Excessive miR-27 expression impairs regulatory T cell-mediated immunological tolerance [CD4cre miR-23 clusterTg Tr]

MicroRNAs (miRNAs) are tightly regulated in the immune system, as aberrant expression of miRNAs often results in hematopoietic malignancies and autoimmune diseases. Previously, elevated levels of miR-27 in T cells isolated from multiple sclerosis patients has been suggested to facilitate disease progression through inhibiting Th2 immunity and promoting pathogenic Th1 responses. Here we demonstrate that while mice with T cell-specific overexpression of miR-27 harbor dysregulated Th1 responses and develop autoimmune pathology, these disease phenotypes are not driven by miR-27 in effector T cells in a cell-autonomous manner but rather resulted from a perturbed regulatory T (Treg) cell compartment. Excessive miR-27 expression in T cells severely impairs Treg cell differentiation. Moreover, Treg cells with exaggerated miR-27-mediated gene regulation exhibit diminished homeostasis and suppressor function in vivo. Mechanistically, miR-27 represses several known as well as previously uncharacterized targets that play critical roles in controlling multiple aspects of Treg cell biology. Collectively, our data show miR-27 functions as a key regulator in Treg cell development and function and suggest that proper regulation of miR-27 is pivotal to safeguard Treg cell-mediated immunological tolerance. Treg cells isolated from mice with T cell-specific overexpression of the entire miR-23 cluster or individual miR-23 family members as well as from mice with T cell-specific deletion of both miR-23a/b clusters.