Epithelial origin of cutaneous anchoring fibrils

A homozygous nonsense mutation identified in COL7A1 in a family with autosomal recessive dystrophic epidermolysis bullosa

Autosomal recessive dystrophic epidermolysis bullosa (RDEB) is a severe form of an inherited skin disorder. RDEB segregates both in an autosomal dominant as well as in an autosomal recessive pattern. It has been shown that both forms of dystrophic epidermolysis bullosa (DEB) are caused by mutations in the COL7A1 gene. In this study, we investigated a consanguineous four-generation family with two individuals displaying the RDEB phenotype. Both patients showed multiple skin erosions, atrophic scares, crusted scaling, and pseudosyndactyly. Whole exome sequencing (WES) was performed to identify the underlying genetic defect, revealing a homozygous nonsense mutation, c.409C>T (p.Arg137*) in COL7A1 in both patients. This variant was validated through Sanger sequencing and confirmed to segregate within the family. This report describes a recurrent nonsense mutation in COL7A1 that leads to a severe form of autosomal recessive dystrophic epidermolysis bullosa. Moreover, this study demonstrates that whole exome sequencing analysis is imperative in resolving clinically and genetically heterogeneous diseases like RDEB. Furthermore, this study expands the mutation spectrum of the COL7A1 gene in distinct populations.

Histological and molecular restoration of type VII collagen in Recessive dystrophic epidermolysis bullosa mouse skin by topical injection of keratinocyte-like cells differentiated from human adipose-derived mesenchymal stromal cells

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin fragility disorder caused by mutations in the COL7A1 gene, which encodes type VII collagen (COL7), the main constituent of anchoring fibrils for attaching the epidermis to the dermis. Persistent skin erosions frequently result in intractable ulcers in RDEB patients. Adipose-derived mesenchymal stromal cells (AD-MSCs) are easily harvested in large quantities and have low immunogenicity. Therefore, they are suitable for clinical use, including applications involving allogeneic cell transplantation. Keratinocyte-like cells transdifferentiated from AD-MSCs (KC-AD-MSCs) express more COL7 than undifferentiated AD-MSCs and facilitate skin wound healing with less contracture. Therefore, these cells can be used for skin ulcer treatment in RDEB patients.

OBJECTIVE

We investigated whether KC-AD-MSCs transplantation ameliorated the RDEB phenotype severity in the grafted skin of a RDEB mouse model (col7a1-null) on the back of the immunodeficient mouse.

METHODS

KC-AD-MSCs were intradermally injected into the region surrounding the skin grafts, and this procedure was repeated after 7 days. After a further 7-day interval, the skin grafts were harvested.

RESULTS

Neodeposition of COL7 and generation of anchoring fibrils at the dermal-epidermal junction were observed, although experiments were based on qualitative.

CONCLUSION

KC-AD-MSCs may correct the COL7 insufficiency, repair defective/reduced anchoring fibrils, and improve skin integrity in RDEB patients.

Transcriptomic landscape of Atlantic salmon (Salmo salar L.) skin

In this study, we present the first spatial transcriptomic atlas of Atlantic salmon skin using the Visium Spatial Gene Expression protocol. We utilized frozen skin tissue from 4 distinct sites, namely the operculum, pectoral and caudal fins, and scaly skin at the flank of the fish close to the lateral line, obtained from 2 Atlantic salmon (150 g). High-quality frozen tissue sections were obtained by embedding tissue in optimal cutting temperature media prior to freezing and sectioning. Further, we generated libraries and spatial transcriptomic maps, achieving a minimum of 80 million reads per sample with mapping efficiencies ranging from 79.3 to 89.4%. Our analysis revealed the detection of over 80,000 transcripts and nearly 30,000 genes in each sample. Among the tissue types observed in the skin, the epithelial tissues exhibited the highest number of transcripts (unique molecular identifier counts), followed by muscle tissue, loose and fibrous connective tissue, and bone. Notably, the widest nodes in the transcriptome network were shared among the epithelial clusters, while dermal tissues showed less consistency, which is likely attributable to the presence of multiple cell types at different body locations. Additionally, we identified collagen type 1 as the most prominent gene family in the skin, while keratins were found to be abundant in the epithelial tissue. Furthermore, we successfully identified gene markers specific to epithelial tissue, bone, and mesenchyme. To validate their expression patterns, we conducted a meta-analysis of the microarray database, which confirmed high expression levels of these markers in mucosal organs, skin, gills, and the olfactory rosette.

Epidermal aspects of type VII collagen: Implications for dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita

Type VII collagen (COL7), a major component of anchoring fibrils in the epidermal basement membrane zone, has been characterized as a defective protein in dystrophic epidermolysis bullosa and as an autoantigen in epidermolysis bullosa acquisita. Although COL7 is produced and secreted by both epidermal keratinocytes and dermal fibroblasts, the role of COL7 with regard to the epidermis is rarely discussed. This review focuses on COL7 physiology and pathology as it pertains to epidermal keratinocytes. We summarize the current knowledge of COL7 production and trafficking, its involvement in keratinocyte dynamics, and epidermal carcinogenesis in COL7 deficiency and propose possible solutions to unsolved issues in this field.

Molecular pathology of the basement membrane zone in heritable blistering diseases:: The paradigm of epidermolysis bullosa

Epidermolysis bullosa (EB), a phenotypically heterogeneous group of skin fragility disorders, is characterized by blistering and erosions with considerable morbidity and mortality. Mutations in as many as 18 distinct genes expressed at the cutaneous basement membrane zone have been shown to be associated with the blistering phenotype, attesting to the role of the corresponding proteins in providing stable association of the epidermis to the dermis through adhesion at the dermo-epidermal basement membrane zone. Thus, different forms of EB have been highly instructive in providing information on the physiological functions of these proteins as integral components of the supramolecular adhesion complexes. In addition, precise information of the underlying genes and distinct mutations in families with EB has been helpful in subclassification of the disease with prognostic implications, as well as for prenatal testing and preimplantation genetic diagnosis. Furthermore, knowledge of the types of mutations is a prerequisite for application of allele-specific treatment approaches that have been recently developed, including read-through of premature termination codon mutations and chaperone-facilitated intracellular transport of conformationally altered proteins to proper physiologic subcellular location. Collectively, EB serves as a paradigm of heritable skin diseases in which significant progress has been made in identifying the underlying genetic bases and associated aberrant pathways leading from mutations to the phenotype, thus allowing application of precision medicine for this, currently intractable group of diseases.

