Ceramide-dependent vesicle secretion modulates the integrated stress response in hematopoietic stem cells

Cellular crosstalk within the bone marrow niche maintains hematopoietic stem and progenitor cell (HSPC) integrity and safeguards lifelong blood and immune cell production. Deeper understanding of reciprocal niche signals governing crucial properties of HSPCs is relevant to the pathophysiology of blood disorders and improving HSPC transplantation. Extracellular vesicles (EVs) are key factors of the HSPC secretome, providing signals that regulate homeostasis and stemness. Here we demonstrate ex vivo blockade of ceramide-dependent vesicle secretion from HSPCs activates an integrated stress response (ISR), promoting downstream mTOR inhibition and metabolic quiescence. Crucially, ceramide-EV depletion leads to striking improvements in long-term transplantation. The aggregate findings link ceramide-dependent EV secretion and the ISR as a regulatory dyad guarding HSPC homeostasis and long-term fitness. Translationally, these data support exploration of ceramide inhibition during ex vivo maintenance of HSPCs for adoptive transfer.