scholarly journals The Neurotransmitter Receptor Gabbr1 Regulates Proliferation and Function of Hematopoietic Stem and Progenitor Cells

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 33-33
Author(s):  
Adedamola Elujoba-Bridenstine ◽  
Lijian Shao ◽  
Katherine Zink ◽  
Laura Sanchez ◽  
Kostandin V. Pajcini ◽  
...  

Hematopoietic stem and progenitor cells (HSPCs) are multipotent cells which differentiate to maintain and replenish blood lineages throughout life. Due to these characteristics, HSPC transplants represent a cure for patients with a variety of hematological disorders. HSPC function and behavior is tightly regulated by various cell types and factors in the bone marrow niche. The nervous system has been shown to indirectly influence hematopoiesis by innervating the niche; however, we present a direct route of HSPC regulation via expression of neurotransmitter receptors on HSPC surface. We have identified Gamma Aminobutyric acid (GABA) receptor B subunit 1 (Gabbr1), a hitherto unknown hematopoietic player, as a regulator of HSPC function. GABBR1 is known to be expressed on human HSPCs (Steidl et al., Blood 2004), however its function in their regulation remains unknown. Based on published RNA-seq data (Nestorowa et al., Blood 2016), we discovered that Gabbr1 is expressed on a subset of HSPCs. We confirmed this expression using RT-qPCR to assay hematopoietic populations in the bone marrow (BM). Surface receptor expression analysis showed that Gabbr1 protein is expressed on a subset of BM HSPCs. To detect GABA, the ligand for Gabbr1 in the BM microenvironment, we utilized imaging mass spectrometry (IMS). We detected regionally specific GABA signal in the endosteal region of the BM. We further identified B cells as a cellular source of GABA in the BM. To understand the role of Gabbr1 in hematopoiesis, we generated CRISPR-Cas9 Gabbr1 null mutants on a C57/BL6 background suitable for hematopoietic studies and studied their hematopoietic phenotype. We discovered a decrease in the absolute number of Lin-Sca1+cKit+ (LSK) HSPCs, but the long-term hematopoietic stem cells (LT-HSCs) remain unaffected. Further analysis of peripheral blood of Gabbr1 null mutants showed decreased white blood cells due to reduced B220+ cells. This differentiation defect was confirmed in an in vitro differentiation assay where Gabbr1 null HSPCs displayed an impaired ability to produce B cells. We show that Gabbr1 null HSCs show diminished reconstitution ability when transplanted in a competitive setting. Reduced Gabbr1 null HSC reconstitution persisted in secondary transplant recipients indicating a cell autonomous role for Gabbr1 in regulating reconstitution of HSCs in transplant recipients. Our results show a crucial role for Gabbr1 in HSPC regulation and may translate to human health as a rare human SNP within the GABBR1 locus that correlates with altered leukocyte counts has been reported (Astle et al., Cell 2016). Our studies indicate an important role for Gabbr1 in HSPC reconstitution and differentiation into B cell lineages. Disclosures No relevant conflicts of interest to declare.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1234-1234
Author(s):  
Robert S Welner ◽  
Giovanni Amabile ◽  
Deepak Bararia ◽  
Philipp B. Staber ◽  
Akos G. Czibere ◽  
...  

