Comparative genomics of neuroglobin reveals its early origins

BACKGROUND

Neuroglobin (Ngb) is a hexacoordinated globin expressed mainly in the central and peripheral nervous system of vertebrates. Although several hypotheses have been put forward regarding the role of neuroglobin, its definite function remains uncertain. Ngb appears to have a neuro-protective role enhancing cell viability under hypoxia and other types of oxidative stress. Ngb is phylogenetically ancient and has a substitution rate nearly four times lower than that of other vertebrate globins, e.g. hemoglobin. Despite its high sequence conservation among vertebrates Ngb seems to be elusive in invertebrates.

PRINCIPAL FINDINGS

We determined candidate orthologs in invertebrates and identified a globin of the placozoan Trichoplax adhaerens that is most likely orthologous to vertebrate Ngb and confirmed the orthologous relationship of the polymeric globin of the sea urchin Strongylocentrotus purpuratus to Ngb. The putative orthologous globin genes are located next to genes orthologous to vertebrate POMT2 similarly to localization of vertebrate Ngb. The shared syntenic position of the globins from Trichoplax, the sea urchin and of vertebrate Ngb strongly suggests that they are orthologous. A search for conserved transcription factor binding sites (TFBSs) in the promoter regions of the Ngb genes of different vertebrates via phylogenetic footprinting revealed several TFBSs, which may contribute to the specific expression of Ngb, whereas a comparative analysis with myoglobin revealed several common TFBSs, suggestive of regulatory mechanisms common to globin genes.

SIGNIFICANCE

Identification of the placozoan and echinoderm genes orthologous to vertebrate neuroglobin strongly supports the hypothesis of the early evolutionary origin of this globin, as it shows that neuroglobin was already present in the placozoan-bilaterian last common ancestor. Computational determination of the transcription factor binding sites repertoire provides on the one hand a set of transcriptional factors that are responsible for the specific expression of the Ngb genes and on the other hand a set of factors potentially controlling expression of a couple of different globin genes.

Spectroelectrochemical characterization of small hemoproteins adsorbed within nanostructured mesoporous ITO electrodes

3D nanostructured transparent indium tin oxide (ITO) electrodes prepared by glancing angle deposition (GLAD) were used for the spectroelectrochemical characterization of cytochrome c (Cyt c) and neuroglobin (Nb). These small hemoproteins, involved as electron-transfer partners in the prevention of apoptosis, are oppositely charged at physiological pH and can each be adsorbed within the ITO network under different pH conditions. The resulting modified electrodes were investigated by UV-visible absorption spectroscopy coupled with cyclic voltammetry. By using nondenaturating adsorption conditions, we demonstrate that both proteins are capable of direct electron transfer to the conductive ITO surface, sharing apparent standard potentials similar to those reported in solution. Preservation of the 3D protein structure upon adsorption was confirmed by resonance Raman (rR) spectroscopy. Analysis of the derivative cyclic voltabsorptograms (DCVA) monitored either in the Soret or the Q bands at scan rates up to 1 V s(-1) allowed us to investigate direct interfacial electron transfer kinetics. From the DCVA shape and scan rate dependences, we conclude that the interaction of Cyt c with the ITO surface is more specific than Nb, suggesting an oriented adsorption of Cyt c and a random adsorption of Nb on the ITO surface. At the same time, Cyt c appears more sensitive to the experimental adsorption conditions, and complete denaturation of Cyt c may occur as evidenced from cross-correlation of rR spectroscopy and spectroelectrochemistry.

[Involvement of cerebral neuroglobin in electroacupuncture preconditioning-induced protection effect in cerebral ischemia-reperfusion rats]

OBJECTIVE

To observe the effect of electroacupuncture (EA) preconditioning on cerebral ischemia and the role of cerebral neuroglobin (NgB) in EA-induced brain protection in focal cerebral ischemia and reperfusion injury (CI/RI) rats.

METHODS

Male SD rats were randomly assigned to sham control, CI/RI 6 h, CI/RI 24 h and CI/RI 72 h groups (n = 6) for observing changes of NgB at different time-points. Additional SD rats were randomly assigned to sham, model, and EA preconditioning (EA-PC) groups (n = 16) for observing changes of cerebral NgB positive cell counts in the ischemic penumbra region 24 h after reperfusion. EA pre-conditioning was applied to "Baihui" (GV 20) for 30 min, once daily for 5 days before CI/RI. CI/RI model was established by occlusion of the right middle cerebral artery and reperfusion for 6 h, 24 h and 72 h respectively. The neurological behavior scores (NBS) of all the rats were evaluated according to Garcia's methods. The cerebral infarct volume was determined by 2,3,5-triphenyltetrazolium chloride (TTC) staining. The number of cerebral NgB positive cells was detected by immunofluorescent staining.

RESULTS

No infarct loci were found in the sham group. The cerebral infarction volume percentage was significantly higher in the model group than in the EA-PC group (P < 0.01), while the NBS was significantly lower in the model group than in the EA-PC group (P < 0.01). The number of cerebral NgB positive cells in the ischemic penumbra was up-regulated 6 h after CI/RI injury, peaked at 24 h and continued at 72 h. Compared with the sham group, the number of cerebral NgB positive cells of the model group was increased significantly, whereas that of the EA-PC group up-regulated further obviously in comparison with the model group (P < 0.01).

CONCLUSION

EA pretreatment has a significant neuroprotective effect on cerebral ischemia-reperfusion, which is closely related to its effect in up-regulating NgB protein expression.

Analysis of neuroglobin mRNA expression in rat brain due to arsenite-induced oxidative stress

Arsenic (As) in drinking water is a toxicant causing several health problems including nervous system disturbance. Neuroglobin (Ngb) is a tissue globin in nervous system playing protective role against oxidative stress in many injuries. This study was to investigate how long arsenite exposure (sodium arsenite 7.5 mg/kg/day) could induce oxidative stress in blood and brain of rats and to determine whether Ngb expression in rat brain changed due to oxidative stress. Results showed that superoxide dismutase (SOD) activity and malondialdehyde (MDA) level in serum and brain homogenates and reactive oxygen species (ROS) generation in red blood cells (RBCs) did not change in the rats exposed to arsenite for 8 weeks. In the rats exposed to arsenite for 16 weeks, SOD activity decreased (serum: P < 0.05; brain homogenates: P < 0.01) and MDA level increased (P < 0.01) in serum and brain homogenates; ROS production increased (P < 0.01) in RBC. When oxidative stress occurred, Ngb mRNA expression did not change in whole brain, cerebral cortex, midbrain, and hippocampus; however, Ngb mRNA expression increased significantly (P < 0.05) in cerebellum compared to the control group. This study suggests that arsenite exposure for 16 weeks can lead to oxidative stress of blood and brain of rats. Ngb may play a protective role in cerebellum when oxidative stress occurs due to arsenite exposure.

