Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease

Bone marrow-derived macrophages and the CNS: An update on the use of experimental chimeric mouse models and bone marrow transplantation in neurological disorders

The central nervous system (CNS) is a very unique system with multiple features that differentiate it from systemic tissues. One of the most captivating aspects of its distinctive nature is the presence of the blood brain barrier (BBB), which seals it from the periphery. Therefore, to preserve tissue homeostasis, the CNS has to rely heavily on resident cells such as microglia. These pivotal cells of the mononuclear lineage have important and dichotomous roles according to various neurological disorders. However, certain insults can overwhelm microglia as well as compromising the integrity of the BBB, thus allowing the infiltration of bone marrow-derived macrophages (BMDMs). The use of myeloablation and bone marrow transplantation allowed the generation of chimeric mice to study resident microglia and infiltrated BMDM separately. This breakthrough completely revolutionized the way we captured these 2 types of mononuclear phagocytic cells. We now realize that microglia and BMDM exhibit distinct features and appear to perform different tasks. Since these cells are central in several pathologies, it is crucial to use chimeric mice to analyze their functions and mechanisms to possibly harness them for therapeutic purpose. This review will shed light on the advent of this methodology and how it allowed deciphering the ontology of microglia and its maintenance during adulthood. We will also compare the different strategies used to perform myeloablation. Finally, we will discuss the landmark studies that used chimeric mice to characterize the roles of microglia and BMDM in several neurological disorders. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Evaluating pathogenic dementia variants in posterior cortical atrophy

Posterior cortical atrophy (PCA) is an understudied visual impairment syndrome most often due to "posterior Alzheimer's disease (AD)" pathology. Case studies detected mutations in PSEN1, PSEN2, GRN, MAPT, and PRNP in subjects with clinical PCA. To detect the frequency and spectrum of mutations in known dementia genes in PCA, we screened 124 European-American subjects with clinical PCA (n = 67) or posterior AD neuropathology (n = 57) for variants in genes implicated in AD, frontotemporal dementia, and prion disease using NeuroX, a customized exome array. Frequencies in PCA of the variants annotated as pathogenic or potentially pathogenic were compared against ∼ 4300 European-American population controls from the NHLBI Exome Sequencing Project. We identified 2 rare variants not previously reported in PCA, TREM2 Arg47His, and PSEN2 Ser130Leu. No other pathogenic or potentially pathogenic variants were detected in the screened dementia genes. In this first systematic variant screen of a PCA cohort, we report 2 rare mutations in TREM2 and PSEN2, validate our previously reported APOE ε4 association, and demonstrate the utility of NeuroX.

Differences in Common Genetic Predisposition to Ischemic Stroke by Age and Sex

Supplemental Digital Content is available in the text.

Evidence from epidemiological studies points to differences in factors predisposing to stroke by age and sex. Whether these arise because of different genetic influences remained untested. Here, we use data from 4 genome-wide association data sets to study the relationship between genetic influence on stroke with both age and sex.

Genetics ignite focus on microglial inflammation in Alzheimer's disease

In the past five years, a series of large-scale genetic studies have revealed novel risk factors for Alzheimer’s disease (AD). Analyses of these risk factors have focused attention upon the role of immune processes in AD, specifically microglial function. In this review, we discuss interpretation of genetic studies.  We then focus upon six genes implicated by AD genetics that impact microglial function: TREM2, CD33, CR1, ABCA7, SHIP1, and APOE. We review the literature regarding the biological functions of these six proteins and their putative role in AD pathogenesis. We then present a model for how these factors may interact to modulate microglial function in AD.

Alzheimer's disease: Unique markers for diagnosis & new treatment modalities

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disease. In humans, AD becomes symptomatic only after brain changes occur over years or decades. Three contiguous phases of AD have been proposed: (i) the AD pathophysiologic process, (ii) mild cognitive impairment due to AD, and (iii) AD dementia. Intensive research continues around the world on unique diagnostic markers and interventions associated with each phase of AD. In this review, we summarize the available evidence and new therapeutic approaches that target both amyloid and tau pathology in AD and discuss the biomarkers and pharmaceutical interventions available and in development for each AD phase.

GWAS of longitudinal amyloid accumulation on 18F-florbetapir PET in Alzheimer's disease implicates microglial activation gene IL1RAP

Brain amyloid deposition is thought to be a seminal event in Alzheimer's disease. To identify genes influencing Alzheimer's disease pathogenesis, we performed a genome-wide association study of longitudinal change in brain amyloid burden measured by (18)F-florbetapir PET. A novel association with higher rates of amyloid accumulation independent from APOE (apolipoprotein E) ε4 status was identified in IL1RAP (interleukin-1 receptor accessory protein; rs12053868-G; P = 1.38 × 10(-9)) and was validated by deep sequencing. IL1RAP rs12053868-G carriers were more likely to progress from mild cognitive impairment to Alzheimer's disease and exhibited greater longitudinal temporal cortex atrophy on MRI. In independent cohorts rs12053868-G was associated with accelerated cognitive decline and lower cortical (11)C-PBR28 PET signal, a marker of microglial activation. These results suggest a crucial role of activated microglia in limiting amyloid accumulation and nominate the IL-1/IL1RAP pathway as a potential target for modulating this process.

Microglial malfunction: the third rail in the development of Alzheimer's disease

Studies of Alzheimer's disease (AD) have predominantly focused on two major pathologies: amyloid-β (Aβ) and hyperphosphorylated tau. These misfolded proteins can accumulate asymptomatically in distinct regions over decades. However, significant Aβ accumulation can be seen in individuals who do not develop dementia, and tau pathology limited to the transentorhinal cortex, which can appear early in adulthood, is usually clinically silent. Thus, an interaction between these pathologies appears to be necessary to initiate and propel disease forward to widespread circuits. Recent multidisciplinary findings strongly suggest that the third factor required for disease progression is an aberrant microglial immune response. This response may initially be beneficial; however, a maladaptive microglial response eventually develops, fueling a feed-forward spread of tau and Aβ pathology.

