Membrane flickering of the human erythrocyte: physical and chemical effectors

Correlating nanoscale motion and ATP production in healthy and favism erythrocytes: a real-time nanomotion sensor study

Introduction

Red blood cells (RBCs) are among the simplest, yet physiologically relevant biological specimens, due to their peculiarities, such as their lack of nucleus and simplified metabolism. Indeed, erythrocytes can be seen as biochemical machines, capable of performing a limited number of metabolic pathways. Along the aging path, the cells' characteristics change as they accumulate oxidative and non-oxidative damages, and their structural and functional properties degrade.

Methods

In this work, we have studied RBCs and the activation of their ATP-producing metabolism using a real-time nanomotion sensor. This device allowed time-resolved analyses of the activation of this biochemical pathway, measuring the characteristics and the timing of the response at different points of their aging and the differences observed in favism erythrocytes in terms of the cellular reactivity and resilience to aging. Favism is a genetic defect of erythrocytes, which affects their ability to respond to oxidative stresses but that also determines differences in the metabolic and structural characteristic of the cells.

Results

Our work shows that RBCs from favism patients exhibit a different response to the forced activation of the ATP synthesis compared to healthy cells. In particular, the favism cells, compared to healthy erythrocytes, show a greater resilience to the aging-related insults which was in good accord with the collected biochemical data on ATP consumption and reload.

Conclusion

This surprisingly higher endurance against cell aging can be addressed to a special mechanism of metabolic regulation that permits lower energy consumption in environmental stress conditions.

Surface model of the human red blood cell simulating changes in membrane curvature under strain

We present mathematical simulations of shapes of red blood cells (RBCs) and their cytoskeleton when they are subjected to linear strain. The cell surface is described by a previously reported quartic equation in three dimensional (3D) Cartesian space. Using recently available functions in Mathematica to triangularize the surfaces we computed four types of curvature of the membrane. We also mapped changes in mesh-triangle area and curvatures as the RBCs were distorted. The highly deformable red blood cell (erythrocyte; RBC) responds to mechanically imposed shape changes with enhanced glycolytic flux and cation transport. Such morphological changes are produced experimentally by suspending the cells in a gelatin gel, which is then elongated or compressed in a custom apparatus inside an NMR spectrometer. A key observation is the extent to which the maximum and minimum Principal Curvatures are localized symmetrically in patches at the poles or equators and distributed in rings around the main axis of the strained RBC. Changes on the nanometre to micro-meter scale of curvature, suggest activation of only a subset of the intrinsic mechanosensitive cation channels, Piezo1, during experiments carried out with controlled distortions, which persist for many hours. This finding is relevant to a proposal for non-uniform distribution of Piezo1 molecules around the RBC membrane. However, if the curvature that gates Piezo1 is at a very fine length scale, then membrane tension will determine local curvature; so, curvatures as computed here (in contrast to much finer surface irregularities) may not influence Piezo1 activity. Nevertheless, our analytical methods can be extended address these new mechanistic proposals. The geometrical reorganization of the simulated cytoskeleton informs ideas about the mechanism of concerted metabolic and cation-flux responses of the RBC to mechanically imposed shape changes.

Differential dielectroscopic data on the relation of erythrocyte membrane skeleton to erythrocyte deformability and flicker

Two dielectric relaxations, βsp (1.5 MHz) and γ1sp (7 MHz), have been detected on spectrin-based membrane skeleton (MS) of red blood cells (RBCs) using the plot of admittance changes at the spectrin denaturation temperature (Ivanov and Paarvanova in Bioelectrochemistry 110: 59-68, 2016, Electrochim Acta 317: 289-300, 2019a). In this study, we treated RBCs and RBC ghost membranes with agents that make membranes rigid and suppress membrane flicker, and studied the effect on βsp and γ1sp relaxations. Diamide (diazene dicarboxylic acid bis-(N,N-dimethylamide)) (up to 0.85 mM), taurine mustard (tris(2-chloroethyl)amine) (up to 2 mM), known to specifically cross-link and stiffen spectrin, and glutaraldehyde (up to 0.044%) all inhibited the relaxations in RBC ghost membranes. Similar inhibition was obtained resealing RBC ghost membranes with 2,3-diphosphoglicerate (up to 15 mM), binding WGA (wheat germ agglutinin) (up to 0.025 mg/ml) to exofacial aspect of RBCs, incubating RBCs in hypotonic (200 mOsm) and hypertonic (600-900 mOsm) media and depleting RBCs of ATP. By contrast, concanavalin A (1 mg/ml) and DIDS (4,4'-diiso-thiocyanato stilbene-2,2'-disulfonic acid) (75 μM, pH 8.2), both known to bind specifically band 3 integral protein of RBCs without effect on RBC membrane rigidity, did not affect the relaxations. We conclude there might be a relation between the strength of dielectric relaxations on MS spectrin and the deformability and flicker of RBC membrane.