Abstract Abstract 1234 Specialized bone marrow (BM) microenvironment niches are essential for hematopoietic stem and progenitor cell maintenance, and recent publications have focused on the leukemic stem cells interaction and placement within those sites. Surprisingly, little is known about how the integrity of this leukemic niche changes the normal stem and progenitor cells behavior and functionality. To address this issue, we started by studying the kinetics and differentiation of normal hematopoietic stem and progenitor cells in mice with Chronic Myeloid Leukemia (CML). CML accounts for ∼15% of all adult leukemias and is characterized by the BCR-ABL t(9;22) translocation. Therefore, we used a novel SCL-tTA BCR/ABL inducible mouse model of CML-chronic phase to investigate these issues. To this end, BM from leukemic and normal mice were mixed and co-transplanted into hosts. Although normal hematopoiesis was increasingly suppressed during the disease progression, the leukemic microenvironment imposed distinct effects on hematopoietic progenitor cells predisposing them toward the myeloid lineage. Indeed, normal hematopoietic progenitor cells from this leukemic environment demonstrated accelerated proliferation with a lack of lymphoid potential, similar to that of the companion leukemic population. Meanwhile, the leukemic-exposed normal hematopoietic stem cells were kept in a more quiescent state, but remained functional on transplantation with only modest changes in both engraftment and homing. Further analysis of the microenvironment identified several cytokines that were found to be dysregulated in the leukemia and potentially responsible for these bystander responses. We investigated a few of these cytokines and found IL-6 to play a crucial role in the perturbation of normal stem and progenitor cells observed in the leukemic environment. Interestingly, mice treated with anti-IL-6 monoclonal antibody reduced both the myeloid bias and proliferation defects of normal stem and progenitor cells. Results obtained with this mouse model were similarly validated using specimens obtained from CML patients. Co-culture of primary CML patient samples and GFP labeled human CD34+CD38- adult stem cells resulted in selective proliferation of the normal primitive progenitors compared to mixed cultures containing unlabeled normal bone marrow. Proliferation was blocked by adding anti-IL-6 neutralizing antibody to these co-cultures. Therefore, our current study provides definitive support and an underlying crucial mechanism for the hematopoietic perturbation of normal stem and progenitor cells during leukemogenesis. We believe our study to have important implications for cancer prevention and novel therapeutic approach for leukemia patients. We conclude that changes in cytokine levels and in particular those of IL-6 in the CML microenvironment are responsible for altered differentiation and functionality of normal stem cells. Disclosures: No relevant conflicts of interest to declare.


Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 217-217
Author(s):  
Karin Golan ◽  
Aya Ludin ◽  
Tomer Itkin ◽  
Shiri Cohen-Gur ◽  
Orit Kollet ◽  
...  

Abstract Hematopoietic stem and progenitor cells (HSPC) are mostly retained in a quiescent, non-motile mode in the bone marrow (BM), shifting to a cycling, differentiating and migratory state on demand. How HSC replenish the blood with new mature leukocytes on a daily basis while maintaining a constant pool of primitive cells in the BM throughout life is not clear. Recently, we reported that the bioactive lipid Sphingosine 1-Phosphate (S1P) regulates HSPC mobilization via ROS signaling and CXCL12 secretion (Golan et al, Blood 2012). We hypothesize that S1P influences the daily circadian egress of HSPC and their proliferation. We report that S1P levels in the blood are increased following initiation of light at the peak of HSPC egress and are reduced towards the termination of light when circulating HSPC reach a nadir. Interestingly, mice with constitutively low S1P plasma levels due to lack of one of the enzymes that generates S1P (Sphingosine kinase 1), do not exhibit fluctuations of HSPC levels in the blood between day and night. We report that HSPC numbers in the BM are also regulated in a circadian manner. Unexpectedly, we found two different daily peaks: one in the morning, following initiation of light, which is accompanied by increased HSPC egress and the other at night after darkness, which is associated with reduced HSPC egress. In both peaks HSPC begin to cycle and differentiate via up-regulation of reactive oxygen species (ROS) however, the night peak had lower ROS levels. Concomitant with the peak of primitive stem and progenitor cells, we also observed (to a larger extent in the night peak), expansion of a rare activated macrophage/monocyte αSMA/Mac-1 population. This population maintains HSPC in a primitive state via COX2/PGE2 signaling that reduces ROS levels and increases BM stromal CXCL12 surface expression (Ludin et al, Nat. Imm. 2012). We identified two different BM peaks in HSPC levels that are regulated by the nervous system via circadian changes in ROS levels. Augmented ROS levels induce HSPC proliferation, differentiation and motility, which take place in the morning peak; however, they need to be restored to normal levels in order to prevent BM HSPC exhaustion. In the night peak, HSPC proliferate with less differentiation and egress, and activated macrophage/monocyte αSMA/Mac-1 cells are increased to restore ROS levels and activate CXCL12/CXCR4 interactions to maintain a HSPC primitive phenotype. Additionally, S1P also regulates HSPC proliferation, thus mice with low S1P levels share reduced hematopoietic progenitor cells in the BM. Interestingly S1P is required more for the HSPC night peak since in mice with low S1P levels, HSPC peak normally during day time but not at darkness. We suggest that the first peak is initiated via elevation of ROS by norepinephrine that is augmented in the BM following light-driven cues from the brain (Mendez-Ferrer at al, Nature 2008). The morning elevated ROS signal induces a decrease in BM CXCL12 levels and up-regulated MMP-9 activity, leading to HSC proliferation, as well as their detachment from their BM microenvironment, resulting in enhanced egress. Importantly, ROS inhibition by N-acetyl cysteine (NAC) reduced the morning HSPC peak. Since norepinephrine is an inhibitor of TNFα, upon light termination norepinephrine levels decrease and TNFα levels are up-regulated. TNFα induces activation of S1P in the BM, leading to the darkness peak in HSPC levels. S1P was previously shown also to induce PGE2 signaling, essential for HSPC maintenance by the rare activated αSMA/Mac-1 population. Indeed, in mice with low S1P levels, we could not detect a peak in COX2 levels in these BM cells during darkness. We conclude that S1P not only induces HSPC proliferation via augmentation of ROS levels, but also activates PGE2/COX2 signaling in αSMA/Mac-1 population to restore ROS levels and prevent HSPC differentiation and egress during the night peak. We hypothesize that the morning HSPC peak, involves proliferation, differentiation and egress, to allow HSPC to replenish the blood circulation with new cells. In contrast, the second HSPC night peak induces proliferation with reduced differentiation and egress, allowing the renewal of the BM HSPC pool. In summary, we identified two daily circadian peaks in HSPC BM levels that are regulated via light/dark cues and concomitantly allow HSPC replenishment of the blood and immune system, as well as maintenance of the HSPC constant pool in the BM. Disclosures: No relevant conflicts of interest to declare.


