The collagen lattice: a model for studying the physiology, biosynthetic function and pharmacology of the skin

Inonotus obliquus Extracts Decreased Expression of MMP1 mRNA via JNK-AP-1 Axis

Inonotus obliquus, which is parasitic on birch and other trees, is a fungus in the family Hymenochaetaceae. In this study, we investigated whether Inonotus obliquus extracts used in traditional medicine were decreased in the expression of matrix metalloproteinases-1 (MMP-1) in the normal human dermal fibroblasts. As shown in our results, extracts of Inonotus obliquus decreased MMP1 expression in oxidative stress-exposed normal human dermal fibroblasts. Additionally, Inonotus obliquus extracts decreased AP-1 transcriptional activity and phospho-JNK in oxidative stress-exposed normal human dermal fibroblasts. Oxidative stress mediated the elevation of MMP1 mRNA expression and was well regulated by the JNK-AP-1 axis. Therefore, the results suggest that Inonotus obliquus extracts decreased MMP1 mRNA expression by regulating JNK-AP-1 axis. Additionally, Inonotus obliquus extracts have the potential to reduce collagen destruction and the formation of wrinkles and to be used as a cosmetic ingredient.

MEPE-derived ASARM peptide inhibits odontogenic differentiation of dental pulp stem cells and impairs mineralization in tooth models of X-linked hypophosphatemia

Mutations in PHEX (phosphate-regulating gene with homologies to endopeptidases on the X-chromosome) cause X-linked familial hypophosphatemic rickets (XLH), a disorder having severe bone and tooth dentin mineralization defects. The absence of functional PHEX leads to abnormal accumulation of ASARM (acidic serine- and aspartate-rich motif) peptide − a substrate for PHEX and a strong inhibitor of mineralization − derived from MEPE (matrix extracellular phosphoglycoprotein) and other matrix proteins. MEPE-derived ASARM peptide accumulates in tooth dentin of XLH patients where it may impair dentinogenesis. Here, we investigated the effects of ASARM peptides in vitro and in vivo on odontoblast differentiation and matrix mineralization. Dental pulp stem cells from human exfoliated deciduous teeth (SHEDs) were seeded into a 3D collagen scaffold, and induced towards odontogenic differentiation. Cultures were treated with synthetic ASARM peptides (phosphorylated and nonphosphorylated) derived from the human MEPE sequence. Phosphorylated ASARM peptide inhibited SHED differentiation in vitro, with no mineralized nodule formation, decreased odontoblast marker expression, and upregulated MEPE expression. Phosphorylated ASARM peptide implanted in a rat molar pulp injury model impaired reparative dentin formation and mineralization, with increased MEPE immunohistochemical staining. In conclusion, using complementary models to study tooth dentin defects observed in XLH, we demonstrate that the MEPE-derived ASARM peptide inhibits both odontogenic differentiation and matrix mineralization, while increasing MEPE expression. These results contribute to a partial mechanistic explanation of XLH pathogenesis: direct inhibition of mineralization by ASARM peptide leads to the mineralization defects in XLH teeth. This process appears to be positively reinforced by the increased MEPE expression induced by ASARM. The MEPE-ASARM system can therefore be considered as a potential therapeutic target.

Wnt-4 potently inhibits capillary outgrowth from rat aorta in 3D culture

Regulation of angiogenesis involves tight cell-to-cell and cell-to-extracellular-matrix interactions. Various reports demonstrate that the Wnt signaling pathways participate in this regulation. Using a three-dimensional aortic ring culture combined with an ex vivo retroviral infection approach, we evaluated the effects of two Wnt growth factors, Wnt-1 and Wnt-4, on the formation and growth of new capillaries. Our results show that Wnt-1 had no effect, whereas Wnt-4 was a potent inhibitor of capillary outgrowth in vitro.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

COMPLEMENTARY ROLES OF MICROTUBULES AND MICROFILAMENTS IN THE LUNG FIBROBLAST-MEDIATED CONTRACTION OF COLLAGEN GELS: DYNAMICS AND THE INFLUENCE OF CELL DENSITY

