Mutant APP Research Articles

Alzheimer's Disease: Exploring the Landscape of Cognitive Decline.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and impaired daily functioning. The pathology of AD is marked by the accumulation of amyloid beta plaques and tau protein tangles in the brain, along with neuroinflammation and synaptic dysfunction. Genetic factors, such as mutations in APP, PSEN1, and PSEN2 genes, as well as the APOE ε4 allele, contribute to increased risk of acquiring AD. Currently available treatments provide symptomatic relief but do not halt disease progression. Research efforts are focused on developing disease-modifying therapies that target the underlying pathological mechanisms of AD. Advances in identification and validation of reliable biomarkers for AD hold great promise for enhancing early diagnosis, monitoring disease progression, and assessing treatment response in clinical practice in effort to alleviate the burden of this devastating disease. In this paper, we analyze data from the CAS Content Collection to summarize the research progress in Alzheimer's disease. We examine the publication landscape in effort to provide insights into current knowledge advances and developments. We also review the most discussed and emerging concepts and assess the strategies to combat the disease. We explore the genetic risk factors, pharmacological targets, and comorbid diseases. Finally, we inspect clinical applications of products against AD with their development pipelines and efforts for drug repurposing. The objective of this review is to provide a broad overview of the evolving landscape of current knowledge regarding AD, to outline challenges, and to evaluate growth opportunities to further efforts in combating the disease.

Gene-variant specific effects of plasma amyloid-β levels in Swedish autosomal dominant Alzheimer disease

BackgroundSeveral blood-based biomarkers offer the opportunity of in vivo detection of brain pathology and neurodegeneration in Alzheimer disease with high specificity and sensitivity, but the performance of amyloid-β (Aβ) measurements remains under evaluation. Autosomal dominant Alzheimer disease (ADAD) with mutations in PSEN1, PSEN2 and APP can be studied as a model for sporadic Alzheimer disease. However, clarifying the genetic effects on the Aβ-levels in different matrices such as cerebrospinal fluid or plasma is crucial for generalizability and utility of data. We aimed to explore plasma Aβ concentrations over the Alzheimer disease continuum in a longitudinal cohort of genetic Alzheimer disease.Methods92 plasma samples were collected from at-risk individuals (n = 47) in a Swedish cohort of ADAD, including 18 mutation carriers (13 APPswe (p.KM670/671NL) MC), 5 PSEN1 (p.H163Y) MC) and 29 non-carriers (NC) as the reference group. Concentrations of Aβ1–38, Aβ1–40 and Aβ1–42 were analyzed in plasma using immunoprecipitation coupled to tandem liquid chromatography mass spectrometry (IP-LC-MS/MS). Cross-sectional and repeated-measures data analyses were investigated family-wise, applying non-parametric tests as well as mixed-effects models.ResultsCross-sectional analysis at baseline showed more than a 3-fold increase in all plasma Aβ peptides in APPswe MC, regardless of clinical status, compared to controls (p < 0.01). PSEN1 (p.H163Y) presymptomatic MC had a decrease of plasma Aβ1–38 compared to controls (p < 0.05). There was no difference in Aβ1–42/1–40 ratio between APPswe MC (PMC and SMC), PSEN1 MC (PMC) and controls at baseline. Notably, both cross-sectional data and repeated-measures analysis suggested that APPswe MC have a stable Aβ1–42/1–40 ratio with increasing age, in contrast to the decrease seen with aging in both controls and PSEN1 (p.H163Y) MC.ConclusionThese data show very strong mutation-specific effects on Aβ profiles in blood, most likely due to a ubiquitous production outside of the CNS. Hence, analyses in an unselected clinical setting might unintentionally disclose genetic status. Furthermore, our findings suggest that the Aβ ratio might be a poor indicator of brain Aβ pathology in selected genetic cases. The very small sample size is a limitation that needs to be considered but reflects the scarcity of longitudinal in vivo data from genetic cohorts.

Characteristics and Transcriptomic Analysis of Cholinergic Neurons Derived from Induced Pluripotent Stem Cells with APP Mutation in Alzheimer's Disease.

