Alzheimer's Disease Individuals Research Articles

Associations between CSF proteins and medial temporal lobe atrophy across the AD continuum

AbstractBackgroundCortical atrophy is a typical feature of Alzheimer´s disease (AD). The biological processes that associate with or possibly lead to atrophy remain largely unexplored. We hypothesized that disease stage would modulate the associations between cerebrospinal fluid (CSF) proteins and regional cortical thickness in individuals with abnormal CSF beta‐amyloid.MethodCognitively normal (CN), mild cognitive impairment (MCI) and AD individuals were selected from ADNI, based on abnormal CSF beta‐amyloid (<192 ng/l). All examined individuals had cortical thickness measurements and CSF proteomic data available (measured with MRM and RBM). Correlations between 217 CSF proteins and cortical thickness in 34 cortical regions (averaged over the left and right hemispheres) were analyzed with linear models, adjusted for age and sex. Interactions for diagnosis were evaluated for each protein‐cortical thickness association. Protein enrichment analysis was performed with Cytoscape ClueGO.ResultWe included 197 individuals (32 CN; 104 MCI; 61 AD) with a mean age 74.8 (SD 7.1) years, 41.6 % women.Cortical thickness declined according to disease progression in 28 brain regions, most significantly in the entorhinal cortex (ANOVA p‐value <0.0001), the middle temporal gyrus (p<0.0001) and the inferior temporal cortex (p<0.0001). 9 proteins, including phospho‐tau and BACE activity, showed interactions for diagnosis in the entorhinal cortex, 12 in the middle temporal gyrus and 19 inferior temporal cortex. These proteins were associated with beta‐amyloid metabolic process, dendritic cell differentiation, and oligodendrocyte development in ClueGO enrichment analyses. A consistent finding was that higher levels of the majority of these CSF proteins correlated with lower cortical thickness in CN, and that these correlations were attenuated with disease progression.ConclusionAlterations in the levels of CSF proteins are associated with cortical atrophy in the medial temporal regions, and the biological processes underlying cortical atrophy seem to begin already in the preclinical stage of AD. These results suggest that therapies targeted at preventing cortical atrophy would need to be initiated already in the CN stage.

TREM2-induced activation of microglia contributes to synaptic resilience in non-demented individuals with Alzheimer's neuropathology.

The existence of individuals who remain cognitively intact despite presenting histopathological signs of Alzheimer's disease (AD), here referred to as "Non demented with AD neuropathology" (NDAN), suggests that some unknown mechanisms are triggered to resist cognitive impairment. Synaptic dysfunction has been identified as one of the major AD causes and it is established that microglia, attracted to plaques, engulf damaged synapses. In this context, exposed phosphatidylserine (ePS) represents a neuronal "eat-me" signal involved in microglial-mediated phagocytosis of damaged synapses. A possible candidate mediator of this process is represented by TREM2, a microglial surface receptor activated by ligands including PS. Based on TREM2 role in the scavenging function of microglia, we hypothesize that an efficient microglial phagocytosis of damaged synapses underlies synaptic resilience in NDAN, thus protecting from memory deficits. Using immunofluorescence microscopy, a comparative study of human post-mortem frontal cortices of aged-matched individuals, AD and NDAN individuals has been performed. The distribution of activated microglia (IBA1 and IBA1/CD68 positive cells) and the expression of phagocytic microglia-related proteins (TREM2 and DAP12) were evaluated. To test the efficacy of microglia in removing debris and damaged synapses, preservation of synapses around plaques was assessed using MAP2 and tubulin βIII as dendritic and axonal markers respectively, and PSD95 as a post synaptic marker. Furthermore, taking advantage of flow cytometry techniques, a study of the ePS using Annexin V assay has been performed. Immunofluorescence analyses indicate higher microglial activation and TREM2 expression in NDAN individuals, as well as preserved axonal and dendritic structure around plaques vs. AD. High levels of PSD95 around NDAN plaques and the colocalization of PSD95 and CD68 may suggest a prompt removal of damaged synapses by hyperactive phagocytic microglia. Annexin V assay on synaptosomes isolated from aged-matched, AD and NDAN individuals indicates changes in the ePS in NDAN individuals, confirming the engulfment of damaged synapses. Our results suggest a higher efficiency of TREM2-induced phagocytic microglia in removing damaged synapses, underlying synaptic resilience in NDAN individuals.

Microglia across the spectrum from homeostatic to disease phenotypes display enhanced inflammatory responses in human postmortem AD brain.

