New approaches and concepts in the study of differentiation of oral epithelia

Gingival spatial analysis reveals geographic immunological variation in a microbiota-dependent and -independent manner

In mucosal barriers, tissue cells and leukocytes collaborate to form specialized niches that support host-microbiome symbiosis. Understanding the spatial organization of these barriers is crucial for elucidating the mechanisms underlying health and disease. The gingiva, a unique mucosal barrier with significant health implications, exhibits intricate tissue architecture and likely contains specialized immunological regions. Through spatial transcriptomic analysis, this study reveals distinct immunological characteristics between the buccal and palate regions of the murine gingiva, impacting natural alveolar bone loss. The microbiota primarily affects gingival immunity in the buccal region. Additionally, a significant influence of the microbiota on the junctional epithelium facing the oral biofilm offers new insights into neutrophil recruitment. The microbiota also regulates the proliferation and barrier-sealing function of the gingival epithelium. This underscores the presence of immunological niches in the gingiva, with the microbiota differentially influencing them, highlighting the high complexity of this oral mucosal barrier.

Loricrin and Cytokeratin Disorganisation in Severe Forms of Periodontitis

OBJECTIVE

The aim of this research was to investigate the role of the cornified epithelium, the outermost layer of the oral mucosa, engineered to prevent water loss and microorganism invasion, in severe forms of periodontitis (stage III or IV, grade C).

METHODS

Porphyromonas gingivalis, a major periodontal disease pathogen, can affect cornified epithelial protein expression through chronic activation of signal transducer and activator of transcription 6 (Stat6). We used a mouse model, Stat6VT, that mimics this to determine the effects of barrier defect on P gingivalis-induced inflammation, bone loss, and cornified epithelial protein expression, and compared histologic and immunohistologic findings with tissues obtained from human controls and patients with stage III and IV, grade C disease. Alveolar bone loss in mice was assessed using micro-computerised tomography, and soft tissue morphology was qualitatively and semi-quantitatively assessed by histologic examination for several proteins, including loricrin, filaggrin, cytokeratin 1, cytokeratin 14, a proliferation marker, a pan-leukocyte marker, as well as morphologic signs of inflammation. Relative cytokine levels were measured in mouse plasma by cytokine array.

RESULTS

In the tissues from patients with periodontal disease, there were greater signs of inflammation (rete pegs, clear cells, inflammatory infiltrates) and a decrease and broadening of expression of loricrin and cytokeratin 1. Cytokeratin 14 expression was also broader and decreased in stage IV. P gingivalis-infected Stat6VT mice showed greater alveolar bone loss in 9 out of 16 examined sites, and similar patterns of disruption to human patients in expression of loricrin and cytokeratins 1 and 14. There were also increased numbers of leukocytes, decreased proliferation, and greater signs of inflammation compared with P gingivalis-infected control mice.

CONCLUSIONS

Our study provides evidence that changes in epithelial organisation can exacerbate the effects of P gingivalis infection, with similarities to the most severe forms of human periodontitis.

High Glucose Induces Late Differentiation and Death of Human Oral Keratinocytes

Keratinocytes are essential cells for wound repair. Impaired oral wound healing is common in diabetic patients with periodontal disease. High glucose, or hyperglycemia, impairs the cellular function of different cell types. However, it is unknown whether high glucose has a detrimental effect on the functions of oral keratinocytes. In the current study, a human gingival keratinocyte cell line, telomerase immortalized gingival keratinocytes (TIGK), was treated with high glucose (24 and 48 mM) for up to 120 h. Proliferation, migration, cell viability, and production of markers of differentiation, growth factors and enzymatic antioxidants were assessed after high glucose treatment. The results showed that high glucose significantly inhibited TIGK proliferation and migration. High glucose also induced significant cell death through apoptosis and necrosis as determined by flow cytometry, especially at 120 h after high glucose treatment. Necrosis was the dominant form of cell death induced. Real-time PCR showed that high glucose treatment upregulated mRNA expression of late keratinocyte differentiation makers, such as keratin 1, 10, 13 and loricrin, and downregulated enzymatic antioxidants, including superoxide dismutase 1, catalase, nuclear factor erythroid 2 -related factor 2, heme oxygenase 1. In conclusion, high glucose impairs the proliferation and migration of oral keratinocytes and likely induces cell death through the promotion of late cell differentiation and down-regulation of enzymatic antioxidants.

Gene profiling in dorso-ventral patterning of mouse tongue development

BACKGROUND

The tongue is a muscular fleshy organ in the oral cavity that is anatomically divided into the dorsal, ventral, anterior, and posterior part. The intricate tissue organisation and diverse origins of the tongue make it a complex organ of the oral cavity.

OBJECTIVES

To reveal the signalling molecules involved in the formation of the dorsal and ventral parts of the tongue through microarray analysis.

METHODS

Dorsal and ventral tongue tissues were isolated from embryonic day 14 mice by micro-dissection. RNA was extracted from the dorsal and ventral tongue tissues separately for microarray analysis. Microarray data were confirmed by quantitative reverse transcription polymerase chain reaction and whole-mount in situ hybridisation.

RESULTS

Microarray analysis revealed expression of 33,793 genes. Of these, 931 genes were found to be equally expressed in both the dorsal and ventral parts of the tongue. On limiting the fold-change cut-off to over 1.5-fold, 725 genes were expressed over 1.5-fold in the ventral part and 1,672 in the dorsal part of the tongue. The qPCR and whole-mount in situ hybridisation revealed the expressions of angiopoietin 2 (Angpt2), fibroblast growth factor 18 (Fgf18), mesenchyme homeobox gene1 (Meox1), and SPARC-related modular calcium binding 2 (Smoc2) in the ventral part of the tongue.

CONCLUSIONS

Numerous signalling molecules can be selected from our microarray results to examine their roles in tongue development and disease model systems. In the near future, the selection of candidate genes and their functional evaluations will be performed through loss- and gain-of-function mutation studies.

Periodontal disease affects oral cancer progression in a surrogate animal model for tobacco exposure

For decades, the link between poor oral hygiene and the increased prevalence of oral cancer has been suggested. Most recently, emerging evidence has suggested that chronic inflammatory diseases from the oral cavity (e.g., periodontal disease), to some extent, play a role in the development of oral squamous cell carcinoma (OSCC). The present study aimed to explore the direct impact of biofilm‑induced periodontitis in the carcinogenesis process using a tobacco surrogate animal model for oral cancer. A total of 42 Wistar rats were distributed into four experimental groups: Control group, periodontitis (Perio) group, 4‑nitroquinoline 1‑oxide (4‑NQO) group and 4NQO/Perio group. Periodontitis was stimulated by placing a ligature subgingivally, while oral carcinogenesis was induced by systemic administration of 4NQO in the drinking water for 20 weeks. It was observed that the Perio, 4NQO and 4NQO/Perio groups presented with significantly higher alveolar bone loss compared with that in the control group. Furthermore, all groups receiving 4NQO developed lesions on the dorsal surface of the tongue; however, the 4NQO/Perio group presented larger lesions compared with the 4NQO group. There was also a modest overall increase in the number of epithelial dysplasia and OSCC lesions in the 4NQO/Perio group. Notably, abnormal focal activation of cellular differentiation (cytokeratin 10‑positive cells) that extended near the basal cell layer of the mucosa was observed in rats receiving 4NQO alone, but was absent in rats receiving 4NQO and presenting with periodontal disease. Altogether, the presence of periodontitis combined with 4NQO administration augmented tumor size in the current rat model and tampered with the protective mechanisms of the cellular differentiation of epithelial cells.

