Effect of cartilage oligomeric matrix protein on mesenchymal chondrogenesis in vitro.
OBJECTIVE
Cartilage oligomeric matrix protein (COMP) mutations have been identified as responsible for two arthritic disorders, multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). However, the function of COMP in chondrogenic differentiation is largely unknown. Our investigation focuses on analyzing the function of normal COMP protein in cartilage biology.


RESULTS
To explore the function of COMP we make use of an in vitro model system for chondrogenesis, consisting of murine C3H10T1/2 mesenchymal cells maintained as a high-density micromass culture and stimulated with bone morphogenetic protein 2 (BMP-2). Under these culture conditions, C3H10T1/2 cells undergo active chondrogenesis in a manner analogous to that of embryonic limb mesenchymal cells, and have been shown to serve as a valid model system to investigate the mechanisms regulating mesenchymal chondrogenesis. Our results indicate that ectopic COMP expression enhances several early aspects of chondrogenesis induced by BMP-2 in this system, indicating that COMP functions in part to positively regulate chondrogenesis. Additionally, COMP has inhibitory effects on proliferation of cells in monolayer. However, at later times in micromass culture, ectopic COMP expression in the presence of BMP-2 causes an increase in apoptosis, with an accompanying reduction in cell numbers in the micromass culture. However, the remaining cells retain their chondrogenic phenotype.


CONCLUSIONS
These data suggest that COMP and BMP-2 signaling converge to regulate the fate of these cells in vitro by affecting both early and late stages of chondrogenesis.
Kipnes
J
J
Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH, MSC 5755 Bldg 13, Rm 3W17, Bethesda, MD 20892, USA.
Carlberg
A L
AL
Loredo
G A
GA
Lawler
J
J
Tuan
R S
RS
Hall
D J
DJ
D000818:Animals; D015152:Blotting, Northern; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D016326:Extracellular Matrix Proteins / Q000502:physiology*; D006023:Glycoproteins / Q000502:physiology*; D017403:In Situ Hybridization; D064235:Matrilin Proteins; D008648:Mesoderm / Q000502:physiology*; D051379:Mice; D012313:RNA / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D016212:Transforming Growth Factor beta
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; C577540:Matn1 protein, mouse; D064235:Matrilin Proteins; D016212:Transforming Growth Factor beta; D012313:RNA