Microglia-mediated neuroinflammation is hypothesized to contribute to disease progression in neurodegenerative diseases such as Alzheimer's Disease (AD). Recent single-cell RNA-seq studies highlight the heterogeneity of microglial subtypes. Since microglia are a relatively small proportion of CNS cells, standard single-cell omics approaches do not fully capture the diversity of microglia in human subjects. Understanding the gene expression and regulatory networks which define the spectrum of microglia phenotypes is critical to identifying specific targets for neuroinflammation modulating therapies. Our study utilized post-mortem brain tissue from 22 total (7 male) participants with an average age of 86.23 years and post-mortem interval of 5.42 hours. Of those individuals, 12 (3 male) had significant AD neuropathic change present in their brains upon postmortem analysis. Nuclei isolated from prefrontal cortex were sorted for PU.1 expression using fluorescence activated nucleus sorting (FANS). The FANS approach yields larger numbers of nuclei annotated as microglia with high quality sequence from each individual. We performed single-nucleus RNA-seq using the 10X Genomics Chromium platform. We isolated more than 4,000 microglia nuclei from each of the 22 participants, facilitating the comparison of profiles at an individual level in addition to group comparisons based on disease state. Unbiased clustering revealed 8 microglia clusters and improved resolution of microglia heterogeneity compared to standard single-cell approaches. Previously identified mouse disease-associated microglia (DAM) genes are not located in a single cluster of human microglia. "DAM" genes are also present in control aged brains. We identify clusters of microglia enriched for biological pathways implicating defined myeloid roles including a cluster of interferon-stimulated microglia as well as a cluster of autophagic/phagocytic microglia. In many, but not all, of our annotated clusters, including that with high expression of homeostatic genes, individuals with AD have greater enrichment of inflammatory pathways using pseudobulk analysis. We demonstrate significant heterogeneity in microglia subtypes in human brain. Regulation of expression in inflammation-related networks is detected in microglia from both control and AD individuals, though enrichment of specific inflammatory pathways differs. This is important as the field looks to target microglia mechanisms for pharmacological intervention while limiting off-target effects.

Microglia subtype transcriptomes differ between Alzheimer Disease and control human postmortem brain samples

AbstractBackgroundMicroglia‐mediated neuroinflammation is hypothesized to contribute to disease progression in neurodegenerative diseases such as Alzheimer’s Disease (AD). Microglia subtypes are complex, with beneficial and harmful phenotypes. Understanding the gene expression networks which define the spectrum of microglia phenotypes is critical to identifying specific targets for neuroinflammation modulating therapies.MethodOur study utilized post‐mortem brain tissue from 22 total (7 male) participants; 12 (3 male) had significant AD neuropathic change. Nuclei isolated from prefrontal cortex were sorted for the myeloid marker PU.1 using fluorescence activated nucleus sorting (FANS). The FANS approach yields larger numbers of nuclei annotated as microglia with high quality sequence from each individual. We performed single‐nucleus RNA‐seq using the 10X Genomics Chromium platform.ResultsWe isolated more than 120,000 microglia nuclei, facilitating group comparisons based on disease state. Unbiased clustering revealed 10 microglia clusters and improved resolution of microglia heterogeneity compared to standard single‐cell approaches. We identify clusters of microglia enriched for biological pathways implicating defined myeloid roles including interferon‐stimulated, endo/lysosomal, neurodegenerative with a “disease‐associated microglia” (DAM) signature, as well as a metabolically active and autophagic cluster. Interestingly, the cluster proportionately enriched for AD individuals’ nuclei is not the DAM cluster but instead one of the clusters in which endo/lysosomal genes are highly upregulated. Furthermore, many of the genes in known AD risk loci are strongly differentially regulated in this AD associated cluster. We also identify a cluster of microglia that is proportionately enriched for control samples with upregulated cell cycle and proliferation genes. Trajectory analysis suggests that the paths AD and control nuclei take from unactivated “homeostatic” to various phenotypic states are also distinct.ConclusionUsing human AD tissue collected with uniform protocols we characterize the transcriptomic profiles of microglia subtypes in human brain. By enriching for myeloid cells prior to analysis we can resolve microglia subtypes revealing the diversity of microglia which are “inflammatory” as well as other microglia subtypes responding with induction of metabolic and lysosomal pathways. Our data identifies subtypes of microglia that are unique to AD and control individuals. These results support the possibility of pharmacological targeting of specific subtypes of microglia to alter AD progression.

