Modulation of erythrocyte membrane mechanical stability by 2,3-diphosphoglycerate in the neonatal poikilocytosis/elliptocytosis syndrome

A Neonatal Patient Diagnosed with a COL4A1 Mutation Presenting with Hemorrhagic Infarction and Severe Jaundice

We report a patient diagnosed with a COL4A1 mutation in the early postnatal period. Patients with early postnatal jaundice, intracranial lesions that are negative for TORCH syndrome, and recurrent hemolytic anemia should be suspected of having a COL4A1/COL4A2 gene mutation.

Unravelling the genetic and phenotypic heterogeneity of SPTA1 gene variants in Hereditary Elliptocytosis and Hereditary Pyropoikilocytosis patients using next-generation sequencing

Hereditary Elliptocytosis (HE) and Hereditary Pyropoikilocytosis (HPP) are clinically and genetically heterogeneous red cell membranopathies that result from the defects in the horizontal linkage between RBC (red blood cell) membrane and cytoskeletal proteins affecting its mechanical stability and deformability thereby reducing its lifespan. The principal defect in HE and HPP is due to dysfunction or deficiency of RBC cytoskeletal proteins namely, α-spectrin (SPTA1), β-spectrin (SPTB) and protein 4.1R (EPB41R). This study reports the genetic and phenotypic heterogeneity of 10 Indian patients (5 with HE and 5 with HPP)harboringSPTA1 gene variants. We used targeted next-generation sequencing (t-NGS) to characterize the causative genetic variants in 10 HE/HPP suspected patients and studied the correlation between the identified variants with their corresponding phenotypic features.t-NGS detected 12 SPTA1 variants, out of which 8 are novel. Nearly all of the detected variants have a damaging effect on the protein stability and function, as shown by the insilico analysis. The possible effect of the detected variants on the protein structure was studied using the HOPE software and DynaMut tools wherever possible. To the best of our knowledge, this is the first report on HE/HPP cases confirmed by a genetic study from India. To conclude, HE is caused by monoallelic mutations while HPP, the more severe form, is typically caused by biallelic (homozygous or compound heterozygous) mutations justifying the phenotypic heterogeneity associated with patients. Moreover, analysis at the molecular level by NGS permits diagnosis in these disorders with highly variable heterogeneity requiring regular transfusions and may facilitate prognostic contemplations.

Novel COL4A1 mutations identified in infants with congenital hemolytic anemia in association with brain malformations

Genetic causes of undiagnosed hemolytic anemia in nineteen patients were analyzed by whole-exome sequencing, and novel COL4A1 variants were identified in four patients (21%). All patients were complicated with congenital malformations of the brain, such as porencephaly or schizencephaly. In these patients, hemolysis became less severe within 2 months after birth, and red cell transfusion was no longer required after 50 days, whereas chronic hemolysis continued.

Dizygotic twins with prolonged jaundice and microcytic, hypochromic, hemolytic anemia with pyropoikilocytosis

Dizygotic twin males, born at 34 weeks gestation, had prolonged jaundice, microcytic, hypochromic anemia, FABarts hemoglobin, elevated end-tidal CO, and blood films consistent with hereditary pyropoikilocytosis. DNA sequencing revealed both had a heterozygous alpha spectrin (SPTA1) mutation (c.460_462dup) inherited from their asymptomatic mother, plus a 3-base pair duplication in alpha globin (HBA2) (c.364_366dupGTG) inherited from their asymptomatic father.

Clinical Diagnosis of Red Cell Membrane Disorders: Comparison of Osmotic Gradient Ektacytometry and Eosin Maleimide (EMA) Fluorescence Test for Red Cell Band 3 (AE1, SLC4A1) Content for Clinical Diagnosis

