Hypoxia differentially regulates the expression of neuroglobin and cytoglobin in rat brain

Transcriptomics of a cytoglobin knockout mouse: Insights from hepatic stellate cells and brain

The vertebrate respiratory protein cytoglobin (Cygb) is thought to exert multiple cellular functions. Here we studied the phenotypic effects of a Cygb knockout (KO) in mouse on the transcriptome level. RNA sequencing (RNA-Seq) was performed for the first time on sites of major endogenous Cygb expression, i.e. quiescent and activated hepatic stellate cells (HSCs) and two brain regions, hippocampus and hypothalamus. The data recapitulated the up-regulation of Cygb during HSC activation and its expression in the brain. Differential gene expression analyses suggested a role of Cygb in the response to inflammation in HSCs and its involvement in retinoid metabolism, retinoid X receptor (RXR) activation-induced xenobiotics metabolism, and RXR activation-induced lipid metabolism and signaling in activated cells. Unexpectedly, only minor effects of the Cygb KO were detected in the transcriptional profiles in hippocampus and hypothalamus, precluding any enrichment analyses. Furthermore, the transcriptome data pointed at a previously undescribed potential of the Cygb- knockout allele to produce cis-acting effects, necessitating future verification studies.

Neuronal Cytoglobin in the Auditory Brainstem of Rat and Mouse: Distribution, Cochlear Projection, and Nitric Oxide Production

Cytoglobin (Cygb), a hemoprotein of the globin family, is expressed in the supportive tissue cells of the fibroblast lineage and in distinct neuronal cell populations. The expression pattern and regulatory parameters of fibroblasts and related cells were studied in organs such as the kidney and liver in a variety of animal models. In contrast, knowledge about cytoglobin-expressing neurons is sparse. Only a few papers described the distribution in the brain as ubiquitous with a restricted number of neurons in focal regions. Although there is evidence for cytoglobin involvement in neuronal hypoxia tolerance, its presence in the auditory system was not studied despite high metabolism rates and oxygen demands of the cochlea and related brainstem centers. In a continuation of a previous study demonstrating Cygb-neurons in, inter alia, auditory regions of the mouse brain, we concentrated on the superior olivary complex (SOC) in the present study. We sought to investigate the distribution, projection pattern and neurochemistry of Cygb-neurons in the SOC. We conducted immunohistochemistry using a Cygb antibody and found that this brainstem region, functionally competent for bilateral hearing and providing cochlear hair cell innervation, contains a considerable number of Cygb-expressing neurons (averaging 2067 ± 211 making up 10 ±1% percent of total neuron number) in rats, and 514 ± 138 (6 ± 1%) in mice. They were observed in all regions of the SOC. Retrograde neuronal tract tracing with Fluorogold injected into the cochlea demonstrated that 1243 ± 100 (6 ± 1% of total neuron number in rat SOC)) were olivocochlear neurons. Approximately 56% of total Cygb neurons were retrogradely labelled, while the majority of olivocochlear neurons of both lateral and medial systems were Cygb-immunoreactive. We also conducted double immunofluorescence staining for Cygb and neuronal nitric oxide synthase (nNOS), the enzyme responsible for nitric oxide production, and observed that cytoglobin in the SOC frequently co-localized with nNOS. Our findings suggest that cytoglobin plays an important physiologic role in the oxygen homeostasis of the peripheral and central auditory nervous system. Further studies, also including transgenic animal models, are required to shed more light on the function(s) of Cygb in neurons, in particular of the auditory system.

Cognitive Deficits Are Attenuated in Neuroglobin Overexpressing Mice Exposed to a Model of Obstructive Sleep Apnea

Background: Obstructive sleep apnea (OSA) is a highly prevalent disease manifesting as intermittent hypoxia during sleep (IH) and is increasingly recognized as being independently associated with neurobehavioral deficits. These deficits may be due to increased apoptosis in the hippocampus and cerebral cortex, as well as increased oxidative stress and inflammation. It has been reported that neuroglobin (Ngb) is upregulated in response to hypoxia-ischemia insults and exhibits a protective role in ischemia-reperfusion brain injury. We hypothesized that transgenic overexpression of Ngb would attenuate spatial learning deficits in a murine model of OSA.

Methods:Wild-type mice and Ngb overexpressing male mice (Ngb-TG) were randomly assigned to either IH or room air (RA) exposures. The effects of IH during the light period on performance in a water maze spatial task were assessed, as well as anxiety and depressive-like behaviors using elevated plus maze (EPM) and forced swim tests. Cortical tissues from all the mice were extracted for biochemical studies for lipid peroxidation.

Results:Ngb TG mice exhibited increased Ngb immunoreactivity in brain tissues and IH did not elicit significant changes in Ngb expression in either Ngb-TG mice or WT mice. On a standard place training task in the water maze, Ngb-TG mice displayed preserved spatial learning, and were protected from the reduced spatial learning performances observed in WT mice exposed to IH. Furthermore, anxiety and depression levels were enhanced in WT mice exposed to IH as compared to RA controls, while alterations emerged in Ngb-TG mice exposed to IH. Furthermore, WT mice, but not Ngb-TG mice had significantly elevated levels of malondialdehyde in cortical lysates following IH exposures.

Conclusions:In a murine model of OSA, oxidative stress responses and neurocognitive and behavioral impairments induced by IH during sleep are attenuated by the neuroprotective effects of Ngb.

Mitochondria targeting by environmental stressors: Implications for redox cellular signaling

Mitochondria are cellular powerhouses as well as metabolic and signaling hubs regulating diverse cellular functions, from basic physiology to phenotypic fate determination. It is widely accepted that reactive oxygen species (ROS) generated in mitochondria participate in the regulation of cellular signaling, and that some mitochondria chronically operate at a high ROS baseline. However, it is not completely understood how mitochondria adapt to persistently high ROS states and to environmental stressors that disturb the redox balance. Here we will review some of the current concepts regarding how mitochondria resist oxidative damage, how they are replaced when excessive oxidative damage compromises function, and the effect of environmental toxicants (i.e. heavy metals) on the regulation of mitochondrial ROS (mtROS) production and subsequent impact.

