apoE-containing Lipoproteins Research Articles

Effect of atorvastatin and niacin/LRPT on apolipoprotein e distribution, metabolism and glycation

Aim: To investigate the influence of apoE genotype on the response to atorvastatin treatment in patients with Type 2 diabetes with nephropathy and the effect of niacin/laropiprant (LRPT) on apoE and glycated apoE concentration and distribution in hyperlipidaemia.Methods: ApoE genotype and the effect of 10mg/day and 80mg/day atorvastatin treatment on apoE concentration were studied in 85 patients with type 2 diabetes with nephropathy. The effect of niacin/LRPT on apoE and glycated apoE was investigated for 36 patients with hyperlipidaemia. Results: After 12 months treatment with atorvastatin, serum apoE concentration decreased significantly in the 80mg/day, but not the 10mg/day group. This decrease was observed in patients with E3 and E4 but not E2 genotype. Hyperlipidaemia did not affect total apoE, but the apoE distribution in HDL and d>1.21g/ml lipoprotein fractions was significantly lower. Glycated apoE was significantly higher in patients with hyperlipidaemia than healthy volunteers (p<0.0001). After 3 months treatment with niacin/LRPT, apoE in apoB?containing lipoproteins (VLDL+LDL) was significantly reduced, but was unchanged in apoA-containing lipoproteins (HDL) compared with treatment with placebo. Niacin/LRPT also had no effect on the elevated glycated apoE observed in patients with hyperlipidaemia.Conclusions: The effect of atorvastatin on total apoE concentration is dependent on the dose of atorvastatin and apoE genotype in patients with type 2 diabetes with nephropathy. Niacin/LRPT has no significant effect on total apoE and glycated apoE, but does influence their distribution in lipoprotein fractions in patients with hyperlipidaemia.

CD68GFP/APOE-/- mouse: A novel model to study macrophage biology in atherosclerosis

CD68GFP/APOE-/- mouse: A novel model to study macrophage biology in atherosclerosis

Disruption of astrocyte-neuron cholesterol cross talk affects neuronal function in Huntington's disease.

In the adult brain, neurons require local cholesterol production, which is supplied by astrocytes through apoE-containing lipoproteins. In Huntington's disease (HD), such cholesterol biosynthesis in the brain is severely reduced. Here we show that this defect, occurring in astrocytes, is detrimental for HD neurons. Astrocytes bearing the huntingtin protein containing increasing CAG repeats secreted less apoE-lipoprotein-bound cholesterol in the medium. Conditioned media from HD astrocytes and lipoprotein-depleted conditioned media from wild-type (wt) astrocytes were equally detrimental in a neurite outgrowth assay and did not support synaptic activity in HD neurons, compared with conditions of cholesterol supplementation or conditioned media from wt astrocytes. Molecular perturbation of cholesterol biosynthesis and efflux in astrocytes caused similarly altered astrocyte-neuron cross talk, whereas enhancement of glial SREBP2 and ABCA1 function reversed the aspects of neuronal dysfunction in HD. These findings indicate that astrocyte-mediated cholesterol homeostasis could be a potential therapeutic target to ameliorate neuronal dysfunction in HD.

B27 Disruption Of Astrocyte-neuron Cholesterol Cross-talk Affects Neuronal Function In Huntington's Disease

Background Circulating or dietary cholesterol is not able to cross the blood-brain barrier (BBB) and cholesterol homeostasis in brain is thought to depend largely on endogenous biosynthesis. Cholesterol biosynthesis and content are reduced in the brain of several models of Huntington’s disease (HD) (Valenza et al ., 2005; 2007; 2010). This cerebral dysfunction is measurable also in HD patients starting from early disease stages (Leoni et al ., 2008; Leoni et al ., 2013). Aims In the adult brain cholesterol-dependent neuronal activities, such as neurite outgrowth and synaptic properties, mainly rely on the transport of cholesterol from astrocytes on ApoE-containing particles (Mauch et al ., 2001). Cholesterol supply to neurons might be reduced in HD astrocytes by contributing to neuronal dysfunction in HD neurons. Methods and results Here we show that primary astrocytes obtained from R6/2 HD mice and from mouse knock-in Neural Stem (NS) cell lines expressing mutant huntingtin produce and release less cholesterol bound to ApoE-containing lipoproteins into the medium, compared to control astrocytes. Accordingly, conditioned medium from wild-type astrocytes (GCMwt), but not from R6/2 astrocytes (GCMHD) or from wt astrocytes depleted of lipoproteins (GCMwt-delip), is able to compensate the defect in neurite outgrowth and to ameliorate synaptic-related properties in HD neurons. In parallel we established a dose-response relationship between cholesterol application and these parameters. Furthermore, results from gain and loss of function experiments in wt and HD primary astrocytes reinforce the notion of an altered cross-talk between astrocytes and neurons which can be rescued experimentally. Conclusions In conclusion, our results suggest that astrocytes carrying the HD mutation are the major responsible of the cholesterol dysfunction in HD as they contribute to supply less cholesterol to the surrounding neurons.

