Regulatory functions of insulin-like growth factor binding proteins in osteoarthritis.

Insulin-like growth factor binding proteins (IGFBPs) are a group of secreted proteins, which bind to IGF-I (and IGF-II) with high affinity and modulate the biological actions of IGFs. Abundant evidence points the importance of the IGF-I/IGFBP system on both cell growth and differentiation. A role for the IGF-I/IGFBP system in the regulation of normal human cartilage has been previously reported. In this context, recent studies suggest an emerging role for IGFBPs in the failure of cartilage during osteoarthritis (OA). Indeed, increased IGFBP levels have been reported in both the articular cartilage and synovial fluid from patients with OA. Overexpression of IGFBPs, by altering the bioavailability and function of IGFs, is likely to deliver IGFs-independent signals for chondrocyte survival. This, at least in part, might explain the degenerative changes of the cartilage in OA. Further studies are necessary to clarify the mechanisms that cause the overexpression of IGFBPs in patients with OA. Advances in our understanding of the relationship between osteoarthritis and the IGF-I/IGFBP system may lead to new treatment strategies for this degenerative disease.