Cloning of a gene bearing missense mutations in early-onset familial Alzheimer's disease

Targeting amyloidogenic proteins through cyclic peptides - A medicinal chemistry perspective

Alzheimer's Disease (AD) is characterized by the formation of amyloid-β (Aβ) in the extracellular region, neurofibrillary tangles (NFTs) in the intracellular region accompanied with neuroinflammation and decreased neurotransmitters in various regions of brain leading to neuroinflammation and neurodegeneration. Of the various bioactive molecules, Cyclic Peptides (CPs) are small circular chains of amino acids that can alter the structure and function of the proteins they interact with. They can be synthesized using chemical or genetic approach leading to the generation of diverse libraries of CPs that are screened for binding with desired target proteins. In AD, CPs can interfere at various levels, by either imitating the structure or altering the conformation of amyloidogenic proteins. They can also interfere with signal transduction by competing with amyloid proteins for various receptors which are involved in AD pathology. This review highlights the application of CPs as scaffolds for the identification of novel small molecules that can interfere with amyloid aggregation or for the formulation of vaccination against AD. Other proteins involved in the pathophysiological pathways of AD that can potentially be targeted for CP design have also been discussed.

Identification of presenilin mutations that have sufficient gamma-secretase proteolytic activity to mediate Notch signaling but disrupt organelle and neuronal health

Mutations that cause familial Alzheimer's disease (AD) are predominantly found in the presenilin (PSEN) encoding genes PSEN1 and PSEN2. While the association of PSEN mutations with familial AD have been known for over 20 years, the mechanism underlying the impact these mutations have on disease is not fully understood. PSENs are phylogenetically conserved proteins that are found in diverse multicellular organisms ranging from plants to humans. PSENs form the proteolytic core of gamma-secretase that is required for cleaving type I transmembrane proteins, such as Notch receptors and the amyloid precursor protein. Importantly, familial AD-associated PSEN mutations are broadly distributed and do not clearly define a specific PSEN function essential for neuronal fitness. Here, using C. elegans as a model organism to study the in vivo functions of PSENs, we confirm that C. elegans PSEN plays a pivotal role in gamma-secretase proteolytic activity as well as maintaining neuronal and organelle health. Notably, we demonstrate that these two functions can be genetically uncoupled. Our research identifies several conserved familial AD-like missense mutations in the endogenous sel-12 gene, which encodes C. elegans PSEN. These mutations preserve sufficient gamma-secretase proteolytic activity to mediate Notch signaling but abolish PSEN's role in supporting neuronal and organelle health. Furthermore, we provide evidence that these familial AD-like missense mutations disrupt mitochondrial calcium regulation, ultimately leading to neuronal dysfunction. These results indicate that C. elegans PSEN plays at least two independent roles: one that mediates gamma-secretase proteolytic activity and another that mediates organelle and neuronal health.

The interaction between neurotransmitter receptor activity and amyloid-β pathology in Alzheimer's disease

The accumulation of amyloid-β (Aβ) peptides is a hallmark of Alzheimer's disease (AD). Central to AD pathology is the production of Aβ peptides through the amyloidogenic processing of amyloid-β protein precursor (AβPP) by β-secretase (BACE-1) and γ-secretase. Recent studies have shifted focus from Aβ plaque deposits to the more toxic soluble Aβ oligomers. One significant way in which Aβ peptides impair neuronal information processing is by influencing neurotransmitter receptor function. These receptors, including adrenergic, acetylcholine, dopamine, 5-HT, glutamate, and gamma-aminobutyric acid (GABA) receptors, play a crucial role in regulating synaptic transmission, which underlies perceptual and cognitive functions. This review explores how Aβ interacts with these key neurotransmitter receptors and how these interactions contribute to neural dysfunction in AD. Moreover, we examine how agonists and antagonists of these receptors influence Aβ pathology, offering new perspectives on potential therapeutic strategies to curb AD progression effectively and improve patients' quality of life.

Microglial MS4A4A Protects against Epileptic Seizures in Alzheimer's Disease

Alzheimer's disease (AD) is a predominant neurodegenerative disorder worldwide, with epileptic seizures being a common comorbidity that can exacerbate cognitive deterioration in affected individuals, thus highlighting the importance of early therapeutic intervention. It is determined that deletion of Ms4a4a, an AD-associated gene, exacerbates seizures in amyloid β (Aβ)-driven AD mouse model. MS4A4A is significantly upregulated in brain lesions in patients with epilepsy. Single-cell sequencing reveals that MS4A4A is highly expressed in microglia within these lesions, linked to enhanced phagocytic activity. Mechanistic investigation delineates that deletion of Ms4a4a impairs microglial phagocytosis, accompanied by diminished calcium influx and disruptions in mitochondrial metabolic fitness. The cytosolic fragment of Ms4a4a is anchored to the cytoskeletal components, supporting its critical role in mediating phagocytosis. Induction of Ms4a4a through central delivery of LNP-Il4 alleviates seizure conditions. Collectively, these findings identify Ms4a4a as a potential therapeutic target for managing seizures in AD treatment.

Alzheimer's Disease and Frontotemporal Dementia: A Review of Pathophysiology and Therapeutic Approaches

Alzheimer's disease (AD) is a devastating form of dementia, with the number of affected individuals rising sharply. The main hallmarks of the disease include amyloid-beta plaque deposits and neurofibrillary tangles consisting of hyperphosphorylated tau protein, besides other pathological features that contribute to the disease's complexity. The causes of sporadic AD are multifactorial and mostly age-related and involve risk factors such as diabetes and cardiovascular or cerebrovascular disorders. Frontotemporal dementia (FTD) is another type of dementia characterized by a spectrum of behaviors, memory, and motor abnormalities and associated with abnormal depositions of protein aggregation, including tau protein. Currently approved medications are symptomatic, and no disease-modifying therapy is available to halt the disease progression. Therefore, the development of multi-targeted therapeutic approaches could hold promise for the treatment of AD and other neurodegenerative disorders, including tauopathies. In this article, we will discuss the pathophysiology of AD and FTD, the proposed hypotheses, and current therapeutic approaches, highlighting the development of novel drug candidates and the progress of clinical trials in this field of research.

Epilepsy and Alzheimer disease: New insights and perspectives

Numerous epidemiological and pathophysiological arguments suggest a bidirectional link between late-onset epilepsy and Alzheimer's disease. However, the temporal and causal relationship between the pathophysiological processes underlying these two conditions remains unclear. It is likely that these connections are complex, requiring consideration of various scenarios of causality and reciprocity. In the absence of targeted therapies that effectively address the progression of both diseases, specific measures can be taken to improve patient care. These include screening for cognitive disorders in patients with late-onset epilepsy, detecting subclinical EEG activity in patients with Alzheimer's disease, and identifying and managing cardiovascular risk factors in both populations. Looking ahead, it is evident that global population aging and the potential demographic surge in these two patient groups will necessitate greater efforts to raise awareness and enhance the training of physicians and healthcare professionals in the emerging field of "epileptogeriatrics".

LMTK2 and CRB1 are two novel risk genes for Alzheimer's disease in Han Chinese

BACKGROUND

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease with a substantial genetic background. However, its underlying genetic architecture remains to be elucidated.

METHODS

In this study, we performed whole-exome sequencing in 282 familial and/or early-onset AD patients and 1086 cognitively normal controls in the Han Chinse populations. According to minor allele frequency, variants were divided into common variants (MAF ≥ 0.01) and rare variants (MAF < 0.01). Common variant-based association analysis and gene-based association test aggregating rare variants were performed by PLINK 1.9 and Sequence Kernel Association Test-Optimal, respectively. We replicated the significant results by using the same AD samples and controls from whole genome sequencing (n = 1879). Furthermore, we determined the functions of the novel AD risk genes in vitro.

RESULTS

Common variants association analysis revealed that APOE rs429358 reached statistical whole-exome significance. Gene-level aggregation testing identified that rare damaging variants in LMTK2 and CRB1 conferred risk to AD. All variants are located in highly conserved amino acid regions and are predicted to be damaging. Furthermore, functional studies showed that LMTK2 rare damaging variants (R234P and S974G) enhanced tau phosphorylation levels, tau aggregates formation, and Aβ generation. Meanwhile, the CRB1 Y556X variant caused incomplete translation of CRB1 protein and increased the Aβ42 level and Aβ42/Aβ40 ratio.

CONCLUSION

Our findings indicated that LMTK2 and CRB1 are two novel AD risk genes in Han Chinese, which may provide promising targets for diagnosis and intervention.

