Myelodysplastic syndromes: the complexity of stem-cell diseases

Blockade of BCL-2 proteins efficiently induces apoptosis in progenitor cells of high-risk myelodysplastic syndromes patients

Deregulated apoptosis is an identifying feature of myelodysplastic syndromes (MDS). Whereas apoptosis is increased in the bone marrow (BM) of low-risk MDS patients, progression to high-risk MDS correlates with an acquired resistance to apoptosis and an aberrant expression of BCL-2 proteins. To overcome the acquired apoptotic resistance in high-risk MDS, we investigated the induction of apoptosis by inhibition of pro-survival BCL-2 proteins using the BCL-2/-XL/-W inhibitor ABT-737 or the BCL-2-selective inhibitor ABT-199. We characterized a cohort of 124 primary human BM samples from MDS/secondary acute myeloid leukemia (sAML) patients and 57 healthy, age-matched controls. Inhibition of anti-apoptotic BCL-2 proteins was specifically toxic for BM cells from high-risk MDS and sAML patients, whereas low-risk MDS or healthy controls remained unaffected. Notably, ABT-737 or ABT-199 treatment was capable of targeting the MDS stem/progenitor compartment in high-risk MDS/sAML samples as shown by the reduction in CD34(+) cells and the decreased colony-forming capacity. Elevated expression of MCL-1 conveyed resistance against both compounds. Protection by stromal cells only partially inhibited induction of apoptosis. Collectively, our data show that the apoptotic resistance observed in high-risk MDS/sAML cells can be overcome by the ABT-737 or ABT-199 treatment and implies that BH3 mimetics might delay disease progression in higher-risk MDS or sAML patients.

Deconstructing innate immune signaling in myelodysplastic syndromes

Overexpression of immune-related genes is widely reported in myelodysplastic syndromes (MDSs), and chronic immune stimulation increases the risk for developing MDS. Aberrant innate immune activation, such as that caused by increased toll-like receptor (TLR) signaling, in MDS can contribute to systemic effects on hematopoiesis, in addition to cell-intrinsic defects on hematopoietic stem/progenitor cell (HSPC) function. This review will deconstruct aberrant function of TLR signaling mediators within MDS HSPCs that may contribute to cell-intrinsic consequences on hematopoiesis and disease pathogenesis. We will discuss the contribution of chronic TLR signaling to the pathogenesis of MDS based on evidence from patients and mouse genetic models.

Exploiting replicative stress to treat cancer

DNA replication in cancer cells is accompanied by stalling and collapse of the replication fork and signalling in response to DNA damage and/or premature mitosis; these processes are collectively known as 'replicative stress'. Progress is being made to increase our understanding of the mechanisms that govern replicative stress, thus providing ample opportunities to enhance replicative stress for therapeutic purposes. Rather than trying to halt cell cycle progression, cancer therapeutics could aim to increase replicative stress by further loosening the checkpoints that remain available to cancer cells and ultimately inducing the catastrophic failure of proliferative machineries. In this Review, we outline current and future approaches to achieve this, emphasizing the combination of conventional chemotherapy with targeted approaches.

Deacetylase inhibitors for the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a diverse group of myeloid disorders, with patients being at risk for cytopenias or progression to acute myeloid leukemia. Several classification and prognostic scoring systems have been developed. High-intensity treatments are not appropriate for all patients. Two demethylating agents, azacitidine and decitabine, are approved for the treatment of MDS, although many patients do not derive long-term benefit and eventually progress. Deacetylase inhibitors have emerged as novel treatment candidates based on mechanistic rationale and preliminary data. This article reviews existing data on MDS treatment and discusses the rationale and potential for combination with deacetylase inhibitors.

Genetics factors associated with myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a clinically and cytogenetically heterogeneous group of clonal diseases. Clonal chromosomal abnormalities are observed in 30-50% of patients with MDS. The deletions are among the most common alterations, and often involve the long arms of chromosomes 5, 7, 8, 13, and 20 and the short arms of chromosomes 12 and 17. The advent of new technologies for the detection of genetic abnormalities led to the description of a new set of recurrent mutations, leading to new insights into the pathophysiology of MDS. The recent recognition that genes involved in the regulation of histone function (EZH2, ASXL1, and UTX) and DNA methylation (DNMT3A, IDH1/IDH2, and TET2) are frequently mutated in MDS, has led to the proposal that there is an important link between genetic and epigenetic alterations in this disease. In fact, regulatory factors have also been considered as miR-143/miR-145, miR-146a, miR-125a and MiR-21. Somatic mutations may influence the clinical phenotype but are not included in current prognostic scoring systems. In recent years research has brought new insights into these diseases, but few of the findings are sufficiently robust to be incorporated into the clinical routine at this time. Thus, the aim of this study was to review the role of genetic factors involved in the diagnosis and development of the different phenotypes of MDS.

Deregulation of innate immune and inflammatory signaling in myelodysplastic syndromes

Myelodysplastic syndromes (MDSs) are a group of heterogeneous clonal hematologic malignancies that are characterized by defective bone marrow (BM) hematopoiesis and by the occurrence of intramedullary apoptosis. During the past decade, the identification of key genetic and epigenetic alterations in patients has improved our understanding of the pathophysiology of this disease. However, the specific molecular mechanisms leading to the pathogenesis of MDS have largely remained obscure. Recently, essential evidence supporting the direct role of innate immune abnormalities in MDS has been obtained, including the identification of multiple key regulators that are overexpressed or constitutively activated in BM hematopoietic stem and progenitor cells. Mounting experimental results indicate that the dysregulation of these molecules leads to abnormal hematopoiesis, unbalanced cell death and proliferation in patients' BM, and has an important role in the pathogenesis of MDS. Furthermore, there is compelling evidence that the deregulation of innate immune and inflammatory signaling also affects other cells from the immune system and the BM microenvironment, which establish aberrant associations with hematopoietic precursors and contribute to the MDS phenotype. Therefore, the deregulation of innate immune and inflammatory signaling should be considered as one of the driving forces in the pathogenesis of MDS. In this article, we review and update the advances in this field, summarizing the results from the most recent studies and discussing their clinical implications.

