Fundamentals of redox regulation in biology

Oxidation–reduction (redox) reactions are central to the existence of life. Reactive species of oxygen, nitrogen and sulfur mediate redox control of a wide range of essential cellular processes. Yet, excessive levels of oxidants are associated with ageing and many diseases, including cardiological and neurodegenerative diseases, and cancer. Hence, maintaining the fine-tuned steady-state balance of reactive species production and removal is essential. Here, we discuss new insights into the dynamic maintenance of redox homeostasis (that is, redox homeodynamics) and the principles underlying biological redox organization, termed the ‘redox code’. We survey how redox changes result in stress responses by hormesis mechanisms, and how the lifelong cumulative exposure to environmental agents, termed the ‘exposome’, is communicated to cells through redox signals. Better understanding of the molecular and cellular basis of redox biology will guide novel redox medicine approaches aimed at preventing and treating diseases associated with disturbed redox regulation. Oxidation–reduction (redox) reactions involving reactive oxygen, nitrogen and sulfur species are vital for life, but excessive oxidant levels contribute to ageing and diseases. This Review explores cellular dynamics of redox homeostasis, such as responses to oxidative and reductive stresses and intracellular and intercellular redox communication pathways.