The cholinergic hypothesis is one of the main theories that describe the pathogenesis of Alzheimer's disease (AD). Cholinergic neurons degenerate early and are severely damaged in AD. Despite extensive research, the causes of cholinergic neuron damage and the underlying molecular changes remain unclear. This study aimed to explore the characteristics and transcriptomic changes in cholinergic neurons derived from human induced pluripotent stem cells (iPSCs) with APP mutation. Peripheral blood mononuclear cells from patients with AD and healthy individuals were reprogrammed into iPSCs. The iPSCs were differentiated into cholinergic neurons. Cholinergic neurons were stained, neurotoxically tested, and electrophysiologically and transcriptomically analyzed. The iPSCs-derived cholinergic neurons from a patient with AD carrying a mutation in APP displayed enhanced susceptibility to Aβ1-42-induced neurotoxicity, characterized by severe neurotoxic effects, such as cell body coagulation and neurite fragmentation. Cholinergic neurons exhibited electrophysiological impairments and neuronal death after 21 days of culture in the AD group. Transcriptome analysis disclosed 883 differentially expressed genes (DEGs, 420 upregulated and 463 downregulated) participating in several signaling pathways implicated in AD pathogenesis. To assess the reliability of RNA sequencing, the expression of 16 target DEGs was validated using qPCR. Finally, the expression of the 8 core genes in different cell types of brain was analyzed by the AlzData database. In this study, iPSCs-derived cholinergic neurons from AD patients with APP mutations exhibit characteristics reminiscent of neurodegenerative disease. Transcriptome analysis revealed the corresponding DEGs and pathways, providing potential biomarkers and therapeutic targets for advancing AD research.

Nonlipogenic ABCA1 Inducers (NLAI) for Alzheimer's Disease Validated in a Mouse Model Expressing Human APOE3/APOE4.

Therapeutics enhancing apolipoprotein (APOE) positive function are a priority, because APOE4 is the major genetic risk factor for Alzheimer's disease (AD). The function of APOE, the key constituent of lipoprotein particles that transport cholesterol and lipids in the brain, is dependent on lipidation by ABCA1, a cell-membrane cholesterol transporter. ABCA1 transcription is regulated by liver X receptors (LXR): agonists have been shown to increase ABCA1, often accompanied by unwanted lipogenesis and elevated triglycerides (TG). Therefore, nonlipogenic ABCA1-inducers (NLAI) are needed. Two rounds of optimization of an HTS hit, derived from a phenotypic screen, gave lead compound 39 that was validated and tested in E3/4FAD mice that express human APOE3/4 and five mutant APP and PSEN1 human transgenes. Treatment with 39 increased ABCA1 expression, enhanced APOE lipidation, and reversed multiple AD phenotypes, without increasing TG. This NLAI/LXR-agonist study is the first in a human APOE-expressing model with hallmark amyloid-β pathology.

Modeling APOE ε4 familial Alzheimer's disease in directly converted 3D brain organoids.

Brain organoids have become a valuable tool for studying human brain development, disease modeling, and drug testing. However, generating brain organoids with mature neurons is time-intensive and often incomplete, limiting their utility in studying age-related neurodegenerative diseases such as Alzheimer's disease (AD). Here, we report the generation of 3D brain organoids from human fibroblasts through direct reprogramming, with simplicity, efficiency, and reduced variability. We also demonstrate that induced brain organoids from APOE ε4 AD patient fibroblasts capture some disease-specific features and pathologies associated with APOE ε4 AD. Moreover, APOE ε4-induced brain organoids with mutant APP overexpression faithfully recapitulate the acceleration of AD-related pathologies, providing a more physiologically relevant and patient-specific model of familial AD. Importantly, transcriptome analysis reveals that gene sets specific to APOE ε4 patient-induced brain organoids are highly similar to those of APOE ε4 post-mortem AD brains. Overall, induced brain organoids from direct reprogramming offer a promising approach for more efficient and controlled studies of neurodegenerative disease modeling.

Amyloid-β peptide signature associated with cerebral amyloid angiopathy in familial Alzheimer’s disease with APPdup and Down syndrome

