ArticlePDF Available

Abstract and Figures

The microenvironment, or niche, surrounding a stem cell largely governs its cellular fate. Two anatomical niches for hematopoietic stem cells (HSCs) have been reported in the bone marrow, but a distinct function for each of these niches remains unclear. Here we report a new role for the adhesion molecule E-selectin expressed exclusively by bone marrow endothelial cells in the vascular HSC niche. HSC quiescence was enhanced and self-renewal potential was increased in E-selectin knockout (Sele(-/-)) mice or after administration of an E-selectin antagonist, demonstrating that E-selectin promotes HSC proliferation and is a crucial component of the vascular niche. These effects are not mediated by canonical E-selectin ligands. Deletion or blockade of E-selectin enhances HSC survival threefold to sixfold after treatment of mice with chemotherapeutic agents or irradiation and accelerates blood neutrophil recovery. As bone marrow suppression is a severe side effect of high-dose chemotherapy, transient blockade of E-selectin is potentially a promising treatment for the protection of HSCs during chemotherapy or irradiation.
HSC quiescence is increased in E-selectin knockout (Sele−/−) mice. (a–c) HSC turnover measured by BrdU incorporation in mice of the indicated genotypes continuously administered BrdU. At set periods of time, the percentage of BrdU incorporation in phenotypic HSCs was measured. (a) Dot plot showing the LKS+ gate within Lin− bone marrow cells (left). BrdU after 3 d of incorporation and CD34 expression on gated LKS+ cells from representative mice (right). Inserted quadrants show percentages of cells in each quadrant of the dot plots. (b) Cytospins of sorted HSCs (LKS+CD34−) stained for BrdU incorporation after 5 d of BrdU administration. Scale bar, 50 μm. (c) Percentage of bone marrow LKS+CD34− HSCs that incorporated BrdU over time. Data are pooled from four separate experiments. ***P < 0.001. (d,e) Cell-cycle analysis of LKS+CD34− HSCs. (d) Typical dot plots of DNA content (Hoechst 33342) plotted versus Ki-67 nuclear antigen staining. The cell-cycle phases were defined as G0 (Ki-67− and 2n DNA), G1 (Ki-67+ and 2n DNA) and S-G2-M (Ki-67+ and DNA >2n). (e) Percentage of LKS+CD34− HSC in phase G0 (quiescence). (f) HSC quiescence in Sele−/− and WT mice as measured by hydroxyurea (HU) in vivo suicide assay. Data shows the number of surviving reconstituting units (RU) per femur after injection with HU or no HU control. (g,h) Rhodamine efflux by HSCs. (g) Contour plot showing Rho efflux and CD48 staining on gated bone marrow LKS+ cells from representative mice. (h) Percentage of bone marrow LKS+ cell able to efflux Rho. Data are pooled from three separate experiments. Each symbol in c,e,f and h represents data for one mouse. All statistical significance was calculated by nonparametric Mann-Whitney test. All data are shown as the mean ± s.d.
