Bone marrow CD169+ macrophages promote the retention of hematopoietic stem and progenitor cells in the mesenchymal stem cell niche

The Lactate Receptor GPR81 is a Mechanism of Leukemia-Associated Macrophage Polarization in the Bone Marrow Microenvironment

Interactions between acute myeloid leukemia (AML) and the bone marrow microenvironment (BMME) are critical to leukemia progression and chemoresistance. Altered metabolite levels in the tumor microenvironment contribute to immunosuppression in solid tumors, while this has not been studied yet in the leukemic BMME. Metabolomics of AML patient bone marrow serum detected elevated metabolites, including lactate, compared to age- and sex-matched controls. Excess lactate has been implicated in solid tumors for inducing suppressive tumor-associated macrophages (TAMs) and correlates with poor prognosis. We describe the role of lactate in the polarization of leukemia-associated macrophages (LAMs) using a murine model of blast crisis chronic myelogenous leukemia (bcCML) and mice genetically lacking the lactate receptor GPR81. LAMs were CD206hi and suppressive in transcriptomics and cytokine profiling. Yet, LAMs had a largely unique expression profile from other types of TAMs. We demonstrate GPR81 signaling as a mechanism of both LAM polarization and the direct support of leukemia cell growth and self-repopulation. Furthermore, LAMs and elevated lactate diminished the function of hematopoietic progenitors and stromal support, while knockout of GPR81 had modest protective effects on the hematopoietic system. We report microenvironmental lactate as a critical driver of AML-induced immunosuppression and leukemic progression, thus identifying GPR81 signaling as an exciting and novel therapeutic target for treating this devastating disease.

Regulation of the hematopoietic stem cell pool by C-Kit-associated trogocytosis

Hematopoietic stem cells (HSCs) are routinely mobilized from the bone marrow (BM) to the blood circulation for clinical transplantation. However, the precise mechanisms by which individual stem cells exit the marrow are not understood. This study identified cell-extrinsic and molecular determinants of a mobilizable pool of blood-forming stem cells. We found that a subset of HSCs displays macrophage-associated markers on their cell surface. Although fully functional, these HSCs are selectively niche-retained as opposed to stem cells lacking macrophage markers, which exit the BM upon forced mobilization. Macrophage markers on HSCs could be acquired through direct transfer by trogocytosis, regulated by receptor tyrosine-protein kinase C-Kit (CD117), from BM-resident macrophages in mouse and human settings. Our study provides proof of concept that adult stem cells utilize trogocytosis to rapidly establish and activate function-modulating molecular mechanisms.

Bone marrow niches for hematopoietic stem cells

Hematopoietic stem cells (HSCs) are the cornerstone of the hematopoietic system. HSCs sustain the continuous generation of mature blood derivatives while self-renewing to preserve a relatively constant pool of progenitors throughout life. Yet, long-term maintenance of functional HSCs exclusively takes place in association with their native tissue microenvironment of the bone marrow (BM). HSCs have been long proposed to reside in fixed and identifiable anatomical units found in the complex BM tissue landscape, which control their identity and fate in a deterministic manner. In the last decades, tremendous progress has been made in the dissection of the cellular and molecular fabric of the BM, the structural organization governing tissue function, and the plethora of interactions established by HSCs. Nonetheless, a holistic model of the mechanisms controlling HSC regulation in their niche is lacking to date. Here, we provide an overview of our current understanding of BM anatomy, HSC localization, and crosstalk within local cellular neighborhoods in murine and human tissues, and highlight fundamental open questions on how HSCs functionally integrate in the BM microenvironment.

Challenges and innovations in hematopoietic stem cell transplantation: exploring bone marrow niches and new model systems

Hematopoietic stem cell transplantation (HSCT) remains an indispensable therapeutic strategy for various hematological diseases. This review discusses the pivotal role of bone marrow (BM) niches in influencing the efficacy of HSCT and evaluates the current animal models, emphasizing their limitations and the need for alternative models. Traditional animal models, mainly murine xenograft, have provided significant insights, but due to species-specific differences, are often constrained from accurately mimicking human physiological responses. These limitations highlight the importance of developing alternative models that can more realistically replicate human hematopoiesis. Emerging models that include BM organoids and BM-on-a-chip microfluidic systems promise enhanced understanding of HSCT dynamics. These models aim to provide more accurate simulations of the human BM microenvironment, potentially leading to improved preclinical assessments and therapeutic outcomes. This review highlights the complexities of the BM niche, discusses the limitations of current models, and suggests directions for future research using advanced model systems. [BMB Reports 2024; 57(8): 352-362].

Remodeling of the bone marrow microenvironment during acute myeloid leukemia progression

Hematopoiesis requires a complex interplay between the hematopoietic stem and progenitor cells and the cells of the bone marrow microenvironment (BMM). The BMM is heterogeneous, with different regions having distinct cellular, molecular, and metabolic composition and function. Studies have shown that this niche is disrupted in patients with acute myeloid leukemia (AML), which plays a crucial role in disease progression. This review provides a comprehensive overview of the components of vascular and endosteal niches and the molecular mechanisms by which they regulate normal hematopoiesis. We also discuss how these niches are modified in the context of AML, into a disease-promoting niche and how the modified niches in turn regulate AML blast survival and proliferation. We focus on mechanisms of modifications in structural and cellular components of the bone marrow (BM) niche by the AML cells and its impact on leukemic progression and patient outcome. Finally, we also discuss mechanisms by which the altered BM niche protects AML blasts from treatment agents, thereby causing therapy resistance in AML patients. We also summarize ongoing clinical trials that target various BM niche components in the treatment of AML patients. Hence, the BM niche represents a promising target to treat AML and promote normal hematopoiesis.

From drosophila to humans: a journey through macrophage development

Macrophages are fascinating immune cells involved in a variety of processes in both health and disease. Although they were first discovered and characterized by their functions as professional phagocytes and antigen-presenting cells, it is now clear that macrophages have multiple roles within embryonic development, tissue homeostasis, regulation of inflammation, and host response to pathogens and tissue insults. Interestingly, macrophages, or macrophage-like cells, exist in a variety of organisms, from echinoderms to humans, and are present also in species that lack an adaptive immune system or hematopoietic stem cells (HSCs). In mammals, macrophages can be generated from bone marrow precursors through a monocyte intermediate, but it is now known that they are also generated during earlier hematopoietic waves in the embryo. Seeding a variety of tissues at different times, macrophages contribute to embryonic organogenesis and tissue homeostasis. Interestingly, in species where embryonic macrophages are generated before HSC specification, they seem to be an important component of the HSC generative microenvironment. There are many excellent reviews reporting the current knowledge on the ontogeny and functions of macrophages in adult tissues. Here, we aim to summarize the current knowledge on the development and functions of embryonic macrophages across the most used animal models, with a special focus on developmental hematopoiesis.