How cell death shapes cancer

Apoptosis has been established as a mechanism of anti-cancer defense. Members of the BCL-2 family are critical mediators of apoptotic cell death in health and disease, often found to be deregulated in cancer and believed to lead to the survival of malignant clones. However, over the years, a number of studies pointed out that a model in which cell death resistance unambiguously acts as a barrier against malignant disease might be too simple. This is based on paradoxical observations made in tumor patients as well as mouse models indicating that apoptosis can indeed drive tumor formation, at least under certain circumstances. One possible explanation for this phenomenon is that apoptosis can promote proliferation critically needed to compensate for cell loss, for example, upon therapy, and to restore tissue homeostasis. However, this, at the same time, can promote tumor development by allowing expansion of selected clones. Usually, tissue resident stem/progenitor cells are a major source for repopulation, some of them potentially carrying (age-, injury- or therapy-induced) genetic aberrations deleterious for the host. Thereby, apoptosis might drive genomic instability by facilitating the emergence of pathologic clones during phases of proliferation and subsequent replication stress-associated DNA damage. Tumorigenesis initiated by repeated cell attrition and repopulation, as confirmed in different genetic models, has parallels in human cancers, exemplified in therapy-induced secondary malignancies and myelodysplastic syndromes in patients with congenital bone marrow failure syndromes. Here, we aim to review evidence in support of the oncogenic role of stress-induced apoptosis.

Cytokine expression patterns and mesenchymal stem cell karyotypes from the bone marrow microenvironment of patients with myelodysplastic syndromes

The purpose of this study was to explore cytokine expression patterns and cytogenetic abnormalities of mesenchymal stem cells (MSCs) from the bone marrow microenvironment of Chinese patients with myelodysplastic syndromes (MDS). Bone marrow samples were obtained from 30 cases of MDS (MDS group) and 30 healthy donors (control group). The expression pattern of cytokines was detected by customized protein array. The karyotypes of MSCs were analyzed using fluorescence in situ hybridization. Compared with the control group, leukemia inhibitory factor, stem cell factor (SCF), stromal cell-derived factor (SDF-1), bone morphogenetic protein 4, hematopoietic stem cell (HSC) stimulating factor, and transforming growth factor-β in the MDS group were significantly downregulated (P<0.05), while interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and programmed death ligand (B7-H1) were significantly upregulated (P<0.05). For chromosome abnormality analysis, the detection rate of abnormal karyotypes (+8, -8, -20, 20q-, -Y, -7, 5q-) was 30% in the MDS group and 0% in the control group. In conclusion, the up- and downregulated expression of these cytokines might play a key role in the pathogenesis of MDS. Among them, SCF and SDF-1 may play roles in the apoptosis of HSCs in MDS; and IFN-γ, TNF-α, and B7-H1 may be associated with apoptosis of bone marrow cells in MDS. In addition, the abnormal karyotypes might be actively involved in the pathogenesis of MDS. Further studies are required to determine the role of abnormal karyotypes in the occurrence and development of MDS.

Combining gene mutation with gene expression data improves outcome prediction in myelodysplastic syndromes

Cancer is a genetic disease, but two patients rarely have identical genotypes. Similarly, patients differ in their clinicopathological parameters, but how genotypic and phenotypic heterogeneity are interconnected is not well understood. Here we build statistical models to disentangle the effect of 12 recurrently mutated genes and 4 cytogenetic alterations on gene expression, diagnostic clinical variables and outcome in 124 patients with myelodysplastic syndromes. Overall, one or more genetic lesions correlate with expression levels of ~20% of all genes, explaining 20–65% of observed expression variability. Differential expression patterns vary between mutations and reflect the underlying biology, such as aberrant polycomb repression for ASXL1 and EZH2 mutations or perturbed gene dosage for copy-number changes. In predicting survival, genomic, transcriptomic and diagnostic clinical variables all have utility, with the largest contribution from the transcriptome. Similar observations are made on the TCGA acute myeloid leukaemia cohort, confirming the general trends reported here.

The myelodysplastic syndromes (MDS) are a heterogeneous group of chronic blood cancers. Here, the authors analyse genomic and gene expression data from MDS patients to investigate how driver mutations alter gene expression, diagnostic clinical variables and survival.

Missing Cells: Pathophysiology, Diagnosis, and Management of (Pan)Cytopenia in Childhood

Peripheral blood cytopenia in children can be due to a variety of acquired or inherited diseases. Genetic disorders affecting a single hematopoietic lineage are frequently characterized by typical bone marrow findings, such as lack of progenitors or maturation arrest in congenital neutropenia or a lack of megakaryocytes in congenital amegakaryocytic thrombocytopenia, whereas antibody-mediated diseases such as autoimmune neutropenia are associated with a rather unremarkable bone marrow morphology. By contrast, pancytopenia is frequently associated with a hypocellular bone marrow, and the differential diagnosis includes acquired aplastic anemia, myelodysplastic syndrome, inherited bone marrow failure syndromes such as Fanconi anemia and dyskeratosis congenita, and a variety of immunological disorders including hemophagocytic lymphohistiocytosis. Thorough bone marrow analysis is of special importance for the diagnostic work-up of most patients. Cellularity, cellular composition, and dysplastic signs are the cornerstones of the differential diagnosis. Pancytopenia in the presence of a normo- or hypercellular marrow with dysplastic changes may indicate myelodysplastic syndrome. More challenging for the hematologist is the evaluation of the hypocellular bone marrow. Although aplastic anemia and hypocellular refractory cytopenia of childhood (RCC) can reliably be differentiated on a morphological level, the overlapping pathophysiology remains a significant challenge for the choice of the therapeutic strategy. Furthermore, inherited bone marrow failure syndromes are usually associated with the morphological picture of RCC, and the recognition of these entities is essential as they often present a multisystem disease requiring different diagnostic and therapeutic approaches. This paper gives an overview over the different disease entities presenting with (pan)cytopenia, their pathophysiology, characteristic bone marrow findings, and therapeutic approaches.

Aging and brain rejuvenation as systemic events

The effects of aging were traditionally thought to be immutable, particularly evident in the loss of plasticity and cognitive abilities occurring in the aged central nervous system (CNS). However, it is becoming increasingly apparent that extrinsic systemic manipulations such as exercise, caloric restriction, and changing blood composition by heterochronic parabiosis or young plasma administration can partially counteract this age-related loss of plasticity in the aged brain. In this review, we discuss the process of aging and rejuvenation as systemic events. We summarize genetic studies that demonstrate a surprising level of malleability in organismal lifespan, and highlight the potential for systemic manipulations to functionally reverse the effects of aging in the CNS. Based on mounting evidence, we propose that rejuvenating effects of systemic manipulations are mediated, in part, by blood-borne ‘pro-youthful’ factors. Thus, systemic manipulations promoting a younger blood composition provide effective strategies to rejuvenate the aged brain. As a consequence, we can now consider reactivating latent plasticity dormant in the aged CNS as a means to rejuvenate regenerative, synaptic, and cognitive functions late in life, with potential implications even for extending lifespan.

