CHONDROCYTES FROM PATIENTS WITH FAMILIAL OSTEOCHONDRITIS DISSECANS EXHIBIT AN ENDOPLASMIC RETICULUM STRESS RESPONSE AND DEFECTIVE MATRIX ASSEMBLY

Familial osteochondritis dissecans (FOCD) is an inherited defect of cartilage and bone characterized by development of large cartilage lesions in multiple joints, short stature and early onset osteoarthritis. We have studied a family from Northern Sweden with FOCD over five generations. All affected family members have a heterozygous missense mutation on exon 17 of the aggrecan gene, resulting in a Val-Met amino acid replacement in the G3 aggrecan C-type lectin domain (CLD). Aggrecan, a major proteoglycan of articular cartilage produced by chondrocytes, has a large protein core richly substituted with sulfated glycosaminoglycan chains. The unique structure, its high concentration within the cartilage extracellular matrix and its ability to form a supermolecular complex with hyaluronan and bind to other matrix proteins all profoundly influence the biomechanical properties of the tissue. Deletion of CLD in a chick aggrecan construct was found to influence its secretion from chondrocytes and human aggrecan c...