Transplantation of alveolar macrophages improves the efficacy of endothelial progenitor cell therapy in mouse model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a severe complication of preterm births, which develops due to exposure to supplemental oxygen and mechanical ventilation. Published studies demonstrated that the number of endothelial progenitor cells (EPC) is decreased in mouse and human BPD lungs and that adoptive transfer of EPC is an effective approach in reversing the hyperoxia-induced lung damage in mouse model of BPD. Recent advancements in macrophage biology identified the specific subtypes of circulating and resident macrophages mediating the developmental and regenerative functions in the lungs. Several studies reported the successful application of macrophage therapy in accelerating the regenerative capacity of damaged tissues and enhancing the therapeutic efficacy of other transplantable progenitor cells. In the present study, we explored the efficacy of combined cell therapy with EPC and resident alveolar macrophages (rAM) in hyperoxia-induced BPD mouse model. rAM and EPC were purified from neonatal mouse lungs and were used for adoptive transfer to the recipient neonatal mice exposed to hyperoxia. Adoptive transfer of rAM alone did not result in engraftment of donor rAM into the lung tissue but increased the mRNA level and protein concentration of proangiogenic CXCL12 chemokine in recipient mouse lungs. Depletion of rAM by chlodronate-liposomes decreased the retention of donor EPC after their transplantation into hyperoxia-injured lungs. Adoptive transfer of rAM in combination with EPC enhanced the therapeutic efficacy of EPC as evidenced by increased retention of EPC, increased capillary density, improved arterial oxygenation, and alveolarization in hyperoxia-injured lungs. Dual therapy with EPC and rAM has promise in human BPD.NEW & NOTEWORTHY Recent studies demonstrated that transplantation of lung-resident endothelial progenitor cells (EPC) is an effective therapy in mouse model of bronchopulmonary dysplasia (BPD). However, key factors regulating the efficacy of EPC are unknown. Herein, we demonstrate that transplantation of tissue-resident alveolar macrophages (rAM) increases CXCL12 expression in neonatal mouse lungs. rAM are required for retention of donor EPC in hyperoxia-injured lungs. Co-transplantation of rAM and EPC improves the efficacy of EPC therapy in mouse BPD model.

How aging influences the gut-bone marrow axis and alters hematopoietic stem cell regulation

The gut microbiome has come to prominence across research disciplines, due to its influence on major biological systems within humans. Recently, a relationship between the gut microbiome and hematopoietic system has been identified and coined the gut-bone marrow axis. It is well established that the hematopoietic system and gut microbiome separately alter with age; however, the relationship between these changes and how these systems influence each other demands investigation. Since the hematopoietic system produces immune cells that help govern commensal bacteria, it is important to identify how the microbiome interacts with hematopoietic stem cells (HSCs). The gut microbiota has been shown to influence the development and outcomes of hematologic disorders, suggesting dysbiosis may influence the maintenance of HSCs with age. Short chain fatty acids (SCFAs), lactate, iron availability, tryptophan metabolites, bacterial extracellular vesicles, microbe associated molecular patterns (MAMPs), and toll-like receptor (TLR) signalling have been proposed as key mediators of communication across the gut-bone marrow axis and will be reviewed in this article within the context of aging.

Hematopoietic Stem Cells and Their Niche in Bone Marrow

Extensive research has explored the functional correlation between stem cells and progenitor cells, particularly in blood. Hematopoietic stem cells (HSCs) can self-renew and regenerate tissues within the bone marrow, while stromal cells regulate tissue function. Recent studies have validated the role of mammalian stem cells within specific environments, providing initial empirical proof of this functional phenomenon. The interaction between bone and blood has always been vital to the function of the human body. It was initially proposed that during evolution, mammalian stem cells formed a complex relationship with the surrounding microenvironment, known as the niche. Researchers are currently debating the significance of molecular-level data to identify individual stromal cell types due to incomplete stromal cell mapping. Obtaining these data can help determine the specific activities of HSCs in bone marrow. This review summarizes key topics from previous studies on HSCs and their environment, discussing current and developing concepts related to HSCs and their niche in the bone marrow.

Systemic and local regulation of hematopoietic homeostasis in health and disease

Hematopoietic stem cells (HSCs) generate all blood cell lineages responsible for tissue oxygenation, life-long hematopoietic homeostasis and immune protection. In adulthood, HSCs primarily reside in the bone marrow (BM) microenvironment, consisting of diverse cell types that constitute the stem cell 'niche'. The adaptability of the hematopoietic system is required to respond to the needs of the host, whether to maintain normal physiology or during periods of physical, psychosocial or environmental stress. Hematopoietic homeostasis is achieved by intricate coordination of systemic and local factors that orchestrate the function of HSCs throughout life. However, homeostasis is not a static process; it modulates HSC and progenitor activity in response to circadian rhythms coordinated by the central and peripheral nervous systems, inflammatory cues, metabolites and pathologic conditions. Here, we review local and systemic factors that impact hematopoiesis, focusing on the implications of aging, stress and cardiovascular disease.

Granulocyte Colony Stimulating Factor-Mobilized Peripheral Blood Mononuclear Cells: An Alternative Cellular Source for Chimeric Antigen Receptor Therapy

Lymphocyte collection by apheresis for CAR-T production usually does not include blood mobilized using granulocyte colony stimulating factor (G-CSF) due to the widespread knowledge that it causes a decrease in the number and functionality of lymphocytes. However, it is used for stem cell transplant, which is a common treatment for hematological malignancies. The growing demand for CAR therapies (CAR-T and NK-CAR), both in research and clinics, makes it necessary to evaluate whether mobilized PBSC products may be potential candidates for use in such therapies. This review collects recent works that experimentally verify the role and functionality of T and NK lymphocytes and the generation of CAR-T from apheresis after G-CSF mobilization. As discussed, T cells do not vary significantly in their phenotype, the ratio of CD4+ and CD8+ remains constant, and the different sub-populations remain stable. In addition, the expansion and proliferation rates are invariant regardless of mobilization with G-CSF as well as the secretion of proinflammatory cytokines and the cytotoxic ability. Therefore, cells mobilized before apheresis are postulated as a new alternative source of T cells for adoptive therapies that will serve to alleviate high demand, increase availability, and take advantage of the substantial number of existing cryopreserved products.

Discovering adaptive features of innate immune memory

Conventionally, it was thought that innate immunity operated through a simple system of nonspecific responses to an insult. However, this perspective now seems overly simplistic. It has become evident that intricate cooperation and networking among various cells, receptors, signaling pathways, and protein complexes are essential for regulating and defining the overall activation status of the immune response, where the distinction between innate and adaptive immunity becomes ambiguous. Given the evolutionary timeline of vertebrates and the success of plants and invertebrates which depend solely on innate immunity, immune memory cannot be considered an innovation of only the lymphoid lineage. Indeed, the evolutionary innate immune memory program is a conserved mechanism whereby innate immune cells can induce a heightened response to a secondary stimulus due to metabolic and epigenetic reprogramming. Importantly, the longevity of this memory phenotype can be attributed to the reprogramming of self-renewing hematopoietic stem cells (HSCs) in the bone marrow, which is subsequently transmitted to lineage-committed innate immune cells. HSCs reside within a complex regulated network of immune and stromal cells that govern their two primary functions: self-renewal and differentiation. In this review, we delve into the emerging cellular and molecular mechanisms as well as metabolic pathways of innate memory in HSCs, which harbor substantial therapeutic promise.

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Unveiling aging dynamics in the hematopoietic system insights from single-cell technologies

As the demographic structure shifts towards an aging society, strategies aimed at slowing down or reversing the aging process become increasingly essential. Aging is a major predisposing factor for many chronic diseases in humans. The hematopoietic system, comprising blood cells and their associated bone marrow microenvironment, intricately participates in hematopoiesis, coagulation, immune regulation and other physiological phenomena. The aging process triggers various alterations within the hematopoietic system, serving as a spectrum of risk factors for hematopoietic disorders, including clonal hematopoiesis, immune senescence, myeloproliferative neoplasms and leukemia. The emerging single-cell technologies provide novel insights into age-related changes in the hematopoietic system. In this review, we summarize recent studies dissecting hematopoietic system aging using single-cell technologies. We discuss cellular changes occurring during aging in the hematopoietic system at the levels of the genomics, transcriptomics, epigenomics, proteomics, metabolomics and spatial multi-omics. Finally, we contemplate the future prospects of single-cell technologies, emphasizing the impact they may bring to the field of hematopoietic system aging research.

