"Caught in the net": the extracellular matrix of the bone marrow in normal hematopoiesis and leukemia

Combinatorial extracellular matrix tissue chips for optimizing mesenchymal stromal cell microenvironment and manufacturing

Despite the therapeutic potential of mesenchymal stromal cells (MSC), there is limited understanding of optimal extracellular matrix (ECM) environments to manufacture these cells. We developed tissue chips to study the effects of multi-factorial ECM environments under manufacturable stiffness ranges and multi-component ECM compositions. Manufacturing qualities of cell expansion potential, immunomodulation, and differentiation capacity were examined. The results show stiffness effects, with 900 kPa substrates supporting higher proliferation and osteogenic differentiation, along with anti-inflammatory IL-10 expression, whereas 150 kPa substrates promoted adipogenic differentiation at 150 kPa, suggesting that optimal ECM environments may differ based on manufacturing goals. ECM biochemistries containing fibronectin and laminin further modulated MSC manufacturing qualities across various stiffnesses. Proteomic and transcriptomic analyses revealed unique ECM combinations that induced higher levels of angiogenic and immunomodulatory cytokines, compared to single factor ECMs. These findings demonstrate that optimized ECM environments enhance MSC manufacturing quality.

The potential link between the development of Alzheimer's disease and osteoporosis

Alzheimer's disease (AD) and osteoporosis (OP) pose distinct but interconnected health challenges, both significantly impacting the aging population. AD, a neurodegenerative disorder characterized by memory impairment and cognitive decline, is primarily associated with the accumulation of abnormally folded amyloid beta (Aβ) peptides and neurofibrillary tangles in the brain. OP, a skeletal disorder marked by low bone mineral density, involves dysregulation of bone remodeling and is associated with an increased risk of fractures. Recent studies have revealed an intriguing link between AD and OP, highlighting shared pathological features indicative of common regulatory pathophysiological pathways. In this article, we elucidate the signaling mechanisms that regulate the pathology of AD and OP and offer insights into the intricate network of factors contributing to these conditions. We also examine the role of bone-derived factors in the progression of AD, underscoring the plausibility of bidirectional communication between the brain and the skeletal system. The presence of amyloid plaques in the brain of individuals with AD is akin to the accumulation of brain Aβ in vascular dementia, pointing towards the need for further investigation of shared molecular mechanisms. Moreover, we discuss the role of bone-derived microRNAs that may regulate the pathological progression of AD, providing a novel perspective on the role of skeletal factors in neurodegenerative diseases. The insights presented here should help researchers engaged in exploring innovative therapeutic approaches targeting both neurodegenerative and skeletal disorders in aging populations.

Stem cell status and prognostic applications of cuproptosis-associated lncRNAs in acute myeloid leukemia

Introduction

Acute myeloid leukemia (AML), a highly heterogeneous hematological malignancy, remains a major challenge in adult oncology. Stem cell research has highlighted the crucial role of long noncoding RNA (lncRNA) in regulating cellular differentiation and self-renewal processes, which are pivotal in AML pathogenesis and therapy resistance.

Methods

This study explores the relationship between cuproptosis-related lncRNAs and AML prognosis, providing novel insights into their impact on hematopoietic stem and progenitor cells.

Results

We collected clinical information from 214 AML patients in our center and analyzed the association between granulocyte recovery after chemotherapy, cuproptosis, and prognosis. Additionally, we developed a prognostic model-the cuproptosis-associated long noncoding RNA prognostic model (CRLPM)-y analyzing data from The Cancer Genome Atlas (TCGA). Patients were stratified into high- and low-risk groups based on CRLPM, revealing significant survival differences. High-risk patients demonstrated lower sensitivity to chemotherapeutic agents such as Axitinib, GSK429286A, Navitoclax, and ZM-447439, underscoring the need for alternative therapeutic strategies.

Discussion

CRLPM offers a promising framework for integrating stem cell-focused approaches into personalized treatment regimens, paving the way for precision medicine in AML management.

In Vitro 3D Models of Haematological Malignancies: Current Trends and the Road Ahead?

Haematological malignancies comprise a diverse group of life-threatening systemic diseases, including leukaemia, lymphoma, and multiple myeloma. Currently available therapies, including chemotherapy, immunotherapy, and CAR-T cells, are often associated with important side effects and with the development of drug resistance and, consequently, disease relapse. In the last decades, it was largely demonstrated that the tumor microenvironment significantly affects cancer cell proliferation and tumor response to treatment. The development of biomimetic, in vitro models may promote the investigation of the interactions between cancer cells and the tumor microenvironment and may help to better understand the mechanisms leading to drug resistance. Although advanced in vitro models have been largely explored in the field of solid tumors, due to the complex nature of the blood cancer tumor microenvironment, the mimicking of haematological malignancies mostly relies on simpler systems, often limited to two-dimensional cell culture, which intrinsically excludes the microenvironmental niche, or to ethically debated animal models. This review aims at reporting an updated overview of state-of-the-art hematological malignancies 3D in vitro models, emphasizing the key features and limitations of existing systems to inspire further research in this underexplored field.

