Fucosterol Promotes Browning in Mouse 3T3-L1 Adipocytes Through HO-1/Nrf2 and AMPK Pathways

Browning of white adipose tissue offers a promising strategy to manage obesity by enhancing thermogenesis and lipid oxidation. Although fucosterol, a phytosterol found in brown seaweeds, has been recognized for its antioxidant and metabolic benefits, its ability to trigger browning has not been previously reported. In this study, we demonstrate for the first time that fucosterol induces adipocyte browning in 3T3-L1 cells. Treatment with fucosterol (10-50 μM) during adipogenic differentiation suppressed lipid accumulation and downregulated adipogenic transcription factors (PPARγ, C/EBPα, SREBP-1), while enhancing lipolysis via increased phosphorylation of HSL and AMPK. Critically, browning markers PRDM16, PGC1α, and UCP1 were robustly upregulated in a dose-dependent manner. Fucosterol also activated the Nrf2/HO-1 antioxidant pathway, as evidenced by increased HO-1 expression and Nrf2 nuclear translocation. Pharmacological inhibition of HO-1 or AMPK reversed these effects, confirming their essential role in fucosterol-induced thermogenic remodeling. Interestingly, despite activation of p38 and ERK MAPKs-often linked to stress signaling-fucosterol reduced pro-inflammatory cytokine levels (IL-6, IL-1β, TNF-α) and elevated antioxidant enzymes (SOD, GPx, CAT), suggesting a non-inflammatory metabolic adaptation. These findings reveal a previously uncharacterized function of fucosterol in promoting adipocyte browning, driven by HO-1/Nrf2 and AMPK pathways, with potential relevance for therapeutic strategies targeting obesity.