GSK-3: tricks of the trade for a multi-tasking kinase

Inhibition of GSK-3β restores delayed gastric emptying in obesity-induced diabetic female mice

Diabetic gastroparesis (DG) is a clinical syndrome characterized by delayed gastric emptying (DGE). Loss of nuclear factor erythroid 2-related factor 2 (Nrf2) is associated with reduced neuronal nitric oxide synthase-α (nNOSα)-mediated gastric motility and DGE. Previous studies have shown that nuclear exclusion and inactivation of Nrf2 is partly regulated by glycogen synthase kinase 3β (GSK-3β). In the current study, the molecular signaling of GSK-3β-mediated Nrf2 activation and its mechanistic role on DG were investigated in high-fat diet (HFD)-induced obese/Type 2 diabetes (T2D) female mice. Adult female C57BL/6J mice were fed with HFD or normal diet (ND) with or without GSK-3β inhibitor (SB 216763, 10 mg/kg body wt ip) start from the 14th wk and continued feeding mice for an additional 3-wk time period. Our results show that treatment with GSK-3β inhibitor SB attenuated DGE in obese/T2D mice. Treatment with SB restored impaired gastric 1) Nrf2 and phase II antioxidant enzymes through PI3K/ERK/AKT-mediated pathway, 2) tetrahydrobiopterin (BH₄, cofactor of nNOS) biosynthesis enzyme dihydrofolate reductase, and 3) nNOSα dimerization in obese/T2 diabetic female mice. SB treatment normalized caspase 3 activity and downstream GSK-3β signaling in the gastric tissues of the obese/T2 diabetic female mice. In addition, GSK-3β inhibitor restored impaired nitrergic relaxation in hyperglycemic conditions. Finally, SB treatment reduced GSK3 marker, pTau in adult primary enteric neuronal cells. These findings emphasize the importance of GSK-3β on regulating gastric Nrf2 and nitrergic mediated gastric emptying in obese/diabetic rodents.NEW & NOTEWORTHY Inhibition of glycogen synthase kinase 3β (GSK-3β) with SB 216763 attenuates delayed gastric emptying through gastric nuclear factor erythroid 2-related factor 2 (Nrf2)-phase II enzymes in high-fat diet-fed female mice. SB 216763 restored impaired gastric PI3K/AKT/ β-catenin/caspase 3 expression. Inhibition of GSK-3β normalized gastric dihydrofolate reductase, neuronal nitric oxide synthase-α expression, dimerization and nitrergic relaxation. SB 216763 normalized both serum estrogen and nitrate levels in female obese/Type 2 diabetes mice. SB 216763 reduced downstream signaling of GSK-3β in enteric neuronal cells in vitro.

Pharmacological inhibition of glycogen synthase kinase 3 increases operant alcohol self-administration in a manner associated with altered pGSK-3β, protein interacting with C kinase and GluA2 protein expression in the reward pathway of male C57BL/6J mice

Glycogen synthase kinase 3 (GSK-3) is a constitutively active serine-threonine kinase that regulates numerous signaling pathways and has been implicated in neurodegenerative and neuropsychiatric diseases. Alcohol exposure increases GSK-3β (ser9) phosphorylation (pGSK-3β); however, few studies have investigated whether GSK-3 regulates the positive reinforcing effects of alcohol, which drive repetitive drug use. To address this goal, male C57BL/6J mice were trained to lever press on a fixed-ratio 4 schedule of sweetened alcohol or sucrose-only reinforcement in operant conditioning chambers. The GSK-3 inhibitor CHIR 99021 (0-10 mg/kg, i.p.) was injected 45 minutes prior to self-administration sessions. After completion of the self-administration dose-effect curve, potential locomotor effects of the GSK-3 inhibitor were assessed. To determine molecular efficacy, CHIR 99021 (10 mg/kg, i.p.) was evaluated on pGSK-3β, GSK-3β, protein interacting with C kinase (PICK1), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA2 subunit protein expression in amygdala, nucleus accumbens (NAcb), and frontal cortex. Results showed that CHIR 99021 (10 mg/kg) dose-dependently increased alcohol reinforced responding with no effect on sucrose self-administration or locomotor activity. CHIR 99021 (10 mg/kg) significantly decreased pGSK-3β expression in all brain regions tested, reduced PICK1 and increased GluA2 total expression only in the NAcb. We conclude that GSK-3 inhibition increased the reinforcing effects of alcohol in mice. This was associated with reduced pGSK-3β and PICK1, and increased GluA2 expression. Given prior results showing that AMPA receptor activity regulates alcohol self-administration, we propose that signaling through the GSK-3/PICK1/GluA2 molecular pathway drives the positive reinforcing effects of the drug, which are required for abuse liability.

Glycogen synthase kinase-3β: a promising candidate in the fight against fibrosis

Fibrosis exists in almost all organs/tissues of the human body, plays an important role in the occurrence and development of diseases and is also a hallmark of the aging process. However, there is no effective prevention or therapeutic method for fibrogenesis. As a serine/threonine (Ser/Thr)-protein kinase, glycogen synthase kinase-3β (GSK-3β) is a vital signaling mediator that participates in a variety of biological events and can inhibit extracellular matrix (ECM) accumulation and the epithelial-mesenchymal transition (EMT) process, thereby exerting its protective role against the fibrosis of various organs/tissues, including the heart, lung, liver, and kidney. Moreover, we further present the upstream regulators and downstream effectors of the GSK-3β pathway during fibrosis and comprehensively summarize the roles of GSK-3β in the regulation of fibrosis and provide several potential targets for research. Collectively, the information reviewed here highlights recent advances vital for experimental research and clinical development, illuminating the possibility of GSK-3β as a novel therapeutic target for the management of tissue fibrosis in the future.

Activation of β-catenin by TGF-β1 promotes ligament-fibroblastic differentiation and inhibits cementoblastic differentiation of human periodontal ligament cells

TGF-β and Wnt/β-catenin signaling pathways are known to be essential for the development of periodontal tissue. In this study, we examined the crosstalk between TGF-β and Wnt/β-catenin signaling in ligament-fibroblastic differentiation of human periodontal ligament cells (hPDLCs). TGF-β1 treatment significantly increased the expression of ligament-fibroblastic markers, but such expression was preventing by treatment with SB431542, a TGF-β type I receptor inhibitor. As well as phosphorylation of Smad3, TGF-β1 increased β-catenin activation. The depletion of β-catenin reduced the expression of ligament-fibroblastic markers, suggesting that β-catenin is essential for ligament differentiation. The effect of TGF-β1 on β-catenin activation did not seem to be much correlated with Wnt stimuli, but endogenous DKK1 was suppressed by TGF-β1, indicating that β-catenin activation could be increased much more by TGF-β1. In addition to DKK1 suppression, Smad3 phosphorylation by TGF-β1 facilitated the nuclear translocation of cytoplasmic β-catenin. In contrast to ligament-fibroblastic differentiation, inhibition of TGF-β1 signaling was needed for cementoblastic differentiation of hPDLCs. BMP7 treatment accompanied by inhibition of TGF-β1 signaling had a synergistic effect on cementoblastic differentiation. In conclusion, β-catenin activation by TGF-β1 caused ligament-fibroblastic differentiation of hPDLCs, and the presence of TGF-β1 stimuli basically determined whether hPDLCs are differentiated into ligament progenitor or cementoblasts.

GSK-3 is an RNA polymerase II phospho-CTD kinase

We have previously found that UV-induced DNA damage causes hyperphosphorylation of the carboxy terminal domain (CTD) of RNA polymerase II (RNAPII), inhibition of transcriptional elongation and changes in alternative splicing (AS) due to kinetic coupling between transcription and splicing. In an unbiased search for protein kinases involved in the AS response to DNA damage, we have identified glycogen synthase kinase 3 (GSK-3) as an unforeseen participant. Unlike Cdk9 inhibition, GSK-3 inhibition only prevents CTD hyperphosphorylation triggered by UV but not basal phosphorylation. This effect is not due to differential degradation of the phospho-CTD isoforms and can be reproduced, at the AS level, by overexpression of a kinase-dead GSK-3 dominant negative mutant. GSK-3 inhibition abrogates both the reduction in RNAPII elongation and changes in AS elicited by UV. We show that GSK-3 phosphorylates the CTD in vitro, but preferentially when the substrate is previously phosphorylated, consistently with the requirement of a priming phosphorylation reported for GSK-3 efficacy. In line with a role for GSK-3 in the response to DNA damage, GSK-3 inhibition prevents UV-induced apoptosis. In summary, we uncover a novel role for a widely studied kinase in key steps of eukaryotic transcription and pre-mRNA processing.

