Date of Award

12-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Regulatory Biology

Department

Biological, Geological, and Environmental Sciences

First Advisor

Williams, Jessica

Second Advisor

Dutta, Ranjan

Third Advisor

Bergmann, Cornelia

Abstract

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease of the central nervous system (CNS). Infiltrating inflammatory immune cells perpetuate demyelination and axonal damage in the CNS and significantly contribute to pathology and clinical deficits. Interferon (IFN)γ is classically described as deleterious in acute CNS autoimmunity, we and others have shown astrocytic IFNγ signaling also has a neuroprotective role. We found IFNγ signaling on astrocytes upregulates subunits of the immunoproteasome (iP) and programmed death ligand 1 (PD-L1), both of which serve protective roles during autoimmunity. Astrocyte-specific knockouts of Ifngr1 resulted in increased clinical severity in the MS murine model, experimental autoimmune encephalomyelitis (EAE). These knockouts resulted in decreases in both iP subunits and PD-L1. In MS tissue, iP expression was enhanced in spinal cord compared to brainstem lesions, which correlated with a decrease in oxidative stress. In vitro, IFNγ stimulation enhanced iP expression, reduced reactive oxygen species burden, and decreased oxidatively damaged and poly-ubiquitinated protein accumulation preferentially in human spinal cord astrocytes, which was abrogated with the use of the iP inhibitor, ONX 0914. During the chronic phase of an MS animal model, experimental autoimmune encephalomyelitis (EAE), ONX 0914 treatment exacerbated disease and led to increased oxidative stress and poly-ubiquitinated protein build-up. Finally, mice with astrocyte-specific loss of the receptor exhibited worsened chronic EAE associated, enhanced lesion size and oxidative stress and poly-ubiquitinated protein accumulation in astrocytes. Using a PD-1/PD-L1 antagonist, we determined that apoptosis was reduced in leukocytes exposed to IFNγ -treated astrocytes in vitro. To further elucidate the role of astrocytic IFNγ signaling on the PD-1/PD-L1 axis in vivo, we induced the EAE model of MS in Aldh1l1- CreERT2, Ifngr1fl/fl mice. Mice with conditional astrocytic deletion of IFNγ receptor exhibited a reduction in PD-L1 expression which corresponded to increased infiltrating leukocytes, particularly from the myeloid lineage, and exacerbated clinical disease. PD-1 agonism reduced EAE severity and CNS-infiltrating leukocytes. Importantly, PD-1 is expressed by myeloid cells surrounding MS lesions. Taken together, our data reveal a protective role for IFNγ in chronic neuroinflammation particularly in astrocytes and identify a novel function of the iP and PD-L1 In astrocytes during CNS autoimmunity.

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