Understanding the Consequences of Chronic Nuclear Alpha-Synuclein Mislocalization in Mice and Mapping Alpha-Synuclein Cell-Specific Topography

Abstract

Parkinson's disease (PD) is the fastest growing neurodegenerative disease worldwide and is characterized by dopaminergic neurodegeneration and the accumulation of intraneuronal alpha-synuclein (αSyn) aggregates. While αSyn is typically known as a presynaptic protein, a small population resides in the nucleus. In PD, nuclear αSyn has been shown to increase relative to age-matched controls, and animal models of nuclear αSyn overexpression exhibit neurotoxicity. However, there is an endogenous population of nuclear αSyn that has been shown to be beneficial in repairing DNA damage, therefore it remains unclear whether the nuclear accumulation of αSyn is neurotoxic or neuroprotective. Previous work modeling the nuclear accumulation of αSyn rely on its overexpression, however αSyn is inherently aggregate-prone, thus clouding phenotypes directly attributable to nuclear αSyn. In this dissertation, we model nuclear αSyn accumulation in a novel mouse model (Sncaᴺᴸˢ), which mislocalizes endogenous αSyn into the nucleus without relying on its overexpression. Sncaᴺᴸˢ mice exhibited significant age-dependent motor deficits, cortical neurodegeneration, and decreased survival rates compared to littermate controls. To gain further insight into the mechanism(s) of nuclear αSyn toxicity, we profiled the nuclear αSyn interactome using TurboID, a proximity labelling assay, in primary cortical neurons. Interestingly, we noted an enrichment of spliceosome and RNA binding proteins and validated Luc7l, an RNA-binding protein, to interact with αSyn and modulate its protein levels. Serendipitously, the Sncaᴺᴸˢ model was also found to be an excellent reporter allele for mapping αSyn topography throughout the mouse. Identifying αSyn topography has been challenging due to its largely pre-synaptic locale, which are notoriously difficult to image and correlate to cell bodies. With αSyn in the nucleus, we were more easily able to map αSyn+ cell density and intensity throughout the brain, spinal cord, retina, and gut. We chronicled the topographical distribution of αSyn across different brain structures, cell types, and throughout the periphery. Surprisingly, all neurons in the stomach and duodenum showed some level of αSyn expression, however to different extents, highlighting the heterogeneity of neurons in the gut. This thesis explores the consequences of constitutive nuclear αSyn accumulation, begins to unravel the molecular mechanisms behind this toxicity, and documents the localization of αSyn-abundant cell types. Altogether, this thesis aims to improve our understanding of αSyn, which will enable a deeper insight into PD and other α-synucleinopathies, ultimately leading to more efficient therapeutics.