Two-dimensional analysis of proteins of rat oral epithelia and epidermis

Filaggrin failure - from ichthyosis vulgaris to atopic eczema and beyond

The main proteinaceous component of the keratohyalin granules within the granular layer keratinocytes of the epidermis is the giant, repetitive polyprotein profilaggrin. When granular layer cells commit to terminal differentiation to form the flattened squames of the stratum corneum, profilaggrin is rapidly cleaved into multiple copies of the 37 kDa filaggrin monomer, which binds to and condenses the keratin cytoskeleton, thereby facilitating cellular compression. Within the stratum corneum, filaggrin is broken down to form natural moisturising factor, a pool of amino acids and derivatives thereof that exerts multiple effects. Filaggrin is therefore essential for normal stratum corneum biogenesis and physiology. In 2006, the McLean group identified the first loss‐of‐function mutations in the filaggrin gene (FLG) as the cause of the common monogenic genodermatosis ichthyosis vulgaris (IV). In parallel, they showed by multiple methods that these mutations, carried by up to 10% of various human populations are the major genetic predisposing factor for atopic dermatitis (eczema) and all of the associated allergic phenotypes that constitute the atopic diathesis. This paradigm‐shifting work showed that skin barrier deficiency is a major early event in the pathophysiology of eczema and allergy.

What is already known?

Filaggrin is a critically important, multifunctional protein required for the normal biogenesis and physiology of the stratum corneum.

What does (recent) work tell us?

Loss‐of‐function mutations in the filaggrin gene are common in the human population and cause clinically dry skin, ichthyosis vulgaris and importantly, are a major genetic predisposing factor for atopic dermatitis and its associated allergic conditions. This work revealed that skin barrier deficiency is the major pathomechanism underlying atopic disease.

Characterisation of the rat oesophagus epithelium antigens defined by the so-called 'antikeratin antibodies', specific for rheumatoid arthritis

OBJECTIVES

An attempt was made to characterise the antigens recognised by serum IgG antibodies directed to the stratum corneum of rat oesophagus epithelium, the so-called 'antikeratin antibodies', which were shown to be highly specific for rheumatoid arthritis (RA) and thus to have an actual diagnostic value.

METHODS

Immunoblotting was performed with RA serum samples on different extracts of rat oesophagus epithelium separated by various monodimensional and two dimensional electrophoreses.

RESULTS

Three low-salt-soluble antigens sensitive to proteinase K and, therefore, of protein nature were identified. Two proteins, with apparent molecular masses of 210 and 120-90 kilodaltons, shared isoelectric points ranging from 5.8 to 8.5; the third protein exhibited isoelectric points from 4.5 to 7.2 while its molecular mass ranged from 130 to 60 kilodaltons. Immunoadsorption of RA serum samples onto cytokeratins extracted from the stratum corneum of rat oesophagus epithelium did not change their immunoreactivity towards the three antigenic proteins. Widely used deglycosylation and dephosphorylation methods failed to modify either the electrophoretic migration of the proteins or their immunoreactivity with RA serum samples.

CONCLUSION

The so-called 'antikeratin antibodies' do not react with cytokeratins. They specifically recognise three late epithelial differentiation proteins which had not been previously described. These proteins may be related to (pro)filaggrin.

Effect of zinc deficiency on keratins in buccal epithelium of rats

Weanling rats fed a zinc-deficient diet (less than 1 part/10(6)) for 4 weeks develop parakeratotic and hyperplastic buccal epithelium with increased mitotic activity. Normal buccal epithelium contains major keratin polypeptides of 56, 46 and 43 kDa. Four-week zinc-deficient rats lacked the 43 kDa keratin. It appears that the 46 and 43 kDa keratins are related, differing as a result of some post-translation modification. A proteolytic cleavage of the 46 kDa keratin to the 43 kDa species is the most likely mechanism. The findings point to a decrease of keratinolytic enzyme activity in the zinc-deficient rats.

