Bone Marrow Failure in RPS19-Deficient Mice Is Partly Caused by p53 Activation and Responds to L-Leucine Treatment

Abstract Abstract 727 Diamond-Blackfan anemia (DBA) is a congenital erythroid hypoplasia associated with physical malformations and predisposition to cancer. Of the many different DBA disease genes known, all encode for ribosomal proteins, suggesting that DBA is a disorder relating to ribosomal biogenesis or function. Among these genes, ribosomal protein S19 (RPS19) is the most frequently mutated (25 % of the patients). The generation of animal models for DBA is pivotal in order to understand the disease mechanisms and to evaluate novel therapies. We have generated two mouse models for RPS19-deficient DBA by taking advantage of RNA interference (Jaako et al. Blood. 2010;116:193. ASH meeting abstract). These models contain RPS19-targeting shRNAs expressed by a doxycycline-responsive promoter downstream of the collagen A1 locus allowing an inducible and dose-dependent regulation of shRNA. As we have previously reported, the induction of RPS19 deficiency results in a reduction in the number of erythrocytes, platelets and white blood cells that with time leads to the exhaustion of hematopoietic stem cells and bone marrow failure. In the current study we have analyzed the role of p53 in RPS19-deficient hematopoiesis by crossing the transgenic mice into Trp53 null background. To isolate the hematopoietic phenotype we transplanted bone marrow cells from these mice into lethally irradiated wild-type recipients. We have previously shown that the severity of the hematopoietic phenotype in transplanted recipients is highly dependent on the level of RPS19 downregulation, and the recipients with low RPS19 expression die 2–3 weeks after induction because of bone marrow failure. Remarkably, the inactivation of Trp53 rescued the early mortality in these recipients. However, although the inactivation of Trp53 completely reversed the erythrocyte and leukocyte numbers in the recipients with intermediate RPS19 downregulation, the recipients with low RPS19 expression still developed a mild anemia and macrocytosis. p53 activation is known to inhibit the AKT/mTOR pathway, a central regulator of cell growth and survival. Although the role of this pathway in DBA pathogenesis remains poorly defined, some patients positively respond to treatment with amino acid L-leucine, a nutrient signal that stimulates mTOR activity. Currently we are studying the role of L-leucine in RPS19-deficient hematopoiesis both in vitro and in vivo. Our preliminary data confirm that L-leucine modestly enhances the proliferation of RPS19-deficient c-Kit -enriched hematopoietic progenitors in vitro (1.2 fold in 8 days), while there is no effect on wild-type cultures. Interestingly, the proliferative response in RPS19-deficient cultures appears more pronounced when cells are cultured in low cytokine concentration (1.6 fold in 8 days). Since primary cells from DBA patients are highly responsive to stem cell factor (SCF), which also mediates its effect partly via PI3K/AKT/mTOR pathway, we are studying whether L-leucine has a synergistic role with SCF enhancing the proliferation of hematopoietic progenitors. Finally, a 15% L-leucine supplement in drinking water partly rescues the erythrocyte and leukocyte number in RPS19-deficient mice. In summary, our results demonstrate a key role of p53 activation in RPS19-deficient DBA, although they also suggest that p53-independent pathways may contribute towards phenotype upon severe RPS19 deficiency. Furthermore, our preliminary data supports the role of L-leucine as a therapeutic agent in the treatment of DBA. Disclosures: No relevant conflicts of interest to declare.

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ASXL2 Is Recurrently Mutated in t(8;21) AML and Regulates Hematopoietic Development

Blood ◽

10.1182/blood.v128.22.1051.1051 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1051-1051

Author(s):

Vikas Madan ◽

Lin Han ◽

Norimichi Hattori ◽

Anand Mayakonda ◽

Qiao-Yang Sun ◽

...

Keyword(s):

