Red cell membrane remodeling in sickle cell anemia. Sequestration of membrane lipids and proteins in Heinz bodies.
In red cells from patients with sickle cell anemia, hemoglobin S denatures and forms Heinz bodies. Binding of Heinz bodies to the inner surface of the sickle cell membrane promotes clustering and colocalization of the membrane protein band 3, outer surface-bound autologous IgG and, to some extent, the membrane proteins glycophorin and ankyrin. Loss of transbilayer lipid asymmetry is also found in certain populations of sickle red cells. The lateral distribution of sickle cell membrane lipids has not been examined, however. In this report, we examine by fluorescence microscopy the incorporation and distribution of the fluorescent phospholipid analogues 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD)-phosphatidylserine and NBD-phosphatidylcholine in sickle red cells. Both phospholipid analogues are observed to accumulate prominently at sites of Heinz bodies. Accumulation at sites of Heinz bodies is also shown by 1,'1-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate, a fluorescent lipid analogue that readily crosses membranes, but not by fluorescein-phosphatidylethanolamine, an analogue that is localized to the outer leaflet of the membrane. Double labeling and confocal microscopy techniques show that NBD-lipids, band 3 protein, protein 4.1, ankyrin, and spectrin are all sequestered within sickle red cells and colocalized at sites of Heinz bodies. We propose that Heinz bodies provide a hydrophobic surface on which sickle red cell membrane lipids and proteins are sequestered.