AG490 prevents cell death after exposure of rat astrocytes to hydrogen peroxide or proinflammatory cytokines: involvement of the Jak2/STAT pathway

Prolactin is an Endogenous Antioxidant Factor in Astrocytes That Limits Oxidative Stress-Induced Astrocytic Cell Death via the STAT3/NRF2 Signaling Pathway

Oxidative stress-induced death of neurons and astrocytes contributes to the pathogenesis of numerous neurodegenerative diseases. While significant progress has been made in identifying neuroprotective molecules against neuronal oxidative damage, little is known about their counterparts for astrocytes. Prolactin (PRL), a hormone known to stimulate astroglial proliferation, viability, and cytokine expression, exhibits antioxidant effects in neurons. However, its role in protecting astrocytes from oxidative stress remains unexplored. Here, we investigated the effect of PRL against hydrogen peroxide (H2O2)-induced oxidative insult in primary cortical astrocyte cultures. Incubation of astrocytes with PRL led to increased enzymatic activity of superoxide dismutase (SOD) and glutathione peroxidase (GPX), resulting in higher total antioxidant capacity. Concomitantly, PRL prevented H2O2-induced cell death, reactive oxygen species accumulation, and protein and lipid oxidation. The protective effect of PRL upon H2O2-induced cell death can be explained by the activation of both signal transducer and activator of transcription 3 (STAT3) and NFE2 like bZIP transcription factor 2 (NRF2) transduction cascades. We demonstrated that PRL induced nuclear translocation and transcriptional upregulation of Nrf2, concurrently with the transcriptional upregulation of the NRF2-dependent genes heme oxygenase 1, Sod1, Sod2, and Gpx1. Pharmacological blockade of STAT3 suppressed PRL-induced transcriptional upregulation of Nrf2, Sod1 and Gpx1 mRNA, and SOD and GPX activities. Furthermore, genetic ablation of the PRL receptor increased astroglial susceptibility to H2O2-induced cell death and superoxide accumulation, while diminishing their intrinsic antioxidant capacity. Overall, these findings unveil PRL as a potent antioxidant hormone that protects astrocytes from oxidative insult, which may contribute to brain neuroprotection.

Targeting the JAK2/STAT3 signaling pathway for chronic pain

Chronic pain is a notable health concern because of its prevalence, persistence, and associated mental stress. Drugs targeting chronic pain with potent abirritation, and minimal side effects remain unidentified. Substantial evidence indicates that the Janus Kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway plays a distinct and critical role in different stages of chronic pain. Aberrant activation of the JAK2/STAT3 signaling pathway is evident in multiple chronic pain models. Moreover, an increasing number of studies have demonstrated that the downregulation of JAK2/STAT3 can attenuate chronic pain in different animal models. In this review, we investigated the mechanism and role of the JAK2/STAT3 signaling pathway in modulating chronic pain. The aberrant activation of JAK2/STAT3 can trigger chronic pain by interacting with microglia and astrocytes, releasing proinflammatory cytokines, inhibiting anti-inflammatory cytokines, and regulating synaptic plasticity. We also retrospectively reviewed current reports on JAK2/STAT3 pharmacological inhibitors that demonstrated their significant therapeutic potential in different types of chronic pain. In summary, our results provide strong evidence that the JAK2/STAT3 signaling pathway is a promising therapeutic target for chronic pain.

Ablation of endothelial Atg7 inhibits ischemia-induced angiogenesis by upregulating Stat1 that suppresses Hif1a expression

Ischemia-induced angiogenesis is critical for blood flow restoration and tissue regeneration, but the underlying molecular mechanism is not fully understood. ATG7 (autophagy related 7) is essential for classical degradative macroautophagy/autophagy and cell cycle regulation. However, whether and how ATG7 influences endothelial cell (EC) function and regulates post-ischemic angiogenesis remain unknown. Here, we showed that in mice subjected to femoral artery ligation, EC-specific deletion of Atg7 significantly impaired angiogenesis, delayed the recovery of blood flow reperfusion, and displayed reduction in HIF1A (hypoxia inducible factor 1 subunit alpha) expression. In addition, in cultured human umbilical vein endothelial cells (HUVECs), overexpression of HIF1A prevented ATG7 deficiency-reduced tube formation. Mechanistically, we identified STAT1 (signal transducer and activator of transcription 1) as a transcription suppressor of HIF1A and demonstrated that ablation of Atg7 upregulated STAT1 in an autophagy independent pathway, increased STAT1 binding to HIF1A promoter, and suppressed HIF1A expression. Moreover, lack of ATG7 in the cytoplasm disrupted the association between ATG7 and the transcription factor ZNF148/ZFP148/ZBP-89 (zinc finger protein 148) that is required for STAT1 constitutive expression, increased the binding between ZNF148/ZFP148/ZBP-89 and KPNB1 (karyopherin subunit beta 1), which promoted ZNF148/ZFP148/ZBP-89 nuclear translocation, and increased STAT1 expression. Finally, inhibition of STAT1 by fludarabine prevented the inhibition of HIF1A expression, angiogenesis, and blood flow recovery in atg7 KO mice. Our work reveals that lack of ATG7 inhibits angiogenesis by suppression of HIF1A expression through upregulation of STAT1 independently of autophagy under ischemic conditions, and suggest new therapeutic strategies for cancer and cardiovascular diseases.Abbreviations: ATG5: autophagy related 5; ATG7: autophagy related 7; atg7 KO: endothelial cell-specific atg7 knockout; BECN1: beclin 1; ChIP: chromatin immunoprecipitation; CQ: chloroquine; ECs: endothelial cells; EP300: E1A binding protein p300; HEK293: human embryonic kidney 293 cells; HIF1A: hypoxia inducible factor 1 subunit alpha; HUVECs: human umbilical vein endothelial cells; IFNG/IFN-γ: Interferon gamma; IRF9: interferon regulatory factor 9; KPNB1: karyopherin subunit beta 1; MAP1LC3A: microtubule associated protein 1 light chain 3 alpha; MEFs: mouse embryonic fibroblasts; MLECs: mouse lung endothelial cells; NAC: N-acetyl-l-cysteine; NFKB1/NFκB: nuclear factor kappa B subunit 1; PECAM1/CD31: platelet and endothelial cell adhesion molecule 1; RELA/p65: RELA proto-oncogene, NF-kB subunit; ROS: reactive oxygen species; SP1: Sp1 transcription factor; SQSTM1/p62: sequestosome 1; STAT1: signal transducer and activator of transcription 1; ULK1: unc-51 like autophagy activating kinase 1; ulk1 KO: endothelial cell-specific ulk1 knockout; VSMCs: mouse aortic smooth muscle cells; WT: wild type; ZNF148/ZFP148/ZBP-89: zinc finger protein 148.

The interplay between HIF-1α and long noncoding GAS5 regulates the JAK1/STAT3 signalling pathway in hypoxia-induced injury in myocardial cells

Background

Long non-coding RNA (lncRNA) GAS5 is associated with hypoxia-induced diseases whereas hypoxia-inducible factor-1α (HIF-1α) plays an important role in hypoxic injury of cells. The current study explores the regulatory functions of GAS5/HIF-1α which co-play in anoxic injury among rat cardiomyocytes H9C2 cells.

Methods

Hypoxia in vitro model was established through anoxic incubation while normal culture of H9C2 cells was considered as control. The expression levels of GAS5 and HIF-1α were quantified through RT-qPCR. CCK-8 was applied to determine cell viability. Cell apoptosis rate was calculated using flow cytometry whereas inflammatory cytokines were detected using ELISA method. The impact of downregulating GAS5 or HIF-1α or both upon hypoxic cells was assessed on the basis of changes in cell viability, apoptosis, and inflammatory response. The activity of JAK1/STAT3 signaling was evaluated through RT-qPCR for mRNA expression. AG490 was introduced to inactivate JAK1/STAT3 pathway and to unveil the impact of JAK1/STAT3 signaling on GAS5/HIF-1α and cell viability, apoptosis and inflammation in hypoxic cells.

Results

The results infer that hypoxia suppressed cell viability, promoted inflammation and apoptosis among H9C2 cells. GAS5 or HIF-1α recorded higher expression in hypoxia-induced cells whereas the cell viability got restored with reduction in inflammation and apoptosis. The downregulation of HIF-1α enhanced the protective effect of knocking down GAS5 in hypoxia H9C2 cells. JAK1/STAT3 signaling pathway got activated in hypoxic cells and was regulated by GAS5 and HIF-1α. The inhibition of signaling pathway increased the cell viability but it decreased both inflammation and apoptosis.

