The impact of the COVID-19 pandemic on neurosurgery in the elderly population in Sweden.

BACKGROUND: The COVID-19 pandemic prompted a refocus of health care resources to acute care which has impacted on the capacity of healthcare systems to conduct neurological surgeries. The elderly population has been shown to be particularly vulnerable to the consequences of the pandemic. Less neurosurgery can result in great impact on public health by increasing morbidity and mortality in patients with malignancies and traumatic injuries. The aim of this study was to investigate the effects of the COVID-19 pandemic on neurosurgical procedures in the elderly population in Sweden. METHODS: In this retrospective observational study, the reported incidence of all neurosurgical procedures registered in the 21 Regions of Sweden during 2015-2021 in people aged 65 year or older was collected. Surgical procedures were classified according to the NOMESCO system of classification. Neurosurgery incidence was defined as the number of NOMESCO associated interventions per 100.000 inhabitants. ICD-10 codes associated with neurosurgery-related diagnoses and deaths were also collected. Expected incidence of neurosurgery, neurosurgery-associated deaths and brain cancer diagnoses was estimated and compared to actual outcomes. Decrease in the incidence of neurosurgery was compared to regional COVID-19 incidence, other types of surgery and surgery waiting times. RESULTS: The incidence of several categories of neurosurgery decreased in Sweden during 2020 and 2021, although not as much as other surgical categories. Women were more affected than men by the decrease in neurosurgery which could be partly explained by a decrease in brain cancer diagnoses amongst women. There was an association between regional decrease in neurosurgery incidence and longer surgery waiting time. COVID-19 incidence in the region did not have an effect on regional decreases in neurosurgery incidence. CONCLUSIONS: The COVID-19 pandemic resulted in a reduction in the number of neurosurgical procedures performed in Sweden during 2020-2021, although not as much as in other European countries. There was regional difference in Sweden with respect to number of surgeries, and waiting time for elective surgeries although there was no increase in mortality.

DEAD Box Helicase 24 Is Increased in the Brain in Alzheimer's Disease and AppN-LF Mice and Influences Presymptomatic Pathology.

At the time of diagnosis, Alzheimer's disease (AD) patients already suffer from significant neuronal loss. The identification of proteins that influence disease progression before the onset of symptoms is thus an essential part of the development of new effective drugs and biomarkers. Here, we used an unbiased 18O labelling proteomics approach to identify proteins showing altered levels in the AD brain. We studied the relationship between the protein with the highest increase in hippocampus, DEAD box Helicase 24 (DDX24), and AD pathology. We visualised DDX24 in the human brain and in a mouse model for Aß42-induced AD pathology-AppNL-F-and studied the interaction between Aß and DDX24 in primary neurons. Immunohistochemistry in the AD brain confirmed the increased levels and indicated an altered subcellular distribution of DDX24. Immunohistochemical studies in AppNL-F mice showed that the increase of DDX24 starts before amyloid pathology or memory impairment is observed. Immunocytochemistry in AppNL-F primary hippocampal neurons showed increased DDX24 intensity in the soma, nucleus and nucleolus. Furthermore, siRNA targeting of DDX24 in neurons decreased APP and Aß42 levels, and the addition of Aß42 to the medium reduced DDX24. In conclusion, we have identified DDX24 as a protein with a potential role in Aß-induced AD pathology.

A glycan epitope correlates with tau in serum and predicts progression to Alzheimer's disease in combination with APOE4 allele status.

