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

Abstract

Objective: Since articular chondrocytes and synovial fibroblasts are particularly responsive to interleukin-1 (IL-1) with respect to stimulation of prostaglandin E2 (PGE2) biosynthesis, we have used them as models to examine feedback modulatory effects of PGE2, which blocks or attenuates the direct effects of IL-1β on cell-specific collagen gene expression. Methods: Immortalized human chondrocytes were developed for studying responses to cytokines and prostaglandins. Regulatory sequences of the type II collagen 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 (iNOS) mRNAs were analyzed by RT-PCR. Results: Previous work has shown that IL-1β inhibits, while prostaglandins stimulate, COL2A1 expression. In different immortalized chondrocyte cell lines, the ability to respond to IL- 1β with increased levels of COX-2, PLA2, and iNOS mRNAs depends upon expression of the differentiated chondrocyte phenotype. Conclusion: Our studies suggest that some IL-1-induced responses in chondrocytes may require differentiation-specific transcription factors that could serve as therapeutic targets for arthritis.