Genetic Analysis of Association Between Calcium Signaling and Hippocampal Activation, Memory Performance in the Young and Old, and Risk for Sporadic Alzheimer Disease

IMPORTANCE

Human episodic memory performance is linked to the function of specific brain regions, including the hippocampus; declines as a result of increasing age; and is markedly disturbed in Alzheimer disease (AD), an age-associated neurodegenerative disorder that primarily affects the hippocampus. Exploring the molecular underpinnings of human episodic memory is key to the understanding of hippocampus-dependent cognitive physiology and pathophysiology.

OBJECTIVE

To determine whether biologically defined groups of genes are enriched in episodic memory performance across age, memory encoding-related brain activity, and AD.

DESIGN, SETTING, AND PARTICIPANTS

In this multicenter collaborative study, which began in August 2008 and is ongoing, gene set enrichment analysis was done by using primary and meta-analysis data from 57 968 participants. The Swiss cohorts consisted of 3043 healthy young adults assessed for episodic memory performance. In a subgroup (n = 1119) of one of these cohorts, functional magnetic resonance imaging was used to identify gene set-dependent differences in brain activity related to episodic memory. The German Study on Aging, Cognition, and Dementia in Primary Care Patients cohort consisted of 763 elderly participants without dementia who were assessed for episodic memory performance. The International Genomics of Alzheimer's Project case-control sample consisted of 54 162 participants (17 008 patients with sporadic AD and 37 154 control participants). Analyses were conducted between January 2014 and June 2015. Gene set enrichment analysis in all samples was done using genome-wide single-nucleotide polymorphism data.

MAIN OUTCOMES AND MEASURES

Episodic memory performance in the Swiss cohort and German Study on Aging, Cognition, and Dementia in Primary Care Patients cohort was quantified by picture and verbal delayed free recall tasks. In the functional magnetic resonance imaging experiment, activation of the hippocampus during encoding of pictures served as the phenotype of interest. In the International Genomics of Alzheimer's Project sample, diagnosis of sporadic AD served as the phenotype of interest.

RESULTS

In the discovery sample, we detected significant enrichment for genes constituting the calcium signaling pathway, especially those related to the elevation of cytosolic calcium (P = 2 × 10-4). This enrichment was replicated in 2 additional samples of healthy young individuals (P = .02 and .04, respectively) and a sample of healthy elderly participants (P = .004). Hippocampal activation (P = 4 × 10-4) and the risk for sporadic AD (P = .01) were also significantly enriched for genes related to the elevation of cytosolic calcium.

CONCLUSIONS AND RELEVANCE

By detecting consistent significant enrichment in independent cohorts of young and elderly participants, this study identified that calcium signaling plays a central role in hippocampus-dependent human memory processes in cognitive health and disease, contributing to the understanding and potential treatment of hippocampus-dependent cognitive pathology.

CD33 modulates TREM2: convergence of Alzheimer loci

Here, we report results from a protein quantitative trait analysis in monocytes from 226 individuals to evaluate cross-talk between Alzheimer loci. We find that the NME8 locus influences PTK2B and that the CD33 risk allele leads to greater TREM2 expression. Further, we observe (1) a decreased TREM1/TREM2 ratio with a TREM1 risk allele, (2) decreased TREM2 expression with CD33 suppression, and (3) elevated cortical TREM2 mRNA expression with amyloid pathology.

Tau phosphorylation regulates the interaction between BIN1's SH3 domain and Tau's proline-rich domain

INTRODUCTION

The application of high-throughput genomic approaches has revealed 24 novel risk loci for Alzheimer's disease (AD). We recently reported that the bridging integrator 1 (BIN1) risk gene is linked to Tau pathology.

RESULTS

We used glutathione S-transferase pull-down assays and nuclear magnetic resonance (NMR) experiments to demonstrate that BIN1 and Tau proteins interact directly and then map the interaction between BIN1's SH3 domain and Tau's proline-rich domain (PRD) . Our NMR data showed that Tau phosphorylation at Thr231 weakens the SH3-PRD interaction. Using primary neurons, we found that BIN1-Tau complexes partly co-localize with the actin cytoskeleton; however, these complexes were not observed with Thr231-phosphorylated Tau species.

CONCLUSION

Our results show that (i) BIN1 and Tau bind through an SH3-PRD interaction and (ii) the interaction is downregulated by phosphorylation of Tau Thr231 (and potentially other residues). Our study sheds new light on regulation of the BIN1/Tau interaction and opens up new avenues for exploring its complex's role in the pathogenesis of AD.

The Rotterdam Study: 2016 objectives and design update

The Rotterdam Study is a prospective cohort study ongoing since 1990 in the city of Rotterdam in The Netherlands. The study targets cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, otolaryngological, locomotor, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. The findings of the Rotterdam Study have been presented in over 1200 research articles and reports (see www.erasmus-epidemiology.nl/rotterdamstudy ). This article gives the rationale of the study and its design. It also presents a summary of the major findings and an update of the objectives and methods.

Bridging the Translation Gap: From Dementia Risk Assessment to Advice on Risk Reduction

Dementia risk reduction is a global health and fiscal priority given the current lack of effective treatments and the projected increased number of dementia cases due to population ageing. There are often gaps among academic research, clinical practice, and public policy. We present information on the evidence for dementia risk reduction and evaluate the progress required to formulate this evidence into clinical practice guidelines. This narrative review provides capsule summaries of current evidence for 25 risk and protective factors associated with AD and dementia according to domains including biomarkers, demographic, lifestyle, medical, and environment. We identify the factors for which evidence is strong and thereby especially useful for risk assessment with the goal of personalising recommendations for risk reduction. We also note gaps in knowledge, and discuss how the field may progress towards clinical practice guidelines for dementia risk reduction.

Can oral infection be a risk factor for Alzheimer's disease?

Alzheimer's disease (AD) is a scourge of longevity that will drain enormous resources from public health budgets in the future. Currently, there is no diagnostic biomarker and/or treatment for this most common form of dementia in humans. AD can be of early familial-onset or sporadic with a late-onset. Apart from the two main hallmarks, amyloid-beta and neurofibrillary tangles, inflammation is a characteristic feature of AD neuropathology. Inflammation may be caused by a local central nervous system insult and/or by peripheral infections. Numerous microorganisms are suspected in AD brains ranging from bacteria (mainly oral and non-oral Treponema species), viruses (herpes simplex type I), and yeasts (Candida species). A causal relationship between periodontal pathogens and non-oral Treponema species of bacteria has been proposed via the amyloid-beta and inflammatory links. Periodontitis constitutes a peripheral oral infection that can provide the brain with intact bacteria and virulence factors and inflammatory mediators due to daily, transient bacteremias. If and when genetic risk factors meet environmental risk factors in the brain, disease is expressed, in which neurocognition may be impacted, leading to the development of dementia. To achieve the goal of finding a diagnostic biomarker and possible prophylactic treatment for AD, there is an initial need to solve the etiological puzzle contributing to its pathogenesis. This review therefore addresses oral infection as the plausible etiology of late-onset AD (LOAD).

