Disruption of Glutathione Homeostasis and Endothelial Apoptosis in Acute Lung Injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are hypoxemic respiratory failure syndromes that can be life threatening. ALI is an acute inflammatory state that leads to increased capillary permeability, pulmonary edema, and increased endothelial apoptosis. ALI can occur in response to a number of insults that either directly or indirectly cause lung injury. The most common indirect insult leading to ALI is the release of lipopolysaccharide (LPS) from the outer bacterial cell wall producing gram negative sepsis. Glutathione (GSH) is a thiol-containing tripeptide that has been shown to help in maintaining cellular redox status. Disruption in GSH homeostasis resulting in induction of endothelial apoptosis and the dysregulation of apoptotic pathways is thought to play an important role in the pathogenesis of ALI. Humanin is a 24-amino acid peptide that appears to be involved in the sequestration of the apoptosis-inducing proteins of the Bcl-2 family. Thus, in this proposal we will investigate the mechanisms by which the disruption of GSH homeostasis in ALI/ARDS leads to endothelial apoptosis with a focus on determining the link between the disruption of mitochondrial function and the loss of humanin activity. Our preliminary data suggest that the disruption GSH homeostasis secondary to a loss of glutathione reductase activity leads to alterations in the redox environment of the mitochondria. This in turn leads to an increase in the generation of mitochondrial reactive oxygen species and the subsequent stimulation of the apoptotic pathway. Apoptotic stimuli cause a decrease in the humanin-Bax interaction and increased translocation of Bax from the cytosol to the mitochondria, where it causes membrane permeabilization. We will compare and contrast the effectiveness of humanin gene delivery to the pulmonary vasculature versus the infusion of antioxidant molecules in stimulating anti-apoptotic signaling and limiting lung injury prior to the induction of ALI. We will also evaluate the potential for stimulating pulmonary endothelial anti-apoptotic pathways in reducing the severity of ALI/ARDS in vivo. Despite great advances in understanding the pathophysiology of ALI/ARDS the available therapies have not led to significant reductions in mortality and survivors suffering reduced quality of life. Thus, a greater understanding of the mechanisms by which these pathways are disrupted could lead to the development of more successful therapies. (AHA Program: Beginning Grant-in-Aid)