Alzheimer’s disease (AD) is characterized by extracellular amyloid plaques containing amyloid-β (Aβ) peptides, intraneuronal neurofibrillary tangles, extracellular neuropil threads, and dystrophic neurites surrounding plaques composed of hyperphosphorylated tau protein (pTau). Aβ can also deposit in blood vessel walls leading to cerebral amyloid angiopathy (CAA). While amyloid plaques in AD brains are constant, CAA varies among cases. The study focuses on differences observed between rare and poorly studied patient groups with APP duplications (APPdup) and Down syndrome (DS) reported to have higher frequencies of elevated CAA levels in comparison to sporadic AD (sAD), most of APP mutations, and controls. We compared Aβ and tau pathologies in postmortem brain tissues across cases and Aβ peptides using mass spectrometry (MS). We further characterized the spatial distribution of Aβ peptides with MS-brain imaging. While intraparenchymal Aβ deposits were numerous in sAD, DS with AD (DS-AD) and AD with APP mutations, these were less abundant in APPdup. On the contrary, Aβ deposits in the blood vessels were abundant in APPdup and DS-AD while only APPdup cases displayed high Aβ deposits in capillaries. Investigation of Aβ peptide profiles showed a specific increase in Aβx-37, Aβx-38 and Aβx-40 but not Aβx-42 in APPdup cases and to a lower extent in DS-AD cases. Interestingly, N-truncated Aβ2-x peptides were particularly increased in APPdup compared to all other groups. This result was confirmed by MS-imaging of leptomeningeal and parenchymal vessels from an APPdup case, suggesting that CAA is associated with accumulation of shorter Aβ peptides truncated both at N- and C-termini in blood vessels. Altogether, this study identified striking differences in the localization and composition of Aβ deposits between AD cases, particularly APPdup and DS-AD, both carrying three genomic copies of the APP gene. Detection of specific Aβ peptides in CSF or plasma of these patients could improve the diagnosis of CAA and their inclusion in anti-amyloid immunotherapy treatments.

Mutational Landscape of Alzheimer's Disease and Frontotemporal Dementia: Regional Variances in Northern, Central, and Southern Italy.

Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD) are the two major neurodegenerative diseases with distinct clinical and neuropathological profiles. The aim of this report is to conduct a population-based investigation in well-characterized APP, PSEN1, PSEN2, MAPT, GRN, and C9orf72 mutation carriers/pedigrees from the north, the center, and the south of Italy. We retrospectively analyzed the data of 467 Italian individuals. We identified 21 different GRN mutations, 20 PSEN1, 11 MAPT, 9 PSEN2, and 4 APP. Moreover, we observed geographical variability in mutation frequencies by looking at each cohort of participants, and we observed a significant difference in age at onset among the genetic groups. Our study provides evidence that age at onset is influenced by the genetic group. Further work in identifying both genetic and environmental factors that modify the phenotypes in all groups is needed. Our study reveals Italian regional differences among the most relevant AD/FTD causative genes and emphasizes how the collaborative studies in rare diseases can provide new insights to expand knowledge on genetic/epigenetic modulators of age at onset.

Role of the Insulin-like Growth Factor System in Neurodegenerative Disease.

The insulin-like growth factor (IGF) system has paracrine and endocrine roles in the central nervous system. There is evidence that IGF signalling pathways have roles in the pathophysiology of neurodegenerative disease. This review focusses on Alzheimer's disease and Parkinson's disease, the two most common neurodegenerative disorders that are increasing in prevalence globally in relation to the aging population and the increasing prevalence of obesity and type 2 diabetes. Rodent models used in the study of the molecular pathways involved in neurodegeneration are described. However, currently, no animal model fully replicates these diseases. Mice with triple mutations in APP, PSEN and MAPT show promise as models for the testing of novel Alzheimer's therapies. While a causal relationship is not proven, the fact that age, obesity and T2D are risk factors in both strengthens the case for the involvement of the IGF system in these disorders. The IGF system is an attractive target for new approaches to management; however, there are gaps in our understanding that first need to be addressed. These include a focus beyond IGF-I on other members of the IGF system, including IGF-II, IGF-binding proteins and the type 2 IGF receptor.

Unveiling the Role of Novel miRNA PC-5P-12969 in Alleviating Alzheimer's Disease.

The intricate and complex molecular mechanisms that underlie the progression of Alzheimer's disease (AD) have prompted a concerted and vigorous research endeavor aimed at uncovering potential avenues for therapeutic intervention. This study aims to elucidate the role of miRNA PC-5P-12969 in the pathogenesis of AD. We assessed the differential expression of miRNA PC-5P-12969 in postmortem AD brains, AD animal and cell models using real-time reverse-transcriptase RT-PCR, we also checked the gene and protein expression of GSK3α and APP. Our investigation revealed a notable upregulation of miRNA PC-5P-12969 in postmortem brains of AD patients, in transgenic mouse models of AD, and in mutant APP overexpressing-HT22 cells. Additionally, our findings indicate that overexpression of miRNA PC-5P-12969 exerts a protective effect on cell survival, while concurrently mitigating apoptotic cell death. Further-more, we established a robust and specific interaction between miRNA PC-5P-12969 and GSK3α. Our luciferase reporter assays provided confirmation of the binding between miRNA PC-5P-12969 and the 3'-UTR of the GSK3α gene. Manipulation of miRNA PC-5P-12969 levels in cellular models of AD yielded noteworthy alterations in the gene and protein expression levels of both GSK3α and APP. Remarkably, the manipulation of miRNA PC-5P-12969 levels yielded significant enhancements in mitochondrial respiration and ATP production, concurrently with a reduction in mitochondrial fragmentation, thus unveiling a potential regulatory role of miRNA PC-5P-12969 in these vital cellular processes. In summary, this study sheds light on the crucial role of miRNA PC-5P-12969 and its direct interaction with GSK3α in the context of AD.

