Key adhesion molecules are present on long podia extended by hematopoietic cells

Epithelial Mesenchymal Transition (EMT) and Associated Invasive Adhesions in Solid and Haematological Tumours

In solid tumours, cancer cells that undergo epithelial mesenchymal transition (EMT) express characteristic gene expression signatures that promote invasive migration as well as the development of stemness, immunosuppression and drug/radiotherapy resistance, contributing to the formation of currently untreatable metastatic tumours. The cancer traits associated with EMT can be controlled by the signalling nodes at characteristic adhesion sites (focal contacts, invadopodia and microtentacles) where the regulation of cell migration, cell cycle progression and pro-survival signalling converge. In haematological tumours, ample evidence accumulated during the last decade indicates that the development of an EMT-like phenotype is indicative of poor disease prognosis. However, this EMT phenotype has not been directly linked to the assembly of specific forms of adhesions. In the current review we discuss the role of EMT in haematological malignancies and examine its possible link with the progression towards more invasive and aggressive forms of these tumours. We also review the known types of adhesions formed by haematological malignancies and speculate on their possible connection with the EMT phenotype. We postulate that understanding the architecture and regulation of EMT-related adhesions will lead to the discovery of new therapeutic interventions to overcome disease progression and resistance to therapies.

Hematopoietic progenitors polarize in contact with bone marrow stromal cells in response to SDF1

The fate of hematopoietic stem and progenitor cells (HSPCs) is regulated by their interaction with stromal cells in the bone marrow. However, the cellular mechanisms regulating HSPC interaction with these cells and their potential impact on HSPC polarity are still poorly understood. Here we evaluated the impact of cell–cell contacts with osteoblasts or endothelial cells on the polarity of HSPC. We found that an HSPC can form a discrete contact site that leads to the extensive polarization of its cytoskeleton architecture. Notably, the centrosome was located in proximity to the contact site. The capacity of HSPCs to polarize in contact with stromal cells of the bone marrow appeared to be specific, as it was not observed in primary lymphoid or myeloid cells or in HSPCs in contact with skin fibroblasts. The receptors ICAM, VCAM, and SDF1 were identified in the polarizing contact. Only SDF1 was independently capable of inducing the polarization of the centrosome–microtubule network.

Morphologic and gene expression analysis of periodontal ligament fibroblasts subjected to pressure

INTRODUCTION

Force application (FA) during orthodontic tooth movement is mediated through periodontal ligament (PDL) fibroblasts. FA on deciduous teeth has an inherent risk of root resorption, which is less in permanent teeth. Currently, the root resorption mechanism is poorly understood. We hypothesized that FA alters the morphology and gene expression of PDL fibroblasts. This study was designed to achieve homogenous PDL fibroblast cultures, establish an in-vitro FA model, analyze fibroblast morphology after FA, and compare the gene expressions of PDL fibroblasts of deciduous and permanent teeth after FA.

METHODS

Fibroblasts were sorted from primary cultures of deciduous and permanent tooth PDLs. Cell viability was evaluated in the Opticell (Thermo Scientific, Waltham, Mass) FA model. Cellular morphology was analyzed using immunofluorescence staining for actin and focal adhesion complexes. Gene expressions of untreated or pressure-treated PDL fibroblasts of deciduous and permanent teeth were compared by gene array and confirmed by real-time polymerase chain reaction.

RESULTS

Cell sorting resulted in cultures containing 98% of PDL fibroblasts. The Opticell model showed 94% cell survival after FA. FA increased fibroblasts' adhesion. Gene arrays and real-time polymerase chain reactions indicated greater up-regulation of DKK2 mRNA in untreated PDL fibroblasts of deciduous teeth and greater up-regulation of ADAMTS1 mRNA in pressurized PDL fibroblasts of deciduous and permanent teeth.

CONCLUSIONS

Cell sorting is an efficient method to establish homogenous PDL fibroblast cultures. Using the Opticell FA model allows the maintenance of excellent cell viability. FA increased the surface adherence of fibroblasts. Up-regulation of ADAMTS1 after FA may indicate its involvement in the remodeling of the periodontium during orthodontic tooth movement. Understanding root resorption mechanisms under FA will help to prevent it during orthodontic treatment.

