PEMT-mediated phospholipid imbalance promotes age-associated metabolic dysfunction-associated steatotic liver disease progression.

Metabolic dysfunction-associated steatotic liver disease [MASLD; previously known as nonalcoholic fatty liver disease (NAFLD)] is a prevalent chronic liver disorder strongly associated with aging, yet the mechanisms underlying age-related hepatic lipid dysregulation remain incompletely defined. This study investigates how aging alters hepatic phospholipid metabolism and the contribution of phosphatidylethanolamine N-methyltransferase (PEMT) to MASLD progression. Here, lipid accumulation was characterized in the livers of 2-, 6-, 12-, 18-, and 24-month-old mice, revealing age-dependent increases in hepatic triacylglycerol (TG), total cholesterol (TC), and lipid droplet formation. Lipidomic analysis revealed a marked imbalance in phospholipid composition, characterized by increased phosphatidylcholine (PC) and decreased phosphatidylethanolamine (PE), resulting in a 2.5-fold increase in the PC/PE ratio in 24-month-old mice compared with 6-month-old controls. Mechanistically, PEMT, a key enzyme regulating PC and PE metabolism, exhibited significantly increased expression (~2.4-fold at the protein level) in aged livers, suggesting a pivotal role in driving the observed phospholipid imbalance in vitro. PEMT inhibition significantly attenuated lipid droplet accumulation by ~30% and reduced intracellular TG levels by ~20% in D-galactose-induced senescent AML12 hepatocytes under lipid stress, compared with nonsilenced senescent controls. These findings suggest that aging-driven PEMT overexpression promotes phospholipid remodeling and hepatic lipid accumulation. By leveraging a natural aging mouse model, our study provides the first evidence linking PEMT activity to age-associated phospholipid dyshomeostasis, revealing a previously unknown mechanistic axis distinct from diet-induced MASLD and offering new therapeutic insights.