Abstract
The identification of direct molecular targets for bioactive dietary components is critical for precision nutrition intervention in metabolic dysfunction-associated steatotic liver disease (MASLD). Fucoxanthin, a marine carotenoid from Sargassum fusiforme, exhibits potent lipid-lowering effects; however, its precise intracellular targets and upstream regulatory mechanisms remain elusive. Herein, using drug affinity responsive target stability (DARTS) coupled with LC-MS/MS, we identified the endoplasmic reticulum (ER) chaperone glucose-regulated protein 78 (GRP78) as a direct binding target of fucoxanthin. Molecular dynamics (MD) simulations and cellular thermal shift assays (CETSA) confirmed a stable interaction, primarily driven by hydrogen bonding at the ARG74 residue. In ob/ob mice and palmitic acid-induced HepG2 cells, fucoxanthin treatment significantly alleviated hepatic steatosis and suppressed ER stress. Mechanistically, the fucoxanthin-GRP78 interaction was found to be indispensable for the subsequent activation of AMP-activated protein kinase (AMPK) signaling. Notably, siRNA-mediated knockdown of GRP78 or pharmacological inhibition of AMPK completely abolished the lipid-lowering and ER stress-relieving effects of fucoxanthin, confirming a causal GRP78-AMPK axis. This study elucidates a novel target-driven mechanism wherein fucoxanthin acts as a GRP78 ligand to restore ER homeostasis and reprogram lipid metabolism. These findings position the fucoxanthin-GRP78 axis as a specific therapeutic target for nutritional strategies against MASLD.