Domain-specific lipid distribution in macrophage plasma membranes

Messages in CD40L are encrypted for residue-specific functions

CD40-CD40-ligand (CD40L) interaction plays crucial immunoregulatory roles, as CD40 signals through different signaling intermediates to convert the messages from CD40L to effector functions. Being a TNFα receptor family member, CD40 binds TNFα receptor-associated factors, assembles signalosome complexes and decrypts the messages from CD40L through different signaling modules to result in residue-specific effector functions. The evidence for such a residue-specific message encryption first came from the CD40L mutations resulting in X-linked hyper-IgM syndrome, as the extent of effects varied with the residue mutated. The structural studies on the CD40-CD40L interaction implied differential involvement of the interacting residues on CD40L in influencing the effector functions. Three lines of evidence indicate the previously implied residue-specific message encryption in CD40L: screening of a dodecameric peptide library for CD40 binders identified two peptides with different sequences resulting in counteractive effector functions in macrophages; a series of CD40L mutants identified that the mutations in these residues selectively affected CD40 signaling and macrophage effector functions; and, a panel of 40-mer peptides, representing the CD40-interacting domain of mouse CD40L, with single substitutions resulted in altered CD40 signaling through various signaling intermediates and effector functions in mouse macrophages. We therefore construct the first-ever message encryption-decryption in a biological receptor-ligand system wherein the CD40L residues that interact with CD40 residues have encrypted messages, which are decoded by CD40 signaling to result in residue-specific effector functions. This review presents a novel perspective of receptor-ligand interaction as a system of message transmission, message decoding by signaling, and its transcription to various read-outs. [250 words].

Cholesterol Depletion and Membrane Deformation by MeβCD and the Resultant Enhanced T Cell Killing

Recent studies have demonstrated the crucial role of cholesterol (Chol) in regulating the mechanical properties and biological functions of cell membranes. Methyl-β-cyclodextrin (MeβCD) is commonly utilized to modulate the Chol content in cell membranes, but there remains a lack of a comprehensive understanding. In this study, using a range of different techniques, we find that the optimal ratio of MeβCD to Chol for complete removal of Chol from a phosphocholine (PC)/Chol mixed membrane with a 1:1 mol ratio is 4.5:1, while the critical MeβCD-to-Chol ratio for membrane permeation falls within the range between 1.5 and 2.4. MeβCD at elevated concentrations induces the formation of fibrils or tubes from a PC membrane. Single lipid tracking reveals that removing Chol restores the diffusion of lipid molecules in the PC/Chol membrane to levels observed in pure PC membranes. Exposure to 5 mM MeβCD for 30 min effectively eliminates Chol from various cell lines, leading to an up to 8-fold enhancement in melittin cytotoxicity over Hela cells and an up to 3.5-fold augmentation of T cell cytotoxicity against B16F10-OVA cells. This study presents a diagram that delineates the concentration- and time-dependent distribution of MeβCD-induced Chol depletion and membrane deformation, which holds significant potential for modulating the mechanical properties of cellular membranes in prospective biomedical applications.

Simulations of naïve and KLA-activated macrophage plasma membrane models

Macrophages (MAs), which play vital roles in human immune responses and lipid metabolisms, are implicated in the development and progression of atherosclerosis, a major contributor to cardiovascular diseases. Specifically, the abnormal lipid metabolism of oxidized low-density lipids (oxLDLs) in MAs is believed to be a crucial factor. However, the precise mechanism by which the MA membrane contributes to this altered lipid metabolism remains unclear. Lipidomic studies have revealed significant differences in membrane composition between various MA phenotypes. This study serves to provide and characterize complex realistic computational models for naïve (M0) and Kdo2-lipid A-activated (M1) state MA. Analyses of surface area per lipid (SA/lip), area compressibility modulus (KA), carbon‑hydrogen order parameter (SCH), electron density profile (EDP), tilt angles, two-dimension radial distribution functions (2D RDFs), mean squared displacement (MSD), hydrogen bonds (H-bonds), lipid clustering, and lipid wobble were conducted for both models. Results indicate that the M1 state MA membrane is more tightly packed, with increased chain order across lipid species, and forms PSM-DOPG-CHOL and PSM-SLPC-CHOL clusters. Importantly, the bilayer thicknesses reported for the models are in good agreement with experimental data for the thicknesses of transmembrane regions for MA integral proteins. These findings validate the described models as physiologically accurate for future computational studies of MA membranes and their residing proteins.

Identification of GPI-anchored protein LYPD1 as an essential factor for odontoblast differentiation in tooth development

Lipid rafts are membrane microdomains rich in cholesterol, sphingolipids, glycosylphosphatidylinositol-anchored proteins (GPI-APs), and receptors. These lipid raft components are localized at the plasma membrane and are essential for signal transmission and organogenesis. However, few reports have been published on the specific effects of lipid rafts on tooth development. Using microarray and single-cell RNA sequencing methods, we found that a GPI-AP, lymphocyte antigen-6/Plaur domain-containing 1 (Lypd1), was specifically expressed in preodontoblasts. Depletion of Lypd1 in tooth germ using an ex vivo organ culture system and in mouse dental pulp (mDP) cells resulted in the inhibition of odontoblast differentiation. Activation of bone morphogenetic protein (BMP) signaling by BMP2 treatment in mDP cells promoted odontoblast differentiation via phosphorylation of Smad1/5/8, while this BMP2-mediated odontoblast differentiation was inhibited by depletion of Lypd1. Furthermore, we created a deletion construct of the C terminus containing the omega site in LYPD1; this site is necessary for localizing GPI-APs to the plasma membrane and lipid rafts. We identified that this site is essential for odontoblast differentiation and morphological change of mDP cells. These findings demonstrated that LYPD1 is a novel marker of preodontoblasts in the developing tooth; in addition, they suggest that LYPD1 is important for tooth development and that it plays a pivotal role in odontoblast differentiation by regulating Smad1/5/8 phosphorylation through its effect as a GPI-AP in lipid rafts.

Cyclodextrins: Only Pharmaceutical Excipients or Full-Fledged Drug Candidates?

Cyclodextrins, representing a versatile family of cyclic oligosaccharides, have extensive pharmaceutical applications due to their unique truncated cone-shaped structure with a hydrophilic outer surface and a hydrophobic cavity, which enables them to form non-covalent host-guest inclusion complexes in pharmaceutical formulations to enhance the solubility, stability and bioavailability of numerous drug molecules. As a result, cyclodextrins are mostly considered as inert carriers during their medical application, while their ability to interact not only with small molecules but also with lipids and proteins is largely neglected. By forming inclusion complexes with cholesterol, cyclodextrins deplete cholesterol from cellular membranes and thereby influence protein function indirectly through alterations in biophysical properties and lateral heterogeneity of bilayers. In this review, we summarize the general chemical principles of direct cyclodextrin-protein interactions and highlight, through relevant examples, how these interactions can modify protein functions in vivo, which, despite their huge potential, have been completely unexploited in therapy so far. Finally, we give a brief overview of disorders such as Niemann-Pick type C disease, atherosclerosis, Alzheimer's and Parkinson's disease, in which cyclodextrins already have or could have the potential to be active therapeutic agents due to their cholesterol-complexing or direct protein-targeting properties.

