Targeting GSK-3 family members in the heart: a very sharp double-edged sword

Unlocking hope: GSK-3 inhibitors and Wnt pathway activation in Alzheimer's therapy

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterised by progressive cognitive decline and the accumulation of amyloid-β plaques and tau tangles. The Wnt signalling pathway known for its crucial role in neurodevelopment and adult neurogenesis has emerged as a potential target for therapeutic intervention in AD. Glycogen synthase kinase-3 beta (GSK-3β), a key regulator of the Wnt pathway, plays a pivotal role in AD pathogenesis by promoting tau hyperphosphorylation and neuroinflammation. Several preclinical studies have demonstrated that inhibiting GSK-3β leads to the activation of Wnt pathway thereby promoting neuroprotective effects, and mitigating cognitive deficits in AD animal models. The modulation of Wnt signalling appears to have multifaceted benefits including the reduction of amyloid-β production, tau hyperphosphorylation, enhancement of synaptic plasticity, and inhibition of neuroinflammation. These findings suggest that targeting GSK-3β to activate Wnt pathway may represent a novel approach for slowing or halting the progression of AD. This hypothesis reviews the current state of research exploring the activation of Wnt pathway through the inhibition of GSK-3β as a promising therapeutic strategy in AD.

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

Zonisamide attenuates pressure overload-induced myocardial hypertrophy in mice through proteasome inhibition

Myocardial hypertrophy is a pathological thickening of the myocardium which ultimately results in heart failure. We previously reported that zonisamide, an antiepileptic drug, attenuated pressure overload-caused myocardial hypertrophy and diabetic cardiomyopathy in murine models. In addition, we have found that the inhibition of proteasome activates glycogen synthesis kinase 3 (GSK-3) thus alleviates myocardial hypertrophy, which is an important anti-hypertrophic strategy. In this study, we investigated whether zonisamide prevented pressure overload-caused myocardial hypertrophy through suppressing proteasome. Pressure overload-caused myocardial hypertrophy was induced in mice by trans-aortic constriction (TAC) surgery. Two days after the surgery, the mice were administered zonisamide (10, 20, 40 mg·kg-1·d-1, i.g.) for four weeks. We showed that zonisamide administration significantly mitigated impaired cardiac function. Furthermore, zonisamide administration significantly inhibited proteasome activity as well as the expression levels of proteasome subunit beta types (PSMB) of the 20 S proteasome (PSMB1, PSMB2 and PSMB5) and proteasome-regulated particles (RPT) of the 19 S proteasome (RPT1, RPT4) in heart tissues of TAC mice. In primary neonatal rat cardiomyocytes (NRCMs), zonisamide (0.3 μM) prevented myocardial hypertrophy triggered by angiotensin II (Ang II), and significantly inhibited proteasome activity, proteasome subunits and proteasome-regulated particles. In Ang II-treated NRCMs, we found that 18α-glycyrrhetinic acid (18α-GA, 2 mg/ml), a proteasome inducer, eliminated the protective effects of zonisamide against myocardial hypertrophy and proteasome. Moreover, zonisamide treatment activated GSK-3 through inhibiting the phosphorylated AKT (protein kinase B, PKB) and phosphorylated liver kinase B1/AMP-activated protein kinase (LKB1/AMPKα), the upstream of GSK-3. Zonisamide treatment also inhibited GSK-3's downstream signaling proteins, including extracellular signal-regulated kinase (ERK) and GATA binding protein 4 (GATA4), both being the hypertrophic factors. Collectively, this study highlights the potential of zonisamide as a new therapeutic agent for myocardial hypertrophy, as it shows potent anti-hypertrophic potential through the suppression of proteasome.

Unraveling the Mystery of Cold Stress-Induced Myocardial Injury

Exposure to low ambient temperature imposes great challenge to human health. Epidemiological evidence has noted significantly elevated emergency admission and mortality rate in cold climate in many regions, in particular, adverse events in cardiovascular system. Cold stress is becoming one of the important risk factors for cardiovascular death. Through recent advance in echocardiography and myocardial histological techniques, both clinical and experimental experiments have unveiled that cold stress triggers a variety of pathological and pathophysiological injuries, including ventricular wall thickening, cardiac hypertrophy, elevated blood pressure, decreased cardiac function, and myocardial interstitial fibrosis. In order to examine the potential mechanism of action behind cold stress-induced cardiovascular anomalies, ample biochemical and molecular biological experiments have been conducted to denote a role for mitochondrial injury, intracellular Ca²⁺ dysregulation, generation of reactive oxygen species (ROS) and other superoxide, altered gene and protein profiles for apoptosis and autophagy, and increased adrenergic receptor sensitivity in cold stress-induced cardiovascular anomalies. These findings suggest that cold stress may damage the myocardium through mitochondrial injury, apoptosis, autophagy, metabolism, oxidative stress, and neuroendocrine pathways. Although the precise nature remains elusive for cold stress-induced cardiovascular dysfunction, endothelin (ET-_A) receptor, endoplasmic reticulum (ER) stress, transient receptor potential vanilloid, mitochondrial-related protein including NRFs and UCP-2, ROS, Nrf2-Keap1 signaling pathway, Bcl-2/Bax, and lipoprotein lipase (LPL) signaling may all play a pivotal role. For myocardial injury evoked by cold stress, more comprehensive and in-depth mechanisms are warranted to better define the potential therapeutic options for cold stress-associated cardiovascular diseases.

Centrosome Reduction Promotes Terminal Differentiation of Human Cardiomyocytes

Centrosome reduction and redistribution of pericentriolar material (PCM) coincides with cardiomyocyte transitions to a post-mitotic and matured state. However, it is unclear whether centrosome changes are a cause or consequence of terminal differentiation. We validated that centrosomes were intact and functional in proliferative human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), consistent with their immature phenotype. We generated acentrosomal hPSC-CMs, through pharmacological inhibition of centriole duplication, and showed that centrosome loss was sufficient to promote post-mitotic transitions and aspects of cardiomyocyte maturation. As Hippo kinases are activated during post-natal cardiac maturation, we pharmacologically activated the Hippo pathway using C19, which was sufficient to trigger centrosome disassembly and relocalization of PCM components to perinuclear membranes. This was due to specific activation of Hippo kinases, as direct inhibition of YAP-TEAD interactions with verteporfin had no effect on centrosome organization. This suggests that Hippo kinase-centrosome remodeling may play a direct role in cardiac maturation.

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Centrosomes are intact and functional in immature human cardiomyocytes

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Centrosome loss promotes maturation of human cardiomyocytes

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Centrosomes are returned with cell cycle reinitiation in post-natal cardiomyocytes

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Hippo kinases promote disassembly and redistribution of centrosomal proteins

Insight into glycogen synthase kinase-3β inhibitory activity of phyto-constituents from Melissa officinalis: in silico studies

Over activity of Glycogen synthase kinase-3β (GSK-3β), a serine/threonine-protein kinase has been implicated in a number of diseases including stroke, type II diabetes and Alzheimer disease (AD). This study aimed to find novel inhibitors of GSK-3β from phyto-constituents of Melissa officinalis with the aid of computational analysis. Molecular docking, induced-fit docking (IFD), calculation of binding free energy via the MM-GBSA approach and Lipinski's rule of five (RO5) were employed to filter the compounds and determine their druggability. Most importantly, the compounds pIC50 were predicted by machine learning-based model generated by AutoQSAR algorithm. The generated model was validated to affirm its predictive model. The best model obtained was Model kpls_desc_38 (R2 = 0.8467 and Q2 = 0.8069), and this external validated model was utilized to predict the bioactivities of the lead compounds. While a number of characterized compounds from Melissa officinalis showed better docking score, binding free energy alongside adherence to RO5 than co-cystallized ligand, only three compounds (salvianolic acid C, ellagic acid and naringenin) showed more satisfactory pIC50. The results obtained in this study can be useful to design potent inhibitors of GSK-3β.

Design, Synthesis, and Biological Evaluation of Novel 7H-[1,2,4]Triazolo[3,4-b][1,3,4]thiadiazine Inhibitors as Antitumor Agents

A series of novel anticancer hydrazinotriazolothiadiazine-based derivatives were designed based on the structure-activity relationship of the previously reported anticancer triazolothiadiazines. These derivatives were synthesized and biologically screened against full NCI-60 cancer cell lines revealing compound 5l with a potential antiproliferative effect. 5l was screened over 16 kinases to study its cytotoxic mechanism which showed to inhibit glycogen synthase kinase-3 β (GSK-3β) with IC₅₀ equal to 0.883 μM and 14-fold selectivity over CDK2. Also, 5l increased active caspase-3 levels, induced cell cycle arrest at the G2-M phase, and increased the percentage of Annexin V-fluorescein isothiocyanate-positive apoptotic cells in PC-3 prostate cancer-treated cells. Molecular docking and dynamics were performed to predict the binding mode of 5l in the GSK-3β ATP binding site. 5l can be utilized as a starting scaffold for developing potential GSK-3β inhibitors.

