Background As circulating autoantibodies and immune complex deposition is a pathological hallmark of systemic lupus erythematosus (SLE), B cell differentiation into plasma cells (PCs) and some T cell subsets functioning as B-cell helpers can be therapeutic target of SLE. Mammalian target of rapamycin (mTOR) signaling is implicated in formation of B cells and germinal centers (GCs).
Objectives We sought out to assess the efficacy of metformin having mTOR inhibiting property, on the development of autoimmunity using Roquinsan/san mice.
Methods 20-week-old male Roquinsan/san (Jackson Laboratory, Bar Harbor, ME, USA) mice were used. The serum concentrations of IgG, IgG1 and dsDNA antibodies were measured using ELISA. To examine the population of B cells, the splenocytes were stained anti-B220- allophycocyanin (APC), anti-CD21-fluorescein isothiocyanate (FITC), anit-CD23-Phycoerythrin (PE), anti-CD138-PE, anti-GL7-FITC. Flow cytometry was performed using a FACSCalibur cytometer. Confocal microscopy was used to identify the subpopulations of B and T cells. Mouse spleen, liver and kidney tissues were obtained 5 weeks after the metformin treatment and were assessed using H&E staining.
Results Oral administration of metformin can inhibit the formation of splenic follicles and inflammations in kidney and liver tissues, and also decrease serum levels of anti-dsDNA antibodies, whereas not affecting serum glucose level. Metformin altered B cell subsets inhibition of CD21highCD23low marginal zone B cells, B220+GL7+GC B cells and B220-CD138+ PCs occurred. Indeed, the formation of GCs were markedly decreased by metformin. The spleens of metformin-treated group demonstrated the significant reduction of ICOS+ follicular helper T (Tfh) cells compared with those of the vehicle-treated group. Furthermore, metformin inhibited Th17 cells and reciprocally induced Treg cells. These alterations of B and T cell subsets by metformin were associated with enhanced AMPK expression and reciprocal inhibitions of mTOR-STAT3 signaling. Furthermore, metformin can induce p53 and Nrf2 activity in splenic CD4+ T cells.
Conclusions Metformin-induced alteration of AMPK-mTOR-STAT3 signaling may exert a therapeutic value on SLE via inhibiting B cells differentiation into PCs and GC formation.
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Acknowledgements This study was supported by a grant of the Korean Health Technology R&D Project, Ministry for Health & Welfare, Republic of Korea (HI14C3417).
Disclosure of Interest None declared