Panzi, C. | Search bioRxiv

bioRxiv2023

Botulinum neurotoxin A modulates the axonal release of pathological tau in hippocampal neurons

Pathological tau aggregates propagate across functionally connected neuronal networks in human neurodegenerative pathologies, such as Alzheimers disease. However, the mechanism underlying this process is poorly understood. Several studies have showed that tau release is dependent on neuronal activity and that pathological tau is found in the extracellular space in free form, as well as in the lumen of extracellular vesicles. We recently showed that metabotropic glutamate receptor activity and the SNAP25 integrity modulate the release of pathological tau from human and mouse synaptosomes. Here, we have leveraged botulinum neurotoxins (BoNTs), which impair neurotransmitter release by cleaving specific synaptic SNARE proteins, to dissect molecular mechanisms related to tau release at synapses. In particular, we have tested the effect of botulinum neurotoxin A (BoNT/A) on the synaptic release of tau in primary mouse neurons. Hippocampal neurons were grown in microfluidic chambers and transduced with lentiviruses expressing human tau (hTau). We found that neuronal stimulation significantly increases the release of mutant hTau, whereas wild-type hTau is unaffected. Importantly, BoNT/A blocks mutant hTau release, indicating that this process is modulated by SNAP25 in intact neurons. These results suggest that BoNTs are potent tools to study the spreading of pathological proteins in neurodegenerative diseases and will play a central role in identifying novel molecular targets for the development of therapeutic interventions to treat tauopathies.

neuroscience↗

bioRxiv2023

The tyrosine phosphatase LAR acts as a receptor of the nidogen-tetanus toxin complex

Tetanus toxin is one of the most potent neurotoxins and is the causative agent of tetanus. This neurotoxin binds to the neuromuscular junction and, after internalisation into motor neurons, undergoes long-distance axonal transport and transcytosis into spinal cord inhibitory interneurons. Inside the cytoplasm of interneurons, the catalytic chain of the toxin blocks neurotransmitter release, leading to spastic paralysis. Whilst the effects of tetanus toxin intoxication have been extensively studied, the molecular composition of its receptor complex is still poorly understood. We have previously shown that the extracellular matrix proteins nidogens are essential for binding of the toxin to the neuromuscular junction. In this study, we show that the tyrosine phosphatase LAR interacts with the nidogen-tetanus toxin complex and enables its uptake into motor neurons. Binding of LAR to the toxin complex is mediated by its fibronectin III domains, which we have harnessed to inhibit tetanus toxin entry into motor neurons. Surprisingly, this function of LAR is independent of its role in regulating the neurotrophic activity of the TrkB receptor, which has previously been shown to augment the axonal transport of signalling endosomes containing tetanus neurotoxin. These findings identify a multi-subunit complex acting as a protein receptor for tetanus neurotoxin, and demonstrate a novel endocytic trafficking route for extracellular matrix proteins in neurons. Our study paves the way for dissecting the molecular mechanisms that control the recognition and uptake of physiological ligands and pathological proteins at the neuronal plasma membrane, as well as their targeting to the axonal retrograde pathway for long-distance transport within the nervous system.

cell biology↗