Transforming the Niche: The Emerging Role of Extracellular Vesicles in Acute Myeloid Leukaemia Progression

Acute myeloid leukaemia (AML) management remains a significant challenge in oncology due to its low survival rates and high post-treatment relapse rates, mainly attributed to treatment-resistant leukaemic stem cells (LSCs) residing in bone marrow (BM) niches. This review offers an in-depth analysis of AML progression, highlighting the pivotal role of extracellular vesicles (EVs) in the dynamic remodelling of BM niche intercellular communication. We explore recent advancements elucidating the mechanisms through which EVs facilitate complex crosstalk, effectively promoting AML hallmarks and drug resistance. Adopting a temporal view, we chart the evolving landscape of EV-mediated interactions within the AML niche, underscoring the transformative potential of these insights for therapeutic intervention. Furthermore, the review discusses the emerging understanding of endothelial cell subsets' impact across BM niches in shaping AML disease progression, adding another layer of complexity to the disease progression and treatment resistance. We highlight the potential of cutting-edge methodologies, such as organ-on-chip (OoC) and single-EV analysis technologies, to provide unprecedented insights into AML-niche interactions in a human setting. Leveraging accumulated insights into AML EV signalling to reconfigure BM niches and pioneer novel approaches to decipher the EV signalling networks that fuel AML within the human context could revolutionise the development of niche-targeted therapy for leukaemia eradication.

Proteomic analysis reveals a potential role for extracellular vesicles within the erythroblastic island niche

Introduction: Erythroblastic island (EBI) macrophages play an essential role in the production and maturation of the vast numbers of red blood cells (RBCs) that are produced throughout life. Their location within the bone marrow makes it difficult to study the cellular and molecular interactions associated with their action so we have used an in vitro model of the EBI niche using macrophages derived from human induced pluripotent stem cells (hiPSCs). We previously demonstrated that the activation of the transcription factor KLF1 enhanced the activity of hiPSC-derived EBI macrophages. Methods: To elucidate the mechanisms associated with EBI-like activity we carried out a quantitative proteomic analysis and assessed the role of extracellular vesicles using Nanosight Tracking analyses and media filtration. Results and Discussion: Gene ontology analysis showed that many of the proteins upregulated by KLF1 were protein-binding factors, some of which were associated with the cell membrane or extracellular vesicles We demonstrated that filtration of macrophage-conditioned media resulted in a reduction in the supportive effects on erythroid cell viability and maturation implying a role for extracellular vesicles but this was not KLF1 dependent. Pathway analyses of the proteomic data revealed that proteins upregulated by KLF1 were associated with the citric acid cycle, pyruvate metabolism and ATP synthesis indicating that KLF1-activated macrophages had a metabolic profile comparable to a pro-reparative phenotype. This study has generated a proteomic dataset that could provide new insights into the role of macrophages within the EBI niche and has indicated a potential role for extracellular vesicles in the differentiation and maturation of RBCs in vitro. Further research will aid in the production of RBCs in vitro for use in disease modelling and cell therapy.

Macrophage heterogeneity in bone metastasis

Previous studies illustrated that macrophage, a type of innate immune cell, plays critical roles in tumour progression and metastasis. Bone is the most frequent site of metastasis for several cancer types including breast, prostate, and lung. In bone metastasis, osteoclast, a macrophage subset specialized in bone resorption, was heavily investigated in the past. Recent studies illustrated that other macrophage subsets, e.g. monocyte-derived macrophages, and bone resident macrophages, promoted bone metastasis independent of osteoclast function. These novel mechanisms further improved our understanding of macrophage heterogeneity in the context of bone metastasis and illustrated new opportunities for future studies.

Fetal liver macrophages contribute to the hematopoietic stem cell niche by controlling granulopoiesis

During embryogenesis, the fetal liver becomes the main hematopoietic organ, where stem and progenitor cells as well as immature and mature immune cells form an intricate cellular network. Hematopoietic stem cells (HSCs) reside in a specialized niche, which is essential for their proliferation and differentiation. However, the cellular and molecular determinants contributing to this fetal HSC niche remain largely unknown. Macrophages are the first differentiated hematopoietic cells found in the developing liver, where they are important for fetal erythropoiesis by promoting erythrocyte maturation and phagocytosing expelled nuclei. Yet, whether macrophages play a role in fetal hematopoiesis beyond serving as a niche for maturing erythroblasts remains elusive. Here, we investigate the heterogeneity of macrophage populations in the murine fetal liver to define their specific roles during hematopoiesis. Using a single-cell omics approach combined with spatial proteomics and genetic fate-mapping models, we found that fetal liver macrophages cluster into distinct yolk sac-derived subpopulations and that long-term HSCs are interacting preferentially with one of the macrophage subpopulations. Fetal livers lacking macrophages show a delay in erythropoiesis and have an increased number of granulocytes, which can be attributed to transcriptional reprogramming and altered differentiation potential of long-term HSCs. Together, our data provide a detailed map of fetal liver macrophage subpopulations and implicate macrophages as part of the fetal HSC niche.

Isolation of Murine Neonatal and Adult Osteomacs to Examine Their Role in the Hematopoietic Niche

Maintenance of hematopoietic stem cell (HSC) function is an orchestrated event between multiple cell types, and crosstalk between these cell types is an essential part of HSC regulation. Among the cell groups of the niche involved in this process are a group of bone-resident macrophages known as osteomacs (OM). Previously, it was demonstrated that OM and osteoblasts contained within neonatal calvarial cells are critical to maintain hematopoietic function. Additionally, interactions between neonatal calvarial cells and megakaryocytes further enhance this hematopoietic activity. In this chapter, we explore one such interaction involving OM and osteoblasts in the hematopoietic niche. We describe a protocol to isolate OM from both neonatal and adult mice, and subsequently use colony-forming assays to demonstrate their interaction with osteoblasts in maintaining HSC function.

Extramedullary hematopoiesis in cancer

Hematopoiesis can occur outside of the bone marrow during inflammatory stress to increase the production of primarily myeloid cells at extramedullary sites; this process is known as extramedullary hematopoiesis (EMH). As observed in a broad range of hematologic and nonhematologic diseases, EMH is now recognized for its important contributions to solid tumor pathology and prognosis. To initiate EMH, hematopoietic stem cells (HSCs) are mobilized from the bone marrow into the circulation and to extramedullary sites such as the spleen and liver. At these sites, HSCs primarily produce a pathological subset of myeloid cells that contributes to tumor pathology. The EMH HSC niche, which is distinct from the bone marrow HSC niche, is beginning to be characterized. The important cytokines that likely contribute to initiating and maintaining the EMH niche are KIT ligands, CXCL12, G-CSF, IL-1 family members, LIF, TNFα, and CXCR2. Further study of the role of EMH may offer valuable insights into emergency hematopoiesis and therapeutic approaches against cancer. Exciting future directions for the study of EMH include identifying common and distinct EMH mechanisms in cancer, infectious diseases, and chronic autoimmune diseases to control these conditions.

