Microtubule-associated Protein Tau Mutations Research Articles

Long Non-Coding RNA Profile in Genetic Symptomatic and Presymptomatic Frontotemporal Dementia: A GENFI Study.

Long non-coding RNAs (lncRNAs) play crucial roles in gene regulation and are implicated in neurodegenerative diseases, including frontotemporal dementia (FTD). However, their expression patterns and potential as biomarkers in genetic FTD involving Chromosome 9 Open Reading Frame (C9ORF72), Microtubule Associated Protein Tau (MAPT), and Progranulin (GRN) genes are not well understood. This study aimed to profile the expression levels of lncRNAs in peripheral blood mononuclear cells collected within the GENetic Frontotemporal dementia Initiative (GENFI). Fifty-three lncRNAs were analyzed with the OpenArray Custom panel, in 131 patients with mutations in C9ORF72, MAPT, and GRN, including 68 symptomatic mutation carriers (SMC) and 63 presymptomatic mutation carriers (PMC), compared with 40 non-carrier controls (NC). Thirty-eight lncRNAs were detectable; the relative expression of NEAT1 and NORAD was significantly higher in C9ORF72 SMC as compared with NC. GAS5 expression was instead significantly lower in the GRN group versus NC. MAPT carriers showed no significant deregulations. No significant differences were observed in PMC. Disease duration did not correlate with lncRNA expression. NEAT1 and NORAD are upregulated in C9ORF72 SMC and GAS5 levels are downregulated in GRN SMC, underlining lncRNAs' relevance in FTD and their potential for biomarker development. Further validation and mechanistic studies are crucial for clinical implications.

P.002 Distinct neuropsychiatric symptom trajectories in frontotemporal dementia across genetic mutations

Background: Frontotemporal dementia (FTD) often presents with varying neuropsychiatric symptoms (NPS), which may differ based on genetic mutations. We hypothesized distinct NPS trajectories in FTD progression among carriers of chromosome 9 open reading frame 72 (C9orf72), progranulin (GRN), and microtubule-associated protein tau (MAPT) mutations. Methods: We analyzed 1662 participants from ALLFTD, including 342 C9orf72, 148 GRN, 168 MAPT mutation carriers, and 1004 noncarriers. We categorized participants into four stages based on CDR plus NACC FTLD global scores: 1) Presymptomatic (consistent CDR=0), 2) Early conversion (CDR increasing from 0 to 0.5), 3) Advanced conversion (CDR increasing from 0.5 to ≥1.0), and 4) Symptomatic (CDR>1.0). The Neuropsychiatric Inventory-Questionnaire (NPI-Q) assessed NPS changes, analyzed using a mixed-effects model, accounting for age and baseline scores. Results: Our results indicated similar NPS trajectories in the presymptomatic stage for all groups. Notably, during early conversion, C9orf72 and GRN carriers exhibited significantly higher NPI-Q score increases than MAPT carriers, primarily in psychosis and hyperactivity domains. In later stages, increases in NPS were similar across groups. Conclusions: This study suggests familial FTD progression, particularly in TDP-43 pathology, may involve more severe NPS like psychosis or hyperactivity, differing from tau pathology or sporadic FTD. Further research is needed to explore these distinct trajectories.

Changes in Oxidised Phospholipids in Response to Oxidative Stress in Microtubule-Associated Protein Tau (MAPT) Mutant Dopamine Neurons.

Microtubule-associated protein Tau (MAPT) is strongly associated with the development of neurodegenerative diseases. In addition to driving the formation of neurofibrillary tangles (NFT), mutations in the MAPT gene can also cause oxidative stress through hyperpolarisation of the mitochondria. This study explores the impact that MAPT mutation is having on phospholipid metabolism in iPSC-derived dopamine neurons, and to determine if these effects are exacerbated by mitochondrial and endoplasmic reticulum stress. Neurons that possessed a mutated copy of MAPT were shown to have significantly higher levels of oxo-phospholipids (Oxo-PL) than wild-type neurons. Oxidation of the hydrophobic fatty acid side chains changes the chemistry of the phospholipid leading to disruption of membrane function and potential cell lysis. In wild-type neurons, both mitochondrial and endoplasmic reticulum stress increased Oxo-PL abundance; however, in MAPT mutant neurons mitochondrial stress appeared to have a minimal effect. Endoplasmic reticulum stress, surprisingly, reduced the abundance of Oxo-PL in MAPT mutant dopamine neurons, and we postulate that this reduction could be modulated through hyperactivation of the unfolded protein response and X-box binding protein 1. Overall, the results of this study contribute to furthering our understanding of the regulation and impact of oxidative stress in Parkinson's disease pathology.

