scholarly journals Selective Aster inhibitors distinguish vesicular and nonvesicular sterol transport mechanisms

2020 ◽  
Vol 118 (2) ◽  
pp. e2024149118
Author(s):  
Xu Xiao ◽  
Youngjae Kim ◽  
Beatriz Romartinez-Alonso ◽  
Kristupas Sirvydis ◽  
Daniel S. Ory ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Ldl Cholesterol ◽  
Regulatory Element ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Transport Mechanisms ◽  
Sterol Transport ◽  
Niemann Pick ◽  
Small Molecule Modulators

The Aster proteins (encoded by the Gramd1a-c genes) contain a ligand-binding fold structurally similar to a START domain and mediate nonvesicular plasma membrane (PM) to endoplasmic reticulum (ER) cholesterol transport. In an effort to develop small molecule modulators of Asters, we identified 20α-hydroxycholesterol (HC) and U18666A as lead compounds. Unfortunately, both 20α-HC and U18666A target other sterol homeostatic proteins, limiting their utility. 20α-HC inhibits sterol regulatory element-binding protein 2 (SREBP2) processing, and U18666A is an inhibitor of the vesicular trafficking protein Niemann–Pick C1 (NPC1). To develop potent and selective Aster inhibitors, we synthesized a series of compounds by modifying 20α-HC and U18666A. Among these, AI (Aster inhibitor)-1l, which has a longer side chain than 20α-HC, selectively bound to Aster-C. The crystal structure of Aster-C in complex with AI-1l suggests that sequence and flexibility differences in the loop that gates the binding cavity may account for the ligand specificity for Aster C. We further identified the U18666A analog AI-3d as a potent inhibitor of all three Aster proteins. AI-3d blocks the ability of Asters to bind and transfer cholesterol in vitro and in cells. Importantly, AI-3d also inhibits the movement of low-density lipoprotein (LDL) cholesterol to the ER, although AI-3d does not block NPC1. This finding positions the nonvesicular Aster pathway downstream of NPC1-dependent vesicular transport in the movement of LDL cholesterol to the ER. Selective Aster inhibitors represent useful chemical tools to distinguish vesicular and nonvesicular sterol transport mechanisms in mammalian cells.

scholarly journals Low-density lipoprotein susceptibility to in vitro oxidation in healthy smokers and nonsmokers

1996 ◽  
Vol 42 (4) ◽  
pp. 524-530 ◽  
Author(s):  
R Siekmeier ◽  
P Wülfroth ◽  
H Wieland ◽  
W Gross ◽  
W März
Keyword(s):  
Body Mass ◽  
Ldl Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Hdl Cholesterol ◽  
Thiobarbituric Acid ◽  
Low Density ◽  
Apo B ◽  
Lag Times

Abstract We analyzed the susceptibility of low-density lipoproteins (LDL) to oxidation in 17 healthy smokers (43.3 +/- 16.8 pack-years) and 19 healthy nonsmokers, matched for age (smokers: 52 +/- 7 years; nonsmokers: 53 +/- 7 years), gender, and relative body mass. Cholesterol, triglycerides, LDL cholesterol, HDL cholesterol, and apolipoprotein (apo) B were not different between smokers and nonsmokers; apo A-I was slightly lower in smokers (one-tailed P = 0.066). To study whether LDL from smokers were prone to in vitro oxidation than LDL from nonsmokers, we measured the time kinetics of diene formation and the production of malondialdehyde during oxidation of LDL in vitro. In smokers and nonsmokers, respectively, the mean (+/-SD) lag times (tinh) of diene formation were 111 +/- 26 and 100 +/- 27 min, the peak rates of diene formation (Vmax) were 5.99 +/- 2.34 and 6.34 +/- 2.30 mmol x min-1 x g-1, and the amounts of dienes produced during the propagation phase (dmax) were 250 +/- 264 and 248 +/- 56 mmol x g-1. Neither the malondialdehyde content of LDL (measured as thiobarbituric acid-reactive substances) before oxidation nor the amount of malondialdehyde generated during oxidation (smokers: 57.0 +/- 14.2 micromol x g-1; nonsmokers: 63.2 +/- 15.2 micromol x g-1 indicated any statistically significant effect of smoking. When nonsmokers and smokers were considered together, the amount of malondialdehyde generated during oxidation correlated with age (nonparametric rs = 0.405), body mass index (r2 = 0.573), and concentrations of apo B (rs = 0.480), cholesterol (rs = 0.448), triglycerides (rs = 0.436), and LDL cholesterol (rs = 0.398). Our data show that smoking is not associated with increased oxidizability of LDL in healthy men and women at ages 42-63 years.

