Mechanical Properties Of Cell Membrane Research Articles

A perspective on modeling pore energy and pulsed electromagnetic field induced cell membrane perforation

Pulsed electric field-induced electroporation has been widely used, but its specific perforation theory has not been fully elucidated. Therefore, this Perspective paper takes as a clue the dynamic development relationship between the pore energy and the pore state in cell membranes. First, based on the contribution of line tension, surface tension, steric repulsion, and applied electric field to pore energy, the theoretical models of reversible electroporation of a microsecond pulsed electric field and irreversible electroporation of a high-frequency nanosecond pulsed electric field are reviewed. Then, the contribution of elastic strain energy to pore energy is increased, and the theoretical model of pulsed electric field electroporation considering the mechanical properties of cell membranes is further reviewed. Based on the contribution of magnetic stress generated by the magnetic field and the gradient magnetic field to pore energy, a theoretical model of cell membrane magnetoporation under the action of a pulsed magnetic field is proposed, which lays a theoretical foundation for the popularization and application of non-contact cell membrane perforation technology.

Model of inverse bleb growth explains giant vacuole dynamics during cell mechanoadaptation.

Cells can withstand hostile environmental conditions manifest as large mechanical forces such as pressure gradients and/or shear stresses by dynamically changing their shape. Such conditions are realized in the Schlemm's canal of the eye where endothelial cells that cover the inner vessel wall are subjected to the hydrodynamic pressure gradients exerted by the aqueous humor outflow. These cells form fluid-filled dynamic outpouchings of their basal membrane called giant vacuoles. The inverses of giant vacuoles are reminiscent of cellular blebs, extracellular cytoplasmic protrusions triggered by local temporary disruption of the contractile actomyosin cortex. Inverse blebbing has also been first observed experimentally during sprouting angiogenesis, but its underlying physical mechanisms are poorly understood. Here, we hypothesize that giant vacuole formation can be described as inverse blebbing and formulate a biophysical model of this process. Our model elucidates how cell membrane mechanical properties affect the morphology and dynamics of giant vacuoles and predicts coarsening akin to Ostwald ripening between multiple invaginating vacuoles. Our results are in qualitative agreement with observations from the formation of giant vacuoles during perfusion experiments. Our model not only elucidates the biophysical mechanisms driving inverse blebbing and giant vacuole dynamics, but also identifies universal features of the cellular response to pressure loads that are relevant to many experimental contexts.

Effect of the mechanical properties of the cell membrane on the transition energy barrier of electroporation

The mechanical properties of the cell membrane play an important role in electroporation. This paper studied the influence of the mechanical properties of the cell membrane on the transition energy of electroporation through both modeling and experiments. An electromechanical coupling model of a single pore on the cell membrane was established in COMSOL, and the effect of elastic strain energy on the formation of pores was analyzed. Additionally, to compare the transition energy barrier of pores for different elastic properties of the cell membrane, electroporation experiments were carried out at different temperatures. The simulation showed that the elastic strain energy of the cell membrane increased the transition energy barrier of the pores. The experiments also showed that the transition energy barrier was larger when the elasticity of the cell membrane is intact, which was in good agreement quantitatively with the simulation results. We demonstrated that the mechanical properties of the cell membrane hinder the pore formation, which may be due to the increase of the transition energy barrier. We analyzed the possible mechanism of the effect of cell membrane mechanical properties on electroporation and found the contribution of cell membrane mechanical properties to electroporation during the delivery of exogenous substances, which can provide guidance for improving therapies in electrochemotherapy.

Atomic force microscopy in the assessment of erythrocyte membrane mechanical properties with exposure to various physicochemical agents

Background: Mechanical properties of cell membranes and their structural organization are considered among the most important biological parameters affecting the functional state of the cell. Under the influence of various pathogenic factors, erythrocyte membranes lose their elasticity. The resulting changes in their biomechanical characteristics is an important, but poorly studied topic. It is of interest to study the deformation of native erythrocytes to a depth compatible with their deformation in the bloodstream.Aim: To investigate the patterns of deep deformation and the particulars of structural organization of native erythrocyte membranes before and after their exposure to physicochemical agents in vitro.Materials and methods: Cell morphology, nanostructure characteristics, and membrane deformation of native erythrocytes in a solution of hemoconservative CPD/SAGM were studied with atomic force microscope NTEGRA Prima. Hemin, zinc ions (Zn2+), and ultraviolet (UV) radiation were used as modifiers. To characterize the membrane stiffness, we measured the force curves F(h), hHz (the depth to which the probe immersion is described by interaction with a homogeneous medium), and the Young's modulus values of the erythrocyte membrane.Results: Exposure to hemin, Zn2+ and UV radiation led to transformation of the cell shape, appearance of topological defects and changes in mechanical characteristics of erythrocyte membranes. Under exposure to hemin, Young's modulus increased from 10±4 kPa to 27.2±8.6 kPa (p<0.001), exposure to Zn2+, to 21.4±8.7 kPa (p=0.002), and UV, to 18.8±5.6 kPa (p=0.001). The hHz value was 815±210 nm for the control image and decreased under exposure to hemin to 420±80 nm (p<0.001), Zn2+, to 370±90 nm (p<0.001), and UV, to 614±120 nm (p=0.001).Conclusion: The results obtained contribute to a deeper understanding of interaction between membrane surfaces of native erythrocytes and small vessel walls. They can be useful in clinical medicine as additional characteristics for assessment of the quality of packed red blood cells, as well as serve as a basis for biophysical studies into the mechanisms of action of oxidative processes of various origins.

