Molecular insights into the role of endosomal recycling in health and disease

Abstract

The endosomal network is a crucial sorting hub in eukaryotic cells, responsible for integrating transmembrane proteins and lipids, termed ‘cargoes’, from multiple input pathways and sorting them for a crucial subsequent fate decision. Cargoes in the endosomal network can either be degraded within the lysosome, or recycled back to an acceptor compartment such as the plasma membrane or trans-Golgi network (TGN). Endosomal sorting complexes that facilitate this process play as central role in the maintenance of cellular homeostasis by regulating a delicate balance between cargo degradation and recycling. Perturbations to endosomal recycling are increasingly associated with disease, many of which are neurodegenerative in their aetiology. 
Recent methodological advances have expanded the understanding of the flux of cargoes through the endosomal network, with hundreds of transmembrane proteins depending upon sequence-dependent sorting for their delivery to the plasma membrane. In this thesis, I utilised proteomics and RNA-sequencing techniques to investigate two key complexes involved in orchestrating endosomal recycling: the retromer complex, and the endosomal SNX-BAR sorting complex promoting exit-1 (ESCPE-1). I identified a multivariate phenotype of endolysosomal dysfunction upon retromer depletion, consistent with complex neurodegenerative phenotypes reported in the literature. By developing a methodology to specifically label trans¬-Golgi network proteins by proximity biotinylation, I also performed a screen to identify retrograde endosome-to-TGN cargo proteins for ESCPE-1, which highlighted Neuropilin-1 as a novel cargo.
The coronavirus disease 2019 (COVID-19) pandemic emerged in 2019 and swept across the globe, causing > 116,000,000 cases and > 2,500,000 deaths worldwide at the time of writing. As part of a collaborative project, we identified Neuropilin-1 as an important host factor for infection by the causative virus, SARS-CoV-2. We showed that SARS-CoV-2 directly binds to Neuropilin-1, and blocking this interaction suppresses infection in cell culture, therefore establishing Neuropilin-1 as an important therapeutic target in the study of COVID-19.

Date of Award	28 Sept 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Pete J Cullen (Supervisor) & Jeremy M Henley (Supervisor)