Abstract 541: Specific Deletion of LDL Receptor--Related Protein on Macrophages Skews Cytokine Production by Invariant Natural Killer T Cells

Invariant Natural Killer T (iNKT) cells are specialized lymphocytes that when activated can regulate chronic inflammatory conditions and atherosclerotic processes. The activation of iNKT cells occurs when glycolipid antigens bind the MHC class-I like molecule CD1d present on antigen presenting cells (APCs). The pathways by which glycolipid antigens target CD1d for presentation and activation of iNKT cells remain unclear, yet the expression of surface receptors associated with lipid homeostasis, such as the LDL receptor (LDLr), have been implicated in the modulation of iNKT cell activation. The LDLr has been shown to modulate this process by binding apoE-containing lipoproteins, which can carry antigenic glycolipids for iNKT cell activation. The LDL receptor-related protein (LRP), a transmembrane receptor from the LDL receptor family of proteins, shares structural homology with LDLr and can bind a number of ligands including apoE-containing lipoproteins. We hypothesized that LRP can play an active role in glycolipid antigen presentation and subsequent activation of iNKT cells. Here, we demonstrate that LRP is preferentially expressed at high levels on F4/80 + macrophages, when compared to other APCs. We also show that a specialized subset of macrophages expressing CD169, known for their ability to present glycolipid antigen to iNKT cells, have increased levels of LRP when compared to CD169 - macrophages. Using mice with a targeted deletion of LRP in macrophages, we observed decreased activation of iNKT cells in vitro (24, 48 hours) and normal IFN-gamma but blunted IL-4 response in vivo. Further flow cytometric analysis showed normal surface expression of CD1d in LRP-cKO macrophages as well as normal uptake of fluorescently labeled glycolipid in vitro . Additionally, analysis of the iNKT cell compartment in LRP-cKO mice revealed intact numbers and percentages of iNKT cells and no homeostatic disruption as evidenced by absence of programmed death-1 and LY-49. Collectively, these data suggest that macrophage LRP contributes to early iNKT cell activation by enhancing early IL-4 responses.

Oxidative Stress and FGF-1 Release from Astrocytes

The brain is an organ to consume highly oxygen and to produce Reactive Oxygen Species (ROS) at high level. ROS facilitate to produce many kinds of peroxide lipids in the lipid-rich brain. Accordingly, it is considered that the brain is an organ to undergo easily oxidative stress. Severe diseases of brain such as Parkinsonism and Alzheimer’s disease are seemingly accompanied with oxidative stress. The construction of protection system against oxidative stress is very important to maintain normal neuron function in the brain. We are studying the production and function of Fibroblast Growth Factor 1 (FGF-1) in astrocytes undergoing oxidative stress. Astrocytes increase FGF-1 release under stressful condition such as oxidative stress and long-term cultured stress. In vitro treatment of rat astrocytes with 100 μM Hydrogen Peroxide (H2O2) for 10 min enhances the release of FGF-1 along with cytosolic proteins such as HSP90, HSP70, PK-Cδ without inducing apoptosis. The treatment with H2O2 enhanced the flow into the cells of exogenous compounds such as trypsin and Rhodamin-phalloidin also, suggesting increase in permeability of plasma membrane in astrocytes treated with H2O2. Oxidative stress suppressed transiently cholesterol synthesis and enhanced cholesterol release from the cell surface, resulted in impairment of the cholesterol metabolism. The change of cholesterol metabolism may participate in the increase in membrane permeability in astrocytes undergone oxidative stress. FGF-1 released from rat astrocytes enhances apoE-containing HDL-like lipoproteins (apoE/HDL) generation of astrocytes in the manner of autocrine action. In this review, we describe physiological significance of FGF-1 released from astrocytes stimulated by oxidative stress to relate with generation of apoE/HDL of astrocytes in the brain.

