Changes in surface carbohydrates of erythrocytes during in vivo aging

Establishing Rules for Self-Adhesion and Aggregation of N-Glycan Sugars Using Virus Glycan Shields

The surfaces of cells and pathogens are covered with short polymers of sugars known as glycans. Complex N-glycans have a core of three mannose sugars with distal repeats of N-acetylglucosamine and galactose sugars terminating with sialic acid (SA). Long-range tough and short-range brittle self-adhesions were observed between SA and mannose residues, respectively, in ill-defined artificial monolayers. We investigated if and how these adhesions translate when the residues are presented in N-glycan architecture with SA at the surface and mannose at the core and with other glycan sugars. Two pseudotyped viruses with complex N-glycan shields were brought together in force spectroscopy (FS). At higher ramp rates, slime-like adhesions were observed between the shields, whereas Velcro-like adhesions were observed at lower rates. The higher approach rates compress the virus as a whole, and the self-adhesion between the surface SA is sampled. At the lower ramp rates, however, the complex glycan shield is penetrated and adhesion from the mannose core is accessed. The slime-like and Velcro-like adhesions were lost when SA and mannose were cleaved, respectively. While virus self-adhesion in forced contact was modulated by glycan penetrability, the self-aggregation of the freely diffusing virus was only determined by the surface sugar. Mannose-terminal viruses self-aggregated in solution, and SA-terminal ones required Ca2+ ions to self-aggregate. Viruses with galactose or N-acetylglucosamine surfaces did not self-aggregate, irrespective of whether or not a mannose core was present below the N-acetylglucosamine surface. Well-defined rules appear to govern the self-adhesion and -aggregation of N-glycosylated surfaces, regardless of whether the sugars are presented in an ill-defined monolayer, or N-glycan, or even polymer architecture.

Membrane lipids and protein-bound carbohydrates status during the maturation of reticulocytes to erythrocytes in type 2 diabetics

BACKGROUND

The reticulocyte maturation process is an ideal model for the study of biochemical alterations seen during final stage of erythropoiesis under disease conditions. In this study, determined whether type 2 diabetes has any effect on membrane lipids and protein-bound carbohydrates during the maturation of reticulocytes to erythrocytes.

SUBJECTS AND METHODS

Lipids (cholesterol and phospholipids) and protein-bound carbohydrates (hexose, hexosamine and sialic acid) were extracted and estimated in plasma, membrane of reticulocytes and erythrocytes from 20 treated but uncontrolled type 2 diabetic volunteers and age matched controls.

RESULTS

Plasma, membranes of reticulocytes and erythrocytes of diabetics showed increase in cholesterol (35.7%, 8.7% and 16.4%); phospholipids (43.4%, 18.8% and 8.2%); hexose (34.1%, 19.3% and 8.2%) and decrease in hexosamine (11.9%, 7.3% and 14.7%); and sialic acid (34.1%, 19.3% and 32.0%) compared to controls. As reticulocytes matured to erythrocytes, cholesterol, phospholipids, hexosamine and sialic acid levels were decreased; C/P ratio and hexose levels were increased in both controls and diabetics. However, these alterations were more intensified in diabetics.

CONCLUSION

These alterations in diabetic patients may indicate the existence of one or both of the following conditions: acceleration of maturation processes and/or decreased red blood cell life span.

Bilirubin binding to normal and modified human erythrocyte membranes: effect of phospholipases, neuraminidase, trypsin and CaCl2

Binding of bilirubin to human erythrocyte membranes was studied after various enzymatic treatments as well as calcium loading. Whereas phospholipase D treatment of erythrocyte membranes resulted in 23% increase in bilirubin binding, phospholipase C-treated membranes showed remarkable enhancement in bilirubin binding. Polar head groups in general and negatively charged phosphate moieties, in particular, of phospholipids of the membrane appear to inhibit a large amount of bilirubin from binding to the membranes. Neuraminidase treatment of the membranes also led to a slight increase in bilirubin binding as compared to untreated membranes. Membrane proteins and carbohydrates seem to play significant regulatory role in bilirubin binding. However, no direct correlation was found between the increase in bilirubin binding and the amount of carbohydrate released upon tryptic digestion of membranes. Increase in bilirubin binding to trypsin-treated membranes can be ascribed to the increase in free bilirubin concentration in the incubation mixture as a result of tryptic hydrolysis of albumin by the membrane-bound tryptic activity. Calcium-loaded erythrocyte membranes also showed remarkable increase in bilirubin binding as a result of negative charge shielding and calcium-induced hydrophobic aggregation. Taken together, these results suggest the inhibitory role of polar head groups of phospholipids (phosphate in particular), carbohydrate and sialic acid in the binding of bilirubin to erythrocyte membranes.

