Acute respiratory distress syndrome (ARDS) is a fatal critical illness with mortality rates remaining greater than twenty percent despite numerous clinical trials. It is therefore essential to better understand the basic mechanisms underpinning its development. ARDS is also unique in that it is a common pathway that occurs after many disease processes that result in critical illness (shock from trauma or sepsis, burns, pancreatitis). As such, ARDS represents an ideal model disease to understand severe critical illness and will studied in the proposed animal and human studies. ARDS is characterized by vascular permeability leading to edema and accumulation of immune cells in the lung. The increased vascular permeability is in part due to dysfunction of endothelial cells and will therefore be the focus of this project. Much work has focused on gene expression and evaluation of the protein levels with little emphasis on changes in RNA splicing. RNA splicing is a basic molecular function that occurs in all cells directly after RNA transcription, but before protein translation in which introns are removed and exons are joined together. Over 90% of human genes with multiple exons have alternative splicing events. With such a high rate of variation from the transcribed gene to the produced protein, splicing must be under exquisite control, particularly in times of critical illness. Numerous proteins are involved in the control of RNA splicing, one of interest is U1-70K. Preliminary data suggests that in the lung there is no difference in gene expression, but rather multiple sites of alternative splicing of U1-70K. This is similar to previous work showing that critical illness (ARDS) leads to alternative splicing of membrane bound proteins resulting in a soluble form. We hypothesize that alternative splicing seen during critical illness alters the protein isoforms of U1-70K in endothelial cells. This change in the isoforms, in turn, results in the microvascular permeability and sequestration of edema and immune cells in the lungs during ARDS. With a better understanding of alternative RNA splicing, the long term goal is to manipulate this mechanism to improve outcomes or better predict resolution or ARDS.