On the role of mechanics in driving mesenchymal-to-epithelial transitions

Measurement of adhesion and traction of cells at high yield (MATCHY) reveals an energetic ratchet driving nephron condensation

Engineering of embryonic strategies for tissue-building has extraordinary promise for regenerative medicine. This has led to a resurgence in interest in the relationship between cell biophysical properties and morphological transitions. However, mapping gene or protein expression data to cell biophysical properties to physical morphogenesis remains challenging with current techniques. Here we present MATCHY (multiplexed adhesion and traction of cells at high yield). MATCHY advances the multiplexing and throughput capabilities of existing traction force and cell-cell adhesion assays using microfabrication and an automated computation scheme with machine learning-driven cell segmentation. Both biophysical assays are coupled with serial downstream immunofluorescence to extract cell type/signaling state information. MATCHY is especially suited to complex primary tissue-, organoid-, or biopsy-derived cell mixtures since it does not rely on a priori knowledge of cell surface markers, cell sorting, or use of lineage-specific reporter animals. We first validate MATCHY on canine kidney epithelial cells engineered for RET tyrosine kinase expression and quantify a relationship between downstream signaling and cell traction. We go on to create a biophysical atlas of primary cells dissociated from the mouse embryonic kidney and use MATCHY to identify distinct biophysical states along the nephron differentiation trajectory. Our data complement expression-level knowledge of adhesion molecule changes that accompany nephron differentiation with quantitative biophysical information. These data reveal an 'energetic ratchet' that explains spatial nephron progenitor cell condensation from the niche as they differentiate, which we validate through agent-based computational simulation. MATCHY offers automated cell biophysical characterization at >104-cell throughput, a highly enabling advance for fundamental studies and new synthetic tissue design strategies for regenerative medicine.

Biological Characteristics and Pathogenesis of Monkeypox Virus: An Overview

Although the smallpox virus has been eradicated worldwide, the World Health Organization (WHO) has issued a warning about the virus's potential to propagate globally. The WHO labeled monkeypox a world public health emergency in July 2022, requiring urgent prevention and treatment. The monkeypox virus is a part of the Poxviridae family, Orthopoxvirus genus, and is accountable for smallpox, which has killed over a million people in the past. Natural hosts of the virus include squirrels, Gambian rodents, chimpanzees, and other monkeys. The monkeypox virus has transmitted to humans through primary vectors (various animal species) and secondary vectors, including direct touch with lesions, breathing particles from body fluids, and infected bedding. The viral particles are ovoid or brick-shaped, 200-250 nm in diameter, contain a single double-stranded DNA molecule, and reproduce only in the cytoplasm of infected cells. Monkeypox causes fever, cold, muscle pains, headache, fatigue, and backache. The phylogenetic investigation distinguished between two genetic clades of monkeypox: the more pathogenic Congo Basin clade and the West Africa clade. In recent years, the geographical spread of the human monkeypox virus has accelerated despite a paucity of information regarding the disease's emergence, ecology, and epidemiology. Using lesion samples and polymerase chain reaction (PCR), the monkeypox virus was diagnosed. In the USA, the improved Ankara vaccine can now be used to protect people who are at a higher risk of getting monkeypox. Antivirals that we have now work well against smallpox and may stop the spread of monkeypox, but there is no particular therapy for monkeypox.

Unlocking cellular plasticity: Enhancing human iPSC reprogramming through bromodomain inhibition and extracellular matrix gene expression regulation

The transformation of fibroblasts into epithelial cells is critical for iPSC reprogramming. In this report, we describe studies with PFI-3, a small molecule inhibitor that specifically targets the bromodomains of SMARCA2/4 and PBRM1 subunit of SWI/SNF complex, as an enhancer of iPSC reprogramming efficiency. Our findings revealed that PFI-3 induces cellular plasticity in multiple human dermal fibroblasts, leading to a mesenchymal-epithelial transition (MET) during iPSC formation. This transition was characterized by the upregulation of E-cadherin expression, a key protein involved in epithelial cell adhesion. Additionally, we identified COL11A1 as a reprogramming barrier and demonstrated COL11A1 knockdown increased reprogramming efficiency. Notably, we found that PFI-3 significantly reduced the expression of numerous extracellular matrix (ECM) genes, particularly those involved in collagen assembly. Our research provides key insights into the early stages of iPSC reprogramming, highlighting the crucial role of ECM changes and cellular plasticity in this process.

Targeting the KRT16-vimentin axis for metastasis in lung cancer

Lung cancer is the most diagnosed malignant cancer and the leading cause of cancer-related deaths worldwide, with advanced stage and metastasis being a major issue. The mechanism leading to metastasis is not yet understood. Here, we found that KRT16 is upregulated in metastatic lung cancer tissues and correlated with poor overall survival. Knockdown of KRT16 inhibits metastasis of lung cancer both in vitro and in vivo. Mechanistically, KRT16 interacts with vimentin, and depletion of KRT16 leads to downregulation of vimentin. KRT16 acquired its oncogenic ability by stabilizing vimentin, and vimentin is required for KRT16-driven metastasis. FBXO21 mediates the polyubiquitination and degradation of KRT16, and vimentin inhibits KRT16 ubiquitination and degradation by impairing its interaction with FBXO21. Significantly, IL-15 inhibits metastasis of lung cancer in a mouse model through upregulation of FBXO21, and the level of IL-15 in circulating serum was significantly higher in nonmetastatic lung cancer patients than in metastatic patients. Our findings indicate that targeting the FBXO21/KRT16/vimentin axis may benefit lung cancer patients with metastasis.

