Lipoprotein Particles in Cerebrospinal Fluid

The brain is the most lipid-rich organ in the body, and the intricate interplay between lipid metabolism and pathologies associated with neurodegenerative disorders is being increasingly recognized. The brain is bathed in cerebrospinal fluid (CSF), which, like plasma, contains lipid-protein complexes called lipoproteins that are responsible for extracellular lipid transport. Multiple CSF lipoprotein populations exist, some of which are produced de novo in the central nervous system and others that appear to be generated from protein constituents that are produced in the periphery. These CSF lipoproteins are thought to play key roles in maintaining lipid homeostasis in the central nervous system, while little else is known due to their limited accessibility and their low abundance in CSF. Recent work has provided new insights into the compositional complexity of CSF lipoprotein families and their metabolism in cerebral circulation. The purpose of this review is to summarize our current state of knowledge on the composition, origin, and metabolism of CSF lipoproteins.

Clinical diversity and molecular mechanism of VPS35L-associated Ritscher-Schinzel syndrome

PURPOSE

The Retriever subunit VPS35L is the third responsible gene for Ritscher-Schinzel syndrome (RSS) after WASHC5 and CCDC22. To date, only one pair of siblings have been reported and their condition was significantly more severe than typical RSS. This study aimed to understand the clinical spectrum and underlying molecular mechanism in VPS35L-associated RSS.

METHODS

We report three new patients with biallelic VPS35L variants. Biochemical and cellular analyses were performed to elucidate disease aetiology.

RESULTS

In addition to typical features of RSS, we confirmed hypercholesterolaemia, hypogammaglobulinaemia and intestinal lymphangiectasia as novel complications of VPS35L-associated RSS. The latter two complications as well as proteinuria have not been reported in patients with CCDC22 and WASHC5 variants. One patient showed a severe phenotype and the other two were milder. Cells established from patients with the milder phenotypes showed relatively higher VPS35L protein expression. Cellular analysis found VPS35L ablation decreased the cell surface level of lipoprotein receptor-related protein 1 and low-density lipoprotein receptor, resulting in reduced low-density lipoprotein cellular uptake.

CONCLUSION

VPS35L-associated RSS is a distinct clinical entity with diverse phenotype and severity, with a possible molecular mechanism of hypercholesterolaemia. These findings provide new insight into the essential and distinctive role of Retriever in human development.

High-density lipoproteins mediate small RNA intercellular communication between dendritic cells and macrophages

HDL are dynamic transporters of diverse molecular cargo and play critical roles in lipid metabolism and inflammation. We have previously reported that HDL transport both host and nonhost small RNAs (sRNA) based on quantitative PCR and sRNA sequencing approaches; however, these methods require RNA isolation steps which have potential biases and may not isolate certain forms of RNA molecules from samples. HDL have also been reported to accept functional sRNAs from donor macrophages and deliver them to recipient endothelial cells; however, using PCR to trace HDL-sRNA intercellular communication has major limitations. The present study aims to overcome these technical barriers and further understand the pathways involved in HDL-mediated bidirectional flux of sRNAs between immune cells. To overcome these technical limitations, SYTO RNASelect, a lipid-penetrating RNA dye, was used to quantify a) overall HDL-sRNA content, b) bidirectional flux of sRNAs between HDL and immune cells, c) HDL-mediated intercellular communication between immune cells, and d) HDL-mediated RNA export changes in disease. Live cell imaging and loss-of-function assays indicate that the endo-lysosomal system plays a critical role in macrophage storage and export of HDL-sRNAs. These results identify HDL as a substantive mediator of intercellular communication between immune cells and demonstrate the importance of endocytosis for recipient cells of HDL-sRNAs. Utilizing a lipid-penetrating RNA-specific fluorescence dye, we were able to both quantify the absolute concentration of sRNAs transported by HDL and characterize HDL-mediated intercellular RNA transport between immune cells.

Abstract 417: Elevation Of Serum Hdl And Apoe Level In A Novel Vps35l Deficient Mouse Model

Aim: Defect of the endosomal protein sorting factor VPS35L causes novel congenital anomalies syndrome, in which cholesterol dysmetabolism is one of the symptoms. To reveal the biochemical mechanisms, the a model mouse was developed and characterized.

Methods: Loss-of-function mutation, N995del, VPS35L knock-in (KI) mice were generated. Serum lipoprotein profiles were assessed by LipoSEARCH™ (Immuno-Biological Laboratories, Japan). For biochemical assays, 70 micro-L of serum was sub-fractionated with Superose 6 column in PBS and total and free cholesterol detected using LabAssay™cholesterol (Fujifilm Wako Chemicals, Japan) and Pureauto™S F-CHO-N (SEKISUI MEDICAL, Japan) assay kits. Negative images of fractioned lipoproteins were observed by TEM (JEM-1400Plus, JEOL, Japan). ApoA-I and apoE in the fractions were determined by use of a mouse apoA1 ELISA PRO kit and a mouse apoE ELISA PRO kit (Mabtech AB, Sweden). Mouse liver total RNA was isolated by ISOGEN (Nippon Gene, Japan) and first-strand cDNA generated using the Invitrogen™ SuperScript™IV First-Strand Synthesis system with random hexamers. For quantitative real-time PCR, the StepOnePlus™ real-time PCR system (Thermo Fisher) was used, and the PCR end product of each well confirmed by the melt curve analysis.

Results: Lipoprotein analysis indicated the KI mice showed 1.9-fold higher total cholesterol than WT mice. LDL-C and HDL-C were increased 2.9- and 1.9-fold compared to WT mice, respectively. ApoA-I levels in the large HDL and HDL fractions were all significantly increased 1.5-, and 1.6-fold, whereas apoE levels were elevated 25-, and 8.4-fold, respectively.

Conclusions: Ablation of VPS35L in MEF(3T3) cells caused loss of endocytosis of the LDL receptor and LRP1, and perhaps even SR-BI, which may lead to increased serum LDL and HDL levels in the loss-of-function KI model mice. Surprisingly. a high level of apoE was detected in KI mice, especially in the HDL fraction. In this case, apoE catabolism became abnormal due to the lack of LRP1 at the cell surface. Abnormal metabolism of apoE may affect the central nervous system or neuron generation. Further examination of the phenotype of this this model mouse line are warranted.

Abstract P111: Effects Of Magnetic Field On Abca1-mediated Cellular Lipid Release And Adult Brain Cell Generation In Mice

Aim: This project aims to explore a novel magnetic field (MF) health care based on the cholesterol metabolism.