Unlocking the therapeutic promise of miRNAs in promoting amyloid-β clearance for Alzheimer's disease

Alzheimer's disease (AD) is a neurological disorder that affects cognition and behavior, accounting for 60-70 % of dementia cases. Its mechanisms involve amyloid aggregates, hyperphosphorylated tau tangles, and loss of neural connections. Current treatments have limited efficacy due to a lack of specific targets. Recently, microRNAs (miRNAs) have emerged as key modulators in AD, regulating gene expression through interactions with mRNA. Dysregulation of specific miRNAs contributes to disease progression by disrupting clearance pathways. Antisense oligonucleotide (ASO)-based therapies show promise for AD treatment, particularly when combined with miRNA mimics or antagonists, targeting complex regulatory networks. However, miRNAs can interact with each other, complicating cellular processes and potentially leading to side effects. Our review emphasizes the role of miRNAs in regulating amyloid-beta (Aβ) clearance and highlights their potential as therapeutic targets and early biomarkers for AD, underscoring the need for further research to enhance their efficacy and safety.

Presenilin 1 hemizygosity has no overt deleterious phenotypic outcomes in sheep: Potential implications for therapeutic targets in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition and one of the most significant medical challenges today. Dominant mutations causing early-onset AD have been identified in the presenilin 1 and 2 (PSEN1 and PSEN2), and the amyloid precursor protein (APP) genes. Either PSEN1 or PSEN2 is required by γ-secretase, a functional complex that cleaves APP to produce amyloid-beta (Aβ) peptides of varying lengths. These mutations result in relative or absolute increases in the longer Aβ peptides (Aβ1-40, Aβ 1-42), which accumulate as plaques, characteristic of both early and late-onset AD. To investigate the effects of modulating PSEN1 expression, we have produced PSEN1 hemizygous sheep. Sheep PSEN and APP genes are highly conserved relative to humans, including the APP proteolytic cleavage sites, and like humans, sheep naturally develop plaques and TAU tangles with age. At five years of age, the PSEN1 hemizygous animals are phenotypically and biochemically normal. Interestingly, the characteristic Aβ peptide levels in their cerebrospinal fluid and plasma remain at wildtype levels, indicating that a 50 % reduction in PSEN1 abundance does not materially affect γ-secretase's APP cleavage activity. These results suggest that generalized regulation of PSEN1 expression is unlikely to be an effective therapeutic approach for AD on its own. However, it does suggest that loss of one PSEN1 allele may be tolerated in higher organisms, with no deleterious side-effects. It is therefore possible that knocking-out or knocking-down one copy of PSEN1 via genetic modification will be tolerated in humans, especially as functional hemizygous humans are present in the population (gnomad). These kinds of therapies could potentially prevent AD caused by dominant gain-of-function mutations in PSEN1.

Presenilin, γ-Secretase, and the Search for Pathogenic Triggers of Alzheimer's Disease

Cerebral plaques of the amyloid β-peptide (Aβ) are a defining pathology in Alzheimer's disease (AD). The amyloid hypothesis of AD pathogenesis has dominated the field for over 30 years, ostensibly validated by rare AD-causing mutations in the substrate and enzyme that produce Aβ. The γ-secretase complex carries out intramembrane proteolysis of the substrate derived from the amyloid precursor protein (APP). Mutations in APP and presenilin, the catalytic component of γ-secretase, typically increase the ratio of aggregation-prone 42-residue Aβ (Aβ42) over the more soluble 40-residue form (Aβ40). Nevertheless, the inability to clarify how Aβ aggregation leads to neurodegeneration, along with poor progress in developing effective AD therapeutics that target Aβ, raises concern about whether Aβ is the primary disease driver. γ-Secretase carries out processive proteolysis on the APP substrate, producing long Aβ peptides that are generally trimmed in tripeptide intervals to shorter secreted peptides. Recent studies on effects of AD-causing mutations on the complicated proteolytic processing of the APP substrate by γ-secretase has led to the discovery that these mutations reduce─but do not abolish─processive proteolysis. Reduced proteolysis is apparently due to stabilization of enzyme-substrate complexes, and these stalled substrate-bound γ-secretase complexes can trigger synaptic degeneration even in the absence of Aβ production. Thus, the stalled process rather than the proteolytic products may be a principal initiator of AD pathogenesis. This new amyloid-independent hypothesis suggests that pharmacological agents that rescue stalled γ-secretase enzyme-substrate complexes might be effective therapeutics for AD prevention and/or treatment.

Circadian rhythms and the light-dark cycle interact to regulate amyloid plaque accumulation and tau phosphorylation in 5xFAD mice

Background

Circadian disruption has long been appreciated as a downstream consequence of Alzheimer's Disease in humans. However, an upstream role for behavioral circadian disruption in regulating AD pathology remains an open question.

Methods

To determine the role of the central circadian clock in the suprachiasmatic nucleus (SCN) in regulating amyloid pathology, we crossed the 5xFAD amyloid mouse model with mice harboring deletion of the critical clock gene Bmal1 in GABAergic neurons using VGAT-iCre, which is expressed in >95% of SCN cells. To examine the role the light-dark cycle in this process, we aged these mice in either regular 12:12 light-dark (LD) or constant darkness (DD) conditions. Transcriptional, behavioral, and physiological rhythms were examined in VGAT-iCre; 5xFAD; Bmal1 fl/fl (VGAT-BMAL1KO;5xFAD) mice under varying light conditions. Amyloid plaque deposition, peri-plaque tau phosphorylation, and other pathology was examined by immunohistochemistry, and transcriptomic changes were examined by high-throughput qPCR.

Results

VGAT-BMAL1KO;5xFAD mice showed loss of SCN BMAL1 expression and severe disruption of behavioral rhythms in both LD and DD, with loss of day-night rhythms in consolidated sleep and blunting of rhythmic clock gene expression in the brain. Surprisingly, VGAT-BMAL1KO;5xFAD mice kept under LD showed reduced total plaque accumulation and peri-plaque tau phosphorylation, compared to Cre-negative controls. These changes were gated by the light-dark cycle, as they were absent in VGAT-BMAL1KO;5xFAD mice kept in DD conditions. Total plaque accumulation was also reduced in control 5xFAD mice kept in DD as compared to LD, suggesting a general effect of light-dark cycle on amyloid aggregation. Expression of murine presenilin 1 (Psen1) -- which catalyzes the processing of sAPPβ into Aβ -- as well as APP cleavage to C-terminal fragments, were suppressed in VGAT-BMAL1KO;5xFAD under LD conditions.

Conclusions

These studies elucidated an interaction between the circadian clock in GABAergic neurons and the light-dark cycle in regulating amyloid pathology and suggest that decoupling the central clock form the light-dark cycle may reduce APP cleavage and plaque formation. These results call into question the proposed simple positive feedback loop between circadian rhythm disruption and Alzheimer's Disease pathology.

Safety and efficacy of long-term gantenerumab treatment in dominantly inherited Alzheimer's disease: an open-label extension of the phase 2/3 multicentre, randomised, double-blind, placebo-controlled platform DIAN-TU trial

BACKGROUND

Amyloid plaque removal by monoclonal antibody therapies slows clinical progression in symptomatic Alzheimer's disease; however, the potential for delaying the onset of clinical symptoms in asymptomatic people is unknown. The Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU) is an ongoing platform trial assessing the safety and efficacy of multiple investigational products in participants with dominantly inherited Alzheimer's disease (DIAD). Based on findings of amyloid removal and downstream biological effects from the gantenerumab group of the platform trial, we continued a 3-year open-label extension (OLE) study to assess the safety and efficacy of long-term treatment with high doses of gantenerumab.

METHODS

The randomised, placebo-controlled, double-blind, phase 2/3 multi-arm trial (DIAN-TU-001) assessed solanezumab or gantenerumab versus placebo in participants who were between 15 years before and 10 years after their estimated years to symptom onset and who had a Clinical Dementia Rating (CDR) global score of 0 (cognitively normal) to 1 (mild dementia). This study was followed by an OLE study of gantenerumab treatment, conducted at 18 study sites in Australia, Canada, France, Ireland, Puerto Rico, Spain, the UK, and the USA. For inclusion in the OLE, participants at risk for DIAD had participated in the double-blind period of DIAN-TU-001 and were required to know their mutation status. We investigated increasing doses of subcutaneous gantenerumab up to 1500 mg every 2 weeks. Due to the lack of a regulatory path for gantenerumab, the study was stopped early after a prespecified interim analysis (when most participants had completed 2 years of treatment) of the clinical measure CDR-Sum of Boxes (CDR-SB). The primary outcome for the final analysis was the amyloid plaque measure 11C-Pittsburgh compound-B positron emission tomography (PiB-PET) standardised uptake value ratio (SUVR [PiB-PET SUVR]) at 3 years, assessed in the modified intention-to-treat group (mITT; defined as participants who received any gantenerumab treatment post-OLE baseline, had at least one PiB-PET SUVR assessment before gantenerumab treatment, and a post-baseline assessment). All participants who received at least one dose of study drug in the OLE were included in the safety analysis. DIAN-TU-001 (NCT01760005) and the OLE (NCT06424236) are registered with ClinicalTrials.gov.

