ABCA7 deficiency causes neuronal dysregulation by altering mitochondrial lipid metabolism.

ABCA7 loss-of-function variants are associated with increased risk of Alzheimer's disease (AD). Using ABCA7 knockout human iPSC models generated with CRISPR/Cas9, we investigated the impacts of ABCA7 deficiency on neuronal metabolism and function. Lipidomics revealed that mitochondria-related phospholipids, such as phosphatidylglycerol and cardiolipin were reduced in the ABCA7-deficient iPSC-derived cortical organoids. Consistently, ABCA7 deficiency-induced alterations of mitochondrial morphology accompanied by reduced ATP synthase activity and exacerbated oxidative damage in the organoids. Furthermore, ABCA7-deficient iPSC-derived neurons showed compromised mitochondrial respiration and excess ROS generation, as well as enlarged mitochondrial morphology compared to the isogenic controls. ABCA7 deficiency also decreased spontaneous synaptic firing and network formation in iPSC-derived neurons, in which the effects were rescued by supplementation with phosphatidylglycerol or NAD+ precursor, nicotinamide mononucleotide. Importantly, effects of ABCA7 deficiency on mitochondria morphology and synapses were recapitulated in synaptosomes isolated from the brain of neuron-specific Abca7 knockout mice. Together, our results provide evidence that ABCA7 loss-of-function contributes to AD risk by modulating mitochondria lipid metabolism.

Metabolome-wide association study on ABCA7 indicates a role of ceramide metabolism in Alzheimer's disease.

Genome-wide association studies (GWASs) have identified genetic loci associated with the risk of Alzheimer's disease (AD), but the molecular mechanisms by which they confer risk are largely unknown. We conducted a metabolome-wide association study (MWAS) of AD-associated loci from GWASs using untargeted metabolic profiling (metabolomics) by ultraperformance liquid chromatography-mass spectrometry (UPLC-MS). We identified an association of lactosylceramides (LacCer) with AD-related single-nucleotide polymorphisms (SNPs) in ABCA7 (P = 5.0 × 10-5 to 1.3 × 10-44). We showed that plasma LacCer concentrations are associated with cognitive performance and genetically modified levels of LacCer are associated with AD risk. We then showed that concentrations of sphingomyelins, ceramides, and hexosylceramides were altered in brain tissue from Abca7 knockout mice, compared with wild type (WT) (P = 0.049-1.4 × 10-5), but not in a mouse model of amyloidosis. Furthermore, activation of microglia increases intracellular concentrations of hexosylceramides in part through induction in the expression of sphingosine kinase, an enzyme with a high control coefficient for sphingolipid and ceramide synthesis. Our work suggests that the risk for AD arising from functional variations in ABCA7 is mediated at least in part through ceramides. Modulation of their metabolism or downstream signaling may offer new therapeutic opportunities for AD.

Relationships between PET and blood plasma biomarkers in corticobasal syndrome.

INTRODUCTION: Corticobasal syndrome (CBS) can result from underlying Alzheimer's disease (AD) pathologies. Little is known about the utility of blood plasma metrics to predict positron emission tomography (PET) biomarker-confirmed AD in CBS. METHODS: A cohort of eighteen CBS patients (8 amyloid beta [Aß]+; 10 Aß-) and 8 cognitively unimpaired (CU) individuals underwent PET imaging and plasma analysis. Plasma concentrations were compared using a Kruskal-Wallis test. Spearman correlations assessed relationships between plasma concentrations and PET uptake. RESULTS: CBS Aß+ group showed a reduced Aß42/40 ratio, with elevated phosphorylated tau (p-tau)181, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) concentrations, while CBS Aß- group only showed elevated NfL concentration compared to CU. Both p-tau181 and GFAP were able to differentiate CBS Aß- from CBS Aß+ and showed positive associations with Aß and tau PET uptake. DISCUSSION: This study supports use of plasma p-tau181 and GFAP to detect AD in CBS. NfL shows potential as a non-specific disease biomarker of CBS regardless of underlying pathology. HIGHLIGHTS: Plasma phosphorylated tau (p-tau)181 and glial fibrillary acidic protein (GFAP) concentrations differentiate corticobasal syndrome (CBS) amyloid beta (Aß)- from CBS Aß+. Plasma neurofilament light concentrations are elevated in CBS Aß- and Aß+ compared to controls. Plasma p-tau181 and GFAP concentrations were associated with Aß and tau positron emission tomography (PET) uptake. Aß42/40 ratio showed a negative correlation with Aß PET uptake.

