Neuropathology of frontotemporal lobar degeneration-tau (FTLD-tau)

Single-nucleus multi-omics identifies shared and distinct pathways in Pick's and Alzheimer's disease

The study of neurodegenerative diseases, particularly tauopathies like Pick's disease (PiD) and Alzheimer's disease (AD), offers insights into the underlying regulatory mechanisms. By investigating epigenomic variations in these conditions, we identified critical regulatory changes driving disease progression, revealing potential therapeutic targets. Our comparative analyses uncovered disease-enriched non-coding regions and genome-wide transcription factor (TF) binding differences, linking them to target genes. Notably, we identified a distal human-gained enhancer (HGE) associated with E3 ubiquitin ligase (UBE3A), highlighting disease-specific regulatory alterations. Additionally, fine-mapping of AD risk genes uncovered loci enriched in microglial enhancers and accessible in other cell types. Shared and distinct TF binding patterns were observed in neurons and glial cells across PiD and AD. We validated our findings using CRISPR to excise a predicted enhancer region in UBE3A and developed an interactive database (http://swaruplab.bio.uci.edu/scROAD) to visualize predicted single-cell TF occupancy and regulatory networks.

Patterns of glucose hypometabolism can help differentiate FTLD-FET from other types of FTLD

INTRODUCTION

FTLD-FET is a newly described subtype of frontotemporal lobar degeneration (FTLD characterized by pathologic inclusions of FET proteins: fused in sarcoma (FUS), Ewing sarcoma, and TATA-binding protein-associated factor 2N (TAF15)). Severe caudate volume loss on MRI has been linked to FTLD-FUS, yet glucose hypometabolism in FTLD-FET has not been studied. We assessed [18F] fluorodeoxyglucose PET (FDG-PET) hypometabolism in FTLD-FET subtypes and compared metabolism to FTLD-tau and FTLD-TDP.

METHODS

We retrospectively reviewed medical records of 26 autopsied FTLD patients (six FTLD-FET, ten FTLD-Tau, and ten FTLD-TDP) who had completed antemortem FDG-PET. We evaluated five regions, caudate nucleus, medial frontal cortex, lateral frontal cortex, and medial temporal using a 0-3 visual rating scale and validated our findings quantitatively using CORTEX-ID suite Z scores.

RESULTS

Of the six FTLD-FET cases (three females) with median age at onset = 36, three were atypical FTLD-U (aFTLD-U) and three were neuronal intermediate filament inclusion disease (NIFID). bvFTD was the most common presentation. Four of the six FTLD cases (3 aFTLD-U + 1 NIFID) showed prominent caudate hypometabolism relatively early in the disease course. FTLD-tau and FTLD-TDP did not show early prominent caudate hypometabolism. Hypometabolism in medial and lateral temporal cortex was associated with FTLD-TDP, while FTLD-tau had normal-minimal regional metabolism.

DISCUSSION

Prominent caudate hypometabolism, especially early in the disease course, appears to be a hallmark feature of the aFTLD-U subtype of FTLD-FET. Assessing caudate and temporal hypometabolism on FDG-PET will help to differentiate FTLD-FET from FTLD-tau and FTLD-TDP.

Incidence of Primary Progressive Apraxia of Speech and Primary Progressive Aphasia in Olmsted County, MN, 2011-2022

BACKGROUND AND OBJECTIVE

No epidemiologic studies have formally assessed the incidence of primary progressive aphasia (PPA) and primary progressive apraxia of speech (PPAOS). Thus, we decided to assess the incidence of these disorders in Olmsted County, MN, between 2011 and 2022, and to characterize clinical, radiographic, and pathologic characteristics of these patients.

METHODS

This was a retrospective examination of data from a population-based cohort of patients with PPA and PPAOS prospectively identified in Olmsted County, MN, from 2011 to 2022. The incidence of PPA among adults (older than 18 years) was calculated for Olmsted County as the number of patients per 100,000 person-years during the study period. The adult population of Olmsted County was determined by the annual catchment population reported by the Rochester Epidemiological Project for each year 2011-2022. A behavioral neurologist verified the clinical diagnoses and determined subtypes.

RESULTS

We identified 10 patients (60% female) within the study period (median age of symptoms onset: 70 years; range: 66-73), 8 with PPA and 2 with PPAOS. Of the 8 patients with PPA (6 female patients, 2 male patients), 2 met criteria for non-fluent variant PPA (nfvPPA), 3 for logopenic variant PPA (lvPPA), and 3 for semantic variant (svPPA). Speech evaluation confirmed the clinical diagnoses in all patients and all showed typical imaging findings consistent with their respective subtype. Six patients (2 PPAOS, 2 nfvPPA, 2 lvPPA) died and 3 underwent autopsy (2 PPAOS, 1 nfvPPA), confirming the pathologic diagnosis of progressive supranuclear palsy. The incidence of PPA + PPAOS was 0.70 persons per 100,000 person-years (95% CI 0.34-1.29 persons per 100,000) during the study period. The incidence of PPAOS was 0.14 persons per 100,000 person-years (95% CI 0.02-0.55 persons per 100,000), whereas for the 8 patients with PPA, the incidence was 0.56 persons per 100,000 person-years (95% CI 0.24-1.10 cases per 100,000). The incidence of nfvPPA was 0.14 persons per 100,000 person-years (95% CI 0.02-0.55), 0.21 persons per 100,000 person-years (95% CI 0.04-0.61) for lvPPA, and 0.21 persons per 100,000 person-years (95% CI 0.04-0.61) for svPPA.

DISCUSSION

As a group, PPA and PPAOS are a relatively rare group of diseases. PPAOS has a slightly lower incidence than PPA as a group but similar incidence to the individual PPA variants.

Clinicopathologic and Neuroimaging Correlations of Nonverbal Oral Apraxia in Patients With Neurodegenerative Disease

BACKGROUND AND OBJECTIVES

Nonverbal oral apraxia (NVOA) is the inability to plan, sequence, and execute voluntary oromotor movements in the absence of weakness. In the context of neurodegenerative disease, it remains unclear whether it is linked to a specific underlying pathologic, clinical, or neuroimaging finding. Thus, we aimed to assess the clinicopathologic and neuroimaging associations of NVOA.

METHODS

We conducted a retrospective study of autopsy-confirmed patients previously assessed through an NVOA evaluation tool with a previously published cutpoint to screen for NVOA. We compared demographic and clinical characteristics and postmortem pathology between those who developed NVOA and those who did not. We also compared clinicopathologic characteristics in mild vs greater than mild NVOA and early vs late-emerging NVOA. SPM12 was used to assess patterns of gray matter loss in NVOA vs non-NVOA with age and sex included as covariates.

RESULTS

A total of 104 patients (median age at symptom onset 63 years, 43% female) were included in the study. 63 (60.6%) developed NVOA. NVOA appeared at a median of 4.3 years from symptom onset. 29% developed NVOA within the first 3 years. Primary progressive apraxia of speech and the nonfluent variant of primary progressive aphasia were the most common baseline diagnoses in the NVOA group while progressive supranuclear palsy (PSP) syndrome and logopenic progressive aphasia (LPA) were the most common in patients without NVOA. Atrophy of the left lateral and medial posterior frontal cortex was related to NVOA. The most common pathologies associated with NVOA were PSP (36.5%) and corticobasal degeneration (CBD) (33.3%). In patients without NVOA, PSP (26.8%) and other pathologies (26.8%) were the most frequent. 11% of patients with NVOA had persistently mild NVOA and were more likely to have baseline diagnoses of LPA, PSP syndrome, or semantic dementia. The most frequent pathologies in this group were Alzheimer disease and PSP. The pathologic associations of greater than mild NVOA were CBD and PSP.

DISCUSSION

NVOA is present in several clinical syndromes. It is most associated with PSP and CBD. NVOA is a manifestation of left lateral and medial posterior frontal cortex damage rather than a particular pathology.

Chromogranin A Deficiency Attenuates Tauopathy by Altering Epinephrine-Alpha-Adrenergic Receptor Signaling

Metabolic disorders such as insulin resistance and hypertension are potential risk factors for aging and neurodegenerative diseases. These conditions are reversed in Chromogranin A knockout (CgA-KO) mice. This study investigates the role of CgA in Alzheimer's disease (AD) and corticobasal degeneration (CBD). CgA ablation in tauopathy mice (hTau) (CgA-KO/hTau) exhibited reduced tau aggregation, spreading, extended lifespan, and improved cognitive function. Transcriptomic and metabolite analysis of mouse cortices revealed altered alpha1-adrenergic receptors (Adra1) and high epinephrine (EPI) levels in hTau mice compared to WT mice, mirroring observations in AD and CBD patients. CgA-KO/hTau mice exhibited a reversal of EPI levels in the cortex and the expression of Adra1, nearly returning them to WT levels. Treatment of hippocampal slices with EPI or Adra1 agonist intensified, while an Adra1 antagonist inhibited tau hyperphosphorylation and aggregation. These findings highlight the interplay between the EPI-Adra signaling system and CgA in tauopathy.

Comparing classic-onset corticobasal syndrome to speech/language-onset corticobasal syndrome

INTRODUCTION

Patients with classic-onset corticobasal syndrome (CBS) present with asymmetric limb apraxia and parkinsonism. We have, however, observed patients who initially present with speech and/or language (SL) problems and several years later develop CBS (i.e., SL-onset CBS). We aimed to compare clinical, neuroimaging and pathological characteristics of classic-onset CBS with SL-onset CBS.

METHODS

We conducted a retrospective cohort study of 62 patients who met criteria for CBS (17 presented with classic-onset CBS and 45 had SL-onset CBS). We compared demographics, clinical characteristics, and grey and white matter volume loss with SPM12 between groups and assessed pathology and corticobasal degeneration (CBD) pathological lesion counts in patients who had died and undergone autopsy.