Cellular and molecular mechanisms of senescent erythrocyte phagocytosis by macrophages. A review

Human red blood cells (RBCs) have a life-span of 120 days in circulation, after which they are phagocytized by resident macrophages. Extensive studies have been undertaken by many investigators in order to elucidate the cellular and molecular mechanisms of the erythrophagocytosis. The critical questions addressed by physiologists, clinicians and biochemists are: 'which of the many traumatic blemishes that appear on the erythrocyte surface as it winds its way through the circulation is the primary signal for clearance of the effete RBC from the circulation?', or 'What is the critical signal that it, and it alone, will activate the resident macrophage to adhere to and engulf it?'. Numerous, and often conflicting, hypotheses have been proposed. Each investigator focusing on but one of the many modifications that afflict the cell surface of the ageing erythrocyte, viz changes in either or both the carbohydrate or peptidic moieties of glycoproteins; abolishment of the pre-existing asymmetry in the lipid bilayer with the exposure of phosphatidylserine residues; or alterations in spectrin, to mention but a few. Many of these investigators also have invoked an intermediary role for auto-immune antibodies that recognise the change(s) on the erythrocyte surface and thereby serve as opsonins as a prelude to the erythrophagocytosis. The objective of the present review is to evaluate the data in support of the various hypotheses, and to submit some of our own recent observations involving the use of flow cytometric procedures that: i) provide evidence that the cell surface sialic acid serves as a determinant of the life-span; ii) characterise the senescent erythrocyte population that is specifically captured and phagocytized by macrophages (utilising the rapid and sensitive procedure we developed for quantification of in vitro erythrophagocytosis); and finally iii) provide evidence for the existence of an alternative pathway that is independent of immunoglobulins.

Flow cytofluorimetric analysis of young and senescent human erythrocytes probed with lectins. Evidence that sialic acids control their life span

Comparing the properties of 'young' and senescent ('aged') O+ erythrocytes isolated by applying ultracentrifugation in a self-forming Percoll gradient, we demonstrate that the sialic acids of membrane glycoconjugates control the life span of erythrocytes and that the desialylation of glycans is responsible for the clearance of the aged erythrocytes. This capture is mediated by a beta-galactolectin present in the membrane of macrophages. The evidence supporting these conclusions is as follows: (1) Analysis by flow cytofluorimetry of the binding of fluorescein isothiocyanate labelled lectins specific for sialic acids shows that the aged erythrocytes bind less WGA, LPA, SNA and MAA than young erythrocytes. The binding of DSA and LCA is not modified. On the contrary, the number of binding sites of UEA-I specific for O antigen and of AAA decreases significantly. PNA and GNA do not bind to erythrocytes. (2) RCA120 as well as Erythrina cristagalli and Erythrina corallodendron lectins specific for terminal beta-galactose residues lead to unexpected and unexplained results with a decrease in the number of lectin binding sites associated with increasing desialylation. (3) The glycoconjugates from the old erythrocytes incorporate more sialic acid than the young cells. This observation results from the determination of the rate of transfer by alpha-2,6-sialyltransferase of fluorescent or radioactive N-acetylneuraminic acid, using as donors CMP-9-fluoresceinyl-NeuAc and CMP-[14C]-NeuAc, respectively. (4) Microscopy shows that the old erythrocytes are captured preferentially by the macrophages relative to the young ones. Fixation of erythrocytes by the macrophage membrane is inhibited by lactose, thus demonstrating the involvement of a terminal beta-galactose specific macrophage lectin. (5) Comparative study of the binding of WGA, LPA, SNA and MAA to the aged erythrocytes and to the in vitro enzymatically desialylated erythrocytes shows that the desialylation rate of aged cells is low but sufficient to lead to their capture by the macrophages.

