Browsing by Subject "hematopoiesis"

Now showing 1 - 6 of 6
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    Ape1 regulates hematopoietic differentiation of embryonic stem cells through its redox functional domain
    (2007-03) Zou, Gang-Ming; Luo, Meihua; Reed, April; Kelley, Mark R.; Yoder, Mervin C.
    Ape1 is a molecule with dual functions in DNA repair and redox regulation of transcription factors. In Ape1-deficient mice, embryos do not survive beyond embryonic day 9, indicating that this molecule is required for normal embryo development. Currently, direct evidence of the role of Ape1 in regulating hematopoiesis is lacking. We used the embryonic stem (ES) cell differentiation system and an siRNA approach to knockdown Ape1 gene expression to test the role of Ape1 in hematopoiesis. Hemangioblast development from ES cells was reduced 2- to 3-fold when Ape1 gene expression was knocked down by Ape1-specific siRNA, as was primitive and definitive hematopoiesis. Impaired hematopoiesis was not associated with increased apoptosis in siRNA-treated cells. To begin to explore the mechanism whereby Ape1 regulates hematopoiesis, we found that inhibition of the redox activity of Ape1 with E3330, a specific Ape1 redox inhibitor, but not Ape1 DNA repair activity, which was blocked using the small molecule methoxyamine, affected cytokine-mediated hemangioblast development in vitro. In summary, these data indicate Ape1 is required in normal embryonic hematopoiesis and that the redox function, but not the repair endonuclease activity, of Ape1 is critical in normal embryonic hematopoietic development.
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    Megakaryocytes: Regulators of Bone Mass and Hematopoiesis
    (Office of the Vice Chancellor for Research, 2016-04-08) Alvarez, Marta B.; Xu, LinLin; Himes, Evan R.; Chitteti, Brahmananda R.; Cheng, Yinghua; Engle, Andrew; Olivos, David; Childress, Paul; Srour, Edward F.; Kacena, Melissa A.
    Emerging evidence demonstrates that megakaryocytes (MK) play a key role in regulating skeletal homeostasis and hematopoiesis. Recent reports show that MK reside in close proximity to hematopoietic stem cells (HSC). Genetic depletion of MK resulted in mitotic activation of HSC suggesting that MK maintain HSC quiescence. Other studies demonstrated that following irradiation, surviving MK migrate to endosteal surfaces where osteoblast (OB) lineage cells dramatically increase and promote engraftment of transplanted HSC. Here we investigated if MK directly impact hematopoiesis or whether they indirectly support HSC function through their interaction with OB-lineage cells. Our data suggests that LSK (Lin-Sca+CD117+, an enriched HSC population) co-cultured with MK and OB generate significantly higher numbers of colony forming cells (HSC function) compared to LSK cocultured with either MK or OB alone. The functionality of this in vitro data was confirmed in vivo with transplantation studies which showed increased engraftment in mice transplanted with LSK cells co-cultured with OB and MK compared to LSK cells co-cultured with OB alone. To test if loss of MK negatively impacts osteoblastogenesis, we generated conditional knockout mice where cMpl, the receptor for the main MK growth factor, thrombopoietin (TPO), was deleted in MK (cMplfl/fl x PF4Cre). Unexpectedly, these mice exhibited a 10-fold increase in platelet numbers, megakaryocytosis, a dramatic expansion of phenotypically defined hematopoietic precursors, and a remarkable 20-fold increase in the bone volume fraction. Collectively, these data indicate that while MK modulate HSC function, this activity is in part mediated through interactions with OB and suggest a complex role for TPO and MK in HSC regulation. While work is needed to further elucidate mechanisms, understanding the coordinated interaction between MK, OB, HSC, and TPO/Mpl should inform the development of novel treatments to enhance HSC recovery following myelosuppressive injuries, as well as bone loss diseases, such as osteoporosis.
