SIRT1 and AROS suppress doxorubicin-induced apoptosis via inhibition of GSK3β activity in neuroblastoma cells

ABSTRACT

SIRT1, the best-characterized member of the sirtuin family of deacetylases, is involved in cancer, apoptosis, inflammation, and metabolism. Active regulator of SIRT1 (AROS) was the first identified direct regulator of SIRT1. An increasing number of reports have indicated that SIRT1 plays an important role in controlling brain tumors. Here, we demonstrated that depletion of SIRT1 and AROS increases doxorubicin-mediated apoptosis in human neuroblastoma SH-SY5Y cells. Glycogen synthase kinase 3β (GSK3β) promoted doxorubicin-mediated apoptosis, but this effect was abolished by overexpression of SIRT1 and AROS. Interestingly, SIRT1 and AROS interacted with GSK3β and increased inhibitory phosphorylation of GSK3β on Ser9. Finally, we determined that AROS cooperates with SIRT1 to suppress GSK3β acetylation. Taken together, our results suggest that SIRT1 and AROS inhibit GSK3β activity and provide additional insight into drug resistance in the treatment of neuroblastoma.     

GRK5 influences the phosphorylation of tau via GSK3β and contributes to Alzheimer's disease

G protein-coupled receptor kinase 5 (GRK5) is a serine/threonine kinase whose dysfunction results in cognitive impairment and Alzheimer-like pathology, including tau hyperphosphorylation. However, the mechanisms whereby GRK5 influences tau phosphorylation remain incompletely understood. In the current study, we showed that GRK5 influenced the phosphorylation of tau via glycogen synthase kinase 3β (GSK3β). The activity of both tau and GSK3β in the hippocampus was increased in aged GRK5-knockout mice, which is consistent with what occurs in APP/PS1 transgenic mice. Furthermore, GRK5 regulated the activity of GSK3β and phosphorylated tau in vitro. Regardless of changes of GRK5 protein levels, tau hyperphosphorylation remained reduced after GSK3β activity was inhibited, suggesting that GRK5 may specifically influence tau hyperphosphorylation by modulating GSK3β activity. Taken together, our findings suggest that GRK5 deficiency contributes to the pathogenesis of Alzheimer's disease by influencing the hyperphosphorylation of tau through the activation of GSK3β.     

GSK3β Regulates Differentiation and Growth Arrest in Glioblastoma

Cancers are driven by a population of cells with the stem cell properties of self-renewal and unlimited growth. As a subpopulation within the tumor mass, these cells are believed to constitute a tumor cell reservoir. Pathways controlling the renewal of normal stem cells are deregulated in cancer. The polycomb group gene Bmi1, which is required for neural stem cell self-renewal and also controls anti-oxidant defense in neurons, is upregulated in several cancers, including medulloblastoma. We have found that Bmi1 is consistently and highly expressed in GBM. Downregulation of Bmi1 by shRNAs induced a differentiation phenotype and reduced expression of the stem cell markers Sox2 and Nestin. Interestingly, expression of glycogen synthase kinase 3 beta (GSK3β), which was found to be consistently expressed in primary GBM, also declined. This suggests a functional link between Bmi1 and GSK3β. Interference with GSK3β activity by siRNA, the specific inhibitor SB216763, or lithium chloride (LiCl) induced tumor cell differentiation. In addition, tumor cell apoptosis was enhanced, the formation of neurospheres was impaired, and clonogenicity reduced in a dose-dependent manner. GBM cell lines consist mainly of CD133-negative (CD133-) cells. Interestingly, ex vivo cells from primary tumor biopsies allowed the identification of a CD133- subpopulation of cells that express stem cell markers and are depleted by inactivation of GSK3β. Drugs that inhibit GSK3, including the psychiatric drug LiCl, may deplete the GBM stem cell reservoir independently of CD133 status.     