The isoelectric point of the human red cell glucose transporter

The isoelectric point (pI) of the human red cell glucose transporter (Glut 1) was determined. Inconsistent values of 6.0, 6.4-6.5 and 8 have been reported earlier. Integral membrane proteins from human red cells were analyzed by two-dimensional electrophoresis with isoelectric focusing and sodium dodecyl sulfate gel electrophoresis (2D-PAGE). A zone of monomeric Glut 1 was found at pH 8.7, but most of the Glut 1 focused at pH 6-7 together with the anion transporter and other components. Purified Glut 1 focused only at pH 8.5 +/- 0.2 (S.D., n = 12) and deglycosylated purified Glut 1 only at pH 8.4 +/- 0.1 (n = 5), as shown by 2D-PAGE. The absence of Glut 1 below pH 8 in the latter cases was confirmed by immunoblotting with a monoclonal antibody. Furthermore, Glut 1 was photoaffinity-labelled with [3H]cytochalasin B and subjected to isoelectric focusing in one dimension. The pI of the labelled Glut 1 was 8.6 +/- 0.3 (n = 11). A pI of 9.1 was calculated for the Glut 1 polypeptide on the basis of amino acid composition and pKa values for amino acid side groups. The sialic acid content of the glycosylated transporter from fresh red cells was determined at approximately 2.1 sialic acid residues per transporter, which corresponds to a calculated pI of 8.8. The pI values of other human glucose transporter polypeptides of the facilitative diffusion type (Glut 2, 3, 4 and 5) were calculated at 8.4, 7.4, 7.1 and 6.2, respectively.

Alcohol intoxication and sialic acid in erythrocyte membrane and in serum transferrin

Microheterogeneity of serum transferrin as well as erythrocyte membrane sialic acid content were examined in alcoholic patients and healthy controls. Both the sialic acid content of erythrocyte membranes and of the circulating transferrin were significantly lower in alcoholic patients than in controls. A moderate daily ethanol intake (less than 80 g) allowed to observe a proportional relationship between alcohol intake and the carbohydrate deficient forms of transferrin, and also a correlation between alcohol intake and the membrane sialic acid content. This supports the hypothesis of ubiquitary alterations of glycosylations in connection to ethanol intoxication. Additional disturbances could explain the absence of correlations between membrane sialic acid, pattern of abnormal forms of serum transferrin, and alcohol intake in heavy alcoholic patients.

Erythrocyte rheology

Two main subjects of erythrocyte rheology, deformation and aggregation, are discussed in detail, on the basis of biochemical structure. The close relationship between the life span (or cell aging) and the rheology of individual erythrocytes is also briefly described. A currently important problem is emphasized, that is, the molecular aspect of the dynamic cytoskeletal structure and the mechanism of its regulation. This concerns not only the rheological function and the survival of circulating erythrocytes, but also the pathophysiology of abnormal erythrocytes.

Binding of lectins to "young" and "old" human erythrocytes

"Old" human erythrocytes showed a 21.2% decrease in cell surface area and a 2% decrease in the number of WGA receptor sites, but a 27% increase in the distribution density of the WGA (lectin) receptor site, when compared with "young" human erythrocytes. For a list of lectin abbreviations, see Materials and methods). Both "young" and "old" erythrocytes exhibited very weak binding activity for 125I-labeled PNA, but there was no difference in binding activity for PNA between "young" erythrocytes and "old" ones. Compared with "young" erythrocytes, decreases in the number and distribution density of receptor sites for five lectins including LPA, Con A, RCA-II, SBA and BPA on the cell surface were observed in aged erythrocytes. "Old" erythrocytes also showed a decrease in the number of PHA-E receptor sites, while the distribution density of the same receptor site remained unchanged. In view of these and other observations, it is thought that human erythrocyte aging is accompanied by elimination of some glycoconjugates which have affinity for six lectins, LPA, Con A, RCA-II, PHA-E, SBA and BPA, whereas no WGA receptor-containing glycoconjugates are released from erythrocyte membranes. Elimination of the glycoconjugates results in shrinkage of erythrocytes to reduce their cell surface areas.

