Coordinate upregulation of cartilage matrix synthesis in fibrin cultures supplemented with exogenous insulin-like growth factor-I

The addition of insulin-like growth factor-I to cartilage cultures is known to stimulate the synthesis of proteoglycan and type-II collagen in explant and monolayer studies. The purpose of this study was to determine the effe cts of long-term supplementation with insulin-like growth factor-I in chond rocytes cultured in fibrin discs as a preliminary investigation to in vivo application of chondrocyte/insulin-like growth factor-I/fibrin grafts to ar ticular-cartilage repair procedures. Chondrocyte-fibrin cultures were maint ained for 14 days, with insulin-like growth factor-I added at varying conce ntrations of 0, 10, 50, or 100 ng/ml medium. Cultures supplemented with 50 or 100 ng of growth factor/ml had increased levels of aggrecan and type-IIB procollagen mRNA, and translation to aggrecan and type-:IIB collagen was c onfirmed by dye-binding assay of total proteoglycan, type-II collagen immun ohistochemistry, and determination of collagen content by highperformance l iquid chromatography. Maintenance of the chondrocyte phenotype during the 1 4 days of culture was confirmed by round cell morphology on routine stainin g,expression of type-II procollagen mRNA on in situ hybridization, evidence of production of pericellular type-II collagen on immunocytochemistry, syn thesis of large-molecular-size aggrecan monomer on CL-2B column chromatogra phy, and lack of appreciable message expression for type I or IIA collagen on Northern blot hybridization. Dose-response effects of insulin-like growt h factor-I on the expression of chondrocyte matrix constituents were most p ronounced at 50 and 100 ng of growth factor per milliliter of medium. These data confirm that (a) culture of chondrocytes for extended periods in thre e-dimensional cultures of fibrin maintains the chondrocyte phenotype and (b ) supplementation with increasing concentrations of insulin-like growth fac tor-I enhances chondrocyte matrix synthesis and may provide a means to enha nce chondrocyte phenotypic stability and function during transplantation gr afting procedures.