Blood ◽  
2017 ◽  
Vol 130 (Suppl_1) ◽  
pp. 96-96
Author(s):  
Marta Derecka ◽  
Senthilkumar Ramamoorthy ◽  
Pierre Cauchy ◽  
Josip Herman ◽  
Dominic Grun ◽  
...  

Abstract Hematopoietic stem and progenitor cells (HSPC) are in daily demand worldwide because of their ability to replenish entire blood system. However, the in vitro expansion of HSPC is still a major challenge since the cues from bone marrow microenvironment remain largely elusive. Signals coming from the bone marrow niche, and specifically mesenchymal stem and progenitor cells (MSPC), orchestrate maintenance, trafficking and stage specific differentiation of HSPCs. Although, it is generally accepted that MSPCs are essential for hematopoietic homeostasis and generating multiple types of stromal cells, the exact transcriptional networks regulating MSPCs are not well established. Early B-cell factor 1 (Ebf1) has been discovered as lineage-specific transcription factor governing B lymphopoiesis. Additionally, it has been shown to play important role in differentiation of adipocytes, which are a niche component supporting hematopoietic regeneration. Thus, in this study we seek to examine if Ebf1 has an alternative function in non-hematopoietic compartment of bone marrow, specifically in mesenchymal stromal cells that maintain proper hematopoiesis. Here, we identified Ebf1 as new transcription regulator of MSPCs activity. Mesenchymal progenitors isolated from Ebf1-/- mice show diminished capacity to form fibroblasticcolonies (CFU-F) indicating reduced self-renewal. Moreover, cells expanded from these colonies display impaired in vitro differentiation towards osteoblasts, chondrocytes and adipocytes. In order to test how this defective MSPCs influence maintenance of HSPCs, we performed long-term culture-initiating cell assay (LTC-IC). After 5 weeks of co-culture of Ebf1-deficient stromal cells with wild type HSPCs we could observe significantly decreased number of cobblestone and CFU colonies formed by primitive HSPCs, in comparison to co-cultures with control stromal cells. Furthermore, in vivo adoptive transfers of wild type HSPCs to Ebf1+/- recipient mice showed a decrease in the absolute numbers of HSPCs in primary recipients and reduced donor chimerism within the HSCP compartment in competitive secondary transplant experiments. Additionally, Prx1-Cre-mediated deletion of Ebf1 specifically in MSPCs of mice leads to reduced frequency and numbers of HSPCs and myeloid cells in the bone marrow. These results confirm that mesenchymal stromal cells lacking Ebf1 render insufficient support for HSPCs to sustain proper hematopoiesis. Interestingly, we also observed a reduced ability of HSPCs sorted from Prx1CreEbf1fl/fl mice to form colonies in methylcellulose, suggesting not only impaired maintenance but also hindered function of these cells. Moreover, HSPCs exposed to Ebf1-deficient niche exhibit changes in chromatin accessibility with reduced occupancy of AP-1, ETS, Runx and IRF motifs, which is consistent with decreased myeloid output seen in Prx1CreEbf1fl/fl mice. These results support the hypothesis that defective niche can cause epigenetic reprograming of HSPCs. Finally, single cell and bulk transcriptome analysis of MSPCs lacking Ebf1 revealed differences in the niche composition and decreased expression of lineage-instructive signals for myeloid cells. Thus, our study establishes Ebf1 as a novel regulator of MSPCs playing a crucial role in the maintenance and differentiation of HSPCs. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1806-1806
Author(s):  
Darlene A. Monlish ◽  
Zev J. Greenberg ◽  
Sima T. Bhatt ◽  
Dagmar Ralphs ◽  
John L. Keller ◽  
...  

