Abstract
Aim: To investigate whether housing temperature influences rat adiposity, and the extent it is modified by diet and/or pregnancy. Housing temperature impacts on brown adipose tissue, that possess a unique uncoupling protein (UCP) 1, which, when activated by reduced ambient temperature, enables rapid heat generation.Methods: We, therefore, examined whether the effects of dietary induced rise in fat mass on interscapular brown fat in female rats were dependent on housing temperature, and whether pregnancy further modulates the response. Four week old rats were either maintained at thermoneutrality (27°C) or at a “standard” cool temperature (20°C), and fed either a control or obesogenic (high in fat and sugar) diet until 10 weeks old. They were then either tissue sampled or mated with a male maintained under the same conditions. The remaining dams were tissue sampled at either 10 or 19 days gestation.Results: Diet had the greatest effect on fat mass at thermoneutrality although, by 19 days gestation, fat weight was similar between groups. Prior to mating, the abundance of UCP1 was higher at 20°C, but was similar between groups during pregnancy. UCP1 mRNA followed a similar pattern, with expression declining to a greater extent in the animals maintained at 20°C.Conclusion: Housing temperature has a marked influence on the effect of dietary induced rise in fat deposition that was modified through gestation. This maybe mediated by the reduction in UCP1 with housing at thermoneutrality prior to pregnancy and could subsequently impact on growth and development of the offspring.
Highlights
The temperature in which laboratory animals are maintained can have a pronounced impact on both metabolic and physiological homeostasis (Maloney et al, 2014). This is important when investigating adipose tissue function, as brown fat is very sensitive to ambient temperature and its activity is enhanced when rats are kept at temperatures below thermoneutrality, i.e., less than 27◦C
Housing temperature will be important in the interpretation of studies investigating the impact of maternal obesity on pregnancy outcomes
We examined the impact of housing temperature on UCP1 in the primary brown adipose tissue (BAT) depot in rodents and the extent to which either protein or gene expression could be modulated by being maintained at a “standard” cool temperature (i.e., 20◦C) or at thermoneutrality (i.e., ∼27◦C)
Summary
The temperature in which laboratory animals are maintained can have a pronounced impact on both metabolic and physiological homeostasis (Maloney et al, 2014) This is important when investigating adipose tissue function, as brown fat is very sensitive to ambient temperature and its activity is enhanced when rats are kept at temperatures below thermoneutrality, i.e., less than 27◦C. The majority of rodent studies show little stimulatory effect of obesity on birth weight (Shankar et al, 2007; Morris and Chen, 2009) and some even show an increased incidence of intra-uterine growth retardation (Howie et al, 2009) This is important as the main consequence of maternal obesity in otherwise apparently healthy women is increased birth weight (Ruager-Martin et al, 2010). Before examining the magnitude of postnatal outcome, it is necessary to establish whether ambient temperature has comparable effects in the mother, to those which have been described primarily in male mice (Stemmer et al, 2015; Xiao et al, 2015; Cui et al, 2016)
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