Hypoxia/reoxygenation differentially modulates NF-kappaB activation and iNOS expression in astrocytes and microglia

CX3CL1/CX3CR1 signal mediates M1-type microglia and accelerates high-altitude-induced forgetting

Introduction

Hypoxia-induced neuronal damage is the primary cause of cognitive impairment induced by high-altitude exposure. Microglia play a crucial regulatory role in the central nervous system (CNS) homeostasis and synaptic plasticity. M1-type polarized microglia are suspected to be responsible for CNS injury under hypoxic conditions, but the exact molecular mechanism is still unelucidated.

Methods

CX3CR1 knock out and wide type mice were exposed to a simulated plateau at 7000 m for 48 h to construct the model of hypobaric hypoxia-induced memory impairment. The memory impairment of mice was assessed by Morris water maze. The dendritic spine density in the hippocampus was examined by Golgi staining. The synapses in the CA1 region and the number of neurons in the DG region were examined by immunofluorescence staining. The synapses in microglia activation and phagocytosis were examined by immunofluorescence. The levels of CX3CL1/CX3CR1 and their downstream proteins were detected. CX3CR1 knockout primary microglia were treated with CX3CL1 combined with 1% O₂. The levels of proteins related to microglial polarization, the uptake of synaptosome and phagocytotic ability of microglia were detected.

Results

In this study, mice exposed to a simulated 7000 m altitude for 48 h developed significant amnesia for recent memories, but no significant change in their anxiety levels was observed. Hypobaric hypoxia exposure (7000 m altitude above sea level for 48 h) resulted in synapse loss in the CA1 region of the hippocampus, but no significant changes occurred in the total number of neurons. Meanwhile, microglia activation, increased phagocytosis of synapses by microglia, and CX3CL1/CX3CR1 signal activation were observed under hypobaric hypoxic exposure. Further, we found that after hypobaric hypoxia exposure, CX3CR1-deficient mice showed less amnesia, less synaptic loss in the CA1 region, and less increase in M1 microglia, compared to their wildtype siblings. CX3CR1-deficient microglia did not exhibit M1-type polarization in response to either hypoxia or CX3CL1 induction. Both hypoxia and CX3CL1 induced the phagocytosis of synapses by microglia through the upregulation of microglial phagocytosis.

Discussion

The current study demonstrates that CX3CL1/CX3CR1 signal mediates the M1-type polarization of microglia under high-altitude exposure and upregulates microglial phagocytosis, which increases the phagocytosis of synapses in the CA1 region of the hippocampus, causing synaptic loss and inducing forgetting.

Opioids and Vitamin C: Known Interactions and Potential for Redox-Signaling Crosstalk

Opioids are among the most widely used classes of pharmacologically active compounds both clinically and recreationally. Beyond their analgesic efficacy via μ opioid receptor (MOR) agonism, a prominent side effect is central respiratory depression, leading to systemic hypoxia and free radical generation. Vitamin C (ascorbic acid; AA) is an essential antioxidant vitamin and is involved in the recycling of redox cofactors associated with inflammation. While AA has been shown to reduce some of the negative side effects of opioids, the underlying mechanisms have not been explored. The present review seeks to provide a signaling framework under which MOR activation and AA may interact. AA can directly quench reactive oxygen and nitrogen species induced by opioids, yet this activity alone does not sufficiently describe observations. Downstream of MOR activation, confounding effects from AA with STAT3, HIF1α, and NF-κB have the potential to block production of antioxidant proteins such as nitric oxide synthase and superoxide dismutase. Further mechanistic research is necessary to understand the underlying signaling crosstalk of MOR activation and AA in the amelioration of the negative, potentially fatal side effects of opioids.

Glutamate Uptake Is Not Impaired by Hypoxia in a Culture Model of Human Fetal Neural Stem Cell-Derived Astrocytes

Hypoxic ischemic injury to the fetal and neonatal brain is a leading cause of death and disability worldwide. Although animal and culture studies suggest that glutamate excitotoxicity is a primary contributor to neuronal death following hypoxia, the molecular mechanisms, and roles of various neural cells in the development of glutamate excitotoxicity in humans, is not fully understood. In this study, we developed a culture model of human fetal neural stem cell (FNSC)-derived astrocytes and examined their glutamate uptake in response to hypoxia. We isolated, established, and characterized cultures of FNSCs from aborted fetal brains and differentiated them into astrocytes, characterized by increased expression of the astrocyte markers glial fibrillary acidic protein (GFAP), excitatory amino acid transporter 1 (EAAT1) and EAAT2, and decreased expression of neural stem cell marker Nestin. Differentiated astrocytes were exposed to various oxygen concentrations mimicking normoxia (20% and 6%), moderate and severe hypoxia (2% and 0.2%, respectively). Interestingly, no change was observed in the expression of the glutamate transporter EAAT2 or glutamate uptake by astrocytes, even after exposure to severe hypoxia for 48 h. These results together suggest that human FNSC-derived astrocytes can maintain glutamate uptake after hypoxic injury and thus provide evidence for the possible neuroprotective role of astrocytes in hypoxic conditions.

Upregulation of CD14 in mesenchymal stromal cells accelerates lipopolysaccharide-induced response and enhances antibacterial properties

Mesenchymal stromal cells (MSCs) have broad-ranging therapeutic properties, including the ability to inhibit bacterial growth and resolve infection. However, the genetic mechanisms regulating these antibacterial properties in MSCs are largely unknown. Here, we utilized a systems-based approach to compare MSCs from different genetic backgrounds that displayed differences in antibacterial activity. Although both MSCs satisfied traditional MSC-defining criteria, comparative transcriptomics and quantitative membrane proteomics revealed two unique molecular profiles. The antibacterial MSCs responded rapidly to bacterial lipopolysaccharide (LPS) and had elevated levels of the LPS co-receptor CD14. CRISPR-mediated overexpression of endogenous CD14 in MSCs resulted in faster LPS response and enhanced antibacterial activity. Single-cell RNA sequencing of CD14-upregulated MSCs revealed a shift in transcriptional ground state and a more uniform LPS-induced response. Our results highlight the impact of genetic background on MSC phenotypic diversity and demonstrate that overexpression of CD14 can prime these cells to be more responsive to bacterial challenge.

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MSCs from different genetic backgrounds have distinct responses to bacteria

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Upregulating CD14 in MSCs enhances LPS-induced response and antibacterial traits

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CD14 upregulation homogenizes MSC transcriptional profiles across individual cells

Intermittent Hypoxia and Effects on Early Learning/Memory: Exploring the Hippocampal Cellular Effects of Pediatric Obstructive Sleep Apnea

This review provides an update on the neurocognitive phenotype of pediatric obstructive sleep apnea (OSA). Pediatric OSA is associated with neurocognitive deficits involving memory, learning, and executive functioning. Adenotonsillectomy (AT) is presently accepted as the first-line surgical treatment for pediatric OSA, but the executive function deficits do not resolve postsurgery, and the timeline for recovery remains unknown. This finding suggests that pediatric OSA potentially causes irreversible damage to multiple areas of the brain. The focus of this review is the hippocampus, 1 of the 2 major sites of postnatal neurogenesis, where new neurons are formed and integrated into existing circuitry and the mammalian center of learning/memory functions. Here, we review the clinical phenotype of pediatric OSA, and then discuss existing studies of OSA on different cell types in the hippocampus during critical periods of development. This will set the stage for future study using preclinical models to understand the pathogenesis of persistent neurocognitive dysfunction in pediatric OSA.

