Synergistic activation of thermogenic adipocytes by a combination of PPARγ activation, SMAD3 inhibition and adrenergic receptor activation ameliorates metabolic abnormalities in rodents.

Aims/hypothesis: To treat obesity and related diseases, considerable effort has gone into developing strategies to convert white adipocytes into thermogenic brown-like adipocytes ('browning'). The purpose of this study was to identify the most efficient signal control for browning.

Methods: To identify the most efficient signal control for browning, we examined rat stromal vascular fraction cells. In addition, physiological changes consequent to signal control were examined in vivo using lean and diet-induced obese (DIO) C57BL/6J mice.

Results: Combined treatment with the peroxisome proliferator-activated receptor γ (PPARγ) agonist rosiglitazone, the SMAD3 inhibitor SIS3 and the adrenergic receptor agonist noradrenaline (norepinephrine) synergistically induced Ucp1, Fgf21 and Cited1 expression, triggering brown adipogenesis. Synergistic induction of Ucp1 by the three agents was negatively regulated by forkhead box O (FOXO)3 via the inhibition of PPARγ-dependent gene transcription. Moreover, the administration of rosiglitazone, SIS3 and the selective β3 adrenergic receptor agonist CL316,243 to DIO mice reduced the amount of body-fat deposits (body weight from day 0 to 14, 12.3% reduction), concomitant with morphological changes in white adipose tissue, an increase in mitochondrial biosynthesis and a marked induction of uncoupling protein 1 (UCP1). Furthermore, administration of the three agents significantly increased serum adiponectin levels (mean 65.56 μg/ml with the three agents vs 20.79 μg/ml in control mice, p < 0.05) and improved glucose and lipid tolerance.

Conclusions/interpretation: These results suggest that the combined regulation of PPARγ, SMAD and the adrenergic receptor signalling pathway synergistically induces brown adipogenesis and may serve as an effective strategy to treat obesity and related diseases, including type 2 diabetes.