Abstract
BackgroundNeuroglobin (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 FindingsNgb-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.SignificanceAccording 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.
Highlights
Hypoxia and ischemic injury are both characterized by reduced oxygen availability in the tissue, which is detrimental for the brain due to its very high metabolic demand [1]
The present study evaluates the effect of hypoxia on neuronal survival and gene regulation in Ngb-null mice leading us to the following conclusions: 1) Ngb is not vital for neuronal survival during hypoxia, but 2) Ngb deficiency has a global aggravating effect on the expression of key hypoxia regulatory genes and 3) Ngb deficiency alters the hypoxia-dependent transcriptional response of genes related to the glycolysis pathway
Ngb-deficient mice Ngb was targeted by introducing LoxP sites into the introns flanking exons 2 and 3, which were subsequently removed by mating Ngb-floxed mice with C57BL/6J Cre deleter mice (Figure 1A, please see section ‘‘Ngb deficient mice’’ in Materials and Methods, for details)
Summary
Hypoxia and ischemic injury are both characterized by reduced oxygen availability in the tissue, which is detrimental for the brain (and heart) due to its very high metabolic demand [1]. Unlike the muscles, where myoglobin can store and facilitate oxygen diffusion from the blood, the brain was believed to lack a similar storage system until Burmester and coworkers [2] discovered a neuron-specific globin, which they named Neuroglobin (Ngb). Notwithstanding the marked differences from myoglobin and at least partly due to reported up-regulation of Ngb expression during hypoxia, it has been proposed that Ngb may have neuroprotective properties during hypoxia in vitro [10,11] and in animal models of ischemia [10,12,13,14,15]. 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. Differential expression was estimated by a novel data analysis approach, which applies non-parametric statistical inference directly to probe level measurements
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
