Region-specific and age-related differences in astrocytes in the human brain.

Astrocyte heterogeneity and its relation to aging in the normal human brain remain poorly understood. We here analyzed astrocytes in gray and white matter brain tissues obtained from donors ranging in age between the neonatal period to over 100 years. We show that astrocytes are differently distributed with higher density in the white matter. This regional difference in cellular density becomes less prominent with age. Additionally, we confirm the presence of morphologically distinct astrocytes, with gray matter astrocytes being morphologically more complex. Notably, gray matter astrocytes morphologically change with age, while white matter astrocytes remain relatively consistent in morphology. Using regional mass spectrometry-based proteomics, we did, however, identify astrocyte specific proteins with regional differences in abundance, reflecting variation in cellular density or expression level. Importantly, the expression of some astrocyte specific proteins region-dependently decreases with age. Taken together, we provide insights into region- and age-related differences in astrocytes in the human brain.

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 ß 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 (ß -0·54 [95% CI -1·94 to 0·87], p=0·45) or disease duration (ß 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 (ß 2·66 [0·63 to 4·70], p=0·011), H1i (ß -3·66 [-6·83 to -0·48], p=0·025), and H1u (ß -5·25 [-10·42 to -0·07], p=0·048); and with disease duration for H1x (ß -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.

Linking acetylated α-Tubulin redistribution to α-Synuclein pathology in brain of Parkinson's disease patients.

Highly specialized microtubules in neurons are crucial to both health and disease of the nervous system, and their properties are strictly regulated by different post-translational modifications, including α-Tubulin acetylation. An imbalance in the levels of acetylated α-Tubulin has been reported in experimental models of Parkinson's disease (PD) whereas pharmacological or genetic modulation that leads to increased acetylated α-Tubulin successfully rescues axonal transport defects and inhibits α-Synuclein aggregation. However, the role of acetylation of α-Tubulin in the human nervous system is largely unknown as most studies are based on in vitro evidence. To capture the complexity of the pathological processes in vivo, we analysed post-mortem human brain of PD patients and control subjects. In the brain of PD patients at Braak stage 6, we found a redistribution of acetylated α-Tubulin, which accumulates in the neuronal cell bodies in subcortical structures but not in the cerebral cortex, and decreases in the axonal compartment, both in putamen bundles of fibres and in sudomotor fibres. High-resolution and 3D reconstruction analysis linked acetylated α-Tubulin redistribution to α-Synuclein oligomerization and to phosphorylated Ser 129 α-Synuclein, leading us to propose a model for Lewy body (LB) formation. Finally, in post-mortem human brain, we observed threadlike structures, resembling tunnelling nanotubes that contain α-Synuclein oligomers and are associated with acetylated α-Tubulin enriched neurons. In conclusion, we support the role of acetylated α-Tubulin in PD pathogenesis and LB formation.

Dissecting the Clinical Heterogeneity and Genotype-Phenotype Correlations of MAPT Mutations: A Systematic Review.

BACKGROUND: Microtubule-associated protein tau (MAPT) mutations are one of the main causes of genetic Frontotemporal dementia (FTD) and are characterised by high clinical heterogeneity. A behavioural variant of FTD is the principal phenotype, but other rarer phenotypes are described, mostly reported as single cases. In this review, we provide an overview of the clinical phenotypes associated with MAPT mutations in order to define their characteristics and explore genotype-phenotype correlations. METHODS: We performed systematic bibliographic research on the Pubmed database, focusing on articles published between 1998 and 2022. We analysed the clinical phenotype of 177 patients carrying MAPT mutations, focusing on the rarest ones. We performed a narrative synthesis of the results. RESULTS: Regarding language phenotypes, the most frequent were the non-fluent variant and the semantic variant of Primary Progressive Aphasia (nfvPPA, svPPA), approximately in the same proportion. Almost 20% of the whole group of patients present a clinical phenotype belonging to the corticobasal syndrome-progressive supranuclear palsy (CBS-PSP) spectrum. While no clear genotype-phenotype correlation could be identified, some mutations were associated with a specific phenotype, while others gave origin to multiple clinical pictures and mixed phenotypes. CONCLUSIONS: A high clinical heterogeneity exists in FTD associated with MAPT mutations without a clear phenotype-genotype correlation in most cases. However, some characteristics can be helpful to drive genetic testing. Deep phenotyping of patients, together with functional studies of single mutations, particularly those associated with atypical phenotypes, are necessary to better understand the biological mechanisms underlying this clinical variability.

