Author ORCID Identifier
Document Type
Dissertation
Date of Award
2022
Degree Name
Doctor of Philosophy (PhD)
Department
Basic Biomedical Science
First Advisor
Kevin Francis
Abstract
The brain is the most cholesterol rich organ in the body, containing ~25% of the body’s total cholesterol content. Due to the blood-brain barrier, cholesterol in the brain is primarily synthesized de novo by astrocytes and transported to neurons. Genetic disorders of cholesterol biosynthetic enzymes result in reduced CNS cholesterol levels and sterol precursor accumulation. Smith-Lemli-Opitz syndrome (SLOS) is caused by mutations in 7-dehydrocholesterol reductase (DHCR7), which is responsible for the reduction of 7- DHC to cholesterol in the final step of the cholesterol biosynthesis pathway. SLOS results in broad neurodevelopmental malformations and neurological deficits. While much work has focused on the neuronal deficits present, the impact of DHCR7 disruption on glial function and immune activation remains unknown. As the predominant cell type within the nervous system, astrocytes critically regulate neurodevelopment and neurological function through processes ranging from cell migration to network-level communication. Immunological activation of astrocytes and subsequent impaired astrocyte function is now recognized as a hallmark pathology and significant contributor to numerous neurological disorders. While altered astrocyte function frequently coincides with changes in astrocyte metabolism, detailed analyses of the metabolic changes which lead to astrocyte immune activation are limited. We demonstrate that Dhcr7 mutant astrocytes display hallmark signs of reactivity, observed through both morphological and transcriptional changes. Dhcr7 astrocytes also exhibit a hyperactive response to glutamate stimulation and correlative changes in calcium flux. Proteomic analyses prove further cellular dysfunction as a result of astrocyte reactivity, including changes in cell adhesion and motility. We further determine that cholesterol impacts are not intrinsic to astrocytes but result from non-cell autonomous effects of Dhcr7 mutant microglia on astrocytes. Similar to astrocytes, Dhcr7 microglia also display morphological and transcriptional changes indicative of a reactive cellular state. Our data suggest astrocyte deficits resulting from astrocyte-microglia crosstalk may contribute to the neurological phenotypes observed in disorders of cholesterol biosynthesis. Additionally, this work also further elucidates the complex role cholesterol and lipid metabolism play within the astrocyte-microglia immune axis and suggest impacts of glial sterol biosynthesis on neurological disease.
Subject Categories
Neuroscience and Neurobiology
Keywords
astrocyte, cholesterol, Dhcr7, microglia, reactivity, Smith-Lemli-Opitz syndrom
Number of Pages
179
Publisher
University of South Dakota
Recommended Citation
Freel, Bethany Ann, "DISRUPTION OF CHOLESTEROL BIOSYNTHESIS CONTRIBUTES TO GLIAL DYSFUNCTION AND DISTURBS ASTROCYTE-MICROGLIA CROSSTALK" (2022). Dissertations and Theses. 307.
https://red.library.usd.edu/diss-thesis/307
