Epidermis as a secretory tissue

Biogenesis of specialized lysosomes in differentiated keratinocytes relies on close apposition with the Golgi apparatus

Intracellular organelles support cellular physiology in diverse conditions. In the skin, epidermal keratinocytes undergo differentiation with gradual changes in cellular physiology, accompanying remodeling of lysosomes and the Golgi apparatus. However, it was not known whether changes in Golgi and lysosome morphology and their redistribution were linked. Here, we show that disassembled Golgi is distributed in close physical apposition to lysosomes in differentiated keratinocytes. This atypical localization requires the Golgi tethering protein GRASP65, which is associated with both the Golgi and lysosome membranes. Depletion of GRASP65 results in the loss of Golgi-lysosome apposition and the malformation of lysosomes, defined by their aberrant morphology, size, and function. Surprisingly, a trans-Golgi enzyme and secretory Golgi cargoes are extensively localized to the lysosome lumen and secreted to the cell surface, contributing to total protein secretion of differentiated keratinocytes but not in proliferative precursors, indicating that lysosomes acquire specialization during differentiation. We further demonstrate that the secretory function of the Golgi apparatus is critical to maintain keratinocyte lysosomes. Our study uncovers a novel form of Golgi-lysosome cross-talk and its role in maintaining specialized secretory lysosomes in differentiated keratinocytes.

Assessment of replication rates of human keratinocytes in engineered skin substitutes grafted to athymic mice

Stable closure of skin wounds with engineered skin substitutes (ESS) requires indefinite mitotic capacity to generate the epidermis. To evaluate whether keratinocytes in ESS exhibit the stem cell phenotype of label retention, ESS (n = 6-9/group) were pulsed with 5-bromo-2'-deoxyuridine (BrdU) in vitro, and after grafting to athymic mice (n = 3-6/group). Pulse and immediate chase in vitro labeled virtually all basal keratinocytes at day 8, with label uptake decreasing until day 22. Label retention in serial chase decreased more rapidly from day 8 to day 22, with a reorganization of BrdU-positive cells into clusters. Similarly, serial chase of labeled basal keratinocytes in vivo decreased sharply from day 20 to day 48 after grafting. Label uptake was assessed by immediate chases of basal keratinocytes, and decreased gradually to day 126, while total labeled cells remained relatively unchanged. These results demonstrate differential rates of label uptake and retention in basal keratinocytes of ESS in vitro and in vivo, and a proliferative phenotype with potential for long-term replication in the absence of hair follicles. Regulation of a proliferative phenotype in keratinocytes of ESS may improve the biological homology of tissue-engineered skin to natural skin, and contribute to more rapid and stable wound healing.

β2AR antagonists and β2AR gene deletion both promote skin wound repair processes

Skin wound healing is a complex process requiring the coordinated, temporal orchestration of numerous cell types and biological processes to regenerate damaged tissue. Previous work has demonstrated that a functional β-adrenergic receptor autocrine/paracrine network exists in skin, but the role of β2-adrenergic receptor (β2AR) in wound healing is unknown. A range of in vitro (single-cell migration, immunoblotting, ELISA, enzyme immunoassay), ex vivo (rat aortic ring assay), and in vivo (chick chorioallantoic membrane assay, zebrafish, murine wild-type, and β2AR knockout excisional skin wound models) models were used to demonstrate that blockade or loss of β2AR gene deletion promoted wound repair, a finding that is, to our knowledge, previously unreported. Compared with vehicle-only controls, β2AR antagonism increased angiogenesis, dermal fibroblast function, and re-epithelialization, but had no effect on wound inflammation in vivo. Skin wounds in β2AR knockout mice contracted and re-epithelialized faster in the first few days of wound repair in vivo. β2AR antagonism enhanced cell motility through distinct intracellular signalling mechanisms and increased vascular endothelial growth factor secretion from keratinocytes. β2AR antagonism promoted wound repair processes in the early stages of wound repair, revealing a possible new avenue for therapeutic intervention.

Constitutive release of cytokines by human oral keratinocytes in an organotypic culture

PURPOSE

The Food and Drug Administration requires an accurate determination of the dose and potency of tissue-engineered or combination products as is required for drugs. This needs to be done as a rapid, quantitative, and noninvasive measurement of biologic function/activity in a way so as not to perturb the tissue-engineered product being developed. The aim of this study was to correlate constitutive release of cytokine(s) from unstimulated cells, at different stages of development, within a 3-dimensional (3D) organotypic ex vivo produced oral mucosa equivalent (EVPOME) to be used for intraoral grafting, with oral keratinocyte cell viability of the EVPOME.

MATERIALS AND METHODS

Tissue culture medium was assayed with an enzyme-linked immunosorbent assay from monolayer culture of oral keratinocytes and a 3D EVPOME to determine the constitutive release of interleukin (IL) 1alpha, IL-6, IL-8, and vascular endothelial growth factor (VEGF). VEGF messenger ribonucleic acid expression by oral keratinocytes within the 3D EVPOME was detected by in situ hybridization at days 4, 7, and 11. The number of viable oral keratinocytes within the EVPOME was extrapolated from VEGF release by use of a modified MTT assay.

