Effects of estrogen on growth and smooth muscle differentiation of vascular wall-resident CD34+ stem/progenitor cells

Abstract Objectives : To investigate the effects of estrogen on growth and smooth muscle cell (SMC)-differentiation of vascular wall-resident CD34 + stem/progenitor cells (VRS/Pcs). Methods and Results : The existence of CD34 + VRS/Pcs was confirmed by immunohistochemistry in the adventitia of arteries of young (2-month-old) and old (24-month-old) female SD rats with less CD34 + adventitial cells detected in the old. The VRS/Pcs isolated from young animals were grown in Stem cell growth medium or induced to differentiate into SMC with PDGF-BB in the presence or absence of 17β-estrodiol (E 2 ). Flow cytometry, RT-qPCR and Western blot showed that E 2 promoted Brdu incorporation of the CD34 + VRS/Pcs growing in Stem cell growth medium; but when the cells were incubated in PDGF-BB, the hormone enhanced their expression of SMC marker SM22. ChIP and IP assays showed that E 2 significantly promoted the binding of pELK1-SRF complex to the promoter of c-fos gene in CD34 + VRS/Pcs growing in the Stem cell growth medium; but when the cells were stimulated with PDGF-BB, an E 2 -enhanced binding of myocardin-SRF to the promoter of SM22 gene was found with enhanced expression of SRC3 and its binding to myocardin. The effects of E 2 above could be blocked by the estrogen receptor antagonist ICI 182,780 or inhibited by SRF-siRNA. Conclusion : Estrogen has dual effects on CD34 + VRS/Pcs. For the undifferentiated VRS/Pcs, it accelerates their proliferation by enhancing binding of pELK1-SRF complex to c-fos gene; while for the differentiating VRS/Pcs, it promotes their differentiation to SMC through a mechanism of SRC3-mediated interaction of myocardin-SRF complex with SM22 gene.