Brain globins in physiology and pathology

Globins are globular proteins for either transport or storage of oxygen which are critical for cellular metabolism. Four globins have been identified in rodent and human brains. Among them, neuroglobin, cytoglobin and hemoglobin chains are constitutively expressed in normal brain, while myoglobin is only expressed in some neurological disorders. Studies on the molecular structure, expression and functional features of these brain globins indicated that they may play crucial roles in maintenance of neural cell survival and activity, including neurons and astrocytes. Their regulation in neurological disorders may help thoroughly understand initiation and progression of ischemia, Alzheimer's disease and glioma, etc. Elucidation of the brain globin functions might remarkably improve medical strategies that sustain neurological homeostasis and treat neurological diseases. Here the expression pattern and functions of brain globins and their involvement in neurological disorders are reviewed.

Neuroglobin in Breast Cancer Cells: Effect of Hypoxia and Oxidative Stress on Protein Level, Localization, and Anti-Apoptotic Function

The over-expression of human neuroglobin (NGB), a heme-protein preferentially expressed in the brain, displays anti-apoptotic effects against hypoxic/ischemic and oxidative stresses enhancing neuron survival. As hypoxic and oxidative stress injury frequently occurs in fast proliferating neoplastic tissues, here, the effect of these stressors on the level, localization, and anti-apoptotic function of NGB in wild type and NGB-stable-silenced MCF-7 breast cancer cells has been assessed. The well-known endogenous NGB inducer 17β-estradiol (E2) has been used as positive control. The median pO2 present in tumor microenvironment of breast cancer patients (i.e., 2% O₂) does not affect the NGB level in breast cancer cells, whereas hydrogen peroxide and lead(IV) acetate, which increase intracellular reactive oxygen species (ROS) level, enhance the NGB levels outside the mitochondria and still activate apoptosis. However, E2-induced NGB up-regulation in mitochondria completely reverse lead(IV) acetate-induced PARP cleavage. These results indicate that the NGB level could represent a marker of oxidative-stress in MCF-7 breast cancer cells; however, the NGB ability to respond to injuring stimuli by preventing apoptosis requires its re-allocation into the mitochondria. As a whole, present data might lead to a new direction in understanding NGB function in cancer opening new avenues for the therapeutic intervention.

Distribution of Cytoglobin in the Mouse Brain

Cytoglobin (Cygb) is a vertebrate globin with so far poorly defined function. It is expressed in the fibroblast cell-lineage but has also been found in neurons. Here we provide, using immunohistochemistry, a detailed study on the distribution of Cygb in the mouse brain. While Cygb is a cytoplasmic protein in active cells of the supportive tissue, in neurons it is located in the cytoplasm and the nucleus. We found the expression of Cygb in all brain regions, although only a fraction of the neurons was Cygb-positive. Signals were of different intensity ranging from faint to very intense. Telencephalic neurons in all laminae of the cerebral cortex (CCo), in the olfactory bulb (in particular periglomerular cells), in the hippocampal formation (strongly stained pyramidal cells with long processes), basal ganglia (scattered multipolar neurons in the dorsal striatum, dorsal and ventral pallidum (VP)), and in the amygdala (neurons with unlabeled processes) were labeled by the antibody. In the diencephalon, we observed Cygb-positive neurons of moderate intensity in various nuclei of the dorsal thalamus, in the hypothalamus, metathalamus (geniculate nuclei), epithalamus with strong labeling of habenular nucleus neurons and no labeling of pineal cells, and in the ventral thalamus. Tegmental neurons stood out by strongly stained somata with long processes in, e.g., the laterodorsal nucleus. In the tectum, faintly labeled neurons and fibers were detected in the superior colliculus (SC). The cerebellum exhibited unlabeled Purkinje-neurons but signs of strong afferent cortical innervation. Neurons in the gray matter of the spinal cord showed moderate immunofluorescence. Peripheral ganglia were not labeled by the antibody. The Meynert-fascicle and the olfactory and optic nerves/tracts were the only Cygb-immunoreactive (Cygb-IR) fiber systems. Notably, we found a remarkable level of colocalization of Cygb and neuronal nitric oxide (NO)-synthase in neurons, which supports a functional association.

Synaptosomal lactate dehydrogenase isoenzyme composition is shifted toward aerobic forms in primate brain evolution

With the evolution of a relatively large brain size in haplorhine primates (i.e. tarsiers, monkeys, apes, and humans), there have been associated changes in the molecular machinery that delivers energy to the neocortex. Here we investigated variation in lactate dehydrogenase (LDH) expression and isoenzyme composition of the neocortex and striatum in primates using quantitative Western blotting and isoenzyme analysis of total homogenates and synaptosomal fractions. Analysis of isoform expression revealed that LDH in synaptosomal fractions from both forebrain regions shifted towards a predominance of the heart-type, aerobic isoform LDH-B among haplorhines as compared to strepsirrhines (i.e. lorises and lemurs), while in the total homogenate of the neocortex and striatum there was no significant difference in LDH isoenzyme composition between the primate suborders. The largest increase occurred in synapse-associated LDH-B expression in the neocortex, with an especially remarkable elevation in the ratio of LDH-B/LDH-A in humans. The phylogenetic variation in the ratio of LDH-B/LDH-A was correlated with species-typical brain mass but not the encephalization quotient. A significant LDH-B increase in the subneuronal fraction from haplorhine neocortex and striatum suggests a relatively higher rate of aerobic glycolysis that is linked to synaptosomal mitochondrial metabolism. Our results indicate that there is a differential composition of LDH isoenzymes and metabolism in synaptic terminals that evolved in primates to meet increased energy requirements in association with brain enlargement.

