Mitochondrial Hexokinase II Promotes Neuronal Survival and Acts Downstream of Glycogen Synthase Kinase-3

Abstract

Mitochondrial alterations are detected in most neurodegenerative disorders and may contribute to the dysfunction and demise of neuronal cells. Because glycogen synthase kinase-3 (GSK-3) is considered to be a critical factor in regulating neuronal cell survival and death, we studied the effects of modulating GSK-3 activity in cultured neurons treated with the mitochondrial inhibitor, rotenone. Interestingly, chronic inhibition of GSK-3 protects against rotenone-induced apoptosis in cultured neuronal cells. In an attempt to elucidate the molecular mechanisms underlying this neuroprotection, we demonstrated that chronic inhibition of GSK-3 reprograms the metabolism of neuronal cells, leading to an enhancement of glycolysis. This effect was accompanied by the induction and accumulation of hexokinase II (HKII) in the mitochondria. Interfering with either the mitochondrial binding of HKII or HKII expression significantly diminished the neuroprotection evoked by GSK-3 inhibition, and importantly, HKII overexpression is sufficient to protect against rotenone-induced cell death. Thus, mitochondrial HKII is a promoter of neuronal survival under the regulation of GSK-3. Furthermore, the neuroprotective effect of HKII may be relevant to neurodegenerative diseases in which glucose hypometabolism and mitochondrial dysfunction are prominent features.Most neurodegenerative diseases share certain common features, including mitochondrial dysfunction (reviewed in Refs. 1, 2) and glucose hypometabolism (3, 4), which may contribute to the selective loss of specific neuronal cell populations (5). Rotenone is an inhibitor of the mitochondrial complex I that has been used extensively as a pesticide (6) and that is suspected to be an environmental trigger of Parkinson disease (7,8). Rotenone has also been employed to develop animal models for Parkinson disease, because animals exposed to rotenone display a parkinsonian-like phenotype with nigrostriatal degeneration and the formation of Lewy body inclusions (9 -11). Furthermore, rotenone has also been used to establish cell models of mitochondrial dysfunction and induced neurodegeneration, because there is compelling evidence showing that neurons exposed to rotenone undergo apoptosis (12)(13)(14).Glycogen synthase kinase-3 (GSK-3) 4 is a multifunctional protein kinase that is involved in several cellular processes, such as the regulation of cell metabolism, apoptosis, transcription, and cytoskeleton dynamics (15, 16). It is well known that inhibition of GSK-3 protects neuronal cells from distinct pro-apoptotic stimuli, such as trophic factor withdrawal, ␤-amyloid exposure, excitotoxicity, or prion peptide-induced cell death (17-20). Thus, GSK-3 has been proposed as a possible therapeutic target for neurodegenerative diseases (21).In this study, we show that chronic inhibition of GSK-3 induces significant protection against rotenone-triggered neuronal cell death. We also demonstrate that this neuroprotection is accompanied by an increase in the translocation of hexokinase II (HKII) to mit...

Evidence for Irreversible Inhibition of Glycogen Synthase Kinase-3β by Tideglusib

“…Cortical neurons from CD-1 mouse embryos of 18-day gestation were obtained and maintained following procedures already described (37). After 4 days in vitro, the cells were treated with 50 M cycloheximide, and at the intended time, they were lysed with buffer containing 10 mM Tris-HCl, pH 7.4, 100 mM NaCl, 1 mM EDTA, 2 mM Na 3 VO 4 , 1% Triton X-100, 10% glycerol, 0.1% SDS, 0.5% sodium deoxycholate, 1 mM PMSF, and the Complete TM protease inhibitor mixture (Roche Applied Science).…”

The Key Roles of GSK-3β in Regulating Mitochondrial Activity

“…HK-II has been demonstrated to significantly reduce the accumulation of Bax in the mitochondria under metabolic stress [61]. GSK-3β phosphorylates VDAC1 and subsequently promotes it to interact with Bax, resulting in disruption of HK-II and VDAC1 interaction [60]. Furthermore, GSK-3β might be involved in regulation of HK-II mRNA expression induced by benzo [a] pyrene [62].…”

“…2) [59]. HK-II has been demonstrated to mainly dock with VDAC1 at mitochondria [60]. Bax mitochondrial accumulation is positively related to mitochondrial dysfunction and mitochondria-dependent apoptosis.…”

Hexokinase activity is required for recruitment of parkin to depolarized mitochondria

“…The recruitment of HK2 to the OMM is enhanced by phosphorylation of HK2 at T473 by Akt (14,26,27). To further understand the mechanism by which HK2 recruits parkin to mitochondria, we used pharmacological and genetic approaches.…”