Tauopathies are a subset of neurodegenerative diseases characterized by abnormal tau inclusions. Specifically, three-repeat tau and four-repeat tau in Alzheimer's disease, three-repeat tau in Pick's ...disease (PiD) and four-repeat tau in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) form amyloid-like fibrous structures that accumulate in neurons and/or glial cells. Amplification and cell-to-cell transmission of abnormal tau based on the prion hypothesis are believed to explain the onset and progression of tauopathies. Recent studies support not only the self-propagation of abnormal tau, but also the presence of conformationally distinct tau aggregates, namely tau strains. Cryogenic electron microscopy analyses of patient-derived tau filaments have revealed disease-specific ordered tau structures. However, it remains unclear whether the ultrastructural and biochemical properties of tau strains are inherited during the amplification of abnormal tau in the brain. In this study, we investigated template-dependent amplification of tau aggregates using a cellular model of seeded aggregation. Tau strains extracted from human tauopathies caused strain-dependent accumulation of insoluble filamentous tau in SH-SY5Y cells. The seeding activity towards full-length four-repeat tau substrate was highest in CBD-tau seeds, followed by PSP-tau and Alzheimer's disease (AD)-tau seeds, while AD-tau seeds showed higher seeding activity than PiD-tau seeds towards three-repeat tau substrate. Abnormal tau amplified in cells inherited the ultrastructural and biochemical properties of the original seeds. These results strongly suggest that the structural differences of patient-derived tau strains underlie the diversity of tauopathies, and that seeded aggregation and filament formation mimicking the pathogenesis of sporadic tauopathy can be reproduced in cultured cells. Our results indicate that the disease-specific conformation of tau aggregates determines the tau isoform substrate that is recruited for templated amplification, and also influences the prion-like seeding activity.
Alzheimer’s disease (AD) is a chronic neurodegenerative disease characterized by pathology of accumulated amyloid β (Aβ) and phosphorylated tau proteins in the brain. Postmortem degradation and ...cellular complexity within the brain have limited approaches to molecularly define the causal relationship between pathological features and neuronal dysfunction in AD. To overcome these limitations, we analyzed the neuron-specific DNA methylome of postmortem brain samples from AD patients, which allowed differentially hypomethylated region of the BRCA1 promoter to be identified. Expression of BRCA1 was significantly up-regulated in AD brains, consistent with its hypomethylation. BRCA1 protein levels were also elevated in response to DNA damage induced by Aβ. BRCA1 became mislocalized to the cytoplasm and highly insoluble in a tau-dependent manner, resulting in DNA fragmentation in both in vitro cellular and in vivo mouse models. BRCA1 dysfunction under Aβ burden is consistent with concomitant deterioration of genomic integrity and synaptic plasticity. The Brca1 promoter region of AD model mice brain was similarly hypomethylated, indicating an epigenetic mechanism underlying BRCA1 regulation in AD. Our results suggest deterioration of DNA integrity as a central contributing factor in AD pathogenesis. Moreover, these data demonstrate the technical feasibility of using neuron-specific DNA methylome analysis to facilitate discovery of etiological candidates in sporadic neurodegenerative diseases.
Tauopathies are the most common type of neurodegenerative proteinopathy, being characterized by cytoplasmic aggregates of hyperphosphorylated tau protein. The formation and morphologies of these tau ...inclusions, the distribution of the lesions and related metabolic changes in cytoplasm differ among different tauopathies. The aim of this study was to examine whether there are differences in the post-translational modifications (PTMs) in the pathological tau proteins. We analyzed sarkosyl-insoluble pathological tau proteins prepared from brains of patients with Alzheimer's disease, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, globular glial tauopathy, and frontotemporal dementia and parkinsonisms linked to chromosome 17 with tau inclusions using liquid chromatography mass spectrometry. In pathological tau proteins associated with a wide range of tauopathies, 170 PTMs in total were identified including new PTMs. Among them, common PTMs were localized in the N- and C-terminal flanking regions of the microtubule binding repeats and PTMs, which were considered to be disease-specific, were found in microtubule binding repeats forming filament core. These suggested that the differences in PTMs reflected the differences in tau filament core structures in each disease.