INTRODUCTION: There is an urgent need for novel blood biomarkers for the detection of Alzheimer's disease (AD). We previously showed that levels of the bisecting N-acetylglucosamine glycan epitope was elevated in cerebrospinal fluid in AD. However, its diagnostic value in blood is unknown. METHODS: We analyzed blood levels of bisecting N-acetylglucosamine and total tau in a retrospective cohort of 233 individuals. Progression to AD was compared between the groups using Cox regression. The predictive value of the biomarkers was determined by logistic regression. RESULTS: Bisecting N-acetylglucosamine correlated with tau levels (p < 0.0001). Individuals with an intermediate tau/bisecting N-acetylglucosamine ratio had elevated AD risk (hazard ratio = 2.06, 95% confidence interval [CI]: 1.18-3.6). Moreover, a combined model including tau/bisecting N-acetylglucosamine ratio, apolipoprotein E (APOE) ε4 status, and Mini-Mental State Examination score predicted future AD (area under the curve = 0.81, 95% CI: 0.68-0.93). DISCUSSION: Bisecting N-acetylglucosamine in combination with tau is a valuable blood biomarker for predicting AD.

Lack of N-glycosylation increases amyloidogenic processing of the amyloid precursor protein.

The amyloid precursor protein (APP) is a ubiquitously expressed type 1 transmembrane protein mostly known for serving as a precursor to the amyloid-ß peptide (Aß), a culprit in Alzheimer disease (AD). However, APP also has important physiological functions by being implicated in, for instance, adhesion, signaling, neuronal development, and synaptic function. Human APP contains 2 N-glycosylation sites, at asparagine (N) 467 (N467) and N496. Here, we studied the role of N-glycosylation on APP trafficking and processing by constructing APP-SNAP plasmid vectors for wildtype APP and N-glycosylation site mutants in which N467 or N496 was replaced by glutamine (Q) and expressed these in HEK293T cells. Lack of either of the 2 N-glycans resulted in a reduction in the size of intracellular APP-SNAP-positive vesicles and a reduction of APP-SNAP in the plasma membrane and lysosomes. Importantly, loss of either of the 2 N-glycans resulted in elevated levels of intracellular as well as secreted Aß42. These data suggest that N-glycans have a major impact on trafficking and processing of APP and could play an important role in the development of AD.

Changes in dementia diagnoses in Sweden during the COVID-19 pandemic.

INTRODUCTION: The COVID-19 pandemic has caused large disruptions to healthcare systems. Refocus on COVID-19 related care might have contributed to indirect effects on other healthcare areas. Care focused on acute conditions have been negatively affected although research into the effects on chronic and care intensive patient groups such as patients with dementia diseases is lacking. In this study we evaluated dementia diagnosis trends in Sweden during 2015-2020 according to International Classification of Disease version 10 coding of common dementia diseases. METHODS: Regional and national statistics in the form of International Classification of Disease version 10 coding, COVID-19 incidence, mortality data, and population census data were collected from the National Institute of Health and Welfare. Logistic regression analysis was performed to identify trends of dementia diagnosis during 2015-2020. Correlation test was performed between COVID-19 incidence, mortality rates, and dementia coding. RESULTS: Dementia diagnosis incidence has been declining since 2015 and further decline was noted in many regions in Sweden during 2020. As COVID-19 incidence increased, fewer cases of dementia were diagnosed, a decrease that differentially impacted women and those who were advanced in age. CONCLUSIONS: Dementia diagnosis incidence in Sweden has been on a decline since 2015. The COVID-19 pandemic caused a further larger decline in dementia diagnosis incidence during 2020. COVID-19 incidence, but not mortality, was associated with decrease in dementia diagnosis incidence. There might be a large number of undiagnosed patients with dementia and healthcare reforms should be enacted to address this. Women and elderly are particularly vulnerable groups.

Changes in mortality trends amongst common diseases during the COVID-19 pandemic in Sweden.

