Urmi Sengupta

Alzheimer brain-derived tau oligomers propagate pathology from endogenous tau

Intracerebral injection of brain extracts containing amyloid or tau aggregates in transgenic animals can induce cerebral amyloidosis and tau pathology. We extracted pure populations of tau oligomers directly from the cerebral cortex of Alzheimer disease (AD) brain. These oligomers are potent inhibitors of long term potentiation (LTP) in hippocampal brain slices and disrupt memory in wild type mice. We observed for the first time that these authentic brain-derived tau oligomers propagate abnormal tau conformation of endogenous murine tau after prolonged incubation. The conformation and hydrophobicity of tau oligomers play a critical role in the initiation and spread of tau pathology in the naïve host in a manner reminiscent of sporadic AD.

Tau oligomers impair memory and induce synaptic and mitochondrial dysfunction in wild-type mice

BackgroundThe correlation between neurofibrillary tangles of tau and disease progression in the brains of Alzheimers disease (AD) patients remains an area of contention. Innovative data are emerging from biochemical, cell-based and transgenic mouse studies that suggest that tau oligomers, a pre-filament form of tau, may be the most toxic and pathologically significant tau aggregate.ResultsHere we report that oligomers of recombinant full-length human tau protein are neurotoxic in vivo after subcortical stereotaxic injection into mice. Tau oligomers impaired memory consolidation, whereas tau fibrils and monomers did not. Additionally, tau oligomers induced synaptic dysfunction by reducing the levels of synaptic vesicle-associated proteins synaptophysin and septin-11. Tau oligomers produced mitochondrial dysfunction by decreasing the levels of NADH-ubiquinone oxidoreductase (electron transport chain complex I), and activated caspase-9, which is related to the apoptotic mitochondrial pathway.ConclusionsThis study identifies tau oligomers as an acutely toxic tau species in vivo, and suggests that tau oligomers induce neurodegeneration by affecting mitochondrial and synaptic function, both of which are early hallmarks in AD and other tauopathies. These results open new avenues for neuroprotective intervention strategies of tauopathies by targeting tau oligomers.

Identification of oligomers at early stages of tau aggregation in Alzheimer's disease

Neurofibrillary tangles (NFTs) are a pathological hallmark of Alzheimers disease (AD); however, the relationship between NFTs and disease progression remains controversial. Analyses of tau animal models suggest that phenotypes coincide with accumulation of soluble aggregated tau species but not the accumulation of NFTs. The pathological role of prefilamentous tau aggregates, e.g., tau oligomeric intermediates, is poorly understood, in part because of methodological challenges. Here, we engineered a novel tau oligomer‐specific antibody, T22, and used it to elucidate the temporal course and biochemical features of oligomers during NFT development in AD brain. We found that tau oligomers in human AD brain samples were 4‐fold higher than those in the controls. We also revealed the role of oligomeric tau conformers in pretangles, neuritic plaques, and neuropil threads in the frontal cortex tissue from AD brains; this analysis uncovers a consistent code that governs tau oligomerization with regard to degree of neuronal cytopathology. These data are the first to characterize the role of tau oligomers in the natural history of NFTs, and they highlight the suitability of tau oligomers as therapeutic targets in AD and related tauopathies.—Lasagna‐Reeves, C. A., Castillo‐Carranza, D. L., Sengupta, U., Troncoso, J., Jackson, G. R., Kayed, R. Identification of oligomers at early stages of tau aggregation in Alzheimers disease. FASEB J. 26, 1946‐1959 (2012). www.fasebj.org

Passive Immunization with Tau Oligomer Monoclonal Antibody Reverses Tauopathy Phenotypes without Affecting Hyperphosphorylated Neurofibrillary Tangles

Recent findings suggest that tau oligomers, which form before neurofibrillary tangles (NFTs), are the true neurotoxic tau entities in neurodegenerative tauopathies, including Alzheimers disease (AD). Studies in animal models of tauopathy suggest that tau oligomers play a key role in eliciting behavioral and cognitive impairments. Here, we used a novel tau oligomer-specific monoclonal antibody (TOMA) for passive immunization in mice expressing mutant human tau. A single dose of TOMA administered either intravenously or intracerebroventricularly was sufficient to reverse both locomotor and memory deficits in a mouse model of tauopathy for 60 d, coincident with rapid reduction of tau oligomers but not phosphorylated NFTs or monomeric tau. Our data demonstrate that antibody protection is mediated by extracellular and rapid peripheral clearance. These findings provide the first direct evidence in support of a critical role for tau oligomers in disease progression and validate tau oligomers as a target for the treatment of AD and other neurodegenerative tauopathies.

