Removal Of Cellular Cholesterol Research Articles

Role of Integrins Involved in Mn2+-Dependent Adhesion to Fibronectin Peptide of Mastocytoma P-815 Cells and Peritoneal Mast Cells

Mn2+-dependent integrin-mediated adhesion to the extracellular matrix is extensively studied, however, its implication in mast cell biology remains unexplored. This study aims to investigate the role of Mn2+ in promoting adhesion in mouse mastocytoma P-815 cells (P-815) and peritoneal mast cells (PMC) to the Arg-Gly-Asp (RGD)-enriched fibronectin peptide (RGD matrix) within the culture medium. Our findings indicate that Mn2+ induces cell adhesion, with optimal results achieved when P-815 were exposed to 2 mM Mn2+ for 30 min at 37ºC, resulting in approximately 40% cell adhesion to the RGD matrix. The Mn2+-dependent P-815 adhesion was inhibited by anti-integrin α4, β1, and β3 subunit function-blocking antibodies, and by the integrin αIIbβ3 antagonist tirofiban, indicating the involvement of integrins α4β1 and αIIbβ3. Similarly, Mn2+-dependent PMC adhesion to the RGD matrix was inhibited by anti-integrin α4, α5, β1, β3, and β7 subunit function-blocking antibodies and tirofiban, demonstrating the involvement of integrins α4β1, α4β7, α5β1, and αIIbβ3. Integrins α4β1 and αIIbβ3 were consistently involved in Mn2+-induced adhesion reactions in both P-815 and PMC, while integrins α4β7 and α5β1 were specifically implicated in the response to PMC only. The addition of the actin inhibitor cytochalasin D, glycosylphosphatidylinositol-anchored protein (GPI-AP) cleaving enzyme phosphatidylinositol-specific phospholipase C, and the PKA inhibitor H-89 significantly reduced Mn2+-dependent P-815 adhesion to the RGD matrix. However, adding the myosin II inhibitor brebbistatin and the RhoA inhibitor Y27632 did not produce the same effect. Furthermore, cellular cholesterol removal with 6-O-α-maltosyl-β cyclodextrin significantly diminished Mn2+-dependent P-815 adhesion, concomitant with a decrease in the expression of integrin α4 and β1 subunits on the cell surface.

Treatment of preeclamptic vessels with pravastatin enhances vessel function and alters caveolae form and distribution through removal of cellular cholesterol

IntroductionPreeclampsia (PE) causes significant maternal and foetal morbidity and mortality. Maternal vascular endothelial dysfunction contributes to PE resulting in systemic organ dysfunction. Symptoms of PE are most effectively alleviated/managed through pre‐term delivery and/or expectant care, highlighting the need for effective therapies to be identified. The potential clinical applications of pravastatin in the treatment of PE has been reported across multiple studies, however the mechanism(s) behind this is have yet to be elucidated [1, 2].AimsThis study aims to investigate the effect of in vitro pravastatin on uterine microvascular endothelial function in PE, specifically its role in modulating caveolae form and distribution and hence vascular function in PEMethodsMyometrial radial arterioles from caesarean‐section normotensive (NT) and PE patients were incubated with pravastatin (2mM/6h) in vitro. Electron microscopy, immunohistochemistry and pressure myography were used to characterize caveolae and vessel structure and function. Parallel studies conducted with methyl‐β‐cyclodextrin (MβCD) (10mM/1h) examined the effects of removing cholesterol on function.ResultsOverall caveolae density/µm is reduced 24% from 5.5 ± 0.1/µm in NT (n=4, P<0.05) to 4.2 ± 0.01/µm (n=4, P<0.05) in PE vessels, a further 31% to 1.9 ± 0.8/µm (n=4, P<0.05) in PE vessels following treatment with pravastatin. Myoendothelial gap junction density/5mm of vessel length is reduced ~215% from 5.7 ± 1.3/5mm in NT (n=3, P<0.05) to 1.8 ± 0.9/5mm (n=3, P<0.05) in PE vessels. Confocal immunohistochemistry showed decreased caveolin‐1 expression in PE arterioles relative to NT with expression redistributed to endothelial cell borders, following treatment with pravastatin expression was reduced a further ~50% in PE vessels (n=6‐8, P<0.05). Functionally, endothelium‐dependent relaxation was inhibited in arteries from PE compared to NT. Inhibition of NOS/COX reduced bradykinin‐induced dilation in arteries from NT but not PE, suggesting NO/PG‐mediated dilation is lost in PE.. Pravastatin incubation restored endothelium‐dependent relaxation in PE samples to NT levels enhancing the NO and IKCa‐mediated components of relaxation. Incubation with MβCD increased sensitivity (LogEC50 from ‐7.37 to ‐8.24, P<0.05) and maximum dilation to bradykinin in arteries from NT (81.7 ± 4.9.% (n=13) to 94.8 ± 5.2 % (n=8), P<0.05), but had no significant effect in arteries from PE (max 65.6 ± 6.4% (n=17) to 86.5 ± 13.5% (n=3), P>0.05).DiscussionThis data suggests treatment of preeclamptic vessels with pravastatin can be associated with improved vessel function as well as modulation of caveolae form and distribution, specifically though the removal of cellular cholesterol.1. Costantine, M. M. & Cleary, M. K. Obstetrics & Gynecology 121, 349‐353, (2013).2. Esteve‐Valverde, E. et al. Obstetrical & Gynecological Survey 73, 40‐55, (2018).

