Cytoskeleton and integrin-mediated adhesion signaling in human CD34+ hemopoietic progenitor cells

Impacts of Organomodified Nanoclays and Their Incinerated Byproducts on Bronchial Cell Monolayer Integrity

Incorporation of engineered nanomaterials (ENMs) into nanocomposites using advanced manufacturing strategies is set to revolutionize diverse technologies. Of these, organomodified nanoclays (ONCs; i.e., smectite clays with different organic coatings) act as nanofillers in applications ranging from automotive to aerospace and biomedical systems. Recent toxicological evaluations increased awareness that exposure to ONC can occur along their entire life cycle, namely, during synthesis, handling, use, manipulation, and disposal. Compared to other ENMs, however, little information exists describing which physicochemical properties contribute to induced health risk. This study conducted high content screening on bronchial epithelial cell monolayers for coupled high-throughput in vitro assessment strategies aimed to evaluate acute toxicity of a library of ONCs (all of prevalent use) prior to and after simulated disposal by incineration. Coating-, incineration status-, and time-dependent effects were considered to determine changes in the pulmonary monolayer integrity, cell transepithelial resistance, apoptosis, and cell metabolism. Results showed that after exposure to each ONC at its half-maximal inhibitory concentration (IC₅₀) there is a material-induced toxicity effect with pristine nanoclay, for instance, displaying acute loss of monolayer coverage, resistance, and metabolism, coupled with increased number of apoptotic cells. Conversely, the other three ONCs tested displayed little loss of monolayer integrity; however, they exhibited differential coating-dependent increased apoptosis and up to 40-45% initial reduction in cell metabolism. Moreover, incinerated byproducts of ONCs exhibited significant loss of monolayer coverage and integrity, increased necrosis, with little evidence of monolayer re-establishment. These findings indicate that characteristics of organic coating type largely determine the mechanism of cytotoxicity and the ability of the monolayer to recover. Use of high content screening coupled with traditional in vitro assays proves to serve as a rapid pulmonary toxicity assessment tool to help define prevention by targeted physicochemical material properties design strategies.

Functional anatomy of the hair follicle: The Secondary Hair Germ

The secondary hair germ (SHG)-a transitory structure in the lower portion of the mouse telogen hair follicle (HF)-is directly involved in anagen induction and eventual HF regrowth. Some crucial aspects of SHG functioning and ontogenetic relations with other HF parts, however, remain undefined. According to recent evidence (in contrast to previous bulge-centric views), the SHG is the primary target of anagen-inducing signalling and a source of both the outer root sheath (ORS) and ascending HF layers during the initial (morphogenetic) anagen subphase. The SHG is comprised of two functionally distinct cell populations. Its lower portion (originating from lower HF cells that survived catagen) forms all ascending HF layers, while the upper SHG (formed by bulge-derived cells) builds up the ORS. The predetermination of SHG cells to a specific morphogenetic fate contradicts their attribution to the "stem cell" category and supports SHG designation as a "germinative" or a "founder" cell population. The mechanisms of this predetermination driving transition of the SHG from "refractory" to the "competent" state during the telogen remain unknown. Functionally, the SHG serves as a barrier, protecting the quiescent bulge stem cell niche from the extensive follicular papilla/SHG signalling milieu. The formation of the SHG is a prerequisite for efficient "precommitment" of these cells and provides for easier sensing and a faster response to anagen-inducing signals. In general, the formation of the SHG is an evolutionary adaptation, which allowed the ancestors of modern Muridae to acquire a specific, highly synchronized pattern of hair cycling.

Designed Surface Topographies Control ICAM-1 Expression in Tonsil-Derived Human Stromal Cells

Fibroblastic reticular cells (FRCs), the T-cell zone stromal cell subtype in the lymph nodes, create a scaffold for adhesion and migration of immune cells, thus allowing them to communicate. Although known to be important for the initiation of immune responses, studies about FRCs and their interactions have been impeded because FRCs are limited in availability and lose their function upon culture expansion. To circumvent these limitations, stromal cell precursors can be mechanotranduced to form mature FRCs. Here, we used a library of designed surface topographies to trigger FRC differentiation from tonsil-derived stromal cells (TSCs). Undifferentiated TSCs were seeded on a TopoChip containing 2176 different topographies in culture medium without differentiation factors, then monitored cell morphology and the levels of ICAM-1, a marker of FRC differentiation. We identified 112 and 72 surfaces that upregulated and downregulated, respectively, ICAM-1 expression. By monitoring cell morphology, and expression of the FRC differentiation marker ICAM-1 via image analysis and machine learning, we discovered correlations between ICAM-1 expression, cell shape and design of surface topographies and confirmed our findings by using flow cytometry. Our findings confirmed that TSCs are mechano-responsive cells and identified particular topographies that can be used to improve FRC differentiation protocols.

Carbon nanotubes physicochemical properties influence the overall cellular behavior and fate

The unique properties of single walled carbon nanotubes (SWCNTs) make them viable candidates for versatile implementation in the next generation of biomedical devices for targeted delivery of chemotherapeutic agents or cellular-sensing probes. Such implementation requires user-tailored changes in SWCNT's physicochemical characteristics to allow for efficient cellular integration while maintaining nanotubes' functionality. However, isolated reports showed that user-tailoring could induce deleterious effects in exposed cells, from decrease in cellular proliferation, to changes in cellular adhesion, generation of reactive oxygen species or phenotypical variations, just to name a few. Before full implementation of SWCNTs is achieved, their toxicological profiles need to be mechanistically correlated with their physicochemical properties to determine how the induced cellular fate is related to the exposure conditions or samples' characteristics. Our study provides a comprehensive analysis of the synergistic cyto- and genotoxic effects resulted from short-term exposure of human lung epithelial cells to pristine (as manufactured) and user-tailored SWCNTs, as a function of their physicochemical properties. Specifically, through a systematic approach we are correlating the nanotube uptake and nanotube-induced cellular changes to the sample's physicochemical characteristics (e.g., metal impurities, length, agglomerate size, surface area, dispersion, and surface functionalization). By identifying changes in active hallmarks involved in cell-cell connections and maintaining epithelial layer integrity, we also determine the role that short-term exposure to SWCNTs plays in the overall cellular fate and cellular transformation. Lastly, we assess cellular structure-function relationships to identify non-apoptotic pathways induced by SWCNTs exposure that could however lead to changes in cellular behavior and cellular transformation. Our results show that the degree of cell transformation is a function of the physicochemical properties of the SWCNT, with the nanotube with higher length, higher metal content and larger agglomerate size reducing cell viability to a larger extent. Such changes in cell viability are also complemented by changes in cell structure, cycle and cell-cell interactions, all responsible for maintaining cell fate.

