Dissociation of actin microfilament organization from acquisition and maintenance of elongated shape of human dermal fibroblasts in three-dimensional collagen gel

Registration of the extracellular matrix components constituting the fibroblastic focus in idiopathic pulmonary fibrosis

The extracellular matrix (ECM) in idiopathic pulmonary fibrosis (IPF) drives fibrosis progression; however, the ECM composition of the fibroblastic focus (the hallmark lesion in IPF) and adjacent regions remains incompletely defined. Herein, we serially sectioned IPF lung specimens constructed into tissue microarrays and immunostained for ECM components reported to be deregulated in IPF. Immunostained sections were imaged, anatomically aligned, and 3D reconstructed. The myofibroblast core of the fibroblastic focus (defined by collagen I, α-smooth muscle actin, and procollagen I immunoreactivity) was associated with collagens III, IV, V, and VI; fibronectin; hyaluronan; and versican immunoreactivity. Hyaluronan immunoreactivity was also present at the fibroblastic focus perimeter and at sites where early lesions appear to be forming. Fibrinogen immunoreactivity was often observed at regions of damaged epithelium lining the airspace and the perimeter of the myofibroblast core but was absent from the myofibroblast core itself. The ECM components of the fibroblastic focus were distributed in a characteristic and reproducible manner in multiple patients. This information can inform the development of high-fidelity model systems to dissect mechanisms by which the IPF ECM drives fibrosis progression.

Tissue engineering approaches for the construction of a completely autologous tendon substitute

Tissue engineering is a multidisciplinary field that involves the application of the principles and methods of engineering and life sciences towards i) the fundamental understanding of structure-function relationships in normal and pathological mammalian tissues and ii) the development of biological substitutes that restore, maintain or improve tissue function. The goal of tissue engineering is to surpass the limitations of conventional treatments based on organ transplantation and biomaterial implantation. The field of tendon tissue engineering is relatively unexplored due to the difficulty in in vitro preservation of tenocyte phenotype. Only recently has mechanobiology allowed us to gain a better understanding of the fundamental role of in vitro mechanical stimuli in maintaining the phenotype of tendinous tissue. This review analyzes the techniques used so far for in vitro regeneration of tendinous tissue.

Characterization of dense artificial connective tissues generated in a newly designed bioreactor

Dense connective tissues were generated simultaneously by accumulating collagen fibrils and fibroblasts on stainless steel mesh using a bioreactor system that we designed. The advantage of our system is that the artificial connective tissues can be generated within 24 hr in the absence of inhibitors against matrix metalloproteinases. The fibroblasts were suspended in 200 mL of Dulbecco's modified Eagle's medium containing 10% fetal bovine serum and 0.5 mg/mL type I collagen. The mixed solution was circulated in two types of bioreactors with cylindrical or vertical configurations to generate luminal or parenchymal tissues, respectively. The gelatin zymography showed that MMPs were first detected in the media after 8 hr from the start of circulation and reached the highest levels on day 3. Glossy white aggregates, 1-3 mm in thickness, depending on the circulation period, accumulated on mesh grids. Fibroblasts were embedded in the network of collagen fibrils and possessed oval nuclei with or without prominent cell processes to form a bipolar shape. We could not observe distended cisternae of the endoplasmic reticula, the Golgi apparatus, or exploded mitochondria, showing hypoxic degenerative alterations of fibroblasts in dense connective tissues. The artificial tissues generated by our system will be useful for biological studies and transplantation therapy.

Keratinocyte differentiation and proliferation are regulated by adhesion to the three-dimensional meshwork structure of type IV collagen

We examined the behavior of human foreskin keratinocytes (HFKs) on reconstituted type IV collagen gel. HFKs survived for several days and the upper layer cells expressed a differentiation marker, involucrin. Apoptosis was induced after involucrin expression while cell proliferation was suppressed. On molecular type IV collagen, integrins shifted from alpha 2 beta 1 to alpha 3 beta 1 during HFK culture. On type IV collagen gel, HFKs initially expressed integrin alpha 2 beta 1, and later expressed integrin alpha 3 beta 1 in the presence of alpha 2 beta 1 did not disappear. Using synthetic peptides, we examined integrin alpha2-mediated adhesion to type IV collagen gel. Addition of synthetic peptide dose-dependently inhibited cell adhesion both on type IV collagen gel and on molecular type IV collagen. On type IV collagen gel, weaker phosphorylation of focal adhesion kinase, paxillin, and Akt was observed compared with the molecular forms. Based on these observations, we think type IV collagen gel is a novel culture substrate that mimics the physiological environment for HFKs.