Abstract Prior studies from our lab and others have demonstrated a role for Toll-like receptor 2 (TLR2) in regulating both normal and premalignant hematopoietic stem and progenitor cells (HSPCs), however the contributions of its binding partners, TLR1 and TLR6, remain unknown. In CD34+ bone marrow cells of patients with myelodysplastic syndrome (MDS), increased TLR2 was associated with lower-risk disease, elevated rates of apoptosis associated with improved prognosis, and enhanced survival. Conversely, increased levels of TLR6, but not TLR1, was associated with higher-risk disease and an increased percentage of bone marrow blasts (Zeng et al., Exp Cell Res 2016 and Wei et al., Leukemia 2013). These data suggest that there may be heterodimer-specific effects of TLR2 signaling on HSPCs influencing disease progression. To elucidate the unique contributions of the heterodimer pairs in MDS pathogenesis and leukemogenesis, we utilized a well-established mouse model of MDS that expresses the NUP98-HOXD13 fusion from the hematopoietic Vav-1 promoter. The "NHD13" mice recapitulate many of the salient features of human MDS and succumb to cytopenias or leukemia by 14 months of age (Lin et al., Blood 2005). Importantly, we observed significantly increased expression of TLRs 1, 2, and 6 on the c-Kit+, Sca-1+, Lineage- ("KSL") HSPCs of the NHD13 mice, similar to the increased expression of these TLRs on CD34+ cells of MDS patients. To begin to delineate the heterodimeric differences, NHD13 mice were treated chronically with either PAM2CSK4 (PAM2), a TLR2/6-specific agonist, or PAM3CSK4 (PAM3), a TLR1/2-specific agonist, to assess the effects on cytopenias and survival. After five months of treatment, a significant increase was observed in the total number of white blood cells in NHD13 mice treated with PAM2 (p=0.007), but not PAM3 (vs. vehicle (water)-treated controls), a finding that was not recapitulated in wild-type (WT) controls. On the contrary, a significant decrease in the total number of platelets in both NHD13 and WT mice treated with PAM3 was observed as compared to vehicle-treated controls (p=0.024 and p=0.011, respectively). Further supporting the existence of heterodimer-specific differences, death was expedited in NHD13 mice treated with PAM2 as compared to those treated with PAM3 (p=0.019), with a median survival of 243 days vs. 338 for the PAM3-treated cohort. The cause of death, as determined by a hematopathologist based on cytology and blast percentage, was most often due to leukemia. To investigate the potential mechanism through which enhanced TLR2/6 signaling accelerates leukemogenesis and death in NHD13 mice, the HSPCs of premalignant NHD13 mice treated with PAM2 or PAM3 were characterized by flow cytometry and evaluated for cell cycling and cell death. Both the total number and frequency of KSL cells were significantly increased in NHD13 mice treated with PAM2 (p=0.007 and p<0.0001, respectively), but not PAM3, vs. water-treated controls. No significant changes were noted in either cell cycling or apoptosis following agonist treatment. A microarray of bone marrow KSL cells revealed that stimulation of the TLR2/6 pathway is associated with an activated c-Myc signature, suggesting that enhanced signaling through this pathway, but not TLR1/2, may enhance leukemogenesis via Myc activation. Further, the expression levels of six downstream targets of c-Myc, including BAX, APEX1, ODC1, FKBP4, NCL, and HSPD1, were significantly increased in both WT and NHD13 mice following PAM2 treatment. Evaluation of serum cytokines also revealed heterodimer-specific alterations, including increased IL-6 levels in NHD13 mice treated with PAM2, but not PAM3. These data corroborate numerous previous reports linking IL-6 to MDS pathogenesis and transformation to acute myeloid leukemia. Ongoing studies involving mass cytometry, IL-6knockout mice, and pharmacological inhibitors of both IL-6 and c-Myc aim to further elucidate the mechanism through which TLR2/6-specific activation accelerates leukemogenesis and death in the NHD13 mouse model of MDS. These studies hope to inform more targeted therapeutics that could potentially delay MDS progression and reduce off-target effects. Disclosures No relevant conflicts of interest to declare.


