Growth factor withdrawal from primary human erythroid progenitors induces apoptosis through a pathway involving glycogen synthase kinase-3 and Bax

Role of Glycogen Synthase Kinase-3 in Interferon-γ-Mediated Immune Hepatitis

Glycogen synthase kinase-3 (GSK-3), a serine/threonine kinase, is a vital glycogen synthase regulator controlling glycogen synthesis, glucose metabolism, and insulin signaling. GSK-3 is widely expressed in different types of cells, and its abundant roles in cellular bioregulation have been speculated. Abnormal GSK-3 activation and inactivation may affect its original bioactivity. Moreover, active and inactive GSK-3 can regulate several cytosolic factors and modulate their diverse cellular functional roles. Studies in experimental liver disease models have illustrated the possible pathological role of GSK-3 in facilitating acute hepatic injury. Pharmacologically targeting GSK-3 is therefore suggested as a therapeutic strategy for liver protection. Furthermore, while the signaling transduction of GSK-3 facilitates proinflammatory interferon (IFN)-γ in vitro and in vivo, the blockade of GSK-3 can be protective, as shown by an IFN-γ-induced immune hepatitis model. In this study, we explored the possible regulation of GSK-3 and the potential relevance of GSK-3 blockade in IFN-γ-mediated immune hepatitis.

LncRNA PPM1A-AS Regulate Tumor Development Through Multiple Signal Pathways in T-Cell Acute Lymphoblastic Leukemia

ALL (Acute lymphoblastic leukemia) is the most common pediatric malignancy and T-ALL (T-cell acute lymphoblastic leukemia) comprises about 15% cases. Compared with B-ALL (B-cell acute lymphoblastic leukemia), the prognosis of T-ALL is poorer, the chemotherapy is easier to fail and the relapse rate is higher. Previous studies mainly focused in Notch1-related long non-coding RNAs (lncRNAs) in T-ALL. Here, we intend to investigate lncRNAs involved in T-ALL covering different subtypes. The lncRNA PPM1A-AS was screened out for its significant up-regulation in 10 T-ALL samples of different subtypes than healthy human thymus extracts. Besides, the PPM1A-AS expression levels in 3 T-ALL cell lines are markedly higher than that in CD45⁺ T cells of healthy human. We further demonstrate that PPM1A-AS can promote cell proliferation and inhibit cell apoptosis in vitro and can influence T-ALL growth in vivo. Finally, we verified that PPM1A-AS can regulate core proteins, Notch4, STAT3 and Akt, of 3 important signaling pathways related to T-ALL. These results confirm that lncRNA PPM1A-AS can act as an oncogene in T-ALL and maybe a potential clinical target of patients resistant to current chemotherapy or relapsed cases.

Current Evidence on the Protective Effects of Recombinant Human Erythropoietin and Its Molecular Variants against Pathological Hallmarks of Alzheimer's Disease

Substantial evidence in the literature demonstrates the pleiotropic effects of the administration of recombinant human erythropoietin (rhEPO) and its molecular variants in different tissues and organs, including the brain. Some of these reports suggest that the chemical properties of this molecule by itself or in combination with other agents (e.g., growth factors) could provide the necessary pharmacological characteristics to be considered a potential protective agent in neurological disorders such as Alzheimer’s disease (AD). AD is a degenerative disorder of the brain, characterized by an aberrant accumulation of amyloid β (Aβ) and hyperphosphorylated tau (tau-p) proteins in the extracellular and intracellular space, respectively, leading to inflammation, oxidative stress, excitotoxicity, and other neuronal alterations that compromise cell viability, causing neurodegeneration in the hippocampus and the cerebral cortex. Unfortunately, to date, it lacks an effective therapeutic strategy for its treatment. Therefore, in this review, we analyze the evidence regarding the effects of exogenous EPOs (rhEPO and its molecular variants) in several in vivo and in vitro Aβ and tau-p models of AD-type neurodegeneration, to be considered as an alternative protective treatment to this condition. Particularly, we focus on analyzing the differential effect of molecular variants of rhEPO when changes in doses, route of administration, duration of treatment or application times, are evaluated for the improved cellular alterations generated in this disease. This narrative review shows the evidence of the effectiveness of the exogenous EPOs as potential therapeutic molecules, focused on the mechanisms that establish cellular damage and clinical manifestation in the AD.

Aldehyde dehydrogenase 2 protects cardiomyocytes against lipotoxicity via the AKT/glycogen synthase kinase 3 beta pathways

Aldehyde dehydrogenase 2, a mitochondrial matrix enzyme, plays a crucial role in protecting the heart against stress, such as ischemia reperfusion and alcohol injury. The present study aimed to investigate the effect of aldehyde dehydrogenase 2 on lipotoxic cardiomyopathy and to explore the possible mechanisms in vitro. Primary cardiomyocytes in the lipotoxic group were treated with oxidatively modified low-density lipoprotein (50 mg/L) for 24 h. Overexpression of aldehyde dehydrogenase 2 was achieved using the aldehyde dehydrogenase 2 activator, Alda-1 (20 μM). We found that cardiomyocyte apoptosis was attenuated by aldehyde dehydrogenase 2 overexpression. In addition, aldehyde dehydrogenase 2 overexpression inhibited the expression of BCL2 associated X, apoptosis regulator (BAX) and caspase 3, while it enhanced protein kinase B (AKT) and glycogen synthase kinase 3 beta (GSK-3β) phosphorylation. The results suggested that aldehyde dehydrogenase 2 is cardioprotective against lipotoxic cardiomyopathy, probably by reducing apoptosis through the AKT/glycogen synthase kinase 3 beta (GSK-3β) pathway. Our findings partially revealed the molecular mechanism of aldehyde dehydrogenase 2's cardioprotective effect against lipotoxic injury, and suggest a new therapeutic strategy to treat lipotoxic cardiomyopathy.

Effects of siRNA-Mediated Knockdown of GSK3β on Retinal Ganglion Cell Survival and Neurite/Axon Growth

There are contradictory reports on the role of the serine/threonine kinase isoform glycogen synthase kinase-3β (GSK3β) after injury to the central nervous system (CNS). Some report that GSK3 activity promotes axonal growth or myelin disinhibition, whilst others report that GSK3 activity prevents axon regeneration. In this study, we sought to clarify if suppression of GSK3β alone and in combination with the cellular-stress-induced factor RTP801 (also known as REDD1: regulated in development and DNA damage response protein), using translationally relevant siRNAs, promotes retinal ganglion cell (RGC) survival and neurite outgrowth/axon regeneration. Adult mixed retinal cell cultures, prepared from rats at five days after optic nerve crush (ONC) to activate retinal glia, were treated with siRNA to GSK3β (siGSK3β) alone or in combination with siRTP801 and RGC survival and neurite outgrowth were quantified in the presence and absence of Rapamycin or inhibitory Nogo-A peptides. In in vivo experiments, either siGSK3β alone or in combination with siRTP801 were intravitreally injected every eight days after ONC and RGC survival and axon regeneration was assessed at 24 days. Optimal doses of siGSK3β alone promoted significant RGC survival, increasing the number of RGC with neurites without affecting neurite length, an effect that was sensitive to Rapamycin. In addition, knockdown of GSK3β overcame Nogo-A-mediated neurite growth inhibition. Knockdown of GSK3β after ONC in vivo enhanced RGC survival but not axon number or length, without potentiating glial activation. Knockdown of RTP801 increased both RGC survival and axon regeneration, whilst the combined knockdown of GSK3β and RTP801 significantly increased RGC survival, neurite outgrowth, and axon regeneration over and above that observed for siGSK3β or siRTP801 alone. These results suggest that GSK3β suppression promotes RGC survival and axon initiation whilst, when in combination with RTP801, it also enhanced disinhibited axon elongation.

GSK3β: a plausible mechanism of cognitive and hippocampal changes induced by erythropoietin treatment in mood disorders?

