COMP-Ang1, a chimeric form of Angiopoietin 1, enhances BMP2-induced osteoblast differentiation and bone formation

Bone. 2010 Feb;46(2):479-86. doi: 10.1016/j.bone.2009.09.019. Epub 2009 Sep 25.


Introduction: Angiogenesis is closely associated with bone formation, especially endochondral ossification. Angiopoietin 1 (Ang1) is a specific growth factor functioning to generate a stable and matured vasculature through the Tie2 receptor/PI3K/AKT pathway. Recently cartilage oligomeric matrix protein (COMP)-Ang1, an Ang1 variant which is more potent than native Ang1 in phosphorylating Tie2 receptor and AKT, was developed. This study was designed to examine the effects of angiogenic COMP-Ang1 on BMP2-induced osteoblast differentiation and bone formation.

Methods: Expression of endogenous Ang-1 and its binding receptor Tie 2 mRNA was examined in osteoblast-like cells and primary mouse calvarial cells by RT-PCR analysis, and was also monitored during osteoblast differentiation induced by BMP-2 and/or ascorbic acid and beta-glycerophosphate. Effects of COMP-Ang-1 on osteoblast differentiation and mineralization were evaluated by alkaline phosphatase (ALP) activity and osteocalcin (OC) production, and Alizarin red stain. For a molecular mechanism, Western blot and OG2 and 6xOSE promoter assays were done. For in vivo evaluation, adenoviral (Ad) vectors containing COMP-Ang-1 or BMP-2 gene were administered into thigh muscle of mice, and after 2 weeks bone formation was analyzed by micro-computed tomography and histology. Angiogenic event of COMP-Ang1 was confirmed by immunofluorescence analysis with anti-CD31 antibody.

Results: Expression of Tie2 receptor was significantly increased in the course of osteoblast differentiation. Treatment or overexpression of COMP-Ang1 enhanced BMP2-induced ALP activity, OC production, and mineral deposition in a dose-dependent manner. In addition, COMP-Ang1 synergistically increased OG2 and 6xOSE promoter activities of BMP2, and sustained p38, Smad and AKT phosphorylation of BMP2. Notably, in vivo intramuscular injection of COMP-Ang1 dose-dependently enhanced BMP2-induced ectopic bone formation with increases in CD31 reactivity.

Conclusions: These results suggest that COMP-Ang1 synergistically enhanced osteoblast differentiation and bone formation through potentiating BMP2 signaling pathways and angiogenesis. Combination of BMP2 and COMP-Ang1 should be clinically useful for therapeutic application to fracture and destructive bone diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiopoietin-1 / genetics
  • Angiopoietin-1 / metabolism
  • Angiopoietin-1 / pharmacology*
  • Animals
  • Bone Morphogenetic Protein 2 / pharmacology*
  • Calcification, Physiologic / drug effects
  • Cell Differentiation / drug effects*
  • Cell Line
  • Extracellular Matrix / drug effects
  • Extracellular Matrix / metabolism
  • Gene Expression Regulation / drug effects
  • Humans
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Osteoblasts / cytology*
  • Osteoblasts / drug effects*
  • Osteoblasts / metabolism
  • Osteogenesis / drug effects*
  • Osteogenesis / genetics
  • Phosphorylation / drug effects
  • Receptor, TIE-2 / genetics
  • Receptor, TIE-2 / metabolism
  • Recombinant Fusion Proteins / pharmacology*
  • Signal Transduction / drug effects
  • Transcription, Genetic / drug effects
  • Transcriptional Activation / drug effects


  • Angiopoietin-1
  • Bone Morphogenetic Protein 2
  • COMP-Ang1 fusion protein
  • Recombinant Fusion Proteins
  • Receptor, TIE-2