Myelin-specific CD4 T effector cells (Teffs), Th1 and Th17 cells, are encephalitogenic in experimental autoimmune encephalomyelitis (EAE), a well-defined murine model of multiple sclerosis (MS) and implicated in MS pathogenesis. Forkhead box O 1 (FoxO1) is a conserved effector molecule in PI3K/Akt signaling and critical in the differentiation of CD4 T cells into T helper subsets. However, it is still unclear whether FoxO1 may be a target for redirecting CD4 T cell differentiation and benefit CNS autoimmunity.
Using a selective FoxO1 inhibitor AS1842856, we determined the effects of FoxO1 inhibition in regulating myelin-specific Th1 and Th17 cells, and the transcriptional balance of T-bet and Foxp3 in myelin-specific CD4 T cells from EAE mice. The effects of AS1842856 in regulating the encephalitogenicity of myelin-specific T cells and the expansion of human Th1 cells from MS patients were also characterized. Furthermore, we characterized the potential role of FoxO1 in mediating PD-1 signaling in CD4 T cells, critical for regulating Teff and Treg cells.
Inhibition of FoxO1 suppressed the differentiation and expansion of Th1 cells. Moreover, the transdifferentiation of Th17 cells into encephalitogenic Th1-like cells was suppressed by FoxO1 inhibition upon reactivation of myelin-specific CD4 T cells from mice with EAE. When FoxO1 was inhibited in myelin-specific CD4 T cells, the transcriptional balance skewed from the Th1 transcription factor T-bet toward the Treg transcription factor Foxp3. Myelin-specific CD4 T cells treated with the FoxO1 inhibitor were less encephalitogenic in adoptive transfer EAE studies compared to control-treated cells. Inhibition of FoxO1 in T cells from MS patients significantly suppressed the expansion of Th1 cells. Furthermore, the immune checkpoint programmed cell death protein-1 (PD-1)-induced Foxp3 expression in CD4 T cells was impaired by FoxO1 inhibition, consistent with a bias toward Treg induction.
These data illustrate an important role of FoxO1 signaling in CNS autoimmunity via regulating autoreactive Teff and Treg balance.