Academic literature on the topic 'BM niche'

The mammalian hematopoietic system is remarkably efficient in meeting an organism’s vital needs, yet is highly sensitive and exquisitely regulated. Much of the organismal control over hematopoiesis comes from the regulation of hematopoietic stem cells (HSCs) by specific microenvironments called niches in bone marrow (BM), where HSCs reside. The experimental studies of the last two decades using the most sophisticated and advanced techniques have provided important data on the identity of the niche cells controlling HSCs functions and some mechanisms underlying niche-HSC interactions. In this review we discuss various aspects of organization and functioning of the HSC cell niche in bone marrow. In particular, we review the anatomy of BM niches, various cell types composing the niche, niches for more differentiated cells, metabolism of HSCs in relation to the niche, niche aging, leukemic transformation of the niche, and the current state of HSC niche modeling in vitro.

Hematopoietic stem cell (HSC) transplantation (HSCT) is required for curative therapy for patients with high-risk hematologic malignancies, and a number of non-malignant disorders including inherited bone marrow failure syndromes (iBMFS). Strategies to enhance bone marrow (BM) niche capacity to engraft donor HSC have the potential to improve HSCT outcome by decreasing graft failure rates and enabling reduction in conditioning intensity and regimen-associated complications. Several studies in animal models of iBMFS have demonstrated that BM niche dysfunction contributes to both the pathogenesis of iBMFS, as well as impaired graft function after HSCT. We hypothesize that such iBMFS mouse models are useful tools for discovering targetable niche elements critical for donor engraftment after HSCT. Here, we report the development of a novel mouse model of Shwachman-Diamond Syndrome (SDS) driven by conditional Sbds deletion, which demonstrates profound impairment of healthy donor hematopoietic engraftment after HSCT due to pathway-specific dysfunctional signaling within SBDS-deficient recipient niches. We first attempted to delete Sbds specifically in mature osteoblasts by crossing Sbdsfl/flmice with Col1a1Cre+mice. However, the Col1a1CreSbdsExc progenies are embryonic lethal at E12-E15 stage due to developmental musculoskeletal abnormalities. Alternatively, we generated an inducible SDS mouse model by crossing Sbdsfl/flmice with Mx1Cre+ mice, and inducing Sbds deletion in Mx1-inducible BM hematopoietic and osteolineage niche cells by polyinosinic-polycytidilic acid (pIpC) administration. Compared with Sbdsfl/flcontrols, Mx1CreSbdsExc mice develop significantly decreased platelet counts, an inverted peripheral blood myeloid/lymphoid cell ratio, and reduced long-term HSC within BM, consistent with stress hematopoiesis seen in BMF and myelodysplastic syndromes. To assess whether inducible SBDS deficiency impacts niche function to engraft donor HSC, we transplanted GFP+ wildtype donor BM into pIpC-treated Mx1CreSbdsExc mice and Sbdsfl/flcontrols after 1100 cGy of total body irradiation (TBI). Following transplantation, Mx1CreSbdsExc recipient mice exhibit significantly higher mortality than controls (Figure 1). The decreased survival was related to primary graft failure, as Mx1CreSbdsExc mice exhibit persistent BM aplasia after HSCT and decreased GFP+ reconstitution in competitive secondary transplantation assays. We next sought to identify the molecular and cellular defects within BM niche cells that contribute to the engraftment deficits in SBDS-deficient mice. We performed RNA-seq analysis on the BM stromal cells from irradiated Mx1CreSbdsExc mice versus controls, and the results revealed that SBDS deficiency in BM niche cells caused disrupted gene expression within osteoclast differentiation, FcγR-mediated phagocytosis, and VEGF signaling pathways. Multiplex ELISA assays showed that the BM niche of irradiated Mx1CreSbdsExc mice expresses lower levels of CXCL12, P-selectin and IGF-1, along with higher levels of G-CSF, CCL3, osteopontin and CCL9 than controls. Together, these results suggest that poor donor HSC engraftment in SBDS-deficient mice is likely caused by alterations in niche-mediated donor HSC homing/retention, bone metabolism, host monocyte survival, signaling within IGF-1 and VEGF pathways, and an increased inflammatory state within BM niches. Moreover, flow cytometry analysis showed that compared to controls, the BM niche of irradiated Mx1CreSbdsExc mice contained far fewer megakaryocytes, a hematopoietic cell component of BM niches that we previously demonstrated to be critical in promoting osteoblastic niche expansion and donor HSC engraftment. Taken together, our data demonstrated that SBDS deficiency in BM niches results in reduced capacity to engraft donor HSC. We have identified multiple molecular and cellular defects in the SBDS-deficient niche contributing to this phenotype. Such niche signaling pathway-specific deficits implicate these pathways as critical for donor engraftment during HSCT, and suggest their potential role as targets of therapeutic approaches to enhance donor engraftment and improve HSCT outcome in any condition for which HSCT is required for cure. Disclosures Olson: Merck: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Miltenyi: Honoraria.

