Apolipoprotein E E3/E4 genotype is associated with an increased risk of type 2 diabetes mellitus complicated with coronary artery disease.

OBJECTIVE: Dyslipidemia is a co-existing problem in patients with diabetes mellitus (DM) and coronary artery disease (CAD), and apolipoprotein E (APOE) plays an important role in lipid metabolism. However, the relationship between the APOE gene polymorphisms and the risk of developing CAD in type 2 DM (T2DM) patients remains controversial. The aim of this study was to assess this relationship and provide a reference for further risk assessment of CAD in T2DM patients. METHODS: The study included 378 patients with T2DM complicated with CAD (T2DM + CAD) and 431 patients with T2DM alone in the case group, and 351 individuals without DM and CAD were set as controls. The APOE rs429358 and rs7412 polymorphisms were genotyped by polymerase chain reaction (PCR) - microarray. Differences in APOE genotypes and alleles between patients and controls were compared. Multiple logistic regression analysis was performed after adjusting for age, gender, body mass index (BMI), history of smoking, and history of drinking to access the relationship between APOE genotypes and T2DM + CAD risk. RESULTS: The frequencies of the APOE ɛ3/ɛ4 genotype and ε4 allele were higher in the T2DM + CAD patients, and the frequencies of the APOE ɛ3/ɛ3 genotype and ε3 allele were lower than those in the controls (all p < 0.05). The T2DM + CAD patients with ɛ4 allele had higher level in low-density lipoprotein cholesterol (LDL-C) than those in patients with ɛ2 and ɛ3 allele (p < 0.05). The results of logistic regression analysis showed that age ≥ 60 years old, and BMI ≥ 24.0 kg/m2 were independent risk factors for T2DM and T2DM + CAD, and APOE ɛ3/ɛ4 genotype (adjusted odds ratio (OR) = 1.93, 95% confidence interval (CI) = 1.18-3.14, p = 0.008) and ɛ4 allele (adjusted OR = 1.97, 95% CI = 1.23-3.17) were independent risk factors for T2DM + CAD. However, the APOE genotypes and alleles were not found to have relationship with the risk of T2DM. CONCLUSIONS: APOE ε3/ε4 genotype and ε4 allele were independent risk factors for T2DM complicated with CAD, but not for T2DM.

Generation of novel anti-apoE monoclonal antibodies that selectively recognize apoE isoforms.

Apolipoprotein E (apoE) is a regulator of lipid metabolism, cholesterol transport, and the clearance and aggregation of amyloid ß in the brain. The three human apoE isoforms apoE2, apoE3, and apoE4 only differ in one or two residues. Nevertheless, the functions highly depend on the isoform types and lipidated states. Here, we generated novel anti-apoE monoclonal antibodies (mAbs) and obtained an apoE4-selective mAb whose epitope is within residues 110-117. ELISA and bio-layer interferometry measurements demonstrated that the dissociation constants of mAbs are within the nanomolar range. Using the generated antibodies, we successfully constructed sandwich ELISA systems, which can detect all apoE isoforms or selectively detect apoE4. These results suggest the usability of the generated anti-apoE mAbs for selective detection of apoE isoforms.

APOE4 genotype and aging impair injury-induced microglial behavior in brain slices, including toward Aß, through P2RY12.

