Ultrastructural observations on the enzymatic activity of keratinosomes

Effects of arotinoid ethyl ester on epithelial differentiation and proliferation

In recent years the search for new retinoids, safer and more potent than the available compounds, has led to the development of arotinoids. In preliminary clinical trials, arotinoid ethyl ester [(E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1- propenyl]benzoic acid ethyl ester; TTNPB ethyl ester] was found to be highly effective in the treatment of severe and etretinate-resistant dermatoses. Using adult hairless mice, embryonic mouse limb-bud cultures and keratinocyte cultures as experimental models, we have performed morphological, autoradiographic and biochemical studies on the effects of arotinoid ethyl ester on epithelial differentiation in vivo and in vitro. Arotinoid ethyl ester stimulates proliferation of both embryonic and adult mouse epidermis. However, it inhibits the differentiation of embryonic epidermis and enhances that of adult epidermis. Arotinoid ethyl ester induces a decrease in the cyclic AMP content of cholera toxin-stimulated keratinocytes but fails to alter cyclic AMP concentrations in keratinocytes not treated with cholera toxin.

Cohesion and desquamation of epidermal stratum corneum

This article attempts to provide a comprehensive review on the roles of various classes of molecules in the cohesion and desquamation of the stratum corneum. In the first part of this monograph we review the field of epidermal differentiation in vivo and vitro, describing the expression and functions of a number of key structural molecules that characterize the process. In the second part we emphasize terminal differentiation and the biogenesis of the stratum corneum. The stratum corneum is a cell layer unique to fully differentiated squamous epithelia such as skin. While it is a dead stratum, it nevertheless is in a homeostatic process of continual shedding and renewal in synchrony with basal cell replication. It is also a degradative layer containing many proteinases and glycosidases in which a variety of intracellular and intercellular macromolecules are degraded. We highlight the molecules localized within the intercorneal matrix that are most likely to play a role in cohesion and desquamation, including: glycoproteins, lipids and enzymes. Because it is difficult to study the stratum corneum and desquamation in the native tissue, we discuss a number of model systems that have been used. The stratum corneum can be dispersed into single squames in different ways; these include mechanical dispersion as well as agents such as detergents and enzymes. The solubilized molecules and the structures remaining can then be studied as to their specific roles in desquamation. Using this approach it is possible to reconstitute multilayered structures that resemble a real stratum corneum. We have shown that glycoproteins play a key role in squame reaggregation and that this process can be modulated with amino sugars in a lectin-like fashion. Cohesion and desquamation can also be studied in tissue culture. Depending on the culture system, the extent of terminal differentiation and squame accumulation varies. Yet desquamation does not normally occur. It can be induced however by the inclusion of exogenous agents such as IFN-gamma which are found in the native epidermis but are absent in vitro. Modulation of desquamation by other exogenous agents is likely to yield further knowledge of how shedding occurs in vivo. Insight has also come from studies of scaling skin disorders. The glycoprotein and lipid profiles are altered in the stratum corneum in many diseases of aberrant terminal differentiation. A number of abnormalities in the levels of cytokines and growth factors have also been reported in the lesional tissue of such diseases.(ABSTRACT TRUNCATED AT 400 WORDS)

An electron microscopic study of experimentally-induced comedo and effects of vitamin A acid on comedo formation

The mechanisms of comedogenesis and comedolysis were investigated at the ultrastructural level after applying oleic acid (OA) only, or oleic acid together with vitamin A acid (VAA), to rabbit ears daily for two weeks. 1) In the follicular epithelium of the experimentally-induced comedo (EIC) by OA, several ultrastructural changes similar to those in human comedo were observed. EIC in rabbit ears appeared to be induced both by the hyperkeratinization of the follicular epithelium and by the delayed desquamation of horny cells due to the persistence of intercellular binding apparatus. 2) VAA strongly inhibited the formation of EIC. In the follicular epithelium, two different types of changes, non-cohesive hyperkeratinization and inhibition of keratinization, were observed. These represent the cell injury and recovery stages, respectively. VAA induced the disturbance of follicular epithelial keratinization and reduction of intercellular bindings between horny cells. These effects might prevent the cohesion and accumulation of horny cells and inhibit EIC formation. 3) The number of Odland bodies (Ods) showed an inverse correlation with the cohesion of horny layer. These findings support the theory that Ods have a desquamating function as extracellular lysosomes. The change in Ods would also contribute to both EIC formation by OA and the inhibition by VAA. In addition, VAA caused a characteristic increase in Ods with lamellar structures. It is suggested that Ods with lamellar structures have a desquamating function.

