Abstract 317: Differential Role of Estrogen Receptors Alpha and Beta in Estradiol (E2) Enhanced Contribution of Bone Marrow-Derived Endothelial Progenitor Cells to Neovascularization after Ischemic Injury
Background and Aim: E2 modulates the kinetics of circulating endothelial progenitor cells (EPCs) and favorably impacts neovascularization after ischemic injury. However, the role of estrogen receptor alpha (ERa) and beta (ERb), is largely unknown in this process. The aim of this study is to investigate the role of the estrogen receptors in E2-induced, EPC-mediated neovascularization. Methods and Results: In response to E2, EPC proliferation and migration activities in vitro were severely impaired in EPCs cultured from ERa-knockout mice (ERaKO EPCs)(migration p<0.001, proliferation p<0.001) and moderately impaired in ERbKO EPCs (p=0.03, p<0.001), as compared to wild type (WT) EPCs. In vivo, both tissue homing and EPC mobilization from bone marrow were significantly impaired in ERaKO (homing p<0.001, mobilization p<0.01) and ERbKO (p=0.03, p=0.02) vs. WT mice in mouse acute myocardial infarction (MI) models. Capillary density at the border zone of ischemic myocardium, was also significantly reduced in WT mice with ERaKO-bone marrow transplantation (BMT) vs. WT mice with WT-BMT (p<0.001). In these experiments, ERaKO EPCs had a more prominent phenotype than ERbKO EPCs. ERa mRNA was more abundantly expressed on EPCs when compared to ERb mRNA by quantitative RT-PCR, confirmed by FITC-conjugated estrogen binding studies. Quantitative RT-PCR for cultured-EPCs revealed that VEGF-A was significantly down-regulated in ERaKO EPCs, as compared to WT EPCs (p<0.001). On ischemic myocardium in mice with MI and ERaKO EPC injection, VEGF protein expression at the border zone around the injected EPCs was lower, compared with mice with MI and WT EPC injection. On the other hand, in ERbKO EPCs, SDF-1 and MMP-9 mRNAs were significantly low (p=0.01). Blocking experiment showed that MMP-9 expression was regulated by SDF-1-CXCR4 axis in cultured EPCs. SDF-1 and MMP-9 protein expression was lower on ischemic myocardium in mice with MI and ERbKO EPC injection, compared with mice with MI and WT EPC injection. Conclusion: ERa and ERb mediate expression of different angiogenic molecules, revealing different mechanisms of E2 effect on EPC biology.