Dynamics of TGF-β induced epithelial-to-mesenchymal transition monitored by Electric Cell-Substrate Impedance Sensing

Classifying contaminated cell cultures using time series features

We examine the use of time series data, derived from Electric Cell-substrate Impedance Sensing (ECIS), to differentiate between standard mammalian cell cultures and those infected with a mycoplasma organism. With the goal of easy visualization and interpretation, we perform low-dimensional feature-based classification, extracting application-relevant features from the ECIS time courses. We can achieve very high classification accuracy using only two features, which depend on the cell line under examination. Initial results also show the existence of experimental variation between plates and suggest types of features that may prove more robust to such variation. Our paper is the first to perform a broad examination of ECIS time course features in the context of detecting contamination; to combine different types of features to achieve classification accuracy while preserving interpretability; and to describe and suggest possibilities for ameliorating plate-to-plate variation.

Time-Series Clustering of Single-Cell Trajectories in Collective Cell Migration

Simple Summary

In this study, we normalized trajectories containing both mesenchymal and epithelial cells to remove the effect of cell location on clustering, and performed a dimensionality reduction on the time series data before clustering. When the clustering results were superimposed on the trajectories prior to normalization, the results still showed similarities in location, indicating that this method can find cells with similar migration patterns. These data highlight the reliability of this method in identifying consistent migration patterns in collective cell migration.

Abstract

Collective invasion drives multicellular cancer cells to spread to surrounding normal tissues. To fully comprehend metastasis, the methodology of analysis of individual cell migration in tissue should be well developed. Extracting and classifying cells with similar migratory characteristics in a colony would facilitate an understanding of complex cell migration patterns. Here, we used electrospun fibers as the extracellular matrix for the in vitro modeling of collective cell migration, clustering of mesenchymal and epithelial cells based on trajectories, and analysis of collective migration patterns based on trajectory similarity. We normalized the trajectories to eliminate the effect of cell location on clustering and used uniform manifold approximation and projection to perform dimensionality reduction on the time-series data before clustering. When the clustering results were superimposed on the trajectories before normalization, the results still exhibited positional similarity, thereby demonstrating that this method can identify cells with similar migration patterns. The same cluster contained both mesenchymal and epithelial cells, and this result was related to cell location and cell division. These data highlight the reliability of this method in identifying consistent migration patterns during collective cell migration. This provides new insights into the epithelial–mesenchymal interactions that affect migration patterns.

Optical Cellular Micromotion: A New Paradigm to Measure Tumor Cells Invasion within Gels Mimicking the 3D Tumor Environments

Measuring tumor cell invasiveness through 3D tissues, particularly at the single-cell level, can provide important mechanistic understanding and assist in identifying therapeutic targets of tumor invasion. However, current experimental approaches, including standard in vitro invasion assays, have limited physiological relevance and offer insufficient insight into the vast heterogeneity in tumor cell migration through tissues. To address these issues, here the concept of optical cellular micromotion is reported on, where digital holographic microscopy is used to map the optical nano- to submicrometer thickness fluctuations within single-cells. These fluctuations are driven by the dynamic movement of subcellular structures including the cytoskeleton and inherently associated with the biological processes involved in cell invasion within tissues. It is experimentally demonstrated that the optical cellular micromotion correlates with tumor cells motility and invasiveness both at the population and single-cell levels. In addition, the optical cellular micromotion significantly reduced upon treatment with migrastatic drugs that inhibit tumor cell invasion. These results demonstrate that micromotion measurements can rapidly and non-invasively determine the invasive behavior of single tumor cells within tissues, yielding a new and powerful tool to assess the efficacy of approaches targeting tumor cell invasiveness.