A single epidermal stem cell strategy for safe ex vivo gene therapy

There is a widespread agreement from patient and professional organisations alike that the safety of stem cell therapeutics is of paramount importance, particularly for ex vivo autologous gene therapy. Yet current technology makes it difficult to thoroughly evaluate the behaviour of genetically corrected stem cells before they are transplanted. To address this, we have developed a strategy that permits transplantation of a clonal population of genetically corrected autologous stem cells that meet stringent selection criteria and the principle of precaution. As a proof of concept, we have stably transduced epidermal stem cells (holoclones) obtained from a patient suffering from recessive dystrophic epidermolysis bullosa. Holoclones were infected with self-inactivating retroviruses bearing a COL7A1 cDNA and cloned before the progeny of individual stem cells were characterised using a number of criteria. Clonal analysis revealed a great deal of heterogeneity among transduced stem cells in their capacity to produce functional type VII collagen (COLVII). Selected transduced stem cells transplanted onto immunodeficient mice regenerated a non-blistering epidermis for months and produced a functional COLVII. Safety was assessed by determining the sites of proviral integration, rearrangements and hit genes and by whole-genome sequencing. The progeny of the selected stem cells also had a diploid karyotype, was not tumorigenic and did not disseminate after long-term transplantation onto immunodeficient mice. In conclusion, a clonal strategy is a powerful and efficient means of by-passing the heterogeneity of a transduced stem cell population. It guarantees a safe and homogenous medicinal product, fulfilling the principle of precaution and the requirements of regulatory affairs. Furthermore, a clonal strategy makes it possible to envision exciting gene-editing technologies like zinc finger nucleases, TALENs and homologous recombination for next-generation gene therapy.

High Local Concentrations of Intradermal MSCs Restore Skin Integrity and Facilitate Wound Healing in Dystrophic Epidermolysis Bullosa

Dystrophic epidermolysis bullosa (DEB) is an incurable skin fragility disorder caused by mutations in the COL7A1 gene, coding for the anchoring fibril protein collagen VII (C7). Life-long mechanosensitivity of skin and mucosal surfaces is associated with large body surface erosions, chronic wounds, and secondary fibrosis that severely impede functionality. Here, we present the first systematic long-term evaluation of the therapeutic potential of a mesenchymal stromal cell (MSC)-based therapy for DEB. Intradermal administration of MSCs in a DEB mouse model resulted in production and deposition of C7 at the dermal-epidermal junction, the physiological site of function. The effect was dose-dependent with MSCs being up to 10-fold more potent than dermal fibroblasts. MSCs promoted regeneration of DEB wounds via normalization of dermal and epidermal healing and improved skin integrity through de novo formation of functional immature anchoring fibrils. Additional benefits were gained by MSCs' anti-inflammatory effects, which led to decreased immune cell infiltration into injured DEB skin. In our setting, the clinical benefit of MSC injections lasted for more than 3 months. We conclude that MSCs are viable options for localized DEB therapy. Importantly, however, the cell number needed to achieve therapeutic efficacy excludes the use of systemic administration.

Type IV collagen is a novel DEJ biomarker that is reduced by radiotherapy

The dental basement membrane (BM) is composed of collagen types IV, VI, VII, and XVII, fibronectin, and laminin and plays an inductive role in epithelial-mesenchymal interactions during tooth development. The BM is degraded and removed during later-stage tooth morphogenesis; however, its original position defines the location of the dentin-enamel junction (DEJ) in mature teeth. We recently demonstrated that type VII collagen is a novel component of the inner enamel organic matrix layer contiguous with the DEJ. Since it is frequently co-expressed with and forms functional complexes with type VII collagen, we hypothesized that type IV collagen should also be localized to the DEJ in mature human teeth. To identify collagen IV, we first evaluated defect-free erupted teeth from various donors. To investigate a possible stabilizing role, we also evaluated extracted teeth exposed to high-dose radiotherapy--teeth that manifest post-radiotherapy DEJ instability. We now show that type IV collagen is a component within the morphological DEJ of posterior and anterior teeth from individuals aged 18 to 80 yr. Confocal microscopy revealed that immunostained type IV collagen was restricted to the 5- to 10-µm-wide optical DEJ, while collagenase treatment or previous in vivo tooth-level exposure to > 60 Gray irradiation severely reduced immunoreactivity. This assignment was confirmed by Western blotting with whole-tooth crown and enamel extracts. Without reduction, type IV collagen contained macromolecular α-chains of 225 and 250 kDa. Compositionally, our results identify type IV collagen as the first macromolecular biomarker of the morphological DEJ of mature teeth. Given its network structure and propensity to stabilize the dermal-epidermal junction, we propose that a collagen-IV-enriched DEJ may, in part, explain its well-known fracture toughness, crack propagation resistance, and stability. In contrast, loss of type IV collagen may represent a biochemical rationale for the DEJ instability observed following oral cancer radiotherapy.

Cell therapy in dermatology

Harnessing the regenerative capacity of keratinocytes and fibroblasts from human skin has created new opportunities to develop cell-based therapies for patients. Cultured cells and bioengineered skin products are being used to treat patients with inherited and acquired skin disorders associated with defective skin, and further clinical trials of new products are in progress. The capacity of extracutaneous sources of cells such as bone marrow is also being investigated for its plasticity in regenerating skin, and new strategies, such as the derivation of inducible pluripotent stem cells, also hold great promise for future cell therapies in dermatology. This article reviews some of the preclinical and clinical studies and future directions relating to cell therapy in dermatology, particularly for inherited skin diseases associated with fragile skin and poor wound healing.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

The structure and organization of lanceolate mechanosensory complexes at mouse hair follicles

In mouse hairy skin, lanceolate complexes associated with three types of hair follicles, guard, awl/auchene and zigzag, serve as mechanosensory end organs. These structures are formed by unique combinations of low-threshold mechanoreceptors (LTMRs), Aβ RA-LTMRs, Aδ-LTMRs, and C-LTMRs, and their associated terminal Schwann cells (TSCs). In this study, we investigated the organization, ultrastructure, and maintenance of longitudinal lanceolate complexes at each hair follicle subtype. We found that TSC processes at hair follicles are tiled and that individual TSCs host axonal endings of more than one LTMR subtype. Electron microscopic analyses revealed unique ultrastructural features of lanceolate complexes that are proposed to underlie mechanotransduction. Moreover, Schwann cell ablation leads to loss of LTMR terminals at hair follicles while, in contrast, TSCs remain associated with hair follicles following skin denervation in adult mice and, remarkably, become re-associated with newly formed axons, indicating a TSC-dependence of lanceolate complex maintenance and regeneration in adults.

DOI:http://dx.doi.org/10.7554/eLife.01901.001

Many mammals, such as cats, mice, and sea lions, have long whiskers that are particularly sensitive to touch. However, the hairs that cover the skin of most mammals are also important touch detectors. These hairs grow from follicles that are connected to the ends of the nerve cells that detect and convey touch information to the central nervous system. In mice, three main types of hair follicle—guard hairs, awl hairs, and zigzag hairs—are associated with combinations of three types of nerve endings. Much remains to be understood about how hair follicles and nerve cell endings—which are wrapped by cells called terminal Schwann cells—interact via structures called lanceolate complexes.