Deep eutectic solvents as cryoprotective agents for mammalian cells

Cryopreservation has facilitated numerous breakthroughs including assisted reproductive technology, stem cell therapies, and species preservation. Successful cryopreservation requires the addition of cryoprotective agents to protect against freezing damage and dehydration. For decades, cryopreservation has largely relied on the same two primary agents: dimethylsulfoxide and glycerol. However, both of these are toxic which limits their use for cells destined for clinical applications. Furthermore, these two agents are ineffective for hundreds of cell types, and organ and tissue preservation has not been achieved. The research presented here shows that deep eutectic solvents can be used as cryoprotectants. Six deep eutectic solvents were explored for their cryoprotective capacity towards mammalian cells. The solvents were tested for their thermal properties, including glass transitions, toxicity, and permeability into mammalian cells. A deep eutectic solvent made from proline and glycerol was an effective cryoprotective agent for all four cell types tested, even with extended incubation prior to freezing. This deep eutectic solvent was more effective and less toxic than its individual components, highlighting the importance of multi-component systems. Cells were characterised post-thawing using atomic force microscopy and confocal microscopy. Molecular dynamics simulations support the biophysical parameters obtained by experimentation. This is one of the first times that this class of solvents has been systematically tested for cryopreservation of mammalian cells and as such this research opens the way for the development of potentially thousands of new cryoprotective agents that can be tailored to specific cell types. The demonstrated capacity of cells to be incubated with the deep eutectic solvent at 37 °C for hours prior to freezing without significant loss of viability is a major step toward the storage of organs and tissues.

The Role of Membrane Lipids in Light-Activation of Drosophila TRP Channels

Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP₂) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP₃). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts, compelling evidence of the involvement of DAG accumulation, PIP₂ depletion or IP₃-mediated Ca²⁺ release in light activation of the TRP/TRPL channels are still lacking. Exogeneous application of poly unsaturated fatty acids (PUFAs), a product of DAG hydrolysis was demonstrated as an efficient way to activate the Drosophila TRP/TRPL channels. However, compelling evidence for the involvement of PUFAs in physiological light-activation of the TRP/TRPL channels is still lacking. Light-induced mechanical force generation was measured in photoreceptor cells prior to channel opening. This mechanical force depends on PLC activity, suggesting that the enzymatic activity of PLC converting PIP₂ into DAG generates membrane tension, leading to mechanical gating of the channels. In this review, we will present the roles of membrane lipids in light activation of Drosophila TRP channels and present the many advantages of this model system in the exploration of TRP channel activation under physiological conditions.

Functions of Sphingolipids in Pathogenesis During Host-Pathogen Interactions

Sphingolipids are a class of membrane lipids that serve as vital structural and signaling bioactive molecules in organisms ranging from yeast to animals. Recent studies have emphasized the importance of sphingolipids as signaling molecules in the development and pathogenicity of microbial pathogens including bacteria, fungi, and viruses. In particular, sphingolipids play key roles in regulating the delicate balance between microbes and hosts during microbial pathogenesis. Some pathogens, such as bacteria and viruses, harness host sphingolipids to promote development and infection, whereas sphingolipids from both the host and pathogen are involved in fungus-host interactions. Moreover, a regulatory role for sphingolipids has been described, but their effects on host physiology and metabolism remain to be elucidated. Here, we summarize the current state of knowledge about the roles of sphingolipids in pathogenesis and interactions with host factors, including how sphingolipids modify pathogen and host metabolism with a focus on pathogenesis regulators and relevant metabolic enzymes. In addition, we discuss emerging perspectives on targeting sphingolipids that function in host-microbe interactions as new therapeutic strategies for infectious diseases.

Effect of High-Density Lipoprotein from Healthy Subjects and Chronic Kidney Disease Patients on the CD14 Expression on Polymorphonuclear Leukocytes

In uremic patients, high-density lipoprotein (HDL) loses its anti-inflammatory features and can even become pro-inflammatory due to an altered protein composition. In chronic kidney disease (CKD), impaired functions of polymorphonuclear leukocytes (PMNLs) contribute to inflammation and an increased risk of cardiovascular disease. This study investigated the effect of HDL from CKD and hemodialysis (HD) patients on the CD14 expression on PMNLs. HDL was isolated using a one-step density gradient centrifugation. Isolation of PMNLs was carried out by discontinuous Ficoll-Hypaque density gradient centrifugation. CD14 surface expression was quantified by flow cytometry. The activity of the small GTPase Rac1 was determined by means of an activation pull-down assay. HDL increased the CD14 surface expression on PMNLs. This effect was more pronounced for HDL isolated from uremic patients. The acute phase protein serum amyloid A (SAA) caused higher CD14 expression, while SAA as part of an HDL particle did not. Lipid raft disruption with methyl-β-cyclodextrin led to a reduced CD14 expression in the absence and presence of HDL. HDL from healthy subjects but not from HD patients decreased the activity of Rac1. Considering the known anti-inflammatory effects of HDL, the finding that even HDL from healthy subjects increased the CD14 expression was unexpected. The pathophysiological relevance of this result needs further investigation.

Mechanistic Insights into Trop2 Clustering on Lung Cancer Cell Membranes Revealed by Super-resolution Imaging

The transmembrane glycoprotein Trop2 plays important roles in various types of human cancers, especially lung cancer. Although it has been found to form clusters on cancer cell membranes, the factors that affect its clustering are not yet fully understood. Here, using direct stochastic optical reconstruction microscopy (dSTORM), we found that Trop2 generated more, larger, and denser clusters on apical cell membranes than on basal membranes and that the differences might be related to the different membrane structures. Moreover, dual-color dSTORM imaging revealed significant colocalization of Trop2 and lipid rafts, and methyl-β-cyclodextrin disruption dramatically impaired the formation of Trop2 clusters, indicating a key role of lipid rafts in Trop2 clustering. Additionally, depolymerization of the actin cytoskeleton decreased Trop2 cluster numbers and areas, revealing that actin can stabilize the clusters. More importantly, stimulation of Trop2 in cancer cells hardly changed the cluster morphology, suggesting that Trop2 is activated and forms clusters in cancer cells. Altogether, our work links the spatial organization of Trop2 to different membrane structures and Trop activation and uncovers the essential roles of lipid rafts and actin in Trop2 cluster maintenance.

