Management of severely injured patients is challenging because Multiple Organ Dysfunction Syndrome may advance relentlessly even if the initial insult is controlled. However, a series of reports point to the prospect that mitochondrial (mt)-associated pathways play a central role. Specifically, it has been discovered that oxidative mtDNA damage is both cytotoxic and leads to its fragmentation into proinflammatory mtDNA Damage Associated Molecular Patterns with the potential to disseminate injury to distant organs. Against this background, the goal of this project is to provide insight into the origin, characteristics, and biological effects of mtDNA DAMPs in the setting of trauma-related MODS as a prelude for translating mtDNA- directed therapies into clinical application. We will use a clinically-relevant porcine model of MODS induced by hemorrhage with truncal ischemia and reperfusion to address three Aims. Because conventional strategies for analysis of circulating mtDNA DAMPs use PCR to quantify sequences of about 200 bp in length, it is likely that the most prevalent or biologically relevant mtDNA DAMP species have not been identified. In addition, there are tissue-specific differences in mtDNA sequences that may dictate sequence characteristics of circulating mtDNA DAMPs. Accordingly, Aim 1 will define sequence characteristics of mtDNA DAMPs released during the evolution of trauma-related MODS and test the hypothesis that unique variant signatures of circulating mtDNA can be traced to specific organs and that fail.
The second aim addresses the origin of mtDNA fragments accumulating in the circulation after trauma. In this regard, it has been known for decades that interuption of mesenteric lymphatic drainage forestalls MODS, thus supporting the concept that the liver- gut-mesenteric axis could be a major source of circulating mtDNA DAMPs, perhaps stimulating mtDNA DAMP production in other organs.
Aim 2 will therefore test the hypotheses that in trauma, mtDNA DAMPs are present in the mesenteric lymphatic drainage and that an intact mesenteric lymphatic drainage system is required for systemic mtDNA DAMP accumulation and MODS. Finally, prevention or reversal of mtDNA damage with novel fusion protein constructs targeting DNA repair enzymes to mitochondria and pharmacological enhancement of mtDNA DAMP degradation with a repurposed agent, DNase1, forestalls IR injury in rodents. Importantly, however, neither of these strategies have been explored in a clinically-relevant animal model. As a consequence, critical mechanistic insight, particularly the purported operation of a feed- forward pathway linking mtDNA damage to mtDNA DAMP production, is unavailable. Accordingly, to provide information needed for translation of mtDNA-directed therapies into clinical application, Aim 3 will use test the hypothesis that mt-targeted Ogg1 and DNase1, given alone or in combination, alter disposition of circulating mtDNA DAMPs and suppress MODS.
Laboratory experiments in rodent models and observational studies in severely injured human subjects show that mitochondrial (mt) DNA damage and attendant formation of pro-inflammatory (mtDNA fragments, termed mtDNA Damage Associated Molecular Patterns (DAMPs), are closely associated with clinical outcomes. Little is known, however, about the organs from which mtDNA DAMPs originate, about their molecular characteristics, and about whether mtDNA damage and DAMP formation are pharmacologic targets that could have clinical utility. Accordingly, the goal of this project is to use a rational porcine model of MODS to provide insight into the origin, characteristics, and biological effects of mtDNA DAMPs as a prelude for translating mtDNA-directed therapies into clinical application.