Evaluation of Endothelial Cell Adhesion onto Different Protein/Gold Electrodes by EIS

To study cell attachment to biomaterials, several proteins such as fibronectin, collagen IV, heparin, immunoglobulin G, and albumin have been deposited onto polystyrene adsorbed on a self-assembled monolayer (silane or thiol) on glass or gold, respectively. The different steps of this multilayer assembly have been characterized by electrochemical impedance spectroscopy (EIS). These data are compared to those of adhesion rate, viability percentage, and cytoskeleton labeling for a better understanding of the cell adhesion process to each protein. All the proteins are endothelial cell adhering biomolecules but not with the same features. A linear relationship has been established between adhesion rate and resistance of the endothelial cell/protein interface for all negatively charged proteins.

Electrical probing of endothelial cell behaviour on a fibronectin/polystyrene/thiol/gold electrode by Faradaic electrochemical impedance spectroscopy (EIS)

The electrochemical impedance spectroscopy (EIS) technique has been shown to be an effective tool for monitoring endothelial cell behaviour on a multilayer functionalised gold electrode. Polystyrene, a reproducible model substrate, is deposited as a thin layer on a thiol functionalised gold electrode. Fibronectin, a protein promoting endothelial cell adhesion, is then adsorbed on the polystyrene surface. The different steps of this multilayer assembly are characterized by Faradaic impedance. The charge transfer resistance and the capacitance for the total layer are modified at each step according to the electrical properties of each layer. This gives the endothelial cells' electrical state in terms of its resistive and capacitive properties. In this study, the endothelial cell layer presents a specific charge transfer resistance equal to 1.55 kOmega cm(2) with no large defects in the cell layer, and a specific capacitance equal to few microF cm(-2) explained by the existence of pseudopods. These electrical properties are correlated to the endothelial cell viability, adhesion and cytoskeleton organization.

Three-dimensional coculture of endometrial cancer cells and fibroblasts in human placenta derived collagen sponges and expression matrix metalloproteinases in these cells

OBJECTIVE

Collagen gel constitutes a valuable tool for the study of cell-matrix interactions; however, it is sometimes difficult to use the gel, in which tumor and stromal cells are cocultured, for immunohistochemistry, because it is easily broken during the process of fixation and embedding in paraffin, especially after long-term culture.

METHODS

To examine the interaction between endometrial cancer cells and fibroblasts in tumor invasion, we carried out three-dimensional (3-D) coculture of various endometrial cancer cell lines and fibroblasts in human placenta derived collagen sponges and analyzed the expression and localization of matrix metalloproteinases (MMP) and plasminogen activators (PA) in these cells by immunohistochemistry.

RESULTS

After 4 weeks of culture on the collagen sponges, endometrial cancer cells composed stratiform or glandular structures on the layer of extracellular matrix, which was composed from fibloblasts and extracellular matrix. Compared to Ishikawa cells, which were rarely invasive, HEC-1A and HEC-1BE and cocultured fibroblasts showed high invasiveness and strong expression of some proteins. In cell line HEC-1BE, MMP-1, -7, and -9, MT1-MMP, tissue inhibitors of metalloproteinases 2, and uPA showed intensive staining in both cancer cells and fibroblasts by immunohistochemistry. HEC-1A cells and cocultured fibroblasts showed expression patterns similar to those of HEC-1BE.

CONCLUSION

These results suggested that expression of MMPs and uPA was accelerated in fibroblasts surrounded by cancer cells. We believe that our 3-D coculture system has merit in that the interaction between cancer cells and stromal cells can be visually analyzed by immunohistochemistry and that experiments for a long period, at least 2 weeks, are possible. Furthermore, it is expected that some animal, e.g., nude mouse, experiments can be replaced by experiments using this culture system.

