Activation of Non-Canonical Immune Signalling Pathways Drives Marrow Failure in a Murine Model of MDS

Abstract The Myelodysplastic Syndromes (MDS) are the most common hematological malignancies arising from stem/progenitor cells. MDS is characterized by ineffective hematopoiesis in one or more lineages of the bone marrow, resulting in peripheral cytopenias and the propensity to progress to either acute myeloid leukemia (AML) or bone marrow failure (BMF). The most common cytogenetic aberration associated with MDS is deletion of the long arm of chromosome 5. Many of the molecular events involved in the development of del(5q) MDS have been elucidated including haploinsufficiency of the gene encoding the ribosomal protein RPS14, responsible for the anemia observed, and haploinsufficency of the miRNAs miR-145 and miR-146a, which together target the innate immune signaling pathway, specifically, the Toll-like receptor-4 (TLR-4)signalling pathway. It has been demonstrated that overexpression of a target of miR-146a,TRAF6, in mouse bone marrow can recapitulate the phenotype of del(5q) MDS including the cytopenias and progression to BMF or AML. However, enforced expression of TIRAP, a miR-145 target gene, results in rapid BMF independent of TRAF6. The molecular and cellular mechanisms responsible for the differential outcome of overexpression of two genes that act within the same signalling pathway remain to be fully understood. We have identified several differentially expressed cytokines, including interferon gamma (IFNγ) and interleukin-10 (IL-10), following TIRAP overexpression compared with TRAF6 overexpression. Promoter methylation analysis has shown hypermethylation of key adaptors and signal transducers that lie between TIRAP and TRAF6 in the TLR-4 signalling pathway, suggesting activation of different pathways by TIRAP and TRAF6 overexpression. Indeed, blockade of TRAF6 and MyD88 did not inhibit TIRAP induced expression of these cytokines, suggesting that IFNγ and IL-10 production occurs in a TRAF6 and MyD88 independent manner. We identified IFNγ as the critical effector cytokine responsible for TIRAP mediated marrow failure. Gene set enrichment analysis has shown an enrichment of an IFNγ signature in MDS patients with a low risk of transformation to AML compared to healthy controls. Furthermore, interferon signatures were highly enriched in MDS patients compared to patients with AML, suggesting an important role for IFNγ signaling in driving MDS progression toward marrow failure as opposed to leukemic progression. IFNγ has been shown to inhibit components of the bone marrow niche by blocking RANK signalling in stromal cells such as osteoclast progenitors. Using coculture of TIRAP expressing bone marrow cells with the RAW264.7 monocyte cell line, a cell line that is capable of differentiation into osteoclasts, we found an inhibition in the ability of these cells to form osteoclasts compared to control. This provides the first line of evidence suggesting that immune signalling defects arising from genetic perturbations in the hematopoietic stem cell compartment can result in stem cell niche dysfunction leading to marrow failure. Disclosures No relevant conflicts of interest to declare.

Download Full-text

IFNy Stimulation Induces Hematopoietic Stem Cell Homing and Niche Relocalization

Blood ◽

10.1182/blood-2019-130555 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3726-3726

Author(s):

Marcus A Florez ◽

Katie A Matatall ◽

Laura Ortinau ◽

Roman Jaksik ◽

Marek Kimmel ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cell ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Terminal Differentiation ◽

