Biochemistry (Moscow), Supplement Series A: Membrane and Cell Biology最新文献

In this work we investigated the rearrangements in the cristae structure and possible connection of these changes with the level of MICOS proteins in rat liver mitochondria in experimentally induced hyperthyroidism. A model of hyperthyroidism (HT) was induced by chronic administration of thyroxine. A change in the structure of liver mitochondria of hyperthyroid rats (HR) was found to consist of swollen organelles with a slightly altered number of cristae. A part of mitochondria (13%) in HR had vacuolized matrix with simultaneously reduced number of cristae. An increase in the protein levels of MIC 60, MIC 25, and MIC 19 was shown in the HT condition, while the quantity of MIC 10 was unchanged. In turn, the levels of SAMM 50 and OPA1 were reduced in HR. The data obtained indicate that excess thyroid hormones cause partial changes in the structure of liver mitochondria and reduce the content of SAMM50 and OPA1 proteins, which can be considered as possible targets for investigating therapeutic strategies for metabolic disorders associated with mitochondrial dysfunction.

Erythropoietin (EPO) is a hormone that plays a dual role: it regulates erythropoiesis and works as a neuroprotector, the synthesis of which is activated by brain cells in response to hypoxia. Several clinical trials showed that administration of EPO against anemia caused the improvement of cognitive brain functions, however the mechanisms of this action have not yet been characterized. Recently, the usage of Carbamylated darbepoetin (CdEpo), which is neuroprotective but lacks hematopoietic activity and has a more prolonged half-life, has become an attractive tool. The influence of administration of 100 ng/mL CdEpo on the activity and ultrastructural organization of mature hippocampal cultures in normoxic conditions was assessed. It was found that the application of CdEpo in normoxic conditions causes a negative neurotropic influence on neuronal activity that was measured via calcium imaging. Calcium imaging data revealed that CdEpo caused a decrease in the frequency of calcium oscillations; however, the duration of calcium events slightly increased. The decrease in neuronal activity upon administration of CdEpo coincided with compartment-dependent ultrastructural changes. In axons, there was an increase in total mitochondrial area with a decrease in mitochondrial and endoplasmic reticulum contact surface, and in neuronal soma, there was an increase in the surface of intermitochondrial contacts.

The trigeminovascular system plays a pivotal role in the generation of nociceptive activity, which underlies pain in migraine and includes trigeminal nerve afferents, dura mater vessels, and mast cells. Adenosine triphosphate (ATP) is one of the main mediators of the interaction between vessels, nerve endings, and mast cells. ATP activates P2X3 receptors of trigeminal nerve afferents and P2X7 receptors of mast cells. 24-Hydroxycholesterol is the primary brain cholesterol metabolite synthesized by neurons and is capable of freely entering the bloodstream by crossing the blood–brain barrier. The purpose of this study was to examine the impact of 24-hydroxycholesterol on the electrical activity of trigeminal nerve afferents triggered by ATP application and on the mast cells degranulation in rat brain meninges. The electrical activity of the trigeminal nerve was recorded using an extracellular electrode in a rat hemiskull preparation, mast cells were stained with toluidine blue. 24-Hydroxycholesterol had no direct effect on the frequency of action potentials of trigeminal nerve but suppressed the response triggered by ATP application. Furthermore, incubation of meninges in 24-hydroxycholesterol resulted in a reduction in mast cell degranulation in response to ATP. Therefore, 24-hydroxycholesterol prevented the activation of trigeminal afferents either directly by reducing the activity of ionotropic ATP receptors or indirectly by stabilizing mast cells.

Formation of through conducting defects—pores—in the lipid bilayer affects many processes in living cells and can lead to strong changes in cellular metabolism. Pore formation is a complex topological rearrangement and occurs in several stages: first, a hydrophobic through pore is formed, then it is reconstructed into a hydrophilic pore with a curved edge, the expansion of which leads to membrane rupture. Pore formation does not occur spontaneously, since it requires significant energy costs associated with membrane deformation. The evolution of the system is associated with overcoming one or two energy barriers, the ratio of their heights affects the stability of the pore and the probability of its formation. We study the effect of membrane curvature on the height of the energy barrier for the transition of a pore to a metastable hydrophilic state. We apply the theory of elasticity of lipid membranes and generalize the model of pore formation in flat membranes to the case of arbitrary curvature. We show that the barrier for pore formation decreases by 8k_BT when the radius of curvature decreases from 1000 to 10 nm, which facilitates the formation of a metastable pore. Our results are consistent with experimental data and can be used to model complex processes occurring in curved regions of living cell membranes.

