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

Hibernating arctic ground squirrels ( Urocitellus parryii ), overwintering in frozen soils, maintain large gradients between ambient temperature ( T a ) and body temperature ( T b ) by substantially increasing metabolic rate during torpor while maintaining a subzero T b . We used quantitative revers...

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Bibliographic Details
Published in:Journal of Experimental Biology
Main Authors: Williams, Cory T., Goropashnaya, Anna V., Buck, C. Loren, Fedorov, Vadim B., Kohl, Franziska, Lee, Trixie N., Barnes, Brian M.
Format: Text
Language:English
Published: Company of Biologists 2011
Subjects:
Research Articles
Arctic
permafrost
Urocitellus parryii
Online Access:http://jeb.biologists.org/cgi/content/short/214/8/1300
https://doi.org/10.1242/jeb.052159
Description
Summary:Hibernating arctic ground squirrels ( Urocitellus parryii ), overwintering in frozen soils, maintain large gradients between ambient temperature ( T a ) and body temperature ( T b ) by substantially increasing metabolic rate during torpor while maintaining a subzero T b . We used quantitative reverse-transcription PCR (qRT-PCR) to determine how the expression of 56 metabolic genes was affected by season (active in summer vs hibernating), metabolic load during torpor (imposed by differences in T a : +2 vs –10°C) and hibernation state (torpid vs after arousal). Compared with active ground squirrels sampled in summer, liver from hibernators showed 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 and ELOVL6 ), 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 glycogen synthesis ( GSY1 ) in liver showing consistent differences in expression levels between temperature treatments. Despite the more than eightfold increase in energetic demand associated with defending T b during torpor at a T a of –10 vs +2°C, transcript levels in liver and brown adipose tissue differed little. Our results are inconsistent with a hypothesized switch to use of non-lipid fuels when ambient temperatures drop below freezing.

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