The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including embryonic development, wound healing, and immune responses. However, cell migration is also a key mechanism in cancer enabling these cancer cells to detach from the primary tumor to start metastatic spreading. Within the past years various cell migration assays have been developed to analyze the migratory behavior of different cell types. Because the locomotory behavior of cells markedly differs between a two-dimensional (2D) and three-dimensional (3D) environment it can be assumed that the analysis of the migration of cells that are embedded within a 3D environment would yield in more significant cell migration data. The advantage of the described 3D collagen matrix migration assay is that cells are embedded within a physiological 3D network of collagen fibers representing the major component of the extracellular matrix. Due to time-lapse video microscopy real cell migration is measured allowing the determination of several migration parameters as well as their alterations in response to pro-migratory factors or inhibitors. Various cell types could be analyzed using this technique, including lymphocytes/leukocytes, stem cells, and tumor cells. Likewise, also cell clusters or spheroids could be embedded within the collagen matrix concomitant with analysis of the emigration of single cells from the cell cluster/ spheroid into the collagen lattice. We conclude that the 3D collagen matrix migration assay is a versatile method to analyze the migration of cells within a physiological-like 3D environment.
20 Related JoVE Articles!
Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells
Institutions: University of California, Davis.
The physiological electric field serves specific biological functions, such as directing cell migration in embryo development, neuronal outgrowth and epithelial wound healing. Applying a direct current electric field to cultured cells in vitro
induces directional cell migration, or galvanotaxis. The 2-dimensional galvanotaxis method we demonstrate here is modified with custom-made poly(vinyl chloride) (PVC) chambers, glass surface, platinum electrodes and the use of a motorized stage on which the cells are imaged. The PVC chambers and platinum electrodes exhibit low cytotoxicity and are affordable and re-useable. The glass surface and the motorized microscope stage improve quality of images and allow possible modifications to the glass surface and treatments to the cells. We filmed the galvanotaxis of two non-tumorigenic, SV40-immortalized prostate cell lines, pRNS-1-1 and PNT2. These two cell lines show similar migration speeds and both migrate toward the cathode, but they do show a different degree of directionality in galvanotaxis. The results obtained via this protocol suggest that the pRNS-1-1 and the PNT2 cell lines may have different intrinsic features that govern their directional migratory responses.
Cellular Biology, Issue 94, Cell biology, Prostate cells, cell migration, electric field, galvanotaxis, time-lapse imaging
A Three-dimensional Tissue Culture Model to Study Primary Human Bone Marrow and its Malignancies
Institutions: Purdue University, University of Alberta, Cross Cancer Institute.
Tissue culture has been an invaluable tool to study many aspects of cell function, from normal development to disease. Conventional cell culture methods rely on the ability of cells either to attach to a solid substratum of a tissue culture dish or to grow in suspension in liquid medium. Multiple immortal cell lines have been created and grown using such approaches, however, these methods frequently fail when primary cells need to be grown ex vivo
. Such failure has been attributed to the absence of the appropriate extracellular matrix components of the tissue microenvironment from the standard systems where tissue culture plastic is used as a surface for cell growth. Extracellular matrix is an integral component of the tissue microenvironment and its presence is crucial for the maintenance of physiological functions such as cell polarization, survival, and proliferation. Here we present a 3-dimensional tissue culture method where primary bone marrow cells are grown in extracellular matrix formulated to recapitulate the microenvironment of the human bone (rBM system). Embedded in the extracellular matrix, cells are supplied with nutrients through the medium supplemented with human plasma, thus providing a comprehensive system where cell survival and proliferation can be sustained for up to 30 days while maintaining the cellular composition of the primary tissue. Using the rBM system we have successfully grown primary bone marrow cells from normal donors and patients with amyloidosis, and various hematological malignancies. The rBM system allows for direct, in-matrix real time visualization of the cell behavior and evaluation of preclinical efficacy of novel therapeutics. Moreover, cells can be isolated from the rBM and subsequently used for in vivo
transplantation, cell sorting, flow cytometry, and nucleic acid and protein analysis. Taken together, the rBM method provides a reliable system for the growth of primary bone marrow cells under physiological conditions.
Medicine, Issue 85, extracellular matrix, 3D culture, bone marrow, hematological malignancies, primary cell culture, tumor microenvironment
Tissue Engineering of Tumor Stromal Microenvironment with Application to Cancer Cell Invasion
Institutions: University of Dundee, A*Star, Singapore.