Progesterone regulates reproductive processes and affects many functions of various non-reproductive organs. Its effects in mammals and humans are mediated by nuclear (nPRs) and membrane progesterone receptors (mPRs). The action of progesterone through different types of receptors differs significantly and also has tissue-specific features. The expression of known types and subtypes of progesterone receptors in tissues of male and female rats has not been sufficiently studied. The aim of this work was to investigate the expression of five mPRs genes and nPRs gene, as well as membrane component of progesterone receptor PGRMC1 in reproductive organs and in 17 non-reproductive tissues of male and female rats by reverse transcription followed by real-time PCR. A high level of nPRs gene expression has been found not only in reproductive organs of female rats (uterus, ovary, mammary glands), but also in seminal vesicles of male rats, in the brain and trachea of both sexes, in blood vessels and in the pancreas of females. The highest level of expression of mPRs genes of all subtypes was in the testes, while expression of the gene encoding nPRs was practically undetectable in them. Expression of genes encoding mPRs was also detected in the liver and spleen of male and female rats, while expression of the gene encoding nPRs was at the background level. No expression of nPRs, mPRs and membrane component of progesterone receptor (PGRMC1) genes was detected in muscle, and its level was very low in heart in animals of both sexes. Nuclear and membrane receptor mRNA expression in non-reproductive tissues in rats has been shown to be sex-dependent. Transcription of nPRs and three subtypes of mPRs (α, β, δ) was predominant in females, and two subtypes of mPRs (γ, ε) were predominant in males. Evidence for the presence of progesterone receptors in tissues not involved in reproduction supports the action of progesterone on these organs. The high mRNA levels of various progesterone receptors in male rat tissues such as pancreas, lung, kidney, and trachea suggest an important physiological role of progestins not only in females but also in males, which is still poorly understood. The paper also discusses the known functions of progesterone receptors in the tissues studied.

Despite the fact that the current situation with COVID-19 incidence is not an emergency, new strains of SARS-CoV-2 coronavirus continue to appear in the world, some of them with higher virulence compared to 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 model of the familial AD, using the 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 for detection of neurons (marker MAP2) and astroglia (marker GFAP) it was found that 24 h after 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 turned out to be 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 were studied. It was shown that administration of YB-1, an endogenous multifunctional 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. These results suggest that YB-1 and cell therapy using MMSCs are promising options for the development of new effective methods to prevent the pathologic effects of the virus on brain tissue, which is an important link in the treatment of SARS-CoV-2 virus infection.

The transport of protons between the membrane boundary and water can be hindered by the presence of a high potential barrier, which affects their transport across the membrane performed by membrane proteins. To estimate the rate of proton transport across this barrier, photoactivatable compounds whose molecules can adsorb on the membrane boundary and release protons upon excitation are used. We studied such a compound, sodium 2-methoxy-5-nitrophenyl sulfate (MNPS). Its molecule is able to adsorb on a lipid bilayer membrane (BLM) as an 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. Slow changes in potential were measured using the intramembrane field compensation method, while fast changes were measured using an electrometric amplifier. When the light was switched on, the potential increased rapidly, and when it was switched off, it 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 by a factor of ten. These results indicate that the reaction of proton release during the excitation of MNPS molecules occurs both on the membrane surface and in the water near it. The binding at the membrane of protons released by the reaction of MNPS in water provides the major contribution to the change in electrostatic potential at the membrane boundary, considerably exceeding the contribution of MNPS anions released by the reaction at the membrane.

