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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 18 O 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 Aβ42-induced AD pathology- App NL-F -and studied the interaction between Aβ 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 App NL-F mice showed that the increase of DDX24 starts before amyloid pathology or memory impairment is observed. Immunocytochemistry in App NL-F primary hippocampal neurons showed increased DDX24 intensity in the soma, nucleus and nucleolus. Furthermore, siRNA targeting of DDX24 in neurons decreased APP and Aβ42 levels, and the addition of Aβ42 to the medium reduced DDX24. In conclusion, we have identified DDX24 as a protein with a potential role in Aβ-induced AD pathology.

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., (© 2024. The Author(s).)

Background: The N-glycan structure bisecting N-acetylglucosamine (bisecting GlcNAc) is present on several N-glycans that are elevated in Alzheimer's disease (AD), and previous studies have shown that bisecting GlcNAc levels correlate with total tau and phospho-tau181 in cerebrospinal fluid at early stages of AD. A recent population-based study showed that bisecting GlcNAc correlates with total tau also in blood and that this correlation could predict conversion to dementia., Objective: In this study, we have further investigated how bisecting GlcNAc relates to total tau and phospho-tau 181 in cerebrospinal fluid samples from controls and cases with early cognitive deficits, stratified by amyloid/tau status and gender., Methods: Relative levels of bisecting GlcNAc in cerebrospinal fluid were measured by an enzyme-linked lectin assay in individuals with subjective cognitive decline, mild cognitive impairment and controls from the Norwegian Dementia Disease Initiation cohort., Results: As in our previous study, the correlation between bisecting GlcNAc and total tau or phospho-tau181 was particularly strong in the subjective cognitive decline group. The correlation was observed in amyloid negative and tau negative as well as amyloid positive and tau positive individuals, both in females and in males. Interestingly, among the amyloid negative and tau negative individuals, the correlation was observed in individuals with subjective cognitive decline but not in the controls., Conclusions: Thus, bisecting GlcNAc could be a biomarker for early cognitive decline.

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., (© 2023 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

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., (© 2022. The Author(s).)

Amyloid A (AA) amyloidosis occurs spontaneously in many mammals and birds, but the prevalence varies considerably among different species, and even among subgroups of the same species. The Blue fox and the Gray fox seem to be resistant to the development of AA amyloidosis, while Island foxes have a high prevalence of the disease. Herein, we report on the identification of AA amyloidosis in the Red fox (Vulpes vulpes). Edman degradation and tandem MS analysis of proteolyzed amyloid protein revealed that the amyloid partly was composed of full-length SAA. Its amino acid sequence was determined and found to consist of 111 amino acid residues. Based on inter-species sequence comparisons we found four residue exchanges (Ser31, Lys63, Leu71, Lys72) between the Red and Blue fox SAAs. Lys63 seems unique to the Red fox SAA. We found no obvious explanation to how these exchanges might correlate with the reported differences in SAA amyloidogenicity. Furthermore, in contrast to fibrils from many other mammalian species, the isolated amyloid fibrils from Red fox did not seed AA amyloidosis in a mouse model., (© 2017 The Protein Society.)

There are around 30 human diseases associated with protein misfolding and amyloid formation, each one caused by a certain protein or peptide. Many of these diseases are lethal and together they pose an enormous burden to society. The prion protein has attracted particular interest as being shown to be the pathogenic agent in transmissible diseases such as kuru, Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. Whether similar transmission could occur also in other amyloidoses such as Alzheimer's disease, Parkinson's disease and serum amyloid A amyloidosis is a matter of intense research and debate. Furthermore, it has been suggested that novel biomaterials such as artificial spider silk are potentially amyloidogenic. Here, we provide a brief introduction to amyloid, prions and other proteins involved in amyloid disease and review recent evidence for their potential transmission. We discuss the similarities and differences between amyloid and silk, as well as the potential hazards associated with protein-based biomaterials., (© 2016 The Association for the Publication of the Journal of Internal Medicine.)

Oligomers formed by the amyloid β-peptide (Aβ) are pathogens in Alzheimer's disease. Increased knowledge on the oligomerization process is crucial for understanding the disease and for finding treatments. Ideally, Aβ oligomerization should be studied in solution and at physiologically relevant concentrations, but most popular techniques of today are not capable of such analyses. We demonstrate here that the combination of Förster Resonance Energy Transfer and Fluorescence Correlation Spectroscopy (FRET-FCS) has a unique ability to detect small subpopulations of FRET-active molecules and oligomers. FRET-FCS could readily detect a FRET-active oligonucleotide present at levels as low as 0.5% compared to FRET-inactive dye molecules. In contrast, three established fluorescence fluctuation techniques (FCS, FCCS, and PCH) required fractions between 7 and 11%. When applied to the analysis of Aβ, FRET-FCS detected oligomers consisting of less than 10 Aβ molecules, which coexisted with the monomers at fractions as low as 2 ± 2%. Thus, we demonstrate for the first time direct detection of small fractions of Aβ oligomers in solution at physiological concentrations. This ability of FRET-FCS could be an indispensable tool for studying biological oligomerization processes, in general, and for finding therapeutically useful oligomerization inhibitors.

Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid beta-protein (Abeta). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zinc-binding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against Abeta. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu(78) in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against Abeta-(1-42), Abeta-(1-40), and Abeta Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 A resolution of AtPreP allowed us to identify Cys(90) and Cys(527) that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial Abeta by hPreP may potentially be of importance in the pathology of Alzheimer disease.

The tetrapeptide KFFE is one of the shortest amyloid fibril-forming peptides described. Herein, we have investigated how the structural environment of this motif affects polymerization. Using a turn motif (YNGK) or a less rigid sequence (AAAK) to fuse two KFFE tetrapeptides, we show by several biophysical methods that the amyloidogenic properties are strongly dependent on the structural environment. The dodecapeptide KFFEAAAKKFFE forms abundant thick fibril bundles. Freshly dissolved KFFEAAAKKFFE is monomeric and shows mainly disordered secondary structure, as evidenced by circular dichroism, NMR spectroscopy, hydrogen/deuterium exchange measurements, and molecular modeling studies. In sharp contrast, the dodecapeptide KFFEYNGKKFFE does not form fibrils but folds into a stable beta-hairpin. This structure can oligomerize into a stable 12-mer and multiples thereof, as shown by size exclusion chromatography, sedimentation analysis, and electrospray mass spectrometry. These data indicate that the structural context in which a potential fibril forming sequence is present can prevent fibril formation by favoring self-limiting oligomerization over polymerization.

Amyloid beta-peptide (Abeta) deposition in brain is important in the development of Alzheimer's disease (AD). Neprilysin (NEP) appears to be the major Abeta degrading enzyme in vivo and reduced mRNA levels of NEP correlates with increased plaque density. We hypothesized that alterations in the NEP promoter region may alter NEP expression and thus be involved in the AD process. We investigated three putative important regions in the NEP promoter region; two dinucleotide-repeats (CA and GT) and a 480 base pair fragment. With fragment analysis and sequencing, 164 early-onset and 152 late-onset Swedish AD cases and 109 non-demented controls were investigated. No significant difference in the distribution of promoter polymorphisms between AD cases and controls were found in this study.

Amyloid fibrils in which specific proteins have polymerized into a cross-beta-sheet structure are found in about 20 diseases. In contrast to the close structural similarity of fibrils formed in different amyloid diseases, the structures of the corresponding native proteins differ widely. We show here that peptides as short as 4 residues with the sequences KFFE or KVVE can form amyloid fibrils that are practically identical to fibrils formed in association with disease, as judged by electron microscopy and Congo red staining. In contrast, KLLE or KAAE do not form fibrils. The fibril-forming KFFE and KVVE show partial beta-strand conformation in solution, whereas the non-fibril-forming KLLE and KAAE show random structure only, suggesting that inherent propensity for beta-strand conformation promotes fibril formation. The peptides KFFK or EFFE do not form fibrils on their own but do so in an equimolar mixture. Thus, intermolecular electrostatic interactions, either between charged dipolar peptides or between complementary charges of co-fibrillating peptides favor fibril formation.

Aortic medial amyloid is a form of localized amyloid that occurs in virtually all individuals older than 60 years. The importance and impact of the amyloid deposits are unknown. In this study we have purified a 5.5-kDa aortic medial amyloid component, by size-exclusion chromatography and RP-HPLC, from three individuals, and we have shown by amino acid sequence analysis that the amyloid is derived from an integral proteolytic fragment of lactadherin. Lactadherin is a 364-aa glycoprotein, previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane. The multidomain protein has a C-terminal domain showing homology to blood coagulation factors V and VIII. We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. Our result is supported by the specific labeling of aortic medial amyloid in light and electron microscopy with two rabbit antisera raised against two synthetic peptides corresponding to different parts of medin. By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. Furthermore, one of the synthetic peptides forms amyloid-like fibrils in vitro. Lactadherin was not previously known to be an amyloid precursor protein or to be expressed in aortic tissue. The structure of lactadherin may implicate an important regulatory function in the aorta.

