UC San Diego

Although brown adipose tissue (BAT) has recently become a topic of interest due to its newfound presence in adult humans, the morphology brown adipocytes and expression of uncoupling protein 1 (UCP1) during developmental embryonic and postpartum time frames remains unclear. Additionally, little is known about how maternal obesity affects BAT development in fetal offspring. We selected pups of C57BL/6J dams from E15.5 through P30.5 under standard pregnancy conditions. Interscapular BAT (iBAT) samples were taken and analyzed using hematoxylin and eosin staining, western blotting for anti-UCP1, and fluorescent imaging using UCP1-creER mT/mG transgenic construct. We placed C57BL/6J dams on 60% high fat calorie content diets 3 months before gestation and analyzed UCP1 content in pups using immunohistochemistry for anti-UCP1. Analysis on pup iBAT during standard pregnancies along our perinatal time frame revealed a linearly significant decrease in cell density and increase in adipocyte area. Moreover, both iBAT mass ratio to body weight and UCP1 protein expression spiked on P0.5 and eventually diminished. UCP1-creER mT/mG fluorescent imaging revealed UCP1 gene activity as early as E18.5. Maternal obesity increased UCP1 expression in iBAT at birth. Our study provides foundational information into the structural morphology of perinatal iBAT and the starting time point of UCP1 expression. We also find maternal obesity causes an increase in UCP1 expression during postpartum development in pups.