Now, using a combination of genetics, microscopy and surgical procedures, Li and Ginty have studied these structures in unprecedented detail, and revealed some intriguing structural differences among the three types of hair follicles. Zigzag follicles—which make up the fur undercoat—are associated with fewer terminal Schwann cells than are awl follicles, whilst guard hair follicles have the most. High-resolution analyses revealed that distinct combinations of sensory nerve endings were associated with different types of hair follicle cells—which may underlie the unique responses of the different hair follicle types when the hairs are deflected. Furthermore, an individual terminal Schwann cell can be associated with more than one type of nerve ending, adding another layer of intricacy to the detection of hair movements.

Killing the terminal Schwann cells in mice caused a complete loss of sensory nerve endings at hair follicles, which suggests that these cells are essential for maintaining the connection between the hair follicles and nerve cell endings. Interestingly, surgically removing nerve endings from the skin did not lead to a loss of terminal Schwann cells, and the nerve endings eventually grew back and reconnected with the hair follicles.

In addition to shedding new light on the structures of lanceolate complexes in different types of hair follicles, the findings of Li and Ginty suggest that terminal Schwann cells maintain the nerve endings at hair follicles and guide their regeneration after damage. Uncovering the molecular mechanisms that control these processes represents an important next step in this research.

DOI:http://dx.doi.org/10.7554/eLife.01901.002

Generation of keratinocytes from normal and recessive dystrophic epidermolysis bullosa-induced pluripotent stem cells

Embryonic stem cells (ESCs) have an unlimited proliferative capacity and extensive differentiation capability. They are an alternative source for regenerative therapies with a potential role in the treatment of several human diseases. The clinical use of ESCs, however, has significant ethical and biological obstacles related to their derivation from embryos and potential for immunological rejection, respectively. These disadvantages can be circumvented by the alternative use of induced pluripotent stem cells (iPSCs), which are generated from an individual's (autologous) somatic cells by exogenous expression of defined transcription factors and have biological characteristics similar to ESCs. In recent years, patient-specific iPSCs have been generated to study disease mechanisms and develop iPSC-based therapies. The development of iPSC-based therapies for skin diseases requires successful differentiation of iPSCs into cellular components of the skin, including epidermal keratinocytes. Here, we succeeded in generating iPSCs not only from normal human fibroblasts but also from fibroblasts isolated from the skin of two patients with recessive dystrophic epidermolysis bullosa. Moreover, we differentiated both of these iPSCs into keratinocytes with high efficiency, and generated 3D skin equivalents using iPSC-derived keratinocytes, suggesting that they were fully functional. Our studies indicate that autologous iPSCs have the potential to provide a source of cells for regenerative therapies for specific skin diseases.

Potential of fibroblast cell therapy for recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited skin-blistering disorder caused by mutations in the COL7A1 gene that lead to reduced type-VII collagen and defective anchoring fibrils at the dermal-epidermal junction (DEJ). Presently there are no effective treatments for this disorder. Recent mouse studies have shown that intradermal injections of normal human fibroblasts can generate new human type-VII collagen and anchoring fibrils at the DEJ. To assess potential clinical benefits in humans, we gave single intradermal injections of allogeneic fibroblasts to five subjects with RDEB. We noted increased type-VII collagen at the DEJ at 2 weeks and at 3 months following injection and increased anchoring fibrils, although none of these had normal morphology. No adverse effects, clinical or immunopathologic, were noted. We believe the major effect of allogeneic fibroblasts is to increase the recipients' own COL7A1 mRNA levels with greater deposition of mutant type-VII collagen at the DEJ and formation of additional rudimentary anchoring fibrils. Nevertheless, this mutant protein may be partially functional and capable of increasing adhesion at the DEJ. This is the first study demonstrating that intradermal injections of allogeneic fibroblasts have therapeutic potential in human subjects with RDEB.

Effects of fibroblasts and microenvironment on epidermal regeneration and tissue function in long-term skin equivalents

In vitro generated skin models find growing interest as promising tools in basic research and clinical application in regenerative medicine. Here, we present further details of an improved long-term skin equivalent (SE) enabling mechanistic studies on skin reconstruction and epidermal function. Growth conditions of fibroblasts in a 3D scaffold were analysed to optimise the dermal microenvironment by providing an authentic dermal matrix for regular tissue reconstruction and function of cocultured keratinocytes. These SEs demonstrate sustained epidermal viability - over 12 weeks - with regular differentiation as substantiated by in vivo-like patterns of all differentiation products, exemplified here by the cornified envelope components loricrin and repetin. The continuous expression of all major tight junction components in the granular layer, shown here for ZO-1 in coherence with the presence of epidermal barrier lipids, and ultrastructural accumulation of lamellar bodies, collectively indicate proper epidermal barrier structures. Remarkably, cocultured keratinocytes exerted an ongoing proliferation-stimulating effect on fibroblasts colonising the scaffold comparable to a cocktail of fibroblast growth factors. Consequently, precultivation of dermal equivalents (DEs) in basal or growth factor-enriched media had only minor effects on the quality of epidermal regeneration in cocultures. As to the role of fibroblast numbers, complete absence of dermal cells resulted in atrophic epithelia but the effect of cell numbers as low as 5 x 10(4)cells/cm(2) on epidermal tissue quality equalled that of the standard density (2 x 10(5)cells/cm(2)). Surprisingly, precultivation of fibroblasts in the DEs for 7 days (standard) showed no better effect on epidermal tissue reformation as compared to 2 days whereas a precultivation period of 14 days resulted in atrophic epidermal and dermal tissue development. These data demonstrate, (i) the strict dependence of epidermal tissue regeneration on the presence of fibroblasts, (ii) the mutual keratinocyte-fibroblast interactions for cell proliferation and organogenesis, and (iii) the importance of the proper microenvironment for epidermal tissue function and supposedly for establishment of a stem cell niche in vitro.

Amnia for intractable skin ulcers with recessive dystrophic epidermolysis bullosa: report of three cases

Recessive dystrophic epidermolysis bullosa (RDEB) is a disease characterized by recurrent blistering and chronic ulceration of the skin. In these patients, recurrent blisters frequently result in intractable skin ulcers due to impaired wound healing caused by mutations in the type VII collagen gene and malnutrition as well as by increased collagenase activity. To evaluate the efficacy of amnia for intractable ulcers in RDEB, we treated RDEB patients with amnia. The amniotic membrane was simply placed on the cleansed wound surface. The procedure was repeated once a week for up to 10 weeks. As a result, wound conditions improved remarkably after treatment with amnia for 2-10 weeks in all the patients, resulting in total re-epithelization of the ulcers. Amnia could be an effective therapy for intractable skin ulcers in RDEB patients, and should be considered as a re-emerging therapeutic option for the disease.