Contact probing of prestressed adhesive membranes of living cells.

Atomic force microscopy (AFM) studies of living biological cells is one of main experimental tools that enable quantitative measurements of deformation of the cells and extraction of information about their structural and mechanical properties. However, proper modelling of AFM probing and related adhesive contact problems are of crucial importance for interpretation of experimental data. The Johnson-Kendall-Roberts (JKR) theory of adhesive contact has often been used as a basis for modelling of various phenomena including cell-cell interactions. However, strictly speaking the original JKR theory is valid only for contact of isotropic linearly elastic spheres, while the cell membranes are often prestressed. For the first time, effects caused by molecular adhesion for living cells are analytically studied taking into account the mechanical properties of cell membranes whose stiffness depends on the level of the tensile prestress. Another important question is how one can extract the work of adhesion between the probe and the cell. An extended version of the Borodich-Galanov method for non-direct extraction of elastic and adhesive properties of contacted materials is proposed to apply to experiments of cell probing. Evidently, the proposed models of adhesive contact for cells with prestressed membranes do not cover all types of biological cells because the structure and properties of the cells may vary considerably. However, the obtained results can be applied to many types of smooth cells and can be used to describe initial stages of contact and various other processes when effects of adhesion are of crucial importance. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Measurement of dynamic membrane mechanosensation using optical tweezers.

Many cellular processes are orchestrated by dynamic changes in the plasma membrane to form membrane projections and endocytic vesicles in response to extracellular environmental changes. Our previous studies show that ARF6-ACAP4-ezrin signaling regulates membrane dynamics and curvature in response to EGF stimulation. However, there is no quantitative measurement to relate molecular organization of membrane cytoskeletal remodeling to stimulus-elicited mechanosensation on the plasma membrane. Optical tweezers is a powerful tool in the study of membrane tension. Comparing to pulling out an entire membrane tether at one time, the step-like method is more efficient because multiple relaxation curves can be obtained from one membrane tether. Fewer models describe relaxation curves to characterize mechanical properties of cell membrane. Here we establish a new method to measure the membrane relaxation curve of HeLa cells judged by the relationship between membrane tether diameter and tensions. We obtained effective viscosities and static tensions by fitting relaxation curves to our model. We noticed the delicate structure of relaxation curves contains information of cytoskeletal remodeling and lateral protein diffusion. Our study established a quantitative measure to characterize the mechanosensation of epithelial cells in response to stimulus-elicited membrane dynamics.

Interferon-Induced Transmembrane Protein 3 Blocks Fusion of Diverse Enveloped Viruses by Altering Mechanical Properties of Cell Membranes.

Interferon-induced transmembrane protein 3 (IFITM3) potently inhibits entry of diverse enveloped viruses by trapping the viral fusion at a hemifusion stage, but the underlying mechanism remains unclear. Here, we show that recombinant IFITM3 reconstituted into lipid vesicles induces negative membrane curvature and that this effect maps to its small amphipathic helix (AH). We demonstrate that AH (i) partitions into lipid-disordered domains where IAV fusion occurs, (ii) induces negative membrane curvature, and (iii) increases lipid order and membrane stiffness. These effects on membrane properties correlate with the fusion-inhibitory activity, as targeting the ectopically expressed AH peptide to the cytoplasmic leaflet of the cell plasma membrane diminishes IAV-cell surface fusion induced by exposure to acidic pH. Our results thus imply that IFITM3 inhibits the transition from hemifusion to full fusion by imposing an unfavorable membrane curvature and increasing the order and stiffness of the cytoplasmic leaflet of endosomal membranes. Our findings reveal a universal mechanism by which cells block entry of diverse enveloped viruses.

