Rescue of Aging-Dependent Reduction of Claudin-10b Expression by Glutamate in Mouse Intestinal MCE301 Cells

Paracellular permeability of mineral ions and water in the intestines is restricted by claudins (CLDNs), which are key components of tight junctions (TJs). Glutamate (Glu) plays a role in regulating absorption mechanisms in the intestines, but the effect on paracellular permeability remains unclear. In mouse intestine-derived MCE301 cells, Glu treatment increased the mRNA levels of CLDN10b, while the levels of other CLDNs and zonula occludens-1, a scaffolding protein in TJs, remained unchanged. Similar results were obtained in rat intestine-derived IEC6 cells without CLDN1 and CLDN15. Glu also increased the protein level and TJ localization of CLDN10. The Glu-induced increase in CLDN10b mRNA expression was suppressed by knockdown of taste receptor type 1, T1R1 and T1R3. Glu treatment stimulated Ca²⁺ influx, which was inhibited by BAPTA, a Ca²⁺ chelator, and ebselen, a voltage-dependent Ca²⁺ channel inhibitor. Furthermore, the upregulation of CLDN10b mRNA by Glu was inhibited by BAPTA, ebselen, and rapamycin, an inhibitor of mammalian target of rapamycin (mTOR). These results suggest that Glu upregulates CLDN10b expression in MCE301 cells mediated by a T1R1/T1R3-Ca²⁺-mTOR signaling pathway. The mRNA levels of CLDN10b were decreased in the colon of aged mice and MCE301 cells treated with tenovin-1 (Ten-1), an inducer of cellular senescence. Glu reversed the Ten-1-induced reduction of CLDN10b mRNA and restored paracellular barrier function. These results suggest that Glu enhances the intestinal paracellular barrier function through the regulation of CLDN10b expression.