Increased Expression of α‐Synuclein Impairs Trafficking of the Essential SNARE Protein Synaptobrevin‐2

ABSTRACT α‐Synuclein is a presynaptic protein that has been extensively studied for its role in Parkinson's disease. Multiplication and missense variants in the gene encoding α‐synuclein are causes of familial PD, and aggregated α‐synuclein is a major component of Lewy bodies and Lewy neurites, the histopathological hallmark of the disease. However, the native function of α‐synuclein remains unclear, though several lines of evidence suggest it modulates presynaptic function. α‐Synuclein binds the vesicular SNARE protein synaptobrevin‐2/VAMP2, and increased levels of α‐synuclein potentiate SNARE complex levels without impacting exocytic rate. Given the essential role of synaptobrevin‐2 in synaptic function we sought to examine how increased expression of α‐synuclein, at levels observed in familial synucleinopathies with SNCA triplication, impacts the trafficking of this essential SNARE protein. Modest (approximately 2‐fold) overexpression of α‐synuclein in cultured murine hippocampal neurons caused a slowing in the endocytic retrieval of synaptobrevin‐2, without impacting either the targeting of the protein to synapses or altering endocytosis. We also show that α‐synuclein is not working antagonistically with the synaptobrevin‐2 chaperone synaptophysin, and likely acts at least partially via direct binding to synaptobrevin‐2. Finally, increased expression of α‐synuclein induces synaptic depression upon repeated neuronal depolarisation, in a manner requiring binding to synaptobrevin‐2. We reveal α‐synuclein as a modulator of synaptobrevin‐2 endocytic trafficking and highlight perturbed SNARE protein trafficking as a potential contributor to synaptic dysfunction and neuronal health in Parkinson's disease. image