Small proteoglycans from different regions of the fibrocartilaginous temporomandibular joint disc

Abstract

Proteoglycans were isolated from two zones--the periphery and the inner zone--of bovine temporomandibular joint articular discs and separated into two pools by gel-filtration. Proteoglycans in the low molecular mass pool were further resolved by hydrophobic affinity chromatography into two groups identified by cyanogen bromide peptide analysis, amino acid analysis and amino-terminal sequence analysis as PGI (biglycan) and PGII (decorin). These two proteoglycans were isolated in approximately equal proportions from the 'inner' disc tissue but PGII predominated in the 'outer' tissue. Direct chemical analysis showed that the glycosaminoglycan chains on both PGI and PGII were high in iduronate (64-68% of total uronic acid). The dermatan sulfate chains on proteoglycans from the inner disc tissue were longer than those from the outer tissue. Comparison of the galactosamine contents of the intact proteoglycans with electrophoretic mobilities of the isolated dermatan sulfate chains showed that the PGI from the disc carries two dermatan sulfate chains. Inclusion of disc DS-PGI in a solution of soluble type I collagen lengthened the lag-phase, steepened the turbidity-time curve and increased the final opacity attained during fibril formation in vitro. The median fibril diameter and the range of diameters were both higher in the presence of DS-PGI. By contrast, disc DS-PGII reduced the slope of the turbidity-time curve but had little effect on the final turbidity or the fibril diameter.