Ischemic preconditioning, insulin, and morphine all cause hexokinase redistribution

Abstract

Association of hexokinase (HK) with mitochondria preserves mitochondrial integrity and is an important mechanism by which cancer cells are protected against hypoxic conditions. Maintenance of mitochondrial integrity also figures prominently as a major characteristic of many cardioprotective manipulations. In this study, we provide evidence that cardioprotective interventions may promote HK redistribution from the cytosol to the mitochondria in the heart. Isolated Langendorff-perfused rat hearts (n = 6/group) were subjected to normoxic perfusion (control, Con), three 5-min ischemia-reperfusion periods (ischemic preconditioning, IPC), 1 U/l insulin (Ins), or 1 microM morphine (Mor). Hearts were immediately homogenized and centrifuged to obtain whole cell, cytosolic, and mitochondrial fractions. HK, lactate dehydrogenase (LDH), and citrate synthase (CS) enzyme activities were determined. No change in LDH or CS present in the cytosol fraction relative to whole cell activity was observed with any of the cardioprotective interventions. By contrast, HK present in the cytosol fraction relative to whole cell activity decreased significantly (P < 0.05) with all cardioprotective interventions, from 0.58 +/- 0.03 (Con) to 0.46 +/- 0.04 (IPC), 0.41 +/- 0.01 (Ins), and 0.45 +/- 0.02 (Mor). In addition, HK relative to CS activity in the mitochondrial fraction increased significantly with cardioprotection, from 0.15 +/- 0.001 (Con) to 0.21 +/- 0.002 (IPC), 0.18 +/- 0.003 (Ins), and 0.21 +/- 0.005 (Mor). Our novel data suggest that well-known cardioprotective interventions share a common end-effector mechanism of cytosolic HK translocation. Association of HK with mitochondria may promote inhibition of the mitochondrial permeability transition pore and thereby reduce cell death and apoptosis.

Akt mediates mitochondrial protection in cardiomyocytes through phosphorylation of mitochondrial hexokinase-II

“…25,27,35 Our experiments reveal that the total amount of HK-II found in the mitochondrial fraction is increased by Akt activation (Figure 7a). The current study also shows that activated Akt redistributes to mitochondria and that it associates with and phosphorylates mitochondrial HK-II.…”

“…Interestingly ischemic preconditioning, as well as insulin and morphine (interventions known to activate Akt) were recently reported to increase mitochondrial hexokinase activity in the heart. 35 Thus it will be of interest to determine in future studies whether HK-II phosphorylation by Akt leads to changes in the avidity with which HK-II associates with cardiac mitochondria.…”

Hexokinase II integrates energy metabolism and cellular protection: Akting on mitochondria and TORCing to autophagy

“…79,97 In the heart, in which HK-II is the predominant isoform, mitoHK-II activity is known to be increased by many cardioprotective interventions such as insulin, morphine and ischemic preconditioning. [119][120][121] Given that Akt leads to increased mitoHK-II, we explored the possibility that Akt directly phosphorylates HK-II. Our previous study revealed that HK-II, but not HK-I or HK-III, has an Akt consensus sequence at position Thr473 (RARQKT*), which is preserved in mouse, rat and human.…”

Mitochondrial hexokinase and cardioprotection of the intact heart

“…In 2005, the first study was performed that examined whether short, reversible periods of ischemia resulting in ischemic preconditioning, was associated with HK translocation to the mitochondria within the intact heart (Zuurbier et al 2005). It was demonstrated that hexokinase activity decreased in the cytosol, whereas it increased in the mitochondrial compartment of the ischemic preconditioned heart.…”