Distribution of histidine-rich basic protein, a possible keratin matrix protein, in rat oral epithelium

Peptidylarginine deiminase is involved in maintaining the cornified oral mucosa of rats

BACKGROUND AND OBJECTIVE

Epithelial cells derived from different regions exhibit marked differences in their differentiation capacity, allowing them to provide a suitable protective barrier. We aimed to clarify the role of peptidylarginine deiminase (PAD) in modifying the key epidermal proteins filaggrin (FLG) and keratin 1 (K1) during stratification of the rat palate and buccal mucosa.

MATERIAL AND METHODS

We performed immunofluorescence, immunoblotting, PAD activity assays and 2-dimensional electrophoresis, and developed an organotypic culture model.

RESULTS

PAD1 expression was highest in the palate, whereas PAD2, PAD3 and PAD4 expression was highest in the skin, suggesting the tissue-specific expression of PAD isozymes that leads to differences in calcium dependency. Immunoblotting showed that the FLG monomer, as well as its degradation products and precursor (proFLG), were most abundantly expressed in the skin but had low expression in the palate, whereas only faint proFLG expression was detected in the buccal mucosa. FLG and K1 were colocalized with PAD1 and were likely to be citrullinated in the cornified layers of the skin; this colocalization was not detected on the palatal surface, and dot-like presence of proFLG that might be citrullinated and that of PAD1 were found in the granules of the palate. Organotypic models derived from the rat palate revealed that PAD inhibition reduced the breakdown of FLG, increased its association with K1 together with epithelial compaction, and decreased permeability in a dye permeability assay. Conversely, PAD stimulation had the opposite effects.

CONCLUSION

Citrullination is likely a protein modification that plays an important role in maintaining the structure and function of oral cornified mucosa in a way that is distinctly different from that of the skin.

Tissue markers of potentially malignant human oral epithelial lesions

Tissue markers of potential malignancy have been sought for many years. Cell surface markers, particularly blood group and histocompatibility antigens, have shown great promise and several squamous carcinoma antigens have been identified--but not fully studied in potentially malignant lesions. Growth factors and receptors also need further study. Cytoplasmic markers of potential malignancy have been examined and, of these, keratins, filaggrin, and some carcinoma antigens show most promise. Nuclear analyses have promise but are time-consuming and expensive. Image cytometric analyses appear to be sensitive and predictive: oncogene and tumour suppressor analyses remain to be fully evaluated. New investigative techniques at the cellular and molecular level show increasing promise at defining potentially malignant oral epithelial lesions but more prospective studies are required.

Fine structure of the dorsal lingual epithelium of the crab-eating monkey, Macaca irus

Light and electron microscopic observations of the dorsal lingual epithelium of the crab-eating monkey, Macaca irus, revealed three different regions: the epithelium on the anterior side of the filiform papillae, the epithelium on the posterior side of the filiform papillae, and the interpapillar epithelium. Whereas the basal and suprabasal cells are similar throughout, differences characterize the intermediate and surface layers. Keratohyalin granules appear predominantly in the intermediate layer of the epithelium on the anterior side of filiform papillae. In the epithelium on the posterior side of the filiform papillae, no keratohyalin granules are seen and, instead, tonofibrils are prominent. The cells begin to be significantly flattened. In the interpapillar epithelium, no keratohyalin granules and tonofibrils are seen, and the tonofilaments occupy almost the entire cytoplasm of the cells of the intermediate and surface layers, with the cells having larger volumes in these layers.

Fine structure of the dorsal lingual epithelium of the domestic, newborn kitten, Felis catus

The tip and the body of the tongue of the domestic kitten, Felis catus, were examined by light and transmission electron microscopy. On the tip of the tongue, no filiform papillae were observed, but the connective tissue papillae of the lamina propria were recognized. On the lingual body, there were filiform papillae composed of an anterior, a posterior and interpapillar epithelium. Under the transmission electron microscope, the epithelium on the tip of the kitten tongue was found to be of the stratified squamous type. The epithelium contained no cells filled with keratin fibers. In the lingual body, the interpapillar epithelium contained very few keratohyalin granules, and no cells with keratin fibers. In the epithelium on the anterior side of the filiform papillae, numerous keratohyalin granules appeared in the intermediate layer. In the surface layer, a thin layer of typical keratinized cells was visible. In the epithelium on the posterior side of the filiform papillae, a thick layer of keratinized cells was located on the surface layer.

Biosynthetic pathways of filaggrin and loricrin--two major proteins expressed by terminally differentiated epidermal keratinocytes

We have used immunoelectron microscopy to map the biosynthetic pathways of loricrin and filaggrin in epidermal keratinocytes at successive stages of differentiation in newborn mouse skin. The filaggrin epitope is first detected in large, irregularly shaped, keratohyalin granules (F-granules) in the stratum granulosum, and then distributed throughout the cytoplasms of the innermost layers of stratum corneum cells. We conclude that the poly-protein filaggrin precursor is first accumulated in F-granules, from which it is subsequently released and processed into filaggrin, and becomes associated with the densely packed bundles of keratin filaments inside stratum corneum cells. Its diminished visibility in the outer layers correlates with the known degradation of filaggrin to free amino acids. Loricrin is first detected in small round keratohyalin granules (L-granules), and subsequently at the periphery of cells throughout the stratum corneum. Labeling of purified keratinocyte envelopes establishes that this loricrin epitope is exposed only at their inner (cytoplasmic) surface. Thus loricrin is initially accumulated in L-granules, to be released at a specifically programmed stage of keratinocyte maturation, and incorporated into the covalently cross-linked lining of the cell envelope. Since loricrin is rich in cysteine, L-granules account for the sulfur-rich keratohyalin granules described earlier. Proposals are made to rationalize why, subsequent to synthesis, filaggrin precursor and loricrin should be segregated both from each other and from the rest of the cytoplasm.

