Behavioral and Neuropathological Phenotyping of the Tau58/2 and Tau58/4 Transgenic Mouse Models for FTDP-17

Simple Summary: The tau protein normally functions to maintain the stability of microtubules, the cellular cytoskeleton that provides structure and shape to eukaryotic cells. Tau protein malfunction is a core feature of a group of neurodegenerative diseases labeled 'tauopathies' that include, among others, Alzheimer's disease and frontotemporal dementia, with parkinsonism linked to chromosome 17 (FTDP-17). In these disorders, abnormally hyperphosphorylated tau is accumulated in intraneuronal tangles, disturbing normal cellular function and acting as the basis of neurofibrillary degeneration and dementia. FTDP-17 is indeed a form of frontotemporal dementia or frontotemporal degeneration characterized by a loss of nerve cells in areas of the brain called the frontal and temporal lobes. Over time, this cell loss affects personality, behavior, language, and movement. Valid animal models are vital to enhance our understanding of molecular disease mechanisms and as preclinical tools to identify novel treatment targets and to screen the efficacy of novel drug candidates or other therapeutic approaches. We report the validity of two genetically modified mouse models that express a mutated form of human tau protein associated with FTDP-17. With aging, both lines developed progressively worsening tau-related pathology, cognitive decline, and behavioral changes reminiscent of the symptom profile of FTDP-17 patients. Background: The Tau58/2 and Tau58/4 mouse lines expressing 0N4R tau with a P301S mutation mimic aspects of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). In a side-by-side comparison, we report the age-dependent development of cognitive, motor, and behavioral deficits in comparison with the spatial-temporal evolution of cellular tau pathology in both models. Methods: We applied the SHIRPA primary screen and specific neuromotor, behavioral, and cognitive paradigms. The spatiotemporal development of tau pathology was investigated immunohistochemically. Levels of sarkosyl-insoluble paired helical filaments were determined via a MesoScale Discovery biomarker assay. Results: Neuromotor impairments developed from age 3 months in both models. On electron microscopy, spinal cord neurofibrillary pathology was visible in mice aged 3 months; however, AT8 immunoreactivity was not yet observed in Tau58/4 mice. Behavioral abnormalities and memory deficits occurred at a later stage (>9 months) when tau pathology was fully disseminated throughout the brain. Spatiotemporally, tau pathology spread from the spinal cord via the midbrain to the frontal cortex, while the hippocampus was relatively spared, thus explaining the late onset of cognitive deficits. Conclusions: Our findings indicate the face and construct validity of both Tau58 models, which may provide new, valuable insights into the pathologic effects of tau species in vivo and may consequently facilitate the development of new therapeutic targets to delay or halt neurodegenerative processes occurring in tauopathies.