Sepsis is a medical emergency of life-threatening organ dysfunction due to a dysregulated host response to infection. In the United States, over one million people are hospitalized with sepsis or septic shock every year, including >75,000 children. Multiple organ dysfunction syndrome (MODS) is the most common cause of death for children with sepsis. Although most children who develop sepsis recover with appropriate conventional care, ~20% develop MODS, and one in five of these children with sepsis-induced MODS still die. For this high-risk subset, we have no cure and care is largely supportive. Widespread alterations in the ability of mitochondria to supply sufficient energy for normal cellular activities has been implicated as a key pathologic event leading to MODS in sepsis. Using a protocol optimized to measure mitochondrial respiration and content in peripheral blood mononuclear cells (PBMC), our group discovered that children with prolonged sepsis- induced MODS are more likely to have persistent mitochondrial dysfunction. This proposal builds on our prior work to test the hypothesis that low mitochondrial respiration in PBMCs is caused by abnormal mitochondrial quality control processes (biogenesis, fission, fusion, and mitophagy) that normally restore and maintain mitochondrial health. The resulting mitochondrial dysfunction, through release of mitochondrial DNA (mtDNA) into the cytosol, can then activate inflammatory pathways that sustain inflammation and organ dysfunction in children with sepsis.
In Aim 1, we will determine which changes in mitochondrial quality control are associated with recovery versus persistence of low mitochondrial respiration in children with sepsis. We will enroll 106 children with sepsis-induced MODS and measure mitochondrial respiration, redox state, content, biogenesis, fission, fusion, and mitophagy on days 1, 3, 5, and 7 of illness.
In Aim 2, we will determine if the persistence of PBMC mitochondrial dysfunction activates three inflammatory pathway (cGAS-STING, TLR-9, and inflammasome) that sense release of mtDNA into the cytosol.
In Aim 3, we will test whether mitochondrial dysfunction, abnormal mitochondrial quality control, or activation of inflammatory pathways are associated with the severity or duration of MODS in children with sepsis. As part of Aims 1 and 2, we will also conduct a parallel set of in vitro experiments to test the utility of lipopolysaccharide- and lipoteichoic acid-stimulation of EBV-transformed lymphoblasts as a potential translational platform for future therapeutic investigation and to establish cytosolic mtDNA as one mechanism through which mitochondria can promote inflammation in sepsis.
These aims address the NICHD?s interest in ?studies focused on mitochondrial dysfunction as a pathophysiologic process of MODS?with potential to advance to translational and clinical projects.? By understanding why mitochondrial dysfunction persists in some children and how this can lead to sustained inflammation and MODS, we will identify new potential therapeutic targets for children with prolonged MODS, the leading cause of death in sepsis for which we currently have no cure.
Sepsis is the most common cause of multiple organ dysfunction syndrome (MODS), and sepsis-induced MODS is a leading cause of prolonged hospitalization and death for children. We previously found that children with prolonged MODS also have persistent immune cell mitochondrial dysfunction. Through the proposed study, we will now determine if mechanisms that normally restore and maintain mitochondrial health are abnormal in children with prolonged sepsis-induced MODS, leading to persistent mitochondrial dysfunction that then sustains inflammation and increases severity and duration of organ dysfunction.
