MicroRNAs and immunomodulation by vitamin D

Li, Danyang (2019). MicroRNAs and immunomodulation by vitamin D. University of Birmingham. Ph.D.

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Abstract

The active form of vitamin D, 1,25(OH)\(_2\)D3, plays well-established roles in calcium regulation and bone formation. 1,25(OH)\(_2\)D3 is also thought to exert immunoregulatory effects upon cells of the innate (dendritic cell) and adaptive (T cell) immune systems, that may impact health and disease. In recent years, the role of 1,25(OH)\(_2\)D3 has been implicated in autoimmune diseases such as rheumatoid arthritis (RA). 1,25(OH)\(_2\)D3 brings about genetic and epigenetic changes within immune cells, the latter which may include effects of microRNAs (miRNAs); small non-coding RNAs with an important regulatory role.

To study the role of 1,25(OH)\(_2\)D3 on miRNAs in RA, we utilised n=20 (RA) and n=7 (reactive arthritis, ReA) matched patient serum and synovial fluid (SF) samples to derive measurements of vitamin D metabolite concentrations by LC-MS/MS, vitamin D binding protein abundance by ELISA, and circulating miRNA expression by qPCR. To study the role of 1,25(OH)\(_2\)D3 on miRNAs in healthy immune cells, we also generated \(in\) \(vitro\) models of dendritic cells (DC) and CD4+ T cells, treated with 1,25(OH)\(_2\)D3 or vehicle at different stages of development. An unbiased array approach was then used to screen 372 miRNAs closely related to inflammation in the DC and T cell models. Bioinformatic analyses were used to identify predicted gene targets of significantly regulated miRNAs in both DC and T cells.

Results showed that 1,25(OH)\(_2\)D3 in SF was low or undetectable in 13/20 RA and 4/7 ReA samples. MiR-146a and miR-155 was up-regulated in RA SF compared to serum, but did not significantly correlate with RA disease markers. In DC, miR-155 but not miR-146a was up-regulated by LPS-induced cell maturation in the presence or absence of 1,25(OH)\(_2\)D3. Global down-regulation of miRNAs was observed after either short or long-term treatment of DC with 1,25(OH)\(_2\)D3. This was due, in part, to suppression of expression for miRNA processing genes. In contrast to DC, global miRNA down-regulation was not observed in T cells treated with 1,25(OH)\(_2\)D3. Notably, MiR-155 was up-regulated by cell activation but not 1,25(OH)\(_2\)D3, and miR-212-3p was up-regulated by activation and 1,25(OH)\(_2\)D3.

Together, these results suggest that any 1,25(OH)\(_2\)D3 generated within the synovial microenvironment may be restricted to the cells involved in immunoregulation within this tissue. The role of miR-146a and miR-155 in immune cells is still unclear; it is unlikely that these miRNAs are actively mediating gene silencing to cause inflammation within the local environment, but rather they are maintained as a reserve of miRNAs not associated with their target gene. Global down-regulation of miRNAs following 1,25(OH)\(_2\)D3 in DC, but not T cells, suggests a role for 1,25(OH)\(_2\)D3-mediated miRNA down-regulation as opposed to decreased miRNA synthesis. Coupled with bioinformatic tools and gene ontology analysis, there is potential to identify novel roles for 1,25(OH)\(_2\)D3-responsive miRNAs in the prediction and pathogenesis of inflammatory disease.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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