Exploitation of the fibrinolytic system by B-cell acute lymphoblastic leukemia and its therapeutic targeting

Fibrinolysis influences the mobilization of hematopoietic stem cells from their bone marrow microenvironment (BMM). Here we show that activation of plasmin, a key fibrinolytic agent, by annexin A2 (ANXA2) distinctly impacts progression of BCR-ABL1+ B-cell acute lymphoblastic leukemia (B-ALL) via modulation of the extracellular matrix (ECM) in the BMM. The dense ECM in a BMM with decreased plasmin activity entraps insulin-like growth factor (IGF) 1 and reduces mTORC2-dependent signaling and proliferation of B-ALL cells. Conversely, B-ALL conditions the BMM to induce hepatic generation of plasminogen, the plasmin precursor. Treatment with ε-aminocaproic acid (EACA), which inhibits plasmin activation, reduces tumor burden and prolongs survival, including in xenogeneic models via increased fibronectin in the BMM. Human data confirm that IGF1 and fibronectin staining in trephine biopsies are correlated. Our studies suggest that fibrinolysis-mediated ECM remodeling and subsequent growth factor release influence B-ALL progression and inhibition of this process by EACA may be beneficial as adjunct therapy.

Mechanisms of Germline Stem Cell Competition across Species

In this review, we introduce the concept of cell competition, which occurs between heterogeneous neighboring cell populations. Cells with higher relative fitness become "winners" that outcompete cells of lower relative fitness ("losers"). We discuss the idea of super-competitors, mutant cells that expand at the expense of wild-type cells. Work on adult stem cells (ASCs) has revealed principles of neutral competition, wherein ASCs can be stochastically lost and replaced, and of biased competition, in which a winning ASC with a competitive advantage replaces its neighbors. Germline stem cells (GSCs) are ASCs that are uniquely endowed with the ability to produce gametes and, therefore, impact the next generation. Mechanisms of GSC competition have been elucidated by studies in Drosophila gonads, tunicates, and the mammalian testis. Competition between ASCs is thought to underlie various forms of cancer, including spermatocytic tumors in the human testis. Paternal age effect (PAE) disorders are caused by de novo mutations in human GSCs that increase their competitive ability and make them more likely to be inherited, leading to skeletal and craniofacial abnormalities in offspring. Given its widespread effects on human health, it is important to study GSC competition to elucidate how cells can become winners or losers.

Heterotypic interaction promotes asymmetric division of human hematopoietic progenitors

Hematopoietic stem and progenitor cells (HSPCs) give rise to all cell types of the hematopoietic system through various processes, including asymmetric divisions. However, the contribution of stromal cells of the hematopoietic niches in the control of HSPC asymmetric divisions remains unknown. Using polyacrylamide microwells as minimalist niches, we show that specific heterotypic interactions with osteoblast and endothelial cells promote asymmetric divisions of human HSPCs. Upon interaction, HSPCs polarize in interphase with the centrosome, the Golgi apparatus, and lysosomes positioned close to the site of contact. Subsequently, during mitosis, HSPCs orient their spindle perpendicular to the plane of contact. This division mode gives rise to siblings with unequal amounts of lysosomes and of the differentiation marker CD34. Such asymmetric inheritance generates heterogeneity in the progeny, which is likely to contribute to the plasticity of the early steps of hematopoiesis.

Liquid Overlay and Collagen-Based Three-Dimensional Models for In Vitro Investigation of Multiple Myeloma

Multiple myeloma (MM) clones reside in the bone marrow (BM), which plays a role in its survival and development. The interactions between MM and their neighboring mesenchymal stromal cells (MSCs) have been shown to promote MM growth and drug resistance. However, those interactions are often missing or misrepresented in traditional two-dimensional (2D) culture models. Application of novel three-dimensional (3D) models might recapitulate the BM niche more precisely, which will offer new insights into MM progression and survival. Here, we aimed to establish two 3D models, based on MSC spheroids and collagen droplets incorporating both MM cells and MSCs with the goal of replicating the native myeloma context of the BM niche. This approach revealed that although MSCs can spontaneously assemble spheroids with altered metabolic traits, MSC spheroid culture does not support the integration of MM cells. On the contrary, collagen-droplet culture supported the growth of both cell types. In collagen, MSC proliferation was reduced, with the correlating decrease in ATP production and Ki-67 expression, which might resemble in vivo conditions, rather than 2D abundance of nutrients and space. MSCs and MMs were distributed homogenously throughout the collagen droplet, with an apparent CXCL12 expression in MSCs. In addition, the response of MM cells to bortezomib was substantially reduced in collagen, indicating the importance of 3D culture in the investigation of myeloma cell behavior, as drug resistance is one of the most pertinent issues in cancer therapy.

