In vivo transcriptome changes of human white blood cells in response to vitamin D

In the vitamin D intervention study VitDbol (NCT02063334) blood samples were drawn directly before an oral bolus (2000 μg vitamin D₃) and 24 h later. The focus of phase II of VitDbol was the transcriptome-wide analysis of the effects of vitamin D gene expression in human peripheral blood mononuclear cells (PBMCs). All five participants responded in an individual fashion to the bolus by increases in serum levels of the vitamin D metabolites 25-hydroxyvitamin D₃ (25(OH)D₃) and 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃). RNA sequencing identified 15.040 commonly expressed genes in PBMCs, 702 (4,7%) of which were significantly (p < 0,05) affected by the vitamin D₃ bolus. KEGG pathway analysis suggested that these genes are involved in general protein translation, monocyte differentiation and cellular growth control. Previously published transcriptome-wide studies in comparable cell systems confirmed 234 of the 702 vitamin D target genes, leaving many genes, such as HLA-A and HLA-C, as novel discoveries. Interestingly, in vivo stimulated PBMCs of this study showed a larger number of common vitamin D target genes with the monocytic cell line THP-1 than with in vitro stimulated PBMCs. The expression pattern of vitamin D target genes differed significantly between individuals and the average expression change can serve as a marker for vitamin D responsiveness. In conclusion, this study demonstrates that under in vivo conditions changes in 25(OH)D₃ and 1,25(OH)₂D₃ serum concentrations alter the expression of more than 700 vitamin D target genes in human leukocytes.