MAPT Mutations V337M and N297K Alter Organelle Trafficking in Frontotemporal Dementia Patient-Specific Motor Neurons.

Frontotemporal dementia (FTD) is a neurodegenerative disease characterized by the progressive loss of neurons mainly in the frontal and temporal lobes of the brain. Mutations (e.g., V337M, N297K) in the microtubule-associated protein TAU (MAPT) are responsible 5-20% of familial FTD cases and have been associated with defects in organelle trafficking that plays a critical role in the proper function of cells, including transport of essential molecules and degradation of waste products. Due to the critical role of TAU mutations in microtubule stabilization and organelle transportation, it is of great interest to study these molecular mechanisms to develop effective therapeutic strategies. Therefore, herein, we analyzed mitochondrial and lysosomal trafficking in disease-specific spinal motor neurons by using live cell imaging in undirected (uncompartmentalized) and directed (compartmentalized) cell culture systems. While V337M neurons only expressed 3R TAU, the N297K mutant neurons expressed both 3R and 4R TAU. Axonal trafficking was affected differentially in V337M and N297 MAPT mutated neurons. These findings suggest that the MAPT mutations V337M and N297K impaired axon physiology differentially, which highlights the need for mutation- and/or 3R/4R TAU-specific therapeutic approaches.

The MAPT P.G324L and P.A406G mutations are associated with progressive supranuclear palsy with atypical features

IntroductionProgressive supranuclear palsy (PSP) is an atypical parkinsonism caused by the intracerebral aggregation of the microtubule-associated protein tau (MAPT) which is encoded by MAPT gene. Although PSP is a sporadic disease, MAPT mutations have been reported in rare cases. MethodsAmong 190 patients with PSP who were recruited by the Neurodegenerative Research Group at Mayo Clinic during 2009–2023, we identified two patients who fulfilled diagnostic criteria for PSP-Richardson's syndrome (PSP-RS) and harbor novel MAPT mutations. To better investigate the potential effects of these mutations, we compared the clinical, and neuroimaging characteristics of these two patients to 20 randomly selected patients with PSP-RS without a MAPT mutation. ResultsMAPT c.1024G > A, p. Glu342Lys, and MAPT c.1217 G > A, p. Arg406Gln mutations were found in 2 men who developed PSP-RS with atypical features at the ages of 60 and 62 years, respectively. Glu342Lys mutation was associated with features resembling alpha-synucleinopathies (autonomic dysfunction, dream enactment behavior), while both mutations were associated with features suggestive of Alzheimer's disease with poorer performance on tests of episodic memory. Comparison of 18F-flortaucipir uptake between the two MAPT mutation cases with 20 patients without a mutation revealed increased signal on flortaucipir-PET in bilateral medial temporal lobe regions (amygdala, entorhinal cortices, hippocampus, parahippocampus) but not in PSP-related regions (globus pallidum, midbrain, superior frontal cortex and dentate nucleus of the cerebellum). ConclusionGlu342Lys and Arg406Gln mutations appear to modify the PSP-RS phenotype by targeting the medial temporal lobe regions resulting in more memory loss and greater flortaucipir uptake.

Development and characterization of a robust in vitro disease cell line to study tauopathies

