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iPSC-derived microglia as a model of immune dysfunction in neurodegenerative diseases

Bunga, Aurelien 2018. iPSC-derived microglia as a model of immune dysfunction in neurodegenerative diseases. PhD Thesis, Cardiff University.
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It is now increasingly evident that neurodegenerative diseases such as Alzheimer’s disease (AD) and Huntington’s disease (HD) trigger immune activation within the CNS and activate innate immune responses, which are primarily driven by microglia. HD is caused by a CAG repeat expansion in the huntingtin gene (HTT), leading to translation of an aberrant and pathogenic mutant HTT. Studies in mouse models have shown that HD microglia acquire a hyper-reactive inflammatory phenotype, mediated by a gain of toxicity of mutant HTT. Using a HD induced pluripotent stem cell (iPSC) line containing 109 CAG repeats in the HTT gene, microglia-like cells were generated with the aim of characterising their phenotype. RNA sequencing was used to explore the microglial-specific transcriptional changes associated with mutant HTT and pathway analysis carried out to predict any downstream processes affected in the HD109 microglia. Several immune-related functions including chemotaxis and phagocytosis were subsequently identified as dysregulated or impaired. However, upon functional assay validation, no phenotypic abnormalities were manifest in the HD109 microglia, with comparisons made against WT Kolf2 and isogenic HD109 corrected iPSC-derived microglia. Similarly, the in vitro microglia did not exhibit the inflammatory phenotype characteristic of diseased HD microglia and other immune cells. Loss-of-function variants in the microglia-enriched gene encoding ATP-binding cassette transporter A7 (ABCA7) increase Alzheimer’s disease risk. Although it has been suggested to play a role in amyloid beta phagocytosis, the precise role of ABCA7 in AD pathogenesis remains unknown. To that end, ABCA7 knockout iPSCs were generated using CRISPR/Cas9 and in preliminary results, loss-of-function mutations in ABCA7 were found to impair phagocytosis of E. coli bioparticles and regulate in vitro microglial inflammatory responses. This thesis demonstrates that iPSC-derived microglia can serve as a platform for exploring the inflammatory pathways mediating microglial involvement in AD and HD pathogenesis, thus enabling in-depth mechanistic studies that bridge the gap between clinical and animal models.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Biosciences
Neuroscience and Mental Health Research Institute (NMHRI)
Uncontrolled Keywords: microglia; Huntington's; iPSC differentiation; Alzheimer's
Funders: Wellcome Trust
Date of First Compliant Deposit: 30 May 2019
Last Modified: 30 Mar 2021 12:57

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