Alterations of the structure and/or amount of glycans present on proteins are associated with many diseases. We previously demonstrated that changes in N-glycans alter Aβ production. In the present ...study, we focused on the relationship between Alzheimer's disease (AD) and O-glycan, another type of glycan. The UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferase (GalNAc-T) family functions in the first step of mucin-type O-glycan synthesis. Analysis of the expression of GalNAc-Ts in the human brain using real-time PCR revealed that the expression of several GalNAc-Ts was altered with sporadic AD progression. Three of these GalNAc-Ts (GalNAc-T1, GalNAc-T4 and GalNAc-T6) were transfected into HEK293T cells to examine their impact on Aβ production. Transfection of GalNAc-T6 significantly reduced both Aβ1-40 and Aβ1-42 generation, but GalNAc-T1 and GalNAc-T4 only reduced Aβ1-40 generation. Although these three GalNAc-Ts exhibited enzymatic activities on soluble amyloid precursor protein (APP), the GalNAc transferase activity of GalNAc-T6 to APP was most prominent. The expression of α-secretase and β-secretase was slightly altered in the transfected cells, but the activities of α-secretase and β-secretase were not significantly altered. These data suggest that excess O-glycosylation on APP by GalNAc-T6 inhibits Aβ production.
Abstract
The dual-hit hypothesis of Parkinson’s disease (PD) originally postulated that a neurotropic pathogen leads to formation of α-synuclein pathology in the olfactory bulb (OB) and dorsal motor ...nucleus of the vagus (DMV) and then invades the brain from these two entry points. Little work has been conducted to validate an important underlying premise for the dual-hit hypothesis, namely that the initial Lewy pathology does arise simultaneously in the OB and the enteric nervous system (ENS) plexuses and DMV at the earliest disease stage. We conducted a focused re-analysis of two postmortem datasets, which included large numbers of mild Lewy body disease (LBD) cases. We found that cases with α-synuclein pathology restricted to the peripheral autonomic nervous system and/or lower brainstem (early body-first LBD cases) very rarely had any OB pathology, suggesting that Lewy pathology commonly arises in the ENS without concomitant involvement of the OB. In contrast, cases with mild amygdala-predominant Lewy pathology (early brain-first LBD cases) nearly always showed OB pathology. This is compatible with the first pathology being triggered in the OB or amygdala followed by secondary spreading to connected structures, but without early involvement of the ENS or lower brainstem. These observations support that the pathologic process starts in
either
the olfactory bulb
or
the ENS, but rarely in the olfactory bulb and gut simultaneously. More studies on neuropathological datasets are warranted to reproduce these findings. The agreement between the revised single-hit hypothesis and the recently proposed brain-first vs. body-first model of LBD is discussed.
Abstract
Lemur tail kinase 1 (LMTK1), previously called apoptosis-associated tyrosine kinase (AATYK), is an endosomal Ser/Thr kinase. We recently reported that LMTK1 regulates axon outgrowth, ...dendrite arborization and spine formation via Rab11-mediated vesicle transport. Rab11, a small GTPase regulating recycling endosome trafficking, is shown to be associated with late-onset Alzheimer’s disease (LOAD). In fact, genome-wide association studies identified many proteins regulating vesicle transport as risk factors for LOAD. Furthermore, LMTK1 has been reported to be a risk factor for frontotemporal dementia. Then, we hypothesized that LMTK1 contributes to AD development through vesicle transport and examined the effect of LMTK1 on the cellular localization of AD-related proteins, amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE1). The β-cleavage of APP by BACE1 is the initial and rate-limiting step in Aβ generation. We found that LMTK1 accumulated BACE1, but not APP, to the perinuclear endosomal compartment, whereas the kinase-negative(kn) mutant of LMTK1A did not. The β-C-terminal fragment was prone to increase under overexpression of LMTK1A kn. Moreover, the expression level of LMTK1A was reduced in AD brains. These results suggest the possibility that LMTK1 is involved in AD development through the regulation of the proper endosomal localization of BACE1.
Graphical Abstract
Graphical Abstract
Two motor neuron diseases, amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), are caused by distinct genes involved in RNA metabolism, TDP‐43 and FUS/TLS, and SMN, respectively. ...However, whether there is a shared defective mechanism in RNA metabolism common to these two diseases remains unclear. Here, we show that TDP‐43 and FUS/TLS localize in nuclear Gems through an association with SMN, and that all three proteins function in spliceosome maintenance. We also show that in ALS, Gems are lost, U snRNA levels are up‐regulated and spliceosomal U snRNPs abnormally and extensively accumulate in motor neuron nuclei, but not in the temporal lobe of FTLD with TDP‐43 pathology. This aberrant accumulation of U snRNAs in ALS motor neurons is in direct contrast to SMA motor neurons, which show reduced amounts of U snRNAs, while both have defects in the spliceosome. These findings indicate that a profound loss of spliceosome integrity is a critical mechanism common to neurodegeneration in ALS and SMA, and may explain cell‐type specific vulnerability of motor neurons.
This paper reveals the importance of nuclear Gems and spliceosomal U snRNPs in motor neuron survival common to ALS and SMA.
Accumulation of phosphorylated α‐synuclein in the central and peripheral nervous systems is a histological hallmark of Lewy body disease (LBD), including Parkinson's disease (PD), dementia with Lewy ...bodies (DLB), and LB‐related pure autonomic failure. The submandibular gland is employed as a biopsy site for detecting Lewy pathology; however, the incidence of Lewy pathology in this region in autopsy‐proven LBD cases at all stages from an aged Japanese cohort remains unclear. To validate the utility of Lewy pathology of the submandibular gland as a diagnostic biomarker for LBD, we investigated the submandibular gland Lewy pathology in autopsied patients. To determine the specificity, we prospectively evaluated the submandibular gland in 64 consecutive autopsied patients. To determine the sensitivity, we retrospectively assessed the submandibular gland in 168 consecutive autopsied patients who had prodromal or clinical LBD. In the prospective study, Lewy pathology was found in 21 of 64 patients, and nine of those 21 patients had the submandibular gland Lewy pathology. No Lewy pathology was found in 43 patients without CNS Lewy pathology, giving a specificity of 100%. In the retrospective study, Lewy pathology of the submandibular gland was detected in 126 of 168 patients. The sensitivity was 89.1% in PD and 75.4% in DLB. The sensitivity increased with disease progression. These findings support the utility of the submandibular gland biopsy for the pathological diagnosis of LBD.
A long non-coding RNA (lncRNA), nuclear-enriched abundant transcript 1_2 (NEAT1_2), constitutes nuclear bodies known as "paraspeckles". Mutations of RNA binding proteins, including TAR DNA-binding ...protein-43 (TDP-43) and fused in sarcoma/translocated in liposarcoma (FUS/TLS), have been described in amyotrophic lateral sclerosis (ALS). ALS is a devastating motor neuron disease, which progresses rapidly to a total loss of upper and lower motor neurons, with consciousness sustained. The aim of this study was to clarify the interaction of paraspeckles with ALS-associated RNA-binding proteins, and to identify increased occurrence of paraspeckles in the nucleus of ALS spinal motor neurons.
In situ hybridization (ISH) and ultraviolet cross-linking and immunoprecipitation were carried out to investigate interactions of NEAT1_2 lncRNA with ALS-associated RNA-binding proteins, and to test if paraspeckles form in ALS spinal motor neurons. As the results, TDP-43 and FUS/TLS were enriched in paraspeckles and bound to NEAT1_2 lncRNA directly. The paraspeckles were localized apart from the Cajal bodies, which were also known to be related to RNA metabolism. Analyses of 633 human spinal motor neurons in six ALS cases showed NEAT1_2 lncRNA was upregulated during the early stage of ALS pathogenesis. In addition, localization of NEAT1_2 lncRNA was identified in detail by electron microscopic analysis combined with ISH for NEAT1_2 lncRNA. The observation indicating specific assembly of NEAT1_2 lncRNA around the interchromatin granule-associated zone in the nucleus of ALS spinal motor neurons verified characteristic paraspeckle formation.
NEAT1_2 lncRNA may act as a scaffold of RNAs and RNA binding proteins in the nuclei of ALS motor neurons, thereby modulating the functions of ALS-associated RNA-binding proteins during the early phase of ALS. These findings provide the first evidence of a direct association between paraspeckle formation and a neurodegenerative disease, and may shed light on the development of novel therapeutic targets for the treatment of ALS.
Lewy bodies (LBs) and glial cytoplasmic inclusions (GCIs) are specific aggregates found in Parkinson's disease (PD) and multiple system atrophy (MSA), respectively. These aggregates mainly consist of ...α-synuclein (α-syn) and have been reported to propagate in the brain. In animal experiments, the fibrils of α-syn propagate similarly to prions but there is still insufficient evidence to establish this finding in humans. Here, we analysed the protein structure of these aggregates in the autopsy brains of patients by synchrotron Fourier-transform infrared micro-spectroscopy (FTIRM) analysis without extracting or artificially amplifying the aggregates. As a result, we found that the content of the β-sheet structure in LBs in patients with PD was significantly higher than that in GCIs in patients with MSA (52.6 ± 1.9% in PD vs. 38.1 ± 0.9% in MSA, P < 0.001). These structural differences may provide clues to the differences in phenotypes of PD and MSA.
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