AbstractBackgroundTauopathies, such as frontotemporal dementia (FTD) and Alzheimer’s dimentia (AD), are neurodegenerative diseases characterized by the pathological aggregation of paired helical filaments (PHFs) or neurofibrillary tangles (NFTs) within neurons and glia, leading to cell death1. PHFs and NFTs are formed by aggregation of hyperphosphorylated tau1. Mutations in the microtubule‐associated protein tau (MAPT) gene result in tauopathies. Moreover, FTD is a common clinical syndrome of 4 repeat (4R) tauopathies, as defined by aggregation of tau protein isoforms with four microtubule binding domains2. Here, we aimed to develop and characterize a physiologically relevant and robust in vitro FTD model, to aid the future development of FTD disease therapeutics.MethodUsing CRISPR‐Cas9 gene editing technology, familial mutations MAPT P301S and N279K underlying AD/FTD3 were engineered into an iPSC line that carries the opti‐oxTM technology and can rapidly be reprogrammed into glutamatergic neurons4. By means of immunocytochemistry we characterized b‐amyloid oligomer treated neurons, and neurons with the MAPT mutations to assess tau hyperphosphorylation.ResultThe CRISPR‐edited MAPT neurons can mature and show a healthy morphology. b‐amyloid oligomers (dose dependently) induce tau hyperphosphorylation in wild type glutamatergic neurons. Total tau expression is reduced in MAPT P301S homozygous and N279K heterozygous cells when compared to wild type cells. The MAPT P301S cells also show hyperphosphorylation for p‐tau 217, p‐tau202/205, and p‐tau404, and the N279K cells show hyperphosphorylation for p‐tau202/205, and p‐tau404.ConclusionThe elevated p‐tau to total tau ratio measured by the immunocytochemistry assay indicates the potential of at least two cell lines as possible disease models to aid future research into developing AD/FTD disease therapeutics.

Parkinson-ALS with a novel MAPT variant

The mutations on microtubule associated protein tau (MAPT) gene manifest clinically with behavioural frontotemporal dementia (FTD), parkinsonism, such as progressive supranuclear palsy and corticobasal degeneration, and rarely with amyotrophic lateral sclerosis (ALS). FTD-parkinsonism and FTD-ALS are clinical overlaps included in the spectrum of MAPT mutation’s phenotypes. The mutations on MAPT gene cause the dysfunction of tau protein determining its accumulation in neurofibrillary tangles. Recent data describe frequently the co-occurrence of the aggregation of tau protein and α-synuclein in patients with parkinsonism and Parkinson disease (PD), suggesting an interaction of the two proteins in determining neurodegenerative process. The sporadic description of PD-ALS clinical complex, known as Brait–Fahn–Schwarz disease, supports the hypothesis of common neuropathological pathways between different disorders. Here we report the case of a 54-year-old Italian woman with idiopathic PD later complicated by ALS carrying a novel MAPT variant (Pro494Leu). The variant is characterized by an amino acid substitution and is classified as damaging for MAPT functions. The case supports the hypothesis of tau dysfunction as the basis of multiple neurodegenerative disorders.

Network Connectivity Alterations across the MAPT Mutation Clinical Spectrum.

Microtubule-associated protein tau (MAPT) mutations cause frontotemporal lobar degeneration, and novel biomarkers are urgently needed for early disease detection. We used task-free functional magnetic resonance imaging (fMRI) mapping, a promising biomarker, to analyze network connectivity in symptomatic and presymptomatic MAPT mutation carriers. We compared cross-sectional fMRI data between 17 symptomatic and 39 presymptomatic carriers and 81 controls with (1) seed-based analyses to examine connectivity within networks associated with the 4 most common MAPT-associated clinical syndromes (ie, salience, corticobasal syndrome, progressive supranuclear palsy syndrome, and default mode networks) and (2) whole-brain connectivity analyses. We applied K-means clustering to explore connectivity heterogeneity in presymptomatic carriers at baseline. Neuropsychological measures, plasma neurofilament light chain, and gray matter volume were compared at baseline and longitudinally between the presymptomatic subgroups defined by their baseline whole-brain connectivity profiles. Symptomatic and presymptomatic carriers had connectivity disruptions within MAPT-syndromic networks. Compared to controls, presymptomatic carriers showed regions of connectivity alterations with age. Two presymptomatic subgroups were identified by clustering analysis, exhibiting predominantly either whole-brain hypoconnectivity or hyperconnectivity at baseline. At baseline, these two presymptomatic subgroups did not differ in neuropsychological measures, although the hypoconnectivity subgroup had greater plasma neurofilament light chain levels than controls. Longitudinally, both subgroups showed visual memory decline (vs controls), yet the subgroup with baseline hypoconnectivity also had worsening verbal memory and neuropsychiatric symptoms, and extensive bilateral mesial temporal gray matter decline. Network connectivity alterations arise as early as the presymptomatic phase. Future studies will determine whether presymptomatic carriers' baseline connectivity profiles predict symptomatic conversion. ANN NEUROL 2023;94:632-646.