Endogenous reactive oxygen species and nitric oxide have opposite roles in regulating HIF-1alpha expression in hypoxic astrocytes

Ischemic stroke results in cerebral tissue hypoxia and increased expression of hypoxia-inducible factor (HIF), which is critically implicated in ischemic brain injury. Understanding the mechanisms of HIF-1alpha regulation in the ischemic brain has been an important research focus. The generation of both nitric oxide (NO) and reactive oxygen species (ROS) is increased under hypoxic/ischemic conditions and each of them has been independently shown to regulate HIF-1alpha expression. In this study, we investigated the cross-effects of NO and ROS on the expression of HIF-1alpha in hypoxic astrocytes. Exposure of astrocytes to 2 h-hypoxia remarkably increased HIF-1alpha protein levels, which was accompanied by increased NO and ROS production. Decreasing ROS with NAC, NADPH oxidase inhibitor DPI, or SOD mimetic MnTMPyP decreased hypoxia-induced HIF-1alpha protein accumulation and increased NO level in hypoxic astrocytes. The NO synthase (NOS) inhibitor L-NAME inhibited ROS generation, which led to a reduction in hypoxia-induced HIF-1alpha protein expression. Although NOS inhibitor or ROS scavengers alone reduced HIF-1alpha protein levels, the reduction was reversed when NOS inhibitor and ROS scavenger present together. The NO scavenger PTIO increased hypoxia-induced HIF-1alpha protein expression and ROS production, while HIF-1alpha protein level was decreased in the presence of NO scavenger and ROS scavenger together. These results suggest that ROS, NO, and their interaction critically contribute to the regulation of hypoxia-induced HIF-1alpha protein accumulation under hypoxic condition. Furthermore, our results indicate that hypoxia-induced NO generation may represent an endogenous mechanism for balancing ROS-mediated hypoxic stress, as reflected by inhibiting hypoxia-induced HIF-1alpha protein accumulation.

Integrative Bioinformatics Analysis of iNOS/NOS2 in gastric and colorectal cancer

Objective The aim of the present work was to investigate the expression of nitric oxide synthase 2 (iNOS/ NOS2) in colorectal and gastric cancers and evaluate its association with patient’s prognosis by integrated bioinformatics analysis.

Methods The data for present study was obtained from the TCGA, GTEx, and STRING database. iNOS/NOS2 mRNA expression in normal tissue and colorectal, and gastric cancer tissuea were investigated through the GTEx and TCGA database. iNOS/NOS2 gene mutations and frequency were analyzed in the TCGA database using the cBioPortal online data analysis tool. The protein-protein interaction (PPI) network of iNOS/NOS2 was constructed by STRING database. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway of iNOS/NOS2 and relevant proteins involved in the PPI network were enriched and demonstrated by the bubble plot. Comparison of the overall survival(OS) and disease free survival(DFS) between samples expressing high and low levels of iNOS/NOS2 was analysis based on the TCGA databases through the GEPIA online data analysis tool.

Results For colon adenocarcinoma (COAD) and rectal adenocarcinoma(READ) iNOS/NOS2 mRNA expression levels in tumor tissue were significant higher than those of corresponding normal colorectal tissue (p<0.05). iNOS/NOS2 mutations were identified in both colorectal cancer and gastric cancer. Missense substitutions and synonymous substitution were the top two mutation types for colorectal and gastric cancer. The top positive and negative co-expressed genes correlated with iNOS/ NOS2 were TRIM40 (rpearson=0.56, p<0.05) and GDPD5 (rpearson=-0.41, p<0.05) in colorectal cancer respectively andCASP5 (rpearson=0.63,p<0.05) and PIAS3 (rpearson=-0.43,p<0.05) in gastric cancer. Twenty one proteins were included in the PPI network with 51 nodes and 345 edges which indicated the PPI enrichment wassignificant (p=1.0e-16). The KEGG of the included genes were mainly enriched in metabolic pathway and Jak-STAT signaling pathway. There was a significant difference indisease free survival (DFS) between samples expressing high and low iNOS/NOS2 (HR=0.37, p=0.044) in rectal cancer. The difference was not statistical between iNOS/NOS2 high and low expressing groups for overall survival(OS) or DFS in the colon cancer or gastric cancer(p>0.05).

Conclusions iNOS/NOS2 mRNA isup-regulated in tumor tissue compared to corresponding normal tissue in colorectal and gastric cancer which implement it in the development of colorectal and gastric cancers.

Regulatory mechanisms and therapeutic potential of microglial inhibitors in neuropathic pain and morphine tolerance

Microglia are important cells involved in the regulation of neuropathic pain (NPP) and morphine tolerance. Information on their plasticity and polarity has been elucidated after determining their physiological structure, but there is still much to learn about the role of this type of cell in NPP and morphine tolerance. Microglia mediate multiple functions in health and disease by controlling damage in the central nervous system (CNS) and endogenous immune responses to disease. Microglial activation can result in altered opioid system activity, and NPP is characterized by resistance to morphine. Here we investigate the regulatory mechanisms of microglia and review the potential of microglial inhibitors for modulating NPP and morphine tolerance. Targeted inhibition of glial activation is a clinically promising approach to the treatment of NPP and the prevention of morphine tolerance. Finally, we suggest directions for future research on microglial inhibitors.

Dectin-1/Syk signaling triggers neuroinflammation after ischemic stroke in mice

Background

Dendritic cell-associated C-type lectin-1 (Dectin-1) receptor has been reported to be involved in neuroinflammation in Alzheimer’s disease and traumatic brain injury. The present study was designed to investigate the role of Dectin-1 and its downstream target spleen tyrosine kinase (Syk) in early brain injury after ischemic stroke using a focal cortex ischemic stroke model.

Methods

Adult male C57BL/6 J mice were subjected to a cerebral focal ischemia model of ischemic stroke. The neurological score, adhesive removal test, and foot-fault test were evaluated on days 1, 3, 5, and 7 after ischemic stroke. Dectin-1, Syk, phosphorylated (p)-Syk, tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS) expression was analyzed via western blotting in ischemic brain tissue after ischemic stroke and in BV2 microglial cells subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) injury in vitro. The brain infarct volume and Iba1-positive cells were evaluated using Nissl’s and immunofluorescence staining, respectively. The Dectin-1 antagonist laminarin (LAM) and a selective inhibitor of Syk phosphorylation (piceatannol; PIC) were used for the intervention.

Results

Dectin-1, Syk, and p-Syk expression was significantly enhanced on days 3, 5, and 7 and peaked on day 3 after ischemic stroke. The Dectin-1 antagonist LAM or Syk inhibitor PIC decreased the number of Iba1-positive cells and TNF-α and iNOS expression, decreased the brain infarct volume, and improved neurological functions on day 3 after ischemic stroke. In addition, the in vitro data revealed that Dectin-1, Syk, and p-Syk expression was increased following the 3-h OGD and 0, 3, and 6 h of reperfusion in BV2 microglial cells. LAM and PIC also decreased TNF-α and iNOS expression 3 h after OGD/R induction.

Conclusion

Dectin-1/Syk signaling plays a crucial role in inflammatory activation after ischemic stroke, and further investigation of Dectin-1/Syk signaling in stroke is warranted.

Uncoupled Endothelial Nitric Oxide Synthase Enhances p-Tau in Chronic Traumatic Encephalopathy Mouse Model

AIMS

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease thought to be caused by repetitive traumatic brain injury (TBI) and subconcussive injuries. While hyperphosphorylation of tau (p-Tau), which is attributed to astrocytic tangles (ATs) and neurofibrillary tangles, is known to be involved in CTE, there are limited neuropathological or molecular data. By utilizing repetitive mild TBI (rmTBI) mouse models, our aim was to examine the pathological changes of CTE-associated structures, specifically the ATs.

