Megakaryocyte-derived excessive transforming growth factor β1 inhibits proliferation of normal hematopoietic stem cells in acute myeloid leukemia

SARS-CoV-2 infection modifies the transcriptome of the megakaryocytes in the bone marrow

ABSTRACT

Megakaryocytes (MKs), integral to platelet production, predominantly reside in the bone marrow (BM) and undergo regulated fragmentation within sinusoid vessels to release platelets into the bloodstream. Inflammatory states and infections influence MK transcription, potentially affecting platelet functionality. Notably, COVID-19 has been associated with altered platelet transcriptomes. In this study, we investigated the hypothesis that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection could affect the transcriptome of BM MKs. Using spatial transcriptomics to discriminate subpopulations of MKs based on proximity to BM sinusoids, we identified ∼19 000 genes in MKs. Machine learning techniques revealed that the transcriptome of healthy murine BM MKs exhibited minimal differences based on proximity to sinusoid vessels. Furthermore, at peak SARS-CoV-2 viremia, when the disease primarily affected the lungs, MKs were not significantly different from those from healthy mice. Conversely, a significant divergence in the MK transcriptome was observed during systemic inflammation, although SARS-CoV-2 RNA was never detected in the BM, and it was no longer detectable in the lungs. Under these conditions, the MK transcriptional landscape was enriched in pathways associated with histone modifications, MK differentiation, NETosis, and autoimmunity, which could not be explained by cell proximity to sinusoid vessels. Notably, the type I interferon signature and calprotectin (S100A8/A9) were not induced in MKs under any condition. However, inflammatory cytokines induced in the blood and lungs of COVID-19 mice were different from those found in the BM, suggesting a discriminating impact of inflammation on this specific subset of cells. Collectively, our data indicate that a new population of BM MKs may emerge through COVID-19-related pathogenesis.

Unveiling novel insights in acute myeloid leukemia through single-cell RNA sequencing

Acute myeloid leukemia (AML) is a complex and heterogeneous group of aggressive hematopoietic stem cell disease. The presence of diverse and functionally distinct populations of leukemia cells within the same patient's bone marrow or blood poses a significant challenge in diagnosing and treating AML. A substantial proportion of AML patients demonstrate resistance to induction chemotherapy and a grim prognosis upon relapse. The rapid advance in next generation sequencing technologies, such as single-cell RNA-sequencing (scRNA-seq), has revolutionized our understanding of AML pathogenesis by enabling high-resolution interrogation of the cellular heterogeneity in the AML ecosystem, and their transcriptional signatures at a single-cell level. New studies have successfully characterized the inextricably intertwined interactions among AML cells, immune cells and bone marrow microenvironment and their contributions to the AML development, therapeutic resistance and relapse. These findings have deepened and broadened our understanding the complexity and heterogeneity of AML, which are difficult to detect with bulk RNA-seq. This review encapsulates the burgeoning body of knowledge generated through scRNA-seq, providing the novel insights and discoveries it has unveiled in AML biology. Furthermore, we discuss the potential implications of scRNA-seq in therapeutic opportunities, focusing on immunotherapy. Finally, we highlight the current limitations and future direction of scRNA-seq in the field.

The roles and mechanisms of TGFB1 in acute myeloid leukemia chemoresistance

Relapsed or Refractory (R/R) Acute Myeloid Leukemia (AML) patients usually have very poor prognoses, and drug-resistance is one of the major limiting factors. In this study, we aimed to explore the functions of Transforming Growth Factor-β1 (TGFB1) in AML drug-resistance. First, TGFB1 levels in serum and bone marrow are higher in R/R patients compared with newly diagnosed patients, this phenomenon could be due to different sources of secreted TGFB1 according to immunohistochemistry of marrow biopsies. Similarly, TGFB1 expression in AML drug-resistant cell lines is higher than that in their parental cell lines, and blocking the TGFB signaling pathway by specific inhibitors decreased resistance to chemotherapeutic agents. On the other hand, exogenous TGFB1 can also promote AML parental cells senescence and chemotherapy resistance. Next, we found SOX4 level is upregulated in drug-resistant cells, and parental cells treated with exogenous TGFB1 induced upregulation of SOX4 levels. Interference of SOX4 expression by siRNA diminished the TGFB1-induced sensitivity to chemotherapeutic agents. Finally, we conduct metabolomic analysis and find Alanine, aspartate and glutamate metabolism pathway, and Glycerophospholipid metabolism pathway are decreased after inhibiting TGFB signaling pathway or interfering SOX4 expression. This study concludes that TGFB1 level in R/R AML patients and drug-resistant strains is significantly increased. Blocking the TGFB signaling pathway can enhance the chemosensitivity of drug-resistant cells by suppressing SOX4 expression and metabolic reprogramming.