Expression of hair-related keratins in a soft epithelium: subpopulations of human and mouse dorsal tongue keratinocytes express keratin markers for hair-, skin- and esophageal-types of differentiation

The dorsal surfaces of mammalian tongues are covered with numerous projections known as filiform papillae whose morphology varies in different species. Using a panel of monoclonal antibodies to keratins as probes, we have established that, in both human and mouse, the interpapillary epithelia express mainly the "esophageal-type" keratins, while the papillary epithelia express "skin-type" keratins as well as some keratins reacting with a monoclonal antibody (AE13) to hair keratins. The AE13-reactive proteins of the mouse were found to be very similar to those of authentic mouse hair keratins. However, the corresponding protein of human tongue appears to be different from all known human keratins. This protein has a MW of 51K; it is relatively acidic; it is sulfhydryl-rich, as revealed by iodoacetic acid-induced charge and apparent size shift; it shares an epitope with all the known acidic human hair keratins; and it is associated with keratin fibrils in vivo. This protein may therefore be regarded as a novel type I "hard" keratin. These data establish that mammalian dorsal tongue epithelia can be divided into at least three compartments that undergo mainly "esophageal-", "skin-" and "hair"-types of differentiation. Different keratin filaments, e.g., those of the esophageal- and hair-types, exhibit strikingly different degrees of lateral aggregation, which can potentially account for the different physical strength and rigidity of various cellular compartments. Our data also suggest the possibility that variations in papillary structure in human and mouse may arise from different spatial arrangements of specific keratinocytes, and/or from the expression of specialized hair-related keratins.

The morphological details of globular keratohyalin granules

In quickly dividing epithelia such as that of the tongue, keratohyalin formation takes place in globular keratohyalin granules (KHG). This is in contrast with the irregular KHG as seen in normal, slowly dividing epidermis. The morphogenesis of the globular KHG is explained in this study. In small KHG, dense aggregates of ribosomes can be seen at the site of blebs. It is suggested that these blebs framed with ribosomes are internalized giving rise to "dense homogeneous deposits" or "single granules". Lipid droplets occur in the upper spinous and horny layer. Globular KHG also contain variable amounts of lipids, and the lipid content seems to be inversely related to the protein content, dependent on the degree of cell differentiation or on the rate of cell turnover. It is suggested that in epithelia with a high cell turnover few rigid keratohyalin components are dispersed in lipids, which maintain a globular shape due to the surface tension.

Immunologic localization of filaggrin in human oral epithelia and correlation with keratinization

Localization of filaggrin, a human epithelial structural protein, was investigated by indirect-immunofluorescence microscopy of oral mucosa. Thirty specimens were tested, 10 each of palate, gingiva, and buccal mucosa. Orthokeratinized and parakeratinized specimens displayed immunofluorescence within the stratum corneum, stratum granulosum, and upper stratum spinosum. Within the stratum corneum, the reaction was diffuse. Within the stratum granulosum and spinosum, the reaction was in a granular pattern, in a perinuclear position. Several of the nonkeratinized specimens had a negative reaction; however, most displayed a very weak, scattered reaction in a granular pattern within the most superficial cells. The presence of filaggrin in keratinized palate was confirmed by immunoblot studies with the same antibody. Profilaggrin was detectable in representative nonkeratinized and parakeratinized oral tissues, as well as in keratinized palatal epithelium. The localization of filaggrin is consistent with its possible function as the interfilamentous matrix protein within cells of the stratum corneum, and with its derivation from a cross-reactive precursor protein stored in keratohyaline granules. A strong positive correlation was found between the degree of keratinization and the amount of immunofluorescence; therefore, filaggrin and related antigens may be useful and sensitive marker proteins for epithelial keratinization.

Immunohistochemical localization of keratin in the taste buds of rat vallate papillae

Keratin detected with anti-human whole keratin serum, raised in rabbits by injection of the isolated human whole keratin, was used as a histologic marker to study the origin of the cells in taste buds. Rat vallate papillae, including surrounding tissue, were processed for indirect immunofluorescent staining of ketatin. In the taste buds, most basal cells and some of the elongated cells were immunoreactive with anti-keratin serum, showing that most taste-bud cells, if not all, originate from cells of epithelial origin.

Composite keratohyaline granules in palmoplantar keratoderma: an ultrastructural study

We report the results of an ultrastructural study of the hyperkeratotic epidermis in 23 cases of palmoplantar keratoderma (PPK) comprising 8 inherited keratoderma, 8 keratoderma climactericum in menopausal women and 7 symptomatic keratoderma. In all but one of the cases of inherited PPK and keratoderma climactericum, composite keratohyalin (KH) granules were found in granular cells of the interductal epidermis, which were similar to those found in the rat and in some other conditions. In the cases of symptomatic keratoderma, e.g. secondary to eczema, the appearance of the KH granules did not differ from that of granules observed in two normal plantar skin samples. While the real role played by these granules is unknown, they could constitute a differentiation marker of intraepidermal duct cells, and their abundance in PPK suggest that intraepidermal sweat ducts may play a part in PPK histogenesis.