RESULTS

Our rmTBI mouse models showed symptoms of depressive behavior and memory deficit, alongside an increased p-Tau expression in their neurons and astrocytes in both the hippocampus and cortex. rmTBI induced oxidative stress in endothelial cells and nitric oxide (NO) generation in astrocytes, which were mediated by hypoxia and increased hypoxia-inducible factor 1-α (HIF1α). There was also correlated decreased regional cerebral tissue perfusion units, mild activation of astrocytes and NFκB phosphorylation, increased expression of inducible nitric oxide synthase (iNOS), increased endothelial nitric oxide synthase (eNOS) uncoupling with decreased tetrahydrobiopterin, and increased expression of nitrotyrosine, NADPH oxidase 2 (Nox2)/nuclear factor (erythroid-derived 2) factor 2 (Nrf2) signaling proteins. Combined, these effects induced peroxynitrite formation and hyperphosphorylation of tau in the hippocampus and cortex toward the formation of ATs.

INNOVATION

Our model features molecular pathogenesis events of CTE with clinically relevant latency periods. In particular, this is the first demonstration of an increased astrocytic iNOS expression in an in vivo model.

CONCLUSION

We propose a novel mechanism of uncoupled eNOS and NO contribution to Tau phosphorylation and AT formation in rmTBI brain, toward an increased molecular understanding of the pathophysiology of human CTE.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Mechanisms of microglial activation in models of inflammation and hypoxia: Implications for chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) is a hallmark of sleep apnoea, a condition associated with diverse clinical disorders. CIH and sleep apnoea are characterized by increased reactive oxygen species formation, peripheral and CNS inflammation, neuronal death and neurocognitive deficits. Few studies have examined the role of microglia, the resident CNS immune cells, in models of CIH. Thus, little is known concerning their direct contributions to neuropathology or the cellular mechanisms regulating their activities during or following pathological CIH. In this review, we identify gaps in knowledge regarding CIH-induced microglial activation, and propose mechanisms based on data from related models of hypoxia and/or hypoxia-reoxygenation. CIH may directly affect microglia, or may have indirect effects via the periphery or other CNS cells. Peripheral inflammation may indirectly activate microglia via entry of pro-inflammatory molecules into the CNS, and/or activation of vagal afferents that trigger CNS inflammation. CIH-induced release of damage-associated molecular patterns from injured CNS cells may also activate microglia via interactions with pattern recognition receptors expressed on microglia. For example, Toll-like receptors activate mitogen-activated protein kinase/transcription factor pathways required for microglial inflammatory gene expression. Although epigenetic effects from CIH have not yet been studied in microglia, potential epigenetic mechanisms in microglial regulation are discussed, including microRNAs, histone modifications and DNA methylation. Epigenetic effects can occur during CIH, or long after it has ended. A better understanding of CIH effects on microglial activities may be important to reverse CIH-induced neuropathology in patients with sleep disordered breathing.

Intermittent hypoxia-induced cardiorespiratory long-term facilitation: A new role for microglia

Intermittent hypoxia induces plasticity in neural networks controlling breathing and cardiovascular function. Studies demonstrate that mechanisms causing cardiorespiratory plasticity rely on intracellular signalling pathways that are activated by specific neurotransmitters. Peptides such as serotonin, PACAP and orexin are well-known for their physiological significance in regulating the cardiorespiratory system. Their receptor counterparts are present in cardiorespiratory centres of the brainstem medulla and spinal cord. Microglial cells are also important players in inducing plasticity. The phenotype and function of microglial cells can change based on the physiological state of the central nervous system. Here, we propose that in the autonomic nuclei of the ventral brainstem the relationship between neurotransmitters and neurokines, neurons and microglia determines the overall neural function of the central cardiorespiratory system.

Combustion smoke-induced inflammation in the olfactory bulb of adult rats

BACKGROUND

The damaging effect of combustion smoke inhalation on the lung is widely reported but information on its effects on the olfactory bulb is lacking. This study sought to determine the effects of smoke inhalation on the olfactory bulb, whose afferent input neurons in the nasal mucosa are directly exposed to external stimuli, such as smoke.

METHODS

Adult male Sprague-Dawley rats were subjected to combustion smoke inhalation and sacrificed at different time points. Changes in olfactory bulb proteins including vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), Na+-K+-Cl- cotransporter 1 (NKCC1), glial fibrillary acidic protein (GFAP), and aquaporin-4 (AQP4) were evaluated by Western blot analysis. In addition, ELISA was conducted for cytokine and chemokine levels, and double immunofluorescence labeling was carried out for GFAP/VEGF, GFAP/AQP4, NeuN/nNOS, GFAP/NKCC1, NeuN/NKCC1, GFAP/Rhodamine isothiocyanate (RITC), and transferase dUTP nick end labeling (TUNEL). Aminoguanidine was administered to determine the effects of iNOS inhibition on the targets probed after smoke inhalation.

RESULTS

The results showed a significant increase in VEGF, iNOS, eNOS, nNOS, NKCC1, and GFAP expression in the bulb tissues, with corresponding increases in inflammatory cytokines and chemokines after smoke inhalation. Concurrent to this was a drastic increase in AQP4 expression and RITC permeability. Aminoguanidine administration decreased the expression of iNOS and RITC extravasation after smoke inhalation. This was coupled with a significant reduction in incidence of TUNEL + cells that was not altered with administration of L-NG-nitroarginine methyl ester (L-NAME).

CONCLUSIONS

These findings suggest that the upregulation of iNOS in response to smoke inhalation plays a major role in the olfactory bulb inflammatory pathophysiology, along with a concomitant increase in pro-inflammatory molecules, vascular permeability, and edema. Overall, these findings indicate that the olfactory bulb is vulnerable to smoke inhalation.

Induction of peroxiredoxin 1 by hypoxia regulates heme oxygenase-1 via NF-κB in oral cancer

Overexpression of peroxiredoxin 1 (Prx1) has been observed in numerous cancers including oral squamous cell carcinoma (OSCC). The precise molecular mechanism of up-regulation of Prx1 in carcinogenesis, however, is still poorly understood. The objective of this study is to investigate the relationship between Prx1 and hypoxia, and potential mechanism(s) of Prx1 in OSCC cell line SCC15 and xenograft model. We treated wild-type and Prx1 knockdown SCC15 cells with transient hypoxia followed by reoxygenation. We detected the condition of hypoxia, production of reactive oxygen species (ROS), and expression and/or activity of Prx1, heme oxygenase 1 (HO-1) and nuclear factor-kappa B (NF-κB). We found that hypoxia induces ROS accumulation, up-regulates Prx1, increases NF-κB translocation and DNA binding activity, and down-regulates HO-1 in vitro. In Prx1 knockdown cells, the expression level of HO-1 was increased, while NFκB translocation and DNA binding activity were decreased after hypoxia or hypoxia/reoxygenation treatment. Moreover, we mimicked the dynamic oxygenation tumor microenvironment in xenograft model and assessed the above indices in tumors with the maximal diameter of 2 mm, 5 mm, 10 mm or 15 mm, respectively. Our data showed that tumor hypoxic condition and expression of Prx1 are significantly associated with tumor growth. The expression of HO-1 and NF-κB, and NF-κB DNA binding activity were significantly elevated in 15 mm tumors, and the level of 8-hydroxydeoxyguanosine was increased in 10 mm and 15 mm tumors, compared to those in size of 2 mm. The results from this study provide experimental evidence that overexpression of Prx1 is associated with hypoxia, and Prx1/NF-κB/HO-1 signaling pathway may be involved in oral carcinogenesis.

Combustion smoke-induced inflammation in the cerebellum and hippocampus of adult rats

AIMS

The effect of combustion smoke inhalation on the respiratory system is widely reported but its effects on the central nervous system remain unclear. Here, we aimed to determine the effects of smoke inhalation on the cerebellum and hippocampus which are areas vulnerable to hypoxia injury.