Bone Marrow Niche ◽

Hematopoietic Stem ◽

Bm Niche ◽

The Impact

Interferon gamma (IFNy) is a pro-inflammatory cytokine that is upregulated during chronic infections and chronic diseases, such as aplastic anemia, and has been associated with pancytopenia and diminished hematopoiesis. Studies have shown that IFNy negatively regulates hematopoietic stem cell (HSC) homeostasis by decreasing self-renewal and promoting terminal differentiation. The tight regulation of HSC homeostasis is dependent upon the bone marrow (BM) microenvironment, or BM niche. The BM niche is composed of a network of cell types that provide elaborate cell-cell interactions, cellular metabolites, transcriptional regulators, and local and distant humoral and neural signals that allow for hematopoietic homeostasis. In particular, CXCL12-abundant reticular (CAR) cells are vital to HSC maintenance, as depletion of CXCL12, or its receptor, leads to HSC depletion. However, the mechanism which IFNy activates HSCs and influences its interaction with the BM niche is unknown. We hypothesize that IFNy promotes HSC terminal differentiation and loss of quiescence by altering HSC interactions with the BM niche. To assess changes in HSC interactions with the BM niche upon IFNy stimulation, we performed intravital imaging using CXCL12 GFP reporter mice before and after administration of recombinant IFNy. We found that HSCs stimulated with IFNy were significantly distanced from CAR cells compared to pre-treated controls. There was no change in distance with IFNy-receptor deficient HSCs, suggesting that movement away from the CAR cells was due to a cell autonomous IFNy-dependent mechanism. We performed gene expression analysis and transwell migration assays on HSCs from IFNy treated mice, and determined that there was no change in CXCL12 receptor (CXCR4) expression upon IFNy treatment, and IFNy did not alter migration towards CXCL12. These results suggest that HSC re-localization upon IFNy is independent of CXCL12 signaling. To explore the mechanism by which IFNy induces re-localization of HSCs, we first performed microarray analysis on HSCs from IFNy stimulated mice to assess what surface proteins were changed upon IFNy treatment. While there was no change in common HSC receptors thought to influence HSC homeostasis (cKit, Cdh2, Mpl, Itgb1, Itbg2, Itga4, and Itga1), we observed an increase in expression of bone marrow stromal antigen 2 (BST2). To explore the impact of BST2 on HSC homeostasis, quantification and proliferation analysis was performed on HSCs from Bst2-/- mice. Interestingly, Bst2-/- HSCs were significantly less proliferative and more abundant compared to controls. These studies suggest that BST2 may play a role in maintaining HSC homeostasis. The functional role of BST2 in cellular movement and adhesion has been studied in cancer. Increased BST2 expression has been associated with promoting the migration, adhesion and metastasis of various cancer cells. Since migration and adhesion is important for HSC homing, we assessed the effects of IFNy on HSC homing. Hematopoietic progenitors from IFNy-treated mice homed to the bone marrow with greater efficiency than PBS-treated controls, whereas progenitors from IFNy-receptor-deficientmice showed a decrease in homing. Additionally, WBM from IFNyR-/- had reduced engraftment than wildtype, consistent with a role for IFNy signaling in promoting HSC homing. The impact of BST2 on homing is currently being explored. In summary, we show that IFNy induces re-localization of HSCs away from quiescence-promoting CAR cells within the bone marrow niche via a mechanism that is independent of CXCL12 signaling. We further show that IFNy promotes HSC homing. The increased expression of BST2 on IFNy-stimulated HSCs appears to impact HSC proliferation and abundance in the bone marrow. Thus, BST2 may play a role in HSC activation and exit from quiescence. Expanding our understanding of the mechanism that drives HSC activation and terminal differentiation has important implications for patients who develop pancytopenia or bone marrow failure due to chronic inflammation. Disclosures No relevant conflicts of interest to declare.

Download Full-text

Apoptosis and the DNA Damage Response: The Role of the RB Tumor Suppressor Pathway in Oxidative Stress Responses in the Hematopoietic System.

Blood ◽

10.1182/blood.v114.22.sci-15.sci-15 ◽

2009 ◽

Vol 114 (22) ◽

pp. SCI-15-SCI-15

Author(s):

Kay F. Macleod

Keyword(s):

