apoE Isoforms Research Articles

Molecular Dynamics of Apolipoprotein Genotypes APOE4 and SNARE Family Proteins and Their Impact on Alzheimer’s Disease

Alzheimer’s disease is a chronic neurodegenerative disorder characterized by progressive memory loss and a significant impact on quality of life. The APOE ε4 allele is a major genetic contributor to AD pathogenesis, with synaptic dysfunction being a central hallmark in its pathophysiology. While the role of APOE4 in reducing SNARE protein levels has been established, the underlying molecular mechanisms of this interaction remain obscure. Our research employs molecular dynamics simulations to analyze interactions between APOE4 and APOE3 isoforms and the synaptic proteins VAMP2, SNAP25, and SYNTAXIN1, which play crucial roles in the presynaptic membrane. Our findings reveal that APOE4 significantly destabilizes the SNARE complex, suppresses its structural dynamics, and reduces hydrogen bonding, consequently partially hindering neurotransmitter release—a very likely discovery for elucidating synaptic dysfunction in Alzheimer’s disease. We identified that APOE4 exhibits a diminished affinity for the SNARE complex in comparison to APOE3. This observation suggests that APOE4 may play a role in modulating the stability of the SNARE complex, potentially impacting the progression and occurrence of Alzheimer’s disease through free energy analysis. This work highlights the perturbations in synaptic function mediated by APOE4, which may offer novel insights into the molecular underpinnings of AD. By elucidating the molecular interplay between APOE4 and the SNARE complex, our study not only enhances our comprehension of AD’s synaptic pathology but also paves the way for devising innovative therapeutic interventions, such as targeting the APOE4–SNARE complex interaction or to restore neurotransmitter release.

The Apoprotein E4 isotype does not affect the severity of COVID-19 infection and other flu-like syndromes.

Introduction. Apolipoprotein E (ApoE), especially the ApoE4 isotype, is suggested to influence the severity of respiratory viral infections; however, this association is still unclear.Hypothesis. The presence of allele ε4 impacts the development of flu-like syndromes.Aim. This study aimed to evaluate the impact of the Apo E4 isoform on the severity and duration of flu-like syndromes, including the coronavirus disease COVID-19.Methodology. This study comprised 280 individuals presenting flu-like symptoms, all genotyped for ApoE isoforms. Data were collected on clinical course, comorbidities, nutritional status, biochemical and inflammatory markers, SARS-CoV-2 reverse transcription PCR results and disease severity (mild, moderate or severe) according to the World Health Organization criteria. The individuals were analysed as a whole and within subgroups based on the SARS-CoV-2-positive (COVID-19 group) or SARS-CoV-2-negative (flu-like syndrome group) test.Results. The frequency of the ε4 allele was similar across the whole population and in both the COVID-19 and flu-like syndrome subgroups (17 and 18%, respectively). No differences were seen in sex, age range, self-reported skin colour, body mass index (BMI), number of comorbidities, vaccination status, biochemical, cytokine and lipid profiles (except for total cholesterol) in the flu-like group when ε4 allele carriers and non-carriers were compared. In the COVID-19 group, the ε4 allele did not correlate with disease severity or duration, number of comorbidities or inflammatory biomarkers. While gender distribution was equal in the overall COVID-19 population, male gender strongly correlated with COVID-19 severity. Multivariate analysis showed that older individuals, male gender, higher BMI and the presence of comorbidities were linked to increased chances of developing moderate and severe disease. IL-4 was the only factor found to reduce the risk of severe COVID-19.Conclusion. The presence of one ɛ4 allele showed no association with the duration and severity of flu-like syndromes, including COVID-19. Nonetheless, SARS-CoV-2-positive individuals tend to be older men with a higher BMI and a tendency to be overweight or with obesity. Regarding COVID-19 severity, BMI, male sex and the number of associated comorbidities were the factors that increased the chance of developing a more severe form of COVID-19.

Characterization of the N- and C-terminal domain interface of the three main apoE isoforms: A combined quantitative cross-linking mass spectrometry and molecular modeling study.