A comprehensive analysis of cell-autonomous and non-cell-autonomous regulation of myeloid leukemic cells: The prospect of developing novel niche-targeting therapies

Leukemic cells (LCs) arise from the hematopoietic stem/and progenitor cells (HSCs/HSPCs) and utilize cues from the bone marrow microenvironment (BMM) for their regulation in the same way as their normal HSC counterparts. Mesenchymal stromal cells (MSCs), a vital component of the BMM promote leukemogenesis by creating a protective and immune-tolerant microenvironment that can support the survival of LCs, helping them escape chemotherapy, thereby resulting in the relapse of leukemia. Conversely, MSCs also induce apoptosis in the LCs and inhibit their proliferation by interfering with their self-renewal potential. This review discusses the work done so far on cell-autonomous (intrinsic) and MSCs-mediated non-cell-autonomous (extrinsic) regulation of myeloid leukemia with a special focus on the need to investigate the extrinsic regulation of myeloid leukemia to understand the contrasting role of MSCs in leukemogenesis. These mechanisms could be exploited to formulate novel therapeutic strategies that specifically target the leukemic microenvironment.

Interlukin-4 weakens resistance to stress injury and megakaryocytic differentiation of hematopoietic stem cells by inhibiting Psmd13 expression

Thrombocytopenia is a major and fatal complication in patients with acute myeloid leukemia (AML), which results from disrupted megakaryopoiesis by leukemic niche and blasts. Our previous research revealed that elevated interleukin-4 (IL-4) in AML bone marrow had adverse impact on multiple stages throughout megakaryopoiesis including hematopoietic stem cells (HSCs), but the specific mechanism remains unknown. In the present study, we performed single-cell transcriptome analysis and discovered activated oxidative stress pathway and apoptosis pathway in IL-4Rαhigh versus IL-4Rαlow HSCs. IL-4 stimulation in vitro led to apoptosis of HSCs and down-regulation of megakaryocyte-associated transcription factors. Functional assays displayed higher susceptibility of IL-4Rαhigh HSCs to tunicamycin and irradiation-induced apoptosis, demonstrating their vulnerability to endoplasmic reticulum (ER) stress injury. To clarify the downstream signaling of IL-4, we analyzed the transcriptomes of HSCs from AML bone marrow and found a remarkable down-regulation of the proteasome component Psmd13, whose expression was required for megakaryocytic-erythroid development but could be inhibited by IL-4 in vitro. We knocked down Psmd13 by shRNA in HSCs, and found their repopulating capacity and megakaryocytic differentiation were severely compromised, with increased apoptosis in vivo. In summary, our study uncovered a previous unrecognized regulatory role of IL-4-Psmd13 signaling in anti-stress and megakaryocytic differentiation capability of HSCs.

Chemotherapy-induced thrombocytopenia: literature review

Chemotherapy-induced thrombocytopenia (CIT) is a common condition that frequently results in reduced chemotherapy dosages, postponed treatment, bleeding, and unfavorable oncological outcomes. At present, there is no clear suggestions for preventing or treating CIT. Thrombopoietin (TPO) replacement therapy has been invented and used to treat CIT to promote the production of megakaryocytes and stimulate the formation of platelets. However, this treatment is limited to the risk of immunogenicity and cancer progression. Therefore, an unmet need exists for exploring alternatives to TPO to address the clinical issue of CIT. Application of appropriate therapeutic drugs may be due to understanding the potential mechanisms of CIT. Studies have shown that chemotherapy significantly affects various cells in bone marrow (BM) microenvironment, reduces their ability to support normal hematopoiesis, and may lead to BM damage, including CIT in cancer patients. This review focuses on the epidemiology and treatment of cancer patients with CIT. We also introduce some recent progress to understand the cellular and molecular mechanisms of chemotherapy inhibiting normal hematopoiesis and causing thrombocytopenia.

A novel Boolean network inference strategy to model early hematopoiesis aging

Hematopoietic stem cell (HSC) aging is a multifactorial event leading to changes in HSC properties and functions, which are intrinsically coordinated and affect the early hematopoiesis. To better understand the mechanisms and factors controlling these changes, we developed an original strategy to construct a Boolean model of HSC differentiation. Based on our previous scRNA-seq data, we exhaustively characterized active transcription modules or regulons along the differentiation trajectory and constructed an influence graph between 15 selected components involved in the dynamics of the process. Then we defined dynamical constraints between observed cellular states along the trajectory and using answer set programming with in silico perturbation analysis, we obtained a Boolean model explaining the early priming of HSCs. Finally, perturbations of the model based on age-related changes revealed important deregulations, such as the overactivation of Egr1 and Junb or the loss of Cebpa activation by Gata2. These new regulatory mechanisms were found to be relevant for the myeloid bias of aged HSC and explain the decreased transcriptional priming of HSCs to all mature cell types except megakaryocytes.

