Presence of secretory group IIa and V phospholipase A2 and cytosolic group IValpha phospholipase A2 in chondrocytes from patients with rheumatoid arthritis.

Both secretory and cytosolic phospholipase A2 enzymes have been implicated in the pathogenesis of arthritis in animal models, but the exact expression patterns of the enzymes in diseased human joint tissue are uncertain. We investigated the messenger RNA expression of group IIa, IValpha and V phospholipase A2 and localized the presence of group IIa and IValpha phospholipase A2 at protein levels in articular cartilage from patients with rheumatoid arthritis, osteoarthritis and patients with non-arthritic joints. Both group IIa phospholipase A2 messenger RNA and protein were detected in all samples independent of diagnosis, but were far more prominent in cartilage from rheumatoid arthritis samples. In cartilage with rheumatoid arthritis, the enzyme was detected both within the chondrocytes and in the extracellular matrix, whereas only few osteoarthritic cartilage samples showed positive staining in the matrix. In the cartilage matrix of non-arthritic controls, group IIa phospholipase A2 was totally absent. Messenger RNA for the group IValpha and V phospholipase A2 was, except for one osteoarthritic cartilage sample, exclusively detected in rheumatoid arthritic cartilage. For group IValpha phospholipase A2 this was also confirmed at the protein level. These results suggest that each phospholipase A2 enzyme has distinct roles in both healthy and diseased joint tissue, and that the diversity and amount of enzyme correlate with the grade of inflammation and disease severity.