Showing papers on "Sterol published in 2011"
TL;DR: The yeast Kes1p/Osh4p protein functions as a sterol/PI(4)P exchanger between lipid membranes, which suggests the possibility of creating a sterOL gradient via phosphoinositide metabolism.
Abstract: Osh/Orp proteins transport sterols between organelles and are involved in phosphoinositide metabolism. The link between these two aspects remains elusive. Using novel assays, we address the influence of membrane composition on the ability of Osh4p/Kes1p to extract, deliver, or transport dehydroergosterol (DHE). Surprisingly, phosphatidylinositol 4-phosphate (PI(4)P) specifically inhibited DHE extraction because PI(4)P was itself efficiently extracted by Osh4p. We solve the structure of the Osh4p-PI(4)P complex and reveal how Osh4p selectively substitutes PI(4)P for sterol. Last, we show that Osh4p quickly exchanges DHE for PI(4)P and, thereby, can transport these two lipids between membranes along opposite routes. These results suggest a model in which Osh4p transports sterol from the ER to late compartments pinpointed by PI(4)P and, in turn, transports PI(4)P backward. Coupled to PI(4)P metabolism, this transport cycle would create sterol gradients. Because the residues that recognize PI(4)P are conserved in Osh4p homologues, other Osh/Orp are potential sterol/phosphoinositol phosphate exchangers.
329 citations
TL;DR: ORP5 works together with Niemann Pick C-1 to facilitate exit of cholesterol from endosomes and lysosomes.
Abstract: Oxysterol-binding protein (OSBP) and its related proteins (ORPs) constitute a large and evolutionarily conserved family of lipid-binding proteins that target organelle membranes to mediate sterol signaling and/or transport. Here we characterize ORP5, a tail-anchored ORP protein that localizes to the endoplasmic reticulum. Knocking down ORP5 causes cholesterol accumulation in late endosomes and lysosomes, which is reminiscent of the cholesterol trafficking defect in Niemann Pick C (NPC) fibroblasts. Cholesterol appears to accumulate in the limiting membranes of endosomal compartments in ORP5-depleted cells, whereas depletion of NPC1 or both ORP5 and NPC1 results in luminal accumulation of cholesterol. Moreover, trans-Golgi resident proteins mislocalize to endosomal compartments upon ORP5 depletion, which depends on a functional NPC1. Our results establish the first link between NPC1 and a cytoplasmic sterol carrier, and suggest that ORP5 may cooperate with NPC1 to mediate the exit of cholesterol from endosomes/lysosomes.
278 citations
TL;DR: The general features of HMGR regulation, including a requirement for the HMGR-binding protein Insig, are remarkably conserved between mammals and ascomycetous fungi, including S. cerevisiae and S. pombe.
241 citations
TL;DR: Upon infection, the authors' immune cells produce a small protein called interferon, which in turn signals a protective response through a series of biochemical reactions that involves lowering the cells' ability to make cholesterol by targeting a gene essential for controlling the pathway for cholesterol metabolism.
Abstract: Little is known about the protective role of inflammatory processes in modulating lipid metabolism in infection. Here we report an intimate link between the innate immune response to infection and regulation of the sterol metabolic network characterized by down-regulation of sterol biosynthesis by an interferon regulatory loop mechanism. In time-series experiments profiling genome-wide lipid-associated gene expression of macrophages, we show a selective and coordinated negative regulation of the complete sterol pathway upon viral infection or cytokine treatment with IFNγ or β but not TNF, IL1β, or IL6. Quantitative analysis at the protein level of selected sterol metabolic enzymes upon infection shows a similar level of suppression. Experimental testing of sterol metabolite levels using lipidomic-based measurements shows a reduction in metabolic output. On the basis of pharmacologic and RNAi inhibition of the sterol pathway we show augmented protection against viral infection, and in combination with metabolite rescue experiments, we identify the requirement of the mevalonate-isoprenoid branch of the sterol metabolic network in the protective response upon statin or IFNβ treatment. Conditioned media experiments from infected cells support an involvement of secreted type 1 interferon(s) to be sufficient for reducing the sterol pathway upon infection. Moreover, we show that infection of primary macrophages containing a genetic knockout of the major type I interferon, IFNβ, leads to only a partial suppression of the sterol pathway, while genetic knockout of the receptor for all type I interferon family members, ifnar1, or associated signaling component, tyk2, completely abolishes the reduction of the sterol biosynthetic activity upon infection. Levels of the proteolytically cleaved nuclear forms of SREBP2, a key transcriptional regulator of sterol biosynthesis, are reduced upon infection and IFNβ treatment at both the protein and de novo transcription level. The reduction in srebf2 gene transcription upon infection and IFN treatment is also found to be strictly dependent on ifnar1. Altogether these results show that type 1 IFN signaling is both necessary and sufficient for reducing the sterol metabolic network activity upon infection, thereby linking the regulation of the sterol pathway with interferon anti-viral defense responses. These findings bring a new link between sterol metabolism and interferon antiviral response and support the idea of using host metabolic modifiers of innate immunity as a potential antiviral strategy.
