Focal adhesion protein abnormalities in myelodysplastic mesenchymal stromal cells

The mesenchymal compartment in myelodysplastic syndrome: Its role in the pathogenesis of the disorder and its therapeutic targeting

Myelodysplastic syndromes include a broad spectrum of malignant myeloid disorders that are characterized by dysplastic ineffective hematopoiesis, reduced peripheral blood cells counts and a high risk of progression to acute myeloid leukemia. The disease arises primarily because of accumulating chromosomal, genetic and epigenetic changes as well as immune-mediated alterations of the hematopoietic stem cells (HSCs). However, mounting evidence suggests that aberrations within the bone marrow microenvironment critically contribute to myelodysplastic syndrome (MDS) initiation and evolution by providing permissive cues that enable the abnormal HSCs to grow and eventually establish and propagate the disease. Mesenchymal stromal cells (MSCs) are crucial elements of the bone marrow microenvironment that play a key role in the regulation of HSCs by providing appropriate signals via soluble factors and cell contact interactions. Given their hematopoiesis supporting capacity, it has been reasonable to investigate MSCs' potential involvement in MDS. This review discusses this issue by summarizing existing findings obtained by in vitro studies and murine disease models of MDS. Furthermore, the theoretical background of targeting the BM-MSCs in MDS is outlined and available therapeutic modalities are described.

Impairment of FOXM1 expression in mesenchymal cells from patients with myeloid neoplasms, de novo and therapy-related, may compromise their ability to support hematopoiesis

Bone marrow mesenchymal stem cells (BM-MSCs) exhibit multiple abnormalities in myelodysplastic syndromes (MDS) and acute myeloid leukemias (AML), including reduced proliferative and clonogenic capacity, altered morphology, impaired immunoregulatory properties and capacity to support hematopoiesis. Here, we investigated expression of the FOXM1 gene, a transcription factor driving G2/M gene expression, in BM-MSCs isolated from patients with MDS and AML, de novo and therapy-related, compared to BM-MSCs isolated from healthy donors (HD). We observed a statistically significant downregulation of FOXM1 expression in BM-MSCs isolated from MDS and AML patients, as compared to controls. In parallel, expression of FOXM1 mitotic targets (CCNB1, CDC20, PLK1 and NDC80) was suppressed in patients' BM-MSCs, as compared to HD. No differences in the expression of FOXM1 and its mitotic targets were observed in BM-mononuclear cells from the different sources. From a functional standpoint, silencing of FOXM1 mRNA in healthy MSC induced a significant decrease in the expression of its targets. In this line, healthy MSC silenced for FOXM1 showed an impaired ability to support hematopoiesis in vitro. These findings suggest that deregulation of FOXM1 may be involved in the senescent phenotype observed in MSC derived from myeloid neoplasms.

Nature or Nurture? Role of the Bone Marrow Microenvironment in the Genesis and Maintenance of Myelodysplastic Syndromes

Myelodysplastic syndrome (MDS) are clonal haematopoietic stem cell (HSC) disorders driven by a complex combination(s) of changes within the genome that result in heterogeneity in both clinical phenotype and disease outcomes. MDS is among the most common of the haematological cancers and its incidence markedly increases with age. Currently available treatments have limited success, with <5% of patients undergoing allogeneic HSC transplantation, a procedure that offers the only possible cure. Critical contributions of the bone marrow microenvironment to the MDS have recently been investigated. Although the better understanding of the underlying biology, particularly genetics of haematopoietic stem cells, has led to better disease and risk classification; however, the role that the bone marrow microenvironment plays in the development of MDS remains largely unclear. This review provides a comprehensive overview of the latest developments in understanding the aetiology of MDS, particularly focussing on understanding how HSCs and the surrounding immune/non-immune bone marrow niche interacts together.

