ApoE Mice Research Articles

APOE4 expression confers a mild, persistent reduction in neurovascular function in the visual cortex and hippocampus of awake mice

Vascular factors are known to be early and important players in Alzheimer’s disease (AD) development, however the role of the ε4 allele of the Apolipoprotein (APOE) gene (a risk factor for developing AD) remains unclear. APOE4 genotype is associated with early and severe neocortical vascular deficits in anaesthetised mice, but in humans, vascular and cognitive dysfunction are focused on the hippocampal formation and appear later. How APOE4 might interact with the vasculature to confer AD risk during the preclinical phase represents a gap in existing knowledge. To avoid potential confounds of anaesthesia and to explore regions most relevant for human disease, we studied the visual cortex and hippocampus of awake APOE3 and APOE4-TR mice using 2-photon microscopy of neurons and blood vessels. We found mild vascular deficits: vascular density and functional hyperaemia were unaffected in APOE4 mice, and neuronal or vascular function did not decrease up to late middle-age. Instead, vascular responsiveness was lower, arteriole vasomotion was reduced and neuronal calcium signals during visual stimulation were increased. This suggests that, alone, APOE4 expression is not catastrophic but stably alters neurovascular physiology. We suggest this state makes APOE4 carriers more sensitive to subsequent insults such as injury or beta amyloid accumulation.

Humanized APOE genotypes influence lifespan independently of tau aggregation in the P301S mouse model of tauopathy

Apolipoprotein (APOE) E4 isoform is a major risk factor of Alzheimer’s disease and contributes to metabolic and neuropathological abnormalities during brain aging. To provide insights into whether APOE4 genotype is related to tau-associated neurodegeneration, we have generated human P301S mutant tau transgenic mice (PS19) that carry humanized APOE alleles (APOE2, APOE3 or APOE4). In aging mice that succumbed to paralysis, PS19 mice homozygous for APOE3 had the longest lifespan when compared to APOE4 and APOE2 homozygous mice (APOE3 > APOE4 ~ APOE2). Heterozygous mice with one human APOE and one mouse Apoe allele did not show any variations in lifespan. At end-stage, PS19 mice homozygous for APOE3 and APOE4 showed equivalent levels of phosphorylated tau burden, inflammation levels and ventricular volumes. Compared to these cohorts, PS19 mice homozygous for APOE2 showed lower induction of phosphorylation on selective epitopes, though the effect sizes were small and variable. In spite of this, the APOE2 cohort showed shorter lifespan relative to APOE3 homozygous mice. None of the cohorts accumulated appreciable levels of phosphorylated tau compartmentalized in the insoluble cell fraction. RNAseq analysis showed that the induction of immune gene expression was comparable across all the APOE genotypes in PS19 mice. Notably, the APOE4 homozygous mice showed additional induction of transcripts corresponding to the Alzheimer’s disease-related plaque-induced gene signature. In human Alzheimer’s disease brain tissues, we found no direct correlation between higher burden of phosphorylated tau and APOE4 genotype. As expected, there was a strong correlation between phosphorylated tau burden with amyloid deposition in APOE4-positive Alzheimer’s disease cases. Overall, our results indicate that APOE3 genotype may confer some resilience to tauopathy, while APOE4 and APOE2 may act through multiple pathways to increase the pathogenicity in the context of tauopathy.

Amelioration of Cognitive and Olfactory System Deficits in APOE4 Transgenic Mice with DHA Treatment.