RESULTS

Both VEGF release level and the number of viable cells in the monolayer cultures and 3D EVPOME as measured by MTT assay significantly increased in a time-dependent manner (P < .001, r = 0.743).

CONCLUSION

These results suggest that the increasing detectable levels of VEGF associated with the increasing number of viable cells in the EVPOME may provide a useful noninvasive/nondestructive means of assessing both cellular viability (dose) and biologic function/activity (potency) of a combination cell-based device such as the EVPOME.

TGF-β1 gene polymorphism in psoriasis vulgaris

Overexpression of TGF-beta(1) has been implicated in the pathology of many inflammatory diseases, including psoriasis. This study was performed to investigate the association between TGF-beta(1) single nucleotide polymorphism and susceptibility for psoriasis vulgaris. DNA from 78 patients with psoriasis vulgaris and 74 healthy volunteers was investigated. Polymorphism of TGF-beta(1) gene in codon 10 (T/C) and codon 25 (G/C) was evaluated by PCR-SSP and the results were compared between group of psoriatic patients, divided into early onset of psoriasis (type I) and late onset of psoriasis (type II) subgroups, and control healthy subjects. Frequencies in genotypes were similar between patients and control group (p >0.7), but between type I and type II psoriasis patients highly significant difference was found (p <0.0003). Higher frequency of CC/GG (intermediate producer) and TC/GG (high producer) was noted in the type I group, but the second high producer genotype (TT/GG) was more common in type II group. Also between type II psoriasis patients and healthy controls statistically significant difference was found (p <0.000001). In analyzing frequencies of carriage and alleles no significant differences were found. TGF-beta(1) gene polymorphism in codon 10 and 25 is not associated with susceptibility to psoriasis vulgaris, but may be important for the type of the disease.

Corneal epithelial stem cell delivery using cell sheet engineering: not lost in transplantation

Cell-based therapies have now generated significant interest as novel drug delivery systems, with various adult cell types used in treating a wide range of diseases. To overcome the limits that restrict treatments for corneal surface dysfunction, corneal epithelial stem cells expanded ex vivo have been applied as an alternative approach. While previous studies used various carrier substrates, we present a novel method using cell sheet engineering with temperature-responsive culture dishes to create carrier-free corneal epithelial stem cell sheets that can be transplanted without sutures. Results from clinical trials reveal successful transplantation with the recovery of lost visual acuity in all cases. Cell sheet engineering, therefore, presents a novel method for the delivery of corneal epithelial stem cells, and can also be applied for other approaches of cellular therapeutics.

Epidermis promotes dermal fibrosis: role in the pathogenesis of hypertrophic scars

Hypertrophic scarring is a pathological process characterized by fibroblastic hyperproliferation and by excessive deposition of extracellular matrix components. It has been hypothesized that abnormalities in epidermal-dermal crosstalk explain this pathology. To test this hypothesis, a tissue-engineered model of self-assembled reconstructed skin was used in this study to mimic interactions between dermal and epidermal cells in normal or pathological skin. These skin equivalents were constructed using three dermal cell types: normal wound (Wmyo) or hypertrophic wound (Hmyo) myofibroblasts and normal skin fibroblasts (Fb). Epidermis was reconstructed with normal skin keratinocytes (NK) or hypertrophic scar keratinocytes (HK). In the absence of keratinocytes, Hmyo formed a thicker dermis than Wmyo. When seeded with NK, the dermal thickness of Hmyo (121.2 +/- 31.4 microm vs 196.2 +/- 27.8 microm) and Fb (43.7 +/- 7.1 microm vs 83.6 +/- 16.3 microm) dermis was significantly (p < 0.05) reduced, while that of Wmyo (201.5 +/- 15.7 microm vs 160.7 +/- 21.1 microm) was increased. However, the presence of HK always induced significantly thicker dermis formation than observed with NK (Wmyo: 238.8 +/- 25.9 microm; Hmyo: 145.5 +/- 22.4 microm; Fb: 74.2 +/- 11.2 microm). These results correlated with collagen and MMP-1 secretion and with cell proliferation, which were increased when keratinocytes were added, except for the collagen secretion of Hmyo and Fb in the presence of NK. The level of dermal apoptosis was not different when epidermis was added to the dermis (<1% in each category). These observations strongly suggest that hypertrophic scar keratinocytes play a role in the development of pathological fibrosis by influencing the behaviour of dermal cells.