17β-Oestradiol anti-inflammatory effects in primary astrocytes require oestrogen receptor β-mediated neuroglobin up-regulation

Neuroglobin (Ngb), so named after its initial discovery in brain neurones, has received great attention as a result of its neuroprotective effects both in vitro and in vivo. Recently, we demonstrated that, in neurones, Ngb is a 17β-oestradiol (E(2) ) inducible protein that is pivotal for hormone-induced anti-apoptotic effects against H(2) O(2) toxicity. The involvement of Ngb in other brain cell populations, as well as in other neuroprotective effects of E(2) , is completely unknown at present. We demonstrate Ngb immunoreactivity in reactive astrocytes located in the proximity of a penetrating cortical injury in vivo and the involvement of Ngb in the E(2) -mediated anti-inflammatory effect in primary cortical astrocytes. Upon binding to oestrogen receptor (ER)β, E(2) enhances Ngb levels in a dose-dependent manner. Although with a lesser degree than E(2) , the pro-inflammatory stimulation with lipopolysaccharide (LPS) also induces the increase of Ngb protein levels via nuclear factor-(NF)κB signal(s). Moreover, a negative cross-talk between ER subtypes and NFκB signal(s) has been demonstrated. In particular, ERα-activated signals prevent the NFκB-mediated Ngb increase, whereas LPS impairs the ERβ-induced up-regulation of Ngb. Therefore, the co-expression of both ERα and ERβ is pivotal for mediating E(2) -induced Ngb expression in the presence of NFκB-activated signals. Interestingly, Ngb silencing prevents the effect of E(2) on the expression of inflammatory markers (i.e. interleukin 6 and interferon γ-inducible protein 10). Ngb can be regarded as a key mediator of the different protective effects of E(2) in the brain, including protection against oxidative stress and the control of inflammation, both of which are at the root of several neurodegenerative diseases.

Hypoxia and hypoxia mimetics decrease aquaporin 5 (AQP5) expression through both hypoxia inducible factor-1α and proteasome-mediated pathways

The alveolar epithelium plays a central role in gas exchange and fluid transport, and is therefore critical for normal lung function. Since the bulk of water flux across this epithelium depends on the membrane water channel Aquaporin 5 (AQP5), we asked whether hypoxia had any effect on AQP5 expression. We show that hypoxia causes a significant (70%) decrease in AQP5 expression in the lungs of mice exposed to hypoxia. Hypoxia and the hypoxia mimetic, cobalt, also caused similar decreases in AQP5 mRNA and protein expression in the mouse lung epithelial cell line MLE-12. The action of hypoxia and cobalt on AQP5 transcription was demonstrated by directly quantifying heternonuclear RNA by real-time PCR. Dominant negative mutants of Hypoxia Inducible Factor (HIF-1α) and HIF-1α siRNA blocked the action of cobalt, showing that HIF-1α is a key component in this mechanism. The proteasome inhibitors, lactacystin or proteasome inhibitor-III completely abolished the effect of hypoxia and cobalt both at the protein and mRNA level indicating that the proteasome pathway is probably involved not only for the stability of HIF-1α protein, but for the stability of unidentified transcription factors that regulate AQP5 transcription. These studies reveal a potentially important physiological mechanism linking hypoxic stress and membrane water channels.

The anti-apoptotic role of neuroglobin

The small heme-protein neuroglobin is expressed at high concentrations in certain brain neurons and in the rod cells of the retina. This paper reviews the many studies which have recently identified a protective role for neuroglobin, in a wide range of situations involving apoptotic cell death. The origins of this protective mechanism are discussed in terms of both experimental results and computational modeling of the intrinsic pathway of apoptosis, which shows that neuroglobin can intervene in this process by a reaction with released mitochondrial cytochrome c. An integrated model, based on the various molecular actions of both neuroglobin and cytochrome c, is developed, which accounts for the cellular distribution of neuroglobin.

Effect of permanent middle cerebral artery occlusion on Cytoglobin expression in the mouse brain

Cytoglobin, a new member of the mammalian heme-globin family has been shown to bind oxygen and to have cell protective properties in vitro. Cytoglobin is specifically expressed in a subpopulation of brain neurons. Based on hypoxia-induced up regulation and proposed scavenging of reactive oxygen species Cytoglobin was suggested as a candidate for pharmaceutical stroke treatment. Since production of reactive oxygen species is a hallmark of ischemia, we hypothesized that Cytoglobin expression would be increased and that Cytoglobin expressing neurons would be spared after ischemic injury. Twenty male C57BL/6J mice were used in the experimental design. Ten were sham operated and ten were given permanent middle cerebral artery occlusion (pMCAo). All animals were euthanized after 24h. From each group, three animals were used for histology and seven for QRT-PCR and western blotting. Immunohistochemical examination of the ischemic penumbra revealed neither changes in Cytoglobin immunoreactivity nor any changes in expression in the necrotic infarct area. The lack of expression change was confirmed by western blotting and QRT-PCR showing no significant difference between sham and pMCAo operated mice. This suggests that Cytoglobin is likely not important for global neuronal protection following ischemia and the role of Cytoglobin in relation to endogenous neuroprotection remains unresolved.