The functional interplay of transcription factors and cell adhesion molecules in experimental myelodysplasia including hematopoietic stem progenitor compartment

Myelodysplastic syndrome is a heterogenous group of disorder with clonal dysregulated hematopoiesis characterized by bone marrow failure, cytogenetic and molecular abnormalities and variable risk of progression to acute myeloid leukemia (AML). The bone marrow niche plays a major role in maintaining the homeostasis and is often injured by the chemotherapeutic drugs leading to catastrophic consequences like myelodysplastic syndrome. In the present study, we made an attempt to find out the osteoblastic niche related alterations in the myelodysplastic bone marrow through mainly flowcytometric and fluorescent microscopic studies. We have also checked the condition of the myelodysplastic bone through micro computed tomography. The results revealed that the affected osteoblasts of the myelodysplastic bone marrow compelled the hematopoietic stem cell to come out of quiescence and become actively proliferating, and in this scenario the decline in expression of cell adhesion molecules like N-Cadherin, Intercellular adhesion molecule 1 (ICAM) and upregulated focal adhesion kinase (FAK) played a major role. The hike in number of osteoclasts in myelodysplastic cases than control also shattered the balance between bone formation and resorption ratio. We have recorded a dysregulated expression of transcription factors GATA2 and CEBPα (CCAAT-enhancer-binding-protein) in the hematopoietic stem progenitor compartment of the myelodysplastic bone marrow, the main reason behind the presence of abnormal myeloblasts in myelodysplastic cases. Collectively, we can say the coordinated perturbations in the osteoblastic niche, cell adhesion molecules together with the transcription factors has resulted in the uncontrolled proliferation of hematopoietic stem cell, dysregulated myelopoiesis, early trafficking of hematopoietic progenitors to blood compartment and at the same time pancytopenic peripheral blood conditions during the progression of N-Ethyl N Nitroso Urea (ENU) induced myelodysplasia.

Menatetrenone facilitates hematopoietic cell generation in a manner that is dependent on human bone marrow mesenchymal stromal/stem cells

Vitamin K2 in the form of menatetrenone has clinical benefits for osteoporosis and cytopenia. Given the dominant role of mesenchymal-osteolineage cells in the regulation of hematopoiesis, we investigated whether menatetrenone alters the hematopoiesis-supportive capability of human bone marrow mesenchymal stromal/stem cells (BM-MSCs). Menatetrenone up-regulated fibronectin protein expression in BM-MSCs without affecting their proliferation and differentiation capabilities. In addition, menatetrenone treatment of BM-MSCs enhanced generation of the CD34⁺ cell population in co-cultures through acceleration of the cell cycle. This effect was associated with cell-cell interactions mediated by VLA-4 and fibronectin. This proposal was supported by cytokine array and quantitative real-time PCR analyses, in which there were no significant differences between the expression levels of hematopoiesis-associated soluble factors in naïve and menatetrenone-treated BM-MSCs. Profiling of hematopoietic cells in co-cultures with menatetrenone-treated BM-MSCs demonstrated that they included significantly more CD34⁺CD38⁺ hematopoietic progenitor cells and cells skewed toward myeloid and megakaryocytic lineages than those in co-cultures with untreated BM-MSCs. Notably, myelodysplastic syndrome-derived cells were induced to undergo apoptosis when co-cultured with BM-MSCs, and this effect was enhanced by menatetrenone. Overall, our findings indicate that pharmacological treatment with menatetrenone bestows a unique hematopoiesis-supportive capability on BM-MSCs, which may contribute to the clinical improvement of cytopenia.

Evaluation of bone marrow microenvironment could change how myelodysplastic syndromes are diagnosed and treated

Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic disorders. However, the therapies used against the hematopoietic stem cells clones have limited efficacy; they slow the evolution toward acute myeloid leukemia rather than stop clonal evolution and eradicate the disease. The progress made in recent years regarding the role of the bone marrow microenvironment in disease evolution may contribute to progress in this area. This review presents the recent updates on the role of the bone marrow microenvironment in myelodysplastic syndromes pathogenesis and tries to find answers regarding how this information could improve myelodysplastic syndromes diagnosis and therapy.

