GSK-3: Functional Insights from Cell Biology and Animal Models

Drosophila melanogaster as a Model for Diabetes Type 2 Progression

Drosophila melanogaster has been used as a very versatile and potent model in the past few years for studies in metabolism and metabolic disorders, including diabetes types 1 and 2. Drosophila insulin signaling, despite having seven insulin-like peptides with partially redundant functions, is very similar to the human insulin pathway and has served to study many different aspects of diabetes and the diabetic state. Yet, very few studies have addressed the chronic nature of diabetes, key for understanding the full-blown disease, which most studies normally explore. One of the advantages of having Drosophila mutant viable combinations at different levels of the insulin pathway, with significantly reduced insulin pathway signaling, is that the abnormal metabolic state can be studied from the onset of the life cycle and followed throughout. In this review, we look at the chronic nature of impaired insulin signaling. We also compare these results to the results gleaned from vertebrate model studies.

Drosophila RSK Influences the Pace of the Circadian Clock by Negative Regulation of Protein Kinase Shaggy Activity

Endogenous molecular circadian clocks drive daily rhythmic changes at the cellular, physiological, and behavioral level for adaptation to and anticipation of environmental signals. The core molecular system consists of autoregulatory feedback loops, where clock proteins inhibit their own transcription. A complex and not fully understood interplay of regulatory proteins influences activity, localization and stability of clock proteins to set the pace of the clock. This study focuses on the molecular function of Ribosomal S6 Kinase (RSK) in the Drosophila melanogaster circadian clock. Mutations in the human rsk2 gene cause Coffin–Lowry syndrome, which is associated with severe mental disabilities. Knock-out studies with Drosophila ortholog rsk uncovered functions in synaptic processes, axonal transport and adult behavior including associative learning and circadian activity. However, the molecular targets of RSK remain elusive. Our experiments provide evidence that RSK acts in the key pace maker neurons as a negative regulator of Shaggy (SGG) kinase activity, which in turn determines timely nuclear entry of the clock proteins Period and Timeless to close the negative feedback loop. Phosphorylation of serine 9 in SGG is mediated by the C-terminal kinase domain of RSK, which is in agreement with previous genetic studies of RSK in the circadian clock but argues against the prevailing view that only the N-terminal kinase domain of RSK proteins carries the effector function. Our data provide a mechanistic explanation how RSK influences the molecular clock and imply SGG S9 phosphorylation by RSK and other kinases as a convergence point for diverse cellular and external stimuli.

β-Elemene inhibits the proliferation of primary human airway granulation fibroblasts by down-regulating canonical Wnt/β-catenin pathway

Benign airway stenosis is a clinical challenge because of recurrent granulation tissues. Our previous study proved that a Chinese drug, β-elemene, could effectively inhibit the growth of fibroblasts cultured from hyperplastic human airway granulation tissues, which could slow down the progression of this disease. The purpose of the present study is to find out the mechanism for this effect. We cultured fibroblasts from normal human airway tissues and human airway granulation tissues. These cells were cultured with 160 μg/ml normal saline (NS), different doses of β-elemene, or 10 ng/ml canonical Wnt/β-catenin pathway inhibitor (Dickkopf-1, DKK-1). The proliferation rate of cells and the expression of six molecules involved in canonical Wnt/β-catenin pathway, Wnt3a, glycogen synthase kinase-3β (GSK-3β), β-catenin, α-smooth muscle actin (α-SMA), transforming growth factor-β (TGF-β), and Collagen I (Col-I), were measured. At last, we used canonical Wnt/β-catenin pathway activator (LiCl) to further ascertain the mechanism of β-elemene. Canonical Wnt/β-catenin pathway is activated in human airway granulation fibroblasts. β-Elemene didn't affect normal human airway fibroblasts; however, it had a dose-responsive inhibitive effect on the proliferation and expression of Wnt3a, non-active GSK-3β, β-catenin, α-SMA, TGF-β, and Col-I of human airway granulation fibroblasts. More importantly, it had the same effect on the expression and nuclear translocation of active β-catenin. All these effects were similar to 10 ng/ml DKK-1 and could be attenuated by 10 mM LiCl. Thus, β-elemene inhibits the proliferation of primary human airway granulation fibroblasts by down-regulating canonical Wnt/β-catenin pathway. This pathway is possibly a promising target to treat benign tracheobronchial stenosis.

Anti-helminthic niclosamide inhibits Ras-driven oncogenic transformation via activation of GSK-3

Despite the importance of Ras oncogenes as a therapeutic target in human cancer, their ‘undruggable’ tertiary structures limit the effectiveness of anti-Ras drugs. Canonical Wnt signaling contributes to Ras activity by glycogen synthase kinase 3 (GSK-3)-dependent phosphorylation at the C-terminus and subsequent degradation. In the accompanying report, we show that the anti-helminthic niclosamide directly binds to GSK-3 and inhibits Axin functions in colon cancer cells, with reversion of Snail-mediated epithelial-mesenchymal transition. In this study, we report that niclosamide effectively suppresses Ras and nuclear NFAT activities regardless of the mutational status of Ras at nM levels. Mechanistically, niclosamide increased endogenous GSK-3 activity, shortening the half-life of mutant Ras. Further, niclosamide activates Raf-1 kinase inhibitory protein, a downstream target of Snail repressor. Niclosamide treatment attenuates Ras-induced oncogenic potential in vitro and in vivo. These findings provide a clinically available repositioned Ras inhibitor as well as a novel strategy for inhibiting the Ras via GSK-3.

Protein S-Nitrosylation Controls Glycogen Synthase Kinase 3β Function Independent of Its Phosphorylation State

RATIONALE

GSK-3β (glycogen synthase kinase 3β) is a multifunctional and constitutively active kinase known to regulate a myriad of cellular processes. The primary mechanism to regulate its function is through phosphorylation-dependent inhibition at serine-9 residue. Emerging evidence indicates that there may be alternative mechanisms that control GSK-3β for certain functions.

OBJECTIVES

Here, we sought to understand the role of protein S-nitrosylation (SNO) on the function of GSK-3β. SNO-dependent modulation of the localization of GSK-3β and its ability to phosphorylate downstream targets was investigated in vitro, and the network of proteins differentially impacted by phospho- or SNO-dependent GSK-3β regulation and in vivo SNO modification of key signaling kinases during the development of heart failure was also studied.

METHODS AND RESULTS

We found that GSK-3β undergoes site-specific SNO both in vitro, in HEK293 cells, H9C2 myoblasts, and primary neonatal rat ventricular myocytes, as well as in vivo, in hearts from an animal model of heart failure and sudden cardiac death. S-nitrosylation of GSK-3β significantly inhibits its kinase activity independent of the canonical phospho-inhibition pathway. S-nitrosylation of GSK-3β promotes its nuclear translocation and access to novel downstream phosphosubstrates which are enriched for a novel amino acid consensus sequence motif. Quantitative phosphoproteomics pathway analysis reveals that nuclear GSK-3β plays a central role in cell cycle control, RNA splicing, and DNA damage response.