RESULTS

Median age at CBS diagnosis was 66.4 years in classic-onset CBS and 73.6 years in SL-onset CBS. Classic-onset CBS had higher frequencies of dystonia, myoclonus, and alien limb phenomenon, while SL-onset CBS had a higher frequency of vertical supranuclear gaze palsy. Both groups showed smaller frontoparietal volumes than controls, with SL-onset CBS having greater volume loss in the left supplementary motor area than classic-onset CBS. All three classic-onset CBS cases with autopsy (100 %) had CBD pathology while 8/21 of SL-onset CBS cases (38 %) had CBD. Pathological lesion burden (including astrocytic plaques) did not differ between classic-onset and SL-onset CBS.

CONCLUSION

Classic-onset and SL-onset CBS appear to be different syndromes, with the former being a more profuse motor syndrome. The more widespread volume loss in SL-onset CBS likely reflects longer disease course.

Pharmacotherapies for the Treatment of Progressive Supranuclear Palsy: A Narrative Review

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder resulting from the deposition of misfolded and neurotoxic forms of tau protein in specific areas of the midbrain, basal ganglia, and cortex. It is one of the most representative forms of tauopathy. PSP presents in several different phenotypic variations and is often accompanied by the development of concurrent neurodegenerative disorders. PSP is universally fatal, and effective disease-modifying therapies for PSP have not yet been identified. Several tau-targeting treatment modalities, including vaccines, monoclonal antibodies, and microtubule-stabilizing agents, have been investigated and have had no efficacy. The need to treat PSP and other tauopathies is critical, and many clinical trials investigating tau-targeted treatments are underway. In this review, the PubMed database was queried to collect information about preclinical and clinical research on PSP treatment. Additionally, the US National Library of Medicine's ClinicalTrials.gov website was queried to identify past and ongoing clinical trials relevant to PSP treatment. This narrative review summarizes our findings regarding these reports, which include potential disease-modifying drug trials, modifiable risk factor management, and symptom treatments.

G272V and P301L Mutations Induce Isoform Specific Tau Mislocalization to Dendritic Spines and Synaptic Dysfunctions in Cellular Models of 3R and 4R Tau Frontotemporal Dementia

Tau pathologies are detected in the brains of some of the most common neurodegenerative diseases including Alzheimer's disease (AD), Lewy body dementia (LBD), chronic traumatic encephalopathy (CTE), and frontotemporal dementia (FTD). Tau proteins are expressed in six isoforms with either three or four microtubule-binding repeats (3R tau or 4R tau) due to alternative RNA splicing. AD, LBD, and CTE brains contain pathological deposits of both 3R and 4R tau. FTD patients can exhibit either 4R tau pathologies in most cases or 3R tau pathologies less commonly in Pick's disease, which is a subfamily of FTD. Here, we report the isoform-specific roles of tau in FTD. The P301L mutation, linked to familial 4R tau FTD, induces mislocalization of 4R tau to dendritic spines in primary hippocampal cultures that were prepared from neonatal rat pups of both sexes. Contrastingly, the G272V mutation, linked to familial Pick's disease, induces phosphorylation-dependent mislocalization of 3R tau but not 4R tau proteins to dendritic spines. The overexpression of G272V 3R tau but not 4R tau proteins leads to the reduction of dendritic spine density and suppression of mEPSCs in 5-week-old primary rat hippocampal cultures. The decrease in mEPSC amplitude caused by G272V 3R tau is dynamin-dependent whereas that caused by P301L 4R tau is dynamin-independent, indicating that the two tau isoforms activate different signaling pathways responsible for excitatory synaptic dysfunction. Our 3R and 4R tau studies here will shed new light on diverse mechanisms underlying FTD, AD, LBD, and CTE.

Stepwise Functional Brain Architecture Correlates with Atrophy in Progressive Supranuclear Palsy

BACKGROUND

Stepwise functional connectivity (SFC) detects whole-brain functional couplings of a selected region of interest at increasing link-step topological distances.

OBJECTIVE

This study applied SFC to test the hypothesis that stepwise architecture propagating from the disease epicenter would shape patterns of brain atrophy in patients with progressive supranuclear palsy-Richardson's syndrome (PSP-RS).

METHODS

Thirty-six patients with PSP-RS and 44 age-matched healthy control subjects underwent brain magnetic resonance imaging on a 3-T scanner. The disease epicenter was defined as the peak of atrophy observed in an independent cohort of 13 cases with postmortem confirmation of PSP pathology and used as seed region for SFC analysis. First, we explored SFC rearrangements in patients with PSP-RS, as compared with age-matched control subjects. Subsequently, we tested SFC architecture propagating from the disease epicenter as a determinant of brain atrophy distribution.

RESULTS

The disease epicenter was identified in the left midbrain tegmental region. Compared with age-matched control subjects, patients with PSP-RS showed progressively widespread decreased SFC of the midbrain with striatal and cerebellar regions through direct connections and sensorimotor cortical regions through indirect connections. A correlation was found between average link-step distance from the left midbrain in healthy subjects and brain volumes in patients with PSP-RS (r = 0.38, P < 0.001).

CONCLUSIONS

This study provides comprehensive insights into the topology of functional network rearrangements in PSP-RS and demonstrates that the brain architectural topology, as described by SFC propagating from the disease epicenter, shapes the pattern of atrophic changes in PSP-RS. Our findings support the view of a network-based pathology propagation in this primary tauopathy. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Chromogranin A (CgA) Deficiency Attenuates Tauopathy by Altering Epinephrine-Alpha-Adrenergic Receptor Signaling

Our previous studies have indicated that insulin resistance, hyperglycemia, and hypertension in aged wild-type (WT) mice can be reversed in mice lacking chromogranin-A (CgA-KO mice). These health conditions are associated with a higher risk of Alzheimer's disease (AD). CgA, a neuroendocrine secretory protein has been detected in protein aggregates in the brains of AD patients. Here, we determined the role of CgA in tauopathies, including AD (secondary tauopathy) and corticobasal degeneration (CBD, primary tauopathy). We found elevated levels of CgA in both AD and CBD brains, which were positively correlated with increased phosphorylated tau in the frontal cortex. Furthermore, CgA ablation in a human P301S tau (hTau) transgenic mice (CgA-KO/hTau) exhibited reduced tau aggregation, resistance to tau spreading, and an extended lifespan, coupled with improved cognitive function. Transcriptomic analysis of mice cortices highlighted altered levels of alpha-adrenergic receptors (Adra) in hTau mice compared to WT mice, akin to AD patients. Since CgA regulates the release of the Adra ligands epinephrine (EPI) and norepinephrine (NE), we determined their levels and found elevated EPI levels in the cortices of hTau mice, AD and CBD patients. CgA-KO/hTau mice exhibited reversal of EPI levels in the cortex and the expression of several affected genes, including Adra1 and 2, nearly returning them to WT levels. Treatment of hippocampal slice cultures with EPI or an Adra1 agonist intensified, while an Adra1 antagonist inhibited, tau hyperphosphorylation and aggregation. These findings reveal a critical role of CgA in regulation of tau pathogenesis via the EPI-Adra signaling axis.

Tau liquid-liquid phase separation: At the crossroads of tau physiology and tauopathy

Abnormal deposition of tau in neurons is a hallmark of Alzheimer's disease and several other neurodegenerative disorders. In the past decades, extensive efforts have been made to explore the mechanistic pathways underlying the development of tauopathies. Recently, the discovery of tau droplet formation by liquid-liquid phase separation (LLPS) has received a great deal of attention. It has been reported that tau condensates have a biological role in promoting and stabilizing microtubule (MT) assembly. Furthermore, it has been hypothesized that the transition of phase-separated tau droplets to a gel-like state and then to fibrils is associated with the pathology of neurodegenerative diseases. In this review, we outline LLPS, the structural disorder that facilitates tau droplet formation, the effects of posttranslational modification of tau on condensate formation, the physiological function of tau droplets, the pathways from droplet to toxic fibrils, and the therapeutic strategies for tauopathies that might evolve from toxic droplets. We expect a deeper understanding of tau LLPS will provide additional insights into tau physiology and tauopathies.

The clinical importance of suspected non-Alzheimer disease pathophysiology

The development of biomarkers for Alzheimer disease (AD) has led to the origin of suspected non-AD pathophysiology (SNAP) - a heterogeneous biomarker-based concept that describes individuals with normal amyloid and abnormal tau and/or neurodegeneration biomarker status. In this Review, we describe the origins of the SNAP construct, along with its prevalence, diagnostic and prognostic implications, and underlying neuropathology. As we discuss, SNAP can be operationalized using different biomarker modalities, which could affect prevalence estimates and reported characteristics of SNAP in ways that are not yet fully understood. Moreover, the underlying aetiologies that lead to a SNAP biomarker profile, and whether SNAP is the same in people with and without cognitive impairment, remains unclear. Improved insight into the clinical characteristics and pathophysiology of SNAP is of major importance for research and clinical practice, as well as for trial design to optimize care and treatment of individuals with SNAP.

Pathologic and cognitive correlates of plasma biomarkers in neurodegenerative disease

INTRODUCTION

We investigate pathological correlates of plasma phosphorylated tau 181 (p-tau181), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) across a clinically diverse spectrum of neurodegenerative disease, including normal cognition (NormCog) and impaired cognition (ImpCog).

METHODS

Participants were NormCog (n = 132) and ImpCog (n = 461), with confirmed β-amyloid (Aβ+/-) status (cerebrospinal fluid, positron emission tomography, autopsy) and single molecule array plasma measurements. Logistic regression and receiver operating characteristic (ROC) area under the curve (AUC) tested how combining plasma analytes discriminated Aβ+ from Aβ-. Survival analyses tested time to clinical dementia rating (global CDR) progression.

RESULTS

Multivariable models (p-tau+GFAP+NfL) had the best performance to detect Aβ+ in NormCog (ROCAUC = 0.87) and ImpCog (ROCAUC = 0.87). Survival analyses demonstrated that higher NfL best predicted faster CDR progression for both Aβ+ (hazard ratio [HR] = 2.94; p = 8.1e-06) and Aβ- individuals (HR = 3.11; p = 2.6e-09).

DISCUSSION

Combining plasma biomarkers can optimize detection of Alzheimer's disease (AD) pathology across cognitively normal and clinically diverse neurodegenerative disease.

