Hsp90 mediates insulin‐like growth factor 1 and interleukin‐1β signaling in an age‐dependent manner in equine articular chondrocytes

Abstract

Objective. Many metabolic processes in chondrocytes thought to contribute to age-related changes in the extracellular matrix are influenced by known roles of Hsp90. Age-related decreases in the level of Hsp90 have been documented in numerous cell types and could contribute to cartilage degeneration. The aim of this study was to investigate the roles of age and Hsp90 in insulin-like growth factor 1 (IGF-1) and interleukin-1␤ (IL-1␤) signaling in chondrocytes.Methods. Levels of Hsp90 messenger RNA (mRNA) and protein, with respect to age, were determined by quantitative real-time polymerase chain reaction (PCR) and Western blot analysis, respectively. The Hsp90 inhibitor geldanamycin (50 nM, 100 nM, or 500 nM) was used to assess age-related responses to Hsp90 with concurrent IGF-1 or IL-1␤ stimulation of chondrocytes. Quantitative real-time PCR was used to measure COL2A1 and matrix metalloproteinase 13 (MMP13) gene expression; Western blot analysis was performed to determine the phosphorylation status of p42/44 and Akt/protein kinase B.Results. The effects of Hsp90 inhibition with geldanamycin were concentration dependent. Inhibition of Hsp90 with 100 nM or 500 nM geldanamycin blocked IGF-1-induced cell proliferation, Akt and p42/44 activation, and COL2A1 expression. Basal and IL-1␤-induced up-regulation of MMP13 mRNA was blocked by all concentrations of geldanamycin tested. Gain-offunction assays with Hsp90 resulted in increased expression of MMP13 mRNA.Conclusion. These results suggest that Hsp90 is involved in opposing signaling pathways of cartilage homeostasis, and that catabolic responses are more sensitive to Hsp90 inhibition than are anabolic responses. Further studies are needed to determine the role of Hsp90 inhibition in osteoarthritis in order to assess its potential as a therapeutic target.

Direct regulation of IGF-binding protein 1 promoter by interleukin-1β via an insulin- and FoxO-1-independent mechanism

“…IL-1␤ in particular has been shown to downregulate the expression of insulin receptor substrate-1 and to inhibit Akt phosphorylation (5,17,24,27,45,52). This present study also found a substantial decline in the magnitude of insulin-induced Akt activation in the presence of IL-1␤.…”

Intra-Articular Injections for the Treatment of Osteoarthritis: Focus on the Clinical Use of Several Regimens

“…In animal models, Insulin like growth factor-I has led to enhanced repair of extensive cartilage defects and protection of the synovial membrane from chronic inflammation (Fortier & Miller, 2006;Goodrich et al, 2007). However, studies of human articular cartilage indicate that serum Insulin like growth factor-1 levels and chondrocyte responsiveness to Insulin like growth factor-1 diminish progressively with age (Ashton & Matheson, 1979;Boehm et al, 2007;Fortier & Miller, 2006;Loeser et al, 2002;Loeser et al, 2000;Trippel, 1995) This finding suggests that a simultaneous decrease in the amount of Insulin like growth factor-1 available and a reduced ability of cells to respond to the remaining Insulin like growth factor may produce cartilage that is less capable of maintaining its structural and functional integrity. Insulin like growth factor non-responsiveness has been further observed to exist in chondrocytes from arthritic cartilage or in the presence of inflammation (Verschure et al, 1996).…”

Biochemical Mediators Involved in Cartilage Degradation and the Induction of Pain in Osteoarthritis

“…Gruber and colleagues found that the addition of IGF-1 increased cell survival upon experimental induction of apoptosis in spine disc annulus fibrosus cells (180), consistent with the anti-catabolic capacity of IGF-1 in both intervertebral disc (IVD) and articular cartilage tissues. Despite its potent anabolic and anti-catabolic effects on normal cartilage tissue, however, IGF-1 appears to have a diminished ability to stimulate ECM formation and decrease catabolism with both age (181,182) and OA (68,149,181). There appears to be an uncoupling of IGF-1 responsiveness in OA, as IGF-1 is able to stimulate matrix synthesis but is unable to decrease matrix catabolism (183).…”