Progressive Supranuclear Palsy Brains Research Articles

Discriminative power of multi‐PET tracer approach targeting reactive astrogliosis, tau pathology, and dopaminergic impairment in 4R primary tauopathies

AbstractBackgroundThe 4R tauopathies corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are described as dementias with parkinsonian syndrome. Even if they are proven to represent clinically different entities, their complex neuropathology and common hallmarks often make the differential clinical diagnosis of CBD and PSP challenging. The highly entangled astrocytic and tau pathologies observed in these diseases are however displaying unique disparities which might unravel specific neuropathological profiles for each disease. The multi‐PET tracer approach applied in the present study in postmortem brain tissue might provide new mechanistic insights. We recently demonstrated that the second‐generation tau PET tracer, 3H‐PI2620 had a discriminative potential in CBD, PSP, and Alzheimer’s disease (AD) brains (Malarte et al. Mol. Psychiatry. 2022). To further understand the interaction between tau spatial distribution and its potential effects on astrocytic reactivity, we conducted a comparative multi‐tracer investigation in CBD, PSP, AD, and control brains using novel tau and astrocytic tracers. To gain a deeper insight into the relationship between tau, astrogliosis, and concomitant motor impairments, we also studied the interaction with the dopaminergic system.MethodWe performed autoradiography studies on large frozen hemispherical brain tissue of CBD, PSP, AD, and control cases using the tau PET tracer 3H‐PI2620, in comparison to astrocytic tracers (3H‐BU99008 and 3H‐Deprenyl) and dopaminergic tracers (3H‐Raclopride and 3H‐FE‐PE2I). We also analyzed the regional distribution of these tracers in small adjacent frozen brain sections of pathologically specific brain regions (globus pallidus, putamen, caudate, frontal cortex, medulla oblongata). We also performed saturation studies with 3H‐BU99008 and 3H‐Deprenyl on CBD and PSP brain homogenatesResultOur preliminary results are promising and suggest high astrogliosis measured by 3H‐BU99008 and 3H‐Deprenyl in large frozen autoradiography in CBD and PSP brains, and with different binding intensities in different brain regions comparable with regional 3H‐PI2620 binding. 3H‐BU99008 and 3H‐Deprenyl both highlighted two binding sites in the putamen of CBD cases, but only one site in PSP.ConclusionOngoing multi‐PET tracer studies targeting different pathological hallmarks of CBD and PSP tauopathies will improve differentiation and provide new knowledge regarding the spatial distribution of tau and its correlation with astrogliosis and the dopaminergic system in primary tauopathies.

Discriminative power of multi‐PET tracer approach targeting reactive astrogliosis, tau pathology, and dopaminergic impairment in 4R primary tauopathies

AbstractBackgroundThe 4R tauopathies corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are described as dementias with parkinsonian syndrome. Even if they are proven to represent clinically different entities, their complex neuropathology and common hallmarks often make the differential clinical diagnosis of CBD and PSP challenging. The highly entangled astrocytic and tau pathologies observed in these diseases are however displaying unique disparities which might unravel specific neuropathological profiles for each disease. The multi‐PET tracer approach applied in the present study in postmortem brain tissue might provide new mechanistic insights. We recently demonstrated that the second‐generation tau PET tracer, 3H‐PI2620 had a discriminative potential in CBD, PSP, and Alzheimer’s disease (AD) brains (Malarte et al. Mol. Psychiatry. 2022). To further understand the interaction between tau spatial distribution and its potential effects on astrocytic reactivity, we conducted a comparative multi‐tracer investigation in CBD, PSP, AD, and control brains using novel tau and astrocytic tracers. To gain a deeper insight into the relationship between tau, astrogliosis, and concomitant motor impairments, we also studied the interaction with the dopaminergic system.MethodWe performed autoradiography studies on large frozen hemispherical brain tissue of CBD, PSP, AD, and control cases using the tau PET tracer 3H‐PI2620, in comparison to astrocytic tracers (3H‐BU99008 and 3H‐Deprenyl) and dopaminergic tracers (3H‐Raclopride and 3H‐FE‐PE2I). We also analyzed the regional distribution of these tracers in small adjacent frozen brain sections of pathologically specific brain regions (globus pallidus, putamen, caudate, frontal cortex, medulla oblongata). We also performed saturation studies with 3H‐BU99008 and 3H‐Deprenyl on CBD and PSP brain homogenatesResultOur preliminary results are promising and suggest high astrogliosis measured by 3H‐BU99008 and 3H‐Deprenyl in large frozen autoradiography in CBD and PSP brains, and with different binding intensities in different brain regions comparable with regional 3H‐PI2620 binding. 3H‐BU99008 and 3H‐Deprenyl both highlighted two binding sites in the putamen of CBD cases, but only one site in PSP.ConclusionOngoing multi‐PET tracer studies targeting different pathological hallmarks of CBD and PSP tauopathies will improve differentiation and provide new knowledge regarding the spatial distribution of tau and its correlation with astrogliosis and the dopaminergic system in primary tauopathies.