OBJECTIVE: It has been found that COVID-19 increases deaths within common diseases in countries that have implemented strict lockdowns. In order to elucidate the proper national response to a pandemic, the mortality rates within COVID-19 and various diseases need to be studied in countries whose pandemic response differ. Sweden represents a country with lax pandemic restrictions, and we aimed to study the effects of COVID-19 on historical mortality rates within common diseases during 2020. METHODS: Regression models and moving averages were used to predict expected premature mortality per the ICD-10 during 2020 using historical data sets. Predicted values were then compared to recorded premature mortality to identify changes in mortality trends. RESULTS: Seasonal increased mortality was found within neurological diseases. Infectious diseases, tumours and cardiac disease mortality rates decreased compared to expected outcome. CONCLUSIONS: Changes in mortality trends were observed for several common diseases during the COVID-19 pandemic. Neurological and cardiac conditions, infections and tumours are examples of diseases that were heavily affected by the pandemic. The indirect effects of COVID-19 on certain patient populations should be considered when determining pandemic impact.

The N-glycan profile in cortex and hippocampus is altered in Alzheimer disease.

Protein glycosylation is crucial for the central nervous system and brain functions, including processes that are defective in Alzheimer disease (AD) such as neurogenesis, synaptic function, and memory formation. Still, the roles of glycans in the development of AD are relatively unexplored. Glycomics studies of cerebrospinal fluid (CSF) have previously shown altered glycosylation pattern in patients with different stages of cognitive impairment, including AD, compared to healthy controls. As a consequence, we hypothesized that the glycan profile is altered in the brain of patients with AD and analyzed the asparagine-linked (N-linked) glycan profile in hippocampus and cortex in AD and control brain. Glycans were enzymatically liberated from brain glycoproteins and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Eleven glycans showed significantly different levels in hippocampus compared to cortex in both control and AD brain. Two glycans in cortex and four in hippocampus showed different levels in AD compared to control brain. All glycans that differed between controls and AD brain had similar structures with one sialic acid, at least one fucose and a confirmed or potential bisecting N-acetylglucosamine (GlcNAc). The glycans that were altered in AD brain differed from those that were altered in AD CSF. One glycan found to be present in significantly lower levels in both hippocampus and cortex in AD compared to control contained a structurally and functionally interesting epitope that we assign as a terminal galactose decorated with fucose and sialic acid. Altogether, these studies suggest that protein glycosylation is an important component in the development of AD and warrants further studies.

Engineered Human Induced Pluripotent Cells Enable Genetic Code Expansion in Brain Organoids.

Human induced pluripotent stem cell (hiPSC) technology has revolutionized studies on human biology. A wide range of cell types and tissue models can be derived from hiPSCs to study complex human diseases. Here, we use PiggyBac-mediated transgenesis to engineer hiPSCs with an expanded genetic code. We demonstrate that genomic integration of expression cassettes for a pyrrolysyl-tRNA synthetase (PylRS), pyrrolysyl-tRNA (PylT) and the target protein of interest enables site-specific incorporation of a non-canonical amino acid (ncAA) in response to an amber stop codon. Neural stem cells, neurons and brain organoids derived from the engineered hiPSCs continue to express the amber suppression machinery and produce ncAA-bearing reporter. The incorporated ncAA can serve as a minimal bioorthogonal handle for further modifications by labeling with fluorescent dyes. Site-directed ncAA mutagenesis will open a wide range of applications to probe and manipulate proteins in brain organoids and other hiPSC-derived cell types and complex tissue models.

Live Cell FRET Imaging Reveals Amyloid ß-Peptide Oligomerization in Hippocampal Neurons.

Amyloid ß-peptide (Aß) oligomerization is believed to contribute to the neuronal dysfunction in Alzheimer disease (AD). Despite decades of research, many details of Aß oligomerization in neurons still need to be revealed. Förster resonance energy transfer (FRET) is a simple but effective way to study molecular interactions. Here, we used a confocal microscope with a sensitive Airyscan detector for FRET detection. By live cell FRET imaging, we detected Aß42 oligomerization in primary neurons. The neurons were incubated with fluorescently labeled Aß42 in the cell culture medium for 24 h. Aß42 were internalized and oligomerized in the lysosomes/late endosomes in a concentration-dependent manner. Both the cellular uptake and intracellular oligomerization of Aß42 were significantly higher than for Aß40. These findings provide a better understanding of Aß42 oligomerization in neurons.

