Publications by authors named "Rebekka K Schneider"

54 Publications

Heterogeneous bone-marrow stromal progenitors drive myelofibrosis via a druggable alarmin axis.

Cell Stem Cell 2021 Apr 9;28(4):637-652.e8. Epub 2020 Dec 9.

Department of Hematology, Erasmus Medical Center, Rotterdam 3015GD, the Netherlands; Department of Cell Biology, Institute for Biomedical Engineering, Faculty of Medicine, RWTH Aachen University, Pauwelsstrasse 30, 52074 Aachen, Germany; Oncode Institute, Erasmus Medical Center, Rotterdam 3015GD, the Netherlands. Electronic address:

Functional contributions of individual cellular components of the bone-marrow microenvironment to myelofibrosis (MF) in patients with myeloproliferative neoplasms (MPNs) are incompletely understood. We aimed to generate a comprehensive map of the stroma in MPNs/MFs on a single-cell level in murine models and patient samples. Our analysis revealed two distinct mesenchymal stromal cell (MSC) subsets as pro-fibrotic cells. MSCs were functionally reprogrammed in a stage-dependent manner with loss of their progenitor status and initiation of differentiation in the pre-fibrotic and acquisition of a pro-fibrotic and inflammatory phenotype in the fibrotic stage. The expression of the alarmin complex S100A8/S100A9 in MSC marked disease progression toward the fibrotic phase in murine models and in patient stroma and plasma. Tasquinimod, a small-molecule inhibiting S100A8/S100A9 signaling, significantly ameliorated the MPN phenotype and fibrosis in JAK2V617F-mutated murine models, highlighting that S100A8/S100A9 is an attractive therapeutic target in MPNs.
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http://dx.doi.org/10.1016/j.stem.2020.11.004DOI Listing
April 2021

Malignant Transformation Involving Mutations Identified in a Leukemic Progression Model of Severe Congenital Neutropenia.

Cell Rep Med 2020 Aug 25;1(5):100074. Epub 2020 Aug 25.

Department of Hematology, Erasmus University Medical Center, Rotterdam 3015 CN, the Netherlands.

Severe congenital neutropenia (SCN) patients treated with CSF3/G-CSF to alleviate neutropenia frequently develop acute myeloid leukemia (AML). A common pattern of leukemic transformation involves the appearance of hematopoietic clones with CSF3 receptor () mutations in the neutropenic phase, followed by mutations in before AML becomes overt. To investigate how the combination of CSF3 therapy and and mutations contributes to AML development, we make use of mouse models, SCN-derived induced pluripotent stem cells (iPSCs), and SCN and SCN-AML patient samples. CSF3 provokes a hyper-proliferative state in / mutant hematopoietic progenitors but does not cause overt AML. Intriguingly, an additional acquired driver mutation in causes elevated CXXC4 and reduced TET2 protein levels in murine AML samples. Expression of multiple pro-inflammatory pathways is elevated in mouse AML and human SCN-AML, suggesting that inflammation driven by downregulation of TET2 activity is a critical step in the malignant transformation of SCN.
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http://dx.doi.org/10.1016/j.xcrm.2020.100074DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7659587PMC
August 2020

Decoding myofibroblast origins in human kidney fibrosis.

Nature 2021 01 11;589(7841):281-286. Epub 2020 Nov 11.

Division of Nephrology and Clinical Immunology, RWTH Aachen University, Aachen, Germany.

Kidney fibrosis is the hallmark of chronic kidney disease progression; however, at present no antifibrotic therapies exist. The origin, functional heterogeneity and regulation of scar-forming cells that occur during human kidney fibrosis remain poorly understood. Here, using single-cell RNA sequencing, we profiled the transcriptomes of cells from the proximal and non-proximal tubules of healthy and fibrotic human kidneys to map the entire human kidney. This analysis enabled us to map all matrix-producing cells at high resolution, and to identify distinct subpopulations of pericytes and fibroblasts as the main cellular sources of scar-forming myofibroblasts during human kidney fibrosis. We used genetic fate-tracing, time-course single-cell RNA sequencing and ATAC-seq (assay for transposase-accessible chromatin using sequencing) experiments in mice, and spatial transcriptomics in human kidney fibrosis, to shed light on the cellular origins and differentiation of human kidney myofibroblasts and their precursors at high resolution. Finally, we used this strategy to detect potential therapeutic targets, and identified NKD2 as a myofibroblast-specific target in human kidney fibrosis.
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http://dx.doi.org/10.1038/s41586-020-2941-1DOI Listing
January 2021

Macrophage frequency in the bone marrow correlates with morphologic subtype of myeloproliferative neoplasm.

Ann Hematol 2021 Jan 26;100(1):97-104. Epub 2020 Oct 26.

Institute of Pathology, University Hospital Bonn, Bonn, Germany.