232 citations
TL;DR: In the absence of enzymatic catalysis in a pathway usually termed "autoxidation", which has been known for almost a century and observed under various experimental conditions, the susceptibility of cholesterol to non-enzymatic oxidation has raised considerable interest in the function of oxysterols as biological effectors and potential biomarkers for the non-invasive study of oxidative stress in vivo as discussed by the authors.
203 citations
TL;DR: The increased sensitivity of BODIPY-cholesterol assay coupled with the simplicity of measuring fluorescence results in a sensitive, high-throughput assay that can screen large numbers of sera, and thus establish the relationship between cholesterol efflux and atherosclerosis.
179 citations
01 Jan 2011
TL;DR: The susceptibility of cholesterol to non-enzymatic oxidation has raised considerable interest in the function of oxysterols as biological effectors and potential biomarkers for the non-invasive study of oxidative stress in vivo.
Abstract: Cholesterol has many functions, including those that affect biophysical properties of membranes, and is a precursor to hormone synthesis. These actions are governed by enzymatic pathways that modify the sterol nucleus or the isooctyl tail. The addition of oxygen to the cholesterol backbone produces its derivatives known as oxysterols. In addition to having an enzymatic origin, oxysterols can be formed in the absence of enzymatic catalysis in a pathway usually termed “autoxidation,” which has been known holesterol autoxidation xidative stress for almost a century and observed under various experimental conditions. Autoxidation of cholesterol can occur through reactions initiated by free radical species, such as those arising from the superoxide/hydrogen peroxide/hydroxyl radical system and by non-radical highly reactive oxygen species such as singlet oxygen, HOCl, and ozone. The susceptibility of cholesterol to non-enzymatic oxidation has raised considerable interest in the function of oxysterols as biological effectors and potential biomarkers for the non-invasive study of oxidative stress in vivo. © 2011 Elsevier Ireland Ltd. All rights reserved.
173 citations
TL;DR: Genetic approaches have provided insights into the diversity of sterol and sphingolipid functions in eukaryotes providing evidence that these two lipid classes function together, and advances in lipidomics and subcellular fractionation should improve this situation.
Abstract: Sterols and sphingolipids are considered mainly eukaryotic lipids even though both are present in some prokaryotes, with sphingolipids being more widespread than sterols Both sterols and sphingolipids differ in their structural features in vertebrates, plants, and fungi Interestingly, some invertebrates cannot synthesize sterols de novo and seem to have a reduced dependence on sterols Sphingolipids and sterols are found in the plasma membrane, but we do not have a clear picture of their precise intracellular localization Advances in lipidomics and subcellular fractionation should help to improve this situation Genetic approaches have provided insights into the diversity of sterol and sphingolipid functions in eukaryotes providing evidence that these two lipid classes function together Intermediates in sphingolipid biosynthesis and degradation are involved in signaling pathways, whereas sterol structures are converted to hormones Both lipids have been implicated in regulating membrane trafficking
164 citations
TL;DR: A mini-review classifies the popular cholesterol-lowering nutraceuticals and functional foods, and explores their underlying mechanisms.
