Human erythrocyte shape regulation: interaction of metabolic and redox status

The Blood Bag Plasticizer Di-2-Ethylhexylphthalate Causes Red Blood Cells to Form Stomatocytes, Possibly by Inducing Lipid Flip-Flop

Background

During storage of red blood cell (RBC) concentrates, the plasticizer di-2-ethylhexylphthalate (DEHP) that keeps the blood bags soft leaches out and can be taken up by the RBCs. DEHP is known to be beneficial for the RBC storage quality, but the molecular mechanisms of the action are unknown.

Methods

Aqueous suspensions of DEHP were added to RBCs in buffer. The morphological effects were observed on RBCs from 5 donors. Flow cytometry with annexin A5 binding was used to measure the exposed phosphatidylserine.

Results

DEHP induced the formation of stomatocytes at concentrations as low as ng/ml, provided that the cell suspension was also sufficiently dilute. Some spherocytes, which were susceptible to lysis, were also formed; after lysis, RBC ghosts were seen to continue the transition to the cup-shaped stomatocyte form. Incubation with DEHP increased the exposed phosphatidylserine, an effect that was also observed in the presence of vanadate, which inhibits the ATP-dependent translocases that maintain the membrane's lipid asymmetry.

Conclusions

DEHP can have an active effect on RBC shape, instead of just preventing the storage-related shape changes. The effect appears to be mediated by increased flip-flop of lipids between the leaflets of the RBC membrane.

NMR q-space analysis of canonical shapes of human erythrocytes: stomatocytes, discocytes, spherocytes and echinocytes

q-Space plots obtained experimentally using pulsed field-gradient stimulated echo (PGSTE) nuclear magnetic resonance (NMR) spectroscopy from water diffusing in red blood cells (RBCs) of different canonical (distinct variant) morphologies have "signature" features. The experimental q-space plots from suspensions of stomatocytes, echinocytes and spherocytes generated chemically had no diffraction features; in contrast a sample of blood from a patient with hereditary spherocytosis showed diffraction minima. To understand the forms of q-space plots, mathematical/geometrical models of discocytes, stomatocytes, echinocytes and spherocytes were used as restricting boundaries in simulations of water diffusion with Monte Carlo random walks. These simulations indicated that diffusion-diffraction minima are expected for each of the cell shapes considered. The absence of diffusion-diffraction minima in stomatocytes generated by dithiothreitol treatment was surmised to be due to non-alignment of the cells with the magnetic field of the NMR spectrometer. Differential interference contrast microscopy images of the chemically generated spherocyte and echinocyte suspensions showed them to be heterogeneous in cell shape. Therefore, we concluded that the shape heterogeneity caused the loss of the diffusion-diffraction features, which were observed in the more homogeneous sample from a patient with hereditary spherocytosis, and in the simulations of homogeneous cell suspensions. This understanding of factors that affect q-space plots from RBC suspensions will assist morphological studies of other cell and tissue types.

Tetracysteine-based fluorescent tags to study protein localization and trafficking in Plasmodium falciparum-infected erythrocytes

Plasmodium falciparum (Pf) malaria parasites remodel host erythrocytes by placing membranous structures in the host cell cytoplasm and inserting proteins into the surrounding erythrocyte membranes. Dynamic imaging techniques with high spatial and temporal resolutions are required to study the trafficking pathways of proteins and the time courses of their delivery to the host erythrocyte membrane.

METHODOLOGY AND FINDINGS

Using a tetracysteine (TC) motif tag and TC-binding biarsenical fluorophores (BAFs) including fluorescein arsenical hairpin (FlAsH) and resorufin arsenical hairpin (ReAsH), we detected knob-associated histidine-rich protein (KAHRP) constructs in Pf-parasitized erythrocytes and compared their fluorescence signals to those of GFP (green fluorescent protein)-tagged KAHRP. Rigorous treatment with BAL (2, 3 dimercaptopropanol; British anti-Lewisite) was required to reduce high background due to nonspecific BAF interactions with endogenous cysteine-rich proteins. After this background reduction, similar patterns of fluorescence were obtained from the TC- and GFP-tagged proteins. The fluorescence from FlAsH and ReAsH-labeled protein bleached at faster rates than the fluorescence from GFP-labeled protein.

CONCLUSION

While TC/BAF labeling to Pf-infected erythrocytes is presently limited by high background signals, it may offer a useful complement or alternative to GFP labeling methods. Our observations are in agreement with the currently-accepted model of KAHRP movement through the cytoplasm, including transient association of KAHRP with Maurer's clefts before its incorporation into knobs in the host erythrocyte membrane.