A novel tool for the unbiased characterization of epithelial monolayer development in culture

The function of an epithelial tissue is intertwined with its architecture. Epithelial tissues are often described as pseudo-two-dimensional, but this view may be partly attributed to experimental bias: many model epithelia, including cultured cell lines, are easiest to image from the "top-down." We measured the three-dimensional architecture of epithelial cells in culture and found that it varies dramatically across cultured regions, presenting a challenge for reproducibility and cross-study comparisons. We therefore developed a novel tool (Automated Layer Analysis, "ALAn") to characterize architecture in an unbiased manner. Using ALAn, we find that cultured epithelial cells can organize into four distinct architectures and that architecture correlates with cell density. Cells exhibit distinct biological properties in each architecture. Organization in the apical-basal axis is determined early in monolayer development by substrate availability, while disorganization in the apical-basal axis arises from an inability to form substrate connections. Our work highlights the need to carefully control for three-dimensional architecture when using cell culture as a model system for epithelial cell biology and introduces a novel tool, built on a set of rules that can be widely applied to epithelial cell culture.

Role of fibroblast plasticity and heterogeneity in modulating angiogenesis and healing in the diabetic foot ulcer

Chronic diabetic foot ulcers (DFUs) are an important clinical issue faced by clinicians despite the advanced treatment strategies consisting of wound debridement, off-loading, medication, wound dressings, and keeping the ulcer clean. Non-healing DFUs are associated with the risk of amputation, increased morbidity and mortality, and economic stress. Neo-angiogenesis and granulation tissue formation are necessary for physiological DFU healing and acute inflammation play a key role in healing. However, chronic inflammation in association with diabetic complications holds the ulcer in the inflammatory phase without progressing to the resolution phase contributing to non-healing. Fibroblasts acquiring myofibroblasts phenotype contribute to granulation tissue formation and angiogenesis. However, recent studies suggest the presence of five subtypes of fibroblast population and of changing density in non-healing DFUs. Further, the association of fibroblast plasticity and heterogeneity with wound healing suggests that the switch in fibroblast phenotype may affect wound healing. The fibroblast phenotype shift and altered function may be due to the presence of chronic inflammation or a diabetic wound microenvironment. This review focuses on the role of fibroblast plasticity and heterogeneity, the effect of hyperglycemia and inflammatory cytokines on fibroblasts, and the interaction of fibroblasts with other cells in diabetic wound microenvironment in the perspective of DFU healing. Next, we summarize secretory, angiogenic, and angiostatic phenotypes of fibroblast which have been discussed in other organ systems but not in relation to DFUs followed by the perspective on the role of their phenotypes in promoting angiogenesis in DFUs.

Physical and biological advances in endothelial cell-based engineered co-culture model systems

Scientific knowledge in the field of cell biology and mechanobiology heavily leans on cell-based in vitro experiments and models that favor the examination and comprehension of certain biological processes and occurrences across a variety of environments. Cell culture assays are an invaluable instrument for a vast spectrum of biomedical and biophysical investigations. The quality of experimental models in terms of simplicity, reproducibility, and combinability with other methods, and in particular the scale at which they depict cell fate in native tissues, is critical to advancing the knowledge of the comprehension of cell-cell and cell-matrix interactions in tissues and organs. Typically, in vitro models are centered on the experimental tinkering of mammalian cells, most often cultured as monolayers on planar, two-dimensional (2D) materials. Notwithstanding the significant advances and numerous findings that have been accomplished with flat biology models, their usefulness for generating further new biological understanding is constrained because the simple 2D setting does not reproduce the physiological response of cells in natural living tissues. In addition, the co-culture systems in a 2D stetting weakly mirror their natural environment of tissues and organs. Significant advances in 3D cell biology and matrix engineering have resulted in the creation and establishment of a new type of cell culture shapes that more accurately represents the in vivo microenvironment and allows cells and their interactions to be analyzed in a biomimetic approach. Contemporary biomedical and biophysical science has novel advances in technology that permit the design of more challenging and resilient in vitro models for tissue engineering, with a particular focus on scaffold- or hydrogel-based formats, organotypic cultures, and organs-on-chips, which cover the purposes of co-cultures. Even these complex systems must be kept as simplified as possible in order to grasp a particular section of physiology too very precisely. In particular, it is highly appreciated that they bridge the space between conventional animal research and human (patho)physiology. In this review, the recent progress in 3D biomimetic culturation is presented with a special focus on co-cultures, with an emphasis on the technological building blocks and endothelium-based co-culture models in cancer research that are available for the development of more physiologically relevant in vitro models of human tissues under normal and diseased conditions. Through applications and samples of various physiological and disease models, it is possible to identify the frontiers and future engagement issues that will have to be tackled to integrate synthetic biomimetic culture systems far more successfully into biomedical and biophysical investigations.

The transcriptomic landscape of caudal cell mass in different developmental stages of the chick embryo

INTRODUCTION

The caudal cell mass (CCM) is an aggregate of undifferentiated pluripotent cells and the main player in secondary neurulation. Previous studies have elucidated the dynamic fate of the multipotent cell lineages, with a recent interest in the neuromesodermal progenitors. However, a transcriptomic analysis of the CCM during secondary neurulation has not been performed yet.

METHODS

We analyzed RNA sequencing data of CCM samples at three different developmental stages of chicken embryos; HH16 (largest CCM phase), HH20 (secondary neural tube formation phase), and HH28 (degeneration phase).

RESULTS

The transcriptomic profiles were clearly distinguishable according to developmental stage, and HH20 was shown to have not only intermediate, but also unique properties in secondary neurulation. A total of 10,666 differentially expressed genes, including FGF18 and GDF11, were identified and enriched in several gene ontologies related to embryogenesis or organogenesis. We also found that genes encoding transcription factors, such as TWIST2, IRX4, HOXB4, HOXD13, LIN28A, CDX4, and Brachyury, were among the top-ranked differentially expressed genes.

CONCLUSION

Through transcriptomic profiling, we provided a picture of the developmental process of the CCM. We identified several key molecules or pathways involved in secondary neurulation and the pathogenesis of related diseases.