Methods: Mouse peritoneal macrophages foam cells were incubated in CO 2 -independent culture medium containing apoA-I and were exposed in a MF (0.4 T) using the electromagnet of EPR spectrometer. C57BL/6N mice (8 week-old) were peritoneally injected F-ara-EdU (133μg/g mouse body weight) then exposed to MF under the identical condition. Mouse plasma, cerebrospinal fluid, liver and brain were harvested on the 28 th day. Lipoprotein profiles were examined enzymatic detection followed by a gel-permeable-HPLC (Skylight Biotech Inc.). Amyloid β40 and β42 levels were determined by WAKO ELISA kit. Fixed mouse brain sections (40um) were prepared by Leica CM1900 cryostat. Alexa fluor® 488 conjugates were link to F-ara-EdU by a click chemistry method and fluor positive nucleus images were captured by a confocal super resolution SpinSR10 (Olympus, Inc.).

Results: ABCA1-apoA-I mediated cellular cholesterol release was not affected or reduced by the exposure in the MF of 0.4 T. The Pcsk9 expression showed significant reduction in the hepatocytes. Reduction of Abca1 expression and increase of Scarb1 were obtained non significantly. The newly generated hippocampal dentate gyrus cells in the control mice group and the MF exposed group were 1.6±1.17, and 0.47±0.62 cells per dentate gyrus section, respectively (P=0.003) despite bulk of new cells in olfactory bulbs in the both groups.

Discussions: No substantial increase in cellular cholesterol export was observed by MF irradiation of mouse peritoneal macrophage cells. In addition, the lipoprotein profile showed a decrease in HDL cholesterol even after 28 days. As a result of gene expression in the liver, a decrease in ABCA1 expression and an increase in SR-BI expression inferred reduction of HDL. The number of new cells detected in the granular zone and the subgranular zone in the dentate gyrus of the hippocampus was significantly reduced in the mice subjected to the MF treatment. In the future, it is necessary to investigate in detail whether these newborn cells are neuron or glial cells.

Apolipoprotein A-I in mouse cerebrospinal fluid derives from the liver and intestine via plasma high-density lipoproteins assembled by ABCA1 and LCAT

Apolipoprotein (apo) A-I, the major structural protein of high-density lipoprotein (HDL), is present in human and mouse cerebrospinal fluid (CSF) despite its lack of expression in brain cells. To identify the origin of apoA-I in CSF, we generated intestine-specific and liver-specific Apoa1 knockout mice (Apoa1^ΔInt and Apoa1^Δliv mice, respectively). Lipoprotein profiles of Apoa1^ΔInt and Apoa1^ΔLiv mice resembled those of control littermates, whereas knockout of Apoa1 in both intestine and liver (Apoa1^ΔIntΔLiv ) resulted in a 60-percent decrease in HDL-cholesterol levels, thus strongly mimicking the Apoa1^-/- mice. Immunoassays revealed that mouse apoA-I was not present in the CSF of the Apoa1^ΔIntΔLiv mice. Furthermore, apoA-I levels in CSF were highly correlated with plasma spherical HDL levels, which were regulated by ABCA1 and LCAT. Collectively, these results suggest that apoA-I protein in CSF originates in liver and small intestine and is taken up from the plasma.

LDL uptake-dependent phosphatidylethanolamine translocation to the cell surface promotes fusion of osteoclast-like cells

Osteoporosis is associated with vessel diseases attributed to hyperlipidemia, and bone resorption by multinucleated osteoclasts is related to lipid metabolism. In this study, we generated low-density lipoprotein receptor (LDLR)/lectin-like oxidized LDL receptor-1 (LOX-1, also known as Olr1) double knockout (dKO) mice. We found that, like LDLR single KO (sKO), LDLR/LOX-1 dKO impaired cell-cell fusion of osteoclast-like cells (OCLs). LDLR/LOX-1 dKO and LDLR sKO preosteoclasts exhibited decreased uptake of LDL. The cell surface cholesterol levels of both LDLR/LOX-1 dKO and LDLR sKO osteoclasts were lower than the levels of wild-type OCLs. Additionally, the amount of phosphatidylethanolamine (PE) on the cell surface was attenuated in LDLR/LOX-1 dKO and LDLR sKO preosteoclasts, whereas the PE distribution in wild-type OCLs was concentrated on the filopodia in contact with neighboring cells. Abrogation of the ATP binding cassette G1 (ABCG1) transporter, which transfers PE to the cell surface, caused decreased PE translocation to the cell surface and subsequent cell-cell fusion. The findings of this study indicate the involvement of a novel cascade (LDLR∼ABCG1∼PE translocation to cell surface∼cell-cell fusion) in multinucleation of OCLs.

Selective Correction of Genotype Yield by Probucol in HDL-Deficient Mice Propagation

Aim: Probucol is a controversial drug to inhibit ATP-binding cassette transporter A1 (ABCA1) and to exhibit some positive clinical effects such as regression of xanthomas. It reportedly rescues female infertility in scavenger receptor BI-deficient mice. Here, we investigated the effect of probucol on propagation in HDL-deficient mice as alternative models for impaired HDL-mediated cholesterol delivery.

Methods: Propagation of ABCA1-deficient (Abca1−/−) mice and lecithin: cholesterol acyltransferase (LCAT)-deficient (Lcat−/−) mice were quantitatively observed under the probucol treatment.

Results:Abca1−/− and Lcat−/− mice appear with negligible plasma HDL concentration. Upon backcrossing Abc1+/− with the Abc1−/− mice and cross-breeding between Abc1+/− mice, the numbers of Abc1−/− weaned pups were reduced to 54.7% and to 57.1% from those expected by Mendelian genetics, respectively. Similarly, Lcat-/-weaned pups decreased to 67.7% and to 35.9% but only in the male. Probucol severely reduced plasma HDL-cholesterol to 5% in the wild-type mice, but showed no effects on their propagation. Probucol corrected the deflections of the genotype distribution in the weaned pups recovery in the LCAT-deficient mice propagation but not in the ABCA1-deficient mice while plasma HDL was kept negligible. Probucol had no effect on cholesterol content in the steroidogenic organs of the HDL-deficient mice, while it somewhat increased plasma corticosterone and expression of adrenal cortex HMG-CoA reductase, StAR, cytochrome P450scc, and VKORC1 indicating increase in the synthesis of cholesterol and steroid hormones and in vitamin K turn-over. However, no evident mechanistic background was indicated.

Conclusions: Probucol corrected deflection of genotype distribution in propagation of the LCAT-deficient mice but not the ABCA1-deficient mice at the weaning stage, apparently not through normalization of hypoalphalipo-proteinemia.

Reconstituted Discoidal High-Density Lipoproteins: Bioinspired Nanodiscs with Many Unexpected Applications

PURPOSE OF REVIEW

Summarize the initial discovery of discoidal high-density lipoprotein (HDL) in human plasma and review more recent innovations that span the use of reconstituted nanodisc HDL for membrane protein characterization to its use as a drug carrier and a novel therapeutic agent for cardiovascular disease.

