Abstract We have previously shown that metformin, a biguanide commonly used for the treatment of type 2 diabetes, has robust protective effects against cigarette smoke (CS)- induced lung pathologies including accelerated aging, apoptosis, inflammation, and oxidative stress in mice and in individuals with emphysema-dominant COPD. Alveolar epithelial cell injury contributes to structural damage in emphysema with alveolar type 2 epithelial (AT2) cells crucial in promoting lung re-epithelization and maintenance of surfactant synthesis after such injuries. AT2 cells are the most metabolically active cells of the alveoli and use fatty acid oxidation (FAO, which occurs mainly in mitochondria) as fuel. We here show that AT2 cells are the main target of metformin’s protective effects against CS-induced lung damage, by reducing AT2 oxidative stress burden and improving AT2 FAO and mitochondrial function. In this proposal, we will test the central hypothesis that metformin protects AT2 cells against CS-induced dysfunction and emphysema by ameliorating dysfunctional AT2 cell mitochondrial metabolism and FAO. We will also prove that, by improving FAO in AT2 cells, metformin rescues mitochondria from CS-induced dysfunction. To test these hypotheses, we will pursue complementary Specific Aims. Aim #1 will test the hypothesis that metformin improves AT2 function in a CS-induced emphysema model by partial binding of mitochondrial complex 1 (MTC) of the electron transport chain. Using CS-exposed mice lacking a functional MTC1 subunit, and + metformin, we will analyze the effects of metformin on AT2 cell function by assessing mitochondrial function/stress, and AT2 surfactant synthesis and regenerative functional capacity. In Aim #2, will test the hypothesis that metformin improves AT2 function in a CS-induced emphysema model by restoring FAO improving lipid metabolism and mitochondrial function in AT2 cells. Using CS-exposed mice lacking CPT1A, a key enzyme in FAO, and + metformin, we will determine the protective effects of metformin on AT2 cell surfactant synthesis and regenerative functional capacity by assessing lipid metabolism, FAO oxidation and mitochondrial function/stress. In Aim #3, we will use fresh lung samples from individuals with COPD and controls recruited prospectively to confirm our preclinical finding that metformin protects the lung against CS and COPD pathologies by ameliorating AT2 cell FAO and mitochondrial impairment and thus AT2 cell function. Simultaneously, using fresh and frozen blood from samples from the same patients and from well-characterized existing COPD patients’ cohorts, we will also investigate the circulating lipidomic profile associated with the use of metformin as a marker of metformin efficacy in a selected subset of COPD patients. The characterization of the effects of metformin on FAO in a preclinical emphysema model, and in patients with emphysema will pave the way to new strategies targeting a selected category of patie...