Keratinocyte-fibroblast interactions in wound healing

Cutaneous tissue repair aims at restoring the barrier function of the skin. To achieve this, defects need to be replaced by granulation tissue to form new connective tissue, and epithelial wound closure is required to restore the physical barrier. Different wound-healing phases are recognized, starting with an inflammation-dominated early phase giving way to granulation tissue build-up and scar remodeling after epithelial wound closure has been achieved. In the granulation tissue, mesenchymal cells are maximally activated, cells proliferate, and synthesize huge amounts of extracellular matrix. Epithelial cells also proliferate and migrate over the provisional matrix of the underlying granulation tissue, eventually closing the defect. This review focuses on the role of keratinocyte-fibroblast interactions in the wound-healing process. There is ample evidence that keratinocytes stimulate fibroblasts to synthesize growth factors, which in turn will stimulate keratinocyte proliferation in a double paracrine manner. Moreover, fibroblasts can acquire a myofibroblast phenotype under the control of keratinocytes. This depends on a finely tuned balance between a proinflammatory or a transforming growth factor (TGF)-beta-dominated environment. As the phenotype of fibroblasts from different tissues or body sites becomes better defined, we may understand their individual contribution in wound healing in more detail and possibly explain different clinical outcomes.

Epidermal homeostasis in long-term scaffold-enforced skin equivalents

Epidermal homeostasis is understood as the maintenance of epidermal tissue structure and function by a fine tuned regulatory mechanism balancing proliferation and cell loss by desquamation and apoptosis. The lack of appropriate experimental models has largely prevented a better understanding of the regulatory mechanisms controlling epidermal tissue homeostasis in human skin. Keratinocyte culture studies had revealed a strict dependency of regular epidermal differentiation on dermal interactions only accomplishable in three-dimensional skin models. As major drawbacks, conventional models, employing collagen hydrogels as dermal equivalents (DEs) exhibit a rather poor stability and limited lifespan. Here, we present an improved stabilized in vitro-model for long-term growth and differentiation of keratinocytes providing the basis for tissue homeostasis. Keratinocytes were grown on DEs reinforced by modified hyaluronic acid fibers (Hyalograft-3D) and colonized with skin fibroblasts, producing genuine dermis-type matrix. These skin equivalents (SEs) develop superior epidermal architecture with regular differentiation and ultrastructure. Critical aspects of differentiation, still unbalanced in early stages, are renormalized, most strikingly the coexpression of keratins K1/K10, downregulation of regeneration-associated keratins (K16), and restriction of K15 to the basal layer. The strict localization of integrins to basal cells underlining restored tissue polarity, the drop of keratinocyte growth rates towards physiological levels and the rapid formation of a mature basement membrane with abundant anchoring fibrils are altogether features fulfilling the criteria of tissue homeostasis. Therefore, these scaffold-based SEs not only allow for studying homeostasis control but also for the first time provide proper experimental conditions for establishing a stem cell niche in vitro.

Interactions between fibroblasts and keratinocytes in morphogenesis of dermal epidermal junction in a model of reconstructed skin

De novo dermal epidermal junction morphogenesis was studied in a skin model including dermal fibroblasts and epidermal keratinocytes. Sequential gene expression, protein deposition, and localization of basement membrane zone components were studied during 15 days. The morphogenesis of dermal epidermal junction is characterized by an implementation of the different components and then a subsequent plateau phase occurring at day 11. Three groups of genes were identified depending on cellular origin and expression profile: 1/genes of fibroblastic origin (col I alpha1, col III alpha1, nidogen, and fibrillin 1); 2/genes expressed in fibroblasts and keratinocytes with symmetrical expression pattern between both cell types (col IV alpha1, col VII alpha1, and tenascin C); 3/laminin beta3 only expressed in keratinocytes. Use of modified organotypic models excluding one cell type revealed a tight interplay between fibroblasts and keratinocytes for synthesis and localization of the components of dermal epidermal junction. Keratinocytes downregulated mRNA and proteins of fibroblastic origin, upregulated col VII in fibroblasts and were absolutely required for dermal-epidermal junction localization of fibroblastic proteins. Fibroblasts downregulated mRNA of keratinocytes and were needed for extracellular secretion and correct localization of type VII collagen and laminin 5.

Fibroblasts as Target Cells for DEB Gene Therapy

Dystrophic epidermolysis bullosa (DEB) is due to mutations in the type VII collagen (C7) gene. Potential therapies for DEB include (i) ex vivo gene therapy and (ii) intradermal injection of gene-corrected DEB fibroblasts, lentiviral vectors expressing C7 or recombinant C7 itself. With regard to molecular engineering, the dermal fibroblast has advantages over epidermal keratinocytes for delivering C7 to DEB patients.

Authentic fibroblast matrix in dermal equivalents normalises epidermal histogenesis and dermoepidermal junction in organotypic co-culture

Besides medical application as composite skin grafts, in vitro constructed skin equivalents (SEs) or organotypic co-cultures represent valuable tools for cutaneous biology. Major drawbacks of conventional models, employing collagen hydrogels as dermal equivalents (DEs), are a rather poor stability and limited life span, restricting studies to early phases of skin regeneration. Here we present an improved stabilised in vitro model actually providing the basis for skin-like homeostasis. Keratinocytes were grown on dermal equivalents (DEs) reinforced by modified hyaluronic acid fibres (Hyalograft-3D) and colonised with skin fibroblasts, producing genuine dermis-type matrix. These SEs developed a superior epidermal architecture with regular differentiation and ultrastructure, which occurred also faster than in SEs based on collagen-DEs. Critical aspects of differentiation, still unbalanced in early stages, were perfectly re-normalised, most strikingly the co-expression of keratins K1/K10 and downregulation of regeneration-associated keratins such as K16. The restriction of integrin and K15 distribution as well as keratinocyte proliferation to the basal layer underlined the restored tissue polarity, while the drop of growth rates towards physiological levels implied finally accomplishment of homeostasis. This correlated to faster basement membrane (BM) formation and ultrastructurally defined dermo-epidermal junction including abundant anchoring fibrils for strong tissue connection. Whereas the fibroblasts in the scaffold initially secreted a typical provisional regenerative matrix (fibronectin, tenascin), with time collagens of mature dermis (type I and III) were accumulating giving rise to an in vivo-like matrix with regularly organised bundles of striated collagen fibrils. In contrast to the more catabolic state in conventional DEs, the de novo reconstruction of genuine dermal tissue seemed to be a key element for maintaining prolonged normal keratinocyte proliferation (followed up to 8 wks), fulfilling the criteria of tissue-homeostasis, and possibly providing a stem cell niche.

