Compromised wound tissue oxygenation has been long recognized as a key limiting factor in healing. Oxygen homeostasis has therefore been the center of major attention in wound healing research. Current findings indicate that a significant fraction of oxygen at the wound site is utilized to generate reactive oxygen species (ROS). ROS are classically described as accidental metabolic by-products, and are generally thought to be deleterious. The phagocyte NADPH oxidase deliberately generates ROS in transient bursts to kill pathogens. High concentrations of H2O2 (equal to or more than 1%) are used clinically for wound disinfection. However, there is a general agreement that at these doses H2O2 is harsh to regenerating cells and may not benefit overall healing. The recent discovery of another family of NADPH oxidases, the Nox/Duox family, provides additional examples of deliberate generation of ROS by non-phagocytic cells at the wound site. Upon induction, these cells generate low-levels of ROS on a sustained basis. Recent data support that such low concentration of ROS can regulate specific key redox-sensitive signaling processes most of which can be directly linked to wound healing. This proposal rests on our striking observation that genetic as well as pharmacological approaches to deliver low concentrations of ROS promote dermal wound angiogenesis, contraction and closure. Such low concentrations of ROS did not influence wound infection status. Strategies to decompose ROS at the wound site impaired healing. Taken together, these observations led to the hypothesis that resisting infection is not the sole role of ROS at the wound-site, and that ROS drives redox-signaling to support healing. Indeed, congenital defect in human NADPH oxidase results in impaired wound healing and antibiotics alone cannot correct such defect. We have observed that NADPH oxidase deficient transgenic mice suffer from impaired dermal healing even under infection-free conditions; the impairment is corrected by low-dose ROS delivery. Our working hypothesis is that ROS generated by wound-related cells (low-ROS by Nox; and residual ROS in the aftermath of phagocyte respiratory burst) support earlyphase acute wound healing by inducing redox-sensitive signal transduction pathways. Our long-term objective is to understand this new aspect of wound tissue oxygen homeostasis. We seek to illuminate the significance of redoxsensitive processes in wound healing, and to design redox-based strategies to promote healing. To test the stated hypothesis we propose the following three specific aims using standard models of murine acute dermal wound and in vitro culture of dermal microvascular endothelial cells: Aim 1. Investigate the role of ROS in excisional dermal wound vascularization, contraction and repair; Aim 2. Determine the significance of NADPH oxidases at the wound site; and Aim 3. Characterize the redox-sensitive mechanisms that regulate wound angiogenesis.