Haematopoietic stem cells niches: Interrelations between structure and function

Kinetics of leukemic cells in 3D culture with stromal cells and with arginine deprivation stress

Previously, we established a three-dimensional (3D) bone marrow culture system that maintains normal hematopoiesis, including prolongation of hematopoietic stem cell proliferation and differentiation. To analyze the role of bone marrow stromal cells that compose the microenvironment, the growth of a leukemic cell line (K562) in the 3D condition and with arginine deprivation stress was compared with two-dimensional stromal cell monolayers (2D) and suspension cultures without stromal cells (stroma (-)). Arginine is essential for the proliferation and differentiation of erythrocytes. The proliferation and differentiation of K562 cells cultured in the 3D system were stabilized compared with cells in 2D or stroma (-). Furthermore, the number of K562 cells in the G₀/G₁ phase in 3D was increased significantly compared with cells grown in 2D or stroma (-). Interestingly, the mRNA expression of various hematopoietic growth factors of stromal cells in 3D was not different from 2D, even though supportive activity on K562 cell growth was observed in the arginine deprivation condition. Thus, the hematopoietic microenvironment involves multi-dimensional and complex systems including biochemical and physiochemical factors that regulate quiescence, proliferation, activation, and differentiation of normal hematopoietic cells and cloned leukemic cells. Our 3D culture system may be a valuable new tool for investigating leukemic cell-stromal cell interactions in vitro.

Neuropeptide Y improves cisplatin-induced bone marrow dysfunction without blocking chemotherapeutic efficacy in a cancer mouse model

Cisplatin is the most effective and widely used chemo-therapeutic agent for many types of cancer. Unfortunately, its clinical use is limited by its adverse effects, notably bone marrow suppression leading to abnormal hematopoiesis. We previously revealed that neuropeptide Y (NPY) is responsible for the maintenance of hematopoietic stem cell (HSC) function by protecting the sympathetic nervous system (SNS) fibers survival from chemotherapy-induced bone marrow impairment. Here, we show the NPY-mediated protective effect against bone marrow dysfunction due to cisplatin in an ovarian cancer mouse model. During chemotherapy, NPY mitigates reduction in HSC abundance and destruction of SNS fibers in the bone marrow without blocking the anticancer efficacy of cisplatin, and it results in the restoration of blood cells and amelioration of sensory neuropathy. Therefore, these results suggest that NPY can be used as a potentially effective agent to improve bone marrow dysfunction during cisplatin-based cancer therapy.

Thrombopoiesis is spatially regulated by the bone marrow vasculature

In mammals, megakaryocytes (MKs) in the bone marrow (BM) produce blood platelets, required for hemostasis and thrombosis. MKs originate from hematopoietic stem cells and are thought to migrate from an endosteal niche towards the vascular sinusoids during their maturation. Through imaging of MKs in the intact BM, here we show that MKs can be found within the entire BM, without a bias towards bone-distant regions. By combining in vivo two-photon microscopy and in situ light-sheet fluorescence microscopy with computational simulations, we reveal surprisingly slow MK migration, limited intervascular space, and a vessel-biased MK pool. These data challenge the current thrombopoiesis model of MK migration and support a modified model, where MKs at sinusoids are replenished by sinusoidal precursors rather than cells from a distant periostic niche. As MKs do not need to migrate to reach the vessel, therapies to increase MK numbers might be sufficient to raise platelet counts.Megakaryocyte maturation is thought to occur as the cells migrate from a vessel-distant (endosteal) niche to the vessel within the bone. Here, the authors show that megakaryocytes represent largely sessile cells in close contact with the vasculature and homogeneously distributed in the bone marrow.

Neuropeptide Y Induces Hematopoietic Stem/Progenitor Cell Mobilization by Regulating Matrix Metalloproteinase-9 Activity Through Y1 Receptor in Osteoblasts

Hematopoietic stem/progenitor cell (HSPC) mobilization is an essential homeostatic process regulated by the interaction of cellular and molecular components in bone marrow niches. It has been shown by others that neurotransmitters released from the sympathetic nervous system regulate HSPC egress from bone marrow to peripheral blood. In this study, we investigate the functional role of neuropeptide Y (NPY) on this process. NPY deficient mice had significantly impaired HSPC mobilization due to increased expression of HSPC maintenance factors by reduction of matrix metalloproteinase-9 (MMP-9) activity in bone marrow. Pharmacological or endogenous elevation of NPY led to decrease of HSPC maintenance factors expression by activating MMP-9 in osteoblasts, resulting in HSPC mobilization. Mice in which the Y1 receptor was deleted in osteoblasts did not exhibit HSPC mobilization by NPY. Furthermore, NPY treatment in ovariectomized mice caused reduction of bone loss due to HSPC mobilization. These results suggest a new role of NPY on HSPC mobilization, as well as the potential therapeutic application of this neuropeptide for stem cell-based therapy. Stem Cells 2016;34:2145-2156.