Dynamic Monitoring of EMT in CTCs as an Indicator of Cancer Metastasis

Epithelial to mesenchymal transition (EMT) results in the genesis of circulating tumor cells (CTCs) from tumor sites and promotes the metastatic capability of CTCs in circulation. In this study, we develop a multiplex surface-enhanced Raman scattering nanotechnology for comprehensive characterization of EMT-associated phenotypes in CTCs, to monitor cancer metastasis. We observe the downregulation of the CTC marker (EpCAM) and the epithelial marker (E-cadherin), as well as the upregulation of a mesenchymal marker (N-cadherin) and a stem cell marker (ABCB5) during the transforming growth factor-β-induced EMT process in breast cancer cell line models. Additionally, we also find changes in the heterogeneity levels of these selected markers in cells. With this method, we successfully detect the presence of disease in samples from breast cancer patients and characterize EMT-associated phenotypes in their CTCs. Overall, this approach and findings provide a new means for monitoring the EMT process in cancer, insights into the detailed mechanistic progress of the diseases, and have potential for detecting the early occurrence of cancer metastasis.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) – particularly by cancer-associated fibroblasts – on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

A non-contact impedimetric biosensing system for classification of toxins associated with cytotoxicity testing

We report on a novel impedance spectroscopy measurement and data analysis technique for cytotoxicity testing. The technique combines non-contact measurement with real-time impedance data analysis based on the toxin dose dependency of the outputs, making it suitable for high throughput screening. A multi-electrode array was designed and fabricated such that a standard well plate could be positioned above the electrodes, negating the requirement for bespoke culture wells with integrated electrodes. For cytotoxicity testing, endothelial cells, type ECV304, within the wells were exposed to various concentrations of 3 toxins, dimethyl sulphoxide, cadmium chloride and saponin, which exhibit different modes of action on cells. Impedance spectra were recorded every 30 min over a 24 h period. From the spectra 'toxin maps' were produced which presented the correlation between impedance output and dose of toxin versus frequency and time. The results demonstrated characteristic toxin maps for each toxin and significantly differences between the three toxins studied. Using complementary measurement methods, we showed that these differences in toxin maps related to morphological and physiological changes in the cells due to the differing mode of action of each toxin.

An evaluation of the impact of clinical bacterial isolates on epithelial cell monolayer integrity by the electric Cell-Substrate Impedance Sensing (ECIS) method

Virulence is the relative capacity of a pathogenic microorganism to cause damage in susceptible host cells such as those found in airway passages and the gut. In this study, the effect of clinical bacterial isolates on the monolayer integrity of cultured human alveolar basal epithelial cells (A549) was evaluated using the Electric Cell-Substrate Impedance Sensing (ECIS) system. ECIS is a morphological biosensor which records electrical properties of cell-covered microelectrodes in an AC circuit including impedance (ohm), resistance (ohm), and capacitance (μFarad). In the current study, fluctuations in the electrical properties of cell-covered microelectrodes reflect dynamic changes in cell morphology resulting from disrupted cell monolayers following exposure to bacteria. Using the ECIS system, real-time changes of cell morphology and disruption of monolayer integrity of cell-cultures in vitro were revealed for A549 cells infected with either Pseudomonas aeruginosa, ESBL Escherichia coli, Staphylococcus aureus (MRSA), or Enterococcus (VRE). We determined empirically that the optimal signal response was obtained for resistance (ohm) measurements at 4000 hertz. Following infection of A549 cells, the data revealed that Pseudomonas aeruginosa resulted in little change in microelectrode resistance (ohm @4 kHz) as compared to pathogen-free controls within the first 12 h. In contrast, E. coli, MRSA, and VRE caused significant changes in electrode resistance (ohm @4 kHz) values in the infected cells compared to controls over the first 5 h. Resistance (ohm @4 kHz) changes were also observed in cell monolayers infected with different bacterial concentrations for all isolates over 24 h. The highest concentration of bacteria caused the measured resistance (ohm @4 kHz) to drop faster than its' immediate lower concentration, suggesting a dose-dependent effect. Compared to live bacteria, cells exposed to heat-killed bacteria did not show significant changes in resistance (ohm @4 kHz) over 48 h post-exposure. Functionally, cytokine responses were different between cells treated with live and heat-killed bacteria. Of note, live bacteria induced IFNγ, IL-13, and IL-1β production in A549 cells, whereas heat-killed bacteria induced IL-8 production suggesting a differential interaction with cells that could reveal the underlying causes of resistance (ohm @4 kHz) changes. Our findings indicate that ECIS provides a means to quantify, automate, and measure bacterial virulence, which may have broader implications governing the course of treatment compared to traditional methods alone.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) - particularly by cancer-associated fibroblasts - on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