Possible role of Malassezia furfur in psoriasis: modulation of TGF-beta1, integrin, and HSP70 expression in human keratinocytes and in the skin of psoriasis-affected patients

BACKGROUND

Psoriasis is a disease characterized by an abnormal pattern of keratinocyte growth and differentiation. Malassezia furfur forms part of the normal human skin flora. It may also be involved in the pathogenesis of psoriasis. To define the role of M. furfur in the pathogenesis of psoriasis, we investigated how M. furfur regulates molecules involved in cell migration and proliferation. The experiments were performed using human keratinocytes and skin biopsies from M. furfur-positive and -negative psoriasis-affected patients. In addition, we examined the signal transduction mechanisms involved.

MATERIALS AND METHODS

Western blot analysis was performed on human keratinocytes lysates treated or untreated with M. furfur and on biopsies from healthy and psoriasis patients. Signal transduction mechanisms involved were evaluated by electrophoretic mobility shift assay using the AP-1 inhibitor curcumin.

RESULTS

We found that M. furfur up-regulates transforming growth factor-beta1 (TGF-beta1), integrin chain, and HSP70 expression in human keratinocytes via AP-1-dependent mechanism. In the biopsies of M. furfur-positive psoriasis-affected patients, an increase in TGF-beta1, integrin chains, and HSP70 expression was found.

CONCLUSION

Our data suggest that M. furfur can induce the overproduction of molecules involved in cell migration and hyperproliferation, thereby favoring the exacerbation of psoriasis.

Isolation and clonal analysis of human epidermal keratinocyte stem cells in long-term culture

We developed a procedure for growing normal epidermal keratinocyte stem cells isolated from a single punch biopsy of adult human skin in long-term culture. Primary skin epithelial cells were maintained in collagen-coated plates with irradiated human neonatal foreskin fibroblasts (line HPI.1) as a feeder for more than 120 days, approximately 115 population doublings, without signs of replicative senescence. Clonal analysis revealed the presence of holoclones, meroclones, and paraclones. Only emerging colonies with high proliferative potentials and extensive capacities for division (holoclones and meroclones) were subcultured, favoring the expansion of stem cells and progenitors capable of prolonged self-maintenance when subcloned, thus accounting for the prevailing long-term proliferation of the original culture. We found that meroclones included bipotent progenitors capable of generating both keratinocytes and mucin-producing cells. The numbers of these cells were greater after confluence, suggesting that commitment for their differentiation occurred late in the life of a single clone. On a three-dimensional gelatin matrix and on a collagen layer containing the fibroblast feeder, cells isolated from the expansion of holoclones and meroclones formed stratified cohesive layers of keratinocytes that were able to further differentiate, as in normal skin. These results indicate that our procedure will serve as a valuable tool to study expansion of epidermal stem cells as well as the growth mechanisms and cell products associated with their growth and differentiation.

Keratinocytes Promote Proliferation and Inhibit Apoptosis of the Underlying Fibroblasts: An Important Role in the Pathogenesis of Keloid

Interactions between epidermal keratinocytes and dermal fibroblasts play an important role in regulating tissue homeostasis and repair. Nevertheless, little is known about the role of keratinocytes in the pathogenesis of keloid. In this study, we investigated the influence of normal skin- and keloid-derived keratinocytes on normal skin- and keloid-derived fibroblasts utilizing a serum-free indirect coculture system. The keloid-derived fibroblasts showed a greater proliferation and minimal apoptosis when cocultured with normal skin- or keloid-derived keratinocytes, and the results were most significant in the latter. This difference was not observed when the fibroblasts were treated with conditioned medium obtained from normal skin- and keloid-derived keratinocytes. Nevertheless, conditioned medium-treated groups showed more proliferation and less apoptosis compared to the nonconditioned medium-treated control groups. We also analyzed the profile of factors involved in cell growth and apoptosis in fibroblasts cocultured with keratinocytes. Extracellular signal-regulated kinase and c-Jun N-terminal kinase phosphorylations and expression of Bcl-2 and transforming growth factor-beta1 were all significantly upregulated in the fibroblasts cocultured with keloid-derived keratinocytes. Together, these results strongly suggest that the overlying keratinocytes of the keloid lesion play an important role in keloidogenesis by promoting more proliferation and less apoptosis in the underlying fibroblasts through paracrine and double paracrine effects.

Synchronous activation of ERK and phosphatidylinositol 3-kinase pathways is required for collagen and extracellular matrix production in keloids