Fibroblasts are important cellular components in wound healing, scar formation, and fibrotic disorders; and the fibroblast-populated collagen-gel (FPCG) model allows examination of fibroblast behavior in an in vitro three-dimensional environment similar to that in vivo. Contraction of free-floating FPCGs depends on an active and dynamic cytoskeleton, and the contraction dynamics are highly influenced by cell density. We investigated mechanistic differences between high- and low-cell density FPCG contraction by evaluating contraction dynamics in detail, using specific cytoskeletal disruptors. Collagen gels were seeded with human lung fibroblasts at either high (HD) or low (LD) density, and incubated with or without cytoskeletal disruptors colchicine (microtubules) or cytochalasin D (microfilaments). Gel area was measured daily. FPCG contraction curves were essentially sigmoidal, featuring an initial period of no contraction (lag phase), followed by a period of rapid contraction (log phase). Contraction curves of HD-FPCGs were distinct from those of LD-FPCGs. For example, HD-FPCGs had a negligible lag phase (compared with 3 d for LD-FPCGs) and exhibited a higher rate of log-phase contraction. Both colchicine and cytochalasin dose-dependently inhibited contraction but specifically affected different phases of contraction in HD- and LD-FPCGs; and colchicine inhibited LD-FPCGs much more than HD-FPCGs. The data indicate that LD- and HD-FPCGs contract through different primary mechanisms. Microtubules and microfilaments are both complementarily and dynamically involved in the contraction of FPCGs, and cell density influences primary cytoskeletal mechanisms. These results provide valuable information about fibroblast behavior in healing and fibrosis, and may suggest novel treatment options.

MAP kinase pathways involving hsp27 regulate fibroblast-mediated wound contraction

BACKGROUND

Heat shock protein 27 (hsp27) has been shown to modulate actin arrays in a manner dependent on its phosphorylation status. Hsp27 is phosphorylated by mitogen-activated protein kinase-activated protein kinase 2/3, which is regulated by mitogen-activated protein (MAP) kinases. We hypothesize that hsp27 phosphorylation modulates wound contraction.

MATERIALS AND METHODS

In these studies, a specific p38 MAP kinase inhibitor, SB203580, and a specific MAPK/extracellular signal-regulated kinase kinase 1,2 inhibitor, PD98059, were used to inhibit kinase activity. The effect of MAP kinase inhibitors was tested using a tissue culture model, the fibroblast-populated collagen lattice (FPCL) contraction assay, and a rat full-thickness skin defect model of wound healing. Hsp27 phosphorylation status was determined by isoelectric focus and Western blot analysis.

RESULTS

We show here that hsp27 phosphorylation correlates with FPCL contraction and with contraction in vivo. In the tissue culture model, each inhibitor reduced FPCL contraction and hsp27 phosphorylation. Hsp27 phosphorylation correlated with both p38 and ERK1, 2 activation. Hsp27 was highly phosphorylated in the wound edge during wound healing in a rat in vivo model. The phosphorylation status was highest in the granulation tissue. Treatment with both kinase inhibitors significantly delayed wound contraction in vivo, which correlated with inhibition of hsp27 phosphorylation.

CONCLUSIONS

This study demonstrates that ERK and p38 kinase cascades play important roles in wound contraction. Additionally, these data implicate hsp27 as being a key molecule in modulating the effects of these kinases.

Multistep production of bioengineered skin substitutes: sequential modulation of culture conditions

Many studies are being conducted to define the role of growth factors in cutaneous physiology in order to add cytokines in a timely fashion for optimal tissue engineering of skin. This study is aimed at developing a multistep approach for the production of bioengineered skin substitutes, taking into account the effects of various growth factors according to the culture time. The use of a serum-supplemented medium throughout the whole culture period of skin substitutes was compared to the sequential use of specific additives at defined culture steps. Histological analysis revealed that serum was necessary for keratinocyte proliferation and migration on dermal substitutes during the first 2 d after their seeding. However, the serum-free medium presented some advantages when supplemented with different additives at specific culture steps. Interestingly, ascorbic acid added to the dermal substitutes before and after keratinocyte seeding maintained their cuboidal morphology in the basal epidermal layer. In the absence of serum, collagen matrix degradation slowed down, and a better multilayered epidermal organization was obtained, notably with retinoic acid. Stratum corneum formation was also enhanced by fatty acids. Thus, sequential addition of exogenous factors to the medium used to produce skin substitutes can improve their structural features and functional properties in vitro.

