Glycogen Synthase Kinase-3 Isoforms Research Articles

Cardiac fibroblast GSK-3α aggravates ischemic cardiac injury by promoting fibrosis, inflammation, and impairing angiogenesis.

Myocardial infarction (MI) is the leading cause of death worldwide. Glycogen synthase kinase-3 (GSK-3) has been considered to be a promising therapeutic target for cardiovascular diseases. GSK-3 is a family of ubiquitously expressed serine/threonine kinases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Previously, our group identified that cardiac fibroblast (FB) GSK-3β acts as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of FB-GSK-3α in MI pathology is not defined. To determine the role of FB-GSK-3α in MI-induced adverse cardiac remodeling, GSK-3α was deleted specifically in the residential fibroblast or myofibroblast (MyoFB) using tamoxifen (TAM) inducible Tcf21 or Periostin (Postn) promoter-driven Cre recombinase, respectively. Echocardiographic analysis revealed that FB- or MyoFB-specific GSK-3α deletion prevented the development of dilative remodeling and cardiac dysfunction. Morphometrics and histology studies confirmed improvement in capillary density and a remarkable reduction in hypertrophy and fibrosis in the KO group. We harvested the hearts at 4weeks post-MI and analyzed signature genes of adverse remodeling. Specifically, qPCR analysis was performed to examine the gene panels of inflammation (TNFα, IL-6, IL-1β), fibrosis (COL1A1, COL3A1, COMP, Fibronectin-1, Latent TGF-β binding protein 2), and hypertrophy (ANP, BNP, MYH7). These molecular markers were essentially normalized due to FB-specific GSK-3α deletion. Further molecular studies confirmed that FB-GSK-3α could regulate NF-kB activation and expression of angiogenesis-related proteins. Our findings suggest that FB-GSK-3α plays a critical role in the pathological cardiac remodeling of ischemic hearts, therefore, it could be therapeutically targeted.

In Silico-Motivated Discovery of Novel Potent Glycogen Synthase-3 Inhibitors: 1-(Alkyl/arylamino)-3H-naphtho[1,2,3-de]quinoline-2,7-dione Identified as a Scaffold for Kinase Inhibitor Development.

Glycogen synthase kinase-3 (GSK-3) isoforms α and β have diverse roles within cell biology, and have been linked with multiple diseases that include prominent CNS conditions such as Alzheimer's disease and several psychiatric disorders. In this study, motivated by computation, we aimed to identify novel ATP-binding site inhibitors of GSK-3 with CNS-active potential. A ligand screening (docking) protocol against GSK-3β was first optimized, employing an active/decoy benchmarking set, with the final protocol selected based on statistical performance analysis. The optimized protocol involved pre-filtering of ligands using a three-point 3D-pharmacophore, followed by Glide-SP docking applying hinge region hydrogen bonding constraints. Using this approach, the Biogenic subset of the ZINC15 compound database was screened, focused on compounds with potential for CNS-activity. Twelve compounds (generation I) were selected for experimental validation using in vitro GSK-3β binding assays. Two hit compounds, 1 and 2, with 6-amino-7H-benzo[e]perimidin-7-one and 1-(phenylamino)-3H-naphtho[1,2,3-de]quinoline-2,7-dione type scaffolds were identified with IC50 values of 1.63 µM and 20.55 µM, respectively. Ten analogues of 2 (generation II) were selected for structure activity relationship (SAR) analysis and revealed four low micromolar inhibitors (<10 µM), with 19 (IC50 = 4.1 µM)~five times more potent than initial hit compound 2. Selectivity screening of low micromolar inhibitors 14 and 19 (comparing aryl- and alkyl-substituents) against 10 homologous kinases revealed unique selectivity profiles, with both compounds more potent against the GSK-3α isoform (IC50s~2 µM) and, additionally, inhibitors of PKBβ (IC50s < 25 µM). Compound 14 also inhibited ERK2 and 19, PKCγ, but generally good selectivity for GSK-3 isoforms over the other kinases was observed. The compounds had excellent predicted oral bioavailability and CNS-activity profiles, presenting promising candidates for future testing in cellular models of disease.

Fibroblast GSK-3α Promotes Fibrosis via RAF-MEK-ERK Pathway in the Injured Heart.