Apolipoprotein E (apoE) polymorphism is associated with different pathologies such as atherosclerosis and Alzheimer's disease. Knowledge of the three-dimensional structure of apoE and isoform-specific structural differences are prerequisites for the rational design of small molecule structure modulators that correct the detrimental effects of pathological isoforms. In this study, cross-linking mass spectrometry (XL-MS) targeting Asp, Glu and Lys residues was used to explore the intramolecular interactions in the E2, E3 and E4 isoforms of apoE. The resulting quantitative XL-MS data combined with molecular modeling revealed isoform-specific characteristics of the N- and C-terminal domain interfaces as well as the isoform-dependent dynamic equilibrium of these interfaces. Finally, the data identified a network of salt bridges formed by R61-R112-E109 residues in the N-terminal helical bundle as a modulator of the interaction with the C-terminal domain making this network a potential drug target.

Impaired Cerebrospinal Fluid Lipoprotein-Mediated Cholesterol Delivery to Neurons in Alzheimer's Disease.

In the central nervous system, apolipoprotein (APO) E-containing high-density lipoprotein (HDL)-like particles mediate the transport of glial-derived cholesterol to neurons, which is essential for neuronal membrane remodeling and maintenance of the myelin sheath. Despite this, the role of HDL-like cholesterol trafficking on Alzheimer's disease (AD) pathogenesis remains poorly understood. We aimed to examine cholesterol transport via HDL-like particles in cerebrospinal fluid (CSF) of AD patients compared to control individuals. Additionally, we explored the ability of reconstituted HDL containing different APOE isoforms to regulate cholesterol transport. We evaluated the capacity of CSF HDL-like particles to facilitate radiolabeled unesterified cholesterol efflux from A172 human glioblastoma astrocytes and to deliver cholesterol to SH-SY5Y human neuronal cells. The HDL-like proteome in the AD and control groups was analyzed by liquid chromatography-mass spectrometry (LC-MS/MS). Reconstituted HDL nanoparticles were prepared by combining phospholipids and cholesterol with human APOE3 or APOE4, followed by radiolabeling with unesterified cholesterol. Our results showed that cholesterol efflux from astrocytes to CSF were similar between AD patients and controls, both under baseline conditions and after activation of ATP-binding cassette transporters A1 and G1. However, CSF HDL-like particle-mediated neuronal cholesterol uptake was significantly reduced in the AD group. LC-MS/MS analysis identified 775 proteins associated with HDL-like particles in both groups, with no major alterations in proteins linked to cholesterol metabolism. However, 27 proteins involved in non-cholesterol-related processes were differentially expressed. Notably, synthetic reconstituted HDL particles containing APOE4 exhibited reduced capacity to deliver cholesterol to neurons compared to those with APOE3. These findings indicate that CSF HDL-like particles from patients with AD demonstrate impaired cholesterol delivery to neurons. Our study highlights APOE4 as a critical contributor to abnormal neuronal cholesterol uptake in AD pathophysiology.

Synthesis and Characterization of Transferrin and Cell-Penetrating Peptide-Functionalized Liposomal Nanoparticles to Deliver Plasmid ApoE2 In Vitro and In Vivo in Mice.

Alzheimer's disease (AD) is a prevalent neurodegenerative condition characterized by the aggregation of amyloid-β plaques and neurofibrillary tangles in the brain, leading to synaptic dysfunction and neuronal degeneration. Recently, new treatment approaches involving drugs such as donanemab and lecanemab have been introduced for AD. However, these drug regimens have been associated with adverse effects, leading to the exploration of gene therapy as a potential treatment option. The apolipoprotein E (ApoE) isoforms (ApoE2, ApoE3, and ApoE4) play pivotal roles in AD pathology, with ApoE2 known for its protective effects against AD, making it a promising candidate for gene therapy interventions. However, delivering therapeutics across the blood-brain barrier (BBB) remains a crucial challenge in treating neurological disorders. Liposomes, lipid-based vesicles, are effective nanocarriers due to their ability to shield therapeutics from degradation, though they often lack specificity for brain delivery. To address this issue, liposomes were functionalized with cell-penetrating peptides such as penetratin (Pen), cingulin (Cgn), and a targeting ligand transferrin (Tf). This modification strategy aimed to enhance the delivery of therapeutic ApoE2 plasmids across the BBB to neurons, thereby increasing the level of ApoE2 protein expression. Experimental findings demonstrated that dual-functionalized liposomes (CgnTf and PenTf) exhibited higher cellular uptake, biodistribution, and transfection efficiency than single-functionalized (Pen, Cgn, or Tf) and nonfunctionalized liposomes. In vitro studies using primary neuronal cells, bEnd.3 cells, and primary astrocytes consistently supported these findings. Following a single dose treatment via tail vein administration in C57BL6/J mice, in vivo biodistribution results showed significantly higher biodistribution levels in the brain (∼12% ID/gram of tissue) for dual-functionalized liposomes. Notably, treatment with dual-functionalized liposomes resulted in a 2-fold increase in ApoE2 expression levels compared to baseline levels. These findings highlight the potential of dual-functionalized liposomes as an efficacious delivery system for ApoE2 gene therapy in AD, highlighting a promising strategy to address the disease's underlying mechanisms.

