Apolipoprotein E Isoforms Research Articles

Effects of APOE isoforms in diabetic nephropathy patients of South India.

Diabetic nephropathy (DN) is a grave complication and the most common renal dysfunction of diabetes mellitus. Genetic factors, including Apolipoprotein E (APOE) isoforms, have been implicated in the pathogenesis of DN. A total of 577 type 2 Diabetes mellitus subjects were categorized into diabetes non-nephropathic (Controls: n = 321), diabetes nephropathic (DN: n = 256) groups. Demographic, clinical, and biochemical parameters including age, BMI, lipid profiles (TC, LDL-C, HDL-C, TG), glucose metabolism (plasma glucose, HbA1c, serum insulin), renal function (UACR, PCR), and blood pressure (SBP, DBP) were assessed. APOE variant frequencies were determined using restriction fragment length polymorphism (RFLP) analysis, validated against Hardy-Weinberg equilibrium (HWE), and statistically correlated with each clinical and biochemical parameter. The DN group had an increased prevalence of hypertension, fatty liver, and dyslipidemia compared to the Control group. Biochemical analyses revealed elevated levels of TC (213.41mg/dL vs. 189.32mg/dL), LDL-C (134.46mg/dL vs. 107.56mg/dL), and reduced HDL-C (58.13mg/dL vs. 65.32mg/dL) in DN cases compared to Controls (all p < 0.0001). The APOE variants distribution showed a significant increase in E2 allele frequency (69.1% vs. 15.3%) and corresponding homozygous genotype (E2/2: 42.2% vs. 5.6%) in DN cohorts. The study found a higher frequency of E2 allele in the DN group compared to Controls, though no statistically significant risk of DN was linked to this allele. The results suggest a potential association for APOE polymorphisms, requiring broader studies to clarify the role of APOE polymorphisms in DN susceptibility.

IPSC-derived blood-brain barrier modeling reveals APOE isoform-dependent interactions with amyloid beta

BackgroundThree common isoforms of the apolipoprotein E (APOE) gene - APOE2, APOE3, and APOE4 - hold varying significance in Alzheimer’s Disease (AD) risk. The APOE4 allele is the strongest known genetic risk factor for late-onset Alzheimer’s Disease (AD), and its expression has been shown to correlate with increased central nervous system (CNS) amyloid deposition and accelerated neurodegeneration. Conversely, APOE2 is associated with reduced AD risk and lower CNS amyloid burden. Recent clinical data have suggested that increased blood-brain barrier (BBB) leakage is commonly observed among AD patients and APOE4 carriers. However, it remains unclear how different APOE isoforms may impact AD-related pathologies at the BBB.MethodsTo explore potential impacts of APOE genotypes on BBB properties and BBB interactions with amyloid beta, we differentiated isogenic human induced pluripotent stem cell (iPSC) lines with different APOE genotypes into both brain microvascular endothelial cell-like cells (BMEC-like cells) and brain pericyte-like cells. We then compared the effect of different APOE isoforms on BBB-related and AD-related phenotypes. Statistical significance was determined via ANOVA with Tukey’s post hoc testing as appropriate.ResultsIsogenic BMEC-like cells with different APOE genotypes had similar trans-endothelial electrical resistance, tight junction integrity and efflux transporter gene expression. However, recombinant APOE4 protein significantly impeded the “brain-to-blood” amyloid beta 1–40 (Aβ40) transport capabilities of BMEC-like cells, suggesting a role in diminished amyloid clearance. Conversely, APOE2 increased amyloid beta 1–42 (Aβ42) transport in the model. Furthermore, we demonstrated that APOE-mediated amyloid transport by BMEC-like cells is dependent on LRP1 and p-glycoprotein pathways, mirroring in vivo findings. Pericyte-like cells exhibited similar APOE secretion levels across genotypes, yet APOE4 pericyte-like cells showed heightened extracellular amyloid deposition, while APOE2 pericyte-like cells displayed the least amyloid deposition, an observation in line with vascular pathologies in AD patients.ConclusionsWhile APOE genotype did not directly impact general BMEC or pericyte properties, APOE4 exacerbated amyloid clearance and deposition at the model BBB. Conversely, APOE2 demonstrated a potentially protective role by increasing amyloid transport and decreasing deposition. Our findings highlight that iPSC-derived BBB models can potentially capture amyloid pathologies at the BBB, motivating further development of such in vitro models in AD modeling and drug development.

