Overexpression of osteopontin in rheumatoid synovial mononuclear cells is associated with joint inflammation, not with genetic polymorphism

OBJECTIVE: Osteopontin (OPN) is thought to play an important role in rheumatoid synovitis. We investigated the expression of OPN in rheumatoid synovial fluid mononuclear cells (SFMC) and its potential association with genetic polymorphism of the OPN gene and joint inflammation in rheumatoid arthritis (RA). METHODS: 1. The expression of OPN mRNA in peripheral blood mononuclear cells (PBMC) and SFMC of patients with RA was analyzed quantitatively by real-time polymerase chain reaction (PCR). Results were analyzed in paired PBMC and SFMC and control PBMC. 2. Six single nuclear acid polymorphisms of the OPN gene were genotyped in a cohort of 192 Chinese patients with RA and controls (n = 288) by restriction fragment length polymorphism PCR or direct DNA sequencing. 3. SF derived from RA patients was examined for the stimulating effect on mRNA expression of the OPN gene in PBMC. RESULTS: The expression of OPN gene was significantly increased in SFMC and, to a lesser degree, in PBMC of patients with RA compared to control PBMC (p < 0.01). However, the prevalence of OPN genotype and allele frequencies at the selected positions did not differ significantly between RA patients and the control group (p > 0.05). Further characterization indicated that SF known to contain a variety of proinflammatory factors significantly stimulated mRNA expression of OPN in PBMC obtained from RA patients or healthy controls. CONCLUSION: Overexpression of OPN mRNA in SFMC is associated with proinflammatory factors produced in inflamed joints, but not with OPN genetic polymorphisms. OPN gene polymorphisms do not correlate with susceptibility to RA.