Extracellular matrix proteins of human epidermal keratinocytes and feeder 3T3 cells

In vitro toxicity of fine and coarse particulate matter on the skin, ocular and lung microphysiological cell-culture systems

Particulate matter (PM) has been associated with adverse effects on human health, causing allergies, skin and eye irritation and corrosion, respiratory tract irritation, headaches, bronchoconstriction, cardiopulmonary diseases such as asthma, chronic obstructive pulmonary disease (COPD), lung cancer, reproductive problems, premature deaths, and epigenetic changes that lead to a wide variety of cancers, among other health conditions. The air quality in the Medellín - Colombia presents fluctuations that oscillate between the maximum permissible levels established at the national level and by the WHO, which represents a latent risk to people's health. Although important efforts have been made to quantify the different levels of pollution and administrative measures have been established to mitigate air pollution, little research work has been done to establish the relationship between these levels of pollutants and the effects on biological systems. The objective of the present research was to make a morphological and chemical characterization of particulate matter (PM) captured with a commercial air filter and a electrospun nanofiber membrane and evaluate the cytotoxicity of the each PM extracts in monolayer and co-culture models which recreate microphysiological systems of lung, skin and cornea and propose the possible cellular interactions that lead the cytotoxic response of the chemical compounds found in particulate matter in cities. The morphology and elemental chemical characterization were done with scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM - EDS). For the polycyclic aromatic hydrocarbons detection was made with a chromatographic method accoupled to mass spectrometer. Finally, the cytotoxicity was made in monolayers of A549, HEK001, and SIRC cell lines and microphysiological systems consisting of two-cell layer construct to resemble the interaction between fibroblast and epithelial cells that comprises naturally the corneal, skin and lung tissue. We performed three different cocultures models with BALB/3T3 clone A31 as a feeder layer, using porous Transwell® inserts in the in-contact and non-contact way. Monolayer and co-culture models were exposed to coarse and fine PM (1, 2, and 5 mg/mL) and the cell viability was evaluated at 24 h using an MTT assay. The electrospun nanofibers membranes demonstrates higher efficiency to capture PM with different sizes and high concentration of polycyclic aromatic hydrocarbons, heavy metals, and other chemical compounds responsible of many human diseases. Cytotoxic effects of MP were observed in all models at higher concentration; however, models exposed to fine PM exhibited a significant reduction in cell viability compared to those exposed to coarse PM. In addition, multilayer models are more resistant to PM exposure than monolayer models. Furthermore, the study indicated that, depending on the seeding strategy, different results might be observed: the non-contact model showed higher resistance to PM exposure than in-contact for SIRC and HEK001, but A549 monolayers showed the highest viability response. This study demonstrates the usefulness of applying co-culture models to assess environmental pollutant toxicity, in addition to being a potential alternative method to animal testing for risk assessment.

Characterization of Pseudogymnoascus destructans conidial adherence to extracellular matrix: Association with fungal secreted proteases and identification of candidate extracellular matrix binding proteins

Pseudogymnoascus destructans is the etiological agent of white-nose syndrome (WNS), a fungal skin infection of hibernating bats. Pathophysiology of the disease involves disruption of bat metabolism and hibernation patterns, which subsequently causes premature emergence and mortality. However, information on the mechanism(s) and virulence factors of P. destructans infection is minimally known. Typically, fungal adherence to host cells and extracellular matrix (ECM) is the critical first step of the infection. It allows pathogenic fungi to establish colonization and provides an entry for invasion in host tissues. In this study, we characterized P. destructans conidial adherence to laminin and fibronectin. We found that P. destructans conidia adhered to laminin and fibronectin in a dose-dependent, time-dependent and saturable manner. We also observed changes in the gene expression of secreted proteases, in response to ECM exposure. However, the interaction between fungal conidia and ECM was not specific, nor was it facilitated by enzymatic activity of secreted proteases. We therefore further investigated other P. destructans proteins that recognized ECM and found glyceraldehyde-3-phosphate dehydrogenase and elongation factor 1-alpha among the candidate proteins. Our results demonstrate that P. destructans may use conidial surface proteins to recognize laminin and fibronectin and facilitate conidial adhesion to ECM. In addition, other non-specific interactions may contribute to the conidial adherence to ECM. However, the ECM binding protein candidates identified in this study highlight additional potential fungal virulence factors worth investigating in the P. destructans mechanism of infection in future studies.

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

Conditional reprogramming: next generation cell culture

Long-term primary culture of mammalian cells has been always difficult due to unavoidable senescence. Conventional methods for generating immortalized cell lines usually require manipulation of genome which leads to change of important biological and genetic characteristics. Recently, conditional reprogramming (CR) emerges as a novel next generation tool for long-term culture of primary epithelium cells derived from almost all origins without alteration of genetic background of primary cells. CR co-cultures primary cells with inactivated mouse 3T3-J2 fibroblasts in the presence of RHO-related protein kinase (ROCK) inhibitor Y-27632, enabling primary cells to acquire stem-like characteristics while retain their ability to fully differentiate. With only a few years' development, CR shows broad prospects in applications in varied areas including disease modeling, regenerative medicine, drug evaluation, drug discovery as well as precision medicine. This review is thus to comprehensively summarize and assess current progress in understanding mechanism of CR and its wide applications, highlighting the value of CR in both basic and translational researches and discussing the challenges faced with CR.

Conditional reprogramming: Modeling urological cancer and translation to clinics

Patient-derived models, including cell models (organoids and conditionally reprogrammed cells [CRCs]) and patient-derived xenografts, are urgently needed for both basic and translational cancer research. Conditional reprogramming (CR) technique refers to a co-culture system of primary human normal or tumor cells with irradiated murine fibroblasts in the presence of a Rho-associated kinase inhibitor to allow the primary cells to acquire stem cell properties and the ability to proliferate indefinitely in vitro without any exogenous gene or viral transfection. Considering its robust features, the CR technique may facilitate cancer research in many aspects. Under in vitro culturing, malignant CRCs can share certain genetic aberrations and tumor phenotypes with their parental specimens. Thus, tumor CRCs can promisingly be utilized for the study of cancer biology, the discovery of novel therapies, and the promotion of precision medicine. For normal CRCs, the characteristics of normal karyotype maintenance and lineage commitment suggest their potential in toxicity testing and regenerative medicine. In this review, we discuss the applications, limitations, and future potential of CRCs in modeling urological cancer and translation to clinics.

Protocol for the long-term culture of human primary keratinocytes from the normal colorectal mucosa

Procedures for in vitro culturing of human primary keratinocytes from normal colon mucosa specimens have not been fully feasible, thus far. The protocol described herein allows primary keratinocytes from small tissue fragments of colorectal mucosa biopsies to grow in vitro. The procedure develops in three steps: (a) the enzymatic digestion of the tissue biopsy; (b) the use of cloning rings to purify primary keratinocyte colonies, (c) a defined keratinocyte medium to grow these cells in long-term culture. Our cultural method enables normal primary keratinocytes to be obtained by simple and rapid techniques. In our culture condition, primary keratinocytes express specific epithelial markers. Colorectal mucosa keratinocyte colonies require approximately 2 weeks to grow. Compared with previous approaches, our protocol provides a valuable model of study for human primary keratinocytes from normal colorectal (NCR) mucosa both at the cellular and molecular levels. It is well known, that different mutations occurring during the multistep process of carcinogenesis in the NCR mucosa, are strictly associated to the onset/progression of the colorectal carcinoma. On this ground, normal keratinocytes grown with our protocol, may represent an innovative tool to investigate the mechanisms that lead to colorectal carcinoma and other diseases. Our innovative procedure may allow to perform comparative investigations between normal and pathological colorectal cells.