156 citations
TL;DR: The concept that neurons continuously acquire C from interstitial fluid to permit plasma membrane turnover and remodeling is supported, and continuous infusion into the ventricular system of npc1−/− animals between 3 and 7 weeks of age normalized the biochemical abnormalities and completely prevented the expected neurodegeneration.
Abstract: While unesterified cholesterol (C) is essential for remodeling neuronal plasma membranes, its role in certain neurodegenerative disorders remains poorly defined. Uptake of sterol from pericellular fluid requires processing that involves two lysosomal proteins, lysosomal acid lipase, which hydrolyzes C esters, and NPC1 (Niemann-Pick type C1). In systemic tissues, inactivation of either protein led to sterol accumulation and cell death, but in the brain, inactivation of only NPC1 caused C sequestration and neurodegeneration. When injected into the CNS of the npc1 −/− mouse, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), a compound known to prevent this C accumulation, diffused throughout the brain and was excreted with a t ½ of 6.5 h. This agent caused suppression of C synthesis, elevation of C esters, suppression of sterol regulatory-binding protein 2 (SREBP2) target genes, and activation of liver X receptor-controlled genes. These findings indicated that HP-β-CD promoted movement of the sequestered C from lysosomes to the metabolically active pool of C in the cytosolic compartment of cells in the CNS. The ED 50 for this agent in the brain was ∼0.5 mg/kg, and the therapeutic effect lasted >7 d. Continuous infusion of HP-β-CD into the ventricular system of npc1 −/− animals between 3 and 7 weeks of age normalized the biochemical abnormalities and completely prevented the expected neurodegeneration. These studies support the concept that neurons continuously acquire C from interstitial fluid to permit plasma membrane turnover and remodeling. Inactivation of NPC1 leads to lysosomal C sequestration and neurodegeneration, but this is prevented by the continuous, direct administration of HP-β-CD into the CNS.
147 citations
TL;DR: The identified SIRT2 inhibitor reduced cholesterol in cultured naïve neuronal cells and brain slices from wild-type mice and provides a clear opportunity for lead optimization and drug development, targeting metabolic dysfunctions in CNS disorders where abnormal cholesterol homeostasis is implicated.
Abstract: Sirtuin 2 (SIRT2) deacetylase-dependent inhibition mediates neuroprotective reduction of cholesterol biosynthesis in an in vitro Huntington's disease model. This study sought to identify the first brain-permeable SIRT2 inhibitor and to characterize its cholesterol-reducing properties in neuronal models. Using biochemical sirtuin deacetylation assays, we screened a brain-permeable in silico compound library, yielding 3-(1-azepanylsulfonyl)-N-(3-bromphenyl)benzamide as the most potent and selective SIRT2 inhibitor. Pharmacokinetic studies demonstrated brain-permeability but limited metabolic stability of the selected candidate. In accordance with previous observations, this SIRT2 inhibitor stimulated cytoplasmic retention of sterol regulatory element binding protein-2 and subsequent transcriptional downregulation of cholesterol biosynthesis genes, resulting in reduced total cholesterol in primary striatal neurons. Furthermore, the identified inhibitor reduced cholesterol in cultured naive neuronal cells and brain slices from wild-type mice. The outcome of this study provides a clear opportunity for lead optimization and drug development, targeting metabolic dysfunctions in CNS disorders where abnormal cholesterol homeostasis is implicated.
TL;DR: It is concluded that the role of Osh proteins in non‐vesicular sterol transport between the PM, ER and lipid droplets is either minimal, or subsumed by other mechanisms and that Osh proteins regulate the organization of sterols at the PM.
