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BackgroundBridging Integrator 1 (BIN1) is the second most important Alzheimer’s disease (AD) risk gene, but its physiological roles in neurons and its contribution to brain pathology remain largely elusive. In this work, we show that BIN1 plays a critical role in the regulation of calcium homeostasis, electrical activity, and gene expression of glutamatergic neurons.MethodsWe generated 3D cerebral organoids and 2D enriched neuronal cell cultures from isogenicBIN1wild-type (WT), heterozygous (HET) and homozygous knockout (KO) human-induced pluripotent stem cells (hiPSCs). Using single-cell RNA-sequencing, biochemical assays, immunocytochemistry and multi-electrode array(MEA) electrophysiology, we characterized the molecular and functional consequences of reduced BIN1 expression in different neural cell types.ResultsWe show thatBIN1is mainly expressed by oligodendrocytes and glutamatergic neurons of cerebral organoids, like in the human brain. BothBIN1HET and KO cerebral organoids show specific transcriptional alterations, mainly associated with ion transport and synapses in glutamatergic neurons. We then demonstrate thatBIN1cell-autonomously regulates gene expression in glutamatergic neurons by using a novel protocol to generate pure culture of human-derived induced neurons (hiNs). Using this system, we also show that BIN1 plays a key role in the regulation of neuronal calcium transients and electrical activity via its interaction with the L-type voltage-gated calcium channel Cav1.2.BIN1KO hiNs show reduced activity-dependent internalization and higher Cav1.2expression compared to WT hiNs. Pharmacological treatment with clinically relevant doses of nifedipine, a calcium channel blocker, partly rescues neuronal electrical and gene expression alterations inBIN1KO glutamatergic neurons. Further, we show that transcriptional alterations inBIN1KO hiNs affecting biological processes related to calcium homeostasis are also present in glutamatergic neurons of the human brain at late stages of AD pathology.ConclusionsTogether, our findings suggest that BIN1-dependent alterations in neuronal properties could contribute to AD pathophysiology and that treatment with low doses of clinically approved calcium blockers should be considered as an option to dampen disease onset and progression.

BackgroundGenetic variants within the APOE locus may modulate Alzheimer’s disease (AD) risk independently or in conjunction with APOE*2/3/4 genotypes. Identifying such variants and mechanisms would importantly advance our understanding of APOE pathophysiology and provide critical guidance for AD therapies aimed at APOE. The APOE locus however remains relatively poorly understood in AD, owing to multiple challenges that include its complex linkage structure and uncertainty in APOE*2/3/4 genotype quality. Here, we present a novel APOE*2/3/4 filtering approach and showcase its relevance on AD risk association analyses for the rs439401 variant, which is located 1,801 base pairs downstream of APOE and has been associated with a potential regulatory effect on APOE.MethodsWe used thirty-two AD-related cohorts, with genetic data from various high-density single- nucleotide polymorphism microarrays, whole-genome sequencing, and whole-exome sequencing. Study participants were filtered to be ages 60 and older, non-Hispanic, of European ancestry, and diagnosed as cognitively normal or AD (n=65,701). Primary analyses investigated AD risk in APOE*4/4 carriers. Additional supporting analyses were performed in APOE*3/4 and 3/3 strata. Outcomes were compared under two different APOE*2/3/4 filtering approachesResultsUsing more conventional APOE*2/3/4 filtering criteria (approach 1), we showed that, when in- phase with APOE*4, rs439401 was variably associated with protective effects on AD case-control status. However, when applying a novel filter that increases certainty of the APOE*2/3/4 genotypes by applying more stringent criteria for concordance between the provided APOE genotype and imputed APOE genotype (approach 2), we observed that all significant effects were lost.ConclusionsWe showed that careful consideration of APOE genotype and appropriate sample filtering were crucial to robustly interrogate the role of the APOE locus on AD risk. Our study presents a novel APOE filtering approach and provides important guidelines for research into the APOE locus, as well as for elucidating genetic interaction effects with APOE*2/3/4.