Quantitative and Kinetic Proteomics Reveal ApoE Isoform-dependent Proteostasis Adaptations in Mouse Brain.

Apolipoprotein E (ApoE) polymorphisms modify the risk of Alzheimer's disease with ApoE4 strongly increasing and ApoE2 modestly decreasing risk relative to the control ApoE3. To investigate how ApoE isoforms alter risk, we measured changes in proteome homeostasis in transgenic mice expressing a human ApoE gene (isoform 2, 3, or 4). The regulation of each protein's homeostasis is observed by measuring turnover rate and abundance for that protein. We identified 4849 proteins and tested for ApoE isoform-dependent changes in the homeostatic regulation of ~2700 ontologies. In the brain, we found that ApoE4 and ApoE2 both lead to modified regulation of mitochondrial membrane proteins relative to the wild-type control ApoE3. In ApoE4 mice, lack of cohesion between mitochondrial membrane and matrix proteins suggests that dysregulation of proteasome and autophagy is reducing protein quality. In ApoE2, proteins of the mitochondrial matrix and the membrane, including oxidative phosphorylation complexes, had a similar increase in degradation which suggests coordinated replacement of the entire organelle. In the liver we did not observe these changes suggesting that the ApoE-effect on proteostasis is amplified in the brain relative to other tissues. Our findings underscore the utility of combining protein abundance and turnover rates to decipher proteome regulatory mechanisms and their potential role in biology.

Optimized prime editing of the Alzheimer's disease-associated APOE4 mutation.

Gene editing strategies to safely and robustly modify the Alzheimer's disease-associated APOE4 isoform are still lacking. Prime editing (PE) enables the precise introduction of genetic variants with minimal unintended editing and without donor templates. However, it requires optimization for each target site and has not yet been applied to APOE4 gene editing. Here, we screened PE guide RNA (pegRNA) parameters and PE systems for introducing the APOE4 variant and applied the optimized PE strategy to generate disease-relevant human induced pluripotent stem cell models. We show that introducing a single-nucleotide difference required for APOE4 correction inhibits PE activity. To advance efficient and robust genome engineering of precise genetic variants, we further present a reliable PE enrichment strategy based on diphtheria toxin co-selection. Our work provides an optimized and reproducible genome engineering pipeline to generate APOE4 disease models and outlines novel strategies to accelerate genome editing in cellular disease model generation.

Lipoprotein(a) concentrations and cardiovascular disease in patients with chronic kidney disease: Results from the German Chronic Kidney Disease study.

