Structure of the cortical cytoskeleton in fibers of postural muscles and cardiomyocytes of mice after 30-day 2-g centrifugation

Increased H3K9me3 and F-Actin Reorganization in the Rapid Adaptive Response to Hypergravity in Human T Lymphocytes

Our study explored the impact of hypergravity on human T cells, which experience additional acceleration forces beyond Earth's gravity due to various factors, such as pulsatile blood flow, and technology, such as high-performance aircraft flights or spaceflights. We investigated the histone modifications Histone 3 lysine 4 and 9 trimethylation (H3K4me3 and H3K9me3, respectively), as well as the structural and cytoskeletal organization of Jurkat T cells in response to hypergravity. Histone modifications play a crucial role in gene regulation, chromatin organization and DNA repair. In response to hypergravity, we found only minimal changes of H3K4me3 and a rapid increase in H3K9me3, which was sustained for up to 15 min and then returned to control levels after 1 h. Furthermore, rapid changes in F-actin fluorescence were observed within seconds of hypergravity exposure, indicating filament depolymerization and cytoskeletal restructuring, which subsequently recovered after 1 h of hypergravity. Our study demonstrated the rapid, dynamic and adaptive cellular response to hypergravity, particularly in terms of histone modifications and cytoskeletal changes. These responses are likely necessary for maintaining genome stability and structural integrity under hypergravity conditions as they are constantly occurring in the human body during blood cell circulation.

Transcriptional Response in Human Jurkat T Lymphocytes to a near Physiological Hypergravity Environment and to One Common in Routine Cell Culture Protocols

Cellular effects of hypergravity have been described in many studies. We investigated the transcriptional dynamics in Jurkat T cells between 20 s and 60 min of 9 g hypergravity and characterized a highly dynamic biphasic time course of gene expression response with a transition point between rapid adaptation and long-term response at approximately 7 min. Upregulated genes were shifted towards the center of the nuclei, whereby downregulated genes were shifted towards the periphery. Upregulated gene expression was mostly located on chromosomes 16-22. Protein-coding transcripts formed the majority with more than 90% of all differentially expressed genes and followed a continuous trend of downregulation, whereas retained introns demonstrated a biphasic time-course. The gene expression pattern of hypergravity response was not comparable with other stress factors such as oxidative stress, heat shock or inflammation. Furthermore, we tested a routine centrifugation protocol that is widely used to harvest cells for subsequent RNA analysis and detected a huge impact on the transcriptome compared to non-centrifuged samples, which did not return to baseline within 15 min. Thus, we recommend carefully studying the response of any cell types used for any experiments regarding the hypergravity time and levels applied during cell culture procedures and analysis.

Drosophila melanogaster Oocytes after Space Flight: The Early Period of Adaptation to the Force of Gravity

The effect of space flight factors and the subsequent adaptation to the Earth's gravity on oocytes is still poorly understood. Studies of mammalian oocytes in space present significant technical difficulties; therefore, the fruit fly Drosophila melanogaster is a convenient test subject. In this study, we analyzed the structure of the oocytes of the fruit fly Drosophila melanogaster, the maturation of which took place under space flight conditions (the "Cytomehanarium" experiment on the Russian Segment of the ISS during the ISS-67 expedition). The collection of the oocytes began immediately after landing and continued for 12 h. The flies were then transferred onto fresh agar plates and oocyte collection continued for the subsequent 12 h. The stiffness of oocytes was determined by atomic force microscopy and the content of the cytoskeletal proteins by Western blotting. The results demonstrated a significant decrease in the stiffness of oocytes in the flight group compared to the control (26.5 ± 1.1 pN/nm vs. 31.0 ± 1.8 pN/nm) against the background of a decrease in the content of some cytoskeletal proteins involved in the formation of microtubules and microfilaments. This pattern of oocyte structure leads to the disruption of cytokinesis during the cleavage of early embryos.