Number and distribution density of ABH and MN antigen sites on young and old human erythrocyte surfaces

There were no differences in the number of A and M antigen sites between young and old human erythrocyte surfaces. No essential differences in the number of A1, N and Vicia graminea N antigen sites could be observed between young and old erythrocytes. The number of B and H antigen sites on cell surface was significantly higher in young erythrocytes than in old ones. The distribution density of A and M antigen sites on young erythrocyte was remarkably higher than that on old ones. Compared with young erythrocytes, significant increases in the distribution density of A1, B, H, N and Vicia graminea N antigen sites were observed in aged erythrocytes. It is suggested from these and other observations that human erythrocyte aging is accompanied by elimination of a small amount of B and H antigens from cell membranes, while A, A1, M, N and Vicia graminea N antigens are not released from cell membranes during in vivo aging.

Co-clustering of denatured hemoglobin with band 3: its role in binding of autoantibodies against band 3 to abnormal and aged erythrocytes

Precipitates of hemoglobin, termed Heinz bodies, occur in a fraction of erythrocytes after removal of the spleen and are also observed in aged erythrocytes. This implies that precipitates of hemoglobin might play a particular role in senescent cell recognition. By using immunofluorescence microscopy, evidence is presented in splenectomized patients and in several patients with unstable (mutant) hemoglobins that membrane-attached Heinz bodies are associated with both clusters of the anion channel, band 3, and clusters of surface-bound immunoglobulins (IgG). In 75% of the cases of unstable hemoglobin, such as sickle cell anemia or hemoglobin Köln disease, the level of cell-bound IgG (measured by 125I-labeled staphylococcal protein A) was increased severalfold above the level found in healthy controls. Immunoblot analysis identified the major fraction of cell-bound IgG to be directed to band 3. These observations indicate copolymerization of denatured hemoglobin with the cytoplasmic domain of band 3, which may cause band 3 to form clusters. These clusters probably serve as thermodynamically favored binding sites for autoantibodies in serum, which promote elimination of the erythrocytes by the immune system. Thus, erythrocytes may be removed from circulation when hemoglobin begins to denature and the cells begin to fail in their main function of oxygen transport.

Cell surface alterations during blood-storage characterized by artificial aggregation of washed red blood cells

Aggregation measurement of washed human erythrocytes (RBC) were carried out in a NaCl-PBS solution under laminar shear conditions. Artificial aggregation of fresh and stored erythrocytes was caused by decreased pH and reduced ionic strength and characterized by collision efficiency alpha. Generally, the collision efficiency alpha of stored erythrocytes rises with the increased storage time. Such an aggregation technique might be useful to detect and quantify changes of the membrane and/or the surface structure due to aging and/or storage.

Erythrocyte membrane phosphorylation in aging rats

By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the protein profile and autophosphorylation of plasma membranes of red cells from 3-, 9-, 18-, and 30-month-old rats was examined. No major changes in SDS-PAGE protein profiles were noticeable. However, endogenous (auto) and exogenous phosphorylation in the presence of (gamma-32P)ATP showed an age-dependent increase in 32P uptake. pH optimum was between 8.0 and 9.0 for all age groups. Cyclic AMP was without effect on either endogenous or exogenous phosphorylation. Further analysis of the autophosphorylation reaction by quantification of autoradiograms obtained from SDS-PAGE gels displayed an age-dependent increase in phosphorylation of bands 2, 3, 4.1, and 4.5 [nomenclature of Fairbanks et al. Biochemistry 10:2606, 1971] and of several other minor bands. The data imply that alteration in red cell membranes may occur during aging of rats causing an enhancement in endogenous kinase activity and possibly in the number of phosphate acceptor sites as well.

Erythrocyte deformability in aging

Blood viscosity and the deformability and other properties of erythrocytes were compared among 60-, 150-, 320- and 710-day-old rats. Blood viscosity was remarkably higher in the 320- and 710-day old rats than in those 60- and 150 days' old. Measurement by the capillary centrifugal method showed that the deformability of erythrocytes is significantly decreased with age. The increase in blood viscosity with aging could be attributed to the decrease in erythrocyte deformation. Osmotic fragility and the number of higher density erythrocytes also increase with age. The negative surface charge in erythrocytes obtained from old rats was higher than in those from younger rats.