Constructing an in vitro cornea from cultures of the three specific corneal cell types

This paper presents a reliable method for establishing pure cultures of the three types of corneal cells. This is believed to be the first time, corneal cells have been cultured from fetal pig corneas. Cell growth studies were performed in different media. Subcultures of the three corneal cell types were passaged until the 30th generation without their showing signs of senescence. For engineering an in vitro cornea, corneal epithelial cells were cultured over corneal stromal cells in an artificial biomatrix of collagen with an underlying layer of corneal endothelial cells. The morphology, histology, and differentiation of the in vitro cornea were investigated to determine the degree of comparability to the cornea in vivo. The in vitro construct displayed signs of transition to an organotypic phenotype of which the most prominent was the formation of two basement membranes.

Tissue-engineered human skin substitutes developed from collagen-populated hydrated gels: clinical and fundamental applications

The field of tissue engineering has opened several avenues in biomedical sciences, through ongoing progress. Skin substitutes are currently optimised for clinical as well as fundamental applications. The paper reviews the development of collagen-populated hydrated gels for their eventual use as a therapeutic option for the treatment of burn patients or chronic wounds: tools for pharmacological and toxicological studies, and cutaneous models for in vitro studies. These skin substitutes are produced by culturing keratinocytes on a matured dermal equivalent composed of fibroblasts included in a collagen gel. New biotechnological approaches have been developed to prevent contraction (anchoring devices) and promote epithelial cell differentiation. The impact of dermo-epidermal interactions on the differentiation and organisation of bio-engineered skin tissues has been demonstrated with human skin cells. Human skin substitutes have been adapted for percutaneous absorption studies and toxicity assessment. The evolution of these human skin substitutes has been monitored in vivo in preclinical studies showing promising results. These substitutes could also serve as in vitro models for better understanding of the immunological response and healing mechanism in human skin. Thus, such human skin substitutes present various advantages and are leading to the development of other bio-engineered tissues, such as blood vessels, ligaments and bronchi.

Keratinocytes contract human dermal extracellular matrix and reduce soluble fibronectin production by fibroblasts in a skin composite model

Composites of human de-epidermised acellular dermis and normal adult human keratinocytes and fibroblasts were examined for the ability of cells to contract these composites. Image analysis of the outline of the composites showed that, in this model, keratinocytes alone or in the presence of fibroblasts caused highly significant contraction (of the order of 25% by day 12). There was no significant contraction of the dermis with fibroblasts alone or in the absence of cells. The presence or absence of basement membrane antigens did not influence the effect of keratinocytes on dermal contraction. Analysis of the conditioned media from these composites showed that the greatest fibronectin production was seen with fibroblasts alone in the presence of basement membrane. Keratinocytes alone produced little fibronectin irrespective of the presence of the basement membrane. If keratinocytes were present with fibroblasts, however, then fibronectin production was significantly reduced both in the presence and absence of the basement membrane, indicating that keratinocytes modify dermal fibroblast extracellular matrix production. This study shows that while keratinocytes and fibroblasts are clearly influencing each other's activity in this human skin composite model, under the circumstances we describe it is the keratinocyte and not the fibroblast which causes contraction of the human de-epidermised acellular dermis.

Development of a skin model based on insoluble fibrillar collagen

A biocompatible, 3-dimensional, noncontracting, crosslinked collagen matrix was adapted to promote differentiation of epidermal keratinocytes. To produce the matrix, a 3% wt/wt dispersion of insoluble bovine collagen containing 5 mg polylysine/g collagen in 0.001 N HCl was blended, lyophilized, and crosslinked using a dehydrothermal technique. Matrices 4 cm2 and 3 mm thick were seeded with human dermal fibroblasts (1 x 10(5)/cm2). After 5 days in culture, the matrices were seeded with human epidermal keratinocytes (1 x 10(5)/cm2). The cultures were grown submerged for 1 week and raised to the liquid/air interface for 3 weeks to promote epidermal differentiation. Based on morphology and immunological staining with antibodies for human involucrin, keratin 1 (k1), filaggrin, and loricrin, the state of differentiation of the epidermal layer was nearly equivalent to that seen with cultures grown on contracted collagen lattices produced according to the methodology described in the literature and similar to the pattern produced in normal neonatal foreskin. These results demonstrate the usefulness of an in vitro skin model employing a crosslinked collagen matrix that permits the incorporation of additional covalently linked bioactive molecules during matrix formation.