Single Cell in a Gravity Field

The exploration of deep space or other bodies of the solar system, associated with a long stay in microgravity or altered gravity, requires the development of fundamentally new methods of protecting the human body. Most of the negative changes in micro- or hypergravity occur at the cellular level; however, the mechanism of reception of the altered gravity and transduction of this signal, leading to the formation of an adaptive pattern of the cell, is still poorly understood. At the same time, most of the negative changes that occur in early embryos when the force of gravity changes almost disappear by the time the new organism is born. This review is devoted to the responses of early embryos and stem cells, as well as terminally differentiated germ cells, to changes in gravity. An attempt was made to generalize the data presented in the literature and propose a possible unified mechanism for the reception by a single cell of an increase and decrease in gravity based on various deformations of the cortical cytoskeleton.

Mouse and Fly Sperm Motility Changes Differently under Modelling Microgravity

Sperm motility is essential for the natural fertilization process in most animal species. Despite the fact that evolution took place under conditions of constant gravity, the motility of spermatozoa of insects and mammals under microgravity conditions changes in different ways. In this work, an attempt was made to explain this effect. The sperm motility of the fruit fly Drosophila melanogaster and the mouse was evaluated after exposure to a random positioning machine for 6 h. Sodium fluoride was used to inhibit serine/threonine phosphatases, sodium orthovanadate was used to inhibit tyrosine phosphatases, and 6-(dimethylamino)purine was used to inhibit protein kinases. The results obtained indicate that simulated microgravity leads to an increase in the speed of movement of fly spermatozoa by 30% (p < 0.05), and this effect is blocked by sodium fluoride. In contrast, a 29% (p < 0.05) decrease in the speed of movement of mouse spermatozoa under simulated microgravity is prevented by 6-(dimethylamino)purine. Moreover, after 6 h of exposure, the content of tubulin cytoskeleton and actin proteins remains at the control level in the spermatozoa of flies and mice. However, the content of the actin-binding protein alpha-actinin in fly sperm decreases by 29% (p < 0.05), while in mouse sperm, the relative content of alpha-actinin1 increases by 94% (p < 0.05) and alpha-actinin4 by 121% (p < 0.05) relative to the control, as determined by 6 simulated microgravity tests. It can be assumed that the effect of simulated microgravity on the motility of mammalian spermatozoa is mediated through the regulation of phosphorylation and that of insects through the regulation of dephosphorylation of motor proteins; moreover, the development of a response to changes in external mechanical conditions has a different time scale.

DNA Methylation of Mouse Testes, Cardiac and Lung Tissue During Long-Term Microgravity Simulation

Under microgravity, the gene expression levels vary in different types of cells; however, the reasons for this have not been sufficiently studied. The aim of this work was to evaluate the methylation of CpG islands in the promoter regions of the genes encoding some cytoskeletal proteins, the total methylation and 5 hmC levels, and the levels of enzymes that regulate these processes in the testes, heart, and lungs in mice after a 30-day microgravity modeling by antiorthostatic suspension and after a subsequent 12-hour recovery as well as in the corresponding control group and identical groups treated with essential phospholipids. The obtained results indicate that under modeling microgravity in the examined tissues a decrease of cytoskeletal gene expression (mainly in the heart and lungs tissues) correlated with an increase in the CpG islands methylation and an increase of the expression (mainly in the testes tissue) - with a decrease of the CpG-methylation, despite of the fact that in the examined tissues took place a decrease of the content methylases and demethylases. But the deacetylase HDAC1 content increased in the heart and lungs tissues and decreased in the testes, letting us suggest its participation in the regulation of the methylation level under microgravity conditions.

β-Actin shows limited mobility and is required only for supraphysiological insulin-stimulated glucose transport in young adult soleus muscle