[Changes of neuroglobin in the pathologic process of contusion and laceration of brain in children]

OBJECTIVE

To study the role of neuroglobin (Ngb) in the pathologic process of contusion and laceration of brain in children.

METHODS

The proteins in the brain tissue were extracted by two-dimensional gel electrophoresis in 3 children undergoing brain ventricular neoplasms resection (normal brain tissue) and in 8 children with contusion and laceration of brain. The image analysis was done using the PDQuest 7.0 software. The differential protein spots were detected and analyzed with Applied Biosystems Voyager System 4307 MALDI-TOF Mass Spectrometer and bioinformatical skills. Ngb expression in the brain tissue was measured using immunohistochemisty. Ngb expression in plasma was measured using ELISA in 15 children with contusion and laceration of brain and 10 healthy children.

RESULTS

Expression maps of the brain tissue were established by two-dimensional gel electrophoresis in children with contusion and laceration of brain and healthy children. Six differential protein spots were found and 5 of them were identified by mass spectrum. Immunohistochemisty assay showed that Ngb expression in the brain tissue in children with contusion and laceration of brain was significantly higher than in normal controls (P<0.05). ELISA results showed that Ngb expression in the plasma increased significantly 6, 12, 18, 24 and 48 hours after trauma in children with contusion and laceration of brain compared with healthy children (P<0.01).

CONCLUSIONS

Ngb may play an important role in the pathologic process of contusion and laceration of brain in children.

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.

Circadian behaviour in neuroglobin deficient mice

Neuroglobin (Ngb), a neuron-specific oxygen-binding globin with an unknown function, has been proposed to play a key role in neuronal survival. We have previously shown Ngb to be highly expressed in the rat suprachiasmatic nucleus (SCN). The present study addresses the effect of Ngb deficiency on circadian behavior. Ngb-deficient and wild-type (wt) mice were placed in running wheels and their activity rhythms, endogenous period and response to light stimuli were investigated. The effect of Ngb deficiency on the expression of Period1 (Per1) and the immediate early gene Fos was determined after light stimulation at night and the neurochemical phenotype of Ngb expressing neurons in wt mice was characterized. Loss of Ngb function had no effect on overall circadian entrainment, but resulted in a significantly larger phase delay of circadian rhythm upon light stimulation at early night. A light-induced increase in Per1, but not Fos, gene expression was observed in Ngb-deficient mice. Ngb expressing neurons which co-stored Gastrin Releasing Peptide (GRP) and were innervated from the eye and the geniculo-hypothalamic tract expressed FOS after light stimulation. No PER1 expression was observed in Ngb-positive neurons. The present study demonstrates for the first time that the genetic elimination of Ngb does not affect core clock function but evokes an increased behavioural response to light concomitant with increased Per1 gene expression in the SCN at early night.

Transgenic overexpression of neuroglobin attenuates formation of smoke-inhalation-induced oxidative DNA damage, in vivo, in the mouse brain

Acute inhalation of combustion smoke causes neurological deficits in survivors. Inhaled smoke includes carbon monoxide, noxious gases, and a hypoxic environment, which disrupt oxygenation and generate free radicals. To replicate a smoke-inhalation scenario, we developed an experimental model of acute exposure to smoke for the awake mouse/rat and detected induction of biomarkers of oxidative stress. These include inhibition of mitochondrial respiratory complexes and formation of oxidative DNA damage in the brain. DNA damage is likely to contribute to neuronal dysfunction and progression of brain injury. In the search for strategies to attenuate the smoke-initiated brain injury, we produced a transgenic mouse overexpressing the neuronal globin protein neuroglobin. Neuroglobin was neuroprotective in diverse models of ischemic/hypoxic/toxic brain injuries. Here, we report lesser inhibition of respiratory complex I and reduced formation of smoke-induced DNA damage in neuroglobin transgenic compared to wild-type mouse brain. DNA damage was assessed using the standard comet assay, as well as a modified comet assay done in conjunction with an enzyme that excises oxidized guanines that form readily under conditions of oxidative stress. Both comet assays revealed that overexpressed neuroglobin attenuates the formation of oxidative DNA damage, in vivo, in the brain. These findings suggest that elevated neuroglobin exerts neuroprotection, in part, by decreasing the impact of acute smoke inhalation on the integrity of neuronal DNA.

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.

[Recent data about the role of hypothalamic suprachiasmatic nucleus in circadian organization of physiological functions]

The suprachiasmatic nucleus is the primary circadian pacemaker in mammals. In turn, the suprachiasmatic nucleus influences circadian physiology, endocrinology and behavior via the synchronization of local oscillators that are operative in the cells of most organs and tissues. Thus circadian pacemaker may play an important role in psychiatric disorders and in psychotherapeutic drugs effect. In this review, we summarize data about the suprachiasmatic nuclei anatomy, physiology and pharmacological sensitivity.

Neuroglobin is an endogenous neuroprotectant for retinal ganglion cells against glaucomatous damage

Neuroglobin (NGB), a newly discovered member of the globin superfamily, may regulate neuronal survival under hypoxia or oxidative stress. Although NGB is greatly expressed in retinal neurons, the biological functions of NGB in retinal diseases remain largely unknown. We investigated the role of NGB in an experimental model of glaucoma, a neurodegenerative disorder that usually involves elevation of intraocular pressure (IOP). Elevated IOP is thought to induce oxidative stress in retinal ganglion cells (RGCs), thereby causing RGC death and, eventually, blindness. We found that NGB plays a critical role in increasing RGC resistance to ocular hypertension and glaucomatous damage. Elevation of IOP stimulated a transient up-regulation of endogenous NGB in RGCs. Constitutive overexpression of NGB in transgenic mice prevented RGC damage induced by glutamate cytotoxicity in vitro and/or by chronic IOP elevation in vivo. Moreover, overexpression of NGB attenuated ocular hypertension-induced superoxide production and the associated decrease in ATP levels in mice, suggesting that NGB acts as an endogenous neuroprotectant to reduce oxidative stress and improve mitochondrial function, thereby promoting RGC survival. Thus, NGB may modulate RGC susceptibility to glaucomatous neural damage. Manipulating the expression and bioactivity of NGB may represent a novel therapeutic strategy for glaucoma.