Tau seed amplification assay reveals relationship between seeding and pathological forms of tau in Alzheimer’s disease brain

Tau seed amplification assays (SAAs) directly measure the seeding activity of tau and would therefore be ideal biomarkers for clinical trials targeting seeding-competent tau in Alzheimer’s disease (AD). However, the precise relationship between tau seeding measured by SAA and the levels of pathological forms of tau in the AD brain remains unknown. We developed a new tau SAA based on full-length 0N3R tau with sensitivity in the low fg/ml range and used it to characterize 103 brain samples from three independent cohorts. Tau seeding clearly discriminated between AD and control brain samples. Interestingly, seeding was absent in Progressive Supranuclear Palsy (PSP) putamen, suggesting that our tau SAA did not amplify 4R tau aggregates from PSP brain. The specificity of our tau SAA for AD brain was further supported by analysis of matched hippocampus and cerebellum samples. While seeding was detected in hippocampus from Braak stages I-II, no seeding was present in AD cerebellum that is devoid of tau inclusions. Analysis of 40 middle frontal gyrus samples encompassing all Braak stages showed that tau SAA seeding activity gradually increased with Braak stage. This relationship between seeding activity and the presence of tau inclusions in AD brain was further supported by robust correlations between tau SAA results and the levels of phosphorylated tau212/214, phosphorylated tau181, aggregated tau, and sarkosyl-insoluble tau. Strikingly, we detected tau seeding in the middle frontal gyrus already at Braak stage II-III, suggesting that tau SAA can detect tau pathology earlier than conventional immunohistochemical staining. In conclusion, our data suggest a quantitative relationship between tau seeding activity and pathological forms of tau in the human brain and provides an important basis for further development of tau SAA for accessible human samples.

Cross species systems biology discovers glial DDR2, STOM, and KANK2 as therapeutic targets in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative parkinsonian disorder characterized by cell-type-specific tau lesions in neurons and glia. Prior work uncovered transcriptome changes in human PSP brains, although their cell-specificity is unknown. Further, systematic data integration and experimental validation platforms to prioritize brain transcriptional perturbations as therapeutic targets in PSP are currently lacking. In this study, we combine bulk tissue (n = 408) and single nucleus RNAseq (n = 34) data from PSP and control brains with transcriptome data from a mouse tauopathy and experimental validations in Drosophila tau models for systematic discovery of high-confidence expression changes in PSP with therapeutic potential. We discover, replicate, and annotate thousands of differentially expressed genes in PSP, many of which reside in glia-enriched co-expression modules and cells. We prioritize DDR2, STOM, and KANK2 as promising therapeutic targets in PSP with striking cross-species validations. We share our findings and data via our interactive application tool PSP RNAseq Atlas (https://rtools.mayo.edu/PSP_RNAseq_Atlas/). Our findings reveal robust glial transcriptome changes in PSP, provide a cross-species systems biology approach, and a tool for therapeutic target discoveries in PSP with potential application in other neurodegenerative diseases.

Understanding reactive astrogliosis in degenerative proteinopathies through the lens of postmortem brain imaging techniques