Conclusions

GAS5 and HIF-1α could regulate hypoxic injury in H9C2 cells through JAK1/STAT3 signaling pathway. This scenario suggests that the inhibitors of GAS5 and HIF-1α may synergize with AG-490 to protect myocardial cells from hypoxic injury.

Eltrombopag inhibits Type I interferon-mediated antiviral signaling by decreasing cellular iron

Thrombocytopenia is common among patients with viral hepatitis, limiting the use of antiviral therapy. Eltrombopag (EP) is a thrombopoietin receptor (TPO-R) agonist that has been approved for treatment of immune thrombocytopenia patients with hepatitis virus infection. Interferon-α (IFN-α) plays a crucial role in the antiviral response, and is recommended as the first-line agent for chronic hepatitis B patients. Here, we investigated whether EP inhibits the production of IFN-stimulated genes (ISGs) induced by IFN-α through the TPO-R-independent pathway by mediating reactive oxygen species production by iron chelation. Our results assessed the inhibitory effect of EP on IFN-α signaling, which contributes to the downregulation of ISGs produced by monocytes and sheds light on the underlying mechanisms using iron chelation to treat patients with hepatitis-related immunological thrombocytopenia.

Acupuncture attenuates cognitive deficits through α7nAChR mediated anti-inflammatory pathway in chronic cerebral hypoperfusion rats

AIMS

Chronic cerebral hypoperfusion (CCH) elicits inflammatory response, which contributes to the pathology of cognitive impairment. Several studies demonstrate that the alpha-7 nicotinic acetylcholine receptor (α7nAChR) can be a key component to modulate the inflammatory responses. We have reported previously that acupuncture attenuated cognitive deficits induced by CCH. In present study, whether effect of acupuncture was related to α7nAChR mediated anti-inflammatory pathway in CCH rats was further explored.

MAIN METHODS

Acupuncture was performed in CCH rats induced by bilateral common carotid arteries occlusion. Neuronal injury, the activation of microglia, the release of inflammatory cytokines, the expression of α7nAChR, and the activation of JAK2/STAT3 signaling pathways were detected. Cognitive function and central inflammation were evaluated after the intraperitoneal injection of an α7nAChR agonist PNU282987, or intracerebroventricular injection of an α7nAChR antagonist α-bungarotoxin (α-BGT).

KEY FINDINGS

We found that there were neuronal damage and inflammation, accompanied with the decreased expressions of α7nAChR in the hippocampus under CCH condition. Acupuncture inhibited neuronal damage, activation of microglia, and inflammatory cytokines. The expressions of α7nAChR, together with its downstream JAK2/STAT3 pathways were up regulated by acupuncture. PNU282987 mimicked the anti-inflammatory and neuroprotective effects as well as the cognitive improvements of acupuncture. Meanwhile, the benefit effects of acupuncture above were blocked by α-BGT.

SIGNIFICANCE

It was demonstrated that acupuncture promoted cognitive function and afforded neuroprotective effects against inflammation via activation of α7nAChR and its downstream JAK2-STAT3 pathway in CCH rats. It provides a new insight for acupuncture as an anti-inflammatory intervention for cognitive impairment.

Redox Regulation of STAT1 and STAT3 Signaling

STAT1 and STAT3 are nuclear transcription factors that regulate genes involved in cell cycle, cell survival and immune response. The cross-talk between these signaling pathways determines how cells integrate the environmental signals received ultimately translating them in transcriptional regulation of specific sets of genes. Despite being activated downstream of common cytokine and growth factors, STAT1 and STAT3 play essentially antagonistic roles and the disruption of their balance directs cells from survival to apoptotic cell death or from inflammatory to anti-inflammatory responses. Different mechanisms are proposed to explain this yin-yang relationship. Considering the redox aspect of STATs proteins, this review attempts to summarize the current knowledge of redox regulation of STAT1 and STAT3 signaling focusing the attention on the post-translational modifications that affect their activity.

Hydroxysafflor Yellow A mitigated myocardial ischemia/reperfusion injury by inhibiting the activation of the JAK2/STAT1 pathway

Hydroxysafflor Yellow A (HSYA) may reduce ischemia/reperfusion (I/R) injury. However, the underlying molecular mechanisms remain unclear. The present study explored the effect and the mechanisms of HSYA on myocardial injury in vivo and in vitro. Myocardial infarct size was assessed by Evans blue/2,3,5‑triphenyltetrazoliumchloride staining. Levels of cardiac troponin I (cTnI), interleukin‑6 (IL‑6), lactate dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA) were measured using commercial kits. Alteration of mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) generation was determined by fluorescent signals. Apoptosis was detected by terminal deoxynucleotidyl‑transferase‑mediated dUTP nick‑end labeling staining, flow cytometry assay and caspase‑3 activity. Expression levels of the apoptosis‑associated proteins were detected by reverse transcription quantitative polymerase chain reaction and western blot analysis. In vivo, animals treated with HSYA presented less severe myocardial injury and decreased janus kinase 2 (JAK2)/signal transducer and activator of transcription 1 (STAT1) activity, improved antioxidant capacity and decreased apoptosis. In vitro, compared with the hypoxia (H)/reoxygenation (R) + HSYA group, AG490 and S1491 treatment decreased the releases of cTnI, IL‑6 and LDH and enhanced the resistance to oxidative stress by maintaining MMP and decreasing ROS generation. In addition, AG490 and S1491 were also identified to alleviate the H/R‑induced apoptosis by inhibiting caspase 3 activity and modulating the expression levels of cleaved caspase‑3, tumor necrosis factor receptor superfamily member 6 (Fas), Fas ligand, B‑cell lymphoma 2 (Bcl‑2) and Bcl‑2‑associated X protein. These data suggested that inactivation of the JAK2/STAT1 pathway strengthened the HSYA‑induced protective effect in H/R‑induced myocardial injury. In conclusion, the treatment of HSYA was effective in decreasing IR‑induced myocardial injury, and this may be largely dependent on the JAK2/STAT1 pathway. Therefore, the present study provided a potential strategy to prevent myocardial I/R injury.

Inhibition of cerebral ischemia/reperfusion injury-induced apoptosis: nicotiflorin and JAK2/STAT3 pathway

Nicotiflorin is a flavonoid extracted from Carthamus tinctorius. Previous studies have shown its cerebral protective effect, but the mechanism is undefined. In this study, we aimed to determine whether nicotiflorin protects against cerebral ischemia/reperfusion injury-induced apoptosis through the JAK2/STAT3 pathway. The cerebral ischemia/reperfusion injury model was established by middle cerebral artery occlusion/reperfusion. Nicotiflorin (10 mg/kg) was administered by tail vein injection. Cell apoptosis in the ischemic cerebral cortex was examined by hematoxylin-eosin staining and terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Bcl-2 and Bax expression levels in ischemic cerebral cortex were examined by immunohistochemial staining. Additionally, p-JAK2, p-STAT3, Bcl-2, Bax, and caspase-3 levels in ischemic cerebral cortex were examined by western blot assay. Nicotiflorin altered the shape and structure of injured neurons, decreased the number of apoptotic cells, down-regulates expression of p-JAK2, p-STAT3, caspase-3, and Bax, decreased Bax immunoredactivity, and increased Bcl-2 protein expression and immunoreactivity. These results suggest that nicotiflorin protects against cerebral ischemia/reperfusion injury-induced apoptosis via the JAK2/STAT3 pathway.

Role of JAK-STAT pathway in reducing cardiomyocytes hypoxia/reoxygenation injury induced by S1P postconditioning

This experiment was designed to explore the protection of sphingosine1-phosphate (S1P) postconditioning on rat myocardial cells injured by hypoxia/reoxygenation acting via the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signal pathway. The data showed that S1P could significantly increase cell viability, lower the rate of apoptosis, decrease the content of lactate dehydrogenase (LDH) and caspase3 activity in the culture medium, increase the activity of total superoxide dismutase (T-SOD) and manganese superoxide dismutase (Mn-SOD), reduce the loss of mitochondrial membrane potential and the fluorescence intensity of intracellular calcium, as well as increase the phosphorylation of JAK2 and STAT3 in comparison with the H/R group. When the JAK inhibitor AG490 or the STAT inhibitor stattic were added, the effects of S1P were inhibited. Our date shows that S1P protects H9c2 cells from hypoxia/reoxygenation injury and that the protection by S1P was inhibited by AG490 and stattic. Therefore S1P protects H9c2 cells against hypoxia/reoxygenation injury via the JAK-STAT pathway.

