Role Of GSK-3β Research Articles

Targeting Glycogen Synthase Kinase‐3β for Therapeutic Benefit against Oxidative Stress in Alzheimer′s Disease: Involvement of the Nrf2‐ARE Pathway

Specific regions of the Alzheimer's disease (AD) brain are burdened with extracellular protein deposits, the accumulation of which is concomitant with a complex cascade of overlapping events. Many of these pathological processes produce oxidative stress. Under normal conditions, oxidative stress leads to the activation of defensive gene expression that promotes cell survival. At the forefront of defence is the nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor that regulates a broad spectrum of protective genes. Glycogen synthase kinase-3β (GSK-3β) regulates Nrf2, thus making this kinase a potential target for therapeutic intervention aiming to boost the protective activation of Nrf2. This paper aims to review the neuroprotective role of Nrf2 in AD, with special emphasis on the role of GSK-3β in the regulation of the Nrf2 pathway. We also examine the potential of inducing GSK-3β by small-molecule activators, dithiocarbamates, which potentially exert their beneficial therapeutic effects via the activation of the Nrf2 pathway.

Intersecting Chemical Genomic and Genetic Screens Identifies Glycogen Synthase Kinase-3α (GSK-3α) as a Modulator of Differentiation In Acute Myeloid Leukemia

AbstractAbstract 1000The treatment of acute myeloid leukemia (AML) poses a vexing challenge despite an improved understanding of its molecular pathogenesis. A two-hit theory has been proposed for the pathogenesis of AML where the first hit imparts a proliferation defect and the second a block in differentiation. Drug discovery efforts for AML, however, have largely focused on the proliferation defect. Using the intersection of chemical biology and high-throughput genetic screening we sought to identify new AML differentiation targets by measuring the induction of a complex gene expression signature of myeloid maturation. We performed two independent small molecule library screens and a high-throughput shRNA screen for perturbations that induce differentiation in AML cells. We measured this differentiation signature using the previously described gene expression-based high-throughput screening (GE-HTS) approach in which gene expression signatures serve as surrogates for different biological states. Glycogen Synthase Kinase-3 (GSK-3) emerged as a target at the intersection of these three screens. GSK-3 is a multifunctional serine threonine kinase involved in diverse cellular processes including differentiation, signal transduction, cell cycle regulation and proliferation, with an emerging role in human leukemia. We demonstrate that the GSK-3 inhibitors scoring in the primary screens indeed induce the differentiation signature with a dose-response in AML cell lines. In order to further validate GSK-3 as a target, we extended testing to lithium chloride and SB216763, two commonly used GSK-3 inhibitors not in the original screens. Both of these molecules induced AML differentiation as measured by gene expression and morphological changes in multiple AML cell lines and in primary patient blasts in vitro. GSK-3 is expressed as two highly homologous but non-redundant isoforms, GSK-3α and GSK-3β, with small molecule inhibitors non-selectively reported to target both. In order to further validate the findings of the small molecule library screens, we performed a high-throughput shRNA screen targeting the human kinome for shRNAs that induce differentiation. Multiple hairpins against GSK-3α scored. In secondary testing of four AML cell lines, we found that genetic loss of GSK-3α induced differentiation as measured by induction of the complex gene expression signature, alterations in genome-wide expression, and morphological changes associated with maturation. Moreover, colony formation in methylcellulose was impeded. These effects could be rescued with a GSK-3α cDNA immune to the effects of the shRNA, further supporting the on-target activity of the hairpin. In contrast, GSK-3β-directed hairpins induced minimal differentiation. We next extended testing to an in vivo U937 orthotopic model of AML. While pan-GSK-3 inhibition with lithium chloride treatment did not demonstrate efficacy in this model, inhibition of GSK-3α with shRNA attenuated development of disease compared to an shRNA control. We hypothesize that the rise in β-catenin with pan-inhibition of GSK-3 may attenuate the response to lithium in vivo. In contrast, isolated knockdown of GSK-3α does not induce β-catenin. While much of the prior cancer literature has focused on the role of GSK-3β in human malignancy, these studies suggest a role for GSK-3α in AML differentiation and support a role for GSK-3α-directed targeted therapy. Disclosures:No relevant conflicts of interest to declare.