Neprilysin Confers Genetic Susceptibility to Alzheimer's Disease in Han Chinese

Alzheimer's disease (AD) is a progressive neurodegenerative disease, with increasing incidence all over the world. Amyloid-β (Aβ) was considered to be the original cause to AD, and many reported pathogenic or risk genes for AD were located in the Aβ generation and degradation pathways. Neprilysin (NEP), insulin-degrading enzyme (IDE), and matrix metalloprotease-9 (MMP-9) are the most important Aβ-degrading proteases. Accumulating genetic evidence suggested that single nucleotide polymorphisms (SNPs) of these genes confer susceptibility to AD in Caucasian populations. In this study, we screened eight SNPs within these three Aβ-degrading protease genes in 1475 individuals of two independent Han Chinese case-control cohorts. SNP rs1816558 of NEP was found to be significantly associated with AD after adjustment for ε4 allele of the apolipoprotein E gene (APOEε4) and the Bonferroni correction. The remaining variants were not associated with risk of AD in Han Chinese sample set. Further data mining revealed that messenger RNA (mRNA) level of NEP substantially increased during the development of AD and was positively correlated with APP expression. The combined results indicated that NEP confers genetic susceptibility to AD in Han Chinese populations.

The Alzheimer's disease risk factor CD2AP maintains blood-brain barrier integrity

CD2-associated protein (CD2AP) is a leading genetic risk factor for Alzheimer's disease, but little is known about the function of CD2AP in the brain. We studied CD2AP(-/-) mice to address this question. Because CD2AP(-/-) mice normally die by 6 weeks from nephrotic syndrome, we used mice that also express a CD2AP transgene in the kidney, but not brain, to attenuate this phenotype. CD2AP-deficient mice had no behavioral abnormalities except for mild motor and anxiety deficits in a subset of CD2AP(-/-) mice exhibiting severe nephrotic syndrome, associated with systemic illness. Pentylenetetrazol (PTZ)-induced seizures occurred with shorter latency in CD2AP(-/-) mice, but characteristics of these seizures on electroencephalography were not altered. As CD2AP is expressed in brain-adjacent endothelial cells, we hypothesized that the shorter latency to seizures without detectably different seizure characteristics may be due to increased penetration of PTZ related to compromised blood-brain barrier integrity. Using sodium fluorescein extravasation, we found that CD2AP(-/-) mice had reduced blood-brain barrier integrity. Neither seizure severity nor blood-brain barrier integrity was correlated with nephrotic syndrome, indicating that these effects are dissociable from the systemic illness associated with CD2AP deficiency. Confirming this dissociation, wild-type mice with induced nephrotic syndrome maintained an intact blood-brain barrier. Taken together, our results support a role of CD2AP in mediating blood-brain barrier integrity and suggest that cerebrovascular roles of CD2AP could contribute to its effects on Alzheimer's disease risk.

Dissecting Complex and Multifactorial Nature of Alzheimer's Disease Pathogenesis: a Clinical, Genomic, and Systems Biology Perspective

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and other cognitive functions. AD can be classified into familial AD (FAD) and sporadic AD (SAD) based on heritability and into early onset AD (EOAD) and late onset AD (LOAD) based on age of onset. LOAD cases are more prevalent with genetically complex architecture. In spite of significant research focused on understanding the etiological mechanisms, search for diagnostic biomarker(s) and disease-modifying therapy is still on. In this article, we aim to comprehensively review AD literature on established etiological mechanisms including role of beta-amyloid and apolipoprotein E (APOE) along with promising newer etiological factors such as epigenetic modifications that have been associated with AD suggesting its multifactorial nature. As genomic studies have recently played a significant role in elucidating AD pathophysiology, a systematic review of findings from genome-wide linkage (GWL), genome-wide association (GWA), genome-wide expression (GWE), and epigenome-wide association studies (EWAS) was conducted. The availability of multi-dimensional genomic data has further coincided with the advent of computational and network biology approaches in recent years. Our review highlights the importance of integrative approaches involving genomics and systems biology perspective in elucidating AD pathophysiology. The promising newer approaches may provide reliable means of early and more specific diagnosis and help identify therapeutic interventions for LOAD.

How strong is the relationship between glaucoma, the retinal nerve fibre layer, and neurodegenerative diseases such as Alzheimer's disease and multiple sclerosis?

Glaucoma is a neurodegenerative disorder with established relationships with ocular structures such as the retinal nerve fibre layer (RNFL) and the ganglion cell layer (GCL). Ocular imaging techniques such as optical coherence tomography (OCT) allow for quantitative measurement of these structures. OCT has been used in the monitoring of glaucoma, as well as investigating other neurodegenerative conditions such as Alzheimer's disease (AD) and multiple sclerosis (MS). In this review, we highlight the association between these disorders and ocular structures (RNFL and GCL), examining their usefulness as biomarkers of neurodegeneration. The average RNFL thickness loss in patients with AD is 11 μm, and 7 μm in MS patients. Most of the studies investigating these changes are cross-sectional. Further longitudinal studies are required to assess sensitivity and specificity of these potential ocular biomarkers to neurodegenerative disease progression.

Genetic Interactions Explain Variance in Cingulate Amyloid Burden: An AV-45 PET Genome-Wide Association and Interaction Study in the ADNI Cohort

Alzheimer's disease (AD) is the most common neurodegenerative disorder. Using discrete disease status as the phenotype and computing statistics at the single marker level may not be able to address the underlying biological interactions that contribute to disease mechanism and may contribute to the issue of “missing heritability.” We performed a genome-wide association study (GWAS) and a genome-wide interaction study (GWIS) of an amyloid imaging phenotype, using the data from Alzheimer's Disease Neuroimaging Initiative. We investigated the genetic main effects and interaction effects on cingulate amyloid-beta (Aβ) load in an effort to better understand the genetic etiology of Aβ deposition that is a widely studied AD biomarker. PLINK was used in the single marker GWAS, and INTERSNP was used to perform the two-marker GWIS, focusing only on SNPs with p ≤ 0.01 for the GWAS analysis. Age, sex, and diagnosis were used as covariates in both analyses. Corrected p values using the Bonferroni method were reported. The GWAS analysis revealed significant hits within or proximal to APOE, APOC1, and TOMM40 genes, which were previously implicated in AD. The GWIS analysis yielded 8 novel SNP-SNP interaction findings that warrant replication and further investigation.

