title: Alpha9beta1: a novel osteoclast integrin that regulates osteoclast formation and function.
abstract: We identified a previously unknown integrin, alpha(9)beta(1), on OCLs and their precursors. Antibody to alpha(9) inhibited OCL formation in human marrow cultures, and OCLs from alpha(9) knockout mice had a defect in actin ring reorganization and an impaired bone resorption capacity.
  
  
  BACKGROUND
  Integrins play important roles in osteoclast (OCL) formation and function. Mature OCLs mainly express alpha(v)beta(3) integrin, a heterodimer adhesion receptor that has been implicated in osteoclastic bone resorption. We identified ADAM8, a disintegrin and metalloproteinase, as a novel stimulator of OCL differentiation and showed that the disintegrin domain of ADAM8 mediated its effects on OCL formation. Because the disintegrin domain of ADAM8 does not bind Arg-Gly-Asp (RGD) sequences, we determined which integrin bound ADAM8 and characterized its role in OCL formation and activity.
  
  
  METHODS
  Chinese hamster ovary cells (CHO) expressing different integrin subunits were tested for their capacity to bind the disintegrin domain of ADAM8. Mouse or human bone marrow cells and purified OCL precursors were tested for alpha(9)beta(1) integrin expression by Western blot, immunocytochemistry, and real-time RT-PCR. A monoclonal antibody to human alpha(9) was used to block alpha(9)beta(1) on OCL precursors stimulated by 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] or RANKL. Vertebrae of 7-day-old alpha(9)(-/-) mice and wildtype (WT) littermates were compared using bone histomorphometry and 3D microCT analysis.
  
  
  RESULTS
  Alpha(9) integrin was expressed by mouse and human bone marrow-derived OCLs and their precursors. Importantly, the anti-alpha(9) antibody inhibited human OCL formation stimulated by 1alpha,25(OH)(2)D(3) or RANKL dose-dependently. Furthermore, analysis of OCLs formed in marrow cultures from alpha(9)(-/-) mice showed that the OCLs formed were more contracted and formed significantly less bone resorption pits on dentin slices. Histologic analysis of alpha(9)(-/-) vertebrae showed thickened trabecular regions and retained cartilage within vertebral bodies of alpha(9)(-/-) mice. 3D microCT analysis of alpha(9)(-/-) vertebrae also showed a significant increase in trabecular bone volume/total tissue volume and a tendency for decreased trabecular separation compared with WT mice.
  
  
  CONCLUSIONS
  These results support a previously unknown role for alpha(9)beta(1) integrin in OCL formation and function.
authors.affiliation: Medicine-Hematology/Oncology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Rao
authors.forename: Ganwei
authors.initials: G
authors.lastname: Lu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kajiya
authors.forename: Veronica
authors.initials: V
authors.lastname: Garcia-Palacios
authors.forename: Noriyoshi
authors.initials: N
authors.lastname: Kurihara
authors.forename: Judy
authors.initials: J
authors.lastname: Anderson
authors.forename: Ken
authors.initials: K
authors.lastname: Patrene
authors.forename: Dean
authors.initials: D
authors.lastname: Sheppard
authors.forename: Harry C
authors.initials: HC
authors.lastname: Blair
authors.forename: Jolene J
authors.initials: JJ
authors.lastname: Windle
authors.forename: Sun Jin
authors.initials: SJ
authors.lastname: Choi
authors.forename: G David
authors.initials: GD
authors.lastname: Roodman
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001862:Bone Resorption; D016466:CHO Cells; D002454:Cell Differentiation; D006224:Cricetinae; D003599:Cytoskeleton / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000166:cytology / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D039302:Integrin alphaVbeta3; D016023:Integrins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C113256:integrin alpha 9 beta 1; D051722:ADAM Proteins; C489402:Adam8 protein, mouse