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Deeper understanding of the cellular and molecular pathways regulating hematopoiesis is critical to maximize the therapeutic potential of hematopoietic stem cells (HSCs) in curative procedures including hematopoietic stem cell transplantation (HST). We have recently identified mast cells (MCs) as therapeutically-targetable components of the HSC niche. Here, we demonstrate that mice lacking MCs display peripheral neutrophilia, expansion of bone marrow (BM) HSC populations, resistance to repeated 5-fluorouracil (5-FU) administration, and a BM genetic signature primed for hematopoietic proliferation. MC deficiency functionally altered both the hematopoietic and the stromal compartment of the BM as hematopoietic reconstitution was accelerated in wildtype mice that received MC deficient BM and in MC deficient recipients that received wildtype BM. Finally, we demonstrate that mice treated at steady state with the MC stabilizing agent ketotifen exhibit increased BM cellularity as well as expansion of phenotypic HSC populations. This work provides novel mechanistic rationale to explore mast cells as a target to enhance human BM transplants. Additionally, the potential of repurposing FDA approved mast cell targeting therapies to promote hematopoietic regeneration may provide well-tolerated treatment strategies at a fraction of the cost and development time.

Emerging evidence implicates the eicosanoid molecule prostaglandin E2 (PGE2) in conferring a regenerative phenotype to multiple organ systems following tissue injury. As aging is in part characterized by loss of tissue stem cells’ regenerative capacity, we tested the hypothesis that the prostaglandin-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) contributes to the diminished organ fitness of aged mice. Here we demonstrate that genetic loss of 15-PGDH (Hpgd) confers a protective effect on aging of murine hematopoietic and gastrointestinal (GI) tissues. Aged mice lacking 15-PGDH display increased hematopoietic output as assessed by peripheral blood cell counts, bone marrow and splenic stem cell compartments, and accelerated post-transplantation recovery compared to their WT counterparts. Loss of Hpgd expression also resulted in enhanced GI fitness and reduced local inflammation in response to colitis. Together these results suggest that 15-PGDH negatively regulates aged tissue regeneration, and that 15-PGDH inhibition may be a viable therapeutic strategy to ameliorate age-associated loss of organ fitness.