AbstractBackgroundThe discovery and validation of biomarkers beyond amyloid‐β and tau is now considered as a research priority in the Alzheimer’s disease (AD) field. In this context, astrocytes ‘key homeostatic cells’ in the central nervous system (CNS) are potential targets thanks to their swift response in AD pathology. Astrocytes tend to changes in brain physiology after CNS injury/insults via a specific defence response called reactive astrogliosis. The role of astrocytes in AD pathology is still under examination, however recent studies have openly suggested that reactive astrogliosis is an early event which may precede other hallmarks of the disease. In our recent work, we have speculated, based on clinical/translational in vivo and in vitro brain imaging studies, that there are two waves, ‘first (early) and second (late)’, of reactive astrogliosis in AD pathology with a distinct, close‐knit relationship with other pathological markers. Reactive astrogliosis also seems to play a critical role in other proteinopathies, such as progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). The PET imaging field is advancing very fast and different astrocytic‐tracers are now available, such as 11C‐Deprenyl (DED) and SMBT‐1 (both targeting MAO‐B) as well as 11C‐BU99008 (detect imidazoline2 binding sites), which we believe is of utmost relevance to shed more light on the role of reactive astrogliosis, including astrocytic heterogeneity and improve our understanding of the underlying mechanism in these proteinopathies.MethodWe used a mixed battery of specialized in vitro radioligand binding assays (saturation and competition studies in brain tissues) and large frozen human brain section autoradiography in AD, PSP, CBD and control brains.ResultIn our studies, we demonstrated that BU99008 could visualize reactive astrogliosis and target multiple binding sites in AD brain. We observed that BU99008 and DED varied in their binding behavior in AD and control brains, suggesting that they might be targeting a specific state/or a different sub‐population of astrocytes.ConclusionPostmortem brain imaging techniques are valuable tools for validation (pre‐clinical) of novel PET‐tracers. Our ongoing studies in PSP and CBD brains as well as with SMBT‐1 will provide deeper insight into the role of reactive astrogliosis in these deadly diseases.

Rare Genetic Risk in Progressive Supranuclear Palsy

AbstractBackgroundGenetic risk in common variants have been identified for Progressive Supranuclear Palsy (PSP), but common variants only account for a portion of disease heritability. A proportion of the remaining disease heritability is likely contributed by rare variants identifiable via sequencing. Leveraging whole‐genome sequencing of 1719 PSP cases and 2940 controls from the Alzheimer’s Disease Sequencing Project, we detected single nucleotide variants (SNVs), insertion/deletions (INDELs), and copy number variants (CNVs). Note that all samples are non‐Hispanic whites with identity by descent (IBD) >0.25, and no outlier is >6 standard deviation in the principal component analysis. We conducted association analysis for variants, genes and gene sets to identify rare genetic risk for PSP.MethodAfter quality control (variants and genotypes notated PASS by the calling algorithms), we detected 85,228,234 rare SNVs/INDELs and 163,987 rare CNVs (minor allele frequency (MAF) < 1%). For rare SNVs/INDELs, the Sequence Kernel Association Test Optimized was performed to identify rare genetic PSP risk from protein truncating variants (PTV) and damaging missense variants (MAF<0.01%) in both protein coding genes and gene sets that were previously associated with PSP based on protein co‐expression networks. For rare CNVs, a permutation‐based association test implemented in Plink was performed to identify CNVs associated with PSP.ResultCombining protein truncating variants (PTV) and damaging missense variants, we identified one genome‐wide significant gene, FBXO38 (FDR = 0.0003, OR = 1.78). We also found enrichment of PTVs and damaging missense variants in genes comprising the C2 module, a neuronal module previously identified in post mortem PSP brain (FDR = 0.0016). For CNV analysis, there were 17 significant deletions and 2 significant duplications that were associated with PSP (Padjust < 0.05). The deletion (18:58488230‐58488489) in ALPK2, which has been identified as an Alzheimer’s Disease risk gene, was the only CNV that conferred a higher‐risk for PSP. Particularly, one deletion (17:46009357‐46009595) was in linkage disequilibrium with MAPT H2 haplotype which has been associated various neurodegenerative diseases including PSP.ConclusionWe identified several new genes and a protein co‐expression network in which risk variants were associated with PSP. These genes and pathways provide potential candidate drug targets for future investigation.

Cell-Specific Dysregulation of Iron and Oxygen Homeostasis as a Novel Pathophysiology in PSP.

Progressive supranuclear palsy (PSP) is a 4R-tauopathy showing heterogeneous tau cytopathology commencing in the globus pallidus (GP) and the substantia nigra (SN), regions also associated with age-related iron accumulation. Abnormal iron levels have been extensively associated with tau pathology in neurodegenerative brains, however, its role in PSP pathogenesis remains yet unknown. We perform the first cell type-specific evaluation of PSP iron homeostasis and the closely related oxygen homeostasis, in relation to tau pathology in human postmortem PSP brains. In brain regions vulnerable to PSP pathology (GP, SN, and putamen), we visualized iron deposition in tau-affected and unaffected neurons, astroglia, oligodendrocytes, and microglia, using a combination of iron staining with immunolabelling. To further explore molecular pathways underlying our observations, we examined the expression of key iron and oxygen homeostasis mRNA transcripts and proteins. We found astrocytes as the major cell type accumulating iron in the early affected regions of PSP, highly associated with cellular tau pathology. The same regions are affected by dysregulated expression of alpha and beta hemoglobin and neuroglobin showing contrasting patterns. We discovered changes in iron and oxygen homeostasis-related gene expression associated with aging of the brain, and identified dysregulated expression of rare neurodegeneration with brain iron accumulation (NBIA) genes associated with tau pathology to distinguish PSP from the healthy aging brain. We present novel aspects of PSP pathophysiology highlighting an overlap with NBIA pathways. Our findings reveal potential novel targets for therapy development and have implications beyond PSP for other iron-associated neurodegenerative diseases. ANN NEUROL 2023;93:431-445.

