Investigating synaptic tau localisation in neurodegeneration using Expansion Microscopy

Abstract

Tauopathies are a class of neurodegenerative diseases characterised by the progressive
accumulation of misfolded tau protein into neurofibrillary tangles (NFTs). The dissociation of
tau from microtubules disrupts axonal transport whilst intracellular NFTs displace organelles
resulting in cell death. Evidence from mouse tauopathy models (i.e. rTg4510) indicate that
prior to substantial NFT accumulation, tau is mislocated to synapses. This correlates
temporally with an early disruption to synaptic function in rTg4510 mice, and it has been
hypothesised that synaptic tau presence could contribute to the early synapse loss that occurs
in tauopathy-driven neurodegeneration.
Previous studies aiming to resolve pathological tau at dendritic spines have been limited by
light resolution. However, in recent years, a new technique, Expansion Microscopy (ExM),
has been established by which fixed tissue and cell samples can be physically expanded 4.0-
4.5 fold to enable imaging of subcellular structures probed with fluorophores on conventional
light microscopes.
Here, Protein Retention Expansion Microscopy (ProExM) has been optimised and applied to
fixed brain tissue slices from 4-month-old rTg4510 mice, with the purpose of increasing the
resolution of cell ultrastructure so that tau fibrils at synapses could be identified. rTg4510
fixed tissue was immunolabelled for tau and synaptic markers and expanded via ProExM. It
was shown that ExM is effective in increasing the resolution of molecular tau fibrils. In
addition, tau fibrils were localised to some putative synapses however these findings were
still limited by resolution.
The full potential of ExM has not yet been fully realised, and future studies could utilise
updated ExM protocols with higher expansion factors to further improve the resolution of
synaptic tau. By identifying synaptic tau presence in mouse models of neurodegeneration, the
relationship between mislocated synaptic tau and the disruption of synaptic function early in
tauopathies could be elucidated.

Date of Award	2 Dec 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Michael Ashby (Supervisor) & Jack R Mellor (Supervisor)