FINDINGS

Of 74 participants who were recruited into the OLE study between June 3, 2020, and April 22, 2021, 73 were enrolled and received gantenerumab treatment. 47 (64%) stopped dosing due to early termination of the study by the sponsor, and 13 (18%) prematurely discontinued the study for other reasons; 13 people completed 3 years of treatment. The mITT group for the primary analysis comprised 55 participants. At the interim analysis, the hazard ratio for clinical decline of CDR-SB in asymptomatic mutation carriers was 0·79 (n=53 [95% CI 0·47 to 1·32]) for participants who were treated with gantenerumab in either the double-blind or OLE period (Any Gant), and 0·53 (n=22 [0·27 to 1·03]) for participants who were treated with gantenerumab the longest (Longest Gant). At the final analysis, the adjusted mean change from OLE baseline to year 3 in PiB-PET SUVR was -0·71 SUVR (95% CI -0·88 to -0·53, p<0·0001). Amyloid-related imaging abnormalities occurred in 53% (39 of 73) of participants: 47% (34 of 73) with microhaemorrhages, 30% (22 of 73) with oedema, and 6% (five of 73) were associated with superficial siderosis. No treatment-associated macrohaemorrhages or deaths occurred.

INTERPRETATION

Partial or short-term amyloid removal did not show significant clinical effects. However, long-term full amyloid removal potentially delayed symptom onset and dementia progression. Our conclusions are limited due to the OLE design and use of external controls and need to be confirmed in long-term trials.

FUNDING

National Institute on Aging, Alzheimer's Association, GHR Foundation, and F Hoffmann-La Roche/Genentech.

Risk of Alzheimer's disease in Down syndrome: Insights gained by multi-omics

Individuals with Down syndrome (DS) are highly susceptible to Alzheimer's disease (AD). The integration of genomics, transcriptomics, epigenomics, proteomics, and metabolomics enables unprecedented understanding of DS-AD, offering a detailed picture of this complex issue. The vast -omics data also present challenges that reflect the complexity of genetic information flow. These studies nonetheless reveal critical mechanisms behind AD risk, including unique observations in DS that differ from those seen in the general population and familial dominant AD. In addition, the correlations between the AD polygenic risk score and proteins related to female infertility and autoimmune thyroiditis corroborate clinical observations. Metabolomic data reveal disrupted metabolic networks, offering prospects for a dynamic score to create specialized nutritional interventions. By adopting a multidimensional perspective with integrated reductionism, the evolving landscape presents an opportunity to identify promising directions for developing precision strategies to mitigate the impact of AD in the DS population. HIGHLIGHTS: Individuals with Down syndrome (DS) are highly susceptible to Alzheimer's disease (AD). DS-AD is characterized by its polygenic nature, extending beyond chromosome 21 with significant contributions from various chromosomes. DS-AD also presents unique features that differ from those observed in the general population and familial dominant AD. Our review consolidates key findings from genomics, transcriptomics, epigenomics, proteomics, and metabolomics, providing a comprehensive view of the molecular mechanisms underlying DS-AD. We highlight promising research directions to further elucidate the pathogenesis of DS-AD.

Navigating the blurred boundary: Neuropathologic changes versus clinical symptoms in Alzheimer's disease, and its consequences for research in genetics

During decades scientists tried to unveil the genetic architecture of Alzheimer's disease (AD), recurring to increasingly larger sample numbers for genome-wide association studies (GWAS) in hope for higher statistical gains. Here, a retrospective look on the most prominent GWAS was performed, focusing on the quality of the diagnosis associated with the used data and databases. Different methods for AD diagnosis (or absence) carry different levels of accuracy and certainty applied to both subsets of cases and controls. Furthermore, the different phenotypes included in these databases were explored, as several incorporate other ageing comorbidities and might be encompassing many confounding agents as well. Age of the samples' donors and origin populations were also investigated as these could be biasing factors in posterior analyses. A tendency for looser diagnostic methods in more recent GWAS was observed, where greater datasets of individuals are analyzed, which may have been hampering the discovery of associated genetic variants. Specifically for AD, a diagnostic method conveying a clinical outcome may be distinct from the disease neuropathological assessment, since the first has a practical perspective that not necessarily needs a confirmation. Due to its properties and complex diagnosis, this work highlights the importance of the neuropathological confirmation of AD (or its absence) in the subjects considered for research purposes to avoid reaching statistically weak and/or misleading conclusions that may trigger further studies with powerless groundwork.

Genetic risk for neurodegenerative conditions is linked to disease-specific microglial pathways

Genome-wide association studies have identified thousands of common variants associated with an increased risk of neurodegenerative disorders. However, the noncoding localization of these variants has made the assignment of target genes for brain cell types challenging. Genomic approaches that infer chromosomal 3D architecture can link noncoding risk variants and distal gene regulatory elements such as enhancers to gene promoters. By using enhancer-to-promoter interactome maps for human microglia, neurons, and oligodendrocytes, we identified cell-type-specific enrichment of genetic heritability for brain disorders through stratified linkage disequilibrium score regression. Our analysis suggests that genetic heritability for multiple neurodegenerative disorders is enriched at microglial chromatin contact sites, while schizophrenia heritability is predominantly enriched at chromatin contact sites in neurons followed by oligodendrocytes. Through Hi-C coupled multimarker analysis of genomic annotation (H-MAGMA), we identified disease risk genes for Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis and schizophrenia. We found that disease-risk genes were overrepresented in microglia compared to other brain cell types across neurodegenerative conditions and within neurons for schizophrenia. Notably, the microglial risk genes and pathways identified were largely specific to each disease. Our findings reinforce microglia as an important, genetically informed cell type for therapeutic interventions in neurodegenerative conditions and highlight potentially targetable disease-relevant pathways.

Multi-Targeting Phytochemicals for Alzheimer's Disease

Alzheimer's disease (AD) is a type of neurodegenerative illness in which β-amyloid (Aβ) and tau protein accumulate in neurons in the form of tangles. The pathophysiological pathway of AD consists of Aβ-amyloid peptides, tau proteins, and oxidative stress in neurons and increased neuro-inflammatory response. Food and Drug Administration in the United States has authorized various drugs for the effective treatment of AD, which include galantamine, rivastigmine, donepezil, memantine, sodium oligomannate, lecanemab, and aducanumab. The major disadvantage of these drugs is that they only provide "symptomatic" relief. They are most effective in the early stages or for mild to moderate cases of the disease, but are not suitable for long-term use. Besides conventional therapies, phytochemicals have the potential to stop the progression of AD. According to research, the use of potential phytochemicals against AD has gained attention due to their potent anti-inflammatory, antioxidant, anti-hyperphosphorylation of the tau protein, metal chelation, and anti-amyloid properties. This study seeks to provide an up-to-date compilation of the most current and promising breakthroughs in AD therapy using phytochemicals. It could be concluded that phytochemicals light serve as an effective therapy for AD. However, more mechanistic investigations are needed to determine the clinical implications of phytochemicals in AD treatment.

Multi-omics analyses of early-onset familial Alzheimer's disease and Sanfilippo syndrome zebrafish models reveal commonalities in disease mechanisms

Sanfilippo syndrome (mucopolysaccharidosis type III, MPSIII) causes childhood dementia, while Alzheimer's disease is the most common type of adult-onset dementia. There is no cure for either of these diseases, and therapeutic options are extremely limited. Increasing evidence suggests commonalities in the pathogenesis of these diseases. However, a direct molecular-level comparison of these diseases has never been performed. Here, we exploited the power of zebrafish reproduction (large families of siblings from single mating events raised together in consistent environments) to conduct sensitive, internally controlled, comparative transcriptome and proteome analyses of zebrafish models of early-onset familial Alzheimer's disease (EOfAD, psen1Q96_K97del/+) and MPSIIIB (nagluA603fs/A603fs) within single families. We examined larval zebrafish (7 days post fertilisation), representing early disease stages. We also examined the brains of 6-month-old zebrafish, which are approximately equivalent to young adults in humans. We identified substantially more differentially expressed genes and pathways in MPS III zebrafish than in EOfAD-like zebrafish. This is consistent with MPS III being a rapidly progressing and earlier onset form of dementia. Similar changes in expression were detected between the two disease models in gene sets representing extracellular matrix receptor interactions in larvae, and the ribosome and lysosome pathways in 6-month-old adult brains. Cell type-specific changes were detected in MPSIIIB brains at 6 months of age, likely reflecting significant disturbances of oligodendrocyte, neural stem cell, and inflammatory cell functions and/or numbers. Our 'omics analyses have illuminated similar disease pathways between EOfAD and MPS III indicating where efforts to find mutually effective therapeutic strategies can be targeted.

