Estrogen receptors α and β mediate contribution of bone marrow-derived endothelial progenitor cells to functional recovery after myocardial infarction

Background-Estradiol (E-2) modulates the kinetics of circulating endothelial progenitor cells (EPCs) and favorably affects neovascularization after ischemic injury. However, the roles of estrogen receptors alpha(ER alpha) and beta(ER beta) in EPC biology are largely unknown. Methods and Results-In response to E-2, migration, tube formation, adhesion, and estrogen-responsive element dependent gene transcription activities were severely impaired in EPCs obtained from ER alpha-knockout mice (ER alpha KO) and moderately impaired in ER beta KO EPCs. The number of ER alpha KO EPCs (42.4 +/- 1.5; P < 0.001) and ER beta KO EPCs (55.4 +/- 1.8; P=0.03) incorporated into the ischemic border zone was reduced as compared with wild-type (WT) EPCs (72.5 +/- 1.3). In bone marrow transplantation (BMT) models, the number of mobilized endogenous EPCs in E-2-treated mice was significantly reduced in ER alpha KO BMT (WT mice transplanted with ER alpha KO bone marrow) (2.03 +/- 0.18%; P=0.004 versus WT BMT) and ER beta KO BMT (2.62 +/- 0.07%; P=0.02 versus WT) compared with WT BMT (2.87 +/- 0.13%) (WT to WT BMT as control) mice. Capillary density at the border zone of ischemic myocardium also was significantly reduced in ER alpha KO BMT and ER alpha KO BMT compared with WT mice (WT BMT, 1718 +/- 75/mm(2); ER alpha KO BMT, 1107 +/- 48/mm(2); ER beta KO BMT, 1567 +/- 50/mm(2)). ER alpha mRNA was expressed more abundantly on EPCs compared with ER beta. Moreover, vascular endothelial growth factor was significantly downregulated on ER alpha KO EPCs compared with WT EPCs both in vitro and in vivo. Conclusions-Both ER alpha and ER beta contribute to E-2-mediated EPC activation and tissue incorporation and to preservation of cardiac function after myocardial infarction. ER alpha plays a more prominent role in this process. Moreover, ER alpha contributes to upregulation of vascular endothelial growth factor, revealing possible mechanisms of an effect of E-2 on EPC biology. Finally, these data provide additional evidence of the importance of bone marrow-derived EPC phenotype in ischemic tissue repair.