Nonuniform loss of membrane glycoconjugates during in vivo aging of human erythrocytes: studies of normal and diabetic red cell saccharides

Changes occurring in membrane saccharides during the in vivo aging of normal human erythrocytes have been evaluated after the fractionation of the red cells into five age groups by density gradient centrifugation. The glycoconjugate fractions studied included sialoglycoproteins, macroglycolipids, low-molecular-weight glycolipids, and Band 3 glycoproteins. All of the carbohydrate constituents of the membrane were found to decrease relative to the total ghost protein as a function of cell age, with the most substantial losses occurring in the macroglycolipids (50%) and Band 3 glycoprotein (30%); the smallest changes were observed in the sialoglycoproteins (13%). No preferential loss of sialic acid or other peripheral sugars was found, making unlikely the importance of glycosidase action in the removal of sugars from the membrane. It is suggested that the changes observed in the composition of the ghosts during aging are best explained by a loss of membrane segments enriched in glycoproteins and glycolipids and deficient in internally located molecules such as spectrin. Analyses were also performed on the glycoconjugate fractions from diabetic erythrocytes separated according to cell age. These erythrocytes, which had glycosylated hemoglobin values twice those of normals, had somewhat smaller amounts of membrane-bound carbohydrate. The difference between diabetic and normal erythrocytes was greatest when young cells were examined (diabetic to normal = 0.93), suggesting that the known increased turnover of red cells in diabetes leads to an early loss of membrane constituents.

Identification of a receptor for senescent erythrocytes on liver macrophages

Isolated rat liver macrophages adherent to culture dishes phagocytize selectively senescent rat erythrocytes as well as in vitro aged rat erythrocytes but not young or freshly isolated erythrocytes. Since in vitro aged erythrocytes lack cell bound antibodies and phagocytosis occurs in serum free medium, antibodies do not appear to play a role. Phagocytosis as well as binding of old erythrocytes to liver macrophages is inhibited by N-acetyl-D-galactosamine and related monosaccharides (1-25 mM range) and by corresponding synthetic glycoproteins (10(-6)-10(-10) M range) but not by D-mannose or N-acetyl-D-glucosamine. We conclude that recognition and phagocytosis of senescent and in vitro aged erythrocytes is mediated by the galactose particle receptor on rat liver macrophages.

Energy depletion retards the loss of membrane transport during reticulocyte maturation

The effect of metabolic depletion on the maturation-associated loss of membrane functions has been studied by using sheep reticulocytes incubated in vitro at 37 degrees C for periods up to 41 hr. ATP was either maintained with glucose, adenosine plus inosine, or depleted with 2-deoxyglucose plus arsenate. Two membrane transport systems were studied: Na+-dependent glycine transport activity and the sodium pump, estimated from measurements of the number of [3H]ouabain binding sites per cell. Both transport systems were decreased during maturation. However, the decrease was much less in ATP-depleted cells compared to ATP-replete cells. It is concluded that the loss of certain functions during reticulocyte maturation is retarded by metabolic depletion.

Binding of Leishmania promastigotes to macrophages

Leishmania tropica promastigotes are easily attached to and engulfed by C3H peritoneal macrophages in vitro at 37 degrees C. Different sugars at 0.3-0.5 M inhibited in vitro the attachment of L. tropica promastigotes to C3H peritoneal macrophages with lactose (Gal-beta [1 leads to 4]Glc) being the most efficient. Inhibition of attachment is also affected by pre-treatment of promastigotes with galactose oxidase. Oligosaccharides extending from promastigote and amastigote cell surfaces contain an important proportion of non-reducing galactose as does the carbohydrate-rich factor (EF) excreted by promastigotes of L. tropica and L. donovani. This study suggests that Leishmania, an obligatory intracellular parasite, uses as a means of entering the host cell a cellular mechanism similar to that used in the removal of damaged cells from blood circulation. This mechanism is assumed to take advantage of the exposed sugars, particularly the exposed non-reducing galactose, on the parasite surface during the stage of attachment. Once the parasite is inside the cell, the EF it produces might have a protective function, being inhibitory to some of the host cell lysosomal enzymes.

