Generation of phenotypically aged phosphatidylserine-expressing erythrocytes by dilauroylphosphatidylcholine-induced vesiculation

In vitro stored red blood cells (RBC) and RBC artificially induced to vesiculate by incubation with dilauroylphosphatidyl-choline were monitored for age- and vesiculation-dependent changes in cell density, membrane lipid asymmetry, and their ability to be recognized and cleared by reticuloendothelial cells. RBC demonstrated a progressive increase in density on self-forming Percoll gradients upon vesiculation and in vitro "aging." Uptake of vesiculated RBC by in vitro cultivated macrophages was increased threefold over non-vesiculated control RBC. The clearance rate of dense vesiculated RBC was biphasic and contained a rapid component and a slower second component consistent with the clearance rates of normal control populations. Determination of phosphatidylserine (PS) in the outer leaflet of RBC by the PS-dependent prothrombinase assay revealed that PS redistributed to the cell's outer leaflet upon in vitro storage and vesiculation. Inhibition of PS movement by oxidation of membrane sulfhydryls with pyridyldithioethylamine resulted in higher prothrombinase levels and enhanced clearance of vesiculated RBC. These experiments suggest that vesiculation contributes to alterations in membrane lipid asymmetry and cell density characteristic of the aged RBC phenotype.     

Time-course investigation of SAGM-stored leukocyte-filtered red bood cell concentrates: from metabolism to proteomics

Background

Results from recent, highly debated, retrospective studies raised concerns and prompted considerations about further testing the quality of long stored red blood cells from a biochemical standpoint.

Design and Methods

We performed an integrated mass spectrometry-based metabolomics and proteomics time-course investigation on SAGM-stored red blood cells. In parallel, structural changes during storage were monitored through scanning electron microscopy.

Results

We detected increased levels of glycolytic metabolites over the first 2 weeks of storage. From day 14 onwards, we observed a significant consumption of all metabolic species, and diversion towards the oxidative phase of the pentose phosphate pathway. These phenomena coincided with the accumulation of reactive oxygen species and markers of oxidation (protein carbonylation and malondialdehyde accumulation) up to day 28. Proteomics evidenced changes at the membrane protein level from day 14 onwards. Changes included fragmentation of membrane structural proteins (spectrin, band 3, band 4.1), membrane accumulation of hemoglobin, anti-oxidant enzymes (peroxiredoxin-2) and chaperones. While the integrity of red blood cells did not show major deviations at day 14, at day 21 scanning electron microscope images revealed that 50% of the erythrocytes had severely altered shape. We could correlate the scanning electron microscopy observations with the onset of vesiculation, through a proteomics snapshot of the difference in the membrane proteome at day 0 and day 35. We detected proteins involved in vesicle formation and docking to the membrane, such as SNAP alpha.

Conclusions

Biochemical and structural parameters did not show significant alterations in the first 2 weeks of storage, but then declined constantly from day 14 onwards. We highlighted several parallelisms between red blood cells stored for a long time and the red blood cells of patients with hereditary spherocytosis.     

Growth of Plasmodium falciparum in human erythrocytes containing abnormal membrane proteins.

To evaluate the role of erythrocyte (RBC) membrane proteins in the invasion and maturation of Plasmodium falciparum, we have studied, in culture, abnormal RBCs containing quantitative or qualitative membrane protein defects. These defects included hereditary spherocytosis (HS) due to decreases in the content of spectrin [HS(Sp+)], hereditary elliptocytosis (HE) due to protein 4.1 deficiency [HE(4.1(0))], HE due to a spectrin alpha I domain structural variant that results in increased content of spectrin dimers [HE(Sp alpha I/65)], and band 3 structural variants. Parasite invasion, measured by the initial uptake of [3H]hypoxanthine 18 hr after inoculation with merozoites, was normal in all of the pathologic RBCs. In contrast, RBCs from six HS(Sp+) subjects showed marked growth inhibition that became apparent after the first or second growth cycle. Preincubation of HS(Sp+) RBCs in culture for 3 days did not alter these results. Normal parasite growth was observed in RBCs from one HS subject with normal membrane spectrin content. The extent of decreased parasite growth in HS(Sp+) RBCs closely correlated with the extent of RBC spectrin deficiency (r = 0.90). Homogeneous subpopulations of dense HS RBCs exhibited decreased parasite growth to the same extent as did HS whole blood. RBCs from four HE subjects showed marked parasite growth inhibition, the extent of which correlated with the content of spectrin dimers (r = 0.94). RBCs from two unrelated subjects with structural variants of band 3 sustained normal parasite growth. Decreased growth in the pathologic RBCs was not the result of decreased ATP or glutathione levels or of increased RBC hemolysis. We conclude that abnormal parasite growth in these RBCs is not the consequence of metabolic or secondary defects. Instead, we suggest that a functionally and structurally normal host membrane is indispensable for parasite growth and development.     

