Beyond the epithelium: Cadherin function in fibrous connective tissues

Autocrine IL-6 drives cell and extracellular matrix anisotropy in scar fibroblasts

Fibrosis is associated with dramatic changes in extracellular matrix (ECM) architecture of unknown etiology. Here we exploit keloid scars as a paradigm to understand fibrotic ECM organization. We reveal that keloid patient fibroblasts uniquely produce a globally aligned ECM network in 2-D culture as observed in scar tissue. ECM anisotropy develops after rapid initiation of a fibroblast supracellular actin network, suggesting that cell alignment initiates ECM patterning. Keloid fibroblasts produce elevated levels of IL-6, and autocrine IL-6 production is both necessary and sufficient to induce cell and ECM alignment, as evidenced by ligand stimulation of normal dermal fibroblasts and treatment of keloid fibroblasts with the function blocking IL-6 receptor monoclonal antibody, tocilizumab. Downstream of IL-6, supracellular organization of keloid fibroblasts is controlled by activation of cell-cell adhesion. Adhesion formation inhibits contact-induced cellular overlap leading to nematic organization of cells and an alignment of focal adhesions. Keloid fibroblasts placed on isotropic ECM align the pre-existing matrix, suggesting that focal adhesion alignment leads to active anisotropic remodeling. These results show that IL-6-induced fibroblast cooperativity can control the development of a nematic ECM, highlighting both IL-6 signaling and cell-cell adhesions as potential therapeutic targets to inhibit this common feature of fibrosis.

Hydroxytyrosol as a Promising Ally in the Treatment of Fibromyalgia

Fibromyalgia (FM) is a chronic and highly disabling syndrome, which is still underdiagnosed, with controversial treatment. Although its aetiology is unknown, a number of studies have pointed to the involvement of altered mitochondrial metabolism, increased oxidative stress and inflammation. The intake of extra virgin olive oil, and particularly of one of its phenolic compounds, hydroxytyrosol (HT), has proven to be protective in terms of redox homeostatic balance and the reduction of inflammation. In this context, using a proteomic approach with nanoscale liquid chromatography coupled to tandem mass spectrometry, the present study analysed: (i) Changes in the proteome of dermal fibroblasts from a patient with FM versus a healthy control, and (ii) the effect of the treatment with a nutritional relevant dose of HT. Our results unveiled that fibroblast from FM show a differential expression in proteins involved in the turnover of extracellular matrix and oxidative metabolism that could explain the inflammatory status of these patients. Moreover, a number of these proteins results normalized by the treatment with HT. In conclusion, our results support that an HT-enriched diet could be highly beneficial in the management of FM.

Galectin-1 and Galectin-3 and Their Potential Binding Partners in the Dermal Thickening of Keloid Tissues

Keloids are defined histopathologically as an inflammatory disorder characterized by exhibiting numerous fibroblasts, abnormal vascularization, increased number of proinflammatory immune cells as well as uncontrolled cell proliferation, and exacerbated and disorganized deposition of extracellular matrix (ECM) molecules. Importantly, many of these ECM molecules display N- and O-linked glycan residues and are considered as potential targets for galectin-1 (Gal-1) and galectin-3 (Gal-3). Nevertheless, the presence and localization of Gal-1 and Gal-3 as well as the interactions with some of their binding partners in keloid tissues have not been considered. Here, we show that in the dermal thickening of keloids, versican, syndecan-1, fibronectin, thrombospondin-1, tenascin C, CD44, integrin β1, and N-cadherin were immunolocalized in the elongated fibroblasts that were close to the immune cell infiltrate, attached to collagen bundles, and around the microvasculature and in some immune cells. We also show that Gal-1 and Gal-3 were present in the cytoplasm and along the cell membrane of some fibroblasts and immune and endothelial cells of the dermal thickening. We suggest that Gal-1 and Gal-3, in concert with some of the ECM molecules produced by fibroblasts and by immune cells, counteract the inflammatory response in keloids. We also proposed that Gal-1 and Gal-3 through their binding partners may form a supramolecular structure at the cell surface of fibroblasts, immune cells, endothelial cells, and in the extracellular space that might influence the fibroblast morphology, adhesion, proliferation, migration, and survival as well as the inflammatory responses.