Microglia are highly dynamic cells that play a critical role in tissue homeostasis through the surveillance of brain parenchyma and response to cues associated with damage. Aging and APOE4 genotype are the strongest risk factors for Alzheimer's disease (AD), but how they affect microglial dynamics remains unclear. Using ex vivo confocal microscopy, we analyzed microglial dynamic behaviors in the entorhinal cortex (EC) and hippocampus CA1 of 6-, 12-, and 21-month-old mice APOE3 or APOE4 knock-in mice expressing GFP under the CX3CR1 promoter. To study microglia surveillance, we imaged microglia baseline motility for 20 min and measured the extension and retraction of processes. We found that APOE4 microglia exhibited significantly less brain surveillance (27%) compared to APOE3 microglia in 6-month-old mice; aging exacerbated this deficit. To measure microglia response to damage, we imaged process motility in response to ATP, an injury-associated signal, for 30 min. We found APOE4 microglia extended their processes significantly slower (0.9 µm/min, p < 0.005) than APOE3 microglia (1.1 µm/min) in 6-month-old animals. APOE-associated alterations in microglia motility were observed in 12- and 21-month-old animals, and this effect was exacerbated with aging in APOE4 microglia. We measured protein and mRNA levels of P2RY12, a core microglial receptor required for process movement in response to damage. We found that APOE4 microglia express significantly less P2RY12 receptors compared to APOE3 microglia despite no changes in P2RY12 transcripts. To examine if the effect of APOE4 on the microglial response to ATP also applied to amyloid ß (Aß), we infused locally Hi-Lyte Fluor 555-labeled Aß in acute brain slices of 6-month-old mice and imaged microglia movement for 2 h. APOE4 microglia showed a significantly slower (p < 0.0001) process movement toward the Aß, and less Aß coverage at early time points after Aß injection. To test whether P2RY12 is involved in process movement in response to Aß, we treated acute brain slices with a P2RY12 antagonist before Aß injection; microglial processes no longer migrated towards Aß. These results provide mechanistic insights into the impact of APOE4 genotype and aging in dynamic microglial behaviors prior to gross Aß pathology and could help explain how APOE4 brains are more susceptible to AD pathogenesis.

Investigating the synergistic effects of hormone replacement therapy, apolipoprotein E and age on brain health in the UK Biobank.

Global prevalence of Alzheimer's Disease has a strong sex bias, with women representing approximately two-thirds of the patients. Yet, the role of sex-specific risk factors during midlife, including hormone replacement therapy (HRT) and their interaction with other major risk factors for Alzheimer's Disease, such as apolipoprotein E (APOE)-e4 genotype and age, on brain health remains unclear. We investigated the relationship between HRT (i.e., use, age of initiation and duration of use) and brain health (i.e., cognition and regional brain volumes). We then consider the multiplicative effects of HRT and APOE status (i.e., e2/e2, e2/e3, e3/e3, e3/e4 and e4/e4) via a two-way interaction and subsequently age of participants via a three-way interaction. Women from the UK Biobank with no self-reported neurological conditions were included (N = 207,595 women, mean age = 56.25 years, standard deviation = 8.01 years). Generalised linear regression models were computed to quantify the cross-sectional association between HRT and brain health, while controlling for APOE status, age, time since attending centre for completing brain health measure, surgical menopause status, smoking history, body mass index, education, physical activity, alcohol use, ethnicity, socioeconomic status, vascular/heart problems and diabetes diagnosed by doctor. Analyses of structural brain regions further controlled for scanner site. All brain volumes were normalised for head size. Two-way interactions between HRT and APOE status were modelled, in addition to three-way interactions including age. Results showed that women with the e4/e4 genotype who have used HRT had 1.82% lower hippocampal, 2.4% lower parahippocampal and 1.24% lower thalamus volumes than those with the e3/e3 genotype who had never used HRT. However, this interaction was not detected for measures of cognition. No clinically meaningful three-way interaction between APOE, HRT and age was detected when interpreted relative to the scales of the cognitive measures used and normative models of ageing for brain volumes in this sample. Differences in hippocampal volume between women with the e4/e4 genotype who have used HRT and those with the e3/e3 genotype who had never used HRT are equivalent to approximately 1-2 years of hippocampal atrophy observed in typical health ageing trajectories in midlife (i.e., 0.98%-1.41% per year). Effect sizes were consistent within APOE e4/e4 group post hoc sensitivity analyses, suggesting observed effects were not solely driven by APOE status and may, in part, be attributed to HRT use. Although, the design of this study means we cannot exclude the possibility that women who have used HRT may have a predisposition for poorer brain health.

Effects of the ApoE genotype on cognitive function in aging mice fed with a high-fat diet and the protective potential of n-3 polyunsaturated fatty acids.

