Early-onset Familial Alzheimer's Disease Research Articles

A Comprehensive Machine Learning Framework for the Exact Prediction of the Age of Onset in Familial and Sporadic Alzheimer's Disease.

Machine learning (ML) algorithms are widely used to develop predictive frameworks. Accurate prediction of Alzheimer’s disease (AD) age of onset (ADAOO) is crucial to investigate potential treatments, follow-up, and therapeutic interventions. Although genetic and non-genetic factors affecting ADAOO were elucidated by other research groups and ours, the comprehensive and sequential application of ML to provide an exact estimation of the actual ADAOO, instead of a high-confidence-interval ADAOO that may fall, remains to be explored. Here, we assessed the performance of ML algorithms for predicting ADAOO using two AD cohorts with early-onset familial AD and with late-onset sporadic AD, combining genetic and demographic variables. Performance of ML algorithms was assessed using the root mean squared error (RMSE), the R-squared (R2), and the mean absolute error (MAE) with a 10-fold cross-validation procedure. For predicting ADAOO in familial AD, boosting-based ML algorithms performed the best. In the sporadic cohort, boosting-based ML algorithms performed best in the training data set, while regularization methods best performed for unseen data. ML algorithms represent a feasible alternative to accurately predict ADAOO with little human intervention. Future studies may include predicting the speed of cognitive decline in our cohorts using ML.

In-Frame and Frameshift Mutations in Zebrafish Presenilin 2 Affect Different Cellular Functions in Young Adult Brains.

Background:Mutations in PRESENILIN 2 (PSEN2) cause early onset familial Alzheimer’s disease (EOfAD) but their mode of action remains elusive. One consistent observation for all PRESENILIN gene mutations causing EOfAD is that a transcript is produced with a reading frame terminated by the normal stop codon—the “reading frame preservation rule”. Mutations that do not obey this rule do not cause the disease. The reasons for this are debated.Objective:To predict cellular functions affected by heterozygosity for a frameshift, or a reading frame-preserving mutation in zebrafish psen2 using bioinformatic techniques.Methods:A frameshift mutation (psen2N140fs) and a reading frame-preserving (in-frame) mutation (psen2T141 _ L142delinsMISLISV) were previously isolated during genome editing directed at the N140 codon of zebrafish psen2 (equivalent to N141 of human PSEN2). We mated a pair of fish heterozygous for each mutation to generate a family of siblings including wild type and heterozygous mutant genotypes. Transcriptomes from young adult (6 months) brains of these genotypes were analyzed.Results:The in-frame mutation uniquely caused subtle, but statistically significant, changes to expression of genes involved in oxidative phosphorylation, long-term potentiation and the cell cycle. The frameshift mutation uniquely affected genes involved in Notch and MAPK signaling, extracellular matrix receptor interactions and focal adhesion. Both mutations affected ribosomal protein gene expression but in opposite directions.Conclusion:A frameshift and an in-frame mutation at the same position in zebrafish psen2 cause discrete effects. Changes in oxidative phosphorylation, long-term potentiation and the cell cycle may promote EOfAD pathogenesis in humans.

Clinicopathological correlations and cholinesterase expression in early-onset familial Alzheimer's disease with the presenilin 1 mutation, Leu235Pro

In sporadic Alzheimer's disease (SpAD), acetylcholinesterase and butyrylcholinesterase, co-regulators of acetylcholine, are associated with β-amyloid plaques and tau neurofibrillary tangles in patterns suggesting a contribution to neurotoxicity. This association has not been explored in early-onset familial Alzheimer's disease (FAD). We investigated whether cholinesterases are observed in the neuropathological hallmarks in FAD expressing the presenilin 1 Leu235Pro mutation. Brain tissues from three FAD cases and one early-onset SpAD case were stained and analyzed for β-amyloid, tau, α-synuclein, acetylcholinesterase and butyrylcholinesterase. AD pathology was prominent throughout the rostrocaudal extent of all 4 brains but α-synuclein-positive neurites were present in only one familial case. In FAD and SpAD cases, cholinergic activity was associated with plaques and tangles but not with α-synuclein pathology. Both cholinesterases showed similar or decreased plaque staining than detected with β-amyloid immunostaining but greater plaque deposition than observed with thioflavin-S histofluorescence. Acetylcholinesterase and butyrylcholinesterase are highly associated with AD pathology in inherited disease and both may represent specific diagnostic and therapeutic targets for all AD forms.