Olfactory dysfunction and atrophy of olfactory brain regions are observed early in mild cognitive impairment and Alzheimer disease. Despite substantial evidence showing neuroprotective effects in MCI/AD with treatment of docosahexaenoic acid (DHA), an omega-3 fatty acid, few studies have assessed DHA and its effects on the olfactory system deficits. We therefore performed structural (MRI), functional (olfactory behavior, novel object recognition), and molecular (markers of apoptosis and inflammation) assessments of APOE4 and wild-type mice ± DHA treatment at 3, 6, and 12 months of age. Our results demonstrate that APOE4 mice treated with the control diet show recognition memory deficits, abnormal olfactory habituation, and discrimination abilities and an increase in IBA-1 immunoreactivity in the olfactory bulb. These phenotypes were not present in APOE4 mice treated with a DHA diet. Alterations in some brain regions' weights and/or volumes were observed in the APOPE4 mice and may be due to caspase activation and/or neuroinflammatory events. These results suggest that the consumption of a diet rich in DHA may provide some benefit to E4 carriers but may not alleviate all symptoms.

Allelic variation within the major APOE CpG island affects its methylation in the brain of targeted replacement mice expressing human APOE

•The number of cytosine-phosphate-guanine (CpG) sites differs due to sequence variation in the human apolipoprotein E (APOE) gene.•APOE DNA methylation is allele-dependently altered corresponding to the total number of CpG pairs in the brain of APOE targeted replacement mice (APOE εpsilon 4 > εpsilon 3 > εpsilon 2).•Binding of the methyl-CpG binding protein 2 to genomic APOE was in trend less pronounced in the brain of APOE4 mice.

Abstract 584: Myeloid Kruppel-like Factor 14 Mediates Sexual Dimorphism Of Abdominal Aortic Aneurysm Via Estrogen Receptor β

Rationale: Abdominal aortic aneurysm (AAA) is an irreversible degenerative disease of the abdominal aorta. Monocytes/macrophages are important mediators of inflammation and proteolysis during AAA development. In both human and rodent models, AAA has strong sexual dimorphism with a 4-6-fold higher prevalence in males than females, largely attributed to the estrogen/estrogen receptor signaling pathway. Krüppel-Like Factor 14 (KLF14) mediates anti-inflammatory response during disease pathogenesis and shows sexual heterogeneity in human genetic studies. However, whether and how KLF14 regulates sexual dimorphism during AAA progression has largely been unknown. Objective: Herein, we generated a novel insight into the anti-inflammatory effect and sexual dimorphic regulation of KLF14 during AAA pathogenesis. Methods and Results: We induced AAA model in myeloid cell-specific Klf14 knockout mice in ApoE -deficient background ( Klf14 LysM ApoE -/- ) and their littermate control mice ( Klf14 fl/fl ApoE -/- ). Klf14 deficiency in macrophages completely abrogated the sexual dimorphism observed in control mice by showing higher AAA incidence with more macrophage infiltration and more severe elastin degradation in female mice. Mechanistically, KLF14 upregulates the transcription of estrogen receptors, especially ESR2 , in macrophages. Perhexiline, a KLF14 inducer, induces Esr2 expression dependent on Klf14 and exerts an anti-inflammatory effect partially dependent on Esr2 in macrophages. Furthermore, Klf14 or Esr2 deficiency in macrophages abolished the protective effect of exogenous estradiol (E 2 ) treatment in male control mice. Conclusions: These studies provide evidence that Klf14 deficiency within myeloid lineage cells accelerated AAA development in female mice, resulting in the loss of sexual dimorphism in AAA pathogenesis. KLF14 showed protective effects, likely via transcriptionally regulating ESR2 expression and suppressing inflammation.

Exercise-induced upregulation of APOE expression is attenuated by dietary supplementation with resveratrol