LATS kinases and SLUG regulate the transition to advanced stage in aggressive oral cancer cells

The epithelial-to-mesenchymal transition (EMT) is a critical process by which cancer cells acquire malignant features. However, the molecular mechanism and functional implications of EMT and the mesenchymal-to-epithelial transition (MET) in tumor progression remain elusive. In this study, we established two aggressive cancer cell lines from the human oral cancer cell line SAS, mesenchymal-like SAS-m4 and epithelial-like SAS-δ. SAS-δ is a revertant cell obtained by inducing MET in SAS-m4. SAS-δ, but not SAS-m4, exhibited abnormal cell growth, including piled-up overgrowth and invasive tumor formation in the tongues of nude mice, suggesting that SAS-δ represented more advanced cancer cells than the parental SAS cells. EMT-related transcriptional factor SLUG is phosphorylated at T208 and partly stabilized by the Hippo pathway kinases, LATS1 and LATS2. Depletion of SLUG promoted the invasive activity of SAS-δ by increasing the protein levels of LATS1/2 and the proportion of the phosphorylated form among total SLUG protein. Our results suggest that the LATS1/2-SLUG axis regulates the transition of SAS cells to the advanced stage via repeated switching between EMT and MET. Therefore, an anti-SLUG-pT208 antibody would be valuable not alone as a malignant tumor marker antibody but also as a prognostic tool for patients with malignant disease.

Epithelial-Mesenchymal Plasticity Induced by Discontinuous Exposure to TGFβ1 Promotes Tumour Growth

Simple Summary

In this manuscript, we used a non-genetically manipulated EMT/MET cell line model to demonstrate that epithelial mesenchymal plasticity occurring in normal cells generates co-existing phenotypically and functionally divergent cell subpopulations which result in fast growing tumours in vivo.

Abstract

Transitions between epithelial and mesenchymal cellular states (EMT/MET) contribute to cancer progression. We hypothesize that EMT followed by MET promotes cell population heterogeneity, favouring tumour growth. We developed an EMT model by on and off exposure of epithelial EpH4 cells (E-cells) to TGFβ1 that mimics phenotypic EMT (M-cells) and MET. We aimed at understanding whether phenotypic MET is accompanied by molecular and functional reversion back to epithelia by using RNA sequencing, immunofluorescence (IF), proliferation, wound healing, focus formation and mamosphere formation assays as well as cell xenografts in nude mice. Phenotypic reverted epithelial cells (RE-cells) obtained after MET induction presented epithelial morphologies and proliferation rates resembling E cells. However, the RE transcriptomic profile and IF staining of epithelial and mesenchymal markers revealed a uniquely heterogeneous mixture of cell subpopulations with a high self-renewal ability. RE cell heterogeneity was stably maintained for long periods after TGFβ1 removal both in vitro and in large tumours derived from the nude mice. Overall, we show that phenotypic reverted epithelial cells (RE cells) do not return to the molecular and functional epithelial state and present mesenchymal features related to aggressiveness and cellular heterogeneity that favour tumour growth in vivo. This work strengthens epithelial cell reprogramming and cellular heterogeneity fostered by inflammatory cues as a tumour growth-promoting factor in vivo.

Andrographolide inhibits the growth of human osteosarcoma cells by suppressing Wnt/β-catenin, PI3K/AKT and NF-κB signaling pathways

Osteosarcoma (OS) is an aggressive malignant skeletal tumor characterized by an extremely poor prognosis and a high tendency to recur. The frequently used anti-OS chemotherapy regents are often limited by drug resistance and severe adverse events. It is urgent to develop more effective, tolerable and safe drugs for the treatment of OS. Andrographolide (AG), a diterpenoid lactone isolated from Andrographis paniculata, has been proved to possess anti-tumor activity against several human cancer types. In this current study, we evaluated the inhibitory effect of AG on human OS cells and probed the possible mechanism. We found that AG inhibited the proliferation of human OS cells and blocked cell cycle at G2/M phase. Furthermore, AG impeded the migration and invasion, while promoted the apoptosis of human OS cells. Moreover, we found that AG inhibited OS growth and lung metastasis in orthotopic transplantation model. Mechanistically, we demonstrated that AG suppressed the activity of Wnt/β-catenin, PI3K/AKT and NF-κB signaling pathways. Notably, we validated that AG synergized with the inhibitors of Wnt/β-catenin, PI3K/AKT and NF-κB to suppress the proliferation, migration and invasion of human OS cells. Collectively, our study conclusively demonstrates that AG inhibits the growth of human OS cells, thus, may be a promising candidate for the treatment of OS.

Therapeutic Potential of Microvesicles in Cell Therapy and Regenerative Medicine of Ocular Diseases With an Especial Focus on Mesenchymal Stem Cells-Derived Microvesicles

These days, mesenchymal stem cells (MSCs), because of immunomodulatory and pro-angiogenic abilities, are known as inevitable factors in regenerative medicine and cell therapy in different diseases such as ocular disorder. Moreover, researchers have indicated that exosome possess an essential potential in the therapeutic application of ocular disease. MSC-derived exosome (MSC-DE) have been identified as efficient as MSCs for treatment of eye injuries due to their small size and rapid diffusion all over the eye. MSC-DEs easily transfer their ingredients such as miRNAs, proteins, and cytokines to the inner layer in the eye and increase the reconstruction of the injured area. Furthermore, MSC-DEs deliver their immunomodulatory cargos in inflamed sites and inhibit immune cell migration, resulting in improvement of autoimmune uveitis. Interestingly, therapeutic effects were shown only in animal models that received MSC-DE. In this review, we summarized the therapeutic potential of MSCs and MSC-DE in cell therapy and regenerative medicine of ocular diseases.

