| First Author | Sarafian TA | Year | 2017 |
| Journal | J Neurosci Res | Volume | 95 |
| Issue | 9 | Pages | 1871-1887 |
| PubMed ID | 28117497 | Mgi Jnum | J:268174 |
| Mgi Id | MGI:6268880 | Doi | 10.1002/jnr.24024 |
| Citation | Sarafian TA, et al. (2017) Stimulation of synaptoneurosome glutamate release by monomeric and fibrillated alpha-synuclein. J Neurosci Res 95(9):1871-1887 |
| abstractText | The alpha-synuclein protein exists in vivo in a variety of covalently modified and aggregated forms associated with Parkinson's disease (PD) pathology. However, the specific proteoform structures involved with neuropathological disease mechanisms are not clearly defined. Since alpha-synuclein plays a role in presynaptic neurotransmitter release, an in vitro enzyme-based assay was developed to measure glutamate release from mouse forebrain synaptoneurosomes (SNs) enriched in synaptic endings. Glutamate measurements utilizing SNs from various mouse genotypes (WT, over-expressers, knock-outs) suggested a concentration dependence of alpha-synuclein on calcium/depolarization-dependent presynaptic glutamate release from forebrain terminals. In vitro reconstitution experiments with recombinant human alpha-synuclein proteoforms including monomers and aggregated forms (fibrils, oligomers) produced further evidence of this functional impact. Notably, brief exogenous applications of fibrillated forms of alpha-synuclein enhanced SN glutamate release but monomeric forms did not, suggesting preferential membrane penetration and toxicity by the aggregated forms. However, when applied to brain tissue sections just prior to homogenization, both monomeric and fibrillated forms stimulated glutamate release. Immuno-gold and transmission electron microscopy (TEM) detected exogenous fibrillated alpha-synuclein associated with numerous SN membranous structures including synaptic terminals. Western blots and immuno-gold TEM were consistent with SN internalization of alpha-synuclein. Additional studies revealed no evidence of gross disruption of SN membrane integrity or glutamate transporter function by exogenous alpha-synuclein. Overall excitotoxicity, due to enhanced glutamate release in the face of either overexpressed monomeric alpha-synuclein or extrasynaptic exposure to fibrillated alpha-synuclein, should be considered as a potential neuropathological pathway during the progression of PD and other synucleinopathies. (c) 2017 Wiley Periodicals, Inc. |