Trabecular Meshwork Cholesterol Levels Regulate Actin Polymerization and Tunneling Nanotubes

Trabecular meshwork (TM) tissue is made of highly contractile mechanosensitive cells regulating aqueous humor (AH) outflow facility and intraocular pressure (IOP). Increased actin‐mediated contraction of TM elevates IOP causing glaucoma and irreversible blindness. This study aims at understanding the role of cholesterol in regulating actin dynamics in human TM (HTM) cells. To test this, HTM cells were treated with SiR‐Actin in serum‐free media overnight and F‐actin changes were recorded using live‐cell time‐lapse (5 min interval) confocal imaging before and during exposure to ‐ A) 10mM methyl‐β‐cyclodextrin (MβCD) for 1h for acute removal of cellular cholesterol, B) 100μM cholesterol‐saturated MβCD (MβCD‐CHOL) for 1h to enrich cholesterol, and C) 10mM MβCD for 1h followed by cholesterol supplementation using MβCD‐CHOL for 1h. F‐actin fluorescence intensity changes were calculated and unpaired t‐test was used for statistical analyses and results were significant if p<0.05 with a sample size of n= 4‐57. HTM cells plated on coverslips were treated as A – C as mentioned above, cholesterol and lipid synthesis inhibitors for 24h ‐ D) 100μM atorvastatin and E) 20μM fatostatin, respectively, F) actin polymerization disruptor ‐ 10μM cytochalasin D (CYTD) for 1h, G) 10μM CYTD for 1h followed by 100μM MβCD‐CHOL for 1h, H) microtubule disruptor ‐ 1μM demecolcine (DEM) for 1h, I) 1μM DEM for 1h followed by 100μM MβCD‐CHOL for 1h. Cells without treatment were used as control. After all these treatments, cells were fixed and immunofluorescence (IF) was performed to check for cholesterol using filipin, F‐actin by phalloidin, focal adhesion (FA) localization based on ‐ vinculin and paxillin distribution. Further F‐actin/G‐actin in vitro assay was performed to quantify the changes in actin polymerization under the conditions A – I compared to the control. The imaging analysis showed cholesterol removal significantly decreased F‐actin fluorescence intensity from 20min sustaining up to 1h and decreased the FA distribution. Cholesterol supplementation led to partial rescue of actin and FA indicating the re‐establishment of actin cytoskeleton and increased tunneling nanotube structures enhancing the cell‐cell communication (Figure 1). Moreover, IF results show that atorvastatin and fatostatin decreased F‐actin and FA distribution. CYTD disrupted F‐actin network leaving remnant filament ends and decreased FA but cholesterol enrichment increased F‐actin branches formed at ~70‐degree angle indicating Arp2/3 activation. DEM treatment increased F‐actin and FA, and cholesterol enrichment induced thick F‐actin filaments. These results were confirmed by quantitative F/G‐actin ratio decrease and increase upon cholesterol removal and enrichment, respectively. Additionally, supplementing cholesterol after removal increased the ratio compared to solely removing cholesterol. Interestingly, F/G‐actin ratio increased under CYTD treatment indicating that CYTD disrupted longer actin filaments but helped polymerization of newly formed actin filaments. Finally, DEM treatment increased F/G‐actin ratio, which was further increased by cholesterol enrichment. This systematic evaluation of cholesterol modulation on TM actin cytoskeleton polymerization identifies the significance of maintaining membrane and cellular cholesterol levels and cellular communication for achieving IOP homeostasis.