Effect of hydrogen peroxide on normal and acatalasemic mouse erythrocytes

OBJECTIVES

Normal and acatalasemic mouse erythrocytes were used to clarify the relationship between oxidative damage in H2O2-treated erythrocytes and catalase activity.

DESIGN & METHODS

Generation of hydrolysis-resistant erythrocytes and hemolysis were examined. The osmotic fragility test, the negative charges and the number of membrane-flickering erythrocytes among the H2O2-treated erythrocytes were investigated.

RESULTS

Small amounts of hydrolysis-resistant mouse erythrocytes were generated by treatment with 0.1 mM H2O2, and the amount of acatalasemic erythrocytes was larger than untreated controls. Hemolysis in the acatalasemic erythrocytes was observed 30 min after the addition of the H2O2. A drastic increase in hydrolysis-resistant erythrocytes and a loss of membrane proteins in the acatalasemic erythrocytes were found as a result of the addition of 1 mM H2O2. Hemolysis in normal erythrocytes was observed at 3 mM H2O2.

CONCLUSIONS

Catalase is a potent H2O2-scavenger even in acatalasemic mouse erythrocytes. It is concluded that the drastic increase of hydrolysis-resistant erythrocytes is induced by a loss of membrane function and is associated with the low catalase activity in these cells.

Heat damage of cytoskeleton in erythrocytes increases membrane roughness and cell rigidity

The intensity of erythrocyte membrane fluctuations was studied by laser interference microscopy (LIM), which provide information about mechanical properties of the erythrocyte membrane. Atomic force microscopy (AFM) was used to study erythrocyte surface relief; it is related to the cytoskeleton structure of erythrocyte membrane. Intact human erythrocytes and erythrocytes with a destroyed cytoskeleton were used. According to the obtained results, cytoskeleton damage induced by heating up to 50 °С results in a reduced intensity of cell membrane fluctuations compared to non-treated cells (20.6 ± 10.2 vs. 30.5 ± 5.5 nm, correspondingly), while the roughness of the membrane increases (4.5 ± 1.5 vs. 3.4 ± 0.5 nm, correspondingly).

Accelerating metabolism and transmembrane cation flux by distorting red blood cells

Under static conditions, mammalian red blood cells (RBCs) require a continuous supply of energy, typically via glucose, to maintain their biconcave disc shape. Mechanical distortion, in a complementary way, should lead to increased energy demand that is manifest in accelerated glycolysis. The experimental challenge in observing this phenomenon was met by reversibly and reproducibly distorting the cells and noninvasively measuring glycolytic flux. This was done with a gel-distorting device that was coupled with ¹³C nuclear magnetic resonance (NMR) spectroscopy. We measured [3-¹³C]l-lactate production from [1,6-¹³C]d-glucose in the RBCs suspended in gelatin gels, and up to 90% rate enhancements were recorded. Thus, for the first time, we present experiments that demonstrate the linkage of mechanical distortion to metabolic changes in whole mammalian cells. In seeking a mechanism for the linkage between shape and energy supply, we measured transmembrane cation flux with Cs⁺ (as a K⁺ congener) using ¹³³Cs NMR spectroscopy, and the cation flux was increased up to fivefold. The postulated mechanism for these notable (in terms of whole-body energy consumption) responses is stimulation of Ca-adenosine triphosphatase by increased transmembrane flux of Ca²⁺ via the channel protein Piezo1 and increased glycolysis because its flux is adenosine triphosphate demand-regulated.

Membrane flickering of the human erythrocyte: constrained random walk used with Bayesian analysis

The involvement of adenosine triphosphate (ATP) in erythrocyte (red blood cell; RBC) membrane flickering is of particular interest, because ATP turnover in the cell as a whole is not yet fully accounted for. We sought the origins of flickering by deriving a mathematical model of it, on the basis of the idea of thermally driven collisions of small molecules with the membrane, which responds like an over-damped spring. The model gave simulated responses that were similar to a constrained random walk and had the same frequency-spectral characteristics of membrane displacement as those recorded from RBCs by use of differential interference contrast light microscopy. Bayesian analysis was used as the basis for determination, from experimental results, of the values of the parameters in the model. The analysis was used in the accompanying article in which we investigated the response of membrane flickering to different effector molecules and physicochemical conditions. The results implied ATP was involved only indirectly in membrane flickering.