G-CSF-induced hematopoietic stem cell mobilization from the embryonic hematopoietic niche does not require neutrophils and macrophages

Hematopoietic stem cell transplantation requires the collection of hematopoietic cells from patients or stem cell donors. Granulocyte colony-stimulating factor (G-CSF) is widely used in the clinic to mobilize hematopoietic stem and progenitor cells (HSPCs) from the adult bone marrow niche into circulation, allowing a collection of HSPCs from the blood. The mechanism by which G-CSF acts to mobilize HSPCs is unclear, with some studies showing a direct stimulation of stem cells and others suggesting that myeloid cells are required. In this study, we developed a heat-inducible G-CSF transgenic zebrafish line to study HSPC mobilization in vivo. Live imaging of HSPCs after G-CSF induction revealed an increase in circulating HSPCs, demonstrating a successful HSPC mobilization. These mobilized HSPCs went on to prematurely colonize the kidney marrow, the adult zebrafish hematopoietic niche. We eliminated neutrophils or macrophages using a nitroreductase-based cell ablation system and found that G-CSF still mobilizes HSPCs from the niche. Our findings indicate that neutrophils and macrophages are not required for G-CSF-induced HSPC mobilization from the embryonic hematopoietic niche.

Bone marrow macrophages are involved in the ineffective hematopoiesis of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of heterogeneous myeloid clonal disorders characterized by ineffective hematopoiesis. Accumulating evidence has shown that macrophages (MΦs) are important components in the regulation of tumor progression and hematopoietic stem cells (HSCs). However, the roles of bone marrow (BM) MΦs in regulating normal and malignant hematopoiesis in different clinical stages of MDS are largely unknown. Age-paired patients with lower-risk MDS (N = 15), higher-risk MDS (N = 15), de novo acute myeloid leukemia (AML) (N = 15), and healthy donors (HDs) (N = 15) were enrolled. Flow cytometry analysis showed increased pro-inflammatory monocyte subsets and a decreased classically activated (M1) MΦs/alternatively activated (M2) MΦs ratio in the BM of patients with higher-risk MDS compared to lower-risk MDS. BM MФs from patients with higher-risk MDS and AML showed impaired phagocytosis activity but increased migration compared with lower-risk MDS group. AML BM MΦs showed markedly higher S100A8/A9 levels than lower-risk MDS BM MΦs. More importantly, coculture experiments suggested that the HSC supporting abilities of BM MΦs from patients with higher-risk MDS decreased, whereas the malignant cell supporting abilities increased compared with lower-risk MDS. Gene Ontology enrichment comparing BM MΦs from lower-risk MDS and higher-risk MDS for genes was involved in hematopoiesis- and immunity-related pathways. Our results suggest that BM MΦs are involved in ineffective hematopoiesis in patients with MDS, which indicates that repairing aberrant BM MΦs may represent a promising therapeutic approach for patients with MDS.

Contribution of the TIME in BCP-ALL: the basis for novel approaches therapeutics

The bone marrow (BM) niche is a microenvironment where both immune and non-immune cells functionally interact with hematopoietic stem cells (HSC) and more differentiated progenitors, contributing to the regulation of hematopoiesis. It is regulated by various signaling molecules such as cytokines, chemokines, and adhesion molecules in its microenvironment. However, despite the strict regulation of BM signals to maintain their steady state, accumulating evidence in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) indicates that leukemic cells can disrupt the physiological hematopoietic niche in the BM, creating a new leukemia-supportive microenvironment. This environment favors immunological evasion mechanisms and the interaction of these cells with the development and progression of BCP-ALL. With a growing understanding of the tumor immune microenvironment (TIME) in the development and progression of BCP-ALL, current strategies focused on "re-editing" TIME to promote antitumor immunity have been developed. In this review, we summarize how TIME cells are disrupted by the presence of leukemic cells, evading immunosurveillance mechanisms in the BCP-ALL model. We also explore the crosstalk between TIME and leukemic cells that leads to treatment resistance, along with the most promising immuno-therapy strategies. Understanding and further research into the role of the BM microenvironment in leukemia progression and relapse are crucial for developing more effective treatments and reducing patient mortality.

Stromal bone marrow fibroblasts and mesenchymal stem cells support acute myeloid leukaemia cells and promote therapy resistance

The bone marrow (BM) is the primary site of adult haematopoiesis, where stromal elements (e.g. fibroblasts and mesenchymal stem cells [MSCs]) work in concert to support blood cell development. However, the establishment of an abnormal clone can lead to a blood malignancy, such as acute myeloid leukaemia (AML). Despite our increased understanding of the pathophysiology of the disease, patient survival remains suboptimal, mainly driven by the development of therapy resistance. In this review, we highlight the importance of bone marrow fibroblasts and MSCs in health and acute myeloid leukaemia and their impact on patient prognosis. We discuss how stromal elements reduce the killing effects of therapies via a combination of contact-dependent (e.g. integrins) and contact-independent (i.e. secreted factors) mechanisms, accompanied by the establishment of an immunosuppressive microenvironment. Importantly, we underline the challenges of therapeutically targeting the bone marrow stroma to improve acute myeloid leukaemia patient outcomes, due to the inherent heterogeneity of stromal cell populations. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Haematopoietic stem cell health in sickle cell disease and its implications for stem cell therapies and secondary haematological disorders

Gene modification of haematopoietic stem cells (HSCs) is a potentially curative approach to sickle cell disease (SCD) and offers hope for patients who are not eligible for allogeneic HSC transplantation. Current approaches require in vitro manipulation of healthy autologous HSC prior to their transplantation. However, the health and integrity of HSCs may be compromised by a variety of disease processes in SCD, and challenges have emerged in the clinical trials of gene therapy. There is also concern about increased susceptibility to haematological malignancies during long-term follow up of patients, and this raises questions about genomic stability in the stem cell compartment. In this review, we evaluate the evidence for HSC deficits in SCD and then discuss their potential causation. Finally, we suggest several questions which need to be addressed in order to progress with successful HSC manipulation for gene therapy in SCD.

Spatial mapping of human hematopoiesis at single-cell resolution reveals aging-associated topographic remodeling

ABSTRACT

The spatial anatomy of hematopoiesis in the bone marrow (BM) has been extensively studied in mice and other preclinical models, but technical challenges have precluded a commensurate exploration in humans. Institutional pathology archives contain thousands of paraffinized BM core biopsy tissue specimens, providing a rich resource for studying the intact human BM topography in a variety of physiologic states. Thus, we developed an end-to-end pipeline involving multiparameter whole tissue staining, in situ imaging at single-cell resolution, and artificial intelligence-based digital whole slide image analysis and then applied it to a cohort of disease-free samples to survey alterations in the hematopoietic topography associated with aging. Our data indicate heterogeneity in marrow adipose tissue (MAT) content within each age group and an inverse correlation between MAT content and proportions of early myeloid and erythroid precursors, irrespective of age. We identify consistent endosteal and perivascular positioning of hematopoietic stem and progenitor cells (HSPCs) with medullary localization of more differentiated elements and, importantly, uncover new evidence of aging-associated changes in cellular and vascular morphologies, microarchitectural alterations suggestive of foci with increased lymphocytes, and diminution of a potentially active megakaryocytic niche. Overall, our findings suggest that there is topographic remodeling of human hematopoiesis associated with aging. More generally, we demonstrate the potential to deeply unravel the spatial biology of normal and pathologic human BM states using intact archival tissue specimens.