Gene Expression ◽

Bone Marrow ◽

Research Funding ◽

Hematopoietic Differentiation ◽

Wild Type ◽

Flow Cytometric ◽

Deficient Mice

Abstract Chromosomal translocation t(8;21) (q22;q22) leading to generation of oncogenic RUNX1-RUNX1T1 fusion is a cytogenetic abnormality observed in about 10% of acute myelogenous leukemia (AML). Studies in animal models and recent next generation sequencing approaches have suggested cooperativity of secondary genetic lesions with t(8;21) in inducing leukemogenesis. In this study, we used targeted and whole exome sequencing of 93 cases (including 30 with matched relapse samples) to profile the mutational landscape of t(8;21) AML at initial diagnosis and post-therapy relapse. We identified recurrent mutations of KIT, TET2, MGA, FLT3, NRAS, DHX15, ASXL1 and KMT2Dgenes in this subtype of AML. In addition, high frequency of truncating alterations in ASXL2 gene (19%) also occurred in our cohort. ASXL2 is a member of mammalian ASXL family involved in epigenetic regulation through recruitment of polycomb or trithorax complexes. Unlike its closely related homolog ASXL1, which is mutated in several hematological malignancies including AML, MDS, MPN and others; mutations of ASXL2 occur specifically in t(8;21) AML. We observed that lentiviral shRNA-mediated silencing of ASXL2 impaired in vitro differentiation of t(8;21) AML cell line, Kasumi-1, and enhanced its colony forming ability. Gene expression analysis uncovered dysregulated expression of several key hematopoiesis genes such as IKZF2, JAG1, TAL1 and ARID5B in ASXL2 knockdown Kasumi-1 cells. Further, to investigate implications of loss of ASXL2 in vivo, we examined hematopoiesis in Asxl2 deficient mice. We observed an age-dependent increase in white blood cell count in the peripheral blood of Asxl2 KO mice. Myeloid progenitors from Asxl2 deficient mice possessed higher re-plating ability and displayed altered differentiation potential in vitro. Flow cytometric analysis of >1 year old mice revealed increased proportion of Lin-Sca1+Kit+ (LSK) cells in the bone marrow of Asxl2 deficient mice, while the overall bone marrow cellularity was significantly reduced. In vivo 5-bromo-2'-deoxyuridine incorporation assay showed increased cycling of LSK cells in mice lacking Asxl2. Asxl2 deficiency also led to perturbed maturation of myeloid and erythroid precursors in the bone marrow, which resulted in altered proportions of mature myeloid populations in spleen and peripheral blood. Further, splenomegaly was observed in old ASXL2 KO mice and histological and flow cytometric examination of ASXL2 deficient spleens demonstrated increased extramedullary hematopoiesis and myeloproliferation compared with the wild-type controls. Surprisingly, loss of ASXL2 also led to impaired T cell development as indicated by severe block in maturation of CD4-CD8- double negative (DN) population in mice >1 year old. These findings established a critical role of Asxl2 in maintaining steady state hematopoiesis. To gain mechanistic insights into its role during hematopoietic differentiation, we investigated changes in histone marks and gene expression affected by loss of Asxl2. Whole transcriptome sequencing of LSK population revealed dysregulated expression of key myeloid-specific genes including Mpo, Ltf, Ngp Ctsg, Camp and Csf1rin cells lacking Asxl2 compared to wild-type control. Asxl2 deficiency also caused changes in histone modifications, specifically H3K27 trimethylation levels were decreased and H2AK119 ubiquitination levels were increased in Asxl2 KO bone marrow cells. Global changes in histone marks in control and Asxl2 deficient mice are being investigated using ChIP-Sequencing. Finally, to examine cooperativity between the loss of Asxl2 and RUNX1-RUNX1T1 in leukemogenesis, KO and wild-type fetal liver cells were transduced with retrovirus expressing AML1-ETO 9a oncogene and transplanted into irradiated recipient mice, the results of this ongoing study will be discussed. Overall, our sequencing studies have identified ASXL2 as a gene frequently altered in t(8;21) AML. Functional studies in mouse model reveal that loss of ASXL2 causes defects in hematopoietic differentiation and leads to myeloproliferation, suggesting an essential role of ASXL2 in normal and malignant hematopoiesis. *LH and NH contributed equally Disclosures Ogawa: Takeda Pharmaceuticals: Consultancy, Research Funding; Sumitomo Dainippon Pharma: Research Funding; Kan research institute: Consultancy, Research Funding.

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Distinct Roles of Lymphotoxin α and the Type I Tumor Necrosis Factor (TNF) Receptor in the Establishment of Follicular Dendritic Cells from Non–Bone Marrow–derived Cells

Journal of Experimental Medicine ◽

10.1084/jem.186.12.1997 ◽

1997 ◽

Vol 186 (12) ◽

pp. 1997-2004 ◽

Cited By ~ 92

Author(s):

Mitsuru Matsumoto ◽

Yang-Xin Fu ◽

Hector Molina ◽

Guangming Huang ◽

Jinho Kim ◽

...

Keyword(s):

Bone Marrow ◽

Dendritic Cells ◽

Tumor Necrosis ◽

Type I ◽

Follicular Dendritic Cells ◽

Wild Type ◽

Lymphotoxin Α ◽

Deficient Mice ◽

Necrosis Factor

In mice deficient in either lymphotoxin α (LT-α) or type I tumor necrosis factor receptor (TNFR-I), organized clusters of follicular dendritic cells (FDC) and germinal centers (GC) are absent from the spleen. We investigated the role of LT-α and TNFR-I in the establishment of spleen FDC and GC structure by using reciprocal bone marrow (BM) transfer. When LT-α–deficient mice were reconstituted with wild-type BM, FDC organization and the ability to form GC were restored, indicating that the LT-α–expressing cells required to establish organized FDC are derived from BM. The role of LT-α in establishing organized FDC structure was further investigated by the transfer of complement receptor 1 and 2 (CR1/2)–deficient BM cells into LT-α–deficient mice. Organized FDC were identified with both the FDC-M1 and anti-CR1 monoclonal antibodies in these BM-chimeric mice, indicating that these cells were derived from the LT-α–deficient recipient. Thus, expression of LT-α in the BM-derived cells, but not in the non–BM-derived cells, is required for the maturation of FDC from non-BM precursor cells. In contrast, when TNFR-I–deficient mice were reconstituted with wild-type BM, they showed no detectable FDC clusters or GC formation. This indicates that TNFR-I expression on non–BM-derived cellular components is necessary for the establishment of these lymphoid structures. TNFR-I–deficient BM was able to restore FDC organization and GC formation in LT-α–deficient mice, indicating that formation of these structures does not require TNFR-I expression on BM-derived cells. The data in this study demonstrate that FDC organization and GC formation are controlled by both LT-α–expressing BM-derived cells and by TNFR-I-expressing non–BM-derived cells.

