By Pooja Toshniwal PahariaReviewed by Lexie CornerMay 7 2025A recent Nature Communications study explored how synaptic vesicle (SV) composition changes with age and α-synuclein (αSyn)-related disease. The researchers focused on the role of αSyn in maintaining synaptic health, with the goal of informing therapies that could restore normal function by adjusting αSyn levels.
This protein, known for accumulating in Lewy bodies, is a key driver of neurodegeneration in disorders such as Parkinson’s disease (PD).
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Synapses are the communication points between neurons, where neurotransmitters are released to transmit signals. Two core processes—exocytosis and endocytosis—regulate this transmission.
Exocytosis releases neurotransmitters by fusing SVs with the presynaptic membrane, while endocytosis recycles SVs for future use. Both processes are known to decline with age and are further disrupted in neurodegenerative diseases. Alpha-synuclein is a presynaptic protein that helps regulate SV availability, which is essential for efficient neurotransmission.
About the Study
The researchers examined SV protein and lipid composition in mice to model changes linked to aging and αSyn-related pathology.
They studied three groups:
- Wild-type (WT) mice with natural aging
- αSyn knockout (αSynKO) mice that lack both mouse and human αSyn
- αSynBAC mice expressing human αSyn in the absence of the mouse version
Brain samples were collected at 1, 3, and 10 months of age. To isolate SVs, brain tissue was first processed using SDS-PAGE for protein extraction and subcellular fractionation. Crude SV fractions were then analyzed using quantitative proteomics, including high-pH reverse-phase (hpRP) chromatography and nanoscale LC-MS (nanoLC-MS).
Lipid composition was studied using reversed-phase LC-MS and pathway mapping through BioPAN analysis. Transmission electron microscopy (TEM) provided visual data on synaptic terminal size, SV density, number of docked vesicles, and active zone dimensions.
To complement this, sucrose density gradient centrifugation was used to assess how SV proteins were distributed within the isolated fractions, linking molecular findings to structural observations from TEM.
Results
The study identified previously unreported proteomic and lipidomic changes in synaptic vesicles (SVs) linked to aging and α-synuclein-related disease. These changes may impact SV membrane curvature, increase lipid packing defects, elevate phosphatidylserine (PS) levels on cytosolic leaflets, and disrupt PS-protein interactions. Monomeric α-synuclein is known to induce membrane curvature and respond to lipid packing defects, suggesting that its loss may contribute to synaptic dysfunction.
The ultrastructural findings of wild-type, αSynBAC, and αSynKO mice suggest that the loss of α-synuclein function may contribute to synaptic disruption.
While synaptic vesicles of WT mice remained stable with aging, αSynKO and αSynBAC mice SV demonstrated increased density, reduced active zone length, fewer docked SVs, and smaller terminals. Additionally, the αSynBAC mice exhibited increased SV clusters, resulting from human α-synuclein phosphorylation at the Ser129 site, a pathologic hallmark of synucleinopathies.
In the proteomic analysis, all mice showed increased exocytosis-related proteins such as syntaxin-1B, mammalian uncoordinated-18-1 (Munc-18-1), and endocytosis-related bridging integrator 1 (Bin1). In addition, αSynKO mice showed increased levels of calcium-dependent secretion activator 2 (CADPS2), synapsin, adaptor-related protein complex 1 subunit beta-1 (AP1B1), phosphatidylinositol binding clathrin assembly protein (PICALM), and decreased levels of V-type proton ATPase (vATPase) subunits V0d1 and V0F1.
CADPS2 and synapsin mediate exocytosis, AP1B1 and PICALM regulate endocytosis, and vATPase enzymes control SV acidity. Genomic mutations in CADPS2, PICALM, and Bin1 occur in neurodegenerative disorders, implying the significance of SV proteins and potential applications of αSyn-related therapies to improve neurotransmission.
Compared to αSynKO mice, αSynBAC mice showed contrasting findings. Changes unique to αSynKO mice included an upsurge in N-ethylmaleimide-sensitive fusion protein (NSF)-related exocytosis, whereas ATPase phospholipid transporting 8A1 (ATP8A1)-related exocytotic processes increased only in the αSynBAC group.
In the lipidomic analysis, WT mice showed reduced expression of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine with concomitant increases in lysoPC, lysoPS, and ATP8A1. In addition to these effects, αSynBAC mice demonstrated increased lysoPE and reduced ratios of lipids to proteins. The αSynKO mice exhibited lipid profiles opposite to those of αSynBAC mice.
Among the animals, only αSynBAC mice revealed a considerable age-dependent reduction in total lipid level, with the most pronounced changes in unsaturated lipids. The PD lipidome comprises increased lysoPC, sphingolipid, cholesterol, diacylglycerol (DAG), and decreased PC and PE. The findings highlight the link between αSyn-induced synaptic changes and neurodegenerative disorders.
The team found an age-associated increase in SV2, an integral synaptic vesicle protein, in the brain samples obtained from the αSynKO and αSynBAC groups, with the highest levels in αSynBAC animals. They also observed increases in vesicular glutamate transporter 3 (vGluT3) levels in the αSynBAC group at 10 months and in the expression of the vesicular monoamine transporter 2 (vMAT2) in the αSynBAC group. These age-associated changes result from SV acidification and phospholipid metabolism. Taken together, αSynKO and αSynBAC mice have reduced synaptic strength.
Overall, the findings show that loss or dysfunction of α-synuclein disrupts SV composition and function. This disruption impairs neurotransmitter release and highlights the importance of α-synuclein in maintaining synaptic health, offering a potential target for therapies in neurodegenerative conditions.
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Journal Reference
Gao, V., et al. Synaptic vesicle-omics in mice captures signatures of aging and synucleinopathy. Nat Commun 16, 4079 (2025), DOI: 10.1038/s41467-025-59441-7, https://www.nature.com/articles/s41467-025-59441-7
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