Abstract

Introduction: Ischemia/reperfusion (I/R) injury occurs after coronary revascularization, contributing to infarct size. Circulating mitochondrial DNA (mtDNA) levels are elevated in acute myocardial infarction (MI) patients, and act as Damage Associated Molecular Patterns (mtDNA DAMP), which are recognized by the Toll-like receptor 9 (TLR9), initiating pro-inflammatory responses. Prior studies have shown that loss of TLR9 prevents I/R injury in isolated mouse hearts. However, mtDNA DAMP levels have not been measured in ST-elevation MI (STEMI) patients, and whether blocking TLR9 in mice can reduce I/R injury remains unknown. Hypothesis: MtDNA DAMP levels serve as markers of STEMI related cardiac injury. Blocking the activation of TLR9 will decrease cardiac I/R injury. Methods: MtDNA DAMP levels in serum were measured pre- and 24 hours post- PCI in 55 STEMI patients and 37 healthy controls by qPCR. To evaluate the role of TLR9 on I/R injury, ODN2088 was used to block TLR9 receptor, wild type and TLR9 germline KO mice were subjected to close-chest I/R surgery with minimal systemic inflammation. The cardiac systolic function and infarct size were assessed. Immune cells were isolated from the injured left ventricle and spleens and detected by flow cytometry. Results: Pre- PCI mtDNA DAMP levels were increased ~200 folds in STEMI patients compared to healthy controls. After PCI, the elevated mtDNA DAMP levels reduced significantly, while the troponin T levels increased, suggesting mtDNA is an early marker of MI. Compared with negative ODN, ODN2088 treatment at reperfusion reduced infarct size and total leukocytes, myeloid cells, neutrophils and TNF-α + cells, and a trend of reduced IL-1β + cells, and there was no difference in IL-6 + cells, total macrophages and residential macrophages. Loss of TLR9 in male and female mice significantly reduced infarct size by ~40% and preserved the systolic function. Meanwhile, there is no difference between genders. Conclusions: Circulating mtDNA DAMP level is an early marker of STEMI and may predict the success of PCI. Blocking the mtDNA DAMP-TLR9 signaling pathway during reperfusion significantly reduces I/R injury, indicating it is a viable therapy to mitigate cardiac I/R injury after prompt coronary revascularization.