Established and novel methods of interrogating two-dimensional cell migration

Electric Cell-Substrate Impedance Sensing as a Tool to Characterize Wound Healing Dynamics

The electric cell-substrate impedance sensing (ECIS) is a well-established technique that allows for the real-time monitoring of cell cultures growing on gold-electrodes embedded in culture dishes. Its foundation lays on the insulating effect that cells present against the free-flow of electrons, as these passive electrical properties generate a characteristic complex impedance spectrum when a small-amplitude, non-invasive alternating current (AC) is provided through the electrodes, the living cells, and the culture media in the culture ware. In addition, it possesses the ability to create a wound that is highly confined to the electrode area by simply increasing the amplitude of the AC current in dependence of the pre-resistor strength for a defined pulse duration and at a specific frequency. Therefore, it represents a controlled and reproducible tool to carry out in vitro wound healing experiments. Accordingly, in this methods protocol, the use of the ECIS will be described in the context of the wound healing research: cardiac 3T3 fibroblasts will be wounded and their recovery dynamics analyzed based on the typical methodologies applied to the processing of ECIS data. In addition, cellular micromotions will be evaluated. Finally, fluorescence immunostaining of ECIS samples will be described in order to showcase the potential of the ECIS in combination with other well-established techniques to add further knowledge depth to the understanding of the complex wound healing dynamics.

Chronic Wound Healing Models

In this paper, we review and analyze the commonly available wound healing models reported in the literature and discuss their advantages and issues, considering their relevance and translational potential to humans. Our analysis includes different in vitro and in silico as well as in vivo models and experimental techniques. We further explore the new technologies in the study of wound healing to provide an all encompassing review of the most efficient ways to proceed with wound healing experiments. We revealed that there is not one model of wound healing that is superior and can give translatable results to human research. Rather, there are many different models that have specific uses for studying certain processes or stages of wound healing. Our analysis suggests that when performing an experiment to assess stages of wound healing or different therapies to enhance healing, one must consider not only the species that will be used but also the type of model and how this can best replicate the physiology or pathophysiology in humans.

Bifurcation analysis of critical values for wound closure outcomes in wound healing experiments

A nonlinear partial differential equation containing a nonlocal advection term and a diffusion term is analyzed to study wound closure outcomes in wound healing experiments. There is an extensive literature of similar models for wound healing experiments. In this paper we study the character of wound closure in these experiments in terms of the sensing radius of cells and the force of cell-cell adhesion. We prove a bifurcation result which differentiates uniform closure of the wound from nonuniform closure of the wound, based on a critical value [Formula: see text] of the force of cell-cell adhesion parameter [Formula: see text]. For [Formula: see text] the steady state solution [Formula: see text] of the model is stable and the wound closes uniformly. For [Formula: see text] the steady state solution [Formula: see text] of the model is unstable and the wound closes nonuniformly. We provide numerical simulations of the model to illustrate our results.

A Novel In Vitro Wound Healing Assay Using Free-Standing, Ultra-Thin PDMS Membranes

Advances in polymer science have significantly increased polymer applications in life sciences. We report the use of free-standing, ultra-thin polydimethylsiloxane (PDMS) membranes, called CellDrum, as cell culture substrates for an in vitro wound model. Dermal fibroblast monolayers from 28- and 88-year-old donors were cultured on CellDrums. By using stainless steel balls, circular cell-free areas were created in the cell layer (wounding). Sinusoidal strain of 1 Hz, 5% strain, was applied to membranes for 30 min in 4 sessions. The gap circumference and closure rate of un-stretched samples (controls) and stretched samples were monitored over 4 days to investigate the effects of donor age and mechanical strain on wound closure. A significant decrease in gap circumference and an increase in gap closure rate were observed in trained samples from younger donors and control samples from older donors. In contrast, a significant decrease in gap closure rate and an increase in wound circumference were observed in the trained samples from older donors. Through these results, we propose the model of a cell monolayer on stretchable CellDrums as a practical tool for wound healing research. The combination of biomechanical cell loading in conjunction with analyses such as gene/protein expression seems promising beyond the scope published here.

Water-Air Interface to Mimic In Vitro Tumoral Cell Migration in Complex Micro-Environments

The long-known role of cell migration in physiological and pathological contexts still requires extensive research to be fully understood, mainly because of the intricate interaction between moving cells and their surroundings. While conventional assays fail to capture this complexity, recently developed 3D platforms better reproduce the cellular micro-environment, although often requiring expensive and time-consuming imaging approaches. To overcome these limitations, we developed a novel approach based on 2D micro-patterned substrates, compatible with conventional microscopy analysis and engineered to create micro-gaps with a length of 150 µm and a lateral size increasing from 2 to 8 µm, where a curved water-air interface is created on which cells can adhere, grow, and migrate. The resulting hydrophilic/hydrophobic interfaces, variable surface curvatures, spatial confinements, and size values mimic the complex micro-environment typical of the extracellular matrix in which aggressive cancer cells proliferate and migrate. The new approach was tested with two breast cancer cell lines with different invasive properties. We observed that invasive cells (MDA-MB-231) can align along the pattern and modify both their morphology and their migration rate according to the size of the water meniscus, while non-invasive cells (MCF-7) are only slightly respondent to the surrounding micro-environment. Moreover, the selected pattern highlighted a significative matrix deposition process connected to cell migration. Although requiring further optimizations, this approach represents a promising tool to investigate cell migration in complex environments.

Reciprocity of Cell Mechanics with Extracellular Stimuli: Emerging Opportunities for Translational Medicine

Human cells encounter dynamic mechanical cues in healthy and diseased tissues, which regulate their molecular and biophysical phenotype, including intracellular mechanics as well as force generation. Recent developments in bio/nanomaterials and microfluidics permit exquisitely sensitive measurements of cell mechanics, as well as spatiotemporal control over external mechanical stimuli to regulate cell behavior. In this review, the mechanobiology of cells interacting bidirectionally with their surrounding microenvironment, and the potential relevance for translational medicine are considered. Key fundamental concepts underlying the mechanics of living cells as well as the extracelluar matrix are first introduced. Then the authors consider case studies based on 1) microfluidic measurements of nonadherent cell deformability, 2) cell migration on micro/nano-topographies, 3) traction measurements of cells in three-dimensional (3D) matrix, 4) mechanical programming of organoid morphogenesis, as well as 5) active mechanical stimuli for potential therapeutics. These examples highlight the promise of disease diagnosis using mechanical measurements, a systems-level understanding linking molecular with biophysical phenotype, as well as therapies based on mechanical perturbations. This review concludes with a critical discussion of these emerging technologies and future directions at the interface of engineering, biology, and medicine.

