Celastrol mediates Th17 and Treg cell generation via metabolic signaling

A T helper 17 (Th17) cell/regulatory T (Treg) cell imbalance is involved in many immune disorders and diseases. Celastrol, a Chinese herbal compound that has anti-inflammatory and immunosuppressive properties, has been indicated to suppress T cell proliferation and Th17 cell induction, while facilitating Forkhead box P3 (Foxp3) expression and Treg cell generation. In this study, we explored the impact and mechanism of celastrol on Th17 cell/induced Treg (iTreg) cell induction. CD4⁺CD25^- T cells were purified, stimulated with anti-CD3 and anti-CD28 antibodies, and polarized in vitro to generate Th17 or iTreg cells in the presence or absence of celastrol. Initially, we determined that Interleukin (IL)-17 expression by celastrol-treated Th17 was significantly decreased compared with untreated cells; however, the frequency of Foxp3⁺ cells was increased in celastrol-treated cells. We verified that celastrol inhibited phospho-STAT3 expression in cultured Th17 cells and up-regulated phospho-STAT5 expression in iTreg cells. Furthermore, T cells treated with celastrol were more likely to participate in FAO metabolism instead of glycolysis. Celastrol suppressed the expression of glucose transporter, Glut1, and the rate-limiting enzyme, HK2, in addition to mTOR, HIF-1α, c-Myc and Akt expression in Th17 cells. Conversely, celastrol promoted FAO of lipids by up-regulating CPT1A and AMPKα expression in iTreg cells. Our results suggest that celastrol suppresses Th17 cell induction, while promoting the generation of iTreg cells. We found that celastrol inhibits glycolysis in Th17 cells and promotes FAO by iTreg cells, suggesting that celastrol could mediate the metabolism of Th17 and iTreg cells.