The ultrastructure of the interfollicular epidermis of the hairless (hr/hr) mouse. III. Desmosomal transformation during keratinization

Aberrant distribution patterns of corneodesmosomal components of tape-stripped corneocytes in atopic dermatitis and related skin conditions (ichthyosis vulgaris, Netherton syndrome and peeling skin syndrome type B)

BACKGROUND

Atopic dermatitis (AD), Netherton syndrome (NS) and peeling skin syndrome type B (PSS) may show some clinical phenotypic overlap. Corneodesmosomes are crucial for maintaining stratum corneum integrity and the components' localization can be visualized by immunostaining tape-stripped corneocytes. In normal skin, they are detected at the cell periphery.

OBJECTIVE

To determine whether AD, NS, PSS and ichthyosis vulgaris (IV) have differences in the corneodesmosomal components' distribution and corneocytes surface areas.

METHODS

Corneocytes were tape-stripped from a control group (n=12) and a disease group (37 AD cases, 3 IV cases, 4 NS cases, and 3 PSS cases), and analyzed with immunofluorescent microscopy. The distribution patterns of corneodesmosomal components: desmoglein 1, corneodesmosin, and desmocollin 1 were classified into four types: peripheral, sparse diffuse, dense diffuse and partial diffuse. Corneocyte surface areas were also measured.

RESULTS

The corneodesmosome staining patterns were abnormal in the disease group. Other than in the 3 PSS cases, all three components showed similar patterns in each category. In lesional AD skin, the dense diffuse pattern was prominent. A high rate of the partial diffuse pattern, loss of linear cell-cell contacts, and irregular stripping manners were unique to NS. Only in PSS was corneodesmosin staining virtually absent. The corneocyte surface areas correlated significantly with the rate of combined sparse and dense diffuse patterns of desmoglein 1.

CONCLUSION

This method may be used to assess abnormally differentiated corneocytes in AD and other diseases tested. In PSS samples, tape stripping analysis may serve as a non-invasive diagnostic test.

Tight junctions in the stratum corneum explain spatial differences in corneodesmosome degradation

To maintain stratum corneum integrity while simultaneously desquamating at a steady rate, degradation of corneodesmosomes must proceed in a controlled manner. It is unknown why corneodesmosomes are present only at the cell periphery in the upper stratum corneum. To explore this, we studied distributions of three major corneodesmosomal components, corneodesmosin, desmoglein 1 and desmocollin 1 in normal adult human epidermis. Immunofluorescent microscopy studies of skin surface corneocytes detected all three components only at the cell edges. Immunoelectron microscopy revealed selective loss of these components at the central areas starting from the deep cornified layers. We hypothesized that tight junctions (TJs) formed in the superficial granular layer may prevent protease access by functioning as a barrier between the peripheral and the central intercellular spaces in the stratum corneum. Ultrastructural examination demonstrated TJs up to the junctions between the seventh and the eighth deepest cornified layers. Immunoelectron microscopy also detected clusters of occludin and claudin-1 immunolabels at the cell periphery, and kallikrein 7 immunolabels outside of TJs in the lower cornified layers. With colloidal lanthanum nitrate perfusion assay of stripped stratum corneum, the tracer was excluded from TJ domains. Taken together, we propose that TJs inhibit access of proteases to the peripheral corneodesmosomes forming the structural basis for the basket-weave-like appearance of the stratum corneum.

Gerbilline cholesteatoma development Part I: Epithelial migration pattern and rate on the gerbil tympanic membrane: comparisons with human and guinea pig

OBJECTIVE

To determine the migration rate and pattern for keratin on the tympanic membrane (TM) of the gerbil and guinea pig in comparison to human data and determine which species is an appropriate model for investigating the relationship of epithelial clearance to cholesteatoma formation.

STUDY DESIGN AND SETTING

Ink drops were placed on the TM and their locations plotted daily.

RESULTS

Gerbils demonstrated a radial migration pattern away from the umbo, identical to that reported for humans, although the rate was 0.32 mm/day-3 times the human rate of 0.1 mm/day. Guinea pigs were significantly different from gerbils and humans, with a rate of 0.79 mm/day and a pattern of superior/inferior migration without anterior-posterior movement.

CONCLUSION

Gerbils more closely resemble humans in rate and pattern of epithelial migration.

SIGNIFICANCE

Gerbils represent the most appropriate model for determining the relationship between keratin migration and cholesteatoma formation.