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.

Neuroglobin and myoglobin in non-small cell lung cancer: expression, regulation and prognosis

Globins are respiratory proteins involved in oxygen metabolism, which is a critical factor in tumor growth and progression. The status of neuroglobin and myoglobin is largely unknown in human malignancies, including lung cancer. The aim of this study was to explore mRNA expression profiles, potential regulatory mechanisms and clinicopathological associations of neuroglobin and myoglobin in non-small cell lung cancer (NSCLC). We screened 208 surgically resected NSCLC specimens and a panel of lung normal and cancer cell lines. The mRNA expression of neuroglobin, myoglobin and hypoxia markers (HIF1α and VEGFa) was measured with qRTPCR, while neuroglobin promoter methylation was assessed with Pyrosequencing. Neuroglobin and myoglobin were upregulated in the tumor samples compared to normal tissue (p=1.3×10(-22) and p=1.9×10(-9), respectively). Neuroglobin was more frequently overexpressed in squamous cell carcinomas (SqCCL) than adenocarcinomas. Overexpression of myoglobin was more profound in adenocarcinomas, which correlated with poor survival (p=0.013). Neuroglobin promoter was hypermethylated in 30.8% of NSCLC cases, which correlated with neuroglobin mRNA downregulation. The epigenetic regulation of neuroglobin was confirmed by treating lung cell lines with 5'azadeoxycytidine and/or trichostatin A. Expression of both genes correlated with the expression of HIF1α (neuroglobin: p=3.8×10(-5), myoglobin: p=1.1×10(-11)). Myoglobin expression was also associated to that of VEGFa (p=2.1×10(-7)). Hypoxia-dependent upregulation of both globins was validated in vitro. In summary, neuroglobin and myoglobin overexpression in NSCLC is associated with histological subtype, hypoxia and, in case of neuroglobin - epigenetic regulation. Myoglobin expression may have potential significance in the prognostication of lung adenocarcinomas.

Electron transfer function versus oxygen delivery: a comparative study for several hexacoordinated globins across the animal kingdom

Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O(2) and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O(2) as for Ngb and Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O(2) actually binding to the iron atom, since the heme is oxidized by O(2) faster than the time for distal histidine dissociation. These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally different from that of pentacoordinated globins.

Module M1 of zebrafish neuroglobin acts as a structural and functional protein building block for a cell-membrane-penetrating activity

Neuroglobin (Ngb) is a recently discovered vertebrate globin that is expressed in the brain and can reversibly bind oxygen. Mammalian Ngb is involved in neuroprotection during oxidative stress that occurs, for example, during ischemia and reperfusion. Recently, we found that zebrafish, but not human, Ngb can translocate into cells. Moreover, we demonstrated that a chimeric ZHHH Ngb protein, in which the module M1 of human Ngb is replaced by the corresponding region of zebrafish Ngb, can penetrate cell membranes and protect cells against oxidative stress-induced cell death, suggesting that module M1 of zebrafish Ngb is important for protein transduction. Furthermore, we recently showed that Lys7, Lys9, Lys21, and Lys23 in module M1 of zebrafish Ngb are crucial for protein transduction activity. In the present study, we have investigated whether module M1 of zebrafish Ngb can be used as a building block to create novel cell-membrane-penetrating folded proteins. First, we engineered a chimeric myoglobin (Mb), in which module M1 of zebrafish Ngb was fused to the N-terminus of full-length human Mb, and investigated its functional and structural properties. Our results showed that this chimeric Mb protein is stable and forms almost the same heme environment and α-helical structure as human wild-type Mb. In addition, we demonstrated that chimeric Mb has a cell-membrane-penetrating activity similar to zebrafish Ngb. Moreover, we found that glycosaminoglycan is crucial for the cell-membrane-penetrating activity of chimeric Mb as well as that of zebrafish Ngb. These results enable us to conclude that such module substitutions will facilitate the design and production of novel functional proteins.

Probing the role of the internal disulfide bond in regulating conformational dynamics in neuroglobin

In this report, we demonstrate that the internal disulfide bridge in human neuroglobin modulates structural changes associated with ligand photo-dissociation from the heme active site. This is evident from time-resolved photothermal studies of CO photo-dissociation, which reveal a 13.4+/-0.9 mL mol(-1) volume expansion upon ligand photo-release from human neuroglobin, whereas the CO dissociation from rat neuroglobin leads to a significantly smaller volume change (DeltaV=4.6+/-0.3 mL mol(-1)). Reduction of the internal disulfide bond in human neuroglobin leads to conformational changes (reflected by DeltaV) nearly identical to those observed for rat Ngb. Our data favor the hypothesis that the disulfide bond between Cys46 and Cys55 modulates the functioning of human neuroglobin.

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.

[The neuroglobin expression when retinal ganglion cells death in acute rats' retina ischemia]

OBJECTIVE

To investigate the intra-retinal expression of neuroglobin (Ngb) and death of retinal ganglion cells (RGCs) in acute retina ischemia rats.

METHODS

It was an experimental study. The acute retina ischemia model was established by specific hypothesised left retina artery of Sprague-Dawley rats. Forty rats were divided into four groups (0, 15, 30, 60 min) by the time of retina ischemia. Every group has 10 rats, in one group random 3 rats were detected by Western blotting; 4 rats were detected by ganglion cell counted by hematoxylin and eosin stain and immunohistochemistry fluorescence intensity analysis. The rest 3 rats were detected by Western blotting. The difference among different data were analyzed statistically by One-factor analysis of variance and LSD-t analysis.

RESULTS

The intra-retinal expression of Ngb reached maximum after acute ischemia 15 minute (P = 0.000). then the expression began decreasing. After 30 minute acute ischemia, the expression of Ngb had approached normal (P = 0.728), while, the cell number of RGCs began lower than 0 min group (P = 0.011); after 60 minute acute ischemia, the expression of Ngb had been obviously lower than 0 min group (P = 0.001), the cell number of RGCs had been further lower than 0 min group (P = 0.000). The expression of Ngb in RGCs layer was highest in rat retina. The expression in inner plexiform layer and external plexiform layer were lower than the former. The expression of Ngb RGCs was mostly intracytoplasm. After 30 minute acute ischemia, the expression of Ngb were detected in mitochondrial outer compartment and mitochondrial cristae, but in cytoplasm of inner nuclear layer and outer nuclear layer the Ngb was not found.