Dehydrocostuslactone suppresses angiogenesis in vitro and in vivo through inhibition of Akt/GSK-3β and mTOR signaling pathways

The traditional Chinese medicine component dehydrocostuslactone (DHC) isolated from Saussurea costus (Falc.) Lipschitz, has been shown to have anti-cancer activity. Angiogenesis is an essential process in the growth and progression of cancer. In this study, we demonstrated, for the first time, the anti-angiogenic mechanism of action of DHC to be via the induction of cell cycle progression at the G0/G1 phase due to abrogation of the Akt/glycogen synthase kinase-3β (GSK-3β)/cyclin D1 and mTOR signaling pathway. First, we demonstrated that DHC has an anti-angiogenic effect in the matrigel-plug nude mice model and an inhibitory effect on human umbilical vein endothelial cell (HUVEC) proliferation and capillary-like tube formation in vitro. DHC caused G0/G1 cell cycle arrest, which was associated with the down-regulation of cyclin D1 expression, leading to the suppression of retinoblastoma protein phosphorylation and subsequent inhibition of cyclin A and cdk2 expression. With respect to the molecular mechanisms underlying the DHC-induced cyclin D1 down-regulation, this study demonstrated that DHC significantly inhibits Akt expression, resulting in the suppression of GSK-3β phosphorylation and mTOR expression. These effects are capable of regulating cyclin D1 degradation, but they were significantly reversed by constitutively active myristoylated (myr)-Akt. Furthermore, the abrogation of tube formation induced by DHC was also reversed by overexpression of Akt. And the co-treatment with LiCl and DHC significantly reversed the growth inhibition induced by DHC. Taken together, our study has identified Akt/GSK-3β and mTOR as important targets of DHC and has thus highlighted its potential application in angiogenesis-related diseases, such as cancer.     

Design of potent and selective GSK3β inhibitors with acceptable safety profile and pharmacokinetics

From potent and selective inhibitors of GSK3β displaying CYP1A2 inhibition and poor PK properties, mostly linked to metabolic instability and in vivo hydrolysis of the amide bond, we were able to obtain safe and orally available inhibitors with good half lives.     

PKCε promotes cardiac mitochondrial and metabolic adaptation to chronic hypobaric hypoxia by GSK3β inhibition

PKCε is central to cardioprotection. Sub-proteome analysis demonstrated co-localization of activated cardiac PKCε (aPKCε) with metabolic, mitochondrial, and cardioprotective modulators like hypoxia-inducible factor 1α (HIF-1α). aPKCε relocates to the mitochondrion, inactivating glycogen synthase kinase 3β (GSK3β) to modulate glycogen metabolism, hypertrophy and HIF-1α. However, there is no established mechanistic link between PKCε, p-GSK3β and HIF1-α. Here we hypothesized that cardiac-restricted aPKCε improves mitochondrial response to hypobaric hypoxia by altered substrate fuel selection via a GSK3β/HIF-1α-dependent mechanism. aPKCε and wild-type (WT) mice were exposed to 14 days of hypobaric hypoxia (45 kPa, 11% O(2)) and cardiac metabolism, functional parameters, p-GSK3β/HIF-1α expression, mitochondrial function and ultrastructure analyzed versus normoxic controls. Mitochondrial ADP-dependent respiration, ATP production and membrane potential were attenuated in hypoxic WT but maintained in hypoxic aPKCε mitochondria (P < 0.005, n = 8). Electron microscopy revealed a hypoxia-associated increase in mitochondrial number with ultrastructural disarray in WT versus aPKCε hearts. Concordantly, left ventricular work was diminished in hypoxic WT but not aPKCε mice (glucose only perfusions). However, addition of palmitate abrogated this (P < 0.05 vs. WT). aPKCε hearts displayed increased glucose utilization at baseline and with hypoxia. In parallel, p-GSK3β and HIF1-α peptide levels were increased in hypoxic aPKCε hearts versus WT. Our study demonstrates that modest, sustained PKCε activation blunts cardiac pathophysiologic responses usually observed in response to chronic hypoxia. Moreover, we propose that preferential glucose utilization by PKCε hearts is orchestrated by a p-GSK3β/HIF-1α-mediated mechanism, playing a crucial role to sustain contractile function in response to chronic hypobaric hypoxia.     