CONCLUSIONS

The results indicate that SNO has a differential effect on the location and activity of GSK-3β in the cytoplasm versus the nucleus. SNO modification of GSK-3β occurs in vivo and could contribute to the pathobiology of heart failure and sudden cardiac death.

SIRT2 deacetylase regulates the activity of GSK3 isoforms independent of inhibitory phosphorylation

Glycogen synthase kinase 3 (GSK3) is a critical regulator of diverse cellular functions involved in the maintenance of structure and function. Enzymatic activity of GSK3 is inhibited by N-terminal serine phosphorylation. However, alternate post-translational mechanism(s) responsible for GSK3 inactivation are not characterized. Here, we report that GSK3α and GSK3β are acetylated at Lys246 and Lys183, respectively. Molecular modeling and/or molecular dynamics simulations indicate that acetylation of GSK3 isoforms would hinder both the adenosine binding and prevent stable interactions of the negatively charged phosphates. We found that SIRT2 deacetylates GSK3β, and thus enhances its binding to ATP. Interestingly, the reduced activity of GSK3β is associated with lysine acetylation, but not with phosphorylation at Ser9 in hearts of SIRT2-deficient mice. Moreover, GSK3 is required for the anti-hypertrophic function of SIRT2 in cardiomyocytes. Overall, our study identified lysine acetylation as a novel post-translational modification regulating GSK3 activity.

Progesterone attenuates airway remodeling and glucocorticoid resistance in a murine model of exposing to ozone

Airway remodeling is a vital component of chronic obstructive pulmonary disease (COPD). Despite the broad anti-inflammation effects of glucocorticoids, they exhibit relatively little therapeutic benefit in COPD, indicating the accelerating demands of new agents for COPD. We aim to explore the effect of progesterone on airway remodeling in a murine modeling of exposing to ozone and to further examine the potential effect of progesterone on glucocorticoid insensitivity. C57/BL6 mice were exposed to ozone for 12 times over 6 weeks, and were administered with progesterone alone or combined with budesonide (BUD) after each exposure until the 10th week. The peribronchial collagen deposition was measured. The protein levels of MMP8 and MMP9 in bronchoalveolar lavage fluid (BALF) and lungs were assessed. Western blot analysis was used to detect the levels of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), a-smooth muscle actin (α-SMA), glycogen synthase kinase-3β (GSK-3β). The expression of VEGF and histone deacetylase 2 (HDAC2) in the lung were determined by Immunohistochemical analyses. We observe that progesterone attenuates the peribronchial collagen deposition, as well as the expression of MMP8, MMP9, HIF-1α, VEGF, α-SMA, and GSK-3β in BALF or lung tissues. Progesterone or BUD monotherapy has no effect on HDAC2 production. Progesterone combines with BUD induce dramatically enhanced effects. Thus, these results demonstrate novel roles of progesterone for the pathogenesis and airway remodeling in COPD. Progesterone plus BUD administration exerts more significant inhibition on airway remodeling with dose-independent. Additionally, progesterone may, to some extent, improve the glucocorticoid insensitivity.

Small Molecules for Neural Stem Cell Induction

Generation of induced pluripotent stem cells (iPSCs) from other somatic cells has provided great hopes for transplantation therapies. However, these cells still cannot be used for clinical application due to the low reprogramming and differentiation efficiency beside the risk of mutagenesis and tumor formation. Compared to iPSCs, induced neural stem cells (iNSCs) are easier to terminally differentiate into neural cells and safe; thus, iNSCs hold more opportunities than iPSCs to treat neural diseases. On the other hand, recent studies have showed that small molecules (SMs) can dramatically improve the efficiency of reprogramming and SMs alone can even convert one kind of somatic cells into another, which is much safer and more effective than transcription factor-based methods. In this study, we provide a review of SMs that are generally used in recent neural stem cell induction studies, and discuss the main mechanisms and pathways of each SM.

Modulation of GSK3β autoinhibition by Thr-7 and Thr-8

Glycogen synthase kinase 3β (GSK-3β) is a pivotal signaling node that regulates a myriad of cellular functions and is deregulated in many pathological conditions, making it an attractive therapeutic target. Inhibitory Ser-9 phosphorylation of GSK3β by AKT is an important mechanism for negative regulation of GSK3β activity upon insulin stimulation. Here, we report that Thr-7 and Thr-8 residues located in the AKT/PKB substrate consensus sequence on GSK3β are essential for insulin-stimulated Ser-9 phosphorylation in vivo and for GSK3β inactivation. Intestinal cell kinase (ICK) phosphorylates GSK3β Thr-7 in vitro and in vivo. Thr-8 phosphorylation partially inhibits GSK3β, but Thr-7 phosphorylation promotes GSK3β activity and blocks phospho-Ser-9-dependent GSK3β autoinhibition. Our findings uncover novel mechanistic and signaling inputs involved in the autoinhibition of GSK3β.

Peripheral Administration of GSK-3β Antisense Oligonucleotide Improves Learning and Memory in SAMP8 and Tg2576 Mouse Models of Alzheimer's Disease

Glycogen synthase kinase (GSK)-3β is a multifunctional protein that has been implicated in the pathological characteristics of Alzheimer's disease (AD), including the heightened levels of neurofibrillary tangles, amyloid-beta (Aβ), and neurodegeneration. We have previously shown that an antisense oligonucleotide directed at the Tyr 216 site on GSK-3β (GAO) when injected centrally can decrease GSK-3β levels, improve learning and memory, and decrease oxidative stress. In addition, we showed that GAO can cross the blood-brain barrier. Herein the impact of peripherally administered GAO in both the non-transgenic SAMP8 and transgenic Tg2576 (APPswe) models of AD were examined respective to learning and memory. Brain tissues were then evaluated for expression changes in the phosphorylated-Tyr 216 residue, which leads to GSK-3β activation, and the phosphorylated-Ser9 residue, which reduces GSK-3β activity. SAMP8 GAO-treated mice showed improved acquisition and retention using aversive T-maze, and improved declarative memory as measured by the novel object recognition (NOR) test. Expression of the phosphorylated-Tyr 216 was decreased and the phosphorylated-Ser9 was increased in GAO-treated SAMP8 mice. Tg2576 GAO-treated mice improved acquisition and retention in both the T-maze and NOR tests, with an increased phosphorylated-Ser9 GSK-3β expression. Results demonstrate that peripheral administration of GAO improves learning and memory, corresponding with alterations in GSK-3β phosphorylation state. This study supports peripherally administered GAO as a viable means to mediate GSK-3β activity within the brain and a possible treatment for AD.

