Simulated Microgravity Inhibited the Proliferation of Bovine Muscle Satellite Cells

This study aimed to assess the effects of simulated microgravity (SMG) on bovine muscle satellite cells (bSCs). The results demonstrated that bSCs maintained a fibroblast-like morphology throughout SMG exposure from day 3 to day 7. However, cells in the SMG group exhibited reduced proliferation compared to the control group, as indicated by lower cell density at both time points. In contrast, cell viability was higher in the SMG group than in the control group. Cell cycle analysis revealed a higher proportion of SMG-treated bSCs in the G0/G1 phase and a lower proportion in the S phase at day 3, suggesting cell cycle arrest at an early stage. Interestingly, by day 7, the percentage of cells in the S phase increased in the SMG group and exceeded that of the control group, indicating a partial recovery of proliferative activity. Western blot analysis showed decreased expression of key cell cycle-related proteins, including cyclin A1/A2, cyclin D1, and CDK2, in SMG-treated cells compared to controls at the early stage. Notably, cyclin D1 and CDK2 expression levels were upregulated at the later stage under SMG conditions. Additionally, nuclear morphology in SMG-treated bSCs displayed enlargement and irregularity. Overall, these findings suggest that SMG initially suppresses bSC proliferation by inducing cell cycle arrest, but cells can partially retrieve their proliferative capacity at later stages, potentially through upregulation of cell cycle regulatory proteins.