Bioengineered Wound Healing Skin Models: The Role of Immune Response and Endogenous ECM to Fully Replicate the Dynamic of Scar Tissue Formation In Vitro

The healing of deep skin wounds is a complex phenomenon evolving according with a fine spatiotemporal regulation of different biological events (hemostasis, inflammation, proliferation, remodeling). Due to the spontaneous evolution of damaged human dermis toward a fibrotic scar, the treatment of deep wounds still represents a clinical concern. Bioengineered full-thickness skin models may play a crucial role in this direction by providing a deep understanding of the process that leads to the formation of fibrotic scars. This will allow (i) to identify new drugs and targets/biomarkers, (ii) to test new therapeutic approaches, and (iii) to develop more accurate in silico models, with the final aim to guide the closure process toward a scar-free closure and, in a more general sense, (iv) to understand the mechanisms involved in the intrinsic and extrinsic aging of the skin. In this work, the complex dynamic of events underlaying the closure of deep skin wound is presented and the engineered models that aim at replicating such complex phenomenon are reviewed. Despite the complexity of the cellular and extracellular events occurring during the skin wound healing the gold standard assay used to replicate such a process is still represented by planar in vitro models that have been largely used to identify the key factors regulating the involved cellular processes. However, the lack of the main constituents of the extracellular matrix (ECM) makes these over-simplistic 2D models unable to predict the complexity of the closure process. Three-dimensional bioengineered models, which aim at recreating the closure dynamics of the human dermis by using exogenous biomaterials, have been developed to fill such a gap. Although interesting mechanistic effects have been figured out, the effect of the inflammatory response on the ECM remodelling is not replicated yet. We discuss how more faithful wound healing models can be obtained by creating immunocompetent 3D dermis models featuring an endogenous ECM.

Cancer cell migration on straight, wavy, loop and grid microfibre patterns

Cell migration plays an important role in physiological and pathological processes where the fibrillar morphology of extracellular matrices (ECM) could regulate the migration dynamics. To mimic the morphological characteristics of fibrillar matrix structures, low-voltage continuous electrospinning was adapted to construct straight, wavy, looped and gridded fibre patterns made of polystyrene (of fibre diameter ca. 3 μm). Cells were free to explore their different shapes in response to the directly-adhered fibre, as well as to the neighbouring patterns. For all the patterns studied, analysing cellular migration dynamics of MDA-MB-231 (a highly migratory breast cancer cell line) demonstrated two interesting findings: first, although cells dynamically adjust their shapes and migration trajectories in response to different fibrillar environments, their average step speed is minimally affected by the fibre global pattern; secondly, a switch in behaviour was observed when the pattern features approach the upper limit of the cell body's minor axis, reflecting that cells' ability to divert from an existing fibre track is limited by the size along the cell body's minor axis. It is therefore concluded that the upper limit of cell body's minor axis might act as a guide for the design of microfibre patterns for different purposes of cell migration.

Analysis of Migration and Invasion in Ewing Sarcoma

The metastasis is a complex, well-orchestrated process, which includes migration from the primary tumor and invasion into secondary locations as main features. In Ewing sarcoma, metastasis is the main determinant of malignancy, with ~30% of patients presenting with metastatic disease at diagnosis. Therefore, analyzing migration and invasion in different experimental settings in vitro is key to understanding this disease. Among the variety of possible techniques to study migration, this chapter described the methods of wound healing (migration in 2D) and transwell (migration through a porous membrane in response to a given stimulus). Additionally, this chapter includes a variation of the transwell protocol that allows for the analysis of cell invasion through a gel matrix in response to stimulus.

The epithelial-mesenchymal transition and the cytoskeleton in bioengineered systems

The epithelial-mesenchymal transition (EMT) is intrinsically linked to alterations of the intracellular cytoskeleton and the extracellular matrix. After EMT, cells acquire an elongated morphology with front/back polarity, which can be attributed to actin-driven protrusion formation as well as the gain of vimentin expression. Consequently, cells can deform and remodel the surrounding matrix in order to facilitate local invasion. In this review, we highlight recent bioengineering approaches to elucidate EMT and functional changes in the cytoskeleton. First, we review transitions between multicellular clusters and dispersed individuals on planar surfaces, which often exhibit coordinated behaviors driven by leader cells and EMT. Second, we consider the functional role of vimentin, which can be probed at subcellular length scales and within confined spaces. Third, we discuss the role of topographical patterning and EMT via a contact guidance like mechanism. Finally, we address how multicellular clusters disorganize and disseminate in 3D matrix. These new technologies enable controlled physical microenvironments and higher-resolution spatiotemporal measurements of EMT at the single cell level. In closing, we consider future directions for the field and outstanding questions regarding EMT and the cytoskeleton for human cancer progression. Video Abstract.

Creating wounds in cell monolayers using micro-jets

Many wound-healing assays are used in cell biology and biomedicine; they are often labor intensive and/or require specialized and costly equipment. We describe a contactless method to create wounds with any imaginable 2D pattern in cell monolayers using the micro-jets of either media or an immiscible and biocompatible fluorocarbon (i.e., FC40). We also combine this with another method that allows automation and multiplexing using standard Petri dishes. A dish is filled with a thin film of media overlaid with FC40, and the two liquids are reshaped into an array of microchambers within minutes. Each chamber in such a grid is isolated from others by the fluid walls of FC40. Cells are now added, allowed to grow into a monolayer, and wounds are created using the microjets; then, healing is monitored by microscopy. As arrays of chambers can be made using media and Petri dishes familiar to biologists, and as dishes fit seamlessly into their incubators, microscopes, and workflows, we anticipate that this assay will find wide application in wound healing.

A practical toolkit to study aspects of the metastatic cascade in vitro

While metastasis - the spread of cancer from the primary location to distant sites in the body - remains the principle cause of cancer death, it is incompletely understood. It is a complex process, requiring the metastatically successful cancer cell to negotiate a formidable series of interconnected steps, which are described in this paper. For each step, we review the range of in vitro assays that may be used to study them. We also provide a range of detailed, step-by-step protocols that can be undertaken in most modestly-equipped laboratories, including methods for converting qualitative observations into quantitative data for analysis. Assays include: (1) a gelatin degradation assay to study the ability of endothelial cells to degrade extracellular matrix during tumour angiogenesis; (2) the morphological characterisation of cells undergoing epithelial-mesenchymal transition (EMT) as they acquire motility; (3) a 'scratch' or 'wound-healing' assay to study cancer cell migration; (4) a transwell assay to study cancer cell invasion through extracellular matrix; and (5) a static adhesion assay to examine cancer cell interactions with, and adhesion to, endothelial monolayers. This toolkit of protocols will enable researchers who are interested in metastasis to begin to focus on defined aspects of the process. It is only by further understanding this complex, fascinating and clinically relevant series of events that we may ultimately devise ways of better treating, or even preventing, cancer metastasis. The assays may also be of more broad interest to researchers interested in studying aspects of cellular behaviour in relation to other developmental and disease processes.

Two high-yield complementary methods to sort cell populations by their 2D or 3D migration speed

The potential to migrate is one of the most fundamental functions for various epithelial, mesenchymal, and immune cells. Image analysis of motile cell populations, both primary and cultured, typically reveals an intercellular variability in migration speeds. However, cell migration chromatography, the sorting of large populations of cells based on their migratory characteristics, cannot be easily performed. The lack of such methods has hindered our understanding of the direct correlation between the capacity to migrate and other cellular properties. Here, we report two novel, easily implementable and readily scalable methods to sort millions of live migratory cancer and immune cells based on their spontaneous migration in two-dimensional and three-dimensional microenvironments, respectively. Correlative downstream transcriptomic, molecular and functional tests reveal marked differences between the fast and slow subpopulations in patient-derived cancer cells. We further employ our method to reveal that sorting the most migratory cytotoxic T lymphocytes yields a pool of cells with enhanced cytotoxicity against cancer cells. This phenotypic assay opens new avenues for the precise characterization of the mechanisms underlying hither to unexplained heterogeneities in migratory phenotypes within a cell population, and for the targeted enrichment of the most potent migratory leukocytes in immunotherapies.