Mitigating RANKL-induced cholesterol overload in macrophages with β-cyclodextrin-threaded polyrotaxanes suppresses osteoclastogenesis.

Free cholesterol acts as an endogenous agonist for estrogen-related receptor α (ERRα), a nuclear receptor that regulates osteoclastogenesis. Because stimulation of macrophages with receptor activator of nuclear factor κB ligand (RANKL) induces an overload of free cholesterol and activates ERRα, we hypothesized that direct removal of cellular cholesterol would suppress osteoclastogenesis. In this study, the effect of 2-hydroxypropyl β-cyclodextrin (HP-β-CD), a highly water-soluble cyclic glucopyranose, and β-CD-threaded polyrotaxanes (PRXs), supramolecular polymers designed to release threaded β-CDs in acidic lysosomes, on RANKL-induced cholesterol overload and osteoclast differentiation of murine macrophage-like RAW264.7 cells were investigated. PRXs suppressed RANKL-induced cholesterol overload. Additionally, RANKL-induced osteoclast differentiation of RAW264.7 cells was inhibited by PRXs. In contrast, HP-β-CD did not reduce cholesterol levels or inhibit osteoclast differentiation in RAW264.7 cells. Gene expression analysis of osteoclast markers suggested that PRXs suppress only the early stage of osteoclast differentiation, as PRXs cannot be internalized into multinucleated osteoclasts. However, modification of PRXs with cell-penetrating peptides facilitated their cellular uptake into multinucleated osteoclasts and inhibited osteoclast maturation. Thus, PRXs are promising candidates for inhibiting osteoclast differentiation by suppressing cholesterol overload and may be useful for treating osteoporosis or other bone defects caused by the overactivity of osteoclasts.

Probing the Structure–Function relationship and amyloidogenic propensities in natural variants of apolipoprotein A-I

BackgroundApolipoprotein A-I (apoA-I) protects against atherosclerosis and participates in the removal of excess cellular cholesterol from peripheral organs. Several naturally occurring apoA-I mutations are associated with familial systemic amyloidosis, with deposition of amyloid aggregates in peripheral organs, resulting in multiple organ failure. Systematic studies on naturally occurring variants are needed to delineate their roles and involvement in pathogenesis. MethodsWe performed a comparative structure–function analysis of five naturally occurring apoA-I variants and the wild-type protein. Circular dichroism, Fourier-transform infrared spectroscopy, thioflavin T and congo red fluorescence assays, thermal, chemical, and proteolytic stability assays, and 1,2-Dimyristoyl-sn-glycero-3-phosphocholine clearance analyses were used to assess the effects of mutations on the structure, function, stability, aggregation, and proteolytic susceptibility of the proteins to explore the mechanisms underlying amyloidosis and hypercholesterolemia. ResultsWe observed structural changes in the mutants independent of fibril formation, suggesting the influence of the surrounding environment. The mutants were involved in aggregate formation to varying degree; L170P, R173P, and V156E showed an increased propensity to aggregate under different physiological conditions. β sheet formation indicates that L170P and R173P participate in amyloid formation. Compared to WT, V156E and L170P exhibited higher capacity for lipid clearance. ConclusionsThe selected point mutations, including those outside the hot spot regions of apoA-I structure, perturb the physiochemical and conformational behavior of the protein, influencing its function. General significanceThe study provides insights into the structure–function relationships of naturally occurring apoA-I variants outside the hot spot mutation sites.

Gypenosides mediate cholesterol efflux and suppress oxidized LDL induced inflammation in retinal pigment epithelium cells

Age-related macular degeneration (AMD) is a predominant cause of visual deficit in aged population. Abnormal accumulation of cholesterol, including oxidized low-density lipoprotein (oxLDL), underneath the retinal pigment epithelium (RPE) cells contributes to the development of AMD. Gypenosides (Gyp) are glycosides extracted from Gynostemma pentaphyllum and have demonstrated protective effects against inflammation and oxidative stress. To determine the therapeutic potential of Gyp for AMD, we investigated its effect on cholesterol trafficking and metabolism and assessed the protective function of Gyp against oxLDL-induced damage in RPE cells. Cholesterol efflux to high-density lipoprotein (HDL) and human serum was significantly increased in RPE cells treated with Gyp when compared to untreated control cells. Expression of cholesterol metabolism (CYP27A1, CYP46A1) and trafficking (TSPO, ABCA1 and ABCG1) genes was also markedly increased in Gyp-treated RPE cells. OxLDL-treated RPE cells had significantly increased cholesterol accumulation and lipid droplet formation. There were marked increases in reactive oxygen species (ROS) generation and proinflammatory cytokines via NF-κB activation in RPE cells treated with oxLDL, while incubation with Gyp rectified these changes. These findings provide pharmacological evidence that Gyp has the potential to treat patients with early onset AMD by promoting cellular cholesterol removal from RPE cells and inhibiting inflammation and oxidative stress.

