Re-evaluation of the structural integrity of red-cell glycoproteins during aging in vivo and nutrient deprivation

On the association of lipid rafts to the spectrin skeleton in human erythrocytes

Lipid rafts are local inhomogeneities in the composition of the plasma membrane of living cells, that are enriched in sphingolipids and cholesterol in a liquid-ordered state, and proteins involved in receptor-mediated signalling. Interactions between lipid rafts and the cytoskeleton have been observed in various cell types. They are isolated as a fraction of the plasma membrane that resists solubilization by nonionic detergents at 4°C (detergent-resistant membranes, DRMs). We have previously described that DRMs are anchored to the spectrin-based membrane skeleton in human erythrocytes and can be released by increasing the pH and ionic strength of the solubilization medium with sodium carbonate. It was unexplained why this carbonate treatment was necessary and why this requirement was not reported by other workers in this area. We show here that when contaminating leukocytes are present in erythrocyte preparations that are subjected to detergent treatment, the isolation of DRMs can occur without the requirement for carbonate treatment. This is due to the uncontrolled breakdown of erythrocyte membrane components by hydrolases that are released from contaminating neutrophils that lead to proteolytic disruption of the supramolecular assembly of the membrane skeleton. Results presented here corroborate the concept that DRMs are anchored to the membrane skeleton through electrostatic interactions that most likely involve the spectrin molecule.

Oxidation state of glutathione and membrane proteins in human red cells of different age

In this study the oxidation state of glutathione and membrane proteins was analyzed in red cells of different age in basal conditions. Red cells of different age were prepared by centrifugation and separated according to their density by two procedures: on self-forming gradients of autologous plasma (Murphy's procedure) and on discontinuous Stractan gradients. The efficiency of the two procedures in the isolation of senescent cells was compared. The results indicate that, despite the evidence that total cell GSH decreases with aging, its concentration, evaluated in the cell preparations of different ages, remains constant throughout the red cell life, when correlated with cell water content. Glutathione disulfide concentration increases with aging. The oxidation state of membrane proteins does not seem to change during the red cell life span.

Role of spleen in hereditary spherocytosis: evidence for increased in vitro proteolysis of red cell membrane

In vitro proteolysis of red cell membranes has been studied by means of electrophoretic separation on SDS-polyacrylamide gel of solubilized ghost proteins and subsequent densitometry of separated, stained bands; the amounts of major membrane proteins were measured in ghosts either with inhibited or with allowed proteolysis in the following cases: 15 patients suffering from hereditary spherocytosis (HS) with variable degree of spleen enlargement, eight cirrhotic patients with spleen enlargement and 12 healthy blood donors as control group. Proteolysis was present to a greater extent in HS patients with larger splenomegaly, lesser in HS with smaller splenomegaly, and was comparable to healthy controls both in splenectomized HS and in patients with spleen enlargement due to liver cirrhosis. The results suggest the involvement of splenomegaly in the enhancement of in vitro proteolysis in HS red cell membrane; it is probably attributable to joint effects of the damage induced in red cells by prolonged retention within haemolysing spleen together with the abnormalities genetically affecting the structure of HS red cell membrane.

Evidence for membrane protein oxidation during in vivo aging of human erythrocytes

Oxidative lesions to membrane proteins were studied in human erythrocytes of different age and were evaluated on ghost membrane preparations by assaying thiol and methionine sulphoxide groups, and in situ on intact cells, after treating erythrocytes with the fluorochrome N-(7-dimethyl-amino-4-methyl-coumarinyl) maleimide (DACM). DACM reacts with thiol groups and the amount of this reagent bound by membrane proteins was quantified after SDS-PAGE separation. Results obtained show that during aging of normal cells the oxidative state of membrane proteins increases: this was better shown by the assay of methionine sulphoxide residues rather than by the thiol titration, when studies were carried out on ghost membranes. After separation of individual membrane proteins by SDS-PAGE, decreased accessibility of DACM to thiol groups of band 3 and of the main proteins of the membrane skeleton was evident in senescent erythrocytes. These results show that during aging, band 3 and membrane skeleton proteins undergo conformational changes and/or oxidation. Similar results were obtained when thiol distribution was studied in membrane proteins separated by SDS-PAGE in both reducing and non-reducing conditions.