Neuroglobin, a novel target for endogenous neuroprotection against stroke and neurodegenerative disorders

Brain neurons and tissues respond to sublethal injury by activating endogenous protective pathways. Recently, following the failure of a large number of clinical trials for protective strategies against stroke that aim to inhibit a specific ischemia response pathway, endogenous neuroprotection has emerged as a more promising and hopeful strategy for development of therapeutics against stroke and neurodegenerative disorders. Neuroglobin (Ngb) is an oxygen-binding globin protein that is highly and specifically expressed in brain neurons. Accumulating evidence have clearly demonstrated that Ngb is an endogenous neuroprotective molecule against hypoxic/ischemic and oxidative stress-related insults in cultured neurons and animals, as well as neurodegenerative disorders such as Alzheimer’s disease, thus any pharmacological strategy that can up-regulate endogenous Ngb expression may lead to novel therapeutics against these brain disorders. In this review, we summarize recent studies about the biological function, regulation of gene expression, and neuroprotective mechanisms of Ngb. Furthermore, strategies for identification of chemical compounds that can up-regulate endogenous Ngb expression for neuroprotection against stroke and neurodegenerative disorders are discussed.

Levels of neuroglobin in serum and neurocognitive impairments in Chinese patients with obstructive sleep apnea

PURPOSE

The impact of different severities of obstructive sleep apnea (OSA) on cognition has not well been documented. Neuroglobin, a recently discovered vertebrate protein, shows a neuroprotective function to modulate hypoxic-ischemic brain injury. This study investigated the cognitive function of patients with varying OSA severities and intended to explore the relationship between levels of neuroglobin in serum and cognitive deficits of OSA.

METHODS

Sixty Chinese adults aged 18-59 years old were enrolled and categorized into four groups based on apnea-hypopnea index (AHI): primary snoring (n = 7), mild (n = 13), moderate (n = 20), and severe (n = 20) OSA groups. Computer-based neurocognitive tests (including calculation, memory, and attention) and Epworth sleepiness scale were administered before polysomnographic monitoring, and blood sample was taken the next morning. Concentrations of serum neuroglobin were measured using ELISA.

RESULTS

No significant difference was observed in cognitive function regardless of OSA severities, but patients with moderate and severe OSA presented significantly more sleepiness than patients with primary snoring and mild OSA. Memory significantly correlated with time spent with oxygen saturation below 90 % during nighttime (T < 90 %), as well as oxygen desaturation index, AHI, or NREM sleep. Calculation correlated significantly with sleepiness and respiratory arousal index. Levels of neuroglobin in serum of patients with varying OSA severities were significant elevated than that of patients with primary snoring. No relationship was found between the neurobehavioral ability index of neurocognitive tests and serum neuroglobin concentrations after controlling for gender, age, and BMI, whereas the unique association between levels of neuroglobin in serum and the scores of auditory digit span test was noted.

CONCLUSIONS

Our findings suggest that different neurocognitive domains might specifically correlate to either sleepiness or hypoxemia. Changes of concentrations of neuroglobin in serum may possibly be used as an indicator to monitor the brain damage of OSA. Further investigations are needed to explore the relationship between regulation of neuroglobin in serum and severity of brain damage in OSA.

Neuroglobin-deficiency exacerbates Hif1A and c-FOS response, but does not affect neuronal survival during severe hypoxia in vivo

BACKGROUND

Neuroglobin (Ngb), a neuron-specific globin that binds oxygen in vitro, has been proposed to play a key role in neuronal survival following hypoxic and ischemic insults in the brain. Here we address whether Ngb is required for neuronal survival following acute and prolonged hypoxia in mice genetically Ngb-deficient (Ngb-null). Further, to evaluate whether the lack of Ngb has an effect on hypoxia-dependent gene regulation, we performed a transcriptome-wide analysis of differential gene expression using Affymetrix Mouse Gene 1.0 ST arrays. Differential expression was estimated by a novel data analysis approach, which applies non-parametric statistical inference directly to probe level measurements.

PRINCIPAL FINDINGS

Ngb-null mice were born in expected ratios and were normal in overt appearance, home-cage behavior, reproduction and longevity. Ngb deficiency had no effect on the number of neurons, which stained positive for surrogate markers of endogenous Ngb-expressing neurons in the wild-type (wt) and Ngb-null mice after 48 hours hypoxia. However, an exacerbated hypoxia-dependent increase in the expression of c-FOS protein, an immediate early transcription factor reflecting neuronal activation, and increased expression of Hif1A mRNA were observed in Ngb-null mice. Large-scale gene expression analysis identified differential expression of the glycolytic pathway genes after acute hypoxia in Ngb-null mice, but not in the wts. Extensive hypoxia-dependent regulation of chromatin remodeling, mRNA processing and energy metabolism pathways was apparent in both genotypes.

SIGNIFICANCE

According to these results, it appears unlikely that the loss of Ngb affects neuronal viability during hypoxia in vivo. Instead, Ngb-deficiency appears to enhance the hypoxia-dependent response of Hif1A and c-FOS protein while also altering the transcriptional regulation of the glycolytic pathway. Bioinformatic analysis of differential gene expression yielded novel predictions suggesting that chromatin remodeling and mRNA metabolism are among the key regulatory mechanisms when adapting to prolonged hypoxia.

Cytoglobin: biochemical, functional and clinical perspective of the newest member of the globin family

Since the discovery of cytoglobin (Cygb) a decade ago, growing amounts of data have been gathered to characterise Cygb biochemistry, functioning and implication in human pathologies. Its molecular roles remain under investigation, but nitric oxide dioxygenase and lipid peroxidase activities have been demonstrated. Cygb expression increases in response to various stress conditions including hypoxia, oxidative stress and fibrotic stimulation. When exogenously overexpressed, Cygb revealed cytoprotection against these factors. Cygb was shown to be upregulated in fibrosis and neurodegenerative disorders and downregulated in multiple cancer types. CYGB was also found within the minimal region of a hereditary tylosis with oesophageal cancer syndrome, and its expression was reduced in tylotic samples. Recently, Cygb has been shown to inhibit cancer cell growth in vitro, thus confirming its suggested tumour suppressor role. This article aims to review the biochemical and functional aspects of Cygb, its involvement in various pathological conditions and potential clinical utility.

