Selective miRNA disruption in Tregs leads to uncontrolled autoimmunity

A new Treg-specific, FoxP3-GFP-hCre BAC transgenic was crossed to a conditional Dicer knock-out mouse strain to analyze the role of microRNAs (miRNA) in the development and function of regulatory T cells (Tregs). Although thymic Tregs developed normally in this setting, the cells showed evidence of altered differentiation and dysfunction in the periphery. Dicer-deficient Treg lineage cells failed to remain stable as a subset of cells down-regulated the Treg-specific transcription factor, FoxP3, while the majority expressed altered levels of multiple genes and proteins (including Neuropilin 1, GITR and CTLA-4) associated with the Treg fingerprint. In fact, a significant percentage of the Treg lineage cells took on a Th memory phenotype including increased levels of CD127, IL-4, and interferon-g. Importantly, Dicer-deficient Tregs lost suppression activity in vivo; the mice rapidly developed fatal systemic autoimmune disease resembling the FoxP3 knockout phenotype. These results support a central role for miRNAs in maintaining the stability of differentiated Treg function in vivo and homeostasis of the adaptive immune system.

6