Catch bond interaction allows cells to attach to strongly hydrated interfaces

Hyaluronans are a class of glycosaminoglycans that are widespread in the mammalian body and serve a variety of functions. Their most striking characteristic is their pronounced hydrophilicity and their capability to inhibit unspecific adhesion when present at interfaces. Catch-bond interactions are used by the CD44 receptor to interact with this inert material and to roll on the surfaces coated with hyaluronans. In this minireview, the authors discuss the general properties of hyaluronans and the occurrence and relevance of the CD44 catch-bond interaction in the context of hematopoiesis, cancer development, and leukemia.

Adhesion of human haematopoietic (CD34+) stem cells to human liver compartments is integrin and CD44 dependent and modulated by CXCR3 and CXCR4

BACKGROUND/AIMS

Haematopoietic stem cells (HSC) have previously been shown in some studies to migrate to damaged and diseased liver where a small proportion will engraft. Such cells can promote liver repair in rodent models of liver injury and lead to improved liver function in uncontrolled clinical studies. In order to maximize the engraftment of cells for clinical applications it is necessary to understand the molecular mechanisms that regulate stem cell recruitment and retention. Our aim therefore was to determine which factors where involved in adhesion of circulating HSC to liver endothelium and sequestration around epithelial cells within the liver.

METHODS

We examined the ability of CD34+ populations from peripheral and mobilized blood and the CD34-expressing cell line KG1a to bind to human hepatic sinusoidal endothelial (HSEC) and biliary epithelial cells (BEC) in vitro.

RESULTS

We report that all CD34(+) populations express alpha4beta1, beta2 integrins and CD44. Liver tissue sections and primary liver cells expressed the corresponding ligands VCAM-1/fibronectin, ICAM-1 and CD44. Pertussis toxin was shown to decrease binding of CD34(+) cells and the cells migrated to CXCR3 and CXCR4 ligands.

CONCLUSIONS

CD34(+) populations use alpha4beta1, beta2 integrins and CD44 receptors to bind to the ligands VCAM-1/fibronectin, ICAM-1, and hyaluronic acid expressed on sinusoidal vessels in tissue sections and to primary human HSEC. Binding to BEC was mediated by the interaction of beta1 and beta2 integrins with VCAM-1 and ICAM-1 respectively. A role for chemokines is supported by our finding that pertussis toxin inhibits CD34(+) cell adhesion to BEC and HSEC and by the ability of CD34(+) cells to migrate to CXCR3 and CXCR4 ligands.

Application of nanosilver surface modification to RO membrane and spacer for mitigating biofouling in seawater desalination

Biofouling is one the most critical problems in seawater desalination plants and science has not yet found effective ways to control it. Silver compounds and ions are historically recognized for their effective antimicrobial activity. Nanosilver particles have been applied as a biocide in many aspects of disinfection, including healthcare products and water treatment. This study proposes an innovative biofouling control approach by surface modification of the RO membrane and spacer with nanosilver coating. A chemical reduction method was used for directly coating nanosilver particles on the membrane sheet and spacer. The surface-modified membrane and spacer were tested for their antifouling performance in a cross-flow flat-sheet membrane cell, which is a part of a pilot plant in Wukan desalination plant. The silver-coating membranes and spacers, along with an unmodified membrane sheet, were tested in the membrane cell and compared on the basis of their antifouling performance. Permeate flux decline and salt rejection was continuously monitored through the testing period. Meanwhile regrowth of microbial populations on the membrane cell was quantified by a unique microbial counting every three to four days. The results showed that both silver-coated membrane (Ag-cM) with uncoated spacer and silver-coated spacer (Ag-cS) with uncoated membrane performed better than the unmodified membrane and spacer (Un-MS), in terms of much slower decrease in permeate flux and TDS rejection. However, the effect of silver-coated spacer on antimicrobial activity was more lasting. In the silver-coated spacer test, there was almost no multiplication of cells detected on the membrane during the whole testing period. Besides, the cells adhering to the membrane seemed to lose their activity quickly. According to the RO performance and microbial growth morphology, the nanosilver coating technology is valuable for use in biofouling control in seawater desalination.

