Viral Delivery of Non-Mutated Human Truncated Tau to Neurons Recapitulates Key Features of Human Tauopathy in Wild-Type Mice

BACKGROUND

Neuronal accumulation of hyperphosphorylated and truncated tau aggregates is one of the major defining factors and key drivers of neurodegeneration in Alzheimer's disease and other tauopathies.

OBJECTIVE

We developed an AAV-induced model of tauopathy mediated by human truncated tau protein without familial frontotemporal dementia-related mutations to study tau propagation and the functional consequences of tau pathology.

METHODS

We performed targeted transductions of the hippocampus or entorhinal cortex in adult mice followed by histological analysis to study the progression of hippocampal tau pathology and tau spreading. We performed behavioral analysis of mice with AAV-induced hippocampal tau pathology.

RESULTS

AAV-induced hippocampal tau pathology was characterized by tau hyperphosphorylation (AT8 positivity), sarkosyl insolubility, and the presence of neurofibrillary tangles. AAV-induced tau pathology was associated with microgliosis and hypertrophic astrocytes in the absence of cognitive deficits. Additionally, the co-expression of mCherry fluorescent protein and human truncated tau enabled us to detect both local spreading of human tau and spreading from the entorhinal cortex to the synaptically connected dentate gyrus.

CONCLUSION

Targeted delivery of AAV with truncated tau protein into subcortical and cortical structures of mammalian brains represents an efficient approach for creating temporally and spatially well-defined tau pathology suitable for in vivo studies of tau propagation and neuronal circuit deficits in Alzheimer's disease.

Targeting Mitophagy in Alzheimer's Disease

Mitochondria perform many essential cellular functions including energy production, calcium homeostasis, transduction of metabolic and stress signals, and mediating cell survival and death. Maintaining viable populations of mitochondria is therefore critical for normal cell function. The selective disposal of damaged mitochondria, by a pathway known as mitophagy, plays a key role in preserving mitochondrial integrity and quality. Mitophagy reduces the formation of reactive oxygen species and is considered as a protective cellular process. Mitochondrial dysfunction and deficits of mitophagy have important roles in aging and especially in neurodegenerative disorders such as Alzheimer's disease (AD). Targeting mitophagy pathways has been suggested to have potential therapeutic effects against AD. In this review, we aim to briefly discuss the emerging concepts on mitophagy, molecular regulation of the mitophagy process, current mitophagy detection methods, and mitophagy dysfunction in AD. Finally, we will also briefly examine the stimulation of mitophagy as an approach for attenuating neurodegeneration in AD.

Neuropathological changes and cognitive deficits in rats transgenic for human mutant tau recapitulate human tauopathy

The assembly of tau protein into abnormal filaments and brain cell degeneration are characteristic of a number of human neurodegenerative diseases, including Alzheimer's disease and frontotemporal dementia and parkinsonism linked to chromosome 17. Several murine models have been generated to better understand the mechanisms contributing to tau assembly and neurodegeneration. Taking advantage of the more elaborate central nervous system and higher cognitive abilities of the rat, we generated a model expressing the longest human tau isoform (2N4R) with the P301S mutation. This transgenic rat line, R962-hTau, exhibits the main features of human tauopathies, such as: age-dependent increase in inclusions comprised of aggregated-tau, neuronal loss, global neurodegeneration as reflected by brain atrophy and ventricular dilation, alterations in astrocytic and microglial morphology, and myelin loss. In addition, substantial deficits across multiple memory and learning paradigms, including novel object recognition, fear conditioning and Morris water maze tasks, were observed at the time of advanced tauopathy. These results support the concept that progressive tauopathy correlates with brain atrophy and cognitive impairment.