Bone marrow (BM) fibrosis in myeloproliferative neoplasms (MPNs) is associated with a poor prognosis. The development of myelofibrosis and differentiation of mesenchymal stromal cells to profibrotic myofibroblasts depends on macrophages. Here, we compared macrophage frequencies in BM biopsies of MPN patients and controls (patients with non-neoplastic processes), including primary myelofibrosis (PMF, n = 18), essential thrombocythemia (ET, n = 14), polycythemia vera (PV, n = 12), and Philadelphia chromosome-positive chronic myeloid leukemia (CML, n = 9). In PMF, CD68-positive macrophages were greatly increased compared to CML (p = 0.017) and control BM (p < 0.001). Similar findings were observed by CD163 staining (PMF vs. CML: p = 0.017; PMF vs. control: p < 0.001). Moreover, CD68-positive macrophages were increased in PV compared with ET (p = 0.009) and reactive cases (p < 0.001). PMF had higher frequencies of macrophages than PV (CD68: p < 0.001; CD163: p < 0.001) and ET (CD68: p < 0.001; CD163: p < 0.001). CD163 and CD68 were often co-expressed in macrophages with stellate morphology in Philadelphia chromosome-negative MPN, resulting in a sponge-like reticular network that may be a key regulator of unbalanced hematopoiesis in the BM space and may explain differences in cellularity and clinical course.
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http://dx.doi.org/10.1007/s00277-020-04304-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782416PMC
January 2021

Increased CXCL4 expression in hematopoietic cells links inflammation and progression of bone marrow fibrosis in MPN.

Blood 2020 10;136(18):2051-2064

Department of Hematology, Erasmus Medical Center Cancer Institute, Rotterdam, The Netherlands.

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) that leads to progressive bone marrow (BM) fibrosis. Although the cellular mutations involved in the pathogenesis of PMF have been extensively investigated, the sequential events that drive stromal activation and fibrosis by hematopoietic-stromal cross-talk remain elusive. Using an unbiased approach and validation in patients with MPN, we determined that the differential spatial expression of the chemokine CXCL4/platelet factor-4 marks the progression of fibrosis. We show that the absence of hematopoietic CXCL4 ameliorates the MPN phenotype, reduces stromal cell activation and BM fibrosis, and decreases the activation of profibrotic pathways in megakaryocytes, inflammation in fibrosis-driving cells, and JAK/STAT activation in both megakaryocytes and stromal cells in 3 murine PMF models. Our data indicate that higher CXCL4 expression in MPN has profibrotic effects and is a mediator of the characteristic inflammation. Therefore, targeting CXCL4 might be a promising strategy to reduce inflammation in PMF.
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http://dx.doi.org/10.1182/blood.2019004095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7678060PMC
October 2020

Inflammatory bone marrow microenvironment.

Hematology Am Soc Hematol Educ Program 2019 12;2019(1):294-302

Department of Hematology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands.

Self-renewing hematopoietic stem cells and their progeny, lineage-specific downstream progenitors, maintain steady-state hematopoiesis in the bone marrow (BM). Accumulating evidence over the last few years indicates that not only primitive hematopoietic stem and progenitor cells (HSPCs), but also cells defining the microenvironment of the BM (BM niche), sense hematopoietic stress signals. They respond by directing and orchestrating hematopoiesis via not only cell-intrinsic but also cell-extrinsic mechanisms. Inflammation has many beneficial roles by activating the immune system in tissue repair and as a defense mechanism. However, chronic inflammation can have detrimental effects by stressing HSPCs, leading to cell (DNA) damage resulting in BM failure or even to leukemia. Emerging data have demonstrated that the BM microenvironment plays a significant role in the pathogenesis of hematopoietic malignancies, in particular, through disrupted inflammatory signaling, specifically in niche (microenvironmental) cells. Clonal selection in the context of microenvironmental alterations can occur in the context of toxic insults (eg, chemotherapy), not only aging but also inflammation. In this review, we summarize mechanisms that lead to an inflammatory BM microenvironment and discuss how this affects normal hematopoiesis. We pay particular attention to the process of aging, which is known to involve low-grade inflammation and is also associated with age-related clonal hematopoiesis and potentially malignant transformation.
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http://dx.doi.org/10.1182/hematology.2019000045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6913454PMC
December 2019

Sequentially inducible mouse models reveal that Npm1 mutation causes malignant transformation of Dnmt3a-mutant clonal hematopoiesis.

Leukemia 2019 07 28;33(7):1635-1649. Epub 2019 Jan 28.

The Jackson Laboratory, Bar Harbor, ME, USA.

Clonal hematopoiesis (CH) is a common aging-associated condition with increased risk of hematologic malignancy. Knowledge of the mechanisms driving evolution from CH to overt malignancy has been hampered by a lack of in vivo models that orthogonally activate mutant alleles. Here, we develop independently regulatable mutations in DNA methyltransferase 3A (Dnmt3a) and nucleophosmin 1 (Npm1), observed in human CH and AML, respectively. We find Dnmt3a mutation expands hematopoietic stem and multipotent progenitor cells (HSC/MPPs), modeling CH. Induction of mutant Npm1 after development of Dnmt3a-mutant CH causes progression to myeloproliferative disorder (MPD), and more aggressive MPD is observed with longer latency between mutations. MPDs uniformly progress to acute myeloid leukemia (AML) following transplant, accompanied by a decrease in HSC/MPPs and an increase in myeloid-restricted progenitors, the latter of which propagate AML in tertiary recipient mice. At a molecular level, progression of CH to MPD is accompanied by selection for mutations activating Ras/Raf/MAPK signaling. Progression to AML is characterized by additional oncogenic signaling mutations (Ptpn11, Pik3r1, Flt3) and/or mutations in epigenetic regulators (Hdac1, Idh1, Arid1a). Together, our study demonstrates that Npm1 mutation drives evolution of Dnmt3a-mutant CH to AML and rate of disease progression is accelerated with longer latency of CH.
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http://dx.doi.org/10.1038/s41375-018-0368-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6609470PMC
July 2019

Rps14, Csnk1a1 and miRNA145/miRNA146a deficiency cooperate in the clinical phenotype and activation of the innate immune system in the 5q- syndrome.