Imatinib and nilotinib inhibit hematopoietic progenitor cell growth, but do not prevent adhesion, migration and engraftment of human cord blood CD34+ cells

Background

The availability of tyrosine kinase inhibitors (TKIs) has considerably changed the management of Philadelphia chromosome positive leukemia. The BCR-ABL inhibitor imatinib is also known to inhibit the tyrosine kinase of the stem cell factor receptor, c-Kit. Nilotinib is 30 times more potent than imatinib towards BCR-ABL in vitro. Studies in healthy volunteers and patients with chronic myelogenous leukemia or gastrointestinal stromal tumors have shown that therapeutic doses of nilotinib deliver drug levels similar to those of imatinib. The aim of this study was to compare the inhibitory effects of imatinib and nilotinib on proliferation, differentiation, adhesion, migration and engraftment capacities of human cord blood CD34⁺ cells.

Design and Methods

After a 48-hour cell culture with or without TKIs, CFC, LTC-IC, migration, adhesion and cell cycle analysis were performed. In a second time, the impact of these TKIs on engraftment was assessed in a xenotransplantation model using NOD/SCID/IL-2Rγ (null) mice.

Results

TKIs did not affect LTC-IC frequencies despite in vitro inhibition of CFC formation due to inhibition of CD34⁺ cell cycle entry. Adhesion of CD34⁺ cells to retronectin was reduced in the presence of either imatinib or nilotinib but only at high concentrations. Migration through a SDF-1α gradient was not changed by cell culture in the presence of TKIs. Finally, bone marrow cellularity and human chimerism were not affected by daily doses of imatinib and nilotinib in a xenogenic transplantation model. No significant difference was seen between TKIs given the equivalent affinity of imatinib and nilotinib for KIT.

Conclusions

These data suggest that combining non-myeloablative conditioning regimen with TKIs starting the day of the transplantation could be safe.

To stay or to leave: Stem cells and progenitor cells navigating the S1P gradient

Most hematopoietic stem progenitor cells (HSPCs) reside in bone marrow (BM), but a small amount of HSPCs have been found to circulate between BM and tissues through blood and lymph. Several lines of evidence suggest that sphingosine-1-phosphate (S1P) gradient triggers HSPC egression to blood circulation after mobilization from BM stem cell niches. Stem cells also visit certain tissues. After a temporary 36 h short stay in local tissues, HSPCs go to lymph in response to S1P gradient between lymph and tissue and eventually enter the blood circulation. S1P also has a role in the guidance of the primitive HSPCs homing to BM in vivo, as S1P analogue FTY720 treatment can improve HSPC BM homing and engraftment. In stress conditions, various stem cells or progenitor cells can be attracted to local injured tissues and participate in local tissue cell differentiation and tissue rebuilding through modulation the expression level of S1P₁, S1P₂ or S1P₃ receptors. Hence, S1P is important for stem cells circulation in blood system to accomplish its role in body surveillance and injury recovery.

Alpha1 and beta1 integrins enhance the homing and differentiation of cultured prostate cancer stem cells

CD133(+) prostate cancer stem cells (PCSCs) have recently been identified in human prostate cancer tissues. The present study reports the integrin profile of prostate cancer progenitor cells and the role of alpha(1) and beta(1) integrins in the homing and differentiation of PCSCs in vitro. PCSCs were isolated from the tissue specimens of patients with prostate cancer and the expression of surface integrins and adhesion patterns were determined. Our analysis of the expression of surface integrins and their adhesion patterns of prostate cancer stem cells derived from prostate cancer tissues revealed that the levels of beta(1) and alpha(2)beta(1) integrins were significantly higher (P < 0.05) than those of the other integrins. By contrast, peripheral blood-derived CD133(+) cells from prostate cancer patients showed a high level of expression (P < 0.01) of alpha(2)beta(1), alpha(v)beta(3), alpha(v)beta(5), beta(1) and alpha(1) integrins and a minimal expression of alpha(4)beta(1) integrins. Moreover, CD133(+) cells derived from both prostate cancer tissues and peripheral blood exhibited an increased degree of attachment to extracellular matrix proteins (P < 0.001) and a high expression level of alpha(2)beta(1) integrin. In vitro experiments using blocking antibodies indicated that alpha(1) and beta(1) integrins have a role in the homing and differentiation of PCSCs. This is the first report to suggest the importance of integrins in mediating the homing and differentiation of PCSCs.

Hematopoietic stem cells: ex-vivo expansion and therapeutic potential for myocardial ischemia

Despite recent advances in cardiovascular medicine, ischemic heart disease remains the major cause of death in the United States and abroad. Cell-based therapy for degenerative diseases like myocardial ischemia using stem cells is currently under serious investigation. Various types of stem cells are being considered to be candidates for cell transplantation in cell-based therapy. Hematopoietic stem cells are one of the most promising cell types as several studies demonstrated their ability to improve ischemic cardiac functions by enhancing neovascularization and by reducing the total size of scar tissue. However, in order to procure sufficient numbers of functional stem cells, ex-vivo expansion technology became critically important. In this review, we focus on the state-of-the-art ex-vivo technology for the expansion of hematopoietic stem cells, and the underlying mechanisms regulating stem cell self-renewal as well as differentiation.

Olfactory epithelium progenitors: insights from transgenic mice and in vitro biology

The rodent olfactory epithelium (OE) is capable of prolonged neurogenesis, beginning at E10 in the embryo and continuing throughout adulthood. Significant progress has been made over the last 10 years in revealing the signals that drive induction, differentiation and survival of its Olfactory Receptor Neurons (ORNs). Our understanding of the identity of specific progenitors or precursors that respond to these signals is, however, less well developed, and the search is still on for the elusive, definitive multipotent neuro-glial OE "Stem cell". Here, we review several lines of evidence that support the existence of a heterogeneous population of neural and glial progenitors in the olfactory mucosa, and highlight the differences in the identity and activity of progenitors found in the embryonic and adult OE. In particular, we show how recent advances in mouse transgenesis, and in the development of in vitro assays of progenitor activity, have helped to demonstrate the existence of multiple classes of olfactory mucosa-based progenitors.