Crosstalk between GSK-3β-actuated molecular cascades and myocardial physiology

The finding of "glycogen synthase kinase-3" (GSK-3) was initially identified as a protein kinase that phosphorylate and inhibited glycogen synthase. However, it was soon discovered that GSK-3 also has significant impact in regulation of truly astonishing number of critical intracellular signaling pathways ranging from regulation of cell growth, neurology, heart failure, diabetes, aging, inflammation, and cancer. Recent studies have validated the feasibility of targeting GSK-3 for its vital therapeutic potential to maintain normal myocardial homeostasis, conversely, its loss is incompatible with life as it can abrupt cell cycle and endorse fatal cardiomyopathy. The current study focuses on its expanding therapeutic action in myocardial tissue, concentrating primarily on its role in diabetes-associated cardiac complication, apoptosis and metabolism, heart failure, cardiac hypertrophy, and myocardial infarction. The current report also includes the finding of our previous investigation that has shown the impact of GSK-3β inhibitor against diabetes-associated myocardial injury and experimentally induced myocardial infarction. We have also discussed some recent identified GSK-3β inhibitors for their cardio-protective potential. The crosstalk of various underlying mechanisms that highlight the significant role of GSK-3β in myocardial pathophysiology have been discussed in the present report. For these literatures, we will rely profoundly on our previous studies and those of others to reconcile some of the deceptive contradictions in the literature.

Roles of GSK-3 and β-Catenin in Antiviral Innate Immune Sensing of Nucleic Acids

The rapid activation of the type I interferon (IFN) antiviral innate immune response relies on ubiquitously expressed RNA and DNA sensors. Once engaged, these nucleotide-sensing receptors use distinct signaling modules for the rapid and robust activation of mitogen-activated protein kinases (MAPKs), the IκB kinase (IKK) complex, and the IKK-related kinases IKKε and TANK-binding kinase 1 (TBK1), leading to the subsequent activation of the activator protein 1 (AP1), nuclear factor-kappa B (NF-κB), and IFN regulatory factor 3 (IRF3) transcription factors, respectively. They, in turn, induce immunomodulatory genes, allowing for a rapid antiviral cellular response. Unlike the MAPKs, the IKK complex and the IKK-related kinases, ubiquitously expressed glycogen synthase kinase 3 (GSK-3) α and β isoforms are active in unstimulated resting cells and are involved in the constitutive turnover of β-catenin, a transcriptional coactivator involved in cell proliferation, differentiation, and lineage commitment. Interestingly, studies have demonstrated the regulatory roles of both GSK-3 and β-catenin in type I IFN antiviral innate immune response, particularly affecting the activation of IRF3. In this review, we summarize current knowledge on the mechanisms by which GSK-3 and β-catenin control the antiviral innate immune response to RNA and DNA virus infections.

Advanced Evolution of Pathogenesis Concepts in Cardiomyopathies

Cardiomyopathy is a group of heterogeneous cardiac diseases that impair systolic and diastolic function, and can induce chronic heart failure and sudden cardiac death. Cardiomyopathy is prevalent in the general population, with high morbidity and mortality rates, and contributes to nearly 20% of sudden cardiac deaths in younger individuals. Genetic mutations associated with cardiomyopathy play a key role in disease formation, especially the mutation of sarcomere encoding genes and ATP kinase genes, such as titin, lamin A/C, myosin heavy chain 7, and troponin T1. Pathogenesis of cardiomyopathy occurs by multiple complex steps involving several pathways, including the Ras-Raf-mitogen-activated protein kinase-extracellular signal-activated kinase pathway, G-protein signaling, mechanotransduction pathway, and protein kinase B/phosphoinositide 3-kinase signaling. Excess biomechanical stress induces apoptosis signaling in cardiomyocytes, leading to cell loss, which can induce myocardial fibrosis and remodeling. The clinical features and pathophysiology of cardiomyopathy are discussed. Although several basic and clinical studies have investigated the mechanism of cardiomyopathy, the detailed pathophysiology remains unclear. This review summarizes current concepts and focuses on the molecular mechanisms of cardiomyopathy, especially in the signaling from mutation to clinical phenotype, with the aim of informing the development of therapeutic interventions.

Targeted disruption of glycogen synthase kinase-3β in cardiomyocytes attenuates cardiac parasympathetic dysfunction in type 1 diabetic Akita mice

Type 1 diabetic Akita mice develop severe cardiac parasympathetic dysfunction that we have previously demonstrated is due at least in part to an abnormality in the response of the end organ to parasympathetic stimulation. Specifically, we had shown that hypoinsulinemia in the diabetic heart results in attenuation of the G-protein coupled inward rectifying K channel (GIRK) which mediates the negative chronotropic response to parasympathetic stimulation due at least in part to decreased expression of the GIRK1 and GIRK4 subunits of the channel. We further demonstrated that the expression of GIRK1 and GIRK4 is under the control of the Sterol Regulatory element Binding Protein (SREBP-1), which is also decreased in response to hypoinsulinemia. Finally, given that hyperactivity of Glycogen Synthase Kinase (GSK)3β, had been demonstrated in the diabetic heart, we demonstrated that treatment of Akita mice with Li⁺, an inhibitor of GSK3β, increased parasympathetic responsiveness and SREBP-1 levels consistent with the conclusion that GSK3β might regulate IKACh via an effect on SREBP-1. However, inhibitor studies were complicated by lack of specificity for GSK3β. Here we generated an Akita mouse with cardiac specific inducible knockout of GSK3β. Using this mouse, we demonstrate that attenuation of GSK3β expression is associated with an increase in parasympathetic responsiveness measured as an increase in the heart rate response to atropine from 17.3 ± 3.5% (n = 8) prior to 41.2 ± 5.4% (n = 8, P = 0.017), an increase in the duration of carbamylcholine mediated bradycardia from 8.43 ± 1.60 min (n = 7) to 12.71 ± 2.26 min (n = 7, P = 0.028) and an increase in HRV as measured by an increase in the high frequency fraction from 40.78 ± 3.86% to 65.04 ± 5.64 (n = 10, P = 0.005). Furthermore, patch clamp measurements demonstrated a 3-fold increase in acetylcholine stimulated peak IKACh in atrial myocytes from GSK3β deficiency mice compared with control. Finally, western blot analysis of atrial extracts from knockout mice demonstrated increased levels of SREBP-1, GIRK1 and GIRK4 compared with control. Taken together with our prior observations, these data establish a role of increased GSK3β activity in the pathogenesis of parasympathetic dysfunction in type 1 diabetes via the regulation of IKACh and GIRK1/4 expression.

Roles of Glycogen Synthase Kinase-3 (GSK-3) in Cardiac Development and Heart Disease

Glycogen synthase kinase-3 (GSK-3) is a cytoplasmic serine/threonine protein kinase which is known to regulate a variety of cellular processes through a number of signaling pathways important for cell proliferation, stem cell renewal, apoptosis and development. Although GSK-3 exists in a variety of tissues, this kinase plays very important roles in the heart to control its development through the formation of heart and cardiomyocyte proliferation. GSK-3 is also recognized as one of the main molecules that control cardiac hypertrophy and fibrosis. Therefore, GSK-3 could be an attractive target for the development of new drugs to cure cardiac diseases. The present review summarizes the roles of GSK-3 in the signaling pathways and the heart, and discusses the possibility of new drug development targeting this kinase.

Quercetin Prevents In Vivo and In Vitro Myocardial Hypertrophy Through the Proteasome-GSK-3 Pathway

PURPOSE

Quercetin, a flavonoid, has been reported to ameliorate cardiovascular diseases, such as cardiac hypertrophy. However, the mechanism is not completely understood. In this study, a mechanism related to proteasome-glycogen synthesis kinase 3 (GSK-3) was elucidated in rats and primary neonatal cardiomyocytes.

METHODS

Rats were subjected to sham or constriction of abdominal aorta surgery groups and treated with or without quercetin for 8 weeks. Angiotensin II (Ang II)-induced primary cardiomyocytes were cultured with quercetin treatment or not for 48 h. Echocardiography, real-time RT-PCR, histology, immunofluorescence, and Western blotting were conducted. Proteasome activities were also detected using a fluorescent peptide substrate.