HIGHLIGHTS

Participants were clinically heterogeneous, with autopsy- or biomarker-confirmed Aβ. Combining plasma p-tau181, GFAP, and NfL improved diagnostic accuracy for Aβ status. Diagnosis by plasma biomarkers is more accurate in amnestic AD than nonamnestic AD. Plasma analytes show independent associations with tau PET and post mortem Aβ/tau. Plasma NfL predicted longitudinal cognitive decline in both Aβ+ and Aβ- individuals.

Cell autonomous microglia defects in a stem cell model of frontotemporal dementia

Neuronal dysfunction has been extensively studied as a central feature of neurodegenerative tauopathies. However, across neurodegenerative diseases, there is strong evidence for active involvement of immune cells like microglia in driving disease pathophysiology. Here, we demonstrate that tau mRNA and protein are expressed in microglia in human brains and in human induced pluripotent stem cell (iPSC)-derived microglia like cells (iMGLs). Using iMGLs harboring the MAPT IVS10+16 mutation and isogenic controls, we demonstrate that a tau mutation is sufficient to alter microglial transcriptional states. We discovered that MAPT IVS10+16 microglia exhibit cytoskeletal abnormalities, stalled phagocytosis, disrupted TREM2/TYROBP networks, and altered metabolism. Additionally, we found that secretory factors from MAPT IVS10+16 iMGLs impact neuronal health, reducing synaptic density in neurons. Key features observed in vitro were recapitulated in human brain tissue and cerebrospinal fluid from MAPT mutations carriers. Together, our findings that MAPT IVS10+16 drives cell-intrinsic dysfunction in microglia that impacts neuronal health has major implications for development of therapeutic strategies.

MAPT H2 haplotype and risk of Pick's disease in the Pick's disease International Consortium: a genetic association study

BACKGROUND

Pick's disease is a rare and predominantly sporadic form of frontotemporal dementia that is classified as a primary tauopathy. Pick's disease is pathologically defined by the presence in the frontal and temporal lobes of Pick bodies, composed of hyperphosphorylated, three-repeat tau protein, encoded by the MAPT gene. MAPT has two distinct haplotypes, H1 and H2; the MAPT H1 haplotype is the major genetic risk factor for four-repeat tauopathies (eg, progressive supranuclear palsy and corticobasal degeneration), and the MAPT H2 haplotype is protective for these disorders. The primary aim of this study was to evaluate the association of MAPT H2 with Pick's disease risk, age at onset, and disease duration.

METHODS

In this genetic association study, we used data from the Pick's disease International Consortium, which we established to enable collection of data from individuals with pathologically confirmed Pick's disease worldwide. For this analysis, we collected brain samples from individuals with pathologically confirmed Pick's disease from 35 sites (brainbanks and hospitals) in North America, Europe, and Australia between Jan 1, 2020, and Jan 31, 2023. Neurologically healthy controls were recruited from the Mayo Clinic (FL, USA, or MN, USA between March 1, 1998, and Sept 1, 2019). For the primary analysis, individuals were directly genotyped for the MAPT H1-H2 haplotype-defining variant rs8070723. In a secondary analysis, we genotyped and constructed the six-variant-defined (rs1467967-rs242557-rs3785883-rs2471738-rs8070723-rs7521) MAPT H1 subhaplotypes. Associations of MAPT variants and MAPT haplotypes with Pick's disease risk, age at onset, and disease duration were examined using logistic and linear regression models; odds ratios (ORs) and β coefficients were estimated and correspond to each additional minor allele or each additional copy of the given haplotype.

FINDINGS

We obtained brain samples from 338 people with pathologically confirmed Pick's disease (205 [61%] male and 133 [39%] female; 338 [100%] White) and 1312 neurologically healthy controls (611 [47%] male and 701 [53%] female; 1312 [100%] White). The MAPT H2 haplotype was associated with increased risk of Pick's disease compared with the H1 haplotype (OR 1·35 [95% CI 1·12 to 1·64], p=0·0021). MAPT H2 was not associated with age at onset (β -0·54 [95% CI -1·94 to 0·87], p=0·45) or disease duration (β 0·05 [-0·06 to 0·16], p=0·35). Although not significant after correcting for multiple testing, associations were observed at p less than 0·05: with risk of Pick's disease for the H1f subhaplotype (OR 0·11 [0·01 to 0·99], p=0·049); with age at onset for H1b (β 2·66 [0·63 to 4·70], p=0·011), H1i (β -3·66 [-6·83 to -0·48], p=0·025), and H1u (β -5·25 [-10·42 to -0·07], p=0·048); and with disease duration for H1x (β -0·57 [-1·07 to -0·07], p=0·026).

INTERPRETATION

The Pick's disease International Consortium provides an opportunity to do large studies to enhance our understanding of the pathobiology of Pick's disease. This study shows that, in contrast to the decreased risk of four-repeat tauopathies, the MAPT H2 haplotype is associated with an increased risk of Pick's disease in people of European ancestry. This finding could inform development of isoform-related therapeutics for tauopathies.

FUNDING

Wellcome Trust, Rotha Abraham Trust, Brain Research UK, the Dolby Fund, Dementia Research Institute (Medical Research Council), US National Institutes of Health, and the Mayo Clinic Foundation.

Synaptic alterations associated with disrupted sensory encoding in a mouse model of tauopathy

Synapse loss is currently the best biological correlate of cognitive decline in Alzheimer's disease and other tauopathies. Synapses seem to be highly vulnerable to tau-mediated disruption in neurodegenerative tauopathies. However, it is unclear how and when this leads to alterations in function related to the progression of tauopathy and neurodegeneration. We used the well-characterized rTg4510 mouse model of tauopathy at 5-6 months and 7-8 months of age, respectively, to study the functional impact of cortical synapse loss. The earlier age was used as a model of prodromal tauopathy, with the later age corresponding to more advanced tau pathology and presumed progression of neurodegeneration. Analysis of synaptic protein expression in the somatosensory cortex showed significant reductions in synaptic proteins and NMDA and AMPA receptor subunit expression in rTg4510 mice. Surprisingly, in vitro whole-cell patch clamp electrophysiology from putative pyramidal neurons in layer 2/3 of the somatosensory cortex suggested no functional alterations in layer 4 to layer 2/3 synaptic transmission at 5-6 months. From these same neurons, however, there were alterations in dendritic structure, with increased branching proximal to the soma in rTg4510 neurons. Therefore, in vivo whole-cell patch clamp recordings were utilized to investigate synaptic function and integration in putative pyramidal neurons in layer 2/3 of the somatosensory cortex. These recordings revealed a significant increase in the peak response to synaptically driven sensory stimulation-evoked activity and a loss of temporal fidelity of the evoked signal to the input stimulus in rTg4510 neurons. Together, these data suggest that loss of synapses, changes in receptor expression and dendritic restructuring may lead to alterations in synaptic integration at a network level. Understanding these compensatory processes could identify targets to help delay symptomatic onset of dementia.

Probe-dependent Proximity Profiling (ProPPr) Uncovers Similarities and Differences in Phospho-Tau-Associated Proteomes Between Tauopathies

Tauopathies represent a diverse group of neurodegenerative disorders characterized by the abnormal aggregation of the microtubule-associated protein tau. Despite extensive research, the precise mechanisms underlying the complexity of different types of tau pathology remain incompletely understood. Here we describe an approach for proteomic profiling of aggregate-associated proteomes on slides with formalin-fixed, paraffin-embedded (FFPE) tissue that utilizes proximity labelling upon high preservation of aggregate morphology, which permits the profiling of pathological aggregates regardless of their size. To comprehensively investigate the common and unique protein interactors associated with the variety of tau lesions present across different human tauopathies, Alzheimer's disease (AD), corticobasal degeneration (CBD), Pick's disease (PiD), and progressive supranuclear palsy (PSP), were selected to represent the major tauopathy diseases. Implementation of our widely applicable Probe-dependent Proximity Profiling (ProPPr) strategy, using the AT8 antibody, permitted identification and quantification of proteins associated with phospho-tau lesions in well-characterized human post-mortem tissue. The analysis revealed both common and disease-specific proteins associated with phospho-tau aggregates, highlighting potential targets for therapeutic intervention and biomarker development. Candidate validation through high-resolution co-immunofluorescence of distinct aggregates across disease and control cases, confirmed the association of retromer complex protein VPS35 with phospho-tau lesions across the studied tauopathies. Furthermore, we discovered disease-specific associations of proteins including ferritin light chain (FTL) and the neuropeptide precursor VGF within distinct pathological lesions. Notably, examination of FTL-positive microglia in CBD astrocytic plaques indicate a potential role for microglial involvement in the pathogenesis of these tau lesions. Our findings provide valuable insights into the proteomic landscape of tauopathies, shedding light on the molecular mechanisms underlying tau pathology. This first comprehensive characterization of tau-associated proteomes across different tauopathies enhances our understanding of disease heterogeneity and provides a resource for future functional investigation, as well as development of targeted therapies and diagnostic biomarkers.

In vivo PET classification of tau pathologies in patients with frontotemporal dementia

Frontotemporal dementia refers to a group of neurodegenerative disorders with diverse clinical and neuropathological features. In vivo neuropathological assessments of frontotemporal dementia at an individual level have hitherto not been successful. In this study, we aim to classify patients with frontotemporal dementia based on topologies of tau protein aggregates captured by PET with 18F-florzolotau (aka 18F-APN-1607 and 18F-PM-PBB3), which allows high-contrast imaging of diverse tau fibrils in Alzheimer's disease as well as in non-Alzheimer's disease tauopathies. Twenty-six patients with frontotemporal dementia, 15 with behavioural variant frontotemporal dementia and 11 with other frontotemporal dementia phenotypes, and 20 age- and sex-matched healthy controls were included in this study. They underwent PET imaging of amyloid and tau depositions with 11C-PiB and 18F-florzolotau, respectively. By combining visual and quantitative analyses of PET images, the patients with behavioural variant frontotemporal dementia were classified into the following subgroups: (i) predominant tau accumulations in frontotemporal and frontolimbic cortices resembling three-repeat tauopathies (n = 3), (ii) predominant tau accumulations in posterior cortical and subcortical structures indicative of four-repeat tauopathies (n = 4); (iii) amyloid and tau accumulations consistent with Alzheimer's disease (n = 4); and (iv) no overt amyloid and tau pathologies (n = 4). Despite these distinctions, clinical symptoms and localizations of brain atrophy did not significantly differ among the identified behavioural variant frontotemporal dementia subgroups. The patients with other frontotemporal dementia phenotypes were also classified into similar subgroups. The results suggest that PET with 18F-florzolotau potentially allows the classification of each individual with frontotemporal dementia on a neuropathological basis, which might not be possible by symptomatic and volumetric assessments.

