Defining how phospholipid signaling networks control Th17 differentiation and effector function - Defining how phospholipid signaling networks control Th17 differentiation and effector function Autoimmune diseases represent a substantial public health burden, affecting over 7% of the population (23.5 million people) and incurring costs upward of 1 billion dollars per year in the US alone. The adaptive immune system generates an autoreactive response when self-tolerance mechanisms are broken. In this autoreactive cascade, proinflammatory CD4+ T cell populations develop, damage host tissues, and cause disease pathology. In autoimmune diseases, including MS and rheumatoid arthritis, the ratio of proinflammatory Th17 to regulatory T cells (Treg) skews towards elevated Th17. Recent work suggests that reestablishing a healthy Treg/Th17 balance has therapeutic potential for autoimmune diseases. The required cytokines and transcription factors that program Treg versus Th17 differentiation are well established. Much less is known about the intracellular signaling networks that drive Th17 differentiation. Identifying signaling proteins essential for Th17s and dispensable for Tregs represent “vulnerable liabilities” to target with small molecule inhibitors. In our recent publication, we systematically apply phosphoproteomics to profile kinase signaling during Treg versus Th17 differentiation. Our foundational phosphoproteomics datasets identify many new signaling circuits representing new basic T cell biology and provide possible targets for drug therapies to block proinflammatory Th17 cells while maintaining Treg function. We determined that phosphatidylinositol kinase, PIKFYVE, was differentially regulated during Treg versus Th17 differentiation. Our biochemical analysis reveals that PI(3,5)P2 synthesis, the product of PIKFYVE, is upregulated explicitly during Th17 differentiation, arguing that PI(3,5)P2 is an essential signaling molecule specific to the Th17 differentiation program. Blocking PIKFYVE diminished Th17 differentiation and disease in the experimental autoimmune encephalomyelitis (EAE) model. Our findings serve as a solid rationale for mechanistically defining how PIKFYVE/PI(3,5)P2 promotes Th17 differentiation and EAE disease. Inhibiting PIKFYVE is as effective at diminishing EAE disease as some FDA-approved therapeutics for MS, establishing PIKFYVE/PI(3,5)P2 as a high impact target. Based on our published and preliminary data, we propose the central hypothesis that PIKFYVE/PI(3,5)P2 is required for Th17 differentiation and EAE pathology. We will determine how PIKFYVE/PI(3,5)P2 regulates immune cell function in the EAE model. This analysis will determine if genetic deletion of PIKFYVE in CD4+ T cells downmodulates Th17 differentiation in the EAE model and reduces neuroinflammation. We will also determine if blocking PIKFYVE diminishes effector T cell function. Additionally, will determine the molecular mechanisms by which PIKFYVE/PI(3,5)P2 regulates Th17 differentiation. This analysis will identify how PIKFYVE regulates kinase networks and transcriptional programs to support Th17 differentiation. Completing this work will define the importance of PIKFYVE in T cell biology and inform therapeutic strategies for autoimmune diseases caused by Th17 cells.