Oxidative Stress ◽

Bone Marrow ◽

Stem Cell ◽

Tumor Suppressor ◽

Bone Marrow Failure ◽

Bone Marrow Niche ◽

Hematopoietic Stem ◽

Hematopoietic System ◽

Protein Levels ◽

Replicative Stress

Abstract Abstract SCI-15 Exposure to pro-oxidants and defects in repair of oxidative base damage is associated with disease and aging and also contributes to the development of anemia, bone marrow failure and hematopoietic malignancies. Our work examines the role of the RB tumor suppressor pathway in the response of the hematopoietic system to oxidative stress and DNA damage. Evidence from mouse models has identified a role for the Rb protein (pRb) in the regulation of hematopoiesis through cell intrinsic functions in blood cell types but also through effects on the bone marrow microenvironment (Spike et al, 2004; Walkley et al, 2007; Daria et al, 2008). Such models have also demonstrated that pRb is required under stress conditions but not under conditions of steady state hematopoiesis (Spike et al, 2004; Spike et al, 2007; Daria et al, 2008). In particular, pRb was required to modulate the response of the hematopoietic system to replicative stress and hypoxia (Spike et al, 2007; Daria et al, 2008). To explain the mechanisms underlying these unique properties of pRb in hematopoiesis, we hypothesized that pRb protein levels are regulated by oxidative stress, including hypoxia and ROS generated as a consequence of stem cell location in the bone marrow niche or in response to replicative stress induced by agents such as 5-fluorouracil. Notably, hypoxia within the bone marrow niche has been reported to promote stem cell expansion and we postulated that this may be due to reduced pRb protein levels in response to hypoxia. We present evidence that pRb protein levels are regulated in wild-type bone marrow in response to replicative stress and that this in turn modulates expansion of stem cells and myeloid progenitors and also impacts end-stage differentiation in the erythroid lineage. Acetylation of pRb stabilized the protein in an active conformation while de-acetylation de-stabilized the protein and promoted pRb protein turnover and increased progenitor cell proliferation. We will present on-going studies that examine how hypoxia and/or ROS affects hematopoietic stem cell proliferation, self-renewal and differentiation in vivo as a function of pRb protein levels using conditional mouse models. The significance of our findings for bone marrow failure in human patients will be discussed. References Spike, B.T. et al. The Rb tumor suppressor is required for stress erythropoiesis. The EMBO J. 2004: 23, 4319-29. Spike, B.T., Dibling, B.C. & Macleod, K.F. Hypoxic stress underlies defects in erythroblast island formation in the Rb null mouse. Blood 2007; 110, 2173-81. Walkley, C.R., Shea, J.M., Sims, N.A., Purton, L.E. & Orkin, S.H. Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment. Cell 2007; 129, 1081-95. Daria, D. et al. The retinoblastoma tumor suppressor is a critical intrinsic regulator for hematopoietic stem and progenitor cells under stress. Blood 2008; 111, 1894-902. Funding: The author is grateful to the J.P. McCarthy Foundation, the Aplastic Anemia and MDS International Foundation and the National Heart Lung & Blood Institute (RO1 HL080262) for funding of work in her laboratory relating to oxidative stress, erythropoiesis and hematopoietic diseases. Disclosures No relevant conflicts of interest to declare.

Download Full-text

G-CSF Treatment Induces Toll-Like Receptor Signaling and Regulates Hematopoietic Stem Cell Function

Blood ◽

10.1182/blood.v122.21.1181.1181 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1181-1181 ◽

Cited By ~ 1

Author(s):

Laura G. Schuettpelz ◽

Joshua N. Borgerding ◽

Priya Gopalan ◽

Matt Christopher ◽

Molly Romine ◽

...

Keyword(s):

Bone Marrow ◽

Cell Function ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Intestinal Flora ◽

Enrichment Analysis ◽

Gene Set Enrichment Analysis ◽

Tlr Signaling ◽

Hematopoietic Stem

Abstract Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are unclear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect. RNA profiling and flow cytometry studies of HSCs from G-CSF treated mice show that multiple toll- like receptors (TLRs) are upregulated in HSCs upon G-CSF treatment, and gene set enrichment analysis shows enhancement of TLR signaling in G-CSF-treated HSCs. G-CSF-induced expansion of phenotypic HSCs is reduced in mice lacking the TLR signaling adaptors MyD88 or Trif, and the induction of quiescence is abrogated in mice lacking these adaptors. Furthermore, loss of TLR4 mitigates the G-CSF-mediated HSC repopulating defect. Interestingly, baseline HSC function is also dependent on TLR signaling. We show that HSC long-term repopulating activity is enhanced in Tlr4-/- and MyD88-/- mice, but not Trif-/- mice. One potential source of TLR ligands affecting HSC function in the bone marrow is the gut microbiota. Indeed, we show that in mice treated with antibiotics to suppress intestinal flora, G-CSF induced HSC quiescence and hematopoietic progenitor mobilization are attenuated. Moreover, in germ free mice, HSC long-term repopulating activity is enhanced. Collectively these data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling. Our finding of enhanced TLR signaling upon G-CSF treatment, and the mitigation of G-CSF’s effects in mice deficient for TLR signaling or commensal organisms, suggest that TLR antagonists and/or agonists may ultimately be used clinically to enhance engraftment following bone marrow transplantation or applied toward the treatment of patients with bone marrow failure. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Rpl22 Deficiency Predisposes Hematopoietic Stem and Progenitor Cells to Leukemogenesis

Blood ◽

10.1182/blood.v126.23.899.899 ◽

2015 ◽

Vol 126 (23) ◽

pp. 899-899 ◽

Cited By ~ 1

Author(s):

Bryan Harris ◽

Jaqueline Perrigoue ◽

Rachel M. Kessel ◽

Shawn Fahl ◽

Stephen Matthew Sykes ◽

...