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FIP1L1/PDGFRa Synergizes with SCF/c-Kit Signaling To Induce Systemic Mastocytosis in a Chronic Eosinophilic Leukemia Murine Model

Blood ◽

10.1182/blood.v110.11.1540.1540 ◽

2007 ◽

Vol 110 (11) ◽

pp. 1540-1540

Author(s):

Yoshiyuki Yamada ◽

Jose A. Cancelas ◽

Eric B. Brandt ◽

Abel Sanchez-Aguilera ◽

Melissa McBride ◽

...

Keyword(s):

Bone Marrow ◽

Small Intestine ◽

Murine Model ◽

Fusion Gene ◽

Systemic Mastocytosis ◽

Wild Type ◽

Chronic Eosinophilic Leukemia

Abstract Systemic mastocytosis (SM) associated with chronic eosinophilic leukemia (CEL)/hypereosinophilic syndrome (HES) is a result of expression of the Fip1-like1 (FIP1L1)/platelet-derived growth factor receptor alpha (PDGFRa) (F/P) fusion gene. We have previously described a murine CEL/HES model (CEL-like mice) induced by F/P fusion gene transduction and T-cell overexpression of IL-5 (Yamada Y et al., Blood 2006). We have now validated a preclinical murine model of F/P-induced SM/CEL and analyzed the pathogenesis of SM in this model. F/P+ mast cells (MC, defined as EGFP+/c-kit+/FceRI+) were significantly increased in the small intestine, bone marrow (BM) and spleen of CEL-like mice compared to wild-type mice (Table). CEL-like mice also developed cutaneous MC infiltration. In addition, mMCP-1 serum levels, which correlate well with MC expansion and activation in vivo, were significantly higher in CEL-like mice than in wild-type mice (64,000 ± 23,800 and 38 ± 41.4 pg/ml, respectively). F/P induces increased expansion of BM-derived MC in vitro (∼2,000-fold) and F/P+ BM-derived MC survive longer than wild-type MC in cytokine-deprived medium (28.0 ± 2.3% vs. 8.7 ± 3.1% 7AAD−/Annexin V− cells after 48 hours). This correlated with increased Akt phosphorylation in the F/P+ MC. Since c-kit mutations are the most frequent cause of SM, we analyzed the possible synergistic role of SCF and F/P signaling. F/P and SCF/c-kit signaling indeed synergize in the development of BM-derived MC (16-fold greater expansion than in the absence of SCF) and F/P+ BM-derived MC showed a 3.7-fold greater migratory response to SCF than wild-type BM-derived MC. In order to determine the role of SCF/c-kit signaling in F/P+ MC development, activation and tissue infiltration in vivo,these responses were evaluated in mice that were treated with a blocking anti-c-kit blocking antibody, ACK-2, or an isotype-matched control antibody. ACK-2 treatment suppressed intestinal MC infiltration and elevated plasma levels of mMCP-1 induced by F/P expression by 95 ± 6.0% and 98 ± 0.76%, respectively, whereas MC and plasma mMCP-1 were completely undetectable in wild-type mice treated with ACK2. This suggests that SCF/c-kit interactions may synergize with F/P to induce SM. In summary, mice with CEL-like disease also develop SM. F/P-induced SM is a result of increased in vivo MC proliferation, survival, activation and tissue infiltration. SCF/c-kit signaling synergizes with F/P in vivo and in vitro to promote mast cell development, activation and survival. EGFP+/c-kit+/FcεRI+ cell frequency in tissues of control and CEL-like mice (%) Control mice CEL-like mice Small intestine 1.0±0.95 47±21.4* Bone marrow 0.2±0.14 3±1.9* Spleen 0.05±0.01 3±0.8*

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G-CSF Mediated Decrease in Bone-Marrow SDF-1 Level Is Neutrophil Dependent but CD26 Independent

Blood ◽

10.1182/blood.v112.11.3469.3469 ◽

2008 ◽

Vol 112 (11) ◽

pp. 3469-3469

Author(s):

Pratibha Singh ◽

Seiji Fukuda ◽

Janardhan Sampath ◽

Louis M. Pelus

Keyword(s):

