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The transmission of tau pathology has been proposed as one of the major mechanisms for the spatiotemporal spreading of tau pathology in neurodegenerative diseases. Over the last decade, studies have demonstrated that targeting total or pathological tau using tau antibodies can mitigate the development of tau pathology in tauopathy or Alzheimer's disease (AD) mouse models, and multiple tau immunotherapy agents have progressed to clinical trials. Tau antibodies are believed to inhibit the internalization of pathologic seeds and/or block seed elongation after seed internalization. To further address the mechanism of tau antibody inhibition of pathological spread, we conducted immunotherapy studies in mouse primary neurons and wild-type mice (females) seeded with AD patient-derived tau to induce the formation and spreading of tau pathology. Notably, we evaluated the effect of a mouse tau-specific antibody (mTau8) which does not interact with AD-tau seeds in these models. Our results show that mTau8 crosses the blood-brain barrier at levels similar to other antibodies and effectively decreases AD-tau-seeded tau pathology in vitro and in vivo. Importantly, our data suggest that mTau8 binds to endogenous intraneuronal mouse tau, thereby inhibiting the elongation of internalized tau seeds. These findings provide valuable insights into the possible mechanism underlying antibody-based therapies for treating tauopathies. Significance Statement The transmission of tau pathology plays key role in the pathoclinical progression of tauopathy. Studies have shown that tau antibody treatment can mitigate tau pathology in transgenic and spreading models of tauopathy. To explore the mechanisms involved in this procedure, we conducted immunotherapy studies on human tau seeds induced tau spreading models using a mouse tau-specific antibody (mTau8), which does not interact with human-tau seeds. Our findings in the study enhance our understanding of antibody-based therapies for tauopathies., (Copyright © 2024 the authors.)

Alzheimer's disease (AD) and many other neurodegenerative diseases are characterized by pathological aggregation of the protein tau. These tau aggregates spread in a stereotypical spatiotemporal pattern in the brain of each disease, suggesting that the misfolded tau can recruit soluble monomers to adopt the same pathological structure. To investigate whether recruited tau indeed adopts the same structure and properties as the original seed, here we template recombinant full-length 0N3R tau, 0N4R tau, and an equimolar mixture of the two using sarkosyl-insoluble tau extracted from AD brain and determine the structures of the resulting fibrils using cryoelectron microscopy. We show that these cell-free amplified tau fibrils adopt the same molecular structure as the AD paired-helical filament (PHF) tau but are unable to template additional monomers. Therefore, the PHF structure alone is insufficient for defining the pathological properties of AD tau, and other biochemical components such as tau posttranslational modifications, other proteins, polyanionic cofactors, and salt are required for the prion-like serial propagation of tauopathies., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Inclusions comprised of microtubule-associated protein tau (tau) are implicated in a group of neurodegenerative diseases, collectively known as tauopathies, that include Alzheimer's disease (AD). The spreading of misfolded tau "seeds" along neuronal networks is thought to play a crucial role in the progression of tau pathology. Consequently, restricting the release or uptake of tau seeds may inhibit the spread of tau pathology and potentially halt the advancement of the disease. Previous studies have demonstrated that the Mammalian Suppressor of Tauopathy 2 (MSUT2), an RNA binding protein, modulates tau pathogenesis in a transgenic mouse model. In this study, we investigated the impact of MSUT2 on tau pathogenesis using tau seeding models. Our findings indicate that the loss of MSUT2 mitigates human tau seed-induced pathology in neuron cultures and mouse models. In addition, MSUT2 regulates many gene transcripts, including the Adenosine Receptor 1 (A1AR), and we show that down regulation or inhibition of A1AR modulates the activity of the "ArfGAP with SH3 Domain, Ankyrin Repeat, and PH Domain 1 protein" (ASAP1), thereby influencing the internalization of pathogenic tau seeds into neurons resulting in reduction of tau pathology., (© 2024. The Author(s).)