Abstract: Sterol transport between the endoplasmic reticulum (ER) and plasma membrane (PM) occurs by an ATP-dependent, non-vesicular mechanism that is presumed to require sterol transport proteins (STPs). In Saccharomyces cerevisiae, homologues of the mammalian oxysterol-binding protein (Osh1–7) have been proposed to function as STPs. To evaluate this proposal we took two approaches. First we used dehydroergosterol (DHE) to visualize sterol movement in living cells by fluorescence microscopy. DHE was introduced into the PM under hypoxic conditions and observed to redistribute to lipid droplets on growing the cells aerobically. Redistribution required ATP and the sterol acyltransferase Are2, but did not require PM-derived transport vesicles. DHE redistribution occurred robustly in a conditional yeast mutant (oshΔ osh4-1ts) that lacks all functional Osh proteins at 37°C. In a second approach we used a pulse-chase protocol to analyze the movement of metabolically radiolabeled ergosterol from the ER to the PM. Arrival of radiolabeled ergosterol at the PM was assessed in isolated PM-enriched fractions as well by extracting sterols from intact cells with methyl-β-cyclodextrin. These experiments revealed that whereas ergosterol is transported effectively from the ER to the PM in Osh-deficient cells, the rate at which it moves within the PM to equilibrate with the methyl-β-cyclodextrin extractable sterol pool is slowed. We conclude (i) that the role of Osh proteins in nonvesicular sterol transport between the PM, ER and lipid droplets is either minimal, or subsumed by other mechanisms and (ii) that Osh proteins regulate the organization of sterols at the PM.
TL;DR: This work reviews how sterols act through evolutionarily ancient mechanisms to control these processes through feed-forward and feedback mechanisms.
Abstract: Sterol metabolites are critical signaling molecules that regulate metabolism, development, and homeostasis. Oxysterols, bile acids (BAs), and steroids work primarily through cognate sterol-responsive nuclear hormone receptors to control these processes through feed-forward and feedback mechanisms. These signaling pathways are conserved from simple invertebrates to mammals. Indeed, results from various model organisms have yielded fundamental insights into cholesterol and BA homeostasis, lipid and glucose metabolism, protective mechanisms, tissue differentiation, development, reproduction, and even aging. Here, we review how sterols act through evolutionarily ancient mechanisms to control these processes.
TL;DR: Q-TOF MS/MS provides a comprehensive strategy for sterol lipid quantification that can be adapted to other tandem mass spectrometers and is far more sensitive than GC or HPLC.
TL;DR: The expression of a small sterol transport protein, STARD4, is regulated by cholesterol levels, providing an additional layer of regulation in the cholesterol homeostatic mechanism.
Abstract: Nonvesicular transport of cholesterol plays an essential role in the distribution and regulation of cholesterol within cells, but it has been difficult to identify the key intracellular cholesterol transporters. The steroidogenic acute regulatory-related lipid-transfer (START) family of proteins is involved in several pathways of nonvesicular trafficking of sterols. Among them, STARD4 has been shown to increase intracellular cholesteryl ester formation and is controlled at the transcriptional level by sterol levels in cells. We found that STARD4 is very efficient in transporting sterol between membranes in vitro. Cholesterol levels are increased in STARD4-silenced cells, while sterol transport to the endocytic recycling compartment (ERC) and to the endoplasmic reticulum (ER) are enhanced upon STARD4 overexpression. STARD4 silencing attenuates cholesterol-mediated regulation of SREBP-2 activation, while its overexpression amplifies sterol sensing by SCAP/SREBP-2. To analyze STARD4's mode of action, we compared sterol transport mediated by STARD4 with that of a simple sterol carrier, methyl-β-cyclodextrin (MCD), when STARD4 and MCD were overexpressed or injected into cells. Interestingly, STARD4 and cytosolic MCD act similarly by increasing the rate of transfer of sterol to the ERC and to the ER. Our results suggest that cholesterol transport mediated by STARD4 is an important component of the cholesterol homeostasis regulatory machinery.
TL;DR: It is shown that solute transporters for tryptophan and arginine are functional, whereas the export of weak organic acids via Pdr12p, a multi-drug resistance family member, is not, which reveals a sterol function that is probably dependent upon a precise sterol structure.
TL;DR: The development, optimization and validation of a methodology to determine nine key steroid hormones expressed in the steroidogenesis in biological fluids and the accuracy was 50–112% in the range 0.10 to 2.00 ng/mL.
Abstract: This paper presents the development, optimization and validation of a methodology to determine nine key steroid hormones (viz. pregnenolone, progesterone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, estrone, 17α-estradiol and 17β-estradiol) expressed in the steroidogenesis in biological fluids. The analytical method allows for the determination of steroid hormones in blood plasma and serum down to 0.08-0.16 ng/mL for estrogens, 0.20-0.36 ng/mL for androgens and 0.36-0.43 ng/mL for progestagens. These limits of detection were obtainable using a two-step solid-phase clean-up for fractionation and elimination of interfering lipids (fatty acids, phospholipids, glycerides and sterols) from the steroid hormones. The accuracy of the method was 50-112% in the range 0.10 to 2.00 ng/mL.
