Membrane Localization of Piezo1 in the Context of Its Role in the Regulation of Red Blood Cell Volume.

Piezo1 is a membrane nonspecific cation channel involved in red blood cells (RBCs) in the regulation of their volume. Recently, it was shown that it is distributed on the RBC membrane in a nonuniform manner. Here it is shown that it is possible to interpret the lateral distribution of Piezo1 molecules on RBC membrane by the curvature dependent Piezo1-bilayer interaction which is the consequence of the mismatch between the intrinsic principal curvatures of the Piezo1 trimer and the principal curvatures of the membrane at Piezo1's location but without its presence.

Theoretical Bases for the Role of Red Blood Cell Shape in the Regulation of Its Volume.

The red blood cell (RBC) membrane contains a mechanosensitive cation channel Piezo1 that is involved in RBC volume homeostasis. In a recent model of the mechanism of its action it was proposed that Piezo1 cation permeability responds to changes of the RBC shape. The aim here is to review in a descriptive manner different previous studies of RBC behavior that formed the basis for this proposal.

A Model of Piezo1-Based Regulation of Red Blood Cell Volume.

A red blood cell (RBC) performs its function of adequately carrying respiratory gases in blood by its volume being ∼60% of that of a sphere with the same membrane area. For this purpose, human and most other vertebrate RBCs regulate their content of potassium (K) and sodium (Na) ions. The focus considered here is on K efflux through calcium-ion (Ca)-activated Gárdos channels.

Investigating cell functioning by theoretical analysis of cell-to-cell variability.

Here we discuss cell-to-cell variability in isogenic cell populations on the basis of an analogy between the processes of vesicle self-reproduction and cell self-replication. A short review of the theoretical analysis of vesicle self-reproduction is presented to indicate that this process only occurs under the fulfillment of specific criteria: causal relations between the values of vesicle variables involved in its growth and division, and the parameters of the environment. It is shown that when division is asymmetric, both vesicle birth size and interdivision times are variable.

A novel strain energy relationship for red blood cell membrane skeleton based on spectrin stiffness and its application to micropipette deformation.

Red blood cell (RBC) membrane skeleton is a closed two-dimensional elastic network of spectrin tetramers with nodes formed by short actin filaments. Its three-dimensional shape conforms to the shape of the bilayer, to which it is connected through vertical linkages to integral membrane proteins. Numerous methods have been devised over the years to predict the response of the RBC membrane to applied forces and determine the corresponding increase in the skeleton elastic energy arising either directly from continuum descriptions of its deformation, or seeking to relate the macroscopic behavior of the membrane to its molecular constituents.

Curvature-dependent protein-lipid bilayer interaction and cell mechanosensitivity.

Cells respond to applied external forces through different mechanosensitive processes, with many of them based on the interaction between membrane-embedded proteins and their lipid environments. This interaction can depend on membrane curvature at the location of such proteins. Here we elucidate the general characteristics of a macroscopically defined protein-lipid bilayer interaction based on a mismatch between the shape of the protein surface and the surrounding membrane curvature.

Mechanical and molecular basis for the symmetrical division of the fission yeast nuclear envelope.

In fission yeast Schizosaccharomyces pombe, the nuclear envelope remains intact throughout mitosis and undergoes a series of symmetrical morphological changes when the spindle pole bodies (SPBs), embedded in the nuclear envelope, are pushed apart by elongating spindle microtubules. These symmetrical membrane shape transformations do not correspond to the shape behavior of an analogous system based on lipid vesicles. Here we report that the symmetry of the dividing fission yeast nucleus is ensured by SPB-chromosome attachments, as loss of kinetochore clustering in the vicinity of SPBs results in the formation of abnormal asymmetric shapes with long membrane tethers.

Sorting of integral membrane proteins mediated by curvature-dependent protein-lipid bilayer interaction.

Cell membrane proteins, both bound and integral, are known to preferentially accumulate at membrane locations with curvatures favorable to their shape. This is mainly due to the curvature dependent interaction between membrane proteins and their lipid environment. Here, we analyze the effects of the protein-lipid bilayer interaction energy due to mismatch between the protein shape and the principal curvatures of the surrounding bilayer.