Secondary Protein Aggregates in Neurodegenerative Diseases: Almost the Rule Rather than the Exception.

The presence of protein aggregates is a hallmark of many neurodegenerative diseases, including Parkinson's disease (PD), Alzheimer's disease (AD), and frontotemporal lobar degeneration (FTLD). Traditionally, each disease has been associated with the aggregation of specific proteins, which serve as disease-specific biomarkers. For example, aggregates of α-synuclein (α-syn) are found in α-synucleinopathies such as PD, dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Similarly, AD is characterized by aggregates of amyloid-beta (Aß) and tau proteins. However, it has been observed that these protein aggregates can also occur in other neurodegenerative diseases, contributing to disease progression. For instance, α-syn aggregates have been detected in AD, Down syndrome, Huntington's disease, prion diseases, and various forms of FTLD. Similarly, Aß aggregates have been found in conditions like DLB and PD. Tau aggregates, in addition to being present in primary tauopathies, have been identified in prion diseases, α-synucleinopathies, and cognitively healthy aged subjects. Finally, aggregates of TDP-43, typically associated with FTLD and amyotrophic lateral sclerosis (ALS), have been observed in AD, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), MSA, DLB, and other neurodegenerative diseases. These findings highlight the complexity of protein aggregation in neurodegeneration and suggest potential interactions and common mechanisms underlying different diseases. A deeper understating of this complex scenario may eventually lead to the identification of a better elucidation of the pathogenetic mechanisms of these devastating conditions and hopefully new therapeutic stragegies.

Impact of seed amplification assay and surface-enhanced Raman spectroscopy combined approach on the clinical diagnosis of Alzheimer's disease.

BACKGROUND: The current diagnosis of Alzheimer's disease (AD) is based on a series of analyses which involve clinical, instrumental and laboratory findings. However, signs, symptoms and biomarker alterations observed in AD might overlap with other dementias, resulting in misdiagnosis. METHODS: Here we describe a new diagnostic approach for AD which takes advantage of the boosted sensitivity in biomolecular detection, as allowed by seed amplification assay (SAA), combined with the unique specificity in biomolecular recognition, as provided by surface-enhanced Raman spectroscopy (SERS). RESULTS: The SAA-SERS approach supported by machine learning data analysis allowed efficient identification of pathological Aß oligomers in the cerebrospinal fluid of patients with a clinical diagnosis of AD or mild cognitive impairment due to AD. CONCLUSIONS: Such analytical approach can be used to recognize disease features, thus allowing early stratification and selection of patients, which is fundamental in clinical treatments and pharmacological trials.

24-Hydroxycholesterol Induces Tau Proteasome-Dependent Degradation via the SIRT1/PGC1α/Nrf2 Pathway: A Potential Mechanism to Counteract Alzheimer's Disease.

Considerable evidence indicates that cholesterol oxidation products, named oxysterols, play a key role in several events involved in Alzheimer's disease (AD) pathogenesis. Although the majority of oxysterols causes neuron dysfunction and degeneration, 24-hydroxycholesterol (24-OHC) has recently been thought to be neuroprotective also. The present study aimed at supporting this concept by exploring, in SK-N-BE neuroblastoma cells, whether 24-OHC affected the neuroprotective SIRT1/PGC1α/Nrf2 axis. We demonstrated that 24-OHC, through the up-regulation of the deacetylase SIRT1, was able to increase both PGC1α and Nrf2 expression and protein levels, as well as Nrf2 nuclear translocation. By acting on this neuroprotective pathway, 24-OHC favors tau protein clearance by triggering tau ubiquitination and subsequently its degradation through the ubiquitin-proteasome system. We also observed a modulation of SIRT1, PGC1α, and Nrf2 expression and synthesis in the brain of AD patients with the progression of the disease, suggesting their potential role in neuroprotection. These findings suggest that 24-OHC contributes to tau degradation through the up-regulation of the SIRT1/PGC1α/Nrf2 axis. Overall, the evidence points out the importance of avoiding 24-OHC loss, which can occur in the AD brain, and of limiting SIRT1, PGC1α, and Nrf2 deregulation in order to prevent the neurotoxic accumulation of hyperphosphorylated tau and counteract neurodegeneration.