The pro-neurotrophin receptor sortilin is a major neuronal APOE receptor for catabolism of amyloid-β peptide in the brain

Sortilin is a member of the VPS10P domain receptor gene family, a class of sorting and signalling receptors in neurons. This gene family also includes SORLA/LR11, the neuronal sorting factor for APP. Sortilin has been shown to constitute an essential component of the receptor complex that transmits pro-neurotrophin-dependent death signals in neurons. In previous studies, sortilin-dependent pro-neurotrophin signalling has been implicated in regulation of neuronal viability during normal development and aging. Also, sortilin activity has been shown to control neuronal cell death and survival in spinal cord injury. Remarkably, up-regulation of pro-neurotrophins has been observed under conditions of neurodegeneration. These findings led us to hypothesize that sortilin signaling may not only control neuronal viability during acute but also during chronic distress of the nervous system as in Alzheimer’s disease (AD). Here, we have used mice with targeted sortilin gene disruption to address the consequences of impaired receptor activity for APP processing, structural and functional integrity of the brain, as well as AD pathology in vivo. When crossed with two different AD models (PDAPP, 5xFAD), sortilin-deficient mice showed a robust increase in Aβ levels in brain compared with control animals. Surprisingly, the levels of soluble APP products were not altered in sortilin-deficient mice, nor were the levels of Aβ-degrading enzymes, neprilysin and insulin-degrading enzyme, suggesting an impairment of Aβ clearance pathways. Apolipoprotein (APO) E is the major risk factor for sporadic Alzheimer disease. Among other functions, APOE is proposed to sequester neurotoxic amyloid-β peptides (Aβ) in the brain, delivering them to cellular catabolism via neuronal APOE receptors. In this study, we identified the pro-neurotrophin receptor sortilin as major endocytic pathway for clearance of apoliporotein E (APOE)/Aβ complexes in neurons. Sortilin binds APOE with high affinity. Lack of receptor expression in mice results in accumulation of APOE and of Aβ in the brain, and in aggravated plaque burden. Also, primary neurons lacking sortilin exhibit significantly impaired uptake of APOE/Aβ complexes despite proper expression of other APOE receptors. In spite of higher than normal brain APOE levels, sortilin-deficient animals display anomalies in brain lipid metabolism seen in APOE-deficient mice, indicating functional deficiency in cellular APOE uptake pathways. Taken together, our findings identified sortilin as an essential neuronal pathway for APOE-containing lipoproteins in vivo and suggest an intriguing link between Aβ catabolism and pro-neurotrophin signaling converging on this receptor.

Killing Two Birds With One Stone, Maybe

Connections between glucose and lipid metabolism have long been recognized. It is well known that impaired glucose metabolism, particularly in diabetes mellitus, influences plasma levels of both apoB- and apoAI-containing lipoproteins and induces an abnormal lipid phenotype known as atherogenic dyslipidemia.1 This is characterized by high triglycerides, low high-density lipoprotein (HDL), and elevated low-density lipoprotein (LDL) particle concentration attributable to a preponderance of smaller-sized LDL. These effects are seen as secondary to the insulin-resistant state and caused by its interference with the lipid homeostatic mechanisms, including increased secretion of apoB-containing lipoproteins and reduced lipolysis of triglyceride-rich particles. However, a direct influence of primary abnormalities in lipid metabolism on glucose homeostatic mechanisms is not commonly recognized, with the exception of subjects with extreme hypertriglyceridemia caused by lipoprotein lipase deficiency, where diabetes mellitus may develop during periods of uncontrolled dyslipidemia, and control of glucose levels is achieved by adjustment of triglycerides.2 Although lipotoxicity is known to harm many tissues and cells, the presence of common dyslipidemia is not considered as a risk factor for changes in insulin sensitivity by liver, muscle, or adipose tissue, or in insulin production by the pancreatic beta cell. Article, see p 167 In the past few years, this general concept has been challenged with the recognition that membrane cholesterol levels regulate insulin exocytosis from beta cells. In particular, the absence of the main cellular cholesterol transporter, ABCA1, drastically reduces insulin output.3,4 Because ABCA1 controls the first step in the extracellular process known as reverse cholesterol transport, mediated by the circulating HDL particle, this suggests that natural or drug-induced changes in HDL metabolism or composition may influence the ability of beta cells to respond to physiological stimuli, including glucose. Hence, it is possible that in some instances diabetes mellitus development may be accelerated …

