Temporal changes in the markers of ribosome biogenesis in rat soleus muscle under simulated microgravity

Skeletal muscle inactivity due to real or simulated microgravity results in a significant atrophy of muscle fibers. One of the key causes of disuse atrophy is a decrease in the rate of muscle protein synthesis (MPS). MPS is dependent not only on translational efficiency but also on the number of ribosomes available for translation (translational capacity), however a time course for biomarkers of ribosome biogenesis during muscle disuse remains understudied. The aim of the study was to analyze temporal changes in the regulators/markers of ribosome biogenesis in rat soleus muscle during the course of disuse. Rats were subjected to hindlimb unloading (HU) for 1, 3, 7 and 14 days. 18S + 28S rRNA content was assessed by gel-electrophoresis; expression levels of 45S pre-rRNA and c-Myc were determined by RT-PCR and the rate of MPS was measured using SUnSET method. The content of 18S + 28S rRNA and total RNA as well as 45S pre-rRNA expression significantly decreased after 1-day HU and remained diminished for the entire unloading period. c-Myc mRNA expression was downregulated following 1, 3 and 7 days of HU, but did not significantly differ from control after 14-day HU. MPS showed a progressive decrease from the 3rd to 14th day of HU. Thus, a decrease in MPS in rat soleus during 3-, 7- and 14-day HU was accompanied by downregulation of the key markers of translational capacity. •The study revealed temporal alterations in ribosome biogenesis in rat soleus muscle during simulated microgravity.•A decrease in 45S pre-rRNA expression in rat soleus was observed at both early and later stages of simulated microgravity.•A decline in 18S+28S rRNA and total RNA in rat soleus was detected after 1, 3, 7 and 14 days of simulated microgravity.•A significant reduction in c-Myc expression in rat soleus was observed following 1, 3 and 7 days of simulated microgravity.