The Mechanism Of Osteoblastic CXCL9 In The Uncoupled Bone Formation And Resorption In Postmenopausal Osteoporosis

BackgroundEstrogen deficiency leads to bone loss in postmenopausal osteoporosis,because bone formation,albeit enhanced,fails to keep pace with the stimulated osteoclastic bone resorption.The mechanism driving this uncoupling is central to the pathogenesis of postmenopausal osteoporosis and vital for development of new drugs to restore the remodeling balance,which,however,remains poorly understood.We previously found that CXCL9 secreted by osteoblasts inhibited osteogenesis in bone,while the roles of CXCL9 on osteoclastic bone resorption and postmenopausal osteoporosis are unclear.ObjectiveThe aim of this study was to explore the effect of osteoblastic CXCL9 on the differentiation of osteoblast and osteoclast and its role in OVX induced postmenopausal osteoporosis.MethodsThe mouse model of osteoporosis induced by OVX was established.CXCL9 and ELISA assay were used to explore the expression and secretion of CXCL9 in the bone tissue of Sham and OVX mice.CXCL9 neutralizing antibody and vehicle were injected into the distal femoral bone marrow cavity of OVX mice,and the changes of bone mass were detected by micro-CT;Osteocalcin immunofluorescence and TRAP staining were used to detect the effect of CXCL9 on the differentiation of osteoblasts and osteoclasts in vivo.Brdu assay was used to detect the effect of CXCL9 on the proliferation of osteoblasts in vitro,and the effect of CXCL9 on osteoblast differentiation was detected by western blot and ALP staining.We treated BMMs with conditional medium collected from osteoblasts interfered with CXCL9 expression,to detect the effect of osteoblast-derived CXCL9 on the adhesion,migration and differentiation of osteoclast progenitor cells.BMMs were treated with CXCR3 and ERK antagonists to prove that CXCL9 acted on osteoclasts through CXCR3/ERK signal pathway.We treated mouse primary osteoblasts with estradiol and fulvestrant(estrogen receptor antagonist)respectively and examined CXCL9 expression and secretion.ResultsHere we found that CXCL9 was expressed and secreted increasingly in O VX mice bone.Neutralizing CXCL9 in bone marrow alleviated bone loss in the mice by stimulating bone formation as well as inhibiting bone resorption.In vitro,CXCL9 secreted from osteoblasts facilitated osteoclast precursors adhesion,migration and their differentiation into mature osteoclasts.The positive role of osteoblastic CXCL9 on osteoclasts were all eliminated by blocking CXCR3/ERK signaling in osteoclasts.Estrogen negatively regulated CXCL9 expression and secretion in osteoblasts,explaining the increased CXCL9 concentration in OVX mice bone.ConclusionOur study illustrates the roles of CXCL9 in inhibiting bone formation and stimulating bone resorption in postmenopausal osteoporotic bone,therefore bringing a new therapeutic target to the treatment of postmenopausal osteoporosis.