Hematopoietic and stromal DMP1-Cre labeled cells form a unique niche in the bone marrow

Skeletogenesis and hematopoiesis are interdependent. Niches form between cells of both lineages where microenvironmental cues support specific lineage commitment. Because of the complex topography of bone marrow (BM), the identity and function of cells within specialized niches has not been fully elucidated. Dentin Matrix Protein 1 (DMP1)-Cre mice have been utilized in bone studies as mature osteoblasts and osteocytes express DMP1. DMP1 has been identified in CXCL12+ cells and an undefined CD45+ population. We crossed DMP1-Cre with Ai9 reporter mice and analyzed the tdTomato+ (tdT+) population in BM and secondary hematopoietic organs. CD45+tdT+ express myeloid markers including CD11b and are established early in ontogeny. CD45+tdT+ cells phagocytose, respond to LPS and are radioresistant. Depletion of macrophages caused a significant decrease in tdT+CD11b+ myeloid populations. A subset of CD45+tdT+ cells may be erythroid island macrophages (EIM) which are depleted after G-CSF treatment. tdT+CXCL12+ cells are in direct contact with F4/80 macrophages, express RANKL and form a niche with B220+ B cells. A population of resident cells within the thymus are tdT+ and express myeloid markers and RANKL. In conclusion, in addition to targeting osteoblast/osteocytes, DMP1-Cre labels unique cell populations of macrophage and stromal cells within BM and thymus niches and expresses key microenvironmental factors.

The TLR2/TLR6 ligand FSL-1 mitigates radiation-induced hematopoietic injury in mice and nonhuman primates

Thrombocytopenia, hemorrhage, anemia, and infection are life-threatening issues following accidental or intentional radiation exposure. Since few therapeutics are available, safe and efficacious small molecules to mitigate radiation-induced injury need to be developed. Our previous study showed the synthetic TLR2/TLR6 ligand fibroblast stimulating lipopeptide (FSL-1) prolonged survival and provided MyD88-dependent mitigation of hematopoietic acute radiation syndrome (H-ARS) in mice. Although mice and humans differ in TLR number, expression, and function, nonhuman primate (NHP) TLRs are like those of humans; therefore, studying both animal models is critical for drug development. The objectives of this study were to determine the efficacy of FSL-1 on hematopoietic recovery in small and large animal models subjected to sublethal total body irradiation and investigate its mechanism of action. In mice, we demonstrate a lack of adverse effects, an easy route of delivery (subcutaneous) and efficacy in promoting hematopoietic progenitor cell proliferation by FSL-1. NHP given radiation, followed a day later with a single subcutaneous administration of FSL-1, displayed no adversity but showed elevated hematopoietic cells. Our analyses revealed that FSL-1 promoted red blood cell development and induced soluble effectors following radiation exposure. Cytologic analysis of bone marrow aspirates revealed a striking enhancement of mononuclear progenitor cells in FSL-1-treated NHP. Combining the efficacy of FSL-1 in promoting hematopoietic cell recovery with the lack of adverse effects induced by a single administration supports the application of FSL-1 as a viable countermeasure against H-ARS.

Repopulating Kupffer cells originate directly from hematopoietic stem cells

BACKGROUND

Kupffer cells (KCs) originate from yolk-sac progenitors before birth. Throughout adulthood, they self-maintain independently from the input of circulating monocytes (MOs) at a steady state and are replenished within 2 weeks after having been depleted, but the origin of repopulating KCs in adults remains unclear. The current paradigm dictates that repopulating KCs originate from preexisting KCs or monocytes, but there remains a lack of fate-mapping evidence.

METHODS

We first traced the fate of preexisting KCs and that of monocytic cells with tissue-resident macrophage-specific and monocytic cell-specific fate-mapping mouse models, respectively. Secondly, we performed genetic lineage tracing to determine the type of progenitor cells involved in response to KC-depletion in mice. Finally, we traced the fate of hematopoietic stem cells (HSCs) in an HSC-specific fate-mapping mouse model, in the context of chronic liver inflammation induced by repeated carbon tetrachloride treatment.

RESULTS

By using fate-mapping mouse models, we found no evidence that repopulating KCs originate from preexisting KCs or MOs and found that in response to KC-depletion, HSCs proliferated in the bone marrow, mobilized into the blood, adoptively transferred into the liver and differentiated into KCs. Then, in the chronic liver inflammation context, we confirmed that repopulating KCs originated directly from HSCs.

CONCLUSION

Taken together, these findings provided in vivo fate-mapping evidence that repopulating KCs originate directly from HSCs, which presents a completely novel understanding of the cellular origin of repopulating KCs and shedding light on the divergent roles of KCs in liver homeostasis and diseases.

Oncofetal reprogramming in tumor development and progression: novel insights into cancer therapy

Emerging evidence indicates that cancer cells can mimic characteristics of embryonic development, promoting their development and progression. Cancer cells share features with embryonic development, characterized by robust proliferation and differentiation regulated by signaling pathways such as Wnt, Notch, hedgehog, and Hippo signaling. In certain phase, these cells also mimic embryonic diapause and fertilized egg implantation to evade treatments or immune elimination and promote metastasis. Additionally, the upregulation of ATP-binding cassette (ABC) transporters, including multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 1 (MRP1), and breast cancer-resistant protein (BCRP), in drug-resistant cancer cells, analogous to their role in placental development, may facilitate chemotherapy efflux, further resulting in treatment resistance. In this review, we concentrate on the underlying mechanisms that contribute to tumor development and progression from the perspective of embryonic development, encompassing the dysregulation of developmental signaling pathways, the emergence of dormant cancer cells, immune microenvironment remodeling, and the hyperactivation of ABC transporters. Furthermore, we synthesize and emphasize the connections between cancer hallmarks and embryonic development, offering novel insights for the development of innovative cancer treatment strategies.

The impact of diabetes mellitus on hematopoietic stem cell mobilization, a-single center cohort study

BACKGROUND

Factors such as age, underlying hematological disease, chemotherapy and radiotherapy used, and bone marrow infiltration may cause mobilization failure. Several preclinical observed that diabetes mellitus (DM) leads to profound remodeling of the hematopoietic stem cell (HSC) niche, resulting in the impaired release of HSCs. We aim to examine the effect of DM on HSC mobilization and to investigate whether there is a relationship between complications developing in the DM process and drugs used to treat DM and mobilization failure.

METHODS

In Erciyes University Bone Marrow Transplantation Unit, 218 patients who underwent apheresis for stem cell mobilization between 2011 and 2021 were evaluated retrospectively. One hundred and nine patients had a diagnosis of DM, and 109 did not.

RESULTS

Mobilization failure developed in 17 (15.6 %) of the patients in the DM group, while it developed in 7 (6.4 %) patients in the non-DM group (p = 0.03). CD34+ stem cell count was 8.05 (1.3-30.2) × 106/kg in the DM group, while it was 8.2 (1.7-37.3) × 106/kg in the other group (p = 0.55). There was no statistically significant relationship between glucose and hemoglobin A1c levels and the amount of CD34+ cells (p = 0.83 and p = 0.14, respectively). Using sulfonylurea was the only independent predictor of mobilization failure (OR 5.75, 95 % CI: 1.38-24.05, p = 0.02).

CONCLUSION

DM should be considered a risk factor for mobilization failure. Further research is needed fully to understand the mechanisms underlying the mobilization failure effects of sulfonylureas and to develop strategies to improve stem cell mobilization in diabetic patients.

Haematopoietic stem cell numbers are not solely determined by niche availability

Haematopoietic stem cells (HSCs) reside in specialized microenvironments, also referred to as niches, and it has been widely believed that HSC numbers are determined by the niche size alone 1-5 . However, the vast excess of the number of niche cells over that of HSCs raises questions about this model. We initially established a mathematical model of niche availability and occupancy, which predicted that HSC numbers are restricted at both systemic and local levels. To address this question experimentally, we developed a femoral bone transplantation system, enabling us to increase the number of available HSC niches. We found that the addition of niches does not alter total HSC numbers in the body, regardless of whether the endogenous (host) niche is intact or defective, suggesting that HSC numbers are limited at the systemic level. Additionally, HSC numbers in transplanted wild-type femurs did not increase beyond physiological levels when HSCs were mobilized from defective endogenous niches to the periphery, indicating that HSC numbers are also constrained at the local level. Our study demonstrates that HSC numbers are not solely determined by niche availability, thereby rewriting the long-standing model for the regulation of HSC numbers.