Discriminative binding of tau PET tracers PI2620, MK6240 and RO948 in Alzheimer’s disease, corticobasal degeneration and progressive supranuclear palsy brains

Recent mechanistic and structural studies have challenged the classical tauopathy classification approach and revealed the complexity and heterogeneity of tau pathology in Alzheimer’s disease (AD) and primary tauopathies such as corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), progressing beyond distinct tau isoforms. In this multi-tau tracer study, we focused on the new second-generation tau PET tracers PI2620, MK6240 and RO948 to investigate this tau complexity in AD, CBD, and PSP brains using post-mortem radioligand binding studies and autoradiography of large and small frozen brain sections. Saturation binding studies indicated multiple binding sites for 3H-PI2620 in AD, CBD and PSP brains with different binding affinities (Kd ranging from 0.2 to 0.7 nM) and binding site densities (following the order: BmaxAD > BmaxCBD > BmaxPSP). Competitive binding studies complemented these findings, demonstrating the presence of two binding sites [super-high affinity (SHA): IC50(1) = 8.1 pM; and high affinity (HA): IC50(2) = 4.9 nM] in AD brains. Regional binding distribution studies showed that 3H-PI2620 could discriminate between AD (n = 6) and control cases (n = 9), especially in frontal cortex and temporal cortex tissue (p < 0.001) as well as in the hippocampal region (p = 0.02). 3H-PI2620, 3H-MK6240 and 3H-RO948 displayed similar binding behaviour in AD brains (in both homogenate competitive studies and one large frozen hemispherical brain section autoradiography studies) in terms of binding affinities, number of sites and regional patterns. Our small section autoradiography studies in the frontal cortex of CBD (n = 3) and PSP brains (n = 2) showed high specificity for 3H-PI2620 but not for 3H-MK6240 or 3H-RO948. Our findings clearly demonstrate different binding properties among the second-generation tau PET tracers, which may assist in further understanding of tau heterogeneity in AD versus non-AD tauopathies and suggests potential for development of pure selective 4R tau PET tracers.

Site-Specific Phospho-Tau Aggregation-Based Biomarker Discovery for AD Diagnosis and Differentiation.

Tau aggregates are present in multiple neurodegenerative diseases known as "tauopathies," including Alzheimer's disease (AD), Pick's disease (PiD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). Such misfolded tau aggregates are therefore potential sources for tauopathy biomarker discovery. Using the tau antibody screening approach targeting high-molecular-weight misfolded tau aggregates, we tested several tau antibodies and a comprehensive set of site-specific phospho-tau (p-tau) antibodies targeting tau phosphorylation sites showing high frequencies in AD subjects. Our screens revealed that site-specific p-tau antibodies can not only differentiate AD from non-AD brains, but also discriminate AD from rare tauopathies PiD, PSP, and CBD brains. Differential detection of tau aggregates identified several novel p-tau sites as potential new biomarkers. As a proof-of-principle example, we showed that p-tau198 is a novel promising AD biomarker with sensitivity and specificity comparable with the existing biomarkers p-tau181 and p-tau217. Our results demonstrated that p-tau198 detection can not only differentiate AD from non-AD controls, but also diagnose AD from related 4R tauopathies PSP and CBD with AUCs of 0.96-0.99 (95% CI ranges from 0.90 to 1.00). Promisingly, p-tau198 was able to discriminate mild cognitive impairment from cognitively normal brains with an AUC of 0.75 (95% CI = 0.58-0.92). Our work provides a new avenue for developing diagnosis and differentiation tools for AD and related tauopathies.

Actin-binding protein filamin-A drives tau aggregation and contributes to progressive supranuclear palsy pathology.