A sensitive S-Trap-based approach to the analysis of T cell lipid raft proteome

The analysis of T cell lipid raft proteome is challenging due to the highly dynamic nature of rafts and the hydrophobic character of raft-resident proteins. We explored an innovative strategy for bottom-up lipid raftomics based on suspension-trapping (S-Trap) sample preparation. Mouse T cells were prepared from splenocytes by negative immunoselection, and rafts were isolated by a detergent-free method and OptiPrep gradient ultracentrifugation. Microdomains enriched in flotillin-1, LAT, and cholesterol were subjected to proteomic analysis through an optimized protocol based on S-Trap and high pH fractionation, followed by nano-LC-MS/MS. Using this method, we identified 2,680 proteins in the raft-rich fraction and established a database of 894 T cell raft proteins. We then performed a differential analysis on the raft-rich fraction from nonstimulated versus anti-CD3/CD28 T cell receptor (TCR)-stimulated T cells. Our results revealed 42 proteins present in one condition and absent in the other. For the first time, we performed a proteomic analysis on rafts from ex vivo T cells obtained from individual mice, before and after TCR activation. This work demonstrates that the proposed method utilizing an S-Trap-based approach for sample preparation increases the specificity and sensitivity of lipid raftomics.

Protamine sulphate coated poly (lactide-co-glycolide) nanoparticles of MUC-1 peptide improved cellular uptake and cytokine release in mouse antigen presenting cells

AIM

MUC-1-peptide (M-1-pep) loaded poly (lactide-co-glycolide) nanoparticles were coated with protamine sulphate (PS), M-1-pep-PS-P-NPs for targeting antigen presenting cells (APCs) to evoke cytokine release.

METHODS AND RESULTS

M-1-pep-PS-P-NPs were tailored by emulsion-diffusion evaporation method and characterised in vitro under a set of rigorous parameters. The average particle size and zeta potential of optimised M-1-pep-PS-P-B-NPs was measured to be 132.21 ± 30.71 nm and 6.29 ± 0.71 mV, significantly (p < 0.01) higher than 71.24 ± 17.76-nm and -43.41 ± 3.37 mV of M-1-pep-P-NPs. Further, 50-μg/ml concentration of M-1-pep-PS-P-B-NPs displayed 82.4% cellular uptake in RAW 264.7 cells calculated in setting of fluorescence intensity significantly (p < 0.05) elevated than 63.1% of M-1-pep-P-NPs. Consistent to quantitative results, M-1-pep-PS-P-B-NPs also confirmed advanced cellular uptake (CU) in RAW 264.7 cells in contrast to M-1-pep-P-NPs suppose to be through multiple mechanisms including phagocytosis and clathrin mediated endocytosis.

CONCLUSION

M-1-pep-PS-P-B-NPs must be evaluated in vivo through inhalation route of administration for antitumor prospective in lung cancer xenograft model.

Isolation of Lipid Rafts from Cultured Mammalian Cells and Their Lipidomics Analysis

Lipid rafts are distinct liquid-ordered domains of plasma membranes of most eukaryotic cells providing platform for signaling pathways. Lipid composition of rafts is critical for their structural integrity and for regulation of signaling pathways originating from rafts. Here we provide a protocol to isolate lipid rafts from cultured human and animal cells and comprehensively analyse their lipid composition.

Modulation of Transient Receptor Potential C Channel Activity by Cholesterol

Changes of cholesterol level in the plasma membrane of cells have been shown to modulate ion channel function. The proposed mechanisms underlying these modulations include association of cholesterol to a single binding site at a single channel conformation, association to a highly flexible cholesterol binding site adopting multiple poses, and perturbation of lipid rafts. These perturbations have been shown to induce reversible targeting of mammalian transient receptor potential C (TRPC) channels to the cholesterol-rich membrane environment of lipid rafts. Thus, the observed inhibition of TRPC channels by methyl-β-cyclodextrin (MβCD), which induces cholesterol efflux from the plasma membrane, may result from disruption of lipid rafts. This perturbation was also shown to disrupt multimolecular signaling complexes containing TRPC channels. The Drosophila TRP and TRP-like (TRPL) channels belong to the TRPC channel subfamily. When the Drosophila TRPL channel was expressed in S2 or HEK293 cells and perfused with MβCD, the TRPL current was abolished in less than 100 s, fitting well the fast kinetic phase of cholesterol sequestration experiments in cells. It was thus suggested that the fast kinetics of TRPL channel suppression by MβCD arise from disruption of lipid rafts. Accordingly, lipid raft perturbation by cholesterol sequestration could give clues to the function of lipid environment in TRPC channel activity and its mechanism.

The molecular mechanism of robust macrophage immune responses induced by PEGylated molybdenum disulfide

Molybdenum disulfide (MoS2), a representative hexagonal transition metal dichalcogenide (TMD), has been extensively exploited in biomedical applications due to its unique physicochemical properties and biocompatibility. However, the lack of adequate data regarding how MoS2 activates immunological responses of macrophages remains a key concern for its risk assessment. Here, we employ a combined theoretical and experimental approach to investigate the interactions of MoS2 and PEGylated MoS2 (MoS2-PEG) with macrophages. We first perform molecular dynamics simulations to examine the atomic-detailed interactions of MoS2 and MoS2-PEG nanoflakes with a realistic model of the macrophage membrane. We show that a small MoS2 nanoflake (edge length of 2.86 nm) is capable of penetrating the macrophage membrane independent of its concentration. We also demonstrate that when initiated with a corner point-on configuration, the surface-bound PEG chains of MoS2-PEG hinder its membrane insertion process, leading to a prolonged passage through the membrane. Moreover, when placed in a face-on arrangement initially, the MoS2-PEG exhibits a lower binding free energy than pristine MoS2 after its adsorption on the membrane surface. The PEG chains can even insert and get buried in the outer leaflet of the membrane, providing additional contact for membrane adsorption. Our flow cytometric experiments then show that the responses of macrophages to either MoS2-PEG or MoS2 are significantly higher than that of the control (no nanomaterial stimulus), with MoS2-PEG eliciting stronger cytokine secretion than the pristine MoS2. The characteristics of slower/prolonged membrane penetration and stronger membrane adsorption of MoS2-PEG compared to pristine MoS2 explain why it triggers more sustained stimulation and higher cytokine secretion in macrophages as observed in our experiments. Our findings reveal the underlying molecular mechanism of how MoS2-PEG influences the immune responses and suggest its potential applications in nanomedicine involving immune stimulation.