Hemoglobin-spectrin complexes: interference with spectrin tetramer assembly as a mechanism for compartmentalization of band 1 and band 2 complexes

The irreducible complexation of hemoglobin with spectrin is a natural phenomenon of red blood cell aging, positively correlating with increasing cell density and decreasing cell deformability. The current study begins to address the role of these complexes in the disruption of membrane skeletal physiology and structure. The effect of bound hemoglobin on spectrin dimer self-association was investigated in vitro. The extent of conversion of isolated spectrin dimers to tetramers was evaluated as a function of peroxide-induced globin complexation before the conversion incubations. The incremental accumulation of tetramer was observed to decrease with increasing peroxide concentration used in the globin complexation step. The role of oxidized heme in this process was made apparent by the inability of carboxyhemoglobin to inhibit tetramer accumulation. A Western blot analysis of naturally formed globin-spectrin conjugates demonstrated irreducible complexes of globin with both bands 1 and 2. The complexes are tentatively designated "h1" and "h2". This analysis also demonstrated that h1 is completely extractable from cell ghosts, whereas h2 is only 50% extractable. These findings are incorporated into a hypothesis linking globin-spectrin complexation and the consequent inhibition of spectrin dimer self-association to the clustered band 3 senescence antigen (Low et al, Science 227:531, 1985).     

Interaction of erythroid spectrin with hemoglobin variants: implications in beta-thalassemia

Among the few studies, producing contradictory results, done on the interaction of erythroid membrane skeletal spectrin with hemoglobin (Hb), none has been able to provide a quantitative estimate of the association of spectrin with Hb. In this work, studies on the interactions of erythroid spectrin with Hb have been elaborated upon using a novel fluorescence technique. The concentration-dependent change in the fluorescence intensity of fluorescein-conjugated spectrin (F-spectrin) in presence of oxy-Hb indicated binding with a dissociation constant of approximately 20 microM that has been directly evaluated from the increase in the extent of quenching of the fluorescein fluorescence of F-spectrin by reverse titration with the increasing concentrations of different Hb samples isolated from both normal and beta-thalassemic patients. The Hb compositions, with major components of the normal HbA, the fetal HbF, and the variant HbA2, of each individual were estimated using the Variant HPLC device of Bio-Rad. Results of the present study indicated that the dissociation constant, K(d), of spectrin binding to Hb decreased from 19.5 +/- 2 microM in normal individuals to of 6.5 +/- 0.5 microM in the presence of 73% HbA2 along with coeluted variants in the blood samples of patients suffering from beta-thalassemia, indicating differential interactions of the Hb variants with spectrin.     

Improved red blood cell preservation correlates with decreased loss of bands 3, 4.1, acetylcholinestrase, and lipids in microvesicles

