Dr. Scott L. Weiss, Assistant Professor of Anesthesia, Critical Care, and Pediatrics at the University of Pennsylvania (UPenn) and The Children's Hospital of Philadelphia (CHOP), is committed to his development as a translational scientist studying mitochondrial dysfunction in sepsis, with a particular focus on pediatrics. More than 75,000 children develop sepsis-associated organ dysfunction in the United States each year with over 10 estimated deaths per day and an annual cost of $4.8 billion. Acquired mitochondrial dysfunction can impair cellular bioenergetics and has been implicated as a proximate cause of organ dysfunction in sepsis. If early mitochondrial dysfunction results in organ injury in patients with sepsis, then therapies targeting this pathway could improve outcomes. The candidate's immediate goal is to determine if changes in mitochondrial function are associated with clinical outcomes in sepsis-associated multi-organ dysfunction syndrome (MODS). His long-term goal is to improve outcomes for children with sepsis using therapies targeted to fundamental pathobiology developed through translational research. This career development award will utilize a multidisciplinary network of research and mentorship to ensure the cross-training in clinical research and laboratory methods needed for the translational study of mitochondrial dysfunction in sepsis. This will include close mentorship from both local and international expert scientists in mitochondrial biology, sepsis, and patient-oriented research, coursework focusing on clinical trial design and advanced statistics, and classroom and laboratory experiences to expand his knowledge of mitochondrial biology. To address the lack of a pragmatic tool to measure mitochondrial dysfunction in critically ill children, the candidate has previously demonstrated that circulating blood mononuclear cells (MNCs) exhibit mitochondrial dysfunction in pediatric septic shock and that these blood-based measures correlate with mitochondrial dysfunction in other vital organ systems within an animal model of shock. As an easily accessible cell type in clinical practice, blood MNCs could provide a window into a systemic process affecting vital organ systems and impart insight into a mechanism of sepsis-induced immune dysregulation. The goal of the current research is to determine if mitochondrial dysfunction in blood MNCs is indicative of systemic organ dysfunction and immune dysregulation in pediatric sepsis. Aim 1 will determine whether mitochondrial dysfunction measured in blood mononuclear cells is associated with vital organ dysfunction in pediatric sepsis in a prospective cohort study of 200 critically ill children with sepsis. The exposure in ths study will be presence versus absence of mitochondrial dysfunction. The primary outcome will be organ failure-free days; secondary outcomes will be prolonged organ dysfunction, new and progressive MODS (NPMODS), shock-free days, ventilator-free days, length of stay, mortality, and functional status. Aim 2 will test the association of mitochondrial dysfunction in MNCs with the development of immune dysregulation and changes in inflammatory signals in sepsis. Aim 3 will investigate four compelling mechanisms of mitochondrial dysfunction-increased reactive oxygen species, decreased electron transport system complex activity, aberrant mitochondrial turnover, and decreased mitochondrial gene expression. In summary, the plan outlined in this application will provide an outstanding early career research experience within a rich environment supported by world-class mentorship that will prepare the candidate to become an independent investigator. Completion of the proposed aims will provide the foundation to study if quantifiable deficits in mitochondrial function can inform risk-stratification and targeted mitochondrial-based therapies in critical illness.