Distinct roles of integrins alpha6 and alpha4 in homing of fetal liver hematopoietic stem and progenitor cells

Homing of hematopoietic stem cells (HSCs) into the bone marrow (BM) is a prerequisite for establishment of hematopoiesis during development and following transplantation. However, the molecular interactions that control homing of HSCs, in particular, of fetal HSCs, are not well understood. Herein, we studied the role of the alpha6 and alpha4 integrin receptors for homing and engraftment of fetal liver (FL) HSCs and hematopoietic progenitor cells (HPCs) to adult BM by using integrin alpha6 gene-deleted mice and function-blocking antibodies. Both integrins were ubiquitously expressed in FL Lin(-)Sca-1(+)Kit(+) (LSK) cells. Deletion of integrin alpha6 receptor or inhibition by a function-blocking antibody inhibited FL LSK cell adhesion to its extracellular ligands, laminins-411 and -511 in vitro, and significantly reduced homing of HPCs to BM. In contrast, the anti-integrin alpha6 antibody did not inhibit BM homing of HSCs. In agreement with this, integrin alpha6 gene-deleted FL HSCs did not display any homing or engraftment defect compared with wild-type littermates. In contrast, inhibition of integrin alpha4 receptor by a function-blocking antibody virtually abrogated homing of both FL HSCs and HPCs to BM, indicating distinct functions for integrin alpha6 and alpha4 receptors during homing of fetal HSCs and HPCs.

T-, B- and NK-lymphoid, but not myeloid cells arise from human CD34+CD38−CD7+ common lymphoid progenitors expressing lymphoid-specific genes

Hematopoietic stem cells in the bone marrow (BM) give rise to all blood cells. According to the classic model of hematopoiesis, the differentiation paths leading to the myeloid and lymphoid lineages segregate early. A candidate 'common lymphoid progenitor' (CLP) has been isolated from CD34(+)CD38(-) human cord blood cells based on CD7 expression. Here, we confirm the B- and NK-differentiation potential of CD34(+)CD38(-)CD7(+) cells and show in addition that this population has strong capacity to differentiate into T cells. As CD34(+)CD38(-)CD7(+) cells are virtually devoid of myeloid differentiation potential, these cells represent true CLPs. To unravel the molecular mechanisms underlying lymphoid commitment, we performed genome-wide gene expression profiling on sorted CD34(+)CD38(-)CD7(+) and CD34(+)CD38(-)CD7(-) cells. Interestingly, lymphoid-affiliated genes were mainly upregulated in the CD7(+) population, while myeloid-specific genes were downregulated. This supports the hypothesis that lineage commitment is accompanied by the shutdown of inappropriate gene expression and the upregulation of lineage-specific genes. In addition, we identified several highly expressed genes that have not been described in hematopoiesis before.

Gene stage-specific expression in the microenvironment of pediatric myelodysplastic syndromes

Using cDNA microarray assays we have observed a clear difference in the gene expression pattern between bone marrow stromal cells obtained from healthy children (CT) and from pediatric patients with either myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) associated with MDS (MDS-AML). The global gene function profiling analysis indicated that in the pediatric MDS microenvironment the disease stages may be characterized mainly by underexpression of genes associated with biological processes such as transport. Furthermore, a subset of downregulated genes related to endocytosis and protein secretion was able to discriminate MDS from MDS-AML.

Expansion of engrafting human hematopoietic stem/progenitor cells in three-dimensional scaffolds with surface-immobilized fibronectin

An efficient and practical ex vivo expansion methodology for human hematopoietic stem/progenitor cells (HSPCs) is critical in realizing the potential of HSPC transplantation in treating a variety of hematologic disorders and as a supportive therapy for malignant diseases. We report here an expansion strategy using a three-dimensional (3D) scaffold conjugated with an extracellular matrix molecule, fibronectin (FN), to partially mimic the hematopoietic stem cell niche. FN-immobilized 3D polyethylene terephthalate (PET) scaffold was synthesized and evaluated for HSPC expansion efficiency, in comparison with a FN-immobilized 2D PET substrate and a 3D scaffold with FN supplemented in the medium. Covalent conjugation of FN produced substrate and scaffold with higher cell expansion efficiency than that on their unmodified counterparts. After 10 days of culture in serum-free medium, human umbilical cord blood CD34+ cells cultured in FN-conjugated scaffold yielded the highest expansion of CD34+ cells (approximately 100 fold) and long-term culture initiating cells (approximately 47-fold). The expanded human CD34+ cells successfully reconstituted hematopoiesis in NOD/SCID mice. This study demonstrated the synergistic effect between the three-dimensionality of the scaffold and surface-conjugated FN, and the potential of this FN-conjugated 3D scaffold for ex vivo expansion of HSPCs.

Despite Inhibition of Hematopoietic Progenitor Cell Growth In Vitro, the Tyrosine Kinase Inhibitor Imatinib Does Not Impair Engraftment of Human CD133+Cells into NOD/SCIDβ2mNullMice

There is potential interest for combining allogeneic hematopoietic cell transplantation (HCT), and particularly allogeneic HCT with a nonmyeloablative regimen, to the tyrosine kinase inhibitor imatinib (Glivec; Novartis, Basel, Switzerland, http://www.novartis.com) in order to maximize anti-leukemic activity against Philadelphia chromosome-positive leukemias. However, because imatinib inhibits c-kit, the stem cell factor receptor, it could interfere with bone marrow engraftment. In this study, we examined the impact of imatinib on normal progenitor cell function. Imatinib decreased the colony-forming capacity of mobilized peripheral blood human CD133(+) cells but not that of long-term culture-initiating cells. Imatinib also decreased the proliferation of cytokine-stimulated CD133(+) cells but did not induce apoptosis of these cells. Expression of very late antigen (VLA)-4, VLA-5, and CXCR4 of CD133(+) cells was not modified by imatinib, but imatinib decreased the ability of CD133(+) cells to migrate. Finally, imatinib did not decrease engraftment of CD133(+) cells into irradiated nonobese diabetic/severe combined immunodeficient/beta2m(null) mice conditioned with 3 or 1 Gy total body irradiation. In summary, our results suggest that, despite inhibition of hematopoietic progenitor cell growth in vitro, imatinib does not interfere with hematopoietic stem cell engraftment.