Neuropathological hallmarks of Alzheimer's disease in centenarians, in the context of aging.

Alzheimer's Disease (AD) is characterized by accumulation of amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs). With increasing age these neuropathological hallmarks are also present in the brains of non-demented individuals. Here, we investigated neuropathological hallmarks in cognitively healthy centenarians in the context of aging. Amyloid phases, Braak stages (NFTs) and CERAD scores (neuritic plaques, NPs) and brain weights of 53 well-phenotyped self-reported cognitively healthy centenarians (aged 100-115) were compared with 1,503 brains from AD- (age 37-102) and non-demented donors (age 16-99). Global cognitive performance (MMSE score) in centenarians was assessed on average 0.83 years before death and correlations with the pathologies were assessed when separating the centenarians on MMSE alone or in combination with AD pathology presence. With increasing age-at-death, average AD neuropathology load increases in non-demented individuals, and decreases in AD cases, converging at around 100 years of age. Of all non-demented centenarians (MMSE score ≥26 at last visit), 50% fulfilled pathology criteria for AD and had intermediate levels of AD neuropathology, and one centenarian (5%) was free of AD pathology. Among centenarians, Amyloid phases, CERAD scores, or brain weight did not correlate with MMSE score. Braak stages varied widely, but did not exceed Braak stage IV. Moreover, Braak stage correlated with cognitive performance (p=0.049). Neuropathology-loads in AD and non-demented individuals converge at 100 years, suggesting that the levels of these pathologies are a common consequence of aging. A large proportion of cognitively healthy centenarians fulfil pathological criteria for AD. These findings suggest that centenarians can have high levels of cognitive health despite the presence of pathology. This may be attributed to the prolonged functioning of cellular processes that maintain brain health in these unique individuals.

Hippocampal transcriptomic profiling of Alzheimer’s disease patients and mouse models: Differences and similarities

Rodent models of Alzheimer's disease (AD) have provide invaluable insights on AD pathophysiology in the past decades. Therefore, the evaluation of similarities between models and human pathology can improve AD research. Here, we compared hippocampal transcriptomic profiles of human late onset-AD (LOAD) and early-onset AD (EOAD) individuals with three mouse models (hAβ-KI, APP/PS1 and 5xFAD) to evaluate transcriptomic similarities between these animal models and human pathology. While APP/PS1 and 5xFAD are well established EOAD models, hAβ-KI was recently introduced as a potential LOAD model. We hypothesized that APP/PS1 and 5xFAD will have more similiatires to EOAD human AD and hAβ-KI with human LOAD. Five publicly available human AD/cognitively unimpaired transcriptomic profiles were collected from GEO (https://www.ncbi.nlm.nih.gov/geo/), merged and submitted to differential expression analysis (DEA) and functional enrichment analysis (FEA) using R. APP/PS1 mouse model RNAseq data from two datasets (GSE149661 and GSE145907) were also collected. Finally, RNAseq data of 5xFAD and hAβ-KI mouse models were obtained from AMP-AD Knowledge Portal (https://www.synapse.org/) using synapser and synapserutils packages. All animal models were submitted to DEA and FEA. DEA identified 1164, 3261 and 1782 differentially expressed genes (DEGs) for the comparisons between hAβ-KI, 5xFAD and APP/PS1 mutants versus wild type controls, respectively. The hAβ-KI mice model exhibited more DEGs in common with LOAD than with EOAD patients. Interestingly, APP/PS1 and 5xFAD mice also presented more DEGs in common with LOAD than with EOAD patients. However, 5xFAD showed significantly higher DEGs intersection with EOAD than with hAβ-KI and APP/PS1. FEA of Gene Ontology biological processes revealed 92% overlap of terms enriched in hAβ-KI with LOAD, but only 32% with EOAD. Unexpectedly, both 5xFAD and APP/PS1 presented more than 75% of their enriched terms in common with LOAD patients compared to ∼45% in EOAD. New animal models are being introduced constantly to better simulate AD pathology. Hence, the evaluation of their overlap with human pathology is paramount. We found that the new hAβ-KI shows a good fit towards LOAD, as was its original purpose. APP/PS1 and 5xFAD on the other hand, were less optimal than expected to model EOAD.

Vaccination against the broadly expressed microbial antigen PNAG prevents cognitive decline in the APP-PS1 mouse model of Alzheimer's disease.