Lipoprotein(a) (Lp(a)) is a causal, genetically determined risk factor for cardiovascular disease (CVD) in the general population. Patients with chronic kidney disease (CKD) have an increased CVD risk and elevated Lp(a) concentrations. Only a few studies on Lp(a) were performed in persons with mild-to-moderate CKD; none of them used genetic variants to explore potential causal associations. This study aims to investigate the association of measured and genetically predicted Lp(a) concentrations on prevalent and incident CVD events in the German Chronic Kidney Disease (GCKD) study. The study included 5043 participants of European ancestry with an estimated glomerular filtration rate (eGFR) between 30 and 60mL/min/1.73m2 or an eGFR >60mL/min/1.73m2 in the presence of overt albuminuria with a follow-up of 6.5 years. With each 10mg/dL higher Lp(a) concentration, odds for prevalent CVD (1290 events) increased 1.065-fold (95%CI: 1.042-1.088, p<0.001). The risk was significantly higher in patients with Lp(a) ≥50mg/dL but most pronounced in Lp(a) ≥70mg/dL (odds ratio=1.775 [1.409-2.231], p<0.001) compared to Lp(a) <30mg/dL. Each 10mg/dL higher Lp(a) concentration and Lp(a) ≥70mg/dL increased the risk for incident 3-point major adverse cardiovascular events (MACEs) (474 events): hazard ratio [HR]=1.037 [1.009-1.067], p=0.009 and HR=1.335 [1.001-1.781], p=0.050), respectively. Similar results were obtained for 4-point MACE (653 events). Analyses based on apo(a) isoforms and genetically predicted Lp(a) concentrations led to even stronger associations. In patients with mild-to-severe CKD, elevated Lp(a) concentrations and genetic determinants of Lp(a) concentrations are significantly associated with CVD at baseline and during follow-up, independent of traditional risk factors.

Evidence of recent evolutionary selection at eQTLs for APOE

AbstractBackgroundLate‐onset Alzheimer Disease (LOAD) risk and prevalence differ by ancestral group. Furthermore, the frequency of APOE‐4 and its effect size on LOAD risk also differ by ancestry group. If these patterns are a function of evolutionary history, we may find ancestry group‐specific evidence of recent selection at the APOE locus or APOE eQTLs. This could provide us with additional insights into APOE function, specifically its pleiotropic effects and ethnic specific mechanisms of disease.MethodsWe used chromosome 19 sequence data from 2,504 unrelated individuals in 26 populations from the latest release of the 1000 Genomes Data (phased 30x coverage build 38 data), and we ran separate selection analyses in each population. We calculated two selection measures based on Extension of Haplotype Homozygosity (EHH): iHS (integrated haplotype score) and nSL (number of segregating sites by length). Scores were then normalized in bins of similar allele frequency (AF) to account for frequency effects on EHH. Loci in the top 1% of |iHS| and |nSL| scores were considered evidence of selection.ResultsAmong the two SNPs defining the APOE isoforms and 27 SNPs defining APOE EQTLs (29 sites in total) we observed 9 APOE eQTLs in the top 1% of iHS and three in the top 1% of nSL. Two SNPS demonstrated evidence of selection in both scores: rs1628394 in Kinh Vietnamese (in a SIPA1L3 intron) and rs2909088 in Han Chinese (in a ZFP30 intron). Neither of the APOE SNPs showed evidence of selection in any population.ConclusionsWe identified evidence of recent natural selection in APOE eQTLs in two East Asian populations: rs1628394 in Kinh Vietnamese and rs2909088 in Han Chinese. Prior work has established that rs1628394 is nominally associated with LOAD (p = 2.45 × 10‐3) and the genome Aggregation Database indicates that it is common in Africans (AF = 0.63), less common in Europeans (AF = 0.33), and least common in East Asians (AF = 0.13). The second SNP, rs2909088, is not associated with LOAD, but it is also less common in East Asians (AFEuropean = 0.87, AFAfrican = 0.69, and AFEastAsian = 0.38). Recent selection at rs1628394 may be enhancing the impact of APOE4 on LOAD development in Kinh Vietnamese.

