mTOR coordinates transcriptional programs and mitochondrial metabolism of activated Treg subsets to protect tissue homeostasis

Regulatory T (Treg) cells derived from the thymus (tTreg) and periphery (pTreg) play central and distinct roles in immunosuppression, but mechanisms governing the generation and activation of Treg subsets in vivo remain uncertain. Here, we report that mechanistic target of rapamycin (mTOR) unexpectedly supports the homeostasis and functional activation of tTreg and pTreg cells. Further, mTOR signaling is crucial for programming activated Treg cell effector function to protect immune tolerance and tissue homeostasis. Treg-specific deletion of mTOR drives spontaneous TH2 responses and altered barrier tissue homeostasis, associated with reductions in both thymic derived effector Treg (eTreg) and pTreg cells. Mechanistically, mTOR acts downstream of antigenic signals to drive IRF4 expression and mitochondrial metabolism, and accordingly, disruption of mitochondrial metabolism severely impairs Treg cell suppressive function and their homeostasis in tissues. Collectively, our results demonstrate that mTOR coordinates transcriptional and metabolic programs in activated Treg subsets to mediate tissue homeostasis We used microarrays to explore global gene expression profiles in unstimulated cTreg cells or cTreg cells activated in the presence or absence of mTOR inhibitors Torin 1 and PP242. YFP+CD4+CD62L+iCD44- cTreg cells from Foxp3-YFP+ transgenic mice were sort-purified from peripheral lymphoid tissues and cultured in vitro. cTreg cells were activated using anti-CD3 and anti-CD28 antibodies in the presence of recombinant IL-2 for 20h and simultaneously treated with vehicle (DMSO), Torin 1 (50 nM) or PP242 (500 nM) before extraction of total RNA for microarray analysis. Biological triplicates of each treatment group were analyzed.