Biologičeskie membrany

Specific patterns of lipid distribution in cell membranes determine their structural and signaling roles, and ensure the integrity and functionality of the plasma membrane and cell organelles. Recent advances in the development of recombinant lipid biosensors and imaging techniques allow direct observation of the distribution, movement, and dynamics of lipids within cells, significantly expanding the understanding of lipid functions and their involvement in cellular and subcellular processes. In this review, we summarize the data related to the development and application of recombinant protein sensors for various lipids in cell membranes.

The transfer of protons between the surface of lipid membrane and water can be slowed down by the presence of a high potential barrier, which affects the functioning of proton-transporting proteins. To evaluate the rate of the proton transfer across the barrier, the photoactivatable compounds that can adsorb on the membrane boundary and release protons upon excitation are used. One of these compounds, which we studied earlier, sodium salt of 2-methoxy-5-nitrophenylsulfate (MNPS), was used in this work. The molecule of MNPS can adsorb on the bilayer lipid membrane (BLM) as anion and release sulfate and proton upon excitation with UV light, becoming an electroneutral product. Upon illumination of the BLM, on one side of which MNPS anions were adsorbed, changes in the electrostatic potential at the membrane–water interface were observed. The slow changes of the potential were measured by the intramembrane field compensation method and the fast changes, by the operational amplifier as an electrometer. When the light was switched on, the potential increased rapidly, and when the light was switched off, the potential slowly returned to its initial value. The rate of rapid potential increase depended on the lipid composition of BLM, buffer concentration, and pH of the medium. The dependence of this rate on pH was different for BLMs formed from phosphatidylcholine and its mixture with phosphatidylserine. With increasing buffer concentration, the rate decreased tens of times. The results obtained indicate that the reaction of proton release formed during the excitation of MNPS molecules occurs both on the membrane surface and in the water near it. The main contribution to the change in the electrostatic potential at the membrane boundary is given by protons bound at its surface from the reaction in water.

Controlled formation of through pores in bilayer lipid membranes is a key stage of various biotechnological techniques. Excess energy of the pore edge is characterized by line tension, the value of which determines the overall stability of the membrane with respect to pore formation. The practically important pore size is on the order of a few nanometers. It is impossible to study such pores by direct optical methods, but they can, in principle, be visualized by atomic force microscopy. This method uses a solid support on which the lipid bilayer is held due to the interaction of one of the monolayers with it. In this work, we theoretically investigated the effect of the presence of the support on the value of the line tension of the pore edge. It was assumed that the line tension is determined by the energy of elastic deformations of the membrane at the edge. Various regimes of membrane interaction with the support were considered: from a free-standing membrane (complete absence of interaction) to the case of infinitely strong adhesion of the membrane to the support. The calculation results show that the relative change in the line tension of the pore edge within such variation of the intensity of the interaction of the membrane with the support is less than 3.5%. Thus, the developed theoretical model predicts an extremely weak effect of the interaction with the support on the magnitude of the line tension–the main energy characteristic of the pore edge.

Although the current COVID-19 incidence situation is not an emergency, more new strains of SARS-CoV-2 coronavirus continue to emerge worldwide, some of which are more virulent than the original virus. Studies have shown that patients with Alzheimer's disease (AD) had a high risk of severe COVID-19, but the molecular and cellular mechanism of this predisposition is not fully elucidated. In this study, we developed a cellular model of the initial stage of COVID-19 on primary hippocampal culture of 5xFAD mice, a familial AD model, using a specific ACE2 receptor inhibitor, MLN-4760. This model is based on the experimentally proven decrease in ACE2 receptor activity observed in COVID-19 patients due to internalization of the receptor inside the cell after binding to coronavirus. Using immunochemical staining with specific antibodies to detect neurons (marker MAP2) and astroglia (marker GFAP), it was found that 24 h after the addition of MLN-4760 (0.2 nmol per 1 mL of medium) to the culture medium, there was a decrease in the density of astrocytes and neurons, a change in their morphology with a sharp reduction in the length and density of neurites, which led to the death of the cell culture. The transgenic culture was more sensitive to the effect of the inhibitor compared to the control hippocampal culture of native mice. In the second part of the study the possibilities of preventing the destructive effect of MLN-4760 on the hippocampal culture condition were studied. It was shown that administration of YB-1, an endogenous polyfunctional stress protein, promoted restoration of cell culture structure and resulted in stimulation of neurite growth and astroglia activation. Introduction of multipotent mesenchymal stromal cells (MMSCs) after ACE2 blockade was also accompanied by improved culture survival, restoration of cell morphology, and increased density of astrocytes and neurons. The obtained results indicate that YB-1 and cell therapy using MMSCs are promising options for the development of new effective methods to prevent the pathological effect of the virus on brain tissue, which is an important link in the treatment of infection caused by SARS-CoV-2 virus.