The travel diaries of tetanus and botulinum neurotoxins.

Tetanus (TeNT) and botulinum (BoNT) neurotoxins, the causative agents of tetanus and botulism, respectively, are the most potent toxic molecules known to mankind. This extreme potency is attributed to: i) their specificity for essential components of the neurotransmitter release machinery present at vertebrate synapses, and ii) their high-affinity targeting to motor neurons by binding to polysialogangliosides and protein receptors. Comprising the clostridial neurotoxin family, TeNT and BoNTs engage distinct surface receptors and intracellular sorting pathways in neurons. BoNTs bind to the intraluminal domain of specific synaptic vesicle proteins that are exposed to the extracellular milieu upon exocytosis, and are taken up by synaptic vesicle recycling. A sizeable proportion of BoNT molecules remain at the neuromuscular junction, where their protease moiety is released into the cytoplasm, blocking synaptic transmission and causing flaccid paralysis. In contrast, TeNT undergoes binding to specific components of the basal membrane at the neuromuscular junction, is endocytosed into motor neurons and sorted to axonal signalling endosomes. Following this, TeNT is transported to the soma of motor neurons located in the spinal cord or brainstem, and then transcytosed to inhibitory interneurons, where it blocks synaptic transmission. TeNT-induced impairment of inhibitory input leads to hyperactivity of motor neurons, causing spastic paralysis, which is the hallmark of tetanus. This review examines the molecular mechanisms leading to the entry, sorting and intracellular trafficking of TeNT and BoNTs.

A neuroprotective astrocyte state is induced by neuronal signal EphB1 but fails in ALS models.

Astrocyte responses to neuronal injury may be beneficial or detrimental to neuronal recovery, but the mechanisms that determine these different responses are poorly understood. Here we show that ephrin type-B receptor 1 (EphB1) is upregulated in injured motor neurons, which in turn can activate astrocytes through ephrin-B1-mediated stimulation of signal transducer and activator of transcription-3 (STAT3). Transcriptional analysis shows that EphB1 induces a protective and anti-inflammatory signature in astrocytes, partially linked to the STAT3 network. This is distinct from the response evoked by interleukin (IL)-6 that is known to induce both pro inflammatory and anti-inflammatory processes. Finally, we demonstrate that the EphB1-ephrin-B1 pathway is disrupted in human stem cell derived astrocyte and mouse models of amyotrophic lateral sclerosis (ALS). Our work identifies an early neuronal help-me signal that activates a neuroprotective astrocytic response, which fails in ALS, and therefore represents an attractive therapeutic target.