Large-scale gene expression changes in APP/PSEN1 and GFAP mutation models exhibit high congruence with Alzheimer's disease.

Alzheimer's disease (AD) is a complex neurodegenerative disorder with both genetic and non-genetic causes. Animal research models are available for a multitude of diseases and conditions affecting the central nervous system (CNS), and large-scale CNS gene expression data exist for many of these. Although there are several models specifically for AD, each recapitulates different aspects of the human disease. In this study we evaluate over 500 animal models to identify those with CNS gene expression patterns matching human AD datasets. Approaches included a hypergeometric based scoring system that rewards congruent gene expression patterns but penalizes discordant gene expression patterns. The top two models identified were APP/PS1 transgenic mice expressing mutant APP and PSEN1, and mice carrying a GFAP mutation that is causative of Alexander disease, a primary disorder of astrocytes in the CNS. The APP/PS1 and GFAP models both matched over 500 genes moving in the same direction as in human AD, and both had elevated GFAP expression and were highly congruent with one another. Also scoring highly were the 5XFAD model (with five mutations in APP and PSEN1) and mice carrying CK-p25, APP, and MAPT mutations. Animals with the APOE3 and 4 mutations combined with traumatic brain injury ranked highly. Bulbectomized rats scored high, suggesting anosmia could be causative of AD-like gene expression. Other matching models included the SOD1G93A strain and knockouts for SNORD116 (Prader-Willi mutation), GRID2, INSM1, XBP1, and CSTB. Many top models demonstrated increased expression of GFAP, and results were similar across multiple human AD datasets. Heatmap and Uniform Manifold Approximation Plot results were consistent with hypergeometric ranking. Finally, some gene manipulation models, including for TYROBP and ATG7, were identified with reversed AD patterns, suggesting possible neuroprotective effects. This study provides insight for the pathobiology of AD and the potential utility of available animal models.

IPSC-derived PSEN2 (N141I) astrocytes and microglia exhibit a primed inflammatory phenotype

BackgroundWidescale evidence points to the involvement of glia and immune pathways in the progression of Alzheimer’s disease (AD). AD-associated iPSC-derived glial cells show a diverse range of AD-related phenotypic states encompassing cytokine/chemokine release, phagocytosis and morphological profiles, but to date studies are limited to cells derived from PSEN1, APOE and APP mutations or sporadic patients. The aim of the current study was to successfully differentiate iPSC-derived microglia and astrocytes from patients harbouring an AD-causative PSEN2 (N141I) mutation and characterise the inflammatory and morphological profile of these cells.MethodsiPSCs from three healthy control individuals and three familial AD patients harbouring a heterozygous PSEN2 (N141I) mutation were used to derive astrocytes and microglia-like cells and cell identity and morphology were characterised through immunofluorescent microscopy. Cellular characterisation involved the stimulation of these cells by LPS and Aβ42 and analysis of cytokine/chemokine release was conducted through ELISAs and multi-cytokine arrays. The phagocytic capacity of these cells was then indexed by the uptake of fluorescently-labelled fibrillar Aβ42.ResultsAD-derived astrocytes and microglia-like cells exhibited an atrophied and less complex morphological appearance than healthy controls. AD-derived astrocytes showed increased basal expression of GFAP, S100β and increased secretion and phagocytosis of Aβ42 while AD-derived microglia-like cells showed decreased IL-8 secretion compared to healthy controls. Upon immunological challenge AD-derived astrocytes and microglia-like cells showed exaggerated secretion of the pro-inflammatory IL-6, CXCL1, ICAM-1 and IL-8 from astrocytes and IL-18 and MIF from microglia.ConclusionOur study showed, for the first time, the differentiation and characterisation of iPSC-derived astrocytes and microglia-like cells harbouring a PSEN2 (N141I) mutation. PSEN2 (N141I)-mutant astrocytes and microglia-like cells presented with a ‘primed’ phenotype characterised by reduced morphological complexity, exaggerated pro-inflammatory cytokine secretion and altered Aβ42 production and phagocytosis.