C1 CAGE detects transcription start sites and enhancer activity at single-cell resolution

Single-cell transcriptomic profiling is a powerful tool to explore cellular heterogeneity. However, most of these methods focus on the 3′-end of polyadenylated transcripts and provide only a partial view of the transcriptome. We introduce C1 CAGE, a method for the detection of transcript 5′-ends with an original sample multiplexing strategy in the C1^TM microfluidic system. We first quantifiy the performance of C1 CAGE and find it as accurate and sensitive as other methods in the C1 system. We then use it to profile promoter and enhancer activities in the cellular response to TGF-β of lung cancer cells and discover subpopulations of cells differing in their response. We also describe enhancer RNA dynamics revealing transcriptional bursts in subsets of cells with transcripts arising from either strand in a mutually exclusive manner, validated using single molecule fluorescence in situ hybridization.

Single-cell transcriptomic profiling allows the exploration of cellular heterogeneity but commonly focuses on the 3′-end of the transcript. Here the authors introduce C1 CAGE, which detects the 5′ transcript end in a multiplexed microfluidic system.

Combining stem cell-derived hepatocytes with impedance sensing to better predict human drug toxicity

Background: The liver plays a central role in human drug metabolism. To model drug metabolism, the major cell type of the liver, the hepatocyte, is commonly used. Hepatocytes can be derived from human and animal sources, including pluripotent stem cells. Cell-based models have shown promise in modeling human drug exposure. The assays used in those studies are normally 'snap-shot' in nature, and do not provide the complete picture of human drug exposure. Research design and methods: In this study, we employ stem cell-derived hepatocytes and impedance sensing to model human drug toxicity. This impedance-based stem cell assay reports hepatotoxicity in real time after treatment with compounds provided by industry. Results: Using electric cell-substrate impedance Sensing (ECIS), we were able to accurately measure drug toxicity post-drug exposure in real time and more quickly than gold standard biochemical assays. Conclusions: ECIS is robust and non-destructive methodology capable of monitoring human drug exposure with superior performance to current gold standard 'snapshot' assays. We believe that the methodology presented within this article could prove valuable in the quest to better predict off-target effects of drugs in humans.

Real-Time Bioimpedance Sensing of Antifibrotic Drug Action in Primary Human Cells

Fibrotic diseases are among the most serious health issues with severe burdens due to their chronic nature and a large number of patients suffering from the debilitating effects and long-term sequelae. Collagenase treatment is a nonsurgical option but has limited results. To date, there is no potent noninvasive solution for fibrosis. Part of the reason for this is the lack of appropriate in vitro live cell screening tools to assess the efficacy of new therapeutical agents. Here, we demonstrate the utility of a cell-based electrochemical impedance biosensor platform to screen the efficacy of potential antifibrotic compounds. The platform employs a label-free and noninvasive strategy to detect the progression of fibrosis and the potency of the antifibrotic molecules in real-time. The fundamental principle that governs this novel system is that dynamic changes in cell shape and adhesion during fibrosis can be measured accurately by monitoring the changes in the impedance. This is achieved by growing the cells on a transparent interdigitated indium tin oxide (ITO) electrodes. It was demonstrated by monitoring the efficacy of a model antifibrotic compound, PXS64, on cells collected from patients with Dupuytren's contracture. We confirmed the validity of the developed biochemical impedance biosensor as an tool for in vitro screening of antifibrotic compounds and provided quantitative information on subcellular influences of the examined chemical molecules using correlative microscopy analyses that monitor the average cell area, cell morphology, and the amount and directionality of the deposited extracellular matrix protein collagen and measurement of cytosolic Ca²⁺ changes.