The ApoE4 allele is the strongest genetic determinant for Alzheimer's disease (AD), while obesity is a strong environmental risk for AD. The modulatory effect of the ApoE genotype on aging-related cognitive function in tandem with a high-fat diet (HFD) remains uncertain. This study aimed to elucidate the effects of ApoE3/ApoE4 genotypes in aged mice exposed to a HFD, and the benefits of n-3 polyunsaturated fatty acids (PUFAs) from fish oil. Remarkably, the HFD led to weight gain and lipid accumulation, more pronounced in ApoE3 mice, while ApoE4 mice experienced exacerbated cerebral insulin resistance, neuroinflammation, and oxidative stress. Critically, n-3 PUFAs modulated the cerebral insulin signaling via the IRS-1/AKT/GLUT4 pathway, mitigated microglial hyperactivity, and reduced IL-6 and MDA levels, thereby counteracting cognitive deficits. These findings highlight the contrasting impacts of ApoE genotypes on aging mice exposed to a HFD, supporting n-3 PUFAs as a strategic nutritional intervention for brain health, especially for ApoE4 carriers.

The Role of Impaired Receptor Trafficking in Mediating the Pathological Effects of APOE4 in Alzheimer's Disease.

BACKGROUND: Apolipoprotein E4 (APOE4) is the most prevalent genetic risk factor of Alzheimer's disease. Several studies suggest that APOE4 binding to its receptors is associated with their internalization and accumulation in intracellular compartments. Importantly, this phenomenon also occurs with other, non-ApoE receptors. Based on these observations, we hypothesized that APOE4 pathological effects are mediated by impairment in the life cycle of distinct receptors (APOER2, LRP1, IR, VEGFR). OBJECTIVE: To examine the effects of APOE genotype on receptors protein levels and compartmentalization. METHODS: Primary mouse neurons were prepared from APOE3 or APOE4 targeted replacement mice, or APOE-KO mice. Specific receptors protein levels were evaluated in these neurons, utilizing immunofluorescent staining. Additionally, surface membrane protein levels of those receptors were assessed by cell surface biotinylation assay and ELISA. Receptors' colocalization with intracellular compartments was assessed by double staining and confocal microscopy, followed by colocalization analysis. Finally, LRP1 or APOER2 were knocked-down with CRISPR/Cas9 system to examine their role in mediating APOE4 effects on the receptors. RESULTS: Our results revealed lower receptors' levels in APOE4, specifically on the membrane surface. Additionally, APOE4 affects the compartmentation of these receptors in two patterns: the first was observed with LRP1 and was associated with decreased receptor levels in numerous intracellular compartments. The second was obtained with the other receptors and was associated with their accumulation in early endosomes and their decrease in the late endosomes. CONCLUSIONS: These results provide a unifying mechanism, in which APOE4 drives the down regulation of various receptors, which plays important roles in distinct APOE4 related pathological processes.

Apolipoprotein E isoforms and their Cys-thiol modifications impact LRP1-mediated metabolism of triglyceride-rich lipoproteins.

The low-density lipoprotein (LDL) receptor-related protein (LRP)1 participates in the metabolism of apolipoprotein (apo) E-containing lipoproteins (apoE-LP). We investigated the effects of modifications of cysteine (Cys)-thiol of apoE on LRP1-mediated metabolism. Among the three isoforms, apoE2-LP exhibited the lowest affinity for LRP1 but was significantly catabolized, whereas apoE4-LP was sufficiently bound to LRP1 but showed the lowest catabolic capability. The reduction enhanced the binding and suppressed the catabolism of apoE3-LP, but had no effect on apoE2-LP. The formation of disulfide-linked complexes with apoAII suppressed binding, but enhanced the catabolism of apoE2-LP. Redox modifications of apoE-Cys-thiol may modulate the LRP1-mediated metabolism of apoE2- or apoE3-LP, but not apoE4-LP. The failure of this function may be involved in the pathophysiology of dyslipidemia.

Amelioration of Tau and ApoE4-linked glial lipid accumulation and neurodegeneration with an LXR agonist.

Apolipoprotein E (APOE) is a strong genetic risk factor for late-onset Alzheimer's disease (LOAD). APOE4 increases and APOE2 decreases risk relative to APOE3. In the P301S mouse model of tauopathy, ApoE4 increases tau pathology and neurodegeneration when compared with ApoE3 or the absence of ApoE. However, the role of ApoE isoforms and lipid metabolism in contributing to tau-mediated degeneration is unknown. We demonstrate that in P301S tau mice, ApoE4 strongly promotes glial lipid accumulation and perturbations in cholesterol metabolism and lysosomal function. Increasing lipid efflux in glia via an LXR agonist or Abca1 overexpression strongly attenuates tau pathology and neurodegeneration in P301S/ApoE4 mice. We also demonstrate reductions in reactive astrocytes and microglia, as well as changes in cholesterol biosynthesis and metabolism in glia of tauopathy mice in response to LXR activation. These data suggest that promoting efflux of glial lipids may serve as a therapeutic approach to ameliorate tau and ApoE4-linked neurodegeneration.

