Showing papers on "Sterol published in 2009"
TL;DR: High rates of de novo cholesterol synthesis in the glia and neurons provide the sterol necessary for early brain development in the mouse and human, respectively.
Abstract: The average amount of cholesterol in the whole animal equals approximately 2100 mg/kg body weight, and 15% and 23% of this sterol in the mouse and human, respectively, is found in the central nervous system. There is no detectable uptake across the blood-brain barrier of cholesterol carried in lipoproteins in the plasma, even in the newborn. However, high rates of de novo cholesterol synthesis in the glia and neurons provide the sterol necessary for early brain development. Once a stable brain size is achieved in the adult, cholesterol synthesis continues, albeit at a much lower rate, and this synthesis is just balanced by the excretion of an equal amount of sterol, either as 24(S)-hydroxycholesterol or, presumably, as cholesterol itself.
282 citations
TL;DR: Progress is reviewed in studying the effects of phytosterols/phytostanols on cholesterol homeostasis by affecting sterol regulatory element-binding protein (SREBP)-2 processing and liver X receptor (LXR) regulatory pathways and the molecular mechanisms involved.
256 citations
TL;DR: The hypothesis that the few bacteria that harbor homologs of the sterol pathway have likely acquired these via horizontal gene transfer from eukaryotes is supported, and a potential candidate for the elusive enzyme performing C-3 ketoreduction in land plants and probably in other eUKaryotic phyla is proposed.
Abstract: The availability of complete genomes from a wide sampling of eukaryotic diversity has allowed the application of phylogenomics approaches to study the origin and evolution of unique eukaryotic cellular structures, but these are still poorly applied to study unique eukaryotic metabolic pathways. Sterols are a good example because they are an essential feature of eukaryotic membranes. The sterol pathway has been well dissected in vertebrates, fungi, and land plants. However, although different types of sterols have been identified in other eukaryotic lineages, their pathways have not been fully characterized. We have carried out an extensive analysis of the taxonomic distribution and phylogeny of the enzymes of the sterol pathway in a large sampling of eukaryotic lineages. This allowed us to tentatively indicate features of the sterol pathway in organisms where this has not been characterized and to point out a number of steps for which yet-to-discover enzymes may be at work. We also inferred that the last eukaryotic common ancestor already harbored a large panel of enzymes for sterol synthesis and that subsequent evolution over the eukaryotic tree occurred by tinkering, mainly by gene losses. We highlight a high capacity of sterol synthesis in the myxobacterium Plesiocystis pacifica, and we support the hypothesis that the few bacteria that harbor homologs of the sterol pathway have likely acquired these via horizontal gene transfer from eukaryotes. Finally, we propose a potential candidate for the elusive enzyme performing C-3 ketoreduction (ERG27 equivalent) in land plants and probably in other eukaryotic phyla.
236 citations
TL;DR: Although still poorly characterized in many trafficking routes, several potential sterol transport proteins have been described in detail; as a result, molecular mechanisms for sterols transport among membranes start to be appreciated.
217 citations
TL;DR: The data demonstrate that intestinal excretion represents a quantitatively important route for fecal removal of neutral sterols independent of biliary secretion in mice, and support the concept that the intestine substantially contributes to reverse cholesterol transport.
207 citations
TL;DR: Using lipid analysis by mass spectrometry and a genetic approach on mutants in sterol metabolism, it is shown that cells adjust their membrane composition in response to mutant sterol structures preferentially by changing their sphingolipid composition.
Abstract: Sterols and sphingolipids are limited to eukaryotic cells, and their interaction has been proposed to favor formation of lipid microdomains. Although there is abundant biophysical evidence demonstrating their interaction in simple systems, convincing evidence is lacking to show that they function together in cells. Using lipid analysis by mass spectrometry and a genetic approach on mutants in sterol metabolism, we show that cells adjust their membrane composition in response to mutant sterol structures preferentially by changing their sphingolipid composition. Systematic combination of mutations in sterol biosynthesis with mutants in sphingolipid hydroxylation and head group turnover give a large number of synthetic and suppression phenotypes. Our unbiased approach provides compelling evidence that sterols and sphingolipids function together in cells. We were not able to correlate any cellular phenotype we measured with plasma membrane fluidity as measured using fluorescence anisotropy. This questions whether the increase in liquid order phases that can be induced by sterol–sphingolipid interactions plays an important role in cells. Our data revealing that cells have a mechanism to sense the quality of their membrane sterol composition has led us to suggest that proteins might recognize sterol–sphingolipid complexes and to hypothesize the coevolution of sterols and sphingolipids.
