Neuritogenic actions of botulinum neurotoxin A on cultured motor neurons.
Botulinum neurotoxins (BoNTs) are extremely potent neuromuscular poisons that act through soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein cleavage to inhibit neurotransmitter release. The ability of BoNT serotype A (BoNT/A) to eliminate localized transmitter release at extremely low doses is well characterized. In the current study, we investigated the less understood characteristic of BoNT/A to induce nerve outgrowth, sometimes referred to as sprouting. This phenomenon is generally considered a secondary response to the paralytic actions of BoNT/A, and other potential factors that may initiate this sprouting have not been investigated. Alternatively, we hypothesized that BoNT/A induces sprouting through presynaptic receptor activation that is independent of its known intracellular actions on the soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) synaptosomal associated protein of 25 kDa (SNAP-25). To test this, the effects of BoNT/A application on neurite outgrowth were examined using primary cultures enriched with motor neurons isolated from embryonic mouse spinal cord. In this system, BoNT/A potently stimulated neuritogenesis at concentrations as low as 0.01 nM. The neuritogenic effects of BoNT/A exposure were concentration dependent and antagonized by Triticum vulgaris lectin, a known competitive antagonist of BoNT. Similar results were observed with the isolated BoNT/A binding domain, revealing that neuritogenesis could be initiated solely by the binding actions of BoNT/A. In addition, the presence or absence of SNAP-25 cleavage by BoNT/A was not a determinant factor in BoNT/A-induced neuritogenesis. Collectively, these results suggest that binding of BoNT/A to the motor neuronal membrane activates neuritogenesis through as yet undetermined intracellular pathway(s), independent of its known action on vesicular release.
Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA. coffield@uga.edu
Julie A
JA
Coffield
Xiuzhen
X
Yan
D000818:Animals; D019274:Botulinum Toxins, Type A / Q000494:pharmacology*; D002478:Cells, Cultured; D022162:Cytoplasmic Vesicles / Q000378:metabolism / Q000382:microbiology / Q000502:physiology; D053595:Embryonic Stem Cells / Q000166:cytology / Q000382:microbiology / Q000502:physiology*; D005260:Female; D007424:Intracellular Fluid / Q000382:microbiology / Q000502:physiology; D051379:Mice; D009046:Motor Neurons / Q000166:cytology / Q000382:microbiology / Q000502:physiology*; D016501:Neurites / Q000382:microbiology / Q000502:physiology*; D055495:Neurogenesis / Q000502:physiology*; D011247:Pregnancy; D015398:Signal Transduction / Q000502:physiology
D019274:Botulinum Toxins, Type A