Leptin activation was dependent on the AMPKα/STAT3 pathway. (A) Relative mRNA expression of the BAT markers UCP-1, PGC1α, PRDM-16, DIO-2, and CD36 in differentiated C3H10T1/2 cells treated with vehicle, leptin or PNS. (B) Western blot analyses of PRDM-16, PGC1α, leptin, and phosphorylated STAT3 and AMPKα protein levels in differentiated C3H10T1/2 cells. β-actin was used as a loading control. (C) The efficiency of the siRNA-mediated depletion of AMPKα and STAT3 in beige cells treated with leptin was determined by immunoblotting. (D) Representative fluorescence images showing the expression of UCP-1 (red) and the status of lipid droplets stained with BODIPY 493/503 (green) in the siRNA-treated cells after induction. Scale bar: 20 µm.