A Scarless Healing Tale: Comparing Homeostasis and Wound Healing of Oral Mucosa With Skin and Oesophagus

Epithelial tissues are the most rapidly dividing tissues in the body, holding a natural ability for renewal and regeneration. This ability is crucial for survival as epithelia are essential to provide the ultimate barrier against the external environment, protecting the underlying tissues. Tissue stem and progenitor cells are responsible for self-renewal and repair during homeostasis and following injury. Upon wounding, epithelial tissues undergo different phases of haemostasis, inflammation, proliferation and remodelling, often resulting in fibrosis and scarring. In this review, we explore the phenotypic differences between the skin, the oesophagus and the oral mucosa. We discuss the plasticity of these epithelial stem cells and contribution of different fibroblast subpopulations for tissue regeneration and wound healing. While these epithelial tissues share global mechanisms of stem cell behaviour for tissue renewal and regeneration, the oral mucosa is known for its outstanding healing potential with minimal scarring. We aim to provide an updated review of recent studies that combined cell therapy with bioengineering exporting the unique scarless properties of the oral mucosa to improve skin and oesophageal wound healing and to reduce fibrotic tissue formation. These advances open new avenues toward the ultimate goal of achieving scarless wound healing.

Modulation of radiation-induced oral mucositis (mouse) by dermatan sulfate: effects on differentiation processes

PURPOSE

During head and neck cancer radiotherapy, oral mucositis is the most frequent early side effect. Systemic dermatan sulfate (DS) administration has been shown to significantly decrease oral mucosal radiation reactions during daily fractionated irradiation (IR) in an established mouse model. The aim of this study was to investigate the mechanism of the oral epithelial differentiation process, during IR alone and in combination with DS treatment in the same mouse model.

METHODS

Fractionated IR 5 × 3 Gy/week was given to the snouts of mice over two weeks, either alone (IR) or in combination with daily DS treatment of 4 mg/kg (IR + DS). Groups of mice (n = 3) were sacrificed every second day over the course of 14 days in both experimental arms. Their tongue was excised and subjected to immunohistochemical processing.

RESULTS

In the p16 analysis as a proliferation marker, the difference between IR alone and IR + DS in the germinal (proliferation) layer was not significant, not stimulating the proliferation process. For the p21 analysis as a differentiation marker on the functional (differentiation) layer, the difference between IR alone and IR + DS arms was significant, indicating that DS inhibited the differentiation process. In the cytokeratin (CK) analysis as the indicator of cellular skeletal integrity, the percentage of antibody-positive cells was above the normal level in both experimental arms and significantly superior in the IR + DS arm.

CONCLUSION

The mucosal protective activity of DS, instead of stimulating proliferation, is based on prevention of cell loss by a combination of effects leading to the inhibition of cellular differentiation and an increase in the expression of epithelial mechanical strength between intercellular mechanical junctions.

Oral Mucosal Epithelial Cells

Cellular Phenotype and Apoptosis: The function of epithelial tissues is the protection of the organism from chemical, microbial, and physical challenges which is indispensable for viability. To fulfill this task, oral epithelial cells follow a strongly regulated scheme of differentiation that results in the formation of structural proteins that manage the integrity of epithelial tissues and operate as a barrier. Oral epithelial cells are connected by various transmembrane proteins with specialized structures and functions. Keratin filaments adhere to the plasma membrane by desmosomes building a three-dimensional matrix.

Cell-Cell Contacts and Bacterial Influence: It is known that pathogenic oral bacteria are able to affect the expression and configuration of cell-cell junctions. Human keratinocytes up-regulate immune-modulatory receptors upon stimulation with bacterial components. Periodontal pathogens including P. gingivalis are able to inhibit oral epithelial innate immune responses through various mechanisms and to escape from host immune reaction, which supports the persistence of periodontitis and furthermore is able to affect the epithelial barrier function by altering expression and distribution of cell-cell interactions including tight junctions (TJs) and adherens junctions (AJs).

In the pathogenesis of periodontitis a highly organized biofilm community shifts from symbiosis to dysbiosis which results in destructive local inflammatory reactions.

Cellular Receptors: Cell-surface located toll like receptors (TLRs) and cytoplasmatic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) belong to the pattern recognition receptors (PRRs). PRRs recognize microbial parts that represent pathogen-associated molecular patterns (PAMPs).

A multimeric complex of proteins known as inflammasome, which is a subset of NLRs, assembles after activation and proceeds to pro-inflammatory cytokine release.

Cytokine Production and Release: Cytokines and bacterial products may lead to host cell mediated tissue destruction. Keratinocytes are able to produce diverse pro-inflammatory cytokines and chemokines, including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-α. Infection by pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) can induce a differentiated production of these cytokines.

Immuno-modulation, Bacterial Infection, and Cancer Cells: There is a known association between bacterial infection and cancer. Bacterial components are able to up-regulate immune-modulatory receptors on cancer cells. Interactions of bacteria with tumor cells could support malignant transformation an environment with deficient immune regulation.

The aim of this review is to present a set of molecular mechanisms of oral epithelial cells and their reactions to a number of toxic influences.

Anisomycin, a JNK and p38 activator, suppresses cell-cell junction formation in 2D cultures of K38 mouse keratinocyte cells and reduces claudin-7 expression, with an increase of paracellular permeability in 3D cultures

Keratinocytes in the oral mucosal epithelium, which is a non-keratinized stratified epithelium, are exposed to various stimuli from the oral cavity. JNK and p38 are stress-activated mitogen-activated protein kinases (MAPKs) that are phosphorylated by various stimuli and are involved in the assembly and disassembly of tight junctions (TJs) in keratinocytes. Therefore, we investigated the effects of stress-activated MAPKs on TJs in a mouse keratinocyte cell line during cell-cell junction formation in two-dimensional (2D) cultures or stratification to form non-keratinized epithelium in 3D cultures. In 2D cultures, calcium induced zipper-like staining for ZO-1 at 2 h and string-like staining for ZO-1 at 12 h, which indicated immature and mature cell-cell junctions, respectively. Anisomycin (AM), a JNK and p38 activator, inhibited formation of string-like staining for ZO-1, whereas inhibition of JNK, but not p38, after AM treatment restored string-like staining for ZO-1, although claudins (CLDNs) 4, 6, and 7 did not completely colocalize to ZO-1-positive sites. In 3D cultures, AM treatment for 2 weeks activated only p38, suppressed flattening of the superficial cells, removed CLDN7 from ZO-1-positive spots on the surface of 3D cultures, which represent TJs, and decreased transepithelial electrical resistance. Thus, short-term AM treatment inhibited maturation of cell-cell junctions by JNK, but not p38, activation. p38 activation by long-term AM treatment affected morphology of stratified structures and paracellular permeability, which was increased by CLDN7 removal from TJs. Various chronic stimuli that activate stress-activated MAPKs may weaken the keratinocyte barrier and be involved in TJ-related diseases.

Construction and characterization of human oral mucosa equivalent using hyper-dry amniotic membrane as a matrix

BACKGROUND

Human amniotic membrane(HAM) as a graft material has been used in various fields. Hyper-dry amniotic membrane (HD-AM) is a novel dried amniotic membrane that is easy to handle and can be preserved at room temperature without time limitation. The purpose of this study was to investigate the useful properties of HD-AM in reconstruction of the oral mucosa.

METHODS

Human oral keratinocytes were isolated and seeded on HD-AM in serum-free culture system. Oral mucosa equivalent (OME) was developed and transplanted onto full-thickness wound on athymic mice. The wound healing was analyzed and the OME both before and after transplantation was analyzed with hematoxylin-eosin staining and immunohistochemical staining for Cytokines 10 (CK10), Cytokines 16 (CK16), and Ivolucrin (IVL).