Myelodysplastic syndromes

Myelodysplastic syndromes are clonal marrow stem-cell disorders, characterised by ineffective haemopoiesis leading to blood cytopenias, and by progression to acute myeloid leukaemia in a third of patients. 15% of cases occur after chemotherapy or radiotherapy for a previous cancer; the syndromes are most common in elderly people. The pathophysiology involves cytogenetic changes with or without gene mutations and widespread gene hypermethylation at advanced stages. Clinical manifestations result from cytopenias (anaemia, infection, and bleeding). Diagnosis is based on examination of blood and bone marrow showing blood cytopenias and hypercellular marrow with dysplasia, with or without excess of blasts. Prognosis depends largely on the marrow blast percentage, number and extent of cytopenias, and cytogenetic abnormalities. Treatment of patients with lower-risk myelodysplastic syndromes, especially for anaemia, includes growth factors, lenalidomide, and transfusions. Treatment of higher-risk patients is with hypomethylating agents and, whenever possible, allogeneic stem-cell transplantation.

Prognostic value of isocitrate dehydrogenase mutations in myelodysplastic syndromes: a retrospective cohort study and meta-analysis

Background

Recent genomic sequencing efforts have identified a number of recurrent mutations in myelodysplastic syndromes (MDS) that may contribute to disease progression and overall survival, including mutations in isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2).

Methods

Pretreatment bone marrow (BM) samples were acquired from mononuclear cells in 146 adult patients with de novo MDS from January 2006 to June 2013. Polymerase chain reaction (PCR) and direct sequencing were performed on exon 4 of IDH1/2 genes and mutation status was correlated with overall survival (OS) and leukemia-free survival (LFS). We then performed a meta-analysis combining previously published and current studies to explore the effect of IDH mutations on OS and LFS in MDS.

Results

In our study, somatic mutations of either IDH gene were discovered in 11 MDS patients (7.53%) and were significantly correlated with poorer OS (P = 0.007). IDH mutations were specifically associated with a poorer OS in the intermediate-1 risk group by the International Prognostic Scoring System (IPSS) (P = 0.039). In addition, we discovered decitabine achieved a better therapeutic effect compared to other treatments in IDH mutation-positive patients (P = 0.023). We identified six previous studies of IDH mutations in MDS. A meta-analysis of these studies included 111 MDS patients IDH mutations and 1671 MDS patients with wild-type IDH1/2. The hazard ratios (HRs) of OS and LFS for patients with IDH mutations were 1.62 (95% CI, 1.27–2.09) and 2.21 (95% CI, 1.48–3.30), respectively.

Conclusion

The results from our study and the meta-analysis provide firm evidence that IDH mutations are significantly associated with poorer clinical outcomes in MDS. Identification of IDH mutations may be pivotal for better risk stratification in MDS patients and improving IPSS score. Additionally, hypomethylating agents may be an effective treatment option for MDS patients with IDH mutations.

In Brief: (mis)splicing in disease

Splicing of pre-mRNAs is a crucial step in the gene expression pathway. Disruption of splicing has been linked to the pathogenesis of several human diseases and is particularly widespread in cancer. Recently, a number of mutations affecting genes of the core spliceosome machinery have been identified in haematological malignancies, yet the effect of such mutations on RNA splicing is unclear. A better understanding of how mis-splicing contributes to malignancies may provide diagnostic or prognostic information and new drug targets for therapeutic approaches.

MLL3 is a haploinsufficient 7q tumor suppressor in acute myeloid leukemia

Recurring deletions of chromosome 7 and 7q [-7/del(7q)] occur in myelodysplastic syndromes and acute myeloid leukemia (AML) and are associated with poor prognosis. However, the identity of functionally relevant tumor suppressors on 7q remains unclear. Using RNAi and CRISPR/Cas9 approaches, we show that an ∼50% reduction in gene dosage of the mixed lineage leukemia 3 (MLL3) gene, located on 7q36.1, cooperates with other events occurring in -7/del(7q) AMLs to promote leukemogenesis. Mll3 suppression impairs the differentiation of HSPC. Interestingly, Mll3-suppressed leukemias, like human -7/del(7q) AMLs, are refractory to conventional chemotherapy but sensitive to the BET inhibitor JQ1. Thus, our mouse model functionally validates MLL3 as a haploinsufficient 7q tumor suppressor and suggests a therapeutic option for this aggressive disease.

Identification of campath-1 (CD52) as novel drug target in neoplastic stem cells in 5q-patients with MDS and AML

PURPOSE

The CD52-targeted antibody alemtuzumab induces major clinical responses in a group of patients with myelodysplastic syndromes (MDS). The mechanism underlying this drug effect remains unknown.

EXPERIMENTAL DESIGN

We asked whether neoplastic stem cells (NSC) in patients with MDS (n = 29) or acute myelogenous leukemia (AML; n = 62) express CD52.

RESULTS

As assessed by flow cytometry, CD52 was found to be expressed on NSC-enriched CD34(+)/CD38(-) cells in 8/11 patients with MDS and isolated del(5q). In most other patients with MDS, CD52 was weakly expressed or not detectable on NSC. In AML, CD34(+)/CD38(-) cells displayed CD52 in 23/62 patients, including four with complex karyotype and del(5q) and one with del(5q) and t(1;17;X). In quantitative PCR (qPCR) analyses, purified NSC obtained from del(5q) patients expressed CD52 mRNA. We were also able to show that CD52 mRNA levels correlate with EVI1 expression and that NRAS induces the expression of CD52 in AML cells. The CD52-targeting drug alemtuzumab, was found to induce complement-dependent lysis of CD34(+)/CD38(-)/CD52(+) NSC, but did not induce lysis in CD52(-) NSC. Alemtuzumab also suppressed engraftment of CD52(+) NSC in NSG mice. Finally, CD52 expression on NSC was found to correlate with a poor survival in patients with MDS and AML.

CONCLUSIONS

The cell surface target Campath-1 (CD52) is expressed on NSC in a group of patients with MDS and AML. CD52 is a novel prognostic NSC marker and a potential NSC target in a subset of patients with MDS and AML, which may have clinical implications and may explain clinical effects produced by alemtuzumab in these patients.

