Abstract
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.
Highlights
One of the most medically significant challenges to long-term space missions, including ones to other planets, such as Mars, is manifested muscle atrophy, which does not allow the performance of necessary work after landing on the surface of a body in space
The transversal stiffness of rat soleus muscle fibers after 6 hours of suspension did not differ from the control group level for the corresponding legs: there were no differences between groups without lecithin «C» (3.08 ± 0.10 pN/nm) and «HS» (3.17 ± 0.08 pN/nm) as well as between groups with lecithin «C+L» (3.78 ± 0.11 pN/nm) and «HS+L» (3.53 ± 0.09 pN/nm) (Fig 2)
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» was increased by 200% compared with that of group «C», and beta-tubulin increased by 100%
Summary
One of the most medically significant challenges to long-term space missions, including ones to other planets, such as Mars, is manifested muscle atrophy, which does not allow the performance of necessary work after landing on the surface of a body in space. Exposure to microgravity conditions for long periods of time has been shown to result in significant weight loss and atrophic changes in the soleus muscle [1,2,3]. A decrease in functional capacity has been reported for the entire muscle [4,5] and its isolated fibers [6]. It is clear that a decrease in the functional potential of postural muscles when exposed to microgravity conditions occurs when the integrity of basic structural and functional muscle tissue units, such as a muscle fiber (single cell) is disrupted. Mechanisms of the mechanoreception of different cells, including muscle cells, still remain unclear
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