Brain-Decellularized ECM-Based 3D Myeloid Sarcoma Platform: Mimicking Adaptive Phenotypic Alterations in the Brain

Leukemia circulates in the bloodstream and induces various symptoms and complications. Occasionally, these cells accumulate in non-marrow tissues, forming a tumor-like myeloid sarcoma (MS). When the blast-stage leukemia cells invade the brain parenchyma, intracranial MS occurs, leading to a challenging prognosis owing to the limited penetration of cytostatic drugs into the brain and the development of drug resistance. The scarcity of tissue samples from MS makes understanding the phenotypic changes occurring in leukemia cells within the brain environment challenging, thereby hindering development of effective treatment strategies for intracranial MS. This study presents a novel 3D in vitro model mimicking intracranial MS, employing a hydrogel scaffold derived from the brain-decellularized extracellular matrix in which suspended leukemia cells are embedded, simulating the formation of tumor masses in the brain parenchyma. This model reveals marked phenotypic changes in leukemia cells, including altered survival, proliferation, differentiation, and cell cycle regulation. Notably, proportion of dormant leukemia stem cells increases and expression of multidrug resistance genes is upregulated, leading to imatinib resistance, mirroring the pathological features of in vivo MS tissue. Furthermore, suppression of ferroptosis is identified as an important characteristic of intracranial MS, providing valuable insights for the development of targeted therapeutic strategies.

Intravital Microscopy to Study the Effect of Matrix Metalloproteinase Inhibition on Acute Myeloid Leukemia Cell Migration in the Bone Marrow

Hematopoiesis is the process through which all mature blood cells are formed and takes place in the bone marrow (BM). Acute myeloid leukemia (AML) is a blood cancer of the myeloid lineage. AML progression causes drastic remodeling of the BM microenvironment, making it no longer supportive of healthy hematopoiesis and leading to clinical cytopenia in patients. Understanding the mechanisms by which AML cells shape the BM to their benefit would lead to the development of new therapeutic strategies. While the role of extracellular matrix (ECM) in solid cancer has been extensively studied during decades, its role in the BM and in leukemia progression has only begun to be acknowledged. In this context, intravital microscopy (IVM) gives the unique insight of direct in vivo observation of AML cell behavior in their environment during disease progression and/or upon drug treatments. Here we describe our protocol for visualizing and analyzing MLL-AF9 AML cell dynamics upon systemic inhibition of matrix metalloproteinases (MMP), combining confocal and two-photon microscopy and focusing on cell migration.

Reactive oxygen species downregulate dystroglycans in the megakaryocytes of rats with arterial hypertension

Hypertension is a multifactorial disease characterized by vascular and renal dysfunction, cardiovascular remodeling, inflammation, and fibrosis, all of which are associated with oxidative stress. We previously demonstrated cellular reactive oxygen species (ROS) imbalances may impact the structural and biochemical functions of blood cells and reported downregulation of β-dystroglycan (β-Dg) and overexpression of the epithelial sodium channel (ENaC) contribute to the pathophysiology of hypertension. In this study, we aimed to determine the expression of dystroglycans (Dg) and ENaC in platelet progenitors (megakaryocytes) and their surrounding niches. Thin sections of bone marrow from 5- and 28-week-old spontaneous hypertensive rats (SHR) were compared to age-matched normotensive rats (WKY). Cytometry and immunohistochemical assays demonstrated an oxidative environment in SHR bone marrow, characterized by high levels of myeloperoxidase and 3-nitrotyrosine and downregulation of peroxiredoxin II. In addition, transmission electron micrography and confocal microscopy revealed morphological changes in platelets and Mgks from SHR rats, including swollen mitochondria. Quantitative qRT-PCR assays confirmed downregulation of Dg mRNA and immunohistochemistry and western-blotting validated low expression of β-Dg, mainly in the phosphorylated form, in Mgks from 28-week-old SHR rats. Moreover, we observed a progressive increase in β-1 integrin expression in Mgks and extracellular matrix proteins in Mgk niches in SHR rats compared to WKY controls. These results indicate accumulation of ROS promotes oxidative stress within the bone marrow environment and detrimentally affects cellular homeostasis in hypertensive individuals.

