Study of the glycome of synovial mast cells in normal tissues, osteoarthritis and rheumatoid arthritis reveals MGAT5 activity in these and endochondral cells

Mast cells and angiogenesis play roles in the synovium of both osteoarthritis and rheumatoid disease but precise mechanisms are unclear. In a study of the glycome of human synovial biopsies from normal, osteoarthritic and rheumatoid disease cases mast cell numbers were increased in both osteoarthritic and rheumatoid disease synovial samples (the latter more than the former). Both mast cells and endothelial cells expressed receptors for the lectinPhaseolus vulgarisleukagglutinin (lPHA). Endothelial cells only expressed receptors forPsophocarpus tetragonolobus(PTL-II). Mast cells and angiogenesis are, therefore, likely to have a common pathogenetic mechanism in osteoarthritis and rheumatoid synovitis, the difference being one of degree. lPHA receptor expression in both mast cells and endothelial cells indicates βl,6N–acetylglucosaminyl (GlcNAc) – transferase V (GnTaseV/MGAT5) activity. This provides a linkage between mast cells and endothelial cell proliferation. Endothelial cells show core 1 O-glycosylation (positive PTL-II staining) which is probably necessary for the formation of competent tubular structures and for continuing vascular integrity.