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    Prostaglandin E₂ promotes recovery of hematopoietic stem and progenitor cells after radiation exposure
    (2014-07-11) Stilger, Kayla N.; Broxmeyer, Hal E.; Kacena, Melissa A.; Srour, Edward F.; Pelus, Louis
    The hematopoietic system is highly proliferative, making hematopoietic stem and progenitor cells (HSPC) sensitive to radiation damage. Total body irradiation and chemotherapy, as well as the risk of radiation accident, create a need for countermeasures that promote recovery of hematopoiesis. Substantive damage to the bone marrow from radiation exposure results in the hematopoietic syndrome of the acute radiation syndrome (HS-ARS), which includes life-threatening neutropenia, lymphocytopenia, thrombocytopenia, and possible death due to infection and/or hemorrhage. Given adequate time to recover, expand, and appropriately differentiate, bone marrow HSPC may overcome HS-ARS and restore homeostasis of the hematopoietic system. Prostaglandin E2 (PGE2) is known to have pleiotropic effects on hematopoiesis, inhibiting apoptosis and promoting self-renewal of hematopoietic stem cells (HSC), while inhibiting hematopoietic progenitor cell (HPC) proliferation. We assessed the radiomitigation potential of modulating PGE2 signaling in a mouse model of HS-ARS. Treatment with the PGE2 analog 16,16 dimethyl PGE2 (dmPGE2) at 24 hours post-irradiation resulted in increased survival of irradiated mice compared to vehicle control, with greater recovery in HPC number and colony-forming potential measured at 30 days post-irradiation. In a sublethal mouse model of irradiation, dmPGE2-treatment at 24 hours post-irradiation is associated with enhanced recovery of HSPC populations compared to vehicle-treated mice. Furthermore, dmPGE2-treatment may also act to promote recovery of the HSC niche through enhancement of osteoblast-supporting megakaryocyte (MK) migration to the endosteal surface of bone. A 2-fold increase in MKs within 40 um of the endosteum of cortical bone was seen at 48 hours post-irradiation in mice treated with dmPGE2 compared to mice treated with vehicle control. Treatment with the non-steroidal anti-inflammatory drug (NSAID) meloxicam abrogated this effect, suggesting an important role for PGE2 signaling in MK migration. In vitro assays support this data, showing that treatment with dmPGE2 increases MK expression of the chemokine receptor CXCR4 and enhances migration to its ligand SDF-1, which is produced by osteoblasts. Our results demonstrate the ability of dmPGE2 to act as an effective radiomitigative agent, promoting recovery of HSPC number and enhancing migration of MKs to the endosteum where they play a valuable role in niche restoration.
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    Regulation of Constitutive Tip110 Expression in Human Cord Blood CD34+ Cells Through Selective Usage of the Proximal and Distal Polyadenylation Sites Within the 3′Untranslated Region
    (Liebert, 2018) Liu, Ying; Huang, Xinxin; Timani, Khalid A.; Broxmeyer, Hal E.; He, Johnny J.; Microbiology and Immunology, School of Medicine
    Tip110 plays important roles for stem cell pluripotency and hematopoiesis. However, little is known about the regulatory mechanisms of Tip110 expression in this process. In this study, we first showed that constitutive Tip110 expression was cell proliferation and differentiation dependent and self-regulated in both human cord blood CD34+ cells. Using a series of molecular techniques, we found that ectopic Tip110 expression led to increased constitutive Tip110 expression through its 3′-untranslated region (3′UTR), specifically through preferential usage of proximal polyadenylation sites within its 3′UTR in cells, including human cord blood CD34+ cells, which indeed led to an increased number of CD34+ cells during differentiation of those cells. Lastly, we showed that Tip110 protein interacted with cleavage stimulation factor 64 (CstF64) protein and that more CstF64 was recruited to the promixal polyadenylation site than the distal polyadenylation site within its 3′UTR. These finding together demonstrates that constitutive Tip110 expression is regulated, at least in part, through its interaction with CstF64, recruitment of CstF64 to, and selective usage of those two polyadenylation sites within its 3′UTR.
