Transgenic Expression of Osteoactivin/gpnmb Enhances Bone Formation In Vivo and Osteoprogenitor Differentiation Ex Vivo

• Published in: Journal of cellular physiology Vol. 231; no. 1; pp. 72 - 83
• Main Authors: Frara, Nagat, Abdelmagid, Samir M., Sondag, Gregory R., Moussa, Fouad M., Yingling, Vanessa R., Owen, Thomas A., Popoff, Steven N., Barbe, Mary F., Safadi, Fayez F.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01-01-2016; Wiley Subscription Services, Inc
• Subjects: Animals; Bone and Bones - metabolism; Bone Density - physiology; Bone Remodeling - genetics; Bone Remodeling - physiology; Bone Resorption - metabolism; Cell Differentiation - genetics; Cell Differentiation - physiology; Eye Proteins - genetics; Eye Proteins - metabolism; Melanoma; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Mice, Transgenic; Osteoblasts - cytology; Osteoclasts - cytology; Osteogenesis - genetics; Protein-Serine-Threonine Kinases - metabolism; Receptors, Transforming Growth Factor beta - metabolism
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.25020

Initial identification of osteoactivin (OA)/glycoprotein non‐melanoma clone B (gpnmb) was demonstrated in an osteopetrotic rat model, where OA expression was increased threefold in mutant bones, compared to normal. OA mRNA and protein expression increase during active bone regeneration post‐fracture, and primary rat osteoblasts show increased OA expression during differentiation in vitro. To further examine OA/gpnmb as an osteoinductive agent, we characterized the skeletal phenotype of transgenic mouse overexpressing OA/gpnmb under the CMV‐promoter (OA‐Tg). Western blot analysis showed increased OA/gpnmb in OA‐Tg osteoblasts, compared to wild‐type (WT). In OA‐Tg mouse femurs versus WT littermates, micro‐CT analysis showed increased trabecular bone volume and thickness, and cortical bone thickness; histomorphometry showed increased osteoblast numbers, bone formation and mineral apposition rates in OA‐Tg mice; and biomechanical testing showed higher peak moment and stiffness. Given that OA/gpnmb is also over‐expressed in osteoclasts in OA‐Tg mice, we evaluated bone resorption by ELISA and histomorphometry, and observed decreased serum CTX‐1 and RANK‐L, and decreased osteoclast numbers in OA‐Tg, compared to WT mice, indicating decreased bone remodeling in OA‐Tg mice. The proliferation rate of OA‐Tg osteoblasts in vitro was higher, compared to WT, as was alkaline phosphatase staining and activity, the latter indicating enhanced differentiation of OA‐Tg osteoprogenitors. Quantitative RT‐PCR analysis showed increased TGF‐β1 and TGF‐β receptors I and II expression in OA‐Tg osteoblasts, compared to WT. Together, these data suggest that OA overexpression has an osteoinductive effect on bone mass in vivo and stimulates osteoprogenitor differentiation ex vivo. J. Cell. Physiol. 230: 72–83, 2016. © 2015 Wiley Periodicals, Inc.