RECENT FINDINGS

Using a wide variety of biophysical techniques, the structure and composition of endogenous discoidal HDL have now largely been solved. This has led to the development of new methods for the in vitro reconstitution of nanodisc HDL, which have proven to have a wide variety of biomedical applications. Nanodisc HDL has been used as a platform for mimicking the plasma membrane for the reconstitution and investigation of the structures of several plasma membrane proteins, such as cytochrome P450s and ABC transporters. Nanodisc HDL has also been designed as drug carriers to transport amphipathic, as well as hydrophobic small molecules, and has potential therapeutic applications for several diseases. Finally, nanodisc HDL itself like native discoidal HDL can mediate cholesterol efflux from cells and are currently being tested in late-stage clinical trials for cardiovascular disease. The discovery of the characterization of native discoidal HDL has inspired a new field of synthetic nanodisc HDL, which has offered a growing number of unanticipated biomedical applications.

Abstract 397: Cotinine, but Not Nicotine, Increased ApoA-I Mediated HDL Synthesis in THP-1 Cells

Aim: Cotinine is known as a stable metabolite of nicotine, the plasma half-life is over 20-30 hrs. Here, we evaluated its characteristic properties on the apoA-I mediated HDL generation.

Method: Cotinine (5.6 to 11.2μM), or nicotine (5 to 150μM) were supplemented to medium and co-incubated with apoA-I (10μg/mL) for 18 hrs with THP-1 cells to determine their effect on efflux activity. Cellular ACAT accessible cholesterol pool size was determined by [ 14 C]oleic acid labeling of cells for 60 min immediately after removal of the culture medium. The culture medium and the cellular lipids were extracted by organic solvents and cholesterol and phospholipids content were determined. Nicotine was administered orally as an aqueous solution (10 μM) to C57BL/6 mice for 10 days and the plasma lipoprotein profiles were measured by gel-HPLC (tandem TSK-lipopropak XL ) with online enzymatic lipid assay system (Skylight biotech, Inc.).

Results: Supplementation of nicotine into the medium showed no effect on the apoA-I mediated cellular cholesterol release from THP-1 cells. On the other hand, cotinine increased apoA-I mediated cellular cholesterol efflux 2.8 fold. ACAT accessible cholesterol pool size was dramatically decreased to 80% and 58% of control with 5 and 10 μM cotinine treatment, respectively, indicating that cotinine effectively increased apoA-I/ABCA1 mediated cellular cholesterol efflux. Mice with oral nicotine administration showed increased plasma HDL by 11.4% (50.1±4.4 and 55.8±3.9 mg/dL for control and nicotine treatment, respectively).

Conclusions: Cotinine increased apoA-I mediated cellular cholesterol efflux in THP-1 cells. The cellular ACAT accessible cholesterol pool size reduction is one of the early reactions of apoA-I/ABCA1 mediated cellular cholesterol efflux. Cotinine seemingly modifies cellular factor/factors to induce a change in cholesterol distribution. Mice administrated oral nicotine may convert the compound to cotinine by CYP2A6 and aldehyde oxidase activities in their liver, and which likely increased HDL generation. Further experiments are necessary to examine the direct effect of cotinine on the ABCA1 transporter for increasing HDL assembly system.

Charged Residues in the C-Terminal Domain of Apolipoprotein A-I Modulate Oligomerization

Charged residues of the C-terminal domain of human apolipoprotein A-I (apoA-I) were targeted by site-directed mutagenesis. A series of mutant proteins was engineered in which lysine residues (Lys 195, 206, 208, 226, 238, and 239) or glutamate residues (Glu 234 and 235) were replaced by glutamine. The amino acid substitutions did not result in changes in secondary structure content or protein stability. Cross-linking and size-exclusion chromatography showed that the mutations resulted in reduced self-association, generating a predominantly monomeric apoA-I when five or six lysine residues were substituted. The rate of phosphatidylcholine vesicle solubilization was enhanced for all variants, with approximately a threefold rate enhancement for apoA-I lacking Lys 206, 208, 238, and 239, or Glu 234 and 235. Single or double mutations did not change the ability to protect lipolyzed low density lipoprotein from aggregation, but variants lacking >4 lysine residues were less effective in preventing lipoprotein aggregation. ApoA-I mediated cellular lipid efflux from wild-type mice macrophage foam cells was decreased for the variant with five lysine mutations. However, this protein was more effective in releasing cellular phosphatidylcholine and sphingomyelin from Abca1-null mice macrophage foam cells. This suggests that the mutations caused changes in the interaction with ABCA1 transporters and that membrane microsolubilization was primarily responsible for lipid efflux in cells lacking ABCA1. Taken together, this study indicates that ionic interactions in the C-terminal domain of apoA-I favor self-association and that monomeric apoA-I is more active in solubilizing phospholipid bilayers.

Abstract 571: Short Term Taste Preference for Cholesterol Rich Diet in ABCA1 Null Mice

Background: Plasma HDL particle is one of the essential player for maintaining cholesterol homeostasis in mammal. Even though cholesterol can be ubiquitously biosynthesized upon requirement, cholesterol in diet is efficiently used to maintain cholesterol homeostasis which implicates existence of sensing system for cholesterol in diet. The study of taste preference on cholesterol was not well explored. In this project we examined taste preference in mice using a novel method called dual diet test (DDT) system.

Methods: Chow pellets of 1.2% cholesterol or 0.02% Acesulfame potassium (AmK, calorie-free sweet molecule) were prepared based on standard mouse chow, CE-2(0.2% cholesterol, Crea Japan). The mouse chow tray was divided into three sections. Water nozzle was set in the center section. Each chow was weighed then set ether right or left section. One session was composed by 1-3 days and remaining chow was weighed to calculate consumption of each chow diet. The diet position was switched randomly at each session. The operation was performed between ZT9-ZT10 when mice were less active in a day. To avoid social isolation stress, 2-5 littermates were placed per cage.

Results: C56B/6 wild type mice and LCAT null mice significantly preferred 1.2% cholesterol containing chow compared to control chow during 6 sessions by 18-28 weeks old littermates (n=16, n=8, respectively). These mice also significantly preferred AmK-chow compared to the control chow. ABCA1 null and ABCA1 heterozygote mice exhibited significance on the preference of 1.2% cholesterol in the first 3 sessions but not for the later sessions. Repeating the experiment after interval period improved their cholesterol preference in ABCA1 null mice. No gender difference was observed. Preferences to AmK-chow were significant in all trials.

Conclusions: The preference in higher cholesterol or sweet in diet were detected at this novel DDT system, significantly. In ABCA1 null or heterozygote mice, long-term preferences to high cholesterol diet were abolished perhaps due to their lack of focus on cholesterol-rich chow of which less reward to these mice. In this experiment, mice synchronized in consuming higher cholesterol containing diet indicating mice are sensing cholesterol as a preferred tastant.