2018 ◽  
Vol 27 (21) ◽  
pp. 1494-1506 ◽  
Author(s):  
Sofieke E. Klamer ◽  
Yvonne L. Dorland ◽  
Marion Kleijer ◽  
Dirk Geerts ◽  
William E. Lento ◽  
...  

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3417-3417
Author(s):  
Cesar Nombela-Arrieta ◽  
Gregory Pivarnik ◽  
Beatrice Winkel ◽  
Brendan Harley ◽  
John E Mahoney ◽  
...  

Abstract Abstract 3417 The identification of specific microenvironments, in which Hematopoietic Stem and Progenitor Cells (HSPCs), reside within the BM is a major challenge in stem cell biology. Yet the extreme rarity of HSCs, their dynamic nature, and the lack of unique specific markers to identify them, have precluded an accurate definition of HSC niches to date. Using Laser Scanning Cytometry, a powerful emerging quantitative imaging technology that enables analysis of whole femoral sections at the single cell level, we have mapped the global distribution of hematopoietic stem and progenitor cells within femoral bone marrow cavities, and analyzed their inmediate surrounding microenvironment. Systematic mapping of the global distribution of endogenous HSPC-enriched populations in the BM, revealed an accumulation of these cells inside endosteal regions (ER <100μm from inner bone surface), but not necessarily in contact with endosteal surfaces. Interestingly, the vast majority of HSPCs were found in direct association with BM micrrovessels, further supporting previous work, which suggested bone marrow endothelium as a major component of HSPC niches. By employing a novel imaging approach, we provide a three-dimensional (3D) microscopic overview of the unique BM vascular network found in endosteal zones, which contain the transition of bone-lining arterioles and capillaries to the sinusoidal network. Of note, HSPC association to vascular structures is not restricted to sinusoids. A significant fraction of HSPCs lied adjacent to non-sinusoidal endothelium. Using five-color imaging cytometry and pimonidazole incorporation, we have assessed the hypoxic state of HSPCs in different BM microenvironments. Our in situ analysis reveals that intracellular hypoxia is a hallmark of HSPCs, independent of their distance to bone surfaces, and more importantly, regardless of their perivascular localization. These studies provide unequivocal anatomical evidence for the intrinsic rather than environmental regulation of intracellular hypoxia in HSPCs and challenge the hypothesis of a “super hypoxic” HSPC niche. Disclosures: No relevant conflicts of interest to declare.


Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 5048-5048
Author(s):  
Kam Tong Leung ◽  
Yorky Tsin Sik Wong ◽  
Karen Li ◽  
Kathy Yuen Yee Chan ◽  
Xiao-Bing Zhang ◽  
...  