Preclinical validation of a potent γ-secretase modulator for Alzheimer’s disease prevention

A potent γ-secretase modulator (GSM) has been developed to circumvent problems associated with γ-secretase inhibitors (GSIs) and to potentially enable use in primary prevention of early-onset familial Alzheimer's disease (EOFAD). Unlike GSIs, GSMs do not inhibit γ-secretase activity but rather allosterically modulate γ-secretase, reducing the net production of Aβ42 and to a lesser extent Aβ40, while concomitantly augmenting production of Aβ38 and Aβ37. This GSM demonstrated robust time- and dose-dependent efficacy in acute, subchronic, and chronic studies across multiple species, including primary and secondary prevention studies in a transgenic mouse model. The GSM displayed a >40-fold safety margin in rats based on a comparison of the systemic exposure (AUC) at the no observed adverse effect level (NOAEL) to the 50% effective AUC or AUCeffective, the systemic exposure required for reducing levels of Aβ42 in rat brain by 50%.

Early-onset familial Alzheimer's disease in a family with mutation of presenilin 2 gene.

Alzheimer's disease (AD) is the most common senile neurodegenerative disease characterized by progressive cognitive dysfunction, psychological and behavioral abnormalities, and impaired ability of activities of daily living. A family with a total of 3 patients were admitted to the Department of Neurology of Xiangya Hospital, Central South University in 2018. The proband showed memory decline as the presenting symptoms, and subsequently showed psychological and behavioral abnormalities, personality changes, seizures, and motor retardation. Definite diagnosis of early-onset familial AD (EOFAD) with missense mutation of presenilin 2 (PSEN2) (c.715A>G p.M239V) was established by whole exome sequencing (WES) technology. We reported the mutation in Chinese Han population for the first time, which expanded the mutation spectrum ofPSEN2 gene and aid to enrich the characterization of clinical phenotype in EOFAD associated to PSEN2 mutations. Patients with early onset age and complex clinical manifestations of AD can be diagnosed with the help of genetic testing to avoid misdiagnosis.

Familial Alzheimer’s disease mutations in amyloid protein precursor alter proteolysis by γ-secretase to increase amyloid β-peptides of ≥45 residues

Production of amyloid β-protein (Aβ) is carried out by the membrane-embedded γ-secretase complex. Mutations in the transmembrane domain of amyloid β-protein precursor (APP) associated with early-onset familial Alzheimer's disease (FAD) can alter the ratio of aggregation-prone 42-residue Aβ (Aβ42) to 40-residue Aβ (Aβ40). However, APP substrate is proteolyzed processively by γ-secretase along two pathways: Aβ49→Aβ46→Aβ43→Aβ40 and Aβ48→Aβ45→Aβ42→Aβ38. Effects of FAD mutations on each proteolytic step are unknown, largely due to difficulties in detecting and quantifying longer Aβ peptides. To address this, we carried out systematic and quantitative analyses of all tri- and tetrapeptide coproducts from proteolysis of wild-type and 14 FAD-mutant APP substrates by purified γ-secretase. These small peptides, including FAD-mutant forms, were detected by tandem mass spectrometry and quantified by establishing concentration curves for each of 32 standards. APP intracellular domain (AICD) coproducts were quantified by immunoblot, and the ratio of AICD products corresponding to Aβ48 and Aβ49 was determined by mass spectrometry. Levels of individual Aβ peptides were determined by subtracting levels of peptide coproducts associated with degradation from those associated with production. This method was validated for Aβ40 and Aβ42 by specific ELISAs and production of equimolar levels of Aβ and AICD. Not all mutant substrates led to increased Aβ42/40. However, all 14 disease-causing mutations led to inefficient processing of longer forms of Aβ ≥ 45 residues. In addition, the effects of certain mutations provided insight into the mechanism of processive proteolysis: intermediate Aβ peptides apparently remain bound for subsequent trimming and are not released and reassociated.

Alzheimer's disease: a tale of two diseases?