Heart failure is the leading cause of mortality, morbidity, and health care expenditures worldwide. Numerous studies have implicated GSK-3 (glycogen synthase kinase-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms seem to play overlapping, unique and even opposing functions in the heart. Previously, we have shown that of the 2 isoforms of GSK-3, cardiac fibroblast GSK-3β acts as a negative regulator of myocardial fibrosis in the ischemic heart. However, the role of cardiac fibroblast-GSK-3α in the pathogenesis of cardiac diseases is completely unknown. To define the role of cardiac fibroblast-GSK-3α in myocardial fibrosis and heart failure, GSK-3α was deleted from fibroblasts or myofibroblasts with tamoxifen-inducible Tcf21- or Postn-promoter-driven Cre recombinase. Control and GSK-3α KO mice were subjected to cardiac injury and heart parameters were evaluated. The fibroblast kinome mapping was carried out to delineate molecular mechanism followed by in vivo and in vitro analysis. Fibroblast-specific GSK-3α deletion restricted fibrotic remodeling and preserved function of the injured heart. We observed reductions in cell migration, collagen gel contraction, α-SMA protein levels, and expression of ECM genes in TGFβ1-treated KO fibroblasts, indicating that GSK-3α is required for myofibroblast transformation. Surprisingly, GSK-3α deletion did not affect SMAD3 activation, suggesting the profibrotic role of GSK-3α is SMAD3 independent. The molecular studies confirmed decreased ERK signaling in GSK-3α-KO CFs. Conversely, adenovirus-mediated expression of a constitutively active form of GSK-3α (Ad-GSK-3αS21A) in fibroblasts increased ERK activation and expression of fibrogenic proteins. Importantly, this effect was abolished by ERK inhibition. GSK-3α-mediated MEK-ERK activation is a critical profibrotic signaling circuit in the injured heart, which operates independently of the canonical TGF-β1-SMAD3 pathway. Therefore, strategies to inhibit the GSK-3α-MEK-ERK signaling circuit could prevent adverse fibrosis in diseased hearts.

Abstract EC106: Cardiac Fibroblast GSK-3α Aggravates Ischemic Cardiac Injury By Promoting Fibrosis, Inflammation, And Impairing Angiogenesis

Background: Myocardial Infarction (MI) is the leading cause of death worldwide. Numerous studies from our lab and others have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 is a family of ubiquitously expressed serine/threonine kinases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Previously our group has identified that cardiac fibroblast (CF) GSK-3β acts as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK-3α in MI-induced adverse cardiac remodeling is not defined. Methods and Results: To determine the role of CF-GSK-3α in MI-induced adverse cardiac remodeling, GSK-3α was deleted specifically in the activated fibroblast/myofibroblast using tamoxifen (TAM)-inducible Periostin promoter-driven Cre recombinase system. At 12 weeks of age, mice were fed with TAM diet. After 1 week of TAM treatment, control (GSK-3α fl/fl Cre -/- ) and KO (GSK-3α fl/fl Cre +/- ) mice were subjected to permanent LAD ligation (MI) surgery. Echocardiographic analysis revealed that control mice developed severe systolic dysfunction and dilative cardiac remodeling post-MI. These MI-induced pathologies were remarkably prevented by myofibroblast-specific GSK-3α deletion. To further confirm the role of CF-GSK-3α in processes contributing to cardiac remodeling, we harvested the hearts at 4 weeks post-MI and analyzed signature genes of adverse remodeling. Specifically, qPCR analysis was performed to examine the gene panels of inflammation (TNFα, IL-6, IL-1β), fibrosis (COL1A1, COL3A1, COMP), and angiogenesis (VEGFR2, CD31, HIF-1α). As expected, ischemic injury induced the expression of inflammation and fibrosis-related genes in the control group. In contrast, CF-GSK-3α KO hearts did not display any of these hallmarks. Another critical feature of adverse cardiac remodeling is impaired angiogenesis. Indeed, the CF-GSK-3α KO hearts were protected from MI-induced reduction in angiogenesis-related genes. Taken together, our findings support a driving role of CF-GSK-3α in MI-induced adverse cardiac remodeling. Conclusion: Our findings suggest a critical role of CF-GSK-3α in pathological cardiac remodeling and heart failure that could be therapeutically targeted for future clinical applications.

Pathobiology and Therapeutic Relevance of GSK-3 in Chronic Hematological Malignancies.