Enhancement of FGF-1 release along with cytosolic proteins from rat astrocytes by hydrogen peroxide

We previously observed that the production and release of fibroblast growth factor (FGF-1) are increased in rat astrocytes during in vitro long-term culture, that FGF-1 enhances the generation of apoE-containing high density lipoproteins (apoE/HDL), and that the wound healing of brain cryoinjury delays in apoE-deficient mouse. The detail mechanism underlying these phenomena remains unknown. In this study, we examined effects of oxidative stress on release of FGF-1 from cultured rat astrocytes.The treatment of rat astrocytes with 100µM hydrogen peroxide (H2O2) for 10min enhanced FGF-1 release without inducing apoptosis. The conditioned medium prepared from the cells cultured in a fresh medium after the treatment with H2O2 had the FGF-1-like activities, which enhanced cholesterol synthesis, signalings to phosphorylate Akt and ERK, and apoE secretion. The oxidative stress induced by H2O2 enhanced the release of cytosolic proteins such as HSP70 and HSP90 in addition to FGF-1. Antioxidants such as ascorbic acid and ebselen suppressed the release of cytosolic proteins induced by H2O2 treatment. The addition of lipoproteins such as low density lipoproteins (LDL), furthermore, canceled H2O2-induced release of FGF-1 and cytosolic proteins. Proteolysis of cytosolic proteins in the H2O2-treated rat astrocytes was enhanced in the presence of exogenous trypsin, which was attenuated by the pretreatment with LDL, suggesting that H2O2 increases the permeability of the membrane of cells, which was prevented by the addition of lipoproteins. These findings suggest that oxidative stress is one of the candidates which triggers FGF-1 release from astrocytes in the brain, and that the lipid homeostasis in the cell membrane may regulate H2O2-induced release of FGF-1.

The neuronal membrane as a key factor in neurodegeneration

The neuronal membrane as a key factor in neurodegeneration

Lipid Abnormalities in Patients with Chronic Kidney Disease: Implications for the Pathophysiology of Atherosclerosis

Cardiovascular disease is increased in patients with chronic kidney disease (CKD) and is the principle cause of morbidity and mortality in these patients. In patients with stage 5 CKD, structural changes in the myocardium have been implicated as the principle cardiovascular processes leading to this increase in morbidity and mortality, while atherosclerotic events including acute myocardial infarction and strokes are responsible for approximately 10-15% of cardiovascular deaths. Dyslipidemia is common in CKD patients and is usually not characterized by elevated cholesterol levels, except in patients with marked proteinuria. Increased triglyceride levels in conjunction with decreased high-density lipoprotein levels are the commonest qualitative abnormality. Characteristically, abnormalities in the metabolism of apolipoprotein (apo) B-containing lipoproteins have been described, including both gut derived (apoB-48) as well as those produced by hepatic synthesis (apoB-100). A decrease in enzymatic delipidation as well as reduced receptor removal of these lipoproteins both contribute to the increased levels of these apo-B-containing particles and their remnants (which are believed to be highly atherogenic). Abnormalities in the metabolism of apoA-containing lipoproteins are also present and these changes contribute to the lower levels of HDL seen. Qualitative abnormalities of these HDL particles may be associated with cellular oxidative injury and contribute to a pro-inflammatory, pro-thrombotic milieu that is frequently present in CKD patients.

Cardiovascular Protection by ApoE and ApoE-HDL Linked to Suppression of ECM Gene Expression and Arterial Stiffening

Arterial stiffening is a risk factor for cardiovascular disease, but how arteries stay supple is unknown. Here, we show that apolipoprotein E (apoE) and apoE-containing high-density lipoprotein (apoE-HDL) maintain arterial elasticity by suppressing the expression of extracellular matrix genes. ApoE interrupts a mechanically driven feed-forward loop that increases the expression of collagen-I, fibronectin, and lysyl oxidase in response to substratum stiffening. These effects are independent of the apoE lipid-binding domain and transduced by Cox2 and miR-145. Arterial stiffness is increased in apoE null mice. This stiffening can be reduced by administration of the lysyl oxidase inhibitor BAPN, and BAPN treatment attenuates atherosclerosis despite highly elevated cholesterol. Macrophage abundance in lesions is reduced by BAPN in vivo, and monocyte/macrophage adhesion is reduced by substratum softening in vitro. We conclude that apoE and apoE-containing HDL promote healthy arterial biomechanics and that this confers protection from cardiovascular disease independent of the established apoE-HDL effect on cholesterol.

