Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs.
Androgens have benefits, such as promoting muscle growth, but also significant costs, including suppression of immune function. In many species, these trade-offs in androgen action are reflected in regulated androgen production, which is typically highest only in reproductive males. However, all non-reproductive Arctic ground squirrels, irrespective of age and sex, have high levels of androgens prior to hibernating at sub-zero temperatures. Androgens appear to be required to make muscle in summer, which, together with lipid, is then catabolized during overwinter. By contrast, most hibernating mammals catabolize only lipid. We tested the hypothesis that androgen action is selectively enhanced in Arctic ground squirrel muscle because of an upregulation of androgen receptors (ARs). Using Western blot analysis, we found that Arctic ground squirrels have AR in skeletal muscle more than four times that of Columbian ground squirrels, a related southern species that overwinters at approximately 0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph nodes was equivalent in both species. Brain AR was also modestly but significantly increased in Arctic ground squirrel relative to Columbian ground squirrel. These results are consistent with the hypothesis that tissue-specific AR regulation prior to hibernation provides a mechanism whereby Arctic ground squirrels obtain the life-history benefits and mitigate the costs associated with high androgen production.
Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada M1C 1A4 boonstra@utsc.utoronto.ca.
Rudy
R
Boonstra
Department of Psychology and Cell and Systems Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.
Kaiguo
K
Mo
Department of Psychology and Cell and Systems Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.
Douglas Ashley
DA
Monks
D000416:Alberta; D000728:Androgens / Q000378:metabolism*; D000818:Animals; D001110:Arctic Regions; D015153:Blotting, Western / Q000662:veterinary; D001921:Brain / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006605:Hibernation; D008198:Lymph Nodes / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics* / Q000378:metabolism; D012589:Sciuridae / Q000502:physiology*; D013045:Species Specificity; D015874:Yukon Territory
D000728:Androgens; D011944:Receptors, Androgen
adrenal androgens; androgen receptors; life-history trade-offs; muscle anabolism and catabolism