While amyloid-β lies upstream of tau pathology in Alzheimer’s disease, key drivers for other tauopathies, including progressive supranuclear palsy (PSP), are largely unknown. Various tau mutations are known to facilitate tau aggregation, but how the nonmutated tau, which most cases with PSP share, increases its propensity to aggregate in neurons and glial cells has remained elusive. Here, we identified genetic variations and protein abundance of filamin-A in the PSP brains without tau mutations. We provided in vivo biochemical evidence that increased filamin-A levels enhance the phosphorylation and insolubility of tau through interacting actin filaments. In addition, reduction of filamin-A corrected aberrant tau levels in the culture cells from PSP cases. Moreover, transgenic mice carrying human filamin-A recapitulated tau pathology in the neurons. Our data highlight that filamin-A promotes tau aggregation, providing a potential mechanism by which filamin-A contributes to PSP pathology.

Analysis of modular gene co-expression networks reveals molecular pathways underlying Alzheimer's disease and progressive supranuclear palsy.

A comprehensive understanding of the pathological mechanisms involved at different stages of neurodegenerative diseases is key for the advance of preventive and disease-modifying treatments. Gene expression alterations in the diseased brain is a potential source of information about biological processes affected by pathology. In this work, we performed a systematic comparison of gene expression alterations in the brains of human patients diagnosed with Alzheimer’s disease (AD) or Progressive Supranuclear Palsy (PSP) and animal models of amyloidopathy and tauopathy. Using a systems biology approach to uncover biological processes associated with gene expression alterations, we could pinpoint processes more strongly associated with tauopathy/PSP and amyloidopathy/AD. We show that gene expression alterations related to immune-inflammatory responses preponderate in younger, whereas those associated to synaptic transmission are mainly observed in older AD patients. In PSP, however, changes associated with immune-inflammatory responses and synaptic transmission overlap. These two different patterns observed in AD and PSP brains are fairly recapitulated in animal models of amyloidopathy and tauopathy, respectively. Moreover, in AD, but not PSP or animal models, gene expression alterations related to RNA splicing are highly prevalent, whereas those associated with myelination are enriched both in AD and PSP, but not in animal models. Finally, we identify 12 AD and 4 PSP genetic risk factors in cell-type specific co-expression modules, thus contributing to unveil the possible role of these genes to pathogenesis. Altogether, this work contributes to unravel the potential biological processes affected by amyloid versus tau pathology and how they could contribute to the pathogenesis of AD and PSP.

Non-invasive imaging of tau-targeted probe uptake by whole brain multi-spectral optoacoustic tomography

PurposeAbnormal tau accumulation within the brain plays an important role in tauopathies such as Alzheimer’s disease and frontotemporal dementia. High-resolution imaging of tau deposits at the whole-brain scale in animal disease models is highly desired.MethodsWe approached this challenge by non-invasively imaging the brains of P301L mice of 4-repeat tau with concurrent volumetric multi-spectral optoacoustic tomography (vMSOT) at ~ 115 μm spatial resolution using the tau-targeted pyridinyl-butadienyl-benzothiazole derivative PBB5 (i.v.). In vitro probe characterization, concurrent vMSOT and epi-fluorescence imaging of in vivo PBB5 targeting (i.v.) was performed in P301L and wild-type mice, followed by ex vivo validation using AT-8 antibody for phosphorylated tau.ResultsPBB5 showed specific binding to recombinant K18 tau fibrils by fluorescence assay, to post-mortem Alzheimer’s disease brain tissue homogenate by competitive binding against [11C]PBB3 and to tau deposits (AT-8 positive) in post-mortem corticobasal degeneration and progressive supranuclear palsy brains. Dose-dependent optoacoustic and fluorescence signal intensities were observed in the mouse brains following i.v. administration of different concentrations of PBB5. In vivo vMSOT brain imaging of P301L mice showed higher retention of PBB5 in the tau-laden cortex and hippocampus compared to wild-type mice, as confirmed by ex vivo vMSOT, epi-fluorescence, multiphoton microscopy, and immunofluorescence staining.ConclusionsWe demonstrated non-invasive whole-brain imaging of tau in P301L mice with vMSOT system using PBB5 at a previously unachieved ~ 115 μm spatial resolution. This platform provides a new tool to study tau spreading and clearance in a tauopathy mouse model, foreseeable in monitoring tau targeting putative therapeutics.

Alzheimer's disease and progressive supranuclear palsy share similar transcriptomic changes in distinct brain regions.

