Estrogens (E2) regulate expression and response of 1,25-dihydroxyvitamin D3 receptors in bone cells: changes with aging and hormone deprivation.
Studies on the effect of estrogens (E(2)) on the expression of vitamin D receptor (VDR) and its bioresponse in bone have demonstrated that E(2) modulate activity and increase the number of VDRs in vitro; however, no in vivo studies have been pursued to assess this interaction. Our study identifies the changes in the number of VDR-expressing cells in bone of C57BL/6J young and old oophorectomized mice (4 and 24 months) with and without 17beta estradiol (E(2)) replacement. A total of 36 mice were sacrificed; both tibiae and femora were isolated and VDR expression was quantified by Northern blot, immunohistochemistry, immunofluorescence, and flow cytometry. Among the intact mice there was a significant difference in the number of VDR-expressing osteoblasts between young (68%) and old (56%) (p<0.04). In young oophorectomized mice the number of VDR-expressing osteoblasts decreased from 68% to 46% after oophorectomy and recovered to 72% after E(2) administration (p<0.02), while in the group of old mice, the number of VDR-expressing osteoblasts decreased from 56% to 48% after oophorectomy (p<0.01) and recovered to 85% after E(2) administration (p<0.001). Our results show that VDR expression in bone decreases with aging and estrogen deprivation but recovers after E(2) supplementation in both young and old mice with a more significant level of response in older bone. To evaluate the level of VDR bioresponse to E(2) we assessed the effect of E(2) supplementation to human osteoblasts (N-976) in vitro. Northern blot showed a significant up-regulation of VDR expression in E(2) treated cells as compared to non-treated cells (p<0.05). We also assessed the previously known anti-apoptotic effect of vitamin D in osteoblasts in vitro after serum deprivation by using either E(2), E(2)+1,25(OH)(2)D(3), or 1,25(OH)(2)D(3) alone. We found a lower number of apoptotic cells and longer cell survival after 48 h of treatment with 1,25(OH)(2)D(3)+E(2) as compared to 1,25(OH)(2)D(3) or E(2) alone (p<0.002). In summary, our results demonstrate that E(2) increases VDR expression in bone in vivo and potentiate the bioresponse of VDR in osteoblasts in vitro.
Duque
Gustavo
G
Calcium Research Laboratory, Department of Medicine, McGill University, Que., Montreal, Canada. gduque@po-box.mcgill.ca
El Abdaimi
Khadija
K
Macoritto
Michael
M
Miller
Marilyn M
MM
Kremer
Richard
R
D000375:Aging / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001854:Bone Marrow Cells / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism*; D004967:Estrogens / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D006728:Hormones / Q000172:deficiency*; D006801:Humans; D020287:In Situ Nick-End Labeling; D051379:Mice; D008810:Mice, Inbred C57BL; D009929:Organ Size; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010052:Ovariectomy; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism*; D014599:Uterus / Q000033:anatomy & histology
D004967:Estrogens; D006728:Hormones; D018167:Receptors, Calcitriol