146 DIFFERENTIAL EXPRESSION OF TRANSCELLULAR CALCIUM TRANSPORT AND PARACELLULAR TIGHT JUNCTION GENES IN THE PLACENTAE OF CALBINDIN-D9k, -D28k AND -D9k/D28k KNOCKOUT MICE

Abstract

The placenta has many essential roles in the maintenance of pregnancy and homeostasis. Calcium transport and regulation are also controlled by the placenta. In general, calcium transport is divided into an active transcellular pathway and a passive paracellular pathway. Transient receptor potential cation channel subfamily V member 5/6 (TRPV5/6), calbindin-D9k/-28k (CaBP-9k/-28k) and Na⁺/Ca²⁺ exchanger (NCX1) are involved in the transcellular pathway. The paracellular pathway is determined by the expression of tight junction genes, such as occludin, claudins and ZO-1. In this study, we analysed the difference in calcium transport in the placentae of CaBP-9k and CaBP-28k knockout (KO) mice compared with that of wild-type (WT) mice. Placentae were collected and used for mRNA and protein evaluation from 9 mice of each type (a total of 36 mice). All mice were killed on gestational Day 19. We confirmed mRNA expression by RT-qPCR and protein expression by Western blot analysis. The data were statistically analysed by one-way ANOVA using Tukey's test. In the transcellular pathway, the expression levels of NCX1 and TPRV6 were shown to be significantly increased in KO mice compared with WT mice. In the paracellular pathway, occluding, which is directly related to permeability, mRNA and protein expression was significantly increased in single KO mice compared with WT, but not in double KO mice. Claudin-4, which is a cation barrier, mRNA and protein expression patterns were significantly decreased in single KO mice compared with WT, but not in double KO mice. These results imply that the disability of calcium buffering due to CaBP-9k or CaBP-28k KO may lead to an accelerated transcellular pathway. In addition, a single KO of calcium-binding proteins may lead to decreased paracellular permeability to weaken the leakage of calcium through the tight junction and may also lead to increased cation selectivity of tight junctions. Taken together, these results might indicate that KO of calcium-binding proteins may induce activation of a compensating transcellular pathway in the placenta of mice and a paracellular pathway may support the maintenance of calcium homeostasis.