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    The Role of Osteomacs in Regulating Stem Cell Function and the Hematopoietic Niche
    (2020-02) Mohamad, Safa F.; Srour, Edward F.; Bruzzaniti, Angela; Haneline, Laura S.; Pelus, Louis M.; Kacena, Melissa A.
    Maintenance of hematopoietic stem cell (HSC) function is an orchestrated event requiring the participation of multiple cell types within the hematopoietic niche. Among the key cellular components of the niche are a group of specialized bone-resident macrophages known as osteomacs (OM). Reported here is a detailed characterization of OM and description of discriminating phenotypic and functional properties that clearly distinguish OM from bone marrow-derived macrophages (BM Mφ). Furthermore, it was established that OM support hematopoiesis enhancing activity of osteoblasts and that this activity was augmented by megakaryocytes. Serial transplantation demonstrated that HSC repopulating potential was best maintained by in vitro cultures containing OM, osteoblasts and megakaryocytes. Interestingly, BM Mφ were unable to mediate the same hematopoiesis enhancing activity regardless of whether megakaryocytes were present in co-culture or not. Subsequently, to understand the importance of networking between the residents of the niche, 3D tissue cytometry was performed on fixed and stained unperturbed bone marrow sections. This approach identified the spatial relationships between OM, osteoblasts, megakaryocytes and HSC within the niche and defined parameters, under which these cell types coexist in undamaged bone marrow. In addition, single cell mRNAseq and CyTOF was performed to assess genetic and proteomic expression changes in OM following their interaction with megakaryocytes. These studies revealed the upregulation of CD166 and embigin on OM via osteoblast and megakaryocyte interactions. Clonogenic assays were conducted to examine the impact of these molecules in hematopoietic function. When these assays were initiated with CD166 KO OM or shRNA-mediated embigin knockdown OM, it was established that loss of these surface molecules on OM caused a decline in the normal OM-mediated hematopoietic enhancing activity. Conversely, recombinant CD166 and embigin partially substituted for OM activity thus identifying potential mediators through which OM maintain hematopoietic function. This data, for the first time, reveal intimate spatial interactions between OM, osteoblasts, megakaryocytes and HSC in the hematopoietic niche. They also illustrate the importance of crosstalk between OM, osteoblasts and megakaryocytes and reveal novel mediators such as CD166 and embigin that cooperate with other elements of the niche to support HSC function.
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    Toll-like receptor signaling in hematopoietic stem and progenitor cells
    (Wolters Kluwer, 2019-07) Capitano, Maegan L.; Microbiology and Immunology, School of Medicine
    Purpose of review The innate immune system is essential in the protection against microbial infection and facilitating tissue repair mechanisms. During these stresses, the maintenance of innate immune cell numbers through stress-induced or emergency hematopoiesis is key for our survival. One major mechanism to recognize danger signals is through the activation of Toll-like receptors (TLRs) on the surface of hematopoietic cells, including hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC), and nonhematopoietic cells, which recognize pathogen-derived or damaged-induced compounds and can influence the emergency hematopoietic response. This review explores how direct pathogen-sensing by HSC/HPC regulates hematopoiesis, and the positive and negative consequences of these signals. Recent findings Recent studies have highlighted new roles for TLRs in regulating HSC and HPC differentiation to innate immune cells of both myeloid and lymphoid origin and augmenting HSC and HPC migration capabilities. Most interestingly, new insights as to how acute versus chronic stimulation of TLR signaling regulates HSC and HPC function has been explored. Summary Recent evidence suggests that TLRs may play an important role in many inflammation-associated diseases. This suggests a possible use for TLR agonists or antagonists as potential therapeutics. Understanding the direct effects of TLR signaling by HSC and HPC may help regulate inflammatory/danger signal-driven emergency hematopoiesis.