A novel signaling pathway for regulation of ATP‐binding cassette transporter A1 expression

The objective of this study is to characterize the signaling pathway for regulation of ATP‐binding cassette transporter A1 (ABCA1) expression. Quantitative real‐time RT‐PCR assay and Western blot analysis revealed that treatment of macrophages with reelin, apolipoprotein E (ApoE) or ApoE‐containing lipoproteins increased ABCA1 mRNA and protein expression. In addition, these reagents significantly increased the level of phosphorylated disabled‐1 (Dab1), phosphatidylinositol 3‐kinase (PI3K), protein kinase C‐æ (PKC‐æ), and specificity protein 1 (Sp1), increased the amount of Sp1 bound to the ABCA1 promoter, and induced PKC‐æ binding with Sp1. Mutation of the Sp1 binding site in the ABCA1 promoter suppressed the ABCA1 promoter activity induced by reelin, ApoE or ApoE‐containing lipoproteins. The upregulation effect of these reagents on ABCA1 expression was suppressed by: 1) knockdown of Dab1, very low‐density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2) with siRNAs, 2) inhibition of PI3K and PKC with kinase inhibitors, 3) overexpression of kinase‐dead PKC‐æ, and 4) inhibition of Sp1 DNA‐binding with mithramycin A. These results, together with the known function of these signaling proteins, suggest that ABCA1 expression can be upregulated by activation of the VLDLR/ApoER2‐Dab1‐PI3K‐PKCæ‐Sp1 signaling cascade.Grant support: SC1HL101431 (HY) and R01HL089382 (ZMG).

Clinical Study on the Effect of Simvastatin on Paraoxonase Activity

Human paraoxonase (PON1) is a serum high-density lipoprotein-associated phosphotriesterase. High-density lipoprotein (HDL) plays the role of a carrier and the site of action of this enzyme. According to a majority of authors, PON1 acts as an antioxidant, preventing low-density lipoprotein (LDL) peroxidation. However, due to the fact that in vivo serum PON1 is predominantly associated with HDL, its major physiological role might be to protect HDL, rather than LDL, from oxidation. Nevertheless, the physiological substrate of PON1 still remains to be discovered. The objective of this study was to determine changes in PON1 activity during treatment with simvastatin (CAS 79902-63-9, Lipex) in patients with type IIa and/or IIb hyperlipoproteinemia. PON1 activity was assessed in 32 patients with hyperlipoproteinemia type IIa or IIb with an LDL cholesterol concentration higher than 4.2 mmol/l. Patients received simvastatin in a daily dose of 20 mg. The lipid status and PON1 activity were assessed at baseline, as well as 3 and 6 months after the beginning of treatment. The study demonstrated a statistically significant lipid lowering effect of simvastatin on total and LDL cholesterol, and an increase in PON1 activity in patients with both types of hyperlipoproteinemia. No statistically significant correlation was observed either between changes in PON1 activity and HDL, HDL2, HDL3 and LDL cholesterol and triglyceride levels, or between their first differences in patients with both type IIa and IIb hyperlipoproteinemia. The obtained results suggest that the antioxidant properties of simvastatin might be caused by a mechanism independent of apoAI-containing lipoprotein concentration. The antioxidant properties of simvastatin, which play an important role in HDL protection from oxidation, could be the mechanism inducing the increase in PON1 activity.