Age-development changes in susceptibility of erythrocytes to perfringolysin O

Susceptibility to perfringolysin O of erythrocytes from mice of different ages was examined. Erythrocytes of mice younger than 5 weeks' old were more resistant to the toxin than those of young adult and adult mice. Erythrocytes of aged mice were about 3.5 times more susceptible to the toxin than erythrocytes from 4-week-old mice. The membrane cholesterol content of erythrocytes appeared to be maintained at a constant level throughout the ages of mice examined. About 5% of the total membrane cholesterol was supposed to provide receptor sites for the toxin from an experiment in which cholesterol was specifically extracted by liposomes. It was demonstrated in this experiment that susceptibility of erythrocytes to the toxin was lost in proportion to the reduction in the toxin binding. The susceptibility, however, of erythrocytes from young or aged mice was much lower or higher than expected from the changes in toxin binding. Therefore, two possibilities were raised to account for age-related alterations in the susceptibility of erythrocytes; not only expansion of a particular compartment of membrane cholesterol as a toxin receptor but also some activation of intracellular reactions leading to hemolysis might occur in senescence.

Effects of diabetes and high fat-high cholesterol diet on plasma lipid levels and on erythrocyte membrane composition

Erythrocyte membrane composition was studied in rats subjected to experimental hyperlipidemia and/or hyperglycemia by means of 6 weeks of high fat (40% w/w)-high cholesterol (5% w/w)diet with and without 8 weeks of streptozotocin-induced diabetes. High fat-high cholesterol diet lowered plasma glucose levels in control and in diabetic animals. While the atherogenic diet produced only hypercholesterolemia, the same diet fed to diabetic animals produced both hypercholesterolemia and hypertriglyceridemia. The membrane protein content was lower in diabetic rats than in controls, while the cholesterol and phospholipids were higher in diabetic rat erythrocyte membranes. Feeding the atherogenic diet increased membrane lipid levels in only nondiabetic animals. The total carbohydrate content of the membranes was greater in diabetic animals than controls. Difference in relative proportion of individual sugars, e.g., galactose, mannose, glucose, and fucose of the membranes was observed between diabetic and control groups. These observations suggest that rat erythrocyte membrane composition is altered both in hyperglycemic and hyperlipidemic conditions, and may provide a useful model for evaluating lipid carbohydrate abnormalities of membrane structures in diabetes mellitus.

In vivo ageing of human erythrocytes and cell-surface labeling by D-galactose oxidase and sodium borotritide

Young and old, human erythrocytes, separated in vitro according to their age in vivo, were radioactively labeled at the cell-surface D-galactosyl and 2-acetamido-2-deoxy-D-galactosyl residues by treatment with D-galactose oxidase, followed by reduction with sodium borotritide. The labeling was quantitatively determined for each type of erythrocyte by measuring the molar amounts of borohydride necessary for the complete reduction of the oxidized residues. The number of surface residues per blood-group A+ erythrocyte was found to be 37.6 +/- 1.8 x 10(6) (n = 8) for young, 21.8 +/- 4.9 x 10(6) (n = 8) for old, and 24.8 +/- 6.4 x 10(6) (n = 8) for middle-aged erythrocytes, indicating a significant decrease of the residues during ageing.

Membrane asymmetry. A survey and critical appraisal of the methodology. I. Methods for assessing the asymmetric orientation and distribution of proteins

This and the companion article are aimed at surveying the methods used for the study of membrane asymmetry. The techniques employed for the assessment of the asymmetric distribution and orientation of membrane proteins are reviewed in this article, whereas those pertaining to the unequal distribution of lipids are detailed in the companion paper. The use of immunological techniques and lectins, functions of proteins and their perturbations, chemical reagents, enzymatic isotopic labeling and enzymatic cleavage of membrane proteins and physical techniques are discussed and illustrated using recent examples of their application. Whenever appropriate, problems involving crypticity and non-availability or non-reactivity of functional sites, relevant chemical functions or protein fragments to appropriate ligands, reagents or modifying enzymes are envisaged and possible modification of the exposure of proteins during preparation of ghosts and other drawbacks are discussed, the use of different techniques and control experiments in conjunction is recommended for a more realistic assessment of the distribution and orientation of proteins.