18F‐fluorodeoxyglucose‐positron emission tomography Findings in Patients with Genetic Frontotemporal Dementia

AbstractBackgroundMutations in microtubule‐associated protein tau (MAPT), granulin (GRN), and hexanucleotide expansion repeat in the open reading frame of chromosome 9 (C9orf72) are found in 60% of familial frontotemporal dementia (FTD) cases. The current study aims to delineate brain regions with reduced glucose metabolism in patients with genetic FTD in comparison with cognitively normal controls.Methods(18)F‐ fluorodeoxyglucose (FDG)‐positron emission tomography (PET) images were retrospectively obtained from 17 genetic FTD patients. All patients were symptomatic at the time of imaging, and the autopsy was available for 13. Pittsburgh compound B (PiB) amyloid PET scans were done for 13 patients (Table 1). FDG‐PET was collected at Lawrence Berkeley National Laboratory on a PET or PET‐CT scanner as six 5‐min frames acquired 30 min post tracer injection. Standard Uptake Value Ratio (SUVR) images were created for each patient using pons as a reference region. W‐score (age‐adjusted Z‐score) maps were created for each patient’s FDG SUVR using a group of neurologically unimpaired controls (N=74, Mean age 65+16, 41 female) as reference.ResultOn review of single‐subject w‐maps, all patients with MAPT mutation showed hypometabolism in the anteromedial temporal lobes with 66% showing anterolateral temporal hypometabolism and 33% in the frontal and dorsolateral parietal lobes. Hypometabolism in temporal lobes was seen in all GRN patients and 75% had frontal and parietal hypometabolism in an asymmetric pattern. 80% of theC9orf72 patients had hypometabolism in anteromedial temporal and orbitofrontal regions. 60% showed hypometabolism in dorsolateral prefrontal, medial frontal, and anterolateral temporal lobes. Posterior temporal, posterior cingulate, parietal lobe, cerebellum, insula, thalamus, and caudate were hypometabolic in less than 40% of the C9orf72 patients (Figure 1).On group‐level analysis, compared to controls, patients with C9orf72 showed hypometabolism in the frontotemporal regions, cerebellum and thalamus. Hypometabolism in the frontotemporal and parietal regions was seen with GRN mutation. MAPT mutation carriers showed frontal and anteromedial temporal hypometabolism (Figure 2).ConclusionHypometabolism in the posterior regions and cerebellum is more suggestive of C9orf72 repeat expansion. An asymmetric pattern of hypometabolism was seen in all GRN mutation carriers. MAPT mutation resulted in a greater degree of hypometabolism in the anterior medial temporal lobes.

Optogenetic model of tau aggregation for tauopathies

AbstractBackgroundAlzheimer’s disease (AD) and >20 other dementias, termed tauopathies, are pathologically defined by insoluble aggregates of the microtubule‐associated protein tau (MAPT). A predictive relationship between the onset and progression of clinical AD symptoms correlates with post‐translational modifications of tau in cerebrospinal fluid and tau aggregation in the brains of AD patients. However, the biological basis for the transition of tau from a microtubule‐associated protein to an insoluble aggregate and the precise relationship between tau aggregation and neuronal dysfunction remains unknown. Recent studies have reported the development of photo‐inducible systems to control protein aggregation using photo‐oligomerizable proteins that self‐associate upon exposure to blue light. We hypothesized that the development of a photo‐inducible system, which permits temporal control of tau aggregation, would provide a novel tool to study the cause and consequence of tau aggregation.MethodsWe fused Vivid (VVD), a photoreceptor that self‐associates upon exposure to blue light, to full‐length (2N4R) tau, termed optoTAU. In addition, we generated optoTAU plasmids that contain other MAPT isoforms (e.g., 0N4R, 1N4R) and pro‐ and anti‐aggregation mutations in MAPT. We investigated the effect of blue stimulation on the soluble and insoluble aggregation of optoTAU in a cellular and neuronal model by immunoblot and immunocytochemical analysis.ResultsOptoTAU permits temporal control of tau aggregation that faithfully reproduces the isoform‐specific and dementia‐associated aggregation properties of tau. OptoTAU provides a platform to visualize the transition of tau from a soluble to an insoluble aggregate in a cellular model of tau aggregation.ConclusionsOptoTAU is a biologically‐relevant model to investigate modifiers of tau pathobiology in AD and other tauopathies and is a drug discovery platform to identify pharmacological modifiers of tau aggregation.

Circulating Non-Coding RNA Levels Are Altered in Autosomal Dominant Frontotemporal Dementia.