METHODS

Adult male Sprague-Dawley rats were subjected to combustion smoke inhalation and sacrificed at 0.5, 3, 24 and 72 h after exposure. The cerebellum and hippocampus were subjected to Western analysis for VEGF, iNOS, eNOS, nNOS and AQP4 expression; ELISA analysis for cytokine and chemokine levels; and immunohistochemistry for GFAP/AQP4, RECA-1/RITC and TUNEL. Aminoguanidine (AG) was administered to determine the effects of iNOS after smoke inhalation.

RESULTS

Both the cerebellum and hippocampus showed a significant increase in VEGF, iNOS, eNOS, nNOS and AQP4 expression with corresponding increases in inflammatory cytokines and chemokines and increased AQP4 expression and RITC permeability after smoke exposure. AG was able to decrease the expression of iNOS, followed by VEGF, eNOS, nNOS, RITC and AQP4 after smoke exposure. There was also a significant increase in TUNEL+ cells in the cerebellum and hippocampus which were not significantly reduced by AG. Beam walk test revealed immediate deficits after smoke inhalation which was attenuated with AG.

CONCLUSION

The findings suggest that iNOS plays a major role in the central nervous system inflammatory pathophysiology after smoke inhalation exposure with concomitant increase in proinflammatory molecules, vascular permeability and oedema, for which the cerebellum appears to be more vulnerable to smoke exposure than the hippocampus.

Inhibition of interleukin-1β production by extracellular acidification through the TDAG8/cAMP pathway in mouse microglia

Interleukin-1β (IL-1β) is released from activated microglia and involved in the neurodegeneration of acute and chronic brain disorders, such as stroke and Alzheimer's disease, in which extracellular acidification has been shown to occur. Here, we examined the extracellular acidic pH regulation of IL-1β production, especially focusing on TDAG8, a major proton-sensing G-protein-coupled receptor, in mouse microglia. Extracellular acidification inhibited lipopolysaccharide -induced IL-1β production, which was associated with the inhibition of IL-1β cytoplasmic precursor and mRNA expression. The IL-1β mRNA and protein responses were significantly, though not completely, attenuated in microglia derived from TDAG8-deficient mice compared with those from wild-type mice. The acidic pH also stimulated cellular cAMP accumulation, which was completely inhibited by TDAG8 deficiency. Forskolin and a cAMP derivative, which specifically stimulates protein kinase A (PKA), mimicked the proton actions, and PKA inhibitors reversed the acidic pH-induced IL-1β mRNA expression. The acidic pH-induced inhibitory IL-1β responses were accompanied by the inhibition of extracellular signal-related kinase and c-Jun N-terminal kinase activities. The inhibitory enzyme activities in response to acidic pH were reversed by the PKA inhibitor and TDAG8 deficiency. We conclude that extracellular acidic pH inhibits lipopolysaccharide-induced IL-1β production, at least partly, through the TDAG8/cAMP/PKA pathway, by inhibiting extracellular signal-related kinase and c-Jun N-terminal kinase activities, in mouse microglia.

P2X4 receptors expressed on microglial cells in post-ischemic inflammation of brain ischemic injury

Post-ischemic inflammation is an essential step in the progression of brain ischemia injury. P2X4 receptors are the predominant purinergic P2X receptor subtypes expressed on immune and neural cells. The subtype traffic between intracellular compartments and the plasma membrane form protein interactions with each other to regulate ATP-dependent signaling. The P2X4 receptors expressed on microglial cells have been reported to be involved in the inflammatory response of many central nervous system diseases. However, the mechanism that activates microglial cells and the role of P2X4 receptor expressed in microglial cells in the ischemic brain remains to be clarified. Here we provide a review for understanding and exploring converging lines of evidence for involvement of P2X4 receptors expressed on microglial cells in the post-ischemic inflammation in the brain ischemic injury.

Glial modulators as potential treatments of psychostimulant abuse

Glia (including astrocytes, microglia, and oligodendrocytes), which constitute the majority of cells in the brain, have many of the same receptors as neurons, secrete neurotransmitters and neurotrophic and neuroinflammatory factors, control clearance of neurotransmitters from synaptic clefts, and are intimately involved in synaptic plasticity. Despite their prevalence and spectrum of functions, appreciation of their potential general importance has been elusive since their identification in the mid-1800s, and only relatively recently have they been gaining their due respect. This development of appreciation has been nurtured by the growing awareness that drugs of abuse, including the psychostimulants, affect glial activity, and glial activity, in turn, has been found to modulate the effects of the psychostimulants. This developing awareness has begun to illuminate novel pharmacotherapeutic targets for treating psychostimulant abuse, for which targeting more conventional neuronal targets has not yet resulted in a single, approved medication. In this chapter, we discuss the molecular pharmacology, physiology, and functional relationships that the glia have especially in the light in which they present themselves as targets for pharmacotherapeutics intended to treat psychostimulant abuse disorders. We then review a cross section of preclinical studies that have manipulated glial processes whose behavioral effects have been supportive of considering the glia as drug targets for psychostimulant-abuse medications. We then close with comments regarding the current clinical evaluation of relevant compounds for treating psychostimulant abuse, as well as the likelihood of future prospects.

S-nitrosylation: specificity, occupancy, and interaction with other post-translational modifications

SIGNIFICANCE

S-nitrosylation (SNO) has been identified throughout the body as an important signaling modification both in physiology and a variety of diseases. SNO is a multifaceted post-translational modification, in that it can either act as a signaling molecule itself or as an intermediate to other modifications.

RECENT ADVANCES AND CRITICAL ISSUES

Through extensive SNO research, we have made progress toward understanding the importance of single cysteine-SNO sites; however, we are just beginning to explore the importance of specific SNO within the context of other SNO sites and post-translational modifications. Additionally, compartmentalization and SNO occupancy may play an important role in the consequences of the SNO modification.

FUTURE DIRECTIONS

In this review, we will consider the context of SNO signaling and discuss how the transient nature of SNO, its role as an oxidative intermediate, and the pattern of SNO, should be considered when determining the impact of SNO signaling.

Microglia-derived proinflammatory cytokines tumor necrosis factor-alpha and interleukin-1beta induce Purkinje neuronal apoptosis via their receptors in hypoxic neonatal rat brain

The developing cerebellum is extremely vulnerable to hypoxia which can damage the Purkinje neurons. We hypothesized that this might be mediated by tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) derived from activated microglia as in other brain areas. One-day-old rats were subjected to hypoxia following, which the expression changes of various proteins in the cerebellum including hypoxia inducible factor-1α, TNF-α, IL-1β, TNF-R1 and IL-1R1 were analyzed. Following hypoxic exposure, TNF-α and IL-1β immunoexpression in microglia was enhanced coupled by that of TNF-R1 and IL-1R1 in the Purkinje neurons. Along with this, hypoxic microglia in vitro showed enhanced release of TNF-α and IL-1β whose receptor expression was concomitantly increased in the Purkinje neurons. In addition, nitric oxide (NO) level was significantly increased in the cerebellum and cultured microglia subjected to hypoxic exposure. Moreover, cultured Purkinje neurons treated with conditioned medium derived from hypoxic microglia underwent apoptosis but the incidence was significantly reduced when the cells were treated with the same medium that was neutralized with TNF-α/IL-1β antibody. We conclude that hypoxic microglia in the neonatal cerebellum produce increased amounts of NO, TNF-α and IL-1β which when acting via their respective receptors could induce Purkinje neuron death.