A comprehensive understanding of the pathological mechanisms involved at different stages of neurodegenerative diseases is key for the advance of preventive and disease-modifying treatments. Gene expression alterations in the diseased brain is a potential source of information about biological processes affected by pathology. In this work, we performed a systematic comparison of gene expression alterations in the brains of human patients diagnosed with Alzheimer’s disease (AD) or Progressive Supranuclear Palsy (PSP) and animal models of amyloidopathy and tauopathy. Using a systems biology approach to uncover biological processes associated with gene expression alterations, we could pinpoint processes more strongly associated with tauopathy/PSP and amyloidopathy/AD. We show that gene expression alterations related to immune-inflammatory responses preponderate in younger, whereas those associated to synaptic transmission are mainly observed in older AD patients. In PSP, however, changes associated with immune-inflammatory responses and synaptic transmission overlap. These two different patterns observed in AD and PSP brains are fairly recapitulated in animal models of amyloidopathy and tauopathy, respectively. Moreover, in AD, but not PSP or animal models, gene expression alterations related to RNA splicing are highly prevalent, whereas those associated with myelination are enriched both in AD and PSP, but not in animal models. Finally, we identify 12 AD and 4 PSP genetic risk factors in cell-type specific co-expression modules, thus contributing to unveil the possible role of these genes to pathogenesis. Altogether, this work contributes to unravel the potential biological processes affected by amyloid versus tau pathology and how they could contribute to the pathogenesis of AD and PSP.

Genome-wide association studies (GWAS) have identified more than 75 genetic risk loci for Alzheimer’s Disease (AD), however for a substantial portion of these loci the genetic variants or genes directly involved in AD risk remain to be found. A GWAS locus defined by the index SNP rs1476679 inZCWPW1is one of the largest AD loci as the association signal spans 56 potential risk genes. The three most compelling candidate genes in this locus areZCWPW1, PILRAandPILRB, based on genetic, transcriptomic, and proteomic evidence. We performed amplicon-based target enrichment and next-generation sequencing of the exons, exon-intron boundaries, and UTRs ofZCWPW1, PILRAandPILRBon an Illumina MiSeq platform in 1048 Flanders-Belgian late-onset AD patients and 1037 matched healthy controls. Along with the single-marker association testing, the combined effect of Sanger-validated rare variants was evaluated in SKAT-O. No common variants (n= 40) were associated with AD. We identified 20 validated deleterious rare variants (MAF < 1%, CADD score ≥ 20), 14 of which inZCWPW1. This included 4 predicted loss-of-function (LoF) mutations that were exclusively found in patients (P= 0.011). Haplotype sharing analysis revealed distant common ancestors for two LoF mutations. Single-molecule long-read Nanopore sequencing analysis unveiled that all LoF mutations are phased with the risk haplotype in the locus. Our results support the recent report for the role of ultra-rare LoFZCWPW1variants in AD and suggest a potential risk mechanism for AD throughZCWPW1haploinsufficiency.

SUMMARYThe Bridging Integrator 1 (BIN1) gene is a major susceptibility gene for Alzheimer’s disease (AD). Deciphering its pathophysiological role is challenging due to its numerous isoforms. Here we observed in Drosophila that human BIN1 isoform1 (BIN1iso1) overexpression, contrary to BIN1iso8 and BIN1iso9, induced an accumulation of endosomal vesicles and neurodegeneration. Systematic search for endosome regulators able to prevent BIN1iso1-induced neurodegeneration indicated that a defect at the early endosome level is responsible for the neurodegeneration. In human induced neurons (hiNs) and cerebral organoids, BIN1 knock-out resulted in the narrowing of early endosomes. This phenotype was rescued by BIN1iso1 but not BIN1iso9 expression. Finally, BIN1iso1 overexpression also led to an increase in the size of early endosomes and neurodegeneration in hiNs. Altogether, our data demonstrate that the AD susceptibility gene BIN1, and especially BIN1iso1, contributes to early-endosome size deregulation, which is an early pathophysiological hallmark of AD pathology.