Histologic and electron microscopic characterization of the antiperinuclear factor antigen

The presence of the antiperinuclear factor, an autoantibody that recognizes cytoplasmic antigens, was detected in sera from patients with rheumatoid arthritis (59%), seronegative rheumatoid arthritis (36%), systemic lupus erythematosus (46%), systemic sclerosis (26%), and in nonautoimmune controls (10%). The antigenic perinuclear granules were found in the stratum intermedium layer of the buccal mucosa. Granules exhibited histologic features of nucleoproteins, stained for ribonucleoprotein, and showed the ultrastructural characteristics of aggregated rough endoplasmic reticulum. The antiperinuclear factor may recognize a common autoantigen in connective tissue disease.

Morphological variations and population density of membrane-coating granules in human gingival sulcular epithelium

Surgically excised specimens of sulcular wall with minimal inflammatory response as judged by clinical then histological criteria were processed for electron microscopy. The specimens were divided into crestal, middle and cervical areas of the sulcular epithelium. The highest concentration of membrane-coating granules was found in the upper spinous cell layers of sulcular epithelium. The profiles of these granules showed examples of both classical keratinized (lamellated) and non-keratinized (non-lamellated) forms but also other appearances that were not derived from them through differences in the plane of section. The population of granules decreased between the crestal and cervical zones, and the decrease in number was marked for the lamellated granules. This decrease in numbers of membrane-coating granules, together with the wider intercellular spaces, may be the reason why the sulcular epithelium is most permeable in the cervical region.

Association of a basic 25K protein with membrane coating granules of human epidermis

Keratinocytes of the upper granular layers contain unique round-to-oval granules, 100-500 nm in diameter, in their peripheral cytoplasm. These granules (known as membrane coating granules [MCG], or lamellar granules) fuse with the apical cell surface of uppermost granular cells and discharge their contents into the intercellular space, where they are believed to play a role in establishing the permeability barrier of the epidermis and possibly in regulating the orderly desquamation of terminally differentiated keratinocytes. Using two monoclonal antibodies originally prepared against hair follicle antigens, we have identified a 25K epidermal protein in association with both MCG-like granules in the peripheral cytoplasm of granular cells as well as MCG-derived intercellular material. This protein is relatively basic (pI greater than 8), largely aqueous soluble, methionine deficient, and is relatively abundant in epidermis (comprising up to approximately 0.1% of soluble proteins). Its distribution is restricted to the granular layer of keratinized (cornified) stratified squamous epithelia. The identification of this protein component opens new avenues for studying the molecular mechanisms underlying the establishment of permeability barrier and/or regulation of desquamation.

Lipid composition and acid hydrolase content of lamellar granules of fetal rat epidermis

Lipids and acid hydrolases have been characterized in a subcellular fraction, enriched with lamellar granules (LG), derived from fetal rat epidermis. This fraction contains 23% glycosyl ceramides and ceramides, 15% free sterols, and 34% phospholipids. The lipid/protein ratio is 2.0. The sterols and sphingolipids were present in proportions similar to those previously reported in stratum corneum. These findings provide direct biochemical evidence for the widely accepted hypothesis that stratum corneum lipids are derived from exocytosis of lamellar granules into the intercellular space. The LG fraction was enriched in certain acid hydrolases including glucosidase, acid phosphatase, phospholipases A, and sphingomyelinase; other acid hydrolases, i.e., amino-glycosidases, glactosidase and aryl sulfatase (pH 5.5), and steroid sulfatase were not preferentially localized in this fraction. By modulation of phospholipids, glycolipids, and proteins in the membrane regions of stratum corneum, the acid hydrolases of LG may play a role relevant to the function and desquamation of stratum corneum.

Lamellar body-enriched fractions from neonatal mice: preparative techniques and partial characterization

Several problems have frustrated the isolation of lamellar bodies (LB) from mammalian epidermis. We obtained pellets enriched in intact LB by utilizing the staphylococcal epidermolytic toxin to provide intact, outer epidermal sheets, by controlled homogenization in a cell disrupter, and by passage of homogenates through a graded series of nuclepore filters (Science 221:962, 1983). Such preparations contained more intact LB than did fractions prepared by a variety of differential or sucrose/metrizamide discontinuous centrifugation methods. Initial characterization of the enzymatic content of this fraction revealed it to be enriched in certain hydrolytic enzymes (acid phosphatase, carboxypeptidase, cathepsin B, acid lipase, sphingomyelinase, and phospholipase A), but strikingly depleted in all sulfatases, beta-glucuronidase, and the non-lysosomal protease, plasminogen activator. Thus, LB show some properties of lysosomes, although certain characteristic lysosomal enzymes are strikingly absent. Lamellar body fractions contained 2-3 times more lipid per unit weight than did homogenates, and were enriched in phospholipids, free sterols, and glycosphingolipids, but not in other neutral lipids or ceramides. In summary, whereas some of the enzymes in LB could participate in the metabolism of LB lipid precursors to hydrophobic barrier constituents, others may attack intercellular constituents, ultimately resulting in desquamation. The lipid profile of these organelles suggests that they deliver precursors of permeability barrier lipids to intercellular domains.