Mechanistic insights into GLUT1 activation and clustering revealed by super-resolution imaging

The glucose transporter GLUT1, a plasma membrane protein that mediates glucose homeostasis in mammalian cells, is responsible for constitutive uptake of glucose into many tissues and organs. Many studies have focused on its vital physiological functions and close relationship with diseases. However, the molecular mechanisms of its activation and transport are not clear, and its detailed distribution pattern on cell membranes also remains unknown. To address these, we first investigated the distribution and assembly of GLUT1 at a nanometer resolution by super-resolution imaging. On HeLa cell membranes, the transporter formed clusters with an average diameter of ∼250 nm, the majority of which were regulated by lipid rafts, as well as being restricted in size by both the cytoskeleton and glycosylation. More importantly, we found that the activation of GLUT1 by azide or MβCD did not increase its membrane expression but induced the decrease of the large clusters. The results suggested that sporadic distribution of GLUT1 may facilitate the transport of glucose, implying a potential association between the distribution and activation. Collectively, our work characterized the clustering distribution of GLUT1 and linked its spatial structural organization to the functions, which would provide insights into the activation mechanism of the transporter.

Macrophages Shed Excess Cholesterol in Unique Extracellular Structures Containing Cholesterol Microdomains

Supplemental Digital Content is available in the text.

Objective—

Cells use various mechanisms to maintain cellular cholesterol homeostasis including efflux of cholesterol from the cellular plasma membrane to cholesterol acceptors such as HDLs (high-density lipoproteins). Little is known about the transfer of cholesterol from cells into the extracellular matrix. Using a unique monoclonal antibody that detects ordered cholesterol arrays (ie, cholesterol micro[or nano]-domains), we previously identified that particles containing these cholesterol domains accumulate in the extracellular matrix during cholesterol enrichment of human monocyte-derived macrophages and are found in atherosclerotic lesions. In this study, we further investigate these deposited particles containing cholesterol microdomains and discover their unexpected morphology.

Approach and Results—

Although appearing spherical at the resolution of the conventional fluorescence microscope, super-resolution immunofluorescence and atomic force microscopy of in situ cholesterol microdomains, and immunoelectron microscopy of isolated cholesterol microdomains revealed that the microdomains are not vesicles or 3-dimensional crystals but rather appear as branching irregularly shaped deposits of varying size. These cholesterol microdomain-containing deposits are shed from the plasma membrane into the extracellular matrix.

Conclusions—

To date, research on cellular excretion of excess cholesterol has demonstrated cellular cholesterol efflux in the form of membranous vesicles and discoidal HDL particles released into the fluid-phase medium. Shedding of plasma membrane cholesterol microdomains provides an additional mechanism for cells such as macrophages to maintain plasma membrane cholesterol homeostasis. Furthermore, recognition that macrophages shed cholesterol microdomains into the extracellular matrix is important to our understanding of extracellular buildup of cholesterol in atherosclerosis.

Influence of omega-3 polyunsaturated fatty acids from fish oil or meal on the structure of lipid microdomains in bovine luteal cells

Biological membranes are composed of a lipid bilayer and proteins that form lipid microdomains. This study examined the effects of fish byproducts on lipid-protein interactions within lipid microdomains of bovine luteal cells. In Exp. 1 and 2, luteal cells were prepared from corpora lutea (CL; n = 4 to 8) collected at an abattoir. Exp. 1 was conducted to optimize ultrasonication in a detergent-free protocol for isolation of lipid microdomains. A power setting of 10 to 20% was effective in isolating lipid microdomains from bulk lipid. In Exp. 2, cells were cultured in control medium or fish oil to determine influence of fish oil on distribution of lipid microdomain markers and prostaglandin F_2α (FP) receptors. Cells treated with fish oil had a smaller percentage of microdomain markers and FP receptor in microdomains (P < 0.05). In Exp. 3 and 4, cells were prepared from mid-cycle CL obtained from cows supplemented with corn gluten meal (n = 4) or fish meal (n = 4). Exp. 3 examined effects of dietary supplementation on distribution of lipid microdomain markers and FP receptor and Exp. 4 on fatty acid composition within lipid microdomains. A smaller percentage of lipid microdomain markers and FP receptor was detected in microdomains of cells collected from fish meal supplemented animals (P < 0.05). In Exp. 4, a greater percentage of omega-3 polyunsaturated fatty acids was detected in bulk lipid from fish meal supplemented cows (P < 0.05). Results show that fish byproducts influence lipid-protein interactions in lipid microdomains in bovine luteal cells.

High cholesterol in lipid rafts reduces the sensitivity to EGFR-TKI therapy in non-small cell lung cancer

Overcoming EGFR-TKI resistant which has the initial enthusiasm over substantial clinical responses is a formidable challenge on nowadays. In this study, we showed that cholesterol level in lipid rafts in gefitinib resistant non-small cell lung cancer (NSCLC) cell lines was remarkably higher than gefitinib sensitive cell line, and depletion of cholesterol increased gefitinib sensitivity. Furthermore, cholesterol-depleted enhanced gefitinib inhibit phosphorylation of EGFR, Akt-1, MEK1/2, and ERK1/2 and these were reversed in cholesterol add-back experiments. Gefitinib resistant cell lines showed high affinity of gefitinib and EGFR when cholesterol was depleted. Therefore, targeting cholesterol combined with EGFR-TKI is potentially a novel therapeutic strategy for gefitinib resistant treatment.

The effect of sterol structure upon clathrin-mediated and clathrin-independent endocytosis

Ordered lipid domains (rafts) in plasma membranes have been hypothesized to participate in endocytosis based on inhibition of endocytosis by removal or sequestration of cholesterol. To more carefully investigate the role of the sterol in endocytosis, we used a substitution strategy to replace cholesterol with sterols that show various raft-forming abilities and chemical structures. Both clathrin-mediated endocytosis of transferrin and clathrin-independent endocytosis of clustered placental alkaline phosphatase were measured. A subset of sterols reversibly inhibited both clathrin-dependent and clathrin-independent endocytosis. The ability of a sterol to support lipid raft formation was necessary for endocytosis. However, it was not sufficient, because a sterol lacking a 3β-OH group did not support endocytosis even though it had the ability to support ordered domain formation. Double bonds in the sterol rings and an aliphatic tail structure identical to that of cholesterol were neither necessary nor sufficient to support endocytosis. This study shows that substitution using a large number of sterols can define the role of sterol structure in cellular functions. Hypotheses for how sterol structure can similarly alter clathrin-dependent and clathrin-independent endocytosis are discussed.

Methyl-β-cyclodextrin modulates thapsigargin-induced store-dependent Ca2+ entry in macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that preincubation of macrophages with methyl-β-cyclodextrin, inducing cholesterol extraction from membranes and raft disruption, leads to significant inhibition of thapsigargin-induced store-dependent Ca²⁺ entry in rat peritoneal macrophages. In contrast, macrophage treatment with methyl-β-cyclodextrin after Ca²⁺ entry mechanisms were activated by store depletion by thapsigargin application leads to potentiation of subsequent store-dependent Ca²⁺ entry. The results suggest that intact lipid rafts are necessary for the activation but not the maintenance of store-dependent Ca²⁺ entry in macrophages.