RESULTS

Echocardiography showed that quercetin prevented constriction of abdominal aorta-induced cardiac hypertrophy and improved the cardiac diastolic function. In addition, quercetin also significantly reduced the Ang II-induced hypertrophic surface area and atrial natriuretic factor (ANF) mRNA level in primary cardiomyocytes. Proteasome activities were obviously inhibited in the quercetin-treated group both in vivo and in vitro. Quercetin also decreased the levels of proteasome subunit beta type (PSMB) 1, PSMB2, and PSMB5 of the 20S proteasome as well as the levels of proteasome regulatory particle (Rpt) 1 and Rpt4 of the 19S proteasome. In particular, the PSMB5 level in the nucleus was reduced after quercetin treatment. Furthermore, phosphorylated GSK-3α/β (inactivation of GSK-3) was decreased, which means that GSK-3 activity was increased. The phosphorylation levels of upstream AKT (PKB (protein kinase B)) and liver kinase B1/AMP activated protein kinase (LKB1/AMPKα) and those of downstream extracellular signal-regulated kinase (ERK), histone H3, β-catenin, and GATA binding protein 4 (GATA4) were reduced after quercetin treatment, while hypertrophy was reversed after treatment with the GSK-3 inhibitor.

CONCLUSION

In summary, quercetin prevents cardiac hypertrophy, which is related to proteasome inhibition and activation of GSK-3α/β. Upstream (AKT, LKB1/AMPKα) and downstream hypertrophic factors, such as ERK, histone H3, β-catenin, and GATA4, may also be involved.

Habitual aerobic exercise and circulating proteomic patterns in healthy adults: relation to indicators of healthspan

Habitual aerobic exercise enhances physiological function and reduces risk of morbidity and mortality throughout life, but the underlying molecular mechanisms are largely unknown. The circulating proteome reflects the intricate network of physiological processes maintaining homeostasis and may provide insight into the molecular transducers of the health benefits of physical activity. In this exploratory study, we assessed the plasma proteome (SOMAscan proteomic assay; 1,129 proteins) of healthy sedentary or aerobic exercise-trained young women and young and older men ( n = 47). Using weighted correlation network analysis to identify clusters of highly co-expressed proteins, we characterized 10 distinct plasma proteomic modules (patterns). In healthy young (24 ± 1 yr) men and women, 4 modules were associated with aerobic exercise status and 1 with participant sex. In healthy young and older (64 ± 2 yr) men, 5 modules differed with age, but 2 of these were partially preserved at young adult levels in older men who exercised; among all men, 4 modules were associated with exercise status, including 3 of the 4 identified in young adults. Exercise-linked proteomic patterns were related to pathways involved in wound healing, regulation of apoptosis, glucose-insulin and cellular stress signaling, and inflammation/immune responses. Importantly, several of the exercise-related modules were associated with physiological and clinical indicators of healthspan, including diastolic blood pressure, insulin resistance, maximal aerobic capacity, and vascular endothelial function. Overall, these findings provide initial insight into circulating proteomic patterns modulated by habitual aerobic exercise in healthy young and older adults, the biological processes involved, and their relation to indicators of healthspan. NEW & NOTEWORTHY This is the first study to assess the relation between plasma proteomic patterns and aerobic exercise status in healthy adults. Weighted correlation network analysis identified 10 distinct proteomic modules, including 5 patterns specific for exercise status. Additionally, 5 modules differed with aging in men, two of which were preserved in older exercising men. Exercise-associated modules included proteins related to inflammation, stress pathways, and immune function and correlated with clinical and physiological indicators of healthspan.

The cardioprotective effect of dexmedetomidine on regional ischemia/reperfusion injury in type 2 diabetic rat hearts

BACKGROUND

Dexmedetomidine (DEX) is an α₂-adrenergic receptor agonist commonly used during perioperative periods due to its sedation and analgesia effect. It is confirmed that DEX has cardioprotective effects against ischemia/reperfusion (I/R) injury. We investigated whether DEX administration is beneficial to type 2 diabetic rats subjected to I/R injury.

METHODS

The diabetes model was established by providing a high-fat diet for 2 weeks followed by injecting 35 mg/kg streptozotocin (STZ). The myocardial I/R model consisted of left anterior descending coronary artery occlusion for 30 min followed by reperfusion for two-hours. DEX was administered before ischemia; alternatively, yohimbine was administered with or without DEX before ischemia. At the end of reperfusion, the rats were sacrificed, and hearts were isolated for histology. The levels of glycogen synthase kinase-3β (GSK-3β) and phosphorylated GSK-3β (p-GSK-3β) were quantitatively analyzed. The infarct size was measured via Evans Blue and 2,3,5‑triphenyltetrazolium chloride (TTC) staining. Plasma samples were collected to measure the levels of cardiac Troponin T (cTnT). Arrhythmia scores were recorded during the first few minutes of reperfusion.

RESULTS

DEX preconditioning significantly reduced myocardial infarct size, arrhythmia scores and the plasma cTnT levels, and increased the p-GSK-3β levels. All of these protective effects of DEX were reversed by co-administration of yohimbine.

CONCLUSIONS

These results suggested that DEX preconditioning exerted a cardioprotective effect against regional I/R injury in diabetic rats.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

Cyclin D2 is a critical mediator of exercise-induced cardiac hypertrophy

A number of signaling pathways underlying pathological cardiac hypertrophy have been identified. However, few studies have probed the functional significance of these signaling pathways in the context of exercise or physiological pathways. Exercise studies were performed on females from six different genetic mouse models that have been shown to exhibit alterations in pathological cardiac adaptation and hypertrophy. These include mice expressing constitutively active glycogen synthase kinase-3β (GSK-3βS9A), an inhibitor of CaMK II (AC3-I), both GSK-3βS9A and AC3-I (GSK-3βS9A/AC3-I), constitutively active Akt (myrAkt), mice deficient in MAPK/ERK kinase kinase-1 (MEKK1-/-), and mice deficient in cyclin D2 (cyclin D2-/-). Voluntary wheel running performance was similar to NTG littermates for five of the mouse lines. Exercise induced significant cardiac growth in all mouse models except the cyclin D2-/- mice. Cardiac function was not impacted in the cyclin D2-/- mice and studies using a phospho-antibody array identified six proteins with increased phosphorylation (greater than 150%) and nine proteins with decreased phosphorylation (greater than 33% decrease) in the hearts of exercised cyclin D2-/- mice compared to exercised NTG littermate controls. Our results demonstrate that unlike the other hypertrophic signaling molecules tested here, cyclin D2 is an important regulator of both pathologic and physiological hypertrophy. Impact statement This research is relevant as the hypertrophic signaling pathways tested here have only been characterized for their role in pathological hypertrophy, and not in the context of exercise or physiological hypertrophy. By using the same transgenic mouse lines utilized in previous studies, our findings provide a novel and important understanding for the role of these signaling pathways in physiological hypertrophy. We found that alterations in the signaling pathways tested here had no impact on exercise performance. Exercise induced cardiac growth in all of the transgenic mice except for the mice deficient in cyclin D2. In the cyclin D2 null mice, cardiac function was not impacted even though the hypertrophic response was blunted and a number of signaling pathways are differentially regulated by exercise. These data provide the field with an understanding that cyclin D2 is a key mediator of physiological hypertrophy.

The Impact of Chronic Glycogen Synthase Kinase-3 Inhibition on Remodeling of Normal and Pre-Diabetic Rat Hearts

PURPOSE

There is an ongoing search for new drugs and drug targets to treat diseases like Alzheimer's disease, cancer and type 2 diabetes (T2D). Both obesity and T2D are characterized by the development of a cardiomyopathy associated with increased hypertension and compensatory left ventricular hypertrophy. Small, specific glycogen synthase kinase-3 (GSK-3) inhibitors were developed to replace lithium chloride for use in psychiatric disorders. In addition, they were advocated as treatment for T2D since GSK-3 inhibition improves blood glucose handling. However, GSK-3 is a regulator of hypertrophic signalling in the heart via phosphorylation of NFATc3 and β-catenin respectively. In view of this, we hypothesized that chronic inhibition of GSK-3 will induce myocardial hypertrophy or exacerbate existing hypertrophy.

METHODS

Rats with obesity-induced prediabetes were treated orally with GSK-3 inhibitor (CHIR118637 (CT20026)), 30 mg/kg/day for the last 8 weeks of a 20-week diet high in sugar content vs a control diet. Biometric and biochemical parameters were measured, echocardiography performed and localization and co-localization of NFATc3 and GATA4 determined in cardiomyocytes.