The Stromal Activity of Mesenchymal Stromal Cells

SUMMARY: The mechanism that regulates self-renewal and differentiation of hematopoietic stem cells (HSC) is a central question in stem cell biology that might ultimately lead to reliable protocols for in vitro expansion of HSC. Cellular fate is governed by cell-cell interaction with the microenvironment in the bone marrow, the stem cell niche. Mesenchymal stromal cells (MSC) are precursors of the cellular components, and they secrete extracellular matrix proteins of the bone marrow stroma. Therefore, MSC feeder layer might provide a suitable in vitro model system for the stem cell niche. In vitro assays demonstrate that MSC maintain the stem cell function of HSC and that MSC from bone marrow have a higher hematopoiesis supportive activity than MSC from adipose tissue. Co-cultivation with MSC might pave the way for expansion of long-term repopulating HSC, and various clinical trials indicate that co-transplantation of HSC and MSC might enhance engraftment. Thus, MSC are promising tools to elucidate the underlying mechanism of the cellular microenvironment. The large variety of preparative protocols for isolation and cultivation of MSC affects their stromal activity. Standardized isolation methods and molecular characterization of MSC are of utmost importance for reproducible isolation of hematopoiesis supportive stromal cells and for their potential clinical application.

Adhesion of human hematopoietic progenitor cells to mesenchymal stromal cells involves CD44

BACKGROUND

Direct cell-cell contact between hematopoietic progenitor cells (HPC) and their cellular microenvironment is essential for maintenance of 'stemness'. We have previously demonstrated that a feeder layer of human mesenchymal stromal cells (MSC) could provide a surrogate model as a niche for human HPC. Maintenance of long-term culture-initiating cells was significantly lower on fibroblasts.

METHODS

Adhesion of HPC to MSC was further analyzed using our recently described adhesion assay based on gravitational force upon inversion and in combination with specific antibodies against CD44.

RESULTS

Adhesion of KG1a and CD34+ cells was significantly reduced by administration of a monoclonal CD44 antibody and for KG1a to a greater extent than for CD34+ cells. Interaction of HPC and MSC was further analyzed by laser scanning confocal microscopy. CD44 was located on the uropod of CD34+ cells at the site of contact with MSC and both cell types were interwoven by a network of fibronectin.

CONCLUSION

Various adhesion proteins, including CD44, are involved in the contact of human HPC and human MSC and further analysis of the relative significance and interaction of these proteins will be crucial for the understanding of the mechanism of this specific cell-cell interaction.

The many facets of SDF-1alpha, CXCR4 agonists and antagonists on hematopoietic progenitor cells

Stromal cell-derived factor-1alpha (SDF-1α) has pleiotropic effects on hematopoietic progenitor cells (HPCs). We have monitored podia formation, migration, proliferation, and cell-cell adhesion of human HPC under the influence of SDF-1α, a peptide agonist of CXCR4 (CTCE-0214), a peptide antagonist (CTCE-9908), and a nonpeptide antagonist (AMD3100). Whereas SDF-1α induced migration of CD34⁺ cells in a dose-dependent manner, CTCE-0214, CTCE-9908, and AMD3100 did not induce chemotaxis in this concentration range albeit the peptides CTCE-0214 and CTCE-9908 increased podia formation. Cell-cell adhesion of HPC to human mesenchymal stromal cells was impaired by the addition of SDF-1α, CTCE-0214, and AMD3100. Proliferation was not affected by SDF-1α or its analogs. Surface antigen detection of CXCR4 was reduced upon treatment with SDF-1α or AMD3100 and it was enhanced by CTCE-9908. Despite the fact that all these molecules target the same CXCR4 receptor, CXCR4 agonists and antagonists have selective effects on different functions of the natural molecule.

