Effects of extracellular matrices on human keratinocyte adhesion and growth and on its secretion and deposition of fibronectin in culture

Porcine mesothelium matrix as a biomaterial for wound healing applications

The increasing economic burden of wound healing in healthcare systems requires the development of functional therapies. Xenografts with preserved extracellular matrix (ECM) structure and biofunctional components overcome major limitations of autografts and allografts (e.g. availability) and artificial biomaterials (e.g. foreign body response). Although porcine mesothelium is extensively used in clinical practice, it is under-investigated for wound healing applications. Herein, we compared the biochemical and biological properties of the only two commercially available porcine mesothelium grafts (Meso Biomatrix® and Puracol® Ultra ECM) to traditionally used wound healing grafts (Endoform™, ovine forestomach and MatriStem®, porcine urinary bladder) and biomaterials (Promogran™, collagen/oxidized regenerated cellulose). The Endoform™ and the Puracol® Ultra ECM showed the highest (p<0.05) soluble collagen and elastin content. The MatriStem® had the highest (p<0.05) basic fibroblast growth factor (FGFb) content, whereas the Meso Biomatrix® had the highest (p<0.05) transforming growth factor beta-1 (TGF-β1) and vascular endothelial growth factor (VEGF) content. All materials showed tissue-specific structure and composition. The Endoform™ and the Meso Biomatrix® had some nuclei residual matter. All tissue grafts showed similar (p>0.05) response to enzymatic degradation, whereas the Promogran™ was not completely degraded by matrix metalloproteinase (MMP)-8 and was completely degraded by elastase. The Promogran™ showed the highest (p<0.05) permeability to bacterial infiltration. The Promogran™ showed by far the lowest dermal fibroblast and THP-1 attachment and growth. All tested materials showed significantly lower (p<0.05) tumor necrosis factor-alpha (TNF-α) expression than the lipopolysaccharides group. The MatriStem® and the Puracol® Ultra ECM promoted the highest (p<0.05) number of micro-vessel formation, whereas the Promogran™ the lowest (p<0.05). Collectively, these data confer that porcine mesothelium has the potential to be used as a wound healing material, considering its composition, resistance to enzymatic degradation, cytocompatibility, and angiogenic potential.

Peptide-Functionalized Hydrogels Modulate Integrin Expression and Stemness in Adult Human Epidermal Keratinocytes

The extracellular matrix (ECM) controls keratinocyte proliferation, migration, and differentiation through β-integrin signaling. Wound-healing research requires expanding cells in vitro while maintaining replicative capacity; however, early terminal differentiation under traditional culture conditions limits expansion. Here, a design of experiments approach identifies poly(ethylene glycol)-based hydrogel formulations with mechanical properties (elastic modulus, E = 20.9 ± 0.56 kPa) and bioactive peptide sequences that mimic the epidermal ECM. These hydrogels enable systematic investigation of the influence of cell-binding domains from fibronectin (RGDS), laminin (YIGSR), and collagen IV (HepIII) on keratinocyte stemness and β1 integrin expression. Quantification of 14-day keratin protein expression shows four hydrogels improve stemness compared to standard techniques. Three hydrogels increase β1 integrin expression, demonstrating a positive linear relationship between stemness and β1 integrin expression. Multifactorial statistical analysis predicts an optimal peptide combination ([RGDS] = 0.67 mm, [YIGSR] = 0.13 mm, and [HepIII] = 0.02 mm) for maintaining stemness in vitro. Best-performing hydrogels exhibit no decrease in Ki-67-positive cells compared to standards (15% decrease, day 7 to 14; p < 0.05, Tukey Test). These data demonstrate that precisely designed hydrogel biomaterials direct integrin expression and promote proliferation, improving the regenerative capability of cultured keratinocytes for basic science and translational work.

In Vitro Evaluation of 3T3 and MDBK Cells Attachment and Proliferation on Collagen and Fibronectin Immobilized Nonwoven Polylactide Matrices

Fibroblast-like, 3T3 (Mouse Swiss Albino) and epithelial-like MDBK (Madine Darby Bovine Kidney) cells were selected as model cell lines and the adhesion of these cells on nonwoven poly DL-lactide (PDLLA) matrices were investigated. PDLLA was synthesized by ring-opening polymerization of DL-lactide. Nonwoven PDLLA matrices were prepared by an extrusion/winding process. Surface modification of these matrices was achieved by glow-discharge treatment, which was followed by glutaraldehyde incorporation. Biologically modification was performed by immobilization of collagen and/or fibronectin for cell attachment and proliferation. Adhesion values of fibroblast-like and epithelial-like cells after incubation for 2 h was 90 and 85% of initial cells, respectively. The 3T3 cells grown on PDLLA, after 11 days of incubation, was 9 105 cells while the control group was 1.2 106 cells. MDBK cells grown on the same polymeric matrices were determined to be 1.5 106 cells and 1.8 106cells for the control group. These results indicate that biodegradable nonwoven PDLLA matrices can be used for adhesion and proliferation of primary cell cultures and that implants of polymer-cells composites can be used in wound healing. An important advantage of these matrices is that a second surgical operation is not necessary to remove the implant due to the biodegradation of polymer in tissue.