Conformation-specific antibodies against multiple amyloid protofibril species from a single amyloid immunogen.

We engineered and employed a chaperone-like amyloid-binding protein Nucleobindin 1 (NUCB1) to stabilize human islet amyloid polypeptide (hIAPP) protofibrils for use as immunogen in mice. We obtained multiple monoclonal antibody (mAb) clones that were reactive against hIAPP protofibrils. A secondary screen was carried out to identify clones that cross-reacted with amyloid beta-peptide (Aß42) protofibrils, but not with Aß40 monomers. These mAbs were further characterized in several in vitro assays, in immunohistological studies of a mouse model of Alzheimer's disease (AD) and in AD patient brain tissue. We show that mAbs obtained by immunizing mice with the NUCB1-hIAPP complex cross-react with Aß42, specifically targeting protofibrils and inhibiting their further aggregation. In line with conformation-specific binding, the mAbs appear to react with an intracellular antigen in diseased tissue, but not with amyloid plaques. We hypothesize that the mAbs we describe here recognize a secondary or quaternary structural epitope that is common to multiple amyloid protofibrils. In summary, we report a method to create mAbs that are conformation-sensitive and sequence-independent and can target more than one type of protofibril species.

Isopeptide and ester bond ubiquitination both regulate degradation of the human dopamine receptor 4.

How an optimal level of human dopamine D4 receptor (hD4R) is maintained in synaptic membranes is not known. We show here that hD4R is ubiquitinated in primary neurons. We go on to show that ubiquitin is attached to hD4R through isopeptide and ester bonds. When lysine (Lys) residues of the hD4R are substituted with arginine (Arg) residues, cellular hD4R protein levels increase. A synergistic effect on hD4R levels is noted when cytoplasmic serine (Ser) and threonine (Thr) residues are mutated. Chloroquine, an inhibitor of lysosomal degradation, did not have an effect on hD4R protein levels. However, treatment with bortezomib, an inhibitor of the 20S proteasome, caused a dose-dependent increase in hD4R protein levels. The effect of bortezomib was attenuated in the receptor variants that lacked Lys or Ser/Thr residues, and the hD4R mutant that lacked 17 cytoplasmic Lys, Ser, and Thr residues was nearly insensitive to bortezomib treatment. We conclude that both isopeptide and ester bond ubiquitination regulate proteasomal degradation of hD4R.

Maturation and processing of the amyloid precursor protein is regulated by the potassium/sodium hyperpolarization-activated cyclic nucleotide-gated ion channel 2 (HCN2).

The toxic amyloid ß-peptide (Aß) is a key player in Alzheimer Disease (AD) pathogenesis and selective inhibition of the production of this peptide is sought for. Aß is produced by the sequential cleavage of the Aß precursor protein (APP) by ß-secretase (to yield APP-C-terminal fragment ß (APP-CTFß) and soluble APPß (sAPPß)) and γ-secretase (to yield Aß). We reasoned that proteins that associate with γ-secretase are likely to regulate Aß production and to be targets of pharmaceutical interventions and therefore performed a pull-down assay to screen for such proteins in rat brain. Interestingly, one of the purified proteins was potassium/sodium hyperpolarization-activated cyclic nucleotide-gated ion channel 2 (HCN2), which has been shown to be involved in epilepsy. We found that silencing of HCN2 resulted in decreased secreted Aß levels. To further investigate the mechanism behind this reduction, we also determined the levels of full-length APP, sAPP and APP-CTF species after silencing of HCN2. A marked reduction in sAPP and APP-CTF, as well as glycosylated APP levels was detected. Decreased Aß, sAPP and APP-CTF levels were also detected after treatment with the HCN2 inhibitor ZD7288. These results indicate that the effect on Aß levels after HCN2 silencing or inhibition is due to altered APP maturation or processing by ß-secretase rather than a direct effect on γ-secretase. However, HCN2 and γ-secretase were found to be in close proximity, as evident by proximity ligation assay and immunoprecipitation. In summary, our results indicate that silencing or inhibition of HCN2 affects APP processing and thereby could serve as a potential treatment strategy.