In vitro production of functional immune cells derived from human hematopoietic stem cells

Hematopoietic stem cells (HSC) from cord blood are potentially high sources for transplantation due to their low immunogenicity and the presence of the multipotent cells. These cells are capable of differentiating to produce various lineages of blood cells under specific conditions. We have enriched highly purified CD34⁺ cells from cord blood, determined in vitro growth of the cells in culture systems in the absence (condition A) or presence of GM-CSF and G-CSF (condition B), and determined the profile of immune cells during the period of cultivation by using flow cytometry. PhytohemagglutininA (PHA) was used as a mitogen to stimulate T lymphocytes derived from hematopoietic stem cells. GM-CSF and G-CSF prolonged the survival of the growing cells and also maintained expansion of cells in blastic stage. By day 12 of cultivation, when cell numbers peaked, various types of immune cells had appeared (CD14⁺ cells, CD40⁺HLA-DR⁺ cells, CD3⁺CD56⁺ cells, CD19⁺ cells, CD3⁺CD4⁺ cells, CD3⁺CD8⁺cells and CD3-CD56⁺). A significantly higher percentage of monocytes (p = 0.002) were observed under culture with GM-CSF, G-CSF when compared with culture without GM-CSF, G-CSF. In addition, T lymphocytes derived from HSC responded to 50 µg/ml of PHA. This is the first report showing the complete differentiation and proliferation of immune cells derived from CD34⁺ HSC under in vitro culture conditions. Lymphocytes, monocytes, dendritic cells and polymorph nuclear cells derived from HSC in vitro are unique, and thus may benefit various studies such as innate immunity and pathophysiology of immune disorders.

Primo-Vascular System as Presented by Bong Han Kim

In the 1960s Bong Han Kim discovered and characterized a new vascular system. He was able to differentiate it clearly from vascular blood and lymph systems by the use of a variety of methods, which were available to him in the mid-20th century. He gave detailed characterization of the system and created comprehensive diagrams and photographs in his publications. He demonstrated that this system is composed of nodes and vessels, and it was responsible for tissue regeneration. However, he did not disclose in detail his methods. Consequently, his results are relatively obscure from the vantage point of contemporary scientists. The stains that Kim used had been perfected and had been in use for more than 100 years. Therefore, the names of the stains were directed to the explicit protocols for the usage with the particular cells or molecules. Traditionally, it was not normally necessary to describe the method used unless it is significantly deviated from the original method. In this present work, we have been able to disclose staining methods used by Kim.

Kinetics of hematopoietic stem cells and supportive activities of stromal cells in a three-dimensional bone marrow culture system

In the bone marrow, hematopoietic cells proliferate and differentiate in close association with a three-dimensional (3D) hematopoietic microenvironment. Previously, we established a 3D bone marrow culture system. In this study, we analyzed the kinetics of hematopoietic cells, and more than 50% of hematopoietic progenitor cells, including CFU-Mix, CFU-GM and BFU-E in 3D culture were in a resting (non-S) phase. Furthermore, we examined the hematopoietic supportive ability of stromal cells by measuring the expression of various mRNAs relevant to hematopoietic regulation. Over the 4 weeks of culture, the stromal cells in the 3D culture are not needlessly activated and "quietly" regulate hematopoietic cell proliferation and differentiation during the culture, resulting in the presence of resting hematopoietic stem cells in the 3D culture for a long time. Thus, the 3D culture system may be a new tool for investigating hematopoietic stem cell-stromal cell interactions in vitro.

