Elastin in oral connective tissue modulates the keratinization of overlying epithelium

Aim: One of the most discernable differences between keratinized and non-keratinized oral mucosas is the quantity of elastin they contain in the connective tissues. Whether elastin modulates the keratin expression of oral epithelial cells is unknown. Methods: Four specimens containing both keratinized and non-keratinized mucosas were processed for immunohistochemical (IHC) stainings for elastin and four keratins. Six keratinized and non-keratinized portions of oral mucosas were dissected and cultured on an organ culture system. Purified elastin and elastase were added separately to the media. After 14 days, the mucosas were examined for four keratin expressions. Cell cultures of keratinized and non-keratinized gingival fibroblasts were established and tested for elastin expression. Oral mucosa equivalents were then engineered and tested for keratin expression. Results: Keratinized epithelium exclusively expressed keratin-1 and -10 (K1/10), while non-keratinized epithelium expressed keratin-4 and -13 (K4/13). Only non-keratinized fibroblasts expressed elastin in cell culture. Both the native and the engineered keratinized gingiva changed phenotypes and expressed K4/13 when treated with exogenous elastin. On the contrary, the native non-keratinized mucosa started to express K1/10 when elastase eradicated inherent elastin. Conclusions: Our study demonstrated that the elastin in the oral connective tissue is important for the non-keratinized phenotypes of overlaying epithelium.