Membrane-Wrapped Nanoparticles for Enhanced Chemotherapy of Acute Myeloid Leukemia

This work reports the development of a biomimetic membrane-wrapped nanoparticle (MWNP) platform for targeted chemotherapy of acute myeloid leukemia (AML). Doxorubicin (DOX), a chemotherapeutic used to treat leukemias, lymphomas, and other cancers, was encapsulated in polymeric NPs that were coated with cytoplasmic membranes derived from human AML cells. The release rate of DOX from the MWNPs was characterized under both storage and physiological conditions, with faster release observed at pH 5.5 than pH 7.4. The system was then introduced to AML cell cultures to test the functionality of the released DOX cargo as compared to DOX delivered freely or via NPs coated with poly(ethylene glycol) (PEG). The MWNPs delivered DOX in an efficient and targeted manner, inducing up to 80% apoptosis in treated cells at a dose of 5 μM, compared to 15% for free DOX and 17% for DOX-loaded PEG-coated NPs at the same drug concentration. The mechanism of cell death was confirmed as DNA double-strand breaks through a γH2A.X assay, indicating that the released DOX retained its expected mechanism of action. These findings designate MWNPs as a robust drug delivery system with great potential for future development in treatments of AML and other blood cancers.

Hematopoietic Stem and Progenitor Cells (HSPCs) and Hematopoietic Microenvironment: Molecular and Bioinformatic Studies of the Zebrafish Models

Hematopoietic stem cells (HSCs) reside in a specialized microenvironment in a peculiar anatomic location which regulates the maintenance of stem cells and controls its functions. Recent scientific progress in experimental technologies have enabled the specific detection of epigenetic factors responsible for the maintenance and quiescence of the hematopoietic niche, which has improved our knowledge of regulatory mechanisms. The aberrant role of RNA-binding proteins and their impact on the disruption of stem cell biology have been reported by a number of recent studies. Despite recent modernization in hematopoietic microenvironment research avenues, our comprehension of the signaling mechanisms and interactive pathways responsible for integration of the hematopoietic niche is still limited. In the past few decades, zebrafish usage with regards to exploratory studies of the hematopoietic niche has expanded our knowledge for deeper understanding of novel cellular interactions. This review provides an update on the functional roles of different genetic and epigenetic factors and molecular signaling events at different sections of the hematopoietic microenvironment. The explorations of different molecular approaches and interventions of latest web-based tools being used are also outlined. This will help us to get more mechanistic insights and develop therapeutic options for the malignancies.

Megakaryocyte Diversity in Ontogeny, Functions and Cell-Cell Interactions

Hematopoietic stem cells (HSCs) rely on local interactions in the bone marrow (BM) microenvironment with stromal cells and other hematopoietic cells that facilitate their survival and proliferation, and also regulate their functions. HSCs and multipotent progenitor cells differentiate into lineage-specific progenitors that generate all blood and immune cells. Megakaryocytes (Mks) are hematopoietic cells responsible for producing blood platelets, which are essential for normal hemostasis and blood coagulation. Although the most prominent function of Mks is platelet production (thrombopoiesis), other increasingly recognized functions include HSC maintenance and host immune response. However, whether and how these diverse programs are executed by different Mk subpopulations remains poorly understood. This Perspective summarizes our current understanding of diversity in ontogeny, functions and cell-cell interactions. Cumulative evidence suggests that BM microenvironment dysfunction, partly caused by mutated Mks, can induce or alter the progression of a variety of hematologic malignancies, including myeloproliferative neoplasms (MPNs) and other disorders associated with tissue scarring (fibrosis). Therefore, as an example of the heterogeneous functions of Mks in malignant hematopoiesis, we will discuss the role of Mks in the onset and progression of BM fibrosis. In this regard, abnormal interactions between of Mks and other immune cells might directly contribute to fibrotic diseases. Overall, further understanding of megakaryopoiesis and how Mks interact with HSCs and immune cells has potential clinical implications for stem cell transplantation and other therapies for hematologic malignancies, as well as for treatments to stimulate platelet production and prevent thrombocytopenia.

Three-Dimensional Avian Hematopoietic Stem Cell Cultures as a Model for Studying Disease Pathogenesis