Macrophage LRP1 Suppresses Neo-Intima Formation during Vascular Remodeling by Modulating the TGF-β Signaling Pathway

BackgroundVascular remodeling in response to alterations in blood flow has been shown to modulate the formation of neo-intima. This process results from a proliferative response of vascular smooth muscle cells and is influenced by macrophages, which potentiate the development of the intima. The LDL receptor-related protein 1 (LRP1) is a large endocytic and signaling receptor that recognizes a number of ligands including apoE-containing lipoproteins, proteases and protease-inhibitor complexes. Macrophage LRP1 is known to influence the development of atherosclerosis, but its role in vascular remodeling has not been investigated.Methodology/Principal FindingsTo define the contribution of macrophage LRP1 to vascular remodeling, we generated macrophage specific LRP1-deficient mice (macLRP1-/-) on an LDL receptor (LDLr) knock-out background. Using a carotid ligation model, we detected a 2-fold increase in neointimal thickening and a 2-fold increase in the intima/media ratio in macLRP1-/- mice. Quantitative RT-PCR arrays of the remodeled vessel wall identified increases in mRNA levels of the TGF-β2 gene as well as the Pdgfa gene in macLRP1-/- mice which could account for the alterations in vascular remodeling. Immunohistochemistry analysis revealed increased activation of the TGF-β signaling pathway in macLRP1-/- mice. Further, we observed that LRP1 binds TGF-β2 and macrophages lacking LRP1 accumulate twice as much TGF-β2 in conditioned media. Finally, TNF-α modulation of the TGF-β2 gene in macrophages is attenuated when LRP1 is expressed. Together, the data reveal that LRP1 modulates both the expression and protein levels of TGF-β2 in macrophages.Conclusions/SignificanceOur data demonstrate that macrophage LRP1 protects the vasculature by limiting remodeling events associated with flow. This appears to occur by the ability of macrophage LRP1 to reduce TGF-β2 protein levels and to attenuate expression of the TGF-β2 gene resulting in suppression of the TGF-β signaling pathway.

Preferential interactions between ApoE-containing lipoproteins and Aβ revealed by a detection method that combines size exclusion chromatography with non-reducing gel-shift

The association between apolipoprotein E (apoE) and amyloid-β peptide (Aβ) may significantly impact the function of both proteins, thus affecting the etiology of Alzheimer's disease (AD). However, apoE/Aβ interactions remain fundamentally defined by the stringency of the detection method. Here we use size exclusion chromatography (SEC) as a non-stringent approach to the detection of apoE/Aβ interactions in solution, specifically apoE and both endogenous and exogenous Aβ from plasma, CSF and astrocyte conditioned media. By SEC analysis, Aβ association with plasma and CNS lipoproteins is apoE-dependent. While endogenous Aβ elutes to specific human plasma lipoproteins distinct from those containing apoE, it is the apoE-containing lipoproteins that absorb excess amounts of exogenous Aβ40. In human CSF, apoE, endogenous Aβ and phospholipid elute in an almost identical profile, as do apoE, exogenous Aβ and phospholipid from astrocyte conditioned media. Combining SEC fractionation with subsequent analysis for SDS-stable apoE/Aβ complex reveals that apoE-containing astrocyte lipoproteins exhibit the most robust interactions with Aβ. Thus, standardization of the methods for detecting apoE/Aβ complex is necessary to determine its functional significance in the neuropathology characteristic of AD. Importantly, a systematic understanding of the role of apoE-containing plasma and CNS lipoproteins in Aβ homeostasis could potentially contribute to identifying a plasma biomarker currently over-looked because it has multiple components.

The Modulating Effect of Mechanical Changes in Lipid Bilayers Caused by ApoE-Containing Lipoproteins on Aβ Induced Membrane Disruption

A major feature of Alzheimer's disease (AD), a late-onset neurodegenerative disorder, is the ordered aggregation of the β-amyloid peptide (Aβ) into fibrils that comprise extracellular neuritic plaques found in the disease brain. One of many potential pathways for Aβ toxicity may be modulation of lipid membrane function. Here, we show by in situ atomic force microscopy (AFM) that astrocyte secreted lipoprotein particles (ASLPs) containing different isoforms of apolipoprotein E (apoE), of which the apoE4 allele is a major risk factor for the development of AD, can protect total brain lipid extract bilayers from Aβ(1-40) induced disruption. The apoE4 allele was less effective in protecting lipid bilayers from disruption compared with apoE3. Size analysis of apoE-containing ASLPs and mechanical studies of bilayer properties revealed that apoE-containing ASLPs modulate the mechanical properties of bilayers by acquiring some bilayer components (most likely cholesterol and/or oxidatively damaged lipids). Measurement of bilayer mechanical properties was accomplished with scanning probe acceleration microscopy (SPAM). These measurements demonstrated that apoE4 was also less effective in modulating mechanical properties of bilayers in comparison with apoE3. This ability of apoE to alter the mechanical properties of lipid membranes may represent a potential mechanism for the suppression of Aβ(1-40) induced bilayer disruption.

