Chlorine (Cl2) is a highly irritant and reactive gas produced in large quantities throughout the world and used extensively for pulp bleaching, waste sanitation and in the manufacturing of various pharmaceuticals. It also poses a significant threat to public health when inhaled. Exposure to Cl2, released into the atmosphere during transportation and industrial accidents, as well as acts of terrorism resulted in significant morbidity and mortality to both humans and animals. There is no safe exposure to Cl2: Even domestic exposure to low levels of Cl2 may result in wheezing and exacerbate the clinical outcome of asthma and chronic obstructive pulmonary disease. When inhaled, Cl2 first reacts with antioxidants in the lung epithelial lining fluid (ELF); when antioxidants are depleted, it fors relatively stable adducts with proteins, components of the extracellular matrix and unsaturated fatty acids which then proceed to prolong the toxicity of the initial Cl2 exposure and contribute t the long term pathology. In this proposal we will test the hypothesis that these secondary reactive species target the mitochondrion and so decrease mitochondrial quality and cause bioenergetic dysfunction which delays tissue recovery and repair. Based upon these data we hypothesize that mitochondria are a critical target for Cl2 toxicity in lung epithelial cells and te combined strategy of preventing mitochondrial oxidative damage by mitochondrial targeted antioxidants (such as MitoQ) with enhancing mitophagy (by rapamycin and trehalose), will be beneficial in ameliorating Cl2 toxicity. This hypothesis will be tested by completing the in vitro and in vivo studies highlighted in these two highly integrated specific aims: SA-1: Determine the mechanisms and physiological sequelae of mitochondria injury and autophagy following exposure of human airway cells to Cl2 in vitro. SA-2: Determine if post Cl2 administration of MitoQ, rapamycin and trehalose in mice decreases Cl2 induced mortality and lung injury and improves mitochondrial bioenergetics function. Completion of these experiments will provide the rational basis for additional studies to establish effective therapies for a major environmental and public health threat to humans.