Background: Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD). These mutations elevate the LRRK2 kinase activity, making LRRK2 kinase inhibitors an attractive therapeutic. LRRK2 kinase activity has been consistently linked to specific cell signaling pathways, mostly related to organelle trafficking and homeostasis, but its relationship to PD pathogenesis has been more difficult to define. LRRK2-PD patients consistently present with loss of dopaminergic neurons in the substantia nigra but show variable development of Lewy body or tau tangle pathology. Animal models carrying LRRK2 mutations do not develop robust PD-related phenotypes spontaneously, hampering the assessment of the efficacy of LRRK2 inhibitors against disease processes. We hypothesized that mutations in LRRK2 may not be directly related to a single disease pathway, but instead may elevate the susceptibility to multiple disease processes, depending on the disease trigger. To test this hypothesis, we have previously evaluated progression of α-synuclein and tau pathologies following injection of proteopathic seeds. We demonstrated that transgenic mice overexpressing mutant LRRK2 show alterations in the brain-wide progression of pathology, especially at older ages., Methods: Here, we assess tau pathology progression in relation to long-term LRRK2 kinase inhibition. Wild-type or LRRK2 G2019S knock-in mice were injected with tau fibrils and treated with control diet or diet containing LRRK2 kinase inhibitor MLi-2 targeting the IC50 or IC90 of LRRK2 for 3-6 months. Mice were evaluated for tau pathology by brain-wide quantitative pathology in 844 brain regions and subsequent linear diffusion modeling of progression., Results: Consistent with our previous work, we found systemic alterations in the progression of tau pathology in LRRK2 G2019S mice, which were most pronounced at 6 months. Importantly, LRRK2 kinase inhibition reversed these effects in LRRK2 G2019S mice, but had minimal effect in wild-type mice, suggesting that LRRK2 kinase inhibition is likely to reverse specific disease processes in G2019S mutation carriers. Additional work may be necessary to determine the potential effect in non-carriers., Conclusions: This work supports a protective role of LRRK2 kinase inhibition in G2019S carriers and provides a rational workflow for systematic evaluation of brain-wide phenotypes in therapeutic development., (© 2024. The Author(s).)

Alzheimer's disease (AD) is defined by intracellular neurofibrillary tangles formed by the microtubule-associated protein tau and extracellular plaques formed by the β-amyloid peptide. AD tau tangles contain a mixture of tau isoforms with either four (4R) or three (3R) microtubule-binding repeats. Here we use solid-state NMR to determine how 4R and 3R tau isoforms mix at the molecular level in AD tau aggregates. By seeding differentially isotopically labeled 4R and 3R tau monomers with AD brain-derived tau, we measured intermolecular contacts of the two isoforms. The NMR data indicate that 4R and 3R tau are well mixed in the AD-tau seeded fibrils, with a 60:40 incorporation ratio of 4R to 3R tau and a small homotypic preference. The AD-tau templated 4R tau, 3R tau, and mixed 4R and 3R tau fibrils exhibit no structural differences in the rigid β-sheet core or the mobile domains. Therefore, 4R and 3R tau are fluently recruited into the pathological fold of AD tau aggregates, which may explain the predominance of AD among neurodegenerative disorders., (© 2022. The Author(s).)

Alzheimer's disease (AD) is a neurodegenerative disorder that exhibits pathological changes in both tau and synaptic function. AD patients display increases in hyperphosphorylated tau and synaptic activity. Previous studies have individually identified the role of NR2B subunit-containing NMDA receptors in AD related synaptic dysfunction and aggregated tau without reconciling the conflicting differences and implications of NR2B expression. Inhibition of extrasynaptically located NR2B mitigates tau pathology in AD models, whereas the inhibition of synaptic NR2B replicates tau-associated hyperactivity. This suggests that a simultaneous increase in extrasynaptic NR2B and decrease in synaptic NR2B may be responsible for tau pathology and synaptic dysfunction, respectively. The synaptic location of NR2B is regulated by casein kinase 2 (CK2), which is highly expressed in AD patients. Here, we used patient brains diagnosed with AD, corticobasal degeneration, progressive supranuclear palsy or Pick's disease to characterize CK2 expression across these diverse tauopathies. Human derived material was also utilized in conjunction with cultured hippocampal neurons in order to investigate AD-induced changes in NR2B location. We further assessed the therapeutic effect of CK2 inhibition on NR2B synaptic distribution and tau pathology. We found that aberrant expression of CK2, and synaptically translocated NR2B, is unique to AD patients compared to other tauopathies. Increased CK2 was also observed in AD-tau treated neurons in addition to the mislocalization of NR2B receptors. Tau burden was alleviated in vitro by correcting synaptic:extrasynaptic NR2B function. Restoring NR2B physiological expression patterns with CK2 inhibition and inhibiting the function of excessive extrasynaptic NR2B with Memantine both mitigated tau accumulation in vitro. However, the combined pharmacological treatment promoted the aggregation of tau. Our data suggests that the synaptic:extrasynaptic balance of NR2B function regulates AD-tau pathogenesis, and that the inhibition of CK2, and concomitant prevention of NR2B mislocalization, may be a useful therapeutic tool for AD patients., (© 2022. The Author(s).)