RESULTS

Oral keratinocytes spread and proliferated well on HD-AM. Two weeks after air-lifting, OME had formed with good differentiation and morphology. We confirmed immunohistochemically that the expression of CK10 was positive in all suprabasal layers, as was CK16 in the upper layers, while IVL was present in all cell layers. Three weeks after transplantation to athymic mice, the newly generated tissue had survived well with the smallest contraction. The epithelial cells of newly generated tissue expressed CK10 throughout in all suprabasal layers, IVL was mainly in the granular layer, and CK16 positive cells were observed in all spinous layer and granular layer but were not expressed in the mouse skin, all of which were similar to native gingival mucosa.

CONCLUSIONS

The OME with HD-AM as a matrix revealed a good morphology and stable wound healing. This study demonstrates that HD-AM is a useful and feasible biomaterial for oral mucosa reconstruction.

Regeneration of Vocal Fold Mucosa Using Tissue-Engineered Structures with Oral Mucosal Cells

OBJECTIVES

Scarred vocal folds result in irregular vibrations during phonation due to stiffness of the vocal fold mucosa. To date, a completely satisfactory corrective procedure has yet to be achieved. We hypothesize that a potential treatment option for this disease is to replace scarred vocal folds with organotypic mucosa. The purpose of this study is to regenerate vocal fold mucosa using a tissue-engineered structure with autologous oral mucosal cells.

STUDY DESIGN

Animal experiment using eight beagles (including three controls).

METHODS

A 3 mm by 3 mm specimen of canine oral mucosa was surgically excised and divided into epithelial and subepithelial tissues. Epithelial cells and fibroblasts were isolated and cultured separately. The proliferated epithelial cells were co-cultured on oriented collagen gels containing the proliferated fibroblasts for an additional two weeks. The organotypic cultured tissues were transplanted to the mucosa-deficient vocal folds. Two months after transplantation, vocal fold vibrations and morphological characteristics were observed.

RESULTS

A tissue-engineered vocal fold mucosa, consisting of stratified epithelium and lamina propria, was successfully fabricated to closely resemble the normal layered vocal fold mucosa. Laryngeal stroboscopy revealed regular but slightly small mucosal waves at the transplanted site. Immunohistochemically, stratified epithelium expressed cytokeratin, and the distributed cells in the lamina propria expressed vimentin. Elastic Van Gieson staining revealed a decreased number of elastic fibers in the lamina propria of the transplanted site.

CONCLUSION

The fabricated mucosa with autologous oral mucosal cells successfully restored the vocal fold mucosa. This reconstruction technique could offer substantial clinical advantages for treating intractable diseases such as scarring of the vocal folds.

Keratin and S100 calcium-binding proteins are major constituents of the bovine teat canal lining

The bovine teat canal provides the first-line of defence against pathogenic bacteria infecting the mammary gland, yet the protein composition and host-defence functionality of the teat canal lining (TCL) are not well characterised. In this study, TCL collected from six healthy lactating dairy cows was subjected to two-dimensional electrophoresis (2-DE) and mass spectrometry. The abundance and location of selected identified proteins were determined by western blotting and fluorescence immunohistochemistry. The variability of abundance among individual cows was also investigated. Two dominant clusters of proteins were detected in the TCL, comprising members of the keratin and S100 families of proteins. The S100 proteins were localised to the teat canal keratinocytes and were particularly predominant in the cornified outermost layer of the teat canal epithelium. Significant between-animal variation in the abundance of the S100 proteins in the TCL was demonstrated. Four of the six identified S100 proteins have been reported to have antimicrobial activity, suggesting that the TCL has additional functionality beyond being a physical barrier to invading microorganisms. These findings provide new insights into understanding host-defence of the teat canal and resistance of cows to mastitis.

Constitution and in vivo test of micro-porous tubular scaffold for esophageal tissue engineering

Current clinical techniques in treating long-gap esophageal defects often lead to complications and high morbidity. Aiming at long-gap synthetic esophageal substitute, we had synthesized a biodegradable copolymer, poly(L-lactide-co-caprolactone) (PLLC), with low glass transition temperature. In this work, we developed a tubular PLLC porous scaffold using a self-designed tubular mold and thermal induced phase separation (TIPS) method. In order to enhance the interaction between tissue and scaffold, fibrin, a natural fibrous protein derived from blood fibrinogen, was coated on the scaffold circumferential surface. The fibrin density was measured to be 1.23 ± 0.04 mg/cm2. Primary epithelial cell culture demonstrated the improved in vitro biocompatibility. In animal study with partial scaffold implantation, in situ mucosa regeneration was observed along the degradation of the scaffold. These indicate that fibrin incorporated PLLC scaffold can greatly improve epithelial regeneration in esophagus repair, therefore serve as a good candidate for long-term evaluation of post-implantation at excision site.

In-vivo nonlinear optical microscopy (NLOM) of epithelial-connective tissue interface (ECTI) reveals quantitative measures of neoplasia in hamster oral mucosa

The epithelial-connective tissue interface (ECTI) plays an integral role in epithelial neoplasia, including oral squamous cell carcinoma (OSCC). This interface undergoes significant alterations due to hyperproliferating epithelium that supports the transformation of normal epithelium to precancers and cancer. We present a method based on nonlinear optical microscopy to directly assess the ECTI and quantify dysplastic alterations using a hamster model for oral carcinogenesis. Neoplastic and non-neoplastic normal mucosa were imaged in-vivo by both multiphoton autofluorescence microscopy (MPAM) and second harmonic generation microscopy (SHGM) to obtain cross-sectional reconstructions of the oral epithelium and lamina propria. Imaged sites were biopsied and processed for histopathological grading and measurement of ECTI parameters. An ECTI shape parameter was calculated based on deviation from the linear geometry (ΔLinearity) seen in normal mucosa was measured using MPAM-SHGM and histology. The ECTI was readily visible in MPAM-SHGM and quantitative shape analysis showed ECTI deformation in dysplasia but not in normal mucosa. ΔLinearity was significantly (p < 0.01) higher in dysplasia (0.41±0.24) than normal (0.11±0.04) as measured in MPAM-SHGM and results were confirmed in histology which showed similar trends in ΔLinearity. Increase in ΔLinearity was also statistically significant for different grades of dysplasia. In-vivo ΔLinearity measurement alone from microscopy discriminated dysplasia from normal tissue with 87.9% sensitivity and 97.6% specificity, while calculations from histology provided 96.4% sensitivity and 85.7% specificity. Among other quantifiable architectural changes, a progressive statistically significant increase in epithelial thickness was seen with increasing grade of dysplasia. MPAM-SHGM provides new noninvasive ways for direct characterization of ECTI which may be used in preclinical studies to investigate the role of this interface in early transformation. Further development of the method may also lead to new diagnostic approaches to differentiate non-neoplastic tissue from precancers and neoplasia, possibly with other cellular and layer based indicators of abnormality.