Overexpression of miR-125a in myelodysplastic syndrome CD34+ cells modulates NF-κB activation and enhances erythroid differentiation arrest

Myelodysplastic syndromes (MDS) are characterized by impaired proliferation and differentiation of hematopoietic stem cells. The participation of toll-like receptor (TLR)-mediated signaling in MDS is well documented. Increased TLR signaling leads to the constitutive activation of NF-κB, which mediates inflammation, cell proliferation and apoptosis. In addition, the TLR pathway induces the expression of miRNAs which participate in the fine-tuning of the inflammatory response. miRNAs also regulate other biological processes, including hematopoiesis. miR-125a and miR-125b are known modulators of hematopoiesis and are abnormally expressed in several hematologic malignancies. However, little is known about their role in MDS. NF-κB-activating ability has been described for both miRNAs. We studied the role of miR-125a/miR-125b in MDS and their relationship with TLR signaling and hematopoietic differentiation. Our results indicate that miR-125a is significantly overexpressed in MDS patients and correlates negatively with patient survival. Expression of miR-99b, which is clustered with miR-125a, is also directly correlated with prognosis of MDS. Both miR-125a and miR-99b activated NF-κB in vitro; however, we observed a negative correlation between miR-99b expression and the levels of TLR2, TLR7 and two downstream genes, suggesting that NF-κB activation by the miRNA cluster occurs in the absence of TLR signaling. We also show that TLR7 is negatively correlated with patient survival in MDS. In addition, our data suggest that miR-125a may act as an NF-κB inhibitor upon TLR stimulation. These results indicate that miR-125a is involved in the fine-tuning of NF-κB activity and that its effects may depend on the status of the TLR pathway. Furthermore, we observed that miR-125a inhibits erythroid differentiation in leukemia and MDS cell lines. Therefore, this miRNA could serve as a prognostic marker and a potential therapeutic target in MDS.

Nuclear Nox4-derived reactive oxygen species in myelodysplastic syndromes

A role for intracellular ROS production has been recently implicated in the pathogenesis and progression of a wide variety of neoplasias. ROS sources, such as NAD(P)H oxidase (Nox) complexes, are frequently activated in AML (acute myeloid leukemia) blasts and strongly contribute to their proliferation, survival, and drug resistance. Myelodysplastic syndromes (MDS) comprise a heterogeneous group of disorders characterized by ineffective hematopoiesis, with an increased propensity to develop AML. The molecular basis for MDS progression is unknown, but a key element in MDS disease progression is the genomic instability. NADPH oxidases are now recognized to have specific subcellular localizations, this targeting to specific compartments for localized ROS production. Local Nox-dependent ROS production in the nucleus may contribute to the regulation of redox-dependent cell growth, differentiation, senescence, DNA damage, and apoptosis. We observed that Nox1, 2, and 4 isoforms and p22phox and Rac1 subunits are expressed in MDS/AML cell lines and MDS samples, also in the nuclear fractions. Interestingly, Nox4 interacts with ERK and Akt1 within nuclear speckle domain, suggesting that Nox4 could be involved in regulating gene expression and splicing factor activity. These data contribute to the elucidation of the molecular mechanisms used by nuclear ROS to drive MDS evolution to AML.

A review of the mitochondrial and glycolytic metabolism in human platelets and leukocytes: implications for their use as bioenergetic biomarkers

The assessment of metabolic function in cells isolated from human blood for treatment and diagnosis of disease is a new and important area of translational research. It is now becoming clear that a broad range of pathologies which present clinically with symptoms predominantly in one organ, such as the brain or kidney, also modulate mitochondrial energetics in platelets and leukocytes allowing these cells to serve as “the canary in the coal mine” for bioenergetic dysfunction. This opens up the possibility that circulating platelets and leukocytes can sense metabolic stress in patients and serve as biomarkers of mitochondrial dysfunction in human pathologies such as diabetes, neurodegeneration and cardiovascular disease. In this overview we will describe how the utilization of glycolysis and oxidative phosphorylation differs in platelets and leukocytes and discuss how they can be used in patient populations. Since it is clear that the metabolic programs between leukocytes and platelets are fundamentally distinct the measurement of mitochondrial function in distinct cell populations is necessary for translational research.

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Monocytes, lymphocytes, neutrophils and platelets have distinct bioenergetic programs that regulate energy production.

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Platelets and monocytes exhibit a high level of aerobic glycolysis and mitochondrial respiration.

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Lymphocytes have a low glycolytic capacity while neutrophils have little or no detectable oxidative phosphorylation.

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The levels of mitochondrial complex IV and III subunits differ substantially between lymphocytes, monocytes and platelets.

Animal models to test hiPS-derived hepatocytes in the context of inherited metabolic liver diseases

Human induced pluripotent stem (hiPS) cells are established following reprogramming of somatic cells from a wide variety of tissues. Given the scarcity of adult human hepatocytes, hiPS-derived hepatocytes would be a valuable source of cells to study differentiation programs, model patient-specific diseases, test drug toxicities, and cell transplantation therapies. Although hiPS-derived hepatocytes are extensively characterized in cell culture assays, testing these cells in animal models is necessary to fully evaluate their differentiation profile and their lack of tumorigenicity. Immunodeficient mouse models harboring liver damage are effective hosts in which xenogeneic hepatocytes can engraft, proliferate, and participate in liver regeneration, thus constituting a stringent test of hepatocyte functionality. The in vivo evaluation of disease-specific hiPS-derived hepatocytes should broaden our understanding of the cellular and molecular processes involved in inherited metabolic liver disease phenotypes. Herein, we detail our methods to test the functions of hiPS-derived hepatocytes in the context of the immunodeficient Rag2(-/-)IL2Rγc(-/-)Alb-uPAtg mouse model.

Arsenic disulfide-triggered apoptosis and erythroid differentiation in myelodysplastic syndrome and acute myeloid leukemia cell lines

OBJECTIVES

Effects of arsenic disulfide (As2S2) were investigated by focusing on growth inhibition, apoptosis induction, and erythroid differentiation in MDS-L, F-36p and HL-60 cells, derived from myelodysplastic syndrome (MDS), MDS/acute myeloid leukemia (AML), and de novo AML, respectively.

METHODS

Cell viability was determined by MTT assay. Apoptosis induction was analyzed using Annexin V/propidium iodide staining. Erythroid differentiation was assessed by the expression level of CD235a, a marker for detection of the erythroid cell lineage. The activation of p38 MAPK and the expression profile of apoptosis-related proteins Bcl-2 and Bid were analyzed using western blot.

RESULTS

As2S2 inhibited cell growth of these cell lines. Of note, the IC50 value of As2S2 in MDS-L cells was comparable to that in F-36p cells, and was half of that in HL-60 cells. A dose-dependent decrease in cell viability and concomitant increase in the percentage of apoptotic cells were observed in F-36p cells treated with 8 and 16 µM As2S2 for 72 hours. However, similar phenomena were only observed in HL-60 cells when treated with as high as 16 µM As2S2. Furthermore, As2S2 exerted more potent erythroid differentiation-inducing activity on F-36p cells than HL-60 cells. Interestingly, negative correlation between p38 MAPK signaling pathway and As2S2-induced erythroid differentiation was observed in HL-60 cells. Treatment with relatively high concentration of As2S2 resulted in the downregulation of Bcl-2 and Bid proteins in HL-60 cells.