IκBα deficiency in brain leads to elevated basal neuroinflammation and attenuated response following traumatic brain injury: implications for functional recovery

Background

The transcription factor NFκB is an important mediator of cell survival and inflammation in the immune system. In the central nervous system (CNS), NFκB signaling has been implicated in regulating neuronal survival following acute pathologic damage such as traumatic brain injury (TBI) and stroke. NFκB is normally bound by the principal inhibitory protein, IκBα, and sequestered in the cytoplasm. Activation of NFκB requires the degradation of IκBα, thereby freeing NFκB to translocate to the nucleus and activate the target genes. Mice deficient in IκBα display deregulated and sustained NFκB activation and early postnatal lethality, highlighting a critical role of IκBα in NFκB regulation.

Results

We investigated the role of IκBα in regulating NFκB activity in the brain and the effects of the NFκB/IκBα pathway in mediating neuroinflammation under both physiological and brain injury conditions. We report that astrocytes, but not neurons, exhibit prominent NFκB activity, and that basal NFκB activity in astrocytes is elevated in the absence of IκBα. By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development. However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated. This leads to impaired inflammatory responses following TBI and worsened brain damage including higher blood brain barrier permeability, increased injury volumes and enlarged ventricle volumes.

Conclusions

We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation. We further demonstrate that IκBα plays an important role in regulating NFκB activity in the brain and a robust NFκB/IκBα-mediated neuroinflammatory response immediately following TBI is beneficial.

Intracerebral lipopolysaccharide induces neuroinflammatory change and augmented brain injury in growth-restricted neonatal rats

INTRODUCTION

Intrauterine growth restriction (IUGR) alters fetal development and is associated with neurodevelopmental abnormalities. We hypothesized that growth restriction from reduced intrauterine perfusion would predispose neonatal rats to subsequent inflammatory brain injury.

METHODS

In this study, IUGR was achieved by induced placental insufficiency in pregnant rats at 14 days of gestation. IUGR offspring and sham-operated control pups were subsequently injected with intracerebral lipopolysaccharide (LPS) as a model of periventricular leukomalacia (PVL).

RESULTS

LPS similarly elevates proinflammatory cytokines in the brains of both IUGR and control rat pups. However, the chemokines cytokine-induced neutrophil chemoattractant-1 (CINC-1) and macrophage chemoattractant protein-1 (MCP-1), as well as microglia activation, were significantly higher in LPS-treated IUGR rat pups as compared with LPS-treated controls. In addition to the unique brain inflammatory response, IUGR rat pups demonstrated increased brain damage with an increased number of apoptotic cells, larger lateral ventricular size, and more severe impairment of myelination.

DISCUSSION

This study provides evidence that placental insufficiency may sensitize the innate immune system in the immature brain and reveals a possible link between brain inflammation and injury.

In vivo regulation of the heme oxygenase-1 gene in humanized transgenic mice

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation producing equimolar amounts of carbon monoxide, iron, and biliverdin. Induction of HO-1 is a beneficial response to tissue injury in diverse animal models of diseases including acute kidney injury. In vitro analysis has shown that the human HO-1 gene is transcriptionally regulated by changes in chromatin conformation but whether such control occurs in vivo is not known. To enable such analysis, we generated transgenic mice, harboring an 87-kb bacterial artificial chromosome expressing human HO-1 mRNA and protein and bred these mice with HO-1 knockout mice to generate humanized BAC transgenic mice. This successfully rescued the phenotype of the knockout mice including reduced birth rates, tissue iron overload, splenomegaly, anemia, leukocytosis, dendritic cell abnormalities and survival after acute kidney injury induced by rhabdomyolysis or cisplatin nephrotoxicity. Transcription factors such as USF1/2, JunB, Sp1, and CTCF were found to associate with regulatory regions of the human HO-1 gene in the kidney following rhabdomyolysis. Chromosome Conformation Capture and ChIP-loop assays confirmed this in the formation of chromatin looping in vivo. Thus, these bacterial artificial chromosome humanized HO-1 mice are a valuable model to study the human HO-1 gene providing insight to the in vivo architecture of the gene in acute kidney injury and other diseases.

Roles of activated microglia in hypoxia induced neuroinflammation in the developing brain and the retina

Amoeboid microglial cells (AMCs) in the developing brain display surface receptors and antigens shared by the monocyte-derived tissue macrophages. Activation of AMCs in the perinatal brain has been associated with periventricular white matter damage in hypoxic-ischemic conditions. The periventricular white matter, where the AMCs preponderate, is selectively vulnerable to hypoxia as manifested by death of premyelinating oligodendrocytes and degeneration of axons leading to neonatal mortality and long-term neurodevelopmental deficits. AMCs respond vigorously to hypoxia by producing excess amounts of inflammatory cytokines e.g. the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) along with glutamate, nitric oxide (NO) and reactive oxygen species which collectively cause oligodendrocyte death, axonal degeneration as well as disruption of the immature blood brain barrier. A similar phenomenon is observed in the hypoxic developing cerebellum in which activated AMCs induced Purkinje neuronal death through production of TNF-α and IL-1β via their respective receptors. Hypoxia is also implicated in retinopathy of prematurity in which activation of AMCs has been shown to cause retinal ganglion cell death through production of TNF-α and IL-1β and NO. Because AMCs play a pivotal role in hypoxic injuries in the developing brain affecting both neurons and oligodendrocytes, a fuller understanding of the underlying molecular mechanisms of microglial activation under such conditions would be desirable for designing of a novel therapeutic strategy for management of hypoxic damage.

Nitric oxide production by endothelin-1 enhances astrocytic migration via the tyrosine nitration of matrix metalloproteinase-9

The deleterious effects of endothelin-1 (ET-1) in the central nervous system (CNS) include disturbance of water homeostasis and blood-brain barrier (BBB) integrity. In the CNS, ischemic injury elicits ET-1 release from astrocytes, behaving through G-protein coupled ET receptors. These considerations raise the question of whether ET-1 influences cellular functions of astrocytes, the major cell type that provides structural and functional support for neurons. Uncontrolled nitric oxide (NO) production has been implicated in sterile brain insults, neuroinflammation, and neurodegenerative diseases, which involve astrocyte activation and neuronal death. However, the detailed mechanisms of ET-1 action related to NO release on rat brain astrocytes (RBA-1) remain unknown. In this study, we demonstrate that exposure of astrocytes to ET-1 results in the inducible nitric oxide synthase (iNOS) up-regulation, NO production, and matrix metalloproteinase-9 (MMP-9) activation in astrocytes. The data obtained with Western blot, reverse transcription-PCR (RT-PCR), and immunofluorescent staining analyses showed that ET-1-induced iNOS expression and NO production were mediated through an ET(B)-dependent transcriptional activation. Engagement of G(i/o)--and G(q) -coupled ET(B) receptors by ET-1 led to activation of c-Src-dependent phosphoinositide 3-kinase (PI3K)/Akt and p42/p44 mitogen-activated protein kinase (MAPK) and then activated transcription factor nuclear factor-κB (NF-κB). The activated NF-κB was translocated into nucleus and thereby promoted iNOS gene transcription. Ultimately, NO production stimulated by ET-1 enhanced the migration of astrocytes through the tyrosine nitration of MMP-9. Taken together, these results suggested that in astrocytes, activation of NF-κB by ET(B)-dependent c-Src, PI3K/Akt, and p42/p44 MAPK signalings is necessary for ET-1-induced iNOS gene up-regulation.

JSH-23 targets nuclear factor-kappa B and reverses various deficits in experimental diabetic neuropathy: effect on neuroinflammation and antioxidant defence

AIM

Nuclear factor-kappa B (NF-κB) being reported to play an important role in the pathogenesis of diabetic neuropathy is believed to be a central mechanism involved in the genesis and promulgation of inflammatory insult. Here we have targeted the nuclear translocation of NF-κB using JSH-23 to elucidate its role in diabetic neuropathy.