Abstract 2419: Lipid droplets promote glioblastoma cell growth through maintaining cholesterol homeostasis mediated by autophagy

Abstract Lipid droplets (LDs) have been studied as the major storage site of neutral lipids for decades, especially in the progression of metabolic diseases. Recently, the functions of LDs in cancers have begun to gain significant attention. Here, we provide evidence that LDs promote glioblastoma (GBM) cell growth through autophagy mediated maintenance of cholesterol homeostasis. Our data showed that LDs in tumor tissues from GBM patients are engulfed by autophagic vacuoles and lysosomes. Cellular cholesterol deprivation or removal of plasma membrane cholesterol by methyl-β-cyclodextrin (MβCD) activates autophagy to hydrolyze LDs to support GBM cell survival, whereas inhibition of autophagy blocks transportation of cholesterol to plasma membrane, leading to cell death. Fluorescence imaging reveals direct trafficking of LD-stored cholesterol to the plasma membrane through autophagic liberation. Our data demonstrate that LDs serve as cholesterol reservoir for GBM cell growth, suggesting that targeting LD-autophagy-cholesterol homeostasis metabolic pathway represents a potential means to treat GBM and other malignancies. Citation Format: Feng Geng, Xiang Cheng, Chunming Cheng, Arnab Chakravarti, Deliang Guo. Lipid droplets promote glioblastoma cell growth through maintaining cholesterol homeostasis mediated by autophagy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2419.

Retinal pigment epithelium cholesterol efflux mediated by the 18 kDa translocator protein, TSPO, a potential target for treating age-related macular degeneration.

Cholesterol accumulation beneath the retinal pigment epithelium (RPE) cells is supposed to contribute the pathogenesis of age-related macular degeneration (AMD). Cholesterol efflux genes (APOE and ABCA1) were identified as risk factors for AMD, although how cholesterol efflux influences accumulation of this lipid in sub-RPE deposits remains elusive. The 18 kDa translocator protein, TSPO, is a cholesterol-binding protein implicated in mitochondrial cholesterol transport. Here, we investigate the function of TSPO in cholesterol efflux from the RPE cells. We demonstrate in RPE cells that TSPO specific ligands promoted cholesterol efflux to acceptor (apo)lipoprotein and human serum, while loss of TSPO resulted in impaired cholesterol efflux. TSPO-/- RPE cells also had significantly increased production of reactive oxygen species (ROS) and upregulated expression of proinflammatory cytokines (IL-1β and TNFα). Cholesterol (oxidized LDL) uptake and accumulation were markedly increased in TSPO-/- RPE cells. Finally, in aged RPE cells, TSPO expression was reduced and cholesterol efflux impaired. These findings provide a new pharmacological concept to treat early AMD patients by stimulating cellular cholesterol removal with TSPO specific ligands or by overexpression of TSPO in RPE cells.

Plaque-hyaluronidase-responsive high-density-lipoprotein-mimetic nanoparticles for multistage intimal-macrophage-targeted drug delivery and enhanced anti-atherosclerotic therapy.