While there is ample evidence for a role of the microbiota in cognitive decline in Alzheimer's Disease (AD), there is little insight into how the microbiota mediates neuronal dysfunction and cognitive decline. A conserved surface polysaccharide, poly-N-acetyl glucosamine (PNAG) is produced by a broad range of microbial cells, but not mammals. We have detected the presence of PNAG-positive, likely microbiota-derived cells or fragments closely associated with amyloid-ß deposits in the brains of deceased AD individuals and cognitively impaired APP-PS1 mice, but not non-AD controls. These fragments potentially provide an inflammatory stimulus critical for neural tissue destruction and cognitive impairment. We tested whether vaccination against PNAG prevented microbial access to brains of APP-PS1 mice and impacted cognitive decline. Microbial factors were detected with a human IgG monoclonal antibody (MAb) to PNAG in brain tissues from human AD and APP/PS1 mice. Two cohorts of APP/PS1 mice and wild type (WT) littermate controls were vaccinated with either a PNAG vaccine (5GlcNH2 -TT) or TT (tetanus toxin) only as a control, five times starting at either 5 weeks or 5 months of age. Only PNAG-immunized mice made specific antibodies over the experimental period. Water T maze testing of mice was performed at 12-15 months of age. Brains were harvested to detect both PNAG and amyloid-ß immunohistochemically. PNAG-positive microbial factors were elevated in areas with amyloid-ß deposits in brain tissue from human AD cases and APP/PS1 mice. Non-AD age- and sex-matched controls had little detectable brain PNAG, even around amyloid-ß deposits. Active PNAG vaccination at both 5 weeks and 5 months of age prevented cognitive decline in APP-PS1 mice. Only 10% or 30% of non-immune APP/PS1 mice reached criteria by day 5 of reversal, respectively, compared to 90% and 100% of PNAG vaccinated APP/PS1 mice. Immunohistochemistry indicated decreased presence of PNAG-positive material in PNAG vaccinated mice and a modest reduction in amyloid-ß deposits. Antibodies to PNAG induced at 5 weeks or 5 months of age prevented cognitive decline and brain pathology in APP/PS1 mice, suggesting that microbial factors that enter the brain are critical for cognitive decline that may be prevented by vaccination.

Urine dicarboxylic acids are metabolic biomarkers of early Alzheimer’s disease

AbstractBackgroundWe previously identified urine dicarboxylic acids (DCA) of carbon length 4‐9 as candidate biomarkers of probable Alzheimer’s disease (AD) and energy dysregulation, and found their levels correlated with hippocampal volume. Our aim was to evaluate these initial findings in a second cohort.MethodStudy participants (> 65 years) were classified clinically as cognitively healthy (CH, n=188) or with probable AD (n=66) based on Uniform Data System‐3 of the National Alzheimer’s Coordinating Center criteria. Cerebrospinal fluid (CSF) amyloid ß42 (A) and phospho‐ tau (T) levels were measured by validated immunoassay. Urine was collected in a “spot” sample after a 12 h overnight fast; target DCAs were detected using gas chromatography coupled with negative ion chemical ionization mass spectrometry and each DCA was normalized to deuterated internal standards and to a percent of total fatty acids.ResultThe mean of short‐chain DCA’s (C4‐C5) were higher in CH (44.38% ±17.79) compared to AD individuals (34.79% ±12.39) (p=0.0002), while the long‐chain DCA’s (C7‐C9) were lower for CH (34.70% ±16.88) when compared to AD individuals (45.22% ±15.11) (p<0.0001). DCA levels in the subset of CH participants with A+/T+ were in a transition to the levels of the AD group and C4‐C5 and C7‐C9 differed from those with A‐/T‐ biomarkers (p=0.0001). Combining results into a ratio of short‐ to long‐chain DCAs distinguished the A‐/T‐ (2.330 ±2.144) from the A+/T+ group (1.178 ±0.946); p<0.0001. ROC curve of the DCA ratio between CH‐NAT and AD is 82%. Study participant clinical and DCA groups were not significantly correlated with the common confounders of age, sex, education or ApoE genotype.ConclusionOur data extends our initial finding that urine DCA measures have potential as biomarkers of AD pathology, including for cognitively healthy individuals who are positive for CSF AT biomarkers. We propose that measurement of urine DCAs provides a new approach to screen for metabolic fluctuations in early AD and to monitor the effect of novel therapies in clinical trials. While studies are needed, including with other populations, varied clinical classifications, simplified chemistry, this data supports DCA biomarkers for widespread screening since the necessary urine sample is available from everyone.