Filaggrin expression in cutaneous and mucosal human papillomavirus induced lesions

A series of 32 human papillomavirus induced lesions derived from epidermis and mucosa was studied for the modulation of filaggrin-profilaggrin (F-PF) expression according to the degree of virus infection as compared to normal skin and mucosa biopsies. This investigation was carried out on frozen sections using indirect immunofluorescence for filaggrin detection and group specific viral antigen and by in situ hybridization with biotinylated probes for viral DNA detection and typing. The 9 cutaneous warts showed an increase of F-PF expression in upper layer cells as compared to normal epidermis, which could be related to the high production of virus (viral antigen and HPV types 1 or 2). The 5 condyloma acuminata displayed also an enhanced expression of these components which was located in several upper layers but virus infection was confirmed in 2 of them with HPV types 6, 11 or 16. The 6 laryngeal papillomas exhibited a granular reactivity pattern for F-PF in suprabasal cell layers with an increase in the upper layers; viral antigen was found in 4 cases and HPV DNA types 6, 11 or 16 were detected in 4 specimens. Conversely among 12 cervical intraepithelial neoplasia, F-PF was expressed only in very superficial layers in few cases, without any correlation with the DNA detection (6, 11 or 16, 18). Taken together these data are suggestive of an intense expression of F-PF in benign lesions which can replicate the virus and a discrete or an absent expression of these components in premalignant or malignant lesions.

Site-specific distribution of epithelial cell-surface carbohydrates in rat oral mucosa

The binding of two fluorescein-labelled lectins to epithelial cell surfaces was examined microspectrofluorimetrically in rat oral mucosa. Griffonia simplicifolia (GS-I-B4), which is specific for alpha-D-galactosyl end groups, labelled only basal cells, while Ulex europaeus (UEA-I), which is specific for alpha-L-fucosyl groups, labelled only spinous cells. The degree of binding of the lectins was dependent on the lectin concentration and the lectin pH. Different sites were examined. The labelling of basal cells by GS-I-B4 was maximal on the lateral borders of the tongue, and the fluorescence diminished medially; in contrast, the UEA-I labelling of the corresponding spinous cells was of undiminished intensity in the mediolateral direction across the entire lingual epithelium. There was a gradual increase in the binding of GS-I-B4 and UEA-I towards the posterior aspect of the tongue. In the mid-palate, there was stronger staining both of basal cells by GS-I-B4 and of spinous cells by UEA-I in the gingivae as compared to the centre of the palate. In anteroposterior sections of the fore- and mid-palate, the fluorescence intensity of basal cells was inversely related to that of spinous cells, with maximal labelling of basal cells by GS-I-B4 and corresponding minimal binding of spinous cells by UEA-I being evident at the crests of the transverse rugae, and the opposite pattern of staining by both lectins being noted at the bases of the rugae.(ABSTRACT TRUNCATED AT 250 WORDS)

Staining patterns of rodent squamous epithelia by monoclonal anti-keratin antibodies

Anti-keratin staining patterns were examined by immunofluorescence in the epidermis, oral mucosa and forestomach of rats and mice by monoclonal antibodies AE1 and AE2. In contrast to human tissues enzymatic pretreatment of sections was necessary even when fresh-frozen tissue was used, suggesting masking of the antigens in vivo. AE1 stained the cytoplasm of spinous cells in most epithelia, whereas basal cell staining varied. AE2 showed suprabasal cytoplasmic staining in epidermis, forestomach and palate, whereas the other epithelia were stained only in keratohyalin granules and membranes of cornified cells. In some epithelia a small number of irregularly distributed basal cells stained positive with AE2, indicating heterogeneity in the basal cell compartment. Thus, the anti-keratin staining pattern varies both regionally and, as earlier shown in human epithelium, with the stage of maturation of cells within a given epithelium. The present study provides a basis for further studies of epithelial differentiation during normal and pathologic development.

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.

Keratin proteins in human oral mucosa

We have examined the keratin proteins in normal human oral mucosa from 6 different regions including hard palate, buccal mucosa, tongue, gingiva and floor of the mouth. Urea-dithiothreitol extracts of EDTA separated epithelia were analysed by SDS-PAGE and immunoblotting. Eight samples from each region were investigated and showed very little individual variation in the keratin profile on Coomasie Blue-stained gels. The keratinizing hard palate and gingiva expressed identical patterns and resembled the pattern of epidermis from the flank region. The normally non-keratinizing buccal mucosa and the mucosa of the floor of the mouth expressed polypeptides distinctly different from those of the keratinizing epithelia and lacked the high molecular weight keratins. The dorsal surface of the tongue and the commissure region showed a pattern intermediate between keratinizing and non-keratinizing epithelia. The greater sensitivity of the immunoblotting technique revealed that the non-keratinizing epithelia synthesized one of the high molecular polypeptides and that the tongue produced all the bands found in keratinizing epithelia, but in very small quantities. There are, thus, distinct differences in the keratin expression of oral epithelia which are related to the pattern of keratinization assessed histologically.