B cell acute lymphoblastic leukemia (B-ALL) blasts hijack the bone marrow (BM) microenvironment to form chemoprotective leukemic BM “niches,” facilitating chemoresistance and, ultimately, disease relapse. However, the ability to dissect these evolving, heterogeneous interactions among distinct B-ALL subtypes and their varying BM niches is limited with current in vivo methods. Here, we demonstrated an in vitro organotypic “leukemia-on-a-chip” model to emulate the in vivo B-ALL BM pathology and comparatively studied the spatial and genetic heterogeneity of the BM niche in regulating B-ALL chemotherapy resistance. We revealed the heterogeneous chemoresistance mechanisms across various B-ALL cell lines and patient-derived samples. We showed that the leukemic perivascular, endosteal, and hematopoietic niche-derived factors maintain B-ALL survival and quiescence (e.g., CXCL12 cytokine signal, VCAM-1/OPN adhesive signals, and enhanced downstream leukemia-intrinsic NF-κB pathway). Furthermore, we demonstrated the preclinical use of our model to test niche-cotargeting regimens, which may translate to patient-specific therapy screening and response prediction.

Abstract Bone marrow (BM) niche-derived signals are critical for facilitating engraftment after hematopoietic stem cell (HSC) transplantation (HSCT). HSCT is required for restoration of hematopoiesis in patients with inherited BM failure syndromes (iBMFSs). Shwachman-Diamond syndrome (SDS) is a rare iBMFS associated with mutations in SBDS. Previous studies have demonstrated that SBDS deficiency in osteolineage niche cells causes BM dysfunction that promotes leukemia development. However, it is unknown whether BM niche defects caused by SBDS deficiency also impair efficient engraftment of healthy donor HSC after HSCT, a hypothesis that could explain morbidity noted after clinical HSCT for patients with SDS. Here, we report a mouse model with inducible Sbds deletion in hematopoietic and osteolineage cells. Primary and secondary BM transplantation (BMT) studies demonstrated that SBDS deficiency within BM niches caused poor donor hematopoietic recovery and specifically poor HSC engraftment after myeloablative BMT. We have also identified multiple molecular and cellular defects within niche populations that are driven by SBDS deficiency and are accentuated by or develop specifically after myeloablative conditioning. These abnormalities include altered frequencies of multiple niche cell subsets, including mesenchymal lineage cells, macrophages, and endothelial cells; disruption of growth factor signaling, chemokine pathway activation, and adhesion molecule expression; and p53 pathway activation and signals involved in cell cycle arrest. Taken together, this study demonstrates that SBDS deficiency profoundly impacts recipient hematopoietic niche function in the setting of HSCT, suggesting that novel therapeutic strategies targeting host niches could improve clinical HSCT outcomes for patients with SDS.

Hematopoietic stem cells (HSCs) reside in specialized bone marrow (BM) niches regulated by the sympathetic nervous system (SNS). Here, we have examined whether mononuclear phagocytes modulate the HSC niche. We defined three populations of BM mononuclear phagocytes that include Gr-1hi monocytes (MOs), Gr-1lo MOs, and macrophages (MΦ) based on differential expression of Gr-1, CD115, F4/80, and CD169. Using MO and MΦ conditional depletion models, we found that reductions in BM mononuclear phagocytes led to reduced BM CXCL12 levels, the selective down-regulation of HSC retention genes in Nestin+ niche cells, and egress of HSCs/progenitors to the bloodstream. Furthermore, specific depletion of CD169+ MΦ, which spares BM MOs, was sufficient to induce HSC/progenitor egress. MΦ depletion also enhanced mobilization induced by a CXCR4 antagonist or granulocyte colony-stimulating factor. These results highlight two antagonistic, tightly balanced pathways that regulate maintenance of HSCs/progenitors in the niche during homeostasis, in which MΦ cross talk with the Nestin+ niche cell promotes retention, and in contrast, SNS signals enhance egress. Thus, strategies that target BM MΦ hold the potential to augment stem cell yields in patients that mobilize HSCs/progenitors poorly.