194 citations
TL;DR: It is proposed that the modification of lipid composition could affect membrane stability and the abundance or activity of plasma membrane proteins such as aquaporins or H(+)-ATPase, which would provide a mechanism for controlling water permeability and for acclimation to salinity stress.
178 citations
TL;DR: It is shown that the cholesterol transport defect in NPC1 mutant cells is restricted to lysosomal export, and other cholesterol transport pathways appear normal, including the movement of cholesterol from the plasma membrane to the ER after treatment of cells with 25-hydroxycholesterol or sphingomyelinase.
Abstract: A handoff model has been proposed to explain the egress from lysosomes of cholesterol derived from receptor-mediated endocytosis of LDL. Cholesterol is first bound by soluble Niemann-Pick C2 (NPC2) protein, which hands off the cholesterol to the N-terminal domain of membrane-bound NPC1. Cells lacking NPC1 or NPC2 accumulate LDL-derived cholesterol in lysosomes and fail to deliver LDL cholesterol to the endoplasmic reticulum (ER) for esterification by acyl-CoA acyltransferase (ACAT) and for inhibition of sterol regulatory element-binding protein cleavage. Here, we support this model by showing that the cholesterol transport defect in NPC1 mutant cells is restricted to lysosomal export. Other cholesterol transport pathways appear normal, including the movement of cholesterol from the plasma membrane to the ER after treatment of cells with 25-hydroxycholesterol or sphingomyelinase. The NPC1 or NPC2 block in cholesterol delivery to the ER can be overcome by 2-hydroxypropyl-β-cyclodextrin, which leads to a marked increase in ACAT-mediated cholesterol esterification. The buildup of cholesteryl esters in the cytosol is expected to be much less toxic than the buildup of free cholesterol in the lysosomes of patients with mutations in NPC1 or NPC2.
169 citations
TL;DR: The results show that the mitochondrial membrane as well as the membrane lining the protozoan cell body and flagellum are the main targets, and apoptosis-like and autophagic processes induced by several of the inhibitors tested led to parasite death.
Abstract: Sterols are constituents of the cellular membranes that are essential for their normal structure and function. In mammalian cells, cholesterol is the main sterol found in the various membranes. However, other sterols predominate in eukaryotic microorganisms such as fungi and protozoa. It is now well established that an important metabolic pathway in fungi and in members of the Trypanosomatidae family is one that produces a special class of sterols, including ergosterol, and other 24-methyl sterols, which are required for parasitic growth and viability, but are absent from mammalian host cells. Currently, there are several drugs that interfere with sterol biosynthesis (SB) that are in use to treat diseases such as high cholesterol in humans and fungal infections. In this review, we analyze the effects of drugs such as (a) statins, which act on the mevalonate pathway by inhibiting HMG-CoA reductase, (b) bisphosphonates, which interfere with the isoprenoid pathway in the step catalyzed by farnesyl diphosphate synthase, (c) zaragozic acids and quinuclidines, inhibitors of squalene synthase (SQS), which catalyzes the first committed step in sterol biosynthesis, (d) allylamines, inhibitors of squalene epoxidase, (e) azoles, which inhibit C14-demethylase, and (f) azasterols, which inhibit -sterol methyltransferase (SMT). Inhibition of this last step appears to have high selectivity for fungi and trypanosomatids, since this enzyme is not found in mammalian cells. We review here the IC50 values of these various inhibitors, their effects on the growth of trypanosomatids (both in axenic cultures and in cell cultures), and their effects on protozoan structural organization (as evaluted by light and electron microscopy) and lipid composition. The results show that the mitochondrial membrane as well as the membrane lining the protozoan cell body and flagellum are the main targets. Probably as a consequence of these primary effects, other important changes take place in the organization of the kinetoplast DNA network and on the protozoan cell cycle. In addition, apoptosis-like and autophagic processes induced by several of the inhibitors tested led to parasite death.
