed at optimizing in-stent reendothelialization.