RESULTS

Obesity initiated myocardial hypertrophy, evidenced by increased ventricular mass (1.158 ± 0.029 vs 0.983 ± 0.03 g) and enlarged cardiomyocytes (18.86 ± 2.25 vs 14.92 ± 0.50um(2)) in association with increased end-diastolic diameter (EDD = 8.48 ± 0.11 vs 8.15 ± 0.10 mm). GSK-3 inhibition (i) increased ventricular mass only in controls (1.075 ± 0.022 g) and (ii) EDD in both groups (controls: 8.63 ± 0.07; obese: 8.72 ± 0.15 mm) (iii) localized NFATc3 and GATA4 peri-nuclearly.

CONCLUSION

Indications of onset of myocardial hypertrophy in both control and obese rats treated with a GSK-3 inhibitor were found. It remains speculation whether these changes were adaptive or maladaptive.

Remote ischemic preconditioning differentially attenuates post-ischemic cardiac arrhythmia in streptozotocin-induced diabetic versus nondiabetic rats

Background

Sudden cardiac death (SCD), a leading cause of global mortality, most commonly arises from a substrate of cardiac ischemia, but requires an additional trigger. Diabetes mellitus (DM) predisposes to SCD even after adjusting for other DM-linked cardiovascular pathology such as coronary artery disease. We previously showed that remote liver ischemia preconditioning (RLIPC) is highly protective against cardiac ischemia reperfusion injury (IRI) linked ventricular arrhythmias and myocardial infarction, via induction of the cardioprotective RISK pathway, and specifically, inhibitory phosphorylation of GSK-3β (Ser 9).

Methods

We evaluated the impact of acute streptozotocin-induced DM on coronary artery ligation IRI-linked ventricular arrhythmogenesis and RLIPC therapy in rats.

Results

Post-IRI arrhythmia induction was similar in nondiabetic and DM rats, but, unexpectedly, DM rats exhibited lower incidence of SCD during reperfusion (41 vs. 100%), suggesting uncontrolled hyperglycemia does not acutely predispose to SCD. RLIPC was highly effective in both nondiabetic and DM rats at reducing incidence and duration of, and increasing latency to, all classes of ventricular tachyarrhythmias. In contrast, atrioventricular block (AVB) was highly responsive to RLIPC in nondiabetic rats (incidence reduced from 72 to 18%) but unresponsive in DM rats. RISK pathway induction was similar in nondiabetic and DM rats, thus not explaining the DM-specific resistance of AVB to therapy.

Conclusions

Our findings uncover important acute DM-specific differences in responsiveness to remote preconditioning for ventricular tachyarrhythmias versus AVB, which may have clinical significance given that AVB is a malignant arrhythmia twofold more common in human diabetics than nondiabetics, and correlated to plasma glucose levels >10 mmol/L.

Pharmacophore-based screening and drug repurposing exemplified on glycogen synthase kinase-3 inhibitors

The current study was conducted to elaborate a novel pharmacophore model to accurately map selective glycogen synthase kinase-3 (GSK-3) inhibitors, and perform virtual screening and drug repurposing. Pharmacophore modeling was developed using PHASE on a data set of 203 maleimides. Two benchmarking validation data sets with focus on selectivity were assembled using ChEMBL and PubChem GSK-3 confirmatory assays. A drug repurposing experiment linking pharmacophore matching with drug information originating from multiple data sources was performed. A five-point pharmacophore model was built consisting of a hydrogen bond acceptor (A), hydrogen bond donor (D), hydrophobic (H), and two rings (RR). An atom-based 3D quantitative structure-activity relationship (QSAR) model showed good correlative and satisfactory predictive abilities (training set [Formula: see text]; test set: [Formula: see text]; whole data set: stability [Formula: see text]). Virtual screening experiments revealed that selective GSK-3 inhibitors are ranked preferentially by Hypo-1, but fail to retrieve nonselective compounds. The pharmacophore and 3D QSAR models can provide assistance to design novel, potential GSK-3 inhibitors with high potency and selectivity pattern, with potential application for the treatment of GSK-3-driven diseases. A class of purine nucleoside antileukemic drugs was identified as potential inhibitor of GSK-3, suggesting the reassessment of the target range of these drugs.

GSK-3β controls NF-kappaB activity via IKKγ/NEMO

The NF-κB signaling pathway is central for the innate immune response and its deregulation is found in multiple disorders such as autoimmune, chronic inflammatory and metabolic diseases. IKKγ/NEMO is essential for NF-κB activation and NEMO dysfunction in humans has been linked to so-called progeria syndromes, which are characterized by advanced ageing due to age-dependent inflammatory diseases. It has been suggested that glycogen synthase kinase-3β (GSK-3β) participates in NF-κB regulation but the exact mechanism remained incompletely understood. In this study, we identified NEMO as a GSK-3β substrate that is phosphorylated at serine 8, 17, 31 and 43 located within its N-terminal domain. The kinase forms a complex with wild-type NEMO while point mutations of NEMO at the specific serines abrogated GSK-3β binding and subsequent phosphorylation of NEMO resulting in its destabilization. However, K63-linked polyubiquitination was augmented in mutated NEMO explaining an increased binding to IKKα and IKKβ. Even IκBα was found degraded. Still, TNFα-stimulated NF-κB activation was impaired pointing towards an un-controlled signalling process. Our data suggest that GSK-3β is critically important for ordered NF-κB signalling through modulation of NEMO phosphorylation.

Effects of mutations in Wnt/β-catenin, hedgehog, Notch and PI3K pathways on GSK-3 activity-Diverse effects on cell growth, metabolism and cancer

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that participates in an array of critical cellular processes. GSK-3 was first characterized as an enzyme that phosphorylated and inactivated glycogen synthase. However, subsequent studies have revealed that this moon-lighting protein is involved in numerous signaling pathways that regulate not only metabolism but also have roles in: apoptosis, cell cycle progression, cell renewal, differentiation, embryogenesis, migration, regulation of gene transcription, stem cell biology and survival. In this review, we will discuss the roles that GSK-3 plays in various diseases as well as how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTOR, Ras/Raf/MEK/ERK, Wnt/beta-catenin, hedgehog, Notch and TP53. Mutations that occur in these and other pathways can alter the effects that natural GSK-3 activity has on regulating these signaling circuits that can lead to cancer as well as other diseases. The novel roles that microRNAs play in regulation of the effects of GSK-3 will also be evaluated. Targeting GSK-3 and these other pathways may improve therapy and overcome therapeutic resistance.

Induction of Human iPSC-Derived Cardiomyocyte Proliferation Revealed by Combinatorial Screening in High Density Microbioreactor Arrays

Inducing cardiomyocyte proliferation in post-mitotic adult heart tissue is attracting significant attention as a therapeutic strategy to regenerate the heart after injury. Model animal screens have identified several candidate signalling pathways, however, it remains unclear as to what extent these pathways can be exploited, either individually or in combination, in the human system. The advent of human cardiac cells from directed differentiation of human pluripotent stem cells (hPSCs) now provides the ability to interrogate human cardiac biology in vitro, but it remains difficult with existing culture formats to simply and rapidly elucidate signalling pathway penetrance and interplay. To facilitate high-throughput combinatorial screening of candidate biologicals or factors driving relevant molecular pathways, we developed a high-density microbioreactor array (HDMA) – a microfluidic cell culture array containing 8100 culture chambers. We used HDMAs to combinatorially screen Wnt, Hedgehog, IGF and FGF pathway agonists. The Wnt activator CHIR99021 was identified as the most potent molecular inducer of human cardiomyocyte proliferation, inducing cell cycle activity marked by Ki67, and an increase in cardiomyocyte numbers compared to controls. The combination of human cardiomyocytes with the HDMA provides a versatile and rapid tool for stratifying combinations of factors for heart regeneration.

Loss of Adult Cardiac Myocyte GSK-3 Leads to Mitotic Catastrophe Resulting in Fatal Dilated Cardiomyopathy

RATIONALE

Cardiac myocyte-specific deletion of either glycogen synthase kinase (GSK)-3α and GSK-3β leads to cardiac protection after myocardial infarction, suggesting that deletion of both isoforms may provide synergistic protection. This is an important consideration because of the fact that all GSK-3-targeted drugs, including the drugs already in clinical trial target both isoforms of GSK-3, and none are isoform specific.

OBJECTIVE

To identify the consequences of combined deletion of cardiac myocyte GSK-3α and GSK-3β in heart function.

