Phosphorylated Tau Pathology Research Articles

TDP‐43 promotes pathological tau phosphorylation and selective neurotoxicity in C. elegans

AbstractBackgroundTDP‐43‐positive inclusions are present in disease‐affected neurons in over half of patients with Alzheimer’s disease (AD). AD patients with TDP‐43 pathology have worsened clinical outcomes and increased neurodegeneration, but the molecular mechanisms underlying this are unknown.MethodsWe have developed new models of multi‐pathology AD by combining tau and TDP‐43 or tau and Aβ in C. elegans neurons. To characterize these transgenic animals, we measured changes in behavioral outcomes, pathological protein accumulation, and neuron loss. We further tested whether the potent tau modifier sut‐2 influences synergistic neurotoxicity exhibited by tau and TDP‐43 co‐expression.ResultsTDP‐43 promotes tau but not Aβ neurotoxicity, resulting in enhanced uncoordinated locomotion, neuronal dysfunction, pathological protein accumulation, and selective neurodegeneration through aging. Synergism between tau and TDP‐43 is rescued by sut‐2 loss‐of‐function.ConclusionsCharacterizing the relationship between TDP‐43 and tau in vivo is critical to understand and ultimately treat mixed pathology AD. Studies of this novel model of tau and TDP‐43 combined proteotoxicity provide insights into mechanisms underlying tau and TDP‐43 synergistic neurotoxicity. The identification of sut‐2 as a robust modifier of co‐expressed tau and TDP‐43 implicates TDP‐43 as an enhancer of tau toxicity.

The impact of cerebrovascular disease on blood‐based biomarkers of Alzheimer’s disease

AbstractBackgroundThe development of ultrasensitive assays for blood‐based biomarkers may allow for detection of Alzheimer’s disease (AD)‐related pathology in large‐scale community‐based cohorts. We previously showed in the Washington Heights Inwood Columbia Aging Project (WHICAP) an association of plasma biomarker concentrations with clinical and pathological AD diagnosis, and that MRI markers of cerebrovascular disease, particularly parietal lobe white matter hyperintensities (WMH), increase the risk and progression of clinical AD. Here, we test the hypothesis that cerebrovascular disease has a direct impact on AD‐related pathology by examining the association of MRI markers of cerebrovascular disease and plasma biomarker concentrations in WHICAP.MethodAmong 300 WHICAP participants with available structural MRI (mean age 81.87+6.45 years, 67% women, 33.3% non‐Hispanic white, 33.3% African American, 33.3% Hispanic, 42% with cognitive impairment) we used SIMOA and MSD technology to measure plasma concentrations of Aβ42, Aβ40, ptau181, ptau217, total tau, and NfL from banked plasma samples. MRI scans were analyzed for regional WMH, presence of infarct, and presence of microbleeds. We first examined bivariate correlations between MRI cerebrovascular measures and plasma biomarker concentrations. For markers that were associated, we conducted demographically adjusted analyses and examined interactions with cognitive diagnostic status.ResultIncreased parietal lobe WMH, specifically, was associated with higher ptau181 (r=0.21, p=0.008) and ptau217 (r=0.13, p=0.05) concentrations. Increased WMH in frontal, temporal, and parietal regions was associated with increased NfL concentrations (rs=0.21‐0.25, ps<0.001‐0.002). Presence of one or more microbleed was associated with increased NfL (r=0.19, p=0.02). In adjusted models the associations of regional WMH with ptau181 and NfL concentrations were independent of and did not interact with diagnosis.ConclusionMarkers of small vessel cerebrovascular disease, particularly parietal lobe WMH, are associated with AD blood‐based biomarkers of phosphorylated tau pathology and neurodegeneration.

Amelioration of tau related pathology with a novel anti‐prion protein monoclonal antibody in an AD mouse model