Risk for late-onset Alzheimer’s disease (LOAD) is driven by multiple loci primarily identified by genome-wide association studies, many of which are common variants with minor allele frequencies (MAF)> 0.01. To identify additional common and rare LOAD risk variants, we performed a GWAS on 25,170 LOAD subjects and 41,052 cognitively normal controls in 44 datasets from the International Genomics of Alzheimer’s Project (IGAP). Existing genotype data was imputed using the dense, high-resolution Haplotype Reference Consortium (HRC) r1.1 reference panel. Stage 1 associations of P−5 were meta-analyzed with the European Alzheimer’s Disease Biobank (EADB) (n=20,301 cases; 21,839 controls) (stage 2 combined IGAP and EADB). An expanded meta-analysis was performed using a GWAS of parental AD/dementia history in the UK Biobank (UKBB) (n=35,214 cases; 180,791 controls) (stage 3 combined IGAP, EADB, and UKBB). Common variant (MAF≥0.01) associations were identified for 29 loci in stage 2, including novel genome-wide significant associations at TSPAN14 (P=2.33×10−12), SHARPIN (P=1.56×10−9), and ATF5/SIGLEC11 (P=1.03×10−8), and newly significant associations without using AD proxy cases in MTSS1L/IL34 (P=1.80×10−8), APH1B (P=2.10×10−13), and CLNK (P=2.24×10−10). Rare variant (MAFAPOE and TREM2, and a novel association of a rare variant (rs143080277; MAF=0.0054; P=2.69×10−9) in NCK2, further strengthened with the inclusion of UKBB data in stage 3 (P=7.17×10−13). Single-nucleus sequence data shows that NCK2 is highly expressed in amyloid-responsive microglial cells, suggesting a role in LOAD pathology.

Toxoplasma gondiiis a eukaryotic parasite that forms latent cysts in the brain of immunocompetent individuals. The latent parasite infection of the immune-privileged central nervous system is linked to most complications. With no drug currently available to eliminate the latent cysts in the brain of infected hosts, the consequences of neurons’ long-term infection are unknown. It has long been known thatT. gondiispecifically differentiates into a latent form (bradyzoite) in neurons, but how the infected neuron responds to the infection remains to be elucidated. We have established a newin vitromodel resulting in the production of mature bradyzoite cysts in brain cells. Using dual, host and parasite RNA-seq, we characterized the dynamics of differentiation of the parasite, revealing the involvement of key pathways in this process. Moreover, we identified how the infected brain cells responded to the parasite infection revealing the drastic changes that take place. We showed that neuronal-specific pathways are strongly affected, with synapse signaling being particularly affected, especially glutamatergic synapse signaling. The establishment of this newin vitromodel allows investigating both the dynamics of parasite differentiation and the specific response of neurons to the long-term infection by this parasite.

SUMMARYThe endoplasmic reticulum (ER) is a central eukaryotic organelle with a tubular network made of hairpin proteins linked by hydrolysis of GTP nucleotides. Among post-translational modifications initiated at the ER level, glycosylation is the most common reaction. However, our understanding of the impact of glycosylation on ER structure remains unclear. Here, we show that Exostosin-1 (EXT1) glycosyltransferase, an enzyme involved inN-glycosylation, is a key regulator of ER morphology and dynamics. We have integrated multi-omics data and super-resolution imaging to characterize the broad effect of EXT1 inactivation, including ER shape-dynamics-function relationships in mammalian cells. We have observed that, inactivating EXT1 induces cell enlargement and enhances metabolic switches such as protein secretion. In particular, suppressing EXT1 in mouse thymocytes causes developmental dysfunctions associated to ER network extension. Our findings suggest that EXT1 drives glycosylation reactions involving ER structural proteins and high-energy nucleotide sugars, which might also apply to other organelles.

