Treg sensitivity to FasL and relative IL-2 deprivation drive idiopathic aplastic anemia immune dysfunction.

Idiopathic aplastic anemia (AA) has 2 key characteristics: an autoimmune response against hematopoietic stem/progenitor cells and regulatory T-cells (Tregs) deficiency. We have previously demonstrated reduction in a specific subpopulation of Treg in AA, which predicts response to immunosuppression. The aims of the present study were to define mechanisms of Treg subpopulation imbalance and identify potential for therapeutic intervention. We have identified 2 mechanisms that lead to skewed Treg composition in AA: first, FasL-mediated apoptosis on ligand interaction; and, second, relative interleukin-2 (IL-2) deprivation. We have shown that IL-2 augmentation can overcome these mechanisms. Interestingly, when high concentrations of IL-2 were used for in vitro Treg expansion cultures, AA Tregs were able to expand. The expanded populations expressed a high level of p-BCL-2, which makes them resistant to apoptosis. Using a xenograft mouse model, the function and stability of expanded AA Tregs were tested. We have shown that these Tregs were able to suppress the macroscopic clinical features and tissue manifestations of T-cell-mediated graft-versus-host disease. These Tregs maintained their suppressive properties as well as their phenotype in a highly inflammatory environment. Our findings provide an insight into the mechanisms of Treg reduction in AA. We have identified novel targets with potential for therapeutic interventions. Supplementation of ex vivo expansion cultures of Tregs with high concentrations of IL-2 or delivery of IL-2 directly to patients could improve clinical outcomes in addition to standard immunosuppressive therapy.

miR-181c-BRK1 axis plays a key role in actin cytoskeleton-dependent T cell function.

MicroRNAs are short endogenous noncoding RNAs that play pivotal roles in a diverse range of cellular processes. The miR-181 family is important in T cell development, proliferation, and activation. In this study, we have identified BRK1 as a potential target of miR-181c using a dual selection functional assay and have showed that miR-181c regulates BRK1 by translational inhibition. Given the importance of miR-181 in T cell function and the potential role of BRK1 in the involvement of WAVE2 complex and actin polymerization in T cells, we therefore investigated the influence of miR-181c-BRK1 axis in T cell function. Stimulation of PBMC derived CD3+ T cells resulted in reduced miR-181c expression and up-regulation of BRK1 protein expression, suggesting that miR-181c-BRK1 axis is important in T cell activation. We further showed that overexpression of miR-181c or suppression of BRK1 resulted in inhibition of T cell activation and actin polymerization coupled with defective lamellipodia generation and immunological synapse formation. Additionally, we found that BRK1 silencing led to reduced expressions of other proteins in the WAVE2 complex, suggesting that the impairment of T cell actin dynamics was a result of the instability of the WAVE2 complex following BRK1 depletion. Collectively, we demonstrated that miR-181c reduces BRK1 protein expression level and highlighted the important role of miR-181c-BRK1 axis in T cell activation and actin polymerization-mediated T cell functions.