Transcriptional profile of thymic and splenic regulatory T cells, sufficient and deficient in miR-181a

MicroRNAs (miRNAs) are expressed from a class of small non-protein coding RNA molecules. Growing evidence shows that miRNAs are potent mediators of post-transcriptional gene silencing and emerged to be critical in the regulation of innate and adaptive immune responses (Ansel KM, Immunol Rev 2013, p5; Baumjohann D, Nature Rev Immunol 2013, p666). MicroRNA-181a (miR-181a) constitutes the most prominently expressed miRNA species in DP thymocytes (Neilson JR, Genes Dev 2007, p578; Kirigin FF, JI 2012, p3257) and has been associated with modulating TCR signal strength via targeting serine/threonine as well as tyrosine phosphatases (Li Q-J, Cell 2007, p147). Consequently, elevated expression of miR-181a results in reduced phosphatase activity and increased TCR signal strength. The effect of aberrant expression of miR-181a on TCR signaling has been already analyzed employing short-term assays and in vitro organ cultures. Our group started to investigate the consequences of miR-181a/b-1 deletion on T cell development in vivo in the steady state. To this end, we developed a new mouse model - miR-181a/b-1 knockout mice (Zietara N et al, PNAS 2013b). During investigations of the immune system of miR-181a/b-1 deficient mice we discovered that these miRNAs are critical for the development of invariant natural killer (NK) T cells. Such cells are known to be selected by a high affinity agonist ligands, thus they are particularly sensitive to the modulation of TCR signaling thresholds, which is achieved by miR-181a/b-1 (Zietara N et al, PNAS 2013b). Furthermore we hypothesized that similar regulation might apply for the other T cell populations selected under high TCR signal strength, like Treg cells. Thus our current research focuses on the role of miR-181a/b-1 during Treg cell development in the thymus as well as on their function in the periphery.

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