Phosphodiesterase SMPDL3B Gene Expression as Independent Outcome Prediction Marker in Localized Prostate Cancer

Current outcome prediction markers for localized prostate cancer (PCa) are insufficient. The impact of the lipid-modifying Sphingomyelin Phosphodiesterase Acid Like 3B (SMPDL3B) in PCa is unknown. Two cohorts of patients with PCa who underwent radical prostatectomy (n = 40, n = 56) and benign prostate hyperplasia (BPH) controls (n = 8, n = 11) were profiled for SMPDL3B expression with qRT-PCR. Publicly available PCa cohorts (Memorial Sloane Kettering Cancer Centre (MSKCC; n = 131, n = 29 controls) and The Cancer Genome Atlas (TCGA; n = 497, n = 53 controls)) served for validation. SMPDL3B's impact on proliferation and migration was analyzed in PC3 cells by siRNA knockdown. In both cohorts, a Gleason score and T stage independent significant overexpression of SMPDL3B was seen in PCa compared to BPH (p < 0.001 each). A lower expression of SMPDL3B was associated with a shorter overall survival (OS) (p = 0.005) in long term follow-up. A SMPDL3B overexpression in PCa tissue was confirmed in the validation cohorts (p < 0.001 each). In the TCGA patients with low SMPDL3B expression, biochemical recurrence-free survival (p = 0.011) and progression-free interval (p < 0.001) were shorter. Knockdown of SMPDL3B impaired PC3 cell migration but not proliferation (p = 0.0081). In summary, SMPLD3B is highly overexpressed in PCa tissue, is inversely associated with localized PCa prognosis, and impairs PCa cell migration.

In vitro cell migration quantification method for scratch assays

The scratch assay is an in vitro technique used to assess the contribution of molecular and cellular mechanisms to cell migration. The assay can also be used to evaluate therapeutic compounds before clinical use. Current quantification methods of scratch assays deal poorly with irregular cell-free areas and crooked leading edges which are features typically present in the experimental data. We introduce a new migration quantification method, called 'monolayer edge velocimetry', that permits analysis of low-quality experimental data and better statistical classification of migration rates than standard quantification methods. The new method relies on quantifying the horizontal component of the cell monolayer velocity across the leading edge. By performing a classification test on in silico data, we show that the method exhibits significantly lower statistical errors than standard methods. When applied to in vitro data, our method outperforms standard methods by detecting differences in the migration rates between different cell groups that the other methods could not detect. Application of this new method will enable quantification of migration rates from in vitro scratch assay data that cannot be analysed using existing methods.

A Semiautomated, Phenotypic, In Vitro Scratch Assay for Assessing Retinal Pigment Epithelial Cell Wound Healing

Purpose: Age-related macular degeneration leads to retinal pigment epithelium (RPE) cell death and loss of central vision. In vivo studies have shown that the RPE layer has an innate, but limited, ability to repopulate atrophic areas. We aimed to establish a semiautomated, in vitro, wound healing assay workflow for targeted screening of compounds able to influence RPE wound healing. Methods: The ARPE-19 phenotype was evaluated using bright-field microscopy, immunocytochemistry, and quantitative real-time polymerase chain reaction. ARPE-19 monolayers were simultaneously scratched in a 96-well format and treated with Hoechst-33342 and an array of compounds. Initial wound dimensions and wound healing were subsequently evaluated using the EVOS FL Auto 2.0 imaging platform combined with automated image analyses. Results: Long-term cultured ARPE-19 cells displayed a more in vivo RPE-like phenotype compared with recently seeded or short-term cultured cells. No statistical difference of initial scratch width was observed between short-term and long-term cultured cells, but more wells were excluded from analyses in total in the latter case due to scratch width, scratch smoothness, and imaging errors. Furthermore, the previous time spent in continuous culture had an effect on the observation of an altered wound healing response to different treatment conditions. Conclusions: We have established a semiautomated, 96-well format, in vitro wound healing assay with a reproducible workflow. This would enable screening of a significant number of compounds and greatly advances the potential of identifying novel therapeutics that may enhance the innate ability of RPE cells to repopulate atrophic areas.

A novel magnet-based scratch method for standardisation of wound-healing assays

A novel magnetic scratch method achieves repeatability, reproducibility and geometric control greater than pipette scratch assays and closely approximating the precision of cell exclusion assays while inducing the cell injury inherently necessary for wound healing assays. The magnetic scratch is affordable, easily implemented and standardisable and thus may contribute toward better comparability of data generated in different studies and laboratories.

Local cell coordination does not alter individual cell migration during collective migration but does impact cellular exchange events

Coordinated cell re-organization is critical to ensure correct tissue morphogenesis for a number of important embryonic and tissue repair events, however the mechanisms that govern cells coordination during collective movements, particularly in situations where cells are spatially restricted by their neighbours, are not well understood. Here we assessed cell re-organization in monolayers of retinal epithelial cells (ARPE-19) to determine if cells that coordinate with their neighbours exhibit differential migration properties to non-coordinating cells and participate differently in local cell re-organization of the tissue sheet. From global tracking analysis, we determined that the movement profiles of cells were indistinguishable regardless of whether or not they were a part of multicellular streams. Using high magnification live imaging of cell membranes, we also characterized the localized geometry and organization of a monolayer (cell area, number of nearest neighbours, aspect ratio, internal cell angles) during cell re-organization in both streaming and non-streaming regions. Consistent with our global migration analysis, we observed no differences in cell sheet geometry and organization in streaming versus non-streaming regions. We did however observe that cells executed T1-like transitions to exchange position within the space-limited monolayer and that exchange events consistently involved at least one non-streaming cell. Our data suggests a model in which cell movement within the sheet is limited by neighbour exchange events and likely cells transition between streaming and non-streaming regimes to facilitate these neighbour exchange events while maintaining the integrity of the sheet.

Mechanical forces in cell monolayers

In various physiological processes, the cell collective is organized in a monolayer, such as seen in a simple epithelium. The advances in the understanding of mechanical behavior of the monolayer and its underlying cellular and molecular mechanisms will help to elucidate the properties of cell collectives. In this Review, we discuss recent in vitro studies on monolayer mechanics and their implications on collective dynamics, regulation of monolayer mechanics by physical confinement and geometrical cues and the effect of tissue mechanics on biological processes, such as cell division and extrusion. In particular, we focus on the active nematic property of cell monolayers and the emerging approach to view biological systems in the light of liquid crystal theory. We also highlight the mechanosensing and mechanotransduction mechanisms at the sub-cellular and molecular level that are mediated by the contractile actomyosin cytoskeleton and cell-cell adhesion proteins, such as E-cadherin and α-catenin. To conclude, we argue that, in order to have a holistic understanding of the cellular response to biophysical environments, interdisciplinary approaches and multiple techniques - from large-scale traction force measurements to molecular force protein sensors - must be employed.