Phenotypically concordant distribution of pick bodies in aphasic versus behavioral dementias

Pick's disease (PiD) is a subtype of the tauopathy form of frontotemporal lobar degeneration (FTLD-tau) characterized by intraneuronal 3R-tau inclusions. PiD can underly various dementia syndromes, including primary progressive aphasia (PPA), characterized by an isolated and progressive impairment of language and left-predominant atrophy, and behavioral variant frontotemporal dementia (bvFTD), characterized by progressive dysfunction in personality and bilateral frontotemporal atrophy. In this study, we investigated the neocortical and hippocampal distributions of Pick bodies in bvFTD and PPA to establish clinicopathologic concordance between PiD and the salience of the aphasic versus behavioral phenotype. Eighteen right-handed cases with PiD as the primary pathologic diagnosis were identified from the Northwestern University Alzheimer's Disease Research Center brain bank (bvFTD, N = 9; PPA, N = 9). Paraffin-embedded sections were stained immunohistochemically with AT8 to visualize Pick bodies, and unbiased stereological analysis was performed in up to six regions bilaterally [middle frontal gyrus (MFG), superior temporal gyrus (STG), inferior parietal lobule (IPL), anterior temporal lobe (ATL), dentate gyrus (DG) and CA1 of the hippocampus], and unilateral occipital cortex (OCC). In bvFTD, peak neocortical densities of Pick bodies were in the MFG, while the ATL was the most affected in PPA. Both the IPL and STG had greater leftward pathology in PPA, with the latter reaching significance (p < 0.01). In bvFTD, Pick body densities were significantly right-asymmetric in the STG (p < 0.05). Hippocampal burden was not clinicopathologically concordant, as both bvFTD and PPA cases demonstrated significant hippocampal pathology compared to neocortical densities (p < 0.0001). Inclusion-to-neuron analyses in a subset of PPA cases confirmed that neurons in the DG are disproportionately burdened with inclusions compared to neocortical areas. Overall, stereological quantitation suggests that the distribution of neocortical Pick body pathology is concordant with salient clinical features unique to PPA vs. bvFTD while raising intriguing questions about the selective vulnerability of the hippocampus to 3R-tauopathies.

Diagnostic and therapeutic targeting of pathological tau proteins in neurodegenerative disorders

Tauopathies, characterized by fibrillar tau accumulation in neurons and glial cells, constitute a major neuropathological category of neurodegenerative diseases. Neurofibrillary tau lesions are strongly associated with cognitive deficits in these diseases, but the causal mechanisms underlying tau-induced neuronal dysfunction remain unresolved. Recent advances in cryo-electron microscopy examination have revealed various core structures of tau filaments from different tauopathy patients, which can be used to classify tauopathies. In vivo visualization of tau pathology is now available using several tau positron emission tomography tracers. Among these radioprobes, PM-PBB3 allows high-contrast imaging of tau deposits in the brains of patients with diverse disorders and tauopathy mouse models. Selective degradation of pathological tau species by the ubiquitin-proteasome system or autophagy machinery is a potential therapeutic strategy. Alternatively, the non-cell-autonomous clearance of pathological tau species through neuron-glia networks could be reinforced as a disease-modifying treatment. In addition, the development of neuroinflammatory biomarkers is required for understanding the contribution of immunocompetent cells in the brain to preventing neurodegeneration. This review provides an overview of the current research and development of diagnostic and therapeutic agents targeting divergent tau pathologies.

Glial reactivity and T cell infiltration in frontotemporal lobar degeneration with tau pathology

Frontotemporal lobar degeneration with tau (FTLD-tau) is a group of tauopathies that underlie ∼50% of FTLD cases. Identification of genetic risk variants related to innate/adaptive immunity have highlighted a role for neuroinflammation and neuroimmune interactions in FTLD. Studies have shown microglial and astrocyte activation together with T cell infiltration in the brain of THY-Tau22 tauopathy mice. However, this remains to be confirmed in FTLD-tau patients. We conducted a detailed post-mortem study of FTLD-tau cases including 45 progressive supranuclear palsy with clinical frontotemporal dementia, 33 Pick's disease, 12 FTLD-MAPT and 52 control brains to characterize the link between phosphorylated tau (pTau) epitopes and the innate and adaptive immunity. Tau pathology was assessed in the cerebral cortex using antibodies directed against: Tau-2 (phosphorylated and unphosphorylated tau), AT8 (pSer202/pThr205), AT100 (pThr212/pSer214), CP13 (pSer202), PHF1 (pSer396/pSer404), pThr181 and pSer356. The immunophenotypes of microglia and astrocytes were assessed with phenotypic markers (Iba1, CD68, HLA-DR, CD64, CD32a, CD16 for microglia and GFAP, EAAT2, glutamine synthetase and ALDH1L1 for astrocytes). The adaptive immune response was explored via CD4+ and CD8+ T cell quantification and the neuroinflammatory environment was investigated via the expression of 30 inflammatory-related proteins using V-Plex Meso Scale Discovery. As expected, all pTau markers were increased in FTLD-tau cases compared to controls. pSer356 expression was greatest in FTLD-MAPT cases versus controls (P < 0.0001), whereas the expression of other markers was highest in Pick's disease. Progressive supranuclear palsy with frontotemporal dementia consistently had a lower pTau protein load compared to Pick's disease across tau epitopes. The only microglial marker increased in FTLD-tau was CD16 (P = 0.0292) and specifically in FTLD-MAPT cases (P = 0.0150). However, several associations were detected between pTau epitopes and microglia, supporting an interplay between them. GFAP expression was increased in FTLD-tau (P = 0.0345) with the highest expression in Pick's disease (P = 0.0019), while ALDH1L1 was unchanged. Markers of astrocyte glutamate cycling function were reduced in FTLD-tau (P = 0.0075; Pick's disease: P < 0.0400) implying astrocyte reactivity associated with a decreased glutamate cycling activity, which was further associated with pTau expression. Of the inflammatory proteins assessed in the brain, five chemokines were upregulated in Pick's disease cases (P < 0.0400), consistent with the recruitment of CD4+ (P = 0.0109) and CD8+ (P = 0.0014) T cells. Of note, the CD8+ T cell infiltration was associated with pTau epitopes and microglial and astrocytic markers. Our results highlight that FTLD-tau is associated with astrocyte reactivity, remarkably little activation of microglia, but involvement of adaptive immunity in the form of chemokine-driven recruitment of T lymphocytes.

TDP-43 dysregulation of polyadenylation site selection is a defining feature of RNA misprocessing in ALS/FTD and related disorders

Nuclear clearance and cytoplasmic aggregation of the RNA-binding protein TDP-43 are observed in many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and fronto- temporal dementia (FTD). Although TDP-43 dysregulation of splicing has emerged as a key event in these diseases, TDP-43 can also regulate polyadenylation; yet, this has not been adequately studied. Here, we applied the dynamic analysis of polyadenylation from RNA-seq (DaPars) tool to ALS/FTD transcriptome datasets, and report extensive alternative polyadenylation (APA) upon TDP-43 alteration in ALS/FTD cell models and postmortem ALS/FTD neuronal nuclei. Importantly, many identified APA genes highlight pathways implicated in ALS/FTD pathogenesis. To determine the functional significance of APA elicited by TDP-43 nuclear depletion, we examined microtubule affinity regulating kinase 3 (MARK3). Nuclear loss of TDP-43 yielded increased expression of MARK3 transcripts with longer 3'UTRs, resulting in greater transcript stability and elevated MARK3 protein levels, which promotes increased neuronal tau S262 phosphorylation. Our findings define changes in polyadenylation site selection as a previously unrecognized feature of TDP-43-driven disease pathology in ALS/FTD and highlight a potentially novel mechanistic link between TDP-43 dysfunction and tau regulation.

Modulation of Tau Pathology in Alzheimer's Disease by Dietary Bioactive Compounds

Tau is a microtubule-associated protein essential for microtubule assembly and stability in neurons. The abnormal intracellular accumulation of tau aggregates is a major characteristic of brains from patients with Alzheimer's disease (AD) and other tauopathies. In AD, the presence of neurofibrillary tangles (NFTs), which is composed of hyperphosphorylated tau protein, is positively correlated with the severity of the cognitive decline. Evidence suggests that the accumulation and aggregation of tau cause synaptic dysfunction and neuronal degeneration. Thus, the prevention of abnormal tau phosphorylation and elimination of tau aggregates have been proposed as therapeutic strategies for AD. However, currently tau-targeting therapies for AD and other tauopathies are limited. A number of dietary bioactive compounds have been found to modulate the posttranslational modifications of tau, including phosphorylation, small ubiquitin-like modifier (SUMO) mediated modification (SUMOylation) and acetylation, as well as inhibit tau aggregation and/or promote tau degradation. The advantages of using these dietary components over synthetic substances in AD prevention and intervention are their safety and accessibility. This review summarizes the mechanisms leading to tau pathology in AD and highlights the effects of bioactive compounds on the hyperphosphorylation, aggregation and clearance of tau protein. The potential of using these bioactive compounds for AD prevention and intervention is also discussed.

First-In-Human Safety, Tolerability, and Pharmacokinetics of Single and Multiple Doses of AZP2006, A Synthetic Compound for the Treatment of Alzheimer's Disease and Related Diseases

Background

Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) are major neurodegenerative conditions with tau pathology in common but distinct symptoms-AD involves cognitive decline while PSP affects balance and eye movement. Progranulin (PGRN) is a growth factor implicated in neurodegenerative diseases, including AD and PSP. AZP2006, a synthetic compound, targets tauopathies by stabilizing PGRN levels and reducing tau aggregation and neuroinflammation.

