Comprehensive cornified envelope protein profile of odontogenic keratocysts clarifies the characteristics of non-keratinized oral epithelium

BACKGROUND

Odontogenic keratocysts constitute 10%-20% of odontogenic cysts and exhibit a distinctive corrugated parakeratinized lining epithelium. Considering that cornified envelope formation is an important phenomenon during keratinocyte differentiation, this study aimed to clarify the characteristics of cornified envelope formation in odontogenic keratocysts.

METHODS

We investigated the cellular distribution of cornified envelope-related proteins (transglutaminases and their substrates), as well as the upstream regulatory protein c-Fos, by immunohistochemical analysis of the lining epithelium of 20 odontogenic keratocysts. We examined the corresponding mRNA levels by quantitative polymerase chain reaction. Ten dentigerous cysts served as control non-keratinized cysts.

RESULTS

The distributions of transglutaminase and their substrates except loricrin and small protein-rich protein 1a significantly differed between odontogenic keratocysts and dentigerous cysts. There was no significant difference in c-Fos expression between odontogenic keratocysts and dentigerous cysts. The mRNA levels of transglutaminases and their substrates were significantly higher in odontogenic keratocysts than in dentigerous cysts. However, c-Fos mRNA levels did not significantly differ between groups.

CONCLUSION

Surprisingly, the overall appearance of cornified envelope-related proteins of odontogenic keratocysts was consistent with the characteristics of non-keratinized oral mucosa identified in previous studies. These findings indicate that the contribution of cornified envelope-related molecules in odontogenic keratocysts is similar to that in non-keratinized oral epithelium, rather than keratinized oral epithelium, suggesting that odontogenic keratocysts are not genuine keratinized cysts. The upregulation of cornified envelope-related genes in odontogenic epithelium could be an important pathognomonic event during odontogenic keratocyst development.

Contribution of transglutaminases and their substrate proteins to the formation of cornified cell envelope in oral mucosal epithelium

Cornified envelope formation is crucial for the final differentiation of keratinized epithelium. However, the mechanisms of cornified envelope formation in the oral epithelium remain unclear. The aim of this study was to clarify the differences in the distribution and expression of cornified envelope related proteins and genes between keratinized and non-keratinized oral epithelia. We immunohistochemically investigated the distribution patterns of transglutaminase 1 (TG1), transglutaminase 3 (TG3), and their substrate proteins involucrin (IVL), loricrin (LOR), and small proline rich proteins (SPRs), in 19 keratinized and 14 non-keratinized oral epithelium samples. TG1 and TG3 mRNA levels were investigated in both types of epithelium by real time reverse transcription polymerase chain reaction (RT-PCR) using paraffin-embedded specimens. Data were analyzed to identify factors involved in cornified envelope formation. We demonstrate that 11 localization patterns show statistically significant differences between keratinized and non-keratinized oral epithelia. These factors clearly drove the separation of the two groups during cluster analysis. TG1 mRNA levels in keratinized oral epithelium were significantly higher than those in non-keratinized oral epithelium. In conclusion, the characteristic distribution of transglutaminases and their substrates and the mRNA levels of TG1 can regulate cornified envelope formation in keratinized oral epithelium, together with the contribution of TG3 first reported in this paper.

Transglutaminases in autoimmune and inherited skin diseases: The phenomena of epitope spreading and functional compensation

Transglutaminases (TGs) are structurally and functionally related enzymes that modify the post-translational structure and activity of proteins or peptides, and thus are able to turn on or switch off their function. Depending on location and activities, TGs are able to modify the signalling, the function and the fate of cells and extracellular connective tissues. Besides mouse models, human diseases enable us to appreciate the function of various TGs. In this study, skin diseases induced by genetic damages or autoimmune targeting of these enzymes will be discussed. TG1, TG3 and TG5 contribute to the cutaneous barrier and thus to the integrity and function of epidermis. TGM1 mutations related to autosomal recessive ichthyosis subtypes, TGM5 mutations to a mild epidermolysis bullosa phenotype and as novelty TGM3 mutation to uncombable hair syndrome will be discussed. Autoimmunity to TG2, TG3 and TG6 may develop in a few of those genetically determined individuals who lost tolerance to gluten, and manifest as coeliac disease, dermatitis herpetiformis or gluten-dependent neurological symptoms, respectively. These gluten responder diseases commonly occur in combination. In autoimmune diseases, the epitope spreading is remarkable, while in some inherited pathologies, a unique compensation of the lost enzyme function is noted.

Platelet-Released Growth Factors Induce Differentiation of Primary Keratinocytes

Autologous thrombocyte concentrate lysates, for example, platelet-released growth factors, (PRGFs) or their clinically related formulations (e.g., Vivostat PRF®) came recently into the physicians' focus as they revealed promising effects in regenerative and reparative medicine such as the support of healing of chronic wounds. To elucidate the underlying mechanisms, we analyzed the influence of PRGF and Vivostat PRF on human keratinocyte differentiation in vitro and on epidermal differentiation status of skin wounds in vivo. Therefore, we investigated the expression of early (keratin 1 and keratin 10) and late (transglutaminase-1 and involucrin) differentiation markers. PRGF treatment of primary human keratinocytes decreased keratin 1 and keratin 10 gene expression but induced involucrin and transglutaminase-1 gene expression in an epidermal growth factor receptor- (EGFR-) dependent manner. In concordance with these results, microscopic analyses revealed that PRGF-treated human keratinocytes displayed morphological features typical of keratinocytes undergoing terminal differentiation. In vivo treatment of artificial human wounds with Vivostat PRF revealed a significant induction of involucrin and transglutaminase-1 gene expression. Together, our results indicate that PRGF and Vivostat PRF induce terminal differentiation of primary human keratinocytes. This potential mechanism may contribute to the observed beneficial effects in the treatment of hard-to-heal wounds with autologous thrombocyte concentrate lysates in vivo.