… 
PSGL-1 and CD44 receptors do not mediate the effects of E-selectin on HSC cycling. (a) Static adhesion assay of sorted bone marrow LKS+ cells on immobilized recombinant selectins. Shown are the percentages of adherent cells compared to input cells. In all cases, 97–100% of the input cells adhered to immobilized recombinant mouse VCAM-1 in parallel wells. Data are the mean ± s.d. for triplicate wells. (b) E-selectin (Esel)-IgM binding assay. A suspension of bone marrow cells was stained for the indicated cell-surface antigens and then incubated with a preformed complex of E-selectin–IgM and CY5-labeled antibody to IgM. Shown are overlays of E-selectin binding to CD11b+Gr1+/low neutrophils and monocytes (top left, Gr1+/low) and to gated LKS+ cells (top right). Black line, WT; bold gray line, Selplg−/−Cd44−/− (KO); light gray filled line, EDTA negative control. Also shown is a histogram (bottom) of the percentage of gated cells that bound E-selectin–IgM. Data are the mean ± s.d. n = 6 mice per group. ***P < 0.001. (c) Three-day BrdU incorporation plotted relative to CD34 expression in gated LKS+ cells in WT and Selplg−/−Cd44−/− mice. Inserted quadrants show percentages of cells in each quadrant of the dot plots. (d) Timecourse of BrdU incorporation in gated bone marrow LKS+CD34− cells. Bars are the mean ± s.d. NS, not significant. (e) Rho efflux by HSCs. Contour plot showing Rho efflux plotted against CD48 staining on gated bone marrow LKS+ cells from representative WT and Selplg−/−Cd44−/− mice. (f) Percentage of bone marrow LKS+ cells able to efflux Rho. (g) E-selectin pulldown experiments. Lysates of Lin−Kit+ cells from Selplg−/−Cd44−/− mice were incubated with recombinant mouse E-selectin–huIgG1–Fc (Esel-IgG) or control (IgG)-coated beads, pulled down, eluted with EDTA and western blotted with a rabbit antibody to ESL-1. MW, molecular weight. (h) Binding of LKS+ cells from WT and Selplg−/−Cd44−/− mice to recombinant human E-selectin–IgM (top histograms) and P-selectin–IgM (bottom histograms) after an overnight incubation with or without PPMP, as measured by flow cytometry. Data are the mean ± s.d. (triplicate wells, three repeats). Each symbol in d and f represents data from a single mouse. All statistical significance was determined by nonparametric Mann-Whitney test.
… 
Content may be subject to copyright.
A preview of the PDF is not available
... However, BMM or "niche"-mediated resistance may be associated with extrinsic cytokines or chemokines, such as CXC chemokine receptor 4 (CXCR4)/CXC motif ligand 12 (CXCL12) and endothelial (E)-selectin (CD62E)/E-selectin ligands (E-selectin-L). Both CXCR4 and E-selectin ligands are crucial for directing leukocyte or hematopoietic stem cell (HSC) homing to BMM 10,11 . In addition, the hypoxic condition (1-3% O 2 ) in BMM can trigger the upregulation of genes glycosylating E-selectin-L such as fucosyltransferase VII (FUT7) and sialyltransferase ST3Gal-I (ST3O) through the hypoxiainducible factor (HIF)1-α---a key transcriptional factor induced by hypoxia, known to be involved in the synthesis of the carbohydrate ligands for E-selectin and associated with resistance to therapy in AML 12,13 . ...
... CXCR4 is overexpressed in 25%-30% of AML patients, and high CXCR4 expression is correlated with a shorter overall survival duration and a higher probability of relapse in both FLT3-ITD and FLT3-wild-type AML [13][14][15] . Two principal ligands for E-selectin are found on HSC: the sialofucosylated glycoform of the CD44 protein-hematopoietic cell E-/L-selectin ligand (HCELL) and P-selectin glycoprotein ligand-1 (PSGL-1; CD162) 11,[16][17][18][19][20] . All these E-selectin ligands on tumor cells contain the sialyl-Lewis x or a (sLe x/a ) glyco-epitopes, which are recognized by E-selectin in a highly speci c fashion 21,22 . ...
Preprint
Full-text available
CXC chemokine receptor 4 (CXCR4)/CXC motif ligand 12 (CXCL12) and E-(endothelial)-selectin/E-selectin ligands (E-selectin-L) axes play critical roles in leukemia cell homing to the bone marrow niche and are closely associated with resistance to FLT3-targeted therapy in FLT3 -mutant acute myeloid leukemia (AML) patients. Hence, it is imperative to co-target CXCR4/E-selectin/FLT3 in FLT3 mutant AML. Herein, we determined whether FLT3 inhibition modulates CXCR4/E-selectin-L levels and whether co-targeting CXCR4/E-selectin enhances the anti-leukemia effects and reduces bone marrow niche-mediated resistance in FLT3-targeted therapy. Our results demonstrate that CXCR4/E-selectin-L are transcriptionally upregulated by FLT3 inhibition. Concomitant blockage of CXCR4/E-selectin with the dual inhibitor GMI-1359 disrupts leukemia cell homing and migration to bone marrow niches. Combination treatment with GMI-1359 and quizartinib significantly reduced leukemia cell burden and extended mouse survival in a patient derived xenograft AML mouse model. These findings provide pre-clinical rationale for combined CXCR4/E-selectin/FLT3 targeting in FLT3 -mutant AML.