ABCA7 haplodeficiency disturbs microglial immune responses in the mouse brain.

Carrying premature termination codons in 1 allele of the ABCA7 gene is associated with an increased risk for Alzheimer's disease (AD). While the primary function of ABCA7 is to regulate the transport of phospholipids and cholesterol, ABCA7 is also involved in maintaining homeostasis of the immune system. Since inflammatory pathways causatively or consequently participate in AD pathogenesis, we studied the effects of Abca7 haplodeficiency in mice on brain immune responses under acute and chronic conditions. When acute inflammation was induced through peripheral lipopolysaccharide injection in control or heterozygous Abca7 knockout mice, partial ABCA7 deficiency diminished proinflammatory responses by impairing CD14 expression in the brain. On breeding to AppNL-G-F knockin mice, we observed increased amyloid-ß (Aß) accumulation and abnormal endosomal morphology in microglia. Taken together, our results demonstrate that ABCA7 loss of function may contribute to AD pathogenesis by altering proper microglial responses to acute inflammatory challenges and during the development of amyloid pathology, providing insight into disease mechanisms and possible treatment strategies.

Apolipoprotein E regulates lipid metabolism and α-synuclein pathology in human iPSC-derived cerebral organoids.

APOE4 is a strong genetic risk factor for Alzheimer's disease and Dementia with Lewy bodies; however, how its expression impacts pathogenic pathways in a human-relevant system is not clear. Here using human iPSC-derived cerebral organoid models, we find that APOE deletion increases α-synuclein (αSyn) accumulation accompanied with synaptic loss, reduction of GBA levels, lipid droplet accumulation and dysregulation of intracellular organelles. These phenotypes are partially rescued by exogenous apoE2 and apoE3, but not apoE4. Lipidomics analysis detects the increased fatty acid utilization and cholesterol ester accumulation in apoE-deficient cerebral organoids. Furthermore, APOE4 cerebral organoids have increased αSyn accumulation compared to those with APOE3. Carrying APOE4 also increases apoE association with Lewy bodies in postmortem brains from patients with Lewy body disease. Our findings reveal the predominant role of apoE in lipid metabolism and αSyn pathology in iPSC-derived cerebral organoids, providing mechanistic insights into how APOE4 drives the risk for synucleinopathies.

ApoE (Apolipoprotein E) in Brain Pericytes Regulates Endothelial Function in an Isoform-Dependent Manner by Modulating Basement Membrane Components.

OBJECTIVE: The ε4 allele of the APOE gene (APOE4) is the strongest genetic risk factor for Alzheimer disease when compared with the common ε3 allele. Although there has been significant progress in understanding how apoE4 (apolipoprotein E4) drives amyloid pathology, its effects on amyloid-independent pathways, in particular cerebrovascular integrity and function, are less clear. Approach and Results: Here, we show that brain pericytes, the mural cells of the capillary walls, differentially modulate endothelial cell phenotype in an apoE isoform-dependent manner. Extracellular matrix protein induction, tube-like structure formation, and barrier formation were lower with endothelial cells cocultured with pericytes isolated from apoE4-targeted replacement (TR) mice compared with those from apoE3-TR mice. Importantly, aged apoE4-targeted replacement mice had decreased extracellular matrix protein expression and increased plasma protein leakages compared with apoE3-TR mice. CONCLUSIONS: ApoE4 impairs pericyte-mediated basement membrane formation, potentially contributing to the cerebrovascular effects of apoE4.

Dual-Modified Liposome for Targeted and Enhanced Gene Delivery into Mice Brain.