Objective

Evaluate the safety, tolerability, and pharmacokinetics of AZP2006.

Methods

A first-in-Human phase 1 study comprised a single ascending dose (SAD) and a multiple ascending dose study (MAD). The SAD study included 64 healthy male volunteers and tested singles oral doses of 3 to 500 mg of AZP2006 free base equivalent or placebo. In the MAD study, 24 healthy male volunteers were administered oral doses of 30, 60, and 120 mg per day of AZP2006 or placebo for 10 days.

Results

No serious adverse events were observed. Clinical, biological, and electrocardiogram findings were non-relevant. Nineteen minor adverse events resolved before study completion. The safety profile indicated no specific risks. The multiple ascending dose study was halted, and the optional dose level of 180 mg was not performed due to high levels of M2 metabolite in plasma that necessitated additional preclinical evaluation of M2. Both AZP2006 and its M2 metabolite were quickly absorbed and widely distributed in tissues. Exposure increased more than proportionally with dose.

Conclusions

AZP2006 had a favorable safety profile and was rapidly absorbed. Elevated M2 metabolite levels necessitated further studies to clarify excretion and metabolism mechanisms.

The emerging complexity of molecular pathways implicated in mouse self-grooming behavior

Rodent self-grooming is an important complex behavior, and its deficits are translationally relevant to a wide range of neuropsychiatric disorders. Here, we analyzed a comprehensive dataset of 227 genes whose mutations are known to evoke aberrant self-grooming in mice. Using these genes, we constructed the network of their established protein-protein interactions (PPI), yielding several distinct molecular clusters related to postsynaptic density, the Wnt signaling, transcription factors, neuronal cell cycle, NOS neurotransmission, microtubule regulation, neuronal differentiation/trafficking, neurodevelopment and mitochondrial function. Utilizing further bioinformatics analyses, we also identified novel central ('hub') proteins within these clusters, whose genes may also be implicated in aberrant self-grooming and other repetitive behaviors in general. Untangling complex molecular pathways of this important behavior using in silico approaches contributes to our understanding of related neurological disorders, and may suggest novel potential targets for their pharmacological or gene therapy.

Synaptic density affects clinical severity via network dysfunction in syndromes associated with frontotemporal lobar degeneration

There is extensive synaptic loss from frontotemporal lobar degeneration, in preclinical models and human in vivo and post mortem studies. Understanding the consequences of synaptic loss for network function is important to support translational models and guide future therapeutic strategies. To examine this relationship, we recruited 55 participants with syndromes associated with frontotemporal lobar degeneration and 24 healthy controls. We measured synaptic density with positron emission tomography using the radioligand [11C]UCB-J, which binds to the presynaptic vesicle glycoprotein SV2A, neurite dispersion with diffusion magnetic resonance imaging, and network function with task-free magnetic resonance imaging functional connectivity. Synaptic density and neurite dispersion in patients was associated with reduced connectivity beyond atrophy. Functional connectivity moderated the relationship between synaptic density and clinical severity. Our findings confirm the importance of synaptic loss in frontotemporal lobar degeneration syndromes, and the resulting effect on behaviour as a function of abnormal connectivity.

Site-Specific Ubiquitination of Tau Amyloids Promoted by the E3 Ligase CHIP

Post-translational modifications of Tau are emerging as key players in determining the onset and progression of different tauopathies such as Alzheimer's disease, and are recognized to mediate the structural diversity of the disease-specific Tau amyloids. Here we show that the E3 ligase CHIP catalyzes the site-specific ubiquitination of Tau filaments both in vitro and in cellular models, proving that also Tau amyloid aggregates are direct substrate of PTMs. Transmission electron microscopy and mass spectrometry analysis on ubiquitin-modified Tau amyloids revealed that the conformation of the filaments restricts CHIP-mediated ubiquitination to specific positions of the repeat domain, while only minor alterations in the structure of the fibril core were inferred using seeding experiments in vitro and in a cell-based tauopathy model. Overexpression of CHIP significantly increased the ubiquitination of exogenous PHF, proving that the ligase can interact and modify Tau aggregates also in a complex cellular environment.

Functional network collapse in neurodegenerative disease

Cognitive and behavioral deficits in Alzheimer's disease (AD) and frontotemporal dementia (FTD) result from brain atrophy and altered functional connectivity. However, it is unclear how atrophy relates to functional connectivity disruptions across dementia subtypes and stages. We addressed this question using structural and functional MRI from 221 patients with AD (n=82), behavioral variant FTD (n=41), corticobasal syndrome (n=27), nonfluent (n=34) and semantic (n=37) variant primary progressive aphasia, and 100 cognitively normal individuals. Using partial least squares regression, we identified three principal structure-function components. The first component showed overall atrophy correlating with primary cortical hypo-connectivity and subcortical/association cortical hyper-connectivity. Components two and three linked focal syndrome-specific atrophy to peri-lesional hypo-connectivity and distal hyper-connectivity. Structural and functional component scores predicted global and domain-specific cognitive deficits. Anatomically, functional connectivity changes reflected alterations in specific brain activity gradients. Eigenmode analysis identified temporal phase and amplitude collapse as an explanation for atrophy-driven functional connectivity changes.

[18F]PI-2620 Binding Patterns in Patients with Suspected Alzheimer Disease and Frontotemporal Lobar Degeneration

Tau PET has enabled the visualization of paired helical filaments of 3 or 4 C-terminal repeat tau in Alzheimer disease (AD), but its ability to detect aggregated tau in frontotemporal lobar degeneration (FTLD) spectrum disorders is uncertain. We investigated 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5c']dipyridine ([18F]PI-2620), a newer tracer with ex vivo evidence for binding to FTLD tau, in a convenience sample of patients with suspected FTLD and AD using a static acquisition protocol and parametric SUV ratio (SUVr) images. Methods: We analyzed [18F]PI-2620 PET data from 65 patients with clinical diagnoses associated with AD or FTLD neuropathology; most (60/65) also had amyloid-β (Aβ) PET. Scans were acquired 30-60 min after injection; SUVr maps (reference, inferior cerebellar cortex) were created for the full acquisition and for 10-min truncated sliding windows (30-40, 35-45,…50-60 min). Age- and sex-adjusted z score maps were computed for each patient, relative to 23 Aβ-negative cognitively healthy controls (HC). Mean SUVr in the globus pallidus, substantia nigra, subthalamic nuclei, dentate nuclei, white matter, and temporal gray matter was extracted for the full and truncated windows. Results: Patients with suspected AD neuropathology (Aβ-positive patients with mild cognitive impairment or AD dementia) showed high-intensity temporoparietal cortex-predominant [18F]PI-2620 binding. At the group level, patients with clinical diagnoses associated with FTLD (progressive supranuclear palsy with Richardson syndrome [PSP Richardson syndrome], corticobasal syndrome, and nonfluent-variant primary progressive aphasia) exhibited higher globus pallidus SUVr than did HCs; pallidal retention was highest in the PSP Richardson syndrome group, in whom SUVr was correlated with symptom severity (ρ = 0.53, P = 0.05). At the individual level, only half of PSP Richardson syndrome, corticobasal syndrome, and nonfluent-variant primary progressive aphasia patients had a pallidal SUVr above that of HCs. Temporal SUVr discriminated AD patients from HCs with high accuracy (area under the receiver operating characteristic curve, 0.94 [95% CI, 0.83-1.00]) for all time windows, whereas discrimination between patients with PSP Richardson syndrome and HCs using pallidal SUVr was fair regardless of time window (area under the receiver operating characteristic curve, 0.77 [95% CI, 0.61-0.92] at 30-40 min vs. 0.81 [95% CI, 0.66-0.96] at 50-60 min; P = 0.67). Conclusion: [18F]PI-2620 SUVr shows an intense and consistent signal in AD but lower-intensity, heterogeneous, and rapidly decreasing binding in patients with suspected FTLD. Further work is needed to delineate the substrate of [18F]PI-2620 binding and the usefulness of [18F]PI2620 SUVr quantification outside the AD continuum.

Structural correlates of survival in progressive supranuclear palsy

INTRODUCTION

Many studies of the Richardson's syndrome phenotype of progressive supranuclear palsy (PSP) have elucidated regions of progressive atrophy and neural correlates of clinical severity. However, the neural correlates of survival and how these differ according to variant phenotypes are poorly understood. We set out to identify structural changes that predict severity and survival from scanning date to death.

METHODS

Structural magnetic resonance imaging data from 112 deceased people with clinically defined 'probable' or 'possible' PSP were analysed. Neuroanatomical regions of interest volumes, thickness and area were correlated with 'temporal stage', defined as the ratio of time from symptom onset to death, time from scan to death ('survival from scan'), and in a subset of patients, clinical severity, adjusting for age and total intracranial volume. Forty-nine participants had post mortem confirmation of the diagnosis.

RESULTS

Using T1-weighted magnetic resonance imaging, we confirmed the midbrain, and bilateral cortical structural correlates of contemporary disease severity. Atrophy of the striatum, cerebellum and frontotemporal cortex correlate with temporal stage and survival from scan, even after adjusting for severity. Subcortical structure-survival relationships were stronger in Richardson's syndrome than variant phenotypes.

CONCLUSIONS

Although the duration of PSP varies widely between people, an individual's progress from disease onset to death (their temporal stage) reflects atrophy in striatal, cerebellar and frontotemporal cortical regions. Our findings suggest magnetic resonance imaging may contribute to prognostication and stratification of patients with heterogenous clinical trajectories and clarify the processes that confer mortality risk in PSP.

