Fucoxanthin Ameliorates MASLD by Directly Targeting GRP78 to Restore ER Homeostasis and Activate AMPK Signaling

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.