Frontotemporal Dementia (FTD) represents a highly heritable neurodegenerative disorder. Most of the heritability is caused by autosomal dominant mutations in the Microtubule-Associated Protein Tau (MAPT), Progranulin (GRN), and the pathologic exanucleotide expansion of C9ORF72 genes. At the pathological level, either the tau or the TAR DNA-binding protein (TDP-43) account for almost all cases of FTD. Pathogenic mechanisms are just arising, and the emerging role of non-coding RNAs (ncRNAs), such as microRNAs (miRNA) and long non-coding RNAs (lncRNAs), have become increasingly evident. Using specific arrays, an exploratory analysis testing the expression levels of 84 miRNAs and 84 lncRNAs has been performed in a population consisting of 24 genetic FTD patients (eight GRN, eight C9ORF72, and eight MAPT mutation carriers), eight sporadic FTD patients, and eight healthy controls. The results showed a generalized ncRNA downregulation in patients carrying GRN and C9ORF72 when compared with the controls, with statistically significant results for the following miRNAs: miR-155-5p (Fold Change FC: 0.45, p = 0.037 FDR = 0.52), miR-15a-5p (FC: 0.13, p = 0.027, FDR = 1), miR-222-3p (FC: 0.13, p = 0.027, FDR = 0.778), miR-140-3p (FC: 0.096, p = 0.034, FRD = 0.593), miR-106b-5p (FC: 0.13, p = 0.02, FDR = 0.584) and an upregulation solely for miR-124-3p (FC: 2.1, p = 0.01, FDR = 0.893). Conversely, MAPT mutation carriers showed a generalized robust upregulation in several ncRNAs, specifically for miR-222-3p (FC: 22.3, p = 7 × 10-6, FDR = 0.117), miR-15a-5p (FC: 30.2, p = 0.008, FDR = 0.145), miR-27a-3p (FC: 27.8, p = 6 × 10-6, FDR = 0.0005), miR-223-3p (FC: 18.9, p = 0.005, FDR = 0.117), and miR-16-5p (FC: 10.9, p = 5.26 × 10-5, FDR = 0.001). These results suggest a clear, distinctive pattern of dysregulation among ncRNAs and specific enrichment gene pathways between mutations associated with the TDP-43 and tau pathologies. Nevertheless, these preliminary results need to be confirmed in a larger independent cohort.

Reconfigured metabolism brain network in asymptomatic microtubule-associated protein tau mutation carriers: a graph theoretical analysis

BackgroundStudies exploring topological properties of the metabolic network during the presymptomatic stage of genetic frontotemporal dementia (FTD) are scarce. However, such knowledge is important for understanding brain function and disease pathogenesis. Therefore, we aimed to explore FTD-specific patterns of metabolism topology reconfiguration in microtubule-associated protein tau (MAPT) mutation carriers before the onset of symptoms.MethodsSix asymptomatic carriers of the MAPT P301L mutation were compared with 12 non-carriers who all belonged to the same family of FTD. For comparison, we included 32 behavioral variant FTD (bvFTD) patients and 33 unrelated healthy controls. Each participant underwent neuropsychological assessments, genetic testing, and a hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI) scan. Voxel-wise gray matter volumes and standardized uptake value ratios were calculated and compared for structural MRI and fluorodeoxyglucose (FDG)-PET, separately. The sparse inverse covariance estimation method (SICE) was applied to topological properties and metabolic connectomes of brain functional networks derived from 18F-FDG PET/MRI data. Independent component analysis was used to explore the metabolic connectivity of the salience (SN) and default mode networks (DMN).ResultsThe asymptomatic MAPT carriers performed normal global parameters of the metabolism network, whereas bvFTD patients did not. However, we revealed lost hubs in the ventromedial prefrontal, orbitofrontal, and anterior cingulate cortices and reconfigured hubs in the anterior insula, precuneus, and posterior cingulate cortex in asymptomatic carriers compared with non-carriers, which overlapped with the comparisons between bvFTD patients and controls. Similarly, significant differences in local parameters of these nodes were present between asymptomatic carriers and non-carriers. The reduction in the connectivity of lost hub regions and the enhancement of connectivity between reconfigured hubs and components of the frontal cortex were marked during the asymptomatic stage. Metabolic connectivity within the SN and DMN was enhanced in asymptomatic carriers compared with non-mutation carriers but reduced in bvFTD patients relative to controls.ConclusionsOur findings showed that metabolism topology reconfiguration, characterized by the earliest involvement of medial prefrontal areas and active compensation in task-related regions, was present in the presymptomatic phase of genetic FTD with MAPT mutation, which may be used as an imaging biomarker of increased risk of FTD.

