Hematopoietic Progenitor Cell Fate Research Articles

1024 - EPIGENETIC CONTROL OF MYELOID CELL DEVELOPMENT BY THE TRANSCRIPTION FACTOR IRF8

Differentiation of hematopoietic stem and progenitor cells to various types of blood cells is a process of establishing cell type-specific gene expression patterns. We have been investigating the mechanism of myeloid cell development from a viewpoint of gene expression control by transcription factors, particularly IRF8. In Irf8–/– mice, mononuclear phagocyte progenitors are accumulated, and these progenitors do not efficiently differentiate into monocytes (Mos) or dendritic cells (DCs) but instead, give rise to a large number of neutrophils. Accordingly, the loss of IRF8 causes immunodeficiency and chronic myeloid leukemia-like neutrophilia in mice and humans. Recently, we found that a novel 3’ enhancer is responsible for high Irf8 expression in the DC lineage. Deletion of this enhancer in vivo resulted in the loss of classical DC1s (cDC1s) and somehow surprisingly, caused a significant increase in Mo counts. Thus, the expression level of IRF8 determines the fate of myeloid progenitors; absence, low, or high expression of IRF8 promotes differentiation towards neutrophils, Mos, or DCs, respectively. We also analyzed enhancer landscape dynamics and the genome-wide behavior of IRF8 during the development of mononuclear phagocytes in vivo. While IRF8 does not immediately change the global gene expression pattern in the mononuclear phagocyte progenitors, it does establish their enhancer landscapes by cooperating or antagonizing with other transcription factors, thereby preparing for future gene expression. Furthermore, we found that IRF8 is weakly expressed in a subpopulation of lymphoid-primed multipotent progenitors and leads to early lineage specification towards cDC1s by regulating chromatin states before inducing major transcriptional changes. We are now investigating the 3D chromatin structure dynamics and the role of IRF8 during myeloid development. Collectively, these results illustrate that the epigenetic changes induced by key transcription factors such as IRF8 determine the fate of hematopoietic progenitor cells before establishing gene expression patterns.

Hematological findings in non-treated and gamma-irradiated mice deficient for MIC-1/GDF15.

Several members of the TGF-beta family are known to effectively regulate the fate of hematopoietic progenitor cells in a complex and context-dependent manner. Growth differentiation factor-15 (GDF15) is a divergent member of the TGF-beta family. This stress-induced cytokine has been proposed to possess immunomodulatory functions and its high expression is often associated with progression of a variety of pathological conditions. GDF15 is also induced by chemotherapy and irradiation. Very few fundamental studies have been published regarding the effect of GDF15 in hematopoiesis. In this study, we analyzed the hematological status of untreated and gamma-irradiated mice deficient for GDF15 as a result of genetic knock-out (KO), in order to clarify the regulatory role of GDF15 in hematopoiesis. Significant differences between GDF15 KO mice and their pertinent WT controls were found in the parameters of blood monocyte numbers, blood platelet size, and distribution width, as well as in the values of bone marrow granulocyte/macrophage progenitor cells. Different tendencies of some hematological parameters in the GDF15 KO mice in normal conditions and those under exposure of the mice to ionizing radiation were registered. These findings are discussed in the context of the GDF15 gene function and its lack under conditions of radiation-induced damage.

Functional and molecular characterization of mouse Gata2-independent hematopoietic progenitors

AbstractThe Gata2 transcription factor is a pivotal regulator of hematopoietic cell development and maintenance, highlighted by the fact that Gata2 haploinsufficiency has been identified as the cause of some familial cases of acute myelogenous leukemia/myelodysplastic syndrome and in MonoMac syndrome. Genetic deletion in mice has shown that Gata2 is pivotal to the embryonic generation of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). It functions in the embryo during endothelial cell to hematopoietic cell transition to affect hematopoietic cluster, HPC, and HSC formation. Gata2 conditional deletion and overexpression studies show the importance of Gata2 levels in hematopoiesis, during all developmental stages. Although previous studies of cell populations phenotypically enriched in HPCs and HSCs show expression of Gata2, there has been no direct study of Gata2 expressing cells during normal hematopoiesis. In this study, we generate a Gata2Venus reporter mouse model with unperturbed Gata2 expression to examine the hematopoietic function and transcriptome of Gata2 expressing and nonexpressing cells. We show that all the HSCs are Gata2 expressing. However, not all HPCs in the aorta, vitelline and umbilical arteries, and fetal liver require or express Gata2. These Gata2-independent HPCs exhibit a different functional output and genetic program, including Ras and cyclic AMP response element-binding protein pathways and other Gata factors, compared with Gata2-dependent HPCs. Our results, indicating that Gata2 is of major importance in programming toward HSC fate but not in all cells with HPC fate, have implications for current reprogramming strategies.

Impact of Erythropoietin Modulation Using Hyperbaric Oxygen on Umbilical Cord Blood CD34+ Cell Homing

Background: Previously, we demonstrated that host pre-treatment with hyperbaric oxygen (HBO) improves engraftment of umbilical cord blood (UCB) CD34+ cells in a transplant murine model. Recent data suggest that erythropoietin (EPO) determines the fate of hematopoietic progenitor cells in favor of erythroid differentiation. Herein, we evaluated mechanisms underlying the favorable effect of HBO therapy on UCB CD34+ cell engraftment. We hypothesized that HBO modulates EPO which in turn enhances UCB CD34 homing to the marrow, thereby enhancing engraftment. Materials/methods: We examined EPO receptor (EPOR) expression on UCB CD34+ cells by flow cytometry and western blot. Transmigration assays were used to evaluate EPO effects on UCB CD34+ cell migration toward Stromal Cell-Derived Factor 1 (SDF-1; CXCL12) which has been shown to mediate CD34+ chemotaxis to the marrow. Using an NSG transplant murine model, we evaluated serum EPO levels by ELISA and early UCB bone marrow/spleen homing by flow cytometry. Bone marrow UCB cell differentiation was examined 1 and 2 weeks post-transplant using CFU-assay. Results: We found that on average 17.6 (4.9-38.7) % of CD34+ enriched UCB cells express EPOR. EPOR expression was confirmed by western blot. The percentage of EPOR positive cells was significantly higher in hematopoietic stem cells (HSC) defined as Lin- CD34+ CD38- CD45RA- CD90+ CD49f+ (45.7+/-1.4) compared to hematopoietic progenitor cells defined as Lin- CD34+ CD38+ (25.1+/-0.7) and multipotent progenitors defined as Lin- CD34+ CD38- CD45RA- CD90- CD49f- (27.2+/-0.3). Also, exposure of UCB CD34+ cells to EPO during cell culture inhibited their migration toward SDF-1 (Figure-1). HBO treated mice demonstrated significantly lower serum EPO blood levels compared to control mice (727.4+/- 42.02 versus1576 +/- 80.90 pg/mL, p <0.0001) measured 3-hours post-transplant. A higher percentage of human CD34+ was seen in the bone marrow of HBO treated mice 3-hours post-transplant (6.8+/-1.0 versus 3.4+/-0.6), p=0.01). HBO treated mice demonstrated significantly lower numbers of BFU-E ( 26.7+/-8.7 versus 75.3+/-19.3, p =0.043) and increasing numbers of CFU-G/M (166.0+/-27.9 versus 74.8+/-32.6, p =0.05). Conclusions: EPOR is enriched in UCB HSC. HBO lowers host blood EPO and as a result improves UCB CD34+ cell early bone marrow homing and enhances myeloid differentiation. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.