The impact of rare genetic variants on Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disease with a strong genetic component. Although autosomal dominant mutations and common risk variants in AD risk have been extensively studied, the genetic underpinning of polygenic AD remains incompletely understood. Rare variants could elucidate part of the missing heritability in AD. Rare variant research gained momentum with the discovery of a rare variant in TREM2, along with loss-of-function variants in ABCA7 and SORL1, and has come into full bloom in recent years. Not only has the number of rare variant discoveries increased through large-scale whole-exome and genome sequencing studies, improved imputation in genome-wide association studies and increased focus on understudied populations, the number of studies mapping the functional effects of several of these rare variants has also significantly increased, leading to insights in the pathogenesis of AD and drug development. Here we provide a comprehensive overview of the known and novel rare variants implicated in AD risk, highlighting how they shine new light on AD pathophysiology and provide new inroads for drug development. We will review their impact on individual, familial and population levels, and discuss the potential and challenges of rare variants in genetic risk prediction.

The Spectrum of Genetic Risk in Alzheimer Disease

Alzheimer disease (AD), the most common dementing syndrome in the United States, is currently established by the presence of amyloid-β and tau protein biomarkers in the setting of clinical cognitive impairment. These straightforward diagnostic parameters belie an immense complexity of genetic architecture underlying risk and presentation in AD. In this review, we provide a focused overview of the current state of AD genetics. We discuss the discovery of familial autosomal dominant genes, the identification of candidate genes associated with AD, and genetic variants conferring higher risk of developing AD compared with the general population. In particular, we discuss important features of AD risk due to the APOE ε4 allele. In addition to risk, we describe how the field has made headway understanding genetic factors that may protect from AD. The biological implications and practical limitations of information gleaned from genome-wide association studies in AD over the years are also discussed. The readers will have an up-to-date understanding of where we are in our efforts to understand the layers of genetic complexity in AD.

An overview of the genes and biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and neurodegenerative disease characterized by neurofibrillary tangles (NFTs) and amyloid plaque. Familial AD is caused by mutations in the APP, PSEN1, and PSEN2 genes and these mutations result in the early onset of the disease. Sporadic AD usually affects older adults over the age of 65 years and is, therefore classified as late-onset AD (LOAD). Several risk factors associated with LOAD including the APOE gene have been identified. Moreover, GWAS studies have identified a wide array of genes and polymorphisms that are associated with LOAD risk. Currently, the diagnosis of AD involves the evaluation of memory and personality changes, cognitive impairment, and medical and family history to rule out other diseases. Laboratory tests to assess the biomarkers in the body fluids as well as MRI, CT, and PET scans to analyze the presence of plaques and NFTs are also included in the diagnosis of AD. It is important to diagnose AD before the onset of clinical symptoms, i.e. during the preclinical stage, to delay the progression and for better management of the disease. Research has been conducted to identify biomarkers of AD in the CSF, serum, saliva, and urine during the preclinical stage. Current research has identified several biomarkers and potential biomarkers in the body fluids that enhance diagnostic accuracy. Aside from genetics, other factors such as diet, physical activity, and lifestyle factors may influence the risk of developing AD. Clinical trials are underway to find potential biomarkers, diagnostic measures, and treatments for AD mainly in the preclinical stage. This review provides an overview of the genes and biomarkers of AD.

Inflammatory signaling pathways in Alzheimer's disease: Mechanistic insights and possible therapeutic interventions

The complex pathophysiology of Alzheimer's disease (AD) poses challenges for the development of therapies. Recently, neuroinflammation has been identified as a key pathogenic mechanism underlying AD, while inflammation has emerged as a possible target for the management and prevention of AD. Several prior studies have demonstrated that medications modulating neuroinflammation might lessen AD symptoms, mostly by controlling neuroinflammatory signaling pathways such as the NF-κB, MAPK, NLRP3, etc, and their respective signaling cascade. Moreover, targeting these inflammatory modalities with inhibitors, natural products, and metabolites has been the subject of intensive research because of their anti-inflammatory characteristics, with many studies demonstrating noteworthy pharmacological capabilities and potential clinical applications. Therefore, targeting inflammation is considered a promising strategy for treating AD. This review comprehensively elucidates the neuroinflammatory mechanisms underlying AD progression and the beneficial effects of inhibitors, natural products, and metabolites in AD treatment.

Alzheimer's disease: insights into pathology, molecular mechanisms, and therapy

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. This condition casts a significant shadow on global health due to its complex and multifactorial nature. In addition to genetic predispositions, the development of AD is influenced by a myriad of risk factors, including aging, systemic inflammation, chronic health conditions, lifestyle, and environmental exposures. Recent advancements in understanding the complex pathophysiology of AD are paving the way for enhanced diagnostic techniques, improved risk assessment, and potentially effective prevention strategies. These discoveries are crucial in the quest to unravel the complexities of AD, offering a beacon of hope for improved management and treatment options for the millions affected by this debilitating disease.

Safety and efficacy of long-term gantenerumab treatment in dominantly inherited Alzheimer's disease: an open label extension of the phase 2/3 multicentre, randomised, double-blind, placebo-controlled platform DIAN-TU Trial

Background

Amyloid-plaque removal by monoclonal antibody therapies slows clinical progression in symptomatic Alzheimer's disease; however, the potential for delaying the onset of clinical symptoms in asymptomatic people is unknown. The Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU) is an ongoing platform trial assessing the safety and efficacy of multiple investigational products in participants with dominantly inherited Alzheimer's disease (DIAD) caused by mutations. On the basis of findings of amyloid removal and downstream biological effects from the gantenerumab arm of the platform trial, we continued a 3-year open-label extension (OLE) study to assess the safety and efficacy of long-term treatment with high doses of gantenerumab.

Methods

The randomised, placebo-controlled, double-blind, phase 2/3 multi-arm trial (DIAN-TU-001) assessed solanezumab or gantenerumab versus placebo in participants who were between 15 years before to 10 years after their estimated years to symptom onset and had a Clinical Dementia Rating (CDR) global score of 0 (cognitively normal) to 1 (mild dementia). This study was followed by an OLE study of gantenerumab treatment, conducted at 18 study sites in Australia, Canada, France, Ireland, Puerto Rico, Spain, the UK, and USA. For inclusion in the OLE, participants at risk for DIAD had participated in the double-blind period of DIAN-TU-001 and were required to know their mutation status. We investigated increasing doses of gantenerumab up to 1500 mg subcutaneous every 2 weeks. Due to the lack of a regulatory path for gantenerumab, the study was stopped early after a pre-specified interim analysis (when most participants had completed 2 years of treatment) of the clinical measure CDR-SB. The primary outcome for the final analysis was the amyloid plaque measure PiB-PET SUVR at 3 years, assessed in the modified intention to treat population (defined as participants who received any gantenerumab treatment post-OLE baseline, had at least one PiB-PET SUVR assessment prior to gantenerumab treatment, and a post-baseline assessment). All participants who received at least one dose of study drug in the OLE were included in the safety analysis. DIAN-TU-001 (NCT01760005) and the OLE (NCT06424236) are registered with clinicaltrials.gov.

Findings

Of 74 participants who were recruited into the OLE study between June 3, 2020 and April 22, 2021, 73 were enrolled and received gantenerumab treatment. 47 (64%) stopped dosing due to early termination of the study by the sponsor, and 13 (18%) prematurely discontinued the study for other reasons. The mITT population for the primary analysis comprised 55 participants. At the interim analysis, the hazard ratio for clinical decline of CDR-SB in asymptomatic mutation carriers was 0.79 (n=53, 95% CI 0.47 to 1.32) for participants who were treated with gantenerumab in either the double-blind or OLE period (Any Gant), and 0.53 (n=22, 0.27 to 1.03) for participants who were treated with gantenerumab the longest (Longest Gant). At the final analysis, the adjusted mean change from OLE baseline to year 3 in PiB-PET SUVR was -0.71 SUVR (95% CI -0.88 to -0.53, p<0.0001). Amyloid-related imaging abnormalities occurred in 53% (39/73) of participants: 47% (34/73) with microhaemorrhages, 30% (22/73) with oedema, and 6% (5/73) were associated with symptoms. No treatment-associated macrohaemorrhages or deaths occurred.

Interpretation

Partial or short-term amyloid removal did not show significant clinical effects. However, long-term full amyloid removal potentially delayed symptom onset and dementia progression. Conclusions are limited due to the OLE design and use of external controls and need to be confirmed in long term trials.

Funding

National Institutes on Aging, Alzheimer's Association, GHR, F. Hoffmann-La Roche, Ltd/Genentech.

Lipidome disruption in Alzheimer's disease brain: detection, pathological mechanisms, and therapeutic implications

Alzheimer's disease (AD) is among the most devastating neurodegenerative disorders with limited treatment options. Emerging evidence points to the involvement of lipid dysregulation in the development of AD. Nevertheless, the precise lipidomic landscape and the mechanistic roles of lipids in disease pathology remain poorly understood. This review aims to highlight the significance of lipidomics and lipid-targeting approaches in the diagnosis and treatment of AD. We summarized the connection between lipid dysregulation in the human brain and AD at both genetic and lipid species levels. We briefly introduced lipidomics technologies and discussed potential challenges and areas of future advancements in the lipidomics field for AD research. To elucidate the central role of lipids in converging multiple pathological aspects of AD, we reviewed the current knowledge on the interplay between lipids and major AD features, including amyloid beta, tau, and neuroinflammation. Finally, we assessed the progresses and obstacles in lipid-based therapeutics and proposed potential strategies for leveraging lipidomics in the treatment of AD.