The intracellular amyloid beta-peptide (A beta) binding protein, ERAB, a member of the short-chain dehydrogenase/reductase (SDR) family, is known to mediate apoptosis in different cell lines and to be a class II hydroxyacyl-CoA dehydrogenase. The A beta peptide inhibits the enzymatic reaction in a mixed type fashion with a Ki of 1.2 micromol/l and a KiES of 0.3 micromol/l, using 3-hydroxybutyryl-CoA. The peptide region necessary for inhibition comprises residues 12-24 of A beta1-40, covering the 16-20 fragment, which is the minimum sequence for the blockade of A beta polymerization, but that minimal fragment is not sufficient for more than marginal inhibition. The localization of ERAB to the endoplasmic reticulum and mitochondria suggests a complex interaction with components of the programmed cell death machinery. The interaction of A beta with ERAB further links oxidoreductase activity with both apoptosis and amyloid toxicity.

Background: The accumulation of fibrillar deposits of amyloid beta-peptide (Abeta) in brain parenchyma and cerebromeningeal blood vessels is a key step in the pathogenesis of Alzheimer's disease. In this report, polymerization of Abeta was studied using fluorescence correlation spectroscopy (FCS), a technique capable of detecting small molecules and large aggregates simultaneously in solution., Results: The polymerization of Abeta dissolved in Tris-buffered saline, pH 7.4, occurred above a critical concentration of 50 microM and proceeded from monomers/dimers into two discrete populations of large aggregates, without any detectable amount of oligomers. The aggregation showed very high cooperativity and reached a maximum after 40 min, followed by an increase in the amount of monomers/dimers and a decrease in the size of the large aggregates. Electron micrographs of samples prepared at the time for maximum aggregation showed a mixture of an amorphous network and short diffuse fibrils, whereas only mature amyloid fibrils were detected after one day of incubation. The aggregation was reduced when Abeta was incubated in the presence of Abeta ligands, oligopeptides previously shown to inhibit fibril formation, and aggregates were partly dissociated after the addition of the ligands., Conclusions: The polymerization of Abeta is a highly cooperative process in which the formation of very large aggregates precedes the formation of fibrils. The entire process can be inhibited and, at least in early stages, partly reversed by Abeta ligands.

In Alzheimer's disease (AD), one of the cardinal neuropathological signs is deposition of amyloid, primarily consisting of the amyloid beta-peptide (Abeta). Structural variants of AD-associated Abeta peptides have been difficult to purify by high-resolution chromatographic techniques. We therefore developed a novel chromatographic protocol, enabling high-resolution reverse-phase liquid chromatography (RPLC) purification of Abeta variants displaying very small structural differences. By using a combination of size-exclusion chromatography and the novel RPLC protocol, Abeta peptides extracted from AD amyloid were purified and subsequently characterized. Structural analysis by microsequencing and electrospray-ionization mass spectrometry revealed that the RPLC system resolved a complex mixture of Abeta variants terminating at either residue 40 or 42. Abeta variants differing by as little as one amino acid residue could be purified rapidly to apparent homogeneity. The resolution of the system was further illustrated by its ability to separate the structural isomers of Abeta1-40. The present chromatography system might provide further insight into the role of N-terminally and posttranslationally modified Abeta variants, because each variant can now be studied individually.

Genetic evidence suggests a role for apolipoprotein E (apoE) in Alzheimer's disease (AD) amyloidogenesis. Here, amyloid-associated apoE from 32 AD patients was purified and characterized. We found that brain amyloid-associated apoE apparently exists not as free molecules but as complexes with polymers of the amyloid beta peptide (A beta). Brain A beta-apoE complexes were detected irrespective of the apoE genotype, and similar complexes could be mimicked in vitro. The fine structure of purified A beta-apoE complexes was fibrillar, and immunogold labeling revealed apoE immunoreactivity along the fibrils. Thus, we conclude that A beta-apoE complexes are principal components of AD-associated brain amyloid and that the data presented here support a role for apoE in the pathogenesis of AD.

The Alzheimer a beta amyloid precursor protein is metabolized by at least two secretory pathways. One generates the A beta peptide and the other a N-terminally truncated A beta fragment termed p3 that is considered non-amyloidogenic. However, direct evidence is missing. We have undertaken to synthesize and purify p3. Pure p3 polymerizes in vitro, forming a lattice with an ultrastructure distinct from the linear fibrils of A beta. In contrast to amyloid, polymerized p3 does not bind thioflavine T. It is therefore concluded that amino acids in the N-terminal part of the A beta molecule are required for formation of typical amyloid fibrils and that the metabolic pathway generating p3 probably is non-amyloidogenic