Mood disorders are associated with significant psychosocial and occupational disability. It is estimated that major depressive disorder (MDD) will become the second leading cause of disability worldwide by 2020. Existing pharmacological and psychological treatments are limited for targeting cognitive dysfunctions in mood disorders. However, growing evidence from human and animal studies has shown that treatment with erythropoietin (EPO) can improve cognitive function. A recent study involving EPO-treated patients with mood disorders showed that the neural basis for their cognitive improvements appeared to involve an increase in hippocampal volume. Molecular mechanisms underlying hippocampal changes have been proposed, including the activation of anti-apoptotic, antioxidant, pro-survival and anti-inflammatory signalling pathways. The aim of this review is to describe the potential importance of glycogen synthase kinase 3-beta (GSK3β) as a multi-potent molecular mechanism of EPO-induced hippocampal volume change in mood disorder patients. We first examine published associations between EPO administration, mood disorders, cognition and hippocampal volume. We then highlight evidence suggesting that GSK3β influences hippocampal volume in MDD patients, and how this could assist with targeting more precise treatments particularly for cognitive deficits in patients with mood disorders. We conclude by suggesting how this developing area of research can be further advanced, such as using pharmacogenetic studies of EPO treatment in patients with mood disorders.

Glycogen synthase kinase-3 and alternative splicing

Glycogen synthase kinase-3 (GSK-3) is a highly conserved negative regulator of receptor tyrosine kinase, cytokine, and Wnt signaling pathways. Stimulation of these pathways inhibits GSK-3 to modulate diverse downstream effectors that include transcription factors, nutrient sensors, glycogen synthesis, mitochondrial function, circadian rhythm, and cell fate. GSK-3 also regulates alternative splicing in response to T-cell receptor activation, and recent phosphoproteomic studies have revealed that multiple splicing factors and regulators of RNA biosynthesis are phosphorylated in a GSK-3-dependent manner. Furthermore, inhibition of GSK-3 alters the splicing of hundreds of mRNAs, indicating a broad role for GSK-3 in the regulation of RNA processing. GSK-3-regulated phosphoproteins include SF3B1, SRSF2, PSF, RBM8A, nucleophosmin 1 (NPM1), and PHF6, many of which are mutated in leukemia and myelodysplasia. As GSK-3 is inhibited by pathways that are pathologically activated in leukemia and loss of Gsk3 in hematopoietic cells causes a severe myelodysplastic neoplasm in mice, these findings strongly implicate GSK-3 as a critical regulator of mRNA processing in normal and malignant hematopoiesis. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Processing > Splicing Regulation/Alternative Splicing RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Leonurine protects cardiac function following acute myocardial infarction through anti‑apoptosis by the PI3K/AKT/GSK3β signaling pathway

Leonurine is a compound derived from Herba leonuri, which has been reported to protect cardiac tissue against ischemic injury via antioxidant and anti‑apoptosis effects. The present study investigated whether these effects may be applied to acute myocardial infarction (MI) and examined the underlying mechanisms of leonurine treatment. A rat model of MI was induced by coronary artery ligation. Leonurine was administered at 15 mg/kg/day by oral gavage following the onset of MI. Rats in the sham group and the saline group were administered with an equal volume of saline. Echocardiography, Masson's trichrome staining, and terminal‑deoxynucleotidyl transferase‑mediated dUTP nick end labeling assays were performed 28 days post MI. The expression of B‑cell lymphoma‑2 and Bax were assessed by western blot analysis and reverse transcription‑quantitative polymerase chain reaction. Phosphoinositide 3‑kinase (PI3K), protein kinase B and glycogen synthase kinase‑3β (GSK3β) protein expression were investigated by western blot analysis. Leonurine significantly alleviated collagen deposition and MI size, inhibited cell apoptosis and improved myocardial function. This was accompanied by significantly increased levels of phosphorylated (p)‑PI3K, p‑AKT, p‑GSK3β and Bcl‑2, as well as significantly decreased levels of caspase3, cleaved‑caspase3 and Bax following MI. The results demonstrated that leonurine exerts potent cardio‑protective effects in a rat model of MI by inducing anti‑apoptotic effects by activating the PI3K/AKT/GSK3β signaling pathway.

Topiramate mitigates 3-nitropropionic acid-induced striatal neurotoxicity via modulation of AMPA receptors

Prevalence of glutamate receptor subunit 2 (GluR2)-lacking alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors is a hallmark of excitotoxicity-related neurodegenerative diseases. Topiramate (TPM) is a structurally novel anticonvulsant with a well-known modulatory effects on AMPA/kainate subtypes of glutamate receptors. The present study aimed at investigating the neuroprotective potential of TPM on 3-nitropropionic acid (3-NP)-induced striatal neurodegeneration and Huntington's disease-like symptoms. Rats were injected with 3-NP (10 mg/kg/i.p.) for 14 days. TPM (50 mg/kg/p.o.) was given once a day, 1 h before 3-NP. TPM amended 3-NP induced changes in neurobehavioral performance, striatal neurotransmitters levels and histopathological injury. 3-NP control rats showed a significant ablation in the mRNA expression of Ca²⁺-impermeable Glu2R subunit along with an elevation in its regulatory protein (protein interacting with C kinase-1) PICK1, an effect that was largely reversed by TPM. TPM in addition, enhanced the phosphorylation of the protein kinase B/glycogen synthase kinase-3β/cAMP response element binding protein (Akt/GSK-3β/CREB) cue. Moreover, improvement in oxidative status, suppression of caspase-3 activity and restoration of striatal BDNF were noticed following treatment with TPM. The current study revealed that TPM boosted the neuroprotective (Akt/GSK-3β/CREB) pathway by its negative modulatory effect on AMPA glutamate receptors as well as its direct antioxidant property.

Erythropoietin ameliorates diabetes-associated cognitive dysfunction in vitro and in vivo

Several studies indicate that erythropoietin (EPO) has remarkable neuroprotective effects in various central nervous system disorders, while little is known about the effects of EPO in diabetes-associated cognitive dysfunction. Therefore, the present study aimed to investigate whether EPO ameliorates diabetes-associated cognitive dysfunction in vivo and in vitro. We investigated the protective effects of EPO on high-glucose (HG)-induced PC12 cell death and oxidative stress. The effects of EPO (300 U/kg administered three times a week for 4 weeks) on diabetes-associated cognitive decline were investigated in diabetic rats. EPO significantly increased cell viability, increased the activity of superoxide dismutase, decreased the production of malondialdehyde and reactive oxygen species, and decreased the apoptosis rate. Additionally, LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, abolished the protective effects of EPO in HG-treated PC12 cells. In diabetic rats, EPO prevented deficits in spatial learning and memory in the Morris water maze test. The results of real-time PCR and Western blotting showed that EPO upregulated EPO receptor, PI3K, and phosphorylated Akt2 relative to unphosphorylated Akt2 (p-Akt2/Akt2) and downregulated glycogen synthase kinase-3β (GSK-3β). These studies demonstrate that EPO is an effective neuroprotective agent in the context of diabetes-associated cognitive dysfunction and show that this effect involves the PI3K/Akt/GSK-3β pathway.

Protective Effect of Minocycline Against Ketamine-Induced Injury in Neural Stem Cell: Involvement of PI3K/Akt and Gsk-3 Beta Pathway

It has been suggested that ketamine cause injury during developing brain. Minocycline (MC) could prevent neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals in models of neurodegenerative diseases. Here we investigated the protective effect of MC against ketamine-induced injury in neural stem cells (NSCs) from neonatal rat. Ketamine (100 μM/L) significantly inhibited NSC proliferation, promoted their differentiation into astrocytes and suppressed neuronal differentiation of NSCs. Moreover, the apoptotic level was increased following ketamine exposure. MC pretreatment greatly enhanced cell viability, decreased caspase-3-like activity, even reversed the differentiation changes caused by ketamine. To elucidate a possible mechanism of MC' neuroprotective effect, we investigated the phosphatidylinositol 3-kinase (PI3K) pathway using LY294002, a specific PI3K inhibitor. Immunoblotting revealed that MC enhanced the phosphorylation/activation of Akt and phosphorylation/inactivation of glycogen synthase kinase-3beta (Gsk-3β). Our results suggest that PI3K/Akt and Gsk-3β pathway are involved in the neuroprotective effect of MC.

