Identification and characterization of versican/PG-M aggregates in cartilage

Versican/PG-M is a large chondroitin sulfate proteoglycan of the extracellular matrix with a common domain structure to aggrecan and is present in cartilage at low levels. Here, we characterized cartilage versican during development and growth. Immunostaining showed that versican was mainly localized in the interterritorial zone of the articular surface at 2 weeks in mice, whereas aggrecan was in the pericellular zone of prehypertrophic and hypertrophic cells of the growth plate. Although its transcription level rapidly diminished during growth, versican remained in the articular cartilage. Biochemical analysis of normal articular cartilage and aggrecan-null cartilage from cmd (cartilage matrix deficiency)/cmd mice revealed that versican was present as a proteoglycan aggregate with both link protein and hyaluronan. Chondroitin sulfate chains of versican digested with chondroitinase ABC contained 71% nonsulfated and 28% 4-sulfated unsaturated disaccharides, whereas those of aggrecan contained 25% nonsulfated and 70% 4-sulfated. Link protein overexpression in chondrocytic N1511 cells at the early stage of differentiation, in which versican is expressed, enhanced versican deposition in the matrix and prevented subsequent aggrecan deposition. These results suggest that versican is present as an aggregate distinct from the aggrecan aggregate and may play specific roles in the articular surface.