Glycogen synthase kinase-3 (GSK-3) is an evolutionarily conserved, ubiquitously expressed, multifunctional serine/threonine protein kinase involved in the regulation of a variety of physiological processes. GSK-3 comprises two isoforms (α and β) which were originally discovered in 1980 as enzymes involved in glucose metabolism via inhibitory phosphorylation of glycogen synthase. Differently from other proteins kinases, GSK-3 isoforms are constitutively active in resting cells, and their modulation mainly involves inhibition through upstream regulatory networks. In the early 1990s, GSK-3 isoforms were implicated as key players in cancer cell pathobiology. Active GSK-3 facilitates the destruction of multiple oncogenic proteins which include β-catenin and Master regulator of cell cycle entry and proliferative metabolism (c-Myc). Therefore, GSK-3 was initially considered to be a tumor suppressor. Consistently, GSK-3 is often inactivated in cancer cells through dysregulated upstream signaling pathways. However, over the past 10–15 years, a growing number of studies highlighted that in some cancer settings GSK-3 isoforms inhibit tumor suppressing pathways and therefore act as tumor promoters. In this article, we will discuss the multiple and often enigmatic roles played by GSK-3 isoforms in some chronic hematological malignancies (chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, and B-cell non-Hodgkin’s lymphomas) which are among the most common blood cancer cell types. We will also summarize possible novel strategies targeting GSK-3 for innovative therapies of these disorders.

Glycogen Synthase Kinase-3 Isoform Variants and Their Inhibitory Phosphorylation in Human Testes and Spermatozoa.

To clarify (phospho-) glycogen synthase kinase-3 (GSK3) isoform variants in the germline and soma of human testes and spermatozoa. GSK3 isoform variants in normospermatogenic and Sertoli cell-only (SCO) testicular biopsies and spermatozoa were examined. In normospermatogenic testes, GSK3α and GSK3β variants 1 and 2 different in low complexity region (LCR) were expressed and their levels were decreased in SCO testes. GSK3β variant 3 was only expressed in SCO testes. GSK3β as well as GSK3α, the dominant isoforms in testes were decreased in SCO testes. In normospermatogenic testes, GSK3β were found in spermatogonia and markedly decreased in meiotic germ cells in which GSK3α was dominant. p-GSK3α/β were marginal in spermatogonia and early spermatocytes. In SCO testes, GSK3α/β immunoreactivity in seminiferous epithelia was weaker than those of normospermatogenic testes whereas p-GSK3α/β(Ser) immunoreactivity was visibly increased in Sertoli cells. GSK3α was dominant in ejaculated spermatozoa in which GSK3α and p-GSK3α(Ser) were found in the head, midpiece, and tail. In acrosome-reacted spermatozoa, GSK3α was found in the equatorial region of head, midpiece, and tail, and p-GSK3α(Ser) was only found in midpiece. During sperm capacitation, p-GSK3α(Ser) was significantly increased together with phosphotyrosine proteins and motility. In human male germ cells, GSK3 isoforms different in LCRs switch from GSK3β to GSK3α during meiotic entry, suggesting the isoform-specific roles of GSK3α and GSK3β in meiosis and stemness or proliferation of spermatogonia, respectively. In dormant Sertoli cells of SCO testes kinase activity of GSK3 might be downregulated via inhibitory phosphorylation. In spermatozoa, inhibitory phosphorylation of GSK3α might be coupled with activation of motility during capacitation.

Underlying mechanisms of glucocorticoid-induced \u03b2-cell death and dysfunction: a new role for glycogen synthase kinase 3

Glucocorticoids (GCs) are widely prescribed for their anti-inflammatory and immunosuppressive properties as a treatment for a variety of diseases. The use of GCs is associated with important side effects, including diabetogenic effects. However, the underlying mechanisms of GC-mediated diabetogenic effects in β-cells are not well understood. In this study we investigated the role of glycogen synthase kinase 3 (GSK3) in the mediation of β-cell death and dysfunction induced by GCs. Using genetic and pharmacological approaches we showed that GSK3 is involved in GC-induced β-cell death and impaired insulin secretion. Further, we unraveled the underlying mechanisms of GC-GSK3 crosstalk. We showed that GSK3 is marginally implicated in the nuclear localization of GC receptor (GR) upon ligand binding. Furthermore, we showed that GSK3 regulates the expression of GR at mRNA and protein levels. Finally, we dissected the proper contribution of each GSK3 isoform and showed that GSK3β isoform is sufficient to mediate the pro-apoptotic effects of GCs in β-cells. Collectively, in this work we identified GSK3 as a viable target to mitigate GC deleterious effects in pancreatic β-cells.

