Neutral sphingomyelinase blockade enhances hematopoietic stem cell fitness through an integrated stress response

Hematopoietic stem and progenitor cell (HSPC) transplantation serves as a curative therapy for many benign and malignant hematopoietic disorders and as a platform for gene therapy. However, growing needs for ex vivo manipulation of HSPC-graft products are limited by barriers in maintaining critical self-renewal and quiescence properties. The role of sphingolipid metabolism in safeguarding these essential cellular properties has been recently recognized, but not yet widely explored. Here, we demonstrate that pharmacologic and genetic inhibition of neutral sphingomyelinase 2 (nSMase-2) leads to sustained improvements in long-term competitive transplantation efficiency after ex vivo culture. Mechanistically, nSMase-2 blockade activates a canonical integrated stress response (ISR) and promotes metabolic quiescence in human and murine HSPCs. These adaptations result in part from disruption in sphingolipid metabolism that impairs the release of nSMase-2-dependent extracellular vesicles (EVs). The aggregate findings link EV trafficking and the ISR as a regulatory dyad guarding HSPC homeostasis and long-term fitness. Translationally, transient nSMase-2 inhibition enables ex vivo graft manipulation with enhanced HSPC potency.

Automated summary

This study demonstrates that inhibition of nSMase-2 can significantly improve the transplantation efficiency of HSPC after ex vivo culture. The blockade of nSMase-2 activates ISR and promotes metabolic quiescence, partly due to disrupted sphingolipid metabolism that impairs the release of nSMase-2-dependent EVs. These findings reveal the importance of EV trafficking and ISR in maintaining HSPC homeostasis and long-term fitness, and suggest that transient nSMase-2 inhibition can enhance HSPC potency during ex vivo graft manipulation.