CONCLUSION

Ngb quickly steps-up when RGCs die in acute retina ischemia, and mainly expresses intracytoplasm of RGCs. It has tense relationships with nerve cells' survival in hypoxia.

Neuroglobin genetic polymorphisms and their relationship to functional outcomes after traumatic brain injury

Neuroglobin has shown rich neuroprotective effects against cerebral hypoxia, and therefore has the potential to impact outcomes after traumatic brain injury (TBI). However, to date an association between genetic variation within the human neuroglobin (NGB) gene and recovery post-TBI has not been reported. The purpose of this study was to explore the relationship between NGB genotypes and outcomes (as assessed by the Glasgow Outcome Scale [GOS], the Disability Rating Scale [DRS], and the Neurobehavioral Rating Scale-Revised [NRS-R]) after severe TBI. Genotyping using TaqMan allele discrimination for two tagging single nucleotide polymorphisms (tSNPs) that represent the two haplotype blocks for NGB (rs3783988 and rs10133981) was completed on DNA obtained from 196 Caucasian patients recovering from severe TBI. Patients were dichotomized based on the presence of the variant allele for each tSNP. Chi-square and Fisher's exact tests were used to compare characteristics between groups. Multivariate linear regression was used to examine NGB tSNPs and recovery from severe TBI. Subjects with the TT genotype (wild-type) for rs3783988 were more likely to have better GOS and DRS scores at 3, 6, 12, and 24 months, while rs10133981 genotype was not significantly related to functional outcome. After controlling for age, gender, and Glasgow Coma Scale (GCS) score, those subjects with the rs3783988 TT genotype had more than a 2.65-times greater likelihood of better functional outcomes than individuals with genotypes harboring a variant allele. Data suggest that the haplotype block represented by rs3783988 in NGB appears to influence recovery after severe TBI. Represented within this haplotype block of NGB is the region that codes for the oxygen-binding portion of NGB.

An antiapoptotic neuroprotective role for neuroglobin

Cell death associated with mitochondrial dysfunction is common in acute neurological disorders and in neurodegenerative diseases. Neuronal apoptosis is regulated by multiple proteins, including neuroglobin, a small heme protein of ancient origin. Neuroglobin is found in high concentration in some neurons, and its high expression has been shown to promote survival of neurons in vitro and to protect brain from damage by both stroke and Alzheimer's disease in vivo. Early studies suggested this protective role might arise from the protein's capacity to bind oxygen or react with nitric oxide. Recent data, however, suggests that neither of these functions is likely to be of physiological significance. Other studies have shown that neuroglobin reacts very rapidly with cytochrome c released from mitochondria during cell death, thus interfering with the intrinsic pathway of apoptosis. Systems level computational modelling suggests that the physiological role of neuroglobin is to reset the trigger level for the post-mitochondrial execution of apoptosis. An understanding of the mechanism of action of neuroglobin might thus provide a rational basis for the design of new drug targets for inhibiting excessive neuronal cell death.

Spectroscopic study on acid-induced unfolding and refolding of apo-neuroglobin

pH-induced unfolding and refolding of apo-neuroglobin (apo-Ngb) were investigated by UV, fluorescence, circular dichroism (CD) spectra and light scattering measurements. Results revealed that apo-Ngb became partially unfolded at around pH 5.0, with evidences from a red shift in the fluorescence spectra, a decrease in the far-UV CD and a sharp peak in the light scattering intensity. Further lowering of the pH reversed these effects, suggesting that apo-Ngb folds back to a compact state. At pH 2.0, the apo-Ngb forms a folding intermediate known as molten globule (MG), which is possessed of native-like secondary structure and almost complete loss of tertiary structure. Based on these results, the acid-induced denaturation pathway of apo-Ngb can be illustrated from the native state (N), via a partially unfolded state (U(A)) to the molten globule state (MG).

Neuroglobin protects nerve cells from apoptosis by inhibiting the intrinsic pathway of cell death

In the past few years, overwhelming evidence has accrued that a high level of expression of the protein neuroglobin protects neurons in vitro, in animal models, and in humans, against cell death associated with hypoxic and amyloid insult. However, until now, the exact mechanism of neuroglobin's protective action has not been determined. Using cell biology and biochemical approaches we demonstrate that neuroglobin inhibits the intrinsic pathway of apoptosis in vitro and intervenes in activation of pro-caspase 9 by interaction with cytochrome c. Using systems level information of the apoptotic signalling reactions we have developed a quantitative model of neuroglobin inhibition of apoptosis, which simulates neuroglobin blocking of apoptosome formation at a single cell level. Furthermore, this model allows us to explore the effect of neuroglobin in conditions not easily accessible to experimental study. We found that the protection of neurons by neuroglobin is very concentration sensitive. The impact of neuroglobin may arise from both its binding to cytochrome c and its subsequent redox reaction, although the binding alone is sufficient to block pro-caspase 9 activation. These data provides an explanation the action of neuroglobin in the protection of nerve cells from unwanted apoptosis.

[An experimental research of neuroglobin expression changes and neural apoptosis after traumatic brain injury]

OBJECTIVE

To study the expression changes of neuroglobin in rats with the model of diffuse traumatic brain injury and explore the relationship between the neuroglobin and neuron apoptosis in traumatic brain injury.

METHODS

The diffuse traumatic brain injury of rats was induced by the Marmarou's 'weight-drop' device. And the immunohistochemical technique was used to detect the expression changes of neuroglobin and neuron apoptosis in rat brain at different time points post-injury.

RESULTS

The expression of neuroglobin increased twice and reached peaks at 2 hours and 72 hours post-injury respectively. And the increased expression of neuroglobin from 30 minutes to 1 hour post-injury and from 48 hours to 72 hours post-injury accompanied with the decreased expression ratio of Bax to Bcl-2.

CONCLUSION

The increased expression of neuroglobin in traumatic brain injury informed us that neuroglobin had anti-apoptosis action in post-injury neuron. It could protect the neuron from traumatic stress and secondary ischemia and hypoxia insults during ultra-early and acute stages.