Sporadic late-onset Alzheimer’s disease (SLOAD) and familial early-onset Alzheimer’s disease (FEOAD) associated with dominant mutations in APP, PSEN1 and PSEN2, are thought to represent a spectrum of the same disorder based on near identical behavioral and histopathological features. Hence, FEOAD transgenic mouse models have been used in past decades as a surrogate to study SLOAD pathogenic mechanisms and as the gold standard to validate drugs used in clinical trials. Unfortunately, such research has yielded little output in terms of therapeutics targeting the disease’s development and progression. In this short review, we interrogate the widely accepted view of one, dimorphic disease through the prism of the Bmi1+/– mouse model and the distinct chromatin signatures observed between SLOAD and FEOAD brains.

Brain Transcriptome Analysis of a Protein-Truncating Mutation in Sortilin-Related Receptor 1 Associated With Early-Onset Familial Alzheimer's Disease Indicates Early Effects on Mitochondrial and Ribosome Function.

The early cellular stresses leading to Alzheimer's disease (AD) remain poorly understood because we cannot access living, asymptomatic human AD brains for detailed molecular analyses. Sortilin-related receptor 1 (SORL1) encodes a multi-domain receptor protein genetically associated with both rare, early-onset familial AD (EOfAD) and common, sporadic, late-onset AD (LOAD). SORL1 protein has been shown to act in the trafficking of the amyloid β A4 precursor protein (AβPP) that is proteolysed to form one of the pathological hallmarks of AD, amyloid-β (Aβ) peptide. However, other functions of SORL1 in AD are less well understood. To investigate the effects of heterozygosity for an EOfAD-like mutation in SORL1 on the brain transcriptome of young-adult mutation carriers using zebrafish as a model organism. We performed targeted mutagenesis to generate an EOfAD-like mutation in the zebrafish orthologue of SORL1 and performed RNA-sequencing on mRNA isolated from the young adult brains of siblings in a family of fish either wild type (non-mutant) or heterozygous for the EOfAD-like mutation. We identified subtle differences in gene expression indicating changes in mitochondrial and ribosomal function in the mutant fish. These changes appear to be independent of changes in mitochondrial content or the expression of AβPP-related proteins in zebrafish. These findings provided evidence supporting that EOfAD mutations in SORL1 affect mitochondrial and ribosomal function and provide the basis for future investigation elucidating the nature of these effects.

Clinico‐genetic study of two Japanese pedigrees with hereditary spastic paraparesis and Alzheimer's disease

AbstractBackgroundMutations in the SPG4/SPAST gene are the major cause of hereditary spastic paraplegias (HSPs), a group of genetic disorders leading to progressive spasticity and weakness of the lower limbs. Alzheimer's disease (AD) is a degenerative disorder of the central nervous system. Early‐onset familial AD (EOFAD) accounts for 3‐5% of all AD cases and denotes families in which onset is reliably before age 60 to 65 years and often before age 55 years. The present study reports a second Japanese pedigree in which a SPG4/SPAST mutation co‐segregates with HSP and EOFAD.MethodWhole exome sequencing (WES), Sanger sequencing, Multiplex Ligation dependent Probe Amplification (MLPA) analysis, bioinformatics, neurological evaluation, diagnostic imaging, and pathological assessment. An SPG4/SPAST Japanese family with similar genotype‐phenotype findings was already described by our research team. Haplotype analysis was conducted on the two pedigrees.ResultOne Japanese man was diagnosed as certainly affected by slowly progressive autosomal dominant HSP, according to the Harding criteria. The age at onset of the first motor symptoms was 31 years. At 52 years, phenotype was complicated by cognitive impairment; a diagnosis of probable EOFAD following the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS‐ADRDA) criteria was formulated. The case was definite Alzheimer’s disease (autopsy proven): the brain pathology revealed plaques with a congophilic core and neuritic pathology. Both the brother and the son of the proband revealed the same initial symptoms of dementia and HSP was diagnosed, respectively, at age 55 and 34 years. WES revealed in all the patients a heterozygous change in SPAG4/SPAST. MLPA analysis excluded the presence of deletions/duplications in SPG4/SPAST. Haplotype analysis disclosed a founder effect for the mutation in the two families sharing the same clinico‐genetic characteristics. Bioinformatic analyses and population study confirm a pathogenetic role of such mutation. Screening of PS1, PS2, and bAPP genes did not reveal any coding mutation. No affected subject carried out APOE genotype ε4/ε3 or ε4/ε4.ConclusionThis work describes the second Japanese family with a SPAG4/SPAST mutation and association of HSP and EOFAD. A possible founder effect was confirmed by haplotype analysis.