The development of neuropharmaceutical gene delivery systems requires strategies to obtain efficient and effective brain targeting as well as blood-brain barrier (BBB) permeability. A brain-targeted gene delivery system based on a transferrin (Tf) and cell-penetrating peptide (CPP) dual-functionalized liposome, CPP-Tf-liposome, was designed and investigated for crossing BBB and permeating into the brain. We selected three sequences of CPPs [melittin, Kaposi fibroblast growth factor (kFGF), and penetration accelerating sequence-R8] and compared their ability to internalize into the cells and, subsequently, improve the transfection efficiency. Study of intracellular uptake indicated that liposomal penetration into bEnd.3 cells, primary astrocytes, and primary neurons occurred through multiple endocytosis pathways and surface modification with Tf and CPP enhanced the transfection efficiency of the nanoparticles. A coculture in vitro BBB model reproducing the in vivo anatomophysiological complexity of the biologic barrier was developed to characterize the penetrating properties of these designed liposomes. The dual-functionalized liposomes effectively crossed the in vitro barrier model followed by transfecting primary neurons. Liposome tissue distribution in vivo indicated superior ability of kFGF-Tf-liposomes to overcome BBB and reach brain of the mice after single intravenous administration. These findings demonstrate the feasibility of using strategically designed liposomes by combining Tf receptor targeting with enhanced cell penetration as a potential brain gene delivery vector. SIGNIFICANCE STATEMENT: Rational synthesis of efficient brain-targeted gene carrier included modification of liposomes with a target-specific ligand, transferrin, and with cell-penetrating peptide to enhance cellular internalization. Our study used an in vitro triple coculture blood-brain barrier (BBB) model as a tool to characterize the permeability across BBB and functionality of designed liposomes prior to in vivo biodistribution studies. Our study demonstrated that rational design and characterization of BBB permeability are efficient strategies for development of brain-targeted gene carriers.

Nerve Growth Factor Gene Delivery across the Blood-Brain Barrier to Reduce Beta Amyloid Accumulation in AD Mice.

The therapeutic potential of the nerve growth factor (NGF) gene using brain-targeted liposomal nanoparticles was investigated for the treatment of Alzheimer's disease (AD). We designed brain-targeted gene delivery systems with prolonged systemic circulation and enhanced cellular penetration by conjugating the transferrin (Tf) ligand and the penetratin (Pen) peptide to liposomes via a 1, 2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) phospholipid. In vitro characterization studies showed that the nanoparticles had homogeneous particle size and positive zeta potential and were able to protect the plasmid DNA against enzymatic degradation. In vivo brain targeting efficiency of designed liposomes was mimicked using an in vitro triple coculture blood-brain barrier (BBB) model. Liposomal nanoparticles dual-modified with Tf and Pen encasing plasmid NGF efficiently crossed the in vitro BBB model and, subsequently, transfected the primary neuronal cells. Increasing NGF expression in primary neuronal cells following treatment with liposomes increased the levels of the presynaptic marker synaptophysin in vitro. A dose-response study in vivo was performed in order to select the appropriate dose of plasmid NGF to induce significant NGF expression and, consequently, a therapeutic effect. Administration of PenTf-liposomes containing pNGF to amyloid precursor protein (APP)/PS1 mice (aged 3 months) for 4 weeks (one injection per week) significantly decreased (p < 0.05) the levels of toxic soluble and insoluble Aß peptides as compared to those levels in untreated APP/PS1 mice. Additionally, the treatment stimulated cell proliferation and increased the levels of synaptic markers, synaptophysin and PSD-95. These data suggest the therapeutic potential of PenTf-liposome-mediated NGF gene therapy, and this system can be considered a candidate for the treatment of AD.

Selective loss of cortical endothelial tight junction proteins during Alzheimer's disease progression.

