The core function of hematopoietic stem and progenitor cells (HSPCs) is to provide lifelong production of all lineages of the blood and immune cells. The mechanisms that modulate HSPC homeostasis and lineage-biasing are not fully understood. Growing evidence implicates the aryl hydrocarbon receptor (AHR), an environment sensing transcription factor, as a regulator of hematopoiesis. AHR ligands modulate the frequency of mature hematopoietic cells in the bone marrow and periphery, while HSPCs from mice lacking AHR (AHR KO) have increased proliferation. Yet, whether AHR modulates HSPC lineage potential and directs differentiation towards specific lineage-biased progenitors is not well understood. Our current study revealed that AHR-KO mice have an increased proportion of myeloid-biased HSCs and myeloid-biased multipotent progenitors (MPP3) cells. Utilizing inducible AHR knockout mice (iAHR-KO), it was discovered that acute deletion of AHR doubled the number of MPP3 cells and altered the composition of downstream lineage-committed progenitors, such as increased frequency of pre-granulocyte/monocyte committed progenitors. Furthermore, in-vivo antagonism of the AHR led to a 2.5-fold increase in the number of MPP3 cells and promoted myeloid-biased differentiation. Using hematopoietic-specific conditional AHR knockout mice (AHRVav1) revealed that increased frequency of myeloid-biased HSCs and myeloid-biased progenitors are driven by AHR signaling that is intrinsic to the hematopoietic compartment. These findings demonstrate that the AHR plays a pivotal role in regulating steady-state hematopoiesis, influencing HSPC homeostasis and lineage potential. Additionally, the data presented provide potential insight into how deliberate modulation of AHR signaling could help with the treatment of a broad ranges of diseases that require the hematopoietic compartment.

Recent evidence suggests that the environment-sensing transcription factor aryl hydrocarbon receptor (AHR) is an important regulator of hematopoiesis. Yet, the mechanisms and extent of AHR-mediated regulation within the most primitive hematopoietic cells, hematopoietic stem and progenitor cells (HSPCs), are poorly understood. Through a combination of transcriptomic and flow cytometric approaches, this study provides new insight into how the AHR influences hematopoietic stem and progenitor cells. Comparative analysis of intraphenotypic transcriptomes of hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells from AHR knockout (AHR KO) and wild type mice revealed significant differences in gene expression patterns. Notable among these were differences in expression of cell cycle regulators, specifically an enrichment of G2/M checkpoint genes when Ahr was absent. This included the regulator Aurora A kinase (Aurka, AurA). Analysis of AurA protein levels in HSPC subsets using flow cytometry, in combination with inducible AHR KO or in vivo AHR antagonism, showed that attenuation of AHR increased levels of AurA in HSCs and lineage-biased MPP cells. Overall, these data highlight a potential novel mechanism by which AHR controls HSC homeostasis and HSPC differentiation. These findings advance the understanding of how AHR influences and regulates primitive hematopoiesis.

Recent evidence suggests that the environment-sensing transcription factor aryl hydrocarbon receptor (AHR) is an important regulator of hematopoiesis. Yet, the mechanisms and extent of AHR-mediated regulation within the most primitive hematopoietic cells, hematopoietic stem and progenitor cells (HSPCs), are poorly understood. Through a combination of transcriptomic and flow cytometric approaches, this study provides new insight into how the AHR influences HSPCs. Comparative analysis of intraphenotypic transcriptomes of hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells from AHR knockout (AHR KO) and wild-type (WT) mice revealed significant differences in gene expression patterns. Notable among these were differences in expression of cell cycle regulators, specifically an enrichment of G2/M checkpoint genes when Ahr was absent. This included the regulator Aurora A kinase ( Aurka , AurA). Interrogation of AurA protein levels in HSPC subsets using flow cytometry, in combination with inducible AHR KO or in vivo AHR antagonism showed that attenuation of AHR increased levels of AurA in HSCs and lineage-biased MPP cells. Overall, these data highlight a potential novel mechanism by which AHR controls HSC homeostasis and HSPC differentiation. These findings advance the understanding of how AHR influences and regulates primitive hematopoiesis. Highlights (max 85 characters): AHR alters gene expression during HSC-MPP transition. Transcriptomic analysis shows AHR regulation of key G2/M phase regulators Inducible AHR KO mice show increased AurA levels in HSPC populations Acute antagonism of AHR increased AurA levels across multiple HSPC populations