METHODS

JSH-23 (1 and 3 mg/kg) was administered for 2 weeks in diabetic rats, after 6 weeks of diabetes induction using streptozotocin (55 mg/kg) as diabetogenic agent. Functional (motor nerve conduction velocity and blood flow), behavioural (mechanical hyperalgesia), biochemical [malondialdehyde, glutathione, tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels] and NF-κB translocation studies (western blot technique) were then undertaken.

RESULTS

JSH-23 treatment significantly reversed the nerve conduction and nerve blood flow deficits seen in diabetic animals. Reduction in mechanical pain threshold was also partially corrected by the treatment. Protein expression studies showed that nuclear translocation of p65/p50 subunit was inhibited by JSH-23 treatment in the sciatic nerve. The treatment also lowered the elevated IL-6, TNF-α, cyclo-oxygenase (COX-2) and inducible nitric oxide synthase (iNOS) levels/expression, indicating reduction in the inflammatory damage of the sciatic nerve. Apart from these effects, JSH-23 also increased Nrf2 and hemeoxygenase-1 (HO-1) levels which could imply its potential in increasing the strength of antioxidant defence.

CONCLUSION

We observed that NF-κB inhibition partially reversed functional, behavioural and biochemical deficits with JSH-23 treatment. This study substantiates the role of NF-κB activation in the aetiology of diabetic neuropathy and protection afforded by inhibition of NF-κB by JSH-23, which can be attributed to its effect on neuroinflammation and oxidative stress.

The anti-inflammatory effects of dimethyl fumarate in astrocytes involve glutathione and haem oxygenase-1

DMF (dimethyl fumarate) exerts anti-inflammatory and pro-metabolic effects in a variety of cell types, and a formulation (BG-12) is being evaluated for monotherapy in multiple sclerosis patients. DMF modifies glutathione (GSH) levels that can induce expression of the anti-inflammatory protein HO-1 (haem oxygenase-1). In primary astrocytes and C6 glioma cells, BG-12 dose-dependently suppressed nitrite production induced by either LI [LPS (lipopolysaccharide) at 1 μg/ml plus IFNγ (interferon γ) at 20 units/ml] or a mixture of pro-inflammatory cytokines, with greater efficacy in C6 cells. BG-12 reduced NOS2 (nitric oxide synthase 2) mRNA levels and activation of a NOS2 promoter, reduced nuclear levels of NF-κB (nuclear factor κB) p65 subunit and attenuated loss of IκBα (inhibitory κBα) in both cell types, although with greater effects in astrocytes. In astrocytes, LI decreased mRNA levels for GSHr (GSH reductase) and GCL (c-glutamylcysteine synthetase), and slightly suppressed GSHs (GSH synthetase) mRNAs. Co-treatment with BG-12 prevented those decreased and increased levels above control values. In contrast, LI reduced GSHp (GSH peroxidase) and GCL in C6 cells, and BG-12 had no effect on those levels. BG-12 increased nuclear levels of Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2), an inducer of GSH-related enzymes, in astrocytes but not C6 cells. In astrocytes, GSH was decreased by BG-12 at 2 h and increased at 24 h. Prior depletion of GSH using buthionine-sulfoximine increased the ability of BG-12 to reduce nitrites. In astrocytes, BG-12 increased HO-1 mRNA levels and effects on nitrite levels were blocked by an HO-1 inhibitor. These results demonstrate that BG-12 suppresses inflammatory activation in astrocytes and C6 glioma cells, but with distinct mechanisms, different dependence on GSH and different effects on transcription factor activation.

Cultured adult porcine astrocytes and microglia express functional interferon-γ receptors and exhibit toxicity towards SH-SY5Y cells

In vitro cultures of various glial cell types are common systems used to model neuroinflammatory processes associated with age-dependent human neurodegenerative diseases. Even though most researchers choose to use neonatal rodent brain tissues as the source of glial cells, there are significant variations in glial cell functions that are species and age dependent. It has been established that human and swine immune systems have a number of similarities, which suggests that cultured porcine microglia and astrocytes may be good surrogates for human glial cell types. Here we describe a method that could be used to prepare more than 90% pure microglia and astrocyte cultures derived from adult porcine tissues. We demonstrate that both microglia and astrocytes derived from adult porcine brains express functional interferon-γ receptors (IFN-γ-R) and CD14. They become toxic towards SH-SY5Y neuroblastoma cells when exposed to proinflammatory mediators. Upon such stimulation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ), adult porcine microglia, but not astrocytes, secrete tumor necrosis factor-α (TNF-α) while both cell types do not secrete detectable levels of nitric oxide (NO). Comparison of our experimental data with previously published studies indicates that adult porcine glial cultures have certain functional characteristics that make them similar to human glial cells. Therefore adult porcine glial cells may be a useful model system for studies of human diseases associated with adulthood and advanced age. Adult porcine tissues are relatively easy to obtain in most countries and could be used as a reliable and inexpensive source of cultured cells.

Microglia in ischemic brain injury

Microglia are resident CNS immune cells that are active sensors in healthy brain and versatile effectors under pathological conditions. Cerebral ischemia induces a robust neuroinflammatory response that includes marked changes in the gene-expression profile and phenotype of a variety of endogenous CNS cell types (astrocytes, neurons and microglia), as well as an influx of leukocytic cells (neutrophils, macrophages and T-cells) from the periphery. Many molecules and conditions can trigger a transformation of surveying microglia to microglia of an alerted or reactive state. Here we review recent developments in the literature that relate to microglial activation in the experimental setting of in vitro and in vivo ischemia. We also present new data from our own laboratory demonstrating the direct effects of in vitro ischemic conditions on the microglial phenotype and genomic profile. In particular, we focus on the role of specific molecular signaling systems, such as hypoxia inducible factor-1 and Toll-like receptor-4, in regulating the microglial response in this setting. We then review histological and novel radiological data that confirm a key role for microglial activation in the setting of ischemic stroke in humans. We also discuss recent progress in the pharmacologic and molecular targeting of microglia in acute ischemic stroke. Finally, we explore how recent studies on ischemic preconditioning have increased interest in pre-emptively targeting microglial activation in order to reduce stroke severity.

Hypoxia regulates iNOS expression in human normal peritoneal and adhesion fibroblasts through nuclear factor kappa B activation mechanism

OBJECTIVE

To determine the mechanism by which hypoxia increases expression of iNOS in human normal peritoneal and adhesion fibroblasts.

DESIGN

Prospective experimental study.

SETTING

University medical center.

PATIENT(S)

Primary cultures of fibroblasts from normal peritoneum and adhesion tissues.

INTERVENTION(S)

Hypoxia-treated cells.

MAIN OUTCOME MEASURE(S)

We used real-time reverse transcription-polymerase chain reaction to quantify mRNA levels of iNOS and nuclear factor kappa B (NF-kappaB). Western blots were used to determine iNOS, NF-kappaB, IkappaB-alpha, and phospho-IkappaB expression levels in normal peritoneal and adhesion fibroblasts in response to hypoxia.

RESULT(S)

Hypoxia resulted in a significant increase in iNOS and NF-kappaB expression in normal and adhesion fibroblasts. Furthermore, both cell types manifested lower levels of NF-kappaB, cytoplasmic phospho-IkappaB-alpha, and iNOS proteins. In contrast, they manifested higher levels of cytoplasmic IkappaB-alpha and IkappaB-alpha/NF-kappaB ratios as well as a phosphorylated-IkappaB-alpha/NF-kappaB ratio. Under hypoxic conditions, both cell types exhibited significantly decreased cytoplasmic NF-kappaB, IkappaB-alpha levels, and significantly increased cytoplasmic phospho-IkappaB-alpha, iNOS, and NF-kappaB protein levels.

