Hypomethylation of long interspersed nucleotide element-1 in peripheral mononuclear cells of juvenile systemic lupus erythematosus patients in China

Abstract

Aim: Methylation abnormalities in T lymphocytes have been reported to correlate with systemic lupus erythematosus (SLE). Previous studies identified hypomethylation in the promoter of several genes linked to SLE. Long interspersed nucleotide element-1 (LINE-1) constitutes 17-25% of the human genome, and LINE-1 hypomethylation has been reported in SLE. Limited information is available regarding LINE-1 methylation in juvenile SLE (JSLE).

Method: Methylation levels of LINE-1 in peripheral blood mononuclear cells (PBMCs) from 59 JSLE and 47 control samples were examined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Total homocysteine (tHcy) concentrations in plasma were measured by immunoassay.

Results: Significant hypomethylation of LINE-1 was observed in PBMCs from JSLE patients (60.93% in cases compared with 62.88% in controls, P = 0.001). Significant LINE-1 hypomethylation was observed in active SLE compared to controls (60.66% vs. 62.88%, P = 0.001). According to other clinical parameters, a significant correlation was found between LINE-1 methylation levels and the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2000) of the cases (r = -0.285, P = 0.032). The risk of JSLE increased with decreasing levels of LINE-1 methylation, with an odds ratio of 14.5 (95% CI: 2.8-75.6, P = 0.002). Cases had significantly higher plasma concentrations of tHcy than controls (15.11 vs. 11.02 μmol/L, P = 0.028); the correlation between LINE-1 methylation levels and tHcy was significant (r = -0.4, P = 0.013). Correlations between methylation levels of LINE-1 and complement component 3 were significant (r = 0.317, P = 0.044; r = 0.387, P = 0.031, in total JSLE and active JSLE, respectively).

Conclusion: Hypomethylation of LINE-1 is associated with risk of JSLE, and LINE-1 methylation levels were related to disease activity and clinical manifestations. The correlation between tHcy levels and LINE-1 methylation was significant.

Keywords: juvenile; long interspersed nucleotide element-1; methylation; systemic lupus erythematosus.