Zinc Chloride Transiently Maintains Mouse Embryonic Stem Cell Pluripotency by Activating Stat3 Signaling

An improved understanding of the pluripotency maintenance of embryonic stem (ES) cells is important for investigations of early embryo development and for cell replacement therapy, but the mechanism behind pluripotency is still incompletely understood. Recent findings show that zinc, an essential trace element in humans, is critically involved in regulating various signaling pathways and genes expression. However, its role in ES cell fate determination remains to be further explored. Here we showed that 2μM zinc chloride (ZnCl₂) transiently maintained mouse ES cell pluripotency in vitro. The cultured mouse ES cells remained undifferentiated under 2μM ZnCl₂ treatment in leukemia inhibitory factor (LIF) withdrawal, retinoic acid (RA) or embryoid bodies (EBs) differentiation assays. In addition, ZnCl₂ increased pluripotency genes expression and inhibited differentiation genes expression. Further mechanistic studies revealed that ZnCl₂ transiently activated signal transducers and activators of transcription 3 (Stat3) signaling through promoting Stat3 phosphorylation. Inhibition of Stat3 signaling abrogated the effects of ZnCl₂ on mouse ES cell pluripotency. Taken together, this study demonstrated a critical role of zinc in the pluripotency maintenance of mouse ES cells, as well as an important regulator of Stat3 signaling.

Pwp1 is required for the differentiation potential of mouse embryonic stem cells through regulating Stat3 signaling

Leukemia inhibitory factor/Stat3 signaling is critical for maintaining the self-renewal and differentiation potential of mouse embryonic stem cells (mESCs). However, the upstream effectors of this pathway have not been clearly defined. Here, we show that periodic tryptophan protein 1 (Pwp1), a WD-40 repeat-containing protein associated with histone H4 modification, is required for the exit of mESCs from the pluripotent state into all lineages. Knockdown (KD) of Pwp1 does not affect mESC proliferation, self-renewal, or apoptosis. However, KD of Pwp1 impairs the differentiation potential of mESCs both in vitro and in vivo. PWP1 chromatin immunoprecipitation-seq results revealed that the PWP1-occupied regions were marked with significant levels of H4K20me3. Moreover, Pwp1 binds to sites in the upstream region of Stat3. KD of Pwp1 decreases the level of H4K20me3 in the upstream region of Stat3 gene and upregulates the expression of Stat3. Furthermore, Pwp1 KD mESCs recover their differentiation potential through suppressing the expression of Stat3 or inhibiting the tyrosine phosphorylation of STAT3. Together, our results suggest that Pwp1 plays important roles in the differentiation potential of mESCs.

Calcium Contributes to the Cytotoxic Interaction Between Diclofenac and Cytokines

Diclofenac (DCLF) is a widely used non-steroidal anti-inflammatory drug that is associated with idiosyncratic, drug-induced liver injury (IDILI) in humans. The mechanisms of DCLF-induced liver injury are unknown; however, patients with certain inflammatory diseases have an increased risk of developing IDILI, which raises the possibility that immune mediators play a role in the pathogenesis. DCLF synergizes with the cytokines tumor necrosis factor-alpha (TNF) and interferon-gamma (IFN) to cause hepatocellular apoptosis in vitro by a mechanism that involves activation of the endoplasmic reticulum (ER) stress response pathway and of the mitogen-activated protein kinases, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK). DCLF also causes an increase in intracellular calcium (Ca(++)) in hepatocytes, but the role of this in the cytotoxic synergy between DCLF and cytokines is unknown. We tested the hypothesis that Ca(++) contributes to DCLF/cytokine-induced cytotoxic synergy. Treatment of HepG2 cells with DCLF led to an increase in intracellular Ca(++) at 6 and 12 h, and this response was augmented in the presence of TNF and IFN at 12 h. The intracellular Ca(++) chelator BAPTA/AM reduced cytotoxicity and caspase-3 activation caused by DCLF/cytokine cotreatment. BAPTA/AM also significantly reduced DCLF-induced activation of the ER stress sensor, protein kinase RNA-like ER kinase (PERK), as well as activation of JNK and ERK. Treatment of cells with an inositol trisphosphate receptor antagonist almost completely eliminated DCLF/cytokine-induced cytotoxicity and decreased DCLF-induced activation of PERK, JNK, and ERK. These findings indicate that Ca(++) contributes to DCLF/cytokine-induced cytotoxic synergy by promoting activation of the ER stress-response pathway and JNK and ERK.

Cyclovirobuxinum D suppresses lipopolysaccharide-induced inflammatory responses in murine macrophages in vitro by blocking JAK-STAT signaling pathway

AIM

Cyclovirobuxinum D (CVB-D), an alkaloid isolated from the Chinese medicinal plant Buxus microphylla, has been found to be effective to treat cardiac insufficiency, arrhythmias and coronary heart disease. In the present study, we investigated the effects of CVB-D on the inflammatory responses in lipopolysaccharide (LPS)-stimulated murine macrophages in vitro and the underlying mechanisms.

METHODS

Murine macrophage cell line RAW264.7 cells were incubated in the presence of LPS (0.1 μg/mL) for 24 h. The cell viability was measured using MTT assay. The release of NO and cytokines were detected using the Griess test and ELISA, respectively. The mRNA and protein levels were determined using RT-PCR and Western blot, respectively. Reporter gene assays were used to analyze the transcriptional activity of NF-κB.

RESULTS

Treatment of RAW264.7 cells with CVB-D (25-300 μmol/L) did not affect the cell viability. Pretreatment with CVB-D (50, 100 and 200 μmol/L) concentration-dependently decreased NO release and iNOS expression in LPS-treated RAW264.7 cells (its IC50 value in inhibition of NO production was 144 μmol/L). CVB-D also concentration-dependently inhibited the secretion and mRNA expression of IL-1β and IL-6 in LPS-treated RAW264.7 cells. Furthermore, CVB-D remarkably inhibited the phosphorylation of STAT1 and STAT3, as well as JAK2 in LPS-treated RAW264.7 cells, but did not affect the activation of NF-κB and MAPKs pathways. Pretreatment with the JAK2 specific inhibitor AG490 (30 μmol/L) produced similar effects on NO release and iNOS expression in LPS-treated RAW264.7 cells.

CONCLUSION

CVB-D exerts anti-inflammatory effects in LPS-stimulated murine macrophages in vitro at least in part by blocking the JAK-STAT signaling pathway. The anti-inflammatory actions of CVB-D may contribute to its cardioprotection.

Aspirin-triggered Lipoxin A4 attenuates mechanical allodynia in association with inhibiting spinal JAK2/STAT3 signaling in neuropathic pain in rats

Aspirin-triggered Lipoxin A4 (ATL), as a Lipoxin A4 (LXA4) epimer, is endogenously produced by aspirin-acetylated cycloxygenase-2 (COX-2) and plays a vital role in endogenous anti-inflammation via the LXA4 receptor (ALX). Recent investigations have indicated that spinal neuroinflammation and the activation of the Janus Kinase 2 (JAK2)/Signal Transducers and Transcription Activators 3 (STAT3) signaling pathway are involved in neuropathic pain states. However, the effect of ATL on neuroinflammation and JAK2/STAT3 signaling in chronic constriction injury (CCI)-induced neuropathic pain in rats has not been well-studied. The present study demonstrated the anti-inflammatory and analgesic effect of ATL on neuropathic pain and assessed the role of spinal JAK2/STAT3 signaling on the effect of ATL. Intrathecal administration of ATL significantly attenuated mechanical allodynia via spinal ALX and inhibited the upregulation of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) on day 7 of CCI surgery. In addition, ATL markedly suppressed the upregulation of p-STAT3 induced by the neuropathic pain. Blockade of JAK2-STAT3 signaling with intrathecal administration of the JAK2 inhibitor AG490 or the STAT3 inhibitor S3I-201 clearly reduced mechanical allodynia and the upregulation of pro-inflammatory cytokines in CCI rats. Interestingly, inhibition of JAK2/STAT3 signaling via ATL or the specific signaling inhibitor (AG49, S3I-201) further promoted the increased expression of suppressor of cytokine signaling 3 (SOCS3) mRNA in the spinal cord induced by CCI surgery. Taken together, our results suggested that the analgesic effect of ATL was mediated by inhibiting spinal JAK2/STAT3 signaling and hence the spinal neuroinflammation in CCI rats.