Interferon-Induced Transmembrane Protein 3 Blocks Fusion of Diverse Enveloped Viruses by Locally Altering Mechanical Properties of Cell Membranes

Interferon-induced transmembrane protein 3 (IFITM3) potently inhibits entry of diverse enveloped viruses by trapping the viral fusion at a hemifusion stage, but the underlying mechanism remains unclear. Here, we show that recombinant IFITM3 reconstituted into lipid vesicles induces negative membrane curvature and that this effect maps to its small amphipathic helix (AH). We demonstrate that AH: (i) partitions into lipid-disordered domains where IAV fusion occurs, (ii) induces negative membrane curvature, and (iii) increases lipid order and membrane stiffness. Additionally, replacing the IFITM3 AH with AH from an unrelated protein did not compromise its antiviral activity. These effects on membrane properties correlate with the fusion-inhibitory activity, as exogenous addition of AH to insulin-producing cells reduces glucose-stimulated insulin secretion. Our results thus imply that IFITM3 inhibits the transition from hemifusion to full fusion by imposing an unfavorable membrane curvature and increasing the order and stiffness of the cytoplasmic leaflet of endosomal membranes.

PyOIF: Computational tool for modelling of multi-cell flows in complex geometries

A user ready, well documented software package PyOIF contains an implementation of a robust validated computational model for cell flow modelling. The software is capable of simulating processes involving biological cells immersed in a fluid. The examples of such processes are flows in microfluidic channels with numerous applications such as cell sorting, rare cell isolation or flow fractionation. Besides the typical usage of such computational model in the design process of microfluidic devices, PyOIF has been used in the computer-aided discovery involving mechanical properties of cell membranes. With this software, single cell, many cell, as well as dense cell suspensions can be simulated. Many cell simulations include cell-cell interactions and analyse their effect on the cells. PyOIF can be used to test the influence of mechanical properties of the membrane in flows and in membrane-membrane interactions. Dense suspensions may be used to study the effect of cell volume fraction on macroscopic phenomena such as cell-free layer, apparent suspension viscosity or cell degradation. The PyOIF module is based on the official ESPResSo distribution with few modifications and is available under the terms of the GNU General Public Licence. PyOIF is based on Python objects representing the cells and on the C++ computational core for fluid and interaction dynamics. The source code is freely available at GitHub repository, runs natively under Linux and MacOS and can be used in Windows Subsystem for Linux. The communication among PyOIF users and developers is maintained using active mailing lists. This work provides a basic background to the underlying computational models and to the implementation of interactions within this framework. We provide the prospective PyOIF users with a practical example of simulation script with reference to our publicly available User Guide.

Changes in the physicochemical properties of fish cell membranes during cellular senescence.

Fish cell lines are widely used for the studies of developmental biology, virology, biology of aging, and nutrition physiology. However, little is known about their physicochemical properties. Here, we report the phospholipid compositions and mechanical properties of cell membranes derived from freshwater, anadromous and marine fish species. Biophysical analyses revealed that fish cell lines have highly deformable cell membranes with significantly low membrane tensions and Young's moduli compared with those of mammalian cell lines. The induction of cellular senescence by DNA demethylation using 5-Aza-2'-deoxycytidine significantly reduced the deformability of fish cell membrane, but hydrogen peroxide-induced oxidative stress did not affect the deformability. Mass spectrometry analysis of phospholipids revealed that the level of phosphatidylethanolamine molecules containing polyunsaturated fatty acids significantly increased during the 5-Aza-2'-deoxycytidine-induced cellular senescence. Fish cell lines provide a useful model system for studying the changes in the physicochemical properties of cell membranes during cellular senescence.Abbreviations: 2D-TLC: two-dimensional thin layer chromatography; 5-Aza-dC: 5-Aza-2'-deoxycytidine; DHA: docosahexaenoic acid; EPA: eicosapentaenoic acid; FBS: fetal bovine serum; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PI: phosphatidylinositol; PS: phosphatidylserine; PUFA: polyunsaturated fatty acid; SA-β-gal: senescence-associated beta-galactosidase; SM: sphingomyelin.

