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Hibernating above the permafrost: effects of ambient temperature and season on expression of metabolic genes in liver and brown adipose tissue of arctic ground squirrels

TitleHibernating above the permafrost: effects of ambient temperature and season on expression of metabolic genes in liver and brown adipose tissue of arctic ground squirrels
Publication TypeJournal Article
Year of Publication2011
AuthorsWilliams, CT, Goropashnaya, AV, Buck, LC, Fedorov, VB, Kohl, F, Lee, TN, Barnes, BM
JournalThe Journal of Experimental Biology
Volume214
Pagination1300–1306
Abstract

Hibernating arctic ground squirrels (Urocitellus parryii), overwintering in frozen soils, maintain large gradients between ambienttemperature (Ta) and body temperature (Tb) by substantially increasing metabolic rate during torpor while maintaining a subzeroTb. We used quantitative reverse-transcription PCR (qRT-PCR) to determine how the expression of 56 metabolic genes wasaffected by season (active in summer vs hibernating), metabolic load during torpor (imposed by differences in Ta: +2 vs –10°C)and hibernation state (torpid vs after arousal). Compared with active ground squirrels sampled in summer, liver from hibernatorsshowed increased expression of genes associated with fatty acid catabolism (CPT1A, FABP1 and ACAT1), ketogenesis (HMGCS2)and gluconeogenesis (PCK1) and decreased expression of genes associated with fatty acid synthesis (ACACB, SCD andELOVL6), amino acid metabolism, the urea cycle (PAH, BCKDHA and OTC), glycolysis (PDK1 and PFKM) and lipid metabolism(ACAT2). Stage of hibernation (torpid vs aroused) had a much smaller effect, with only one gene associated with glycogensynthesis (GSY1) in liver showing consistent differences in expression levels between temperature treatments. Despite the morethan eightfold increase in energetic demand associated with defending Tb during torpor at a Ta of –10 vs +2°C, transcript levels inliver and brown adipose tissue differed little. Our results are inconsistent with a hypothesized switch to use of non-lipid fuelswhen ambient temperatures drop below freezing.

DOI10.1242/jeb.052159
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