Rac GTPases differentially integrate signals regulating hematopoietic stem cell localization

The molecular events that regulate engraftment and mobilization of hematopoietic stem cells and progenitors (HSC/Ps) are still incompletely defined. We have examined the role of the Rho GTPases Rac1 and Rac2 in HSC engraftment and mobilization. Rac1, but not the hematopoietic-specific Rac2, is required for the engraftment phase of hematopoietic reconstitution, because Rac1(-/-) HSCs did not rescue in vivo hematopoiesis after transplantation, but deletion of Rac1 after engraftment did not impair steady-state hematopoiesis. Rac1(-/-) HSC/Ps showed impaired spatial localization to the endosteum but near-normal homing to the medullary cavity in vivo. Interaction with the bone marrow microenvironment in vitro was markedly altered. Whereas post-engraftment deletion of Rac1 alone did not impair hematopoiesis, deficiency of both Rac1 and Rac2 led to massive mobilization of HSCs from the marrow associated with ineffective hematopoiesis and intense selection for Rac-expressing HSCs. This mobilization was reversible by re-expression of Rac1. In addition, a rationally designed, reversible small-molecule inhibitor of Rac activation led to transient mobilization of engraftable HSC/Ps. Rac proteins thus differentially regulate engraftment and mobilization phenotypes, suggesting that these biological processes and steady-state hematopoiesis are biochemically separable and that Rac proteins may be important molecular targets for stem cell modification.

Integrin profile and in vivo homing of human smooth muscle progenitor cells

BACKGROUND

Recently, we identified circulating smooth muscle progenitor cells (SPCs) in human peripheral blood. The integrin profile of such progenitors is currently unknown and may affect their in vivo homing characteristics. In this study, we determined the integrin profile of vascular progenitors and SPC adhesion to extracellular matrix (ECM) proteins in vitro and in vivo.

METHODS AND RESULTS

SPCs and endothelial progenitor cells (EPCs) were isolated from peripheral blood of healthy human subjects, and expression of surface integrins and adhesion to several vascular ECM proteins were determined. Homing of SPCs in vivo to specific ECM protein was determined by intracoronary infusion of fluorescent SPCs into porcine coronary arteries containing a fibronectin-coated mesh stent. SPCs had high expression of beta1 integrin, moderate expression of alpha1, low levels of alpha(v)beta3, and did not express alpha(v)beta5, beta2, alpha2beta1, or alpha4beta1 integrins. In contrast, EPCs had high expression of alpha2beta1, alpha(v)beta3, alpha(v)beta5, beta1, and alpha1 and minimal expression of alpha4beta1. Moreover, SPCs showed increased adherence to fibronectin and collagen type I compared with vitronectin, consistent with their integrin profile, and demonstrated a similar degree of in vivo attachment to fibronectin-coated mesh.

CONCLUSIONS

These data for the first time show a spectrum of integrin expression on vascular progenitors and suggest the potential importance of integrins in mediating adherence of SPCs to specific ECM both in vitro and in vivo.

Expression of focal adhesion kinase in acute myeloid leukemia is associated with enhanced blast migration, increased cellularity, and poor prognosis

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase playing an important role in cell motility and survival. However, very little is known about FAK in normal and leukemic myeloid cells. In this study, FAK protein expression and mRNA were detected in 25 of 60 cases (42%) of acute myeloid leukemia (AML). Whereas FAK was expressed in 46% of CD34+ AML cells, it was not detected in normal purified CD34+ cells. Conversely, the FAK homologue proline-rich tyrosine kinase 2 (PYK2) was found to be expressed both in normal and leukemic myeloid cells. When expressed, FAK displayed phosphorylation on Tyr-397, an important step for its activation. Moreover, FAK expression was correlated with the phosphorylation of PYK2 on Tyr-881, a critical site for the PYK2 function in cell migration. FAK+ AML cells displayed significantly higher migration capacities and resistance to daunorubicin, compared with FAK- cells. The implication of FAK in both cell motility and drug resistance was demonstrated by small interfering RNA experiments with the FAK-positive KG1 cell line. However, adhesion on fibronectin efficiently protected FAK- AML cells from daunorubicin-mediated killing, suggesting that cellular adhesion mediated-drug resistance is not mediated by FAK. Finally, in a retrospective cohort of 60 AML patients, FAK expression was significantly correlated with high blast cell count, early death, and shorter survival rate. Altogether, this study shows that FAK is aberrantly expressed and activated in about half of the cases of AML and suggests that FAK may contribute to the regulation of AML cell transit from the marrow to blood compartment and that it may influence clinical outcome.

Fast hematopoietic recovery after bone marrow engraftment needs physiological proximity of stromal and stem cells

Relatively slow hematopoietic recovery after isolated bone marrow (I-BM) engraftment is probably caused by a disrupted microenvironment of stromal and stem cells. Thus, we compared the kinetics of hematopoietic recovery of lethally irradiated rats that received I-BM versus vascularized BM (V-BM). Total body irradiated (TBI; 8 Gy) Lewis (LEW; RT1(1)) rats were either injected IV with syngeneic sex-mismatched 80 x 10(6) I-BM or transplanted with 80 x 10(6) V-BM in orthotopic hind limb grafts. Ten days later, peripheral blood (PB) and mesenteric lymph nodes (MLN) of these recipients were examined for the presence of donor-derived hematopoietic cells with a panel of monoclonal antibodies by FACS. To detect male cells in sex-mismatched female recipients, PCR was performed using male Y chromosome primers. When examined in PB and MLN, recipients transplanted with V-BM displayed significantly faster recovery of leukocytes (CD43+), monocytes (CD14+), and T cells (CD5+) in comparison with I-BM recipients. In addition, only V-BM (but not I-BM) groups contained stroma-like male-positive cells in PB and MLN. Our results suggest that V-BM transplants provided superior hematopoietic recovery in comparison to I-BM transplants. We postulated that close proximity between stromal and stem cells in V-BM is essential for efficient repopulation with progenitors of different lines of leukocytes.