Leukemia 2019 07 16;33(7):1759-1772. Epub 2019 Jan 16.

Department of Hematology, Oncology, Hemostaseology, and Stem Cell Transplantation, RWTH Aachen University, Aachen, Germany.

RPS14, CSNK1A1, and miR-145 are universally co-deleted in the 5q- syndrome, but mouse models of each gene deficiency recapitulate only a subset of the composite clinical features. We analyzed the combinatorial effect of haploinsufficiency for Rps14, Csnk1a1, and miRNA-145, using mice with genetically engineered, conditional heterozygous inactivation of Rps14 and Csnk1a1 and stable knockdown of miR-145/miR-146a. Combined Rps14/Csnk1a1/miR-145/146a deficiency recapitulated the cardinal features of the 5q- syndrome, including (1) more severe anemia with faster kinetics than Rps14 haploinsufficiency alone and (2) pathognomonic megakaryocyte morphology. Macrophages, regulatory cells of erythropoiesis and the innate immune response, were significantly increased in Rps14/Csnk1a1/miR-145/146a deficient mice as well as in 5q- syndrome patient bone marrows and showed activation of the innate immune response, reflected by increased expression of S100A8, and decreased phagocytic function. We demonstrate that Rps14/Csnk1a1/miR-145 and miR-146a deficient macrophages alter the microenvironment and induce S100A8 expression in the mesenchymal stem cell niche. The increased S100A8 expression in the mesenchymal niche was confirmed in 5q- syndrome patients. These data indicate that intrinsic defects of the 5q- syndrome hematopoietic stem cell directly alter the surrounding microenvironment, which in turn affects hematopoiesis as an extrinsic mechanism.
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http://dx.doi.org/10.1038/s41375-018-0350-3DOI Listing
July 2019

Puzzling pieces of chromosome 7 loss or deletion.

Blood 2018 06;131(26):2871-2872

Erasmus MC Cancer Institute.

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http://dx.doi.org/10.1182/blood-2018-04-844746DOI Listing
June 2018

Parabiosis and single-cell RNA sequencing reveal a limited contribution of monocytes to myofibroblasts in kidney fibrosis.

JCI Insight 2018 05 3;3(9). Epub 2018 May 3.

Division of Nephrology, Department of Medicine and Department of Cell Biology, Washington University School of Medicine, St. Louis, Missouri, USA.

Fibrosis is the common final pathway of virtually all chronic injury to the kidney. While it is well accepted that myofibroblasts are the scar-producing cells in the kidney, their cellular origin is still hotly debated. The relative contribution of proximal tubular epithelium and circulating cells, including mesenchymal stem cells, macrophages, and fibrocytes, to the myofibroblast pool remains highly controversial. Using inducible genetic fate tracing of proximal tubular epithelium, we confirm that the proximal tubule does not contribute to the myofibroblast pool. However, in parabiosis models in which one parabiont is genetically labeled and the other is unlabeled and undergoes kidney fibrosis, we demonstrate that a small fraction of genetically labeled renal myofibroblasts derive from the circulation. Single-cell RNA sequencing confirms this finding but indicates that these cells are circulating monocytes, express few extracellular matrix or other myofibroblast genes, and express many proinflammatory cytokines. We conclude that this small circulating myofibroblast progenitor population contributes to renal fibrosis by paracrine rather than direct mechanisms.
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http://dx.doi.org/10.1172/jci.insight.99561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6012505PMC
May 2018

Increased neutrophil extracellular trap formation promotes thrombosis in myeloproliferative neoplasms.

Sci Transl Med 2018 04;10(436)

Division of Hematology, Brigham and Women's Hospital, Boston, MA 02115, USA.

Thrombosis is a major cause of morbidity and mortality in Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), clonal disorders of hematopoiesis characterized by activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling. Neutrophil extracellular trap (NET) formation, a component of innate immunity, has been linked to thrombosis. We demonstrate that neutrophils from patients with MPNs are primed for NET formation, an effect blunted by pharmacological inhibition of JAK signaling. Mice with conditional knock-in of , the most common molecular driver of MPN, have an increased propensity for NET formation and thrombosis. Inhibition of JAK-STAT signaling with the clinically available JAK2 inhibitor ruxolitinib abrogated NET formation and reduced thrombosis in a deep vein stenosis murine model. We further show that expression of PAD4, a protein required for NET formation, is increased in -expressing neutrophils and that PAD4 is required for -driven NET formation and thrombosis in vivo. Finally, in a population study of more than 10,000 individuals without a known myeloid disorder, -positive clonal hematopoiesis was associated with an increased incidence of thrombosis. In aggregate, our results link expression to NET formation and thrombosis and suggest that JAK2 inhibition may reduce thrombosis in MPNs through cell-intrinsic effects on neutrophil function.
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http://dx.doi.org/10.1126/scitranslmed.aan8292DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6442466PMC
April 2018

The identification of fibrosis-driving myofibroblast precursors reveals new therapeutic avenues in myelofibrosis.

Blood 2018 05 23;131(19):2111-2119. Epub 2018 Mar 23.

Department of Hematology, Erasmus Medical Center Cancer Institute, Rotterdam, The Netherlands; and.