AbstractBackgroundA number of studies have shown that amyloid β oligomers (Aβo) mediate their toxicity, in part, via the cellular prion protein (PrPC) on the surface of neurons. We hypothesized that tau oligomers may also mediate toxicity and spread of pathology via PrPC. We have generated a novel monoclonal anti‐PrP antibody (TW1) and assessed the efficacy of passive immunization with this antibody in a mouse model of AD with only tau related pathology.MethodHTau/PS1 transgenic AD model mice were injected at 5 months of age intraperitoneally once a week with TW1 from the age of 5 months. Control mice received only saline. Their behavior was assessed at 8 months of age and brain tissue subsequently harvested for analysis at 9 monthsResultThe treated and control mice did not show any significant differences in sensorimotor testing. Significant statistical differences were observed with the novel object recognition test in the immunized mice on percentage time spent in zones (two tailed, t‐test p = 0.0019). On the closed field symmetrical maze immunized mice performed significantly better (Day1: two tailed t‐test p=0.0001; Day2: two tailed t‐test p=0.0015; Day3: two tailed t‐test p=0.0002). Fifty percent less tau pathology was observed in the dentate gyrus with PHF‐1 immunolabeling (two tailed t‐test p= 0.02) and a 60% reduction was seen in the piriform cortex (two‐tailed, t‐test p=0.01) in treated vs control animals. CP13 immunolabeling showed a significant difference in the piriform cortex (p=0.02, two‐tailed t‐test) in treated mice versus controls. There was no significant difference in astrogliosis or microgliosis in treated versus control mice. Western blots using PHF‐1 showed that TW1 therapy reduced phosphorylated tau pathology (two‐tailed t‐test p=0.03) and improved the ratio of pathological soluble tau to tubulin (two‐tailed t‐test p=0.0006). The same effect were observed with the CP13 antibody (two‐tailed t‐test p=0.0007) and improved the ratio CP13/tubulin (two tailed, t‐test p=0.0014).ConclusionThese results indicate that passive immunization with the TW1 antibody can significantly decrease tau pathology and improve cognition in a transgenic mouse model of AD.

Longitudinal 18F-MK-6240 tau tangles accumulation follows Braak stages

Tracking longitudinal tau tangles accumulation across the Alzheimer's disease continuum is crucial to better understand the natural history of tau pathology and for clinical trials. Although the available first-generation tau PET tracers detect tau accumulation in symptomatic individuals, their nanomolar affinity offers limited sensitivity to detect early tau accumulation in asymptomatic subjects. Here, we hypothesized the novel subnanomolar affinity tau tangles tracer 18F-MK-6240 can detect longitudinal tau accumulation in asymptomatic and symptomatic subjects. We studied 125 living individuals (65 cognitively unimpaired elderly amyloid-β-negative, 22 cognitively unimpaired elderly amyloid-β-positive, 21 mild cognitive impairment amyloid-β-positive and 17 Alzheimer's disease dementia amyloid-β-positive individuals) with baseline amyloid-β 18F-AZD4694 PET and baseline and follow-up tau 18F-MK-6240 PET. The 18F-MK-6240 standardized uptake value ratio (SUVR) was calculated at 90-110 min after tracer injection and the cerebellar crus I was used as the reference region. In addition, we assessed the in vivo18F-MK-6240 SUVR and post-mortem phosphorylated tau pathology in two participants with Alzheimer's disease dementia who died after the PET scans. We found that the cognitively unimpaired amyloid-β-negative individuals had significant longitudinal tau accumulation confined to the PET Braak-like stage I (3.9%) and II (2.8%) areas. The cognitively unimpaired amyloid-β-positive individuals showed greater tau accumulation in Braak-like stage I (8.9%) compared with later Braak stages. The patients with mild cognitive impairment and those who were Alzheimer's dementia amyloid-β-positive exhibited tau accumulation in Braak regions III-VI but not I-II. Cognitively impaired amyloid-β-positive individuals that were Braak II-IV at baseline displayed a 4.6-7.5% annual increase in tau accumulation in the Braak III-IV regions, whereas those who were cognitively impaired amyloid-β-positive Braak V-VI at baseline showed an 8.3-10.7% annual increase in the Braak regions V-VI. Neuropathological assessments confirmed PET-based Braak stages V-VI in the two brain donors. Our results suggest that the 18F-MK-6240 SUVR is able to detect longitudinal tau accumulation in asymptomatic and symptomatic Alzheimer's disease. The highest magnitude of 18F-MK-6240 SUVR accumulation moved from the medial temporal to sensorimotor cortex across the disease clinical spectrum. Trials using the 18F-MK-6240 SUVR in cognitively unimpaired individuals would be required to use regions of interest corresponding to early Braak stages, whereas trials in cognitively impaired subjects would benefit from using regions of interest associated with late Braak stages. Anti-tau trials should take into consideration an individual's baseline PET Braak-like stage to minimize the variability introduced by the hierarchical accumulation of tau tangles in the human brain. Finally, our post-mortem findings supported use of the 18F-MK-6240 SUVR as a biomarker to stage tau pathology in patients with Alzheimer's disease.

New RNA-Based Breakthroughs in Alzheimer's Disease Diagnosis and Therapeutics.

