Regulation and localization of transient receptor potential melastatin 2 in rat uterus

The transient receptor potential channels are membrane-binding proteins that are nonselectively permeable for cations, such as Ca(2+) and Mg(2+), in numerous mammalian cells. The extracellular or intracellular ions play key roles in physiological functions including muscle contraction, cytokine production, insulin release, and apoptosis. Although transient receptor potential melastatin (TRPM) channels are implicated in nonreproductive tissues, the presence of TRPM2 has been reported in endometrium of uterus. To examine whether the expression of TRPM2 gene in uterus is due to gonadal steroid hormones or hormone-independent effect, the uterine TRPM2 gene was monitored in uterus of mature rat during estrous cycle and of immature rat after treatment with gonadal steroid estrogen (E2), progesterone (P4) with/without estrogen receptor antagonist Imperial Chemical Industries (ICI) 182780. We examined real-time polymerase chain reaction, Western blot, and immunohistochemistry to demonstrate the expression and localization of the uterine TRPM2 gene. The level of TRPM2 messenger RNA and protein are dramatically induced at proestrus, then dropped to base line levels at metestrus, and restored its level at diestrus. The results imply that uterine TRPM2 expression levels are regulated by gonadal steroid hormone E2. Moreover, the E2-induced TRPM2 expression is inhibited by cotreatment with ICI 182780 or P4. Furthermore, the immune-reactive TRPM2 is observed in myometrium and stromal cell of endometrium and also showed alterations in TRPM2 expression during estrus cycle. This study suggests that TRPM2 may be involved in calcium absorption or uterine contraction and the latter may be related to implantation or labor by endogenous sex steroid hormones.