Comparative study of the organisation and phenotypes of bladder interstitial cells in human, mouse and rat

With most research on interstitial cells (IC) in the bladder being conducted on animal models, it remains unclear whether all structural and functional data on IC from animal models can be translated to the human context. This prompted us to compare the structural and immunohistochemical properties of IC in bladders from mouse, rat and human. Tissue samples were obtained from the bladder dome and subsequently processed for immunohistochemistry and electron microscopy. The ultrastructural properties of IC were compared by means of electron microscopy and IC were additionally characterized with single/double immunohistochemistry/immunofluorescence. Our results reveal a similar organization of the IC network in the upper lamina propria (ULP), the deep lamina propria (DLP) and the detrusor muscle in human, rat and mouse bladders. Furthermore, despite several similarities in IC phenotypes, we also found several obvious inter-species differences in IC, especially in the ULP. Most remarkably in this respect, ULP IC in human bladder predominantly displayed a myoid phenotype with abundant presence of contractile micro-filaments, while those in rat and mouse bladders showed a fibroblast phenotype. In conclusion, the organization of ULP IC, DLP IC and detrusor IC is comparable in human, rat and mouse bladders, although several obvious inter-species differences in IC phenotypes were found. The present data show that translating research data on IC in laboratory animals to the human setting should be carried out with caution.

Inhibition of c-Myc expression accounts for an increase in the number of multinucleated cells in human cervical epithelial cells

The present study aimed to explore the mechanisms by which c-Myc is involved in mitotic catastrophe. HeLa-630 is a cell line stably silenced for c-Myc expression that was established in the laboratory of the School of Radiation Medicine and Protection. Multinucleated cells were observed in this line, and gene expression analysis was utilized to examine differences in gene expression in these cells compared with in the control cells transfected with the control plasmid. Gene ontology analysis was performed for differentially expressed genes. Expression profile analyses revealed that cells with silenced c-Myc exhibited abnormal expression patterns of genes involved in various functions, including the regulation of microtubule nucleation, centrosome duplication, the formation of pericentriolar material, DNA synthesis and metabolism, protein metabolism and the regulation of ion concentrations. Pathway analyses of differentially expressed genes demonstrated that these genes were primarily involved in diverse signal transduction pathways, including not only the adherens junction pathway, the transforming growth factor-β signaling pathway and the Wnt signaling pathway, among others, but also signaling pathways with roles in cytokine and immune regulation. The proportion of multinucleated cells with multipolar spindles was significantly higher in silenced c-Myc cells as compared with the control cells, and this discrepancy became more pronounced following cell irradiation. The inhibition of c-Myc in tumors may account for the radiosensitization of certain tumor cell types.

N-cadherin adhesive interactions modulate matrix mechanosensing and fate commitment of mesenchymal stem cells

During mesenchymal development, the microenvironment gradually transitions from one that is rich in cell-cell interactions to one that is dominated by cell-ECM (extracellular matrix) interactions. Because these cues cannot readily be decoupled in vitro or in vivo, how they converge to regulate mesenchymal stem cell (MSC) mechanosensing is not fully understood. Here, we show that a hyaluronic acid hydrogel system enables, across a physiological range of ECM stiffness, the independent co-presentation of the HAVDI adhesive motif from the EC1 domain of N-cadherin and the RGD adhesive motif from fibronectin. Decoupled presentation of these cues revealed that HAVDI ligation (at constant RGD ligation) reduced the contractile state and thereby nuclear YAP/TAZ localization in MSCs, resulting in altered interpretation of ECM stiffness and subsequent changes in downstream cell proliferation and differentiation. Our findings reveal that, in an evolving developmental context, HAVDI/N-cadherin interactions can alter stem cell perception of the stiffening extracellular microenvironment.

