The role of MutL complexes in CAG repeat expansion in a human iPSC model of Huntington’s disease

Stone, Joseph 2024. The role of MutL complexes in CAG repeat expansion in a human iPSC model of Huntington’s disease. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Huntington’s disease (HD) is a progressive neurodegenerative disease caused by an expanded CAG repeat in exon 1 of the HTT gene. The CAG repeats inherited by HD individuals expand further in some somatic tissues and this somatic expansion is most prevalent in the medium spiny neurons (MSNs) of the striatum. MSNs are the most vulnerable cell type in HD with patient brains showing characteristic striatal atrophy postmortem. Somatic expansion has been implicated as a key driver of disease, making targeting somatic expansion a potential therapeutic avenue to treat HD; a disease that currently does not have any disease modifying therapies. The molecular mechanism facilitating somatic CAG repeat expansion has not yet been fully elucidated, but results from human genetics studies and experiments using mouse and cell models of HD have implicated DNA repair, in particular mismatch repair. Here we show that the MutL complexes play a key role in potentiating somatic CAG repeat expansion. These complexes consist of 3 heterodimers: MutLα (MLH1-PMS2), MutLβ (MLH1-PMS1) and MutLγ (MLH1-MLH3), with MutLα playing a key role in mismatch repair. We have used CRISPR-Cas9 gene editing technology to knock out each of the MutL genes in a patient derived induced pluripotent stem cell (iPSC) model of HD that demonstrates somatic CAG repeat expansion in culture. We have found that MLH1, PMS1 and MLH3 are critical potentiators of somatic expansion in this model, whereas PMS2 is not critical but does facilitate expansion. To further this work, we have developed a more disease relevant patient-derived differentiated glutamatergic cortical neuron model of somatic CAG repeat expansion. Together, this work helps to elucidate the molecular mechanism potentiating somatic CAG repeat expansion informing the development of therapeutics targeting somatic expansion in HD.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Medicine
Funders:	Medical Research Council
Date of First Compliant Deposit:	14 March 2025
Last Modified:	14 Mar 2025 13:49
URI:	https://orca.cardiff.ac.uk/id/eprint/176882

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