Mammalian prions are lethal pathogens composed of fibrillar assemblies of misfolded prion protein. Human prion diseases are rare and usually rapidly fatal neurodegenerative disorders, the most common being sporadic Creutzfeldt-Jakob disease (sCJD). Variants in the gene that encodes prion protein (PRNP) are strong risk factors for sCJD, but although the condition has heritability similar to other neurodegenerative disorders, no other risk loci have yet been confirmed. By genome-wide association in European ancestry populations, we found three replicated loci (cases n=5208, within PRNP, STX6, and GAL3ST1) and two further unreplicated loci were significant in gene-wide tests (within PDIA4, BMERB1). Exome sequencing in 407 sCJD cases, conditional and transcription analyses suggest that associations at PRNP and GAL3ST1 are likely to be caused by common variants that alter the protein sequence, whereas risk variants in STX6 and PDIA4 associate with increased expression of the major transcripts in disease-relevant brain regions. Alteration of STX6 expression does not modify prion propagation in a neuroblastoma cell model of mouse prion infection. We went on to analyse the proteins histologically in diseased tissue and examine the effects of risk variants on clinical phenotypes using deep longitudinal clinical cohort data. Risk SNPs in STX6, a protein involved in the intracellular trafficking of proteins and vesicles, are shared with progressive supranuclear palsy, a neurodegenerative disease associated with the misfolded protein tau. We present the first evidence of statistically robust associations in sporadic human prion disease that implicate intracellular trafficking and sphingolipid metabolism.

Alzheimers disease (AD) is the leading cause of dementia in aging individuals. However pathophysiological processes involved in the brain are still poorly understood. Among numerous strategies, a comprehensive overview of gene expression alterations in the diseased brain has been proposed to help for a better knowledge of the disease processes. In this work, we compared the differential expression of genes in different regions (temporal and frontal lobes) of the brain of healthy and AD adult subjects using data from three large studies: MAYO Clinic; Mount Sinai Brain Bank (MSBB) and ROSMAP. We show that gene expression is dramatically altered in the temporal lobe (TL), but not in the frontal lobe (FL), suggesting regional specificities in transcriptional alterations. Moreover, we show that a large set of genes undetected in the classical differential expression (DEG) analysis show alterations in the transcript usage ratio in AD, i.e. differential isoform fractions. Interestingly, the number of genes with differential transcript usage (gDTUs) is highest at advanced Braak stages and correlates with altered expression of genes associated with the splicing machinery. Using single-cell RNA sequencing (scRNAseq) data, we further assigned DEGs and gDTUs to individual cell types of the adult brain and observed similar signatures per cell type as to other two scRNAseq studies in AD. Lastly, we show that 52 out of 116 genes located in the loci associated with AD risk and expressed in the adult human brain present DEG and/or gDTUs in the TL, whereas only 13 are altered in the FL of AD patients. Among those altered genes, we detect an increased expression of APP isoforms containing the Kunitz protease inhibitor (KPI) domain, which is associated with plaque deposition. Altogether, our work proposes a novel integrative strategy to analyze transcriptional data in AD based on both gene/transcript expression and cell-type specificities.

Recent meta-analyses of genome-wide association studies identified a number of genetic risk factors of Alzheimer’s disease; however, little is known about the mechanisms by which they contribute to the pathological process. As synapse loss is observed at the earliest stage of Alzheimer’s disease, deciphering the impact of Alzheimer’s risk genes on synapse formation and maintenance is of great interest. In this paper, we report a microfluidic co-culture device that physically isolates synapses from pre- and postsynaptic neurons and chronically exposes them to toxic amyloid-beta (Aβ) peptides secreted by model cell lines overexpressing wild-type or mutated (V717I) amyloid precursor protein (APP). Co-culture with cells overexpressing mutated APP exposed the synapses of primary hippocampal neurons to Aβ1-42 molecules at nanomolar concentrations and induced a significant decrease in synaptic connectivity, as evidenced by distance-based assignment of postsynaptic puncta to presynaptic puncta. Treating the cells with antibodies that target different forms of Aβ suggested that low molecular weight oligomers are the likely culprit. As proof of concept, we demonstrate that overexpression of protein tyrosine kinase 2 beta (Pyk2) –an Alzheimer’s disease genetic risk factor involved in synaptic plasticity and shown to decrease in Alzheimer’s disease brains at gene expression and protein levels–selectively in postsynaptic neurons is protective against Aβ1-42-induced synaptotoxicity. In summary, our lab-on-a-chip device provides a physiologically-relevant model of Alzheimer’s disease-related synaptotoxicity, optimal for assessing the impact of risk genes in pre- and postsynaptic compartments.

