Pereira 2015 Abstract MiPschool London 2015

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Ischaemia but not in vitro dissociation of heart mitochondrial-bound hexokinase II affects organelle physiology and morphology.

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Pereira GC, Parker JE, Halestrap AP (2015)

Event: MiPschool London 2015

Cell injury at reperfusion after ischaemia presents a major clinical problem. Recently, we demonstrated that hexokinase II (HK2) dissociation from mitochondria during cardiac ischaemia correlates with cytochrome c (cyt c) loss, oxidative stress and subsequent reperfusion injury [1]. Furthermore, phosphocreatine output was depressed after ischaemia suggesting broken contact sites between inner and outer mitochondrial membranes, while others have reported that contact sites breakage induces cyt c redistribution and is associated with HK2 release [2]. However, it remains unclear whether HK2 release is the primary signal mediating ischaemia-induced mitochondrial damage. Here we assess whether HK2 depletion in vitro can mimic all the ischaemic events leading to mitochondrial damage.

Isolated hearts from Wistar rats were subject to control retrograde perfusion (pre-ischaemia), 30 min global ischaemia or to ischaemic pre-conditioning (IPC) followed by ischaemia. During isolation of mitochondria through standard methods, a portion of the sample was treated with 10 mM glucose-6-phosphate (G6P) at pH 6.3 to promote dissociation of HK2 [1]. We demonstrate that HK2 dissociation has no effect on mitochondrial respiration (± ADP addition) regardless of the perfusion protocol. Moreover, HK2 depletion alone does not promote cyt c release. Surprisingly, complete removal of HK2 neither enhanced mPTP opening nor altered inhibition by cyclosporine A under either energised or de-energised conditions. Inner mitochondrial morphology was assessed indirectly by monitoring light scattering (LS) in the presence of ANT ligands [3]. The amplitude of LS changes exhibited by end-ischaemia mitochondria was smaller suggesting broken contact sites. This effect was prevented by IPC but was not mimicked by in vitro HK2 depletion.

In conclusion, we were unable to replicate ischaemia-induced effects on mitochondrial function by promoting HK2 dissociation in vitro. This implies that release of mitochondrial-bound HK2 in vivo, rather than mediating mitochondrial damage directly, sensitizes mitochondria to other damaging factors.

Keywords: HK2

O2k-Network Lab: UK Bristol Halestrap AP


Labels: MiParea: mt-Medicine, Patients 

Stress:Ischemia-reperfusion  Organism: Rat  Tissue;cell: Heart  Preparation: Intact organ 





Affiliations

School Biochem, Bristol Univ, UK. - goncalo.pereira@ucl.ac.uk

References and Support

This work was supported by a Programme Grant from the British Heart Foundation (RG/08/001/24717)

  1. Pasdois P, Parker JE, Halestrap AP (2012) Extent of mitochondrial hexokinase II dissociation during ischemia correlates with mitochondrial cytochrome c release, reactive oxygen species production, and infarct size on reperfusion. J Am Heart Assoc 2(:e005645.
  2. Vyssokikh M, Zorova L, Zorov D, Heimlich G, Jürgensmeier J, Schreiner D, Brdiczka D (2004) The intra-mitochondrial cytochrome c distribution varies correlated to the formation of a complex between VDAC and the adenine nucleotide translocase: this affects Bax-dependent cytochrome c release. Biochim Biophys Acta. 1644:27-36.
  3. Klingenberg M, Grebe K, Scherer B (1971) Opposite effects of bongkrekic acid and atractyloside on the adenine nucleotides induced mitochondrial volume changes and on the efflux of adenine nucleotides. FEBS Lett 16(4):253-6