Three-dimensional (3D) cell culture is attracting increasing attention today because it can mimic tissue environments and provide more realistic results than do conventional cell cultures. On the other hand, very little attention has been given to using 3D cell cultures in the field of avian cell biology. Although mimicking the bone marrow niche is a classic challenge of mammalian stem cell research, experiments have never been conducted in poultry on preparing in vitro the bone marrow niche. It is well known, however, that all diseases cause immunosuppression and target immune cells and their development. Hematopoietic stem cells (HSC) reside in the bone marrow and constitute a source for immune cells of lymphoid and myeloid origins. Disease prevention and control in poultry are facing new challenges, such as greater use of alternative breeding systems and expanding production of eggs and chicken meat in developing countries. Moreover, the COVID-19 pandemic will draw greater attention to the importance of disease management in poultry because poultry constitutes a rich source of zoonotic diseases. For these reasons, and because they will lead to a better understanding of disease pathogenesis, in vivo HSC niches for studying disease pathogenesis can be valuable tools for developing more effective disease prevention, diagnosis, and control. The main goal of this review is to summarize knowledge about avian hematopoietic cells, HSC niches, avian immunosuppressive diseases, and isolation of HSC, and the main part of the review is dedicated to using 3D cell cultures and their possible use for studying disease pathogenesis with practical examples. Therefore, this review can serve as a practical guide to support further preparation of 3D avian HSC niches to study the pathogenesis of avian diseases.

Granulocytes Negatively Regulate Secretion of Transforming Growth Factor β1 by Bone Marrow Mononuclear Cells via Secretion of Erythropoietin Receptors in the Milieu

In my previous study, I demonstrated that bone marrow-derived mononuclear cells (BM MNCs) secrete copious amounts of Transforming Growth Factor β1 (TGFβ1) in response to erythropoietin (EPO). In this study, I investigated the principal cell type involved in the process. I found that a large percentage of various marrow cells, but not their mature counterparts present in the peripheral blood, express EPO-receptors (EPO-R). Cell depletion experiments showed that depletion of Glycophorin positive erythroblasts and CD41⁺ megakaryocytes - the prime suspects - did not affect the EPO-mediated TGFβ1 secretion by the BM MNCs. However, individual depletion of CD2⁺ T lymphocytes, CD14⁺ monocyte/macrophages, and CD19⁺ B cells affected the TGFβ1 secretion by EPO-primed MNCs: depletion of CD2⁺ cells had the most striking effect. Unexpectedly, and most interestingly, depletion of CD15⁺ granulocytes led to a significant increase in the TGFβ1 secretion by both naïve and EPO-primed BM MNCs, suggesting that these cells negatively regulate the process. Mechanistically, I show that the CD15⁺ cells exert this regulatory effect via secretion of both full-length and soluble EPO-R in the milieu. Overall my results, for the first time, unravel an in-built regulatory mechanism prevailing in the BM microenvironment that regulates the secretion of TGFβ1 by controlling EPO-EPO-R interaction.My data could be relevant in understanding the pathophysiology of several conditions associated with deregulated production of TGFβ1 in the marrow compartment.

Single-cell analysis of ploidy and the transcriptome reveals functional and spatial divergency in murine megakaryopoiesis

Megakaryocytes (MKs), the platelet progenitor cells, play important roles in hematopoietic stem cell (HSC) maintenance and immunity. However, it is not known whether these diverse programs are executed by a single population or by distinct subsets of cells. Here, we manually isolated primary CD41+ MKs from the bone marrow (BM) of mice and human donors based on ploidy (2N-32N) and performed single-cell RNA sequencing analysis. We found that cellular heterogeneity existed within 3 distinct subpopulations that possess gene signatures related to platelet generation, HSC niche interaction, and inflammatory responses. In situ immunostaining of mouse BM demonstrated that platelet generation and the HSC niche-related MKs were in close physical proximity to blood vessels and HSCs, respectively. Proplatelets, which could give rise to platelets under blood shear forces, were predominantly formed on a platelet generation subset. Remarkably, the inflammatory responses subpopulation, consisting generally of low-ploidy LSP1+ and CD53+ MKs (≤8N), represented ∼5% of total MKs in the BM. These MKs could specifically respond to pathogenic infections in mice. Rapid expansion of this population was accompanied by strong upregulation of a preexisting PU.1- and IRF-8-associated monocytic-like transcriptional program involved in pathogen recognition and clearance as well as antigen presentation. Consistently, isolated primary CD53+ cells were capable of engulfing and digesting bacteria and stimulating T cells in vitro. Together, our findings uncover new molecular, spatial, and functional heterogeneity within MKs in vivo and demonstrate the existence of a specialized MK subpopulation that may act as a new type of immune cell.

A clinical prediction model identifies a subgroup with inferior survival within intermediate risk acute myeloid leukemia

Intermediate risk acute myeloid leukemia (AML) comprises around 50% of AML patients and is featured with heterogeneous clinical outcomes. The study aimed to generate a prediction model to identify intermediate risk AML patients with an inferior survival. We performed targeted next generation sequencing analysis for 121 patients with 2017 European LeukemiaNet-defined intermediate risk AML, revealing 122 mutated genes, with 24 genes mutated in > 10% of patients. A prognostic nomogram characterized by white blood cell count ≥10×10⁹/L at diagnosis, mutated DNMT3A and genes involved in signaling pathways was developed for 110 patients who were with clinical outcomes. Two subgroups were identified: intermediate low risk (ILR; 43.6%, 48/110) and intermediate high risk (IHR; 56.4%, 62/110). The model was prognostic of overall survival (OS) and relapse-free survival (RFS) (OS: Concordance index [C-index]: 0.703, 95%CI: 0.643-0.763; RFS: C-index: 0.681, 95%CI 0.620-0.741), and was successfully validated with two independent cohorts. Allogeneic hematopoietic stem cell transplantation (alloHSCT) reduced the relapse risk of IHR patients (3-year RFS: alloHSCT: 40.0±12.8% vs. chemotherapy: 8.6±5.8%, P= 0.010). The prediction model can help identify patients with an unfavorable prognosis and refine risk-adapted therapy for intermediate risk AML patients.