Two Weeks of Variable Stress Increases Gamma-H2AX Levels in the Mouse Bed Nucleus of the Stria Terminalis

Recent reports demonstrate that DNA damage is induced, and rapidly repaired, in circuits activated by experience. Moreover, stress hormones are known to slow DNA repair, suggesting that prolonged stress may result in persistent DNA damage. Prolonged stress is known to negatively impact physical and mental health; however, DNA damage as a factor in stress pathology has only begun to be explored. Histone H2A-X phosphorylated at serine 139 (γH2AX) is a marker of DNA double-strand breaks (DSB), a type of damage that may lead to cell death if unrepaired. We hypothesized that a 14-day period of variable stress exposure sufficient to alter anxiety-like behavior in male C57BL/6J mice would produce an increase in γH2AX levels in the bed nucleus of the stria terminalis (BNST), a region implicated in anxiety and stress regulation. We observed that 14 days of variable stress, but not a single stress exposure, was associated with increased levels of γH2AX 24 h after termination of the stress paradigm. Further investigation found that phosphorylation levels of a pair of kinases associated with the DNA damage response, glycogen synthase kinase 3 β (GSK3β) and p38 mitogen-activated protein kinase (MAPK) were also elevated following variable stress. Our results suggest that unrepaired DNA DSBs and/or repetitive attempted repair may represent an important component of the allostatic load that stress places on the brain.

Pseudomonas aeruginosa mannose-sensitive hemagglutinin inhibits proliferation and invasion via the PTEN/AKT pathway in HeLa cells

We investigated the effects of Pseudomonas aeruginosa mannose-sensitive hemagglutinin (PA-MSHA) on the proliferation and invasion of human cervical cancer cell lines, as well as the molecular pathways underlying these effects. MTT cell proliferation assays revealed a time- and concentration-dependent cytotoxic effect of PA-MSHA on HeLa cells but not H8 cells. Flow cytometry with propidium iodide and annexin-V-fluorescein isothiocyanate labeling (FITC) indicated that various concentrations of PA-MSHA could induce apoptosis and G2-M cell cycle arrest in HeLa cells. PA-MSHA also impaired the migration and invasion abilities of HeLa cells in Wound healing and Transwell invasion assays. Western blot results demonstrated that PA-MSHA reduced the expression of p-AKT, p-GSK3β, BCL-2, Vimentin and β-catenin, but increased the levels of PTEN, BAD, BAX and E-cadherin in HeLa cells. Importantly, PTEN siRNA induced the activity of p-AKT, while PA-MSHA partly inhibited this induction, indicating that PA-MSHA may reduce the cell proliferation and invasion potential by activating PTEN and thus inhibiting the AKT pathway in vitro. These data suggest the potential application of PA-MSHA to the treatment of human cervical cancer.

Glycogen synthase kinase-3 and its inhibitors: Potential target for various therapeutic conditions

Glycogen Synthase Kinase-3 (GSK-3) is a serine/threonine kinase which is ubiquitously expressed and is regarded as a regulator for various cellular events and signalling pathways. It exists in two isoforms, GSK-3α and GSK-3β and can phosphorylate a wide range of substrates. Aberrancy in the GSK-3 activity can lead to various diseases like Alzheimer's, diabetes, cancer, neurodegeneration etc., rendering it an attractive target to develop potent and specific inhibitors. The present review focuses on the recent developments in the area of GSK-3 inhibitors and also enlightens its therapeutic applicability in various disease conditions.

GSK3β Controls mTOR and Prosurvival Signaling in Neurons

Glycogen synthase kinases-3β (GSK3β) is a key regulator of cell homeostasis. In neurons, GSK3β contributes to control of neuronal transmission and plasticity. Despite extensive studies in non-neuronal cells, crosstalk between GSK3β and other signaling pathways remains not well defined in neurons. In the present study, we report that GSK3β positively affected the activity of effectors of mammalian target of rapamycin complex 1 (mTORC1) and complex 2 (mTORC2), in mature neurons in vitro and in vivo. GSK3β also promoted prosurvival signaling and attenuated kainic acid-induced apoptosis. Our study identified GSK3β as a positive regulator of prosurvival signaling, including the mTOR pathway, and indicates the possible neuroprotective role of GSK3β in models of pharmacologically induced excitotoxicity.

Melatonin attenuates phosgene-induced acute lung injury via the upregulation Wnt/β-catenin pathway

The aim of this study was to assess the therapeutic effect of melatonin in phosgene induced acute lung injury (ALI) and to explore the related mechanisms. A rat model of phosgene induced ALI was established and the severity of the ALI was evaluated by wet/dry (W:D) ratio of lung weight, bronchoalveolar lavage (BAL) fluid cell counts and inflammatory cytokines. The rats were administrated with elatonin (MT), ulinastatin (UTI), p38 inhibitor and NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) alone or in combination. We found that MT in combination with UTI significantly improved the severity of ALI and the activation of Wnt/β-catenin signaling was involved in beneficial effect of MT. MT may be used as a therapeutic adjuvant for phosgene induced ALI.

Prenatal Alcohol Exposure Leads to Enhanced Serine 9 Phosphorylation of Glycogen Synthase Kinase-3β (GSK-3β) in the Hippocampal Dentate Gyrus of Adult Mouse

BACKGROUND

The goal of this study was to evaluate the expression and serine 9 phosphorylation of glycogen synthase kinase (GSK-3β) within the adult hippocampal dentate gyrus (DG) in a preclinical mouse model of fetal alcohol spectrum disorders. GSK-3β is a multifunctional kinase that modulates many hippocampal processes affected by gestational alcohol, including synaptic plasticity and adult neurogenesis. GSK-3β is a constitutively active kinase that is negatively regulated by phosphorylation at the serine 9 residue.

METHODS

We utilized a well-characterized limited access "drinking-in-the-dark" paradigm of prenatal alcohol exposure (PAE) and measured p(Ser9)GSK-3β and total GSK-3β within adult DG by Western blot analysis. In addition, we evaluated the expression pattern of both p(Ser9)GSK-3β and total GSK-3β within the adult hippocampal dentate of PAE and control mice using high-resolution confocal microscopy.

RESULTS

Our findings demonstrate a marked 2.0-fold elevation of p(Ser9)GSK-3β in PAE mice, concomitant with a more moderate 36% increase in total GSK-3β. This resulted in an approximate 63% increase in the p(Ser9)GSK-3β/GSK-3β ratio. Immunostaining revealed robust GSK-3β expression within Cornu Ammonis (CA) pyramidal neurons, hilar mossy cells, and a subset of GABAergic interneurons, with low levels of expression within hippocampal progenitors and dentate granule cells.

CONCLUSIONS

These findings suggest that PAE may lead to a long-term disruption of GSK-3β signaling within the DG, and implicate mossy cells, GABAergic interneurons, and CA primary neurons as major targets of this dysregulation.

