The role of beta-synuclein in synaptic vesicle release

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PROJECT SUMMARY/ABSTRACT α-Synuclein (αSyn) and β-synuclein (βSyn) are abundantly expressed proteins found throughout the vertebrate nervous system. αSyn aggregation is pathologically associated with Parkinson’s disease (PD), multiple system atrophy, Lewy body dementia (LBD), and many other synucleinopathies. βSyn is known to be involved in neu- rodegenerative diseases such as LBD, diffuse Lewy body disease, Gaucher’s disease, and PD, but almost nothing is known about its function physiologically. Preliminary data demonstrate that direct interaction of βSyn with αSyn results in reduced synaptic vesicle binding of αSyn, potentially affecting αSyn function in the brain. The objective of this proposal is to delineate the functional consequences of the interaction of βSyn with αSyn for a neuron. The central hypothesis of this proposal, based on strong preliminary data, is that βSyn reduces αSyn’s ability to support SNARE-complex assembly, synaptic vesicle clustering and thereby neuro- transmitter release. The rationale for these studies is that understanding the effects of βSyn on αSyn function may lead to a novel understanding of synuclein function in the brain, and may lie the groundwork for the devel- opment of novel therapeutic strategies for combating synucleinopathies by modulating βSyn instead of αSyn directly. Guided by preliminary data, this hypothesis will be tested in two specific aims: Aim 1) Determine the effect of βSyn on αSyn-mediated SNARE-complex assembly and synaptic vesicle clustering, and Aim 2) Deter- mine how βSyn affects neuronal activity. In the first aim, SNARE-complex levels and synaptic vesicle cluster- ing will be quantified as a function of varied αSyn/βSyn ratios, in P40 WT and βSyn KO mouse brain tissue punches of select brain regions, and in primary neurons with varied βSyn levels. In the second aim, changes to spontaneous and evoked neurotransmitter release in βSyn KO neuronal cultures lentivirally expressing in- creasing amounts of βSyn will be measured, using a microelectrode array and synaptopHluorin experiments. We expect βSyn to reduce αSyn-mediated SNARE-complex assembly and synaptic vesicle clustering. We also expect βSyn to reduce the effect of αSyn on synaptic vesicle release and cycling, due to restraining αSyn away from synaptic vesicles and towards a more soluble and functionally inactive pool. This research is significant because understanding the molecular mechanism of how βSyn functions broadens our understanding of the function of all synucleins, and may provide insight into αSyn dysfunction in synucleinopathies. Previous work focused on eliminating αSyn from neurons was has shown to be detrimental. Altering βSyn instead of aSyn directly may provide a potential therapeutic avenue, but much research remains to be done. This research is innovative because of (1) its novel hypothesis that βSyn affects αSyn function, (2) the proposed study directly addresses the lack of knowledge into the molecular function of βSyn and its effect on αSyn, which could open up avenues of research for new synucleinopathies therapeutics, and (3) its multidisciplinary approach combin- ing biochemical and cell biological approaches to gain insight into the physiological function of βSyn.