Del1: A new protein in the superficial layer of articular cartilage

Articular cartilage contains four distinct zones, extending from the surfac e to the subchondral bone. Freshly isolated chondrocytes from the superfici al zone of articular cartilage retain a collagenase-P-resistant cell-associ ated matrix. In the studies described here, the protein Del1 was identified as a component of the cell-associated matrix of superficial zone chondrocy tes from adult bovine articular cartilage. Very little Del1 was associated with freshly isolated deep zone chondrocytes. Western blot analysis of arti cular cartilage cell and tissue extracts using polyclonal antibodies specif ic for Del1 showed Del1 was present in an insoluble cell-associated fractio n. Extracts of the superficial zone of articular cartilage were found to be enriched in Del1 compared to the deeper layers of the tissue. Immunohistoc hemical staining of full-thickness articular cartilage with anti-Del1 antib odies also showed an enrichment of Del1 in the superficial zone. These obse rvations are the first to describe the protein Del1 in a nonendothelial, no nfetal tissue. (C) 2001 Academic Press.