Glycogen synthesis and beyond, a comprehensive review of GSK3 as a key regulator of metabolic pathways and a therapeutic target for treating metabolic diseases.

Glycogen synthase kinase‐3 (GSK3) is a highly evolutionarily conserved serine/threonine protein kinase first identified as an enzyme that regulates glycogen synthase (GS) in response to insulin stimulation, which involves GSK3 regulation of glucose metabolism and energy homeostasis. Both isoforms of GSK3, GSK3α, and GSK3β, have been implicated in many biological and pathophysiological processes. The various functions of GSK3 are indicated by its widespread distribution in multiple cell types and tissues. The studies of GSK3 activity using animal models and the observed effects of GSK3‐specific inhibitors provide more insights into the roles of GSK3 in regulating energy metabolism and homeostasis. The cross‐talk between GSK3 and some important energy regulators and sensors and the regulation of GSK3 in mitochondrial activity and component function further highlight the molecular mechanisms in which GSK3 is involved to regulate the metabolic activity, beyond its classical regulatory effect on GS. In this review, we summarize the specific roles of GSK3 in energy metabolism regulation in tissues that are tightly associated with energy metabolism and the functions of GSK3 in the development of metabolic disorders. We also address the impacts of GSK3 on the regulation of mitochondrial function, activity and associated metabolic regulation. The application of GSK3 inhibitors in clinical tests will be highlighted too. Interactions between GSK3 and important energy regulators and GSK3‐mediated responses to different stresses that are related to metabolism are described to provide a brief overview of previously less‐appreciated biological functions of GSK3 in energy metabolism and associated diseases through its regulation of GS and other functions.

GSK-3: a multifaceted player in acute leukemias.

Glycogen synthase kinase 3 (GSK-3) consists of two isoforms (α and β) that were originally linked to glucose metabolism regulation. However, GSK-3 is also involved in several signaling pathways controlling many different key functions in healthy cells. GSK-3 is a unique kinase in that its isoforms are constitutively active, while they are inactivated mainly through phosphorylation at Ser residues by a variety of upstream kinases. In the early 1990s, GSK-3 emerged as a key player in cancer cell pathophysiology. Since active GSK-3 promotes destruction of multiple oncogenic proteins (e.g., β-catenin, c-Myc, Mcl-1) it was considered to be a tumor suppressor. Accordingly, GSK-3 is frequently inactivated in human cancer via aberrant regulation of upstream signaling pathways. More recently, however, it has emerged that GSK-3 isoforms display also oncogenic properties, as they up-regulate pathways critical for neoplastic cell proliferation, survival, and drug-resistance. The regulatory roles of GSK-3 isoforms in cell cycle, apoptosis, DNA repair, tumor metabolism, invasion, and metastasis reflect the therapeutic relevance of these kinases and provide the rationale for combining GSK-3 inhibitors with other targeted drugs. Here, we discuss the multiple and often conflicting roles of GSK-3 isoforms in acute leukemias. We also review the current status of GSK-3 inhibitor development for innovative leukemia therapy.

GSK3α, not GSK3β, drives hippocampal NMDAR-dependent LTD via tau-mediated spine anchoring.

Glycogen synthase kinase-3 (GSK3) is an important signalling protein in the brain and modulates different forms of synaptic plasticity. Neuronal functions of GSK3 are typically attributed to one of its two isoforms, GSK3β, simply because of its prevalent expression in the brain. Consequently, the importance of isoform-specific functions of GSK3 in synaptic plasticity has not been fully explored. We now directly address this question for NMDA receptor-dependent long-term depression (LTD) in the hippocampus. Here, we specifically target the GSK3 isoforms with shRNA knock-down in mouse hippocampus and with novel isoform-selective drugs to dissect their roles in LTD. Using electrophysiological and live imaging approaches, we find that GSK3α, but not GSK3β, is required for LTD. The specific engagement of GSK3α occurs via its transient anchoring in dendritic spines during LTD induction. We find that the major GSK3 substrate, the microtubule-binding protein tau, is required for this spine anchoring of GSK3α and mediates GSK3α-induced LTD. These results link GSK3α and tau in a common mechanism for synaptic depression and rule out a major role for GSK3β in this process.