Using spatial filters to study regional reorganization of brain connectivity in familial early onset AD (PSEN1 E280A)

AbstractBackgroundThe most common cause of familial early onset Alzheimer Disease (AD) are the PSEN1 mutations. One of the largest family carriers of the mutation lives in Antioquia, Colombia. The study of mutation carriers provides a unique opportunity to characterize the preclinical changes and the brain reorganization strategies associated with predisposition to AD. The Electroencephalography (EEG) has an enormous potential to study the neurophysiological changes in neurodegenerative processes with promising clinical applications. During the 2012 – 2019 period different studies on a large database of high‐density EEG from PSEN1 E280A carriers were done trying to identify early changes that could be preclinical biomarkers of ADMethodA sample of 83 participants, belonging to families with genetic risk for AD by PSEN1 E280A mutation was included. They were distributed in three groups; asymptomatic carriers (AC, n=27), asymptomatic non‐carriers (ANC, n=33) and a symptomatic group with Mild Cognitive Impairment (SYMP, n=23). We used a 60 channel EEG for recording the brain electrical activity. The relative power values were obtained using Matlab’s chronux toolbox. The results obtained using a workflow based on Independent Component Analysis (ICA), introduced to improve the spatial resolution given by EEG, are discussed. A two‐parameter non‐parametric T‐test was used to calculate the statistical significance of the relative power among the populations analyzed.ResultThe comparison of carriers of PSEN1 E280A mutation and non‐carriers, show altered brain function even in asymptomatic stage complementing previous findings using functional Magnetic Resonance Imaging or Positron Emission Tomography. Regions, like the Precuneus, can be screened across the neurodegenerative process, offering new potential biomarkers of AD. The multivariate analysis of brain sources show generalized impairment in the brain connectivity for asymptomatic subjects. The results found using the workflow were compared with alternatives approaches of analysis, based on scalp EEG or data obtained through inverse solution methods, corroborating the findings.ConclusionThe neurophysiological correlates found opens the possibility of studying new biomarkers in AD based in EEG. The workflow proposed could be used in other neurodegenerative diseases or other brain mapping problems based in EEG.

Cognitive profile and motor phenotype in Mexican patients with familial early onset Alzheimer disease with the p. Ala431Glu variant of the PSEN1 gene

AbstractBackgroundGiven the deleterious consequences for patients and families with autosomal dominant AD, it is necessary to identify individuals at risk in preclinical phases, with the objective of include them in clinical intervention trialsMethodWe included 11 DNA samples from patients diagnosed with FAD and 9 DNA samples with of patients with EAD, which were analyzed by clinical exome sequencing in Nextera Next Seq equipment. Results are reported on a case‐by‐case basis for genomics, cognitive, neuropsychiatric, motor, and functional evaluations.ResultWe identify 9 carriers of the pathogenic variant p. Ala431Glu of the PSEN1 gene and in 4 of these patients, more than one uncertain significance variant was identified in the ANO5, TYROBP, ALS2, WASHC5, ABCA7, TOMM40, CLU, ATP7B, USH2A genes. In 5 patients we identify another pathogenic variants in PSEN1 gene. Estimated age at onset (AAO) in carriers of A431E variant was 40.6 ± 3.1 years, while in the Non A431E group was 46 ± 11.6. Patients with E431E variant had the worst performance at the beginning and in his last evaluation in all the cognitive tests. The most striking differences were in MMSE (16.3 ± 6.1 and 9.4 ± 6.2 vs 18.1 ± 2.1 and 11.9 ± 4.7) and PHFV tests (4 ± 5.2 and 1.33 ± 2.2 vs 6.1 ± 0.2 and 2.6 ± 2). The most frequent neuropsychiatric symptoms in A431E group was depression, anxiety and irritability, while in the EAD was apathy. Near to 40% of patients A431E has motor symptoms at baseline, and this percentage increased to 80% in the latest evaluation. This group had a high frequency of stiffness, tremor and spastic gait and in EAD the most consistent symptom was postural tremor. The motor‐symptom profile is presented in Figure 1.ConclusionA high frequency of the Jalisco variant is reported in Mexican patients with FAD. This variant is related to early onset of symptoms, rapid progression, as well as a high frequency of motor symptoms. This makes it necessary to consider their identification of this variant as a first step in the diagnostic algorithm of this type of population. The identification of patients carrying this variant requires correct genetic counseling and makes them candidates to enroll in international clinical trials of pharmacological intervention.

