Paired Helical Filament Tau Research Articles

Higher Angiotensin II Type 1 Receptor Levels and Activity in the Postmortem Brains of Older Persons with Alzheimer's Dementia.

Aging is a key risk factor in Alzheimer's dementia (AD) development and progression. The primary dementia-protective benefits of angiotensin II subtype 1 receptor (AT1R) blockers are believed to arise from systemic effects on blood pressure. However, a brain-specific renin-angiotensin system (b-RAS) exists, which can be altered by AT1R blockers. Brain RAS acts mainly through 3 angiotensin receptors: AT1R, AT2R, and AT4R. Changes in these brain angiotensin receptors may accelerate the progression of AD. Using postmortem frontal cortex brain samples of age- and sex-matched cognitively normal individuals (n = 30) and AD patients (n = 30), we sought to dissect the b-RAS changes associated with AD and assess how these changes correlate with brain markers of oxidative stress, inflammation, and mitochondrial dysfunction as well as amyloid-β and paired helical filament tau pathologies. Our results show higher protein levels of the pro-inflammatory AT1R and phospho-ERK (pERK) in the brains of AD participants. Brain AT1R levels and pERK correlated with higher oxidative stress, lower cognitive performance, and higher tangle and amyloid-β scores. This study identifies molecular changes in b-RAS and offers insight into the role of b-RAS in AD-related brain pathology.

PET imaging biomarkers: What is the outlook for their role in research, trials, and practice?

AbstractBackgroundPositron emission tomography (PET) imaging is an increasingly widespread tool for the identification of Alzheimer’s disease (AD) pathophysiology. PET biomarkers of Aβ and tau pathology, together with fluid biomarkers and ex vivo pathology validation, have enabled detection of early regional changes and identification of individuals who are unimpaired but on the AD pathway. This presentation will address the changing and complementary role of PET biomarkers in relation to fluid biomarkers in AD clinical trials, research, and practice.MethodRecent PET imaging work from natural history studies targeting Aβ and tau pathology will be reviewed, with an emphasis on early detection of dynamic regional changes in unimpaired individuals in relation to fluid biomarkers and cognition. Relationships between Aβ and tau PET measurements to other biomarkers and pathology will be discussed, as well as the status of emerging PET markers of inflammation and synaptic integrity.ResultA key unique feature of PET imaging is that it offers a regionally‐specific view of fibrillar Aβ and paired helical filament (PHF) tau pathology in vivo. Initial Aβ and tau changes are detectable over a decade before the onset of clinically‐relevant cognitive symptoms. There is a predictable time course of Aβ and tau change over the course of disease, and regional tau accumulation predicts local neurodegenerative changes. In symptomatic individuals, inferolateral temporal tau accumulation is sensitive to AD and useful for differential diagnosis. However, tau accumulation is also highly variable even among symptomatic Aβ+ individuals, likely due to co‐pathology and the influence of poorly understood factors such as age, sex, genetics, and cardiovascular risk. There are a number of technical and cost considerations for successful implementation of PET relative to other biomarkers in research, trials, and clinical practice.ConclusionEarly, regionally‐specific Aβ and tau PET measurements predict downstream neurodegeneration and cognitive decline. Such early changes represent an opportunity for therapeutic intervention, but identification of individuals who are unimpaired but at risk remains challenging. Additional longitudinal research and development of PET biomarkers for other disease targets will address open questions about how AD develops.

Higher angiotensin II type 1 receptor (AT1 R) levels and activity in the postmortem brains of older persons with Alzheimer's disease.