The measurement of band 3 (AE1, SLC4A1, CD233) content of red cells by eosin-5- maleimide (EMA) staining is swiftly replacing conventional osmotic fragility (OF) test as a tool for laboratory confirmation of hereditary spherocytosis across the globe. Our group has systematically evaluated the EMA test as a method to screen for a variety of anemias in the last 10 years, and compared these results to those obtained with the osmotic gradient ektacytometry (osmoscans) which we have used over three decades. Our overall experience allowed us to characterize the distinctive patterns with the two tests in several congenital erythrocyte membrane disorders, such as hereditary spherocytosis (HS), hereditary elliptocytosis (HE), Southeast Asian Ovalocytosis (SAO), hereditary pyropoikilocytosis (HPP) variants, erythrocyte volume disorders, various red cell enzymopathies, and hemoglobinopathies. A crucial difference between the two methodologies is that osmoscans measure red blood cell deformability of the entire sample of RBCs, while the EMA test examines the band 3 content of individual RBCs. EMA content is influenced by cell size as smaller red cells have lower amount of total membrane than larger cells. The SAO mutation alters the EMA binding site resulting in a lower EMA MCF even as the band 3 content itself is unchanged. Thus, EMA scan results should be interpreted with caution and both the histograms and dot plots should be analyzed in the context of the clinical picture and morphology.

Algorithmic evaluation of hereditary erythrocytosis: Pathways and caveats

Multiple algorithms have been published for the evaluation of hereditary erythrocytosis (HE). Typical entry points begin after excluding the more common acquired conditions through investigations of clinical history and assessment of cardiac, pulmonary, or vascular system disorders. Prior exclusion of JAK2 mutations, particularly the common JAK2 V617F mutation, is indicated in adults but less so in pediatric populations. Key decision trees are based on serum erythropoietin levels and p50 results. Recent data reveal some overlap in clinical presentation and laboratory findings in erythrocytosis. Caveats to consider when using algorithmic approaches are discussed.

Inherited hemolytic anemia: a possessive beginner's guide

Significant advances have been made in diagnosis and clinical management of inherited red cell membrane disorders that result in hemolytic anemia. Membrane structural defects lead to hereditary spherocytosis (HS) and hereditary elliptocytosis (HE), whereas altered membrane transport function accounts for hereditary xerocytosis (HX) and hereditary overhydrated stomatocytosis (OHS). The degrees of membrane loss and resultant increases in cell sphericity determine the severity of anemia in HS and HE, and splenectomy leads to amelioration of anemia by increasing the circulatory red cell life span. Alterations in cell volume as a result of disordered membrane cation permeability account for reduced life span red cells in HX and OHS. Importantly, splenectomy is not beneficial in these 2 membrane transport disorders and is not recommended because it is ineffective and may lead to an increased risk of life-threatening thrombosis. Rational approaches are now available for the diagnosis and management of these inherited red cell disorders, and these will be discussed in this review.

Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders

Hereditary spherocytosis and elliptocytosis are the two most common inherited red cell membrane disorders resulting from mutations in genes encoding various red cell membrane and skeletal proteins. Red cell membrane, a composite structure composed of lipid bilayer linked to spectrin-based membrane skeleton is responsible for the unique features of flexibility and mechanical stability of the cell. Defects in various proteins involved in linking the lipid bilayer to membrane skeleton result in loss in membrane cohesion leading to surface area loss and hereditary spherocytosis while defects in proteins involved in lateral interactions of the spectrin-based skeleton lead to decreased mechanical stability, membrane fragmentation and hereditary elliptocytosis. The disease severity is primarily dependent on the extent of membrane surface area loss. Both these diseases can be readily diagnosed by various laboratory approaches that include red blood cell cytology, flow cytometry, ektacytometry, electrophoresis of the red cell membrane proteins, and mutational analysis of gene encoding red cell membrane proteins.

Low-level mercury can enhance procoagulant activity of erythrocytes: a new contributing factor for mercury-related thrombotic disease

BACKGROUND

Associations between cardiovascular diseases and mercury have been frequently described, but underlying mechanisms are poorly understood.

OBJECTIVES

We investigate the procoagulant activation of erythrocytes, an important contributor to thrombosis, by low-level mercury to explore the roles of erythrocytes in mercury-related cardiovascular diseases.

METHODS

We used freshly isolated human erythrocytes and ex vivo and in vivo thrombosis models in rats to investigate mercury-induced procoagulant activity.