Role of N-cadherin in proliferation, migration, and invasion of germ cell tumours

Germ cell tumors (GCTs) are the most common malignancies in young men. Most patients with GCT can be cured with cisplatin-based combination chemotherapy, even in metastatic disease. In case of therapy resistance, prognosis is usually poor. We investigated the potential of N-cadherin inhibition as a therapeutic strategy. We analyzed the GCT cell lines NCCIT, NTERA-2, TCam-2, and the cisplatin-resistant sublines NCCIT-R and NTERA-2R. Effects of a blocking antibody or siRNA against N-cadherin on proliferation, migration, and invasion were investigated. Mouse xenografts of GCT cell lines were analyzed by immunohistochemistry for N-cadherin expression. All investigated GCT cell lines were found to express N-cadherin protein in vitro and in vivo. Downregulation of N-cadherin in vitro leads to a significant inhibition of proliferation, migration, and invasion. N-cadherin-downregulation leads to a significantly higher level of pERK. N-cadherin-inhibition resulted in significantly higher rates of apoptotic cells in caspase-3 staining. Expression of N-cadherin is preserved in cisplatin-resistant GCT cells, pointing to an important physiological role in cell survival. N-cadherin-downregulation results in a significant decrease of proliferation, migration, and invasion and stimulates apoptosis in cisplatin-naive and resistant GCT cell lines. Therefore, targeting N-cadherin may be a promising therapeutic approach, particularly in cisplatin-resistant, therapy refractory and metastatic GCT.

Immunohistochemical Analysis of Collagen IV and Laminin Expression in Spontaneous Melanoma Regression in the Melanoma-Bearing Libechov Minipig

Spontaneous regression (SR) of human melanoma is a rare, well-documented phenomenon that is not still fully understood. Its detailed study cannot be performed in patients due to ethical reasons. Using the Melanoma-bearing Libechov Minipig (MeLiM) animals of various ages (from 3 weeks to 8 months) we implemented a long-term monitoring of melanoma growth and SR. We focused on immunohistochemical detection of two important extracellular matrix proteins, collagen IV and laminin, which are associated with cancer. We showed that SR of melanoma is a highly dynamic process. The expression of collagen IV and laminin correlated with changes in population of melanoma cells. Tumours of 3-week-old animals consisted primarily of melanoma cells with a granular expression of collagen IV and laminin around them. Thereafter, melanoma cells were gradually destroyed and tumour tissue was rebuilt into the connective tissue. Collagen IV expression slightly increased in tumours of 10-week-old pigs showing extracellular fibrous appearance. In tumours of older animals, areas lacking melanoma cells demonstrated a low expression and areas still containing melanoma cells a high expression of both proteins. We considered the age of 10 weeks as a turning point in the transition between tumour growth and SR of the MeLiM melanoma.

N-cadherin negatively regulates collective Drosophila glial migration via actin cytoskeleton remodeling

Cell migration is an essential and highly regulated process. During development, glia and neurons migrate over long distances, in most cases collectively, to reach their final destination and build the sophisticated architecture of the nervous system, the most complex tissue of the body. Collective migration is highly stereotyped and efficient, defects in the process leading to severe human diseases that include mental retardation. This dynamic process entails extensive cell communication and coordination, hence the real challenge is to analyze it in the whole organism and at cellular resolution. We here investigate the impact of the N-cadherin adhesion molecule on collective glial migration using the Drosophila developing wing and cell-type specific manipulation of gene expression. We show that N-cadherin timely accumulates in glial cells and that its levels affect migration efficiency. N-cadherin works as a molecular brake in a dosage dependent manner by negatively controlling actin nucleation and cytoskeleton remodeling through α/β catenins. This is the first in vivo evidence for N-cadherin negatively and cell autonomously controlling collective migration.

Membrane-type 1 matrix metalloproteinase regulates fibronectin assembly and N-cadherin adhesion

Fibronectin matrix formation requires the increased cytoskeletal tension generated by cadherin adhesions, and is suppressed by membrane-type 1 matrix metalloproteinase (MT1-MMP). In a co-culture of Rat1 fibroblasts and MT1-MMP-silenced HT1080 cells, fibronectin fibrils extended from Rat1 to cell-matrix adhesions in HT1080 cells, and N-cadherin adhesions were formed between Rat1 and HT1080 cells. In control HT1080 cells contacting with Rat1 fibroblasts, cell-matrix adhesions were formed in the side away from Rat1 fibroblasts, and fibronectin assembly and N-cadherin adhesions were not formed. The role of N-cadherin adhesions in fibronectin matrix formation was studied using MT1-MMP-silenced HT1080 cells. MT1-MMP knockdown promoted fibronectin matrix assembly and N-cadherin adhesions in HT1080 cells, which was abrogated by double knockdown with either integrin β1 or fibronectin. Conversely, inhibition of N-cadherin adhesions by its knockdown or treatment with its neutralizing antibody suppressed fibronectin matrix formation in MT1-MMP-silenced cells. These results demonstrate that fibronectin assembly initiated by MT1-MMP knockdown results in increase of N-cadherin adhesions, which are prerequisite for further fibronectin matrix formation.