Role and regulation of Glycogen synthase kinase-3 beta in bovine spermatozoa

The serine/threonine kinase Glycogen synthase kinase 3 (GSK-3) is a master switch that regulates a multitude of cellular pathways, including the acrosome reaction in sperm. In epididymal sperm cells, for example, GSK-3 activity correlates with inhibition of motility-yet no direct pathways connecting GSK-3 activation with loss of motility have been described. Indeed, the details of how GSK-3 is regulated during sperm capacitation and the acrosome reaction remains obscure. To this end, we addressed the involvement of the GSK-3 beta isoform in several known pathways that contribute to motility and the acrosome reaction. We established that Protein kinase A (PKA) is the main regulator of GSK-3β in sperm, as pre-treatment of cells with a GSK-3 inhibitor prior to addition of H89, an inhibitor of PKA, attenuated the motility loss induced by blocking PKA activity. Both induced and spontaneous acrosome reactions also occurred less frequently in sperm treated with GSK-3 inhibitors. Finally, we observed a slow decline in phosphorylation of GSK-3β on Ser 9, which represents an inhibited state, during sperm capacitation; this phenotype is reversed during the induced acrosome reaction, in parallel to activation of Protein phosphatase 1. These results suggest that maintenance of sperm motility and acrosome reaction timing are mediated by PKA through the regulation of GSK-3 beta activity. Mol. Reprod. Dev. 84: 8-18, 2017. © 2016 Wiley Periodicals, Inc.

Probing the PI3K/Akt/mTor pathway using 31P-NMR spectroscopy: routes to glycogen synthase kinase 3

Akt is an intracellular signalling pathway that serves as an essential link between cell surface receptors and cellular processes including proliferation, development and survival. The pathway has many downstream targets including glycogen synthase kinase3 which is a major regulatory kinase for cell cycle transit as well as controlling glycogen synthase activity. The Akt pathway is frequently up-regulated in cancer due to overexpression of receptors such as the epidermal growth factor receptor, or mutation of signalling pathway kinases resulting in inappropriate survival and proliferation. Consequently anticancer drugs have been developed that target this pathway. MDA-MB-468 breast and HCT8 colorectal cancer cells were treated with inhibitors including LY294002, MK2206, rapamycin, AZD8055 targeting key kinases in/associated with Akt pathway and the consistency of changes in ³¹P-NMR-detecatable metabolite content of tumour cells was examined. Treatment with the Akt inhibitor MK2206 reduced phosphocholine levels in MDA-MB-468 cells. Treatment with either the phosphoinositide-3-kinase inhibitor, LY294002 and pan-mTOR inhibitor, AZD8055 but not pan-Akt inhibitor MK2206 increased uridine-5′-diphosphate-hexose cell content which was suppressed by co-treatment with glycogen synthase kinase 3 inhibitor SB216763. This suggests that there is an Akt-independent link between phosphoinositol-3-kinase and glycogen synthase kinase3 and demonstrates the potential of ³¹P-NMR to probe intracellular signalling pathways.

Potential beneficial role for endothelin in scleroderma vasculopathy: inhibition of endothelial apoptosis by type B endothelin-receptor signaling

Objectives

Microvascular endothelial cell (MVEC) apoptosis is considered to be a key event in the pathogenesis of systemic sclerosis (SSc), an increased expression of endothelin-1 (ET1) is also well recognized in the disease. ET1 is thought to exert deleterious effects on the vasculature by virtue of its known vasospastic, proliferative and fibrotic effects, yet ET1 can act as a survival factor for a variety of cells, including MVEC. The aim of this study is to investigate if ET1 signaling protects SSc-MVECs from apoptosis.

Methods

The expression levels of ET1-receptor genes: Endothelin Receptor Type A gene (EDNRA) and Endothelin Receptor Type B gene (EDNRB), and the effects of selective Endothelin Receptor Type A (ETA) antagonists, selective Endothelin Receptor Type B (ETB), and dual ETA/B antagonist in the presence and/or absence of ET1 on control and SSc-MVEC apoptosis were examined.

Results

Significant increase in the expression of ETA and ETB was noted in SSc-MVECs. Growth factors withdrawal (GFW) resulted in a significant apoptosis that was considerably reduced by the addition ET1. The addition of ETA-receptor antagonists did not affect ET1 anti-apoptotic effects, while the nonselective ETA/B or the selective ETB-receptor antagonists blocked the anti-apoptotic effects of ET1. Finally, an upregulation of the proapoptotic gene BAX after GFW was noted that was normalized by the addition of ET1.

Conclusions

The results suggest that ET1 mediates an anti-apoptotic effect through engaging the ETB receptors in MVECs. Therefore, it appears that selective ETA antagonism may have an advantage over the non-selective ET1-receptor antagonists in SSc vasculopathy, particularly in the early stages of the disease when MVEC apoptosis is rampant.

The role of Akt (protein kinase B) and protein kinase C in ischemia-reperfusion injury

Stroke is a leading cause of long-term disability and death in the United States. Currently, tissue plasminogen activator (tPA), is the only Food and Drug Administration-approved treatment for acute ischemic stroke. However, the use of tPA is restricted to a small subset of acute stroke patients due to its limited 3-h therapeutic time window. Given the limited therapeutic options at present and the multi-factorial progression of ischemic stroke, emphasis has been placed on the discovery and use of combination therapies aimed at various molecular targets contributing to ischemic cell death. Protein kinase C (PKC) and Akt (protein kinase B) are serine/threonine kinases that play a critical role in mediating ischemic-reperfusion injury and cellular growth and survival, respectively. The present review will examine the role of PKC and Akt in the cellular response to ischemic-reperfusion injury.

Glycogen synthase kinase-3 beta (GSK-3β) signaling: Implications for Parkinson's disease

Glycogen synthase kinase 3 (GSK-3) dysregulation plays an important role in the pathogenesis of numerous disorders, affecting the central nervous system (CNS) encompassing both neuroinflammation and neurodegenerative diseases. Several lines of evidence have illustrated a key role of the GSK-3 and its cellular and molecular signaling cascades in the control of neuroinflammation. Glycogen synthase kinase 3 beta (GSK-3β), one of the GSK-3 isomers, plays a major role in neuronal apoptosis and its inhibition decreases expression of alpha-Synuclein (α-Synuclein), which make this kinase an attractive therapeutic target for neurodegenerative disorders. Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. Thus, understanding the role of GSK-3β in PD will enhance our knowledge of the basic mechanisms underlying the pathogenesis of this disorder and facilitate the identification of new therapeutic avenues. In recent years, GSK-3β has been shown to play essential roles in modulating a variety of cellular functions, which have prompted efforts to develop GSK-3β inhibitors as therapeutics. In this review, we summarize GSK-3 signaling pathways and its association with neuroinflammation. Moreover, we highlight the interaction between GSK-3β and several cellular processes involved in the pathogenesis of PD, including the accumulation of α-Synuclein aggregates, oxidative stress and mitochondrial dysfunction. Finally, we discuss about GSK-3β inhibitors as a potential therapeutic strategy in PD.

Galectin-3 mediates bone marrow microenvironment-induced drug resistance in acute leukemia cells via Wnt/β-catenin signaling pathway

BACKGROUND

Acute leukemia is currently the major cause of death in hematological malignancies. Despite the rapid development of new therapies, minimal residual disease (MRD) continues to occur and leads to poor outcomes. The leukemia niche in the bone marrow microenvironment (BMM) is thought to be responsible for such MRD development, which can lead to leukemia drug resistance and disease relapse. Consequently further investigation into the way in which the leukemia niche interacts with acute leukemia cells (ALCs) and development of strategies to block the underlying process are expected to improve disease prognosis. Recent studies indicated that galectin-3 (gal-3) might play a pivotal role in this process. Thus we aimed to elucidate the exact role played by gal-3 in this process and clarify its mechanism of action.

METHODS

We used human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) to mimic the leukemia BMM in vitro, and investigated their effects on drug resistance of ALCs and the possible mechanisms involved, with particular emphasis on the role of gal-3.