SK-N-MC cell death occurs by distinct molecular mechanisms in response to hydrogen peroxide and superoxide anions: involvements of JAK2-STAT3, JNK, and p38 MAP kinases pathways

Oxidative stress plays a vital role in the pathogenesis of neurodegenerative diseases. Nerve cells are incessantly exposed to environmental stresses leading to overproduction of some harmful species like reactive oxygen species (ROS). ROS including hydrogen peroxide and superoxide anion are potent inducers of various signaling pathways encompassing MAPKs and JAK-STAT pathways. In the current study, we scrutinized the effects of hydrogen peroxide and/or menadione (superoxide anion generator) on JNK/p38-MAPKs and JAK2-STAT3 pathways to elucidate the mechanism(s) by which each oxidant modulated the above-mentioned pathways leading to SK-N-MC cell death. Our results delineated that hydrogen peroxide and superoxide anion radical induced distinct responses as we showed that STAT3 and p38 were activated in response to hydrogen peroxide, but not superoxide anion radicals indicating the specificity in ROS-induced signaling pathways activations and behaviors. We also observed that menadione induced JNK-dependent p53 expression and apoptotic death in SK-N-MC cells while H2O2-induced JNK activation was p53 independent. Thus, we declare that ROS type has a key role in selective instigation of JNK/p38-MAPKs and JAK2-STAT3 pathways in SK-N-MC cells. Identifying these differential behaviors and mechanisms of hydrogen peroxide and superoxide anion functions illuminates the possible therapeutic targets in the prevention or treatment of ROS-induced neurodegenerative diseases such as Alzheimer's disease.

NFκB and STAT3 synergistically activate the expression of FAT10, a gene counteracting the tumor suppressor p53

Chronic inflammation is one of the main causes of cancer, yet the molecular mechanism underlying this effect is not fully understood. In this study, we identified FAT10 as a potential target gene of STAT3, the expression of which is synergistically induced by NFκB co-stimulation. STAT3 binding stabilizes NFκB on the FAT10 promoter and leads to maximum induction of FAT10 gene expression. Increased FAT10 represses the transcriptional activity of the tumor suppressor p53, a protein that accelerates the protein degradation of FAT10. This FAT10-p53 double-negative regulation is critical in the control of tumorigenesis, as overexpressed FAT10 facilitates the tumor progression in the solid tumor model. In conclusion, transcriptional synergy between STAT3 and NFκB functions to put weight on FAT10 in the mutually inhibitory FAT10-p53 regulatory loop and thus favors tumorigenesis under inflammatory conditions.

New role of JAK2/STAT3 signaling in endothelial cell oxidative stress injury and protective effect of melatonin

Previous studies have shown that the JAK2/STAT3 signaling pathway plays a regulatory role in cellular oxidative stress injury (OSI). In this study, we explored the role of the JAK2/STAT3 signaling pathway in hydrogen peroxide (H₂O₂)-induced OSI and the protective effect of melatonin against (H₂O₂)-induced injury in human umbilical vein endothelial cells (HUVECs). AG490 (a specific inhibitor of the JAK2/STAT3 signaling pathway) and JAK2 siRNA were used to manipulate JAK2/STAT3 activity, and the results showed that AG490 and JAK2 siRNA inhibited OSI and the levels of p-JAK2 and p-STAT3. HUVECs were then subjected to H₂O₂ in the absence or presence of melatonin, the main secretory product of the pineal gland. Melatonin conferred a protective effect against H₂O₂, which was evidenced by improvements in cell viability, adhesive ability and migratory ability, decreases in the apoptotic index and reactive oxygen species (ROS) production and several biochemical parameters in HUVECs. Immunofluorescence and Western blotting showed that H₂O₂ treatment increased the levels of p-JAK2, p-STAT3, Cytochrome c, Bax and Caspase3 and decreased the levels of Bcl2, whereas melatonin treatment partially reversed these effects. We, for the first time, demonstrate that the inhibition of the JAK2/STAT3 signaling pathway results in a protective effect against endothelial OSI. The protective effects of melatonin against OSI, at least partially, depend upon JAK2/STAT3 inhibition.

AG490 improves the survival of human myoblasts in vitro and in vivo

Cell therapies consist in transplanting healthy cells into a disabled tissue with the goal to repopulate it and restore its function at least partially. In muscular diseases, most of the time, myoblasts are chosen for their expansion capacity in culture. Nevertheless, cell transplantation has limitations, among them, death of the transplanted cells, during the days following the graft. One possibility to counteract this problem is to enhance the proliferation of the transplanted myoblasts before their fusion with the existing muscle fibers. AG490 is a specific inhibitor of janus tyrosine kinase 2 (JAK2). The hypothesis is to block myoblast differentiation with AG490, thus permitting their proliferation. The inhibition of myoblast fusion by AG490 was confirmed in this study by gene expression and with a myosin heavy chain staining (MyHC). Moreover, cell survival was estimated by flow cytometry. AG490 was found to protect myoblasts in vitro from apoptosis induced by H(2)O(2) or by preventing attachment of cells to their substrate. Finally, in an in vivo model of muscle regeneration, when AG490 was coinjected with the myoblasts their survival was increased by 45% at 5 days after their transplantation.

Interleukin 6 protects H(2)O(2)-induced cardiomyocytes injury through upregulation of prohibitin via STAT3 phosphorylation

OBJECTIVE

Hydrogen peroxide (H(2)O(2)) is a potent reactive oxygen species that causes cardiomyocytes injury. As an important cytokine, interleukin 6 (IL-6) has cardioprotective effects as it plays an essential role in the late phase of preconditioning. Our work is to investigate if IL-6 preconditioning has protective effects on neonatal rat ventricular cardiomyocytes in response to H(2)O(2) and its underlying mechanism.

METHODS

Gel-based comparative proteomic approach along with small interfering RNA (siRNA) and Western blot analysis was used to analyse mechanisms of IL-6 preconditioning on H(2)O(2)-induced neonatal rat ventricular cardiomyocytes injury.

RESULTS

IL-6 preconditioning protected cardiomyocytes against H(2)O(2)-induced cell death. Proteomic analysis showed that IL-6 pretreatment further increased the expression of prohibitin and improved the viability of cardiomyocytes exposed to H(2)O(2). Knocking down of prohibitin with siRNA abrogated this protection by increasing apoptosis rate. Tyrosine kinase inhibitor AG490 decreased signal transducers and activators of transcription 3 (STAT3) phosphorylation and down-regulated prohibitin expression in cardiomyocytes pretreated with IL-6 and exposed to H(2)O(2), which further dampened the protective effects of IL-6 preconditioning.

CONCLUSION

Our results provide direct evidence that prohibitin is a protective factor of IL-6 preconditioning in H(2)O(2)-induced neonatal rat ventricular cardiomyocytes death. The upregulation of prohibitin by IL-6 is, at least, partially regulated through STAT3 phosphorylation.

The potential role of JAK2/STAT3 pathway on the anti-apoptotic effect of recombinant human erythropoietin (rhEPO) after experimental traumatic brain injury of rats

Previous studies indicate that administration of recombinant human erythropoietin (rhEPO) protects cortical neurons following traumatic brain injury (TBI). The mechanisms of rhEPO's neuroprotection are complex and interacting, including anti-apoptosis. Here we aim to demonstrate the role of janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway on the anti-apoptotic effect of rhEPO in Feeney free falling TBI model. Activation of JAK2/STAT3 in pericontusional cortex was analyzed among rats in Sham, TBI, TBI+rhEPO, TBI+rhEPO+AG490 groups (rhEPO: 5000 U/kg day; JAK2 inhibitor AG490: 5 mg/kg day, intraperitoneal) through Western blotting, electrophoretic mobility shift assay. Bcl-2 and Bcl-xl expression (Q-PCR, Western blotting) and cell apoptosis (TUNEL) in pericontusional cortex were also detected in each group. As a result, we found that TBI could activate JAK2 and STAT3, and increase cell apoptosis in pericontusional cortex. RhEPO enhanced the expression of p-JAK2 and p-STAT3, up-regulated the mRNA and protein levels of Bcl-2 and Bcl-xl, followed by increased cell survival. Moreover, AG490 attenuated rhEPO's neuroprotection by down-regulating rhEPO-induced activation of JAK2/STAT3, and inhibiting Bcl-2 and Bcl-xl. These results suggest the essential role of JAK2/STAT3 pathway on the anti-apoptotic benefit of post-TBI rhEPO treatment.