Alterations in desmosome size and number coincide with the loss of keratinocyte cohesion in skin with homozygous and heterozygous defects in the desmosomal protein plakophilin 1

Recessive mutations in the desmosomal plaque protein plakophilin 1 (PkP1) underlie ectodermal dysplasia/skin fragility syndrome (MIM 604536). We undertook an immunohistochemical and quantitative electron microscopic examination of suprabasal desmosomes from 4 skin samples from 3 PkP1 deficient patients, an unaffected carrier with a PKP1 heterozygous acceptor splice site mutation and 5 healthy control subjects. Desmosomal plaque size (>50 desmosomes per individual) and frequency (>20 high power fields, HPF) were assessed. Compared with controls, desmosomes were reduced dramatically both in size (49%) and frequency (61%) in the lower suprabasal layers (LSB) in PkP1 null patients (P<0.01). In the LSB compartment of the heterozygous carrier, corresponding reductions were 37% and 20%, respectively (P<0.01). Surprisingly, the PkP1 null patient's upper suprabasal layer, (USB), desmosome size was larger (59%, P<0.01) than the control value, and showed increased desmoglein 1 and PkP2 USB staining. The USB desmosome frequency in PKP1 null patients was similar to the LSB compartment (but reduced by 43% compared to USB controls). The carrier showed no difference in the USB desmosome size and frequency compared with the controls (P>0.05). The PKP1 null patients showed poorly developed inner and outer desmosomal plaques. Thus, both the patients and unaffected carrier showed reductions in the LSB desmosome size and number; despite only PkP1 null patients exhibiting any phenotype. These findings attest to the molecular recruiting and stabilizing roles of PkP1 in desmosome formation, particularly in the LSB compartment.

Antigen retrieval of loricrin epitopes at desmosomal areas of cornified cell envelopes: an immunoelectron microscopic analysis

Cell envelopes (CEs) are insoluble, chemically and mechanically tough structures formed during terminal differentiation of keratinocytes, providing skin with a protective barrier against the environment. They are 15 to 20 nm thick structures beneath the plasma membrane and continuous with desmosomal attachment plaques. Sequential deposition of several proteins including involucrin and loricrin leads to a gradual increase in envelope thickness and rigidity. Cross-linking of desmosomal components to other CE-proteins has been demonstrated and desmosomes in the cornified cells have been regarded as a part of CEs. Our previous immunoelectron microscopy studies showed that desmosomal areas of granular cells were loricrin-positive, but those in cornified cells were negative. We asked whether this is due to epitope masking and applied trypsin digestion of the electron microscopy sections to retrieve the possibly masked epitopes. Since this treatment made desmosomal structures obscure, one side of the sections was stained with anti-desmoglein antibody as an indicator of desmosomes. Trypsin was applied on the other side followed by immunolabeling with anti-loricrin antibody. Trypsin digestion indeed unmasked the loricrin epitopes in the desmoglein-positive desmosomal areas of CEs. It seems therefore that loricrin is first accumulated at the desmosomes before the CE-assembly and cross-linking of loricrin occurs at the desmosomal areas of CEs as well as at the non-desmosomal areas.

Osmium tetroxide and ruthenium tetroxide are complementary reagents for the preparation of epidermal samples for transmission electron microscopy

Ruthenium tetroxide and osmium tetroxide were compared as post-fixatives in the preparation of human epidermis for transmission electron microscopic examination. Both reagents revealed characteristic lamellar granules within the granular layer and extruded lamellar granule contents in the upper granular layer. The transformation of the granule contents into multilamellar sheets at the interface between the granular and cornified layers and the persistence of these sheets through all levels of the stratum corneum were demonstrated only with ruthenium tetroxide fixation. Therefore, the reactivity of osmium tetroxide with isolated epidermal lipids was examined. The failure of osmium tetroxide to reveal membrane structures in the stratum corneum can be explained by its inability to react with many of the lipid components of these membranes, rather than to selective removal of lipids during tissue processing, as was formerly believed. Ruthenium tetroxide, a stronger oxidizing agent than osmium tetroxide, overcomes this problem but has other severe limitations as a post-fixative.

Evidence for a role of corneodesmosin, a protein which may serve to modify desmosomes during cornification, in stratum corneum cell cohesion and desquamation

Corneodesmosin, defined as the protein recognized by the monoclonal antibody G36-19, is a recently described late differentiation protein of human cornified epithelium. In the stratum corneum it is localized in the extracellular parts of modified desmosomes (corneodesmosomes) and adjacent parts of the cornified cell envelope. The aim of the present study was to investigate whether corneodesmosin undergoes changes in the stratum corneum which can be related to the cohesive state of the tissue and to desquamation. Extracts of plantar stratum corneum from various tissue levels and tape-stripped non-palmoplantar stratum corneum were analysed by immunoblotting with G36-19. In addition, the fate of corneodesmosin during shedding of surface cells in a recently described in vitro model of desquamation in plantar stratum corneum was investigated and compared with the degradation of the desmosomal protein desmoglein I in this system. The apparent molecular weights of the major G36-19-positive components in plantar stratum corneum ranged between 33 and 48 kDa. The components with the highest molecular weights were predominant in the deepest tissue layers. In the intermediate tissue layers G36-19-positive components of molecular weight 33-36, 39 and 44-48 kDa were found. There seemed to be a further degradation of the 33 to 36-kDa components in the most superficial parts of the tissue. In surface cells dissociated in vivo as well as in vitro no G36-19-positive components with molecular weights above 36 kDa were detected. Results from analyses of nonpalmoplantar stratum corneum suggested that corneodesmosin is degraded in this tissue in a way that may be similar to that in plantar stratum corneum.(ABSTRACT TRUNCATED AT 250 WORDS)