PSEN1 M139L mutation in a Chinese pedigree with early‐onset familial Alzheimer's disease

AbstractBackgroundpresenilin 1(PSEN1) is the most common gene associated with familial Alzheimer's disease. we reported a case with M139L mutation of PSEN1 which was reported as pathogenic mutation in February 2019.Methodchose an early‐onset Alzheimer's patient (proband) and her family (I‐V generation) as the research object. clinical and imaging data of the proband and her family members were collected. High throughput second generation exon sequencing and sanger method was used to analyze the gene of the proband.Result1. Proband clinical characteristic: The proband (IV8) started to progressive memory loss, especially short‐term memory at 38 years old. She can't work because of memory problem. Now she lives on her own, can use mobile phone and APP, drive, remember familiar roads, but cannot shop, take bus to new place, handle own finances. The MMSE score was 27/30, and the MOCA score was 20/30 (delayed recall, time orientation, visuospatial disfunction, calculation) (Figure 1). Brain Magnetic Resonance Imaging suggested hippocampal atrophy (Figure 2). 2. Family phenotypic distribution (Figure 3): The onset age of Alzheimer's disease in this family was early, starting between 38 and 55 years old. The first and prominent clinical manifestations were memory loss, followed by orientation and executive function impairment. Movement disorder appears later or does not appear. It may have mild anxiety or depression. 3. Gene results (Figure 4): a heterozygotic mutation was found in the exon region of the PSEN1 gene: c.415A>T (adenine > thymine), resulting in an amino acid change of p.139l (methionine > leucine).ConclusionWe reported the early onset familial Alzheimer's disease caused by M139L mutation of PSEN1 in Han Chinese family which was helpful to enrich the clinical phenotypic characteristics of early onset familial Alzheimer's disease associated with PSEN1 mutation.

Retinal Imaging Findings in Carriers With PSEN1-Associated Early-Onset Familial Alzheimer Disease Before Onset of Cognitive Symptoms

Individuals with autosomal dominant mutations for Alzheimer disease are valuable in determining biomarkers present prior to the onset of cognitive decline, improving the ability to diagnose Alzheimer disease as early as possible. Optical coherence tomography (OCT) has surfaced as a potential noninvasive technique capable of analyzing central nervous system tissues for biomarkers of Alzheimer disease. To evaluate whether OCT can detect early retinal alterations in carriers of the presenilin 1 (PSEN1 [OMIM 104311]) E280A mutation who are cognitively unimpaired. A cross-sectional imaging study conducted from July 13, 2015, to September 16, 2020, included 10 carriers of the PSEN1 E280A mutation who were cognitively unimpaired and 10 healthy noncarrier family members, all leveraged from a homogenous Colombian kindred. Statistical analysis was conducted from September 9, 2017, to September 16, 2020. Mixed-effects multiple linear regression was performed to compare the thickness values of the whole retina and individual retinal layers on OCT scans between mutation carriers and noncarriers. Simple linear-effects and mixed-effects multiple linear regression models were used to assess whether age was an effect modifier for PSEN1 mutation of amyloid β levels and retinal thickness, respectively. Fundus photographs were used to compare the number of arterial and venous branch points, arterial and venous tortuosity, and fractal dimension. This study included 10 carriers of the PSEN1 E280A mutation who were cognitively unimpaired (7 women [70%]; mean [SD] age, 36.3 [8.1] years) and 10 healthy noncarrier family members (7 women [70%]; mean [SD] age, 36.4 [8.2] years). Compared with noncarrier controls, PSEN1 mutation carriers who were cognitively unimpaired had a generalized decrease in thickness of the whole retina as well as individual layers detected on OCT scans, with the inner nuclear layer (outer superior quadrant, β = -3.06; P = .007; outer inferior quadrant, β = -2.60; P = .02), outer plexiform layer (outer superior quadrant, β = -3.44; P = .03), and outer nuclear layer (central quadrant, β = -8.61; P = .03; inner nasal quadrant, β = -8.39; P = .04; inner temporal quadrant, β = -9.39; P = .02) showing the greatest amount of statistically significant thinning. Age was a significant effect modifier for the association between PSEN1 mutation and amyloid β levels in cortical regions (β = 0.03; P = .001) but not for the association between PSEN1 mutation and retinal thickness. No statistical difference was detected in any of the vascular parameters studied. These findings suggest that OCT can detect functional and morphologic changes in the retina of carriers of familial Alzheimer disease who are cognitively unimpaired several years before clinical onset, suggesting that OCT findings and retinal vascular parameters may be biomarkers prior to the onset of cognitive decline.