Neuroglobin expression in ischemic stroke

BACKGROUND AND PURPOSE

We investigated whether neuroglobin, a neuronal protein that protects neurons from hypoxic-ischemic injury, is upregulated in ischemic stroke.

METHODS

Neuroglobin immunoreactivity was measured in brain tissue from control subjects and patients with ischemic stroke.

RESULTS

Neuroglobin was detected in several brain areas, and its expression was increased in the cortical peri-infarct region after stroke.

CONCLUSIONS

Ischemic stroke increases expression of the neuroprotective protein neuroglobin, suggesting neuroglobin may represent a novel target for stroke therapy.

Failure of apoptosis-inducing factor to act as neuroglobin reductase

Neuroglobin (Ngb) is a hexacoordinate globin expressed in the nervous system of vertebrates, where it protects neurons against hypoxia. Ferrous Ngb has been proposed to favor cell survival by scavenging NO and/or reducing cytochrome c released into the cytosol during hypoxic stress. Both catalytic functions require an as yet unidentified Ngb-reductase activity. Such an activity was detected both in tissue homogenates of human brain and liver and in Escherichia coli extracts. Since NADH:flavorubredoxin oxidoreductase from E. coli, that was shown to reduce ferric Ngb, shares sequence similarity with the human apoptosis-inducing factor (AIF), AIF has been proposed by us as a candidate Ngb reductase. In this study, we tested this hypothesis and show that the Ngb-reductase activity of recombinant human AIF is negligible and hence incompatible with such a physiological function.

The structure of neuroglobin at high Xe and Kr pressure reveals partial conservation of globin internal cavities

Neuroglobin (Ngb) is a hexacoordinate globin expressed in the brain of vertebrates. Ferrous Ngb binds dioxygen with high affinity and the O(2) adduct is able to scavenge NO. Convincing in vitro and in vivo data indicate that Ngb is involved in neuroprotection during hypoxia and ischemia. The 3D structure of Ngb reveals the presence of a wide internal cavity connecting its heme active site with the bulk. To explore the role of this "tunnel" in the control of ligand binding, we determined the structure of metNgb and NgbCO equilibrated with Xe or Kr. We show four docking sites for Xe (only two for Kr); two of the four Xe sites are within the large cavity. They are only partially conserved in globins, since the two proximal Xe sites identified in myoglobin (Xe1 and Xe2) are absent in Ngb, as well as in cytoglobin. The Xe docking sites in Ngb map a pathway within the protein matrix, leading to the heme, which becomes more accessible in the ligand-bound species. This may be of significance in connection with the redox chemistry that may be the primary function of this hexacoordinate globin.

Translocation and neuroprotective properties of transactivator-of-transcription protein-transduction domain-neuroglobin fusion protein in primary cultured cortical neurons

Ngb (neuroglobin) is a newly discovered hexaco-ordinate globin that is expressed in vertebrate brain and peripheral nervous systems. Expression of Ngb increases in response to oxygen deprivation and protects neurons from hypoxia in vitro and in vivo. However, the lack of its transduction ability into cells resulted in limited neuroprotection. To educe its neuroprotection under hypoxia, a cell-permeable Ngb fusion protein was generated. A rat brain Ngb gene was cloned and fused with a gene fragment encoding the nine-amino-acid TAT PTD (transactivator-of-transcription protein-transduction domain; RKKRRQRRR) of HIV-1 in a prokaryotic expression vector to generate a genetic in-frame N-terminal hexahistidine-tagged) TAT PTD-Ngb fusion protein. It was expressed in soluble form in Escherichia coli BL21(DE3)plysS and purified with Ni(2+)-affinity chromatography. The results showed that the purified fusion protein TAT PTD-Ngb can enter into the primary cultured cortical neurons in a dose-dependent manner when added exogenously to the culture media and can be detected in cells within 48 h. The cell viability under hypoxia was increased and apoptosis induced by hypoxia was decreased after TAT PTD-Ngb was transduced into cortical neurons. The results provide a clue for the research of Ngb and suggest that transduction of TAT PTD-Ngb may be one of the ways for the therapy of CNS (central nervous system) diseases, especially cerebrovascular diseases and neurodegenerative diseases.

[Expression of neuroglobin in rats with brain injury induced by LPS]

OBJECTIVE

To investigate the expression of neuroglobin (Ngb) in frontal cortex, cerebrospinal fluid (CSF) and serum in rats with brain injury induced by LPS and to elucidate its significance.

METHODS

Seventy adult Sprague-Dawley rats were randomly divided into LPS (n = 60, with injection of 0.1 mg/kg LPS into cistern) and control (C, n = 10, with injection of equal volume of isotonic saline into cistern) groups, with 10 rats in each group. The plasma, CSF as well as frontal cortex from sacrificed rats were collected in LPS group at 3, 6, 12, 24, 48, 72 post injection hour (PIH), with 10 rats at each time point. The protein expression of Ngb was measured by enzyme-linked immunosorbent assay (ELISA) and Western blot. Expression of Ngb in frontal cortex was determined by SP. Water content of frontal cortex was assessed by drying method. The correlation among Ngb contents in serum, CSF, frontal cortex and water content of frontal cortex was analyzed with multiple comparison.

RESULTS

Ngb expression (by ELISA): Ngb expression of frontal cortex, CSF, and serum in LPS group was higher than that in C group at each time point, and it peaked at48 PBH (35.4 +/- 3.9, 22.7 +/- 3.1, 14.4 +/- 2.8 ng/mL, respectively, P < 0.01). Ngb expression (by Western blot): Ngb protein with relative molecular mass of 17 x 10(3) was observed in each group. Ngb expression detected by Western blot was similar to that detected by ELISA. Brain water content was significantly greater in LPS group than that of C group at 6-72 PIH (P < 0.01), and it peaked at 48 PBH (83.3 +/- 1.9)%. Ngb contents in serum, CSF, frontal cortex, and water content of frontal cortex were positively correlated with multiple comparison ( y = 0.631-0.719, P < 0.01).

CONCLUSIONS

Up-regulation of Ngb expression in brain injury induced by LPS is correlated with duration after challenge of LPS.