Dementia is described as the fifth leading cause of death worldwide and Alzheimer’s disease (AD) is recognized as the most common, causing a huge impact on health costs and quality of patients’ lives. The main hallmarks that are commonly associated with the pathologic process are amyloid deposition, pathologic Tau phosphorylation and neurodegeneration. It is still unclear how these events are linked to the disease progression, due to the complex pathologic mechanisms. Nevertheless, several hypotheses have been proposed for a better understanding of AD. The AD diagnosis is performed by using a combination of several tools to detect β-amyloid peptide (Aβ) deposits and modifications in cognitive performance, sometimes being expensive and invasive. In the treatment field, there is still an absence of effective treatments to delay or stop the progression of the disease, with most of the approved drugs used to relieve symptoms, and all of them with significant adverse side effects. Considering all limitations, the need to establish new and more effective diagnostic and therapeutic strategies becomes clear. This review aims not only to describe the disease and its impact but also to collect the currently available diagnostic and therapeutic strategies, highlighting new promising RNA-based strategies for AD.

Roscovitine, a Cyclin-Dependent Kinase-5 Inhibitor, Decreases Phosphorylated Tau Formation and Death of Retinal Ganglion Cells of Rats after Optic Nerve Crush.

Tauopathies are neurodegenerative diseases characterized by abnormal metabolism of misfolded tau proteins and are progressive. Pathological phosphorylation of tau occurs in the retinal ganglion cells (RGCs) after optic nerve injuries. Cyclin-dependent kinase-5 (Cdk5) causes hyperphosphorylation of tau. To determine the roles played by Cdk5 in retinal degeneration, roscovitine, a Cdk5 inhibitor, was injected intravitreally after optic nerve crush (ONC). The neuroprotective effect of roscovitine was determined by the number of Tuj-1-stained RGCs on day 7. The change in the levels of phosphorylated tau, calpain-1, and cleaved α-fodrin was determined by immunoblots on day 3. The expression of P35/P25, a Cdk5 activator, in the RGCs was determined by immunohistochemistry. The results showed that roscovitine reduced the level of phosphorylated tau by 3.5- to 1.6-fold. Calpain-1 (2.1-fold) and cleaved α-fodrin (1.5-fold) were increased on day 3, suggesting that the calpain signaling pathway was activated. P35/P25 was accumulated in the RGCs that were poorly stained by Tuj-1. Calpain inhibition also reduced the increase in phosphorylated tau. The number of RGCs decreased from 2191 ± 178 (sham) to 1216 ± 122 cells/mm2 on day 7, and roscovitine preserved the level at 1622 ± 130 cells/mm2. We conclude that the calpain-mediated activation of Cdk5 is associated with the pathologic phosphorylation of tau.

G protein-coupled receptor kinases are associated with Alzheimer's disease pathology.

Alzheimer's disease (AD) is characterised by extracellular deposition of amyloid-β (Aβ) in amyloid plaques and intracellular aggregation and accumulation of hyperphosphorylated tau in neurofibrillary tangles (NFTs). Although several kinases have been identified to contribute to the pathological phosphorylation of tau, kinase-targeted therapies for AD have not been successful in clinical trials. Critically, the kinases responsible for numerous identified tau phosphorylation sites remain unknown. G protein-coupled receptor (GPCR) kinases (GRKs) have recently been implicated in phosphorylation of non-GPCR substrates, for example, tubulin and α-synuclein, and in neurological disorders, including schizophrenia and Parkinson's disease. Accordingly, we investigated the involvement of GRKs in the pathophysiology of AD. We performed a comprehensive immunohistochemical and biochemical analysis of the ubiquitously expressed GRKs, namely, GRK2, 3, 5 and 6, in postmortem human brain tissue of control subjects and AD patients. GRKs display unique cell-type-specific expression patterns in neurons, astrocytes and microglia. Levels of GRKs 2, 5 and 6 are specifically decreased in the CA1 region of the AD hippocampus. Biochemical evidence indicates that the GRKs differentially associate with total, soluble and insoluble pools of tau in the AD brain. Complementary immunohistochemical studies indicate that the GRKs differentially colocalise with total tau, phosphorylated tau and NFTs. Notably, GRKs 3 and 5 also colocalise with amyloid plaques. These studies establish a link between GRKs and the pathological phosphorylation and accumulation of tau and amyloid pathology in AD brains and suggest a novel role for these kinases in regulation of the pathological hallmarks of AD.