Regional variations of cell surface carbohydrates in human oral stratified epithelium

The distribution of blood group carbohydrate chains with antigen A, B, H type 2 chain (A and B precursor), and N-acetyllactosamine (H type 2 precursor) specificity was studied in human oral epithelium from different anatomical regions. These represented various epithelial differentiation patterns such as non-keratinized, parakeratinized, and orthokeratinized stratified squamous epithelium. The material included buccal and palatal epithelium from 20 persons with blood group A or O, gingival, and alveolar epithelium from 10 persons with blood group A or B, and buccal metaplastically keratinized epithelium from nine blood group A, two blood group B, and nine blood group O individuals. The blood group carbohydrate chains were examined in tissue sections by immunofluorescence microscopy. The A and B blood group antigens were detected by human blood group sera, and antigen H type 2 chains and N-acetyllactosamine by murine monoclonal antibodies. Each antigen showed a similar staining pattern in buccal and alveolar epithelium (non-keratinized) which differed considerably from that seen in palatal and gingival epithelium (ortho- and parakeratinized). The expression of blood group antigens A or B and the precursor antigen H type 2 chains in metaplastically keratinized buccal epithelium was found to differ significantly from that seen in normal non-keratinized buccal epithelium. The regional variations demonstrated in cell surface carbohydrates are suggested to reflect differences in tissue differentiation.

Electrophoretic study of keratin polypeptides in chemically-induced oral carcinomas in the hamster

Comparison was made of the electrophoretic keratin polypeptide patterns of normal hard palate epithelia from three hamsters and of eight palatal squamous cell carcinomas induced by 7,12-dimethylbenz(a)anthracene (DMBA) treatment. Keratin polypeptides from normal epithelia had a molecular weight range of about 48,000 to 70,000. In the tumour extracts, the large polypeptides (above 61,000) found in the normal epithelia were absent, but the majority of other small polypeptides below 61,000 were expressed. Three as yet undefined polypeptides, in the range of 40,000 to 70,000, were detected in tumour extracts, but not in extracts of normal palatal mucosa. The keratin polypeptide electrophoretic alterations in carcinomas of hamster palatal mucosa are similar to those reported for extra-oral carcinomas in other animal species.

Keratin pattern in human and buccal and hard palate mucosa

As a preliminary study the keratin proteins of human oral stratified epithelia from buccal mucosa and hard palate were investigated using SDS-PAGE technique. The keratinized hard palate consistently showed six polypeptides varying in molecular weight from 47 to 67 k daltons, whereas the nonkeratinized buccal epithelium lacked the larger polypeptides and showed three polypeptides with molecular weight from 50 to 56 k daltons. The individual variations in the SDS-gel pattern from eight clinically normal individuals were restricted to minor quantitative differences.

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

The indirect fluorescent-antibody technique was used to locate histidine-rich basic protein, filaggrin. In the newborn, immunofluorescence was seen in the cornified layers and in keratohyalin granules throughout the mouth using antibody specific for epidermal filaggrin, a distribution similar to that in epidermis where it is thought that filaggrin functions as the keratin matrix protein. In the adult immunofluorescence was in keratohyalin granules of palate, buccal and tongue epithelium but in the stratum corneum was limited to the soft palate with weak, patchy areas in the densely keratinized epithelium of the hard palate and tongue. Immunofluorescence was delineated at the boundary between the soft and hard palates. A protein apparently identical to epidermal filaggrin was identified in extracts of newborn palate by its mobility on sodium dodecyl sulphate-polyacrylamide gels and subsequent reaction with the antibody used for immunofluorescent studies. This protein was not detected in extracts of adult oral epithelia. Both newborn and adult tissues contained high mol. wt cross-reactive protein, suggestive of the filaggrin-precursor protein extractable from keratohyalin granules. The distribution of filaggrin was consistent with its function as a keratin matrix protein in the newborn oral epithelium and some less densely keratinized regions of the adult. However, in the adult mouth, filaggrin is not detectable in the stratum corneum of the most densely keratinized regions. Thus, the protein must be lost or its antigenic sites altered with maturation of the animal, depending on the type and extent of keratinization.