Increasing evidence has highlighted the pivotal role that intimal macrophage (iMΦ) plays in the pathophysiology of atherosclerotic plaques, which represents an attractive target for atherosclerosis treatment. In this work, to address the insufficient specificity of conventional reconstituted high-density lipoprotein (rHDL) for iMΦ and its limited cholesterol efflux ability, we designed a hyaluronan (HA)-anchored core–shell rHDL. This nanoparticle achieved efficient iMΦ-targeted drug delivery via a multistage-targeting approach, and excellent cellular cholesterol removal. It contained a biodegradable poly (lactic-co-glycolic acid) (PLGA) core within a lipid bilayer, and apolipoprotein A-I (apoA-I) absorbing on the lipid bilayer was covalently decorated with HA. The covalent HA coating with superior stability and greater shielding was favorable for not only minimizing the liver uptake but also facilitating the accumulation of nanoparticles at leaky endothelium overexpressing CD44 receptors in atherosclerotic plaques. The ultimate iMΦ homing was achieved via apoA-I after HA coating degraded by hyaluronidase (HAase) (abundant in atherosclerotic plaque). The multistage-targeting mechanism was revealed on the established injured endothelium–macrophage co-culture dynamic system. Upon treatment with HAase in vitro, the nanoparticle HA-(C)-PLGA-rHDL exhibited a greater cholesterol efflux capacity compared with conventional rHDL (2.43-fold). Better targeting efficiency toward iMΦ and attenuated liver accumulation were further proved by results from ex vivo imaging and iMΦ-specific fluorescence localization. Ultimately, HA-(C)-PLGA-rHDL loaded with simvastatin realized the most potent anti-atherogenic efficacies in model animals over other preparations. Thus, the HAase-responsive HDL-mimetic nanoparticle was shown in this study to be a promising nanocarrier for anti-atherogenic therapy, in the light of efficient iMΦ-targeted drug delivery and excellent function of mediating cellular cholesterol efflux.

Ethanol Inhibits High-Affinity Immunoglobulin E Receptor (FcεRI) Signaling in Mast Cells by Suppressing the Function of FcεRI-Cholesterol Signalosome.

Ethanol has multiple effects on biochemical events in a variety of cell types, including the high-affinity immunoglobulin E receptor (FcεRI) signaling in antigen-activated mast cells. However, the underlying molecular mechanism remains unknown. To get better understanding of the effect of ethanol on FcεRI-mediated signaling we examined the effect of short-term treatment with non-toxic concentrations of ethanol on FcεRI signaling events in mouse bone marrow-derived mast cells. We found that 15 min exposure to ethanol inhibited antigen-induced degranulation, calcium mobilization, expression of proinflammatory cytokine genes (tumor necrosis factor-α, interleukin-6, and interleukin-13), and formation of reactive oxygen species in a dose-dependent manner. Removal of cellular cholesterol with methyl-β-cyclodextrin had a similar effect and potentiated some of the inhibitory effects of ethanol. In contrast, exposure of the cells to cholesterol-saturated methyl-β-cyclodextrin abolished in part the inhibitory effect of ethanol on calcium response and production of reactive oxygen species, supporting lipid-centric theories of ethanol action on the earliest stages of mast cell signaling. Further studies showed that exposure to ethanol and/or removal of cholesterol inhibited early FcεRI activation events, including tyrosine phosphorylation of the FcεRI β and γ subunits, SYK kinases, LAT adaptor protein, phospholipase Cγ, STAT5, and AKT and internalization of aggregated FcεRI. Interestingly, ethanol alone, and particularly in combination with methyl-β-cyclodextrin, enhanced phosphorylation of negative regulatory tyrosine 507 of LYN kinase. Finally, we found that ethanol reduced passive cutaneous anaphylactic reaction in mice, suggesting that ethanol also inhibits FcεRI signaling under in vivo conditions. The combined data indicate that ethanol interferes with early antigen-induced signaling events in mast cells by suppressing the function of FcεRI-cholesterol signalosomes at the plasma membrane.

The role of the lymphatic system in cholesterol transport.

Reverse cholesterol transport (RCT) is the pathway for removal of peripheral tissue cholesterol and involves transport of cholesterol back to liver for excretion, starting from cellular cholesterol efflux facilitated by lipid-free apolipoprotein A1 (ApoA1) or other lipidated high-density lipoprotein (HDL) particles within the interstitial space. Extracellular cholesterol then is picked up and transported through the lymphatic vasculature before entering into bloodstream. There is increasing evidence supporting a role for enhanced macrophage cholesterol efflux and RCT in ameliorating atherosclerosis, and recent data suggest that these processes may serve as better diagnostic biomarkers than plasma HDL levels. Hence, it is important to better understand the processes governing ApoA1 and HDL influx into peripheral tissues from the bloodstream, modification and facilitation of cellular cholesterol removal within the interstitial space, and transport through the lymphatic vasculature. New findings will complement therapeutic strategies for the treatment of atherosclerotic vascular disease.