Antihypoxic effects of neuroglobin in hypoxia-preconditioned mice and SH-SY5Y cells

This work aims at investigating the neuroprotective effects of neuroglobin (Ngb) in vivo and in vitro. RT-PCR and Western blotting were used to examine Ngb mRNA and protein levels in the mouse cortex after acute and repeated exposure to hypoxia. The cDNAs of mouse Ngb were cloned and transfected into SH-SY5Y cells to examine Ngb function in vitro. Expression of Ngb and mRNA was upregulated in the cortex of mice preconditioned by repetitive exposure to hypoxia. Tolerance to hypoxia of Ngb-transformed SH-SY5Y cells was enhanced. These results suggest that Ngb might be involved in hypoxic preconditioning which protects neurons from hypoxic injury.

[Study on the distribution and location of neuroglobin in human tissues and cells]

OBJECTIVE

To explore the distribution and location of neuroglobin (NGB) and its function in human tissues and cells.

METHODS

The distribution and localization of NGB in human tissues and cells were examined by immunohistochemical method.

RESULTS

NGB-positive cells were mainly distributed in neurons of central nervous system and peripheral nervous system, and some in endocrine tissues and genital system. NGB-immunoreactive product located in the cytoplasm of these cells.

CONCLUSION

The expression of NGB in human nervous tissues, some endocrine tissues and genital system suggested that NGB might play an important role in the utilizations of oxygen and physiological functions.

Expression, purification, and crystallization of neuro- and cytoglobin

Neuroglobin and cytoglobin, members of the globin family, are present in vertebrate cells at very low concentrations. As the function of both proteins is still a matter of debate, it is very important to be able to produce and purify these proteins, and in general all members of the globin family, to homogeneity. For this purpose, this chapter describes the expression of neuro- and cytoglobin by E. coli and its preparative purification. These proteins are then used in crystallization experiments. Also an analytical purification strategy is discussed in detail.

Neuroglobin in the rat brain: localization

Neuroglobin (Ngb) is a neuronal hemeprotein similar to myoglobin and hemoglobin and shares their capability for oxygen binding. It has thus been proposed that Ngb acts as an oxygen reservoir or combats reactive oxygen species. In the present study, we investigated the Ngb expression pattern in the rat brain using immunohistochemistry, in situ hybridization, and quantitative real-time PCR (qRT-PCR). This revealed the interesting finding that Ngb expression is restricted to a few neurone populations, many of which are involved in the sleep-wake cycle, circadian regulation or food regulation. In the forebrain we found intense Ngb expression in neurones in the piriform cortex, the central and medial amygdala, the medial preoptic area, the suprachiasmatic nucleus (SCN), the hypothalamic paraventricular nucleus, the perifornical nucleus, the lateral hypothalamus. Within the mid- and hindbrain Ngb expressing neurones were found in the laterodorsal tegmental nucleus, the pedunculo pontine tegmental nucleus, the locus coeruleus, and the lateral parabrachial nucleus. In the medulla oblongata Ngb expressing neurones were found in the nucleus of the solitary tract. The qRT-PCR data showed a diurnal variation of Ngb mRNA in the SCN, having a peak in the day time (light-period) and nadir during night (dark-period).

Neuroglobin in the rat brain (II): co-localisation with neurotransmitters

In an accompanying article, we found that neuroglobin (Ngb) was expressed in a few well-defined nuclei in the rat brain. Here, we show by use of immunohistochemistry and in situ hybridisation (ISH) that Ngb co-localise with several specific neurotransmitters. Ngb co-localise consistently with tyrosine hydroxylase (TH) in the noradrenergic/adrenergic A1/C1 and A2/C2; the noradrenergic A5, A6 and A7. Ngb were not observed to co-localise TH in the dopaminergic A8-A16 cell populations. Ngb were only seen to co-localise with choline acetyltransferase (ChAT) in the laterodorsal tegmental nucleus (LDTg) and in the pontine tegmental nucleus (PPTg). Many Ngb-ir neurones co-localised with neuronal nitric oxide synthase (nNOS) in the LDTg, whereas fewer Ngb-ir neurones co-localise nNOS in the anterior basomedial (BMA) and the posterodorsal medial (MePD) amygdaloid nucleus, in the medial preoptic area (MPA) and in part of the lateral hypothalamus (LH). Ngb-ir neurones co-localise heme oxygenase 1 (HO-1) in the LDTg and locus coeruleus. Ngb-ir neurones co-localise hypocretin-1 (Hcrt1) in the perifornical (PeF) and perifornical lateral hypothalamus (PeFLH). Within the LH, Ngb-ir neurones co-localised melanin concentration hormone (MCH). A few Ngb-ir perikarya in the paraventricular hypothalamic nucleus (PVN) co-localised arginine vasopressin (aVP). Ngb were not observed to co-localise with serotonin, vasointestinal peptide (VIP), or cocaine amphetamine-regulated transcript (CART) at any places. In the present study, we found no evidence that one or more particular neurotransmitters are coupled 100% to Ngb or that Ngb is coupled 100% to a specific neurotransmitter. Based on these findings, we suggest that Ngb could be involved in some sort of regulation of the sleep-wake cycle. Secondly, that Ngb in some neurones is involved in regulation of gaseous neurotransmission, and that this in any given case only involves a subset of neurones. To us this indicates that the cellular and physiological function of Ngb in different subsets of neurones might not be identical, or that all neurones containing Ngb has one thing in common that we at presently not are aware of.

Neuroglobin attenuates beta-amyloid neurotoxicity in vitro and transgenic Alzheimer phenotype in vivo

Neuroglobin (Ngb), a vertebrate globin expressed primarily in neurons, is induced by and protects against neuronal hypoxia and cerebral ischemia. To investigate the spectrum and mechanism of Ngb's neuroprotective action, we studied the effect of transgenic overexpression of Ngb on NMDA and beta-amyloid (Abeta) toxicity in murine cortical neuron cultures in vitro and on the phenotype of Alzheimer's disease (AD) transgenic (APP(Sw,Ind)) mice. Compared with cortical neuron cultures from wild-type mice, cultures from Ngb-overexpressing transgenic (Ngb-Tg mice) were resistant to the toxic effects of NMDA and Abeta(25-35), as measured by polarization of cell membrane lipid rafts, mitochondrial aggregation, lactate dehydrogenase release, and nuclear fragmentation. In addition, compared with APP(Sw,Ind) mice, double-transgenic (Ngb-Tg x APP(Sw,Ind)) mice showed reductions in thioflavin-S-stained extracellular Abeta deposits, decreased levels of Abeta(1-40) and Abeta(1-42), and improved behavioral performance in a Y-maze test of spontaneous alternations. These findings suggest that the spectrum of Ngb's neuroprotective action extends beyond hypoxic-ischemic insults. Ngb may protect neurons from NMDA and Abeta toxicity by inhibiting the formation of a death-signaling membrane complex, and interventions that increase Ngb expression could have therapeutic application in AD and other neurodegenerative disorders.

