The small proteoglycans of cartilage matrix.

The small proteoglycans (PGs) of cartilage matrix represent a small fraction of the total mass of PGs, but with a small size they can be present in equivalent moles to the large PGs. Three types of PGs with a wide skeletal and extraskeletal distribution, biglycan (PGI), decorin (PGII) and fibromodulin have distinct but homologous core proteins containing leucin-rich sequences. Carbohydrate substituants (one or two chondroitin sulfate/dermatan sulfate chains for decorin and biglycan respectively, chains of keratan sulfate for fibromodulin and oligosaccharides) present variations from tissue to tissue and with age and other factors. Decorin and fibromodulin appear to interact with collagen and to participate in the regulation of collagen matrices. In vitro experiments indicate a role for small PGs in adhesion, multiplication, differentiation, and migration of cells. Recent data on molecular biology of the small PGs contribute to a better understanding of their functions and make the evaluation of their role in hereditary diseases.