Abstract 285: High Throughput Profiling of Gsk3α Regulated Fibroblast Kinome Reveals Raf as a Mediator of Fibrosis in Failing Heart

Background: Heart failure is the leading cause of mortality, morbidity, and healthcare expenditures worldwide. Numerous studies have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Recently our group has identified cardiac fibroblast (CF) GSK3β as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK3α in cardiac pathophysiology is unknown. Methods and Results: GSK3α was deleted specifically from cardiac fibroblasts or myofibroblasts with tamoxifen-inducible TCF21- or periostin- promoter-driven Cre recombinase. At 2 months of age, WT and KO mice were subjected to cardiac injury, and heart functions were monitored by serial echocardiography. Histological analysis and morphometric studies were performed at 8 weeks post-injury. In both settings, GSK3α deletion restricted fibrotic remodeling and improved cardiac function. To investigate underlying mechanisms, we examined the effect of GSK3α deletion on myofibroblast transformation and pro-fibrotic TGFβ1-SMAD3 signaling in vitro . WT and KO mouse embryonic fibroblasts (MEFs) were treated with TGFβ1. Indeed, a significant reduction in cell migration, collagen gel contraction, and α-SMA expression in TGFβ1 treated KO MEFs confirmed that GSK3α is required for myofibroblast transformation. Surprisingly, GSK3α deletion had no effect on SMAD3 activation, indicating the pro-fibrotic role of GSK3α is SMAD3 independent. At 4 weeks post-injury, total proteins were isolated from CFs of WT and KO animals, and kinome profiling was performed by utilizing PamStation®12 high throughput microarray platform. The upstream kinase analysis identified the downregulation of RAF family kinase activity in GSK3α-KO-CFs. Moreover, mapping of significantly altered kinases against literature annotated interactions generated ERK-centric networks. These findings are consistent with previous studies that implicated ERK in fibrotic diseases across multiple organs. Conclusion: CF-GSK3α plays a causal role in the cardiac pathophysiology that could be therapeutically targeted for future clinical applications.

Modulated Expression of the Protein Kinase GSK3 in Motor and Dopaminergic Neurons Increases Female Lifespan in Drosophila melanogaster.

Most eukaryotic genes express multiple transcripts and proteins, and a sophisticated gene expression strategy plays a crucial role in ensuring the cell-specificity of genetic information and the correctness of phenotypes. The Drosophila melanogaster gene shaggy encodes several isoforms of the conserved glycogen synthase kinase 3 (GSK3), which is vitally important for multiple biological processes. To characterize the phenotypic effects of differential shaggy expression, we explored how the multidirectional modulation of the expression of the main GSK3 isoform, Shaggy-PB, in different tissues and cells affects lifespan. To this end, we used lines with transgenic constructs that encode mutant variants of the protein. The effect of shaggy misexpression on lifespan depended on the direction of the presumed change in GSK3 activity and the type of tissue/cell. The modulation of GSK3 activity in motor and dopaminergic neurons improved female lifespan but caused seemingly negative changes in the structural (mitochondrial depletion; neuronal loss) and functional (perturbed locomotion) properties of the nervous system, indicating the importance of analyzing the relationship between lifespan and healthspan in invertebrate models. Our findings provide new insights into the molecular and cellular bases of lifespan extension, demonstrating that the fine-tuning of transcript-specific shaggy expression in individual groups of neurons is sufficient to provide a sex-specific increase in survival and slow aging.

The Glycogen Synthase Kinase-3 in the Regulation of Ion Channels and Cellular Carriers.

Glycogen synthase kinase-3 (GSK-3) is a highly evolutionarily conserved and ubiquitously expressed serine/threonine kinase, an enzyme protein profoundly specific for glycogen synthase (GS). GSK-3 is involved in various cellular functions and physiological processes, including cell proliferation, differentiation, motility, and survival as well as glycogen metabolism, protein synthesis, and apoptosis. There are two isoforms of human GSK-3 (named GSK-3α and GSK-3β) encoded by two distinct genes. Recently, GSK-3β has been reported to function as a powerful regulator of various transport processes across the cell membrane. This kinase, GSK-3β, either directly or indirectly, may stimulate or inhibit many different types of transporter proteins, including ion channel and cellular carriers. More specifically, GSK-3β-sensitive cellular transport regulation involves various calcium, chloride, sodium, and potassium ion channels, as well as a number of Na+-coupled cellular carriers including excitatory amino acid transporters EAAT2, 3 and 4, high-affinity Na+ coupled glucose carriers SGLT1, creatine transporter 1 CreaT1, and the type II sodium/phosphate cotransporter NaPi-IIa. The GSK-3β-dependent cellular transport regulations are a part of the kinase functions in numerous physiological and pathophysiological processes. Clearly, additional studies are required to examine the role of GSK-3β in many other types of cellular transporters as well as further elucidating the underlying mechanisms of GSK-3β-mediated cellular transport regulation.