Alzheimer's disease (AD) is the most common cause of dementia. Although multiple potential etiologies have been proposed, no clear aging-related etiological mechanisms have been identified. Renin Angiotensin system (RAS) is a hormonal system that is implicated in blood pressure control and has been suggested as a potential contributor to the development of AD. Here, using postmortem frontal cortex brain samples of age- and sex-matched cognitively normal individuals (n=30) and AD patients (n=30), we sought to examine the brain specific RAS (b-RAS) differences with AD and how these findings correlate with brain AD pathologies. Samples were obtained from the Rush Memory and Aging Project. We measured angiotensinogen, renin, and ACE gene expression by qPCR and both gene expression and protein levels of Angiotensin II receptor type 1, 2, and 4 and their downstream signaling pathway (pERK, eNOS, and nNOS) by qPCR and Western blot. Brain cytokines (IL6, TNFα, IFNγ, and IL1β) and oxidative stress (OS) marker (protein carbonyl) as well as average paired helical filaments-tau and β-amyloid load were used as specific markers of AD pathology. Our results demonstrate an increase in both gene and protein expression (2.47 folds p=0.01, median0.59 (range1.99) vs. 0.47 (1.95) p=0.03, respectively) and signaling activity (0.35 (11.41) vs. 0.04 (1.84), p<0.01) of AT1 R in AD. We have not observed any significant changes in other RAS components. Our data show that higher AT1 R levels correlate with OS (r=0.301 p=0.01) and β-amyloid load (r=0.245 p=0.04), while higher pERK levels negatively correlate with MN (r=-0.239 p=0.03) and positively correlate with total tangle (r=0.413 p<0.01) and amyloid (r=0.208 p=0.02) scores. Finally, mRNA, protein, and pERK levels of AT1 R were negatively correlated with global cognitive function (GCF) scores (r=-0.216 p=0.05, r=-0.258 p=0.02, r=-0.376 p<0.01, respectively) and were associated with greater decline in GCF (r=0.265 p=0.02, r=0.223 p=0.04, respectively) in all subjects. This study highlights molecular changes in b-RAS and offers insight into the association of these changes with brain pathology in AD. These findings can be important in shedding light on the benefits of RAS-modulating drugs in AD.

Tau fibril with membrane lipids: Insight from computational modeling and simulations.

The microtubule-binding protein tau has been the center of researches concerning Alzheimer’s disease (AD) due to several clinical trials of β-amyloid therapies failing recently. The availability of the tau fibril structure from AD brain enables computational modeling studies to calculate binding affinities with different ligands. In this study, the tau paired helical filaments (PHF-Tau) (PDB ID: 5O3L) was used as receptor and interactions with the lipids: 3-alpha-cholesterol; 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; and C18:1 sphingomyelin, were explored with molecular docking, molecular dynamics, and natural bond orbital analysis. Docking sites upon solvation of the protein with transferable interatomic potential-3 points reveal the amphipathic nature of PHF-Tau and molecular dynamics simulations show that the embedded phosphocholine at the tail side gives high potential energy values with some amino acids forming H-bond interactions.

PI-2620 Lead Optimization Highlights the Importance of Off-Target Assays to Develop a PET Tracer for the Detection of Pathological Aggregated Tau in Alzheimer's Disease and Other Tauopathies.

The first candidate PI-2014 was tested in healthy controls and subjects with Alzheimer's disease (AD). As PI-2014 displayed off-target binding to monoamine oxidase A (MAO-A), a new lead with improved binding to Tau and decreased MAO-A binding was required. For compound optimization, Tau binding assays based on both human AD brain homogenate and Tau-paired helical filaments were employed. Furthermore, two MAO-A screening assays based on (1) human-recombinant MAO-A and (2) displacement of 2-fluoro-ethyl-harmine from mouse brain homogenate were employed. Removing the N-methyl group from the tricyclic core resulted in compounds displaying improved Tau binding. For the final round of optimization, the cyclic amine substituents were replaced by pyridine derivatives. PI-2620 (2-(2-fluoropyridin-4-yl)-9H-pyrrolo[2,3-b:4,5-c']dipyridine) emerged as a best candidate displaying high Tau binding, low MAO-A binding, high brain uptake, and fast and complete brain washout. Furthermore, PI-2620 showed Tau binding on brain sections from corticobasal degeneration, progressive supranuclear palsy, and Pick's disease.

Phosphorylation-Induced Structural Reorganization in Tau-Paired Helical Filaments.

Taupathies involve the deposition of abnormal tau protein into neurofibrillary tangles (NFTs) in the human brain. The abnormally hyperphosphorylated tau dissociates from microtubules and forms insoluble aggregates known as paired helical filaments (PHFs), highlighting the importance of post-translational modifications in taupathies. The present study examines the factors responsible for the structural stability of PHFs in native as well as in phosphorylated and O-GlcNAcylated tau. We carried out molecular dynamics simulations on the R3-R4 repeat domains of the human tau protein to gain atomic insights into the key noncovalent interactions responsible for their unique dimeric C-shaped structure. The structural effects upon post-translational modification were found to be prominent for phosphorylation when compared with O-GlcNAcylation. O-GlcNAcylated tau was found to retain the "C conformation" observed in the native tau PHF, whereas upon phosphorylation, we observed a conformational transition to a more opened "H conformation". We found that this conformational transition is brought about by the loss of a key salt bridge between Lys353 and Asp358 due to the phosphorylation at Ser356 that results in the reorganization of the dimeric interface.