RESULTS

In our study, we demonstrated that hBM-MSCs induced gal-3 up-regulation, promoting β-catenin stabilization and thus activating the Wnt/β-catenin signaling pathway in ALCs, which is critical in cytotoxic drug resistance of leukemia. This effect could be reversed by addition of gal-3 short hairpin RNA (shRNA). We also found that up-regulation of gal-3 promoted Akt and glycogen synthase kinase (GSK)-3β phosphorylation, thought to constitute a cross-bridge between gal-3 and Wnt signaling.

CONCLUSIONS

Our results suggest that gal-3, a key factor mediating BMM-induced drug resistance, could be a novel therapeutic target in acute leukemia.

GSK-3 – at the crossroads of cell death and survival

Glycogen synthase kinase 3 (GSK-3) is involved in various signaling pathways controlling metabolism, differentiation and immunity, as well as cell death and survival. GSK-3 targets transcription factors, regulates the activity of metabolic and signaling enzymes, and controls the half-life of proteins by earmarking them for degradation. GSK-3 is unique in its mode of substrate recognition and the regulation of its kinase activity, which is repressed by pro-survival phosphoinositide 3-kinase (PI3K)–AKT signaling. In turn, GSK-3 exhibits pro-apoptotic functions when the PI3K–AKT pathway is inactive. Nevertheless, as GSK-3 is crucially involved in many signaling pathways, its role in cell death regulation is not uniform, and in some situations it promotes cell survival. In this Commentary, we focus on the various aspects of GSK-3 in the regulation of cell death and survival. We discuss the effects of GSK-3 on the regulation of proteins of the BCL-2 family, through which GSK-3 exhibits pro-apoptotic activity. We also highlight the pro-survival activities of GSK-3, which are observed in the context of nuclear factor κB (NFκB) signaling, and we discuss how GSK-3, by impacting on cell death and survival, might play a role in diseases such as cancer.

Intranasal formulation of erythropoietin (EPO) showed potent protective activity against amyloid toxicity in the Aβ₂₅₋₃₅ non-transgenic mouse model of Alzheimer's disease

Erythropoietin (EPO) promotes neurogenesis and neuroprotection. We here compared the protection induced by two EPO formulations in a rodent model of Alzheimer's disease (AD): rHu-EPO and a low sialic form, Neuro-EPO. We used the intracerebroventricular administration of aggregated Aβ₂₅₋₃₅ peptide, a non-transgenic AD model. rHu-EPO was tested at 125-500 µg/kg intraperitoneally and Neuro-EPO at 62-250 µg/kg intranasally (IN). Behavioural procedures included spontaneous alternation, passive avoidance, water-maze and object recognition, to address spatial and non-spatial, short- and long-term memories. Biochemical markers of Aβ₂₅₋₃₅ toxicity in the mouse hippocampus were examined and cell loss in the CA1 layer was determined. rHu-EPO and Neuro-EPO led to a significant prevention of Aβ₂₅₋₃₅-induced learning deficits. Both EPO formulations prevented the induction of lipid peroxidation in the hippocampus, showing an antioxidant activity. rHu-EPO (250 µg/kg) or Neuro-EPO (125 µg/kg) prevented the Aβ₂₅₋₃₅-induced increase in Bax level, TNFα and IL-1β production and decrease in Akt activation. A significant prevention of the Aβ₂₅₋₃₅-induced cell loss in CA1 was also observed. EPO is neuroprotective in the Aβ₂₅₋₃₅ AD model, confirming its potential as an endogenous neuroprotection system that could be boosted for therapeutic efficacy. We here identified a new IN formulation of EPO showing high neuroprotective activity. Considering its efficacy, ease and safety, IN Neuro-EPO is a new promising therapeutic agent in AD.

Combined inhibition of PI3K and activation of MAPK p38 signaling pathways trigger erythroid alternative splicing switch of 4.1R pre-mRNA in DMSO-induced erythroleukemia cells

There is increasing evidence showing that many extracellular cues modulate pre-mRNA alternative splicing, through different signaling pathways. We here show that 4.1R exon 16 splicing is altered in response to specific signals. The switch from erythroblastic isoform lacking exon 16 to mature erythrocytic isoform containing this exon is tightly regulated during late erythroid differentiation, and blocage of this splicing switch in erythroleukemia cells is seen as a consequence of the deregulation of important regulatory pathways. We support that combined inhibition of PI3K and activation of p38 signaling pathways impinge on erythroid 4.1R pre-mRNA alternative splicing switch, and on cell differentiation as witnessed by hemoglobin production. By contrast, MEK/ERK signaling appeared not to affect neither cell hemoglobin production nor erythroid 4.1R pre-mRNA splicing. We also found that the signal-induced alternative splicing is not typically distinctive of EPO-non-responsive cells, but operates in EPO-responsive cells as well. Pre-mRNA splicing is a major regulatory mechanism at the crossroad between transcription and translation. We here provide evidence that inhibition of PI3K activates the splicing switch in a promoter-dependent manner, whereas p38 activation induces this event in a promoter-independent fashion. Our data further support that constitutive activation of EPO-R by the viral protein gp55 and the short form of the tyrosine kinase receptor Stk, transduces PI3K proliferation signal, but not MAPK p38 differentiation signal. Concurrently, this work lend credence to the concept that DMSO triggers transient activation of p38 signaling and irreversible inhibition of PI3K/AKT signaling pathway, hence uncovering an old conundrum regarding the mechanism by which DMSO induces erythroleukemia cell differentiation.

Netrin-1 protects hypoxia-induced mitochondrial apoptosis through HSP27 expression via DCC- and integrin α6β4-dependent Akt, GSK-3β, and HSF-1 in mesenchymal stem cells

Netrin (Ntn) has the potential to be successfully applied as an anti-apoptotic agent with a high affinity for tissue, for therapeutic strategies of umbilical cord blood-derived mesenchymal stem cells (UCB-MSC), although the mechanism by which Ntn-1 protects hypoxic injury has yet to be identified. Therefore, the present study examined the effect of Ntn-1 on hypoxia-induced UCB-MSC apoptosis, as well as the potential underlying mechanisms of its protective effect. Hypoxia (72 h) reduced cell viability (MTT reduction, and [³H]-thymidine incorporation) and cell number, and induced apoptosis (annexin and/or PI positive), which were reversed by Ntn-1 (10 ng/ml). Moreover, Ntn-1 decreased the increase of hypoxia-induced Bax, cleaved caspase-9, and -3, but blocked the decrease of hypoxia-reduced Bcl-2. Next, in order to examine the Ntn-1-related signaling cascade in the protection of hypoxic injury, we analyzed six Ntn receptors in UCB-MSC. We identified deleted in colorectal cancer (DCC) and integrin (IN) α6β4, except uncoordinated family member (UNC) 5A–C, and neogenin. Among them, IN α6β4 only was detected in lipid raft fractions. In addition, Ntn-1 induced the dissociation of DCC and APPL-1 complex, thereby stimulating the formation of APPL-1 and Akt2 complex. Ntn-1 also reversed the hypoxia-induced decrease of Akt and glycogen synthase kinase 3β (GSK-3β) phosphorylation, which is involved in heat shock factor-1 (HSF-1) expression. Ntn-1-induced phospho-Akt and -GSK-3β were inhibited by DCC function-blocking antibody, IN a6b4 function-blocking antibody, and the Akt inhibitor. Hypoxia and/or Ntn-1 stimulated heat shock protein (HSP)27 expression, which was blocked by HSF-1-specific small interfering RNA (siRNA). Furthermore, HSP27-specific siRNA reversed the Ntn-1-induced increase of phospho-Akt. Additionally, HSP27-specific siRNA attenuated the Ntn-1-reduced loss of mitochondrial membrane injury via the inhibition of cytochrome c (cyt c) release and formation of cyt c and HSP27 complex. Moreover, the inhibition of each signaling protein attenuated Ntn-1-induced blockage of apoptosis. In conclusion, Ntn-1-induced HSP27 protected hypoxic injury-related UCB-MSC apoptosis through DCC- and IN α6β4-dependent Akt, GSK-3β, and HSF-1 signaling pathways.