Metabolomic changes in Caenorhabditis elegans lifespan mutants as evident from GC–EI–MS and GC–APCI–TOF–MS profiling

Lifespan mutants of the nematode Caenorhabditis elegans are a much studied aging model, however, aging-related changes at the metabolome level remain largely unexplored. To identify metabolic features connected to mitochondrial dysfunction, a hallmark of aging and age-related disease, we analyzed a short-lived mitochondrial mutant (mev-1(kn1)), a long-lived mutant with enhanced cellular maintenance (ife-2(ok306)) and the novel double mutant ife-2(ok306);mev-1(kn1) which is normal-lived, possibly through attenuation of the metabolic mev-1 phenotype. Metabolomic analysis involved coupled gas chromatography–mass spectrometry with electron ionization (GC–EI–MS) and, in addition, recently introduced GC with soft atmospheric pressure chemical ionization coupled to time-of-flight mass spectrometry (GC–APCI–TOF–MS) to yield complementary mass spectrometric information for enhanced metabolite annotation. Multivariate analysis allowed distinction of mev-1 and ife-2 mutants from the wild type, while suggesting still another, distinct metabolic phenotype for the ife-2;mev-1 double mutant. In mev-1(kn1), disturbed energy metabolism was indicated by upset TCA cycle homeostasis, elevated glycolytic substrate and lactic acid levels as well as depletion of free amino acids pools. Surprisingly, these mitochondrially related changes were retained in the ife-2;mev-1 mutant, as were highly elevated levels of the dipeptide glycylproline indicative of increased collagen catabolism. However, the double mutant reverted mev-1(kn1) changes in uric acid and long-chain fatty alcohol metabolism, two pathways connected to the peroxisomal compartment. Our results are in line with recent evidence for a critical role of this organelle in aging and demonstrate the usefulness of non-targeted metabolomics approaches for detecting complex metabolic changes in the study of mitochondrial dysfunction.     

Inhibition of GSK 3β Activity Is Associated with Excessive EZH2 Expression and Enhanced Tumour Invasion in Nasopharyngeal Carcinoma

Background

Enhancer of zeste homolog 2 (EZH2) has been shown to contribute to tumour development and/or progression. However, the signalling pathway underlying the regulation of EZH2 in nasopharyngeal carcinoma (NPC) remains unclear. Since EZH2 contains the putative Glycogen synthase kinase 3 beta (GSK3β) phosphorylation motif ADHWDSKNVSCKNC (591) and may act as a possible substrate of GSK-3β, it is possible that inactivation of GSK3β may lead to excessive EZH2 expression in NPC.

Method

We first examined the expression of EZH2 and phosphorylated GSK3β (p-GSK3β) by immunohistochemical staining in NPC samples. Then, we evaluated the interaction of GSK3β and EZH2 using immunoprecipitation and immune blot. Moreover, we determined the effect of inhibition of GSK3β activity on EZH2 expression and tumor invasiveness in NPC cell lines in vitro. Finally, we evaluated the invasive properties of NPC cells after knocking down EZH2 expression with EZH2 siRNA.

Results

We found that expression of EZH2 correlated with phosphorylated GSK3β (p-GSK3β) at Ser 9 (an inactivated form of GSK3β) in human nasopharyngeal carcinoma (NPC) samples. We also provided evidence that GSK3β is able to interact with EZH2 using immunoprecipitation and immune blot. Furthermore, we found that inhibition of GSK3β activity can lead to upregulation of EZH2 in NPC cell lines in vitro, with enhanced local invasiveness. By knocking down EZH2 expression with EZH2 siRNA, we found that these invasive properties were EZH2 dependent.

Conclusion

Our findings indicate that GSK3β inactivation may account for EZH2 overexpression and subsequent tumour progression, and this mechanism might be a potential target for NPC therapy.     

