Vitamin D controls the capacity of human dendritic cells to induce functional regulatory T cells by regulation of glucose metabolism

Tolerogenic dendritic cells (tolDCs) instruct regulatory T cells (Tregs) to dampen autoimmunity. Active vitamin D-3 (1 alpha,25-dihydroxyvitamin D-3; 1 alpha,25(OH)(2)D-3) imprints human monocyte-derived DCs with tolerogenic properties by reprogramming their glucose metabolism. Here we identify the glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 (PFKFB4) as a critical checkpoint and direct transcriptional target of 1 alpha,25(OH)(2)D-3 in determining the tolDC profile. Using tracer metabolomics, we show that PFKFB4 activity is essential for glucose metabolism, especially for glucose oxidation, which is elevated upon 1 alpha,25(OH)(2)D-3 exposure. Pharmacological inhibition of PFKFB4 reversed the 1 alpha,25(OH)(2)D-3-mediated shift in metabolism, DC profile and function, as determined by expression of inhibitory surface markers and secretion of regulatory cytokines and factors. Moreover, PFKFB4 inhibition in 1 alpha,25(OH)(2)D-3-treated DCs blocked their hallmark capacity to induce suppressive Tregs. This work demonstrates that alterations in the bioenergetic metabolism of immune cells are central to the immunomodulatory effects induced by 1 alpha,25(OH)(2)D-3.