The effects of epidermal keratinocytes and dermal fibroblasts on the formation of cutaneous basement membrane in three-dimensional culture systems

The cutaneous basement membrane (BM) plays an important role in normal and pathological conditions. However, few studies have addressed the formation of the cutaneous BM using three-dimensional culture systems. In this study, to elucidate the effects of human epidermal keratinocytes and dermal fibroblasts on the formation of the cutaneous BM, keratinocytes were cultured on several dermal substrates in the presence or absence of fibroblasts at the air-liquid interface. After 2 weeks of culture, immunohistochemical stainings for the components of the BM and electron microscopic studies of the BM zone (BMZ) were performed. In cultures of keratinocytes alone on dead reticular dermis or collagen gel without fibroblasts, beta4 integrin chain, laminin, type IV and VII collagens were all expressed. However, ultrastructurally, BMZ was not formed. In cultures of keratinocytes on fibroblast-populated collagen matrix, laminin, and type IV and VII collagens were expressed more strongly than in the absence of fibroblasts. In addition, elements of the BMZ such as hemidesmosomes, lamina lucida, lamina densa and anchoring fibrils were formed, although it was still incomplete. In the culture of keratinocytes alone on de-epidermized dermis (DED) (surface up), beta4 integrin chain, laminin, and type IV and VII collagens were strongly expressed. Also, the BMZ appeared similar to that in normal skin. In cocultures of keratinocytes and fibroblasts on DED or cultures of keratinocytes on DED combined with fibroblast-populated collagen matrix, type IV collagen was expressed more strongly than in cultures of keratinocytes alone. Ultrastructurally, similar findings to those of cultures of keratinocytes alone on DED were seen. Interestingly, when keratinocytes and fibroblasts were cocultured on DED, some fibroblasts were seen in the upper dermis as a result of migration into the dermis through partial loss of the lamina densa. These results show that keratinocytes produce most of the components of the BM such as laminin, and type IV and VII collagens. In addition, fibroblasts stimulate the expression of the components of the BM and the formation of a BMZ, suggesting that fibroblasts may produce laminin, and type IV and VII collagens or influence the effects of keratinocytes on the formation of the BM through a keratinocyte-fibroblast interaction.

Transcriptional Control of the Mouse Col7a1 Gene in Keratinocytes: Basal and Transforming Growth Factor-β Regulated Expression

Anchoring fibrils at the cutaneous basement membrane zone of the stratified squamous epithelia are essential to maintaining skin integrity, as absence of these structures leads to the chronic blistering disease, dystrophic epidermolysis bullosa. Type VII collagen, the major component of anchoring fibrils, is synthesized primarily by basal keratinocytes and to a lesser degree by dermal fibroblasts. To elucidate the transcriptional control elements of the type VII collagen gene (Col7a1), 3 kb of 5' flanking sequence of the mouse gene was cloned, sequenced, and fused to the chloramphenicol acetyltransferase reporter gene. Promoter deletion analyses revealed that 560 bp of Col7a1 5' flanking sequence was sufficient and necessary for basal level of transcription in cultured murine keratinocytes. Mutagenesis of DNA sequences with similarity to consensus binding sites for transcription factors, including Sp1/Sp3, AP2, AP1, and Smads, within the p-560Col7a1 promoter/chloramphenicol acetyltransferase construct, coupled with DNA binding assays, revealed the importance of these sites for basal Col7a1 expression. The effect of transforming growth factor beta, an activator of Col7a1 expression in keratinocytes and dermal fibroblasts, was examined using the same Col7a1 promoter/chloramphenicol acetyltransferase constructs. These analyses demonstrated that transforming growth factor beta1 stimulation of Col7a1 transcription is dependent on a putative interaction between Smads and AP1. Interestingly, the Smad-like binding site was essential for both basal and transforming growth factor beta1 stimulated Col7a1 transcription. Collectively, these findings attest to the complex regulation of Col7a1 transcription in epidermal keratinocytes.

Normal and Gene-Corrected Dystrophic Epidermolysis Bullosa Fibroblasts Alone Can Produce Type VII Collagen at the Basement Membrane Zone

Type VII collagen is synthesized and secreted by both human keratinocytes and fibroblasts. Although both cell types can secrete type VII collagen, it is thought that keratinocytes account for type VII collagen at the dermal-epidermal junction (DEJ). In this study, we examined if type VII collagen secreted solely by dermal fibroblasts could be transported to the DEJ. We established organotypic, skin-equivalent cultures composed of keratinocytes from patients with recessive dystrophic epidermolysis bullosa (RDEB) and normal dermal fibroblasts. Immuno-labeling of skin equivalent sections with the anti-type VII collagen antibody revealed tight linear staining at the DEJ. RDEB fibroblasts, were gene-corrected to make type VII collagen and used to regenerate human skin on immune-deficient mice. The human skin generated by gene-corrected RDEB fibroblasts or normal human fibroblasts combined with RDEB keratinocytes restored type VII collagen expression at the DEJ in vivo. Further, intradermal injection of normal human or gene-corrected RDEB fibroblasts into mouse skin resulted in the stable expression of human type VII collagen at the mouse DEJ. These data demonstrate that human dermal fibroblasts alone are capable of producing type VII collagen at the DEJ, and it is possible to restore type VII collagen gene expression in RDEB skin in vivo by direct intradermal injection of fibroblasts.

The cellular origins of the linear IgA disease target antigens: an indirect immunofluorescence study using cultured human keratinocytes and fibroblasts

BACKGROUND

Linear IgA disease (LAD) is an IgA-mediated subepidermal immunobullous disease of adults and children, with heterogeneous immunopathology. Objectives To investigate to what extent the cellular origins of the target antigens account for the heterogeneity of the immune response in LAD.

METHODS

Forty-nine adult and 33 childhood LAD sera were studied. Immunofluorescence was carried out to determine the expression of the LAD antigens by normal human keratinocytes, fibroblasts and mixed cultures of keratinocytes and fibroblasts. Immunoblotting was performed to determine the localization of the LAD target antigens in tissue extracts (48 adult and 31 childhood sera) and cell extracts (21 adult and 10 childhood sera).

RESULTS

Thirty-one adult and 13 childhood LAD sera bound proteins expressed by human keratinocytes; of these sera, 15 adult and four childhood LAD sera also recognized proteins expressed by fibroblasts. A single adult serum was positive on fibroblasts alone. Seventeen adult and 20 childhood sera were negative on both cell types. There was a modest increase (9%) in the detection of the IgA autoantibodies on keratinocytes and fibroblasts grown together in mixed culture. Immunoblotting showed that the LAD target antigens could be detected in cell as well as in tissue extracts.

