Kv1.3 deletion induces Foxo1 expression independently of Foxp3 and biases Th cells toward an immunoregulatory phenotype (P5127)

Myelin-reactive Th cells in patients with multiple sclerosis (MS) express Kv1.3, a voltage-gated K+ channel essential for Th cell activation and function. Recently, we have demonstrated that Kv1.3 deletion prevents experimental autoimmune encephalomyelitis, a murine model of MS, by inducing a regulatory Th cell phenotype independently of Foxp3. However, the mechanism by which Th cells with regulatory properties develop in the absence of Kv1.3 remains unclear. Foxo1 has been shown to function in induction of tolerance and in Treg cell lineage commitment. Foxo1 nuclear exclusion is induced in effector Th cells by downstream T cell receptor (TCR) signaling. Herein, we demonstrate an increase in nuclear Foxo1, with concomitant reduction in T-bet, in Kv1.3 KO Th cells. Surprisingly, Kv1.3 deletion does not impair TCR-induced intracellular Ca2+ flux or the activation of the Ca2+-sensitive transcription factor NF-AT. Instead, the absence of Kv1.3 leads to p56lck relocalization from TCR to the IL-2R complex, thereby contributing to the increase in Foxo1 and the differentiation of Treg cells in the absence of changes in Foxp3 expression. Herein, we demonstrate that regulatory Th cells are generated in the absence of Kv1.3 as a consequence of disrupted TCR signaling during formation of the immunological synapse, rather than impaired Ca2+ flux, resulting in upregulation of Foxo1. These data highlight Foxo1 as a novel target for induction of Treg cells in autoimmune diseases such as MS.