Exposure to High Glucose Concentration Decreases Cell Surface ABCA1 and HDL Biogenesis in Hepatocytes

Aim: To study atherosclerosis risk in diabetes, we investigated ATP-binding cassette transporter A1 (ABCA1) expression and high-density lipoprotein (HDL) biogenesis in the liver and hepatocytes under hyperglycemic conditions.

Methods and Results: In streptozotocin-induced diabetic mice, plasma HDL decreased while ABCA1 protein increased without changing its mRNA in the liver, only in the animals that responded to the treatment to show hypoinsulinemia and fasting hyperglycemia but not in the poor responders not showing those. To study the mechanism for this finding, hepatocytes were isolated from the control and diabetic mice, and they showed no difference in expression of ABCA1 protein, its mRNA, and HDL biogenesis in 1 g/l d-glucose but showed decreased HDL biogenesis in 4.5 g/l d-glucose although ABCA1 protein increased without change in its mRNA. Similar findings were confirmed in HepG2 cells with d-glucose but not with l-glucose. Thus, these cell models reproduced the in vivo findings in hyperglycemia. Labeling of cell surface protein revealed that surface ABCA1 decreased in high concentration of d-glucose in HepG2 cells despite the increase of cellular ABCA1 while not with l-glucose. Immunostaining of ABCA1 in HepG2 cells demonstrated the decrease of surface ABCA1 but increase of intracellular ABCA1 with high d-glucose. Clearance of ABCA1 was retarded both in primary hepatocytes and HepG2 cells exposed to high d-glucose but not to l-glucose, being consistent with the decrease of surface ABCA1.

Conclusions: It is suggested that localization of ABCA1 to the cell surface is decreased in hepatocytes in hyperglycemic condition to cause decrease of HDL biogenesis.

Efficacy of Eculizumab Therapy for Atypical Hemolytic Uremic Syndrome Recurrence and Antibody-Mediated Rejection Progress After Renal Transplantation With Preformed Donor-Specific Antibodies: Case Report

Atypical hemolytic uremic syndrome (aHUS) develops as the result of unregulated complement progression and precipitates de novo thrombotic microangiopathy. Plasma therapy is used to control the progression of the complement cascade, but that therapy is not effective in all patients and is accompanied by risk of infection and/or allergy. Eculizumab has been reported as an efficient therapy for aHUS. We report the case of a 35-year old woman who underwent effective eculizumab therapy for aHUS recurrence and antibody-mediated rejection (AMR) progress after renal transplantation with preformed donor-specific antibodies (DSA). She developed end-stage renal disease due to suspicious IgA nephropathy at age 33 years. Kidney transplantation was performed at age 35 years, and aHUS recurred 2 weeks later, leading to the progressive hemolytic anemia and renal dysfunction. Therefore, she underwent plasma therapy several times. Because it was difficult to continue to plasma therapy for severe allergy, eculizumab was proposed as an alternate therapy. Treatment with eculizumab was initiated 36 days after renal transplantation. After 3 years of eculizumab treatment, and without plasma therapy, schistocytes decreased, haptoglobin increased to within normal limits, creatinine levels stabilized, and no further episodes of diarrhea were reported. At protocol biopsy 1 year after transplantation, she was diagnosed with C4d-negative subclinical AMR. However, her pathologic findings at follow-up biopsy 3 years after transplantation were recovered. We conclude that eculizumab alone, without plasma therapy, is sufficient to treat recurrence of aHUS and AMR due to DSA after renal transplantation and to maintain long-term graft function.

ABCG1 and ABCG4 Suppress γ-Secretase Activity and Amyloid β Production

ATP-binding cassette G1 (ABCG1) and ABCG4, expressed in neurons and glia in the central nervous system, mediate cholesterol efflux to lipid acceptors. The relationship between cholesterol level in the central nervous system and Alzheimer's disease has been reported. In this study, we examined the effects of ABCG1 and ABCG4 on amyloid precursor protein (APP) processing, the product of which, amyloid β (Aβ), is involved in the pathogenesis of Alzheimer's disease. Expression of ABCG1 or ABCG4 in human embryonic kidney 293 cells that stably expressed Swedish-type mutant APP increased cellular and cell surface APP levels. Products of cleavage from APP by α-secretase and by β-secretase also increased. The levels of secreted Aβ, however, decreased in the presence of ABCG1 and ABCG4, but not ABCG4-KM, a nonfunctional Walker-A lysine mutant. In contrast, secreted Aβ levels increased in differentiated SH-SY5Y neuron-like cells in which ABCG1 and ABCG4 were suppressed. Furthermore, Aβ42 peptide in the cerebrospinal fluid from Abcg1 null mice significantly increased compared to the wild type mice. To examine the underlying mechanism, we analyzed the activity and distribution of γ-secretase. ABCG1 and ABCG4 suppressed γ-secretase activity and disturbed γ-secretase localization in the raft domains where γ-secretase functions. These results suggest that ABCG1 and ABCG4 alter the distribution of γ-secretase on the plasma membrane, leading to the decreased γ-secretase activity and suppressed Aβ secretion. ABCG1 and ABCG4 may inhibit the development of Alzheimer's disease and can be targets for the treatment of Alzheimer's disease.

Abstract 434: LDL-like Particles in HDL Density Have Small Diameters and Stimulate Macrophages Similar to LDL

We have been detected small portion of LDL-like lipoprotein in HDL density (1.063 <d< 1.21 g/mL) from human plasma. This β-migrating lipoprotein has affinity to Dextrin Sulfate (DS) column of which use for LDL apheresis (LA-15, Kanenka Medix Corp, Japan). Here, we isolated and examined character of this human dense LDL (d-LDL) isolated by ultracentrifugation and DS column then evaluated its potential on mouse macrophages foam cell development. Protein composition of d-LDL fraction detected by SDS-PAGE was similar to LDL fraction rather than HDL DS (remaining after DS column). This d-LDL particle size was measured by Transmission Electron Microscopic-negative staining method (JEM-1011J, x200,000) and this digital image data were further analyzed by Developer Toolbox TM (GE Healthcare) for particle area and diameter. The calibration speed of average 420.4 lipoprotein particles per 2440 x 3571 pixels image was less than 10 sec by this program. The d-LDL contained smaller particles compared to the LDL fraction, significantly. Small dense LDL (sdLDL) detected by DENKA assay system revealed increased sdLDL/LDL ratio in HDL DS fraction than d-LDL or LDL fractions. Perhaps, the sdLDL has low affinity to the DS column. In the other hand, Lp(a) was highly bound to DS column. The acetylated LDLs (ac-LDL, ac-d-LDL) were load on mouse peritoneal resident macrophage for 48 hrs to produce the foam cells. Both acetylated LDLs successfully induced foam cells while cellular choline labeled phosphatidylcholine was twice as high as in ac-d-LDL treated foam cells. The cholesterol content in the macrophage was also increased by ac-d-LDL. d-LDL fraction was re-isolated by “masked” DS column from non-specifically bound plasma proteins (d-LDL ri ). Difference of phospholipid synthesis during macrophages foam cell development was abolished between by ac-LDL and by ac-d-LDL ri . Thus, original DS-Cellulose column bounds LDL but also inducer/inducers of macrophage lipid synthesis from human plasma HDL fraction. These results indicate LDL-like lipoprotein in HDL fraction, d-LDL, has smaller diameter than LDL. The acetylated d-LDL ri activated phospholipid synthesis in mouse peritoneal macrophage as the same extent to Ac-LDL.