CONCLUSIONS

Our results have shown that normal human keratinocytes and fibroblasts in culture express the LAD target antigens. LAD sera (with a single exception) bound antigens expressed by keratinocytes alone or by both keratinocytes and fibroblasts. The principal pattern of expression in keratinocytes was cytoplasmic, similar to that demonstrated by polyclonal antibodies to the 180-kDa bullous pemphigoid antigen (BP180). This reflects the pivotal role of BP180 in LAD. The finding that LAD antigens are expressed by both human keratinocytes and fibroblasts in culture may explain the heterogeneity of the target antigens, and may be a contributory factor in the immunopathology of the disease.

The architecture of a collagen coating on a synthetic polymer influences epithelial adhesion

The current study sought to identify a collagen coating methodology for application to polymer surfaces that would provide for the development of adhesive structures responsible for the sustained adhesion of corneal epithelial tissue. We compared an uncoated microporous polycarbonate surface and equivalent surfaces coated with either covalently immobilized collagen I or chemically crosslinked collagen I gel in a corneal explant outgrowth assay over 21 days. Electron microscopy was used to examine the formation of hemidesmosomes, basal lamina, and anchoring fibrils at the tissue-polymer interface. The crosslinked collagen gel preparation supported the overlying epithelial tissue across the pore openings and allowed for the formation of identifiable basal lamina, hemidesmosomes, and anchoring fibrils between the epithelial tissue and the polymer surface. Hemidesmosomal plaque, but no basal lamina or anchoring fibril formation, occurred on the uncoated surface or on that coated with covalently immobilized collagen I. We propose that the collagen matrix provided by the crosslinked collagen gel was reorganized by the epithelial tissue and that this, combined with the secretion of ECM molecules, served to limit the diffusion of basement membrane components, which permitted an increase in the local concentration of these molecules, which favored the assembly of epithelial adhesive structures.

Purification and partial amino acid sequence of proteins from human epidermal keratinocyte conditioned medium

Keratinocytes are the main cell type of the epidermis. They secrete a variety of proteins and peptides that have diverse roles in epidermal physiology. In this report, we present purification and partial amino acid sequence of LEKTI, a serine proteinase inhibitor, and DAN (NO3) zinc-finger protein, a tumor suppressor protein of neuroblastoma, from human keratinocyte conditioned medium. Epidermal keratinocytes were isolated from human foreskin and serially passaged in a defined medium (MSBM). At confluence of the fourth passage, MSBM medium was replaced with protein-free Dulbecco's modified Eagle medium/F12 (DMEM:F12) 3:1 base medium and collected every 24 h for 4 days. Medium was pooled and concentrated using a stirred cell concentrator. Concentrated medium was diluted 1:1 in 50 mM sodium phosphate, pH 8 buffer, and loaded onto a preparative heparin affinity column. Proteins/peptides were purified from heparin column passthrough by the combination of preparative and analytical FPLC-based gel filtration chromatography and reversed-phase HPLC. Samples electroblotted onto a PVDF support were sequenced by Edman degradation in a gas-phase sequencing system.

Regulated cutaneous gene delivery: the skin as a bioreactor

Epidermal keratinocytes can secrete polypeptides into the bloodstream, and they can be easily expanded in culture and genetically modified. It is thus possible to use epidermal keratinocytes for the systemic delivery of transgene products. Here we review the development of epidermal secretory systems, from cultured keratinocytes to skin grafts and transgenic mouse models. We also discuss a gene-switch approach for regulated cutaneous gene delivery.

Systemic replacement therapy from genetically modified epidermal keratinocytes

Epidermal keratinocytes are a potential vehicle for gene transfer and systemic delivery. We review data showing that epidermis-secreted protein does indeed reach the circulation, and we discuss factors that bear upon the issue of how much protein epidermal keratinocytes can deliver to the circulation.

A partial catalog of proteins secreted by epidermal keratinocytes in culture

Proteins secreted by epidermal keratinocytes are known to engage in functions other than those directly associated with barrier formation. We have used a previously published culture model to collect proteins secreted by adult human epidermal keratinocytes. Electrophoresis and microsequencing allowed us to identify 20 proteins. The list of proteins includes those known to be produced by keratinocytes (beta-2 microglobulin, betaIG-H3, calgranulin A, cathepsin B and D, E-cadherin, gelatinase B, gelsolin, interstitial collagenase, laminin B2t, plasminogen activator inhibitor-1, protein 14-3-3epsilon, SCC antigen, stratifin, and translationally controlled tumor protein) as well as those not previously known to be secreted by keratinocytes (epididymis secretory protein, maspin, and anti-neoplastic urinary protein). In addition, two proteins were identified that are not known to be secreted (glutathione-S-transferase and heat shock protein 27/28 kDa). The varied nature of the proteins identified suggests that epidermal keratinocytes have physiologic functions that have yet to be identified.

Dynamics of basement membrane formation by keratinocyte-fibroblast interactions in organotypic skin culture

The cutaneous basement membrane zone, composed of numerous macromolecules, plays a multifunctional role in tissue regeneration and maintenance. To elucidate the cellular origin and dynamics of basement membrane formation, de novo synthesis, deposition, and ultrastructural assembly of its components were analyzed in organotypic cultures of adult skin keratinocytes on collagen gels with or without collagen-embedded dermal cells. Collagen IV and laminin-1 deposition occurred only in the presence of mesenchymal cells: patchy at day 4 and continuous after 1 week. Chain-specific mRNA expression started at day 2 in both keratinocytes and fibroblasts. It steadily increased up to day 10, however, with a reciprocal induction pattern, mRNA abundance shifting from keratinocytes to fibroblasts. On the other hand, laminin-5 staining was first observed at day 4, but in keratinocyte both mono- and cocultures. This was followed by nidogen, which was detected in cocultures but also in dermal monocultures. Laminin-5 protein persisted throughout day 21, whereas nidogen steadily increased in intensity. Expression kinetics revealed high levels of laminin-5 transcripts early and in keratinocytes only, whereas nidogen was expressed later and predominantly in fibroblasts. Although basement membrane protein deposition was continuous at day 14, the ultrastructural organization was still fragmentary, eventually normalizing at 3 weeks. These data demonstrate a dynamic interaction and cooperation of epithelial and mesenchymal skin cells in basement membrane formation. This interaction is supposedly mediated via diffusible factors. Our findings further extend the scope of epithelial-mesenchymal interactions stressing that both cell compartments are essential to constitute a tissue-specific extracellular matrix structure.

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.