Oxidative stress-associated shape transformation and membrane proteome remodeling in erythrocytes of end stage renal disease patients on hemodialysis

This study was designed to evaluate the oxidative stress status of erythrocytes and its association with cellular ultrastructure and membrane proteome modifications in patients with end stage renal disease (ESRD) on hemodialysis (HD). For that purpose, we studied red blood cells' (RBCs) modifications in twelve non-diabetic ESRD patients that were responsive in erythropoietin therapy. Intracellular ROS levels were measured by fluorometry, RBCs ultra-structure was examined by electron microscopy, while the membrane proteome by electrophoresis and immunoblotting. Compared to the healthy subjects, the uremic RBCs exhibited significantly increased ROS accumulation. Dialysis partially ameliorated the basal ROS levels but triggered cellular sensitivity to exogenous oxidative stimuli. Common membrane modifications involved loss, aggregation, fragmentation and carbonylation of critical components as well as over-expression of stress markers. HD significantly contributed to membrane proteome remodeling, especially for aquaporin-1, peroxiredoxin-2 and ubiquitinated proteins. The intracellular redox status and the closely associated membrane modifications seemed to be related to membrane instability, loss of surface area through vesiculation, echinocytosis and stomatocytosis. Our data evinced a network of interactions among the uremic toxins, the RBCs membrane composition and the cellular shape modifications in ESRD, which is developed around a core of oxidative provocations and cellular responses.

Extensive electroporation abolishes experimentally induced shape transformations of erythrocytes: a consequence of phospholipid symmetrization?

As shown in earlier work (M.M. Henszen et al., Mol. Membr. Biol. 14 (1997) 195-204), exposure of erythrocytes to single brief electric field pulses (5-7 kV cm(-1)) enhances the transbilayer mobility of phospholipids and produces echinocytes which can subsequently be transformed into stomatocytes in an ATP-dependent process. These shape transformations arise from partly reversible changes of the transbilayer disposition of phospholipids, in agreement with the bilayer couple concept. Extensive membrane modification by repetitive (</=20) field pulses followed by 20 h incubation at 37 degrees C is now shown to produce discocytic cells which are resistant to many established shape-transforming treatments, including (A) single electric field pulses, Ca(2+) incorporation and exposure to membrane active amphiphiles, but also (B) metabolic depletion, binding of band 3 ligands, alkaline pH and contact with glass surfaces. The suppression of type A effects can readily be interpreted by a complete symmetrization of the phospholipids in extensively field pulse-modified cells which prevents shape transformations related to the asymmetric disposition of the phospholipids. This symmetrization could be further substantiated by more direct determinations of the transbilayer distribution of phospholipids. Suppression of shape transformations of type B may indicate an involvement of phospholipid asymmetry in these processes on a yet unknown mechanistic basis. Alternatively we discuss field pulse-induced alterations of the disposition of peripheral proteins or of the conformation of integral membrane proteins as mechanisms interfering with shape transformations of type B.

Electric field pulses induce reversible shape transformation of human erythrocytes

Electric field pulses > 2-3 kV cm-1, long known to induce membrane poration and fusion of erythrocytes as well as to enhance the transbilayer mobility of phospholipids and to perturb aminophospholipid asymmetry, are shown to induce, at 0 degree C, transformation of the discocytic cells into echinocytes and spheroechinocytes. The extent of transformation increases with strength, duration and number of pulses. Its time course is biphasic, a major rapid phase (t/2 approximately 5 s) being followed by a minor one, lasting for 2-3 h. Shape transformation goes along with the exofacial exposure of phosphatidylserine (PS), detected by FITC-annexin V binding and quantified by a calibration curve established via externally inserted dilauroylphosphatidylserine. Incubation of these echinocytes at 37 degrees C leads to a rapid recovery of the discocytic shape followed by slower formation of stomatocytes. Shape recovery is temperature dependent (Ea approximately 100 kJ/mol), and can be impaired by depletion of ATP or Mg++ and by addition of vanadate or fluoride. Shape recovery and stomatocyte formation go along with a rapid loss of annexin binding in about 45% of the cells while the rest maintains its binding capacity. In the presence of vanadate, annexin binding increases in all cells. The results are discussed in the light of the bilayer couple concept of erythrocyte shape and the enhanced transverse mobility of phospholipids. Echinocyte formation is most likely caused by the reorientation of endofacial aminophospholipids to the outer leaflet of the bilayer. Shape recovery and stomatocyte formation probably result from a continuous reinternalization of PS via the ATP dependent aminophospholipid translocase, but may also be supported by downhill movement of PC to the inner leaflet and by other yet unidentified processes.

Dithiothreitol stimulates the activity of the plasma membrane aminophospholipid translocator

Metabolic depletion induces human erythrocytes to crenate, a shape change that is reversed when ATP is regenerated by nutrient supplementation. In the presence of the sulfhydryl reducing agent dithiothreitol (DTT), this shape reversal is exaggerated, proceeding beyond normal discoid morphology to stomatocytic forms. DTT-induced stomatocytosis does not correlate consistently with alterations in cell ATP, spectrin phosphorylation, or phosphoinositide metabolism (Truong, H.-T.N., Ferrell, J.E., Jr. and Huestis, W.H. (1986) Blood 67, 214-221). The effect of DTT on outer-to-inner-monolayer transport of aminophospholipids was examined by monitoring shape changes induced by dilauroylphosphatidylserine (DLPS). Stomatocytosis induced by transport of this exogenous lipid to the membrane inner monolayer is accelerated and exaggerated by DTT. The effect of DTT on DLPS translocation is reversible and temperature dependent, consistent with the intervention of reducing agents in the activity of the aminophospholipid translocator. These findings bear on the relationship between cell redox status and shape regulation.