Glycogen synthase kinase-3ß supports serotonin transporter function and trafficking in a phosphorylation-dependent manner

Serotonin (5-HT) transporter (SERT) plays a crucial role in serotonergic transmission in the central nervous system, and any aberration causes serious mental illnesses. Nevertheless, the cellular mechanisms that regulate SERT function and trafficking are not entirely understood. Growing evidence suggests that several protein kinases act as modulators. Here, we delineate the molecular mechanisms by which glycogen synthase kinase-3ß (GSK3ß) regulates SERT. When mouse striatal synaptosomes were treated with the GSK3α/ß inhibitor CHIR99021, we observed a significant increase in SERT function, V_max , surface expression with a reduction in 5-HT K_m and SERT phosphorylation. To further study how the SERT molecule is affected by GSK3α/ß, we used HEK-293 cells as a heterologous expression system. As in striatal synaptosomes, CHIR99021 treatment of cells expressing wild-type hSERT (hSERT-WT) resulted in a time and dose-dependent elevation of hSERT function with a concomitant increase in the V_max and surface transporters because of reduced internalization and enhanced membrane insertion; silencing GSK3α/ß in these cells with siRNA also similarly affected hSERT. Converting putative GSK3α/ß phosphorylation site serine at position 48 to alanine in hSERT (hSERT-S48A) completely abrogated the effects of both the inhibitor CHIR99021 and GSK3α/ß siRNA. Substantiating these findings, over-expression of constitutively active GSK3ß with hSERT-WT, but not with hSERT-S48A, reduced SERT function, V_max , surface density, and enhanced transporter phosphorylation. Both hSERT-WT and hSERT-S48A were inhibited similarly by PKC activation or by inhibition of Akt, CaMKII, p38 MAPK, or Src kinase. These findings provide new evidence that GSK3ß supports basal SERT function and trafficking via serine-48 phosphorylation.

[Value of ginsenoside Rb1 in alleviating coronary artery lesion in a mouse model of Kawasaki disease]

OBJECTIVE

To study the effect and related signaling pathways of ginsenoside Rb1 in the treatment of coronary artery lesion (CAL) in a mouse model of Kawasaki disease (KD).

METHODS

BALB/c mice were randomly divided into a control group, a model group, an aspirin group, a low-dose ginsenoside Rb1 group (50 mg/kg), and a high-dose ginsenoside Rb1 group (100 mg/kg), with 12 mice in each group. All mice except those in the control group were given intermittent intraperitoneal injection of 10% bovine serum albumin to establish a mouse model of KD. The mice in the aspirin group, the low-dose ginsenoside Rb1 group, and the high-dose ginsenoside Rb1 group were given the corresponding drug by gavage for 20 days after modeling. Hematoxylin and eosin staining was used to observe the pathological changes of coronary artery tissue. ELISA was used to measure the levels of the inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in serum and coronary artery tissue. Western blot was used to measure the relative expression levels of proteins involved in the regulation of the AMPK/mTOR autophagy signaling pathway and the PI3K/Akt oxidative stress signaling pathway in coronary artery tissue.

RESULTS

The observation of pathological sections showed that compared with the model group, the high-dose ginsenoside Rb1 group had significant improvement in the symptoms of vascular wall thickening, intimal edema, fiber rupture, and inflammatory infiltration of endothelial cells. Compared with the control group, the model and low-dose ginsenoside Rb1 groups had significant increases in the levels of TNF-α, IL-6, and IL-1β in serum and coronary artery tissue (P<0.05); the model group had significant increases in the expression levels of P-AMPK/AMPK, P-mTOR/mTOR, and P-P70S6/P70S6 in coronary artery tissue (P<0.05) and significant reductions in the expression levels of P-PI3K/PI3K, P-AKT/AKT, and P-GSK-3β/GSK-3β in coronary artery tissue (P<0.05). Compared with the model group, the aspirin group and the high-dose ginsenoside Rb1 group had significant reductions in the levels of TNF-α, IL-6, and IL-1β (P<0.05); the low- and high-dose ginsenoside Rb1 groups had significant reductions in the expression levels of P-AMPK/AMPK, P-mTOR/mTOR, and P-P70S6/P70S6 (P<0.05) in a dose-dependent manner between the two groups (P<0.05); the low-dose ginsenoside Rb1 group had no significant change in the expression level of P-PI3K/PI3K (P>0.05) and had significant increases in the expression levels of P-AKT/AKT and P-GSK-3β/GSK-3β (P<0.05), while the high-dose ginsenoside Rb1 group had significant increases in the relative protein expression levels of the above three proteins (P<0.05). Compared with the low-dose ginsenoside Rb1 group, the aspirin group and the high-dose ginsenoside Rb1 group had significant reductions in the levels of TNF-α, IL-6, and IL-1β (P<0.05); the high-dose ginsenoside Rb1 group had significant increases in the expression levels of P-PI3K/PI3K and P-AKT/AKT (P<0.05).

CONCLUSIONS

Ginsenoside Rb1 can effectively alleviate CAL in a mouse model of KD in a dose-dependent manner, possibly by regulating the AMPK/mTOR/P70S6 autophagy signaling pathway to inhibit CAL inflammation and regulating the PI3K/AKT/GSK-3β oxidative stress signaling pathway to exert a biological activity of protection against coronary artery endothelial cell injury.

[Value of ginsenoside Rb1 in alleviating coronary artery lesion in a mouse model of Kawasaki disease]

OBJECTIVE

To study the effect and related signaling pathways of ginsenoside Rb1 in the treatment of coronary artery lesion (CAL) in a mouse model of Kawasaki disease (KD).

METHODS

BALB/c mice were randomly divided into a control group, a model group, an aspirin group, a low-dose ginsenoside Rb1 group (50 mg/kg), and a high-dose ginsenoside Rb1 group (100 mg/kg), with 12 mice in each group. All mice except those in the control group were given intermittent intraperitoneal injection of 10% bovine serum albumin to establish a mouse model of KD. The mice in the aspirin group, the low-dose ginsenoside Rb1 group, and the high-dose ginsenoside Rb1 group were given the corresponding drug by gavage for 20 days after modeling. Hematoxylin and eosin staining was used to observe the pathological changes of coronary artery tissue. ELISA was used to measure the levels of the inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in serum and coronary artery tissue. Western blot was used to measure the relative expression levels of proteins involved in the regulation of the AMPK/mTOR autophagy signaling pathway and the PI3K/Akt oxidative stress signaling pathway in coronary artery tissue.

RESULTS

The observation of pathological sections showed that compared with the model group, the high-dose ginsenoside Rb1 group had significant improvement in the symptoms of vascular wall thickening, intimal edema, fiber rupture, and inflammatory infiltration of endothelial cells. Compared with the control group, the model and low-dose ginsenoside Rb1 groups had significant increases in the levels of TNF-α, IL-6, and IL-1β in serum and coronary artery tissue (P<0.05); the model group had significant increases in the expression levels of P-AMPK/AMPK, P-mTOR/mTOR, and P-P70S6/P70S6 in coronary artery tissue (P<0.05) and significant reductions in the expression levels of P-PI3K/PI3K, P-AKT/AKT, and P-GSK-3β/GSK-3β in coronary artery tissue (P<0.05). Compared with the model group, the aspirin group and the high-dose ginsenoside Rb1 group had significant reductions in the levels of TNF-α, IL-6, and IL-1β (P<0.05); the low- and high-dose ginsenoside Rb1 groups had significant reductions in the expression levels of P-AMPK/AMPK, P-mTOR/mTOR, and P-P70S6/P70S6 (P<0.05) in a dose-dependent manner between the two groups (P<0.05); the low-dose ginsenoside Rb1 group had no significant change in the expression level of P-PI3K/PI3K (P>0.05) and had significant increases in the expression levels of P-AKT/AKT and P-GSK-3β/GSK-3β (P<0.05), while the high-dose ginsenoside Rb1 group had significant increases in the relative protein expression levels of the above three proteins (P<0.05). Compared with the low-dose ginsenoside Rb1 group, the aspirin group and the high-dose ginsenoside Rb1 group had significant reductions in the levels of TNF-α, IL-6, and IL-1β (P<0.05); the high-dose ginsenoside Rb1 group had significant increases in the expression levels of P-PI3K/PI3K and P-AKT/AKT (P<0.05).

