Presenilin-1 mutations in Alzheimer's disease

Cryo-EM structures of cotton wool plaques' amyloid β and of tau filaments in dominantly inherited Alzheimer disease

Cotton wool plaques (CWPs) have been described as features of the neuropathologic phenotype of dominantly inherited Alzheimer disease (DIAD) caused by some missense and deletion mutations in the presenilin 1 (PSEN1) gene. CWPs are round, eosinophilic amyloid-β (Aβ) plaques that lack an amyloid core and are recognizable, but not fluorescent, in Thioflavin S (ThS) preparations. Amino-terminally truncated and post-translationally modified Aβ peptide species are the main component of CWPs. Tau immunopositive neurites may be present in CWPs. In addition, neurofibrillary tangles coexist with CWPs. Herein, we report the structure of Aβ and tau filaments isolated from brain tissue of individuals affected by DIAD caused by the PSEN1 V261I and A431E mutations, with the CWP neuropathologic phenotype. CWPs are predominantly composed of type I Aβ filaments present in two novel arrangements, type Ic and type Id; additionally, CWPs contain type I and type Ib Aβ filaments. Tau filaments have the AD fold, which has been previously reported in sporadic AD and DIAD. The formation of type Ic and type Id Aβ filaments may be the basis for the phenotype of CWPs. Our data are relevant for the development of PET imaging methodologies to best detect CWPs in DIAD.

Effect of astaxanthin in type-2 diabetes -induced APPxhQC transgenic and NTG mice

OBJECTIVES

Aggregation and misfolding of amyloid beta (Aβ) and tau proteins, suggested to arise from post-translational modification processes, are thought to be the main cause of Alzheimer's disease (AD). Additionally, a plethora of evidence exists that links metabolic dysfunctions such as obesity, type 2 diabetes (T2D), and dyslipidemia to the pathogenesis of AD. We thus investigated the combinatory effect of T2D and human glutaminyl cyclase activity (pyroglutamylation), on the pathology of AD and whether astaxanthin (ASX) treatment ameliorates accompanying pathophysiological manifestations.

METHODS

Male transgenic AD mice, APPxhQC, expressing human APP751 with the Swedish and the London mutation and human glutaminyl cyclase (hQC) enzyme and their non-transgenic (NTG) littermates were used. Both APPxhQC and NTG mice were allocated to 3 groups, control, T2D-control, and T2D-ASX. Mice were fed control or high fat diet ± ASX for 13 weeks starting at an age of 11-12 months. High fat diet fed mice were further treated with streptozocin for T2D induction. Effects of genotype, T2D induction, and ASX treatment were evaluated by analysing glycemic readouts, lipid concentration, Aβ deposition, hippocampus-dependent cognitive function and nutrient sensing using immunosorbent assay, ELISA-based assays, western blotting, immunofluorescence staining, and behavioral testing via Morris water maze (MWM), respectively.

RESULTS

APPxhQC mice presented a higher glucose sensitivity compared to NTG mice. T2D-induced brain dysfunction was more severe in NTG compared to the APPxhQC mice. T2D induction impaired memory functions while increasing hepatic LC3B, ABCA1, and p65 levels in NTG mice. T2D induction resulted in a progressive shift of Aβ from the soluble to insoluble form in APPxhQC mice. ASX treatment reversed T2D-induced memory dysfunction in NTG mice and in parallel increased hepatic pAKT while decreasing p65 and increasing cerebral p-S6rp and p65 levels. ASX treatment reduced soluble Aβ38 and Aβ40 and insoluble Aβ40 levels in T2D-induced APPxhQC mice.

CONCLUSIONS

We demonstrate that T2D induction in APPxhQC mice poses additional risk for AD pathology as seen by increased Aβ deposition. Although ASX treatment reduced Aβ expression in T2D-induced APPxhQC mice and rescued T2D-induced memory impairment in NTG mice, ASX treatment alone may not be effective in cases of T2D comorbidity and AD.

Closest horizons of Hsp70 engagement to manage neurodegeneration

Our review seeks to elucidate the current state-of-the-art in studies of 70-kilodalton-weighed heat shock proteins (Hsp70) in neurodegenerative diseases (NDs). The family has already been shown to play a crucial role in pathological aggregation for a wide spectrum of brain pathologies. However, a slender boundary between a big body of fundamental data and its implementation has only recently been crossed. Currently, we are witnessing an anticipated advancement in the domain with dozens of studies published every month. In this review, we briefly summarize scattered results regarding the role of Hsp70 in the most common NDs including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). We also bridge translational studies and clinical trials to portray the output for medical practice. Available options to regulate Hsp70 activity in NDs are outlined, too.

A Review on Integrated ZnO-Based SERS Biosensors and Their Potential in Detecting Biomarkers of Neurodegenerative Diseases

Surface-enhanced Raman spectroscopy (SERS) applications in clinical diagnosis and spectral pathology are increasing due to the potential of the technique to bio-barcode incipient and differential diseases via real-time monitoring of biomarkers in fluids and in real-time via biomolecular fingerprinting. Additionally, the rapid advancements in micro/nanotechnology have a visible influence in all aspects of science and life. The miniaturization and enhanced properties of materials at the micro/nanoscale transcended the confines of the laboratory and are revolutionizing domains such as electronics, optics, medicine, and environmental science. The societal and technological impact of SERS biosensing by using semiconductor-based nanostructured smart substrates will be huge once minor technical pitfalls are solved. Herein, challenges in clinical routine testing are addressed in order to understand the context of how SERS can perform in real, in vivo sampling and bioassays for early neurodegenerative disease (ND) diagnosis. The main interest in translating SERS into clinical practice is reinforced by the practical advantages: portability of the designed setups, versatility in using nanomaterials of various matter and costs, readiness, and reliability. As we will present in this review, in the frame of technology readiness levels (TRL), the current maturity reached by semiconductor-based SERS biosensors, in particular that of zinc oxide (ZnO)-based hybrid SERS substrates, is situated at the development level TRL 6 (out of 9 levels). Three-dimensional, multilayered SERS substrates that provide additional plasmonic hot spots in the z-axis are of key importance in designing highly performant SERS biosensors for the detection of ND biomarkers.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

11C-PiB PET can underestimate brain amyloid-β burden when cotton wool plaques are numerous

