Investigating the synaptic mechanisms of the spread of wild type and P301S 1N4R human tau in in vitro and in vivo models

Abstract

AbstractBackgroundTau aggregates propagate across functionally connected neuronal networks in tauopathies as Alzheimer’s disease. However, the mechanisms underlying this process are poorly understood. Different studies showed that tau release is dependent on neuronal activity and that pathological tau can be found in the extracellular space confined in extracellular vesicles or in a free form. We recently showed that metabotropic glutamate receptors and SNAP25 modulate the release of pathologic tau from human and mouse synaptosomes. Here, with the use of blocking agents such as botulinum neurotoxins (BoNTs), we plan to test the effect on the synaptic release of tau in vitro and in vivo. BoNTs enter synapses and cleave specific synaptic SNARE proteins, impairing synaptic vesicle fusion and release. We aim at demonstrating the potential of BoNTs as tools to study neurodegenerative diseases.MethodsPrimary mouse hippocampal neurons were cultured in microfluidic chambers, transduced with lentiviruses expressing human tau (hTau) isoforms, and treated with BoNTs and stimulators. ELISA was used to quantify hTau in the culture media. AAVs expressing hTau were injected in the vitreous of wild‐type mice, and BoNT type A (BoNT/A) was injected in the superior colliculus (SC). Retina, SC and lateral geniculate nucleus (LGN) were analysed through immunohistochemistry.ResultsOverexpression of hTau in primary neurons increases the expression of synaptic markers as compared to non‐transduced cells, while any difference is detected between wild‐type and P301S hTau. Neuronal stimulation significantly increases the release of P301S hTau, whereas BoNT/A blocks it. Preliminary in vivo data show no difference in the expression and transfer of wild type and P301S hTau in the SC and LGN. The ongoing analysis of BoNT/A injected mice will reveal any effect on tau spread in the brain.ConclusionsThe release of hTau is modulated by specific SNARE proteins and differs depending on the isoform in vitro. The use of BoNT/A in vivo will help us to clarify the mechanisms modulating tau release in a complex system. Moreover, with the use of other BoNTs, we will provide novel insights into the mechanisms of synaptic tau release and identify novel molecular targets for the development of therapeutic interventions to treat tauopathies.