Li Nan, An Lili, Hang Haiying
Key Laboratory for Protein and Peptide Pharmaceuticals, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China.
Key Laboratory for Protein and Peptide Pharmaceuticals, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
PLoS One. 2015 Apr 27;10(4):e0125236. doi: 10.1371/journal.pone.0125236. eCollection 2015.
Microgravity is a major stress factor that astronauts have to face in space. In the past, the effects of microgravity on genomic DNA damage were studied, and it seems that the effect on genomic DNA depends on cell types and the length of exposure time to microgravity or simulated microgravity (SMG). In this study we used mouse embryonic stem (MES) and mouse embryonic fibroblast (MEF) cells to assess the effects of SMG on DNA lesions. To acquire the insight into potential mechanisms by which cells resist and/or adapt to SMG, we also included Rad9-deleted MES and Mdc1-deleted MEF cells in addition to wild type cells in this study. We observed significant SMG-induced DNA double strand breaks (DSBs) in Rad9-/- MES and Mdc1-/- MEF cells but not in their corresponding wild type cells. A similar pattern of DNA single strand break or modifications was also observed in Rad9-/- MES. As the exposure to SMG was prolonged, Rad9-/- MES cells adapted to the SMG disturbance by reducing the induced DNA lesions. The induced DNA lesions in Rad9-/- MES were due to SMG-induced reactive oxygen species (ROS). Interestingly, Mdc1-/- MEF cells were only partially adapted to the SMG disturbance. That is, the induced DNA lesions were reduced over time, but did not return to the control level while ROS returned to a control level. In addition, ROS was only partially responsible for the induced DNA lesions in Mdc1-/- MEF cells. Taken together, these data suggest that SMG is a weak genomic DNA stress and can aggravate genomic instability in cells with DNA damage response (DDR) defects.
微重力是宇航员在太空中必须面对的一个主要应激因素。过去，人们研究了微重力对基因组DNA损伤的影响，似乎微重力对基因组DNA的影响取决于细胞类型以及暴露于微重力或模拟微重力（SMG）的时间长度。在本研究中，我们使用小鼠胚胎干细胞（MES）和小鼠胚胎成纤维细胞（MEF）来评估SMG对DNA损伤的影响。为了深入了解细胞抵抗和/或适应SMG的潜在机制，在本研究中，除了野生型细胞外，我们还纳入了Rad9基因敲除的MES细胞和Mdc1基因敲除的MEF细胞。我们观察到，在Rad9基因敲除的MES细胞和Mdc1基因敲除的MEF细胞中，SMG诱导了显著的DNA双链断裂（DSB），但在相应的野生型细胞中未观察到。在Rad9基因敲除的MES细胞中也观察到了类似的DNA单链断裂或修饰模式。随着暴露于SMG时间的延长，Rad9基因敲除的MES细胞通过减少诱导的DNA损伤来适应SMG干扰。Rad9基因敲除的MES细胞中诱导的DNA损伤是由SMG诱导的活性氧（ROS）引起的。有趣的是，Mdc1基因敲除的MEF细胞仅部分适应了SMG干扰。也就是说，诱导的DNA损伤随时间减少，但并未恢复到对照水平，而ROS恢复到了对照水平。此外，ROS仅部分导致了Mdc1基因敲除的MEF细胞中诱导的DNA损伤。综上所述，这些数据表明，SMG是一种较弱的基因组DNA应激因素，可加剧具有DNA损伤应答（DDR）缺陷的细胞中的基因组不稳定性。