Viscoelasticity, Like Forces, Plays a Role in Mechanotransduction

Viscoelasticity and its alteration in time and space has turned out to act as a key element in fundamental biological processes in living systems, such as morphogenesis and motility. Based on experimental and theoretical findings it can be proposed that viscoelasticity of cells, spheroids and tissues seems to be a collective characteristic that demands macromolecular, intracellular component and intercellular interactions. A major challenge is to couple the alterations in the macroscopic structural or material characteristics of cells, spheroids and tissues, such as cell and tissue phase transitions, to the microscopic interferences of their elements. Therefore, the biophysical technologies need to be improved, advanced and connected to classical biological assays. In this review, the viscoelastic nature of cytoskeletal, extracellular and cellular networks is presented and discussed. Viscoelasticity is conceptualized as a major contributor to cell migration and invasion and it is discussed whether it can serve as a biomarker for the cells’ migratory capacity in several biological contexts. It can be hypothesized that the statistical mechanics of intra- and extracellular networks may be applied in the future as a powerful tool to explore quantitatively the biomechanical foundation of viscoelasticity over a broad range of time and length scales. Finally, the importance of the cellular viscoelasticity is illustrated in identifying and characterizing multiple disorders, such as cancer, tissue injuries, acute or chronic inflammations or fibrotic diseases.

Cell and Tissue Nanomechanics: From Early Development to Carcinogenesis

Cell and tissue nanomechanics, being inspired by progress in high-resolution physical mapping, has recently burst into biomedical research, discovering not only new characteristics of normal and diseased tissues, but also unveiling previously unknown mechanisms of pathological processes. Some parallels can be drawn between early development and carcinogenesis. Early embryogenesis, up to the blastocyst stage, requires a soft microenvironment and internal mechanical signals induced by the contractility of the cortical actomyosin cytoskeleton, stimulating quick cell divisions. During further development from the blastocyst implantation to placenta formation, decidua stiffness is increased ten-fold when compared to non-pregnant endometrium. Organogenesis is mediated by mechanosignaling inspired by intercellular junction formation with the involvement of mechanotransduction from the extracellular matrix (ECM). Carcinogenesis dramatically changes the mechanical properties of cells and their microenvironment, generally reproducing the structural properties and molecular organization of embryonic tissues, but with a higher stiffness of the ECM and higher cellular softness and fluidity. These changes are associated with the complete rearrangement of the entire tissue skeleton involving the ECM, cytoskeleton, and the nuclear scaffold, all integrated with each other in a joint network. The important changes occur in the cancer stem-cell niche responsible for tumor promotion and metastatic growth. We expect that the promising concept based on the natural selection of cancer cells fixing the most invasive phenotypes and genotypes by reciprocal regulation through ECM-mediated nanomechanical feedback loop can be exploited to create new therapeutic strategies for cancer treatment.

Stress generation, relaxation and size control in confined tumor growth

Experiments on tumor spheroids have shown that compressive stress from their environment can reversibly decrease tumor expansion rates and final sizes. Stress release experiments show that nonuniform anisotropic elastic stresses can be distributed throughout. The elastic stresses are maintained by structural proteins and adhesive molecules, and can be actively relaxed by a variety of biophysical processes. In this paper, we present a new continuum model to investigate how the growth-induced elastic stresses and active stress relaxation, in conjunction with cell size control feedback machinery, regulate the cell density and stress distributions within growing tumors as well as the tumor sizes in the presence of external physical confinement and gradients of growth-promoting chemical fields. We introduce an adaptive reference map that relates the current position with the reference position but adapts to the current position in the Eulerian frame (lab coordinates) via relaxation. This type of stress relaxation is similar to but simpler than the classical Maxwell model of viscoelasticity in its formulation. By fitting the model to experimental data from two independent studies of tumor spheroid growth and their cell density distributions, treating the tumors as incompressible, neo-Hookean elastic materials, we find that the rates of stress relaxation of tumor tissues can be comparable to volumetric growth rates. Our study provides insight on how the biophysical properties of the tumor and host microenvironment, mechanical feedback control and diffusion-limited differential growth act in concert to regulate spatial patterns of stress and growth. When the tumor is stiffer than the host, our model predicts tumors are more able to change their size and mechanical state autonomously, which may help to explain why increased tumor stiffness is an established hallmark of malignant tumors.

Molecular and Mechanical Cues for Somite Periodicity

Somitogenesis refers to the segmentation of the paraxial mesoderm, a tissue located on the back of the embryo, into regularly spaced and sized pieces, i.e., the somites. This periodicity is important to assure, for example, the formation of a functional vertebral column. Prevailing models of somitogenesis are based on the existence of a gene regulatory network capable of generating a striped pattern of gene expression, which is subsequently translated into periodic tissue boundaries. An alternative view is that the pre-pattern that guides somitogenesis is not chemical, but of a mechanical origin. A striped pattern of mechanical strain can be formed in physically connected tissues expanding at different rates, as it occurs in the embryo. Here we argue that both molecular and mechanical cues could drive somite periodicity and suggest how they could be integrated.

E-Cadherin: An Important Functional Molecule at Respiratory Barrier Between Defence and Dysfunction

While breathing, many microorganisms, harmful environmental particles, allergens, and environmental pollutants enter the human airways. The human respiratory tract is lined with epithelial cells that act as a functional barrier to these harmful factors and provide homeostasis between external and internal environment. Intercellular epithelial junctional proteins play a role in the formation of the barrier. E-cadherin is a calcium-dependent adhesion molecule and one of the most important molecules involved in intercellular epithelial barier formation. E-cadherin is not only physical barrier element but also regulates cell proliferation, differentiation and the immune response to environmental noxious agents through various transcription factors. In this study, we aimed to review the role of E-cadherin in the formation of airway epithelial barier, its status as a result of exposure to various environmental triggers, and respiratory diseases associated with its dysfunction. Moreover, the situations in which its abnormal activation can be noxious would be discussed.