TL;DR: CYP3A synthesizes a significant amount of 25-hydroxycholesterol and may participate in the regulation of lipid metabolism, and the significance of CYP3A on the production of25-hydroxylation is demonstrated.
TL;DR: Whether the serum markers are valid indicators of cholesterol metabolism in various conditions is compared to find out and it is worth using several instead of only one precursor and absorption sterol marker for making conclusions of altered synthesis or absorption of cholesterol.
Abstract: Aims To study the whole-body cholesterol metabolism in man, cholesterol synthesis and absorption need to be measured. Because of the complicated methods of the measurements, new approaches were developed including the analysis of serum non-cholesterol sterols. In current lipidologic papers and even in intervention studies, serum non-cholesterol sterols are frequently used as surrogate markers of cholesterol metabolism without any validation to the absolute metabolic variables. The present review compares serum non-cholesterol sterols with absolute measurements of cholesterol synthesis and absorption in published papers to find out whether the serum markers are valid indicators of cholesterol metabolism in various conditions. Data synthesis During statin treatment, during interventions of dietary fat, and in type 2 diabetes the relative and absolute variables of cholesterol synthesis and absorption were frequently but not constantly correlated with each other. In some occasions, especially in subjects with apolipoprotein E3/4 and E4/4 phenotypes, the relative metabolic markers were even more sensitive than the absolute ones to reflect changes in cholesterol metabolism during dietary interventions. Even in general population at very high absorption the homeostasis of cholesterol metabolism is disturbed damaging the validity of the serum markers. Conclusions It is worth using several instead of only one precursor and absorption sterol marker for making conclusions of altered synthesis or absorption of cholesterol, and even then the presence of at least some absolute measurement is valuable. During consumption of plant sterol-enriched diets and in situations of interfered cholesterol homeostasis the relative markers do not adequately reflect cholesterol metabolism. Accordingly, the validity of the relative markers of cholesterol metabolism should not be considered as self-evident.
TL;DR: It turns out that not only was there great similarity between the fatty acid profiles of corn oil and sesame oil but also there were not too many differences for the sterol profiles, which demonstrated that only one of these profiles was unreliable for indentifying oil origin and authenticity.
Abstract: The similarities and differences of eight vegetable oils produced in China were investigated in terms of their fatty acid, sterol, and tocopherol compositions and subsequent data processing by hierarchical clustering analysis and principal component analysis. The lipid profiles, acquired by analytical techniques tailored to each lipid class, revealed great similarities among the fatty acid profiles of corn and sesame oil as well as few differences in their sterol profiles. It turns out that not only was there great similarity between the fatty acid profiles of corn oil and sesame oil but also there were not too many differences for the sterol profiles. Sunflower and tea-seed oil showed similar sterol compositions, while the tea-seed oil tocopherol was very similar to palm oil. The results demonstrated that the use of only one of these profiles was unreliable for indentifying oil origin and authenticity. In contrast, the use of the sterol or tocopherol profile together with the fatty acid profile more accurately discriminates these oils.
TL;DR: It is demonstrated that plasma membrane-localized NPC1L1 binds exogenous cholesterol via its NTD, and facilitates the formation of NPC1 L1-flotillin-cholesterol membrane microdomains that are then internalized into cells through the clathrin-AP2 pathway.
TL;DR: The finding that 7-dehydrocholesterol is a precursor of 7-ketocholesterol has relevance to an inborn error of metabolism known as Smith-Lemli-Opitz syndrome (SLOS) caused by defective cholesterol biosynthesis.
TL;DR: The results suggest that the nature of membrane sterols governs the mechanical behavior of the PM during hyperosmotic perturbation, and a relationship between hydric stress resistance and thenature of PM sterols is suggested.