Bone Marrow ◽

Magnetic Beads ◽

Critical Role ◽

Alternative Mechanism ◽

Wild Type ◽

Hematopoietic Stem ◽

Osteoblast Activity

Abstract Interaction of CXCR4 expressed on hematopoietic stem and progenitor cells (HSPC) with bone-marrow stromal SDF-1 is believed to play a central role in retention or mobilization of HSPC. Recently, a mobilization regimen of G-CSF was shown to decrease osteoblast number resulting in reduced levels of bone-marrow SDF-1, however the detailed mechanism leading to this reduction is currently unknown. It is unlikely that G-CSF directly regulates osteoblast SDF-1 production since osteoblasts do not express G-CSF receptor. Proteolytic cleavage of SDF-1 by peptidase CD26 in the bone-marrow may be an alternative mechanism responsible for reduction of SDF-1 level. Although CD26 can cleave SDF-1 in vitro, direct evidence of SDF-1 cleavage by CD26 in vivo during G-CSF induced HSPC mobilization has not been demonstrated. We previously demonstrated that neutrophils are required for G-CSF induced HSPC mobilization and that CD26 expression on neutrophils, rather than HSPC, is critical for mobilization. To more fully understand the role of CD26 in altering SDF-1 protein/activity during G-CSF induced HSPC mobilization, we quantitated bone-marrow SDF-1 levels in CD26−/− and wild-type CD26+/+ mice by ELISA during G-CSF administration. A standard 4 day G-CSF mobilization regimen (100 μg/kg bid, sc × 4 days) decreased bone-marrow total SDF-1 from 4.55±0.3 to 0.52±0.06 ng/femur in wild-type CD26+/+ mice (8.7-fold) and from 4.51±0.3 to 0.53±0.05 ng/femur (8.5-fold) in CD26−/− mice. However, despite an equivalent decrease in SDF-1, total CFU mobilization and the absolute number of mobilized SKL cells were decreased (3.1 and 2.0 fold lower, respectively) in CD26−/− mice compared to wild-type CD26+/+ controls. These results suggest that the decrease in total SDF-1 level in marrow seen following G-CSF treatment is independent of CD26. Cytological examination of bone-marrow smears showed that the reduction in SDF-1 levels in bone-marrow of both wild-type CD26+/+ and CD26−/− mice following G-CSF administration correlated with an increase in total absolute bone-marrow neutrophil cell number, suggesting a role for neutrophils in modulation of SDF-1 protein. To determine if neutrophils affect osteoblast SDF-1 production, bone marrow Gr-1+ neutrophils from wild-type CD26+/+ and CD26−/− mice were purified using anti-Ly6G magnetic beads and co-cultured with MC3T3-E1 preosteoblasts in vitro. Gr-1+ neutrophils from both wild-type and CD26−/− mice decreased pre-osteoblast SDF-1 production by similar amounts (15.4-fold vs 14.8-fold respectively), while Gr-1 neg cells from both wild-type CD26+/+ or CD26−/− were without effect on SDF-1 levels. Similarly, Gr-1+ neutrophils from both wild-type and CD26−/− mice decreased SDF-1 produced by MC3T3-E1-derived osteoblasts from 1.85±0.3 to 0.52±0.06 ng/ml (3.5 fold) and 0.56±0.07 ng/ml (3.3 fold) respectively, with Gr-1neg cells having no effect. Gr-1+ neutrophils either from wild-type or CD26−/− mice, but not Gr-1neg cells, significantly induced apoptosis of MC3T3-E1 cells as measured by Annexin-V staining (70.5%±10.2 vs 71.2%±12.5 for wild-type CD26+/+ and CD26−/− neutrophils respectively) and significantly inhibited osteoblast activity (20-fold vs 20.6-fold for CD26+/+ and CD26−/− neutrophils respectively) as measured by osteocalcin expression. Furthermore, irrespective of G-CSF treatment, an inverse correlation between absolute neutrophil number and SDF-1 protein levels was observed, suggesting that G-CSF induces neutrophil expansion but does not directly affect SDF-1 production. Collectively, these results provide additional support for the critical role of neutrophils in G-CSF induced mobilization and strongly suggested that neutrophils directly regulate bone-marrow SDF-1 levels independent of CD26 activity.

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Podocalyxin Negatively Regulates Stress Myelopoiesis, Directly Binds Rap-1A and Modulates Its G-CSF-Induced Activity

Blood ◽

10.1182/blood.v126.23.1184.1184 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1184-1184

Author(s):

Pan Li ◽

Rose McGlauflin ◽

Amanda J Favreau ◽

Edward Jachimowicz ◽

Calvin Vary ◽

...