Individuals with familial Alzheimer's disease due to PSEN1 mutations develop high cortical fibrillar amyloid-β load but often have lower cortical 11C-Pittsburgh compound B (PiB) retention than Individuals with sporadic Alzheimer's disease. We hypothesized this is influenced by limited interactions of Pittsburgh compound B with cotton wool plaques, an amyloid-β plaque type common in familial Alzheimer's disease but rare in sporadic Alzheimer's disease. Histological sections of frontal and temporal cortex, caudate nucleus and cerebellum were obtained from 14 cases with sporadic Alzheimer's disease, 12 cases with familial Alzheimer's disease due to PSEN1 mutations, two relatives of a PSEN1 mutation carrier but without genotype information and three non-Alzheimer's disease cases. Sections were processed immunohistochemically using amyloid-β-targeting antibodies and the fluorescent amyloid stains cyano-PiB and X-34. Plaque load was quantified by percentage area analysis. Frozen homogenates from the same brain regions from five sporadic Alzheimer's disease and three familial Alzheimer's disease cases were analysed for 3H-PiB in vitro binding and concentrations of amyloid-β1-40 and amyloid-β1-42. Nine sporadic Alzheimer's disease, three familial Alzheimer's disease and three non-Alzheimer's disease participants had 11C-PiB PET with standardized uptake value ratios calculated using the cerebellum as the reference region. Cotton wool plaques were present in the neocortex of all familial Alzheimer's disease cases and one sporadic Alzheimer's disease case, in the caudate nucleus from four familial Alzheimer's disease cases, but not in the cerebellum. Cotton wool plaques immunolabelled robustly with 4G8 and amyloid-β42 antibodies but weakly with amyloid-β40 and amyloid-βN3pE antibodies and had only background cyano-PiB fluorescence despite labelling with X-34. Relative to amyloid-β plaque load, cyano-Pittsburgh compound B plaque load was similar in sporadic Alzheimer's disease while in familial Alzheimer's disease it was lower in the neocortex and the caudate nucleus. In both regions, insoluble amyloid-β1-42 and amyloid-β1-40 concentrations were similar in familial Alzheimer's disease and sporadic Alzheimer's disease groups, while 3H-PiB binding was lower in the familial Alzheimer's disease than the sporadic Alzheimer's disease group. Higher amyloid-β1-42 concentration associated with higher 3H-PiB binding in sporadic Alzheimer's disease but not familial Alzheimer's disease. 11C-PiB retention correlated with region-matched post-mortem amyloid-β plaque load; however, familial Alzheimer's disease cases with abundant cotton wool plaques had lower 11C-PiB retention than sporadic Alzheimer's disease cases with similar amyloid-β plaque loads. PiB has limited ability to detect amyloid-β aggregates in cotton wool plaques and may underestimate total amyloid-β plaque burden in brain regions with abundant cotton wool plaques.

Biological and methodological complexities of beta-amyloid peptide: Implications for Alzheimer's disease research

Although controversial, the amyloid cascade hypothesis remains central to the Alzheimer's disease (AD) field and posits amyloid-beta (Aβ) as the central factor initiating disease onset. In recent years, there has been an increase in emphasis on studying the role of low molecular weight aggregates, such as oligomers, which are suggested to be more neurotoxic than fibrillary Aβ. Other Aβ isoforms, such as truncated Aβ, have also been implicated in disease. However, developing a clear understanding of AD pathogenesis has been hampered by the complexity of Aβ biochemistry in vitro and in vivo. This review explores factors contributing to the lack of consistency in experimental approaches taken to model Aβ aggregation and toxicity and provides an overview of the different techniques available to analyse Aβ, such as electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, dye-based assays, size exclusion chromatography, mass spectrometry and SDS-PAGE. The review also explores how different types of Aβ can influence Aβ aggregation and toxicity, leading to variation in experimental outcomes, further highlighting the need for standardisation in Aβ preparations and methods used in current research.

In Silico Inhibition of BACE-1 by Selective Phytochemicals as Novel Potential Inhibitors: Molecular Docking and DFT Studies

BACKGROUND

Alzheimer's Disease (AD) has become the most common age-dependent disease of dementia. The trademark pathologies of AD are the presence of amyloid aggregates in neurofibrils. Recently phytochemicals being considered as potential inhibitors against various neurodegenerative, antifungal, antibacterial and antiviral diseases in human beings.

OBJECTIVE

This study targets the inhibition of BACE-1 by phytochemicals using in silico drug discovery analysis.

METHODS

A total of 3150 phytochemicals were collected from almost 25 different plants through literature assessment. The ADMET studies, molecular docking and density functional theory (DFT) based analysis were performed to analyze the potential inhibitory properties of these phytochemicals.

RESULTS

The ADMET and docking results exposed seven compounds that have high potential as an inhibitory agent against BACE-1 and show binding affinity >8.0 kcal/mol against BACE-1. They show binding affinity greater than those of various previously reported inhibitors of BACE-1. Furthermore, DFT based analysis has shown high reactivity for these seven phytochemicals in the binding pocket of BACE- 1, based on ELUMO, EHOMO and Kohn-Sham energy gap. All seven phytochemicals were testified (as compared to experimental ones) as novel inhibitors against BACE-1.

CONCLUSION

Out of seven phytochemicals, four were obtained from plant Glycyrrhiza glabra i.e. Shinflavanone, Glabrolide, Glabrol and PrenyllicoflavoneA, one from Huperzia serrate i.e. Macleanine, one from Uncaria rhynchophylla i.e. 3a-dihydro-cadambine and another one was from VolvalerelactoneB from plant Valeriana-officinalis. It is concluded that these phytochemicals are suitable candidates for drug/inhibitor against BACE-1, and can be administered to humans after experimental validation through in vitro and in vivo trials.

Tau Protein Interaction Partners and Their Roles in Alzheimer's Disease and Other Tauopathies

Tau protein plays a critical role in the assembly, stabilization, and modulation of microtubules, which are important for the normal function of neurons and the brain. In diseased conditions, several pathological modifications of tau protein manifest. These changes lead to tau protein aggregation and the formation of paired helical filaments (PHF) and neurofibrillary tangles (NFT), which are common hallmarks of Alzheimer's disease and other tauopathies. The accumulation of PHFs and NFTs results in impairment of physiological functions, apoptosis, and neuronal loss, which is reflected as cognitive impairment, and in the late stages of the disease, leads to death. The causes of this pathological transformation of tau protein haven't been fully understood yet. In both physiological and pathological conditions, tau interacts with several proteins which maintain their proper function or can participate in their pathological modifications. Interaction partners of tau protein and associated molecular pathways can either initiate and drive the tau pathology or can act neuroprotective, by reducing pathological tau proteins or inflammation. In this review, we focus on the tau as a multifunctional protein and its known interacting partners active in regulations of different processes and the roles of these proteins in Alzheimer's disease and tauopathies.

Personalized Healthcare for Dementia

Dementia is one of the most common health problems affecting older adults, and the population with dementia is growing. Dementia refers to a comprehensive syndrome rather than a specific disease and is characterized by the loss of cognitive abilities. Many factors are related to dementia, such as aging, genetic profile, systemic vascular disease, unhealthy diet, and physical inactivity. As the causes and types of dementia are diverse, personalized healthcare is required. In this review, we first summarize various diagnostic approaches associated with dementia. Particularly, clinical diagnosis methods, biomarkers, neuroimaging, and digital biomarkers based on advances in data science and wearable devices are comprehensively reviewed. We then discuss three effective approaches to treating dementia, including engineering design, exercise, and diet. In the engineering design section, recent advances in monitoring and drug delivery systems for dementia are introduced. Additionally, we describe the effects of exercise on the treatment of dementia, especially focusing on the effects of aerobic and resistance training on cognitive function, and the effects of diets such as the Mediterranean diet and ketogenic diet on dementia.