Lysophospholipids synergistically promote primitive hematopoietic cell chemotaxis via a mechanism involving Vav 1

Hematopoiesis is sustained by the proliferation and development of an extremely low number of hematopoietic stem cells resident in the bone marrow. These stem cells can migrate from their bone marrow microenvironment and can be found at low levels in the peripheral blood. The factors that regulate egress or ingress of the stem cells from the marrow include cytokines and chemokines. This process of stem cell trafficking is fundamental to both stem cell biology and stem cell transplantation. We show that primitive hematopoietic cells with cobblestone area-forming cell activity express receptors for and display enhanced motility in response to a new class of stem cell agonists, namely lysophospholipids. These agents synergistically promote chemokine-stimulated cell chemotaxis, a process that is crucial in stem cell homing. The response to lysophospholipids is mediated by Rac, Rho, and Cdc42 G proteins and the hematopoietic-specific guanyl nucleotide exchange factor Vav 1. Inhibitor studies also show a critical role for phosphatidylinositol 3 kinase (PI3K). Lipid mediators, therefore, regulate the critical process of primitive hematopoietic cell motility via a PI3K- and Vav-dependent mechanism and may govern stem cell movement in vivo. These results are of relevance to understanding stem cell trafficking during bone marrow transplantation.

Acute myeloid leukemia

In this chapter, Drs. Keating and Willman review recent advances in our understanding of the pathophysiology of acute myeloid leukemia (AML) and allied conditions, including the advanced myelodysplastic syndromes (MDS), while Drs. Goldstone, Avivi, Giles, and Kantarjian focus on therapeutic data with an emphasis on current patient care and future research studies. In Section I, Dr. Armand Keating reviews the role of the hematopoietic microenvironment in the initiation and progression of leukemia. He also discusses recent data on the stromal, or nonhematopoietic, marrow mesenchymal cell population and its possible role in AML. In Section II, Drs. Anthony Goldstone and Irit Avivi review the current role of stem cell transplantation as therapy for AML and MDS. They focus on data generated on recent Medical Research Council studies and promising investigation approaches. In Section III, Dr. Cheryl Willman reviews the current role of molecular genetics and gene expression analysis as tools to assist in AML disease classification systems, modeling of gene expression profiles associated with response or resistance to various interventions, and identifying novel therapeutic targets. In Section IV, Drs. Hagop Kantarjian and Francis Giles review some promising agents and strategies under investigation in the therapy of AML and MDS with an emphasis on novel delivery systems for cytotoxic therapy and on targeted biologic agents.

Activation of Rac and tyrosine phosphorylation of cytokine receptors induced by cross-linking of integrin alpha4beta1 and cell adhesion in hematopoietic cells

Adhesion of hematopoietic cells, mainly through alpha4beta1 and alpha5beta1 integrins, to the bone marrow microenvironment may play important roles in regulation of hematopoiesis. However, the mechanisms for signaling, outside-in signaling, have largely remained to be established. We demonstrate here that cross-linking of alpha4beta1 by anti-alpha4 antibody induces tyrosine phosphorylation of Pyk2, Shc, and Cbl as well as binding of the adaptor protein CrkL with Cbl in a murine hematopoietic cell line, 32D/EpoR-Wt. Furthermore, cross-linking of alpha4beta1 induced activation of the Rho family small GTPase Rac, which was enhanced by induced overexpression of CrkL and was inhibited by the phosphatidylinositol 3(')-kinase (PI3K) inhibitor LY294002. In addition, adhesion of 32D/EpoR-Wt cells to immobilized H-296, a recombinant fibronectin peptide specific for alpha4beta1, induced tyrosine phosphorylation of Jak2, the erythropoietin receptor (EpoR), and the IL-3 receptor beta subunit as well as Pyk2, Shc, and Cbl. Tyrosine phosphorylation of Jak2 and EpoR was also induced in a human leukemic cell line, UT-7, by adhesion to immobilized H-296. However, adhesion of 32D/EpoR-PM4 cells, expressing the W282R mutant EpoR defective in coupling with Jak2, to immobilized H-296 failed to induce tyrosine phosphorylation of the mutant EpoR. These results implicate CrkL in PI3K-dependent activation of Rac by outside-in signaling from alpha4beta1 and suggest that adhesion through alpha4beta1 further activates cytokine receptor-associated Jak2 to induce phosphorylation of these receptors.

Laminin isoform-specific promotion of adhesion and migration of human bone marrow progenitor cells

Laminins are alphabetagamma heterotrimeric extracellular proteins that regulate cellular functions by adhesion to integrin and nonintegrin receptors. Laminins containing alpha4 and alpha5 chains are expressed in bone marrow, but their interactions with hematopoietic progenitors are unknown. We studied human bone marrow cell adhesion to laminin-10/11 (alpha5beta1gamma1/alpha5beta2gamma1), laminin-8 (alpha4beta1gamma1), laminin-1 (alpha1beta1gamma1), and fibronectin. About 35% to 40% of CD34(+) and CD34(+)CD38(-) stem and progenitor cells adhered to laminin-10/11, and 45% to 50% adhered to fibronectin, whereas they adhered less to laminin-8 and laminin-1. Adhesion of CD34(+)CD38(-) cells to laminin-10/11 was maximal without integrin activation, whereas adhesion to other proteins was dependent on protein kinase C activation by 12-tetradecanoyl phorbol-13-acetate (TPA). Fluorescence-activated cell-sorting (FACS) analysis showed expression of integrin alpha6 chain on most CD34(+) and CD34(+)CD38(-) cells. Integrin alpha6 and beta1 chains were involved in binding of both cell fractions to laminin-10/11 and laminin-8. Laminin-10/11 was highly adhesive to lineage-committed myelomonocytic and erythroid progenitor cells and most lymphoid and myeloid cell lines studied, whereas laminin-8 was less adhesive. In functional assays, both laminin-8 and laminin-10/11 facilitated stromal-derived factor-1alpha (SDF-1alpha)-stimulated transmigration of CD34(+) cells, by an integrin alpha6 receptor-mediated mechanism. In conclusion, we demonstrate laminin isoform-specific adhesive interactions with human bone marrow stem, progenitor, and more differentiated cells. The cell-adhesive laminins affected migration of hematopoietic progenitors, suggesting a physiologic role for laminins during hematopoiesis.