Neuroproteomics of cognitively healthy centenarians in the context of aging and Alzheimer's disease.

Aging is often accompanied by neurodegenerative diseases such as Alzheimer's disease (AD), and their associated neuropathological hallmarks. Few individuals are able to maintain cognitive health until extreme ages, such as cognitively healthy centenarians, despite displaying substantial pathology in their brains. Here we report on a unique and large single-center proteomics study providing insight into proteome changes occurring with AD and aging. We investigate which mechanisms could be involved in maintaining cognitive health at extreme ages in the presence of pathology. We performed quantitative proteomics on middle temporal lobe tissue for a cohort of 61 non-demented and 91 AD individuals across the age-continuum, and 58 centenarians from the 100-plus Study. We performed enrichment analyses for cell-types and GO-terms using multiple approaches (Figure 1). We identified 3,448 proteins, among which proteins associated with AD Braak stage or age. 472 proteins were associated with Braak stages, independent of age. Cell-type enrichment revealed that with increasing Braak stages, the abundance of astrocytic proteins increased while the abundance of neuronal proteins decreased. Among centenarians we identified 13 proteins that that differ in abundance from AD cases with the same Braak stage (IV). These included ubiquitin, cytoskeletal and synaptic proteins. Additionally, we identified 174 age-related proteins in non-demented controls. Of these, 97 were expressed in centenarians at levels different from those predicted for their age. Cell-type enrichment revealed that the abundance of oligodendrocytic proteins decreased with age, whereas the abundance of astrocytic proteins was increased with age and Braak stage. Progressive AD stages are associated with increased abundance of astrocytic- and lower abundance of neuronal proteins, while healthy aging is associated with a lower abundance of oligodendrocytic proteins and higher abundance of astrocytic proteins. In this study we identified proteins in the centenarians that deviate in level from prediction based on age. How these proteins act on cognition needs to be investigated further. Centenarian-specific proteins at Braak stage IV may indicate mechanisms protecting against cognitive decline, whereas the centenarian-specific age-related proteins might indicate processes that prevent adverse brain aging.

Gut microbiome alterations in Alzheimer’s patients from Kazakhstan

AbstractBackgroundRecent studies strongly suggest that gut microbiome is capable of influencing brain functions and contribute to the development of Alzheimer’s disease (AD). However, only few studies have characterized the human gut microbiome communities associated with AD. Moreover, reported changes in the gut microbiomes in AD patients from different countries are not similar. Therefore, more research is needed in order to reveal the relationships existing between human microbiomes and AD in different ethnic populations. Here, we report the first pilot case‐control study of diversity and composition of gut microbiomes isolated from the patients diagnosed with AD in comparison with healthy seniors from the Central Asian region.MethodMicrobial DNA was isolated from fecal samples of the patients with confirmed AD (n=11) and healthy age‐ and gender‐matched individuals (n=13). The composition of gut microbiomes were characterized by 16S ribosomal RNA MiSeq sequencing. Data analysis was performed using less operational taxonomic units scripts (LotuS) and R (v4.03).ResultOur results demonstrated that gut microbiota of AD individuals had overall higher α‐diversity compared to healthy controls, although this difference was not significant. The absence of statistical power might be explained by a low sample size. However, we have found significant differences of bacterial abundance at class, order and genus levels. At class level the amount of Bacilli was depleted in AD group; at order level, the relative abundance of Oscillospirales increased, while the abundance of Lactobacillales decreased in AD patients. Among bacterial genera, microbiomes of AD participants were characterized by a preponderance of unknown_Prevotellaceae and unknown_Ruminococcaceae. Linear discriminant analysis (LDA) has revealed that the relative abundances of Eubacterium coprostanoligenes group, Rikenellaceae RC9 gut group, Bacilli RF39, Oscillospirales UCG‐011 were significantly different in AD patients compared to healthy participants.ConclusionStudying the gut microbiome alterations in AD patients is of considerable interest. By focusing on the mechanism of interactions between human microbiota and the brain, we can uncover new pathophysiological pathways leading to the onset and progression of AD, evaluate the contributions of environment and lifestyle to the increase in prevalence of dementia and develop practical recommendations for the prevention and treatment of this severe pathology.

Postural Sway Characteristics Are Affected by Alzheimer's Disease.