Presenilin1 familial Alzheimer disease mutants inactivate EFNB1- and BDNF-dependent neuroprotection against excitotoxicity by affecting neuroprotective complexes of N-methyl-d-aspartate receptor

Excitotoxicity is thought to play key roles in brain neurodegeneration and stroke. Here we show that neuroprotection against excitotoxicity by trophic factors EFNB1 and brain-derived neurotrophic factor (called here factors) requires de novo formation of 'survival complexes' which are factor-stimulated complexes of N-methyl-d-aspartate receptor with factor receptor and presenilin 1. Absence of presenilin 1 reduces the formation of survival complexes and abolishes neuroprotection. EPH receptor B2- and N-methyl-d-aspartate receptor-derived peptides designed to disrupt formation of survival complexes also decrease the factor-stimulated neuroprotection. Strikingly, factor-dependent neuroprotection and levels of the de novo factor-stimulated survival complexes decrease dramatically in neurons expressing presenilin 1 familial Alzheimer disease mutants. Mouse neurons and brains expressing presenilin 1 familial Alzheimer disease mutants contain increased amounts of constitutive presenilin 1-N-methyl-d-aspartate receptor complexes unresponsive to factors. Interestingly, the stability of the familial Alzheimer disease presenilin 1-N-methyl-d-aspartate receptor complexes differs from that of wild type complexes and neurons of mutant-expressing brains are more vulnerable to cerebral ischaemia than neurons of wild type brains. Furthermore, N-methyl-d-aspartate receptor-mediated excitatory post-synaptic currents at CA1 synapses are altered by presenilin 1 familial Alzheimer disease mutants. Importantly, high levels of presenilin 1-N-methyl-d-aspartate receptor complexes are also found in post-mortem brains of Alzheimer disease patients expressing presenilin 1 familial Alzheimer disease mutants. Together, our data identify a novel presenilin 1-dependent neuroprotective mechanism against excitotoxicity and indicate a pathway by which presenilin 1 familial Alzheimer disease mutants decrease factor-depended neuroprotection against excitotoxicity and ischaemia in the absence of Alzheimer disease neuropathological hallmarks which may form downstream of neuronal damage. These findings have implications for the pathogenic effects of familial Alzheimer disease mutants and therapeutic strategies.

Are N- and C-terminally truncated Aβ species key pathological triggers in Alzheimer's disease?

The histopathology of Alzheimer's disease (AD) is characterized by neuronal loss, neurofibrillary tangles, and senile plaque formation. The latter results from an exacerbated production (familial AD cases) or altered degradation (sporadic cases) of 40/42-amino acid-long β-amyloid peptides (Aβ peptides) that are produced by sequential cleavages of Aβ precursor protein (βAPP) by β- and γ-secretases. The amyloid cascade hypothesis proposes a key role for the full-length Aβ42 and the Aβ40/42 ratio in AD etiology, in which soluble Aβ oligomers lead to neurotoxicity, tau hyperphosphorylation, aggregation, and, ultimately, cognitive defects. However, following this postulate, during the last decade, several clinical approaches aimed at decreasing full-length Aβ42 production or neutralizing it by immunotherapy have failed to reduce or even stabilize AD-related decline. Thus, the Aβ peptide (Aβ40/42)-centric hypothesis is probably a simplified view of a much more complex situation involving a multiplicity of APP fragments and Aβ catabolites. Indeed, biochemical analyses of AD brain deposits and fluids have unraveled an Aβ peptidome consisting of additional Aβ-related species. Such Aβ catabolites could be due to either primary enzymatic cleavages of βAPP or secondary processing of Aβ itself by exopeptidases. Here, we review the diversity of N- and C-terminally truncated Aβ peptides and their biosynthesis and outline their potential function/toxicity. We also highlight their potential as new pharmaceutical targets and biomarkers.

Complexity and Selectivity of γ-Secretase Cleavage on Multiple Substrates: Consequences in Alzheimer's Disease and Cancer

The processing of the amyloid-β protein precursor (AβPP) by β- and γ-secretases is a pivotal event in the genesis of Alzheimer's disease (AD). Besides familial mutations on the AβPP gene, or upon its overexpression, familial forms of AD are often caused by mutations or deletions in presenilin 1 (PSEN1) and 2 (PSEN2) genes: the catalytic components of the proteolytic enzyme γ-secretase (GS). The "amyloid hypothesis", modified over time, states that the aberrant processing of AβPP by GS induces the formation of specific neurotoxic soluble amyloid-β (Aβ) peptides which, in turn, cause neurodegeneration. This theory, however, has recently evidenced significant limitations and, in particular, the following issues are debated: 1) the concept and significance of presenilin's "gain of function" versus "loss of function"; and 2) the presence of several and various GS substrates, which interact with AβPP and may influence Aβ formation. The latter consideration is suggestive: despite the increasing number of GS substrates so far identified, their reciprocal interaction with AβPP itself, even in the AD field, is significantly unexplored. On the other hand, GS is also an important pharmacological target in the cancer field; inhibitors or GS activity are investigated in clinical trials for treating different tumors. Furthermore, the function of AβPP and PSENs in brain development and in neuronal migration is well known. In this review, we focused on a specific subset of GS substrates that directly interact with AβPP and are involved in its proteolysis and signaling, by evaluating their role in neurodegeneration and in cell motility or proliferation, as a possible connection between AD and cancer.

Passive Aβ Immunotherapy: Current Achievements and Future Perspectives

Passive immunotherapy has emerged as a very promising approach for the treatment of Alzheimer’s disease and other neurodegenerative disorders, which are characterized by the misfolding and deposition of amyloid peptides. On the basis of the amyloid hypothesis, the majority of antibodies in clinical development are directed against amyloid β (Aβ), the primary amyloid component in extracellular plaques. This review focuses on the current status of Aβ antibodies in clinical development, including their characteristics and challenges that came up in clinical trials with these new biological entities (NBEs). Emphasis is placed on the current view of common side effects observed with passive immunotherapy, so-called amyloid-related imaging abnormalities (ARIAs), and potential ways to overcome this issue. Among these new ideas, a special focus is placed on molecules that are directed against post-translationally modified variants of the Aβ peptide, an emerging approach for development of new antibody molecules.

Iatrogenic Creutzfeldt-Jakob disease with Amyloid-β pathology: an international study

The presence of pathology related to the deposition of amyloid-β (Aβ) has been recently reported in iatrogenic Creutzfeldt-Jakob disease (iCJD) acquired from inoculation of growth hormone (GH) extracted from human cadaveric pituitary gland or use of cadaveric dura mater (DM) grafts.To investigate this phenomenon further, a cohort of 27 iCJD cases - 21 with adequate number of histopathological sections - originating from Australia, France, Italy, and the Unites States, were examined by immunohistochemistry, amyloid staining, and Western blot analysis of the scrapie prion protein (PrPSc), and compared with age-group matched cases of sporadic CJD (sCJD), Alzheimer disease (AD) or free of neurodegenerative diseases (non-ND).Cases of iCJD and sCJD shared similar profiles of proteinase K-resistant PrPSc with the exception of iCJD harboring the "MMi" phenotype. Cerebral amyloid angiopathy (CAA), either associated with, or free of, Thioflavin S-positive amyloid core plaques (CP), was observed in 52% of 21 cases of iCJD, which comprised 37.5% and 61.5% of the cases of GH- and DM-iCJD, respectively. If only cases younger than 54 years were considered, Aβ pathology affected 41%, 2% and 0% of iCJD, sCJD and non-ND, respectively. Despite the patients' younger age CAA was more severe in iCJD than sCJD, while Aβ diffuse plaques, in absence of Aβ CP, populated one third of sCJD. Aβ pathology was by far most severe in AD. Tau pathology was scanty in iCJD and sCJD.In conclusion, (i) despite the divergences in the use of cadaveric GH and DM products, our cases combined with previous studies showed remarkably similar iCJD and Aβ phenotypes indicating that the occurrence of Aβ pathology in iCJD is a widespread phenomenon, (ii) CAA emerges as the hallmark of the Aβ phenotype in iCJD since it is observed in nearly 90% of all iCJD with Aβ pathology reported to date including ours, and it is shared by GH- and DM-iCJD, (iii) although the contributions to Aβ pathology of other factors, including GH deficiency, cannot be discounted, our findings increase the mounting evidence that this pathology is acquired by a mechanism resembling that of prion diseases.

