Methylation of receptor activator of nuclear factor kappa ligand (RANKL) gene in rheumatoid arthritis patients

BackgroundRheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by synovitis, cartilage damage and bone resorption. Methylation of deoxyribonucleic acid plays a crucial role in repressing gene expression. Receptor activator of nuclear factor-kappa ligand (RANKL) controls bone homeostasis.Aim of the workTo assess the serum level of RANKL and its gene promoter methylation in RA patients and to determine its association with clinical characteristics and disease activity.Patients and methodsThe study included 40 RA patients and 40 control. The disease activity score (DAS28) was assessed. Frequency of RANKL gene promoter methylation was determined by quantitative methylation specific PCR (QMSP) and serum RANKL level by enzyme linked immunosorbant assay (ELISA).ResultsPatients mean age was 46.8 ± 10.6 years, 36 females and 4 males (F:M 9:1) with median disease duration 4.5 years. Positive rheumatoid factor, anti-cyclic citrullinated peptide and C-reactive protein were present in 65 %, 75 % and 55 % of cases. Methylation percentage of RANKL gene promoter was significantly lower in patients (3.4 %) than in controls (3.7 %)(p = 0.035) while serum level was significantly increased in patients (9.1 ng/ml,5.3–11.8 ng/ml) than in controls (5.7 ng/ml, 4.5–8 ng/ml)(p = 0.003). RANKL methylation frequency was inversely associated with serum level (rs = -0.21,p = 0.06). There was no significant correlation of RANKL serum level and methylation with DAS28 (r = 0.03,p = 0.87 and r = 0.06,p = 0.73 respectively). RANKL serum level (>9.5 ng/ml) and methylation percentage (≤9%) significantly discriminate RA cases from control (sensitivity 47.5 %, specificity 91.9 %; p = 0.001 and sensitivity 100 %, specificity 40 %; p = 0.03 respectively).ConclusionRA patients expressed elevated serum RANKL with low methylation.