Keloid fibroproliferation appears to be influenced by epithelial-mesenchymal interactions between keloid keratinocytes (KKs) and keloid fibroblasts (KFs). Keloid and normal fibroblasts exhibit accelerated proliferation and collagen I and III production in co-culture with KKs compared with single cell culture or co-culture with normal keratinocytes. ERK and phosphatidylinositol 3-kinase (PI3K) pathway activation has been observed in excessively proliferating KFs in co-culture with KKs. We hypothesized that ERK and PI3K pathways might be involved in collagen and extracellular matrix production in KFs. To test our hypothesis, four samples of KFs were co-cultured in defined serum-free medium with KKs for 2-5 days. KF cell lysate was subjected to Western blot analysis. Compared with KF single cell culture, phospho-ERK1/2 and downstream phospho-Elk-1 showed up-regulation in the co-culture groups, as did phospho-PI3K and phospho-Akt-1, indicating ERK and PI3K pathway activation. Western blotting of the conditioned medium demonstrated increased collagen I-III, laminin beta2, and fibronectin levels. Addition of the MEK1/2-specific inhibitor U0126 or the PI3K-specific inhibitor LY294002 (but not p38 kinase and JNK inhibitors) completely nullified collagen I-III production and significantly decreased laminin beta2 and fibronectin secretion. In the presence of the MEK1/2 or PI3K inhibitor, fibronectin demonstrated changes in molecular mass reflected by faster in-gel migration. These data strongly suggest that synchronous activation of both the ERK and PI3K pathways is essential for collagen I-III and laminin beta2 production. These pathways additionally appear to affect the side chain attachments of fibronectin. Modulation of these pathways may suggest a direction for keloid therapy.

Role of IGF system of mitogens in the induction of fibroblast proliferation by keloid-derived keratinocytes in vitro

Keloids are proliferative dermal growths representing a pathological wound-healing response. We report high proliferation rates in normal (NF) and keloid-derived fibroblasts (KF) cocultured with keloid-derived keratinocytes (KK). IGF binding protein (IGFBP)-3 mRNA and secreted IGFBP-3 in conditioned media were increased in NF cocultured with KK compared with NF but markedly reduced in KF cocultured with KK or normal keratinocytes (NK). IGFBP-2 and IGFBP-4 mRNA levels were elevated, whereas IGFBP-5 mRNA was decreased in KF cocultured with KK or NK. Significant increases in IGFBP-2 and -4 mRNA in KF cocultured with KK did not correlate with protein secretion. Downstream IGF signaling cascade components, phospho-Raf, phospho-MEK1/2, phospho-MAPK, PI-3 kinase, phospho-Akt, and phospho-Elk-1, were elevated in KF cocultured with KK. Addition of recombinant human IGFBP-3 or antibodies against IGF-I or IGF-IR significantly inhibited proliferation of KF. The bioavailability of IGF-I may be related to the levels of IGFBP-3 produced, which in turn influences KF proliferation, suggesting that modulation of IGF-I, IGF-IR, and IGFBP-3, individually or in combination, may represent novel approaches to the treatment of keloids.

Fibroblasts cocultured with keloid keratinocytes: normal fibroblasts secrete collagen in a keloidlike manner

Keloid scars represent a pathological response to cutaneous injury, reflecting a new set point between synthesis and degradation biased toward extracellular matrix (ECM) collagen accumulation. Using a serum-free two-chamber coculture model, we recently demonstrated a significant increase in normal fibroblast proliferation when cocultured with keloid-derived keratinocytes. We hypothesized that similar keratinocyte-fibroblast interactions might influence fibroblast collagen production and examined conditioned media and cell lysate from coculture for collagen I and III production by Western blot, allied with Northern analysis for procollagen I and III mRNA. Normal fibroblasts cocultured with keloid keratinocytes produced increased soluble collagen I and III with a corresponding increase in procollagen I and III mRNA transcript levels. This was associated with decreased insoluble collagen from cell lysate. When keloid fibroblasts were cocultured with keloid keratinocytes, both soluble and insoluble collagen were increased with associated procollagen III mRNA upregulation. Transmission electron microscopy of normal fibroblasts cocultured with keloid keratinocytes showed an ECM appearance similar to in vivo keloid tissue, an appearance not seen when normal fibroblasts were cocultured with normal keratinocytes.

Principles and practices for treatment of cutaneous wounds with cultured skin substitutes

BACKGROUND

Skin substitutes prepared from cultured skin cells and biopolymers may reduce requirements for donor skin autograft, and have been shown to be effective in treatment of excised burns, burn scars, and congenital skin lesions.

DATA SOURCES

Cultured skin substitutes (CSS) generate skin phenotypes (epidermal barrier, basement membrane) in the laboratory, and restore tissue function and systemic homeostasis. Healed skin is smooth, soft and strong, but develops irregular degrees of pigmentation. Quantitative analysis demonstrates that CSS closes 67 times the area of the donor skin, compared to less than 4 times for split-thickness skin autograft.

CONCLUSIONS

CSS reduce requirements for donor skin autograft for closure of excised, full-thickness cutaneous wounds, and demonstrate qualitative outcome that is not different from meshed, split-thickness autograft. These results offer reductions in morbidity and mortality for the treatment of burns and chronic wounds, and for cutaneous reconstruction.

