Modulation of gene expression in heart and liver of hibernating black bears (Ursus americanus)

Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
BMC Genomics (Impact Factor: 3.99). 03/2011; 12(1):171. DOI: 10.1186/1471-2164-12-171
Source: PubMed


Hibernation is an adaptive strategy to survive in highly seasonal or unpredictable environments. The molecular and genetic basis of hibernation physiology in mammals has only recently been studied using large scale genomic approaches. We analyzed gene expression in the American black bear, Ursus americanus, using a custom 12,800 cDNA probe microarray to detect differences in expression that occur in heart and liver during winter hibernation in comparison to summer active animals.
We identified 245 genes in heart and 319 genes in liver that were differentially expressed between winter and summer. The expression of 24 genes was significantly elevated during hibernation in both heart and liver. These genes are mostly involved in lipid catabolism and protein biosynthesis and include RNA binding protein motif 3 (Rbm3), which enhances protein synthesis at mildly hypothermic temperatures. Elevated expression of protein biosynthesis genes suggests induction of translation that may be related to adaptive mechanisms reducing cardiac and muscle atrophies over extended periods of low metabolism and immobility during hibernation in bears. Coordinated reduction of transcription of genes involved in amino acid catabolism suggests redirection of amino acids from catabolic pathways to protein biosynthesis. We identify common for black bears and small mammalian hibernators transcriptional changes in the liver that include induction of genes responsible for fatty acid β oxidation and carbohydrate synthesis and depression of genes involved in lipid biosynthesis, carbohydrate catabolism, cellular respiration and detoxification pathways.
Our findings show that modulation of gene expression during winter hibernation represents molecular mechanism of adaptation to extreme environments.

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Available from: Vadim B Fedorov
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    • "We also observed that total bile acid levels in the serum were lower in the winter with large reductions in primary and conjugated bile acids (Figure 2G;Table S2 ). Notably, expression of the ratelimiting enzyme of bile acid production CYP7A1 is reduced in the liver of hibernating mammals (Fedorov et al., 2011; Otis et al., 2011), and the microbiota contributes to modifications of bile acids (Sayin et al., 2013). Bile acids promote lipid uptake and respond to food intake. "
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    • "The array data were transformed with quantile normalization (Bolstad et al. 2003), and a one-way ANOVA test was used to select genes that exhibited significant differences between hibernating and summer-active animals. Similar to experiments with other tissues (Fedorov et al. 2011), a P-value <0.05 and |log 2 FC | >0.5 were set as cut-offs for significant differences in expressed genes, where FC is fold change (the mean expression value in the hibernating animals divided by the mean expression value in the summer-active animals as the criteria for differentially expressed genes as previously reported for other tissues (Fedorov et al. 2009, 2011)). The false discovery rate (FDR) was calculated using random permutation as described by Storey & Tibshirani (2003). "
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