The bone-marrow niche in MDS and MGUS: implications for AML and MM

Several haematological malignancies, including multiple myeloma (MM) and acute myeloid leukaemia (AML), have well-defined precursor states that precede the development of overt cancer. MM is almost always preceded by monoclonal gammopathy of undetermined significance (MGUS), and at least a quarter of all patients with myelodysplastic syndromes (MDS) have disease that evolves into AML. In turn, MDS are frequently anteceded by clonal haematopoiesis of indeterminate potential (CHIP). The acquisition of additional genetic and epigenetic alterations over time clearly influences the increasingly unstable and aggressive behaviour of neoplastic haematopoietic clones; however, perturbations in the bone-marrow microenvironment are increasingly recognized to have key roles in initiating and supporting oncogenesis. In this Review, we focus on the concept that the haematopoietic neoplasia-microenvironment relationship is an intimate rapport between two partners, provide an overview of the evidence supporting a role for the bone-marrow niche in promoting neoplasia, and discuss the potential for niche-specific therapeutic targets.

DICER1 gene and miRNA dysregulation in mesenchymal stem cells of patients with myelodysplastic syndrome and acute myeloblastic leukemia

Multipotent mesenchymal stem cells (MSC) are key components of the bone marrow (BM) microenvironment. The contribution of this microenvironment to the pathophysiology of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) is not well defined. A recent study in mice demonstrated that DICER1 gene deletion in osteoprogenitor cells from the BM microenvironment suppressed osteogenic differentiation and induced MDS and AML-like haematological findings. The present study evaluated the expression profiles of microRNAs (miRNAs) and DICER1 gene in BM-derived MSC of patients with AML (n=12), MDS (n=10) and healthy controls (HC) (n=8).miRNA expression profiles were analyzed by microarray and confirmations were performed using quantitative real-time PCR (qRT-PCR). Patient MSC displayed impaired proliferative and differentiation potential compared to HC. DICER1 gene expression was lower in MSC from MDS and AML patients than HC and some differentially expressed miRNAs indicated the potential involvement of DICER1 in the pathogenesis of MDS and AML. qRT-PCR confirmation revealed down-regulated miRNAs (hsa-miR-30d-5p, hsa-miR-222-3p and hsa-miR-30a-3p in MDS; hsa-miR-1275, hsa-miR-4725-5p and hsa-miR-143-3p in AML) and over-expressed miRNAs (hsa-miR-4462 in MDS; hsa-miR-134-5p and hsa-miR-874-3p in AML) in MDS and AML. Thus, our findings validate the results of the aforementioned animal study and demonstrate downregulation of DICER1 gene and abnormal miRNA profile in MDS and AML, which may have implications for understanding MDS and AML pathogenesis and contribute to developing targeted treatment strategies.

Mesenchymal Stem Cells in Myeloid Malignancies: A Focus on Immune Escaping and Therapeutic Implications

The importance of the bone marrow microenvironment forming the so-called niche in physiologic hemopoiesis is largely known, and recent evidences support the presence of stromal alterations from the molecular to the cytoarchitectural level in hematologic malignancies. Various alterations in cell adhesion, metabolism, cytokine signaling, autophagy, and methylation patterns of tumor-derived mesenchymal stem cells have been demonstrated, contributing to the genesis of a leukemic permissive niche. This niche allows both the ineffective haematopoiesis typical of myelodysplastic syndromes and the differentiation arrest, proliferation advantage, and clone selection which is the hallmark of acute myeloid leukemia. Furthermore, the immune system, both adaptive and innate, encompassing mesenchymal-derived cells, has been shown to take part to the leukemic niche. Here, we critically review the state of art about mesenchymal stem cell role in myelodysplastic syndromes and acute myeloid leukemia, focusing on immune escaping mechanisms as a target for available and future anticancer therapies.

