Quercetin Upregulates Uncoupling Protein 1 in White/Brown Adipose Tissues through Sympathetic Stimulation

Uncoupling protein 1 (UCP1) plays an important role in increasing energy expenditure; thus, it is being considered as a new target for preventing obesity and metabolic complications. In this study, we investigated the effect of quercetin, a naturally occurring flavonoid, on UCP1 expression in white/brown adipose tissues (WAT/BAT). Mice were fed a high-fat diet (HFD) supplemented with or without dietary quercetin for 9 weeks, and 3T3-L1 adipocytes were treated with quercetin. Expression of UCP1 and other thermogenic genes/proteins was measured by real-time polymerase chain reaction and/or Western blotting. Dietary quercetin supplementation increased the level of UCP1 in both WAT and/or BAT of HFD-fed obese mice, which was accompanied by upregulated mRNA levels of thermogenesis-related genes. Quercetin supplementation enhanced the plasma norepinephrine level and tended to upregulate mRNA level in the WAT of HFD-fed obese mice, accompanied by AMP-activated protein kinase (AMPK) activation. Moreover, quercetin enhanced UCP1 expression in 3T3-L1 adipocytes, and this was blunted by treatment with a peroxisome proliferator-activated receptor gamma (PPARγ) antagonist. These findings suggest that quercetin upregulates UCP1, implying increased WAT browning and BAT activity, via activation of the AMPK/PPARγ pathway through sympathetic stimulation. Quercetin may be useful for preventing obesity and metabolic complications.