title: Extracellular mtDNA activates NF-κB via toll-like receptor 9 and induces cell death in cardiomyocytes.
abstract: Acute myocardial infarction (AMI) causes sterile inflammation, which exacerbates tissue injury. Elevated levels of circulating mitochondrial DNA (mtDNA) have been associated with AMI. We hypothesized that mtDNA triggers an innate immune response via TLR9 and NF-κB activation, causing cardiomyocyte injury. Murine cardiomyocytes express TLR9 mRNA and protein and were able to internalize fluorescently labeled mouse mtDNA. Incubation of human embryonic kidney cells with serum from AMI patients containing naturally elevated levels of mtDNA induced TLR9-dependent NF-κB activity. This effect was mimicked by isolated mtDNA. mtDNA activated NF-κB in reporter mice both in vivo and in isolated cardiomyocytes. Moreover, incubation of isolated cardiomyocytes with mtDNA induced cell death after 4 and 24 h. Laser confocal microscopy showed that incubation of cardiomyocytes with mtDNA accelerated mitochondrial depolarization induced by reactive oxygen species. In contrast to mtDNA, isolated total DNA did not activate NF-κB nor induce cell death. In conclusion, mtDNA can induce TLR9-dependent NF-κB activation in reporter cells and activate NF-κB in cardiomyocytes. In cardiomyocytes, mtDNA causes mitochondrial dysfunction and death. Endogenous mtDNA in the extracellular space is a danger signal with direct detrimental effects on cardiomyocytes.
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.|Department of Emergency Medicine and Intensive Care, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, UiO, Oslo, Norway.
authors.forename: Marte
authors.initials: M
authors.lastname: Bliksøen
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.
authors.forename: Lars Henrik
authors.initials: LH
authors.lastname: Mariero
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.
authors.forename: May Kristin
authors.initials: MK
authors.lastname: Torp
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.
authors.forename: Anton
authors.initials: A
authors.lastname: Baysa
authors.affiliation: Cardiovascular Research Group, Department of Medical Biology, Faculty of Health Sciences, University of Tromsø, Tromsø, Norway.
authors.forename: Kirsti
authors.initials: K
authors.lastname: Ytrehus
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.
authors.forename: Fred
authors.initials: F
authors.lastname: Haugen
authors.affiliation: Center for Heart Failure Research, UiO, Oslo, Norway.|Department of Cardiology, Center for Clinical Heart Research, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, UiO, Oslo, Norway.
authors.forename: Ingebjørg
authors.initials: I
authors.lastname: Seljeflot
authors.affiliation: Department of Emergency Medicine and Intensive Care, Oslo University Hospital, Oslo, Norway.|Institute of Clinical Medicine, UiO, Oslo, Norway.
authors.forename: Jarle
authors.initials: J
authors.lastname: Vaage
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway.|Center for Heart Failure Research, UiO, Oslo, Norway.
authors.forename: Guro
authors.initials: G
authors.lastname: Valen
authors.affiliation: Department of Molecular Medicine, Faculty of Medicine, Institute of Basic Medical Sciences, University of Oslo (UiO), Oslo, Norway. k.o.stenslokken@medisin.uio.no.|Center for Heart Failure Research, UiO, Oslo, Norway. k.o.stenslokken@medisin.uio.no.|Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Science, Postbox 1103, Blindern, 0317, Oslo, Norway. k.o.stenslokken@medisin.uio.no.
authors.forename: Kåre-Olav
authors.initials: KO
authors.lastname: Stensløkken
mesh_terms: D000818:Animals; D016923:Cell Death / Q000502:physiology; D004272:DNA, Mitochondrial / Q000378:metabolism*; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology*; D032383:Myocytes, Cardiac / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D051217:Toll-Like Receptor 9 / Q000378:metabolism*
chemical_list: D004272:DNA, Mitochondrial; D016328:NF-kappa B; D051217:Toll-Like Receptor 9
keywords: Inflammation; Mitochondrial DNA; Myocardial infarction; NF-κB; TLR9; mtDNA