MicroRNA-146a Deficiency Protects NOD Mice from Autoimmune Diabetes by Enhancing c-Rel-Dependent Regulatory T Cell Function

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by T-cell mediated destruction of pancreatic islet {beta}-cells with genetic, environmental, and molecular triggers involved in disease pathogenesis. Patients with T1D have elevated serum levels of microRNA146a (miR146a). Polymorphisms in the miR146a gene that result in reduced expression of miR146a are associated with protection from T1D. We studied physiological regulators of miR146a expression and found that both hyperglycemia and elevated O-GlcNAcylation increased miR146a expression in T cells. Peripheral blood mononuclear cells (PBMCs) from T1D patients showed increased miR146a and O-GlcNAc transferase (OGT) expression, suggesting increased O-GlcNAcylation may promote miR146a expression in T1D patients. To determine the genetic and developmental role of miR146a in T1D, we generated miR146a-knockout (KO) non-obese diabetic (NOD) mice and found that absence of miR146a significantly protected NOD mice from spontaneous autoimmune diabetes. While we found no impact of miR146a knockout on general hematopoietic parameters and immune cell populations, remarkably, immune cell infiltration into the pancreas was significantly attenuated. Protection from autoimmune diabetes in miR146a-KO NOD mice was associated with increased regulatory T (Treg) cells in the spleen and pancreatic lymph node. Mechanistically, absence of miR146a increased NF-{kappa}B c-Rel expression in Treg cells and enhanced c-Rel binding at the Forkhead box protein P3 (FOXP3) promoter, which positively regulated Treg cell development and suppressor function, offering protection from T1D in miR146a-KO NOD mice. Our findings reveal miR146a as a key regulator of Treg cell-mediated immune tolerance through controlling NF-{kappa}B c-Rel-dependent FOXP3 expression and suggest targeting miR146a as a potential strategy to restore peripheral tolerance in T1D.