Collagen metabolism and basement membrane formation in cultures of mouse mammary epithelial cells. Induction of 'assembly' on fibrillar type I collagen substrata

Properties of a bovine collagen type I membrane for guided bone regeneration applications

Dental implant treatment requires an available bone volume in the implantation site to ensure the implant’s mechanical stability. When the bone volume is insufficient, one must resort to surgical means such as guided bone regeneration (GBR). In GBR surgery, bone grafts and membranes are used. The objective of this work is to manufacture and characterize the in vitro and in vivo properties of resorbable collagen type I membranes (Green Membrane®) for GBR. Membrane surface morphology was characterized by SEM and roughness was measured using an interferometric noncontact 3D system. In vivo skin sensitization and toxicity tests have been performed on Wistar rats. Bone defects were prepared in 24 adult male rats, filled with biomaterials (Blue Bone® and Bio Oss®) and covered with collagen membranes to maintain the mechanical stability of the site for bone regeneration. The incisions were closed with simple stitches; and 60 days after the surgery, the animals were euthanized. Results showed that the analyzed membrane was homogeneous, with collagen fiber webs and open pores. It had no sign of cytotoxicity and the cells at the insertion site showed no bone morphological changes. There was no tissue reaction and no statistical difference between Blue Bone® and Bio Oss® groups. The proposed membrane has no cytotoxicity and displays a biocompatibility profile that makes it suitable for GBR.

Factors implicated in the assessment of aminolevulinic acid-induced protoporphyrin IX fluorescence

BACKGROUND

Photodynamic therapy and photodiagnosis of cancer requires preferential accumulation of fluorescent photosensitizers in tumors. Clinical evidence documents feasibility of ALA-based photodiagnosis for tumor detection. However, false positive results and large variations in fluorescence intensities are also reported. Furthermore, selective accumulation of fluorescent species of photosensitizers in tumor cell lines, as compared to normal ones, when cultured in vitro, is not always observed. To understand this discrepancy we analyzed the impact of various factors on the intensity of detected PpIX fluorescence.

METHODS

Impacts of cell type, mitochondrial potential, cell-cell interactions and relocalization of PpIX among different cell types in co-cultures of different cell lines were analyzed by confocal microscopy and flow cytometry. Fluorescence spectroscopy was used to estimate absolute amounts of ALA-induced PpIX in individual cell lines. Immunofluorescence staining was applied to evaluate the ability of cell lines to produce collagen.

RESULTS

Higher ALA-induced PpIX fluorescence in cancer cell lines as compared to normal ones was not detected by all the methods used. Mitochondrial activity was heterogeneous throughout the cell monolayers and could not be clearly correlated with PpIX fluorescence. Positive collagen staining was detected in all cell lines tested.

CONCLUSIONS

Contrary to in vivo situation, ALA-induced PpIX production by cell lines in vitro may not result in higher PpIX fluorescence signals in tumor cells than in normal ones. We suggest that a combination of several properties of tumor tissue, instead of tumor cells only, is responsible for increased ALA-induced PpIX fluorescence in solid tumors.

GENERAL SIGNIFICANCE

Understanding the reasons of increased ALA-induced PpIX fluorescence in tumors is necessary for reliable ALA-based photodiagnosis, which is used in various oncological fields.

Issues to be considered when studying cancer in vitro

Various cancer treatment approaches have shown promising results when tested preclinically. The results of clinical trials, however, are often disappointing. While searching for the reasons responsible for their failures, the relevance of experimental and preclinical models has to be taken into account. Possible factors that should be considered, including cell modifications during in vitro cultivation, lack of both the relevant interactions and the structural context in vitro have been summarized in the present review.

Substrate viscosity enhances correlation in epithelial sheet movement

The movement of the epithelium plays vital roles in the development and renewal of complex tissues, from the separation of tissues in the early embryo, to turnover in the homeostasis of the gastrointestinal mucosa. Yet, despite its importance, a clear interpretation of the mechanism for collective motion in epithelial sheets remains elusive. This interpretation is prohibited by the lack of understanding of the relationship between motion and cell-cell contact, and their mediation by the mechanical properties of the underlying substrate. To better mimic physiological substrates that have inherent viscosity, we probe this relationship using polydimethylsiloxane, a substrate whose mechanical properties can be tuned from predominantly elastic to viscous by altering its cross-linking content. We therefore characterize the comparative spatiotemporal correlations in cell velocity during the movement of an epithelial monolayer as a function of the viscoelasticity of the substrate. Our results show that high correlation in cell velocity is achieved when the substrate G''(ω) is ~0.4 × G'(ω). This correlation is driven by a balance between cell-cell contact and the adhesion and contraction of the extracellular matrix. For G'(ω) > G'(ω), this balance shifts, and contraction of the tissue drives the substrate to flow, further elevating the correlation in movement.

Culturing keratinocytes and fibroblasts in a three-dimensional mesh results in epidermal differentiation and formation of a basal lamina-anchoring zone

The purpose of this study was to characterize an in vitro co-culture model in which fibroblasts grown in a three-dimensional nylon mesh were recombined with human keratinocytes. The cultures were kept for 3 and 5 weeks and then processed for electron microscopy. Keratinocytes showed reconstruction of an epidermis consisting of a basal layer with hemidesmosomes, a stratified epithelium with tonofilaments and desmosomes, a granular layer with keratinosomes and keratohyaline granules, and a transitional stratum corneum. Anchoring filaments, lamina densa, anchoring fibrils, bundles of elastin-associated microfibrils (diameters 10 nm) and fine collagen fibrils were formed. Collagen fibrils near the epidermis were much thinner than those in the lower levels. The present study shows that the dermal model containing metabolically active fibroblasts in their natural environment will support epidermal morphogenesis and differentiation including the formation of a basal lamina and anchoring zone.