... The pathophysiology of leukostasis in AML is also unclear in the wider literature [72]. However, two prominent theories involving endothelial selectins that adhere leukemic blasts to the vascular endothelium have been identified to play a vital role in the development of leukostasis in conjunction with chemotherapy resistance and Leukemic Stem Cells (LSC) [71][72][73][74][75]. Furthermore, increased blood viscosity and reduced deformability of myeloid blasts in contrast to lymphoid blasts and mature myeloid cells have been attributed to a disruption in the microcirculation resulting in the risk of end-organ damage [72,[76][77][78]. ...
Article
Full-text available
Acute Myeloid Leukemia (AML) is a malignant clonal hematopoietic stem cell disorder of the myeloid lineage that results in the infiltration of abnormal hematopoietic cells of the system in the bone marrow and haematological periphery. AML presents with a wide range of often unremarkable symptoms. However, it can rapidly become fatal due to complications, including hyperleukocytosis, which can lead to Disseminated Intravascular Coagulation (DIC), tumour lysis syndrome, leukostasis, and end-organ injury. Leukostasis occurs when the White Blood Cell (WBC) count is high enough to result in vascular congestion and lead to end-organ dysfunction. Leukostasis is relatively common and occurs in 15-45% of AML patients with hyperleukocytosis. Alarmingly, if left untreated, leukostasis is associated with a mortality rate of 20 to 40 per cent. The varied symptomatology, high mortality and common presentation of leukostasis in hyperleukocytic AML patients highlight the importance of raising awareness of leukostasis in clinical settings. Thus, it is crucial to report identified cases of hyperleukocytosis and leukostasis to improve diagnostic accuracy and health outcomes. Therefore, we report a case of hyperleukocytosis in a 62-year-old female with AML who presented to our rural emergency department with a four-week history of cough.
... Both cell types play different roles in the modulation of BM niche (97). SECs are the compartments of more permeable sinusoidal vessels and secrete high levels of CXCL12 as well as E-selectin that regulate HSC homing (96,98). On the contrary, AECs are the compartments of arteriolar vessels which have low penetration and ensure a relatively hypoxic environment (99,100). ...
Article
Full-text available
Acute myeloid leukemia (AML) arises from the cells of myeloid lineage and is the most frequent leukemia type in adulthood accounting for about 80% of all cases. The most common treatment strategy for the treatment of AML includes chemotherapy, in rare cases radiotherapy and stem cell and bone marrow transplantation are considered. Immune checkpoint proteins involve in the negative regulation of immune cells, leading to an escape from immune surveillance, in turn, causing failure of tumor cell elimination. Immune checkpoint inhibitors (ICIs) target the negative regulation of the immune cells and support the immune system in terms of anti-tumor immunity. Bone marrow microenvironment (BMM) bears various blood cell lineages and the interactions between these lineages and the noncellular components of BMM are considered important for AML development and progression. Administration of ICIs for the AML treatment may be a promising option by regulating BMM. In this review, we summarize the current treatment options in AML treatment and discuss the possible application of ICIs in AML treatment from the perspective of the regulation of BMM.
... MSC separation and expansion are easy to perform; besides, their cell properties are stable after expansion, and MSCs have homing to inflammatory sites, multidirectional differentiation ability, and immunoregulatory properties; they can also regulate the proliferation and differentiation of HSC by secreting Eselectin (13), cytochemokines, and crosstalk molecules, such as Jagged1 and CXCL12 (14)(15)(16), and this regulation also depends on the tight spatial localization of MSC and vascular endothelial cells (17). ...
