ABSTRACT
<p><b>PURPOSE</b>Microgravity is known to cause endothelium dysfunction in astronauts returning from spaceflight. We aimed to reveal the regulatory mechanism in alterations of human endothelial cells after simulated microgravity (SMG).</p><p><b>METHODS</b>We utilized the rotary cell culture system (RCCS-1) to explore the subsequent effects of SMG on human umbilical vein endothelial cells (HUVECs).</p><p><b>RESULTS</b>SMG-treated HUVECs appeared obvious growth inhibition after return to normal gravity, which might be attributed to a set of responses including alteration of cytoskeleton, decreased cell adhesion capacity and increased apoptosis. Expression levels of mTOR and its downstream Apaf-1 were increased during subsequent culturing after SMG. miR-22 was up-regulated and its target genes SRF and LAMC1 were down-regulated at mRNA levels. LAMC1 siRNAs reduced cell adhesion rate and inhibited stress fiber formation while SRF siRNAs caused apoptosis.</p><p><b>CONCLUSION</b>SMG has the subsequent biological effects on HUVECs, resulting in growth inhibition through mTOR signaling and miR-22-mediated mechanism.</p>