Early-Onset Alzheimer Disease (EOAD) With Aphasia: A Case Report

Background: Alzheimer's disease (AD) is traditionally subdivided into early onset (EOAD) and late onset (LOAD). EOAD has an onset before age 65 years and accounts for 1-5% of all cases. Two main presentation types of AD are familial and sporadic. Case presentation: The authors present the case of a 68-year-old retired white man, with a college level educational background. At 55 years of age, the patient presented cognitive decline with short-term memory impairment and slowed, hesitant speech. At 57 years, he was unable to remember the way to work, exhibiting spatial disorientation. PET-CT: revealed hypometabolism and atrophy in the left temporal lobe and posterior region of the parietal lobes. Disease course: Evolving with difficulties in comprehension and sentence repetition over past 3 years and with global aphasia in past 6 months, beyond progressive memory impairment. Discussion: Possibly due to the young age and atypical presentation, and the diagnosis of EOAD is often delayed. To the best of our knowledge, this case can be classified as a sporadic EOAD with aphasia. Clinical variant and neuroimaging findings were crucial to the diagnosis and treatment of this atypical presentation of AD.

N-Terminally Truncated Amyloid-β(11-40/42) Cofibrillizes with its Full-Length Counterpart: Implications for Alzheimer's Disease

Amyloid-β peptide (Aβ) isoforms of different lengths and aggregation propensities coexist in vivo. These different isoforms are able to nucleate or frustrate the assembly of each other. N-terminally truncated Aβ_(11-40) and Aβ_(11-42) make up one fifth of plaque load yet nothing is known about their interaction with full-length Aβ_(1-40/42) . We show that in contrast to C-terminally truncated isoforms, which do not co-fibrillize, deletions of ten residues from the N terminus of Aβ have little impact on its ability to co-fibrillize with the full-length counterpart. As a consequence, N-terminally truncated Aβ will accelerate fiber formation and co-assemble into short rod-shaped fibers with its full-length Aβ counterpart. This has implications for the assembly kinetics, morphology, and toxicity of all Aβ isoforms.

A critical concentration of N-terminal pyroglutamylated amyloid beta drives the misfolding of Ab1-42 into more toxic aggregates

A wide consensus based on robust experimental evidence indicates pyroglutamylated amyloid-β isoform (AβpE3-42) as one of the most neurotoxic peptides involved in the onset of Alzheimer's disease. Furthermore, AβpE3-42 co-oligomerized with excess of Aβ1-42, produces oligomers and aggregates that are structurally distinct and far more cytotoxic than those made from Aβ1-42 alone. Here, we investigate quantitatively the influence of AβpE3-42 on biophysical properties and biological activity of Aβ1-42. We tested different ratios of AβpE3-42/Aβ1-42 mixtures finding a correlation between the biological activity and the structural conformation and morphology of the analyzed mixtures. We find that a mixture containing 5% AβpE3-42, induces the highest disruption of intracellular calcium homeostasis and the highest neuronal toxicity. These data correlate to an high content of relaxed antiparallel β-sheet structure and the coexistence of a population of big spheroidal aggregates together with short fibrils. Our experiments provide also evidence that AβpE3-42 causes template-induced misfolding of Aβ1-42 at ratios below 33%. This means that there exists a critical concentration required to have seeding on Aβ1-42 aggregation, above this threshold, the seed effect is not possible anymore and AβpE3-42 controls the total aggregation kinetics.

Isoglutaminyl cyclase contributes to CCL2-driven neuroinflammation in Alzheimer's disease

The brains of Alzheimer’s disease (AD) patients are characterized by deposits of Abeta peptides and by accompanying chronic inflammation. Here, we provide evidence that the enzyme isoglutaminyl cyclase (isoQC) is a novel factor contributing to both aspects of AD pathology. Two putative substrates of isoQC, N-truncated Abeta peptides and the monocyte chemoattractant chemokine CCL2, undergo isoQC-catalyzed pyroglutamate (pGlu) modification. This triggers Abeta aggregation and facilitates the biological activity of CCL2, which collectively results in the formation of high molecular weight Abeta aggregates, glial cell activation, neuroinflammation and neuronal cell death. In mouse brain, we found isoQC to be neuron-specifically expressed in neocortical, hippocampal and subcortical structures, localized to the endoplasmic reticulum and Golgi apparatus as well as co-expressed with its substrate CCL2. In aged APP transgenic Tg2576 mice, both isoQC and CCL2 mRNA levels are up-regulated and isoQC and CCL2 proteins were found to be co-induced in Abeta plaque-associated reactive astrocytes. Also, in mouse primary astrocyte culture, a simultaneous up-regulation of isoQC and CCL2 expression was revealed upon Abeta and pGlu-Abeta stimulation. In brains of AD patients, the expression of isoQC and CCL2 mRNA and protein is up-regulated compared to controls and correlates with pGlu-Abeta load and with the decline in mini-mental state examination. Our observations provide evidence for a dual involvement of isoQC in AD pathogenesis by catalysis of pGlu-Abeta and pGlu-CCL2 formation which mutually stimulate inflammatory events and affect cognition. We conclude that isoQC inhibition may target both major pathological events in the development of AD.

Extracellular vesicles in Alzheimer's disease: friends or foes? Focus on aβ-vesicle interaction

The intercellular transfer of amyloid-β (Aβ) and tau proteins has received increasing attention in Alzheimer’s disease (AD). Among other transfer modes, Aβ and tau dissemination has been suggested to occur through release of Extracellular Vesicles (EVs), which may facilitate delivery of pathogenic proteins over large distances. Recent evidence indicates that EVs carry on their surface, specific molecules which bind to extracellular Aβ, opening the possibility that EVs may also influence Aβ assembly and synaptotoxicity. In this review we focus on studies which investigated the impact of EVs in Aβ-mediated neurodegeneration and showed either detrimental or protective role for EVs in the pathology.

The Ubiquitin-Proteasome System and Molecular Chaperone Deregulation in Alzheimer's Disease

One of the shared hallmarks of neurodegenerative diseases is the accumulation of misfolded proteins. Therefore, it is suspected that normal proteostasis is crucial for neuronal survival in the brain and that the malfunction of this mechanism may be the underlying cause of neurodegenerative diseases. The accumulation of amyloid plaques (APs) composed of amyloid-beta peptide (Aβ) aggregates and neurofibrillary tangles (NFTs) composed of misfolded Tau proteins are the defining pathological markers of Alzheimer's disease (AD). The accumulation of these proteins indicates a faulty protein quality control in the AD brain. An impaired ubiquitin-proteasome system (UPS) could lead to negative consequences for protein regulation, including loss of function. Another pivotal mechanism for the prevention of misfolded protein accumulation is the utilization of molecular chaperones. Molecular chaperones, such as heat shock proteins (HSPs) and FK506-binding proteins (FKBPs), are highly involved in protein regulation to ensure proper folding and normal function. In this review, we elaborate on the molecular basis of AD pathophysiology using recent data, with a particular focus on the role of the UPS and molecular chaperones as the defensive mechanism against misfolded proteins that have prion-like properties. In addition, we propose a rational therapy approach based on this mechanism.