Case study on the pathophysiology of Fabry disease: abnormalities of cellular membranes can be reversed by substrate reduction in vitro

It is still not entirely clear how α-galactosidase A (GAA) deficiency translates into clinical symptoms of Fabry disease (FD). The present communication investigates the effects of the mutation N215S in FD on the trafficking and processing of lysosomal GAA and their potential association with alterations in the membrane lipid composition. Abnormalities in lipid rafts (LRs) were observed in fibroblasts isolated from a male patient with FD bearing the mutation N215S. Interestingly, LR analysis revealed that the distribution of cholesterol and flotillin-2 are distinctly altered in the Fabry fibroblasts when compared with that of the wild-type cells. Furthermore, increased levels of glycolipid globotriaosylceramide 3 (Gb3) and sphingomyelin (SM) were observed in non-raft membrane fractions of Fabry cells. Substrate reduction with N-butyldeoxynojirimycin (NB-DNJ) in vitro was capable of reversing these abnormalities in this patient. These data led to the hypothesis that alterations of LRs may contribute to the pathophysiology of Morbus Fabry. Furthermore, it may be suggested that substrate reduction therapy with NB-DNJ might be a promising approach for the treatment of GAA deficiency at least for the selected patients.

Methyl-β-cyclodextrin inhibits Ca2+-responses induced by glutoxim and molixan in macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that methyl-β-cyclodextrin, inducing cholesterol extraction from membranes and raft disruption, significantly inhibits glutoxim- and molixan-induced Ca²⁺-responses in rat peritoneal macrophages. The results suggest that intact rafts are necessary for signaling cascade induced by glutoxim or molixan and leading to intracellular Ca²⁺ concentration increase in macrophages.

Acute exposure to apolipoprotein A1 inhibits macrophage chemotaxis in vitro and monocyte recruitment in vivo

Apolipoprotein A1 (apoA1) is the major protein component of high-density lipoprotein (HDL) and has well documented anti-inflammatory properties. To better understand the cellular and molecular basis of the anti-inflammatory actions of apoA1, we explored the effect of acute human apoA1 exposure on the migratory capacity of monocyte-derived cells in vitro and in vivo. Acute (20-60 min) apoA1 treatment induced a substantial (50-90%) reduction in macrophage chemotaxis to a range of chemoattractants. This acute treatment was anti-inflammatory in vivo as shown by pre-treatment of monocytes prior to adoptive transfer into an on-going murine peritonitis model. We find that apoA1 rapidly disrupts membrane lipid rafts, and as a consequence, dampens the PI3K/Akt signalling pathway that coordinates reorganization of the actin cytoskeleton and cell migration. Our data strengthen the evidence base for therapeutic apoA1 infusions in situations where reduced monocyte recruitment to sites of inflammation could have beneficial outcomes.

CD14 Is a Co-Receptor for TLR4 in the S100A9-Induced Pro-Inflammatory Response in Monocytes

The cytosolic Ca²⁺-binding S100A9 and S100A8 proteins form heterodimers that are primarily expressed in human neutrophils and monocytes. We have recently shown that S100A9 binds to TLR4 in vitro and induces TLR4-dependent NF-κB activation and a pro-inflammatory cytokine response in monocytes. In the present report we have further investigated the S100A9-mediated stimulation of TLR4 in monocytes. Using transmission immunoelectron microscopy, we detected focal binding of S100A9 to monocyte membrane subdomains containing the caveolin-1 protein and TLR4. Furthermore, the S100A9 protein was detected in early endosomes of the stimulated cells, indicating that the protein could be internalized by endocytosis. Although stimulation of monocytes with S100A9 was strictly TLR4-dependent, binding of S100A9 to the plasma membrane and endocytosis of S100A9 was still detectable and coincided with CD14 expression in TLR4-deficient cells. We therefore investigated whether CD14 would be involved in the TLR4-dependent stimulation and could show that the S100A9-induced cytokine response was inhibited both in CD14-deficient cells and in cells exposed to CD14 blocking antibodies. Further, S100A9 was not internalized into CD14-deficient cells suggesting a direct role of CD14 in endocytosis of S100A9. Finally, we could detect satiable binding of S100A9 to CD14 in surface plasmon resonance experiments. Taken together, these results indicate that CD14 is a co-receptor of TLR4 in the S100A9-induced cytokine response.

The ontogeny of P-glycoprotein in the developing human blood-brain barrier: implication for opioid toxicity in neonates

BACKGROUND

Neonates have been shown to have a heightened sensitivity to the central depressive effects of opioids compared to older infants and adults. The limited development of P-glycoprotein (P-gp) may limit the ability of the neonate to efflux morphine from the brain back to the systemic circulation. The objective of the study was to determine the ontogeny of P-gp in the human brain.

METHODS

Postmortem cortex samples from gestational age (GA) 20-26 wk, GA 36-40 wk, postnatal age (PNA) 0-3 mo, PNA 3-6 mo, and adults were immunostained for P-gp.

RESULTS

The intensity of P-gp staining in adults was significantly higher compared to at GA 20-26 wk (P < 0.05), GA 36-40 wk (P < 0.05), and PNA 0-3 mo (P < 0.05). P-gp intensity at GA 20-26 wk (P < 0.05), GA 36-40 wk (P < 0.05), and PNA 0-3 mo (P < 0.05) was significantly lower compared to at PNA 3-6 mo.

CONCLUSION

P-gp expression in the brain is limited at birth, increases with postnatal maturation, and reaches adult levels at ~3-6 mo of age. Given the immaturity of blood-brain barrier (BBB) P-gp after birth, morphine may concentrate in the brain. This provides mechanistic support to life threatening opioid toxicity seen with maternal codeine use during breastfeeding.

Surface hydrolysis of sphingomyelin by the outer membrane protein Rv0888 supports replication of Mycobacterium tuberculosis in macrophages

Sphingomyelinases secreted by pathogenic bacteria play important roles in host-pathogen interactions ranging from interfering with phagocytosis and oxidative burst to iron acquisition. This study shows that the Mtb protein Rv0888 possesses potent sphingomyelinase activity cleaving sphingomyelin, a major lipid in eukaryotic cells, into ceramide and phosphocholine, which are then utilized by Mtb as carbon, nitrogen and phosphorus sources, respectively. An Mtb rv0888 deletion mutant did not grow on sphingomyelin as a sole carbon source anymore and replicated poorly in macrophages indicating that Mtb utilizes sphingomyelin during infection. Rv0888 is an unusual membrane protein with a surface-exposed C-terminal sphingomyelinase domain and a putative N-terminal channel domain that mediated glucose and phosphocholine uptake across the outer membrane in an M. smegmatis porin mutant. Hence, we propose to name Rv0888 as SpmT (sphingomyelinase of Mycobacterium tuberculosis). Erythrocyte membranes contain up to 27% sphingomyelin. The finding that Rv0888 accounts for half of Mtb's hemolytic activity is consistent with its sphingomyelinase activity and the observation that Rv0888 levels are increased in the presence of erythrocytes and sphingomyelin by 5- and 100-fold, respectively. Thus, Rv0888 is a novel outer membrane protein that enables Mtb to utilize sphingomyelin as a source of several essential nutrients during intracellular growth.

