Xu et al. · Acta Neuropathologica · 2024
MSUT2 regulates tau spreading via adenosinergic signaling mediated ASAP1 pathway in neurons
Xu Hong, Qiu Qi, Hu Peng, Hoxha Kevt'her, Jang Elliot, O'Reilly Mia, Kim Christopher, He Zhuohao, Marotta Nicholas, Changolkar Lakshmi, Zhang Bin, Wu Hao, Schellenberg Gerard D., Kraemer Brian, Luk Kelvin C., Lee Edward B., Trojanowski John Q., Brunden Kurt R., Lee Virginia M.-Y.
The study
What was asked, and what was found
Xu et al., Acta Neuropathologica, 2024 asked how tau pathology moves from neuron to neuron, and what controls the step where a misfolded tau seed is taken into a healthy cell. Earlier work had shown that losing the RNA binding protein MSUT2 reduces tau pathology in mice that overexpress mutant human tau, but overexpression models cannot separate the spreading of pathology from its production. The authors therefore used seeding models, adding tau extracted from the brains of people who had Alzheimer's disease, corticobasal degeneration or progressive supranuclear palsy to mouse primary neurons and to mouse brain, with no tau overexpression anywhere.
The knockdowns were done with self-delivering AUMsilence sdASOs, obtained from AUM BioTech and diluted into the culture medium at 1 μM on day 2 in vitro, against a scramble control and a buffer arm. Six independent sequences against MSUT2 were validated first, and all six lowered MSUT2 protein. Treated neurons then developed less tau pathology from all three human seed types, while alpha synuclein aggregation was unaffected. Live imaging with labelled seeds showed why: treated neurons took up fewer tau seeds and moved fewer into acidic compartments, so the effect sits upstream of aggregation, at entry.
Single nucleus sequencing of MSUT2 knockout neurons pointed to the adenosine A1 receptor, and further oligonucleotides tested that chain link by link. Knocking down the A1 receptor reproduced both the drop in seeded pathology and the drop in seed uptake, while knocking down the A2A receptor did not. Knocking down ASAP1, which the paper describes as a potential genetic risk factor for progressive supranuclear palsy, or its partner FIP3, did the same. Measuring three other routes into the neuron showed that only macropinocytosis changed, so the pathway is specific. The study rests on five separate messenger RNA knockdowns in primary neurons, each one added to the medium.
Key findings
- Six independent self-delivering AUMsilence sdASOs against MSUT2 each cut MSUT2 protein in wild-type mouse primary neurons, so the effect was reproduced across sequences rather than resting on one.(Results, MSUT2 regulates pathogenic tau internalization in neurons)
- Knocking MSUT2 down reduced tau inclusions seeded by brain material from three different human tauopathies, while leaving alpha synuclein aggregates untouched, which shows the effect is specific to tau rather than a general block on aggregation.(Results, MSUT2 regulates pathogenic tau internalization in neurons)
- Live imaging of labelled tau seeds showed the knockdown works upstream of aggregation: treated neurons took up fewer seeds and moved fewer of them into acidic compartments.(Results, MSUT2 regulates pathogenic tau internalization in neurons)
- Oligonucleotides against the adenosine A1 receptor reproduced the MSUT2 result, cutting both seeded tau pathology and seed uptake, while oligonucleotides against the A2A receptor did not, which placed the A1 receptor rather than adenosine signalling in general downstream of MSUT2.(Results)
- Two further knockdowns, of ASAP1 and of FIP3, also cut seeded tau pathology and seed uptake, completing a chain from an RNA binding protein through a receptor to the machinery of macropinocytosis.(Results)
- Selectivity was tested directly by measuring three other routes into the neuron, and only the macropinocytosis marker moved, so the knockdown changed how tau specifically gets in rather than shutting down uptake in general.(Results, MSUT2 regulates pathogenic tau internalization in neurons)
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