scholarly journals Rab8-dependent Recycling Promotes Endosomal Cholesterol Removal in Normal and Sphingolipidosis Cells

2007 ◽  
Vol 18 (1) ◽  
pp. 47-56 ◽  
Author(s):  
Matts D. Linder ◽  
Riikka-Liisa Uronen ◽  
Maarit Hölttä-Vuori ◽  
Peter van der Sluijs ◽  
Johan Peränen ◽  
...  
Keyword(s):  
Cholesterol Efflux ◽  
Ldl Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Receptor Activation ◽  
Cholesterol Esterification ◽  
Rab Gtpase ◽  
Cell Periphery ◽  
Regulatory Machinery ◽  
Niemann Pick

The mechanisms by which low-density lipoprotein (LDL)-cholesterol exits the endocytic circuits are not well understood. The process is defective in Niemann–Pick type C (NPC) disease in which cholesterol and sphingolipids accumulate in late endosomal compartments. This is accompanied by defective cholesterol esterification in the endoplasmic reticulum and impaired ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux. We show here that overexpression of the recycling/exocytic Rab GTPase Rab8 rescued the late endosomal cholesterol deposition and sphingolipid mistrafficking in NPC fibroblasts. Rab8 redistributed cholesterol from late endosomes to the cell periphery and stimulated cholesterol efflux to the ABCA1-ligand apolipoprotein A-I (apoA-I) without increasing cholesterol esterification. Depletion of Rab8 from wild-type fibroblasts resulted in cholesterol deposition within late endosomal compartments. This cholesterol accumulation was accompanied by impaired clearance of LDL-cholesterol from endocytic circuits to apoA-I and could not be bypassed by liver X receptor activation. Our findings establish Rab8 as a key component of the regulatory machinery that leads to ABCA1-dependent removal of cholesterol from endocytic circuits.

scholarly journals Interplay between Asters/GRAMD1s and phosphatidylserine in intermembrane transport of LDL cholesterol

2022 ◽  
Vol 119 (2) ◽  
pp. e2120411119
Author(s):  
Michael N. Trinh ◽  
Michael S. Brown ◽  
Joachim Seemann ◽  
Gonçalo Vale ◽  
Jeffrey G. McDonald ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Ldl Cholesterol ◽  
Chinese Hamster Ovary Cells ◽  
Low Density Lipoprotein ◽  
Chinese Hamster ◽  
Density Lipoprotein ◽  
Cholesterol Esterification ◽  
Gene Encoding ◽  
Ovary Cells ◽  
Genes Encoding

Low-density lipoprotein (LDL) delivers cholesterol to mammalian cells through receptor-mediated endocytosis. The LDL cholesterol is liberated in lysosomes and transported to the plasma membrane (PM) and from there to the endoplasmic reticulum (ER). Excess ER cholesterol is esterified with a fatty acid for storage as cholesteryl esters. Recently, we showed that PM-to-ER transport of LDL cholesterol requires phosphatidylserine (PS). Others showed that PM-to-ER transport of cholesterol derived from other sources requires Asters (also called GRAMD1s), a family of three ER proteins that bridge between the ER and PM by binding to PS. Here, we use a cholesterol esterification assay and other measures of ER cholesterol delivery to demonstrate that Asters participate in PM-to-ER transport of LDL cholesterol in Chinese hamster ovary cells. Knockout of the gene encoding PTDSS1, the major PS-synthesizing enzyme, lowered LDL-stimulated cholesterol esterification by 85%, whereas knockout of all three Aster genes lowered esterification by 65%. The reduction was even greater (94%) when the genes encoding PTDSS1 and the three Asters were knocked out simultaneously. We conclude that Asters participate in LDL cholesterol delivery from PM to ER, and their action depends in large part, but not exclusively, on PS. The data also indicate that PS participates in another delivery pathway, so far undefined, that is independent of Asters.

scholarly journals Sorting nexin 17 (SNX17) links endosomal sorting to Eps15 homology domain protein 1 (EHD1)–mediated fission machinery