Keyword(s):

Bone Marrow ◽

Functional Role ◽

Blood Analysis ◽

Wild Type ◽

Hematopoietic Progenitors ◽

Gm Csf ◽

Peripheral Blood Analysis ◽

Specific Deletion

Abstract Podocalyxin (PodxL) is a CD34 family member previously identified to mark hematopoietic stem cells (HSCs) and other progenitor cells. Previously, we discovered PodxL as a potent erythropoietin (EPO) response gene and demonstrated to promote egression of immature reticulocytes from bone marrow into circulation. PodxL is upregulated in several cancers, including myeloid and lymphoid leukemia. Herein, we aim to define the functional role of PodxL in hematopoiesis - specifically myelopoiesis - by employing conditional PodxL knock out (KO) mouse models. Hematopoietic-specific deletion was achieved using Cre mice with a Vav1 driver and myeloid-specific deletion was achieved with Lyzm2 - Cre driver. We confirmed the deletion of exons 3-7 at the gene, transcript and protein levels using PCR, RT-qPCR and western blotting, respectively. Peripheral blood analysis revealed no difference in blood cell lineages for either KO mouse strain. At steady state, colony forming unit-granulocyte/macrophage (CFU-GM) assay also showed no difference between the KO strains and wild type. In order to examine the functional role of PodxL during stress myelopoiesis, PodxL-/- ; Vav1-Cre mice were treated with 5-Fluorouracil (5FU), a chemotherapeutic agent induces myeloablation. Notably, during rebound of neutrophils, the PodxL-/- ; Vav1-Cre mice showed a sharp increase in neutrophil counts at day 12.5, which at later time points reverted to normal levels comparable to wild type mice. Previously, our in silico analyses combined with outcomes from truncated EpoR knock-in alleles had revealed that PodxL is a potential STAT5 transcriptional target. Here, we tested if G-CSF induces PodxL expression in hematopoietic progenitors. In vivo, G-CSF significantly induced PodxL expression four fold. We then tested the role of PodxL in G-CSF induced neutrophil formation in vivo. Both KO strains (Podxl-/-;Vav1-Cre and Podxl-/-;Lyzm2-Cre) and wild type were treated with G-CSF (125ug/kg/day) for 5 days. Peripheral blood analysis revealed increased neutrophil and monocyte levels in the PodxL-/-;Vav1-Cremice. In order to then determine a possible role of PodxL at the progenitor level, CFU-GM assays were performed. PodxL-/- ; lyzm2-Cre mice had increased colony forming capabilities but there was no difference in PodxL-/-;Vav1-Cre mice compared to wild type. Our results imply that PodxL is playing a negative regulatory role in stress myelopoiesis. Interestingly, the deletion of PodxL in hematopoietic progenitors (Vav1-Cre) resulted in enhanced migration of neutrophils, whereas deletion of PodxL in myeloid compartment (Lyzm2-Cre) resulted in decreased neutrophil migration. This may be in part due to a compensatory effect by CD34 in the hematopoietic compartment. To dissect the molecular mechanism of PodxL during stress myelopoiesis, upon in vivo G-CSF treatment, bone marrow derived hematopoietic progenitors were isolated and PodxL protein was immunoprecipitated. LC-MS/MS proteomic analysis was performed to identify the interacting partners with PodxL. Rap-1A, a small GTPase and member of the RAS family, was among the top interacting proteins. Rap-1A has been shown to promote adhesion and migration of myeloid cells. The association of PodxL with Rap-1A was further confirmed in hematopoietic progenitors by immunoprecipitation and western blotting. To determine if the interaction of PodxL directly regulates Rap-1A activity, a GTP-Rap-1A activity assay was performed in response to G-CSF, GM-CSF and IL-3. Rap-1A activity was significantly elevated in hematopoietic progenitors upon G-CSF treatment in PodxL-/-:Vav1-Cre mice compared to wild type, followed by IL3; however, GM-CSF did not affect Rap-1A activity. In conclusion, our results indicate an important functional role for PodxL in stress myelopoiesis, a function likely mediated via Rap-1A. A complete understanding of the PodxL/Rap-1A axis may reveal important molecular insights into G-CSF-induced mobilization of neutrophils and provide mechanistic understanding into the pathological role of PodxL in aggressive cancers, including leukemia, which in turn may facilitate identification of novel therapeutic targets in PodxL associated cancers. Disclosures No relevant conflicts of interest to declare.

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Analysis of Leukemogenic Effects of RUNX1 and CSF3R Mutations Using Congenital Neutropenia (CN)/AML Patient-Derived Induced Pluripotent Stem Cells (iPSCs)

Blood ◽

10.1182/blood.v128.22.404.404 ◽

2016 ◽

Vol 128 (22) ◽

pp. 404-404

Author(s):

Benjamin Dannenmann ◽

Maksim Klimiankou ◽

Christian Lindner ◽

Azadeh Zahabi ◽

Regine Bernhard ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Pluripotent Stem Cells ◽