Emerging drugs for the treatment of diabetic ulcers

INTRODUCTION

Diabetic ulcers are chronic nonhealing ulcerations that despite the available medical tools still result in high amputation rates. Growing evidence suggests that alteration of the biochemical milieu of the chronic wound plays a significant role in impaired diabetic wound healing.

AREAS COVERED

The basic pathophysiology and the conventional treatment strategy of diabetic foot ulcers have been reviewed in the first section. In the second part, the most up-to-date bench and translational research in the field are described. The third section focuses on the drugs currently under development and the ongoing clinical trials evaluating their safety and efficacy. Finally, the major drug development issues and the possible scientific approaches to overcome them are analyzed.

EXPERT OPINION

Significant strides in understanding the chronic wound development have led to the development of topical therapies to address aberrant expression of growth factors and overexpression of inflammatory cytokines. Current research in the laboratory suggests that while decreased growth factor expression occurs at the local wound level, increased systemic serum levels of growth factors suggest growth factor resistance.

Fibroblast morphogenesis on 3D collagen matrices: the balance between cell clustering and cell migration

Fibroblast clusters have been observed in tissues under a variety of circumstances: in fibrosis and scar, in the formation of hair follicle dermal papilla, and as part of the general process of mesenchymal condensation that takes place during development. Cell clustering has been shown to depend on features of the extracellular matrix, growth factor environment, and mechanisms to stabilize cell-cell interactions. In vitro studies have shown that increasing the potential for cell-cell adhesion relative to cell-substrate adhesion promotes cell clustering. Experimental models to study fibroblast clustering have utilized centrifugation, hanging drops, and substrata with poorly adhesive, soft and mechanically unstable properties. In this review, we summarize work on a new, highly tractable, cell clustering research model in which human fibroblasts are incubated on the surfaces of collagen matrices. Fibroblast clustering occurs under procontractile growth factor conditions (e.g., serum or the serum lipid agonist lysophosphatidic acid) but not under promigratory growth factor conditions (e.g., platelet-derived growth factor) and can be reversed by switching growth factor environments. Cell contraction plays a dual role in clustering to bring cells closer together and to stimulate cells to organize fibronectin into a fibrillar matrix. Binding of fibroblasts to a shared fibronectin fibrillar matrix stabilizes clusters, and fragmentation of the fibrillar matrix occurs when growth factor conditions are switched to promote cell dispersal.

N-cadherin expression in malignant germ cell tumours of the testis

BACKGROUND

Testicular germ cell tumours (TGCTs) are the most common malignancy in young men aged 18-35 years. They are clinically and histologically subdivided into seminomas and non-seminomas. Cadherins are calcium-dependent transmembrane proteins of the group of adhesion proteins. They play a role in the stabilization of cell-cell contacts, the embryonic morphogenesis, in the maintenance of cell polarity and signal transduction. N-cadherin (CDH2), the neuronal cadherin, stimulates cell-cell contacts during migration and invasion of cells and is able to suppress tumour cell growth.

METHODS

Tumour tissues were acquired from 113 male patients and investigated by immunohistochemistry, as were the three TGCT cell lines NCCIT, NTERA-2 and Tcam2. A monoclonal antibody against N-cadherin was used.

RESULTS

Tumour-free testis and intratubular germ cell neoplasias (unclassified) (IGCNU) strongly expressed N-cadherin within the cytoplasm. In all seminomas investigated, N-cadherin expression displayed a membrane-bound location. In addition, the teratomas and yolk sac tumours investigated also differentially expressed N-cadherin. In contrast, no N-cadherin could be detected in any of the embryonal carcinomas and chorionic carcinomas examined. This expression pattern was also seen in the investigated mixed tumours consisting of seminomas, teratomas, and embryonal carcinoma.