The impact of genetic variability on Alzheimer's therapies: obstacles for pharmacogenetic progress

INTRODUCTION

Genetic load influences the therapeutic response to conventional drugs in Alzheimer's disease (AD). Pharmacogenetics (PGx) is the best option to reduce drug-drug interactions and adverse drug reactions in patients undergoing polypharmacy regimens. However, there are important limitations that make it difficult to incorporate pharmacogenetics into routine clinical practice.

AREAS COVERED

This article analyzes the pharmacogenetic apparatus made up of pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes responsible for the efficacy and safety of pharmacological treatment, the impact of genetic load on the outcome of multifactorial treatments, and practical aspects for the effective use of PGx.

EXPERT OPINION

Over 120 genes are closely associated with AD. There is an accumulation of cerebrovascular (CVn) and neurodegenerative (ADn) genes in AD. APOE-4 carriers accumulate more deleterious genetic load related to other CVn and ADn genes, develop the disease earlier, and are at a biological disadvantage compared to APOE-4 non-carriers. CYP2D6-PMs and APOE-4 carriers are the worst responders to anti-dementia drugs. Some limitations hinder the implementation of PGx in clinical practice, including lack of pharmacogenetic information for many drugs, low number of genes in PGx screening protocols, and educational deficiencies in the medical community regarding PGx and genomic medicine.

Connecting the Dots: Gender, Sexuality, and Societal Influences on Cognitive Aging and Alzheimer's Disease

Alzheimer's disease (AD) has many etiologies and the impact of gender on AD changes throughout time. As a consequence of advancements in precision medical procedures and methodology, Alzheimer's disease is now better understood and treated. Several risk factors may be addressed to lower one's chances of developing Alzheimer's disease or associated dementia (ADRD). The presence of amyloid-α protein senile plaques, intracellular tau protein neurofibrillary tangles (NfTs), neurodegeneration, and neuropsychiatric symptoms (NPS) characterizes Alzheimer's disease. NPS is common in persons with Alzheimer's disease dementia, although its presentation varies widely. Gender differences might explain this clinical variability. The fundamental goal of this review is to 1) emphasize the function of old age, sex, and gender in the development of Alzheimer's disease, dementia, and ADRD, and 2) explain the importance of sexual hormones, education, and APOE (Apolipoprotein E) status. This is a narrative summary of new ideas and concepts on the differences in the chance of developing dementia or Alzheimer's disease between men and women. A more thorough examination of risk and protective variables in both men and women might hasten research into the epidemiology of neurological illnesses such as dementia and Alzheimer's disease. Similarly, future preventive efforts should target men and women separately.

Association of common and rare variants with Alzheimer's disease in more than 13,000 diverse individuals with whole-genome sequencing from the Alzheimer's Disease Sequencing Project

INTRODUCTION

Alzheimer's disease (AD) is a common disorder of the elderly that is both highly heritable and genetically heterogeneous.

METHODS

We investigated the association of AD with both common variants and aggregates of rare coding and non-coding variants in 13,371 individuals of diverse ancestry with whole genome sequencing (WGS) data.

RESULTS

Pooled-population analyses of all individuals identified genetic variants at apolipoprotein E (APOE) and BIN1 associated with AD (p < 5 × 10-8). Subgroup-specific analyses identified a haplotype on chromosome 14 including PSEN1 associated with AD in Hispanics, further supported by aggregate testing of rare coding and non-coding variants in the region. Common variants in LINC00320 were observed associated with AD in Black individuals (p = 1.9 × 10-9). Finally, we observed rare non-coding variants in the promoter of TOMM40 distinct of APOE in pooled-population analyses (p = 7.2 × 10-8).

DISCUSSION

We observed that complementary pooled-population and subgroup-specific analyses offered unique insights into the genetic architecture of AD.

HIGHLIGHTS

We determine the association of genetic variants with Alzheimer's disease (AD) using 13,371 individuals of diverse ancestry with whole genome sequencing (WGS) data. We identified genetic variants at apolipoprotein E (APOE), BIN1, PSEN1, and LINC00320 associated with AD. We observed rare non-coding variants in the promoter of TOMM40 distinct of APOE.

Genetics and Neuropathology of Neurodegenerative Dementias

OBJECTIVE

This article provides an overview of the current understanding of the genetic and pathologic features of neurodegenerative dementias, with an emphasis on Alzheimer disease and related dementias.

LATEST DEVELOPMENTS

In recent years, there has been substantial progress in genetic research, contributing significant knowledge to our understanding of the molecular risk factors involved in neurodegenerative dementia syndromes. Several genes have been linked to monogenic forms of dementia (eg, APP, PSEN1, PSEN2, SNCA, GRN, C9orf72, MAPT) and an even larger number of genetic variants are known to influence susceptibility for developing dementia. As anti-amyloid therapies for patients with early-stage Alzheimer disease have entered the clinical arena, screening for the apolipoprotein E ε4 high-risk allele has come into focus, emphasizing the importance of genetic counseling. Similarly, advances in the pathologic classifications of neurodegenerative dementia syndromes and molecular pathology highlight their heterogeneity and overlapping features and provide insights into the pathogenesis of these conditions.

ESSENTIAL POINTS

Recent progress in neurogenetics and molecular pathology has improved our understanding of the complex pathogenetic changes associated with neurodegenerative dementias, facilitating improved disease modeling, enhanced diagnostics, and individualized counseling. The hope is that this knowledge will ultimately pave the way for the development of novel therapeutics.

Is the Relationship Between Cardiovascular Disease and Alzheimer's Disease Genetic? A Scoping Review

BACKGROUND/OBJECTIVES

Cardiovascular disease (CVD) and Alzheimer's disease (AD) are two diseases highly prevalent in the aging population and often co-occur. The exact relationship between the two diseases is uncertain, though epidemiological studies have demonstrated that CVDs appear to increase the risk of AD and vice versa. This scoping review aims to examine the current identified overlapping genetics between CVDs and AD at the individual gene level and at the shared pathway level.

METHODS

Following PRISMA-ScR guidelines for a scoping review, we searched the PubMed and Scopus databases from 1990 to October 2024 for articles that involved (1) CVDs, (2) AD, and (3) used statistical methods to parse genetic relationships.

RESULTS

Our search yielded 2918 articles, of which 274 articles passed screening and were organized into two main sections: (1) evidence of shared genetic risk; and (2) shared mechanisms. The genes APOE, PSEN1, and PSEN2 reportedly have wide effects across the AD and CVD spectrum, affecting both cardiac and brain tissues. Mechanistically, changes in three main pathways (lipid metabolism, blood pressure regulation, and the breakdown of the blood-brain barrier (BBB)) contribute to subclinical and etiological changes that promote both AD and CVD progression. However, genetic studies continue to be limited by the availability of longitudinal data and lack of cohorts that are representative of diverse populations.

CONCLUSIONS

Highly penetrant familial genes simultaneously increase the risk of CVDs and AD. However, in most cases, sets of dysregulated genes within larger-scale mechanisms, like changes in lipid metabolism, blood pressure regulation, and BBB breakdown, increase the risk of both AD and CVDs and contribute to disease progression.

Missense and loss-of-function variants at GWAS loci in familial Alzheimer's disease

BACKGROUND

Few rare variants have been identified in genetic loci from genome-wide association studies (GWAS) of Alzheimer's disease (AD), limiting understanding of mechanisms, risk assessment, and genetic counseling.

METHODS

Using genome sequencing data from 197 families in the National Institute on Aging Alzheimer's Disease Family Based Study and 214 Caribbean Hispanic families, we searched for rare coding variants within known GWAS loci from the largest published study.

RESULTS

Eighty-six rare missense or loss-of-function (LoF) variants completely segregated in 17.5% of families, but in 91 (22.1%) families Apolipoprotein E (APOE)-𝜀4 was the only variant segregating. However, in 60.3% of families, APOE 𝜀4, missense, and LoF variants were not found within the GWAS loci.

DISCUSSION

Although APOE 𝜀4and several rare variants were found to segregate in both family datasets, many families had no variant accounting for their disease. This suggests that familial AD may be the result of unidentified rare variants.

HIGHLIGHTS

Rare coding variants from GWAS loci segregate in familial Alzheimer's disease. Missense or loss of function variants were found segregating in nearly 7% of families. APOE-𝜀4 was the only segregating variant in 29.7% in familial Alzheimer's disease. In Hispanic and non-Hispanic families, different variants were found in segregating genes. No coding variants were found segregating in many Hispanic and non-Hispanic families.