Measurement of mechanical properties of naked cell membranes using atomic force microscope puncture test

Cell membrane defines the physical boundary of the cell, maintains their shape and volume, and meanwhile dominates the cells response to mechanical force. There are many limitations in the mechanical analysis of naked cell membrane, such as cell condition, the supporting of cytoskeleton and cytoplasm. To reduce these influences, non-supported membrane was prepared on high-ordered pore array silicon substrate. Rupture forces and Young's modulus of three non-supported membranes, red blood cell membrane, somatic cell (MDCK) membrane and phospholipids membrane, are obtained quantitatively using AFM puncture tests. Results indicate that the sequence of both rupture forces and Young's modulus of the three membranes is MDCK cell membrane > red blood cell membrane > phospholipids membrane. The determinant of naked cell membrane's mechanical properties is the constituent of membrane itself, including the quantity and distribution of membrane proteins. Focused on the distribution of membrane proteins, two proposed models of cell membrane—the semi-mosaic model of red blood cell membrane and the Protein Layer-Lipid-Protein Island (PLLPI) model of nucleated mammalian cell membrane can be used to explain the different mechanical properties of naked cell membranes.

Characteristics of phospholipid vesicles enhanced by adhesion on an annular region.

Phospholipid vesicle membranes are simple models used to study the mechanical properties of cell membranes. The shapes of flaccid vesicles can exhibit very diverse forms. When researching very flaccid vesicles, axisymmetrical vesicles with the membranes adhered to an annular region can also be observed. A phase diagram of such shapes was studied for different values of the vesicle parameters, i.e., the adhesion constant, the vesicle volume-to-membrane ratio, the volume ratio between the polar and the equatorial parts, and the equilibrium difference between the membrane monolayers. The energies of the annular shapes with respect to the vesicle parameters were closely examined and compared with the energies of the discocyte and stomatocyte shapes. The requirements for the existence of such annular shapes were also given for adhesion-free vesicle membranes. The results show that the adhesion between the lipid bilayers stabilizes the observed shapes, which belong to the locally stable branch of the annular vesicles. The value obtained for the adhesion constant of the SOPC membrane is 3×10^{-9}J/m^{2}.

Membrane Mechanical Properties Regulate the Effect of Strain on Spontaneous Electrophysiology in Human iPSC-Derived Neurons

Peripheral nerves contain neuron fibers vital for movement and sensation and are subject to continuous elongation and compression during everyday movement. At supraphysiological strains conduction blocks occur, resulting in permanent or temporary loss of function. The mechanisms underpinning these alterations in electrophysiological activity remain unclear; however, there is evidence that both ion channels and network synapses may be affected through cell membrane transmitted strain. The aim of this work was to quantify the changes in spontaneous activity resulting from application of uniaxial strain in a human iPS-derived motor neuron culture model, and to investigate the role of cell membrane mechanical properties during cell straining. Increasing strain in a custom-built cell-stretching device caused a linear decrease in spontaneous activity, and no immediate recovery of activity was observed after strain release. Imaging neuronal membranes with c-Laurdan showed changes to the lipid order in neural membranes during deformation with a decrease in lipid packing. Neural cell membrane stiffness can be modulated by increasing cholesterol content, resulting in reduced stretch-induced decrease of membrane lipid packing and in a reduced decrease in spontaneous activity caused by mechanical strain. Together these results indicate that the mechanism whereby cell injury causes impaired transmission of neural impulses may be governed by the mechanical state of the cell membrane, and contribute to establishing a direct relationship between neural uniaxial straining and loss of spontaneous neural activity.

TRP Channels as Sensors of Chemically-Induced Changes in Cell Membrane Mechanical Properties.

Transient Receptor Potential ion channels (TRPs) have been described as polymodal sensors, being responsible for transducing a wide variety of stimuli, and being involved in sensory functions such as chemosensation, thermosensation, mechanosensation, and photosensation. Mechanical and chemical stresses exerted on the membrane can be transduced by specialized proteins into meaningful intracellular biochemical signaling, resulting in physiological changes. Of particular interest are compounds that can change the local physical properties of the membrane, thereby affecting nearby proteins, such as TRP channels, which are highly sensitive to the membrane environment. In this review, we provide an overview of the current knowledge of TRP channel activation as a result of changes in the membrane properties induced by amphipathic structural lipidic components such as cholesterol and diacylglycerol, and by exogenous amphipathic bacterial endotoxins.

Effects of electroformation protocol parameters on quality of homogeneous GUV populations

Giant unilamellar vesicles (GUVs) have become one of extensively studied biological bilayer models especially when investigating topological and mechanical properties of cell membranes. They are also used to visualize membrane-related phenomena. However, the method of preparation and the effects of parameters of preparation on the vesicular structure are extensively varied. Therefore, it is important to understand how the process of formation of GUVs influences the outcome population, as it can influence the outcome of the experiment that is planned. Therefore, in this study, we investigated the effects of protocol parameters of electroformation on properties of homogeneous population of POPC GUVs. The parameters investigated in this study are duration of electroformation, usage of electrodes and frequency of applied AC field and its voltage. The properties investigated, which can be used to describe GUV populations are average diameter of vesicle, the amount of lipid molecules in population, and structure of vesicles. According to our results, prolonged time (greater than 4 h) does not influence outcome; however, parameters of applied electrical field (voltage and frequency) did significantly influence the properties of obtained POPC GUV populations.