Discriminatory ability of next-generation tau PET tracers for Alzheimer's disease.

A next generation of tau PET tracers for the imaging of Alzheimer’s disease and other dementias has recently been developed. Whilst the new compounds have now entered clinical studies, there is limited information available to assess their suitability for clinical applications. Head-to-head comparisons are urgently needed to understand differences in the radiotracer binding profiles. We characterized the binding of the tau tracers PI2620, RO948, MK6240 and JNJ067 in human post-mortem brain tissue from a cohort of 25 dementia cases and age-matched controls using quantitative phosphorimaging with tritium-labelled radiotracers in conjunction with phospho-tau specific immunohistochemistry. The four radiotracers depicted tau inclusions composed of paired helical filaments with high specificity, both in cases with Alzheimer’s disease and in primary tauopathy cases with concomitant Alzheimer’s disease pathology. In contrast, cortical binding to primary tauopathy in cases without paired helical filament tau was found to be within the range of age-matched controls. Off-target binding to monoamine oxidase B has been overcome, as demonstrated by heterologous blocking studies in basal ganglia tissue. The high variability of cortical tracer binding within the Alzheimer’s disease group followed the same pattern with each tracer, suggesting that all compounds are suited to differentiate Alzheimer’s disease from other dementias.

Insight Into Seeded Tau Fibril Growth From Molecular Dynamics Simulation of the Alzheimer's Disease Protofibril Core.

Aggregates of the microtubule associated tau protein are a major constituent of neurofibrillary lesions that define Alzheimer’s disease (AD) pathology. Increasing experimental evidence suggests that the spread of tau neurofibrillary tangles results from a prion-like seeding mechanism in which small oligomeric tau fibrils template the conversion of native, intrinsically disordered, tau proteins into their pathological form. By using atomistic molecular dynamics (MD) simulations, we investigate the stability and dissociation thermodynamics of high-resolution cryo-electron microscopy (cryo-EM) structures of both the AD paired-helical filament (PHF) and straight filament (SF). Non-equilibrium steered MD (SMD) center-of-mass pulling simulations are used to probe the stability of the protofibril structure and identify intermolecular contacts that must be broken before a single tau peptide can dissociate from the protofibril end. Using a combination of exploratory metadynamics and umbrella sampling, we investigate the complete dissociation pathway and compute a free energy profile for the dissociation of a single tau peptide from the fibril end. Different features of the free energy surface between the PHF and SF protofibril result from a different mechanism of tau unfolding. Comparison of wild-type tau PHF and post-translationally modified pSer356 tau shows that phosphorylation at this site changes the dissociation free energy surface of the terminal peptide. These results demonstrate how different protofibril morphologies template the folding of endogenous tau in distinct ways, and how post-translational modification can perturb the folding mechanism.

The accumulation rate of tau aggregates is higher in females and younger amyloid-positive subjects.

