Interleukin-7 stimulates secretion of S100A4 by activating the JAK/STAT signaling pathway in human articular chondrocytes.
OBJECTIVE
S100A4 has been shown to be increased in osteoarthritic (OA) cartilage and to stimulate chondrocytes to produce matrix metalloproteinase 13 (MMP-13) through activation of the receptor for advanced glycation end products (RAGE). The aim of this study was to examine the mechanism of S100A4 secretion by chondrocytes.


METHODS
Human articular chondrocytes isolated from ankle cartilage were stimulated with 10 ng/ml of interleukin-1beta (IL-1beta), IL-6, IL-7, or IL-8. Cells were pretreated with either a JAK-3 inhibitor, brefeldin A, or cycloheximide. Immunoblotting with phospho-specific antibodies was used to determine the activation of signaling proteins. Secretion of S100A4 was measured in conditioned media by immunoblotting, and MMP-13 was measured by enzyme-linked immunosorbent assay.


RESULTS
Chondrocyte secretion of S100A4 was observed after treatment with IL-6 or IL-8 but was much greater in cultures treated with equal amounts of IL-7 and was not observed after treatment with IL-1beta. IL-7 activated the JAK/STAT pathway, with increased phosphorylation of JAK-3 and STAT-3, leading to increased production of S100A4 and MMP-13. Overexpression of a dominant-negative RAGE construct inhibited the IL-7-mediated production of MMP-13. Pretreatment of chondrocytes with a JAK-3 inhibitor or with cycloheximide blocked the IL-7-mediated secretion of S100A4, but pretreatment with brefeldin A did not.


CONCLUSIONS
IL-7 stimulates chondrocyte secretion of S100A4 via activation of JAK/STAT signaling, and then S100A4 acts in an autocrine manner to stimulate MMP-13 production via RAGE. Since both IL-7 and S100A4 are up-regulated in OA cartilage and can stimulate MMP-13 production by chondrocytes, this signaling pathway could contribute to cartilage destruction during the development of OA.
Yammani
Raghunatha R
RR
Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA. ryammani@wfubmc.edu
Long
David
D
Loeser
Richard F
RF
D020126:Brefeldin A / Q000494:pharmacology; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D015851:Interleukin-7 / Q000502:physiology*; D053612:Janus Kinases / Q000378:metabolism*; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D000067759:Receptor for Advanced Glycation End Products / Q000378:metabolism; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins / Q000378:metabolism*; D050791:STAT Transcription Factors / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
D015851:Interleukin-7; D011500:Protein Synthesis Inhibitors; D000067759:Receptor for Advanced Glycation End Products; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins; D050791:STAT Transcription Factors; C077591:S100A4 protein, human; D020126:Brefeldin A; D003513:Cycloheximide; D053612:Janus Kinases; D053509:Matrix Metalloproteinase 13