The role of GSK3β in NSC proliferation and neural differentiation in the brain of rats prenatally exposured to valproic acid

The role of GSK3β in NSC proliferation and neural differentiation in the brain of rats prenatally exposured to valproic acid

Suppression of Neurotensin Receptor Type 1 Expression and Function by Histone Deacetylase Inhibitors in Human Colorectal Cancers

Neurotensin, a gut peptide, stimulates the growth of colorectal cancers that possess the high-affinity neurotensin receptor (NTR1). Sodium butyrate (NaBT) is a potent histone deacetylase inhibitor (HDACi) that induces growth arrest, differentiation, and apoptosis of colorectal cancers. Previously, we had shown that NaBT increases nuclear GSK-3beta expression and kinase activity; GSK-3beta functions as a negative regulator of extracellular signal-regulated kinase (ERK) signaling. The purpose of our current study was to determine: (a) whether HDACi alters NTR1 expression and function, and (b) the role of GSK-3beta/ERK in NTR1 regulation. Human colorectal cancers with NTR1 were treated with various HDACi, and NTR1 expression and function were assessed. Treatment with HDACi dramatically decreased endogenous NTR1 mRNA, protein, and promoter activity. Overexpression of GSK-3beta decreased NTR1 promoter activity (> 30%); inhibition of GSK-3beta increased NTR1 expression in colorectal cancer cells, indicating that GSK-3beta is a negative regulator of ERK and NTR1. Consistent with our previous findings, HDACi significantly decreased phosphorylated ERK while increasing GSK-3beta. Selective MAP/ERK kinase/ERK inhibitors suppressed NTR1 mRNA expression in a time- and dose-dependent fashion, and reduced NTR1 promoter activity by approximately 70%. Finally, pretreatment with NaBT prevented neurotensin-mediated cyclooxygenase-2 and c-myc expression and attenuated neurotensin-induced interleukin-8 expression. HDACi suppresses endogenous NTR1 expression and function in colorectal cancer cell lines; this effect is mediated, at least in part, through the GSK-3beta/ERK pathway. The downregulation of NTR1 in colorectal cancers may represent an important mechanism for the anticancer effects of HDACi.

Role of GSK3β in behavioral abnormalities and tau hyperphosphorylation in olfactory bulbectomized rats

Role of GSK3β in behavioral abnormalities and tau hyperphosphorylation in olfactory bulbectomized rats

Inhibition of Glycogen Synthase Kinase 3β (GSK3β) Decreases Inflammatory Responses in Brain Endothelial Cells

Immune mediators and leukocyte engagement of brain microvascular endothelial cells (BMVECs) contribute to blood-brain barrier impairment during neuroinflammation. Glycogen synthase kinase 3beta (GSK3beta) was recently identified as a potent regulator of immune responses in in vitro systems and animal models. However, the role of GSK3beta in regulation of immune endothelial functions remains undetermined. Here we evaluated the effect of GSK3beta inhibition on the regulation of inflammatory responses in BMVECs. A focused PCR gene array of 84 genes was performed to identify the cytokine and chemokine gene expression profile in tumor necrosis factor (TNF) alpha-stimulated BMVECs after GSK3beta inactivation by specific inhibitors. Fifteen of 39 genes induced by TNFalpha stimulation were down-regulated after GSK3beta inhibition. Genes known to contribute to neuroinflammation that were most negatively affected by GSK3beta inactivation included IP-10/CXCL10, MCP-1/CCL2, IL-8/CXCL8, RANTES/CCL5, and Groalpha/CXCL1. GSK3beta suppression resulted in diminished secretion of these proinflammatory mediators by inflamed BMVECs detected by ELISA. GSK3beta inhibition in BMVECs reduced adhesion molecule expression as well as monocyte adhesion to and migration across cytokine stimulated BMVEC monolayers. Interactions of monocytes with TNFalpha-activated BMVECs led to barrier disruption, and GSK3beta suppression in the endothelium restored barrier integrity. GSK3beta inhibition in vivo substantially decreased leukocyte adhesion to brain endothelium under inflammatory conditions. In summary, inhibition of GSK3beta emerges as an important target for stabilization of the blood-brain barrier in neuroinflammation.