In earlier studies we have shown that a final concentration of 0.69% glycerol in blood mixed with an experimental additive solution, EAS 25, improves the in vitro quality and in vivo survival of red blood cells (RBCs). The objective of this study was to determine if the better preservation of RBCs in EAS 25 is correlated with the improved maintenance of membrane lipids and proteins and decreased vesiculation. Split units of RBCs were stored in Adsol or EAS 25 (mmol/L: adenine 2/2, dextrose 122/110, mannitol 42/55, glycerol 0/150, NaCl 154/50). After 12 weeks storage, RBC and microvesicle membranes were analyzed for cholesterol, phospholipid, diphenyl hexatriene fluorescence anisotropy, and acetylcholinesterase (AchE) activity. Bands 3 and 4.1 were identified in the microvesicle membranes by immunoblotting. The RBC membrane cholesterol, phospholipids, and AchE remained higher in EAS 25 than in Adsol (P < .001). Vesicle membrane lipids and AchE in EAS 25 were significantly less than in Adsol (P < .001). The fluidity of stored cells in both the solutions was greater than the prestorage samples. Immunoblotting analyses showed that bands 3 and 4.1 were greatly reduced in the microvesicle membranes shed by the RBCs stored in EAS 25 compared with those formed in Adsol.     

Molecular basis of spectrin deficiency in hereditary pyropoikilocytosis

Hereditary pyropoikilocytosis (HPP) is a recessively inherited hemolytic anemia characterized by severe poikilocytosis and red blood cell fragmentation. HPP red blood cells are partially deficient in spectrin and contain a mutant alpha or beta-spectrin that is defective in terms of spectrin self-association. Although the nature of the latter defect has been studied in considerable detail and many mutations of alpha-spectrin and beta spectrin have been identified, the molecular basis of spectrin deficiency is unknown. Here we report two mechanisms underlying spectrin deficiency in HPP. The first mechanism involves a thalassemia-like defect characterized by a reduced synthesis of alpha-spectrin as shown by studies involving synthesis of spectrin in two unrelated HPP probands and their parents: One parent carries the elliptocytogenic spectrin mutation, whereas the other parent is fully asymptomatic. Peripheral blood mononuclear cells as a source of erythroid burst-forming unit (BFUe) were cultured in a two-phase liquid culture system that gives rise to terminally differentiated erythroblasts. Pulse-labeling studies of an equal number of erythroblasts or morphologically identical maturity showed that the synthesis of alpha-spectrin as well as the mRNA levels as measured by the competitive polymerase chain reaction (PCR) method are markedly reduced in the presumed asymptomatic carriers and the HPP probands. In contrast, the synthesis and mRNA levels of beta-spectrin were normal. These results constitute a direct demonstration of an alpha-spectrin synthetic defect in a subset of asymptomatic carriers of HPP and HPP probands. The second mechanism underlying spectrin deficiency involves increased degradation of mutant spectrin before its assembly on the membrane. This is evidenced by pulse labeling studies of erythroblasts from a patient with HPP associated with a homozygous state for spectrin alpha I/46 mutation (leu-pro mutation at AA 207 of alpha-spectrin). These studies showed that although spectrin is synthesized in the cytosol in normal amounts, the rate of turnover of alpha-spectrin is faster resulting in about 40% to 50% reduced assembly of alpha-spectrin and beta-spectrin on the membrane. Thus, spectrin deficiency in this case is at least in part caused by increased susceptibility of the mutant spectrin to degradation before its assembly on the membrane. We conclude that at least two separate mechanisms underlie the molecular basis of spectrin deficiency in HPP.     

Spontaneous vesiculation of phospholipids: a simple and quick method of forming unilamellar vesicles.

Phosphatidic acid dispersions in H2O vesiculate when the pH is increased transiently (less than 2 min) from approximately 3 to 10.5-11. The same phenomenon is observed in mixed dispersions of phosphatidylcholine and phosphatidic acid in H2O when the pH is increased from approximately 3 to 7 to 8. With phosphatidic acid, this treatment produces small closed unilamellar vesicles (200-600 A) from 50-60% of the total phospholipid, with the remainder present as large unilamellar vesicles and multilamellar structures. The extent of vesiculation depends on the pH that the dispersion is exposed to. With mixed phospholipid dispersions, similar vesicles are obtained; in addition to pH, the extent of vesiculation depends on the phosphatidylcholine/phosphatidic acid (wt/wt) ratio; as this ratio increases, the percentage of small unilamellar vesicles formed decreases. The short exposure of the phospholipids to high pH does not cause lipid degradation, as assessed by thin-layer chromatography; hence, the formation of degradation products can be ruled out as being responsible for the spontaneous vesiculation. Ionization of the phosphate group, resulting in a high surface charge density, may be an important factor in the spontaneous vesiculation. The proportion of phospholipid present as small unilamellar vesicles was determined by gel filtration on Sepharose 4B and by 1H NMR. The small vesicles gave rise to a reasonably well resolved high-resolution NMR spectrum. A good correlation was found between the proportion of phospholipid giving rise to the high resolution spectrum, as derived from spectral intensity measurements, and the proportion present as small unilamellar vesicles, as derived from gel filtration.     

