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Lipid rafts are assumed to undergo biologically important size-modulations from nanorafts to microrafts. Due to the complexity of cellular membranes, model systems become important tools, especially for the investigation of the factors affecting "raft-like" Lo domain size and the search for Lo nanodomains as precursors in Lo microdomain formation. Because lipid compositional change is the primary mechanism by which a cell can alter membrane phase behavior, we studied the effect of the ganglioside GM1 concentration on the Lo/Ld lateral phase separation in PC/SM/Chol/GM1 bilayers. GM1 above 1mol % abolishes the formation of the micrometer-scale Lo domains observed in GUVs. However, the apparently homogeneous phase observed in optical microscopy corresponds in fact, within a certain temperature range, to a Lo/Ld lateral phase separation taking place below the optical resolution. This nanoscale phase separation is revealed by fluorescence spectroscopy, including C12NBD-PC self-quenching and Laurdan GP measurements, and is supported by Gaussian spectral decomposition analysis. The temperature of formation of nanoscale Lo phase domains over an Ld phase is determined, and is shifted to higher values when the GM1 content increases. A "morphological" phase diagram could be made, and it displays three regions corresponding respectively to Lo/Ld micrometric phase separation, Lo/Ld nanometric phase separation, and a homogeneous Ld phase. We therefore show that a lipid only-based mechanism is able to control the existence and the sizes of phase-separated membrane domains. GM1 could act on the line tension, "arresting" domain growth and thereby stabilizing Lo nanodomains., (Copyright © 2014 Elsevier B.V. All rights reserved.)

KV10.1 potassium channels are implicated in a variety of cellular processes including cell proliferation and tumour progression. Their expression in over 70% of human tumours makes them an attractive diagnostic and therapeutic target. Although their physiological role in the central nervous system is not yet fully understood, advances in their precise cell localization will contribute to the understanding of their interactions and function. We have determined the plasma membrane (PM) distribution of the KV10.1 protein in an enriched mouse brain PM fraction and its association with cholesterol- and sphingolipid-rich domains. We show that the KV10.1 channel has two different populations in a 3:2 ratio, one associated to and another excluded from Detergent Resistant Membranes (DRMs). This distribution of KV10.1 in isolated PM is cholesterol- and cytoskeleton-dependent since alteration of those factors changes the relationship to 1:4. In transfected HEK-293 cells with a mutant unable to bind Ca(2+)/CaM to KV10.1 protein, Kv10.1 distribution in DRM/non-DRM is 1:4. Mean current density was doubled in the cholesterol-depleted cells, without any noticeable effects on other parameters. These results demonstrate that recruitment of the KV10.1 channel to the DRM fractions involves its functional regulation., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Objectives: This study aimed to evaluate the agreement between blood spot and plasma chitotriosidase using the economic substrate 4-methylumbelliferyl-β-D-N,N',N"-triacetylchitotrioside, and to investigate the utility of the blood spot assay for the wide scale screening for lysosomal storage disorders among the clinically suspected., Design and Methods: Blinded blood spot samples were compared with the corresponding plasma levels in 199 children (56 with confirmed diagnoses of ten different lysosomal storage disorders, 73 normal controls and 70 pathological controls). Several performance criteria (limit of detection, linearity, within-run and day-to-day precision and sample stability) were also evaluated., Results: Plasma assay performed better by most criteria; however, blood spot performance was quite satisfactory. Quantitative values of the two methods can't be used interchangeably based on their 95% limits of agreement. Diagnostic sensitivity and specificity derived from ROC curves were 75.0 and 85.3% for the plasma assay and 71.4 and 79.0% for the blood spot assay, respectively. Cohen's kappa was 0.72 (95% CI: 0.616-0.821) denoting a good categorical agreement between the two methods., Conclusion: The clinical use of blood spot chitotriosidase for the screening of lysosomal storage disorders can be quite practical, provided proper cut-off values are determined for each lab., (© 2013.)

This work aims at elucidating the relation between morphological and physicochemical properties of different ataxin-3 (ATX3) aggregates and their cytotoxicity. We investigated a non-pathological ATX3 form (ATX3Q24), a pathological expanded form (ATX3Q55), and an ATX3 variant truncated at residue 291 lacking the polyQ expansion (ATX3/291Δ). Solubility, morphology and hydrophobic exposure of oligomeric aggregates were characterized. Then we monitored the changes in the intracellular Ca(2+) levels and the abnormal Ca(2+) signaling resulting from aggregate interaction with cultured rat cerebellar granule cells. ATX3Q55, ATX3/291Δ and, to a lesser extent, ATX3Q24 oligomers displayed similar morphological and physicochemical features and induced qualitatively comparable time-dependent intracellular Ca(2+) responses. However, only the pre-fibrillar aggregates of expanded ATX3 (the only variant which forms bundles of mature fibrils) triggered a characteristic Ca(2+) response at a later stage that correlated with a larger hydrophobic exposure relative to the two other variants. Cell interaction with early oligomers involved glutamatergic receptors, voltage-gated channels and monosialotetrahexosylganglioside (GM1)-rich membrane domains, whereas cell interaction with more aged ATX3Q55 pre-fibrillar aggregates resulted in membrane disassembly by a mechanism involving only GM1-rich areas. Exposure to ATX3Q55 and ATX3/291Δ aggregates resulted in cell apoptosis, while ATX3Q24 was substantially innocuous. Our findings provide insight into the mechanisms of ATX3 aggregation, aggregate cytotoxicity and calcium level modifications in exposed cerebellar cells., (© 2013.)