Corrigendum: PMCA-based detection of prions in the olfactory mucosa of patients with sporadic Creutzfeldt-Jakob disease.

[This corrects the article DOI: 10.3389/fnagi.2022.848991.].

Spontaneous intracerebral haemorrhage associated with early-onset cerebral amyloid angiopathy and Alzheimer's disease neuropathological changes five decades after cadaveric dura mater graft.

Cerebral amyloid angiopathy (CAA) is a small vessel disease, causing spontaneous intracerebral hemorrhage (ICH) in the elderly. It is strongly associated with Alzheimer disease (AD), as most CAA patients show deposition of Aß-i.e. the basic component of parenchymal Alzheimer amyloid deposits-in the cerebral vessels. Iatrogenic early-onset CAA has been recently identified in patients with a history of traumatic brain injury or other cerebral as well as extra-cerebral lesions that led to neurosurgery or other medical procedures as intravascular embolization by cadaveric dura mater extracts many years before the first ICH event. In those patients, a transmission of Aß seeds from neurosurgical instruments or from cadaveric dura mater exposure was suggested. We report a 51-year-old woman with unremarkable family history who presented abruptly with aphasia and right hemiparesis. A cerebral left lobar haemorrhagic stroke was documented by neuroimaging. Accurate anamnesis revealed a neurosurgical procedure with cadaveric dura mater graft at the age of 2 years for an arachnoid cyst. The neuropathological examination of the cerebral parietal biopsy showed severe amyloid angiopathy in many leptomeningeal and cortical vessels, as well as abundant parenchymal Aß deposits, neurofibrillary tangles and neuropil threads. The mechanism involved in the human-to-human transmission of the Aß proteinopathy remains to be clarified. In our patient the cadaver derived dura used for grafting is a very strong candidate as the source of the transmission. A systematic monitoring of individuals who have had neurosurgical procedures in early life, especially those involving cadaveric dural grafts, is required to determine the ratio of those affected by CAA many years later and unaffected. Moreover, our report confirms that in addition to vascular and parenchymal Aß pathology, neurofibrillary changes indistinguishable from AD may develop in specific conditions with long latency period from the neurosurgical or embolization procedure.

Semantic and right temporal variant of FTD: Next generation sequencing genetic analysis on a single-center cohort.

Semantic and right temporal variant of frontotemporal dementia (svFTD and rtvFTD) are rare clinical phenotypes in which, in most cases, the underlying pathology is TDP-43 proteinopathy. They are usually sporadic disorders, but recent evidences suggest a higher frequency of genetic mutations for the right temporal versus the semantic variant. However, the genetic basis of these forms is not clear. In this study we performed a genetic screening of a single-center cohort of svFTD and rtvFTD patients, aiming at identifying the associated genetic variants. A panel of 73 dementia candidate genes has been analyzed by NGS target sequencing including both causal and risk/modifier genes in 23 patients (15 svFTD and 8 rtvFTD) and 73 healthy age-matched controls. We first performed a single variant analysis considering rare variants and then a gene-based aggregation analysis to evaluate the cumulative effects of multiple rare variants in a single gene. We found 12 variants in nearly 40% of patients (9/23), described as pathogenic or classified as VUS/likely pathogenic. The overall rate was higher in svFTD than in rtvFTD. Three mutations were located in MAPT gene and single mutations in the following genes: SQSTM1, VCP, PSEN1, TBK1, OPTN, CHCHD10, PRKN, DCTN1. Our study revealed the presence of variants in genes involved in pathways relevant for the pathology, especially autophagy and inflammation. We suggest that molecular analysis should be performed in all svFTD and rtvFTD patients, to better understand the genotype-phenotype correlation and the pathogenetic mechanisms that could drive the clinical phenotypes in FTD.

The PINK1 p.Asn521Thr Variant Is Associated with Earlier Disease Onset in GRN/C9orf72 Frontotemporal Lobar Degeneration.