Trisomy 21 ◽

Bone Marrow Failure ◽

Hematopoietic Cells ◽

Hematopoietic Progenitors ◽

Congenital Neutropenia ◽

Induced Pluripotent

Abstract Severe congenital neutropenia (CN) is a pre-leukemic bone marrow failure syndrome. Recently we reported a high frequency of cooperating RUNX1 and CSF3R mutations in CN patients that developed AML or MDS. Only a combination of these two mutations induced elevated proliferation and diminished myeloid differentiation of CD34+ cells in vitro. To confirm these clinical data in an in vitro model, we generated human induced pluripotent stem cells (hiPSCs) from PBMNCs of a CN patient harbouring p.C151Y mutation in ELANE after acquisition of AML. During GCSF treatment, this patient acquired G-CSFRmutation p.Q741*, which leads to a truncated G-CSF receptor and was detected six years prior to overt AML. Three years later, he acquired an additional RUNX1 (p.R139G) mutation, which is located in the RUNT-homology domain (RHD). Subsequently, he developed AML (FAB M1) with trisomy 21. Reprogramming of PBMNCs isolated from the time-point of AML (ca. 80 % of AML blasts) resulted in the generation of hiPSCs clones harbouring either only ELANE p.C151Y mutation (CN-iPSC clone, derived from non-leukemia PBMNCs) or additional CSF3R and RUNX1 mutations and trisomy 21 (CN/AML-iPSC clone, derived from AML blasts), which was subsequently validated by Sanger sequencing and by digital PCR. These iPSCs clones have been tested for their pluripotency and self-renewal capacity. Both iPSC clones expressed the pluripotent stem cell surface markers SSEA-4 and TRA-1-60 and displayed alkaline phosphatase activity. Further they highly expressed mRNA of the pluripotent stem cell markers SOX2, ABCG2, DNMT and NANOG and were able to differentiate into all three germ layers (meso-, endo- and ectoderm). Embryoid body (EB)-based hematopoietic / neutrophilic differentiation of CN-iPS clones using serum-free APEL stem cell differentiation medium showed comparable amounts of CD34+ and CD33+ cells, but ~ 2-fold reduction of CD16+ cells, compared to healthy donor (HD) iPSCs. CN/AML-iPSCs were not able to differentiate into mature granulocytes at all and revealed 10-fold reduced counts of CD34+ and CD33+hematopoietic cells. Morphological examinations of Giemsa-stained cytospin slides confirmed these results. Additionally, CN/AML-iPSCs showed a highly reduced number of CFU-G and CFU-GM colonies in CFU-Assay. To investigate the intracellular mechanisms of leukemogenic transformation in CN, we analyzed gene expression profiles of hematopoietic cells generated from CN-iPSCs vs CN/AML-iPSCs and HD-iPSCs for various time points of differentiation in our EB based-system. Our previous microarray-based analysis of bone marrow CD33+ cells of this CN/AML patient revealed that genes overexpressed in early hematopoietic stem/progenitor cells (HSPCs) as compared to more mature progenitors, such as DNTT, BAALC, CD34, HPGDS, NPR3 and PROM1 were strongly upregulated in CN/AML blasts harbouring both RUNX1 and CSF3R mutations, as compared to the cells prior to leukemia development. Intriguingly, elevated expression of these genes was described previously in RUNX1-mutated de novo AML blasts (Mendler et al., JCO 2012). This genetic signature suggests transformation of hematopoietic progenitors carrying mutated CSF3R into more primitive hematopoietic progenitors after aquisition of RUNX1mutation. We were able to confirm markedly increase of mRNA levels of these genes in hematopoietic cells derived from CN/AML-iPSCs, as compared to CN-iPSCs. In addition, we found that hematopoietic cells of both CN-iPSCs and CN/AML-iPSCs revealed increased expression of unfolded-protein response (UPR) genes DDIT3 (CHOP), ATF4 and ATF6, as compared to HD-iPSCs. Activation of UPR in hematopoietic cells of CN-ELANEpatients has been previously described by our and other groups. CN/AML-iPSC-derived hematopoietic progenitor cells expressed RUNX1 mRNA at least two-fold higher, as compared to HD- or CN-iPSC-derived cells. In summary, we established an in vitro cellular model of leukemogenic transformation in CN patients using CN/AML-patient derived hiPSCs that confirmed clinical data of Skokowa et al. (Blood 123:2550, 2014) on a cooperative leukemogenic effect of CSF3R and RUNX1 mutations. Comprehensive analysis of hematopoiesis using this iPSCs model will give us a deeper view into this highly complex signaling network operating during leukemogenic transformation of HSCs in pre-leukemic bone marrow failure syndromes. Disclosures No relevant conflicts of interest to declare.

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Direct contact between human primitive hematopoietic progenitors and bone marrow stroma is not required for long-term in vitro hematopoiesis

Blood ◽

10.1182/blood.v79.11.2821.bloodjournal79112821 ◽

1992 ◽

Vol 79 (11) ◽

pp. 2821-2826 ◽

Cited By ~ 2

Author(s):

CM Verfaillie

Keyword(s):

Bone Marrow ◽

Direct Contact ◽

Hematopoietic Progenitors ◽

Proliferation And Differentiation ◽

Bone Marrow Cultures ◽

Marrow Stroma ◽

Blood Elements

Long-term bone marrow cultures support both differentiation and conservation of primitive human hematopoietic progenitors in the absence of exogenous cytokines. It is believed that hematopoiesis in such cultures requires direct contact between hematopoietic progenitors and stroma. In the present study, we demonstrate that primitive progenitors physically separated from the stromal layer by a 0.45- microns microporous membrane continue to generate differentiated progenitors for at least 8 weeks. Moreover, primitive progenitors are conserved to a greater extent under these conditions, as when cultured in direct contact with the stroma. However, excessive production of granulocyte-macrophage progenitors occurs when primitive progenitors are not allowed to interact directly with the stroma. Thus, direct contact between hematopoietic and stromal cells is not required for either differentiation or conservation of primitive hematopoietic progenitors but is essential for the regulated production of mature blood elements. These findings can now be used to define the role of diffusible factors and cell-cell or cell-extracellular matrix adhesion events in the regulation of conservation, proliferation, and differentiation of primitive human hematopoietic progenitors in vitro.

