Investigating Aβ toxicity and binding to neurons from differentiated human stem cells
AuthorTan, Marsha Siok Hui
AffiliationPharmacology and Therapeutics
Document TypePhD thesis
Access StatusOpen Access
© 2019 Marsha Siok Hui Tan
Alzheimer’s disease (AD) is a neurodegenerative disease that is pathologically characterized by abnormal deposition of extracellular amyloid plaques and intraneuronal neurofibrillary tangles. The deposition of these aggregated proteins causes progressive brain atrophy resulting from gradual synaptic loss and neuronal cell death. Although the aetiology of AD remains elusive, studies have shown that amyloid beta (Aβ) peptide, a cleavage product from amyloid precursor protein (APP), is a key protein causing AD pathogenesis. Recent studies have identified how the presence of soluble low molecular weight Aβ oligomers in the brain correlate best with synaptic loss, and they are a better predictor of disease progression compared to the presence of amyloid plaques or neurofibrillary tangles. In the AD brain, neuronal subpopulations appear to exhibit different levels of vulnerability to Aβ, particularly the basal forebrain cholinergic and hippocampal glutamatergic neurons, while GABAergic neurons appear to remain unaffected till later disease stages. Current treatments based on knowledge gathered from mouse models targeting the cholinergic and glutamatergic systems only alleviate symptoms and are ineffective in halting disease progression. Therefore, we hypothesize that Aβ exerts its neurotoxic effect by binding to a subpopulation of mature neurons. To address this, human embryonic stem cells (hESCs) were differentiated into mature glutamatergic and GABAergic neurons and cultured up to 12 weeks. These cultures were treated fortnightly with soluble synthetic Aβ peptide for 96 hrs. We found that Aβ bound to neurites in culture, altered gene expression and neurotoxicity was more pronounced in 6-week old glutamatergic than GABAergic cultures. Further investigations in determining the specific toxic species of Aβ oligomers revealed that 12 week old cultures were more susceptible to Aβ oligomer induced toxicity, with Aβ dimers being most toxic to glutamatergic neurons while GABAergic neurons were most susceptible to Aβ tetramers. In summary, we successfully established a simple hESC based model to study Aβ toxicity. Our findings also highlight the importance of using relevant human cell-based models to study AD pathogenesis as well as identify potential AD modifying therapeutic strategies.
Keywordsneurodegeneration; Alzheimer's Disease; human embryonic stem cells; glutamatergic neurons; GABAergic neurons; neuronal differentiation; Aβ toxicity; Aβ binding
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