Simulated microgravity influences circadian rhythm of NIH3T3 cells

Gravity heavily influences living organisms on earth including their circadian rhythm, which is fundamentally important for coordinately physiology in organisms as diverse as cyanobacteria, fungus and humans. Numerous researches have revealed that microgravity in outer space can affect circadian rhythm of astronauts and rodent animals, but the mechanism remains unknown. Using rotary cell culture system to simulate microgravity environment, we investigated the role of simulated microgravity in regulating the circadian rhythm of NIH3T3 cells. Our experiments found that simulated microgravity can not only influence the mRNA level of some core circadian genes, but also modify the circadian rhythm of <i>Per1</i> and <i>Per2</i> synchronized after phorbol myristate acetate treatment. Remarkably, MEK/ERK pathway was transiently activated after a 2-h simulated microgravity treatment, with a significant upregulation of <i>Kras</i>, <i>Raf1</i> and p-ERK1/ERK2. Moreover, U0126, a selective inhibitor of MEK/ERK pathway, could disrupt the circadian rhythm of <i>Per1</i> and <i>Per2</i> synchronized after simulated microgravity treatment. Together, our results unveil that simulated microgravity could act like a zeitgeber to influence the circadian rhythm of NIH3T3 by acting on MEK/ERK pathway, indicating that MEK/ERK pathway may act as a bridge which connects cells mechanotransduction pathway and circadian rhythm regulation.