CONCLUSION(S)

Hypoxia increases iNOS expression by a mechanism involving activation of NF-kappaB. The ratio of IkappaB-alpha/NF-kappaB or IkappaB-alpha/p-IkappaB-alpha can be used to monitor activation.

Tumor necrosis factor receptor 1 induces interleukin-6 upregulation through NF-kappaB in a rat neuropathic pain model

Peripheral nerve injury resulting in neuropathic pain induces the upregulation of interleukin (IL)-6 and tumor necrosis factor-alpha, which binds to tumor necrosis factor receptor 1 (TNFR1) and induces NF-kappaB and p38 MAPK activation in the spinal cord and dorsal root ganglia (DRG). We here investigated whether TNFR1 regulates IL-6 expression through NF-kappaB or p38 MAPK activations in the spinal cord and DRG in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal treatment with a TNFR1 antisense oligonucleotide (ASO) significantly inhibited CCI-elevated IKKs phosphorylation, IkB-alpha degradation, the nuclear translocation, phosphorylation, and DNA-binding activity of NF-kappaB, p38 MAPK activation, and IL-6 mRNA and protein expression in the spinal cord and DRG. Interestingly, CCI remarkably elevated IKKalpha and p65 phosphorylations in the spinal cord rather than in the DRG. In addition, NF-kappaB decoy, but not p38 MAPK inhibitor, SB203580 reduced CCI-elevated IL-6 expression in the spinal cord and DRG. Therefore, these data suggest that TNFR1 induces IL-6 upregulation and neuropathic pain through NF-kappaB, but not p38 MAPK activation in the spinal cord and DRG and that the NF-kappaB/IL-6 pathways in the DRG may be less dependent on TNFR1 than the spinal cord pathway.

The transcription factor Nrf2 is a therapeutic target against brain inflammation

Because chronic neuroinflammation is a hallmark of neurodegenerative diseases and compromises neuron viability, it is imperative to discover pharmacologic targets to modulate the activation of immune brain cells, the microglia. In this study, we identify the transcription factor Nrf2, guardian of redox homeostasis, as such target in a model of LPS-induced inflammation in mouse hippocampus. Nrf2 knockout mice were hypersensitive to the neuroinflammation induced by LPS, as determined by an increase in F4/80 mRNA and protein, indicative of an increase in microglial cells, and in the inflammation markers inducible NO synthase, IL-6, and TNF-alpha, compared with the hippocampi of wild-type littermates. The aliphatic isothiocyanate sulforaphane elicited an Nrf2-mediated antioxidant response in the BV2 microglial cell line, determined by flow cytometry of cells incubated with the redox sensitive probe dihydrodichlorofluorescein diacetate, and by the Nrf2-dependent induction of the phase II antioxidant enzyme heme oxygenase-1. Animals treated with sulforaphane displayed a 2-3-fold increase in heme oxygenase-1, a reduced abundance of microglial cells in the hippocampus and an attenuated production of inflammation markers (inducible NO synthase, IL-6, and TNF-alpha) in response to LPS. Considering that release of reactive oxygen species is a property of activated microglia, we propose a model in which late induction of Nrf2 intervenes in the down-regulation of microglia. This study opens the possibility of targeting Nrf2 in brain as a means to modulate neuroinflammation.

Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

Given that erythropoietin (EPO) is no longer believed to have exclusive biological activity in the hematopoietic system, EPO is now considered to have applicability in a variety of nervous system disorders that can overlap with vascular disease, metabolic impairments, and immune system function. As a result, EPO may offer efficacy for a broad number of disorders that involve Alzheimer's disease, cardiac insufficiency, stroke, trauma, and diabetic complications. During a number of clinical conditions, EPO is robust and can prevent metabolic compromise, neuronal and vascular degeneration, and inflammatory cell activation. Yet, use of EPO is not without its considerations especially in light of frequent concerns that may compromise clinical care. Recent work has elucidated a number of novel cellular pathways governed by EPO that can open new avenues to avert deleterious effects of this agent and offer previously unrecognized perspectives for therapeutic strategies. Obtaining greater insight into the role of EPO in the nervous system and elucidating its unique cellular pathways may provide greater cellular viability not only in the nervous system but also throughout the body.

Erythropoietin and oxidative stress

Unmitigated oxidative stress can lead to diminished cellular longevity, accelerated aging, and accumulated toxic effects for an organism. Current investigations further suggest the significant disadvantages that can occur with cellular oxidative stress that can lead to clinical disability in a number of disorders, such as myocardial infarction, dementia, stroke, and diabetes. New therapeutic strategies are therefore sought that can be directed toward ameliorating the toxic effects of oxidative stress. Here we discuss the exciting potential of the growth factor and cytokine erythropoietin for the treatment of diseases such as cardiac ischemia, vascular injury, neurodegeneration, and diabetes through the modulation of cellular oxidative stress. Erythropoietin controls a variety of signal transduction pathways during oxidative stress that can involve Janus-tyrosine kinase 2, protein kinase B, signal transducer and activator of transcription pathways, Wnt proteins, mammalian forkhead transcription factors, caspases, and nuclear factor kappaB. Yet, the biological effects of erythropoietin may not always be beneficial and may be poor tolerated in a number of clinical scenarios, necessitating further basic and clinical investigations that emphasize the elucidation of the signal transduction pathways controlled by erythropoietin to direct both successful and safe clinical care.

Triple play: promoting neurovascular longevity with nicotinamide, WNT, and erythropoietin in diabetes mellitus

Oxidative stress is a principal pathway for the dysfunction and ultimate destruction of cells in the neuronal and vascular systems for several disease entities, not promoting the ravages of oxidative stress to any less of a degree than diabetes mellitus. Diabetes mellitus is increasing in incidence as a result of changes in human behavior that relate to diet and daily exercise and is predicted to affect almost 400 million individuals worldwide in another two decades. Furthermore, both type 1 and type 2 diabetes mellitus can lead to significant disability in the nervous and cardiovascular systems, such as cognitive loss and cardiac insufficiency. As a result, innovative strategies that directly target oxidative stress to preserve neuronal and vascular longevity could offer viable therapeutic options to diabetic patients in addition to more conventional treatments that are designed to control serum glucose levels. Here we discuss the novel application of nicotinamide, Wnt signaling, and erythropoietin that modulate cellular oxidative stress and offer significant promise for the prevention of diabetic complications in the nervous and vascular systems. Essential to this process is the precise focus upon diverse as well as common cellular pathways governed by nicotinamide, Wnt signaling, and erythropoietin to outline not only the potential benefits, but also the challenges and possible detriments of these therapies. In this way, new avenues of investigation can hopefully bypass toxic complications, or at the very least, avoid contraindications that may limit care and offer both safe and robust clinical treatment for patients.

The Wnt signaling pathway: aging gracefully as a protectionist?

No longer considered to be exclusive to cellular developmental pathways, the Wnt family of secreted cysteine-rich glycosylated proteins has emerged as versatile targets for a variety of conditions that involve cardiovascular disease, aging, cancer, diabetes, neurodegeneration, and inflammation. In particular, modulation of Wnt signaling may fill a critical void for the treatment of disorders that impact upon both cellular survival and cellular longevity. Yet, in some scenarios, Wnt signaling can become the catalyst for disease development or promote cell senescence that can compromise clinical utility. This double edge sword in regards to the role of Wnt and its signaling pathways highlights the critical need to further elucidate the cellular mechanisms governed by Wnt in conjunction with the development of robust pharmacological ligands that may open new avenues for disease treatment. Here we discuss the influence of the Wnt pathway during cell survival, metabolism, and aging in order for one to gain a greater insight for the novel role of Wnt signaling as well as exemplify its unique cellular pathways that influence both normal physiology and disease.

