Internalization and proteolytic action of botulinum toxins in CNS neurons and astrocytes

Abstract: Tetanus and botulinum toxins bind and are internalized at the neuromuscular junction. Botulinum neurotoxins (BoNTs) enter the cytosol at the motor nerve terminal; tetanus neurotoxin (TeNT) proceeds retroax-onally inside the motor axon to reach the spinal cord inhibitory interneurons. Although the major target of BoNTs is the peripheral cholinergic terminals, CNS neu-rons are susceptible to intoxication as well. We investi-gated the route of entry and the proteolytic activity of BoNT/B and BoNT/F in cultured hippocampal neurons and astrocytes. We show that, differently from TeNT, which enters hippocampal neurons via the process of synaptic vesicle (SV) recycling, BoNTs are internalized and cleave the substrate synaptobrevin/VAMP2 via a process independent of synaptic activity. Labeling of liv