Adhesion of hematopoietic progenitor cells to human mesenchymal stem cells as a model for cell−cell interaction

OBJECTIVE

The significant role of direct contact between hematopoietic progenitor cells (HPC) and the cellular microenvironment for maintaining "stemness" has been demonstrated. Human mesenchymal stem cell (MSC) feeder layers represent a surrogate model for this interaction. Specific adhesion molecules are responsible for this cell-cell contact.

METHODS

To define cell-cell contact between HPC and MSC, we have studied adhesive interaction of various fractions of HPC by using a novel assay based on gravitational force upon inversion. Adherent and nonadherent cells were separated and further analyzed with regard to gene expression and long-term hematopoietic culture initiating cell (LTC-IC) frequency.

RESULTS

HPC subsets with higher self-renewing capacity demonstrated significantly higher adherence to human MSC (CD34(+) vs CD34(-), CD34(+)/CD38(-) vs CD34(+)/CD38(+), slow dividing fraction vs fast dividing fraction). LTC-IC frequency was significantly higher in the adherent fraction than in the nonadherent fraction. Furthermore, genes coding for adhesion proteins and extracellular matrix were higher expressed in the adherent subsets of CD34(+) cells (fibronectin 1, cadherin 11, vascular cell adhesion molecule-1, connexin 43, integrin beta-like 1, and TGFBI).

CONCLUSION

In this study we have demonstrated that primitive subsets of HPC have higher affinity to human MSC. The essential role of specific junction proteins for stabilization of cell-cell contact is indicated by their significant higher expression.

Bone marrow niche and leukemia

Mounting evidence indicates that human cancers may originate from malignant transformation of stem cells. The most convincing proof is found in acute myeloid leukemia, where only a small subset of slowly dividing cells was able to induce transplantable acute myeloid leukemia. Normal hematopoietic stem cells (HSC) are characterized by their unlimited ability to self-renew, give rise to a multitude of cells that exhibit more differentiated features, and show slow division kinetics. Using human HSC and mesenchymal stromal cells (MSC) as models, we and others have demonstrated the vital role of the cellular niche in maintaining the self-renewing capacity, that is, "stemness" of HSC. Without direct contact with the cellular niche, HSC tend to differentiate and lose their stemness. Similar to their normal counterparts, leukemia stem cells divide slowly and maintain their self-renewal capacity through interaction with the niche. As a consequence, they are resistant to conventional chemotherapy strategies that target rapidly dividing cells. Thus it is of utmost importance to understand the interaction between cellular niche and normal HSC as well as between leukemia stem cells and the niche to provide a basis for more efficient treatment strategies.

Hematopoietic Progenitor Cells and Cellular Microenvironment: Behavioral and Molecular Changes upon Interaction

Cell-cell contact between stem cells and cellular determinants of the microenvironment plays an essential role in controlling cell division. Using human hematopoietic progenitor cells (CD34+/CD38-) and a stroma cell line (AFT024) as a model, we have studied the initial behavioral and molecular sequel of this interaction. Time-lapse microscopy showed that CD34+/CD38- cells actively migrated toward and sought contact with stroma cells and 30% of them adhered firmly to AFT024 stroma through the uropod. CD44 and CD34 are colocalized at the site of contact. Gene expression profiles of CD34+/CD38- cells upon cultivation with or without stroma for 16, 20, 48, or 72 hours were analyzed using our human genome cDNA microarray. Chk1, egr1, and cxcl2 were among the first genes upregulated within 16 hours. Genes with the highest upregulation throughout the time course included tubulin genes, ezrin, c1qr1, fos, pcna, mcm6, ung, and dnmt1, genes that play an essential role in reorganization of the cytoskeleton system, stabilization of DNA, and methylation patterns. Our results demonstrate directed migration of CD34+/CD38- cells toward AFT024 and adhesion through the uropod and that upon interaction with supportive stroma, reorganization of the cytoskeleton system, regulation of cell division, and maintenance of genetic stability represent the most essential steps.