Old proteins - new locations: myoglobin, haemoglobin, neuroglobin and cytoglobin in solid tumours and cancer cells

AIM

The unexpected identification of myoglobin (MB) in breast cancer prompted us to evaluate the clinico-pathological value of MB, haemoglobin (HB) and cytoglobin (CYGB) in human breast carcinoma cases. We further screened for the presence of neuroglobin (NGB) and CYGB in tumours of diverse origin, and assessed the O(2) -response of HB, MB and CYGB mRNAs in cancer cell lines, to better elicit the links between this ectopic globin expression and tumour hypoxia.

METHODS

Breast tumours were analysed by immunohistochemistry for HB, MB and CYGB and correlated with clinico-pathological parameters. Screening for CYGB and NGB mRNA expression in tumour entities was performed by hybridization, quantitative PCR (qPCR) and bioinformatics. Hypoxic or anoxic responses of HB, MB and CYGB mRNAs was analysed by qPCR in human Hep3B, MCF7, HeLa and RCC4 cancer cell lines.

RESULTS

78.8% of breast cancer cases were positive for MB, 77.9% were positive for HB and 55.4% expressed CYGB. The closest correlation with markers of hypoxia was observed for CYGB. Compared to the weakly positive status of MB in healthy breast tissues, invasive tumours either lost or up-regulated MB. Breast carcinomas showed the tendency to silence CYGB. HB was not seen in normal tissues and up-regulated in tumours. Beyond breast malignancies, expression levels of NGB and CYGB mRNAs were extremely low in brain tumours (glioblastoma, astrocytoma). NGB was not observed in non-brain tumours. CYGB mRNA, readily detectable in breast cancer and other tumours, is down-regulated in lung adenocarcinomas. Alpha1 globin (α1 globin) and Mb were co-expressed in MCF7 and HeLa cells; CYGB transcription was anoxia-inducible in Hep3B and RCC4 cells.

CONCLUSIONS

This is the first time that HB and CYGB are reported in breast cancer. Neither NGB nor CYGB are systematically up-regulated in tumours. The down-regulated CYGB expression in breast and lung tumours is in line with a tumour-suppressor role. Each of the screened cancer cells expresses at least one globin (i.e. main globin species: CYGB in Hep3B; α1 globin + MB in MCF7 and HeLa). Thus, globins exist in a wide variety of solid tumours. However, the generally weak expression of the endogenous proteins in the cancer argues against a significant contribution to tumour oxygenation. Future studies should consider that cancer-expressed globins might function in ways not directly linked to the binding and transport of oxygen.

Promotion of liver and lung tumorigenesis in DEN-treated cytoglobin-deficient mice

Cytoglobin (Cygb) is a recently discovered vertebrate globin with molecular characteristics that are similar to myoglobin. To study the biological function of Cygb in vivo, we generated Cygb knockout mice and investigated their susceptibility to N,N-diethylnitrosamine (DEN)-induced tumorigenesis. Four-week-old male mice were administered DEN in drinking water at a dose of 25 ppm for 25 weeks or 0.05 ppm for 36 weeks. Cygb deficiency promoted the DEN-induced development of liver and lung tumors. All Cygb(+/-) and Cygb(-/-) mice treated with 25-ppm DEN exhibited liver tumors, compared with 44.4% of their wild-type counterparts. Lung tumors were present only in Cygb-deficient mice. More than 40% of Cygb(-/-) mice developed liver and lung tumors at the nontoxic dose of DEN (0.05 ppm), which did not induce tumors in wild-type mice. Cygb loss was associated with increased cancer cell proliferation, elevated extracellular signal-regulated kinase and Akt activation, overexpression of IL-1β, IL-6, Tnfα, and Tgfβ3 mRNAs, and hepatic collagen accumulation. Cygb-deficient mice also exhibited increased nitrotyrosine formation and dysregulated expression of cancer-related genes (cyclin D2, p53, Pak1, Src, Cdkn2a, and Cebpa). These results suggest that Cygb deficiency induces susceptibility to cancer development in the liver and lungs of mice exposed to DEN. Thus, globins such as Cygb will shed new light on the biological features of organ carcinogenesis.

Protection by neuroglobin and cell-penetrating peptide-mediated delivery in vivo: a decade of research. Comment on Cai et al: TAT-mediated delivery of neuroglobin protects against focal cerebral ischemia in mice. Exp Neurol. 2011; 227(1): 224-31

Over the last decade, numerous studies have suggested that neuroglobin is able to protect against the effects of ischemia. However, such results have mostly been based on models using transgenic overexpression or viral delivery. As a therapy, new technology would need to be applied to enable delivery of high concentrations of neuroglobin shortly after the patient suffers the stroke. An approach to deliver proteins in ischemia in vivo in a timely manner is the use of cell-penetrating peptides (CPP). CPP have been used in animal models for brain diseases for about a decade as well. In a recent issue of Experimental Neurology, Cai and colleagues test the effect of CPP-coupled neuroglobin in an in vivo stroke model. They find that the fusion protein protects the brain against the effect of ischemia when applied before stroke onset. Here, a concise review of neuroglobin research and the application of CPP peptides in hypoxia and ischemia is provided.

Neuroglobin protects neurons against oxidative stress in global ischemia

Neuroglobin (Ngb) is a recently discovered globin that affords protection against hypoxic/ischemic-induced cell injury in brain. Hypoxic/ischemic injury is associated with accumulation of reactive oxygen species (ROS) and/or reactive nitrogen species (RNS). In previous studies, we found that Ngb has antioxidative properties, and protects PC-12 cells against hypoxia- and β-amyloid-induced cell death. To further delineate the potential role of Ngb in protection against cerebral ischemia-reperfusion injury in vivo, we developed a transgenic mouse line that overexpresses Ngb. Hippocampal ischemia-reperfusion injury was induced by a 10-minute bilateral occlusion of the common carotid arteries, and the animal brains were assessed 3 days later. CA1 neural injury was determined by cresyl violet staining. Lipid peroxidation was assessed using a malonyldialdehyde assay kit, whereas ROS/RNS accumulation was determined by Het staining in the CA1 hippocampal region. Hippocampal Ngb mRNA and protein expressions were assessed by reverse transcriptase-PCR and western blotting, respectively. Neuroglobin was successfully overexpressed in the hippocampus of Ngb transgenic mice. After ischemia-reperfusion, CA1 ROS/RNS production and lipid peroxidation were markedly decreased in Ngb transgenic mice compared with wild-type mice. Furthermore, CA1 neuronal injury was also markedly reduced. Thus, Ngb may confer protection against ischemia-reperfusion injury in the brain through its intrinsic antioxidant properties.