Neuropathological staging studies have suggested that tau pathology spreads through the brain in Alzheimer's disease (AD) and other tauopathies, but it is unclear how neuroanatomical connections, spatial proximity, and regional vulnerability contribute. In this study, we seed tau pathology in the brains of nontransgenic mice with AD tau and quantify pathology development over 9 months in 134 brain regions. Network modeling of pathology progression shows that diffusion through the connectome is the best predictor of tau pathology patterns. Further, deviations from pure neuroanatomical spread are used to estimate regional vulnerability to tau pathology and identify related gene expression patterns. Last, we show that pathology spread is altered in mice harboring a mutation in leucine-rich repeat kinase 2. While tau pathology spread is still constrained by anatomical connectivity in these mice, it spreads preferentially in a retrograde direction. This study provides a framework for understanding neuropathological progression in tauopathies., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

The microtubule-associated protein tau (tau) forms hyperphosphorylated aggregates in the brains of tauopathy patients that can be pathologically and biochemically defined as distinct tau strains. Recent studies show that these tau strains exhibit strain-specific biological activities, also referred to as pathogenicities, in the tau spreading models. Currently, the specific pathogenicity of human-derived tau strains cannot be fully recapitulated by synthetic tau preformed fibrils (pffs), which are generated from recombinant tau protein. Reproducing disease-relevant tau pathology in cell and animal models necessitates the use of human brain-derived tau seeds. However, the availability of human-derived tau is extremely limited. Generation of tau variants that can mimic the pathogenicity of human-derived tau seeds would significantly extend the scale of experimental design within the field of tauopathy research. Previous studies have demonstrated that in vitro seeding reactions can amplify the beta-sheet structure of tau protein from a minute quantity of human-derived tau. However, whether the strain-specific pathogenicities of the original, human-derived tau seeds are conserved in the amplified tau strains has yet to be experimentally validated. Here, we used biochemically enriched brain-derived tau seeds from Alzheimer's disease (AD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) patient brains with a modified seeding protocol to template the recruitment of recombinant 2N4R (T40) tau in vitro. We quantitatively interrogated efficacy of the amplification reactions and the pathogenic fidelity of the amplified material to the original tau seeds using recently developed sporadic tau spreading models. Our data suggest that different tau strains can be faithfully amplified in vitro from tau isolated from different tauopathy brains and that the amplified tau variants retain their strain-dependent pathogenic characteristics.

Background: Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD) and are also associated with genetic risk in idiopathic PD. Mutations in LRRK2, including the most common p.G2019S lead to elevated kinase activity, making LRRK2 kinase inhibitors prime targets for therapeutic development. However, the role of LRRK2 kinase activity in PD pathogenesis has remained unclear. While essentially all LRRK2-PD patients exhibit dopaminergic neuron loss, many of these patients do not have α-synuclein Lewy bodies in their brains. So, what is the neuropathological substrate of LRRK2-PD? Tau has emerged as a possible candidate due to the presence of tau pathology in the majority of LRRK2 mutation carriers and reports of hyperphosphorylated tau in LRRK2 animal models., Objective: In the current study, we aim to address whether a mutation in LRRK2 changes the cell-autonomous seeding of tau pathology in primary neurons. We also aim to assess whether LRRK2 kinase inhibitors are able to modulate tau pathology., Methods/results: Treatment of primary neurons with LRRK2 kinase inhibitors leads to prolonged kinase inhibition but does not alter tau pathology induction. The lack of an effect of LRRK2 kinase activity was further confirmed in primary neurons expressing LRRK2G2019S and with two different forms of pathogenic tau. In no case was there more than a minor change in tau pathology induction., Conclusion: Together, our results indicate that LRRK2 kinase activity is not playing a major role in the induction of tau pathology in individual neurons. Understanding the impact of LRRK2 kinase inhibitors on pathology generation is important as kinase inhibitors move forward in clinical trials.

