The Absence of Claudin-10 in the Enamel Organ Alters Its Integrity

Rare disorders related to tight junction (TJ) proteins have been associated with amelogenesis imperfecta. Pathogenic variants of CLDN10, encoding claudin-10b, a cation transport pore, cause the autosomal recessive HELIX syndrome (Hypohidrosis, Electrolyte imbalance, hypoLacrymia, Ichthyosis, Xerostomia). Patients exhibit salivary dysfunction and rapid enamel wear after tooth eruption. Since Cldn10 is expressed in the dental epithelium, this study explores the role of claudin-10b in amelogenesis. We analyzed amelogenesis in constitutive and conditional Cldn10 knockout (KO) murine models, comparing the findings to human HELIX enamel. First, analysis of constitutive Cldn10 knockout (KO) mice, which die within a few hours after birth, showed that claudin-10 is present at the plasma membrane of the stratum intermedium but not at the TJs during the secretory stage. Its absence altered gene expression related to ion transport and pH control, although without major disturbance in cell polarization or enamel matrix synthesis. Examination of later stages of amelogenesis in epithelium-targeted conditional Cldn10 KO mice showed that claudin-10 is present in the papillary layer at the maturation stage. In its absence, the pH of the enamel matrix was more basic during early maturation, suggesting that claudin-10 determines enamel matrix pH. However, at later stage of the maturation process, the pH was corrected and the resulting enamel did not show major structural or elemental alterations. These later findings were confirmed by exploring the enamel of Cldn10 KO transplanted tooth germs, which have developed in a controlled mineral environment. Nevertheless, higher contents of aluminum were detected in the enamel of transplanted germs and in human HELIX enamel, suggesting that claudin-10 deficiency may lead to a loss of enamel organ integrity. These data suggest that while salivary dysfunction is the main cause of enamel wear in HELIX, claudin-10 plays a direct role in amelogenesis by determining pH and enamel organ integrity.