Effects of the extracellular matrix on fetal choroid plexus epithelial cells: changes in morphology and multicellular organization do not affect gene expression

We have developed a primary culture system for fetal mouse choroid plexus epithelial cells which maintains their differentiated phenotype. When grown on a reconstituted basement membrane substrate (Matrigel) epithelial cells formed aggregates which became embedded in the matrix and developed into characteristic and highly reproducible multicellular vesicular structures. These vesicles consisted of a squamous layer of epithelial cells with extensive attachment to the matrix substrate, surrounding a fluid-filled lumen. Electron microscopy showed that cells comprising these vesicles had a high degree of membrane specialization and polarized morphology which in many respects mimicked the in vivo morphology. Biochemical analyses demonstrated that under these culture conditions the tissue-specific pattern of gene expression of fetal choroid plexus epithelium was maintained. After 6 days in culture these cells contained approximately the same amount of transthyretin mRNA as the 12.5-day choroid plexus in vivo, and the level of total RNA per cell, which is proportional to the protein synthetic capability of the cells, was also maintained. The pattern of protein secretion was also very similar to that generated by fetal mouse choroid plexus cells in vivo. In contrast choroid plexus epithelial cells attached poorly to collagen I gels. Heterogeneous aggregates were formed in which cell-cell interactions were more extensive than cell-substrate interactions, and in no cases was a central lumen observed. Cells on the surface of large aggregates showed some evidence of membrane polarization, while the majority of cells in the cultures exhibited little evidence of polarized morphology. Despite the striking difference in morphology and multicellular organization these cells still expressed high levels of transthyretin mRNA and maintained the same pattern of protein synthesis as cells cultured on Matrigel. These results indicate that the basement membrane is important for the organization of choroid plexus epithelial cells into a functional epithelium in vitro and thus presumably the maintenance of the integrity of the blood-brain barrier in vivo. In contrast to several other epithelial systems which have been studied, the type of extracellular matrix does not appear to directly influence tissue-specific gene expression by choroid plexus epithelial cells. Thus the level of gene expression is not dependent on the cytoarchitecture and multicellular organization of this cell type.

Expression of extracellular matrix components is regulated by substratum

Reconstituted basement membranes and extracellular matrices have been demonstrated to affect, positively and dramatically, the production of milk proteins in cultured mammary epithelial cells. Here we show that both the expression and the deposition of extracellular matrix components themselves are regulated by substratum. The steady-state levels of the laminin, type IV collagen, and fibronectin mRNAs in mammary epithelial cells cultured on plastic dishes and on type I collagen gels have been examined, as has the ability of these cells to synthesize, secrete, and deposit laminin and other, extracellular matrix proteins. We demonstrate de novo synthesis of a basement membrane by cells cultured on type I collagen gels which have been floated into the medium. Expression of the mRNA and proteins of basement membranes, however, are quite low in these cultures. In contrast, the levels of laminin, type IV collagen, and fibronectin mRNAs are highest in cells cultured on plastic surfaces, where no basement membrane is deposited. It is suggested that the interaction between epithelial cells and both basement membrane and stromally derived matrices exerts a negative influence on the expression of mRNA for extracellular matrix components. In addition, we show that the capacity for lactational differentiation correlates with conditions that favor the deposition of a continuous basement membrane, and argue that the interaction between specialized epithelial cells and stroma enables them to create their own microenvironment for accurate signal transduction and phenotypic function.

The preservation and regeneration of cilia on human nasal epithelial cells cultured in vitro

Dissociated human nasal epithelial cells from nasal polyps were cultured in Ham's F12-DME 1/1 supplemented with NU-serum 10%, choleratoxin (10 ng/ml), retinoic acid (10(-7) M) and antibiotics. In monolayer cultures, the epithelial cells grew to confluency on collagen gels, became squamous, and lost their cilia within 2-6 weeks. In suspension cultures, epithelial cell sheaths formed stable vesicles and aggregates. These maintained a respiratory-type morphology and normal ciliary activity for over 6 months. When deciliated, squamous cells from monolayer cultures were brought in suspension, a respiratory-type morphology with cilia reappeared. This in vitro ciliogenesis resulted in normal and coordinated ciliary activity observed for more than 5 months.

Study of basement membrane formation in dermal-epidermal recombinants in vitro

Two different dermal-epidermal recombinants were prepared in vitro and used to study the synthesis and formation of basement membrane. The first was obtained by culturing keratinocytes on the surface of a collagen lattice populated by fibroblasts. The second was prepared by coculture of both keratinocytes and fibroblasts in a collagen lattice. After 6 weeks of culture, the basal lamina was observed with electron microscopy only if keratinocytes were cultivated on top of the collagen lattice populated by fibroblasts. In the second model, however, type IV collagen, laminin, and pemphigoid bullosa antigen could be detected by immunofluorescence as well as synthesis of type IV collagen in the culture, but no basement membrane was observed by electron microscopy. These data demonstrate that, in vitro, basement membrane formation depends not only on the presence of the macromolecular components but also on the culture conditions.