Anomia is present pre-symptomatically in frontotemporal dementia due to MAPT mutations

IntroductionA third of frontotemporal dementia (FTD) is caused by an autosomal-dominant genetic mutation in one of three genes: microtubule-associated protein tau (MAPT), chromosome 9 open reading frame 72 (C9orf72) and progranulin (GRN). Prior studies of prodromal FTD have identified impaired executive function and social cognition early in the disease but few have studied naming in detail.MethodsWe investigated performance on the Boston Naming Test (BNT) in the GENetic Frontotemporal dementia Initiative cohort of 499 mutation carriers and 248 mutation-negative controls divided across three genetic groups: C9orf72, MAPT and GRN. Mutation carriers were further divided into 3 groups according to their global CDR plus NACC FTLD score: 0 (asymptomatic), 0.5 (prodromal) and 1 + (fully symptomatic). Groups were compared using a bootstrapped linear regression model, adjusting for age, sex, language and education. Finally, we identified neural correlates of anomia within carriers of each genetic group using a voxel-based morphometry analysis.ResultsAll symptomatic groups performed worse on the BNT than controls with the MAPT symptomatic group scoring the worst. Furthermore, MAPT asymptomatic and prodromal groups performed significantly worse than controls. Correlates of anomia in MAPT mutation carriers included bilateral anterior temporal lobe regions and the anterior insula. Similar bilateral anterior temporal lobe involvement was seen in C9orf72 mutation carriers as well as more widespread left frontal atrophy. In GRN mutation carriers, neural correlates were limited to the left hemisphere, and involved frontal, temporal, insula and striatal regions.ConclusionThis study suggests the development of early anomia in MAPT mutation carriers, likely to be associated with impaired semantic knowledge. Clinical trials focused on the prodromal period within individuals with MAPT mutations should use language tasks, such as the BNT for patient stratification and as outcome measures.

Generation of an induced pluripotent stem cell line (ICNDXHi001-A) from a patient with frontotemporal dementia carrying a heterozygous mutation c.796C > G (p.L266V) in MAPT

Frontotemporal dementia (FTD) caused by microtubule-associated protein tau (MAPT) mutations is not rare and is almost fully penetrant. However, no disease-modifying treatment for FTD is currently available. Here, we demonstrated the establishment and characterization of a novel human induced pluripotent stem cell (iPSC) line ICNDXHi001-A from a patient with FTD carrying genetic variant MAPT c.796C > G (p.L266V). The generated cell line showed trilineage differentiation potential, expression of pluripotency markers, a normal karyotype, and retention of MAPT mutation. The study provides a useful model to further elucidate the underlying mechanisms of FTD and to facilitate novel therapy development.

Investigating changes in the proteostasis capabilities of iPSC‐neurons during development and in FTD using iPSC‐neurons with MAPT mutations

AbstractBackgroundMutations in microtubule‐associated protein tau (MAPT) gene are causative of Frontotemporal Dementia (FTD). Many of the features associated with the development of tau pathology, e.g high levels of tau phosphorylation, are also present in early development. iPSC‐neurons have gene expression signatures similar to fetal neurons, and iPSC‐neurons with MAPT mutations do not develop tau aggregates. We hypothesise that iPSC‐neurons are resistant to developing tau aggregates due to high activity levels of the proteostasis network during early development. To test this hypothesis, we investigated the levels of proteasome subunits in developing iPSC derived neurons and measured the proteasome activity of iPSC‐neurons throughout development. To test whether manipulation of proteostasis in iPSC‐neurons could lead to tau pathology we treated cells with a proteasome inhibitor, and measured changes in total and phosphorylated tau, proteasome subunits and autophagy regulators.MethodsHuman cortical neurons were derived from isogenic iPSCs with the following MAPT genotypes: WT, 10+16 monoallelic, 10+16 biallelic and 10+16/P301S biallelic. RNA and protein analysis of proteasome subunits was performed by qPCR and Western blot at during neuronal development (DIV 0, 10, 30 and 100) and after proteasome inhibition treatments.ResultsWe show that proteasome activity decreases during the differentiation of iPSCs to cortical neurons, accompanied by a reduction in levels of the proteasome regulatory subunits Rpt6 and Rpn6. Proteasome inhibition in WT neurons does not lead to a significant change in total or phosphorylated tau levels but resulted in an increase in the autophagy associated protein BAG3, together with an induction of tau cleaved by caspase‐3 at Asp421.ConclusionProteasome activity decreases during the differentiation of iPSCs into neurons, which may be due to a reduction in in proteasome regulators. Our results suggest that proteasome inhibition causes an increase in tau cleavage which may be preferentially cleared through the autophagy pathway. The ability of these ‘fetal‐like’ neurons to adapt and upregulate their protein clearance system may be enhanced compared to FTD brain tissue. In ongoing work we are investigating proteasome expression and activity in FTD post‐mortem tissue as well as the localisation and interactions of tau and the proteasome after proteasome inhibition treatments.

