In vivo modeling of stress erythropoiesis through targeted gene editing of rat hematopoietic stem cells

In response to anemia, the erythroid lineage significantly expands. This growth is driven by extramedullary erythropoiesis in mice, but is additionally regulated within the bone marrow (BM) of rats, a process likely conserved in humans due to similar BM architecture. This process is, however, mostly elusive. We identified E-cadherin to mark the expansion of the erythroid lineage in BM from anemic rats. To explore the regulation of erythropoiesis in the BM in response to anemia, we studied the role of E-cadherin in the erythroid lineage of rats. As genetic methods to model erythropoiesis in rats are limited, we established a rat BM transplant model that, combined with CRISPR/Cas9 genome editing, enabled us to examine the control of E-cadherin in BM in response to anemia. We identified CD90+CD44+CD45R- cells to contain hematopoietic stem and progenitor cells (HSPCs) in rats. CD90+CD44+CD45R--enriched HSPCs can be efficiently edited using CRISPR/Cas9, which, upon transplant, induce high BM chimerism. Importantly, we identified that recovery from irradiation-induced anemia involves 2 phases. Phase 1 is marked by expansion of erythroid precursors in the BM, supported by extramedullary erythropoiesis in the spleen. This phase is followed by a second phase, characterized by accelerated terminal differentiation, which is selectively controlled in the BM. Finally, we discovered that genetic inactivation of hematopoietic-expressed E-cadherin delays recovery from radiation-induced anemia. Our work provides novel means to expand our knowledge on hematology, and the opportunity to dissect the molecular regulation underlying the erythroid response(s) to anemia in BM, using rat models.