ADAM10 and BACE1 are localized to synaptic vesicles.

Synaptic degeneration and accumulation of the neurotoxic amyloid ß-peptide (Aß) in the brain are hallmarks of Alzheimer disease. Aß is produced by sequential cleavage of the amyloid precursor protein (APP), by the ß-secretase ß-site APP cleaving enzyme 1 (BACE1) and γ-secretase. However, Aß generation is precluded if APP is cleaved by the α-secretase ADAM10 instead of BACE1. We have previously shown that Aß can be produced locally at the synapse. To study the synaptic localization of the APP processing enzymes we used western blotting to demonstrate that, compared to total brain homogenate, ADAM10 and BACE1 were greatly enriched in synaptic vesicles isolated from rat brain using controlled-pore glass chromatography, whereas Presenilin1 was the only enriched component of the γ-secretase complex. Moreover, we detected ADAM10 activity in synaptic vesicles and enrichment of the intermediate APP-C-terminal fragments (APP-CTFs). We confirmed the western blotting findings using in situ proximity ligation assay to demonstrate close proximity of ADAM10 and BACE1 with the synaptic vesicle marker synaptophysin in intact mouse primary hippocampal neurons. In contrast, only sparse co-localization of active γ-secretase and synaptophysin was detected. These results indicate that the first step of APP processing occurs in synaptic vesicles whereas the final step is more likely to take place elsewhere.

Tumor biomarker glycoproteins in the seminal plasma of healthy human males are endogenous ligands for DC-SIGN.

DC-SIGN is an immune C-type lectin that is expressed on both immature and mature dendritic cells associated with peripheral and lymphoid tissues in humans. It is a pattern recognition receptor that binds to several pathogens including HIV-1, Ebola virus, Mycobacterium tuberculosis, Candida albicans, Helicobacter pylori, and Schistosoma mansoni. Evidence is now mounting that DC-SIGN also recognizes endogenous glycoproteins, and that such interactions play a major role in maintaining immune homeostasis in humans and mice. Autoantigens (neoantigens) are produced for the first time in the human testes and other organs of the male urogenital tract under androgenic stimulus during puberty. Such antigens trigger autoimmune orchitis if the immune response is not tightly regulated within this system. Endogenous ligands for DC-SIGN could play a role in modulating such responses. Human seminal plasma glycoproteins express a high level of terminal Lewis(x) and Lewis(y) carbohydrate antigens. These epitopes react specifically with the lectin domains of DC-SIGN. However, because the expression of these sequences is necessary but not sufficient for interaction with DC-SIGN, this study was undertaken to determine if any seminal plasma glycoproteins are also endogenous ligands for DC-SIGN. Glycoproteins bearing terminal Lewis(x) and Lewis(y) sequences were initially isolated by lectin affinity chromatography. Protein sequencing established that three tumor biomarker glycoproteins (clusterin, galectin-3 binding glycoprotein, prostatic acid phosphatase) and protein C inhibitor were purified by using this affinity method. The binding of DC-SIGN to these seminal plasma glycoproteins was demonstrated in both Western blot and immunoprecipitation studies. These findings have confirmed that human seminal plasma contains endogenous glycoprotein ligands for DC-SIGN that could play a role in maintaining immune homeostasis both in the male urogenital tract and the vagina after coitus.

What Can N-glycomics and N-glycoproteomics of Cerebrospinal Fluid Tell Us about Alzheimer Disease?