Validation of Various Pan‐ApoE and Isoform‐Specific ApoE Antibodies

AbstractBackgroundApolipoprotein E (ApoE) exists in three protein isoforms: E2, E3, and E4, which differ by only one or two amino acids. These slight differences profoundly effect protein structure and function, allowing each isoform to differentially impact Alzheimer’s Disease (AD) risk. Relative to the most common E3 isoform, E4 dramatically increases risk, while E2 confers a substantial decrease in risk. The close similarity between protein isoforms makes it difficult to develop isoform‐specific antibodies that are reliable and selective. Here, we aim to validate and optimize a number of common, commercially available ApoE antibodies to determine isoform specificity.MethodControl samples included plasma and brain collected from APOE knockout (KO), homozygous E2, E3 and E4 humanized APOE (hAPOE) mice, and human plasma from all 6 possible APOE genotypes. Western blotting was used on plasma and brain homogenates to determine isoform specificity of E2, E3, or E4 antibodies. Commercial antibodies tested included pan‐ApoE antibodies from Cell Signaling Technologies (CST) and Abcam, ApoE4 antibodies from Novus and CST, ApoE2 antibodies from CST, and ApoE3 antibodies from Abcam and Novus. Additionally, pan‐ApoE antibodies were kindly gifted to us by collaborators (Drs. Lammich and Haass, LMU) and tested. Antibodies were also tested for use in immunohistochemistry (IHC) using hAPOE and APOE KO mouse brain sections (30 uM).ResultDespite the ApoE3 antibodies being marketed as isoform‐specific, they did not show efficacy in either application. Commercial pan‐ApoE antibodies were outperformed by the LMU antibodies, but still showed efficacy. When used for western blotting, the CST ApoE4 and ApoE2 antibodies showed clear isoform specificity in hAPOE mouse and human samples. While none of the isoform‐specific antibodies passed controls for IHC purposes, multiple pan‐ApoE antibodies were variably effective for staining of brain tissue.ConclusionThese data identify several isoform‐specific ApoE antibodies that are reliable and selective across multiple sample types and applications; albeit some display higher affinity for one application over another. Overall, we hope these results will provide AD researchers with important resources that are crucial for visualizing and quantifying ApoE isoform distribution in heterozygote individuals and across a number of AD models, systems, and studies.

Effects of COVID-19 virus-like particles on the behavioral and cognitive performance of human apolipoprotein E targeted replacement mice.

The effects of viral infections might be apolipoprotein E (apoE) isoform-dependent. In humans, there are three major apoE isoforms, E2, E3, and E4. E4 is associated with the enhanced entry of several viruses into the brain and their disease progression. A concern of infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the development of post-acute COVID-19 syndrome, also known as long COVID. Genetic risk factors for developing long COVID were reported. In this study, we used virus-like particles (VLPs) that include expression of the SARS-CoV-2 nucleocapsid (N), membrane (M), and envelope (E) structural proteins together with S. In the current study, we used human E2, E3, and E4 targeted replacement mice to assess whether these VLPs affect body weight, behavioral and cognitive performance, and circadian body temperatures. Using VLPs allow working outside an ABSL-3 facility. The effects of VLPs on some behavioral measures were apoE isoform-dependent, with the E2 mice being more affected than E3 or E4 mice. The overall decreased activity in the open field containing objects in week 2 indicate that VLPs can also reduce activity levels in an apoE isoform-independent fashion. The results of the current study indicate that even in the absence of viral replication, detrimental effects of VLPs on behavioral measures and circadian body temperatures are seen.

Klebsiella pneumoniae infection increases risk of Alzheimer's Disease in the UK Biobank cohort.

Infections, including bacterial pathogens, have been implicated in Alzheimer's disease (AD) risk. Klebsiella pneumoniae (K. pneumoniae) is a common hospital-acquired pathogen associated with significant inflammation, which may contribute to neurodegeneration. This study investigates the relationship between K. pneumoniae infections and AD in the UK Biobank cohort. Using UK Biobank data, we assessed AD diagnoses based on linked healthcare records and identified K. pneumoniae infections using ICD-10 codes B96.1 and J15.0. A cohort of 502,494 participants was analyzed for AD incidence in relation to demographic factors, educational years, APOE isoforms, and history of K. pneumoniae infection. Logistic regression was used to assess the association between K. pneumoniae infection and AD risk. AD incidence was significantly higher among participants with a history of K. pneumoniae infection (1.0%) compared to those without (0.2%; p < 0.001, Fisher's exact test two tailed). Logistic regression analysis revealed that K. pneumoniae infection was associated with an increased risk of AD (OR = 3.32, p < 0.001), independent of age, sex, education, and APOE isoform. Additionally, AD risk was higher among ε4ε4 carriers and increased with age but decreased with additional years of education. Our findings suggest that K. pneumoniae infection may be an independent risk factor for AD. This association underscores the need for further research into infection control and its role in mitigating neurodegenerative disease risk, particularly in populations susceptible to healthcare-associated infections.