Distribution and synthesis of type VII collagen in oral squamous cell carcinoma

The distribution of the basement membrane anchoring fibril component type VII collagen was studied in oral squamous cell carcinoma by using in situ hybridization and immunohistochemical methods. The expression of type VII collagen in oral normal mucosa, lichen planus and epithelial dysplasias was also investigated. In squamous cell carcinomas, the signals for type VII collagen mRNA were located exclusively in malignant peripheral cells in tumour islands and in fibroblast-like cells among the stromal tissue. In normal buccal mucosa, type VII collagen mRNA expression was located in basal epithelial cells. In oral lichen planus and epithelial dysplasias, the signals for type VII collagen mRNA were also located in basal keratinocytes; however, the signal was especially strong in some epithelial cells. In oral squamous cell carcinomas, the linear immunohistochemical staining pattern of type VII collagen was noted surrounding partly squamous epithelial tumour cell islands, and a large number of tumour cells showed a cytoplasmic staining reaction using the type VII collagen antibody. Some fibroblast-like stromal cells also showed a positive immunostaining reaction. In conclusion, the results of this study indicate that a high synthesis level, but an impaired distribution of type VII collagen, are highly characteristic of squamous epithelial tumour cells.

Differential expression of collagens XII and XIV in human skin and in reconstructed skin

Collagens XII and XIV localize near the surface of collagen fibrils and may be involved in epithelial-mesenchymal interactions as well as in the modulation of tissue biomechanical properties. Moreover, human skin fibroblasts cultured in monolayer are known to lose their ability to produce collagen XIV and to switch the transcription of collagen XII from the small splice variant (220 kDa) to the large (320 kDa), whereas the small form is the main form found in human skin. We have investigated the expression patterns of these two molecules in human skin as a function of donor age and anatomic site, by using immunohistology with specific monoclonal antibodies. We demonstrated changes in the expression patterns of collagens XII and XIV in human skin after birth. Moreover, in adult scalp skin, very strong staining of collagen XII fibril bundles was observed around hair follicles, in association with very low expression of collagen XIV. We also investigated the expression of collagens XII and XIV by fibroblasts and keratinocytes cultured in a reconstructed skin. In these culture conditions, fibroblasts recovered their ability to produce collagen XIV and re-expressed the small splice variant of collagen XII. These results could be explained by the deposition of large amounts of collagen fibrils by fibroblasts in this culture system. Thus, the re-expression of these collagens suggests that the deposition of banded collagen fibrils is a pre-requisite for the expression of collagen XIV and small variant of collagen XII.

A GT-rich sequence binding the transcription factor Sp1 is crucial for high expression of the human type VII collagen gene (COL7A1) in fibroblasts and keratinocytes

Type VII collagen is the major component of anchoring fibrils, structural elements that stabilize the attachment of the basement membrane to the underlying dermis. In this study, we have dissected the human type VII collagen gene (COL7A1) promoter to characterize the cis-elements responsible for the expression of the gene in cultured fibroblasts and keratinocytes. Using transient cell transfections with various 5' end deletion COL7A1 promoter/chloramphenicol acetyltransferase reporter gene plasmid constructs, we determined that the region between nucleotides -524 and -456, relative to the transcription start site, is critical for high promoter activity in both cell types studied. Gel mobility shift assays using several DNA fragments spanning this region identified a GT-rich sequence between residues -512 and -505, necessary for the binding of nuclear proteins to this region of the promoter. Point mutations abolished the binding of nuclear proteins in gel shift assays and drastically diminished the activity of the promoter in transient cell transfections. Supershift assays with antibodies against various transcription factors including Sp1, Sp3, c-Jun/AP-1, and AP-2, and competition experiments with oligonucleotides containing consensus sequences for Sp1 and AP-1 binding identified Sp1 as the transcription factor binding to this region of the COL7A1 promoter. Indeed, recombinant human Sp1 was shown to bind the COL7A1 promoter GT-rich element but not its mutated form in gel mobility shift assays. In addition, co-transfection of pPacSp1, an expression vector for Sp1, together with the COL7A1 promoter/chloramphenicol acetyltransferase construct into Sp1-deficient Drosophila Schneider SL2 cells unequivocally demonstrated that Sp1 is essential for high expression of the COL7A1 gene. These data represent the first in-depth analysis of the human COL7A1 promoter transcriptional control.

Characterization of a 50-kDa component of epithelial basement membranes using GDA-J/F3 monoclonal antibody

Using the monoclonal antibody GDA-J/F3, a 50-kDa noncollagenous component of human skin basement membrane zone was identified. Immunofluorescence stainings of normal human skin with the GDA-J/F3 antibody showed a linear fluorescence decorating the basement membrane zone. With immunoelectron microscopy, the epitope was localized to the insertion points of the anchoring fibrils into the lamina densa. The antigen is distinct from collagen VII, from the main structural protein of the anchoring fibrils, and from several other structural molecules of the basement membrane zone, because the GDA-J/F3 antibody did not react with purified basement membrane components in vitro. In serum-free cultures, the antigen was synthesized and secreted by normal and transformed human keratinocytes and to a lesser extent by normal human skin fibroblasts. Immunoprecipitation of radiolabeled epithelial cell-conditioned medium with the GDA-J/F3 antibody yielded two polypeptides that migrated on SDS-polyacrylamide gel electrophoresis with apparent molecular masses of 46 and 50 kDa under nonreducing conditions. Using reducing gels, only the 50-kDa polypeptide was observed. The antigen was resistant to digestion with bacterial collagenase but sensitive to trypsin and pepsin. It also bound to heparin and DEAE cellulose at low ionic strength and alkaline pH. These findings indicate that the GDA-J/F3 antigen is a small globular disulphide-bonded protein with a potential to interact with basement membrane proteoglycans. Integration of the GDA-J/F3 antigen into the histoarchitecture of the dermo-epidermal junction is dependent on the presence of collagen VII, because the GDA-J/F3 epitope was missing in several patients with a genetic blistering disorder of the skin, epidermolysis bullosa dystrophica, who lacked collagen VII and anchoring fibrils.

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

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

Basement membrane proteoglycans are of epithelial origin in rodent skin

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

Keratin expression in discoid lupus erythematosus

21 lesions from 16 patients with discoid lupus erythematosus (DLE) were examined immunohistologically using monoclonal antibodies to keratins (K). Markers of basal epithelial cells (the keratin conformation specific basal markers LH6 and LH8), differentiating keratinocytes (K1 and K10), hyperproliferating keratinocytes (K16) and panepidermal keratin (K14), were used. A monoclonal antibody to type VII collagen was used as a guide to the state of the basement membrane zone (BMZ). Keratin distribution in DLE differed from controls. Suprabasal cells were labelled by LH6 in 95% of specimens (19/20) and LH8 in 79% (15/19) in contrast to the basal distribution in normal skin. Reduction of suprabasal LL017 (K1) expression was seen in 59% (10/17) of lesions. An increase of LL025 (K16) expression was seen in 33% (5/15) of specimens. Where LL025 (K16) expression was increased, LL017 (K1) expression was reduced in 80% (4/5). Dermal colloid bodies expressed both basal and suprabasal keratins and were present at sites of maximal basement membrane disruption. These findings are consistent with a model of DLE in which there is an increase in the proliferative basal compartment. This compartment and the associated BMZ suffer fragmentation and loss of colloid bodies to the dermis which express a range of keratins not uniformly associated with basal keratinocytes.