Mitochondrial Quality Control in Alzheimer's Disease: Insights from Caenorhabditis elegans Models

Alzheimer's disease (AD) is a complex neurodegenerative disorder that is classically defined by the extracellular deposition of senile plaques rich in amyloid-beta (Aβ) protein and the intracellular accumulation of neurofibrillary tangles (NFTs) that are rich in aberrantly modified tau protein. In addition to aggregative and proteostatic abnormalities, neurons affected by AD also frequently possess dysfunctional mitochondria and disrupted mitochondrial maintenance, such as the inability to eliminate damaged mitochondria via mitophagy. Decades have been spent interrogating the etiopathogenesis of AD, and contributions from model organism research have aided in developing a more fundamental understanding of molecular dysfunction caused by Aβ and toxic tau aggregates. The soil nematode C. elegans is a genetic model organism that has been widely used for interrogating neurodegenerative mechanisms including AD. In this review, we discuss the advantages and limitations of the many C. elegans AD models, with a special focus and discussion on how mitochondrial quality control pathways (namely mitophagy) may contribute to AD development. We also summarize evidence on how targeting mitophagy has been therapeutically beneficial in AD. Lastly, we delineate possible mechanisms that can work alone or in concert to ultimately lead to mitophagy impairment in neurons and may contribute to AD etiopathology.

Brain aging and Alzheimer's disease, a perspective from non-human primates

Brain aging is compared between Cercopithecinae (macaques and baboons), non-human Hominidae (chimpanzees, orangutans, and gorillas), and their close relative, humans. β-amyloid deposition in the form of senile plaques (SPs) and cerebral β-amyloid angiopathy (CAA) is a frequent neuropathological change in non-human primate brain aging. SPs are usually diffuse, whereas SPs with dystrophic neurites are rare. Tau pathology, if present, appears later, and it is generally mild or moderate, with rare exceptions in rhesus macaques and chimpanzees. Behavior and cognitive impairment are usually mild or moderate in aged non-human primates. In contrast, human brain aging is characterized by early tau pathology manifested as neurofibrillary tangles (NFTs), composed of paired helical filaments (PHFs), progressing from the entorhinal cortex, hippocampus, temporal cortex, and limbic system to other brain regions. β-amyloid pathology appears decades later, involves the neocortex, and progresses to the paleocortex, diencephalon, brain stem, and cerebellum. SPs with dystrophic neurites containing PHFs and CAA are common. Cognitive impairment and dementia of Alzheimer's type occur in about 1-5% of humans aged 65 and about 25% aged 85. In addition, other proteinopathies, such as limbic-predominant TDP-43 encephalopathy, amygdala-predominant Lewy body disease, and argyrophilic grain disease, primarily affecting the archicortex, paleocortex, and amygdala, are common in aged humans but non-existent in non-human primates. These observations show that human brain aging differs from brain aging in non-human primates, and humans constitute the exception among primates in terms of severity and extent of brain aging damage.

Rotating magnetic field improves cognitive and memory impairments in APP/PS1 mice by activating autophagy and inhibiting the PI3K/AKT/mTOR signaling pathway

Alzheimer's disease (AD) is a geriatric disorder that can be roughly classified into sporadic AD and hereditary AD. The latter is strongly associated with genetic factors, and its treatment poses greater challenges compared to sporadic AD. Rotating magnetic fields (RMF) is a non-invasive treatment known to have diverse biological effects, including the modulation of the central nervous system and aging. However, the impact of RMF on hereditary AD and its underlying mechanism remain unexplored. In this study, we exposed APP/PS1 mice to RMF (2 h/day, 0.2 T, 4 Hz) for a duration of 6 months. The results demonstrated that RMF treatment significantly ameliorated their cognitive and memory impairments, attenuated neuronal damage, and reduced amyloid deposition. Furthermore, RNA-sequencing analysis revealed a significant enrichment of autophagy-related genes and the PI3K/AKT-mTOR signaling pathway. Western blotting further confirmed that RMF activated autophagy and suppressed the phosphorylation of proteins associated with the PI3K/AKT/mTOR signaling pathway in APP/PS1 mice. These protective effects and the underlying mechanism were also observed in Aβ25-35-exposed HT22 cells. Collectively, our findings indicate that RMF improves cognitive and memory dysfunction in APP/PS1 mice by activating autophagy and inhibiting the PI3K/AKT/mTOR signaling pathway, thus highlighting the potential of RMF as a clinical treatment for hereditary AD.

Alzheimer's disease induced neurons bearing PSEN1 mutations exhibit reduced excitability

Alzheimer's disease (AD) is a devastating neurodegenerative condition that affects memory and cognition, characterized by neuronal loss and currently lacking a cure. Mutations in PSEN1 (Presenilin 1) are among the most common causes of early-onset familial AD (fAD). While changes in neuronal excitability are believed to be early indicators of AD progression, the link between PSEN1 mutations and neuronal excitability remains to be fully elucidated. This study examined iPSC-derived neurons (iNs) from fAD patients with PSEN1 mutations S290C or A246E, alongside CRISPR-corrected isogenic cell lines, to investigate early changes in excitability. Electrophysiological profiling revealed reduced excitability in both PSEN1 mutant iNs compared to their isogenic controls. Neurons bearing S290C and A246E mutations exhibited divergent passive membrane properties compared to isogenic controls, suggesting distinct effects of PSEN1 mutations on neuronal excitability. Additionally, both PSEN1 backgrounds exhibited higher current density of voltage-gated potassium (Kv) channels relative to their isogenic iNs, while displaying comparable voltage-gated sodium (Nav) channel current density. This suggests that the Nav/Kv imbalance contributes to impaired neuronal firing in fAD iNs. Deciphering these early cellular and molecular changes in AD is crucial for understanding disease pathogenesis.

Recording γ-secretase activity in living mouse brains

γ-Secretase plays a pivotal role in the central nervous system. Our recent development of genetically encoded Förster resonance energy transfer (FRET)-based biosensors has enabled the spatiotemporal recording of γ-secretase activity on a cell-by-cell basis in live neurons in culture. Nevertheless, how γ-secretase activity is regulated in vivo remains unclear. Here, we employ the near-infrared (NIR) C99 720-670 biosensor and NIR confocal microscopy to quantitatively record γ-secretase activity in individual neurons in living mouse brains. Intriguingly, we uncovered that γ-secretase activity may influence the activity of γ-secretase in neighboring neurons, suggesting a potential 'cell non-autonomous' regulation of γ-secretase in mouse brains. Given that γ-secretase plays critical roles in important biological events and various diseases, our new assay in vivo would become a new platform that enables dissecting the essential roles of γ-secretase in normal health and diseases.

A golden age of muscarinic acetylcholine receptor modulation in neurological diseases

Over the past 40 years, the muscarinic acetylcholine receptor family, particularly the M1-receptor and M4-receptor subtypes, have emerged as validated targets for the symptomatic treatment of neurological diseases such as schizophrenia and Alzheimer disease. However, despite considerable effort and investment, no drugs have yet gained clinical approval. This is largely attributable to cholinergic adverse effects that have halted the majority of programmes and resulted in a waning of interest in these G-protein-coupled receptor targets. Recently, this trend has been reversed. Driven by advances in structure-based drug design and an appreciation of the optimal pharmacological properties necessary to deliver clinical efficacy while minimizing adverse effects, a new generation of M1-receptor and M4-receptor orthosteric agonists and positive allosteric modulators are now entering the clinic. These agents offer the prospect of novel therapeutic solutions for 'hard to treat' neurological diseases, heralding a new era of muscarinic drug discovery.

Association of MME gene polymorphisms with susceptibility to Alzheimer's disease in an Iranian population

Background

the MME gene encodes a membrane metalloendopeptidase, known as neprilysin (NEP). There are no reports on the potential implications of MME gene polymorphisms on the risk of Alzheimer's disease (AD) in the Iranian population. In this study, we studied the potential association of two single nucleotide polymorphisms (SNPs), rs6797911 and rs3736187, in the MME gene and the risk of developing AD in an Iranian population.

Methods

This case-control study comprised 120 AD-diagnosed patients and 120 healthy individuals without any prior family history of AD. The patient and control groups were matched for major demographic and health characteristics. Genotyping was performed by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR).

Results

All patients included in this study were assessed by an experienced neurologist to exclude cases with other forms of dementia based on a brain computed tomography scan and other clinical findings. There were no significant differences in demographic and health characteristics including sex, diabetes, blood pressure, and cigarette smoking status between case and control groups (p > 0.05). However, the age difference appeared significant. Both SNPs were significantly associated with the risk of AD in our study population. The rs3736187 (T > C, 3:155168489) was strongly associated with AD risk under the log-additive model (OR = 1.67, CI = 1.18-2.37, p-value = 0.003). The rs6797911 (T > A, 3:155144601) also showed a significant association with AD risk under the dominant model (TT vs. TA and AA, OR = 3.37, CI = 1.86-6.1, p-value <0.001).

