The role of microRNAs in allergic airways disease and T cell biology

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and their cellular expression is differentially regulated at various developmental and functional stages. The objective of my PhD research was to assess 1) whether miRNAs are differentially regulated in an ovalbumin-induced model of allergic airways disease, 2) whether corticosteroid (dexamethasone) treatment alters miRNA expression, 3) whether miRNAs play a functional role in disease development, 4) whether miRNAs are differentially regulated in Th cell differentiation and 5) whether miRNAs play a functional role in Th cell differentiation and function. To address these questions, we performed miRNA profiling on the lungs of allergic mice and compared these profiles to lung profiles from dexamethasone-treated mice and non-allergic controls, using miRNA microarray analysis and real-time PCR. We generated distinct miRNA signatures and identified 29 miRNAs that showed significantly altered expression in allergic lungs. Analysis of predicted miRNA targets revealed novel target genes with altered mRNA expression and demonstrated synergistic miRNA regulation within allergic lungs. Using antagomirs, we inhibited the function of two specific miRNAs (mmu-miR-155-5p and mmu-miR-449a-5p) in the airway wall and investigated the effect on hallmark features of allergic airways disease. While antagomir administration successfully reduced expression of targeted miRNAs, it failed to induce alterations to disease phenotype, suggesting multiple miRNAs regulate changes associated with allergic disease. We further show that antagomir delivery to the lung achieves only variable efficacy across different cell types. While antagomir delivery efficiently reduced specific miRNA expression in myeloid cells, lymphocytes are only partially targeted, suggesting that therapeutic targeting of miRNA function in lymphocytes may require a different approach. We further performed miRNA profiling in naive and effector Th cells in vitro and identified a global up-regulation of miRNA expression in activated Th cells. Using antagomirs, we inhibited the function of several miRNAs and again found that antagomir delivery to Th cells proves inadequate for suppression of target miRNA expression.