EFFECTS OF TRANSFORMING GROWTH-FACTOR-BETA ON PROTEOGLYCAN SYNTHESIS BY CELL AND EXPLANT CULTURES DERIVED FROM THE KNEE-JOINT MENISCUS

Repair of meniscal tears depends in part upon the ability of the resid ent fibrochondrocytes to produce new extracellular matrix molecules in cluding proteoglycans. Three culture systems have been used to investi gate proteoglycan production by meniscal fibrochondrocytes from the in ner, middle and outer zones of medial and lateral menisci of the sheep stifle joint. Cultures of meniscal explants, monolayered cells, and c ells encapsulated in alginate beads were labeled with (SO4H2)-S-35 for 48 h in the absence and presence of tranforming growth factor beta (T GF beta) and the proteoglycans were analysed by Sephacryl S-1000 chrom atography. In general, the lateral meniscus produced more proteoglycan than the medial. Explants from the inner and middle zones produced pr edominantly aggrecan-like proteoglycan, together with a smaller proteo glycan population eluting with an average distribution coefficient of around 0.65. The outer meniscal zones synthesized less proteoglycan ov erall, the majority of which consisted of the smaller proteoglycans. T hese characteristic proteoglycan size profiles obtained with explant c ultures also were preserved when cells isolated from the respective zo nes were cultured in alginate beads. Monolayer cell cultures, however, produced almost entirely small proteoglycans, regardless of their zon e of origin. Chromatography of chondroitinase AC and ABC digested samp les indicated that the small proteoglycan population comprised mostly dermatan sulphate-containing proteoglycans. In all meniscal zones and in all culture systems, TGF beta stimulated proteoglycan production by up to 100% and the proteoglycans were slightly larger. TGF beta also stimulated cell division in fibrochondrocyte monolayer cultures. Long term intermittent stimulation of alginate bead cultures with TGF beta resulted in large increases in proteoglycan synthesis, increased aggre gation of large proteoglycan monomers, and an increase in the producti on of the larger of two small proteoglycans, putatively, biglycan.