Vast numbers of differentially expressed genes and perturbed networks have been identified in Alzheimer’s disease (AD), however, neither disease nor brain region specificity of these transcriptome alterations has been explored. Using RNA-Seq data from 231 temporal cortex and 224 cerebellum samples from patients with AD and progressive supranuclear palsy (PSP), a tauopathy, we identified a striking correlation in the directionality and magnitude of gene expression changes between these 2 neurodegenerative proteinopathies. Further, the transcriptomic changes in AD and PSP brains ware highly conserved between the temporal and cerebellar cortices, indicating that highly similar transcriptional changes occur in pathologically affected and grossly less affected, albeit functionally connected, areas of the brain. Shared up- or downregulated genes in AD and PSP are enriched in biological pathways. Many of these genes also have concordant protein changes and evidence of epigenetic control. These conserved transcriptomic alterations of 2 distinct proteinopathies in brain regions with and without significant gross neuropathology have broad implications. AD and other neurodegenerative diseases are likely characterized by common disease or compensatory pathways with widespread perturbations in the whole brain. These findings can be leveraged to develop multifaceted therapies and biomarkers that address these common, complex, and ubiquitous molecular alterations in neurodegenerative diseases.

Dysregulated coordination of MAPT exon 2 and exon 10 splicing underlies different tau pathologies in PSP and AD.

Understanding regulation of MAPT splicing is important to the etiology of many nerurodegenerative diseases, including Alzheimer disease (AD) and progressive supranuclear palsy (PSP), in which different tau isoforms accumulate in pathologic inclusions. MAPT, the gene encoding the tau protein, undergoes complex alternative pre-mRNA splicing to generate six isoforms. Tauopathies can be categorized by the presence of tau aggregates containing either 3 (3R) or 4 (4R) microtubule-binding domain repeats (determined by inclusion/exclusion of exon 10), but the role of the N-terminal domain of the protein, determined by inclusion/exclusion of exons 2 and 3 has been less well studied. Using a correlational screen in human brain tissue, we observed coordination of MAPT exons 2 and 10 splicing. Expressions of exon 2 splicing regulators and subsequently exon 2 inclusion are differentially disrupted in PSP and AD brain, resulting in the accumulation of 1N4R isoforms in PSP and 0N isoforms in AD temporal cortex. Furthermore, we identified different N-terminal isoforms of tau present in neurofibrillary tangles, dystrophic neurites and tufted astrocytes, indicating a role for differential N-terminal splicing in the development of disparate tau neuropathologies. We conclude that N-terminal splicing and combinatorial regulation with exon 10 inclusion/exclusion is likely to be important to our understanding of tauopathies.

Understanding the transcriptional (dys)regulation in progressive supranuclear palsy

Progressive Supranuclear Palsy (PSP) is an incurable, neurodegenerative parkinsonian disorder characterized by tau proteinopathy in multiple brain cell types. We previously reported global gene expression changes associated with neuropathologic endophenotypes in PSP. In this study, we expanded this work to brain RNA sequence (RNAseq) transcriptome data from two independent cohorts and assessed both bulk and analytically deconvoluted transcriptome integrated with other omics data from humans and mice to discover dysregulated genes and networks in PSP. Transcriptome was measured in 408 temporal cortex samples from two independent cohorts of PSP and control brains, all of which had quantitative neuropathology scores. Differentially expressed genes (DEG) were identified using both bulk and analytically deconvoluted transcriptome for each brain cell type. Weighted Gene Co-expression Network Analysis (WGCNA) was used to construct modules, which were annotated for enrichment of Gene Ontology terms and cell type markers. We sought validations using a multitude of complementary datasets, including PSP GWAS, eQTL, proteome data and tau transgenic mouse models. There were 22,560 genes detected in both cohorts of which 1,709 were significantly differentially expressed. Among the DEGs, 721 genes also had nominal associations with one or more neuropathology endophenotypes. Additionally, 104 of the bulk DEGs were also differentially expressed in one of the brain cell types, i.e. were cell-intrinsic DEGs (CI-DEGs). There were 23 co-expression network modules, 10 of which were enriched for brain cell type markers; 8 of these also demonstrated enrichment of CI-DEGs of the corresponding cell-type. Importantly, 3 of these 8 modules also associated with PSP diagnosis. The most significant modules were enriched for oligodendrocyte and astrocyte genes and CI-DEGs. Most notably, we identified one module with enrichment of oligodendrocyte gene markers that are likewise downregulated in PSP. This module was also enriched with myelin gene expression changes identified in oligodendrocyte CI-DEGs. The expression profile of PSP brain changes in a cell-specific manner. Astrocyte and oligodendrocyte gene expression appears most impacted in PSP. Our findings implicate novel genes and pathways which underlie disease risk and neuropathology in PSP and may serve as novel therapeutic and biomarker targets.