Bioenergetic programming of macrophages by the apolipoprotein A-I mimetic peptide 4F

The apoA-I (apolipoprotein A-I) mimetic peptide 4F favours the differentiation of human monocytes to an alternatively activated M2 phenotype. The goal of the present study was to test whether the 4F-mediated differentiation of MDMs (monocyte-derived macrophages) requires the induction of an oxidative metabolic programme. 4F treatment induced several genes in MDMs that play an important role in lipid metabolism, including PPARγ (peroxisome-proliferator-activated receptor γ) and CD36. Addition of 4F was associated with a significant increase in FA (fatty acid) uptake and oxidation compared with vehicle treatment. Mitochondrial respiration was assessed by measurement of the OCR (oxygen-consumption rate). 4F increased basal and ATP-linked OCR as well as maximal uncoupled mitochondrial respiration. These changes were associated with a significant increase in ΔΨm (mitochondrial membrane potential). The increase in metabolic activity in 4F-treated MDMs was attenuated by etomoxir, an inhibitor of mitochondrial FA uptake. Finally, addition of the PPARγ antagonist T0070907 to 4F-treated MDMs reduced the expression of CD163 and CD36, cell-surface markers for M2 macrophages, and reduced basal and ATP-linked OCR. These results support our hypothesis that the 4F-mediated differentiation of MDMs to an anti-inflammatory phenotype is due, in part, to an increase in FA uptake and mitochondrial oxidative metabolism.

Giant plasma membrane vesicles: models for understanding membrane organization

The organization of eukaryotic membranes into functional domains continues to fascinate and puzzle cell biologists and biophysicists. The lipid raft hypothesis proposes that collective lipid interactions compartmentalize the membrane into coexisting liquid domains that are central to membrane physiology. This hypothesis has proven controversial because such structures cannot be directly visualized in live cells by light microscopy. The recent observations of liquid-liquid phase separation in biological membranes are an important validation of the raft hypothesis and enable application of the experimental toolbox of membrane physics to a biologically complex phase-separated membrane. This review addresses the role of giant plasma membrane vesicles (GPMVs) in refining the raft hypothesis and expands on the application of GPMVs as an experimental model to answer some of key outstanding problems in membrane biology.

Apolipoprotein E derived HDL mimetic peptide ATI-5261 promotes nascent HDL formation and reverse cholesterol transport in vitro

Modulation of the reverse cholesterol transport (RCT) pathway may provide a therapeutic target for the prevention and treatment of atherosclerotic cardiovascular disease (CVD). In the present study, we evaluated a novel 26-amino acid apolipoprotein mimetic peptide (ATI-5261) designed from the carboxyl terminal of apoE, in its ability to mimic apoA-I functionality in RCT in vitro. Our data shows that nascent HDL-like (nHDL) particles generated by incubating cells over-expressing ABCA1 with ATI-5261 increase the rate of specific ABCA1 dependent lipid efflux, with high affinity interactions with ABCA1. We also show that these nHDL particles interact with membrane micro-domains in a manner similar to nHDL apoA-I. These nHDL particles then interact with the ABCG1 transporter and are remodeled by plasma HDL-modulating enzymes. Finally, we show that these mature HDL-like particles are taken up by SR-BI for cholesterol delivery to liver cells. This ATI-5621-mediated process mimics apoA-I and may provide a means to prevent cholesterol accumulation in the artery wall. In this study, we propose an integrative physiology approach of HDL biogenesis with the synthetic peptide ATI-5261. These experiments provide new insights for potential therapeutic use of apolipoprotein mimetic peptides.

Proteomics of plasma membrane microdomains

Plasma membrane microdomains represent subcompartments of the plasma membrane characterized by a specific lipid and protein composition. The recognition of microdomains in nearly all the eukaryotic membranes has accredited them with specialized functions in health and disease. Several proteomic studies have recently addressed the specific composition of plasma membrane microdomains, and will be reviewed in this paper. Peculiar information has been obtained, but a comprehensive view of the main protein classes required to define the microdomain proteome is still missing. The achievement of this information is slowed by the difficulties encountered in resolving and analyzing hydrophobic proteins, but it could help in understanding the overall function of plasma membrane microdomains and their involvement in human pathology.

Regulation of pattern recognition receptors by the apolipoprotein A-I mimetic peptide 4F

OBJECTIVE

The apolipoprotein A-I (apoA-I) mimetic peptide 4F favors the differentiation of human monocytes to an anti-inflammatory phenotype and attenuates lipopolysaccharide (LPS)-induced inflammatory responses. We investigated the effects of LPS on the Toll-like receptor (TLR) signaling pathway in 4F-differentiated monocyte-derived macrophages.

METHODS AND RESULTS

Monocyte-derived macrophages were pretreated with 4F or vehicle for 7 days. 4F downregulated cell-surface TLRs (4, 5, and 6) as determined by flow cytometry. 4F attenuated the LPS-dependent upregulation of genes encoding TLR1, 2, and 6 and genes of the MyD88-dependent (CD14, MyD88, TRAF6, interleukin-1 receptor-associated kinase 4, and inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase beta) and MyD88-independent (interferon regulatory factor 3, TANK-binding kinase 1, and Toll-interleukin 1 receptor domain-containing adaptor-inducing interferon-β) pathways as determined by microarray analysis and quantitative reverse transcriptase polymerase chain reaction. Functional analyses of monocyte-derived macrophages showed that 4F reduced LPS-dependent TLR4 recycling, phosphorylation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha, activation and translocation of nuclear factor-κB and inhibited the secretion of tumor necrosis factor-α and interleukin-6 induced by LPS or lipoteichoic acid. These changes were associated with depletion of cellular cholesterol and caveolin, components of membrane lipid rafts.

CONCLUSIONS

These data suggest that disruption of rafts by 4F alters the assembly of TLR-ligand complexes in cell membranes and inhibits proinflammatory gene expression in monocyte-derived macrophages, thus attenuating the responsiveness of macrophages to LPS.

