title: Botulinum neurotoxin A impairs neurotransmission following retrograde transynaptic transport.
abstract: The widely used botulinum neurotoxin A (BoNT/A) blocks neurotransmission via cleavage of the synaptic protein SNAP-25 (synaptosomal-associated protein of 25 kDa). Recent evidence demonstrating long-distance propagation of SNAP-25 proteolysis has challenged the idea that BoNT/A remains localized to the injection site. However, the extent to which distant neuronal networks are impacted by BoNT/A retrograde trafficking remains unknown. Importantly, no studies have addressed whether SNAP-25 cleavage translates into structural and functional changes in distant intoxicated synapses. Here we show that the BoNT/A injections into the adult rat optic tectum result in SNAP-25 cleavage in retinal neurons two synapses away from the injection site, such as rod bipolar cells and photoreceptors. Retinal endings displaying cleaved SNAP-25 were enlarged and contained an abnormally high number of synaptic vesicles, indicating impaired exocytosis. Tectal injection of BoNT/A in rat pups resulted in appearance of truncated-SNAP-25 in cholinergic amacrine cells. Functional imaging with calcium indicators showed a clear reduction in cholinergic-driven wave activity, demonstrating impairments in neurotransmission. These data provide the first evidence for functional effects of the retrograde trafficking of BoNT/A, and open the possibility of using BoNT/A fragments as drug delivery vehicles targeting the central nervous system.
authors.affiliation: CNR Neuroscience Institute, via G. Moruzzi 1, Pisa, 56124, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Restani
authors.forename: Elena
authors.initials: E
authors.lastname: Novelli
authors.forename: David
authors.initials: D
authors.lastname: Bottari
authors.forename: Paola
authors.initials: P
authors.lastname: Leone
authors.forename: Ilaria
authors.initials: I
authors.lastname: Barone
authors.forename: Lucia
authors.initials: L
authors.lastname: Galli-Resta
authors.forename: Enrica
authors.initials: E
authors.lastname: Strettoi
authors.forename: Matteo
authors.initials: M
authors.lastname: Caleo
mesh_terms: D000818:Animals; D019274:Botulinum Toxins, Type A / Q000494:pharmacology*; D020013:Calcium Signaling; D051381:Rats; D020318:Rats, Long-Evans; D055351:Retinal Neurons / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D050825:Synaptosomal-Associated Protein 25 / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D019274:Botulinum Toxins, Type A; C545476:incobotulinumtoxinA