Investigating the fetal origins of myeloid-biased hematopoietic stem cells

PROJECT ABSTRACT Hematopoietic stem cells (HSCs) play a crucial role in maintaining blood cell production throughout life and are essential for therapeutic interventions such as HSC transplantation. At a young age, HSC produce sufficient amounts of blood cells of both myeloid and lymphoid linages. However, with aging, there is a dramatic shift in HSC lineage output towards myeloid cells at the expense of naive lymphocyte production, leading to compromised immune function and increased susceptibility to hematologic disorders. While this age-associated change has been largely attributed to alterations in the adult HSC compartment, emerging evidence suggests that lineage biases may originate early in life during fetal development. Recent findings from our lab have identified a subset of HSCs marked by the surface marker Neogenin-1 (Neo1), which exhibit a myeloid-biased lineage output. Utilizing our unique reporter mouse line in which long-term HSCs are marked by mCherry expression under the regulation of the Hoxb5 gene, and transplantation experiments, my preliminary data indicate that Hoxb5 +Neo1+ HSCs are present in fetal hematopoietic tissues and contribute to the myeloid- biased HSC population in adults. Building upon this discovery, my proposed research aims to elucidate the developmental origin and functional characteristics of Hoxb5+Neo1+ myeloid- biased HSCs (my-HSCs) that are present in the fetal liver. Through comprehensive analyses of embryonic and extra-embryonic hematopoietic sites, I will investigate the localization and frequency of Hoxb5+Neo1+-expressing HSCs during prenatal development. I will employ advanced techniques such as flow cytometry, immunofluorescence, transplantation, and single-cell RNA sequencing to characterize the transcriptional landscapes of Hoxb5 +Neo1+ HSCs and their progeny throughout development and aging. Additionally, lineage tracing and HSC subset depletion experiments will be performed to determine the contribution of Hoxb5 +Neo1+ fetal HSCs to the population of my-HSCs in adulthood. Overall, this study aims to uncover the developmental origins of my-HSCs and their implications for hematopoietic aging. By understanding the mechanisms underlying HSC lineage biases, we hope to pave the way for future therapeutic interventions aimed at preserving or restoring balanced hematopoiesis in aging individuals.