The Alzheimer's therapeutic PBT2 promotes amyloid-β degradation and GSK3 phosphorylation via a metal chaperone activity

Impaired metal ion homeostasis causes synaptic dysfunction and treatments for Alzheimer's disease (AD) that target metal ions have therefore been developed. The leading compound in this class of therapeutic, PBT2, improved cognition in a clinical trial with AD patients. The aim of the present study was to examine the cellular mechanism of action for PBT2. We show PBT2 induces inhibitory phosphorylation of the α- and β-isoforms of glycogen synthase kinase 3 and that this activity is dependent on PBT2 translocating extracellular Zn and Cu into cells. This activity is supported when Aβ:Zn aggregates are the source of extracellular Zn and adding PBT2 to Aβ:Zn preparations promotes Aβ degradation by matrix metalloprotease 2. PBT2-induced glycogen synthase kinase 3 phosphorylation appears to involve inhibition of the phosphatase calcineurin. Consistent with this, PBT2 increased phosphorylation of other calcineurin substrates, including cAMP response element binding protein and Ca2?/calmodulin-dependent protein kinase. These data demonstrate PBT2 can decrease Aβ levels by sequestering the Zn that promotes extracellular formation of protease resistant Aβ:Zn aggregates, and that subsequent intracellular translocation of the Zn by PBT2 induces cellular responses with synapto-trophic potential. Intracellular translocation of Zn and Cu via the metal chaperone activity of PBT2 may be an important mechanism by which PBT2 improves cognitive function in people with AD.     

The cardioprotective effect of dihydromyricetin prevents ischemia–reperfusion-induced apoptosis in vivo and in vitro via the PI3K/Akt and HIF-1α signaling pathways

Reperfusion therapy is widely used to treat acute myocardial infarction (AMI). However, further injury to the heart induced by rapidly initiating reperfusion is often encountered in clinical practice. A lack of pharmacological strategies in clinics limits the prognosis of patients with myocardial ischemia-reperfusion injury (MIRI). Dihydromyricetin (DMY) is one of the most abundant components in vine tea, commonly known as the tender stems and leaves of Ampelopsis grossedentata. The aim of this study was to evaluate the cardioprotection of DMY against myocardial ischemia-reperfusion (I/R) injury and to further investigate the underlying mechanism. An I/R injury was induced by left anterior descending coronary artery occlusion in adult male rats in vivo and a hypoxia–reoxygenation (H/R) injury in H9c2 cardiomyocytes in vitro. We found that DMY pretreatment provided significant protection against I/R-induced injury, including enhanced antioxidant capacity and inhibited apoptosis in vivo and in vitro. This effect correlated with the activation of the PI3K/Akt and HIF-1α signaling pathways. Conversely, blocking Akt activation with the PI3K inhibitor LY294002 effectively suppressed the protective effects of DMY against I/R-induced injury. In addition, the PI3K inhibitor partially blocked the effects of DMY on the upregulation of Bcl-2, Bcl-xl, procaspase-3, -8, and -9 protein expression and the downregulation of HIF-1α, Bnip3, Bax, Cyt-c, cleaved caspase-3, -8, and -9 protein expression. Collectively, these results showed that DMY decreased the apoptosis and necrosis by I/R treatment, and PI3K/Akt and HIF-1α plays a crucial role in protection during this process. These observations indicate that DMY has the potential to exert cardioprotective effects against I/R injury and the results might be important for the clinical efficacy of AMI treatment.     

Silencing of IncRNA LBX2-AS1 suppresses glioma cell proliferation and metastasis through the Akt/GSK3β pathway in vitro

Long non-coding RNAs (IncRNAs) have been proposed to play pivotal roles in the tumorigenesis of various malignant tumors.Previous studies have found that IncRNA...     