The ε4 variant of the Apolipoprotein E gene (APOE4) is the most prevalent genetic risk factor for Alzheimer’s disease (AD). Approximately 25% of people carry at least one copy of the variant which increases risk of AD two-to-three-fold relative to those who carry the ε3 variant. Low ApoE levels are typically reported in Alzheimer’s patients and animal studies have reveal lower levels of ApoE in ε4 carriers relative to ε3 carriers. Therefore, reduced ApoE levels has been associated with increased risk for dementia. Physical exercise and active lifestyles are well-accepted therapeutic strategies for the prevention or delay of Alzheimer’s disease and other dementias, Additionally, there is growing evidence that the consumption of antioxidant nutritional supplements may also be therapeutic and slow progression of AD. But the effect of physical activity or antioxidant intake on APOE expression is not well-studied.The objective of this study is to determine the impact of exercise and resveratrol intake on APOE expression. We hypothesized that both resveratrol intake and exercise would increase APOE expression in brain with an additive effect when combined. Targeted replacement mice, homozygous for either APOE3 or APOE4 were randomized into four groups based on activity and resveratrol dietary supplementation: sedentary standard, sedentary resveratrol, exercise standard, and exercise resveratrol. Exercised groups were subjected to daily treadmill running for 8 weeks. Resveratrol treated groups were fed a chow supplemented with resveratrol. Results showed that exercise induced a significant increase in ApoE protein in brain cortex of both APOE3 and APOE4 mice. Resveratrol treatment alone had no significant effect on brain APOE expression, but in combination with exercise, attenuated the exercise-induced increase. While biochemical variations between APOE3 and APOE4 mice likely contribute to the differential risk for AD, the exercise-induced increase in ApoE levels in both genotypes supports a role for APOE in the therapeutic mechanisms of exercise. The timing of antioxidant supplementation in conjunction with exercise interventions should be critically considered to ensure best therapeutic efficacy of exercise. This research was supported by NIH grants R25AG047843 and 2U54MD007597-31 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Allelic modulation of mesenteric artery mechanical properties in young and adult APOE3 and APOE4 mice

Previous studies from our lab have demonstrated age-related changes in vascular structure/function in posterior cerebral arteries (PCA) and left common carotid artery (CA) in male and female mice expressing human-ApoE targeted replacement of APOE3 (B6.129P2-Apoetm2(APOE*3)MaeN8) and APOE4 (B6.129P2-Apoetm3(APOE*4)Mae N8) (Taconic Labs). Therefore, we hypothesized that similar changes may be observed in the peripheral circulation. We isolated 3rd-order mesenteric arteries (MA) from young (Y, 3 to 4 mo) and adult (A, 7 to 10 mo), male and female mice expressing hPOE3 and hAPOE4. Mesenteric artery segments (5-8 mm in length) were isolated and cannulated on an arteriograph to assess vascular mechanical properties (lumen diameter (LD), wall thickness (WT), wall cross-sectional area (CSA), wall:lumen ratio (WL), distensibility (Dist), and stress/strain (SvS) under passive conditions (Ca2+-free Krebs + diltiazem) at intraluminal pressures ranging from 10-140 mmHg. Data were analyzed using two-way ANOVA, Student’s t-test, and analysis of nonlinear fit. Values were considered statistically different at P<0.05. Our data indicate that LD was greater in YE4 compared to YE3 mice (P<0.05), but was smaller in AE4 compared to AE3 mice (P<0.05). WT and WL was greater in YE3 mice compared to YE4 mice (P<0.05), but greater in AE4 compared to AE3 mice (P<0.05). While Dist was similar between YE3 and YE4 mice, AE4 mice exhibited less Dist than AE3 mice (P<0.05). Interestingly, distensibility increased between YE3 and AE3 mice (P<0.05), but was not significantly different between YE4 and AE4 mice. While compliance was similar between YE3 and YE4 mice, and similar between AE3 and AE4 mice, AE4 mice displayed decreased compliance compared to YE4 mice. No difference was seen between YE3 and AE3 mice. Wall stress was greater in YE4 mice compared to YE3 mice, but smaller in AE4 mice compared to AE3 mice (P<0.05), and an analogous pattern was observed in Einc for young and adult mice (P<0.05). These data indicate contrasting patterns of age-related vascular changes between allelotypes. Furthermore, these preliminary findings suggest that MA from A E4 mice exhibit a trend toward a hypertensive phenotype. Support: ABRC/ADHS18-205211 (DME, CBJ), Arizona Alzheimer's Consortium (funded by the Arizona Department of Health Services, Contract No. CTR040636) and matching funds from Midwestern University (DME), Biomedical Sciences Program (JF, KW, JD, DME), Biomedical Sciences Start-up Funds (DME) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Berberine is a potential alternative for metformin with good regulatory effect on lipids in treating metabolic diseases

