The high affinity ALK1-ligand BMP9 induces a hypertrophy-like state in chondrocytes that is antagonized by TGFbeta1
SourceOsteoarthritis and Cartilage, 23, 6, (2015), pp. 985-95
Article / Letter to editor
Display more detailsDisplay less details
Osteoarthritis and Cartilage
SubjectRadboudumc 5: Inflammatory diseases RIMLS: Radboud Institute for Molecular Life Sciences
OBJECTIVE: In osteoarthritic cartilage, expression of the receptor ALK1 correlates with markers of deleterious chondrocyte hypertrophy. Recently, bone morphogenetic protein 9 (BMP9) was identified as a high affinity ligand for ALK1. Therefore, we studied if BMP9 signaling results in expression of hypertrophy markers in chondrocytes. Furthermore, because transforming growth factorss1 (TGFbeta1) is a well known anti-hypertrophic factor, the interaction between BMP9 and TGFbeta1 signaling was also studied. DESIGN: Primary chondrocytes were isolated from bovine cartilage and stimulated with BMP9 and/or TGFbeta1 to measure intracellular signaling via pSmads with the use of Western blot. Expression of Smad-responsive genes or hypertrophy-marker genes was measured using qPCR. To confirm observations on TGFbeta/Smad3 responsive genes, a Smad3-dependent CAGA12-luc transcriptional reporter assay was performed in the chondrocyte G6 cell line. RESULTS: In primary chondrocytes, BMP9 potently induced phosphorylation of Smad1/5 and Smad2 to a lesser extent. BMP9-induced Smad1/5 phosphorylation was rapidly (2 h) reflected in gene expression, whereas Smad2 phosphorylation was not. Remarkably, BMP9 and TGFbeta1 dose-dependently synergized on Smad2 phosphorylation, and showed an additive effect on expression of Smad3-dependent genes like bSerpine1 after 24 h. The activation of the TGFbeta/Smad3 signaling cascade was confirmed using the CAGA12-luc transcriptional reporter. BMP9 selectively induced bAlpl and bColX expression, which are considered early markers of cellular hypertrophy, but this was potently antagonized by addition of a low dose of TGFbeta1. CONCLUSIONS: This study shows that in vitro in chondrocytes, BMP9 potently induces pSmad1/5 and a chondrocyte hypertrophy-like state, which is potently blocked by TGFbeta1. This observation underlines the importance of TGFbeta1 in maintenance of chondrocyte phenotype.
Upload full text
Use your RU credentials (u/z-number and password) to log in with SURFconext to upload a file for processing by the repository team.