Surveillance of Myelodysplastic Syndrome via Migration Analyses of Blood Neutrophils: A Potential Prognostic Tool

Autonomous migration is a central characteristic of immune cells, and changes in this function have been correlated to the progression and severity of diseases. Hence, the identification of pathologically altered leukocyte migration patterns might be a promising approach for disease surveillance and prognostic scoring. However, because of the lack of standardized and robust assays, migration patterns have not been clinically exploited so far. In this study, we introduce an easy-to-use and cross-laboratory, standardized two-dimensional migration assay for neutrophil granulocytes from peripheral blood. By combining time-lapse video microscopy and automated cell tracking, we calculated the average migration of neutrophils from 111 individual participants of the German Heinz Nixdorf Recall MultiGeneration study under steady-state, formyl-methionyl-leucyl-phenylalanine-, CXCL1-, and CXCL8-stimulated conditions. Comparable values were obtained in an independent laboratory from a cohort in Belgium, demonstrating the robustness and transferability of the assay. In a double-blinded retrospective clinical analysis, we found that neutrophil migration strongly correlated with the Revised International Prognostic Scoring System scoring and risk category of myelodysplastic syndrome (MDS) patients. In fact, patients suffering from high-risk subtypes MDS with excess blasts I or II displayed highly significantly reduced neutrophil migration. Hence, the determination of neutrophil migration patterns might represent a useful tool in the surveillance of MDS. Taken together, we suggest that standardized migration assays of neutrophils and other leukocyte subtypes might be broadly applicable as prognostic and surveillance tools for MDS and potentially for other diseases.

Optimized Scratch Assay for In Vitro Testing of Cell Migration with an Automated Optical Camera

Cell migration is an important process that influences many aspects of health, such as wound healing and cancer, and it is, therefore, crucial for developing methods to study the migration. The scratch assay has long been the most common in vitro method to test compounds with anti- and pro-migration properties because of its low cost and simple procedure. However, an often-reported problem of the assay is the accumulation of cells across the edge of the scratch. Furthermore, to obtain data from the assay, images of different exposures must be taken over a period of time at the exact same spot to compare the movements of the migration. Different analysis programs can be used to describe the scratch closure, but they are labor intensive, inaccurate, and forces cycles of temperature changes. In this study, we demonstrate an optimized method for testing the migration effect, e.g. with the naturally occurring proteins Human- and Bovine-Lactoferrin and their N-terminal peptide Lactoferricin on the epithelial cell line HaCaT. A crucial optimization is to wash and scratch in PBS, which eliminates the aforementioned accumulation of cells along the edge. This could be explained by the removal of cations, which have been shown to have an effect on keratinocyte cell-cell connection. To ensure true detection of migration, pre-treating with mitomycin C, a DNA synthesis inhibitor, was added to the protocol. Finally, we demonstrate the automated optical camera, which eliminates excessive temperature cycles, manual labor with scratch closure analysis, while improving on reproducibility and ensuring analysis of identical sections of the scratch over time.

Controlled microenvironments to evaluate chemotactic properties of cultured Müller glia

Emerging therapies have begun to evaluate the abilities of Müller glial cells (MGCs) to protect and/or regenerate neurons following retina injury. The migration of donor cells is central to many reparative strategies, where cells must achieve appropriate positioning to facilitate localized repair. Although chemical cues have been implicated in the MGC migratory responses of numerous retinopathies, MGC-based therapies have yet to explore the extent to which external biochemical stimuli can direct MGC behavior. The current study uses a microfluidics-based assay to evaluate the migration of cultured rMC-1 cells (as model MGC) in response to quantitatively-controlled microenvironments of signaling factors implicated in retinal regeneration: basic Fibroblast Growth factor (bFGF or FGF2); Fibroblast Growth factor 8 (FGF8); Vascular Endothelial Growth Factor (VEGF); and Epidermal Growth Factor (EGF). Findings indicate that rMC-1 cells exhibited minimal motility in response to FGF2, FGF8 and VEGF, but highly-directional migration in response to EGF. Further, the responses were blocked by inhibitors of EGF-R and of the MAPK signaling pathway. Significantly, microfluidics data demonstrate that changes in the EGF gradient (i.e. change in EGF concentration over distance) resulted in the directional chemotactic migration of the cells. By contrast, small increases in EGF concentration, alone, resulted in non-directional cell motility, or chemokinesis. This microfluidics-enhanced approach, incorporating the ability both to modulate and asses the responses of motile donor cells to a range of potential chemotactic stimuli, can be applied to potential donor cell populations obtained directly from human specimens, and readily expanded to incorporate drug-eluting biomaterials and combinations of desired ligands.

Overexpressing TPTE2 (TPIP), a homolog of the human tumor suppressor gene PTEN, rescues the abnormal phenotype of the PTEN-/- mutant

One possible approach to normalize mutant cells that are metastatic and tumorigenic, is to upregulate a functionally similar homolog of the mutated gene. Here we have explored this hypothesis by generating an overexpressor of TPTE2 (TPIP), a homolog of PTEN, in PTEN-/- mutants, the latter generated by targeted mutagenesis of a human epithelial cell line. Overexpression of TPTE2 normalized phenotypic changes associated with the PTEN mutation. The PTEN-/- -associated changes rescued by overexpressing TPTE2 included 1) accelerated wound healing in the presence or absence of added growth factors (GFs), 2) increased division rates on a 2D substrate in the presence of GFs, 3) adhesion and viability on a 2D substrate in the absence of GFs, 4) viability in a 3D Matrigel model in the absence of GFs and substrate adhesion 5) loss of apoptosis-associated annexin V cell surface binding sites. The results justify further exploration into the possibility that upregulating TPTE2 by a drug may reverse metastatic and tumorigenic phenotypes mediated in part by a mutation in PTEN. This strategy may also be applicable to other tumorigenic mutations in which a homolog to the mutated gene is present and can substitute functionally.

Linear array of multi-substrate tracts for simultaneous assessment of cell adhesion, migration, and differentiation

Cell migration, which is central to a wide variety of life processes, involves integration of the extracellular matrix (ECM) with the internal cytoskeleton and motor proteins via receptors spanning the plasma membrane. Cell migration can be induced by a variety of signals, including gradients of external soluble molecules, differences in ECM composition, or electrical gradients. Current in vitro methods to study cell migration only test one substrate at a time. Here, we present a method for assessing cell adhesion, migration, and differentiation in up to 20 different test conditions simultaneously, using only minute amounts of target substrate. Our system, which we call the linear array of multi-substrate cell migration assay (LAMA), has two configurations for direct comparison of one or two cell types in response to an array of ECM constituents under the same culture conditions. This culture model utilizes only nanogram amounts of test substrates and a minimal number of cells, which maximizes the use of limited and expensive test reagents. Moreover, LAMA can also be used for high-throughput screening of potential pharmaceuticals that target ECM-dependent cell behavior and differentiation.