Human APOE4 Protects High-Fat and High-Sucrose Diet Fed Targeted Replacement Mice against Fatty Liver Disease Compared to APOE3.

Recent genome- and exome-wide association studies suggest that the human APOE ε4 allele protects against non-alcoholic fatty liver disease (NAFLD), while ε3 promotes hepatic steatosis and steatohepatitis. The present study aimed at examining the APOE genotype-dependent development of fatty liver disease and its underlying mechanisms in a targeted replacement mouse model. Male mice expressing the human APOE3 or APOE4 protein isoforms on a C57BL/6J background and unmodified C57BL/6J mice were chronically fed a high-fat and high-sucrose diet to induce obesity. After 7 months, body weight gain was more pronounced in human APOE than endogenous APOE expressing mice with elevated plasma biomarkers suggesting aggravated metabolic dysfunction. APOE3 mice exhibited the highest liver weights and, compared to APOE4, massive hepatic steatosis. An untargeted quantitative proteome analysis of the liver identified a high number of proteins differentially abundant in APOE3 versus APOE4 mice. The majority of the higher abundant proteins in APOE3 mice could be grouped to inflammation and damage-associated response, and lipid storage, amongst others. Results of the targeted qRT-PCR and Western blot analyses contribute to the overall finding that APOE3 as opposed to APOE4 promotes hepatic steatosis, inflammatory- and damage-associated response signaling and fibrosis in the liver of obese mice. Our experimental data substantiate the observation of an increased NAFLD-risk associated with the human APOEε3 allele, while APOEε4 appears protective. The underlying mechanisms of the protection possibly involve a higher capacity of nonectopic lipid deposition in subcutaneous adipose tissue and lower hepatic pathogen recognition in the APOE4 mice.

Higher Neuronal Facilitation and Potentiation with APOE4 Suppressed by Angiotensin II.

Progressive hippocampal degeneration is a key component of Alzheimer's disease (AD) progression. Therefore, identifying how hippocampal neuronal function is modulated early in AD is an important approach to eventually prevent degeneration. AD-risk factors and signaling molecules likely modulate neuronal function, including APOE genotype and angiotensin II. Compared to APOE3, APOE4 increases AD risk up to 12-fold, and high levels of angiotensin II are hypothesized to disrupt neuronal function in AD. However, the extent that APOE and angiotensin II modulates the hippocampal neuronal phenotype in AD-relevant models is unknown. To address this issue, we used electrophysiological techniques to assess the impact of APOE genotype and angiotensin II on basal synaptic transmission, presynaptic, and post-synaptic activity in mice that express human APOE3 (E3FAD) or APOE4 (E4FAD) and overproduce Aß. We found that compared to E3FAD mice, E4FAD mice have lower synaptic activity, but higher levels of paired-pulse facilitation (PPF) and long-term potentiation (LTP) in the Schaffer Collateral Commissural Pathway (SCCP) of the hippocampus. We also found that exogenous angiotensin II has a profound inhibitory effect on hippocampal LTP in both E3FAD and E4FAD mice. Collectively, our data suggests that APOE4 and Aß are associated with a hippocampal phenotype comprised of lower basal activity and higher responses to high-frequency stimulation, the latter of which is suppressed by angiotensin II. These novel data suggest a potential mechanistic link between hippocampal activity, APOE4 genotype, and angiotensin II in AD.

Neuronal Stem Cells from Late-Onset Alzheimer Patients Show Altered Regulation of Sirtuin 1 Depending on Apolipoprotein E Indicating Disturbed Stem Cell Plasticity.