Abstract 530: Cardiac Fibroblast GSK-3α Contributes to Ventricular Remodeling and Dysfunction of the Failing Heart

Background: Heart failure is the leading cause of mortality, morbidity, and healthcare expenditures worldwide. Numerous studies from our lab and others have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms appear to play overlapping, unique and even opposing functions in the heart. Recently our group has identified cardiac fibroblast (CF) GSK-3β as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK-3α in cardiac pathophysiology is poorly understood. Methods and Results: To determine the role of CF-GSK-3α in the pathogenesis of heart failure, GSK -3α was deleted specifically from mouse resident cardiac fibroblast or myofibroblast with tamoxifen-inducible TCF21- or periostin (Postn)- promoter-driven Cre recombinase. At 2 months of age, WT and KO mice were subjected to cardiac injury and heart functions were monitored by serial echocardiography. Histological analysis and morphometric studies were performed at 8 weeks post-injury. In TCF21-KO mice, deletion of GSK-3α from resident cardiac fibroblasts significantly restricted pressure overload-induced adverse cardiac remodeling and improved cardiac function. Consistently, in Postn-KO mice, deletion of GSK-3α from myofibroblasts remarkably reduced LV scar circumference and prevented cardiac dysfunction post-MI. To gain the mechanistic insights of observed GSK-3α mediated fibrotic remodeling, we examined the effect of GSK-3α deletion on myofibroblast transformation and profibrotic TGF-β1-SMAD3 signaling in vitro . WT and GSK-3α KO mouse embryonic fibroblasts (MEFs) were treated with TGF-β1 (10 ng/mL). Indeed, a significant reduction in cell migration, collagen gel contraction, and α-SMA expression in TGF-β1 treated GSK-3α KO MEF confirmed that GSK-3α is required for myofibroblast transformation. Surprisingly, GSK-3α deletion had no effect on TGF-β1 induced SMAD3 activation indicating the potential involvement of GSK-3α in eliciting SMAD3 independent profibrotic response. Conclusion: These findings suggest the causal role of CF-GSK3α in the cardiac remodeling of the injured heart that could be a therapeutically targeted for the future clinical applications.

Disordered Expression of shaggy, the Drosophila Gene Encoding a Serine-Threonine Protein Kinase GSK3, Affects the Lifespan in a Transcript-, Stage-, and Tissue-Specific Manner.

GSK3 (glycogen synthase kinase 3) is a conserved protein kinase governing numerous regulatory pathways. In Drosophila melanogaster, GSK3 is encoded by shaggy (sgg), which forms 17 annotated transcripts corresponding to 10 protein isoforms. Our goal was to demonstrate how differential sgg transcription affects lifespan, which GSK3 isoforms are important for the nervous system, and which changes in the nervous system accompany accelerated aging. Overexpression of three sgg transcripts affected the lifespan in a stage- and tissue-specific way: sgg-RA and sgg-RO affected the lifespan only when overexpressed in muscles and in embryos, respectively; the essential sgg-RB transcript affected lifespan when overexpressed in all tissues tested. In the nervous system, only sgg-RB overexpression affected lifespan, causing accelerated aging in a neuron-specific way, with the strongest effects in dopaminergic neurons and the weakest effects in GABAergic neurons. Pan-neuronal sgg-RB overexpression violated the properties of the nervous system, including the integrity of neuron bodies; the number, distribution, and structure of mitochondria; cytoskeletal characteristics; and synaptic activity. Such changes observed in young individuals indicated premature aging of their nervous system, which paralleled a decline in survival. Our findings demonstrated the key role of GSK3 in ensuring the link between the pathology of neurons and lifespan.

Hepatic Expression of Phosphorylated Kinase Akt and Glycogen Synthase Kinase-3 Isoforms in Patients with Chronic Hepatitis C.