161 citations
TL;DR: It is demonstrated that the membrane order and occurrence of voids are determinants of membrane rigidity and hypersensitivity to a drug, and the relevance of drug permeability is considered.
149 citations
TL;DR: Niemann-Pick C1 Like 1 (NPC1L1) has been identified and characterized as an essential protein in the intestinal cholesterol absorption process and is a critical intestinal sterol uptake transporter which influences whole body cholesterol homeostasis.
TL;DR: A graphical model is presented, which describes the growth of an herbivore in a system with two potentially limiting resources, and implies that herbivores are frequently limited by two or more essential nutrients simultaneously.
Abstract: Empirical data providing evidence for a colimitation of an herbivore by two or more essential nutrients are scarce, particularly in regard to biochemical resources. Here, a graphical model is presented, which describes the growth of an herbivore in a system with two potentially limiting resources. To verify this model, life-history experiments were conducted with the herbivore Daphnia magna feeding on the picocyanobacterium Synechococcus elongatus, which was supplemented with increasing amounts of cholesterol either in the presence or the absence of saturating amounts of eicosapentaenoic acid (EPA). For comparison, D. magna was raised on diets containing different proportions of S. elongatus and the cholesterol- and EPA-rich eukaryotic alga Nannochloropsis limnetica. Somatic and population growth of D. magna on a sterol- and EPA-deficient diet was initially constrained by the absence of sterols. With increased sterol availability, a colimitation by EPA became apparent and when the sterol requirements were met, the growth-limiting factor was shifted from a limitation by sterols to a limitation by EPA. These data imply that herbivores are frequently limited by two or more essential nutrients simultaneously. Hence, the concept of colimitation has to be incorporated into models assessing nutrient-limited growth kinetics of herbivores to accurately predict demographic changes and population dynamics.
TL;DR: The findings suggest that ApoE4 may not by itself alter sterol or sphingolipid metabolism in the brain under normal conditions, but that other neuropathologic changes of Alzheimer's are required to unmask the effect of Apo epsilon 4, and to perturb sterol and sphingoipid biochemistry.
TL;DR: It is shown that cyp125 is essential for R.’jostii RHA1 to grow on 3‐hydroxysterols such as cholesterol, but not on3‐oxo sterol derivatives, and that CYP125 performs an obligate first step in cholesterol degradation.
Abstract: P>The cyp125 gene of Rhodococcus jostii RHA1 was previously found to be highly upregulated during growth on cholesterol and the orthologue in Mycobacterium tuberculosis (rv3545c) has been implicated in pathogenesis. Here we show that cyp125 is essential for R. jostii RHA1 to grow on 3-hydroxysterols such as cholesterol, but not on 3-oxo sterol derivatives, and that CYP125 performs an obligate first step in cholesterol degradation. The involvement of cyp125 in sterol side-chain degradation was confirmed by disrupting the homologous gene in Rhodococcus rhodochrous RG32, a strain that selectively degrades the cholesterol side-chain. The RG32 Omega cyp125 mutant failed to transform the side-chain of cholesterol, but degraded that of 5-cholestene-26-oic acid-3 beta-ol, a cholesterol catabolite. Spectral analysis revealed that while purified ferric CYP125(RHA1) was <10% in the low-spin state, cholesterol (K(D)app = 0.20 +/- 0.08 mu M), 5 alpha-cholestanol (K(D)app = 0.15 +/- 0.03 mu M) and 4-cholestene-3-one (K(D)app = 0.20 +/- 0.03 mu M) further reduced the low spin character of the haem iron consistent with substrate binding. Our data indicate that CYP125 is involved in steroid C26-carboxylic acid formation, catalysing the oxidation of C26 either to the corresponding carboxylic acid or to an intermediate state.
TL;DR: New experimental data has accumulated supporting the contention that side-chain oxysterols are involved in some LXR-mediated regulation in vivo, at least in some biological systems, and these findings will be critically reviewed here.
TL;DR: Questions are now beginning to emerge from the study of a newly discovered family of transcription-regulating proteins called sterol regulatory element binding proteins.