Abstract 546: SR-BI Functions on Plasma HDL Homeostasis -low Plasma preβHDL Level in SR-BI Null Mice by 2D PAGE Analysis

ApoA-I-ABCA1 mediated HDL synthesis is major source of plasma preβHDL generation. Lipid free apoA-I is mainly provided from newly synthesized from liver, small intestinal cells and the other hand, apoA-I is also provided from deflated HDL result of transferring cholesterylester into target cells via SR-BI. To evaluate the contribution of SR-BI on reverse cholesterol transport at plasma preβHDL synthesis, first, plasma from SR-BI null mice and wild type mice were analyzed by 2D-gel and compared. The anti-mouse apoA-I peptide (134-140AA, N-Asp-Val-Glu-Leu-Tyr-Arg-Gln-C) polyclonal antibody were further purified by mouse apoA-I-Sepharose then used for detection of HDL subclasses developed by 2D-gel, combination of agarose gel and native gradient PAGE. Ten μL of tail blood from each mouse were collected into microtubes containing NEM, EDTA and ascorbic acid. Plasma was kept in ice then the first electrophoresis by PALAGON LIPO gel was performed within 3 hours of harvest of blood. PreβHDL in SR-BI null mice was significantly reduced (13.78±3.58 μg protein/mL plasma, P=0.00153). The other hand, preβHDL of ABCG1 null mice (37.46±13.803, P=0.423) was the same as in wild type mice plasma (38.48±13.58). To detect the origin of apoA-I on this preβHDL, 125I labeled apoA-I HDL injection of apoA-I on plasma preβHDL, 2D gel analyses were performed followed by 125I-apoA-I-HDL injection. 125I-preβHDL spot was detected early as 2 hours to 6 hours in wild type mice plasma, indicating apoA-I recycling to the new preβHDL particle. The other hand in SR-BI null mice plasma, the 125I-preβHDL spot was only detected between 6 hours to 24 hours. The loss of SR-BI protein delayed reproduction of preβHDL in plasma in mice. This result indicates SR-BI functions as provider of preβHDL possibly both free apoA-I for ABCA1 mediated preβHDL synthesis and also directly supply preβHDL particles in mice plasma.

Encephalitis caused by human herpesvirus-6B in pancreas-after-kidney transplantation

Human herpesvirus-6 (HHV-6) is a common pathogen among children, classically presenting with fever and rash that resolves without specific therapy. HHV-6 can be reactivated in the immunosuppressed patient. After bone marrow and solid organ transplantation, HHV-6 has been linked to various clinical syndromes, including undifferentiated febrile illness, encephalitis, myelitis, hepatitis, pneumonitis, and bone marrow suppression. However, HHV-6 encephalitis after pancreatic transplant has rarely been reported. Early diagnosis and treatment of HHV-6 encephalitis may be important for affected patients. We report the case of a 53-year-old pancreas-after-kidney transplant recipient who initially presented with high fever and confusion 3 weeks after operation. We managed to save the patient's life and preserve the pancreas graft function. We also review previously reported cases of HHV-6B encephalitis in solid organ transplant recipients.

Abstract 231: ABCG1 Null and SR-BI Null Mice Reduced Plasma HDL Uptake by the Liver and Small Intestine

Aim: To reveal cholesterol transport via non-liver excretion pathway of plasma HDL-cholesterol, we focused on small intestinal and kidney in hyper- and hypo-lipoproteinemia model mice.

Method: Mouse plasma was collected within EDTA coated tubes. Plasma lipoprotein profiles were measured by size exclusion HPLC and plasma preβHDL level was detected by immno-blotting of 2D PAGE by anti-mouse apoA-I peptide polyclonal antibody. Mouse HDL was co-incubated with 3H-cholesteryl oleyl ether (CEt) presence of CETP containing human plasma proteins for 48 hrs. The (100μL) of 3H-CEt-HDL was injected trough tail vein in anesthetized mice. 30μL of blood was collected each time point to chase the radioactivity, Mice organs were harvested after 3 hrs of the injection. Since lack of cellular catabolic pathway, CEt within the cells remained. For the immunohistochemical study, mouse was anesthetized and perfused thoroughly with PBS/5mM EDTA followed by 4% PFA/0.1M PB for the fixation. Leica CM1850 Cryostat was used for sectioning (thickness 16 μm). The sections were incubated in PBS containing 5% skim milk, 0.5% Triton X-100 and 5% inactivated normal horse serum for 3 hrs at room temperature, then incubated with primary antibodies (anti-SR-BI antibody diluted to 1:10,000) for overnight at 4°C. Secondary antibodies (Alexa fluor594) dissolved in the same blocking solution were applied to the sections for 90 min at room temperature. The fluorescence samples were observed by Nikon A1RSi confocal microscopy system.

Results and conclusion: HDL derived CEt in intestinal cells were significantly reduced in ABCG1 null and SR-BI null mice during this experimental period. The other hand, kidney radioactivity showed no difference. Interestingly, preβHDL in SR-BI null mice was reduced by 2D western blotting of anti-mouse apoA-I peptide. Indicates that reduced speed of the plasma apoA-I recycling in SR-BI null mice, it may also cause reduced uptake of HDL-CEt by alternative pathway. Here we show that strong SR-BI-immunoreactivity was also found in the basolateral membrane and even higher intensity in some region. SR-BI located at the basolateral membrane may function as HDL-CE receptor in the small intestine.