Role of GSK-3β in hepatocellular carcinoma cell migration

Objective To study the effects of GSK-3β on the migration ability of hepatocellular carcinoma cells. Methods Inhibition tests with specific inhibitors of GSK -3 ( LiCl and SB216763) and transfection with different plasmids( GSK-3β WT,GSK-3β S9A,and GID5 -6) were used to alter the activity of GSK -3β. The migration ability of SMMC-7221 and Hep3B cells was observed using wound healing assay,transwell assay and the microtubule-organizing center ( MTOC) test before and after treatment. Immunocytochemistry was used to investigate the distribution of phospho-GSK-3β. Results Wound healing assay showed that LiCl and SB216763 decreased the migration of SMMC-7721 cells by 36. 44% and 41. 78% ,respectively; and decreased the migration of Hep3B cells by both 26. 66%. Transfection with GSK-3β WT increased the expression of GSK-3β and pGSK-3β,and the migration rate of SMMC-7721 cells decreased to 61. 27%. Transfection with GSK-3β S9A increased GSK-3β expression and had no noticeable influence on pGSK -3β expression,and the migration rate of SMMC-7721 cells decreased to 38. 61%. Transfection with GID5-6 had no noticeable influence on GSK-3β and increased pGSK-3β expression,and the migration rate decreased to 36. 49%. Immunocytochemical staining showed that LiCl blocked pGSK-3β accumulation on cell edge as that in normally cultured cells. MTOC test showed that the MTOC positive rate was above 60% in Hep3B cells before adding inhibitors of GSK-3β,and it decreased after exposure to the inhibitors. Conclusion GSK-3β plays an important role in migration of hepatocellular carcinoma cells. Inhibitors of GSK-3β can affect the polarization and decrease the migration ability of hepatocellular carcinoma cells.

Inhibition of glycogen synthase kinase-3β prevents activation of focal adhesion kinase after ischemia/reperfusion of the rat lung

Recent studies on the mechanisms of ischemic preconditioning in myocardial tissue have presented convincing evidence that multiple protective pathways converge on inhibition of glycogen synthase kinase-3β (GSK-3β). To directly address the role of GSK-3β in ischemia and reperfusion (I/R) of the lung, a rat model of left lung in situ ischemia was used. The specific non-competitive inhibitor of GSK-3β, TDZD-8, was injected (3 mg/kg, vehicle in controls) 5 min before the left lung hilum was occluded for 60 min. Animals in the ischemia group underwent the same treatment, but without administration of TDZD-8. Lung functional and biochemical parameters were determined at time points 15 min and 60 min reperfusion. Treatment with TDZD-8 improved gas exchange (arterial pO2), but I/R-induced inflammation (plasma interleukin-6, leukocyte invasion) was not affected. The I/R cycle induced a rapid (15 min reperfusion) increase of protein tyrosine phosphorylation, including the activating phosphorylation of focal adhesion kinase at Tyr397, Tyr407, Tyr577, and Tyr861, and the non-receptor kinase Src at Tyr416. The phosphorylation was blocked by the GSK inhibitor. This effect may be related to the reduced plasma level of the strong effector of focal adhesion kinase, transforming growth factor-β1, in the TDZD group. The underlying mechanisms are elusive, but they deserve further investigation, especially in relation to the early increase of lung permeability in this rat model of I/R injury. In conclusion, the results suggest that inhibition of GSK-3β improves rat lung function during an I/R cycle, but only during the early reperfusion phase.

P3.31. Role of GSK-3β as a negative regulator of epithelial-mesenchymal transition in oral cancer cells

P3.31. Role of GSK-3β as a negative regulator of epithelial-mesenchymal transition in oral cancer cells

S1624 Inhibition of Sustained Smooth Muscle Contraction By PKA and PKG Is Mediated By Phosphorylation of Gα 13 and Inhibition of Gα 13-Dependent Activation of RHOA

