Differential effects of local application of BMP-2 or TGF-beta 1 on both articular cartilage composition and osteophyte formation.
OBJECTIVE
The related molecules bone morphogenetic protein-2 (BMP-2) and transforming growth factor beta-1 (TGF-beta 1) have both been shown to stimulate chondrocyte proteoglycan (PG) synthesis in vitro. We investigated the in-vivo effects of these factors on articular cartilage PG metabolism.


METHODS
Several doses of BMP-2 or TGF-beta 1 were injected into the murine knee joint, once or repeatedly. Patellar cartilage PG synthesis was measured by [35S]-sulfate incorporation and reverse transcriptase polymerase chain reaction (RT-PCR). PG content was analyzed by measuring safranin O staining intensity on histologic sections.


RESULTS
A single injection of 200 ng BMP-2 induced a much earlier and more impressive stimulation of articular cartilage PG synthesis, than 200 ng TGF-beta 1. RT-PCR revealed that both factors upregulated mRNA of aggrecan more than that of biglycan and decorin. However, 21 days after a single injection of 200 ng TGF-beta 1 PG synthesis still was significantly increased, while stimulation by BMP-2 only lasted for 3 to 4 days. Stimulation by BMP-2 could be prolonged to at least 2 weeks by triple injections of 200 ng each, at alternate days. Remarkably, even after this intense exposure to BMP-2, stimulation of PG synthesis was not reflected in long-lasting enhancement of PG content of articular cartilage. In contrast, even a single injection with 200 ng of TGF-beta 1 induced prolonged enhancement of PG content. After repeated injections, both BMP-2 and TGF-beta 1 induced chondrogenesis at specific sites. 'Chondrophytes' induced by BMP-2 were found predominantly in the region where the growth plates meet the joint space, while those triggered by TGF-beta 1 originated from the periosteum also at sites remote from the growth plates.


CONCLUSIONS
BMP-2 and TGF-beta stimulate PG synthesis and PG content with different kinetics, and these factors have different chondro-inductive properties.
van Beuningen
H M
HM
Department of Rheumatology, University Hospital Nijmegen, The Netherlands. h.vanbeuningen@reuma.azn.nl
Glansbeek
H L
HL
van der Kraan
P M
PM
van den Berg
W B
WB
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D001842:Bone and Bones / Q000378:metabolism; D002358:Cartilage, Articular / Q000187:drug effects*; D003094:Collagen / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005355:Fibrosis / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011509:Proteoglycans / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D015854:Up-Regulation / Q000502:physiology
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D011509:Proteoglycans; D016212:Transforming Growth Factor beta; D003094:Collagen