RESULTS

Prolonged exposure to low-dose mercuric ion (Hg(2+); 0.25-5 microM for 1-48 hr) induced erythrocyte shape changes from discocytes to echinocytes to spherocytes, accompanied by microvesicle (MV) generation. These MVs and remnant erythrocytes expressed phosphatidylserine (PS), an important mediator of procoagulant activation. Hg(2+) inhibited flippase, an enzyme that recovers PS into the inner leaflet of the cell membrane, and activated scramblase, an enzyme that alters lipid asymmetry in the cell membrane. Consistent with these activity changes, Hg(2+) increased intracellular calcium and depleted ATP and protein thiol. A thiol supplement reversed Hg(2+)-induced MV generation and PS exposure and inhibited the increase in calcium ion (Ca(2+)) and depletion of ATP, indicating that free-thiol depletion was critical to Hg(2+)-mediated procoagulant activity. The procoagulant activity of Hg(2+)-treated erythrocytes was demonstrated by increased thrombin generation and endothelial cell adhesion. We further confirmed Hg(2+)-mediated procoagulant activation of erythrocytes in ex vivo and in vivo rat thrombosis models, where Hg(2+) treatment (0.5-2.5 mg/kg) increased PS exposure and thrombus formation significantly.

CONCLUSION

This study demonstrated that mercury could provoke procoagulant activity in erythrocytes through protein-thiol depletion-mediated PS exposure and MV generation, ultimately leading to enhanced thrombosis.

Erythrocyte signal transduction pathways, their oxygenation dependence and functional significance

Erythrocytes play a key role in human and vertebrate metabolism. Tissue O2 supply is regulated by both hemoglobin (Hb)-O2 affinity and erythrocyte rheology, a key determinant of tissue perfusion. Oxygenation-deoxygenation transitions of Hb may lead to re-organization of the cytoskeleton and signalling pathways activation/deactivation in an O2-dependent manner. Deoxygenated Hb binds to the cytoplasmic domain of the anion exchanger band 3, which is anchored to the cytoskeleton, and is considered a major mechanism underlying the oxygenation-dependence of several erythrocyte functions. This work discusses the multiple modes of Hb-cytoskeleton interactions. In addition, it reviews the effects of Mg2+, 2,3-diphosphoglycerate, NO, shear stress and Ca2+, all factors accompanying the oxygenation-deoxygenation cycle in circulating red cells. Due to the extensive literature on the subject, the data discussed here, pertain mainly to human erythrocytes whose O2 affinity is modulated by 2,3-diphosphoglycerate, ectothermic vertebrate erythrocytes that use ATP, and to bird erythrocytes that use inositol pentaphosphate.

Hereditary elliptocytosis: spectrin and protein 4.1R

Hereditary elliptocytosis (HE) is a common disorder of erythrocyte shape, occurring especially in individuals of African and Mediterranean ancestry, presumably because elliptocytes confer some resistance to malaria. The principle lesion in HE is mechanical weakness or fragility of the erythrocyte membrane skeleton due to defects in alpha-spectrin, beta-spectrin, or protein 4.1. Numerous mutations have been described in the genes encoding these proteins, including point mutations, gene deletions and insertions, and mRNA processing defects. Several mutations have been identified in a number of individuals on the same genetic background, suggesting a "founder effect." The majority of HE patients are asymptomatic, but some may experience hemolytic anemia, splenomegaly, and intermittent jaundice.

Rhabdomyolysis and severe haemolytic anaemia, hepatic dysfunction and intestinal osteopathy due to hypophosphataemia in a patient after Billroth II gastrectomy

Hypophosphataemic syndromes lead to appreciable morbidity and mortality. A deficiency or lack of phosphate leads to tissue hypoxia and disruption of cellular function, which may cause severe clinical complications. We present various manifestations of hypophosphataemia; in all cases, diagnosis was delayed due to lack of follow-up. We present the case of a patient with rhabdomyolysis, severe haemolytic anaemia, hepatic dysfunction and intestinal osteopathy due to hypophosphataemia complicated by gastric Billroth II anastomosis surgery. We also review the literature concerning hypophosphataemic conditions. In conclusion, the determination of serum calcium and phosphate levels should be included in the routine follow-up of Billroth II anastomosed patients.