Far from Health: The Bone Marrow Microenvironment in AML, A Leukemia Supportive Shelter

Acute myeloid leukemia (AML) is the second most common leukemia among children. Although significant progress in AML therapy has been achieved, treatment failure is still associated with poor prognosis, emphasizing the need for novel, innovative therapeutic approaches. To address this major obstacle, extensive knowledge about leukemogenesis and the complex interplay between leukemic cells and their microenvironment is required. The tremendous role of this bone marrow microenvironment in providing a supportive and protective shelter for leukemic cells, leading to disease development, progression, and relapse, has been emphasized by recent research. It has been revealed that the interplay between leukemic cells and surrounding cellular as well as non-cellular components is critical in the process of leukemogenesis. In this review, we provide a comprehensive overview of recently gained knowledge about the importance of the microenvironment in AML whilst focusing on promising future therapeutic targets. In this context, we describe ongoing clinical trials and future challenges for the development of targeted therapies for AML.

Megakaryoblastic leukemia: a study on novel role of clinically significant long non-coding RNA signatures in megakaryocyte development during treatment with phorbol ester

Acute megakaryocytic leukemia (AMKL) is one of the rarest sub-types of acute myeloid leukemia (AML). AMKL is characterized by high proliferation of megakaryoblasts and myelofibrosis of bone marrow, this disease is also associated with poor prognosis. Previous analyses have reported that the human megakaryoblastic cells can be differentiated into cells with megakaryocyte (MK)-like characteristics by phorbol 12-myristate 13-acetate (PMA). However, little is known about the mechanism responsible for regulating this differentiation process. We performed long non-coding RNA (lncRNA) profiling to investigate the differently expressed lncRNAs in megakaryocyte blast cells treated with and without PMA and examined those that may be responsible for the PMA-induced differentiation of megakaryoblasts into MKs. We found 30 out of 90 lncRNA signatures to be differentially expressed after PMA treatment of megakaryoblast cells, including the highly expressed JPX lncRNA. Further, in silico lncRNA-miRNA and miRNA-mRNA interaction analysis revealed that the JPX is likely involved in unblocking the expression of TGF-β receptor (TGF-βR) by sponging oncogenic miRNAs (miR-9-5p, miR-17-5p, and miR-106-5p) during MK differentiation. Further, we report the activation of TGF-βR-induced non-canonical ERK1/2 and PI3K/AKT pathways during PMA-induced MK differentiation and ploidy development. The present study demonstrates that TGF-βR-induced non-canonical ERK1/2 and PI3K/AKT pathways are associated with PMA-induced MK differentiation and ploidy development; in this molecular mechanism, JPX lncRNA could act as a decoy for miR-9-5p, miR-17-5p, and miR-106-5p, titrating them away from TGF-βR mRNAs. Importantly, this study reveals the activation of ERK1/2 and PI3K/AKT pathway in PMA-induced Dami cell differentiation into MK. The identified differentially expressed lncRNA signatures may facilitate further study of the detailed molecular mechanisms associated with MK development. Thus, our data provide numerous targets with therapeutic potential for the modulation of the differentiation of megakaryoblastic cells in AMKL.

Role and clinical significance of TGF‑β1 and TGF‑βR1 in malignant tumors (Review)

The appearance and growth of malignant tumors is a complicated process that is regulated by a number of genes. In recent years, studies have revealed that the transforming growth factor-β (TGF-β) signaling pathway serves an important role in cell cycle regulation, growth and development, differentiation, extracellular matrix synthesis and immune response. Notably, two members of the TGF-β signaling pathway, TGF-β1 and TGF-β receptor 1 (TGF-βR1), are highly expressed in a variety of tumors, such as breast cancer, colon cancer, gastric cancer and hepatocellular carcinoma. Moreover, an increasing number of studies have demonstrated that TGF-β1 and TGF-βR1 promote proliferation, migration and epithelial-mesenchymal transition of tumor cells by activating other signaling pathways, signaling molecules or microRNAs (miRs), such as the NF-κB signaling pathway and miR-133b. In addition, some inhibitors targeting TGF-β1 and TGF-βR1 have exhibited positive effects in in vitro experiments. The present review discusses the association between TGF-β1 or TGF-βR1 and tumors, and the development of some inhibitors, hoping to provide more approaches to help identify novel tumor markers to restrain and cure tumors.

