Glutathione restricts serine metabolism to preserve regulatory T cell function

Regulatory T cells (Tregs) maintain immune homeostasis and prevent autoimmunity. Serine can stimulate glutathione (GSH) synthesis and feeds into the one-carbon metabolic cycle essential for effector T cell (Teff) responses. However, serine’s functions, linkage to GSH, and role in stress responses in Tregs are unknown. Here we show, using mice with Treg-specific ablation of the catalytic subunit of glutamate cysteine ligase (Gclc), that GSH loss in Tregs alters serine import and synthesis, and that the integrity of this feedback loop is critical for Treg suppressive capacity. Although Gclc-ablation does not impair Treg differentiation, the mutant mice develop severe spontaneous autoimmunity and show enhanced anti-tumor responses. Gclc-deficient Tregs exhibit increased serine metabolism, mTOR activation and proliferation but FoxP3 was downregulated. Limitation of cellular serine in vitro and in vivo restores FoxP3 expression and suppressive capacity to Gclc-deficient Tregs. Our work reveals an unexpected role for GSH in restricting serine availability to preserve Treg functionality. Here, we freshly isolated Tregs from WT and mutant mice (indicated as nTregs) as well as differentiate naïve CD4+ T cells from both WT and mutant mice into induced Tregs (indicated as iTregs)