Investigation of the influence of keloid-derived keratinocytes on fibroblast growth and proliferation in vitro

Keloids are disfiguring, proliferative scars that represent a pathological response to cutaneous injury. The overabundant extracellular matrix formation, largely from collagen deposition, is characteristic of these lesions and has led to investigations into the role of the fibroblast in its pathogenesis. Curiously, the role of the epidermis in extracellular matrix collagen deposition of normal skin has been established, but a similar hypothesis in keloids has not been investigated. The aim of this study was to investigate the influence of keloid epithelial keratinocytes on the growth and proliferation of normal fibroblasts in an in vitro serum-free co-culture system. A permeable membrane separated two chambers; the upper chamber contained a fully differentiated stratified epithelium derived from the skin of excised earlobe keloid specimens, whereas the lower chamber contained a monolayer of normal or keloid fibroblasts. Both cell types were nourished by serum-free medium from the lower chamber. Epithelial keratinocytes from five separate earlobe keloid specimens were investigated. Four sets of quadruplicates were performed for each specimen co-cultured with normal fibroblasts or keloid-derived fibroblasts. Controls consisted of (1) normal keratinocytes co-cultured with normal fibroblasts, and (2) fibroblasts grown in serum-free media in the absence of keratinocytes in the upper chamber. Fibroblasts were indirectly quantified by 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay, with results confirmed by DNA content measurement, at days 1 and 5 after the co- culture initiation.Significantly, increased proliferation was seen in fibroblasts co-cultured with keloid keratinocytes, as compared with the normal keratinocyte controls at day 5 (analysis of variance, p < 0.001). These results strongly suggest that the overlying epidermal keratinocytes of the keloid may have an important, previously unappreciated role in keloid pathogenesis using paracrine or epithelial-mesenchymal signaling.

Can we produce a human corneal equivalent by tissue engineering?

Tissue engineering is progressing rapidly. Bioengineered substitutes are already available for experimental applications and some clinical purposes such as skin replacement. This review focuses on the development of reconstructed human cornea in vitro by tissue engineering. Key elements to consider in the corneal reconstruction, such as the source for epithelial cells and keratocytes, are discussed and the various steps of production are presented. Since one application of this human model is to obtain a better understanding of corneal wound healing, the mechanisms of this phenomenon as well as the function played both by membrane-bound integrins and components from the extracellular matrix have also been addressed. The analysis of integrins by immunohistofluorescence labelling of our reconstructed human cornea revealed that beta(1), alpha(3), alpha(5), and alpha(6) integrin subunits were expressed but alpha(4) was not. Laminin, type VII collagen and fibronectin were also detected. Finally, the future challenges of corneal reconstruction by tissue engineering are discussed and the tremendous applications of such tissue produced in vitro for experimental as well as clinical purposes are considered.

Effects of microgravity on growing cultured skin constructs

Understanding the cellular, chemical, and physical responses of cells to stimuli is critical to successfully engineering tissue. The effect of culturing a living skin equivalent (LSE) in a submerged microgravity environment was investigated. LSEs were developed by culturing normal human epidermal keratinocyte (NHEK) on a submerged fibroblast and type 1 collagen gel matrix. Once formed, LSEs were brought up to the air/liquid interface, and after 4 days, the cultures were maintained in either (a) a normal air/liquid interface (S), (b) resubmerged in media (R), (c) folded on themselves to enclose the keratinized layer (F/R), or (d) cut into 2-4-mm fragments and suspended in a state of microgravity in a NASA-designed bioreactor (B). All groups were cultured for an average of 3 additional days. LSEs were processed for histologic evaluation. Skin cells were stained for cytokeratin to evaluate function. Images were digitally captured and processed for analysis. Parameters, including epithelial thickness, cellular areas, nuclear number, nuclear area, cytoplasmic area, and stained cytokeratin areas were measured. Removing the air/media interface significantly increased the number of NHEKs present in the skin; microgravity greatly enhanced this effect (p < 0.0001). No significant difference in cellular function as measured by protein expression [stained cytokeratin area (micro(2)) per cell] was found among the groups, though the ratio of nuclear area was significantly increased in all three groups as compared to the S group (p = 0.00227). In the case of the R and F/R groups, this appears due to the loss of the NHEK layer associated with those groups. Additionally, significant nuclear hypertrophy was demonstrated in the B group (p < 0.0001), and cellular hyperplasia was measured in all submerged groups as compared to static (p < 0.0001). Elimination of the air/liquid interface enhanced proliferation of keratinocytes. This effect was further enhanced in the presence of microgravity. No significant effect on cell function was noted with the use of this microgravity environment. We hypothesize that the increased epidermal contact plays a role in this proliferation. Microgravity is also associated with nuclear and cellular hypertrophy over and above that of the submersion methods.

Gene therapy and dermatology: more than just skin deep

BACKGROUND

Recent advances in the molecular characterization of dermatologic disease have substantively augmented the understanding of the pathogenetic processes underlying disorders of the skin. This new knowledge coupled with progress in gene delivery technologies has paved the way for introducing cutaneous gene therapy into the dermatologic therapeutic armamentorium.

