Antioxidant proteins and reactive oxygen species are decreased in a murine epidermal side population with stem cell-like characteristics

Reactive oxygen species (ROS) and antioxidants are essential to maintain a redox balance within tissues and cells. Intracellular ROS regulate key cellular functions such as proliferation, differentiation and apoptosis through cellular signaling, and response to injury. The redox environment is particularly important for stem/progenitor cells, as their self-renewal and differentiation has been shown to be redox sensitive. However, not much is known about ROS and antioxidant protein function in freshly isolated keratinocytes, notably the different keratinocyte subpopulations. Immunostaining of neonatal cutaneous sections revealed that antioxidant enzymes [catalase, SOD2, gluthatione peroxidase-1 (GPx)] and ROS are localized predominantly to the epidermis. We isolated keratinocyte subpopulations and found lower levels of SOD2, catalase and GPx, as well as decreased SOD and catalase activity in an epidermal side population with stem cell-like characteristics (EpSPs) compared to more differentiated (Non-SP) keratinocytes. EpSPs also exhibited less mitochondrial area, fewer peroxisomes and produced lower levels of ROS than Non-SPs. Finally, EpSPs were more resistant to UV radiation than their progeny. Together, our data indicate ROS and antioxidant levels are decreased in stem-like EpSPs.