Abstract 108: Probucol Rescued Reproduction of LCAT Null Male Mice

Low plasma HDL mice, such as lecitin:cholesterol acyltransferase null mice (Lcat-null), Abca1- null mice and ABCA1 inactivator, probucol-fed mice have significantly low cholesterol content in their adrenal glands and ovaries. Cholesterylester content in brain of male LCAT null mice was significantly reduced while in female the content was not change compare to wild type mice. The reproduction of Lcat-null male pups was reduced to 31% of that expected by Mendelian genetics. Gender ratio in reproduction of wild type, ABCA1 null, and ABCG1null mice were 1 to1 in the same mating condition. Supplement of vitamin E in feeding chow increased vitamin E level in plasma and recovered reproduction defect of male LCAT null mice. Thus, plasma HDL is important lipoprotein to carry hydrophobic vitamin to steroidgenetic cells. Furthermore, although 0.2% probucol-fed mice reduced its plasma HDL only to 5% within 2 weeks, probucol-fed mice reproduced normally. This result suggesting some beneficial function may occur in this chow treatment. So that, we fed 0.2% probucol containing chow to LCAT (+/-) mice during their mating and found recovery of gender ratio in the weaned mice. HMGCoA reductase expression was increased in adrenal gland of probucol fed mice indicate cholesterol de novo synthesis may increased to support cholesterol requirement for steroid synthesis during reproduction. Probucol incorporated HDL (1.00 ug probucol / ug HDL-protein) derived probucol into NCI-H295 human adrenal cortex cell (0.73±0.12 ug probucol / mg cellular protein) and the expression of HMGCoA reductase was significantly increased compared to βactin housekeeping gene expression. Both FC and CE contents in the brain of probucol fed mice were significantly increased. Effect of probucol on cholesterol homeostasis in steroidgenic cells and neuronal cells will be examined in the future study.

Abstract 411: An Anion-Exchange Chromatography Isolated Subfraction of Mouse Apolipoprotein A-I Is Unable to Activate Cellular Cholesterol Release from Mouse Peritoneal Macrophage Foam Cells

Aim: Human and mouse plasma apoA-I separate on anion exchange chromatography (6M urea) in distinct subfractions. To investigate the nature of this diversity, we analyzed the protein subfractions by IEF and Urea-PAGE, and compared their ability to generate HDL in vitro.

Methods: Human and mouse plasma HDLs were delipidated then applied to an DE52 ion-exchange column and eluted by 30-60mM Tris-HCl, pH7.80 containing 6M urea. Mouse, human, and recombinant apoA-Is were analyzed by IEF (Ettan IPGphor3) followed by CBB protein staining. Urea-PAGE analysis was performed with 14% acrylamide gel in 6M urea buffer. ApoA-Is abilities to efflux cholesterol from mouse peritoneal foam cells and to shift the size of the ACAT-accessible cholesterol pool were determined.

Results: Human plasma and recombinant human apoA-I showed two apoA-I subtypes by IEF and Urea-PAGE analysis; whereas HDL from C57BL/6 and 129SV mice contained three apoA-Is at pI=5.37, 5.31, 5.27 (mP3-1, mP2, mP3-3), and pI=5.44, 5.37, 5.32, respectively. Subfractions mP2 and mP3-3 were isolated on a DE52 column and, despite their difference in pI, were able to mediate cellular cholesterol efflux at levels similar to human plasma apoA-Is. Subfraction mP3-1, with the highest pI, eluted between mP2 and mP3-3 on DE-52 column. Interestingly, for both mouse strains, mP3-1 showed very poor cholesterol efflux and the incorporation of 14C-oleic acid to cellular CE was significantly higher when compared to mP2 and mP3-3.

Conclusion: We found that differences in the pI of anion-exchange chromatography apoA-I subfractions did not directly affect HDL generation except for mouse subtype mP3-1. mP3-1 binds strongly to the anionic DE52 resin, probably by hydrophobic interaction, and is unable to mediate cellular cholesterol efflux. Further investigation of the nature of the differences in these apoA-I subtypes will provide insights on factors that may be implicated in the biogenesis of HDL in vivo.

Protein-energy malnutrition halts hemopoietic progenitor cells in the G0/G1 cell cycle stage, thereby altering cell production rates

Protein energy malnutrition (PEM) is a syndrome that often results in immunodeficiency coupled with pancytopenia. Hemopoietic tissue requires a high nutrient supply and the proliferation, differentiation and maturation of cells occur in a constant and balanced manner, sensitive to the demands of specific cell lineages and dependent on the stem cell population. In the present study, we evaluated the effect of PEM on some aspects of hemopoiesis, analyzing the cell cycle of bone marrow cells and the percentage of progenitor cells in the bone marrow. Two-month-old male Swiss mice (N = 7-9 per group) were submitted to PEM with a low-protein diet (4%) or were fed a control diet (20% protein) ad libitum. When the experimental group had lost about 20% of their original body weight after 14 days, we collected blood and bone marrow cells to determine the percentage of progenitor cells and the number of cells in each phase of the cell cycle. Animals of both groups were stimulated with 5-fluorouracil. Blood analysis, bone marrow cell composition and cell cycle evaluation was performed after 10 days. Malnourished animals presented anemia, reticulocytopenia and leukopenia. Their bone marrow was hypocellular and depleted of progenitor cells. Malnourished animals also presented more cells than normal in phases G0 and G1 of the cell cycle. Thus, we conclude that PEM leads to the depletion of progenitor hemopoietic populations and changes in cellular development. We suggest that these changes are some of the primary causes of pancytopenia in cases of PEM.

Pathologic and immunologic profiles of a limited form of neuromyelitis optica with myelitis

BACKGROUND

Neuromyelitis optica (NMO) is a demyelinating syndrome characterized by myelitis and optic neuritis. Detection of anti-NMO immunoglobulin G antibody that binds to aquaporin-4 (AQP4) water channels allows the diagnosis of a limited form of NMO in the early stage with myelitis, but not optic neuritis. However, the detailed clinicopathologic features and long-term course of this limited form remain elusive.

METHODS

We investigated 8 patients with the limited form of NMO with myelitis in comparison with 9 patients with the definite form.

RESULT

All patients with limited and definite form showed uniform relapsing-remitting courses, with no secondary progressive courses. Pathologic findings of biopsy specimens from the limited form were identical to those of autopsy from the definite form, demonstrating extremely active demyelination of plaques, extensive loss of AQP4 immunoreactivity in plaques, and diffuse infiltration by macrophages containing myelin basic proteins with thickened hyalinized blood vessels. Moreover, the definite form at the nadir of relapses displayed significantly higher amounts of the inflammatory cytokines interleukin (IL)-1beta and IL-6 in CSF than the limited form and multiple sclerosis.

CONCLUSION

This consistency of pathologic findings and uniformity of courses indicates that aquaporin 4-specific autoantibodies as the initiator of the neuromyelitis optica (NMO) lesion consistently play an important common role in the pathogenicity through the entire course, consisting of both limited and definite forms, and NMO continuously displays homogeneity of pathogenic effector immune mechanisms through terminal stages, whereas multiple sclerosis should be recognized as the heterogeneous 2-stage disease that could switch from inflammatory to degenerative phase. This report is a significant description comparing the pathologic and immunologic data of limited NMO with those of definite NMO.