Glutamine- and phosphate-containing hypotonic storage media better maintain erythrocyte membrane physical properties

We have shown that red blood cell (RBC) adenosine-5'-triphosphate (ATP) is better maintained and that there is less hemolysis and K+ leakage in hypotonic experimental additive solutions (EASs) containing glutamine and glutamine plus phosphate (Pi) than in the conventional additive solution Adsol during blood bank storage. The objective of this study was to determine if the beneficial effect produced in these media correlates with better preservation of RBC membrane properties including lipid content, phospholipid organization, aminophospholipid transport (flippase), and prothrombin converting activity. Aliquots of packed RBCs were stored in EASs containing adenine, glucose, sodium chloride, and mannitol, with 10 mmol/L glutamine (EAS 44) or with 10 mmol/L glutamine and 20 mmol/L Pi(EAS 45), or in Adsol. RBC membranes were studied after 0, 28, 42, and 84 days of storage, and vesicle membranes were studied after 84 days. RBC cholesterol and phospholipid content remained significantly greater (P < .01) in EASs than in Adsol. The degree of membrane vesiculation was more than 50% lower in EASs than in Adsol (P < .01). After 42 days of storage, the accessibility of phosphatidylethanolamine to phospholipases was approximately 1.5 times greater for Adsol and EAS 44 samples than for EAS 45 samples (43.5% v 28%). The rates of phosphatidylserine transport were 43% to 70% lower for stored cells but were not dependent on storage media. The amounts of bands 3 and 4.1 in the microvesicle membranes were not statistically different in any of the preparations. These results suggest that storage of RBCs in glutamine and Pi-medium better maintains ATP, lipid content, and phospholipid asymmetry and results in decreased vesiculation.     

Loss of phospholipid membrane asymmetry and sialylated glycoconjugates from erythrocyte surface in haemoglobin E beta-thalassaemia

This study aimed to investigate any correlation between the extent of phosphatidylserine (PS) asymmetry and sialylated glycoconjugate levels with the faster clearance of circulating erythrocytes in haemoglobin E (HbE) β-thalassaemia. Erythrocytes from peripheral blood samples of different HbEβ-thalassaemia patients showed loss of PS asymmetry measured by annexin V binding using flow cytometry. Maximum PS exposure was found when HbE was 50–60% and HbF was <20% indicating a possible correlation with severity of the disease. Separation of erythrocytes into aged and younger cells showed higher loss of PS asymmetry in the younger erythrocytes of HbEβ-thalassaemia patients when compared with normal blood, where PS asymmetry was lost only in the older cells. Sialylated glycoconjugate measurement using the lectins wheatgerm agglutinin and pokeweed mitogen showed loss of sialic acid and N -acetyl- d -glucosamine-bearing glycoproteins in the order normal相似文献   

Vesiculation of sickle erythrocytes during thermal stress

Since it is not known why sickle RBCs tend to undergo microvesiculation, we have investigated their susceptibility to thermal stress. While normal RBCs start to vesiculate at 49.0 +/- 0 degrees C (n = 14), sickle RBCs begin to vesiculate at 47.9 +/- 0.5 degrees C, with a range of 46.5 to 48.5 degrees C (n = 14). This abnormality is reproduced by treating normal RBCs with phenazine methosulfate (PMS), which stimulates the excess intracellular generation of superoxide characteristic of sickle RBCs. For PMS-treated RBCs, there is a strong correlation between membrane protein thiol oxidation and vesiculation temperature (r = .977, P less than .001). The abnormal vesiculation temperature of both unmanipulated sickle RBCs and PMS-treated RBCs is significantly improved by treatment of the RBCs with dithiothreitol. The most dense sickle RBCs are most prone to vesiculation during thermal stress, and they are the subpopulation having the greatest amount of thiol oxidation. We conclude that the tendency of sickle RBCs to vesiculate during thermal stress is further evidence for functional abnormality of the RBC cytoskeleton due to thiol oxidation.     

