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

Abstract

Akt activation supports survival of cardiomyocytes against ischemia/reperfusion, which induces cell death through opening of the mitochondrial permeability transition pore (PT-pore). Mitochondrial depolarization induced by treatment of cardiomyocytes with H 2 0 2 is prevented by activation of Akt with leukemia inhibitory factor (LIF). This protective effect is observed even when cardiomyocytes treated with LIF are permeabilized and mitochondrial depolarization is elicited by elevating Ca 2 þ . Cell fractionation studies demonstrate that LIF treatment increases both total and phosphorylated Akt in the mitochondrial fraction. Furthermore, the association of Akt with HK-II is increased by LIF. HK-II contains consensus sequences for phosphorylation by Akt and LIF treatment induces PI3K-and Akt-dependent HK-II phosphorylation. Addition of recombinant kinase-active Akt to isolated adult mouse heart mitochondria stimulates phosphorylation of HK-II and concomitantly inhibits the ability of Ca 2 þ to induce cytochrome c release. This protection is prevented when HK-II is dissociated from mitochondria by incubation with glucose 6-phosphate or HK-II-dissociating peptide. Finally LIF increases HK-II association with mitochondria and dissociation of HK-II from mitochondria attenuates the protective effect of LIF on H 2 0 2 -induced mitochondrial depolarization in cardiomyocytes. We conclude that Akt has a direct effect at the level of the mitochondrion, which is mediated via phosphorylation of HK-II and results in protection of mitochondria against oxidant or Ca 2 þ -stimulated PT-pore opening.

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

“…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. 97 We found that Akt, activated by receptor agonists, translocates to mitochondria and phosphorylates HK-II at Thr473, a critical step in Akt-mediated mitoHK-II increase and protection in cardiomyocytes 79,97 (Figure 3). Other studies also support that Akt increases mitoHK-II in cardiac and non-cardiac cells.…”

“…We and others have also reported that an increase in mitoHK-II has an inhibitory effect on Ca 2+ -and ROS-induced mPTP opening and that a large dissociation of mitoHK-II sensitizes mPTP opening and cell death. 77,80,82,83,[96][97][98] A series of studies have demonstrated that mitoHK-II has an ability to decrease ROS generation at mitochondria to prevent opening of the mPTP. 77,80,82,84,99 As mentioned earlier, mitoHK ensures tight coupling of glucose phosphorylation and mitochondrial ATP generation.…”

“…94 Further, mitoHK-II increased by Akt overexpression confers protection in Bax/Bak null cells, suggesting inhibition of mPTP 93 and our previous work in cardiomyocytes also showed that Akt activation increases the level of mitoHK-II leading to inhibition of mPTP opening and cell death. 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.…”

“…Akt mediated increases in HK-II expression and mitochondrial association support the growth response through efficient energy production 4,17,18 as well as preserving mitochondrial integrity. 3,15,28,76,77,79,80,93,96,97,118,178 In contrast, regulation of the pentose phosphate pathway or glycogenesis by HKs is considered as a cytosolic event. Thus Akt-mediated phosphorylation endows HK-II with diverse and complex roles to regulate energy production versus storage, and cell growth and survival by changing its intracellular localization.…”

Metabolic reprogramming of the tumor

“…Second, it brings it physically closer to OXPHOS-derived ATP, thus increasing the rate at which glucose phosphorylation can occur (Kroemer and Pouyssegur, 2008). Finally, it prevents mitochondrial depolarization and cytochrome-c release, thus participating in the anti-apoptotic effects of AKT (Miyamoto et al, 2008).…”