Differentiation of regulatory Treg (Treg) in the periphery is critical to control inflammatory processes. Although polarization of inducible Treg (iTreg) often occurs in an inflammatory environment, the effects exerted by inflammation on human iTreg differentiation have not been extensively studied. We observed that IL-1β significantly reduced the frequency of FOXP3+ T cells under iTreg-polarizing conditions. Mechanistically, we show that IL-1β activated mTORC1 and downstream upregulated hypoxia inducible factor-1 (HIF-1α) expression. Using specific inhibitors, we demonstrated that both steps were critical in the deleterious effect of IL-1β on Treg differentiation. Chemical stabilization of HIF-1α by Dimethyloxalylglycine (DMOG) also significantly impaired iTreg differentiation. Interestingly, while IL-1β-treated cells exhibited only minor changes in metabolism, DMOG treatment decreased iTreg mitochondrial respiration and increased their glycolytic capacity. In conclusion, exposure to inflammatory stimuli profoundly inhibits human Treg differentiation HIF-1α dependent, suggesting that targeting HIF-1α could be a strategy to foster iTreg differentiation in an inflammatory milieu. However, IL-1β deleterious effect does not appear to be completely driven by metabolic changes. These data thus suggest that several mechanisms contribute to the regulation of iTreg differentiation, but the timing and respective requirement for each pathway vary depending on the milieu in which iTreg differentiate.

The transcription factor hypoxia inducible factor‐1α (HIF‐1α) mediates the metabolic adaptation of cells to hypoxia and T‐helper cell fate. However, HIF‐1α regulation in CD4+ T cells (T cells) remains elusive. Here we observed that depletion of oxygen (O2⩽2%) alone was not sufficient to induce HIF‐1α expression in T cells. However, when hypoxic T cells were stimulated, HIF‐1α was expressed and this was dependent on nuclear factor‐κB‐ and nuclear factor of activated T cell (NFAT)‐mediated transcriptional upregulation of Hif‐1α mRNA. HIF‐1α upregulation could be blocked by drugs inhibiting NF‐κB, NFAT or mammalian target of rapamycin precluding CD4+ T‐cell stimulation or translation in T cells, as well as by blocking transcription. CD3, CD28, phorbol‐12‐myristat‐13‐acetat (PMA) or ionomycin‐stimulated T cells did not express HIF‐1α under normoxic conditions. In conclusion, regulation of HIF‐1α expression in CD4+ T cells in hypoxia gravely relies on its transcriptional upregulation and subsequent enhanced protein stabilization.

The central oxygen sensitive transcription factor HIF-1α has been implicated in the differentiation of n(T(reg)) and Th17 cells and to orchestrate metabolic changes of activated T cells. However, data on the functional relevance of HIF-1α and Hox, in general, for nT(reg)-suppressive activity and T cell function in primary human cells are still missing. Therefore, we analyzed the effect of Hox and HIF-1α on human T(res), n(Treg), and Th17 cells. Under Hox, nT(reg)-mediated suppression of T(res) proliferation, CD25 expression, and secretion of IFN-γ were significantly reduced, whereas expression levels of VEGF, TNF-α, and IL-10 were significantly increased. In contrast to observations in mice, Th17 lineage commitment, as determined by RORγt expression, was not affected by activation or inhibition of HIF-1α expression using DMOG or YC-1 treatment, respectively. Nevertheless, the secretion of IL-17A was increased by DMOG and reduced by YC-1 under Th17-skewing conditions in a dose- dependent manner. In conclusion, Hox and HIF-1α substantially influence human T cell-mediated immune responses by modulation of nT(reg)-suppressive function and IL-17A secretion by Th17 cells.