Induction of interleukin-1 in articular cartilage by explantation and cutting.
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.


CONCLUSIONS
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.
Gruber
Johann
J
Imperial College School of Medicine, London, UK.
Vincent
Tonia L
TL
Hermansson
Monika
M
Bolton
Mark
M
Wait
Robin
R
Saklatvala
Jeremy
J
D000818:Animals; D002358:Cartilage, Articular / Q000502:physiology*; D019902:Chondrocytes / Q000378:metabolism; D046508:Culture Techniques; D007375:Interleukin-1 / Q000032:analysis* / Q000235:genetics; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases / Q000032:analysis; D020928:Mitogen-Activated Protein Kinases / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D015398:Signal Transduction / Q000502:physiology; D013552:Swine; D048051:p38 Mitogen-Activated Protein Kinases
D007375:Interleukin-1; D012333:RNA, Messenger; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases