Visualizing in deceased COVID-19 patients how SARS-CoV-2 attacks the respiratory and olfactory mucosae but spares the olfactory bulb.

Anosmia, the loss of smell, is a common and often the sole symptom of COVID-19. The onset of the sequence of pathobiological events leading to olfactory dysfunction remains obscure. Here, we have developed a postmortem bedside surgical procedure to harvest endoscopically samples of respiratory and olfactory mucosae and whole olfactory bulbs. Our cohort of 85 cases included COVID-19 patients who died a few days after infection with SARS-CoV-2, enabling us to catch the virus while it was still replicating. We found that sustentacular cells are the major target cell type in the olfactory mucosa. We failed to find evidence for infection of olfactory sensory neurons, and the parenchyma of the olfactory bulb is spared as well. Thus, SARS-CoV-2 does not appear to be a neurotropic virus. We postulate that transient insufficient support from sustentacular cells triggers transient olfactory dysfunction in COVID-19. Olfactory sensory neurons would become affected without getting infected.

The probabilistic model of Alzheimer disease: the amyloid hypothesis revised.

The current conceptualization of Alzheimer disease (AD) is driven by the amyloid hypothesis, in which a deterministic chain of events leads from amyloid deposition and then tau deposition to neurodegeneration and progressive cognitive impairment. This model fits autosomal dominant AD but is less applicable to sporadic AD. Owing to emerging information regarding the complex biology of AD and the challenges of developing amyloid-targeting drugs, the amyloid hypothesis needs to be reconsidered. Here we propose a probabilistic model of AD in which three variants of AD (autosomal dominant AD, APOE ε4-related sporadic AD and APOE ε4-unrelated sporadic AD) feature decreasing penetrance and decreasing weight of the amyloid pathophysiological cascade, and increasing weight of stochastic factors (environmental exposures and lower-risk genes). Together, these variants account for a large share of the neuropathological and clinical variability observed in people with AD. The implementation of this model in research might lead to a better understanding of disease pathophysiology, a revision of the current clinical taxonomy and accelerated development of strategies to prevent and treat AD.

Encephalocraniocutaneous lipomatosis phenotype associated with mosaic biallelic pathogenic variants in the NF1 gene.

Encephalocraniocutaneous lipomatosis (ECCL) is a sporadic congenital condition characterised by ocular, cutaneous and central nervous system involvement. Mosaic activating variants in FGFR1 and KRAS have been reported in several individuals with this syndrome. We report on a patient with neurofibromatosis type 1 (NF1) with a germline pathogenic variant in the NF1 gene and an ECCL phenotype, suggesting ECCL to be part of a spectrum of malformations associated with NF1 pathogenic variants. An anatomical hemispherectomy was performed for intractable epilepsy. Through genetic analysis of blood, cerebral tissue and giant cell lesions in both jaws, we identified the germline NF1 pathogenic variant in all samples and a second-hit pathogenic NF1 variant in cerebral tissue and both giant cell lesions. Both NF1 variants were located on different alleles resulting in somatic mosaicism for a biallelic NF1 inactivation originating in early embryogenesis (second-hit mosaicism or Happle type 2 mosaicism). The biallelic deficit in NF1 in the left hemicranium explains the severe localised, congenital abnormality in this patient. Identical first and second-hit variants in a giant cell lesion of both upper and lower jaws provide confirmatory evidence for an early embryonic second hit involving at least the neural crest. We suggest that the ECCL phenotype may be part of a spectrum of congenital problems associated with mosaic NF1 nullisomy originating during early embryogenesis. The biallelic NF1 inactivation during early embryogenesis mimics the severe activation of the RAS-MAPK pathway seen in ECCL caused by embryonic mosaic activating FGFR1 and KRAS variants in the cranial region. We propose that distinct mechanisms of mosaicism can cause the ECCL phenotype through convergence on the RAS-MAPK pathway.

Regulated cell death and its role in Alzheimer's disease and amyotrophic lateral sclerosis.

Despite considerable research efforts, it is still not clear which mechanisms underlie neuronal cell death in neurodegenerative diseases. During the last 20 years, multiple pathways have been identified that can execute regulated cell death (RCD). Among these RCD pathways, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-related cell death, and lysosome-dependent cell death have been intensively investigated. Although RCD consists of numerous individual pathways, multiple common proteins have been identified that allow shifting from one cell death pathway to another. Another layer of complexity is added by mechanisms such as the endosomal machinery, able to regulate the activation of some RCD pathways, preventing cell death. In addition, restricted axonal degeneration and synaptic pruning can occur as a result of RCD activation without loss of the cell body. RCD plays a complex role in neurodegenerative processes, varying across different disorders. It has been shown that RCD is differentially involved in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), among the most common neurodegenerative diseases. In AD, neuronal loss is associated with the activation of not only necroptosis, but also pyroptosis. In ALS, on the other hand, motor neuron death is not linked to canonical necroptosis, whereas pyroptosis pathway activation is seen in white matter microglia. Despite these differences in the activation of RCD pathways in AD and ALS, the accumulation of protein aggregates immunoreactive for p62/SQSTM1 (sequestosome 1) is a common event in both diseases and many other neurodegenerative disorders. In this review, we describe the major RCD pathways with clear activation in AD and ALS, the main interactions between these pathways, as well as their differential and similar involvement in these disorders. Finally, we will discuss targeting RCD as an innovative therapeutic concept for neurodegenerative diseases, such as AD and ALS. Considering that the execution of RCD or "cellular suicide" represents the final stage in neurodegeneration, it seems crucial to prevent neuronal death in patients by targeting RCD. This would offer valuable time to address upstream events in the pathological cascade by keeping the neurons alive.

Retina pathology as a target for biomarkers for Alzheimer's disease: Current status, ophthalmopathological background, challenges, and future directions.

There is emerging evidence that amyloid beta protein (Aß) and tau-related lesions in the retina are associated with Alzheimer's disease (AD). Aß and hyperphosphorylated (p)-tau deposits have been described in the retina and were associated with small amyloid spots visualized by in vivo imaging techniques as well as degeneration of the retina. These changes correlate with brain amyloid deposition as determined by histological quantification, positron emission tomography (PET) or clinical diagnosis of AD. However, the literature is not coherent on these histopathological and in vivo imaging findings. One important reason for this is the variability in the methods and the interpretation of findings across different studies. In this perspective, we indicate the critical methodological deviations among different groups and suggest a roadmap moving forward on how to harmonize (i) histopathologic examination of retinal tissue; (ii) in vivo imaging among different methods, devices, and interpretation algorithms; and (iii) inclusion/exclusion criteria for studies aiming at retinal biomarker validation.

Primary retinal tauopathy: A tauopathy with a distinct molecular pattern.

BACKGROUND: Phosphorylated tau (p-tau) accumulation, a hallmark of Alzheimer's disease (AD), can also be found in the retina. However, it is uncertain whether it is linked to AD or another tauopathy. METHODS: Retinas from 164 individuals, with and without AD, were analyzed for p-tau accumulation and its relationship with age, dementia, and vision impairment. RESULTS: Retinal p-tau pathology showed a consistent pattern with four stages and a molecular composition distinct from that of cerebral tauopathies. The stage of retinal p-tau pathology correlated with age (r = 0.176, P = 0.024) and was associated with AD (odds ratio [OR] 3.193; P = 0.001), and inflammation (OR = 2.605; P = 0.001). Vision impairment was associated with underlying eye diseases (ß = 0.292; P = 0.001) and the stage of retinal p-tau pathology (ß = 0.192; P = 0.030) in a linear regression model. CONCLUSIONS: The results show the presence of a primary retinal tauopathy that is distinct from cerebral tauopathies.

Pyroptosis in Alzheimer's disease: cell type-specific activation in microglia, astrocytes and neurons.

The major neuropathological hallmarks of Alzheimer's disease (AD) are amyloid ß (Aß) plaques and neurofibrillary tangles (NFT), accompanied by neuroinflammation and neuronal loss. Increasing evidence is emerging for the activation of the canonical NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome in AD. However, the mechanisms leading to neuronal loss in AD and the involvement of glial cells in these processes are still not clear. The aim of this study was to investigate the contribution of pyroptosis, a pro-inflammatory mechanism of cell death downstream of the inflammasome, to neurodegeneration in AD. Immunohistochemistry and biochemical analysis of protein levels were performed on human post-mortem brain tissue. We investigated the presence of cleaved gasdermin D (GSDMD), the pyroptosis effector protein, as well as the NLRP3 inflammasome-forming proteins, in the medial temporal lobe of 23 symptomatic AD, 25 pathologically defined preclinical AD (p-preAD) and 21 non-demented control cases. Cleaved GSDMD was detected in microglia, but also in astrocytes and in few pyramidal neurons in the first sector of the cornu ammonis (CA1) of the hippocampus and the temporal cortex of Brodmann area 36. Only microglia expressed all NLRP3 inflammasome-forming proteins (i.e., ASC, NLRP3, caspase-1). Cleaved GSDMD-positive astrocytes and neurons exhibited caspase-8 and non-canonical inflammasome protein caspase-4, respectively, potentially indicating alternative pathways for GSDMD cleavage. Brains of AD patients exhibited increased numbers of cleaved GSDMD-positive cells. Cleaved GSDMD-positive microglia and astrocytes were found in close proximity to Aß plaques, while cleaved GSDMD-positive neurons were devoid of NFTs. In CA1, NLRP3-positive microglia and cleaved GSDMD-positive neurons were associated with local neuronal loss, indicating a possible contribution of NLRP3 inflammasome and pyroptosis activation to AD-related neurodegeneration. Taken together, our results suggest cell type-specific activation of pyroptosis in AD and extend the current knowledge about the contribution of neuroinflammation to the neurodegenerative process in AD via a direct link to neuron death by pyroptosis.

Seeding, maturation and propagation of amyloid ß-peptide aggregates in Alzheimer's disease.

Alzheimer's disease is neuropathologically characterized by the deposition of the amyloid ß-peptide (Aß) as amyloid plaques. Aß plaque pathology starts in the neocortex before it propagates into further brain regions. Moreover, Aß aggregates undergo maturation indicated by the occurrence of post-translational modifications. Here, we show that propagation of Aß plaques is led by presumably non-modified Aß followed by Aß aggregate maturation. This sequence was seen neuropathologically in human brains and in amyloid precursor protein transgenic mice receiving intracerebral injections of human brain homogenates from cases varying in Aß phase, Aß load and Aß maturation stage. The speed of propagation after seeding in mice was best related to the Aß phase of the donor, the progression speed of maturation to the stage of Aß aggregate maturation. Thus, different forms of Aß can trigger propagation/maturation of Aß aggregates, which may explain the lack of success when therapeutically targeting only specific forms of Aß.

Cerebral amyloid angiopathy: Neuropathological diagnosis, link to Alzheimer's disease and impact on clinics.

Cerebral amyloid angiopathy (CAA) is the most frequent cause of lobar hemorrhages in the brains of elderly individuals. It is characterized by the deposition of amyloidogenic proteins in the vessel wall of leptomeningeal and/or intracerebral blood vessels. Different proteins can cause CAA. Most frequently, the amyloid ß protein (Aß) is found to be deposited in CAA and indicates a link to Alzheimer's disease, because Aß is known to be deposited in amyloid plaques characteristic of Alzheimer's disease. Among other proteins that can also cause CAA, transthyretin (TTR) is the most important one because TTR amyloidosis can be successfully treated. Therefore, it is essential to diagnose TTR-related CAA even in biopsies taken in the context of cerebral hematoma evacuations if possible. The current "Boston criteria version 2.0" for the diagnosis of CAA highlight the importance of autopsy for the definite diagnosis of CAA and biopsies for the diagnosis of probable CAA. Here, we discuss the implications of Aß-related and non-Aß-related forms of CAA for their current diagnostic relevance also in the context of neurodegenerative diseases as well as the implications of the Boston criteria version 2.0 for neuropathological diagnosis.

Fetal brain maceration score on postmortem magnetic resonance imaging vs. conventional autopsy.

BACKGROUND: Postmortem fetal magnetic resonance imaging (MRI) has been on the rise since it was proven to be a good alternative to conventional autopsy. Since the fetal brain is sensitive to postmortem changes, extensive tissue fixation is required for macroscopic and microscopic assessment. Estimation of brain maceration on MRI, before autopsy, may optimize histopathological resources. OBJECTIVE: The aim of the study is to develop an MRI-based postmortem fetal brain maceration score and to correlate it with brain maceration as assessed by autopsy. MATERIALS AND METHODS: This retrospective single-center study includes 79 fetuses who had postmortem MRI followed by autopsy. Maceration was scored on MRI on a numerical severity scale, based on our brain-specific maceration score and the whole-body score of Montaldo. Additionally, maceration was scored on histopathology with a semiquantitative severity scale. Both the brain-specific and the whole-body maceration imaging scores were correlated with the histopathological maceration score. Intra- and interobserver agreements were tested for the brain-specific maceration score. RESULTS: The proposed brain-specific maceration score correlates well with fetal brain maceration assessed by autopsy (τ = 0.690), compared to a poorer correlation of the whole-body method (τ = 0.452). The intra- and interobserver agreement was excellent (correlation coefficients of 0.943 and 0.864, respectively). CONCLUSION: We present a brain-specific postmortem MRI maceration score that correlates well with the degree of fetal brain maceration seen at histopathological exam. The score is reliably reproduced by different observers with different experience.

Neuronal loss of the nucleus basalis of Meynert in primary progressive aphasia is associated with Alzheimer's disease neuropathological changes.

INTRODUCTION: Imaging studies indicated basal forebrain reduction in primary progressive aphasia (PPA), which might be a candidate marker for cholinergic treatment. Nucleus basalis of Meynert (nbM) neuronal loss has been reported, but a systematic quantitative neuropathological assessment including the three clinical PPA variants is lacking. METHODS: Quantitative assessment of neuronal density and pathology was performed on nbM tissue of 47 cases: 15 PPA, constituting the different clinicopathological phenotypes, 14 Alzheimer's disease (AD), and 18 cognitively normals. RESULTS: Group-wise, reduced nbM neuronal density was restricted to AD. At the individual level, semantic variant PPA with underlying AD neuropathological change (ADNC) had lower neuronal densities, while those with frontotemporal lobar degeneration (FTLD) transactive response DNA binding protein 43 kDa (TDP-43) type C pathology were unaffected. Higher Braak stages and increased numbers of nbM-related pretangles were associated with nbM neuronal loss. DISCUSSION: nbM neuronal loss in PPA is related to ADNC. This study cautions against overinterpreting MRI-based basal forebrain volumes in non-AD PPA as neuronal loss.

CRISPR/Cas9 screen in human iPSC-derived cortical neurons identifies NEK6 as a novel disease modifier of C9orf72 poly(PR) toxicity.

INTRODUCTION: The most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are hexanucleotide repeats in chromosome 9 open reading frame 72 (C9orf72). These repeats produce dipeptide repeat proteins with poly(PR) being the most toxic one. METHODS: We performed a kinome-wide CRISPR/Cas9 knock-out screen in human induced pluripotent stem cell (iPSC) -derived cortical neurons to identify modifiers of poly(PR) toxicity, and validated the role of candidate modifiers using in vitro, in vivo, and ex-vivo studies. RESULTS: Knock-down of NIMA-related kinase 6 (NEK6) prevented neuronal toxicity caused by poly(PR). Knock-down of nek6 also ameliorated the poly(PR)-induced axonopathy in zebrafish and NEK6 was aberrantly expressed in C9orf72 patients. Suppression of NEK6 expression and NEK6 activity inhibition rescued axonal transport defects in cortical neurons from C9orf72 patient iPSCs, at least partially by reversing p53-related DNA damage. DISCUSSION: We identified NEK6, which regulates poly(PR)-mediated p53-related DNA damage, as a novel therapeutic target for C9orf72 FTD/ALS.

Increased pyroptosis activation in white matter microglia is associated with neuronal loss in ALS motor cortex.

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of motor neurons in the motor cortex, brainstem, and spinal cord. Although ALS is considered a motor neuron disorder, neuroinflammation also plays an important role. Recent evidence in ALS disease models indicates activation of the inflammasome and subsequent initiation of pyroptosis, an inflammatory type of cell death. In this study, we determined the expression and distribution of the inflammasome and pyroptosis effector proteins in post-mortem brain and spinal cord from ALS patients (n = 25) and controls (n = 19), as well as in symptomatic and asymptomatic TDP-43A315T transgenic and wild-type mice. Furthermore, we evaluated its correlation with the presence of TDP-43 pathological proteins and neuronal loss. Expression of the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, pyroptosis effector protein cleaved Gasdermin D (GSDMD), and IL-18 was detected in microglia in human ALS motor cortex and spinal cord, indicative of canonical inflammasome-triggered pyroptosis activation. The number of cleaved GSDMD-positive precentral white matter microglia was increased compared to controls and correlated with a decreased neuronal density in human ALS motor cortex. Neither of this was observed in the spinal cord. Similar results were obtained in TDP-43A315T mice, where microglial pyroptosis activation was significantly increased in the motor cortex upon symptom onset, and correlated with neuronal loss. There was no significant correlation with the presence of TDP-43 pathological proteins both in human and mouse tissue. Our findings emphasize the importance of microglial NLRP3 inflammasome-mediated pyroptosis activation for neuronal degeneration in ALS and pave the way for new therapeutic strategies counteracting motor neuron degeneration in ALS by inhibiting microglial inflammasome/pyroptosis activation.

Classification of 18F-Flutemetamol scans in cognitively normal older adults using machine learning trained with neuropathology as ground truth.

PURPOSE: End-of-life studies have validated the binary visual reads of 18F-labeled amyloid PET tracers as an accurate tool for the presence or absence of increased neuritic amyloid plaque density. In this study, the performance of a support vector machine (SVM)-based classifier will be tested against pathological ground truths and its performance determined in cognitively healthy older adults. METHODS: We applied SVM with a linear kernel to an 18F-Flutemetamol end-of-life dataset to determine the regions with the highest feature weights in a data-driven manner and to compare between two different pathological ground truths: based on neuritic amyloid plaque density or on amyloid phases, respectively. We also trained and tested classifiers based on the 10% voxels with the highest amplitudes of feature weights for each of the two neuropathological ground truths. Next, we tested the classifiers' diagnostic performance in the asymptomatic Alzheimer's disease (AD) phase, a phase of interest for future drug development, in an independent dataset of cognitively intact older adults, the Flemish Prevent AD Cohort-KU Leuven (F-PACK). A regression analysis was conducted between the Centiloid (CL) value in a composite volume of interest (VOI), as index for amyloid load, and the distance to the hyperplane for each of the two classifiers, based on the two pathological ground truths. A receiver operating characteristic analysis was also performed to determine the CL threshold that optimally discriminates between neuritic amyloid plaque positivity versus negativity, or amyloid phase positivity versus negativity, within F-PACK. RESULTS: The classifiers yielded adequate specificity and sensitivity within the end-of-life dataset (neuritic amyloid plaque density classifier: specificity of 90.2% and sensitivity of 83.7%; amyloid phase classifier: specificity of 98.4% and sensitivity of 84.0%). The regions with the highest feature weights corresponded to precuneus, caudate, anteromedial prefrontal, and also posterior inferior temporal and inferior parietal cortex. In the cognitively normal cohort, the correlation coefficient between CL and distance to the hyperplane was -0.66 for the classifier trained with neuritic amyloid plaque density, and -0.88 for the classifier trained with amyloid phases. This difference was significant. The optimal CL cut-off for discriminating positive versus negative scans was CL = 48-51 for the different classifiers (area under the curve (AUC) = 99.9%), except for the classifier trained with amyloid phases and based on the 10% voxels with highest feature weights. There the cut-off was CL = 26 (AUC = 99.5%), which closely matched the CL threshold for discriminating phases 0-2 from 3-5 based on the end-of-life dataset and the neuropathological ground truth. DISCUSSION: Among a set of neuropathologically validated classifiers trained with end-of-life cases, transfer to a cognitively normal population works best for a classifier trained with amyloid phases and using only voxels with the highest amplitudes of feature weights.

Antiviral treatment with fluoxetine for rituximab-associated chronic echovirus 13 meningoencephalitis and myofasciitis.

BACKGROUND AND PURPOSE: Enterovirus infections pose a serious threat for patients with humoral deficiencies and may be lethal, whilst the efficacy of proposed treatment options such as corticosteroids, intravenous immunoglobulins and fluoxetine remains debated. METHODS: Viral clearance was investigated in a patient with rituximab-induced B-cell depletion and chronic echovirus 13 (E13) meningoencephalitis/myofasciitis in response to intravenous immunoglobulins and fluoxetine using sequential semi-quantitative E13 viral load measurements by real-time reverse transcription polymerase chain reaction. Fluoxetine concentrations in plasma and cerebrospinal fluid were determined by liquid chromatography mass spectrometry. RESULTS: Intravenous immunoglobulins appeared ineffective in this case of E13 infection, whereas virus clearance in cerebrospinal fluid was obtained after 167 days of oral fluoxetine. Since treatment with corticosteroids resulted in a flare of symptoms, rechallenge with viral load measurements was not attempted. CONCLUSION: In this report of a patient with rituximab-associated chronic echovirus 13 meningoencephalitis, viral clearance in response to single treatment options is assessed for the first time. Our observations further support the in vivo efficacy of fluoxetine against enteroviral infections. More research is needed to establish its efficacy in different enterovirus strains.

Maturation of neuronal AD-tau pathology involves site-specific phosphorylation of cytoplasmic and synaptic tau preceding conformational change and fibril formation.

In Alzheimer's disease (AD), tau-protein undergoes a multi-step process involving the transition from a natively unfolded monomer to large, aggregated structures such as neurofibrillary tangles (NFTs). However, it is not yet clear which events initiate the early preclinical phase of AD tauopathy and whether they have impact on the propagation of tau pathology in later disease stages. To address this question, we analyzed the distribution of tau species phosphorylated at T231, S396/S404 and S202/T205, conformationally modified at the MC1 epitope and fibrillary tau detected by the Gallyas method (Gallyas-tau), in the brains of 15 symptomatic and 20 asymptomatic cases with AD pathology as well as of 19 nonAD cases. As initial tau lesions, we identified phosphorylated-T231-tau diffusely distributed within the somatodendritic compartment (IC-tau) and phosphorylated-S396/pS404-tau in axonal lesions of the white matter and in the neuropil (IN-tau). The subcellular localization of pT231-tau in the cell body and pS396/pS404-tau in the presynapse was confirmed in hP301L mutant Drosophila larvae. Phosphorylated-S202/T205-tau, MC1-tau and Gallyas-tau were negative for these lesions. IC- and IN-tau were observed in all analyzed regions of the human brain, including early affected regions in nonAD cases (entorhinal cortex) and late affected regions in symptomatic AD cases (cerebellum), indicating that tau pathology initiation follows similar processes when propagating into previously unaffected regions. Furthermore, a sequence of AD-related maturation of tau-aggregates was observed, initiated by the appearance of IC- and IN-tau, followed by the formation of pretangles exhibiting pT231-tau, pS396/pS404-tau and pS202/pT205-tau, then by MC1-conformational tau, and, finally, by the formation of Gallyas-positive NFTs. Since cases classified as nonAD [Braak NFT stages < I (including a-1b)] already showed IC- and IN-tau, our findings suggest that these lesions are a prerequisite for the development of AD.

Sequence of proteome profiles in preclinical and symptomatic Alzheimer's disease.

Proteome profile changes in Alzheimer's disease (AD) brains have been reported. However, it is unclear whether they represent a continuous process, or whether there is a sequential involvement of distinct proteins. To address this question, we used mass spectrometry. We analyzed soluble, dispersible, sodium dodecyl sulfate, and formic acid fractions of neocortex homogenates (mainly Brodmann area 17-19) from 18 pathologically diagnosed preclinical AD, 17 symptomatic AD, and 18 cases without signs of neurodegeneration. By doing so, we identified four groups of AD-related proteins being changed in levels in preclinical and symptomatic AD cases: early-responding, late-responding, gradually-changing, and fraction-shifting proteins. Gene ontology analysis of these proteins and all known AD-risk/causative genes identified vesicle endocytosis and the secretory pathway-related processes as an early-involved AD component. In conclusion, our findings suggest that subtle changes involving the secretory pathway and endocytosis precede severe proteome changes in symptomatic AD as part of the preclinical phase of AD. The respective early-responding proteins may also contribute to synaptic vesicle cycle alterations in symptomatic AD.

Necrosome complex detected in granulovacuolar degeneration is associated with neuronal loss in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by a specific pattern of neuropathological changes, including extracellular amyloid ß (Aß) deposits, intracellular neurofibrillary tangles (NFTs), granulovacuolar degeneration (GVD) representing cytoplasmic vacuolar lesions, synapse dysfunction and neuronal loss. Necroptosis, a programmed form of necrosis characterized by the assembly of the necrosome complex composed of phosphorylated proteins, i.e. receptor-interacting serine/threonine-protein kinase 1 and 3 (pRIPK1 and pRIPK3) and mixed lineage kinase domain-like protein (pMLKL), has recently been shown to be involved in AD. However, it is not yet clear whether necrosome assembly takes place in brain regions showing AD-related neuronal loss and whether it is associated with AD-related neuropathological changes. Here, we analyzed brains of AD, pathologically defined preclinical AD (p-preAD) and non-AD control cases to determine the neuropathological characteristics and distribution pattern of the necrosome components. We demonstrated that all three activated necrosome components can be detected in GVD lesions (GVDn+, i.e. GVD with activated necrosome) in neurons, that they colocalize with classical GVD markers, such as pTDP-43 and CK1δ, and similarly to these markers detect GVD lesions. GVDn + neurons inversely correlated with neuronal density in the early affected CA1 region of the hippocampus and in the late affected frontal cortex layer III. Additionally, AD-related GVD lesions were associated with AD-defining parameters, showing the strongest correlation and partial colocalization with NFT pathology. Therefore, we conclude that the presence of the necrosome in GVD plays a role in AD, possibly by representing an AD-specific form of necroptosis-related neuron death. Hence, necroptosis-related neuron loss could be an interesting therapeutic target for treating AD.

Binding of [18F]AV1451 in post mortem brain slices of semantic variant primary progressive aphasia patients.

PURPOSE: In vivo tau-PET tracer retention in the anterior temporal lobe of patients with semantic variant primary progressive aphasia (SV PPA) has consistently been reported. This is unexpected as the majority of these patients have frontotemporal lobar degeneration TDP (FTLD-TDP). METHODS: We conducted an in vitro [18F]AV1451 autoradiography binding study in five cases with a clinical diagnosis of SV PPA constituting the range of pathologies (i.e., three FTLD-TDP, one Alzheimer's disease (AD), and one Pick's disease (PiD)). Binding was compared with two controls without neurodegeneration, two typical AD, one corticobasal syndrome with underlying AD, and one frontotemporal dementia behavioral variant with FTLD-TDP. The effect of blocking with the authentic reference material and with the MAO-B inhibitor deprenyl was assessed. Immunohistochemistry was performed on adjacent cryosections. RESULTS: Absence of specific [18F]AV1451 binding was observed for all three SV PPA FTLD-TDP cases. The absence of binding in controls as well as the successful blocking with authentic AV1451 in cases with tauopathy demonstrated specificity of the [18F]AV1451 signal for tau. The specific [18F]AV1451 binding was highest in AD, followed by PiD. This binding colocalized with the respective tau lesions and could not be blocked by deprenyl. Similar pilot findings were obtained with [18F]THK5351. CONCLUSION: In vitro autoradiography showed no [18F]AV1451 binding in SV PPA due to FTLD-TDP, while specific binding was present in SV PPA due to AD and PiD. The discrepancy between in vitro and in vivo findings remains to be explained. The discordance is not related to [18F]AV1451 idiosyncrasies as [18F]THK5351 findings were similar.

Aß-induced acceleration of Alzheimer-related τ-pathology spreading and its association with prion protein.

Extracellular deposition of amyloid ß-protein (Aß) in amyloid plaques and intracellular accumulation of abnormally phosphorylated τ-protein (p-τ) in neurofibrillary tangles (NFTs) represent pathological hallmark lesions of Alzheimer's disease (AD). Both lesions develop in parallel in the human brain throughout the preclinical and clinical course of AD. Nevertheless, it is not yet clear whether there is a direct link between Aß and τ pathology or whether other proteins are involved in this process. To address this question, we crossed amyloid precursor protein (APP) transgenic mice overexpressing human APP with the Swedish mutation (670/671 KM → NL) (APP23), human wild-type APP (APP51/16), or a proenkephalin signal peptide linked to human Aß42 (APP48) with τ-transgenic mice overexpressing human mutant 4-repeat τ-protein with the P301S mutation (TAU58). In 6-month-old APP23xTAU58 and APP51/16xTAU58 mice, soluble Aß was associated with the aggravation of p-τ pathology propagation into the CA1/subiculum region, whereas 6-month-old TAU58 and APP48xTAU58 mice neither exhibited significant amounts of p-τ pathology in the CA1/subiculum region nor displayed significant levels of soluble Aß in the forebrain. In APP23xTAU58 and APP51/16xTAU58 mice showing an acceleration of p-τ propagation, Aß and p-τ were co-immunoprecipitated with cellular prion protein (PrPC). A similar interaction between PrPC, p-τ and Aß was observed in human AD brains. This association was particularly noticed in 60% of the symptomatic AD cases in our sample, suggesting that PrPC may play a role in the progression of AD pathology. An in vitro pull-down assay confirmed that PrPC is capable of interacting with Aß and p-τ. Using a proximity ligation assay, we could demonstrate proximity (less than ~ 30-40 nm distance) between PrPC and Aß and between PrPC and p-τ in APP23xTAU58 mouse brain as well as in human AD brain. Proximity between PrPC and p-τ was also seen in APP51/16xTAU58, APP48xTAU58, and TAU58 mice. Based on these findings, it is tempting to speculate that PrPC is a critical player in the interplay between Aß and p-τ propagation at least in a large group of AD cases. Preexisting p-τ pathology interacting with PrPC, thereby, appears to be a prerequisite for Aß to function as a p-τ pathology accelerator via PrPC.