Deletion of von Hippel-Lindau in glomerular podocytes results in glomerular basement membrane thickening, ectopic subepithelial deposition of collagen {alpha}1{alpha}2{alpha}1(IV), expression of neuroglobin, and proteinuria

Vascular endothelial growth factor, which is critical for blood vessel formation, is regulated by hypoxia inducible transcription factors (HIFs). A component of the E3 ubiquitin ligase complex, von Hippel-Lindau (VHL) facilitates oxygen-dependent polyubiquitination and proteasomal degradation of HIFalpha subunits. Hypothesizing that deletion of podocyte VHL would result in HIFalpha hyperstabilization, we crossed podocin promoter-Cre transgenic mice, which express Cre recombinase in podocytes beginning at the capillary loop stage of glomerular development, with floxed VHL mice. Vascular patterning and glomerular development appeared unaltered in progeny lacking podocyte VHL. However, urinalysis showed increased albumin excretion by 4 weeks when compared with wild-type littermates with several sever cases (>1000 microg/ml). Many glomerular ultrastructural changes were seen in mutants, including focal subendothelial delamination and widespread podocyte foot process broadening, and glomerular basement membranes (GBMs) were significantly thicker in 16-week-old mutants compared with controls. Moreover, immunoelectron microscopy showed ectopic deposition of collagen alpha1alpha2alpha1(IV) in GBM humps beneath podocytes. Significant increases in the number of Ki-67-positive mesangial cells were also found, but glomerular WT1 expression was significantly decreased, signifying podocyte death and/or de-differentiation. Indeed, expression profiling of mutant glomeruli suggested a negative regulatory feedback loop involving the HIFalpha prolyl hydroxylase, Egln3. In addition, the brain oxygen-binding protein, Neuroglobin, was induced in mutant podocytes. We conclude that podocyte VHL is required for normal maintenance of podocytes, GBM composition and ultrastructure, and glomerular barrier properties.

Neuroglobin, cytoglobin, and transcriptional profiling of hypoxia-related genes in the rat cerebellum after prenatal chronic very mild carbon monoxide exposure (25 ppm)

The expression of neuroglobin (Ngb) and cytoglobin (Cygb), two recently discovered globins with a potential neuroprotective activity against hypoxia and oxidative stress, was investigated in the cerebellum of young rats (postnatal day 20) after being exposed to chronic mild carbon monoxide (CO) at 25 ppm during prenatal (group A), prenatal and postnatal (group B), the postnatal period only (group C), and air (group D). The expression of genes associated with hypoxia signaling pathways was also investigated in the rat cerebella by real-time RT-PCR after CO exposure. Ngb and Cygb mRNAs did not change in any CO-exposed group. Quantitative immunohistochemistry showed no significant change in Ngb protein; however, there was a significant increase of Cygb protein in rats from groups A, B, and C when compared with group D. In group B, genes related to the generation of reactive oxygen species (Nos2) and lipid metabolism (Apat2) were upregulated. In contrast, no changes were found in the expression of 8 genes typically upregulated by hypoxic conditions (Angptl4, Arnt2, Casp1, Crebbp, Hif1a, Hif3a, Mt3, or Vegfa) in any CO-exposed group, suggesting that hypoxia-related gene expression is not altered by this mild CO exposure. Cygb but not Ngb may protect cerebellar cells from the chronic presence of CO exposure during prenatal and postnatal development.

Neuroglobin expression in the cochlea of rat pups exposed to chronic very mild carbon monoxide (25ppm) in air during and after the prenatal period

The distribution of neuroglobin (Ngb) was investigated in the normal rat cochlea using immunohistochemistry and non-radioactive insitu hybridization. We also determined whether chronic, very mild CO exposure at 25ppm in air over the gestational and postnatal period alters the expression of Ngb. Pregnant rats were exposed chronically to CO from gestational days 5-20. Four groups were made as follows: prenatal exposure to CO only; prenatal exposure to CO followed by postnatal exposure from postnatal days (5) P5 to P20; rat pups were exposed to CO from P5 to P20; controls (air without CO). In normal adult rats and control group pups, Ngb was found in spiral ganglia neurons, fibrocytes of the spiral ligament, and supporting cells of the organ of Corti. Ngb was not present in the stria vascularis and the inner and outer hair cells. At P20 Ngb immunoreactivity and transcript expression decreased in spiral ganglia neurons and the spiral ligament in the prenatal and pre- and postnatal groups. This decrease was not observed in the postnatal group. Ngb-IR did not decrease in supporting cells in any CO group. Cytochrome-C immunoreactivity followed Ngb distribution in normal controls and CO treated groups. A decrease in Ngb in spiral ganglia neurons and rat spiral ligament, but not in supporting cells, following CO exposure supports the idea that chronic, mild exposure to CO may create a vulnerable cellular environment predisposed to adverse cochlear development.