Serum proprotein convertase subtilisin/kexin type 9 concentration is not increased by plant stanol ester consumption in normo- to moderately hypercholesterolaemic non-obese subjects. The BLOOD FLOW intervention study

Proprotein convertase subtilisin/kexin type9 (PCSK9) regulates low-density lipoprotein (LDL) cholesterol (LDL-C) metabolism by targeting LDL receptors for degradation. Statins increase serum PCSK9 concentration limiting the potential of statins to reduce LDL-C, whereas ezetimibe, inhibitor of cholesterol absorption, has ambiguous effects on circulating PCSK9 levels. Plant stanols also reduce cholesterol absorption, but their effect on serum PCSK9 concentration is not known. Therefore, we performed a controlled, randomized, double-blind study, in which 92 normo- to moderately hypercholesterolaemic subjects (35 males and 57 females) consumed vegetable-oil spread 20g/day enriched (plant stanol group, n=46) or not (control group, n=46) with plant stanols 3g/day as ester for 6 months. Fasting blood samples were drawn at baseline and at the end of the study. Serum PCSK9 concentration was analysed with Quantikine Elisa Immunoassay, serum and lipoprotein lipids enzymatically and serum non-cholesterol sterols with GLC. At baseline, PCSK9 concentration varied from 91 to 716ng/ml with a mean value of 278±11 (S.E.M.) ng/ml with no gender difference. It correlated with serum and LDL-C, serum triglycerides, age, body mass index (BMI) and plasma glucose concentration, but not with variables of cholesterol metabolism when adjusted to serum cholesterol. Plant stanols reduced LDL-C by 10% from controls (P<0.05), but PCSK9 levels were unchanged and did not differ between the groups. In conclusion, the present study demonstrated for the first time that inhibition of cholesterol absorption with plant stanol esters did not affect serum PCSK9 concentration. Thus, plant stanol esters provide an efficient dietary means to lower LDL-C without interfering with the PCSK9 metabolism and in this regard the LDL receptor-mediated cellular cholesterol uptake and removal.

The Effects of Phellinus linteus Polysaccharide Extracts on Cholesterol Efflux in Oxidized Low-Density Lipoprotein–Loaded THP-1 Macrophages

The removal of excess cellular cholesterol is critical for maintaining cellular cholesterol homeostasis. Phellinus linteus polysaccharide extracts (PLPEs) is an immunomudulatory agent with a molecular weight of 153 kd. Here,...

Phosphatidylcholine-Mediated Aqueous Diffusion of Cellular Cholesterol Down-Regulates the ABCA1 Transporter in Human Skin Fibroblasts.

ATP-binding cassette protein A1 (ABCA1) is a cholesterol transporter that contributes to the active transport/removal of excess cellular cholesterol. ABCA1 expression is up-regulated when cells accumulate cholesterol.AimsThe purpose of this study was to determine any correlation between extracellular phospholipid levels and ABCA1 expression and function.MethodologyHuman foreskin fibroblasts were incubated with cholesterol alone or cholesterol and phosphatidylcholine. Total RNA was isolated and subjected to end-point RT-PCR to compare ABCA1 transcript levels. Cell lysates were subjected to Western blot analysis to compare ABCA1 protein levels. Cells were loaded with radiolabeled cholesterol and cellular cholesterol efflux was measured in the presence and absence of apoE, a cholesterol acceptor. ApoE-dependent efflux was calculated as a measure of ABCA1-mediated efflux.ResultsHere we show that incubation of cholesterol-loaded human skin fibroblasts with L-α-phosphatidylcholine (PC) decreases ABCA1 mRNA and protein levels by 93% and 57%, respectively, compared to cells loaded with cholesterol alone. Similarly, PC treatment results in a 25% reduction in ABCG1 mRNA levels compared to cells treated with cholesterol alone, but there is no change in SR-BI transcript levels. Subsequent incubation of phospholipid-treated cells with a cholesterol acceptor such as apoE for 24 hours shows a 65% reduction in ABCA1-mediated cholesterol efflux compared to efflux in cells not treated with PC. During the lipid treatment itself, there is a 2.7-fold greater loss of cholesterol from PC treated cells compared to cells treated with cholesterol alone. Measurement of cholesterol in cellular lipid extracts reveals that cells incubated in the presence of phosphatidylcholine are significantly depleted of cholesterol having only 20% of the cholesterol compared to cells loaded with cholesterol alone.ConclusionThus, phosphatidylcholine facilitates removal of cellular cholesterol, thereby negating the cholesterol-dependent induction of ABCA1 message, protein and function.