A, valproic acid, apicidin and MS275). NTR1 mRNA and protein expression was assessed by Northern and Western blots, respectively. NTR1 promoter activity was assessed by luciferase assay. (ii) The role of GSK-3β and ERK signaling pathways was determined using the selective inhibitors SB-216763 (for GSK-3β) and U0126 or PD98059 (for MEK/ERK) as well as siRNA to GSK-3β. (iii) To assess the functional effects of HDACI regulation of NTR, the effect of NaBT on NT-mediated induction of COX-2, c-myc and IL-8 expression was assessed by Northern blot and RNase protection assay. RESULTS. (i) Treatment with all HDACIs resulted in the potent down-regulation of endogenous NTR1 mRNA, protein and promoter activity. Northern blot analyses showed that HDACIs down-regulate NTR1 mRNA in a time-and dose-dependent fashion in all five NTR1-positive cell lines. Notably, NTR1mRNAwas dramatically decreased after 4 h of NaBT treatment in HT29 cells suggesting that NTR1 may be a direct target gene of HDACIs. (ii) Overexpression of GSK-3β decreased NTR1 promoter activity (> 30%); inhibition of GSK-3β increased NTR1 expression in HT29 and SW480 cells, indicating that GSK-3β is a negative regulator of ERK and NTR1. Consistent with our previous findings, HDACIs significantly decreased phosphorylated ERK while increasing GSK-3β. Selective MEK/ERK inhibitors suppressed NTR1 mRNA expression in a timeand dose-dependent fashion, and reduced NTR1 promoter activity by ~70%. (iii) Pretreatment with NaBT prevented NT-mediated COX-2 and c-myc expression and attenuated NT-induced IL-8 expression. CONCLUSIONS. HDACIs suppress endogenous NTR1 expression and function in CRC cell lines; this effect may involve both a direct and/or an indirect mechanism through the GSK-3β/ERK pathway. The down-regulation of NTR1 in CRCs may represent an important mechanism for the anti-cancer effects of HDACIs.

TNF-induced activation of pulmonary microvessel endothelial cells: a role for GSK3β

The hypothesis tested was PKCalpha mediates the phosphorylation of glycogen synthetase kinase 3beta (GSK3beta) and that the GSK3beta inhibition modulates the response to tumor necrosis factor-alpha (TNF) in rat pulmonary microvessel endothelial cells (PMEC). PMEC were treated with TNF for 4.0 h (100 ng/ml) or vehicle. First, to assess the role of PKCalpha in the phosphorylation of GSK3beta (i.e., an indicator of GSK3beta inhibition), PMEC were pretreated with 1) nonsense-RNA-PKCalpha, 2) siRNA-PKCalpha, and 3) the PKC inhibitor Gö6983. In the nonsense RNA-PKCalpha+TNF and TNF groups, there was increased phosphorylated GSK3beta-Ser9 that did not occur in the Gö6983+TNF group. In the TNF groups, there was a significant correlation between PKCalpha protein and phosphorylated GSK3beta-Ser9 that did not occur in the groups without TNF. Second, to assess the role of GSK3beta in beta-catenin activity, PMEC were pretreated with 1) wild-type (w) GSK3beta plasmid to enhance GSK3beta activity, 2) kinase dead (kd)-GSK3beta plasmid, and 3) the GSK3beta inhibitor SB-216763. In the TNF group, there was increased unphosphorylated beta-catenin-Ser37/33 compared with the control group. In the GSK3beta-inhibited groups (i.e., SB-216763 and kdGSK3beta) +/- TNF, the unphosphorylated beta-catenin-Ser37/33 was similar to the TNF group. In the GSK3beta-enhanced group +/- TNF, the unphosphorylated beta-catenin-Ser37/33 was similar to the control. Finally, PMEC were also treated with TOPflash, a beta-catenin-dependent promoter luciferase reporter, or the mutant construct FOPflash, 2 days before treatment with TNF. In the TNF group, there was an increased TOPflash/FOPflash activity ratio compared with the control group. In the GSK3beta-inhibited groups (i.e., SB-216763 and kdGSK3beta) +/- TNF, the TOPflash/FOPflash activity ratio was similar to the TNF group. In the GSK3beta-enhanced group +/- TNF, the TOPflash/FOPflash activity ratio was similar to the control. The data indicate that TNF induces endothelial activation that is modulated by a PKCalpha-dependent inhibition of GSK3beta.