The vestibular system, responsible for balance, is affected by Alzheimer's disease (AD). In this paper, linear and non-linear balance features were used to assess the postural stability of 13 AD individuals at mild stages in comparison with 16 healthy controls. Utilizing two accelerometers, the anterior-posterior (AP) and medial-lateral (ML) sways were recorded from the T2 vertebrae and lateral malleolus of participants standing on a solid and soft foam surface under both eyes-open and eyes-closed conditions. From the recorded signals, four features were extracted and used for statistical analysis: Number of Position Changes (NPC), Number of Non-Zero Accelerations (NNZA), Katz, and Higuchi fractal dimensions (KFD and HFD, respectively). The results show: 1) postural stability is significantly worse for the eyes-closed compared to eyes-open condition (P<0.05 for all features except HFD) as well as whilst standing on soft foam compared to the solid surface (P<0.05 for all features) in both groups; 2) balance perturbations were larger for AP sway than ML on both solid and foam surfaces in both groups (P<0.05 for NPC and NNZA); and 3) stationary balance is significantly poorer for AD individuals compared to controls (P<0.05 for all features). These observations show that both linear and non-linear characteristics of postural stability data have the potentials to be used as objective diagnostic aids for the detection of AD.

Mitochondrial Electron Transport Chain Protein Abnormalities Detected in Plasma Extracellular Vesicles in Alzheimer's Disease.

Mitochondria provide energy to neurons through oxidative phosphorylation and eliminate Reactive Oxygen Species (ROS) through Superoxide Dismutase 1 (SOD1). Dysfunctional mitochondria, manifesting decreased activity of electron transport chain (ETC) complexes and high ROS levels, are involved in Alzheimer’s disease (AD) pathogenesis. We hypothesized that neuronal mitochondrial dysfunction in AD is reflected in ETC and SOD1 levels and activity in plasma neuron-derived extracellular vesicles (NDEVs). We immunoprecipitated NDEVs targeting neuronal marker L1CAM from two cohorts: one including 22 individuals with early AD and 29 control subjects; and another including 14 individuals with early AD and 14 control subjects. In the first cohort, we measured levels of complexes I, III, IV, ATP synthase, and SOD1; in the second cohort, we measured levels and catalytic activity of complexes IV and ATP synthase. AD individuals had lower levels of complexes I (p < 0.0001), III (p < 0.0001), IV (p = 0.0061), and V (p < 0.0001), and SOD1 (p < 0.0001) compared to controls. AD individuals also had lower levels of catalytic activity of complex IV (p = 0.0214) and ATP synthase (p < 0.0001). NDEVs confirm quantitative and functional abnormalities in ECT complexes and SOD1 previously observed in AD models and during autopsy, opening the way for using them as biomarkers for mitochondrial dysfunction in AD.

Differing glial expression profiles as a meaningful measure of earliest stages of Alzheimer's disease (AD) pathogenesis

Neuroinflammatory dysfunction is a well-known phenomenon encountered in brains of demented AD individuals, but little is known about its role in earliest stages of AD pathogenesis. We assessed glial immunoreactivity in brain regions where tau burden was just about to develop and evaluated differing expression profiles in cognitively diverging individuals.

Dense core vesicle markers in CSF and cortical tissues of patients with Alzheimer\u2019s disease

BackgroundNew fluid biomarkers for Alzheimer's disease (AD) that reveal synaptic and neural network dysfunctions are needed for clinical practice and therapeutic trial design. Dense core vesicle (DCV) cargos are promising cerebrospinal fluid (CSF) indicators of synaptic failure in AD patients. However, their value as biomarkers has not yet been determined.MethodsImmunoassays were performed to analyze the secretory proteins prohormone convertases PC1/3 and PC2, carboxypeptidase E (CPE), secretogranins SgIII and SgII, and Cystatin C in the cerebral cortex (n = 45, provided by Bellvitge University Hospital) and CSF samples (n = 66, provided by The Sant Pau Initiative on Neurodegeneration cohort) from AD patients (n = 56) and age-matched controls (n = 55).ResultsIn AD tissues, most DCV proteins were aberrantly accumulated in dystrophic neurites and activated astrocytes, whereas PC1/3, PC2 and CPE were also specifically accumulated in hippocampal granulovacuolar degeneration bodies. AD individuals displayed an overall decline of secretory proteins in the CSF. Interestingly, in AD patients, the CSF levels of prohormone convertases strongly correlated inversely with those of neurodegeneration markers and directly with cognitive impairment status.ConclusionsThese results demonstrate marked alterations of neuronal-specific prohormone convertases in CSF and cortical tissues of AD patients. The neuronal DCV cargos are biomarker candidates for synaptic dysfunction and neurodegeneration in AD.