Focusing the amyloid cascade hypothesis on N-truncated Abeta peptides as drug targets against Alzheimer's disease

Although N-truncated Aβ variants are known to be the main constituent of amyloid plaques in the brains of patients with Alzheimer’s disease, their potential as targets for pharmacological intervention has only recently been investigated. In the last few years, the Alzheimer field has experienced a paradigm shift with the ever increasing understanding that targeting amyloid plaques has not led to a successful immunotherapy. On the other hand, there can be no doubt that the amyloid cascade hypothesis is central to the etiology of Alzheimer’s disease, raising the question as to why it is apparently failing to translate into the clinic. In this review, we aim to refocus the amyloid hypothesis integrating N-truncated Aβ peptides based on mounting evidence that they may represent better targets than full-length Aβ. In addition to Aβ peptides starting with an Asp at position 1, a variety of different N-truncated Aβ peptides have been identified starting with amino residue Ala-2, pyroglutamylated Glu-3, Phe-4, Arg-5, His-6, Asp-7, Ser-8, Gly-9, Tyr-10 and pyroglutamylated Glu-11. Certain forms of N-truncated species are better correlates for early pathological changes found pre-symptomatically more often than others. There is also evidence that, together with full-length Aβ, they might be physiologically detectable and are naturally secreted by neurons. Others are known to form soluble aggregates, which have neurotoxic properties in transgenic mouse models. It has been clearly demonstrated by several groups that some N-truncated Aβs dominate full-length Aβ in the brains of Alzheimer’s patients. We try to address which of the N-truncated variants may be promising therapeutic targets and which enzymes might be involved in the generation of these peptides

Abundance of Aβ₅-x like immunoreactivity in transgenic 5XFAD, APP/PS1KI and 3xTG mice, sporadic and familial Alzheimer's disease

Background

According to the modified amyloid hypothesis the main event in the pathogenesis of Alzheimer’s disease (AD) is the deposition of neurotoxic amyloid β-peptide (Aβ) within neurons. Additionally to full-length peptides, a great diversity of N-truncated Aβ variants is derived from the larger amyloid precursor protein (APP). Vast evidence suggests that Aβ_x-42 isoforms play an important role triggering neurodegeneration due to its high abundance, amyloidogenic propensity and toxicity. Although N-truncated and Aβ_x-42 species have been pointed as crucial players in AD etiology, the Aβ_5-x isoforms have not received much attention.

Results

The present study is the first to show immunohistochemical evidence of Aβ_5-x in familial cases of AD (FAD) and its distribution in APP/PS1KI, 5XFAD and 3xTG transgenic mouse models. In order to probe Aβ_5-x peptides we generated the AB5-3 antibody. Positive plaques and congophilic amyloid angiopathy (CAA) were observed among all the FAD cases tested carrying either APP or presenilin 1 (PS1) mutations and most of the sporadic cases of AD (SAD). Different patterns of Aβ_5-x distribution were found in the mouse models carrying different combinations of autosomal mutations in the APP, PS1 and Tau genes. All of them showed extracellular Aβ deposits but none CAA. Additionally, they were all affected by a severe amyloid pathology in the hippocampus among other areas. Interestingly, neither 5XFAD nor APP/PS1KI showed any evidence for intraneuronal Aβ_5-x.

Conclusions

Different degrees of Aβ_5-x accumulations can be found in the transgenic AD mouse models and human cases expressing the sporadic or the familial form of the disease. Due to the lack of intracellular Aβ_5-x, these isoforms might not be contributing to early mechanisms in the cascade of events triggering AD pathology. Brain sections obtained from SAD cases showed higher Aβ_5-x–immunoreactivity in vascular deposits than in extracellular plaques, while both are equally important in the FAD cases. The difference may rely on alternative mechanisms involving Aβ_5-x peptides and operating in a divergent way in the late and early onset forms of the disease.

BACE2 degradation mediated by the macroautophagy-lysosome pathway

Neuritic plaque is the pathological hallmark in Alzheimer's disease (AD). Amyloid-β protein (Aβ), the central component of neuritic plaques, is generated from amyloid-β precursor protein (APP) by β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. β-site APP cleaving enzyme 2 (BACE2), a homolog of BACE1, functions differently from BACE1 in APP processing. BACE1 is the β-secretase essential for Aβ production, and BACE2, a θ-secretase, cleaves APP within the Aβ domain, preventing Aβ production. Elucidation of the mechanism underlying BACE2 degradation is important for defining its biological features and its potential role in Alzheimer's disease drug development. In this report we first showed that the half-life of BACE2 is approximately 20 h. Lysosomal inhibition increased BACE2 protein levels whereas proteasomal inhibition had no effect on BACE2 protein expression. Furthermore, we identified that macroautophagy mediated BACE2 degradation. Finally, we showed that lysosomal inhibition increased BACE2 cleavage of APP. Taken together, our in vitro study showed that BACE2 is degraded through the macrophagy-lysosome pathway and that lysosomal inhibition affects BACE2 processing of APP. Modulation of BACE2 degradation via the lysosomal pathway could be a new target for AD drug development.

The Arctic AβPP mutation leads to Alzheimer's disease pathology with highly variable topographic deposition of differentially truncated Aβ

BACKGROUND

The Arctic mutation (p.E693G/p.E22G)fs within the β-amyloid (Aβ) region of the β-amyloid precursor protein gene causes an autosomal dominant disease with clinical picture of typical Alzheimer's disease. Here we report the special character of Arctic AD neuropathology in four deceased patients.

RESULTS

Aβ deposition in the brains was wide-spread (Thal phase 5) and profuse. Virtually all parenchymal deposits were composed of non-fibrillar, Congo red negative Aβ aggregates. Congo red only stained angiopathic vessels. Mass spectrometric analyses showed that Aβ deposits contained variably truncated and modified wild type and mutated Aβ species. In three of four Arctic AD brains, most cerebral cortical plaques appeared targetoid with centres containing C-terminally (beyond aa 40) and variably N-terminally truncated Aβ surrounded by coronas immunopositive for Aβx-42. In the fourth patient plaque centres contained almost no Aβ making the plaques ring-shaped. The architectural pattern of plaques also varied between different anatomic regions. Tau pathology corresponded to Braak stage VI, and appeared mainly as delicate neuropil threads (NT) enriched within Aβ plaques. Dystrophic neurites were scarce, while neurofibrillary tangles were relatively common. Neuronal perikarya within the Aβ plaques appeared relatively intact.

CONCLUSIONS

In Arctic AD brain differentially truncated abundant Aβ is deposited in plaques of variable numbers and shapes in different regions of the brain (including exceptional targetoid plaques in neocortex). The extracellular non-fibrillar Aβ does not seem to cause overt damage to adjacent neurons or to induce formation of neurofibrillary tangles, supporting the view that intracellular Aβ oligomers are more neurotoxic than extracellular Aβ deposits. However, the enrichment of NTs within plaques suggests some degree of intra-plaque axonal damage including accumulation of hp-tau, which may impair axoplasmic transport, and thereby contribute to synaptic loss. Finally, similarly as the cotton wool plaques in AD resulting from exon 9 deletion in the presenilin-1 gene, the Arctic plaques induced only modest glial and inflammatory tissue reaction.