Morphological alterations and increased resistance to hemolysis in t-butyl hydroperoxide incubated RBC from elderly subjects

The response of human red blood cells (RBC) to oxidative stress has been studied with the aim to evaluate any difference in the behavior of cells from young and old subjects. Thus, RBC from 5 young (27 +/- 2 years) and 5 old (80 +/- 5 years) individuals have been treated with the organic peroxide t-butyl hydroperoxide (TBHP). The two groups behaved differently: after 4 hrs of incubation in 0.5 mM TBHP, RBC from young donors showed a higher level of hemolysis; instead, RBC from old individuals showed abnormal morphologies, being absent in unstressed RBC, with constriction and budding, which could be identified as poikilocytosis. The same abnormal forms are found in patients with spectrin mutation, leading us to hypothesize that TBHP causes damage to the cytoskeletal spectrin. This suggests that poikilocytosis might be an early stage of red blood cell hemolysis because their presence is associated to a lower level of hemolysis.

Elevated 2,3-diphosphoglycerate concentrations and alteration of structural integrity in the erythrocytes of Indian cases of visceral leishmaniasis

The visceral leishmaniasis (VL) known as kala-azar in India is characterized by severe anaemia. The anaemia seems to be the result, at least in part, of the relatively short life-time of the erythrocytes, which have weakened cell membranes, possibly because of elevated concentrations of 2,3-diphosphoglycerate (2,3-DPG). There is a negative correlation (r = 0.91; P < 0.01) between erythrocytic 2,3-DPG concentrations and the blood concentration of haemoglobin, and the erythrocytes from infected patients display higher osmotic fragility than those from uninfected controls. Spectrofluorometry, using 1,6-diphenyl 1,3,5-hexatriene as a probe, indicated that fluorescence depolarization and microviscosity are also higher in the erythrocytic membranes from VL cases than in those from the controls. The cholesterol/phospholipid ratio is also relatively high in the membranes from the VL cases and there is degradation of the skeletal components and the major integral protein (band 3). The enhanced concentration of 2,3-DPG may be related to the altered structural integrity of the erythrocytes and this may lead to anisocytosis and the reduction in the erythrocytic half life.

Recurrent fatal hydrops fetalis associated with a nucleotide substitution in the erythrocyte beta-spectrin gene

We studied a kindred in which four third-trimester fetal losses occurred, associated with severe Coombs-negative hemolytic anemia and hydrops fetalis. Postmortem examination of two infants revealed extensive extramedullary erythropoiesis. Studies of erythrocytes and erythrocyte membranes from the parents revealed abnormal erythrocyte membrane mechanical stability as well as structural and functional abnormalities in spectrin, the principal structural protein of the erythrocyte membrane. Genetic studies identified a point mutation of the beta-spectrin gene, S2019P, in a region of beta spectrin that is critical for normal spectrin function. Both parents and two living children were heterozygous for this mutation; three infants dying of hydrops fetalis were homozygous for this mutation. In an in vitro assay using recombinant peptides, the mutant beta-spectrin peptide demonstrated a significant abnormality in its ability to interact with alpha spectrin. This is the first description of a molecular defect of the erythrocyte membrane associated with hydrops fetalis.

Molecular basis of clinical and morphological heterogeneity in hereditary elliptocytosis (HE) with spectrin alpha I variants

The impaired ability of spectrin dimers to self-associate into tetramers is one of the most frequent defects associated with hereditary elliptocytosis (HE) and its more serious form, hereditary pyropoikylocytosis (HPP). We previously described four proteic variants of the spectrin (Sp) alpha I tryptic domain associated with the Sp dimer self-association defect (Sp alpha I/78, Sp alpha I/74, Sp alpha I/65, Sp alpha I/46 variants). Following the characterization of proteic variants, genomic molecular defects were identified and most of the mutations appeared to lie either in or near the self-association site, i.e. in the alpha I tryptic domain or in the beta I tryptic domain. The clinical severity of these different mutations varies considerably and ranges from asymptomatic to severe haemolytic disease such as in heterozygous HPP patients and in some homozygous HE patients. Studies of 113 patients from 61 HE families showed a correlation among parameters and showed which factors modulate the clinical expression of the molecular defect. Our analysis indicated that the clinical expression was directly correlated with the severity of the spectrin dimer self-association defect as evaluated by the increase in the Sp dimer percentage found in the 4 degrees C extract. A critical threshold of 40-50% of unassembled Sp dimer was determined; above that, patients exhibited severe haemolysis requiring splenectomy. The percentage of Sp dimer depends, in turn, on two factors: (i) the nature of the variant in relation to the position of the mutation versus the tetramerization site; (ii) the relative amount of mutant spectrin present in the membrane (ranging from 15% to 80% in heterozygous patients). As for the severity of haemolysis, the ghost mechanical stability to shear stress, as measured by ektacyometer, was also found to depend on the Sp dimer self-association defect. In contrast, the decrease in erythrocyte deformability was not related to the amount of unassembled Sp dimer but appeared to be correlated with the amount of mutant spectrin whatever the variant. Concerning erythrocyte morphology and the number of elliptocytes, the Sp alpha I/65 variant appears to be the most 'elliptocytogenic' variant, indicating that erythrocyte shape abnormality is not linked to the Sp dimer self-association defect.