The development of tau-PET allows paired helical filament tau pathology to be visualized in vivo. Increased knowledge about conditions affecting the rate of tau accumulation could guide the development of therapies halting the progression of Alzheimer's disease. However, the factors modifying the rate of tau accumulation over time in Alzheimer's disease are still largely unknown. Large-scale longitudinal cohort studies, adjusting for baseline tau load, are needed to establish such risk factors. In the present longitudinal study, 419 participants from four cohorts in the USA (Avid 05e, n = 157; Expedition-3, n = 82; ADNI, n = 123) and Sweden (BioFINDER, n = 57) were scanned repeatedly with tau-PET. The study participants were cognitively unimpaired (n = 153), or patients with mild cognitive impairment (n = 139) or Alzheimer's disease dementia (n = 127). Participants underwent two to four tau-PET (18F-flortaucipir) scans with a mean (± standard deviation) of 537 (±163) days between the first and last scan. The change in tau-PET signal was estimated in temporal meta- and neocortical regions of interest. Subject specific tau-PET slopes were predicted simultaneously by age, sex, amyloid status (determined by amyloid-β PET), APOE ε4 genotype, study cohort, diagnosis and baseline tau load. We found that accelerated increase in tau-PET signal was observed in amyloid-β-positive mild cognitive impairment (3.0 ± 5.3%) and Alzheimer's disease dementia (2.9 ± 5.7%), respectively, when compared to either amyloid-β-negative cognitively unimpaired (0.4 ± 2.7%), amyloid-β-negative mild cognitive impairment (-0.4 ± 2.3%) or amyloid-β-positive cognitively unimpaired (1.2 ± 2.8%). Tau-PET uptake was accelerated in females (temporal region of interest: t = 2.86, P = 0.005; neocortical region of interest: t = 2.90, P = 0.004), younger individuals (temporal region of interest: t = -2.49, P = 0.013), and individuals with higher baseline tau-PET signal (temporal region of interest: t = 3.83, P < 0.001; neocortical region of interest: t = 5.01, P < 0.001). Tau-PET slopes decreased with age in amyloid-β-positive subjects, but were stable by age in amyloid-β-negative subjects (age × amyloid-β status interaction: t = -2.39, P = 0.018). There were no effects of study cohort or APOE ε4 positivity. In a similar analysis on longitudinal amyloid-β-PET (in ADNI subjects only, n = 639), we found significant associations between the rate of amyloid-β accumulation and APOE ε4 positivity, older age and baseline amyloid-β positivity, but no effect of sex. In conclusion, in this longitudinal PET study comprising four cohorts, we found that the tau accumulation rate is greater in females and younger amyloid-β-positive individuals, while amyloid-β accumulation is greater in APOE ε4 carriers and older individuals. These findings are important considerations for the design of clinical trials, and might improve our understanding of factors associated with faster tau aggregation and spread.

Conformation-selective tau monoclonal antibodies inhibit tau pathology in primary neurons and a mouse model of Alzheimer\u2019s disease

BackgroundThe 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.MethodsWe 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.ResultsDMR7 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.ConclusionsThese 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.

Inferior temporal tau is associated with accelerated prospective cortical thinning in clinically normal older adults

Neurofibrillary tau tangles are a hallmark pathology of Alzheimer's disease (AD) and are more closely associated with AD-related cortical atrophy and symptom severity than amyloid-beta (Aβ). However, studies regarding the effect of tau on longitudinal cortical thinning, particularly in healthy aging and preclinical AD, have been limited in number due to the relatively recent introduction of in vivo PET tracers for imaging tau pathology. Here, we investigate [18F]-flortaucipir (FTP, a marker of paired helical filament tau) PET as a predictor of atrophy in healthy aging and preclinical AD. We examine longitudinal structural MRI brain imaging data, retrospectively and prospectively relative to FTP imaging, using piecewise linear mixed-effect models with time centered at each participant's FTP-PET session. Participants include 111 individuals from the Harvard Aging Brain Study who underwent at least three MRI sessions over an average of 4.46 years and one FTP-PET at the approximate midpoint of the observation period. Our primary analyses focus on inferior temporal (IT) FTP standardized uptake value ratios and longitudinal FreeSurfer defined cortical regions of interest. Relationships were also explored using other regional FTP measures (entorhinal, composite, and local), within high and low Pittsburgh compound-B (PiB) PET groups, and with longitudinal subcortical volume. Strong associations between IT FTP and cortical thinning were found, most notably in temporal, midline, and prefrontal regions, with stronger effects generally observed in the prospective as compared to retrospective time frame. Significant differences between prospective and retrospective rates of thinning were found in the inferior and middle temporal gyri, cingulate areas, as well as pars orbitalis such that higher IT FTP was associated with greater prospective rates of thinning. Within the high PiB group, significant differences between prospective and retrospective rates of thinning were similarly observed. However, no consistent pattern of tau-related change in cortical thickness within the low PiB group was discerned. These results provide support for the hypothesis that tau pathology is a driver of future atrophy as well as provide additional evidence for tau-PET as an effective AD biomarker for interventional clinical trials.