The effect of different collagens and of proteoglycan on the retraction of collagen lattice

The effect of various collagens and proteoglycan on the formation and retraction of collagen lattices was tested. The most rapid aggregation of collagen molecules was observed by the use of the least cross-linked collagen fractions (ie pepsin-digested calf skin collagen type I). Lattices formed with more cross-linked collagens (acid soluble collagen-ASC, type III) contracted slowly and less intensively. Unpurified pepsinized cartilage extract containing collagen types II, IX and XI, some glycoproteins and proteoglycans formed lattices rather well. On the contrary, purified collagen type II as well as polymeric collagen (solubilized by denaturing conditions) did not form lattices at all. The lattice formation and retraction was intensified by addition of proteoglycan into the culture medium. The authors suggest that the kinetics of the lattice formation and retraction depends on the amount of collagen cross-links and the concentration of proteoglycan in the culture medium.

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.

Different regulation of collagen I gene transcription in three-dimensional lattice cultures

Human skin fibroblasts were cultivated in confluent monolayers, retracting collagen lattices, retracting fibrin lattices and non-retracting fibrin lattices and the expression of messenger RNA specific for the alpha 1 chain of type I procollagen comparatively studied by Northern blot and dot blot hybridization. Two factors contribute to the lower level of procollagen messenger RNA in collagen lattices: the retraction and the nature of the fibrillar protein that constitutes the lattices. Fibrin lattices, when they do not retract, make as much collagen and procollagen mRNA as monolayer confluent cells.

A new technique to study the mechanical properties of collagen lattices

A new technique to study the mechanical properties of collagen lattices or dermal equivalents is described. With the help of the load-extension curve obtained with a uniaxial traction apparatus, a stiffness modulus varying from 0.06 to 1 MPa is calculated from the studied parameters (duration of culture, collagen and fibroblast concentration). The technique is presented as a new tool for testing the effect of pharmacological agents on the mechanical properties of the skin.

Variability in the retraction of collagen lattices by scleroderma fibroblasts--relationship to protein synthesis and clinical data

Skin fibroblasts from 18 scleroderma patients were seeded into collagen lattices and their ability to retract their substratum was compared with that of control fibroblasts from healthy donors. When considered as a whole, scleroderma fibroblasts retracted lattices earlier and more intensely than controls. Analysis of individual results demonstrated that morphea and diffuse systemic sclerosis (dSSc) fibroblasts had different kinetics of lattice retraction. Fibroblasts which contracted lattices more intensely than controls were found to produce increased levels of fibronectin. A comparison of the retraction of collagen lattices by fibroblasts from involved (IS) and uninvolved skin (US) of the same patients (n = 4) showed that those from IS retracted the lattices more than fibroblasts from normal donors, whereas a high variability was found with fibroblasts from US. The increased retraction of collagen lattices seems to be a feature of the more severe forms of scleroderma.

Effects of amiprilose hydrochloride on the components of human skin equivalents

Amiprilose hydrochloride has been shown to inhibit the proliferation of a number of hyperproliferative cell types including psoriatic skin cells. In the present study, the effects of amiprilose hydrochloride on human tissue equivalents were examined by incubating a) dermal equivalents, b) skin equivalents in the process of epidermalization, and c) mature skin equivalents, with varying concentrations of the drug. In all three models amiprilose hydrochloride concentrations of 0.1% (wt/vol) and lower were not toxic to fibroblasts and keratinocytes and did not interfere with the differentiation of the skin equivalent and the developing skin equivalent. When tested in dermal equivalents, concentrations of amiprilose hydrochloride between 0.1 and 0.5% resulted in changes in fibroblast morphology with development of large intracellular vacuoles, and concentrations greater than 5% were toxic. In mature skin equivalents, in addition to changes in fibroblast morphology, amiprilose hydrochloride in concentrations of 1 to 10% affected the epidermis. When 0.5% amiprilose hydrochloride was present in the developing skin equivalent during differentiation, the epidermal keratinocytes were also affected. Thus the morphology of basal keratinocytes was modified, the differentiation was incomplete, and the dermal-epidermal attachment was compromised. These studies suggest the possibility of an extracellular mechanism of action of amiprilose hydrochloride and delineate acceptable dosage ranges for the potential drug.

