Oxidative stress under ambient and physiological oxygen tension in tissue culture

Oxygen (O₂) levels range from 2-9% in vivo. However, cell culture experiments are performed at atmospheric O₂ levels (21%). Oxidative stress due to generation of reactive oxygen species (ROS) in cells cultured at higher than physiological levels is implicated in multitude of deleterious effects including DNA damage, genomic instability and senescence. In addition, oxidative stress activates redox sensitive transcription factors related to inflammatory signaling and apoptotic signaling. Furthermore, several chromatin-modifying enzymes are affected by ROS, potentially impacting epigenetic regulation of gene expression. While primary cells are cultured at lower O₂ levels due to their inability to grow at higher O₂, the immortalized cells, which display no such apparent growth difficulties, are typically cultured at 21% O₂. This review will provide an overview of issues associated with increased oxygen levels in in vitro cell culture and point out the benefits of using lower levels of oxygen tension even for immortalized cells.