title: Loss of Huntingtin stimulates capture of retrograde dense-core vesicles to increase synaptic neuropeptide stores.
abstract: The Huntington's disease protein Huntingtin (Htt) regulates axonal transport of dense-core vesicles (DCVs) containing neurotrophins and neuropeptides. DCVs travel down axons to reach nerve terminals where they are either captured in synaptic boutons to support later release or reverse direction to reenter the axon as part of vesicle circulation. Currently, the impact of Htt on DCV dynamics in the terminal is unknown. Here we report that knockout of Drosophila Htt selectively reduces retrograde DCV flux at proximal boutons of motoneuron terminals. However, initiation of retrograde transport at the most distal bouton and transport velocity are unaffected suggesting that synaptic capture rate of these retrograde DCVs could be altered. In fact, tracking DCVs shows that retrograde synaptic capture efficiency is significantly elevated by Htt knockout or knockdown. Furthermore, synaptic boutons contain more neuropeptide in Htt knockout larvae even though bouton size, single DCV fluorescence intensity, neuropeptide release in response to electrical stimulation and subsequent activity-dependent capture are unaffected. Thus, loss of Htt increases synaptic capture as DCVs travel by retrograde transport through boutons resulting in reduced transport toward the axon and increased neuropeptide in the terminal. These results therefore identify native Htt as a regulator of synaptic capture and neuropeptide storage.
authors.affiliation: Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
authors.forename: Dinara
authors.initials: D
authors.lastname: Bulgari
authors.affiliation: Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Deitcher
authors.affiliation: Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15261, USA. Electronic address: elevitan@pitt.edu.
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Levitan
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D055786:Gene Knockout Techniques; D000071058:Huntingtin Protein / Q000378:metabolism*; D009046:Motor Neurons / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; C542005:Htt protein, Drosophila; D000071058:Huntingtin Protein; D009479:Neuropeptides
keywords: Axonal transport; Huntingtin; Neuromuscular junction; Synapse