Abstract RGS family proteins are known to negatively regulate G-protein-coupled receptor signaling through their GTPase-accelerating activity. In several types of hematopoietic cells (e.g., B lymphocytes and megakaryocytes), responses to stromal cell-derived factor-1 (SDF-1) are subjected to regulation by R4 subfamily RGS proteins. However, their expression patterns and functional roles in hematopoietic stem and progenitor cells (HSC) are poorly characterized. Here, we showed that human CD34+ HSC derived from cord blood (CB, n = 10) expressed 7 out of 10 R4 RGS proteins at mRNA level (RGS1-3, 5, 13, 16 and 18), whereas expressions of RGS4, 8 and 21 were undetectable. Exposure of CB CD34+ cells to SDF-1 significantly increased RGS1, 2, 13 and 16 expressions and decreased RGS3 and 18 expressions (P ≤ 0.0402, n = 5). Expressions of RGS1, 13 and 16 were significantly higher in bone marrow (BM, n = 10) CD34+ cells when compared to mobilized peripheral blood (MPB, n = 5) CD34+ cells (P ≤ 0.0160), while RGS3 and 18 expressions were lower in BM CD34+ cells (P ≤ 0.0471), suggesting a SDF-1- and niche-dependent regulation of RGS expressions. To investigate the potential involvement of RGS proteins in SDF-1-mediated homing-related functions, we introduced RGS overexpression constructs into CB CD34+ cells by lentiviral transduction. With >80% transduction efficiency, we showed that overexpression of RGS1, 13 and 16 but not RGS2 significantly inhibited migration of CD34+ cells to a SDF-1 gradient (P ≤ 0.0391, n = 4-5). Similarly, RGS1, 13 and 16 overexpression suppressed SDF-1-induced Akt phosphorylation (n = 2), but none of them affected SDF-1-mediated actin polymerization (n = 3). In the NOD/SCID mouse xenotransplantation model, preliminary results showed that bone marrow homing was impaired in RGS1- (16.3% reduction), RGS13- (12.7% reduction) or RGS16-overexpressing CD34+ cells (33.7% reduction). Taken together, we provided the first evidence that expressions of R4 RGS proteins are regulated by the SDF-1/CXCR4 axis in human CD34+ HSC. We also presented evidence that specific R4 RGS proteins (RGS1, 13 and 16) negatively regulate in vitro SDF-1-mediated responses and in vivo homing of CD34+ cells, suggesting that RGS proteins may serve as a feedback mechanism to regulate SDF-1/CXCR4 signaling. Strategies to inhibit RGS signaling could thus be a potential method for enhancing efficiency of HSC homing and long-term engraftment, which is particularly important in the setting of CB transplantation. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 357-357
Author(s):  
Angela Stoddart ◽  
Jianghong Wang ◽  
Chunmei Hu ◽  
Anthony A. Fernald ◽  
Elizabeth M. Davis ◽  
...  

Abstract A del(5q) is frequently noted in MDS, AML, and therapy-related myeloid neoplasms (t-MN) following alkylating agent therapy. Mutation/loss of the TP53 is gene found in 80% of t-MNs with a del(5q). Recent studies suggest that TP53 mutations are found at a low frequency in hematopoietic stem/progenitor cells (HSPCs) in adults (Xie et al., Nat Med 20:1472, 2014; Genovese et al., NEJM 371:2477, 2014; Jaiswal et al., NEJM 371:2488, 2014), and chemotherapy confers a selective growth advantage to these rare clones (Wong et al., Nature 518:552, 2015). We previously established a mouse model for t-MN with a del(5q) and showed that haploinsufficiency of two del(5q) genes, Egr1 and Apc, cooperate with loss of function of the Trp53 (p53) gene to induce myeloid neoplasms in mice. Specifically, transplantation of Egr1+/-, Apcdel/+ bone marrow (BM) cells transduced with p53 shRNAs into wild type (WT) recipients resulted in the development of a transplantable AML, characterized by a complex karyotype and genetic instability, in 17% of mice. There is growing evidence that microenvironment perturbations play a major role in the malignant process; however, the effect of cytotoxic therapy on HSPCs as well as the BM niche is not well understood. Using our mouse model of t-MN with a del(5q), we explored the effects of ENU, an alkylating agent, on both HSPCs and the BM microenvironment by exposing both donor and recipient mice to ENU (Panel 1 in the figure). In mice transplanted with Egr1+/-, Apcdel/+, p53 shRNA HSPCs, exposure to ENU strikingly decreased survival (median survival: 200d vs. not reached) and increased the incidence of AML or MDS with multilineage dysplasia (73% vs. 17%). In the absence of p53 knockdown (i.e., control shRNA), mice survived longer (370d vs. 200d, P = 0.0014); however, 100% of mice developed MDS with dyserythropoiesis. None developed AML, suggesting that loss of p53 function is critical for leukemic transformation (Panel 2). Loss of both del(5q) genes, EGR1 and APC, was necessary to develop AML. Compared to mice transplanted with Egr1+/-, Apcdel/+, p53 shRNA HSPCs, mice transplanted with Egr1+/-, p53 shRNA HSPCs survived longer (369 d vs. 200 d, P = 0.0117) and only 40% of mice developed MDS with dysgranulopoiesis and/or dyserythropoiesis (Panel 3). None developed AML. Thus, severity of disease increases with loss of more than one del(5q) gene. Finally, to determine the separate effects of alklating agent therapy on HSPCs vs. the niche, we treated either the recipient or donor mice with ENU. Whereas ENU exposure to both donor and recipient resulted in a profound expansion of p53 shRNA+ cells and the development of MDS/AML in 73% of mice, ENU exposure of either donor or recipient led to only modest expansion of p53 shRNA+ cells and none of the mice developed MDS or AML. This suggests that the clonal expansion of cells with loss of multiple 5q genes and p53 is likely promoted by cytotoxic exposure to the cells themselves, as well as exposure to the surrounding niche cells. t-MN patients with a del(5q) typically present with trilineage dysplasia implicating all three hematopoietic cell lineages (erythroid, myeloid, and megakaryocytic) in the dysplastic process. Our mouse models shed light on some of the key genes on 5q, as well as the environmental exposure, that contributes to trilineage dysplasia in patients. Finally, our data suggests that t-MN is a "disease of the tissue", and the expansion of mutant HSPCs, e.g., with TP53 mutations, likely results from the combined effects of cytotoxic therapy on the hematopoietic cells themselves, as well as the BM microenvironment that supports hematopoiesis Figure 1. Figure 1. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 3895-3895
Author(s):  
Michael A Schmid ◽  
Dior Baumjohann ◽  
Markus G Manz

