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Leptin Receptor, a Surface Marker for a Subset of Highly Engrafting Long-term Functional Hematopoietic Stem Cells

ABSTRACT: The hematopoietic system is sustained by a rare population of hematopoietic stem cells (HSCs), which emerge during early fetal development and then reside in the hypoxic niche of the adult bone marrow microenvironment. Although leptin receptor (Lepr)-expressing stromal cells are well-studied as critical regulators of murine hematopoiesis, the biological implications of Lepr expression on HSCs remain largely unexplored. We hypothesized that Lepr+HSCs are functionally different from other HSCs. Using in vitro and in vivo experimental approaches, we demonstrated that Lepr further differentiates SLAM HSCs into two distinct populations; Lepr+HSCs engrafted significantly higher than Lepr-HSCs and self-renewed more extensively as noted in secondary transplants. To determine how molecular pathways and gene expression profiles affect their functional differences, we performed bulk RNA-sequencing on purified Lepr+HSC/MPP and Lepr-HSC/MPP cells. Our results showed that Lepr+HSCs were characterized by a proinflammatory transcriptomic profile enriched for Type-I Interferon and Interferon-gamma (IFN-γ) response pathways, which are known to be critical for the emergence of HSCs in fetal life. Gene set analyses indicated that Lepr+HSCs were more highly enriched for genes associated with long-term HSCs whereas Lepr-HSCs’ expression profiles were more closely related to progenitors. We conclude that although Lepr+HSCs represent a minor subset of HSCs, they are highly engrafting cells that possess embryonic-like transcriptomic characteristics, and that Lepr can serve as a useful marker for functional long term HSCs, which may have potential clinical applicability.

ORGANISM(S): Mus musculus

PROVIDER: GSE158393 | GEO | 2020/10/30

REPOSITORIES: GEO

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Project description:Hematopoietic stem cells (HSCs) are at the basis of the hematopoietic hierarchy. Their ability to self-renew and differentiate is strictly controlled by molecular signals produced by their surrounding micorenvironments composed of stromal cells. HSCs first emerge in the AGM (Aorta Gonads Mesonephros) region, amplify in the fetal liver (FL) and are maintained in the adult bone marrow (BM). To further characterize the molecular program of the HSC niches, we have compared the global transcriptome of HSC-supportive and non-supportive stromal clones established from the AGM, FL and BM. Hematopoietic stem cells (HSCs) are at the basis of the hematopoietic hierarchy. Their ability to self-renew and differentiate is strictly controlled by molecular signals produced by their surrounding micorenvironments composed of stromal cells. HSCs first emerge in the AGM (Aorta Gonads Mesonephros) region, amplify in the fetal liver (FL) and are maintained in the adult bone marrow (BM). To further characterize the molecular program of the HSC niches, we have compared the global transcriptome of HSC-supportive line from Fetal Calvaria (OP9) and non-supportive stromal clones from fetal liver (BFC). Hematopoietic stem cells (HSCs) are at the basis of the hematopoietic hierarchy. Their ability to self-renew and differentiate is strictly controlled by molecular signals produced by their surrounding micorenvironments composed of stromal cells. HSCs first emerge in the AGM (Aorta Gonads Mesonephros) region, amplify in the fetal liver (FL) and are maintained in the adult bone marrow (BM). To further characterize the molecular program of the HSC niches, we have compared the global transcriptome of HSC-supportive and non-supportive stromal clones established from fetal liver. We took advantage of stromal clones established from the AGM, FL and BM and tested for their ability to support or not HSCs ex vivo. RNA were extracted from confluent stromal cultures or sorted cells and used for hybridization of Affymetrix (mouse gene 1.0 ST) microarrays.

Project description:Disrupting mutations of the RUNX1 gene are found in 10% of patients with myelodysplasia (MDS) and 30% of patients with acute myeloid leukemia (AML). Previous studies have revealed an increase in hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells in conditional Runx1-knockout (KO) mice, but the molecular mechanism is unresolved. We investigated the myeloid progenitor (MP) compartment in KO mice, arguing that disruptions at the HSC/MPP level may be amplified in downstream cells. We demonstrate that the MP compartment is increased more than fivefold in Runx1 KO mice, with a prominent skewing toward megakaryocyte (Meg) progenitors. Runx1- deficient granulocyte-macrophage progenitors are characterized by increased cloning capacity, impaired development into mature cells, and HSC and Meg transcription signatures. An HSC/MPP subpopulation expressing Meg markers was also increased in Runx1-deficient mice. Rescue experiments coupled with transcriptome analysis and Runx1 DNA-binding assays demonstrated that commitment is marked by Runx1 suppression of genes encoding adherence and motility proteins (Tek, Jam3, Plxnc1, Pcdh7, and Selp) that support HSCâMeg interactions with the BM niche. In vitro assays confirmed that enforced Tek expression in HSCs/MPPs increases Meg output. Interestingly, besides this key repressor function of Runx1 to control lineage decisions and cell numbers in progenitors, our study also revealed a critical activating function in erythroblast differentiation, in addition to its known importance in Meg and granulocyte/monocyte (G/M) maturation. Thus both repressor and activator functions of Runx1 at multiple hematopoietic stages and lineages likely contribute to the tumor suppressor activity in MDS and AML. GMP were isolated either from Runx1+/+-Tg(vav-Cre) and Runx1fl/fl-Tg(vav-Cre) mice or from mice transplanted with Runx1fl/fl-Tg(vav-Cre) progenitors engineered to express GFP with RUNX1-ERt2 or ERt2. RUNX1-ERt2 activity was induced by i.p. injection of tamoxifen on 3 consecutive days prior to GMP isolation.

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Leptin Receptor, a Surface Marker for a Subset of Highly Engrafting Long-term Functional Hematopoietic Stem Cells

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