APOE from astrocytes restores Alzheimer’s Aβ-pathology and DAM-like responses in APOE deficient microglia

The major genetic risk factor for Alzheimer’s disease (AD), APOE4, accelerates beta-amyloid (Aβ) plaque formation, but whether this is caused by APOE expressed in microglia or astrocytes is debated. We express here the human APOE isoforms in astrocytes in an Apoe-deficient AD mouse model. This is not only sufficient to restore the amyloid plaque pathology but also induces the characteristic transcriptional pathological responses in Apoe-deficient microglia surrounding the plaques. We find that both APOE4 and the protective APOE2 from astrocytes increase fibrillar plaque deposition, but differentially affect soluble Aβ aggregates. Microglia and astrocytes show specific alterations in function of APOE genotype expressed in astrocytes. Our experiments indicate a central role of the astrocytes in APOE mediated amyloid plaque pathology and in the induction of associated microglia responses.

Therapeutic Challenges Derived from the Interaction Among Apolipoprotein E, Cholesterol, and Amyloid in Alzheimer's Disease.

The isoform E4 of the Apolipoprotein E (ApoE) represents one of the strongest genetic risk factors for late-onset Alzheimer's disease (AD). ApoE has key roles in cholesterol transport and amyloid-β (Aβ) metabolism, which are both central to AD pathogenesis. The E4 isoform has been implicated in reduced cholesterol homeostasis, increased Aβ aggregation, and heightened tau phosphorylation, contributing to amyloid plaques and neurodegeneration. This manuscript examines the complex interactions among ApoE isoforms, cholesterol metabolism, and amyloid pathology. Moreover, the therapeutic challenges associated with lipid-lowering agents (e.g., statins, PCSK9 inhibitors), anti-amyloid immunotherapies, and anticoagulants are described, focusing on ApoE4 carriers. Decision-making challenges are discussed by analyzing the pros and cons of these therapies.

Analyzing the Role of Specific Damage-Associated Molecular Patterns-Related Genes in Osteoarthritis and Investigating the Association between β-Amyloid and Apolipoprotein E Isoforms

Introduction: Osteoarthritis (OA) is a prevalent chronic joint disorder. It is characterized by an immune response that maintains a low level of inflammation throughout its progression. During OA, cartilage degradation leads to the release of damage-associated molecular patterns (DAMPs), which intensify the inflammatory response. β-Amyloid is a well-recognized DAMP in OA, can interact with APOE isoforms. Methods: This study identified DAMPs-related genes in OA using bioinformatics techniques. Additionally, we examined the expression levels of β-amyloid and apolipoprotein E (ApoE) isoforms by enzyme-linked immunosorbent assay. Results: We identified 10 key genes by machine learning techniques. Immune infiltration analysis revealed upregulation of various immune cell types in OA cartilage, underscoring the critical role of inflammation in OA pathogenesis. In the validation study, elevated serum levels of β-amyloid in knee osteoarthritis (KOA) patients were confirmed, showing positive correlations with ApoE2 and ApoE4. Notably, ApoE3 was identified as an independent protective factor against KOA. Conclusion: In this bioinformatics analysis, we identified the DAMPs-related genes of KOA and explored their potential functions and regulatory networks. The high expression of β-amyloid in KOA was confirmed by experiments, and the correlation between β-amyloid and ApoE2, ApoE4 in KOA was revealed for the first time, this provides a new way to explore the pathogenesis of KOA and to study the therapeutic targets of KOA.