Neurodegeneration in Alzheimer's disease (AD) is closely associated with the accumulation of pathologic tau aggregates in the form of neurofibrillary tangles. We found that a p.Asp395Gly mutation in VCP (valosin-containing protein) was associated with dementia characterized neuropathologically by neuronal vacuoles and neurofibrillary tangles. Moreover, VCP appeared to exhibit tau disaggregase activity in vitro, which was impaired by the p.Asp395Gly mutation. Additionally, intracerebral microinjection of pathologic tau led to increased tau aggregates in mice in which p.Asp395Gly VCP mice was knocked in, as compared with injected wild-type mice. These findings suggest that p.Asp395Gly VCP is an autosomal-dominant genetic mutation associated with neurofibrillary degeneration in part owing to reduced tau disaggregation, raising the possibility that VCP may represent a therapeutic target for the treatment of AD., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Background: The spread of tau pathology in Alzheimer's disease (AD) is mediated by cell-to-cell transmission of pathological tau seeds released from neurons that, upon internalization by recipient neurons, template the misfolding of naïve cellular tau, thereby propagating fibrillization. We hypothesize that anti-tau monoclonal antibodies (mAbs) that selectively bind to pathological tau seeds will inhibit propagation of tau aggregates and reduce the spread of tau pathology in vivo., Methods: We inoculated mice with human AD brain-derived extracts containing tau paired helical filaments (AD-tau) and identified two novel mAbs, DMR7 and SKT82, that selectively bind to a misfolded pathological conformation of tau relative to recombinant tau monomer. To evaluate the effects of these mAbs on the spread of pathological tau in vivo, 5xFAD mice harboring significant brain Aβ plaque burden were unilaterally injected with AD-tau in the hippocampus, to initiate the formation of neuritic plaque (NP) tau pathology, and were treated weekly with intraperitoneal (i.p.) injections of DMR7, SKT82, or IgG isotype control mAbs., Results: DMR7 and SKT82 bind epitopes comprised of the proline-rich domain and c-terminal region of tau and binding is reduced upon disruption of the pathological conformation of AD-tau by chemical and thermal denaturation. We found that both DMR7 and SKT82 immunoprecipitate pathological tau and significantly reduce the seeding of cellular tau aggregates induced by AD-tau in primary neurons by 60.5 + 13.8% and 82.2 + 8.3%, respectively, compared to IgG control. To investigate the mechanism of mAb inhibition, we generated pH-sensitive fluorophore-labeled recombinant tau fibrils seeded by AD-tau to track internalization of tau seeds and demonstrate that the conformation-selective tau mAbs inhibit the internalization of tau seeds. DMR7 and SKT82 treatment reduced hyperphosphorylated NP tau as measured with AT8 immunohistochemistry (IHC) staining, but did not achieve statistical significance in the contralateral cortex and SKT82 significantly reduced tau pathology in the ipsilateral hippocampus by 24.2%; p = 0.044., Conclusions: These findings demonstrate that conformation-selective tau mAbs, DMR7 and SKT82, inhibit tau pathology in primary neurons by preventing the uptake of tau seeds and reduce tau pathology in vivo, providing potential novel therapeutic candidates for the treatment of AD.

One hallmark of neurodegenerative diseases is the intracellular accumulation of hyperphosphorylated tau protein, a neuronal microtubule-associated protein, into structures known as neurofibrillary tangles. Tauopathies are heterogeneous neurodegenerative diseases caused by the misfolding of the tau protein. It has been previously shown that the tau protein can spread from cell to cell in a prion-like manner. Tauopathies can be sporadic or familial, with the identification of pathogenic mutations in the microtubule-associated protein tau gene on chromosome 17 in the familial cases. Different frontotemporal dementia with parkinsonism-17 (FTDP-17) cases are associated with varying clinical presentations and types of neuropathology. We previously demonstrated that insoluble tau extracted from sporadic tauopathy human brains contain distinct tau strains, which underlie the heterogeneity of these diseases. Furthermore, these tau strains seeded tau aggregates that resemble human tau neuropathology in nontransgenic and 6hTau mice in vivo. Here, we show insoluble tau from human brains of FTDP-17 cases transmit different patterns of neuronal and glial tau pathology in vivo, similar to the sporadic tauopathies. This suggests that each of these tau mutations has unique properties that underlie the heterogeneity of FTDP-17 cases., (© 2020 American Association of Neuropathologists, Inc. All rights reserved.)

