Abstract 16049: PKA Phosphorylation Regulates Frataxin Mitochondrial Targeting in Pressure Overload-Induced Cardiac Hypertrophy
Background Frataxin (Fr) is a mitochondrial protein whose genetic deficiency causes ataxia often associated with pathological left ventricular hypertrophy. Recently, phosphorylation sites for cAMP-dependent Protein Kinase A (PKA) have been recognized important for Fr cleavage and mitochondrial targeting. Whether altered phosphorylation of Fr might affect mitochondrial function and cell survival is currently unknown.
Methods In order to test the role of Fr phosphorylation on Fr cleavage, mitochondrial function and cell survival, we used rat neonatal cardiomyocytes and a mouse model of cardiac hypertrophy induced by 12 weeks of transverse aortic constriction (TAC).
Results In cardiomyocytes, activation of PKA by isoproterenol induced Fr phosphorylation and increased its mitochondrial targeting. These effects could be prevented by the pre-treatment with the beta-blocker metoprolol or the PKA inhibitor H89. Interestingly, synthetic peptides competitively displacing the mitochondrial A Kinase Anchor Protein 121 (AKAP121) reduced Fr phosphorylation and mitochondrial targeting, promoted mitochondrial dysfunction, increased ROS generation and apoptotic cell death. Next, to test the in vivo role of Fr in the development of heart failure, phosphorylation, processing and mitochondrial targeting of Fr was evaluated in SHAM and TAC hearts. As expected, TAC hearts were characterized by increased myocardial mass, left ventricular dysfunction, significant down-regulation of βARs. In the same hearts, mitochondrial targeting of PKA was significantly reduced. Although pressure overload did not significantly change Fr mRNA levels, it was associated with reduced phosphorylation and mitochondrial localization of Fr, with mitochondrial dysfunction, and increased mitochondrial generation of reactive oxygen species leading to cell death.
Conclusions These data demonstrate that mitochondrial localization of Fr depends on its level of phosphorylation, which reflects the efficiency of mitochondrial cAMP signalling. Post-translational modifications of Fr may represent an important new mechanism for mitochondrial adaptation to stress, and a new pathogenic mechanism in the development of heart failure.
- © 2011 by American Heart Association, Inc.