Apolipoprotein E in Alzheimer's Disease: Focus on Synaptic Function and Therapeutic Strategy.

Synaptic dysfunction is a critical pathological feature in the early phase of Alzheimer's disease (AD) that precedes typical hallmarks of AD, including beta-amyloid (Aβ) plaques and neurofibrillary tangles. However, the underlying mechanism of synaptic dysfunction remains incompletely defined. Apolipoprotein E (APOE) has been shown to play a key role in the pathogenesis of AD, and the ε4 allele of APOE remains the strongest genetic risk factor for sporadic AD. Itiswidelyrecognizedthat APOE4 accelerates the development of Aβ andtau pathology in AD. Recent studies have indicated that APOE affects synaptic function through a variety of pathways. Here, we summarize the mechanism of modulating synapses by various APOE isoforms and demonstrate the therapeutic potential by targeting APOE4 for AD treatment.

APOE genotype modifies microglial immunometabolism

AbstractBackgroundMetabolic dysfunction and neuroinflammation characterize Alzheimer’s disease (AD), but it is unclear if these two facets of the disease are linked. The E4 allele of Apolipoprotein E (APOE) is the strongest genetic risk factor for late‐onset AD and is associated with increased neuroinflammation. Recent data from our lab and others show that E4 is also associated with increased aerobic glycolysis. These two findings may be intrinsically linked through the concept of ‘immunometabolism’ ‐ an emerging paradigm that implicates increased glycolysis as a core requirement during pro‐inflammatory activation, whereas increased oxidative phosphorylation is required for anti‐inflammatory responses.MethodPrimary microglia from mice expressing human APOE isoforms were stimulated with a combination of interferon‐γ and tumor necrosis factor‐α, two pro‐inflammatory cytokines implicated in AD. Metabolic responses were measured using the Agilent Seahorse platform and targeted metabolomics. In addition, we performed single‐cell RNA sequencing on brains from APOE targeted replacement mice at 3‐, 10‐, and 18 months of age. APOE targeted replacement mice were also crossed to the 5x Familial Alzheimer’s Disease model and brains were analyzed by spatial transcriptomics.ResultSeahorse revealed increased glycolysis and decreased mitochondrial respiration in E4 microglia. Targeted metabolomics revealed increased lactate and succinate in E4 microglia, metabolites known to accumulate in pro‐inflammatory macrophages. Aged E4 brains were found to harbor a metabolically distinct cluster of microglia that expressed a signature similar to the established ‘disease associated microglia’ (DAM) phenotype, even in the absence of neuropathology. SCENIC regulon analysis linked this cluster to the transcription network of HIF1a. Ongoing experiments targeting the HIF1a pathway seek to correct the E4‐associated increased aerobic glycolysis and excess pro‐inflammatory cytokine secretion.ConclusionOur findings reveal that inflammatory stimulation, age, and amyloid each induce a distinct metabolic response in E4 microglia. The accumulation of lactate and succinate and increased glycolysis in E4 microglia indicate altered metabolic preference conducive to pro‐inflammatory activation, whereas the decreased mitochondrial respiration may preclude effective anti‐inflammatory responses. We propose that this altered metabolism skews E4 microglia towards a phenotype that favors chronic neuroinflammation and neurodegeneration. Thus, reprogramming metabolism in E4 microglia may provide a novel therapeutic avenue for the treatment of AD.

Carboxyl truncation of α-synuclein occurs early and is influenced by human APOE genotype in transgenic mouse models of α-synuclein pathogenesis

Post-translational modifications to the carboxyl (C) terminus domain of α-synuclein can play an important role in promoting the pathologic aggregation of α-synuclein. Various cleavages that diminish this highly charged, proline-rich region can result in exposure of hydrophobic, aggregation-prone regions, thereby accelerating the aggregation kinetics of α-synuclein into misfolded, pathologic forms. C-terminally truncated forms of α-synuclein are abundant in human diseased brains compared to controls, suggesting a role in disease pathogenesis. Factors that alter the homeostatic proteolytic processing of α-synuclein may ultimately tip the balance towards a progressive disease state. Apolipoprotein E (APOE) has been implicated in the acceleration of cognitive impairment in patients with Lewy body diseases. The APOE4 isoform has been found to cause dysregulation in the endosomal–lysosomal pathway, which could result in altered α-synuclein degradation as a potential mechanism for promoting its pathologic misfolding. Herein, we investigate the spatiotemporal accumulation of C-terminally truncated α-synuclein in a seeded and progressive mouse model of synucleinopathy. Furthermore, we study how this process is influenced in the context of mice that are altered to express either the human APOE3 or APOE4 isoforms. We found that specific C-terminal truncation of α-synuclein occurs at early stages of pathogenesis. We also found that proteolytic processing of this domain differs across various brain regions and is influenced by the presence of different human APOE isoforms. Our data demonstrate an early pathogenic role for C-terminally truncated α-synuclein, and highlight the influence of APOE isoforms in modulating its impact.