Heat Stress Reduces Sperm Motility via Activation of Glycogen Synthase Kinase-3α and Inhibition of Mitochondrial Protein Import

The adverse effects of high environmental temperature exposure on animal reproductive functions have been concerned for many decades. However, the molecular basis of heat stress (HS)-induced decrease of sperm motility has not been entirely elucidated. We hypothesized that the deteriorate effects of HS may be mediated by damage of mitochondrial function and ATP synthesis. To test this hypothesis, we use mature boar sperm as model to explore the impacts of HS on mitochondrial function and sperm motility. A 6 h exposure to 42°C (HS) induced significant decrease in sperm progressive motility. Concurrently, HS induced mitochondrial dysfunction that is indicated by decreased of membrane potential, respiratory chain complex I and IV activities and adenosine triphosphate (ATP) contents. Exogenous ATP abolished this effect suggesting that reduced of ATP synthesis is the committed step in HS-induced reduction of sperm motility. At the molecular level, the mitochondrial protein contents were significantly decreased in HS sperm. Notably, the cytochrome c oxidase subunit 4, which was synthesized in cytoplasm and translocated into mitochondria, was significantly lower in mitochondria of HS sperm. Glycogen synthase kinase-3α (GSK3α), a negative regulator of sperm motility that is inactivated by Ser21 phosphorylation, was dephosphorylated after HS. The GSK3α inhibitor CHIR99021 was able to abolish the effects of HS on sperm and their mitochondria. Taken together, our results demonstrate that HS affects sperm motility through downregulation of mitochondrial activity and ATP synthesis yield, which involves dephosphorylation of GSK3α and interference of mitochondrial remodeling.

Phosphoproteomics reveals that glycogen synthase kinase-3 phosphorylates multiple splicing factors and is associated with alternative splicing

Glycogen synthase kinase-3 (GSK-3) is a constitutively active, ubiquitously expressed protein kinase that regulates multiple signaling pathways. In vitro kinase assays and genetic and pharmacological manipulations of GSK-3 have identified more than 100 putative GSK-3 substrates in diverse cell types. Many more have been predicted on the basis of a recurrent GSK-3 consensus motif ((pS/pT)XXX(S/T)), but this prediction has not been tested by analyzing the GSK-3 phosphoproteome. Using stable isotope labeling of amino acids in culture (SILAC) and MS techniques to analyze the repertoire of GSK-3-dependent phosphorylation in mouse embryonic stem cells (ESCs), we found that ∼2.4% of (pS/pT)XXX(S/T) sites are phosphorylated in a GSK-3-dependent manner. A comparison of WT and Gsk3a;Gsk3b knock-out (Gsk3 DKO) ESCs revealed prominent GSK-3-dependent phosphorylation of multiple splicing factors and regulators of RNA biosynthesis as well as proteins that regulate transcription, translation, and cell division. Gsk3 DKO reduced phosphorylation of the splicing factors RBM8A, SRSF9, and PSF as well as the nucleolar proteins NPM1 and PHF6, and recombinant GSK-3β phosphorylated these proteins in vitro RNA-Seq of WT and Gsk3 DKO ESCs identified ∼190 genes that are alternatively spliced in a GSK-3-dependent manner, supporting a broad role for GSK-3 in regulating alternative splicing. The MS data also identified posttranscriptional regulation of protein abundance by GSK-3, with ∼47 proteins (1.4%) whose levels increased and ∼78 (2.4%) whose levels decreased in the absence of GSK-3. This study provides the first unbiased analysis of the GSK-3 phosphoproteome and strong evidence that GSK-3 broadly regulates alternative splicing.

Developmental neurotoxicity of the hippocampus following in utero exposure to methylmercury: impairment in cell signaling

In this study, we assessed some hippocampal signaling cascades and behavioral impairments in 30-day-old rat pups prenatally exposed to methylmercury (MeHg). Pregnant rats were exposed to 1.0 or 2.0 mg/kg MeHg by gavage in alternated days from gestational day 5 until parturition. We found increased anxiety-like and decreased exploration behavior evaluated by open field test and deficit of both short- and long-term memories by novel object recognition task, respectively, in MeHg-treated pups. Downregulated PI3K/Akt/mTOR pathway and activated/hypophosphorylated (Ser9) GSK3β in MeHg-treated pups could be upstream of hyperphosphorylated Tau (Ser396) destabilizing microtubules and contributing to neural dysfunction in the hippocampus of these rats. Hyperphosphorylated/activated p38MAPK and downregulated phosphoErk1/2 support a role for mitogen-activated protein kinase (MAPK) cascade on MeHg neurotoxicity. Decreased receptor of advanced glycation end products (RAGE) immunocontent supports the assumption that downregulated RAGE/Erk1/2 pathway could be involved in hypophosphorylated lysine/serine/proline (KSP) repeats on neurofilament subunits and disturbed axonal transport. Downregulated myelin basic protein (MBP), the major myelin protein, is compatible with dysmyelination and neurofilament hypophosphorylation. Increased glial fibrillary acidic protein (GFAP) levels suggest reactive astrocytes, and active apoptotic pathways BAD/BCL-2, BAX/BCL-XL, and caspase 3 suggest cell death. Taken together, our findings get light on important signaling mechanisms that could underlie the behavioral deficits in 30-day-old pups prenatally exposed to MeHg.

In vivo regulation of glycogen synthase kinase 3β activity in neurons and brains

Glycogen synthase kinase 3β (GSK3β) is a multifunctional protein kinase involved in many cellular activities including development, differentiation and diseases. GSK3β is thought to be constitutively activated by autophosphorylation at Tyr216 and inactivated by phosphorylation at Ser9. The GSK3β activity has previously been evaluated by inhibitory Ser9 phosphorylation, but it does not necessarily indicate the kinase activity itself. Here, we applied the Phos-tag SDS-PAGE technique to the analysis of GSK3β phosphoisotypes in cells and brains. There were three phosphoisotypes of GSK3β; double phosphorylation at Ser9 and Tyr216, single phosphorylation at Tyr216 and the nonphosphorylated isotype. Active GSK3β with phosphorylation at Tyr216 represented half or more of the total GSK3β in cultured cells. Although levels of phospho-Ser9 were increased by insulin treatment, Ser9 phosphorylation occurred only in a minor fraction of GSK3β. In mouse brains, GSK3β was principally in the active form with little Ser9 phosphorylation, and the phosphoisotypes of GSK3β changed depending on the regions of the brain, age, sex and disease conditions. These results indicate that the Phos-tag SDS-PAGE method provides a simple and appropriate measurement of active GSK3β in vivo, and the activity is regulated by the mechanism other than phosphorylation on Ser9.

Molecular regulation and pharmacological targeting of the β-catenin destruction complex

The β‐catenin destruction complex is a dynamic cytosolic multiprotein assembly that provides a key node in Wnt signalling regulation. The core components of the destruction complex comprise the scaffold proteins axin and adenomatous polyposis coli and the Ser/Thr kinases casein kinase 1 and glycogen synthase kinase 3. In unstimulated cells, the destruction complex efficiently drives degradation of the transcriptional coactivator β‐catenin, thereby preventing the activation of the Wnt/β‐catenin pathway. Mutational inactivation of the destruction complex is a major pathway in the pathogenesis of cancer. Here, we review recent insights in the regulation of the β‐catenin destruction complex, including newly identified interaction interfaces, regulatory elements and post‐translationally controlled mechanisms. In addition, we discuss how mutations in core destruction complex components deregulate Wnt signalling via distinct mechanisms and how these findings open up potential therapeutic approaches to restore destruction complex activity in cancer cells.