Brain transcriptome analysis reveals subtle effects on mitochondrial function and iron homeostasis of mutations in the SORL1 gene implicated in early onset familial Alzheimer\u2019s disease

To prevent or delay the onset of Alzheimer’s disease (AD), we must understand its molecular basis. The great majority of AD cases arise sporadically with a late onset after 65 years of age (LOAD). However, rare familial cases of AD can occur due to dominant mutations in a small number of genes that cause an early onset prior to 65 years of age (EOfAD). As EOfAD and LOAD share similar pathologies and disease progression, analysis of EOfAD genetic models may give insight into both subtypes of AD. Sortilin-related receptor 1 (SORL1) is genetically associated with both EOfAD and LOAD and provides a unique opportunity to investigate the relationships between both forms of AD. Currently, the role of SORL1 mutations in AD pathogenesis is unclear. To understand the molecular consequences of SORL1 mutation, we performed targeted mutagenesis of the orthologous gene in zebrafish. We generated an EOfAD-like mutation, V1482Afs, and a putatively null mutation, to investigate whether EOfAD-like mutations in sorl1 display haploinsufficiency by acting through loss-of-function mechanisms. We performed mRNA-sequencing on whole brains, comparing wild type fish with their siblings heterozygous for EOfAD-like or putatively loss-of-function mutations in sorl1, or transheterozygous for these mutations. Differential gene expression analysis identified a small number of differentially expressed genes due to the sorl1 genotypes. We also performed enrichment analysis on all detectable genes to obtain a more complete view on changes to gene expression by performing three methods of gene set enrichment analysis, then calculated an overall significance value using the harmonic mean p-value. This identified subtle effects on expression of genes involved in energy production, mRNA translation and mTORC1 signalling in both the EOfAD-like and null mutant brains, implying that these effects are due to sorl1 haploinsufficiency. Surprisingly, we also observed changes to expression of genes occurring only in the EOfAD-mutation carrier brains, suggesting gain-of-function effects. Transheterozygosity for the EOfAD-like and null mutations (i.e. lacking wild type sorl1), caused apparent effects on iron homeostasis and other transcriptome changes distinct from the single-mutation heterozygous fish. Our results provide insight into the possible early brain molecular effects of an EOfAD mutation in human SORL1. Differential effects of heterozygosity and complete loss of normal SORL1 expression are revealed.

Modeling the \u03b2-secretase cleavage site and humanizing amyloid-beta precursor protein in rat and mouse to study Alzheimer\u2019s disease