APOE genotype modifies microglial immunometabolism

AbstractBackgroundMetabolic dysfunction and neuroinflammation characterize Alzheimer’s disease (AD), but it is unclear if these two facets of the disease are linked. The E4 allele of Apolipoprotein E (APOE) is the strongest genetic risk factor for late‐onset AD and is associated with increased neuroinflammation. Recent data from our lab and others show that E4 is also associated with increased aerobic glycolysis. These two findings may be intrinsically linked through the concept of ‘immunometabolism’ ‐ an emerging paradigm that implicates increased glycolysis as a core requirement during pro‐inflammatory activation, whereas increased oxidative phosphorylation is required for anti‐inflammatory responses.MethodPrimary microglia were isolated from targeted replacement mice expressing human APOE isoforms and stimulated with pro‐inflammatory (lipopolysaccharide (LPS); IFNγ + TNFα) or anti‐inflammatory (IL‐10; IL‐4 + IL‐13) cytokines. Metabolic responses were measured using the Agilent Seahorse platform and targeted metabolomics. We also performed single‐cell RNA sequencing on brains from APOE targeted replacement mice at 3‐, 10‐, and 18 months of age +/‐ LPS.ResultSeahorse revealed increased glycolysis and decreased mitochondrial respiration in E4 microglia. Targeted metabolomics revealed increased lactate and succinate in E4 microglia, metabolites known to accumulate in pro‐inflammatory macrophages. Aged E4 brains were uniquely found to harbor a metabolically distinct subcluster of microglia that expressed a signature similar to the established ‘disease associated microglia’ phenotype, even in the absence of neuropathology. SCENIC regulon analysis linked this cluster to the transcription network of HIF1a, and increased expression of HIF1a was validated in E4 microglia. In LPS‐treated animals, two distinct microglia subclusters emerged in E4 brains that were defined by altered expression of genes relating to oxidative phosphorylation and mitochondrial function.ConclusionOur findings reveal that age and LPS treatment induce a distinct metabolic response in E4 microglia. The accumulation of lactate and succinate and increased glycolysis in E4 microglia indicate altered metabolic preference conducive to pro‐inflammatory activation, whereas the decreased mitochondrial respiration may preclude effective anti‐inflammatory responses. We propose that this altered metabolism skews E4 microglia towards a phenotype that favors chronic neuroinflammation and neurodegeneration. Thus, reprogramming metabolism in E4 microglia may provide a novel therapeutic avenue for the treatment of AD.

Impact of Testosterone Deficiency on Adipose Tissue Metabolic Activity and Plasma Lipoprotein and Glucose Homeostasis: The Role of Apolipoprotein E2 and E4 Isoforms

Background: Recent findings indicate that testosterone deficiency (TD) affects key metabolic processes, such as lipid and carbohydrate metabolism. Apolipoprotein E (APOE) is the natural ligand for the low-density lipoprotein receptor (LDLR). The natural APOE isoforms APOE3 and APOE4 have a high affinity for LDLR, while APOE2 exhibits impaired binding to the receptor and an inability to promote lipoprotein remnant clearance. Previous work indicated that LDLR modulates the effects of TD on adipose tissue mitochondrial metabolic activity. Here, we investigated how APOE2 or APOE4 expression influences the effects of TD on plasma lipid and glucose homeostasis and white adipose tissue and brown adipose tissue (BAT) mitochondrial metabolic activity. Materials and Methods: APOE2 knock-in (Apoe2knock-in) and APOE4 knock-in (Apoe4knock-in) mice were subjected to surgical castration or sham operation. Mice were fed western-type diet for a period of 12 weeks, and a series of analyses were performed on live animals or specimens collected at the end of the study. Results: TD results in body weight loss only in Apoe4knock-in mice. Castrated Apoe2knock-in mice show much reduced BAT mitochondrial uncoupling protein 1 (Ucp1) and CytC expression, which may explain the body weight difference between castrated Apoe2knock-in and Apoe4knock-in mice. The reduced body weight gain in castrated APOE4-expressing mice did not alleviate the already much impaired glucose tolerance of these mice or their hepatic triglyceride levels. Quite strikingly, in both mouse strains hypogonadism brings about negative effects on lipoprotein metabolism, manifested by different disturbances. Conclusions: TD is associated with distinct metabolic abnormalities, which depend on the APOE isoform expressed.