High dengue virus load differentially modulates human microvascular endothelial barrier function during early infection

Plasma leakage is the main pathophysiological feature in severe dengue, resulting from altered vascular barrier function associated with an inappropriate immune response triggered upon infection. The present study investigated functional changes using an electric cell-substrate impedance sensing system in four (brain, dermal, pulmonary and retinal) human microvascular endothelial cell (MEC) lines infected with purified dengue virus, followed by assessment of cytokine profiles and the expression of inter-endothelial junctional proteins. Modelling of changes in electrical impedance suggests that vascular leakage in dengue-infected MECs is mostly due to the modulation of cell-to-cell interactions, while this loss of vascular barrier function observed in the infected MECs varied between cell lines and DENV serotypes. High levels of inflammatory cytokines (IL-6 and TNF-α), chemokines (CXCL1, CXCL5, CXCL11, CX3CL1, CCL2 and CCL20) and adhesion molecules (VCAM-1) were differentially produced in the four infected MECs. Further, the tight junctional protein, ZO-1, was down-regulated in both the DENV-1-infected brain and pulmonary MECs, while claudin-1, PECAM-1 and VE-cadherin were differentially expressed in these two MECs after infection. Non-purified virus stock was also studied to investigate the impact of virus stock purity on dengue-specific immune responses, and the results suggest that virus stock propagated through cell culture may include factors that mask or alter the DENV-specific immune responses of the MECs. The findings of the present study show that high DENV load differentially modulates human microvascular endothelial barrier function and disrupts the function of inter-endothelial junctional proteins during early infection with organ-specific cytokine production.

A microfabricated 96-well wound-healing assay

This article presents a microfabricated 96-well wound-healing assay enabling high-throughput measurement of cellular migration capabilities. Within each well, the middle area is the wound region, made of microfabricated gold surface with self-assembled PEG repellent for cell seeding. After the formation of a cellular confluent monolayer around the wound region, collagen solution was applied to form three-dimensional matrix to cover the PEG surface, initiating the wound-healing process. By interpreting the numbers of migrated cells into the wound regions as a function of specific stimuli with different concentrations, EC50 (half-maximal effective concentration) was obtained. Using H1299 as a model, values of EC50 were quantified as 8% and 160 ng/ml for fetal bovine serum and CXCL12, respectively. In addition, the values of EC50 were demonstrated not to be affected by variations in compositions of extracellular matrix and geometries of wounds, which can thus be regarded as an intrinsic marker. Furthermore, the migration capabilities of a second cell type (HeLa) were characterized by the developed wound-healing assay, producing EC50 of 2% when fetal bovine serum was used as the stimuli. These results validated the proposed high-throughput wound-healing assay, which may function as an enabling tool in studying cellular capabilities of migration and invasion. © 2017 International Society for Advancement of Cytometry.

Stereolithographic printing of ionically-crosslinked alginate hydrogels for degradable biomaterials and microfluidics

3D printed biomaterials with spatial and temporal functionality could enable interfacial manipulation of fluid flows and motile cells. However, such dynamic biomaterials are challenging to implement since they must be responsive to multiple, biocompatible stimuli. Here, we show stereolithographic printing of hydrogels using noncovalent (ionic) crosslinking, which enables reversible patterning with controlled degradation. We demonstrate this approach using sodium alginate, photoacid generators and various combinations of divalent cation salts, which can be used to tune the hydrogel degradation kinetics, pattern fidelity, and mechanical properties. This approach is first utilized to template perfusable microfluidic channels within a second encapsulating hydrogel for T-junction and gradient devices. The presence and degradation of printed alginate microstructures were further verified to have minimal toxicity on epithelial cells. Degradable alginate barriers were used to direct collective cell migration from different initial geometries, revealing differences in front speed and leader cell formation. Overall, this demonstration of light-based 3D printing using non-covalent crosslinking may enable adaptive and stimuli-responsive biomaterials, which could be utilized for bio-inspired sensing, actuation, drug delivery, and tissue engineering.

The EEF1A2 gene expression as risk predictor in localized prostate cancer

Background

Besides clinical stage and Gleason score, risk-stratification of prostate cancer in the pretherapeutic setting mainly relies on the serum PSA level. Yet, this is associated with many uncertainties. With regard to therapy decision-making, additional markers are needed to allow an exact risk prediction. Eukaryotic translation elongation factor 1 alpha 2 (EEF1A2) was previously suggested as driver of tumor progression and potential biomarker. In the present study its functional and prognostic relevance in prostate cancer was investigated.

Methods

EEF1A2 expression was analyzed in two cohorts of patients (n = 40 and n = 59) with localized PCa. Additionally data from two large expression dataset (MSKCC, Cell, 2010 with n = 131 localized, n = 19 metastatic PCa and TCGA provisional data, n = 499) of PCa patients were reanalyzed. The expression of EEF1A2 was correlated with histopathology features and biochemical recurrence (BCR). To evaluate the influence of EEF1A2 on proliferation and migration of metastatic PC3 cells, siRNA interference was used. Statistical significance was tested with t-test, Mann-Whitney-test, Pearson correlation and log-rank test.

Results

qRT-PCR revealed EEF1A2 to be significantly overexpressed in PCa tissue, with an increase according to tumor stage in one cohort (p = 0.0443). In silico analyses in the MSKCC cohort confirmed the overexpression of EEF1A2 in localized PCa with high Gleason score (p = 0.0142) and in metastatic lesions (p = 0.0038). Patients with EEF1A2 overexpression had a significantly shorter BCR-free survival (p = 0.0028). EEF1A2 expression was not correlated with serum PSA levels. Similar results were seen in the TCGA cohort, where EEF1A2 overexpression only occurred in tumors with Gleason 7 or higher. Patients with elevated EEF1A2 expression had a significantly shorter BCR-free survival (p = 0.043). EEF1A2 knockdown significantly impaired the migration, but not the proliferation of metastatic PC3 cells.

Conclusion

The overexpression of EEF1A2 is a frequent event in localized PCa and is associated with histopathology features and a shorter biochemical recurrence-free survival. Due to its independence from serum PSA levels, EEF1A2 could serve as valuable biomarker in risk-stratification of localized PCa.

Multicellular tumor invasion and plasticity in biomimetic materials

Cancer cell invasion through the extracellular matrix is associated with metastatic spread and therapeutic resistance. In carcinomas, the detachment and dissemination of individual cells has been associated with an epithelial-mesenchymal transition, but tumors can also invade using collective, multicellular phenotypes. This malignant tumor progression is also associated with alignment and stiffening of the surrounding extracellular matrix. Historically, tumor invasion has been investigated using 2D monolayer culture, small animal models or patient histology. These assays have been complemented by the use of natural biomaterials such as reconstituted basement membrane and collagen I. More recently, engineered materials with well-defined physical, chemical and biomolecular properties have enabled more controlled microenvironments. In this review, we highlight recent developments in multicellular tumor invasion based on microfabricated structures or hydrogels. We emphasize the role of interfacial geometries, biomaterial stiffness, matrix remodeling, and co-culture models. Finally, we discuss future directions for the field, particularly integration with precision measurements of biomaterial properties and single cell heterogeneity, standardization and scale-up of these platforms, as well as integration with patient-derived samples.