Collagen Immobilization onto P(EGDMA/HEMA) Microbeads for Cell Affinity Systems

Both nonswellable and swellable poly(EGDMA/HEMA) microbeads were produced by suspension copolymerization. These microbeads were modified by immobilization of a spacer-arm (hexamethylene diamine, HMDA) and collagen. The optimal values for modifications were as follows: sodium periodate concentration: 0.467 × 10-2 mmol/mL; HMDA concentration: 3.5 × 10-2 mmol/mL; and glutaraldehyde concentration: 0.70 × 106 mmol/mL. Adsorption of collagen onto plain and periodate oxidized poly(EGDMA/HEMA) microbeads were similar, 0.25 and 0.50 mg collagen/g polymer, respectively. Collagen immobilization on poly(EGDMA/HEMA) microbeads was studied at various temperatures, times, and pH by using protein solution containing various amounts of proteins. The optimal values for immobilizations were as follows: the initial collagen concentration: 0.25 mg/mL; temperature: 4°C; pH 7; and the immobilization time; 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to these unmodified and modified microbeads. The attachments of 3T3 and MDBK cells, especially to the collagen immobilized swellable microbeads were very high. Almost 96% of the 3T3 cells available in the cell culture medium became attached to these microbeads (2297 ± 122 cells per mg of polymer). There was no significant effect by swelling on cell attachment.

Cell Growth on Poly(EGDMA/HEMA) Based Microbeads

Poly(EGDMA/HEMA) copolymeric microbeads were prepared by suspension polymerization. A comonomer, i.e., HEMA, was included in the formula in order to provide functional hydroxyl groups on the microbead surfaces. Toluene was used in the polymerization formulations to introduce porosity into the matrix. Hydroxyl groups were first oxidized with NaIO4, and then two biological molecules, namely collagen and fibronectin were immobilized by using glutaraldehyde. A spacer-arm, i.e., hexamethylene diamine, was also used in some cases. More protein molecules were immobilized onto more swellable microbeads using spacer-arm. Higher amounts of collagen were immobilized, more than fibronectin immobilization. Growth of two cell lines, 3T3 and MDBK, on these microbeads with a wide variety of surface properties was studied in vitro culture media. Growths of both cells even onto the plain microbeads were significant. More cell proliferation occurred with the more swellable microbeads. More cells proliferated on the microbeads carrying fibronectin covalently attached onto the microbeads through spacer-arm molecules. Fibronectin was better than collagen for promoting high proliferation. The mathematical model proposed successfully simulated the growth kinetics.

Expression and Distribution of Laminin, Fibronectin and Tenascin is Stage Dependently Modulated in the Skin of Chronic Venous Insufficiency

Objective:

The regulation of tissue remodelling is a function of extracellular matrix (ECM) deposition. Our aim was to determine the expression and distribution pattern of the ECM proteins laminin, fibronectin and tenascin in all stages of chronic venous insufficiency (CVI) from telangiectases to ulceration.

Methods:

In punch biopsies of 25 patients with various stages of CVI and five healthy volunteers, ECM proteins were stained using indirect immunofluroescence. The staining pattern in the affected skin was evaluated by two independent, double-blinded investigators by microscopic examination.

Results:

In specimens of healthy skin or skin with telangiectases or pigmentation, a faint and partly inhomogeneous ECM staining pattern was detected in the upper dermis. In venous eczema, lipodermatosclerosis and venous leg ulcers, an increased expression and a wide-meshed distribution pattern throughout the dermis was observed for laminin, fibronectin and tenascin. Fragmentation of ECM components was first observed in venous eczema, persisting in the more severe stages of CVI. Laminin staining revealed unusual streak-like distributions in the papillary dermis, pronounced in Pigmentation and lipodermatosclerosis and diminished in leg ulcers.

Conclusions:

Our results indicate an important role of laminin, fibronectin and tenascin, and in particular of their proteolytic fragments, in the early phases of CVI, such as venous eczema, by creating permissive environments for cell migration and differentiation, essential for wound healing.

AGE-modified collagens I and III induce keratinocyte terminal differentiation through AGE receptor CD36: epidermal-dermal interaction in acquired perforating dermatosis

To clarify the molecular mechanism underlying the transepidermal extrusion of dermal collagen in acquired perforating dermatosis (APD) associated with diabetes mellitus and renal failure, we studied the interaction between advanced glycation end product (AGE)-modified extracellular matrix proteins and keratinocytes (KCs) in a cell culture system. The expression of involucrin (INV) and keratin 10 was significantly enhanced in normal human KCs grown on AGE-modified collagen I or III compared with cells grown on unmodified collagen I or III. Glycated collagens I and III preferentially induced the expression of AGE receptor CD36, but not of other AGE receptors. KCs induced to terminal differentiation demonstrated markedly elevated CD36 expression. Glycated collagen I- and III-induced INV expression was partially blocked by the anti-CD36 antibody (Ab). These substrates also induced epidermal matrix metalloproteinase 9 (MMP-9) expression. Lesional skin from APD patients reacted moderately or strongly with the anti-CD36 Ab as well as the anti-MMP-9 Ab in the epidermal cells surrounding the collagenous materials being eliminated. These results suggest that exposing KCs to AGE-modified interstitial collagen (types I and III) by scratching induces terminal differentiation of KCs via the AGE receptor (CD36), leading to the upward movement of KCs together with glycated collagen.