N-truncated amyloid β (Aβ) 4-42 forms stable aggregates and induces acute and long-lasting behavioral deficits

N-truncated Aβ_4-42 is highly abundant in Alzheimer disease (AD) brain and was the first Aβ peptide discovered in AD plaques. However, a possible role in AD aetiology has largely been neglected. In the present report, we demonstrate that Aβ_4-42 rapidly forms aggregates possessing a high aggregation propensity in terms of monomer consumption and oligomer formation. Short-term treatment of primary cortical neurons indicated that Aβ_4-42 is as toxic as pyroglutamate Aβ_3-42 and Aβ_1-42. In line with these findings, treatment of wildtype mice using intraventricular Aβ injection induced significant working memory deficits with Aβ_4-42, pyroglutamate Aβ_3-42 and Aβ_1-42. Transgenic mice expressing Aβ_4-42 (Tg4-42 transgenic line) developed a massive CA1 pyramidal neuron loss in the hippocampus. The hippocampus-specific expression of Aβ_4-42 correlates well with age-dependent spatial reference memory deficits assessed by the Morris water maze test. Our findings indicate that N-truncated Aβ_4-42 triggers acute and long-lasting behavioral deficits comparable to AD typical memory dysfunction.

Central amyloid-β-specific single chain variable fragment ameliorates Aβ aggregation and neurotoxicity

Anti-amyloid-β immunotherapies are a promising therapeutic approach for the treatment and prevention of Alzheimer's disease (AD). Single chain antibody fragments (scFv) are an attractive alternative to whole antibodies due to their small size, single polypeptide format and inability to stimulate potentially undesirable Fc-mediated immune effector functions. We have generated the scFv derivative of anti-Aβ monoclonal antibody, 1E8, known to target residues 17-22 of Aβ. Here we show that the soluble 1E8 scFv binds to the central region of Aβ with an affinity of ~55 nM and significantly reduces fibril formation of Aβ(1-42). Furthermore, 1E8 scFv ameliorates Aβ(1-42)-mediated toxicity in the PC12 cell line and murine primary neuronal cultures. This ability to both target the central region of Aβ and prevent Aβ(1-42) neurotoxicity in vitro makes it a promising therapeutic antibody building block for further functionalization, toward the treatment of AD.

Distinct patterns of APP processing in the CNS in autosomal-dominant and sporadic Alzheimer disease

Autosomal-dominant Alzheimer disease (ADAD) is a genetic disorder caused by mutations in Amyloid Precursor Protein (APP) or Presenilin (PSEN) genes. Studies from families with ADAD have been critical to support the amyloid cascade hypothesis of Alzheimer disease (AD), the basis for the current development of amyloid-based disease-modifying therapies in sporadic AD (SAD). However, whether the pathological changes in APP processing in the CNS in ADAD are similar to those observed in SAD remains unclear. In this study, we measured β-site APP-cleaving enzyme (BACE) protein levels and activity, APP and APP C-terminal fragments in brain samples from subjects with ADAD carrying APP or PSEN1 mutations (n = 18), patients with SAD (n = 27) and age-matched controls (n = 22). We also measured sAPPβ and BACE protein levels, as well as BACE activity, in CSF from individuals carrying PSEN1 mutations (10 mutation carriers and 7 non-carrier controls), patients with SAD (n = 32) and age-matched controls (n = 11). We found that in the brain, the pattern in ADAD was characterized by an increase in APP β-C-terminal fragment (β-CTF) levels despite no changes in BACE protein levels or activity. In contrast, the pattern in SAD in the brain was mainly characterized by an increase in BACE levels and activity, with less APP β-CTF accumulation than ADAD. In the CSF, no differences were found between groups in BACE activity or expression or sAPPβ levels. Taken together, these data suggest that the physiopathological events underlying the chronic Aβ production/clearance imbalance in SAD and ADAD are different. These differences should be considered in the design of intervention trials in AD.

Alzheimer's disease related markers, cellular toxicity and behavioral deficits induced six weeks after oligomeric amyloid-β peptide injection in rats

Alzheimer’s disease (AD) is a neurodegenerative pathology associated with aging characterized by the presence of senile plaques and neurofibrillary tangles that finally result in synaptic and neuronal loss. The major component of senile plaques is an amyloid-β protein (Aβ). Recently, we characterized the effects of a single intracerebroventricular (icv) injection of Aβ fragment (25–35) oligomers (oAβ_25–35) for up to 3 weeks in rats and established a clear parallel with numerous relevant signs of AD. To clarify the long-term effects of oAβ_25–35 and its potential role in the pathogenesis of AD, we determined its physiological, behavioral, biochemical and morphological impacts 6 weeks after injection in rats. oAβ_25–35 was still present in the brain after 6 weeks. oAβ_25–35 injection did not affect general activity and temperature rhythms after 6 weeks, but decreased body weight, induced short- and long-term memory impairments, increased corticosterone plasma levels, brain oxidative (lipid peroxidation), mitochondrial (caspase-9 levels) and reticulum stress (caspase-12 levels), astroglial and microglial activation. It provoked cholinergic neuron loss and decreased brain-derived neurotrophic factor levels. It induced cell loss in the hippocampic CA subdivisions and decreased hippocampic neurogenesis. Moreover, oAβ_25–35 injection resulted in increased APP expression, Aβ_1–42 generation, and increased Tau phosphorylation. In conclusion, this in vivo study evidenced that the soluble oligomeric forms of short fragments of Aβ, endogenously identified in AD patient brains, not only provoked long-lasting pathological alterations comparable to the human disease, but may also directly contribute to the progressive increase in amyloid load and Tau pathology, involved in the AD physiopathology.

Inhibition of GSK3β-mediated BACE1 expression reduces Alzheimer-associated phenotypes

Deposition of amyloid β protein (Aβ) to form neuritic plaques in the brain is the pathological hallmark of Alzheimer's disease (AD). Aβ is generated from sequential cleavages of the β-amyloid precursor protein (APP) by the β- and γ-secretases, and β-site APP-cleaving enzyme 1 (BACE1) is the β-secretase essential for Aβ generation. Previous studies have indicated that glycogen synthase kinase 3 (GSK3) may play a role in APP processing by modulating γ-secretase activity, thereby facilitating Aβ production. There are two highly conserved isoforms of GSK3: GSK3α and GSK3β. We now report that specific inhibition of GSK3β, but not GSK3α, reduced BACE1-mediated cleavage of APP and Aβ production by decreasing BACE1 gene transcription and expression. The regulation of BACE1 gene expression by GSK3β was dependent on NF-κB signaling. Inhibition of GSK3 signaling markedly reduced Aβ deposition and neuritic plaque formation, and rescued memory deficits in the double transgenic AD model mice. These data provide evidence for regulation of BACE1 expression and AD pathogenesis by GSK3β and that inhibition of GSK3 signaling can reduce Aβ neuropathology and alleviate memory deficits in AD model mice. Our study suggests that interventions that specifically target the β-isoform of GSK3 may be a safe and effective approach for treating AD.