Effect of plasma membrane cholesterol depletion on glucose transport regulation in leukemia cells

GLUT1 is the predominant glucose transporter in leukemia cells, and the modulation of glucose transport activity by cytokines, oncogenes or metabolic stresses is essential for their survival and proliferation. However, the molecular mechanisms allowing to control GLUT1 trafficking and degradation are still under debate. In this study we investigated whether plasma membrane cholesterol depletion plays a role in glucose transport activity in M07e cells, a human megakaryocytic leukemia line. To this purpose, the effect of cholesterol depletion by methyl-β-cyclodextrin (MBCD) on both GLUT1 activity and trafficking was compared to that of the cytokine Stem Cell Factor (SCF). Results show that, like SCF, MBCD led to an increased glucose transport rate and caused a subcellular redistribution of GLUT1, recruiting intracellular transporter molecules to the plasma membrane. Due to the role of caveolae/lipid rafts in GLUT1 stimulation in response to many stimuli, we have also investigated the GLUT1 distribution along the fractions obtained after non ionic detergent treatment and density gradient centrifugation, which was only slightly changed upon MBCD treatment. The data suggest that MBCD exerts its action via a cholesterol-dependent mechanism that ultimately results in augmented GLUT1 translocation. Moreover, cholesterol depletion triggers GLUT1 translocation without the involvement of c-kit signalling pathway, in fact MBCD effect does not involve Akt and PLCγ phosphorylation. These data, together with the observation that the combined MBCD/SCF cell treatment caused an additive effect on glucose uptake, suggest that the action of SCF and MBCD may proceed through two distinct mechanisms, the former following a signalling pathway, and the latter possibly involving a novel cholesterol dependent mechanism.

Evidence for the presence of functional lipid rafts in immune cells of ectothermic organisms

The role of lipid rafts in non-mammalian leukocytes has been scarcely investigated. We performed biochemical and functional analysis of lipid rafts in fish leukocytes. Fish Flotillin-1 and a fish GM1-like molecule (fGM1-L) were found in low density detergent-resistant membranes (LD-DRM) in goldfish macrophages and catfish B lymphocytes, similarly to mammals. The presence of flotillin-1 and fGM1-L in LD-DRM was sensitive to increased detergent concentrations, and cholesterol extraction. Confocal microscopy analysis of flotillin-1 and fGM1-L in fish leukocytes showed a distinctive punctuated staining pattern, suggestive of pre-existing rafts. Confocal microscopy analysis of macrophages showed that the membrane of phagosomes containing serum-opsonized zymosan was enriched in fGM1-L, and zymosan phagocytosis was reduced after cholesterol extraction. The presence of flotillin-1 and fGM1-L in LD-DRM, the microscopic evidence of flotillin-1 and fGM1-L on fish macrophages and B-cells, and the sensitivity of phagocytosis to cholesterol extraction, indicate that lipid rafts are biochemically and functionally similar in leukocytes from fish and mammals.

Curvature factor and membrane solubilization, with particular reference to membrane rafts

The composition of membrane rafts (cholesterol/sphingolipid-rich domains) cannot be fully deduced from the analysis of a detergent-resistant membrane fraction after solubilization in Triton X-100 at 4°C. It is hypothesized that the membrane curvature-dependent lateral distribution of membrane components affects their solubilization. The stomatocytogenic, Triton X-100, cannot effectively solubilize membrane components, especially with regard to the outward membrane curvature.

Lipid rafts: a signalling platform linking lipoprotein metabolism to atherogenesis

Lipid rafts are microdomains of the plasma membrane which are enriched in cholesterol and sphingolipids. They serve as a platform for signal transduction, in particular during immune and inflammatory responses. As hypercholesterolemia and inflammation are two key elements of atherogenesis, it is conceivable that the cholesterol and cholesterol oxide content of lipid rafts might influence the inflammatory signalling pathways, thus modulating the development of atherosclerosis. In support of this emerging view, lipid rafts have been shown to be involved in several key steps of atherogenesis, such as the oxysterol-mediated apoptosis of vascular cells, the blunted ability of high density lipoproteins (HDL) to exert anti-inflammatory effects, and the exacerbated secretion of pro-inflammatory cytokines by immune cells. Additional studies are now required to address the relative contribution of lipid raft abnormalities to the pathophysiology of atherosclerosis and cardiovascular disease.

Replication of simulated prebiotic amphiphile vesicles controlled by experimental lipid physicochemical properties

We present a new embodiment of the graded autocatalysis replication domain (GARD) for the growth, replication and evolution of lipid vesicles based on a semi-empirical foundation using experimentally measured kinetic values of selected extant lipid species. Extensive simulations using this formalism elucidated the details of the dependence of the replication and properties of the vesicles on the physicochemical properties and concentrations of the lipids, both in the environment and in the vesicle. As expected, the overall concentration and number of amphiphilic components strongly affect average replication time. Furthermore, variations in acyl chain length and unsaturation of vesicles also influence replication rate, as do the relative concentrations of individual lipid types. Understanding of the dependence of replication rates on physicochemical parameters opens a new direction in the study of prebiotic vesicles and lays the groundwork for future studies involving the competition between lipid vesicles for available amphiphilic monomers.

Fatty acid and peptide profiles in plasma membrane and membrane rafts of PUFA supplemented RAW264.7 macrophages

The eukaryotic cell membrane possesses numerous complex functions, which are essential for life. At this, the composition and the structure of the lipid bilayer are of particular importance. Polyunsaturated fatty acids may modulate the physical properties of biological membranes via alteration of membrane lipid composition affecting numerous physiological processes, e.g. in the immune system. In this systematic study we present fatty acid and peptide profiles of cell membrane and membrane rafts of murine macrophages that have been supplemented with saturated fatty acids as well as PUFAs from the n-3, the n-6 and the n-9 family. Using fatty acid composition analysis and mass spectrometry-based peptidome profiling we found that PUFAs from both the n-3 and the n-6 family have an impact on lipid and protein composition of plasma membrane and membrane rafts in a similar manner. In addition, we found a relation between the number of bis-allyl-methylene positions of the PUFA added and the unsaturation index of plasma membrane as well as membrane rafts of supplemented cells. With regard to the proposed significance of lipid microdomains for disease development and treatment our study will help to achieve a targeted dietary modulation of immune cell lipid bilayers.