Studies in skeletal muscle cell cultures suggest that the cortical actin cytoskeleton is a major requirement for insulin-stimulated glucose transport, implicating the β-actin isoform, which in many cell types is the main actin isoform. However, it is not clear that β-actin plays such a role in mature skeletal muscle. Neither dependency of glucose transport on β-actin nor actin reorganization upon glucose transport have been tested in mature muscle. To investigate the role of β-actin in fully differentiated muscle, we performed a detailed characterization of wild type and muscle-specific β-actin knockout (KO) mice. The effects of the β-actin KO were subtle; however, we confirmed the previously reported decline in running performance of β-actin KO mice compared with wild type during repeated maximal running tests. We also found insulin-stimulated glucose transport into incubated muscles reduced in soleus but not in extensor digitorum longus muscle of young adult mice. Contraction-stimulated glucose transport trended toward the same pattern, but the glucose transport phenotype disappeared in soleus muscles from mature adult mice. No genotype-related differences were found in body composition or glucose tolerance or by indirect calorimetry measurements. To evaluate β-actin mobility in mature muscle, we electroporated green fluorescent protein (GFP)-β-actin into flexor digitorum brevis muscle fibers and measured fluorescence recovery after photobleaching. GFP-β-actin showed limited unstimulated mobility and no changes after insulin stimulation. In conclusion, β-actin is not required for glucose transport regulation in mature mouse muscle under the majority of the tested conditions. Thus, our work reveals fundamental differences in the role of the cortical β-actin cytoskeleton in mature muscle compared with cell culture.

Cytoskeleton structure and total methylation of mouse cardiac and lung tissue during space flight

The purpose of this work was to evaluate the protein and mRNA expression levels of multiple cytoskeletal proteins in the cardiac and lung tissue of mice that were euthanized onboard the United States Orbital Segment of the International Space Station 37 days after the start of the SpaceX-4 mission (September 2014, USA). The results showed no changes in the cytoskeletal protein content in the cardiac and lung tissue of the mice, but there were significant changes in the mRNA expression levels of the associated genes, which may be due to an increase in total genome methylation. The mRNA expression levels of DNA methylases, the cytosine demethylases Tet1 and Tet3, histone acetylase and histone deacetylase did not change, and the mRNA expression level of cytosine demethylase Tet2 was significantly decreased.

Novel insights into cardiomyocytes provided by atomic force microscopy

Cardiovascular diseases (CVDs) are the number one cause of death globally, therefore interest in studying aetiology, hallmarks, progress and therapies for these disorders is constantly growing. Over the last decades, the introduction and development of atomic force microscopy (AFM) technique allowed the study of biological samples at the micro- and nanoscopic level, hence revealing noteworthy details and paving the way for investigations on physiological and pathological conditions at cellular scale. The present work is aimed to collect and review the literature on cardiomyocytes (CMs) studied by AFM, in order to emphasise the numerous potentialities of this approach and provide a platform for researchers in the field of cardiovascular diseases. Original data are also presented to highlight the application of AFM to characterise the viscoelastic properties of CMs.

The Development Of Drosophila Melanogaster under Different Duration Space Flight and Subsequent Adaptation to Earth Gravity

In prospective human exploration of outer space, the need to preserve a species over several generations under changed gravity conditions may arise. This paper demonstrates our results in the creation of the third generation of fruit fly Drosophila melanogaster (third-stage larvae) during the 44.5-day space flight (Foton-M4 satellite (2014, Russia)), then the fourth generation on Earth and the fifth generation again in conditions of the 12-day space flight (2014, in the Russian Segment of the ISS). The species preserves fertility despite a number of changes in the level of expression and content of cytoskeletal proteins, which are the key components of the cleavage spindle and the contractile ring of cells. The results of transcriptome screening and space analysis of cytoskeletal proteins show that the exposure to weightless conditions leads to the increased transcription of metabolic genes, cuticle components and the decreased transcription of genes involved in morphogenesis, cell differentiation, cytoskeletal organization and genes associated with the plasma membrane. "Subsequent" exposure to the microgravity for 12 days resulted in an even more significant increase/decrease in the transcription of the same genes. On the contrary, the transition from the microgravity conditions to the gravity of Earth leads to the increased transcription of genes whose products are involved in the morphogenesis, cytoskeletal organization, motility of cells and transcription regulation, and to the decreased transcription of cuticle genes and proteolytic processes.

Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention

Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.