Caffeic acid phenylethyl ester and MG132, two novel nonconventional chemotherapeutic agents, induce apoptosis of human leukemic cells by disrupting mitochondrial function

The ability to modulate balance between cell survival and death is recognized for its great therapeutic potential. Therefore, research continues to focus on elucidation of cell machinery and signaling pathways that control cell proliferation and apoptosis. Conventional chemotherapeutic agents often have a cytostatic effect over tumor cells. New natural or synthetic chemotherapeutic agents have a wider spectrum of interesting antitumor activities that merit in-depth studies. In the present work, we aimed at characterizing the molecular mechanism leading to induction of cell death upon treatment of the lymphoblastoid cell line PL104 with caffeic acid phenylethyl ester (CAPE), MG132 and two conventional chemotherapeutic agents, doxorubicine (DOX) and vincristine (VCR). Our results showed several apoptotic hallmarks such as phosphatidylserine (PS) exposure on the outer leaflet of the cell membrane, nuclear fragmentation, and increase sub-G1 DNA content after all treatments. In addition, all four drugs downregulated survivin expression. CAPE and both chemotherapeutic agents reduced Bcl-2, while only CAPE and MG132 significantly increased Bax level. CAPE and VCR treatment induced the collapse of mitochondrial membrane potential (∆ψm). All compounds induced cytochrome c release from mitochondrial compartment to cytosol. However, only MG132 caused the translocation of Smac/DIABLO. Except for VCR treatment, all other drugs increased reactive oxygen species (ROS) production level. All treatments induced activation of caspases 3/7, but only CAPE and MG132 led to the activation of caspase 9. In conclusion, our results indicate that CAPE and MG132 treatment of PL104 cells induced apoptosis through the mitochondrial intrinsic pathway, whereas the apoptotic mechanism induced by DOX and VCR may proceed through the extrinsic pathway.

Specific deletion of glycogen synthase kinase-3β in the renal proximal tubule protects against acute nephrotoxic injury in mice

Renal proximal tubular damage and repair are hallmarks of acute kidney injury. Because glycogen synthase kinase-3β (GSK-3β) is an important cellular regulator of survival and proliferation, we determined its role during injury and recovery of proximal tubules in a mercuric chloride-induced nephrotoxic model of acute kidney injury. Renal proximal tubule-specific GSK-3β knockout mice exposed to mercuric chloride had improved survival and renal function compared to wild type mice. Apoptosis, measured by TUNEL staining, Bax activation, and caspase 3 cleavage were all reduced in the knockout mice. The restoration of renal structure, function, and cell proliferation was also accelerated in the GSK-3β knockout mice. This enhanced repair, evidenced by increased Ki-67 and BrdU staining, along with increased cyclin D1 and c-myc levels, was recapitulated by treatment of wild type mice with the small-molecule GSK-3 inhibitor TDZD-8 following injury. This confirmed that hastened repair in the knockout mice was not merely due to lower initial injury levels. Thus, inhibition of GSK-3β prior to nephrotoxic insult protects from renal injury. Such treatment after acute kidney injury may accelerate repair and regeneration.

Differential proteomic analysis of human erythroblasts undergoing apoptosis induced by epo-withdrawal

The availability of Erythropoietin (Epo) is essential for the survival of erythroid progenitors. Here we study the effects of Epo removal on primary human erythroblasts grown from peripheral blood CD34(+) cells. The erythroblasts died rapidly from apoptosis, even in the presence of SCF, and within 24 hours of Epo withdrawal 60% of the cells were Annexin V positive. Other classical hallmarks of apoptosis were also observed, including cytochrome c release into the cytosol, loss of mitochondrial membrane potential, Bax translocation to the mitochondria and caspase activation. We adopted a 2D DIGE approach to compare the proteomes of erythroblasts maintained for 12 hours in the presence or absence of Epo. Proteomic comparisons demonstrated significant and reproducible alterations in the abundance of proteins between the two growth conditions, with 18 and 31 proteins exhibiting altered abundance in presence or absence of Epo, respectively. We observed that Epo withdrawal induced the proteolysis of the multi-functional proteins Hsp90 alpha, Hsp90 beta, SET, 14-3-3 beta, 14-3-3 gamma, 14-3-3 epsilon, and RPSA, thereby targeting multiple signaling pathways and cellular processes simultaneously. We also observed that 14 proteins were differentially phosphorylated and confirmed the phosphorylation of the Hsp90 alpha and Hsp90 beta proteolytic fragments in apoptotic cells using Nano LC mass spectrometry. Our analysis of the global changes occurring in the proteome of primary human erythroblasts in response to Epo removal has increased the repertoire of proteins affected by Epo withdrawal and identified proteins whose aberrant regulation may contribute to ineffective erythropoiesis.

Mild hyperthermia promotes and accelerates development and maturation of erythroid cells

Hyperthermia treatment has at times been associated with increased platelet levels in humans. The heat shock protein HSP70, which can be induced by hyperthermia in megakaryocytes and erythrocytes, was recently shown to protect GATA-1 from degradation and to be required for erythroid differentiation. Based on these findings, we hypothesize that mild hyperthermia (MH), such as fever (39°C), could impact the differentiation of hematopoietic progenitors into erythrocytes and their subsequent maturation. Cell growth and erythroid differentiation increased dramatically in cord blood CD34(+) cell cultures incubated under MH. Erythroid maturation was also strongly promoted, which resulted in an increased proportion of hemoglobinized and enucleated erythroids. The rise in erythroid development was traced to a strong synergistic activity between MH and erythropoietin (EPO). The molecular basis for this potent synergy appears to originate from the capacity of MH to increase the basal activation of several signaling molecules downstream of the EPO receptor and the transcriptional activity of GATA-1. Moreover, the potent impact of MH on erythroid development was found be dependent on increased intracellular levels of reactive oxygen species. Thus, fever-like temperatures can promote the differentiation of progenitors along the erythroid lineage and accelerate their maturation through normal regulatory circuitry.

GSK3 as a Sensor Determining Cell Fate in the Brain

Glycogen synthase kinase 3 (GSK3) is an unusual serine/threonine kinase that controls many neuronal functions, including neurite outgrowth, synapse formation, neurotransmission, and neurogenesis. It mediates these functions by phosphorylating a wide range of substrates involved in gene transcription, metabolism, apoptosis, cytoskeletal dynamics, signal transduction, lipid membrane dynamics, and trafficking, amongst others. This complicated list of diverse substrates generally follow a more simple pattern: substrates negatively regulated by GSK3-mediated phosphorylation favor a proliferative/survival state, while substrates positively regulated by GSK3 favor a more differentiated/functional state. Accordingly, GSK3 activity is higher in differentiated cells than undifferentiated cells and physiological (Wnt, growth factors) and pharmacological inhibitors of GSK3 promote the proliferative capacity of embryonic stem cells. In the brain, the level of GSK3 activity influences neural progenitor cell proliferation/differentiation in neuroplasticity and repair, as well as efficient neurotransmission in differentiated adult neurons. While defects in GSK3 activity are unlikely to be the primary cause of neurodegenerative diseases, therapeutic regulation of its activity to promote a proliferative/survival versus differentiated/mature functional environment in the brain could be a powerful strategy for treatment of neurodegenerative and other mental disorders.

Glycogen synthase kinase-3β is a prosurvival signal for the maintenance of human mast cell homeostasis

Homeostasis of mature tissue-resident mast cells is dependent on the relative activation of pro- and antiapoptotic regulators. In this study, we investigated the role of glycogen synthase kinase 3β (GSK3β) in the survival of neoplastic and nonneoplastic human mast cells. GSK3β was observed to be phosphorylated at the Y(216) activating residue under resting conditions in both the neoplastic HMC1.2 cell line and in peripheral blood-derived primary human mast cells (HuMCs), suggesting constitutive activation of GSK3β in these cells. Lentiviral-transduced short hairpin RNA knockdown of GSK3β in both the HMC1.2 cells and HuMCs resulted in a significant reduction in cell survival as determined with the MTT assay. The decrease in stem cell factor (SCF)-mediated survival in the GSK3β knockdown HuMCs was reflected by enhancement of SCF withdrawal-induced apoptosis, as determined by Annexin V staining and caspase cleavage, and this was associated with a pronounced reduction in SCF-mediated phosphorylation of Src homology 2 domain-containing phosphatase 2 and ERK1/2 and reduced expression of the antiapoptotic proteins Bcl-xl and Bcl-2. These data show that GSK3β is an essential antiapoptotic factor in both neopastic and nontransformed primary human mast cells through the regulation of SCF-mediated Src homology 2 domain-containing phosphatase 2 and ERK activation. Our data suggest that targeting of GSK3β with small m.w. inhibitors such as CHIR 99021 may thus provide a mechanism for limiting mast cell survival and subsequently decreasing the intensity of the allergic inflammatory response.