Cerebrovascular Dysfunction in Alzheimer's Disease and Transgenic Rodent Models.

Alzheimer's Disease (AD) and Alzheimer's Disease-Related Dementia (ADRD) are the primary causes of dementia that has a devastating effect on the quality of life and is a tremendous economic burden on the healthcare system. The accumulation of extracellular beta-amyloid (Aβ) plaques and intracellular hyperphosphorylated tau-containing neurofibrillary tangles (NFTs) in the brain are the hallmarks of AD. They are also thought to be the underlying cause of inflammation, neurodegeneration, brain atrophy, and cognitive impairments that accompany AD. The discovery of APP, PS1, and PS2 mutations that increase Aβ production in families with early onset familial AD led to the development of numerous transgenic rodent models of AD. These models have provided new insight into the role of Aβ in AD; however, they do not fully replicate AD pathology in patients. Familial AD patients with mutations that elevate the production of Aβ represent only a small fraction of dementia patients. In contrast, those with late-onset sporadic AD constitute the majority of cases. This observation, along with the failure of previous clinical trials targeting Aβ or Tau and the modest success of recent trials using Aβ monoclonal antibodies, has led to a reappraisal of the view that Aβ accumulation is the sole factor in the pathogenesis of AD. More recent studies have established that cerebral vascular dysfunction is one of the earliest changes seen in AD, and 67% of the candidate genes linked to AD are expressed in the cerebral vasculature. Thus, there is an increasing appreciation of the vascular contribution to AD, and the National Institute on Aging (NIA) and the Alzheimer's Disease Foundation recently prioritized it as a focused research area. This review summarizes the strengths and limitations of the most commonly used transgenic AD animal models and current views about the contribution of Aβ accumulation versus cerebrovascular dysfunction in the pathogenesis of AD.

Selective induction of Rab9-dependent alternative mitophagy using a synthetic derivative of isoquinoline alleviates mitochondrial dysfunction and cognitive deficits in Alzheimer's disease models.

Rationale: Promotion of mitophagy is considered a promising strategy for the treatment of neurodegenerative diseases including Alzheimer's disease (AD). The development of mitophagy-specific inducers with low toxicity and defined molecular mechanisms is essential for the clinical application of mitophagy-based therapy. The aim of this study was to investigate the potential of a novel small-molecule mitophagy inducer, ALT001, as a treatment for AD. Methods: ALT001 was developed through chemical optimization of an isoquinolium scaffold, which was identified from a chemical library screening using a mitophagy reporter system. In vitro and in vivo experiments were conducted to evaluate the potential of ALT001 as a mitophagy-targeting therapeutic agent and to investigate the molecular mechanisms underlying ALT001-induced mitophagy. The therapeutic effect of ALT001 was assessed in SH-SY5Y cells expressing mutant APP and mouse models of AD (5×FAD and PS2APP) by analyzing mitochondrial dysfunction and cognitive defects. Results: ALT001 specifically induces mitophagy both in vitro and in vivo but is nontoxic to mitochondria. Interestingly, we found that ALT001 induces mitophagy through the ULK1-Rab9-dependent alternative mitophagy pathway independent of canonical mitophagy pathway regulators such as ATG7 and PINK1. Importantly, ALT001 reverses mitochondrial dysfunction in SH-SY5Y cells expressing mutant APP in a mitophagy-dependent manner. ALT001 induces alternative mitophagy in mice and restores the decreased mitophagy level in a 5×FAD AD model mouse. In addition, ALT001 reverses mitochondrial dysfunction and cognitive defects in the PS2APP and 5×FAD AD mouse models. AAV-mediated silencing of Rab9 in the hippocampus further confirmed that ALT001 exerts its therapeutic effect through alternative mitophagy. Conclusion: Our results highlight the therapeutic potential of ALT001 for AD via alleviation of mitochondrial dysfunction and indicate the usefulness of the ULK1-Rab9 alternative mitophagy pathway as a therapeutic target.