Lipoprotein glomerulopathy: what is known? Literature review

The review is devoted to the important problem of contemporary nephrology — lipoprotein glomerulopathy (LPG), a rare glomerular disorder leading to nephrotic syndrome and/or chronic kidney failure (CKF). The article highlights the primary genetic defect in LPG associated with heterozygous mutations of the apolipoprotein E (ApoE) gene in the low‑density lipoprotein (LDL) binding site with the corresponding receptor, which increases the affinity of mutant ApoE‑containing lipoproteins to the glomerular capillary wall. The article presents data from population‑based studies on the prevalence of LPG and current understanding of its pathogenesis, in particular, the main pathogenetic link — damage to the structure and function of ApoE due to heterozygous mutations of the ApoE gene. The participation of ApoE‑containing lipoproteins, which include ApoE isoforms, in the formation of glomerular deposits, lipoprotein thrombi in the lumen of glomerular capillaries, as well as the role of macrophages in the pathogenesis of renal lipidosis is considered. Histological picture typical for LPG, intraglomerular and extrarenal factors of its development, and features of serum lipid spectrum accompanying the clinical course of LPG are described. Diagnostic criteria of LPG, clinical manifestations of this glomerular disorder, prognosis in LPG, its complications and some co-morbid states associated with LPG are given. Special attention is paid for the treatment of LPG, without which the disease is progressing to a terminal CKF. Some possibilities of contemporary lipid lowering agents (fibrates, nicotinic acid derivates, statins, monoclonal antibodies to apolipoprotein CIII) in correction of lipid disorders associated with LPG are discussed. Some perspective agents that could be applied in patients with LPG (inhibitors of natrium-dependent glucose co-transporter 2, antioxidants, anticonvulsant topiramate) after special trials are enumerated. Some attention is paid to other treatment measures in LPG, such as LDL-apheresis with heparin‑induced extracorporal precipitation, staphylococcal protein-A immunoadsorption therapy, and renal transplantation. Necessity is emphasized of further experimental and clinical studies that will allow to enlarge updated ideas about the etiology and pathogenesis of LPG, improve its diagnostics and treatment efficacy.

Readdressing the Localization of Apolipoprotein E (APOE) in Mitochondria-Associated Endoplasmic Reticulum (ER) Membranes (MAMs): An Investigation of the Hepatic Protein-Protein Interactions of APOE with the Mitochondrial Proteins Lon Protease (LONP1), Mitochondrial Import Receptor Subunit TOM40 (TOMM40) and Voltage-Dependent Anion-Selective Channel 1 (VDAC1).

As a component of circulating lipoproteins, APOE binds to cell surface receptors mediating lipoprotein metabolism and cholesterol transport. A growing body of evidence, including the identification of a broad variety of cellular proteins interacting with APOE, suggests additional independent functions. Investigating cellular localization and protein-protein interactions in cultured human hepatocytes, we aimed to contribute to the elucidation of hitherto unnoted cellular functions of APOE. We observed a strong accumulation of APOE in MAMs, equally evident for the two major isoforms APOE3 and APOE4. Using mass spectrometry proteome analyses, novel and previously noted APOE interactors were identified, including the mitochondrial proteins TOMM40, LONP1 and VDAC1. All three interactors were present in MAM fractions, which we think initially facilitates interactions with APOE. LONP1 is a protease with chaperone activity, which migrated to MAMs in response to ER stress, displaying a reinforced interaction with APOE. We therefore hypothesize that APOE may help in the unfolded protein response (UPR) by acting as a co-chaperone in cooperation with LONP1 at the interface of mitochondria and ER membranes. The interaction of APOE with the integral proteins TOMM40 and VDAC1 may point to the formation of bridging complexes connecting mitochondria with other organelles.

Analysis of early effects of human APOE isoforms on Alzheimer’s disease and type III hyperlipoproteinemia pathways using knock-in rat models with humanized APP and APOE

APOE is a major genetic factor in late-onset Alzheimer’s disease (LOAD), with APOE4 increasing risk, APOE3 acting as neutral, and APOE2 offering protection. APOE also plays key role in lipid metabolism, affecting both peripheral and central systems, particularly in lipoprotein metabolism in triglyceride and cholesterol regulation. APOE2 is linked to Hyperlipoproteinemia type III (HLP), characterized by mixed hypercholesterolemia and hypertriglyceridemia due to impaired binding to Low-Density Lipoproteins receptors. To explore the impact of human APOE isoforms on LOAD and lipid metabolism, we developed Long-Evans rats with human APOE2, APOE3, or APOE4 in place of rat Apoe. These rats were crossed with those carrying a humanized App allele to express human Aβ, which is more aggregation-prone than rodent Aβ, enabling the study of human APOE-human Aβ interactions. In this study, we focused on 80-day-old adolescent rats to analyze early changes that may be associated with the later development of LOAD. We found that APOE2hAβ rats had the highest levels of APOE in serum and brain, with no significant transcriptional differences among isoforms, suggesting variations in protein translation or stability. Aβ43 levels were significantly higher in male APOE4hAβ rats compared to APOE2hAβ rats. However, no differences in Tau or phosphorylated Tau levels were observed across the APOE isoforms. Neuroinflammation analysis revealed lower levels of IL13, IL4 and IL5 in APOE2hAβ males compared to APOE4hAβ males. Neuronal transmission and plasticity tests using field Input-Output (I/O) and long-term potentiation (LTP) recordings showed increased excitability in all APOE-carrying rats, with LTP deficits in APOE2hAβand APOE4hAβ rats compared to ApoehAβ and APOE3hAβ rats. Additionally, a lipidomic analysis of 222 lipid molecular species in serum samples showed that APOE2hAβ rats displayed elevated triglycerides and cholesterol, making them a valuable model for studying HLP. These rats also exhibited elevated levels of phosphatidylglycerol, phosphatidylserine, phosphatidylethanolamine, sphingomyelin, and lysophosphatidylcholine. Minimal differences in lipid profiles between APOE3hAβ and APOE4hAβ rats reflect findings from mouse models. Future studies will include comprehensive lipidomic analyses in various CNS regions and at older ages to further validate these models and explore the effects of APOE isoforms on lipid metabolism in relation to AD pathology.

