1,25-dihydroxyvitamin D3 is an autonomous regulator of the transcriptional changes leading to a tolerogenic dendritic cell phenotype.

Activation of vitamin D receptor (VDR) by 1,25-dihydroxyvitamin D(3) (1,25-vitD) reprograms dendritic cells (DC) to become tolerogenic. Previous studies suggested that 1,25-vitD could inhibit the changes brought about by differentiation and maturation of DCs. Underpinning the described phenotypic and functional alterations, there must be 1,25-vitD-coordinated transcriptional events. However, this transcriptional program has not been systematically investigated, particularly not in a developmental context. Hence, it has not been explored how 1,25-vitD-regulated genes, particularly the ones bringing about the tolerogenic phenotype, are connected to differentiation. We conducted global gene expression analysis followed by comprehensive quantitative PCR validation to clarify the interrelationship between 1,25-vitD and differentiation-driven gene expression patterns in developing human monocyte-derived and blood myeloid DCs. In this study we show that 1,25-vitD regulates a large set of genes that are not affected by differentiation. Interestingly, several genes, impacted both by the ligand and by differentiation, appear to be regulated by 1,25-vitD independently of the developmental context. We have also characterized the kinetics of generation of 1,25-vitD by using three early and robustly regulated genes, the chemokine CCL22, the inhibitory receptors CD300LF and CYP24A1. We found that monocyte-derived DCs are able to turn on 1,25-vitD sensitive genes in early phases of differentiation if the precursor is present. Our data collectively suggest that exogenous or endogenously generated 1,25-vitD regulates a large set of its targets autonomously and not via inhibition of differentiation and maturation, leading to the previously characterized tolerogenic state.