2020 ◽  
Vol 295 (12) ◽  
pp. 3837-3850 ◽  
Author(s):  
Kanika Dhawan ◽  
Naava Naslavsky ◽  
Steve Caplan
Keyword(s):  
Mammalian Cells ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Surface Rendering ◽  
Sorting Nexin ◽  
Density Lipoprotein Receptor ◽  
Endosomal Membranes ◽  
Domain Protein ◽  
Eps15 Homology Domain

Following endocytosis, receptors that are internalized to sorting endosomes are sorted to different pathways, in part by sorting nexin (SNX) proteins. Notably, SNX17 interacts with a multitude of receptors in a sequence-specific manner to regulate their recycling. However, the mechanisms by which SNX17-labeled vesicles that contain sorted receptors bud and undergo vesicular fission from the sorting endosomes remain elusive. Recent studies suggest that a dynamin-homolog, Eps15 homology domain protein 1, catalyzes fission and releases endosome-derived vesicles for recycling to the plasma membrane. However, the mechanism by which EHD1 is coupled to various receptors and regulates their recycling remains unknown. Here we sought to characterize the mechanism by which EHD1 couples with SNX17 to regulate recycling of SNX17-interacting receptors. We hypothesized that SNX17 couples receptors to the EHD1 fission machinery in mammalian cells. Coimmunoprecipitation experiments and in vitro assays provided evidence that EHD1 and SNX17 directly interact. We also found that inducing internalization of a SNX17 cargo receptor, low-density lipoprotein receptor–related protein 1 (LRP1), led to recruitment of cytoplasmic EHD1 to endosomal membranes. Moreover, surface rendering and quantification of overlap volumes indicated that SNX17 and EHD1 partially colocalize on endosomes and that this overlap further increases upon LRP1 internalization. Additionally, SNX17-containing endosomes were larger in EHD1-depleted cells than in WT cells, suggesting that EHD1 depletion impairs SNX17-mediated endosomal fission. Our findings help clarify our current understanding of endocytic trafficking, providing significant additional insight into the process of endosomal fission and connecting the sorting and fission machineries.

scholarly journals NPC1L1 Facilitates Sphingomyelin Absorption and Regulates Diet-Induced Production of VLDL/LDL-associated S1P

Nutrients ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2641
Author(s):  
Yoshihide Yamanashi ◽  
Tappei Takada ◽  
Hideaki Yamamoto ◽  
Hiroshi Suzuki
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cholesterol Absorption ◽  
In Vivo Studies ◽  
Lipid Mediator ◽  
Low Density ◽  
Dependent Manner ◽  
Niemann Pick

Niemann-Pick C1-Like 1 (NPC1L1) is a cholesterol importer and target of ezetimibe, a cholesterol absorption inhibitor used clinically for dyslipidemia. Recent studies demonstrated that NPC1L1 regulates the intestinal absorption of several fat-soluble nutrients, in addition to cholesterol. The study was conducted to reveal new physiological roles of NPC1L1 by identifying novel dietary substrate(s). Very low-density lipoprotein and low-density lipoprotein (VLDL/LDL) are increased in Western diet (WD)-fed mice in an NPC1L1-dependent manner, so we comprehensively analyzed the NPC1L1-dependent VLDL/LDL components. Apolipoprotein M (apoM), a binding protein of sphingosine-1-phosphate (S1P: a lipid mediator), and S1P were NPC1L1-dependently increased in VLDL/LDL by WD feeding. S1P is metabolized from sphingomyelin (SM) and SM is abundant in WD, so we focused on intestinal SM absorption. In vivo studies with Npc1l1 knockout mice and in vitro studies with NPC1L1-overexpressing cells revealed that SM is a physiological substrate of NPC1L1. These results suggest a scenario in which dietary SM is absorbed by NPC1L1 in the intestine, followed by SM conversion to S1P and, after several steps, S1P is exported into the blood as the apoM-bound form in VLDL/LDL. Our findings provide insight into the functions of NPC1L1 for a better understanding of sphingolipids and S1P homeostasis.

scholarly journals The complexity of lipoprotein (a) lowering by PCSK9 monoclonal antibodies

