Abstract 9344: Myocardial Uncoupling Protein-2 Expression Depolarizes the Inner Membrane Potential of Mitochondria and Reduces Maximal Superoxide Levels
Background: Myocardial expression of uncoupling protein (UCP)-2 is increased by peroxisome proliferator-activated receptor (PPAR) gamma stimulation with pioglitazone (PIO). We characterized the effects of PIO on the inner membrane potential of mitochondria and measured superoxide levels from wild type (WT) and UCP-2 knock-out (KO) mouse hearts. We hypothesized that chronic PIO would increase UCP-2 content and improve tolerance to ex vivo anoxia.
Methods: WT and UCP-2 KO mice were fed chow with or without PIO (3 mg/day) and sacrificed at 3 weeks. Heart mitochondria were isolated and UCP-2 protein content was measured. Membrane potential was measured with tetraphenylphosphonium and maximal superoxide acccumulation during complex III inhibition with antimycin A was measured with dihydroethidium. State 3 respiration and the respiratory control index (State3/State2; RCI) were measured in isolated mitochondria at baseline and following 10 min. anoxia from WT and UCP-2 KO mice fed PIO.
Results: PIO increased UCP-2 content in WT hearts by >2-fold while no expression was observed in UCP-2 KO mice. PIO decreased the inner membrane potential in WT hearts from −166±4 to −147±6mV (P<0.05) with no effect in UCP-2 KO hearts (−180±4 and −182±3 mV respectively; NS). Superoxide levels were lower with the reduced inner membrane potential in response to increased UCP-2 content in WT mice (Figure). Post-anoxia, State 3 respiration was higher (231±61 versus 93±12 nmol O2/min/mg; P<0.05) and the RCI was greater (2.37±0.18 versus 1.43±0.13; P<0.05) in WT versus UCP-2 KO mice given PIO.
Conclusion: These data establish an important relationship between inner membrane potential of mitochondria and maximal superoxide production in relationship to UCP-2 expression in heart tissue. Mitochondria from hearts with increased UCP-2 expression demonstrate improved State 3 respiration post-anoxia and the mechanism likely relates to an anti-oxidant effect.
- © 2010 by American Heart Association, Inc.