Adsorption and photochemical reactions of pyranine on a bilayer lipid membrane (BLM) have been studied by measuring electrostatic potentials at the membrane–water interface. The dependence of the electrostatic potentials due to the adsorption of pyranine on its concentration in solution is described by the Gouy–Chapman theory assuming that anions with three charged groups are adsorbed on the membrane. No significant changes in the boundary potential were found when BLM with pyranine adsorbed on it was illuminated. Significant changes in the potential were observed if molecules of styryl dyes di-4-ANEPPS or RH-421 were adsorbed on BLM in addition to pyranine. The sign and magnitude of these changes correspond to the disappearance of the dipole potential created by styryl dye molecules on the BLM. The rate of potential disappearance was proportional to pyranine concentration and illumination intensity. The disappearance of the potential can be caused either by the binding of protons released from the pyranine molecule to the dye mo-lecules with their subsequent desorption from the BLM or by their destruction. Pyranine and styryl dye molecules can form complexes at the BLM boundary. This is evidenced by experiments in which the sum of the potential changes caused by their adsorption separately differed significantly from the change in the boundary potential during their simultaneous adsorption. The kinetics of the disappearance of the dipole potential of BLM with styryl dyes upon excitation of pyranine turned out to be similar to that observed earlier with another compound, 2-methoxy-5-nitrophenyl sodium sulfate, which releases protons at the membrane boundary upon illumination (Konstantinova et al., 2021. Biochem. (Mosc.), Suppl. Series A: Membr. Cell Biol. 15 (2), 142–146). This suggests that it is associated with the desorption of dye molecules from the membrane, due to the binding of protons released from excited pyranin molecules to them.

In this work the effect of changing extracellular potassium concentration ([K⁺]_o) on spontaneous and evoked burst activity of glutamatergic neurons in the mouse hippocampus was investigated using the whole-cell patch clamp technique. It was shown that the increase of [K⁺]_o from 3 to 8.5 mM (potassium load): (1) induced spontaneous tonic and pacemaker burst activity in CA1 pyramidal cells (20% and 10% of total cells, respectively) but did not result in the emergence of pacemaker granule cells in the dentate gyrus (DG). (2) Similarly, potassium load increased the evoked burst activity of CA1 pyramidal cells and, paradoxically, suppressed the burst activity of DG granule cells over the entire range of current steps from 10 to 200 pA. (3) Potassium load caused a rightward shift of the current–voltage (I/V) curves in both cell types, decreasing the reversal potential E_rev and increasing the slope of the I/V curves (amplitudes of inward currents at voltages from –100 mV to –70 mV) in the CA1 and DG neurons 2–3- and 4–5-fold, respectively. (4) Potassium load produced an opposite effect on outward currents, causing a significant increase in current amplitude in pyramidal cells and a decrease in granule cells (at membrane voltages above 0 mV). The inward and outward currents of DG neurons were 4–4.5 times higher than those of CA1 neurons. The possible involvement of potassium-activated and other potassium-conducting channels in different excitability responses of glutamatergic CA1 and DG neurons under potassium load is discussed. The high sensitivity of CA1 pyramidal cells to potassium load compared to DG granule cells may play an important role in hyperexcitation of neuronal networks during epileptogenesis.

The review considers the data available in the literature on myoglobin expression in various tumors and cell lines of non-muscle tumor cells and on the influence of hypoxia, reactive oxygen and nitrogen species, hormones, growth factors, gender, and age on this process. The effect of tumor myoglobin on cellular processes such as oxidative stress, inhibition of mitochondrial respiration by nitric oxide, and fatty acid metabolism is also analyzed, both during endogenous expression of small amounts (~1 μM) of myoglobin and overexpression of the protein (~150 μM) due to incorporation of the myoglobin gene into the tumor cell genome. It is concluded that hypoxia-induced intrinsic expression of low concentrations of myoglobin, due to its ability to utilize reactive oxygen and nitrogen species that can damage tumor cells, ensures their better survival by promoting tumor progression and metastasis. Accordingly, this expression of myoglobin is generally associated with a more aggressive tumor type, poor prognosis for the course and outcome of the disease, and may thus serve as a “marker” of an aggressive malignancy. In contrast, artificial overexpression of myoglobin can significantly inhibit tumor development and improve disease course by switching cancer cell metabolism from tumor-specific glycolysis to oxidative phosphorylation inherent in healthy tissue. Myoglobin overexpression may thus be an effective therapeutic tool in oncology.