OBJECTIVE

This review article includes an overview of the current strategies for delivery of gene therapy with an emphasis on the potential role of cutaneous gene delivery in the treatment of skin and systemic diseases.

CONCLUSIONS

Accessibility for gene delivery, clinical evaluation, and topical modulation of gene expression render the skin a very attractive tissue for therapeutic gene delivery. However, there are several key hurdles to be overcome before cutaneous gene therapy becomes a viable clinical option. These include difficulties in inducing sustained expression of the desired gene in vivo, the challenge of targeting genes to long-lived stem cells, and the difficulty in achieving specific and uniform transfer to different compartments of the skin. However, these problems are not insurmountable and will likely be resolved in conjunction with ongoing advances in delineating gene expression profiles and other molecular properties of the skin, strategies for stem cell isolation, and improved approaches to regulating gene delivery and expression. These advances should create the framework for translating the enormous potential of cutaneous gene therapy into the clinical arena and, thereby, substantively improving the management of both cutaneous and systemic disease.

Skin substitutes from cultured cells and collagen-GAG polymers

Engineering skin substitutes provides a potential source of advanced therapies for the treatment of acute and chronic wounds. Cultured skin substitutes (CSS) consisting of human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates have been designed and tested in preclinical and clinical studies. Cell culture techniques follow general principles of primary culture and cryopreservation in liquid nitrogen for long-term storage. Biopolymer substrates are fabricated from xenogeneic (bovine) collagen and glycosaminoglycan that are lyophilised for storage until use. At maturity in air-exposed culture, CSS develop an epidermal barrier that is not statistically different from native human skin, as measured by surface electrical capacitance. Preclinical studies in athymic mice show rapid healing, expression of cytokines and regulation of pigmentation. Clinical studies in burn patients demonstrate a qualitative outcome with autologous skin that is not different from 1:4 meshed, split-thickness autograft skin, and with a quantitative advantage over autograft skin in the ratio of healed skin to biopsy areas. Chronic wounds resulting from diabetes or venous stasis have been closed successfully with allogeneic CSS prepared from cryopreserved skin cells. These results define the therapeutic benefits of cultured skin substitutes prepared with skin cells from the patient or from cadaver donors. Future directions include genetic modification of transplanted cells to improve wound healing transiently or to deliver gene products systemically.

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.

Therapeutic gene delivery to the skin

The skin represents a site for treatment of cutaneous and systemic disease and is the most accessible somatic tissue for therapeutic gene transfer in humans. Monogenic hereditary skin diseases, such as ichthyosis and epidermolysis bullosa subtypes, and disorders characterized by low levels of polypeptides in the systemic circulation, are current central foci of efforts in cutaneous-gene transfer. Additional efforts center on the treatment of wounds and malignancies. Recent developments in models of gene delivery to the skin underscore key challenges that must be met before successful treatment of human disease by cutaneous gene delivery can be achieved.

Regulation of parathyroid hormone-related protein secretion and mRNA expression in normal human keratinocytes and a squamous carcinoma cell line

Parathyroid hormone-related protein (PTHrP) has been identified as a causative factor in the pathogenesis of humoral hypercalcemia of malignancy (HHM). The regulation and mechanisms of PTHrP secretion in most normal and malignant cells are unknown. PTHrP secretion, mRNA expression, and transcription were measured in neoplastic human squamous carcinoma cells (A253) and normal human foreskin keratinocytes (NHFK) by radioimmunoassay, RNase protection assay, and transient transfections of the 5'-flanking region of human PTHrP in a luciferase expression vector. Mechanisms of PTHrP secretion were investigated using chemicals (monensin, colchicine, cytochalasin B, guanosine 5'-[gamma-thio]triphosphate (GTPgammaS)) that interfere with or facilitate intracellular transport. Monensin inhibited PTHrP secretion in both NHFK and A253 cells. Ultrastructurally, monensin caused dilatation of rough endoplasmic reticulum and the formation of numerous cytoplasmic secretory vacuoles in both cell lines. Colchicine decreased PTHrP production in NHFK cells and stimulated PTHrP production and mRNA levels in A253 cells. Colchicine also stimulated transcription of the PTHrP-luciferase reporter gene. Cytochalasin B stimulated PTHrP secretion and mRNA expression in A253 cells, but had no effect in NHFK cells. GTPgammaS had no effect on PTHrP secretion in either cell line. It was concluded that PTHrP secretion is dependent on the constitutive movement of secretory vesicles to the cytoplasmic membrane and regulation of PTHrP secretion and mRNA expression are altered in squamous carcinoma cells compared to normal human keratinocytes in vitro.

