Effects of transforming growth factor beta on proteoglycan synthesis by cell and explant cultures derived from the knee joint meniscus

Abstract

Repair of meniscal tears depends in part upon the ability of the resident fibrochondrocytes to produce new extracellular matrix molecules including proteoglycans. Three culture systems have been used to investigate proteoglycan production by meniscal fibrochondrocytes from the inner, middle and outer zones of medial and lateral menisci of the sheep stifle joint. Cultures of meniscal explants, monolayered cells, and cells encapsulated in alginate beads were labeled with 35SO4H2 for 48 h in the absence and presence of transforming growth factor beta (TGF beta) and the proteoglycans were analysed by Sephacryl S-1000 chromatography. In general, the lateral meniscus produced more proteoglycan than the medial. Explants from the inner and middle zones produced predominantly aggrecan-like proteoglycan, together with a smaller proteoglycan population eluting with an average distribution coefficient of around 0.65. The outer meniscal zones synthesized less proteoglycan overall, the majority of which consisted of the smaller proteoglycans. These characteristic proteoglycan size profiles obtained with explant cultures also were preserved when cells isolated from the respective zones were cultured in alginate beads. Monolayer cell cultures, however, produced almost entirely small proteoglycans, regardless of their zone of origin. Chromatography of chondroitinase AC and ABC digested samples 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 aggregation of large proteoglycan monomers, and an increase in the production of the larger of two small proteoglycans, putatively, biglycan.