Promoting epithelium regeneration for esophageal tissue engineering through basement membrane reconstitution

Scaffolds mimicking hierarchical features of native extracellular matrices may facilitate cell growth and anatomical tissue regeneration. In our previous study, esophageal basement membrane (BM) was shown to be composed of interwoven fibers with mean diameter of 66 ± 24 nm (range 28-165 nm) and with abundant pores of unequal sizes. The main extracellular matrix (ECM) contents found in porcine esophageal BM were collagen IV, laminin, entactin, and proteoglycans. In this work, biodegradable polycaprolactone (PCL) and silk fibroin (SF) were spun with electrospinning technology, both individually and in combination, to fabricate fibrous scaffolds with diameters between 64 and 200 nm. The surface morphologies of PCL, PCL/SF, and SF scaffolds were observed under scanning electron microscopy. Their mechanical properties were tested and the cytocompatibility was evaluated in vitro via culture of primary epithelial cells (ECs). The SF or PCL/SF scaffold favorably promoted epithelial cell attachment and proliferation comparing with PCL scaffold. However, mitochondrial activity of epithelial cells was greatly promoted when major BM proteins were coated onto the electrospun scaffold to provide an ECM-like structure. Results from in vivo tests revealed that the electrospun scaffolds coated with BM protein possess good biocompatibility and capability to promote epithelium regeneration.

Oral cytokeratins in health and disease

The dynamics of oral mucosa is known by its inherent defensive nature. Certain areas demand tough shield when subjected to mechanical insults. This is met by structural scaffolding material referred as cytoskeleton comprised of intracellular protein filaments called cytokeratins in the surface squames of oral epithelia. They also equally contribute towards the architecture of odontogenic apparatus and salivary gland. Differentiation of epithelial cells within stratified epithelia regulates the expression of specific keratin gene. Any mutation in, or autoantibodies to keratins, desmosomal and cornified envelope proteins is translated into genetic and acquired human disorders. Sound knowledge of structural proteins, their expression, distribution and function plays a vital role in acquainting with these disorders and their application as differentiation markers. Thus, they form an integral aid in diagnostic pathology and may be instrumental in the future interventions by gene therapy. This review focuses on basics to current updates on oral cytokeratins with an emphasis on the genetic and acquired disorders of cytokeratins with oral implications.

Downregulation of keratin 76 expression during oral carcinogenesis of human, hamster and mouse

Background

Keratins are structural marker proteins with tissue specific expression; however, recent reports indicate their involvement in cancer progression. Previous study from our lab revealed deregulation of many genes related to structural molecular integrity including KRT76. Here we evaluate the role of KRT76 downregulation in oral precancer and cancer development.

Methods

We evaluated KRT76 expression by qRT-PCR in normal and tumor tissues of the oral cavity. We also analyzed K76 expression by immunohistochemistry in normal, oral precancerous lesion (OPL), oral squamous cell carcinoma (OSCC) and in hamster model of oral carcinogenesis. Further, functional implication of KRT76 loss was confirmed using KRT76-knockout (KO) mice.

Results

We observed a strong association of reduced K76 expression with increased risk of OPL and OSCC development. The buccal epithelium of DMBA treated hamsters showed a similar trend. Oral cavity of KRT76-KO mice showed preneoplastic changes in the gingivobuccal epithelium while no pathological changes were observed in KRT76 negative tissues such as tongue.

Conclusion

The present study demonstrates loss of KRT76 in oral carcinogenesis. The KRT76-KO mice data underlines the potential of KRT76 being an early event although this loss is not sufficient to drive the development of oral cancers. Thus, future studies to investigate the contributing role of KRT76 in light of other tumor driving events are warranted.

Oral epithelial stem cells in tissue maintenance and disease: the first steps in a long journey

The identification and characterization of stem cells is a major focus of developmental biology and regenerative medicine. The advent of genetic inducible fate mapping techniques has made it possible to precisely label specific cell populations and to follow their progeny over time. When combined with advanced mathematical and statistical methods, stem cell division dynamics can be studied in new and exciting ways. Despite advances in a number of tissues, relatively little attention has been paid to stem cells in the oral epithelium. This review will focus on current knowledge about adult oral epithelial stem cells, paradigms in other epithelial stem cell systems that could facilitate new discoveries in this area and the potential roles of epithelial stem cells in oral disease.

Establishment and characterization of a telomerase immortalized human gingival epithelial cell line

BACKGROUND AND OBJECTIVE

Gingival keratinocytes are used in model systems to investigate the interaction between periodontal bacteria and the epithelium in the initial stages of the periodontal disease process. Primary gingival epithelial cells (GECs) have a finite lifespan in culture before they enter senescence and cease to replicate, while epithelial cells immortalized with viral proteins can exhibit chromosomal rearrangements. The aim of this study was to generate a telomerase immortalized human gingival epithelial cell line and compare its in vitro behaviour to that of human GECs.

MATERIAL AND METHODS

Human primary GECs were immortalized with a bmi1/hTERT combination to prevent cell cycle triggers of senescence and telomere shortening. The resultant cell-line, telomerase immortalized gingival keratinocytes (TIGKs), were compared to GECs for cell morphology, karyotype, growth and cytokeratin expression, and further characterized for replicative lifespan, expression of toll-like receptors and invasion by P. gingivalis.

RESULTS

TIGKs showed morphologies, karyotype, proliferation rates and expression of characteristic cytokeratin proteins comparable to GECs. TIGKs underwent 36 passages without signs of senescence and expressed transcripts for toll-like receptors 1-6, 8 and 9. A subpopulation of cells underwent stratification after extended time in culture. The cytokeratin profiles of TIGK monolayers were consistent with basal cells. When allowed to stratify, cytokeratin profiles of TIGKs were consistent with suprabasal cells of the junctional epithelium. Further, TIGKs were comparable to GECs in previously reported levels and kinetics of invasion by wild-type P. gingivalis and an invasion defective ΔserB mutant.

CONCLUSION

Results confirm bmi1/hTERT immortalization of primary GECs generated a robust cell line with similar characteristics to the parental cell type. TIGKs represent a valuable model system for the study of oral bacteria interactions with host gingival cells.

Keratinization and its disorders

Keratins are a diverse group of structural proteins that form the intermediate filament network responsible for maintaining the structural integrity of keratinocytes. In humans, there are around 30 keratin families divided into two groups, namely, acidic and basic keratins, which are arranged in pairs. They are expressed in a highly specific pattern related to the epithelial type and stage of cellular differentiation. A total of 54 functional genes exist which codes for these keratin families. The expression of specific keratin genes is regulated by the differentiation of epithelial cells within the stratifying squamous epithelium. Mutations in most of these genes are now associated with specific tissue fragility disorders which may manifest both in skin and mucosa depending on the expression pattern. The keratins and keratin-associated proteins are useful as differentiation markers because their expression is both region specific and differentiation specific. Antibodies to keratin are considered as important tissue differentiation markers and therefore are an integral aid in diagnostic pathology. The present review discusses the structure of keratin, the various types of keratin and their distribution and the disorders associated with keratinization with special emphasis on the disorders of the oral cavity. A brief note on the clinical significance of keratin is also mentioned.

The lytic activation of KSHV during keratinocyte differentiation is dependent upon a suprabasal position, the loss of integrin engagement, and calcium, but not the interaction of cadherins

We previously found that KSHV (HHV-8) lytic activation occurs during differentiation of oral keratinocytes in organotypic raft cultures. To further investigate the spatial and temporal aspects of KSHV lytic activation and the roles of integrins, cadherins, and calcium, we used rKSHV.219-infected primary oral keratinocytes in submerged, suspension, and direct suprabasal plating, models of differentiation. We found that early keratinocyte differentiation did not activate lytic KSHV in cells attached to a substratum, with activation only occurring in suprabasal cells. Temporally, KSHV lytic expression occurred between the expression of early and late differentiation markers. Keratinocytes differentiated in suspension culture, which mimics substratum loss that occurs with stratification, activated lytic KSHV. This lytic activation was inhibited by integrin engagement, showing that integrins are a control point for KSHV reactivation. A role for cadherins was not found. Elevated extracellular calcium was necessary, but not sufficient, for lytic activation.