3D organotypic cultures of epithelial cells on a matrix embedded with mesenchymal cells are widely used to study epithelial cell differentiation and invasion. Rat tail type I collagen and/or matrix derived from Engelbreth-Holm-Swarm mouse sarcoma cells have been traditionally employed as the substrates to model the matrix or stromal microenvironment into which mesenchymal cells (usually fibroblasts) are populated. Although experiments using such matrices are very informative, it can be argued that due to an overriding presence of a single protein (such as in type I Collagen) or a high content of basement membrane components and growth factors (such as in matrix derived from mouse sarcoma cells), these substrates do not best reflect the contribution to matrix composition made by the stromal cells themselves. To study native matrices produced by primary dermal fibroblasts isolated from patients with a tumor prone, genetic blistering disorder (recessive dystrophic epidermolysis bullosa), we have adapted an existing native matrix protocol to study tumor cell invasion. Fibroblasts are induced to produce their own matrix over a prolonged period in culture. This native matrix is then detached from the culture dish and epithelial cells are seeded onto it before the entire coculture is raised to the air-liquid interface. Cellular differentiation and/or invasion can then be assessed over time. This technique provides the ability to assess epithelial-mesenchymal cell interactions in a 3D setting without the need for a synthetic or foreign matrix with the only disadvantage being the prolonged period of time required to produce the native matrix. Here we describe the application of this technique to assess the ability of a single molecule expressed by fibroblasts, type VII collagen, to inhibit tumor cell invasion.
Biomedical Engineering, Issue 85, tumor microenvironment, stromal fibroblasts, extracellular matrix, tissue engineering, dermal equivalent, collagen, native matrix
Cell Population Analyses During Skin Carcinogenesis
Institutions: Indiana University.
Cancer development is a multiple-step process involving many cell types including cancer precursor cells, immune cells, fibroblasts and endothelial cells. Each type of cells undergoes signaling and functional changes during carcinogenesis. The current challenge for many cancer researchers is to dissect these changes in each cell type during the multiple-step process in vivo
. In the last few years, the authors have developed a set of procedures to isolate different cell populations during skin cancer development using K14creER/R26-SmoM2YFP
mice. The procedure is divided into 6 parts: 1) generating appropriate mice for the study (K14creER+
mice in this protocol); 2) inducing SmoM2YFP
expression in mouse skin; 3) preparing mouse skin biopsies; 4) isolating epidermis from skin; 5) preparing single cells from epidermis; 6) labeling single cell populations for flow cytometry analysis. Generation of sufficient number of mice with the right genotype is the limiting step in this protocol, which may take up to two months. The rest of steps take a few hours to a few days. Within this protocol, we also include a section for troubleshooting. Although we focus on skin cancer, this protocol may be modified to apply for other animal models of human diseases.
Cancer Biology, Issue 78, Medicine, Cellular Biology, Molecular Biology, Biomedical Engineering, Genetics, Anatomy, Physiology, Oncology, Cocarcinogenesis, animal models, Skin cancer, basal cell carcinoma, hedgehog, smoothened, keratinocyte, cancer, carcinogenesis, cells, cell culture, animal model
Imaging G-protein Coupled Receptor (GPCR)-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum
Institutions: National Institute of Allergy and Infectious Diseases, National Institutes of Health.
Many eukaryotic cells can detect gradients of chemical signals in their environments and migrate accordingly 1
. This guided cell migration is referred as chemotaxis, which is essential for various cells to carry out their functions such as trafficking of immune cells and patterning of neuronal cells 2, 3
. A large family of G-protein coupled receptors (GPCRs) detects variable small peptides, known as chemokines, to direct cell migration in vivo 4
. The final goal of chemotaxis research is to understand how a GPCR machinery senses chemokine gradients and controls signaling events leading to chemotaxis. To this end, we use imaging techniques to monitor, in real time, spatiotemporal concentrations of chemoattractants, cell movement in a gradient of chemoattractant, GPCR mediated activation of heterotrimeric G-protein, and intracellular signaling events involved in chemotaxis of eukaryotic cells 5-8
. The simple eukaryotic organism, Dictyostelium discoideum
, displays chemotaxic behaviors that are similar to those of leukocytes, and D. discoideum
is a key model system for studying eukaryotic chemotaxis. As free-living amoebae, D. discoideum
cells divide in rich medium. Upon starvation, cells enter a developmental program in which they aggregate through cAMP-mediated chemotaxis to form multicullular structures. Many components involved in chemotaxis to cAMP have been identified in D. discoideum
. The binding of cAMP to a GPCR (cAR1) induces dissociation of heterotrimeric G-proteins into Gγ and Gβγ subunits 7, 9, 10
. Gβγ subunits activate Ras, which in turn activates PI3K, converting PIP2
on the cell membrane 11-13
serve as binding sites for proteins with pleckstrin Homology (PH) domains, thus recruiting these proteins to the membrane 14, 15
. Activation of cAR1 receptors also controls the membrane associations of PTEN, which dephosphorylates PIP3
to PIP2 16, 17
. The molecular mechanisms are evolutionarily conserved in chemokine GPCR-mediated chemotaxis of human cells such as neutrophils 18
. We present following methods for studying chemotaxis of D. discoideum cells
. 1. Preparation of chemotactic component cells. 2. Imaging chemotaxis of cells in a cAMP gradient. 3. Monitoring a GPCR induced activation of heterotrimeric G-protein in single live cells. 4. Imaging chemoattractant-triggered dynamic PIP3
responses in single live cells in real time. Our developed imaging methods can be applied to study chemotaxis of human leukocytes.
