Transforming growth factor-β1 stimulates synthesis of proteoglycan aggregates in calf articular cartilage organ cultures

Abstract

Previous work showed that transforming growth factor-β1 (TGF-β1), added alone to bovine cartilage organ cultures, stimulated [ 35S]sulfate incorporation into macromolecular material but did not investigate the fidelity of the stimulated system to maintain synthesis of cartilage-type proteoglycans. This paper provides evidence that chondrocytes synthesize the appropriate proteoglycan matrix under TGF-β1 stimulation: (i) there is a coordinated increase in hyaluronic acid and proteoglycan monomer synthesis, (ii) link-stable proteoglycan aggregates are assembled, (iii) the hybrid chondroitin sulfate/ keratan sulfate monomeric species is synthesized, and (iv) there is an increase in protein core synthesis. Some variation in glycosylation patterns was observed when proteoglycans synthesized under TGF-β1 stimulation were compared to those synthesized under basal conditions. Thus comparing TGF-β1 to basal samples respectively, the monomers were larger ( K av on Sepharose CL-2B = 0.29 vs 0.41), the chondroitin sulfate chains were longer by ~3.5 kDa, the percentage of total glycosaminoglycan in keratan sulfate increased slightly from ~4% (basal) to ~6%, and the unsulfated disaccharide decreased from 28% (basal) to 12%. All of these variations are in the direction of a more anionic proteoglycan. Since the ability of proteoglycans to confer resiliency to the cartilage matrix is directly related to their anionic nature, these changes would presumably have a beneficial effect on tissue function.