Myofibroblasts are fibrosis-driving cells and are well characterized in solid organ fibrosis, but their role and cellular origin in bone marrow fibrosis remains obscure. Recent work has demonstrated that Gli1 and LepR mesenchymal stromal cells (MSCs) are progenitors of fibrosis-causing myofibroblasts in the bone marrow. Genetic ablation of Gli1 MSCs or pharmacologic targeting of hedgehog (Hh)-Gli signaling ameliorated fibrosis in mouse models of myelofibrosis (MF). Moreover, pharmacologic or genetic intervention in platelet-derived growth factor receptor α () signaling in stromal cells suppressed their expansion and ameliorated MF. Improved understanding of cellular and molecular mechanisms in the hematopoietic stem cell niche that govern the transition of MSCs to myofibroblasts and myofibroblast expansion in MF has led to new paradigms in the pathogenesis and treatment of MF. Here, we highlight the central role of malignant hematopoietic clone-derived megakaryocytes in reprogramming the hematopoietic stem cell niche in MF with potential detrimental consequences for hematopoietic reconstitution after allogenic stem cell transplantation, so far the only therapeutic approach in MF considered to be curative. We and others have reported that targeting Hh-Gli signaling is a therapeutic strategy in solid organ fibrosis. Data indicate that targeting Gli proteins directly inhibits Gli1 cell proliferation and myofibroblast differentiation, which results in reduced fibrosis severity and improved organ function. Although canonical Hh inhibition (eg, smoothened [Smo] inhibition) failed to improve pulmonary fibrosis, kidney fibrosis, or MF, the direct inhibition of Gli proteins ameliorated fibrosis. Therefore, targeting Gli proteins directly might be an interesting and novel therapeutic approach in MF.
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http://dx.doi.org/10.1182/blood-2018-02-834820DOI Listing
May 2018

Understanding deregulated cellular and molecular dynamics in the haematopoietic stem cell niche to develop novel therapeutics for bone marrow fibrosis.

J Pathol 2018 06 19;245(2):138-146. Epub 2018 Apr 19.

Department of Haematology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands.

Bone marrow fibrosis is the continuous replacement of blood-forming cells in the bone marrow with excessive scar tissue, leading to failure of the body to produce blood cells and ultimately to death. Myofibroblasts are fibrosis-driving cells and are well characterized in solid organ fibrosis, but their role and cellular origin in bone marrow fibrosis have remained obscure. Recent work has demonstrated that Gli1 and leptin receptor mesenchymal stromal cells are progenitors of fibrosis-causing myofibroblasts in the bone marrow. Genetic ablation or pharmacological inhibition of Gli1 mesenchymal stromal cells ameliorated fibrosis in mouse models of myelofibrosis. Conditional deletion of the platelet-derived growth factor (PDGF) receptor-α (PDGFRA) gene (Pdgfra) and inhibition of PDGFRA by imatinib in leptin receptor stromal cells suppressed their expansion and ameliorated bone marrow fibrosis. Understanding the cellular and molecular mechanisms in the haematopoietic stem cell niche that govern the mesenchymal stromal cell-to-myofibroblast transition and myofibroblast expansion will be critical to understand the pathogenesis of bone marrow fibrosis in both malignant and non-malignant conditions, and will guide the development of novel therapeutics. In this review, we summarize recent discoveries of mesenchymal stromal cells as part of the haematopoietic niche and as myofibroblast precursors, and discuss potential therapeutic strategies in the specific targeting of fibrotic transformation in bone marrow fibrosis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.
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http://dx.doi.org/10.1002/path.5078DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5969225PMC
June 2018

Mesenchymal Stem Cells in Fibrotic Disease.

Cell Stem Cell 2017 08;21(2):166-177

Institute of Life Sciences, Wenzhou University, Wenzhou University-Wenzhou Medical University Collaborative Innovation Center of Biomedicine, Wenzhou, Zhejiang, China; Excellence Cluster Cardio-Pulmonary System (ECCPS), Universities of Giessen and Marburg Lung Center (UGMLC), Justus-Liebig-University Giessen, German Center for Lung Research (DZL), Giessen, Germany. Electronic address:

Fibrosis is associated with organ failure and high mortality and is commonly characterized by aberrant myofibroblast accumulation. Investigating the cellular origin of myofibroblasts in various diseases is thus a promising strategy for developing targeted anti-fibrotic treatments. Recent studies using genetic lineage tracing technology have implicated diverse organ-resident perivascular mesenchymal stem cell (MSC)-like cells and bone marrow-MSCs in myofibroblast generation during fibrosis development. In this Review, we give an overview of the emerging role of MSCs and MSC-like cells in myofibroblast-mediated fibrotic disease in the kidney, lung, heart, liver, skin, and bone marrow.
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http://dx.doi.org/10.1016/j.stem.2017.07.011DOI Listing
August 2017

Gli1 Mesenchymal Stromal Cells Are a Key Driver of Bone Marrow Fibrosis and an Important Cellular Therapeutic Target.

Cell Stem Cell 2017 06 27;20(6):785-800.e8. Epub 2017 Apr 27.