Desmosome differentiation during epidermal cornification: new observations obtained from intermediate voltage electron microscopy

Human epidermis was examined under 400-kV intermediate voltage electron microscopy using epon sections cut 5-8 times thicker than usual ultrathin sections. Asymmetry of desmosomal structures occurred as cells became cornified. Electron-dense proteins deposited at the inner leaflet of the plasma membrane of corneocytes do not extend into the desmosomal area, which connects to granular cells. Stereo micrographs revealed the existence of two different cellular elements at the cell surface confirming that the plasma membrane first thickened in areas without desmosomes. Examination of the three-dimensional nature of desmosomes and keratin-filament aggregation without serial sectioning and/or selecting a strict angle of the tissues will allow us to extend our ultrastructural knowledge.

Quantitative immunohistochemical analysis of keratins and desmoplakins in human gingiva and peri-implant mucosa

Quantitative immunohistochemistry was used to compare the distributions of keratins and desmoplakins in human gingiva and peri-implant mucosa (three specimens each). In gingiva, keratin 1 (a marker of cornification) and desmoplakins I & II (markers of desmosomes) stained most heavily in granular strata followed by corneal strata; keratin 13, a marker of non-cornifying stratified squamous cells, stained most heavily in suprabasal strata of oral sulcular epithelium. Keratin 19, a marker for junctional epithelium, stained the basal stratum of oral sulcular epithelium most heavily. In peri-implant mucosa, the patterns of staining were similar, except that staining for desmoplakins I & II was generally significantly reduced compared with gingiva, and junctional epithelium co-expressed keratins 13 and 19. Peri-implant junctional epithelial cells attached to titanium implant abutments were removed by trypsin/EDTA digestion, and also exhibited co-expression of keratins 13 and 19. Inflammatory cell infiltration was associated with reduction of keratin 1 staining in gingiva. The data indicate that the epithelia of gingiva and peri-implant mucosa are not composed of identical cell populations.

Desmosomes, corneosomes and desquamation. An ultrastructural study of adult pig epidermis

We recently developed a pig skin model to determine the role of corneosomes (modified desmosomes in the stratum corneum) and extracellular lipids in desquamation. The present study provides control morphometric data on the morphological changes in desmosomes and corneosomes leading to desquamation in adult pig epidermis in vivo. The extracellular space within desmosomes gradually widened from the basal to the granular layer, and decreased slightly in the stratum corneum. Mid-dense line broadening, and increased electron density of the distal light layers, coincided with membrane-coating granule extrusion in the outer granular layer. Corneocyte attachment correlated with corneosome distribution. Compactum packing was relatively tight and corneosomes were numerous. Cohesion was mainly peripheral in the disjunctum, and corneosomes were restricted to corneocyte edges. Adhesion had a tongue-and-groove appearance with corneosomes riveting corneocyte peripheries into a lipped groove on adjoining cells. Cells shed by peeling radially towards the lipped groove, and corneosomes decreased from lower to upper disjunctum. Corneosome breakdown commenced with an electron lucent band forming between the plug and lipid envelope. The plug was then unzipped from the lipid envelope and degraded. Corneosomes did not form squamosomes.

Biochemical changes in desmosomes of bovine muzzle epidermis during differentiation

Biochemical changes taking place in desmosomes during differentiation have been studied. Bovine muzzle epidermis was sliced horizontally into 6 layers, 0.2 mm thick, and desmosomes were isolated from each layer. These were then analyzed by polyacrylamide gel electrophoresis. The electrophoretic patterns of desmosomal proteins from the 6 layers were found to be qualitatively similar to each other, but there was an increase in the ratio of the amount of 150 kD glycoprotein (desmoglein I) relative to 240 and 210 kD proteins (desmoplakins) in the upper layers of the epidermis. This finding was supported by the similar increase observed in electrophoretic patterns of proteins extracted directly from each layer of the epidermis in electrophoretic sample buffer. In order to study the fate of desmosomal components in the stratum corneum, serial skin surface biopsies were stained with antisera against desmosomal components using indirect immunofluorescence techniques. This experiment showed that desmosomal proteins and glycoproteins persist in the stratum corneum but quantitatively decrease in the outer layers. This decrease may play a significant role in desquamation.