Lecithin Prevents Cortical Cytoskeleton Reorganization in Rat Soleus Muscle Fibers under Short-Term Gravitational Disuse

The aim of this study was to prevent the cortical cytoskeleton reorganization of rat soleus muscle fibers under short-term gravitational disuse. Once a day, we injected the right soleus muscle with 0.5 ml lecithin at a concentration of 200 mg/ml and the left soleus muscle with a diluted solution in an equal volume for 3 days prior to the experiment. To simulate microgravity conditions in rats, an anti-orthostatic suspension was used according to the Ilyin-Novikov method modified by Morey-Holton et al. for 6 hours. The following groups of soleus muscle tissues were examined: «C», «C+L», «HS», and «HS+L». The transversal stiffness of rat soleus muscle fibers after 6 hours of suspension did not differ from that of the control group for the corresponding legs; there were no differences between the groups without lecithin «C» and «HS» or between the groups with lecithin «C+L» and «HS+L». However, lecithin treatment for three days resulted in an increase in cell stiffness; in the «C+L» group, cell stiffness was significantly higher by 22.7% (p < 0.05) compared with that of group «C». The mRNA content of genes encoding beta- and gamma-actin and beta-tubulin did not significantly differ before and after suspension in the corresponding groups. However, there was a significant increase in the mRNA content of these genes after lecithin treatment: the beta-actin and gamma-actin mRNA content in group «C+L» increased by 200% compared with that of group «C», and beta-tubulin increased by 100% (as well as the mRNA content of tubulin-binding proteins Ckap5, Tcp1, Cct5 and Cct7). In addition, desmin mRNA content remained unchanged in all of the experimental groups. As a result of the lecithin injections, there was a redistribution of the mRNA content of genes encoding actin monomer- and filament-binding proteins in the direction of increasing actin polymerization and filament stability; the mRNA content of Arpc3 and Lcp1 increased by 3- and 5-fold, respectively, but the levels of Tmod1 and Svil decreased by 2- and 5-fold, respectively. However, gravitational disuse did not result in changes in the mRNA content of Arpc3, Tmod1, Svil or Lcp1. Anti-orthostatic suspension for 6 hours resulted in a decrease in the mRNA content of alpha-actinin-4 (Actn4) and alpha-actinin-1 (Actn1) in group «HS» compared with that of group «C» by 25% and 30%, respectively, as well as a decrease and increase in the ACTN4 protein content in the membrane and cytoplasmic fractions, respectively. Lecithin injection resulted in an increase in the Actn1 and Actn4 mRNA content in group «C+L» by 1.5-fold and more than 2-fold, respectively, compared with the levels in group «C». Moreover, in group «HS+L», the mRNA content did not change in these genes compared with the levels in group «C+L», and the ACTN4 protein content in the membrane and cytoplasmic fractions also remained unchanged. Thus, lecithin prevented the reduction of Actn1 and Actn4 mRNA and the migration of ACTN4 from the cortical cytoskeleton to the cytoplasm.

Effects of chronic hypergravity: from adaptive to deleterious responses in growing mouse skeleton

One of the most important but least studied environmental factors playing a major role in bone physiology is gravity. While the knowledge of deleterious effects of microgravity on the skeleton is expanding, little is known about hypergravity and its osteogenic potential. Centrifugation was used to assess effects of 21-day continuous 2- or 3-g acceleration on femur and L2-vertebra of 7-wk-old male C57BL/6 mice. Under 3 g, body mass growth slowed down, and deleterious skeletal effects were found (P < 0.05 compared with control): cortical thinning, osteoclasts surface increase (+41% in femur, +20% in vertebra), and bone formation rate decrease (-34% in femur, -38% in vertebra). A 2-g centrifugation did not reduce body mass and improved trabecular volume (+18% in femur, +13% in vertebra) and microarchitecture (+32% connectivity density in femur, +9% trabecular thickness in vertebra, P < 0.05 compared with control). Centrifugation at 2 g also decreased osteoclast surfaces (-36% in femur, -16% in vertebra) and increased the extent of mineralized surfaces (+31% in femur, +48% in vertebra, P < 0.05 compare to control). Quantitative immunohistochemistry revealed an increase of dentin matrix acidic phosphoprotein 1 (DMP1) and decrease of sclerostin (+60% and -35% respectively, P < 0.001 compared with control) in the femur cortex of 2-g mice. In the distal femur metaphysis, the number and volume of blood vessels increased by 22 and 44%, respectively (P < 0.05 compared with control). In conclusion, the effects of continuous hypergravity were bone compartment-specific and depended on the gravity level, with a threshold between beneficial 2-g and deleterious 3-g effects.