The Molecular Efficacy of CRISPR-Cas9 in TreatingAlzheimer’s Disease

Alzheimer’s disease (AD), a highly complicated type of neurodegenerative diseases is the brain ailment characterized by the progressive decline in mental function influencing millions of people globally. In spite the developments in molecular biology, it is not fully understood what causes this disease. Mutations in APP, PSEN1, and PSEN2 symptomize AD by building amyloid-beta, a plaque formed in the brains by which neurons communication is hindered triggering cognitive decline, neuronal impairment, and death. Current advances in gene editing have provided new insights into the significant genetic factors take part in the progress of AD. CRISPR-Cas9 is a cutting-edge genome-editing tool used to provide sincere efforts to target and silence infective proteins linked with AD. The main goal of this research is to assess the potential of CRISPR Cas9, as a treatment for Alzheimer’s disease (AD) in addition to reviewing genes for both early and late onset AD.

Towards A Cell Biology of Alzheimer’s Disease

In many neurodegenerative disorders, including Alzheimer's Disease (AD), the dysfunction of multiple cell types causes neuronal cell death, but the precise cellular processes involved remain incompletely understood for any neurodegenerative disease. Strikingly, synapses are often affected early during pathogenesis, probably because presynaptic terminals are distant outstations of neurons that are the most vulnerable part of a neuron. In AD, multiple mutations in APP and presenilin genes cause rare familial cases, while the ApoE4 variant of the ApoE gene represents the strongest genetic risk factor for sporadic AD in the general population. APP and presenilin gene mutations are thought to induce AD pathogenesis by overproducing pathogenic Abeta variants, and ApoE4 is thought to influence Abeta clearance, but how Abeta might incite AD pathogenesis and how ApoE4 might predispose to AD pathogenesis remains incompletely understood. Moreover, compelling evidence implicates microglial and possibly astrocytic dysfunction in AD pathogenesis. In my lab, we have taken a cell-biological approach to these questions with a focus on synapses because of their prominent role in AD, recognizing that synapse impairments in AD may also be secondary to microglial dysfunction. We have examined how pathogenic APP mutations, chronic impairments of presenilin function, or ApoE4 may act on synapses, using human neurons trans-differentiated from ES and iPS cells as a model. In my presentation, I will discuss the current status of this project which is far from providing a definitive account of AD pathogenesis but may offer a basis for understanding the most basic processes underlying such pathogenesis.

Atypical presentations of autosomal dominant familial Alzheimer’s disease: insights into genetic, neuropathological and clinical heterogeneity

AbstractBackgroundAutosomal dominant familial Alzheimer’s disease (ADAD), caused by APP, PSEN1 and PSEN2 mutations, is clinically and pathologically similar to sporadic AD, with both typically presenting with memory impairment. However as in sporadic AD, atypical phenotypes and neuropathological heterogeneity occur, including variable vascular Aβ deposition as cerebral amyloid angiopathy (CAA). Investigating relationships between clinical, genetic and neuropathological heterogeneity in ADAD may provide insights into pathophysiological pathways relevant to AD in general.Methods256 symptomatic individuals from ADAD families seen at our Centre were included in a survival analysis, with detailed clinical phenotype data available for 138 (101 PSEN1, 37 APP). 33 of these individuals underwent brain donation (24 PSEN1, 9 APP), all demonstrating end‐stage AD pathology. Frontal and occipital cortex sections were stained immunohistochemically for Aβ and vessel counts used to determine the proportion of cortical and leptomeningeal blood vessels affected by CAA.ResultsAge at onset was, on average, seven years younger for PSEN1 than APP mutations and was influenced by mutation much more than survival was. Atypical (non‐amnestic) cognitive presentations with initial behavioral, language, dyscalculic or dysexecutive symptoms, and atypical clinical features (pyramidal, extrapyramidal and cerebellar signs) were more common in PSEN1 than APP cases, particularly those with post‐codon 200 mutations. Atypical cognitive presentations were associated with longer survival. There was some indication that APOE4 carriers had longer survival and that this effect may be restricted to PSEN1. In the post‐mortem cohort, atypical cognitive presentations occurred in 15%. Additional neurological features comprised myoclonus (45%), seizures (21%), pyramidal signs (21%) and extrapyramidal signs (15%), one individual had cerebellar signs. Increased frontal cortical and leptomeningeal CAA occurred in individuals with pyramidal and extrapyramidal signs, and in PSEN1 post‐codon 200 compared to pre‐codon 200 mutations. Atypical cognitive presentations were associated with increased frontal cortical CAA.ConclusionsPhenotypic heterogeneity in ADAD is influenced by causative gene and mutation type, and atypical clinical presentations are associated with increased CAA. Exploring mechanisms by which certain mutations drive Aβ deposition towards the vasculature, and how these may be impacted by other genetic factors and by therapies targeting Aβ, is an important direction for future research.