Genetic frontotemporal lobar degeneration (FTLD) is characterized by heterogeneous phenotypic expression, with a disease onset highly variable even in patients carrying the same mutation. Herein we investigated if variants in lysosomal genes modulate the age of onset both in FTLD due to GRN null mutations and C9orf72 expansion. In a total of 127 subjects (n = 74 GRN mutations and n = 53 C9orf72 expansion carriers), we performed targeted sequencing of the top 98 genes belonging to the lysosomal pathway, selected based on their high expression in multiple brain regions. We described an earlier disease onset in GRN/C9orf72 pedigrees in subjects carrying the p.Asn521Thr variant (rs1043424) in PTEN-induced kinase 1 (PINK1), a gene that is already known to be involved in neurodegenerative diseases. We found that: (i) the PINK1 rs1043424 C allele is significantly associated with the age of onset; (ii) every risk C allele increases hazard by 2.11%; (iii) the estimated median age of onset in homozygous risk allele carriers is 10-12 years earlier than heterozygous/wild type homozygous subjects. A replication study in GRN/C9orf72 negative FTLD patients confirmed that the rs1043424 C allele was associated with earlier disease onset (-5.5 years in CC versus A carriers). Understanding the potential mechanisms behind the observed modulating effect of the PINK1 gene in FTLD might prove critical for identifying biomarkers and/or designing drugs to modify the age of onset, especially in GRN/C9orf72-driven disease.

Pathological 25 kDa C-Terminal Fragments of TDP-43 Are Present in Lymphoblastoid Cell Lines and Extracellular Vesicles from Patients Affected by Frontotemporal Lobar Degeneration and Neuronal Ceroidolipofuscinosis Carrying a GRN Mutation.

Frontotemporal lobar degeneration (FTLD) is a complex disease, characterized by progressive degeneration of frontal and temporal lobes. Mutations in progranulin (GRN) gene have been found in up to 50% of patients with familial FTLD. Abnormal deposits of post-translationally-modified TAR DNA-binding protein of 43 kDa (TDP-43) represent one of the main hallmarks of the brain pathology. To investigate in peripheral cells the presence of the different TDP-43 forms, especially the toxic 25 kDa fragments, we analyzed lymphoblastoid cell lines (LCLs) and the derived extracellular vesicles (EVs) from patients carrying a GRN mutation, together with wild-type (WT) healthy controls. After characterizing EV sizes and concentrations by nanoparticle tracking analysis, we investigated the levels of different forms of the TDP-43 protein in LCLs and respective EVs by Western blot. Our results showed a trend of concentration decreasing in EVs derived from GRN-mutated LCLs, although not reaching statistical significance. A general increase in p-TDP-43 levels in GRN-mutated LCLs and EVs was observed. In particular, the toxic 25 kDa fragments of p-TDP-43 were only present in GRN-mutated LCLs and were absent in the WT controls. Furthermore, these fragments appeared to be more concentrated in EVs than in LCLs, suggesting a relevant role of EVs in spreading pathological molecules between cells.

Approaching the Gut and Nasal Microbiota in Parkinson's Disease in the Era of the Seed Amplification Assays.

Parkinson's disease (PD) is a neurodegenerative disorder often associated with pre-motor symptoms involving both gastrointestinal and olfactory tissues. PD patients frequently suffer from hyposmia, hyposalivation, dysphagia and gastrointestinal dysfunctions. During the last few years it has been speculated that microbial agents could play a crucial role in PD. In particular, alterations of the microbiota composition (dysbiosis) might contribute to the formation of misfolded α-synuclein, which is believed to be the leading cause of PD. However, while several findings confirmed that there might be an important link between intestinal microbiota alterations and PD onset, little is known about the potential contribution of the nasal microbiota. Here, we describe the latest findings on this topic by considering that more than 80% of patients with PD develop remarkable olfactory deficits in their prodromal disease stage. Therefore, the nasal microbiota might contribute to PD, eventually boosting the gut microbiota in promoting disease onset. Finally, we present the applications of the seed amplification assays to the study of the gut and olfactory mucosa of PD patients, and how they could be exploited to investigate whether pathogenic bacteria present in the gut and the nose might promote α-synuclein misfolding and aggregation.

A novel bio-inspired strategy to prevent amyloidogenesis and synaptic damage in Alzheimer's disease.