Isolation and propagation of keratinocytes derived from Cashmere goat fetus

The study was conducted to isolate epidermal keratinocytes from Cashmere goat fetus with the aim to develop suitable conditions for keratinocyte cultivation and propagation. The methods developed for keratinocyte culture include (i) use of a feeder-layer of mitotically inactivated fibroblasts obtained from goat and mouse fetal skin, (ii) use of a substrate such as collagen IV, or (iii) without use of any substrate. Epidermal cell removal was established by enzymatically separating keratinocytes from 12 to 16 weeks aged fetal skin tissues treated with 0.125% trypsin solution overnight at 4 degrees C. The cells were maintained in all culture conditions with serum containing medium. Keratinocyte multiplication and proliferation were comparable in different culture conditions and the improved cellular attachment and growth have been obtained in cultures on feeder layers. Colony forming keratinocytes on feeder layer were heterogeneous in their growth potential. In feeder free conditions, high cellular density was required at plating for sub-cultivation as their poor attachment in culture dishes. This study reports the comparative efficacy of different culture conditions for keratinocyte isolation and in vitro propagation originating from Cashmere goat fetus.

Transduction of beta3 integrin subunit cDNA confers on human keratinocytes the ability to adhere to gelatin

alphavbeta3 is a multiligand integrin receptor that interacts with fibrinogen (FG), fibrin (FB), fibronectin (FN), vitronectin (VN), and denatured collagen. We previously reported that cultured normal human keratinocytes, like in vivo keratinocytes, do not express alphavbeta3 on the cell surface, and do not adhere to and migrate on FG and FB. Furthermore, we reported that human keratinocytes transduced with beta3 integrin subunit cDNA by a retrovirus-mediated transduction method express alphavbeta3 on the cell surface and adhere to FG, FB, FN, and VN significantly compared with beta-galactosidase (beta-gal) cDNA-transduced keratinocytes (control). In this study, we determined whether these beta3 integrin subunit cDNA-transduced keratinocytes or normal human keratinocytes adhere to denatured collagen (gelatin) using a 1 h cell adhesion assay. beta3 cDNA-transduced keratinocytes adhered to gelatin, whereas no significant adhesion was observed with the control cells (beta-gal cDNA-transduced keratinocytes and normal human keratinocytes). The adhesion to gelatin was inhibited by LM609, a monoclonal antibody to alphavbeta3, and RGD peptides but not by normal mouse IgG1 nor RGE peptides. Thus, transduction of beta3 integrin subunit cDNA confers on human keratinocytes the ability to adhere to denatured collagen (gelatin) as well as to FG, FB, VN, and FN. Otherwise, normal human keratinocytes do not adhere to gelatin. These data support the idea that beta3 cDNA-transduced human keratinocytes can be a good material for cultured epithelium to achieve better take rate with acute or chronic wounds, in which FG, FB, and denatured collagen are abundantly present.

Minute changes in composition of polymer substrates produce amplified differences in cell adhesion and motility via optimal ligand conditioning

We explored the interplay between substratum chemistry of polymeric materials and surface-adsorbed ligand concentration (human plasma fibronectin) in the control of cell adhesion and cell motility. We found that small changes in the chemical composition of a polymeric substratum had different effects on cellular motility--depending on the concentration of preadsorbed fibronectin. We used two tyrosine-derived polyarylates, poly(DTD diglycolate) and poly(DTD glutarate), as substrata for the seeding of NIH-3T3 fibroblasts. The only compositional difference between the two test polymers was that one single oxygen atom in the polymer backbone of poly(DTD diglycolate) had been substituted by a methylene group in the backbone of poly(DTD glutarate), The two polymers had closely matched hydrophobicity and physical properties. Flat, spin-coated surfaces of these polymers were pretreated with different concentrations of human plasma fibronectin (0-20 microg/ml). After seeding with NIH-3T3 fibroblasts, we examined the adhesion and motility behavior of these cells. We found that NIH-3T3 fibroblasts migrated significantly faster on poly(DTD diglycolate), but only when the polymer surfaces were pretreated with intermediate concentrations of fibronectin. Only at these intermediate levels of ligand conditioning, did the presence of an extra oxygen atom in the backbone of poly(DTD diglycolate) relative to poly(DTD glutarate) (i) alter the overall organization/concentration of the fibronectin; (ii) weaken cell attachment strength and inhibited excessive cell spreading; and (iii) promote cell motility kinetics. These findings indicate that the biological effect of minute changes in substratum chemistry is critically dependent on the level of surface-adsorbed cell-binding ligands.

Type II Collagen Accumulation in Overlying Dermo-Epidermal Junction of Pilomatricoma Is Mediated by Bone Morphogenetic Protein 2 and 4

