Estradiol improves behavior in FAD transgenic mice that express APOE3 but not APOE4 after ovariectomy.

Increasing evidence suggests that female individuals have a higher Alzheimer's disease (AD) risk associated with post-menopausal loss of circulating estradiol (E2). However, clinical data are conflicting on whether E2 lowers AD risk. One potential contributing factor is APOE. The greatest genetic risk factor for AD is APOE4, a factor that is pronounced in female individuals post-menopause. Clinical data suggests that APOE impacts the response of AD patients to E2 replacement therapy. However, whether APOE4 prevents, is neutral, or promotes any positive effects of E2 is unclear. Therefore, our goal was to determine whether APOE modulates the impact of E2 on behavior and AD pathology in vivo. To that end, mice that express human APOE3 (E3FAD) or APOE4 (E4FAD) and overproduce Aß42 were ovariectomized at either 4 months (early) or 8 months (late) and treated with vehicle or E2 for 4 months. In E3FAD mice, we found that E2 mitigated the detrimental effect of ovariectomy on memory, with no effect on Aß in the early paradigm and only improved learning in the late paradigm. Although E2 lowered Aß in E4FAD mice in the early paradigm, there was no impact on learning or memory, possibly due to higher Aß pathology compared to E3FAD mice. In the late paradigm, there was no effect on learning/memory and Aß pathology in E4FAD mice. Collectively, these data support the idea that, in the presence of Aß pathology, APOE impacts the response to E2 supplementation post-menopause.

CETP inhibition enhances monocyte activation and bacterial clearance and reduces streptococcus pneumonia-associated mortality in mice.

Sepsis is a leading cause of mortality worldwide, and pneumonia is the most common cause of sepsis in humans. Low levels of high-density lipoprotein cholesterol (HDL-C) levels are associated with an increased risk of death from sepsis, and increasing levels of HDL-C by inhibition of cholesteryl ester transfer protein (CETP) decreases mortality from intraabdominal polymicrobial sepsis in APOE*3-Leiden.CETP mice. Here, we show that treatment with the CETP inhibitor (CETPi) anacetrapib reduced mortality from Streptococcus pneumoniae-induced sepsis in APOE*3-Leiden.CETP and APOA1.CETP mice. Mechanistically, CETP inhibition reduced the host proinflammatory response via attenuation of proinflammatory cytokine transcription and release. This effect was dependent on the presence of HDL, leading to attenuation of immune-mediated organ damage. In addition, CETP inhibition promoted monocyte activation in the blood prior to the onset of sepsis, resulting in accelerated macrophage recruitment to the lung and liver. In vitro experiments demonstrated that CETP inhibition significantly promoted the activation of proinflammatory signaling in peripheral blood mononuclear cells and THP1 cells in the absence of HDL; this may represent a mechanism responsible for improved bacterial clearance during sepsis. These findings provide evidence that CETP inhibition represents a potential approach to reduce mortality from pneumosepsis.

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.

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.

Apolipoprotein E secreted by astrocytes forms antiparallel dimers in discoidal lipoproteins.

The Apolipoprotein E gene (APOE) is of great interest due to its role as a risk factor for late-onset Alzheimer's disease. ApoE is secreted by astrocytes in the central nervous system in high-density lipoprotein (HDL)-like lipoproteins. Structural models of lipidated ApoE of high resolution could aid in a mechanistic understanding of how ApoE functions in health and disease. Using monoclonal Fab and F(ab')2 fragments, we characterize the structure of lipidated ApoE on astrocyte-secreted lipoproteins. Our results provide support for the "double-belt" model of ApoE in nascent discoidal HDL-like lipoproteins, where two ApoE proteins wrap around the nanodisc in an antiparallel conformation. We further show that lipidated, recombinant ApoE accurately models astrocyte-secreted ApoE lipoproteins. Cryogenic electron microscopy of recombinant lipidated ApoE further supports ApoE adopting antiparallel dimers in nascent discoidal lipoproteins.

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.

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.

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.

Apolipoprotein E3 functionalized lipid-drug conjugated nanoparticles of Levetiracetam for enhanced delivery to the brain: In-vitro cell line studies and in-vivo study.