Good Cop, Bad Cop: Profiling the Immune Landscape in Multiple Myeloma

Multiple myeloma (MM) is a dyscrasia of plasma cells (PCs) characterized by abnormal immunoglobulin (Ig) production. The disease remains incurable due to a multitude of mutations and structural abnormalities in MM cells, coupled with a favorable microenvironment and immune suppression that eventually contribute to the development of drug resistance. The bone marrow microenvironment (BMME) is composed of a cellular component comprising stromal cells, endothelial cells, osteoclasts, osteoblasts, and immune cells, and a non-cellular component made of the extracellular matrix (ECM) and the liquid milieu, which contains cytokines, growth factors, and chemokines. The bone marrow stromal cells (BMSCs) are involved in the adhesion of MM cells, promote the growth, proliferation, invasion, and drug resistance of MM cells, and are also crucial in angiogenesis and the formation of lytic bone lesions. Classical immunophenotyping in combination with advanced immune profiling using single-cell sequencing technologies has enabled immune cell-specific gene expression analysis in MM to further elucidate the roles of specific immune cell fractions from peripheral blood and bone marrow (BM) in myelomagenesis and progression, immune evasion and exhaustion mechanisms, and development of drug resistance and relapse. The review describes the role of BMME components in MM development and ongoing clinical trials using immunotherapeutic approaches.

In vitro simulation of the acute lymphoblastic leukemia niche: a critical view on the optimal approximation for drug testing

Acute lymphoblastic leukemia with the worst prognosis is related to minimal residual disease. Minimal residual disease not only depends on the individual peculiarities of leukemic clones but also reflects the protective role of the acute lymphoblastic leukemia microenvironment. In this review, we discuss in detail cell-to-cell interactions in the 2 leukemic niches, more explored bone marrow and less studied extramedullary adipose tissue. A special emphasis is given to multiple ways of interactions of acute lymphoblastic leukemia cells with the bone marrow or extramedullary adipose tissue microenvironment, indicating observed differences in B- and T-cell-derived acute lymphoblastic leukemia behavior. This analysis argued for the usage of coculture systems for drug testing. Starting with a review of available sources and characteristics of acute lymphoblastic leukemia cells, mesenchymal stromal cells, endothelial cells, and adipocytes, we have then made an update of the available 2-dimensional and 3-dimensional systems, which bring together cellular elements, components of the extracellular matrix, or its imitation. We discussed the most complex available 3-dimensional systems like "leukemia-on-a-chip," which include either a prefabricated microfluidics platform or, alternatively, the microarchitecture, designed by using the 3-dimensional bioprinting technologies. From our analysis, it follows that for preclinical antileukemic drug testing, in most cases, intermediately complex in vitro cell systems are optimal, such as a "2.5-dimensional" coculture of acute lymphoblastic leukemia cells with niche cells (mesenchymal stromal cells, endothelial cells) plus matrix components or scaffold-free mesenchymal stromal cell organoids, populated by acute lymphoblastic leukemia cells. Due to emerging evidence for the correlation of obesity and poor prognosis, a coculture of adipocytes with acute lymphoblastic leukemia cells as a drug testing system is gaining shape.

CD44 in Bone Metastasis Development: A Key Player in the Fate Decisions of the Invading Cells?

A participant in key developmental processes, the adhesion glycoprotein CD44 is also expressed in several types of malignancies and can promote metastasis. In addition, the expression of CD44 isoforms in different types of cancer such as prostate and breast cancers may facilitate bone metastases by enhancing tumorigenicity, osteomimicry, cell migration, homing to bone, and anchorage within the bone specialized domains. Moreover, there is evidence that the CD44-ICD fragments in breast cancer cells may promote the cells' osteolytic nature. Yet the mechanisms by which CD44 and its downstream effectors promote the establishment of these cells within the bone are not fully elucidated. In this review, we summarize the current data on the roles played by CD44 in cancer progression and bone metastasis and the possible effects of its interaction with the different components of the bone marrow milieu.

Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

As an important treatment for acute myeloid leukemia, allogeneic hematopoietic stem cell transplantation (allo-HSCT) plays an important role in reducing relapse and improving long-term survival. With rapid advancements in basic research in molecular biology and immunology and with deepening understanding of the biological characteristics of hematopoietic stem cells, allo-HSCT has been widely applied in clinical practice. During allo-HSCT, preconditioning, the donor, and the source of stem cells can be tailored to the patient's conditions, greatly broadening the indications for HSCT, with clear survival benefits. However, the risks associated with allo-HSCT remain high, i.e. hematopoietic reconstitution failure, delayed immune reconstitution, graft-versus-host disease, and post-transplant relapse, which are bottlenecks for further improvements in allo-HSCT efficacy and have become hot topics in the field of HSCT. Other bottlenecks recognized in the current treatment of individuals diagnosed with acute myeloid leukemia and subjected to allo-HSCT include the selection of the most appropriate conditioning regimen and post-transplantation management. In this paper, we reviewed the progress of relevant research regarding these aspects.