METHODS AND RESULTS

We generated tamoxifen-inducible cardiac myocyte-specific mice lacking both GSK-3 isoforms (double knockout). We unexpectedly found that cardiac myocyte GSK-3 is essential for cardiac homeostasis and overall survival. Serial echocardiographic analysis reveals that within 2 weeks of tamoxifen treatment, double-knockout hearts leads to excessive dilatative remodeling and ventricular dysfunction. Further experimentation with isolated adult cardiac myocytes and fibroblasts from double-knockout implicated cardiac myocytes intrinsic factors responsible for observed phenotype. Mechanistically, loss of GSK-3 in adult cardiac myocytes resulted in induction of mitotic catastrophe, a previously unreported event in cardiac myocytes. Double-knockout cardiac myocytes showed cell cycle progression resulting in increased DNA content and multinucleation. However, increased cell cycle activity was rivaled by marked activation of DNA damage, cell cycle checkpoint activation, and mitotic catastrophe-induced apoptotic cell death. Importantly, mitotic catastrophe was also confirmed in isolated adult cardiac myocytes.

CONCLUSIONS

Together, our findings suggest that cardiac myocyte GSK-3 is required to maintain normal cardiac homeostasis, and its loss is incompatible with life because of cell cycle dysregulation that ultimately results in a severe fatal dilated cardiomyopathy.

Kcne2 deletion attenuates acute post-ischaemia/reperfusion myocardial infarction

AIMS

Most cardiac arrhythmia-associated genes encode ion channel subunits and regulatory proteins that are also expressed outside the heart, suggesting that diseases linked to their disruption may be multifactorial. KCNE2 is a ubiquitously expressed potassium channel β subunit associated with cardiac arrhythmia, atherosclerosis, and myocardial infarction (MI) in human populations. Here, we tested the hypothesis that Kcne2 disruption in mice would influence the acute outcome of experimentally induced MI.

METHODS AND RESULTS

One-year-old male Kcne2⁺/⁺ and Kcne2⁻/⁻ mice were subjected to cardiac ischaemia/reperfusion injury (IRI) by left anterior descending coronary artery ligation. After reperfusion (3 h), infarct size and markers of tissue damage were quantified. Unexpectedly, post-reperfusion, Kcne2⁻/⁻ mice exhibited 40% lower infarct size, decreased myocardial apoptosis and damage, and more than two-fold lower serum levels of damage markers, lactate dehydrogenase and creatine kinase, than Kcne2⁺/⁺ mice. Kcne2 deletion, despite increasing normalized heart weight and prolonging baseline QTc by 70%, helped preserve post-infarct cardiac function (quantified by a Millar catheter), with parameters including left ventricular maximum pressure, max dP/dt (P < 0.01), contractility index, and pressure/time index (P < 0.05) all greater in Kcne2⁻/⁻ compared with Kcne2⁺/⁺ mice. Western blotting indicated two-fold-increased glycogen synthase kinase 3β (GSK-3β) phosphorylation (inactivation) before and after IRI (P < 0.05) in Kcne2⁻/⁻ mice compared with Kcne2⁺/⁺ mice. GSK-3β inhibition by SB216763 mimicked in Kcne2⁺/⁺ mice the cardioprotective effects of Kcne2 deletion, but did not further enhance them in Kcne2⁻/⁻mice, suggesting that GSK-3β inactivation was a primary cardioprotective mechanism arising from Kcne2 deletion.

CONCLUSIONS

Kcne2 deletion preconditions the heart, attenuating the acute tissue damage caused by an imposed IRI. The findings contribute further evidence that genetic disruption of arrhythmia-associated ion channel genes has cardiac ramifications beyond abnormal electrical activity.

Protein kinase G signaling in cardiac pathophysiology: Impact of proteomics on clinical trials

The protective role of cyclic guanosine monophosphate (cGMP)-stimulated protein kinase G (PKG) in the heart makes it an attractive target for therapeutic drug development to treat a variety of cardiac diseases. Phosphodiesterases degrade cGMP, thus phosphodiesterase inhibitors that can increase PKG are of translational interest and the subject of ongoing human trials. PKG signaling is complex, however, and understanding its downstream phosphorylation targets and upstream regulation are necessary steps toward safe and efficacious drug development. Proteomic technologies have paved the way for assays that allow us to peer broadly into signaling minutia, including protein quantity changes and phosphorylation events. However, there are persistent challenges to the proteomic study of PKG, such as the impact of the expression of different PKG isoforms, changes in its localization within the cell, and alterations caused by oxidative stress. PKG signaling is also dependent upon sex and potentially the genetic and epigenetic background of the individual. Thus, the rigorous application of proteomics to the field will be necessary to address how these effectors can alter PKG signaling and interfere with pharmacological interventions. This review will summarize PKG signaling, how it is being targeted clinically, and the proteomic challenges and techniques that are being used to study it.

How do kinases contribute to tonicity-dependent regulation of the transcription factor NFAT5?

NFAT5 plays a critical role in maintaining the renal functions. Its dis-regulation in the kidney leads to or is associated with certain renal diseases or disorders, most notably the urinary concentration defect. Hypertonicity, which the kidney medulla is normally exposed to, activates NFAT5 through phosphorylation of a signaling molecule or NFAT5 itself. Hypotonicity inhibits NFAT5 through a similar mechanism. More than a dozen of protein and lipid kinases have been identified to contribute to tonicity-dependent regulation of NFAT5. Hypertonicity activates NFAT5 by increasing its nuclear localization and transactivating activity in the early phase and protein abundance in the late phase. The known mechanism for inhibition of NFAT5 by hypotonicity is a decrease of nuclear NFAT5. The present article reviews the effect of each kinase on NFAT5 nuclear localization, transactivation and protein abundance, and the relationship among these kinases, if known. Cyclosporine A and tacrolimus suppress immune reactions by inhibiting the phosphatase calcineurin-dependent activation of NFAT1. It is hoped that this review would stimulate the interest to seek explanations from the NFAT5 regulatory pathways for certain clinical presentations and to explore novel therapeutic approaches based on the pathways. On the basic science front, this review raises two interesting questions. The first one is how these kinases can specifically signal to NFAT5 in the context of hypertonicity or hypotonicity, because they also regulate other cellular activities and even opposite activities in some cases. The second one is why these many kinases, some of which might have redundant functions, are needed to regulate NFAT5 activity. This review reiterates the concept of signaling through cooperation. Cells need these kinases working in a coordinated way to provide the signaling specificity that is lacking in the individual one. Redundancy in regulation of NFAT5 is a critical strategy for cells to maintain robustness against hypertonic or hypotonic stress.

Fine-Tuning of the RIG-I-Like Receptor/Interferon Regulatory Factor 3-Dependent Antiviral Innate Immune Response by the Glycogen Synthase Kinase 3/β-Catenin Pathway

Induction of an antiviral innate immune response relies on pattern recognition receptors, including retinoic acid-inducible gene 1-like receptors (RLR), to detect invading pathogens, resulting in the activation of multiple latent transcription factors, including interferon regulatory factor 3 (IRF3). Upon sensing of viral RNA and DNA, IRF3 is phosphorylated and recruits coactivators to induce type I interferons (IFNs) and selected sets of IRF3-regulated IFN-stimulated genes (ISGs) such as those for ISG54 (Ifit2), ISG56 (Ifit1), and viperin (Rsad2). Here, we used wild-type, glycogen synthase kinase 3α knockout (GSK-3α(-/-)), GSK-3β(-/-), and GSK-3α/β double-knockout (DKO) embryonic stem (ES) cells, as well as GSK-3β(-/-) mouse embryonic fibroblast cells in which GSK-3α was knocked down to demonstrate that both isoforms of GSK-3, GSK-3α and GSK-3β, are required for this antiviral immune response. Moreover, the use of two selective small-molecule GSK-3 inhibitors (CHIR99021 and BIO-acetoxime) or ES cells reconstituted with the catalytically inactive versions of GSK-3 isoforms showed that GSK-3 activity is required for optimal induction of antiviral innate immunity. Mechanistically, GSK-3 isoform activation following Sendai virus infection results in phosphorylation of β-catenin at S33/S37/T41, promoting IRF3 DNA binding and activation of IRF3-regulated ISGs. This study identifies the role of a GSK-3/β-catenin axis in antiviral innate immunity.

Astaxanthin induces angiogenesis through Wnt/β-catenin signaling pathway

OBJECTIVE

In the present study, we sought to elucidate whether astaxanthin contributes to induce angiogenesis and its mechanisms.

MATERIALS AND METHODS

To this end, we examined the role of astaxanthin on human brain microvascular endothelial cell line (HBMEC) and rat aortic smooth muscle cell (RASMC) proliferation, invasion and tube formation in vitro. For study of mechanism, the Wnt/β-catenin signaling pathway inhibitor IWR-1-endo was used. HMBECs and RASMCs proliferation were tested by cell counting. Scratch adhesion test was used to assess the ability of invasion. A matrigel tube formation assay was performed to test capillary tube formation ability. The Wnt/β-catenin pathway activation in HMBECs and RASMCs were tested by Western blot.

