Mitochondrial DAMPs in sterile inflammation after acute
myocardial infarction
Torp, M-K.1, Heiestad, C.1, Flatebø, T.1, Ranheim, T.2,3,4, Yndestad, Y. 2,3,4, and Stensløkken,
K-O.1,3
1
Division of Physiology, Institute of Basic Medical Sciences, University of Oslo
Research Institute of Internal Medicine, Oslo University Hospital Rikshospitalet
3
Center for Heart Failure Research, University of Oslo
4
KG Jebsen Center for Inflammation Research, University of Oslo
2
BACKGROUND:
Acute myocardial infarction causes necrosis and initiate a local sterile inflammation, which is activated
by Damage-Associated Molecular Patterns (DAMPs). Based on the endosymbiotic theory the
mitochondria have an evolutionary bacterial origin and the cardiomyocyte volume consists of 30%
mitochondria. Our research group has shown that mitochondrial DNA are involved in reducing viability
of cardiac cells and activates the innate immune system. Moreover, other mitochondrial molecules
have been characterized as DAMPs, including the mitochondrial N-formyl proteins. Thus, we
hypothesized that the viability of cardiomyocytes and cardiac fibroblasts are reduced when they are
stimulated with mitochondrial debris compared to mitochondria poor cardiac debris.
METHODS:
Cardiac mitochondria and mitochondria poor cardiac debris were isolated from C57BI6 male mice
hearts. The purity of the isolation was verified by western blotting and endotoxin tested. The
cardiomyocytes were exposed to mitochondrial debris, mitochondria poor cardiac debris, or the Nformyl peptide receptor (Fpr) agonist fMLP for 24 h. Cardiomyocytes stained with propidium iodide
(necrotic nuclei) were investigated for viability with High-Throughput microscopy. The expression of
Fprs and cytokines were investigated by quantitative real-time PCR.
PRELIMINARY RESULTS:
Cardiomyocytes stimulated with 10 μg/ml mitochondrial debris showed a significant increased number
of propidium iodide positive nuclei compared to control. Whereas, cardiomyocytes stimulated with 20
μg/ml mitochondria poor cardiac debris showed no changes. The Fpr genes were not expressed in
cardiomyocytes nor cardiac fibroblasts. However, an increased expression was shown in postmyocardial infarction hearts, which may indicate increased infiltration of leukocytes. Cardiomyocytes
stimulated with fMLP showed no decrease in viability compared to control. Additionally, at mRNA level,
no tested innate immune genes were upregulated in fMLP stimulated cardiomyocytes.
CONCLUSIONS:
Mitochondrial debris appears to have a considerably larger effect on cardiomyocyte viability than
mitochondria poor cardiac debris. This appears not to be affected by the N-formyl peptides.