Regenerating human epithelia with cultured stem cells: feeder cells, organoids and beyond

More than 40 years ago, Howard Green's laboratory developed a method for long-term expansion of primary human epidermal keratinocytes by co-culture with 3T3 mouse embryonic fibroblasts. This was a breakthrough for in vitro cultivation of cells from human skin and later for other epithelia: it led to the first stem cell therapy using cultured cells and has vastly increased our understanding of epithelial stem cell biology. In recent years, new methods to expand epithelial cells as three-dimensional organoids have provided novel means to investigate the functions of these cells in health and disease. Here, we outline the history of stratified epithelial stem cell culture and the application of cultured epithelial cells in clinical therapies. We further discuss the derivation of organoids from other types of epithelia and the challenges that remain for the translation of novel stem cell therapies toward clinical use.

Epidermal grafting for wound healing: a review on the harvesting systems, the ultrastructure of the graft and the mechanism of wound healing

Epidermal grafting for wound healing involves the transfer of the epidermis from a healthy location to cover a wound. The structural difference of the epidermal graft in comparison to the split-thickness skin graft and full-thickness skin graft contributes to the mechanism of effect. While skin grafting is an epidermal transfer, little is known about the precise mechanism of wound healing by epidermal graft. This paper aims to explore the evolution of the epidermal graft harvesting system over the last five decades, the structural advantages of epidermal graft for wound healing and the current hypotheses on the mechanism of wound healing by epidermal graft. Three mechanisms are proposed: keratinocyte activation, growth factor secretion and reepithelialisation from the wound edge. We evaluate and explain how these processes work and integrate to promote wound healing based on the current in vivo and in vitro evidence. We also review the ongoing clinical trials evaluating the efficacy of epidermal graft for wound healing. The epidermal graft is a promising alternative to the more invasive conventional surgical techniques as it is simple, less expensive and reduces the surgical burden for patients in need of wound coverage.

The Interaction Between Human Papillomaviruses and the Stromal Microenvironment

Human papillomaviruses (HPVs) are small, double-stranded DNA viruses that replicate in stratified squamous epithelia and cause a variety of malignancies. Current efforts in HPV biology are focused on understanding the virus-host interactions that enable HPV to persist for years or decades in the tissue. The importance of interactions between tumor cells and the stromal microenvironment has become increasingly apparent in recent years, but how stromal interactions impact the normal, benign life cycle of HPVs, or progression of lesions to cancer is less understood. Furthermore, how productively replicating HPV impacts cells in the stromal environment is also unclear. Here we bring together some of the relevant literature on keratinocyte-stromal interactions and their impacts on HPV biology, focusing on stromal fibroblasts, immune cells, and endothelial cells. We discuss how HPV oncogenes in infected cells manipulate other cells in their environment, and, conversely, how neighboring cells may impact the efficiency or course of HPV infection.

Epigenetic Regulation of Epidermal Stem Cell Biomarkers and Their Role in Wound Healing

As an actively renewable tissue, changes in skin architecture are subjected to the regulation of stem cells that maintain the population of cells responsible for the formation of epidermal layers. Stems cells retain their self-renewal property and express biomarkers that are unique to this population. However, differential regulation of the biomarkers can initiate the pathway of terminal cell differentiation. Although, pockets of non-clarity in stem cell maintenance and differentiation in skin still exist, the influence of epigenetics in epidermal stem cell functions and differentiation in skin homeostasis and wound healing is clearly evident. The focus of this review is to discuss the epigenetic regulation of confirmed and probable epidermal stem cell biomarkers in epidermal stratification of normal skin and in diseased states. The role of epigenetics in wound healing, especially in diseased states of diabetes and cancer, will also be conveyed.

Focal-adhesion-independent integrin-αv regulation of FAK and c-Myc is necessary for 3D skin formation and tumor invasion

Integrins play crucial roles in epithelial adhesion, proliferation, wound healing and cancer. In the epidermis, the roles of many integrin subunits are incompletely defined and mechanistic details regarding their functions are lacking. We performed a multiplexed small hairpin (sh)RNA screen to define roles for each subunit in human organotypic skin. We show that integrin-αv (also known as ITGAV) heterodimers are essential for epidermal generation, with integrin-αv loss driving a keratinocyte G1-S cell cycle block. Surprisingly, integrin αv is not localized within keratinocyte focal adhesions, and instead maintains proliferation by controlling cellular (c)-Myc translation through FAK, p38β and p90RSK1. These phenotypes depend only on the binding partners of integrin-αv--integrin β5 and integrin β6 (also known as ITGB5 and ITGB6, respectively). Through inducible depletion of integrin αv in both normal organotypic epidermis and Ras-driven invasive neoplasia, we show that integrin αv is required for de novo tissue generation and neoplastic invasion but that it is dispensable for epidermal maintenance. Heterodimers of integrin αv with integrin β5 (integrin αvβ5) or integrin β6 (integrin αvβ6) are required to similar extents for neoplastic invasion, thus identifying integrin αvβ5 and integrin αvβ6 heterodimers as potential therapeutic targets for epidermal squamous cell carcinoma.

Occurrence and control of sporadic proliferation in growth arrested Swiss 3T3 feeder cells

Growth arrested Swiss mouse embryonic 3T3 cells are used as feeders to support the growth of epidermal keratinocytes and several other target cells. The 3T3 cells have been extensively subcultured owing to their popularity and wide distribution in the world and, as a consequence selective inclusion of variants is a strong possibility in them. Inadvertently selected variants expressing innate resistance to mitomycin C may continue to proliferate even after treatment with such growth arresting agents. The failure of growth arrest can lead to a serious risk of proliferative feeder contamination in target cell cultures. In this study, we passaged Swiss 3T3 cells (CCL-92, ATCC) by different seeding densities and incubation periods. We tested the resultant cultures for differences in anchorage-independent growth, resumption of proliferation after mitomycin C treatment and occurrence of proliferative feeder contaminants in an epidermal keratinocyte co-culture system. The study revealed subculture dependent differential responses. The cultures of a particular subculture procedure displayed unique cell size distribution and disintegrated completely in 6 weeks following mitomycin C treatment, but their repeated subculture resulted in feeder regrowth as late as 11 weeks after the growth arrest. In contrast, mitomycin C failed to inhibit cell proliferation in cultures of the other subculture schemes and also in a clone that was established from a transformation focus of super-confluent culture. The resultant proliferative feeder cells contaminated the keratinocyte cultures. The anchorage-independent growth appeared in late passages as compared with the expression of mitomycin C resistance in earlier passages. The feeder regrowth was prevented by identifying a safe subculture protocol that discouraged the inclusion of resistant variants. We advocate routine anchorage-independent growth assay and absolute confirmation of feeder disintegration to qualify feeder batches and caution on the use of fetal bovine serum.

Agarose overlay selectively improves macrocolony formation and radiosensitivity assessment in primary fibroblasts

PURPOSE

Primary fibroblasts are not suitable for in vitro macrocolony assay due to their inability to form distinct colonies. Here we present a modification of agarose overlay that yielded extensive improvement in their colony formation and assessment of radiosensitivity.

MATERIALS AND METHODS

Macrocolony formation was assessed in primary human fibroblasts VH10 and HDFn with or without overlay using 0.5% agarose in growth medium at 24 h post-seeding. Malignant human cell lines (A549, U87) and transformed non-malignant fibroblasts (AA8 hamster, MRC5 human) were used for comparison.

RESULTS

Agarose overlay caused significant improvement marked by early appearance (one week) of distinct colonies with high cell density and multifold higher plating efficiency than conventional macrocolony assay in VH10 and HDFn human fibroblasts. Compared to conventional assay or feeder cell supplementation, agarose overlay resulted in broader cell morphology due to improved adherence, and yielded more compact colonies. Gamma-radiation dose-response survival curves could be successfully generated for both fibroblast cell lines using this method, which yielded no such effects in the transformed/malignant cell lines tested.

CONCLUSION

This easy and inexpensive 'agarose overlay technique' significantly and selectively improves the fibroblast plating efficiency, thus considerably reducing time and effort to greatly benefit the survival studies on primary fibroblasts.

