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. 2017 Jan 3;12(1):e0169366.
doi: 10.1371/journal.pone.0169366. eCollection 2017.

Transcriptome Analysis Identifies Key Metabolic Changes in the Hooded Seal (Cystophora Cristata) Brain in Response to Hypoxia and Reoxygenation

Free PMC article

Transcriptome Analysis Identifies Key Metabolic Changes in the Hooded Seal (Cystophora Cristata) Brain in Response to Hypoxia and Reoxygenation

Mariana Leivas Müller Hoff et al. PLoS One. .
Free PMC article


The brain of diving mammals tolerates low oxygen conditions better than the brain of most terrestrial mammals. Previously, it has been demonstrated that the neurons in brain slices of the hooded seal (Cystophora cristata) withstand hypoxia longer than those of mouse, and also tolerate reduced glucose supply and high lactate concentrations. This tolerance appears to be accompanied by a shift in the oxidative energy metabolism to the astrocytes in the seal while in terrestrial mammals the aerobic energy production mainly takes place in neurons. Here, we used RNA-Seq to compare the effect of hypoxia and reoxygenation in vitro on brain slices from the visual cortex of hooded seals. We saw no general reduction of gene expression, suggesting that the response to hypoxia and reoxygenation is an actively regulated process. The treatments caused the preferential upregulation of genes related to inflammation, as found before e.g. in stroke studies using mammalian models. Gene ontology and KEGG pathway analyses showed a downregulation of genes involved in ion transport and other neuronal processes, indicative for a neuronal shutdown in response to a shortage of O2 supply. These differences may be interpreted in terms of an energy saving strategy in the seal's brain. We specifically analyzed the regulation of genes involved in energy metabolism. Hypoxia and reoxygenation caused a similar response, with upregulation of genes involved in glucose metabolism and downregulation of the components of the pyruvate dehydrogenase complex. We also observed upregulation of the monocarboxylate transporter Mct4, suggesting increased lactate efflux. Together, these data indicate that the seal brain responds to the hypoxic challenge by a relative increase in the anaerobic energy metabolism.

Conflict of interest statement

The authors have declared that no competing interests exist.


Fig 1
Fig 1. Venn diagram showing the unique and shared DE genes in hypoxia and hypoxia/reoxygenation treated brain slices of the hooded seal.
(A) Upregulated genes, (B) downregulated genes.
Fig 2
Fig 2. Heat map of gene expression in the visual cortex and brain slices from the hooded seal.
(A) Hierarchical clustering of the regulated genes in the differentially treated brain slices and the visual cortex. (B) Hierarchical clustering of the top 20 up- and top 20 downregulated genes shared between hypoxia/reoxygenation and the normoxia control.
Fig 3
Fig 3. Gene ontology analyses of hypoxia and hypoxia/reoxygenation-regulated genes in seal brain slices.
GO analysis in the domain "molecular function" of the significantly up- (A) and down- (B) regulated genes in the hooded seal brain slices after 1 h hypoxia (black) and after 1 h hypoxia followed by 20 min reoxygenation (white). The analyses of the GO terms in the categories "biological process" and "protein class" are given in S3 and S4 Figs.
Fig 4
Fig 4. Regulation of enzymes of the energy metabolism enzymes in hooded seal cortex in response to hypoxia and reoxygenation.
Upregulated genes are indicated by a green plus (+), downregulated genes are indicated by a red minus (-). All genes show the same patterns of regulation, except Cox5a and Cox5b, which were only regulated by hypoxia, and Atp5i, Sucla2, and Idh3g, which were only found regulated after reoxygenation. Thick arrows represent the reactions that may be favored by the regulations observed here. See S3 Table for abbreviations and details.
Fig 5
Fig 5. Expression levels of components of the pyruvate dehydrogenase (PDH) complex.
The RPKM values of Pdha1, Pdhx, Dlat and Dld show significant downregulation in the seal brain slices after hypoxia and hypoxia/reoxygenation (N = 3). Error bars represent standard deviations. Statistical significance was indicated by one-way ANOVA associated with Tukey's multiple comparison tests; different letters indicate statistically significant differences.

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Grant support

This study has been supported by the Deutsche Forschungsgemeinschaft (Bu956/12). MLMH is supported by a fellowship for Ph.D. by the German Academic Exchange Service (DAAD) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)/Brazil (5125/11-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.