Background During osteoporosis, bone mesenchymal stem cells (BMSCs) lineage commitment shifts to adipocytes, causing fat accumulation and bone loss in the skeleton. Seeking drugs that could reverse the adipocyte fate determination of BMSCs is critical for osteoporosis therapy. As a traditional Chinese medicine, Rhizoma Curculiginis (Xianmao) has been used to treat bone diseases and promote bone healing, while the effective constituent of it and the underlying mechanisms are unknown. Objectives The aim of this study is to unveil the role of orcinol glucoside (OG), one constituent of Rhizoma Curculiginis, in osteoporosis and BMSCs lineage commitment and to explore the underlying mechanisms. Methods Micro-CT and three-point bending test were performed to determine the effect of OG on bone structure and strength. qT-PCR and Western blot were performed to determine the expression of osteogenic or adipogenic differentiation markers in BMSCs. Mineralization in differentiated BMSCs was assessed by Alizarin Red staining, and lipid accumulation in the cells was evaluated by Oil Red O staining. All measurements were performed at least three times. Results OG prevented bone loss by stimulating bone formation and attenuating fat formation in bone. In vitro, OG promoted osteoblastic differentiation and inhibited adipogenic differentiation of BMSCs. Inhibition of Wnt/β-catenin by ICG-001 significantly reversed the effect of OG on osteogenic and adipogenic differentiation of BMSCs. Conclusion Our study demonstrated the role of OG in alleviating bone loss and fat accumulation in osteoporotic bone, therefore bringing a new therapeutic means to the treatment of osteoporosis.

Introduction Estrogen 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, 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 osteoporosis are unclear. Materials and Methods Postmenopausal osteoporosis mouse model was established by bilateral surgical ovariectomy (OVX). In situ hybridization was performed to detect Cxcl9 mRNA expression in bone. ELISA assay was conducted to assess Cxcl9 concentrations in bone and serum. Cxcl9 activity was blocked by its neutralizing antibody. Micro-CT was performed to determine the effects of Cxcl9 neutralization on bone structure. Cell Migration and adhesion assay were conducted to evaluate the effects of Cxcl9 on osteoclast activity. TRAP staining and Western blot were performed to assess osteoclast differentiation. CXCR3 antagonist NBI-74,330 or ERK antagonist SCH772984 was administered to osteoclast to study the effects of Cxcl9 on CXCR3/ERK signaling. Results Cxcl9 was expressed and secreted increasingly in OVX mice bone. Neutralizing Cxcl9 in bone marrow prevented bone loss in the mice by facilitating 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 was 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. Conclusion Our study illustrates the roles of Cxcl9 in inhibiting bone formation and stimulating bone resorption in osteoporotic bone, therefore providing a possible therapeutic target to the treatment of postmenopausal osteoporosis.

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