Metformin suppresses systemic autoimmunity in Roquinsan/san mice through inhibiting B cell differentiation into plasma cells via regulation of AMPK/mTOR/STAT3

Circulating autoantibodies and immune complex deposition are pathological hallmarks of systemic lupus erythematosus (SLE). B cell differentiation into plasma cells (PCs) and some T cell subsets that function as B cell helpers can be therapeutic targets of SLE. Mechanistic target of rapamycin (mTOR) signaling is implicated in the formation of B cells and germinal centers (GCs). We assessed the effect of metformin, which inhibits mTOR, on the development of autoimmunity using Roquinsan/san mice. Oral administration of metformin inhibited the formation of splenic follicles and inflammation in kidney and liver tissues. It also decreased serum levels of anti-dsDNA Abs without affecting serum glucose levels. Moreover, metformin inhibited CD21high CD23low marginal zone B cells, B220+GL7+ GC B cells, B220-CD138+ PCs, and GC formation. A significant reduction in ICOS+ follicular helper T cells was found in the spleens of the metformin-treated group compared with the vehicle-treated group. In addition, metformin inhibited Th17 cells and induced regulatory T cells. These alterations in B and T cell subsets by metformin were associated with enhanced AMPK expression and inhibition of mTOR-STAT3 signaling. Furthermore, metformin induced p53 and NF erythroid-2-related factor-2 activity in splenic CD4⁺ T cells. Taken together, metformin-induced alterations in AMPK-mTOR-STAT3 signaling may have therapeutic value in SLE by inhibiting B cell differentiation into PCs and GCs.