PROJECT SUMMARY
This application is for F31 support for Rachel Underwood for the remainder of her PhD training.
Parkinson's disease (PD) is the second most common neurodegenerative disorder that causes tremendous
economic and social burden worldwide. Alpha-synuclein (asyn) is the key protein component of intracellular
aggregates termed Lewy bodies, the pathological hallmark of Parkinson's disease2. In its non-native form,
asyn is thought to propagate throughout the brain in a prion-like fashion: when released, it can be taken up by
surrounding neurons to cause aggregation and cell death by inducing the misfolding of endogenous asyn3-6.
However, the mechanism that regulates the release and spread of asyn is poorly understood. aSyn release
has previously been shown to involve exosomal and non-exosomal pathways involving endosomes which are
tightly regulated by a family of GTPase proteins termed Rabs8-12. Rab27b is a GTPase protein that regulates
protein secretion through both exosomal and non-exosomal pathways and is highly expressed in the human
brain13-15. In addition, Rab27b polymorphisms have been associated with a higher motor neuron disease risk in
GWAS studies16. Rab27b transcriptional dysregulation has also been associated with other neurological
disorders including Alzheimer's disease, Dementia with Lewy Bodies and X-linked dystonia parkinsonism
syndrome17-19. Our data shows that Rab27b expression is increased in human PD postmortem brain tissue in
comparison to age-matched healthy controls (Fig. 4). Our preliminary data also indicates that Rab27b
modulates the release of asyn in vitro (Fig. 5). Our central hypothesis is that Rab27b promotes asyn-
mediated neurotoxicity by inducing the release and spread of toxic asyn species.
The goal of this proposal is to determine the effects of Rab27b on asyn release, spread, and paracrine
toxicity. In Aim 1, we will test if Rab27b regulates asyn release and toxicity in a paracrine tetracycline-inducible
asyn cell model, in which asyn, upon induction with doxycycline, is released into the conditioned media (CM)
and induces cell death when transferred to separately cultured neurons. We will use knockdown and dominant
negative technology to test if Rab27b regulates asyn release, clearance, and toxicity in this model. In Aim 2,
we will test if Rab27b regulates asyn aggregation, spread, and neurotoxicity in cellular and in vivo asyn fibril
based PD models. If our hypothesis is true, Rab27b may prove to be a useful research tool and a potential
target for therapeutic intervention to reduce asyn propagation in PD.