Linked Articles

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc

The role of hypernitrosylation in the pathogenesis and pathophysiology of neuroprogressive diseases

There is a wealth of data indicating that de novo protein S-nitrosylation in general and protein transnitrosylation in particular mediates the bulk of nitric oxide signalling. These processes enable redox sensing and facilitate homeostatic regulation of redox dependent protein signalling, function, stability and trafficking. Increased S-nitrosylation in an environment of increasing oxidative and nitrosative stress (O&NS) is initially a protective mechanism aimed at maintaining protein structure and function. When O&NS becomes severe, mechanisms governing denitrosylation and transnitrosylation break down leading to the pathological state referred to as hypernitrosylation (HN). Such a state has been implicated in the pathogenesis and pathophysiology of several neuropsychiatric and neurodegenerative diseases and we investigate its potential role in the development and maintenance of neuroprogressive disorders. In this paper, we propose a model whereby the hypernitrosylation of a range of functional proteins and enzymes lead to changes in activity which conspire to produce at least some of the core abnormalities contributing to the development and maintenance of pathology in these illnesses.

GSK-3Beta-Dependent Activation of GEF-H1/ROCK Signaling Promotes LPS-Induced Lung Vascular Endothelial Barrier Dysfunction and Acute Lung Injury

The bacterial endotoxin or lipopolysaccharide (LPS) leads to the extensive vascular endothelial cells (EC) injury under septic conditions. Guanine nucleotide exchange factor-H1 (GEF-H1)/ROCK signaling not only involved in LPS-induced overexpression of pro-inflammatory mediator in ECs but also implicated in LPS-induced endothelial hyper-permeability. However, the mechanisms behind LPS-induced GEF-H1/ROCK signaling activation in the progress of EC injury remain incompletely understood. GEF-H1 localized on microtubules (MT) and is suppressed in its MT-bound state. MT disassembly promotes GEF-H1 release from MT and stimulates downstream ROCK-specific GEF activity. Since glycogen synthase kinase (GSK-3beta) participates in regulating MT dynamics under pathologic conditions, we examined the pivotal roles for GSK-3beta in modulating LPS-induced activation of GEF-H1/ROCK, increase of vascular endothelial permeability and severity of acute lung injury (ALI). In this study, we found that LPS induced human pulmonary endothelial cell (HPMEC) monolayers disruption accompanied by increase in GSK-3beta activity, activation of GEF-H1/ROCK signaling and decrease in beta-catenin and ZO-1 expression. Inhibition of GSK-3beta reduced HPMEC monolayers hyper-permeability and GEF-H1/ROCK activity in response to LPS. GSK-3beta/GEF-H1/ROCK signaling is implicated in regulating the expression of beta-catenin and ZO-1. In vivo, GSK-3beta inhibition attenuated LPS-induced activation of GEF-H1/ROCK pathway, lung edema and subsequent ALI. These findings present a new mechanism of GSK-3beta-dependent exacerbation of lung micro-vascular hyper-permeability and escalation of ALI via activation of GEF-H1/ROCK signaling and disruption of intracellular junctional proteins under septic condition.

α-Synuclein binds to the ER-mitochondria tethering protein VAPB to disrupt Ca2+ homeostasis and mitochondrial ATP production

α-Synuclein is strongly linked to Parkinson’s disease but the molecular targets for its toxicity are not fully clear. However, many neuronal functions damaged in Parkinson’s disease are regulated by signalling between the endoplasmic reticulum (ER) and mitochondria. This signalling involves close physical associations between the two organelles that are mediated by binding of the integral ER protein vesicle-associated membrane protein-associated protein B (VAPB) to the outer mitochondrial membrane protein, protein tyrosine phosphatase-interacting protein 51 (PTPIP51). VAPB and PTPIP51 thus act as a scaffold to tether the two organelles. Here we show that α-synuclein binds to VAPB and that overexpression of wild-type and familial Parkinson’s disease mutant α-synuclein disrupt the VAPB-PTPIP51 tethers to loosen ER–mitochondria associations. This disruption to the VAPB-PTPIP51 tethers is also seen in neurons derived from induced pluripotent stem cells from familial Parkinson’s disease patients harbouring pathogenic triplication of the α-synuclein gene. We also show that the α-synuclein induced loosening of ER–mitochondria contacts is accompanied by disruption to Ca²⁺ exchange between the two organelles and mitochondrial ATP production. Such disruptions are likely to be particularly damaging to neurons that are heavily dependent on correct Ca²⁺ signaling and ATP.

GSK3 and its interactions with the PI3K/AKT/mTOR signalling network

Glycogen Synthase Kinase-3 (GSK3 or GSK-3) is a promiscuous protein kinase and its phosphorylation of its diverse substrates has major influences on many areas of physiology and pathology, including cellular metabolism, lineage commitment and neuroscience. GSK3 was one of the first identified substrates of the heavily studied oncogenic kinase AKT, phosphorylation by which inhibits GSK3 activity via the formation of an autoinhibitory pseudosubstrate sequence. This has led to investigation of the role of GSK3 inhibition as a key component of the cellular responses to growth factors and insulin, which stimulate the class I PI 3-Kinases and in turn AKT activity and GSK3 phosphorylation. GSK3 has been shown to phosphorylate several upstream and downstream components of the PI3K/AKT/mTOR signalling network, including AKT itself, RICTOR, TSC1 and 2, PTEN and IRS1 and 2, with the potential to apply feedback control within the network. However, it has been clear for some time that functionally distinct, insulated pools of GSK3 exist which are regulated independently, so that for some GSK3 substrates such as β-catenin, phosphorylation by GSK3 is not controlled by input from PI3K and AKT. Instead, as almost all GSK3 substrates require a priming phosphorylated residue to be 4 amino acids C-terminal to the Ser/Thr phosphorylated by GSK3, the predominant form of regulation of the activity of GSK3 often appears to be through control over these priming events, specific to individual substrates. Therefore, a major role of GSK3 can be viewed as an amplifier of the electrostatic effects on protein function which are caused by these priming phosphorylation events. Here we discuss these different aspects to GSK3 regulation and function, and the functions of GSK3 as it integrates with signalling through the PI3K-AKT-mTOR signalling axis.

AKT/PKB Signaling: Navigating the Network

The Ser and Thr kinase AKT, also known as protein kinase B (PKB), was discovered 25 years ago and has been the focus of tens of thousands of studies in diverse fields of biology and medicine. There have been many advances in our knowledge of the upstream regulatory inputs into AKT, key multifunctional downstream signaling nodes (GSK3, FoxO, mTORC1), which greatly expand the functional repertoire of AKT, and the complex circuitry of this dynamically branching and looping signaling network that is ubiquitous to nearly every cell in our body. Mouse and human genetic studies have also revealed physiological roles for the AKT network in nearly every organ system. Our comprehension of AKT regulation and functions is particularly important given the consequences of AKT dysfunction in diverse pathological settings, including developmental and overgrowth syndromes, cancer, cardiovascular disease, insulin resistance and type 2 diabetes, inflammatory and autoimmune disorders, and neurological disorders. There has also been much progress in developing AKT-selective small molecule inhibitors. Improved understanding of the molecular wiring of the AKT signaling network continues to make an impact that cuts across most disciplines of the biomedical sciences.