Molecular Biology, Issue 55, Chemotaxis, directional sensing, GPCR, PCR, G-proteins, signal transduction, Dictyostelium discoideum
The Cell-based L-Glutathione Protection Assays to Study Endocytosis and Recycling of Plasma Membrane Proteins
Institutions: Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine.
Membrane trafficking involves transport of proteins from the plasma membrane to the cell interior (i.e.
endocytosis) followed by trafficking to lysosomes for degradation or to the plasma membrane for recycling. The cell based L-glutathione protection assays can be used to study endocytosis and recycling of protein receptors, channels, transporters, and adhesion molecules localized at the cell surface. The endocytic assay requires labeling of cell surface proteins with a cell membrane impermeable biotin containing a disulfide bond and the N-hydroxysuccinimide (NHS) ester at 4 ºC - a temperature at which membrane trafficking does not occur. Endocytosis of biotinylated plasma membrane proteins is induced by incubation at 37 ºC. Next, the temperature is decreased again to 4 ºC to stop endocytic trafficking and the disulfide bond in biotin covalently attached to proteins that have remained at the plasma membrane is reduced with L-glutathione. At this point, only proteins that were endocytosed remain protected from L-glutathione and thus remain biotinylated. After cell lysis, biotinylated proteins are isolated with streptavidin agarose, eluted from agarose, and the biotinylated protein of interest is detected by western blotting. During the recycling assay, after biotinylation cells are incubated at 37 °C to load endocytic vesicles with biotinylated proteins and the disulfide bond in biotin covalently attached to proteins remaining at the plasma membrane is reduced with L-glutathione at 4 ºC as in the endocytic assay. Next, cells are incubated again at 37 °C to allow biotinylated proteins from endocytic vesicles to recycle to the plasma membrane. Cells are then incubated at 4 ºC, and the disulfide bond in biotin attached to proteins that recycled to the plasma membranes is reduced with L-glutathione. The biotinylated proteins protected from L-glutathione are those that did not recycle to the plasma membrane.
Basic Protocol, Issue 82, Endocytosis, recycling, plasma membrane, cell surface, EZLink, Sulfo-NHS-SS-Biotin, L-Glutathione, GSH, thiol group, disulfide bond, epithelial cells, cell polarization
In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration
Institutions: Harvard Medical School, MGH for Children, Massachusetts General Hospital.
Mucosal surfaces serve as protective barriers against pathogenic organisms. Innate immune responses are activated upon sensing pathogen leading to the infiltration of tissues with migrating inflammatory cells, primarily neutrophils. This process has the potential to be destructive to tissues if excessive or held in an unresolved state. Cocultured in vitro
models can be utilized to study the unique molecular mechanisms involved in pathogen induced neutrophil trans-epithelial migration. This type of model provides versatility in experimental design with opportunity for controlled manipulation of the pathogen, epithelial barrier, or neutrophil. Pathogenic infection of the apical surface of polarized epithelial monolayers grown on permeable transwell filters instigates physiologically relevant basolateral to apical trans-epithelial migration of neutrophils applied to the basolateral surface. The in vitro
model described herein demonstrates the multiple steps necessary for demonstrating neutrophil migration across a polarized lung epithelial monolayer that has been infected with pathogenic P. aeruginosa
(PAO1). Seeding and culturing of permeable transwells with human derived lung epithelial cells is described, along with isolation of neutrophils from whole human blood and culturing of PAO1 and nonpathogenic K12 E. coli
(MC1000). The emigrational process and quantitative analysis of successfully migrated neutrophils that have been mobilized in response to pathogenic infection is shown with representative data, including positive and negative controls. This in vitro
model system can be manipulated and applied to other mucosal surfaces. Inflammatory responses that involve excessive neutrophil infiltration can be destructive to host tissues and can occur in the absence of pathogenic infections. A better understanding of the molecular mechanisms that promote neutrophil trans-epithelial migration through experimental manipulation of the in vitro
coculture assay system described herein has significant potential to identify novel therapeutic targets for a range of mucosal infectious as well as inflammatory diseases.
Infection, Issue 83, Cellular Biology, Epithelium, Neutrophils, Pseudomonas aeruginosa, Respiratory Tract Diseases, Neutrophils, epithelial barriers, pathogens, transmigration
Revealing the Cytoskeletal Organization of Invasive Cancer Cells in 3D
Institutions: Institut Curie.
