Date of Award

Spring 2022

Project Type

Dissertation

Program or Major

Genetics

Degree Name

Doctor of Philosophy

First Advisor

Xuanmao Chen

Second Advisor

Sherine Elsawa

Third Advisor

Subhash Minocha

Abstract

In the last two decades, primary cilia have become recognized as tiny sensory organelles with considerable physiological function including regulation of cell division and modulation of transduction pathways. Scientists build on former discoveries, identifying new connections and accentuating the value of primary cilia in disease and intercellular signaling. Astrocytes, the most numerous cell type within the brain, act in support of neurons and maintain neurological health by providing neurotrophic factors and removing synaptic debris. These cells are particularly significant in reparations following neural injury and diseases, altering shape and function to protect healthy tissue. Astrocytes display primary cilia, yet little is understood about the function of this organelle within these cells. My dissertation research sought to determine the morphological changes of astrocytic primary cilia under neuropathological conditions, such as brain injury and epilepsy, and explore electroencephalogram activity under anesthesia in a mouse model of Alzheimer’s disease (AD). This research comprised of three major projects: (1) identifying morphological and condition-based differences between neuronal and astrocytic primary cilia, (2) evaluating the implications of Arl13B during cortical injury, and (3) quantifying EEG waveform pattern in an AD mouse model for distinctions indicative of the presence of the disease prior to the phenotypic onset. Immunohistochemistry was used to explore morphological differences and alterations in primary cilia associated with cell-type and the development of astrocytic reactivity. Cortical injury procedures were used to form a localized astrocytic response in Arl13B loss-of-function and gain-of-function strains, as well as an IFT88 knockout strain to compare the role of Arl13B in glial scarring. Electroencephalogram/electromyogram (EEG/EMG) recordings were furthermore used to substantiate seizure activity in a strain of mice prone to epileptic behavior. Finally, the APP23 mouse, a murine model of AD, was exposed to isoflurane anesthesia while EEG waveform was recorded. These recordings were filtered and processed via Brainstorm, a MATLAB graphical interface, and analyzed for Power Spectral Density, Burst Suppression Density, and Phase Amplitude Coupling. Results of morphological changes in cilia were consistent with the hypothesis that similarly to neuronal primary cilia, astrocytic cilia are implicated under reactive conditions assessed by morphological changes. Immunohistochemical analysis also revealed regional and strain differences of primary cilia. However, comparison of Loss-of-Function and Gain-of-Function studies did not collectively support the hypothesis that the ciliary protein Arl13B is a functionally relevant component of GFAP-based neurological repair one week following injury, although injured tissue did consistently show heightened Arl13B close to cortical lesion. Finally, EEG waveform analysis of a mouse model of AD during exposure to anesthesia revealed 3-4-month-old mice show a statistically significant difference in levels of Burst Suppression Density during anesthesia and Power Spectral Densities of Delta, Theta, and Alpha. These results support the potential foundation of waveform analysis during anesthesia as a prudent diagnostic tool to allow for early diagnosis of the disease. This research elucidates (1) the role of astrocytic primary cilia in the pathogenic brain, (2) relevance of Arl13B in brain injury, and (3) provides a possible basis for quantifiable hallmarks of AD in EEG waveform under isoflurane-induced anesthesia.

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