A novel inhibitor of focal adhesion signaling induces caspase-independent cell death in diffuse large B-cell lymphoma

Focal adhesion (FA) proteins have been associated with transformation, migration, metastasis, and poor outcome in many neoplasias. We previously showed that these proteins were inhibited by E7123, a new celecoxib derivative with antitumor activity, in acute myeloid leukemia. However, little is known about FAs in diffuse large B cell lymphoma (DLBCL). This paper aimed to determine whether E7123 was effective against DLBCL and whether FAs were involved in its action. We evaluated the cytotoxicity and mechanism of action of E7123 and celecoxib in DLBCL cell lines. We also assessed the E7123 in vivo activity in a DLBCL xenograft model and studied FA signaling in primary DLBCL patient samples. We found that E7123 showed higher antitumor effect than celecoxib against DLBCL cells. Its mechanism of action involved deregulation of FA, AKT, and Mcl-1 proteins, a pathway that is activated in some patient samples, apoptosis-inducing factor release and induction of caspase-independent cell death. Moreover, E7123 showed suppression of in vivo tumor growth. These findings indicate that E7123 is effective against DLBCL in vitro and in vivo, with a mechanism of action that differs from that of most current therapies for this malignancy. Our results support further preclinical evaluation of E7123.

The HIV-1-specific protein Casp8p41 induces death of infected cells through Bax/Bak

Casp8p41, a novel protein generated when HIV-1 protease cleaves caspase 8, independently causes NF-κB activation, proinflammatory cytokine production, and cell death. Here we investigate the mechanism by which Casp8p41 induces cell death. Immunogold staining and electron microscopy demonstrate that Casp8p41 localizes to mitochondria of activated primary CD4 T cells, suggesting mitochondrial involvement. Therefore, we assessed the dependency of Casp8p41-induced death on Bax/Bak and caspase 9. In wild-type (WT) mouse embryonic fibroblast (MEF) cells, Casp8p41 causes rapid mitochondrial depolarization (P < 0.001), yet Casp8p41 expression in Bax/Bak double-knockout (DKO) MEF cells does not. Similarly, caspase 9-deficient T cells (JMR cells), which express Casp8p41, undergo minimal cell death, whereas reconstituting these cells with caspase 9 (F9 cells) restores Casp8p41 cytotoxicity (P < 0.01). The infection of caspase 9-deficient cells with a green fluorescent protein (GFP) HIV-1 reporter virus results in cell death in 32% of infected GFP-positive cells, while the restoration of caspase 9 expression in these cells restores infected-cell killing to 68% (P < 0.05), with similar levels of viral replication between infections. Our data demonstrate that Casp8p41 requires Bax/Bak to induce mitochondrial depolarization, which leads to caspase 9 activation following either Casp8p41 expression or HIV-1 infection. This understanding allows the design of strategies to interrupt this form of death of HIV-1-infected cells.

Regulation of cell survival mechanisms in Alzheimer's disease by glycogen synthase kinase-3

A pivotal role has emerged for glycogen synthase kinase-3 (GSK3) as an important contributor to Alzheimer's disease pathology. Evidence for the involvement of GSK3 in Alzheimer's disease pathology and neuronal loss comes from studies of GSK3 overexpression, GSK3 localization studies, multiple relationships between GSK3 and amyloid β-peptide (Aβ), interactions between GSK3 and the microtubule-associated tau protein, and GSK3-mediated apoptotic cell death. Apoptotic signaling proceeds by either an intrinsic pathway or an extrinsic pathway. GSK3 is well established to promote intrinsic apoptotic signaling induced by many insults, several of which may contribute to neuronal loss in Alzheimer's disease. Particularly important is evidence that GSK3 promotes intrinsic apoptotic signaling induced by Aβ. GSK3 appears to promote intrinsic apoptotic signaling by modulating proteins in the apoptosis signaling pathway and by modulating transcription factors that regulate the expression of proteins involved in apoptosis. Thus, GSK3 appears to contribute to several neuropathological mechanisms in Alzheimer's disease, including apoptosis-mediated neuronal loss.

Glycogen synthase kinase-3 regulates endoplasmic reticulum (ER) stress-induced CHOP expression in neuronal cells

Endoplasmic reticulum (ER) stress, often resulting from cellular accumulation of misfolded proteins, occurs in many neurodegenerative disorders, in part because of the relatively long lifetime of neurons. Excessive accumulation of misfolded proteins activates the unfolded protein response (UPR) that dampens protein synthesis and promotes removal of misfolded proteins to support survival of ER-stressed cells. However, the UPR also initiates apoptotic signaling to kill cells if recovery is not achieved. Thus, there is much interest in identifying determinants of the life-death switch and interventions that promote recovery and survival. One intervention that has consistently been shown to protect cells from ER stress-induced apoptosis is application of inhibitors of glycogen synthase kinase-3 (GSK3). Therefore, we examined where in the UPR pathway GSK3 inhibitors intercede to impede signaling towards apoptosis. Apoptosis following UPR activation can be mediated by activation of two transcription factors, ATF4 and ATF6, that activate expression of the death-inducing transcription factor C/EBP homologous protein (CHOP/GADD153) following ER stress. We found that ER stress activated ATF6 and ATF4, but these responses were not inhibited by pretreatment with GSK3 inhibitors. However, inhibition of GSK3 effectively reduced the expression of CHOP, and this was apparent in several types of neural-related cells and was evident after application of several structurally diverse GSK3 inhibitors. Therefore, reduction of CHOP activation provides one mechanism by which inhibitors of GSK3 are capable of shifting cell fate towards survival instead of apoptosis following ER stress.

Erythropoietin improves the survival of fat tissue after its transplantation in nude mice

Background

Autologous transplanted fat has a high resorption rate, providing a clinical challenge for the means to reduce it. Erythropoietin (EPO) has non-hematopoietic targets, and we hypothesized that EPO may improve long-term fat graft survival because it has both pro-angiogenic and anti-apoptotic properties. We aimed to determine the effect of EPO on the survival of human fat tissue after its transplantation in nude mice.

Methodology/Principal Findings

Human fat tissue was injected subcutaneously into immunologically-compromised nude mice, and the grafts were then treated with either 20 IU or 100 IU EPO. At the end of the 15-week study period, the extent of angiogenesis, apoptosis, and histology were assessed in the fat grafts. The results were compared to vascular endothelial growth factor (VEGF)-treated and phosphate-buffered saline (PBS)-treated fat grafts. The weight and volume of the EPO-treated grafts were higher than those of the PBS-treated grafts, whose weights and volumes were not different from those of the VEGF-treated grafts. EPO treatment also increased the expression of angiogenic factors and microvascular density, and reduced inflammation and apoptosis in a dose-dependent manner in the fat grafts.

Conclusions/Significance

Our data suggest that stimulation of angiogenesis by a cluster of angiogenic factors and decreased fat cell apoptosis account for potential mechanisms that underlie the improved long-term survival of fat transplants following EPO treatment.

Effect of mood stabilizers on gene expression in lymphoblastoid cells

Lithium and valproate are widely used as effective mood stabilizers for the treatment of bipolar disorder. To elucidate the common molecular effect of these drugs on non-neuronal cells, we studied the gene expression changes induced by these drugs. Lymphoblastoid cell cultures derived from lymphocytes harvested from three healthy subjects were incubated in medium containing therapeutic concentrations of lithium (0.75 mM) or valproate (100 microg ml(-1)) for 7 days. Gene expression profiling was performed using an Affymetrix HGU95Av2 array containing approximately 12,000 probe sets. We identified 44 and 416 genes that were regulated by lithium and valproate, respectively. Most of the genes were not commonly affected by the two drugs. Among the 18 genes commonly altered by both drugs, vascular endothelial growth factor A (VEGFA), which is one of the VEGF gene isoforms, showed the largest downregulation. Our findings indicate that these two structurally dissimilar mood stabilizers, lithium, and valproate, alter VEGFA expression. VEGFA might be a useful biomarker of their effects on peripheral tissue.