Cytochalasin D induces edema formation and lowering of interstitial fluid pressure in rat dermis

The increased capillary fluid filtration required to create a rapid edema formation in acute inflammation can be generated by lowering the interstitial fluid pressure (P(IF)). The lowering of P(IF) appears to involve dynamic beta(1)-integrin-mediated interactions between dermal cells and extracellular matrix fibers. The present study specifically investigates the role of the cell cytoskeleton, i.e., the contractile apparatus of cells, in controlling P(IF) in rat skin as the integrins are linked to both the cytoskeleton and the extracellular matrix. P(IF) was measured using a micropuncture technique in the dorsal skin of the hind paw at a depth of 0.2--0.5 mm and following the induction of circulatory arrest with the intravenous injection of KCl in pentobarbital anesthesia. This procedure prevented the transcapillary flux of fluid and protein leading to edema formation in acute inflammation, which in turn can increase the P(IF) and therefore potentially mask a decrease of P(IF). Control P(IF) (n = 42) averaged -0.8 +/- 0.5 (means +/- SD) mmHg. In the first group of experiments, subdermal injection of 2 microl cytochalasin D, a microfilament-disrupting drug, lowered P(IF) to an average of -2.8 +/- 0.7 mmHg within 40 min postinjection (P < 0.05 compared with control). Subdermal injection of vehicle (10% DMSO in PBS or PBS alone) did not change the P(IF) (P > 0.05). Lowering of the P(IF) was not observed after the injection of colchicine or nocodazole, which specifically disrupts microtubuli in cultured cells. In the second group of experiments, 2 microl of cytochalasin D injected subdermally into rats with intact circulation increased the total tissue water (TTW) and albumin extravasation rate (E(ALB)) by 0.7 +/- 0.2 and 0.4 +/- 0.3 ml/g dry wt, respectively (P < 0.05 compared with vehicle). Nocodazole and colchicine did not significantly alter the TTW or E(ALB) compared with the vehicle (P > 0.05). Taken together, these findings strongly suggest that the connective tissue cells can participate in control of P(IF) via the actin filament system. In addition, the observation that subdermal injection of cytochalasin D lowered P(IF) indicates that a dynamic assembly and disassembly of actin filaments also occurs in the cells of dermal tissues in vivo.

Effect of type XII or XIV collagen NC-3 domain on the human dermal fibroblast migration into reconstituted collagen gel

Type XII and XIV collagens localize near the surface of banded collagen fibrils and most likely work as a molecular bridge between collagen fibrils. We have shown that both collagens can modulate the interactions between collagen fibrils, allowing fibroblasts to act upon the fibrils to vary the deformability. In the present study the effect of the globular domains (collagenase-resistant domains) of type XII and XIV collagens (XII-NC-3 and XIV-NC-3) on the migration of fibroblasts into the reconstituted type I collagen gel was investigated. Cell attachment and proliferation on the collagen gel were unaffected. The migration of fibroblasts into the gel was increased proportionally to the concentration of collagen. We found that XII-NC-3 and XIV-NC-3 domains caused decreases in the numbers of fibroblasts that migrated into the gel. Heat treatment of XII-NC-3 and XIV-NC-3 or the addition of polyclonal antibodies eliminated the suppressive activity on fibroblast migration, showing that the intact conformation of NC-3 domain is important for suppression of migration. The results suggest that both NC-3 domains influence the deformability of type I collagen fibril networks, which may cause the change in fibroblast migration.

An interleukin-1 loop is induced in human skin fibroblasts upon stress relaxation in a three-dimensional collagen gel but is not involved in the up-regulation of matrix metalloproteinase 1

The integrin-mediated stress relaxation as it occurs in a retracting three-dimensional collagen gel (RCG) is accompanied by a large up-regulation of the interstitial collagenase, matrix metalloproteinase 1 ((MMP-1), EC 3.4.24.7), regulated notably by interleukin-1 (IL-1), phorbol esters, and cytoskeleton-disrupting drugs as cytochalasin D (CD). The repression of MMP-1 up-regulation in RCG by cycloheximide suggested the participation in the regulation process of a de novo synthesized intermediary component. We demonstrate here that culture of human skin fibroblasts in RCG or in CD- and 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated monolayers resulted in the activation of an IL-1 autocrine feedback loop that was switched off by the naturally occurring IL-1 receptor antagonist (IL-1RA), a blocker of the common IL-1 receptor. The IL-1RA did not suppress the MMP-1 up-regulation induced in RCG nor in CD-treated cells, indicating that the up-regulation of MMP-1 and the IL-1 autocrine loop occurred in an independent way, while the TPA-induced MMP-1 expression was suppressed by the receptor antagonist. The RCG- as well as the TPA-, IL-1-, and CD-induced up-regulation of both MMP-1 and IL-1 was totally suppressed by protein tyrosine kinases inhibitors. In contrast bisindoylmaleimide, at a concentration (5 microM) that inhibits the TPA-induced protein kinase C activity, suppressed the CD-induced MMP-1 expression but did not or barely altered that induced in RCG or by IL-1. None of the other tested inhibitors of a variety of signaling pathways including those used by integrins was able to suppress the RCG or CD-induced MMP-1. These results point to a potent regulation of MMP-1 by mechanical stress relaxation, a process depending on de novo protein synthesis and occurring independently of the activation of an IL-1 autocrine feedback loop.