Frequency and magnitude of intermittent hypoxia modulate endothelial wound healing in a cell culture model of sleep apnea

Intermittent hypoxia (IH) has been implicated in the cardiovascular consequences of obstructive sleep apnea (OSA). However, the lack of suitable experimental systems has precluded assessment as to whether IH is detrimental, protective, or both for the endothelium. The aim of the work was to determine the effects of frequency and amplitude of IH oxygenation swings on aortic endothelial wound healing. Monolayers of human primary endothelial cells were wounded and subjected to constant oxygenation (1%, 4%, 13%, or 20% O₂) or IH at different frequencies (0.6, 6, or 60 cycles/h) and magnitude ranges (13-4% O₂ or 20-1% O₂), using a novel well-controlled system, with wound healing being measured after 24 h. Cell monolayer repair was similar at 20% O₂ and 13% O₂, but was considerably increased (approximately twofold) in constant hypoxia at 4% O₂ The magnitude and frequency of IH considerably modulated wound healing. Cycles ranging 13-4% O₂ at the lowest frequency (0.6 cycles/h) accelerated endothelial wound healing by 102%. However, for IH exposures consisting of 20% to 1% O₂ oscillations, wound closure was reduced compared with oscillation in the 13-4% range (by 74% and 44% at 6 cycles/h and 0.6 cycles/h, respectively). High-frequency IH patterns simulating severe OSA (60 cycles/h) did not significantly modify endothelial wound closure, regardless of the oxygenation cycle amplitude. In conclusion, the frequency and magnitude of hypoxia cycling in IH markedly alter wound healing responses and emerge as key factors determining how cells will respond in OSA.NEW & NOTEWORTHY Intermittent hypoxia (IH) induces cardiovascular consequences in obstructive sleep apnea (OSA) patients. However, the vast array of frequencies and severities of IH previously employed in OSA-related experimental studies has led to controversial results on the effects of IH. By employing an optimized IH experimental system here, we provide evidence that the frequency and magnitude of IH markedly alter human aortic endothelial wound healing, emerging as key factors determining how cells respond in OSA.

Electrical Stimulation Increases Random Migration of Human Dermal Fibroblasts

Exogenous electrical stimulation (ES) has been investigated as a therapy for chronic wounds, as the skin produces currents and electrical fields (EFs) during wound healing. ES therapies operate by applying small EFs to the skin to mimic the transepithelial potentials that occur during the granulation phase of wound healing. Here, we investigated the effect of short duration (10 min) ES on the migration of HDFs using various magnitudes of physiologically relevant EFs. We modeled cutaneous injury by culturing HDFs in custom chambers that allowed the application of ES and then performed timelapse microscopy on a standard wound model. Using MATLAB to process cell coordinate data, we determined that the cells were migrating randomly and fit mean squared displacement data to the persistent random walk equation using nonlinear least squares regression analysis. Results indicated that application of 25-100 mV/mm DC EFs to HDFs on either uncoated or FN-coated surfaces demonstrated no significant changes in viability or proliferation. Of significance is that the HDFs increased random migration behavior under some ES conditions even after 10 min, providing a mechanism to enhance wound healing.

RAB27A, RAB27B and VPS36 are downregulated in advanced prostate cancer and show functional relevance in prostate cancer cells

Paracrine and long-range signaling via extracellular vesicles, such as exosomes and microvesicles, is deemed crucial for tumorigenesis, invasion and spread of solid tumors. The ESCRT machinery (endosomal sorting complexes required for transport) and Rab-proteins act as key players in vesicular trafficking and secretion. Yet, their role in prostate cancer (PCa) is unknown. Therefore, this study aimed to elucidate the relevance of these components in PCa. In silico reanalysis of genes with known involvement in vesicular trafficking and secretion in an existing microarray dataset revealed low expression of RAB27A, RAB27B and VPS36 to be predictive for reduced BCR-free survival in patients with localized PCa (p=0.033, 0.025 and 0.005). In the same microarray dataset underexpression of RAB27A, RAB27B and VPS36 was seen in distant metastases (p<0.001; p=0.003; p<0.001). This was consistent in two further microarray datasets. qRT-PCR-validation in two independent cohorts of PCa specimens (n=90) showed low expression of VPS36 in PCa tissue (p=0.023), especially in castration-resistant tumors (p=0.002). In all five datasets there were significant correlations between the expression of at least two of the candidates. Upon knockdown of VPS36 an increase of RAB27A and RAB27B expression, but not vice versa, was observed in both prostate and breast cancer cells (PC3, MDA-MB‑231). In PC3 cell knockdown of RAB27B and VPS36 dramatically reduced colony formation (-52.2%, p<0.001; -71.1%, p<0.001) and, controversial to reports in other tumor entities, increased the release of extracellular particles (+25.3%, p=0.014; +45.6%, p<0.001). Taken together RAB27A, RAB27B and VPS36 are frequently underexpressed in advanced PCa and are inversely correlated with PCa outcome. There seems to be a close relationship in the expression of RAB27A, RAB27B and VPS36, with RAB27A and RAB27B being dependent on VPS36. Changes in colony formation and particle release upon RNAi indicate an involvement in paracrine cell-cell communication.

Inference of Internal Stress in a Cell Monolayer

We combine traction force data with Bayesian inversion to obtain an absolute estimate of the internal stress field of a cell monolayer. The method, Bayesian inversion stress microscopy, is validated using numerical simulations performed in a wide range of conditions. It is robust to changes in each ingredient of the underlying statistical model. Importantly, its accuracy does not depend on the rheology of the tissue. We apply Bayesian inversion stress microscopy to experimental traction force data measured in a narrow ring of cohesive epithelial cells, and check that the inferred stress field coincides with that obtained by direct spatial integration of the traction force data in this quasi one-dimensional geometry.

A simple non-perturbing cell migration assay insensitive to proliferation effects

Migration is a fundamental cellular behavior that plays an indispensable role in development and homeostasis, but can also contribute to pathology such as cancer metastasis. Due to its relevance to many aspects of human health, the ability to accurately measure cell migration is of broad interest, and numerous approaches have been developed. One of the most commonly employed approaches, because of its simplicity and throughput, is the exclusion zone assay in which cells are allowed to migrate into an initially cell-free region. A major drawback of this assay is that it relies on simply counting cells in the exclusion zone and therefore cannot distinguish the effects of proliferation from migration. We report here a simple modification to the exclusion zone migration assay that exclusively measures cell migration and is not affected by proliferation. This approach makes use of a lineage-tracing vital stain that is retained through cell generations and effectively reads out migration relative to the original, parental cell population. This modification is simple, robust, non-perturbing, and inexpensive. We validate the method in a panel of cell lines under conditions that inhibit or promote migration and demonstrate its use in normal and cancer cell lines as well as primary cells.