Skin repair using a porcine collagen I/III membrane--vascularization and epithelization properties

BACKGROUND

Collagen membranes have been developed to overcome the problem of limited availability of skin grafts. Vascularization and restricted functional epithelization limit the success of bioartificial constructs.

OBJECTIVE

To compare the vascularization, epithelization, and integration of a porcine collagen I/III membrane with that of split-thickness skin grafts on skin wounds.

MATERIALS AND METHODS

In 21 adult pigs, full-thickness skin defects on the rear side of the ear healed by split-thickness skin grafting, by covering with the membrane, or by free granulation. Skin samples on postoperative days 1, 3, 7, 14, 21, and 28 were evaluated histologically (hematoxylin-eosin, Sirius Red) and using immunohistochemistry (cytokeratin 5/6, transforming growth factor beta receptor (TGFbetaR-III) and immunoblot (TGFbeta(1,3), Smad2/3). Epithelial thickness and TGFbetaR-III-positive capillary area were quantitatively assessed.

RESULTS

Epithelization and vascularization in the membrane group were not significantly different from in the group treated with a split-thickness skin graft. Free granulation showed significantly slower epithelization and vascularization (p<.05). TGFbeta(1) and Smad2/3 complex expression were high during free granulation. Matrix was distinguishable until day 7.

CONCLUSIONS

This membrane serves as a suitable full-thickness dermal substitute, because the membrane is vascularized faster than free granulation tissue and enables early epithelization.

State of differentiation defines buccal epithelial cell affinity for cross-linking to Candida albicans Hwp1

Candida albicans utilizes mammalian cell-associated transglutaminase (TGase) activity to adhere covalently to human buccal epithelial cells (BECs) through Hyphal Wall Protein 1. Little is known about the factors leading to the identity and appearance of Hwp1 binding partners on cells lining the oral cavity. The observation that BECs vary in their ability to attach to C. albicans germ tubes and to bind recombinant Hwp1 (rHwp1) suggested that differentiation may play a role in affinity for germ tube attachment. Individual BECs were characterized for differentiation status and rHwp1 binding. rHwp1 bound to the more terminally differentiated cells displaying SPR3 and keratin 13 but not to less differentiated cells with abundant involucrin. Sequential expression of involucrin followed by SPR3 in oral keratinocytes was demonstrated using stratified organotypic cultures and a feeder layer system with the OKF6/TERT-2 cell line. Increased cross-linking of the lysine analogue 5-(biotinamido)pentylamine to cultured OKF6/TERT-2 cell proteins accompanied this increased expression of SPR3. Western blot analysis demonstrated the presence of rHwp1 cross-links to proteins from BECs or from OKF6/TERT-2 cells that had been mechanically dislodged from culture dishes. Therefore, the differentiation of SPR3 positive from involucrin positive cells is correlated with the acquisition of affinity for cross-linking to rHwp1 and covalent adhesion of germ tubes to BECs.

Distinctive molecular composition of human gingival interdental papilla

BACKGROUND

Gingiva is composed of attached and marginal (free) gingiva and interdental papilla. Increasing esthetic demands in dentistry have created a need to restore all parts of the gingiva. However, the interdental papilla has limited regeneration potential compared to other parts of the gingiva. It also is more susceptible to gingival overgrowth, suggesting that it has distinct cellular and molecular properties from other parts of the gingiva. Very little is known about the possible differences in the molecular composition of different parts of the gingiva.

METHODS

We compared the expression of a set of key molecules in interdental papilla and marginal gingiva from seven healthy subjects by immunohistochemical staining.

RESULTS

In the interdental papilla, immunoreactivity for integrin alphavbeta6 and cytokeratin 19 in the oral epithelium was significantly higher than in marginal gingiva. Expression of type I procollagen, extra domain A (EDA) and extra domain B (EDB) fibronectin isoforms, tenascin-C, transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF), and the signaling molecule son-of-sevenless (SOS)-1 also were increased in the interdental papilla. The expression of small leucine-rich proteoglycans decorin, biglycan, fibromodulin, and lumican in the interdental papilla was partially different from the marginal gingiva.

CONCLUSIONS

Molecular composition of the interdental papilla is distinct from marginal gingiva. Increased expression of molecules normally induced in wound healing (alphavbeta6 integrin, fibronectin-EDB and -EDA, tenascin-C, type I procollagen, TGF-beta, CTGF, and SOS-1) suggests that the cells in the interdental papilla are in an activated state and/or inherently display a specific phenotype resembling wound healing.

Cytokeratin expression in palatal and marginal mucosa of cleft palate patients

OBJECTIVE

The margin of a palatal cleft is a unique anatomical site since the palatal mucosa is continuous with the nasal or nasopharyngeal mucosa. The aim of this study was to compare the expression patterns of cytokeratins and basal membrane components of the mucosa in the area of the cleft.

DESIGN

Biopsies from the mucosa of the hard palate and from the cleft margin in the soft palate were obtained from five patients during the primary surgical closure of the cleft. The tissues were processed for haematoxylin-eosin staining and for immunohistochemistry. Antibodies against the cytokeratins (CK) 4, 7, 8, 10, 13, 16 and 18, and the basal membrane components heparan sulphate (HS) and collagen type IV (CIV) were used for immunostaining.

RESULTS

The nasopharyngeal epithelium was thinner than the epithelium of the soft palatal mucosa, and showed less interpapillary ridges. The nasopharyngeal epithelium was stratified but expressed the keratins of a simple epithelium (CK 7, 8 and 18). The expression pattern abruptly changed into that of a typical non-keratinized stratified epithelium (CK 4, 13) at the transition to the soft palatal epithelium. The epithelium of the hard palate was a fully differentiated, keratinized and stratified epithelium (CK 10, 16). The basal membrane was thinner in the nasopharyngeal epithelium, which might be related to the presence of abundant inflammatory cells.

CONCLUSION

The area around the palatal cleft showed three different types of epithelium. There was an abrupt transition in phenotype of the epithelium from the oral side to the nasopharyngeal side.

Organotypic human oral tissue models for toxicological studies

Three-dimensional models of the human oral epithelia have been developed to test the irritation of oral-care products and to provide systems to study the pathology of the oral cavity. The in vitro tissue models, cultured using normal oral epithelial cells and serum free medium, adopt a buccal or gingival phenotype. The buccal tissue (designated ORL-200) is 8-12 cell layers thick and non-cornified; the gingival tissue (designated GIN-100) is 9-13 layers thick and cornified at the apical surface. The tissues express cytokeratins 13 and 14 similar to their corresponding native oral tissues. The MTT viability assay was used to assess inter-lot and intra-lot reproducibility. The MTT average intra-lot coefficient of variation (CV) was less than 10% for both tissues and the time required to reduce tissue viability by 50% (ET-50) following application of 1% Triton-X 100 averaged 1.02+/-0.33 h (n=26) and 7.97+/-0.80 h (n=14) for the buccal and gingival tissues, respectively. The utility of the buccal tissue for irritation studies was examined by testing prototype dentifrice formulations and commercially available products including mouthwashes, toothpastes, and oral cleansers. Use of the MTT ET-50 assay and cytokine release clearly differentiated between the formulations and the oral care products. In conclusion, the oral tissue models represent highly reproducible, non-animal means to screen the irritation potential of newly developed oral care products and should be useful to study the innate immunity, biology, and pathology of the oral mucosa.