Increase in Frequency of Myeloid-Derived Suppressor Cells in the Bone Marrow of Myeloproliferative Neoplasm: Potential Implications in Myelofibrosis

The Philadelphia-negative myeloproliferative neoplasms (MPNs), defined as clonal disorders of the hematopoietic stem cells, are characterized by the proliferation of mature myeloid cells in the bone marrow and a chronic inflammatory status impacting the initiation, progression, and symptomatology of the malignancies. There are three main entities defined as essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF), and genetically classified by JAK2^V617F, CALR, or MPL mutations. In MPNs, due to the overproduction of inflammatory cytokines by the neoplastic cells and non-transformed immune cells, chronic inflammation may provoke the generation and expansion of myeloid-derived suppressors cells (MDSCs) that highly influence the adaptive immune response. Although peripheral blood MDSC levels are elevated, their frequency in the bone marrow of MPNs patients is not well elucidated yet. Our results indicated increased levels of total (T)-MDSCs (CD33⁺HLA-DR^-/low) and polymorphonuclear (PMN)-MDSCs (CD33⁺/HLA-DR^low/CD15⁺/CD14^-) in the bone marrow and peripheral blood of all three types of MPNs malignancies. However, these bone marrow MDSCs-increased frequencies did not correlate with the clinical parameters, such as hepatomegaly, leukocytes, hemoglobin, or platelet levels, or with JAK2 and CALR mutations. Besides, bone marrow MDSCs, from ET, PV, and PMF patients, exhibited immunosuppressive function, determined as T-cell proliferation inhibition. Notably, the highest T-MDSCs and PMN-MDSC levels were found in PMF samples, and the increased MDSCs frequency strongly correlated with the degree of myelofibrosis. Thus, these data together indicate that the immunosuppressive MDSCs population is increased in the bone marrow of MPNs patients and may be implicated in generating a fibrotic microenvironment.

AML-derived extracellular vesicles negatively regulate stem cell pool size: A step toward bone marrow failure

PURPOSE OF THE STUDY

Long-term repopulating hematopoietic stem cells (LTR-HSCs) have been previously shown to reside in close proximity to osteoblasts, where they take shelter in the bone marrow (BM) microenvironment against cytotoxic and apoptotic stimuli. Nevertheless, the function of the HSC niche is believed to undergo an adaptive evolutionary modification during leukemogenesis. Recent studies have demonstrated that leukemic clones can impact BM homing through extracellular vesicle (EV) secretion. However, the exact mechanism driving BM conversion is still unclear. In the present study, the human osteoblast cell line (MG-63) were subjected to various concentration of sera-derived EVs of patients with acute myeloid leukemia (AML) and healthy volunteers to assess if they are associated strongly enough to alter the expression pattern of cross-talk molecules involved in niche interactions.

METHOD

To gain a brief insight into the EVs secretion criteria, we first conducted a comparative analysis of sera-derived EVs by dynamic light scattering (DLS), transmission electron microscopy (TEM), and Bradford assay. After incubating MG-63 cell lines with increasing concentrations of the EVs, Trypan-blue and microculture tetrazolium test (MTT) assays were used to evaluate the cell survival, logarithmic growth, and metabolic activity. Finally, the expression levels of OPN, ANGPT-1, and JAG-1 transcripts were evaluated through the qRT-PCR technique.

RESULTS

Here, we report that AML-derived EVs can affect the viability, cell growth, and metabolic activity of the human osteoblasts cell line (MG-63) compared to those that received healthy-derived EVs. We also found that leukemic EVs tend to induce overexpression of OPN but reduce the expression of ANGPT-1 and JAG-1 genes in the osteoblast transcriptome, which may provide a potential context imposing selective suppression of HSC pool size.

CONCLUSION

These findings extend the general concept of a novel mechanism in which leukemic EVs would make it possible to create a specialized pre-metastatic microenvironment in the interest of tumor expansion, allowing leukemic clones to overcome their HSCs counterparts.