Investigating astrocytes as mediators of tau spread.

Highly phosphorylated tau aggregates spread in a prion-like manner through tauopathy brain. Increasing evidence suggests that astrocytes may influence tau spread, with recent data describing mechanisms of tau uptake my astrocytes. However, the efficiency of uptake of different disease-associated tau species is not well defined, nor is the effects of tau uptake on astrocyte reactivity and function. We have investigated the relationship between tau seeds and reactive astrocytes in htau mice and in human astrocyte cultures. Tau was isolated from human postmortem control (CTRL), Alzheimer's disease (AD), progressive supranuclear palsy (PSP) and Pick's disease (PiD) brain and injected intraperitoneally into 4-month old wild-type and htau mice. Brains and other tissues were collected for biochemical and immunohistochemical analysis of tau aggregated burden in different brain regions when mice reached 18 months of age. Human iPSC-derived astrocytes and iNPC-astrocytes were established and their gene and protein expression profiles characterised. Aggregated tau was isolated from postmortem human brain for spiking into astrocyte cultures. Cells were analysed for efficiency of tau uptake and astrocyte reactivity. Peripheral injection of brain extracts from AD, PSP and PiD brain resulted in regional differences in the patterns of tau aggregate accumulation in htau mouse brain. Tau pathology was commonly associated with reactive astrocytes. Cultures of human iPSC-derived astrocytes and iNPC-astrocytes that express mature astrocyte markers were established. Both types of cell culture were found to internalise tau extracts from human postmortem brain. Furthermore, preliminary analysis indicates alterations in astrocyte reactivity following tau uptake. Our data suggests that neurons in different regions are selectively vulnerable to tau aggregates from different tauopathies. Our human astrocyte cultures demonstrate that astrocytes can internalise tau seeds and alter their reactivity and potentially their functions. Further investigations will determine the mechanisms of tau uptake and the downstream effects on astrocyte signalling and functional changes, providing further insights into how astrocytes may affect the spread of tau and potentially contribute to selective regional vulnerability in tauopathies.

Stem cell models of primary tauopathies reveal defects in synaptic function.

Primary tauopathies are characterized neuropathologically by inclusions containing abnormal forms of the microtubule-associated protein tau (MAPT) and clinically by diverse neuropsychiatric, cognitive, and motor impairments. Autosomal dominant mutations in the MAPT gene cause heterogeneous forms of frontotemporal lobar degeneration with tauopathy (FTLD-Tau). Common and rare variants in the MAPT gene increase the risk for sporadic FTLD-Tau, including progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). We generated a collection of fibroblasts from 140 MAPT mutation/risk variant carriers, PSP, CBD, and cognitively normal controls; 31 induced pluripotent stem cell (iPSC) lines from MAPT mutation carriers, non-carrier family members, and autopsy-confirmed PSP patients; 33 genome engineered iPSCs that were corrected or mutagenized; and forebrain neural progenitor cells (NPCs). To begin to identify the genes and pathways that are dysregulated in primary tauopathies, we performed transcriptomic analyses in induced pluripotent stem cell (iPSC)-derived neurons carrying MAPT p.R406W and CRISPR/Cas9-corrected isogenic controls. We found that the expression of the MAPT p.R406W mutation was sufficient to create a significantly different transcriptomic profile compared with that of the isogeneic controls and to cause the differential expression of 328 genes. Sixty-one of these genes were also differentially expressed between MAPT p.R406W carriers and control brains. Twelve of these genes are also differentially expressed between PSP and control brains. Together, these genes are enriched for pathways involved in GABA-mediated signaling and synaptic function, which may contribute to the pathogenesis of FTLD-tau and other primary tauopathies. Here, we present a resource of fibroblasts, iPSCs, and NPCs with comprehensive clinical histories that can be accessed by the scientific community for disease modeling and development of novel therapeutics for tauopathies.

Molecular Processing of Tau Protein in Progressive Supranuclear Palsy: Neuronal and Glial Degeneration.