Kinetics and symmetry of divisions of hematopoietic stem cells

To fulfill the dual abilities to self-renew and to differentiate into cells of multiple lineages, stem cells must undergo, at some stage, asymmetric divisions to generate cells to sustain the stem cell pool as well as the various progeny cells of the distinct lineages. A central question in developmental biology is how a single cell can divide to produce two progeny cells that adopt different fates. Different daughter cells can theoretically arise by uneven distribution of determinants upon cell division, i.e., due to intrinsic factors, or become different upon subsequent exposure to environmental signals, i.e., due to extrinsic factors. Recent advances in the understanding of stem cell biology in Drosophila and murine models have served as a model for hematopoietic stem cell (HSC) development. Provided with advances in molecular and cellular biology, we have gained insight into the mechanisms governing self-renewing asymmetric divisions of primitive HSC. Direct contact with cellular determinants in the niche has been shown to play an essential role in the balance between self-renewing asymmetric division versus differentiation. Identification of the molecular interactions between stem cells and their niche will lead to an understanding of the mechanisms controlling the long-term destiny of stem cells. Ultimately, molecular signals triggered by adhesion and junction complexes are probably responsible for the specific adoption of differentiation pathways.

Reversible switching of expression of c-kit and Pax-5 in immature hematopoietic progenitor cells by stromal cells

OBJECTIVE

Bone marrow stromal cells provide the microenvironment for self-renewal and differentiation of hematopoietic stem/progenitor cells through complex cell-cell interaction. To elucidate the regulatory mechanisms of hematopoiesis by stromal cells, we established a novel stroma-dependent hematopoietic cell line and explored the phenotypic changes regulated by the two stromal cells.

MATERIALS AND METHODS

DFC-28 cells clonally established from long-term bone marrow culture of C57BL/6 mice were sustained by coculture on MSS62 cells (mouse spleen stromal cell line). When DFC-28 cells were transferred to TBR31-1 cells (mouse bone marrow stromal cell line), their phenotypic changes were analyzed by flow cytometry and reverse transcriptase polymerase chain reaction.

RESULTS

DFC-28 cells on MSS62 cells exhibited surface phenotypes of the immature hematopoietic progenitor cells (Lin(-)AA4.1(+)c-kit(+)Sca-1(-)). By stroma-replacement from MSS62 cells to TBR31-1 cells, DFC-28 cells were differentiated into very early B-lymphoid stage characterized by c-kit down-regulation and induction of BP-1 and B-lymphoid-associated genes (Pax-5, CD19, TdT, Rag-1, and Rag-2). In addition, the differentiation phenotypes reverted to the immature state characterized by c-kit induction and down-regulation of BP-1 and B-lymphoid-associated genes by replacing stroma back to MSS62 from TBR31-1. Interleukin-7 stimulation and conditioned medium of TBR31-1 cells were ineffective in converting the differentiation phenotypes of DFC-28 cells.

CONCLUSIONS

The results demonstrate that the differentiation phenotypes and growth potential of stroma-dependent hematopoietic progenitor cells we established could be reversibly controlled via direct contact with stromal cells in the microenvironment.

Murine Sca-1(+)/Lin(-) cells and human KG1a cells exhibit multiple pseudopod morphologies during migration

OBJECTIVE

The migration of primitive hematopoietic cells has been studied mostly via population-based assays while the actual mechanisms of cell motion have been defined by tracking individual mature cells. In this report, we examined individual immature hematopoietic cells to determine if any notable differences in migration mechanisms exist due to the primitive nature of the cells.

MATERIALS AND METHODS

Murine cells of the Sca-1(+)/Lin(-) phenotype were isolated from C57BL/6 mice using Miltenyi bead purification and flow cytometric sorting. These cells were then observed for long periods of time with an environmentally controlled time-lapse microscope system in either multiwell plates or micropore transwell chambers. Experiments were also performed with the human KG1a immature hematopoietic cell line.