2017 ◽  
Vol 131 (4) ◽  
pp. 261-268 ◽  
Author(s):  
Gilles Lambert ◽  
Aurélie Thedrez ◽  
Mikaël Croyal ◽  
Stéphane Ramin-Mangata ◽  
David Couret ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Ldl Cholesterol ◽  
Scientific Literature ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Lipoprotein A ◽  
Pcsk9 Inhibition

Since 2012, clinical trials dedicated to proprotein convertase subtilisin kexin type 9 (PCSK9) inhibition with monoclonal antibodies (mAbs) have unambiguously demonstrated robust reductions not only in low-density lipoprotein (LDL) cholesterol (LDL-C) but also in lipoprotein (a) [Lp(a)] levels. The scientific literature published prior to those studies did not provide any evidence for a link between PCSK9 and Lp(a) metabolism. More recent investigations, either in vitro or in vivo, have attempted to unravel the mechanism(s) by which PCSK9 mAbs reduce circulating Lp(a) levels, with some showing a specific implication of the LDL receptor (LDLR) in Lp(a) clearance whereas others found no significant role for the LDLR in that process. This elusive pathway appears clearly distinct from that of the widely prescribed statins that also enhance LDLR function but do not lower circulating Lp (a) levels in humans. So how does PCSK9 inhibition with mAbs reduce Lp(a)? This still remains to be established.

scholarly journals Rutin and Quercetin Decrease Cholesterol in HepG2 Cells but Not Plasma Cholesterol in Hamsters by Oral Administration

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3766
Author(s):  
Ning Liang ◽  
Yuk-Man Li ◽  
Zouyan He ◽  
Wangjun Hao ◽  
Yimin Zhao ◽  
...  
Keyword(s):  
Oral Administration ◽  
Hepg2 Cells ◽  
Cholesterol Metabolism ◽  
Plasma Cholesterol ◽  
Regulatory Element ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
In Vivo Studies

Rutin (R) and quercetin (Q) are two widespread dietary flavonoids. Previous studies regarding the plasma cholesterol-lowering activity of R and Q generated inconsistent results. The present study was therefore carried out to investigate the effects of R and Q on cholesterol metabolism in both HepG2 cells and hypercholesterolemia hamsters. Results from HepG2 cell experiments demonstrate that both R and Q decreased cholesterol at doses of 5 and 10 µM. R and Q up-regulated both the mRNA and protein expression of sterol regulatory element binding protein 2 (SREBP2), low-density lipoprotein receptor (LDLR), and liver X receptor alpha (LXRα). The immunofluorescence study revealed that R and Q increased the LDLR expression, while only Q improved LDL-C uptake in HepG2 cells. Results from hypercholesterolemia hamsters fed diets containing R (5.5 g/kg diet) and Q (2.5 g/kg diet) for 8 weeks demonstrate that both R and Q had no effect on plasma total cholesterol. In the liver, only Q reduced cholesterol significantly. The discrepancy between the in vitro and in vivo studies was probably due to a poor bioavailability of flavonoids in the intestine. It was therefore concluded that R and Q were effective in reducing cholesterol in HepG2 cells in vitro, whereas in vivo, the oral administration of the two flavonoids had little effect on plasma cholesterol in hamsters.

Lack of Correlation between the Maximum Low-Density Lipoprotein (Ldl) Receptor Activity of Blood Lymphocytes and Plasma LDL Concentration in Normal Men

1983 ◽  
Vol 65 (1) ◽  
pp. 95-98 ◽  
Author(s):  
C. Cortese ◽  
P. R. Turner ◽  
C. B. Marenah ◽  
U. Sule ◽  
S. Price ◽  
...  
Keyword(s):  
Ldl Cholesterol ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Receptor Activity ◽  
Cholesterol Concentration ◽  
Low Density ◽  
Blood Lymphocytes ◽  
Wide Range

1. Measurements were made of the maximal low-density lipoprotein (LDL) receptor activities of blood lymphocytes from 81 healthy men with a wide range of plasma LDL cholesterol concentrations (1.45-7.55 mmol/l). 2. Receptor activity was quantified by measuring the degradation of 125I-labelled LDL (10 μg of protein/ml) to trichloroacetic acid-soluble material during a 6 h incubation, after derepression of the lymphocytes for 72 h in lipoprotein-deficient medium. 3. No significant correlation existed between LDL receptor activity in vitro and plasma LDL cholesterol concentration in vivo (r = −0.08).

