Chondrocyte innate immune myeloid differentiation factor 88-dependent signaling drives procatabolic effects of the endogenous Toll-like receptor 2/Toll-like receptor 4 ligands low molecular weight hyaluronan and high mobility group box chromosomal protein 1 in mice

Arthritis Rheum. 2010 Jul;62(7):2004-12. doi: 10.1002/art.27475.


Objective: Toll-like receptor 2 (TLR-2)/TLR-4-mediated innate immunity serves as a frontline antimicrobial host defense, but also modulates tissue remodeling and repair responses to endogenous ligands released during low-grade inflammation. We undertook the present study to assess whether the endogenous TLR-2/TLR-4 ligands low molecular weight hyaluronan (LMW-HA) and high mobility group box chromosomal protein 1 (HMGB-1), which are increased in osteoarthritic (OA) joints, drive procatabolic chondrocyte responses dependent on TLR-2 and TLR-4 signaling through the cytosolic adaptor myeloid differentiation factor 88 (MyD88).

Methods: We studied mature femoral head cap cartilage explants and immature primary knee articular chondrocytes from TLR-2/TLR-4-double-knockout, MyD88-knockout, and congenic wild-type mice. Generation of nitric oxide (NO), degradation of hyaluronan, release of HMGB-1, matrix metalloproteinase 3 (MMP-3), and MMP-13, and protein expression of type X collagen were assessed by Griess reaction and Western blotting analyses. Expression of messenger RNA for type II and type X collagen, MMP-13, and RUNX-2 was examined by real-time quantitative reverse transcription-polymerase chain reaction.

Results: Interleukin-1beta and TLR-2 and TLR-4 ligands induced both HMGB-1 release from chondrocytes and extracellular LMW-HA generation in normal chondrocytes. TLR-2/TLR-4(-/-) and MyD88(-/-) mouse cartilage explants and chondrocytes lost the capacity to mount procatabolic responses to both LMW-HA and HMGB-1, demonstrated by >95% suppression of NO production (P < 0.01), and attenuated induction of MMP-3 and MMP-13. Combined deficiency of TLR-2/TLR-4, or of MyD88 alone, also attenuated release of NO and blunted induction of MMP-3 and MMP-13 release. MyD88 was necessary for HMGB-1 and hyaluronidase 2 (which generates LMW-HA) to induce chondrocyte hypertrophy, which is implicated in OA progression.

Conclusion: MyD88-dependent TLR-2/TLR-4 signaling is essential for procatabolic responses to LMW-HA and HMGB-1, and MyD88 drives chondrocyte hypertrophy. Therefore, LMW-HA and HMGB-1 act as innate immune cytokine-like signals with the potential to modulate chondrocyte differentiation and function in OA progression.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Biomarkers / metabolism
  • Cartilage, Articular / cytology
  • Cartilage, Articular / metabolism
  • Cell Enlargement
  • Chondrocytes / cytology
  • Chondrocytes / metabolism*
  • Female
  • Gene Expression
  • Gene Expression Regulation
  • HMGB2 Protein / metabolism*
  • Hyaluronic Acid / metabolism*
  • Male
  • Matrix Metalloproteinase 13 / genetics
  • Matrix Metalloproteinase 13 / metabolism
  • Matrix Metalloproteinase 3 / genetics
  • Matrix Metalloproteinase 3 / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Molecular Weight
  • Myeloid Differentiation Factor 88
  • Nitric Oxide / metabolism
  • Signal Transduction
  • Toll-Like Receptor 2 / metabolism*
  • Toll-Like Receptor 4 / metabolism*


  • Biomarkers
  • HMGB2 Protein
  • Myeloid Differentiation Factor 88
  • Tlr2 protein, mouse
  • Tlr4 protein, mouse
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Nitric Oxide
  • Hyaluronic Acid
  • Matrix Metalloproteinase 13
  • Matrix Metalloproteinase 3