Abstract Abstract 3895 Dendritic cells (DCs), the key antigen-presenting cell population, continuously need to be regenerated from bone marrow (BM) hematopoietic stem and progenitor cells. Common dendritic progenitors (CDP) were previously shown to efficiently generate DCs in lymphoid and non-lymphoid tissues. How the dissemination of bone marrow (BM) DC-progenitors to peripheral tissues is regulated upon demand remains elusive to date. Acute microbial infections are sensed via Toll-like receptors (TLR). Recent studies showed that stem and progenitor cells express TLRs. We found that CDPs in the BM of mice express relative high levels of Tlr2, Tlr4 and Tlr9, and hypothesized that these might be involved in regulating CDP migration. CDPs in steady-state expressed high levels of Cxcr4, but no, or low Ccr7. Upon direct stimulation with the respective TLR-agonists in vitro, CDPs rapidly down-regulated Cxcr4 and up-regulated Ccr7 mRNA and protein. CDPs that were stimulated with TLR-agonists for only 2 h preferentially homed to the lymph nodes (LN) in expense of BM in steady-state recipients. When TLR-agonists were injected subcutaneously, CDPs gave rise to increased numbers of plasmacytoid DCs, classical DCs, and DCs with a skin-derived migratory phenotype in inflamed LNs on day 4. This was not due to increased proliferative activity. Injecting the CXCR4 antagonist AMD3100 demonstrated that the retention of CDPs in the BM depends on CXCR4. Furthermore, CCR7 was important for the engraftment of CDP-derived DCs into LNs in steady-state and during inflammation. In conclusion, DC progenitors in the bone marrow are capable to directly sense TLR-agonists via their cognate receptors in systemic infections. This results in differential expression of chemokine receptors and consecutive migration of DC-progenitors to inflamed LNs. This mechanism helps to restore DC subsets during ongoing immune responses and to return to DC homeostasis once the inflammation ceases. Disclosures: No relevant conflicts of interest to declare.


Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 4789-4789
Author(s):  
Xuejun Zhu ◽  
Zhongfa Yang ◽  
Junling Wang ◽  
Alan G. Rosmarin

Abstract Abstract 4789 Dendritic cells (DCs) play key roles in mediating innate and acquired immune responses. DCs have a short half life in peripheral organs and are derived constitutively from bone marrow hematopoietic stem cells (HSCs) and Flt3+ progenitors. Cytokine signaling from Flt3 is crucial for stimulation of DC development. Previous studies demonstrated that injection of Flt3 ligand (Flt3L) in mouse caused a transient, but substantial increase in DC development. The effects of long-term activation of Flt3 signaling with physiological levels of Flt3L, however, have not yet been defined. Transgenic mice with constitutively activated Flt3 signaling were generated by replacing the Flt3 alleles with a mutant version Flt3ITD. Both mature DCs and DC progenitors increased modestly in Flt3ITD mice; both lymphoid and myeloid derived DCs were increased compared with wild type mice. Although the level of DCs in Flt3ITD mice did not reach the high levels in mice injected with Flt3L, the effect of Flt3ITD on DC development was consistent and long-lasting. Thus, activation of Flt3 signaling by different mechanisms led to distinct responses of bone marrow stem and progenitor cells for DC development. Flt3ITD mice provide a unique model to analyze DC differentiation from bone marrow stem and progenitor cells at physiological levels of Flt3L. Disclosures: No relevant conflicts of interest to declare.


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