Cell-Substrate Dynamics of the Epithelial-to-Mesenchymal Transition

The biological process of the epithelial-to-mesenchymal transition (EMT) allows epithelial cells to enhance their migratory and invasive behavior and plays a key role in embryogenesis, fibrosis, wound healing, and metastasis. Among the multiple biochemical changes from an epithelial to a mesenchymal phenotype, the alteration of cellular dynamics in cell-cell as well as cell-substrate contacts is crucial. To determine these variations over the whole time scale of the EMT, we measure the cell-substrate distance of epithelial NMuMG cells during EMT using our newly established metal-induced energy transfer (MIET) microscopy, which allows one to achieve nanometer axial resolution. We show that, in the very first hours of the transition, the cell-substrate distance increases substantially, but later in the process after reaching the mesenchymal state, this distance is reduced again to the level of untreated cells. These findings relate to a change in the number of adhesion points and will help to better understand remodeling processes associated with wound healing, embryonic development, cancer progression, or tissue regeneration.

Crosstalk of cardiomyocytes and fibroblasts in co-cultures

Electromechanical function of cardiac muscle depends critically on the crosstalk of myocytes with non-myocytes. Upon cardiac fibrosis, fibroblasts translocate into infarcted necrotic tissue and alter their communication capabilities. In the present in vitro study, we determined a multiple parameter space relevant for fibrotic cardiac tissue development comprising the following essential processes: (i) adhesion to substrates with varying elasticity, (ii) dynamics of contractile function, and (iii) electromechanical connectivity. By combining electric cell-substrate impedance sensing (ECIS) with conventional optical microscopy, we could measure the impact of fibroblast–cardiomyocyte ratio on the aforementioned parameters in a non-invasive fashion. Adhesion to electrodes was quantified via spreading rates derived from impedance changes, period analysis allowed us to measure contraction dynamics and modulations of the barrier resistance served as a measure of connectivity. In summary, we claim that: (i) a preferred window for substrate elasticity around 7 kPa for low fibroblast content exists, which is shifted to stiffer substrates with increasing fibroblast fractions. (ii) Beat frequency decreases nonlinearly with increasing fraction of fibroblasts, while (iii) the intercellular resistance increases with a maximal functional connectivity at 75% fibroblasts. For the first time, cardiac cell–cell junction density-dependent connectivity in co-cultures of cardiomyocytes and fibroblasts was quantified using ECIS.

Impedance analysis of GPCR-mediated changes in endothelial barrier function: overview and fundamental considerations for stable and reproducible measurements

The past 20 years has seen significant growth in using impedance-based assays to understand the molecular underpinning of endothelial and epithelial barrier function in response to physiological agonists and pharmacological and toxicological compounds. Most studies on barrier function use G protein-coupled receptor (GPCR) agonists which couple to fast and transient changes in barrier properties. The power of impedance-based techniques such as electric cell-substrate impedance sensing (ECIS) resides in its ability to detect minute changes in cell layer integrity label-free and in real-time ranging from seconds to days. We provide a comprehensive overview of the biophysical principles, applications, and recent developments in impedance-based methodologies. Despite extensive application of impedance analysis in endothelial barrier research, little attention has been paid to data analysis and critical experimental variables, which are both essential for signal stability and reproducibility. We describe the rationale behind common ECIS data presentation and interpretation and illustrate practical guidelines to improve signal intensity by adapting technical parameters such as electrode layout, monitoring frequency, or parameter (resistance versus impedance magnitude). Moreover, we discuss the impact of experimental parameters, including cell source, liquid handling, and agonist preparation on signal intensity and kinetics. Our discussions are supported by experimental data obtained from human microvascular endothelial cells challenged with three GPCR agonists, thrombin, histamine, and sphingosine-1-phosphate.