Metformin (MTF) and berberine (BBR) share several therapeutic benefits in treating metabolic-related disorders. However, as the two agents have very different chemical structure and bioavailability in oral route, the goal of this study is to learn their characteristics in treating metabolic disorders. The therapeutic efficacy of BBR and MTF was systemically investigated in the high fat diet feeding hamsters and/or ApoE(-/-) mice; in parallel, gut microbiota related mechanisms were studied for both agents. We discovered that, although both two drugs had almost identical effects on reducing fatty liver, inflammation and atherosclerosis, BBR appeared to be superior over MTF in alleviating hyperlipidemia and obesity, but MTF was more effective than BBR for the control of blood glucose. Association analysis revealed that the modulation of intestinal microenvironment played a crucial role in the pharmacodynamics of both drugs, in which their respective superiority on the regulation of gut microbiota composition and intestinal bile acids might contribute to their own merits on lowering glucose or lipids. This study shows that BBR may be a good alternative for MTF in treating diabetic patients, especially for those complicated with dyslipidemia and obesity.

Advancing age increases the size and severity of spontaneous atheromas in mouse models of atherosclerosis

Using multiple mouse models, we explored the impact of aging on the size and severity of atherosclerotic lesions. In young, middle-aged and old apolipoprotein E knockout mice (ApoE−/−) fed an atherogenic diet (AD) for 3–8 weeks, plaque/atheroma formation in the descending aorta and aortic root, and atheroma development in the carotid in response to partial carotid ligation (PCL) were assessed. Total and LDL cholesterol, and triglycerides were higher in old compared to both other age groups, regardless of AD duration. Aortic plaque burden increased with AD duration in all ages. The size and plaque morphology grade of aortic root atheromas was higher with age; however, there was no effect of age on the size or severity of carotid atheromas after PCL. We additionally induced hyperlipidemia in young and old C57BL/6 mice by adeno-associated virus mediated upregulation of LDL receptor regulator, Pcsk9, and 5 weeks of AD. Despite lower cholesterol in old compared to young Pcsk9 mice, there was a greater size and severity of aortic root atheromas in old mice. However, like the ApoE−/− mice, there was no effect of age on size or severity of PCL-induced carotid artery atheromas in Pcsk9 mice. Together, these results suggest that aging increases the size and severity of spontaneous aortic atheromas.

Differential splicing of neuronal genes in a Trem2*R47H mouse model mimics alterations associated with Alzheimer’s disease

BackgroundMolecular characterization of late-onset Alzheimer’s disease (LOAD), the leading cause of age-related dementia, has revealed transcripts, proteins, and pathway alterations associated with disease. Assessing these postmortem signatures of LOAD in experimental model systems can further elucidate their relevance to disease origins and progression. Model organisms engineered with human genetic factors further link these signatures to disease-associated variants, especially when studies are designed to leverage homology across species. Here we assess differential gene splicing patterns in aging mouse models carrying humanized APOE4 and/or the Trem2*R47H variant on a C57BL/6J background. We performed a differential expression of gene (DEG) and differential splicing analyses on whole brain transcriptomes at multiple ages. To better understand the difference between differentially expressed and differentially spliced genes, we evaluated enrichment of KEGG pathways and cell-type specific gene signatures of the adult brain from each alteration type. To determine LOAD relevance, we compared differential splicing results from mouse models with multiple human AD splicing studies.ResultsWe found that differentially expressed genes in Trem2*R47H mice were significantly enriched in multiple AD-related pathways, including immune response, osteoclast differentiation, and metabolism, whereas differentially spliced genes were enriched for neuronal related functions, including GABAergic synapse and glutamatergic synapse. These results were reinforced by the enrichment of microglial genes in DEGs and neuronal genes in differentially spliced genes in Trem2*R47H mice. We observed significant overlap between differentially spliced genes in Trem2*R47H mice and brains from human AD subjects. These effects were absent in APOE4 mice and suppressed in APOE4.Trem2*R47H double mutant mice relative to Trem2*R47H mice.ConclusionsThe cross-species observation that alternative splicing observed in LOAD are present in Trem2*R47H mouse models suggests a novel link between this candidate risk gene and molecular signatures of LOAD in neurons and demonstrates how deep molecular analysis of new genetic models links molecular disease outcomes to a human candidate gene.