Synapse disruption in AD brain: Evidence for early pathological clustering of the group I metabotropic glutamate receptor 5

deficits in APP transgenic mice. Furthermore, Abca1 knockout mice were shown to have a significant decrease of apolipoprotein E (apoE) and apolipoprotein A-I (apoA-I) in the brain.Methods: In this study we have examined Abeta clearance and transport from the brain in Abca1ko mice. Single apoE and apoA-I knockout mice were used as controls.Results:Our data demonstrate that among the genotypes that were tested, Abca1ko mice have the highest level of amyloid plaques and cognitive deficits. The increased amyloid load and memory deficits in Abca1-ko mice correlated to decreased clearance of A-beta as measured by microdialysis experiments. In addition, the transport of radioactive labeled A-beta through blood brain barrier was decreased in Abca1-ko as compared to Abca1-wt mice and single knockout mice. Our in vitro experiments show that apoE-containing lipoproteins isolated from Abca1wt astrocytes are lipid-rich and decrease A-beta aggregation. In contrast, apoE-containing lipoproteins isolated from Abca1ko cells are lipid-poor and do not affect A-beta aggregation. Conclusions: In conclusion, our in vivo and in vitro data suggest that lack of Abca1 increases A-beta aggregation thus preventing its clearance from the brain ultimately leading to cognitive decline.

Domains of apoE4 required for the biogenesis of apoE-containing HDL

Introduction. We have studied the functions of truncated apoE4 forms in vitro and in vivo in order to identify the domains of apoE4 required for the biogenesis of apoE-containing high-density lipoprotein (HDL). Results. We have found that apoE4-185, -202, -229, or -259 could promote ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux in vitro, although less efficiently than Full-length apoE4, and had diminished capacity to activate lecithin cholesterol acyltransferase (LCAT). Formation of HDL in vivo was assessed by various methods following gene transfer in apolipoprotein A-I−/− × apoE−/− mice. Fast protein liquid chromatography of plasma showed that the truncated apoE forms, except apoE4-185, generated an apoE-containing HDL peak. Two-dimensional gel electrophoresis of plasma and electron microscopy showed that truncated apoE forms generated distinct HDL subpopulations and formed discoidal HDL particles which could be converted to spherical by co-administration of truncated apoE4-202 and LCAT. Conclusion. Overall, the in-vivo and in-vitro data are consistent and indicate that apoE4-185 is the shortest truncated form that supports formation of discoidal apoE4-containing HDL particles.

The effect of decreasing renal function on lipoprotein profiles

Progressive chronic kidney disease (CKD) is accompanied by dyslipidemia that is characterized by increased concentrations of intact and partially metabolized ApoB and ApoC-III-containing triglyceride-rich lipoproteins in very low-density lipoprotein, intermediate density lipoprotein (IDL) and low-density lipoprotein. The purpose of the present study was to characterize the distribution of individual discrete lipoprotein subclasses in relation to the glomerular filtration rate (GFR) in nondiabetic CKD subjects. Fifty-one subjects (33 patients with CKD and 18 asymptomatic subjects) with GFR ranging from 12 to 120 mL/min were studied. Individual ApoA- and ApoB-containing lipoprotein subclasses (Lp) were determined in plasma by sequential immunoaffinity chromatography and subsequent determination of apolipoprotein composition by electroimmunoassays. GFR was measured as plasma clearance of iohexol or (51)Cr-ethylenediaminetetraacetic acid. There were no changes in concentrations of ApoA-containing lipoproteins with decreasing GFR. The levels of ApoB-containing lipoproteins increased significantly with decreasing GFR. There was a moderate increase of cholesterol-rich LpB and a 3-fold increase of ApoB- and ApoC-III-containing lipoproteins in subjects in the two lowest quintiles of GFR. This was accompanied by a significant increase of plasma ApoC-III. Reduced renal function is associated with a complex alteration of the lipoprotein profile that is predominantly characterized by increased concentrations of triglyceride-rich lipoprotein subclasses containing both ApoB and ApoC-III.