Objective: 

Myocardial injury may activate the innate immune system by activation of nuclear factor kappa B (NFB) via toll-like receptors (TLRs). Mitochondria are evolutionary endosymbiots and mitochondrial DNA (mtDNA) might contain bacterial molecular motifs, potentially causing a TLR9 mediated, NFB-dependent inflammation. We hypothesize that mtDNA is damaged and released during myocardial ischemia-reperfusion injury and evokes an immune response.

Methods and materials: 

Patients: 

Blood was sampled for mtDNA extraction from 20 patients with acute myocardial infarction and 10 patients with stable angina pectoris undergoing percutaneous coronary intervention (PCI).

Mice: 

Isolated, perfused hearts were were subjected to global ischemia and reperfusion (n=10). Coronary effluents and hearts were collected for mtDNA extraction and evaluation with real time PCR.

Cells: 

Human embryonic kidney cells (HEK293lucTLR9/elam), stably transfected with TLR9 reporting elam luciferase activity upon NFB activation, were incubated with vehicle, nuclear DNA (nDNA), mtDNA or TLR9 agonist (CpG-DNA) for 24 hours. Luciferase activity was photometrically assessed.

Results: 

Patients with myocardial infarction had increased release of mtDNA 3 hours after PCI compared to patients with stable angina (p< 0.01). There was a correlation between infarct size (measured by MRI) and mtDNA release (p =0.01). Ischemic-reperfused mouse hearts had evidence of mtDNA damage (p =0.01), and mtDNA was released into the perfusate (p =0.0015). mtDNA and CpG-DNA activated luciferase activity in HEK293lucTLR9/elam cells (p< 0.0001) indicating TLR9 dependent NFB signaling leading to elam expression.

Conclusion: 

Ischemiareperfusion caused mtDNA damage in the heart and leakage of mtDNA into the circulation. mtDNA stimulated HEK293lucTLR9/elam cells in a NFB dependent manner.