WNT Signaling Modifies Barrier Functions of Junctional and Pocket Epithelium

The aims of this study were 1) to determine how ligature-induced periodontitis (LIP) disrupts barrier functions of the junctional epithelium (JE); 2) to determine, using a genetic approach, the necessity of Wnt signaling for JE barrier functions; and 3) to test, using a biochemical strategy, whether a WNT therapeutic is sufficient to improve barrier functions of a pocket epithelium. In a murine model of LIP, quantitative analyses performed at multiple time points assessed epithelial apoptosis; expression of attachment proteins laminin 5 and β4 integrin, inflammation, and bone resorption. Axin2^CreERT2/+; R26R^mTmG/+ mice were used to evaluate how LIP impacted Wnt-responsive cells and their progeny, and K14^CreERT2/+;Wls^fl/fl mice were used to determine whether Wnt signaling was required for JE barrier functions. In some cases, LIP was followed by a recovery period to assess molecular changes in pocket epithelium, and in a subset of these mice, a liposomal formulation of human WNT3A protein (L-WNT3A) was tested for its effects on early repair dynamics in pocket epithelium. LIP triggered apoptosis, significantly reduced expression of laminin 5 and β4 integrin in the JE, and disrupted the Wnt-responsive compartment; these epithelial changes were accompanied by inflammation and alveolar bone resorption. Reepithelialization occurred even with a ligature present, but this pocket epithelium had compromised barrier functions. Wntless (Wls) deletion was sufficient to convert a JE into pocket epithelium, while topical L-WNT3A treatment was sufficient to increase hemidesmosomal protein expression in pocket epithelium and reduce inflammation at early time points. LIP destroys barrier functions and thus converts a JE into pocket epithelium. Deletion of epithelial Wls demonstrates that this conversion is a Wnt-dependent event. L-WNT3A restores some early barrier features to pocket epithelium; future studies will focus on the durability of these effects.