Hyaline protoplasmic astrocytopathy of neocortex

Eosinophilic inclusions in the cytoplasm of protoplasmic astrocytes of the neocortex, usually in the clinical setting of epilepsy and/or psychomotor retardation, were first recognized and illustrated by Alois Alzheimer in 1910. Traditional special stains have failed to elucidate the specific nature of these inclusions. Ultrastructurally, the material was composed predominantly of highly electron-dense, non-membrane-bound, granular material distinct from Rosenthal fibers. Immunohistochemical examination has been informative but also sometimes inconsistent; it has recently been suggested that they may represent a filaminopathy (filamin A). We examined 5 cases with neocortical eosinophilic inclusions (3 autopsies, 2 surgical resections) using a standardized immunohistochemical protocol at a single institution. The specimens were immunostained with 32 antibodies to 30 potentially relevant proteins using several antigen retrieval protocols. We confirmed the presence of filamin A in these inclusions, but several additional proteins, particularly cytoglobin and glutamate transporter 1, were also identified. By electron microscopy in 2 cases, the granular fine structure of the inclusions was confirmed; mitochondria adjacent to, and perhaps within, the inclusions that contained many pleomorphic vesicular and membranous elements were also noted in 1 case. The pathophysiologic relevance of these proteins and the clinical significance of the hyaline inclusions are discussed.

Association between Ngb polymorphisms and ischemic stroke in the Southern Chinese Han population

Background

Neuroglobin (Ngb), one of novel members of the globin superfamily, is expressed predominantly in brain neurons, and appears to modulate hypoxic-ischemic insults. The mechanisms underlying Ngb-mediated neuronal protection are still unclear. For it is one of the candidate protective factors for ischemic stroke, we conducted a case-control study to clarify the association of Ngb polymorphisms with ischemic stroke in the Southern Chinese Han population.

Methods

355 cases and 158 controls were recruited. With brain imaging, cases were subdivided into large-artery atherosclerosis (LVD) and small-vessel occlusion (SVD) stroke. PCR amplified all the four exons of Ngb and flanking intron sequence for each exon. Genotyping for Ngb was achieved by direct sequencing and mismatched PCR-RFLP. Polymorphisms were studied both individually and as haplotypes in each group and subgroup which subdivided according to gender or age.

Results

Two intronic polymorphisms 89+104 c>t and 322-110 (6a)>5a were identified. The allele frequency of 89+104 t was decreased in stroke cases. The protective effect seems to be more pronounced in subgroups of female patients and age > 60 years. Also, we have confirmed decreased LDL-C level and reduced hypertension and hypercholesterolemia in 89+104 t allele carriers. In contrast, the 322-110 (6a)>5a genotype distribution was similar between cases and controls. However, the haplotype 89+104 c>t/322-110 (6a)>5a was related with LVD and SVD stroke. The haplotype c-5a was more frequent in both LVD and SVD groups while t-6a was more frequent in controls.

Conclusion

Ngb polymorphism 89+104 t had protective effects on LVD and SVD in the Southern Chinese Han population. A "hitchhiking" effect was observed for the 89+104 t/322-110 (6a) genotype combination especially for LVD.

Expression and hypoxic up-regulation of neuroglobin in human glioblastoma cells

Neuroglobin is a recently identified globin molecule that is expressed predominantly in the vertebrate brain. Neuroglobin expression increases in oxygen-deprived neurons, suggesting it protects neurons from ischemic cell death. We report that neuroglobin transcript and protein are expressed in human glioblastoma cells, and that this expression increases in hypoxia in vitro. We also show that neuroglobin is up-regulated in hypoxic microregions of glioblastoma tumor xenografts. Our finding of hypoxic up-regulation of neuroglobin in human glioblastoma cells may provide insight into how tumor cells adapt to and survive in hypoxic microenvironments.

Identification of protein radicals formed in the human neuroglobin-H2O2 reaction using immuno-spin trapping and mass spectrometry

Neuroglobin (Ngb) is a recently discovered protein that shows only minor sequence similarity with myoglobin and hemoglobin but conforms to the typical 3-over-3 alpha-helical fold characteristic of vertebrate globins. An intriguing feature of Ngb is its heme hexacoordination in the absence of external ligands, observed both in the ferrous and in the ferric (met) forms. In Ngb, the imidazole of a histidine residue (His-64) in the distal position, above the heme plane, provides the sixth coordination bond. In this work, a valine residue was introduced at position 64 (H64V variant) to clarify the possible role(s) of the distal residue in protecting the heme iron of Ngb from attack by strong oxidants. SDS-PAGE analyses revealed that the oxidation of the H64V variant of metNgb by H 2O 2 resulted in the formation of dimeric and trimeric products in contrast to the native protein. Dityrosine cross-links were shown by their fluorescence to be present in the oligomeric products. When the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was included in the reaction mixture, nitrone adducts were detected by immuno-spin trapping. The specific location of the DMPO adducts on the H64V variant protein was determined by a mass spectrometry method that combines off-line immuno-spin trapping and chromatographic procedures. This method revealed Tyr-88 to be the site of modification by DMPO. The presence of His-64 in the wild-type protein results in the nearly complete loss of detectable radical adducts. Together, the data support the argument that wild-type Ngb is protected from attack by H 2O 2 by the coordinated distal His.

Neuroglobin protects PC12 cells against oxidative stress

Neuroglobin (Ngb) is a newly discovered globin in the vertebrate brain that exhibits neuroprotection against hypoxic/ischemic injury. Hypoxic/ischemic brain injury is associated with accumulation of reactive oxygen species (ROS) and/or reactive nitrogen species (RNS), and antioxidants or ROS scavengers promote cell survival. Therefore, Ngb may serve as a scavenger of toxic reactive species, such as hydrogen peroxide. To examine the anti-oxidative role of neuroglobin, PC12 cells were transfected with wild type and mutant (H64 V/H96A) Ngb for 48 h and then treated with H2O2 (0.1, 0.2 and 0.4 mM) for 6 h. Ngb siRNA decreased the H2O2-induced Ngb expression and exacerbated H2O2-induced cell injury. Transient transfection of Ngb induced dose-dependent increases in Ngb protein expression and did not alter SOD, GPX, and catalase activities. Overexpression of wild type Ngb, but not of mutant Ngb, significantly attenuated H2O2-induced ROS/RNS accumulation and lipid peroxidation, decreased H2O2-induced mitochondrial dysfunction and apoptosis, and promoted overall cell survival. Thus, Ngb plays a protective role against oxidative stress, which appears to be primarily mediated by intrinsic Ngb antioxidant properties.