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Loss of Gfi1 Impedes Development of T-Cell Lymphoma upon Exposure to N-ethyl-N-nitrosourea but Predisposes to Severe Myleodysplastic Changes.

Blood ◽

10.1182/blood.v110.11.2221.2221 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2221-2221

Author(s):

Cyrus Khandanpour ◽

Ulrich Duehrsen ◽

Tarik Möröy

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Dna Damage ◽

T Cell ◽

Bone Marrow Cells ◽

Cell Lymphoma ◽

Wild Type ◽

Hematopoietic Stem ◽

Deficient Mice

Abstract Exogenous toxic substances often cause the initiation and development of leukemia and lymphoma by acting as mutagens. N-ethyl-N-nitrosourea (ENU) is a paradigmatic example for such a substance, which introduces point mutations in the genome through DNA damage and repair pathways. ENU is widely used to experimentally induce T-cell lymphomas in mice. We have used ENU to investigate whether the hematopoietic transcription factor Gfi1 is required for lymphomagenesis. The Gfi1 gene was originally discovered as a proviral target gene and a series of experiments with transgenic mice had suggested a role of Gfi1 as a dominant oncogene with the ability to cooperate with Myc and Pim genes in the generation of T-cell lymphoma. In addition, Gfi1 deficient mice showed a defect in T-cell maturation but also aberration in myeloid differentiation and an accumulation of myelomonocytic cells. ENU was administered i.p. once a week for three weeks with a total dose of 300mg/kg to wild type (wt) and Gfi1 null mice. Wild type mice (12/12) predominantly developed T-cell tumors and rarely acute myeloid leukemia, as expected. However, only 2/8 Gfi1 −/− mice succumbed to lymphoid neoplasia; they rather showed a severe dysplasia of the bone marrow that was more pronounced than in wt controls. These changes in Gfi1 null mice were accompanied by a dramatic decrease of the LSK (Lin-, Sca1- and c-Kit+) bone marrow fraction that contains hematopoietic stem cells and by a higher percentage (18%) of bone marrow cells, not expressing any lineage markers (CD4, CD 8, Ter 119, Mac1, Gr1, B220, CD3). In particular, we found that the LSK subpopulation of Gfi1 deficient mice showed a noticeable increase in cells undergoing apoptosis suggesting a role of Gfi1 in hematopoietic stem cell survival. In addition, Gfi1−/− bone marrow cells and thymic T-cells were more sensitive to DNA damage such as radiation and exposure to ENU than their wt counterparts pointing to a role of Gfi1 in DNA damage response. Our results indicate that Gfi1 is required for development of T-cell tumors and that a loss of Gfi1 may sensitize hematopoietic cells and possibly hematopoietic stem cells for programmed cell death. Further studies have to show whether interfering with Gfi1 expression or function might represent a tool in the therapy of leukemia.

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Lentiviral FANCA Vectors Pseudotyped with a Modified Prototype Foamy Viral Envelope Corrects Murine Fanca−/− Hematopoietic Stem Cells with Reduced Toxicity.

Blood ◽

10.1182/blood.v110.11.1677.1677 ◽

2007 ◽

Vol 110 (11) ◽

pp. 1677-1677

Author(s):

