Synaptophysin sustains presynaptic performance by preserving vesicular synaptobrevin-II levels

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Physiology

Background:

• Synaptic vesicles (SVs) contain abundant synaptophysin and synaptobrevin-II (sybII).
• SybII is vital for SV fusion, while synaptophysin is implicated in sybII trafficking and retrieval.
• Synaptophysin knockout neurons show minimal impact on neurotransmission, suggesting compensatory mechanisms.

Purpose of the Study:

• To investigate the role of synaptophysin in maintaining synaptic function during periods of high neuronal activity.
• To test the hypothesis that synaptophysin's importance is revealed under conditions of repeated synaptic vesicle turnover.

Main Methods:

• Primary cultures of synaptophysin knockout neurons were subjected to repeated neuronal stimulation.
• Synaptic vesicle fusion events were monitored using vesicular glutamate transporter-pHluorin.
• Vesicular sybII levels were assessed via immunofluorescence and Western blotting.

Main Results:

• Repeated neuronal activity in synaptophysin knockout neurons led to a significant decrease in SV fusion events.
• Vesicular sybII levels were also significantly reduced in the absence of synaptophysin under these conditions.
• Exogenous synaptophysin expression rescued presynaptic performance, and exogenous sybII fully restored SV fusion events.

Conclusions:

• Synaptophysin is essential for sustaining SV fusion and vesicular sybII levels during repetitive SV turnover.
• The findings suggest synaptophysin's primary role is to facilitate efficient sybII retrieval, thereby supporting sustained neurotransmitter release.
• This highlights synaptophysin's critical contribution to synaptic plasticity and maintaining neurotransmission under demanding activity levels.