Clonal analysis of stably transduced human epidermal stem cells in culture

We have transduced normal human keratinocytes with retroviral constructs expressing a bacterial beta-galactosidase (beta-gal) gene or a human interleukin-6 (hIL-6) cDNA under control of a long terminal repeat. Efficiency of gene transfer averaged approximately 50% and 95% of clonogenic keratinocytes for beta-gal and hIL-6, respectively. Both genes were stably integrated and expressed for more than 150 generations. Clonal analysis showed that both holoclones and their transient amplifying progeny expressed the transgene permanently. Southern blot analysis on isolated clones showed that many keratinocyte stem cells integrated multiple proviral copies in their genome and that the synthesis of the exogenous gene product in vitro was proportional to the number of proviral integrations. When cohesive epidermal sheets prepared from stem cells transduced with hIL-6 were grafted on athymic animals, the serum levels of hIL-6 were strictly proportional to the rate of secretion in vitro and therefore to the number of proviral integrations. The possibility of specifying the level of transgene expression and its permanence in a homogeneous clone of stem cell origin opens new perspectives in the long-term treatment of genetic disorders.

Expression of interleukin-1alpha, interleukin-6, and basic fibroblast growth factor by cultured skin substitutes before and after grafting to full-thickness wounds in athymic mice

OBJECTIVES

Cultured skin substitutes (CSSs), consisting of human keratinocytes and human fibroblasts attached to collagen-glycosaminoglycan substrates, have been demonstrated to cover wounds, and may release detectable quantities of growth factors that promote wound healing.

MATERIALS AND METHODS

Basic fibroblast growth factor (bFGF), interleukin-1alpha (IL-1alpha), and interleukin-6 (IL-6) were assayed by enzyme linked immunosorbent assay and immunohistochemistry in CSSs in vitro and at days 1, 3, 7, 14, and 21 after grafting to full-thickness wounds in athymic mice.

MEASUREMENTS AND MAIN RESULTS

When isolated cells were tested, IL-1alpha was found to come primarily from the keratinocytes, whereas bFGF was from the fibroblasts. Combinations of both cell types in the CSSs resulted in a synergistic enhancement of IL-6 expression. Quantities of all three cytokines from CSSs were greater in vitro compared with in vivo levels at all time points after grafting. bFGF increased from day 1 to day 7, and then remained relatively constant until day 21. At day 3 maximal levels of IL-1alpha were observed. By day 7, IL-1alpha decreased to approximately 40% of maximal levels, and subsequently increased until day 21. IL-6 levels were highest at day 7 after grafting. All cytokines had reached elevated levels during the time of wound revascularization (days 3-7).

CONCLUSIONS

The sequence of cytokine synthesis in the wounds (i.e., rapid IL-1alpha increase followed by IL-6 expression) parallels serum levels reported after a septic challenge. These findings support the hypothesis that the wound is a source of systemic cytokines.

Stimulation of human keratinocyte proliferation through growth factor exchanges with dermal fibroblasts in vitro

Progress in biotechnology has led to new therapeutic approaches in various fields of human health care, such as the autologous grafting of cultured epidermal cell sheets on burned patients. These cultures depend on various parameters but growth factors are of paramount importance. Cutaneous cells are known to secrete various growth factors in vivo, although only a few have been identified. The aim of this study was to determine if such factors are secreted from human cutaneous cells in culture, to evaluate their effects on epidermal cell proliferation in vitro and to analyse them on SDS-PAGE. Human skin fibroblasts and keratinocytes were co-cultured for 8-10 days using a Costar trans-filter system. Dermo-epidermal cooperation was observed in such a co-culture system through the exchange of secretion products in the culture medium. Epidermal cell growth and metabolic activities were highly stimulated in co-culture (2-fold and 1.5-fold, respectively, P < 0.02) compared to the control. The de novo synthesis of secretion products, notably of a protein of about 40 kDa, was specifically induced in co-culture. The identification of new keratinocyte growth factors could accelerate graftable epidermal sheet production in vitro for human wound coverage and possibly enhance wound healing in vivo.

Comparative assessment of cultured skin substitutes and native skin autograft for treatment of full-thickness burns

OBJECTIVE

Comparison of cultured skin substitutes (CSSs) and split-thickness autograft (STAG) was performed to assess whether the requirement for autologous skin grafts may be reduced in the treatment of massive burns.

SUMMARY BACKGROUND DATA

Cultured skin substitutes consisting of collagen-glycosaminoglycan substrates populated with autologous fibroblasts and keratinocytes have been demonstrated to close full-thickness skin wounds in athymic mice and to express normal skin antigens after closure of excised wounds in burn patients.

METHODS

Data were collected from 17 patients between days 2 and 14 to determine incidence of exudate, incidence of regrafting, coloration, keratinization, and percentage of site covered by graft (n = 17). Outcome was evaluated on an ordinal scale (0 = worst; 10 = best) beginning at day 14, with primary analyses at 28 days (n = 10) and 1 year (n = 4) for erythema, pigmentation, epithelial blistering, surface roughness, skin suppleness, and raised scar.

