Our lab was the first to report a key role of osteoactivin (OA/GPNMB) in osteoblast differentiation and bone formation. We reported that OA/GPNMB is expressed ...
Mutation in OA/GPNMB Inhibits Bone Resorption in vivo and Osteoclast Differentiationin vitro Categories: Osteoclasts Bone, Cartilage and Connective Tissue Matrix & Development Growth Factors, Cytokines and Immunomodulators Poster Sessions, Presentation Number: SU0256 Session: Poster Session II and Poster Tours Sunday, October 14, 2012 11:30 AM - 1:30 PM, Minneapolis Convention Center, Discovery Hall-Hall B * Samir Abdelmagid, Joyce Y Belcher, Carlynn A Fulp, Fouad M Moussa, Roshanak Razmpour, Fabiola DelCarpio Cano, Steven Popoff, Fayez Safadi Our lab was the first to report a key role of osteoactivin (OA/GPNMB) in osteoblast differentiation and bone formation. We reported that OA/GPNMB is expressed during osteoblast differentiation in vitro. We also showed that injection of recombinant (r) OA into the femur medullary space stimulated osteogenesis in vivo. Recent report showed that OA/GPNMB is expressed in osteoclasts (OC). In this study, we were interested to examine the functional role of OA/GPNMB during osteoclastogenesis. Immunofluorescent localization of OA/GPNMB in multinucleated osteoclasts (mOC) (≥ 3 nuclei) showed co-localization of OA/GPNMB protein with actin ring and β3 integrin. In addition, we tested the effects of rOA on osteoclastogenesis using bone marrow-derived hematopoietic cells. rOA protein enhanced RANKL-mediated osteoclastogenesis in a dose dependent manner measured by TRAP activity, total number and size of OC. Our laboratory obtained a mouse model with a natural mutation in the OA/GPNMB gene encoding a truncated protein with defective function and skeletal phenotype. Characterization of the bone phenotype by micro-CT analysis showed decreased bone volume and trabecular number in 8-week old mutant compared to wild-type (WT). Histomorphometric analysis showed no difference in the total number of TRAP-positive OC; however, mOC were significantly increased in number in OA/GPNMB mutant compared to WT. Although, the size of mOC was not changed; however, the mOC surface over bone surface was decreased in the mutant compared to WT, suggesting defective bone resorption in OA/GPNMB mutant mice. Transmission electron microscopy analysis demonstrated an abnormality in the ruffled border of mOC in OA/GPNMB mutant compared to WT. Defective OC function was confirmed by decreased levels of CTX in sera from OA/GPNMB mutant compared to WT. Next, we examined OC differentiation derived from OA/GPNMB mutant and WT mice ex vivo. TRAP-positive mOC number and activity were dramatically reduced in OA/GPNMB mutant compared to WT. Next, we examined adhesion of OA/GPNMB mutant and WT mOC over vitronectin. Interestingly, we found decreased adhesion of mOC and focal adhesion kinase (FAK) activity in OA/GPNMB mutant mOC compared to WT. Collectively; our data suggest that defective mOC in OA/GPNMB mutant mice is mediated at least in part, by OC adhesion and FAK activation pathway. Further studies are warranted to investigate the mechanism(s) of OA/GPNMB in osteoclastogenesis and bone remodeling. Disclosures: None * Presenting Authors(s): Samir Abdelmagid, Northeast Ohio Medical University, USA
