Abstract 15957: Impaired Mitochondrial RIRR and Network Excitability in Failing Cardiomyocytes
Background: Previous studies in healthy guinea pig cardiomyocytes have shown that reactive oxygen species (ROS) produced by a few mitochondria exposed to laser flash can propagate to neighboring mitochondria, generating cell-wide network oscillations via ROS induced ROS release (RIRR). How mitochondria of failing myocytes exhibit RIRR and network oscillations in response to oxidative stress is unknown. We hypothesized that in heart failure, a decrease in mitochondrial network connection/tethering is associated with impaired laser flash-induced RIRR and ROS propagation.
Methods: Ascending aortic constriction in the guinea pig produces LV dilatation and decreased ejection fraction at 8 weeks. Cardiomyocytes were isolated and studied with two-photon and confocal microscopies to determine the basal oxidative stress level in myocytes and the propensity of cells to undergo metabolic oscillation as a function of initial oxidative stress. We also examined the dynamics of mitochondrial network oscillations triggered by local laser flash. Finally, we measured mitochondrial fusion protein expressions, i.e., mitofusins 1 and 2 (Mfn1 and Mfn2), by western blot in sham and failing myocardium.
Results: Cardiomyocytes isolated from failing LVs had a higher propensity to depolarize in response to laser flash compared to sham cardiomyocytes (90% vs. 76%, p<0.05). Failing cardiomyocytes also had higher baseline ROS levels and lower reduced glutathione levels vs. shams. Intriguingly, failing cell mitochondrial network had dyssynchronous depolarizations and oscillations and lower rate of RIRR mediated depolarization wave propagation. Consistent with impaired RIRR/mitochondrial dynamics in failing cells, mitochondrial network ultrastructure was disorganized and Mfn1 and Mfn2 expressions were decreased.
Conclusion: Mitochondria of failing myocytes exhibit higher levels of oxidative stress with a lower RIRR and network excitability that is associated with impaired mitochondrial tethering and disorganized ultrastructure. Future studies will determine whether these alterations are causes or consequences of heart failure.
- © 2013 by American Heart Association, Inc.