CONCLUSIONS

N-cadherin expression can be used to differentiate embryonal carcinomas and chorionic carcinomas from other histological subtypes of TGCT.

GPR56 in cancer progression: current status and future perspective

Cell adhesion is a critical process during cancer progression and is mediated by transmembrane receptors. Recently, GPR56, a member of the adhesion family of G protein-coupled receptors, was established as a new type of adhesion receptor that binds to extracellular matrix proteins and shown to play inhibitory roles in melanoma progression. Further studies revealed that the extracellular portion and the seven transmembrane domains of GPR56 function antagonistically to regulate VEGF production and angiogenesis via a signaling pathway mediated by PKCα. Tissue transglutaminase was identified as the first extracellular matrix protein that binds to GPR56. It is a crosslinking enzyme in the extracellular matrix but is also expressed in the cytosol. Tissue transglutaminase plays pleiotropic roles in cancer progression. Whether and how it might mediate GPR56-regulated cancer progression awaits further investigation.

N-cadherin is overexpressed in Crohn's stricture fibroblasts and promotes intestinal fibroblast migration

BACKGROUND

Intestinal fibroblasts mediate stricture formation in Crohn's disease (CD). Transforming growth factor-β₁ (TGF-β₁) is important in fibroblast activation, while cell attachment and migration is regulated by the adhesion molecule N-cadherin. The aim of this study was to investigate the expression and function of N-cadherin in intestinal fibroblasts in patients with fibrostenosing CD.

METHODS

Intestinal fibroblasts were cultured from seromuscular biopsies from patients undergoing resection for terminal ileal fibrostenosing CD (n = 14) or controls patients (n = 8). N-cadherin expression was assessed using Western blot and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Fibroblasts were stimulated with TGF-β₁ and selective pathway inhibitors Y27632, PD98050, and LY294002 were used to examine the Rho/ROCK, ERK-1/2, and Akt signaling pathways, respectively. Cell migration was assessed using a scratch wound assay. N-cadherin was selectively overexpressed using a plasmid.

RESULTS

Fibroblasts from fibrostenosing CD express increased constitutive N-cadherin mRNA and protein and exhibit enhanced basal cell migration relative to those from directly adjacent normal bowel. Control fibroblasts treated with TGF-β₁ induced N-cadherin in a dose-dependent manner which was inhibited by Rho/ROCK and Akt pathway modulation. Control fibroblasts exhibited enhanced cell migration in response to treatment with TGF-β₁ or transfection with an N-cadherin plasmid.

CONCLUSIONS

Fibroblasts from strictures in CD express increased constitutive N-cadherin and exhibit enhanced basal cell migration. TGF-β₁ is a potent inducer of N-cadherin in intestinal fibroblasts resulting in enhanced cell migration. The TGF-β₁-mediated induction of N-cadherin may potentiate Crohn's stricture formation.

N-cadherin cell-cell adhesion complexes are regulated by fibronectin matrix assembly

Fibronectin is a principal component of the extracellular matrix. Soluble fibronectin molecules are assembled into the extracellular matrix as insoluble, fibrillar strands via a cell-dependent process. In turn, the interaction of cells with the extracellular matrix form of fibronectin stimulates cell functions critical for tissue repair. Cross-talk between cell-cell and cell-extracellular matrix adhesion complexes is essential for the organization of cells into complex, functional tissue during embryonic development and tissue remodeling. Here, we demonstrate that fibronectin matrix assembly affects the organization, composition, and function of N-cadherin-based adherens junctions. Using fibronectin-null mouse embryonic myofibroblasts, we identified a novel quaternary complex composed of N-cadherin, β-catenin, tensin, and actin that exists in the absence of a fibronectin matrix. In the absence of fibronectin, homophilic N-cadherin ligation recruited both tensin and α5β1 integrins into nascent cell-cell adhesions. Initiation of fibronectin matrix assembly disrupted the association of tensin and actin with N-cadherin, released α5β1 integrins and tensin from cell-cell contacts, stimulated N-cadherin reorganization into thin cellular protrusions, and decreased N-cadherin adhesion. Fibronectin matrix assembly has been shown to recruit α5β1 integrins and tensin into fibrillar adhesions. Taken together, these studies suggest that tensin serves as a common cytoskeletal link for integrin- and cadherin-based adhesions and that the translocation of α5β1 integrins from cell-cell contacts into fibrillar adhesions during fibronectin matrix assembly is a novel mechanism by which cell-cell and cell-matrix adhesions are coordinated.

