<p>Metabolic dysfunction-associated steatohepatitis (MASH) is a serious chronic liver disease, in which ferroptosis has been identified as a crucial triggering event. However, the precise mechanisms of ferroptosis activation in MASH have not been fully disclosed. Herein, we found a positive association between macrophage Notch1 activation and hepatocyte ferroptosis in MASH patients and mice. Further, macrophage-specific Notch1 knockout (Notch1^M-KO) mice showed ameliorative MASH symptoms, including less liver injury, lipid accumulation, inflammation, and collagen deposition. These mice also exhibited reduced hepatocyte ferroptosis, evidenced by decreased Fe²⁺ levels and expression of pro-ferroptosis genes (<i>Hamp</i> and <i>Ptgs2</i>) and higher expression of anti-ferroptosis genes (<i>Gpx4</i> and <i>Slc7a11</i>), as well as improved mitochondrial structure. Moreover, hepatocytes that received exosomes from Notch1-deficient macrophages exhibited decreased ferroptosis, while the tail vein infusion of Notch1-activated macrophage exosomes aggravated ferroptosis and MASH symptoms, identifying the role of macrophage Notch1-exosomes in promoting hepatocyte ferroptosis under MASH. Mechanistically, we discovered that macrophage Notch1 activation increased the level of exosomal miR-142a-3p by miRNA sequencing and decreased its target gene TIPE2, and confirmed that the inhibition of miR-142a-3p upregulated the Notch1 activation-induced TIPE2 decrease. Besides, overexpression of TIPE2 in hepatocytes inhibited ferroptosis. Collectively, our findings uncover a novel mechanism by which Notch1 activation in hepatic macrophages promotes hepatocyte ferroptosis through the exosomal miR-142a-3p/TIPE2 axis in MASH. We revealed a novel insight into hepatocyte ferroptosis activation from the perspective of macrophage, and discovered a pivotal role of macrophage Notch1 in hepatocyte ferroptosis during MASH progression, highlighting a potential therapeutic target for MASH treatment.</p> Graphical abstract <p></p>