Determinants of astrocytic pathology in stem cell models of primary tauopathies

Astrocytic tau aggregates are seen in several primary and secondary tauopathies, including progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and chronic traumatic encephalopathy (CTE). In all of these diseases, astrocytic tau consists mostly of the longer (4R) tau isoform, even when adjacent neuronal aggregates consist of a mixture of 3- and 4R tau, as in CTE. Even the rare astrocytic tau aggregates seen in Pick's disease appear to contain both 3R and 4R tau. The reasons for this, and the mechanisms by which astrocytic tau aggregates form, remain unclear. We used a combination of RNA in situ hybridization and immunofluorescence in post-mortem human brain tissue, as well as tau uptake studies in human stem cell-derived astrocytes, to determine the origins of astrocytic tau in 4R tauopathies. We found no differences in tau mRNA expression between diseases or between tau positive and negative astrocytes within PSP. We then found that stem cell-derived astrocytes preferentially take up long isoform (4R) recombinant tau and that this uptake is impaired by induction of reactivity with inflammatory stimuli or nutritional stress. Astrocytes exposed to either 3R or 4R tau also showed downregulation of genes related to astrocyte differentiation. Our findings suggest that astrocytes preferentially take up neuronal 4R tau from the extracellular space, potentially explaining why 4R tau is the predominant isoform in astrocytic tau aggregates.

Longitudinal characterization of patients with progressive apraxia of speech without clearly predominant phonetic or prosodic speech features

Most recent studies of progressive apraxia of speech (PAOS) have focused on patients with phonetic or prosodic predominant PAOS to understand the implications of the presenting clinical phenotype. Patients without a clearly predominating speech quality, or mixed AOS, have been excluded. Given the implications for disease progression, it is important to understand these patients early in the disease course to inform appropriate education and prognostication. The aim of this study was to describe a cohort of ten patients with initially mixed PAOS and how their clinical course evolves. Four patients were rated prosodic predominant later on (mild AOS at first visit); five were later designated phonetic (four with more than mild AOS at first visit); one was judged mixed at all visits. The study suggests patients without a clear predominance of speech featuresshould still be included in PAOS studies and thought of on the continuum of the disease spectrum.

Behavioral and neuropathological characterization over the adult lifespan of the human tau knock-in mouse

Tau is a microtubule-associated protein with a diverse functional repertoire linked to neurodegenerative disease. Recently, a human tau knock-in (MAPT KI) mouse was developed that may overcome many limitations associated with current animal models used to study tau. In MAPT KI mice, the entire murine Mapt gene was replaced with the human MAPT gene under control of the endogenous Mapt promoter. This model represents an ideal in vivo platform to study the function and dysfunction of human tau protein. Accordingly, a detailed understanding of the effects MAPT KI has on structure and function of the CNS is warranted. Here, we provide a detailed behavioral and neuropathological assessment of MAPT KI mice. We compared MAPT KI to wild-type (WT) C57BL/6j mice in behavioral assessments of anxiety, attention, working memory, spatial memory, and motor performance from 6 to 24 months (m) of age. Using immunohistological and biochemical assays, we quantified markers of glia (microglia, astrocytes and oligodendrocytes), synaptic integrity, neuronal integrity and the cytoskeleton. Finally, we quantified levels of total tau, tau isoforms, tau phosphorylation, and tau conformations. MAPT KI mice show normal cognitive and locomotor behavior at all ages, and resilience to mild age-associated locomotor deficits observed in WT mice. Markers of neuronal and synaptic integrity are unchanged in MAPT KI mice with advancing age. Glial markers are largely unchanged in MAPT KI mice, but glial fibrillary acidic protein is increased in the hippocampus of WT and MAPT KI mice at 24 m. MAPT KI mice express all 6 human tau isoforms and levels of tau remain stable throughout adulthood. Hippocampal tau in MAPT KI and WT mice is phosphorylated at serine 396/404 (PHF1) and murine tau in WT animals displays more PHF1 phosphorylation at 6 and 12 m. Lastly, we extended previous reports showing that MAPT KI mice do not display overt pathology. No evidence of other tau phosphorylation residues (AT8, pS422) or abnormal conformations (TNT2 or TOC1) associated with pathogenic tau were detected. The lack of overt pathological changes in MAPT KI mice make this an ideal platform for future investigations into the function and dysfunction of tau protein in vivo.

Interaction of Proteins Involved in Neuronal Proteinopathies

Proteinopathy is characterized by the accumulation of aggregates of a specific protein in a target organ, tissue, or cell. The aggregation of the same protein can cause different pathologies as single protein can adopt various amyloidogenic, disease-specific conformations. The conformation governs the interaction of amyloid aggregates with other proteins that are prone to misfolding and, thus, determines disease-specific spectrum of concomitant pathologies. In this regard, a detailed description of amyloid protein conformation as well as spectrum of its interaction with other proteins become a key point for drafting of precise description of the disease. The majority of clinical cases of neuronal proteinopathies is caused by the aggregation of rather limited range of amyloidogenic proteins. Here, we provided the characterization of pathologies, related to the aggregation of amyloid β peptide, tau protein, α-synuclein, TDP-43, and amylin, giving a short description of pathologies themselves, recent advances in elucidation of misfolded protein conformation, with emphasis on those protein aggregates extracted from biological samples, what is known about the interaction of this proteins, and the influence of this interaction on the progression of underlying disease and comorbidities.

Analysis of Genetic and MRI Changes, Blood Markers, and Risk Factors in a Twin Pair Discordant of Progressive Supranuclear Palsy

Background and Objectives: Progressive supranuclear palsy (PSP) is a neurodegenerative disease, a tauopathy, which results in a wide clinical spectrum of neurological symptoms. The diagnosis is mostly based on clinical signs and neuroimaging; however, possible biomarkers for screening have been under investigation, and the role of the gut microbiome is unknown. The aim of our study was to identify potential blood biomarkers and observe variations in the gut microbiome within a PSP discordant monozygotic twin pair. Materials and Methods: Anthropometric measurements, neuropsychological tests, and the neurological state were evaluated. Blood was collected for metabolic profiling and for the detection of neurodegenerative and vascular biomarkers. Both the gut microbiome and brain MRI results were thoroughly examined. Results: We found a relevant difference between alpha-synuclein levels and moderate difference in the levels of MMP-2, MB, Apo-A1, Apo-CIII, and Apo-H. With respect to the ratios, a small difference was observed for ApoA1/SAA and ApoB/ApoA1. Using a microbiome analysis, we also discovered a relative dysbiosis, and the MRI results revealed midbrain and frontoparietal cortical atrophy along with a reduction in overall brain volumes and an increase in white matter lesions in the affected twin. Conclusions: We observed significant differences between the unaffected and affected twins in some risk factors and blood biomarkers, along with disparities in the gut microbiome. Additionally, we detected abnormalities in brain MRI results and alterations in cognitive functions.

Novel Conformation-Dependent Tau Antibodies Are Modulated by Adjacent Phosphorylation Sites

Tau proteins within the adult central nervous system (CNS) are found to be abnormally aggregated into heterogeneous filaments in neurodegenerative diseases, termed tauopathies. These tau inclusions are pathological hallmarks of Alzheimer's disease (AD), Pick's disease (PiD), corticobasal degeneration (CBD), and progressive supranuclear palsy (PSP). The neuropathological hallmarks of these diseases burden several cell types within the CNS, and have also been shown to be abundantly phosphorylated. The mechanism(s) by which tau aggregates in the CNS is not fully known, but it is hypothesized that hyperphosphorylated tau may precede and further promote filament formation, leading to the production of these pathological inclusions. In the studies herein, we generated and thoroughly characterized two novel conformation-dependent tau monoclonal antibodies that bind to residues Pro218-Glu222, but are sensitive to denaturing conditions and highly modulated by adjacent downstream phosphorylation sites. These epitopes are present in the neuropathological hallmarks of several tauopathies, including AD, PiD, CBD, and PSP. These novel antibodies will further enable investigation of tau-dependent pathological inclusion formation and enhance our understanding of the phosphorylation signatures within tauopathies with the possibility of new biomarker developments.

Frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is one of the most common causes of early-onset dementia and presents with early social-emotional-behavioural and/or language changes that can be accompanied by a pyramidal or extrapyramidal motor disorder. About 20-25% of individuals with FTLD are estimated to carry a mutation associated with a specific FTLD pathology. The discovery of these mutations has led to important advances in potentially disease-modifying treatments that aim to slow progression or delay disease onset and has improved understanding of brain functioning. In both mutation carriers and those with sporadic disease, the most common underlying diagnoses are linked to neuronal and glial inclusions containing tau (FTLD-tau) or TDP-43 (FTLD-TDP), although 5-10% of patients may have inclusions containing proteins from the FUS-Ewing sarcoma-TAF15 family (FTLD-FET). Biomarkers definitively identifying specific pathological entities in sporadic disease have been elusive, which has impeded development of disease-modifying treatments. Nevertheless, disease-monitoring biofluid and imaging biomarkers are becoming increasingly sophisticated and are likely to serve as useful measures of treatment response during trials of disease-modifying treatments. Symptomatic trials using novel approaches such as transcranial direct current stimulation are also beginning to show promise.

Expression of tau and phosphorylated tau in the brain of normal and hemiparkinsonian rhesus macaques

Tau is a neuronal protein involved in microtubule stabilization and intracellular vesicle transport in axons. In neurodegenerative disorders termed "tauopathies," like Alzheimer's and Parkinson's disease, tau becomes hyperphosphorylated and forms intracellular inclusions. Rhesus macaques are widely used for studying ageing processes and modeling neurodegenerative disorders, yet little is known about endogenous tau expression in their brains. In this study, immunohistochemical methods were used to map and characterize total tau, 3R- and 4R-tau isoforms, and phosphorylated tau (pThr231-tau and pSer202/Thr205-tau/AT8) expression bilaterally in 16 brain regions of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian adult rhesus macaques. Tau-immunoreactivity (-ir), including both 3R and 4R isoforms, was observed throughout the brain, with varying regional intensities. The anterior cingulate cortex, entorhinal cortex, and hippocampus displayed the most robust tau-ir, while the subthalamic nucleus and white matter regions had minimal expression. Tau was present in neurons of gray matter regions; it was preferentially observed in fibers of the globus pallidus and substantia nigra and in cell bodies of the thalamus and subthalamic nucleus. In white matter regions, tau was abundantly present in oligodendrocytes. Additionally, neuronal pThr231-tau-ir was abundant in all brain regions, but not AT8-ir. Differences in regional and intracellular protein expression were not detected between control subjects and both brain hemispheres of MPTP-treated animals. Specifically, tau-ir in the substantia nigra of all subjects colocalized with GABAergic neurons. Overall, this report provides an in-depth characterization of tau expression in the rhesus macaque brain to facilitate future investigations for understanding and modeling tau pathology in this species.