RESULTS

Sites treated with CSSs had increased incidence of exudate (p = 0.06) and decreased percentage of engraftment (p < 0.05) compared with STAG. Outcome parameters during the first year showed no differences in erythema, blistering, or suppleness. Pigmentation was greater, scar was less raised, but regrafting was more frequent in CSS sites than STAG. No differences in qualitative outcomes were found after 1 year, and antibodies to bovine collagen were not detected in patient sera.

CONCLUSIONS

These results suggest that outcome of engrafted CSSs is not different from STAG and that increased incidence of regrafting is related to decreased percentage of initial engraftment. Increased rates of engraftment of CSSs may lead to improved outcome for closure of burn wounds, allow greater availability of materials for grafting, and reduce requirements for donor skin autograft.

Transforming growth factor-beta 1 modulates beta 1 and beta 5 integrin receptors and induces the de novo expression of the alpha v beta 6 heterodimer in normal human keratinocytes: implications for wound healing

The molecular mechanism underlying the promotion of wound healing by TGF-beta 1 is incompletely understood. We report that TGF-beta 1 regulates the regenerative/migratory phenotype of normal human keratinocytes by modulating their integrin receptor repertoire. In growing keratinocyte colonies but not in fully stratified cultured epidermis, TGF-beta 1: (a) strongly upregulates the expression of the fibronectin receptor alpha 5 beta 1, the vitronectin receptor alpha v beta 5, and the collagen receptor alpha 2 beta 1 by differentially modulating the synthesis of their alpha and beta subunits; (b) downregulates the multifunctional alpha 3 beta 1 heterodimer; (c) induces the de novo expression and surface exposure of the alpha v beta 6 fibronectin receptor; (d) stimulates keratinocyte migration toward fibronectin and vitronectin; (e) induces a marked perturbation of the general mechanism of polarized domain sorting of both beta 1 and beta 4 dimers; and (f) causes a pericellular redistribution of alpha v beta 5. These data suggest that alpha 5 beta 1, alpha v beta 6, and alpha v beta 5, not routinely used by keratinocytes resting on an intact basement membrane, act as "emergency" receptors, and uncover at least one of the molecular mechanisms responsible for the peculiar integrin expression in healing human wounds. Indeed, TGF-beta 1 reproduces the integrin expression pattern of keratinocytes located at the injury site, particularly of cells in the migrating epithelial tongue at the leading edge of the wound. Since these keratinocytes are inhibited in their proliferative capacity, these data might account for the apparent paradox of a TGF-beta 1-dependent stimulation of epidermal wound healing associated with a growth inhibitory effect on epithelial cells.

Levels of skin-derived antileukoproteinase (SKALP)/elafin in serum correlate with disease activity during treatment of severe psoriasis with cyclosporin A

The epidermal serine proteinase inhibitor SKALP (also known as elafin), directed against human leukocyte elastase and proteinase 3, is strongly induced in suprabasal keratinocytes during inflammation. The presence of SKALP/elafin in urine has been demonstrated for several inflammatory skin disorders, such as psoriasis, erythroderma, and erysipelas. In this study we investigated whether SKALP/elafin levels in serum and urine of psoriatic patients can be used as a marker for disease activity during treatment. Patients with severe chronic disabling psoriasis were treated for 16 weeks with cyclosporin A, which resulted in a marked clinical improvement as measured with the PASI score. SKALP/elafin levels both in serum and urine were determined with an enzyme-linked immunosorbent assay (ELISA). Measurements were performed at the start of the cyclosporin A treatment, and after regular intervals up to 16 weeks. The results indicate that 1) SKALP/elafin determination in serum rather than in urine is the preferred method, because the decrease in serum SKALP levels during therapy is more pronounced and correlated better with the clinical course of the patients; 2) SKALP/elafin levels in serum decreased during cyclosporin A treatment (p < 0.05); and 3) SKALP/elafin levels in serum correlate with the PASI score (p < 0.01). We conclude that SKALP/elafin measurement in serum of patients with severe psoriasis provides a tool for monitoring disease activity.

Epidermis: an attractive target tissue for gene therapy

Important advances have been made within the past several years in understanding diseases at the molecular and cellular levels, which may enable the application of somatic gene therapy to a wide variety of genetic and acquired diseases. The initial clinical trials involving somatic gene therapy have demonstrated that gene transfer into human subjects can be performed safely and with public acceptance. This review focuses on use of the epidermis as a target tissue for gene therapy and assesses various delivery systems for both ex vivo and in vivo approaches. In addition, we discuss candidate diseases that may be amenable to epidermal gene therapy and the advantages of employing transgenic mouse model systems to test the efficacy of a given gene therapy prior to clinical trials.

Annular skin eruptions

Preview Skin eruptions often occur in annular patterns. Fungal infections are one of the most common causes of ring-shaped eruptions, but annular patterns form in many other skin conditions as well. Dr Bart describes, illustrates, and discusses the causes and treatments of 24 disorders that can result in rings on the skin.