Reactivity and endogenous modification by nitrite and hydrogen peroxide: does human neuroglobin act only as a scavenger?

NGB (human neuroglobin), a recently discovered haem protein of the globin family containing a six-co-ordinated haem, is expressed in nervous tissue, but the physiological function of NGB is currently unknown. As well as playing a role in neuronal O2 homoeostasis, NGB is thought to act as a scavenger of reactive species. In the present study, we report on the reactivity of metNGB (ferric-NGB), which accumulates in vivo as a result of the reaction of oxyNGB (oxygenated NGB) with NO, towards NO2- and H2O2. NO2- co-ordination of the haem group accounts for the activity of metNGB in the nitration of phenolic substrates. The two different metNGB forms, with and without the internal disulfide bond between Cys46 (seventh residue on the inter-helix region between helices C and D) and Cys55 (fifth residue on helix D), exhibit different reactivity, the former being more efficient in activating NO2-. The kinetics of the reactions, the NO2--binding studies and the analysis of the nitrated products from different substrates all support the hypothesis that metNGB is able to generate an active species with the chemical properties of peroxynitrite, at pathophysiological concentrations of NO2- and H2O2. Without external substrates, the targets of the reactive species generated by the metNGB/NO2-/H2O2 system are endogenous tyrosine (resulting in the production of 3-nitrotyrosine) and cysteine (oxidized to sulfinic acid and sulfonic acid) residues. These endogenous modifications were characterized by HPLC-MS/MS (tandem MS) analysis of metNGB after reaction with NO2- and H2O2 under various conditions. The internal S-S bond affects the functional properties of the protein. Therefore metNGB acts not only as scavenger of toxic species, but also as a target of the self-generated reactive species. Self-modification of the protein may be related to or inhibit its postulated neuroprotective activity.

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.

Neuroglobin dynamics observed with ultrafast 2D-IR vibrational echo spectroscopy

Neuroglobin (Ngb), a protein in the globin family, is found in vertebrate brains. It binds oxygen reversibly. Compared with myoglobin (Mb), the amino acid sequence has limited similarity, but key residues around the heme and the classical globin fold are conserved in Ngb. The CO adduct of Ngb displays two CO absorption bands in the IR spectrum, referred to as N(3) (distal histidine in the pocket) and N(0) (distal histidine swung out of the pocket), which have absorption spectra that are almost identical with the Mb mutants L29F and H64V, respectively. The Mb mutants mimic the heme pocket structures of the corresponding Ngb conformers. The equilibrium protein dynamics for the CO adduct of Ngb are investigated by using ultrafast 2D-IR vibrational echo spectroscopy by observing the CO vibration's spectral diffusion (2D-IR spectra time dependence) and comparing the results with those for the Mb mutants. Although the heme pocket structure and the CO FTIR peak positions of Ngb are similar to those of the mutant Mb proteins, the 2D-IR results demonstrate that the fast structural fluctuations of Ngb are significantly slower than those of the mutant Mbs. The results may also provide some insights into the nature of the energy landscape in the vicinity of the folded protein free energy minimum.

On optima: The case of myoglobin-facilitated oxygen diffusion

The process of myoglobin/leghemoglobin-facilitated oxygen diffusion is adapted to function in different environments in diverse organisms. We enquire how the functional parameters of the process are optimized in particular organisms. The ligand-binding properties of the proteins, myoglobin and plant symbiotic hemoglobins, we discover, suggest that they have been adapted under genetic selection pressure for optimal performance. Since carrier-mediated oxygen transport has probably evolved independantly many times, adaptation of diverse proteins for a common functionality exemplifies the process of convergent evolution. The progenitor proteins may be built on the myoglobin scaffold or may be very different.

Molecular dynamics simulation of deoxy and carboxy murine neuroglobin in water

Globins are respiratory proteins that reversibly bind dioxygen and other small ligands at the iron of a heme prosthetic group. Hemoglobin and myoglobin are the most prominent members of this protein family. Unexpectedly a few years ago a new member was discovered and called neuroglobin (Ngb), being predominantly expressed in the brain. Ngb is a single polypeptide of 151 amino acids and despite the small sequence similarity with other globins, it displays the typical globin fold. Oxygen, nitric oxide, or carbon monoxide can displace the distal histidine which, in ferrous Ngb as well as in ferric Ngb, is bound to the iron, yielding a reversible adduct. Recent crystallographic data on carboxy Ngb show that binding of an exogenous ligand is associated to structural changes involving heme sliding and a topological reorganization of the internal cavities; in particular, the huge internal tunnel that connects the bulk with the active site, peculiar to Ngb, is heavily reorganized. We report the results of extended (90 ns) molecular dynamics simulations in water of ferrous deoxy and carboxy murine neuroglobin, which are both coordinated on the distal site, in the latter case by CO and in the former one by the distal His(64)(E7). The long timescale of the simulations allowed us to characterize the equilibrated protein dynamics and to compare protein structure and dynamical behavior coupled to the binding of an exogenous ligand. We have characterized the heme sliding motion, the topological reorganization of the internal cavities, the dynamics of the distal histidine, and particularly the conformational change of the CD loop, whose flexibility depends ligand binding.

Micro-resonance Raman study of optically trapped Escherichia coli cells overexpressing human neuroglobin

We describe the possibility of using a microresonance Raman spectrometer combined with a microfluidic system and optical tweezers to study Escherichia coli (E. coli) overexpressing wild type (wt) neuroglobin (NGB) and its E7Leu mutant, respectively. NGB is a recently discovered heme protein and its function still is a matter of debate. So far, the protein has been studied in its purified form, and in vivo measurements on the single cell level could give more information. To study the feasibility of the combined techniques, the possibilities of the setup are investigated by taking spectra from single cells and clusters of cells. We find that the microresonance Raman technique enables studies of the wt NGB protein in a living cell under fluctuating aerobic and anaerobic conditions. E. coli cells overexpressing wt NGB are stable, and the reversible oxygenation-deoxygenation can be studied over a long period of time. Further, the experiment indicates the presence of an enzymatic system in the bacteria reducing the ferric form NGB. The study of E. coli cells overexpressing E7Leu NGB, on the other hand, gives insight into limiting factors of the setup, such as cell lysis, photoinduced chemistry, and protein concentrations.