Peripheral apolipoprotein E proteins and their binding to LRP1 antagonize Alzheimer’s disease pathogenesis in the brain during peripheral chronic inflammation

C-reactive protein (CRP) impacts apolipoprotein E4 (ApoE4) allele to increase Alzheimer’s disease (AD) risk. However, it is unclear how the ApoE protein and its binding to LRP1 are involved. We found that ApoE2 carriers had the highest but ApoE4 carriers had the lowest concentrations of blood ApoE in both humans and mice; blood ApoE concentration was negatively associated with AD risk. Elevation of peripheral monomeric CRP (mCRP) reduced the expression of ApoE in ApoE2 mice, while it decreased ApoE-LRP1 binding in the brains of ApoE4 mice that was characterized by Proximity Ligation Assay. Both serum ApoE and brain ApoE-LRP1 binding were positively associated with the expression of pericytes that disappeared after mCRP treatment, and negatively associated with brain tauopathy and neuroinflammation in the presence of mCRP. In ApoE-/- mice, mCRP reduced the brain expression levels of synaptophysin and PSD95 and the positive relationship between ApoE-LRP1 binding and synaptophysin or PSD95 expression disappeared. Our study suggests that blood ApoE protects against AD pathogenesis by binding to LRP1 during peripheral chronic inflammation.

CCR5 deficiency normalizes TIMP levels, working memory, and gamma oscillation power in APOE4 targeted replacement mice

The APOE4 allele increases the risk for Alzheimer's disease (AD) in a dose-dependent manner and is also associated with cognitive decline in non-demented elderly controls. In mice with targeted gene replacement (TR) of murine APOE with human APOE3 or APOE4, the latter show reduced neuronal dendritic complexity and impaired learning. APOE4 TR mice also show reduced gamma oscillation power, a neuronal population activity which is important to learning and memory. Published work has shown that brain extracellular matrix (ECM) can reduce neuroplasticity as well as gamma power, while attenuation of ECM can instead enhance this endpoint. In the present study we examine human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 individuals and brain lysates from APOE3 and APOE4 TR mice for levels of ECM effectors that can increase matrix deposition and restrict neuroplasticity. We find that CCL5, a molecule linked to ECM deposition in liver and kidney, is increased in CSF samples from APOE4 individuals. Levels of tissue inhibitor of metalloproteinases (TIMPs), which inhibit the activity of ECM-degrading enzymes, are also increased in APOE4 CSF as well as astrocyte supernatants brain lysates from APOE4 TR mice. Importantly, as compared to APOE4/wild-type heterozygotes, APOE4/CCR5 knockout heterozygotes show reduced TIMP levels and enhanced EEG gamma power. The latter also show improved learning and memory, suggesting that the CCR5/CCL5 axis could represent a therapeutic target for APOE4 individuals.

The effects of age, genotype and diet on hippocampal subfield iron dysregulation and Alzheimer's disease biomarkers in an ApoE mouse model.