Division of Nephrology and Clinical Immunology, RWTH Aachen University, 52074 Aachen, Germany. Electronic address:

Bone marrow fibrosis (BMF) develops in various hematological and non-hematological conditions and is a central pathological feature of myelofibrosis. Effective cell-targeted therapeutics are needed, but the cellular origin of BMF remains elusive. Here, we show using genetic fate tracing in two murine models of BMF that Gli1 mesenchymal stromal cells (MSCs) are recruited from the endosteal and perivascular niche to become fibrosis-driving myofibroblasts in the bone marrow. Genetic ablation of Gli1 cells abolished BMF and rescued bone marrow failure. Pharmacological targeting of Gli proteins with GANT61 inhibited Gli1 cell expansion and myofibroblast differentiation and attenuated fibrosis severity. The same pathway is also active in human BMF, and Gli1 expression in BMF significantly correlates with the severity of the disease. In addition, GANT61 treatment reduced the myofibroblastic phenotype of human MSCs isolated from patients with BMF, suggesting that targeting of Gli proteins could be a relevant therapeutic strategy.
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http://dx.doi.org/10.1016/j.stem.2017.03.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6485654PMC
June 2017

Physiologic Expression of Sf3b1(K700E) Causes Impaired Erythropoiesis, Aberrant Splicing, and Sensitivity to Therapeutic Spliceosome Modulation.

Cancer Cell 2016 09;30(3):404-417

Division of Hematology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA. Electronic address:

More than 80% of patients with the refractory anemia with ring sideroblasts subtype of myelodysplastic syndrome (MDS) have mutations in Splicing Factor 3B, Subunit 1 (SF3B1). We generated a conditional knockin mouse model of the most common SF3B1 mutation, Sf3b1(K700E). Sf3b1(K700E) mice develop macrocytic anemia due to a terminal erythroid maturation defect, erythroid dysplasia, and long-term hematopoietic stem cell (LT-HSC) expansion. Sf3b1(K700E) myeloid progenitors and SF3B1-mutant MDS patient samples demonstrate aberrant 3' splice-site selection associated with increased nonsense-mediated decay. Tet2 loss cooperates with Sf3b1(K700E) to cause a more severe erythroid and LT-HSC phenotype. Furthermore, the spliceosome modulator, E7017, selectively kills SF3B1(K700E)-expressing cells. Thus, SF3B1(K700E) expression reflects the phenotype of the mutation in MDS and may be a therapeutic target in MDS.
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http://dx.doi.org/10.1016/j.ccell.2016.08.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5023069PMC
September 2016

Adventitial MSC-like Cells Are Progenitors of Vascular Smooth Muscle Cells and Drive Vascular Calcification in Chronic Kidney Disease.

Cell Stem Cell 2016 11 8;19(5):628-642. Epub 2016 Sep 8.

Division of Nephrology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.

Mesenchymal stem cell (MSC)-like cells reside in the vascular wall, but their role in vascular regeneration and disease is poorly understood. Here, we show that Gli1 cells located in the arterial adventitia are progenitors of vascular smooth muscle cells and contribute to neointima formation and repair after acute injury to the femoral artery. Genetic fate tracing indicates that adventitial Gli1 MSC-like cells migrate into the media and neointima during athero- and arteriosclerosis in ApoE mice with chronic kidney disease. Our data indicate that Gli1 cells are a major source of osteoblast-like cells during calcification in the media and intima. Genetic ablation of Gli1 cells before induction of kidney injury dramatically reduced the severity of vascular calcification. These findings implicate Gli1 cells as critical adventitial progenitors in vascular remodeling after acute and during chronic injury and suggest that they may be relevant therapeutic targets for mitigation of vascular calcification.
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http://dx.doi.org/10.1016/j.stem.2016.08.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5097006PMC
November 2016

Core Circadian Clock Genes Regulate Leukemia Stem Cells in AML.

Cell 2016 Apr;165(2):303-16

Department of Medicine, Division of Hematology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA; Broad Institute of Harvard University and MIT, Cambridge, MA 02142, USA; Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02215, USA. Electronic address:

Leukemia stem cells (LSCs) have the capacity to self-renew and propagate disease upon serial transplantation in animal models, and elimination of this cell population is required for curative therapies. Here, we describe a series of pooled, in vivo RNAi screens to identify essential transcription factors (TFs) in a murine model of acute myeloid leukemia (AML) with genetically and phenotypically defined LSCs. These screens reveal the heterodimeric, circadian rhythm TFs Clock and Bmal1 as genes required for the growth of AML cells in vitro and in vivo. Disruption of canonical circadian pathway components produces anti-leukemic effects, including impaired proliferation, enhanced myeloid differentiation, and depletion of LSCs. We find that both normal and malignant hematopoietic cells harbor an intact clock with robust circadian oscillations, and genetic knockout models reveal a leukemia-specific dependence on the pathway. Our findings establish a role for the core circadian clock genes in AML.
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http://dx.doi.org/10.1016/j.cell.2016.03.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4826477PMC
April 2016

Mutant Calreticulin Requires Both Its Mutant C-terminus and the Thrombopoietin Receptor for Oncogenic Transformation.

Cancer Discov 2016 Apr 7;6(4):368-81. Epub 2016 Mar 7.

Division of Hematology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts. Broad Institute, Cambridge, Massachusetts. Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts.

Unlabelled: Somatic mutations in calreticulin (CALR) are present in approximately 40% of patients with myeloproliferative neoplasms (MPN), but the mechanism by which mutant CALR is oncogenic remains unclear. Here, we demonstrate that expression of mutant CALR alone is sufficient to engender MPN in mice and recapitulates the disease phenotype of patients with CALR-mutant MPN. We further show that the thrombopoietin receptor MPL is required for mutant CALR-driven transformation through JAK-STAT pathway activation, thus rendering mutant CALR-transformed hematopoietic cells sensitive to JAK2 inhibition. Finally, we demonstrate that the oncogenicity of mutant CALR is dependent on the positive electrostatic charge of the C-terminus of the mutant protein, which is necessary for physical interaction between mutant CALR and MPL. Together, our findings elucidate a novel paradigm of cancer pathogenesis and reveal how CALR mutations induce MPN.

