Differential expression of membrane-anchored proteoglycans in rabbit articular chondrocytes cultured in monolayers and in alginate beads. Effect of transforming growth factor- β1

Abstract

Cell-surface proteoglycans (PGs) were extracted with Triton X-100 from rabbit articular chondrocytes cultured in monolayers and in alginate beads. They were first purified on DEAE-Trisacryl columns and the proportion of hydrophobic PGs was determined by both Octyl-Sepharose chromatography and partitioning in Triton X-114. These two methods revealed that the proportion of hydrophobic PGs was higher in monolayer culture system as compared to alginate beads (24 and 15%, respectively). Characterization of the PGs by Sepharose CL 6B gel filtration followed by electrophoresis indicated that the PGs isolated from monolayers were composed of three chondroitin sulfate (CS) PGs (core proteins of 180, 100 and 50 kDa) and a heparan sulfate (HS) PG (core protein of 60 kDa). In the alginate system, CSPGs with core proteins of 180, 45 and 32 kDa were observed, but no HSPG was present. In parallel, the effect of TGF- β on the distribution of membrane-associated PGs was studied. The results showed that the synthesis of cell-surface PGs was stimulated by TGF- β in monolayers whereas it was inhibited in alginate beads, but the amount of hydrophobic PGs was not altered by the growth factor. These data clearly indicate that TGF- β induces a differential expression of the PG families present at the cell surface. Taken together, the results reveal the complex regulation of cell-surface PG distribution, which obviously depends on the culture method used and suggest that rabbit articular chondrocytes may differentially respond to extracellular ligands according to their morphological state and environment.