Fibroblast movements during contraction of collagen lattices--a quantitative study using a new three-dimensional time-lapse technique with phase-contrast laser scanning microscopy

In this study we assessed the behavior of fibroblasts during contraction of collagen lattices. We applied a new technique for three-dimensional time-lapse studies of movements of living cells using phase-contrast laser scanning microscopy. Five anchored and five floating collagen lattices were studied regarding the activity of cells during a 7-h period of active contraction. Three-dimensional reconstructions of the fibroblasts and their extensions were made from datasets of 16-26 "optical sections" 5 microm apart recorded hourly during the period of measurements. The distance between fibroblast nuclei in the floating lattices decreased by a mean of 6.8 microm, but remained constant in the anchored group. Only minor variations were found in the angle between a line connecting any two nuclei and the tangent of the lattice margin. The lengths of the cellular extensions continuously changed by shortening and extending, and an increasing number of intercellular contacts were established with time. The angle between the extensions and the periphery of the lattice varied continually, and no distinct pattern of arrangement of the extensions was seen. In conclusion, we have shown in living cells in vitro that fibroblasts do not appear to move around within lattices during contraction but rather send out and withdraw cellular extensions continuously. This speaks against cellular locomotion or movement as a main feature of contraction. Time-lapse scanning laser microscopy has also been shown to be a suitable method to study cellular behavior quantitatively in three dimensions during lattice contraction.

Mechano-sensing and mechano-reaction of soft connective tissue cells

One main function of the connective tissues is to provide cells with a mechanically resistant attachment support required for survival, division and differentiation. All cells contain membrane-anchored attachment proteins able to recognize specific chemical motifs in the extracellular macromolecules forming the supporting scaffold, made of various types of collagen, adhesive glycoproteins, elastin, proteoglycans, etc... These cell-matrix interactions are mainly mediated by receptors of the integrins family, heterodimeric molecules made of an extracellular domain connected through a transmembrane sequence to an intracytoplasmic tail. Upon recognition of the extracellular ligand, the clustering and activation of the integrins result in the recruitment of a complex of proteins and formation of the focal adhesion plaque, containing both cytoskeletal and catalytic signaling molecules. Activation results in polymerization of actin and formation of stress fibers. These structures establish a physical link between the extracellular matrix components and the cytoskeleton through the integrins providing a continuous path acting as a mechanotransducer. This connection is used by the cells to perform their mechanical functions as adhesion, migration and traction. In vitro experimental models using fibroblasts in a collagen gel demonstrate that cells are in mechanical equilibrium with their support which regulates their replicative and biosynthetic phenotype. The present review discusses the molecular structures operating in the transmission of the mechanical messages from the support to the connective tissue cells, and their effect on the cellular machinery. We present arguments for investigating these mechanisms in understanding the perception of reduced gravity and the resulting reaction leading to microgravity induced pathologies.

Deposition of collagen fibril bundles by long-term culture of fibroblasts in a collagen sponge

Human fibroblasts cultured for 10 days in a collagen sponge migrated through the pores of the sponge and expressed a moderate mitotic activity, which stabilized after 10 days, and a high collagen and protein synthesis. Between 10 and 27 days, the newly synthesized collagen filled the pores of the sponge. This matrix accumulation induced a delayed decrease of collagen and protein synthesis. Finally, after 27 days of culture, the fibroblasts expressed low biosynthetic activities similar to the ones exhibited in vivo. The newly synthesized matrix was highly differentiated, as shown by the presence of a dense network of quarter-staggered collagen fibrils (42 nm +/- 6 nm in diameter) surrounding the cells. The size and the shape of these fibrils demonstrated that the newly synthesized procollagen was fully processed in collagen by removal of their N- and C-terminal propeptides. Moreover, these fibrils were packed in bundles organized into an interwoven network that mimics the pattern of the papillary dermis. These findings show that fibroblasts cultured for one month in a collagen sponge construct large amounts of a highly differentiated connective tissue.