Polycythemia vera erythroid precursors exhibit increased proliferation and apoptosis resistance associated with abnormal RAS and PI3K pathway activation

OBJECTIVE

Polycythemia vera (PV) is characterized by erythrocytosis associated with the presence of the activating JAK2(V617F) mutation in a variable proportion of hematopoietic cells. JAK2(V617F) is detected in other myeloproliferative neoplasms, does not appear to be the PV-initiating event, and its specific role in deregulated erythropoiesis in PV is incompletely understood. We investigated the pathogenesis of PV to characterize abnormal proliferation and apoptosis responses and aberrant oncogenic pathway activation in primary PV erythroid precursors.

MATERIALS AND METHODS

Peripheral blood CD34(+) cells isolated from PV patients and healthy controls were grown in liquid culture to expand a population of primary erythroblasts for experiments designed to analyze cellular proliferation, apoptosis, JAK2(V617F) mutation status, cytokine-dependent protein phosphorylation and gene expression profiling using Affymetrix microarrays.

RESULTS

The survival and proliferation of PV erythroblasts were growth factor-dependent under strict serum-free conditions requiring both erythropoietin (EPO) and stem cell factor. PV erythroblasts exhibited EPO hypersensitivity and enhanced cellular proliferation associated with increased EPO-mediated extracellular signal-regulated kinases 1 and 2 phosphorylation. EPO-induced AKT phosphorylation was observed in PV but not normal erythroblasts, an effect associated with apoptosis resistance in PV erythroblasts. Analysis of gene expression and oncogenic pathway activation signatures revealed increased RAS (p<0.01) and phosphoinositide-3 kinase (p<0.05) pathway activation in PV erythroblasts.

CONCLUSION

Deregulated erythropoiesis in PV involves EPO hypersensitivity and apoptosis resistance of erythroid precursor cells associated with abnormally increased activation of RAS-ERK and phosphoinositide-3 kinase-AKT pathways. These data suggest that investigation of the mechanisms of abnormal RAS and phosphoinositide-3 kinase pathway activation in erythroblasts may contribute to our understanding of the molecular pathogenesis of PV.

Inhibiting glycogen synthase kinase-3 reduces endotoxaemic acute renal failure by down-regulating inflammation and renal cell apoptosis

BACKGROUND AND PURPOSE

Excessive inflammation and apoptosis are pathological features of endotoxaemic acute renal failure. Activation of glycogen synthase kinase-3 (GSK-3) is involved in inflammation and apoptosis. We investigated the effects of inhibiting GSK-3 on lipopolysaccharide (LPS)-induced acute renal failure, nuclear factor-kappaB (NF-kappaB), inflammation and apoptosis.

EXPERIMENTAL APPROACH

The effects of inhibiting GSK-3 with inhibitors, including lithium chloride (LiCl) and 6-bromo-indirubin-3'-oxime (BIO), on LPS-treated (15 mg x kg(-1)) C3H/HeN mice (LiCl, 40 mg x kg(-1) and BIO, 2 mg x kg(-1)) and LPS-treated (1 microg x mL(-1)) renal epithelial cells (LiCl, 20 mM and BIO, 5 microM) were studied. Mouse survival was monitored and renal function was analysed by histological and serological examination. Cytokine and chemokine production, and cell apoptosis were measured by enzyme-linked immunosorbent assay and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling staining, respectively. Activation of NF-kappaB and GSK-3 was determined by immunostaining and Western blotting, respectively.

KEY RESULTS

Mice treated with GSK-3 inhibitors showed decreased mortality, renal tubular dilatation, vacuolization and sloughing, blood urea nitrogen, creatinine and renal cell apoptosis in response to endotoxaemia. Inhibiting GSK-3 reduced LPS-induced tumour necrosis factor-alpha (TNF-alpha) and CCL5/RANTES (released upon activation of normal T-cells) in vivo in mice and in vitro in murine kidney cortical collecting duct epithelial M1 cells. Inhibiting GSK-3 did not block TNF-alpha-induced cytotoxicity in rat kidney proximal tubular epithelial NRK52E or in M1 cells.

CONCLUSIONS AND IMPLICATIONS

These results suggest that GSK-3 inhibition protects against endotoxaemic acute renal failure mainly by down-regulating pro-inflammatory TNF-alpha and RANTES.

G-CSF- and erythropoietin-based cell therapy: a promising strategy for angiomyogenesis in myocardial infarction

Granulocyte colony-stimulating factor (G-CSF) and erythropoietin are two cytokines that have been demonstrated to improve cardiac function and perfusion in myocardial infarction. G-CSF was initially evaluated as a stem cell mobilizer and erythropoietin as a cytoprotective agent. However, both cytokines have direct cytoprotective effects and stem cell-mobilizing ability. Direct cytoprotective effects of both cytokines are commonly mediated by the Jak-STAT pathway. In preclinical study, G-CSF and erythropoietin improved cardiac function and perfusion by angiomyogenesis and protection of cardiomyocytes in myocardial infarction. However, results from recent clinical trials did not support beneficial effects of cytokine therapy with G-CSF or erythropoietin alone in patients with myocardial infarction. Further studies are required to elucidate the mechanism of action and to improve therapeutic efficacy by employing novel strategies, such as combined cytokines.

Erythropoietin prevents PC12 cells from 1-methyl-4-phenylpyridinium ion-induced apoptosis via the Akt/GSK-3beta/caspase-3 mediated signaling pathway

Apoptosis is a contributing cause of dopaminergic neuron loss in Parkinson disease. Recent work has shown that erythropoietin (EPO) offers protection against apoptosis in a wide variety of tissues. We demonstrate that exposure of PC12 cells to 1-methyl-4-phenylpyridinium ion (MPP(+)) with recombinant human EPO, significantly decreased apoptosis as measured by TUNEL and caspase-3 activity when compared to MPP(+) treatment alone. EPO induced sustained phosphorylation of Akt and its substrate, GSK-3beta, reduced caspase-3 activities in PC12 cells. The anti-apoptotic effect of EPO was abrogated by co-treatment with LY294002, the specific blocker of phosphatidylinositol 3-kinase (PI3K). The effects of EPO on GSK-3beta and caspase-3 activities were also blocked by LY294002. LiCl, the inhibitor of GSK-3beta, downregulated the caspase-3 activity and blocked the apoptosis induced by MPP(+). Finally, we determined that EPO transiently activated the ERK signaling pathway, but PD98059, a specific inhibitor of ERK, does not alter the survival effect of EPO in this model system. Thus, these findings indicate that EPO protects against apoptosis in PC12 cells exposed to MPP(+), through the Akt/GSK-3beta/caspase-3 signaling pathway, but the ERK pathway is not involved in the EPO-dependent survival enhancing effect in this model system.

GSK-3beta acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 in ceramide-induced mitochondrial apoptosis

The signaling of glycogen synthase kinase-3beta (GSK-3beta) has been implicated in stress-induced apoptosis. However, the pro-apoptotic role of GSK-3beta is still unclear. Here, we show the involvement of GSK-3beta in ceramide-induced mitochondrial apoptosis. Ceramide induced GSK-3beta activation via protein dephosphorylation at serine 9. We previously reported that ceramide induced caspase-2 and caspase-8 activation, Bid cleavage, mitochondrial damage, and apoptosis. In this study, we found that caspase-2 activation and the subsequent apoptotic events were abolished by the GSK-3beta inhibitors lithium chloride and SB216763, and by GSK-3beta knockdown using short interfering RNA. We also found that ceramide-activated protein phosphatase 2A (PP2A) indirectly caused GSK-3beta activation, and that the PP2A-regulated PI 3-kinase-Akt pathway was involved in GSK-3beta activation. These results indicate a role for GSK-3beta in ceramide-induced apoptosis, in which GSK-3beta acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 and caspase-8.