Conclusion

There is a strong association between MME gene polymorphisms and susceptibility to AD in the Iranian population. Amyloid-β (Aβ) can serve as a substrate for the NEP metalloendopeptidase, the product of the MME gene. However, the mechanistic understanding of how these genetic variations affect NEP expression, function, and consequently susceptibility to AD, is poorly understood. Further research is required to fully understand the exact implication of MME gene variations on AD, particularly in a larger, ethnicity-diverse population.

A familial Alzheimer's disease associated mutation in presenilin-1 mediates amyloid-beta independent cell specific neurodegeneration

Mutations in the presenilin (PS) genes are a predominant cause of familial Alzheimer's disease (fAD). An ortholog of PS in the genetic model organism Caenorhabditis elegans (C. elegans) is sel-12. Mutations in the presenilin genes are commonly thought to lead to fAD by upregulating the expression of amyloid beta (Aβ), however this hypothesis has been challenged by recent evidence. As C. elegans lack amyloid beta (Aβ), the goal of this work was to examine Aβ-independent effects of mutations in sel-12 and PS1/PS2 on behaviour and sensory neuron morphology across the lifespan in a C. elegans model. Olfactory chemotaxis experiments were conducted on sel-12(ok2078) loss-of-function mutant worms. Adult sel-12 mutant worms showed significantly lower levels of chemotaxis to odorants compared to wild-type worms throughout their lifespan, and this deficit increased with age. The chemotaxis phenotype in sel-12 mutant worms is rescued by transgenic over-expression of human wild-type PS1, but not the classic fAD-associated variant PS1C410Y, when expression was driven by either the endogenous sel-12 promoter (Psel-12), a pan-neuronal promoter (Primb-1), or by a promoter whose primary expression was in the sensory neurons responsible for the chemotaxis behavior (Psra-6, Podr-10). The behavioural phenotype was also rescued by over-expressing an atypical fAD-linked mutation in PS1 (PS1ΔS169) that has been reported to leave the Notch pathway intact. An examination of the morphology of polymodal nociceptive (ASH) neurons responsible for the chemotaxis behavior also showed increased neurodegeneration over time in sel-12 mutant worms that could be rescued by the same transgenes that rescued the behaviour, demonstrating a parallel with the observed behavioral deficits. Thus, we report an Aβ-independent neurodegeneration in C. elegans that was rescued by cell specific over-expression of wild-type human presenilin.

Updates in Alzheimer's disease: from basic research to diagnosis and therapies

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized pathologically by extracellular deposition of β-amyloid (Aβ) into senile plaques and intracellular accumulation of hyperphosphorylated tau (pTau) as neurofibrillary tangles. Clinically, AD patients show memory deterioration with varying cognitive dysfunctions. The exact molecular mechanisms underlying AD are still not fully understood, and there are no efficient drugs to stop or reverse the disease progression. In this review, we first provide an update on how the risk factors, including APOE variants, infections and inflammation, contribute to AD; how Aβ and tau become abnormally accumulated and how this accumulation plays a role in AD neurodegeneration. Then we summarize the commonly used experimental models, diagnostic and prediction strategies, and advances in periphery biomarkers from high-risk populations for AD. Finally, we introduce current status of development of disease-modifying drugs, including the newly officially approved Aβ vaccines, as well as novel and promising strategies to target the abnormal pTau. Together, this paper was aimed to update AD research progress from fundamental mechanisms to the clinical diagnosis and therapies.

Generation of a gene-corrected human isogenic iPSC line from an Alzheimer's disease iPSC line carrying the PSEN1 H163R mutation

We report the generation of a gene-edited human induced pluripotent stem cell (iPSC) line from an Alzheimer's disease patient-derived iPSC line harbouring the PSEN1 H163R mutation. This line demonstrates pluripotent stem cell morphology, expression of pluripotency markers, and maintains a normal karyotype.

Cortical neurodegeneration caused by Psen1 mutations is independent of Aβ

Mutations in the PSEN genes are the major cause of familial Alzheimer's disease, and presenilin (PS) is the catalytic subunit of γ-secretase, which cleaves type I transmembrane proteins, including the amyloid precursor protein (APP) to release Aβ peptides. While PS plays an essential role in the protection of neuronal survival, PSEN mutations also increase the ratio of Aβ42/Aβ40. Thus, it remains unresolved whether PSEN mutations cause AD via a loss of its essential function or increases of Aβ42/Aβ40. Here, we test whether the knockin (KI) allele of Psen1 L435F, the most severe FAD mutation located closest to the active site of γ-secretase, causes age-dependent cortical neurodegeneration independent of Aβ by crossing various Psen mutant mice to the App-null background. We report that removing Aβ completely through APP deficiency has no impact on the age-dependent neurodegeneration in Psen mutant mice, as shown by the absence of effects on the reduced cortical volume and decreases of cortical neurons at the ages of 12 and 18 mo. The L435F KI allele increases Aβ42/Aβ40 in the cerebral cortex while decreasing de novo production and steady-state levels of Aβ42 and Aβ40 in the presence of APP. Furthermore, APP deficiency does not alleviate elevated apoptotic cell death in the cerebral cortex of Psen mutant mice at the ages of 2, 12, and 18 mo, nor does it affect the progressive microgliosis in these mice. Our findings demonstrate that Psen1 mutations cause age-dependent neurodegeneration independent of Aβ, providing further support for a loss-of-function pathogenic mechanism underlying PSEN mutations.

PSEN2 Mutations May Mimic Frontotemporal Dementia: Two New Case Reports and a Review

BACKGROUND

Monogenic Alzheimer's disease (AD) has severe health and socioeconomic repercussions. Its rarest cause is presenilin 2 (PSEN2) gene mutations. We present two new cases with presumed PSEN2-AD with unusual clinical and neuroimaging findings in order to provide more information on the pathophysiology and semiology of these patients.

METHODS

Women aged 69 and 62 years at clinical onset, marked by prominent behavioral and language dysfunction, progressing to severe dementia within three years were included. The complete study is depicted. In addition, a systematic review of the PSEN2-AD was performed.

RESULTS

Neuroimaging revealed pronounced frontal white matter hyperintensities (WMH) and frontotemporal atrophy/hypometabolism. The genetic study unveiled PSEN2 variants: c.772G>A (p.Ala258Thr) and c.1073-2_1073-1del. Both cerebrospinal fluid (CSF) and experimental blood biomarkers shouldered AD etiology.

CONCLUSIONS

Prominent behavioral and language dysfunction suggesting frontotemporal dementia (FTD) may be underestimated in the literature as a clinical picture in PSEN2 mutations. Thus, it may be reasonable to include PSEN2 in genetic panels when suspecting FTDL. PSEN2 mutations may cause striking WMH, arguably related to myelin disruption induced by amyloid accumulation.

Alzheimer's Disease Neuropathological Change in Aged Non-Primate Mammals

Human brain aging is characterized by the production and deposition of β-amyloid (Aβ) in the form of senile plaques and cerebral amyloid angiopathy and the intracellular accumulation of hyper-phosphorylated tau (Hp-tau) to form neurofibrillary tangles (NFTs) and dystrophic neurites of senile plaques. The process progresses for years and eventually manifests as cognitive impairment and dementia in a subgroup of aged individuals. Aβ is produced and deposited first in the neocortex in most aged mammals, including humans; it is usually not accompanied by altered behavior and cognitive impairment. Hp-tau is less frequent than Aβ pathology, and NFTs are rare in most mammals. In contrast, NFTs are familiar from middle age onward in humans; NFTs first appear in the paleocortex and selected brain stem nuclei. NFTs precede for decades or years Aβ deposition and correlate with dementia in about 5% of individuals at the age of 65 and 25% at the age of 85. Based on these comparative data, (a) Aβ deposition is the most common Alzheimer's disease neuropathological change (ADNC) in the brain of aged mammals; (b) Hp-tau is less common, and NFTs are rare in most aged mammals; however, NFTs are the principal cytoskeletal pathology in aged humans; (c) NFT in aged humans starts in selected nuclei of the brain stem and paleocortical brain regions progressing to the most parts of the neocortex and other regions of the telencephalon; (d) human brain aging is unique among mammalian species due to the early appearance and dramatic progression of NFTs from middle age onward, matching with cognitive impairment and dementia in advanced cases; (e) neither mammalian nor human brain aging supports the concept of the amyloid cascade hypothesis.