Amyloid pathology and synaptic loss in pathological aging.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory dysfunction and cognitive decline. Pathological aging (PA) describes patients who are amyloid-positive but cognitively unimpaired at time of death. Both AD and PA contain amyloid plaques dominated by amyloid β (Aβ) peptides. In this study, we investigated and compared synaptic protein levels, amyloid plaque load, and Aβ peptide patterns between AD and PA. Two cohorts of post-mortem brain tissue were investigated. In the first, consisting of controls, PA, AD, and familial AD (FAD) individuals, synaptic proteins extracted with tris(hydroxymethyl)aminomethane-buffered saline (TBS) were analyzed. In the second, consisting of tissue from AD and PA patients from three different regions (occipital lobe, frontal lobe, and cerebellum), a two-step extraction was performed. Five synaptic proteins were extracted using TBS, and from the remaining portion Aβ peptides were extracted using formic acid. Subsequently, immunoprecipitation with several antibodies targeting different proteins/peptides was performed for both fractions, which were subsequently analyzed by mass spectrometry. The levels of synaptic proteins were lower in AD (and FAD) compared with PA (and controls), confirming synaptic loss in AD patients. The amyloid plaque load was increased in AD compared with PA, and the relative amount of Aβ40 was higher in AD while for Aβ42 it was higher in PA. In AD loss of synaptic function was associated with increased plaque load and increased amounts of Aβ40 compared with PA cases, suggesting that synaptic function is preserved in PA cases even in the presence of Aβ.

Systematic Identification of circRNAs in Alzheimer's Disease.

Mammalian circRNAs are covalently closed circular RNAs often generated through backsplicing of precursor linear RNAs. Although their functions are largely unknown, they have been found to influence gene expression at different levels and in a wide range of biological processes. Here, we investigated if some circRNAs may be differentially abundant in Alzheimer’s Disease (AD). We identified and analyzed publicly available RNA-sequencing data from the frontal lobe, temporal cortex, hippocampus, and plasma samples reported from persons with AD and persons who were cognitively normal, focusing on circRNAs shared across these datasets. We identified an overlap of significantly changed circRNAs among AD individuals in the various brain datasets, including circRNAs originating from genes strongly linked to AD pathology such as DOCK1, NTRK2, APC (implicated in synaptic plasticity and neuronal survival) and DGL1/SAP97, TRAPPC9, and KIF1B (implicated in vesicular traffic). We further predicted the presence of circRNA isoforms in AD using specialized statistical analysis packages to create approximations of entire circRNAs. We propose that the catalog of differentially abundant circRNAs can guide future investigation on the expression and splicing of the host transcripts, as well as the possible roles of these circRNAs in AD pathogenesis.

Differentiation of Amyloid Plaques Between Alzheimer's Disease and Non-Alzheimer's Disease Individuals Based on Gray-Level Co-occurrence Matrix Texture Analysis.

Amyloid plaques, one of the main hallmarks of Alzheimer's disease (AD), are classified into diffuse (associated with cognitive impairment) and dense-core types (a common finding in brains of people without Alzheimer's disease (non-AD) and without impaired cognitive function) based on their morphology. We tried to determine the usability of gray-level co-occurrence matrix (GLCM) texture parameters of homogeneity and heterogeneity for the differentiation of amyloid plaque images obtained from AD and non-AD individuals. Images of amyloid-β (Aβ) immunostained brain tissue samples were obtained from the Aging, Dementia and Traumatic Brain Injury Project. A total of 1,039 plaques were isolated from different brain regions of 69 AD and non-AD individuals and used for further GLCM analysis. Images of Aβ stained plaques show higher values of heterogeneity parameters and lower values of homogeneity parameters in AD patients, and vice versa in non-AD patients. Additionally, GLCM analysis shows differences in Aβ plaque texture between different brain regions in non-AD patients and correlates with variables that characterize patient's dementia status. The present study shows that GLCM texture analysis is an efficient method to discriminate between different types of amyloid plaques based on their morphology and thus can prove as a valuable tool in the neuropathological investigation of dementia.

Clustering Alzheimer's Disease Gene Expression Dataset Reveals Underlying Sexually Dimorphic and Disease Status Profiles.