Stem cell maintenance in a different niche

To overcome the difficulty of controlling stem cell fate and function in applications to regenerative medicine, a number of alternative approaches have been made. Recent reports demonstrate that a non-cellular niche modulating the biophysical microenvironment with chemical factors can support stem cell self-renewal. In our previous studies, early establishment was executed to optimize biophysical factors and it was subsequently found that the microgeometry of the extracellular matrix made huge differences in stem cell behavior and phenotype. We review here a three-dimensional, non-cellular niche designed to support stem cell self-renewal. The characteristics of stem cells under the designed system are further discussed.

Classical human epidermal keratinocyte cell culture

It has been more than 30 years since the serial cultivation of human keratinocytes in monolayer culture was first described by Rheinwald and Green. Initially, isolation of primary keratinocytes from disaggregated human skin tissue and subsequent propagation was promoted through use of replication-inactivated murine fibroblast feeder layers. Since then numerous advances have been made to the cultivation of human keratinocytes in both two-dimensional monolayer and three-dimensional organotypic culture. Monolayer culture facilitates keratinocyte proliferation, whereas organotypic culturing techniques promote keratinocyte differentiation using conditions permissive for stratification. The protocols presented here describe traditional culturing methods, providing guidance for isolation and serial cultivation of primary human keratinocytes and dermal fibroblasts, as well as the use of these cells types for generation of stratified skin tissue.

Analysis of the factors that limit the ability of feeder cells to maintain the undifferentiated state of human embryonic stem cells

Human embryonic stem cell (hESC) culture is routinely performed using inactivated mouse embryonic fibroblasts (MEFs) as a feeder cell layer (FL). Although these cells maintain pluripotency of hESCs, the molecular basis for this is unknown. Objectives of this study were to determine whether timing between MEF inactivation and their use as a FL influenced hESC growth and differentiation, and to begin defining the mechanism(s) involved. hESCs were plated on MEFs prepared 1 (MEF-1), 4 (MEF-4), and 7 (MEF-7) days earlier. hESC colony morphology and Oct3/4 expression levels were evaluated to determine the influence of different FLs. Significant enhancement of hESC growth (self-renewal) was observed on MEF-1 compared with MEF-4 and/or MEF-7. Conditioned media (CM) collected from MEF-1 supported significantly better hESC growth in a FL-free system compared to MEF-7 CM. Effects of MEFs on hESC growth were not caused by differences in cell density or viability, although indications of apoptosis were observed in MEF-7. Scanning electron microscopy demonstrated that MEF-7 were morphologically distinct from MEF-1 and MEF-4. Microarray analysis identified 19 genes related to apoptosis with significantly different levels of expression between MEF-1 and MEF-7. Several differentially expressed RNAs had gene ontology classifications associated with extracellular matrix (ECM) structural constituents and growth factors. Because members of Wnt signaling pathway were identified in the array analysis, we examined the ability of the Wnt1 CM and secreted frizzled-related proteins to affect hESC growth and differentiation. The addition of Wnt1 CM to both MEF-1 and MEF-7 significantly increased the number of undifferentiated colonies, while the addition of Sfrps promoted differentiation. Together, these results suggest that microenvironment, ECM, and soluble factors expressed by MEF-1 are significantly better at maintaining self-renewal and pluripotency of hESCs. Our findings have important implications in the optimization of hESC culture when MEFs are used as FL or CM is used in FL-free culture.

Microfabricated poly(ethylene glycol) templates enable rapid screening of triculture conditions for cardiac tissue engineering

The purpose of this study was to design a simple system for cultivation of micro-scale cardiac organoids and investigate the effects of cellular composition on the organoid function. We hypothesized that cultivation of cardiomyocytes (CM) on preformed networks of fibroblasts (FB) and endothelial cells (EC) would enhance the structural and functional properties of the organoids, compared to simultaneously seeding the three cell types or cultivating enriched CM alone. Microchannels for cell seeding were created by photopolymerization of poly(ethylene glycol) diacrylate. In the preculture group the channels were seeded with a mixture of NIH 3T3 FB and D4T EC, following by addition of neonatal rat CM after 2 days of FB/EC preculture. The control microchannels were seeded simultaneously with FB/EC/CM (simultaneous triculture) or with enriched CM alone (enriched CM). Preculture resulted in cylindrical, contractile, and compact cardiac organoids that contained elongated CM expressing connexin-43 and cardiac troponin I. In contrast, simultaneous triculture resulted in noncontractile organoids with clusters of CM growing separately from elongated FBs and ECs. The staining for Connexin-43 was absent in the simultaneous triculture group. When fixed or frozen FB/EC were utilized as a preculture substrate for CM, noncontractile organoids were obtained; while preculture on a single cell type (either FB or EC) resulted in contractile organoids but with inferior properties compared to preculture with both FB/EC. These results emphasize the importance of living cells, presence of both nonmyocyte cell types as well as sequential seeding approach for cultivation of functional multicell type cardiac organoids.

Cloned embryos from semen. Part 1: in vitro proliferation of epithelial cells on embryonic fibroblasts after isolation from semen by gradient centrifugation

Although epithelial-like somatic cells have been previously isolated from semen, cell proliferation rates were low. Culture of whole semen samples resulted in loss of potentially valuable spermatozoa. The aims of the present study were to: (1) isolate somatic cells from semen, while preserving sperm viability, and (2) optimize in vitro culture conditions for semen-derived epithelial cells. Density gradient centrifugation of washed ejaculates of two rams (Ovis aries) (n = 24) and one eland bull (Taurotragus oryx) (n = 4) was performed using a three-layer discontinuous Percoll column consisting of 90% (P-90), 50% (P-50), and 20% (P-20) Percoll. In vitro culture and Trypan Blue staining indicated that live somatic cells settled in the P-20 layer. Nonmotile spermatozoa were recovered at the P-50 and P-90 interfaces, whereas motile spermatozoa were collected in the pellet from the P-90 layer. Subsequently, somatic cells isolated from the P-20 layer were plated either on inactivated 3T3 mouse embryonic fibroblast feeder layers, collagen-coated plates with 3T3 feeder cell inserts, or on collagen-coated plates. Initial somatic cell plating was similar among treatments, but proliferation significantly increased when cocultured with 3T3 cells (feeder or insert). Furthermore, two different types of epithelial cells were obtained. The exact origin of the cells in the male reproduction system is uncertain and probably variable. The present method of cell isolation and in vitro culture may be of value for preserving endangered species. Specifically, cells isolated and cultured from cryopreserved semen of nonliving males could be used for producing embryos by somatic cell nuclear transfer.

Fibromodulin gene is expressed in human epidermal keratinocytes in culture and in human epidermis in vivo

Fibromodulin is a small leucine-rich proteoglycan that has a central role in the maintenance of collagen fibrils structure, and in regulation of TGF-beta biological activity. Although, it is mainly found in cartilage and tendon, little is known regarding the expression of the fibromodulin gene in other cell types. By RT-PCR, real time PCR and immunohistochemistry, we describe the expression of the fibromodulin gene and the presence of the protein in human epidermal keratinocytes (HEK), both in culture and in normal human epidermis. Our results show, for the first time, that fibromodulin gene is constantly expressed in HEK during culture time. Immunostaining showed that fibromodulin is located intracytoplasmically in basal and stratified keratinocytes of the growing colonies, confluent cultures, and epidermis in vivo. The expression and intracellular localization of fibromodulin in HEK is a new finding and opens new possible biological roles for the SLRP family.

