Coneys, Rachel; (2024) Investigating the role of molecular chaperones in amyotrophic lateral sclerosis and frontotemporal dementia. Doctoral thesis (Ph.D), UCL (University College London).

Text Coneys Thesis 2024.pdf - Accepted Version Access restricted to UCL open access staff until 1 May 2025. Download (7MB)

Abstract

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two devastating neurodegenerative diseases that exhibit significant genetic and pathological overlap. Nuclear clearance and cytoplasmic deposition of the RNA binding protein TDP-43 is seen in the majority of ALS and FTD patients, resulting in disrupted RNA and protein homeostasis. Molecular chaperones act within protein quality control networks to prevent and respond to aberrant proteostasis. Recent exome sequencing identified loss-of-function mutations in the molecular chaperone, DNAJC7, as a novel gene implicated in ALS risk, while the chaperone DNAJB1 has been identified by the Isaacs laboratory as a modifier of dipeptide repeat protein (DPR) toxicity, associated with C9orf72-ALS/FTD. Here, I sought to identify how loss of DNAJC7 contributes to ALS risk and how DNAJB1 exerts neuroprotective effects against C9orf72-associated toxicity. To do so, I first developed and characterised new iPSC models of ALS/FTD and employed TurboID-proximity labelling to elucidate the pathways in which DNAJC7 and DNAJB1 act. Using mass spectrometry, I identified both known and novel interactors of the two proteins, including other members of the molecular chaperone network. Components of the DNA damage response, namely HERC2, NEURL4 and USP11 were identified as novel neuronal interactors of DNAJC7, while AGTPBP1, a protein involved in axonal regeneration, was identified as a novel interacting partner of DNAJB1. To further define how loss of DNAJC7 specifically affects disease-specific pathways, I developed a neuronal model of DNAJC7 knockdown and report loss of DNAJC7 results in aberrant localisation of TDP-43 and the emergence of cryptic exons in STMN2 and UNC13A. Finally, I show how loss of DNAJC7 impacts the DNA damage response in neurons. Specifically, I observed increased expression of p53’s target genes, including those associated with apoptotic pathways, following DNAJC7 knockdown. Additionally, in neurons with reduced DNAJC7, increased ubiquitinated γH2AX was observed, which we postulate is a result of disruption to DNAJC7s interactions with HERC2 and/or USP11. Overall, the work presented in this thesis attempts to ascertain how molecular chaperones may be acting to protect against ALS and FTD, to enhance our understanding of disease mechanisms and hopefully contribute to the development of novel therapies.

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