Cell migration has traditionally been studied in 2D substrates. However, it has become increasingly evident that there is a need to study cell migration in more appropriate 3D environments, which better resemble the dimensionality of the physiological processes in question. Migratory cells can substantially differ in their morphology and mode of migration depending on whether they are moving on 2D or 3D substrates. Due to technical difficulties and incompatibilities with most standard protocols, structural and functional analysis of cells embedded within 3D matrices still remains uncommon. This article describes methods for preparation and imaging of 3D cancer cell cultures, either as single cells or spheroids. As an appropriate ECM substrate for cancer cell migration, we use nonpepsinized rat tail collagen I polymerized at room-temperature and fluorescently labeled to facilitate visualization using standard confocal microscopes. This work also includes a protocol for 3D immunofluorescent labeling of endogenous cell cytoskeleton. Using these protocols we hope to contribute to a better description of the molecular composition, localization, and functions of cellular structures in 3D.
Medicine, Issue 80, TAMRA, collagen, 3D matrix, spheroids, F-actin, microtubules
Efficient Production and Purification of Recombinant Murine Kindlin-3 from Insect Cells for Biophysical Studies
Institutions: University of Oxford.
Kindlins are essential coactivators, with talin, of the cell surface receptors integrins and also participate in integrin outside-in signalling, and the control of gene transcription in the cell nucleus. The kindlins are ~75 kDa multidomain proteins and bind to an NPxY motif and upstream T/S cluster of the integrin β-subunit cytoplasmic tail. The hematopoietically-important kindlin isoform, kindlin-3, is critical for platelet aggregation during thrombus formation, leukocyte rolling in response to infection and inflammation and osteoclast podocyte formation in bone resorption. Kindlin-3's role in these processes has resulted in extensive cellular and physiological studies. However, there is a need for an efficient method of acquiring high quality milligram quantities of the protein for further studies. We have developed a protocol, here described, for the efficient expression and purification of recombinant murine kindlin-3 by use of a baculovirus-driven expression system in Sf9 cells yielding sufficient amounts of high purity full-length protein to allow its biophysical characterization. The same approach could be taken in the study of the other mammalian kindlin isoforms.
Virology, Issue 85, Heterologous protein expression, insect cells, Spodoptera frugiperda, baculovirus, protein purification, kindlin, cell adhesion
A Quantitative Evaluation of Cell Migration by the Phagokinetic Track Motility Assay
Institutions: Louisiana State University Health Sciences Center, Louisiana State University Health Sciences Center, SUNY Upstate Medical University, Louisiana State University Health Sciences Center.
Cellular motility is an important biological process for both unicellular and multicellular organisms. It is essential for movement of unicellular organisms towards a source of nutrients or away from unsuitable conditions, as well as in multicellular organisms for tissue development, immune surveillance and wound healing, just to mention a few roles1,2,3
. Deregulation of this process can lead to serious neurological, cardiovascular and immunological diseases, as well as exacerbated tumor formation and spread4,5
. Molecularly, actin polymerization and receptor recycling have been shown to play important roles in creating cellular extensions (lamellipodia), that drive the forward movement of the cell6,7,8
. However, many biological questions about cell migration remain unanswered.
The central role for cellular motility in human health and disease underlines the importance of understanding the specific mechanisms involved in this process and makes accurate methods for evaluating cell motility particularly important. Microscopes are usually used to visualize the movement of cells. However, cells move rather slowly, making the quantitative measurement of cell migration a resource-consuming process requiring expensive cameras and software to create quantitative time-lapsed movies of motile cells. Therefore, the ability to perform a quantitative measurement of cell migration that is cost-effective, non-laborious, and that utilizes common laboratory equipment is a great need for many researchers.
The phagokinetic track motility assay utilizes the ability of a moving cell to clear gold particles from its path to create a measurable track on a colloidal gold-coated glass coverslip9,10
. With the use of freely available software, multiple tracks can be evaluated for each treatment to accomplish statistical requirements. The assay can be utilized to assess motility of many cell types, such as cancer cells11,12
, skeletal muscle cells14
, endothelial cells17
, and monocytes10,18-22
. The protocol involves the creation of slides coated with gold nanoparticles (Au°) that are generated by a reduction of chloroauric acid (Au3+
) by sodium citrate. This method was developed by Turkevich et al.
and then improved in the 1970s by Frens et al.24,25
. As a result of this chemical reduction step, gold particles (10-20 nm in diameter) precipitate from the reaction mixture and can be applied to glass coverslips, which are then ready for use in cellular migration analyses9,26,27
In general, the phagokinetic track motility assay is a quick, quantitative and easy measure of cellular motility. In addition, it can be utilized as a simple high-throughput assay, for use with cell types that are not amenable to time-lapsed imaging, as well as other uses depending on the needs of the researcher. Together, the ability to quantitatively measure cellular motility of multiple cell types without the need for expensive microscopes and software, along with the use of common laboratory equipment and chemicals, make the phagokinetic track motility assay a solid choice for scientists with an interest in understanding cellular motility.
Immunology, Issue 70, Microbiology, Cellular Biology, Molecular Biology, gold nanoparticles, coverslips, cell migration, quantitative cell movement, microscopy, motility, assay
Induction and Analysis of Epithelial to Mesenchymal Transition
Institutions: R&D Systems, Inc., R&D Systems, Inc..