Plasminogen-mediated activation and release of hepatocyte growth factor from extracellular matrix

Interventions that enhance plasminogen activation within the lung consistently limit the fibrosis that follows alveolar injury. However, this protective effect cannot be attributed solely to accelerated clearance of fibrin that forms as a provisional matrix after lung injury. To explore other mechanisms, we considered interactions between the plasminogen activation system and hepatocyte growth factor (HGF). HGF is known to have antifibrotic activity, but to do so, it must be both released from its sites of sequestration within extracellular matrix (ECM) and activated by proteolytic cleavage. A recent study using bleomycin-exposed mice showed that manipulations of the plasminogen activation system influenced the amount of free HGF within bronchoalveolar lavage fluid without affecting total lung HGF mRNA or protein. To elucidate the mechanisms, we studied the role of plasminogen activation in fibroblast-mediated HGF release and activation. We found that NIH3T3 and mouse lung fibroblasts release ECM-bound HGF in a plasminogen-dependent fashion. The plasminogen effect was lost when lung fibroblasts from urokinase-type plasminogen activator (uPA)-deficient mice were used, and was increased by fibroblasts from plasminogen activator inhibitor (PAI)-1-deficient mice. Plasminogen addition to NIH3T3 or mouse lung fibroblasts increased conversion of pro-HGF to its active form. The plasminogen effect on activation was lost when uPA-deficient fibroblasts were used and accentuated by PAI-1-deficient fibroblasts. In conjunction with the previous in vivo study, these results suggest that plasminogen activation can protect the lung against fibrosis by increasing the availability of active HGF.

[In vitro three-dimensional reconstruction of human bladder mucosa]

OBJECTIVE

The purpose of this study is to apply the in vitro keratinocyte culture techniques and the tissue engineering principles to human urothelium, to reconstruct an in vitro three-dimensional human bladder mucosa, suitable for grafting.

MATERIAL AND METHODS

Biopsy specimens of human bladder mucosa were obtained from patients undergoing suprapubic prostatectomy, in vitro cultured and finally, an immunohistochemical study was made.

RESULTS

A three-dimensional in vitro tissue was obtained, composed of a bio-artificial submucosa (fibrin gel and fibroblast) where the uroepithelial cells were seeding. We used a biodegradable polyglycolic acid mesh to facilitate the tissue manipulation and implantation. An immature epithelium was obtained with a weak immunostaining to cytokeratins. The immunohistochemical study could not demonstrate the development of basement membrane.

CONCLUSIONS

In vitro keratinocyte culture techniques could be applied to other epithelial tissues like the urothelium. We obtained a three-dimensional in vitro tissue suitable for grafting in a relatively short time, which needs the matrix interactions in order to mature.

Endothelial extracellular matrix: biosynthesis, remodeling, and functions during vascular morphogenesis and neovessel stabilization

The extracellular matrix (ECM) is critical for all aspects of vascular biology. In concert with supporting cells, endothelial cells (ECs) assemble a laminin-rich basement membrane matrix that provides structural and organizational stability. During the onset of angiogenesis, this basement membrane matrix is degraded by proteinases, among which membrane-type matrix metalloproteinases (MT-MMPs) are particularly significant. As angiogenesis proceeds, ECM serves essential functions in supporting key signaling events involved in regulating EC migration, invasion, proliferation, and survival. Moreover, the provisional ECM serves as a pliable scaffold wherein mechanical guidance forces are established among distal ECs, thereby providing organizational cues in the absence of cell-cell contact. Finally, through specific integrin-dependent signal transduction pathways, ECM controls the EC cytoskeleton to orchestrate the complex process of vascular morphogenesis by which proliferating ECs organize into multicellular tubes with functional lumens. Thus, the composition of ECM and therefore the regulation of ECM degradation and remodeling serves pivotally in the control of lumen and tube formation and, finally, neovessel stability and maturation.

[Experimental study about viability of autologous free graft in vitro cultivated urinary epithelium]

OBJECTIVE

The purpose of this study is to apply the in vitro keratinocyte culture techniques and the tissue engineering principles to urothelium, to obtain a three-dimensional autologous tissue suitable for grafting. We also showed the viability of free graft cultured urothelium in an experimental model.

MATERIAL AND METHODS

An animal experimental model was designed to apply the techniques of cellular culture and tissue engineering. Biopsy specimens of bladder mucosa were obtained, in vitro cultured and posteriorly implanted in each animal. We established three groups based on different follow-up periods (7, 14 and 30 days), and made a final histomorphological study to demonstrate the viability of the graft at the end of its respective follow-up period.

RESULTS

A three-dimensional in vitro tissue was obtained, composed of a bio-artificial submucosa (fibrin gel and fibroblast) where the uroepithelial cells were seeding; a biodegradable polyglycolic acid mesh was used to facilitate the tissue manipulation and implantation. In the morphological study all the implants appeared viable, but the grafts with longer implantations periods were better conformed, showing a tisular structure with multiple cellular layers.

CONCLUSIONS

In vitro keratinocyte culture techniques could be applied to other epithelial tissues as the urothelium. We obtained a three-dimensional in vitro tissue suitable for grafting in a relatively short time. The histological study demonstrated that free autologous urothelial graft is totally viable, opening future clinics applications.

A three-dimensional cell culture model for bovine endometrium: regeneration of a multicellular spheroid using ascorbate

The development of a multicellular spheroid comprising bovine endometrial epithelial cells (BEE) and bovine endometrial stromal cells (BES) is described in this study. The BES were cultured to confluence in medium with L -ascorbic acid phosphate magnesium salt n -hydrate (AsA-P) which stimulates collagen synthesis in BES. The BEE were co-cultured on a BES cell-sheet for 24h before detachment of the cell-sheet to generate a hetero-spheroid. After EDTA treatment and agitating with pipette, the floating cell-sheet shrank and became an aggregated cell mass in a few days; it finally formed a round-shaped hetero-spheroid composed of BES and BEE. Histological examination found that hetero-spheroids were covered with BEE on the outer layer. When cell viability was examined with TUNEL (terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling), no positive signal was detected in the spheroid for up to 10 days. Immunofluorescence observations showed that spheroids contained abundant extracellular matrices, including type-I, -III, -IV collagen, fibronectin, and laminin. PGF(2alpha) produced by hetero-spheroids in response to oxytocin was significantly higher than those produced by monolayer cultured BEE (P< 0.05). MMPs were not detected in media from spheroids cultured for 5 days after detachment of the cell sheet. These results indicate that bovine endometrial cells have the capacity to regenerate as a multicellular spheroid after treatment with ascorbate in vitro. The spheroid displays an endometrium-mimic feature. Thus, we conclude that spheroids formed by BES and BEE are a useful in vitro model of bovine endometrium.

Keratins and the keratinocyte activation cycle

In wound healing and many pathologic conditions, keratinocytes become activated: they turn into migratory, hyperproliferative cells that produce and secrete extracellular matrix components and signaling polypeptides. At the same time, their cytoskeleton is also altered by the production of specific keratin proteins. These changes are orchestrated by growth factors, chemokines, and cytokines produced by keratinocytes and other cutaneous cell types. The responding intracellular signaling pathways activate transcription factors that regulate expression of keratin genes. Analysis of these processes led us to propose the existence of a keratinocyte activation cycle, in which the cells first become activated by the release of IL-1. Subsequently, they maintain the activated state by autocrine production of proinflammatory and proliferative signals. Keratins K6 and K16 are markers of the active state. Signals from the lymphocytes, in the form of Interferon-gamma, induce the expression of K17 and make keratinocytes contractile. This enables the keratinocytes to shrink the provisional fibronectin-rich basement membrane. Signals from the fibroblasts, in the form of TGF-beta, induce the expression of K5 and K14, revert the keratinocytes to the healthy basal phenotype, and thus complete the activation cycle.

Lack of intrinsic polarity in the ligand-binding ability of keratinocyte beta1 integrins

Within the basal layer of the epidermis the beta1 integrins have a pericellular distribution. Two monoclonal antibodies, 15/7 and 12G10, that detect a conformation of the beta1 integrin subunit that is induced following cation or ligand occupancy selectively recognized beta1 integrins at the basement membrane zone in vivo and in focal adhesions of cultured keratinocytes; they did not recognize integrins on the apical and upper lateral membranes of basal keratinocytes nor integrins on the suprabasal keratinocytes of hyperproliferative epidermis. Inhibition of intercellular adhesion did not induce the 15/7 epitope on the lateral and apical membrane domains. The surface distribution of the epitopes was consistent with the antibodies acting as reporters of ligand-binding; in addition, the 15/7 epitope was exposed on unglycosylated, immature beta1 integrins. Although the apical membrane of basal keratinocytes is not normally in contact with extracellular matrix proteins, we found that it was capable of binding fibronectin-coated beads and that the 15/7 epitope was exposed on plasma membrane in contact with the beads. When a chimeric molecule consisting of the extracellular domain of CD8 and the cytoplasmic domain of the beta1 integrin subunit, used to mimic a constitutively active beta1 heterodimer, was introduced into keratinocytes it localized to the basal, lateral and apical membrane domains. We conclude that although the conformation of the keratinocyte beta1 integrins differs between the basal and the lateral/apical membrane domains there is no intrinsic polarity in the ligand binding potential of the receptors.