Tauopathies are characterized by abnormal accumulation of tau protein in neurons and glia. In Alzheimer's disease (AD), tau aggregates in neurons, while in corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), tau also aggregates in astrocytes and oligodendrocytes. We previously demonstrated that human CBD and PSP tauopathy lysates (CBD-tau and PSP-tau) contain distinct tau strains that propagate neuronal and glial tau aggregates in nontransgenic (nonTg) mouse brain. Yet the mechanism of glial tau transmission is unknown. Here, we developed a novel mouse model to knock down tau in neurons to test for glial tau transmission. While oligodendroglial tau pathology propagated across the mouse brain in the absence of neuronal tau pathology, astrocytic tau pathology did not. Oligodendroglial tau aggregates propagated along white matter tracts independently of neuronal axons, and resulted in oligodendrocyte cell loss. Thus, glial tau pathology has significant functional consequences independent of neuronal tau pathology., (© 2019 Narasimhan et al.)

The deposition of pathological tau is a common feature in several neurodegenerative tauopathies. Although equal ratios of tau isoforms with 3 (3R) and 4 (4R) microtubule-binding repeats are expressed in the adult human brain, the pathological tau from different tauopathies have distinct isoform compositions and cell type specificities. The underlying mechanisms of tauopathies are unknown, partially due to the lack of proper models. Here, we generate a new transgenic mouse line expressing equal ratios of 3R and 4R human tau isoforms (6hTau mice). Intracerebral injections of distinct human tauopathy brain-derived tau strains into 6hTau mice recapitulate the deposition of pathological tau with distinct tau isoform compositions and cell type specificities as in human tauopathies. Moreover, through in vivo propagation of these tau strains among different mouse lines, we demonstrate that the transmission of distinct tau strains is independent of strain isoform compositions, but instead intrinsic to unique pathological conformations.

Identification of multiple immune-related genetic risk factors for sporadic AD (sAD) have put the immune system center stage in mechanisms underlying this disorder. Comprehensive analysis of microglia in different stages of AD in human brains revealed microglia activation to follow the progression of AD neuropathological changes and requiring the co-occurrence of beta-Amyloid (Aβ) and tau pathology. Carriers of AD-associated risk variants in TREM2 (Triggering receptor expressed on myeloid cells 2) showed a reduction of plaque-associated microglia and a substantial increase in dystrophic neurites and overall pathological tau compared with age and disease stage matched AD patients without TREM2 risk variants. These findings were substantiated by digital spatial profiling of the plaque microenvironment and targeted gene expression profiling on the NanoString nCounter system, which revealed striking brain region dependent differences in immune response patterns within individual cases. The demonstration of profound brain region and risk-variant specific differences in immune activation in human AD brains impacts the applicability of immune-therapeutic approaches for sAD and related neurodegenerative diseases.

Pathological tau aggregates in Alzheimer's disease (AD) and frontotemporal lobar degeneration-tau (FTLD-tau) adopt distinct conformations differentiated by the AD-tau specific monoclonal antibody (mAb) GT-38 that are not readily visualized using phosphorylation-specific anti-tau mAbs. To determine the extent of co-morbid AD-tau pathology in FTLD-tau, we performed immunohistochemical (IHC) staining with GT-38 and assigned Braak stages of AD-tau in a cohort 180 FTLD-tau cases consisting of corticobasal degeneration (CBD; n = 49), progressive supranuclear palsy (PSP; n = 109), and Pick's disease (PiD; n = 22). Nearly two-thirds of patients (n = 115 of 180, 63.8%) with FTLD-tau had some degree of comorbid AD-tau pathology and 20.5% of the FTLD-tau cohort had Braak stage ≥B2, consistent with medium-to-high-level AD neuropathological change (ADNPC). The PSP group had the highest frequency of medium-high AD-tau pathology compared to other tauopathies (PSP = 31/109, 28.4%; Picks = 2/22, 9.1%, CBD = 4/49, 8.2%) but neuropathological diagnosis was not found to be a significant independent predictor of medium-high AD Braak stage in a multivariate model after accounting for age at death (OR = 1.09; 95% CI = 1.03-1.15; p = 0.002) and CERAD plaque scores (OR = 3.75, 95% CI = 1.58-8.89; p = 0.003), suggesting there is no predilection for a specific FTLD tauopathy to develop AD-tau co-pathology after accounting for age. Patients with FTLD-tau who had, clinically significant, medium-high AD-tau pathology had significantly higher antemortem CSF levels of both total-tau (t-tau; mean = 89.98 pg/ml, SD = 36.70 pg/ml) and phosphorylated-tau (p-tau; mean = 20.45 pg/ml, SD = 9.31 pg/ml) compared to patients with negligible-low AD-tau, t-tau (mean = 43.04 pg/ml, SD = 25.40 pg/ml) and p-tau (mean = 11.90 pg/ml, SD = 4.48 pg/ml) (p ≤ 0.001 both). Finally, in an exploratory analysis in our largest pathology group (PSP) we find an association of GT-38 AD-tau Braak stage with lower baseline MMSE (p = 0.03). Together, these finding validate the use of GT-38 to selectively detect AD-tau pathology in the context of FTLD-tau and provides a novel tool to investigate associations of clinical phenotypes amongst co-morbid tauopathies.