Immunohistochemical and mutation analyses demonstrate that procollagen VII is processed to collagen VII through removal of the NC-2 domain

Collagen VII is the major structural constituent of anchoring fibrils in the skin. It is synthesized as a procollagen that is larger than the collagen deposited in the tissue. In this study, we investigated the conversion of procollagen VII to collagen VII in human skin and in cutaneous cells in vitro and identified the propeptide using domain-specific antibodies. For this purpose, two bacterial fusion proteins containing unique sequences of the carboxy-terminal globular NC-2 domain of procollagen VII were prepared, and polyclonal antibodies raised against them. Immunoblotting showed that the anti-NC2 antibodies reacted with procollagen VII isolated from cultured keratinocytes, but not with collagen VII extracted from the skin. Immunohistochemical experiments with the NC-2 antibodies revealed a strong reaction in cultured keratinocytes, but the basement membrane zone of normal skin remained negative. The staining could not be rendered positive by chemical or enzymatic unmasking of potential hidden epitopes in the skin, indicating that most of the NC-2 domain is absent from normal skin. In contrast, a positive staining with NC-2 antibodies was observed in the skin of a patient with NC-2 antibodies was observed in the skin of a patient with dystrophic epidermolysis bullosa, who carried a 14-bp deletion at one of the intro-exon junctions of the collagen VII gene. This aberration led to an in-frame skipping of exon 115 from the mRNA and eliminated 29 amino acids from the NC-2 domain which include the putative cleavage site for the physiological processing enzyme, procollagen C-proteinase. The results indicate that in normal human skin, the removal of the NC-2 domain from procollagen VII precedes its deposition at the dermal-epidermal junction. Furthermore, they suggest that an aberration in the procollagen VII cleavage interferes with the normal fibrillogenesis of the anchoring fibrils.

Expression of epithelial adhesion proteins and integrins in chronic inflammation

Epithelial cell behavior in chronic inflammation is poorly characterized. During inflammation of tooth-supporting structures (periodontal disease), increased proliferation of epithelial cells into the inflamed connective tissue stroma is commonly seen. In some areas ulceration and degeneration take place. We studied alterations in the expression of adhesion molecules and integrins during chronic periodontal inflammation. In inflamed tissue, laminin-1 and type IV collagen were still present in the basement membrane and surrounding blood vessels, but they were also found extravascularly in inflamed connective tissue stroma. Type VII collagen and laminin-5 (also known as kalinin, epiligrin, or nicein) were poorly preserved in the basement membrane zone, but both were found in unusual streak-like distributions in the subepithelial connective tissue stroma in inflamed tissue. Both fibronectin and tenascin were substantially decreased in chronically inflamed connective tissue, showing only punctate staining at the basement membrane zone. Integrins of the beta 1 family showed two distinct staining patterns in epithelial cells during chronic inflammation; focal losses of beta 1 integrins (alpha 2 beta 1 and alpha 3 beta 1) were found in most areas, while in other areas the entire pocket epithelium was found to be strongly positive for beta 1 integrins. No members of the alpha v integrin family were found in any epithelia studied. Expression of the alpha 6 beta 4 integrin was high in basal cells of healthy tissue, but weak in epithelium associated with chronic inflammation. Chronic inflammation therefore involves alterations in both adhesion proteins and integrins expressed by epithelial cells. Basement membrane components found at abnormal sites in stroma in chronic inflammation might serve as new adhesive ligands for various cell types in inflamed stroma.

Destruction of the epithelial anchoring system in lichen planus

To find out whether the epithelial anchoring system shows any alterations in lichen planus, we examined the distribution of type VII collagen, alpha 6 beta 4 integrin, and kalinin in lesions of lichen planus. These molecules were chosen because they are structural components of anchoring fibrils, hemidesmosome-associated complexes, and anchoring filaments. The localization of type VII collagen in lichen planus was strikingly different from that in nonaffected mucosa or dermis or in other mucocutaneous lesions. In the normal mucosa, type VII collagen was localized only at the basement membrane zone. In lichen planus, type VII collagen was present not only in the basement membrane area but also in streaked patterns deep in the connective tissue. The hemidesmosome-associated complex, alpha 6 beta 4 integrin, was localized at the basal aspect of basal epithelial cells of nonaffected sites, but was diffuse and discontinuous in lichen planus lesions. Most of the basal keratinocytes, however, stained for this integrin. Kalinin staining was discontinuous in lichen planus lesions. Often, finger-like projections of kalinin staining were found protruding into the connective tissue stroma. Kalinin was localized at the basement membrane zone of the nonaffected tissue and other mucocutaneous lesions. These results indicate that in cutaneous and mucosal lichen planus, the epithelial anchoring system is disturbed.

Expression of basement membrane type IV collagen and type IV collagenases (MMP-2 and MMP-9) in human fetal teeth

Formation and degradation of dental basement membrane (BM) are important for tooth development. Data on the expression of genes for type IV collagen (the major structural component of the BM) and type IV collagenases [MMP-2 (72 kDa) and MMP-9 (92 kDa)], enzymes that degrade type IV collagen during human tooth development, are lacking. We studied expression of type IV collagen and the MMP-2 and MMP-9 in human fetal teeth (from the 13th to the 20th gestational weeks, covering cap stage through early hard tissue formation). During cap and bell stages, in situ hybridization located transcripts for alpha 1 type IV collagen chain in the fibroblasts surrounding the enamel organ. No alpha 1 type IV collagen chain mRNA was detected in tooth germ epithelium or dental papilla. However, type IV collagen immunoreactivity was observed in BM underlying the dental epithelium up to the appositional stage. Transcripts for MMP-2 were located mostly in the cells of the dental papilla and follicle. Transient expression of MMP-2 mRNA was observed in the inner enamel epithelium of late cap/early bell-stage teeth. During early apposition, a high level of MMP-2 was confined to secretory odontoblasts. Transcripts for MMP-9 were detected by the sensitive reverse-transcription polymerase chain reaction (RT-PCR) in developing teeth. Thus, in dental BM, alpha 1 type IV collagen chain may be of mesenchymal cell origin. Further, MMP-2 but not MMP-9 may participate in remodeling and degradation of BM during human tooth morphogenesis.