Complex CD44 splicing combinations in synovial fibroblasts from arthritic joints

CD44 is a broadly expressed cell surface glycoprotein which is the major cell surface receptor for the glycosaminoglycan, hyaluronan. In humans, alternative splicing of up to 9 variant exons (v2-v10) into CD44 mRNA, together with posttranslational modification via glycosylation and chondroitin sulfate attachment has the potential of generating a large number of CD44 isoforms. Insertion of these various exons has the potential to change the functional capacities of the molecule and has implications in disease. We have analyzed CD44 splice variant expression in cultured VCAM-1-positive synovial fibroblasts isolated from patients with osteo- or rheumatoid arthritis and from normal synovium. Rheumatoid and osteoarthritic tissue express CD44 splice variants at the cell surface level. At the mRNA level exons v3, v6, v7, v8, v9 and v10 were detected in different splicing combinations. Rheumatoid tissue showed high expression, osteoarthritic tissues showed great variation. In contrast, non-inflamed tissue showed no splicing events. Our results indicate that the nature of CD44 splice variant expression may be linked to the inflammatory state of the synovial joint.