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K de Jong

Publications and source records attributed to K de Jong.

18 recordsLinked to original sources
PubMed2001

Short survival of phosphatidylserine-exposing red blood cells in murine sickle cell anemia.

Several transgenic murine models for sickle cell anemia have been developed that closely reproduce the biochemical and physiological disorders in the human disease. A comprehensive characterization is described of hematologic parameters of mature red blood cells, reticulocytes, and red cell precursors in the bone marrow and spleen of a murine sickle cell model in which erythroid cells expressed exclusively human alpha, gamma, and betaS globin. Red cell survival was dramatically decreased in these anemic animals, partially compensated by considerable enhancement in erythropoietic activity. As in humans, these murine sickle cells contain a subpopulation of phosphatidylserine-exposing cells that may play a role in their premature removal. Continuous in vivo generation of this phosphatidylserine-exposing subset may have a significant impact on the pathophysiology of sickle cell disease.

Anemia, Sickle Cell↗
PubMed2001

Characterization of the phosphatidylserine-exposing subpopulation of sickle cells.

Phosphatidylserine (PS), exclusively present in the inner monolayer of the normal red blood cell (RBC) membrane, is exposed in subpopulations of sickle cells. PS-exposing RBCs were found predominantly among the densest and the very light sickle cells. Within the light RBC fraction, PS exposure was found on reticulocytes, transferrin receptor-expressing reticulocytes, and mature RBCs. The last subset contained low-density valinomycin-resistant RBCs, previously shown to have high Na(+) and low K(+) content. This subpopulation contained the highest percentage of PS-exposing cells. The PS-exposing sickle cells did not show the sustained high cytosolic Ca(++) levels that have been shown to activate scramblase activity. Data from this study indicate that PS exposure can occur at different stages in the life of the sickle RBC and that it correlates with the loss of aminophospholipid translocase activity, the only common denominator of the PS-exposing cells. The additional requirement of scramblase activation may occur during transient increases in cytosolic Ca(++). (Blood. 2001;98:860-867)

Anemia, Sickle Cell↗
PubMed2001

Glycophorin A dimerization and band 3 interaction during erythroid membrane biogenesis: in vivo studies in human glycophorin A transgenic mice.

Band 3 and glycophorin A (GPA) are the 2 most abundant integral proteins in the human erythrocyte membrane. Earlier studies suggested that the 2 proteins may associate not only in the mature erythrocyte membrane, but also during their posttranslational processing and intracellular trafficking. The purpose of this study was to directly examine the GPA-band 3 interaction in vivo and determine the nature of this association during erythroid membrane biogenesis. Transgenic mice were generated expressing the human glycophorin A gene and were used to examine how the induction of human GPA expression affected the levels of murine GPA and band 3 expression in the red cell membrane. Murine GPA expression was reduced in erythrocytes expressing human GPA, whereas the level of band 3 expression remained constant, implying a tight coupling of band 3 and GPA expression in the membrane of mature red cells. In vivo GPA dimerization was not modulated solely by the GPA transmembrane motif, but the distance between this motif and the basic residues on the cytoplasmic side of the transmembrane domain may also be important. In addition, GPA monomers with varying degrees of glycosylation dimerized, providing clear evidence that carbohydrate structures on the extracellular domain do not affect dimerization. The association between the multiple transmembrane-spanning protein, band 3, and the single transmembrane-spanning sialoglycoprotein, GPA, may serve as a model for interactions of other multi-pass and single-pass polypeptides during membrane biogenesis.

Animals↗
PubMed1999

Hereditary spherocytosis and elliptocytosis erythrocytes show a normal transbilayer phospholipid distribution.

Phosphatidylserine (PS) asymmetry was determined in red blood cells from patients with hereditary spherocytosis and elliptocytosis. No PS-exposing subpopulations were detected using the very sensitive method with fluorescently labeled annexin V. Treatment with N-ethylmaleimide or adenosine triphosphate (ATP) depletion to inactivate the flipase did not lead to formation of PS-exposing subpopulations in these cells, but elevated intracellular calcium levels did lead to extensive scrambling of the PS asymmetry. Although interactions of the membrane skeleton with the phospholipid bilayer have been suggested to stabilize the asymmetric distribution of PS across the bilayer, our data show that red blood cells with a severely damaged membrane skeleton are able to preserve asymmetry, even under conditions in which restoration of the asymmetric distribution is excluded. Moreover, the loss of membrane asymmetry in these cells requires active scrambling involving high levels of intracellular calcium as in normal cells. Our data show that the severe disorder of the membrane skeleton found in these cells does not affect the activity of flipase or scramblase, indicating that these proteins are not regulated by, nor coupled to the membrane skeleton assembly, and that possible thrombotic events in spherocytosis patients are not likely associated with altered PS topology of the red blood cells.