Allogeneic hematopoietic stem cell (HSC) transplantation (HSCT) is currently the leading strategy to manage acute myeloid leukemia (AML). However, treatment-related morbidity limits the patient generalizability of HSCT use, and the survival of leukemic stem cells (LSCs) within protective areas of the bone marrow (BM) continues to lead to high relapse rates. Despite growing appreciation for the significance of the LSC microenvironment, it has remained unresolved whether LSCs preferentially situate within normal HSC niches or whether their niche requirements are more promiscuous. Here, we provide functional evidence that the spatial localization of phenotypically primitive human AML cells is restricted to niche elements shared with their normal counterparts, and that their intrinsic ability to initiate and retain occupancy of these niches can be rivaled by healthy hematopoietic stem and progenitor cells (HSPCs). When challenged in competitive BM repopulation assays, primary human leukemia-initiating cells (L-ICs) can be consistently outperformed by HSPCs for BM niche occupancy in a cell dose-dependent manner that ultimately compromises long-term L-IC renewal and subsequent leukemia-initiating capacity. The effectiveness of this approach could be demonstrated using cytokine-induced mobilization of established leukemia from the BM that facilitated the replacement of BM niches with transplanted HSPCs. These findings identify a functional vulnerability of primitive leukemia cells, and suggest that clinical development of these novel transplantation techniques should focus on the dissociation of L-IC–niche interactions to improve competitive replacement with healthy HSPCs during HSCT toward increased survival of patients.

The bone marrow (BM) is the primary site of postnatal hematopoiesis and hematopoietic stem cell (HSC) maintenance. The BM HSC niche is an essential microenvironment which evolves and responds to the physiological demands of HSCs. It is responsible for orchestrating the fate of HSCs and tightly regulates the processes that occur in the BM, including self-renewal, quiescence, engraftment, and lineage differentiation. However, the BM HSC niche is disturbed following hematological stress such as hematological malignancies, ionizing radiation, and chemotherapy, causing the cellular composition to alter and remodeling to occur. Consequently, hematopoietic recovery has been the focus of many recent studies and elucidating these mechanisms has great biological and clinical relevance, namely to exploit these mechanisms as a therapeutic treatment for hematopoietic malignancies and improve regeneration following BM injury. The sympathetic nervous system innervates the BM niche and regulates the migration of HSCs in and out of the BM under steady state. However, recent studies have investigated how sympathetic innervation and signaling are dysregulated under stress and the subsequent effect they have on hematopoiesis. Here, we provide an overview of distinct BM niches and how they contribute to HSC regulatory processes with a particular focus on neuronal regulation of HSCs under steady state and stress hematopoiesis.

Hematopoietic stem and progenitor cells (HSPCs) are frequently located around the bone marrow (BM) vasculature. These so-called perivascular niches regulate HSC function both in health and disease, but they have been poorly studied in humans due to the scarcity of models integrating complete human vascular structures. Herein, we propose the stromal vascular fraction (SVF) derived from human adipose tissue as a cell source to vascularize 3D osteoblastic BM niches engineered in perfusion bioreactors. We show that SVF cells form self-assembled capillary structures, composed by endothelial and perivascular cells, that add to the osteogenic matrix secreted by BM mesenchymal stromal cells in these engineered niches. In comparison to avascular osteoblastic niches, vascularized BM niches better maintain immunophenotypically-defined cord blood (CB) HSCs without affecting cell proliferation. In contrast, HSPCs cultured in vascularized BM niches showed increased CFU-granulocyte-erythrocyte-monocyte-megakaryocyte (CFU-GEMM) numbers. The vascularization also contributed to better preserve osteogenic gene expression in the niche, demonstrating that niche vascularization has an influence on both hematopoietic and stromal compartments. In summary, we have engineered a fully humanized and vascularized 3D BM tissue to model native human endosteal perivascular niches and revealed functional implications of this vascularization in sustaining undifferentiated CB HSPCs. This system provides a unique modular platform to explore hemato-vascular interactions in human healthy/pathological hematopoiesis.

