MON-011 NALCN Expression Is Regulated by Progesterone and Estrogen in Human Myometrial Smooth Muscle Cells

During pregnancy, the uterus transitions from a quiescent state to a highly contractile, excitable state. Both ion channels and hormones are essential for this transition. We recently identified that the Na(+) leak channel, non-selective (NALCN) contributes to a leak current in human MSMCs and mice lacking NALCN have prolonged and dysfunctional labor. Additionally, NALCN levels change throughout mouse pregnancy suggesting regulation by hormones of pregnancy, specifically estrogen and progesterone. Here, we tested the hypothesis that P4, a pro-quiescent hormone, and E2, a pro-contractile hormone, regulate NALCN expression and current in the myometrium. In a human immortalized myometrial cells (HM6ERMS2), using qPCR we measured a 2.3 fold decrease and a 5.6 fold increase in NALCN mRNA expression in the presence of E2 and P4, respectively. These findings were also confirmed when NALCN protein expression were measured by immunoblot. Conversely, treatment with the ER antagonist, ICI 182,780, significantly increased NALCN mRNA expression, while treatment with the PR antagonist RU486 significantly decreased NALCN mRNA expression suggesting E2 and P4 work through their respective receptors to regulate NALCN. P4 differentially regulates myometrial activity depending on which progesterone receptor is activated: PRA, promotes contractility, whereas PRB promotes quiescence. Thus to study the effect of each PR, we used a human myometrial cell line stably expressing PRA or PRB, and measured similar increases in NALCN mRNA expression in both cell lines treated with P4. To determine the functional consequences of E2 and P4, we measured NALCN-dependent leak current in MSMCs using whole cell patch clamping. We observed that E2 significantly inhibited while P4 significantly enhanced NALCN current. Finally, we identified estrogen response and progesterone response elements (ERE and PRE) in the NALCN promoter and showed that the PREs contributed to P4 regulation while the ERE did not contribute to the regulation of NALCN expression using luciferase based promoter assays. Overall, our findings show that NALCN is upregulated by P4, the pro-quiescent hormone, and downregulated by E2, the pro-contractile hormone. This data reveals a new mechanism by which NALCN is regulated in the myometrium and may suggest a novel role for NALCN during pregnancy. Further investigation into these novel roles can provide an insight into potential targets to modulate uterine quiescence and contractility.