The Effect of FTY720 on Sphingolipid Imbalance and Cognitive Decline in Aged EFAD Mice.

During Alzheimer's disease (AD) progression, there is a decline in the bioactive sphingolipid sphingosine-1-phosphate (S1P). Previous research showed that FTY720, an S1P mimetic, prevented cognitive decline and reduced ceramide levels in transgenic mice with familial AD carrying the human APOE4 gene (E4FAD) at 6-7 months of age. The objective of this study is to explore the protective effects of FTY720 at late-stage AD. Male mice aged 9.5 to 10.5 months were orally administered FTY720 (0.1 mg/kg) via oral gavage for 6 weeks. A pre-test of water maze was used for evaluating the pathological status. After 4 weeks of administration, memory, locomotion, and anxiety were assessed. Cortex samples were analyzed for amyloid-β (Aβ) and sphingolipid levels. Compared with APOE3 mice, APOE4, E3FAD and E4FAD mice exhibited significant memory deficits. After 6 weeks administration, FTY720 did not alleviate memory deficits in EFAD mice. Lipid analysis revealed that S1P was significantly reduced in EFAD mice (E3FAD or E4FAD) compared to controls (APOE3 and APOE4). Ceramide level alterations were predominantly dependent on APOE isoforms rather than AD transgenes. Interestingly, Cer (d18 : 1/22 : 1) was elevated in APOE4 mice compared to APOE3, and FTY720 reduced it. E4FAD and APOE4 mice exhibited significant spatial memory deficits and higher ceramide concentrations compared to APOE3 mice. FTY720 did not reverse memory deficits in E4FAD and APOE4 mice but reduced specific ceramide species. This study provides insights into the association between sphingolipids and APOE4 in advanced AD stages, exploring potential therapeutic targeting of sphingolipid metabolism.

The influences of ApoE isoforms on endothelial adherens junctions and actin cytoskeleton responding to mCRP

Apolipoprotein E4 (ApoE4) plays an important role responding to monomeric C-reactive protein (mCRP) via binding to CD31 leading to cerebrovascular damage and Alzheimer’s disease (AD). Using phosphor-proteomic profiling, we found altered cytoskeleton proteins in the microvasculature of AD brains, including increased levels of hyperphosphorylated tau (pTau) and the actin-related protein, LIMA1. To address the hypothesis that cytoskeletal changes serve as early pathological signatures linked with CD31 in brain endothelia in ApoE4 carriers, ApoE4 knock-in mice intraperitoneal injected with mCRP revealed that mCRP increased the expressions of phosphorylated CD31 (pCD31) and LIMA1, and facilitate the binding of pCD31 to LIMA1. mCRP combined with recombinant APOE4 protein decreased interaction of CD31 and VE-Cadherin at adherens junctions (AJs), along with altered the expression of various actin cytoskeleton proteins, causing microvasculature damage. Notably, the APOE2 protein attenuated these changes. Overall, our study demonstrates that ApoE4 responds to mCRP to disrupt the endothelial AJs which link with the actin cytoskeleton and this pathway could play a key role in the barrier dysfunction leading to AD risk.