Expression of mRNA for type IV collagen alpha1, alpha5 and alpha6 chains by cultured dermal fibroblasts from patients with X-linked Alport syndrome

COL4A5 mutations causing X-linked Alport syndrome (XLAS) are frequently associated with absence of the alpha3, alpha4,alpha5 and alpha6 chains of type IV collagen from basement membranes and increased amounts of the alpha1(IV) and alpha2(IV) chains in glomerular basement membrane. Although many COL4A5 mutations have been described in XLAS, the mechanisms by which these mutations influence the basement membrane appearance of chains other than alpha5(IV) remain poorly understood. In this study, we used dermal fibroblasts from eight normal individuals and nine males with XLAS to test the hypotheses that COL4A5 mutations increase transcription of COL4A1 and suppress transcription of COL4A6. Ribonuclease protection assays revealed that alpha1(IV), alpha5(IV) and alpha6(IV) transcripts were expressed in cultures of dermal fibroblasts. The mRNA levels for alpha1(IV) in eight of nine patients with XLAS were not increased compared to controls; one patient with a large COL4A5 deletion showed significant elevation of alpha1(IV) mRNA levels. No differences in steady-state mRNA levels for alpha6(IV) were found when XLAS fibroblasts were compared with controls, even though little or no alpha6(IV) protein was detectable at the dermal-epidermal junction by immunofluorescence study. This finding suggests that post-transcriptional events account for the absence of alpha6(IV) in the Alport dermal-epidermal junction.

Adipose tissue extracellular matrix: newly organized by adipocytes during differentiation

The distribution of eight types of extracellular matrix (ECM) proteins (type I-VI) collagen, laminin and fibronectin) in the skeletal muscle of Japanese Black cattle was determined by indirect immunofluorescence using specific antibodies against each protein. ECM proteins were well organized in the intramuscular connective tissue: type I, II, III collagen and fibronectin were localized primarily in the perimysium, type V and VI collagen in both the perimysium and endomysium, and type IV collagen and laminin were virtually confined to the endomysium. In the loose connective tissue holding the adipocytes together to form a tissue mass between the muscular bundles, seven of the ECM proteins not type II collagen were relatively abundant in a disordered arrangement. Further analysis by in vitro immunocytochemical staining also demonstrated that a stromal-vascular preadipocyte cell line (BIP cell), derived from Japanese Black cattle, synthesized various ECMs in much the same way as fibroblasts. Exponentially growing BIP cells with a fibroblastic phenotype were found to produce type II, V, and VI collagens, in addition to the other previously identified connective tissue glycoproteins of mouse 3T3 preadipocytes. When confluent preadipocyte cultures were stimulated with adipogenic medium, a fibrillar network of ECM was observed to bridge the intercellular space and connect adjacent cell surfaces. During adipocyte differentiation, type III collagen and laminin were arranged in a non-fibrous structure, and type-II collagen was only barely detected. These results are supported by the staining of the adipose tissue, where all ECM proteins studied except type II collagen were stained intensely. These data indicate that in vivo under conditions permissive for adipose conversion, the production and organization of ECM, accompanied by hyperplasia and hypertrophy of precursor cells, gives rise to adipose tissue in skeletal muscle with its own ECM products. These data further suggest that each ECM protein might have some role for the adipocytes in forming tissue.

Epidermal signal transduction and transcription factor activation in activated keratinocytes

In the area of biology, many laboratories around the world are dissecting and characterizing signal transduction mechanisms and transcription factors responsive to various growth factors and cytokines, in various cell types. However, because of the differences in systems used, it is not clear whether these systems coexist, whether they interact meaningfully, and what their relative roles are. Epidermal keratinocytes are the perfect cell type in which to integrate this knowledge, because in these cells these mechanisms are known to be relevant. Keratinocytes both produce and respond to growth factors and cytokines, especially in pathological conditions and during wound healing, when the physiology of keratinocytes is altered in a way specified by the presence of a subset growth factors and cytokines. In fact, growth factors and cytokines cause the major changes in gene expression and keratinocyte behavior in various cutaneous diseases. In some cases, such as in wound healing, these responses are highly beneficial; in others, such as in psoriasis, they are pathological. It is not clear at present which are operating in which conditions, which are important for the healing process and which are harmful. Growth factors and cytokines affect keratinocytes sometimes simultaneously, at other times individually. In this manuscript we describe the signal transduction pathways responsible for the effects of interferons, the EGF/TGF alpha family and the TNF alpha/IL-1 family of signaling molecules. We also describe the important transcription factors known to be functional in epidermis, with particular emphasis on those factors that are activated by growth factors and cytokines. Finally, we describe what is known about transcriptional regulation of keratin genes, especially those specifically expressed in pathological processes in the epidermis. We expect that the enhanced understanding of the pathways regulating gene expression in keratinocytes will identify the pharmacological targets, the signal transducing proteins and the corresponding transcription factors, used by growth factors and cytokines. This research will led to development of compounds precisely aimed at those targets, allowing us to isolate and inhibit the harmful side effects of growth factors and cytokines. Such compounds should lead to highly specific and therefore more effective treatments of the cutaneous disorders in which these pathways play significant roles.

Cultured human keratinocytes express tropoelastin

We detected elastin mRNA in cultured normal human keratinocytes by RNase protection assay. The content of elastin mRNA was estimated at approximately one-twentieth of that of cultured skin fibroblasts. Tropoelastin polypeptide with a molecular weight of 68 kDa was detected in the preparation of culture medium of normal human keratinocytes by western blot assays using anti-tropoelastin antibody. Immunohistochemical studies also demonstrated positive staining in cultured normal human keratinocytes as well as in skin fibroblasts. The expression of elastin by normal human keratinocytes was found to reach a maximum level at the quiescent phase of keratinocyte growth. When normal human keratinocytes were cultured on tropoelastin-coated dishes, their growth potential was greatly suppressed compared with other matrix protein-coated dishes. These results suggest that cultured normal human keratinocytes can actively synthesize elastin and that keratinocyte elastin may act as a growth-regulator for keratinocytes.

There is temporal and spatial expression of alpha1 (IV), alpha2 (IV), alpha5 (IV), alpha6 (IV) collagen chains and beta1 integrins during the development of the basal lamina in an "in vitro" skin model

Temporal and spatial expression of alpha1 (IV), alpha2 (IV), alpha3 (IV), alpha4 (IV), alpha5 (IV), and alpha6 (IV) collagen chains was studied during the formation of the basal lamina in an "in vitro" skin model. A sequential study was performed at 7-d and 14-d cultures (lamina densa absent) and at 28-, 36-, and 56-d cultures (lamina densa present). Expression of beta1, beta4, alpha1, alpha2, alpha3, alpha5, alpha6 integrin subunits and co-localization with collagen IV was studied by regular and laser confocal indirect immunofluorescence microscopy. mRNA expression of alpha2 (IV) and alpha6 (IV) chains was estimated by northern blots. The earliest expression of alpha1 (IV) and alpha2 (IV) collagen chains was noted in 7-d cultures restricted to basal keratinocytes. At 14-d cultures, alpha1 (IV) and alpha2 (IV) chains were noted in basal keratinocytes and as a broad band (10 microm) in the adjacent dermis. At this stage 80% of the alpha2 (IV) mRNA was expressed in the dermis and 20% in the epidermis. At 28-, 36-, and 56-d cultures the alpha1 (IV) and alpha2 (IV) chains were present in a linear distribution at the epidermo-dermal junction and in the upper dermis. The alpha6 (IV) collagen chains were expressed much later at 36-d cultures and the alpha5 (IV) at 56 d, both mostly in a linear distribution but also in the adjacent dermis. Alpha6 (IV) mRNA was demonstrated in the dermis of 36-d cultures. There was co-localization of collagen IV and beta1 integrin subunits in 14-d cultures at the matrix site of keratinocytes. Functional perturbation studies with AIIB2 monoclonal antibody (anti-beta1 subunits) and competitive inhibition with a collagen cyanogen bromide digestion derived fragment (CB3[IV]) that contains the collagen IV ligand for alpha1beta1, alpha2beta1 integrins, altered the pattern of collagen IV deposition.