Article
Full-text available
Myelodysplastic syndrome (MDS) is a common hematological malignant disease, characterized by malignant hematopoietic stem cell proliferation in the bone marrow (BM); clinically, it mainly manifests clinically mainly by as pathological hematopoiesis, hemocytopenia, and high-risk transformation to acute leukemia. Several studies have shown that the BM microenvironment plays a critical role in the progression of MDS. In this study, we specifically evaluated mesenchymal stromal cells (MSCs) that exert immunomodulatory effects in the BM microenvironment. This immunomodulatory effect occurs through direct cell-cell contact and the secretion of soluble cytokines or micro vesicles. Several researchers have compared MSCs derived from healthy donors to low-risk MDS-associated bone mesenchymal stem cells (BM-MSCs) and have found no significant abnormalities in the MDS-MSC phenotype; however, these cells have been observed to exhibit altered function, including a decline in osteoblastic function. This altered function may promote MDS progression. In patients with MDS, especially high-risk patients, MSCs in the BM microenvironment regulate immune cell function, such as that of T cells, B cells, natural killer cells, dendritic cells, neutrophils, myeloid-derived suppressor cells (MDSCs), macrophages, and Treg cells, thereby enabling MDS-associated malignant cells to evade immune cell surveillance. Alterations in MDS-MSC function include genomic instability, microRNA production, histone modification, DNA methylation, and abnormal signal transduction and cytokine secretion.
... Additionally, endothelial cells have been shown to support HSC maintenance by providing factors, such as CXCL12, SCF, angiopoietin, fibroblast growth factor (FGF) 2, and Delta-like 1 [19,33]. Furthermore, removal of E-selectin from endothelial cells increased HSC quiescence and self-renewal, confirming that E-selectin also supports HSC function [34]. ...
Article
Full-text available
Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.
... Bone marrow endothelial cells (BMECs) play a key role in restoring hematopoiesis following radiation injury in part by secretion of hematopoietic cytokines such as G-CSF, EGF, pleiotrophin, jagged-1, CCL5 and E-selection [13,[58][59][60][61][62][63]. Indeed, genetic gain and loss of function models have demonstrated the necessity of the BM vascular niche for hematopoietic regeneration following radiation injury. ...
Article
Full-text available
As the single cell lining of the heart and all blood vessels, the vascular endothelium serves a critical role in maintaining homeostasis via control of vascular tone, immune cell recruitment, and macromolecular transit. For victims of acute high-dose radiation exposure, damage to the vascular endothelium may exacerbate the pathogenesis of acute and delayed multi-organ radiation toxicities. While commonalities exist between radiation-induced endothelial dysfunction in radiosensitive organs, the vascular endothelium is known to be highly heterogeneous as it is required to serve tissue and organ specific roles. In keeping with its organ and tissue specific functionality, the molecular and cellular response of the endothelium to radiation injury varies by organ. Therefore, in the development of medical countermeasures for multi-organ injury, it is necessary to consider organ and tissue-specific endothelial responses to both injury and candidate mitigators. The purpose of this review is to summarize the pathogenesis of endothelial dysfunction following total or near total body irradiation exposure at the level of individual radiosensitive organs.
... Since the interplay between leukemic blasts and the bone marrow microenvironment has shown to affect chemotherapy resistance in AML, targeting the TME interactions in AML has been the focus of several preclinical studies and early phase clinical trials [23,24]. Examples include inhibitors of CXCR4 [25,26], VLA-4 [27,28] and E-selectin [29], which are being evaluated in clinical trials. ...
... Both arteriolar and sinusoidal BMECs play a pivotal, instructive role on HSC by regulating quiescence, self-renewal and trafficking [4][5][6] . BMECs are key for hematopoietic regeneration following radiation and chemotherapy [7][8][9] and are active participants in malignant hematopoiesis [10][11][12][13] . Thus, a deeper understanding of BMECs, their diversity and crosstalk with HSC and other BM cell types, will lead to the identification of novel therapeutic targets. ...