Keyword(s):

Gene Expression ◽

Bone Marrow ◽

Stem Cell ◽

Ribosomal Protein ◽

Cell Function ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Ectopic Expression ◽

Hematopoietic Stem ◽

Increased Risk

Abstract Mutations and deletions in ribosomal proteins are associated with a group of diseases termed ribosomopathies. Collectively, these diseases are characterized by ineffective hematopoiesis, bone marrow failure, and an increased risk of developing myelodysplastic syndrome (MDS) and subsequently acute myeloid leukemia (AML). This observation highlights the role of dysregulation of this class of proteins in the development and progression of myeloid neoplasms. Analysis of gene expression in CD34+ hematopoietic stem cells (HSC) from 183 MDS patients demonstrated that ribosomal protein L22 (Rpl22) was the most significantly reduced ribosomal protein gene in MDS. Interestingly, we observed that AML patients with lower expression of Rpl22 had a significant reduction in their survival (TCGA cohort, N=200, Log Rank P value <0.05). To assess the mechanism of reduced expression, we developed a FISH probe complementary to the RPL22 locus and assessed for deletion of this locus in an independent set of 104 MDS/AML bone marrow samples. Strikingly, we found that RPL22 deletion was enriched in high-risk MDS and secondary AML cases. We, therefore, sought to investigate whether reduced Rpl22 expression played a causal in leukemogenesis. Using Rpl22-/- mice, we found that Rpl22-deficiency resulted in a constellation of phenotypes resembling MDS. Indeed, Rpl22-deficiency causes a macrocytic reduction in red blood cells, dysplasia in the bone marrow, and an expansion of the early hematopoietic stem and progenitor compartment (HSPC). Since MDS has been described as a disease originating from the stem cell compartment, we next sought to determine if the hematopoietic defects were cell autonomous and resident in Rpl22-/- HSC. Competitive transplantation revealed that Rpl22-/- HSC exhibited pre-leukemic characteristics including effective engraftment, but a failure to give rise to downstream mature blood cell lineages. Importantly, there was a strong myeloid bias in those downstream progeny derived form Rpl22-/- HSC. Because human MDS frequently progresses to AML, we examined the potential for Rpl22-deficient HSC to be transformed upon ectopic expression of the MLL-AF9 oncogenic fusion. Indeed, Rpl22-deficient HSPC exhibited an increased predisposition to transformation both in vitro and in vivo, in MLL-AF9 knockin mice. To determine how Rpl22-deficiency increased the transformation potential of HSC, we performed whole transcriptome analysis on Rpl22-/- HSC. Interestingly, four expression signatures were observed that were consistent with the altered behavior exhibited by Rpl22-/- HSC. Rpl22-deficient HSC exhibited increased expression of: 1) genes associated with stem cell function, consistent with the basal expansion and effective engraftment of Rpl22-/- HSC upon adoptive transfer; 2) markers of the myeloid lineage, providing a potential explanation for the myeloid bias exhibited by Rpl22-/- HSC; 3) cell cycle regulators, consistent with the increased proliferation exhibited by Rpl22-/- HSC; and 4) components of the mitochondrial respiratory chain, a metabolic program on which leukemic stem cell function depends. Together, these data suggest that Rpl22 controls a program of gene expression that regulates the predisposition of HSPC to myeloid transformation. Disclosures No relevant conflicts of interest to declare.

Download Full-text

Hematological Disorders in Human Patients with Son Mutations

Blood ◽

10.1182/blood-2019-130616 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3709-3709

Author(s):

Lana Vukadin ◽

Jung-Hyun Kim ◽

Tara Bly Hackwelder ◽

Nathan Ungerleider ◽

Erik Flemington ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Rna Splicing ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Regulation Of Transcription ◽