Exploring Protein Structure with RasMol, a Free Online Tool

Understanding the structural and functional relationships of proteins is an important concept of biology. Therefore, we had Gordon State College students in the biochemistry class of spring 2019 apply and evaluate a hands-on bioinformatics activity, using the free bioinformatics program, RasMol. This module was designed to help students understand the relationships of a protein to a specific disease, and in this paper, we have chosen to discuss apolipoprotein E (APOE) relationships to Alzheimer’s disease since some of the students had an interest in neurobiochemistry. During the learning module, students were asked to identify structural differences among the APOE isoforms. Overall, 20 out of 27 students (74.1%) evaluated the instructional value of the RasMol program positively after being surveyed. Student feedback also suggested they learned more about the molecular structure of APOE using RasMol. Therefore, utilization of free computer bioinformatics activities encourages students to apply logical, real-world solutions to biological problems.

Mesenteric Artery Reactivity in Young APOE3 and APOE4 Mice

IntroductionVariant isoforms of apolipoprotein E (APOE) are risk factors for both Alzheimer’s disease (AD) and cardiovascular disease (CVD), with the APOE4 isoform increasing risk compared to the most common isoform, APOE3. Allelotype alters cerebral artery reactivity and cardiac indices in aged animals (ongoing studies in our lab), yet little is known about how allelotype affects systemic circulation. Thus, we hypothesized that APOE allelotype alters mesenteric arteries (MA) in mice. We determined the mechanical characteristics and vascular reactivity of 3rd‐order MA isolated from young (Y, 3 to 4 mo), male and female mice expressing human‐ApoE targeted replacement of APOE3 (B6.129P2‐Apoetm2(APOE*3)Mae N8) and APOE4 (B6.129P2‐Apoetm3(APOE*4)Mae N8) (Taconic Labs).MethodsMAs were isolated, cleaned of connective tissue, cut into 8mm segments, and cannulated in an arteriograph chamber to assess vascular reactivity via myogenic tone (MT) and phenylephrine (PE)‐induced constriction (1µM). Passive mechanical properties assessed at intraluminal pressures of 10mm Hg to 140mm Hg included lumen diameter, wall thickness, wall tension, stress vs pressure, distensibility and arterial stress/strain. Data were analyzed using two‐way ANOVA and Students t‐test.ResultsMT was greater in E3 mice compared to E4 mice (P&lt;0.001). K+‐ and PE‐induced constriction were similar between E3 mice and E4 mice. Subtle, yet significant changes were observed in passive mechanical properties. Lumen diameter and wall tension was greater in E4 mice compared E3 mice (P&lt;0.01). Wall thickness was greater in E3 mice vs E4 mice (P&lt;0.05). Stress vs pressure was greater in E4 mice vs E3 mice (P&lt;0.05). E4 mice tended to have greater stress vs pressure and distensibility values than E3 mice, but they did not reach statistical significance. Finally, stress vs strain values in MA from E3 mice and E4 mice were similar.Summary/ConclusionsThese data indicate allelotype alters MA vascular reactivity and structural properties. Additional studies are warranted to determine whether these changes in systemic circulation persist with ageing and contribute to altered cerebral and cardiac structure/function observed in ongoing studies in our lab.

APOE4 dysregulates autophagy in cultured cells.

Human APOE4 (apolipoprotein E4 isoform) is a powerful genetic risk factor for late-onset Alzheimer disease (AD). Many groups have investigated the effect of APOE4 on the degradation of amyloid β (Aβ), the main component of plaques found in the brains of AD patients. However, few studies have focused on the degradation of APOE itself. We investigated the lysosomal trafficking of APOE in cells and found that APOE from the post-Golgi compartment is degraded through an autophagic process requiring the lysosomal membrane protein LAMP2A. We found that APOE4 accumulates in enlarged lysosomes, alters autophagic flux, and changes the proteomic contents of lysosomes following internalization. This dysregulated lysosomal trafficking may represent one of the mechanisms that contributes to AD pathogenesis.