Porcine mononuclear cells adhere to human fibronectin independently of very late antigen-5: implications for donor-specific tolerance induction in xenotransplantation

To combat the shortage of donor organs, transplantation across species barriers has been proposed. Induction of tolerance would overcome the substantial immunologic barriers to xenotransplantation and would avoid the chronic use of immunosuppressive agents. Successful transplantation of hematopoietic cells induces robust specific tolerance to donor antigens in allogeneic and xenogeneic models. The beta1 integrin class of adhesion molecules and their interactions with extracellular matrix components are thought to be integral to the engraftment and maturation of hematopoietic stem cells. We therefore examined the efficacy of porcine very late antigen-5 (VLA-5) and VLA-4 interactions with the human extracellular matrix (ECM) protein, fibronectin. Peripheral blood mononuclear cells (PBMCs) from humans and miniature swine were flourochrome labeled and adhesion to plates coated with whole human fibronectin (whFN) or its 120 KDa fragment containing the VLA-5 binding region was determined. Flow cytometry and immuno- precipitation were used to identify a monoclonal antibody that cross-reacted on porcine VLA-5. Human and pig PBMC adhesion to human fibronectin (hFN) or 120 kDa fragment-coated plates was assessed following incubation with control ab, anti-VLA-4, anti-VLA-5, or soluble fibronectin. Using rabbit complement, cells expressing VLA-5 were purged from PBMC preparations before performing the adhesion assay. Porcine and human PBMC both adhered to hFN in a divalent cation-dependent and activation-dependent manner. Adhesion to hFN of human but not pig PBMC was blocked by anti-VLA-5 monoclonal antibody SAM-1, although this mAb immunoprecipitated a heterodimeric cell surface molecule (155/135 kDa) resembling VLA-5 from pig PBMC. Complement-mediated depletion of VLA-5-expressing cells ablated specific binding of human but not porcine cells to hFN and its 120 kDa fragment. Addition of soluble fibronectin was capable of blocking adhesion of PBMC of both species to hFN. Anti-VLA-4 reduced the binding of PBMC from both species to hFN to a similar extent. Human and pig cells can specifically adhere to hFN and its 120 kDa fragment, suggesting that this critical cell-ECM interaction is preserved across species. While human cells exclusively use VLA-5 for binding to the 120 kDa fragment, porcine cells could not be shown to adhere to whFN or its 120 kDa fragment via VLA-5. However, porcine VLA-4 is capable of mediating adhesion to human FN. We conclude that disparities in the adhesive interactions of beta1 integrins may be a barrier to the use of porcine hematopoietic stem cell transplantation as a means of inducing donor-specific tolerance in the pig to human species combination.

Homing and clonogenic outgrowth of CD34(+) peripheral blood stem cells: a role for L-selectin?

OBJECTIVE

After transplantation of hematopoietic stem cells, adhesion molecules play a major role in the multistep process of engraftment in which L-selectin is suggested to be of relevance. A positive correlation previously was found between the number of reinfused L-selectin(+) stem cells and platelet recovery. In the present study, we determined the role of L-selectin in different engraftment steps, i.e., adhesion to endothelial cells, migration, and clonogenic outgrowth by in vitro assays that closely mimic the in vivo situation.

MATERIALS AND METHODS

Flow adhesion and migration experiments were performed using the human bone marrow endothelial cell line 4LHBMEC and isolated peripheral CD34(+) cells with or without blocking of L-selectin-ligand interaction. Various clonogenic assays, including serum-free colony-forming unit-megakaryocytes (CFU-MK) and burst-forming unit-megakaryocytes (BFU-MK), were performed with sorted L-selectin(+)L-selectin(-) cells or in the presence of antibodies.

RESULTS

Blocking of L-selectin on CD34(+) cells did not significantly affect rolling over and firm adhesion to 4LHBMEC. In addition, no role for L-selectin was found in transendothelial migration experiments. Finally, in clonogenic outgrowth of sorted or anti-L-selectin monoclonal antibody-incubated CD34(+) cells, no key role for L-selectin expression could be defined in BFU-MK and CFU-MK assays.

CONCLUSION

Using in vitro assays for CD34(+) stem cell adhesion, migration, and clonogenic capacity, we were not able to define a major role for L-selectin.

Decreased stroma adhesion capacity of CD34+ progenitor cells from mobilized peripheral blood is not lineage- or stage-specific and is associated with low beta 1 and beta 2 integrin expression

Molecular mechanisms leading to mobilization of hematopoietic cells from bone marrow (BM) to peripheral blood (PB) involve modulation of adhesion molecule expression on these cells that probably result in changes in adhesion capacity to the microenvironment. However, it is not clear whether these changes involve different stages or lineages of progenitor cells. In this study, we compared the capacity of mature and immature clonogenic progenitor cells from granulocyte colony-stimulating factor (G-CSF)-mobilized PB and normal BM CD34+ cells to adhere to complete marrow stroma. This functional capacity was assessed concurrently with molecular expression on CD34+ cells of integrins VLA-4 (alpha 4/beta 1), VLA-5 (alpha 5/beta 1), and LFA-1 (alpha L/beta 2) by interindividual (between mobilized PB and normal BM) and intraindividual (between mobilized PB and steady-state BM and PB in the same patient) analysis. The proportion of adherent clonogenic progenitor cells was significantly lower in PB than in BM, not only for total progenitor cells but also for mature and immature progenitor cells, and the difference was found for granulocytic and particularly for erythroid lineages. The lower adhesion capacity of PB CD34+ cells to stroma was associated with decreased expression (signal/noise MFI ratio) of integrin alpha 4, beta 1, alpha L, and beta 2 chains whereas that of alpha 5 chain did not differ from BM cells with the lowest expression level. Similar differences in integrin expression levels were also found between mobilized PB and steady-state BM CD34+ cells in the same patient except for the alpha L chain. Moreover, we demonstrated for the first time a strong positive correlation between mobilizing capacity and expression levels on mobilized CD34+ cells for the LFA-1 alpha L chain but not for VLA-4 or VLA-5. In conclusion, the decreased adhesion capacity of mobilized PB progenitor cells to stroma involves different maturation stages and different lineages. This is associated with down-regulation of integrins VLA-4 and LFA-1, but mobilizing capacity appears positively correlated with LFA-1 levels.