Impact of MAPT mutations on transcriptomic signatures of FTLD brains and patient‐derived pluripotent cell models

AbstractBackgroundMutations in the microtubule‐associated protein tau (MAPT) cause heterogeneous forms of frontotemporal lobar dementia with tau inclusions (FTLD‐tau). Yet the pathogenic events linked to disease remain poorly understood. This study aimed to identify genes and pathways that lead to FTLD‐tau.MethodTo identify the earliest genes and pathways that are dysregulated in FTLD‐tau, we identified differentially expressed genes in RNA‐seq data generated from induced pluripotent stem cell (iPSC)–derived cortical neurons carrying MAPT R406W, MAPT P301L, and MAPT IVS10+16 and isogenic, controls and brain tissue samples from progressive supranuclear palsy (PSP) and control brains. We then identified pathological pathways and drug targets that were enriched among the differentially expressed genes.ResultsWe identified 275 genes that were differentially expressed in iPSC–derived cortical neurons from MAPT R406W carriers compared to isogenic controls, MAPT IVS10+16 carriers compared to isogenic controls, and MAPT P301L carriers compared with isogenic controls. These commonly dysregulated genes were enriched for pathways involving synaptic function, neuronal development, and endolysosomal function. A subset of these genes were also changed in brains from human subjects with PSP compared to normal control brains. Finally, a subset of genes, enriched in glutamate receptor signaling, were altered across the mutant neurons and significantly changed with tau accumulation in a mouse model of tauopathy (Tau‐P301L mice).ConclusionThe results from this study demonstrate that iPSC‐derived neurons capture molecular processes that occur in human brains and can be used to model disease and point to common molecular pathways driven by 3 distinct MAPT mutations

A phase 1b, randomized, double‐blind, placebo‐controlled, parallel cohort safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary efficacy study of intravenously infused BIIB092 in patients with four different primary tauopathy syndromes

AbstractBackgroundAggregation of insoluble tau is a key autopsy finding in several neurodegenerative conditions including corticobasal syndrome (CBS), non‐fluent variant primary progressive aphasia (nfvPPA), frontotemporal lobar degeneration due to microtubule‐associated protein tau (MAPT) mutation, and traumatic encephalopathy syndrome (TES). Monoclonal‐antibody (mAb) therapies may promote clearance of pathogenic tau species, but differing protein isoforms and conformations may limit the affinity of mAbs for tau epitopes in distinct tauopathy syndromes. A “basket trial” allows for efficient investigation of drug target engagement in distinct diseases sharing common causative molecular alterations. We assessed the safety, tolerability, pharmacokinetic profile, and pharmacodynamic effects of BIIB092 (gosuranemab), a mAb targeting an N‐terminal tau epitope, in a basket trial enrolling participants with 4 different tauopathy syndromes: CBS, nfvPPA, symptomatic MAPT mutations, and TES. We also explored BIIB092’s effects on CSF, MRI and clinical measures of disease severity.MethodN=25 participants were randomized approximately 3:1 to monthly intravenous infusions of 2000 mg BIIB092 (8 CBS, 4 nfvPPA, 4 MAPT, 2 TES) or placebo (CBS, 2 nfvPPA, 1 MAPT, 1 TES) for up to 6 months of double‐blind therapy. Subsequently 14 participants received monthly open label infusions for up to 6 months. Plasma, CSF, exploratory clinical measures, and volumetric imaging were collected at baseline, week 12, and week 24 of the double‐blind portion of the trial.ResultThe study was terminated by Biogen in December 2019 (following negative results in a phase 2 in progressive supranuclear palsy), prior to completion of planned enrollment or treatment in recruited participants. Adverse events were more frequent in participants randomized to BIIB092 (83%) compared to placebo (28%), though no adverse events were attributed to study drug. In all patients randomized to BIIB092, we observed 90% reduction in detectable CSF N‐terminal tau epitopes at weeks 12 (mean ‐96.9%, SD 2.0) and 24 (mean ‐97.0%, SD 1.9) of the blinded treatment period. Analyses of other secondary and exploratory endpoints are underway.ConclusionSix months of BIIB092 treatment was well tolerated and appears to bind to the N‐terminal epitopes in individuals with four different tauopathy syndromes.

