EFFECTS OF GROWTH-FACTORS AND INTERLEUKIN-1-ALPHA ON PROTEOGLYCAN ANDTYPE-II COLLAGEN TURNOVER IN BOVINE NASAL AND ARTICULAR CHONDROCYTE PELLET CULTURES

The aim of this study was to investigate the effects of insulin-like g rowth factor-I, transforming growth factor-beta (TGF-beta), and interl uekin-1 alpha (IL-1 alpha) on the deposition and degradation of a cart ilage-like matrix in high-density pellet cultures of adult bovine chon drocytes. Proteoglycan was determined by toluidine blue staining and c olorimetric assay. Type II collagen was determined by immunohistochemi cal staining and its unwinding in situ by a recently developed immunoa ssay. Bovine nasal chondrocytes cultured as pellets deposited a well-o rganized extracellular matrix of proteoglycan and type II collagen. In sulin-like growth factor-I (2-10 ng/ml) increased the synthesis and in corporation into the matrix of both these proteins. TGF-beta (2-10 ng/ ml) also increased proteoglycan synthesis. However it inhibited proteo glycan deposition, presumably through increased degradation of the mol ecule, as shown by increased release of aggrecan fragments into the ti ssue culture medium. TGF-beta had no effect on type II collagen deposi tion. In pellet cultures of bovine nasal or articular chondrocytes, 20 ng/ml IL-1 alpha induced a significant degradation of both proteoglyc an and type II collagen. The effect on collagen clearly involved prote olytic cleavage of its triple helix because there was an increase in t he proportion of unwound type II collagen in the matrix, as well as a loss of total type II collagen. In explant cultures of intact bovine a rticular cartilage, incubation with 50 ng/ml IL-1 alpha stimulated sig nificant degradation of the proteoglycan but no degradation of the typ e II collagen. These results demonstrate that although the articular c hondrocytes are capable of degrading type II collagen when isolated, t hey do not do so in situ, presumably because of some inherent property of the mature extracellular matrix. This study demonstrates the utili ty of pellet cultures when investigating chondrocyte-mediated turnover of cartilage matrix and its modulation by cytokines and growth factor s.