High-Molecular-Weight Paired Helical Filaments from Alzheimer Brain Induces Seeding of Wild-Type Mouse Tau into an Argyrophilic 4R Tau Pathology in Vivo

In Alzheimer disease, the development of tau pathology follows neuroanatomically connected pathways, suggesting that abnormal tau species might recruit normal tau by passage from cell to cell. Herein, we analyzed the effect of stereotaxic brain injection of human Alzheimer high-molecular-weight paired helical filaments (PHFs) in the dentate gyrus of wild-type and mutant tau THY-Tau22 mice. After 3 months of incubation, wild-type and THY-Tau22 mice developed an atrophy of the dentate gyrus and a tau pathology characterized by Gallyas and tau-positive grain-like inclusions into granule cells that extended in the hippocampal hilus and eventually away into the alveus, and the fimbria. Gallyas-positive neuropil threads and oligodendroglial coiled bodies were also observed. These tau inclusions were composed only of mouse tau, and were immunoreactive with antibodies to 4R tau, phosphotau, misfolded tau, ubiquitin, and p62. Although local hyperphosphorylation of tau was increased in the dentate gyrus in THY-Tau22 mice, the development of neurofibrillary tangles made of mutant human tau was not accelerated in the hippocampus, indicating that wild-type human PHFs were inefficient in seeding tau aggregates made of G272V/P301S mutant human tau. Our results indicate thus that injection of human wild-type Alzheimer PHF seeded aggregation of wild-type murine tau into an argyrophilic 4R tau pathology, and constitutes an interesting model independent of expression of a mutant tau protein.