BackgroundThree amino acid differences between rodent and human APP affect medically important features, including β-secretase cleavage of APP and Aβ peptide aggregation (De Strooper et al., EMBO J 14:4932-38, 1995; Ueno et al., Biochemistry 53:7523-30, 2014; Bush, 2003, Trends Neurosci 26:207–14). Most rodent models for Alzheimer’s disease (AD) are, therefore, based on the human APP sequence, expressed from artificial mini-genes randomly inserted in the rodent genome. While these models mimic rather well various biochemical aspects of the disease, such as Aβ-aggregation, they are also prone to overexpression artifacts and to complex phenotypical alterations, due to genes affected in or close to the insertion site(s) of the mini-genes (Sasaguri et al., EMBO J 36:2473-87, 2017; Goodwin et al., Genome Res 29:494-505, 2019). Knock-in strategies which introduce clinical mutants in a humanized endogenous rodent APP sequence (Saito et al., Nat Neurosci 17:661-3, 2014) represent useful improvements, but need to be compared with appropriate humanized wildtype (WT) mice.MethodsComputational modelling of the human β-CTF bound to BACE1 was used to study the differential processing of rodent and human APP. We humanized the three pivotal residues we identified G676R, F681Y and R684H (labeled according to the human APP770 isoform) in the mouse and rat genomes using a CRISPR-Cas9 approach. These new models, termed mouse and rat Apphu/hu, express APP from the endogenous promotor. We also introduced the early-onset familial Alzheimer’s disease (FAD) mutation M139T into the endogenous Rat Psen1 gene.ResultsWe show that introducing these three amino acid substitutions into the rodent sequence lowers the affinity of the APP substrate for BACE1 cleavage. The effect on β-secretase processing was confirmed as both humanized rodent models produce three times more (human) Aβ compared to the original WT strain. These models represent suitable controls, or starting points, for studying the effect of transgenes or knock-in mutations on APP processing (Saito et al., Nat Neurosci 17:661-3, 2014). We introduced the early-onset familial Alzheimer’s disease (FAD) mutation M139T into the endogenous Rat Psen1 gene and provide an initial characterization of Aβ processing in this novel rat AD model.ConclusionThe different humanized APP models (rat and mouse) expressing human Aβ and PSEN1 M139T are valuable controls to study APP processing in vivo allowing the use of a human Aβ ELISA which is more sensitive than the equivalent system for rodents. These animals will be made available to the research community.

Gene mutations associated with early onset familial Alzheimer's disease in China: An overview and current status.

BackgroundMutations of three causative genes, namely presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP), have been identified as the major causes of early‐onset familial Alzheimer's disease (EOFAD). The prevalence of causative gene mutations in patients with EOFAD has been reported in previous studies worldwide but remains unclear in China. The patients with these known mutations always show considerable clinical phenotypic variability. However, to date, there have been no detailed descriptions of the clinical phenotypes associated with these Chinese EOFAD mutations. Thus, the aim of this study was to describe all of the known mutations in three EOFAD causative genes and genotype–phenotype correlations in Chinese patients with EOFAD.MethodWe systematically searched the PubMed, MEDLINE, CNKI, VIP, and WAN‐FANG databases to find Chinese EOFAD mutations in reports from inception through May 2020.ResultWe identified 31 studies reporting mutations of three causative genes in China. 10 mutations in APP gene, 27 mutations in PSEN1 gene and six mutations in PSEN2 were discovered in Chinese EOFAD. This review summarized all these probably pathogenic mutations as well as its clinical features. To the best of our knowledge, this is the first systemic review of causative gene mutations in patients with EOFAD in China.ConclusionThe analysis of the genetic and clinical phenotype correlations in this review supports the idea that the clinical phenotype might be influenced by specific genetic defects. It also suggests genetic testing and genotype–phenotype correlations are important for the accurate diagnosis and for understanding disease‐associated pathways and might also improve disease therapy and prevention.

Early-Onset Familial Alzheimer Disease Variant PSEN2 N141I Heterozygosity is Associated with Altered Microglia Phenotype.

Background:Early-onset familial Alzheimer disease (EOFAD) is caused by heterozygous variants in the presenilin 1 (PSEN1), presenilin 2 (PSEN2), and APP genes. Decades after their discovery, the mechanisms by which these genes cause Alzheimer’s disease (AD) or promote AD progression are not fully understood. While it is established that presenilin (PS) enzymatic activity produces amyloid-β (Aβ), PSs also regulate numerous other cellular functions, some of which intersect with known pathogenic drivers of neurodegeneration. Accumulating evidence suggests that microglia, resident innate immune cells in the central nervous system, play a key role in AD neurodegeneration.Objective:Previous work has identified a regulatory role for PS2 in microglia. We hypothesized that PSEN2 variants lead to dysregulated microglia, which could further contribute to disease acceleration. To mimic the genotype of EOFAD patients, we created a transgenic mouse expressing PSEN2 N141I on a mouse background expressing one wildtype PS2 and two PS1 alleles.Results:Microglial expression of PSEN2 N141I resulted in impaired γ-secretase activity as well as exaggerated inflammatory cytokine release, NFκB activity, and Aβ internalization. In vivo, PS2 N141I mice showed enhanced IL-6 and TREM2 expression in brain as well as reduced branch number and length, an indication of “activated” morphology, in the absence of inflammatory stimuli. LPS intraperitoneal injection resulted in higher inflammatory gene expression in PS2 N141I mouse brain relative to controls.Conclusion:Our findings demonstrate that PSEN2 N141I heterozygosity is associated with disrupted innate immune homeostasis, suggesting EOFAD variants may promote disease progression through non-neuronal cells beyond canonical dysregulated Aβ production.