Comparison between fibroblast wound healing and cell random migration assays in vitro

Cell migration plays a key role in many biological processes, including cancer growth and invasion, embryogenesis, angiogenesis, inflammatory response, and tissue repair. In this work, we compare two well-established experimental approaches for the investigation of cell motility in vitro: the cell random migration (CRM) and the wound healing (WH) assay. In the former, extensive tracking of individual live cells trajectories by time-lapse microscopy and elaborate data processing are used to calculate two intrinsic motility parameters of the cell population under investigation, i.e. the diffusion coefficient and the persistence time. In the WH assay, a scratch is made in a confluent cell monolayer and the closure time of the exposed area is taken as an easy-to-measure, empirical estimate of cell migration. To compare WH and CRM we applied the two assays to investigate the motility of skin fibroblasts isolated from wild type and transgenic mice (TgPED) overexpressing the protein PED/PEA-15, which is highly expressed in patients with type 2 diabetes. Our main result is that the cell motility parameters derived from CRM can be also estimated from a time-resolved analysis of the WH assay, thus showing that the latter is also amenable to a quantitative analysis for the characterization of cell migration. To our knowledge this is the first quantitative comparison of these two widely used techniques.

In vitro wound healing assays – state of the art

Wound healing is essential for the restoration of the barrier function of the skin. During this process, cells at the wound edges proliferate and migrate, leading to re-epithelialization of the wound surface. Wound healing assays are used to study the molecular mechanisms of wound repair, as well as in the investigation of potential therapeutics and treatments for improved healing. Numerous models of wound healing have been developed in recent years. In this review, we focus on in vitro assays, as they allow a fast, cost-efficient and ethical alternative to animal models. This paper gives a general overview of 2-dimensional (2D) cell monolayer assays by providing a description of injury methods, as well as an evaluation of each assay’s strengths and limitations. We include a section reviewing assays performed in 3-dimensional (3D) culture, which employ bioengineered skin models to capture complex wound healing mechanics like cell-matrix interactions and the interplay of different cell types in the healing process. Finally, we discuss in detail available software tools and algorithms for data analysis.

Establishing correlations in the en-mass migration of dermal fibroblasts on oriented fibrillar scaffolds

Wound healing proceeds via fibroblast migration along three dimensional fibrillar substrates with multiple angles between fibers. We have developed a technique for preparation of three dimensional fibrillar scaffolds with where the fiber diameters and the angles between adjacent fiber layers could be precisely controlled. Using the agarose droplet method we were able to make accurate determinations of the dependence of the migration speed, focal adhesion distribution, and nuclear deformation on the fiber diameter, fiber spacing, and angle between adjacent fiber layers. We found that on oriented single fiber layers, whose diameters exceeded 1 μm, large focal adhesion complexes formed in a linear arrangement along the fiber axis and cell motion was highly correlated. On multi layered scaffolds most of the focal adhesion sites reformed at the junction points and the migration speed was determined by the angle between adjacent fiber layers, which followed a parabolic function with a minimum at 30°. On these surfaces we observed a 25% increase in the number of focal adhesion points and a similar decrease in the degree of nuclear deformation, both phenomena associated with decreased mobility. These results underscore the importance of substrate morphology on the en-mass migration dynamics.

STATEMENT OF SIGNIFICANCE

En-mass fibroblast migration is an essential component of the wound healing process which can determine rate and scar formation. Yet, most publications on this topic have focused on single cell functions. Here we describe a new apparatus where we designed three dimensional fibrillar scaffolds with well controlled angles between junction points and highly oriented fiber geometries. We show that the motion of fibroblasts undergoing en-mass migration on these scaffolds can be controlled by the substrate topography. Significant differences in cell morphology and focal adhesions was found to exist between cells migrating on flat versus fibrillar scaffolds where the migration speed was found to be a function of the angle between fibers, the fiber diameter, and the distance between fibers.

Techniques and assays for the study of angiogenesis

The importance of studying angiogenesis, the formation of new blood vessels from pre-existing vessels, is underscored by its involvement in both normal physiology, such as embryonic growth and wound healing, and pathologies, such as diabetes and cancer. Treatments targeting the molecular drive of angiogenesis have been developed, but many of the molecular mechanisms that mediate vascularization, as well as how these mechanisms can be targeted in therapy, remain poorly understood. The limited capacity to quantify angiogenesis properly curtails our molecular understanding and development of new drugs and therapies. Although there are a number of assays for angiogenesis, many of them strip away its important components and/or limit control of the variables that direct this highly cooperative and complex process. Here we review assays commonly used in endothelial cell biology and describe the progress toward development of a physiologically realistic platform that will enable a better understanding of the molecular and physical mechanisms that govern angiogenesis.

Normal and tumoral melanocytes exhibit q-Gaussian random search patterns

In multicellular organisms, cell motility is central in all morphogenetic processes, tissue maintenance, wound healing and immune surveillance. Hence, failures in its regulation potentiates numerous diseases. Here, cell migration assays on plastic 2D surfaces were performed using normal (Melan A) and tumoral (B16F10) murine melanocytes in random motility conditions. The trajectories of the centroids of the cell perimeters were tracked through time-lapse microscopy. The statistics of these trajectories was analyzed by building velocity and turn angle distributions, as well as velocity autocorrelations and the scaling of mean-squared displacements. We find that these cells exhibit a crossover from a normal to a super-diffusive motion without angular persistence at long time scales. Moreover, these melanocytes move with non-Gaussian velocity distributions. This major finding indicates that amongst those animal cells supposedly migrating through Lévy walks, some of them can instead perform q-Gaussian walks. Furthermore, our results reveal that B16F10 cells infected by mycoplasmas exhibit essentially the same diffusivity than their healthy counterparts. Finally, a q-Gaussian random walk model was proposed to account for these melanocytic migratory traits. Simulations based on this model correctly describe the crossover to super-diffusivity in the cell migration tracks.

Motility of select ovarian cancer cell lines: effect of extra-cellular matrix proteins and the involvement of PAK2

The interaction between tumor cells and extracellular matrix (ECM) proteins influences cell migration and the invasive behavior of cancer cells. In this study, we provide experimental evidence that collagen I and fibronectin affect ovarian cancer cell migration. In vitro wound healing assays and transwell migration assays were used to measure both total wound healing and directionality of individually migrating OV2008 and C13 ovarian cancer cells on glass, collagen I and fibronectin. Involvement of p21-activated kinase 2 (Pak2) in the motility of these cell lines was investigated using a chemical inhibitor as well as siRNA transfection. Culturing ovarian cancer cells on collagen type I (COLL) increased the migratory ability of OV2008 and C13 cells by increasing the directional migration of cells. In contrast, fibronectin (FN) decreased the migratory ability of OV2008 cells by reducing their ability to migrate directionally. When both cell lines are cultured on COLL and treated with increasing concentrations of a PAK inhibitor (IPA-3), there is a dose-dependent response such that there is a decrease in migration with an increase in inhibitor concentration. Further experiments utilizing PAK2 knockdown via siRNA transfection demonstrated significantly reduced migration of OV2008 cells on COLL as compared to those receiving control siRNA. In conclusion, our results indicate that FN and COLL affect the motility of the selected ovarian cancer cells lines and the effect of COLL is likely mediated, at least in part, by PAK2. A better understanding of the molecular events that contribute to tumor invasion and metastasis is crucial for developing novel treatment strategies to improve the long-term survival of women with ovarian cancer. As PAK2 is involved in motility, it should be further explored as a pro-metastatic gene in ovarian cancer.