Abstract 15438: Serum Proprotein Convertase Subtilisin/Kexin Type 9 Levels Are Not Increased by Plant Stanol Ester Consumption

Introduction: Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a critical role in regulating cholesterol metabolism mainly by binding to LDL receptors targeting them for degradation. Statins, inhibitors of cholesterol synthesis, increase the serum PCSK9 concentration limiting the potential of statins to reduce LDL cholesterol (C) concentration, whereas ezetimibe, an inhibitor of cholesterol absorption, has ambiguous effects on circulating PCSK9 levels. Plant stanols lower LDL-C by inhibiting cholesterol absorption, but their effect on serum PCSK9 concentration is not known. Hypothesis: We assessed the hypothesis that consumption of plant stanol esters lowers LDL-C without increasing circulating PCSK9 levels. Methods: Ninety-two normo- and mildly hypercholesterolemic subjects, 35 men and 57 women (mean age 50.8±1.0 (SE) years) were randomly divided into plant stanol ester (STANOL) (n=46) and control (n=46) groups. They consumed spread enriched with (STANOL group) and without (control group) plant stanol (3g /d) ester in a double-blind intervention for six months. Serum lipids and lipoproteins were analysed enzymatically and serum PCSK9 concentration was quantitated with Quantikine Elisa Immunoassay at baseline and after the intervention. Results: At baseline, serum PCSK9 levels correlated positively with LDL-C in the whole study population. Serum total, LDL-C and non-HDL-C concentrations, similar between the study groups at baseline, declined by 7%,10%, and 11% at the end of the intervention in the STANOL group compared with the control group (p&lt; 0.001, for all). The baseline serum PCSK9 concentrations were similar between the groups (STANOL 284±16 ng/ml, controls 273±16 ng/ml, ns). At the end of the intervention, serum PCSK9 concentrations were unchanged from baseline in both groups and did not differ between the groups (STANOL 293 ±15 ng/ml, controls 309±16 ng/ml, ns). Conclusion: In conclusion, plant stanol ester consumption does not affect the circulating PCSK9 concentration. Thus, plant stanols provide an efficient dietary means to lower LDL-C concentration without interfering with the LDL receptor-mediated cellular cholesterol uptake and removal.

Evidence for the presence of lipid-free monomolecular apolipoprotein A-1 in plasma

The first step in reverse cholesterol transport is a process by which lipid-free or lipid-poor apoA-1 removes cholesterol from cells through the action of ATP binding cassette transporter A1 at the plasma membrane. However the structure and composition of lipid-free or -poor apoA-1 in plasma remains obscure. We previously obtained a monoclonal antibody (MAb) that specifically recognizes apoA-1 in preβ1-HDL, the smallest apoA-1-containing particle in plasma, which we used to establish a preβ1-HDL ELISA. Here, we purified preβ1-HDL from fresh normal plasma using said antibody, and analyzed the composition and structure. ApoA-1 was detected, but neither phospholipid nor cholesterol were detected in the purified preβ1-HDL. Only globular, not discoidal, particles were observed by electron microscopy. In nondenaturing PAGE, no difference in the mobility was observed between the purified preβ1-HDL and original plasma preβ1-HDL, or between the preβ1-HDL and lipid-free apoA-1 prepared by delipidating HDL. In sandwich ELISA using two anti-preβ1-HDL MAbs, reactivity with intact plasma preβ1-HDL was observed in ELISA using two MAbs with distinct epitopes but no reactivity was observed in ELISA using a single MAb, and the same phenomenon was observed with monomolecular lipid-free apoA-1. These results suggest that plasma preβ1-HDL is lipid-free monomolecular apoA-1.

Cholesterol dependence of Newcastle Disease Virus entry

Lipid rafts are membrane microdomains enriched in cholesterol, sphingolipids, and glycolipids that have been implicated in many biological processes. Since cholesterol is known to play a key role in the entry of some other viruses, we investigated the role of cholesterol and lipid rafts in the host cell plasma membrane in Newcastle Disease Virus (NDV) entry. We used methyl-β-cyclodextrin (MβCD) to deplete cellular cholesterol and disrupt lipid rafts. Our results show that the removal of cellular cholesterol partially reduces viral binding, fusion and infectivity. MβCD had no effect on the expression of sialic acid containing molecule expression, the NDV receptors in the target cell. All the above-described effects were reversed by restoring cholesterol levels in the target cell membrane. The HN viral attachment protein partially localized to detergent-resistant membrane microdomains (DRMs) at 4°C and then shifted to detergent-soluble fractions at 37°C. These results indicate that cellular cholesterol may be required for optimal cell entry in NDV infection cycle.