Differential toxicity, conformation and morphology of typical initial aggregation states of Aβ1-42 and Aβpy3-42 beta-amyloids

Among the different species of water-soluble β-peptides (Aβ1-42, Aβ1-40 and N-terminal truncated Aβ-peptides), Aβpy3-42 is thought to play a relevant role in Alzheimer's pathogenesis due to its abundance, resistance to proteolysis, fast aggregation kinetics, dynamic structure and high neurotoxicity. To evaluate the specific structural characteristics and neurotoxicity of Aβpy3-42, we separated different aggregation states of Aβ1-42 and Aβpy3-42 using fast protein liquid chromatography, isolating in both cases three peaks that corresponded to sa (small), ma (medium) and la (large) aggregates. Conformational analysis, by circular dichroism showed a prevailing random coil conformation for sa and ma, and typical β-sheet conformation for la. AFM and TEM show differential structural features between the three aggregates of a given β-peptide and among the aggregate of the two β-peptides. The potential toxic effects of the different aggregates were evaluated using human neuroblastoma SH-SY5Y cells in the MTT reduction, in the xCELLigence System, and in the Annexin V binding experiments. In the case of Aβ1-42 the most toxic aggregate is la, while in the case of Aβpy3-42 both sa and la are equally toxic. Aβ aggregates were found to be internalized in the cells, as estimated by confocal immunofluorescence microscopy, with a higher effect observed for Aβpy3-42, showing a good correlation with the toxic effects. Together these experiments allowed the discrimination of the intermediate states more responsible of oligomer toxicity, providing new insights on the correlation between the aggregation process and the toxicity and confirming the peculiar role in the pathogenesis of Alzheimer disease of Aβpy3-42 peptide.

N-Terminal pyroglutamate formation of Aβ38 and Aβ40 enforces oligomer formation and potency to disrupt hippocampal long-term potentiation

Pyroglutamate (pGlu)-modified amyloid peptides have been identified in sporadic and familial forms of Alzheimer's disease (AD) and the inherited disorders familial British and Danish Dementia (FBD and FDD). In this study, we characterized the aggregation of amyloid-β protein Aβ37, Aβ38, Aβ40, Aβ42 and ADan species in vitro, which were modified by N-terminal pGlu (pGlu-Aβ3-x, pGlu-ADan) or possess the intact N-terminus (Aβ1-x, ADan). The pGlu-modification confers rapid formation of oligomers and short fibrillar aggregates. In accordance with these observations, the pGlu-modified Aβ38, Αβ40 and Αβ42 species inhibit hippocampal long term potentiation of synaptic response, but pGlu-Aβ3-42 showing the highest effect. Among the unmodified Aβ peptides, only Aβ1-42 exhibites such propensity, which was similar to pGlu-Aβ3-38 and pGlu-Aβ3-40. Likewise, the amyloidogenic peptide pGlu-ADan impaired synaptic potentiation more pronounced than N-terminal unmodified ADan. The results were validated using conditioned media from cultivated HEK293 cells, which express APP variants favoring the formation of Aβ1-x, Aβ3-x or N-truncated pGlu-Aβ3-x species. Hence, we show that the ability of different amyloid peptides to impair synaptic function apparently correlates to their potential to form oligomers as a common mechanism. The pGlu-modification is apparently mediating a higher surface hydrophobicity, as shown by 1-anilinonaphtalene-8-sulfonate fluorescence, which enforces potential to interfere with neuronal physiology.

Neurodegeneration in Alzheimer disease: role of amyloid precursor protein and presenilin 1 intracellular signaling

Alzheimer disease (AD) is a heterogeneous neurodegenerative disorder characterized by (1) progressive loss of synapses and neurons, (2) intracellular neurofibrillary tangles, composed of hyperphosphorylated Tau protein, and (3) amyloid plaques. Genetically, AD is linked to mutations in few proteins amyloid precursor protein (APP) and presenilin 1 and 2 (PS1 and PS2). The molecular mechanisms underlying neurodegeneration in AD as well as the physiological function of APP are not yet known. A recent theory has proposed that APP and PS1 modulate intracellular signals to induce cell-cycle abnormalities responsible for neuronal death and possibly amyloid deposition. This hypothesis is supported by the presence of a complex network of proteins, clearly involved in the regulation of signal transduction mechanisms that interact with both APP and PS1. In this review we discuss the significance of novel finding related to cell-signaling events modulated by APP and PS1 in the development of neurodegeneration.

Regulation of β-site APP-cleaving enzyme 1 gene expression and its role in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder leading to dementia. Neuritic plaques are the hallmark neuropathology in AD brains. Proteolytic processing of amyloid-β precursor protein at the β site by beta-site amyloid-β precursor protein-cleaving enzyme 1 (BACE1) is essential to generate Aβ, a central component of the neuritic plaques. BACE1 is increased in some sporadic AD brains, and dysregulation of BACE1 gene expression plays an important role in AD pathogenesis. This review will focus on the regulation of BACE1 gene expression at the transcriptional, post-transcriptional, translation initiation, translational and post-translational levels, and its role in AD pathogenesis. Further studies on BACE1 gene expression regulation will greatly contribute to our understanding of AD pathogenesis and reveal potential novel approaches for AD prevention and drug development.

Pyroglutamate amyloid-β (Aβ): a hatchet man in Alzheimer disease

Pyroglutamate-modified amyloid-β (Aβ(pE3)) peptides are gaining considerable attention as potential key participants in the pathology of Alzheimer disease (AD) due to their abundance in AD brain, high aggregation propensity, stability, and cellular toxicity. Transgenic mice that produce high levels of Aβ(pE3-42) show severe neuron loss. Recent in vitro and in vivo experiments have proven that the enzyme glutaminyl cyclase catalyzes the formation of Aβ(pE3). In this minireview, we summarize the current knowledge on Aβ(pE3), discussing its discovery, biochemical properties, molecular events determining formation, prevalence in the brains of AD patients, Alzheimer mouse models, and potential as a target for therapy and as a diagnostic marker.

A window into the heterogeneity of human cerebrospinal fluid Aβ peptides

The initiating event in Alzheimer's disease (AD) is an imbalance in the production and clearance of amyloid beta (Aβ) peptides leading to the formation of neurotoxic brain Aβ assemblies. Cerebrospinal Fluid (CSF), which is a continuum of the brain, is an obvious source of markers reflecting central neuropathologic features of brain diseases. In this review, we provide an overview and update on our current understanding of the pathobiology of human CSF Aβ peptides. Specifically, we focused our attention on the heterogeneity of the CSF Aβ world discussing (1) basic research studies and what has been translated to clinical practice, (2) monomers and other soluble circulating Aβ assemblies, and (3) communication modes for Aβ peptides and their microenvironment targets. Finally, we suggest that Aβ peptides as well as other key signals in the central nervous system (CNS), mainly involved in learning and hence plasticity, may have a double-edged sword action on neuron survival and function.

Potent amyloidogenicity and pathogenicity of Aβ43

The amyloid-β peptide Aβ42 is known to be a primary amyloidogenic and pathogenic agent in Alzheimer's disease. However, the role of Aβ43, which is found just as frequently in the brains of affected individuals, remains unresolved. We generated knock-in mice containing a pathogenic presenilin-1 R278I mutation that causes overproduction of Aβ43. Homozygosity was embryonic lethal, indicating that the mutation involves a loss of function. Crossing amyloid precursor protein transgenic mice with heterozygous mutant mice resulted in elevated Aβ43, impairment of short-term memory and acceleration of amyloid-β pathology, which accompanied pronounced accumulation of Aβ43 in plaque cores similar in biochemical composition to those observed in the brains of affected individuals. Consistently, Aβ43 showed a higher propensity to aggregate and was more neurotoxic than Aβ42. Other pathogenic presenilin mutations also caused overproduction of Aβ43 in a manner correlating with Aβ42 and with the age of disease onset. These findings indicate that Aβ43, an overlooked species, is potently amyloidogenic, neurotoxic and abundant in vivo.

