Estrogen blocks parathyroid hormone (PTH)-stimulated osteoclast-like cell formation by selectively affecting PTH-responsive cyclic adenosine monophosphate pathway.
Several lines of evidence have previously indicated that estrogen inhibits PTH-induced bone resorption in vivo and in vitro. However, its mechanism remains unknown. Therefore, the present study was performed to investigate the effect of estrogen on PTH-stimulated osteoclast-like cell formation and clarify its mechanism. 17 beta-estradiol (17 beta-E2) significantly antagonized osteoclast-like cell formation stimulated by 10(-8) M human (h) PTH-(1-34) as well as 10(-8) M hPTH-related peptide (PTHrP)-(1-34)in osteoblast-containing mouse bone cell cultures. The conditioned medium derived from osteoblastic SaOS-2 cells or MC3T3-E1 cells pretreated with both PTH-(1-34) (10(-8)M) and 17 beta-E2(10(-8)M) stimulated osteoclast-like cell formation from hemopoietic blast cells more weakly than conditioned medium from cells pretreated with PTH-(1-34) alone. Moreover, 10(-8) M 17 beta-E2 significantly blocked the formation of osteoclast-like cells stimulated by 10(-8) M hPTH-(1-34) in spleen cell cultures derived from 5-fluorouracil-pretreated mice. On the other hand, 10(-8) M 17 beta-E2 significantly inhibited osteoclast-like cell formation stimulated by dbcAMP (10(-4)M) and Sp-cAMPS (10(-4)M), as well as forskolin (10(-5)M) in mouse bone cell cultures. In contrast, 10(-8)M 17 beta-E2 did not affect PMA (10(-7)M)-, A23187 (10(-7)M)-, or BAYK-8644 (5 x 10(-6) M)-stimulated osteoclast-like cell formation. In conclusion, the present study demonstrated that estrogen inhibits PTH-stimulated osteoclast-like cell formation by directly acting on hemopoietic blast cells as well as by indirectly acting on them via osteoblasts. The inhibitory effects of estrogen on PTH-stimulated osteoclast-like cell formation seemed to be mediated through blocking the cAMP-dependent protein kinase pathway but not by blocking calcium/protein kinase C.
Kaji
H
H
Department of Medicine, Kobe University School of Medicine, Japan.
Sugimoto
T
T
Kanatani
M
M
Nasu
M
M
Chihara
K
K
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D005472:Fluorouracil / Q000494:pharmacology; D006801:Humans; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects*; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000494:pharmacology; D015290:Second Messenger Systems; D013154:Spleen / Q000166:cytology / Q000187:drug effects; D019379:Teriparatide
C470121:PTHLH protein, human; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D011506:Proteins; D019379:Teriparatide; D004958:Estradiol; D003994:Bucladesine; D000242:Cyclic AMP; D011494:Protein Kinases; D005472:Fluorouracil