Synovial glycosidases in joint diseases

Abstract

We have shown earlier that certain synovial fluid exoglycosidases are predictors of rheumatoid arthritis and are capable of depleting the articular cartilage in glycosamino-glycans. In the current study we investigated the expression of several glycosidases and glycosidase-like molecules including hexosaminidase (Hex), glucuronidase (Gus), hyaluronidase (Hyal), klotho and the chitinase-like human cartilage glycoprotein 39 (Hc-gp39) in synovial fluid and membrane samples as well as synovial fibroblast strains of patients with osteoarthritis (OA) and rheumatoid arthritis (RA). The gene expression of the chitinase like Hc-gp 39 was by far the highest among the tested genes both in synovial fibroblasts and synovial membrane samples. HexA gene was characterized by the second strongest gene expression, followed by the expression of HexB, GusB, Hyal1 and KLOTHO in a decreasing sequence of order. The only significant difference was found in the gene expression of Hyal1 of the RA and OA patients. Synovial membrane homogenates were characterized by high β-D-N-acetyl-glucosaminidase, β-D-N-acetyl-galactosaminidase and β-D-glucuronidase expression as compared to the synovial fluid samples. We found that while synovial fibroblasts appeared the primary sources of the β-D-N-acetyl-glucosaminidase and β-D-N-acetyl-galactosaminidase enzymes, they produced relatively low amounts of β-D-glucuronidase. There was no significant difference in the activities associated with the synovial membrane and synovial fibroblast of OA and RA patients. Using fluorescent substrates of β-D-glucuronidase we found stronger enzyme activities in OA fibroblasts as compared to those isolated from patients with RA. Furthermore, we found that β-D-glucuronidase activity was associated with microparticles found in the supernatants of synovial fibroblast of both RA and OA patients. We also tested if cytokines, implicated in the pathomechanism of RA, regulated the expression of the above enzymes. While IL-17 had no effect, TNF-alpha markedly upregulated the expression of the KLOTHO gene.