Pilomatricoma consists of the cells differentiating towards hair matrix cells. Immunohistochemical study revealed the deposition of type II collagen in the overlying dermo-epidermal junction (DEJ) of this benign tumor. Proalpha(1)(II) mRNA was detected by RT-PCR in the overlying epidermal layer but not in the dermal layer prepared from the lesional skin of pilomatricoma. The neutral salt-soluble proteins extracted from the tumor of pilomatricoma induced proalpha(1)(II) mRNA in the cultured human keratinocytes but not in the cultured dermal fibroblasts. Bone morphogenetic protein 2 or 4 (BMP2 or 4) was immunohistochemically detected in some shadow cells of pilomatricoma. Recombinant BMP2 and BMP4 were found to induce proalpha(1)(II) mRNA concentration dependently in the cultured human keratinocytes but not in the cultured fibroblasts. Proalpha(1)(II) mRNA induced by BMP2 and in cultured keratinocytes contained exon 2, indicating that the mRNA species is non-chondrogenic type IIA form. The results strongly suggest that BMP2 or 4 expressed in pilomatricoma is responsible for the induction of proalpha(1)(II) collagen mRNA in the overlying epidermal cells resulting in the deposition of type II collagen in the DEJ. When human keratinocytes were cultured on type II collagen substratum in vitro, the cell proliferation was accelerated at the early period of culture but was inhibited at the late period of culture, whereas the cell proliferation was persistently accelerated by type I or IV collagen substratum. Type II collagen deposition in the DEJ may potentially exert profound effects on keratinocyte proliferation and differentiation.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

PEG-variant biomaterials as selectively adhesive protein templates: model surfaces for controlled cell adhesion and migration

Our study focused on the role of poly(ethylene glycol) (PEG) in actively regulating the biological responsiveness of protein-adsorbed biomaterials. To this end, we designed PEG-variant biomaterials from a family of tyrosine/PEG-derived polycarbonates to present surfaces ranging from low to intermediate levels of PEG concentration, below the PEG level requisite for complete abolition of protein adsorption. We analyzed the effect of PEG concentration on the amount, conformation and bioactivity of an adsorbed model protein, fibronectin, and on the attachment, adhesion strength and motility of L929 fibroblasts. Our results demonstrate that low levels of PEG can regulate not only the extent but also the conformation and specific bioactivity of adsorbed fibronectin. As the PEG concentration was increased from 0 to 6 mol%, the amount of adsorbed fibronectin decreased linearly yet the fibronectin conformation was altered such that the overall bioactivity of adsorbed fibronectin was uncompromised. We report that the degree of cell attachment varied with PEG concentration in a manner similar to the dependence of fibronectin bioactivity on PEG. In contrast, the nature of cell adhesion strength dependence on PEG paralleled the pattern observed for fibronectin surface concentration. Our studies also indicated that the rate of cell migration was inversely correlated with PEG concentration over a narrow range of PEG concentration. Overall, these results highlight the striking ability of PEG-variant biomaterials to systematically regulate the behavior of adsorbed cell adhesion proteins and, consequently, effect cell functions.

Substrate-adsorbed collagen and cell secreted fibronectin concertedly induce cell migration on poly(lactide-glycolide) substrates

Limited epithelial cell migration on synthetic polymeric biomaterials, such as polyesters, presents a serious challenge to their use as scaffolds for artificial skin analogs. The mechanisms by which a physiologic matrix interface on such polymers may regulate and promote cell migration under 'activated conditions' were the focus of this study. We have quantified the migration behavior of epidermal growth factor (EGF) stimulated epidermal keratinocytes on 50:50 poly-D,L(lactide-glycolide) (PLGA) substrates, following exogenous and cell-derived substrate conditioning based on the model matrix proteins, collagen and fibronectin. We report that 'non-conditioned' PLGA substrates elicited poor levels of keratinocyte migration. However, keratinocyte migration was significantly enhanced upon the adsorption of type I collagen, and was only weakly enhanced with fibronectin adsorption. Molecular analysis of the mechanism of enhanced migration on collagen-PLGA substrates showed that keratinocyte migration was sensitive to cell-derived fibronectin conditioning, but not to cell-secreted collagen conditioning. Fibronectin control of cell migration on collagen-PLGA was found to be both stoichiometric and biologically specific, mediated via adhesion involving keratinocyte alpha v integrin receptors. Based on our results, we propose a unique paradigm for induction of cell migration on a non-physiologic synthetic polymer using concerted interactions between primary, polymer-instructed matrix remodeling and secondary, cell-derived matrix remodeling.

A potential cell affinity sorbent: fibronectin carrying poly(EGDMA/HEMA) microbeads

Both non-swellable and swellable poly(EGDMA/HEMA) microbeads were produced by suspension copolymerization. These microbeads were modified by immobilization of a spacer-arm (hexamethylene diamine, HMDA) and fibronectin. The optimal values for modifications were as follows: the sodium periodate concentration 1.0 mg ml(-1); the HMDA concentration 4 mg ml(-1); and the glutaraldehyde concentration 0.070 microg ml(-1). Adsorption of fibronectin onto the plain and periodate-oxidized poly(EGDMA/HEMA) microbeads were very similar, and were 0.025-0.035 mg fibronectin per g polymer, respectively. Fibronectin immobilization on poly(EGDMA/HEMA) microbeads were studied at different temperature, time and pH using single protein solution containing different amount of proteins. The optimal values for immobilizations were as follows: the initial fibronectin concentration 0.1 mg ml; temperature + 25 degrees C; pH 7; the immobilization time 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to these unmodified and modified microbeads. The attachments of both 3T3 and MDBK cells, especially to the fibronectin-immobilized swellable microbeads, were very high. Almost 96% of the 3T3 cells available in the cell culture medium did attach to these microbeads (2345 +/- 98 cells per mg of polymer).

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.

