Purpose:Microgravity is known to cause endothelium dysfunction in astronauts reting from spaceflight.We aimed to reveal the regulatory mechanism in alterations of human endothelial cells after simulated microgravity (SMG).Methods:We utilized the rotary cell culture system (RCCS-1) to explore the subsequent effects of SMG on human umbilical vein endothelial cells (HUVECs).Results:SMG-treated HUVECs appeared obvious growth inhibition after ret 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.Conclusion:SMG has the subsequent biological effects on HUVECs,resulting in growth inhibition through mTOR signaling and miR-22-mediated mechanism.