Date Published: May 16, 2018
Publisher: Public Library of Science
Author(s): Irina V. Ogneva, Sergey S. Loktev, Vladimir N. Sychev, Mohammad R. K. Mofrad.
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.
Under microgravity conditions, there are different negative changes in the skeletal, muscle and cardiovascular systems. Animal experiments have facilitated the investigation of the structural changes in the myocardium and skeletal muscles that arise during space flights.
The influence of the changes in external mechanical conditions, particularly gravity changes, on the cells of organisms that have evolved in Earth’s gravity conditions is still poorly understood. The main difficulty is the extrapolation of ground experimental data to the prediction of results under weightlessness conditions. Previous experiments conducted under space flight conditions were limited by the fact that the biomaterial of the flight animals could only be fixed after landing, usually occurring a few hours after the landing [1–7, 13]. Therefore, this experiment is the first in the history of human space exploration with the unique opportunity to fix mouse biomaterial under space flight conditions. Comparing these results with the results obtained after the BION-M Biosatellite No. 1 flight of the same length, a number of deductions can be made regarding the structural changes in the cells as a result of the early period of readaptation to Earth’s gravity.
Our study, in which murine biomaterial was fixed for the first time under space flight conditions (after 37 days of weightlessness), showed no changes in the cytoskeletal protein contents in the cardiac and lung tissue of mice. At the same time, there were significant changes in the mRNA content, which, on the one hand, indicates changes in translation efficiency and/or proteolysis levels that act to maintain normal levels of proteins and on the other hand, indicates the alteration of the expression levels of genes encoding cytoskeletal proteins, perhaps as a result of the total genome methylation increase. The mRNA contents of the DNA methylases, the cytosine demethylases Tet1 and Tet3, histone acetylase and histone deacetylase were unchanged, and the mRNA content of the cytosine demethylase Tet2 was significantly decreased, which could cause changes in the total methylation level.