An investigation into the potential of extracellular matrix factors for attachment and proliferation of human keratinocytes on skin substitutes

The purpose of this investigation was to assess the potential of commercially available extracellular matrix proteins, as enhancers of human keratinocyte attachment and proliferation, with a view to their incorporation into a skin equivalent. The following substrates were studied: type I and type IV collagen, fibronectin, gelatin and laminin. Human keratinocytes were cultured in low-calcium, serum-free medium. The number of cells attached to each substrate, observed under phase-contrast inverted microscopy in randomly selected fields of view, were counted 2 h afterseeding. Measurements of growth rate and colony-forming efficiency were made at 24-h intervals. None of the substrates tested were found to have an effect significant enough to warrant further investigation or inclusion into skin equivalent.

Influence of extracellular matrix proteins on human keratinocyte attachment, proliferation and transfer to a dermal wound model

The aim of this study was to investigate whether prior culture of cells on ECM proteins might positively influence the performance of keratinocytes when cells are transferred to a dermal in vitro wound bed model. Keratinocytes were cultured using a method for producing cultured epithelial autografts for severely burned patients (essentially using Green's medium, a mitogen-rich medium containing fetal calf serum, cholera toxin, EGF, insulin, transferrin and triiodothyronine). Cells were cultured either on irradiated 3T3 fibroblasts (as in the standard Rheinwald and Green technique) or, alternatively, on collagen I, collagen IV, matrigel, RGD, vitronectin or fibronectin. Under these conditions matrigel, collagen I and IV enhanced initial attachment, RGD, vitronectin, fibronectin and irradiated 3T3 fibroblasts did not. Proliferation of cells was positively influenced by matrigel, collagen I and IV and irradiated 3T3 fibroblasts; of these, however, only matrigel and 3T3 fibroblasts had sustained significant effects on keratinocyte proliferation over 4 days. Cells on fibronectin showed significantly reduced proliferation. An acellular non-viable dermis was then used to mimic the homograft allodermis onto which cultured epithelial autograft sheets are grafted clinically and cells cultured on the various ECM proteins for 96 h were transferred to this in vitro wound model. None of the substrates enhanced keratinocyte performance on this model. It was concluded that under these conditions some ECM proteins can significantly affect keratinocyte attachment and, to a lesser extent, proliferation but that the culture of keratinocytes on these ECM proteins does not appear to confer any lasting benefit to the attachment of these keratinocytes to an in vitro wound-bed model.

Agarose gel keratinocyte outgrowth system as a model of skin re-epithelization: requirement of endogenous acetylcholine for outgrowth initiation

To better understand the mechanisms of skin re-epithelization, we developed a simple technique that assays the outgrowth of human keratinocytes. Second-passage foreskin keratinocytes were inoculated at high cell density into 3-mm wells cut from agarose gels in standard 6-well tissue culture dishes. The cells settled on the dish bottom and formed a confluent colony. The cells at the periphery of the colony flattened, spread their cytoplasm, and moved away over the dish surface under the agarose gel. The morphology of migrating keratinocytes was observed microscopically through the transparent agarose, and the migration distance was measured after the gels were removed and after cells were fixed and stained. To determine which cell activities were involved in the outgrowth, the effects of cholinergic compounds on keratinocyte outgrowth were compared with their effects on keratinocyte proliferation, cell-plastic attachment, and spreading measured in separate sets of experiments. Outgrowth was inhibited by the specific inhibitor of acetylcholine synthesis bromoacetylcholine (0.05 mM) and restored by 5 mM exogenous acetylcholine. The irreversible muscarinic antagonist propylbenzilylcholine mustard (0.05 mM) abolished the restorative effects of exogenous acetylcholine, and also inhibited outgrowth of intact keratinocytes. In keratinocyte cell cultures, bromoacetylcholine stopped cell division. Propylbenzilylcholine mustard increased cell number, but interfered with cell-plastic attachment and spreading. This suggests that cell-matrix attachment, spreading, and locomotion of human keratinocytes, but not mitosis, mediate the earliest stages of skin re-epithelization, and that endogenous acetylcholine regulates these keratinocyte functions. Specifically, keratinocyte acetylcholine is required to initiate outgrowth.

Study of blood compatible polymers. III. Copolymers of N-benzyl, N-(2-hydroxyethyl) acrylamide and 2-hydroxyethyl methacrylate

Copolymerization of 2-hydroxyethyl methacrylate (HEMA) and N-benzyl, N-(2-hydroxyethyl) acrylamide (BENAAm) was carried out at different mole ratios of the monomers to obtain copolymers of varying composition. BENAAm content of the copolymers varies between 13 and 70%. Investigation of the interaction of rabbit platelets with these polymer surfaces showed that copolymers with higher BENAAm content inhibit the platelet deformation. Human umbilical cord fibroblast cells proliferated very well on the copolymer surfaces. The cell growth rate on polyHEMA was relatively low. Maximum cell growth was observed on the copolymer having 87% HEMA.