Alzheimer's Genetic Risk Intensifies Neurocognitive Slowing Associated with Diabetes in Non-Demented Older Adults

Introduction

We examine interactive and intensification effects of type 2 diabetes (T2D) with APOE and an Alzheimer's disease genetic risk score (GRS) on neurocognitive speed performance and change in nondemented older adults.

Methods

In an accelerated longitudinal design, we used latent growth modeling to test moderators of level and change in a neurocognitive speed latent variable for 628 adults (baseline median age = 69.0) followed over 9 years. The GRS was compiled using the cumulative risk of APOE, CLU, CR1, and PICALM.

Results

First, T2D predicted slower speed performance at centering age (75). Second, no predictive effects were associated with APOE or GRS. Third, a significant interaction showed that high risk from both T2D and GRS was selectively associated with steeper longitudinal slowing than all comparison cross-domain risk groups.

Discussion

Higher AD-related genetic risk intensified deleterious effects of diabetes on neurocognitive slowing in nondemented aging beyond the independent influence of APOE.

Nucleic acid-based risk factors and biomarkers: a future perspective on their use and development in Alzheimer's disease

As our population lives longer the impact of Alzheimer's disease threatens to exert socioeconomic influences across generations. We now know that by the manifestation of memory problems, the neuropathological processes associated with Alzheimer's disease have progressed in the brain for over a decade. This represents an opportunity for medicine - a window to detect, diagnose and treat to prevent the onset of these cognitive symptoms. To achieve these goals we need the confluence of safe effective treatments and an improved ability to identify individuals at highest risk for the disease as early as possible. We will touch on current work in that arena and discuss the future of diagnostic and risk assessment capabilities through the use of nucleic acid-based measurements.

De novo deleterious genetic variations target a biological network centered on Aβ peptide in early-onset Alzheimer disease

We hypothesized that de novo variants (DNV) might participate in the genetic determinism of sporadic early-onset Alzheimer disease (EOAD, onset before 65 years). We investigated 14 sporadic EOAD trios first by array-comparative genomic hybridization. Two patients carried a de novo copy number variation (CNV). We then performed whole-exome sequencing in the 12 remaining trios and identified 12 non-synonymous DNVs in six patients. The two de novo CNVs (an amyloid precursor protein (APP) duplication and a BACE2 intronic deletion) and 3/12 non-synonymous DNVs (in PSEN1, VPS35 and MARK4) targeted genes from a biological network centered on the Amyloid beta (Aβ) peptide. We showed that this a priori-defined genetic network was significantly enriched in amino acid-altering DNV, compared with the rest of the exome. The causality of the APP de novo duplication (which is the first reported one) was obvious. In addition, we provided evidence of the functional impact of the following three non-synonymous DNVs targeting this network: the novel PSEN1 variant resulted in exon 9 skipping in patient's RNA, leading to a pathogenic missense at exons 8-10 junction; the VPS35 missense variant led to partial loss of retromer function, which may impact neuronal APP trafficking and Aβ secretion; and the MARK4 multiple nucleotide variant resulted into increased Tau phosphorylation, which may trigger enhanced Aβ-induced toxicity. Despite the difficulty to recruit Alzheimer disease (AD) trios owing to age structures of the pedigrees and the genetic heterogeneity of the disease, this strategy allowed us to highlight the role of de novo pathogenic events, the putative involvement of new genes in AD genetics and the key role of Aβ network alteration in AD.

A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome

Down syndrome, which arises in individuals carrying an extra copy of chromosome 21, is associated with a greatly increased risk of early-onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP)--an Alzheimer disease risk factor--although the possession of extra copies of other chromosome 21 genes may also play a part. Further study of the mechanisms underlying the development of Alzheimer disease in people with Down syndrome could provide insights into the mechanisms that cause dementia in the general population.

The genetic landscape of Alzheimer disease: clinical implications and perspectives

The search for the genetic factors contributing to Alzheimer disease (AD) has evolved tremendously throughout the years. It started from the discovery of fully penetrant mutations in Amyloid precursor protein, Presenilin 1, and Presenilin 2 as a cause of autosomal dominant AD, the identification of the ɛ4 allele of Apolipoprotein E as a strong genetic risk factor for both early-onset and late-onset AD, and evolved to the more recent detection of at least 21 additional genetic risk loci for the genetically complex form of AD emerging from genome-wide association studies and massive parallel resequencing efforts. These advances in AD genetics are positioned in light of the current endeavor directing toward translational research and personalized treatment of AD. We discuss the current state of the art of AD genetics and address the implications and relevance of AD genetics in clinical diagnosis and risk prediction, distinguishing between monogenic and multifactorial AD. Furthermore, the potential and current limitations of molecular reclassification of AD to streamline clinical trials in drug development and biomarker studies are addressed.

Genet Med18 5, 421–430.

Genetic Control of Chromatin States in Humans Involves Local and Distal Chromosomal Interactions

Deciphering the impact of genetic variants on gene regulation is fundamental to understanding human disease. Although gene regulation often involves long-range interactions, it is unknown to what extent non-coding genetic variants influence distal molecular phenotypes. Here, we integrate chromatin profiling for three histone marks in lymphoblastoid cell lines (LCLs) from 75 sequenced individuals with LCL-specific Hi-C and ChIA-PET-based chromatin contact maps to uncover one of the largest collections of local and distal histone quantitative trait loci (hQTLs). Distal QTLs are enriched within topologically associated domains and exhibit largely concordant variation of chromatin state coordinated by proximal and distal non-coding genetic variants. Histone QTLs are enriched for common variants associated with autoimmune diseases and enable identification of putative target genes of disease-associated variants from genome-wide association studies. These analyses provide insights into how genetic variation can affect human disease phenotypes by coordinated changes in chromatin at interacting regulatory elements.

