Download Mitochondrial debris reduce viability of healthy cardiomyocytes

Mitochondrial debris reduce viability of healthy
cardiomyocytes
Torp, M-K. 1,3, Li,Y.1,3, Flatebø, T.1, Ranheim, T.2,3,4, Yndestad, A.2,3,4, and Stensløkken, K-O.1,3
1Division
of Physiology, Institute of Basic Medical Sciences, University of Oslo
Institute of Internal Medicine, Oslo University Hospital Rikshospitalet
3Center for Heart Failure Research, University of Oslo
4KG Jebsen Center for Inflammation Research, University of Oslo
2Research
Background: Acute myocardial infarction results in necrosis and initiation of sterile inflammation
activated by Damage-Associated Molecular Patterns (DAMPs).Mitochondria are of bacterial origin,
displaying bacterial traits in their DNA and proteins. Moreover, the cardiomyocyte volume consists of
30% mitochondria. Our research group has recently showed that mitochondrial DNA induces cell
death and activates the innate immune system in cardiomyocytes. In this study, we hypothesize that
mitochondrial constituents in general, or N-formyl-peptides specifically, are detrimental to cardiac cells.
Methods: Cardiac mitochondria were isolated from C57BI6 male mice and this debris was utilized as
agonists for isolated adult mouse cardiomyocytes and cardiac fibroblasts. The cardiomyocytes were
stimulated with increasing concentrations of mitochondrial debris or the N-formyl-peptide receptor
(Fpr) agonist fMLP. Cardiomyocytes were also exposed to 40 minutes hypoxia and 2h re-oxygenation.
Cell death was investigated with High-Throughput microscopy. The cardiac fibroblasts were exposed
to mitochondrial debris and sampled in time intervals. Expression and release of cytokines were
measured by qPCR and ELISA.
Preliminary Results: Cardiomyocytes exposed to normoxic conditions showed a significant increase
in cell death when stimulated with 100 µg/ml mitochondrial debris compared to control. In addition,
hypoxic conditions significantly increased cell death of cardiomyocytes at lower concentrations of
mitochondrial debris (10 µg/ml). Moreover, cardiomyocytes and cardiac fibroblasts exposed to
mitochondrial debris showed a significant dose-dependent increase in Interleukin-6 production.
Absolute quantification of Fpr genes revealed no expression in cardiomyocytes or cardiac fibroblasts.
However, the receptors were expressed in mRNA extracted from PBS perfused mouse hearts possibly
indicating presence of tissue resident macrophages. Cardiomyocytes stimulated with fMLP showed no
significant decrease in viability compared to control.
Conclusion: Mitochondrial debris reduced the viability of the cardiomyocytes, and gave an
inflammatory response in cardiomyocytes and cardiac fibroblasts. This response appears not to be
mediated through the Fpr.