A significant portion of brain-tumor patients suffer from 'brain-tumor-related epilepsy (BTE)' which results in depression, anxiety and hampered quality of life. Conventional anti-epileptic drugs indicate negative interaction with other drugs augmenting the poor outcome of overall therapy. Levetiracetam (LVM) has evidenced effectiveness for BTE but its hydrophilicity restricts the passage into blood-brain barrier. The majority of lipid nanoparticles fails to load hydrophilic drug sufficiently. Therefore, lipid-drug conjugates (LDC) were synthesized using stearic acid via amide bond formation confirmed by FTIR and NMR. The nanoparticles of synthesized LDC were prepared by solvent injection method followed by functionalization with Apolipoprotein E3 (ApoE3@LDC-NP). The nanoparticles were characterized by DSC, XRD, particle size (131.6 ± 1.24 nm), zeta potential (-15.6 ± 0.09 mV), and for storage stability. In-vitro release study indicated initial burst release of 20 ± 0.63 % followed by sustained release up to 30 h (66 ± 1.40 %) for ApoE3@LDC-NP. The cell-line study on HEK293 indicated no significant cytotoxic effect and greater cell uptake through U87MG cell line. The pharmacokinetic and bio-distribution study indicated 2.5-fold greater brain-targeting of ApoE3@LDC-NP as compared to LVM solution. It proved safe in the haemolysis study and exhibited the absence of tissue necrosis. Thus, ApoE3@LDC-NP might be a promising approach for effective brain-targeting of LVM for improved clinical response in BTE.

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.

ApoE3 Anchored Liposomal Delivery of Rivastigmine for Brain Delivery: Formulation, Characterization, and In Vivo Pharmacokinetic Evaluation.

Rivastigmine hydrogen tartrate (RHT) is an acetylcholinesterase (AChE) inhibitor used in the management of Alzheimer's disease (AD). RHT is a BCS class-I drug that undergoes significant first-pass metabolism. Permeating a hydrophilic drug through the brain remains a major challenge in brain delivery. In this study, the RHT was incorporated inside the hydrophilic core of liposomes (LPS) and then coated with the ApoE3. ApoE3-coated RHT-loaded liposomes (ApoE3-RHT-LPS) were fabricated through the thin film hydration method using DSPE-PEG. The coating of LPS with ApoE3 enhances brain uptake and improves Aß clearance. The results obtained from the physicochemical characterization demonstrated that ApoE3-RHT-LPS shows a particle size of 128.6 ± 2.16 nm and a zeta potential of 16.6 ± 1.19. The % entrapment efficiency and % drug loading were found to be 75% and 17.84%, respectively. The data obtained from TEM and SEM studies revealed that the particle size of the LPS was less than 200 nm. An in vitro AChE assay was performed, and the results demonstrated the AChE inhibitory potential of ApoE3-RHT-LPS. Through the intravenous route, an in vivo pharmacokinetic study of formulation displayed improved brain uptake of RHT by ~ 1.3-fold than pure RHT due to ApoE3 coating. In vivo, biodistribution studies in vital organs suggested that the biodistribution of RHT to the liver was significantly reduced (p < 0.001), signifying an increase in the drug's half-life and blood circulation time. All research findings suggested that ApoE3 coating and LPS strategy are proven effective for improving the brain uptake of RHT designed for the management of 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.

ApoE4-dependent lysosomal cholesterol accumulation impairs mitochondrial homeostasis and oxidative phosphorylation in human astrocytes.

Recent developments in genome sequencing have expanded the knowledge of genetic factors associated with late-onset Alzheimer's disease (AD). Among them, genetic variant ε4 of the APOE gene (APOE4) confers the greatest disease risk. Dysregulated glucose metabolism is an early pathological feature of AD. Using isogenic ApoE3 and ApoE4 astrocytes derived from human induced pluripotent stem cells, we find that ApoE4 increases glycolytic activity but impairs mitochondrial respiration in astrocytes. Ultrastructural and autophagy flux analyses show that ApoE4-induced cholesterol accumulation impairs lysosome-dependent removal of damaged mitochondria. Acute treatment with cholesterol-depleting agents restores autophagic activity, mitochondrial dynamics, and associated proteomes, and extended treatment rescues mitochondrial respiration in ApoE4 astrocytes. Taken together, our study provides a direct link between ApoE4-induced lysosomal cholesterol accumulation and abnormal oxidative phosphorylation.

Apolipoprotein E-containing HDL decreases caspase-dependent apoptosis of memory regulatory T lymphocytes.