RESULTS

Murine Sca-1(+)/Lin(-) immature hematopoietic cells and human KG1a cells were observed to exhibit a variety of mechanisms/morphologies during migration, which include the classic "hand mirror" shape; broad, flat lamellipodia; trailing uropodia; dynamic filopodia; and retraction fibers. Time-lapse observations of transmembrane assays revealed long, thin magnupodia passing through the pores, while other measurements show magnupods can generate forces capable of accelerating a cell to a velocity of 5 microns/minute.

CONCLUSION

Many of these mechanisms have been reported separately for differentiated cells; however, we show that immature hematopoietic cells are capable of exhibiting all of these mechanisms of migration. These data provide insight into the loss of phenotypic functions as stem cells differentiate.

Multiple personalities: synaptic target cells as introverts and extroverts

The intricate process of wiring a neuronetwork requires a high degree of accuracy in the communication between pre- and post-synaptic cells. While presynaptic cells have been widely recognized for their dynamic role in synaptic matchmaking, post-synaptic cells have historically been overlooked as passive targets. Recent studies in the Drosophila embryonic neuromuscular system provide compelling evidence that post-synaptic cells participate actively in the synaptogenic process. Endocytosis allows them to quickly modify the array of molecular cues they provide on their surfaces and the extension of dynamic filopodia allows post-synaptic cells to engage in direct long-distance communication. By making use of familiar cellular mechanisms such as endocytosis and filopodia formation, post-synaptic cells may be able to communicate more effectively with potential synaptic partners.

Intercellular adhesion can be visualized using fluorescently labeled fibrosarcoma HT1080 cells cocultured with hematopoietic cell lines or CD34(+) enriched human mobilized peripheral blood cells

BACKGROUND

Intercellular contacts between adjacent cells migrating over each other are important in many cellular processes. However, it has been difficult to visualize and identify dynamic intercellular adhesions between migrating cells in situ.

METHODS

Two fluorescent membrane dyes, PKH2 and PKH26 for staining HT1080 and hematopoietic cells and cell lines, and an automated fluorescence microscopy system were used to monitor intercellular adhesion.

RESULTS

Cellular extensions connecting two or more adjacent cells were visualized, showing the intercellular adhesion between migrating cells for minutes and up to hours. After cells adhered to each other, followed by cell migration in different directions, cellular extensions were dragged from the pivotal contact points in different focal planes. CD34(+)-enriched mobilized peripheral blood cells and six hematopoietic cell lines showed intercellular connections in cocultures with HT1080. However, the frequency of intercellular connections was variable in different cocultures. A cell density of about 3.1 x 10(4) cells/cm(2) for both cell lines in cocultures provided an adequate number of cells in each field of view, showing up to four intercellular connections per 100 total cells plated.

DISCUSSION

The tools derived from this study will open new areas of investigation for understanding the mechanism of the intercellular adhesion process.

Extension of osmolality-induced podia is observed from fluorescently labeled hematopoietic cell lines in hyperosmotic medium

BACKGROUND

Since the description of long podia extended by hematopoietic cells and cell lines, the reliable elicitation of podia extensions is needed to study these podia systemically. In this study, hyperosmotic stress was considered as an elicitor.

METHODS

Using two fluorescent membrane dyes PKH2 and PKH26, and an automated fluorescence microscopy system, morphological changes of seven human cell lines (six hematopoietic, one fibrosarcoma) at different osmolalities were monitored. Presence of surface molecules on the hyperosmolality-induced podia (osmopodia) was examined.

RESULTS

In hyperosmotic medium, cells shrank rapidly, followed by osmopodia extension. Cells exhibited variable number (up to five) and length (up to longer than 100 microm) of osmopodia in about 1 h. Dead cells did not extend podia. Frequency, length, and number of podia were variable among cell lines studied. CD44 and CD45 were not present on the osmopodia, although they were present on the cell surface, showing that osmopodia characteristics differ from the podia observed previously in isotonic media. The osmopodia extension process was shown to be reversible upon repeated osmolality changes.

CONCLUSIONS

Osmopodia extended by human hematopoietic cell lines display a newly observed cellular morphology and provide a tool for investigation of dynamic cellular response to environmental changes.