98 THE EXPRESSION OF TIGHT JUNCTION GENES IN THE PLACENTA BY CALCIUM OR VITAMIN D DEFICIENCY IN WILD TYPE AND CaBP-9k OR CaBP-28k KNOCKOUT MICE

Abstract

The placenta is responsible for calcium transport from mother to fetus. Tight junction genes are responsible for the passive paracellular pathway, which is one of the major calcium transport pathways. Therefore, we examined whether the tight junction genes are differently expressed in the placenta by calcium, vitamin D, or both deficiency. We also investigated the correlation between transcellular transport and paracellular transport by using calbindin-D9k (CaBP-9k), calbindin-D28K (CaBP-28k), or both knockout (KO) mice. We administrated C57BL/6 wild type and CaBP-D9K, CaBP-D28K KO, or both mice with calcium, vitamin D, or both deficiency diets for 19 days (during pregnant Day 0 to 18). The expression levels and localization of tight junction genes including zona occludens 1 (Zo-1), junction adhesion molecules A (Jam-A), and claudins (Cldn) were tested. The mRNA and protein expression of these genes were investigated by real-time PCR and Western blotting assay. Five samples from 3 animals for each treated group were used and the data analyzed using a one-way ANOVA. P-values <0.05 were considered statistically significant. The localization of the genes was also examined by immunohistochemistry. The mRNA and protein expressions of Cldn1 were increased in calcium and calcium/vitamin D deficient CaBP-D9K KO mice and in calcium/vitamin D deficient CaBP-D9/28K mice, whereas those of Zo-1 and Jam-A were not affected. Gene Cldn5 mRNA expression showed a decrease in CaBP-9k, CaBP-28k, or both KO mice compared with wild type mice. Interestingly, Cldn5 mRNA expression was augmented in vitamin D or calcium deficient CaBP-D9K KO mice. Other tested Cldns did not show significant changes in any dietary or CaBP KO conditions. All the tight junction genes were localized in the trophoblast layer of the placenta. Taken together, the expression of tight junction genes was dynamically regulated by different dietary conditions and in the condition that transcellular calcium transport was altered by ablation of CaBPs, suggesting that these genes were involved in the placental calcium homeostasis.