Synucleins represent a conserved family of small proteins that include α-, β-, and
γ- isoforms, which are highly expressed in neurons of the vertebrate nervous system. The
normal function of these proteins is not well understood. However, in humans α-
synuclein dysfunction is causatively linked to Parkinson’s Disease (PD), where it
abnormally accumulates in neuronal cell bodies as protein aggregates that are associated
with neuronal death. Although the associations between synuclein accumulation and
cellular death are established in PD, the extent to which this occurs in other contexts,
such as neuronal injury, is unknown. Furthermore, the effects of synuclein aggregation
on the function of synapses, where synuclein is normally localized, are not well
understood. To address these questions I took advantage of the experimentally accessible
nervous system of the sea lamprey (Petromyzon marinus). I used molecular cloning and
phylogenetic analyses to characterize three lamprey synuclein orthologues, one of which
is highly expressed within a class of neurons called the giant reticulospinal (RS) neurons.
Spinal cord injury induces the accumulation of synuclein protein only within a population
of poor surviving RS neurons, and this accumulation is correlated with cellular death.
Thus, similar to PD, the abundance of synuclein protein is associated with neuronal
toxicity. In a related project, I demonstrated that elevating synuclein levels at synapses, such as occurs in PD, is deleterious to synaptic function through an inhibition of synaptic
vesicle (SV) recycling. By injecting excess synuclein protein directly into the axons of
giant RS neurons, and analyzing the ultrastructural morphology of synapses, I have
shown that clathrin-mediated synaptic vesicle endocytosis was greatly inhibited. The
conserved N-terminal domain was sufficient to inhibit vesicle recycling, and injecting
synuclein mutants with disrupted N-terminal α-helices caused reduced defects in SV
recycling. Therefore the α-helical structure of the N-terminus is necessary to inhibit SV
recycling at early stages of clathrin-mediated endocytosis. Binding interactions with
clathrin-mediated endocytosis components, such as the phosphoinositide lipid PI(4)P
support this hypothesis. These studies provide a better understanding of the mechanisms
by which synuclein dysfunction leads to neuronal death after injury and synaptic
dysfunction in PD and other synuclein-associated diseases. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2012-08-6276 |
| Date | 03 October 2012 |
| Creators | Busch, David James |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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