Microgravity inhibition of lipopolysaccharide-induced tumor necrosis factor-α expression in macrophage cells

Microgravity environments in space can cause major abnormalities in human physiology, including decreased immunity. The underlying mechanisms of microgravity-induced inflammatory defects in macrophages are unclear. RAW264.7 cells and primary mouse macrophages were used in the present study. Lipopolysaccharide (LPS)-induced cytokine expression in mouse macrophages was detected under either simulated microgravity or 1g control. Freshly isolated primary mouse macrophages and RAW264.7 cells were cultured in a standard simulated microgravity situation using a rotary cell culture system (RCCS-1) and 1g control conditions. The cytokine expression was determined by real-time PCR and ELISA assays. Western blots were used to investigate the related intracellular signals. LPS-induced tumor necrosis factor-alpha (TNF-alpha) expression, but not interleukin-1 beta expression, in mouse macrophages was significantly suppressed under simulated microgravity. The molecular mechanism studies showed that LPS-induced intracellular signal transduction including phosphorylation of IKK and JNK and nuclear translocation of NF-kappa B in macrophages was identical under normal gravity and simulated microgravity. Furthermore, TNF-alpha mRNA stability did not decrease under simulated microgravity. Finally, we found that heat shock factor-1 (HSF1), a known repressor of TNF-alpha promoter, was markedly activated under simulated microgravity. Short-term treatment with microgravity caused significantly decreased TNF-alpha production. Microgravity-activated HSF1 may contribute to the decreased TNF-alpha expression in macrophages directly caused by microgravity, while the LPS-induced NF-kappa B pathway is resistant to microgravity.