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OBJECTIVE: To investigate the effect of explantation and fine cutting of articular cartilage upon intracellular inflammatory signaling pathways and expression of interleukin-1 (IL-1). METHODS: Cartilage from porcine metacarpophalangeal joints was cultured in serum-free medium. Tissue extracts were examined for ERK activation by phosphorylated-Western blotting, for JNK and p38 MAPK activity by kinase assay, and for IkappaBalpha. IL-1alpha and IL-1beta messenger RNA (mRNA) was measured by reverse transcriptase-polymerase chain reaction. IL-1 activity was measured by the induction of serum amyloid A protein in cultured chondrocytes. RESULTS: All 3 MAPKs (p38, JNK, and ERK) were rapidly activated upon dissection and explantation of the cartilage. IL-1alpha and IL-1beta mRNA was also induced: the speed and magnitude of induction were increased if the explants had been finely cut. IL-1 activity that could be inhibited by IL-1 receptor antagonist or antibodies to IL-1alpha was found in extracts of explants cultured for 20 hours or lysates of cells isolated from them. This activity was likely due to intracellular proIL-1alpha that was not secreted. ProIL-1beta would not be detected because it is biologically inactive. The mechanism of inflammatory signaling pathway activation underlying the induction of IL-1 is unknown. CONCLUSION: Explantation and cutting of articular cartilage activates intracellular inflammatory signaling pathways and induces expression of mRNA for IL-1alpha and IL-1beta. Biologically active IL-1alpha protein was detectable in cartilage lysates and was probably intracellular proIL-1alpha. We were unable to show that IL-1 was secreted by chondrocytes.

Original publication




Journal article


Arthritis rheum

Publication Date





2539 - 2546


Animals, Cartilage, Articular, Chondrocytes, Culture Techniques, Interleukin-1, JNK Mitogen-Activated Protein Kinases, MAP Kinase Kinase 4, Mitogen-Activated Protein Kinase Kinases, Mitogen-Activated Protein Kinases, RNA, Messenger, Signal Transduction, Swine, p38 Mitogen-Activated Protein Kinases