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 (1α，25-dihydroxyvitamin D; 1α，25(OH)D) 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 1α，25(OH)D 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 1α，25(OH)D exposure. Pharmacological inhibition of PFKFB4 reversed the 1α，25(OH)D-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 1α，25(OH)D-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 1α，25(OH)D.