Cellular functions are usually associated with the activity of proteins and nucleic acids. Recent studies have shown that lipids modulate the localization and activity of key membrane-associated signal transduction proteins, thus regulating the cell's physiology. Membrane Lipid Therapy aims to reverse cell dysfunctions (i.e., diseases) by modulating the activity of membrane signaling proteins through regulation of the lipid bilayer structure. The present work shows the ability of a series of 2-hydroxyfatty acid (2OHFA) derivatives, varying in the acyl chain length and degree of unsaturation, to regulate the membrane lipid structure. These molecules have shown greater therapeutic potential than their natural non-hydroxylated counterparts. We demonstrated that both 2OHFA and natural FAs induced reorganization of lipid domains in model membranes of POPC:SM:PE:Cho, modulating the liquid-ordered/liquid-disordered structures ratio and the microdomain lipid composition. Fluorescence spectroscopy, confocal microscopy, Fourier transform infrared spectroscopy and differential detergent solubilization experiments showed a destabilization of the membranes upon addition of the 2OHFAs and FAs which correlated with the observed disordering effect. The changes produced by these synthetic fatty acids on the lipid structure may constitute part of their mechanism of action, leading to changes in the localization/activity of membrane proteins involved in signaling cascades, and therefore modulating cell responses., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Lysosomes are membrane-enclosed organelles containing acid hydrolases. They mediate a variety of physiological processes, such as cellular clearance, lipid homeostasis, energy metabolism and pathogen defence. Lysosomes can secrete their content through a process called lysosome exocytosis in which lysosomes fuse with the plasma membrane realising their content into the extracellular milieu. Lysosomal exocytosis is not only responsible for the secretion of lysosomal enzymes, but it also has a crucial role in the plasma membrane repair. Recently, it has been demonstrated that lysosome response to the physiologic signals is regulated by the transcription factor EB (TFEB). In particular, lysosomal secretion is transcriptionally regulated by TFEB which induces both the docking and fusion of lysosomes with the plasma membrane. In this work we demonstrated that TFEB nuclear translocation is accompanied by an increase of mature glycohydrolases β-hexosaminidase and β-galactosidase on cell surface. This evidence contributes to elucidate an unknown TFEB biological function leading the lysosomal glycohydrolases on plasma membrane., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Previously, we demonstrated that eicosapentaenoic acid enhanced ethanol-induced oxidative stress and cell death in primary rat hepatocytes via an increase in membrane fluidity and lipid raft clustering. In this context, another n-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA), was tested with a special emphasis on physical and chemical alteration of lipid rafts. Pretreatment of hepatocytes with DHA reduced significantly ethanol-induced oxidative stress and cell death. DHA protection could be related to an alteration of lipid rafts. Indeed, rafts exhibited a marked increase in membrane fluidity and packing defects leading to the exclusion of a raft protein marker, flotillin. Furthermore, DHA strongly inhibited disulfide bridge formation, even in control cells, thus suggesting a disruption of protein-protein interactions inside lipid rafts. This particular spatial organization of lipid rafts due to DHA subsequently prevented the ethanol-induced lipid raft clustering. Such a prevention was then responsible for the inhibition of phospholipase C-γ translocation into rafts, and consequently of both lysosome accumulation and elevation in cellular low-molecular-weight iron content, a prooxidant factor. In total, the present study suggests that DHA supplementation could represent a new preventive approach for patients with alcoholic liver disease based upon modulation of the membrane structures., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Enterotoxigenic Escherichia coli (ETEC) is a significant source of morbidity and mortality worldwide. One major virulence factor released by ETEC is the heat-labile enterotoxin LT, which is structurally and functionally similar to cholera toxin. LT consists of five B subunits carrying a single catalytically active A subunit. LTB binds the monosialoganglioside G(M1), the toxin's host receptor, but interactions with A-type blood sugars and E. coli lipopolysaccharide have also been identified within the past decade. Here, we review the regulation, assembly, and binding properties of the LT B-subunit pentamer and discuss the possible roles of its numerous molecular interactions.

The plasma membrane of mammalian cells is composed of a great variety of different lipids which are laterally organized into lipid domains. The segregation of lipids into domains has been studied in great detail in vesicles but domain formation of lipids in the plasma membrane of live cells is still unclear. We have previously used fluorescence lifetime imaging microscopy to study the colocalization of the receptor for EGF with the ganglioside GM1 and the GPI-anchored green fluorescent protein. Here we have used this technology to study the effect of EGF on the organization of GM1 in the plasma membrane. Our data show that stimulation of the cell with EGF induces rapidly a strong increase in colocalization of GM1 molecules, suggesting the formation of large lipid domains. These results support the notion that activation of EGFR signaling may result in the formation of signaling platforms.

A frozen section technique for frog oocytes was developed without using any organic solvent. It was applied to examine the distribution of acidic glycosphingolipids (ganglioside GM1 and sulfatide) in Xenopus oocytes, eggs and embryos by indirect immunofluorescence microscopy with specific monoclonal antibodies against the acidic glycolipids. Although glycolipids are generally present on the cell surface, GM1 and sulfatide were distributed in the cytoplasm of animal and vegetal hemispheres, respectively, of the fully grown oocytes and oviposited and fertilized eggs. In blastula, GM1 was present on the cell boundaries and in the Golgi of the blastomeres of animal hemisphere and marginal zone, whereas the staining of the outermost layer of animal blastomeres became faint or negligible at stage 9. Sulfatide in blastula was still observed in vegetal blastomeres. In gastrula, GM1 was distributed in the inner layer of ectoderm and the involuting mesoderm. In neurula, GM1 was concentrated in the dorsal midline including the closing neural tube, notochord and somites, while sulfatide was present in endoderm. The unique distribution of GM1 and sulfatide in oocytes, eggs and early embryos may help to elucidate one aspect of the biochemical bases laid on the animal-vegetal polarity.