Bone marrow vasculature advanced in vitro models for cancer and cardiovascular research

Cardiometabolic diseases and cancer are among the most common diseases worldwide and are a serious concern to the healthcare system. These conditions, apparently distant, share common molecular and cellular determinants, that can represent targets for preventive and therapeutic approaches. The bone marrow plays an important role in this context as it is the main source of cells involved in cardiovascular regeneration, and one of the main sites of liquid and solid tumor metastasis, both characterized by the cellular trafficking across the bone marrow vasculature. The bone marrow vasculature has been widely studied in animal models, however, it is clear the need for human-specific in vitro models, that resemble the bone vasculature lined by endothelial cells to study the molecular mechanisms governing cell trafficking. In this review, we summarized the current knowledge on in vitro models of bone marrow vasculature developed for cardiovascular and cancer research.

Nestin+ Mesenchymal Stromal Cells Fibrotic Transition Mediated by CD169+ Macrophages in Bone Marrow Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (cGVHD) involves multiple organs, but little is known about bone marrow (BM) alterations caused by cGVHD. In mice and humans, we found that cGVHD is associated with BM fibrosis resulting in T cell infiltration, IgG deposition, and hematopoietic dysfunction. Macrophages and Nestin+ mesenchymal stromal cells (MSCs) participated in the process of BM fibrosis during BM cGVHD development. BM macrophage numbers were significantly increased in mice and humans with BM fibrosis associated with cGVHD. Amplified macrophages produced TGF-β1, which recruited Nestin+ MSCs forming clusters, and Nestin+ MSCs later differentiated into fibroblasts, a process mediated by increased TGF-β/Smad signaling. TLR4/MyD88-mediated activation of endoplasmic reticulum (ER) stress in macrophages is associated with fibrosis by increasing Nestin+ MSC migration and differentiation into fibroblasts. Depletion of macrophages by clodronate-containing liposomes and inhibition of ER stress by 4-phenylbutyric acid reversed BM fibrosis by inhibiting fibroblast differentiation. These studies provide insights into the pathogenesis of BM fibrosis during cGVHD development.

Human umbilical cord blood-derived mesenchymal stem cells restored hematopoiesis by improving radiation induced bone marrow niche remodeling in rats

BACKGROUND

Functional hematopoiesis is governed by the bone marrow (BM) niche, which is compromised by radiotherapy, leading to radiation induced BM failure. The aim of this study was to demonstrate the radiation induced pathological remodeling of the niche and the efficacy of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) in restoring hematopoiesis via improvement of the niche.

METHODS

Thirty male Wistar rats were equally assigned to three groups: control (CON), irradiated (IR), and IR+hUCB-MSCs. Biochemical, histopathological and immunohistochemical analyses were performed to detect collagen type III and IV, Aquaporin 1+ sinusoidal endothelial cells and immature hematopoietic cells, CD11c+ dendritic cells, Iba1+ macrophages, CD9+ megakaryocytes, Sca-1+, cKit+, CD133 and N-cadherin+ hematopoietic stem and progenitor cells, CD20+, Gr1+ mature hematopoietic cells, in addition to ki67+ proliferation, Bcl-2+ anti-apoptotic, caspase-3+ apoptotic, TNF-α+ inflammatory cells. Histoplanimetry data were statistically analyzed using the one-way analysis of variance followed by the post hoc Duncan's test. Moreover, Pearson's correlation was used to assess the correlation between various parameters.

RESULTS

In comparison to the IR group, the IR+hUCB-MSCs group showed restored cell populations and extracellular collagen components of the BM niche with significant increase in hematopoietic stem, progenitor, mature and proliferating cells, and a considerable decrease in apoptotic and inflammatory cells. Furthermore, highly significant correlations between BM niche and blood biochemical, histopathological, and immunohistochemical parameters were observed.

CONCLUSION

hUCB-MSCs restored functional hematopoiesis through amelioration of the BM niche components via reduction of oxidative stress, DNA damage, inflammation, and apoptosis with upregulation of cellular proliferation.

Genetically modified IL2 bone-marrow-derived myeloid cells reprogram the glioma immunosuppressive tumor microenvironment

Gliomas are one of the leading causes of cancer-related death in the adolescent and young adult (AYA) population. Two-thirds of AYA glioma patients are affected by low-grade gliomas (LGGs), but there are no specific treatments. Malignant progression is supported by the immunosuppressive stromal component of the tumor microenvironment (TME) exacerbated by M2 macrophages and a paucity of cytotoxic T cells. A single intravenous dose of engineered bone-marrow-derived myeloid cells that release interleukin-2 (GEMys-IL2) was used to treat mice with LGGs. Our results demonstrate that GEMys-IL2 crossed the blood-brain barrier, infiltrated the TME, and reprogrammed the immune cell composition and transcriptome. Moreover, GEMys-IL2 extended survival in an LGG immunocompetent mouse model. Here, we report the efficacy of an in vivo approach that demonstrates the potential for a cell-mediated innate immunotherapy designed to enhance the recruitment of activated effector T and natural killer cells within the glioma TME.

Role of chemokines in T-cell acute lymphoblastic Leukemia: From pathogenesis to therapeutic options

T-cell acute lymphoblastic leukemia (T-ALL) is a highly heterogeneous and aggressive subtype of hematologic malignancy, with limited therapeutic options due to the complexity of its pathogenesis. Although high-dose chemotherapy and allogeneic hematopoietic stem cell transplantation have improved outcomes for T-ALL patients, there remains an urgent need for novel treatments in cases of refractory or relapsed disease. Recent research has demonstrated the potential of targeted therapies aimed at specific molecular pathways to improve patient outcomes. Chemokine-related signals, both upstream and downstream, modulate the composition of distinct tumor microenvironments, thereby regulating a multitude of intricate cellular processes such as proliferation, migration, invasion and homing. Furthermore, the progress in research has made significant contributions to precision medicine by targeting chemokine-related pathways. This review article summarizes the crucial roles of chemokines and their receptors in T-ALL pathogenesis. Moreover, it explores the advantages and disadvantages of current and potential therapeutic options that target chemokine axes, including small molecule antagonists, monoclonal antibodies, and chimeric antigen receptor T-cells.

Sulfated Polysaccharide Regulates the Homing of HSPCs in a BMP-2-Triggered In Vivo Osteo-Organoid

Hematopoietic stem cell transplantation (HSCT) is a well-established method for a variety of acquired and congenital diseases. However, the limited number and sources of therapeutic hematopoietic stem/progenitor cells (HSPCs) hinder the further application of HSCT. A BMP-2 triggered in vivo osteo-organoid that is previously reported, serves as a kind of stem cell biogenerator, for obtaining therapeutic HSPCs via activating the residual regenerative capacity of mammals using bioactive biomaterials. Here, it is demonstrated that targeting the homing signaling of HSPCs elevates the proportions and biological functions of HSPCs in the in vivo osteo-organoid. Notably, it is identified that sulfonated chito-oligosaccharide, a degradation product of sulfonated chitosan, specifically elevates the expression of endothelial protein C receptor on HSPCs and vascular cell adhesion molecule-1 on macrophages in the in vivo osteo-organoid, ultimately leading to the production of adequate therapeutic HSPCs. This in vivo osteo-organoid approach has the potential to provide an alternative HSPCs source for HSCT and benefits more patients.

