Ageing is a process correlated with cellular stress and increased risks of neurodegenerative diseases, in particular Alzheimer’s disease (AD), which is accompanied with severe cognitive and memory impairments. Both ageing and AD affect many brain regions and thus induce brain malfunctions. Among the brain regions, the entorhinal cortex (EC) has drawn more and more attentions due to its pivotal role in cognition and memory functions as well as its vulnerability to ageing process and AD neuropathology. Synaptic and neuronal degenerations, which are also manifest features of AD, occur in the EC during the ageing process and at the early stage of AD. In addition, both pathological hallmarks of AD, namely abnormal accumulation of β-amyloid (Aβ) and hyperphosphorlation of tau proteins, initially appear in the EC and then progress to other brain regions such as the hippocampus and the neocortex. Glial alterations in AD and ageing process have been considered as secondary event to neuronal changes. Nevertheless, accumulating evidence indicates the relevant and primary involvement of astroglia, which is responsible for brain homeostasis, in AD and ageing. In this thesis, we have focused on the astroglial alterations in the EC during the progression of AD in an animal model of the disease as well as in ageing process in non-transgenic control mice. We have used the triple transgenic mouse model of AD (3xTg-AD), which is the most relevant animal model of AD and resembles the spatiotemporal progression of human AD pathology. Our results revealed cytoskeletal atrophy of astrocytes in the EC of 3xTg-AD animals (Chapter 3), shown by significant decrease in GFAP surface and volume. This astroglial alteration began at very early age (1 month) and sustained till more advanced age (12 month). Moreover, Aβ plaques did not trigger astrogliosis, and there was rare presence of GFAP labelled astrocytes in the vicinity of Aβ deposition. This may reflect the relative indifference of astroglia in the EC and thus explain the susceptibility of the EC at the early stage of AD. To study whether astroglial atrophy in cytoskeleton compromise astrocytic function in glutamate homeostasis, we investigated the expression of glutamine synthetase (GS), which is specifically expressed in astrocytes and is critical for glutamate balance (Chapter 4). Our results showed constant GS expression and the density of GS positive astrocytes in the EC. However, dual labelling of GS and GFAP revealed 3 different subsets of astrocytes, being GS-, GFAP-, GS/GFAP- positive astrocytes. The morphology of GS-IR cells, measured by surface and volume, did not change in spite of the evident GFAP atrophy. Therefore, GFAP atrophy does not disturb glutamate homeostasis in the EC, suggesting diverse functional populations of astrocytes, which may show distinct responses during AD progression. In addition we also analysed astroglial changes during the ageing process in the EC and its major projection area, the hippocampus (Chapter 5). Astrocytes in the hippocampus exhibited prominent hypertrophy, shown by increased GFAP whereas entorhinal astrocytes in the EC had profound reduction in GFAP expression. This may implicate heterogeneous astrocytic responses to ageing in different brain regions. The general atrophy of astrocytes in the EC of 3xTg-AD mice and aged controls, suggests astroglial atrophy may results in reduced astrocytic coverage and modulation of synapses, accounting for the synaptic dysfunction in ageing and AD.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:568620 |
| Date | January 2013 |
| Creators | Yeh, Chia-Yu |
| Contributors | Verkhratsky, Alexej; Rodriguez Arellano, Jose |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/cortical-astroglial-atrophy-in-ageing-and-alzheimers-disease(626eda4f-5713-4308-b8f9-7a89e51a9193).html |
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