Heterozygous Deletion ◽

Hematopoietic Stem ◽

Hematological Disorders ◽

Hematopoietic Lineage

Precise regulation of transcription and RNA splicing is critical for controlling hematopoietic cell fate determination and lineage differentiation. Alteration of expression of lineage-specific transcription factors and several core spliceosome components in hematopoietic malignancies highlight the significance of abnormal transcription and RNA splicing as disease-causing factors. Our group previously demonstrated that SON, a large nuclear speckle protein possessing dual abilities to bind both DNA and RNA, functions as a splicing factor as well as a transcriptional repressor. We recently identified heterozygous loss-of-function mutations in the SON gene from children with intellectual disability and developmental delay often with a broad spectrum of other congenital anomalies. The disorder caused by SON haploinsufficiency has been designated as ZTTK syndrome (Zhu-Tokita-Takenouchi-Kim syndrome; OMIM #617140). The majority of the mutations found in these patients are frameshift or nonsense mutations which cause degradation of the mutation-bearing transcript. While the most prominent features of these patients are brain malformations and musculoskeletal abnormalities, we identified various hematological disorders from children with ZTTK syndrome. Notable symptoms include bone marrow failure, severe anemia, immunoglobulin deficiency, thalassemia, polycythemia, polycythemia vera, stroke due to blood clots, and leukocytopenia. Apart from the ZTTK syndrome, SON is known to be upregulated in acute myeloid leukemia (AML) patients and is correlated to altered hematopoietic differentiation. To investigate how altered SON expression affects hematopoiesis, we generated a mouse line with the Son gene deleted specifically in the hematopoietic lineage. Homozygous deletion of Son in hematopoietic lineage led to embryonic lethality, indicating that SON expression in blood cells is indispensable during development. Mice with heterozygous deletion of Son in the hematopoietic lineage were viable and born without notable defects or sign of diseases. However, there is a significant decrease in bone marrow cellularity in the mice with heterozygous deletion of Son. Furthermore, Son haploinsufficiency decreased the size of the lineage negative (Lin-) cell population and short-term hematopoietic stem cell (ST-HSC) population with a concurrent increase in megakaryocyte/erythrocyte lineage-biased multipotent progenitors (MPP2) within hematopoietic stem/progenitor cells. These findings suggest that the level of Son expression potentially affects stem cell maintenance and MPP lineage bias, and the distortion of the subpopulation balance within hematopoietic stem/progenitors is possibly linked to multiple hematological disorders. Our ongoing analyses of hematopoiesis and gene expression changes using this mouse model will expand our knowledge about the role of SON in several hematological disorders and benefit clinical practice for ZTTK syndrome patients. Disclosures No relevant conflicts of interest to declare.

Download Full-text

MT1-MMP Regulates Hematopoiesis Through HIF-Mediated Chemo-/Cytokine Release From the Bone Marrow Niche,

Blood ◽

10.1182/blood.v118.21.3409.3409 ◽

2011 ◽

Vol 118 (21) ◽

pp. 3409-3409

Author(s):

Chiemi Nishida ◽

Kaori Kusubata ◽

Yoshihiko Tashiro ◽

Ismael Gritli ◽

Aki Sato ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Cell Fate ◽

Conflicts Of Interest ◽

Stem Cell Differentiation ◽

Cell Phenotype ◽

Bone Marrow Niche ◽

Matrix Remodeling ◽

Hematopoietic Stem

Abstract Abstract 3409 Stem cells reside in a physical niche, a particular microenvironment. The organization of cellular niches has been shown to play a key role in regulating normal stem cell differentiation, stem cell maintenance and regeneration. Various stem cell niches have been shown to be hypoxic, thereby maintaining the stem cell phenotype, e.g. for hematopoietic stem cells (HSCs) or cancer stem cells. The bone marrow (BM) niche is a rich reservoir for tissue-specific pluripotent HSCs. Proteases, such as matrix metalloproteinases (MMPs) can modulate stem cell fate due to their proteolytic or non-proteolytic functions (abilities). We have investigated the role of membrane-type1 matrix metalloproteinase (MT1-MMP), known for its role in pericellular matrix remodeling and cell migration, in hematopoiesis. MT1-MMP is highly expressed in HSCs and stromal cells. In MT1-MMP−/− mice, release of kit ligand (KitL), stromal cell derived factor-1 (SDF-1/CXCL12), erythropoietin (Epo) and interleukin-7 were impaired resulting in erythroid, myeloid and T and B lymphoid differentiation. Addition of exogenous rec. KitL and rec. SDF-1 restored hematopoiesis in vivo and in vitro. Further mechanistic studies revealed that MT1-MMP in a non-proteolytic manner activates the HIF-1 pathway, thereby inducing the transcription of the HIF-responsive genes KitL, SDF-1 and Epo. These results suggested MT1-MMP as a critical regulator of postnatal hematopoiesis, which as a modulator of the HIF pathway alters critical hematopoietic niche factors necessary for terminal differentiation and or migration. Thus, our results indicate that MT1-MMP as a key molecular link between hypoxia and the regulation of vital HSC niche factors. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Growth Factor Independence 1b (Gfi1b) Regulates The Commitment, Differentiation and Expansion Of Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v122.21.2433.2433 ◽

