4-hydroxybenzoic acid induces browning of white adipose tissue through the AMPK-DRP1 pathway in HFD-induced obese mice

Background: Beige adipocytes have physiological functions similar to brown adipocytes, which are available to increase energy expenditure through uncoupling protein 1 (UCP1) within mitochondria. Recently, many studies showed white adipocytes can undergo remodeling into beige adipocytes, called "browning", by increasing fusion and fission events referred to as mitochondrial dynamics. Purpose: In this study, we aimed to investigate the browning effects of 4-hydroxybenzoic acid (4-HA), one of the major compounds of black raspberries. Methods: We examined the mechanism underlying the browning properties of 4-HA focusing on UCP1-dependent non-shivering thermogenesis in 3T3-L1 white adipocytes, high-fat diet (HFD)-induced obese male C57BL/6J mice, and cold-exposed male C57BL/6J mice. Results: 4-HA treatment elevates browning markers such as UCP1, T-Box transcription factor 1, and PR domain containing 16, mitochondrial function factors like oxidative phosphorylation complex as well as mitochondrial dynamic-related factors like phosphorylated dynamin-related protein 1 (p-DRP1), DRP1, and mitofusin 1 in 3T3L1 white adipocytes, which were also confirmed in inguinal white adipose tissue (iWAT) of HFD-induced obese mice. Mdivi-1 blocked the increased DRP1-mediated mitochondrial fission by 4-HA, and even the browning effect of 4-HA was abolished. Furthermore, 4-HA increased AMP-activated protein kinase (AMPK) in both the 3T3-L1 white adipocytes and iWAT of HFD-induced obese mice. Inhibition of AMPK with Compound C also blocked the 4-HA-induced mitochondrial fission and browning effect. Conclusions: 4-HA induces the browning of white adipocytes into beige adipocytes by regulating the DRP1mediated mitochondrial dynamics through AMPK. These findings suggest that 4-HA could serve as a therapeutic candidate for obesity and related metabolic disorders.