Plasma levels of HDL cholesterol are inversely associated with CVD progression. It is becoming increasingly clear that HDL plays important roles in immunity that go beyond its traditionally understood roles in lipid transport. We previously reported that HDL interaction with regulatory T cells (Treg) protected them from apoptosis, which could be a mechanism underlying the broad anti-inflammatory effect of HDL. Herein, we extend our work to show that HDL interacts mainly with memory Treg, particularly with the highly suppressive effector memory Treg, by limiting caspase-dependent apoptosis in an Akt-dependent manner. Reconstitution experiments identified the protein component of HDL as the primary driver of the effect, though the most abundant HDL protein, apolipoprotein A-I (APOA1), was inactive. In contrast, APOE-depleted HDL failed to rescue effector memory Treg, suggesting the critical role of APOE proteins. HDL particles reconstituted with APOE, and synthetic phospholipids blunted Treg apoptosis at physiological concentrations. The APOE3 and APOE4 isoforms were the most efficient. Similar results were obtained when lipid-free recombinant APOEs were tested. Binding experiments showed that lipid-free APOE3 bound to memory Treg but not to naive Treg. Overall, our results show that APOE interaction with Treg results in blunted caspase-dependent apoptosis and increased survival. As dysregulation of HDL-APOE levels has been reported in CVD and obesity, our data bring new insight on how this defect may contribute to these diseases.

Endothelial Cell APOE3 Regulates Neurovascular, Neuronal, and Behavioral Function.

BACKGROUND: Specialized brain endothelial cells and human APOE3 are independently important for neurovascular function, yet whether APOE3 expression by endothelial cells contributes to brain function is currently unknown. In the present study, we determined whether the loss of endothelial cell APOE3 impacts brain vascular and neural function. METHODS: We developed APOE3fl/fl/Cdh5(PAC)-CreERT2+/- (APOE3Cre+/-) and APOE3fl/fl/Cdh5(PAC)-CreERT2-/- (APOE3Cre-/-, control) mice and induced endothelial cell APOE3 knockdown with tamoxifen at ≈4 to 5 weeks of age. Neurovascular and neuronal function were evaluated by biochemistry, immunohistochemistry, behavioral testing, and electrophysiology at 9 months of age. RESULTS: We found that the loss of endothelial APOE3 expression was sufficient to cause neurovascular dysfunction including higher permeability and lower vessel coverage in tandem with deficits in spatial memory and fear memory extinction and a disruption of cortical excitatory/inhibitory balance. CONCLUSIONS: Our data collectively support the novel concept that endothelial APOE3 plays a critical role in the regulation of the neurovasculature, neural circuit function, and behavior.

Detection of early Alzheimer's disease-like molecular alterations in a mouse model expressing human ApoE4.

The E4 allele of apolipoprotein E (ApoE4) is a key genetic risk factor for late-onset Alzheimer's disease (AD), increasing the risk of developing the disease by up to three-fold. However, the mechanisms by which ApoE4 contributes to AD pathogenesis are poorly understood. Here, we utilize a mouse model expressing either human ApoE3 or human ApoE4 to examine the effects of the E4 allele on a wide range of genetic and molecular pathways that are altered in early AD pathology. We demonstrate that ApoE4-expressing mice begin to show early differential expression of multiple genes, leading to alterations in downstream pathways related to neural cell maintenance, insulin signaling, amyloid processing and clearance, and synaptic plasticity. These alterations may result in the earlier accumulation of pathological proteins such as ß-amyloid that may build up within cells, leading to the accelerated degeneration of neurons and astrocytes as observed in ApoE4-positive individuals. We also examine the metabolic effects associated with a high-fat diet (HFD) in male ApoE4-expressing mice compared with regular chow diet (RD) fed mice at different ages. We found that young ApoE4-expressing mice fed HFD developed metabolic disturbances, such as elevated weight gain, blood glucose, and plasma insulin levels that cumulatively have been observed to increase the risk of AD in humans. Taken together, our results reveal early pathways that could mediate ApoE4-related AD risk and may help identify more tractable therapeutic targets for treating ApoE4-associated AD.

Inducible and Conditional Activation of Adult Neurogenesis Rescues Cadmium-Induced Hippocampus-Dependent Memory Deficits in ApoE4-KI Mice.