CONCLUSIONS

Ginsenoside Rb1 can effectively alleviate CAL in a mouse model of KD in a dose-dependent manner, possibly by regulating the AMPK/mTOR/P70S6 autophagy signaling pathway to inhibit CAL inflammation and regulating the PI3K/AKT/GSK-3β oxidative stress signaling pathway to exert a biological activity of protection against coronary artery endothelial cell injury.

Intermittent fasting promotes adult hippocampal neuronal differentiation by activating GSK-3β in 3xTg-AD mice

Moderate dietary restriction can ameliorate age-related chronic diseases such as Alzheimer's disease (AD) by increasing the expression of neurotrophic factors and promoting neurogenesis in the brain. Glycogen synthase kinase-3β (GSK-3β) signaling is essential for the coordination of progenitor cell proliferation and differentiation during brain development. The mechanisms by which GSK-3β is involved in dietary restriction-induced neurogenesis and cognitive improvement remain unclear. Six-month-old male 3xTg-AD and wild-type mice were fed on alternate days (intermittent fasting, IF) or ad libitum (AL) for 3 months. GSK-3β activity was regulated by bilaterally infusing lentiviral vectors carrying siRNA targeting GSK-3β into the dentate gyrus region of the hippocampus. Intermittent fasting promoted neuronal differentiation and maturation in the dentate gyrus and ameliorated recognized dysfunction in 3xTg-AD mice. These effects were reversed by siRNA targeting GSK-3β. After intermittent fasting, the insulin and protein kinase A signaling pathways were inhibited, while the adenosine monophosphate-activated protein kinase and brain-derived neurotrophic factor pathways were activated. These findings suggest that intermittent fasting can promote neuronal differentiation and maturation in the hippocampus by activating GSK-3β, thus improving learning and memory.

Neurobiology of glycine transporters: From molecules to behavior

Glycine transporters (GlyTs) are Na⁺/Cl^--dependent neurotransmitter transporters, responsible for l-glycine uptake into the central nervous system. GlyTs are members of the solute carrier family 6 (SLC6) and comprise glycine transporter type 1 (SLC6A9; GlyT1) and glycine transporter type 2 (SLC6A5; Glyt2). GlyT1 and GlyT2 are expressed on both astrocytes and neurons, but their expression pattern in brain tissue is foremost related to neurotransmission. GlyT2 is markedly expressed in brainstem, spinal cord and cerebellum, where it is responsible for glycine uptake into glycinergic and GABAergic terminals. GlyT1 is abundant in neocortex, thalamus and hippocampus, where it is expressed in astrocytes, and involved in glutamatergic neurotransmission. Consequently, inhibition of GlyT1 transporters can modulate glutamatergic neurotransmission through NMDA receptors, suggesting an alternative therapeutic strategy. In this review, we focus on recent progress in the understanding of GlyTs role in brain function and in various diseases, such as epilepsy, hyperekplexia, neuropathic pain, drug addiction, schizophrenia and stroke, as well as in neurodegenerative disorders.

The Role of GSK3β in T Lymphocytes in the Tumor Microenvironment

Immunotherapy options for patients with cancer have emerged following decades of research on immune responses against tumors. Most treatments in this category harness T cells with specificity for tumor associated antigens, neoantigens, and cancer-testis antigens. GSK3β is a serine-threonine kinase with the highest number of substrates and multifaceted roles in cell function including immune cells. Importantly, inhibitors of GSK3β are available for clinical and research use. Here, we review the possible role of GSK3β in the immune tumor microenvironment, with goal to guide future research that tests GSK3β inhibition as an immunotherapy adjunct.

The Effects of PK11195 and Protoporphyrin IX Can Modulate Chronic Alcohol Intoxication in Rat Liver Mitochondria under the Opening of the Mitochondrial Permeability Transition Pore

Decades of active research have shown that mitochondrial dysfunction, the associated oxidative stress, impaired anti-stress defense mechanisms, and the activation of the proapoptotic signaling pathways underlie pathological changes in organs and tissues. Pathologies caused by alcohol primarily affect the liver. Alcohol abuse is the cause of many liver diseases, such as steatosis, alcoholic steatohepatitis, fibrosis, cirrhosis, and, potentially, hepatocellular cancer. In this study, the effect of chronic alcohol exposure on rat liver mitochondria was investigated. We observed an ethanol-induced increase in sensitivity to calcium, changes in the level of protein kinase Akt and GSK-3β phosphorylation, an induction of the mitochondrial permeability transition pore (mPTP), and strong alterations in the expression of mPTP regulators. Moreover, we also showed an enhanced effect of PK11195 and PPIX, on the parameters of the mPTP opening in rat liver mitochondria (RLM) isolated from ethanol-treated rats compared to the RLM from control rats. We suggest that the results of this study could help elucidate the mechanisms of chronic ethanol action on the mitochondria and contribute to the development of new therapeutic strategies for treating the effects of ethanol-related diseases.

Protective effect of Hydroxysafflor Yellow A on cerebral ischemia reperfusion-injury by regulating GSK3β-mediated pathways

Ischemia-reperfusion (I/R) injury is accompanied by high mortality and morbidity. Unfortunately, there are few effective therapeutic medicines and strategies to enhance its outcome. Hydroxysafflor Yellow A (HSYA) exerts multiple biological activities and has potential protective effects against I/R injury in the brain, liver and heart. However, its underlying mechanism is still unclear. Here, we investigated whether HSYA modulates apoptosis and neuro-inflammation through the Glycogen synthase kinase-3β(GSK3β)-mediated pathway in a transient middle cerebral artery occlusion (MCAO) rat model and oxygen/glucose deprivation (OGD)-challenged primary neuronal cultures both in vivo and in vitro. Male Wistar rats were subjected to MCAO for 2 h, followed by 24 h of reperfusion. HSYA was administered 15 min after occlusion, SB216763 (GSK3β inhibitor) was injected to the left ventricle of the rat 6 h prior to MCAO. After 24 h of perfusion, apoptosis-associated protein and inflammatory markers were detected by western blotting. Meanwhile, terminal-deoxynucleotidyl transferase mediated nick end labeling(TUNEL) assay was used to evaluate the number of apoptotic cells in OGD-challenged neurons, cleaved caspase-3 were evaluated by Immunofluorescence (IF). Our data indicated that HSYA administration reduced infarct volume, decreased neurological deficit scores, elevated GSK3β phosphorylation and inhibited the activation of iNOS, NF-κB, and capase-3 in the penumbra of I/R rats. Moreover, blockade of GSK3β partly reversed the protective effect of HSYA on I/R by regulating NF-κB and caspase-3 both in vivo and in vitro. Collectively, we found that HSYA ameliorates I/R injury through its anti-inflammatory and anti-apoptotic effects via modulation of GSK-3β phosphorylation.

GSK3β Modulates Timing-Dependent Long-Term Depression Through Direct Phosphorylation of Kv4.2 Channels

Spike timing-dependent plasticity (STDP) is a form of activity-dependent remodeling of synaptic strength that underlies memory formation. Despite its key role in dictating learning rules in the brain circuits, the molecular mechanisms mediating STDP are still poorly understood. Here, we show that spike timing-dependent long-term depression (tLTD) and A-type K+ currents are modulated by pharmacological agents affecting the levels of active glycogen-synthase kinase 3 (GSK3) and by GSK3β knockdown in layer 2/3 of the mouse somatosensory cortex. Moreover, the blockade of A-type K+ currents mimics the effects of GSK3 up-regulation on tLTD and occludes further changes in synaptic strength. Pharmacological, immunohistochemical and biochemical experiments revealed that GSK3β influence over tLTD induction is mediated by direct phosphorylation at Ser-616 of the Kv4.2 subunit, a molecular determinant of A-type K+ currents. Collectively, these results identify the functional interaction between GSK3β and Kv4.2 channel as a novel mechanism for tLTD modulation providing exciting insight into the understanding of GSK3β role in synaptic plasticity.