Biglycan as a mediator of proinflammatory response and target for MDS and sAML therapy

Myelodysplastic syndromes (MDS) and their progression to secondary acute myeloid leukemia (sAML) are associated with an altered protein expression including extracellular matrix (ECM) components thereby promoting an inflammatory environment. Since the role of the proteoglycan biglycan (BGN) as an inflammatory mediator has not yet been investigated in both diseases and might play a role in disease progression, its expression and/or function was determined in cell lines and bone marrow biopsies (BMBs) of MDS and sAML patients and subpopulations of MDS stem cells by Western blot and immunohistochemistry. The bone marrow (BM) microenvironment was analyzed by multispectral imaging, patients' survival by Cox regression. ROC curves were assessed for diagnostic value of BGN. All cell lines showed a strong BGN surface expression in contrast to only marginal expression levels in mononuclear cells and CD34⁺ cells from healthy donors. In the MDS-L cell line, CD34^-CD33⁺ and CD34⁺CD33⁺ blast subpopulations exhibited a differential BGN surface detection. Increased BGN mediated inflammasome activity of CD34^-CD33⁺TLR4⁺ cells was observed, which was inhibited by direct targeting of BGN or NLRP3. BGN was heterogeneously expressed in BMBs of MDS and sAML, but was not detected in control biopsies. BGN expression in BMBs positively correlated with MUM1⁺ and CD8⁺, but negatively with CD33⁺TLR4⁺ cell infiltration and was accompanied by a decreased progression-free survival of MDS patients. BGN-mediated inflammasome activation appears to be a crucial mechanism in MDS pathogenesis implicating its use as suitable biomarker and potential therapeutic target. Abbreviations: Ab, antibody; alloSCT, allogenic stem cell transplant; AML, acute myeloid leukemia; BGN, biglycan; BM, bone marrow; BMB, bone marrow biopsy; casp1, caspase 1; CTLA-4, cytotoxic T lymphocyte-associated protein 4; DAMP, danger-associated molecular pattern; ECM, extracellular matrix; FCS, fetal calf serum; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HD, healthy donor; HSPC, hematopoietic stem and progenitor cell; HSC, hematopoietic stem cell; IFN, interferon; IHC, immunohistochemistry; IL, interleukin; MDS, myelodysplastic syndrome; MPN, myeloproliferative neoplasm; MSI, multispectral imaging; NGS, next-generation sequencing; NLRP3, NLR family pyrin domain containing 3; OS, overall survival; PBMC, peripheral blood mononuclear cell; PD-1, programmed cell death protein 1; PD-L1, programmed death-ligand 1, PFS, progression-free survival; PRR, pattern recognition receptor; SC, stem cell; SLRP, small leucine-rich proteoglycan; TGF, transforming growth factor; TIRAP, toll/interleukin 1 receptor domain-containing adapter protein; TLR, toll-like receptor; Treg, regulatory T cell.

Bone marrow mesenchymal stromal cell-derived extracellular matrix displays altered glycosaminoglycan structure and impaired functionality in Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) comprise a heterogeneous group of hematologic malignancies characterized by clonal hematopoiesis, one or more cytopenias such as anemia, neutropenia, or thrombocytopenia, abnormal cellular maturation, and a high risk of progression to acute myeloid leukemia. The bone marrow microenvironment (BMME) in general and mesenchymal stromal cells (MSCs) in particular contribute to both the initiation and progression of MDS. However, little is known about the role of MSC-derived extracellular matrix (ECM) in this context. Therefore, we performed a comparative analysis of in vitro deposited MSC-derived ECM of different MDS subtypes and healthy controls. Atomic force microscopy analyses demonstrated that MDS ECM was significantly thicker and more compliant than those from healthy MSCs. Scanning electron microscopy showed a dense meshwork of fibrillar bundles connected by numerous smaller structures that span the distance between fibers in MDS ECM. Glycosaminoglycan (GAG) structures were detectable at high abundance in MDS ECM as white, sponge-like arrays on top of the fibrillar network. Quantification by Blyscan assay confirmed these observations, with higher concentrations of sulfated GAGs in MDS ECM. Fluorescent lectin staining with wheat germ agglutinin and peanut agglutinin demonstrated increased deposition of N-acetyl-glucosamine GAGs (hyaluronan (HA) and heparan sulfate) in low risk (LR) MDS ECM. Differential expression of N-acetyl-galactosamine GAGs (chondroitin sulfate, dermatan sulfate) was observed between LR- and high risk (HR)-MDS. Moreover, increased amounts of HA in the matrix of MSCs from LR-MDS patients were found to correlate with enhanced HA synthase 1 mRNA expression in these cells. Stimulation of mononuclear cells from healthy donors with low molecular weight HA resulted in an increased expression of various pro-inflammatory cytokines suggesting a contribution of the ECM to the inflammatory BMME typical of LR-MDS. CD34⁺ hematopoietic stem and progenitor cells (HSPCs) displayed an impaired differentiation potential after cultivation on MDS ECM and modified morphology accompanied by decreased integrin expression which mediate cell-matrix interaction. In summary, we provide evidence for structural alterations of the MSC-derived ECM in both LR- and HR-MDS. GAGs may play an important role in this remodeling processes during the malignant transformation which leads to the observed disturbance in the support of normal hematopoiesis.

