Project Summary/Abstract
As our population ages, neurodegenerative disorders such as Parkinson disease (PD) comprise a major
societal burden. While mechanisms for PD etiology are still emerging, evidence of mitochondrial dysfunction in
the pathogenesis of this disease is abundant. Another component of PD pathology is the protein a-synuclein
(a-syn); it is found within Lewy Body inclusions, yet causes of cellular toxicity remain unclear. A strategy that
mitochondria employ for managing stress is to engage the mitochondrial unfolded protein response (UPRmt),
which coordinates nuclear expression of chaperones and proteases that translocate to the mitochondria to
handle damaged and/or unfolded proteins. When activated in response to acute stressors, the UPRmt re-
establishes homeostasis and promotes cell survival. However, it can become dysregulated when challenged
with a long-term genetic stressor such as misfolded a-syn and becomes cytotoxic. Notably, molecular variants
of a-syn can interact with TOMM20, an outer mitochondrial membrane protein, and initiate a physical block of
mitochondrial protein import. We speculate that the increased UPRmt response observed in a-syn-expressing
neurons is a consequence of blocked mitochondrial import. Although attention to a role for mitochondrial
quality control in neurodegenerative disease has proven increasingly insightful, there is a pivotal gap that
remains to be addressed in demonstrating a direct functional correlation between dysregulated UPRmt activity
and neurodegeneration. Importantly, our research illustrates an insidious aspect of mitochondrial signaling in
which the UPRmt pathway exacerbates disruption of dopaminergic neurons in vivo, resulting in the neuron loss
characteristic of PD. Our approach exploits the expedience of genetic manipulation in Caenorhabditis elegans
research, and the rigor with which large, isogenic populations can be scored for neurodegeneration with
unprecedented accuracy, at the single-neuron level. We will systematically investigate combinations of
transgenic worms co-expressing structural variants of a-syn and transcription factors that activate the UPRmt to
discern functional requirements for UPRmt activation with neurodegeneration as the primary endpoint. The
studies in Aim 1 will investigate the hypothesis that the a-syn-TOMM20 mitochondrial import block triggers the
UPRmt pathway and will explore a role for dopamine in potentially exacerbating the deleterious consequences
of this process. As a distinct strategy, Aim 2 will involve the identification of molecular components associated
with UPRmt signaling through a forward genetic screening strategy that takes advantage of a strain we have
generated that reveals an uncharacterized compensatory mechanism for UPRmt induction. Phenotypic
bioassays and genetic screening using C. elegans are routinely conducted by undergraduates in our lab and
will serve as an excellent training opportunity for students through this R15 proposal. These studies represent
a timely and mechanistic strategy towards defining nuclear-mitochondrial dynamics, specifically with respect to
dopaminergic neurodegeneration, with potential to inform a translational path for therapeutic development.