Impaired Expression of Focal Adhesion Kinase in Mesenchymal Stromal Cells from Low-Risk Myelodysplastic Syndrome Patients

The pathogenic role of mesenchymal stromal cells (MSCs) in myelodysplastic syndromes (MDS) development and progression has been investigated by numerous studies, yet, it remains controversial in some aspects (1, 2). In the present study, we found distinct features of MSCs from low-risk (LR)-MDS stromal microenvironment as compared to those from healthy subjects. At the molecular level, focal adhesion kinase, a key tyrosine kinase in control of cell proliferation, survival, and adhesion process, was found profoundly suppressed in expression and activation in LR-MDS MSC. At a functional level, LR-MDS MSCs showed impaired growth and clonogenic capacity, which were independent of cellular senescence and apoptosis. The pro-adipogenic differentiation and attenuated osteogenic capacity along with reduced SDF-1 expression could be involved in creating an unfavorable microenvironment for hematopoiesis. In conclusion, our experiments support the theory that the stromal microenvironment is fundamentally altered in LR-MDS, and these preliminary data offer a new perspective on LR-MDS pathophysiology.

Downregulation of MMP1 in MDS-derived mesenchymal stromal cells reduces the capacity to restrict MDS cell proliferation

The role of mesenchymal stromal cells (MSCs) in the pathogenesis of myelodysplastic syndromes (MDS) has been increasingly addressed, but has yet to be clearly elucidated. In this investigation, we found that MDS cells proliferated to a greater extent on MDS-derived MSCs compared to normal MSCs. Matrix metalloproteinase 1(MMP1), which was downregulated in MDS-MSCs, was identified as an inhibitory factor of MDS cell proliferation, given that treatment with an MMP1 inhibitor or knock-down of MMP1 in normal MSCs resulted in increased MDS cell proliferation. Further investigations indicated that MMP1 induced apoptosis of MDS cells by interacting with PAR1 and further activating the p38 MAPK pathway. Inhibition of either PAR1 or p38 MAPK can reverse the apoptosis-inducing effect of MMP1. Taken together, these data indicate that downregulation of MMP1 in MSCs of MDS patients may contribute to the reduced capacity of MSCs to restrict MDS cell proliferation, which may account for the malignant proliferation of MDS cells.

Mesenchymal stromal cells in myeloid malignancies

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are clonal myeloid disorders characterized by hematopoietic insufficiency. As MDS and AML are considered to originate from genetic and molecular defects of hematopoietic stem and progenitor cells (HSPC), the main focus of research in this field has focused on the characterization of these cells. Recently, the contribution of BM microenvironment to the pathogenesis of myeloid malignancies, in particular MDS and AML has gained more interest. This is based on a better understanding of its physiological role in the regulation of hematopoiesis. Additionally, it was demonstrated as a ‘proof of principle’ that genetic disruption of cells of the mesenchymal or osteoblastic lineage can induce MDS, MPS or AML in mice. In this review, we summarize the current knowledge about the contribution of the BM microenvironment, in particular mesenchymal stromal cells (MSC) to the pathogenesis of AML and MDS. Furthermore, potential models integrating the BM microenvironment into the pathophysiology of these myeloid disorders are discussed. Finally, strategies to therapeutically exploit this knowledge and to interfere with the crosstalk between clonal hematopoietic cells and altered stem cell niches are introduced.