In Vitro Models of Bone Marrow Remodelling and Immune Dysfunction in Space: Present State and Future Directions

Spaceflight affects the body on every level. Reports on astronaut health identify bone marrow remodelling and dysfunction of the innate immune system as significant health risks of long-term habitation in space. Microgravity-induced alterations of the bone marrow induce physical changes to the bone marrow stem cell niche. Downstream effects on innate immunity are expected due to impaired hematopoiesis and myelopoiesis. To date, few studies have investigated these effects in real microgravity and the sparsely available literature often reports contrasting results. This emphasizes a need for the development of physiologically relevant in vitro models of the bone marrow stem cell niche, capable of delivering appropriate sample sizes for robust statistics. Here, we review recent findings on the impact of spaceflight conditions on innate immunity in in vitro and animal models and discusses the latest in vitro models of the bone marrow stem cell niche and their potential translatability to gravitational biology research.

4-Methylumbelliferone induces antitumor effects independently of hyaluronan synthesis inhibition in human acute leukemia cell lines

AIMS

Despite continuous improvement in the treatment of acute leukemia, new therapies are still needed to overcome resistance and reduce adverse effects. The aim of this work was to study the tumor-suppressive effects of 4-methylumbelliferone (4MU) in human acute leukemia cell lines. In addition, we aimed to address the extent of these effects in relation to the inhibition of hyaluronic acid (HA) synthesis.

MAIN METHODS

HA levels were measured by an ELISA-like assay. Human acute leukemia cell lines were treated with 4MU, HA or their combination. Cell proliferation was assessed by the [³H]-Tdr uptake assay, metabolic activity by the XTT assay and cell death was determined by DAPI, AO/EB and AnnexinV-PE/7-AAD staining. Senescence induction was evaluated by SA-β-Gal and C12FDG staining. Total and surface RHAMM expression levels were assessed by flow cytometry and fluorescence microscopy.

KEY FINDINGS

4MU reduced metabolic activity and inhibited cell proliferation in all leukemia cells, and these effects were explained by the induction of senescence or cell death depending on the cell line evaluated. Exogenous HA failed to prevent most of the tumor-suppressive effects observed. Results from this work suggest that the tumor-suppressive effects exerted by 4MU would be explained by HA-synthesis-independent mechanisms.

SIGNIFICANCE

These findings broaden the knowledge of 4MU as a potential treatment in acute leukemia. We report for the first time the existence of tumor-suppressive effects of 4MU on human acute leukemia cell lines that are independent of its role as HA-synthesis inhibitor.

Adult stem cell niches for tissue homeostasis

Adult stem cells are fundamental to maintain tissue homeostasis, growth, and regeneration. They reside in specialized environments called niches. Following activating signals, they proliferate and differentiate into functional cells that are able to preserve tissue physiology, either to guarantee normal turnover or to counteract tissue damage caused by injury or disease. Multiple interactions occur within the niche between stem cell‐intrinsic factors, supporting cells, the extracellular matrix, and signaling pathways. Altogether, these interactions govern cell fate, preserving the stem cell pool, and regulating stem cell proliferation and differentiation. Based on their response to body needs, tissues can be largely classified into three main categories: tissues that even in normal conditions are characterized by an impressive turnover to replace rapidly exhausting cells (blood, epidermis, or intestinal epithelium); tissues that normally require only a basal cell replacement, though able to efficiently respond to increased tissue needs, injury, or disease (skeletal muscle); tissues that are equipped with less powerful stem cell niches, whose repairing ability is not able to overcome severe damage (heart or nervous tissue). The purpose of this review is to describe the main characteristics of stem cell niches in these different tissues, highlighting the various components influencing stem cell activity. Although much has been done, more work is needed to further increase our knowledge of niche interactions. This would be important not only to shed light on this fundamental chapter of human physiology but also to help the development of cell‐based strategies for clinical therapeutic applications, especially when other approaches fail.

Notch Signaling in the Bone Marrow Lymphopoietic Niche

Lifelong mammalian hematopoiesis requires continuous generation of mature blood cells that originate from Hematopoietic Stem and Progenitor Cells (HSPCs) situated in the post-natal Bone Marrow (BM). The BM microenvironment is inherently complex and extensive studies have been devoted to identifying the niche that maintains HSPC homeostasis and supports hematopoietic potential. The Notch signaling pathway is required for the emergence of the definitive Hematopoietic Stem Cell (HSC) during embryonic development, but its role in BM HSC homeostasis is convoluted. Recent work has begun to explore novel roles for the Notch signaling pathway in downstream progenitor populations. In this review, we will focus an important role for Notch signaling in the establishment of a T cell primed sub-population of Common Lymphoid Progenitors (CLPs). Given that its activation mechanism relies primarily on cell-to-cell contact, Notch signaling is an ideal means to investigate and define a novel BM lymphopoietic niche. We will discuss how new genetic model systems indicate a pre-thymic, BM-specific role for Notch activation in early T cell development and what this means to the paradigm of lymphoid lineage commitment. Lastly, we will examine how leukemic T-cell acute lymphoblastic leukemia (T-ALL) blasts take advantage of Notch and downstream lymphoid signals in the pathological BM niche.