Abstract: Mammalian cells use an exquisitely sensitive mechanism to control the amount of cholesterol and fatty acids in their membranes. This process relies on a feedback system that adjusts the rates of transcription of genes encoding the low density lipoprotein receptor and multiple enzymes in the cholesterol and fatty acid biosynthetic pathways. When cellular cholesterol levels are depleted, these genes are all transcribed in abundant amounts, and their transcription is repressed when sterols build up within the cell. Until recently, the mechanism of this regulation was elusive. How do cells sense the level of a membrane-embedded lipid such as cholesterol and how is this information transmitted to the nucleus where gene transcription is regulated? Answers are now beginning to emerge from the study of a newly discovered family of transcription-regulating proteins called sterol regulatory element binding proteins.
TL;DR: Structural and catalytic properties of a potential M. tuberculosis drug target enzyme are revealed, and the likely mode by which the host-derived substrate is bound and hydroxylated is revealed.
TL;DR: It is proposed that sterols play an essential role in the localization of NADPH oxidases required for regulation of reactive oxygen species, stomatal responses and drought tolerance, as RHD2 NADPH oxidation is de-localized in dry2/sqe1-5 root hairs.
Abstract: Squalene epoxidase enzymes catalyse the conversion of squalene into 2,3-oxidosqualene, the precursor of cyclic triterpenoids. Here we report that the Arabidopsis drought hypersensitive/squalene epoxidase 1-5 (dry2/sqe1-5) mutant, identified by its extreme hypersensitivity to drought stress, has altered stomatal responses and root defects because of a point mutation in the SQUALENE EPOXIDASE 1 (SQE1) gene. GC-MS analysis indicated that the dry2/sqe1-5 mutant has altered sterol composition in roots but wild-type sterol composition in shoots, indicating an essential role for SQE1 in root sterol biosynthesis. Importantly, the stomatal and root defects of the dry2/sqe1-5 mutant are associated with altered production of reactive oxygen species. As RHD2 NADPH oxidase is de-localized in dry2/sqe1-5 root hairs, we propose that sterols play an essential role in the localization of NADPH oxidases required for regulation of reactive oxygen species, stomatal responses and drought tolerance.
TL;DR: Their role in the regulation of cellular and plasma cholesterol levels is investigated, including data that suggest that squalene synthase may be involved in the etiology of hypercholesterolemia.
Abstract: High levels of plasma low-density lipoprotein cholesterol (LDL-C) are a significant risk factor for heart disease. Statins (3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors) have been extensively used to treat high-plasma LDL-C levels and are effective in preventing heart disease. However, statins can be associated with adverse side effects in some patients and do not work effectively in others. As an alternative to statins, the development of cholesterol-lowering agents that directly inhibit squalene synthase have shown promise. Clinical studies have shown that squalene synthase inhibitors are effective in lowering plasma levels of total cholesterol and LDL-C. Squalene synthase plays an important role in the cholesterol biosynthesis pathway as it is responsible for the flow of metabolites into either the sterol or the non-sterol branches of the pathway. In addition, variants of the squalene synthase gene appear to modulate plasma cholesterol levels in human populations and therefore may be linked to cardiovascular disease. In this review, we examine squalene synthase and the gene that codes for it (farnesyldiphosphate farnesyltransferase 1). In particular, we investigate their role in the regulation of cellular and plasma cholesterol levels, including data that suggest that squalene synthase may be involved in the etiology of hypercholesterolemia.
Journal Article•
TL;DR: It is concluded that M. tuberculosis metabolizes cholesterol throughout the course of infection, and that degradation of this sterol is crucial for bacterial persistence.