Bone Marrow Immunity and Myelodysplasia

Myelodysplastic syndrome (MDS) is characterized by an ineffective hematopoiesis with production of aberrant clones and a high cell apoptosis rate in bone marrow (BM). Macrophages are in charge of phagocytosis. Innate Immune cells and specific T cells are in charge of immunosurveillance. Little is known on BM cell recruitment and activity as BM aspirate is frequently contaminated with peripheral blood. But evidences suggest an active role of immune cells in protection against MDS and secondary leukemia. BM CD8⁺ CD28⁻ CD57⁺ T cells are directly cytotoxic and have a distinct cytokine signature in MDS, producing TNF-α, IL-6, CCL3, CCL4, IL-1RA, TNFα, FAS-L, TRAIL, and so on. These tools promote apoptosis of aberrant cells. On the other hand, they also increase MDS-related cytopenia and myelofibrosis together with TGFβ. IL-32 produced by stromal cells amplifies NK cytotoxicity but also the vicious circle of TNFα production. Myeloid-derived suppressing cells (MDSC) are increased in MDS and have ambiguous role in protection/progression of the diseases. CD33 is expressed on hematopoietic stem cells on MDS and might be a potential target for biotherapy. MDS also has impact on immunity and can favor chronic inflammation and emergence of autoimmune disorders. BM is the site of hematopoiesis and thus contains a complex population of cells at different stages of differentiation from stem cells and early engaged precursors up to almost mature cells of each lineage including erythrocytes, megakaryocytes, myelo-monocytic cells (monocyte/macrophage and granulocytes), NK cells, and B cells. Monocytes and B cell finalize their maturation in peripheral tissues or lymph nodes after migration through the blood. On the other hand, T cells develop in thymus and are present in BM only as mature cells, just like other well vascularized tissues. BM precursors have a strong proliferative capacity, which is usually associated with a high risk for genetic errors, cell dysfunction, and consequent cell death. Abnormal cells are prone to destruction through spontaneous apoptosis or because of the immunosurveillance that needs to stay highly vigilant. High rates of proliferation or differentiation failures lead to a high rate of cell death and massive release of debris to be captured and destroyed (1). Numerous macrophages reside in BM in charge of home-keeping. They have a high capacity of phagocytosis required for clearing all these debris.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Mesenchymal stromal cell density is increased in higher grade myelodysplastic syndromes and independently predicts survival

OBJECTIVES

We retrospectively tested the prognostic and diagnostic significance of CD271+ mesenchymal stromal cell (MSC) density in cytopenic patients who underwent bone marrow biopsy to evaluate for myelodysplastic syndromes (MDS).

METHODS

CD271+ MSC density was quantitated by automated image analysis of tissue microarray cores in 125 cytopenic patients: 40 lower grade MDS (<5% marrow blasts), 24 higher grade MDS, and 61 benign.

RESULTS

CD271+ MSC density was increased in higher grade MDS compared with benign (P = .006) and lower grade MDS (P = .02). CD271+ MSC density was predictive of survival among patients with MDS independent of Revised International Prognostic Scoring System (IPSS-R), history of transfusion, therapy-related MDS, and fibrosis (hazard ratio, 3.4; P < .001). Among low or intermediate IPSS-R patients, median survival was significantly shorter in the high CD271+ MSC density group (47 vs 18 months, P < .02).

CONCLUSIONS

High CD271+ MSC density is characteristic of higher grade MDS and is associated with poor risk independent of known prognostic factors.

Down-regulation of Dicer1 promotes cellular senescence and decreases the differentiation and stem cell-supporting capacities of mesenchymal stromal cells in patients with myelodysplastic syndrome

