The present study aimed to determine the effect of thyroid hormone dysfunction
on brown adipose tissue activity and white adipose tissue browning in mice.
Twenty randomized female C57BL/6NTac mice per treatment group housed at room
temperature were rendered hypothyroid or hyperthyroid. In-vivo small animal
18F-FDG PET/MRI was performed to determine the effects of hypo- and
hyperthyroidism on BAT mass and BAT activity. Ex-vivo14C-acetate loading assay
and assessment of thermogenic gene and protein expression permitted analysis
of oxidative and thermogenic capacities of WAT and BAT of eu-, hyper and
hypothyroid mice. 18F-FDG PET/MRI revealed a lack of brown adipose tissue
activity in hypothyroid mice, whereas hyperthyroid mice displayed increased
BAT mass alongside enhanced 18F-FDG uptake. In white adipose tissue of both,
hyper- and hypothyroid mice, we found a significant induction of thermogenic
genes together with multilocular adipocytes expressing UCP1. Taken together,
these results suggest that both the hyperthyroid and hypothyroid state
stimulate WAT thermogenesis most likely as a consequence of enhanced
adrenergic signaling or compensation for impaired BAT function, respectively
