Expression and regulation of toll-like receptor 2 by IL-1β and fibronectin fragments in human articular chondrocytes

Objective: The objective of this study was to examine expression and regulation of Toll-like receptor 2 (TLR2) in human articular chondrocytes Methods: Human articular chondrocytes were enzymatically isolated from normal and osteoarthritic knee cartilage. Immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to assess the expression of toll-like receptors. Following stimulation of chondrocytes in vitro by IL-1 beta and fibronectin proteolytic fragments, the relative levels of mRNA for TLR2 were determined by quantitative real-time PCR. MyD88 activation and nuclear factor-B-K (NF-B-K) translocation were evaluated by immunoprecipitation and electrophoretic mobility shift assay, respectively. Results: Human articular chondrocytes mainly expressed TLR1, 2, 5 by RT-PCR. Protein expression of TLR2 was also identified in adult human articular cartilage. TLR2 was upregulated following IL-1 beta and fibronectin proteolytic fragments stimulation in primary cultures of osteoarthritic articular chondrocytes. Fibronectin proteolytic fragments-induced TLR2 upregulation involved an IL-1 beta autocrine/paracrine pathway. Conclusions: TLR2 is expressed in human articular cartilage and is upregulated by proarthritic agents including IL-1 beta and fibronectin fragments. Signaling through TLR is a novel pro-inflammatory mechanism in osteoarthritis and targeting of these signaling pathways may be of value in treatment of degenerative joint disease. (c) 2005 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.