Abstract: Mycobacterium tuberculosis (MTB) acquisition and utilization of nutrients within the host cell is poorly understood, although it has been hypothesized that host lipids probably play an important role in MTB survival. Cholesterol has recently been identified as an important lipid for mycobacterial infection. The mce4 transport system is required for cholesterol import into bacterial cells, and deletion of mce4 locus resulted in severe attenuation in a chronic mouse model of infection. However, it has remained unclear what additional bacterial functions were required for utilization of this sterol. We have found that the igr locus, which was previously found essential for intracellular growth and virulence of MTB, is required for cholesterol metabolism: igr-deficient bacteria cannot grow using cholesterol as a primary carbon source. The growth-inhibitory effect of cholesterol in vitro depends on cholesterol import, as the delta igr mutant growth defect during the early phase of disease is completely suppressed by mutating mce4, implicating cholesterol intoxication as the primary mechanism of attenuation. We conclude that M. tuberculosis metabolizes cholesterol throughout the course of infection, and that degradation of this sterol is crucial for bacterial persistence.
TL;DR: It is concluded that hamsters but not rats shall be chosen as a model to study efficacy of cholesterol-lowering functional foods because hamsters synthesize and excrete cholesterol and bile acids in a manner similar to that in humans.
Abstract: Rats and hamsters are commonly used rodents to test the efficacy of cholesterol-lowering functional foods. In general, a diet containing 1% cholesterol for rats whereas a diet containing 0.1% cholesterol for hamsters is used to induce the hypercholesterolemia. The present study was carried out to compare hamsters with rats as a hypercholesterolemia model. Golden Syrian hamsters and Sprague Dawley rats were randomly divided into four groups and fed one of the four diets containing 0-0.9% cholesterol. Results demonstrated that serum total cholesterol (TC) in hamsters was raised 73-81% higher than that in rats fed the same cholesterol diets. Unlike rats in which HDL-C accounted very little for serum TC, the lipoprotein profile in hamsters was closer to that in humans. We investigated interaction of higher cholesterol diets with 3-hydroxy-3-methylglutary-CoA (HMG-CoA) reductase, low-density lipoprotein receptor (LDL-R) and cholesterol-7alpha-hydroxylase (CYP7A1), sterol regulatory element binding protein-2 (SREBP-2), and liver X receptor (LXR-alpha). Results showed hamsters and rats metabolized cholesterol differently. In view that hamsters synthesize and excrete cholesterol and bile acids in a manner similar to that in humans, it is concluded that hamsters but not rats shall be chosen as a model to study efficacy of cholesterol-lowering functional foods.
TL;DR: Oxysterol binding protein-related protein 2 (ORP2) has been shown to be a sterol receptor present on cytoplasmic lipid droplets (LDs) as mentioned in this paper.
TL;DR: The data indicate that Ost alpha-Ost beta is essential for bile acid and sterol disposition, and suggest that the carrier may be involved in human conditions related to imbalances in bile acids or lipid homeostasis.
Abstract: The organic solute and steroid transporter, Ost alpha-Ost beta, is an unusual heteromeric carrier that appears to play a central role in the transport of bile acids, conjugated steroids, and structurally-related molecules across the basolateral membrane of many epithelial cells. The transporter's substrate specificity, transport mechanism, tissue distribution, subcellular localization, transcriptional regulation, as well as the phenotype of the recently characterized Ost alpha-deficient mice all strongly support this model. In particular, the Ost alpha-deficient mice display a marked defect in intestinal bile acid and conjugated steroid absorption; a decrease in bile acid pool size and serum bile acid levels; altered intestinal, hepatic and renal disposition of known substrates of the transporter; and altered serum triglyceride, cholesterol, and glucose levels. Collectively, the data indicate that Ost alpha-Ost beta is essential for bile acid and sterol disposition, and suggest that the carrier may be involved in human conditions related to imbalances in bile acid or lipid homeostasis.
TL;DR: Mechanistic insight into the role of plant sterols during endocytosis and the establishment of cell polarity has been obtained and first steps towards in vivo characterization of sterol-enriched membrane domains have been taken.
TL;DR: It is concluded that 14alpha-methyl-3,6-diol is insufficient to pack the plasma membrane, allowing water penetration, which is consistent with membrane disorder after fluconazole administration, and the role of ergosterol in maintaining membrane heterogeneity and preventing water penetration as well as maintaining the rigidity of the plasma lipid region.
