Research Projects

Lysosomes are a heterogeneous collection of membrane-bound compartments, canonically known as the recycling center of the cell for their role in cargo degradation and recycling of the building blocks for de novo macromolecular synthesis. Lysosome dysfunction strongly contributes to and is likely even causative of the pathology of certain neurodegenerative disorders such as Parkinson’s disease, frontotemporal dementia, and Alzheimer's disease. Rabs, Arfs, and Arls (Arf-like) are small GTP-binding (G) proteins of the Ras superfamily that act as master regulators of vesicular transport pathways. Previous research from our lab has revealed that Arl8b, a small G protein of the Arl family, recruits its downstream effectors to mediate fusion of late endosomes and autophagosomes with lysosomes and lysosome motility on microtubule tracks. In a previous study, we identified a role for Arl8b in the sorting of hydrolases, which are essential for the degradative capacity of lysosomes. We found that Arl8b interacts with RUFY1, a motor adaptor that mediates dynein-dependent endosomes to TGN retrieval of cation-independent mannose-6-phosphate receptor (CI-M6PR), which captures lysosomal hydrolases from the TGN for their delivery to lysosomes (Rawat et al., J Cell Biol. 2023). We obtained SNX29 as a potential hit in the screen for RUFY1 interaction partners, which we have validated as part of our preliminary data. As there are no studies on SNX29 localization and function, and as the SNX family of proteins is known to have endocytic regulatory roles, we decided to characterize SNX29 to gain insights into its cellular function. Preliminary data from our work shows that SNX29 depletion results in significantly reduced lysosome function in cargo degradation, likely resulting from defects in lysosomal cargo sorting, including cathepsins. This proposal aims to provide mechanistic insights into understanding the function of this uncharacterized sorting nexin and provide fundamental insights into the process of lysosome biogenesis and function, impairment in which results in neurodegenerative and other genetic disorders. There are GWAS studies linking SNX29 variants to various neuronal disorders; however, the existing literature does not reveal whether the identified SNX29 variants are indeed loss-of-function and whether the disease is a manifestation of compromised SNX29 function. As objective #1 of this proposal, we aim to understand what the determinants of SNX29 membrane localization are on early endosomes and how SNX29 regulates cargo trafficking. Lysosomal cargo such as lysosomal glycoproteins, V-ATPase subunits, and mTORC1 activation complex are localized on a subset of EEA1+ early endosomes. As objective #2 of this proposal, we will characterize SNX29 interaction with Arl8b and investigate the significance of their binding in lysosomal cargo sorting from early endosomes. Several members of the Sorting Nexin (SNX) family are known to undergo phosphorylation, which often alters their interactions with membranes and other proteins, affecting their functions. Through objective #3 of this proposal, we will determine how SNX29 phosphorylation impacts its localization and function in cargo trafficking from early endosomes. Excitingly, the disordered propensity score analysis suggests a significant amount of intrinsically disordered segments in SNX29. We propose to analyze the phase separation properties of SNX29 and its significance for early endosomal cargo trafficking. This is a fundamental basic science (cell biology) proposal with application in the biomedical sciences. The proposal aims to gain mechanistic insights into the cellular role of a protein known as SNX29 and understand its significance in regulating protein degradation by lysosomes. Based on our strong expertise in lysosome biology and a body of literature from our lab on mechanisms regulating lysosome function, we are well suited to address the objectives of this proposal.