title: Adiponectin stimulates RANKL and inhibits OPG expression in human osteoblasts through the MAPK signaling pathway.
abstract: Our study indicates that recombinant adiponectin induced RANKL and inhibited OPG expression in human osteoblasts through the AdipoR1/p38 MAPK pathway, and these responses contributed to the adiponectin-induced osteoclasts formation in the co-culture of osteoblast and peripheral blood monocytes systems. These findings showed that adiponectin increased osteoclast formation indirectly through stimulating RANKL and inhibiting OPG production in osteoblasts. It also suggests the pharmacological nature of recombinant adiponectin that indirectly induces osteoclasts formation.
  
  
  BACKGROUND
  Recently, adiponectin has emerged as an element in the regulation of bone metabolism, but the mechanism remains. This study was undertaken to investigate the action of adiponectin on osteoclastogenesis through revealing RANKL and osteoprotegerin (OPG) expression in osteoblasts and osteoclast formation.
  
  
  METHODS
  Real-time quantitative PCR and ELISA were used to detect RANKL and OPG mRNA and protein expression in cultured human osteoblasts. The involved signal pathway was studied using mitogen-activated protein kinase (MAPK) inhibitor and adiponectin receptor 1 (AdipoR1) siRNA. The effects of recombinant adiponectin on osteoclasts formation also were examined in the co-culture systems of osteoblast and peripheral blood monocytes (PBMCs) systems or purified CD14 + PBMCs cultures.
  
  
  RESULTS
  Our study showed that recombinant adiponectin induced RANKL and inhibited OPG mRNA expression in human osteoblasts in a dose- and time-dependent manner. Adiponectin also increased soluble RANKL and decreased OPG secretion in osteoblasts conditioned media. Suppression of AdipoR1 with siRNA abolished the adiponectin-regulated RANKL and OPG mRNA expression in osteoblasts. Furthermore, pretreatment of osteoblasts with the MAPK inhibitor SB203580 abolished adiponectin-regulated RANKL and OPG mRNA expression. Adiponectin induced osteoclast formation in the co-culture systems of osteoblast and PBMCs systems, and OPG entirely blocked this response. However, adiponectin had no direct effect on the differentiation of osteoclast precursor purified CD14 + PBMCs.
  
  
  CONCLUSIONS
  These data indicate that recombinant adiponectin induced RANKL and inhibited OPG expression in human osteoblasts through the AdipoR1/p38 MAPK pathway, and these responses contributed to the adiponectin-induced osteoclast formation in the co-culture of osteoblast and PBMCs systems. These findings showed that adiponectin increased osteoclast formation indirectly through stimulating RANKL and inhibiting OPG production in osteoblasts. It suggests the pharmacological nature of recombinant adiponectin that indirectly induces osteoclasts formation.
authors.affiliation: Institute of Endocrinology and Metabolism, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, China.
authors.forename: Xiang-Hang
authors.initials: XH
authors.lastname: Luo
authors.forename: Li-Juan
authors.initials: LJ
authors.lastname: Guo
authors.forename: Hui
authors.initials: H
authors.lastname: Xie
authors.forename: Ling-Qing
authors.initials: LQ
authors.lastname: Yuan
authors.forename: Xian-Ping
authors.initials: XP
authors.lastname: Wu
authors.forename: Hou-De
authors.initials: HD
authors.lastname: Zhou
authors.forename: Er-Yuan
authors.initials: EY
authors.lastname: Liao
mesh_terms: D052242:Adiponectin / Q000494:pharmacology*; D002454:Cell Differentiation; D018920:Coculture Techniques; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D020935:MAP Kinase Signaling System; D009000:Monocytes / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010010:Osteoclasts / Q000378:metabolism; D053244:Osteoprotegerin / Q000378:metabolism*; D053245:RANK Ligand / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D054419:Receptors, Adiponectin; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: C475418:ADIPOR1 protein, human; D052242:Adiponectin; D018950:Lipopolysaccharide Receptors; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D054419:Receptors, Adiponectin; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C505688:TNFSF11 protein, human; D048051:p38 Mitogen-Activated Protein Kinases