While the accumulation and aggregation of amyloid-ß and tau are central events in the pathogenesis of Alzheimer's disease, there is increasing evidence that cerebrovascular pathology is also abundant in Alzheimer's disease brains. In brain capillaries, endothelial cells are connected closely with one another through transmembrane tight junction proteins forming the blood-brain barrier. Because the blood-brain barrier tightly regulates the exchange of molecules between brain and blood and maintains brain homeostasis, its impairment is increasingly recognized as a critical factor contributing to Alzheimer's disease pathogenesis. However, the pathological relationship between blood-brain barrier properties and Alzheimer's disease progression in the human brain is not fully understood. In this study, we show that the loss of cortical tight junction proteins is a common event in Alzheimer's disease, and is correlated with synaptic degeneration. By quantifying the amounts of major tight junction proteins, claudin-5 and occludin, in 12 brain regions dissected from post-mortem brains of normal ageing (n = 10), pathological ageing (n = 14) and Alzheimer's disease patients (n = 19), we found that they were selectively decreased in cortical areas in Alzheimer's disease. Cortical tight junction proteins were decreased in association with the Braak neurofibrillary tangle stage. There was also a negative correlation between the amount of tight junction proteins and the amounts of insoluble Alzheimer's disease-related proteins, in particular amyloid-ß40, in cortical areas. In addition, the amount of tight junction proteins in these areas correlated positively with those of synaptic markers. Thus, loss of cortical tight junction proteins in Alzheimer's disease is associated with insoluble amyloid-ß40 and loss of synaptic markers. Importantly, the positive correlation between claudin-5 and synaptic markers, in particular synaptophysin, was present independent of insoluble amyloid-ß40, amyloid-ß42 and tau values, suggesting that loss of cortical tight junction proteins and synaptic degeneration is present, at least in part, independent of insoluble Alzheimer's disease-related proteins. Collectively, these results indicate that loss of tight junction proteins occurs predominantly in the neocortex during Alzheimer's disease progression. Further, our findings provide a neuropathological clue as to how endothelial tight junction pathology may contribute to Alzheimer's disease pathogenesis in both synergistic and additive manners to typical amyloid-ß and tau pathologies.

In vitro and in vivo characterization of CPP and transferrin modified liposomes encapsulating pDNA.

The limitations imposed on brain therapy by the blood-brain barrier (BBB) have warranted the development of carriers that can overcome and deliver therapeutic agents into the brain. We strategically designed liposomal nanoparticles encasing plasmid DNA for efficient transfection and translocation across the in vitro BBB model as well as in vivo brain-targeted delivery. Liposomes were surface modified with two ligands, cell-penetrating peptide (PFVYLI or R9F2) for enhanced internalization into cells and transferrin (Tf) ligand for targeting transferrin-receptor expressed on brain capillary endothelial cells. Dual-modified liposomes encapsulating pDNA demonstrated significantly (P < 0.05) higher in vitro transfection efficiency compared to single-modified nanoparticles. R9F2Tf-liposomes showed superior ability to cross in vitro BBB and, subsequently, transfect primary neurons. Additionally, these nanoparticles crossed in vivo BBB and reached brain parenchyma of mice (6.6%) without causing tissue damage. Transferrin receptor-targeting with enhanced cell penetration is a relevant strategy for efficient brain-targeted delivery of genes.

Tau and apolipoprotein E modulate cerebrovascular tight junction integrity independent of cerebral amyloid angiopathy in Alzheimer's disease.

INTRODUCTION: Cerebrovascular pathologies including cerebral amyloid angiopathy (CAA) and blood-brain barrier (BBB) dysregulation are prominent features in the majority of Alzheimer's disease (AD) cases. METHODS: We performed neuropathologic and biochemical studies on a large, neuropathologically confirmed human AD cohort (N = 469). Amounts of endothelial tight junction proteins claudin-5 (CLDN5) and occludin (OCLN), and major AD-related molecules (amyloid beta [Aß40], Aß42, tau, p-tau, and apolipoprotein E) in the temporal cortex were assessed by ELISA. RESULTS: Higher levels of soluble tau, insoluble p-tau, and apolipoprotein E (apoE) were independently correlated with lower levels of endothelial tight junction proteins CLDN5 and OCLN in AD brains. Although high Aß40 levels, APOE ε4, and male sex were predominantly associated with exacerbated CAA severity, those factors did not influence tight junction protein levels. DISCUSSION: Refining the molecular mechanisms connecting tau, Aß, and apoE with cerebrovascular pathologies is critical for greater understanding of AD pathogenesis and establishing effective therapeutic interventions for the disease.

