AbstractMonocytes are innate immune cells that play a central role in the initiation, propagation and resolution of inflammation. In rheumatoid arthritis monocytes contribute to pathology by producing inflmmatory mediators and interacting with adaptive immune cells. miRNAs are short non-coding strands of RNA that negatively regulate mRNA by binding to the target 3’UTR. miRNA expression has previously been reported to be dysregulated in monocytes from the synovial fluid from patients with RA. Previous work has shown that over-expression of miR-155 induce a pro-inflammatory effect in monocytes. This PhD thesis project aimed to investigate the regulation of miR-155 and miR-210 in health and disease, the effect of miR-155 and miR-210 over-expression in healthy human CD14+ monocytes and investigating the transcriptional signature of miR-155 transfected monocytes.
Expression of miR-155 and miR-210 was significantly increased in CD14+ monocytes from the synovial fluid from patients with RA or PsA. Upon activation with a pro-inflammatory stimuli such as LPS or synovial fluid from RA patients, healthy CD14+ monocytes increased the expression of miR-155 and miR-210.
miR-155 and miR-210 mimics were transfected into healthy CD14+ monocytes to investigate their function. Over-expression of miR-155 induced the spontaneous production of the cytokines TNFα, IL-6, IL-8 and IL-10, increased resistance to spontaneous apoptosis and increased the expression of HLA-DR, CD86, CD80, CD40 and PD-L1. Finally, CD4+ T cells co-cultured with miR-155 transfected monocytes had a higher frequency of cells that expressed IL-10 and IFNγ in a PDL1:PD1 independent manner. In contrast, miR-210 over-expression did not have an effect of CD14+ monocyte cytokine production, survival or phenotype.
To better understand the transcriptional signature of miR-155 transfected CD14+ monocytes RNA-sequencing was carried out. miR-155 significantly differentially expressed 1,690 genes in CD14+ monocytes. This list of genes was used in conjunction with a list of predicted target genes of miR-155 and a list of genes down-regulated in synovial fluid CD14+ cells from RA patients to identify predicted target genes of miR-155 that are down-regulated in RA. This generated a list of 15 potential target genes previously undescribed in the context of RA.
These data indicate that miR-155 has a pro- and anti-inflammatory effect in CD14+ monocytes, with an increased production of pro-inflammatory cytokines, increased expression of co-stimulatory markers. However, the increased expression of the co-inhibitory marker PD-L1 and ability to polarise CD4+ T cells to express more IL-10 suggest that miR-155 may also play a role in resolving inflammation. Better understanding of miR-155 function in monocytes could provide therapeutic targets in a disease setting.
|Date of Award
|1 Feb 2021
|Leonie Taams (Supervisor)