Neuroglobin protects against nitric oxide toxicity

Abstract

Neuroglobin (Ngb) is a novel vertebrate globin expressed principally in neurons. Ngb expression is induced by hypoxia and ischemia, and Ngb protects neurons against these insults. The mechanism of Ngb's protective action is unknown, but its ability to bind NO suggests that NO scavenging might be involved. To test this hypothesis, we treated wild type and Ngb-transfected HN33 (mouse hippocampal neuron × N18TG2 neuroblastoma) cells with NO donors and compared their sensitivity to NO-induced cell death. Ngb overexpression shifted concentration-toxicity curves to the right, indicating reduced susceptibility to NO or is metabolites. The results suggest that the ability of Ngb to neutralize the neurotoxic effects of reactive nitrogen species may be an important contributor to its neuroprotective properties. KeywordsNeuroglobin; nitric oxide; hypoxia Neuroglobin (Ngb) is a monomeric globin that is distantly related to hemoglobin and myoglobin and is expressed predominantly in brain neurons [3]. Ngb expression is induced by neuronal hypoxia and cerebral ischemia [21] and Ngb, in turn, appears to modulate hypoxicischemic brain injury. Thus, enhancing Ngb expression reduces-and knocking down Ngb expression increases-hypoxic neuronal injury in vitro [21] and ischemic cerebral injury in vivo [22]. In addition, Ngb-overexpressing transgenic mice are resistant to cerebral infarction from occlusion of the middle cerebral artery [10,11]. Ngb also reduces the toxicity of H 2 O 2 [5], paraquat [5] and β-amyloid [13] in vitro. However, the mechanisms that underlie neuroprotection by Ngb are unknown.Ancestral globins served primarily as NO oxygenases, converting NO to nitrate, whereas their O 2 -transporting function evolved later [20]. This primordial oxygenase activity is still apparent in the capacity of hemoglobin [6] and myoglobin [4] to scavenge NO, and appears to have pathophysiological significance, since overexpression of inducible NO synthase (NOS) causes heart failure in myoglobin-knockout mice [7]. Because Ngb binds NO [23], its neuroprotective action may also relate to NO scavenging [1,8].Several lines of evidence point to a connection between Ngb and NO. In addition to the ability of Ngb to bind NO [23], some studies have shown parallelism between the distribution of Ngb and of neuronal NOS (nNOS) [15], and NOS expression is increased in several tissues of Ngboverexpressing transgenic mice [11]. Autooxidation of Ngb yields NgbO 2 , which is thought to react rapidly with NO to form a peroxynitrite (ONOO − )-bound intermediate that decays to * To whom correspondence should be addressed: dgreenberg@buckinstitute.org Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered ...

Neuroglobin, estrogens, and neuroprotection

“…Despite the cellular mechanisms remain poorly defined and still controversial, many in vivo studies performed in Ngb-overexpressing transgenic mice, in primary neurons, and in cultured cell lines sustain the neuroprotective role played by Ngb (35,41,44,72,76,78,79). In Ngb-overexpressing transgenic animals, the size of cerebral infarct is drastically reduced (79,80), and the cell survival is enhanced under conditions of Alzheimer disease, anoxia, and oxygen and glucose deprivation (69,73,78,79).…”

Silencing neuroglobin enhances neuronal vulnerability to oxidative injury by down-regulating 14-3-3γ

“…Another proposed function of Ngb is the protection of neuronal cells from various pathological insults. Overexpression of Ngb prevents cell death from hypoxia, ischemia, NO, amyloid beta, and H 2 O 2 insults [11,[18][19][20] . However, the administration of penetrating Ngb directly to SH-SY5Y cells does not confer protection from oxygen and glucose deprivation [21] .…”

Ligand migration through the internal hydrophobic cavities in human neuroglobin

“…Strong evidences suggest that the neuroprotective effect of Ngb might be directly or indirectly associated with an NO scavenging activity (12). The increased resistance of cultured mice neurons overexpressing Ngb to toxic concentrations of NO seems to support this mechanism (13). However, the efficiency of Ngb as a NO dioxygenase in vitro is comparable to that of other globins, both pentacoordinated and hexacoordinated (8), and only the characterization of a specific reductase system in neuronal cells will confirm this role.…”