Microglia mediated neuroinflammation - signaling regulation and therapeutic considerations with special reference to some natural compounds

Neuroinflammation plays a central role in multiple neurodegenerative diseases and neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), cerebral ischemic injury etc. In this connection, microglia, the key players in the central nervous system, mediate the inflammatory response process. In brain injuries, activated microglia can clear the cellular debris and invading pathogens and release neurotrophic factors; however, prolonged microglia activation may cause neuronal death through excessive release of inflammatory mediators. Therefore, it is of paramount importance to understand the underlying molecular mechanisms of microglia activation to design an effective therapeutic strategy to alleviate neuronal injury. Recent studies have shown that some natural compounds and herbal extracts possess anti-inflammatory properties that may suppress microglial activation and ameliorate neuroinflammation and hence are neuroprotective. In this review, we will update some of the common signaling pathways that regulate microglia activation. Among the various signaling pathways, the Notch-1, mitogen-activated protein kinases (MAPKs), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) have been reported to exacerbate microglia mediated neuroinflammation that is implicated in different neuropathological diseases. The search for natural compounds or agents, specifically those derived from natural herbal extracts such as Gastrodin, scutellarin, RG1 etc. has been the focus of many of our recent studies because they have been found to regulate microglia activation. The pharmacological effects of these agents and their potential mechanisms for regulating microglia activation are systematically reviewed here for a fuller understanding of their biochemical action and therapeutic potential for treatment of microglia mediated neuropathological diseases.

ABHD11 Is Critical for Embryonic Stem Cell Expansion, Differentiation and Lipid Metabolic Homeostasis

Growing evidence supports the notion that lipid metabolism is critical for embryonic stem cell (ESC) maintenance. Recently, α/β-hydrolase domain-containing (ABHD) proteins have emerged as novel pivotal regulators in lipid synthesis or degradation while their functions in ESCs have not been investigated. In this study, we revealed the role of ABHD11 in ESC function using classical loss and gain of function experiments. Knockout of Abhd11 hampered ESC expansion and differentiation, triggering the autophagic flux and apoptosis. In contrast, Abhd11 overexpression exerted anti-apoptotic effects in ESCs. Moreover, Abhd11 knockout disturbed GSK3β/β-Catenin and ERK signaling transduction. Finally, Abhd11 knockout led to the misexpression of key metabolic enzymes related to lipid synthesis, glycolysis, and amino acid metabolism, and ABHD11 contributed to the homeostasis of lipid metabolism. These findings provide new insights into the broad role of ABHD proteins and highlight the significance of regulators of lipid metabolism in the control of stem cell function.

Comparative phosphoproteomic analysis of BR-defective mutant reveals a key role of GhSK13 in regulating cotton fiber development

Brassinosteroid (BR), a steroid phytohormone, whose signaling transduction pathways include a series of phosphorylation and dephosphorylation events, and GSK3s are the main negative regulator kinases. BRs have been shown to play vital roles in cotton fiber elongation. However, the underlying mechanism is still elusive. In this study, fibers of a BR-defective mutant Pagoda 1 (pag1), and its corresponding wild-type (ZM24) were selected for a comparative global phosphoproteome analysis at critical developmental time points: fast-growing stage (10 days after pollination (DPA)) and secondary cell wall synthesis stage (20 DPA). Based on the substrate characteristics of GSK3, 900 potential substrates were identified. Their GO and KEGG annotation results suggest that BR functions in fiber development by regulating GhSKs (GSK3s of Gossypium hirsutum L.) involved microtubule cytoskeleton organization, and pathways of glucose, sucrose and lipid metabolism. Further experimental results revealed that among the GhSK members identified, GhSK13 not only plays a role in BR signaling pathway, but also functions in developing fiber by respectively interacting with an AP2-like ethylene-responsive factor GhAP2L, a nuclear transcription factor Gh_DNF_YB19, and a homeodomain zipper member GhHDZ5. Overall, our phosphoproteomic research advances the understanding of fiber development controlled by BR signal pathways especially through GhSKs, and also offers numbers of target proteins for improving cotton fiber quality.

Calcium Sensing Receptor Inhibits Growth of Human Lung Adenocarcinoma Possibly via the GSK3β/Cyclin D1 Pathway

The effect of calcium sensing receptor (CaSR) on tumor cell proliferation has been studied in several human cancers, and great discrepancies were found in different tumors. However, the role of CaSR in lung adenocarcinomas (LUADs) is not clear. Therefore, we investigated the function of CaSR on regulating the growth of human LUAD and its possible mechanism. The expression of CaSR protein and its relationship with pathological parameters were examined in paraffin sections from 51 LUAD patients, by immunohistochemistry. The results showed that CasR expression was negatively correlated with the Ki-67 index as well as the grade of malignancy in LUAD. Further, CaSR demonstrated an in vitro inhibitory effect on the proliferation of human LUAD A549 cells by regulating CaSR activity with agonist cinacalcet, antagonist NPS2143, or shRNA-CaSR transfection. Tumor xenograft models also verified the in vivo proliferation-inhibiting role of CaSR by subcutaneous injecting A549 cells into nude mice with or without changes of CaSR activity. Molecularly, Western blotting showed that CaSR positively regulated the activity of glycogen synthase kinase 3β (GSK3β), followed by the downregulation of Cyclin D1. We used the dominant negative mutant and the constitutively active mutant plasmid of GSK3β to alter GSK3β activity. Our functional experiments showed that the proliferation-inhibition of CaSR was suppressed by the inactivation of GSK3β and enhanced by the activation of GSK3β. These results suggested that CaSR played a proliferation-inhibiting role in LUAD, at least partially by regulating the GSK3β/Cyclin D1 pathway.

Functional Characterization of VvSK Gene Family in Grapevine (Vitis vinifera L.) Revealing their Role in Berry Ripening

The glycogen synthase kinase 3/shaggy kinase (GSK3) is a serine/threonine kinase that plays important roles in brassinosteroid signaling, abiotic stress responses, cell division, and elongation, etc. In this study, we characterized seven grape GSK3 genes, showing high similarities with homologs from other species including Arabidopsis, white pear, apple, orange, and peach. Gene chip microarray data derived from an online database revealed very diverse developmental and tissue-specific expression patterns of VvSKs. VvSK3 and VvSK7 showed much higher expression levels in almost every tissue compared with other members. VvSK7 was highly enriched in young tissues like berries before the veraison stage, young leaves and green stems, etc., but immediately downregulated after these tissues entered maturation or senescence phases. Prediction of cis-elements in VvSK promoters indicated that VvSKs might be sensitive to light stimulation, which is further confirmed by the qPCR data. Constitutive overexpression of VvSK7 in Arabidopsis leads to dwarf plants that resembles BR-deficient mutants. The photosynthetic rate was significantly reduced in these plants, even though they accumulated more chlorophyll in leaves. Transient overexpression of VvSKs in tomatoes delayed the fruit ripening process, consistent with the observation in grapevine which blocks VvSKs by EBR- or BIKININ-promoted berry expansion and soluble solids accumulation. Data presented in the current study may serve as a theoretical basis for the future application of BRs or related compounds in quality grape production.

Extending Arms of Insulin Resistance from Diabetes to Alzheimer's Disease: Identification of Potential Therapeutic Targets

BACKGROUND & OBJECTIVE

Type 3 diabetes (T3D) is chronic insulin resistant state of brain which shares pathology with sporadic Alzheimer's disease (sAD). Insulin signaling is a highly conserved pathway in the living systems that orchestrate cell growth, repair, maintenance, energy homeostasis and reproduction. Although insulin is primarily studied as a key molecule in diabetes mellitus, its role has recently been implicated in the development of Alzheimer's disease (AD). Severe complications in brain of diabetic patients and metabolically compromised status is evident in brain of AD patients. Underlying shared pathology of two disorders draws a trajectory from peripheral insulin resistance to insulin unresponsiveness in the central nervous system (CNS). As insulin has a pivotal role in AD, it is not an overreach to address diabetic condition in AD brain as T3D. Insulin signaling is indispensable to nervous system and it is vital for neuronal growth, repair, and maintenance of chemical milieu at synapses. Downstream mediators of insulin signaling pathway work as a regulatory hub for aggregation and clearance of unfolded proteins like Aβ and tau.