Epithelial to mesenchymal transition (EMT) is essential for proper morphogenesis during development. Misregulation of this process has been implicated as a key event in fibrosis and the progression of carcinomas to a metastatic state. Understanding the processes that underlie EMT is imperative for the early diagnosis and clinical control of these disease states. Reliable induction of EMT in vitro
is a useful tool for drug discovery as well as to identify common gene expression signatures for diagnostic purposes. Here we demonstrate a straightforward method for the induction of EMT in a variety of cell types. Methods for the analysis of cells pre- and post-EMT induction by immunocytochemistry are also included. Additionally, we demonstrate the effectiveness of this method through antibody-based array analysis and migration/invasion assays.
Molecular Biology, Issue 78, Cellular Biology, Biochemistry, Biomedical Engineering, Stem Cell Biology, Cancer Biology, Medicine, Bioengineering, Anatomy, Physiology, biology (general), Pathological Conditions, Signs and Symptoms, Wounds and Injuries, Neoplasms, Diagnosis, Therapeutics, Epithelial to mesenchymal transition, EMT, cancer, metastasis, cancer stem cell, cell, assay, immunohistochemistry
Modeling Astrocytoma Pathogenesis In Vitro and In Vivo Using Cortical Astrocytes or Neural Stem Cells from Conditional, Genetically Engineered Mice
Institutions: University of North Carolina School of Medicine, University of North Carolina School of Medicine, University of North Carolina School of Medicine, University of North Carolina School of Medicine, University of North Carolina School of Medicine, Emory University School of Medicine, University of North Carolina School of Medicine.
Current astrocytoma models are limited in their ability to define the roles of oncogenic mutations in specific brain cell types during disease pathogenesis and their utility for preclinical drug development. In order to design a better model system for these applications, phenotypically wild-type cortical astrocytes and neural stem cells (NSC) from conditional, genetically engineered mice (GEM) that harbor various combinations of floxed oncogenic alleles were harvested and grown in culture. Genetic recombination was induced in vitro
using adenoviral Cre-mediated recombination, resulting in expression of mutated oncogenes and deletion of tumor suppressor genes. The phenotypic consequences of these mutations were defined by measuring proliferation, transformation, and drug response in vitro
. Orthotopic allograft models, whereby transformed cells are stereotactically injected into the brains of immune-competent, syngeneic littermates, were developed to define the role of oncogenic mutations and cell type on tumorigenesis in vivo
. Unlike most established human glioblastoma cell line xenografts, injection of transformed GEM-derived cortical astrocytes into the brains of immune-competent littermates produced astrocytomas, including the most aggressive subtype, glioblastoma, that recapitulated the histopathological hallmarks of human astrocytomas, including diffuse invasion of normal brain parenchyma. Bioluminescence imaging of orthotopic allografts from transformed astrocytes engineered to express luciferase was utilized to monitor in vivo
tumor growth over time. Thus, astrocytoma models using astrocytes and NSC harvested from GEM with conditional oncogenic alleles provide an integrated system to study the genetics and cell biology of astrocytoma pathogenesis in vitro
and in vivo
and may be useful in preclinical drug development for these devastating diseases.
Neuroscience, Issue 90, astrocytoma, cortical astrocytes, genetically engineered mice, glioblastoma, neural stem cells, orthotopic allograft
Setting-up an In Vitro Model of Rat Blood-brain Barrier (BBB): A Focus on BBB Impermeability and Receptor-mediated Transport
Institutions: VECT-HORUS SAS, CNRS, NICN UMR 7259.
The blood brain barrier (BBB) specifically regulates molecular and cellular flux between the blood and the nervous tissue. Our aim was to develop and characterize a highly reproducible rat syngeneic in vitro
model of the BBB using co-cultures of primary rat brain endothelial cells (RBEC) and astrocytes to study receptors involved in transcytosis across the endothelial cell monolayer. Astrocytes were isolated by mechanical dissection following trypsin digestion and were frozen for later co-culture. RBEC were isolated from 5-week-old rat cortices. The brains were cleaned of meninges and white matter, and mechanically dissociated following enzymatic digestion. Thereafter, the tissue homogenate was centrifuged in bovine serum albumin to separate vessel fragments from nervous tissue. The vessel fragments underwent a second enzymatic digestion to free endothelial cells from their extracellular matrix. The remaining contaminating cells such as pericytes were further eliminated by plating the microvessel fragments in puromycin-containing medium. They were then passaged onto filters for co-culture with astrocytes grown on the bottom of the wells. RBEC expressed high levels of tight junction (TJ) proteins such as occludin, claudin-5 and ZO-1 with a typical localization at the cell borders. The transendothelial electrical resistance (TEER) of brain endothelial monolayers, indicating the tightness of TJs reached 300 ohm·cm2
on average. The endothelial permeability coefficients (Pe) for lucifer yellow (LY) was highly reproducible with an average of 0.26 ± 0.11 x 10-3
cm/min. Brain endothelial cells organized in monolayers expressed the efflux transporter P-glycoprotein (P-gp), showed a polarized transport of rhodamine 123, a ligand for P-gp, and showed specific transport of transferrin-Cy3 and DiILDL across the endothelial cell monolayer. In conclusion, we provide a protocol for setting up an in vitro
BBB model that is highly reproducible due to the quality assurance methods, and that is suitable for research on BBB transporters and receptors.
