Submicrometric Lipid Domains Play Key Roles in Erythrocyte Deformation: From Membrane Bending to Shape Restoration

Abstract

Although direct evidence for lipid domains in living plasma membranes have been recently provided, their existence is still up for debate as their functions remain unclear. Vital imaging of the smooth erythrocyte plasma membrane allowed us to highlight two distinct populations of submicrometric domains with differential cholesterol and sphingomyelin enrichment. We here report direct evidence for the implication of these two domains in key steps of erythrocyte deformation, combining erythrocyte models exhibiting differential membrane curvature (healthy erythrocytes vs erythrocytes from patients with elliptocytosis and spherocytosis, two erythrocyte membrane fragility diseases), (de)stretching biophysical experiments and the decoration of endogenous cholesterol and sphingomyelin by specific fluorescent toxin fragments. Whereas cholesterol-enriched domains were implicated in the generation/maintenance of high membrane curvature areas needed for membrane bending, sphingomyelin-enriched domains were involved in calcium efflux during erythrocyte shape restoration. Our results indicate that cholesterol- and sphingomyelin-enriched domains play distinct key roles in erythrocyte deformation, as confirmed by the specific domain loss upon erythrocyte aging and erythrocyte deformability impairment upon domain abrogation by pharmacological approaches. Thus, whereas cholesterol- and sphingomyelin-enriched domains were so far highly associated, our findings give direct evidence for differential biophysical properties but also distinct physiopathological roles: (i) membrane bending modulators and/or stabilizers (cholesterol-enriched domains), (ii) platforms for protein sorting and/or activation (e.g. calcium efflux pump; sphingomyelin-enriched domains), and (iii) preferential fragility sites for membrane vesiculation (both domains).