Pharmacological inhibition of ABCA1 degradation increases HDL biogenesis and exhibits antiatherogenesis

Expression of ABCA1 is regulated by transcription of the gene and calpain-mediated proteolytic degradation, and inhibition ABCA1 degradation results in increased ABCA1 and HDL biogenesis in vitro. We examined whether this approach could be a potential antiatherogenic treatment. Although probucol inhibits both the activity and degradation of ABCA1, its oxidized products, spiroquinone and diphenoquinone, reduce degradation of ABCA1 without inhibiting its activity or altering transcription of the ABCA1 gene. Accordingly, both compounds enhanced apolipoprotein A-I/ABCA1-dependent generation of HDL in vitro, and increased hepatic ABCA1 and plasma HDL without increasing antioxidant activity in plasma when given to rabbits. Both compounds also decreased vascular lipid deposition in cholesterol-fed rabbits. We therefore conclude that stabilization of ABCA1 against calpain-mediated degradation is a novel and potentially important strategy to increase HDL formation and prevent atherosclerosis. Spiroquinone and diphenoquinone are potential seeds for development of such drugs.

Identification of binding sites for anti-aquaporin 4 antibodies in patients with neuromyelitis optica

OBJECTIVE

Anti-aquaporin 4 antibodies (AQP4-Ab) are specifically detected in patients with neuromyelitis optica. To investigate the role of AQP4-Ab, we examined the antibody binding epitope using human and mouse mutant AQP4.

METHODS

We constructed human and mouse amino acid substitution AQP4 mutants and compared the reactivity with wild-form of human, mouse and rat AQP4.

RESULTS

The decreased intensity of AQP4-Ab staining with mouse AQP4 was recovered to that of human AQP4 with the mouse mutant A228E for 9 of the 10 sera.

CONCLUSIONS

The third extracellular loop of AQP4 is considered to be the major epitope for AQP4-Ab in NMO.

On the mechanism for PPAR agonists to enhance ABCA1 gene expression

Expression of ATP binding cassette transporter A1 (ABCA1), a major regulator of high density lipoprotein (HDL) biogenesis, is known to be up-regulated by the transcription factor liver X receptor (LXR) alpha, and expression is further enhanced by activation of the peroxisome proliferator activated receptors (PPARs). We investigated this complex regulatory network using specific PPAR agonists: four fibrates (fenofibrate, bezafibrate, gemfibrozil and LY518674), a PPAR delta agonist (GW501516) and a PPAR gamma agonist (pioglitazone). All of these compounds increased the expression of LXRs, PPARs and ABCA1 mRNAs, and associated apoA-I-mediated lipid release in THP-1 macrophage, WI38 fibroblast and mouse fibroblast. When mouse fibroblasts lacking expression of PPAR alpha were examined, the effects of fenofibrate and LY518674 were markedly diminished while induction by other ligands were retained. The PPAR alpha promoter was activated by all of these compounds in an LXR alpha-dependent manner, and partially in a PPAR alpha-dependent manner, in mouse fibroblast. The LXR responsive element (LXRE)-luciferase activity was enhanced by all the compounds in an LXR alpha-dependent manner in mouse fibroblast. This activation was exclusively PPAR alpha-dependent by fenofibrate and LY518674, but nonexclusively by the others. We conclude that PPARs and LXRs are involved in the regulation of ABCA1 expression and HDL biogenesis in a cooperative signal transduction pathway.

Biogenesis of HDL by SAA is dependent on ABCA1 in the liver in vivo

Serum amyloid A (SAA) was markedly increased in the plasma and in the liver upon acute inflammation induced by intraperitoneal injection of lipopolysaccharide (LPS) in mice, and SAA in the plasma was exclusively associated with HDL. In contrast, no HDL was present in the plasma and only a small amount of SAA was found in the VLDL/LDL fraction (d < 1.063 g/ml) after the induction of inflammation in ABCA1-knockout (KO) mice, although SAA increased in the liver. Primary hepatocytes isolated from LPS-treated wild-type (WT) and ABCA1-KO mice both secreted SAA into the medium. SAA secreted from WT hepatocytes was associated with HDL, whereas SAA from ABCA1-KO hepatocytes was recovered in the fraction that was >1.21 g/ml. The behavior of apolipoprotein A-I (apoA-I) was the same as that of SAA in HDL biogenesis by WT and ABCA1-KO mouse hepatocytes. Lipid-free SAA and apoA-I both stabilized ABCA1 and caused cellular lipid release in WT mouse-derived fibroblasts, but not in ABCA1-KO mouse-derived fibroblasts, in vitro when added exogenously. We conclude that both SAA and apoA-I generate HDL largely in hepatocytes only in the presence of ABCA1, likely being secreted in a lipid-free form to interact with cellular ABCA1. In the absence of ABCA1, nonlipidated SAA is seemingly removed rapidly from the extracellular space.

Anti-aquaporin 4 antibody in selected Japanese multiple sclerosis patients with long spinal cord lesions

Multiple sclerosis (MS) in Asian populations is often characterized by the selective involvement of the optic nerve (ON) and spinal cord (SP) (OSMS) in contrast to classic MS (CMS), where frequent lesions are observed in the cerebrum, cerebellum or brainstem. In Western countries, inflammatory demyelinating disease preferentially involving the ON and SP is called neuromyelitis optica (NMO). Recently, Lennon et al. discovered that NMO-IgG, shown to bind to aquaporin 4 (AQP4), could be a specific marker of NMO and also of Japanese OSMS whose clinical features were identical to NMO having long spinal cord lesions extending over three vertebral segments (LCL). To examine this antibody in larger populations of Japanese OSMS patients in order to know its epidemiological and clinical spectra, we established an immunohistochemical detection system for the anti-AQP4 antibody (AQP4-Ab) using the AQP4-transfected human embryonic kidney cell line (HEK-293) and confirmed AQP4-Ab positivity together with the immunohistochemical staining pattern of NMO-IgG in approximately 60% of Japanese OSMS patients with LCL. Patients with OSMS without LCL and those with CMS were negative for this antibody. Our results accorded with those of Lennon et al. suggest that Japanese OSMS with LCL may have an underlying pathogenesis in common with NMO.

Serum amyloid A generates high density lipoprotein with cellular lipid in an ABCA1- or ABCA7-dependent manner

Serum amyloid A (SAA) is an amphiphilic helical protein that is found associated with plasma HDL in various pathological conditions, such as acute or chronic inflammation. Cellular lipid release and generation of HDL by this protein were investigated, in comparison with the reactions by apolipoprotein A-I (apoA-I) and several types of cells that appear with various specific profiles of cholesterol and phospholipid release. SAA mediated cellular lipid release from these cells with the same profile as apoA-I. Upregulation of cellular ABCA1 protein by liver X receptor/retinoid X receptor agonists resulted in an increase of cellular lipid release by apoA-I and SAA. SAA reacted with the HEK293-derived clones that stably express human ABCA1 (293/2c) or ABCA7 (293/6c) to generate cholesterol-containing HDL in a similar manner to apoA-I. Dibutyryl cyclic AMP and phorbol 12-myristate 13-acetate, which differentiate apoA-I-mediated cellular lipid release between 293/2c and 293/6c, also exhibited the same differential effects on the SAA-mediated reactions. No evidence was found for the ABCA1/ABCA7-independent lipid release by SAA. Characterization of physicochemical properties of the HDL revealed that SAA-generated HDL particles had higher density, larger diameter, and slower electrophoretic mobility than those generated by apoA-I. These results demonstrate that SAA generates cholesterol-containing HDL directly with cellular lipid and that the reaction is mediated by ABCA1 and ABCA7.