Past and current perspective on new therapeutic targets for Type-II diabetes

Loss of pancreatic β-cell function is a hallmark of Type-II diabetes mellitus (DM). It is a chronic metabolic disorder that results from defects in both insulin secretion and insulin action. Recently, United Kingdom Prospective Diabetes Study reported that Type-II DM is a progressive disorder. Although, DM can be treated initially by monotherapy with oral agent; eventually, it may require multiple drugs. Additionally, insulin therapy is needed in many patients to achieve glycemic control. Pharmacological approaches are unsatisfactory in improving the consequences of insulin resistance. Single therapeutic approach in the treatment of Type-II DM is unsuccessful and usually a combination therapy is adopted. Increased understanding of biochemical, cellular and pathological alterations in Type-II DM has provided new insight in the management of Type-II DM. Knowledge of underlying mechanisms of Type-II DM development is essential for the exploration of novel therapeutic targets. Present review provides an insight into therapeutic targets of Type-II DM and their role in the development of insulin resistance. An overview of important signaling pathways and mechanisms in Type-II DM is provided for the better understanding of disease pathology. This review includes case studies of drugs that are withdrawn from the market. The experience gathered from previous studies and knowledge of Type-II DM pathways can guide the anti-diabetic drug development toward the discovery of clinically viable drugs that are useful in Type-II DM.

GSK3β attenuates TGF-β1 induced epithelial-mesenchymal transition and metabolic alterations in ARPE-19 cells

While TGF-β1 is known to induce epithelial-mesenchymal transition (EMT), a major factor in the pathogenesis of proliferative vitreoretinopathy (PVR), in ARPE-19 cells. The molecular pathways involved in EMT formation have not yet to be fully characterized. In this study, we have found that TGF-β1-mediated induction of EMT in ARPE-19 cells varied in a dose- and time-dependent manner. Specifically, TGF-β1 inhibited GSK-3β by accelerating phosphorylation at ser9. GSK-3β inhibitor or knockdown of GSK-3β resulted in enhanced TGF-β1-mediated EMT, migration and collagen contraction in ARPE-19 cells, which were then abrogated by GSK-3β overexpression and PI3K/AKT inhibitor. Importantly, GSK-3β also mediated metabolic reprogramming in TGF-β1-treated cells. Our results indicate that GSK-3β plays a pivotal role in TGF-β1-mediated EMT in ARPE-19 cells.

Effects of circadian clock genes and health-related behavior on metabolic syndrome in a Taiwanese population: Evidence from association and interaction analysis

Increased risk of developing metabolic syndrome (MetS) has been associated with the circadian clock genes. In this study, we assessed whether 29 circadian clock-related genes (including ADCYAP1, ARNTL, ARNTL2, BHLHE40, CLOCK, CRY1, CRY2, CSNK1D, CSNK1E, GSK3B, HCRTR2, KLF10, NFIL3, NPAS2, NR1D1, NR1D2, PER1, PER2, PER3, REV1, RORA, RORB, RORC, SENP3, SERPINE1, TIMELESS, TIPIN, VIP, and VIPR2) are associated with MetS and its individual components independently and/or through complex interactions in a Taiwanese population. We also analyzed the interactions between environmental factors and these genes in influencing MetS and its individual components. A total of 3,000 Taiwanese subjects from the Taiwan Biobank were assessed in this study. Metabolic traits such as waist circumference, triglyceride, high-density lipoprotein cholesterol, systolic and diastolic blood pressure, and fasting glucose were measured. Our data showed a nominal association of MetS with several single nucleotide polymorphisms (SNPs) in five key circadian clock genes including ARNTL, GSK3B, PER3, RORA, and RORB; but none of these SNPs persisted significantly after performing Bonferroni correction. Moreover, we identified the effect of GSK3B rs2199503 on high fasting glucose (P = 0.0002). Additionally, we found interactions among the ARNTL rs10832020, GSK3B rs2199503, PER3 rs10746473, RORA rs8034880, and RORB rs972902 SNPs influenced MetS (P < 0.001 ~ P = 0.002). Finally, we investigated the influence of interactions between ARNTL rs10832020, GSK3B rs2199503, PER3 rs10746473, and RORB rs972902 with environmental factors such as alcohol consumption, smoking status, and physical activity on MetS and its individual components (P < 0.001 ~ P = 0.002). Our study indicates that circadian clock genes such as ARNTL, GSK3B, PER3, RORA, and RORB genes may contribute to the risk of MetS independently as well as through gene-gene and gene-environment interactions.

Development of [18F]Maleimide-Based Glycogen Synthase Kinase-3β Ligands for Positron Emission Tomography Imaging

Dysregulation of glycogen synthase kinase-3β (GSK-3β) is implicated in the pathogenesis of neurodegenerative and psychiatric disorders. Thus, development of GSK-3β radiotracers for positron emission tomography (PET) imaging is of paramount importance, because such a noninvasive imaging technique would allow better understanding of the link between the activity of GSK-3β and central nervous system disorders in living organisms, and it would enable early detection of the enzyme's aberrant activity. Herein, we report the synthesis and biological evaluation of a series of fluorine-substituted maleimide derivatives that are high-affinity GSK-3β inhibitors. Radiosynthesis of a potential GSK-3β tracer [¹⁸F]10a is achieved. Preliminary in vivo PET imaging studies in rodents show moderate brain uptake, although no saturable binding was observed in the brain. Further refinement of the lead scaffold to develop potent [¹⁸F]-labeled GSK-3 radiotracers for PET imaging of the central nervous system is warranted.

EGb761 Ameliorates Neuronal Apoptosis and Promotes Angiogenesis in Experimental Intracerebral Hemorrhage via RSK1/GSK3β Pathway

Neuronal apoptosis after intracerebral hemorrhage (ICH) plays an essential role in neurological deterioration. Preclinical studies have shown that EGb761, an extract of Ginkgo biloba, is neuroprotective in some other neurological diseases with apoptosis. This study was conducted to investigate the potential neuroprotective effect of EGb761 on neuronal apoptosis in experimental ICH. A model of ICH was induced in C57BL/6 mice by injecting collagenase. EGb761 was administered for 21 days and neurologic behaviors were assessed at 1, 3, 7, 14, and 21 days after ICH. RNAi-mediated knockdown of p90 ribosomal S6 kinase 1 (RSK1) was used to further investigate the role of RSK1 in EGb761-induced neuroprotective effects. Neuronal death was determined by TUNEL staining. The image datasets of neurovascular networks were acquired via micro-optical sectioning tomography (MOST). The glycogen synthase kinase-3β (GSK3β) activity was assayed using commercial kit. Primary cultured cortical neurons were exposed to ferrous iron and treated with EGb761. Apoptotic neurons were counted by flow cytometry. RSK1, GSK3β, phosphorylated-GSK3β (pGSK3β), Bcl2, Bax, cleaved-caspase3 (CC3), and VEGF were measured by Western blot. The pGSK3β was also detected by immunofluorescence staining. We found that mice in EGb761 group performed better on rotarod test. Reduced TUNEL-positive neurons and richer microvascular networks were observed in mice treated with EGb761. EGb761 attenuates neuronal apoptosis induced by ferrous iron counted by flow cytometry in vitro. Decreased GSK3β activity was observed in EGb761-treated mice compared with mice with ICH. EGb761 increased the expression of pGSK3β (Ser9), RSK1 and the Bcl2/Bax ratio, and VEGF and decreased CC3 expression. In conclusion, EGb761 reduces neuronal apoptosis and promotes angiogenesis in experimental intracerebral hemorrhage via RSK1/GSK3β pathway.