Impaired stem cell differentiation and somatic cell reprogramming in DIDO3 mutants with altered RNA processing and increased R-loop levels

Embryonic stem cell (ESC) differentiation and somatic cell reprogramming are biological processes governed by antagonistic expression or repression of a largely common set of genes. Accurate regulation of gene expression is thus essential for both processes, and alterations in RNA processing are predicted to negatively affect both. We show that truncation of the DIDO gene alters RNA splicing and transcription termination in ESC and mouse embryo fibroblasts (MEF), which affects genes involved in both differentiation and reprogramming. We combined transcriptomic, protein interaction, and cellular studies to identify the underlying molecular mechanism. We found that DIDO3 interacts with the helicase DHX9, which is involved in R-loop processing and transcription termination, and that DIDO3-exon16 deletion increases nuclear R-loop content and causes DNA replication stress. Overall, these defects result in failure of ESC to differentiate and of MEF to be reprogrammed. MEF immortalization restored impaired reprogramming capacity. We conclude that DIDO3 has essential functions in ESC differentiation and somatic cell reprogramming by supporting accurate RNA metabolism, with its exon16-encoded domain playing the main role.

Can Human Oral Mucosa Stem Cells Differentiate to Corneal Epithelia?

Human oral mucosa stem cells (hOMSCs) arise from the neural crest, they can self-renew, proliferate, and differentiate to several cell lines and could represent a good source for application in tissue engineering. Because of their anatomical location, hOMSCs are easy to isolate, have multilineage differentiation capacity and express embryonic stem cells markers such as—Sox2, Oct3/4 and Nanog. We have used SHEM (supplemented hormonal epithelial medium) media and cultured hOMSCs over human amniotic membrane and determined the cell’s capacity to differentiate to an epithelial-like phenotype and to express corneal specific epithelial markers—CK3, CK12, CK19, Pan-cadherin and E-cadherin. Our results showed that hOMSCs possess the capacity to attach to the amniotic membrane and express CK3, CK19, Pan-Cadherin and E-Cadherin without induction with SHEM media and expressed CK12 or changed the expression pattern of E-Cadherin to a punctual-like feature when treated with SHEM media. The results observed in this study show that hOMSCs possess the potential to differentiate toward epithelial cells. In conclusion, our results revealed that hOMSCs readily express markers for corneal determination and could provide the ophthalmology field with a therapeutic alternative for tissue engineering to achieve corneal replacement when compared with other techniques. Nevertheless, further studies are needed to develop a predictable therapeutic alternative for cornea replacement.

What we can learn from embryos to understand the mesenchymal-to-epithelial transition in tumor progression

Epithelial plasticity involved the terminal and transitional stages that occur during epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET), both are essential at different stages of early embryonic development that have been co-opted by cancer cells to undergo tumor metastasis. These processes are regulated at multiple instances, whereas the post-transcriptional regulation of key genes mediated by microRNAs is gaining major attention as a common and conserved pathway. In this review, we focus on discussing the latest findings of the cellular and molecular basis of the less characterized process of MET during embryonic development, with special attention to the role of microRNAs. Although we take in consideration the necessity of being cautious when extrapolating the obtained evidence, we propose some commonalities between early embryonic development and cancer progression that can shed light into our current understanding of this complex event and might aid in the design of specific therapeutic approaches.

The role of mechanical interactions in EMT

The detachment of cells from the boundary of an epithelial tissue and the subsequent invasion of these cells into surrounding tissues is important for cancer development and wound healing, and is strongly associated with the epithelial-mesenchymal transition (EMT). Chemical signals, such as TGF-β, produced by surrounding tissue can be uptaken by cells and induce EMT. In this work, we present a novel cell-based discrete mathematical model of mechanical cellular relaxation, cell proliferation, and cell detachment driven by chemically-dependent EMT in an epithelial tissue. A continuum description of the model is then derived in the form of a novel nonlinear free boundary problem. Using the discrete and continuum models we explore how the coupling of chemical transport and mechanical interactions influences EMT, and postulate how this could be used to help control EMT in pathological situations.

Xenopus Deep Cell Aggregates: A 3D Tissue Model for Mesenchymal-to-Epithelial Transition

Mesenchymal-to-epithelial transition (MET) describes the ability of loosely associated migratory cells to form a more adherent sheet-like assembly of cells. MET is a conserved motif occurring throughout organogenesis and plays a key role in regeneration and cancer metastasis, and is the first step in producing induced pluripotent stem cells (iPSCs). To resolve fundamental biological questions about MET, its relation to epithelial-to-mesenchymal transition, and to explore MET's role in tissue assembly and remodeling requires live models for MET that are amenable to experimentation. Many cases of clinically important MET are inferred since they occur deep with the body of the embryo or adult. We have developed a tractable model for MET, where cellular transitions can be directly observed under conditions where molecular, mechanical, and cellular contexts can be controlled experimentally. In this chapter, we introduce a 3-dimensional (3D) tissue model to study MET using Xenopus laevis embryonic mesenchymal cell aggregates.

Actin on and around the Nucleus

Actin plays roles in many important cellular processes, including cell motility, organelle movement, and cell signaling. The discovery of transmembrane actin-binding proteins at the outer nuclear membrane (ONM) raises the exciting possibility that actin can play a role in direct force transmission to the nucleus and the genome at its interior. Actin-dependent nucleus displacement was first described a decade ago. We are now gaining a more detailed understanding of its mechanisms, as well as new roles for actin during mitosis and meiosis, for gene expression, and in the cell's response to mechanical stimuli. Here we review these recent developments, the actin-binding proteins involved, the tissue specificity of these mechanisms, and methods developed to reconstitute and study this interaction in vitro.

Somite Division and New Boundary Formation by Mechanical Strain

Somitogenesis, the primary segmentation of the vertebrate embryo, is associated with oscillating genes that interact with a wave of cell differentiation. The necessity of cell-matrix adherence and embryonic tension, however, suggests that mechanical cues are also involved. To explicitly investigate this, we applied surplus axial strain to live chick embryos. Despite substantial deformations, the embryos developed normally and somite formation rate was unaffected. Surprisingly, however, we observed slow cellular reorganizations of the most elongated somites into two or more well-shaped daughter somites. In what appeared to be a regular process of boundary formation, somites divided and fibronectin was deposited in between. Cell counts and morphology indicated that cells from the somitocoel underwent mesenchymal-epithelial transition; this was supported by a Cellular Potts model of somite division. Thus, although somitogenesis appeared to be extremely robust, we observed new boundary formation in existing somites and conclude that mechanical strain can be morphologically instructive.