DISCUSSION

These results suggest that compared to AML cell line, MDS and MDS/AML cell lines are more sensitive to not only the erythroid differentiation-inducing activity of As2S2, but also its cytotoxicity associated with apoptosis induction. These findings further provide novel insight into As2S2 action toward its use for clinical application in patients with hematological disorders.

Myelodysplastic syndromes: toward a risk-adapted treatment approach

Several classification and scoring systems have been developed in myelodysplastic syndromes (MDS to predict the risk of progression to acute myeloid leukemia and survival. These prognostication models have been also used to inform therapeutic decision-making in a risk-adapted fashion. Patient-related factors such as age, comorbidities, and functional status have to be considered as well. Here we review a risk-guided therapeutic approach for the management of MDS patients. It is anticipated that the improved understanding of the complex pathogenesis of MDS and the recent discovery of important molecular lesions will be translated into novel therapeutic approaches. Additionally, some prognostic aberrations are expected to be incorporated into the prognostic tools with the goal of improving their prognostic precision and therefore allow for a more informed therapeutic decision-making based on the individual's risk profile.

RasGRP Ras guanine nucleotide exchange factors in cancer

RasGRP proteins are activators of Ras and other related small GTPases by the virtue of functioning as guanine nucleotide exchange factors (GEFs). In vertebrates, four RasGRP family members have been described. RasGRP-1 through -4 share many structural domains but there are also subtle differences between each of the different family members. Whereas SOS RasGEFs are ubiquitously expressed, RasGRP proteins are expressed in distinct patterns, such as in different cells of the hematopoietic system and in the brain. Most studies have concentrated on the role of RasGRP proteins in the development and function of immune cell types because of the predominant RasGRP expression profiles in these cells and the immune phenotypes of mice deficient for Rasgrp genes. However, more recent studies demonstrate that RasGRPs also play an important role in tumorigenesis. Examples are skin- and hematological-cancers but also solid malignancies such as melanoma or prostate cancer. These novel studies bring up many new and unanswered questions related to the molecular mechanism of RasGRP-driven oncogenesis, such as new receptor systems that RasGRP appears to respond to as well as regulatory mechanism for RasGRP expression that appear to be perturbed in these cancers. Here we will review some of the known aspects of RasGRP biology in lymphocytes and will discuss the exciting new notion that RasGRP Ras exchange factors play a role in oncogenesis downstream of various growth factor receptors.

Review of therapeutic options and the management of patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a poorly understood group of disorders caused by one or more genetic aberrations in the bone marrow-derived cell line responsible for hematopoiesis. Recent advances in genetic medicine have offered new insights into the epigenesis as well as the prognosis of MDS, but have not resulted in new or improved curative treatment options. Bone marrow transplantation, introduced before the advent of genetic medicine, is still the only potential cure. Advances in other medical and pharmaceutical areas have broadened the scope of supportive care and disease-modifying therapies, and treating physicians now have a broad range of disease management options depending on a patient's likely prognosis. There is now clear evidence that appropriate supportive care and therapeutic intervention can improve progression-free and overall survival of MDS patients.

Age-related changes of healthy bone marrow cell signaling in response to growth factors provide insight into low risk MDS

BACKGROUND

Single Cell Network Profiling (SCNP) is a multiparametric flow cytometry-based assay that quantifiably and simultaneously measures changes in intracellular signaling proteins in response to in vitro extracellular modulators at the single cell level. Myelodysplastic syndrome (MDS) is a heterogeneous clonal disorder of hematopoietic stem cells that occurs in elderly subjects and is characterized by dysplasia and ineffective hematopoiesis. The functional responsiveness of MDS bone marrow (BM) hematopoietic cells, including functionally distinct myeloid and erythroid precursor subsets, to hematopoietic growth factors (HGF) and the relationship of modulated signaling to disease characteristics is poorly understood.

METHODS

SCNP was used first to examine the effects of age on erythropoietin (EPO) and granulocyte colony stimulating factor (GCSF)-induced signaling in myeloid, nucleated red blood cells (nRBC), and CD34 expressing cell subsets in healthy BM (n = 15). SCNP was then used to map functional signaling profiles in low risk (LR) MDS (n = 7) for comparison to signaling in samples from healthy donors and to probe signaling associations within clinically defined subgroups.

RESULTS

In healthy BM samples, signaling responses to HGF were quite homogeneous (i.e., tightly regulated) with age-dependent effects observed in response to EPO but not to GCSF. Despite the relatively small number of samples assayed in the study, LR MDS could be classified into distinct subgroups based on both cell subset frequency and signaling profiles.

CONCLUSIONS

As a correlate of underlying genetic abnormalities, signal transduction analyses may provide a functional and potentially clinically relevant classification of MDS. Further evaluation in a larger cohort is warranted.

The role of splicing factor mutations in the pathogenesis of the myelodysplastic syndromes

Accurate pre-mRNA splicing by the spliceosome is a fundamental cellular mechanism required to remove introns that are present in most protein-coding transcripts. The recent discovery of a variety of somatic spliceosomal mutations in the myelodysplastic syndromes (MDS), a heterogeneous group of myeloid malignancies, has revealed a new leukemogenic pathway involving spliceosomal dysfunction. Spliceosome mutations are found in over half of all MDS patients and are likely founder mutations. The spliceosome mutations are highly specific to MDS and closely related conditions and, to some extent, appear to define distinct clinical phenotypes in MDS. The high frequency of mutations in different components of the RNA splicing machinery in MDS suggests that abnormal RNA splicing is the common consequence of these mutations. The identification of the downstream targets of the spliceosome mutations is an active area of research. Emerging data from the study of the MDS transcriptome suggests that spliceosomal mutations have effects on specific genes, including some previously shown to play a role in MDS pathogenesis. The effects of the spliceosomal mutations on RNA splicing and cell growth have been evaluated only in a limited context to date, however, and the determination of the impact of these mutations in primary human hematopoietic cells is essential in order to elucidate fully the molecular mechanism by which they contribute to MDS pathogenesis.

Oxidative stress leads to increased mutation frequency in a murine model of myelodysplastic syndrome

The myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis, dysplasia, and transformation to acute myeloid leukemia (AML). Although it has been suggested that additional mutations lead to progression of MDS to AML, the causative agent(s) for such mutations remains unclear. Oxidative stress is a potential cause, therefore, we evaluated levels of reactive oxygen species (ROS) in NUP98-HOXD13 (NHD13) transgenic mice, a murine model for MDS. Increased levels of ROS were detected in bone marrow nucleated cells (BMNC) that express CD71, a marker for cell proliferation, as well as immature, lineage negative bone marrow nucleated cells from NHD13 mice. In addition to the increase in ROS, increased DNA double strand breaks and activation of a G2/M phase cell cycle checkpoint were noted in NHD13 BMNC. Finally, using an in vivo assay for mutation frequency, we detected an increased mutation frequency in NHD13 BMNC. These results suggest that oxidative stress may contribute to disease progression of MDS to AML through ineffective repair of DNA damage and acquisition of oncogenic mutations.

