Human chondrocyte culture models for studying cyclooxygenase expression and prostaglandin regulation of collagen gene expression

Objective: Since articular chondrocytes and synovial fibroblasts are partic ularly responsive to interleukin-l (IL-l) with respect to stimulation of pr ostaglandin E-2(PGE(2)) biosynthesis, we have used them as models to examin e feedback modulatory effects of PGE(2), which blocks or attenuates the dir ect effects of IL-1 beta on cell-specific collagen gene expression. Methods: Immortalized human chondrocytes were developed for studying respon ses to cytokines and prostaglandins. Regulatory sequences of the type II co llagen gene (COL2A1) in reporter gene constructs were analyzed in transient transfection experiments. Endogenous expression of COL2A1 mRNA, as well as aggrecan, biglycan, and decorin mRNAs, and IL-1-inducible cyclooxygenase ( COX-2), phospholipase A2 (PLA2), and inducible nitric oxide synthetase (iNO S) mRNAs were analyzed by RT-PCR. Results: Previous work has shown that IL-1 beta inhibits, while prostagland ins stimulate, COL2A1 expression. In different immortalized chondrocyte cel l lines, the ability to respond to IL-1 beta with increased levels of COX-2 , PLA2, and iNOS mRNAs depends upon expression of the differentiated chrond rocyte phenotype. Conclusion: Our studies suggest that some IL-1-induced responses in chondro cytes may require differentiation-specific transcription factors that could serve as therapeutic targets for arthritis.