CONCLUSION

In this review, we discuss the regulatory roles of insulin as a pivotal molecule in brain with the understanding of defective insulin signaling as a key pathological mechanism in sAD. This article also highlights ongoing trials of targeting insulin signaling as a therapeutic manifestation to treat diabetic condition in brain.

Unravelling the Role of Glycogen Synthase Kinase-3 in Alzheimer's Disease-Related Epileptic Seizures

Alzheimer’s disease (AD) is the most common form of dementia. An increasing body of evidence describes an elevated incidence of epilepsy in patients with AD, and many transgenic animal models of AD also exhibit seizures and susceptibility to epilepsy. However, the biological mechanisms that underlie the occurrence of seizure or increased susceptibility to seizures in AD is unknown. Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that regulates various cellular signaling pathways, and plays a crucial role in the pathogenesis of AD. It has been suggested that GSK-3 might be a key factor that drives epileptogenesis in AD by interacting with the pathological hallmarks of AD, amyloid precursor protein (APP) and tau. Furthermore, seizures may also contribute to the progression of AD through GSK-3. In this way, GSK-3 might be involved in initiating a vicious cycle between AD and seizures. This review aims to summarise the possible role of GSK-3 in the link between AD and seizures. Understanding the role of GSK-3 in AD-associated seizures and epilepsy may help researchers develop new therapeutic approach that can manage seizure and epilepsy in AD patients as well as decelerate the progression of AD.

Deregulated PTEN/PI3K/AKT/mTOR signaling in prostate cancer: Still a potential druggable target?

Although the prognosis of patients with localized prostate cancer is good after surgery, with a favorable response to androgen deprivation therapy, about one third of them invariably relapse, and progress to castration-resistant prostate cancer. Overall, prostate cancer therapies remain scarcely effective, thus it is mandatory to devise alternative treatments enhancing the efficacy of surgical castration and hormone administration. Dysregulation of the phosphoinositide 3-kinase pathway has attracted growing attention in prostate cancer due to the highly frequent association of epigenetic and post-translational modifications as well as to genetic alterations of both phosphoinositide 3-kinase and PTEN to onset and/or progression of this malignancy, and to resistance to canonical androgen-deprivation therapy. Here we provide a summary of the biological functions of the major players of this cascade and their deregulation in prostate cancer, summarizing the results of preclinical and clinical studies with PI3K signaling inhibitors and the reasons of failure independent from genomic changes.

Glycogen synthase 3 (GSK-3) regulation of PD-1 expression and and its therapeutic implications

The past few years have witnessed exciting progress in the application of immune check-point blockade (ICB) for the treatment of various human cancers. ICB was first used against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to demonstrate durable anti-tumor responses followed by ICB against programmed cell death-1 (PD-1) or its ligand, PD-L1. Present approaches involve the use of combinations of blocking antibodies against CTLA-4, PD-1 and other inhibitory receptors (IRs) such as TIM3, TIGIT and LAG3. Despite this success, most patients are not cured by ICB therapy and there are limitations to the use of antibodies including cost, tumor penetration, the accessibility of receptors, and clearance from the cell surface as well as inflammatory and autoimmune complications. Recently, we demonstrated that the down-regulation or inhibition of glycogen synthase kinase 3 (GSK-3) down-regulates PD-1 expression in infectious diseases and cancer (Taylor et al., 2016 Immunity 44, 274-86; 2018 Cancer Research 78, 706-717; Krueger and Rudd 2018 Immunity 46, 529-531). In this Review, we outline the use of small molecule inhibitors (SMIs) that target intracellular pathways for co-receptor blockade in cancer immunotherapy.

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.

Structure-Activity Relationships and Molecular Docking Analysis of Mcl-1 Targeting Renieramycin T Analogues in Patient-derived Lung Cancer Cells

Myeloid cell leukemia 1 (Mcl-1) and B-cell lymphoma 2 (Bcl-2) proteins are promising targets for cancer therapy. Here, we investigated the structure-activity relationships (SARs) and performed molecular docking analysis of renieramycin T (RT) and its analogues and identified the critical functional groups of Mcl-1 targeting. RT have a potent anti-cancer activity against several lung cancer cells and drug-resistant primary cancer cells. RT mediated apoptosis through Mcl-1 suppression and it also reduced the level of Bcl-2 in primary cells. For SAR study, five analogues of RT were synthesized and tested for their anti-cancer and Mcl-1- and Bcl-2-targeting effects. Only two of them (TM-(-)-18 and TM-(-)-4a) exerted anti-cancer activities with the loss of Mcl-1 and partly reduced Bcl-2, while the other analogues had no such effects. Specific cyanide and benzene ring parts of RT's structure were identified to be critical for its Mcl-1-targeting activity. Computational molecular docking indicated that RT, TM-(-)-18, and TM-(-)-4a bound to Mcl-1 with high affinity, whereas TM-(-)-45, a compound with a benzene ring but no cyanide for comparison, showed the lowest binding affinity. As Mcl-1 helps cancer cells evading apoptosis, these data encourage further development of RT compounds as well as the design of novel drugs for treating Mcl-1-driven cancers.

GSK3: A Kinase Balancing Promotion and Resolution of Inflammation

GSK3 has been implicated for years in the regulation of inflammation and addressed in a plethora of scientific reports using a variety of experimental (disease) models and approaches. However, the specific role of GSK3 in the inflammatory process is still not fully understood and controversially discussed. Following a detailed overview of structure, function, and various regulatory levels, this review focusses on the immunoregulatory functions of GSK3, including the current knowledge obtained from animal models. Its impact on pro-inflammatory cytokine/chemokine profiles, bacterial/viral infections, and the modulation of associated pro-inflammatory transcriptional and signaling pathways is discussed. Moreover, GSK3 contributes to the resolution of inflammation on multiple levels, e.g., via the regulation of pro-resolving mediators, the clearance of apoptotic immune cells, and tissue repair processes. The influence of GSK3 on the development of different forms of stimulation tolerance is also addressed. Collectively, the role of GSK3 as a kinase balancing the initiation/perpetuation and the amelioration/resolution of inflammation is highlighted.

Chronic mild stress alters synaptic plasticity in the nucleus accumbens through GSK3β-dependent modulation of Kv4.2 channels

Although major depressive disorder (MDD) is highly prevalent, its pathophysiology is poorly understood. Recent evidence suggests that glycogen-synthase kinase 3β (GSK3β) plays a key role in memory formation, yet its role in mood regulation remains controversial. Here, we investigated whether GSK3β activity in the nucleus accumbens (NAc) is associated with depression-like behaviors and synaptic plasticity. We performed whole-cell patch-clamp recordings of medium spiny neurons (MSNs) in the NAc and determined the role of GSK3β in spike timing-dependent long-term potentiation (tLTP) in the chronic unpredictable mild stress (CUMS) mouse model of depression. To assess the specific role of GSK3β in tLTP, we used in vivo genetic silencing by an adeno-associated viral vector (AAV2) short hairpin RNA against GSK3β. In addition, we examined the role of the voltage-gated potassium Kv4.2 subunit, a molecular determinant of A-type K⁺ currents, as a potential downstream target of GSK3β. We found increased levels of active GSK3β and augmented tLTP in CUMS mice, a phenotype that was prevented by selective GSK3β knockdown. Furthermore, knockdown of GSK3β in the NAc ameliorated depressive-like behavior in CUMS mice. Electrophysiological, immunohistochemical, biochemical, and pharmacological experiments revealed that inhibition of the Kv4.2 channel through direct phosphorylation at Ser-616 mediated the GSK3β-dependent tLTP changes in CUMS mice. Our results identify GSK3β regulation of Kv4.2 channels as a molecular mechanism of MSN maladaptive plasticity underlying depression-like behaviors and suggest that the GSK3β-Kv4.2 axis may be an attractive therapeutic target for MDD.