Genetic polymorphisms of apolipoprotein E in nonarteritic anterior ischemic optic neuropathy.

To elucidate the potential role of genetic polymorphisms of apolipoprotein E (APOE) in nonarteritic anterior ischemic optic neuropathy (NAION) and the association between APOE and NAION-induced ocular impairments. A total of 73 NAION patients and 73 sex- and age-matched healthy controls were recruited for the study. Genomic DNA was isolated from peripheral blood samples. The alleles and genotypes of APOE were explored. The interaction between APOE and medical comorbidities was assessed by the multifactor dimensionality reduction (MDR) method. Among 81 affected eyes of NAION patients, an additional association study of APOE isoforms with visual impairments was carried out. The allele and genotype frequencies for APOE showed significant differences when comparing NAION cases and controls. Multivariate analysis adjusted for age, sex, hypertension, dyslipidemia, diabetes mellitus, cardiovascular disease, and cerebrovascular disease revealed that the ε3/ε4 genotype (OR = 3.86, 95% CI = 1.13-13.25, p = 0.032) and ε4 allele (OR = 3.55, 95% CI = 1.05-11.99, p = 0.041) were strong independent risk factors for NAION. Compared to eyes with the ε3/ε3 + ε2/ε4 genotype, individuals with the ε4/ε4 + ε3/ε4 genotype had worse visual field defects (VFDs) and thinner macular ganglion cell complex (mGCC) thicknesses with larger focal loss of volume (FLV) and general loss of volume (GLV). Compared to ε4 noncarriers, ε4 carriers also tended to have more serious VFD and mGCC loss. APOE polymorphisms conferred a significant risk of NAION and were significantly related to ocular impairments caused by NAION.

Familial Hypercholesterolemia: Real-World Data of 1236 Patients Attending a Czech Lipid Clinic. A Retrospective Analysis of Experience in More than 50 years. Part I: Genetics and Biochemical Parameters.

Introduction: The cause of familial hypercholesterolemia (FH) is defect in LDL receptor or familial defect of apolipoprotein B-100 (FDB) or, rarely, defect in proprotein convertase subtilisin/kexin type 9. Identification and treatment of patients with FH improves their prognosis. Our data represent retrospective analysis of 50 years of specialised care in our center. Patients and Methods: A group of 1236 FH patients (841 women, 395 men; 993 study subjects and 243 relatives; mean age 44.8 ± 16.7 years) included 154 FDB patients followed at the Lipid Clinic of the General University Hospital in Prague since the mid-1960s to the present. Clinical diagnosis was based on the Dutch Lipid Clinic Network Criteria. Genetic analysis was performed using PCR-RFLP to detect FDB and apolipoprotein E (APOE) polymorphism. Biochemical data were collected and statistically analysed. Results: At baseline, mean LDL-C and total cholesterol (TC) levels of all FH patients combined were 6.49 ± 1.92 mmol/L and 8.95 ± 1.95 mmol/L, respectively. Their LDL-C levels decreased to 3.26 ± 1.57 mmol/L and TC levels to 5.43 ± 1.69 mmol/L during follow-up. In the subgroup of LDL receptor-mediated FH (non-FDB) patients, baseline LDL-C and TC levels of 6.61 ± 1.95 mmol/L and 9.09 ± 1.97 mmol/L declined to 3.21 ± 1.60 mmol/L and 5.39 ± 1.72 mmol/L, respectively, during follow-up. In the FDB subgroup of patients, baseline levels of LDL-C and TC were 5.57 ± 1.46 mmol/L and 7.88 ± 1.58 mmol/L decreasing to 3.45 ± 0.24 mmol/L and 5.58 ± 1.37 mmol/L, respectively, during follow-up. Differences were also found in the effects of various APOE isoforms on lipid lowering. A significant decrease in lipid parameters was observed with the E2E2 isoform whereas a minimal decrease was seen with the E4E4 and E3E3 isoforms. Conclusion: Whereas, overall, non-FDB patients had higher baseline lipid levels, these levels declined more appreciably compared with FDB patients during follow-up. Our retrospective analysis also found different effects of APOE isoforms on the decrease in lipid levels.

