Hypomethylation of LINE-1 but not Alu in lymphocyte subsets of systemic lupus erythematosus patients

Abstract

BackgroundT lymphocytes from SLE patients have a global decrease in the 5-methylcytosine content. Previous studies have identified hypomethylation in the promoter of several genes but there is limited study in the interspersed repetitive sequences (IRSs). MethodsWe examined and compared the methylation levels of long interspersed nuclear element 1s (LINE-1) and Alu elements in normal and SLE CD4+ T lymphocytes, CD8+ T lymphocytes and B lymphocytes by the combined bisulfite restriction analysis-interspersed repetitive sequences (COBRA-IRS). ResultsHypomethylation of LINE-1 but not Alu was found in CD4+ T lymphocytes, CD8+ T lymphocytes, and B lymphocytes of SLE patient (P=0.005, 0.002, and 0.007, respectively). Moreover, when the SLE patients were divided into active and inactive groups, LINE-1 hypomethylation was more significantly distinguished in both CD4+ and CD8+ T lymphocytes of patients from the active SLE group when compared to the controls. Surprisingly, Alu hypomethylation was also observed in CD8+ T lymphocytes from the inactive SLE group when compared to the normal controls (P=0.0056). ConclusionsThe hypomethylation in each lymphocyte subset of SLE was IRSs specific, mainly found in LINE-1 rather than Alu.