Differential accumulation of tau pathology between reciprocal F1 hybrids of rTg4510 mice

Tau, a family of microtubule-associated proteins, forms abnormal intracellular inclusions, so-called tau pathology, in a range of neurodegenerative diseases collectively known as tauopathies. The rTg4510 mouse model is a well-characterized bitransgenic F1 hybrid mouse model of tauopathy, which was obtained by crossing a Camk2α-tTA mouse line (on a C57BL/6 J background) with a tetO-MAPT*P301L mouse line (on a FVB/NJ background). The aim of this study was to investigate the effects of the genetic background and sex on the accumulation of tau pathology in reciprocal F1 hybrids of rTg4510 mice, i.e., rTg4510 on the (C57BL/6 J × FVB/NJ)F1 background (rTg4510_CxF) and on the (FVB/NJ × C57BL/6 J)F1 background (rTg4510_FxC). As compared with rTg4510_CxF mice, the rTg4510_FxC mice showed marked levels of tau pathology in the forebrain. Biochemical analyses indicated that the accumulation of abnormal tau species was accelerated in rTg4510_FxC mice. There were strong effects of the genetic background on the differential accumulation of tau pathology in rTg4510 mice, while sex had no apparent effect. Interestingly, midline-1 (Mid1) was identified as a candidate gene associated with this difference and exhibited significant up/downregulation according to the genetic background. Mid1 silencing with siRNA induced pathological phosphorylation of tau in HEK293T cells that stably expressed human tau with the P301L mutation, suggesting the role of Mid1 in pathological alterations of tau. Elucidation of the underlying mechanisms will provide novel insights into the accumulation of tau pathology and is expected to be especially informative to researchers for the continued development of therapeutic interventions for tauopathies.

Intravenous administration of mesenchymal stem cells reduces Tau phosphorylation and inflammation in the 3xTg-AD mouse model of Alzheimer's disease

Mesenchymal stem cell (MSC) administration is a novel and promising therapeutic approach for Alzheimer's disease (AD). Focusing on an intervention easily translatable into clinical practice, we administered allogeneic bone marrow-derived MSCs intravenously in a mouse model of AD (3xTg-AD). We systematically evaluated the effects of a single-dose and multiple-doses of MSCs in young and old mice (5 or 10 months old), comparing the short-term and long-term effects after 1, 2, or 7 months of treatment. A single dose of MSCs in young mice attenuated neuroinflammation 1 and 7 months after injection, whereas multiple-doses did not show any effect. Multiple-doses of MSCs (administered at 5 to 12 mo, or 10 to 12 mo) reduced the β-secretase cleavage of the amyloid precursor protein, although levels of Aβ-42 did not change. Most interestingly, multiple doses of MSCs affected tau hyperphosphorylation. MSCs administered in young mice for 7 months decreased the pathological tau phosphorylation at T205, S214, and T231. MSCs administered in old mice for 2 months decreased tau phosphorylation at S396. Our findings show how different timing and frequency of MSC injections can affect and modulate several aspects of the AD-like neuropathology in the 3xTg-AD mouse model, strengthening the concept of fine-tuning MSC therapy for Alzheimer's disease.

Passive Immunization With a Novel Monoclonal Anti-PrP Antibody TW1 in an Alzheimer's Mouse Model With Tau Pathology.

Neurofibrillary tangles (NFTs) are a major pathologic hallmark of Alzheimer’s disease (AD). Several studies have shown that amyloid β oligomers (Aβo) and tau oligomers mediate their toxicity, in part, via binding to cellular prion protein (PrPC) and that some anti-PrP antibodies can block this interaction. We have generated a novel monoclonal anti-PrP antibody (TW1) and assessed the efficacy of passive immunization with it in a mouse model of AD with extensive tau pathology: hTau/PS1 transgenic (Tg) mice. These mice were injected intraperitoneally once a week with TW1 starting at 5 months of age. Behavior was assessed at 8 months of age and brain tissue was subsequently harvested for analysis of treatment efficacy at 9 months. Mice treated with TW1 did not show any significant difference in sensorimotor testing including traverse beam, rotarod, and locomotor activity compared to controls. Significant cognitive benefits were observed with the novel object recognition test (ORT) in the immunized mice (two-tailed, t-test p = 0.0019). Immunized mice also showed cognitive benefits on the closed field symmetrical maze (day 1 two-tailed t-test p = 0.0001; day 2 two-tailed t-test p = 0.0015; day 3 two-tailed t-test p = 0.0002). Reduction of tau pathology was observed with PHF-1 immunohistochemistry in the piriform cortex by 60% (two-tailed t-test p = 0.01) and in the dentate gyrus by 50% (two-tailed t-test p = 0.02) in animals treated with TW1 compared to controls. There were no significant differences in astrogliosis or microgliosis observed between treated and control mice. As assessed by Western blots using PHF-1, the TW1 therapy reduced phosphorylated tau pathology (two-tailed t-test p = 0.03) and improved the ratio of pathological soluble tau to tubulin (PHF1/tubulin; two-tailed t-test p = 0.0006). Reduction of tau pathology also was observed using the CP13 antibody (two-tailed t-test p = 0.0007). These results indicate that passive immunization with the TW1 antibody can significantly decrease tau pathology as assessed by immunohistochemical and biochemical methods, resulting in improved cognitive function in a tau transgenic mouse model of AD.

