title: Uncoupling protein-2 expression and effects on mitochondrial membrane potential and oxidant stress in heart tissue.
abstract: Myocardial uncoupling protein (UCP)-2 is increased with chronic peroxisome proliferator-activated receptor γ (PPARγ) stimulation, but the effect on membrane potential and superoxide is unclear. Wild-type (WT) and UCP-2 knockout (KO) mice were given a 3-week diet of control (C) or the PPARγ agonist pioglitazone (PIO; 50 μg/g-chow per day). In isolated mitochondria, UCP-2 content by Western blots, membrane potential (ΔΨm) by tetraphenylphosphonium (TPP), and relative superoxide levels by dihydroethidium (DHE) were measured. Oxygen respiration was determined at baseline and after 10 min anoxia-reoxygenation. PIO induced a 2-fold increase in UCP-2 and nuclear-bound PGC1α in WT mice with no UCP-2 expression in KO mice. Mitochondrial ΔΨm from WT mice on C and PIO diets was -166±4 mV and -147±6 mV, respectively (P<0.05). These values were lower than in UCP-2 KO mice on C and PIO (-180±4 mV and -180±4 mV, respectively; P<0.05). Maximal complex III inhibitable superoxide from WT mice on C and PIO diets was 22.5±1.3 and 17.8±1.1 AU, respectively (P<0.05), and were lower than UCP-2 KO on C and PIO (32.9±2.3 and 29.2±1.9 AU, respectively; P<0.05). Postanoxia, the respiratory control index (RCI) in mitochondria from WT mice with and without PIO was 2.5±0.3 and 2.4±0.2, respectively, and exceeded that of UCP-2 KO mice on C and PIO (1.2±0.1 and 1.4±0.1, respectively; P<0.05). In summary, chronic PPARγ stimulation leads to depolarization of the inner membrane and reduced superoxide of isolated heart mitochondria, which was critically dependent on increased expression of UCP-2. Thus, UCP-2 expression affords resistance to brief anoxia-reoxygenation.
authors.affiliation: Department of Cardiology & Cardiac Surgery Sections, VA Medical Center, University of Minnesota, Minneapolis, MN 55417, USA.
authors.forename: Jesús A
authors.initials: JA
authors.lastname: Cabrera
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Ziemba
authors.forename: Robert
authors.initials: R
authors.lastname: Colbert
authors.forename: Rosemary F
authors.initials: RF
authors.lastname: Kelly
authors.forename: Michael
authors.initials: M
authors.lastname: Kuskowski
authors.forename: Edgar A
authors.initials: EA
authors.lastname: Arriaga
authors.forename: Wim
authors.initials: W
authors.lastname: Sluiter
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Duncker
authors.forename: Herbert B
authors.initials: HB
authors.lastname: Ward
authors.forename: Edward O
authors.initials: EO
authors.lastname: McFalls
mesh_terms: D000818:Animals; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D018345:Mice, Knockout; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000502:physiology; D024101:Mitochondrial Proteins / Q000378:metabolism*; D018384:Oxidative Stress; D047495:PPAR gamma / Q000819:agonists; D000071246:Uncoupling Protein 2
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D047495:PPAR gamma; C000604390:Ucp2 protein, mouse; D000071246:Uncoupling Protein 2