Current theories regarding accumulation of Alzheimer's disease-related deposits of abnormal intra- and extracellular proteins include reactions to inflammation and mitochondrial dysfunction. In this study, we explored whether age, genotype and inflammation via diet have a greater effect on dysregulatory protein accumulation in any particular subfield of the hippocampus. We stained for ferritin, ferroportin, hyperphosphorylated tau and β-amyloid proteins in the hippocampal region of Apolipoprotein E2 (ApoE2), ApoE3 or ApoE4 mice fed a control diet or a hypothesized inflammation-inducing methionine diet and euthanized at 3, 6, 9 or 12 months. We analysed stains based on hippocampal subfield and compared the protein accumulation levels within each group. We found significantly decreased ferritin expression in ApoE4 mice in the CA1 and Hi regions and decreased ferroportin expression in ApoE4 mice in the Hi region. There was also a significant effect on hyperphosphorylated tau protein levels based upon a given mouse genotype and diet interaction. Additionally, there were nonsignificant trends in each hippocampal subfield of increasing ferroportin and hyperphosphorylated tau after 6months of age and decreasing β-amyloid and ferritin with age. This study identified that there are changes in iron regulatory molecules based on genotype in the Hi and CA1 regions. Our findings also suggest a diet-genotype interaction, which affects levels of specific Alzheimer's disease biomarkers in the hippocampus. Additionally, we identified a trend toward increased ability to clear β-amyloid and decreased ability to clear hyperphosphorylated tau with age in all subfields, in addition to evidence of increasing iron load with time.

GSDME-mediated pyroptosis promotes the progression and associated inflammation of atherosclerosis

Pyroptosis, a type of Gasdermin-mediated cell death, contributes to an exacerbation of inflammation. To test the hypothesis that GSDME-mediated pyroptosis aggravates the progression of atherosclerosis, we generate ApoE and GSDME dual deficiency mice. As compared with the control mice, GSDME−/−/ApoE−/− mice show a reduction of atherosclerotic lesion area and inflammatory response when induced with a high-fat diet. Human atherosclerosis single-cell transcriptome analysis demonstrates that GSDME is mainly expressed in macrophages. In vitro, oxidized low-density lipoprotein (ox-LDL) induces GSDME expression and pyroptosis in macrophages. Mechanistically, ablation of GSDME in macrophages represses ox-LDL-induced inflammation and macrophage pyroptosis. Moreover, the signal transducer and activator of transcription 3 (STAT3) directly correlates with and positively regulates GSDME expression. This study explores the transcriptional mechanisms of GSDME during atherosclerosis development and indicates that GSDME-mediated pyroptosis in the progression of atherosclerosis could be a potential therapeutic approach for atherosclerosis.

Effects of APOE Genotype and Western Diet on Metabolic Phenotypes in Female Mice

Western diets high in sugars and saturated fats have been reported to induce metabolic and inflammatory impairments that are associated with several age-related disorders, including Alzheimer's disease (AD) and type 2 diabetes (T2D). The apolipoprotein E (APOE) genotype is associated with metabolic and inflammatory outcomes that contribute to risks for AD and T2D, with the APOE4 genotype increasing risks relative to the more common APOE3 allele. In this study, we investigated the impacts of the APOE genotype on systemic and neural effects of the Western diet. Female mice with knock-in of human APOE3 or APOE4 were exposed to control or Western diet for 13 weeks. In the control diet, we observed that APOE4 mice presented with impaired metabolic phenotypes, exhibiting greater adiposity, higher plasma leptin and insulin levels, and poorer glucose clearance than APOE3 mice. Behaviorally, APOE4 mice exhibited worse performance in a hippocampal-dependent learning task. In visceral adipose tissue, APOE4 mice exhibited generally higher expression levels of macrophage- and inflammation-related genes. The cerebral cortex showed a similar pattern, with higher expression of macrophage- and inflammation-related genes in APOE4 than APOE3 mice. Exposure to the Western diet yielded modest, statistically non-significant effects on most metabolic, behavioral, and gene expression measures in both APOE genotypes. Interestingly, the Western diet resulted in reduced gene expression of a few macrophage markers, specifically in APOE4 mice. The observed relative resistance to the Western diet suggests protective roles of both female sex and young adult age. Further, the data demonstrate that APOE4 is associated with deleterious systemic and neural phenotypes and an altered response to a metabolic stressor, findings relevant to the understanding of interactions between the APOE genotype and risks for metabolic disorders.

