Temperature-flux induced metabolic adjustments in WAT

Mice have their lowest (basal) metabolic rate when housed at thermoneutrality, which starts above 29 degrees C. Although they eat less, and thus reduce their energy intake, their energy balance remains positive leading to an increased adiposity, especially when fed a high fat diet. However, almost all metabolic mouse studies are performed at standard room temperatures ranging between 20 and 22 degrees C. Previously, we showed that housing mice at thermoneutrality lead to massive increased adiposity, while metabolic dysfunction of white adipose tissue (WAT) was absent. Here, we studied whether an increased metabolic flux through WAT induces cellular stress and underlies tissue dysfunction leading to tissue inflammation. C57BL/6JOlaHsd wildtype male mice, aged 9 weeks, were fed purified low fat diet (BIOCLAIMS, Hoevenaars et al., Genes and Nutrition 2012) for 3 weeks to acclimatize, followed by 12 weeks a BIOCLAIMS high-fat diet (HFD), all at thermoneutrality (29 degrees C). Subsequently, mice were divided into different treatment groups: i) control group, which remained at thermoneutrality for 5 days, ii) 5 days normal housing temperature (22 C degrees) while housed continously in an indirect calorimetry system. At the end of the study, after 2 hours food removal at the start of the light phase, mice were killed immediately by decapitation after taking them out of the indirect calorimetry system. After sacrification, epididymal WAT was immediately dissected and snap frozen in liquid nitrogen. Total RNA was isolated, quantified and qualified, and subsequently used for global gene expression profiling using Agilent 8x60K microarrays.