ERK-1/2 and p38 in the regulation of hypertrophic changes of normal articular cartilage chondrocytes induced by osteoarthritic subchondral osteoblasts.
OBJECTIVE
Previous studies have shown the influence of subchondral bone osteoblasts (SBOs) on phenotypical changes of articular cartilage chondrocytes (ACCs) during the development of osteoarthritis (OA). The molecular mechanisms involved during this process remain elusive, in particular, the signal transduction pathways. The aim of this study was to investigate the in vitro effects of OA SBOs on the phenotypical changes in normal ACCs and to unveil the potential involvement of MAPK signaling pathways during this process.


METHODS
Normal and arthritic cartilage and bone samples were collected for isolation of ACCs and SBOs. Direct and indirect coculture models were applied to study chondrocyte hypertrophy under the influence of OA SBOs. MAPKs in the regulation of the cell-cell interactions were monitored by phosphorylated antibodies and relevant inhibitors.


RESULTS
OA SBOs led to increased hypertrophic gene expression and matrix calcification in ACCs by means of both direct and indirect cell-cell interactions. In this study, we demonstrated for the first time that OA SBOs suppressed p38 phosphorylation and induced ERK-1/2 signal phosphorylation in cocultured ACCs. The ERK-1/2 pathway inhibitor PD98059 significantly attenuated the hypertrophic changes induced by conditioned medium from OA SBOs, and the p38 inhibitor SB203580 resulted in the up-regulation of hypertrophic genes in ACCs.


CONCLUSIONS
The findings of this study suggest that the pathologic interaction of OA SBOs and ACCs is mediated via the activation of ERK-1/2 phosphorylation and deactivation of p38 phosphorylation, resulting in hypertrophic differentiation of ACCs.
Queensland University of Technology, Brisbane, Queensland, Australia.
Indira
I
Prasadam
Stijn
S
van Gennip
Thor
T
Friis
Wei
W
Shi
Ross
R
Crawford
Yin
Y
Xiao
D000328:Adult; D000368:Aged; D000469:Alkaline Phosphatase / Q000235:genetics; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology; D002450:Cell Communication / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000201:enzymology / Q000473:pathology*; D018920:Coculture Techniques; D024121:Collagen Type X / Q000235:genetics; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D006984:Hypertrophy; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008875:Middle Aged; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism / Q000473:pathology*; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D024121:Collagen Type X; D050659:Core Binding Factor Alpha 1 Subunit; D017077:Culture Media, Conditioned; D004791:Enzyme Inhibitors; D005419:Flavonoids; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D000469:Alkaline Phosphatase; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one