Assessing the role of spatial correlations during collective cell spreading

Spreading cell fronts are essential features of development, repair and disease processes. Many mathematical models used to describe the motion of cell fronts, such as Fisher's equation, invoke a mean–field assumption which implies that there is no spatial structure, such as cell clustering, present. Here, we examine the presence of spatial structure using a combination of in vitro circular barrier assays, discrete random walk simulations and pair correlation functions. In particular, we analyse discrete simulation data using pair correlation functions to show that spatial structure can form in a spreading population of cells either through sufficiently strong cell–to–cell adhesion or sufficiently rapid cell proliferation. We analyse images from a circular barrier assay describing the spreading of a population of MM127 melanoma cells using the same pair correlation functions. Our results indicate that the spreading melanoma cell populations remain very close to spatially uniform, suggesting that the strength of cell–to–cell adhesion and the rate of cell proliferation are both sufficiently small so as not to induce any spatial patterning in the spreading populations.

Are in vitro estimates of cell diffusivity and cell proliferation rate sensitive to assay geometry?

Cells respond to various biochemical and physical cues during wound-healing and tumour progression. in vitro assays used to study these processes are typically conducted in one particular geometry and it is unclear how the assay geometry affects the capacity of cell populations to spread, or whether the relevant mechanisms, such as cell motility and cell proliferation, are somehow sensitive to the geometry of the assay. In this work we use a circular barrier assay to characterise the spreading of cell populations in two different geometries. Assay 1 describes a tumour-like geometry where a cell population spreads outwards into an open space. Assay 2 describes a wound-like geometry where a cell population spreads inwards to close a void. We use a combination of discrete and continuum mathematical models and automated image processing methods to obtain independent estimates of the effective cell diffusivity, D, and the effective cell proliferation rate, λ. Using our parameterised mathematical model we confirm that our estimates of D and λ accurately predict the time-evolution of the location of the leading edge and the cell density profiles for both assay 1 and assay 2. Our work suggests that the effective cell diffusivity is up to 50% lower for assay 2 compared to assay 1, whereas the effective cell proliferation rate is up to 30% lower for assay 2 compared to assay 1.

Excess PLAC8 promotes an unconventional ERK2-dependent EMT in colon cancer

The epithelial-to-mesenchymal transition (EMT) transcriptional program is characterized by repression of E-cadherin (CDH1) and induction of N-cadherin (CDH2), and mesenchymal genes like vimentin (VIM). Placenta-specific 8 (PLAC8) has been implicated in colon cancer; however, how PLAC8 contributes to disease is unknown, and endogenous PLAC8 protein has not been studied. We analyzed zebrafish and human tissues and found that endogenous PLAC8 localizes to the apical domain of differentiated intestinal epithelium. Colon cancer cells with elevated PLAC8 levels exhibited EMT features, including increased expression of VIM and zinc finger E-box binding homeobox 1 (ZEB1), aberrant cell motility, and increased invasiveness. In contrast to classical EMT, PLAC8 overexpression reduced cell surface CDH1 and upregulated P-cadherin (CDH3) without affecting CDH2 expression. PLAC8-induced EMT was linked to increased phosphorylated ERK2 (p-ERK2), and ERK2 knockdown restored cell surface CDH1 and suppressed CDH3, VIM, and ZEB1 upregulation. In vitro, PLAC8 directly bound and inactivated the ERK2 phosphatase DUSP6, thereby increasing p-ERK2. In a murine xenograft model, knockdown of endogenous PLAC8 in colon cancer cells resulted in smaller tumors, reduced local invasion, and decreased p-ERK2. Using MultiOmyx, a multiplex immunofluorescence-based methodology, we observed coexpression of cytosolic PLAC8, CDH3, and VIM at the leading edge of a human colorectal tumor, supporting a role for PLAC8 in cancer invasion in vivo.

An introduction to the wound healing assay using live-cell microscopy

The wound healing assay is used in a range of disciplines to study the coordinated movement of a cell population. In this technical review, we describe the workflow of the wound healing assay as monitored by optical microscopy. Although the assay is straightforward, a lack of standardization in its application makes it difficult to compare results and reproduce experiments among researchers. We recommend general guidelines for consistency, including: (1) sample preparation including the creation of the gap, (2) microscope equipment requirements, (3) image acquisition, and (4) the use of image analysis to measure the gap size and its rate of closure over time. We also describe parameters that are specific to the particular research question, such as seeding density and matrix coatings. All of these parameters must be carefully controlled within a given set of experiments in order to achieve accurate and reproducible results.

Collective Cell Migration: A Mechanistic Perspective

Collective cell migration is fundamental to gaining insights into various important biological processes such as wound healing and cancer metastasis. In particular, recent in vitro studies and in silico simulations suggest that mechanics can explain the social behavior of multicellular clusters to a large extent with minimal knowledge of various cellular signaling pathways. These results suggest that a mechanistic perspective is necessary for a comprehensive and holistic understanding of collective cell migration, and this review aims to provide a broad overview of such a perspective.

CellMissy: a tool for management, storage and analysis of cell migration data produced in wound healing-like assays

SUMMARY

Automated image processing has allowed cell migration research to evolve to a high-throughput research field. As a consequence, there is now an unmet need for data management in this domain. The absence of a generic management system for the quantitative data generated in cell migration assays results in each dataset being treated in isolation, making data comparison across experiments difficult. Moreover, by integrating quality control and analysis capabilities into such a data management system, the common practice of having to manually transfer data across different downstream analysis tools will be markedly sped up and made more robust. In addition, access to a data management solution creates gateways for data standardization, meta-analysis and structured public data dissemination. We here present CellMissy, a cross-platform data management system for cell migration data with a focus on wound healing data. CellMissy simplifies and automates data management, storage and analysis from the initial experimental set-up to data exploration.

AVAILABILITY AND IMPLEMENTATION

CellMissy is a cross-platform open-source software developed in Java. Source code and cross-platform binaries are freely available under the Apache2 open source license at http://cellmissy.googlecode.com.

Sensitivity of edge detection methods for quantifying cell migration assays

Quantitative imaging methods to analyze cell migration assays are not standardized. Here we present a suite of two-dimensional barrier assays describing the collective spreading of an initially-confined population of 3T3 fibroblast cells. To quantify the motility rate we apply two different automatic image detection methods to locate the position of the leading edge of the spreading population after , and hours. These results are compared with a manual edge detection method where we systematically vary the detection threshold. Our results indicate that the observed spreading rates are very sensitive to the choice of image analysis tools and we show that a standard measure of cell migration can vary by as much as 25% for the same experimental images depending on the details of the image analysis tools. Our results imply that it is very difficult, if not impossible, to meaningfully compare previously published measures of cell migration since previous results have been obtained using different image analysis techniques and the details of these techniques are not always reported. Using a mathematical model, we provide a physical interpretation of our edge detection results. The physical interpretation is important since edge detection algorithms alone do not specify any physical measure, or physical definition, of the leading edge of the spreading population. Our modeling indicates that variations in the image threshold parameter correspond to a consistent variation in the local cell density. This means that varying the threshold parameter is equivalent to varying the location of the leading edge in the range of approximately 1–5% of the maximum cell density.