Data‐driven comparison of neurodegeneration patterns between autosomal dominant and sporadic late‐onset Alzheimer’s disease

AbstractBackgroundAutosomal dominant Alzheimer’s disease (ADAD) and sporadic late‐onset AD (LOAD) have similar biomarker profiles, supporting a shared pathophysiology. While both ADAD and LOAD are known to be heterogeneous, there are few studies that have compared the heterogeneity of neurodegeneration as indexed by volumetric MRI in LOAD to that of ADAD. Here we apply a data‐driven model of brain atrophy subtypes from LOAD to characterize atrophy within ADAD.MethodWe used cross‐sectional MRI from ADNI (LOAD) and the Estudio de la Enfermaded de Alzheimer en Jalisciences (EEAJ; ADAD). We used 13 cortical and subcortical Freesurfer‐based regions from 1,912 ADNI participants to train a Subtype and Stage Inference (SuStaIn) model of brain atrophy progression within LOAD. We built a three‐subtype model and applied it to subtype and stage 61 EEAJ participants: 47 carriers of the A431E mutation in PSEN1 and 14 carriers of the V717I mutation in APP. To harmonize the two datasets, we removed the effects of age, sex, education years, ICV and study (ADNI vs. EEAJ flag) from each regional volumetric biomarker prior to analysis. We retained 47 of the 61 EEAJ participants with an estimate SuStaIn stage greater than zero (in any subtype) for subsequent analyses.ResultThe progression patterns for each of the three data‐driven brain atrophy subtypes (typical, cortical, subcortical) are presented in Figures 1 A‐C. These are consistent with previous findings in LOAD. We found no difference in the percentage of participants in each subtype between LOAD, ADAD‐PSEN1 and ADAD‐APP groups (χ2 = 1.5, p = 0.84; Figure 1D). Within ADAD, those assigned the typical subtype had a slightly lower average stage of progression than those in the other two subtypes (t = ‐2.0, p = 0.049; Figure 2A). The triangle plot shows the probability of subtype membership is mostly clustered around the typical and cortical subtypes (Figure 2B), while the estimated stages increase dramatically after disease onset, as expected (Figure 2C).ConclusionWe found a comparable distribution of LOAD‐based atrophy subtypes within both the PSEN1 and APP carriers groups in ADAD, showing that heterogeneous neurodegeneration is another commonality between ADAD and LOAD.

Neuronal lipid metabolism genetics and Early‐Onset Alzheimer’s Disease: A systematic review and meta‐analysis of observational studies

AbstractBackgroundEarly Onset Alzheimer’s disease (EOAD) is associated with mutations in APP, PSEN1 and PSEN 2 genes but few studies have assessed its relationship with mutations involved in lipid metabolism and the amyloid cascade. Therefore, this study seeks to determine the association of ABCA7, SORL1 and APOE mutations with EOAD.MethodThe protocol was registered in PROSPERO(CRD42022328366). We included comparative observational studies assessing the association of ABCA7, SORL1 and APOE mutations with the development of EOAD in patients younger than 65 years old. The search strategy was performed in five databases (MEDLINE, Scopus, Web of Science, EMBASE, Opengray) from their inception to May 7th,2022. Abstract and full‐text screening, data extraction and risk of bias (RoB) assessment were performed in duplicates. RoB was assessed with Newcastle‐Ottawa Scale. We performed a random effects meta‐analysis for dichotomous outcomes by using the DerSimoniain Laird method. Effect sizes were reported as odds ratio (OR) with their corresponding 95% confidence intervals (95%CI).ResultA total of 2191 studies were screened and seven studies (n = 8992) were included; one was a retrospective cohort and six were case‐control studies. Three studies had high RoB and four had low RoB. Overall, 60% were female and the mean age ranged from 33.9(SD±17.1) to 57.4(SD±5.6). Three case‐control studies (n = 5098) found a significant association of ABCA7 mutation with EOAD (OR:2.51 95%CI[1.33‐4.73]; tau‐squared = 0.20, I‐squared = 66%). Two case‐control studies (n = 3107) found that SORL1 mutation was not associated with EOAD (OR:3.65 95%CI[0.76‐17.49]; tau‐squared = 1.15, I‐squared = 89%). Two case‐control studies and one cohort study (n = 787) found that APOE4 allelic variant mutation of the APOE gene had significant association with EOAD (OR:13.21; 95%CI[3.81‐45.85]; tau‐squared = 0.90, I‐squared = 75%) and that the APOE2 allelic variant mutation was not associated with EOAD.ConclusionDespite the high heterogeneity in our results and limited number of studies, this study shows that ABCA7 and APOE mutations may be associated with an increased risk of EOAD. Larger high‐quality cohort studies are needed to address this research question.