scholarly journals Effect of phytosterols in the treatment of hypercholesterolemia in adults – systematic review with meta-analysis / Efeitos dos fitoesteróis no tratamento da hipercolesterolemia em adultos – revisão sistemática com metanálise

2021 ◽  
Vol 4 (4) ◽  
pp. 16317-16338
Author(s):  
Rebeca Cirilo De Lima ◽  
Vanessa Souza Mendonça ◽  
Grazielle Vilas Bôas Huguenin
Keyword(s):  
Systematic Review ◽  
Randomized Clinical Trials ◽  
Ldl Cholesterol ◽  
Meta Analysis ◽  
Scientific Evidence ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cochrane Library ◽  
Web Of Service

 Increased plasma total cholesterol (TC) and LDL-cholesterol (low-density lipoprotein) are considered risk factors for coronary disease. Phytosterols are among the dietary options for decreasing serum concentrations of TC and LDL-c by up to 15%.To evaluate the scientific evidence on the use of phytosterols in the treatment of hypercholesterolemia in adults.A systematic meta-analysis of the Medline, Embase, Web of Service, VHL, PUBMED, Scopus, Cochrane Library and LILACS databases was performed between November and December 2016. The PICO strategy was used. Inclusion criteria were randomized clinical trials with adults of both sexes using phytosterols longer than 4 weeks intervention. Exclusion criteria were animal and in vitro studies, humans less than 18 years old and individuals with other diseases (cancer, metabolic syndromes, diabetes mellitus, hypertension, renal disease, liver diseases). The risk of bias was assessed by two reviewers. The primary outcomes investigated were TC and LDL-cholesterol. Statistical analyses were conducted using the RevMan 5.3. The standardized effect size was used to estimate the standardized mean difference and 95% CI of TC and LDL-c.Twenty-seven randomized controlled trials were included in this systematic review and 26 studies in the meta-analysis of TC and LDL-cholesterol. The meta-analyzes showed an association with the reduction in plasma TC (-2.54 [-3.04; -2.03]) and LDL-c (-2.8 [-2.63; -1.53]) after intervention with the vegetable esters.The consumption of 1.5 to 2.0 g/day of phytosterols promotes reduction of TC and LDL-c in hypercholesterolemic individuals, regardless of the way they are consumed.

scholarly journals The intracellular transport of low density lipoprotein-derived cholesterol is defective in Niemann-Pick type C fibroblasts.

1989 ◽  
Vol 108 (5) ◽  
pp. 1625-1636 ◽  
Author(s):  
L Liscum ◽  
R M Ruggiero ◽  
J R Faust
Keyword(s):  
Plasma Membrane ◽  
Intracellular Transport ◽  
Ldl Cholesterol ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cholesterol Transport ◽  
Low Density ◽  
Unesterified Cholesterol ◽  
Type C ◽  
Niemann Pick

Niemann-Pick disease type C (NPC) is characterized by substantial intracellular accumulation of unesterified cholesterol. The accumulation of unesterified cholesterol in NPC fibroblasts cultured with low density lipoprotein (LDL) appears to result from the inability of LDL to stimulate cholesterol esterification in addition to impaired LDL-mediated downregulation of LDL receptor activity and cellular cholesterol synthesis. Although a defect in cholesterol transport in NPC cells has been inferred from previous studies, no experiments have been reported that measure the intracellular movement of LDL-cholesterol specifically. We have used four approaches to assess intracellular cholesterol transport in normal and NPC cells and have determined the following: (a) mevinolin-inhibited NPC cells are defective in using LDL-cholesterol for growth. However, exogenously added mevalonate restores cell growth equally in normal and NPC cells; (b) the transport of LDL-derived [3H]cholesterol to the plasma membrane is slower in NPC cells, while the rate of appearance of [3H]acetate-derived, endogenously synthesized [3H]cholesterol at the plasma membrane is the same for normal and NPC cells; (c) in NPC cells, LDL-derived [3H]cholesterol accumulates in lysosomes to higher levels than normal, resulting in defective movement to other cell membranes; and (d) incubation of cells with LDL causes an increase in cholesterol content of NPC lysosomes that is threefold greater than that observed in normal lysosomes. Our results indicate that a cholesterol transport defect exists in NPC that is specific for LDL-derived cholesterol.

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