The apolipoprotein E (ApoE) gene is a genetic risk factor for late-onset Alzheimer's disease, in which ε4 allele carriers have increased risk compared to the common ε3 carriers. Cadmium (Cd) is a toxic heavy metal and a potential neurotoxicant. We previously reported a gene-environment interaction (GxE) effect between ApoE4 and Cd that accelerates or increases the severity of the cognitive decline in ApoE4-knockin (ApoE4-KI) mice exposed to 0.6 mg/L CdCl2 through drinking water compared to control ApoE3-KI mice. However, the mechanisms underlying this GxE effect are not yet defined. Because Cd impairs adult neurogenesis, we investigated whether genetic and conditional stimulation of adult neurogenesis can functionally rescue Cd-induced cognitive impairment in ApoE4-KI mice. We crossed either ApoE4-KI or ApoE3-KI to an inducible Cre mouse strain, Nestin-CreERTM:caMEK5-eGFPloxP/loxP (designated as caMEK5), to generate ApoE4-KI:caMEK5 and ApoE3-KI:caMEK5. Tamoxifen administration in these mice genetically and conditionally induces the expression of caMEK5 in adult neural stem/progenitor cells, enabling the stimulation of adult neurogenesis in the brain. Male ApoE4-KI:caMEK5 and ApoE3-KI:caMEK5 mice were exposed to 0.6 mg/L CdCl2 throughout the experiment, and tamoxifen was administered once Cd-induced impairment in spatial working memory was consistently observed. Cd exposure impaired spatial working memory earlier in ApoE4-KI:caMEK5 than in ApoE3-KI:caMEK5 mice. In both strains, these deficits were rescued after tamoxifen treatment. Consistent with these behavioral findings, tamoxifen treatment enhanced adult neurogenesis by increasing the morphological complexity of adult-born immature neurons. These results provide evidence for a direct link between impaired spatial memory and adult neurogenesis in this GxE model.

Apolipoprotein E Polymorphism Impacts White Matter Injury Through Microglial Phagocytosis After Experimental Subarachnoid Hemorrhage.

Apolipoprotein E (apoE, protein; APOE, gene), divided into three alleles of E2, E3 and E4 in humans, is associated with the progression of white matter lesion load. However, mechanism evidence has not been reported regarding the APOE genotype in early white matter injury (WMI) under subarachnoid hemorrhage (SAH) conditions. In the present study, we investigated the effects of APOE gene polymorphisms, by constructing microglial APOE3 and APOE4-specific overexpression, on WMI and underlying mechanisms of microglia phagocytosis in a mice model of SAH. A total of 167 male C57BL/6J mice (weight 22-26 g) were used. SAH and bleeding environment were induced by endovascular perforation in vivo and oxyHb in vitro, respectively. Multi-technology approaches, including immunohistochemistry, high throughput sequencing, gene editing for adeno-associated viruses, and several molecular biotechnologies were used to validate the effects of APOE polymorphisms on microglial phagocytosis and WMI after SAH. Our results revealed that APOE4 significantly aggravated the WMI and decreased neurobehavioral function by impairing microglial phagocytosis after SAH. Indicators negatively associated with microglial phagocytosis increased like CD16, CD86 and the ratio of CD16/CD206, while the indicators positively associated with microglial phagocytosis decreased like Arg-1 and CD206. The increased ROS and aggravating mitochondrial damage demonstrated that the damaging effects of APOE4 in SAH may be associated with microglial oxidative stress-dependent mitochondrial damage. Inhibiting mitochondrial oxidative stress by Mitoquinone (mitoQ) can enhance the phagocytic function of microglia. In conclusion, anti-oxidative stress and phagocytosis protection may serve as promising treatments in the management of SAH.

Apolipoprotein E2 Stimulates Protein Synthesis and Promotes Melanoma Progression and Metastasis.

The secreted lipid transporter apolipoprotein E (APOE) plays important roles in atherosclerosis and Alzheimer's disease and has been implicated as a suppressor of melanoma progression. The APOE germline genotype predicts human melanoma outcomes, with APOE4 and APOE2 allele carriers exhibiting prolonged and reduced survival, respectively, relative to APOE3 homozygotes. While the APOE4 variant was recently shown to suppress melanoma progression by enhancing antitumor immunity, further work is needed to fully characterize the melanoma cell-intrinsic effects of APOE variants on cancer progression. Using a genetically engineered mouse model, we showed that human germline APOE genetic variants differentially modulate melanoma growth and metastasis in an APOE2>APOE3>APOE4 manner. The low-density lipoprotein receptor-related protein 1 (LRP1) receptor mediated the cell-intrinsic effects of APOE variants on melanoma progression. Protein synthesis was a tumor cell-intrinsic process differentially modulated by APOE variants, with APOE2 promoting translation via LRP1. These findings reveal a gain-of-function role for the APOE2 variant in melanoma progression, which may aid in predicting melanoma patient outcomes and understanding the protective effect of APOE2 in Alzheimer's disease. SIGNIFICANCE: APOE germline variants impact melanoma progression through disparate mechanisms, such as the protein synthesis-promoting function of the APOE2 variant, indicating that germline genetic variants are causal contributors to metastatic outcomes.