Charcot-Marie-Tooth disease (CMT) is the commonest inherited neuromuscular disorder, which affects the peripheral nervous system leading to nerve degeneration. CMT is categorised into two forms, ‘axonal’ and ‘demyelinating’, which reflects the main site of pathology as the axon or Schwann cells respectively. Over 90 genes have been identified associated with the disease. Among the genes associated with demyelinating CMT, the focus of my thesis is LITAF, mutations in which lead to an autosomal dominant demyelinating CMT known as CMT type 1C. LITAF is a 17 kDa protein likely to be involved in endocytic degradation and trafficking of specific cargo proteins. It contains an N-terminal proline-rich region mediating protein-protein interactions and a C-terminal LITAF domain consisting of a zinc-ribbon structure with a hydrophobic region incorporated. Most of the CMT1C mutations are clustered in this highly conserved LITAF domain. LITAF was predicted to play roles in recruiting ESCRT components and exosome formation, but the precise function remains unclear. Furthermore, why mutations in LITAF lead to CMT is not known. My work therefore focused on characterising the function of the LITAF protein both in health and disease. In my thesis, I first tried to determine the subcellular localisation of LITAF proteins and also investigated the function of the highly conserved C-terminal LITAF domain in targeting protein to the membrane. With regards to the function of LITAF, potential binding partners were screened using the traditional GST pull-down assay and the in-situ proximity labelling assay, BioID. A number of novel potential binding partners were identified in both assays. Among the list of potential binding partners, BAG3 was captured in both pull-down assays and was chosen for further studies. The interaction with LITAF was characterised and the potential role of this interaction in autophagy was investigated. Integrin, which was also captured in the BioID assay, was another protein chosen for further studies. Internalisation and recycling assay were developed to investigate the function of LITAF in integrin trafficking. The potential of CMT mutations in impairing the internalisation of integrin in A431 cells and the difficulty in performing the assays were discussed. Lastly, with patient fibroblasts available in our lab, disease phenotypes were analysed using two types of imaging technique: transmission electron microscopy (TEM) (in collaboration with J. Edgar) and immunofluorescence microscopy. Swollen vacuoles were observed in the TEM images of the patient fibroblasts only, and various uptake assays were performed to identify these enlarged compartments. In summary, this work offers an insight into the function of LITAF both in health and disease as well as identifying potential intracellular binding partners that might shed light on pathogenesis. Furthermore, the modified trafficking assays described in this thesis can be applied to Schwann cell and patient fibroblasts, providing further tools to probe the underlying membrane trafficking pathways that are dysfunctional in CMT.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:744902 |
| Date | January 2018 |
| Creators | Ho, Hon Kwan |
| Contributors | Roberts, Rhys |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.repository.cam.ac.uk/handle/1810/276742 |
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