Hyperphosphorylated Tau, Increased Adenylate Cyclase 5 (ADCY5) Immunoreactivity, but No Neuronal Loss in ADCY5-Dyskinesia.

Adenylate cyclase 5 (ADCY5)-related dyskinesia is a childhood-onset movement disorder. Manifestations vary in frequency and severity and may include chorea, tremor, dystonia, facial twitches, myoclonus, axial hypotonia, and limb hypertonia. Psychosis is likely part of the broader spectrum. ADCY5 is widely expressed in the brain, especially in the striatum. Previous reports of brain autopsies of 2 subjects with likely ADCY5-dyskinesia were limited by the absence of a molecular diagnosis. In 1 case, normal gross pathology was reported. In the other case, ADCY5 expression was not examined and neuropathological findings were confounded by age and comorbidities. To examine ADCY5 expression and neuropathological changes in ADCY5-dyskinesia. An extensive brain autopsy, including immunohistochemical analyses with antibodies to paired helical filament tau, α-synuclein, amyloid-β, microtubule-associated protein 2, and ADCY5, was performed. The patient, with a p.M1029K ADCY5 variant, had severe dyskinesias from early childhood, later recurrent episodes of psychosis, and died at age 46. Gross pathology was unremarkable, but we detected increased immunoreactivity for ADCY5 in neurons in multiple brain regions. Despite no history of brain trauma to suggest chronic traumatic encephalopathy, we found tau deposits in the deep cortical sulci, midbrain, and hippocampus with minimal amyloid pathology and no Lewy bodies. We present the first brain autopsy findings in a molecularly proven case of ADCY5-dyskinesia, showing increased ADCY5 immunoreactivity in neurons and evidence of tau deposition. Additional patients will need to be studied to determine whether increased immunoreactivity for ADCY5 is a signature for ADCY5-dyskinesia and whether this disease has a tauopathy component.

"Tau Protein Targeting Via Radioiodinated Azure A For Brain Theranostics: Radiolabeling, Molecular Docking, in vitro And in vivo Biological Evaluation".

Azure-A is one of the phenothiazines (PTZs) derivatives which for decades have been used as antipsychotic drugs due to good lipophilic characteristics which enable them to pass through the blood brain barrier (BBB), besides the important property of enabeling investigation of the pathological forms of aggregated tau protein found in the neurons of the central nervous system. Radioiodination of Azure-A was carried out via an electrophilic substitution reaction using chloramine-T as oxidizing agent. The influence of various reaction parameters and conditions on radioiodination efficiency was investigated, and a high radiochemical yield of 92.07 ± 0.9 % was obtained. An in vitro cytotoxicity study of iodinated Azure-A on three cell lines (HCT-116, human colon carcinoma cell line; Hep-G2, liver carcinoma cell line and HFB-4, normal human melanocytes) was carried out, and the data revealed that ioiodinated Azure A has no to very low toxic effect. The in vivo biodistribution study of 131 I-Azure A showed a high brain uptake of 6.15 ± 0.09 % injected dose/g tissue organ at 30 minutes post-injection, and its retention in brain remained high up to 2 hours, whereas the clearance from the body appeared to proceed via the renal system. The experimental data were confirmed by the molecular docking studies to predict the effect of radioiodination on the binding affinity of the parent molecule (Azure A) to tau paired helical filaments (PHFs). Both ligands showed better binding to S2 and S3 pockets of (PHFs). Consequently, radioiodinated Azure A seems to be a good candidate as an imaging agent for taupathies such as Alzheimer's disease, chronic traumatic encephalopathy, and corticobasal degeneration. Furthermore, it could be a very potent theranostics agent for brain tumors.

Brain imaging measurements of fibrillar amyloid-β burden, paired helical filament tau burden, and atrophy in cognitively unimpaired persons with two, one, and no copies of the APOE ε4 allele