Expression of fibronectin and integrins in cultured periodontal ligament epithelial cells

The process of attachment of epithelial cells obtained from the porcine periodontal ligament (cell rests of Malassez) to different extracellular matrix proteins and their expression of fibronectin and integrin receptors were studied by means of immunocytochemistry, in situ hybridization, and time-lapse cinemicrography techniques. The cell lines of periodontal ligament epithelial cells (PLE cells) attached to and spread rapidly on fibronectin, vitronectin, and type I collagen. One of the cell lines also attached to laminin, while the other cell line showed poor attachment to both laminin and Matrigel, a basement membrane material. By use of the in situ hybridization technique, some PLE cells were found to express the fibronectin gene strongly. Immunocytochemical staining localized fibronectin in extracellular fibrils and intracellular granules. Fibronectin was also found in the tracks left behind by the cells migrating on the substratum. Arg-gly-asp-ser peptide inhibited the attachment of the PLE cells to fibronectin, laminin, type I collagen, and vitronectin by 47%, 43%, 83%, and 94%, respectively, suggesting that the cell-matrix interactions were partly mediated by receptors related to the integrin family. Antibodies against the beta 1-integrin subunit stained the cell bodies and the plasma membrane projections of spreading cells. After 24 h or longer in culture, beta 1-integrins were localized to the regions of cell-cell contact. Cinemicrography of the arg-gly-asp-ser-peptide-treated cells demonstrated that the spreading and migration of isolated cells were prevented by the peptide. The peptide did not appear to dissociate the cell-cell contacts or interfere with migration of spread-cell colonies.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture techniques for human keratinocytes

The two main approaches developed for in vitro culture of human keratinocytes are reviewed and discussed. The older technique is based on the use of a serum-containing medium and of a feeder-layer of lethally irradiated mouse fibroblasts; the second relies upon serum-free media, in the absence of a feeder-layer. While the former technique is most widely used for the preparation of epithelial sheets for grafting, the latter is best suited for studies on the biological properties of keratinocytes.

Overexpression of extracellular matrix receptors (VLA-3, 5 and 6) on psoriatic keratinocytes

The potential role of adhesion molecules in the pathophysiology of psoriasis was investigated and the pattern of expression of the cell-surface receptors ICAM-1, LFA-3, and VLA-1, 2, 3, 4, 5 and 6 was determined in biopsies of skin from patients with psoriasis (n = 12) and from normal skin (n = 12). There were no differences in the intensity or localization of the adhesion molecules VLA-1, 2 and 4 and LFA-3. In contrast, VLA-3 and VLA-6, which are restricted to the basal keratinocytes in normal skin, were overexpressed in the spinous cells in psoriatic skin. ICAM-1 and VLA-5, which are not expressed by keratinocytes in normal skin, were focally induced, especially in cells above elongated rete ridges and where there was an infiltrate with intraepidermal granulocytes and lymphocytes.

Proliferation of normal human keratinocytes on silicone substrates

Several polydimethylsiloxane elastomers and gels were tested as culture substrates for proliferating normal human epidermal keratinocytes. Growth kinetics of normal human keratinocytes (NHK) and dermal fibroblasts were compared on 'very soft', 'soft' and 'hard' silicone gels, as well as on standard cell culture polystyrene dishes. Water contact angles and chemical compositions (IRFT-HATR) of the different silicone surfaces were found to be equivalent, although very different from standard cell culture polystyrene. The topography of the surfaces as well as the shape of the keratinocytes and fibroblasts grown on the different substrates were visualized by scanning electron microscopy, and compared. Although the surface softness and topography of the substrates differed markedly, dermal fibroblasts proliferated in serum-containing medium in equivalent manner on all substrates. Again no correlation could be found between the characteristics and the attachment of the substrates and rapid proliferation of the epidermal keratinocytes in defined medium. The epidermal keratinocytes spread, secreted a structured extracellular matrix network and grew up to confluence on all silicone substrates (elastomers and gels), except the relatively 'hard' silicone gel; this could be due to a direct interference by the waves observed on the silicone gel surfaces.

Cytokeratin patterns of human oral mucosae in histiotypic culture

In a three-dimensional culture model, oral epithelial differentiation was investigated ultrastructurally and biochemically for cytokeratin expression. Epithelia from the hard palate, gingiva and alveolar mucosa grown on freely floating collagen lattices populated with fibroblasts from homotypic origins, and fed with medium containing 10% delipidized fetal calf serum for 21 days before analysis, stratified and differentiated to basal cuboidal cells, polyhydral spinous cells and elongated superficial cells. The epithelium of palatal origin had non-nucleated superficial cells resembling orthokeratinized cells. The upper spinous cells had keratohyalin-like granules. The corresponding cells of gingival and alveolar mucosal origins retained their nuclei and had smaller numbers of keratohyalin-like granules. Basal cell keratins (CK 5 and 14) and those of hyperproliferation (CK 6 and 16) were consistently found in all epithelia. Furthermore, simple epithelial keratins (CK 18 and 19) were variably expressed by cells from different oral origins. In epithelial cells from the alveolar mucosa, CK 13 and 19 formed major bands, which correlates with their expression in vivo. In contrast, these polypeptides were either absent or formed minor bands in extracts of gingival and hard palatal cells. Although in small quantities, keratins of terminal differentiation (CK 1, 2, 10 and 11) were detected in gels prepared from palatal epithelia. This expression correlates with the higher morphological differentiation of these cells in this model. The model is of interest for studies of epithelial differentiation, as the differentiation markers of keratinized epithelia (CK 1 and 10) were expressed by cells from palatal origin, and those of non-keratinized epithelia (CK 4, 13 and 19) were prominent in cells from alveolar mucosal origin.

