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EMBO J. 2019 Mar 1;38(5). pii: e100116. doi: 10.15252/embj.2018100116. Epub 2019 Feb 7.

Endophilin-A regulates presynaptic Ca2+ influx and synaptic vesicle recycling in auditory hair cells.

Kroll J1,2,3,4, Jaime Tobón LM3,4,5,6,7, Vogl C3,5,7,8, Neef J3,5,6,7, Kondratiuk I1, König M1,3, Strenzke N3,7,9, Wichmann C10,3,7, Milosevic I11,3, Moser T12,5,6,7.

Author information

1
Synaptic Vesicle Dynamics Group, European Neuroscience Institute (ENI), University Medical Center Göttingen, Göttingen, Germany.
2
Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
3
Collaborative Research Center 889, University of Göttingen, Göttingen, Germany.
4
Göttingen Graduate School for Neuroscience and Molecular Biosciences, University of Göttingen, Göttingen, Germany.
5
Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
6
Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
7
Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany.
8
Presynaptogenesis and Intracellular Transport in Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
9
Auditory Systems Physiology Group and InnerEarLab, Department of Otolaryngology, University of Göttingen Medical Center, Göttingen, Germany.
10
Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience, InnerEarLab and Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany carolin.wichmann@med.uni-goettingen.de i.milosevic@eni-g.de tmoser@gwdg.de.
11
Synaptic Vesicle Dynamics Group, European Neuroscience Institute (ENI), University Medical Center Göttingen, Göttingen, Germany carolin.wichmann@med.uni-goettingen.de i.milosevic@eni-g.de tmoser@gwdg.de.
12
Collaborative Research Center 889, University of Göttingen, Göttingen, Germany carolin.wichmann@med.uni-goettingen.de i.milosevic@eni-g.de tmoser@gwdg.de.

Abstract

Ribbon synapses of cochlear inner hair cells (IHCs) operate with high rates of neurotransmission; yet, the molecular regulation of synaptic vesicle (SV) recycling at these synapses remains poorly understood. Here, we studied the role of endophilins-A1-3, endocytic adaptors with curvature-sensing and curvature-generating properties, in mouse IHCs. Single-cell RT-PCR indicated the expression of endophilins-A1-3 in IHCs, and immunoblotting confirmed the presence of endophilin-A1 and endophilin-A2 in the cochlea. Patch-clamp recordings from endophilin-A-deficient IHCs revealed a reduction of Ca2+ influx and exocytosis, which we attribute to a decreased abundance of presynaptic Ca2+ channels and impaired SV replenishment. Slow endocytic membrane retrieval, thought to reflect clathrin-mediated endocytosis, was impaired. Otoferlin, essential for IHC exocytosis, co-immunoprecipitated with purified endophilin-A1 protein, suggestive of a molecular interaction that might aid exocytosis-endocytosis coupling. Electron microscopy revealed lower SV numbers, but an increased occurrence of coated structures and endosome-like vacuoles at IHC active zones. In summary, endophilins regulate Ca2+ influx and promote SV recycling in IHCs, likely via coupling exocytosis to endocytosis, and contributing to membrane retrieval and SV reformation.

KEYWORDS:

electron microscopy; endocytosis; membrane capacitance; ribbon synapse; super‐resolution microscopy

PMID:
30733243
PMCID:
PMC6396150
[Available on 2020-03-01]
DOI:
10.15252/embj.2018100116

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