Elevated Neutrophil-Lymphocyte Ratio is Predictive of Poor Outcomes Following Aneurysmal Subarachnoid Hemorrhage.

Background Recent studies of patients with intracerebral hemorrhage suggest an association between peripheral blood neutrophil-lymphocyte ratio and neurologic deterioration. We aimed to study the prognostic utility of neutrophil-lymphocyte ratio in predicting inpatient mortality in aneurysmal subarachnoid hemorrhage. Methods We conducted a retrospective electronic medical record review of the clinical, laboratory, and radiographic data of patients with aneurysmal subarachnoid hemorrhage 18 years of age or older presenting to the neuroscience intensive care unit from January 1, 2011, to December 31, 2017. Patients with aneurysmal subarachnoid hemorrhage were divided into 2 groups (group 1, alive at discharge; group 2, deceased prior to discharge), and neutrophil-lymphocyte ratio laboratory mean values were recorded for each patient. Our primary outcome measure was inpatient mortality, and our secondary measure was incidence of pneumonia with hospitalization. Results We identified 403 patients with aneurysmal subarachnoid hemorrhage for the study. After exclusion criteria, 44 eligible patients were divided into the 2 groups (group 1, n = 32; group 2, n = 12). Mean neutrophil-lymphocyte ratio for group 1 was 11.53, and for group 2, 17.85 (P < .01). The mean neutrophil-lymphocyte ratio of those who developed pneumonia compared to those who did not was 15.28 versus 12.81, respectively (P = .39). A Kaplan-Meier plot demonstrated increased mortality among patients with a neutrophil-lymphocyte ratio equal to or greater than 12.5 compared to those with a neutrophil-lymphocyte ratio less than 12.5. Conclusions These preliminary data demonstrate that a neutrophil-lymphocyte ratio equal to or greater than 12.5 at admission predict higher inpatient mortality in patients with aneurysmal subarachnoid hemorrhage.

APOE ε4/ε4 diminishes neurotrophic function of human iPSC-derived astrocytes.

The ε4 allele of the APOE gene encoding apolipoprotein E (apoE) is a strong genetic risk factor for aging-related cognitive decline as well as late-onset Alzheimer's disease (AD) compared to the common ε3 allele. In the central nervous system, apoE is produced primarily by astrocytes and functions in transporting lipids including cholesterol to support neuronal homeostasis and synaptic integrity. Although mouse models and corresponding primary cells have provided valuable tools for studying apoE isoform-dependent functions, recent studies have shown that human astrocytes have a distinct gene expression profile compare with rodent astrocytes. Human induced pluripotent stem cells (iPSCs) derived from individuals carrying specific gene variants or mutations provide an alternative cellular model more relevant to humans upon differentiation into specific cell types. Thus, we reprogramed human skin fibroblasts from cognitively normal individuals carrying APOE ε3/ε3 or ε4/ε4 genotype to iPSC clones and further differentiated them into neural progenitor cells and then astrocytes. We found that human iPSC-derived astrocytes secreted abundant apoE with apoE4 lipoprotein particles less lipidated compared to apoE3 particles. More importantly, human iPSC-derived astrocytes were capable of promoting neuronal survival and synaptogenesis when co-cultured with iPSC-derived neurons with APOE ε4/ε4 astrocytes less effective in supporting these neurotrophic functions than those with APOE ε3/ε3 genotype. Taken together, our findings demonstrate APOE genotype-dependent effects using human iPSC-derived astrocytes and provide novel evidence that the human iPSC-based model system is a strong tool to explore how apoE isoforms contribute to neurodegenerative diseases.

ApoE-2 Brain-Targeted Gene Therapy Through Transferrin and Penetratin Tagged Liposomal Nanoparticles.