Aggregation of tau into fibrillar structures within the CNS is a pathological hallmark of a clinically heterogeneous set of neurodegenerative diseases termed tauopathies. Unique misfolded conformations of tau, referred to as strains, are hypothesized to underlie the distinct neuroanatomical and cellular distribution of pathological tau aggregates. Here, we report the identification of novel tau monoclonal antibodies (mAbs) that selectively bind to an Alzheimer disease (AD)-specific conformation of pathological tau. Immunohistochemical analysis of tissue from various AD and nonAD tauopathies demonstrate selective binding of mAbs GT-7 and GT-38 to AD tau pathologies and absence of immunoreactivity for tau aggregates that are diagnostic of corticobasal degenerations (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PiD). In cases with co-occurring AD tauopathy, GT-7 and GT-38 distinguish comorbid AD tau from pathological tau in frontotemporal lobar degeneration characterized by tau inclusions (FTLD-Tau), as confirmed by the presence of both 3 versus 4 microtubule-binding repeat isoforms (3R and 4R tau isoforms, respectively), in AD neurofibrillary tangles but not in the tau aggregates of CBD, PSP, or PiD. These findings support the concept of an AD-specific tau strain. The mAbs described here enable the selective detection of AD tau pathology in nonAD tauopathies., (© 2018 American Association of Neuropathologists, Inc. All rights reserved.)

Alzheimer's disease (AD) is characterized by extracellular amyloid-β (Aβ) plaques and intracellular tau inclusions. However, the exact mechanistic link between these two AD lesions remains enigmatic. Through injection of human AD-brain-derived pathological tau (AD-tau) into Aβ plaque-bearing mouse models that do not overexpress tau, we recapitulated the formation of three major types of AD-relevant tau pathologies: tau aggregates in dystrophic neurites surrounding Aβ plaques (NP tau), AD-like neurofibrillary tangles (NFTs) and neuropil threads (NTs). These distinct tau pathologies have different temporal onsets and functional consequences on neural activity and behavior. Notably, we found that Aβ plaques created a unique environment that facilitated the rapid amplification of proteopathic AD-tau seeds into large tau aggregates, initially appearing as NP tau, which was followed by the formation and spread of NFTs and NTs, likely through secondary seeding events. Our study provides insights into a new multistep mechanism underlying Aβ plaque-associated tau pathogenesis.