Medicine, Issue 88, rat brain endothelial cells (RBEC), mouse, spinal cord, tight junction (TJ), receptor-mediated transport (RMT), low density lipoprotein (LDL), LDLR, transferrin, TfR, P-glycoprotein (P-gp), transendothelial electrical resistance (TEER),
Induction of Adhesion-dependent Signals Using Low-intensity Ultrasound
Institutions: University of Bristol, Smith and Nephew.
In multicellular organisms, cell behavior is dictated by interactions with the extracellular matrix. Consequences of matrix-engagement range from regulation of cell migration and proliferation, to secretion and even differentiation. The signals underlying each of these complex processes arise from the molecular interactions of extracellular matrix receptors on the surface of the cell. Integrins are the prototypic receptors and provide a mechanical link between extracellular matrix and the cytoskeleton, as well as initiating some of the adhesion-dependent signaling cascades. However, it is becoming increasingly apparent that additional transmembrane receptors function alongside the integrins to regulate both the integrin itself and signals downstream. The most elegant of these examples is the transmembrane proteoglycan, syndecan-4, which cooperates with α5
-integrin during adhesion to fibronectin. In vivo
models demonstrate the importance of syndecan-4 signaling, as syndecan-4-knockout mice exhibit healing retardation due to inefficient fibroblast migration1,2
. In wild-type animals, migration of fibroblasts toward a wound is triggered by the appearance of fibronectin that leaks from damaged capillaries and is deposited by macrophages in injured tissue. Therefore there is great interest in discovering strategies that enhance fibronectin-dependent signaling and could accelerate repair processes.
The integrin-mediated and syndecan-4-mediated components of fibronectin-dependent signaling can be separated by stimulating cells with recombinant fibronectin fragments. Although integrin engagement is essential for cell adhesion, certain fibronectin-dependent signals are regulated by syndecan-4. Syndecan-4 activates the Rac1 protrusive signal3
, causes integrin redistribution1
, triggers recruitment of cytoskeletal molecules, such as vinculin, to focal adhesions4
, and thereby induces directional migration3
. We have looked for alternative strategies for activating such signals and found that low-intensity pulsed ultrasound (LIPUS) can mimic the effects of syndecan-4 engagement5
. In this protocol we describe the method by which 30 mW/cm2
, 1.5 MHz ultrasound, pulsed at 1 kHz (Fig. 1
) can be applied to fibroblasts in culture (Fig. 2
) to induce Rac1 activation and focal adhesion formation. Ultrasound stimulation is applied for a maximum of 20 minutes, as this combination of parameters has been found to be most efficacious for acceleration of clinical fracture repair6
. The method uses recombinant fibronectin fragments to engage α5
-integrin, without engagement of syndecan-4, and requires inhibition of protein synthesis by cycloheximide to block deposition of additional matrix by the fibroblasts., The positive effect of ultrasound on repair mechanisms is well documented7,8
, and by understanding the molecular effect of ultrasound in culture we should be able to refine the therapeutic technique to improve clinical outcomes.
Biomedical Engineering, Issue 63, Ultrasound, LIPUS, Focal Adhesion, Syndecan-4, Wound Healing, Extracellular Matrix, Rac1, bioengineering
Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes
Institutions: New York University School of Medicine, New York University School of Medicine.
T lymphocyte adhesion is required for multiple T cell functions, including migration to sites of inflammation and formation of immunological synapses with antigen presenting cells. T cells accomplish regulated adhesion by controlling the adhesive properties of integrins, a class of cell adhesion molecules consisting of heterodimeric pairs of transmembrane proteins that interact with target molecules on partner cells or extracellular matrix. The most prominent T cell integrin is lymphocyte function associated antigen (LFA)-1, composed of subunits αL and β2, whose target is the intracellular adhesion molecule (ICAM)-1. The ability of a T cell to control adhesion derives from the ability to regulate the affinity states of individual integrins. Inside-out signaling describes the process whereby signals inside a cell cause the external domains of integrins to assume an activated state. Much of our knowledge of these complex phenomena is based on mechanistic studies performed in simplified in vitro
model systems. The T lymphocyte adhesion assay described here is an excellent tool that allows T cells to adhere to target molecules, under static conditions, and then utilizes a fluorescent plate reader to quantify adhesiveness. This assay has been useful in defining adhesion-stimulatory or inhibitory substances that act on lymphocytes, as well as characterizing the signaling events involved. Although described here for LFA-1 - ICAM-1 mediated adhesion; this assay can be readily adapted to allow for the study of other adhesive interactions (e.g.