Endothelial to Mesenchymal Transition Contributes to Endothelial Dysfunction in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by lung endothelial cell dysfunction and vascular remodeling. Normally, the endothelium forms an integral cellular barrier to regulate vascular homeostasis. During embryogenesis endothelial cells exhibit substantial plasticity that contribute to cardiac development by undergoing endothelial-to-mesenchymal transition (EndoMT). We determined the presence of EndoMT in the pulmonary vasculature in vivo and the functional effects on pulmonary artery endothelial cells (PAECs) undergoing EndoMT in vitro. Histologic assessment of patients with systemic sclerosis-associated PAH and the hypoxia/SU5416 mouse model identified the presence von Willebrand factor/α-smooth muscle actin-positive endothelial cells in up to 5% of pulmonary vessels. Induced EndoMT in PAECs by inflammatory cytokines IL-1β, tumor necrosis factor α, and transforming growth factor β led to actin cytoskeleton reorganization and the development of a mesenchymal morphology. Induced EndoMT cells exhibited up-regulation of mesenchymal markers, including collagen type I and α-smooth muscle actin, and a reduction in endothelial cell and junctional proteins, including von Willebrand factor, CD31, occludin, and vascular endothelial-cadherin. Induced EndoMT monolayers failed to form viable biological barriers and induced enhanced leak in co-culture with PAECs. Induced EndoMT cells secreted significantly elevated proinflammatory cytokines, including IL-6, IL-8, and tumor necrosis factor α, and supported higher immune transendothelial migration compared with PAECs. These findings suggest that EndoMT may contribute to the development of PAH.

Real-time quantitative monitoring of hiPSC-based model of macular degeneration on Electric Cell-substrate Impedance Sensing microelectrodes

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world. Humanized disease models are required to develop new therapies for currently incurable forms of AMD.

In this work, a tissue-on-a-chip approach was developed through combining human induced pluripotent stem cells, Electric Cell–substrate Impedance Sensing (ECIS) and reproducible electrical wounding assays to model and quantitatively study AMD. Retinal Pigment Epithelium (RPE) cells generated from a patient with an inherited macular degeneration and from an unaffected sibling were used to test the model platform on which a reproducible electrical wounding assay was conducted to model RPE damage. First, a robust and reproducible real-time quantitative monitoring over a 25-day period demonstrated the establishment and maturation of RPE layers on the microelectrode arrays. A spatially controlled RPE layer damage that mimicked cell loss in AMD disease was then initiated. Post recovery, significant differences (P<0.01) in migration rates were found between case (8.6±0.46 μm/h) and control cell lines (10.69±0.21 μm/h). Quantitative data analysis suggested this was achieved due to lower cell–substrate adhesion in the control cell line. The ECIS cell–substrate adhesion parameter (α) was found to be 7.8±0.28 Ω^1/2 cm for the case cell line and 6.5±0.15 Ω^1/2 cm for the control. These findings were confirmed using cell adhesion biochemical assays. The developed disease model-on-a-chip is a powerful platform for translational studies with considerable potential to investigate novel therapies by enabling real-time, quantitative and reproducible patient-specific RPE cell repair studies.

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hiPSC-RPE model was established and characterised on ECIS microelectrode arrays.

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A reproducible electrical wound healing assay was used to mimic RPE cell damage.

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Significant differences in migration rates were found between case and control.

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Cells recovered through mesenchymal migration mirrored by impedance fluctuations.

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Case cell line showed significantly higher adhesion than the control cell line.

The effect of surface charge on nonspecific uptake and cytotoxicity of CdSe/ZnS core/shell quantum dots

In this work, cytotoxicity and cellular impedance response was compared for CdSe/ZnS core/shell quantum dots (QDs) with positively charged cysteamine-QDs, negatively charged dihydrolipoic acid-QDs and zwitterionic D-penicillamine-QDs exposed to canine kidney MDCKII cells. Pretreatment of cells with pharmacological inhibitors suggested that the uptake of nanoparticles was largely due to receptor-independent pathways or spontaneous entry for carboxylated and zwitterionic QDs, while for amine-functionalized particles involvement of cholesterol-enriched membrane domains is conceivable. Cysteamine-QDs were found to be the least cytotoxic, while D-penicillamine-QDs reduced the mitochondrial activity of MDCKII by 20-25%. Although the cell vitality appeared unaffected (assessed from the changes in mitochondrial activity using a classical MTS assay after 24 h of exposure), the binding of QDs to the cellular interior and their movement across cytoskeletal filaments (captured and characterized by single-particle tracking), was shown to compromise the integrity of the cytoskeletal and plasma membrane dynamics, as evidenced by electric cell-substrate impedance sensing.