BACKGROUNDDisentangling the genetic constellation underlying Alzheimer’s disease (AD) is important. Doing so allows us to identify biological pathways underlying AD, point towards novel drug targets and use the variants for individualised risk predictions in disease modifying or prevention trials. In the present work we report on the largest genome-wide association study (GWAS) for AD risk to date and show the combined utility of proven AD loci for precision medicine using polygenic risk scores (PRS).METHODSThree sets of summary statistics were included in our meta-GWAS of AD: an Spanish case-control study (GR@ACE/DEGESCO study, n = 12,386), the case-control study of International Genomics of Alzheimer project (IGAP, n = 82,771) and the UK Biobank (UKB) AD-by-proxy case-control study (n=314,278). Using these resources, we performed a fixed-effects inverse-variance-weighted meta-analysis. Detected loci were confirmed in a replication study of 19,089 AD cases and 39,101 controls from 16 European-ancestry cohorts not previously used. We constructed a weighted PRS based on the 39 AD variants. PRS were generated by multiplying the genotype dosage of each risk allele for each variant by its respective weight, and then summing across all variants. We first validated it for AD in independent data (assessing effects of sub-threshold signal, diagnostic certainty, age at onset and sex) and tested its effect on risk (odds for disease) and age at onset in the GR@ACE/DEGESCO study.FINDINGSUsing our meta-GWAS approach and follow-up analysis, we identified novel genome-wide significant associations of six genetic variants with AD risk (rs72835061-CHRNE, rs2154481-APP, rs876461-PRKD3/NDUFAF7, rs3935877-PLCG2 and two missense variants: rs34173062/rs34674752 in SHARPIN gene) and confirmed a stop codon mutation in the IL34 gene increasing the risk of AD (IL34-Tyr213Ter), and two other variants in PLCG2 and HS3ST1 regions. This brings the total number of genetic variants associated with AD to 39 (excluding APOE). The PRS based on these variants was associated with AD in an independent clinical AD-case control dataset (OR=1.30, per 1-SD increase in the PRS, 95%CI 1.18-1.44, p = 1.1×10−7), a similar effect to that in the GR@ACE/DEGESCO (OR=1.27, 95%CI 1.23-1.32, p = 7.4×10−39). We then explored the combined effects of these 39 variants in a PRS for AD risk and age-at-onset stratification in GR@ACE/DEGESCO. Excluding APOE, we observed a gradual risk increase over the 2% tiles; when comparing the extremes, those with the 2% highest risk had a 2.98-fold (95% CI 2.12–4.18, p = 3.2×10−10) increased risk compared to those with the 2% lowest risk (p = 5.9×10−10). Using the PRS we identified APOE ε33 carriers with a similar risk as APOE ε4 heterozygotes carriers, as well as APOE ε4 heterozygote carriers with a similar risk as APOE ε4 homozygote. Considering age at onset; there was a 9-year difference between median onset of AD the lowest risk group and the highest risk group (82 vs 73 years; p = 1.6×10−6); a 4-year median onset difference (81 vs 77 years; p = 6.9×10−5) within APOE ε4 heterozygotes and a 5.5-year median onset difference (78.5 vs 73 years; p = 4.6×10−5) within APOE ε4 carriers.INTERPRETATIONWe identified six novel genetic variants associated with AD-risk, among which one common APP variant. A PRS of all genetic loci reported to date could be a robust tool to predict the risk and age at onset of AD, beyond APOE alone. These properties make PRS instrumental in selecting individuals at risk in order to apply preventative strategies and might have potential use in diagnostic work-up.