Role of the interaction between Lu/BCAM and the spectrin‐based membrane skeleton in the increased adhesion of hereditary spherocytosis red cells to laminin

Lu/BCAM, the unique erythroid receptor for laminin 511/521, interacts with the erythrocyte membrane skeleton through spectrin binding. It has been reported that Hereditary Spherocytosis red blood cells (HS RBC) exhibit increased adhesion to laminin. We investigated the role of Lu/BCAM–spectrin interaction in the RBC adhesion properties of 2 splenectomised HS patients characterized by 40% spectrin deficiency. Under physiological flow conditions, HS RBC exhibited an exaggerated adhesion to laminin that was completely abolished by soluble Lu/BCAM. Triton extraction experiments revealed that a greater fraction of Lu/BCAM was unlinked to the membrane skeleton of HS RBC, as compared to normal RBC. Disruption of the spectrin interaction site in Lu/BCAM expressed in the transfected K562 cell line resulted in a weakened interaction to the skeleton and an enhanced interaction to laminin. These results demonstrated that the adhesion of HS RBC to laminin was mediated by Lu/BCAM and that its interaction with the spectrin‐based skeleton negatively regulated cell adhesion to laminin. Finally, the results of this study strongly suggest that the reinforced adhesiveness of spectrin‐deficient HS RBC to laminin is partly brought about by an impaired interaction between Lu/BCAM and the membrane skeleton.     

Red blood cell storage in SAGM and AS3: a comparison through the membrane two-dimensional electrophoresis proteome

BACKGROUND: SAGM is currently the standard additive solution used in Europe, while AS-3 is the third additive solution that has been licensed in the USA, and is also the one used in part of Canada. Although AS-3 is based on a saline-adenine-glucose solution, it also contains citrate and phosphate. Storage of red blood cell concentrates in CPD-SAGM is known to lead to the accumulation of a wide series of storage lesions, including membrane protein fragmentation and vesiculation, as we could previously determine through 2-dimensional gel electrophoresis. MATERIALS AND METHODS.: Through 2D-SDS-IEF-polyacrilamide gel electrophoresis we performed a time course analysis (day 0, 21 and 42 of storage) of red blood cell membranes from leukocyte-filtered concentrates either stored in CPD-SAGM or CP2D-AS-3. RESULTS AND DISCUSSION.: From the present study it emerges that the membrane protein profile of red blood cells stored in presence of AS-3 appears to be slightly different from (better than) previous reports on SAGM-stored counterparts. However, the increase of total membrane spot number due to the presence of fragments at day 21 and the significant decrease at day 42 are suggestive of a universal phenomenon which is not efficiently tackled by either of the two additive solutions investigated in the present study. CONCLUSION: To further delve into the storage lesion issue for RBCs stored in AS-3, it would be interesting in the future to assay metabolic changes over storage progression as well.     

Alteration of the erythrocyte membrane skeletal ultrastructure in hereditary spherocytosis, hereditary elliptocytosis, and pyropoikilocytosis