Isoosmotic isolation of rat brain synaptic vesicles, some of which contain tyrosine hydroxylase

Rat brain synaptic vesicles were isoosmotically isolated and examined for Mg(2+)-ATPase [EC 3.6.1.3.] and tyrosine hydroxylase [EC 1.14.16.2.] associated with the synaptic vesicles. Synaptosomes in 0.32 M sucrose were disrupted by freezing and thawing treatment, and the cytosol fraction was fractionated on a Sephacryl S-500 column with a mean exclusion size of 200 nm. Peak I at the void volume was a mixture of large vesicular membranes, small amounts of synaptic vesicles and coated vesicles, etc. Peak II consisted of non- and granulated synaptic vesicles of 35-40 nm diameter, and peak III of soluble proteins. The synaptic vesicles in peak II reacted with antibodies against the H(+)-ATPase A-subunit, vesicular acetylcholine transporter, and vesicular monoamine transporter. However, they showed little Mg(2+)-ATPase activity. Tyrosine hydroxylase was observed in either peak II or III on blotting with an anti-tyrosine hydroxylase antibody. These results imply that tyrosine hydroxylase exists in soluble and bound forms to synaptic vesicles in nerve terminals.

On the hepatic mechanism of HDL assembly by the ABCA1/apoA-I pathway

The mechanism for the assembly of HDL with cellular lipid by ABCA1 and helical apolipoprotein was investigated in hepatocytes. Both HepG2 cells and mouse primary culture hepatocytes produced HDL with apolipoprotein A-I (apoA-I) whether endogenously synthesized or exogenously provided. Probucol, an ABCA1 inactivator, inhibited these reactions, as well as the reversible binding of apoA-I to HepG2. Primary cultured hepatocytes of ABCA1-deficient mice also lacked HDL production regardless of the presence of exogenous apoA-I. HepG2 cells secreted apoA-I into the medium even when ABCA1 was inactivated by probucol, but it was all in a free form as HDL production was inhibited. When a lipid-free apoA-I-specific monoclonal antibody, 725-1E2, was present in the culture medium, production of HDL was suppressed, whether with endogenous or exogenously added apoA-I, and the antibody did not influence HDL already produced by HepG2 cells. We conclude that the main mechanism for HDL assembly by endogenous apoA-I in HepG2 cells is an autocrine-like reaction in which apoA-I is secreted and then interacts with cellular ABCA1 to generate HDL.

Probucol inactivates ABCA1 in the plasma membrane with respect to its mediation of apolipoprotein binding and high density lipoprotein assembly and to its proteolytic degradation

Probucol has been shown to inhibit the release of cellular lipid by helical apolipoprotein and thereby to reduce plasma high density lipoprotein. We attempted to explore the underlying mechanism for this effect in human fibroblast WI-38. Probucol inhibited the apoA-I-mediated cellular lipid release and binding of apoA-I to the cells in a dose-dependent manner. It did not influence cellular uptake of low density lipoprotein, transport of cholesterol to the cell surface whether de novo synthesized or delivered as low density lipoprotein, and overall cellular content of cholesterol, although biosynthesis of lipids from acetate was somewhat increased. Probucol did not affect the mRNA level of ABCA1, and ABCA1 was recovered along with marker proteins for plasma membrane regardless of the presence of probucol. However, the protein level of ABCA1 increased, and the rate of its decay in the presence of cycloheximide was slower in the probucol-treated cells. ABCA1 in the probucol-treated cells was resistant to digestion by calpain but not by trypsin. We concluded that probucol inactivates ABCA1 in the plasma membrane with respect to its function in mediating binding of and lipid release by apolipoprotein and with respect to proteolytic degradation by calpain.

An inhibitor of acylCoA: cholesterol acyltransferase increases expression of ATP-binding cassette transporter A1 and thereby enhances the ApoA-I-mediated release of cholesterol from macrophages

The effect of inhibition of acylCoA: cholesterol acyltransferase (ACAT) was studied on high density lipoprotein (HDL) metabolism. An inhibitor of ACAT, MCC-147, was given mouse peritoneal macrophages and expression of ATP-binding cassette transporter A1 (ABCA1) was examined. ABCA1 was increased both at the mRNA and protein levels, only when the cells are cholesterol-loaded and thereby the inhibitor decreased esterified cholesterol and increased unesterified cholesterol. In this condition, the ACAT inhibitor increased reversible binding of apoA-I to the cells and enhanced apoA-I-mediated release of cellular cholesterol and phospholipid, but did not influence nonspecific cellular cholesterol efflux to lipid microemulsion. It was therefore concluded that the ACAT inhibitor increased the release of cholesterol from the cholesterol-loaded macrophages by increasing the expression of ABCA1, putatively through shifting cholesterol distribution from the esterified to the free compartments.

Potential involvement of dissociated apoA-I in the ABCA1-dependent cellular lipid release by HDL

Helical apolipoproteins of high density lipoprotein (HDL) remove phospholipid and cholesterol from cells and generate HDL particles being mediated by ATP binding cassette transporter A1 (ABCA1). In murine macrophage cell line RAW264 cells, cAMP induced expression of ABCA1, release of cellular phospholipid and cholesterol by apolipoprotein A-I (apoA-I), and reversible binding of apoA-I to the cell. The apoA-I-dependent lipid release was directly proportional to the cAMP-induced binding of apoA-I, and was inhibited 70% by a monoclonal antibody selective to lipid-free apoA-I, 725-1E2. In contrast, apparent cellular cholesterol release to HDL was substantial even without ABCA1 induction, and it was increased only by 27% after the cAMP treatment. The antibody inhibited this increment by 70%. Lipid-free apoA-II liberated apoA-I from HDL by displacement and thereby markedly expanded the cAMP-induced part of the cholesterol release to the HDL-containing medium, and the antibody inhibited this part also by 70%. Binding experiments of the double-labeled reconstituted HDL showed that cAMP induced reversible binding of apoA-I but not the association of cholesteryl ester with the cells. The effect of the antibody on the cellular cholesterol release to the reconstituted HDL was similar to that of the HDL-mediated release. The data implicated that the ABCA1-dependent cholesterol release to HDL is mediated by apoA-I dissociated from HDL.