Co-regulation of p16INK4A and migratory genes in culture conditions that lead to premature senescence in human keratinocytes

Cellular stasis, also known as telomere-independent senescence, prevents many epithelial cells from becoming immortalized by telomerase alone. As human keratinocytes age in culture, protein levels of the tumor suppressor p16INK4a continue to increase, resulting in growth arrest independent of telomere length. Differences in culture conditions have been shown to modulate both p16INK4a expression and replicative capacity of human keratinocytes; however, the mechanism of p16INK4a induction under these conditions is unknown. Using multiple primary keratinocyte cell strains, we verified a delay in p16INK4a induction and an extended lifespan of human keratinocytes when grown in co-culture with post-mitotic fibroblast feeder cells as compared with keratinocytes grown on tissue culture plastic alone. Evaluation of gene expression levels in the two culture conditions by microarray analysis, and subsequent validation, demonstrated that keratinocytes cultured on plastic alone had significantly increased expression of many genes involved in keratinocyte migration and reduced expression levels of genes involved in keratinocyte differentiation. Higher levels of p16INK4a expression were present in cells that also displayed increased amounts of autophosphorylated focal adhesion kinase and urokinase plaminogen activator receptor (uPAR), both markers of keratinocyte migration. Furthermore, when tyrosine phosphorylation or urokinase-type plasminogen activator (uPA)/uPAR function was inhibited, both keratinocyte migration and p16INK4a expression were reduced. Our results indicate that keratinocytes cultured in the absence of feeder cells exhibit a migratory phenotype and suggest that p16INK4a is selectively induced under these conditions by a mechanism involving tyrosine kinase activity and the urokinase plasminogen activation system.

Comparison of differentiation markers between normal and two squamous cell carcinoma cell lines in culture

This study examines differences between cultures of normal human oral epithelial cells and two squamous cell carcinoma cell lines (SCC15 and SCC25) in the expression of structural proteins, adhesion molecules, plasma membrane lipid composition, and intercellular junctions. Based on immunocytochemistry, most normal cell cultures appeared to express more E-cadherin, integrin beta-1, cytokeratin (CK) 14, CK19, and involucrin than SCC cultures. By Western blot analysis, normal cultures expressing high levels of E-cadherin also expressed high levels of involucrin and low levels of CK19. Both SCC cultures demonstrated lower expression of E-cadherin and involucrin, whereas only SCC15 cells showed high levels of CK19. Expression of beta-catenin, an E-cadherin associated protein with potential oncogene function, did not vary among normal and SCC cells. Proportions of saturated fatty acids quantified by thin layer chromatography were higher in the normal cell cultures, than in both SCC cell lines. No morphological differences were evident by transmission electron microscopy (TEM) between normal and SCC cell-cell intercellular junctions. Although no quantitation was attempted, observation suggested that normal cells form more intercellular junctions (TEM observation) and larger intercellular bridges (SEM observation) compared to both SCC cell lines. Of the factors examined, main variations between cultures of normal oral epithelium and the two SCC cell lines examined include the expression of structural and adhesion proteins, lipid composition, and intercellular junctions. The extent of the differences varies according to the stage of terminal differentiation demonstrated by the normal cell cultures.

Recapitulation of oral mucosal tissues in long-term organotypic culture

To test the influence of fibroblasts on epithelial morphology and expression of keratinocyte proteins and barrier lipids, we bioengineered homotypic and heterotypic oral mucosae and skin using cultured adult human cells. Fibroblasts were allowed to modify collagen type I gels for 2 weeks before keratinocytes were added. The organotypic cultures were then grown at the air-liquid interface for 4 weeks. In homotypic combinations, epithelial morphology and protein expression closely mimicked those in vivo. In heterotypic combinations, the morphology resembled that in vivo and keratinocytes expressed their typical markers, except when skin keratinocytes were recombined with alveolar fibroblasts; they expressed K19, K4, and K13, which is similar to oral mucosal epithelia rather than to the epidermis. Morphologically, the stratum corneum layers were typical for the epithelial tissues. Grafting the bioengineered cultures to the backs of Nude mice did not change the results, suggesting that our findings are not merely a culture phenomenon. Lipid profiles of the homotypic combinations mimicked the profiles found in the normal epithelial tissues, except that the engineered alveolar epithelium expressed more ceramide 2 than that in vivo. In the heterotypic combinations, keratinocytes appeared to control the lipid profile, except in the combination of skin keratinocytes with alveolar fibroblasts, wherein the ceramide profile appeared to be partly that of alveolar epithelium and partly that of epidermis. These results suggest that cultured adult fibroblasts and keratinocytes are sufficient to recapitulate graftable oral tissues, and, except for alveolar fibroblasts, the type of fibroblast had little influence on keratinocyte differentiation.

Matrilysin (matrix metalloproteinase-7) expression in human junctional epithelium

Matrilysin is a matrix metalloproteinase expressed in exocrine and mucosal epithelium in many human tissues. Immunohistochemical staining showed that matrilysin is expressed in suprabasal cells of junctional epithelium facing the teeth and in epithelial cell rests of Malassez. No matrilysin expression was seen in the periodontal pocket tissue. In a tissue culture model mimicking junctional epithelium, matrilysin expression was also observed in suprabasal epithelial cells. Of 13 anaerobic oral bacterial species tested, F. nucleatum, F. necrophorum, P. endodontalis, and P. denticola stimulated matrilysin expression in porcine periodontal ligament epithelial cells from 2.5- to 5.7-fold, compared with untreated cells. The enzyme was localized in intracytoplasmic vesicles that also reacted with antibodies against lysosomal membrane protein h-lamp-1. The results indicate that matrilysin may play an important role in the normal physiology of junctional epithelium.

Cytokeratin expression patterns in jaw cyst linings with metaplastic epithelium

BACKGROUND

Cytokeratin (CK) expression patterns have been studied in numerous intact and diseased oral tissues. However, CK expression in metaplastic squamous cells has not been explored in depth and the origin of metaplastic epithelial linings of the jaw cysts has not been sufficiently investigated.

METHODS

We examined CK expression in 46 postoperative maxillary cysts (POMCs) which were lined with pseudostratified columnar cells only, columnar and squamous cells, and squamous cells only, in 13, 30 and 3 cases, respectively.

RESULTS

The expression of CK8, CK13 and CK18 were observed in 39, 9 and all 43 of the columnar epithelial linings, respectively. Metaplastic squamous epithelia expressed more CK13, and less CK18 and CK8. Of the 33 metaplastic linings, 24 expressed CK8, 23 CK13 and 26 linings expressed CK18. The patterns of expression of CK13 and CK18 observed were CK18(+)-CK13(-) in 10 metaplastic linings, CK18(+)-CK13(+) in 16, and CK18(-)-CK13(+) in 7. The expression of CK13- and CK18-mRNA was generally correlated with level of protein expressed. CK18-mRNA expression was observed by in situ hybridization, not only in the 26 metaplastic linings which were positive for CK18 protein, but also in five of the seven metaplastic linings which did not express CK18 protein. In addition, RT-PCR revealed an expression of CK18-mRNA in all metaplastic squamous linings, although the expression level was weaker than that in the columnar epithelial linings. The CK13-mRNA was expressed inversely to the CK18-mRNA.

CONCLUSIONS

These results indicate that CK18-mRNA is preserved through metaplasia, although the protein expression decreased. Metaplastic squamous cells differentiate with a decrease of CK18 and an increase of CK13 expression.

