title: Extent of mitochondrial hexokinase II dissociation during ischemia correlates with mitochondrial cytochrome c release, reactive oxygen species production, and infarct size on reperfusion.
abstract: BACKGROUND
  The mechanisms by which ischemic preconditioning (IP) inhibits mitochondrial permeability transition pore opening and, hence, ischemia-reperfusion injury remain unclear. Here we investigate whether and how mitochondria-bound hexokinase 2 (mtHK2) may exert part of the cardioprotective effects of IP.
  
  
  RESULTS
  Control and IP Langendorff-perfused rat hearts were subject to ischemia and reperfusion with measurement of hemodynamic function and infarct size. Outer mitochondrial membrane (OMM) permeabilization after ischemia was determined by measuring rates of respiration and H2O2 production in the presence and absence of added cytochrome c in isolated mitochondria and permeabilized fibers. IP prevented OMM permeabilization during ischemia and reduced the loss of mtHK2, but not Bcl-xL, observed in control ischemic hearts. By contrast, treatment of permeabilized fibers with glucose-6-phosphate at pH 6.3 induced mtHK2 loss without OMM permeabilization. However, metabolic pretreatments of the perfused heart chosen to modulate glucose-6-phosphate and intracellular pHi revealed a strong inverse correlation between end-ischemic mtHK2 content and infarct size after reperfusion. Loss of mtHK2 was also associated with reduced rates of creatine phosphate generation during the early phase of reperfusion. This could be mimicked in permeabilized fibers after mtHK2 dissociation.
  
  
  CONCLUSIONS
  We propose that loss of mtHK2 during ischemia destabilizes mitochondrial contact sites, which, when accompanied by degradation of Bcl-xL, induces OMM permeabilization and cytochrome c loss. This stimulates reactive oxygen species production and mitochondrial permeability transition pore opening on reperfusion, leading to infarction. Consequently, inhibition of mtHK2 loss during ischemia could be an important mechanism responsible for the cardioprotection mediated by IP and other pretreatments.
authors.affiliation: School of Biochemistry and The Bristol Heart Institute, University of Bristol, Bristol, UK.
authors.forename: Philippe
authors.initials: P
authors.lastname: Pasdois
authors.forename: Joanne Elizabeth
authors.initials: JE
authors.lastname: Parker
authors.forename: Andrew Philip
authors.initials: AP
authors.lastname: Halestrap
mesh_terms: D000818:Animals; D045304:Cytochromes c / Q000378:metabolism*; D004195:Disease Models, Animal; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006439:Hemodynamics; D006593:Hexokinase / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology* / Q000473:pathology; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D009203:Myocardial Infarction / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D015428:Myocardial Reperfusion Injury / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D010539:Permeability; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C494828:Bax protein, rat; C494813:Bcl2l1 protein, rat; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D010725:Phosphocreatine; D019298:Glucose-6-Phosphate; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D006593:Hexokinase