Abstract Body

Tau proteins aggregate into filaments in brain cells in Alzheimer’s disease and tauopathies. Tau immunotherapy is a promising approach. However, tau is also found within brain cells and alternative solutions must be explored. Here, we used fragments of camelid heavy chain-only antibodies (VHHs or single domain antibody fragments) targeting Tau as immuno-modulators of seeding.

Different anti-tau VHHs were screened, and one was selected for its properties to bind microtubule-binding domains, composing the core of Tau fibrils.

This lead VHH was optimized to improve its biochemical and biological properties (intracellular solubility, affinity), resulting in VHH Z70. VHH Z70 was more efficient than the lead to inhibit in vitro Tau aggregation in heparin-induced assays. Expression of VHH Z70 in the Marc Diamond’s HEK cell model of Tau seeding also decreased the FRET signal. Finally, viral vectors encoding VHH Z70 were stereotactically injected in the hippocampus of an established tauopathy mouse seeding model. VHH Z70 demonstrated its capacity to mitigate accumulation of pathological Tau in neuronal cells.

VHH Z70, by targeting Tau inside brain neurons, may be considered as a new immunological tool to target the intra-cellular compartment in Alzheimer’s disease and tauopathies.

Aims

In somes tauopathies, the progression of neurodegeneration follows disease-specific hierarchical progression that may be linked to a prion-like propagation. Indeed, seed-competent tau species spread from cell to cell but the intercellular mechanisms of transfer are unclear. Extracellular vesicles represent a unique intercellular delivery vehicle for transferring pathological species from one neuronal population to another that could explain the differing cell vulnerability seen in tauopathies. Here, we compare tau seeding capacity from vesicles that have been isolated from brain derived fluid of patients with various tauopathies.

Methods

Brain extracts (AD, PSP, PiD, control) were obtained from the Lille Neurobank. Vesicles were characterized (electron microscopy, nanotracking analyses, mass spectrometry, biochemistry). Tau in brain-derived enriched-extracellular vesicles (BD-EVs) was evaluated by ELISA and EM. Seeding mediated by BD-EVs was tested using a cell seeding assay; BD-EVs were injected into the hippocampus of tau transgenic mice and tau lesions quantified (MC1 and AT100).

Results

Whereas vesicles concentration and the tau content did not differ among the tauopathies and controls, we observed considerable heterogeneity in their seeding capacities. The most striking evidence was coming from AD where the BD-EVs clearly contain pathological species that can induce tau lesions in vivo. For PSP and PiD patients, a weak FRET signal was observed which was consistent with neuropathology.

Conclusions

Together, our results support the hypothesis that BD-EVs contain tau variants that may participate to the prion-like propagation of tau pathology in tauopathies. Such observation may lead to reconsider diagnostic and therapeutic strategies.