Apolipoprotein A-1 (apoA-1) deposition in, and release from, the enterocyte brush border: A possible role in transintestinal cholesterol efflux (TICE)?

Transintestinal cholesterol efflux (TICE) has been proposed to represent a non-hepatobiliary route of cholesterol secretion directly “from blood to gut” and to play a physiologically significant role in excretion of neutral sterols, but so far little is known about the proteins involved in the process. We have previously observed that apolipoprotein A-1 (apoA-1) synthesized by enterocytes of the small intestine is mainly secreted apically into the gut lumen during fasting where its assembly into chylomicrons and basolateral discharge is at a minimal level. In the present work we showed, both by immunomicroscopy and subcellular fractionation, that a fraction of the apically secreted apoA-1 in porcine small intestine was not released from the cell surface but instead deposited in the brush border. Cholesterol was detected in immunoisolated microvillar apoA-1, and it was partially associated with detergent resistant membranes (DRMs), indicative of localization in lipid raft microdomains. The apolipoprotein was not readily released from microvillar vesicles by high salt or by incubation with phosphatidylcholine-specific phospholipase C or trypsin, indicating a relatively firm attachment to the membrane bilayer. However, whole bile or taurocholate efficiently released apoA-1 at low concentrations that did not solubilize the transmembrane microvillar protein aminopeptidase N. Based on these findings and the well known role played by apoA-1 in extrahepatic cellular cholesterol removal and reverse cholesterol transport (RCT), we propose that brush border-deposited apoA-1 in the small intestine acts in TICE by mediating cholesterol efflux into the gut lumen.

Cellular membrane cholesterol is required for porcine reproductive and respiratory syndrome virus entry and release in MARC-145 cells

Cholesterol represents one of the key constituents of small, dynamic, sterol- and sphingolipid-enriched domains on the plasma membrane. It has been reported that many viruses depend on plasma membrane cholesterol for efficient infection. In this study, the role of the plasma membrane cholesterol in porcine reproductive and respiratory syndrome virus (PRRSV) infection of MARC-145 cells was investigated. Pretreatment of MARC-145 cells with methyl-β-cyclodextrin (MβCD), a drug used to deplete cholesterol from cellular membrane, significantly reduced PRRSV infection in a dose-dependent manner. This inhibition was partially reversed by supplementing exogenous cholesterol following MβCD treatment, suggesting that the inhibition of PRRSV infection was specifically mediated by removal of cellular cholesterol. Further detailed studies showed that depletion of cellular membrane cholesterol significantly inhibited virus entry, especially virus attachment and release. These results indicate that the presence of cholesterol in the cellular membrane is a key component of PRRSV infection.

Apolipoprotein A-I and A-I mimetic peptides: a role in atherosclerosis

Cardiovascular disease remains a major cause of morbidity and mortality in the westernized world. Atherosclerosis is the underlying cause of most cardiovascular diseases. Atherosclerosis is a slowly evolving chronic inflammatory disorder involving the intima of large and medium sized arteries that is initiated in response to high plasma lipid levels, especially LDL. Cells of both the innate and adaptive immunity are involved in this chronic inflammation. Although high plasma LDL levels are a major contributor to most stages of the evolution of atherosclerosis, HDL and its major protein apoA-I possess properties that attenuate and may even reverse atherosclerosis. Two major functions are the ability to induce the efflux of cholesterol from cells, particularly lipid-loaded macrophages, in the artery wall for transfer to the liver, a process referred to as reverse cholesterol transport, and the ability to attenuate the pro-inflammatory properties of LDL. The removal of cellular cholesterol from lipid-loaded macrophages may also be anti-inflammatory. One of the most promising therapies to enhance the anti-atherogenic, anti-inflammatory properties of HDL is apoA-I mimetic peptides. Several of these peptides have been shown to promote cellular cholesterol efflux, attenuate the production of pro-inflammatory cytokines by macrophages, and to attenuate the pro-inflammatory properties of LDL. This latter effect may be related to their high affinity for oxidized lipids present in LDL. This review discusses the functional properties of the peptides and their effect on experimental atherosclerosis and the results of initial clinical studies in humans.