VLA-4 - fibronectin).
Immunology, Issue 88, Immune System Phenomena, T cell, adhesion, Rap1, integrins, T lymphocytes, ICAM-1
Electric Cell-substrate Impedance Sensing for the Quantification of Endothelial Proliferation, Barrier Function, and Motility
Institutions: Institute for Cardiovascular Research, VU University Medical Center, Institute for Cardiovascular Research, VU University Medical Center.
Electric Cell-substrate Impedance Sensing (ECIS) is an in vitro
impedance measuring system to quantify the behavior of cells within adherent cell layers. To this end, cells are grown in special culture chambers on top of opposing, circular gold electrodes. A constant small alternating current is applied between the electrodes and the potential across is measured. The insulating properties of the cell membrane create a resistance towards the electrical current flow resulting in an increased electrical potential between the electrodes. Measuring cellular impedance in this manner allows the automated study of cell attachment, growth, morphology, function, and motility. Although the ECIS measurement itself is straightforward and easy to learn, the underlying theory is complex and selection of the right settings and correct analysis and interpretation of the data is not self-evident. Yet, a clear protocol describing the individual steps from the experimental design to preparation, realization, and analysis of the experiment is not available. In this article the basic measurement principle as well as possible applications, experimental considerations, advantages and limitations of the ECIS system are discussed. A guide is provided for the study of cell attachment, spreading and proliferation; quantification of cell behavior in a confluent layer, with regard to barrier function, cell motility, quality of cell-cell and cell-substrate adhesions; and quantification of wound healing and cellular responses to vasoactive stimuli. Representative results are discussed based on human microvascular (MVEC) and human umbilical vein endothelial cells (HUVEC), but are applicable to all adherent growing cells.
Bioengineering, Issue 85, ECIS, Impedance Spectroscopy, Resistance, TEER, Endothelial Barrier, Cell Adhesions, Focal Adhesions, Proliferation, Migration, Motility, Wound Healing
Inhibitory Synapse Formation in a Co-culture Model Incorporating GABAergic Medium Spiny Neurons and HEK293 Cells Stably Expressing GABAA Receptors
Institutions: University College London.
Inhibitory neurons act in the central nervous system to regulate the dynamics and spatio-temporal co-ordination of neuronal networks. GABA (γ-aminobutyric acid) is the predominant inhibitory neurotransmitter in the brain. It is released from the presynaptic terminals of inhibitory neurons within highly specialized intercellular junctions known as synapses, where it binds to GABAA
Rs) present at the plasma membrane of the synapse-receiving, postsynaptic neurons. Activation of these GABA-gated ion channels leads to influx of chloride resulting in postsynaptic potential changes that decrease the probability that these neurons will generate action potentials.
During development, diverse types of inhibitory neurons with distinct morphological, electrophysiological and neurochemical characteristics have the ability to recognize their target neurons and form synapses which incorporate specific GABAA
Rs subtypes. This principle of selective innervation of neuronal targets raises the question as to how the appropriate synaptic partners identify each other.
To elucidate the underlying molecular mechanisms, a novel in vitro
co-culture model system was established, in which medium spiny GABAergic neurons, a highly homogenous population of neurons isolated from the embryonic striatum, were cultured with stably transfected HEK293 cell lines that express different GABAA
R subtypes. Synapses form rapidly, efficiently and selectively in this system, and are easily accessible for quantification. Our results indicate that various GABAA
R subtypes differ in their ability to promote synapse formation, suggesting that this reduced in vitro
model system can be used to reproduce, at least in part, the in vivo
conditions required for the recognition of the appropriate synaptic partners and formation of specific synapses. Here the protocols for culturing the medium spiny neurons and generating HEK293 cells lines expressing GABAA
Rs are first described, followed by detailed instructions on how to combine these two cell types in co-culture and analyze the formation of synaptic contacts.
Neuroscience, Issue 93, Developmental neuroscience, synaptogenesis, synaptic inhibition, co-culture, stable cell lines, GABAergic, medium spiny neurons, HEK 293 cell line
Quantitative Analysis of Random Migration of Cells Using Time-lapse Video Microscopy
Institutions: LSU School of Medicine, LSU School of Dentistry, LSU School of Medicine.
Cell migration is a dynamic process, which is important for embryonic development, tissue repair, immune system function, and tumor invasion 1, 2
. During directional migration, cells move rapidly in response to an extracellular chemotactic signal, or in response to intrinsic cues 3
provided by the basic motility machinery. Random migration occurs when a cell possesses low intrinsic directionality, allowing the cells to explore their local environment.
