All ETDs from UAB

Advisory Committee Chair

Talene A Yacoubian

Advisory Committee Members

Matthew Goldberg

David Standaert

Laura Volpicelli-Daley

Elizabeth Sztul

Document Type

Dissertation

Date of Award

2020

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Alpha-synuclein (αsyn) is the key component of proteinaceous aggregates termed Lewy Bodies (LBs) that pathologically define a group of disorders known as synucleinopathies, including Parkinson’s Disease (PD) and Dementia with Lewy Bodies (DLB). αSyn is thought to misfold and spread throughout the brain in a prion-like fashion. Transmission of αsyn necessitates the release of misfolded αsyn from one cell and the uptake of that αsyn by another, in which it templates the misfolding of endogenous αsyn. Identifying regulators of this process is essential to understanding how αsyn propagates and furthers disease progression. In this study, we investigated Rab27 and 14-3-3θ in the regulation of αsyn transmission. Rab27b is one of several GTPases that regulate the endosomal-lysosomal pathway and is implicated in protein secretion and clearance. We used a paracrine αsyn in vitro model to test the impact of Rab27b on αsyn release, clearance, and toxicity. Rab27b knockdown (KD) decreased αsyn secretion through both exosomal and non-exosomal pathways. However, Rab27b KD decreased the autophagic clearance of αsyn and secreted higher molecular weight αsyn, resulting in increased paracrine toxicity. Rab27b is also elevated in PD and DLB brain lysates. We next examined the impact of Rab27a/b double knockout (DKO) in the in vitro and in vivo pre-formed fibril (PFF) models. Rab27 DKO decreased αsyn internalization, aggregation, and neuronal toxicity in vitro. Rab27 DKO in vivo rescued PFF-induced social dominance deficits. Rab27 DKO also decreased αsyn inclusion counts and rescued dopaminergic cell loss in the substantia nigra. 14-3-3 proteins are highly expressed in the brain and have been shown to be protective in multiple synucleinopathy models. We have previously established a neuroprotective role for 14-3-3θ in the in vitro paracrine αsyn and PFF models. Here we further characterized the role for 14-3-3θ in the in vivo PFF model. 14-3-3θ overexpression delayed αsyn aggregation, protected against neuronal cell death and rescued social dominance PFF-induced deficits. Conversely, 14-3-3 inhibition accelerated αsyn aggregation, increased neuronal cell death and exacerbated social dominance deficits in the PFF model. Together these data indicate an essential role for Rab27 and 14-3-3θ in regulating αsyn propagation and warrants further investigation as therapeutic targets for slowing disease progression of synucleinopathies.

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