Toll-like receptors and chondrocytes: the lipopolysaccharide-induced decrease in cartilage matrix synthesis is dependent on the presence of toll-like receptor 4 and antagonized by bone morphogenetic protein 7

Arthritis Rheum. 2007 Jun;56(6):1880-93. doi: 10.1002/art.22637.


Objective: To assess the presence of Toll-like receptors (TLRs) 1-9 in human articular cartilage, and to investigate the effects of lipopolysaccharide (LPS)-induced activation of TLR-4 on biosynthetic activity and matrix production by human articular chondrocytes.

Methods: TLRs 1-9 were assessed in human articular cartilage by reverse transcription-polymerase chain reaction (RT-PCR); TLR-4 was also analyzed by Western blotting and immunohistochemistry. Articular chondrocytes were isolated from human donors and from wild-type or TLR-4(-/-) mice. Chondrocyte monolayer cultures were incubated with interleukin-1beta (IL-1beta) and LPS in the absence or presence of bone morphogenetic protein 7 (BMP-7) and IL-1 receptor antagonist (IL-1Ra). Neosynthesis of sulfated glycosaminoglycans (sGAG) was measured by (35)S-sulfate incorporation. Endogenous gene expression of cartilage markers as well as IL-1beta was examined using RT-PCR. The involvement of p38 kinase or p44/42 kinase (ERK-1/2) in LPS-mediated TLR-4 signaling was investigated by immunoblotting, RT-PCR, and sGAG synthesis.

Results: TLRs 1-9 were found on the messenger RNA (mRNA) level in human articular chondrocytes. The presence of TLR-4 was also observed on the protein level. In murine and human articular chondrocytes, but not in chondrocytes derived from TLR-4(-/-) mice, stimulation with LPS resulted in a decrease in total proteoglycan synthesis. IL-1beta mRNA expression was increased by TLR-4 activation, whereas expression of aggrecan and type II collagen was significantly decreased. The presence of BMP-7 and IL-1Ra antagonized the anti-anabolic effects of LPS. Blocking of p38, but not ERK-1/2, resulted in inhibition of both LPS-mediated IL-1beta gene expression and the negative effects of LPS on matrix biosynthesis.

Conclusion: These data demonstrate the presence of TLRs in human articular cartilage. The suppressive effects of LPS on cartilage biosynthetic activity are dependent on the presence of TLR-4, are governed, at least in part, by an up-regulation of IL-1beta, and are mediated by p38 kinase. These in vitro data indicate an anti-anabolic effect of TLR-4 in articular chondrocytes that may hamper cartilage repair in various joint diseases.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Animals
  • Bone Morphogenetic Protein 7
  • Bone Morphogenetic Proteins / pharmacology*
  • Cartilage Oligomeric Matrix Protein
  • Cells, Cultured
  • Chondrocytes / cytology
  • Chondrocytes / drug effects
  • Chondrocytes / metabolism*
  • Extracellular Matrix Proteins / genetics
  • Extracellular Matrix Proteins / metabolism*
  • Female
  • Gene Expression Regulation / drug effects
  • Glycoproteins / genetics
  • Glycoproteins / metabolism*
  • Humans
  • Interleukin 1 Receptor Antagonist Protein / pharmacology
  • Interleukin-1beta / genetics
  • Interleukin-1beta / physiology
  • Lipopolysaccharides / pharmacology*
  • Matrilin Proteins
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Middle Aged
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism*
  • Toll-Like Receptors / genetics
  • Toll-Like Receptors / metabolism*
  • Transforming Growth Factor beta / pharmacology*
  • p38 Mitogen-Activated Protein Kinases / genetics
  • p38 Mitogen-Activated Protein Kinases / physiology


  • BMP7 protein, human
  • Bone Morphogenetic Protein 7
  • Bone Morphogenetic Proteins
  • Cartilage Oligomeric Matrix Protein
  • Extracellular Matrix Proteins
  • Glycoproteins
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1beta
  • Lipopolysaccharides
  • Matn1 protein, mouse
  • Matrilin Proteins
  • RNA, Messenger
  • TLR4 protein, human
  • TSP5 protein, human
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Toll-Like Receptors
  • Transforming Growth Factor beta
  • p38 Mitogen-Activated Protein Kinases