The role of the nervous system in hematopoietic stem cell mobilization

Hematopoietic stem cells (HSCs) and blood cell progenitors, such as maturing leucocytes, steadily enter from bone marrow (BM) into the circulation under steady-state conditions, and their mobilization is dramatically amplified during stress conditions and by mediators such as granulocyte colony-stimulating factor (G-CSF). This mobilization is dependent upon bone remodeling, the proteolytic enzymes of bone marrow-derived stromal cells, and adhesion molecules such as integrin, but the main mechanisms controlling this traffic are still unclear. The nervous system, as the most important regulator of the body, can affect the mobilization network by secreting catecholamines, so that denervation of catecholaminergic fibers in the BM of mice could lead to declining mobilization in steady state and stress situations, even in the presence of other intact environmental factors in the BM. Thus, due to the importance of the nervous system, we have attempted to give a general overview of how the nervous system is involved in the mobilization of HSCs in this review. Then, we will try to describe the mobilization process induced by the nervous system, which consists of 3 mechanisms: stromal cell-derived factor 1 (SDF-1)/CXC chemokine receptor type 4 (CXCR4), proteolytic enzymes, and bone remodeling.

Absence of sclerostin adversely affects B-cell survival

Increased osteoblast activity in sclerostin-knockout (Sost(-/-)) mice results in generalized hyperostosis and bones with small bone marrow cavities resulting from hyperactive mineralizing osteoblast populations. Hematopoietic cell fate decisions are dependent on their local microenvironment, which contains osteoblast and stromal cell populations that support both hematopoietic stem cell quiescence and facilitate B-cell development. In this study, we investigated whether high bone mass environments affect B-cell development via the utilization of Sost(-/-) mice, a model of sclerosteosis. We found the bone marrow of Sost(-/-) mice to be specifically depleted of B cells because of elevated apoptosis at all B-cell developmental stages. In contrast, B-cell function in the spleen was normal. Sost expression analysis confirmed that Sost is primarily expressed in osteocytes and is not expressed in any hematopoietic lineage, which indicated that the B-cell defects in Sost(-/-) mice are non-cell autonomous, and this was confirmed by transplantation of wild-type (WT) bone marrow into lethally irradiated Sost(-/-) recipients. WT→Sost(-/-) chimeras displayed a reduction in B cells, whereas reciprocal Sost(-/-) →WT chimeras did not, supporting the idea that the Sost(-/-) bone environment cannot fully support normal B-cell development. Expression of the pre-B-cell growth stimulating factor, Cxcl12, was significantly lower in bone marrow stromal cells of Sost(-/-) mice, whereas the Wnt target genes Lef-1 and Ccnd1 remained unchanged in B cells. Taken together, these results demonstrate a novel role for Sost in the regulation of bone marrow environments that support B cells.

Endocannabinoids are expressed in bone marrow stromal niches and play a role in interactions of hematopoietic stem and progenitor cells with the bone marrow microenvironment

Endocannabinoids are lipid signaling molecules that act via G-coupled receptors, CB(1) and CB(2). The endocannabinoid system is capable of activation of distinct signaling pathways on demand in response to pathogenic events or stimuli, hereby enhancing cell survival and promoting tissue repair. However, the role of endocannabinoids in hematopoietic stem and progenitor cells (HSPCs) and their interaction with hematopoietic stem cells (HSC) niches is not known. HSPCs are maintained in the quiescent state in bone marrow (BM) niches by intrinsic and extrinsic signaling. We report that HSPCs express the CB(1) receptors and that BM stromal cells secrete endocannabinoids, anandamide (AEA) (35 pg/10(7) cells), and 2-AG (75.2 ng/10(7) cells). In response to the endotoxin lipopolysaccharide (LPS), elevated levels of AEA (75.6 pg/10(7) cells) and 2-AG (98.8 ng/10(7) cells) were secreted from BM stromal cells, resulting in migration and trafficking of HSPCs from the BM niches to the peripheral blood. Furthermore, administration of exogenous cannabinoid CB(1) agonists in vivo induced chemotaxis, migration, and mobilization of human and murine HSPCs. Cannabinoid receptor knock-out mice Cnr1(-/-) showed a decrease in side population (SP) cells, whereas fatty acid amide hydrolase (FAAH)(-/-) mice, which have elevated levels of AEA, yielded increased colony formation as compared with WT mice. In addition, G-CSF-induced mobilization in vivo was modulated by endocannabinoids and was inhibited by specific cannabinoid antagonists as well as impaired in cannabinoid receptor knock-out mice Cnr1(-/-), as compared with WT mice. Thus, we propose a novel function of the endocannabinoid system, as a regulator of HSPC interactions with their BM niches, where endocannabinoids are expressed in HSC niches and under stress conditions, endocannabinoid expression levels are enhanced to induce HSPC migration for proper hematopoiesis.