PURPOSE: Apolipoprotein E2 (ApoE2) gene therapy is a potential disease-modifying therapy for Alzheimer's disease (AD). We investigated the potential of plasmid encoding ApoE2 loaded brain-targeted functionalized-liposomes for treatment of AD. This was achieved via systemic administration of liposomes entrapping therapeutic gene targeting the brain of mice. METHODS: Targeting and transfection efficiency of designed liposomes were determined in bEnd.3, primary glial and primary neuronal cells. The ability of liposomal formulations to translocate across in vitro blood-brain barrier (BBB) and, thereafter, transfect primary neuronal cells was investigated using in vitro triple co-culture BBB model. We quantified ApoE expression in the brain of mice after single intravenous injection of brain-targeted liposomes loaded with plasmid ApoE2. RESULTS: Dual surface modification enhanced the in vitro transfection efficiency of designed liposomes. Successful delivery of therapeutic gene overcoming BBB by Transferrin-Penetratin- modified liposomes was demonstrated both in vitro and in vivo. Significant (p < 0.05) increase in ApoE levels in the brain of mice was observed after intravenous administration of Tf-Pen-liposomes encasing plasmid ApoE2. CONCLUSION: The results indicate that dual-ligand based liposomal gene delivery systems had both enhanced brain targeting and gene delivery efficiencies. Transferrin-Penetratin modified liposomes for delivery of plasmid ApoE2 has great potential for AD treatment.

5-HT3 Antagonist Ondansetron Increases apoE Secretion by Modulating the LXR-ABCA1 Pathway.

Apolipoprotein E (apoE) is linked to the risk for Alzheimer's disease (AD) and thus has been suggested to be an important therapeutic target. In our drug screening effort, we identified Ondansetron (OS), an FDA-approved 5-HT3 antagonist, as an apoE-modulating drug. OS at low micromolar concentrations significantly increased apoE secretion from immortalized astrocytes and primary astrocytes derived from apoE3 and apoE4-targeted replacement mice without generating cellular toxicity. Other 5-HT3 antagonists also had similar effects as OS, though their effects were milder and required higher concentrations. Antagonists for other 5-HT receptors did not increase apoE secretion. OS also increased mRNA and protein levels of the ATB-binding cassette protein A1 (ABCA1), which is involved in lipidation and secretion of apoE. Accordingly, OS increased high molecular weight apoE. Moreover, the liver X receptor (LXR) and ABCA1 antagonists blocked the OS-induced increase of apoE secretion, indicating that the LXR-ABCA1 pathway is involved in the OS-mediated facilitation of apoE secretion from astrocytes. The effects of OS on apoE and ABCA1 were also observed in human astrocytes derived from induced pluripotent stem cells (iPSC) carrying the APOE ε3/ε3 and APOE ε4/ε4 genotypes. Oral administration of OS at clinically-relevant doses affected apoE levels in the liver, though the effects in the brain were not observed. Collectively, though further studies are needed to probe its effects in vivo, OS could be a potential therapeutic drug for AD by modulating poE metabolism through the LXR-ABCA1 pathway.

Astrocytic LRP1 Mediates Brain Aß Clearance and Impacts Amyloid Deposition.

Accumulation and deposition of amyloid-ß (Aß) in the brain represent an early and perhaps necessary step in the pathogenesis of Alzheimer's disease (AD). Aß accumulation leads to the formation of Aß aggregates, which may directly and indirectly lead to eventual neurodegeneration. While Aß production is accelerated in many familial forms of early-onset AD, increasing evidence indicates that impaired clearance of Aß is more evident in late-onset AD. To uncover the mechanisms underlying impaired Aß clearance in AD, we examined the role of low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. Although LRP1 has been shown to play critical roles in brain Aß metabolism in neurons and vascular mural cells, its role in astrocytes, the most abundant cell type in the brain responsible for maintaining neuronal homeostasis, remains unclear. Here, we show that astrocytic LRP1 plays a critical role in brain Aß clearance. LRP1 knockdown in primary astrocytes resulted in decreased cellular Aß uptake and degradation. In addition, silencing of LRP1 in astrocytes led to downregulation of several major Aß-degrading enzymes, including matrix metalloproteases MMP2, MMP9, and insulin-degrading enzyme. More important, conditional knock-out of the Lrp1 gene in astrocytes in the background of APP/PS1 mice impaired brain Aß clearance, exacerbated Aß accumulation, and accelerated amyloid plaque deposition without affecting its production. Together, our results demonstrate that astrocytic LRP1 plays an important role in Aß metabolism and that restoring LRP1 expression and function in the brain could be an effective strategy to facilitate Aß clearance and counter amyloid pathology in AD.SIGNIFICANCE STATEMENT Astrocytes represent a major cell type regulating brain homeostasis; however, their roles in brain clearance of amyloid-ß (Aß) and underlying mechanism are not clear. In this study, we used both cellular models and conditional knock-out mouse models to address the role of a critical Aß receptor, the low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. We found that LRP1 in astrocytes plays a critical role in brain Aß clearance by modulating several Aß-degrading enzymes and cellular degradation pathways. Our results establish a critical role of astrocytic LRP1 in brain Aß clearance and shed light on specific Aß clearance pathways that may help to establish new targets for AD prevention and therapy.