The Role of Amyloid-β Oligomers in Toxicity, Propagation, and Immunotherapy.

The incidence of Alzheimers disease (AD) is growing every day and finding an effective treatment is becoming more vital. Amyloid-β (Aβ) has been the focus of research for several decades. The recent shift in the Aβ cascade hypothesis from all Aβ to small soluble oligomeric intermediates is directing the search for therapeutics towards the toxic mediators of the disease. Targeting the most toxic oligomers may prove to be an effective treatment by preventing their spread. Specific targeting of oligomers has been shown to protect cognition in rodent models. Additionally, the heterogeneity of research on Aβ oligomers may seem contradictory until size and conformation are taken into account. In this review, we will discuss Aβ oligomers and their toxicity in relation to size and conformation as well as their influence on inflammation and the potential of Aβ oligomer immunotherapy.

Rapid Accumulation of Endogenous Tau Oligomers in a Rat Model of Traumatic Brain Injury POSSIBLE LINK BETWEEN TRAUMATIC BRAIN INJURY AND SPORADIC TAUOPATHIES

Background: Traumatic brain injury (TBI) contributes to the development tauopathy-related dementia. Results: Rapid formation of oligomeric and phosphorylated Tau proteins in a rodent model for TBI. Conclusion: TBI triggers the formation of Tau oligomers, which may represent a link between TBI and sporadic tauopathies. Significance: The results suggest that targeting Tau oligomers may be useful for the prevention of dementia following TBI. Traumatic brain injury (TBI) is a serious problem that affects millions of people in the United States alone. Multiple concussions or even a single moderate to severe TBI can also predispose individuals to develop a pathologically distinct form of tauopathy-related dementia at an early age. No effective treatments are currently available for TBI or TBI-related dementia; moreover, only recently has insight been gained regarding the mechanisms behind their connection. Here, we used antibodies to detect oligomeric and phosphorylated Tau proteins in a non-transgenic rodent model of parasagittal fluid percussion injury. Oligomeric and phosphorylated Tau proteins were detected 4 and 24 h and 2 weeks post-TBI in injured, but not sham control rats. These findings suggest that diagnostic tools and therapeutics that target only toxic forms of Tau may provide earlier detection and safe, more effective treatments for tauopathies associated with repetitive neurotrauma.

Specific Targeting of Tau Oligomers in Htau Mice Prevents Cognitive Impairment and Tau Toxicity Following Injection with Brain-Derived Tau Oligomeric Seeds

Neurodegenerative disease is one of the greatest health crises in the world and as life expectancy rises, the number of people affected will continue to increase. The most common neurodegenerative disease, Alzheimers disease, is a tauopathy, characterized by the presence of aggregated tau, namely in the form of neurofibrillary tangles. Historically, neurofibrillary tangles have been considered the main tau species of interest in Alzheimers disease; however, we and others have shown that tau oligomers may be the most toxic form and the species responsible for the spread of pathology. We developed a novel anti-tau oligomer-specific mouse monoclonal antibody (TOMA) and investigated the potential of anti-tau oligomer passive immunization in preventing the toxicity of tau pathology in Htau mice. We injected pure brain-derived tau oligomers intracerebrally in 3-month-old wild-type and Htau mice and investigated the protective effects of a single 60 μg TOMA injection when compared to the same dose of non-specific IgG and found that TOMA conferred protection against the accumulation of tau oligomers and cognitive deficits for up to 1 month after treatment. Additionally, we injected pure brain-derived tau oligomers intracerebrally in 3-month-old wild-type and Htau mice and treated animals with biweekly injections of 60 μg TOMA or non-specific IgG. We found that long-term administration of TOMA was effective as a preventative therapy, inhibiting oligomeric tau and preserving memory function. These results support the critical role of oligomeric tau in disease progression and validate tau oligomers as a potential drug target.