Some patients with chronic hepatitis C also demonstrate liver steatosis, but the mechanism remains elusive. To analyze the hepatic expression of phosphorylated kinase Akt at Thr 308 and phosphorylated GSK-3 (Glycogen synthase kinase-3) isoforms, GSK3α at Ser 21 and GSK3β at Ser 9, in chronic hepatitis C patients with normal body weight, glucose, and lipid profiles depending on homeostasis model assessment of insulin resistance (HOMA-IR) levels and histological parameters. The study group consisted of 31 patients with chronic hepatitis C. The hepatic expression of kinase Akt (Thr308), GSK3β (Ser9), and GSK3α (Ser21) was measured using Western blot assay. Liver steatosis was observed in 41.93% of patients with HCV infection, in those with increased HOMA-IR index (p = 0.02). However, the hepatic expression of Akt (Thr308), GSK3β (Ser9), and GSK3α (Ser21) was not related to progression of liver steatosis, inflammation, and fibrosis. There was no significant difference in the hepatic expression of kinase Akt (Thr308), GSK3β (Ser9), and GSK3α (Ser21) in relation to HOMA-IR. Liver steatosis was found to be positively associated with HOMA-IR levels in patients with chronic hepatitis C without metabolic disorders. However, the hepatic expression of Akt (Thr308), GSK3β (Ser9), and GSK3α (Ser21) did not correspond to progression of liver disease.

Podocyte GSK3 is an evolutionarily conserved critical regulator of kidney function

Albuminuria affects millions of people, and is an independent risk factor for kidney failure, cardiovascular morbidity and death. The key cell that prevents albuminuria is the terminally differentiated glomerular podocyte. Here we report the evolutionary importance of the enzyme Glycogen Synthase Kinase 3 (GSK3) for maintaining podocyte function in mice and the equivalent nephrocyte cell in Drosophila. Developmental deletion of both GSK3 isoforms (α and β) in murine podocytes causes late neonatal death associated with massive albuminuria and renal failure. Similarly, silencing GSK3 in nephrocytes is developmentally lethal for this cell. Mature genetic or pharmacological podocyte/nephrocyte GSK3 inhibition is also detrimental; producing albuminuric kidney disease in mice and nephrocyte depletion in Drosophila. Mechanistically, GSK3 loss causes differentiated podocytes to re-enter the cell cycle and undergo mitotic catastrophe, modulated via the Hippo pathway but independent of Wnt-β-catenin. This work clearly identifies GSK3 as a critical regulator of podocyte and hence kidney function.

Synthetic Lethality of Wnt Pathway Activation and Asparaginase in Drug-Resistant Acute Leukemias