TL;DR: The sterol profiles of dominant macroalgae occurring in the western Portuguese coast were evaluated and an analytical procedure, involving alkaline hydrolysis and extraction followed by separation by reversed‐phase HPLC–diode array detection (HPLC–DAD), was optimized for the study of their sterols composition.
Abstract: The sterol profiles of dominant macroalgae occurring in the western Portuguese coast were evaluated. An analytical procedure, involving alkaline hydrolysis and extraction followed by separation by reversed-phase HPLC-diode array detection (HPLC-DAD), was optimized for the study of their sterols composition. The validated methodology is short in analysis time (as the compounds are determined in <20 min), sensitive, reproducible, and accurate. It was then successfully applied to the determination of campesterol, cholesterol, desmosterol, ergosterol, fucosterol, stigmasterol, and β-sitosterol in 18 species (three Chlorophyta, five Rhodophyta, and 10 Phaeophyta). The profiles obtained for the several macroalgal species were considerably different. C29 sterols were predominant in Phaeophyta and Chlorophyta (71%-95% of total sterol content), while in Rhodophyta cholesterol content is significantly higher (34%-87%). Among the studied species, Asparagopsis armata Harv. contained the lowest sterol amount (555 mg · kg(-1) dry weight), and Cystoseira tamariscifolia (Huds.) Papenf. the highest one (6,502 mg · kg(-1) dry weight). Data obtained may be helpful in identifying suitable marine sources of sterols, with potential applications in the food and pharmaceutical industries.
TL;DR: In this article, the structure/function characterization of sterol 14α-demethylase (CYP51) from Leishmania infantum was reported, which is the first example of a plant-like 14α methylase.
TL;DR: Deletion of ABCA1 and ABCG1 causes an increased cholesterol content on the inner leaflet of the PM, associated with increased Rac1 PM localization, activation, and impairment of migration and may contribute to the ability of HDL to promote regression of atherosclerosis.
Abstract: Rationale: Reduced plasma cholesterol and increased high-density lipoprotein (HDL) levels promote regression of atherosclerosis, in a process characterized by lipid unloading and emigration of macrophages from lesions. In contrast free cholesterol loading of macrophages leads to imbalanced Rac1/Rho activities and impaired chemotaxis. Objective: To study the role of HDL and the ATP-binding cassette transporters ABCA1 and ABCG1 in modulating the chemotaxis of macrophages. Methods and Results: Abca1 −/− Abcg1 −/− mouse macrophages displayed profoundly impaired chemotaxis both in a Transwell chamber assay and in the peritoneal cavity of wild-type (WT) mice. HDL reversed impaired chemotaxis in free cholesterol–loaded WT macrophages but was without effect in Abca1 −/− Abcg1 −/− cells, whereas cyclodextrin was effective in both. Abca1 −/− Abcg1 −/− macrophages had markedly increased Rac1 activity and increased association of Rac1 with the plasma membrane (PM). Their defective chemotaxis was reversed by a Rac1 inhibitor. To gain a better understanding of the role of transporters in PM cholesterol movement, we measured transbilayer PM sterol distribution. In WT macrophages, the majority of cholesterol was located on the inner leaflet, whereas on upregulation of transporters by liver X receptor activation, PM sterol was shifted to the outer leaflet, where it could be removed by HDL. Abca1 −/− Abcg1 −/− macrophages showed increased PM sterol content and defective redistribution of sterol to the outer leaflet. Conclusions: Deletion of ABCA1 and ABCG1 causes an increased cholesterol content on the inner leaflet of the PM, associated with increased Rac1 PM localization, activation, and impairment of migration. ABCA1 and ABCG1 facilitate macrophage chemotaxis by promoting PM transbilayer cholesterol movement and may contribute to the ability of HDL to promote regression of atherosclerosis.
TL;DR: Reactions using H(2)(18)O(2) established that peroxide is the source of the oxygen introduced in aliphatic hydroxylations, and indicated that oxidation of alcohols to carbonyl and carboxyl groups is produced by successive hydoxylations combined with one dehydration step.
TL;DR: Findings suggest that an increase in bilayer lateral stress is unlikely to underlie the differential ability of cholesterol and related steroids to inhibit BK channels and hypothesize that a cholesterol-recognizing protein surface resides at the BK α subunit itself.
