Hyperoxia shows duration-dependent effects on the lengths of cell cycle phases in fetal cortical neural stem cells.

Fetal neural stem cells (NSCs) physiologically reside under low-oxygen conditions (1%-5% of tissue pO), but are often transferred and maintained under atmospheric oxygen levels of 21% pO (hyperoxia) for investigations. These altered oxygen conditions lead to adaptive changes in NSCs which complicate the interpretation of data. However, the underlying adaption dynamics remain largely enigmatic. Here we investigated short-term hyperoxia effects (5 days in 3% pO followed by 2 days in 21% pO) in comparison to continuous hyperoxia effects (7 days in 21% pO) and physioxic control (7 days in 3% pO). We utilized cortical NSCs to analyze the cell cycle phases by flow cytometry and cumulative BrdU incorporation assay. NSCs showed a severe reduction of cell proliferation when cultivated under continuous hyperoxia, but no changes after short-term hyperoxia. Subsequent cell cycle analysis as assessed by flow cytometry revealed a clear shift of NSCs from G0/G1-phase towards S- or G2/M-phase after both continuous and short-term hyperoxia. However, while cell cycle length was dramatically reduced by short-term hyperoxia, it was increased during continuous hyperoxia. Taken together, our results demonstrate the beneficial effect of physioxia for expanding NSCs and reveal differential effects of short-term hyperoxia compared to continuous hyperoxia.