Tau deposition drives neuropathological, inflammatory and behavioral abnormalities independently of neuronal loss in a novel mouse model

Human Molecular Genetics, 2015, Vol. 24, No. 21 6198–6212 doi: 10.1093/hmg/ddv336 Advance Access Publication Date: 13 August 2015 Original Article ORIGINAL ARTICLE Tau deposition drives neuropathological, inflammatory and behavioral abnormalities independently of neuronal loss in a novel mouse model 1 Department of Neuroscience, Mayo Clinic Jacksonville, 4500 San Pablo Road, Jacksonville, FL 32224, USA and Neurobiology of Disease Graduate Program, Mayo Graduate School, Jacksonville, FL 4500 San Pablo Road, Jacksonville, FL 32224, USA 2 *To whom correspondence should be addressed. Tel: +1 9049532317; Fax: +1 9049537370; Email: (J.F.); Tel: +1 9049532855; Fax: +1 9049537370; Email: (L.P.) Abstract Aberrant tau protein accumulation drives neurofibrillary tangle (NFT) formation in several neurodegenerative diseases. Currently, efforts to elucidate pathogenic mechanisms and assess the efficacy of therapeutic targets are limited by constraints of existing models of tauopathy. In order to generate a more versatile mouse model of tauopathy, somatic brain transgenesis was utilized to deliver adeno-associated virus serotype 1 (AAV1) encoding human mutant P301L-tau compared with GFP control. At 6 months of age, we observed widespread human tau expression with concomitant accumulation of hyperphosphorylated and abnormally folded proteinase K resistant tau. However, no overt neuronal loss was observed, though significant abnormalities were noted in the postsynaptic scaffolding protein PSD95. Neurofibrillary pathology was also detected with Gallyas silver stain and Thioflavin-S, and electron microscopy revealed the deposition of closely packed filaments. In addition to classic markers of tauopathy, significant neuroinflammation and extensive gliosis were detected in AAV1-TauP301L mice. This model also recapitulates the behavioral phenotype characteristic of mouse models of tauopathy, including abnormalities in exploration, anxiety, and learning and memory. These findings indicate that biochemical and neuropathological hallmarks of tauopathies are accurately conserved and are independent of cell death in this novel AAV-based model of tauopathy, which offers exceptional versatility and speed in comparison with existing transgenic models. Therefore, we anticipate this approach will facilitate the identification and validation of genetic modifiers of disease, as well as accelerate preclinical assessment of potential therapeutic targets. Introduction Abnormal deposition of the tau protein is the hallmark feature of tauopathies, which encompasses a growing list of neurodegenerative diseases, including Alzheimer’s disease (AD), frontotemporal dementia (FTD), progressive supranuclear palsy, corticobasal degeneration (CBD) and chronic traumatic encephalopathy (CTE). Additionally, pathogenic mutations in the † C.C. and S.S.K. contributed equally to this study. Received: May 29, 2015. Revised: July 29, 2015. Accepted: August 10, 2015 © The Author 2015. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 6198 Casey Cook2,†, Silvia S. Kang2,†, Yari Carlomagno1, Wen-Lang Lin1, Mei Yue1, Aishe Kurti1, Mitsuru Shinohara1, Karen Jansen-West1, Emilie Perkerson1, Monica Castanedes-Casey1, Linda Rousseau1, Virginia Phillips1, Guojun Bu2, Dennis W. Dickson2, Leonard Petrucelli2, * and John D. Fryer2,* Human Molecular Genetics, 2015, Vol. 24, No. 21 Results Widespread expression of human tau in mice injected with AAV1-TauP301L To assess the ability to model tauopathy with somatic brain transgenesis with AAV1-TauP301L on postnatal day 0, mice were harvested at 6 months of age and the level and distribution of human tau expression evaluated histologically (Fig. 1). Providing a point of reference for the pattern of expression, the level of human tau expression in various brain regions was compared with the commonly utilized rTg4510 mouse tauopathy model (14). As shown in Figure 1, similar to the rTg4510 model (Fig. 1c, f, m–r), a high level of human tau expression was observed in cortical and hippocampal regions in the AAV1-TauP301L model (Fig. 1b, e, g–l). Further increasing the utility of this model, human tau was also highly expressed in other areas of the brain including thalamic and midbrain regions (Fig. 1s–x), enabling the use of the AAV1-TauP301L model to evaluate genetic modifiers of non-cortical tauopathies. In addition, we evaluated human tau expression biochemically to provide an indication of the level of variability, and we observed minimal variation in human tau levels throughout the AAV1-TauP301L cohort (Supplementary Material, Fig. S1a). We also measured human tau levels by a quantitative immunoassay, which demonstrated that the average level of human tau in AAV1Tau P301L mice was 2.37 ± 0.087 ng/µg of brain tissue (mean ± SEM), which is significantly lower than rTg4510 mice that express ∼3.735 ± 0.057 ng/µg of human tau in the brain (Supplementary Material, Fig. S1b). Several markers of neurofibrillary pathology are detected in an AAV model of tauopathy Given that neurofibrillary tangles (NFTs) contain tau species that are abnormally hyperphosphorylated on multiple epitopes, we wanted to determine the degree of tau hyperphosphorylation as well as the level of tau overexpression relative to endogenous tau in the AAV1-TauP301L model (Fig. 2). Strong immunoreactivity for the phospho-tau-specific antibodies PHF1 (pS396/404) and CP13 ( pS202) was observed in hippocampal (Fig. 2a) and cortical (Fig. 2b) regions, in addition to other brain regions (data not shown), indicative of pathological changes in the tau protein. Total tau levels were evaluated biochemically using Tau 5 (Fig. 2c and g), which detects both mouse and human tau independently of phosphorylation state. This analysis revealed that while total tau levels were elevated by approximately 4-fold in AAV1-TauP301L mice (Fig. 2g), the abnormal phosphorylation of tau at the 12E8 epitope (pS262/356) was increased by more than 20-fold (Fig. 2c and f), most likely due to the very low level of phosphorylation at this pathologically relevant epitope under normal conditions. In order to further characterize the pathology in AAV1TauP301L-injected animals, we evaluated immunoreactivity for well-known markers of abnormal conformational changes in the tau protein. The MC1 antibody, which detects a conformational change that occurs early in NFT formation (15,16), labeled inclusions in the hippocampus and cortex (Fig. 3a and b) as well as other brain regions of AAV1-TauP301L mice (data not shown). To detect mature NFT pathology, we pretreated tissue sections with proteinase K and subsequently stained with the conformationaldependent antibody Ab39 (17–19). The strong positivity for Ab39 (...truncated)