The bridging integrator 1 gene (BIN1) is a major genetic risk factor for Alzheimer’s disease (AD). In this report, we investigated how BIN1-dependent pathophysiological processes might be associated with Tau. We first generated a cohort of control and transgenic mice either overexpressing human MAPT (TgMAPT) or both human MAPT and BIN1 (TgMAPT;TgBIN1), which we followed-up from 3 to 15 months. In TgMAPT;TgBIN1 mice short-term memory deficits appeared earlier than in TgMAPT mice; however – unlike TgMAPT mice – TgMAPT;TgBIN1 mice did not exhibit any long-term or spatial memory deficits for at least 15 months. After sacrifice of the cohort at 18 months, immunohistochemistry revealed that BIN1 overexpression prevents both Tau mislocalization and somatic inclusion in the hippocampus, where an increase in BIN1-Tau interaction was also observed. We then sought mechanisms controlling the BIN1-Tau interaction. We developed a high-content screening approach to characterize modulators of the BIN1-Tau interaction in an agnostic way (1,126 compounds targeting multiple pathways), and we identified – among others – an inhibitor of Calcineurin, a Ser/Thr phosphatase. We determined that Calcineurin dephosphorylates BIN1 on a Cyclin-dependent kinase phosphorylation site at T348, promoting the open conformation of the neuronal BIN1 isoform. Phosphorylation of this site increases the availability of the BIN1 SH3 domain for Tau interaction, as demonstrated by nuclear magnetic resonance experiments and in primary neurons. Finally, we observed that the levels of the neuronal BIN1 isoform were decreased in AD brains, whereas phospho-BIN1(T348):BIN1 ratio was increased, suggesting a compensatory mechanism. In conclusion, our data support the idea that BIN1 modulates the AD risk through an intricate regulation of its interaction with Tau. Alteration in BIN1 expression or activity may disrupt this regulatory balance with Tau and have direct effects on learning and memory.

INTRODUCTIONThere is increasing interest in plasma Aβ as an endophenotype and biomarker of Alzheimer’s disease (AD). Identifying the genetic determinants of plasma Aβ levels may elucidate important processes that determine plasma Aβ measures.METHODSWe included 12,369 non-demented participants derived from eight population-based studies. Imputed genetic data and plasma Aβ1-40, Aβ1-42 levels and Aβ1-42/Aβ1-40 ratio were used to perform genome-wide association studies, gene-based and pathway analyses. Significant variants and genes were followed-up for the association with PET Aβ deposition and AD risk.RESULTSSingle-variant analysis identified associations acrossAPOEfor Aβ1-42 and Aβ1-42/Aβ1-40 ratio, andBACE1for Aβ1-40. Gene-based analysis of Aβ1-40 additionally identified associations forAPP,PSEN2,CCKandZNF397. There was suggestive interaction between aBACE1variant andAPOEε4 on brain Aβ deposition.DISCUSSIONIdentification of variants near/in known major Aβ-processing genes strengthens the relevance of plasma-Aβ levels both as an endophenotype and a biomarker of AD.

A genome-wide survival analysis of 14,406 Alzheimer’s disease (AD) cases and 25,849 controls identified eight previously reported AD risk loci and fourteen novel loci associated with age at onset. LD score regression of 220 cell types implicated regulation of myeloid gene expression in AD risk. In particular, the minor allele of rs1057233 (G), within the previously reported CELF1 AD risk locus, showed association with delayed AD onset and lower expression of SPI1 in monocytes and macrophages. SPI1 encodes PU.1, a transcription factor critical for myeloid cell development and function. AD heritability is enriched within the PU.1 cistrome, implicating a myeloid PU.1 target gene network in AD. Finally, experimentally altered PU.1 levels affect the expression of mouse orthologs of many AD risk genes and the phagocytic activity of mouse microglial cells. Our results suggest that lower SPI1 expression reduces AD risk by regulating myeloid gene expression and cell function.