Drug Development Targeting the Glycogen Synthase Kinase-3β (GSK-3β)-Mediated Signal Transduction Pathway: Role of GSK-3β in Myocardial Protection Against Ischemia/Reperfusion Injury

Although reperfusion is required to salvage ischemic myocardium from necrosis, reperfusion per se induces myocardial necrosis. In this “lethal reperfusion injury”, opening of the mitochondrial permeability transition pore (mPTP) upon reperfusion is crucially involved. The mPTP primarily consists of adenine nucleotide translocator (ANT) and voltage-dependent anion channel, and its opening is triggered by binding of cyclophilin-D (CyP-D) to ANT, which increases Ca2+ sensitivity of the mPTP. Recent studies have shown that inactivation of glycogen synthase kinase-3β (GSK-3β) suppresses mPTP opening and protects cardiomyocytes. Multiple intracellular signals relevant to cardiomyocyte protection converge to GSK-3β and inactivate this kinase by phosphorylation. Although the effect of GSK-3β phosphorylation on mPTP structure and function remains unclear, suppression of ANT–CyP-D interaction by binding of phospho-GSK-3β to ANT and reduction in GSK-3β–mediated phosphorylation of p53 may contribute to elevation of the threshold for mPTP opening. Furthermore, a significant inverse correlation was observed between level of phospho-GSK-3β at the time of reperfusion and the extent of myocardium infarction in heart. Together with the infarct size–limiting effect of GSK-3β inhibitors, this finding indicates that phospho-GSK-3β is a determinant of myocardial tolerance against reperfusion-induced necrosis. Thus, GSK-3β appears to be a target of novel therapy for cardioprotection upon reperfusion.

Drug Development Targeting the Glycogen Synthase Kinase-3β (GSK-3β)-Mediated Signal Transduction Pathway: The Role of GSK-3β in the Maintenance of Steady-State Levels of Insulin Receptor Signaling Molecules and Nav1.7 Sodium Channel in Adrenal Chromaffin Cells

Glycogen synthase kinase-3 (GSK-3) is constitutively active in nonstimulated cells, where the majority of its substrates undergo inactivation/proteolysis by phosphorylation. Extracellular stimuli (e.g., insulin) catalyze inhibitory Ser9-phosphorylation of GSK-3β, turning on signaling and causing other biological consequences otherwise constitutively suppressed by GSK-3β. Regulated and dysregulated activities of GSK-3β are pivotal to health, disease, and therapeutics (e.g., insulin resistance, neurodegeneration, tumorigenesis, inflammation); however, the underlying mechanisms of multifunctional GSK-3β remain elusive. In cultured bovine adrenal chromaffin cells, 1) constitutive and negatively-regulated activities of GSK-3β up- and down-regulated insulin receptor, insulin receptor substrate-1 (IRS-1), IRS-2, and Akt levels via controlling proteasomal degradation and protein synthesis; 2) nicotinic receptor/protein kinase C-α (PKC-α) / extracellular signal-regulated kinase (ERK) pathway up-regulated IRS-1 and IRS-2 levels, enhancing insulin-induced the phosphoiNOSitide 3-kinase (PI3K) / Akt / GSK-3β pathway; 3) inhibition of calcineurin by cyclosporin A or FK506 down-regulated IRS-2 level, attenuating insulin-like growth factor-I (IGF-I)-induced ERK and GSK-3β pathways; and 4) insulin, IGF-I or therapeutics (e.g., lithium) up-regulated the voltage-dependent Nav1.7 sodium channel.

Drug Development Targeting the Glycogen Synthase Kinase-3β (GSK-3β)-Mediated Signal Transduction Pathway: Role of GSK-3β in Adult Brain

Glycogen synthase kinase-3β (GSK-3β) is a constitutively active kinase. Since its activation results in neurofibrillary tangle (NFT) deposits in aged and Alzheimer’s disease (AD) brains, GSK-3β may be inhibited under normal conditions but activated under pathological conditions. Given its link to NFT formation, we sought to determine whether GSK-3β exists in the brain as a “pathological time bomb” that promotes disease development. To address this hypothesis, we analyzed GSK-3β heterozygote (GSK+/−) mice, which express GSK-3β at 50% wild-type levels. When tested in the Morris water maze test, GSK+/− mice surprisingly exhibited retrograde amnesia. Further analysis indicated that GSK+/− mice had impaired memory reconsolidation but normal memory consolidation. Therefore, we concluded that GSK-3β activation is required for memory reconsolidation in the adult brain.