Alzheimer's disease: rare variants with large effect sizes

Recent advances in sequencing technology and novel genotyping arrays (focused on low-frequency and coding variants) have made it possible to identify novel coding variants with large effect sizes and also novel genes (TREM2, PLD3, UNC5C, and AKAP9) associated with Alzheimer's disease (AD) risk. The major advantages of these studies over the classic genome-wide association studies (GWAS) include the identification of the functional variant and the gene-driven association. In addition to the large effect size, these studies make it possible to model these variants and genes using cell and animal systems. On the other hand, the underlying population-variability of these very low allele frequency variants poses a great challenge to replicating results. Studies that include very large datasets (>10,000 cases and controls) and combine sequencing and genotyping approaches will lead to the identification of novel genes for Alzheimer's disease.

Differential Recognition Preferences of the Three Src Homology 3 (SH3) Domains from the Adaptor CD2-associated Protein (CD2AP) and Direct Association with Ras and Rab Interactor 3 (RIN3)

CD2AP is an adaptor protein involved in membrane trafficking, with essential roles in maintaining podocyte function within the kidney glomerulus. CD2AP contains three Src homology 3 (SH3) domains that mediate multiple protein-protein interactions. However, a detailed comparison of the molecular binding preferences of each SH3 remained unexplored, as well as the discovery of novel interactors. Thus, we studied the binding properties of each SH3 domain to the known interactor Casitas B-lineage lymphoma protein (c-CBL), conducted a peptide array screen based on the recognition motif PxPxPR and identified 40 known or novel candidate binding proteins, such as RIN3, a RAB5-activating guanine nucleotide exchange factor. CD2AP SH3 domains 1 and 2 generally bound with similar characteristics and specificities, whereas the SH3-3 domain bound more weakly to most peptide ligands tested yet recognized an unusually extended sequence in ALG-2-interacting protein X (ALIX). RIN3 peptide scanning arrays revealed two CD2AP binding sites, recognized by all three SH3 domains, but SH3-3 appeared non-functional in precipitation experiments. RIN3 recruited CD2AP to RAB5a-positive early endosomes via these interaction sites. Permutation arrays and isothermal titration calorimetry data showed that the preferred binding motif is Px(P/A)xPR. Two high-resolution crystal structures (1.65 and 1.11 Å) of CD2AP SH3-1 and SH3-2 solved in complex with RIN3 epitopes 1 and 2, respectively, indicated that another extended motif is relevant in epitope 2. In conclusion, we have discovered novel interaction candidates for CD2AP and characterized subtle yet significant differences in the recognition preferences of its three SH3 domains for c-CBL, ALIX, and RIN3.

Inflammatory Cyclooxygenase Activity and PGE2 Signaling in Models of Alzheimer's Disease

The inflammatory response is a fundamental driving force in the pathogenesis of Alzheimer’s disease (AD). In the setting of accumulating immunogenic Aß peptide assemblies, microglia, the innate immune cells of the brain, generate a non-resolving immune response and fail to adequately clear accumulating Aß peptides, accelerating neuronal and synaptic injury. Pathological, biomarker, and imaging studies point to a prominent role of the innate immune response in AD development, and the molecular components of this response are beginning to be unraveled. The inflammatory cyclooxygenase-PGE₂ pathway is implicated in pre-clinical development of AD, both in epidemiology of normal aging populations and in transgenic mouse models of Familial AD. The cyclooxygenase-PGE₂ pathway modulates the inflammatory response to accumulating Aß peptides through actions of specific E-prostanoid G-protein coupled receptors.

A computational framework for the prioritization of disease-gene candidates

Background

The identification of genes and uncovering the role they play in diseases is an important and complex challenge. Genome-wide linkage and association studies have made advancements in identifying genetic variants that underpin human disease. An important challenge now is to identify meaningful disease-associated genes from a long list of candidate genes implicated by these analyses. The application of gene prioritization can enhance our understanding of disease mechanisms and aid in the discovery of drug targets. The integration of protein-protein interaction networks along with disease datasets and contextual information is an important tool in unraveling the molecular basis of diseases.

Results

In this paper we propose a computational pipeline for the prioritization of disease-gene candidates. Diverse heterogeneous data including: gene-expression, protein-protein interaction network, ontology-based similarity and topological measures and tissue-specific are integrated. The pipeline was applied to prioritize Alzheimer's Disease (AD) genes, whereby a list of 32 prioritized genes was generated. This approach correctly identified key AD susceptible genes: PSEN1 and TRAF1. Biological process enrichment analysis revealed the prioritized genes are modulated in AD pathogenesis including: regulation of neurogenesis and generation of neurons. Relatively high predictive performance (AUC: 0.70) was observed when classifying AD and normal gene expression profiles from individuals using leave-one-out cross validation.

Conclusions

This work provides a foundation for future investigation of diverse heterogeneous data integration for disease-gene prioritization.

Immunopathology of multiple sclerosis

Two decades of clinical experience with immunomodulatory treatments for multiple sclerosis point to distinct immunological pathways that drive disease relapses and progression. In light of this, we discuss our current understanding of multiple sclerosis immunopathology, evaluate long-standing hypotheses regarding the role of the immune system in the disease and delineate key questions that are still unanswered. Recent and anticipated advances in the field of immunology, and the increasing recognition of inflammation as an important component of neurodegeneration, are shaping our conceptualization of disease pathophysiology, and we explore the potential implications for improved healthcare provision to patients in the future.

The Alzheimer disease BIN1 locus as a modifier of GBA-associated Parkinson disease

GBA mutations are among the most common genetic risk factors for Parkinson disease (PD) worldwide. We aimed to identify genetic modifiers of the age at onset (AAO) in GBA-associated PD. The study included a genome-wide discovery phase, including a cohort of 79 patients with the GBA p.N370S mutation, and candidate validation and replication analyses of 8 SNPs in patients with mild (n = 113) and severe (n = 41) GBA mutations. Genotyping was performed using the Affymetrix human SNP 6.0 array and TaqMan assays. In the genome-wide phase, none of the SNPs passed the genome-wide significance threshold. Eight SNPs were selected for further analysis from the top hits. In all GBA-associated PD patients (n = 153), the BIN1 rs13403026 minor allele was associated with an older AAO (12.4 ± 5.9 years later, p = 0.0001), compared to patients homozygous for the major allele. Furthermore, the AAO was 10.7 ± 6.8 years later in patients with mild GBA mutations, (p = 0.005, validation group), and 17.1 ± 2.5 years later in patients with severe GBA mutations (p = 0.01, replication). Our results suggest that alterations in the BIN1 locus, previously associated with Alzheimer disease, may modify the AAO of GBA-associated PD. More studies in other populations are required to examine the role of BIN1-related variants in GBA-associated PD.

