UC Irvine

Evaluating the functional contributions of microglia in host defense and disease in a model of mouse coronavirus-induced neurologic disease

By

Yuting Cheng

Doctor of Philosophy in Biological Science

University of California, Irvine, 2022

Professor Thomas E. Lane, Chair

An important unmet clinical need for multiple sclerosis (MS) patients is an effective method for promoting axonal sparing and remyelination that can ameliorate clinical symptoms associated with demyelination and restore motor function. Previous studies from our laboratory demonstrating an important role for microglia in restricting the severity of demyelination and promoting remyelination in a viral model of demyelination. In brief, intracranial instillation of the neuroadapted JHM strain of mouse hepatitis virus (JHMV, a member of the Coronaviridae family) results in an acute encephalomyelitis followed by a chronic immune-mediated demyelinating disease similar both clinically and histologically with MS. Targeted depletion of microglia via administration of PLX5622, a brain penetrant small molecule antagonist specific for colony-stimulating factor 1 receptor (CSF1R) that efficiently depletes microglia, prior to infection with JHMV resulted in a dramatic increase in the severity of spinal cord demyelination and markedly impaired remyelination. To better understand how microglia impact disease progression in mice persistently infected with JHMV that have established demyelination, PLX5622 was administered to mice at day 14 post-infection (p.i.) and animals remained on drug for 14 days at which point animals were sacrificed and the severity of spinal cord demyelination and remyelination evaluated. Our findings indicate that PLX5622-mediated ablation of microglia for 2 weeks beginning at day 14 p.i. did not lead to an increase in mortality but resulted in a significant (p<0.05) increase in the severity of spinal cord demyelination at day 28 p.i. when compared to control mice. Infiltration of both total and virus-specific CD4+ and CD8+ T cells into the CNS was not affected in response to PLX5622-mediated microglia ablation yet control of viral replication was impaired that correlated with muted expression of MHC class II. Finally, we observed decreased expression of mRNA transcripts encoding remyelination-associated proteins Cystatin F and Lipoprotein lipase. BulkRNAseq analysis of spinal cords indicated that targeting microglia resulted in a dramatic reduction in gene expression profiles associated with cell-mediated immune responses and phagocytosis. These findings indicate that microglia continue to impact control of viral replication within the CNS post-acute phase of disease as well as restrict ongoing demyelination and remyelination in mice persistently infected with JHMV.