Proteomics-large-scale studies of proteins-has over the last decade gained an enormous interest for studies aimed at revealing proteins and pathways involved in disease. To fully understand biological and pathological processes it is crucial to also include post-translational modifications in the "omics". To this end, glycomics (identification and quantification of glycans enzymatically or chemically released from proteins) and glycoproteomics (identification and quantification of peptides/proteins with the glycans still attached) is gaining interest. The study of protein glycosylation requires a workflow that involves an array of sample preparation and analysis steps that needs to be carefully considered. Herein, we briefly touch upon important steps such as sample preparation and preconcentration, glycan release, glycan derivatization and quantification and advances in mass spectrometry that today are the work-horse for glycomics and glycoproteomics studies. Several proteins related to Alzheimer disease pathogenesis have altered protein glycosylation, and recent glycomics studies have shown differences in cerebrospinal fluid as well as in brain tissue in Alzheimer disease as compared to controls. In this review, we discuss these techniques and how they have been used to shed light on Alzheimer disease and to find glycan biomarkers in cerebrospinal fluid.

Neuronal Trafficking of the Amyloid Precursor Protein-What Do We Really Know?

Alzheimer's disease (AD) is the most common type of dementia, contributing to 60-80% of cases. It is a neurodegenerative disease that usually starts symptomless in the first two to three decades and then propagates into a long-term, irreversible disease, resulting in the progressive loss of memory, reasoning, abstraction and language capabilities. It is a complex disease, involving a large number of entangled players, and there is no effective treatment to cure it or alter its progressive course. Therefore, a thorough understanding of the disease pathology and an early diagnosis are both necessary. AD has two significant pathological hallmarks: extracellular senile plaques composed of amyloid ß-peptide (Aß) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein, and the aggregation of Aß, which starts in earlier stages, is usually claimed to be the primary cause of AD. Secretases that cleave Aß precursor protein (APP) and produce neurotoxic Aß reside in distinct organelles of the cell, and current concepts suggest that APP moves between distinct intracellular compartments. Obviously, APP transport and processing are intimately related processes that cannot be dissociated from each other, and, thus, how and where APP is transported determines its processing fate. In this review, we summarize critical mechanisms underlying neuronal APP transport, which we divide into separate parts: (1) secretory pathways and (2) endocytic and autophagic pathways. We also include two lipoprotein receptors that play essential roles in APP transport: sorting-related receptor with A-type repeats and sortilin. Moreover, we consider here some major disruptions in the neuronal transport of APP that contribute to AD physiology and pathology. Lastly, we discuss current methods and technical difficulties in the studies of APP transport.

A Super-Resolved View of the Alzheimer's Disease-Related Amyloidogenic Pathway in Hippocampal Neurons.

BACKGROUND: Processing of the amyloid-ß protein precursor (AßPP) is neurophysiologically important due to the resulting fragments that regulate synapse biology, as well as potentially harmful due to generation of the 42 amino acid long amyloid ß-peptide (Aß42), which is a key player in Alzheimer's disease. OBJECTIVE: Our aim was to clarify the subcellular locations of the fragments involved in the amyloidogenic pathway in primary neurons with a focus on Aß42 and its immediate substrate AßPP C-terminal fragment (APP-CTF). To overcome the difficulties of resolving these compartments due to their small size, we used super-resolution microscopy. METHODS: Mouse primary hippocampal neurons were immunolabelled and imaged by stimulated emission depletion (STED) microscopy, including three-dimensional three-channel imaging, and quantitative image analyses. RESULTS: The first (ß-secretase) and second (γ-secretase) cleavages of AßPP were localized to functionally and distally distinct compartments. The ß-secretase cleavage was observed in early endosomes in soma, where we were able to show that the liberated N- and C-terminal fragments were sorted into distinct vesicles budding from the early endosomes. Lack of colocalization of Aß42 and APP-CTF in soma suggested that γ-secretase cleavage occurs in neurites. Indeed, APP-CTF was, in line with Aß42 in our previous study, enriched in the presynapse but absent from the postsynapse. In contrast, full-length AßPP was not detected in either the pre- or the postsynaptic side of the synapse. Furthermore, we observed that endogenously produced and endocytosed Aß42 were localized in different compartments. CONCLUSION: These findings provide critical super-resolved insight into amyloidogenic AßPP processing in primary neurons.