Background:The multiple appearance phenotypes in Alzheimer’s disease (AD) are manifested in epidemiologic sexual dimorphism, variation in age of onset, progress, and severity of the disease.Objective:In this study, we focused on sexual dimorphism, aiming to untie some of the complex interconnections in AD between sex, disease status, and gene expression profiles. Two strategic decisions guided our study: 1) to value transcriptomic multi-layered profiles over alterations in single genes expression; and 2) to embrace a sexual dimorphism centered approach, as we suspect that transcriptomic profiles may dramatically differ not only between healthy and sick individuals but between men and women as well.Methods:Microarray dataset GSE15222, fulfilling our strict criteria, was retrieved from the GEO repository. We performed cluster analysis for each sex separately, comparing the proportion of healthy and AD individuals in each cluster.Results:We were able to identify a biased, female, AD-typified cluster. Furthermore, we showed that this female AD-typified cluster is highly similar to one of the male clusters. While the female cluster constitutes mostly sick individuals, the male cluster constitutes healthy and sick individuals in almost identical proportion.Conclusion:Our results clearly indicate that similar transcriptomic profiles in the two sexes are “physiologically translated” in to a very different, dramatic outcome. Thus, our results suggest the need for a sex-based and transcriptomic profile-based study, for a better understanding of the onset and progression of AD.

Development and evaluation of a T1 standard brain template for Alzheimer disease.

Patients with Alzheimer disease (AD) and mild cognitive impairment (MCI) have high variability in brain tissue loss, making it difficult to use a disease-specific standard brain template. The objective of this study was to develop an AD-specific three-dimensional (3D) T1 brain tissue template and to evaluate the characteristics of the populations used to form the template. We obtained 3D T1-weighted images from 294 individuals, including 101 AD, 96 amnestic MCI, and 97 cognitively normal (CN) elderly individuals, and segmented them into different brain tissues to generate AD-specific brain tissue templates. Demographic data and clinical outcome scores were compared between the three groups. Voxel-based analyses and regions-of-interest-based analyses were performed to compare gray matter volume (GMV) and white matter volume (WMV) between the three participant groups and to evaluate the relationship of GMV and WMV loss with age, years of education, and Mini-Mental State Examination (MMSE) scores. We created high-resolution AD-specific tissue probability maps (TPMs). In the AD and MCI groups, losses of both GMV and WMV were found with respect to the CN group in the hippocampus (F >44.60, P<0.001). GMV was lower with increasing age in all individuals in the left (r=-0.621, P<0.001) and right (r=-0.632, P<0.001) hippocampi. In the left hippocampus, GMV was positively correlated with years of education in the CN groups (r=0.345, P<0.001) but not in the MCI (r=0.223, P=0.0293) or AD (r=-0.021, P=0.835) groups. WMV of the corpus callosum was not significantly correlated with years of education in any of the three subject groups (r=0.035 and P=0.549 for left, r=0.013 and P=0.821 for right). In all individuals, GMV of the hippocampus was significantly correlated with MMSE scores (left, r=0.710 and P<0.001; right, r=0.680 and P<0.001), while WMV of the corpus callosum showed a weak correlation (left, r=0.142 and P=0.015; right, r=0.123 and P=0.035). A 3D, T1 brain tissue template was created using imaging data from CN, MCI, and AD participants considering the participants' age, sex, and years of education. Our disease-specific template can help evaluate brains to promote early diagnosis of MCI individuals and aid treatment of MCI and AD individuals.

Vitamin D and Folate as Predictors of MMSE in Alzheimer's Disease: A Machine Learning Analysis.

Vitamin D (VD) and micronutrients, including folic acid, are able to modulate both the innate and the adaptive immune responses. Low VD and folic acid levels appear to promote cognitive decline as in Alzheimer’s disease (AD). A machine learning approach was applied to analyze the impact of various compounds, drawn from the blood of AD patients, including VD and folic acid levels, on the Mini-Mental State Exam (MMSE) in a cohort of 108 patients with AD. The first analysis was aimed at predicting the MMSE at recruitment, whereas a second investigation sought to predict the MMSE after a 4 year follow-up. The simultaneous presence of low levels of VD and folic acid allow to predict MMSE, suggestive of poorer cognitive function. Such results suggest that the low levels of VD and folic acid could be associated with more severe cases of cognitive impairment in AD. It could be hypothesized that simultaneous supplementation of VD and folic acid could slow down the progression of cerebral degeneration at least in a subset of AD individuals.