Mitochondrial DNA regulates TNF-alpha mRNA stability
MetadataShow full item record
Sepsis is defined as potentially fatal systemic inflammation, caused by an infection. It is the leading cause of ICU mortality and the 10th leading cause of death in the United States. Several models exist to mimic this disorder, and have demonstrated differential mortality rates between the models as well as the individual animals. Previous studies have shown that elevated levels of plasma mitochondrial DNA (mtDNA) correlated with mortality in septic patients, and cell-free mitochondrial DNA can elicit toll-like receptor mediated immune responses similar to LPS-mediated septicemia. However, the role of mtDNA in the pathophysiology sepsis is still unknown. The focus of this study was to create sepsis in a mouse model using the murine Cecal Ligation and Puncture (CLP) model, and measure plasma mtDNA levels. After CLP was performed on experimental mice, blood plasma was collected 24 hours later. Elevated amounts of circulating mtDNA were detectable in the plasma using real time PCR and cytochrome B2 as a marker of mitochondria. These data were correlated with plasma IL-6 levels, which were used to predict mortality within 5 days of CLP to stratify mice into two populations of those predicted to live or die following the procedure. We also aimed to investigate the effect of mtDNA and mitochondrial debris on naïve mouse macrophages in an in vitro study of the regulation of inflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β). In order to observe the effects of mtDNA on murine macrophages, mitochondria was purified from mouse liver and used to stimulate these cells alongside positive control, LPS. Stimulation with mtDNA and mitochondrial debris resulted in increased levels of TNF-α mRNA in lysed cells as well as their surrounding media as compared to control cells, as well as increased transcript half life as measured over four hours post stimulation with transcription inhibitor actinomycin D. The increases in mRNA half-life elicited by mtDNA were comparable to those observed after LPS addition. Stimulation also caused increased binding of TNF-α mRNA to the RNA binding protein, AUF1, as measured by immunoprecipitation of RNA-protein complexes and assayed for TNF-α binding by PCR. These results demonstrate that mitochondrial damage-associated molecular patterns regulate TNF-α mRNA expression at the post-transcriptional level through AUF1, an mRNA destabilizing factor. This is a novel mechanism that likely contributes to sepsis pathophysiology, and demonstrates the involvement of the mitochondrial fission and fusion balance and its regulation in the sepsis innate immune response.