Ultraviolet B decreases DNA methylation level of CD4+T cells in patients with systemic lupus erythematosus

Objective In the present study, DNA methylation level of CD4+ T cells exposed to ultraviolet B (UVB) was investigated and its potential mechanisms were also explored. Methods CD4+ T cells from 12 cases of healthy subjects and 33 cases of SLE patients were isolated and exposed to different dosages (0, 50, 100 mJ/cm(2)) of UVB. Further, SLE patients were divided into two groups: active SLE group (22 cases, SLEDAI scores > 4) and inactive SLE group (11 cases, SLEDAI scores <= 4). DNA methylation was evaluated by the Methylamp (TM) Global DNA Methylation Quantification Ultra Kit. The mRNA and protein expression levels of DNA methyltransferases (DNMT1 and DNMT3A) were detected by real-time PCR and western blot, respectively. Results The levels of DNA methylation and DNMT3A mRNA in SLE patients were significantly decreased compared with those in healthy subjects at baseline. After different dosages of ultraviolet irradiation (0, 50 and 100 mJ/cm(2)), DNA methylation levels of CD4+ T cells were all reduced in a dose-dependent manner in three subgroups. Additionally, 100 mJ/cm(2) ultraviolet irradiation in active SLE group contributed to a significant decrease of both DNA methylation and DNMT3A mRNA levels in CD4+ T cells. UVB exposure had no significant effects on expression levels of DNMT1 mRNA and protein and DNMT3A protein. Conclusion UVB decreases DNA methylation level of CD4+ T cells in SLE patients probably via inhibiting DNMT3A mRNA expression level, which needs to be further explored.