Although it has been reported that mesenchymal stromal cells are unable to provide sufficient hematopoietic support in myelodysplastic syndrome, the underlying mechanisms remain elusive. In this study, we found that mesenchymal stromal cells from patients with myelodysplastic syndrome displayed a significant increase in senescence, as evidenced by their decreased proliferative capacity, flattened morphology and increased expression of SA-β-gal and p21. Senescent mesenchymal stromal cells from patients had decreased differentiation potential and decreased stem cell support capacity. Gene knockdown of Dicer1, which was down-regulated in mesenchymal stromal cells from patients, induced senescence. The differentiation and stem cell-supporting capacities were significantly inhibited by Dicer1 knockdown. Overexpression of Dicer1 in mesenchymal stromal cells from patients reversed cellular senescence and enhanced stem cell properties. Furthermore, we identified reduced expression in the microRNA-17 family (miR-17-5p, miR-20a/b, miR-106a/b and miR-93) as a potential factor responsible for increased p21 expression, a key senescence mediator, in Dicer1 knockdown cells. Moreover, we found that miR-93 and miR-20a expression levels were significantly reduced in mesenchymal stromal cells from patients and miR-93/miR-20a gain of function resulted in a decrease of cellular senescence. Collectively, the results of our study show that mesenchymal stromal cells from patients with myelodysplastic syndrome are prone to senescence and that Dicer1 down-regulation promotes cellular senescence and decreases the differentiation and stem cell-supporting capacities of mesenchymal stromal cells. Dicer1 down-regulation seems to contribute to the insufficient hematopoietic support capacities of mesenchymal stromal cells from patients with myelodysplastic syndrome.

Serine protease inhibitor kunitz-type 2 is downregulated in myelodysplastic syndromes and modulates cell-cell adhesion

Myelodysplastic syndromes (MDS) are clonal disorders involving hematopoietic stem cells (HSC) characterized by ineffective hematopoiesis. In addition to HSC defects, a defective hematopoiesis supporting capacity of mesenchymal stromal cells (MSCs) in the microenvironment niche has been implicated in MDS pathophysiology. The interaction between the dysfunctional MSCs MDS and HSC regulates diverse adhesion-related processes, such as progenitor cell survival, proliferation, differentiation, and self-renewal. As previously reported, a microarray analysis identified serine protease inhibitor kunitz-type 2 (SPINT2), an inhibitor of hepatocyte growth factor (HGF) activation, to be downregulated in MSCs from MDS patients. To define the role of SPINT2 in MDS hematopoietic microenvironment, an analysis of the effect of SPINT2 silencing in MSCs was carried out. We herein reported significantly lower levels of SPINT2 whereas HGF was expressed at higher levels in MSCs from MDS patients compared with healthy controls. SPINT2 underexpression results in an increased expression, production, and secretion of HGF and stromal cell-derived factor 1 (SDF-1) by MSCs. An increased adhesion of normal HSC or malignant cells onto MSCs silenced for SPINT2 was also observed. The altered MSCs adhesion in SPINT2-knockdown cells was correlated with increased CD49b and CD49d expression and with a decrease in CD49e expression. Our results suggest that the SPINT2 underexpression in the MSC from MDS patients is probably involved in the adhesion of progenitors to the bone marrow niche, through an increased HGF and SDF-1 signaling pathway.

Mesenchymal stem cells in immune-mediated bone marrow failure syndromes

Immune-mediated bone marrow failure syndromes (BMFS) are characterized by ineffective marrow haemopoiesis and subsequent peripheral cytopenias. Ineffective haemopoiesis is the result of a complex marrow deregulation including genetic, epigenetic, and immune-mediated alterations in haemopoietic stem/progenitor cells, as well as abnormal haemopoietic-to-stromal cell interactions, with abnormal release of haemopoietic growth factors, chemokines, and inhibitors. Mesenchymal stem/stromal cells (MSCs) and their progeny (i.e., osteoblasts, adipocytes, and reticular cells) are considered as key cellular components of the bone marrow haemopoietic niche. MSCs may interfere with haemopoietic as well as immune regulation. Evidence suggests that bone marrow MSCs may be involved in immune-mediated BMFS underlying pathophysiology, harboring either native abnormalities and/or secondary defects, caused by exposure to activated marrow components. This review summarizes previous as well as more recent information related to the biologic/functional characteristics of bone marrow MSCs in myelodysplastic syndromes, acquired aplastic anemia, and chronic idiopathic neutropenia.