Vascular cell adhesion molecule-1 (CD106) is cleaved by neutrophil proteases in the bone marrow following hematopoietic progenitor cell mobilization by granulocyte colony-stimulating factor

Mobilized progenitor cells currently represent the most commonly used source of hematopoietic progenitor cells (HPCs) to effect hematopoietic reconstitution following myeloablative chemotherapies. Despite their widespread use, the molecular mechanisms responsible for the enforced egress of HPCs from the bone marrow (BM) into the circulation in response to mobilizing agents such as cytokines remain to be determined. Results of this study indicate that expression of vascular cell adhesion molecule-1 (VCAM-1) is strongly reduced in vivo in the BM during HPC mobilization by granulocyte colony-stimulating factor (G-CSF) and stem cell factor. Two serine proteases, namely, neutrophil elastase and cathepsin G, were identified, which cleave VCAM-1 and are released by neutrophils accumulating in the BM during the course of immobilization induced by G-CSF. The proposal is made that an essential step contributing to the mobilization of HPCs is the proteolytic cleavage of VCAM-1 expressed by BM stromal cells, an event triggered by the degranulation of neutrophils accumulating in the BM in response to the administration of G-CSF.

Cross-talk between alpha(4)beta(1)/alpha(5)beta(1) and c-Kit results in opposing effect on growth and survival of hematopoietic cells via the activation of focal adhesion kinase, mitogen-activated protein kinase, and Akt signaling pathways

Erythroid progenitor cells (EPCs) are deficient in mice lacking either the ligand stem cell factor (SCF), its receptor c-Kit, or beta(1)-integrins. In nonhematopoietic cells, integrins and receptor tyrosine kinases can collaborate to modulate cellular functions, providing evidence for cross-talk between signals emerging from these cell surface molecules. Using specific recombinant fibronectin peptides that contain the binding site for the integrin alpha(4)beta(1) (FN-H296) or alpha(5)beta(1) (FN-CH271) or both alpha(4)beta(1) and alpha(5)beta(1) (FN-CH296), this study investigated the effect of adhesion alone, or in combination with activation of c-Kit, on functional and biochemical outcomes in an EPC line, G1E-ER2, and primary EPCs. G1E-ER2 cells and primary EPCs cultured on FN-CH271 in the presence of c-Kit activation led to a significant increase in proliferation in comparison with cells grown on FN-H296 or FN-CH296. G1E-ER2 cells cultured on FN-H296 or FN-CH296 resulted in significant cell death in comparison to cells grown on FN-CH271. Activation of c-Kit enhanced the survival of G1E-ER2 cells grown on FN-H296 or FN-CH296; however, the rescue was only partial. The reduced survival of G1E-ER2 cells on FN-H296 correlated with reduced activation of Akt and expression of Bcl-2 and Bcl-x(L), whereas increase in proliferation on FN-CH271 correlated with significantly enhanced and sustained activation of focal adhesion kinase (FAK) and extracellular-regulated kinase (ERK) pathways. These data demonstrate that adhesion-induced signals emanating from ligation of alpha(4)beta(1) and alpha(5)beta(1) result in distinct biologic outcomes, including death via alpha(4)beta(1) and survival/proliferation via alpha(5)beta(1). (Blood. 2001;97:1975-1981)

Large populations of non-clonogenic early apoptotic CD34-positive cells are present in frozen-thawed peripheral blood stem cell transplants

Apoptosis is the common cell death pathway which is initiated by a variety of different stimuli. The recognition of early apoptotic events would markedly improve reliability and convenience of apoptosis assays. In the present study the vital stain SytoR 16 in combination with the permeability marker 7-amino actinomycin D, (7-AAD) has been used to identify an early stage of apoptosis, not detected with trypan blue or 7-AAD alone or with conventional apoptosis tests and not consistently and only partly detected by the early apoptosis marker annexin V. The method was established using solid tumour cell lines treated with TNF. Subsequently we applied it to determine apoptotic populations in CD34(+) peripheral blood progenitor cells obtained from growth factor and/or chemotherapy mobilised patients and frozen/thawed according to standard stem cell transplantation protocols. In a cell line model as well as CD34(+) progenitor cells, different subpopulations with decreased SytoR 16 fluorescence (SytoR 16int or SytoR 16low, compared with the normal SytoR 16high) appeared which are not, or only partly, apoptotic using conventional techniques including morphology or 7-AAD staining: eg percentages of SytoR 16(int)/7-AAD(-) and SytoR 16(low)/7-AAD(-) may amount to the majority of cells present in a particular CD34(+) sample. Second, upon further incubation these subpopulations become late apoptotic/secondary necrotic much faster than the unmodified SytoR 16high population, as determined with 7-AAD staining and morphology. Third, these cells have strongly or completely reduced clonogenic capacity for committed (CFU-GM) and early (LTC-IC, determined only for CD34(+) cells) progenitors. This technique needs the inclusion of a blocker of P-glycoprotein, which is highly active in CD34(+) progenitor cells. This prevents the interference of the detection of SytoR16(low) apoptotic cells by SytoR 16low cells resulting from P-glycoprotein activity. By comparison with other apoptosis markers we found that early apoptotic subpopulations were detected in the order SytoR 16 > annexin V > 7-AAD. In conclusion, the combination of SytoR 16 and 7-AAD detects apoptotic events earlier than conventional apoptosis techniques or annexin V. Compared to the presently available viability tests, it allows a much better estimation of the number of viable clonogenic CD34(+) cells after freeze/thawing.