Significance: The mechanism by which CALR mutations induce MPN remains unknown. In this report, we show that the positive charge of the CALR mutant C-terminus is necessary to transform hematopoietic cells by enabling binding between mutant CALR and the thrombopoietin receptor MPL.
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http://dx.doi.org/10.1158/2159-8290.CD-15-1434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4851866PMC
April 2016

Rps14 haploinsufficiency causes a block in erythroid differentiation mediated by S100A8 and S100A9.

Nat Med 2016 Mar 15;22(3):288-97. Epub 2016 Feb 15.

Division of Hematology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.

Impaired erythropoiesis in the deletion 5q (del(5q)) subtype of myelodysplastic syndrome (MDS) has been linked to heterozygous deletion of RPS14, which encodes the ribosomal protein small subunit 14. We generated mice with conditional inactivation of Rps14 and demonstrated an erythroid differentiation defect that is dependent on the tumor suppressor protein p53 (encoded by Trp53 in mice) and is characterized by apoptosis at the transition from polychromatic to orthochromatic erythroblasts. This defect resulted in age-dependent progressive anemia, megakaryocyte dysplasia and loss of hematopoietic stem cell (HSC) quiescence. As assessed by quantitative proteomics, mutant erythroblasts expressed higher levels of proteins involved in innate immune signaling, notably the heterodimeric S100 calcium-binding proteins S100a8 and S100a9. S100a8--whose expression was increased in mutant erythroblasts, monocytes and macrophages--is functionally involved in the erythroid defect caused by the Rps14 deletion, as addition of recombinant S100a8 was sufficient to induce a differentiation defect in wild-type erythroid cells, and genetic inactivation of S100a8 expression rescued the erythroid differentiation defect of Rps14-haploinsufficient HSCs. Our data link Rps14 haploinsufficiency in del(5q) MDS to activation of the innate immune system and induction of S100A8-S100A9 expression, leading to a p53-dependent erythroid differentiation defect.
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http://dx.doi.org/10.1038/nm.4047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4870050PMC
March 2016

An engineered multicomponent bone marrow niche for the recapitulation of hematopoiesis at ectopic transplantation sites.

J Hematol Oncol 2016 Jan 25;9. Epub 2016 Jan 25.

Department of Hematology, Oncology, Hemostaseology and Stem Cell Transplantation, University Hospital Aachen, RWTH Aachen University, Aachen, Germany.

Background: Bone marrow (BM) niches are often inaccessible for controlled experimentation due to their difficult accessibility, biological complexity, and three-dimensional (3D) geometry.

Methods: Here, we report the development and characterization of a BM model comprising of cellular and structural components with increased potential for hematopoietic recapitulation at ectopic transplantation sites. Cellular components included mesenchymal stromal cells (MSCs) and hematopoietic stem and progenitor cells (HSPCs). Structural components included 3D β-tricalcium phosphate (β-TCP) scaffolds complemented with Matrigel or collagen I/III gels for the recreation of the osteogenic/extracellular character of native BM.

Results: In vitro, β-TCP/Matrigel combinations robustly maintained proliferation, osteogenic differentiation, and matrix remodeling capacities of MSCs and maintenance of HSPCs function over time. In vivo, scaffolds promoted strong and robust recruitment of hematopoietic cells to sites of ectopic transplantation, vascularization, and soft tissue formation.

Conclusions: Our tissue-engineered BM system is a powerful tool to explore the regulatory mechanisms of hematopoietic stem and progenitor cells for a better understanding of hematopoiesis in health and disease.
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http://dx.doi.org/10.1186/s13045-016-0234-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4727380PMC
January 2016

Targeting megakaryocytic-induced fibrosis in myeloproliferative neoplasms by AURKA inhibition.

Nat Med 2015 Dec 16;21(12):1473-80. Epub 2015 Nov 16.

Division of Hematology and Oncology, Department of Medicine, Northwestern University, Chicago, Illinois, USA.

Primary myelofibrosis (PMF) is characterized by bone marrow fibrosis, myeloproliferation, extramedullary hematopoiesis, splenomegaly and leukemic progression. Moreover, the bone marrow and spleens of individuals with PMF contain large numbers of atypical megakaryocytes that are postulated to contribute to fibrosis through the release of cytokines, including transforming growth factor (TGF)-β. Although the Janus kinase inhibitor ruxolitinib provides symptomatic relief, it does not reduce the mutant allele burden or substantially reverse fibrosis. Here we show through pharmacologic and genetic studies that aurora kinase A (AURKA) represents a new therapeutic target in PMF. Treatment with MLN8237, a selective AURKA inhibitor, promoted polyploidization and differentiation of megakaryocytes with PMF-associated mutations and had potent antifibrotic and antitumor activity in vivo in mouse models of PMF. Moreover, heterozygous deletion of Aurka was sufficient to ameliorate fibrosis and other PMF features in vivo. Our data suggest that megakaryocytes drive fibrosis in PMF and that targeting them with AURKA inhibitors has the potential to provide therapeutic benefit.
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http://dx.doi.org/10.1038/nm.3995DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4674320PMC
December 2015

Single-cell RNA-seq reveals changes in cell cycle and differentiation programs upon aging of hematopoietic stem cells.