Levels of amyloid β in cerebrospinal fluid predicts cognition five years later: A population‐based study of 70‐year‐olds

AbstractBackgroundFew studies have investigated the relationship between cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease (AD) and later cognitive function in the general population. The aim of this study was to study the association between Aβ42/40‐ratio, total‐tau (t‐tau) and phosfo‐tau (p‐tau) at age 70 and cognition at age 75 in a population‐based sample without dementia at baseline.MethodThe sample was derived from the population‐based Gothenburg H70 Birth Cohort Studies. A representative sample of 70‐year‐olds (N=1203, response rate=72%) were examined between 2014‐2016. A subsample of 316 individuals (26%) consented to a lumbar puncture and were free from dementia at age 70. Data have so far been collected on 72 individuals with CSF‐measures at age 70 and cognitive data at the follow‐up at age 75. CSF measures included Aβ42/Aβ40‐ratio, T‐tau and P‐tau, while cognitive tests comprised the Ray Auditory Verbal Learning Test (RAVLT), Semantic Fluency (animals) and Trail Making Test (TMT) A and B.ResultAt age 70, the prevalence of amyloid pathology was 22.8%, total tau pathology 33.2%, and phosphorylated tau pathology 6.9% in cognitively unimpaired individuals. Lower Aβ42/Aβ40‐ratio at age 70 was associated with lower verbal learning score (p<0.01), lower delayed recall (<0.0001) and lower verbal fluency score (p<0.05) at age 75. Aβ42/Aβ40‐ratio was not significantly associated with TMT, and T‐tau and P‐tau was not significantly related to any of the cognitive measures.ConclusionOur findings indicate that amyloid pathology precedes decline in cognition with at least five years while T‐tau and p‐tau does not.

Does loss of interaction of progranulin and prosaposin promote neurofibrillary tangle development?

AbstractBackgroundProgranulin (PGRN) and prosaposin (PSAP) have lysosomal and neurotrophic properties. Reduced amounts of PGRN in mutant tau‐expressing Alzheimer’s disease (AD) model mice exacerbated phosphorylated tau pathology. The implication of PGRN in tangle formation in AD is not understood nor the association of PSAP with AD. Both features need further research.MethodFixed human brain tissue sections of middle temporal gyrus (MTG) from low plaque (LP)(n=4), high plaque (HP)(n=4) non‐demented (ND), and AD (n=4) cases, and superior frontal gyrus from a presenilin‐1 mutated case and frontal temporal lobar degeneration (FTLD) cases (n=3) with heterozygous granulin mutations were employed in this study. The interaction of PGRN and PSAP was identified with proximity ligation assay (PLA). The colocalization of PGRN and PSAP with tangle was identified by fluorescent immunohistochemistry and triple‐color confocal microscopy with antibodies to phosphorylated tau (p‐tau). PGRN and PSAP fluorescence intensity was measured in p‐tau positive neurons and compared to adjacent p‐tau negative neurons.ResultDifferent p‐tau positive structures were measured and related to the levels of PGRN and PSAP. Extracellular neuropil threads appeared to have no association with these proteins. Reduced levels of PGRN and PSAP were detected in p‐tau positive neurons compared to control neurons in all groups. Average levels of PGRN in control neurons were decreased as disease developed. In the AD group, reduced signals of these proteins were observed overall in neurons without p‐tau, and absent in fully matured neurofibrillary tangles. The levels of PGRN and PSAP negatively correlated with p‐tau immunoreactivity. The presenilin‐1 mutated case with numerous tangles in frontal cortex had absence of PGRN and PSAP in tangles, but colocalization of PGRN and PSAP was evident in adjacent neurons. FTLD cases showed absence of PGRN in most neurons, but continued expression of PSAP. The interaction of PGRN and PSAP in neurons was verified with a PLA assay.ConclusionP‐tau positive neurons had significantly less PGRN and PSAP even in the non‐demented groups, which suggests this could be an early event of tangle formation. The insufficiency of both PGRN and PSAP in neurons might lead to accumulation of p‐tau protein due to deficits in lysosomal activity.

The Crosstalk Between Pathological Tau Phosphorylation and Mitochondrial Dysfunction as a Key to Understanding and Treating Alzheimer's Disease.