Targeting IRAK1 as a therapeutic approach for myelodysplastic syndrome

Myelodysplastic syndromes (MDSs) arise from a defective hematopoietic stem/progenitor cell. Consequently, there is an urgent need to develop targeted therapies capable of eliminating the MDS-initiating clones. We identified that IRAK1, an immune-modulating kinase, is overexpressed and hyperactivated in MDSs. MDS clones treated with a small molecule IRAK1 inhibitor (IRAK1/4-Inh) exhibited impaired expansion and increased apoptosis, which coincided with TRAF6/NF-κB inhibition. Suppression of IRAK1, either by RNAi or with IRAK1/4-Inh, is detrimental to MDS cells, while sparing normal CD34(+) cells. Based on an integrative gene expression analysis, we combined IRAK1 and BCL2 inhibitors and found that cotreatment more effectively eliminated MDS clones. In summary, these findings implicate IRAK1 as a drugable target in MDSs.

Induction of Chromosomal Instability via Telomere Dysfunction and Epigenetic Alterations in Myeloid Neoplasia

Chromosomal instability (CIN) is a characteristic feature of cancer. In this review, we concentrate on mechanisms leading to CIN in myeloid neoplasia, i.e., myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). The pathogenesis of myeloid neoplasia is complex and involves genetic and epigenetic alterations. Chromosome aberrations define specific subgroups and guide clinical decisions. Genomic instability may play an essential role in leukemogenesis by promoting the accumulation of genetic lesions responsible for clonal evolution. Indeed, disease progression is often driven by clonal evolution into complex karyotypes. Earlier studies have shown an association between telomere shortening and advanced MDS and underlined the important role of dysfunctional telomeres in the development of genetic instability and cancer. Several studies link chromosome rearrangements and aberrant DNA and histone methylation. Genes implicated in epigenetic control, like DNMT3A, ASXL1, EZH2 and TET2, have been discovered to be mutated in MDS. Moreover, gene-specific hypermethylation correlates highly significantly with the risk score according to the International Prognostic Scoring System. In AML, methylation profiling also revealed clustering dependent on the genetic status. Clearly, genetic instability and clonal evolution are driving forces for leukemic transformation. Understanding the mechanisms inducing CIN will be important for prevention and for novel approaches towards therapeutic interventions.

Prognostic impact of the number of methylated genes in myelodysplastic syndromes and acute myeloid leukemias treated with azacytidine

The prognostic impact of the aberrant hypermethylation in response to azacytidine (AZA) remains to be determined. Therefore, we have analyzed the influence of the methylation status prior to AZA treatment on the overall survival and clinical response of myeloid malignancies. DNA methylation status of 24 tumor suppressor genes was analyzed by methylation-specific multiplex ligation-dependent probe amplification in 63 patients with myelodysplastic syndromes and acute myeloid leukemia treated with azacytidine. Most patients (73 %) showed methylation of at least one gene, but only 12 % of patients displayed ≥3 methylated genes. The multivariate analysis demonstrated that the presence of a high number (≥2) of methylated genes (P = 0.022), a high WBC count (P = 0.033), or anemia (P = 0.029) were independent prognostic factors associated with shorter overall survival. The aberrant methylation status did not correlate with the response to AZA, although four of the five patients with ≥3 methylated genes did not respond. By contrast, favorable cytogenetics independently influenced the clinical response to AZA as 64.7 % of patients with good-risk cytogenetic abnormalities responded (P = 0.03). Aberrant methylation status influences the survival of patients treated with AZA, being shorter in those patients with a high number of methylated genes.

Treatment of low-risk myelodysplastic syndrome: hematopoietic growth factors erythropoietins and thrombopoietins

The use of erythropoietic growth factors has become standard of care in many countries for lower risk myelodysplastic syndrome (MDS) patients. Throughout a large number of clinical trials, therapy with erythropoietic agents has consistently shown improvement of anemia and reduction of transfusion dependence. There is currently no evidence of safety issues of erythropoietins in MDS, including thrombosis, polycythemia, and progressive disease. Large retrospective comparative analyses have shown no increase in mortality in erythropoietin (EPO)-treated MDS patients. Doses of up to 80,000 IU/wk have successfully been employed and the addition of granulocyte colony-stimulating factor (G-CSF) can benefit previously unresponsive patients. Although several other combination therapies have been tested, apart from G-CSF, none has gained wide clinical acceptance. Thrombopoietic agents can alleviate thrombocytopenia and bleeding symptoms in lower risk MDS patients. However, concerns regarding a higher rate of transformation to acute myeloid leukemia and the fear of increased bone marrow fibrosis during treatment have hampered their clinical development.

Effect of DLK1 on tumorigenesis in CD34+CD38- bone marrow cells in myelodysplastic syndromes

The myelodysplastic syndromes (MDSs) are a group of clonal stem cell disorders resulting from aberrations within hematopoietic stem cells (HSCs), which may lead to the onset of a number of diseases, including acute myeloid leukemia (AML). Recent studies have demonstrated that the expression levels of the DLK1 gene are increased in MDS. In order to determine whether the addition of DLK1 affects tumorigenesis, small interfering (si)RNAs were designed to target DLK1 in order to knockdown its expression in CD34⁺CD38⁻ bone marrow cells in MDS. A lower proliferative rate was observed in the CD34⁺CD38⁻ bone marrow cells following this knockdown of DLK1 expression. The suppression of DLK1 expression resulted in a less aggressive MDS phenotype, which suggests that the upregulation of DLK1 expression may play an oncogenic role in CD34+CD38⁻ bone marrow cells.

Transfemoral balloon expandable aortic valve implantation in a patient with myelodysplastic syndrome

In this case presentation, the transcatheter aortic valve implantation (TAVI) intervention successfully performed on a 76-year-old male patient with severe degenerative aortic stenosis and diagnosed with myelodysplastic syndrome (MDS) is discussed. This case presentation represents the first case on the treatment of severe aortic stenosis on a patient with myelodysplastic syndrome through the use of the TAVI method and may form an alternative to surgery in patients with severe aortic stenosis who have a known haematological disease. For a successful procedure, the patient must be evaluated in cooperation with the haematology clinic and all necessary precautions regarding bleeding and infection complications of the patient must be taken prior to the procedure.