Article
Full-text available
Heterogeneity of endothelial cell (EC) populations reflects their diverse functions in maintaining tissue’s homeostasis. However, their phenotypic, molecular, and functional properties are not entirely mapped. We use the Tie2-CreERT2;Rosa26-tdTomato reporter mouse to trace, profile, and cultivate primary ECs from different organs. As paradigm platform, we use this strategy to study bone marrow endothelial cells (BMECs). Single-cell mRNA sequencing of primary BMECs reveals that their diversity and native molecular signatures is transitorily preserved in an ex vivo culture that conserves key cell-to-cell microenvironment interactions. Macrophages sustain BMEC cellular diversity and expansion and preserve sinusoidal-like BMECs ex vivo. Endomucin expression discriminates BMECs in populations exhibiting mutually exclusive properties and distinct sinusoidal/arterial and tip/stalk signatures. In contrast to arterial-like, sinusoidal-like BMECs are short-lived, form 2D-networks, contribute to in vivo angiogenesis, and support hematopoietic stem/progenitor cells in vitro. This platform can be extended to other organs’ ECs to decode mechanistic information and explore therapeutics. Here Kim et al. show that primary BMECs can be maintained ex vivo as distinct sinusoidal- and arterial-like populations and that the presence of macrophages is critical to preserve their native transcriptomic profiles and functional heterogeneity.
Chapter
The bone microenvironment is a dynamic, specialized region composed of heterogeneous cells, extracellular matrix, soluble growth factors, and cytokines and where these components interact and produce physiological or pathological phenomena. It is the place where various components interact, function, and produce physiological or pathological phenomena. In this part, we introduce bone microenvironment, discuss its role in bone diseases, and review biomaterials used in bone microenvironment.
Article
Full-text available
Hematopoietic stem cells (HSCs) supply all blood cells throughout life by making use of their self-renewal and multilineage differentiation capabilities. A monoclonal antibody raised to the mouse homolog of CD34 (mCD34) was used to purify mouse HSCs to near homogeneity. Unlike in humans, primitive adult mouse bone marrow HSCs were detected in the mCD34 low to negative fraction. Injection of a single mCD34lo/-, c-Kit^+, Sca-1^+, lineage markers negative (Lin^-) cell resulted in long-term reconstitution of the lymphohematopoietic system in 21 percent of recipients. Thus, the purified HSC population should enable analysis of the self-renewal and multilineage differentiation of individual HSCs.
Article
Full-text available
An important factor contributing to hematopoietic stem cell (HSC) mobilization is the ability of mobilizing cytokines and chemotherapy to disturb the cellular components of HSC niches, particularly osteoblasts and their progenitors, and to inhibit the production of HSC supportive cytokines and chemokines. Although the mechanisms by which niche cells are inhibited by mobilizing treatments is still incompletely understood, it has recently emerged that bone marrow macrophages play a critical role in maintaining osteoblasts, bone formation, and the expression of CXCL12, KIT ligand, and angiopoietin-1 necessary to HSC maintenance. In this chapter, we describe how to mobilize HSC into the blood in mice by depleting macrophages with clodronate-loaded liposomes and compare this mode of mobilization to mobilization induced by granulocyte colony-stimulating factor and cyclophosphamide. Detailed methods to analyze mobilization of phenotypic and functional reconstituting HSC are described with examples.
Article
Full-text available
Several cell types have been proposed to create niches for haematopoietic stem cells (HSCs). However, the expression patterns of HSC maintenance factors have not been systematically studied and no such factor has been conditionally deleted from any candidate niche cell. Thus, the cellular sources of these factors are undetermined. Stem cell factor (SCF; also known as KITL) is a key niche component that maintains HSCs. Here, using Scf(gfp) knock-in mice, we found that Scf was primarily expressed by perivascular cells throughout the bone marrow. HSC frequency and function were not affected when Scf was conditionally deleted from haematopoietic cells, osteoblasts, nestin-cre- or nestin-creER-expressing cells. However, HSCs were depleted from bone marrow when Scf was deleted from endothelial cells or leptin receptor (Lepr)-expressing perivascular stromal cells. Most HSCs were lost when Scf was deleted from both endothelial and Lepr-expressing perivascular cells. Thus, HSCs reside in a perivascular niche in which multiple cell types express factors that promote HSC maintenance.