IntroductionWe previously characterized associations between brain imaging measurements of amyloid-β (Aβ) plaque burden and apolipoprotein E (APOE) ε4 gene dose in a small number of cognitively unimpaired late-middle-aged APOE ε4 homozygotes (HMs), heterozygotes (HTs), and noncarriers (NCs). We now characterize cross-sectional Aβ plaque, tau tangle, and cortical atrophy (neurodegeneration) measurements, classifications, and associations with age in a larger number of unimpaired HMs, HTs, and NCs over a wider age range. MethodsWe analyzed 11C Pittsburgh compound B (Aβ) positron emission tomography (PET), flortaucipir (tau) PET, and volumetric magnetic resonance imaging data from 164 study participants of age 47–86 years, including 26 APOE ε4 HMs, 48 HTs, and 90 NCs matched for age and sex. ResultsAβ PET measurements rose, plateaued at the respective ages of 68 and 76, and then declined with age in unimpaired HM and HT groups. Compared with NCs, these two groups began to have significantly higher Aβ PET measurements at ages 62 and 70, respectively, and no longer had significantly higher measurements by ages 71 and 78, respectively. They began to have significantly higher entorhinal cortex tau PET measurements at ages 66 and 70, respectively, and no longer had significantly higher measurements by ages 74 and 78, respectively. Brain atrophy measurements tended to decline slowly with age in all three genetic groups. Their elevated tau PET measurements were attributable to those with positive Aβ PET scans. 41.0%, 18.0%, and 5.0% of the 47- to 70-year-old HMs, HTs, and NCs and 25.0%, 79.0%, and 38.0% of the 71- to 86-year-old HMs, HTs, and NCs had positive Aβ PET scans, and the long-term recall memory scores are significantly higher in the older HMs than in HT and NC groups, suggesting resistance to Aβ deposition in those HMs who remained unimpaired at older ages. ConclusionsThis study provides information about Aβ plaque burden, tau tangle burden, and neurodegeneration in cognitively unimpaired persons at three levels of genetic risk for AD. Unimpaired APOE ε4 HMs can be studied before their 70s to evaluate the understanding of factors, processes, and interventions involved in the predisposition to and prevention of AD, and after their 70s, to discover factors, processes, and interventions involved in the resilience or resistance to and prevention of AD.

Yeast surface display of full-length human microtubule-associated protein tau.

Microtubule-associated protein tau is an intrinsically disordered, highly soluble protein found primarily in neurons. Under normal conditions, tau regulates the stability of axonal microtubules and intracellular vesicle transport. However, in patients of neurodegeneration such as Alzheimer's disease (AD), tau forms neurofibrillary deposits, which correlates well with the disease progression. Identifying molecular signatures in tau, such as posttranslational modification, truncation, and conformational change has great potential to detect earliest signs of neurodegeneration and develop therapeutic strategies. Here, we show that full-length human tau, including the longest isoform found in the adult brain, can be robustly displayed on the surface of yeast Saccharomyces cerevisiae. Yeast-displayed tau binds to anti-tau antibodies that cover epitopes ranging from the N-terminus to the 4R repeat region. Unlike tau expressed in the yeast cytosol, surface-displayed tau was not phosphorylated at sites found in AD patients (probed by antibodies AT8, AT270, AT180, and PHF-1). However, yeast-displayed tau showed clear binding to paired helical filament (PHF) tau conformation-specific antibodies Alz-50, MC-1, and Tau-2. Although the tau possessed a conformation found in PHFs, oligomerization or aggregation into larger filaments was undetected. Taken together, yeast-displayed tau enables robust measurement of protein interactions and is of particular interest for characterizing conformational change.

Head-to-head comparison of tau positron emission tomography tracers [18F]flortaucipir and [18F]RO948

Purpose[18F]flortaucipir binds to paired helical filament tau and accurately identifies tau in Alzheimer’s disease (AD). However, “off-target” binding interferes with the quantification of [18F]flortaucipir in several brain regions. Recently, other tau PET tracers have been developed. Here, we compare [18F]flortaucipir with the novel tau tracer [18F]RO948 head-to-head in vivo.MethodsWe included 18 participants with AD, three with amyloid-β-positive amnestic mild cognitive impairment, and four healthy controls. All underwent [18F]flortaucipir (80–100 min) and [18F]RO948 (70–90) PET scans within approximately 1 month. Four study participants underwent 0–100-min dynamic scanning. Standardized uptake value ratios (SUVRs) were created using an inferior cerebellar reference region.ResultsNeocortical tracer retention was highly comparable using both SUVR and distribution volume ratio-1 values obtained from dynamic scans. However, [18F]RO948 retention was significantly higher in the entorhinal cortex and lower in the basal ganglia, thalamus, and choroid plexus compared with [18F]flortaucipir. Increased off-target binding was observed with age for both tracers. Several cases exhibited strong [18F]RO948 retention in the skull/meninges. This extra-cerebral signal, however, did not affect diagnostic accuracy and remained relatively unchanged when re-examining a subsample after 1 year. Kinetic modeling showed an increase in [18F]flortaucipir SUVR over the scanning interval, compared with a plateau for [18F]RO948.Conclusion[18F]RO948 and [18F]flortaucipir bound comparably in neocortical regions, but [18F]RO948 showed higher retention in the medial temporal lobe and lower intracerebral “off-target” binding. Time-dependent bias of SUVR estimates may prove less of a factor with [18F]RO948, compared with previous tau ligands.