Background:Alzheimer’s disease (AD) and progressive supranuclear palsy (PSP) are examples of neurodegenerative diseases, characterized by abnormal tau inclusions, that are called tauopathies. AD is characterized by highly insoluble paired helical filaments (PHFs) composed of tau with abnormal post-translational modifications. PSP is a neurodegenerative disease with pathological and clinical heterogeneity. There are six tau isoforms expressed in the adult human brain, with repeated microtubule-binding domains of three (3R) or four (4R) repeats. In AD, the 4R:3R ratio is 1:1. In PSP, the 4R isoform predominates. The lesions in PSP brains contain phosphorylated tau aggregates in both neurons and glial cells.Objective:Our objective was to evaluate and compare the processing of pathological tau in PSP and AD.Methods:Double and triple immunofluorescent labeling with antibodies to specific post-translational tau modifications (phosphorylation, truncation, and conformational changes) and thiazin red (TR) staining were carried out and analyzed by confocal microscopy.Results:Our results showed that PSP was characterized by phosphorylated tau in neurofibrillary tangles (NFTs) and glial cells. Tau truncated at either Glu391 or Asp421 was not observed. Extracellular NFTs (eNFTs) and glial cells in PSP exhibited a strong affinity for TR in the absence of intact or phosphorylated tau.Conclusion:Phosphorylated tau was as abundant in PSP as in AD. The development of eNFTs from both glial cells and neuronal bodies suggests that truncated tau species, different from those observed in AD, could be present in PSP. Additional studies on truncated tau within PSP lesions could improve our understanding of the pathological processing of tau and help identify a discriminatory biomarker for AD and PSP.

Iron accumulation in the oculomotor nerve of the progressive supranuclear palsy brain

Abnormal iron accumulation around the substantia nigra (SN) is a diagnostic indicator of Parkinsonism. This study aimed to identify iron-related microarchitectural changes around the SN of brains with progressive supranuclear palsy (PSP) via postmortem validations and in vivo magnetic resonance imaging (MRI). 7 T high-resolution MRI was applied to two postmortem brain tissues, from one normal brain and one PSP brain. Histopathological examinations were performed to demonstrate the molecular origin of the high-resolution postmortem MRI findings, by using ferric iron staining, myelin staining, and two-dimensional laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging. In vivo iron-related MRI was performed on five healthy controls, five patients with Parkinson’s disease (PD), and five patients with PSP. In the postmortem examination, excessive iron deposition along the myelinated fiber at the anterior SN and third cranial nerve (oculomotor nerve) fascicles of the PSP brain was verified by LA-ICP-MS. This region corresponded to those with high R2* values and positive susceptibility from quantitative susceptibility mapping (QSM), but was less sensitive in Perls’ Prussian blue staining. In in vivo susceptibility-weighted imaging, hypointense pixels were observed in the region between the SN and red nucleus (RN) in patients with PSP, but not in healthy controls and patients with PD. R2* and QSM values of such region were significantly higher in patients with PSP compared to those in healthy controls and patients with PD as well (vs. healthy control: p = 0.008; vs. PD: p = 0.008). Thus, excessive iron accumulation along the myelinated fibers at the anterior SN and oculomotor nerve fascicles may be a pathological characteristic and crucial MR biomarker in a brain with PSP.

Post-Mortem 7.0-Tesla Magnetic Resonance Imaging of the Hippocampus in Progressive Supranuclear Palsy with and without Cerebral Amyloid Angiopathy

Introduction and Purpose: Cerebral amyloid angiopathy (CAA) can be observed in patients with progressive supranuclear palsy (PSP), though to a lesser degree than in Alzheimer’s disease. The present post-mortem 7.0-tesla magnetic resonance imaging (MRI) evaluates whether CAA has an influence on the degree of hippocampal atrophy (HA) and on the incidence of associated micro-infarcts (HMIs) and cortical micro-bleeds (HMBs). Material and Methods: Eight brains with PSP-CAA were compared to 20 PSP brains without CAA. In addition to the neuropathological examination, the hippocampus was evaluated on the most representative coronal section with T2 and T2*-weighted MRI sequences. The average degree of HA was determined in both groups. The incidence of HMIs and HMBs was also compared as well as the frequency of cortical micro-infarcts (CoMIs) and cortical micro-bleeds (CoMBs) in the hemispheric neocortex. Results: The neuropathological examination showed a higher incidence of lacunar infarcts in the PSP-CAA brains compared to the PSP ones. With magnetic resonance imaging (MRI), the severity of HA and the incidence of HMIs and HMBs was similar between both groups. Additionally, the frequency of CoMIs and CoMBs in the neocortex was comparable. Conclusions: The association of CAA in PSP brains has no influence on the degree of HA and on the incidence of the small cerebrovascular lesions in the hippocampus as well as in the neocortex.