Alzheimer's disease (AD) is an irreversible neurodegenerative disorder that affects millions of people worldwide. AD pathogenesis is intricate. It primarily involves two main molecular players-amyloid-ß (Aß) and tau-which actually have an intrinsic trend to generate molecular assemblies that are toxic to neurons. Incomplete knowledge of the molecular mechanisms inducing the onset and sustaining the progression of the disease, as well as the lack of valid models to fully recapitulate the pathogenesis of human disease, have until now hampered the development of a successful therapy for AD. The overall experience with clinical trials with a number of potential drugs-including the recent outcomes of studies with monoclonal antibodies against Aß-seems to indicate that Aß-targeting is not effective if it is not accompanied by an efficient challenge of Aß neurotoxic properties. We took advantage from the discovery of a naturally-occurring variant of Aß (AßA2V) that has anti-amyloidogenic properties, and designed a novel bio-inspired strategy for AD based on the intranasal delivery of a six-mer peptide (Aß1-6A2V) retaining the anti-amyloidogenic abilities of the full-length AßA2V variant. This approach turned out to be effective in preventing the aggregation of wild type Aß and averting the synaptic damage associated with amyloidogenesis in a mouse model of AD. The results of our preclinical studies inspired by a protective model already existing in nature, that is the human heterozygous AßA2V carriers which seem to be protected from AD, open the way to an unprecedented and promising approach for the prevention of the disease in humans.

SORL1 gene mutation and octapeptide repeat insertion in PRNP gene in a case presenting with rapidly progressive dementia and cerebral amyloid angiopathy.

BACKGROUND AND PURPOSE: Cerebral amyloid angiopathy (CAA) has been associated with a variety of neurodegenerative disorders, included prion diseases and Alzheimer's disease; its pathophysiology is still largely unknown. We report the case of an 80-year-old man with rapidly progressive dementia and neuroimaging features consistent with CAA carrying two genetic defects in the PRNP and SORL1 genes. METHODS: Neurological examination, brain magnetic resonance imaging (MRI), electroencephalographic-electromyographic (EEG-EMG) polygraphy, and analysis of 14-3-3 and tau proteins, Aß40, and Aß42 in the cerebrospinal fluid (CSF) were performed. The patient underwent a detailed genetic study by next generation sequencing analysis. RESULTS: The patient presented with progressive cognitive dysfunction, generalized myoclonus, and ataxia. Approximately 9 months after symptom onset, he was bed-bound, almost mute, and akinetic. Brain MRI was consistent with CAA. CSF analysis showed high levels of t-tau and p-tau, decreased Aß42, decreased Aß42/Aß40 ratio, and absence of 14.3.3 protein. EEG-EMG polygraphy demonstrated diffuse slowing, frontal theta activity, and generalized spike-waves related to upper limb myoclonus induced by intermittent photic stimulation. Genetic tests revealed the presence of the E270K variant in the SORL1 gene and the presence of a single octapeptide repeat insertion in the coding region of the PRNP gene. CONCLUSIONS: The specific pathogenic contribution of the two DNA variations is difficult to determine without neuropathology; among the possible explanations, we discuss the possibility of their link with CAA. Vascular and degenerative pathways actually interact in a synergistic way, and genetic studies may lead to more insight into pathophysiological mechanisms.

Neurosyphilis Mimicking Behavioral Variant of Frontotemporal Dementia in a 59-Year-Old Man.

We present the case of a man exhibiting a clinical phenotype of behavioral variant of frontotemporal dementia (bvFTD). The man had developed psychiatric disturbances with verbal aggressiveness over a few months, followed by cognitive and frontal behavioral disorders, fulfilling the clinical criteria for bvFTD. Atrophy and hypometabolism in frontotemporal regions were consistent with the diagnosis. However, serum-screening exams for syphilis infection were positive, and CSF analysis, despite a negative Venereal Disease Research Laboratory Test, suggested the diagnosis of neurosyphilis. After specific antibiotic therapy, the man's behavioral abnormalities and cognitive deficits notably improved, confirming neurosyphilis as the cause of the clinical phenotype. The cognitive deficits completely recovered 1 year post therapy and remained stable for 2 years. After ∼2½ years from the first treatment, the man's behavioral disorders mildly worsened, at which time we re-evaluated him. His cognition was stable, and a positive Venereal Disease Research Laboratory Test confirmed the diagnosis of neurosyphilis. With this case, we demonstrated that in some instances, neurosyphilis can mimic frontotemporal dementia. As a cause of treatable dementia, it should be considered in the differential diagnosis of bvFTD, particularly when psychiatric symptoms and a rapid cognitive decline are noted, even in the presence of brain atrophy and/or hypometabolism.