More evidence for association of a rare TREM2 mutation (R47H) with Alzheimer's disease risk

Over 20 risk loci have been identified for late-onset Alzheimer's disease (LOAD), most of which display relatively small effect sizes. Recently, a rare missense (R47H) variant, rs75932628 in TREM2, has been shown to mediate LOAD risk substantially in Icelandic and Caucasian populations. Here, we present more evidence for the association of the R47H with LOAD risk in a Caucasian population comprising 4567 LOAD cases and controls. Our results show that carriers of the R47H variant have a significantly increased risk for LOAD (odds ratio = 7.40, p = 3.66E-06). In addition to Alzheimer's disease risk, we also examined the association of R47H with Alzheimer's disease-related phenotypes, including age-at-onset, psychosis, and amyloid deposition but found no significant association. Our results corroborate those of other studies implicating TREM2 as an LOAD risk locus and indicate the need to determine its biological role in the context of neurodegeneration.

Inflammation in Alzheimer's Disease and Molecular Genetics: Recent Update

Alzheimer's disease (AD) is a complex age-related neurodegenerative disorder of the central nervous system. Since the first description of AD in 1907, many hypotheses have been established to explain its causes. The inflammation theory is one of them. Pathological and biochemical studies of brains from AD individuals have provided solid evidence of the activation of inflammatory pathways. Furthermore, people with long-term medication of anti-inflammatory drugs have shown a reduced risk to develop the disease. After three decades of genetic study in AD, dozens of loci harboring genetic variants influencing inflammatory pathways in AD patients has been identified through genome-wide association studies (GWAS). The most well-known GWAS risk factor that is responsible for immune response and inflammation in AD development should be APOE ε4 allele. However, a growing number of other GWAS risk AD candidate genes in inflammation have recently been discovered. In the present study, we try to review the inflammation in AD and immunity-associated GWAS risk genes like HLA-DRB5/DRB1, INPP5D, MEF2C, CR1, CLU and TREM2.

Clearance systems in the brain-implications for Alzheimer disease

Accumulation of toxic protein aggregates-amyloid-β (Aβ) plaques and hyperphosphorylated tau tangles-is the pathological hallmark of Alzheimer disease (AD). Aβ accumulation has been hypothesized to result from an imbalance between Aβ production and clearance; indeed, Aβ clearance seems to be impaired in both early and late forms of AD. To develop efficient strategies to slow down or halt AD, it is critical to understand how Aβ is cleared from the brain. Extracellular Aβ deposits can be removed from the brain by various clearance systems, most importantly, transport across the blood-brain barrier. Findings from the past few years suggest that astroglial-mediated interstitial fluid (ISF) bulk flow, known as the glymphatic system, might contribute to a larger portion of extracellular Aβ (eAβ) clearance than previously thought. The meningeal lymphatic vessels, discovered in 2015, might provide another clearance route. Because these clearance systems act together to drive eAβ from the brain, any alteration to their function could contribute to AD. An understanding of Aβ clearance might provide strategies to reduce excess Aβ deposits and delay, or even prevent, disease onset. In this Review, we describe the clearance systems of the brain as they relate to proteins implicated in AD pathology, with the main focus on Aβ.

Rare coding mutations identified by sequencing of Alzheimer disease genome-wide association studies loci

Objective

To detect rare coding variants underlying loci detected by genome‐wide association studies (GWAS) of late onset Alzheimer disease (LOAD).

Methods

We conducted targeted sequencing of ABCA7, BIN1, CD2AP, CLU, CR1, EPHA1, MS4A4A/MS4A6A, and PICALM in 3 independent LOAD cohorts: 176 patients from 124 Caribbean Hispanics families, 120 patients and 33 unaffected individuals from the 129 National Institute on Aging LOAD Family Study; and 263 unrelated Canadian individuals of European ancestry (210 sporadic patients and 53 controls). Rare coding variants found in at least 2 data sets were genotyped in independent groups of ancestry‐matched controls. Additionally, the Exome Aggregation Consortium was used as a reference data set for population‐based allele frequencies.

Results

Overall we detected a statistically significant 3.1‐fold enrichment of the nonsynonymous mutations in the Caucasian LOAD cases compared with controls (p = 0.002) and no difference in synonymous variants. A stop‐gain mutation in ABCA7 (E1679X) and missense mutation in CD2AP (K633R) were highly significant in Caucasian LOAD cases, and mutations in EPHA1 (P460L) and BIN1 (K358R) were significant in Caribbean Hispanic families with LOAD. The EPHA1 variant segregated completely in an extended Caribbean Hispanic family and was also nominally significant in the Caucasians. Additionally, BIN1 (K358R) segregated in 2 of the 6 Caribbean Hispanic families where the mutations were discovered.

Interpretation

Targeted sequencing of confirmed GWAS loci revealed an excess burden of deleterious coding mutations in LOAD, with the greatest burden observed in ABCA7 and BIN1. Identifying coding variants in LOAD will facilitate the creation of tractable models for investigation of disease‐related mechanisms and potential therapies. Ann Neurol 2015;78:487–498

The Role of Retromer in Alzheimer's Disease

The retromer complex is an important component of the endosomal protein sorting machinery and mediates protein cargoes from endosomes to the trans-Golgi network (TGN) by retrograde pathway or to the cell surface through recycling pathway. Studies show that retromer and its receptors can make amyloid precursor protein (APP)/β-site APP-cleaving enzyme 1 (BACE1) away endosomes that reduces the production of amyloid β (Aβ). And, tetramer is also found to regulate phagocytic receptors to the plasma membrane of microglia, where some phagocytic receptors take part in Aβ clearance. Therefore, disruption of retromer will increase the production of Aβ. Recently, a plausible relationship between disturbance of retromer and tauopathies is raised. Retromer dysfunction may result in decreasing the clearance of extracellular tau and the level of cathepsin D, which enables tau-induced neurotoxicity. This review article summarizes the structure and function of retromer and its role in pathogenesis of AD. In the end, retromer may provide a potential therapeutic strategy for the treatment of AD.

