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Caspase-6-cleaved tau is relevant in Alzheimer's disease and marginal in four-repeat tauopathies: Diagnostic and therapeutic implications.

  • Author(s): Theofilas, Panos;
  • Piergies, Antonia MH;
  • Oh, Ian;
  • Lee, Yoo Bin;
  • Li, Song Hua;
  • Pereira, Felipe L;
  • Petersen, Cathrine;
  • Ehrenberg, Alexander J;
  • Eser, Rana A;
  • Ambrose, Andrew J;
  • Chin, Brian;
  • Yang, Teddy;
  • Khan, Shireen;
  • Ng, Raymond;
  • Spina, Salvatore;
  • Seeley, Willian W;
  • Miller, Bruce L;
  • Arkin, Michelle R;
  • Grinberg, Lea T
  • et al.

Published Web Location

https://doi.org/10.1111/nan.12819
Abstract

Aim

Tau truncation (tr-tau) by active caspase-6 (aCasp-6) generates tau fragments that may be toxic. Yet the relationship between aCasp-6, different forms of tr-tau and hyperphosphorylated tau (p-tau) accumulation in human brains with Alzheimer's disease (AD) and other tauopathies remains unclear.

Methods

We generated two neoepitope monoclonal antibodies against tr-tau sites (D402 and D13) targeted by aCasp-6. Then, we used five-plex immunofluorescence to quantify the neuronal and astroglial burden of aCasp-6, tr-tau, p-tau and their co-occurrence in healthy controls, AD and primary tauopathies.

Results

Casp-6 activation was strongest in AD and Pick's disease (PiD) but almost absent in 4-repeat (4R) tauopathies. In neurons, the tr-tau burden was much more abundant in AD and PiD than in 4R tauopathies and disproportionally higher when normalising by p-tau pathology. Tr-tau astrogliopathy was detected in low numbers in 4R tauopathies. Unexpectedly, about half of tr-tau positive neurons in AD and PiD lacked p-tau aggregates, a finding we confirmed using several p-tau antibodies.

Conclusions

Early modulation of aCasp-6 to reduce tr-tau pathology is a promising therapeutic strategy for AD and PiD but is unlikely to benefit 4R tauopathies. The large percentage of tr-tau-positive neurons lacking p-tau suggests that many vulnerable neurons to tau pathology go undetected when using conventional p-tau antibodies. Therapeutic strategies against tr-tau pathology could be necessary to modulate the extent of tau abnormalities in AD. The disproportionally higher burden of tr-tau in AD and PiD supports the development of biofluid biomarkers against tr-tau to detect AD and PiD and differentiate them from 4R tauopathies at a patient level.

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