Endocrine Abstracts

The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D), acting via the vitamin D receptor (VDR) is a potent regulator of gene expression, with effects on skeletal and extra-skeletal physiology. We have shown that actions of 1,25D on bone-forming osteoblasts also involve regulation of microRNAs (miRNAs) that play a key role in the functional development of these cells. In the current study, we have investigated miRNAs as mediators of innate and adaptive immune responses to 1,25D. Human peripheral blood mononuclear cells were used to generate models of dendritic cell (DC) maturation and function, and T cell activation and function. DCs matured in the presence of 1,25D, or treated with 1,25D following maturation, showed decreased expression of antigen-presenting marker CD86. Quantitative RT-PCR analysis of 7 candidate miRNAs associated with immune function (miR21, miR29a, miR145, miR146a, miR155, miR627 and let7i) showed miR21 was supressed significantly (0.39-fold) by 1,25D in immature DCs (5 days vehicle culture, followed by 10 nM 1,25D, 24 h), and miR155 was induced significantly (3.66-fold) in tolerogenic DCs after maturation with LPS (6 days culture with 10 nM 1,25D). For studies of adaptive immunity, T cells were activated for 24 h with anti-CD3/CD28 and cytokines (IL-2, TGFβ, IL-1β, IL-6, IL-23) to stimulate VDR expression. In these cells 1,25D (10 nM, 0–72 h) increased the cell-surface antigen CTLA4 and decreased the inflammatory cytokine IFNγ in a time-dependent fashion. This was associated with increased miR29a and miR146a (8 h), miR145 (24 h), and miR627 (48–72 h). These data indicate that miRNAs are important targets for vitamin D in both the innate (DC) and adaptive (T cell) immune systems. Future studies will aim to identify other vitamin D targeted miRNAs using unbiased screening approaches, and will explore the functional impact of these miRNAs on immune regulation by vitamin D.