Migratory and adhesive properties of Xenopus laevis primordial germ cells in vitro

The directional migration of primordial germ cells (PGCs) to the site of gonad formation is an advantageous model system to study cell motility. The embryonic development of PGCs has been investigated in different animal species, including mice, zebrafish, Xenopus and Drosophila. In this study we focus on the physical properties of Xenopus laevis PGCs during their transition from the passive to the active migratory state. Pre-migratory PGCs from Xenopus laevis embryos at developmental stages 17–19 to be compared with migratory PGCs from stages 28–30 were isolated and characterized in respect to motility and adhesive properties. Using single-cell force spectroscopy, we observed a decline in adhesiveness of PGCs upon reaching the migratory state, as defined by decreased attachment to extracellular matrix components like fibronectin, and a reduced adhesion to somatic endodermal cells. Data obtained from qPCR analysis with isolated PGCs reveal that down-regulation of E-cadherin might contribute to this weakening of cell-cell adhesion. Interestingly, however, using an in vitro migration assay, we found that movement of X. laevis PGCs can also occur independently of specific interactions with their neighboring cells. The reduction of cellular adhesion during PGC development is accompanied by enhanced cellular motility, as reflected in increased formation of bleb-like protrusions and inferred from electric cell-substrate impedance sensing (ECIS) as well as time-lapse image analysis. Temporal alterations in cell shape, including contraction and expansion of the cellular body, reveal a higher degree of cellular dynamics for the migratory PGCs in vitro.

Tension monitoring during epithelial-to-mesenchymal transition links the switch of phenotype to expression of moesin and cadherins in NMuMG cells

Structural alterations during epithelial-to-mesenchymal transition (EMT) pose a substantial challenge to the mechanical response of cells and are supposed to be key parameters for an increased malignancy during metastasis. Herein, we report that during EMT, apical tension of the epithelial cell line NMuMG is controlled by cell-cell contacts and the architecture of the underlying actin structures reflecting the mechanistic interplay between cellular structure and mechanics. Using force spectroscopy we find that tension in NMuMG cells slightly increases 24 h after EMT induction, whereas upon reaching the final mesenchymal-like state characterized by a complete loss of intercellular junctions and a concerted down-regulation of the adherens junction protein E-cadherin, the overall tension becomes similar to that of solitary adherent cells and fibroblasts. Interestingly, the contribution of the actin cytoskeleton on apical tension increases significantly upon EMT induction, most likely due to the formation of stable and highly contractile stress fibers which dominate the elastic properties of the cells after the transition. The structural alterations lead to the formation of single, highly motile cells rendering apical tension a good indicator for the cellular state during phenotype switching. In summary, our study paves the way towards a more profound understanding of cellular mechanics governing fundamental morphological programs such as the EMT.

Dielectric spectroscopy as a viable biosensing tool for cell and tissue characterization and analysis

The use of dielectric spectroscopy to carry out real time observations of cells and to extract a wealth of information about their physiological properties has expanded in recent years. This popularity is due to the simple, easy to use, non-invasive and real time nature of dielectric spectroscopy. The ease of integrating dielectric spectroscopy with microfluidic devices has allowed the technology to further expand into biomedical research. Dielectric spectra are obtained by applying an electrical signal to cells, which is swept over a frequency range. This review covers the different methods of interpreting dielectric spectra and progress made in applications of impedance spectroscopy for cell observations. First, methods of obtaining specific electrical properties of cells (cell membrane capacitance and cytoplasm conductivity) are discussed. These electrical properties are obtained by fitting the dielectric spectra to different models and equations. Integrating models to reduce the effects of the electrical double layer are subsequently covered. Impedance platforms are then discussed including electrical cell substrate impedance sensing (ECIS). Categories of ECIS systems are divided into microelectrode arrays, interdigitated electrodes and those that allow differential ECIS measurements. Platforms that allow single cell and sub-single cell measurements are then discussed. Finally, applications of impedance spectroscopy in a range of cell observations are elaborated. These applications include observing cell differentiation, mitosis and the cell cycle and cytotoxicity/cell death. Future applications such as drug screening and in point of care applications are then covered.