Annexin A5↗
PubMed1999

Detection of phosphatidylserine surface exposure on human erythrocytes using annexin V-ferrofluid.

The asymmetric transbilayer distribution of phospholipids in the plasma membrane and the regulation of phosphatidylserine (PS) exposure at the cell surface of animal cells are of high physiological significance. It has been shown previously that annexin V is one of the most sensitive tools with which the presence of small amounts of PS on the outer surface of eukaryotic cells can be detected. We present here the covalent coupling of annexin V molecules to magnetic nanoparticles of maghemite. The resulting annexin V-ferrofluid is used in the magnetic separation of PS exposing cells, as illustrated for human erythrocytes modified in their phospholipid transbilayer asymmetry by the use of a calcium ionophore. Results on stored human erythrocytes and comparison with results obtained using iodinated and fluorescein-labeled annexin V are also presented.

Annexin A5↗
PubMed1998

Membrane phospholipid asymmetry in human thalassemia.

Phospholipid asymmetry in the red blood cell (RBC) lipid bilayer is well maintained during the life of the cell, with phosphatidylserine (PS) virtually exclusively located in the inner monolayer. Loss of phospholipid asymmetry, and consequently exposure of PS, is thought to play an important role in red cell pathology. The anemia in the human thalassemias is caused by a combination of ineffective erythropoiesis (intramedullary hemolysis) and a decreased survival of adult RBCs in the peripheral blood. This premature destruction of the thalassemic RBC could in part be due to a loss of phospholipid asymmetry, because cells that expose PS are recognized and removed by macrophages. In addition, PS exposure can play a role in the hypercoagulable state reported to exist in severe beta-thalassemia intermedia. We describe PS exposure in RBCs of 56 comparably anemic patients with different genetic backgrounds of the alpha- or beta-thalassemia phenotype. The use of fluorescently labeled annexin V allowed us to determine loss of phospholipid asymmetry in individual cells. Our data indicate that in a number of thalassemic patients, subpopulations of red cells circulate that expose PS on their outer surface. The number of such cells can vary dramatically from patient to patient, from as low as that found in normal controls (less than 0.2%) up to 20%. Analysis by fluorescent microscopy of beta-thalassemic RBCs indicates that PS on the outer leaflet is distributed either over the entire membrane or localized in areas possibly related to regions rich in membrane-bound alpha-globin chains. We hypothesize that these membrane sites in which iron carrying globin chains accumulate and cause oxidative damage, could be important in the loss of membrane lipid organization. In conclusion, we report the presence of PS-exposing subpopulations of thalassemic RBC that are most likely physiologically important, because they could provide a surface for enhancing hemostasis as recently reported, and because such exposure may mediate the rapid removal of these RBCs from the circulation, thereby contributing to the anemia.

Annexin A5↗
PubMed1997

Oxidative damage does not alter membrane phospholipid asymmetry in human erythrocytes.

Oxidant-induced damage has been proposed to be the underlying mechanism for loss of membrane phospholipid asymmetry in the erythrocyte membrane. In sickle cell disease, thalassemia, and diabetes as well as in senescent erythrocytes, an apparent correlation between oxidative damage and loss of phosphatidylserine asymmetry has been reported. In the present study, erythrocytes were subjected to various levels of oxidative stress and/or sulfhydryl modifying agents. The transmembrane location of phosphatidylserine (PS) was assessed by FITC-conjugated annexin V labeling and the PS-dependent prothrombinase assay. Transbilayer movement of spin-labeled PS was used to determine aminophospholipid translocase activity. Our data show that cells did not expose PS as the result of oxidative stress induced by phenylhydrazine, hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, or sulfhydryl modification by N-ethylmaleimide (NEM) and diamide, even under conditions that led to severe cellular damage and impairment of aminophospholipid translocase activity. In contrast, the increase of intracellular calcium induced by treatment with calcium and ionophore A23187 leads to a rapid scrambling of the lipid bilayer and the exposure of PS, which can be exacerbated by the inhibition of aminophospholipid translocase activity. Oxidation of the cells with hydrogen peroxide or phenylhydrazine did not affect A23187-induced uptake of calcium, but partly inhibited calcium-induced membrane scrambling. In conclusion, oxidative damage of erythrocytes does not induce exposure of phosphatidylserine on the membrane surface, but can interfere with both aminophospholipid translocase activity and calcium-induced randomization of membrane phospholipids.