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Live chick embryos develop normally under substantial axial strain (>50%)

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Mature somites divide into daughter somites, and fibronectin is deposited in between

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Mesenchymal cells from the somitocoel transition into epithelial border cells

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Mechanical strain can induce border formation and thus affect morphogenesis

Dullard-mediated Smad1/5/8 inhibition controls mouse cardiac neural crest cells condensation and outflow tract septation

The establishment of separated pulmonary and systemic circulation in vertebrates, via cardiac outflow tract (OFT) septation, is a sensitive developmental process accounting for 10% of all congenital anomalies. Neural Crest Cells (NCC) colonising the heart condensate along the primitive endocardial tube and force its scission into two tubes. Here, we show that NCC aggregation progressively decreases along the OFT distal-proximal axis following a BMP signalling gradient. Dullard, a nuclear phosphatase, tunes the BMP gradient amplitude and prevents NCC premature condensation. Dullard maintains transcriptional programs providing NCC with mesenchymal traits. It attenuates the expression of the aggregation factor Sema3c and conversely promotes that of the epithelial-mesenchymal transition driver Twist1. Altogether, Dullard-mediated fine-tuning of BMP signalling ensures the timed and progressive zipper-like closure of the OFT by the NCC and prevents the formation of a heart carrying the congenital abnormalities defining the tetralogy of Fallot.

Tissue mechanics drives regeneration of a mucociliated epidermis on the surface of Xenopus embryonic aggregates

Injury, surgery, and disease often disrupt tissues and it is the process of regeneration that aids the restoration of architecture and function. Regeneration can occur through multiple strategies including stem cell expansion, transdifferentiation, or proliferation of differentiated cells. We have identified a case of regeneration in Xenopus embryonic aggregates that restores a mucociliated epithelium from mesenchymal cells. Following disruption of embryonic tissue architecture and assembly of a compact mesenchymal aggregate, regeneration first restores an epithelium, transitioning from mesenchymal cells at the surface of the aggregate. Cells establish apico-basal polarity within 5 hours and a mucociliated epithelium within 24 hours. Regeneration coincides with nuclear translocation of the putative mechanotransducer YAP1 and a sharp increase in aggregate stiffness, and regeneration can be controlled by altering stiffness. We propose that regeneration of a mucociliated epithelium occurs in response to biophysical cues sensed by newly exposed cells on the surface of a disrupted mesenchymal tissue.

The Role of Calmodulin in Tumor Cell Migration, Invasiveness, and Metastasis

Calmodulin (CaM) is the principal Ca²⁺ sensor protein in all eukaryotic cells, that upon binding to target proteins transduces signals encoded by global or subcellular-specific changes of Ca²⁺ concentration within the cell. The Ca²⁺/CaM complex as well as Ca²⁺-free CaM modulate the activity of a vast number of enzymes, channels, signaling, adaptor and structural proteins, and hence the functionality of implicated signaling pathways, which control multiple cellular functions. A basic and important cellular function controlled by CaM in various ways is cell motility. Here we discuss the role of CaM-dependent systems involved in cell migration, tumor cell invasiveness, and metastasis development. Emphasis is given to phosphorylation/dephosphorylation events catalyzed by myosin light-chain kinase, CaM-dependent kinase-II, as well as other CaM-dependent kinases, and the CaM-dependent phosphatase calcineurin. In addition, the role of the CaM-regulated small GTPases Rac1 and Cdc42 (cell division cycle protein 42) as well as CaM-binding adaptor/scaffold proteins such as Grb7 (growth factor receptor bound protein 7), IQGAP (IQ motif containing GTPase activating protein) and AKAP12 (A kinase anchoring protein 12) will be reviewed. CaM-regulated mechanisms in cancer cells responsible for their greater migratory capacity compared to non-malignant cells, invasion of adjacent normal tissues and their systemic dissemination will be discussed, including closely linked processes such as the epithelial–mesenchymal transition and the activation of metalloproteases. This review covers as well the role of CaM in establishing metastatic foci in distant organs. Finally, the use of CaM antagonists and other blocking techniques to downregulate CaM-dependent systems aimed at preventing cancer cell invasiveness and metastasis development will be outlined.

FoxO3a depletion accelerates cutaneous wound healing by regulating epithelial‑mesenchymal transition through β‑catenin activation

The hysteresis of keratinocyte (KC) re-epithelialization is an important factor resulting in chronic wounds; however, the molecular mechanisms involved in this cellular response remain yet to be completely elucidated. The present study demonstrated the function of transcription factor Forkhead box O3a (FoxO3a) in KC growth and migration functional effects, resulting in restrained KC re-epithelialization during wound healing. In chronic wound tissue samples, the expression of FoxO3a was significantly increased when compared with the acute wound healing group (P<0.01). Overexpressing FoxO3a significantly inhibited, whereas silencing endogenous FoxO3a enhanced, the growth and migration of HaCaT cells in vitro. Further investigation revealed that FoxO3a negatively regulated matrix metalloproteinases 1 and 9, and increased the expression of tissue inhibitor of metalloproteinase 1. In addition, the upregulation of FoxO3a retarded, whereas the downregulation of FoxO3a accelerated, transforming growth factor-β1-induced epithelial-mesenchymal transition in HaCaT cells. Mechanistically, the overexpression of FoxO3a inactivated β-catenin signaling and markedly reduced the levels of nuclear β-catenin. These results reveal a novel mechanism of FoxO3a in regulating KC re-epithelialization, and provide novel targets for the prevention and treatment of chronic wounds.