The role of Janus kinase 2 (JAK2) activation in pneumococcal EstA protein-induced inflammatory response in RAW 264.7 macrophages

In a previous study, we demonstrated pneumococcal EstA-induced inflammatory response through NF-κB and MAPK-dependent pathways. Herein, we tested the hypothesis that the Janus kinase 2 (JAK2) activation and associated signaling cascades may also be involved in EstA-induced inflammatory process in RAW 264.7 macrophages. Our immunoblot analysis indicated EstA-induced activation of JAK2, with the phosphorylated protein detected from 1 to 24 h post-stimulation. As type I interferon (IFN) signaling requires the JAK/STAT pathway, we investigated EstA-induced expression of INF-α4 and INF-β by semi-quantitative and quantitative RT PCR. Our results indicated both concentration- and time-dependent increases in both IFN-α4 and IFN-β mRNA expression after EstA challenge, with the highest fold-increases observed at 4 h and 6 h post-stimulation for IFN-α4 and IFN-β mRNA, respectively. Furthermore, we applied a pharmacological approach to demonstrate the effect of JAK2 inhibition on EstA-induced nitric oxide (NO) and pro-inflammatory cytokine production. The JAK2 inhibitor AG-490 reduced significantly (P < 0.05) EstA-induced NO production and the expression of iNOS mRNA in a concentration-dependent manner. Similarly, EstA-induced IL-1β and IL-6 production and their respective mRNA expression were markedly suppressed by AG-490. However, AG-490 had no inhibitory effect on both mRNA and protein levels of TNF-α. Taken together, we demonstrate that JAK2 activation and IFN I signaling are integral parts of EstA-induced inflammatory process. Further studies will elucidate the interaction of the different signaling pathways, the specific downstream targets of JAK2, the kinetics of cytokine release, and if EstA could induce the pro-inflammatory mediators to the same extent in alveolar macrophages.

Prosurvival role of JAK/STAT and Akt signaling pathways in MPP+-induced apoptosis in neurons

In the present study the role of JAK/STAT and Akt in apoptosis was evaluated in cerebellar granule cells after treatment with the mitochondrial toxin MPP(+). Firstly, we evaluated the role of the prosurvival Akt pathway in MPP(+)-induced apoptosis and found that MPP(+) rapidly reduced the phosphorylation of Akt at Ser473. Since PTEN is an upstream regulator of Akt, its inhibition with bpV(pic) (1-30 μM) should activate Akt, however, it did not attenuate CGC cell death mediated by MPP(+) but protected CGC from apoptosis mediated by S/K deprivation. We also demonstrated that after the treatment with the complex I inhibitor, the expression levels of STAT1 increased and the levels of STAT3 decreased at the time points tested (0.5-8h). Meanwhile, pharmacological inhibition of the JAK/STAT pathway with AG490 (10-40 μM) was neuroprotective, probably due to its antioxidant properties, the Jak2-inhibitor-II potentiated MPP(+) neurotoxicity. Collectively, our data indicate that the treatment of CGC with the neurotoxin MPP(+) decreased two prosurvival pathways: STAT3 and Akt. Meanwhile Akt activation, using a PTEN inhibitor, did not play a prominent role in neuroprotection; loss of STAT3 could be a signal pathway involved in neuroprotection against the Parkinsonian neurotoxin MPP(+).

Effects of IL-6 secreted from astrocytes on the survival of dopaminergic neurons in lipopolysaccharide-induced inflammation

The role of astrocytes in microglia-induced neuronal death remains controversial. In this study, astrocytes and astrocyte-derived conditioned media (ACM) supported the survival of dopaminergic neurons, and the former was more effective than the latter. In the presence of astrocytes, low concentrations of LPS enhanced the survival of dopaminergic neurons, while high concentrations attenuated survival. LPS dramatically induced astrocytes to secrete IL-6 in a dose-dependent manner with no effect on secretion of GDNF. Neuron-astrocyte cultures had highest secretion of GDNF, followed by ACM-treated neuron-enriched cultures. After neuron-astrocyte cultures treated with IL-6-neutralizing antibody, both effects of the enhanced and attenuated survival of dopaminergic neurons were abolished. Our results indicate that astrocytes play a protective role in the LPS-induced damage of dopaminergic neurons in certain circumstances, and the interaction between astrocytes and dopaminergic neurons may enhance the protective effect of astrocytes. Suitable activation of astrocytes increases the protective effect while excessive activation attenuates it, and IL-6 might mediate this dual action. The underlying mechanisms related to the secretion of GDNF and proinflammatory factors warrant further investigation.

Hydrogen peroxide induces the death of astrocytes through the down-regulation of the constitutive nuclear factor-kappaB activity

Nuclear factor-kappaB (NF-kappaB) has a dual role in the promotion or attenuation of cell death. Here, we demonstrated the role of NF-kappaB in the H(2)O(2)-induced death of astrocytes. H(2)O(2) evoked the release of lactate dehydrogenase (LDH), a marker of cell death, and concomitantly decreased the DNA binding and transcriptional activity of NF-kappaB in cultured astrocytes. H(2)O(2)-induced astrocyte death was markedly increased by the co-treatment with pyrrolidinedithiocarbamate, an NF-kappaB inhibitor. Moreover, the elevation of constitutive NF-kappaB activity by overexpressing p65 NF-kappaB subunit attenuated H(2)O(2) toxicity, whereas NF-kappaB inhibition by overexpressing IkappaB potentiated the toxicity. NF-kappaB activity and H(2)O(2) cytotoxicity was further found to be dependent on cell density. Compared with astrocytes in low cell density, those in high cell density exhibited a higher constitutive NF-kappaB activity and a stronger resistance to H(2)O(2) cytotoxicity. These results indicate that the constitutive activity of NF-kappaB in astrocytes is required for their survival under oxidative stress such as H(2)O(2).

Astrocytes are very sensitive to develop innate immune responses to lipid-carried short interfering RNA

Short interfering RNA (siRNA) inhibits the synthesis of specific proteins through RNA interference (RNAi). However, siRNA can induce innate immune responses that are mediated by toll-like receptors (TLRs) in cells of the immune system. Here, we sought to evaluate whether siRNA can induce such responses in glial cells. We examined the effects of various siRNA sequences prepared with lipids (oligofectamine). Lipid-siRNA induced variable degrees of silencing-independent nonspecific effects, e.g. increased Stat1 and Cox-2 expression and release of IL-6 and IP-10 in primary astroglia. This was prevented through chemical modification of siRNA by nucleoside 2'-O-methylation, without impairing specific gene silencing. Lipid-siRNA also induced nonspecific responses in purified astroglia, but not in microglia, or 3T3 cells. The highest TLR7 and TLR3 mRNA expression was found in microglia and purified astroglia, respectively. Accordingly, the TLR3 agonist poly(I:C) (PIC) induced higher release of IFN-beta in primary and purified astroglia than in microglia. As siRNA, PIC induced IP-10, Stat1, VCAM-1, and Cox-2 and increased TLR3 mRNA expression. The effects of lipid-siRNA in purified astrocytes were attenuated after silencing TLR3 or TLR7 expression, and by the PKR inhibitor 2-aminopurine. Furthermore, lipid-siRNA induced the expression of RIG-I. In contrast, siRNA devoid of lipids did not enter the astrocytes, did not silence gene expression, and did not induce Stat1 or Cox-2. The results show that, in astroglia, lipid-siRNA induces innate immune responses that are mediated, at least in part, by intracellular mechanism dependent on TLR7, TLR3, and helicases.

Pien Tze Huang, a composite Chinese traditional herbal extract, affects survival of neuroblastoma cells

Pien Tze Huang is a popular Chinese medicine for liver diseases. In the investigations of possible effects of Pien Tze Huang on the central nervous system, we first studied the in vitro anti-cancer activity of Pien Tze Huang on neuroblastoma cells (SH-SY5Y) as compared with normal fibroblasts (NIH-3T3). Results showed that Pien Tze Huang significantly decreased (p < .05) cell survival of SH-SY5Y as compared to NIH-3T3. Furthermore, the decreases in cell survival of SH-SY5Y were significantly and linearly dose-dependent (p < .05) from 400 to 1,000 microg/ml. This supports further in vivo and animal studies for anti-cancer effect, neuroprotection, and their mechanisms.

