Transcriptional and proteolytic regulation of the insulin-like growth factor-I system of equine articular chondrocytes by recombinant equine interleukin-1β
✍ Scribed by Ryan M. Porter; R. Michael Akers; Rick D. Howard; Kimberly Forsten-Williams
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 282 KB
- Volume
- 209
- Category
- Article
- ISSN
- 0021-9541
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Interleukin‐1 (IL‐1) and insulin‐like growth factor‐I (IGF‐I), which have opposing effects on matrix metabolism within articular cartilage, are thought to play prominent roles in the pathogenesis of osteoarthritis. To better understand the link between these anabolic (IGF‐I) and catabolic (IL‐1) stimuli, we examined exogenous IL‐1 regulation of the IGF‐I signaling system of articular chondrocytes (ACs). Equine ACs from non‐arthritic stifle joints were expanded in monolayer culture, encapsulated for 10 days in alginate beads, and stimulated as high‐density monolayers with recombinant equine IL‐1β (0, 1, 10 ng/ml) for 48 h. IL‐1β enhanced expression of IGF‐IR levels, as determined by both [^125^I]‐IGF‐I binding studies and Western blotting, while reducing the concentration of endogenous IGF‐I detected in conditioned media by radioimmunoassay. Western ligand blotting revealed that chondrocytes primarily secreted IGF binding proteins (IGFBPs) with molecular weights of 28–30 and 32–34 kDa, which were identified as IGFBPs 5 and 2, respectively, and that IL‐1β treatment diminished IGFBP‐2, the prominent homolog in conditioned media. Northern blot analysis suggested IL‐1β regulation of IGF‐I and, to some extent, IGF‐IR was mediated by transcription; however, the cytokine did not affect IGFBP‐2 expression. To test for evidence of proteolysis by matrix metalloproteinases (MMPs), additional cultures were co‐incubated with inhibitors for MMPs 2/9, 3, and 8. IGFBP‐2 suppression was partially reversed by gelatinase (MMP‐2/9) inhibition. In summary, these findings further delineate the role of IL‐1 as a key regulator of the IGF‐I system within articular cartilage, demonstrating that regulation occurs through both direct (transcriptional) and indirect (proteolytic) mechanisms. J. Cell. Physiol. 209: 542–550, 2006. © 2006 Wiley‐Liss, Inc.