Smap1 deficiency perturbs receptor trafficking and predisposes mice to myelodysplasia

The formation of clathrin-coated vesicles is essential for intracellular membrane trafficking between subcellular compartments and is triggered by the ARF family of small GTPases. We previously identified SMAP1 as an ARF6 GTPase-activating protein that functions in clathrin-dependent endocytosis. Because abnormalities in clathrin-dependent trafficking are often associated with oncogenesis, we targeted Smap1 in mice to examine its physiological and pathological significance. Smap1-deficent mice exhibited healthy growth, but their erythroblasts showed enhanced transferrin endocytosis. In mast cells cultured in SCF, Smap1 deficiency did not affect the internalization of c-KIT but impaired the sorting of internalized c-KIT from multivesicular bodies to lysosomes, resulting in intracellular accumulation of undegraded c-KIT that was accompanied by enhanced activation of ERK and increased cell growth. Interestingly, approximately 50% of aged Smap1-deficient mice developed anemia associated with morphologically dysplastic cells of erythroid-myeloid lineage, which are hematological abnormalities similar to myelodysplastic syndrome (MDS) in humans. Furthermore, some Smap1-deficient mice developed acute myeloid leukemia (AML) of various subtypes. Collectively, to our knowledge these results provide the first evidence in a mouse model that the deregulation of clathrin-dependent membrane trafficking may be involved in the development of MDS and subsequent AML.

Development of a high-resolution melting analysis for the detection of the SF3B1 mutations

SF3B1, located on chromosome 2q33.1, encodes a core component of RNA-splicing machinery, and its mutation has been described in myelodysplastic syndromes (MDS) characterized with ring sideroblasts (RS). To explore the reliability and sensitivity of the high-resolution melting analysis (HRMA) technique for the identification of the SF3B1 mutations, mutations in 92 patients with MDS were detected in this study. The sensitivity could reach 5%, obviously higher than the 25% of direct DNA sequencing. A low frequency (5.4%) of SF3B1 mutations were identified in patients with MDS, including three cases of K700E, one case of H662Q, and one case of K666M. Further, SF3B1 mutations were more frequently recurrent in the 33% of patients with MDS characterized with RS, whereas in other subtypes of MDS, only 2.3% of patients were detected with SF3B1 mutations (p=0.006). In conclusion, a rapid, reproducible, sensitive, and high-throughput HRMA assay has been established for the scanning of SF3B1 mutations.

Aberration of p73 promoter methylation in de novo myelodysplastic syndrome

p73, a tumor suppressor gene with significant homology to p53, is hypermethylated in a high percentage of NK-cell lymphoma and B-cell lymphomas patients. Given these data, we sought to study the role of p73 methylation in the pathogenesis of myelodysplastic syndromes (MDS). In this study, the methylation status of the p73 gene promoter was analyzed by methylation-specific polymerase chain reaction (MS-PCR) in bone marrow (BM) samples from 135 adult patients with de novo MDS. The results of MS-PCR were confirmed by bisulfite sequencing. We found that p73 methylation was present in 37% (n = 50) of these cases and methylaiton was correlated significantly with World Health Organization (WHO) subtypes. Patients with advanced stages of WHO subtypes (30 vs. 59%, P = 0.002) exhibited a significantly higher frequency of p73 methylation. Moreover, a decrease in transcription of p73 was accompanied by methylation (P = 0.032) and the decitabine treatment restored the expression of p73. The median survival of patients with p73 methylation was shorter than that for patients without p73 methylation (15 vs. >33 months, P = 0.002). A multivariate analysis also indicated that the p73 methylation status was the independent factor that impacted overall survival (OS) and leukemia-free survival (LFS). However, we failed to find any significant association between p73 methylation and clinical responses to decitabine, a hypomethylating agent that was approved by the US Food and Drug Administration for the treatment of patients with MDS. In conclusion, p73 methylation is common in patients with MDS and indicate poor prognosis. p73 may be a therapeutic target in MDS.

MASL1 induces erythroid differentiation in human erythropoietin-dependent CD34+ cells through the Raf/MEK/ERK pathway

Human erythropoiesis is a dynamic and complex multistep process involving differentiation of early erythroid progenitors into enucleated RBCs. The mechanisms underlying erythropoiesis still remain incompletely understood. We previously demonstrated that erythropoietin-stimulated clone-1, which is selectively expressed in normal human erythroid-lineage cells, shares 99.5% identity with malignant fibrous histiocytoma-amplified sequences with leucine-rich tandem repeats 1 (MASL1). In this study, we hypothesized that the MASL1 gene plays a role in erythroid differentiation, and used a human erythroid cell culture system to explore this concept. MASL1 mRNA and protein expression levels were significantly increased during the erythroid differentiation of CD34(+) cells following erythropoietin (EPO) treatment. Conversely, MASL1 knockdown reduced erythroid differentiation in EPO-treated CD34(+) cells. In addition, MASL1 knockdown interrupted the Raf/MEK/ERK signaling pathway in CD34(+) cells. MASL1 mutant-transfected CD34(+) cells also showed decreased erythroid differentiation. Furthermore, inhibition of the SH3 domain of Son of Sevenless, which is an upstream adapter protein in EPO-induced erythroid differentiation, also reduced MASL1 expression and phosphorylation of Raf/MEK/ERK kinases that consequently reduced erythroid differentiation of EPO-induced CD34(+) cells. Importantly, we also demonstrated that MASL1 interacts physically with Raf1. Taken together, our data provide novel insights into MASL1 regulation of erythropoiesis through the Raf/MEK/ERK pathway.

Spliceosome mutations exhibit specific associations with epigenetic modifiers and proto-oncogenes mutated in myelodysplastic syndrome

The recent identification of acquired mutations in key components of the spliceosome machinery strongly implicates abnormalities of mRNA splicing in the pathogenesis of myelodysplastic syndromes. However, questions remain as to how these aberrations functionally combine with the growing list of mutations in genes involved in epigenetic modification and cell signaling/transcription regulation identified in these diseases. In this study, amplicon sequencing was used to perform a mutation screen in 154 myelodysplastic syndrome patients using a 22-gene panel, including commonly mutated spliceosome components (SF3B1, SRSF2, U2AF1, ZRSR2), and a further 18 genes known to be mutated in myeloid cancers. Sequencing of the 22-gene panel revealed that 76% (n=117) of the patients had mutations in at least one of the genes, with 38% (n=59) having splicing gene mutations and 49% (n=75) patients harboring more than one gene mutation. Interestingly, single and specific epigenetic modifier mutations tended to coexist with SF3B1 and SRSF2 mutations (P<0.03). Furthermore, mutations in SF3B1 and SRSF2 were mutually exclusive to TP53 mutations both at diagnosis and at the time of disease transformation. Moreover, mutations in FLT3, NRAS, RUNX1, CCBL and C-KIT were more likely to co-occur with splicing factor mutations generally (P<0.02), and SRSF2 mutants in particular (P<0.003) and were significantly associated with disease transformation (P<0.02). SF3B1 and TP53 mutations had varying impacts on overall survival with hazard ratios of 0.2 (P<0.03, 95% CI, 0.1-0.8) and 2.1 (P<0.04, 95% CI, 1.1-4.4), respectively. Moreover, patients with splicing factor mutations alone had a better overall survival than those with epigenetic modifier mutations, or cell signaling/transcription regulator mutations with and without coexisting mutations of splicing factor genes, with worsening prognosis (P<0.001). These findings suggest that splicing factor mutations are maintained throughout disease evolution with emerging oncogenic mutations adversely affecting patients' outcome, implicating spliceosome mutations as founder mutations in myelodysplastic syndromes.

