Regulation of Insulin-Like Growth Factor-Binding Protein-5 by Insulin-Like Growth Factor I and Interleukin-1  in Ovine Articular Chondrocytes

Abstract

Insulin-like growth factors (IGFs) contribute to the maintenance of the cartilage matrix by stimulating proteoglycan synthesis. In contrast, interleukin-1 (IL-1), an inflammatory cytokine, suppresses the synthesis of proteoglycans. In pathological conditions the chondrocytes' responsiveness to IGF-I is decreased, and elevated levels of IGF-binding proteins (IGFBPs) have been implicated as a possible cause. The aim of this study was to investigate the effects of IGF-I and IL-1 on IGFBP production by ovine articular chondrocytes (OAC) and the roles of these IGFBPs in the regulation of proteoglycan synthesis. As revealed by Western ligand and immunoblotting, OACs secreted IGFBP-2 and a 24-kDa IGFBP in culture medium under basal conditions. Exposure of the cells to IGF-I for 48 h resulted in the appearance of IGFBP-5 in the medium. Des(1-3)IGF-I, an IGF-I analog with reduced affinity for IGFBPs, also increased the level of IGFBP-5, but to a lesser extent than IGF-I, whereas LR 3 IGF-I, which has virtually no affinity for IGFBPs, had no effect on IGFBP-5. Furthermore, IGFBP-5 underwent a time-dependent limited proteolysis when incubated with OAC-conditioned medium, degrading into 22-and 16-kDa fragments. The degradation of IGFBP-5 was significantly inhibited by IGF-I, but not by des(1-3)IGF-I or LR 3 IGF-I. Basic fibroblast growth factor, transforming growth factor-␤, and plateletderived growth factor had no effect on OAC IGFBPs. However, IL-1␣ increased the IGFBP-5 level in a dose-dependent manner, showing maximum activity at 200 U/ml. Furthermore, IL-1␣, but not IGF-I, induced IGFBP-5 messenger RNA expression, as assessed by Northern blot analysis. Coincubation of IGF-I with IL-1␣ resulted in a substantially increased IGFBP-5 protein level, suggesting a synergism between the mechanisms of action of these two factors. Des(1-3)IGF-I and LR 3 IGF-I were 10 times more potent than IGF-I in stimulating proteoglycan synthesis, indicating inhibition of IGF-I activity by endogenous IGFBPs. IL-1␣ reduced the IGF-I bioactivity, but had no effect on the activities of the IGF-I analogs, thus implying that locally produced IGFBPs, particularly IGFBP-5, which was substantially increased when IGF-I and IL-1␣ were coincubated, mediated the reduction of the IGF-I activity. Our results demonstrate that IGF-I and IL-1␣ synergistically increase the level of IGFBP-5 in OAC by inhibiting the proteolysis and stimulating the expression of IGFBP-5, respectively. Furthermore, the attenuation of IGF-I-stimulated proteoglycan synthesis by IL-1␣ in OAC appears to be mediated by chondrocyte IGFBPs. We conclude that locally produced IGFBPs, in particular IGFBP-5, may play a critical role in the regulation of cartilage matrix degradation in inflammatory and degenerative arthritides. (Endocrinology 139: 2356(Endocrinology 139: -2362(Endocrinology 139: , 1998

Benefits of Recombinant Adeno-Associated Virus (rAAV)-Mediated Insulinlike Growth Factor I (IGF-I) Overexpression for the Long-Term Reconstruction of Human Osteoarthritic Cartilage by Modulation of the IGF-I Axis

“…Of note, we also observed that IGF-I overexpression in OA cartilage in situ was capable of significantly decreasing the expression of IGFBP3 and IGFBP4, two inhibitors of the IGF-I actions (40)(41)(42), while increasing the levels of two of its potentiators (IGFBP5 and its own receptor [IGF-IR]) (42,43), an effect noted at prolonged time points and probably the result of the steady levels of IGF-I production from the rAAV transgene sequence. In this regard, the effects of IGF-I on these components of the IGF-I axis via rAAV in OA cartilage are in good agreement with previous findings when providing IGF-I as a recombinant molecule to articular chondrocytes in vitro (73)(74)(75)(76). Also noteworthy, the elevated, sustained levels of IGF-I produced in OA cartilage via rAAV might have been capable of counteracting the wellknown effects of pathogenic adipokines on the destruction of articular cartilage (3,4).…”

Tumour necrosis factor blockade did not prevent the increase of muscular muscle RING finger-1 and muscle atrophy F-box in arthritic rats

“…The increase in IGFBP-5 in arthritic rats is probably not secondary to the increase in muscular IGF-I, since it has been recently observed in transgenic mice that overexpress IGF-I in muscle that IGFBP-5 mRNA expression was not affected (Musaro et al 2001, Oliver et al 2005. However, the increase in IGFBP-5 in arthritic rats could be secondary to the increase in TNF-a release, since TNF-a can stimulate IGFBP-5 in articular chondrocytes (Sunic et al 1998). Moreover, PEG-sTNFRI administration did not modify TNF-a gene expression in gastrocnemius muscle as it did with the gene expression of IGFBP-5 in this muscle.…”

Differential regulation of IGF-binding proteins in rabbit costal chondrocytes by IGF-I and dexamethasone

“…The first published investigation of IGFBP production by chondrocytes (Froger-Gaillard et al 1989) also reported a dominant, IGF-inducible, 30/31 kDa doublet in rabbit (articular) chondrocytes, although its identity was not established. In contrast, IGFBP-2 was the most abundant species in sheep chondrocytes (Borromeo et al 1996, Sunic et al 1998. IGFBP-3 production was prominent in human articular chondrocytes (Olney et al 1995, DiBattista et al 1996 and weaker in IGF-I-stimulated bovine chondrocytes of various origin (Olney et al 1993).…”