RhoA GTPase oxidation stimulates cell proliferation via nuclear factor-κB activation

Reactive oxygen species (ROS) produced by many kinds of stimuli are essential for cellular signaling including cell proliferation. The dysregulation of ROS, therefore, is related to a variety of diseases including cancer. However, it was not clearly elucidated how ROS regulate cell proliferation and tumorigenesis. In this study, we investigated a mechanism by which the oxidation of RhoA GTPase regulates nuclear factor-κB (NF-κB) and cell proliferation. Hydrogen peroxide activated NF-κB and RhoA GTPase, but did not activate RhoA C16/20A mutant, an oxidation-resistant form. Remarkably, the oxidation of RhoA reduced its affinity towards RhoGDI, leading to the dissociation of RhoA-RhoGDI complex. Si-Vav2, a guanine nucleotide exchange factor (GEF), inhibited RhoA activation upon hydrogen peroxide. The oxidized RhoA (oxRhoA)-GTP was readily bound to IκB kinase γ (IKKγ), whereas oxidized RhoGDI did not bind to IKKγ. The oxRhoA-GTP bound to IKKγ activated IKKβ, leading to IκB phosphorylation and degradation, consequently NF-κB activation. Hydrogen peroxide induced cell proliferation, but RhoA C16/20A mutant suppressed cell proliferation and tumorigenesis. Conclusively, RhoA oxidation at Cys16/20 is critically involved in cell proliferation and tumorigenesis through NF-κB activation in response to ROS.

Inhibition of Glycogen Synthase Kinase 3 Accelerated Liver Regeneration after Acetaminophen-Induced Hepatotoxicity in Mice

Overdose of acetaminophen (APAP) is the leading cause of acute liver failure (ALF) in the United States. Timely initiation of compensatory liver regeneration after APAP hepatotoxicity is critical for final recovery, but the mechanisms of liver regeneration after APAP-induced ALF have not been extensively explored yet. Previous studies from our laboratory have demonstrated that activation of β-catenin signaling after APAP overdose is associated with timely liver regeneration. Herein, we investigated the role of glycogen synthase kinase 3 (GSK3) in liver regeneration after APAP hepatotoxicity using a pharmacological inhibition strategy in mice. Treatment with specific GSK3 inhibitor (L803-mts), starting from 4 hours after 600 mg/kg dose of APAP, resulted in early initiation of liver regeneration in a dose-dependent manner, without modifying the peak regenerative response. Acceleration of liver regeneration was not secondary to alteration of APAP-induced hepatotoxicity, which remained unchanged after GSK3 inhibition. Early cell cycle initiation in hepatocytes after GSK3 inhibition was because of rapid induction of cyclin D1 and phosphorylation of retinoblastoma protein. This was associated with increased activation of β-catenin signaling after GSK3 inhibition. Taken together, our study has revealed a novel role of GSK3 in liver regeneration after APAP overdose and identified GSK3 as a potential therapeutic target to improve liver regeneration after APAP-induced ALF.

Molecular Pathways: Revisiting Glycogen Synthase Kinase-3β as a Target for the Treatment of Cancer

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine protein kinase, is a complex regulator of numerous cellular functions. GSK-3β is a unique kinase which is constitutively active in resting and nonstimulated cells. GSK-3β has been implicated in a wide range of diseases including neurodegeneration, inflammation and fibrosis, noninsulin-dependent diabetes mellitus, and cancer. It is a regulator of NF-κB-mediated survival of cancer cells, which provided a rationale for the development of GSK-3 inhibitors targeting malignant tumors. Recent studies, many of them reported over the past decade, have identified GSK-3β as a potential therapeutic target in more than 15 different types of cancer. Whereas only active GSK-3β is expressed in cancer cell nucleus, aberrant nuclear accumulation of GSK-3β has been identified as a hallmark of cancer cells in malignant tumors of different origin. This review focuses on the preclinical and clinical development of GSK-3 inhibitors and the potential therapeutic impact of targeting GSK-3β in human cancer. Clin Cancer Res; 23(8); 1891-7. ©2017 AACR.

Infections: A Possible Risk Factor for Type 2 Diabetes

Diabetes mellitus is one of the biggest challenges to human health globally, with an estimated 95% of the global diabetic population having type 2 diabetes. Classical causes for type 2 diabetes, such as genetics and obesity, do not account for the high incidence of the disease. Recent data suggest that infections may precipitate insulin resistance via multiple mechanisms, such as the proinflammatory cytokine response, the acute-phase response, and the alteration of the nutrient status. Even pathogen products, such as lipopolysaccharide and peptidoglycans, can be diabetogenic. Therefore, we argue that infections that are known to contribute to insulin resistance should be considered as risk factors for type 2 diabetes.

GSK-3β and MMP-9 Cooperate in the Control of Dendritic Spine Morphology

Changes in the morphology of dendritic spines are prominent during learning and in different neurological and neuropsychiatric diseases, including those in which glycogen synthase kinase-3β (GSK-3β) has been implicated. Despite much evidence of the involvement of GSK-3β in functional synaptic plasticity, it is unclear how GSK-3β controls structural synaptic plasticity (i.e., the number and shape of dendritic spines). In the present study, we used two mouse models overexpressing and lacking GSK-3β in neurons to investigate how GSK-3β affects the structural plasticity of dendritic spines. Following visualization of dendritic spines with DiI dye, we found that increasing GSK-3β activity increased the number of thin spines, whereas lacking GSK-3β increased the number of stubby spines in the dentate gyrus. Under conditions of neuronal excitation, increasing GSK-3β activity caused higher activity of extracellularly acting matrix metalloproteinase-9 (MMP-9), and MMP inhibition normalized thin spines in GSK-3β overexpressing mice. Administration of the nonspecific GSK-3β inhibitor lithium in animals with active MMP-9 and animals lacking MMP-9 revealed that GSK-3β and MMP-9 act in concert to control dendritic spine morphology. Altogether, our data demonstrate that the dysregulation of GSK-3β activity has dramatic consequences on dendritic spine morphology, implicating MMP-9 as a mediator of GSK-3β-induced synaptic alterations.