Neuroglobin: an endogenous neuroprotectant

Cerebral hypoxia and ischemia trigger endogenous protective mechanisms that can prevent or limit brain damage. Understanding these mechanisms may lead to new therapeutic strategies for stroke and related disorders. Neuroglobin (Ngb), a recently discovered protein that is distantly related to hemoglobin and myoglobin, is expressed predominantly in brain neurons, and appears to modulate hypoxic-ischemic brain injury. Evidence includes the observations that neuronal hypoxia and cerebral ischemia induce Ngb expression, that enhancing Ngb expression reduces--and knocking down Ngb expression increases--hypoxic neuronal injury in vitro and ischemic cerebral injury in vivo, and that Ngb-overexpressing transgenic mice are resistant to cerebral infarction. However, the mechanisms that underlie hypoxic induction of Ngb and neuroprotection by Ngb are still unclear.

Hypoxia in the central nervous system

The brain, as a very high energy consumer, is completely reliant on molecular oxygen but because oxygen is dangerous due to toxicity [1], there are mechanisms which allow the brain to exist under low oxygen conditions when 'idling' but increase oxygen delivery when activated. This situation means that the brain can respond naturally to mild hypoxia with acute and chronic adaptive mechanisms. These mechanisms involve systemic and central metabolic and vascular processes that are mediated by hypoxia-inducible factor (HIF)-1. HIF-1-mediated cerebral angiogenesis is completed within 3 weeks of exposure onset and is reversible over the same time frame if normoxia is restored. Hypoxic acclimatizing responses may be significantly impaired with aging and metabolic or vascular disease.

Mitochondrial ferritin expression in adult mouse tissues

Mitochondrial ferritin (FtMt) is a novel ferritin type specifically targeted to mitochondria. It is highly expressed in the human testis and in sideroblasts from patients with sideroblastic anemia, but other organs have not been studied. To study its expression in the main organs of the mouse, we first used RT-PCR and then produced recombinant mouse FtMt and specific antibodies. Immunohistochemistry analyses confirmed that FtMt is highly expressed in mouse testis, particularly in spermatocytes and interstitial Leydig cells. The protein was also identified in other organs including heart, brain, spinal cord, kidney, and pancreatic islet of Langerhans but not in liver and splenocytes, which have iron storage function and express high levels of cytosolic ferritins. Results indicate that the primary function of ferritin FtMt is not involved in storing cellular or body iron, but its association with cell types characterized by high metabolic activity and oxygen consumption suggests a role in protecting mitochondria from iron-dependent oxidative damage.

Cytoglobin Up-regulated by Hydrogen Peroxide Plays a Protective Role in Oxidative Stress

Cytoglobin (Cygb) is a recently discovered intracellular respiratory globin, which exists in all types of cells. It has been suggested that Cygb has a role in protecting cells against oxidative stress. In the present study we have tested this hypothesis. The N2a neuroblastoma cells were exposed to various kinds of insults, including hydrogen peroxide (H(2)O(2)), hypoxia, kainic acid, high extracellular CaCl(2), high osmolarity, UV irradiation and heat shock. Among them, only H(2)O(2)-treatment induced a significant up-regulation of cytoglobin mRNA level. We stably transfected N2a cells with Cygb-siRNA vectors and successfully knocked down Cygb. The Cygb-siRNA could exacerbate cell death upon H(2)O(2)-treatment, as demonstrated by MTT cell viability assay. Thus, Cygb in neuronal cells might be specifically induced under oxidative stress to protect them from death.

Neuroglobin and cytoglobin expression in mice

Although essentially unknown, several functions are hypothesized for neuroglobin and cytoglobin, two new members of the globin family. In this article, we try to shed more light on their possible roles in hypoxia and detoxification of reactive oxygen species in vivo. The relative transcriptional changes of neuroglobin and cytoglobin in a situation of chronic hypoxia in mice were examined using real-time quantitative PCR. The kinetics of the hypoxic expression of neuroglobin (brain, eyes) and cytoglobin (brain, eyes, liver, heart, skeletal muscle) is organ-specific. Moreover, reactive oxygen species production is higher in liver than in the other tissues. In eyes, the negative correlation, after reoxygenation, between neuroglobin protein level and H(2)O(2) concentration is a first proof of a reactive oxygen species-scavenging function for neuroglobin. In addition, apoptotic cell death after hypoxia is for the first time demonstrated in heart and liver.

Neuroglobin-overexpressing transgenic mice are resistant to cerebral and myocardial ischemia

Neuroglobin (Ngb), a protein related to myoglobin and hemoglobin but expressed predominantly in the brain, is induced by neuronal hypoxia and cerebral ischemia and protects against hypoxic or ischemic neuronal injury. We engineered transgenic mice that overexpress murine Ngb under the control of a chicken beta-actin promoter, resulting in enhanced Ngb expression in multiple cell types and multiple tissues, including brain and heart. In Ngb-overexpressing transgenic mice compared with wild-type littermates, the volume of cerebral infarcts after occlusion of the middle cerebral artery was reduced by approximately 30%, and the volume of myocardial infarcts produced by occlusion of the left anterior descending coronary artery was reduced by approximately 25%. Ngb overexpression was associated with enhanced expression of endothelial nitric oxide synthase in vascular endothelial cells. These findings extend prior evidence for cytoprotection by Ngb and suggest both direct (parenchymatous) and indirect (vasomotor) protective mechanisms.