Fibroblast behavior on gels of type I, III, and IV human placental collagens

Various collagens were extracted and purified from human placenta after partial pepsin digestion. We prepared type III + I (57:43), enriched type I, type III, and type IV collagens on an industrial level, and studied their biological properties with MRC5 fibroblast cells. Using the process of contraction of a hydrated collagen lattice described by Bell, we found tha the contraction rate was dependent on collagen type composition. The contraction was faster and more pronounced with pepsinized type I collagen than with pepsinized type III + I (57:43) collagen; the lowest rate was obtained with the pepsinized type III collagen. Using a new technique of collagen cross-linking, a gel was made with type IV collagen. This cross-linking procedure, based on partial oxidation of sugar residues and hydroxylysine by periodic acid, followed by neutralization, resulted in an increased number of natural cross-link bridges between oxidized and nonoxidized collagen molecules, without internal toxic residues. The fibroblasts were unable to contract type IV/IVox collagen gels. The type IV/IVox collagen gel was transparent and its amorphous ultrastructure lacked any visible striated fibrils. Fibroblast cells exhibited atypical behavior in these type IV/IVox collagen gels as evidenced by optical and electron microscopy. The penetration of fibroblasts could be measured. Fibroblasts penetrated faster in type IV/IVox collagen gels than in untreated type III + I collagen gels. The lowest rate of penetration was obtained with cross-linked type III + I gels. Fibroblast proliferation was similar on untreated or cross-linked type III + I collagen gels and slightly increased on type IV/IVox collagen gels, suggesting that this cross-linking procedure was not toxic.

Cell-mediated contraction of collagen lattices in serum-free medium: effect of serum and nonserum factors

This study was conducted to identify a defined, serum-free culture medium that supports cell dependent contraction of a collagen lattice. Collagen lattices were found to contract in cultures containing human foreskin fibroblasts (HFF) or rabbit aortic smooth muscle (RASM) cells incubated in serum-free medium. HFF and RASM cells required different supplements to contract the collagen gels. HFF cultured in Dulbecco's modified Eagle's (DME) medium supplemented with bovine serum albumin (BSA) and either endothelial cell growth supplement (EnGS), insulin (In), or platelet derived growth factor (PDGF) supported collagen lattice contraction. Replacement of BSA with casein without the addition of other supplements improved contraction. In contrast, RASM cells supplemented with BSA, EnGS, In, and PDGF were able to contract collagen gels only minimally. Similar to HFF, RASM cells cultured in DME medium supplemented with casein, but without the addition of other supplements, contracted collagen lattices. HFF-mediated collagen contraction was inhibited by prostaglandins E1 or E2, fibronectin, or ascorbic acid. The reported serum-free model provides a useful in vitro method to investigate the role of serum and nonserum factors regulating cell mediated-contraction of insoluble collagen fibrils.

Cultures of fibroblasts in fibrin lattices: models for the study of metabolic activities of the cells in physiological conditions

Two techniques for fibroblast culture in three-dimensional fibrin matrices (fibrin lattices) were used to study the behavior and metabolism of cells in this physiological support. When the fibrin lattices were prepared in silicone-coated glass petri dishes, fibroblasts induced retraction of lattices to an extent dependent on both cell density and serum concentration, the cells stopped dividing, and their protein and collagen syntheses proceeded at a lower rate, like that in collagen lattices. When fibrin lattices were prepared in plastic petri dishes, the matrix attached to the walls, there was no retraction, and the protein synthesis was very active even as regards collagen. The optimal concentration of ascorbic acid in nonretracting fibrin lattices was lower (10 micrograms/ml) than in monolayers (50 micrograms/ml). The comparison of collagen and fibrin lattices showed that the collagenic nature of the lattice was not compulsory for supporting the phenomenon of retraction and that fibroblasts, when exposed to a stress in a fibrin matrix prevented from retracting, secreted far more collagen.

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.