Differential associations between apolipoprotein E alleles and cerebral myelin content in normative aging

Mounting evidence indicates that myelin breakdown may represent an early phenomenon in neurodegeneration, including Alzheimer's disease (AD). Understanding the factors influencing myelin synthesis and breakdown will be essential for the development and evaluation of therapeutic interventions. In this work, we assessed associations between genetic variance in apolipoprotein E (APOE) and cerebral myelin content. Quantitative magnetic resonance imaging (qMRI) was performed on a cohort of 92 cognitively unimpaired adults ranging in age from 24 to 94 years. We measured whole-brain myelin water fraction (MWF), a direct measure of myelin content, as well as longitudinal and transverse relaxation rates (R1 and R2), sensitive measures of myelin content, in carriers of the APOE ε4 or APOE ε2 alleles and individuals with the ε33 genotype. Automated brain mapping algorithms and statistical models were used to evaluate the relationships between MWF or relaxation rates and APOE isoforms, accounting for confounding variables including age, sex, and race, in several cerebral structures. Our results indicate that carriers of APOE ε2 exhibited significantly higher myelin content, that is, higher MWF, R1 or R2 values, in most brain regions investigated as compared to noncarriers, while ε4 carriers exhibited trends toward lower myelin content compared to noncarriers. Finally, all qMRI metrics exhibited quadratic, inverted U-shape, associations with age; attributed to the development of myelination from young to middle age followed by progressive loss of myelin afterwards. Sex and race effects on myelination were, overall, nonsignificant. These findings suggest that individual genetic background may influence cerebral myelin maintenance. Although preliminary, this work lays the foundation for further investigations to clarify the relationship between APOE genotype and myelination, which may suggest potential targets in treatment or prevention of AD.

Isoform-dependent lysosomal degradation and internalization of apolipoprotein E requires autophagy proteins.

ABSTRACTThe human apolipoprotein E4 isoform (APOE4) is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), and lysosomal dysfunction has been implicated in AD pathogenesis. We found, by examining cells stably expressing each APOE isoform, that APOE4 increases lysosomal trafficking, accumulates in enlarged lysosomes and late endosomes, alters autophagic flux and the abundance of autophagy proteins and lipid droplets, and alters the proteomic contents of lysosomes following internalization. We investigated APOE-related lysosomal trafficking further in cell culture, and found that APOE from the post-Golgi compartment is degraded through autophagy. We found that this autophagic process requires the lysosomal membrane protein LAMP2 in immortalized neuron-like and hepatic cells, and in mouse brain tissue. Several macroautophagy-associated proteins were also required for autophagic degradation and internalization of APOE in hepatic cells. The dysregulated autophagic flux and lysosomal trafficking of APOE4 that we observed suggest a possible novel mechanism that might contribute to AD pathogenesis. This article has an associated First Person interview with the first author of the paper.

Molecular docking analysis of arjunolic acid from Terminalia arjuna with a coronary artery disease target APOE4.

Apo lipoprotein-E (APOE) encoded by APOE gene, is a plasma glycoprotein of 34.15 kDa and has a significant genetic association in coronary artery disease (CAD) progression. The silent epidemic of different cardiovascular diseases including CAD challenges novel therapeutic alternatives to prevent to treat chronic conditions of the disease and its associated complications. It is believed that natural phyto compounds and extracts have been a potential source of treating health conditions and have been practiced since several decades. The aim of the study is to identify phyto compounds having significant cardio protective activity targeting APOE4. Since protein-ligand interactions play a leading role in structure-based drug design, with the help of molecular docking, we selected 20 phyto chemicals present in different plants and investigated their binding affinity against targeted APOE isoforms. Among all selected phytoc ompounds, arjunolic acid, from Terminalia arjuna plant was found as promising candidate for developing therapeutic against APOE4 activated CAD. Findings from the present work could be further studied for clinical evaluations on human to adopt strategies and reduce the prevalence and mortality. Arjunolic acid derivatives can be used as a source of new medication or development of novel compounds in the treatment of CAD.

Inflammatory Pathways Are Impaired in Alzheimer Disease and Differentially Associated With Apolipoprotein E Status.