Amoeboid microglia in the periventricular white matter induce oligodendrocyte damage through expression of proinflammatory cytokines via MAP kinase signaling pathway in hypoxic neonatal rats

Hypoxic injury in the perinatal period results in periventricular white matter (PWM) lesions with axonal damage and oligodendroglial loss. It also alters macrophage function by perpetuating expression of inflammatory mediators. Relevant to this is the preponderance of amoeboid microglial cells (AMC) characterized as active macrophages in the developing PWM. This study aimed to determine if AMC produce proinflammatory cytokines that may be linked to the oligodendroglial loss observed in hypoxic PWM damage (PWMD). Wistar rats (1 day old) were subjected to hypoxia, following which upregulated expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), TNF receptor 1 (TNF-R(1)) and IL-1 receptor 1 (IL-1R(1)) was observed. This was coupled with apoptosis and expression of TNF-R(1) and IL-1R(1) in oligodendrocytes. Primary cultured microglial cells subjected to hypoxia (3% oxygen, 5% CO(2) and 92% nitrogen) showed enhanced expression of TNF-alpha and IL-1beta. Furthermore, mitogen-activated protein (MAP) kinase signaling pathway was involved in the expression of TNF-alpha and IL-1beta in microglia subjected to hypoxia. Our results suggest that following a hypoxic insult, microglial cells in the neonatal rats produce inflammatory cytokines such as TNF-alpha and IL-1beta via MAP kinase signaling pathway. These cytokines are detrimental to oligodendrocytes resulting in PWM lesion.

What is the present pathogenetic concept of glaucomatous optic neuropathy?

Glaucomatous optic neuropathy implies loss of neural tissue, activation of glial cells, tissue remodeling, and change of blood flow. The blood flow reduction is not only secondary but has a primary component. Activation of astrocytes leads to an altered microenvironment. An unstable ocular perfusion, either due to IOP fluctuation or a disturbed autoregulation (due to primary vascular dysregulation syndrome) leads to a mild reperfusion injury. The superoxide (O(2)(-)) anion produced in the mitochondria of the axons, fuses with the nitric oxide (NO) diffusing from the astrocytes, leading to the damaging peroxynitrite (ONOO(-)). It is possible that the diffusion of endothelin and metalloproteinases to the surrounding of the optic nerve head leads to a local vasoconstriction and thereby increases the risk for venous occlusion and weakens the blood-brain barrier, which in extreme situations results in splinter hemorrhages. Activated retinal astrocytes can be visualized clinically. The involvement of primary vascular dysregulation in the pathogenesis of glaucomatous optic neuropathy may explain why women, as well as Japanese, suffer more often from normal-tension glaucoma.

The Src homology 2 domain tyrosine phosphatases SHP-1 and SHP-2: diversified control of cell growth, inflammation, and injury

Interest in the diverse biology of protein tyrosine phosphatases that are encoded by more than 100 genes in the human genome continues to grow at an accelerated pace. In particular, two cytoplasmic protein tyrosine phosphatases composed of two Src homology 2 (SH2) NH2-terminal domains and a C-terminal protein-tyrosine phosphatase domain referred to as SHP-1 and SHP-2 are known to govern a host of cellular functions. SHP-1 and SHP-2 modulate progenitor cell development, cellular growth, tissue inflammation, and cellular chemotaxis, but more recently the role of SHP-1 and SHP-2 to directly control cell survival involving oxidative stress pathways has come to light. SHP-1 and SHP-2 are fundamental for the function of several growth factor and metabolic pathways yielding far reaching implications for disease pathways and disorders such as diabetes, neurodegeneration, and cancer. Although SHP-1 and SHP-2 can employ similar or parallel cellular pathways, these proteins also clearly exert opposing effects upon downstream cellular cascades that affect early and late apoptotic programs. SHP-1 and SHP-2 modulate cellular signals that involve phosphatidylinositol 3-kinase, Akt, Janus kinase 2, signal transducer and activator of transcription proteins, mitogen-activating protein kinases, extracellular signal-related kinases, c-Jun-amino terminal kinases, and nuclear factor-kappaB. Our progressive understanding of the impact of SHP-1 and SHP-2 upon multiple cellular environments and organ systems should continue to facilitate the targeted development of treatments for a variety of disease entities.

p38alpha MAP kinase mediates hypoxia-induced motor neuron cell death: a potential target of minocycline's neuroprotective action

Hypoxia-ischemia (HI) may play a significant role in motor neuron death associated with the pathology of spinal cord injury and, perhaps, amyotrophic lateral sclerosis. The present study employs an in vitro model of HI to investigate the role of a stress kinase pathway, i.e., p38 MAP kinase, in cell death signaling in a motor neuron cell line, i.e., NSC34, subjected to oxygen-glucose deprivation (OGD). Although the neurons were essentially tolerant to either hypoxia (0.2% O(2)) or low glucose (1 mM) alone, more than 60% of them died in response to combined low oxygen and low-glucose exposure. Minocycline, a semi-synthetic tetracycline known for its neuroprotective effects in models of neurodegeneration, afforded substantial (approximately 50%) protection against hypoxic cell death, assessed by lactate dehydrogenase release and flow cytometry, while suppressing OGD-induced p38 MAP kinase activation. An inhibitor of p38 kinase, SB203580, as well as siRNA-mediated down-regulation of p38 kinase elicited an almost complete blockade of OGD-induced cell death. The use of p38 isoform-specific siRNAs further revealed preferential involvement of the alpha over the beta isoform of p38 MAP kinase in hypoxic neuronal cell death in our model.

Glutathione supplementation potentiates hypoxic apoptosis by S-glutathionylation of p65-NFkappaB

In murine embryonic fibroblasts, N-acetyl-L-cysteine (NAC), a GSH generating agent, enhances hypoxic apoptosis by blocking the NFkappaB survival pathway (Qanungo, S., Wang, M., and Nieminen, A. L. (2004) J. Biol. Chem. 279, 50455-50464). Here, we examined sulfhydryl modifications of the p65 subunit of NFkappaB that are responsible for NFkappaB inactivation. In MIA PaCa-2 pancreatic cancer cells, hypoxia increased p65-NFkappaB DNA binding and NFkappaB transactivation by 2.6- and 2.8-fold, respectively. NAC blocked these events without having an effect on p65-NFkappaB protein levels and p65-NFkappaB nuclear translocation during hypoxia. Pharmacological inhibition of the NFkappaB pathway also induced hypoxic apoptosis, indicating that the NFkappaB signaling pathway is a major protective mechanism against hypoxic apoptosis. In cell lysates after hypoxia and treatment with N-ethylmaleimide (thiol alkylating agent), dithiothreitol (disulfide reducing agent) was not able to increase binding of p65-NFkappaB to DNA, suggesting that most sulfhydryls in p65-NFkappaB protein were in reduced and activated forms after hypoxia, thereby being blocked by N-ethylmaleimide. In contrast, with hypoxic cells that were also treated with NAC, dithiothreitol increased p65-NFkappaB DNA binding. Glutaredoxin (GRx), which specifically catalyzes reduction of protein-SSG mixed disulfides, reversed inhibition of p65-NFkappaB DNA binding in extracts from cells treated with hypoxia plus NAC and restored NFkappaB activity. This finding indicated that p65-NFkappaB-SSG was formed in situ under hypoxia plus NAC conditions. In cells, knock-down of endogenous GRx1, which also promotes protein glutathionylation under hypoxic radical generating conditions, prevented NAC-induced NFkappaB inactivation and hypoxic apoptosis. The results indicate that GRx-dependent S-glutathionylation of p65-NFkappaB is most likely responsible for NAC-mediated NFkappaB inactivation and enhanced hypoxic apoptosis.