Clodronate is not protective in lethal viral encephalitis despite substantially reducing inflammatory monocyte infiltration in the CNS

Bone marrow (BM)-derived monocytes induce inflammation and tissue damage in a range of pathologies. In particular, in a mouse model of West Nile virus (WNV) encephalitis (WNE), nitric oxide-producing, Ly6Chi inflammatory monocytes from the BM are recruited to the central nervous system (CNS) and contribute to lethal immune pathology. Reducing the migration of these cells into the CNS using monoclonal antibody blockade, immune-modifying particles or CSF-1R inhibitors reduces neuroinflammation, improving survival and/or clinical outcomes. Macrophages can also be targeted more broadly by administration of clodronate-encapsulated liposomes, which induce apoptosis in phagocytes. In this study, clodronate reduced the inflammatory infiltrate by 70% in WNE, however, surprisingly, this had no effect on disease outcome. More detailed analysis demonstrated a compensatory increase in neutrophils and enhanced activation status of microglia in the brain. In addition, we observed increased numbers of Ly6Chi BM monocytes with an increased proliferative capacity and expression of SCA-1 and CD16/32, potentially indicating output of immature cells from the BM. Once in the brain, these cells were more phagocytic and had a reduced expression of antigen-presenting molecules. Lastly, we show that clodronate also reduces non-myeloid cells in the spleen and BM, as well as ablating red blood cells and their proliferation. These factors likely impeded the therapeutic potential of clodronate in WNE. Thus, while clodronate provides an excellent system to deplete macrophages in the body, it has larger and broader effects on the phagocytic and non-phagocytic system, which must be considered in the interpretation of data.

Consequences of HIV infection in the bone marrow niche

Dysregulation of the bone marrow niche resulting from the direct and indirect effects of HIV infection contributes to haematological abnormalities observed in HIV patients. The bone marrow niche is a complex, multicellular environment which functions primarily in the maintenance of haematopoietic stem/progenitor cells (HSPCs). These adult stem cells are responsible for replacing blood and immune cells over the course of a lifetime. Cells of the bone marrow niche support HSPCs and help to orchestrate the quiescence, self-renewal and differentiation of HSPCs through chemical and molecular signals and cell-cell interactions. This narrative review discusses the HIV-associated dysregulation of the bone marrow niche, as well as the susceptibility of HSPCs to infection by HIV.

Contributions of bone marrow monocytes/macrophages in myeloproliferative neoplasms with JAK2V617F mutation

The classic BCR-ABL1-negative myeloproliferative neoplasm (MPN) is a highly heterogeneous hematologic tumor that includes three subtypes, namely polycythemia vera (PV), essential thrombocytosis (ET), and primary myelofibrosis (PMF). Despite having the same JAK2^V617F mutation, the clinical manifestations of these three subtypes of MPN differ significantly, which suggests that the bone marrow (BM) immune microenvironment may also play an important role. In recent years, several studies have shown that peripheral blood monocytes play an important role in promoting MPN. However, to date, the role of BM monocytes/macrophages in MPN and their transcriptomic alterations remain incompletely understood. The purpose of this study was to clarify the role of BM monocytes/macrophages in MPN patients with the JAK2^V617F mutation. MPN patients with the JAK2^V617F mutation were enrolled in this study. We investigated the roles of monocytes/macrophages in the BM of MPN patients, using flow cytometry, monocyte/macrophage enrichment sorting, cytospins and Giemsa-Wright staining, and RNA-seq. Pearson correlation coefficient analysis was also used to detect the correlation between BM monocytes/macrophages and the MPN phenotype. In the present study, the proportion of CD163⁺ monocytes/macrophages increased significantly in all three subtypes of MPN. Interestingly, the percentages of CD163⁺ monocytes/macrophages are positively correlated with HGB in PV patients and PLT in ET patients. In contrast, the percentages of CD163⁺ monocytes/macrophages are negatively correlated with HGB and PLT in PMF patients. It was also found that CD14⁺CD16⁺ monocytes/macrophages increased and correlated with MPN clinical phenotypes. RNA-seq analyses demonstrated that the transcriptional expressions of monocytes/macrophages in MPN patients are relatively distinct. Gene expression profiles of BM monocytes/macrophages suggest a specialized function in support of megakaryopoiesis in ET patients. In contrast, BM monocytes/macrophages yielded a heterogeneous status in the support or inhibition of erythropoiesis. Significantly, BM monocytes/macrophages shaped an inflammatory microenvironment, which, in turn, promotes myelofibrosis. Thus, we characterized the roles of increased monocytes/macrophages in the occurrence and progression of MPNs. Our findings of the comprehensive transcriptomic characterization of BM monocytes/macrophages provide important resources to serve as a basis for future studies and future targets for the treatment of MPN patients.

ROS-sensitive Crocin-loaded chitosan microspheres for lung targeting and attenuation of radiation-induced lung injury

Radiation-induced lung injury (RILI) is one of the major complications in patients exposed to accidental radiation and radiotherapy for thoracic malignancies. However, there is no reliable radioprotector for effective clinical treatment of RILI so far. Herein, a novel Crocin-loaded chitosan microsphere is developed for lung targeting and attenuation of RILI. The chitosan microspheres are modified with 4-carboxyphenylboronic acid and loaded with the natural antioxidant Crocin-I to give the drug-loaded microspheres (~10 μm). The microspheres possess good biocompatibility in vivo and in vitro. In a mouse model, they exhibit effective passive targeting performance and a long retention time in the lung after intravenous administration. Furthermore, they improve the radioprotective effect of Crocin-I for the treatment of RILI by reducing the level of inflammatory cytokines in bronchoalveolar lavage fluid and by regulating oxidative stress in lung tissues. The targeted agents significantly improved the bioavailability and radioprotection of Crocin-I by the outstanding passive targeting effect. This work may provide a promising strategy for efficient radioprotection on RILI using passive lung targeting microspheres.

M2 macrophages drive leukemic transformation by imposing resistance to phagocytosis and improving mitochondrial metabolism

It is increasingly becoming clear that cancers are a symbiosis of diverse cell types and tumor clones. Combined single-cell RNA sequencing, flow cytometry, and immunohistochemistry studies of the innate immune compartment in the bone marrow of patients with acute myeloid leukemia (AML) reveal a shift toward a tumor-supportive M2-polarized macrophage landscape with an altered transcriptional program, with enhanced fatty acid oxidation and NAD⁺ generation. Functionally, these AML-associated macrophages display decreased phagocytic activity and intra-bone marrow coinjection of M2 macrophages together with leukemic blasts strongly enhances in vivo transformation potential. A 2-day in vitro exposure to M2 macrophages results in the accumulation of CALR^low leukemic blast cells, which are now protected against phagocytosis. Moreover, M2-exposed "trained" leukemic blasts display increased mitochondrial metabolism, in part mediated via mitochondrial transfer. Our study provides insight into the mechanisms by which the immune landscape contributes to aggressive leukemia development and provides alternatives for targeting strategies aimed at the tumor microenvironment.