Tumor Immune Evasion Induced by Dysregulation of Erythroid Progenitor Cells Development

Cancer cells harness normal cells to facilitate tumor growth and metastasis. Within this complex network of interactions, the establishment and maintenance of immune evasion mechanisms are crucial for cancer progression. The escape from the immune surveillance results from multiple independent mechanisms. Recent studies revealed that besides well-described myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs) or regulatory T-cells (Tregs), erythroid progenitor cells (EPCs) play an important role in the regulation of immune response and tumor progression. EPCs are immature erythroid cells that differentiate into oxygen-transporting red blood cells. They expand in the extramedullary sites, including the spleen, as well as infiltrate tumors. EPCs in cancer produce reactive oxygen species (ROS), transforming growth factor β (TGF-β), interleukin-10 (IL-10) and express programmed death-ligand 1 (PD-L1) and potently suppress T-cells. Thus, EPCs regulate antitumor, antiviral, and antimicrobial immunity, leading to immune suppression. Moreover, EPCs promote tumor growth by the secretion of growth factors, including artemin. The expansion of EPCs in cancer is an effect of the dysregulation of erythropoiesis, leading to the differentiation arrest and enrichment of early-stage EPCs. Therefore, anemia treatment, targeting ineffective erythropoiesis, and the promotion of EPC differentiation are promising strategies to reduce cancer-induced immunosuppression and the tumor-promoting effects of EPCs.

Understanding of the crosstalk between normal residual hematopoietic stem cells and the leukemic niche in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease, yet clinically most patients present with pancytopenia resulting from bone marrow failure, predisposing them to life-threatening infections and bleeding. The mechanisms by which AML mediates hematopoietic suppression is not well known. Indeed, much effort has so far been focused on how AML remodels the bone marrow niche to make it a more permissive environment, with less focus on how the remodeled niche affects normal hematopoietic cells. In this perspective, we present evidence of the key role of the bone marrow niche in suppressing hematopoietic stem cells (HSCs) during leukemic progression and provide perspectives on how future research on this topic may be exploited to provide treatments for one of the key complications of AML.

Hematopoietic Stem Cell Niche During Homeostasis, Malignancy, and Bone Marrow Transplantation

Self-renewal and multidirectional differentiation of hematopoietic stem cells (HSCs) are strictly regulated by numerous cellular components and cytokines in the bone marrow (BM) microenvironment. Several cell types that regulate HSC niche have been identified, including both non-hematopoietic cells and HSC-derived cells. Specific changes in the niche composition can result in hematological malignancies. Furthermore, processes such as homing, proliferation, and differentiation of HSCs are strongly controlled by the BM niche and have been reported to be related to the success of hematopoietic stem cell transplantation (HSCT). Single-cell sequencing and in vivo imaging are powerful techniques to study BM microenvironment in hematological malignancies and after HSCT. In this review, we discuss how different components of the BM niche, particularly non-hematopoietic and hematopoietic cells, regulate normal hematopoiesis, and changes in the BM niche in leukemia and after HSCT. We believe that this comprehensive review will provide clues for further research on improving HSCT efficiency and exploring potential therapeutic targets for leukemia.

Inhibition of TGFβ1 and TGFβ3 promotes hematopoiesis in Fanconi anemia

Fanconi anemia (FA) is a chromosome instability syndrome with congenital abnormalities, cancer predisposition and bone marrow failure (BMF). Although hematopoietic stem and progenitor cell (HSPC) transplantation is the recommended therapy, new therapies are needed for FA patients without suitable donors. BMF in FA is caused, at least in part, by a hyperactive growth-suppressive transforming growth factor β (TGFβ) pathway, regulated by the TGFβ1, TGFβ2, and TGFβ3 ligands. Accordingly, the TGFβ pathway is an attractive therapeutic target for FA. While inhibition of TGFβ1 and TGFβ3 promotes blood cell expansion, inhibition of TGFβ2 is known to suppress hematopoiesis. Here, we report the effects of AVID200, a potent TGFβ1- and TGFβ3-specific inhibitor, on FA hematopoiesis. AVID200 promoted the survival of murine FA HSPCs in vitro. AVID200 also promoted in vitro the survival of human HSPCs from patients with FA, with the strongest effect in patients progressing to severe aplastic anemia or myelodysplastic syndrome (MDS). Previous studies have indicated that the toxic upregulation of the nonhomologous end-joining (NHEJ) pathway accounts, at least in part, for the poor growth of FA HSPCs. AVID200 downregulated the expression of NHEJ-related genes and reduced DNA damage in primary FA HSPC in vitro and in in vivo models. Collectively, AVID200 exhibits activity in FA mouse and human preclinical models. AVID200 may therefore provide a therapeutic approach to improving BMF in FA.

