Levels of base excision repair proteins in CD4 + T cells in patients with systemic lupus erythematosus.

OBJECTIVES: Systemic lupus erythematosus (SLE) is a multi-systemic disease with the unknown pathogenic mechanism. DNA demethylation is involved in SLE pathogenesis. Growth arrest and DNA damage inducible 45 alpha (Gadd45a) takes part in the process of DNA demethylation. Gadd45a is a DNA repair-related protein. This study aims to investigate the expressions of some proteins [including activation-induced cytidine deaminase (AID), thymine DNA glycosylase (TDG), and methyl-CpG-binding domain protein 4 (MBD4)] involving in base excision repair (BER) process in CD4+ T cells in patients with SLE, and to analyze the correlations between the above BER proteins and lupus disease.

METHODS: From January 2019 to September 2020, 12 SLE patients and 12 healthy controls were recruited from Second Xiangya Hospital of Central South University. Peripheral blood mononuclear cells (PBMCs) were separated by Ficoll-Hypaque density gradient centrifugation and then CD4+ T cells were isolated via positive selection using Miltenyi beads. We measured the messenger RNA (mRNA) and protein expressions of AID, TDG, and MBD4 by real-time reverse transcription polymerase chain reaction (RT-PCR) and Western blotting, respectively.

RESULTS: In contrast to controls, in SLE CD4+ T cells, the mRNA and protein expressions of AID were elevated (P=0.003, P=0.022, respectively); TDG protein expression was increased (P=0.017); and MBD4 protein level was reduced (P<0.001). No visible distinctions was found in the mRNA expressions of either TDG or MBD4 between the 2 groups (both P>0.05). The mRNA and protein expressions of AID and the protein levels of TDG were positively correlated with SLE disease activity index (SLEDAI). And the mRNA and protein expressions of MBD4 were negatively correlated with SLEDAI.

CONCLUSIONS: In SLE CD4+ T cells, the increased expressions of AID and TDG and the decreased MBD4 expression may participate in SLE pathogenic mechanism.