Funded Studies
Objective/Rationale:
Alpha-synuclein, implicated in Parkinson’s disease, is normally expressed in nerve terminals, from which neurotransmitters are released by fusion of their granule membrane with the cell membrane. Alpha-synuclein has membrane-binding characteristics similar to proteins that modulate the opening (fusion pore) between the fused granule and cell exterior. The opening controls the rate of release of granule proteins to the cell exterior. We will investigate the novel hypothesis that synuclein normally functions to regulate the opening.
Project Description:
We will determine whether the lipid-binding and curvature-inducing characteristics of alpha-synuclein regulate fusion pore expansion and subsequent protein release. First, in cells, we will overexpress alpha-synuclein and mutants that cause disease. We will use a powerful optical technique that we have developed that detects submicroscopic changes in plasma membrane curvature and can visualize the expanding fusion pore at individual fusion events. The relationship between the expanding fusion pore and the rate of specific protein discharge at fusion events will be determined. If alpha-synuclein or mutants inhibit fusion pore expansion, then protein release will be slowed. If it speeds expansion, then proteins that normally are discharge slowly may be more rapidly released.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
If we are correct in our hypothesis that the normal function of alpha-synuclein is to regulate fusion pore expansion and protein release, then the paradigm underlying the investigation of synucleinopathies will change. There will be an increased focus on protein release from neurons, including the biophysical factors that regulate secretion of neurotrophic proteins and how disease-causing alpha-synuclein mutations and gene duplication alter normal function.
Anticipated Outcome:
We anticipate to show that alpha-synuclein regulates the expansion of the initial small-diameter connection of a storage granule with the plasma membrane after fusion, and thereby controls the release of proteins stored within the granule.
Final Outcome
Alpha-synuclein is a sticky protein that clumps in the brains of people with Parkinson's disease (PD). It is also present in the brains of people without PD, but its role is unclear. It is currently believed that alpha-synuclein interacts with lipids, components of membranes that make up the outer layer of the cell as well as packets of protein inside the cell called vesicles. When spilled out of the vesicles outside the cell, these proteins help cells communicate. Alpha-synuclein is believed to interfere with this process. In this study, we aimed to test whether alpha-synuclein controls the size of the hole through which proteins spill out of the vesicle. The results of this study strongly support this hypothesis, indicating that alpha-synuclein slows the release of proteins from vesicles by making the holes smaller.
November 2014