Abstract
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 IκBα. IL‐1α and IL‐1β 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‐1α and IL‐1β 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‐1α 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‐1α that was not secreted. ProIL‐1β 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‐1α and IL‐1β. Biologically active IL‐1α protein was detectable in cartilage lysates and was probably intracellular proIL‐1α. We were unable to show that IL‐1 was secreted by chondrocytes.