The Action Mechanism Of Common Inducers Aggravating Systemic Lupus Erythematosus

Objective: To elucidate the mechanisms of ultraviolet B(UVB), estrogen and human endogenous retroviruses(HERVs) aggravating systemic lupus erythematosus(SLE).Methods:(1) Thirty-five SLE patients and 15 healthy controls were enrolled in the UVB exposure study. CD4+ T cells from SLE patients and healthy controls exposed to different dosages of UVB were analyzed. The global DNA methylation status was measured by flow cytometry analysis. The expression level of DNA methyltransferase 1(DNMT1) was measured by quantitative real-time PCR(q RT-PCR) and Western blotting assay. DNMT1 catalytic activity detection was employed.(2) Thirty women with SLE and 15 female controls were enrolled in the estrogen treatment study. CD4+ T cells exposed to 17β-estradiol were analyzed. The global DNA methylation level and the expression level of DNMT1 were measured. Plasma 17β-estradiol levels were measured by ELISA.(3) Fifteen patients with SLE and 10 healthy controls were enrolled in the study on the HERVs expression. The m RNA expression of 6 selected HERVs was determined by Reverse-transcription PCR(RT-PCR) and q RT-PCR. The methylation status of the long terminal repeats(LTRs) in SLE-related HERVs in CD4+ T cells were investigated by bisulfite sequencing analysis. Furthermore, CD4+ T cells treated with 5-aza-deoxycytidine(5-aza C) and UVB were analyzed.Results:(1) The level of global DNA methylation and DNMT1 m RNA expression in CD4+ T cells from SLE patients were significantly lower than those from the control group. DNA methylation was decreased after UVB exposure in a dosage-dependent manner in SLE patients, but not in the control group. DNMT1 m RNA and protein expression level were not affected by UVB exposure in both SLE patients and healthy controls. DNMT1 catalytic activity was significantly decreased in CD4+ T cells from SLE patients after UVB exposure in a dosage-dependent manner.(2) In female SLE CD4+ T cells, 17β-estradiol downregulated DNMT1 expression at both the m RNA and protein levels, and enhanced global DNA hypomethylation. Plasma 17β-estradiol levels were similar in patients with SLE and controls. The m RNA expression of estrogen receptor α(ERα) was upregulated in SLE CD4+ T cells. Furthermore, the 17β-estradiol-induced downregulation of DNMT1 expression and global DNA hypomethylation were rescued by an ER antagonist.(3) HERV-E m RNA expression was higher in lupus CD4+ T cells than in cells from healthy controls. Additionally, the HERV-E m RNA expression level was positively correlated with SLE disease activity. Furthermore, the HERV-E LTR methylation level was decreased and was negatively correlated to the HERV-E m RNA expression level in lupus CD4+ T cells. Finally, lupus CD4+ T cells showed markedly decreased HERV-E LTR methylation level and increased HERV-E m RNA expression after treatment with 5-aza C or UVB.Conclusions:(1) UVB enhanced DNA hypomethylation of CD4+ T cells in SLE via inhibiting DNMT1 catalytic activity in a dosage-dependent manner.(2) 17β-estradiol enhanced global DNA hypomethylation in female SLE CD4+ T cells via downregulation of DNMT1 expression mediated by ERa overexpression.(3) HERV-E is involved in the development of SLE. HERV-E transcription may be activated via inhibition of LTR methylation in lupus CD4+ T cells.