Exposure to chlorpyrifos during pregnancy differentially affects social behavior and GABA signaling elements in an APOE- and sex-dependent manner in a transgenic mouse model

The massive use of chlorpyrifos (CPF) has been associated with an increased prevalence of neurodevelopmental disorders. Some previous studies have shown that prenatal, but not postnatal, CPF exposure causes social behavior deficits in mice depending on sex while others have found that in transgenic mice models carrying the human apolipoprotein E (APOE) ε3 and ε4 allele confer different vulnerabilities to either behavioral or metabolic disorders after CPF exposure. This study aims to evaluate, in both sexes, how prenatal CPF exposure and APOE genotype impact on social behavior and its relation to changes in GABAergic and glutamatergic systems. For this purpose, apoE3 and apoE4 transgenic mice were exposed through the diet to 0 or 1 mg/kg/day of CPF, between gestational day 12 and 18. A three-chamber test was used to assess social behavior on postnatal day (PND) 45. Then, mice were sacrificed, and hippocampal samples were analyzed to study the gene expression of GABAergic and glutamatergic elements. Results showed that prenatal exposure to CPF impaired social novelty preference and increased the expression of GABA-A α1 subunit in females of both genotypes. In addition, the expression of GAD1, the ionic cotransporter KCC2 and the GABA-A α2 and α5 subunits were increased in apoE3 mice, whereas CPF treatment only accentuated the expression of GAD1 and KCC2. Nevertheless, future research is needed to evaluate whether the influences detected in the GABAergic system are present and functionally relevant in adults and old mice.

The mitochondrial BCKD complex interacts with hepatic apolipoprotein E in cultured cells in vitro and mouse livers in vivo

Background and aimsApolipoprotein E (APOE) is known for its role in lipid metabolism and its association with age-related disease pathology. The aim of the present work was to identify previously unknown functions of APOE based on the detection of novel APOE protein–protein interaction candidates.Approach and resultsAPOE targeted replacement mice and transfected cultured hepatocytes expressing the human isoforms APOE3 and APOE4 were used. For 7 months, APOE3 and APOE4 mice were fed a high-fat and high-sugar diet to induce obesity, while a subgroup was subjected to 30% dietary restriction. Proteomic analysis of coimmunoprecipitation products from APOE mouse liver extracts revealed 28 APOE-interacting candidate proteins, including branched-chain alpha-keto acid dehydrogenase (BCKD) complex subunit alpha (BCKDHA) and voltage-dependent anion-selective channel 1 (VDAC1). The binding of APOE and BCKDHA was verified in situ by proximity ligation assay in cultured cells. The activity of the BCKD enzyme complex was significantly higher in obese APOE4 mice than in APOE3 mice, while the plasma levels of branched-chain amino acids and mTOR signalling proteins were not different. However, the protein–protein interaction with VDAC1 was strongly induced in APOE3 and APOE4 mice upon dietary restriction, suggesting a prominent role of APOE in mitochondrial function.ConclusionsThe protein–protein interactions of APOE with BCKDHA and VDAC1 appear to be of physiological relevance and are modulated upon dietary restriction. Because these are mitochondrial proteins, it may be suggested that APOE is involved in mitochondria-related processes and adaptation to hepatic energy demands.

TRPV1 regulates ApoE4-disrupted intracellular lipid homeostasis and decreases synaptic phagocytosis by microglia

