Astrocytic modulation of neuronal excitability in neurodegeneration

Abstract

The overarching goal of this study is to investigate the functionality of glial cells during the progression of neuronal hyperexcitability in neurodegeneration. Our first aim was to study the potassium clearance process and glial K+ channels in the somatosensory cortex and hippocampus from the 5xFAD mice as a model of AD. In this study, we have used multiple methods, including electrophysiological recordings of astrocytes and neurons from acute brain slices, as well as immunohistochemical, morphological, and molecular analysis to study the [K+]o clearance function of glial cells in different brain regions of young (2 months old) and aged (6 months old) 5xFAD mice. Our data indicate the significant impact of 5xFAD mutations on the decrease in the [K+]o clearance rate in the stratum laconism molecular layer of the hippocampus. Intriguingly, comparing the [K+]o clearance rate from layers II/III of the somatosensory cortex of 5xFAD mice and their aged-matched littermates, we show that neither 5xFAD mutations nor ageing had a significant impact on [K+]o dynamics, indicating regionselective alterations of glial activity in AD. Moreover, we revealed a region-specific pattern in astrocytic reactivity in 5xFAD mice using morphological reconstruction of GFAP-expressing astrocytes from the hippocampus and somatosensory cortex. To correlate changes in the [K+]o clearance rate and the excitability profile of neurons, we patched neurons from the hippocampus of 5xFAD and WT mice and analysed their intrinsic excitability. Interestingly, while 5xFAD mutation affected neuronal excitability in all studied hippocampal layers, only neurons from the stratum laconism molecular layer were hyperexcitable, supporting the correlation between [K+]o clearance dysfunction of glial cells and neuronal excitability. Our second aim was to investigate the impact of neuromodulators on the [K+]o clearance rate in the hippocampal slices of aged WT and 5xFAD mice. Our third aim was to study the [K+]o clearance rate and glial K+ channels in the somatosensory cortex during the progression of paralysis in the superoxide dismutase 1 (SOD1) transgenic mice (G93A) as a mouse model for ALS. Using extracellular and intracellular techniques to analyse [K+]o dynamics, we revealed a significant decrease in the clearance rate at the motor cortex of SOD1 mice, which was region specific, as no significant effect of ageing nor SOD1G93A mutation was noticed in the somatosensory cortex of the same mice. Together, our data from the 5xFAD and SOD1G93A mice indicate a correlation between glial cell dysfunction and shifts in neuronal excitability during neurodegeneration. Also, our results suggest a region-selective glial dysfunction in neurodegeneration, which reflects the heterogeneity of glial cell function and sensitivity at different brain regions. Overall, the data presented in this thesis provides new insights into the region-selective vulnerability of glial cells in neurodegeneration and their impact on nearby neurons. Moreover, the proposed study provides important insight into a relatively new concept that glial cells can actively shape neuronal activity.

Date of Award	2024
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Yossi Buskila (Supervisor) & John Morley (Supervisor)