Microdissected Pyramidal Cell Proteomics of Alzheimer Brain Reveals Alterations in Creatine Kinase B-Type, 14-3-3-γ, and Heat Shock Cognate 71.

Novel insights on proteins involved in Alzheimer's disease (AD) are needed. Since multiple cell types and matrix components are altered in AD, bulk analysis of brain tissue maybe difficult to interpret. In the current study, we isolated pyramidal cells from the cornu ammonis 1 (CA1) region of the hippocampus from five AD and five neurologically healthy donors using laser capture microdissection (LCM). The samples were analyzed by proteomics using 18O-labeled internal standard and nano-high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) for relative quantification. Fold change between AD and control was calculated for the proteins that were identified in at least two individual proteomes from each group. From the 10 cases analyzed, 62 proteins were identified in at least two AD cases and two control cases. Creatine kinase B-type (CKB), 14-3-3-γ, and heat shock cognate 71 (Hsc71), which have not been extensively studied in the context of the human AD brain previously, were selected for further studies by immunohistochemistry (IHC). In hippocampus, semi-quantitative measures of IHC staining of the three proteins confirmed the findings from our proteomic analysis. Studies of the same proteins in the frontal cortex revealed that the alterations remained for CKB and 14-3-3-γ but not for Hsc71. Protein upregulation in CA1 neurons of final stage AD is either a result of detrimental, pathological effects, or from cell-specific protective response mechanisms in surviving neurons. Based on previous findings from experimental studies, CKB and Hsc71 likely exhibit protective effects, whereas 14-3-3-γ may represent a detrimental pathway. These new players could reflect pathways of importance for the development of new therapeutic strategies.

Insights into the changes in the proteome of Alzheimer disease elucidated by a meta-analysis.

Mass spectrometry (MS)-based proteomics is a powerful tool to explore pathogenic changes of a disease in an unbiased manner and has been used extensively in Alzheimer disease (AD) research. Here, by performing a meta-analysis of high-quality proteomic studies, we address which pathological changes are observed consistently and therefore most likely are of great importance for AD pathogenesis. We retrieved datasets, comprising a total of 21,588 distinct proteins identified across 857 postmortem human samples, from ten studies using labeled or label-free MS approaches. Our meta-analysis findings showed significant alterations of 757 and 1,195 proteins in AD in the labeled and label-free datasets, respectively. Only 33 proteins, some of which were associated with synaptic signaling, had the same directional change across the individual studies. However, despite alterations in individual proteins being different between the labeled and the label-free datasets, several pathways related to synaptic signaling, oxidative phosphorylation, immune response and extracellular matrix were commonly dysregulated in AD. These pathways represent robust changes in the human AD brain and warrant further investigation.

Further insight into the roles of the glycans attached to human blood protein C inhibitor.

Protein C inhibitor (PCI) is a 57-kDa glycoprotein that exists in many tissues and secretions in human. As a member of the serpin superfamily of proteins it displays unusually broad protease specificity. PCI is implicated in the regulation of a wide range of processes, including blood coagulation, fertilization, prevention of tumors and pathogen defence. It has been reported that PCI isolated from human blood plasma is highly heterogeneous, and that this heterogeneity is caused by differences in N-glycan structures, N-glycosylation occupancy, and the presence of two forms that differ by the presence or absence of 6 amino acids at the amino-terminus. In this study we have verified that such heterogeneity exists in PCI purified from single individuals, and that individuals of two different ethnicities possess a similar PCI pattern, verifying that the micro-heterogeneity is conserved among humans. Furthermore, we have provided experimental evidence that PCI in both individuals is O-glycosylated on Thr20 with a core type 1 O-glycan, which is mostly NeuAcGalGalNAc. Modeling suggested that the O-glycan attachment site is located in proximity to several ligand-binding sites of the inhibitor.