PI: Jacob I. Sznajder, MD 
Our Program Project Grant focuses on the alveolar epithelium during lung injury. Acute lung injury (ALI) and the Acute Respiratory Distress Syndrome (ARDS) are defined by impairment in the functions of the alveolar-capillary barrier. Alveolar epithelial cell function and barrier integrity are critical to maintaining normal gas exchange. An increase in the permeability of the alveolar epithelium to solutes and a decrease in the ability to actively clear sodium result in increased edema and impaired gas exchange in the lungs. Some patients with acute lung injury also develop disordered repair of the alveolar epithelium which is accompanied by fibroblast proliferation and collagen deposition. Fibroproliferation is associated with prolonged need for mechanical ventilation and development of the multiple organ dysfunction syndrome, a major cause of death in patients with ALI and ARDS. The alveolar epithelium is therefore a critical target for interventions designed to reduce the nearly 40% mortality observed in the estimated 150,000 patients in the U.S who develop acute lung injury and ARDS each year. The hypotheses which underlie the specific aims and experiments of each individual project and which drive the overall program are as follows: - Resolution of alveolar edema is essential for recovery after acute lung injury. Regional tissue hypoxia in the injured lung promotes endocytosis and ubiquitin mediated degradation of the Na,K-ATPase, impairing alveolar fluid clearance.
- Lung injury is associated with regional disruption of alveolar epithelial integrity. Adjacent epithelial cells play a role in re-establishing epithelial integrity through a process that requires the dynamic reorganization of the intermediate filament network.
- Mechanical forces applied to the alveolar epithelium activate signaling pathways through the extracellular matrix including laminin and dystroglycan. Alterations in extracellular matrix stiffness might interfere with these signaling pathways during lung injury and repair.
- A subset of patients with lung injury go on to develop fibroblast proliferation and collagen deposition. This fibroproliferation is associated with poor outcomes. Preventing the activation of the intrinsic apoptotic pathway in alveolar epithelial cells by inhibiting the Bcl-2 protein Bid can prevent the development of fibrosis.
The project investigators bring a wealth of experience to the study of the lung epithelium during injury. Over the last funding period, the projects and cores have developed an abundance of new reagents and procedures including intracellular probes, shRNAs, sophisticated gene delivery systems, advanced cell isolation techniques and transgenic/knockout mice. These reagents are not only proving to be invaluable tools for the ongoing aims but also provide the backbone of the new studies proposed in this continuation. Brief history and rationale for the PPG Historic models of acute lung injury suggested that lung injury follows an orderly, sequential pattern in which damage to the alveolar capillary membrane accompanied by edema formation was followed by active clearance of edema fluid and subsequent repair of the alveolar-capillary membrane with a varying degree of fibrosis. It is now recognized that these processes occur simultaneously in the lung of patient with ARDS and persist throughout the illness. This shift in thinking about ARDS necessitates a shift in the therapeutic paradigm. To enhance the survival of patients with lung injury, a multi-pronged approach is required that simultaneously improves the clearance of edema fluid (Project 1), promotes alveolar epithelial repair over fibrosis (Projects 2 and 3) and prevents the ongoing death of alveolar epithelial cells during injury (Project 4). In this program project, the investigators have focused on the mechanisms by which the alveolar epithelium contributes to the development of lung injury, edema, and fibrosis. Drs. Sznajder, Dada and Ciechanover (Project 1) will examine the mechanisms that regulate Na+ transport in epithelial cells exposed to hypoxia. Drs. Ridge, Goldman, Gottardi and Ciechanover (Project 2) will examine the role of the intermediate filament network, a critical component of the cell cytoskeleton, in the repair of the wounded epithelium. Drs. Jones, Budinger and Glucksberg (Project 3), will examine the mechanisms by which the signaling pathways mediated by interactions between laminin and dystroglycan are modulated by the stiffness of the extracellular matrix and the role that signaling through laminin plays in fibrosis during lung injury. Drs. Chandel, Budinger, and Kamp (Project 4) will extend their observations that mitochondrial-dependent apoptosis is required for fibrosis after bleomycin induced lung injury with a particular focus on signaling by TGF-β1. These four groups of investigators will be supported by the cores. Drs. Dean and Glucksberg will determine the mechanisms by which exposure of epithelial cells to cyclic stretch enhances gene transfer to the alveolar epithelium. The Administrative Core (Core A) will continue to organize the scheduled meetings between the project investigators, schedule and organize outside speakers sponsored by the PPG and facilitate the interaction between project investigators and other core facilities in the University. The Cell Culture Core (Core B) will continue to provide high quality primary alveolar type I and type II cells from rats, mice and humans as well as established alveolar epithelial cell lines to project investigators. The newly established Physiology- Rat/Mouse Core will provide blinded measurements of physiologic outcomes in relevant rat and mouse models of lung injury, breed transgenic and wild-type mice for project investigators and create genetic mouse tools for use by the project investigators and by the pulmonary research community. Collectively, these projects will further enhance our understanding of the mechanisms by which the alveolar epithelium contributes to lung injury and provide strategies to promote alveolar epithelial repair in the injured lung. A summary of the projects and the key personnel is provided in Figure 1. : Project 1: Effects of hypoxia on the alveolar epithelium Project 2: Role of Intermediate Filaments in Alveolar Epithelial Wound Repair Project 3: Laminin mediated alveolar cell mechano-transduction Project 4: Mechanisms of alveolar epithelial apoptosis during acute lung injury Project 5: Gene transfer to the alveolar epithelium: effects of stretch Core A: Administration Core B: Cell Culture and Physiology | 
