Leonard Catherine, Pollet Hélène, Vermylen Christiane, Gov Nir, Tyteca Donatienne, Mingeot-Leclercq Marie-Paule
FACM Unit, Louvain Drug Research Institute & Université Catholique de Louvain, Brussels, Belgium.
CELL Unit, de Duve Institute & Université Catholique de Louvain, Brussels, Belgium.
Cell Physiol Biochem. 2018;48(6):2563-2582. doi: 10.1159/000492700. Epub 2018 Aug 17.
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.
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.
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.
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.
背景/目的：短暂存在的富含胆固醇和鞘脂的纳米级结构域，即脂筏，其特征是与周围脂质相比具有更高的脂质有序性。在此，我们探讨了高度有序脂筏这一开创性概念是否可通过存在胆固醇和鞘磷脂富集程度不同且与红细胞曲率区域相关的脂质结构域来进一步完善。我们还研究了结构域与周围膜（主体）之间脂质有序性差异是如何调控的，以及有序性差异的变化是否参与红细胞变形和囊泡化过程。
我们使用对水合作用和膜堆积敏感的荧光探针劳丹，通过成像模式测定脂质结构域与周围膜的广义极化（GP）值。
劳丹显示，大多数富含鞘磷脂的结构域与红细胞低曲率区域相关，部分富含胆固醇的结构域与高曲率区域相关。在静息状态下，红细胞中的这两种脂质结构域的有序性均低于周围脂质。在红细胞变形（椭圆形红细胞和钙交换刺激）或膜囊泡化（4℃储存）时，脂质结构域的有序性变得高于主体。在衰老过程以及膜脆性疾病（球形红细胞增多症）中，结构域与周围脂质之间脂质有序性差异的增加促成了结构域囊泡化的起始。
结合细胞骨架对膜施加的压力，讨论了结构域 - 主体脂质有序性差异调节对红细胞重塑的关键作用。
