Claudin-10 Decrease in the Submandibular Gland Contributes to Xerostomia

Tight junction proteins play a crucial role in paracellular transport in salivary gland epithelia. It is clear that severe xerostomia in patients with HELIX syndrome is caused by mutations in the claudin-10 gene. However, little is known about the expression pattern and role of claudin-10 in saliva secretion in physical and disease conditions. In the present study, we found that only claudin-10b transcript was expressed in human and mouse submandibular gland (SMG) tissues, and claudin-10 protein was dominantly distributed at the apicolateral membranes of acini in human, rat, and mouse SMGs. Overexpression of claudin-10 significantly reduced transepithelial electrical resistance and increased paracellular transport of dextran and Na⁺ in SMG-C6 cells. In C57BL/6 mice, pilocarpine stimulation promoted secretion and cation concentration in saliva in a dose-dependent increase. Assembly of claudin-10 to the most apicolateral portions in acini of SMGs was observed in the lower pilocarpine (1 mg/kg)-treated group, and this phenomenon was much obvious in the higher pilocarpine (10 mg/kg)-treated group. Furthermore, 7-, 14-, and 21-wk-old nonobese diabetic (NOD) and BALB/c mice were used to mimic the progression of hyposalivation in Sjögren syndrome. Intensity of claudin-10 protein was obviously lower in SMGs of 14- and 21-wk-old NOD mice compared with that of age-matched BALB/c mice. In the cultured mouse SMG tissues, interferon-γ (IFN-γ) downregulated claudin-10 expression. In claudin-10-overexpressed SMG-C6 cells, paracellular permeability was decreased. Furthermore, IFN-γ stimulation increased p-STAT1 level, whereas pretreatment with JAK/STAT1 antagonist significantly alleviated the IFN-γ-induced claudin-10 downregulation. These results indicate that claudin-10 functions as a pore-forming component in acinar epithelia of SMGs, assembly of claudin-10 is required for saliva secretion, and downregulation of claudin-10 induces hyposecretion. These findings may provide new clues to novel therapeutic targets on hyposalivation.