Human keratinocytes adhere to a unique heparin-binding peptide sequence within the triple helical region of type IV collagen

The present studies were aimed at further characterizing the interaction between basement membrane molecules and normal cultured human keratinocytes because of the intimate association between basal keratinocytes and the basement membrane. The studies show that keratinocytes adhere to type IV collagen-coated substrata to a greater degree than substrata coated with similar concentrations of fibronectin and laminin. To further define cell-binding regions within type IV collagen, studies were performed using purified pepsin-generated triple helical fragments of type IV collagen and show that keratinocytes bind to sites within the triple-helical region of type IV collagen. To delineate specific cell adhesion promoting sequences, we studied a series of chemically synthesized peptides derived from the triple-helical region of type IV collagen. One peptide, designated Hep III, which is thirteen amino acids in length and binds heparin, was active in directly promoting keratinocyte adhesion. Furthermore, in competition assays, this peptide in solution was shown to inhibit keratinocyte adhesion to substrata coated with Hep III or intact type IV collagen. These studies show that keratinocytes bind directly to type IV collagen and chemically define a major cell-adhesion-promoting site within the triple helical region.

Fibronectin-cell interactions

Fibronectins are widespread extracellular matrix and body fluid glycoproteins, capable of multiple interactions with cell surfaces and other matrix components. Their structure at a molecular level has been resolved, yet there are still many unanswered questions regarding their biologic activity in vivo. Much data suggests that fibronectins may promote extracellular matrix assembly, and cell adhesion to those matrices. However, one outstanding enigma is that fibronectins may, under different circumstances, promote both cell migration and anchorage. An analysis of the interaction of fibroblasts with proteolytically derived and purified domains of plasma fibronectin revealed that the type of adhesion and the correlated cytoskeletal organization depended on multiple interactions of fibronectin domains with the cell surface. Human dermal fibroblasts were capable of interacting with the integrin-binding domain and both heparin-binding domains of the plasma fibronectin molecule and their interactions determined the type of adhesion. The same principle was seen in a study of the ability of plasma fibronectin to promote basement membrane assembly in an endodermal cell line, PF-HR9. There also, interactions of both heparin- and integrin-binding domains combined to promote the deposition of a proteoglycan, laminin, and type IV collagen-containing basement membrane matrix. The underlying conclusion from our studies is, therefore, that fibronectins may, through their different isotypes, multiple receptors, and varying interaction of one or more domains with those receptors, result in a spectrum of responses in different cell types. The molecular details of this array of biologic activities is not resolved but is the target of much current research.

Cytotoxicity testing of wound dressings using normal human keratinocytes in culture

Comparative cytotoxicity testing of 16 wound dressings of different composition show that normal human keratinocytes (NHK) growing on a fibroblastic feeder layer are as sensitive to toxic materials by direct contact as the confluent MRC5 fibroblasts used for standard cell culture cytotoxicity testing, and slightly more sensitive when extracts of the dressings were tested. After direct contact with each of the cell types, we found effects due to 12 dressing samples (75%), but the extracts of only 6 of them induced changes in cell shape or cell death on NHK, and 4 of them on MRC5 cells. In order to assess the compatibility of these dressings with a pure population of epidermal cells, the cell type responsible for reepidermization of healing wounds, we then tested the sensitivity, both to dressing samples and extracts, of normal human keratinocytes (NHK) grown in chemically defined medium and without a feeder layer: The results show epidermal cytocompatibility of 10 dressing extracts, while 6 others induced cytopathic effects. Three of these extracts specifically damaged epidermal cells and inhibited their proliferation. When comparing the sensitivities of NHK (in defined medium) and MRC5 cells, we observed complete correlation for 75% of the dressings by extract testing and in 94% of the cases after direct contact.

Novel function for beta 1 integrins in keratinocyte cell-cell interactions

We have examined the expression, localization, and function of beta 1 integrins on cultured human epidermal keratinocytes using polyclonal and monoclonal antibodies against the beta 1, alpha 2, alpha 3, and alpha 5 integrin subunits. The beta 1 polypeptide, common to all class 1 integrins, was localized primarily in areas of cell-cell contacts of cultured keratinocytes, as were alpha 2 and alpha 3 polypeptides, suggesting a possible role in cell-cell adhesion for these integrin polypeptides. In contrast, the fibronectin receptor alpha 5 subunit showed no such accumulations in regions of cell-cell contact but was more diffusely distributed in the keratinocyte plasma membrane, consistent with the absence of fibronectin at cell-cell contact sites. Colonies of cultured keratinocytes could be dissociated by treatment with monoclonal antibody specific to the beta 1 polypeptide. Such dissociation of cell-cell contacts also occurred under conditions where the monoclonal antibody had no effect on cell-substrate adhesion. Therefore, beta 1 integrin-dependent cell-cell adhesion can be inhibited without affecting other cell-adhesive interactions. Antibody treatment of keratinocytes maintained in either low (0.15 mM) or high (1.2 mM) CaCl2 also resulted in the loss of organization of intracellular F-actin filaments and beta 1 integrins, even when the anti-beta 1 monoclonal antibody had no dissociating effect on keratinocyte colonies at the higher calcium concentration. Our results indicate that beta 1 integrins play roles in the maintenance of cell-cell contacts between keratinocytes and in the organization of intracellular microfilaments. They suggest that in epithelial cells integrins can function in cell-cell interactions as well as in cell-substrate adhesion.

