The AIM2 Inflammasome Is Activated In Astrocytes During EAE

Abstract

The inflammasomes are a group of pattern recognition receptors (PRRs) with unique characteristics and critical to innate immunity by translating microbial and damage signals into inflammation. While early investigation into inflammasomes focused on their ability to respond to invading pathogens, now inflammasomes are known to collectively respond to a broad range of sterile damage signals. Indeed, several inflammasomes, and most notably the NLRP3 inflammasome, are known to promote pathogenesis of several autoinflammatory conditions, including the autoimmune neuroinflammation which is modeled in the mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). While this association of inflammasomes with EAE is well established, the timing, tissue localization, and cell-specificity of inflammasome activation in the central nervous system (CNS) remains poorly understood during disease. Thus, this dissertation details our investigation into the specific sites and timing of inflammasome activation during EAE, as well as determining which inflammasome is activated in the CNS during disease. The interrogation of inflammasome activation in vivo during disease states required our use of genetically modified mice with fluorescent-protein tagged inflammasome adaptor ASC (ASC-Citrine), which serves as a reporter of active inflammasomes. We identified in situ inflammasome activation in specific CNS cell types of these mice using antibody-based immunofluorescent staining techniques and confocal microscopy, and confirmed the result by genetically modified mice, which allowed cell-specific expression of ASC-Citrine. Further, we used mice genetically deficient in inflammasome components ASC and AIM2 to investigate the involvement of these proteins in disease development. Our study concluded with several insights. Firstly, inflammasome activation occurs in the antigen draining lymph nodes prior to symptom onset during EAE, but inflammasome activation occurs more significantly in the spinal cord at 30 days post induction (dpi) of EAE. Spinal cord inflammasome activation during EAE occurs selectively in radioresistent cells, mainly in astrocytes. Further, this astrocyte inflammasome is dependent on AIM2, and does not result in outcomes, which are canonically observed in myeloid cells, such as release of the inflammatory cytokine, IL-1β. Indeed, AIM2 limits EAE development. Lastly, astrocyte inflammasomes differ morphologically from the traditional structure (known as the “ASC speck”) as seen in macrophages. This dissertation thus expands our understanding of inflammasome activation during EAE, and introduces new areas of investigation into the AIM2 inflammasome during EAE and inflammasome activation in astrocytes.