Sphingosine-1-phosphate signaling inhibition suppresses Th1-like Treg generation by reversing mitochondrial uncoupling

Inflammatory environments induce the generation of dysfunctional IFN{gamma}+T-bet+FOXP3+ Th1-like Tregs, which show defective function and are found in autoimmune conditions including multiple sclerosis (MS). The pathways that control the generation of Th1-like Tregs are not well understood. Sphingosine-1-phosphate (S1P) signaling molecules are upregulated in Th1-like Tregs, and in vivo S1P inhibition with Fingolimod (FTY720) inhibits the expression of genes responsible for Treg plasticity in MS patients. However, the underlying mechanisms are unknown. Here we show that S1P signaling inhibition by FTY720 inhibits the generation of Th1-like Tregs and rescues their suppressive function. These effects are mediated by a decrease in mTORC1 signaling and reversal of the mitochondrial uncoupling that Tregs undergo during their reprogramming into Th1-like Tregs in vitro. Finally, these results are validated in in vivo generated Th1-like Tregs, as the Tregs from MS patients treated with FTY720 display decreased Th1-like Treg frequency, increased suppressive function, and mitochondrial metabolism rebalance. These results highlight the involvement of mitochondrial uncoupling in Treg reprogramming and identify S1P signaling inhibition as a target to suppress the generation of dysfunctional Th1-like Tregs.