Expression and regulation of Toll-like receptor 2 by IL-1beta 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-1beta and fibronectin proteolytic fragments, the relative levels of mRNA for TLR2 were determined by quantitative real-time PCR. MyD88 activation and nuclear factor-kappaB (NF-kappaB) 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-1beta and fibronectin proteolytic fragments stimulation in primary cultures of osteoarthritic articular chondrocytes. Fibronectin proteolytic fragments-induced TLR2 upregulation involved an IL-1beta autocrine/paracrine pathway.


CONCLUSIONS
TLR2 is expressed in human articular cartilage and is upregulated by proarthritic agents including IL-1beta 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.
Su
S-L
SL
Graduate Institute of Medical Science, National Defense Medical Center, Taipei, Taiwan.
Tsai
C-D
CD
Lee
C-H
CH
Salter
D M
DM
Lee
H-S
HS
D000368:Aged; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000276:immunology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000276:immunology*; D005353:Fibronectins / Q000276:immunology; D005786:Gene Expression Regulation; D006801:Humans; D007375:Interleukin-1 / Q000276:immunology*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism*
D005353:Fibronectins; D007375:Interleukin-1; D010446:Peptide Fragments; D012333:RNA, Messenger; D051195:Toll-Like Receptor 2