Genome Res 2015 Dec 1;25(12):1860-72. Epub 2015 Oct 1.

Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02140, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02140, USA.

Both intrinsic cell state changes and variations in the composition of stem cell populations have been implicated as contributors to aging. We used single-cell RNA-seq to dissect variability in hematopoietic stem cell (HSC) and hematopoietic progenitor cell populations from young and old mice from two strains. We found that cell cycle dominates the variability within each population and that there is a lower frequency of cells in the G1 phase among old compared with young long-term HSCs, suggesting that they traverse through G1 faster. Moreover, transcriptional changes in HSCs during aging are inversely related to those upon HSC differentiation, such that old short-term (ST) HSCs resemble young long-term (LT-HSCs), suggesting that they exist in a less differentiated state. Our results indicate both compositional changes and intrinsic, population-wide changes with age and are consistent with a model where a relationship between cell cycle progression and self-renewal versus differentiation of HSCs is affected by aging and may contribute to the functional decline of old HSCs.
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http://dx.doi.org/10.1101/gr.192237.115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4665007PMC
December 2015

Telomere dynamics in patients with del (5q) MDS before and under treatment with lenalidomide.

Leuk Res 2015 Sep 21. Epub 2015 Sep 21.

Department of Hematology, Oncology and Stem Cell Transplantation, Medical Faculty, RWTH Aachen University, Aachen, Germany.

Myelodysplastic syndrome (MDS) associated with an acquired, isolated deletion of chromosome 5q (del (5q) MDS), represent a clonal disorder of hematopoiesis and a clinically distinct entity of MDS. Treatment of del (5q) MDS with the drug lenalidomide has significantly improved quality of life leading to transfusion independence and complete cytogenetic response rates (CCR) in the majority of patients. Telomeres are located at the end of eukaryotic chromosomes and are linked to replicative history/potential as well as genetic (in) stability of hematopoietic stem cells. Here, we analyzed telomere length (TL) dynamics before and under lenalidomide treatment in the peripheral blood and/or bone marrow of del (5q) patients enrolled in the LEMON-5 study (NCT01081431). Hematopoietic cells from del (5q) MDS patients were characterized by significantly shortened TL compared to age-matched healthy controls. Telomere loss was more accelerated in patients with longer disease duration (>2 years) and more pronounced cytopenias. Sequential analysis under lenalidomide treatment revealed that previously shortened TL in peripheral blood cells was significantly "elongated" towards normal levels within the first six months suggesting a shift from clonal del (5q) cells towards normal hematopoiesis in lenalidomide treated MDS patients. Taken together our findings suggest that the development of the del (5q) clone is associated with accelerated telomere shortening at diagnosis. However, upon induction of CCR and reoccurrence of normal hematopoiesis, the lack of a persistent TL deficit argues against telomere-mediated genetic instability neither as a disease-promoting event of del (5q) MDS nor for lenalidomide mediated development of secondary primary malignancies of the hematopoietic system in responding patients.
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http://dx.doi.org/10.1016/j.leukres.2015.09.003DOI Listing
September 2015

Pharmacological GLI2 inhibition prevents myofibroblast cell-cycle progression and reduces kidney fibrosis.

J Clin Invest 2015 Aug 20;125(8):2935-51. Epub 2015 Jul 20.

Chronic kidney disease is characterized by interstitial fibrosis and proliferation of scar-secreting myofibroblasts, ultimately leading to end-stage renal disease. The hedgehog (Hh) pathway transcriptional effectors GLI1 and GLI2 are expressed in myofibroblast progenitors; however, the role of these effectors during fibrogenesis is poorly understood. Here, we demonstrated that GLI2, but not GLI1, drives myofibroblast cell-cycle progression in cultured mesenchymal stem cell-like progenitors. In animals exposed to unilateral ureteral obstruction, Hh pathway suppression by expression of the GLI3 repressor in GLI1+ myofibroblast progenitors limited kidney fibrosis. Myofibroblast-specific deletion of Gli2, but not Gli1, also limited kidney fibrosis, and induction of myofibroblast-specific cell-cycle arrest mediated this inhibition. Pharmacologic targeting of this pathway with darinaparsin, an arsenical in clinical trials, reduced fibrosis through reduction of GLI2 protein levels and subsequent cell-cycle arrest in myofibroblasts. GLI2 overexpression rescued the cell-cycle effect of darinaparsin in vitro. While darinaparsin ameliorated fibrosis in WT and Gli1-KO mice, it was not effective in conditional Gli2-KO mice, supporting GLI2 as a direct darinaparsin target. The GLI inhibitor GANT61 also reduced fibrosis in mice. Finally, GLI1 and GLI2 were upregulated in the kidneys of patients with high-grade fibrosis. Together, these data indicate that GLI inhibition has potential as a therapeutic strategy to limit myofibroblast proliferation in kidney fibrosis.
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http://dx.doi.org/10.1172/JCI74929DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4563736PMC
August 2015

Lenalidomide induces ubiquitination and degradation of CK1α in del(5q) MDS.

Nature 2015 Jul 1;523(7559):183-188. Epub 2015 Jul 1.

Brigham and Women's Hospital, Division of Hematology, Boston, Massachusetts, USA.