N-cadherin acts in concert with Slit1-Robo2 signaling in regulating aggregation of placode-derived cranial sensory neurons

Vertebrate cranial sensory ganglia have a dual origin from the neural crest and ectodermal placodes. In the largest of these, the trigeminal ganglion, Slit1-Robo2 signaling is essential for proper ganglion assembly. Here, we demonstrate a crucial role for the cell adhesion molecule N-cadherin and its interaction with Slit1-Robo2 during gangliogenesis in vivo. A common feature of chick trigeminal and epibranchial ganglia is the expression of N-cadherin and Robo2 on placodal neurons and Slit1 on neural crest cells. Interestingly, N-cadherin localizes to intercellular adherens junctions between placodal neurons during ganglion assembly. Depletion of N-cadherin causes loss of proper ganglion coalescence, similar to that observed after loss of Robo2, suggesting that the two pathways might intersect. Consistent with this possibility, blocking or augmenting Slit-Robo signaling modulates N-cadherin protein expression on the placodal cell surface concomitant with alteration in placodal adhesion. Lack of an apparent change in total N-cadherin mRNA or protein levels suggests post-translational regulation. Co-expression of N-cadherin with dominant-negative Robo abrogates the Robo2 loss-of-function phenotype of dispersed ganglia, whereas loss of N-cadherin reverses the aberrant aggregation induced by increased Slit-Robo expression. Our study suggests a novel mechanism whereby N-cadherin acts in concert with Slit-Robo signaling in mediating the placodal cell adhesion required for proper gangliogenesis.

Promigratory and procontractile growth factor environments differentially regulate cell morphogenesis

Three-dimensional (3D) cell-matrix cultures provide a useful model to analyze and dissect the structural, functional, and mechanical aspects of cell-matrix interactions and motile behavior important for cell and tissue morphogenesis. In the current studies we tested the effects of serum and physiological growth factors on the morphogenetic behavior of human fibroblasts cultured on the surfaces of 3D collagen matrices. Fibroblasts in medium containing serum contracted into clusters, whereas cells in medium containing platelet-derived growth factor (PDGF) were observed to migrate as individuals. The clustering activity of serum appeared to depend on lysophosphatidic acid, required cell contraction based on inhibition by blocking Rho kinase or myosin II, and was reversed upon switching to PDGF. Oncogenic Ras transformed human fibroblasts did not exhibit serum-stimulated cell clustering. Our findings emphasize the importance of cell-specific promigratory and procontractile growth factor environments in the differential regulation of cell motile function and cell morphogenesis.

Adhesion and transcellular migration of neutrophils and B lymphocytes on fibroblasts

During tissue inflammation, infiltrated leukocytes may have physical contacts with fibroblasts. We observed that neutrophils and B lymphocytes adhered in a larger proportion than T cells on cultured fibroblasts. Microscopy showed that adhesion was also characterized by leukocyte engulfment by the fibroblasts. In migration assays, only neutrophils and B lymphocytes were selectively able to migrate through a fibroblast barrier. Adhesion and migration were increased by stimulation with tumor necrosis factor-alpha (TNF-alpha) and phorbol-12-myristate-13-acetate (PMA). Antibodies against ICAM-1/beta2 integrin blocked the interaction of neutrophils to fibroblasts. For B lymphocytes the couple VCAM-1/alpha4 integrin was also involved in this interaction. Human skin fibroblasts presented similar adhesion characteristics as rat cardiac fibroblasts. By measuring the distance between the border of migration holes and cadherin-positive adherens junctions, more than 65% of the holes correspond to the transcellular route over the paracellular route. Furthermore, vimentin staining revealed that the migration holes were highly nested by intermediate filaments in accordance with the transcellular route. Our results demonstrated that engulfment of neutrophils and B lymphocytes by fibroblasts resulted in selective passage by a transcellular route.