Alzheimer disease (AD) is a neurodegenerative disease characterized by a cognitive decline leading to dementia. The most impactful genetic risk factor is apolipoprotein E (APOE). APOE-ε4 significantly increases AD risk, APOE-ε3 is the most common gene variant, and APOE-ε2 protects against AD. However, the underlying mechanisms of APOE-ε4 on AD risk remains unclear, with APOE-ε4 impacting many pathways. We investigated how the APOE isoforms associated with the neuroinflammatory state of the brain with and without AD pathology. Frozen brain tissue from the superior and middle temporal gyrus was analyzed from APOE-ε3/3 (n = 9) or APOE-ε4/4 (n = 10) participants with AD pathology and APOE-ε3/3 (n = 9) participants without AD pathology. We determined transcript levels of 757 inflammatory related genes using the NanoString Human Neuroinflammation Panel. We found significant pathways impaired in APOE-ε4/4-AD individuals compared to APOE-ε3/3-AD. Of interest, expression of genes related to microglial activation (SALL1), motility (FSCN1), epigenetics (DNMT1), and others showed altered expression. Additionally, we performed immunohistochemistry of P2RY12 to confirm reduced microglial activation. Our results suggest APOE-ε3 responds to AD pathology while potentially having a harmful long-term inflammatory response, while APOE-ε4 shows a weakened response to pathology. Overall, APOE isoforms appear to modulate the brain immune response to AD-type pathology.

Apolipoprotein E and Alzheimer disease: pathobiology and targeting strategies.

Polymorphism in the apolipoprotein E (APOE) gene is a major genetic risk determinant of late-onset Alzheimer disease (AD), with the APOE*ε4 allele conferring an increased risk and the APOE*ε2 allele conferring a decreased risk relative to the common APOE*ε3 allele. Strong evidence from clinical and basic research suggests that a major pathway by which APOE4 increases the risk of AD is by driving earlier and more abundant amyloid pathology in the brains of APOE*ε4 carriers. The number of amyloid-β (Aβ)-dependent and Aβ-independent pathways that are known to be differentially modulated by APOE isoforms is increasing. For example, evidence is accumulating that APOE influences tau pathology, tau-mediated neurodegeneration and microglial responses to AD-related pathologies. In addition, APOE4 is either pathogenic or shows reduced efficiency in multiple brain homeostatic pathways, including lipid transport, synaptic integrity and plasticity, glucose metabolism and cerebrovascular function. Here, we review the recent progress in clinical and basic research into the role of APOE in AD pathogenesis. We also discuss how APOE can be targeted for AD therapy using a precision medicine approach.

More severe OA pathology in a humanized mouse model for APOE-ε4 as compared to APOE-ε3: APOE-isoforms as possible risk factor for inflammatory osteoarthritis development?

Purpose: Apolipoprotein E (APOE) is a protein that is closely involved in lipid metabolism. Absence of APOE results in increased serum levels of low-density lipoprotein (LDL) cholesterol, which we previously described to be associated with the development of osteoarthritis (OA) pathology. However, next to its function in lipid metabolism, APOE has been shown to dampen the innate immune system that is strongly involved in the development of OA pathology. In humans, three isoforms of the APOE gene exist (APOE-ε2, APOE-ε3 and APOE-ε4), with different efficacies in suppressing innate immunity (ε2>ε3>ε4). Therefore not surprisingly, the APOE-ε4 isotype has been associated with various inflammation-mediated diseases, including atherosclerosis, Alzheimer’s disease, and multiple sclerosis. However, whether the various APOE isoforms also affect the development of OA remains unknown. Therefore, in the present study we investigated the development of joint pathology after induction of collagenase-induced OA (CIOA) in APOE-ε3 and APOE-ε4 targeted replacement mice. Methods: Wild type, Apoe-/-, and humanized APOE-ε3 and APOE-ε4 targeted replacement mice in which the murine Apoe gene was replaced by the human APOE-ε3 and APOE-ε4 gene, all received a normal diet. CIOA was induced by intra-articular injection of collagenase and mice were sacrificed at day 42 after induction of the model. Serum cholesterol levels were determined using a colorimetric assay. Cartilage degeneration and osteophyte/ectopic bone formation were scored using Safranin O & Fast Green stained sections, representing the entire depth of the joint. Hematoxylin & eosin-stained sections were used to quantify synovial inflammation and chondrocyte death as the percentage of cartilage containing empty lacunae compared to the total cartilage area. Results: Apoe-/-mice showed markedly increased serum LDL levels as compared to their wild type controls (8.90 mmol/L and 0.40 mmol/L, respectively; p<0.001). Moreover, Apoe-/- mice showed significantly increased thickening of the synovium at end-stage OA. Whereas we did not observe differences in cartilage degeneration, we found a strongly increased ectopic bone formation, mainly in the medial collateral ligament. Next, we determined the effects of various human APOE isotypes on the development of joint pathology after induction of CIOA using humanized APOE-ε3 and APOE-ε4 targeted replacement mice. Both mouse strains showed comparable serum LDL levels, which were not raised as compared to wild type mice. Contralateral control joints showed comparable but low synovial inflammation, cartilage degeneration and osteophyte/ectopic bone formation. Interestingly, after induction of CIOA, APOE-ε4 showed increased synovial inflammation as compared to APOE-ε3 mice. In agreement with this finding, we observed significantly increased degeneration of the articular cartilage, which was associated with an increased chondrocyte death. Finally, we found a significantly increased surface area of ectopic bone and osteophyte formation. Conclusions: High LDL cholesterol levels by Apoe deficiency in mice results in increased synovial thickening and ectopic bone formation in end-stage OA. Mice with the human APOE-ε4 gene develop more severe OA pathology as compared to the APOE-ε3 isotype, which is in line with the decreased potency of APOE-ε4 to dampen innate immune responses. This indicates a possible role for the human APOE isotypes as risk factor for the development of OA that needs further investigation.