Abstract: The activity (Po) of large-conductance voltage/Ca(2+)-gated K(+) (BK) channels is blunted by cholesterol levels within the range found in natural membranes. We probed BK channel-forming α (cbv1) subunits in phospholipid bilayers with cholesterol and related monohydroxysterols and performed computational dynamics to pinpoint the structural requirements for monohydroxysterols to reduce BK Po and obtain insights into cholesterol's mechanism of action. Cholesterol, cholestanol, and coprostanol reduced Po by shortening mean open and lengthening mean closed times, whereas epicholesterol, epicholestanol, epicoprostanol, and cholesterol trisnorcholenic acid were ineffective. Thus, channel inhibition by monohydroxysterols requires the β configuration of the C3 hydroxyl and is favored by the hydrophobic nature of the side chain, while having lax requirements on the sterol A/B ring fusion. Destabilization of BK channel open state(s) has been previously interpreted as reflecting increased bilayer lateral stress by cholesterol. Lateral stress is controlled by the sterol molecular area and lipid monolayer lateral tension, the latter being related to the sterol ability to adopt a planar conformation in lipid media. However, we found that the differential efficacies of monohydroxysterols to reduce Po (cholesterol≥coprostanol≥cholestanol>>>epicholesterol) did not follow molecular area rank (coprostanol>>epicholesterol>cholesterol>cholestanol). In addition, computationally predicted energies for cholesterol (effective BK inhibitor) and epicholesterol (ineffective) to adopt a planar conformation were similar. Finally, cholesterol and coprostanol reduced Po, yet these sterols have opposite effects on tight lipid packing and, likely, on lateral stress. Collectively, these findings suggest that an increase in bilayer lateral stress is unlikely to underlie the differential ability of cholesterol and related steroids to inhibit BK channels. Remarkably, ent-cholesterol (cholesterol mirror image) failed to reduce Po, indicating that cholesterol efficacy requires sterol stereospecific recognition by a protein surface. The BK channel phenotype resembled that of α homotetramers. Thus, we hypothesize that a cholesterol-recognizing protein surface resides at the BK α subunit itself.
TL;DR: In this paper, a basal framework of the interactions between sterol, bile salts and phospholipids in aqueous solutions is provided, and new developments are summarized, including mutations in the gene encoding the cholesterol transporter ABCG5-G8 have been found to increase overall gallstone risk.
TL;DR: Feeding plays an essential role in sustaining T. reniformis metabolism during the thermal stress, and enrichment in the δ13C signature of the storage and structural FAs suggests that they were the main compounds respired during the stress to maintain the coral metabolism.
Abstract: This study assesses the combined effect of feeding and short-term thermal stress on various physiological parameters and on the fatty acid, sterol, and alcohol composition of the scleractinian coral Turbinaria reniformis. The compound-specific carbon isotope composition of the lipids was also measured. Under control conditions (26°C), feeding with Artemia salina significantly increased the symbiont density and chlorophyll content and the growth rates of the corals. It also doubled the concentrations of almost all fatty acid (FA) compounds and increased the n-alcohol and sterol contents. δ13C results showed that the feeding enhancement of FA concentrations occurred either via a direct pathway, for one of the major polyunsaturated fatty acid (PUFA) compounds of the food (18:3n-3 FA), or via an enhancement of photosynthate transfer (indirect pathway), for the other coral FAs. Cholesterol (C27Δ5) was also directly acquired from the food. Thermal stress (31°C) affected corals, but differently according to their feeding status. Chlorophyll, protein content, and maximal photosynthetic efficiency of photosystem II (PSII) decreased to a greater extent in starved corals. In such corals, FA concentrations were reduced by 33%, (especially C16, C18 FAs, and n-3 PUFA) and the sterol content by 27% (especially the C28∆5,22 and C28∆5). The enrichment in the δ13C signature of the storage and structural FAs suggests that they were the main compounds respired during the stress to maintain the coral metabolism. Thermal stress had less effect on the lipid concentrations of fed corals, as only FA levels were reduced by 13%, with no major changes in their isotope carbon signatures. In conclusion, feeding plays an essential role in sustaining T. reniformis metabolism during the thermal stress.