A mitotic role for GSK-3β kinase in Drosophila

Glycogen synthase kinase-3β (GSK-3β) is involved in a wide variety of cellular processes, and implicated in a growing list of human diseases. Recent drug inhibition studies have suggested a role for GSK-3β in mitosis in animals. Here, we take an alternative approach to understanding GSK-3β function in mitosis by genetic mutational analysis in Drosophila. GSK-3β function is well conserved between Drosophila (Zw3) and humans, frequently operating similarly in pathways, as diverse as the Wnt signaling and circadian rhythm pathways, and sharing a key role in the development of the neuromuscular junction. Unlike drug inhibitor studies, we find that loss of function mutations of zw3 result in markedly curved, or bent, metaphase spindles that exhibit metaphase delay. These defects do not routinely result in mitotic catastrophe, and argue that Zw3 plays a role in the maintenance of the mitotic spindle, rather than an essential role in spindle morphogenesis. Consistent with a mitotic function, we observe a complex and dynamic localization of Zw3 during cell division. These studies provide genetic data that validate and extend drug inhibition studies on a novel mitotic role for glycogen synthase kinase in the maintenance of the mitotic spindle.

Airway smooth muscle hyperplasia and hypertrophy correlate with glycogen synthase kinase-3β phosphorylation in a mouse model of asthma

Increased airway smooth muscle (ASM) mass, a characteristic finding in asthma, may be caused by hyperplasia or hypertrophy. Cell growth requires increased translation of contractile apparatus mRNA, which is controlled, in part, by glycogen synthase kinase (GSK)-3beta, a constitutively active kinase that inhibits eukaryotic initiation factor-2 activity and binding of methionyl tRNA to the ribosome. Phosphorylation of GSK-3beta inactivates it, enhancing translation. We sought to quantify the contributions of hyperplasia and hypertrophy to increased ASM mass in ovalbumin (OVA)-sensitized and -challenged BALB/c mice and the role of GSK-3beta in this process. Immunofluorescent probes, confocal microscopy, and stereological methods were used to analyze the number and volume of cells expressing alpha-smooth muscle actin and phospho-Ser(9) GSK-3beta (pGSK). OVA treatment caused a 3-fold increase in ASM fractional unit volume or volume density (Vv) (PBS, 0.006 +/- 0.0003; OVA, 0.014 +/- 0.001), a 1.5-fold increase in ASM number per unit volume (Nv), and a 59% increase in volume per cell (Vv/Nv) (PBS, 824 +/- 76 microm(3); OVA, 1,310 +/- 183 mum(3)). In OVA-treated mice, there was a 12-fold increase in the Vv of pGSK (+) ASM, a 5-fold increase in the Nv of pGSK (+) ASM, and a 1.6-fold increase in Vv/Nv. Lung homogenates from OVA-treated mice showed increased GSK-3beta phosphorylation and lower GSK-3beta activity. Both hyperplasia and hypertrophy are responsible for increased ASM mass in OVA-treated mice. Phosphorylation and inactivation of GSK-3beta are associated with ASM hypertrophy, suggesting that this kinase may play a role in asthmatic airway remodeling.

Dissociation of tau toxicity and phosphorylation: role of GSK-3β, MARK and Cdk5 in a Drosophila model

Hyperphosphorylation of tau at multiple sites has been implicated in the formation of neurofibrillary tangles in Alzheimer’s disease; however, the relationship between toxicity and phosphorylation of tau has not been clearly elucidated. Putative tau kinases that play a role in such phosphorylation events include the proline-directed kinases glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (Cdk5), as well as nonproline-directed kinases such as microtubule affinity-regulating kinase (MARK)/PAR-1; however, whether the cascade of events linking tau phosphorylation and neurodegeneration involves sequential action of kinases as opposed to parallel pathways is still a matter of controversy. Here, we employed a well-characterized Drosophila model of tauopathy to investigate the interdependence of tau kinases in regulating the phosphorylation and toxicity of tau in vivo. We found that tau mutants resistant to phosphorylation by MARK/PAR-1 were indeed less toxic than wild-type tau; however, this was not due to their resistance to phosphorylation by GSK-3β/Shaggy. On the contrary, a tau mutant resistant to phosphorylation by GSK-3β/Shaggy retained substantial toxicity and was found to have increased affinity for microtubules compared with wild-type tau. The fly homologs of Cdk5/p35 did not have major effects on tau toxicity or phosphorylation in this model. These data suggest that, in addition to tau phosphorylation, microtubule binding plays a crucial role in the regulation of tau toxicity when misexpressed. These data have important implications for the understanding and interpretation of animal models of tauopathy.

