Abstract 108: Glycolysis, Cardioprotection and Their Modulation by Differential Interactions of Hexokinase I and II with Mitochondria
Rationale: Neonatal heart is more glycolytically active and less susceptible to anoxia/reoxygenation injury than adult heart. Hexokinase (HK) is the first step in glycolysis and its binding to mitochondria is known to be cardioprotective. Since neonatal cardiac myocytes mainly express the HKI isoform, whereas HKII predominates in adults, we explored the functional consequences of such difference.
Objective: To investigate whether differential interactions of HKI and HKII with mitochondria in neonatal (NRVM) and adult rat ventricular myocytes (ARVM) account for their different metabolic profiles and susceptibility to anoxia/reoxygenation injury.
Methods and Results: We performed real-time imaging in isolated NRVM and ARVM expressing the genetically-encoded biosensors FLIPglu-600µM to track intracellular glucose metabolism and YFP-tagged HK constructs to track subcellular HK localization, together with a propidium iodide-based cell death assay. We show that HKI remains bound to mitochondria in both NRVM and ARVM, while HKII distributes between the mitochondria and cytoplasm. Extracellular glucose removal displaced HKII from mitochondria in ARVM, but not in NRVM, whereas iodoacetate (IAA) displaces HKII in both. These differences were associated with a 35-fold greater glycolytic activity and markedly enhanced resistance to anoxia/reoxygenation injury in NVRM. NRVM became comparably susceptible to anoxia/reoxygenation injury only when treated with IAA to suppress HK interaction with mitochondria (whereas glucose removal alone had no effect).
Conclusions: HKs exhibit stronger interaction with mitochondria in NRVM, accounting for their enhanced glycolytic activity and increased resistance to anoxia/reoxygenation injury. HKI may be superior to HKII in protecting the heart because of its stronger interaction with mitochondria.
- © 2012 by American Heart Association, Inc.