Ultrastructural localization of acid phosphatase in nonhuman primate vaginal epithelium

The vagina of the rhesus monkey is lined by a stratified squamous epithelium. However, little is known regarding the cytochemical composition of its cell organelles and the substances found in the intercellular spaces. In this study we have examined the ultrastructural distribution of acid phosphatase in the vaginal epithelium. In basal and parabasal cells reaction product was found in some Golgi cisternae and vesicles and in a variety of cytoplasmic granules. Reaction product was also found in some, but not all, membrane-coating granules. In the upper layers of the epithelium, the membrane-coating granules extruded their contents and acid phosphatase was localized in the intercellular spaces. The possible roles of acid phosphatase in keratinization, desquamation, or modification of substances in the intercellular compartment are discussed.

A morphometric study of alterations in rough endoplasmic reticulum during differentiation in stratified squamous epithelium

Stereological techniques were applied to investigate several structural parameters characterising the rough endoplasmic reticulum (RER) during differentiation in hamster cheek-pouch epithelium. Mucosal samples from five Syrian golden hamsters were obtained and processed for electron microscopy. Following a strict sampling regime, micrographs were obtained from defined basal, spinous and granular layers, and subjected to stereological point and intersection counting procedures. This enabled volume and surface densities, and volume-to-surface ratios of RER to be determined for each cellular layer. From previous estimates of the mean cytoplasmic volume of the "average" basal, spinous and granular cell in this tissue, it was possible to calculate the absolute volume and surface area of RER present in these average cells. Both volume and surface densities of RER decreased between basal and granular layers, whereas the total volume and surface area present in the average spinous and granular cell were both higher than in the average basal cell. These data suggest that RER is being synthesised during epithelial differentiation. In view of the role of the RER in the production of exportable proteins, it is possible that increased amounts of this organelle are required to synthesise the enzymes and glycoproteins found in membrane-coating granules, since these are also seen with increasing frequency in successively higher strata.

A qualitative ultrastructural study of the intercellular spaces between epithelial cells treated in vivo with DMBA

One of the features of epithelial dysplasia at the histological level is known as "loss of cellular adherence" in which adjacent epithelial cells appear more widely separated from each other than in normal tissues. In this study we examine the effects of the carcinogen DMBA on the epithelium of the hamster cheek-pouch with particular emphasis on the dimensions of the intercellular spaces. DMBA-induced lesions were processed for electron microscopy and assigned to hyperplasia, dysplasia and carcinoma groups, using defined criteria on toluidine blue-stained 1 micron Araldite sections. Untreated pouches were used as a control. At the light-microscopical level, intercellular spaces in hyperplastic epithelium appeared similar to those present in untreated tissue but increased progressively in dysplastic and carcinomatous lesions. Spaces were generally wider between basal and spinous cells than between granular cells, although wide variations were observed between tissue blocks demonstrating similar histological features and also within adjacent areas of the same block. At the ultrastructural level, untreated and hyperplastic tissue showed only occasional focal separations of adjacent plasma membranes; these spaces were more frequent between cells of lower strata. In sections from dysplasias and carcinomas, spaces were always extensive and were occupied by numerous villous or foliate membrane-bound cytoplasmic extensions. These were often attached to each other by desmosomes of apparently normal morphology but of a lower frequency than in untreated epithelium. The increased epithelial separation as indicated by the increased intercellular spaces during chemical carcinogenesis may be a result of any or all of the following factors: desmosomal disruption or their failure to develop; the production of cell-surface molecules which are less adhesive; inflammatory oedema and direct alterations on intercellular junctions and cell-surface components by infiltrating inflammatory cells.

Zinc iodide-osmium staining of membrane-coating granules in keratinized and non-keratinized mammalian oral epithelium

Specimens of keratinized and non-keratinized oral epithelium were examined in the electron microscope after being stained with zinc iodide-osmium. In both types of tissue, reaction was seen in unmyelinated nerves, in the specific granules of epithelial Langerhans cells and within lysosome-like organelles and small vesicles associated with Golgi systems. In keratinized epithelia, the reaction was also present in the membrane-coating granules and between the deepest cells of the keratinized layer. In contrast, the membrane-coating granules of non-keratinized epithelia lacked Zn iodide-osmium staining despite the presence of reaction in adjacent Golgi systems. It is suggested that Zn iodide-osmium stains glycolipid or glycoprotein material in the cell. This material is elaborated in the Golgi systems from which lysosomes and the membrane-coating granules of keratinized tissues are probably derived.