Glutaminyl cyclase contributes to the formation of focal and diffuse pyroglutamate (pGlu)-Aβ deposits in hippocampus via distinct cellular mechanisms

In the hippocampal formation of Alzheimer’s disease (AD) patients, both focal and diffuse deposits of Aβ peptides appear in a subregion- and layer-specific manner. Recently, pyroglutamate (pGlu or pE)-modified Aβ peptides were identified as a highly pathogenic and seeding Aβ peptide species. Since the pE modification is catalyzed by glutaminyl cyclase (QC) this enzyme emerged as a novel pharmacological target for AD therapy. Here, we reveal the role of QC in the formation of different types of hippocampal pE-Aβ aggregates. First, we demonstrate that both, focal and diffuse pE-Aβ deposits are present in defined layers of the AD hippocampus. While the focal type of pE-Aβ aggregates was found to be associated with the somata of QC-expressing interneurons, the diffuse type was not. To address this discrepancy, the hippocampus of amyloid precursor protein transgenic mice was analysed. Similar to observations made in AD, focal (i.e. core-containing) pE-Aβ deposits originating from QC-positive neurons and diffuse pE-Aβ deposits not associated with QC were detected in Tg2576 mouse hippocampus. The hippocampal layers harbouring diffuse pE-Aβ deposits receive multiple afferents from QC-rich neuronal populations of the entorhinal cortex and locus coeruleus. This might point towards a mechanism in which pE-Aβ and/or QC are being released from projection neurons at hippocampal synapses. Indeed, there are a number of reports demonstrating the reduction of diffuse, but not of focal, Aβ deposits in hippocampus after deafferentation experiments. Moreover, we demonstrate in neurons by live cell imaging and by enzymatic activity assays that QC is secreted in a constitutive and regulated manner. Thus, it is concluded that hippocampal pE-Aβ plaques may develop through at least two different mechanisms: intracellularly at sites of somatic QC activity as well as extracellularly through seeding at terminal fields of QC expressing projection neurons.

Icariin improves memory impairment in Alzheimer's disease model mice (5xFAD) and attenuates amyloid β-induced neurite atrophy

Essential therapeutic drugs for Alzheimer's disease (AD) have not been developed. Since the neuritic atrophy leading to synaptic losses is one of the critical causes of memory impairment in AD, the effects of several constituents in tonic herbal medicines on neuritic atrophy and memory deficits have been studied. The present study investigated the effects of icariin, a main constituent in Epimedii Herba, a well known tonic crude drug, in an in vitro AD model and transgenic mouse AD model (5xFAD). Amyloid β(1-42)-induced atrophies of axons and dendrites were restored by post-treatment with icariin in rat cortical neurons. Administration of icariin for 8 days (p.o.) improved spatial memory impairment in 5xFAD mice. These novel findings suggest that icariin may improve memory dysfunction in AD and have a potential to extend neurites even when amyloid β-induced neurite atrophy has already occurred.

Molecular biology and pathology of prion strains in sporadic human prion diseases

Prion diseases are believed to propagate by the mechanism involving self-perpetuating conformational conversion of the normal form of the prion protein, PrP(C), to the misfolded, pathogenic state, PrP(Sc). One of the most intriguing aspects of these disorders is the phenomenon of prion strains. It is believed that strain properties are fully encoded in distinct conformations of PrP(Sc). Strains are of practical relevance to human prion diseases as their diversity may explain the unusual heterogeneity of these disorders. The first insight into the molecular mechanisms underlying heterogeneity of human prion diseases was provided by the observation that two distinct disease phenotypes and their associated PrP(Sc) conformers co-distribute with distinct PrP genotypes as determined by the methionine/valine polymorphism at codon 129 of the PrP gene. Subsequent studies identified six possible combinations of the three genotypes (determined by the polymorphic codon 129) and two common PrP(Sc) conformers (named types 1 and 2) as the major determinants of the phenotype in sporadic human prion diseases. This scenario implies that each 129 genotype-PrP(Sc) type combination would be associated with a distinct disease phenotype and prion strain. However, notable exceptions have been found. For example, two genotype-PrP(Sc) type combinations are linked to the same phenotype, and conversely, the same combination was found to be associated with two distinct phenotypes. Furthermore, in some cases, PrP(Sc) conformers naturally associated with distinct phenotypes appear, upon transmission, to lose their phenotype-determining strain characteristics. Currently it seems safe to assume that typical sporadic prion diseases are associated with at least six distinct prion strains. However, the intrinsic characteristics that distinguish at least four of these strains remain to be identified.

BACE1 gene promoter single-nucleotide polymorphisms in Alzheimer's disease

Alzheimer's disease (AD) is the most neurodegenerative disorder leading to dementia. Neuritic plaque formation in brains is a hallmark of AD pathogenesis. Amyloid beta protein (Abeta) is the central component of neuritic plaques. Processing beta-amyloid precursor protein (APP) at the beta-secretase site by the beta-site APP cleaving enzyme 1 (BACE1) is essential for generation of Abeta. Elevation of BACE1 activity and expression has been reported in AD brains. However, no mutation in the BACE1 coding sequence has been identified in AD cases. Human BACE1 expression is tightly regulated at the transcription and translation level. To determine whether there is any single-nucleotide polymorphisms in the BACE1 gene promoter region affecting BACE1 expression in AD pathogenesis, in this study, we screened 2.6 kb of the human BACE1 gene promoter region from late-onset AD patients and found that there was no significant association between single-nucleotide polymorphisms and AD cases.

Distinct glutaminyl cyclase expression in Edinger-Westphal nucleus, locus coeruleus and nucleus basalis Meynert contributes to pGlu-Abeta pathology in Alzheimer's disease

Glutaminyl cyclase (QC) was discovered recently as the enzyme catalyzing the pyroglutamate (pGlu or pE) modification of N-terminally truncated Alzheimer’s disease (AD) Aβ peptides in vivo. This modification confers resistance to proteolysis, rapid aggregation and neurotoxicity and can be prevented by QC inhibitors in vitro and in vivo, as shown in transgenic animal models. However, in mouse brain QC is only expressed by a relatively low proportion of neurons in most neocortical and hippocampal subregions. Here, we demonstrate that QC is highly abundant in subcortical brain nuclei severely affected in AD. In particular, QC is expressed by virtually all urocortin-1-positive, but not by cholinergic neurons of the Edinger–Westphal nucleus, by noradrenergic locus coeruleus and by cholinergic nucleus basalis magnocellularis neurons in mouse brain. In human brain, QC is expressed by both, urocortin-1 and cholinergic Edinger–Westphal neurons and by locus coeruleus and nucleus basalis Meynert neurons. In brains from AD patients, these neuronal populations displayed intraneuronal pE-Aβ immunoreactivity and morphological signs of degeneration as well as extracellular pE-Aβ deposits. Adjacent AD brain structures lacking QC expression and brains from control subjects were devoid of such aggregates. This is the first demonstration of QC expression and pE-Aβ formation in subcortical brain regions affected in AD. Our results may explain the high vulnerability of defined subcortical neuronal populations and their central target areas in AD as a consequence of QC expression and pE-Aβ formation.