Collagen lattice effects on fibroblast arachidonic acid metabolism

Fibroblasts are routinely maintained in vitro on tissue culture plastic, in an environment which is devoid of collagen, the most abundant extracellular protein in dermis. Recent work has shown that by seeding fibroblasts into a collagen matrix, many aspects of their metabolism change dramatically: they stop proliferation, organize and contract the collagen matrix, and secrete much larger quantities of the usual extracellular matrix components. Because so many fibroblast functions are dramatically altered by the presence of the collagen matrix, matrix effects on fibroblast metabolism of arachidonic acid were examined. The studies presented here show that during the period of matrix contraction, metabolism of arachidonate to prostaglandins by fibroblasts is increased sixfold compared to cells plated on plastic, and that this increase is correlated with contraction but does not regulate it. The increase in prostaglandin synthesis is due in part to an increased new synthesis of the rate-limiting enzyme in prostaglandin synthesis, cyclooxygenase. No change in the profile of products the fibroblasts synthesize from arachidonate is induced by the presence of the matrix. After the lattice contraction is complete, the basal arachidonate metabolism of matrix-embedded cells have the same capacity to synthesize PGE2 in response to IL-1 as do cells grown on plastic. However, the response to the hormone agonist bradykinin by the matrix-embedded cells is present on day 1 but not on day 3, the time when cells grown on plastic are most responsive. These data indicate that while basal prostaglandin metabolism is unaffected in quiescent fibroblasts which have been embedded in a collagen matrix, response to hormone agonists may be greatly attenuated. The changes in the metabolism of arachidonate which occur during the process of matrix contraction and organization may play a part in the regulation of wound repair.

Physiological variables affecting collagen lattice contraction by human dermal fibroblasts

Normal human dermal fibroblasts cultured in collagen lattices can compact that matrix by the process known as lattice contraction. That process is a model of the pathological one of scar contracture or wound contraction and is affected by several factors. Lattice contraction is promoted by the addition of adequate amounts of fetal bovine serum to the medium (maximum contraction with 10% serum). The process requires energy, of which glucose and pyruvate have been shown to be adequate sources. When glucose is used as the substrate, the major pathway of energy generation appears to be anaerobic metabolism. When pyruvate is the only substrate, aerobic metabolism may be crucial. The synthesis of DNA is not required for lattice contraction, while protein synthesis is, although the identities of the specific proteins are unknown. Impairment of calcium ion transport inhibits lattice contraction, and the specific inhibition of calmodulin-calcium interactions by W-7 blocks contraction. W-7 at a concentration of 6 x 10(-6) M blocks lattice contraction completely, while it has no effect at any lower concentration. Impairing dynamic microtubule activity impairs contraction. Disrupting microfilaments by cytochalasin B completely blocks lattice contraction. Microfilament function and calcium-calmodulin may be linked by a mechanism involving myosin-ATPase. The process of cell-mediated lattice contraction requires the production of energy, protein synthesis, and a functional cytoskeleton.

Growth and differentiation of 3T3-F442A preadipocytes in three-dimensional gels of native collagen

Three-dimensional gels of native type I collagen have been used as a substrate for growth and differentiation in 3T3 adipocyte precursors. Such hydrated lattices can support a sustained cell growth leading to several 10-fold increases in cell number within 2 weeks. During this period, the cells condense the hydrated collagen lattice to a tissue-like structure one-fourth of the area of the initial gel. From Days 10 to 12, the cells progressively exhibit morphological characteristics of adipocytes and accumulate lipid droplets as evidenced by Oil Red O staining. Lipoprotein lipase activity appears very early; between Days 8 and 22 it sharply increases 15-fold and then remains stable at a very high level (about 30 nmol/min/10(6) cells). The emergence of glycerophosphate dehydrogenase activity is delayed; it becomes detectable at Day 15 and progressively increases up to 700 nmol/min/10(6) cells at Days 35-40. Thus, this adipose tissue equivalent appears to be a potential model for studying adipocyte function.

Epithelial-stromal interactions in the adult bladder: urothelial growth, differentiation, and maturation on culture facsimiles of bladder stroma