A systematic evaluation of hippocampal GABA levels in transgenic mouse models of amyloid and tau

AbstractBackgroundAlzheimer’s disease (AD) is characterized by the extracellular accumulation of amyloid‐β (Aβ) plaques and neuronal deposition of tau tangles, mainly in cortical regions and the hippocampus. Beyond these neuropathological hallmarks, it is suggested that neurotransmission dysfunctions, such as in the γ‐aminobutyric acid (GABA)ergic system, contribute to AD pathophysiology. However, the impact of Aβ and tau in the GABAergic system is still unknown. Thus, we aimed to examine GABA levels in the hippocampus of transgenic mouse models of Aβ and tau.MethodWe systematically reviewed the literature following the PRISMA 2020 guidelines. We searched PubMed and Web of Science databases for studies reporting GABA levels in the 3xTg‐AD and 5xFAD mouse models. These models present APP and PSEN1 mutations, but the 3xTg‐AD also harbors the MAPT P310L tau mutation, which is found in frontotemporal dementia.ResultThe search identified 3,576 articles. Six met the inclusion criteria (n = 26 3xTg‐AD and 26 wild‐type (WT); n = 16 5xFAD and 17 WT). The studies reported no significant differences in the levels of GABA in the hippocampus of 3xTg‐AD mice compared to their WT, but GABA levels decreased as a function of age. By contrast, the 5xFAD mouse model presented higher levels of GABA than their WT littermates.ConclusionHere, we show no significant changes in GABA levels in the hippocampus of 3xTg‐AD mice, whereas the levels of GABA were increased in the 5xFAD. Interestingly, the model harboring APP, PSEN1, and MAPT P310L mutations does not present changes in hippocampal levels of GABA. Our results suggest that Aβ alters GABA levels in the hippocampus, which may be an early change in AD. In addition, hippocampal GABAergic changes seem sensitive to different pathological features of AD.

Accelerated cerebral amyloid angiopathy and vascular alterations in a mixed mouse model of Alzheimer’s disease and cerebral small vessel disease

AbstractBackgroundWhile aging is the primary risk factor for Alzheimer’s disease (AD), emerging evidence suggests that vascular dysfunction, present in cerebral small vessel diseases (CSVD) such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), is also a major contributor for disease progression. Indeed, several studies have provided clinical evidence for a close synergistic relationship between AD and CSVD in cases where both diseases coexist. CSVD can elicit amyloid pathology, while Alzheimer’s‐associated cerebral amyloid angiopathy (CAA) and Ab plaque deposition may lead to concomitant vascular damage. Mutations in genes such as APP, PSEN1, and PSEN2 are not limited to AD, as APP mutations can also cause CAA, while PSEN1 and PSEN2 are involved in Notch3 signaling, a process known to be dysregulated in CADASIL. Here, we aimed to investigate the additive or synergistic effects of amyloid pathology and CADASIL‐related vascular damage on disease progression.MethodTo explore alterations in amyloid and vascular pathology when AD and CADASIL‐related CSVD coexist, we used PET/CT and histology to analyze over time the amyloid deposition in the form of plaques and CAA in a relevant mouse model of AD (5xFAD) carrying the Notch3 C456R mutation that causes CADASIL. Methoxy‐X04, Thioflavin‐S, or 6E10 were used to visualize amyloid accumulation in fixed brain tissues. The progression of microvascular dysfunction and neuroinflammation were assessed by immunofluorescence staining, Western blotting, RNA sequencing, and real‐time PCR.ResultAdult 5xFAD‐Notch3C456R mice showed accelerated parenchymal and vascular amyloid deposition compared to 5xFAD mice. Progressive gliosis and microvascular damage were concomitant to parenchymal and vascular amyloid accumulation. These changes were associated with blood‐brain barrier disruption and reduction in pericyte coverage of cerebral capillaries.ConclusionWe found accelerated amyloid plaque deposition, CAA, gliosis, and vascular damage in a mixed murine model of AD and CADASIL, suggesting that CSVD‐associated vascular changes directly contribute to AD pathology. This model offers novel opportunities to investigate the intricate interplay between CSVD and AD. This research was funded by NIH/NINDS grant RF1NS117486.