Type IV collagen and fibronectin enhance human keratinocyte thymidine incorporation and spreading in the absence of soluble growth factors

In various cell culture systems, extracellular matrix components have been demonstrated to be mitogenic and, in some cases, to substitute for growth factors. In order to study the effects of various matrices on keratinocyte growth, we assessed the incorporation of tritiated thymidine and cell number on short-term cultures of human keratinocytes plated on different substrata. For determination of whether thymidine incorporation by keratinocytes was related to the ability of the cells to attach and spread on the substratum, experiments to determine the percentage of attached and spread cells on each matrix surface were performed. High levels of attachment and incorporation of thymidine with no preferential attachment to a given matrix were evident when the cells were cultured in the presence of growth factors. When growth factors were absent, keratinocytes likewise showed no preferential attachment to a given matrix component, but demonstrated enhanced thymidine incorporation when apposed to type IV collagen or fibronectin in comparison with tissue culture plastic or laminin. In the absence of epidermal growth factor (EGF) and bovine pituitary extract (BPE), increased spreading on type IV collagen and fibronectin was associated with enhanced incorporation of thymidine. In agreement with the thymidine incorporation results, when keratinocytes were cultured for 7 d, cell numbers were increased in cultures plated on type IV collagen only if growth factors were excluded from the medium. When attachment of cells to substrata with or without growth factors was compared, either EGF or BPE enhanced attachment to all of the substrata tested. It is concluded that under suboptimal growth conditions extracellular matrix components can modulate keratinocyte growth. Also, under these conditions, spreading, but not attachment, correlates with growth potential.

Reappearance of an embryonic pattern of fibronectin splicing during wound healing in the adult rat

The adhesive extracellular matrix glycoprotein fibronectin (FN) is thought to play an important role in the cell migration associated with wound healing. Immunolocalization studies show abundant FN in healing wounds; however, these studies cannot define the cellular site(s) of FN synthesis, nor do they distinguish the different and potentially functionally distinct forms of FN that can arise from alternative splicing of the primary gene transcript. To examine these questions of FN synthesis and splicing during wound healing, we have performed in situ hybridization with segment-specific probes on healing wounds in adult rat skin. We find that the FN gene is expressed at increased levels after wounding both in the cells at the base of the wound and in subjacent muscle and dermis lateral to the wound. Interestingly, however, the pattern of splicing of FN mRNA was different in these areas. In adjacent dermis and muscle, the splicing pattern remains identical with that seen in normal adult rat skin, with two of the three spliced segments (EIIIA and EIIIB) excluded from FN mRNA. In contrast, these two segments are included in the FN mRNA present in the cells at the base of the wound. As a result, the mRNA in this region is spliced in a pattern identical with that found during early embryogenesis. The finding that the pattern of FN splicing during wound healing resembles an embryonic pattern suggests that alternative splicing may be used during wound healing as a mechanism to generate forms of FN that may be functionally more appropriate for the cell migration and proliferation associated with tissue repair.

Wound healing for the dermatologic surgeon

An understanding of the basic science of cutaneous wound repair is essential to the dermatologic surgeon for the management of the postoperative wound. This review discusses the stages of wound healing and then applies these principles to the preoperative, intraoperative, and postoperative management of the surgical patient.

Inhibitory effect of gamma interferon on cultured human keratinocyte thrombospondin production, distribution, and biologic activities

Rapidly proliferating keratinocytes (KCs) maintained in low calcium, serum-free medium produce and utilize thrombospondin (TSP) as an attachment and spreading factor. To begin to understand the modulation of KC TSP metabolism, gamma interferon (IFN-gamma), a product of activated T lymphocytes, was added to KC cultures. IFN-gamma was chosen because activated T cells appear at sites of cutaneous injury. Two additional cytokines including tumor necrosis factor (TNF) and IFN-beta were also examined. IFN-gamma (600 U/ml), but not TNF (500 U/ml) or IFN-beta (10(3) U/ml), as single agents decreased KC TSP biosynthesis, secretion, and utilization as an attachment factor. IFN-gamma alone did not detectably decrease TSP mRNA levels suggesting a post-transcriptional effect in KCs. However, the combination of IFN-gamma (600 U/ml) and TNF (500 U/ml) inhibited TSP mRNA production. These results demonstrate the modulation of KC TSP metabolism and biologic activity.

Extracellular matrix modulates the function of human melanocytes but not melanoma cells

Normal human epidermal melanocytes are attached to a basement membrane, a specialized form of extracellular matrix (ECM), located between the epithelium and underlying dermal tissues. To determine whether ECM influences pigmented cell behavior in vitro, human epidermal melanocytes and melanoma cells were cultured on uncoated or ECM-coated plastic culture surfaces, and a comparison was made between growth and function in the presence or absence of ECM. Melanocytes cultured on ECM-coated surfaces developed flatter and larger cell bodies and produced more melanin than melanocytes cultured on uncoated surfaces. In the presence of phorbol-myristate-acetate and cholera toxin, the rate of melanocyte replication was increased by ECM. In the absence of these mitogens, ECM significantly enhanced the adhesiveness of nonproliferating melanocytes. ECM had little or no effect on these parameters (morphology, tyrosinase activity, replication) in a pigmented human malignant melanoma cell line. These findings indicate that normal human epidermal pigment cells have the ability to recognize and respond to matrix signals, whereas this capacity appears to be absent in melanoma cells.