Oxygen-mediated control of the keratinocyte proliferation-differentiation axis

The epidermis differentiates and functions in direct contact with the atmosphere (21% oxygen), leading to the common practice of maintaining primary keratinocytes in vitro at this oxygen level. However, several studies have reported that the in vivo oxygen level within skin is much lower (<10%). We found that 5% oxygen was optimal to obtain both the highest clonogenic potential on feeders and maximum yield in a serum-free, feeder-free system. Whole transcriptomic profiling revealed that oxygen elicits a strong, global differentiation signal, and this occurs as a very early keratinocyte response. This study has implications for standard protocols used in keratinocyte expansion for research and clinical purposes.