PTGER2-β-Catenin Axis Links High Salt Environments to Autoimmunity by Balancing IFNγ and IL-10 in FoxP3+ Regulatory T cells

Foxp3+ regulatory T cells (Tregs) are the central component of peripheral immune tolerance. While dysregulation of the Treg cytokine signature has been observed in autoimmune diseases such as multiple sclerosis (MS) and type 1 diabetes, the regulatory mechanisms balancing pro- and anti-inflammatory cytokine production are not known. Here, we identify imbalance between IFN{gamma} and IL-10 as a shared Treg signature, present in patients with MS and under high salt conditions. By performing RNA-seq analysis on human Treg subpopulations, we identify {beta}-catenin as a key regulator that controls the expression of IFN{gamma} and IL-10. The activated {beta}-catenin signature is enriched specifically in IFN{gamma}+Tregs in humans, and this was confirmed in vivo with Treg-specific {beta}-catenin-stabilized mice exhibiting lethal autoimmunity with a dysfunctional, IFN{gamma}-producing, Treg phenotype. Moreover, we identify PTGER2 as a major factor balancing IFN{gamma} and IL-10 production in the context of a high salt environment, with skewed activation of the {beta}-catenin/SGK1/Foxo axis in IFN{gamma}+Tregs. These findings identify a novel molecular mechanism underlying inflammatory Tregs in human autoimmune disease and reveal a new role for a PTGER2-{beta}-catenin loop in Tregs linking environmental high salt conditions to autoimmunity.