Zejin Sun ◽

Yanzhu Yang ◽

Yan Li ◽

Daisy Zeng ◽

Jingling Li ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Gene Transfer ◽

Ex Vivo ◽

Bone Marrow Failure ◽

Wild Type ◽

Hematopoietic Stem ◽

Ex Vivo Culture

Abstract Fanconi anemia (FA) is a recessive DNA repair disorder characterized by congenital abnormalities, bone marrow failure, genomic instability, and a predisposition to malignancies. As the majority of FA patients ultimately acquires severe bone marrow failure, transplantation of stem cells from a normal donor is the only curative treatment to replace the malfunctioning hematopoietic system. Stem cell gene transfer technology aimed at re-introducing the missing gene is a potentially promising therapy, however, prolonged ex vivo culture of cells, that was utilized in clinical trials with gammaretroviruses, results in a high incidence of apoptosis and at least in mice predisposes the surviving reinfused cells to hematological malignancy. Consequently, gene delivery systems such as lentiviruses that allow a reduction in ex vivo culture time are highly desirable. Here, we constructed a lentiviral vector expressing the human FANCA cDNA and tested the ability of this construct pseudotyped with either VSVG or a modified prototype foamyvirus (FV) envelope to correct Fanca−/− stem and progenitor cells in vitro and in vivo. In order to minimize genotoxic stress due to extended in vitro manipulations, an overnight transduction protocol was utilized where in the absence of prestimulation, murine Fanca−/− bone marrow cKit+ cells were co-cultured for 16h with FANCA lentivirus on the recombinant fibronectin fragment CH296. Transduction efficiency and transfer of lentivirally expressed FANCA was confirmed functionally in vitro by improved survival of consistently approximately 60% of clonogenic progenitors in serial concentrations of mitomycin C (MMC), irregardless of the envelope that was utilized to package the vector. Transduction of fibroblasts was also associated with complete correction of MMC-induced G2/M arrest and biochemically with the restoration of FancD2 mono-ubiquitination. Finally, to functionally determine whether gene delivery by the recombinant lentivirus during such a short transduction period is sufficient to correct Fanca−/− stem cell repopulation to wild-type levels, competitive repopulation experiments were conducted as previously described. Follow-up of up to 8 months demonstrated that the functional correction were also achieved in the hematopoietic stem cell compartment as evidenced by observations that the repopulating ability of Fanca−/− stem cells transduced with the recombinant lentivirus encoding hFANCA was equivalent to that of wild-type stem cells. Importantly, despite the fact that the gene transfer efficiency into cells surviving the transduction protocol were similar for both pseudotypes, VSVG was associated with a 4-fold higher toxicity to the c-kit+ cells than the FV envelope. Thus, when target cell numbers are limited as stem cells are in FA patients, the foamyviral envelope may facilitate overall greater survival of corrected stem cells. Collectively, these data indicate that the lentiviral construct can efficiently correct FA HSCs and progenitor cells in a short transduction protocol overnight without prestimulation and that the modified foamy envelope may have less cytotoxicity than the commonly used VSVG envelope.

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Mir-21 Mediates Hematopoietic Suppression in MDS by Activating TGF-b Signaling,

Blood ◽

10.1182/blood.v118.21.3813.3813 ◽

2011 ◽

Vol 118 (21) ◽

pp. 3813-3813 ◽

Cited By ~ 1

Author(s):

Tushar D. Bhagat ◽

Li Zhou ◽

Lubomir Sokol ◽

Ioannis Mantzaris ◽

Krishna Gundabolu ◽

...

Keyword(s):

Bone Marrow ◽

Binding Sites ◽

Therapeutic Potential ◽

Bone Marrow Failure ◽

Negative Regulator ◽

Locked Nucleic Acid ◽

P Value ◽

Wild Type ◽

Smad2 Phosphorylation

Abstract Abstract 3813 Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis that leads to peripheral cytopenias. TGF-b is a hematopoietic inhibitory cytokine that has been indirectly linked to the pathogenesis of some subsets of MDS. We have shown that smad2, a component of the TGF- signaling pathway, is constitutively activated and upregulated in MDS progenitors (Blood, 112(8):3434; 2008). Since there is conflicting data about upregulation of TGF- b levels in MDS, we next sought to determine the molecular basis of TGF- b pathway activation in this disease. We observed that smad-7, a negative regulator of TGF- b receptor-I kinase, is markedly down regulated in MDS and leads overactivation of the receptor and subsequent smad2 phosphorylation / activation in this disease (Cancer Res, 71(3):955–63). In the present study we wanted to determine the cause of smad7 reduction in MDS. Since microRNA dysregulation has been reported in many malignancies, we explored the 3'UTR of the smad7 gene for putative microRNA binding sites and observed predicted mir-21 and mir-15/16 binding sites that were conserved across species. mir-21 was found to be elevated in a microarray screen in MDS (British J. Haem. 153(1):24–32) and was subsequently found by us to be significantly elevated by qPCR in MDS marrow samples when compared with age matched controls (TTest, N=11 in each group, P Value= 0.02). Luciferase reporters containing wild type and mutant 3' UTR of the smad7 gene were then used to determine whether mir21 was able to directly bind to the predicted sequence in the gene. Enforced expression of mir-21 was able to inhibit the wild type smad7 reporter expression and a mutation of 4 complementary residues in the 3'UTR led to abrogation of this effect, thus demonstrating direct effects of mir-21 on smad7 gene. To test the role of mir-21 in regulating TGF-b signaling in vivo, we used chemically modified, locked nucleic acid (LNA) inhibitors of mir-21. These were used in a TGF-overexpressing transgenic mouse model that develops progressive anemia and dysplasia and thus serves as a model of human bone marrow failure. Treatment with the mir-21 inhibitor led to significant increases in RBC counts when compared to placebo (P value<0.01, T test) and led to increase in smad7 expression and decrease in smad2 phosphorylation in bone marrow progenitors of the treated mice. Finally, mir-21 inhibitor treatment led to increases in erythroid and myeloid colony formation from human MDS bone marrow stem cells, demonstrating its ability in stimulating hematopoiesis in vitro. Taken together, these studies demonstrate that mir-21 mediated reduction in smad-7 contributes to ineffective hematopoiesis in MDS by activating TGF-beta signaling in bone marrow progenitors. Most importantly, these studies illustrate the therapeutic potential of mir-21 inhibitors in this disease. Disclosures: List: Celgene: Consultancy.

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