Identification of plexin A4 as a novel clusterin receptor links two Alzheimer's disease risk genes.

Although abundant genetic and biochemical evidence strongly links Clusterin (CLU) to Alzheimer disease (AD) pathogenesis, the receptor for CLU within the adult brain is currently unknown. Using unbiased approaches, we identified Plexin A4 (PLXNA4) as a novel, high-affinity receptor for CLU in the adult brain. PLXNA4 protein expression was high in brain with much lower levels in peripheral organs. CLU protein levels were significantly elevated in the cerebrospinal fluid (CSF) of Plxna4-/- mice and, in humans, CSF levels of CLU were also associated with PLXNA4 genotype. Human AD brains had significantly increased the levels of CLU protein but decreased levels of PLXNA4 by ∼50%. To determine whether PLXNA4 levels influenced cognition, we analyzed the behaviour of Plxna4+/+, Plxna4+/-, and Plxna4-/- mice. In comparison to WT controls, both Plxna4+/- and Plxna4-/- mice were hyperactive in the open field assay while Plxna4-/- mice displayed a hyper-exploratory (low-anxiety phenotype) in the elevated plus maze. Importantly, both Plxna4+/- and Plxna4-/- mice displayed prominent deficits in learning and memory in the contextual fear-conditioning paradigm. Thus, even a 50% reduction in the level of PLXNA4 is sufficient to cause memory impairments, raising the possibility that memory problems seen in AD patients could be due to reductions in the level of PLXNA4. Both CLU and PLXNA4 have been genetically associated with AD risk and our data thus provide a direct relationship between two AD risk genes. Our data suggest that increasing the levels of PLXNA4 or targeting CLU-PLXNA4 interactions may have therapeutic value in AD.

Multiple system atrophy and apolipoprotein E.

BACKGROUND: Dysregulation of the specialized lipid metabolism involved in myelin synthesis and maintenance by oligodendrocytes has been associated with the unique neuropathology of MSA. We hypothesized that apolipoprotein E, which is associated with neurodegeneration, may also play a role in the pathogenesis of MSA. OBJECTIVE: This study evaluated genetic associations of Apolipoprotein E alleles with risk of MSA and α-synuclein pathology, and also examined whether apolipoprotein E isoforms differentially affect α-synuclein uptake in a oligodendrocyte cell. METHODS: One hundred sixty-eight pathologically confirmed MSA patients, 89 clinically diagnosed MSA patients, and 1,277 control subjects were genotyped for Apolipoprotein E. Human oligodendrocyte cell lines were incubated with α-synuclein and recombinant human apolipoprotein E, with internalized α-synuclein imaged by confocal microscopy and cells analyzed by flow cytometry. RESULTS: No significant association with risk of MSA or was observed for either Apolipoprotein E ɛ2 or ɛ4. α-Synuclein burden was also not associated with Apolipoprotein E alleles in the pathologically confirmed patients. Interestingly, in our cell assays, apolipoprotein E ɛ4 significantly reduced α-synuclein uptake in the oligodendrocytic cell line. CONCLUSIONS: Despite differential effects of apolipoprotein E isoforms on α-synuclein uptake in a human oligodendrocytic cell, we did not observe a significant association at the Apolipoprotein E locus with risk of MSA or α-synuclein pathology. © 2018 International Parkinson and Movement Disorder Society.