Glycogen synthase kinase-3β: a novel therapeutic target for pancreatic cancer

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in the United States with a single-digit 5-year survival rate despite advances in understanding the genetics and biology of the disease. Glycogen synthase kinase-3α (GSK-3α) and GSK-3β are serine/threonine kinases that localize to the cytoplasm, mitochondria and nucleus. Although they are highly homologous within their kinase domains and phosphorylate an overlapping set of target proteins, genetic studies have shown that GSK-3β regulates the activity of several proteins that promote neoplastic transformation. Significantly, GSK-3β is progressively overexpressed during PDAC development where it participates in tumor progression, survival and chemoresistance. Thus, GSK-3β has become an attractive target for treating PDAC.Areas covered: This review summarizes the mechanisms regulating GSK-3β activity, including upstream translational and post-translational regulation, as well as the downstream targets and their functions in PDAC cell growth, metastasis and chemoresistance.Expert opinion: The activity of GSK-3 kinases are considered cell- and context-specific. In PDAC, oncogenic KRas drives the transcriptional expression of the GSK-3β gene, which has been shown to regulate cancer cell proliferation and survival, as well as resistance to chemotherapy. Thus, the combination of GSK-3 inhibitors with chemotherapeutic drugs could be a promising strategy for PDAC.

Transcriptome signatures in the brain of a migratory songbird

Most of the birds's adaptations for migration have a neuroendocrine origin, triggered by changes in photoperiod and the patterns of Earth's magnetic field. Migration phenomenology has been well described in the past decades, yet the genetic structure behind it remains terra incognita. We used RNA-Seq data to investigate which biological functions are linked with the seasonal brain adaptations of a long-distance trans-continental migratory passerine, the Northern Wheatear (Oenanthe oenanthe). We sequenced the wheatear's transcriptomes at three different stages: lean birds, a characteristic phenotype before the onset of migration, during fattening, and at their maximal migratory body mass. We identified a total of 15,357 genes in the brain of wheatears, of which 84 were differentially expressed. These were mostly related to nervous tissue development, angiogenesis, ATP production, innate immune response, and antioxidant protection, as well as GABA and dopamine signalling. The expression pattern of differentially expressed genes is correlated with typical phenotypic changes before migration, such as hyperphagia, migratory restlessness, and a potential increment in the visual and spatial memory capacities. Our work points out, for future studies, biological functions found to be involved in the development of the migratory phenotype -a unique model to study the core of neural, energetic and muscular adaptations for endurance exercise. Comparison of wheatears' transcriptomic data with two other studies with similar goals shows no correlation among the trends in the gene expression. It highlights the complexity and diversity of adaptations for long-distance migration in birds.

Cyclocarya paliurus Polysaccharide Inhibits Glioma Cell U251 Proliferation, Migration, and Invasion and Promotes Apoptosis via the GSK3β/β-Catenin Signaling Pathway

Objective. To investigate the effects of Cyclocarya paliurus polysaccharide (CPP) on the proliferation, migration, invasion, and apoptosis of human glioma U251 cells and further explore the underlying mechanism. Methods. U251 cells were cultured in vitro and treated with various concentrations (25, 50, 75, 100, 125, and 150 μmol/L) of CPP for 24, 48, and 72 h. Cell counting kit-8 was used to detect the activity of cell proliferation. Wound-healing assay, Transwell assay, and flow cytometry were used to measure the effects of CPP on the migration, invasion, and apoptosis of U251 cells, respectively. Western blotting was used to determine the protein expression involved in the GSK3β/β-catenin signaling pathway and its downstream genes related to proliferation, migration, invasion, and apoptosis including Cyr61, CCND1, Vimentin, and Slug. Meanwhile, qRT-PCR was used to detect the mRNA levels of Cyr61, CCND1, Vimentin, and Slug. Results. We found that CPP not only could inhibit the proliferation, migration, and invasion of U251 cells but also promote its apoptosis in vitro. Besides, CPP could significantly inhibit the phosphorylation and decrease the protein levels of GSK3 β at ser9 site (p<0.05), and thus increasing the phosphorylation of β-Catenin at ser33/37 site (p<0.05), resulting in β-Catenin degradation. In addition, we also found that CPP could downregulate the mRNA (p<0.05) and protein expression (p<0.05) of downstream genes of GSK3 β/β-catenin signaling pathway including Cyr61, CCND1, Vimentin, and Slug, which are related to proliferation, migration, invasion, and apoptosis. Conclusion. CPP could inhibit the expression of GSK3β, promote the degradation of β-catenin, and downregulate the levels of GSK3β/β-catenin downstream genes including Cyr61, CCND1, Vimentin, and Slug, which regulate the proliferation, migration, invasion, and apoptosis of glioma cells.

Triptolide potentiates the cytoskeleton-stabilizing activity of cyclosporine A in glomerular podocytes via a GSK3β dependent mechanism

Tripterygium wilfordii Hook F. (TwHF) is a traditional Chinese herb and has a broad spectrum of biological functions including immunosuppression and anti-inflammatory effects. When used in combination with other standard of care medications, such as glucocorticoids and calcineurin inhibitors like cyclosporine A, for treating glomerular diseases, TwHF demonstrates a remarkable dose-sparing effect, the molecular mechanism for which remains largely unknown. In an in vitro model of podocytopathy elicited by a diabetic milieu, triptolide, the major active component of TwHF, at low doses, potentiated the beneficial effect of cyclosporine A, and protected podocytes against diabetic milieu-elicited injury, mitigated cytoskeleton derangement, and preserved podocyte filtration barrier function, entailing a synergistic cytoskeleton-preserving and podocyte protective effect of triptolide and cyclosporine A. Mechanistically, inhibitory phosphorylation of GSK3β, a key molecule recently implicated as a convergence point of podocytopathic pathways, is likely required for the synergistic effect of triptolide and cyclosporine A on podocyte protection, because the synergistic effect was largely blunted in cells expressing the constitutively active GSK3β. Ergo, a synergistic podocyte cytoskeleton-stabilizing mechanism seems to underlie the cyclosporine A-sparing effect of triptolide in glomerulopathies. Combined triptolide and cyclosporine A therapy at reduced doses may be an invaluable regimen for treating diabetic nephropathy.

Tau/MAPT disease-associated variant A152T alters tau function and toxicity via impaired retrograde axonal transport

Mutations in the microtubule-associated protein tau (MAPT) underlie multiple neurodegenerative disorders, yet the pathophysiological mechanisms are unclear. A novel variant in MAPT resulting in an alanine to threonine substitution at position 152 (A152T tau) has recently been described as a significant risk factor for both frontotemporal lobar degeneration and Alzheimer’s disease. Here we use complementary computational, biochemical, molecular, genetic and imaging approaches in Caenorhabditis elegans and mouse models to interrogate the effects of the A152T variant on tau function. In silico analysis suggests that a threonine at position 152 of tau confers a new phosphorylation site. This finding is borne out by mass spectrometric survey of A152T tau phosphorylation in C. elegans and mouse. Optical pulse-chase experiments of Dendra2-tau demonstrate that A152T tau and phosphomimetic A152E tau exhibit increased diffusion kinetics and the ability to traverse across the axon initial segment more efficiently than wild-type (WT) tau. A C. elegans model of tauopathy reveals that A152T and A152E tau confer patterns of developmental toxicity distinct from WT tau, likely due to differential effects on retrograde axonal transport. These data support a role for phosphorylation of the variant threonine in A152T tau toxicity and suggest a mechanism involving impaired retrograde axonal transport contributing to human neurodegenerative disease.

