title: Neuroglobin-deficiency exacerbates Hif1A and c-FOS response, but does not affect neuronal survival during severe hypoxia in vivo.
abstract: 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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Clinical Biochemistry, University of Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark. c.hundahl@gmail.com
authors.forename: Christian Ansgar
authors.initials: CA
authors.lastname: Hundahl
authors.forename: Hendrik
authors.initials: H
authors.lastname: Luuk
authors.forename: Sten
authors.initials: S
authors.lastname: Ilmjärv
authors.forename: Birgitte
authors.initials: B
authors.lastname: Falktoft
authors.forename: Zindy
authors.initials: Z
authors.lastname: Raida
authors.forename: Jonas
authors.initials: J
authors.lastname: Vikesaa
authors.forename: Lennart
authors.initials: L
authors.lastname: Friis-Hansen
authors.forename: Anders
authors.initials: A
authors.lastname: Hay-Schmidt
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002470:Cell Survival; D002843:Chromatin / Q000378:metabolism; D005786:Gene Expression Regulation; D005838:Genotype; D005914:Globins / Q000172:deficiency* / Q000502:physiology*; D006019:Glycolysis; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000502:physiology*; D000078787:Neuroglobin; D009474:Neurons / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*
chemical_list: D002843:Chromatin; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D016760:Proto-Oncogene Proteins c-fos; D005914:Globins