PROJECT SUMMARY/ABSTRACT Environmental inhalation exposures are inherently mixed (gases and particles), yet environmental regulations are still based on single toxicant exposures. Developing and studying the co-exposure scenario in a standardized and controlled fashion will enable a better mechanistic understanding of how environmental exposures result in adverse outcomes. The impact of co-exposures is poorly studied, especially in susceptible populations such as individuals with acute lung injury (ALI). In the absence of such knowledge on environmental co-exposures, it will be very difficult, if not impossible, to reduce the burden of environmental disease and develop effective as well as realistic exposure limits to safeguard public health. The goal of this proposal is to elucidate mechanisms of carbon black (CB; surrogate of the carbon core of ultrafine particles) and ozone (O3) inhalation co-exposure- induced lung injury and modulation of epithelial regeneration in mice following ALI. We will further mechanistically characterize the role of mitochondrial nucleotide-binding oligomerization domain-like Receptor X1 (NLRX1) in these responses. We hypothesize that co-exposure to CB and O3 synergistically increases pulmonary damage by oxidizing the particle surfaces, causing NLRX1 mediated mitochondrial dysfunction and microbial dysbiosis, leading to reprogramming of the alveolar progenitor (AT2) cells for altered alveolar regeneration. Our research plan exclusively combines state of the art inhalation co-exposures, unique mouse models, and 3-D organoid cultures to elucidate the mechanisms of co-exposure induced pulmonary damage in healthy and injured lungs (a susceptibility model). Our preliminary studies demonstrate that O3 and CB inhalation co-exposures synergistically exacerbates lung injury, oxidative stress, inflammation, lung function decline, lung permeability, mitochondrial oxidative phosphorylation, and lung microbial dysbiosis compared to individual exposures. Mice lacking NLRX1 exhibit significantly aggravated inflammatory response after co-exposure. Alveolar type 2 (AT2) cells (alveolar progenitor cells) show significant apoptosis, mitochondrial damage, and impaired ability to form 3-D alveolar organoids after co-exposure. Bleomycin (BLM)-induced lung epithelial injury is significantly increased, while epithelial proliferation is impaired after co-exposure. Our specific aims are 1) to determine synergistic biological activity and mechanisms of lung inflammation after co-exposure, 2) to identify how the altered mechanisms of alveolar injury and alveolar progenitor cell dysfunction contribute to progression and outcome of ALI, and 3) to characterize microbiome-alveolar progenitor cell cross-talk during co-exposure with or without ALI. These studies will delineate genetic (NLRX1) and cellular mechanisms (alveolar progenitor mitochondrial dysfunction and microbial dysbiosis) through which environmental exposures impact ALI outcomes. These findings will be helpful in understanding the impact of co-exposures on adverse lung effects and developing preventive and therapeutic efforts to ameliorate the health impact of air pollution.