Evidence for Anterograde Transport and Transcytosis of Botulinum Neurotoxin A (BoNT/A)

• DOI: 10.1523/jneurosci.2618-11.2011
• Publication Date: 2011-11-02T17:03:41Z
• Authors: Laura Restani; Flavia Antonucci; Laura Gianfranceschi; Chiara Rossi; Ornella Rossetto; Matteo Caleo
• Keywords: Superior Colliculi; Botulinum Toxins; CD11b Antigen; Kainic Acid; Time Factors; Dose-Response Relationship, Drug; Synaptosomal-Associated Protein 25; Neurotoxins; Biological Transport; Nerve Tissue Proteins; Functional Laterality; Rats; 03 medical and health sciences; 0302 clinical medicine; Phosphopyruvate Hydratase; Glial Fibrillary Acidic Protein; Excitatory Amino Acid Agonists; Animals; Rats, Long-Evans; Botulinum Toxins, Type A; Injections, Intraocular; Transcytosis

Botulinum neurotoxin type A (BoNT/A) is a metalloprotease that blocks synaptic transmission via the cleavage of SNAP-25 (synaptosomal-associated protein of 25 kDa). BoNT/A is successfully used in clinical neurology for the treatment of several neuromuscular pathologies and pain syndromes. Despite its widespread use, relatively little is known on BoNT/A intracellular trafficking in neurons. Using the visual pathway as a model system, here we show that catalytically active BoNT/A is capable of undergoing anterograde axonal transport and transcytosis. Following BoNT/A injection into the rat eye, significant levels of BoNT/A-cleaved SNAP-25 appeared in the retinorecipient layers of the superior colliculus (SC). Anterograde propagation of BoNT/A effects required axonal transport, ruling out a systemic spread of the toxin. Cleaved SNAP-25 was present in presynaptic structures of the tectum, but retinal terminals were devoid of the immunoreactivity, indicative of transcytosis. Experiments based on sequential administration of BoNT/A and BoNT/E showed a persistent catalytic activity of BoNT/A in tectal cells following its injection into the retina. Our findings demonstrate that catalytically active BoNT/A is anterogradely transported from the eye to the SC and transcytosed to tectal synapses. These data are important for a more complete understanding of the mechanisms of action of BoNT/A.