Analysis of the responsiveness of isolated adult urothelium to a series of different stromal cell-extracellular matrix combinations demonstrated the capacity of stromal cells to induce and maintain normal patterns of urothelial growth, differentiation, and maturation in vitro. By incorporating embryonic mesenchymal derived (Swiss 3T3) cells into type I collagen matrices, simplified three-dimensional tissue-like facsimiles of bladder stroma were derived. When recombined with sheets of isolated urothelium these facsimiles could approximately reproduce the capacity of natural stromal tissue to support the expression of normal urothelial tissue specific characteristics. In contrast cocultures between urothelia and monolayers of 3T3 cells, applied to the surface of planar collagen substrata could only permit urothelial cell attachment but not growth or differentiation whereas lethally irradiated 3T3 (feeder) cells, under similar experimental conditions, could support the maintenance of an immature or incompletely differentiated urothelium. Conditioned medium elaborated by cultured 3T3 cells could not stimulate further differentiation in urothelia cultured alone on planar collagen substrata. These studies indicate that a significant portion of the regulatory capacity of the stroma in stromal-urothelial interactions can be accounted for by the activities of a closely applied population of stromal cells, provided the cells are viable and presented to the urothelium in a three-dimensional context in combination with collagen. The capacity of embryonic mesenchymal cells to express properties appropriate to the development of a multilayered terminally differentiated urothelium suggests that normal interactions between adult urothelium and stroma are of limited specificity with the urothelium requiring an essential input of permissive signals only.

Fibronectin dependence of the contraction of collagen lattices by human skin fibroblasts

The role of fibronectin in the contraction of collagen lattices by human skin fibroblasts has been investigated. Incubation of lattice cultures in Dulbecco's modified Eagle's medium supplemented with increasing concentrations of non-dialysed or dialysed fetal calf serum demonstrated that the rate of contraction was dependent on non-dialysable serum components. The suppression of contraction observed when fibronectin was eliminated from serum, either by affinity chromatography on gelatin-agarose columns or by precipitation with anti-fibronectin antibodies, showed that fibronectin is critical for the contraction. When collagen lattices were incubated in a serum-free culture medium totally devoid of fibronectin, no contraction occurred. When fibronectin was added to this medium, their contraction was correlated with the concentration of fibronectin added. The contraction was inhibited by cycloheximide, tunicamycin, and monensin. These results demonstrate that the contraction of collagen lattices by human skin fibroblasts is dependent on fibronectin, and that other protein factors synthesized by the cells or contained in serum are also necessary.

Human epidermis reconstructed by culture: is it "normal"?

Human keratinocytes were grown on a dermal equivalent (or lattice) at the liquid-air interface in an attempt to reconstitute a functional epidermis in vitro. Although the multilayered epithelium thus obtained is well differentiated, as shown by the presence of keratohyaline granules and horny layer, several differences from its in vivo counterpart were also observed: In the reconstructed epidermis, basal keratinocytes do not have the cuboidal shape found in vivo; they synthesize bullous pemphigoid antigen and laminin, but the distribution of these antigens is not linear as in vivo; they contain the plasma-membrane antigens restricted to the basal layer in vivo (VM1, BC1), but these antigens are not polarized; lack of polarization is also evidenced by the distribution of actin. Differentiation markers appear but with a topography slightly different from that of epidermis in vivo; the 67-kD keratin does not appear in the first suprabasal layer as in vivo but above; involucrin, which appears in the granular layers in vivo appears as soon as the cells leave the basal layer. psi 3 antigen and fibronectin found in vivo only in hyperproliferative epidermis (wound healing, psoriasis) are detected. Hyperproliferation would also explain the unexpected straining of basal cells by KL1 monoclonal antibody. Because of the potential clinical or pharmacologic use of artificial epidermis, the question of whether the epidermis obtained in vitro can be considered as "normal" is discussed.

A new method for studying epidermalization in vitro

A new method for studying epidermalization in vitro is described. It consists of inserting a punch biopsy that serves as a source of epidermis into dermal equivalent freshly made up, with fibroblasts mixed in a collagen matrix. Fibroblasts cling to collagen fibrils and contract the matrix, leading in 3 days to a resistant dermal equivalent holding the punch biopsy firmly in place. At day 5, a culture medium favouring epidermal growth was used and a fringe of a new epidermis appeared around the punch, the area of which grew linearly with time. This new epidermis showed a pattern of differentiation similar to epidermis in vivo, with cuboidal basal cells, keratohyalin granules, membrane coating granules and the expression of the 65-67 kd keratin subset. The method seems to combine the advantages of the explant technique and of classical keratinocyte cultures, providing the researcher with a large quantity of differentiated epidermis, the pharmacologist with simple and quantitative system in which to study modifications of growth and differentiation of epidermis, and the plastic surgeon with a possible material for skin grafting.