Recording γ-secretase activity in living mouse brains

γ-Secretase plays a pivotal role in the central nervous system. Our recent development of genetically encoded Forster resonance energy transfer (FRET)-based biosensors has enabled the spatiotemporal recording of γ-secretase activity on a cell-by-cell basis in live neurons in culture. Nevertheless, how γ-secretase activity is regulated in vivo remains unclear. Here we employ the near-infrared (NIR) C99 720-670 biosensor and NIR confocal microscopy to quantitatively record γ-secretase activity in individual neurons in living mouse brains. Intriguingly, we uncovered that γ-secretase activity may influence the activity of γ-secretase in neighboring neurons, suggesting a potential "cell non-autonomous" regulation of γ-secretase in mouse brains. Given that γ-secretase plays critical roles in important biological events and various diseases, our new assay in vivo would become a new platform that enables dissecting the essential roles of γ-secretase in normal health and diseases.

Missense and Loss of Function Variants at GWAS Loci in Familial Alzheimer's Disease

BACKGROUND

Few rare variants have been identified in genetic loci from genome wide association studies of Alzheimer's disease (AD), limiting understanding of mechanisms and risk assessment, and genetic counseling.

METHODS

Using genome sequencing data from 197 families in The NIA Alzheimer's Disease Family Based Study, and 214 Caribbean Hispanic families, we searched for rare coding variants within known GWAS loci from the largest published study.

RESULTS

Eighty-six rare missense or loss of function (LoF) variants completely segregated in 17.5% of families, but in 91 (22.1%) of families APOE-e4 was the only variant segregating. However, in 60.3% of families neither APOE-e4 nor missense or LoF variants were found within the GWAS loci.

DISCUSSION

Although APOE-ε4 and several rare variants were found to segregate in both family datasets, many families had no variant accounting for their disease. This suggests that familial AD may be the result of unidentified rare variants.

Multiple Roles of Apolipoprotein E4 in Oxidative Lipid Metabolism and Ferroptosis During the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide and has a great socio-economic impact. Modified oxidative lipid metabolism and dysregulated iron homeostasis have been implicated in the pathogenesis of this disorder, but the detailed pathophysiological mechanisms still remain unclear. Apolipoprotein E (APOE) is a lipid-binding protein that occurs in large quantities in human blood plasma, and a polymorphism of the APOE gene locus has been identified as risk factors for AD. The human genome involves three major APOE alleles (APOE2, APOE3, APOE4), which encode for three subtly distinct apolipoprotein E isoforms (APOE2, APOE3, APOE4). The canonic function of these apolipoproteins is lipid transport in blood and brain, but APOE4 allele carriers have a much higher risk for AD. In fact, about 60% of clinically diagnosed AD patients carry at least one APOE4 allele in their genomes. Although the APOE4 protein has been implicated in pathophysiological key processes of AD, such as extracellular beta-amyloid (Aβ) aggregation, mitochondrial dysfunction, neuroinflammation, formation of neurofibrillary tangles, modified oxidative lipid metabolism, and ferroptotic cell death, the underlying molecular mechanisms are still not well understood. As for all mammalian cells, iron plays a crucial role in neuronal functions and dysregulation of iron homeostasis has also been implicated in the pathogenesis of AD. Imbalances in iron homeostasis and impairment of the hydroperoxy lipid-reducing capacity induce cellular dysfunction leading to neuronal ferroptosis. In this review, we summarize the current knowledge on APOE4-related oxidative lipid metabolism and the potential role of ferroptosis in the pathogenesis of AD. Pharmacological interference with these processes might offer innovative strategies for therapeutic interventions.

The presenilin 1 mutation P436S causes familial Alzheimer's disease with elevated Aβ43 and atypical clinical manifestations

INTRODUCTION

Familial Alzheimer's disease (fAD) is heterogeneous in terms of age at onset and clinical presentation. A greater understanding of the pathogenicity of fAD variants and how these contribute to heterogeneity will enhance our understanding of the mechanisms of AD more widely.

METHODS

To determine the pathogenicity of the unclassified PSEN1 P436S mutation, we studied an expanded kindred of eight affected individuals, with magnetic resonance imaging (MRI) (two individuals), patient-derived induced pluripotent stem cell (iPSC) models (two donors), and post-mortem histology (one donor).

RESULTS

An autosomal dominant pattern of inheritance of fAD was seen, with an average age at symptom onset of 46 years and atypical features. iPSC models and post-mortem tissue supported high production of amyloid beta 43 (Aβ43). PSEN1 peptide maturation was unimpaired.

DISCUSSION

We confirm that the P436S mutation in PSEN1 causes atypical fAD. The location of the mutation in the critical PSEN1 proline-alanine-leucine-proline (PALP) motif may explain the early age at onset despite appropriate protein maturation.

HIGHLIGHTS

PSEN1 P436S mutations cause familial Alzheimer's disease. This mutation is associated with atypical clinical presentation. Induced pluripotent stem cells (iPSCs) and post-mortem studies support increased amyloid beta (Aβ43) production. Early age at onset highlights the importance of the PALP motif in PSEN1 function.

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.

APOE3 Christchurch Heterozygosity and Autosomal Dominant Alzheimer's Disease

BACKGROUND

Variants in APOE and PSEN1 (encoding apolipoprotein E and presenilin 1, respectively) alter the risk of Alzheimer's disease. We previously reported a delay of cognitive impairment in a person with autosomal dominant Alzheimer's disease caused by the PSEN1 E280A variant who also had two copies of the apolipoprotein E3 Christchurch variant (APOE3 Ch). Heterozygosity for the APOE3 Ch variant may influence the age at which the onset of cognitive impairment occurs. We assessed this hypothesis in a population in which the PSEN1 E280A variant is prevalent.

METHODS

We analyzed data from 27 participants with one copy of the APOE3 Ch variant among 1077 carriers of the PSEN1 E280A variant in a kindred from Antioquia, Colombia, to estimate the age at the onset of cognitive impairment and dementia in this group as compared with persons without the APOE3 Ch variant. Two participants underwent brain imaging, and autopsy was performed in four participants.

RESULTS

Among carriers of PSEN1 E280A who were heterozygous for the APOE3 Ch variant, the median age at the onset of cognitive impairment was 52 years (95% confidence interval [CI], 51 to 58), in contrast to a matched group of PSEN1 E280A carriers without the APOE3 Ch variant, among whom the median age at the onset was 47 years (95% CI, 47 to 49). In two participants with the APOE3 Ch and PSEN1 E280A variants who underwent brain imaging, 18F-fluorodeoxyglucose positron-emission tomographic (PET) imaging showed relatively preserved metabolic activity in areas typically involved in Alzheimer's disease. In one of these participants, who underwent 18F-flortaucipir PET imaging, tau findings were limited as compared with persons with PSEN1 E280A in whom cognitive impairment occurred at the typical age in this kindred. Four studies of autopsy material obtained from persons with the APOE3 Ch and PSEN1 E280A variants showed fewer vascular amyloid pathologic features than were seen in material obtained from persons who had the PSEN1 E280A variant but not the APOE3 Ch variant.

CONCLUSIONS

Clinical data supported a delayed onset of cognitive impairment in persons who were heterozygous for the APOE3 Ch variant in a kindred with a high prevalence of autosomal dominant Alzheimer's disease. (Funded by Good Ventures and others.).

Presenilin Deficiency Results in Cellular Cholesterol Accumulation by Impairment of Protein Glycosylation and NPC1 Function

Presenilin proteins (PS1 and PS2) represent the catalytic subunit of γ-secretase and play a critical role in the generation of the amyloid β (Aβ) peptide and the pathogenesis of Alzheimer disease (AD). However, PS proteins also exert multiple functions beyond Aβ generation. In this study, we examine the individual roles of PS1 and PS2 in cellular cholesterol metabolism. Deletion of PS1 or PS2 in mouse models led to cholesterol accumulation in cerebral neurons. Cholesterol accumulation was also observed in the lysosomes of embryonic fibroblasts from Psen1-knockout (PS1-KO) and Psen2-KO (PS2-KO) mice and was associated with decreased expression of the Niemann-Pick type C1 (NPC1) protein involved in intracellular cholesterol transport in late endosomal/lysosomal compartments. Mass spectrometry and complementary biochemical analyses also revealed abnormal N-glycosylation of NPC1 and several other membrane proteins in PS1-KO and PS2-KO cells. Interestingly, pharmacological inhibition of N-glycosylation resulted in intracellular cholesterol accumulation prominently in lysosomes and decreased NPC1, thereby resembling the changes in PS1-KO and PS2-KO cells. In turn, treatment of PS1-KO and PS2-KO mouse embryonic fibroblasts (MEFs) with the chaperone inducer arimoclomol partially normalized NPC1 expression and rescued lysosomal cholesterol accumulation. Additionally, the intracellular cholesterol accumulation in PS1-KO and PS2-KO MEFs was prevented by overexpression of NPC1. Collectively, these data indicate that a loss of PS function results in impaired protein N-glycosylation, which eventually causes decreased expression of NPC1 and intracellular cholesterol accumulation. This mechanism could contribute to the neurodegeneration observed in PS KO mice and potentially to the pathogenesis of AD.