Osteoactivin acts as downstream mediator of BMP-2 effects on osteoblast function

J Cell Physiol. 2007 Jan;210(1):26-37. doi: 10.1002/jcp.20841.

Abstract

Our laboratory previously showed that osteoactivin (OA) is a novel, osteoblast-related glycoprotein that plays a role in osteoblast differentiation and function. The purpose of this study was to examine the regulation of OA expression by BMP-2 and the role OA plays as a downstream mediator of BMP-2 effects in osteoblast function. Using primary osteoblast cultures, we tested different doses of BMP-2 on the regulation of OA expression during osteoblast development. To test whether Smad-1 signaling is responsible for BMP-2 regulation of OA expression, osteoblast cultures were transfected with Smad1 siRNA, treated with 50 ng/ml of BMP-2 and analyzed by Western blot. BMP-2 treatment increased OA mRNA and protein expression in a dose-dependent manner and this upregulation was blocked in Smad1 siRNA transfected cultures. We next examined whether the role of OA as a downstream mediator of BMP-2 effects on osteoblast differentiation and matrix mineralization. Osteoblast cultures were transfected with OA antisense oligonucleotides and treated with 50 ng/ml of BMP-2. Cultures transfected with OA antisense oligonucleotides and treated with BMP-2 showed a reduction of OA expression associated with a significant reduction in early and late differentiation markers induced by BMP-2. Therefore, OA acts, at least in part, as a downstream mediator of BMP-2 effects on osteoblast differentiation and matrix mineralization. Our findings suggest that BMP-2 regulates OA expression through the Smad1 signaling pathway. Our data also emphasize that OA protein acts as a downstream mediator of BMP-2 effects on osteoblast differentiation and function.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Animals, Newborn
  • Bone Morphogenetic Protein 2
  • Bone Morphogenetic Proteins / genetics
  • Bone Morphogenetic Proteins / metabolism
  • Bone Morphogenetic Proteins / pharmacology*
  • Calcification, Physiologic / drug effects
  • Cell Differentiation / drug effects
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Oligonucleotides, Antisense / genetics
  • Oligonucleotides, Antisense / metabolism
  • Osteoblasts / cytology
  • Osteoblasts / drug effects*
  • Osteoblasts / metabolism
  • Osteogenesis / drug effects
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Rats
  • Recombinant Proteins / pharmacology
  • Signal Transduction / drug effects*
  • Smad1 Protein / genetics
  • Smad1 Protein / metabolism*
  • Time Factors
  • Transfection
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism
  • Transforming Growth Factor beta / pharmacology*
  • Up-Regulation / drug effects

Substances

  • Bmp2 protein, rat
  • Bone Morphogenetic Protein 2
  • Bone Morphogenetic Proteins
  • Gpnmb protein, rat
  • Membrane Glycoproteins
  • Oligonucleotides, Antisense
  • RNA, Messenger
  • RNA, Small Interfering
  • Recombinant Proteins
  • Smad1 Protein
  • Transforming Growth Factor beta