Erythrocyte endogenous proteinase activity during blood bank storage

We studied proteolytic alterations of membrane proteins in ghosts derived from human red blood cells, preserved up to 35 days in the liquid state either as whole blood or with additive solution. The study was carried out by performing sodium dodecyl sulfate polyacrylamide gel electrophoresis of stromal proteins from erythrocytes, either previously treated with proteinase inhibitors or previously incubated in conditions promoting proteolysis. To differentiate the effect of erythrocyte from granulocyte proteinases, the investigation was also carried out in leukocyte-free red cell preparations. The results show: (1) the effects of endogenous proteinases on membrane proteins derived from red cells stored under blood bank conditions; (2) a decrease of proteolytic effects in ghosts derived from red cells which have been submitted to a longer storage; (3) a relevant influence of the red cell resuspending medium before lysis on the time-dependent onset and exhaustion of proteolysis in ghosts. The presence of increased proteolysis in ghosts could be regarded as a marker of molecular lesions induced in red cells by storage under blood bank conditions.

Membrane skeleton-bilayer interaction is not the major determinant of membrane phospholipid asymmetry in human erythrocytes

Transbilayer phospholipid distribution, membrane skeleton dissociation/association, and spectrin structure have been analysed in human erythrocytes after subjecting them to heating at 50 degrees C for 15 min. The membrane skeleton dissociation/association was determined by measuring the Tris-induced dissociation of Triton-insoluble membrane skeletons (Triton shells), the spectrin-actin extractability under low ionic conditions, and the binding of spectrin-actin with normal erythrocyte membrane inside-out vesicles (IOVs). The spectrin structure was ascertained by measuring the spectrin dimer-to-tetramer ratio as well as the spectrin tryptophan fluorescence. Both the Tris-induced Triton shell dissociation and the spectrin-actin extractability under low ionic conditions were considerably reduced by the heat treatment. Also, the binding of heated erythrocyte spectrin-actin to IOVs was significantly smaller than that observed with the normal cell spectrin-actin. Further, the quantity of spectrin dimers was appreciably increased in heat-treated erythrocytes as compared to the normal cells. This change in the spectrin dimer-to-tetramer ratio was accompanied by marked changes in the spectrin tryptophan fluorescence. In spite of these heat-induced alterations in structure and bilayer interactions of the membrane skeleton, the inside-outside glycerophospholipid distribution remained virtually unaffected in the heat-treated cells, as judged by employing bee venom and pancreatic phospholipase A2, fluorescamine and Merocyanine 540 as the external membrane probes. These results strongly indicate that membrane bilayer-skeleton interaction is not the major factor in determining the transbilayer phospholipid asymmetry in human erythrocyte membrane.

A lectin-like receptor on murine macrophage is involved in the recognition and phagocytosis of human red cells oxidized by phenylhydrazine

Phenylhydrazine (Phz) is a powerful hemolytic agent which has several effects on both normal and G6PD deficient red blood cells (RBCs). We have studied the mechanism of removal of Phz-damaged human RBCs by murine macrophages. Phagocytosis of Phz-treated RBCs was found to be 50 RBCs/100 mac as compared to 2 RBCs/100 mac of the controls. EGTA and sodium azide inhibited the phagocytosis, indicating a requirement for both calcium ions and energy. Incubation of macrophages with sugars such as D-galactose or D-mannose reduced phagocytosis of Phz-treated RBCs by up to 60%, indicating the involvement of a macrophage lectin-like receptor in the recognition of Phz-treated RBCs. The presence of serum in the phagocytosis assay did not affect either phagocytosis of Phz-treated RBCs or inhibition by sugars. beta-Galactosidase, but not neuraminidase, treatment of RBCs caused a significant inhibition in phagocytosis of Phz-treated RBCs. These results suggest that galactosyl residues are exposed on RBC membrane during oxidation, probably not as a result of desialization. We conclude that Phz-treated RBCs are detected as damaged cells mainly due to sugar changes on their membrane, which are directly recognized by lectin-like receptors on the macrophages.