EMP1 preserves hematopoietic stem cell potential under homeostasis and radiation-induced injury by alleviating ER stress [ER-stress ATAC-seq]

Hematopoietic stem cells (HSCs) play a crucial role in lifelong hematopoiesis by generating all blood lineages. The long-term maintenance of HSCs relies on the regulation of endoplasmic reticulum (ER) stress at a low level. However, the precise control of ER stress in HSCs remains largely unknown. In this study, we demonstrate that suppression of ER stress enhances the in vitro maintenance and in vivo repopulation capacity of HSCs, while also protecting HSCs against radiation-induced injury. Integrated multi-omics analysis has revealed that epithelial membrane protein 1 (Emp1) functions as an ER stress sensor in HSCs. Loss of Emp1 leads to increased 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 dihydroceramides (dhCers), which are a class of sphingolipids. DhCers accumulate in Emp1-deficient HSCs and directly induce protein aggregation. Inhibition of CERS2 significantly restores the maintenance of Emp1-deficient HSCs. Furthermore, Emp1 deficiency renders HSCs more susceptible to radiation, while overexpression of Emp1 or inhibition of CERS2 protects HSCs against radiation-induced injury. These findings highlight the critical role played by the EMP1-CERS2-dhCers axis in constraining ER stress and preserving HSC potential, uncovering a new link between sphingolipid metabolism and HSC homeostasis, and have clinical implications.