The Role of APOE and TREM2 in Alzheimer's Disease-Current Understanding and Perspectives.

Alzheimer’s disease (AD) is the leading cause of dementia worldwide. The extracellular deposits of Amyloid beta (Aβ) in the brain—called amyloid plaques, and neurofibrillary tangles—intracellular tau aggregates, are morphological hallmarks of the disease. The risk for AD is a complicated interplay between aging, genetic risk factors, and environmental influences. One of the Apolipoprotein E (APOE) alleles—APOEε4, is the major genetic risk factor for late-onset AD (LOAD). APOE is the primary cholesterol carrier in the brain, and plays an essential role in lipid trafficking, cholesterol homeostasis, and synaptic stability. Recent genome-wide association studies (GWAS) have identified other candidate LOAD risk loci, as well. One of those is the triggering receptor expressed on myeloid cells 2 (TREM2), which, in the brain, is expressed primarily by microglia. While the function of TREM2 is not fully understood, it promotes microglia survival, proliferation, and phagocytosis, making it important for cell viability and normal immune functions in the brain. Emerging evidence from protein binding assays suggests that APOE binds to TREM2 and APOE-containing lipoproteins in the brain as well as periphery, and are putative ligands for TREM2, thus raising the possibility of an APOE-TREM2 interaction modulating different aspects of AD pathology, potentially in an isoform-specific manner. This review is focusing on the interplay between APOE isoforms and TREM2 in association with AD pathology.

ABCA1 haplodeficiency affects the brain transcriptome following traumatic brain injury in mice expressing human APOE isoforms

Expression of human Apolipoprotein E (APOE) modulates the inflammatory response in an isoform specific manner, with APOE4 isoform eliciting a stronger pro-inflammatory response, suggesting a possible mechanism for worse outcome following traumatic brain injury (TBI). APOE lipidation and stability is modulated by ATP-binding cassette transporter A1 (ABCA1), a transmembrane protein that transports lipids and cholesterol onto APOE. We examined the impact of Abca1 deficiency and APOE isoform expression on the response to TBI using 3-months-old, human APOE3+/+ (E3/Abca1+/+) and APOE4+/+ (E4/Abca1+/+) targeted replacement mice, and APOE3+/+ and APOE4+/+ mice with only one functional copy of the Abca1 gene (E3/Abca1+/−; E4/Abca1+/−). TBI-treated mice received a craniotomy followed by a controlled cortical impact (CCI) brain injury in the left hemisphere; sham-treated mice received the same surgical procedure without the impact. We performed RNA-seq using samples from cortices and hippocampi followed by genome-wide differential gene expression analysis. We found that TBI significantly impacted unique transcripts within each group, however, the proportion of unique transcripts was highest in E4/Abca1+/− mice. Additionally, we found that Abca1 haplodeficiency increased the expression of microglia sensome genes among only APOE4 injured mice, a response not seen in injured APOE3 mice, nor in either group of sham-treated mice. To identify gene networks, or modules, correlated to TBI, APOE isoform and Abca1 haplodeficiency, we used weighted gene co-expression network analysis (WGCNA). The module that positively correlated to TBI groups was associated with immune response and featured hub genes that were microglia-specific, including Trem2, Tyrobp, Cd68 and Hexb. The modules positively correlated with APOE4 isoform and negatively to Abca1 haplodeficient mice represented “protein translation” and “oxidation-reduction process”, respectively. Our results reveal E4/Abca1+/− TBI mice have a distinct response to injury, and unique gene networks are associated with APOE isoform, Abca1 insufficiency and injury.