Interleukin-1 acts via the JNK-2 signaling pathway to induce aggrecan degradation by human chondrocytes

Heba M Ismail, Kazuhiro Yamamoto, Tonia L Vincent, Hideaki Nagase, Linda Troeberg, Jeremy Saklatvala

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69 Citations (Scopus)


OBJECTIVE: Aggrecan enables articular cartilage to bear load and resist compression. Aggrecan loss occurs early in osteoarthritis and rheumatoid arthritis and can be induced by inflammatory cytokines such as interleukin-1 (IL-1). IL-1 induces cleavage of specific aggrecans characteristic of the ADAMTS proteinases. The aim of this study was to identify the intracellular signaling pathways by which IL-1 causes aggrecan degradation by human chondrocytes and to investigate how aggrecanase activity is controlled by chondrocytes.

METHODS: We developed a cell-based assay combining small interfering RNA (siRNA)-induced knockdown with aggrecan degradation assays. Human articular chondrocytes were overlaid with bovine aggrecan after transfection with siRNAs against molecules of the IL-1 signaling pathway. After IL-1 stimulation, released aggrecan fragments were detected with AGEG and ARGS neoepitope antibodies. Aggrecanase activity and tissue inhibitor of metalloproteinases 3 levels were measured by enzyme-linked immunosorbent assay. Low-density lipoprotein receptor-related protein 1 (LRP-1) shedding was analyzed by Western blotting.

RESULTS: ADAMTS-5 is a major aggrecanase in human chondrocytes, regulating aggrecan degradation in response to IL-1. The tumor necrosis factor receptor-associated 6 (TRAF-6)/transforming growth factor β-activated kinase 1 (TAK-1)/MKK-4 signaling axis is essential for IL-1-induced aggrecan degradation, while NF-κB is not. Of the 3 MAPKs (ERK, p38, and JNK), only JNK-2 showed a significant role in aggrecan degradation. Chondrocytes constitutively secreted aggrecanase, which was continuously endocytosed by LRP-1, keeping the extracellular level of aggrecanase low. IL-1 induced aggrecanase activity in the medium in a JNK-2-dependent manner, possibly by reducing aggrecanase endocytosis, because IL-1 caused JNK-2-dependent shedding of LRP-1.

CONCLUSION: The signaling axis TRAF-6/TAK-1/MKK-4/JNK-2 mediates IL-1-induced aggrecanolysis. The level of aggrecanase is controlled by its endocytosis, which may be reduced upon IL-1 stimulation because of LRP-1 shedding.

Original languageEnglish
Pages (from-to)1826-1836
Number of pages11
JournalArthritis & Rheumatology
Issue number7
Early online date16 Mar 2015
Publication statusPublished - Jul 2015


  • ADAM Proteins/physiology
  • ADAMTS5 Protein
  • Aggrecans/metabolism
  • Cells, Cultured
  • Chondrocytes/drug effects
  • Humans
  • Interleukin-1/pharmacology
  • Low Density Lipoprotein Receptor-Related Protein-1/metabolism
  • MAP Kinase Kinase 4/physiology
  • MAP Kinase Kinase 7/physiology
  • MAP Kinase Kinase Kinases/physiology
  • RNA, Small Interfering/pharmacology
  • Signal Transduction/physiology
  • TNF Receptor-Associated Factor 6/physiology

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