117 THE REGULATOR OF THE UTERINE TRPV6 GENE DURING PREGNANCY IN RODENTS

Abstract

Transient receptor potential cation channel, subfamily V, member 6 (TRPV6) is an epithelial Ca²⁺ channel protein expressed in calcium-absorbing organs. Recently it was reported that TRPV6 is expressed in female reproductive organs. The present study was performed to investigate the expression and regulation of uterine and placental TRPV6 during gestation in rats. In the uterus, TRPV6 was moderately expressed at pregnancy day (P) 0 and decreased until P4. Its expression level then peaked at P5, implying that TRPV6 may be involved in embryo implantation. Around P13, uterine TRPV6 expression increased slightly a second time, and then gradually decreased until the end of pregnancy at P21. Tissue localization of TRPV6 expression was determined by immunohistochemistry methods. TRPV6 protein was detected in uterine endothelium layers and glands; however, it was not detected in uterine tissues attached to the placenta. In the placenta, TRPV6 mRNA levels increased in mid-gestation, and the tissue distribution of placental TRPV6 protein suggests that it may play a role in transferring calcium to the fetus during pregnancy. To investigate the pathway(s) mediating TRPV6 expression during pregnancy in rats and mice, steroid hormone antagonists ICI 182 780 (ICI) and RU 486 (RU) were injected prior to maximal TRPV6 expression, as anti-estrogen and anti-progesterone agents, respectively. Pregnant rats (P4 for uterine RNA preparation, P19 for placental RNA preparation) received subcutaneous injections of RU (2.5 mg per rat), ICI (0.5 mg per rat), or a combination of RU and ICI. In addition, ICR-mice at P9 were injected with RU (25 µg per mouse) and/or ICI (2 µg per mouse). We measured level of TRPV6 mRNA transcription using semi-quantitative RT-PCR and real-time PCR. Data were analyzed by nonparametric one-way analysis of variance using the Kruskal-Wallis test, followed by Dunnett's test for multiple comparisons to vehicle. In rats, TRPV6 expression was reduced by RU treatment, and in mice ICI treatment blocked TRPV6 expression. Taken together, these results suggest that progesterone in rats and estrogen in mice act to regulate TRPV6 expression in the uterus and placenta during pregnancy. In conclusion, TRPV6 may play a role in embryo implantation in the uterus and in calcium transport between embryo and mother in the placenta.