RESULTS

Our data suggested that astaxanthin induces angiogenesis by increasing proliferation, invasion and tube formation in vitro. Wnt and β-catenin expression were increased by astaxanthin and counteracted by IWR-1-endo in HMBECs and RASMCs. Tube formation was increased by astaxanthin and counteracted by IWR-1-endo.

CONCLUSIONS

It may be suggested that astaxanthin induces angiogenesis in vitro via a programmed Wnt/β-catenin signaling pathway.

PI3K/SGK1/GSK3β signaling pathway is involved in inhibition of autophagy in neonatal rat cardiomyocytes exposed to hypoxia/reoxygenation by hydrogen sulfide

Excessive autophagy aggravates myocardial ischemia/reperfusion (IR) injury. Hydrogen sulfide (H2S) has been shown to possess a strong cardioprotective effect due to its anti-necrosis, anti-apoptosis, anti-oxidant and anti-inflammatory properties. Our previous study showed that H2S could also protect the myocardium against IR injury through its anti-autophagy effect in vivo, but the underlying mechanism remains unclear. The aim of the present study was to determine whether PI3K/SGK1/GSK3β signaling pathway was involved in the anti-autophagy effect of H2S against myocardial hypoxia/reoxygenation (HR) injury in vitro. Autophagy was significantly increased in cardiomyocytes subjected to HR, but it was down-regulated by H2S (NaHS donor). Blocking PI3K by LY294002 (a PI3K inhibitor) or knocking down SGK1 by SGK1 siRNA augmented autophagy and attenuated the anti-autophagy effect of H2S. However, blocking GSK3β by tws119 (a GSK3β inhibitor) produced an opposite effect. In addition, while treatment of neonatal rat cardiomyocytes with HR reduced cell viability and augmented cell injury, H2S significantly reversed it. Blocking PI3K or knocking down SGK1 aggravated HR injury and weakened the protective effect of H2S, while blocking GSK3β produced an opposite effect. In conclusion, H2S can inhibit autophagy in neonatal rat cardiomyocytes exposed to H/R and exert a cardioprotective effect at least partly by regulating PI3K/SGK1/GSK3β signaling pathway.

Calcineurin B homologous protein 3 negatively regulates cardiomyocyte hypertrophy via inhibition of glycogen synthase kinase 3 phosphorylation

Cardiac hypertrophy is a leading cause of serious heart diseases. Although many signaling molecules are involved in hypertrophy, the functions of some proteins in this process are still unknown. Calcineurin B homologous protein 3 (CHP3)/tescalcin is an EF-hand Ca(2+)-binding protein that is abundantly expressed in the heart; however, the function of CHP3 is unclear. Here, we aimed to identify the cardiac functions of CHP3. CHP3 was expressed in hearts at a wide range of developmental stages and was specifically detected in neonatal rat ventricular myocytes (NRVMs) but not in cardiac fibroblasts in culture. Moreover, knockdown of CHP3 expression using adenoviral-based RNA interference in NRVMs resulted in enlargement of cardiomyocyte size, concomitant with increased expression of a pathological hypertrophy marker ANP. This same treatment elevated glycogen synthase kinase (GSK3α/β) phosphorylation, which is known to inhibit GSK3 function. In contrast, CHP3 overexpression blocked the insulin-induced phosphorylation of GSK3α/β without affecting the phosphorylation of Akt, which is an upstream kinase of GSK3α/β, in HEK293 cells, and it inhibited both IGF-1-induced phosphorylation of GSK3β and cardiomyocyte hypertrophy in NRVMs. Co-immunoprecipitation experiments revealed that GSK3β interacted with CHP3. However, a Ca(2+)-binding-defective mutation of CHP3 (CHP3-D123A) also interacted with GSK3β and had the same inhibitory effect on GSK3α/β phosphorylation, suggesting that the action of CHP3 was independent of Ca(2+). These findings suggest that CHP3 functions as a novel negative regulator of cardiomyocyte hypertrophy via inhibition of GSK3α/β phosphorylation and subsequent enzymatic activation of GSK3α/β.

The GSK-3 family as therapeutic target for myocardial diseases

Glycogen synthase kinase-3 (GSK-3) is one of the few signaling molecules that regulate a truly astonishing number of critical intracellular signaling pathways. It has been implicated in several diseases including heart failure, bipolar disorder, diabetes mellitus, Alzheimer disease, aging, inflammation, and cancer. Furthermore, a recent clinical trial has validated the feasibility of targeting GSK-3 with small molecule inhibitors for human diseases. In the current review, we will focus on its expanding role in the heart, concentrating primarily on recent studies that have used cardiomyocyte- and fibroblast-specific conditional gene deletion in mouse models. We will highlight the role of the GSK-3 isoforms in various pathological conditions including myocardial aging, ischemic injury, myocardial fibrosis, and cardiomyocyte proliferation. We will discuss our recent findings that deletion of GSK-3α specifically in cardiomyocytes attenuates ventricular remodeling and cardiac dysfunction after myocardial infarction by limiting scar expansion and promoting cardiomyocyte proliferation. The recent emergence of GSK-3β as a regulator of myocardial fibrosis will also be discussed. We will review our recent findings that specific deletion of GSK-3β in cardiac fibroblasts leads to fibrogenesis, left ventricular dysfunction, and excessive scarring in the ischemic heart. Finally, we will examine the underlying mechanisms that drive the aberrant myocardial fibrosis in the models in which GSK-3β is specifically deleted in cardiac fibroblasts. We will summarize these recent results and offer explanations, whenever possible, and hypotheses when not. For these studies we will rely heavily on our models and those of others to reconcile some of the apparent inconsistencies in the literature.

GSK-3 as potential target for therapeutic intervention in cancer

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) was initially identified and studied in the regulation of glycogen synthesis. GSK-3 functions in a wide range of cellular processes. Aberrant activity of GSK-3 has been implicated in many human pathologies including: bipolar depression, Alzheimer's disease, Parkinson's disease, cancer, non-insulin-dependent diabetes mellitus (NIDDM) and others. In some cases, suppression of GSK-3 activity by phosphorylation by Akt and other kinases has been associated with cancer progression. In these cases, GSK-3 has tumor suppressor functions. In other cases, GSK-3 has been associated with tumor progression by stabilizing components of the beta-catenin complex. In these situations, GSK-3 has oncogenic properties. While many inhibitors to GSK-3 have been developed, their use remains controversial because of the ambiguous role of GSK-3 in cancer development. In this review, we will focus on the diverse roles that GSK-3 plays in various human cancers, in particular in solid tumors. Recently, GSK-3 has also been implicated in the generation of cancer stem cells in various cell types. We will also discuss how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTORC1, Ras/Raf/MEK/ERK, Wnt/beta-catenin, Hedgehog, Notch and others.

Glycogen synthase kinase-3 (GSK3): regulation, actions, and diseases

Glycogen synthase kinase-3 (GSK3) may be the busiest kinase in most cells, with over 100 known substrates to deal with. How does GSK3 maintain control to selectively phosphorylate each substrate, and why was it evolutionarily favorable for GSK3 to assume such a large responsibility? GSK3 must be particularly adaptable for incorporating new substrates into its repertoire, and we discuss the distinct properties of GSK3 that may contribute to its capacity to fulfill its roles in multiple signaling pathways. The mechanisms regulating GSK3 (predominantly post-translational modifications, substrate priming, cellular trafficking, protein complexes) have been reviewed previously, so here we focus on newly identified complexities in these mechanisms, how each of these regulatory mechanism contributes to the ability of GSK3 to select which substrates to phosphorylate, and how these mechanisms may have contributed to its adaptability as new substrates evolved. The current understanding of the mechanisms regulating GSK3 is reviewed, as are emerging topics in the actions of GSK3, particularly its interactions with receptors and receptor-coupled signal transduction events, and differential actions and regulation of the two GSK3 isoforms, GSK3α and GSK3β. Another remarkable characteristic of GSK3 is its involvement in many prevalent disorders, including psychiatric and neurological diseases, inflammatory diseases, cancer, and others. We address the feasibility of targeting GSK3 therapeutically, and provide an update of its involvement in the etiology and treatment of several disorders.

Chronic high-fat diet-induced obesity decreased survival and increased hypertrophy of rats with experimental eccentric hypertrophy from chronic aortic regurgitation

Background

The composition of a diet can influence myocardial metabolism and development of left ventricular hypertrophy (LVH). The impact of a high-fat diet in chronic left ventricular volume overload (VO) causing eccentric LVH is unknown. This study examined the effects of chronic ingestion of a high-fat diet in rats with chronic VO caused by severe aortic valve regurgitation (AR) on LVH, function and on myocardial energetics and survival.