Although the ε4 allele of the apolipoprotein E (ApoE4) gene has been established as a genetic risk factor for many neurodegenerative diseases, including Alzheimer’s disease, the mechanism of action remains poorly understood. Transient receptor potential vanilloid 1 (TRPV1) was reported to regulate autophagy to protect against foam cell formation in atherosclerosis. Here, we show that ApoE4 leads to lipid metabolism dysregulation in microglia, resulting in enhanced MHC-II-dependent antigen presentation and T-cell activation. Lipid accumulation and inflammatory reactions were accelerated in microglia isolated from TRPV1flox/flox; Cx3cr1cre-ApoE4 mice. We showed that metabolic boosting by treatment with the TRPV1 agonist capsaicin rescued lipid metabolic impairments in ApoE4 neurons and defects in autophagy caused by disruption of the AKT-mTOR pathway. TRPV1 activation with capsaicin reversed ApoE4-induced microglial immune dysfunction and neuronal autophagy impairment. Capsaicin rescued memory impairment, tau pathology, and neuronal autophagy in ApoE4 mice. Activation of TRPV1 decreased microglial phagocytosis of synapses in ApoE4 mice. TRPV1 gene deficiency exacerbated recognition memory impairment and tau pathology in ApoE4 mice. Our study suggests that TRPV1 regulation of lipid metabolism could be a therapeutic approach to alleviate the consequences of the ApoE4 allele.

APOE2 Exacerbates TDP-43 Related Toxicity in the Absence of Alzheimer Pathology.

Recent evidence supports a link between increased TDP-43 burden and the presence of an APOE4 gene allele in Alzheimer's disease (AD); however, it is difficult to conclude the direct effect of APOE on TDP-43 pathology due to the presence of mixed AD pathologies. The goal of this study is to address how APOE isoforms impact TDP-43 pathology and related neurodegeneration in the absence of typical AD pathologies. We overexpressed human TDP-43 via viral transduction in humanized APOE2, APOE3, APOE4 mice, and murine Apoe-knockout (Apoe-KO) mice. Behavior tests were performed across ages. Animals were harvested at 11months of age and TDP-43 overexpression-related neurodegeneration and gliosis were assessed. To further address the human relevance, we analyzed the association of APOE with TDP-43 pathology in 160 postmortem brains from autopsy-confirmed amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with motor neuron disease (FTLD-MND) in the Mayo Clinic Brain Bank. We found that TDP-43 overexpression induced motor function deficits, neuronal loss, and gliosis in the motor cortex, especially in APOE2 mice, with much milder or absent effects in APOE3, APOE4, or Apoe-KO mice. In the motor cortex of the ALS and FTLD-MND postmortem human brains, we found that the APOE2 allele was associated with more severe TDP-43-positive dystrophic neurites. Our data suggest a genotype-specific effect of APOE on TDP-43 proteinopathy and neurodegeneration in the absence of AD pathology, with the strongest association seen with APOE2. ANN NEUROL 2023;93:830-843.

ApoE isoform does not influence skeletal muscle regeneration in adult mice.

Introduction: Apolipoprotein E (ApoE) has been shown to be necessary for proper skeletal muscle regeneration. Consistent with this finding, single-cell RNA-sequencing analyses of skeletal muscle stem cells (MuSCs) revealed that Apoe is a top marker of quiescent MuSCs that is downregulated upon activation. The purpose of this study was to determine if muscle regeneration is altered in mice which harbor one of the three common human ApoE isoforms, referred to as ApoE2, E3 and E4. Methods: Histomorphometric analyses were employed to assess muscle regeneration in ApoE2, E3, and E4 mice after 14days of recovery from barium chloride-induced muscle damage in vivo, and primary MuSCs were isolated to assess proliferation and differentiation of ApoE2, E3, and E4 MuSCs in vitro. Results: There was no difference in the basal skeletal muscle phenotype of ApoE isoforms as evaluated by section area, myofiber cross-sectional area (CSA), and myonuclear and MuSC abundance per fiber. Although there were no differences in fiber-type frequency in the soleus, Type IIa relative frequency was significantly lower in plantaris muscles of ApoE4 mice compared to ApoE3. Moreover, ApoE isoform did not influence muscle regeneration as assessed by fiber frequency, fiber CSA, and myonuclear and MuSC abundance. Finally, there were no differences in the proliferative capacity or myogenic differentiation potential of MuSCs between any ApoE isoform. Discussion: Collectively, these data indicate nominal effects of ApoE isoform on the ability of skeletal muscle to regenerate following injury or the in vitro MuSC phenotype.