Effects of a single dose of erythropoietin on subsequent seizure susceptibility in rats exposed to acute hypoxia at P10

PURPOSE

To determine if posthypoxia treatment with erythropoietin (EPO) has protective effects against subsequent susceptibility to seizure related neuronal injury in rat pups subjected to acute hypoxia at P10.

METHODS

Four groups of rats were manipulated at P10, as described below, then all received kainic acid (KA) (10 mg/kg i.p.) at P29: Hypoxia-NS-KA group (n = 11): subjected to acute hypoxia (down to 4% O2), and then immediately received saline i.p. Hypoxia-EPO-KA group (n = 10): subjected to acute hypoxia and then immediately received EPO (1,000 U/Kg i.p.). Normoxia-NS-KA group (n = 11): sham manipulated and injected with saline. Normoxia-EPO-KA group (n = 10): sham manipulated then immediately injected with EPO (1000 U/Kg i.p.). After receiving KA at P29, all rats were monitored using videotape techniques, and were sacrificed at P31. TUNEL and Hoechst stains to assess for apoptosis, and regular histology for hippocampal cell counts were performed.

RESULTS

Administration of the single dose of erythropoietin directly after an acute hypoxic event at P10 resulted at P29 in increased latency to forelimb clonus seizures, reduced duration of these seizures, protection against hippocampal cell loss, and decreased hippocampal apoptosis in the Hypoxia-EPO-KA group as compared to the Hypoxia-NS-KA group.

CONCLUSION

These data support the presence of favorable protective effects of erythropoietin against the long-term consequences of acute hypoxia in the developing brain and raise the possibility of its investigation as a potential neuroprotective agent after human neonatal hypoxic encephalopathy.

Age-related changes in glycogen synthase kinase 3beta (GSK3beta) immunoreactivity in the central nervous system of rats

Although glycogen synthase kinase 3beta (GSK3beta) is emerging as a prominent drug target in the treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and stroke, very little is known about age-related changes in GSK3beta expression and GSK3beta phosphorylation. Therefore, we examined age-related changes in immunoreactivities for GSK3beta and phosphorylated GSK3beta (pGSK3beta) in the central nervous system. In aged rats, there were significant increases in GSK3beta immunoreactivity in the cell bodies and processes of pyramidal cells in most cortical regions. GSK3beta immunoreactivity was also significantly increased in the pyramidal layer of CA1-3 regions, and the granule cell layer of dentate gyrus. Age-related increases were prominent in lateral septal nuclei, compared to the medial septal nuclei. Interestingly, both GSK3beta and pGSK3beta was increased in the prefrontal cortex, while GSK3beta and pGSK3beta was differentially localized in the cerebellar cortex. The first demonstration of age-related alterations in immunoreactivities for GSK3beta and pGSK3beta in the basal forebrain area and cholinergic projection targets may provide useful data for investigating the pathogenesis of age-related neurodegenerative diseases including AD.

Lithium Treatment Prevents Neurocognitive Deficit Resulting from Cranial Irradiation

Curative cancer treatment regimens often require cranial irradiation, resulting in lifelong neurocognitive deficiency in cancer survivors. This deficiency is in part related to radiation-induced apoptosis and decreased neurogenesis in the subgranular zone of the hippocampus. We show that lithium treatment protects irradiated hippocampal neurons from apoptosis and improves cognitive performance of irradiated mice. The molecular mechanism of this effect is mediated through multiple pathways, including Akt/glycogen synthase kinase-3beta (GSK-3beta) and Bcl-2/Bax. Lithium treatment of the cultured mouse hippocampal neurons HT-22 induced activation of Akt (1.5-fold), inhibition of GSK-3beta (2.2-fold), and an increase in Bcl-2 protein expression (2-fold). These effects were sustained when cells were treated with lithium in combination with ionizing radiation. In addition, this combined treatment led to decreased expression (40%) of the apoptotic protein Bax. The additional genes regulated by lithium were identified by microarray, such as decorin and Birc1f. In summary, we propose lithium treatment as a novel therapy for prevention of deleterious neurocognitive consequences of cranial irradiation.

A small-scale serum-free liquid cell culture model of erythropoiesis to assess the effects of exogenous factors

Anaemia is an important global health problem. Therefore, it is crucial to understand its pathophysiology in various genetic or infectious diseases where dyserythropoiesis is a key pathological feature. To this effect, reproducible and reliable models of erythropoiesis in vitro are much needed as investigative tools. We have developed a serum-free liquid culture model of erythropoiesis using human umbilical cord blood CD34(+) cells cultured in the cytokine combination, interleukin-3 (IL-3), IL-6, stem cell factor (SCF) and erythropoietin (Epo), over 14 days. We found that these culture conditions favored erythroid differentiation over the expansion of the more primitive erythroid precursors. With an initiating culture density of 5x10(4) cells per ml, the nucleated cell fold expansion increased from 7.9+/-3.9 (range 4.5 to 11.1) after 4 days to 2990.2+/-1936.1 (range 626.6 to 6912.0) after 14 days in culture. Day-14 burst-forming unit-erythroid (BFU-E) frequencies peaked at day 4 (24.0+/-8.9%), with a marked decrease in BFU-E burst size as the cultures progressed. Time-course immunophenotypical profiles were characteristically erythroid with a decrease in CD34 expression (from 96.8+/-3.0% at day 0 to 0.8+/-0.8% at day 14), and a concomitant increase in the expression of erythroid-specific markers, CD36, glycophorin A (GpA) and CD71 (from 14.8+/-5.0%, 1.7+/-1.0% and 37.9+/-18.0% to 93.0+/-7.0%, 82.1+/-14.0% and 95.7+/-3.0%, respectively). Morphological studies revealed the presence of normoblasts with the complete absence of reticulocytes and mature erythrocytes after 14 days in culture. Once the culture conditions were optimized, we scaled down our culture model from 24-well plate (large-scale) to 96-well plate cultures (small-scale). We found that the small-scale cultures compared favorably with their large-scale counterpart in terms of erythroid progenitor cell proliferation and differentiation, particularly at low CD34(+) initiating cell doses. By using tumor necrosis factor-alpha (TNF-alpha), a known inhibitor of erythropoiesis, we validated our model system and showed a dose-dependent inhibition of erythroid differentiation with TNF-alpha in our cultures. Therefore, our results demonstrate a small-scale serum-free liquid culture model of erythropoiesis that is comparable with and complements our well-defined large-scale model. Our system would prove useful for screening the effects of exogenous factors on erythropoiesis in vitro.

The paradoxical pro- and anti-apoptotic actions of GSK3 in the intrinsic and extrinsic apoptosis signaling pathways

Few things can be considered to be more important to a cell than its threshold for apoptotic cell death, which can be modulated up or down, but rarely in both directions, by a single enzyme. Therefore, it came as quite a surprise to find that one enzyme, glycogen synthase kinase-3 (GSK3), has the perplexing capacity to either increase or decrease the apoptotic threshold. These apparently paradoxical effects now are known to be due to GSK3 oppositely regulating the two major apoptotic signaling pathways. GSK3 promotes cell death caused by the mitochondrial intrinsic apoptotic pathway, but inhibits the death receptor-mediated extrinsic apoptotic signaling pathway. Intrinsic apoptotic signaling, activated by cell damage, is promoted by GSK3 by facilitation of signals that cause disruption of mitochondria and by regulation of transcription factors that control the expression of anti- or pro-apoptotic proteins. The extrinsic apoptotic pathway entails extracellular ligands stimulating cell-surface death receptors that initiate apoptosis by activating caspase-8, and this early step in extrinsic apoptotic signaling is inhibited by GSK3. Thus, GSK3 modulates key steps in each of the two major pathways of apoptosis, but in opposite directions. Consequently, inhibitors of GSK3 provide protection from intrinsic apoptosis signaling but potentiate extrinsic apoptosis signaling. Studies of this eccentric ability of GSK3 to oppositely influence two types of apoptotic signaling have shed light on important regulatory mechanisms in apoptosis and provide the foundation for designing the rational use of GSK3 inhibitors for therapeutic interventions.