Objective: The goal of this NRSA fellowship is to investigate the role of mitochondrial transcription factor A (Tfam) in mediating mitochondrial biogenesis and preventing organ dysfunction in sepsis and to promote the development of Dr. Keenan as a scientist. Background: Sepsis is the 10th leading cause of death in the United States and the most common cause of multiple organ dysfunction syndromes. In recent years, it has become clear that mitochondrial damage is central to the pathophysiology of sepsis. Mitochondrial biogenesis, or the process of restoring or increasing functional mitochondrial mass in the cell, is critical for cellular recovery following sepsis and has been linked to surviva in critically ill patients. It is regulated by a bi-genomic transcriptional program initiated by a diverse array of stimuli, including inflammation and sepsis, in response to increased cellular energy requirements. Tfam is a nuclear encoded protein that facilitates transcription and replication of mitochondrial DNA. It is a component of the mitochondrial biogenesis program, but its role in mediating mitochondrial biogenesis and preventing organ dysfunction following sepsis has not been characterized. Hypothesis: It is hypothesized that the selective loss of hepatic Tfam upon septic challenge will inhibit mitochondrial biogenesis resulting in increased hepatocyte cell death, worsening hepatic failure, and immune suppression. Methods: The hypothesis will be tested by using a Tfam-knockout mouse model. Specifically, Tfam will be conditionally silenced in the hepatocytes. Sepsis will then be induced by the peritoneal implantation of a S. aureus impregnated fibrin-clot in experimental and wild-type control mice. The mice will be sacrificed at different time points over 48 hours from the time of induction of sepsis and the livers will be harvested. Using real-time PCR, Western blot, and histologic analysis, the activation of mitochondrial biogenesis, related anti- inflammatory pathways, and the extent of hepatocyte damage and dysfunction will be determined. Expected Results: It is expected that the loss of Tfam will result in reduced mitochondrial biogenesis increased organ damage and dysfunction as well as hyper-activation of linked anti-inflammatory pathways. This will demonstrate Tfam essential for the activation of mitochondrial biogenesis and organ protection in sepsis. Confirmation of this hypothesis will form the basis for future experimentation as well as the development of targeted therapies to improve outcomes in sepsis.
Sepsis is the tenth leading cause of death in the United States, and severe sepsis continues to carry a mortality rate of greater than 30%. Effective treatments have not been developed because there is a basic lack of understanding of the cellular and molecular processes underlying sepsis and the cell's response to sepsis. The proposed study intends to gain insight into a critical aspect of the cell's response to sepsis- mitochondrial biogenesis-with the ultimate goal of allowing the development of future targeted therapies for this deadly disease.