Role of GSK3β in behavioral abnormalities induced by serotonin deficiency

We were interested to read the article by Beaulieu et al. (1), suggesting that GSK3β haploinsufficiency counteracts depressive-like behavior in mice expressing a functional TPH2 mutant with a marked decrease in serotonin production. In the figures of the current article, it is clear that GSK3β haploinsufficiency had no antidepressant effect in the tail suspension test in animals without the TPH2 mutant enzyme. However, Beaulieu et al. fail to mention the paper by O'Brien et al. (2), who reported that GSK3β haploinsufficiency alone gives dramatic antidepressant-like effects in the Porsolt swim test, a closely related test for antidepressant behavior. We also have not been able to replicate the results of Beaulieu et al. (see ref. 3). However, it would have seemed essential for the discussion of the current Beaulieu et al. article that they mention the previous report, which found that GSK3β haploinsufficiency is quite sufficient to cause an antidepressant phenotype, in contradiction to their own findings.

Role of GSK3β in behavioral abnormalities induced by serotonin deficiency

Dysregulation of brain serotonin (5-HT) neurotransmission is thought to underlie mental conditions as diverse as depression, anxiety disorders, bipolar disorder, autism, and schizophrenia. Despite treatment of these conditions with serotonergic drugs, the molecular mechanisms by which 5-HT is involved in the regulation of aberrant emotional behaviors are poorly understood. Here, we generated knockin mice expressing a mutant form of the brain 5-HT synthesis enzyme, tryptophan hydroxylase 2 (Tph2). This mutant is equivalent to a rare human variant (R441H) identified in few individuals with unipolar major depression. Expression of mutant Tph2 in mice results in markedly reduced ( approximately 80%) brain 5-HT production and leads to behavioral abnormalities in tests assessing 5-HT-mediated emotional states. This reduction in brain 5-HT levels is accompanied by activation of glycogen synthase kinase 3beta (GSK3beta), a signaling molecule modulated by many psychiatric therapeutic agents. Importantly, inactivation of GSK3beta in Tph2 knockin mice, using pharmacological or genetic approaches, alleviates the aberrant behaviors produced by 5-HT deficiency. These findings establish a critical role of Tph2 in the maintenance of brain serotonin homeostasis and identify GSK3beta signaling as an important pathway through which brain 5-HT deficiency induces abnormal behaviors. Targeting GSK3beta and related signaling events may afford therapeutic advantages for the management of certain 5-HT-related psychiatric conditions.

Not All Hypertrophy Is Created Equal

See related article, pages 1164–1174 Cardiac hypertrophy is the natural response of myocardium to various stressors, including neurohormonal stimuli, hemodynamic overload, and injury. In the face of continued stress, pathological hypertrophy progresses to a loss of cardiomyocytes, the development of fibrosis, and, ultimately, heart failure. Emerging evidence has shown that glycogen synthase kinase-3β (GSK-3β) is an important negative regulator of cardiomyocyte hypertrophy, yet inhibition of GSK-3β has been shown to reduce cell death after ischemia reperfusion. Therefore, it has been difficult to predict what the consequences of chronic inhibition of GSK-3 in the heart would be because it might be a balance between the potential for the aggravation of cardiac hypertrophy versus antiapoptotic effects. In this issue of Circulation Research , Hirotani and colleagues report that sustained inhibition of GSK-3β in postneonatal hearts results in well-compensated “physiologic” cardiac hypertrophy and, most intriguingly, exerts protective effects against the development of “pathological” hypertrophy and heart failure with pressure overload.1 Although there are a number of concerns that need to be addressed before targeting GSK-3 for the treatment of heart failure, this “best of both worlds” outcome provides an interesting and favorable rationale for such intervention. The GSK-3 family of protein kinases is encoded by 2 genes, α and β. They are highly conserved throughout evolution and are critical to the regulation of diverse biological processes ranging from organ development to cell death, including cell growth, cell cycling, cytoskeletal organization, and metabolism.2,3 Furthermore, dysregulation of GSK-3β has been implicated in the pathogenesis of many human diseases including Alzheimer disease, diabetes, and tumorgenesis.4–8 GSK-3α (51 kDa) is the larger of the two and has a glycine-rich N terminus of unknown function. GSK-3β (47 kDa) and α share significant sequence homology (97%) in their kinase domains, however the homology between the …