HIV-1 transactivator protein induction of suppressor of cytokine signaling-2 contributes to dysregulation of IFN{gamma} signaling

HIV infection remains a worldwide threat. HIV-1 transactivator protein Tat is one of the retroviral proteins identified as a key immunomodulator in AIDS pathogenesis. Although the primary function of Tat is to regulate HIV-1 replication in the infected cell, it also dysregulates cytokine production resulting in perturbation of the host immune response and enhancement of the retrovirus survival. Because interferon-gamma (IFNgamma) is a pleiotropic cytokine with potent antiviral and immunoregulatory effects, we investigated whether Tat interferes with the IFNgamma signal transduction in primary monocytes. We demonstrated that Tat impaired the IFNgamma-receptor signaling pathway at the level of STAT1 activation, possibly via Tat-dependent induction of suppressor of cytokine signaling-2 (SOCS-2) activity. We delineated the inhibitory role of SOCS-2 in IFNgamma signaling pathway by overexpression of exogenous SOCS-2 in HEK293 cell. The results showed that SOCS-2 suppressed the IFNgamma-activated STAT1 phosphorylation and consequent IFNgamma-regulated transcription of specific genes. To confirm the role of SOCS2 in the Tat-induced process, we demonstrated that SOCS-2 siRNA in human blood monocytes abrogated the Tat-dependent inhibition of IFNgamma signaling. Our data suggested a possible mechanism implicating the role of SOCS-2 in mediating HIV-1-induced immune evasion and dysregulation of IFNgamma signaling in primary human monocytes.

Preconditioning mediated by sublethal oxygen-glucose deprivation-induced cyclooxygenase-2 expression via the signal transducers and activators of transcription 3 phosphorylation

The signal transducers and activators of transcription (STATs) were found to be essential for cardioprotection. However, their role in preconditioning (PC) neuroprotection remains undefined. Previously, our studies showed that PC mediated a signaling cascade that involves activation of epsilon protein kinase C (varepsilonPKC), extracellular signal-regulated kinase (ERK1/2), and cyclooxygenase-2 (COX-2) pathways. However, the intermediate pathway by which ERK1/2 activates COX-2 was not defined. In this study, we investigated whether the PC-induced signaling pathway requires phosphorylation of STAT isoforms for COX-2 expression. To mimic PC or lethal ischemia, mixed cortical neuron/astrocyte cell cultures were subjected to 1 and/or 4 h of oxygen-glucose deprivation (OGD), respectively. The results indicated serine phosphorylation of STAT3 after PC or varepsilonPKC activation. Inhibition of either varepsilonPKC or ERK1/2 activation abolished PC-induced serine phosphorylation of STAT3. Additionally, inhibition of STAT3 prevented PC-induced COX-2 expression and neuroprotection against OGD. Therefore, our findings suggest that PC signaling cascade involves STAT3 activation after varepsilonPKC and ERK1/2 activation. Finally, we show that STAT3 activation mediates COX-2 expression and ischemic tolerance.

Interleukin-6 induces proliferation in adult spinal cord-derived neural progenitors via the JAK2/STAT3 pathway with EGF-induced MAPK phosphorylation

INTRODUCTION

In a previous study, we observed cell proliferation 3 days after spinal cord injury, and levels of interleukin-6 (IL-6) and epidermal growth factor (EGF) had significantly increased in the region of the injury.

OBJECTIVES

The purpose of the new study described here was to evaluate the roles of IL-6 and EGF after traumatic damage to the spinal cord having isolated neural progenitor cells (NPC) from adult mice.

METHODS AND RESULTS

Evidence provided by the trypan blue dye exclusion assay, 5-bromodeoxyuridine immunoreactivity and Western blot analysis indicated that IL-6 and EGF induced proliferation of these spinal cord-derived NPCs via phosphorylation of Janus-activated kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinases (MAPK), respectively. Combined treatment with IL-6 and EGF accelerated proliferation of cells synergistically and phosphorylation of STAT3 and extracellular signal-regulated kinase 1/2 (Erk1/2). Furthermore, AG490 and AG1478, JAK2 inhibitor and EGFR inhibitor, respectively, prevented the IL-6- and EGF-induced proliferation of the cells. Interestingly, IL-6-activated MAPKs but EGF did not influence JAK2/STAT3 activation; AG490 specifically inhibited IL-6-induced Erk1/2 phosphorylation without affecting IL-6-induced phosphorylation of Raf and MEK1/2. These results indicate that IL-6 is directly involved in Erk1/2 activation via JAK2 and that Erk1/2 provides a signal bridge between the IL-6-induced JAK2/STAT3 pathway and EGF-induced MAPK pathway.

CONCLUSIONS

Our study is the first demonstration of IL-6- and EGF-stimulated proliferation of spinal cord progenitor cells via JAK2/STAT3 and MAPK signalling pathways. These pathways play key roles in repopulation and regeneration of spinal cord tissue after injury. It may represent novel therapeutic targets for pharmacological intervention in central nervous system disease, including spinal cord injury.

Glucose promotes caspase-dependent delayed cell death after a transient episode of oxygen and glucose deprivation in SH-SY5Y cells

Brain ischemia causes neuronal cell death by several mechanisms involving necrotic and apoptotic processes. The contributions of each process depend on conditions such as the severity and duration of ischemia, and the availability of ATP. We examined whether glucose affected the development of apoptosis after transient ischemia, and whether this was sensitive to caspase inhibition. Retinoic acid-differentiated SH-SY5Y human neuroblastoma cells were subjected to oxygen and glucose deprivation for 15 h followed by various periods of reoxygenation in either the presence or absence of glucose. Oxygen and glucose deprivation induced cell death in the hours following reoxygenation, as detected by propidium iodide staining. At the end of the period of oxygen and glucose deprivation, both cytochrome c and apoptosis-inducing factor translocated from mitochondria to cytosol. Reoxygenation in the presence of glucose accelerated cell death, and enhanced caspase-3 activity and apoptosis. The glucose-dependent increase in apoptosis was prevented by treatment with the caspase inhibitor zVAD-fmk, but not with calpeptin, a calpain inhibitor. Nevertheless, both zVAD-fmk and calpeptin decreased cell death in the glucose-treated group. ATP levels dropped dramatically after oxygen and glucose deprivation, but recovered steadily thereafter, and were significantly higher at 6 h of reoxygenation in the glucose-treated group. This indicates that energy recovery may promote the glucose-dependent cell death. We conclude that glucose favours the development of caspase-dependent apoptosis during reoxygenation following oxygen and glucose deprivation.

Oxidative stress on the astrocytes in culture derived from a senescence accelerated mouse strain

Astrocytes are one of the predominant glial cell types in the adult central nervous system functioning as both supportive and metabolic cells for the brain. Our objective in this experiment is to study the direct effects of hydrogen peroxide induced oxidative stress on astrocytes in culture. These astrocytes were derived from both an aged mouse strain (P8) and a matched control strain (R1). The astrocytes for both the P8 and R1 strains were treated with increasing concentrations of hydrogen peroxide. Our results showed that the oxidative stress had a similar effect in both strains of astrocytes; decreases in 3-(4,5-dimethylthiazol-2-yl)-2,2-diphenyltetrazolium bromide (MTT) and glial fibrillary acidic protein (GFAP) levels, and increases in terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) staining, lactate dehydrogenase (LDH) staining, and superoxide dismutase (SOD), caspase-3 and B-cell lymphoma 2-associated protein X (bax) levels. At a hydrogen peroxide concentration of 400 microM , the differences of the above parameters between P8 cultures and R1 cultures were statistically significant (p<0.05). This strongly suggested that astrocytes derived from P8 and R1 strains reacted to oxidative stress with similar mechanisms and consequences. However, the mechanisms were not able to compensate for the oxidative stress in the P8 strain at a hydrogen peroxide concentration of 400 microM. The inability of the P8 astrocytes to counteract the oxidative stress might lead to inadequate protection from neuronal loss possibly resulting in significantly more astrocytic death. Our results suggested that the changes of astrocytes in peroxide detoxification may play a role in aging of the central nervous system, and further aging studies should examine the oxidative status of the samples.

Multiple cysteine residues are implicated in Janus kinase 2-mediated catalysis

The redox regulation of Janus kinase 2 (JAK2) is poorly understood, and there are contradictory reports as to whether the enzyme's activity is inhibited or stimulated by oxidizing conditions in the cell. Here we demonstrate that multiple cysteine residues within the JAK2 catalytic domain may be crucial for enzymatic activity. The enzyme is catalytically inactive when oxidized; activity can be restored via reduction to the thiol state. A series of recombinant variants of JAK2 were overproduced using the baculoviral expression vector system. A truncated variant of JAK2, GST/(NDelta661)rJAK2, provided evidence that the amino-terminal autoinhibitory domain was not essential for direct redox regulation and that only nine cysteine residues were potentially involved. The effect of individually and combinatorially altering these nine cysteines was examined via cysteine-to-serine mutagenesis. This identified four cysteine residues in the catalytic domain (Cys866, Cys917, Cys1094, and Cys1105) that cooperatively maintain JAK2's catalytic competency. Our data are consistent with a direct mechanism for redox regulation of JAK2 via oxidation and reduction of critical cysteine residues.

