Study Of The Damage Effects Of Mitochondrial DNA In Acute Myocardial Infarction And Its Mechanism

Subjectives:The level of mitochondrial DNA(mtDNA)in circulation has been a important indicator of systemic inflammation,cell death and the degree of acute trauma.However,the specific role of mtDNA in acute myocardial infarction remains elusive.This study was designed to examine if mtDNA can be a biomarker of acute myocardial infarction and the damaging effect of mtDNA on cardiomyocytes and to investigate the mechanism.Methods:Plasma nuclear and mtDNA levels were measured by quantitative PCR in 30 AMI patients,15stable angina pectoris control participants(with MI risk),and 15 healthy individuals during the study period.Clinical relative biochemical criterion were measured at the same time.H9c2s cells were incubated with purified mtDNA or nuclear DNA with or without pretreatment by chloroquine(an inhibitor of endosomal receptors like TLR9).The cell viability was tested by MTT.To demonstrate the toxicity of mtDNA,mtDNA fragments were injected into rats 10 min before ischemia for 30 min and reperfusion for 24h.Infarct size was measured by TTC staining.Apoptosis of myocardium was detected by TUNEL staining and caspase-3 activity.The levels of TLR9,p-p38 MAPK,and p38 MAPK were detected by western blotting.Results:The concentrations of mtDNA were significantly higher in the AMI group of hospital day 1 than that in the non-MI controls and healthy individuals(3.754�0.384 ng/?L vs.1.851�0.3483 ng/?L,P<0.05;3.754�0.384 ng/?L vs.0.1517�0.0924 ng/?L,p<0.05)and decreased shortly after PCI.Exogenous mtDNA reduced the viability of H9c2s cells and induced TLR9 expression,caspase 3 activation and p38 mitogen-activated protein kinase(MAPK)phosphorylation.However,these effects were inhibited by chloroquine.In constrast,nuclear DNA did not have these effects.Intravenous injection of mtDNA into rats aggravated ischemia-reperfusion injury and increased the infarction area through TLR9-p38 MAPK activation.Conclusion:MtDNA is released into the circulation by AMI.mtDNA derived from AMI may act as a danger-associated molecular pattern or alarmin and has detrimental effect on myocardium through aggravating ischemia-reperfusion injury via TLR9-p38 MAPK pathway.