Fibroblast elongation and dendritic extensions in constrained versus unconstrained microtissues

Cytoskeletal tension is fundamental to many biological processes, including germ layer sorting during embryogenesis [Krieg et al., 2008]. In vitro, such tension influences cell sorting in self-assembled, 3D microtissues and can be of sufficient magnitude to cause complex-shaped microtissue failure [Dean et al., 2007]. To examine the process of failure under cell-derived tension, we subjected normal human fibroblasts (NHFs) to directed self-assembly [Dean et al., 2007] in micro-molds designed to yield self-constraining microtissues. As cells contracted in this assay, the constrained microtissues narrowed, thinned and ultimately failed at their midpoints. By adding small numbers of GFP+ cells, changes in cell movement and morphology were assessed and compared to those of unconstrained microtissues. We found that cells formed numerous dendritic extensions within an hour of self-assembly and retracted these extensions as they elongated up to 30 times their initial diameter ( approximately 600 microm) just prior to failure. Surprisingly, significant coordination in cell motility was observed over large distances within microtissues. Pharmacologic interventions showed that failure was myosin II and Rho kinase dependent and inhibition of failure resulted in shorter cells with greater numbers of extensions. These findings further our understanding of cellular self-assembly and introduce the use of GFP+ cells with directed self-assembly as a scaffold-free analogue to fibroblast-populated collagen gels (FPCGs).

Cytoskeletal-mediated tension modulates the directed self-assembly of microtissues

The ability of cells to self-assemble into a microtissue such as a spheroid has been attributed mainly to intercellular cohesiveness achieved by the binding of surface membrane proteins such as cadherins. However, highly dynamic and complex cytoskeletal rearrangements are coordinated with these binding events and therefore are likely to participate in self-assembly. By inhibiting such cytoskeletal activity, Y-27632 has been used to prevent and treat fibrotic disease. Here, we used the Rho kinase inhibitor to investigate the role that cellular contraction plays in self-assembly. Normal human fibroblasts (NHFs), Reuber-H35 hepatoma cells (H35s), and mixes of the two (hybrid) were treated with drug during directed self-assembly of microtissues in nonadhesive, micromolded hydrogels. The kinetics of self-assembly of both constrained and unconstrained NHF microtissues were dramatically slowed by the drug, and inhibition was dose responsive and reversible. Although sorting of NHFs and H35s occurred normally in the presence of drug, Y-27632-treated NHFs sorted to the outside of a spheroid when mixed with untreated NHFs. When mixed with H35s in trough micromolds, NHFs could drive spheroid formation from the core of the hybrid microtissues even in small numbers relative to H35s (1:19). These findings demonstrate that cellular contraction controls the kinetics of self-assembly and suggests that NHFs within the core of a microtissue can transmit contractile forces through heterotypic bonds with H35s. The control of directed self-assembly using fibroblasts and contraction inhibitors may be useful for in vitro tissue engineering as well as represent an in vitro model for fibrotic disease.

Changes in regulation of cell-cell adhesion during tumor transformation

Cadherin-mediated cell-cell adhesion defines the integrity of most tissues. Cell-cell adherens junctions are dynamic structures whose functional state is regulated by interactions of cadherin with beta-catenin, p120, and actin cytoskeleton structures. Small GTPases of the Rho family and GTPase Rap1 play the central role in the formation and maintenance of cell-cell adhesion. Aberrant activation of signaling pathways, transcriptional repression of the E-cadherin gene, ectopic expression of N-cadherin, and disturbances in regulation of adhesive and transcriptional functions of beta-catenin stimulate tumor progression.