Lenalidomide is a highly effective treatment for myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)). Here, we demonstrate that lenalidomide induces the ubiquitination of casein kinase 1A1 (CK1α) by the E3 ubiquitin ligase CUL4-RBX1-DDB1-CRBN (known as CRL4(CRBN)), resulting in CK1α degradation. CK1α is encoded by a gene within the common deleted region for del(5q) MDS and haploinsufficient expression sensitizes cells to lenalidomide therapy, providing a mechanistic basis for the therapeutic window of lenalidomide in del(5q) MDS. We found that mouse cells are resistant to lenalidomide but that changing a single amino acid in mouse Crbn to the corresponding human residue enables lenalidomide-dependent degradation of CK1α. We further demonstrate that minor side chain modifications in thalidomide and a novel analogue, CC-122, can modulate the spectrum of substrates targeted by CRL4(CRBN). These findings have implications for the clinical activity of lenalidomide and related compounds, and demonstrate the therapeutic potential of novel modulators of E3 ubiquitin ligases.
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http://dx.doi.org/10.1038/nature14610DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4853910PMC
July 2015

Activated fibronectin-secretory phenotype of mesenchymal stromal cells in pre-fibrotic myeloproliferative neoplasms.

J Hematol Oncol 2014 Dec 14;7:92. Epub 2014 Dec 14.

Department of Oncology, Hematology and Stem cell transplantation, University Hospital Aachen, RWTH Aachen University, Pauwelsstrasse 30, Aachen, 52074, Germany.

We characterized bone marrow stromal cells (BMSC) from patients with pre-fibrotic myeloproliferative neoplasms (MPN). MPN-BMSC showed decreased capacity to stimulate the proliferation of colony-forming units of normal hematopoietic stem and progenitor cells and displayed increased matrix remodelling (in particular fibronectin deposition) compared to control BMSC. This finding was confirmed in pre-fibrotic MPN bone marrow biopsies in a tissue microarray (n = 34), which stained positive for fibronectin in the absence of reticulin as a standard myelofibrosis marker. Fibronectin expression correlated significantly with reduced haemoglobin levels in MPN-patients (p = 0.007; R2 = 0.42). Our data show significant cell-intrinsic alterations in MPN-MSC and suggest that Fibronectin expression might be applicable as a biomarker for the identification of early myelofibrotic transformation in reticulin-negative MPN.
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http://dx.doi.org/10.1186/s13045-014-0092-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4271470PMC
December 2014

Perivascular Gli1+ progenitors are key contributors to injury-induced organ fibrosis.

Cell Stem Cell 2015 Jan 20;16(1):51-66. Epub 2014 Nov 20.

Renal Division, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, Boston, MA 02115, USA; Harvard Stem Cell Institute, Cambridge, MA 02138, USA. Electronic address:

Mesenchymal stem cells (MSCs) reside in the perivascular niche of many organs, including kidney, lung, liver, and heart, although their roles in these tissues are poorly understood. Here, we demonstrate that Gli1 marks perivascular MSC-like cells that substantially contribute to organ fibrosis. In vitro, Gli1(+) cells express typical MSC markers, exhibit trilineage differentiation capacity, and possess colony-forming activity, despite constituting a small fraction of the platelet-derived growth factor-β (PDGFRβ)(+) cell population. Genetic lineage tracing analysis demonstrates that tissue-resident, but not circulating, Gli1(+) cells proliferate after kidney, lung, liver, or heart injury to generate myofibroblasts. Genetic ablation of these cells substantially ameliorates kidney and heart fibrosis and preserves ejection fraction in a model of induced heart failure. These findings implicate perivascular Gli1(+) MSC-like cells as a major cellular origin of organ fibrosis and demonstrate that these cells may be a relevant therapeutic target to prevent solid organ dysfunction after injury.
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http://dx.doi.org/10.1016/j.stem.2014.11.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4289444PMC
January 2015

Distinct effects of concomitant Jak2V617F expression and Tet2 loss in mice promote disease progression in myeloproliferative neoplasms.

Blood 2015 Jan 3;125(2):327-35. Epub 2014 Oct 3.

Division of Hematology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA; Broad Institute, Cambridge, MA.

Signaling mutations (eg, JAK2V617F) and mutations in genes involved in epigenetic regulation (eg, TET2) are the most common cooccurring classes of mutations in myeloproliferative neoplasms (MPNs). Clinical correlative studies have demonstrated that TET2 mutations are enriched in more advanced phases of MPNs such as myelofibrosis and leukemic transformation, suggesting that they may cooperate with JAK2V617F to promote disease progression. To dissect the effects of concomitant Jak2V617F expression and Tet2 loss within distinct hematopoietic compartments in vivo, we generated Jak2V617F/Tet2 compound mutant genetic mice. We found that the combination of Jak2V617F expression and Tet2 loss resulted in a more florid MPN phenotype than that seen with either allele alone. Concordant with this, we found that Tet2 deletion conferred a strong functional competitive advantage to Jak2V617F-mutant hematopoietic stem cells (HSCs). Transcriptional profiling revealed that both Jak2V617F expression and Tet2 loss were associated with distinct and nonoverlapping gene expression signatures within the HSC compartment. In aggregate, our findings indicate that Tet2 loss drives clonal dominance in HSCs, and Jak2V617F expression causes expansion of downstream precursor cell populations, resulting in disease progression through combinatorial effects. This work provides insight into the functional consequences of JAK2V617F-TET2 comutation in MPNs, particularly as it pertains to HSCs.
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http://dx.doi.org/10.1182/blood-2014-04-567024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4287639PMC
January 2015