Immunologic profiles of effector cells and peripheral blood stem cells mobilized with different hematopoietic growth factors

BACKGROUND

Peripheral blood stem cells (PBSC) have become the preferred source of stem cells for autologous transplantation because of the technical advantage and the shorter time to engraftment. Mobilization of CD34(+) cells into the peripheral blood can be achieved by the administration of G-CSF or GM-CSF, or both, alone or in combination with chemotherapy. G-CSF and GM-CSF differ somewhat in the number and composition of CD34(+) cells and effector cells mobilized to the peripheral blood. However, the molecular mechanism underlying the release and engraftment of CD34(+) cells is poorly understood.

PURPOSE

The purpose of this review is to give a recent update on the type and immunological properties of effector cells and CD34(+) cells mobilized by the different growth factors with emphasis on A) mobilization of T cells, natural killer cells, and dendritic cells; B) coexpression of adhesion molecules such as VLA-4 and L-selectin in mobilized PBSC collection, and C) coexpression of CXCR4-the receptor for the stromal-derived differentiation factor 1-with latest information shedding light on the molecular mechanism underlying the release and subsequent engraftment of CD34(+) cells.

CONCLUSIONS

A) The reported suppression of T cell and NK cell functions in PBSC apheresis collections in patients primed with G-CSF or GM-CSF is controversial and may merely reflect low effector cell activity before mobilization. B) A decrease in the expression of adhesion molecules such as VLA-4 and L-selectin is a necessary requirement for the release of CD34(+) cells to the peripheral blood. C) A decrease in the expression of CXCR4 is a necessary requirement for the release of CD34(+) cells to the peripheral blood and correlates with mobilization success.

HERG K+ channels activation during beta(1) integrin-mediated adhesion to fibronectin induces an up-regulation of alpha(v)beta(3) integrin in the preosteoclastic leukemia cell line FLG 29.1

Integrin receptors have been demonstrated to mediate either "inside-to-out" and "outside-to-in" signals, and by this way are capable of regulating many cellular functions, such as cell growth and differentiation, cell migration, and activation. Among the various integrin-centered signaling pathways discovered so far, we demonstrated that the modulation of the electrical potential of the plasma membrane (V(REST)) is an early integrin-mediated signal, which is related to neurite emission in neuroblastoma cells. This modulation is sustained by the activation of HERG K(+) channels, encoded by the ether-à-go-go-related gene (herg). The involvement of integrin-mediated signaling is being discovered in the hemopoietic system: in particular, osteoclasts are generated as well as induced to differentiate by interaction of osteoclast progenitors with the stromal cells, through the involvement of integrin receptors. We studied the effects of cell interaction with the extracellular matrix protein fibronectin (FN) in a human leukemic preosteoclastic cell line (FLG 29.1 cells), which has been demonstrated to express HERG currents. We report here that FLG 29.1 cells indeed adhere to purified FN through integrin receptors, and that this adhesion induces an osteoclast phenotype in these cells, as evidenced by the appearance of tartrate-resistant acid phosphatase, as well as by the increased expression of CD51/alpha(v)beta(3) integrin and calcitonin receptor. An early activation of HERG current (I(HERG)), without any increase in herg RNA or modifications of HERG protein was also observed in FN-adhering cells. This activation is apparently sustained by the beta(1) integrin subunit activation, through the involvement of a pertussis-toxin sensitive G(i) protein, and appears to be a determinant signal for the up-regulation of alpha(v)beta(3) integrin, as well as for the increased expression of calcitonin receptor.

Intercellular communication between bone marrow stromal cells and CD34+ haematopoietic progenitor cells is mediated by connexin 43-type gap junctions

The existence of functional gap junctions between haematopoietic progenitor cells (HPCs) and stromal cells of the haematopoietic microenvironment in the human system is a controversial issue. Primary CD34+ HPCs isolated from leukapheresis products were co-incubated with the human fibroblastoid bone marrow stromal cell line L87/4 in short-term liquid culture. Using the highly sensitive double whole-cell patch-clamp technique, we found that the majority (91%) of CD34+ HPCs are electrically coupled to L87/4 cells. Importantly, efficient coupling was observed within 1 h of the attachment of CD34+ HPCs to plastic adherent L87/4 cells. By comparison, homologous cell pairs formed by L87/4 cells exhibited a significantly higher electric coupling. Analysis of single-channel conductances revealed an electric profile characteristic of connexin 43 (Cx43)-type gap junctions for both homologous and heterologous cell pairs. The Cx phenotype was confirmed using Cx43-specific monoclonal antibodies in a flow cytometric assay and reverse transcription polymerase chain reaction (RT-PCR) for the detection of Cx43 mRNA. Finally, the electrophysiological studies were complemented by dye-transfer experiments using the recently described 'parachute' technique that allows the monitoring of dye diffusion without disruption of the plasma membrane. Taken together, our data indicate that functional Cx43-type gap junctions exist between stromal cells and immature HPCs and, thus, may provide an important regulatory pathway in haematopoiesis.

Membrane-bound macrophage colony-stimulating factor and its receptor play adhesion molecule-like roles in leukemic cells

Membrane-bound macrophage colony-stimulating factor (m-M-CSF) is the membrane form M-CSF by alternative splicing. J6-1 leukemic cell line spontaneously forms cell clusters, whose growth depends on the auto-juxtacrine mediated by m-M-CSF and its receptor (M-CSFR). In this study, M-CSFR isolated from J6-1 cells and recombinant human M-CSF soluble receptor (rh-M-CSFsR) were used to study their effects on J6-1 cells. Both receptors inhibited cell proliferation. Use of M-CSFR monoclonal antibodies, M-CSFR or rh-M-CSFsR to block either M-CSFR or m-M-CSF on cell surface inhibited the cluster forming process, while both receptors stimulated cells adhering to culture plate. Furthermore, M-CSFR and/or rh-M-CSFsR caused multiple cellular changes including cytoplasmic pH, multinuclear cell ratio, antigen expression and cell diameter. A [Ca(2+)] rise was induced within 90 s by both receptors. Western blot experiments showed that rh-M-CSFsR caused tyrosine phosphorylation on multiple cytoplasmic proteins of 45 kDa and 55-90 kDa, which could be blocked by H7. These observations suggested that m-M-CSF and M-CSFR mediate J6-1 cell intercellular adhesion with bi-directional signal transduction, and Ca(2+), protein tyrosine kinases, PKC and/or other H7 sensitive kinase(s) involve in the counter-directional signal transduction.