PTK2 and PTPN11 expression in myelodysplastic syndromes

OBJECTIVE

The aim of this study was to evaluate the expression of protein tyrosine kinase 2 and protein tyrosine phosphatase non-receptor type 11, which respectively encode focal adhesion kinase protein and src homology 2 domain-containing protein-tyrosine phosphatase 2, in hematopoietic cells from patients with myelodysplastic syndromes.

METHODS

Protein tyrosine kinase 2 and tyrosine phosphatase non-receptor type 11 expressions were analyzed by quantitative polymerase chain reaction in bone marrow cells from patients with myelodysplastic syndromes and healthy donors.

RESULTS

Protein tyrosine kinase 2 and tyrosine phosphatase non-receptor type 11 expressions did not significantly differ between normal cells and myelodysplastic cells.

CONCLUSIONS

Our data suggest that despite the relevance of focal adhesion kinase and src homology 2 domain-containing protein-tyrosine phosphatase 2 in hematopoietic disorders, their mRNA expression do not significantly differ between total bone marrow cells from patients with myelodysplastic syndromes and healthy donors.

Mesenchymal stromal cells from patients with myelodyplastic syndrome display distinct functional alterations that are modulated by lenalidomide

The contribution of the bone marrow microenvironment in myelodysplastic syndrome is controversial. We therefore analyzed the functional properties of primary mesenchymal stromal cells from patients with myelodysplastic syndrome in the presence or absence of lenalidomide. Compared to healthy controls, clonality and growth were reduced across all disease stages. Furthermore, differentiation defects and particular expression of adhesion and cell surface molecules (e.g. CD166, CD29, CD146) were detected. Interestingly, the levels of stromal derived factor 1-alpha in patients' cells culture supernatants were almost 2-fold lower (P<0.01) than those in controls and this was paralleled by a reduced induction of migration of CD34(+) hematopoietic cells. Co-cultures of mesenchymal stromal cells from patients with CD34(+) cells from healthy donors resulted in reduced numbers of cobblestone area-forming cells and fewer colony-forming units. Exposure of stromal cells from patients and controls to lenalidomide led to a further reduction of stromal derived factor 1-alpha secretion and cobblestone area formation, respectively. Moreover, lenalidomide pretreatment of mesenchymal stromal cells from patients with low but not high-risk myelodysplastic syndrome was able to rescue impaired erythroid and myeloid colony formation of early hematopoietic progenitors. In conclusion, our analyses support the notion that the stromal microenvironment is involved in the pathophysiology of myelodysplastic syndrome thus representing a potential target for therapeutic interventions.

Insufficient stromal support in MDS results from molecular and functional deficits of mesenchymal stromal cells

Ineffective hematopoiesis is a major characteristic of myelodysplastic syndromes (MDS) causing relevant morbidity and mortality. Mesenchymal stromal cells (MSC) have been shown to physiologically support hematopoiesis, but their contribution to the pathogenesis of MDS remains elusive. We show that MSC from patients across all MDS subtypes (n=106) exhibit significantly reduced growth and proliferative capacities accompanied by premature replicative senescence. Osteogenic differentiation was significantly reduced in MDS-derived MSC, indicated by cytochemical stainings and reduced expressions of Osterix and Osteocalcin. This was associated with specific methylation patterns that clearly separated MDS-MSC from healthy controls and showed a strong enrichment for biological processes associated with cellular phenotypes and transcriptional regulation. Furthermore, in MDS-MSC, we detected altered expression of key molecules involved in the interaction with hematopoietic stem and progenitor cells (HSPC), in particular Osteopontin, Jagged1, Kit-ligand and Angiopoietin as well as several chemokines. Functionally, this translated into a significantly diminished ability of MDS-derived MSC to support CD34+ HSPC in long-term culture-initiating cell assays associated with a reduced cell cycle activity. Taken together, our comprehensive analysis shows that MSC from all MDS subtypes are structurally, epigenetically and functionally altered, which leads to impaired stromal support and seems to contribute to deficient hematopoiesis in MDS.