Methods

Male Wistar rats were divided in four groups: Shams on control or high-fat (HF) diet (15 rats/group) and AR rats fed with the same diets (ARC (n = 56) and ARHF (n = 32)). HF diet was started one week before AR induction and the protocol was stopped 30 weeks later.

Results

As expected, AR caused significant LV dilation and hypertrophy and this was exacerbated in the ARHF group. Moreover, survival in the ARHF group was significantly decreased compared the ARC group. Although the sham animals on HF also developed significant obesity compared to those on control diet, this was not associated with heart hypertrophy. The HF diet in AR rats partially countered the expected shift in myocardial energy substrate preference usually observed in heart hypertrophy (from fatty acids towards glucose). Systolic function was decreased in AR rats but HF diet had no impact on this parameter. The response to HF diet of different fatty acid oxidation markers as well as the increase in glucose transporter-4 translocation to the plasma membrane compared to ARC was blunted in AR animals compared to those on control diet.

Conclusions

HF diet for 30 weeks decreased survival of AR rats and worsened eccentric hypertrophy without affecting systolic function. The expected adaptation of myocardial energetics to volume-overload left ventricle hypertrophy in AR animals seemed to be impaired by the high-fat diet suggesting less metabolic flexibility.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2261-14-123) contains supplementary material, which is available to authorized users.

Inhibition of GSK-3 induces differentiation and impaired glucose metabolism in renal cancer

Glycogen synthase kinase-3 (GSK-3), a constitutively active serine/threonine kinase, is a key regulator of numerous cellular processes ranging from glycogen metabolism to cell-cycle regulation and proliferation. Consistent with its involvement in many pathways, it has also been implicated in the pathogenesis of various human diseases, including type II diabetes, Alzheimer disease, bipolar disorder, inflammation, and cancer. Consequently, it is recognized as an attractive target for the development of new drugs. In the present study, we investigated the effect of both pharmacologic and genetic inhibition of GSK-3 in two different renal cancer cell lines. We have shown potent antiproliferative activity of 9-ING-41, a maleimide-based GSK-3 inhibitor. The antiproliferative activity is most likely caused by G(0)-G(1) and G(2)-M phase arrest as evident from cell-cycle analysis. We have established that inhibition of GSK-3 imparted a differentiated phenotype in renal cancer cells. We have also shown that GSK-3 inhibition induced autophagy, likely as a result of imbalanced energy homeostasis caused by impaired glucose metabolism. In addition, we have demonstrated the antitumor activity of 9-ING-41 in two different subcutaneous xenograft renal cell carcinoma tumor models. To our knowledge, this is the first report describing autophagy induction due to GSK-3 inhibition in renal cancer cells.

Nuclear GSK-3β segregation in desmoid-type fibromatosis

AIMS

Desmoid-type fibromatosis (DF) is a rare benign myofibroblastic neoplasm of the connective tissue that is unable to metastasize but is associated with a high local recurrence rate. Nuclear β-catenin is the most commonly used histological marker of DF; however, clinical and biological predictive markers guiding the treatment and follow-up of DF are still lacking. Normally, β-catenin is regulated by the cytoplasmic multiprotein complex of adenomatous polyposis coli (APC), axin, casein kinase 1α (CK1α), and glycogen synthase kinase 3β (GSK-3β); this phosphorylates and degrades β-catenin, which would otherwise translocate to the nucleus. The aim of this study was to analyse the expression and localization of the β-catenin-protein complex of the Wnt pathway in cells isolated from DF patients.

METHODS AND RESULTS

We isolated cells from biopsies of DF patients, and demonstrated, by immunofluorescence and immunoblot analyses, that it is almost exclusively nuclear GSK-3β that colocalizes and interacts with β-catenin. The nuclear translocation of β-catenin and GSK-3β is not correlated with CTNNB1 mutations. In DF samples, the multiprotein complex is disrupted, as the cytoplasmic localization of APC and axin makes interaction with the nuclear β-catenin and GSK-3β impossible.

CONCLUSIONS

Our data suggest that GSK-3β is an additional DF marker with an important role in the aetiopathogenesis of this entity.

AMP activated protein kinase is indispensable for myocardial adaptation to caloric restriction in mice

Caloric restriction (CR) is a robust dietary intervention known to enhance cardiovascular health. AMP activated protein kinase (AMPK) has been suggested to mediate the cardioprotective effects of CR. However, this hypothesis remains to be tested by using definitive loss-of-function animal models. In the present study, we subjected AMPKα2 knockout (KO) mice and their wild type (WT) littermates to a CR regimen that reduces caloric intake by 20%–40% for 4 weeks. CR decreased body weight, heart weight and serum levels of insulin in both WT and KO mice to the same degree, indicating the effectiveness of the CR protocol. CR activated cardiac AMPK signaling in WT mice, but not in AMPKα2 KO mice. Correspondingly, AMPKα2 KO mice had markedly reduced cardiac function during CR as determined by echocardiography and hemodynamic measurements. The compromised cardiac function was associated with increased markers of oxidative stress, endoplasmic reticulum stress and myocyte apoptosis. Mechanistically, CR down-regulated the expression of ATP5g2, a subunit of mitochondrial ATP synthase, and reduced ATP content in AMPKα2 KO hearts, but not in WT hearts. In addition, CR accelerated cardiac autophagic flux in WT mice, but failed to do so in AMPKα2 KO mice. These results demonstrated that without AMPK, CR triggers adverse effects that can lead to cardiac dysfunction, suggesting that AMPK signaling pathway is indispensible for energy homeostasis and myocardial adaptation to CR, a dietary intervention that normally produces beneficial cardiac effects.

GSK-3α is a central regulator of age-related pathologies in mice

Aging is regulated by conserved signaling pathways. The glycogen synthase kinase-3 (GSK-3) family of serine/threonine kinases regulates several of these pathways, but the role of GSK-3 in aging is unknown. Herein, we demonstrate premature death and acceleration of age-related pathologies in the Gsk3a global KO mouse. KO mice developed cardiac hypertrophy and contractile dysfunction as well as sarcomere disruption and striking sarcopenia in cardiac and skeletal muscle, a classical finding in aging. We also observed severe vacuolar degeneration of myofibers and large tubular aggregates in skeletal muscle, consistent with impaired clearance of insoluble cellular debris. Other organ systems, including gut, liver, and the skeletal system, also demonstrated age-related pathologies. Mechanistically, we found marked activation of mTORC1 and associated suppression of autophagy markers in KO mice. Loss of GSK-3α, either by pharmacologic inhibition or Gsk3a gene deletion, suppressed autophagy in fibroblasts. mTOR inhibition rescued this effect and reversed the established pathologies in the striated muscle of the KO mouse. Thus, GSK-3α is a critical regulator of mTORC1, autophagy, and aging. In its absence, aging/senescence is accelerated in multiple tissues. Strategies to maintain GSK-3α activity and/or inhibit mTOR in the elderly could retard the appearance of age-related pathologies.

Inhibitory phosphorylation of GSK-3β by AKT, PKA, and PI3K contributes to high NaCl-induced activation of the transcription factor NFAT5 (TonEBP/OREBP)

High NaCl activates the transcription factor nuclear factor of activated T cells 5 (NFAT5), leading to increased transcription of osmoprotective target genes. Kinases PKA, PI3K, AKT1, and p38α were known to contribute to the high NaCl-induced increase of NFAT5 activity. We now identify another kinase, GSK-3β. siRNA-mediated knock-down of GSK-3β increases NFAT5 transcriptional and transactivating activities without affecting high NaCl-induced nuclear localization of NFAT5 or NFAT5 protein expression. High NaCl increases phosphorylation of GSK-3β-S9, which inhibits GSK-3β. In GSK-3β-null mouse embryonic fibroblasts transfection of GSK-3β, in which serine 9 is mutated to alanine, so that it cannot be inhibited by phosphorylation at that site, inhibits high NaCl-induced NFAT5 transcriptional activity more than transfection of wild-type GSK-3β. High NaCl-induced phosphorylation of GSK-3β-S9 depends on PKA, PI3K, and AKT, but not p38α. Overexpression of PKA catalytic subunit α or of catalytically active AKT1 reduces inhibition of NFAT5 by GSK-3β, but overexpression of p38α together with its catalytically active upstream kinase, MKK6, does not. Thus, GSK-3β normally inhibits NFAT5 by suppressing its transactivating activity. When activated by high NaCl, PKA, PI3K, and AKT1, but not p38α, increase phosphorylation of GSK-3β-S9, which reduces the inhibitory effect of GSK-3β on NFAT5, and thus contributes to activation of NFAT5.

