Pathogenic Astrocyte Populations in EAE and MS

PROJECT SUMMARY Multiple Sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that constitutes the leading cause of neurologic disability in young adults. Astrocytes, microglia and monocytes play important roles in MS and its model, experimental autoimmune encephalomyelitis (EAE), but the mechanisms that regulate their activity are poorly understood. The study of astrocyte and microglia regulation may identify mechanisms of pathogenesis and therapeutic targets in MS, particularly for the progressive phase of the disease. Our long-term goal is to develop therapies to limit astrocyte pathogenic activities in MS. During the course of our studies we made the following preliminary observations: 1) SigmaR1-IRE1a signaling activates the transcription factor XBP1 in astrocytes, promoting microglial activation, monocyte recruitment to the CNS and disease pathology during EAE; 2) Astrocyte-specific XBP1 knockdown ameliorates EAE; 3) XBP1 is activated in an astrocyte subset in EAE and MS; 4) XBP1 activation in astrocytes is associated to increased VEGF-B signaling 5) Microglia and CNS-recruited monocytes produce VEGF-B during EAE; and 6) VEGF-B produced by microglia boost astrocyte pro-inflammatory activities. We hypothesize that active XBP1 (XBP1s) drives a pathogenic astrocyte subset (XBP1s+ astrocytes) in MS and EAE, which is controlled by microglia- and monocyte-produced VEGF-B. Thus, we propose to study the role of SigmaR1-IRE1a-XBP1 signaling in astrocytes in EAE and MS, and its potential as a therapeutic target. Our specific aims are: SPECIFIC AIM 1: Does XBP1 activation define a subset of pathogenic astrocytes? We propose to: 1) Characterize XBP1s+ astrocytes in EAE using Focused Interrogation of cells by Nucleic acid Detection and Sequencing (FIND-seq) a method, which we developed to study cell subsets in-depth, and 2) Generate a spatiotemporal map of the localization, regulation and cell interactions of XBP1s+ astrocytes and other cell subsets in EAE and MS using MERFISH (Multiplexed error robust fluorescence in situ hybridization). SPECIFIC AIM 2: How do microglia and monocytes control XBP1s+ astrocytes? We propose to: 1) Define the role of VEGF-B produced by microglia and monocytes on the control of XBP1s+ and other astrocyte subsets during EAE, and 2) Identify by NICHE-seq additional pathways involved in the control of XBP1s+ and other astrocyte subsets by microglia and monocytes during EAE. SPECIFIC AIM 3: Is SigmaR1 a therapeutic target to modulate CNS inflammation? We propose to: 1) Evaluate the therapeutic value of the clinical-grade CNS penetrant SigmaR1 antagonist S1RA on EAE, and 2) Define the effects of S1RA on XBP1s+ astrocytes, and other cell subsets in the CNS in EAE. IN SUMMARY, this project studies a novel astrocyte subset, the molecular and cellular mechanisms that control it, its distribution and cell interactions throughout the CNS, and its potential as a therapeutic target in MS.