Direct and remote constriction of membrane necks.

The physical properties of membrane necks are relevant in vesiculation, a process that plays an essential role in cellular physiology. Because the neck's radius is, in general, finite, membrane scission and the consequent pinching off of the vesicle can only occur if it is narrowed to permit the necessary membrane topological reformation. Here we examine, in a simple single phase lipid vesicle, how external forces can promote neck constriction not only by direct compression at the neck but also, counterintuitively, by dilation at remote locations.

Nonlocal membrane bending: a reflection, the facts and its relevance.

About forty years ago it was realized that phospholipid membranes, because they are composed of two layers, exhibit particular, and specific mechanical properties. This led to the concept of nonlocal membrane bending, often called area difference elasticity. We present a short history of the development of the concept, followed by arguments for a proper definition of the corresponding elastic constant.

Partitioning of oleic acid into phosphatidylcholine membranes is amplified by strain.

Partitioning of fatty acids into phospholipid membranes is studied on giant unilamellar vesicles (GUVs) utilizing phase-contrast microscopy. With use of a micropipet, an individual GUV is transferred from a vesicle suspension in a mixed glucose/sucrose solution into an isomolar glycerol solution with a small amount of oleic acid added. Oleic acid molecules intercalate into the phospholipid membrane and thus increase the membrane area, while glycerol permeates into the vesicle interior and thus via osmotic inflation causes an increase of the vesicle volume.

Positioning of integrin β1, caveolin-1 and focal adhesion kinase on the adhered membrane of spreading cells.

We have investigated the relationship between the spreading of anchorage-dependent cells and the surface-density distribution of plasma membrane adhesion proteins. The surface positioning and density of integrin β1, caveolin-1 (cav-1), the phosphorylated caveolin-1 (p-cav-1) and the focal adhesion kinase (FAK) located on the adhering cell membrane (ACM) of HUVEC cells was studied. Imaging with TIRF microscopy was used, which enabled us to observe a few-nanometers-thin section of the cell above the plasma membrane in combination with image-based analyses.

Cellular life could have emerged from properties of vesicles.

It is indicated why it is plausible to assume that the initiation of cellular life was based on properties of vesicles. Vesicle properties relevant for the process of vesicle self-reproduction are revealed. Some open questions related to the idea that vesicle self-reproduction is an evolutionary process that includes the elements of the Darwinian selection are put forward, and some suggestions are made for possible directions of further research.

The dynamics of melittin-induced membrane permeability.

The transport of co-encapsulated solutes through the melittin-induced pores in the membrane of giant phospholipid vesicles was studied, and the characteristics of the pore formation process were modeled. Molecules of two different sizes (dextran and the smaller, fluorescent marker Alexa Fluor) were encapsulated inside the vesicles. The chosen individual vesicles were then transferred by micromanipulation from the stock suspension to the environment with the melittin (MLT).

Stress-free state of the red blood cell membrane and the deformation of its skeleton.

The response of a red blood cell (RBC) to deformation depends on its membrane, a composite of a lipid bilayer and a skeleton, which is a closed, two-dimensional network of spectrin tetramers as its bonds. The deformation of the skeleton and its lateral redistribution are studied in terms of the RBC resting state for a fixed geometry of the RBC, partially aspirated into a micropipette. The geometry of the RBC skeleton in its initial state is taken to be either two concentric circles, a references biconcave shape or a sphere.

Red blood cell shape and deformability in the context of the functional evolution of its membrane structure.

It is proposed that it is possible to identify some of the problems that had to be solved in the course of evolution for the red blood cell (RBC) to achieve its present day effectiveness, by studying the behavior of systems featuring different, partial characteristics of its membrane. The appropriateness of the RBC volume to membrane area ratio for its circulation in the blood is interpreted on the basis of an analysis of the shape behavior of phospholipid vesicles. The role of the membrane skeleton is associated with preventing an RBC from transforming into a budded shape, which could form in its absence due to curvature-dependent transmembrane protein-membrane interaction.