Formation of the hematopoietic stem cell (HSC) niche in bone marrow (BM) is tightly associated with endochondral ossification, but little is known about the mechanisms involved. We used the oc/oc mouse, a mouse model with impaired endochondral ossification caused by a loss of osteoclast (OCL) activity, to investigate the role of osteoblasts (OBLs) and OCLs in the HSC niche formation. The absence of OCL activity resulted in a defective HSC niche associated with an increased proportion of mesenchymal progenitors but reduced osteoblastic differentiation, leading to impaired HSC homing to the BM. Restoration of OCL activity reversed the defect in HSC niche formation. Our data demonstrate that OBLs are required for establishing HSC niches and that osteoblastic development is induced by OCLs. These findings broaden our knowledge of the HSC niche formation, which is critical for understanding normal and pathological hematopoiesis.

Abstract The BM microenvironment and its components regulate hematopoietic stem and progenitor cell (HSC) fate. An abnormality in the BM microenvironment and specific dysfunction of the HSC niche could play a critical role in initiation, disease progression, and response to therapy of BM failure syndromes. Therefore, the identification of changes in the HSC niche in BM failure syndromes should lead to further knowledge of the signals that disrupt the normal microenvironment. In turn, niche disruption may contribute to disease morbidity, resulting in pancytopenia and clonal evolution, and its understanding could suggest new therapeutic targets for these conditions. In this chapter, we briefly review the evidence for the importance of the BM microenvironment as a regulator of normal hematopoiesis, summarize current knowledge regarding the role of dysfunctions in the BM microenvironment in BM failure syndromes, and propose a strategy through which niche stimulation can complement current treatment for myelodysplastic syndrome.