Tau Immunotherapy Modulates Both Pathological Tau and Upstream Amyloid Pathology in an Alzheimer's Disease Mouse Model

In Alzheimers disease (AD), the pathological accumulation of tau appears to be a downstream effect of amyloid β protein (Aβ). However, the relationship between these two proteins and memory loss is unclear. In this study, we evaluated the specific removal of pathological tau oligomers in aged Tg2576 mice by passive immunotherapy using tau oligomer-specific monoclonal antibody. Removal of tau oligomers reversed memory deficits and accelerated plaque deposition in the brain. Surprisingly, Aβ*56 levels decreased, suggesting a link between tau and Aβ oligomers in the promotion of cognitive decline. The results suggest that tau oligomerization is not only a consequence of Aβ pathology but also a critical mediator of the toxic effects observed afterward in AD. Overall, these findings support the potential of tau oligomers as a therapeutic target for AD.

TDP-43 Phosphorylation by casein kinase Iε promotes oligomerization and enhances toxicity in vivo

Dominant mutations in transactive response DNA-binding protein-43 (TDP-43) cause amyotrophic lateral sclerosis. TDP-43 inclusions occur in neurons, glia and muscle in this disease and in sporadic and inherited forms of frontotemporal lobar degeneration. Cytoplasmic localization, cleavage, aggregation and phosphorylation of TDP-43 at the Ser409/410 epitope have been associated with disease pathogenesis. TDP-43 aggregation is not a common feature of mouse models of TDP-43 proteinopathy, and TDP-43 is generally not thought to acquire an amyloid conformation or form fibrils. A number of putative TDP-43 kinases have been identified, but whether any of these functions to regulate TDP-43 phosphorylation or toxicity in vivo is not known. Here, we demonstrate that human TDP-43(Q331K) undergoes cytoplasmic localization and aggregates when misexpressed in Drosophila when compared with wild-type and M337V forms. Coexpression of Q331K with doubletime (DBT), the fly homolog of casein kinase Iε (CKIε), enhances toxicity. There is at best modest basal phosphorylation of misexpressed human TDP-43 in Drosophila, but coexpression with DBT increases Ser409/410 phosphorylation of all TDP-43 isoforms tested. Phosphorylation of TDP-43 in the fly is specific for DBT, as it is not observed using the validated tau kinases GSK-3β, PAR-1/MARK2 or CDK5. Coexpression of DBT with TDP-43(Q331K) enhances the formation of high-molecular weight oligomeric species coincident with enhanced toxicity, and treatment of recombinant oligomeric TDP-43 with rat CKI strongly enhances its toxicity in mammalian cell culture. These data identify CKIε as a potent TDP-43 kinase in vivo and implicate oligomeric species as the toxic entities in TDP-43 proteinopathies.

Characterization of tau oligomeric seeds in progressive supranuclear palsy

BackgroundProgressive supranuclear palsy (PSP) is a neurodegenerative tauopathy which is primarily defined by the deposition of tau into globose-type neurofibrillary tangles (NFT). Tau in its native form has important functions for microtubule dynamics. Tau undergoes alternative splicing in exons 2, 3, and 10 which results in six different isoforms. Products of splicing on exon 10 are the most prone to mutations. Three repeat (3R) and four repeat (4R) tau, like other disease-associated amyloids, can form oligomers which may then go on to further aggregate and form fibrils. Recent studies from our laboratory and others have provided evidence that tau oligomers, not NFTs, are the most toxic species in neurodegenerative tauopathies and seed the pathological spread of tau.ResultsAnalysis of PSP brain sections revealed globose-type NFTs, as well as both phosphorylated and unphosphorylated tau oligomers. Analysis of PSP brains via Western blot and ELISA revealed the presence of increased levels of tau oligomers compared to age-matched control brains. Oligomers were immunoprecipitated from PSP brain and were capable of seeding the oligomerization of both 3R and 4R tau isoforms.ConclusionsThis is the first time tau oligomers have been characterized in PSP. These results indicate that tau oligomers are an important component of PSP pathology, along with NFTs. The ability of PSP brain-derived tau oligomers to seed 3R and 4R tau suggests that these oligomers represent the pathological species responsible for disease propagation and the presence of oligomers in a pure neurodegenerative tauopathy implies a common neuropathological process for tau seen in diseases with other amyloid proteins.