Decreased membrane mechanical stability and in vivo loss of surface area reflect spectrin deficiencies in hereditary spherocytosis

Whereas marked variations in the clinical manifestations of hereditary spherocytosis have long been recognized, we have only recently begun to define the molecular basis for this heterogeneity. An important unanswered question is whether decreased spectrin results in reduced membrane mechanical stability, and if this reduction in membrane mechanical stability can be related to in vivo surface area loss. Using the ektacytometer, we quantitated membrane surface area and stability in erythrocytes from 18 individuals with hereditary spherocytosis and deficiencies of spectrin (30-80% of normal spectrin level). Membrane mechanical stability was reduced and the magnitude of the reductions correlated with the spectrin content. Moreover, the reductions in mechanical stability correlated with in vivo loss of membrane surface area. These data indicate that decreased spectrin content results in reduced membrane mechanical stability and surface area loss in vivo. We conclude that partial deficiencies of spectrin, reductions in membrane mechanical stability, and loss of membrane surface area are directly related and are major features determining the heterogeneous clinical manifestations of hereditary spherocytosis.

Hereditary elliptocytosis, spherocytosis and related disorders: consequences of a deficiency or a mutation of membrane skeletal proteins

The membrane skeleton, a protein lattice that laminates the internal side of the red cell membrane, contains four major proteins: spectrin, actin, protein 4.1 and ankyrin. By mass, the most abundant of these proteins is spectrin, a fibre-like protein composed of two chains, alpha and beta, which are twisted along each other into a heterodimer. At their head region, spectrin heterodimers are assembled into tetramers. At their distal end, these tetramers are interconnected into a two dimensional network by their linkage to oligomers of actin. This interaction is greatly strengthened by protein 4.1. The skeleton is attached to the membrane by ankyrin, a protein that connects the spectrin beta chain to the major transmembrane protein band 3, the anion channel protein. Additional attachment sites are those of protein 4.1 with several glycoproteins, namely glycophorin A and C, as well as direct interactions between spectrin, protein 4.1 and the negatively charged lipids of the inner membrane lipid bilayer. Hereditary spherocytosis, elliptocytosis and pyropoikilocytosis represent a group of disorders that are due to deficiency or dysfunction of one of the membrane skeletal proteins (Fig. 1). Known deficiency states include that of spectrin, ankyrin and protein 4.1. Severe spectrin and ankyrin deficiencies (with decrease in spectrin and ankyrin contents to about 50% of the normal amount) are both rare disorders associated with severe autosomal recessive hereditary spherocytosis. On the other hand, mild spectrin deficiency is found in the majority of patients with autosomal dominant spherocytosis in which the degree of spectrin deficiency correlates with the clinical severity of the disease. Protein 4.1 deficiency, in contrast, is associated with hereditary elliptocytosis, which in certain populations constitutes about 20% of all such patients. Known skeletal protein dysfunctions include mutants of both alpha and beta spectrin that involve the spectrin heterodimer self-association site. These are clinically expressed as hereditary elliptocytosis (HE) and a closely related disorder, hereditary pyropoikilocytosis (HPP). At the level of protein function, this defect can be detected by analysis of the content of spectrin dimers and tetramers in 0 degrees C low ionic strength extracts of red cell membranes. Their structural identification is accomplished by limited proteolytic digestion of spectrin followed by two-dimensional tryptic peptide mapping.(ABSTRACT TRUNCATED AT 400 WORDS)