Quercetin Protects against Okadaic Acid-Induced Injury via MAPK and PI3K/Akt/GSK3β Signaling Pathways in HT22 Hippocampal Neurons

Increasing evidence shows that oxidative stress and the hyperphosphorylation of tau protein play essential roles in the progression of Alzheimer’s disease (AD). Quercetin is a major flavonoid that has anti-oxidant, anti-cancer and anti-inflammatory properties. We investigated the neuroprotective effects of quercetin to HT22 cells (a cell line from mouse hippocampal neurons). We found that Okadaic acid (OA) induced the hyperphosphorylation of tau protein at Ser199, Ser396, Thr205, and Thr231 and produced oxidative stress to the HT22 cells. The oxidative stress suppressed the cell viability and decreased the levels of lactate dehydrogenase (LDH), superoxide dismutase (SOD), mitochondria membrane potential (MMP) and Glutathione peroxidase (GSH-Px). It up-regulated malondialdehyde (MDA) production and intracellular reactive oxygen species (ROS). In addition, phosphoinositide 3 kinase/protein kinase B/Glycogen synthase kinase3β (PI3K/Akt/GSK3β) and mitogen activated protein kinase (MAPK) were also involved in this process. We found that pre-treatment with quercetin can inhibited OA-induced the hyperphosphorylation of tau protein and oxidative stress. Moreover, pre-treatment with quercetin not only inhibited OA-induced apoptosis via the reduction of Bax, and up-regulation of cleaved caspase 3, but also via the inhibition of PI3K/Akt/GSK3β, MAPKs and activation of NF-κB p65. Our findings suggest the therapeutic potential of quercetin to treat AD.     

Triterpenic acids-enriched fraction from Cyclocarya paliurus attenuates insulin resistance and hepatic steatosis via PI3K/Akt/GSK3β pathway

BackgroundNon-alcoholic fatty liver disease (NAFLD) is the most prevalent form of chronic liver diseases. Cyclocarya paliurus (C. paliurus), an edible and medicinal plant in Chinese folk, has been demonstrated to ameliorate diabetes, obesity and lipid metabolism disorders. However, its effects on NAFLD and its potential molecular mechanism have not been clearly expounded.PurposeThe present study was designed to explore the therapeutic potential of triterpenic acids-enriched fraction from C. paliurus (CPT), as well as its underlying mechanism in vivo and in vitro models of NAFLD.MethodsThe metabolic effects and possible molecular mechanism of CPT were examined using HepG2 cells and primary hepatocytes (isolated from C57BL/6 J mice) models of fatty liver induced by palmitic acid (PA) and a high fat diet mouse model.ResultsIn high fat diet-induced C57BL/6 J mice, CPT significantly reduced liver weight index, serum alanine transaminase (ALT), aspartate transaminase (AST), triacylglycerol (TG), total cholesterol (TC) and hepatic TG, TC levels. Moreover, CPT dramatically decreased the contents of blood glucose, insulin, and insulin resistance (HOMA-IR) index. Meanwhile, CPT significantly increased the tyrosine phosphorylation level of IRS and the uptake of 2-deoxyglucose (2DG) in PA-induced HepG2 cells and primary hepatocytes fatty liver models. Furthermore, in PA-induced HepG2 cells and primary hepatocytes, CPT significantly decreased the number of lipid droplets and intracellular TG content. In addition, mechanism investigation showed that CPT increased the phosphorylation of phosphoinositide 3-kinase (PI3K), protein kinase B (Akt) and glycogen synthase-3β (GSK3β) in vivo and in vitro models, which were abrogated by PI3K inhibitor LY294002 in vitro models.ConclusionThese findings indicate that CPT may exert the therapeutic effects on NAFLD via regulating PI3K/Akt/GSK3β pathway.     

