SUN-108 Dose-Dependent Effect of Progesterone on T37i Brown Adipocyte Differentiation

Brown adipose tissue (BAT) is a specialized organ that dissipates energy as heat by a unique mitochondrial protein, uncoupling protein 1 (UCP1). Sex differences on BAT function and abundance have been studied in many species: BAT of female mice has a greater thermogenic function due to a higher mitochondrial capacity than in males, and metabolically active BAT in the PET/CT imaging is more prevalent in women than in men. These sex-specific features are likely driven by sex hormones: estrogen and testosterone. However, the effect of progesterone, a major circulating female sex hormone during luteal phase and pregnancy, has been limitedly studied and available data are conflicting. We aimed to investigate the direct effects of progesterone on BAT differentiation and function using T37i, a female brown adipocyte cell line. T37i cells were differentiated with a standard regimen: 20 nM insulin and 2 nM triiodothyronine, with or without progesterone from 100 nM (a physiological circulating level) to 10 µM. After 9 days of differentiation, cells were collected for analysis or stimulated for 24 hours with 1 µM norepinephrine (NE). Progesterone dose-responsively reduced T37i differentiation. This is reflected by a 30% reduced lipid accumulation (quantified by Oil Red O staining), 37% decreased basal lipolytic activity (determined by glycerol release into the culture media), and decreased expression of adipogenic marker genes: Cd36 65%, Adipoq 68%, and Lep 93% reductions at the highest progesterone concentration. Concerning the thermogenic capacity of T37i cells, progesterone inhibited basal and NE-stimulated expressions of thermogenic genes (baseline Ucp1 98% and Ppargc1a 63% reductions; NE-stimulated Ucp1 97% and Ppargc1a 76% reductions) and reduced the NE-stimulated lipolysis by 50%. Moreover, short-term treatment with progesterone on differentiated T37i cells also reduced Ucp1, Adipoq, and Lep gene expressions. Interestingly, we could not detect Pgr mRNA expression in T37i cells. In conclusion, we demonstrated that progesterone inhibits the T37i brown adipocyte differentiation and thermogenic function, likely independently from the classical progesterone receptor, in a dose-dependent manner. Further studies are required to elucidate the mechanisms how progesterone inhibits BAT differentiation and functions.