Oncogenic Long Noncoding RNA DARS-AS1 in Childhood Acute Myeloid Leukemia by Binding to microRNA-425

OBJECTIVE

Acute myeloid leukemia (AML) represents a hematological cancer. The aim of the investigation was to probe the regulatory relevance of long non-coding RNA (lncRNA) aspartyl-tRNA synthetase anti-sense 1 (DARS-AS1)/microRNA-425 (miR-425)/transforming growth factor-beta 1 (TGFB1) to the development of AML.

METHODS

The DARS-AS1 expression in bone marrow tissues was first analyzed in healthy subjects and AML patients. Subsequently, AML cell lines with DARS-AS1 knockdown were constructed, followed by cell proliferation and apoptosis assays. Afterward, downstream miRNA of DARS-AS1 and target mRNA of the miRNA were analyzed by bioinformatics, and their binding relationships were verified. Functional rescue experiments were then implemented. Finally, activation of the Smad2/3 signaling in MV4-11 and BF-24 cells were detected by western blot.

RESULTS

DARS-AS1 was overexpressed in bone marrow tissues of AML patients and cells, and DARS-AS1 knockdown suppressed the proliferation of AML cells and induced apoptosis. DARS-AS1 bound to and negatively correlated with miR-425. Further results suggested that TGFB1 might be a target gene of miR-425 and could promote Smad2/3 phosphorylation and nuclear translocation. Finally, DARS-AS1 depletion could diminish the tumor volume in vivo.

CONCLUSION

All in all, we highlighted here that DARS-AS1 enhanced the expression of TGFB1 through binding to miR-425 to modulate AML progression via the Smad2/3 pathway, which might perform as a therapeutic target for AML.

Mesenchymal niche remodeling impairs hematopoiesis via stanniocalcin 1 in acute myeloid leukemia

Acute myeloid leukemia (AML) disrupts the generation of normal blood cells, predisposing patients to hemorrhage, anemia, and infections. Differentiation and proliferation of residual normal hematopoietic stem and progenitor cells (HSPCs) are impeded in AML-infiltrated bone marrow (BM). The underlying mechanisms and interactions of residual hematopoietic stem cells (HSCs) within the leukemic niche are poorly understood, especially in the human context. To mimic AML infiltration and dissect the cellular crosstalk in human BM, we established humanized ex vivo and in vivo niche models comprising AML cells, normal HSPCs, and mesenchymal stromal cells (MSCs). Both models replicated the suppression of phenotypically defined HSPC differentiation without affecting their viability. As occurs in AML patients, the majority of HSPCs were quiescent and showed enrichment of functional HSCs. HSPC suppression was largely dependent on secreted factors produced by transcriptionally remodeled MSCs. Secretome analysis and functional validation revealed MSC-derived stanniocalcin 1 (STC1) and its transcriptional regulator HIF-1α as limiting factors for HSPC proliferation. Abrogation of either STC1 or HIF-1α alleviated HSPC suppression by AML. This study provides a humanized model to study the crosstalk among HSPCs, leukemia, and their MSC niche, and a molecular mechanism whereby AML impairs normal hematopoiesis by remodeling the mesenchymal niche.

[Abnormal granulocyte differentiation and the paradoxical switch of transforming growth factor-β1 in breast cancer patients]

OBJECTIVE

To analyze the characteristics of abnormal granulocytic differentiation in breast cancer patients and explore the role of TGF-β1 in granulocytic differentiation of hematopoietic stem cells (HSCs) and tumor development.

METHODS

Blood samples were collected from 52 patients with invasive ductal carcinoma and 47 healthy donors. The distribution of granulocytes was compared between the two groups and the effects of surgery and radiotherapy on granulocytes were analyzed. The relationship between granulocyte abnormalities and the clinicopathological characteristics of the patients was analyzed. Spleen hematopoietic stem cells isolated from normal and tumor-bearing mice were cultured and treated with TGF-β1, and colony formation of the myeloid cells was compared and the proportion of granulocytes was analyzed with flow cytometry.

RESULTS

The white blood cell (WBC) count, neutrophils, total granulocytes, granulocyte ratio in the total WBCs, and neutrophil/lymphocyte ratio (NLR) were significantly increased (P < 0.05), while the eosinophils and its subpopulations were obviously decreased (P < 0.05) in breast cancer patients. Clone formation experiments showed that the numbers of CFU-GM, BFU-E and CFU-M colonies were significantly greater in the spleen cells from tumor-bearing mice than in those from normal mice (P < 0.05). TGF- β1 treatment obviously suppressed clone formation in spleen HSCs from normal mice but significantly promoted the proliferation and granulocyte differentiation of the spleen HSCs from tumor-bearing mice.