Inactivation of GSK3β and activation of NF-κB pathway via Axl represents an important mediator of tumorigenesis in esophageal squamous cell carcinoma

The receptor tyrosine kinase Axl has been described as an oncogene, and its deregulation has been implicated in the progression of several human cancers. While the role of Axl in esophageal adenocarcinoma has been addressed, there is no information about its role in esophageal squamous cell carcinoma (OSCC). In the current report, we identified, for the first time, deregulation of Axl expression in OSCC. Axl is consistently overexpressed in OSCC cell lines and human tumor samples, mainly in advanced stages of the disease. Blockage of Axl gene expression by small interfering RNA inhibits cell survival, proliferation, migration, and invasion in vitro and esophageal tumor growth in vivo. Additionally, repression of Axl expression results in Akt-dependent inhibition of pivotal genes involved in the nuclear factor-kappaB (NF-κB) pathway and in the induction of glycogen synthase kinase 3β (GSK3β) activity, resulting in loss of mesenchymal markers and induction of epithelial markers. Furthermore, treatment of esophageal cancer cells with the Akt inhibitor wortmannin inhibits NF-κB signaling, induces GSK3β activity, and blocks OSCC cell proliferation in an Axl-dependent manner. Taken together, our results establish a clear role for Axl in OSCC tumorigenesis with potential therapeutic implications.     

Knockdown of α-synuclein in cerebral cortex improves neural behavior associated with apoptotic inhibition and neurotrophin expression in spinal cord transected rats

Spinal cord injury (SCI) often causes severe functional impairment with poor recovery. The treatment, however, is far from satisfaction, and the mechanisms remain unclear. By using proteomics and western blot, we found spinal cord transection (SCT) resulted in a significant down-regulation of α-synuclein (SNCA) in the motor cortex of SCT rats at 3 days post-operation. In order to detect the role of SNCA, we used SNCA-ORF/shRNA lentivirus to upregulate or knockdown SNCA expression. In vivo, SNCA-shRNA lentivirus injection into the cerebral cortex motor area not only inhibited SNCA expression, but also significantly enhanced neurons’ survival, and attenuated neuronal apoptosis, as well as promoted motor and sensory function recovery in hind limbs. While, overexpression SNCA exhibited the opposite effects. In vitro, cortical neurons transfected with SNCA-shRNA lentivirus gave rise to an optimal neuronal survival and neurite outgrowth, while it was accompanied by reverse efficiency in SNCA-ORF group. In molecular level, SNCA silence induced the upregulation of Bcl-2 and the downregulation of Bax, and the expression of NGF, BDNF and NT3 was substantially upregulated in cortical neurons. Together, endogenous SNCA play a crucial role in motor and sensory function regulation, in which, the underlying mechanism may be linked to the regulation of apoptosis associated with apoptotic gene (Bax, Bcl2) and neurotrophic factors expression (NGF, BDNF and NT3). These finds provide novel insights to understand the role of SNCA in cerebral cortex after SCT, and it may be as a novel treatment target for SCI repair in future clinic trials.     

GSK3β Overexpression in Dentate Gyrus Neural Precursor Cells Expands the Progenitor Pool and Enhances Memory Skills

In restricted areas of the adult brain, like the subgranular zone of the dentate gyrus (DG), there is continuous production of new neurons. This process, named adult neurogenesis, is involved in important cognitive functions such as memory and learning. It requires the presence of newborn neurons that arise from neuronal stem cells, which divide and differentiate through successive stages in adulthood. In this work, we demonstrate that overexpression of glycogen synthase kinase (GSK) 3β in neural precursor cells (NPCs) using the glial fibrillary acidic protein promoter during DG development produces an increase in the neurogenic process, increasing NPCs numbers. Moreover, the transgenic mice show higher DG volume and increased number of mature granule neurons. In an attempt to compensate for these alterations, glial fibrillary acidic protein/GSK3β-overexpressing mice show increased levels of Dkk1 and sFRP3, two inhibitors of the Wnt-frizzled complex. We have also found behavioral differences between wild type and transgenic mice, indicating a higher rating in memory tasks for GSK3β-overexpressing mice compared with wild type mice. These data indicate that GSK3β is a crucial kinase in NPC physiology and suggest that this molecule plays a key role in the correct development of DG and adult neurogenesis in this region.