2013 ◽

Vol 122 (21) ◽

pp. 2433-2433

Author(s):

Tarik Moroy ◽

Cyrus Khandanpour ◽

Joseph Krongold

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Mouse Bone Marrow ◽

Paracrine Factors ◽

Self Renewal ◽

Hematopoietic Stem

Abstract The efficacy of bone marrow stem cell transplantation is the therapy of choice for many hematopoietic diseases, in particular leukemia and lymphoma. This therapy is critically dependent on the transfer of sufficient numbers of hematopoietic stem cells (HSCs), which possess the capacity for self-renewal and can fully reconstitute the hematopoietic system. As such, the development of techniques for the expansion of fully functional HSCs is of significant clinical interest. By transiently manipulating the factors that govern HSC homeostasis it has been proposed that HSCs can be expanded without the loss of essential stem cell characteristics. Previously we have observed that ablation of the gene encoding the transcription factor Gfi1b in-vivo results in a dramatic expansion and mobilization of hematopoietic stem cells in the bone marrow and periphery. More recent data suggest that the blood mobilization of Gfi1b deficient HSCs is very likely mediated by a deregulation of the integrin expression. These data led us to hypothesize that Gfi1b could be a potential target for ex-vivo treatment and expansion of HSCs. Indeed, when deletion of Gfi1b was induced in whole bone marrow ex-vivo, HSCs showed a significant expansion in both in absolute number and in terms of proportion of bone marrow. We followed HSCs in ex-vivo expansion cultures from mouse bone marrow by tracking expression of the surface marker CD48, which indicates whether an HSC has transitioned to a differentiation committed multi-potent progenitor. We observed that Gfi1b null HSCs expanded without up-regulating CD48 in contrast to wt HSCs. This suggests that Gf11b deficient HSCs underwent symmetric self-renewal type cell divisions at a significantly increased frequency, when compared to wt HSCs. We had previously shown that HSCs lacking Gfi1b cycle at a faster rate than control HSCs. The combination of increased cell division and preferential self-renewal of Gfi1b-/- HSCs indicates that inhibition of Gfi1b may be the ideal strategy for ex-vivo HSC expansion. As well, in accordance with this preference for self-renewal, Gfi1b null HSCs that were cultured under myeloid differentiation conditions remained primarily in an undifferentiated state as defined by a lack of the myeloid surface markers Gr1 and Mac1. These cultures also demonstrated increased long term colony forming capacity versus controls, further supporting an undifferentiated phenotype in Gfi1b-/- cells. Because the stem cell niche is a highly complex and heterogeneous environment we also investigated whether bone marrow in which Gfi1b has been deleted exerts paracrine effects that contributed to HSC expansion. Co-Culture assays demonstrated that Gfi1b-/- bone marrow was able to induce an expansion of progenitors in wild-type bone marrow of more than 10 fold compared to Gfi1b-/+ bone marrow. Interestingly cells co-cultured with Gfi1b null bone marrow also exhibited an overall proliferation advantage after short-term cultures. This suggests that not only does Gfi1b deletion induce HSC expansion via cell intrinsic mechanisms, but also points to the possibility that this occurs through paracrine factors that alter bone marrow homeostasis. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

Alternative Methods of Activation of the Stem Cell Niche Reveal a Spatial Localization of Primitive Cells in the Bone Marrow

Blood ◽

10.1182/blood.v118.21.2396.2396 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2396-2396

Author(s):

