Defective NaCl Reabsorption in Salivary Glands of Eda-Null X-LHED Mice

Mutations in the ectodysplasin A gene ( EDA) cause X-LHED (X-linked hypohidrotic ectodermal dysplasia), the most common human form of ectodermal dysplasia. Defective EDA signaling is linked to hypoplastic development of epithelial tissues, resulting in hypotrichosis, hypodontia, hypohidrosis, and xerostomia. The primary objective of the present study was to better understand the salivary gland dysfunction associated with ectodermal dysplasia using the analogous murine disorder. The salivary flow rate and ion composition of the 3 major salivary glands were determined in adult Eda-deficient Tabby hemizygous male (Ta/Y) and heterozygous female (Ta/X) mice. Submandibular and sublingual glands of Eda-mutant mice were smaller than wild-type littermates, while parotid gland weight was not significantly altered. Fluid secretion by the 3 major salivary glands was essentially unchanged, but the decrease in submandibular gland size was associated with a dramatic loss of ducts in Ta/Y and Ta/X mice. Reabsorption of Na⁺ and Cl^-, previously linked in salivary glands to Scnn1 Na⁺ channels and Cftr Cl^- channels, respectively, was markedly reduced at high flow rates in the ex vivo submandibular glands of Ta/Y mice (~60%) and, to a lesser extent, Ta/X mice (Na⁺ by 14%). Consistent with decreased Na⁺ reabsorption in Ta/Y mice, quantitative polymerase chain reaction analysis detected decreased mRNA expression for Scnn1b and Scnn1g, genes encoding the β and γ subunits, respectively. Moreover, the Na⁺ channel blocker amiloride significantly inhibited Na⁺ and Cl^- reabsorption by wild-type male submandibular glands to levels comparable to those observed in Ta/Y mice. In summary, fluid secretion was intact in the salivary glands of Eda-deficient mice but displayed marked Na⁺ and Cl^- reabsorption defects that correlated with the loss of duct cells and decreased Scnn1 Na⁺ channel expression. These results provide a likely mechanism for the elevated NaCl concentration observed in the saliva of affected male and female patients with X-LHED.