Project Summary The goals of this project are to carry out first-in-human study of the molecule Smad3 to begin to establish if it is important in the pathogenesis of ventilator-induced diaphragm dysfunction (VIDD) in humans, and to use this work to train a promising young investigator to work in translational research. The project will take advantage of the trial design of the parent R01 – a clinical trial focused on the role of Jak/Stat in VIDD -- to focus upon an additional potential effector of VIDD. This project will, it is hoped, provide the basis for further clinical drug development based upon Smad3 as a therapeutic target in VIDD. It is known that MV leads to atrophy and weakness of the diaphragm. Since the diaphragm is primarily responsible for inspiration, its weakness renders it difficult to separate patients from the ventilator. The resulting ventilator dependence often leads to a spiral of other ventilator- associated complications that result in increased morbidity and death. A drug that could be given at the initiation of MV and prevent weakness of the diaphragm would therefore reduce ventilator dependence and complications/deaths in intensive care unit (ICU) patients. The PI’s lab demonstrated that the inter-related molecules Jak and Stat3 are important in the etiology of VIDD in animals, and the parent R01 is studying this in humans by measuring VIDD in subjects randomized to Jak inhibition vs. placebo. However, beyond the Jak/Stat pathway, the lab has also demonstrated that Smad3 appears central to the evolution of VIDD in animals: Smad3 inhibition prevents VIDD in rats. Validation of whether and how Smad3 contributes to human VIDD, by study of human diaphragm biopsies, may provide another therapeutic target: We will take 2 small diaphragm biopsies, 6 hours apart, in patients undergoing esophagectomy, and we will characterize the effects of MV on the activation of Smad3; we will correlate Smad3 activation with VIDD as measured in single, permeabilized, muscle fibers: Aim 1) Study the effect of MV on Smad3 activity in timed, MV human diaphragm biopsies. Aim 2) Study the relationship between Smad3 activity and diaphragm weakness in timed, MV human diaphragm biopsy specimens. This study will thus characterize the relationship between Smad3 activity and diaphragm muscle weakness in humans undergoing MV. The trainee will learn and apply the research skills required for a career in respiratory muscle research at the clinical/laboratory interface. Findings may solidify a novel molecular target for VIDD and support the development of a Smad3 inhibitor that could be tested in a future clinical trial.