Narges M Rashidi ◽

Tassja J Spindler ◽

Lora W Barsky ◽

Gregor B. Adams

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Trabecular Bone ◽

Conflicts Of Interest ◽

Alternative Methods ◽

Cell Populations ◽

Bone Marrow Niche ◽

Hematopoietic Stem ◽

Endosteal Surface ◽

Hsc Niche

Abstract Abstract 2396 Osteoblasts are key constituents of the murine hematopoietic stem cell (HSC) endosteal niche, evidenced by the fact that increasing their activity leads to an increase in the number of HSCs. However, recent studies have also suggested a role of the bone resorbing osteoclast in the HSC niche. In these studies we wished to examine whether activation of the osteoblast or the osteoclast had differing effects on the primitive hematopoietic cell populations. To achieve this we pharmacologically activated osteoclasts and osteoblasts using receptor activator of nuclear factor-κB ligand (RANK-L) and parathyroid hormone (PTH), respectively. Our in vitro results demonstrated that both PTH and RANK-L treatment of bone marrow stromal cell populations activated osteoblasts and osteoclasts. Yet, RANK-L treatment, which is able to expand the osteoclastic population to a much higher degree, demonstrated enhanced support of primitive hematopoietic cells in cobblestone area forming cell assays. We next examined the effects of in vivo treatment with RANK-L and PTH by performing histological analyses to study the effect of these treatments on bone composition, and examining the effects on different HSC sub-populations. These data suggested that the effects of our treatment regimens were different according to the region of the bone, with RANK-L treatment having no effect or leading to a reduction in trabecular bone in the metaphysis, but an increase in bone remodeling activity at the endosteal surface of the cortical bone in the diaphysis, while PTH treatment increases bone formation and remodeling activity both in the diaphysis and the trabecular bone of the metaphysis. Correlating with this was our observations that LT-HSC frequency was increased following RANK-L and PTH treatment, yet an increased ST-HSC frequency was only observed following PTH treatment. Direct examination of HSCs in specific regions of the bone indicated that RANK-L treatment preferentially increased the LT-HSCs in the diaphysis region of the bone marrow, while PTH treatment specifically increased the ST-HSC population in the metaphysis. These data not only reveal a supportive role for osteoclasts in the HSC niche suggesting that osteoclast interaction with osteoblasts is an essential component for maintaining HSC population in the bone marrow niche, they also suggest a possible structural organization for localization of LT-HSC vs. ST-HSCs in the long bone with LT-HSCs being more localized in the endosteal surface of the diaphysis area of the long bones as oppose to the ST-HSCs having a preference for the metaphysis of these bones. Disclosures: No relevant conflicts of interest to declare.

Download Full-text

KIT Blockade Is Sufficient to Sustain Donor Hematopoietic Stem Cell Engraftment in Fanconi Anemia Mice

Blood ◽

10.1182/blood.v126.23.1206.1206 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1206-1206

Author(s):

Shanmuganathan Chandrakasan ◽

Rajeswari Jayavaradhan ◽

Ernst John ◽

Archana Shrestha ◽

Phillip Dexheimer ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cell ◽

Fanconi Anemia ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Conditioning Regimen ◽

Cell Transplant ◽

Hematopoietic Stem ◽

Increased Risk

Abstract Background: Fanconi anemia (FA) is the most common cause of inherited bone marrow failure (BMF). Currently, the only curative option for the BMF in FA is an allogenic hematopoietic stem cell transplant (HSCT). However, due to the underlying DNA repair defect, FA patients poorly tolerate alkylating chemotherapy or irradiation based conditioning, which is necessary for donor engraftment. However, this results in significant short and long term morbidity/mortality and augments the inherent increased risk of malignancies in FA patients. To overcome the adverse effects associated with alkylating conditioning agents, alternate experimental approaches exploiting the inherent hematopoietic stem cell (HSC) defect in FA are of utmost clinical necessity. Objective: To develop a safe KIT blocking antibody (KIT-Ab) based HSCT conditioning regimen for FA that does not involve chemotherapy or irradiation. Method: High purity KIT-Ab was made from the ACK2 hybridoma and its specificity to KIT binding was validated using mast cell assay. Baseline peripheral blood cells and the bone marrow hematopoietic stem and progenitor cell (HSPC) compartment (Lin-Kit+Sca+ and Lin-Kit+Sca+CD150+CD48- cells) of FANCA-/- and FANCD2-/- murine models were analyzed. Mechanistic studies using sorted FA bone marrow HSPC were performed ex vivo. This was followed by definitive primary and secondary transplants experiments following injection of KIT-Ab. Results: Several features of FA hematopoietic stem/progenitor cells (HSPC) suggested their susceptibility to KIT-Ab blockade-mediated killing: (a) Expression of KIT was significantly lower in FANCA-/- HSPC, while expression of its ligand was higher in bone marrow stroma; (b) Moreover, genes associated with apoptosis/senescence, stress and inflammatory signaling that were upregulated in WT-HSPC following KIT-Ab blockade, were upregulated in FANCA-/- HSPC at baseline; (c) Furthermore, FANCA-/- HSPC demonstrated increased susceptibility to KIT-Ab mediated apoptosis and had a reduced proliferative capacity. In-vivo studies following ACK2 injection showed a marked reduction of colony-forming units (CFU-C) from both FANCA-/- and FANCD2-/- mice one week following injection, when compared to WT mice (48% and 76% decrease in CFU-C, respectively). Based on these findings, we evaluated the role of ACK2 as a sole HSCT conditioning regimen in FANCA-/- and FANCD2-/- mice. Indeed, definitive HSCT in both FANCA-/- and FANCD2-/- mice using KIT-Ab based conditioning resulted in donor HSC engraftment with multi-lineage chimerism, which progressively increased to 22-24% by 4-months, and was sustained in secondary transplants. Overall, we show that KIT-blockade alone is an adequate non-genotoxic HSPC-targeted conditioning in FA mice, and its clinical translation could circumvent the extensive transplant-related morbidity/mortality in this disease. Disclosures No relevant conflicts of interest to declare.