Next-generation sequencing - feasibility and practicality in haematology

Next-generation sequencing platforms have evolved to provide an accurate and comprehensive means for the detection of molecular mutations in heterogeneous tumour specimens. Here, we review the feasibility and practicality of this novel laboratory technology. In particular, we focus on the utility of next-generation sequencing technology in characterizing haematological neoplasms and the landmark findings in key haematological malignancies. We also discuss deep-sequencing strategies to analyse the constantly increasing number of molecular markers applied for disease classification, patient stratification and individualized monitoring of minimal residual disease. Although many facets of this assay need to be taken into account, amplicon deep-sequencing has already demonstrated a promising technical performance and is being continuously developed towards routine application in diagnostic laboratories so that an impact on clinical practice can be achieved.

Radiation-induced bone marrow apoptosis, inflammatory bystander-type signaling and tissue cytotoxicity

PURPOSE

A study of irradiated (0.25-2 Gy) murine bone marrow has investigated the relationships between apoptotic responses of cells exposed in vivo and in vitro and between in vivo apoptosis and tissue cytotoxicity.

MATERIALS AND METHODS

The time course of reduction in bone marrow cellularity in vivo was determined by femoral cell counts and apoptosis measurements obtained using three commonly used assays. Inflammatory pro-apoptotic cytokine production at 24 h post-exposure in vivo was investigated using a bystander protocol.

RESULTS

In vivo, there is a dose- and time-dependent non-linear reduction in bone marrow cellularity up to 24 h post- irradiation not directly represented by apoptosis measurements. The majority of cells are killed within 6 h but there is on-going cell loss in vivo up to 24 h post-irradiation in the absence of elevated levels of apoptosis and associated with the induction of cytokines produced in response to the initial tumor protein 53 (p53)-dependent apoptosis.

CONCLUSION

The results demonstrate that small increases in measured apoptosis can reflect significant intramedullary cell death and with apoptotic processes being responsible for pro-inflammatory mechanisms that can contribute to additional on-going cell death. The findings demonstrate the importance of studying tissue responses when considering the mechanisms underlying the consequences of radiation exposures.

Oxidases and reactive oxygen species during hematopoiesis: a focus on megakaryocytes

Reactive oxygen species (ROS), generated as a result of various reactions, control an array of cellular processes. The role of ROS during megakaryocyte (MK) development has been a subject of interest and research. The bone marrow niche is a site of MK differentiation and maturation. In this environment, a gradient of oxygen tension, from normoxia to hypoxia results in different levels of ROS, impacting cellular physiology. This article provides an overview of major sources of ROS, their implication in different signaling pathways, and their effect on cellular physiology, with a focus on megakaryopoiesis. The importance of ROS-generating oxidases in MK biology and pathology, including myelofibrosis, is also described.

Myelodysplastic syndrome hematopoietic stem cell

Myelodysplastic syndromes (MDSs) are clonal hematopoietic stem cell (HSC) malignancies that are characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia (AML). Thus far, few treatments can actually alter the natural history of this disease. Allogeneic stem-cell transplantation for high-risk MDS is becoming the only curative therapy probably because of the improvement of bone marrow transplant procedures. The lack of other options underscores the urgent need to develop new therapy. The prevailing model suggests that genetic and/or epigenetic alterations that occur in HSCs or HSC niche compromise HSC function, resulting in MDS; therefore, MDS HSCs are likely the ideal targets for MDS treatment. Recent encouraging advances--capturing a molecular portrait of the whole genome of MDS CD34(+) cells, including identifying altered signaling pathways and altered microRNAs--have improved our understanding of MDS pathogenesis and provided novel potential clinical targets for MDS. Here, I will briefly review the characteristics of MDS HSCs and discuss the therapeutic promise of targeting MDS HSCs.

Stromal SPARC contributes to the detrimental fibrotic changes associated with myeloproliferation whereas its deficiency favors myeloid cell expansion

In myeloid malignancies, the neoplastic clone outgrows normal hematopoietic cells toward BM failure. This event is also sustained by detrimental stromal changes, such as BM fibrosis and osteosclerosis, whose occurrence is harbinger of a dismal prognosis. We show that the matricellular protein SPARC contributes to the BM stromal response to myeloproliferation. The degree of SPARC expression in BM stromal elements, including CD146+ mesenchymal stromal cells, correlates with the degree of stromal changes, and the severity of BM failure characterizing the prototypical myeloproliferative neoplasm primary myelofibrosis. Using Sparc−/− mice and BM chimeras, we demonstrate that SPARC contributes to the development of significant stromal fibrosis in a model of thrombopoietin-induced myelofibrosis. We found that SPARC deficiency in the radioresistant BM stroma compartment impairs myelofibrosis but, at the same time, associates with an enhanced reactive myeloproliferative response to thrombopoietin. The link betwen SPARC stromal deficiency and enhanced myeloid cell expansion under a myeloproliferative spur is also supported by the myeloproliferative phenotype resulting from the transplantation of defective Apcmin mutant hematopoietic cells into Sparc−/− but not WT recipient BM stroma. Our results highlight a complex influence of SPARC over the stromal and hematopoietic BM response in myeloproliferative conditions.

Splicing factor mutations in myelodysplasia

Myelodysplastic syndromes (MDS) and related myeloid neoplasms are a heterogeneous group of myeloid neoplasms, which frequently terminate in acute myeloid leukemia (AML). During the past decade, a number of gene mutations have been identified in MDS. However, the spectrum of these mutations overlaps largely with that in AML, complicating the understanding of MDS-specific pathogenesis that discriminates MDS from AML. Recently, several groups reported frequent mutations of multiple components of the RNA splicing machinery in MDS and related disorders. Largely specific to myelodysplastic phenotypes, these splicing factor mutations provide a potential clue to better understanding of the pathogenesis of MDS.