THK5351 and flortaucipir PET with pathological correlation in a Creutzfeldt-Jakob disease patient: a case report

BackgroundTHK5351 and flortaucipir tau ligands have high affinity for paired helical filament tau, yet diverse off-target bindings have been reported. Recent data support the hypothesis that THK5351 binds to monoamine oxidase B (MAO-B) expressed from reactive astrocytes and that flortaucipir has an affinity toward MAO-A and B; however, pathological evidence is lacking. We performed a head-to-head comparison of the two tau ligands in a sporadic Creutzfeldt-Jakob disease (CJD) patient and performed an imaging-pathological correlation study.Case presentationA 67-year-old man visited our clinic a history of 6 months of rapidly progressive dementia, visual disturbance, and akinetic mutism. Diffusion-weighted imaging showed cortical diffusion restrictions in the left temporo-parieto-occipital regions. 18F-THK5351 PET, but not 18F-flortaucipir PET showed high uptake in the left temporo-parieto-occipital regions, largely overlapping with the diffusion restricted areas. Cerebrospinal fluid analysis was weakly positive for 14–3-3 protein and pathogenic prion protein was found. The patient showed rapid cognitive decline along with myoclonic seizures and died 13 months after his first visit. A post-mortem study revealed immunoreactivity for PrPsc, no evidence of neurofibrillary tangles, and abundant astrocytosis which was reactive for MAO-B antibody.ConclusionsOur findings add pathological evidence that increased THK5351 uptake in sporadic CJD patients might be caused by an off-target binding driven by its high affinity for MAO-B.

The Influence of Cerebrospinal Fluid Abnormalities and APOE 4 on PHF-Tau Protein: Evidence From Voxel Analysis and Graph Theory.

Mild cognitive impairment (MCI) is a transitional state between the cognitive changes in normal aging and Alzheimer’s disease (AD), which induces abnormalities in specific brain regions. Previous studies showed that paired helical filaments Tau (PHF-Tau) protein is a potential pathogenic protein which may cause abnormal brain function and structure in MCI and AD patients. However, the understanding of the PHF-Tau protein network in MCI patients is limited. In this study, 225 subjects with PHF-Tau Positron Emission Tomography (PET) images were divided into four groups based on whether they carried Apolipoprotein E ε4 (APOE 4) or abnormal cerebrospinal fluid Total-Tau (CSF T-Tau). They are two important pathogenic factors that might cause cognitive function impairment. The four groups were: individuals harboring CSF T-Tau pathology but no APOE 4 (APOE 4−T+); APOE 4 carriers with normal CSF T-Tau (APOE 4+T−); APOE 4 carriers with abnormal CSF T-Tau (APOE 4+T+); and APOE 4 noncarriers with abnormal CSF T-Tau (APOE 4−T−). We explored the topological organization of PHF-Tau networks in these four groups and calculated five kinds of network properties: clustering coefficient, shortest path length, Q value of modularity, nodal centrality and degree. Our findings showed that compared with APOE 4−T− group, the other three groups showed different alterations in the clustering coefficient, shortest path length, Q value of modularity, nodal centrality and degree. Simultaneously, voxel-level analysis was conducted and the results showed that compared with APOE 4−T− group, the other three groups were found increased PHF-Tau distribution in some brain regions. For APOE 4+T+ group, positive correlation was found between the value of PHF-Tau distribution in altered regions and Functional Assessment Questionnaire (FAQ) score. Our results indicated that the effects of APOE 4 and abnormal CSF T-Tau may induce abnormalities of PHF-Tau protein and APOE 4 has a greater impact on PHF-Tau than abnormal CSF T-Tau. Our results may be particularly helpful in uncovering the pathophysiology underlying the cognitive dysfunction in MCI patients.