Download Full-text

The Zebrafish Provides Mechanistic Insights into the Role of Poly(A)-Specific Ribonuclease (PARN) in Hematopoietic Stem Cell (HSC) Homeostasis and Bone Marrow Failure

Blood ◽

10.1182/blood.v126.23.668.668 ◽

2015 ◽

Vol 126 (23) ◽

pp. 668-668

Author(s):

Adam P Deveau ◽

Andrew J Coombs ◽

Santhosh Dhanraj ◽

Gretchen Wagner ◽

Yigal Dror ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cell ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Hematopoietic Stem ◽

Phosphohistone H3 ◽

Biallelic Mutations ◽

Insight Into

Abstract Development of tissues during embryogenesis and their homeostasis after formation are highly regulated by expression of coding and non-coding RNAs. Deadenylation is a core mechanism that regulates RNA function and fate by controlling turnover, abundance and maturation of RNA. Factors that promote or inhibit deadenylation control hematopoietic stem cell (HSC) homeostasis, and inhibition of deadenylation limits differentiation of the HSCs. Importantly, RNA biogenesis has emerged as a mechanism underlying several inherited bone marrow failure syndromes (IBMFSs), such as Diamond Blackfan anemia, dyskeratosis congenita (DC) and Shwachman-Diamond syndrome. Poly(A)-specific ribonuclease (PARN) is a major deadenylation factor and demonstrates high specificity for single-stranded poly (A) tails of various RNA species. We recently identified biallelic mutations in PARN as a cause of hematopoietic failure and profound hypomyelination, similar to the severe form of DC, Hoyeraal-Hreidersson syndrome. We developed a zebrafish model to characterize the hematopoietic phenotype of a patient identified to have severe inherited bone marrow failure resulting from a combined deletion of PARN on one allele and missense mutation in the other. Zebrafish posses a single parn ortholog. Zebrafish parn protein shares homology and high sequence identity (~64%) to its human counterpart. Embryos were injected with either translation start-site or splice-site-blocking morpholino at the one-cell stage. Both morpholino injections resulted in anemic embryos at 48 hours post fertilization (hpf), as evidenced by reduced o-dianisidine staining and gata1 expression by whole-mount in situ hybrization and GFP+ red cell numbers by fluorescence-activated cell sorting (FACS). Morphant embryos also demonstrated reduced expression of myeloid cell markers including l-plastin, myeloperoxidase, and macrophage expressed gene 1 and were leukopenic as evidenced by reduced number of GFP+ myeloid cells. FACS analysis revealed that fluorescently labeled HSCs were increased in parn morphants. Early hematopoietic markers, lmo2 and fli1, expressed in hemogenic and vascular tissue respectively, were also overexpressed in parn morphants. Furthermore, there was reduced global cell proliferation in morphant embryos as determined by phosphohistone H3 antibody staining. These findings suggest that the absence of parn results in a developmental arrest at the HSC stage with an inability to differentiate into leukocyte or erythroid lineages. Similarly, human cell culture data from PARN-deficient HSC/progenitor cells demonstrated markedly reduced colony forming capacity. By modeling parn deficiency in the zebrafish, we validate for the first time an IBMFS that results from biallelic mutations in a major deadenylating protein. Moreover, our zebrafish studies provide insight into the role of parn in maintaining HSC homeostasis/differentiation as the origin of the pancytopenia observed in this patient. Permanent knockouts in the zebrafish using CRISPR/Cas9 technology are underway, which will enable tracking the hematopoietic phenotype into adulthood. These studies have set the stage for critical translational research in a rare form of bone marrow failure as well as new insight into HSC regulation. Disclosures No relevant conflicts of interest to declare.

Download Full-text