Ryu, Daniel

Abstract Understanding the biological functions of tau variants can illuminate differential etiologies of Alzheimer’s disease (AD) and primary tauopathies. Though the end-stage neuropathological attributes of AD and primary tauopathies are similar, the etiology and behavioral outcomes of these diseases follow unique and divergent trajectories. To study the divergent physiological properties of tau variants on a uniform immunogenetic background, we created somatic transgenesis CNS models of tauopathy utilizing neonatal delivery of adeno-associated viruses expressing wild-type (WT) or mutant tau in non-transgenic mice. We selected four different tau variants—WT tau associated with AD, P301L mutant tau associated with frontotemporal dementia (FTD), S320F mutant tau associated with Pick’s disease and a combinatorial approach using P301L/S320F mutant tau. CNS-targeted expression of WT and P301L mutant tau results in robust tau hyperphosphorylation without tangle pathology, gradually developing age-progressive memory deficits. In contrast, the S320F variant, especially in combination with P301L, produces an AD-type tangle pathology, focal neuroinflammation and memory impairment on an accelerated time scale. Using the doubly mutated P301L/S320F tau variant, we demonstrate that combining different mutations can have an additive effect on neuropathologies and associated co-morbidities, possibly hinting at involvement of unique functional pathways. Importantly, we also show that overexpression of wild-type tau as well as an FTD-associated tau variant can lead to cognitive deficits even in the absence of tangles. Together, our data highlights the synergistic neuropathologies and associated cognitive and synaptic alterations of the combinatorial tau variant leading to a robust model of tauopathy.

It has been challenging to produce ex vivo models of the inclusion pathologies that are hallmark pathologies of many neurodegenerative diseases. Using three-dimensional mouse brain slice cultures (BSCs), we have developed a paradigm that rapidly and robustly recapitulates mature neurofibrillary inclusion and Lewy body formation found in Alzheimer’s and Parkinson’s disease, respectively. This was achieved by transducing the BSCs with recombinant adeno-associated viruses (rAAVs) that express α-synuclein or variants of tau. Notably, the tauopathy BSC model enables screening of small molecule therapeutics and tracking of neurodegeneration. More generally, the rAAV BSC “toolkit” enables efficient transduction and transgene expression from neurons, microglia, astrocytes, and oligodendrocytes, alone or in combination, with transgene expression lasting for many months. These rAAV-based BSC models provide a cost-effective and facile alternative to in vivo studies, and in the future can become a widely adopted methodology to explore physiological and pathological mechanisms related to brain function and dysfunction.