Membrane microdomains modulate oligomeric ABCA1 function: impact on apoAI-mediated lipid removal and phosphatidylcholine biosynthesis

Recent studies have identified an ABCA1-dependent, phosphatidylcholine-rich microdomain, called the "high-capacity binding site" (HCBS), that binds apoA-I and plays a pivotal role in apoA-I lipidation. Here, using sucrose gradient fractionation, we obtained evidence that both ABCA1 and [¹²⁵I]apoA-I associated with the HCBS were found localized to nonraft microdomains. Interestingly, phosphatidylcholine (PtdCho) was selectively removed from nonraft domains by apoA-I, whereas sphingomyelin and cholesterol were desorbed from both detergent-resistant membranes and nonraft domains. The modulatory role of cholesterol on apoA-I binding to ABCA1/HCBS was also examined. Loading cells with cholesterol resulted in a drastic reduction in apoA-I binding. Conversely, depletion of membrane cholesterol by methyl-β-cyclodextrin treatment resulted in a significant increase in apoA-I binding. Finally, we obtained evidence that apoA-I interaction with ABCA1 promoted the activation and gene expression of key enzymes in the PtdCho biosynthesis pathway. Taken together, these results provide strong evidence that the partitioning of ABCA1/HCBS to nonraft domains plays a pivotal role in the selective desorption of PtdCho molecules by apoA-I, allowing an optimal environment for cholesterol release and regeneration of the PtdCho-containing HCBS. This process may have important implications in preventing and treating atherosclerotic cardiovascular disease.

Caveolin-1-mediated apolipoprotein A-I membrane binding sites are not required for cholesterol efflux

Caveolin-1 (Cav1), a structural protein required for the formation of invaginated membrane domains known as caveolae, has been implicated in cholesterol trafficking and homeostasis. Here we investigated the contribution of Cav1 to apolipoprotein A-I (apoA-I) cell surface binding and intracellular processing using mouse embryonic fibroblasts (MEFs) derived from wild type (WT) or Cav1-deficient (Cav1(-/-)) animals. We found that cells expressing Cav1 have 2.6-fold more apoA-I binding sites than Cav1(-/-) cells although these additional binding sites are not associated with detergent-free lipid rafts. Further, Cav1-mediated binding targets apoA-I for internalization and degradation and these processes are not correlated to cholesterol efflux. Despite lower apoA-I binding, cholesterol efflux from Cav1(-/-) MEFs is 1.7-fold higher than from WT MEFs. Stimulation of ABCA1 expression with an LXR agonist enhances cholesterol efflux from both WT and Cav1(-/-) cells without increasing apoA-I surface binding or affecting apoA-I processing. Our results indicate that there are at least two independent lipid binding sites for apoA-I; Cav1-mediated apoA-I surface binding and uptake is not linked to cholesterol efflux, indicating that membrane domains other than caveolae regulate ABCA1-mediated cholesterol efflux.

Lipid rafts and cytoskeletal proteins in placental microvilli membranes from preeclamptic and IUGR pregnancies

Intrauterine growth restriction (IUGR) and preeclampsia (PE) are leading causes of perinatal and maternal morbidity and mortality. Previously we reported the expression of lipid rafts in classical microvillous membrane (MVM) and light microvillous membrane (LMVM), two subdomains in apical membrane from the human placental syncytiotrophoblast (hSTB), which constitute the epithelium responsible for maternal-fetal transport. Here the aim was to study the raft and cytoskeletal proteins from PE and IUGR. Microdomains from MVM and LMVM were tested with raft markers (placental alkaline phosphatase, lipid ganglioside, and annexin 2) and a nonraft marker (hTf-R). No changes were detected with those markers in whole purified apical membranes in normal, PE, and IUGR pregnancies; however, their patterns of distribution in lipid rafts were different in PE and IUGR. Cholesterol depletion modified their segregation, confirming their presence in lipid rafts, although unlike normal placenta, in these pathologies there is only one type of microdomain. Additionally, the cytoskeleton proteins actin, ezrin, and cytokeratin-7 showed clear differences between normal and pathological membranes. Cytokeratin-7 expression decreased to 50% in PE, and the distribution between LMVM and MVM (~43 and 57%, respectively) changed in both PE and IUGR, in contrast with the asymmetrical enrichment obtained in normal LMVM (~62%). In conclusion, lipid rafts from IUGR and PE have different features compared to rafts from normal placentae, and this is associated with alterations in the expression and distribution of cytoskeletal proteins.

A potent sphingomyelinase inhibitor from Cordyceps mycelia contributes its cytoprotective effect against oxidative stress in macrophages

A novel water-soluble polysaccharide fraction, CME-1, with a molecular mass of 27.6 kDa and containing mannose and galactose in a respective ratio of 4:6, was prepared from Cordyceps sinensis mycelia and identified by NMR and GC-MS. In the current study, we examined whether CME-1 has anti-inflammatory effects in RAW264.7 cells. The ability of CME-1 to inhibit H(2)O(2)-induced cell death in RAW264.7 cells was assessed by using an MTT assay and annexin V/propidium iodide double staining; we found that CME-1 protected cells against H(2)O(2)-induced injury. H(2)O(2)-induced intracellular oxidative stress and mitochondrial membrane depolarization were also diminished with CME-1 treatment. We evaluated the hydroxyl radical scavenging ability of CME-1 by using the DMPO-electron spin resonance technique, which indicated that CME-1 acts as an intracellular antioxidant in a concentration-dependent manner through a mechanism other than its scavenging activity. Activities of both neutral and acid sphingomyelinases (SMases) were assessed in vitro, and results showed that the CME-1 inhibited activities of both neutral and acid SMases in a concentration-dependent manner. CME-1 reduced H(2)O(2) treatment-elevated C16- and C18-ceramide levels measured by LC/MS/MS in RAW264.7 cells. Results suggest that CME-1 protects RAW264.7 cells against oxidative stress through inhibition of SMase activity and reduction of C16- and C18-ceramide levels.

Echinophilic proteins stomatin, sorcin, and synexin locate outside gangliosideM1 (GM1) patches in the erythrocyte membrane

The detergent (Triton X-100, 4°C)-resistant membrane (DRM)-associated membrane proteins stomatin, sorcin, and synexin (anexin VII) exposed on the cytoplasmic side of membrane were investigated for their lateral distribution in relation to induced ganglioside(M1) (GM1) raft patches in flat (discocytic) and curved (echinocytic) human erythrocyte membrane. In discocytes, no accumulation of stomatin, sorcin, and synexin in cholera toxin subunit B (CTB) plus anti-CTB-induced GM1 patches was detected by fluorescence microscopy. In echinocytes, stomatin, sorcin, and synexin showed a similar curvature-dependent lateral distribution as GM1 patches by accumulating to spiculae induced by ionophore A23187 plus calcium. Stomatin was partly and synexin and sorcin were fully recruited to the spiculae. However, the DRM-associated proteins only partially co-localized with GM1 and were frequently distributed into different spiculae than GM1. The study indicates that stomatin, sorcin, and synexin are echinophilic membrane components that mainly locate outside GM1 rafts in the human erythrocyte membrane. Echinophilicity is suggested to contribute to the DRM association of a membrane component in general.