Effects of the pore-forming agent nystatin on giant phospholipid vesicles.

The effects of the polyene pore-forming agent nystatin were investigated on individual giant unilamellar phospholipid vesicles (GUVs), made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), in different methanol-water solutions using phase-contrast optical microscopy. Three characteristic effects were detected in three different nystatin concentration ranges: vesicle shape changes (between 150 and 250μM); transient, nonspecific, tension pores (between 250 and 400μM); and vesicle ruptures (above 400μM). Both the appearance of the transient tension pores and the vesicle ruptures were explained as being a consequence of the formation of size-selective nystatin channels, whose membrane area density increases with the increasing nystatin concentrations.

Budding of giant unilamellar vesicles induced by an amphitropic protein β2-glycoprotein I.

β(2)-glycoprotein I (β(2)GPI) is a plasma protein capable of binding reversibly to membranes, and is classified among the amphitropic proteins. Part of the protein intercalates into the outer membrane leaflet, altering the difference between the preferred areas of the membrane leaflets, which results in membrane shape transformations. Budding, as a specific example of such shape transformations, was studied using giant unilamellar vesicles.

Vesicle budding and the origin of cellular life.

This Minireview provides an appropriate opportunity to demonstrate the connection between the results of some early experimental and theoretical investigations of vesicle budding and the more recent application of the concepts developed there to the process of vesicle self-reproduction. Herein, we also explain why vesicle budding could have preceded the establishment of cellular life.

Comment on "Thermodynamics of vesicle growth and instability".

Fanelli and McKane [Phys. Rev. E 78, 051406 (2008)] recently described the growth of vesicles due to the accretion of lipid molecules onto their surface in terms of linear irreversible thermodynamics.

Equilibrium mechanics of monolayered epithelium.

In order to fully understand the epithelial mechanics it is essential to integrate different levels of epithelial organization. In this work, we propose a theoretical approach for connecting the macroscopic mechanical properties of a monolayered epithelium to the mechanical properties at the cellular level. The analysis is based on the established mechanical models-at the macroscopic scale the epithelium is described within the mechanics of thin layers, while the cellular level is modeled in terms of the cellular surface (cortical) tension and the intercellular adhesion.

Growth and shape transformations of giant phospholipid vesicles upon interaction with an aqueous oleic acid suspension.

The interaction of two types of vesicle systems was investigated: micrometer-sized, giant unilamellar vesicles (GUVs) formed from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and submicrometer-sized, large unilamellar vesicles (LUVs) formed from oleic acid and oleate, both in a buffered aqueous solution (pH 8.8). Individual POPC GUVs were transferred with a micropipette into a suspension of oleic acid/oleate LUVs, and the shape changes of the GUVs were monitored using optical microscopy.

Time lapse monitoring of CaCo-2 cell shapes and shape dependence of the distribution of integrin β1 and F-actin on their basal membrane.

CaCo-2 cell line is a model system for cell differentiation. For the effective use of CaCo-2 cells, it is important to understand how their growth depends on environmental conditions. The authors grew them on laminin-1, fibronectin, and collagen-1 adsorbed to glass and polystyrene.

Morphology of small aggregates of red blood cells.

Blood can be considered a two-phase liquid composed of plasma as well as cells and cell aggregates. The degree of cell aggregation is an important determinant of blood rheology: The size and shape of the aggregates affect blood viscosity. The microscopic mechanisms of red blood cell adhesion involve a complex interplay of electrostatic, van der Waals, and a range of specific biochemical inter-membrane interactions.

Vesicle self-reproduction: the involvement of membrane hydraulic and solute permeabilities.

Conditions for self-reproduction are sought for a growing vesicle with its growth defined by an exponential increase of vesicle membrane area and by adequate flow of the solution across the membrane. In the first step of the presumed vesicle self-reproduction process, the initially spherical vesicle must double its volume in the doubling time of the membrane area and, through the appropriate shape transformations, attain the shape of two equal spheres connected by an infinitesimally thin neck. The second step involves separation of the two spheres and relies on conditions that cause the neck to be broken.