The membrane skeleton of normal erythrocytes is largely organized into a hexagonal lattice of junctional complexes (JC) crosslinked by spectrin tetramers, and occasional double tetramers and hexamers. To explore possible skeletal alterations in hereditary spherocytosis (HS), elliptocytosis (HE), and pyropoikilocytosis (HPP), we have studied the ultrastructure of the spread membrane skeletons from a subpopulation of HS patients with a partial spectrin deficiency ranging from 43% to 86% of normal levels, and in patients with HPP who, in addition to a mild spectrin deficiency, also carried a mutant spectrin that was dysfunctional, thus reducing the ability of spectrin dimers to assemble into tetramers. Membrane skeletons derived from Triton-treated erythrocyte ghosts were examined by negative staining electron microscopy. HS membrane skeletons contained structural elements, consisting of JC and spectrin filaments similar to the normal skeleton. However, less spectrin filaments interconnected the JC, and the decrease of spectrin filaments attached to JC appeared to correlate with the severity of spectrin deficiency. Only in severe HS associated with severe spectrin deficiency was the loss of spectrin sufficient enough to disrupt the overall skeletal architecture. In contrast, membrane skeletons prepared from red blood cells (RBCs) of subjects with HPP were strikingly different from HS RBCs with a comparable degree of spectrin deficiency. Although HPP RBCs were only mildly deficient in spectrin, their skeletal lattice was grossly disrupted, in contrast to only mild ultrastructural abnormalities of HS membrane skeletons with a nearly identical degree of spectrin deficiency. Skeletons from patients with common mild HE or asymptomatic carriers, carrying the mutant spectrin but having normal spectrin content, exhibited a moderate disruption of the skeletal lattice. We propose that the above differences in skeletal ultrastructure may underlie differences in the biomechanical properties and morphology of HS, HE, and HPP RBCs.     

Spectrin autoantibodies in normal human serum and in polyclonal blood grouping sera

Naturally occurring spectrin autoantibody was detected in normal human sera and in polyclonal blood grouping sera by the immunoblotting technique. The autoantibody seems to be IgG, stable, of high titre and low affinity. It was detected in all sera tested. Preparations of monoclonal antibodies directed against some blood group antigens and anti-A1 lectin reagent were devoid of spectrin autoantibody as expected. This autoantibody may be instrumental in clearing red cell membrane components from the circulation during haemolysis. Care must be exercised in studies designed to determine the association of some blood group antigens with the red cell membrane skeleton, when using polyclonal sera which contain spectrin autoantibodies in addition to the antibodies against the blood group antigen in question.     

Poikilocytic hereditary elliptocytosis associated with spectrin Alexandria: an alpha I/50b Kd variant that is caused by a single amino acid deletion

Hereditary elliptocytosis (HE) is a heterogeneous disorder of red blood cells frequently associated with abnormal limited tryptic digestion of the alpha I domain of spectrin and impaired spectrin dimer self- association. We studied two related individuals with poikilocytic hereditary elliptocytosis (HE) of different severity. Limited tryptic digestion of spectrin from these individuals showed the presence of a variant alpha I/50b Kd peptide at the expense of the normal alpha I/80 Kd peptide. Amino acid sequence analysis of the abnormal peptide showed that the proteolytic cleavage occurred after the arginine at position 470 of the alpha spectrin chain. Spectrin from these patients had an impaired ability to undergo self-association, as evidenced by increased amounts of spectrin dimers in 4 degrees C extracts of erythrocyte membrane from affected individuals. The polymerase chain reaction was used to study the DNA sequence of the alpha spectrin gene encoding the region of the alpha spectrin chain surrounding the abnormal proteolytic cleavage site. We detected the in-frame deletion of the trinucleotide CAT, encoding histidine 469, two amino acid residues to the N-terminal side of the abnormal proteolytic cleavage site between residues 470 and 471. Similar to many other defects of spectrin associated with HE, this deletion occurs in helix three of repeat 5 of the proposed triple helical model of spectrin repeats.     

Interferon-alpha alters spectrin organization in normal and leukemic human B lymphocytes

