Endocrine Abstracts

The hormonally active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D) acting via the vitamin D receptor (VDR) is a potent transcriptional regulator, with effects on skeletal and extra-skeletal physiology. We have shown previously that skeletal responses to 1,25D also involve regulation of microRNAs (miRNAs); small non-coding RNAs with an emerging role in epigenetics. To assess the role of miRNAs in innate immune responses to 1,25D we utilised in vitro models of human mononuclear cell-derived dendritic cell (DC) differentiation and maturation. DCs from n=6 healthy donors were differentiated for 5 days with IL-4 and GM-CSF, with or without 1,25D (10 nM). DCs were then matured for a further 24 hrs with combinations of LPS and/or 1,25D to generate 6 different DC phenotypes (iDC, itolDC, mDC, mtolDC, iDC+1,25D, mDC+1,25D). Candidate miRNA analyses showed that expression of miR155 and let-7i was elevated in mature mDC+1,25D relative to immature iDC+1,25D, underlining the potential for miRNA regulation in DCs. Quantitative RT-PCR array analysis (n=6 donor replicates) of 372 miRNAs closely associated with immune function showed that 44 miRNAs were regulated by LPS alone (>2-fold change), 174 were regulated by 1,25D alone, and 72 by both treatments. MiR-155 and miR-506 were suppressed by 1,25D (P<0.05) after 120 hour treatment in the presence of LPS. Preliminary pathway analysis data of predicted targets for miR-155 and miR-506 showed both miRNAs may target multiple transcripts. These data indicate that miRNAs are important targets for vitamin D in mediating innate immune responses by DCs. We postulate that miRNAs downregulated following 1,25D treatment may be involved in regulating inflammatory responses. Future work will focus on targeted over-expression or knockdown of specific miRNAs to explore the functional impact of these non-coding RNAs in mediating the immunomodulatory effects of vitamin D.