Glycogen synthase kinase-3 regulation of urinary concentrating ability

PURPOSE OF REVIEW

Glycogen synthase kinase-3 (GSK3) is an enzyme that is gaining prominence as a critical signaling molecule in the epithelial cells of renal tubules. This review will focus on recent findings exploring the role of GSK3 in renal collecting ducts, especially its role in urine concentration involving vasopressin signaling.

RECENT FINDINGS

Recent studies using inhibition or tissue-specific gene deletion of GSK3 revealed the mechanism by which GSK3 regulates aquaporin 2 water channels via adenylate cyclase or the prostaglandin-E2 pathway. In other studies, postnatal treatment with lithium, an inhibitor of GSK3, increased cell proliferation and led to microcyst formation in rat kidneys. These studies suggest that loss of GSK3 activity could interfere with renal water transport at two levels. In the short term, it could disrupt vasopressin signaling in collecting duct cells and in the long term it could alter the structure of the collecting ducts, making them less responsive to the hydro-osmotic effects of vasopressin.

SUMMARY

Ongoing studies reveal the crucial role played by GSK3 in the regulation of vasopressin action in the renal collecting ducts and suggest a possible use of GSK3 inhibitors in disease conditions associated with disrupted vasopressin signaling.

Macrophage migration inhibitory factor antagonizes pressure overload-induced cardiac hypertrophy

Macrophage migration inhibitory factor (MIF) functions as a proinflammatory cytokine when secreted from the cell, but it also exhibits antioxidant properties by virtue of its intrinsic oxidoreductase activity. Since increased production of ROS is implicated in the development of left ventricular hypertrophy, we hypothesized that the redox activity of MIF protects the myocardium when exposed to hemodynamic stress. In a mouse model of myocardial hypertrophy induced by transverse aortic coarctation (TAC) for 10 days, we showed that growth of the MIF-deficient heart was significantly greater by 32% compared with wild-type (WT) TAC hearts and that fibrosis was increased by fourfold (2.62 ± 0.2% vs. 0.6 ± 0.1%). Circulating MIF was increased in TAC animals, and expression of MIF receptor, CD74, was increased in the hypertrophic myocardium. Gene expression analysis showed a 10-fold increase (P < 0.01) in ROS-generating mitochondrial NADPH oxidase and 2- to 3-fold reductions (P < 0.01) in mitochondrial SOD2 and mitochondrial aconitase activities, indicating enhanced oxidative injury in the hypertrophied MIF-deficient ventricle. Hypertrophic signaling pathways showed that phosphorylation of cytosolic glycogen synthase kinase-3α was greater (P < 0.05) at baseline in MIF-deficient hearts than in WT hearts and remained elevated after 10-day TAC. In the hemodynamically stressed MIF-deficient heart, nuclear p21(CIP1) increased sevenfold (P < 0.01), and the cytosolic increase of phospho-p21(CIP1) was significantly greater than in WT TAC hearts. We conclude that MIF antagonizes myocardial hypertrophy and fibrosis in response to hemodynamic stress by maintaining a redox homeostatic phenotype and attenuating stress-induced activation of hypertrophic signaling pathways.

Tumor necrosis factor-induced cerebral insulin resistance in Alzheimer's disease links numerous treatment rationales

The evident limitations of the amyloid theory of the pathogenesis of Alzheimer's disease are increasingly putting alternatives in the spotlight. We argue here that a number of independently developing approaches to therapy-including specific and nonspecific anti-tumor necrosis factor (TNF) agents, apolipoprotein E mimetics, leptin, intranasal insulin, the glucagon-like peptide-1 mimetics and glycogen synthase kinase-3 (GSK-3) antagonists-are all part of an interlocking chain of events. All these approaches inform us that inflammation and thence cerebral insulin resistance constitute the pathway on which to focus for a successful clinical outcome in treating this disease. The key link in this chain presently absent is a recognition by Alzheimer's research community of the long-neglected history of TNF induction of insulin resistance. When this is incorporated into the bigger picture, it becomes evident that the interventions we discuss are not competing alternatives but equally valid approaches to correcting different parts of the same pathway to Alzheimer's disease. These treatments can be expected to be at least additive, and conceivably synergistic, in effect. Thus the inflammation, insulin resistance, GSK-3, and mitochondrial dysfunction hypotheses are not opposing ideas but stages of the same fundamental, overarching, pathway of Alzheimer's disease pathogenesis. The insight this provides into progenitor cells, including those involved in adult neurogenesis, is a key part of this approach. This pathway also has therapeutic implications for other circumstances in which brain TNF is pathologically increased, such as stroke, traumatic brain injury, and the infectious disease encephalopathies.

Aldose reductase modulates cardiac glycogen synthase kinase-3β phosphorylation during ischemia-reperfusion

Earlier studies have demonstrated that aldose reductase (AR) plays a key role in mediating ischemia-reperfusion (I/R) injury. Our objective was to investigate if AR mediates I/R injury by influencing phosphorylation of glycogen synthase kinase-3β (p-GSK3β). To investigate this issue, we used three separate models to study the effects of stress injury on the heart. Hearts isolated from wild-type (WT), human expressing AR transgenic (ARTg), and AR knockout (ARKO) mice were perfused with/without GSK3β inhibitors (SB-216763 and LiCl) and subjected to I/R. Ad-human AR (Ad-hAR)-expressing HL-1 cardiac cells were exposed to hypoxia (0.5% O(2)) and reoxygenation (20.9% O(2)) conditions. I/R in a murine model of transient occlusion and reperfusion of the left anterior descending coronary artery (LAD) was used to study if p-GSK3β was affected through increased AR flux. Lactate dehydrogenase (LDH) release and left ventricular developed pressure (LVDP) were measured. LVDP was decreased in hearts from ARTg mice compared with WT and ARKO after I/R, whereas LDH release and apoptotic markers were increased (P < 0.05). p-GSK3β was decreased in ARTg hearts compared with WT and ARKO (P < 0.05). In ARKO, p-GSK3β and apoptotic markers were decreased compared with WT (P < 0.05). WT and ARTg hearts perfused with GSK3β inhibitors improved p-GSK3β expression and LVDP and exhibited decreased LDH release, apoptosis, and mitochondrial pore opening (P < 0.05). Ad-hAR-expressing HL-1 cardiac cells, exposed to hypoxia (0.5% O(2)) and reoxygenation (20.9% O(2)), had greater LDH release compared with control HL-1 cells (P < 0.05). p-GSK3β was decreased and correlated with increased apoptotic markers in Ad-hAR HL-1 cells (P < 0.05). Treatment with phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) inhibitor increased injury demonstrated by increased LDH release in ARTg, WT, and ARKO hearts and in Ad-hAR-expressing HL-1 cells. Cells treated with protein kinase C (PKC) α/β inhibitor displayed significant increases in p-Akt and p-GSK3β expression, and resulted in decreased LDH release. In summary, AR mediates changes in p-GSK3β, in part, via PKCα/β and Akt during I/R.

Acute inhibition of GSK causes mitochondrial remodeling

Recent data have shown that cardioprotection can result in the import of specific proteins into the mitochondria in a process that involves heat shock protein 90 (HSP90) and is blocked by geldanamycin (GD), a HSP90 inhibitor. To test the hypothesis that an alteration in mitochondrial import is a more widespread feature of cardioprotection, in this study, we used a broad-based proteomics approach to investigate changes in the mitochondrial proteome following cardioprotection induced by inhibition of glycogen synthase kinase (GSK)-3. Mitochondria were isolated from control hearts, and hearts were perfused with the GSK inhibitor SB 216763 (SB) for 15 min before isolation of mitochondria. Mitochondrial extracts from control and SB-perfused hearts were labeled with isotope tags for relative and absolute quantification (iTRAQ), and differences in mitochondrial protein levels were determined by mass spectrometry. To test for the role of HSP90-mediated protein import, hearts were perfused in the presence and absence of GD for 15 min before perfusion with SB followed by mitochondrial isolation and iTRAQ labeling. We confirmed that treatment with GD blocked the protection afforded by SB treatment in a protocol of 20 min of ischemia and 40 min of reperfusion. We found 16 proteins that showed an apparent increase in the mitochondrial fraction following SB treatment. GD treatment significantly blocked the SB-mediated increase in mitochondrial association for five of these proteins, which included annexin A6, vinculin, and pyruvate kinase. We also found that SB treatment resulted in a decrease in mitochondrial content of eight proteins, of which all but two are established mitochondrial proteins. To confirm a role for mitochondrial import versus a change in protein synthesis and/or degradation, we measured changes in these proteins in whole cell extracts. Taken together, these data show that SB leads to a remodeling of the mitochondrial proteome that is partially GD sensitive.