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Dynamin controls neuropeptide secretion by organizing dense-core vesicle fusion sites.

ABSTRACT: Synaptic vesicles (SVs) release neurotransmitters at specialized active zones, but release sites and organizing principles for the other major secretory pathway, neuropeptide/neuromodulator release from dense-core vesicles (DCVs), remain elusive. We identify dynamins, yeast Vps1 orthologs, as DCV fusion site organizers in mammalian neurons. Genetic or pharmacological inactivation of all three dynamins strongly impaired DCV exocytosis, while SV exocytosis remained unaffected. Wild-type dynamin restored normal exocytosis but not guanosine triphosphatase-deficient or membrane-binding mutants that cause neurodevelopmental syndromes. During prolonged stimulation, repeated use of the same DCV fusion location was impaired in dynamin 1-3 triple knockout neurons. The syntaxin-1 staining efficiency, but not its expression level, was reduced. αSNAP (α-soluble N-ethylmaleimide-sensitive factor attachment protein) expression restored this. We conclude that mammalian dynamins organize DCV fusion sites, downstream of αSNAP, by regulating the equilibrium between fusogenic and non-fusogenic syntaxin-1 promoting its availability for SNARE (SNAP receptor) complex formation and DCV exocytosis.

SUBMITTER: Moro A

PROVIDER: S-EPMC8139595 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Release of neuropeptides from dense core vesicles (DCVs) is essential for neuromodulation. Compared with the release of small neurotransmitters, much less is known about the mechanisms and proteins contributing to neuropeptide release. By optogenetics, behavioral analysis, electrophysiology, electron microscopy, and live imaging, we show that synapsin SNN-1 is required for cAMP-dependent neuropeptide release in Caenorhabditis elegans hermaphrodite cholinergic motor neurons. In synapsin mutants, behaviors induced by the photoactivated adenylyl cyclase bPAC, which we previously showed to depend on ACh and neuropeptides (Steuer Costa et al., 2017), are altered as in animals with reduced cAMP. Synapsin mutants have slight alterations in synaptic vesicle (SV) distribution; however, a defect in SV mobilization was apparent after channelrhodopsin-based photostimulation. DCVs were largely affected in snn-1 mutants: DCVs were ∼30% reduced in synaptic terminals, and their contents not released following bPAC stimulation. Imaging axonal DCV trafficking, also in genome-engineered mutants in the serine-9 protein kinase A phosphorylation site, showed that synapsin captures DCVs at synapses, making them available for release. SNN-1 colocalized with immobile, captured DCVs. In synapsin deletion mutants, DCVs were more mobile and less likely to be caught at release sites, and in nonphosphorylatable SNN-1B(S9A) mutants, DCVs traffic less and accumulate, likely by enhanced SNN-1 dependent tethering. Our work establishes synapsin as a key mediator of neuropeptide release.SIGNIFICANCE STATEMENT Little is known about mechanisms that regulate how neuropeptide-containing dense core vesicles (DCVs) traffic along the axon, how neuropeptide release is orchestrated, and where it occurs. We found that one of the longest known synaptic proteins, required for the regulation of synaptic vesicles and their storage in nerve terminals, synapsin, is also essential for neuropeptide release. By electrophysiology, imaging, and electron microscopy in Caenorhabditis elegans, we show that synapsin regulates this process by tethering the DCVs to the cytoskeleton in axonal regions where neuropeptides are to be released. Without synapsin, DCVs cannot be captured at the release sites and, consequently, cannot fuse with the membrane, and neuropeptides are not released. We suggest that synapsin fulfills this role also in vertebrates, including humans.

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Dynamin controls neuropeptide secretion by organizing dense-core vesicle fusion sites.

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