Interactions of B-lymphocytes and bone cells in health and disease

Bone remodeling occurs through the interactions of three major cell lineages, osteoblasts, which mediate bone formation, osteocytes, which derive from osteoblasts, sense mechanical force and direct bone turnover, and osteoclasts, which mediate bone resorption. However, multiple additional cell types within the bone marrow, including macrophages, T lymphocytes and B lymphocytes influence the process. The bone marrow microenvironment, which is supported, in part, by bone cells, forms a nurturing network for B lymphopoiesis. In turn, developing B lymphocytes influence bone cells. Bone health during homeostasis depends on the normal interactions of bone cells with other lineages in the bone marrow. In disease state these interactions become pathologic and can cause abnormal function of bone cells and inadequate repair of bone after a fracture. This review summarizes what is known about the development of B lymphocytes and the interactions of B lymphocytes with bone cells in both health and disease.

Dynamic crosstalk between hematopoietic stem cells and their niche from emergence to aging

The behavior of somatic stem cells is regulated by their niche. Interaction between hematopoietic stem cells (HSCs) and their niches are a representative model to understand stem cell-niche interplay. Here, we provide an overview of crosstalk between HSCs and their niches in bone marrow and extramedullary organs following the life journey of HSCs from emergence, development, maturation until aging. We highlight the unique differences of HSC niches in different life stages within various organs focusing on recent literature to propose new speculations and hypotheses.

Cellular niches for hematopoietic stem cells in bone marrow under normal and malignant conditions

Throughout adult life, most lineages of blood cells, including immune cells, are generated from hematopoietic stem cells (HSCs) in the bone marrow. HSCs are thought to require special microenvironments, termed niches, for their maintenance in the bone marrow; however, the identity of the HSC cellular niche has been a subject of long-standing debate. Although diverse candidates have been proposed so far, accumulated studies demonstrate that the bone marrow-specific population of fibroblastic reticular cells with long processes, termed CXC chemokine ligand 12-abundant reticular cells (which overlap strongly with leptin receptor-expressing cells), termed CAR/LepR⁺ cells, are the pivotal cellular component of niches for HSCs and lymphoid progenitors. Sinusoidal endothelial cells (ECs) are also important for hematopoietic homeostasis and regeneration. Hematopoiesis is altered dynamically by various stimuli such as inflammation, infection, and leukemia, all of which affect cellular niches and alter their function. Therefore, it is important to consider situations in which stimuli affect HSCs, either via direct interaction or indirectly via the hematopoietic niches. In this review, the dynamics of cellular niches in the steady state and disease are described, with a focus on CAR/LepR⁺ cells and ECs.

Butyrate-induced IL-22 expression in fish macrophages contributes to bacterial clearance

IL-22 has been characterized as a critical cytokine in maintaining barrier integrity and host immunity. So far, it has been known that IL-22 is mainly produced by lymphoid lineage cells. In the present study, we have thoroughly investigated butyrate-induced production and function of IL-22 in fish macrophages. Our results demonstrated that short-chain fatty acids (SCFAs), major microbiota-derived metabolites, promoted the expression of IL-22 in head kidney macrophages (HKMs) of turbot (Scophthalmus maximus L.). Interestingly, butyrate-mediated intracellular bacterial killing in HKMs diminished when IL-22 expression was interfered. Furthermore, the turbot fed the diet containing sodium butyrate (NaB) exhibited significantly lower mortality after bacterial infection, compared to the fish fed a basal diet. At the meantime, a higher level of IL-22 expression and bactericidal activity was detected in HKMs from the turbot fed NaB-supplemented diet. In addition, NaB treatment promoted the expression of antimicrobial peptides (AMPs) β-defensins in zebrafish (Danio rerio). However, butyrate-induced expression of AMPs was reduced in IL-22 mutant zebrafish compared to wild-type (WT) fish. Meanwhile, NaB treatment was incapable to protect IL-22 mutant fish from bacterial infection as it did in WT zebrafish. Importantly, our results demonstrated that IL-22 expression was remarkably suppressed in macrophage-depleted zebrafish, indicating that macrophage might be a cell source of IL-22 production in vivo. In conclusion, all these findings collectively revealed that SCFAs regulated the production and function of IL-22 in fish macrophages, which facilitated host resistance to bacterial invasion.

Physical and biological advances in endothelial cell-based engineered co-culture model systems

Scientific knowledge in the field of cell biology and mechanobiology heavily leans on cell-based in vitro experiments and models that favor the examination and comprehension of certain biological processes and occurrences across a variety of environments. Cell culture assays are an invaluable instrument for a vast spectrum of biomedical and biophysical investigations. The quality of experimental models in terms of simplicity, reproducibility, and combinability with other methods, and in particular the scale at which they depict cell fate in native tissues, is critical to advancing the knowledge of the comprehension of cell-cell and cell-matrix interactions in tissues and organs. Typically, in vitro models are centered on the experimental tinkering of mammalian cells, most often cultured as monolayers on planar, two-dimensional (2D) materials. Notwithstanding the significant advances and numerous findings that have been accomplished with flat biology models, their usefulness for generating further new biological understanding is constrained because the simple 2D setting does not reproduce the physiological response of cells in natural living tissues. In addition, the co-culture systems in a 2D stetting weakly mirror their natural environment of tissues and organs. Significant advances in 3D cell biology and matrix engineering have resulted in the creation and establishment of a new type of cell culture shapes that more accurately represents the in vivo microenvironment and allows cells and their interactions to be analyzed in a biomimetic approach. Contemporary biomedical and biophysical science has novel advances in technology that permit the design of more challenging and resilient in vitro models for tissue engineering, with a particular focus on scaffold- or hydrogel-based formats, organotypic cultures, and organs-on-chips, which cover the purposes of co-cultures. Even these complex systems must be kept as simplified as possible in order to grasp a particular section of physiology too very precisely. In particular, it is highly appreciated that they bridge the space between conventional animal research and human (patho)physiology. In this review, the recent progress in 3D biomimetic culturation is presented with a special focus on co-cultures, with an emphasis on the technological building blocks and endothelium-based co-culture models in cancer research that are available for the development of more physiologically relevant in vitro models of human tissues under normal and diseased conditions. Through applications and samples of various physiological and disease models, it is possible to identify the frontiers and future engagement issues that will have to be tackled to integrate synthetic biomimetic culture systems far more successfully into biomedical and biophysical investigations.

Serum amyloid A proteins reduce bone mass during mycobacterial infections

Introduction

Osteopenia has been associated to several inflammatory conditions, including mycobacterial infections. How mycobacteria cause bone loss remains elusive, but direct bone infection may not be required.

Methods

Genetically engineered mice and morphometric, transcriptomic, and functional analyses were used. Additionally, inflammatory mediators and bone turnover markers were measured in the serum of healthy controls, individuals with latent tuberculosis and patients with active tuberculosis.

Results and discussion

We found that infection with Mycobacterium avium impacts bone turnover by decreasing bone formation and increasing bone resorption, in an IFNγ- and TNFα-dependent manner. IFNγ produced during infection enhanced macrophage TNFα secretion, which in turn increased the production of serum amyloid A (SAA) 3. Saa3 expression was upregulated in the bone of both M. avium- and M. tuberculosis-infected mice and SAA1 and 2 proteins (that share a high homology with murine SAA3 protein) were increased in the serum of patients with active tuberculosis. Furthermore, the increased SAA levels seen in active tuberculosis patients correlated with altered serum bone turnover markers. Additionally, human SAA proteins impaired bone matrix deposition and increased osteoclastogenesis in vitro. Overall, we report a novel crosstalk between the cytokine-SAA network operating in macrophages and bone homeostasis. These findings contribute to a better understanding of the mechanisms of bone loss during infection and open the way to pharmacological intervention. Additionally, our data and disclose SAA proteins as potential biomarkers of bone loss during infection by mycobacteria.