Abstract 19440: Mitochondrial Localization Unveils a Novel Role for Grk2 in the Regulation of Oxidative Metabolism
BACKGROUND: Recent studies demonstrate the role of the G protein coupled receptor kinase 2 (GRK2) in the control of cellular glucose extraction. Here, we investigate the role of this kinase in ATP production.
METHODS AND RESULTS: By molecular cloning of truncated mutants, we found that GRK2 targets within mitochondrial compartments through means of its RGS homology domain proxymal to the amino-terminus. In HEK-293s, stable overexpression of GRK2, but not its catalytically inactive mutant (GRK2-mut), increases mitochondrial NADHd and cytochrome B gene copies and expression. Reciprocally, we found a reduction in the number of copies and the level of expression of the NADHd and cytocrome B in cultured aorta cells from homozygous floxed GRK2 gene (GRK2f/f) mice, in which GRK2 is removed by adenoviral mediated CRE recombinase (AdCRE) expression (GRK2f/f,Cre). Since increased mitochondrial DNA content associates with elevated oxidative respiratory chain activity, we assessed total and mitochondrial ATP, and found that GRK2 overexpression, but not GRK2-mut, increases total and mitochondrial ATP levels. During acute hypoxia (1 hour) ATP decreases and slowly returns to basal levels after oxygen replenishment. Interestingly, hypoxia promotes a transient increase of mitochondria-associated GRK2 levels, and 15 minutes and 1 hour oxygen replenishment restore the levels of the kinase. GRK2 overexpression attenuates the loss of ATP production during hypoxia. In mice, in GRK2f/f mouse hindlimbs, GRK2 gene deletion by injection of AdCRE in the skeletal muscle causes a significant reduction of ATP levels under basal conditions and impairs the recovery of ATP levels following ischemia/reperfusion.
CONCLUSIONS: The unexpected localization of GRK2 in the mitochondria unveils a positive regulation of the bioenergetic pathway by the kinase.
- © 2010 by American Heart Association, Inc.