Mengjie Li, Qian Ou, Qiang Qin, Jiaxi Chen, Sen Yang, Jie Zhao, Hua Meng, Xu Li, Pinglong Xu, Cunqi Ye, Xiaojian Wang
High-fat diet (HFD) is a risk factor for metabolic dysfunction-associated steatotic liver disease (MASLD), yet the molecular pathways that connect dietary fats to liver dysfunction remain unclear. Here, we discover that hepatic downregulation of Raf kinase inhibitory protein (RKIP) in MASLD patients and male mice is linked to fatty acid uptake, which causes endoplasmic reticulum (ER)-associated degradation of RKIP by inhibiting its S-palmitoylation. Via facilitating the m6A-modified RNA binding of YTHDF1, RKIP is required for the efficient translation of PEMT, an essential enzyme in maintaining phosphatidylcholine (PC) / phosphatidylethanolamine (PE) ratio and ER homeostasis. Hepatocyte-specific RKIP depletion in male mice exacerbates the PC/PE imbalance and ER stress, resulting in lipid droplets accumulation and MASLD progression. Notably, RKIP correlates positively with PEMT protein but inversely with MASLD development. These findings uncover a cellular mechanism of HFD-RKIP-PEMT that underlies diet-induced liver metabolic disease and propose RKIP as a target for MASLD prevention. This study finds HFD downregulates RKIP expression via inhibiting its Spalmitoylation. This impairs translation of PEMT, an essential enzyme for ER lipid homeostasis, exacerbating PC/PE imbalance and ER stress, thereby driving MAFLD progression.