Cell migration is a complex process, in the initial response cell undergoes polarization and extends protrusions in the direction of migration 2
. Traditional methods to measure migration such as the Boyden chamber migration assay is an easy method to measure chemotaxis in vitro
, which allows measuring migration as an end point result. However, this approach neither allows measurement of individual migration parameters, nor does it allow to visualization of morphological changes that cell undergoes during migration.
Here, we present a method that allows us to monitor migrating cells in real time using video - time lapse microscopy. Since cell migration and invasion are hallmarks of cancer, this method will be applicable in studying cancer cell migration and invasion in vitro
. Random migration of platelets has been considered as one of the parameters of platelet function 4
, hence this method could also be helpful in studying platelet functions. This assay has the advantage of being rapid, reliable, reproducible, and does not require optimization of cell numbers. In order to maintain physiologically suitable conditions for cells, the microscope is equipped with CO2
supply and temperature thermostat. Cell movement is monitored by taking pictures using a camera fitted to the microscope at regular intervals. Cell migration can be calculated by measuring average speed and average displacement, which is calculated by Slidebook software.
Cellular Biology, Issue 63, migration, real time, time lapse, video microscopy
Assay for Adhesion and Agar Invasion in S. cerevisiae
Institutions: Princeton University.
Yeasts are found in natural biofilms, where many microorganisms colonize surfaces. In artificial environments, such as surfaces of man-made objects, biofilms can reduce industrial productivity, destroy structures, and threaten human life. 1-3 On the other hand, harnessing the power of biofilms can help clean the environment and generate sustainable energy. 4-8
The ability of S. cerevisiae to colonize surfaces and participate in complex biofilms was mostly ignored until the rediscovery of the differentiation programs triggered by various signaling pathways and environmental cues in this organism. 9, 10 The continuing interest in using S. cerevisiae as a model organism to understand the interaction and convergence of signaling pathways, such as the Ras-PKA, Kss1 MAPK, and Hog1 osmolarity pathways, quickly placed S. cerevisiae in the junction of biofilm biology and signal transduction research. 11-20 To this end, differentiation of yeast cells into long, adhesive, pseudohyphal filaments became a convenient readout for the activation of signal transduction pathways upon various environmental changes. However, filamentation is a complex collection of phenotypes, which makes assaying for it as if it were a simple phenotype misleading. In the past decade, several assays were successfully adopted from bacterial biofilm studies to yeast research, such as MAT formation assays to measure colony spread on soft agar and crystal violet staining to quantitatively measure cell-surface adherence. 12, 21 However, there has been some confusion in assays developed to qualitatively assess the adhesive and invasive phenotypes of yeast in agar.
Here, we present a simple and reliable method for assessing the adhesive and invasive quality of yeast strains with easy-to-understand steps to isolate the adhesion assessment from invasion assessment. Our method, adopted from previous studies, 10, 16 involves growing cells in liquid media and plating on differential nutrient conditions for growth of large spots, which we then wash with water to assess adhesion and rub cells completely off the agar surface to assess invasion into the agar. We eliminate the need for streaking cells onto agar, which affects the invasion of cells into the agar. In general, we observed that haploid strains that invade agar are always adhesive, yet not all adhesive strains can invade agar medium. Our approach can be used in conjunction with other assays to carefully dissect the differentiation steps and requirements of yeast signal transduction, differentiation, quorum sensing, and biofilm formation.
Microbiology, Issue 1, Yeast, Adhesion, Invasion
Human T Lymphocyte Isolation, Culture and Analysis of Migration In Vitro
Institutions: University of Rochester.
The migration of T lymphocytes involves the adhesive interaction of cell surface integrins with ligands expressed on other cells or with extracellular matrix proteins. The precise spatiotemporal activation of integrins from a low affinity state to a high affinity state at the cell leading edge is important for T lymphocyte migration 1
. Likewise, retraction of the cell trailing edge, or uropod, is a necessary step in maintaining persistent integrin-dependent T lymphocyte motility 2
. Many therapeutic approaches to autoimmune or inflammatory diseases target integrins as a means to inhibit the excessive recruitment and migration of leukocytes 3
. To study the molecular events that regulate human T lymphocyte migration, we have utilized an in vitro
system to analyze cell migration on a two-dimensional substrate that mimics the environment that a T lymphocyte encounters during recruitment from the vasculature. T lymphocytes are first isolated from human donors and are then stimulated and cultured for seven to ten days. During the assay, T lymphocytes are allowed to adhere and migrate on a substrate coated with intercellular adhesion molecule-1 (ICAM-1), a ligand for integrin LFA-1, and stromal cell-derived factor-1 (SDF-1). Our data show that T lymphocytes exhibit a migratory velocity of ~15 μm/min. T lymphocyte migration can be inhibited by integrin blockade 1
or by inhibitors of the cellular actomyosin machinery that regulates cell migration 2
Immunology, Issue 40, T lymphocyte, Migration, Integrin, LFA-1, ICAM-1, Chemokine