ABCA7 Deficiency Accelerates Amyloid-ß Generation and Alzheimer's Neuronal Pathology.

In Alzheimer's disease (AD), the accumulation and deposition of amyloid-ß (Aß) peptides in the brain is a central event. Aß is cleaved from amyloid precursor protein (APP) by ß-secretase and γ-secretase mainly in neurons. Although mutations inAPP,PS1, orPS2cause early-onset familial AD,ABCA7encoding ATP-binding cassette transporter A7 is one of the susceptibility genes for late-onset AD (LOAD), in which itsloss-of-functionvariants increase the disease risk. ABCA7 is homologous to a major lipid transporter ABCA1 and is highly expressed in neurons and microglia in the brain. Here, we show that ABCA7 deficiency altered brain lipid profile and impaired memory in ABCA7 knock-out (Abca7(-/-)) mice. When bred to amyloid model APP/PS1 mice, plaque burden was exacerbated by ABCA7 deficit.In vivomicrodialysis studies indicated that the clearance rate of Aß was unaltered. Interestingly, ABCA7 deletion facilitated the processing of APP to Aß by increasing the levels of ß-site APP cleaving enzyme 1 (BACE1) and sterol regulatory element-binding protein 2 (SREBP2) in primary neurons and mouse brains. Knock-down of ABCA7 expression in neurons caused endoplasmic reticulum stress highlighted by increased level of protein kinase R-like endoplasmic reticulum kinase (PERK) and increased phosphorylation of eukaryotic initiation factor 2α (eIF2α). In the brains of APP/PS1;Abca7(-/-)mice, the level of phosphorylated extracellular regulated kinase (ERK) was also significantly elevated. Together, our results reveal novel pathways underlying the association of ABCA7 dysfunction and LOAD pathogenesis. SIGNIFICANCE STATEMENT: Gene variants inABCA7encoding ATP-binding cassette transporter A7 are associated with the increased risk for late-onset Alzheimer's disease (AD). Importantly, we found the altered brain lipid profile and impaired memory in ABCA7 knock-out mice. The accumulation of amyloid-ß (Aß) peptides cleaved from amyloid precursor protein (APP) in the brain is a key event in AD pathogenesis and we also found that ABCA7 deficit exacerbated brain Aß deposition in amyloid AD model APP/PS1 mice. Mechanistically, we found that ABCA7 deletion facilitated the processing of APP and Aß production by increasing the levels of ß-secretase 1 (BACE1) in primary neurons and mouse brains without affecting the Aß clearance rate in APP/PS1 mice. Our study demonstrates a novel mechanism underlying how dysfunctions of ABCA7 contribute to the risk for AD.

Role of LRP1 in the pathogenesis of Alzheimer's disease: evidence from clinical and preclinical studies.

Among the LDL receptor (LDLR) family members, the roles of LDLR-related protein (LRP)1 in the pathogenesis of Alzheimer's disease (AD), especially late-onset AD, have been the most studied by genetic, neuropathological, and biomarker analyses (clinical studies) or cellular and animal model systems (preclinical studies) over the last 25 years. Although there are some conflicting reports, accumulating evidence from preclinical studies indicates that LRP1 not only regulates the metabolism of amyloid-ß peptides (Aßs) in the brain and periphery, but also maintains brain homeostasis, impairment of which likely contributes to AD development in Aß-independent manners. Several preclinical studies have also demonstrated an involvement of LRP1 in regulating the pathogenic role of apoE, whose gene is the strongest genetic risk factor for AD. Nonetheless, evidence from clinical studies is not sufficient to conclude how LRP1 contributes to AD development. Thus, despite very promising results from preclinical studies, the role of LRP1 in AD pathogenesis remains to be further clarified. In this review, we discuss the potential mechanisms underlying how LRP1 affects AD pathogenesis through Aß-dependent and -independent pathways by reviewing both clinical and preclinical studies. We also discuss potential therapeutic strategies for AD by targeting LRP1.