Article
Full-text available
Identification of the precise location, where hematopoietic stem cells (HSCs) reside in the bone marrow, has made a great leap forward with the advance of live time-lapse video 2-photon fluorescent microscopy. These studies have shown that HSCs preferentially resides in the endosteal region of the BM, at an average of two cell diameters from osteoblasts covering endosteal bone surfaces. However, this equipment is very sophisticated and only a very few laboratories can perform these studies. To investigate functional attributes of these niches, we have developed a flow cytometry technique in which mice are perfused with the cell-permeable fluorescent dye Hoechst33342 in vivo before bone marrow cells are collected and antibody stained. This method enables to position phenotypic HSC, multipotent and myeloid progenitors, as well as BM nonhematopoietic stromal cells relative to blood flow in vivo. This technique enables prospective isolation of HSCs based on the in vivo perfusion of the niches in which they reside.
Article
Full-text available
The hematopoietic system is highly proliferative in the bone marrow (BM) due to the short half-life of granulocytes and platelets in the blood. Analysis of cell cycling and cell proliferation in vivo in specific populations of the mouse BM has highlighted some key properties of adult hematopoietic stem cells (HSCs). For instance, despite their enormous proliferation and repopulation potential, most true HSC are deeply quiescent in G(0) phase of the cell cycle and divide very infrequently, while less potent lineage-restricted progenitors divide rapidly to replace the daily consumption of blood leukocytes, erythrocytes, and platelets. In response to stress, e.g., following ablative chemotherapy or irradiation, HSC must enter the cell cycle to rapidly repopulate the BM with progenitors. Due to their extreme rarity in the BM, at least five color flow cytometry for cell surface antigens has to be combined with staining for DNA content and nuclear markers of proliferation to analyze cell cycle and proliferation of HSC in vivo. In this chapter, we describe two methods to stain mouse HSC to (1) distinguish all phases of the cell cycle (G(0), G(1), S, and G(2)/M) and (2) analyze the divisional history of HSC in vivo by incorporation of the thymidine analog 5-bromo-2-deoxyuridine.
Article
Full-text available
Reversible interactions of glycoconjugates on leukocytes with P- and E-selectin on endothelial cells mediate tethering and rolling of leukocytes in inflamed vascular beds, the first step in their recruitment to sites of injury. Although selectin ligands on hematopoietic precursors have been identified, here we review evidence that PSGL-1, CD44, and ESL-1 on mature leukocytes are physiologic glycoprotein ligands for endothelial selectins. Each ligand has specialized adhesive functions during tethering and rolling. Furthermore, PSGL-1 and CD44 induce signals that activate the β2 integrin LFA-1 and promote slow rolling, whereas ESL-1 induces signals that activate the β2 integrin Mac-1 in adherent neutrophils. We also review evidence for glycolipids, CD43, L-selectin, and other glycoconjugates as potential physiologic ligands for endothelial selectins on neutrophils or lymphocytes. Although the physiologic characterization of these ligands has been obtained in mice, we also note reported similarities and differences with human selectin ligands.
Article
Full-text available
Cfr (cysteine-rich fibroblast growth factor receptor) is an Fgf (fibroblast growth factor)-binding protein without a tyrosine kinase. We have shown previously that Cfr is involved in Fgf18 signalling via Fgf receptor 3c. However, as Cfr is also known as Glg (Golgi apparatus protein)-1 or MG-160 and occurs in the Golgi apparatus, it remains unknown how the distribution of Cfr is regulated. In the present study, we performed a mutagenic analysis of Cfr to show that two distinct regions contribute to its distribution and stability. First, the C-terminal region retains Cfr in the Golgi apparatus. Secondly, the Cfr repeats in the extracellular juxtamembrane region destabilizes Cfr passed through the Golgi apparatus. This destabilization does not depend on the cleavage and secretion of the extracellular domain of Cfr. Furthermore, we found that Cfr with a GPI (glycosylphosphatidylinositol) anchor was predominantly expressed on the cell surface in Ba/F3 cells and affected Fgf18 signalling in a similar manner to the full-length Cfr, indicating that the interaction of Cfr with Fgfs on the cell surface is important for its function in Fgf signalling. These results suggest that the expression of Cfr in the Golgi apparatus and on the plasma membrane is finely tuned through two distinct mechanisms for exhibiting different functions.
