SummaryCellular stress responses serve as crucial decision points balancing persistence or culling of hematopoietic stem cells (HSCs) for lifelong blood production. Although strong stressors cull HSCs, the linkage between stress programs and self-renewal properties that underlie human HSC maintenance remains unknown, particularly at quiescence exit when HSCs must also dynamically shift metabolic state. Here, we demonstrate distinct wiring of the sphingolipidome across the human hematopoietic hierarchy and find that genetic or pharmacologic modulation of the sphingolipid enzyme DEGS1 regulates lineage differentiation. Inhibition of DEGS1 in hematopoietic stem and progenitor cells during the transition from quiescence to cellular activation with N-(4-hydroxyphenyl) retinamide activates coordinated stress pathways that coalesce on endoplasmic reticulum stress and autophagy programs to maintain immunophenotypic and functional HSCs. Thus, our work identifies a linkage between sphingolipid metabolism, proteostatic quality control systems, and HSC self-renewal and provides therapeutic targets for improving HSC-based cellular therapeutics.

Dyskeratosis congenita (DC) is a multisystem disorder, with a disruption in telomere biology leading to very short telomeres underpinning its pathophysiology. Bone marrow failure is a key feature in DC and is the leading cause of mortality. Hematopoietic stem cell transplantation (HSCT) is the only curative option for bone marrow failure in DC; however, small case reports and series have suggested a poor outcome after HSCT. We undertook a systematic review of all reported patients with DC who underwent HSCT to better characterize outcome and to identify factors associated with improved survival. The outcome of 109 patients found in the literature was poor, with 5- and 10-year survival estimates of only 57% and 23%, respectively. Patients transplanted after 2000 had improved early survival, with 5-year survival estimates of 70%; however, longer term survival was similar (28%). Pulmonary disease, infection, and graft failure were the leading causes of death. Prognosis after development of pulmonary disease post-HSCT was poor, with only 4 of 15 patients surviving at last follow-up. Multivariate analysis identified age >20 years at HSCT, HSCT before 2000, and alternate donor source to be poor prognostic markers. Reduced-intensity conditioning was not significantly found to be associated with improved survival. This review shows the poor outcome after HSCT in patients with DC and highlights the need for future collaborative clinical trials and extended follow-up of this rare patient population to define whether changes in therapy will lead to improved survival.

Blood cells are organized as a hierarchy with hematopoietic stem cells (HSCs) at the root. The advent of genomic technologies has opened the way for global characterization of the molecular landscape of HSCs and their progeny, both in mouse and human models, at the genetic, transcriptomic, epigenetic, and proteomics levels. Here, we outline our current understanding of the molecular programs that govern human HSCs and how dynamic changes occurring during HSC differentiation are necessary for well-regulated blood formation under homeostasis and upon injury. A large body of evidence is accumulating on how the programs of normal hematopoiesis are modified in acute myeloid leukemia, an aggressive adult malignancy driven by leukemic stem cells. We summarize these findings and their clinical implications.