Abstract: Azole anitifungal drugs such as fluconazole inhibit 14alpha-demethylase. The mechanism of fluconazole action on the plasma membrane is assumed to be ergosterol depletion and accumulation of a toxic sterol, 14alpha-methyl-3,6-diol, that differs in C-6 hydroxylation, B-ring saturation, C-14 methylation, and side-chain modification. Nevertheless, little is known about how these sterol modifications mechanically influence membrane properties and hence fungal viability. Employing time-resolved measurement with a fluorescence anisotropy probe, 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), we demonstrated that fluconazole administration decreased the rigidity of the plasma membrane of Saccharomyces cerevisiae, leading to a dramatic reduction in the order parameter (S) from 0.965 to 0.907 and a 5-fold acceleration of the rotational lipid motion. This suggests that the altered sterol has a deleterious impact on membrane packing, resulting in increased fluidity. Deletion of ERG3 confers hyperresistance to fluconazole by circumventing the accumulation of 14alpha-methyl-3,6-diol and instead produces 14alpha-methylfecosterol lacking the 6-OH group. We found that ERG3 deletion mitigated the fluconazole-induced loss of membrane rigidity with S remaining at a higher value (=0.922), which could contribute to the fluconazole resistance in the erg3Delta mutant. The reduced ability of the 6-OH sterol to stiffen lipid bilayers was supported by the finding that 30 mol % of 6alpha-hydroxy-5alpha-cholestanol marginally increased the S value of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes, while cholesterol and dihydrocholesterol markedly increased it. The decay of the TMA-DPH fluorescence was bimodal in the wild-type strain. This heterogeneity could have arisen from varying degrees of water penetration into the plasma membrane. Fluconazole eliminated the heterogeneity of the dielectric characteristic of the membrane interfacial region, and concomitantly the TMA-DPH lifetime was shortened. Therefore, we conclude that 14alpha-methyl-3,6-diol is insufficient to pack the plasma membrane, allowing water penetration, which is consistent with membrane disorder after fluconazole administration. Our findings illustrate the role of ergosterol in maintaining membrane heterogeneity and preventing water penetration as well as maintaining the rigidity of the plasma membrane interfacial region.
TL;DR: It is clear from the studies reviewed here that small changes in the structure of sphingolipids alter their partitioning between lateral domains substantially, and one of the roles of cholesterol is apparently to modulate the fluidity of the sphingoipid domains and also to help segregate the domains for functional purposes.
TL;DR: It is shown here that graded knockdown of cellular Na/K-ATPase α1 subunit produces a parallel decrease in both caveolin-1 and cholesterol in light fractions of LLC-PK1 cell lysates, demonstrating a novel function of the Na/k-atPase in control of the plasma membrane cholesterol distribution.
TL;DR: It is found that cholesterol primarily affects specific local perturbations of the TM domains such as the helical kink parameters in TM1, TM2 and TM7, and that these local distortions relate to rigid-body motions of the TMs in the TM1-TM2-TM7-H8 bundle.
TL;DR: Data show that activation of PPAR&dgr; stimulates fecal cholesterol excretion in mice, primarily by the two-fold increase in TICE, indicating that this pathway provides an interesting target for the development of drugs aiming at the prevention of atherosclerosis.
TL;DR: This study shows that direct membrane perturbation by side-chain oxysterols is significant and suggests that these membranes perturbations may play a role in the oxysterol regulation of cholesterol homeostasis.
Abstract: Cholesterol is essential for proper function and regulation of eukaryotic membranes, and significant amounts of metabolic energy are dedicated to controlling cellular cholesterol levels. Oxidation products of cholesterol, the oxysterols, are enzymatically produced molecules that play a major role in mediating cholesterol homeostasis through mechanisms which have not yet been fully elucidated. Certain oxysterols are known to have direct effects on membrane permeability and structure, effects that are strikingly different from that of cholesterol. We use molecular dynamics simulations of these oxysterols in 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC) bilayers to explain the structural origins for the differing effects of cholesterol and 25-hydroxycholesterol on bilayer properties. In particular, we demonstrate that the source for these differing perturbations is the much wider range of molecular orientations accessible to 25-hydroxycholesterol when compared to cholesterol. This study shows that direct membrane perturbation by side-chain oxysterols is significant and suggests that these membrane perturbations may play a role in the oxysterol regulation of cholesterol homeostasis.