Involvement of astroglial ceramide in palmitic acid-induced Alzheimer-like changes in primary neurons

A high-fat diet has been shown to significantly increase the risk of the development of Alzheimer's disease (AD), a neurodegenerative disease histochemically characterized by the accumulation of amyloid beta (Abeta) protein in senile plaques and hyperphosphorylated tau in neurofibrillary tangles. Previously, we have shown that saturated free fatty acids (FFAs), palmitic and stearic acids, caused increased amyloidogenesis and tau hyperphosphorylaion in primary rat cortical neurons. These FFA-induced effects observed in neurons were found to be mediated by astroglial FFA metabolism. Therefore, in the present study we investigated the basic mechanism relating astroglial FFA metabolism and AD-like changes observed in neurons. We found that palmitic acid significantly increased de-novo synthesis of ceramide in astroglia, which in turn was involved in inducing both increased production of the Abeta protein and hyperphosphorylation of the tau protein. Increased amyloidogenesis and hyperphoshorylation of tau lead to formation of the two most important pathophysiological characteristics associated with AD, Abeta or senile plaques and neurofibrillary tangles, respectively. In addition to these pathophysiological changes, AD is also characterized by certain metabolic changes; abnormal cerebral glucose metabolism is one of the distinct characteristics of AD. In this context, we found that palmitic acid significantly decreased the levels of astroglial glucose transporter (GLUT1) and down-regulated glucose uptake and lactate release by astroglia. Our present data establish an underlying mechanism by which saturated fatty acids induce AD-associated pathophysiological as well as metabolic changes, placing 'astroglial fatty acid metabolism' at the center of the pathogenic cascade in AD.

Exposure of glia to pro-oxidant agents revealed selective Stat1 activation by H2O2 and Jak2-independent antioxidant features of the Jak2 inhibitor AG490

The JAK/STAT pathway is activated in response to cytokines and growth factors. In addition, oxidative stress can activate this pathway, but the causative pro-oxidant forms are not well identified. We exposed cultures of rat glia to H2O2, FeSO4, nitroprussiate, or paraquat. We assessed oxidative stress by measuring reactive oxygen species (ROS) and oxidated proteins, we determined phosphorylated Stat1 (pStat1), and we evaluated the effect of antioxidants (trolox, propyl gallate, and N-acetylcysteine) and of Jak2 (Janus tyrosine kinases) inhibitors (AG490 and Jak2-Inhibitor-II). Pro-oxidant agents induced ROS and protein oxidation, excluding nitroprussiate that induced protein nitrosylation. H2O2, and to a lesser extent FeSO4, increased the level of pStat1, whereas nitroprussiate and paraquat did not. Trolox and propyl gallate strongly prevented ROS formation but they did not abolish H2O2-induced pStat1. In contrast, NAC did not reduce the level of ROS but it prevented the increase of pStat1 induced by H2O2, evidencing a differential effect on ROS formation and on Stat1 phosphorylation. H2O2 induced pStat1 in mixed glia cultures and, to a lesser extent, in purified astroglia, but not in microglia. Jak2 inhibitors reduced H2O2-induced pStat1, suggesting the involvement of this kinase in the increased phosphorylation of Stat1 by peroxide. Unexpectedly, AG490, but not Jak2-Inhibitor-II, reduced ROS formation, and it abrogated lipid peroxidation in microsomal preparations. Furthermore, AG490 reduced ROS in glial cells that were transfected with siRNA to silence Jak2 expression. These findings reveal previously unrecognized Jak2-independent antioxidant properties of AG490, and show that Jak2-dependent Stat1 activation by peroxide is dissociated from ROS generation.

Mitochondrial glutathione protects against cell death induced by oxidative and nitrative stress in astrocytes

The major cellular antioxidant, glutathione, is mostly localized in the cytosol but a small portion is found in mitochondria. We have recently shown that highly selective depletion of mitochondrial glutathione in astrocytes in culture markedly increased cell death induced by the peroxynitrite donor, 3-morpholino-syndnonimine. The present study was aimed at characterizing the increase in susceptibility arising from mitochondrial glutathione loss and testing the possibility that elevating this metabolite pool above normal values could be protective. The increased vulnerability of astrocytes with depleted mitochondrial glutathione to Sin-1 was confirmed. Furthermore, these cells showed marked increases in sensitivity to hydrogen peroxide and also to high concentrations of the nitric oxide donor, S-nitroso-N-acetyl-penicillamine. The increase in cell death was mostly due to necrosis as indicated by substantially increased release of lactate dehydrogenase and staining of nuclei with propidium iodide but little change in annexin V staining and caspase 3 activation. The enhanced cell loss was blocked by prior restoration of the mitochondrial glutathione content. It was also essentially fully inhibited by treatment with cyclosporin A, consistent with a role for the mitochondrial permeability transition in the development of cell death. Susceptibility to the classical apoptosis inducer, staurosporine, was only affected to a small extent in contrast to the response to the other substances tested. Incubation of normal astrocytes with glutathione monoethylester produced large and long-lasting increases in mitochondrial glutathione content with much smaller effects on the cytosolic glutathione pool. This treatment reduced cell death on exposure to 3-morpholino-syndnonimine or hydrogen peroxide but not S-nitroso-N-acetyl-pencillamine or staurosporine. These findings provide evidence for an important role for mitochondrial glutathione in preserving cell viability during periods of oxidative or nitrative stress and indicate that increases in this glutathione pool can confer protection against some of these stressors.

Angiotensin Receptor Type 1 Blockade in Astroglia Decreases Hypoxia-Induced Cell Damage and TNF Alpha Release

The present study investigated the role of angiotensin receptors (AT-R) in the survival and inflammatory response of astroglia upon hypoxic injury. Exposure of rat astroglial primary cultures (APC) to hypoxic conditions (HC) led to decreased viability of the cells and to a 3.5-fold increase in TNF-alpha release. AT-R type1 (AT1-R) antagonist losartan and its metabolite EXP3174 decrease the LDH release (by 36 +/- 9%; 45 +/- 6%) from APC under HC. Losartan diminished TNF-alpha release (by 40 +/- 15%) and the number of TUNEL-cells by 204 +/- 38% under HC, alone and together with angiotensin II (ATII), while EXP3174 was dependent on ATII for its effect on TNF-alpha. The AT2-R antagonist, PD123.319, did not influence the release of LDH and TNF-alpha under normoxic (NC) and HC. These data suggest that AT1-R may decrease the susceptibility of astrocytes to hypoxic injury and their propensity to release TNF-alpha. AT1-R antagonists may therefore be of therapeutic value during hypoxia-associated neurodegeneration.

Signalling pathways mediating inflammatory responses in brain ischaemia

Stroke causes neuronal necrosis and generates inflammation. Pro-inflammatory molecules intervene in this process by triggering glial cell activation and leucocyte infiltration to the injured tissue. Cytokines are major mediators of the inflammatory response. Pro-inflammatory and anti-inflammatory cytokines are released in the ischaemic brain. Anti-inflammatory cytokines, such as interleukin-10, promote cell survival, whereas pro-inflammatory cytokines, such as TNFalpha (tumour necrosis factor alpha), can induce cell death. However, deleterious effects of certain cytokines can turn to beneficial actions, depending on particular features such as the concentration, time point and the very intricate network of intracellular signals that become activated and interact. A key player in the intracellular response to cytokines is the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway that induces alterations in the pattern of gene transcription. These changes are associated either with cell death or survival depending, among other things, on the specific proteins involved. STAT1 activation is related to cell death, whereas STAT3 activation is often associated with survival. Yet, it is clear that STAT activation must be tightly controlled, and for this reason the function of JAK/STAT modulators, such as SOCS (suppressors of cytokine signalling) and PIAS (protein inhibitor of activated STAT), and phosphatases is most relevant. Besides local effects in the ischaemic brain, cytokines are released to the circulation and affect the immune system. Unbalanced pro-inflammatory and anti-inflammatory plasma cytokine concentrations favouring an 'anti-inflammatory' state can decrease the immune response. Robust evidence now supports that stroke can induce an immunodepression syndrome, increasing the risk of infection. The contribution of individual cytokines and their intracellular signalling pathways to this response needs to be further investigated.