La nicchia staminale ematopoietica è formata da molteplici tipi cellulari che contribuiscono alla regolazione dell’ematopoiesi all’interno del midollo osseo. In alcuni disordini ematopoietici il microambiente midollare risulta alterato, sebbene il suo contributo alla patogenesi non sia ancora chiaro, fornisce supporto alle cellule staminali leucemiche (LSC), a spese delle normali cellule staminali ematopoietiche, e protezione contro i chemioterapici. Dunque, per eradicare le LSC, le strategie terapeutiche devono considerare l’effetto protettivo contro i chemioterapici esercitato dal microambiente midollare oltre alla refrattarietà intrinseca delle LSC alle convenzionali terapie. Nella prima parte di questo progetto di dottorato, abbiamo valutato il ruolo delle cellule stromali mesenchimali (MSC) nella patogenesi dell’anemia aplastica (AA). Le MSC derivate dai pazienti (AA-MSC) sono state caratterizzate in vitro e, soprattutto in vivo, utilizzando il modello di nicchia midollare in vivo recentemente sviluppato dal nostro gruppo di ricerca, basato sull’impianto sottocutaneo di pellet cartilaginei derivati dalle MSC (Serafini et al., Stem Cell Research, 2014). In vitro, le AA-MSC mostravano solo un ridotto potenziale clonogenico senza difetti morfologici, fenotipici, proliferativi e differenziativi. Inoltre, le AA-MSC erano in grado di ricreare una nicchia midollare funzionale in vivo dimostrando un’inalterata capacità di supportare l’ematopoiesi e l’assenza di un loro coinvolgimento nella patogenesi della AA. Nella seconda parte di questo dottorato, abbiamo analizzato gli effetti dell’asparaginasi (ASNase) sulle cellule derivate da pazienti affetti da leucemia mieloide acuta (AML), soprattutto sulle LSC, ed il contributo del microambiente alla resistenza ai chemioterapici. L’ASNase era egualmente efficace contro il bulk delle cellule AML e contro le LSC (CD34+CD38- e CD34+CD38+), mentre l’effetto nei confronti delle cellule ematopoietiche sane era trascurabile. L’azione del farmaco contro le cellule primitive di AML è stato ulteriormente confermato in saggi clonogenici ed in esperimenti effettuati in condizioni di coltura specifiche per il mantenimento delle LSC in vitro. Tuttavia, una nicchia midollare protettiva formata dalle MSC, che esprimono asparagina sintetasi, dai monociti/macrofagi e dai blasti leucemici stessi, che esprimono catepsina B, potrebbe ridurre il potenziale anti-neoplastico del farmaco. Infine, abbiamo testato un nuovo regime di condizionamento (somministrazione di fludarabina in aggiunta all’irraggiamento) in topi SCID-beige, un ceppo poco permissivo per l’engraftment umano. Tale strategia di condizionamento ha incrementato i livelli di engraftment della linea cellulare AML, KG-1, rispetto al solo irraggiamento, e ha permesso di ottenere l’engraftment nel 50% dei blasti AML primari trapiantati. In futuro, vorremmo combinare questo nuovo modello di xenograft così ottenuto con il trapianto di pellet cartilaginei per generare un modello di nicchia AML da poter usare per studiare il microambiente midollare leucemico e per testare promettenti agenti terapeutici contro l’AML, come l’ASNase.
The haematopoietic stem cell (HSC) niche is formed by several cell types which contribute to the regulation of the haematopoiesis within the bone marrow (BM). In pathological conditions, alterations of the BM microenvironment have been reported, but it is still debated whether they are cause or consequence of the disease. Support to leukaemic cells, especially to leukaemic stem cells (LSC), at the expense of normal HSC and protection against chemotherapeutic agents characterise the malignant BM niche. Thus, in order to eradicate LSC, promising therapeutic strategies may consider the chemoprotection exerted by the BM microenvironment in addition to LSC intrinsic features of refractoriness to conventional therapies. In the first part of this PhD project, we investigated the role of mesenchymal stromal cells (MSC) in the pathogenesis of aplastic anaemia (AA). Patient-derived MSC (AA-MSC) were characterised in vitro and, especially, in vivo taking advantage of our recently described in vivo BM niche model, based on the subcutaneous implantation of cartilaginous pellets generated from MSC (Serafini et al., Stem Cell Research, 2014). AA-MSC did not exhibit morphological, phenotypical, proliferative and differentiation defects in vitro. Only a reduced clonogenic potential was observed. Most importantly, they were able to recreate a functional and complete BM niche in vivo, proving their unaltered ability to support haematopoiesis and excluding their involvement in AA pathogenesis. In the second part of this PhD project, we analysed the effects of L-asparaginase (ASNase) on acute myeloid leukaemia (AML) cells, especially on LSC, and the contribution of the microenvironment to chemoresistance. ASNase was equally effective against unfractionated AML cells and against CD34+CD38- and CD34+CD38+ LSC, while slightly affecting healthy haematopoietic cells. The action of the drug against AML primitive cells was confirmed by clonogenic assays and by experiments performed in LSC supportive culture conditions. However, the anti-leukaemic potential of ASNase could be in part counteracted by MSC, expressing asparagine synthetase, and by monocytes/macrophages and blasts themselves, expressing cathepsin B, generating a protective niche. Lastly, we tested a new conditioning regimen based on the addition of fludarabine to irradiation in SCID-beige mice, a poorly permissive strain for human engraftment. The administration of fludarabine after irradiation increased the levels of engraftment of a AML cell line, KG-1, as compared to irradiation only, and it allowed the engraftment in 50% of primary AML blasts transplanted, reproducing human leukaemic infiltration. Thus, we generated a novel AML xenograft model in which we would like to test promising therapeutic agents, as ASNase, and to study different features of the malignant BM niche.

Transformation from electronic commerce business model to social commerce business model empowered manufacturers of niche products to start retail businesses which are operating solely online. The selection of an online sales approach is a part of the online sales process which determines how end customers will be reached. Moreover, the online sales approach determines performance outcome, hence, this selection should be done after meticulous evaluation. This research, after a systematic comparative analysis of the academic literature, explores the omnichannel online sales approach and its relationship with performance outcome in the case of niche products and proposes a theoretical framework for the evaluation of this relationship. The theoretical framework includes financial and qualitative (customer satisfaction and customer loyalty) criteria which allow to evaluate performance outcome created by the omnichannel online sales approach in a holistic way. The performance outcome evaluation results can be used in the decision-making process when deciding whether the chosen omnichannel online sales approach meets the expectations of a business and its customers.