Late-onset Alzheimer's disease (AD) is a complex multifactorial disease. The greatest known risk factor for late-onset AD is the E4 allele of the apolipoprotein E (APOE), while increasing age is the greatest known non-genetic risk factor. The cell type-specific functions of neural stem cells (NSCs), in particular their stem cell plasticity, remain poorly explored in the context of AD pathology. Here, we describe a new model that employs late-onset AD patient-derived induced pluripotent stem cells (iPSCs) to generate NSCs and to examine the role played by APOE4 in the expression of aging markers such as sirtuin 1 (SIRT1) in comparison to healthy subjects carrying APOE3. The effect of aging was investigated by using iPSC-derived NSCs from old age subjects as healthy matched controls. Transcript and protein analysis revealed that genes were expressed differently in NSCs from late-onset AD patients, e.g., exhibiting reduced autophagy-related protein 7 (ATG7), phosphatase and tensin homolog (PTEN), and fibroblast growth factor 2 (FGF2). Since SIRT1 expression differed between APOE3 and APOE4 NSCs, the suppression of APOE function in NSCs also repressed the expression of SIRT1. However, the forced expression of APOE3 by plasmids did not recover differently expressed genes. The altered aging markers indicate decreased plasticity of NSCs. Our study provides a suitable in vitro model to investigate changes in human NSCs associated with aging, APOE4, and late-onset AD.

APOE Christchurch-mimetic therapeutic antibody reduces APOE-mediated toxicity and tau phosphorylation.

INTRODUCTION: We discovered that the APOE3 Christchurch (APOE3Ch) variant may provide resistance to Alzheimer's disease (AD). This resistance may be due to reduced pathological interactions between ApoE3Ch and heparan sulfate proteoglycans (HSPGs). METHODS: We developed and characterized the binding, structure, and preclinical efficacy of novel antibodies targeting human ApoE-HSPG interactions. RESULTS: We found that one of these antibodies, called 7C11, preferentially bound ApoE4, a major risk factor for sporadic AD, and disrupts heparin-ApoE4 interactions. We also determined the crystal structure of a Fab fragment of 7C11 and used computer modeling to predict how it would bind to ApoE. When we tested 7C11 in mouse models, we found that it reduced recombinant ApoE-induced tau pathology in the retina of MAPT*P301S mice and curbed pTau S396 phosphorylation in brains of systemically treated APOE4 knock-in mice. Targeting ApoE-HSPG interactions using 7C11 antibody may be a promising approach to developing new therapies for AD.

APOE3ch alters microglial response and suppresses Aß-induced tau seeding and spread.

A recent case report described an individual who was a homozygous carrier of the APOE3 Christchurch (APOE3ch) mutation and resistant to autosomal dominant Alzheimer's Disease (AD) caused by a PSEN1-E280A mutation. Whether APOE3ch contributed to the protective effect remains unclear. We generated a humanized APOE3ch knock-in mouse and crossed it to an amyloid-ß (Aß) plaque-depositing model. We injected AD-tau brain extract to investigate tau seeding and spreading in the presence or absence of amyloid. Similar to the case report, APOE3ch expression resulted in peripheral dyslipidemia and a marked reduction in plaque-associated tau pathology. Additionally, we observed decreased amyloid response and enhanced microglial response around plaques. We also demonstrate increased myeloid cell phagocytosis and degradation of tau aggregates linked to weaker APOE3ch binding to heparin sulfate proteoglycans. APOE3ch influences the microglial response to Aß plaques, which suppresses Aß-induced tau seeding and spreading. The results reveal new possibilities to target Aß-induced tauopathy.

Generation of the Human iPSC Line from Spontaneous Late-Onset Alzheimer's Disease Patient with ApoE3/3 Genotype and Sex-, Age-, and ApoE-Matched Healthy Control.

Human induced pluripotent stem cell (iPSC) lines were generated from peripheral blood mononuclear cells (PBMCs) isolated from a patient diagnosed with spontaneous late-onset Alzheimer's disease (AD) carrying ApoE3/3 gene and one age-, sex-, and ApoE-matched healthy control. Reprogramming was done using a commercially available Epi5 Reprogramming Kit containing OCT4, SOX2, KLF4, LIN28, and L-MYC as reprogramming factors. The pluripotency of the iPSC lines was verified by the expression of pluripotency markers and by their capacity to differentiate into all three embryonic germ layers in vitro. These newly established iPSC lines offer a valuable platform for in vitro modeling of AD.