Epithelial structural proteins of the skin and oral cavity: function in health and disease

Epithelial tissues function to protect the organism from physical, chemical, and microbial damage and are essential for survival. To perform this role, epithelial keratinocytes undergo a well-defined differentiation program that results in the expression of structural proteins which maintain the integrity of epithelial tissues and function as a protective barrier. This review focuses on structural proteins of the epidermis and oral mucosa. Keratin proteins comprise the predominant cytoskeletal component of these epithelia. Keratin filaments are attached to the plasma membrane via desmosomes, and together these structural components form a three-dimensional array within the cytoplasm of epithelial cells and tissues. Desmosomes contain two types of transmembrane proteins, the desmogleins and desmocollins, that are members of the cadherin family. The desmosomal cadherins are linked to the keratin cytoskeleton via several cytoplasmic plaque proteins, including desmoplakin and plakoglobin (gamma-catenin). Epidermal and oral keratinocytes express additional differentiation markers, including filaggrin and trichohyalin, that associate with the keratin cytoskeleton during terminal differentiation, and proteins such as loricrin, small proline-rich proteins, and involucrin, that are cross-linked into the cornified envelope by transglutaminase enzymes. The importance of these cellular structures is highlighted by the large numbers of genetic and acquired (autoimmune) human disorders that involve mutations in, or autoantibodies to, keratins and desmosomal and cornified envelope proteins. While much progress has been made in the identification of the structural proteins and enzymes involved in epithelial differentiation, regulation of this process is less clear. Both calcium and retinoids influence epithelial differentiation by altering the transcription of target genes and by regulating activity of enzymes critical in epithelial differentiation, such as transglutaminases, proteinases, and protein kinases. These studies have furthered our understanding of how epithelial tissue and cell integrity is maintained and provide a basis for the future treatment of skin and oral disorders by gene therapy and other novel therapeutics.

Modulation of the epidermal growth factor receptor by the human papillomavirus type 16 E5 protein in raft cultures of human keratinocytes

It has been shown that the E5 protein of the human papillomavirus type 16 modulates epidermal growth factor receptor downregulation in monolayer cultures of human keratinocytes and mouse fibroblasts. We have now analysed the effect of this protein on the expression, the distribution and the activation of EGF receptors in raft cultures derived from an E5-transfected human keratinocyte cell line. The epithelia generated in these cultures were stratified and exhibited suprabasal expression of cytokeratins 1 and 10, which are known markers of early epidermal differentiation. In situ hybridization with an antisense riboprobe to the human papilloma virus type 16 E5 protein revealed a homogeneous gene expression within the entire epithelium of E5-transfected but not empty vector-transfected control cultures. Treatment of serum-starved rafts with EGF for 48 hours led to a strong decrease of suprabasal EGF receptors in control cultures, but not in rafts of E5-expressing cells. Under these conditions, no activated receptors were observed in control cultures, but activated receptors were still present in E5-raft cultures. Our results indicate that human papilloma virus type 16 E5-mediated modulation of EGF receptor expression occurs in a time- and structure-dependent manner in epithelial equivalents of human keratinocytes.

Multi-layered periodontal pocket epithelium reconstituted in vitro: histology and cytokeratin profiles

BACKGROUND

In order to study inter-individual differences in bacterial adhesion/invasion of periodontal tissues, an in vitro model for culturing multi-layered pocket epithelium without feeder layers or stromal equivalents (including the evaluation of their cytokeratin profiles) was developed.

METHODS

Pocket epithelium was collected and grown until confluent in Falcon flasks using keratinocyte-serum free medium (KSFM), without a feeder layer. In the second passage, oral keratinocytes were re-grown in a 2 compartment system using either a clear polyester (transwell-clear [TCL]) or a collagen (transwell-col [TCO]) membrane as culture surface. After the first week, the calcium concentration was raised to 1.2 mM and in half the wells, the KSFM was supplemented with 10% fetal calf serum (FCS). Histology and immunohistochemistry were performed after 1, 2, and 3 weeks of additional growth.

RESULTS

In general, all conditions resulted in a structured epithelium consisting of 3 to 5 layers, but important differences were observed between the membrane types and between the media. CK4 was rarely and only lightly expressed while CK18 and 19 (characteristic of junctional epithelium) were very strongly expressed in the older (2 and 3 weeks) cultures. CK13 and 14 (characteristic of any stratifiable epithelial cell) also tended to increase over time; CK13 seemed to be stronger in KSFM with FCS while the contrary was true for CK14. The multi-layer created by the combination TCL/KSFM + 10% FCS resembled a junctional epithelium most, while that grown on TCO without FCS mimicked the sulcular epithelium.

CONCLUSIONS

It seems possible to create a histiotypic culture resembling either periodontal pocket or junctional epithelium without the use of stromal equivalents or feeder layers which make this approach more cumbersome. This multi-layered culture offers a model to investigate the permeability of pocket epithelium and the adhesion and penetration of bacteria under well-defined environmental conditions.

Cellular characterization and successful transfection of serially subcultured normal human esophageal keratinocytes

BACKGROUND

In vitro cell culture models can provide unique insights into squamous epithelial proliferation, differentiation, and neoplastic transformation. Cultures of human esophageal keratinocytes could be advantageous for the study of these processes.

METHODS

Normal human esophageal keratinocytes were cultivated on 3T3 fibroblast feeder layers in vitro and expanded through four serial subcultivations. Confluent tertiary cultures were analyzed by morphological and immunohistochemical techniques to define their basic properties. The ability to transiently transfect cultured esophageal epithelium was tested using a Rous sarcoma virus-luciferase reporter gene by the calcium phosphate and lipofection methods.

RESULTS

Postconfluent cultures displayed a predominantly basal cell phenotype with limited stratification, widespread expression of keratins 5 and 14, and production of attachment specialization proteins such as alpha6beta4 integrin and collagen VII. Terminal differentiation markers (involucrin and transglutaminase) were prematurely expressed. The cells expressed growth factors important in proliferation and differentiation, such as transforming growth factor-beta and interleukin-1beta. Tertiary cultures were successfully transiently transfected with a Rous sarcoma virus-luciferase reporter gene construct.

CONCLUSION

Normal human esophageal cells can be serially passaged through extended numbers of cell generations and transfected by standard methods. This in vitro system may be useful in the study of fundamental cellular processes governing proliferation and differentiation in the esophageal epithelium.

Cultured human sole-derived keratinocyte grafts re-express site-specific differentiation after transplantation

Cultured epithelial autografts (CEA) derived from sole skin were transplanted to full-thickness wounds excised to muscle fascia over a variety of diverse body sites in 12 pediatric patients treated for acute burns or giant congenital nevi. The skin regenerated from the grafts was biopsied from 7 days to 6 years after grafting. The resultant epidermal phenotype was analyzed histologically and by immunohistochemical localization of keratin 9 (K9) as objective evidence of sole-type site-specific differentiation. Expression of K9 was also verified by one-dimensional gel electrophoresis of epidermal cytoskeletal extracts and K9 immunoblot analysis. Grafts prepared from epidermis of axilla; groin or foreskin and transplanted to wounds of comparable depth in an identical manner in the same patients served as controls of postgrafting differentiation. Biopsies of sole skin from amputation specimens from patients of comparable age served as normal positive controls, and biopsies of nonsole skin from patients of comparable age served as normal negative controls. As early as 2 weeks postgrafting, the histologic appearance of sole-derived CEA differed substantively from that of axilla- or groin-derived CEA controls and displayed a phenotype characteristic of sole skin with a thick compact stratum corneum, a thick stratum granulosum, and a distinct stratum lucidum. In sole-derived grafts rete ridges regenerated within 2 months postgrafting, whereas nonsole-derived grafts required 4-6 months for rete ridge regeneration. Once acquired, the sole skin phenotype was maintained long-term by all sole-derived CEA. In vitro, sole-derived keratinocytes synthesized little, if any, K9. However, within 7 days after grafting, K9 synthesis by multiple suprabasal keratinocytes was seen within the epidermis regenerated from sole-derived CEA. Protein of K9 appeared progressively more diffuse throughout the suprabasal layers, attaining a confluent pattern of expression comparable to normal controls of sole skin by 6 to 12 months postgrafting, and the confluent pattern of suprabasal K9 synthesis was maintained long-term. The results demonstrate that site-specific differentiation is an intrinsic property of postnatal human keratinocytes and can be expressed and maintained in a permissive environment in the absence of dermal tissue.