Gait Ignition Failure in JNPL3 Human Tau-mutant Mice.

Cognitive impairments and motor dysfunction are commonly observed behavioral phenotypes in genetic animal models of neurodegenerative diseases. JNPL3 transgenic mice expressing human P301L-mutant tau display motor disturbances with age- and gene dose-dependent development of neurofibrillary tangles, suggesting that tau pathology causes neurodegeneration associated with motor behavioral abnormalities. Although gait ignition failure (GIF), a syndrome marked by difficulty in initiating locomotion, has been described in patients with certain forms of tauopathies, transgenic mouse models mirroring human GIF syndrome have yet to be reported. Using the open field and balance beam tests, here we discovered that JNPL3 homozygous mice exhibit a marked delay of movement initiation. The elevated plus maze excluded the possibility that hesitation to start in JNPL3 mice was caused by enhanced levels of anxiety. Considering the normal gait ignition in rTg4510 mice expressing the same mutant tau in the forebrain, GIF in JNPL3 mice seems to arise from abnormal tau deposition in the hindbrain areas involved in locomotor initiation. Accordingly, immunohistochemistry revealed highly phosphorylated paired helical filament tau in JNPL3 brainstem areas associated with gait initiation. Together, these findings demonstrate a novel behavioral phenotype of impaired gait initiation in JNPL3 mice and underscore the value of this mouse line as a tool to study the neural mechanisms and potential treatments for human GIF syndrome.

Association of Cortical β-Amyloid Protein in the Absence of Insoluble Deposits With Alzheimer Disease

β-Amyloid deposits are a pathologic hallmark of Alzheimer disease (AD). However, the extent to which cortical β-amyloid protein in the absence of insoluble deposits is associated with classic features of AD appear to be unknown. To examine the associations of cortical β-amyloid protein in the absence of insoluble deposits with cognitive decline, neurofibrillary tangles, other age-associated neuropathologic conditions, and APOE. This analysis combines data from 2 community-based clinicopathologic cohort studies of aging. The Religious Orders Study started in 1994, and the Rush Memory and Aging Project started in 1997. Both studies are ongoing. Participants without known dementia were enrolled and agreed to annual clinical evaluations and brain donation after death. Primary analyses focused on individuals without β-amyloid deposits. Data analyses occurred in mid-September 2018. β-Amyloid protein abundance was measured by targeted proteomics using selected reaction monitoring. β-Amyloid deposits were detected using immunohistochemistry. Other neuropathologic indices were quantified via uniform structured evaluation. Linear mixed models were used to examine the association of β-amyloid protein with cognitive decline. Regression models examined the protein associations with neuropathologic outcomes and the APOE genotype. By mid-September 2018, 3575 older persons were enrolled, and 1559 had died and undergone brain autopsy. Proteomic data were collected in 1208 individuals, and 5 with missing cognitive scores were excluded. Of the remaining 1203, primary analyses focused on 148 individuals (12.3%) without β-amyloid deposits. In this group, the mean (SD) age at death was 87.0 (7.0) years, and 84 individuals (56.8%) were women. In the absence of β-amyloid deposits, we did not observe an association of β-amyloid protein with decline in episodic memory, but the protein was associated with faster rates of decline in processing speed (mean [SE] change, -0.014 [0.005]; P = .008) and visuospatial abilities (mean [SE] change, -0.013 [0.005]; P = .006). We did not observe protein association with paired helical filament tau tangle density. The protein was associated with amyloid angiopathy (odds ratio, 1.38 [95% CI, 1.15-1.67]; P < .001) but no other brain pathology. The associations with cognitive decline were unchanged after controlling for amyloid angiopathy. Neither APOE ε4 nor a polygenic Alzheimer risk score was associated with β-amyloid protein. Cortical β-amyloid protein was associated with faster cognitive decline in the absence of β-amyloid deposits, which supports the role of cortical soluble β-amyloid as a neurotoxic agent in aging. The lack of protein association with paired helical filament tau tangles, episodic memory decline, or strong genetic drivers of deposited β-amyloid suggests an underlying neuropathologic change that may differ from that of AD.