Targeting TGFb/IFNy-IRF8 Signaling to Modulate Monocytes and their Crosstalk with Microglia and Astrocytes to Treat Multiple Sclerosis

PROJECT SUMMARY Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS). Despite advances in our understanding of MS pathophysiology, there are minimal disease-modifying treatments or preventions for innate-mediated, secondary-progressive forms of MS. Our long-term goal is to define the role of interactions between microglia and recruited monocytes at different stages of MS and determine which phenotypes and functions lead to progressive forms of MS. We made the following preliminary observations: 1) ITGB8-TGFb signaling regulates astrocyte-microglia crosstalk in neurodegeneration with Irf8 regulation; 2) Deleting microglial Irf8 enhances an MGnD phenotype associated with suppression of TGFb-IFNg upstream regulators; 3) monocytes from SPMS patients have a suppression in IRF8 and induction of neurodegenerative signature; and 4) TGFb-IFNg stimulation restores homeostatic signature in monocytes/macrophages. Based on these findings, we hypothesize that TGFb/IFNg-IRF8 axis induces beneficial microglia and monocyte phenotypes in MS. Here, we propose a multi-disciplinary approach that integrates novel tools, experimental paradigms and our complementary expertise on monocytes, microglia, astrocytes and MS and its pre-clinical models. We will address our hypothesis in the following aims: Aim 1: Investigate the role of TGFb/IFNg-IRF8 signaling in monocytes on the regulation of microglia in MS models. We will 1) Determine the effect of TGFb/IFNg-mediated IRF8 signaling in monocytes on the regulation of microglial phenotypes in EAE and 2) Determine the role of IRF8 in monocytes in the regulation of ITGB8-mediated astrocyte-microglia crosstalk, and 3) Evaluate the effects of monocytes on microglia-astrocytes crosstalk in situ by MERFISH analysis. Aim 2: Modulate microglia-astrocyte crosstalk via IRF8-ITGB8 signaling in MS models. Irf8 deletion polarizes microglia to a neurodegenerative phenotype, activating astrocytes via a Lgals3-ITGB8 negative feedback regulation. To elucidate this crosstalk, we will 1) Conditionally remove IRF8 in pan-microglia during the demyelination stage; 2) Perform fate-map and conditional deletion of Irf8 in MGnD microglia; and 3) Genetically and pharmacologically inhibit ITGB8 in astrocytes. Aim 3: Establish whether modulation of TGFb/IFNg-IRF8 signaling in human monocytes and microglia can serve as a novel therapeutic modality in MS. We will 1) Determine whether restoration of IRF8 signaling via TGFb/IFNg signaling in SPMS monocytes polarizes homeostatic microglia; 2) Elucidate how IRF8 modulation in monocytes affects microglia-astrocyte crosstalk, and whether this effect is ITGB8-dependent; 3) Investigate the role of IRF8 in human microglia and their contribution to demyelination in humanized cuprizone model. IN SUMMARY, this application will elucidate the previously unrecognized role of TGFb/IFNg-IRF8 axis in monocytes-astrocyte-microglia crosstalk in multiple sclerosis progression.