Interferon-alpha (IFN-alpha) regulates the growth, differentiation, and recirculation of normal and malignant B lymphocytes. In this report we examine the effects of IFN-alpha on the distribution of the cytoskeletal protein spectrin in peripheral blood B lymphocytes from normal donors and patients diagnosed with chronic lymphocytic leukemia (CLL) and hairy cell leukemia (HCL). Exposure of normal and leukemic B cells to IFN-alpha in vitro was shown by immunofluorescence microscopy to cause a dose-dependent increase in the percentage of cells containing discrete focal accumulations of spectrin, ie, a single large aggregate or cap-like structure near the plasma membrane. Although the magnitude of this effect was variable among individual patient samples, in some experiments IFN-alpha induced a fourfold increase in the percentage of leukemic B cells exhibiting focal accumulations of spectrin. Spectrin reorganization induced by IFN-alpha was abrogated by the protein synthesis inhibitor cycloheximide. In addition, IFN-alpha increased the total cellular content of spectrin in B-CLL cells by approximately twofold to fourfold. Finally, a role for protein kinase C in mediating the effects of IFN-alpha on spectrin's organization is implicated by studies in which calphostin C inhibited the IFN-induced focal accumulation of spectrin. Taken together, these studies suggest that the immunomodulatory activities of IFN-alpha in normal and malignant B cells involve a change in the organization of the spectrin- based cytoskeleton.     

Spectrin modifications in a heterozygous case of both hereditary elliptocytosis and beta-thalassemia

The clinical and hematological parameters of a patient described here, who inherited the genes of both hereditary elliptocytosis (HE) and beta-thalassemia, seem to reflect a mutual enhancement of the two diseases. The coexistence of the two pathologies is probably also responsible for the observed changes in spectrin: the appearance of an extra spectrin band between tetramers and dimers on denaturing gel electrophoresis and the metabolic-dependent reduction in spectrin amount. It is assumed that the instability of the skeletal network that results from the HE pathology caused increased exposure of the spectrin molecule to oxidative damage that usually occurs in thalassemic red cells. The products of such oxidation may have led to abnormal spectrin associations which finally resulted in the above changes.     

Partial spectrin deficiency in hereditary pyropoikilocytosis

Hereditary pyropoikilocytosis (HPP) is a severe hemolytic anemia in which an instability of the red cell membrane skeleton has been correlated with structural and functional defects of spectrin. We now report that 13 unrelated HPP subjects have approximately 30% less spectrin than normal as evidenced by a decreased spectrin/band 3 ratio. We also examine the role of spectrin degradation as an underlying cause of this partial spectrin deficiency. Our studies demonstrate that the reduced spectrin content of HPP red cells remains constant during in vivo aging of the cells in the peripheral blood, as well as during in vitro incubation. Furthermore, immunoblotting experiments using an affinity-purified antispectrin antibody indicate that there is no loss of spectrin during membrane preparation and also that neither whole HPP red cells nor ghosts nor cytosol contains any abnormal spectrin degradation products. These data suggest that spectrin is not degraded and that it is stable on the membrane of the circulating HPP red cell. In contrast, however, incubation of free spectrin with a lysate of nucleated erythroid precursor cells indicates that HPP alpha I/46 spectrin, but not HPP alpha I/74 spectrin, is more susceptible to proteolytic degradation than a control. These data imply that the decreased spectrin content of HPP is not due to a single defect but that a more complex mechanism is involved. In HPP Sp alpha I/46 subjects, an increased proteolytic degradation in bone marrow erythroid precursors of cytosolic spectrin, prior to its assembly on the membrane, could contribute toward the partial spectrin deficiency.     

Adhesive activity of Lu glycoproteins is regulated by interaction with spectrin

The Lutheran (Lu) and Lu(v13) blood group glycoproteins function as receptors for extracellular matrix laminins. Lu and Lu(v13) are linked to the erythrocyte cytoskeleton through a direct interaction with spectrin. However, neither the molecular basis of the interaction nor its functional consequences have previously been delineated. In the present study, we defined the binding motifs of Lu and Lu(v13) on spectrin and identified a functional role for this interaction. We found that the cytoplasmic domains of both Lu and Lu(v13) bound to repeat 4 of the alpha spectrin chain. The interaction of full-length spectrin dimer to Lu and Lu(v13) was inhibited by repeat 4 of alpha-spectrin. Further, resealing of this repeat peptide into erythrocytes led to weakened Lu-cytoskeleton interaction as demonstrated by increased detergent extractability of Lu. Importantly, disruption of the Lu-spectrin linkage was accompanied by enhanced cell adhesion to laminin. We conclude that the interaction of the Lu cytoplasmic tail with the cytoskeleton regulates its adhesive receptor function.