Neuroglobin, seven years after

Neuroglobin is expressed in vertebrates brain and belongs to a branch of the globin family that diverged early in evolution. Sequence conservation suggests a relevant role in the nervous system, with tight structural restraints. Experiments in vivo and in vitro showed increased hypoxic stress damage upon repressing neuroglobin biosynthesis and improved recovery following overexpression. Neuroglobin shows internal heme hexacoordination, which controls oxygen affinity and kinetics. Neuroglobin concentration, oxygen affinity and enhanced autooxidation question a role in oxygen delivery; thus it was proposed that the neuroprotective effect might be due to radical scavenging or activation of protection mechanisms. Neuroglobin's structure shows a peculiar internal cavity of very large size. Binding of heme ligands is associated to a conformational change involving the heme that "slides" into the pre-existing cavity and makes the sixth coordination position available. These features may pave the way to an understanding of neuroprotection by neuroglobin.

Neuroglobin protects PC12 cells against beta-amyloid-induced cell injury

Excessive accumulation of amyloid beta (Abeta) has been proposed as a pivotal event in the pathogenesis of Alzheimer's disease. Possible mechanisms underlying Abeta-induced neuronal cytotoxicity include excess production of reactive oxidative species (ROS) and apoptosis. Neuroglobin (Ngb), a newly discovered globin in vertebrates that exhibits neuroprotective functions, may have a potential role in scavenging ROS. To examine the potential protective role of Ngb in Abeta-induced cytotoxicity, PC12 cells were treated with Abeta (1-42 fragment) for 24h. Abeta treatments increased ROS production in PC12 cells. Overexpression of Ngb but not Ngb mutant in the PC12 cells significantly attenuated Abeta-induced ROS production and lipids peroxidation. Furthermore, overexpression of Ngb also attenuated Abeta-induced mitochondrial dysfunction and apoptosis, and promoted cell survival in PC12 cells. Therefore, Ngb may act as an intracellular ROS scavenger, and such antioxidant properties may play a protective role against Abeta-induced cell injury.

Intracellular delivery of Neuroglobin using HIV-1 TAT protein transduction domain fails to protect against oxygen and glucose deprivation

Neuroglobin (Ngb) is a heme protein that is primarily localised in the retina and the brain. Its physiological role is largely unknown. It has been reported that its overexpression protects neurons from hypoxia in vitro and in vivo, suggesting that the rapid modulation of the Ngb level in the nerve cells may be a promising stroke treatment strategy. In this study, we used a novel approach to overexpress Ngb and evaluate its ability to promote neuronal survival under hypoxic conditions. We constructed a human recombinant Ngb fused to the cell penetrating peptide (CPP) derived from HIV-1 TAT. Purified recombinant TAT-Ngb was able to efficiently transduce CHO and SHSY5Y cells, when added to the culture media. The potential neuroprotective action of Ngb was then examined by using an in vitro model of ischemia. The two neuronal cell lines RGC-5 and SH-SY5Y were subjected to oxygen glucose deprivation (OGD) after pre-treatment with TAT-Ngb. In both cell types, however, the treatment with the TAT-Ngb fusion protein did not show any effect on cell viability. This discrepancy to earlier reports might be due to the experimental model for oxygen glucose deprivation we employed. Alternatively, intracellular delivery of Ngb by the TAT/CPP might not have beneficial effects in the treatment of ischemic pathology.

A neuroglobin-overexpressing transgenic mouse

Neuroglobin (Ngb) is a recently discovered vertebrate globin expressed primarily in neurons. Ngb expression is induced by hypoxia and ischemia, and Ngb protects neurons from these insults. However, its normal physiological role and the mechanism underlying its neuroprotective action are uncertain. We report production of a transgenic mouse in which Ngb is overexpressed under the control of the chicken beta-actin promoter. This mouse should prove helpful for studying Ngb-mediated effects in vitro and in vivo.

Anoxia or oxygen and glucose deprivation in SH-SY5Y cells: a step closer to the unraveling of neuroglobin and cytoglobin functions

Several studies support the hypothesis that neuroglobin and cytoglobin play a protective role against cell death when cellular oxygen supply is critical. Although the underlying molecular mechanisms are unknown, previous reports suggest that this protection can be realised by the fact that they act as ROS scavengers. In this study, expression of neuroglobin and cytoglobin was evaluated in a human neuroblastoma cell line (SH-SY5Y) under conditions of anoxia or oxygen and glucose deprivation (OGD). The cells could survive prolonged anoxia without significant loss of viability. They became anoxia sensitive when deprived of glucose. OGD induced significant cell death after 16 h resulting in 54% dead cells after 32 h. Necrosis was the main process involved in OGD-induced cell death. After reoxygenation, apoptotic neurons became more abundant. Real-time quantitative PCR and Western blotting revealed that neuroglobin and cytoglobin were upregulated, the former under OGD and the latter under anoxic conditions. Under OGD, cell survival was significantly reduced after inhibiting cytoglobin expression by transfection with antisense ODN. Moreover, cell survival was significantly enhanced by neuroglobin or cytoglobin overexpression. When neuroglobin or cytoglobin protein expression increased or decreased, the H(2)O(2) level was found to be lower or higher, respectively. We conclude that neuroglobin or cytoglobin act as ROS scavengers under ischemic conditions.

Neuroglobin and cytoglobin as potential enzyme or substrate

The possible enzymatic activities of neuro- and cytoglobin as well as their potential function as substrates in enzymatic reactions were studied. Neuro- and cytoglobin are found to show no appreciable superoxide dismutase, catalase, and peroxidase activities. However, the internal disulfide bond (CD7-D5) of human neuroglobin can be reduced by thioredoxin reductase. Furthermore, our in vivo and in vitro studies show that Escherichia coli cells contain an enzymatic reducing system that keeps the heme iron atom of neuroglobin in the Fe(2+) form in the presence of dioxygen despite the high autoxidation rate of the molecule. This reducing system needs a low-molecular-weight compound as co-factor. In vitro tests show that both NADH and NADPH can play this role. Furthermore, the reducing system is not specific for neuroglobin but allows the reduction of the ferric forms of other globins such as cytoglobin and myoglobin. A similar reducing system is present in eukaryotic tissue protein extracts.