Self-assembled Lipid Structures as Model Systems for Studying Electrical and Mechanical Properties of Cell Membranes.

This mini review summarizes our recent works in the development of electrical and mechanical characterization tools for cell membranes. These research topics require the application of physical and chemical characterization tools to biological systems, thus are very interdisciplinary.

Cholesterol Depletion from a Ceramide/Cholesterol Mixed Monolayer: A Brewster Angle Microscope Study.

Cholesterol is crucial to the mechanical properties of cell membranes that are important to cells’ behavior. Its depletion from the cell membranes could be dramatic. Among cyclodextrins (CDs), methyl beta cyclodextrin (MβCD) is the most efficient to deplete cholesterol (Chol) from biomembranes. Here, we focus on the depletion of cholesterol from a C16 ceramide/cholesterol (C16-Cer/Chol) mixed monolayer using MβCD. While the removal of cholesterol by MβCD depends on the cholesterol concentration in most mixed lipid monolayers, it does not depend very much on the concentration of cholesterol in C16-Cer/Chol monolayers. The surface pressure decay during depletion were described by a stretched exponential that suggested that the cholesterol molecules are unable to diffuse laterally and behave like static traps for the MβCD molecules. Cholesterol depletion causes morphology changes of domains but these disrupted monolayers domains seem to reform even when cholesterol level was low.

The role of CD4 on mechanical properties of live cell membrane.

Although much progress has been made in the characterization and identification of CD4 functions, its role in mechanical properties of cell membrane remains largely unknown. Here an atomic force microscopy (AFM) was used to investigate the roles of CD4 in the elasticity of the leukemic human Jurkat (clone E6-1) cell membranes. Analysis of the approach force curves with Hertz model for a completely elastic soft sample measured on the selected CD4+ and CD4- cells showed that CD4+ cell membrane was softer than CD4- one. To confirm that CD4 plays a role in altering cell elasticity, human embryonic kidney 293T cells were transiently transfected with wild type (wt) CD4 plasmid before being used in AFM nanoindentation experiments. The results also demonstrated CD4- membrane was stiffer than CD4+ one suggesting that CD4 integrated into plasma membrane and altered its mechanical properties. The study gives insights into the role of CD4 on cell membrane mechanical characteristics and might be helpful for development of cell biology and medicine.

Dynamics of Membrane Tethers Reveal Novel Aspects of Cytoskeleton-Membrane Interactions in Axons

Mechanical properties of cell membranes are known to be significantly influenced by the underlying cortical cytoskeleton. The technique of pulling membrane tethers from cells is one of the most effective ways of studying the membrane mechanics and the membrane-cortex interaction. In this article, we show that axon membranes make an interesting system to explore as they exhibit both free membrane-like behavior where the tether-membrane junction is movable on the surface of the axons (unlike many other cell membranes) as well as cell-like behavior where there are transient and spontaneous eruptions in the tether force that vanish when F-actin is depolymerized. We analyze the passive and spontaneous responses of axonal membrane tethers and propose theoretical models to explain the observed behavior.

Biomechanical Basis of Alzheimer's Disease and Other Protein Misfolding Diseases: Designing a New AFM Probe to Study Amyloid-Mediated Membrane Disorders

Most important biological interactions with its environment occur at interfaces such as a lipid cellular membrane. These interactions are often dynamic and show time-dependent changes in material properties (e.g, viscoelastic properties). A detailed understanding of biomechanical properties at molecular and subcellular level is vital for basic understanding of normal/abnormal biological processes. Indeed, abnormal changes in the mechanics of biological systems are often indicators of pathophysiological states. For example, amyloid beta peptide (Aβ), a protein present in neural plaques formed in Alzheimer's disease and cholesterol are reported to alter cell membrane mechanical properties leading to neuronal degeneration. Atomic force microscopy (AFM) provides an ideal tool to image the structure and examine the mechanics in physiologically relevant medium. We have created a new cantilevered probe for AFM for the study of nano-to-microscale mechanics of biological interfaces. We used it to examine the role of Aβ1-42 insertion in DPPC lipid monolayers and its effect on the viscoelastic properties that underlie altered membrane fluidity. Real-time analysis of mechanical properties of the model membrane monolayer in the presence of Aβ1-42 shows a decrease in the viscosity of the monolayers over time, consistent with increased membrane fluidity. The finding is consistent with changes in membrane permeability due to Aβ-inserted pores.