Estrogen Regulates Osteoclast Differentiation Through EphB/EphrinB

Postmenopausal osteoporosis (PMOP) frequently occurs in postmenopausal women.The loss of estrogen at menopause causes the bone-resorbing activity of osteoclasts tooutpace the bone-forming activity of osteoblasts. Recently the EphB/EphrinB familyof receptor tyrosine kinases has been shown to play an important role in regulatingbone homeostasis. Therefore, to investigate the estrogen regulate osteoclastdifferentiation by EphB/EphrinB, we isolated and cultured the primary osteoclastsderived from OVX-mice and used estrogen antagonists (ICI182780) and E2to induceRAW264.7cells.Methods:1、RAW264.7cells were divided into3groups: E2, ICI and control group; mRNAand protein were collected after8-day culture and the expression of Ephrin/Eph werecompared by RT-PCR and western bolt;2、Osteoclasts of OVX and sham mice werecultured in the presence of RANKL, and mRNA and protein were collected after 10-day culture and evaluated by RT-PCR and western bolt;3、The osteoclasts of OVXmice were cultured in the presence of EphB4-Fc protein or IgG-Fc.Then the expressionof osteoclast maker was evaluated by RT-PCR and osteoclast differentiation wasassessed by TRAP staining;4、Osteoclasts of OVX and sham mice were cultured in thepresence of RANKL, and mRNA were collected after10-day culture and evaluated byRT-PCR; the osteoclasts of OVX mice were cultured in the presence of EphB2-Fcprotein or IgG-Fc,then the expression of osteoclast maker was evaluated by RT-PCRand osteoclast differentiation was assessed by TRAP staining.Results:1、Compared to the control group, the expression of EphrinB2was increased in E2group and decreased in ICI group,(P<0.01;P<0.05);2、Compared to EphrinB2inosteoclasts of sham mice, the expression of EphrinB2was significantly decreased inovx mice,(P<0.01);3、EphB4-Fc treatment suppressed osteoclast differentiation in ovxmice;4、Compared to EphrinB1in osteoclasts of sham mice, the expression ofEphrinB1was significantly decreased in ovx mice (P<0.01); EphB2-Fc treatmentsuppressed osteoclast differentiation in ovx mice.Conclusion:Estrogen might influence osteoclast differentiation through regulates theexpression of EphrinB2, EphrinB1in osteoclasts; by using EphB4-Fc or EphB2-Fctreatment the activated osteoclasts differentiation was suppressed in ovx mice.