DNA methylation profiling of synovial fluid FLS in rheumatoid arthritis reveals changes common with tissue-derived FLS

Aim: Alterations in DNA methylation contribute to the abnormal phenotype of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA). We profiled genome-wide DNA methylation in these cells from synovial fluid, a more readily accessible source of disease-associated cells. Patients & methods: Genome-wide DNA methylation was interrogated in fluid-derived FLS from five RA and six osteoarthritis patients using Human Methylation 450 Bead Chip and bisulfite pyrosequencing. Results: Array analysis identified 328 CpGs, representing 195 genes, that were differentially methylated between RA and osteoarthritis fluid-derived FLS. Comparison with the genes identified in two independent studies of tissue-derived FLS revealed 73 genes in common (similar to 40%), of which 22 shared identity with both studies. Pyrosequencing confirmed altered methylation of these genes. Conclusion: Synovial fluid-derived RA FLS show methylation changes common with tissue-derived FLS, supporting the use of fluid-derived FLS for future investigations.