Adjustable viscoelasticity allows for efficient collective cell migration

Cell migration is essential for a wide range of biological processes such as embryo morphogenesis, wound healing, regeneration, and also in pathological conditions, such as cancer. In such contexts, cells are required to migrate as individual entities or as highly coordinated collectives, both of which requiring cells to respond to molecular and mechanical cues from their environment. However, whilst the function of chemical cues in cell migration is comparatively well understood, the role of tissue mechanics on cell migration is just starting to be studied. Recent studies suggest that the dynamic tuning of the viscoelasticity within a migratory cluster of cells, and the adequate elastic properties of its surrounding tissues, are essential to allow efficient collective cell migration in vivo. In this review we focus on the role of viscoelasticity in the control of collective cell migration in various cellular systems, mentioning briefly some aspects of single cell migration. We aim to provide details on how viscoelasticity of collectively migrating groups of cells and their surroundings is adjusted to ensure correct morphogenesis, wound healing, and metastasis. Finally, we attempt to show that environmental viscoelasticity triggers molecular changes within migrating clusters and that these new molecular setups modify clusters' viscoelasticity, ultimately allowing them to migrate across the challenging geometries of their microenvironment.

Novel Diphenylamine Analogs Induce Mesenchymal to Epithelial Transition in Triple Negative Breast Cancer

Epithelial to mesenchymal transition (EMT) is a cellular program that converts non-motile epithelial cells into invasive mesenchymal cells. EMT is implicated in cancer metastasis, chemo-resistance, cancer progression, and generation of cancer stem cells (CSCs). Inducing mesenchymal to epithelial transition (MET), the reverse phenomenon of EMT, is proposed as a novel strategy to target triple negative and tamoxifen-resistant breast cancer. Triple negative breast cancer (TNBC) is characterized by the loss of hormone receptors, a highly invasive mesenchymal phenotype, and a lack of targeted therapy. Estrogen receptor-positive breast cancer can be targeted by tamoxifen, an ER antagonist. However, these cells undergo EMT over the course of treatment and develop resistance. Thus, there is an urgent need to develop therapeutic interventions to target these aggressive cancers. In this study, we examined the role of novel diphenylamine analogs in converting the mesenchymal phenotype of MDA-MB-231 TNBC cells to a lesser aggressive epithelial phenotype. Using analog-based drug design, a series of diphenylamine analogs were synthesized and initially evaluated for their effect on E-cadherin protein expression and changes incell morphology, which was quantified by measuring the spindle index (SI) value. Selected compound 1 from this series increases the expression of E-cadherin, a primary marker for epithelial cells, and decreases the mesenchymal markers SOX2, ZEB1, Snail, and vimentin. The increase in epithelial markers and the decrease in mesenchymal markers are consistent with a phenotypic switch from spindle-like morphology to cobblestone-like morphology. Furthermore, Compound 1 decreases spheroid viability, cell migration, and cell proliferation in triple negative BT-549 and tamoxifen-resistant MCF-7 breast cancer cells.

Current Trends and Future Perspective of Mesenchymal Stem Cells and Exosomes in Corneal Diseases

The corneal functions (transparency, refractivity and mechanical strength) deteriorate in many corneal diseases but can be restored after corneal transplantation (penetrating and lamellar keratoplasties). However, the global shortage of transplantable donor corneas remains significant and patients are subject to life-long risk of immune response and graft rejection. Various studies have shown the differentiation of multipotent mesenchymal stem cells (MSCs) into various corneal cell types. With the unique properties of immunomodulation, anti-angiogenesis and anti-inflammation, they offer the advantages in corneal reconstruction. These effects are widely mediated by MSC differentiation and paracrine signaling via exosomes. Besides the cell-free nature of exosomes in circumventing the problems of cell-fate control and tumorigenesis, the vesicle content can be genetically modified for optimal therapeutic affinity. The pharmacology and toxicology, xeno-free processing with sustained delivery, scale-up production in compliant to Good Manufacturing Practice regulations, and cost-effectiveness are the current foci of research. Routes of administration via injection, topical and/or engineered bioscaffolds are also explored for its applicability in treating corneal diseases.

More diversity in epithelial cell polarity: A fruit flies' gut feeling

Multicellular animals face the principle challenge to deal with two distinct compartments: the internal organismal compartment and the external environment. This challenge is met by the differentiation of cell sheets into epithelia, which provide a dynamic barrier in tissues, organs, and organisms. Cell polarity is key to all functions of epithelia, and compromising polarity causes many severe diseases. Within the past 20 years, research on Drosophila melanogaster discovered a conserved molecular machinery that controls epithelial polarity. Recent findings suggest that the textbook Drosophila-based paradigm of the control of epithelial polarity may not be as universal as previously assumed.

This Primer discusses recent research showing that the midgut epithelium of the adult fruit fly differs dramatically from the canonical modes of epithelial cell polarity in main features of its cytoarchitecture and its molecular control mechanisms.

Adipose-derived mesenchymal stem cells formed acinar-like structure when stimulated with breast epithelial cells in three-dimensional culture

Lipotransfer has been applied in breast augmentation surgery for several years and the resident adipose-derived stem cells (ASCs) play an important role in enhancing fat graft survival. However, the interaction between ASCs and mammary epithelium is not fully understood. Many studies have shown that ASCs have a tumor-supportive effect in breast cancer. To the best of our knowledge, this is the first study on the effect of mammary epithelial cells on the human ASCs in 3D culture. ASCs were cultivated on matrigel in the conditioned medium (CM) prepared from a human breast epithelial cell line (HBL-100). The ASCs formed KRT18-positive acini-like structures after stimulation with breast epithelial cells. The expression of epithelial genes (CDH1 and KRT18) was up-regulated while the expression of mesenchymal specific genes (CDH2 and VIM) was down-regulated as determined by qRT-PCR. The stemness marker (CD29) and angiogenic factors (CD31 and VEGF) were also down-regulated as examined by immunofluorescence. In addition, the CM obtained from HBL-100 enhanced the migration and inhibited the adipogenic differentiation of ASCs. These results demonstrate that ASCs have the ability to transform into epithelial-like cells when cultured with mammary epithelial cells. Given these observations, we infer that ASCs have a positive effect on lipotransfer, not only due to their ability to secrete growth factors, but also due to their direct participation in the formation of new breast tissue.