The function of migratory epidermis in the healing of tympanic membrane perforations in guinea-pig. A photographic study

During observations on healing traumatic perforations in guinea-pig tympanic membranes, a specific appearance was seen on the surface of the epidermis as it closed the perforations. In this experiment, this pattern was identified on 15 tympanic membranes in 10 guinea pigs, and serial photography was used to record the healing process in 6 perforations over 5 days. This study shows that epidermis accumulates at the inferior margin of the perforation (the side from which it migrates) and then closes over the defect. Epidermal migration appears to be a key factor in this healing process.

In situ localization of F-actin in the normal and injured guinea-pig tympanic membrane

Although cell migration is an important function of the epithelial cells of the tympanic membrane (TM), little is known about the distribution of the F-actin cytoskeleton, a contractile protein important in cell motility. The purpose of this experiment was to study the in situ localization of F-actin in the epithelial cells of the TM. F-actin, localized using Rhodamine-phalloidin, was present as a thin cortical band at the margin of both the mucosal cells on the inner side of the drum, and the suprabasal cells of the epidermis. The basal cells showed diffuse circumferential F-actin staining sometimes appearing as short microfilaments. Following a full thickness injury, changes in the distribution of F-actin could be observed with in situ localization. While the diffuse F-actin staining of the basal cells was reduced, both long F-actin microfilament bundles extending parallel to the long axis of the cell and focal aggregates of F-actin were prominent. The suprabasal cells became elongated, and while the F-actin remained localized to the cell margin, faint central F-actin microfilaments were observed. The staining of the mucosal cells remained unchanged. This study showed that the guinea pig TM is a useful model to study the distribution of epithelial F-actin in situ under normal and repair conditions, and that the basal cell layer may be important in regulating migration in the epidermis.

Human autoantibodies against a desmosomal core protein in pemphigus foliaceus

Pemphigus foliaceus (PF) is a human autoimmune disease in which antibodies are directed against the cell surface of epidermal cells with resultant blister formation. The histopathology of these blisters indicates that cells have detached from each other, and electron microscopy of early blisters shows diminished numbers, to complete loss, of desmosomes as well as abnormalities of the tonofilament-desmosome complex. In this study we demonstrate that autoantibodies from certain PF patients bind to a desmosomal core glycoprotein called desmoglein (DG) I. Proteins in extracts of normal human epidermis were separated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE), then transferred to nitrocellulose or 2-aminophenylthioether paper for immunoperoxidase staining. Results of these immunoblots indicated that sera from 6 of 13 PF patients specifically and intensely stained an approximately 160,000 mol wt polypeptide, "PF antigen". Such staining was not seen with normal human sera or sera from patients with pemphigus vulgaris or bullous pemphigoid, two autoimmune blistering skin diseases that are clinically, histologically, and immunochemically distinct from PF. However, rabbit antiserum directed against DGI, that was isolated from bovine muzzle desmosomes, stained a polypeptide band which co-migrated with PF antigen. Furthermore, when proteins from extracts of normal human epidermis were electrophoresed in two dimensions (isoelectric focusing, then SDS-PAGE) before transfer to nitrocellulose for immunoperoxidase staining, PF antibodies and antibodies to DGI stained identical spots. Finally, PF sera as well as PF IgG that was affinity purified with PF antigen from normal human epidermis, both selectively bound to DGI extracted from bovine muzzle desmosomes. These studies demonstrate that the human autoantibodies from certain patients with PF, a disease of epidermal cell adhesion, are directed against a desmosomal core protein.

Cohesion of horny cells during comedo formation. An electron microscope study

Cohesion between horny cells was studied in experimentally induced comedones, from the rabbit's external ear canal. It occurred in two different ways: initially, by the persistence of desmosones and desmonosmal bodies (fusiform electron dense bodies), which loosely held the horny cells together; later, and to a lesser extent, by tight junctions, which tightly bound the horny cells together. A gradual decrease in the numbers of membrane coating granules was observed.

The ultrastructure of the interfollicular epidermis of the hairless (hr/hr) mouse. V. The cytoplasm of the horny cells

The ultrastructure of horny cells in the interfollicular epidermis of the hairless mouse and in the mouse with hair has been studied with particular emphasis on changes in the cytoplasm through the horny layer. Horny cells from the two strains have a similar appearance, and the horny layer can be divided into three sublayers, each with a different ultrastructure. It is suggested that in vivo the same arrangement of densely packed filaments and fibrils which represents the keratin pattern in the basal sublayer is preserved throughout the horny layer. However, the filaments and interfilamentous substance seem to undergo a continuous transformation, which possibly results in a disintegration of the filaments when desquamation of the uppermost cell takes place.