GSK-3.BETA., a Therapeutic Target for Cardiomyocyte Protection

Abstract

lycogen synthase kinase-3β (GSK-3β) is a constitutively active 47-kDa Ser/Thr protein kinase that was purified more than 2 decades ago as a kinase that reduces glycogen synthase activity. However, GSK-3β is now known as a multifunctional kinase having more than 40 substrates, playing roles not only in glycogen metabolism but also cell proliferation, growth and death. [1][2][3] To properly execute its functions, GSK-3β has multiple regulatory mechanisms including phosphorylation at Ser and Tyr residues, complex formation with scaffold proteins, priming of substrates and intracellular translocation. Recently, pathophysiological roles of GSK-3β have also received attention because it is involved in common and serious diseases such as Alzheimer's disease, bipolar mood disorder, cancer and ischemia/reperfusion injury. 1,3 In the cardiovascular system, GSK-3β has major roles in glucose metabolism, 4 cardiomyocyte hypertrophy 5 and cell death. The roles of GSK-3β in hypertrophy have recently been reviewed by Sugden et al 5 , so therefore we have focused on the roles of this protein kinase in myocyte death, particularly that after ischemia/ reperfusion. We first briefly overview mechanisms of ischemia/reperfusion injury and then discuss the contribution of GSK-3β to cardiomyocyte death and manipulation of GSK-3β for myocardial protection. Mechanisms of Cardiomyocyte Necrosis During Ischemia/ReperfusionWhen myocardial blood perfusion is interrupted, for example by occluding the coronary artery, ischemic cardiomyocytes suffer from several critical intracellular events that can lead to cell necrosis and/or prime the cells to reperfusion-induced necrosis. First, intracellular level of highenergy phosphate is reduced due to oxygen deficiency. Although ischemic cardiomyocytes cease contraction within a few minutes after the onset of ischemia, adenosine triphosphate (ATP) consumption continues during ischemia mainly by mitochondrial ATPase for maintenance of mitochondrial membrane potential. 6,7 Anaerobic glycolysis supplies ATP during the early period of ischemia, but it is ultimately halted by inhibition of glyceraldehyde phosphate dehydrogenase due to accumulated H + and NADH. 7,8 Second, intracellular Na + accumulates due to Na + influx via Na + -H + exchangers and Na + channels and due to reduced Na + efflux via the Na + -K + pump. [9][10][11] This Na + overload predisposes ischemic cardiomyocytes to Ca 2+ influx by the Na + -Ca 2+ exchanger. Third, Ca 2+ influx via the Na + -Ca 2+ exchanger, reduced Ca 2+ uptake into the sarcoplasmic reticulum and reduced Ca 2+ efflux via the sarcolemmal Ca 2+ pump induce Ca 2+ overload in ischemic cardiomyocytes. 9-12 However, elevation of intracellular Ca 2+ is modest during ischemia because acidosis inhibits the Na + -Ca 2+ exchanger and cytosolic Ca 2+ is taken up by the mitochondria as long as its membrane potential is maintained by use of ATP. [9][10][11]13 Severely ischemic cardiomyocytes ultimately 'starve to death', although sarcolemmal damage by detergent actions of accumulated...

Intracellular zinc release-activated ERK-dependent GSK-3β–p53 and Noxa–Mcl-1 signaling are both involved in cardiac ischemic-reperfusion injury

“…GSK-3b inhibition), which protects the adult-rat heart from I/R injury for 2-4 h. 4,[13][14][15][16] This study showed a link between the Zn 2 þ i release/increase and the activation of GSK-3b, resulting in myocyte apoptosis. We observed an early increase in p-Ser9 GSK-3b levels after Zn 2 þ Figure S2b), we conclude that Zn 2 þ i supplementation-induced early phosphorylation at Ser9 is not necessarily cardioprotective and may induce cytotoxicity after return to normal medium for 4 or 24 h. In support of the above conclusions, Tyr216 phosphorylation is required for nuclear GSK-3b accumulation in neurons and fibroblasts, 17,18 as mutation of Tyr216 to phenylalanine or its dephosphorylation results in less GSK-3b being found in nuclei.…”

“…When the reperfusion injury salvage kinase (RISK) family members PKA, PKB/Akt, PKC, and MEK-ERK are activated by pre-or post-conditioning, a common downstream protein, GSK-3b, is phosphorylated at Ser9, resulting in GSK-3b inhibition (both events occurring within 20 min of the end of conditioning), leading to the inhibition of mPTPs and the salvaging of 20-50% live myocardium. 4,5,[13][14][15][16] A potent GSK-3 inhibitor, SB216763 (SB21), 4,13 had a relatively weak protective effect against H 2 O 2 -, ONOO À -induced myocyte death (Supplementary Figure S2c), but gave better protection against 10 mM Zn 2 þ -induced cell toxicity at 4 h (Figure 2d (TUNEL test) were performed as follows: after ischemia for 40 min, followed by reperfusion for 4 h, myocytes were returned to normal medium without inhibitors for 24 h, then were examined for apoptotic markers. Compared with I/R alone ('I/R', Figure 4b), the presence of 15 mM TPEN at the start of reperfusion for only B20 min ('TPEN (20 min)') markedly inhibited I/R injury at 24 h after TPEN removal, suggesting that the reperfusion-induced initial Zn 2 þ i release (Figure 3b) is important in I/R injury.…”

Integrin-linked kinase mediates force transduction in cardiomyocytes by modulating SERCA2a/PLN function

“…2a). Inactivation of GSK-3b through phosphorylation at Ser9 (pGSK-3b) is cytoprotective in the myocardium 25,26 and is a common readout of ILK activation 27,28 . ILK overexpression caused an increase in phosphorylation of GSK-3b, whereas ILK knockdown by short interfering RNA (siRNA) caused a relative de-phosphorylation of GSK-3b (Fig.…”

Dynamic O-GlcNAcylation and its roles in the cellular stress response and homeostasis

“…For example, deletion of OGT led to reduced OGlcNAcylation of VDAC, sensitizing cells to mitochondrial membrane potential collapse and mPTP formation Jones et al 2008). Notably, formation of the mPTP is also promoted by active GSK3β (Juhaszova et al 2004;Miura and Miki 2009), which is inhibited in some models by stress-induced O-GlcNAcylation (Kazemi et al 2010;Ku et al 2010).…”