Determinants of Astrocytic Pathology in Stem Cell Models of Primary Tauopathies

Astrocytic tau aggregates are seen in several primary and secondary tauopathies, including progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and chronic traumatic encephalopathy (CTE). In all cases, astrocytic tau consists exclusively of the longer (4R) tau isoform, even when adjacent neuronal aggregates consist of a mixture of 3- and 4R tau, as in CTE. The reasons for this and the mechanisms by which astrocytic tau aggregates form remain unclear. We used a combination of RNA in situ hybridization and immunofluorescence in post-mortem human brain tissue, as well as tau uptake studies in human stem cell-derived astrocytes, to determine the origins of astrocytic tau in 4R tauopathies. We found that astrocytes across tauopathies do not upregulate tau mRNA expression between diseases or between tau-positive and -negative astrocytes within PSP. We then found that stem cell-derived astrocytes preferentially take up long isoform (4R) labeled recombinant tau and that this uptake is impaired by induction of reactivity with inflammatory stimuli or nutritional stress. Astrocytes exposed to either 3R or 4R tau also showed downregulation of genes related to astrocyte differentiation. Our findings suggest that astrocytes preferentially take up neuronal 4R tau from the extracellular space, which potentially explains why astrocytic tau aggregates contain only 4R tau, and that tau uptake is impaired by decreased nutrient availability or neuroinflammation, both of which are common in the aging brain.

Tau seeds occur before earliest Alzheimer's changes and are prevalent across neurodegenerative diseases

Tau neurofibrillary tangles are a hallmark of Alzheimer's disease neuropathological change. However, it remains largely unclear how distinctive Alzheimer's disease tau seeds (i.e. 3R/4R) correlate with histological indicators of tau accumulation. Furthermore, AD tau co-pathology is thought to influence features and progression of other neurodegenerative diseases including Lewy body disease; yet measurements of different types of tau seeds in the setting of such diseases is an unmet need. Here, we use tau real-time quaking-induced conversion (RT-QuIC) assays to selectively quantitate 3R/4R tau seeds in the frontal lobe which accumulates histologically identifiable tau pathology at late disease stages of AD neuropathologic change. Seed quantitation across a spectrum of neurodegenerative disease cases and controls indicated tau seeding activity can be detected well before accompanying histopathological indication of tau deposits, and even prior to the earliest evidence of Alzheimer's-related tau accumulation anywhere in the brain. In later stages of AD, 3R/4R tau RT-QuIC measures correlated with immunohistochemical tau burden. In addition, Alzheimer's tau seeds occur in the vast majority of cases evaluated here inclusive of primary synucleinopathies, frontotemporal lobar degeneration and even controls albeit at multi-log lower levels than Alzheimer's cases. α-synuclein seeding activity confirmed synucleinopathy cases and further indicated the co-occurrence of α-synuclein seeds in some Alzheimer's disease and primary tauopathy cases. Our analysis indicates that 3R/4R tau seeds in the mid-frontal lobe correlate with the overall Braak stage and Alzheimer's disease neuropathologic change, supporting the quantitative predictive value of tau RT-QuIC assays. Our data also indicate 3R/4R tau seeds are elevated in females compared to males at high (≥ IV) Braak stages. This study suggests 3R/4R tau seeds are widespread even prior to the earliest stages of Alzheimer's disease changes, including in normal, and even young individuals, with prevalence across multiple neurodegenerative diseases to further define disease subtypes.

Distinct and shared neuropsychiatric phenotypes in FTLD-tauopathies

Frontotemporal lobar degeneration (FTLD) with tau pathology (FTLD-tau) commonly causes dementia syndromes that include primary progressive aphasia (PPA) and behavioral variant frontotemporal dementia (bvFTD). Cognitive decline in PPA and bvFTD is often accompanied by debilitating neuropsychiatric symptoms. In 44 participants with PPA or bvFTD due to autopsy-confirmed FTLD-tau, we characterized neuropsychiatric symptoms at early and late disease stages and determined whether the presence of certain symptoms predicted a specific underlying FTLD-tauopathy. Participants completed annual research visits at the Northwestern University Alzheimer's Disease Research Center. All participants had an initial Global Clinical Dementia Rating (CDR) Scale score ≤ 2, and neuropsychiatric symptoms were evaluated via the Neuropsychiatric Inventory-Questionnaire (NPI-Q). We assessed the frequency of neuropsychiatric symptoms across all participants at their initial and final visits and performed logistic regression to determine whether symptoms predicted a specific FTLD-tau pathologic diagnosis. Across the FTLD-tau cohort, irritability and apathy were most frequently endorsed at initial and final visits, respectively, whereas psychosis was highly uncommon at both timepoints. Irritability at initial visit predicted greater odds of a 4-repeat compared to a 3-repeat tauopathy (OR = 3.95, 95% CI = 1.10-15.83, p < 0.05). Initial sleep disturbance predicted greater odds of progressive supranuclear palsy (PSP) compared to other FTLD-tau subtypes (OR = 10.68, 95% CI = 2.05-72.40, p < 0.01). Appetite disturbance at final evaluation predicted lower odds of PSP (OR = 0.15, 95% CI = 0.02-0.74, p < 0.05). Our findings suggest that characterization of neuropsychiatric symptoms can aid in the prediction of underlying FTLD-tauopathies. Given considerable pathologic heterogeneity underlying dementias, neuropsychiatric symptoms may be useful for differential diagnosis and treatment planning.

Comparative assessment of regional tau distribution by Tau-PET and Post-mortem neuropathology in a representative set of Alzheimer's & frontotemporal lobar degeneration patients

Flortaucipir (FTP) PET is a key imaging technique to evaluate tau burden indirectly. However, it appears to have greater utility for 3R+4R tau found in Alzheimer's disease (AD), compared to other non-AD tauopathies. The purpose of this study is to determine how flortaucipir uptake links to neuropathologically determined tau burden in AD and non-AD tauopathies. We identified nine individuals who had undergone antemortem tau-PET and postmortem neuropathological analyses. The cohort included three patients with low, moderate, and high AD neuropathologic changes (ADNC), five patients with a non-AD tauopathy (one Pick's disease, three progressive supranuclear palsies, and one globular glial tauopathy), and one control without ADNC. We compared regional flortaucipir PET uptake with tau burden using an anti-AT8 antibody. There was a very good correlation between flortaucipir uptake and tau burden in those with ADNC although, in one ADNC patient, flortaucipir uptake and tau burden did not match due to the presence of argyrophilic grains disease. Non-AD patients showed lower flortaucipir uptake globally compared to ADNC patients. In the non-AD patients, some regional associations between flortaucipir uptake and histopathological tau burden were observed. Flortaucipir uptake is strongly linked to underlying tau burden in patients with ADNC but there are instances where they do not match. On-the-other hand, flortaucipir has a limited capacity to represent histopathological tau burden in non-AD patients although there are instances where regional uptake correlates with regional tau burden. There is a definite need for the development of future generations of tau-PET ligands that can detect non-AD tau.

Ultra-Early Screening of Cognitive Decline Due to Alzheimer's Pathology

Alzheimer's pathology can be assessed and defined via Aβ and tau biomarkers. The preclinical period of Alzheimer's disease is long and lasts several decades. Although effective therapies to block pathological processes of Alzheimer's disease are still lacking, downward trends in the incidence and prevalence of dementia have occurred in developed countries. Accumulating findings support that education, cognitive training, physical exercise/activities, and a healthy lifestyle can protect cognitive function and promote healthy aging. Many studies focus on detecting mild cognitive impairment (MCI) and take a variety of interventions in this stage to protect cognitive function. However, when Alzheimer's pathology advances to the stage of MCI, interventions may not be successful in blocking the development of the pathological process. MCI individuals reverting to normal cognitive function exhibited a high probability to progress to dementia. Therefore, it is necessary to take effective measures before the MCI stage. Compared with MCI, an earlier stage, transitional cognitive decline, may be a better time window in which effective interventions are adopted for at-risk individuals. Detecting this stage in large populations relies on rapid screening of cognitive function; given that many cognitive tests focus on MCI detection, new tools need to be developed.

Clinicopathological associations of hemispheric dominance in primary progressive apraxia of speech

OBJECTIVE

Primary progressive apraxia of speech (PPAOS) is associated with imaging abnormalities in the lateral premotor cortex (LPC) and supplementary motor area (SMA). It is not known whether greater involvement of these regions in either hemisphere is associated with demographics, presenting, and/or longitudinal features.

METHODS

In 51 prospectively recruited PPAOS patients who completed [18 F]-fluorodeoxyglucose (FDG) positron emission tomography (PET), we classified patients as left-dominant, right-dominant, or symmetric, based on visual assessment of the LPC and SMA on FDG-PET. SPM and statistical analyses of regional metabolic values were performed. Diagnosis of PPAOS was made if apraxia of speech was present and aphasia absent. Thirteen patients completed ioflupane-123I (dopamine transporter [DAT]) scans. We compared cross-sectional and longitudinal clinicopathological, genetic, and neuroimaging characteristics across the three groups, with area under the receiver-operating curve (AUROC) determined as a measure of effect size.

RESULTS

In all, 49% of the PPAOS patients were classified as left-dominant, 31% as right-dominant, and 20% as symmetric, which was supported by results from the SPM and regional analyses. There were no differences in baseline characteristics. Longitudinally, right-dominant PPAOS showed faster rates of progression of ideomotor apraxia (AUROC 0.79), behavioral disturbances (AUROC 0.84), including disinhibition symptoms (AUROC 0.82) and negative behaviors (AUROC 0.82), and parkinsonism (AUROC 0.75) compared to left-dominant PPAOS. Symmetric PPAOS showed faster rates of dysarthria progression compared to left-dominant (AUROC 0.89) and right-dominant PPAOS (AUROC 0.79). Five patients showed abnormal DAT uptake. Braak neurofibrillary tangle stage differed across groups (p = 0.01).