Neuroprotective Effects of Exercise Treatments After Injury: The Dual Role of Neurotrophic Factors

BACKGROUND

Shared connections between physical activity and neuroprotection have been studied for decades, but the mechanisms underlying this effect of specific exercise were only recently brought to light. Several evidences suggest that physical activity may be a reasonable and beneficial method to improve functional recovery in both peripheral and central nerve injuries and to delay functional decay in neurodegenerative diseases. In addition to improving cardiac and immune functions, physical activity may represent a multifunctional approach not only to improve cardiocirculatory and immune functions, but potentially modulating trophic factors signaling and, in turn, neuronal function and structure at times that may be critical for neurodegeneration and regeneration.

METHODS

Research content related to the effects of physical activity and specific exercise programs in normal and injured nervous system have been reviewed.

RESULTS

Sustained exercise, particularly if applied at moderate intensity and early after injury, exerts anti-inflammatory and pro-regenerative effects, and may boost cognitive and motor functions in aging and neurological disorders. However, newest studies show that exercise modalities can differently affect the production and function of brain-derived neurotrophic factor and other neurotrophins involved in the generation of neuropathic conditions. These findings suggest the possibility that new exercise strategies can be directed to nerve injuries with therapeutical benefits.

CONCLUSION

Considering the growing burden of illness worldwide, understanding of how modulation of neurotrophic factors contributes to exercise-induced neuroprotection and regeneration after peripheral nerve and spinal cord injuries is a relevant topic for research, and represents the beginning of a new non-pharmacological therapeutic approach for better rehabilitation of neural disorders.

Modulation of glycogen synthase kinase-3β following TRAIL combinatorial treatment in cancer cells

Glycogen Synthase Kinase-3β (GSK3β) is a serine/threonine kinase, known to regulate various cellular processes including proliferation, differentiation, survival, apoptosis as well as TRAIL-resistance. Thus pathways that can modulate GSK3β axis are important targets for cancer drug development. Our earlier studies have shown that combinatorial treatment with Troglitazone (TZD) and TRAIL can induce apoptosis in TRAIL-resistant cancer cells. The current studies were undertaken to investigate whether GSK3β pathway was modulated during this apoptosis. Our results indicated an increase in inhibitory GSK3β^Ser9 phosphorylation during apoptosis, mediated via AKT. At a later time, however, TZD alone and TRAIL-TZD combination produced a dramatic reduction of GSK3β expression, which was abolished by cycloheximide. Luciferase assays with GSK3β-luc promoter reporter showed that TZD can effectively antagonize GSK3β promoter activity. Since TZD is a ligand for transcription factor PPARγ and can activate AMPK, we determined their roles on antagonism of GSK3β. Knockdown of PPARγ was unable to restore GSK3β expression or antagonize GSK3β^Ser9 phosphorylation. Although pretreatment with Compound C (pharmacological inhibitor of AMPK) partially rescued GSK3β expression, knockdown of AMPKα1 or α2 alone or in combination were ineffective. These studies suggested a novel PPARγ-AMPK-independent mechanism of targeting GSK3β by TZD, elucidation of which might provide newer insights to improve our understanding of TRAIL-resistance.

The redox sensitive glycogen synthase kinase 3β suppresses the self-protective antioxidant response in podocytes upon oxidative glomerular injury

The redox sensitive glycogen synthase kinase (GSK) 3 has been recently implicated in the pathogenesis of proteinuric glomerulopathy. However, prior studies are less conclusive because they relied solely on chemical inhibitors of GSK3, which provide poor discrimination between the isoforms of GSK3 apart from potential off target activities. In murine kidneys, the β rather than the α isoform of GSK3 was predominantly expressed in glomeruli and distributed intensely in podocytes. By employing the doxycycline-activated Cre-loxP site specific gene targeting system, GSK3β was successfully knocked out (KO) selectively in podocytes in adult mice, resulting in a phenotype no different from control littermates. Electron microscopy of glomeruli in KO mice demonstrated more glycogen accumulation in podocytes but otherwise normal ultrastructures. Upon oxidative glomerular injury induced by protein overload, KO mice excreted significantly less albuminuria and had much attenuated podocytopathy and glomerular damage. The anti-proteinuric and glomerular protective effect was concomitant with diminished accumulation of reactive oxygen species in glomeruli in KO mice, which was likely secondary to a reinforced Nrf2 antioxidant response in podocytes. Collectively, our data suggest that GSK3β is dispensable for glomerular function and histology under normal circumstances but may serve as a therapeutic target for protecting from oxidative glomerular injuries.

2,5-Dimethylcelecoxib prevents pressure-induced left ventricular remodeling through GSK-3 activation

Glycogen synthase kinase-3 (GSK-3) is a crucial regulator of cardiac hypertrophy. We previously reported that 2,5-dimethylcelecoxib (DM-celecoxib), a celecoxib derivative unable to inhibit cyclooxygenase-2, prevented cardiac remodeling by activating GSK-3, resulting in lifespan prolongation in a mouse model of genetic dilated cardiomyopathy. In the present study, we investigated whether DM-celecoxib can also prevent pressure-induced cardiac remodeling and heart failure, elicited by transverse aortic constriction (TAC). Before testing the effects of DM-celecoxib, we compared the effects of TAC on the hearts of wild-type and GSK-3β hetero-deficient (GSK-3β^+/-) mice to determine the role of GSK-3 in cardiac remodeling and heart failure. GSK-3β^+/- mouse hearts exhibited more severe hypertrophy, which was characterized by accelerated interstitial fibrosis, than wild-type mouse hearts after TAC, suggesting that reduced GSK-3β activity aggravates pressure-induced left ventricular remodeling. We subsequently examined the effects of DM-celecoxib on TAC-induced cardiac remodeling. DM-celecoxib inhibited left ventricular systolic functional deterioration, and prevented left ventricular hypertrophy and fibrosis. It also activated GSK-3α and β by inhibiting Akt, suppressing the activity of β-catenin and nuclear factor of activated T-cells and thereby decreasing the expression of the Wnt/β-catenin target gene products fibronectin and matrix metalloproteinase-2. These results suggest that DM-celecoxib is clinically useful for treating pressure-induced heart diseases.

ALS/FTD-associated FUS activates GSK-3β to disrupt the VAPB-PTPIP51 interaction and ER-mitochondria associations

Defective FUS metabolism is strongly associated with amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD), but the mechanisms linking FUS to disease are not properly understood. However, many of the functions disrupted in ALS/FTD are regulated by signalling between the endoplasmic reticulum (ER) and mitochondria. This signalling is facilitated by close physical associations between the two organelles that are mediated by binding of the integral ER protein VAPB to the outer mitochondrial membrane protein PTPIP51, which act as molecular scaffolds to tether the two organelles. Here, we show that FUS disrupts the VAPB-PTPIP51 interaction and ER-mitochondria associations. These disruptions are accompanied by perturbation of Ca(2+) uptake by mitochondria following its release from ER stores, which is a physiological read-out of ER-mitochondria contacts. We also demonstrate that mitochondrial ATP production is impaired in FUS-expressing cells; mitochondrial ATP production is linked to Ca(2+) levels. Finally, we demonstrate that the FUS-induced reductions to ER-mitochondria associations and are linked to activation of glycogen synthase kinase-3β (GSK-3β), a kinase already strongly associated with ALS/FTD.