Mitochondrial ROS Induces Cardiac Inflammation via Damage in Mitochondrial DNA and Stimulation of RAGE Pathway in a Pneumonia-related Sepsis Model
Author(s):
Qun (Sophia) Zang, UT Southwestern Medical Center; Xiao Yao, UT Southwestern Medical Center; Deborah Carlson, UT Southwestern Medical Center; Steven Wolf, UT Southwestern Medical Center; Joseph Minei, UT Southwestern Medical Center
Background: We have previously shown that sepsis impairs cardiac mitochondria, resulting in compromised membrane integrity, an increase in oxidative stress, and a decrease in antioxidant defense using a pneumonia-related sepsis model in rats. Further, when a mitochondria-targeted antioxidant, mitochondria-targeted vitamin E (Mito-Vit-E), was used in this sepsis model, evidence was collected to support that mtROS-mediated mitochondria impairment plays a causative role in myocardial inflammation and cardiac dysfunction during sepsis. Our recent investigation revealed that an important mechanism underling the deteriorative action of mtROS involves damage in mitochondrial DNA (mtDNA) and the activation of TLR9-mtDNA-RAGE pathway in septic hearts.
Hypothesis: Mitochondrial ROS-dependent damage in mtDNA induces cardaic inflammation after sepsis.
Methods: Sepsis was induced in SD rats by intratracheal injection of S. pneumoniae (4x106 CFU/rat). Mito-Vit-E (21.5 micro moles/kg) or vehicle was administered 30 minutes post-inoculation and heart tissue was harvested 24 hours later for analysis.
Results: Sepsis reduced intact mtDNA by 30%, increased mtDNA oxidative modifications, and decreased mitochondria-localized DNA repair enzymes including DNA polymerase gamma, AP endonuclease, 8-oxoguanine glycosylase, and uracil-DNA glycosylase. These changes were not detected in infected animals receiving Mito-Vit-E, indicating mtROS-dependent mtDNA damage in septic hearts. Mito-Vit-E also prevented sepsis-induced defects in mitochondrial respiratory activities and membrane integrity. Furthermore, we detected dramatic increases in cytosolic mtDNA (a type of mitochondrial DAMPs), expression of TLR9 pathway factors MYD88 and RAGE, and interaction between RAGE and one of its ligands TFAM in septic animals. Attenuation of these responses by Mito-Vit-E suggests that mtROS induce inflammation through TLR9. Mito-Vit-E’s anti-inflammatory effect was further demonstrated by decreases in NF-kappa B activation and expression of inflammasome component ASC and cytokine IL-1 beta. Cardiac protection by Mito-Vit-E was shown by reduction in myocardial injury marker troponin-I and amendment of heart morphology after sepsis.
Conclusions: Data suggest that mtROS cause mtDNA damage and induce the activation of TLR9-RAGE pathway, at least partially leading to cardiac inflammation and impairment during sepsis. In addition, the data also suggest that mitochondria-targeted antioxidants represent a potential therapeutic approach for sepsis.