Effect of snuff on cytokeratin expression in oral vestibular sulcus epithelium

Differences in the expression of cytokeratins (CK) in specimens obtained from snuff-affected oral epithelium of the maxillary vestibular sulcus and clinically normal sulcular epithelium were studied by indirect immunofluorescence staining with a panel of monoclonal antibodies (MAbs). CK 14, a marker of stratified squamous epithelium was not seen expressed in 3/11 of the snuff user's specimens. Terminal differentiation markers, typical of cornified epithelia (CK 1, 9, 10 and 11), were detected suprabasally in the snuff user's keratosis but not in the normal control epithelium. The use of snuff seemed to change the CK staining pattern of the mucosa so that it resembles more that of a cornified type of epithelium. Simple epithelial-type CK were included in the study in order to establish the CK profile of the snuff-induced keratosis, for comparison with normal and dysplastic lesions. MAb to CK 7 and 19 showed reactivity in the basal cells and suprabasally whereas the monospecific MAb anti-CK 7 showed suprabasal staining both in the control and affected epithelia. By using MAbs, we found no immunoreactivity against CK 18 either in normal or affected epithelia, whereas we found suprabasal reaction (5/11) against CK 8 in the snuff user's epithelia. The two MAbs demonstrating the expression of CK 19, normally confined to the basal cells of the stratified squamous epithelium, showed variable patterns of expression both in basal cells and suprabasally in the snuff lesions. The results show that use of oral snuff causes some alterations in the CK expression pattern of the affected epithelium. Whether the alterations are indicative of a premalignant change is, however, uncertain. The results encourage further studies on the subject.

Evidence for specific proteolytic cleavage of the N-terminal domain of human profilaggrin during epidermal differentiation

Profilaggrin is a large phosphoprotein that is expressed in the granular cells of epidermis where it is localized in keratohyalin. It consists of multiple copies of single filaggrin units plus N- and C-terminal sequences that differ from filaggrin. Profilaggrin is dephosphorylated and proteolytically processed during terminal differentiation to yield filaggrin, which associates with keratin intermediate filaments to form macrofibrils in the lower layers of the stratum corneum. The N-terminal sequence of human profilaggrin comprises two distinct domains; an acidic A domain of 81 amino acids that binds Ca2+, and a cationic B domain of 212 residues. In this report, we further characterize the N-terminal domain by immunohistochemistry and immunoblot analysis using anti-peptide antibodies raised to the A and B regions. All of these antibodies (n = 4) immunostained keratohyalin in the granular layer of human epidermis and also showed some reaction with the lower stratum corneum. In immunoblot studies, the high molecular weight human profilaggrin reacted with both B domain antibodies whereas it showed a weak and variable reaction with A domain antibodies. In addition to profilaggrin, a cationic 32-kDa protein was detected with all N-terminal antibodies. A similar-sized N-terminal peptide was also produced by in vitro proteolysis of human profilaggrin with endoproteinase 1 (PEP1), a protease involved in processing of mouse profilaggrin, and in cultured rat epidermal keratinocytes transfected with a human profilaggrin cDNA construct. Evidence for at least one additional cleavage within the N-terminal domain is shown by immunoreactivity of smaller (16-20 kDa) acidic and basic proteins with A and B domain antibodies, respectively. These results demonstrate that the N-terminal domain is an integral part of profilaggrin in keratohyalin but is proteolytically cleaved from profilaggrin during the terminal differentiation of keratinocytes to yield a 32-kDa peptide.

A limited role for retinoic acid and retinoic acid receptors RAR alpha and RAR beta in regulating keratin 19 expression and keratinization in oral and epidermal keratinocytes

Different types of stratified squamous epithelia-for example, the "orthokeratinized" epidermis, the "parakeratinized" gingiva, and the "nonkeratinized" oral lining mucosal epithelia-are formed by intrinsically distinct keratinocyte subtypes. These subtypes exhibit characteristic patterns of keratin protein expression in vivo and in culture. Keratin 19 is an informative subtype-specific marker because the basal cells of only nonkeratinizing epithelia express K19 in vivo and in culture. Epidermal keratinocytes normally do not express K19, but can be induced to do so in culture by retinoic acid (RA). Keratinocyte subtypes express the retinoic acid receptor (RAR) beta at levels roughly correlated with their level of K19 expression in culture and their potential for forming a nonkeratinized epithelium in vivo. We tested the hypothesis that the level of RAR beta expressed by a keratinocyte determines its K19 expression and its form of suprabasal differentiation. Normal human epidermal and gingival keratinocytes stably overexpressing either RAR beta or RAR alpha were generated by defective retroviral transduction. Overexpression of either receptor enhanced the RA inducibility of K19 in conventional culture, in that the proportion of the transductants becoming K19+ in response to RA was markedly increased compared with controls. The pattern of differentiation of the epithelium formed in organotypic culture, assessed by basal K19 and suprabasal K1, K4, and filaggrin expression, however, was unaltered by RAR overexpression. Thus, the susceptibility of keratinocytes to regulation of K19 expression by retinoids is conditional, and levels of neither RAR beta nor RAR alpha are limiting to the intrinsic mechanism that specifies alternate differentiation pathways for stratified squamous epithelia.

Keratinocyte gene transfer and gene therapy

Gene therapy has moved beyond the pre-clinical stage to the treatment of a variety of inherited and acquired diseases. For such therapy to be successful, genes must be efficiently delivered to target cells and gene products must be expressed for prolonged periods of time without toxic effects to the host. This may be achieved by means of an in vivo strategy where genes are transferred directly into a host cell, or by means of an ex vivo approach through which cells are removed, cultured, targeted for gene delivery, and grafted back to the host. Several obstacles continue to delay safe and effective clinical application of gene therapy in a variety of target cells. The limited survival of transplanted cells, transient expression of transferred genes, and difficulties in targeting stem cells are technical issues requiring further investigation. Epidermal and oral keratinocytes are potential vehicles for gene therapy. Several features of these tissues can be utilized to achieve delivery of therapeutic gene products for local or systemic delivery. These qualities include: (1) the presence of stem cells; (2) the cell-, strata-, and site-specific regulation of keratinocyte gene expression; (3) tissue accessibility; and (4) secretory capacity. Such features can be exploited by the use of gene therapy strategies to facilitate: (1) identification, enrichment, and targeting of stem cells to ensure the continued presence of the transferred gene; (2) high-level and persistent transgene expression using keratinocyte-specific promoters; (3) tissue access needed for culture and grafting for ex vivo therapy and direct in vivo gene transfer; (4) secretion of transgene product for local or systemic delivery; and (5) monitoring of genetically modified tissue and removal if treatment termination is required. Optimal gene therapy strategies are being tested in a variety of tissues to treat dominant and recessive genetic disorders as well as acquired diseases such as neoplasia and infectious disease. This experience provides a basis for the application of such clinical studies to a spectrum of diseases effecting epidermal and oral keratinocytes. Gene therapy is in an early stage yet holds great promise for its ultimate clinical application.