The chemotherapeutic agent doxorubicin induces brain senescence, with modulation by APOE genotype.

Many cancer patients experience serious cognitive problems related to their treatment, which can greatly affect their quality of life. The molecular mechanisms of this cancer chemotherapy-induced cognitive impairment (CICI) are unknown, thus slowing the development of preventative approaches. We hypothesized that cancer chemotherapies could induce cellular senescence in the brain, creating a pro-inflammatory environment and damaging normal brain communication. We tested this hypothesis using the common chemotherapeutic agent doxorubicin in two independent mouse models. In the first model, we used mice that express tdTomato under the pdkn2a (p16) promoter; p16 is a regulator of cellular senescence, and its upregulation is denoted by the presence of fluorescently tagged cells. Two weeks after exposure to three doses of 5 mg/kg doxorubicin, the number of tdTomato positive cells were increased nearly three-fold in both the cerebral cortex and the hippocampus. tdTomato staining co-localized with neurons, microglia, oligodendrocyte precursor cells, and endothelial cells, but not astrocytes. In the second model, we used APOE knock-in mice, since the APOE4 allele is a risk factor for CICI in humans and mouse models. We isolated RNA from the cerebral cortex of APOE3 and APOE4 mice from one to 21 days after a single dose of 10 mg/kg doxorubicin. Using NanoString analysis of over 700 genes related to neuroinflammation and RT-qPCR analysis of cerebral cortex transcripts, we found two-fold induction of four senescence-related genes at three weeks in the APOE4 mice compared to the APOE3 control mice: p21(cdkn1a), p16, Gadd45a, and Egr1. We conclude that doxorubicin promotes cellular senescence pathways in the brain, supporting the hypothesis that drugs to eliminate senescent cells could be useful in preventing CICI.

Alzheimer's disease phenotype based upon the carrier status of the apolipoprotein E ɛ4 allele.

The apolipoprotein E ɛ4 allele (APOE4) is universally acknowledged as the most potent genetic risk factor for Alzheimer's disease (AD). APOE4 promotes the initiation and progression of AD. Although the underlying mechanisms are unclearly understood, differences in lipid-bound affinity among the three APOE isoforms may constitute the basis. The protein APOE4 isoform has a high affinity with triglycerides and cholesterol. A distinction in lipid metabolism extensively impacts neurons, microglia, and astrocytes. APOE4 carriers exhibit phenotypic differences from non-carriers in clinical examinations and respond differently to multiple treatments. Therefore, we hypothesized that phenotypic classification of AD patients according to the status of APOE4 carrier will help specify research and promote its use in diagnosing and treating AD. Recent reviews have mainly evaluated the differences between APOE4 allele carriers and non-carriers from gene to protein structures, clinical features, neuroimaging, pathology, the neural network, and the response to various treatments, and have provided the feasibility of phenotypic group classification based on APOE4 carrier status. This review will facilitate the application of APOE phenomics concept in clinical practice and promote further medical research on AD.

Microglial APOE4: more is less and less is more.

Apolipoprotein E (APOE) is the single greatest genetic risk factor for late onset Alzheimer's disease (AD). Yet, the cell-specific effects of APOE on microglia function have remained unclear. Fortunately, two comprehensive new studies published in the latest issue of Nature Immunology have employed complementary gain-of-function and loss-of-function approaches to provide critical new insight into the impact of microglial APOE on AD pathogenesis.

A novel apoE-mimetic increases brain apoE levels, reduces Aß pathology and improves memory when treated before onset of pathology in male mice that express APOE3.