Asparaginase, a bacterial enzyme that depletes the nonessential amino acid asparagine, is an integral component of acute leukemia therapy. However, asparaginase resistance is a common clinical problem whose biologic basis is poorly understood. We hypothesized, based on the concept of synthetic lethality, that gain-of-fitness alterations in the drug-resistant cells had conferred a survival advantage that could be exploited therapeutically.To identify molecular pathways that promote fitness of leukemic cells upon treatment with asparaginase, we performed a genome-wide CRISPR/Cas9 loss-of-function screen in the asparaginase-resistant T-ALL cell line CCRF-CEM. Cas9-expressing CCRF-CEM cells were transduced with a genome-wide guide RNA library (Shalem et al. Science343, 84-87, 2014), treated with either vehicle or asparaginase (10 U/L), and guide RNA representation was assessed. Our internal positive control, asparagine synthetase, was the gene most significantly depleted in asparaginase-treated cells (RRA significance score = 1.56 x 10-7), followed closely by two regulators of Wnt signaling, NKD2 and LGR6 (RRA score = 6 x 10-6and 2.19 x 10-5, respectively). To test how these genes regulate Wnt signaling in T-ALL, we transduced CCRF-CEM cells with shRNAs targeting NKD2 or LGR6, or with an shLuciferase control. Knockdown of NKD2 or LGR6 increased levels of active β-catenin, as well as the activity of a TopFLASH reporter of canonical Wnt/β-catenin transcriptional activity (P < 0.0001), indicating that NKD2 and LGR6 are negative regulators of Wnt signaling in these cells. We then validated the screen results using shRNA knockdown of NKD2 or LGR6, which profoundly sensitized these cells to asparaginase (P< 0.0001) and potentiated asparaginase-induced apoptosis (P < 0.0001).Inhibition of glycogen synthase kinase 3 (GSK3) is a key event in Wnt-induced signal transduction. Thus, we tested whether CHIR99021, an ATP-competitive inhibitor of both GSK3 isoforms (GSK3α and GSK3β), could phenocopy the effect of Wnt pathway activation. Pharmacologic inhibition of GSK3 induced significant sensitization to asparaginase across a panel of cell lines representing distinct subtypes of treatment-resistant acute leukemia, including T-ALL, AML and hypodiploid B-ALL (Fig. 1a, b). Importantly, GSK3 inhibition did not sensitize normal hematopoietic progenitors to asparaginase, suggesting a leukemia-specific effect.Wnt-induced sensitization to asparaginase was independent of β-catenin and mTOR activation, because genetic and pharmacologic manipulation of these Wnt targets had no effect on asparaginase response. Instead, it was mediated by Wnt-dependent stabilization of proteins (Wnt/STOP), which inhibits GSK3-dependent protein ubiquitination and proteasomal degradation (Acebron et al. Mol Cell54, 663-674, 2014, Taelman et al. Cell143, 1136-1148, 2010). Indeed,Wnt-induced sensitization to asparaginase was completely blocked by the transduction of leukemia cells with FBXW7 (P < 0.0001), whose overexpression can reverse Wnt/STOP (Acebron et al. Mol Cell54, 663-674; 2014), or by expression of a hyperactive proteasomal subunit ΔN-PSMA4 (P < 0.0001), which globally increases protein degradation (Choi et al. Nat Commun7, 10963, 2016).Although GSK3α and GSK3βare redundant for many of their biologic functions, genetic or pharmacologic inhibition of GSK3α fully phenocopied Wnt-induced sensitization to asparaginase (P < 0.0001), whereas selective inhibition of GSK3β had no effect. We then leveraged the recently developed GSK3α-selective small molecule inhibitor BRD0705 (Wagner et al. Sci Transl Med10, 2018) to test the in vivo therapeutic potential of our findings. Immunodeficient NRG mice were injected with leukemic cells from a primary asparaginase-resistant T-ALL patient derived xenograft, and treatment was begun after confirmation of leukemic engraftment (n=16 mice per group). In vivo, this PDX proved completely resistant to asparaginase or BRD0705 monotherapy, whereas the combination was highly efficacious (median survival of 17 days in vehicle, vs. median not reached at 60 days in combo-treated mice; P < 0.0001; Fig. 2a, b). The combination was also well-tolerated, with no appreciable weight changes or increases in serum bilirubin levels.Our findings provide a molecular rationale for activating Wnt/STOP signaling to improve the therapeutic index of asparaginase. DisclosuresNo relevant conflicts of interest to declare.

Neuroinflammation and aberrant hippocampal plasticity in a mouse model of emotional stress evoked by exposure to ultrasound of alternating frequencies

Emotional stress is a form of stress evoked by processing negative mental experience rather than an organic or physical disturbance and is a frequent cause of neuropsychiatric pathologies, including depression. Susceptibility to emotional stress is commonly regarded as a human-specific trait that is challenging to model in other species. Recently, we showed that a 3-week-long exposure to ultrasound of unpredictable alternating frequencies within the ranges of 20-25 kHz and 25-45 kHz can induce depression-like characteristics in laboratory mice and rats. In an anti-depressant sensitive manner, exposure decreases sucrose preference, elevates behavioural despair, increases aggression, and alters serotonin-related gene expression. To further investigate this paradigm, we studied depression/distress-associated markers of neuroinflammation, neuroplasticity, oxidative stress and the activity of glycogen synthase kinase-3 (GSK-3) isoforms in the hippocampus of male mice. Stressed mice exhibited a decreased density of Ki67-positive and DCX-positive cells in the subgranular zone of hippocampus, and altered expression of brain-derived neurotrophic factor (BDNF), its receptor TrkB, and anti-apoptotic protein kinase B phosphorylated at serine 473 (AktpSer473). The mice also exhibited increased densities of Iba-1-positive cells, increased oxidative stress, increased levels of interleukin-1β (IL-1β), interleukin-6 (IL-6) in the hippocampus and plasma, and elevated activity of GSK-3 isoforms. Together, the results of our investigation have revealed that unpredictable alternating ultrasound evokes behavioural and molecular changes that are characteristic of the depressive syndrome and validates this new and simple method of modeling emotional stress in rodents.

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.