title: Effects of estrogen on stress-induced premature senescence of vascular smooth muscle cells: a novel mechanism for the "time window theory" of menopausal hormone therapy.
abstract: OBJECTIVE
  To investigate the effects of estrogen on stress-induced premature senescence of vascular smooth muscle cells (VSMCs) and the underlying mechanisms.
  
  
  METHODS
  VSMCs of passage 2-3 cultured from young (2 months) and old (18 months) female SD rats were induced into premature senescence by exposure to 150 μmol/L H(2)O(2) in the presence or absence of different concentrations of 17β-estradiol (E(2)). The expression or activation of senescence-associated beta-galactosidase (SA-β-Gal), DcR2, oncogene Ras, p38, PRAK, p53, p21, p16 and Rb was detected by flow cytometry, pull-down assay or Western blot.
  
  
  RESULTS
  Flow cytometry analysis showed that in the VSMCs from young rats pre-administration of E(2) significantly suppressed the H(2)O(2)-induced premature senescence (reducing both percentage of SA-β-Gal positive cells and cellular expression of DcR2) in a dose-dependent manner; these senescent-inhibiting effects of E(2) could be blocked by an estrogen receptor antagonist ICI 182,780 (10(-5)mol/L). Pull-down assay or Western blot analysis revealed that pre-administration of 10(-8)mol/L E(2) significantly reduced the H(2)O(2)-induced activation of oncogene Ras, as well as activity of p16 and p38 MAPK, and expression of PRAK, p53, p21 and p-Rb. Unexpectedly, in the VSMCs from old rats the senescent-inhibiting effect of E(2) disappeared and switched to a senescent-promoting action at 10(-8)mol/L. This senescent-promoting effect could be enhanced by ICI 182,780 and eliminated by a cytochrome P450s inhibitor ABT.
  
  
  CONCLUSIONS
  Estrogen inhibits stress-induced premature senescence of VSMCs from young female through its receptor-mediated suppression of both Ras-p38-PRAK-p53-p21-Rb and Ras-p16-Rb pathways, but this effect disappeared and even more switched to a senescent-promoting action in the cells from old body probably due to a side effect of estrogen metabolites.
authors.affiliation: Department of Anatomy and Embryology, and Center for Medical Research, Wuhan University School of Medicine, 135 Donghu Road, Wuhan 430071, Hubei, China.
authors.forename: Congli
authors.initials: C
authors.lastname: Zhu
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.forename: Yong
authors.initials: Y
authors.lastname: Zheng
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Jian
authors.initials: J
authors.lastname: Song
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Rolfe
authors.forename: Julie H
authors.initials: JH
authors.lastname: Campbell
mesh_terms: D000375:Aging / Q000187:drug effects*; D000818:Animals; D016922:Cellular Senescence / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological
chemical_list: D004958:Estradiol; D006861:Hydrogen Peroxide