PMA treated THP-1-derived-IL-6 promotes EMT of SW48 through STAT3/ERK-dependent activation of Wnt/β-catenin signaling pathway

Colon cancer is one of the most common digestive malignant tumors that leads to high mortality worldwide, and metastasis is the primary cause of cancer-related death. It is well accepted that the epithelial-mesenchymal transition (EMT) plays a key role in the process of metastasis. As a cytokine that macrophage secretes, IL-6 is involved in the progression of tumors, including the invasion and metastasis via kinds of signaling pathways. However, the mechanism of interactions between IL-6, macrophage, EMT and colon cancer is not fully understood. Increased CD68⁺ macrophages and IL-6 level were found in colon tumor as compared to normal colon tissue. Metastatic lymph node showed even more CD68⁺ macrophages and higher IL-6 level than the primary tumor. These results suggested that macrophages and IL-6 play an important role in EMT of colon cancer. In order to investigate the effect of macrophage and IL-6 on EMT of colon cancer, we cultured human colon carcinoma cell line SW48 with conditioned medium (CM) from PMA-stimulated monocyte THP-1 cells and tested for IL-6 dependent EMT pathways. Wound healing assay and Transwell assay were used to analyze cell migration and invasion. Results showed that CM-treated SW48 cells increased IL-6 production and displayed elevated capacity of migration and invasion compared to untreated cells. Increased expressions of EMT markers (N-cadherin, Vimentin and β-catenin) and decreased expression of EMT marker(E-cadherin) were found in CM-treated SW48 cells by Western Blot. The addition of an anti-IL-6 antibody significantly inhibited the increase of EMT markers (Vimentin and β-catenin) as well as cell migration and invasion, suggesting that IL-6 played a critical role in promoting EMT of CM-treated SW48 cells. In addition, we found that the levels of p-STAT3 and p-ERK increased in CM-treated SW48 compared to untreated cells, which can be reversed by AG490, an inhibitor of JAK. In the meantime, the suppression of JAK-associated signaling pathways caused a decrease of β-catenin. In summary, our study suggested that macrophage-induced IL-6 promotes migration and invasion of colon cancer cell via Wnt/β-catenin pathway in STAT3/ERK-dependent way.

Spatiotemporally Controlled Mechanical Cues Drive Progenitor Mesenchymal-to-Epithelial Transition Enabling Proper Heart Formation and Function

During early cardiogenesis, bilateral fields of mesenchymal heart progenitor cells (HPCs) move from the anterior lateral plate mesoderm to the ventral midline, undergoing a mesenchymal-to-epithelial transition (MET) en route to forming a single epithelial sheet. Through tracking of tissue-level deformations in the heart-forming region (HFR) as well as movement trajectories and traction generation of individual HPCs, we find that the onset of MET correlates with a peak in mechanical stress within the HFR and changes in HPC migratory behaviors. Small-molecule inhibitors targeting actomyosin contractility reveal a temporally specific requirement of bulk tissue compliance to regulate heart development and MET. Targeting mutant constructs to modulate contractility and compliance in the underlying endoderm, we find that MET in HPCs can be accelerated in response to microenvironmental stiffening and can be inhibited by softening. To test whether MET in HPCs was responsive to purely physical mechanical cues, we mimicked a high-stress state by injecting an inert oil droplet to generate high strain in the HFR, demonstrating that exogenously applied stress was sufficient to drive MET. MET-induced defects in anatomy result in defined functional lesions in the larval heart, implicating mechanical signaling and MET in the etiology of congenital heart defects. From this integrated analysis of HPC polarity and mechanics, we propose that normal heart development requires bilateral HPCs to undergo a critical behavioral and phenotypic transition on their way to the ventral midline, and that this transition is driven in response to the changing mechanical properties of their endoderm substrate.

ΔNp63α and microRNAs: leveraging the epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is a cellular reprogramming mechanism that is an underlying cause of cancer metastasis. Recent investigations have uncovered an intricate network of regulation involving the TGFβ, Wnt, and Notch signaling pathways and small regulatory RNA species called microRNAs (miRNAs). The activity of a transcription factor vital to the maintenance of epithelial stemness, ΔNp63α, has been shown to modulate the activity of these EMT pathways to either repress or promote EMT. Furthermore, ΔNp63α is a known regulator of miRNA, including those directly involved in EMT. This review discusses the evidence of ΔNp63α as a master regulator of EMT components and miRNA, highlighting the need for a deeper understanding of its role in EMT. This expanded knowledge may provide a basis for new developments in the diagnosis and treatment of metastatic cancer.

Pharmacological and immunological targeting of tumor mesenchymalization

Controlling the spread of carcinoma cells to distant organs is the foremost challenge in cancer treatment, as metastatic disease is generally resistant to therapy and is ultimately incurable for the majority of patients. The plasticity of tumor cell phenotype, in which the behaviors and functions of individual tumor cells differ markedly depending upon intrinsic and extrinsic factors, is now known to be a central mechanism in cancer progression. Our expanding knowledge of epithelial and mesenchymal phenotypic states in tumor cells, and the dynamic nature of the transitions between these phenotypes has created new opportunities to intervene to better control the behavior of tumor cells. There are now a variety of innovative pharmacological approaches to preferentially target tumor cells that have acquired mesenchymal features, including cytotoxic agents that directly kill these cells, and inhibitors that block or revert the process of mesenchymalization. Furthermore, novel immunological strategies have been developed to engage the immune system in seeking out and destroying mesenchymalized tumor cells. This review highlights the relevance of phenotypic plasticity in tumor biology, and discusses recently developed pharmacological and immunological means of targeting this phenomenon.