Aniline Compounds↗
PubMed1996

Phospholipid asymmetry in red blood cells and spectrin-free vesicles during prolonged storage.

Erythrocytes and spectrin-free DMPC-induced vesicles released from the cells were incubated for 3 weeks at 6 degrees C under conditions of metabolic ATP-depletion. Phosphatidylserine (PS) asymmetry was monitored during this period by use of the prothrombinase assay. Prothrombinase activities measured at the beginning of the incubation period indicated that approximately 0.06% of PS was located at the outer layer of the red cell membrane, whereas in DMPC-induced vesicles approximately 1.5% the PS was exposed on the outside. After completion of the incubation period PS exposure on the outside of red cells and vesicles was increased by no more than 5-fold. On the other hand, with vesicles prepared with a significantly increased (4-fold) ATP-content to sustain translocase activity, the incubation process resulted in a surprisingly high (20-fold) increase of PS exposure. With vanadate, an inhibitor of the aminophospholipid translocase, included in the incubation medium, the redistribution of PS was even more pronounced. These observations indicate that PS asymmetry in spectrin-free vesicles can not be directly correlated to either ATP content or translocase activity and suggest that besides the aminophospholipid translocase and the membrane skeleton, other mechanisms must be involved in maintaining phospholipid asymmetry.

Adenosine Triphosphate↗
PubMed1993

Membrane phospholipid asymmetry in DMPC-induced human red cell vesicles.

Vesicles that do not contain spectrin were released from human erythrocytes by incubation with dimyristoylphosphatidylcholine. The transbilayer orientation of membrane phospholipids was subsequently determined by two independent methods. Incubation with phospholipase A2 revealed that the phospholipid asymmetry observed in red blood cells was essentially preserved in vesicles. By use of the prothrombinase assay a still highly asymmetric distribution of phosphatidylserine could be demonstrated in spite of its slightly increased exposure on the vesicle surface. These results show that membrane phospholipid asymmetry can be maintained in a system that does not contain an intact membrane skeleton or spectrin.

Bee Venoms↗
PubMed1991

An articulatory study of consonant-induced vowel duration changes in English.

The effects of voicing, manner, and number of consonants on the duration of previous vowels in English can be created in three ways: by planned expansion or contraction of the entire vowel, by changing the relative timing of consonant and vowel gestures, or by modifying the duration of the closing movement for the consonants. An X-ray microbeam data base of 2 speakers of American English reciting monosyllabic words, which differed in their final consonants and in their position in the accentual structure of the utterance, was studied to evaluate these three accounts. In this data base, vowel duration differences due to the voicing of the following consonants were amplified by the presence of accent. Also, many of the duration differences associated with the following consonants are localized in the later portion of the opening movement, suggesting that subjects often create vowel duration changes by initiating the consonant closing gesture at an earlier or later time relative to the opening gesture.

Humans↗
PubMedDate not supplied

The interplay between prosodic structure and coarticulation.

In this paper we draw on a linguistic model of prosodic structure and a task-dynamic model of speech gestures to account for the interplay of coarticulation and stress in English. We reinterpret results from two experiments in which articulator movements were recorded for utterances varying in pitch accept placement. In the first experiment, jaw kinematics were studied in post-nuclear unaccented and nuclear accented [pap] syllables. The kinematic patterns suggested that gestures in syllables with greater stress (nuclear accented) show less coarticulatory overlap. By contrast, the vowel's low jaw target is undershot in unaccented syllables. Two hypotheses are possible. Either the jaw is lower in stressed syllables so more energy can radiate from the mouth ("sonority expansion") or the jaw is lower to help distinguish the low vowel from other vowels ("hyperarticulation"). Another experiment differentiates the two hypotheses by examining tongue point positions in [put] preceding a [th]. In the more stressed syllables, the tongue dorsum retracts more, likely to make a more distinct back vowel. Also, the amount of assimilation of the alveolar stop to the following dental is reduced. Both results suggest hyperarticulation rather than sonority expansion. Thus, it seems that coarticulation is reduced in stressed syllables, because stressed syllables are hyperarticulated.

Female↗