LEFTY2 inhibits endometrial receptivity by downregulating Orai1 expression and store-operated Ca2+ entry

Madhuri S Salker,B Anne Croy,Md Alauddin,Zoe Webster,Diethelm Wallwiener,Jan J Brosens,Jennifer H Steel,Ni Zeng,Yogesh Singh,Jing Yan,Florian Lang,Jaya Nautiyal,Sara Y Brucker,Ruban R Peter Durairaj,Shaqiu Zhang

doi:10.1007/s00109-017-1610-9

Abstract

Early embryo development and endometrial differentiation are initially independent processes, and synchronization, imposed by a limited window of implantation, is critical for reproductive success. A putative negative regulator of endometrial receptivity is LEFTY2, a member of the transforming growth factor (TGF)-β family. LEFTY2 is highly expressed in decidualizing human endometrial stromal cells (HESCs) during the late luteal phase of the menstrual cycle, coinciding with the closure of the window of implantation. Here, we show that flushing of the uterine lumen in mice with recombinant LEFTY2 inhibits the expression of key receptivity genes, including Cox2, Bmp2, and Wnt4, and blocks embryo implantation. In Ishikawa cells, a human endometrial epithelial cell line, LEFTY2 downregulated the expression of calcium release-activated calcium channel protein 1, encoded by ORAI1, and inhibited store-operated Ca2+ entry (SOCE). Furthermore, LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, as well as YM-58483, inhibited, whereas the Ca2+ ionophore, ionomycin, strongly upregulated COX2, BMP2 and WNT4 expression in decidualizing HESCs. These findings suggest that LEFTY2 closes the implantation window, at least in part, by downregulating Orai1, which in turn limits SOCE and antagonizes expression of Ca2+-sensitive receptivity genes.Key messages•Endometrial receptivity is negatively regulated by LEFTY2.•LEFTY2 inhibits the expression of key murine receptivity genes, including Cox2, Bmp2and Wnt4, and blocks embryo implantation.•LEFTY2 downregulates the expression of Orai1 and inhibits SOCE.•LEFTY2 and the Orai1 blockers 2-APB, MRS-1845, and YM-58483 inhibit COX2, BMP2, and WNT4 expression in endometrial cells.•Targeting LEFTY2 and Orai1 may represent a novel approach for treating unexplained infertility.

Highlights

A transient window of uterine receptivity ensures that embryos implant in an optimal endometrial environment [1]
In order to explore the functional significance of increased LEFTY2 expression, we examined the effect of LEFTY2 on embryo implantation in the mouse uterus
Embryo implantation in mice is a stepwise process that starts with attachment of the blastocysts to the endometrial luminal epithelial layer between 3.5 to 4.5 days postcoitus, triggering decidualization of the underlying stromal cells [35] and closure of the uterine lumen [36].To confirm that LEFTY2

Summary

Introduction

A transient window of uterine receptivity ensures that embryos implant in an optimal endometrial environment [1]. The stromal signals responsible for terminating the window of implantation are not well characterized. A putative candidate is Left-Right Determination Factor 2 (LEFTY2), a cytokine highly expressed by decidualizing stromal cells during the late secretory phase of the menstrual cycle [6], i.e., following closure of the window of implantation and prior to menstruation [7]. Following proteolytic processing of the secreted precursor, LEFTY2 acts as an antagonist of the Nodal signaling pathway by interfering both with the binding of NODAL to the activin receptor and the formation of a receptor complex [9]. Induction of the proprotein convertase (PC) 5/6, which processes LEFTY2, is triggered in the mouse uterus in response to artificial decidualization with oil or upon mechanical injury [11]. In vivo gene transfer of Lefty in the mouse uterus leads to implantation failure [14]. The mechanisms underlying the negative impact of LEFTY2 on endometrial receptivity remain largely unknown

Methods

Results

Conclusion