The long-term maintenance of hematopoietic stem cells (HSCs) relies on the regulation of endoplasmic reticulum (ER) stress at a low level, but the underlying mechanism remains poorly understood. Here, we demonstrate that suppression of ER stress improves the functions of HSCs and protects HSCs against ionizing radiation (IR)-induced injury. We identify epithelial membrane protein 1 (EMP1) as a key regulator that mitigates ER stress in HSCs. Emp1 deficiency leads to the accumulation of protein aggregates and elevated ER stress, ultimately resulting in impaired HSC maintenance and self-renewal. Mechanistically, EMP1 is located within the ER and interacts with ceramide synthase 2 (CERS2) to limit the production of a class of sphingolipids, dihydroceramides (dhCers). DhCers accumulate in Emp1 -deficient HSCs and induce protein aggregation. Furthermore, Emp1 deficiency renders HSCs more susceptible to IR, while overexpression of Emp1 or inhibition of CERS2 protects HSCs against IR-induced injury. These findings highlight the critical role played by the EMP1-CERS2-dhCers axis in constraining ER stress and preserving HSC potential.
Ischemia-reperfusion injury (IRI) remains the leading cause of early graft failure following liver transplantation (LT). Traditional paradigms have centered on hepatocyte death, yet the decisive contribution of liver sinusoidal endothelial cells (LSECs) as the first vascular barrier has long been overlooked. Here, single-cell RNA sequencing of human livers comparing normal controls with those exposed to transplantation-induced IRI, identified EMP1 as the most upregulated gene in LSECs. In LSECs and BRL3A hepatocytes subjected to hypoxia/reoxygenation (H/R), EMP1 silencing with an siRNA, ferroptosis modulation via ferrostatin-1 (Fer-1) or RSL3, and p38 signaling intervention using the p38 activator berberine chloride collectively revealed that EMP1 drives ferroptosis in LSECs in a p38-dependent manner. The results demonstrated that LSECs constituted the predominant hepatic endothelial population, whose numbers decline precipitously after transplantation. EMP1 emerged as the most markedly up-regulated gene in LSECs, correlating closely with the severity of injury. Silencing of EMP1 restored fenestral architecture, reduced VCAM-1 and E-selectin expression levels, suppressed Fe 2+ accumulation and lipid peroxidation, down-regulated ACSL4, and reinstated GPX4, thereby halving the hepatocyte death effects phenocopied by Fer-1 and reversed by RSL3, confirming that ferroptosis as the central mechanism. Furthermore, EMP1 exerted its effects solely via p38 signaling and its depletion selectively abolished p38 phosphorylation, whereas the p38 activator berberine chloride fully reinstated ferroptotic phenotypes and hepatocyte injury. Collectively, these data establish EMP1/p38-driven LSEC ferroptosis as a direct cause of hepatocyte damage, offering a fundamentally new perspective on the pathogenesis of h epatic ischemia reperfusion injury (HIRI) and a novel, potentially targeted therapeutic strategy for its prevention and treatment.
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