CONCLUSIONS

Breast cancer patients have obvious abnormalities in granulocytic differentiation possibly as a result of hematopoietic stem cell differentiation imbalance induced by TGF-β1 and other growth factors produced by the tumor cells. TGF-β1 highlights a paradoxical shift in the regulation of clone formation and granulocytic differentiation of spleen hematopoietic stem cells.

Phosphatidylinositol transfer proteins regulate megakaryocyte TGF-β1 secretion and hematopoiesis in mice

We hypothesized that megakaryocyte (MK) phosphoinositide signaling mediated by phosphatidylinositol transfer proteins (PITPs) contributes to hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC) regulation. Conditional knockout mice lacking PITPs specifically in MKs and platelets (pitpα^-/- and pitpα^-/-/β^-/-) bone marrow (BM) manifested decreased numbers of HSCs, MK-erythrocyte progenitors, and cycling HPCs. Further, pitpα^-/-/β^-/- BM had significantly reduced engrafting capability in competitive transplantation and limiting dilution analysis. Conditioned media (CM) from cultured pitpα^-/- and pitpα^-/-/β^-/- BM MKs contained higher levels of transforming growth factor β1 (TGF-β1) and interleukin-4 (IL-4), among other myelosuppressive cytokines, than wild-type BM MKs. Correspondingly, BM flush fluid from pitpα^-/- and pitpα^-/-/β^-/- mice had higher concentrations of TGF-β1. CM from pitpα^-/- and pitpα^-/-/β^-/- MKs significantly suppressed HPC colony formation, which was completely extinguished in vitro by neutralizing anti-TGF-β antibody, and treatment of pitpα^-/-/β^-/- mice in vivo with anti-TGF-β antibodies completely reverted their defects in BM HSC and HPC numbers. TGF-β and IL-4 synergized to inhibit HPC colony formation in vitro. Electron microscopy analysis of pitpα^-/-/β^-/- MKs revealed ultrastructural defects with depleted α-granules and large, misshaped multivesicular bodies. Von Willebrand factor and thrombospondin-1, like TGF-β, are stored in MK α-granules and were also elevated in CM of cultured pitpα^-/-/β^-/- MKs. Altogether, these data show that ablating PITPs in MKs indirectly dysregulates hematopoiesis in the BM by disrupting α-granule physiology and secretion of TGF-β1.

Sub-Cellular Localization of Metalloproteinases in Megakaryocytes

Metalloproteinases (MMPs) are zinc-dependent endopeptidases that play essential roles as the mediator of matrix degradation and remodeling during organogenesis, wound healing and angiogenesis. Although MMPs were originally identified as matrixin proteases that act in the extracellular matrix, more recent research has identified members of the MMP family in unusual locations within the cells, exerting distinct functions in addition to their established role as extracellular proteases. During thrombopoiesis, megakaryocytes (Mks) sort MMPs to nascent platelets through pseudopodial-like structure known as proplatelets. Previous studies identified gelatinases, MMP-2 and MMP-9, as a novel regulator system of Mks and the platelet function. In this work we have exploited a sensitive immunoassay to detect and quantify multiple MMP proteins and their localization, in conditioned medium and sub-cellular fractions of primary human CD34⁺-derived Mks. We provide evidence that Mks express other MMPs in addition to gelatinases MMP-2 and MMP-9, peculiar isoforms of MMP-9 and MMPs with a novel nuclear compartmentalization.

A vicious interplay between genetic and environmental insults in the etiology of blood cancers

Over the years, the etiology of cancer has been attributed alternatively to genetic and environmental insults. According to the genetic hypothesis, cancer cells arise from the acquisition of mutations that dysregulate the intrinsic mechanisms controlling normal cell growth and survival. In contrast, the environmental hypothesis holds that cancer can be caused by multiple extrinsic challenges that alter normal tissue homeostasis, but may not necessarily involve mutations. It is, however, quite possible that these two mechanisms are not mutually exclusive. According to this third hypothesis, environmental challenges, by mechanisms still poorly understood, may act by imposing a selection pressure that confers a proliferative advantage on cells carrying specific driver mutations, leading to disease initiation. The authors of a brief report published in this journal (Exp Hematol. 2017;56:1-6) tested this third hypothesis experimentally and provide new evidence that chronic inflammation, by increasing tumor necrosis factor (TNF)-α, may positively select malignant hematopoietic stem cells (HSCs) carrying loss-of-function TET2 mutations that switch the TNF-α signaling responses to activate proliferation rather than inducing quiescence. Furthermore, these mutations skew hematopoietic differentiation toward the myelomonocytic lineage and the output of macrophages producing TNF-α constitutively, promoting further environment-independent expansion of the malignant HSCs. These findings support a model in which the formation of a malignant population is triggered by a vicious interplay between genetic (TET2 mutations) and environmental (inflammation) insults, suggesting the need for strategies that target both the malignant cells and their environment.