Mechanisms of endothelial cell protection by blockade of the JAK2 pathway

Inhibition of the JAK2/STAT pathway has been implicated recently in cytoprotective mechanisms in both vascular smooth muscle cells and astrocytes. The advent of JAK2-specific inhibitors provides a practical tool for the study of this pathway in different cellular types. An interest in finding methods to improve endothelial cell (EC) resistance to injury led us to examine the effect of JAK2/STAT inhibition on EC protection. Furthermore, the signaling pathways involved in JAK2/STAT inhibition-related actions were examined. Our results reveal, for the first time, that blockade of JAK2 with the tyrosine kinase inhibitor AG490 strongly protects cultured EC against cell detachment-dependent death and serum deprivation and increases reseeding efficiency. Confirmation of the specificity of the effects of JAK2 inhibition was attained by finding protective effects on transfection with a dominant negative JAK2. Furthermore, AG490 blocked serum deprivation-induced phosphorylation of JAK2. In terms of mechanism, treatment with AG490 induces several relevant responses, both in monolayer and detached cells. These mechanisms include the following: 1) Increase and nuclear translocation of the active, dephosphorylated form of beta-catenin. In functional terms, this translocation is transcriptionally active, and its protective effect is further supported by the stimulation of EC cytoprotection by transfectionally induced excess of beta-catenin. 2) Increase of platelet endothelial cell adhesion molecule (PECAM)/CD31 levels. 3) Increase in total and phosphorylated AKT. 4) Increase in phosphorylated glycogen synthase kinase (GSK)3alpha/beta. The present findings imply potential practical applications of JAK2 inhibition on EC. These applications affect not only EC in the monolayer but also circulating detached cells and involve mechanistic interactions not previously described.

JAK2 and STAT3 activation contributes to neuronal damage following transient focal cerebral ischemia

Increased levels of interleukin-6 (IL-6) play a role in post-ischemic cerebral inflammation. IL-6 binding to its receptors induces phosphorylation of the receptor associated janus kinases (JAKs), and the down-stream signal transducer and activator of transcription (STAT) family of transcription factors, which amplify the IL-6 signal transduction. We evaluated the functional significance of JAK2 and STAT3 activation in focal ischemia-induced neuronal damage. Transient middle cerebral artery occlusion in adult rats led to increased JAK2 and STAT3 phosphorylation in the ipsilateral cortex and striatum after 6-72 h of reperfusion. Fluorescent immunohistochemistry with cell specific markers (NeuN for neurons, glial fibrillary acidic protein for reactive astrocytes and ED1/OX42 for activated macrophages/microglia) showed that both pJAK2 and pSTAT3 staining is predominantly localized in the macrophages/microglia in the post-ischemic brain. Intracerebroventricular infusion of rats with AG490 (a JAK2 phosphorylation inhibitor) prevented the post-ischemic JAK2 and STAT3 phosphorylation and significantly decreased the infarct volume, number of apoptotic cells and neurological deficits, compared to vehicle control. Furthermore, intracerebral injection of siRNA specific for STAT3 led to curtailed STAT3 mRNA expression and phosphorylation, decreased infarct volume, fewer apoptotic cells and improved neurological function following transient middle cerebral artery occlusion. These studies show that JAK2-STAT3 activation plays a role in post-ischemic brain damage.

STAT3 attenuates EGFR-mediated ERK activation and cell survival during oxidant stress in mouse proximal tubular cells

We have shown that renal epithelial cell survival depends on the sustained activation of the extracellular signal-regulated protein kinase (ERK) and lack of this activation was associated with death during oxidative stress. ERK is activated via the canonical epidermal growth factor receptor (EGFR)-Ras-MEK pathway, which could be attenuated by oxidants. We now show that the failure to activate ERK in a sustained manner during severe oxidative stress is owing to the activation of the signal transducer and activator of transcription-3 (STAT3) rather than the failure to activate the EGFR. Tyrosine phosphorylation of the EGFR and STAT3 was studied in hydrogen peroxide (H(2)O(2))-treated mouse proximal tubule (TKPTS) cells or in mouse kidney after ischemia/reperfusion (I/R) injury by Western blotting. STAT3 activation was inhibited by either pharmacologically (AG490) through its upstream janus kinase (JAK2) or by a dominant-negative STAT3 adenovirus. EGFR was inhibited by AG1478. Survival was determined by fluorescence-activated cell sorter analysis and trypan blue exclusion. We found that the EGFR was phosphorylated on its major autophosphorylation site (Tyr1173) regardless of the H(2)O(2) dose. On the other hand, both I/R and severe oxidative stress - but not moderate stress - increased tyrosine phosphorylation of STAT3 in an EGFR and JAK2-dependent manner. Inhibition of JAK2 or STAT3 lead to increased ERK activation and survival of TKPTS cells during severe oxidative stress. Our data suggest a role of tyrosine-phosphorylated STAT3 in the suppression of ERK activation. These data suggest that the STAT3 pathway might represent a new target for improved survival of proximal tubule cells exposed to severe oxidant injury.

Ethanol feeding alters death signaling in the pancreas

OBJECTIVES

Alcohol abuse is a major cause of pancreatitis, which is associated with death of parenchymal cells. The goal of this study was to explore the effects of ethanol on cell death pathways in the pancreas.

METHODS

Adult male Wistar rats were fed with ethanol diets using the Lieber-DeCarli method. Caspase-8, caspase-3, and cathepsin B expression and activity in the pancreas of these animals as well as the signals that regulate their expression were studied using Western blot analysis and specific assays for biochemical enzyme activity.

RESULTS

In the pancreas from rats fed with ethanol, the protein expression and activity of caspase-8 decreased by 48% and 45%, respectively, and caspase-3 activity decreased by 39%. In contrast, cathepsin B protein expression and activity increased with ethanol feeding by 189% and 143%, respectively. Evaluation of the transcriptional regulatory system for caspase-8 and cathepsin B showed that the ethanol effects on these pathways were largely transcriptional.

CONCLUSIONS

Our findings show effects of ethanol on the expression of several signals involved in cell death in the pancreas through alteration of transcriptional regulators. The decrease in caspase expression and increase in cathepsin B expression indicate that ethanol feeding may prevent apoptosis and promote necrosis of pancreatic tissue with stresses that cause pancreatitis.

Interleukin-22, a member of the IL-10 subfamily, induces inflammatory responses in colonic subepithelial myofibroblasts

BACKGROUND & AIMS

Interleukin (IL)-22, a member of the IL-10 subfamily, is a recently identified T-cell-derived cytokine. We investigated IL-22 expression in the inflamed mucosa of patients with inflammatory bowel disease (IBD) and analyzed its biologic activities in human colonic subepithelial myofibroblasts (SEMFs).

METHODS

Mucosal IL-22 expression was evaluated by immunohistochemical procedures. The effects of IL-22 on colonic SEMFs were investigated by cDNA microarrays, Northern blots, enzyme-linked immunosorbent assay, and electrophoretic gel mobility shift assays (EMSAs).

RESULTS

IL-22 was not detectable in normal colonic mucosa. In IBD mucosa, IL-22 expression was detectable in CD4-positive T cells. IL-22-positive cells were increased in ulcerative colitis and even more so in Crohn's disease. IL-22 receptor expression colocalized with a marker of SEMFs. IL-22 did not modulate SEMF proliferation and collagen synthesis. cDNA microarray analyses demonstrated that, in colonic SEMFs, IL-22 increased the messenger RNA (mRNA) expression of inflammatory cytokines (IL-6, IL-8, IL-11, and leukemia inhibitory factor [LIF]), chemokines, and matrix metalloproteinases. IL-22 induced an activation of nuclear factor (NF)-kappaB and activating protein (AP)-1 within 1 hour, and a blockade of NF-kappaB and AP-1 activation markedly reduced IL-22 induction of IL-6, IL-8, IL-11, and LIF mRNA. MAP-kinase inhibitors (PD98059, U0216, and SB202190) significantly reduced IL-22 induction of cytokine secretion. The combination of either IL-17 plus IL-22 or IL-19 plus IL-22 additively up-regulated cytokine secretion.

CONCLUSIONS

IL-22 derived from activated T cells acts on SEMFs to elicit expression of proinflammatory cytokines and matrix-degrading molecules indicating proinflammatory/remodeling roles in IBD.