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.

Impact of MAPT mutations on transcriptomic signatures of FTLD brains and patient-derived pluripotent cell models.

Mutations in the microtubule-associated protein tau (MAPT) cause heterogeneous forms of frontotemporal lobar dementia with tau inclusions (FTLD-tau). Yet, the pathogenic events linked to disease remain poorly understood. This study was aimed at identifying genes and pathways that drive to FTLD-tau. To identify the earliest genes and pathways that are dysregulated in FTLD-tau, we detected differentially expressed genes in RNA-seq data generated from induced pluripotent stem cell (iPSC)-derived cortical neurons carrying MAPT R406W, MAPT P301L, and MAPT IVS10+16 and isogenic, controls and 26 brain tissue samples (3 R406W carriers, 7 IVS10+16, 3 P301L, and 13 unrelated controls). We then identified pathological pathways and drug targets that were enriched among the differentially expressed genes. We identified 61 genes that were differentially expressed in iPSC-derived cortical neurons from MAPT R406W carriers compared with isogenic, control neurons and replicated a subset of these genes in brain tissue from MAPT R406W carriers. We identified 15 genes that were differentially expressed in iPSC-derived cortical neurons from MAPT IVS10+16 carriers compared with isogenic, control neurons and replicated a subset of these genes in brain tissue from MAPT IVS10+16 carriers. We identified 37 genes that were differentially expressed in iPSC-derived cortical neurons from MAPT P301L carriers compared with isogenic, control neurons and replicated a subset of these genes in brain tissue from MAPT P301L carriers. Interestingly, there is little overlap among genes differentially expressed for MAPT R406W, MAPT P301L, and MAPT IVS10+16, which suggests that these mutations may lead to tau aggregation and neurodegeneration by different mechanisms. The results from this study demonstrate that iPSC-derived neurons capture molecular processes that occur in human brains and can be used to model disease.

In Vivo 18 F-APN-1607 Tau Positron Emission Tomography Imaging in MAPT Mutations: Cross-Sectional and Longitudinal Findings.

Frontotemporal lobar degeneration with tauopathy caused by MAPT (microtubule-associated protein tau) mutations is a highly heterogenous disorder. The ability to visualize and longitudinally monitor tau deposits may be beneficial to understand disease pathophysiology and predict clinical trajectories. The aim of this study was to investigate the cross-sectional and longitudinal 18 F-APN-1607 positron emission tomography/computed tomography (PET/CT) imaging findings in MAPT mutation carriers. Seven carriers of MAPT mutations (six within exon 10 and one outside of exon 10) and 15 healthy control subjects were included. All participants underwent 18 F-APN-1607 PET/CT at baseline. Three carriers of exon 10 mutations received follow-up 18 F-APN-1607 PET/CT scans. Standardized uptake value ratio (SUVR) maps were obtained using the cerebellar gray matter as the reference region. SUVR values observed in MAPT mutation carriers were normalized to data from healthy control subjects. A regional SUVR z score ≥ 2 was used as the criterion to define positive 18 F-APN-1607 PET/CT findings. Although the seven study patients had heterogenous clinical phenotypes, all showed a significant 18 F-APN-1607 uptake characterized by high-contrast signals. However, the anatomical localization of tau deposits differed in patients with distinct clinical symptoms. Follow-up imaging data, which were available for three patients, demonstrated worsening trends in patterns of tau accumulation over time, which were paralleled by a significant clinical deterioration. Our data represent a promising step in understanding the usefulness of 18 F-APN-1607 PET/CT imaging for detecting tau accumulation in MAPT mutation carriers. Our preliminary follow-up data also suggest the potential value of 18 F-APN-1607 PET/CT for monitoring the longitudinal trajectories of frontotemporal lobar degeneration caused by MAPT mutations. © 2021 International Parkinson and Movement Disorder Society.