A method for partial purification of lamellar granules from fetal rat epidermis

A subcellular fraction enriched with lamellar granules was obtained from homogenates of fetal rat epidermis by means of density gradient fractionation in metrizamide. 62% of organelles in this fraction were bounded by single membranes and measured 80-130 nm in the shorter diameter. About 10% of these had characteristic lamellae. Other structures in this fraction were larger vesicles (20%) or smaller organelles and vesicles (18%). The fraction had a low buoyant density (1.08-1.10) suggesting a high lipid content and contained a sharply localized peak of acid phosphatase activity. The 80-130 nm organelles reacted with bismuth after oxidation with periodic acid and were positive for acid phosphatase. Other intracellular organelles (e.g., lysosomes, mitochondria, ribosomes) as well as keratin fibrils and keratohyalin were not present. It is concluded that most of this fraction consists of lamellar granules, permitting for the first time detailed investigations of the composition and metabolism of these organelles.

Staining of oral epithelium with the zinc iodide-osmium reaction

Some of the parameters affecting the staining of keratinized oral epithelium with the zinc iodide-osmium reaction were examined using light and electron microscopy and electron probe microanalysis. Factors examined were block size, incubation temperature and the effect of aldehyde prefixation. Large blocks (4 mm cube) were subdivided after incubation and the staining of the centre and edge compared. Generally the reaction was more variable at the edge than in the centre. Small block (1 mm cube) showed a more intense reaction when incubated at 24 degrees C than at 4 degrees C. In all these preparations, final reaction product was seen over Golgi systems, lysosome-like bodies, membrane-coating granules and, in the more intensely stained regions, over endoplasmic reticulum and nuclear membranes as well. In prefixed material, mitochondria were frequently stained in addition to the other organelles. Energy dispersive analysis showed the reaction product to be similar in all preparations and to contain high levels of zinc and osmium but not iodine.

Simultaneous expression of two different types of intermediate sized filaments in mouse keratinocytes proliferating in vitro

The intermediate-sized filaments present in epidermal keratinocytes derived from mouse skin and in an established cell line (HEL) derived from spontaneous transformation of murine keratinocytes grown in vitro, have been examined by immunofluorescence microscopy, using antibodies directed against subunit proteins of different classes of intermediate-sized filaments, as well as by electron microscopy and gel electrophoresis of cytoskeletal preparations highly enriched in intermediate-sized filaments. The keratinocytes derived from neonatal skin, which are capable of only limited replication in vitro, show only a single type of intermediate-sized filaments, i.e., the tonofibril-like arrays of filaments containing prekeratin. HEL cells, which proliferate indefinitely in vitro, retain the tonofilament-like structures typical of differentiated epidermal cells but in addition display intermediate-sized filaments of the vimentin type, i.e., the filament system typically found in mesenchymal and mesenchyme-derived cells. We discuss the possibility that (i) the advent of vimentin-type filaments in epidermal cells in culture is related either to the transformed state or the in vitro growth conditions as such and (ii) other differentiated epithelial cells proliferating in vitro may have more than one system of intermediate-sized filaments.

Cumulative effect of surfactants on cutaneous horny layers: lysosome labilizing action

In order to analyze the role of various surfactants in the abnormal desquamation process of the epidermis in keratodermia type hand dermatitis, the lysosome labilizing effect of surfactants has been investigated by measuring the release of enzymes from lysosomes in vitro using spectrophotometric and gel chromatographic techniques. It has been found that the labilizing effect of surfactants decreases in the order of cationic, anionic, and nonionic surfactants and varies with its alkyl chain length. The relationship of the labilization and skin roughness inducing effect is also discussed.

The light and electron microscopic distribution of acid phosphatase activity in human normal oesophageal epithelium

Acid phosphatase activity in human normal oesophageal epithelium was studied with light and electron microscopic techniques. The maximum activity was found to be in the prickle and lower functional layers. Electron microscopic examination revealed activity to be localized in GERL, lysosomes and membrane coating granules. These last structures probably secreted their content into the intercellular space in the central part of the functional layer. Thick sections (0.5 micron) with tilting showed GERL to consist of anastomosing tubules.

Concanavalin A and ricinus communis receptor sites in normal human oral mucosa

Fluorescein conjugates of concanavalin A (Con-A) and Ricinus communis fraction 120 (RCA120) were shown to bind to the cell surfaces of basal and spinous cell layers in oral buccal mucosa. Palatal epithelium showed distinct binding to basal and spinous cells; cell membranes in the granular layer occasionally bound Con-A and always RCA120. The ultrastructural localization of Con-A binding sites on exfoliated buccal cells was detected by the Con-A peroxidase staining method. The Con-A receptors were seen on the cell surface in association with the outer leaflet of the plasma membrane. The reaction products appeared as a homogeneous, electron-dense layer containing irregularly distributed globules.