The effect of dynamic compression on the response of articular cartilage to insulin-like growth factor-I

Articular cartilage is routinely subjected to mechanical farces and to cell -regulatory molecules, Previous studies have shown that mechanical stimuli can influence articular chondrocyte metabolic activity, and biochemical stu dies have shown that growth factors and cytokines control many of the same cell functions. Little is known, however, of the relationships or interplay , if any, between these two key components of the articular environment. Th is study investigated the comparative and interactive effects of low amplit ude, sinusoidal. dynamic compression: and insulin-like growth factor-I (IGF -I) a polypeptide in synovial fluid that is anabolic for cartilage. In bovi ne patellofemoral cartilage explants, IGF-I increased protein and proteogly can synthesis 90%, and 120%. respectively while dynamic compression increas ed protein and proteoglycan synthesis 40% and 90%, respectively. Stimulatio n by IC;FI was significantly greater than by dynamic compression for both p rotein and proteoglycan synthesis. When applied together, the two stimuli e nhanced protein and proteoglycan synthesis by 180% and 290%, respectively, a degree greater than that achieved by either stimulus alone. IGF-I augment ed protein synthesis with a time constant of 12.2 h. Dynamic compression in creased protein synthesis with a time constant of 2.9 h, a rate significant ly faster than that of IGF-I, suggesting that these signals act via distinc t cell activation pathways. When used together, dynamic compression and IGF -I acted with a time constant of 5.6 h. Thus, dynamic compression accelerat ed the biosynthetic response to IGF-I and increased transport of IGF-I into the articular cartilage matrix, suggesting that, in addition to independen tly stimulating articular chondrocytes, cyclic compression may improve the access of soluble growth factors to these relatively isolated cells. (C) 20 01 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rig hts reserved.