Neurodegenerative proteinopathies characterized by intracellular aggregates of tau proteins, termed tauopathies, include Alzheimer's disease (AD), frontotemporal lobar degeneration (FTLD) with tau pathology (FTLD-tau), and related disorders. Pathological tau proteins derived from human AD brains (AD-tau) act as proteopathic seeds that initiate the templated aggregation of soluble tau upon intracerebral injection into tau transgenic (Tg) and wild-type mice, thereby modeling human tau pathology. In this study, we found that aged Tg mice of both sexes expressing human tau proteins harboring a pathogenic P301L MAPT mutation labeled with green fluorescent protein (T40PL-GFP Tg mouse line) exhibited hyperphosphorylated tau mislocalized to the somatodentritic domain of neurons, but these mice did not develop de novo insoluble tau aggregates, which are characteristic of human AD and related tauopathies. However, intracerebral injections of either T40PL preformed fibrils (PFFs) or AD-tau seeds into T40PL-GFP mice induced abundant intraneuronal pathological inclusions of hyperphosphorylated T40PL-GFP. These injections of pathological tau resulted in the propagation of tau pathology from the injection site to neuroanatomically connected brain regions, and these tau inclusions consisted of both T40PL-GFP and WT endogenous mouse tau. Primary neurons cultured from the brains of neonatal T40PL-GFP mice provided an informative in vitro model for examining the uptake and localization of tau PFFs. These findings demonstrate the seeded aggregation of T40PL-GFP in vivo by synthetic PFFs and human AD-tau and the utility of this system to study the neuropathological spread of tau aggregates. SIGNIFICANCE STATEMENT The stereotypical spread of pathological tau protein aggregates have recently been attributed to the transmission of proteopathic seeds. Despite the extensive use of transgenic mouse models to investigate the propagation of tau pathology in vivo , details of the aggregation process such as the early seeding events leading to new tau pathology have remained elusive. This study validates the use of GFP-labeled tau expressed by neurons in vivo and in vitro as models for investigating mechanisms underlying the seeded transmission of tau pathology as well as tau-focused drug discovery to identify disease-modifying therapies for AD and related tauopathies., (Copyright © 2017 the authors 0270-6474/17/3711485-10$15.00/0.)

Pathological tau aggregates occur in Alzheimer's disease (AD) and other neurodegenerative tauopathies. It is not clearly understood why tauopathies vary greatly in the neuroanatomical and histopathological patterns of tau aggregation, which contribute to clinical heterogeneity in these disorders. Recent studies have shown that tau aggregates may form distinct structural conformations, known as tau strains. Here, we developed a novel model to test the hypothesis that cell-to-cell transmission of different tau strains occurs in nontransgenic (non-Tg) mice, and to investigate whether there are strain-specific differences in the pattern of tau transmission. By injecting pathological tau extracted from postmortem brains of AD (AD-tau), progressive supranuclear palsy (PSP-tau), and corticobasal degeneration (CBD-tau) patients into different brain regions of female non-Tg mice, we demonstrated the induction and propagation of endogenous mouse tau aggregates. Specifically, we identified differences in tau strain potency between AD-tau, CBD-tau, and PSP-tau in non-Tg mice. Moreover, differences in cell-type specificity of tau aggregate transmission were observed between tau strains such that only PSP-tau and CBD-tau strains induce astroglial and oligodendroglial tau inclusions, recapitulating the diversity of neuropathology in human tauopathies. Furthermore, we demonstrated that the neuronal connectome, but not the tau strain, determines which brain regions develop tau pathology. Finally, CBD-tau- and PSP-tau-injected mice showed spatiotemporal transmission of glial tau pathology, suggesting glial tau transmission contributes to the progression of tauopathies. Together, our data suggest that different tau strains determine seeding potency and cell-type specificity of tau aggregation that underlie the diversity of human tauopathies. SIGNIFICANCE STATEMENT Tauopathies show great clinical and neuropathological heterogeneity, despite the fact that tau aggregates in each disease. This heterogeneity could be due to tau aggregates forming distinct structural conformations, or strains. We now report the development of a sporadic tauopathy model to study human tau strains by intracerebrally injecting nontransgenic mice with pathological tau enriched from human tauopathy brains. We show human tau strains seed different types and cellular distributions of tau neuropathology in our model that recapitulate the heterogeneity seen in these human diseases., (Copyright © 2017 the authors 0270-6474/17/3711406-18$15.00/0.)

Filamentous tau aggregates are hallmark lesions in numerous neurodegenerative diseases, including Alzheimer's disease (AD). Cell culture and animal studies showed that tau fibrils can undergo cell-to-cell transmission and seed aggregation of soluble tau, but this phenomenon was only robustly demonstrated in models overexpressing tau. In this study, we found that intracerebral inoculation of tau fibrils purified from AD brains (AD-tau), but not synthetic tau fibrils, resulted in the formation of abundant tau inclusions in anatomically connected brain regions in nontransgenic mice. Recombinant human tau seeded by AD-tau revealed unique conformational features that are distinct from synthetic tau fibrils, which could underlie the differential potency in seeding physiological levels of tau to aggregate. Therefore, our study establishes a mouse model of sporadic tauopathies and points to important differences between tau fibrils that are generated artificially and authentic ones that develop in AD brains., (© 2016 Guo et al.)