Oncogenic Ras-transformed human fibroblasts exhibit differential changes in contraction and migration in 3D collagen matrices

Tractional force exerted by tissue cells in 3D collagen matrices can be utilized for matrix remodeling or cell migration. The interrelationship between these motile processes is not well understood. The current studies were carried out to test the consequences of oncogenic Ras (H-Ras(V12)) transformation on human fibroblast contraction and migration in 3D collagen matrices. Beginning with hTERT-immortalized cells, we prepared fibroblasts stably transformed with E6/E7 and with the combination HPV16 E6/E7 and H-Ras(V12). Oncogenic Ras-transformed cells lost contact inhibition of cell growth, formed colonies in soft agar and were unable to make adherens junctions. We observed no changes in the extent or growth factor dependence of collagen matrix contraction (floating or stress-relaxation) by oncogenic Ras-transformed cells. On the other hand, transformed cells in nested collagen matrices lost not only growth factor selectivity, but also cell-matrix density-dependent inhibition of migration. These findings demonstrate differential regulation of collagen matrix contraction and cell migration in 3D collagen matrices.

The GSK-3/beta-catenin-signalling axis in smooth muscle and its relationship with remodelling

beta-Catenin is a plasma membrane-associated protein that plays a dual role in cellular signalling by stabilizing cadherin mediated cell-cell contact and by regulating TCF-/LEF-mediated gene transcription. Traditionally, the role of beta-catenin in health and disease has mainly been studied in the context of development and uncontrolled cell growth in diseases such as cancer. Recent findings indicate, however, that beta-catenin also plays a significant role in fibro-proliferative diseases of several organ systems and that beta-catenin regulates mitogenic responses of smooth muscle cells. As several diseases of the internal organs are characterized by structural and phenotypic abnormalities of smooth muscle, including increased fibro-proliferative responses, these findings implicate that beta-catenin could play a broad pathophysiological role. This article will review this potential novel role for beta-catenin and associated intracellular signalling in smooth muscle and discuss the hypothesis that it plays a central role in smooth muscle remodelling.

Fibrogenic fibroblasts increase intercellular adhesion strength by reinforcing individual OB-cadherin bonds

We have previously shown that the switch from N-cadherin to OB-cadherin expression increases intercellular adhesion between fibroblasts during their transition from a migratory to a fibrogenic phenotype. Using atomic force microscopy we here show that part of this stronger adhesion is accomplished because OB-cadherin bonds resist approximately twofold higher forces compared with N-cadherin junctions. By assessing the adhesion force between recombinant cadherin dimers and between native cadherins in the membrane of spread fibroblasts, we demonstrate that cadherin bonds are reinforced over time with two distinct force increments. By modulating the degree of lateral cadherin diffusion and F-actin organization we can attribute the resulting three force states to the single-molecule bond rather than to cadherin cluster formation. Notably, association with actin filaments enhances cadherin adhesion strength on the single-molecule level up to threefold; actin depolymerization reduces single-bond strength to the level of cadherin constructs missing the cytoplasmic domain. Hence, fibroblasts reinforce intercellular contacts by: (1) switching from N- to OB-cadherin expression; (2) increasing the strength of single-molecule bonds in three distinct steps; and (3) actin-promoted intrinsic activation of cadherin extracellular binding. We propose that this plasticity adapts fibroblast adhesions to the changing mechanical microenvironment of tissue under remodeling.

Rods, tori, and honeycombs: the directed self-assembly of microtissues with prescribed microscale geometries

It is thought that, due to energy and surface area:volume minimization, the spheroid is the terminal structure of cellular self-assembly. We investigated whether self-assembly could be directed to generate complex-shaped structures. Using micromolded, nonadhesive agarose hydrogels seeded with rat hepatoma (H35s), human fibroblasts (NHFs), or their mix (1:1), we show that cells can self-assemble rods, tori, and honeycombs. We found that in trough-shaped recesses up to 2.2 mm long, H35s readily formed rod-like structures stable at 49% the recess lengths. They also formed intact tori (88%) and fully intact honeycombs structures with patent lumens (9/9) even when released from the mold. In contrast, NHFs in trough features progressed rapidly to spheroids and formed fewer stable tori (30%) and honeycombs (0/9). The 1:1 mix of cells self-assembled rapidly like NHFs but were able to form more stable structures (tori: 30%, honeycombs: 3/9). Experiments with labeled cells in tori and honeycombs revealed that cells self-segregated in these complex structures, with H35s enveloping NHFs, and that NHFs had different morphologies in taut vs. relaxed structures. These data open new possibilities for in vitro tissue models for embryo- and organogenesis study as well as for tissue engineering applications.