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.
Coffield
Julie A
JA
Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA. coffield@uga.edu
Yan
Xiuzhen
X
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