Reconstituted human gingival epithelium: nonsubmerged in vitro model

Many studies have shown that human gingival keratinocytes grown in submerged culture fail to attain optimal differentiation. This study reports an in vitro culture system for oral gingival epithelial cells, in which they are grown at the air-liquid interface, on polycarbonate inserts, in the presence of an NIH-3T3 feeder layer. This model was compared with two submerged culture methods for gingival keratinocytes, on type 1 collagen gel and on an NIH-3T3 feeder layer. Transmission electron microscopy showed an advanced level of stratification (over six layers of cells) for cultures grown at the air-liquid interface. Immunofluorescence and electrophoretic patterns showed the presence of cytokeratins 10 and 11 in cytoskeletal protein extracts of these cultured keratinocytes. In this air-liquid interface culture model, in the presence of NIH-3T3 feeder cells, keratinocytes can achieve an advanced level of stratification and differentiation and a resemblance to in vivo gingiva. The obtention of a highly differentiated epithelium will permit in vitro pharmacological studies and studies on the biocompatability of certain alloys with the superficial periodontium; it will also provide grafts for patients undergoing periodontal surgery.

Characterization of a new in vitro model for studies of reepithelialization in human partial thickness wounds

Reepithelialization of artificial partial thickness wounds made in biopsies of human skin was determined after 3, 5, or 7 d of incubation, submerged or elevated to the air-liquid interface. The biopsies were reepithelialized within 5-7 d, with a more complete epidermal healing in wounds exposed to air. Both types of wounds showed similar time-course in deposition of basement membrane components, as detected by immunofluorescence labeling. Laminin and collagen type VII were deposited underneath the migrating tips, whereas collagen type IV was detected after reepithelialization. Markers of terminal differentiation showed a pattern close to normal in the air-liquid incubated wounds after reepithelialization. Involucrin was detected in the suprabasal regions of the migrating epidermis and thereafter in the upper half of neo-epidermis in the air-liquid incubated wound. Filaggrin could not be detected in the submerged wounds at any time during healing, whereas wounds exposed to air showed a well-differentiated epidermis by Day 7. Tritiated thymidine-incorporation indicated proliferation of epidermal and dermal cells during reepithelialization and a maintained viability, as shown by cultivation of endothelial- and fibroblast-like cells obtained from the dermis 7 d after wounding. Reepithelialization in this human in vitro model is supported by a matrix close to normal with the possibility of extracellular influences and cell-cell interactions and, in addition, the technique is simple and reproducible. Therefore, we suggest this model for studies of regeneration in culture and as a complement to in vivo studies on epidermal healing.

Basement membrane proteoglycans are of epithelial origin in rodent skin

Basement membrane proteoglycans in mammalian skin comprise at least one chondroitin sulfate proteoglycan and heparan sulfate proteoglycans, including perlecan. In this study, the origins of basement membrane chondroitin sulfate proteoglycan and perlecan were investigated both in vivo and in vitro. For in vivo experiments, pieces of newborn rat epidermis obtained by dispase treatment were grafted onto athymic nude mice. Three and six weeks after grafting, immunofluorescence analysis of the grafted skin was carried out, using monoclonal antibodies specific for rat basement membrane chondroitin sulfate proteoglycan and rat and mouse perlecan. While the isolated rat epidermis was shown to completely lack rat basement membrane chondroitin sulfate proteoglycan and rat basement membrane heparan sulfate proteoglycans, including perlecan, immunofluorescence staining of tissue sections from the grafted sites on mice demonstrated the presence of rat basement membrane chondroitin sulfate proteoglycan and rat perlecan on interfollicular and follicular basement membranes including that separating dermal papillae from adjacent hair follicle epithelium. In contrast, the basement membranes of all dermal capillaries were positive for mouse perlecan, but negative for rat basement membrane chondroitin sulfate proteoglycan and rat perlecan, including the basement membranes of papillary dermal capillaries beneath the rat epidermis. These data suggest that basement membrane proteoglycans of the dermal-epidermal junction and hair follicle epithelium are of epidermal (epithelial) origin in vivo. Stratified rat keratinocytes cultured on a collagen matrix at the air-liquid interface showed the synthesis of perlecan, laminin 1, and type IV collagen in basement membranes, but not clearly detectable basement membrane chondroitin sulfate proteoglycan.

Skin fibroblasts are the only source of nidogen during early basal lamina formation in vitro

The purpose of this study was to determine whether nidogen, the linkage protein of the basal lamina, is of epidermal or dermal origin. The development of the basal lamina was studied in an in vitro skin model. Preputial fibroblasts seeded onto a nylon mesh attached, proliferated, and developed a rich extracellular matrix (dermal model). Preputial keratinocytes were added to the dermal model to form a keratinocyte dermal model that ultrastructurally resembled in many respects human skin. Ultrastructural analysis revealed early stages of dermal development, including an incomplete basal lamina, aggregates of dermal filamentous material connecting to the lamina densa, bundles of 10-nm microfibrils, formation of premature hemidesmosomes, anchoring filaments, and anchoring fibrils. The cell origin of nidogen was determined in the dermal model and in the epidermal and dermal components of the keratinocyte dermal model. Specific antibodies and a cDNA probe for nidogen were used for immunofluorescence microscopy, Western and Northern blots, and for in situ hybridization studies. Our data show that fibroblasts are the only source of nidogen during early basal lamina formation. Although fibroblasts can synthesize nidogen and deposit it in the dermal matrix, no basal lamina will form unless they are recombined with keratinocytes. This suggests that the epidermis plays a major regulatory role in the production and assembly of nidogen into the basal lamina.

A novel role for alpha 3 beta 1 integrins in extracellular matrix assembly

To study the biological role of alpha 3 beta 1 integrins in cell adhesion, migration, and in the deposition of extracellular matrix, we stably expressed the human alpha 3 integrin subunit in the alpha 4, alpha 5 integrin deficient CHO cell line B2. The expression of alpha 3 beta 1 integrins enhanced cell adhesion on entactin (also known as nidogen), but not on fibronectin. Using recombinant GST-fusion proteins that span the entire length of the entactin molecule, we located cell adhesive activity to the G2 domain of entactin. These results suggest that the alpha 3 beta 1 integrin functions as an adhesion receptor interacting with the G2 domain of entactin. On the other hand, the expression of alpha 3 beta 1 integrins did not confer the ability to migrate on entactin. Strikingly, the expression of alpha 3 beta 1 dramatically increased the deposition of entactin and fibronectin into the pericellular matrix. This was accompanied by increased binding activity of the 29 kDa amino-terminal domain of fibronectin. Thus, similar to alpha 5 beta 1 integrins, alpha 3 beta 1 integrins can play an important role in modulating the assembly of pericellular matrices. However, unlike fibronectin deposition supported by alpha 5 beta 1, alpha 3 beta 1 supported fibronectin deposition into pericellular matrix was not inhibited by antibodies binding to the RGD containing cell adhesion domain of fibronectin, demonstrating that the two processes are mechanistically distinct. The role of alpha 3 beta 1 in pericellular matrix assembly potentially implicates this receptor in the assembly and/or recognition of entactin-containing pericellular matrices, an observation consistent with its apparent role in the renal glomerulus of the mammalian kidney.

