Thermoneutral Acclimation and FGF21 in Obese Mice

32, 21 week old, male C57BL6/J DIO mice were obtained from the Jackson Laboratories (Bar Harbor, ME), fed 60% high fat diet (Research Diets D12492). Mice were acclimatized for 2 weeks at 72 °F (ambient) then moved to 80 °F that is close to thermoneutral zone, to acclimate another week prior to baseline randomization and subsequent surgery. For experiments at ambient temperature, mice were housed at 72 °F throughout the study. Animals were allocated into 4 groups of n = 8 based on BW and glucose levels to achieve equal distribution of these parameters in each group. On day 0, all animals underwent surgery for the implantation of an Alzet® mini-pump (Model #2002, Durect Corporation) for continuous delivery of either vehicle (PBS) or 0.85 mg/kg/day native FGF21. The iBAT was surgically removed at the time of mini-pump implant in those mice allocated into the X-BAT groups. VO₂ and VCO₂ were measured for 24 hours of fed and 24 hours of fasted conditions using a comprehensive laboratory animal monitoring system (CLAMS) equipped with an Oxymax Open Circuit Calorimeter (Columbus Instruments, Columbus, OH) as previously described (n = 8/group)20 (link)30 (link). RT-PCR One-Step (Qiagen) was used to determine the expression of UCP-1 by standard PCR protocol.