Alzheimer's disease (AD) is the most common progressive neurodegenerative disorder. A defining hallmark of the AD brain is the presence of intraneuronal neurofibrillary tangles (NFTs) which are made up of abnormally modified tau, with aberrant phosphorylation being the most studied posttranslational modification (PTM). Although the accumulation of tau as NFTs is an invariant feature of the AD brain, it has become evident that these insoluble aggregates are likely not the primary pathogenic form of tau, rather soluble forms of tau with abnormal PTMs are the mediators of toxicity. The most prevalent PTM on tau is phosphorylation, with the abnormal modification of specific residues on tau playing a key role in its toxicity. Even though it is widely accepted that tau with aberrant PTMs facilitates neurodegeneration, the precise cellular mechanisms remain unknown. Nonetheless, there is an evolving conceptual framework that an important contributing factor may be selective pathological tau species compromising mitochondrial biology. Understanding the mechanisms by which tau with site-specific PTM impacts mitochondria is crucial for understanding the role tau plays in AD. Here, we provide a brief introduction to tau and its phosphorylation and function in a physiological context, followed by a discussion of the impact of soluble phosphorylated tau species on neuronal processes in general and mitochondria more specifically. We also discuss how therapeutic strategies that attenuate pathological tau species in combination with treatments that improve mitochondrial biology could be a potential therapeutic avenue to mitigate disease progression in AD and other tauopathies.

Differential cross-seeding properties of tau and α-synuclein in mouse models of tauopathy and synucleinopathy.

Co-occurrence of tau and α-synuclein pathologies in a subset of Alzheimer’s disease patients has led to the idea that mixed pathologies may play a unique characteristic role in the Alzheimer’s disease neurodegenerative cascade. To understand the aetiology of such mixed pathologies, we investigated cross-seeding by human recombinant tau and human recombinant α-synuclein fibrillar species in a mouse model of tauopathy (Line PS19) or synucleinopathy (Line M20). Unilateral hippocampal injection of tau fibrils or α-synuclein fibrils, and to a lesser extent tau + α-synuclein copolymer fibrils prepared from co-incubating individual recombinant monomers, induced robust phosphorylated tau pathology in PS19 mice relative to control mice. Though the tau + α-synuclein copolymer fibrils did not modulate induction of pathologies at the site of injection, examination of the whole brain showed that these copolymers exacerbated neuroanatomic transmission of seeded tau pathology compared to tau fibril-injected mice. Only α-synuclein fibrils, but not tau alone or tau + α-synuclein copolymers, triggered modest levels of endogenous phosphorylated α-synuclein pathology. Overall, data from the PS19 mice suggest that human α-synuclein fibrils can efficiently cross-seed human tau and have a modest priming effect on mouse α-synuclein, and the presence of tau fibrils does not exacerbate the priming process. In M20 mice, unilateral hippocampal injection of α-synuclein fibrils or tau fibrils induced robust bilateral phosphorylated α-synuclein pathology, while tau + α-synuclein copolymer injection resulted in restricted phosphorylated α-synuclein pathology predominantly in the ipsilateral cortex. This suggests that human tau fibrils can also induce human α-synuclein pathogenesis, and the presence of combinatorial seeds is not synergistic. None of these aggregates induced phosphorylated tau pathology in M20 mice, showing that mouse tau cannot be primed efficiently by human tau fibrils or human α-synuclein fibrils. Neuropathological analysis of the whole brain of M20 mice showed that tau + α-synuclein copolymer-injected mice had lower abundance of bilaterally transmitted α-synuclein pathologies relative to α-synuclein fibril-injected mice. Thus, the tau + α-synuclein copolymer fibrils show robust transmission properties preferentially in rodent model of tauopathies but not in synucleinopathy, probably signifying an enhanced cooperative relationship between tau and α-synuclein in the tau seeding process. Together, our data highlight the unique cross-seeding properties of tau and αSyn in neurodegenerative proteinopathies.

Mechanisms of Regulation and Diverse Activities of Tau-Tubulin Kinase (TTBK) Isoforms.

