How cytoskeletal impairment in hereditary elliptocytosis and spherocytosis affects erythrocyte membrane composition, organization and deformation

Erythrocytes have a remarkable ability to deform. This deformability depends on a dynamic cytoskeleton but also on surface lipid domains involved in membrane deformation and calcium exchanges. In this work, we investigated whether and how lipid domains are altered and contribute to the pathophysiology of hereditary elliptocytosis and spherocytosis, two erythrocytes diseases caused by cytoskeletal defects. Our results show impairment of the abundance, properties and functionality of the domains involved in calcium exchange. Depending on the disease and its severity, those alterations are accompanied by an overactivation of the plasmatic acid sphingomyelinase, an increase in the intracellular calcium content and an activation of downstream signaling pathways, resulting into impaired membrane asymmetry and increased oxidative stress. This study paves the way towards a better understanding of the molecular mechanisms behind both diseases and opens new perspectives for treatment.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201

Les biais attentionnels envers l’alcool chez les « petits consommateurs » vs « gros consommateurs » dans un environnement virtuel

Introduction : Les personnes dépendantes à l'alcool montrent des biais attentionnels quand elles sont confrontées à des indices liés à l’alcool (Kreusch, Vilenne, & Quertemont, 2013). D’après le modèle de Wiers et al. (2007), les biais attentionnels favoriseraient la consommation répétée de substances. Objectif : Cette étude exploratoire évalue dans quelle mesure la réalité virtuelle fournit un environnement permettant de tester ces biais attentionnels. Hypothèse : Les gros consommateurs d'alcool présentent des biais attentionnels plus fréquents et plus intenses que les petits consommateurs. Méthode : Un questionnaire en ligne permettant de recruter 24 petits et 24 gros consommateurs d’alcool a d’abord été administré afin de présélectionner les sujets. Les participants ont ensuite réalisé une tâche d’immersion dans un environnement virtuel de « bar ». Le nombre de zooms effectués sur les stimuli « bières » et le nombre de commentaires rapportés en lien avec l’alcool étaient mesurés. Directement après l’immersion, la Visual Analogue Craving Scale (VAS) leur était administrée afin d’évaluer leur envie de boire. Résultats : Les « gros consommateurs » présentent davantage de zooms sur les stimuli « bières » que les «petits consommateurs». De plus, les « gros consommateurs » présentent un score plus élevé à la VAS que les «petits consommateurs », ce qui témoignerait d’une envie de consommer plus élevée après l’immersion par rapport aux « petits consommateurs ». Cependant, aucune corrélation significative n’a été mise en avant entre le nombre de zooms effectués et le score à la VAS chez les « gros consommateurs ». Conclusion : En accord avec nos hypothèses, nos résultats ont montré que les gros consommateurs présentent davantage de biais attentionnels envers les stimuli liés à l’alcool que les petits consommateurs ». Cependant, de futures recherches sont nécessaires afin de pouvoir confirmer que la réalité virtuelle fournit un environnement qui permet de tester les biais attentionnels

Recent progress on lipid lateral heterogeneity in plasma membranes: From rafts to submicrometric domains.

The concept of transient nanometric domains known as lipid rafts has brought interest to reassess the validity of the Singer-Nicholson model of a fluid bilayer for cell membranes. However, this new view is still insufficient to explain the cellular control of surface lipid diversity or membrane deformability. During the past decade, the hypothesis that some lipids form large (submicrometric/mesoscale vs nanometric rafts) and stable (>min vs s) membrane domains has emerged, largely based on indirect methods. Morphological evidence for stable submicrometric lipid domains, well-accepted for artificial and highly specialized biological membranes, was further reported for a variety of living cells from prokaryotes to yeast and mammalian cells. However, results remained questioned based on limitations of available fluorescent tools, use of poor lipid fixatives, and imaging artifacts due to non-resolved membrane projections. In this review, we will discuss recent evidence generated using powerful and innovative approaches such as lipid-specific toxin fragments that support the existence of submicrometric domains. We will integrate documented mechanisms involved in the formation and maintenance of these domains, and provide a perspective on their relevance on membrane deformability and regulation of membrane protein distribution

Tuning of differential lipid order between submicrometric domains and surrounding membrane upon erythrocyte reshaping

BACKGROUND/AIMS: Transient nanometric cholesterol- and sphingolipid-enriched domains, called rafts, are characterized by higher lipid order as compared to surrounding lipids. Here, we asked whether the seminal concept of highly ordered rafts could be refined with the presence of lipid domains exhibiting different enrichment in cholesterol and sphingomyelin and association with erythrocyte curvature areas. We also investigated how differences in lipid order between domains and surrounding membrane (bulk) are regulated and whether changes in order differences could participate to erythrocyte deformation and vesiculation. METHODS: We used the fluorescent hydration- and membrane packing-sensitive probe Laurdan to determine by imaging mode the Generalized Polarization (GP) values of lipid domains vs the surrounding membrane. RESULTS: Laurdan revealed the majority of sphingomyelin-enriched domains associated to low erythrocyte curvature areas and part of the cholesterol-enriched domains associated with high curvature. Both lipid domains were less ordered than the surrounding lipids in erythrocytes at resting state. Upon erythrocyte deformation (elliptocytes and stimulation of calcium exchanges) or membrane vesiculation (storage at 4°C), lipid domains became more ordered than the bulk. Upon aging and in membrane fragility diseases (spherocytosis), an increase in the difference of lipid order between domains and the surrounding lipids contributed to the initiation of domain vesiculation. CONCLUSION: The critical role of domain-bulk differential lipid order modulation for erythrocyte reshaping is discussed in relation with the pressure exerted by the cytoskeleton on the membrane

Spatial Relationship and Functional Relevance of Three Lipid Domain Populations at the Erythrocyte Surface.

BACKGROUND/AIMS: Red blood cells (RBC) have been shown to exhibit stable submicrometric lipid domains enriched in cholesterol (chol), sphingomyelin (SM), phosphatidylcholine (PC) or ganglioside GM1, which represent the four main lipid classes of their outer plasma membrane leaflet. However, whether those lipid domains co-exist at the RBC surface or are spatially related and whether and how they are subjected to reorganization upon RBC deformation are not known. METHODS: Using fluorescence and/or confocal microscopy and well-validated probes, we compared these four lipid-enriched domains for their abundance, curvature association, lipid order, temperature dependence, spatial dissociation and sensitivity to RBC mechanical stimulation. RESULTS: Our data suggest that three populations of lipid domains with decreasing abundance coexist at the RBC surface: (i) chol-enriched ones, associated with RBC high curvature areas; (ii) GM1/PC/chol-enriched ones, present in low curvature areas; and (iii) SM/PC/chol-enriched ones, also found in low curvature areas. Whereas chol-enriched domains gather in increased curvature areas upon RBC deformation, low curvature-associated lipid domains increase in abundance either upon calcium influx during RBC deformation (GM1/PC/chol-enriched domains) or upon secondary calcium efflux during RBC shape restoration (SM/PC/chol-enriched domains). Hence, abrogation of these two domain populations is accompanied by a strong impairment of the intracellular calcium balance. CONCLUSION: Lipid domains could contribute to calcium influx and efflux by controlling the membrane distribution and/or the activity of the mechano-activated ion channel Piezo1 and the calcium pump PMCA. Whether this results from lipid domain biophysical properties, the strength of their anchorage to the underlying cytoskeleton and/or their correspondence with inner plasma membrane leaflet lipids remains to be demonstrated