Toll-like receptor 2 ligand mediates the upregulation of angiogenic factor, vascular endothelial growth factor and interleukin-8/CXCL8 in human rheumatoid synovial fibroblasts

Immunol Lett. 2007 Feb 15;108(2):121-8. doi: 10.1016/j.imlet.2006.11.005. Epub 2006 Dec 11.

Abstract

Rheumatoid arthritis (RA) is characterized by infiltrations of inflammatory cells accompanied by neovascularization in the joint. We hypothesized that cell activation via the toll-like receptor (TLR) may be involved in the induction of angiogenic molecules, which are relevant to the pathogenesis of RA. RA fibroblast like synoviocytes (FLS) were stimulated with TLR-2 ligand bacterial peptidoglycan (PGN), TLR-4 ligand lipopolysaccharide (LPS) and various cytokines. Vascular endothelial growth factor (VEGF) and IL-8 were measured by ELISA in culture supernatants; mRNA levels were assessed by RT-PCR and real time PCR. The levels of TLR-2, VEGF and IL-8 were analyzed by dual immunohistochemistry in RA synovium and compared with osteoarthritis (OA). Regulation of MyD88, IRAK4, IRAK1, IRAK-M and TRAF-6 mRNA expression levels by PGN were analyzed by RT-PCR. Phosphorylation of I kappa B alpha was evaluated by western blotting. Levels of VEGF and IL-8 were upregulated in culture supernatants of RA FLS stimulated with PGN, similar to the levels of IL-1beta and IL-17 stimulation. Neutralization of TLR-2 with a blocking monoclonal antibody significantly reduced both VEGF and IL-8 levels (P<0.05), which reflected the functional relevance of TLR-2 activation to the induction of VEGF and IL-8 production. Downstream intracellular signaling following TLR-2 stimulation involved MyD88-IRAK-4-TRAF-6 pathways, resulting in NF-kappaB activation. Thus, TLR-2 activation in RA FLS by microbial constituents could be involved in the induction of VEGF and IL-8 and thereby promote inflammation either directly or via angiogenesis. This possibly contributes to the perpetuation of synovitis in patients with RA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiogenesis Inducing Agents / metabolism*
  • Antibodies / pharmacology
  • Arthritis, Rheumatoid / genetics
  • Arthritis, Rheumatoid / metabolism
  • Arthritis, Rheumatoid / pathology
  • Cells, Cultured
  • Cytokines / pharmacology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism*
  • Gene Expression / drug effects
  • Humans
  • I-kappa B Proteins / metabolism
  • Interleukin-1 Receptor-Associated Kinases / genetics
  • Interleukin-8 / metabolism*
  • Lipopolysaccharides / pharmacology
  • Myeloid Differentiation Factor 88 / genetics
  • NF-kappa B / antagonists & inhibitors
  • NF-kappa B / metabolism
  • Peptidoglycan / pharmacology*
  • Phosphorylation / drug effects
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • TNF Receptor-Associated Factor 6 / genetics
  • Toll-Like Receptor 2 / immunology
  • Toll-Like Receptor 2 / metabolism*
  • Up-Regulation / drug effects
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism*

Substances

  • Angiogenesis Inducing Agents
  • Antibodies
  • CXCL8 protein, human
  • Cytokines
  • I-kappa B Proteins
  • Interleukin-8
  • Lipopolysaccharides
  • MYD88 protein, human
  • Myeloid Differentiation Factor 88
  • NF-kappa B
  • Peptidoglycan
  • RNA, Messenger
  • TLR2 protein, human
  • TNF Receptor-Associated Factor 6
  • Toll-Like Receptor 2
  • VEGFA protein, human
  • Vascular Endothelial Growth Factor A
  • IRAK1 protein, human
  • IRAK3 protein, human
  • IRAK4 protein, human
  • Interleukin-1 Receptor-Associated Kinases