Article
Cell adhesion molecules (CAMs) play a key role in interactions between stromal and hematopoietic cells in bone marrow (BM) and in cell traffic through vascular endothelium. To examine the identity of CAMs involved in these processes in mouse BM, we have investigated the in vivo expression of vascular cell adhesion molecule-1 (VCAM-1) and its counter-receptor, very late antigen-4 (VLA-4). Radioiodinated monoclonal antibodies (MoAbs) detecting VLA-4 and VCAM-1 were injected intravenously. Antibody binding was detected in BM by light and electron microscope radioautography. VCAM-1 labeling was restricted to stromal reticular cells and endothelial cells lining BM sinusoids. VCAM- 1+ reticular cells formed patchy concentrations, especially in subosteal regions, associated with lymphoid, granulocytic, and erythroid cells. After gamma-irradiation to deplete hematopoietic cells, reticular cells and endothelial cells all showed VCAM-1 labeling in apparently increased intensity. VLA-4 labeling was shown by undifferentiated blast cells and lymphohematopoietic cells both in BM cell suspensions and in vivo, especially at reticular cell contact points. The results demonstrate that VCAM-1 is expressed in vivo by certain BM reticular cells, suggesting that the molecule mediates adhesion to multiple lineages of lymphohematopoietic cells. The finding that VCAM-1 is also expressed constitutively by BM sinusoidal endothelium, unlike its inductive expression by endothelia elsewhere, suggests that VCAM-1 and VLA-4 may be involved in regulating the normal cell traffic between BM and the blood stream.
Article
Macrophage inflammatory protein-1 alpha (MIP-1 alpha) has been assessed for its potential in vivo to protect hematopoietic progenitor cells from the cytotoxic effects of a cycle-specific drug--in this case hydroxyurea (HU). Two doses of HU, 7 hours apart, were administered to mice to induce spleen colony-forming unit (CFU-S) cycling and then to kill them during DNA-synthesis. MIP-1 alpha, in a variety of dose and time combinations, was injected before the second dose of HU in an attempt to prevent recruitment or maintain CFU-S quiescence, and thus protect them from the second dose of HU. Without MIP-1 alpha, recovery of the CFU-S population was complete in 7 days. In a dose-dependent manner, MIP-1 alpha either reduced the initial kill and accelerated recovery, or completely protected the CFU-S population. We conclude that MIP-1 alpha does protect multipotent progenitor cells in vivo and that these observations provide a base from which to build practical clinical applications.
Article
Macrophage inflammatory protein-1 alpha (MIP-1 alpha) has been assessed for its potential in vivo to protect hematopoietic progenitor cells from the cytotoxic effects of a cycle-specific drug--in this case hydroxyurea (HU). Two doses of HU, 7 hours apart, were administered to mice to induce spleen colony-forming unit (CFU-S) cycling and then to kill them during DNA-synthesis. MIP-1 alpha, in a variety of dose and time combinations, was injected before the second dose of HU in an attempt to prevent recruitment or maintain CFU-S quiescence, and thus protect them from the second dose of HU. Without MIP-1 alpha, recovery of the CFU-S population was complete in 7 days. In a dose-dependent manner, MIP-1 alpha either reduced the initial kill and accelerated recovery, or completely protected the CFU-S population. We conclude that MIP-1 alpha does protect multipotent progenitor cells in vivo and that these observations provide a base from which to build practical clinical applications.