Tonsil-derived mesenchymal stem cells enhance allogeneic bone marrow engraftment via collagen IV degradation

BACKGROUND

Co-transplantation of bone marrow cells (BMCs) and mesenchymal stem cells (MSCs) is used as a strategy to improve the outcomes of bone marrow transplantation. Tonsil-derived MSCs (TMSCs) are a promising source of MSCs for co-transplantation. Previous studies have shown that TMSCs or conditioned media from TMSCs (TMSC-CM) enhance BMC engraftment. However, the factors in TMSCs that promote better engraftment have not yet been identified.

METHODS

Mice were subjected to a myeloablative regimen of busulfan and cyclophosphamide, and the mRNA expression in the bone marrow was analyzed using an extracellular matrix (ECM) and adhesion molecule-targeted polymerase chain reaction (PCR) array. Nano-liquid chromatography with tandem mass spectrometry, real-time quantitative PCR, western blots, and enzyme-linked immunosorbent assays were used to compare the expression levels of metalloproteinase 3 (MMP3) in MSCs derived from various tissues, including the tonsils, bone marrow, adipose tissue, and umbilical cord. Recipient mice were conditioned with busulfan and cyclophosphamide, and BMCs, either as a sole population or with control or MMP3-knockdown TMSCs, were co-transplanted into these mice. The effects of TMSC-expressed MMP3 were investigated. Additionally, Enzchek collagenase and Transwell migration assays were used to confirm that the collagenase activity of TMSC-expressed MMP3 enhanced BMC migration.

RESULTS

Mice subjected to the myeloablative regimen exhibited increased mRNA expression of collagen type IV alpha 1/2 (Col4a1 and Col4a2). Among the various extracellular matrix-modulating proteins secreted by TMSCs, MMP3 was expressed at higher levels in TMSCs than in other MSCs. Mice co-transplanted with BMCs and control TMSCs exhibited a higher survival rate, weight recovery, and bone marrow cellularity compared with mice co-transplanted with BMCs and MMP3-knockdown TMSCs. Control TMSC-CM possessed higher collagenase activity against collagen IV than MMP3-knockdown TMSC-CM. TMSC-CM also accelerated BMC migration by degrading collagen IV in vitro.

CONCLUSIONS

Collectively, these results indicate that TMSCs enhance BMC engraftment by the secretion of MMP3 for the modulation of the bone marrow extracellular matrix.

Hematopoietic versus leukemic stem cell quiescence: Challenges and therapeutic opportunities

Hematopoietic stem cells (HSC) are responsible for the production of mature blood cells. To ensure that the HSC pool does not get exhausted over the lifetime of an individual, most HSCs are in a state of quiescence with only a small proportion of HSCs dividing at any one time. HSC quiescence is carefully controlled by both intrinsic and extrinsic, niche-driven mechanisms. In acute myeloid leukemia (AML), the leukemic cells overtake the hematopoietic bone marrow niche where they acquire a quiescent state. These dormant AML cells are resistant to chemotherapeutics. Because they can re-establish the disease after therapy, they are often termed as quiescent leukemic stem cells (LSC) or leukemia-initiating cells. While advancements are being made to target particular driver mutations in AML, there is less focus on how to tackle the drug resistance of quiescent LSCs. This review summarises the current knowledge on the biochemical characteristics of quiescent HSCs and LSCs, the intracellular signaling pathways and the niche-driven mechanisms that control quiescence and the key differences between HSC- and LSC-quiescence that may be exploited for therapy.

Understanding the hematopoietic microenvironment in chronic myeloid leukemia: A concise review

Chronic myeloid leukemia (CML) is a myeloproliferative disease that results from the BCR-ABL gene-induced transformation of a primitive hematopoietic cell. This disease has been extensively studied, and, as a result, a very effective therapy has been developed: the tyrosine kinase inhibitors. Although, there is a significant knowledge about the intrinsic biology of CML cells, alterations in their bone marrow microenvironment are not yet completely understood. In this concise review, we summarized recent findings on the composition and function of the bone marrow microenvironment in CML, and their importance in the progression of the disease and treatment resistance.