All‐optical monitoring of excitation–secretion coupling demonstrates that SV2A functions downstream of evoked Ca2+ entry
Open accessAbstract
SV2A, an essential transporter‐like synaptic vesicle protein, is a major target for antiepileptic drugs and a receptor for clostridial neurotoxins including Botox. While SV2A is required for normal levels of evoked neurotransmitter release, the mechanism underlying this role remains unclear. Here, we introduce a new chemogenetic approach for all‐optical monitoring of excitation–secretion coupling, and we demonstrate its use in characterizing the SV2A knockout (KO) phenotype in cultured hippocampal neurons. This method employs the HaloTag system to target a robust small‐molecule Ca 2+ indicator, JF 646–BAPTA, to the presynaptic compartment. The far‐red fluorescence of this indicator enables multiplexing with the fluorescent glutamate sensor iGluSnFR for detection of presynaptic Ca 2+ influx and glutamate release at the same axonal boutons. Evoked glutamate release probability was reduced in SV2A KO neurons without a change in presynaptic Ca 2+ entry, suggesting that SV2A supports vesicle fusion by increasing the functional availability, or efficiency, of the Ca 2+‐regulated membrane fusion machinery. Key points: One of the most prescribed antiepileptic medications, levetiracetam, acts by binding a protein of uncertain molecular function. This transporter‐like protein, SV2A, is trafficked to synaptic vesicles and acts to support neurotransmitter release, but the mechanism underlying this function has not been determined In this study, we sought to establish whether SV2A changes Ca 2+ signalling at nerve terminals, which is a key regulatory system for synaptic vesicle exocytosis. To do so, we adapted new chemogenetic tools to perform all‐optical measurements of presynaptic Ca 2+ and glutamate release in neurons lacking SV2A. Our measurements showed that loss of SV2A reduces glutamate release without reducing Ca 2+ influx at hippocampal nerve terminals, demonstrating that SV2A increases the likelihood that Ca 2+ will trigger synaptic vesicle fusion.
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SV2A aligns vesicle readiness with calcium-triggered fusion, shaping efficiency and timing of exocytosis without altering presynaptic calcium entry.
“Localized to synaptic vesicles, it aligns vesicle readiness with calcium triggered fusion, shaping the efficiency and timing of exocytosis without altering presynaptic calcium entry itself [186,187,188].”
From Synaptic Plasticity—Intrinsic Excitability and Antidepressant Discovery (2026) · cites this paper as [188]
The Abstract and Results report that loss of SV2A reduces evoked glutamate release probability without changing presynaptic Ca2+ entry, supporting its role in the efficiency of calcium-triggered fusion. The Discussion says SV2A’s molecular function remains elusive; the paper does not establish that it aligns vesicle readiness with fusion or controls the timing of exocytosis. The indexed passages provide section labels but no page numbers. (LLM, conf=0.86)
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- Authors
- Bradberry, M. M., & Chapman, E. R.
- Affiliations
- Howard Hughes Medical Institute (US)
- Corresponding author
- Chapman, Edwin R.
- Venue
- The Journal of Physiology
- Publisher
- Wiley
- Published
- 2022-01-13
- Volume
- 600
- Issue
- 3
- Pages
- 645-654
- ISSN
- 0022-3751 (ISSN-L)
- 1469-7793
- PMC
- PMC8810609
- OpenAlex
- W4200055322
- Cited by
- 16
- References
- 44
- Citations by year
- 2026: 1 · 2025: 2 · 2024: 4 · 2023: 5 · 2022: 4
- FWCI
- 1.50
- Type
- journal article
- Language
- en
- Open access
- green
- www.ncbi.nlm.nih.gov
- Locations
- The Journal of Physiology (publishedVersion)
- PubMed (publishedVersion)
- PubMed Central (acceptedVersion)
- Funders
- National Institute of Mental Health (F30MH116580, R01MH061876)
- National Institute of General Medical Sciences (T32GM140935)
- National Institute of Neurological Disorders and Stroke (R35NS097362)
- Topics
- Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Cellular transport and secretion
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Biophysics › Advanced Fluorescence Microscopy Techniques
- Keywords
- SV2A, excitation-secretion coupling, presynaptic calcium entry, glutamate release, synaptic vesicle fusion, vesicle exocytosis, levetiracetam, antiepileptic drugs, HaloTag, iGluSnFR, hippocampal neurons, clostridial neurotoxins, onabotulinumtoxinA
- MeSH terms
- Exocytosis, Synaptic Transmission, Neurons, Synaptic Vesicles, Presynaptic Terminals
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