Transcriptome analysis indicates dominant effects on ribosome and mitochondrial function of a premature termination codon mutation in the zebrafish gene psen2.

PRESENILIN 2 (PSEN2) is one of the genes mutated in early onset familial Alzheimer’s disease (EOfAD). PSEN2 shares significant amino acid sequence identity with another EOfAD-related gene PRESENILIN 1 (PSEN1), and partial functional redundancy is seen between these two genes. However, the complete range of functions of PSEN1 and PSEN2 is not yet understood. In this study, we performed targeted mutagenesis of the zebrafish psen2 gene to generate a premature termination codon close downstream of the translation start with the intention of creating a null mutation. Homozygotes for this mutation, psen2S4Ter, are viable and fertile, and adults do not show any gross psen2-dependent pigmentation defects, arguing against significant loss of γ-secretase activity. Also, assessment of the numbers of Dorsal Longitudinal Ascending (DoLA) interneurons that are responsive to psen2 but not psen1 activity during embryogenesis did not reveal decreased psen2 function. Transcripts containing the S4Ter mutation show no evidence of destabilization by nonsense-mediated decay. Forced expression in zebrafish embryos of fusions of psen2S4Ter 5’ mRNA sequences with sequence encoding enhanced green fluorescent protein (EGFP) indicated that the psen2S4Ter mutation permits utilization of cryptic, novel downstream translation start codons. These likely initiate translation of N-terminally truncated Psen2 proteins lacking late endosomal/lysosomal localization sequences and that obey the “reading frame preservation rule” of PRESENILIN EOfAD mutations. Transcriptome analysis of entire brains from a 6-month-old family of wild type, heterozygous and homozygous psen2S4Ter female siblings revealed profoundly dominant effects on gene expression likely indicating changes in ribosomal, mitochondrial, and anion transport functions.

Accelerated loss of hypoxia response in zebrafish with familial Alzheimer’s disease-like mutation of presenilin 1

Ageing is the major risk factor for Alzheimer's disease (AD), a condition involving brain hypoxia. The majority of early-onset familial AD (EOfAD) cases involve dominant mutations in the gene PSEN1. PSEN1 null mutations do not cause EOfAD. We exploited putative hypomorphic and EOfAD-like mutations in the zebrafish psen1 gene to explore the effects of age and genotype on brain responses to acute hypoxia. Both mutations accelerate age-dependent changes in hypoxia-sensitive gene expression supporting that ageing is necessary, but insufficient, for AD occurrence. Curiously, the responses to acute hypoxia become inverted in extremely aged fish. This is associated with an apparent inability to upregulate glycolysis. Wild-type PSEN1 allele expression is reduced in post-mortem brains of human EOfAD mutation carriers (and extremely aged fish), possibly contributing to EOfAD pathogenesis. We also observed that age-dependent loss of HIF1 stabilization under hypoxia is a phenomenon conserved across vertebrate classes.

Presenilin 1 and APP Gene Mutations in Early-Onset AD Families from a Southeast Region of China.

Early-Onset Familial Alzheimer's Disease (EOFAD) has been reported to be associated with Presenilin 1 (PSEN1), Presenilin 2 (PSEN2), and Amyloid Precursor Protein (APP) genes. The spectrum of mutations in Chinese patients with EOFAD was rarely investigated. To investigate the spectrum of mutations in patients with EOFAD in Chinese population. We performed whole-exome sequencing and described relevant clinical features in a total of 67 subjects from 3 families with EOFAD. A splice mutation (p.S290C) in PSEN1 and a missense mutation (p.V717I) in APP were identified. The variant p. S290C (c.869-2>G) in PSEN1 in Chinese EOAD family revealed different clinical phenotypes when compared with that of Europeans.