Seasonal Cues & Hibernation Alter Expression of Uncoupling Proteins in the Golden Hamster

Abstract

Mammals use shivering and nonshivering thermogenesis (NST) to generate heat in cold environments. Uncoupling protein 1 (UCP1) mediates NST activity in brown fat (BAT); but the roles of UCP2 and 3, homologs of UCP1, are unclear. We measured expression levels of UCP1, 2, & 3 in the golden hamster, M. auratus, during exposure to seasonal changes in photoperiod, temperature and during hibernation. We acclimated hamsters to breeding season conditions [long PP, 14:10 hrs light:dark plus 22 ± 2oC (WA)], to winter preparation conditions [short PP (SPP), 8:16 hrs light:dark plus 22 ± 2oC], and to winter conditions [cold, 6 ± 2oC, plus SPP (CA/SPP)]. After exposure to CA/SPP, some hamsters entered hibernation. Using quantitative real time PCR we measured UCP1, 2, & 3 transcript levels in cervical BAT (CBAT), gastrocnemius & plantaris muscles combined (G/P), soleus (S) muscle, liver and white fat (WAT). We hypothesized that: (1) SPP exposure would increase UCP1 expression, but decrease that of UCP2 & 3; (2) CA/SPP would further increase UCP1 mRNA and initiate increases in UCP2 & 3 expression; and (3) in hibernation, UCP1, 2, & 3 mRNA levels would remain elevated to retain re-warming capability. We found CBAT UCP1 expression did not increase in SPP, but did in CA/SPP and more so in hibernators (P<0.05). Cold also enhanced UCP3 expression in S and CBAT (P<0.05), but not in G/P; and hibernation elevated UCP1 & 2 expression in CBAT, but not in liver or WAT. Thus, in addition to UCP1, UCP2 & 3 may contribute to BAT thermogenesis in hamsters that are cold acclimated or re-warming from hibernation, and that in some muscles, UCP3 may also play a role in cold-induced metabolism.