Tau-tubulin kinase 1 (TTBK1) is a CNS-specific, kinase that has been implicated in the pathological phosphorylation of tau in Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD). TTBK1 is a challenging therapeutic target because it shares a highly conserved catalytic domain with its homolog, TTBK2, a ubiquitously expressed kinase genetically linked to the disease spinocerebellar ataxia type 11. The present study attempts to elucidate the functional distinctions between the TTBK isoforms and increase our understanding of them as distinct targets for the treatment of neurodegenerative disease. We demonstrate that in cortical neurons, TTBK1, not TTBK2, is the isoform responsible for tau phosphorylation at epitopes enriched in tauopathies such as Serine 422. In addition, although our elucidation of the crystal structure of the TTBK2 kinase domain indicates almost identical structural similarity with TTBK1, biochemical and cellular assays demonstrate that the enzymatic activity of these two proteins is regulated by a combination of unique extra-catalytic sequences and autophosphorylation events. Finally, we have identified an unbiased list of neuronal interactors and phosphorylation substrates for TTBK1 and TTBK2 that highlight the unique cellular pathways and functional networks that each isoform is involved in. This data address an important gap in knowledge regarding the implications of targeting TTBK kinases and may prove valuable in the development of potential therapies for disease.

RETRACTED: Inhibition of HDAC3 reverses Alzheimer’s disease-related pathologies in vitro and in the 3xTg-AD mouse model

Alzheimer's disease (AD) is the leading cause of age-related dementia. Neuropathological hallmarks of AD include brain deposition of β-amyloid (Aβ) plaques and accumulation of both hyperphosphorylated and acetylated tau. RGFP-966, a brain-penetrant and selective HDAC3 inhibitor, or HDAC3 silencing, increases BDNF expression, increases histone H3 and H4 acetylation, decreases tau phosphorylation and tau acetylation at disease-associated sites, reduces β-secretase cleavage of the amyloid precursor protein (APP), and decreases Aβ1-42 accumulation in HEK-293 cells overexpressing APP with the double Swedish mutation (HEK/APPsw). In the triple transgenic AD mouse model (3xTg-AD), repeated administration of 3 and 10 mg/kg of RGFP-966 reverses pathological tau phosphorylation at Thr181, Ser202, and Ser396, increases levels of the Aβ degrading enzyme Neprilysin in plasma, decreases Aβ1-42 protein levels in the brain and periphery, and improves spatial learning and memory. Finally, we show that RGFP-966 decreases Aβ1-42 accumulation and both tau acetylation and phosphorylation at disease residues in neurons derived from induced pluripotent stem cells obtained from APOEε4-carrying AD patients. These data indicate that HDAC3 plays an important regulatory role in the expression and regulation of proteins associated with AD pathophysiology, supporting the notion that HDAC3 may be a disease-modifying therapeutic target.

Evaluation of a PET Radioligand to Image O-GlcNAcase in Brain and Periphery of Rhesus Monkey and Knock-Out Mouse.

Accumulation of hyperphosphorylated tau, a microtubule-associated protein, plays an important role in the progression of Alzheimer disease. Animal studies suggest that one strategy for treating Alzheimer disease and related tauopathies may be inhibition of O-GlcNAcase (OGA), which may subsequently decrease pathologic tau phosphorylation. Here, we report the pharmacokinetics of a novel PET radioligand, 18F-LSN3316612, which binds with high affinity and selectivity to OGA. Methods: PET imaging was performed on rhesus monkeys at baseline and after administration of either thiamet-G, a potent OGA inhibitor, or nonradioactive LSN3316612. The density of the enzyme was calculated as distribution volume using a 2-tissue-compartment model and serial concentrations of parent radioligand in arterial plasma. The radiation burden for future studies was based on whole-body imaging of monkeys. Oga∆Br, a mouse brain-specific knockout of Oga, was also scanned to assess the specificity of the radioligand for its target enzyme. Results: Uptake of radioactivity in monkey brain was high (∼5 SUV) and followed by slow washout. The highest uptake was in the amygdala, followed by striatum and hippocampus. Pretreatment with thiamet-G or nonradioactive LSN3316612 reduced brain uptake to a low and uniform concentration in all regions, corresponding to an approximately 90% decrease in distribution volume. Whole-body imaging of rhesus monkeys showed high uptake in kidney, spleen, liver, and testes. In Oga∆Br mice, brain uptake of 18F-LSN3316612 was reduced by 82% compared with control mice. Peripheral organs were unaffected in Oga∆Br mice, consistent with loss of OGA expression exclusively in the brain. The effective dose of 18F-LSN3316612 in humans was calculated to be 22 μSv/MBq, which is typical for 18F-labeled radioligands. Conclusion: These results show that 18F-LSN3316612 is an excellent radioligand for imaging and quantifying OGA in rhesus monkeys and mice. On the basis of these data, 18F-LSN3316612 merits evaluation in humans.

