ROS and oxidative stress in stem cells.

Reactive oxygen species (ROS) are well known to be implicated in various important cellular processes including signaling, regulation of homeostasis, or induction of death. Oxidative stress resulting from increased ROS production and impaired free radical scavenging systems can cause severe damage to biological macromolecules, affecting cell proliferation and causing genomic instability and cellular senescence. Although ROS are involved in a wide range of cellular processes, a limited number of studies have examined the generation and function of ROS in stem cells. It is known that ROS may enhance differentiation of stem cells and facilitate reprogramming into induced pluripotent stem cells (iPSCs), but on the other hand, they are also associated with malignant transformation or premature aging. Stem cells have also been shown to possess defective DNA repair machinery, which may have serious consequences for cells exposed to extensive oxidative stress. Since stem cells are considered as a promising tool in regenerative medicine, it is crucial to know and better understand all the processes related to ROS to prevent potential generation of mutations causing genomic instability and to avoid unwanted ROS-driven differentiation. Thus, the mechanisms by which genomic integrity of stem cells is maintained under oxidative stress and the role of ROS should be elucidated before stem cells finally find their place in clinical applications.