Neutrophils promote Alzheimer's disease-like pathology and cognitive decline via LFA-1 integrin

Inflammation is a pathological hallmark of Alzheimer's disease, and innate immune cells have been shown to contribute to disease pathogenesis. In two transgenic models of Alzheimer's disease (5xFAD and 3xTg-AD mice), neutrophils extravasated and were present in areas with amyloid-β (Aβ) deposits, where they released neutrophil extracellular traps (NETs) and IL-17. Aβ42 peptide triggered the LFA-1 integrin high-affinity state and rapid neutrophil adhesion to integrin ligands. In vivo, LFA-1 integrin controlled neutrophil extravasation into the CNS and intraparenchymal motility. In transgenic Alzheimer's disease models, neutrophil depletion or inhibition of neutrophil trafficking via LFA-1 blockade reduced Alzheimer's disease-like neuropathology and improved memory in mice already showing cognitive dysfunction. Temporary depletion of neutrophils for 1 month at early stages of disease led to sustained improvements in memory. Transgenic Alzheimer's disease model mice lacking LFA-1 were protected from cognitive decline and had reduced gliosis. In humans with Alzheimer's disease, neutrophils adhered to and spread inside brain venules and were present in the parenchyma, along with NETs. Our results demonstrate that neutrophils contribute to Alzheimer's disease pathogenesis and cognitive impairment and suggest that the inhibition of neutrophil trafficking may be beneficial in Alzheimer's disease.

Role of pro-inflammatory cytokines released from microglia in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the brain, which is characterized by the formation of extracellular amyloid plaques (or senile plaques) and intracellular neurofibrillary tangles. However, increasing evidences demonstrated that neuroinflammatory changes, including chronic microgliosis are key pathological components of AD. Microglia, the resident immune cells of the brain, is constantly survey the microenvironment under physiological conditions. In AD, deposition of β-amyliod (Aβ) peptide initiates a spectrum of cerebral neuroinflammation mediated by activating microglia. Activated microglia may play a potentially detrimental role by eliciting the expression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) influencing the surrounding brain tissue. Emerging studies have demonstrated that up-regulation of pro-inflammatory cytokines play multiple roles in both neurodegeneration and neuroprotection. Understanding the pro-inflammatory cytokines signaling pathways involved in the regulation of AD is crucial to the development of strategies for therapy. This review will discuss the mechanisms and important role of pro-inflammatory cytokines in the pathogenesis of AD, and the ongoing drug targeting pro-inflammatory cytokine for therapeutic modulation.

Integrated genomic approaches identify major pathways and upstream regulators in late onset Alzheimer's disease

Previous studies have evaluated gene expression in Alzheimer’s disease (AD) brains to identify mechanistic processes, but have been limited by the size of the datasets studied. Here we have implemented a novel meta-analysis approach to identify differentially expressed genes (DEGs) in published datasets comprising 450 late onset AD (LOAD) brains and 212 controls. We found 3124 DEGs, many of which were highly correlated with Braak stage and cerebral atrophy. Pathway Analysis revealed the most perturbed pathways to be (a) nitric oxide and reactive oxygen species in macrophages (NOROS), (b) NFkB and (c) mitochondrial dysfunction. NOROS was also up-regulated, and mitochondrial dysfunction down-regulated, in healthy ageing subjects. Upstream regulator analysis predicted the TLR4 ligands, STAT3 and NFKBIA, for activated pathways and RICTOR for mitochondrial genes. Protein-protein interaction network analysis emphasised the role of NFKB; identified a key interaction of CLU with complement; and linked TYROBP, TREM2 and DOK3 to modulation of LPS signalling through TLR4 and to phosphatidylinositol metabolism. We suggest that NEUROD6, ZCCHC17, PPEF1 and MANBAL are potentially implicated in LOAD, with predicted links to calcium signalling and protein mannosylation. Our study demonstrates a highly injurious combination of TLR4-mediated NFKB signalling, NOROS inflammatory pathway activation, and mitochondrial dysfunction in LOAD.

Late-onset Alzheimer disease risk variants mark brain regulatory loci

Objective:

To investigate the top late-onset Alzheimer disease (LOAD) risk loci detected or confirmed by the International Genomics of Alzheimer's Project for association with brain gene expression levels to identify variants that influence Alzheimer disease (AD) risk through gene expression regulation.

Methods:

Expression levels from the cerebellum (CER) and temporal cortex (TCX) were obtained using Illumina whole-genome cDNA-mediated annealing, selection, extension, and ligation assay (WG-DASL) for ∼400 autopsied patients (∼200 with AD and ∼200 with non-AD pathologies). We tested 12 significant LOAD genome-wide association study (GWAS) index single nucleotide polymorphisms (SNPs) for cis association with levels of 34 genes within ±100 kb. We also evaluated brain levels of 14 LOAD GWAS candidate genes for association with 1,899 cis-SNPs. Significant associations were validated in a subset of TCX samples using next-generation RNA sequencing (RNAseq).

Results:

We identified strong associations of brain CR1, HLA-DRB1, and PILRB levels with LOAD GWAS index SNPs. We also detected other strong cis-SNPs for LOAD candidate genes MEF2C, ZCWPW1, and SLC24A4. MEF2C and SLC24A4, but not ZCWPW1 cis-SNPs, also associate with LOAD risk, independent of the index SNPs. The TCX expression associations could be validated with RNAseq for CR1, HLA-DRB1, ZCWPW1, and SLC24A4.

Conclusions:

Our results suggest that some LOAD GWAS variants mark brain regulatory loci, nominate genes under regulation by LOAD risk variants, and annotate these variants for their brain regulatory effects.

