Rapamycin Modulate Treg/Th17 Balance via Regulating Metabolic Pathways: A Study in Mice

A regulatory T (Treg) cell/T helper 17 (Th17) cell imbalance is involved in many autoimmune diseases. Rapamycin (Rapa), a clinically used immunosuppressive drug, has been shown to inhibit Th17 cell differentiation but promote Treg cell generation. In this study, we aimed to study the mechanism of Rapa acting on Treg and Th17 cell differentiation. Purified mouse CD4⁺CD25^- T cells were stimulated and polarized in vitro to generate Th17 or Treg cells in the presence or absence of Rapa. We first confirmed that Rapa inhibited the differentiation of Th17 cells and greatly promoted Treg cell generation in vitro. As metabolic pathways play a key role in T cell differentiation, we then detected the metabolic programs in Rapa-treated T cells. We found that Rapa blocked glycolysis in induced Th17 cells, evidenced by reduced glucose uptake, and inhibited expression of glucose transporter 1 and the rate-limiting enzyme HK2. In addition, the expression of c-Myc and of HIF-1α transcription factor, which regulate many genes involved in glycolysis, were inhibited by Rapa. Conversely, Rapa promoted fatty acid oxidation (FAO) metabolism in differentiated Treg cells, with the elevation of FAO product β-hydroxybutyrate, and increased expression of ATGL and CPT1A, the key enzymes of FAO in differentiated Treg cells. The expression of phospho-AMPKα, the key signal in the regulation of FAO, was also promoted in Rapa-treated induced Treg cells. Together, these findings indicated that Rapa abrogated glycolysis in Th17 cells but facilitated FAO in induced Treg cells, which may underlie the mechanism by which Rapa regulates the Treg/Th17 balance.