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Topic

Quantitative analysis of astrocyte properties in a Syrian hamster model of COVID-19

Division of Medical Sciences

Date & location

• Wednesday, November 20, 2024
• 9:00 A.M.
• Medical Sciences Building, Room 150

Examining Committee

Supervisory Committee

• Dr. Leigh Anne Swayne, Division of Medical Sciences, ·¬ÇÑÉçÇø (Supervisor)
• Dr. Craig Brown, Division of Medical Sciences, UVic (Member)
• Dr. Bob Chow, Department of Biology, UVic (Outside Member)

External Examiner

• Dr. Patrick Nahirney, Division of Medical Sciences, UVic

Chair of Oral Examination

• Dr. Helena Petrosova, Department of Biochemistry and Microbiology, UVic

Abstract

COVID-19 (Coronavirus disease 2019), caused by infection with SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2), is primarily a respiratory disease, but it can cause a spectrum of acute and long-term neurological symptoms, like fatigue and impaired cognition. Although there is some debate regarding the underlying mechanisms, there is mounting evidence of neuroinflammation in both animal and human models of COVID-19. Neuroinflammation is commonly associated with astrogliosis, which includes changes in astrocytes, such as increased proliferation and increased distribution of the astrocyte-enriched intermediate filament protein, glial fibrillary acidic protein (GFAP); however, this remains relatively unexplored in the context of COVID-19. To this end, my thesis investigated whether mild COVID-19 respiratory infection induces astrogliosis. I created an unbiased imaging and analysis pipeline to quantify astrocyte changes associated with astrogliosis. My pipeline for astrogliosis quantification involves two measures that are increased in the context of astrogliosis: (1) the distribution of GFAP (i.e., the density of GFAP-positive pixels) and (2) the density of astrocytes (with the astrocyte-specific nuclear marker, SOX9). To implement this pipeline within the context of COVID-19, I collaborated with the Kobasa Lab at the National Microbiology Laboratories. The Kobasa Lab modeled mild, peripheral COVID-19 by intranasal inoculation of Syrian hamsters with SARS-CoV-2. They collected brains at 1, 3, 5, 7, and 31 days post-inoculation (DPI). Following extensive fixation (30 days), they shipped the brains to the ·¬ÇÑÉçÇø. In collaboration with a team of UVic researchers, I sectioned the brains coronally. I then performed immunolabelling with SOX9, GFAP, NeuN, and Hoechst and generated tiled confocal micrographs of entire coronal sections. I then digitally isolated key brain regions involved in cognition and susceptibility to inflammation, including the cortex, the corpus callosum, the dorsal striatum, the hippocampus, and the third ventricle. I then subjected these images to my pipeline for astrogliosis quantification. My analysis revealed a significant increase in GFAP distribution in the cortex of female hamsters at 3 DPI. Similarly, I observed increases in GFAP distribution within the hippocampus and corpus callosum of female hamsters at 3 DPI, although these were not statistically significant. In contrast, SOX9+ cell numbers remained unchanged across DPI in both sexes and across brain regions. These findings suggest that mild peripheral COVID-19 may induce partial and transient astrogliosis, specifically in female hamsters. Additionally, minor fluctuations in Hoechst and NeuN staining across various brain regions and time points suggest possible COVID-19-associated changes in marker expression and/or cell/neuronal density, which require further validation. In conclusion, my findings suggest partial and transient, female-specific astrogliosis response to mild peripheral COVID-19, emphasizing the need to consider regional and temporal factors to understand the neurological impacts of COVID-19.