Direct comparison of a cultured composite skin substitute containing human keratinocytes and fibroblasts to an epidermal sheet graft containing human keratinocytes on athymic mice

This study compares two techniques for making cultured skin substitutes: a composite graft made of human fibroblasts and keratinocytes on a collagen-glycosaminoglycan membrane (CG) and a cultured epidermal cell sheet graft (CEG), without a dermal component. The "take" and quality of these cultured skin substitutes were evaluated by placing them on full-thickness, excised wounds of athymic mice. These cultured skin substitutes were placed onto 2-X-2-cm wounds created on athymic mice. Mice were sacrificed at days 10, 20, and 42 with histologic sections obtained for light, electron, immunofluorescent, and immunohistochemical microscopy. "Take" was determined separately by a direct immunofluorescent stain for human leukocyte ABC antigens. There were ten mice of each graft type with at least two animals sacrificed at each time point. Results showed positive "take" for all animals. Grossly, there was little difference between the two graft types, with the CEG having occasional blister formation. By light microscopy, the CEG had a dissociation of dermis from epidermis until day 42, which was never apparent with the CG. By day 42, the CG had increased dermoepidermal interdigitations similar to rete ridges, with a mature epithelium. Neither of these findings were seen with the CEG. Immunofluorescent and immunohistochemical microscopy for type IV collagen and laminin, as well as electron microscopy, showed similar retardation of basement membrane formation with the CEG. Using this model, the composite graft had significant advantages over the epidermal sheet graft in the closure of full-thickness wounds.

The absence of Harvey ras mutations during development and progression of squamous cell carcinomas of the head and neck

We have examined the incidence of Harvey ras mutations in human squamous cell carcinomas (SCC) of the upper aerodigestive tract using the polymerase chain reaction (PCR) followed by direct sequencing. No mutations were detected at codons 12, 13, 59 or 61 of this gene in any of six papillomas, five erythroplakias, 56 squamous cell carcinomas, and 16 SCC cell lines. Some of the SCC were lymph node metastases (three) or tumours which had recurred following radiotherapy (seven). We conclude that Harvey ras mutations are not a common event in the pathogenesis or recurrence of SCCs from Caucasian subjects, in contrast to the situation with Indian populations (Saranath et al., 1991).

Expression of basement membrane components in skin equivalents--influence of dermal fibroblasts

We have made a skin equivalent constructed of fibroblasts embedded in a type I collagen, with an overlying stratified keratinocyte epithelium to examine formation of the basement membrane. We assessed the influence of the existence and species of fibroblasts in the collagen gel. Cultured human keratinocytes were well attached to the dermal equivalent. Plating efficiency was not clearly different among several types of gel. On the control and mouse fibroblast gel, sheet formation was delayed and epithelial stratification on the human fibroblast gel was more remarkable than on the control gel. On the human fibroblast gel, we observed the expression of basement membrane components (bulbous phemphigoid antigen, laminin, type IV collagen and fibronectin) between the sheet of cultured keratinocytes and the human fibroblast gel earlier than those on the control gel and mouse fibroblast gel. Type VIII collagen was not observed in any of the models at 4 weeks.

Localization of fibronectin in the frog skin

In this review, we present structural and ultrastructural localizations of fibronectin (FN) in the larval and adult skin of the frog (Rana esculenta) either in in vivo or in in vitro conditions. The ventral skin of the tadpole contains membrane-associated FN-plaques disposed around the epidermal and dermal cells during their climactic rearrangement. Moreover, lines of fibrillar FN are detected inside the breaks opened in the derived collagen. The ventral skin of the adult frog reveals FN distributed in the three superimposed tissues forming the skin, i.e. the epidermis, the dermis and the subcutaneous tissue. In vivo, the epidermis is devoid of FN except for the mitochondria-rich cells (MRCs) which contain FN cytoplasmic granules. The dermis reveals two distinct collagenous networks showing FN localizations. A vertically-oriented network formed by thick tracts contains axis of fibrillar FN connecting the upper dermis devoid of FN to the FN-rich subcutaneous tissue. In contiguity with an horizontally-oriented network comprises thin tracts formed by clear spaces separating the superimposed collagen bundles of the dermal stratum compactum. These tracts contain aligned FN-granules. Inside the thick and thin tracts, the dermal and pigment cells present membrane-associated In vitro (in organ culture conditions) MRCs of the epidermis maintain their FN localization and, in addition, the stratum germinativum cells show cytoplasmic FN granules. Epidermal cells, in the vicinity of the cut edges of the cultivated skin fragment, modify their shape and acquire membrane-associated FN-plaques located between desmosomes. The FN localizations in these two collagenous networks of the dermis remain unchanged. In the same way, the FN-rich subcutaneous tissue is unmodified. In summary, the FN distribution in the larval skin is related to the cell rearrangement during the metamorphic climax, and, in the adult skin to the cell migration during the wound healing process and the pigment cell patterning. The cell migration is demonstrated, in organ culture conditions, by antiFN serum used as an experimental tool. FN is an important substrate used in the dermal breaks of the larval skin, and in the dermal tracts of the adult skin, both allowing the dermal and pigment cell migration.

Integrin receptors and RGD sequences in human keratinocyte migration: unique anti-migratory function of alpha 3 beta 1 epiligrin receptor

The migration of keratinocytes over the wound bed plays an important role in the re-epithelialization of cutaneous wounds. However, the mechanisms by which keratinocytes migrate over extracellular matrix components are unknown. In this study, we sought to determine if the RGD sequences in matrix molecules and recognition of these sequences by keratinocytes played a role in the locomotion of keratinocytes. After allowing the cells to attach to the matrix, RGD-containing peptides or control peptides were added to a keratinocyte migration assay. The addition of RGD-containing peptide dramatically inhibited keratinocyte locomotion on a matrix of fibronectin but not on collagen matrices. Therefore, RGD recognition is a critical step for fibronectin-mediated migration but not for collagen-mediated migration. Because the RGD sequences are recognized by cell-surface integrin receptors in a number of cell types, we next examined the roles of integrin receptors in human keratinocyte migration. Using monospecific antibodies that recognize integrin subunits, we found that blocking the beta 1 subunit inhibited the migration of keratinocytes on matrices of fibronectin, interstitial collagen, and basement membrane collagen. Blocking the alpha 5 beta 1 receptor significantly inhibited migration on fibronectin but not on collagen matrices. Conversely, blocking the alpha 2 beta 1 receptor inhibited migration on collagen matrices but not on fibronectin. Blocking the alpha 3 beta 1 receptor uniquely enhanced migration on fibronectin and collagen matrices. In contrast to cells apposed to matrices without the receptor blocked, the enhanced migration in the presence of anti-alpha 3 beta 1 antibody occurred at the later time points of the migration assay. The enhancement of migration by blocking the alpha 3 beta 1 integrin receptor suggests that the interaction of the alpha 3 beta 1 receptor with matrices is associated with immobility.

Feeder cells impart a growth stimulus to recipient epithelial cells by direct contact

Mouse mammary epithelial cells have been shown to proliferate when cultured in the same vessel with lethally irradiated cells of the LA7 rat mammary tumor line. Presented here are experiments that indicate that the LA7 feeder cells stimulate growth of the normal mouse mammary cells by a mechanism that involves direct contact between the two cell types. It is possible that the LA7 feeder cells stimulate proliferation by secretion of a labile growth factor, by secretion of a soluble growth factor in such low concentrations that dilution by travel over a distance makes it less effective, that the stimulus is transduced directly through membrane receptors on the recipient epithelial cells, or that a growth message is sent through gap junctions between cells. This feeder cell system is proposed as an in vitro model for epithelial wound healing.