PLD3 in Alzheimer's Disease: a Modest Effect as Revealed by Updated Association and Expression Analyses

Alzheimer's disease (AD) is the most common form of dementia. Numerous genome-wide association studies (GWASs) have found several AD susceptibility common loci but with limited effect size. Recent next-generation sequencing studies of large AD pedigrees had identified phospholipase D3 (PLD3) p.V232M as the potentially functional rare variant with causal effect. However, four follow-up replication studies (Brief Communications Arising on Nature) questioned that PLD3 V232M might not be so important in AD. In this study, we re-analyzed all public-available genetic (rare and common variants) and expression data of PLD3, and screened coding variants within PLD3 in probands of 18 Han Chinese families with AD, to clarify the exact involvement of PLD3 in AD. Two closest homologues of PLD3, PLD1 and PLD2, were also analyzed to comprehensively understand the role of phospholipase D members in AD. We found that PLD3 variant V232M was associated with AD risk in overall sample sets (∼40,000 subjects) with a modest to moderate effect size (odds ratio [OR] = 1.53). Our results also showed that common variants and mRNA expression alterations of PLD2 play a role in AD genetic risk and pathology. Although we provided a systematic view of the involvement of PLD3 in AD at the genetic, mRNA expression, and protein levels, we could not define the exact causal or essential role of PLD3 rare variants in AD based on currently available data.

CR1 rs3818361 Polymorphism Contributes to Alzheimer's Disease Susceptibility in Chinese Population

Recent genome-wide association studies (GWAS) reported CR1 rs3818361 polymorphism to be an Alzheimer's disease (AD) susceptibility variant in European ancestry. Three independent studies investigated this association in Chinese population. However, these studies reported weak or no significant association. Here, we reinvestigated the association using all the samples from three independent studies in Chinese population (N = 4047, 1244 AD cases and 2803 controls). We also selected three independent studies in European ancestry population (N = 11787, 3939 AD cases and 7848 controls) to evaluate the effect of rs3818361 polymorphism on AD risk in different ethnic backgrounds. In Chinese population, we did not identified significant heterogeneity using additive, recessive, and dominant genetic models. Meta-analysis showed significant association between rs3818361 and AD with P = 6.00E-03 and P = 5.00E-03. We further identified no heterogeneity of rs3818361 polymorphism between Chinese and European populations. We found that rs3818361 polymorphism contributed to AD with similar genetic risk in Chinese and European populations. In summary, this is the first study to show significant association between rs3818361 polymorphism and AD in Chinese population by a meta-analysis method. Our findings indicate that the effect of CR1 rs3818361 polymorphism on AD risk in Chinese cohorts is consistent with the increased risk observed in European AD cohorts.

Genome-wide association analysis on normal hearing function identifies PCDH20 and SLC28A3 as candidates for hearing function and loss

Hearing loss and individual differences in normal hearing both have a substantial genetic basis. Although many new genes contributing to deafness have been identified, very little is known about genes/variants modulating the normal range of hearing ability. To fill this gap, we performed a two-stage meta-analysis on hearing thresholds (tested at 0.25, 0.5, 1, 2, 4, 8 kHz) and on pure-tone averages (low-, medium- and high-frequency thresholds grouped) in several isolated populations from Italy and Central Asia (total N = 2636). Here, we detected two genome-wide significant loci close to PCDH20 and SLC28A3 (top hits: rs78043697, P = 4.71E−10 and rs7032430, P = 2.39E−09, respectively). For both loci, we sought replication in two independent cohorts: B58C from the UK (N = 5892) and FITSA from Finland (N = 270). Both loci were successfully replicated at a nominal level of significance (P < 0.05). In order to confirm our quantitative findings, we carried out RT-PCR and reported RNA-Seq data, which showed that both genes are expressed in mouse inner ear, especially in hair cells, further suggesting them as good candidates for modulatory genes in the auditory system. Sequencing data revealed no functional variants in the coding region of PCDH20 or SLC28A3, suggesting that variation in regulatory sequences may affect expression. Overall, these results contribute to a better understanding of the complex mechanisms underlying human hearing function.

Reduced secreted clusterin as a mechanism for Alzheimer-associated CLU mutations

BACKGROUND

The clusterin (CLU) gene has been identified as an important risk locus for Alzheimer's disease (AD). Although the actual risk-increasing polymorphisms at this locus remain to be identified, we previously observed an increased frequency of rare non-synonymous mutations and small insertion-deletions of CLU in AD patients, which specifically clustered in the β-chain domain of CLU. Nonetheless the pathogenic nature of these variants remained unclear. Here we report a novel non-synonymous CLU mutation (p.I360N) in a Belgian Alzheimer patient and have explored the pathogenic nature of this and 10 additional CLU mutations on protein localization and secretion in vitro using immunocytochemistry, immunodetection and ELISAs.

RESULTS

Three patient-specific CLU mutations in the β-chain (p.I303NfsX13, p.R338W and p.I360N) caused an alteration of the subcellular CLU localization and diminished CLU transport through the secretory pathway, indicative of possible degradation mechanisms. For these mutations, significantly reduced CLU intensity was observed in the Golgi while almost all CLU protein was exclusively present in the endoplasmic reticulum. This was further confirmed by diminished CLU secretion in HEK293T and HEK293 FLp-In cell lines.

CONCLUSIONS

Our data lend further support to the contribution of rare coding CLU mutations in the pathogenesis of neurodegenerative diseases. Functional analyses suggest reduced secretion of the CLU protein as the mode of action for three of the examined CLU mutations. One of those is a frameshift mutation leading to a loss of secreted protein, and the other two mutations are amino acid substitutions in the disulfide bridge region, possibly interfering with heterodimerization of the α- and β-chain of CLU.

Impaired vascular-mediated clearance of brain amyloid beta in Alzheimer's disease: the role, regulation and restoration of LRP1

Amyloid beta (Aβ) homeostasis in the brain is governed by its production and clearance mechanisms. An imbalance in this homeostasis results in pathological accumulations of cerebral Aβ, a characteristic of Alzheimer’s disease (AD). While Aβ may be cleared by several physiological mechanisms, a major route of Aβ clearance is the vascular-mediated removal of Aβ from the brain across the blood-brain barrier (BBB). Here, we discuss the role of the predominant Aβ clearance protein—low-density lipoprotein receptor-related protein 1 (LRP1)—in the efflux of Aβ from the brain. We also outline the multiple factors that influence the function of LRP1-mediated Aβ clearance, such as its expression, shedding, structural modification and transcriptional regulation by other genes. Finally, we summarize approaches aimed at restoring LRP1-mediated Aβ clearance from the brain.