BACKGROUND: Alzheimer's disease (AD) is characterized by cognitive dysfunction and amyloid plaques composed of the amyloid-beta peptide (Aß). APOE is the greatest genetic risk for AD with APOE4 increasing risk up to ~ 15-fold compared to APOE3. Evidence suggests that levels and lipidation of the apoE protein could regulate AD progression. In glia, apoE is lipidated via cholesterol efflux from intracellular pools, primarily by the ATP-binding cassette transporter A1 (ABCA1). Therefore, increasing ABCA1 activity is suggested to be a therapeutic approach for AD. CS-6253 (CS) is a novel apoE mimetic peptide that was developed to bind and stabilize ABCA1 and maintain its localization into the plasma membrane therefore promoting cholesterol efflux. The goal of this study was to determine whether CS could modulate apoE levels and lipidation, Aß pathology, and behavior in a model that expresses human APOE and overproduce Aß. METHODS: In vitro, APOE3-glia or APOE4-glia were treated with CS. In vivo, male and female, E3FAD (5xFAD+/-/APOE3+/+) and E4FAD (5xFAD+/-/APOE4+/+) mice were treated with CS via intraperitoneal injection at early (from 4 to 8 months of age) and late ages (from 8 to 10 months of age). ApoE levels, ABCA1 levels and, apoE lipidation were measured by western blot and ELISA. Aß and amyloid levels were assessed by histochemistry and ELISA. Learning and memory were tested by Morris Water Maze and synaptic proteins were measured by Western blot. RESULTS: CS treatment increased apoE levels and cholesterol efflux in primary glial cultures. In young male E3FAD mice, CS treatment increased soluble apoE and lipid-associated apoE, reduced soluble oAß and insoluble Aß levels as well as Aß and amyloid deposition, and improved memory and synaptic protein levels. CS treatment did not induce any therapeutic benefits in young female E3FAD and E4FAD mice or in any groups when treatment was started at later ages. CONCLUSIONS: CS treatment reduced Aß pathology and improved memory only in young male E3FAD, the cohort with the least AD pathology. Therefore, the degree of Aß pathology or Aß overproduction may impact the ability of targeting ABCA1 to be an effective AD therapeutic. This suggests that ABCA1-stabilizing treatment by CS-6253 works best in conditions of modest Aß levels.

The APOE-R136S mutation protects against APOE4-driven Tau pathology, neurodegeneration and neuroinflammation.

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for late-onset Alzheimer's disease (LOAD), leading to earlier age of clinical onset and exacerbating pathologies. There is a critical need to identify protective targets. Recently, a rare APOE variant, APOE3-R136S (Christchurch), was found to protect against early-onset AD in a PSEN1-E280A carrier. In this study, we sought to determine if the R136S mutation also protects against APOE4-driven effects in LOAD. We generated tauopathy mouse and human iPSC-derived neuron models carrying human APOE4 with the homozygous or heterozygous R136S mutation. We found that the homozygous R136S mutation rescued APOE4-driven Tau pathology, neurodegeneration and neuroinflammation. The heterozygous R136S mutation partially protected against APOE4-driven neurodegeneration and neuroinflammation but not Tau pathology. Single-nucleus RNA sequencing revealed that the APOE4-R136S mutation increased disease-protective and diminished disease-associated cell populations in a gene dose-dependent manner. Thus, the APOE-R136S mutation protects against APOE4-driven AD pathologies, providing a target for therapeutic development against AD.

Cell-autonomous effects of APOE4 in restricting microglial response in brain homeostasis and Alzheimer's disease.

Microglial involvement in Alzheimer's disease (AD) pathology has emerged as a risk-determining pathogenic event. While apolipoprotein E (APOE) is known to modify AD risk, it remains unclear how microglial apoE impacts brain cognition and AD pathology. Here, using conditional mouse models expressing apoE isoforms in microglia and central nervous system-associated macrophages (CAMs), we demonstrate a cell-autonomous effect of apoE3-mediated microglial activation and function, which are negated by apoE4. Expression of apoE3 in microglia/CAMs improves cognitive function, increases microglia surrounding amyloid plaque and reduces amyloid pathology and associated toxicity, whereas apoE4 expression either compromises or has no effects on these outcomes by impairing lipid metabolism. Single-cell transcriptomic profiling reveals increased antigen presentation and interferon pathways upon apoE3 expression. In contrast, apoE4 expression downregulates complement and lysosomal pathways, and promotes stress-related responses. Moreover, in the presence of mouse endogenous apoE, microglial apoE4 exacerbates amyloid pathology. Finally, we observed a reduction in Lgals3-positive responsive microglia surrounding amyloid plaque and an increased accumulation of lipid droplets in APOE4 human brains and induced pluripotent stem cell-derived microglia. Our findings establish critical isoform-dependent effects of microglia/CAM-expressed apoE in brain function and the development of amyloid pathology, providing new insight into how apoE4 vastly increases AD risk.