Coculture of newborn rat skin epidermal cells with Swiss 3T3 cells: Effect of the phases of 3T3 cells on attachment, growth and keratin synthesis of epidermal cells

Swiss albino mouse 3T3 cells in various states were inoculated onto one side of Millipore filters. The other side of the filter was then coated with type I collagen and inoculated with newborn rat skin epidermal cells. On coculture of these cells, the attachment, growth and keratin synthesis of epidermal cells were found to depend on the state of the 3T3 cells: 3T3 cells in the stationary phase of growth were the most effective, followed by those in the logarithmic growth phase, those in the lag phase and plasmolyzed fibroblasts being only slightly effective. The effects of 3T3 cells in different states correlated well with their abilities to synthesize type IV collagen, but not type I collagen: with an increase in type IV collagen synthesis by the 3T3 cells, attachment of epidermal cells to the cell support, and their growth and synthesis of keratins increased. This culture system is concluded to mimic conditions in skin in vivo, and therefore to be suitable for studies on the effects of fibroblasts on the growth of epidermal cells.

Expression of beta 1, beta 3, beta 4, and beta 5 integrins by human epidermal keratinocytes and non-differentiating keratinocytes

We have compared the adhesive properties and integrin expression profiles of cultured human epidermal keratinocytes and a strain of nondifferentiating keratinocytes (ndk). Both cell types adhered to fibronectin, laminin, and collagen types I and IV, but ndk adhered more rapidly and at lower coating concentrations of the proteins. Antibody blocking experiments showed that adhesion of both cell types to fibronectin was mediated by the alpha 5 beta 1 integrin and to laminin by alpha 3 beta 1 in synergy with alpha 2 beta 1. Keratinocytes adhered to collagen with alpha 2 beta 1, but an antibody to alpha 2 did not inhibit adhesion of ndk to collagen. Both cell types adhered to vitronectin by alpha v-containing integrins. Immunoprecipitation of surface-iodinated and metabolically labeled cells showed that in addition to alpha 2 beta 1, alpha 3 beta 1, and alpha 5 beta 1, both keratinocytes and ndk expressed alpha 6 beta 4 and alpha v beta 5. ndk expressed all these integrins at higher levels than normal keratinocytes. ndk, but not normal keratinocytes, expressed alpha v beta 1 and alpha v beta 3; they also expressed alpha 1 beta 1, an integrin that was not consistently detected on normal keratinocytes. Immunofluorescence experiments showed that in stratified cultures of normal keratinocytes integrin expression was confined to cells in the basal layer; terminally differentiating cells were unstained. In contrast, all cells in the ndk population were integrin positive. Our observations showed that the adhesive properties of ndk differ from normal keratinocytes and reflect differences in the type of integrins expressed, the level of expression and the distribution of integrins on the cell surface. ndk thus have a number of characteristics that distinguish them from normal basal keratinocytes.

Growth stimulation of human keratinocytes by tissue inhibitor of metalloproteinases

Human recombinant tissue inhibitor of metalloproteinases (rTIMP) at 0.2-4.6 microM was found to stimulate the growth of normal human keratinocytes, in primary cultures on a plastic support, and to markedly increase their growth on a tridimensional culture system, the skin equivalent, as shown by histology, DNA measurements, and planimetry. In contrast, rTIMP had no effect on the growth of normal human fibroblasts. The growth of keratinocytes on extracellular matrix components produced by keratinocytes cultured in the presence or absence of rTIMP was similar, suggesting that rTIMP does not stimulate keratinocyte growth by modifying either the quantity or the composition of the extracellular matrix deposited. rTIMP was labeled with 125iodine in order to study its interaction with keratinocytes in culture. Binding of (125I) rTIMP to keratinocytes was found to be temperature and time dependent. Under steady-state conditions at 22 degrees C, one class of specific rTIMP binding sites was identified with KD of 8.7 nM and 135,000 sites/cell. Such findings are in keeping with the known potentiating effect of TIMP on erythroid precursors, and indicate that this protein has at least two distinct activities.

Epithelial-mesenchymal interactions enhance expression of collagen VII in vitro

Expression of collagen VII, the major structural protein of the anchoring fibrils, was assessed in vitro using indirect immunofluorescence staining and immunoblotting of collagen VII isolated from cultures. A very low level of expression was observed in monocultures of normal human fibroblasts or keratinocytes, but the expression was greatly stimulated when fibroblasts and keratinocytes were co-cultured. Primary skin explants under culture conditions supporting growth of both cell types, or mixed co-cultures of purified fibroblasts and keratinocytes, exhibited clearly enhanced synthesis of collagen VII, and the intact tissue form of this collagen could be extracted from small co-cultures. Three-dimensional skin equivalents were constructed with fibroblasts embedded in a contracted gel of collagen I and III, with an overlying stratified keratinocyte epithelium. In these equivalents, expression of collagen VII was observed primarily in the lowest epithelial cells, indicating that these cells are the main manufacturers of collagen VII. Laminin and collagen IV were deposited in a linear fashion onto the epithelial-mesenchymal interface. The results suggest that epithelial-mesenchymal interactions, either through physical interactions and/or through soluble mediators, are necessary for efficient synthesis of collagen VII and biogenesis of the anchoring fibrils.

In vitro and post-transplantation differentiation of human keratinocytes grown on the human type IV collagen film of a bilayered dermal substitute

Using human type IV and type I + III collagens and a new, nontoxic cross-linking procedure, we have developed a cell-free bilayered human dermal substitute for organotypic culture and transplantation of human skin keratinocytes. We have studied the formation of the basement membrane, and the differentiation of keratinocytes grown on the type IV collagen layer of this dermal substitute, in vitro and after grafting onto nude mice. These studies demonstrated the formation of essential constituents of the basement membrane in culture: hemidesmosomes and deposition of extracellular matrix on the top of the type IV collagen were observed as early as 6 days after plating of human keratinocytes. Although the keratinocytes formed a well-organized multilayered epithelium, they exhibited limited differentiation when grown submerged in liquid medium. However, the multilayered sheet obtained after 14 days in submerged culture was composed of a regular basal cell layer, several nucleated suprabasal cell layers containing granular cells, and several dense, anucleated cell layers. The grafting experiments have shown a good biocompatibility of the dermal substitute. It is repopulated by fibroblasts, newly synthesized collagen, vessels, and a few mononuclear cells. At Day 14 after grafting, the type IV collagen layer was still present and very dense, and the basement membrane appeared as in culture, with numerous well-structured hemidesmosomes and deposition of extracellular matrix resembling lamina densa. At Day 55 after transplantation, even if the epidermal graft did not exhibit all the characteristics of the normal epidermis in vivo, it was very close to it. At this stage, the basement membrane was complete, with structures clearly indicative of anchoring fibrils. This new dermal substitute offers many advantages. It is stable and easy to handle. Its production is standardized. The oxidation induced by periodic acid led to a nontoxic cross-linked matrix. This dermal substitute is the first one entirely composed of human collagens. The type I + III collagen underlayer is reorganized when grafted. It supports a type IV collagen top layer which offers an excellent substrate for keratinocytes, favors their anchorage, and favors the formation of the basement membrane in vitro. This dermal substitute could be useful for wound coverage or as an in vitro model for toxicological and pharmacological studies.

Secretion of a unique collagen by spontaneously transformed murine keratinocytes (PAM cells) in vitro

A spontaneously transformed murine keratinocyte cell line (PAM cell) was found to secrete two nondisulfide-linked collagenous polypeptides with apparent molecular weight (MW) 190-kd and 120-kd. Pulse-chase experiments indicated that the 190-kd polypeptide was secreted into the culture medium in 2 h and processed to the 120-kd collagen component within 4 h. This process was inhibited by EDTA. The 120-kd polypeptide was sensitive to pepsin, and a 50-kd fragment was produced by a mild pepsin treatment at 4 degrees C. A cyanogen bromide peptide map of the 120-kd polypeptide was distinct from that of types I, II, III, IV, and V collagens. These properties indicate similarities to the type VIII-related collagen produced by human astrocytoma cells. The secretion of the collagen rapidly reached a maximum level on the first day of culture and subsequently declined with cell proliferation. An accelerated processing to the 120-kd polypeptide was observed under culture conditions of high cell density. Similar collagens were also found to be produced by normal human keratinocytes. These results indicate that the 120-kd polypeptide is a potentially functional protein that may participate in the formation of the extracellular matrix of keratinocytes.