title: Distribution and shedding of the membrane phosphatidylserine during maturation and aging of erythroid cells.
abstract: Maturation and aging of erythroid cells are accompanied by extensive remodeling of the membrane and a marked decrease in cell size, processes that are mediated by externalization and shedding of phosphatidylserine (PS). In the present study, we investigated the redistribution of PS in the plasma membrane of erythroid precursors during their maturation and of mature RBCs during senescence, and the involvement of changes in calcium (Ca)-flux in these processes. Maturation was studied by analyzing normal human bone marrow cells as well as cultured human normal erythroid precursors induced by erythropoietin and murine erythroleukemia cells induced by hexamethylene-bisacetamide. Senescence was studied in normal human peripheral RBCs following density fractionation. PS and Ca were determined by flow cytometry using annexin-V and Flu-3, respectively. The outer, inner and shed PS were quantified by a novel two-step binding inhibitory assay. The results indicate a bi-phasic modulation of intracellular Ca and PS externalization/shedding; both of which decreased during maturation and increased during aging. The role of intracellular Ca in PS externalization/shedding was demonstrated by modulating intracellular Ca: Ca was decreased by incubating the cells with an ion chelator (EDTA) or with decreasing concentrations of Ca, whereas treatment with the ionophore A23187 elevated intracellular Ca. The results showed that low Ca resulted in decreased outer and shed PS, whereas high Ca had the opposite effect. The results suggest that PS externalization and shedding are mediated by increased cellular Ca-flux, and that they play an important role in erythroid maturation and RBC senescence.
authors.affiliation: Institute of Drug Research, School of Pharmacy, Department of Hematology, Hadassah-Hebrew University Medical Center, Hebrew University of Jerusalem, Jerusalem, 91120, Israel.
authors.forename: Inna
authors.initials: I
authors.lastname: Freikman
authors.forename: Eitan
authors.initials: E
authors.lastname: Fibach
mesh_terms: D000818:Animals; D016922:Cellular Senescence; D041905:Erythroid Cells / Q000166:cytology*; D005434:Flow Cytometry; D006801:Humans; D008563:Membrane Lipids / Q000378:metabolism*; D051379:Mice; D010718:Phosphatidylserines / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D008563:Membrane Lipids; D010718:Phosphatidylserines