Small Molecule Wnt Pathway Modulators from Natural Sources: History, State of the Art and Perspectives

The Wnt signaling is one of the major pathways known to regulate embryonic development, tissue renewal and regeneration in multicellular organisms. Dysregulations of the pathway are a common cause of several types of cancer and other diseases, such as osteoporosis and rheumatoid arthritis. This makes Wnt signaling an important therapeutic target. Small molecule activators and inhibitors of signaling pathways are important biomedical tools which allow one to harness signaling processes in the organism for therapeutic purposes in affordable and specific ways. Natural products are a well known source of biologically active small molecules with therapeutic potential. In this article, we provide an up-to-date overview of existing small molecule modulators of the Wnt pathway derived from natural products. In the first part of the review, we focus on Wnt pathway activators, which can be used for regenerative therapy in various tissues such as skin, bone, cartilage and the nervous system. The second part describes inhibitors of the pathway, which are desired agents for targeted therapies against different cancers. In each part, we pay specific attention to the mechanisms of action of the natural products, to the models on which they were investigated, and to the potential of different taxa to yield bioactive molecules capable of regulating the Wnt signaling.

The Role of Carcinogenesis-Related Biomarkers in the Wnt Pathway and Their Effects on Epithelial-Mesenchymal Transition (EMT) in Oral Squamous Cell Carcinoma

As oral squamous cell carcinoma (OSCC) can develop from potentially malignant disorders (PMDs), it is critical to develop methods for early detection to improve the prognosis of patients. Epithelial-mesenchymal transition (EMT) plays an important role during tumor progression and metastasis. The Wnt signaling pathway is an intercellular pathway in animals that also plays a fundamental role in cell proliferation and regeneration, and in the function of many cell or tissue types. Specific components of master regulators such as epithelial cadherin (E-cadherin), Vimentin, adenomatous polyposis coli (APC), Snail, and neural cadherin (N-cadherin), which are known to control the EMT process, have also been implicated in the Wnt cascade. Here, we review recent findings on the Wnt signaling pathway and the expression mechanism. These regulators are known to play roles in EMT and tumor progression, especially in OSCC. Characterizing the mechanisms through which both EMT and the Wnt pathway play a role in these cellular pathways could increase our understanding of the tumor genesis process and may allow for the development of improved therapeutics for OSCC.

Interaction between miRNAs and signaling cascades of Wnt pathway in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), a severe problem all over the world and represents around 25% of all total leukemia cases, is generating the need for novel targets against CLL. Wnt signaling cascade regulates cell proliferation, differentiation, and cell death processes. Thus, any alteration of the Wnt signaling pathway protein cascade might develop into various types of cancers, either by upregulation or downregulation of the Wnt signaling pathway protein components. In addition, it is reported that activation of the Wnt signaling pathway is associated with the transcriptional activation of microRNAs (miRNAs) by binding to its promoter region, suggesting feedback regulation. Considering the protein regulatory functions of various miRNAs, they can be approached therapeutically as modulatory targets for protein components of the Wnt signaling pathway. In this article, we have discussed the potential role of miRNAs in the regulation of Wnt signaling pathway proteins related to the pathogenesis of CLL via crosstalk between miRNAs and Wnt signaling pathway proteins. This might provide a clear insight into the Wnt protein regulatory function of various miRNAs and provide a better understanding of developing advanced and promising therapeutic approaches against CLL.

Discovery of suppressors of CRMP2 phosphorylation reveals compounds that mimic the behavioral effects of lithium on amphetamine-induced hyperlocomotion

The effective treatment of bipolar disorder (BD) represents a significant unmet medical need. Although lithium remains a mainstay of treatment for BD, limited knowledge regarding how it modulates affective behavior has proven an obstacle to discovering more effective mood stabilizers with fewer adverse side effects. One potential mechanism of action of lithium is through inhibition of the serine/threonine protein kinase GSK3β, however, relevant substrates whose change in phosphorylation may mediate downstream changes in neuroplasticity remain poorly understood. Here, we used human induced pluripotent stem cell (hiPSC)-derived neuronal cells and stable isotope labeling by amino acids in cell culture (SILAC) along with quantitative mass spectrometry to identify global changes in the phosphoproteome upon inhibition of GSK3α/β with the highly selective, ATP-competitive inhibitor CHIR-99021. Comparison of phosphorylation changes to those induced by therapeutically relevant doses of lithium treatment led to the identification of collapsin response mediator protein 2 (CRMP2) as being highly sensitive to both treatments as well as an extended panel of structurally distinct GSK3α/β inhibitors. On this basis, a high-content image-based assay in hiPSC-derived neurons was developed to screen diverse compounds, including FDA-approved drugs, for their ability to mimic lithium's suppression of CRMP2 phosphorylation without directly inhibiting GSK3β kinase activity. Systemic administration of a subset of these CRMP2-phosphorylation suppressors were found to mimic lithium's attenuation of amphetamine-induced hyperlocomotion in mice. Taken together, these studies not only provide insights into the neural substrates regulated by lithium, but also provide novel human neuronal assays for supporting the development of mechanism-based therapeutics for BD and related neuropsychiatric disorders.

Overview of cannabidiol (CBD) and its analogues: Structures, biological activities, and neuroprotective mechanisms in epilepsy and Alzheimer's disease

Herein, 11 general types of natural cannabinoids from Cannabis sativa as well as 50 (-)-CBD analogues with therapeutic potential were described. The underlying molecular mechanisms of CBD as a therapeutic candidate for epilepsy and neurodegenerative diseases were comprehensively clarified. CBD indirectly acts as an endogenous cannabinoid receptor agonist to exert its neuroprotective effects. CBD also promotes neuroprotection through different signal transduction pathways mediated indirectly by cannabinoid receptors. Furthermore, CBD prevents the glycogen synthase kinase 3β (GSK-3β) hyperphosphorylation caused by Aβ and may be developed as a new therapeutic candidate for Alzheimer's disease.

GAS5, a FoxO1-actived long noncoding RNA, promotes propofol-induced oral squamous cell carcinoma apoptosis by regulating the miR-1297-GSK3β axis

Propofol, an intravenous anaesthetic agent, has been found to exhibit antitumour effects in various kinds of cancer cells. However, the potential roles and regulatory mechanisms of propofol in oral squamous cell carcinoma (OSCC) remain unknown. Herein, we found that propofol inhibits OSCC cell growth and promotes cell apoptosis in a dose- and time-dependent manner. Further mechanistic studies revealed that the long noncoding RNA GAS5 is induced by propofol in OSCC cells. Elevated GAS5 acts as a competing endogenous RNA for miR-1297 and attenuates its inhibitory effect on GSK3β, leading to GSK3β increase and Mcl1 decrease. Additionally, we found that FoxO1 binds to the promoter of GAS5, facilitating its transcription in response to propofol treatment. Thus, these results suggest that propofol exhibits antitumour effects in OSCC cells and that the FoxO1-GAS5-miR-1297-GSK3β axis plays an important role in propofol-induced OSCC cell apoptosis.

Brain Volume-Related Polymorphisms of the Glycogen Synthase Kinase-3β Gene and Their Effect on Antidepressant Treatment in Major Depressive Disorder

BACKGROUND

Glycogen synthase kinase-3β (GSK-3β) polymorphisms are known to influence hippocampal brain tissue volume in individuals with major depressive disorder (MDD). However, the effects of the GSK-3β gene single nucleotide polymorphisms (SNPs) in those receiving antidepressant therapy are unknown.

OBJECTIVES

In the present study, we examined the relationship between brain volume-related SNPs of the GSK-3β gene and antidepressant treatment effects in patients with MDD.

METHODS

Paroxetine, fluvoxamine, or milnacipran was administered to 143 Japanese patients with MDD. Two SNPs of the GSK-3β gene (rs6438552 and rs12630592) that influence brain volume in the hippocampus were genotyped. For the primary outcome, the relationship between genetic variations in the SNPs and the percent change in the Hamilton Rating Scale for Depression (HAM-D) score at week 6 was examined. In addition, rs334558, which has been reported repeatedly, was also genotyped.

RESULTS

There was a significant correlation between the two SNPs and the percent change in the HAM-D scores at week 6 (rs6438552 A/A vs. A/G + G/G: p = 0.016; rs12630592 G/G vs. G/T + T/T: p = 0.016). There was high linkage disequilibrium between the rs6438552 and rs12630592 SNPs. The correlation between high therapeutic response over time and the two SNPs were also confirmed (rs6438552 A/A vs. others: p = 0.031; rs12630592 G/G vs. others: p = 0.031).