Prevalence of preclinical Alzheimer disease

ObjectiveTo determine the prevalence of preclinical Alzheimer disease (AD) according to current classification systems by examining CSF from a representative general population sample of 70-year-olds from Gothenburg, Sweden.MethodThe sample was derived from the population-based H70 Gothenburg Birth Cohort Studies in Gothenburg, Sweden. The participants (n = 322, age 70 years) underwent comprehensive neuropsychiatric, cognitive, and somatic examinations. CSF levels of β-amyloid (Aβ)42, Aβ40, total tau, and phosphorylated tau were measured. Preclinical AD was classified according to criteria of the A/T/N system, Dubois 2016, National Institute on Aging–Alzheimer's Association (NIA-AA) criteria, and International Working Group-2 (IWG-2) criteria. Individuals with Clinical Dementia Rating score >0 were excluded, leaving 259 cognitively unimpaired individuals.ResultsThe prevalence of amyloid pathology was 22.8%, of total tau pathology was 33.2%, and of phosphorylated tau pathology was 6.9%. With the A/T/N system, the prevalence of A+/T−/N− was 13.1%, A+/T−/N+ was 7.3%, A+/T+/N+ was 2.3%, A−/T−/N+ was 18.9%, and A−/T+/N+ was 4.6%. When the Dubois criteria were applied, the prevalence of asymptomatic at risk for AD was 36.7% and of preclinical AD was 9.7%. With the NIA-AA criteria, the prevalence of stage 1 was 13.1% and stage 2 was 9.7%. With the IWG-2 criteria, the prevalence of asymptomatic at risk for AD was 9.7%. The APOE ε4 allele was associated with several of the categories. Men more often had total tau pathology, A+/T−/N+, preclinical AD according to Dubois 2016, asymptomatic at risk for AD according to the IWG-2 criteria, and NIA-AA stage 2.ConclusionThe prevalence of pathologic AD markers was very common (46%) in a representative population sample of 70-year-olds. The clinical implications of these findings need to be scrutinized further in longitudinal studies.

Pathological phosphorylation of tau and TDP-43 by TTBK1 and TTBK2 drives neurodegeneration

BackgroundProgressive neuron loss in the frontal and temporal lobes of the cerebral cortex typifies frontotemporal lobar degeneration (FTLD). FTLD sub types are classified on the basis of neuronal aggregated protein deposits, typically containing either aberrantly phosphorylated TDP-43 or tau. Our recent work demonstrated that tau tubulin kinases 1 and 2 (TTBK1/2) robustly phosphorylate TDP-43 and co-localize with phosphorylated TDP-43 in human postmortem neurons from FTLD patients. Both TTBK1 and TTBK2 were initially identified as tau kinases and TTBK1 has been shown to phosphorylate tau epitopes commonly observed in Alzheimer’s disease and other tauopathies.MethodsTo further elucidate how TTBK1/2 activity contributes to both TDP-43 and tau phosphorylation in the context of the neurodegeneration seen in FTLD, we examined the consequences of elevated human TTBK1/2 kinase expression in transgenic animal models of disease.ResultsWe show that C. elegans co-expressing tau/TTBK1 tau/TTBK2, or TDP-43/TTBK1 transgenes in combination exhibit synergistic exacerbation of behavioral abnormalities and increased pathological protein phosphorylation. We also show that C. elegans co-expressing tau/TTBK1 or tau/TTBK2 transgenes in combination exhibit aberrant neuronal architecture and neuron loss. Surprisingly, the TTBK2/TDP-43 transgenic combination showed no exacerbation of TDP-43 proteinopathy related phenotypes. Additionally, we observed elevated TTBK1/2 protein expression in cortical and hippocampal neurons of FTLD-tau and FTLD-TDP cases relative to normal controls.ConclusionsOur findings suggest a possible etiology for the two most common FTLD subtypes through a kinase activation driven mechanism of neurodegeneration.

Targeting Prion-like Cis Phosphorylated Tau Pathology in Neurodegenerative Diseases.

Tau is a microtubule-associated protein heavily implicated in neurodegenerative diseases collectively known as tauopathies, including Alzheimer’s disease and chronic traumatic encephalopathy. Phosphorylation of tau at Thr231 allows for the isomerization of phosphorylated tau (p-tau) into distinct cis and trans conformations. Cis, but not trans, p-tau is detectable not only in Alzheimer’s disease and chronic traumatic encephalopathy, but also right after traumatic brain injury depending on injury severity and frequency both in humans and animal models. Cis p-tau is not only neurotoxic but also spreads from a neuron to another in a prion-like fashion, functioning as a primary driver of neurodegeneration, which can be effectively neutralized by cis p-tau antibody. This represents an exciting new opportunity for understanding disease development and developing early biomarkers and effective therapies of tauopathies.