CONCLUSIONS

Patients with PPAOS and a right-dominant pattern of hypometabolism on FDG-PET have the fastest rates of decline of behavioral and motor features.

Creating the Pick's disease International Consortium: Association study of MAPT H2 haplotype with risk of Pick's disease

Background

Pick's disease (PiD) is a rare and predominantly sporadic form of frontotemporal dementia that is classified as a primary tauopathy. PiD is pathologically defined by argyrophilic inclusion Pick bodies and ballooned neurons in the frontal and temporal brain lobes. PiD is characterised by the presence of Pick bodies which are formed from aggregated, hyperphosphorylated, 3-repeat tau proteins, encoded by the MAPT gene. The MAPT H2 haplotype has consistently been associated with a decreased disease risk of the 4-repeat tauopathies of progressive supranuclear palsy and corticobasal degeneration, however its role in susceptibility to PiD is unclear. The primary aim of this study was to evaluate the association between MAPT H2 and risk of PiD.

Methods

We established the Pick's disease International Consortium (PIC) and collected 338 (60.7% male) pathologically confirmed PiD brains from 39 sites worldwide. 1,312 neurologically healthy clinical controls were recruited from Mayo Clinic Jacksonville, FL (N=881) or Rochester, MN (N=431). For the primary analysis, subjects were directly genotyped for MAPT H1-H2 haplotype-defining variant rs8070723. In secondary analysis, we genotyped and constructed the six-variant MAPT H1 subhaplotypes (rs1467967, rs242557, rs3785883, rs2471738, rs8070723, and rs7521).

Findings

Our primary analysis found that the MAPT H2 haplotype was associated with increased risk of PiD (OR: 1.35, 95% CI: 1.12-1.64 P=0.002). In secondary analysis involving H1 subhaplotypes, a protective association with PiD was observed for the H1f haplotype (0.0% vs. 1.2%, P=0.049), with a similar trend noted for H1b (OR: 0.76, 95% CI: 0.58-1.00, P=0.051). The 4-repeat tauopathy risk haplotype MAPT H1c was not associated with PiD susceptibility (OR: 0.93, 95% CI: 0.70-1.25, P=0.65).

Interpretation

The PIC represents the first opportunity to perform relatively large-scale studies to enhance our understanding of the pathobiology of PiD. This study demonstrates that in contrast to its protective role in 4R tauopathies, the MAPT H2 haplotype is associated with an increased risk of PiD. This finding is critical in directing isoform-related therapeutics for tauopathies.

Brain Kynurenine Pathway Metabolite Levels May Reflect Extent of Neuroinflammation in ALS, FTD and Early Onset AD

OBJECTIVES

Despite distinct clinical profiles, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients share a remarkable portion of pathological features, with a substantial percentage of patients displaying a mixed disease phenotype. Kynurenine metabolism seems to play a role in dementia-associated neuroinflammation and has been linked to both diseases. We aimed to explore dissimilarities in kynurenine pathway metabolites in these early onset neurodegenerative disorders in a brain-region-specific manner.

METHODS

Using liquid chromatography mass spectrometry (LC-MS/MS), kynurenine metabolite levels were determined in the brain samples of 98 healthy control subjects (n = 20) and patients with early onset Alzheimer's disease (EOAD) (n = 23), ALS (n = 20), FTD (n = 24) or a mixed FTD-ALS (n = 11) disease profile.

RESULTS

Overall, the kynurenine pathway metabolite levels were significantly lower in patients with ALS compared to FTD, EOAD and control subjects in the frontal cortex, substantia nigra, hippocampus and neostriatum. Anthranilic acid levels and kynurenine-to-tryptophan ratios were consistently lower in all investigated brain regions in ALS compared to the other diagnostic groups.

CONCLUSIONS

These results suggest that the contribution of kynurenine metabolism in neuroinflammation is lower in ALS than in FTD or EOAD and may also be traced back to differences in the age of onset between these disorders. Further research is necessary to confirm the potential of the kynurenine system as a therapeutic target in these early onset neurodegenerative disorders.

A prolyl oligopeptidase inhibitor reduces tau pathology in cellular models and in mice with tauopathy

Tauopathies are neurodegenerative diseases that are characterized by accumulation of hyperphosphorylated tau protein, higher-order aggregates, and tau filaments. Protein phosphatase 2A (PP2A) is a major tau dephosphorylating phosphatase, and a decrease in its activity has been demonstrated in tauopathies, including Alzheimer's disease. Prolyl oligopeptidase is a serine protease that is associated with neurodegeneration, and its inhibition normalizes PP2A activity without toxicity under pathological conditions. Here, we assessed whether prolyl oligopeptidase inhibition could protect against tau-mediated toxicity in cellular models in vitro and in the PS19 transgenic mouse model of tauopathy carrying the human tau-P301S mutation. We show that inhibition of prolyl oligopeptidase with the inhibitor KYP-2047 reduced tau aggregation in tau-transfected HEK-293 cells and N2A cells as well as in human iPSC-derived neurons carrying either the P301L or tau-A152T mutation. Treatment with KYP-2047 resulted in increased PP2A activity and activation of autophagic flux in HEK-293 cells and N2A cells and in patient-derived iNeurons, as indicated by changes in autophagosome and autophagy receptor markers; this contributed to clearance of insoluble tau. Furthermore, treatment of PS19 transgenic mice for 1 month with KYP-2047 reduced tau burden in the brain and cerebrospinal fluid and slowed cognitive decline according to several behavioral tests. In addition, a reduction in an oxidative stress marker was seen in mouse brains after KYP-2047 treatment. This study suggests that inhibition of prolyl oligopeptidase could help to ameliorate tau-dependent neurodegeneration.

The Sensitivity of Tau Tracers for the Discrimination of Alzheimer's Disease Patients and Healthy Controls by PET

Hyperphosphorylated tau aggregates, also known as neurofibrillary tangles, are a hallmark neuropathological feature of Alzheimer's disease (AD). Molecular imaging of tau by positron emission tomography (PET) began with the development of [18F]FDDNP, an amyloid β tracer with off-target binding to tau, which obtained regional specificity through the differing distributions of amyloid β and tau in AD brains. A concerted search for more selective and affine tau PET tracers yielded compounds belonging to at least eight structural categories; 18F-flortaucipir, known variously as [18F]-T807, AV-1451, and Tauvid®, emerged as the first tau tracer approved by the American Food and Drug Administration. The various tau tracers differ concerning their selectivity over amyloid β, off-target binding at sites such as monoamine oxidase and neuromelanin, and degree of uptake in white matter. While there have been many reviews of molecular imaging of tau in AD and other conditions, there has been no systematic comparison of the fitness of the various tracers for discriminating between AD patient and healthy control (HC) groups. In this narrative review, we endeavored to compare the binding properties of the various tau tracers in vitro and the effect size (Cohen's d) for the contrast by PET between AD patients and age-matched HC groups. The available tracers all gave good discrimination, with Cohen's d generally in the range of two-three in culprit brain regions. Overall, Cohen's d was higher for AD patient groups with more severe illness. Second-generation tracers, while superior concerning off-target binding, do not have conspicuously higher sensitivity for the discrimination of AD and HC groups. We suppose that available pharmacophores may have converged on a maximal affinity for tau fibrils, which may limit the specific signal imparted in PET studies.

Thioflavin S Staining and Amyloid Formation Are Unique to Mixed Tauopathies

Tau phosphorylation, aggregation, and toxicity are the main drivers of neurodegeneration in multiple tauopathies, including Alzheimer's disease (AD) and frontotemporal lobar degeneration with tau. Although aggregation and amyloid formation are often assumed to be synonymous, the ability of tau aggregates in different diseases to form amyloids in vivo has not been systematically studied. We used the amyloid dye Thioflavin S to look at tau aggregates in mixed tauopathies such as AD and primary age-related tauopathy, as well as pure 3R or 4R tauopathies such as Pick's disease, progressive supranuclear palsy, and corticobasal degeneration. We found that aggregates of tau protein only form thioflavin-positive amyloids in mixed (3R/4R), but not pure (3R or 4R), tauopathies. Interestingly, neither astrocytic nor neuronal tau pathology was thioflavin-positive in pure tauopathies. As most current positron emission tomography tracers are based on thioflavin derivatives, this suggests that they may be more useful for differential diagnosis than the identification of a general tauopathy. Our findings also suggest that thioflavin staining may have utility as an alternative to traditional antibody staining for distinguishing between tau aggregates in patients with multiple pathologies and that the mechanisms for tau toxicity may differ between different tauopathies.

What every neuropathologist needs to know: condensed protocol work-up for clinical dementia syndromes

Concerns about the costs associated with autopsy assessment of Alzheimer disease and related dementias according to 2012 NIA-AA Guidelines have been expressed since the publication of those guidelines. For this reason, we designed and validated a Condensed Protocol for the neuropathologic diagnoses of Alzheimer disease neuropathologic change, Lewy Body disease neuropathologic change, as well as chronic microvascular lesions, hippocampal sclerosis of aging, and cerebral amyloid angiopathy. In this study, the Condensed Protocol is updated to include frontotemporal lobar degeneration [FTLD] tau (corticobasal degeneration, progressive supranuclear palsy, and Pick disease), FTLD-TDP, and limbic-predominant, age-related TDP-43 encephalopathy. The same 20 brain regions are sampled and processed in 5 tissue cassettes, which reduces reagent costs by approximately 65%. Three board-certified neuropathologists were blinded to the original Northwestern University Alzheimer's Disease Research Center Original Protocol neuropathological diagnoses and all clinical history information. The results yielded near uniform agreement with the original comprehensive Alzheimer's Disease Research Center neuropathologic assessments. Diagnostic sensitivity was not impacted. In summary, our recent results show that our updated Condensed Protocol is also an accurate and less expensive alternative to the comprehensive protocols for the additional neuropathologic diagnoses of FTLD Tau and TDP43 proteinopathies.