CONCLUSIONS

Our results suggest that two GSK-3β variants that influence brain volume were associated with changes in the HAM-D scores at week 6 in patients with MDD.

Vitamin C inhibits lipid deposition through GSK-3β/mTOR signaling in the liver of zebrafish

In this study, the mechanism that VC inhibits lipid deposition through GSK-3β/mTOR signaling was investigated in the liver of Danio rerio. The results indicated that 0.5- and 1.0-g/kg VC treatments activated mTOR signaling by inhibiting GSK-3β expression. The mRNA expression of FAS, ACC, and ACL, as well as the content of TG, TC, and NEFA, was decreased by 0.5- and 1.0-g/kg VC treatments. Moreover, to confirm GSK-3β playing a key role in regulating TSC2 and mTOR, GSK-3β RNA was interfered and the activity of GSK-3β was inhibited by 25- and 50-mg/L LiCl treatments, respectively. The results indicated that GSK-3β inactivation played a significant role in inducing mTOR signaling and inhibiting lipid deposition. VC treatments could induce mTOR signaling by inhibiting GSK-3β, and mTOR further participated in regulating lipid deposition by controlling lipid profile in the liver of zebrafish.

DHX33 promotes colon cancer development downstream of Wnt signaling

Colon cancer is one of the most common malignancies in the world; there is no effective therapeutic treatment after surgery. Our previous studies indicate that RNA helicase DHX33 plays a critical role in cell proliferation and cell growth. Here in this study, DHX33 is found to be highly expressed in colon cancer tissues and colon cancer cell lines. Knockdown of DHX33 significantly decreased cell proliferation and triggered apoptosis. Mechanistically, DHX33 was found to transcriptionally control multiple critical genes involved in cell cycle, apoptosis and migration. DHX33 deficiency caused decreased tumor growth for colon cancer cells in a xenograft model in vivo. With Wnt/β-cateninactivator and inhibitors, we further discovered that Wnt/β-catenin pathway regulates DHX33 transcriptionally. This study for the first time demonstratesthe important role of DHX33 in colon cancer development and reveals the underlying molecular mechanism. We also provide the initial evidence for the relationship between DHX33 and Wnt/β-catenin signaling pathway in colon cancer development.

Paneth Cells Respond to Inflammation and Contribute to Tissue Regeneration by Acquiring Stem-like Features through SCF/c-Kit Signaling

IBD syndromes such as Crohn's disease and ulcerative colitis result from the inflammation of specific intestinal segments. Although many studies have reported on the regenerative response of intestinal progenitor and stem cells to tissue injury, very little is known about the response of differentiated lineages to inflammatory cues. Here, we show that acute inflammation of the mouse small intestine is followed by a dramatic loss of Lgr5⁺ stem cells. Instead, Paneth cells re-enter the cell cycle, lose their secretory expression signature, and acquire stem-like properties, thus contributing to the tissue regenerative response to inflammation. Stem cell factor secretion upon inflammation triggers signaling through the c-Kit receptor and a cascade of downstream events culminating in GSK3β inhibition and Wnt activation in Paneth cells. Hence, the plasticity of the intestinal epithelium in response to inflammation goes well beyond stem and progenitor cells and extends to the fully differentiated and post-mitotic Paneth cells.

GSK-3: An important kinase in colon and pancreatic cancers

In this review, the role of glycogen synthase kinase 3 (GSK-3) in pancreatic and colon cancers will be explored. GSK-3 plays a fundamental role in many metabolic processes, primarily as the final enzyme in glycogen synthesis. Active β-catenin represents the final step for the transcription of Wnt target genes. Both GSK-3 and β-catenin are key in the neoplastic transformation and tumorigenesis of human cells. Despite the advances in diagnosis and treatment of pancreatic malignancies, survival remains dismal. Continued poor outcomes are attributable to tumor cell resistance and high frequency of metastatic disease. Survival for patients diagnosed with colon cancer is often excellent, and many patients achieve long term remission. However, the incidence of colon cancers continues to increase, especially among the young. The future use of targeted therapy in pancreatic and colo-rectal cancer utilizing GSK-3 may be promising, pending a more thorough understanding of potential downstream effects. This article is part of a Special Issue entitled: GSK-3 and related kinases in cancer, neurological and other disorders edited by James McCubrey, Agnieszka Gizak and Dariusz Rakus.

GSK-3β-Targeting Fisetin Promotes Melanogenesis in B16F10 Melanoma Cells and Zebrafish Larvae through β-Catenin Activation

Fisetin is found in many fruits and plants such as grapes and onions, and exerts anti-inflammatory, anti-proliferative, and anticancer activity. However, whether fisetin regulates melanogenesis has been rarely studied. Therefore, we evaluated the effects of fisetin on melanogenesis in B16F10 melanoma cell and zebrafish larvae. The current study revealed that fisetin slightly suppressed in vitro mushroom tyrosinase activity; however, molecular docking data showed that fisetin did not directly bind to mushroom tyrosinase. Unexpectedly, fisetin significantly increased intracellular and extracellular melanin production in B16F10 melanoma cells regardless of the presence or absence of α-melanocyte stimulating hormone (α-MSH). We also found that the expression of melanogenesis-related genes such as tyrosinase and microphthalmia-associated transcription factor (MITF), were highly increased 48 h after fisetin treatment. Pigmentation of zebrafish larvae by fisetin treatment also increased at the concentrations up to 200 µM and then slightly decreased at 400 µM, with no alteration in the heart rates. Molecular docking data also revealed that fisetin binds to glycogen synthase kinase-3β (GSK-3β). Therefore, we evaluated whether fisetin negatively regulated GSK-3β, which subsequently activates β-catenin, resulting in melanogenesis. As expected, fisetin increased the expression of β-catenin, which was subsequently translocated into the nucleus. In the functional assay, FH535, a Wnt/β-catenin inhibitor, significantly inhibited fisetin-mediated melanogenesis in zebrafish larvae. Our data suggested that fisetin inhibits GSK-3β, which activates β-catenin, resulting in melanogenesis through the revitalization of MITF and tyrosinase.

The Roles of GSK-3β in Regulation of Retinoid Signaling and Sorafenib Treatment Response in Hepatocellular Carcinoma

Rationale: Glycogen synthase kinase-3β (GSK-3β) plays key roles in metabolism and many cellular processes. It was recently demonstrated that overexpression of GSK-3β can confer tumor growth. However, the expression and function of GSK-3β in hepatocellular carcinoma (HCC) remain largely unexplored. This study is aimed at investigating the role and therapeutic target value of GSK-3β in HCC. Methods: We firstly clarified the expression of GSK-3β in human HCC samples. Given that deviated retinoid signalling is critical for HCC development, we studied whether GSK-3β could be involved in the regulation. Since sorafenib is currently used to treat HCC, the involvement of GSK-3β in sorafenib treatment response was determined. Co-immunoprecipitation, GST pull down, in vitro kinase assay, luciferase reporter and chromatin immunoprecipitation were used to explore the molecular mechanism. The biological readouts were examined with MTT, flow cytometry and animal experiments. Results: We demonstrated that GSK-3β is highly expressed in HCC and associated with shorter overall survival (OS). Overexpression of GSK-3β confers HCC cell colony formation and xenograft tumor growth. Tumor-associated GSK-3β is correlated with reduced expression of retinoic acid receptor-β (RARβ), which is caused by GSK-3β-mediated phosphorylation and heterodimerization abrogation of retinoid X receptor (RXRα) with RARα on RARβ promoter. Overexpression of functional GSK-3β impairs retinoid response and represses sorafenib anti-HCC effect. Inactivation of GSK-3β by tideglusib can potentiate 9-cis-RA enhancement of sorafenib sensitivity (tumor inhibition from 48.3% to 93.4%). Efficient induction of RARβ by tideglusib/9-cis-RA is required for enhanced therapeutic outcome of sorafenib, which effect is greatly inhibited by knocking down RARβ. Conclusions: Our findings demonstrate that GSK-3β is a disruptor of retinoid signalling and a new resistant factor of sorafenib in HCC. Targeting GSK-3β may be a promising strategy for HCC treatment in clinic.