Human chorionic gonadotropin enhances receptivity of fallopian tube through down-regulation of olfactomedin-1

Abstract

Tubal ectopic pregnancy (TEP) occurs in 2 to 5 % of all pregnancy. In humans, TEP may lead to tubal rupture and consequently hemorrhage and maternity death. Various factors, including tubal infection, tubal damage, smoking and in vitro fertilization are associated with TEP. Previous microarray studies suggested that Olfactomedin-1 (Olfm1) is down-regulated in receptive endometrium during the window of implantation. In vitro studies demonstrated that down-regulation of Olfm1 would increase attachment of spheroids (embryo surrogate) onto human endometrial epithelial cells, while recombinant Olfm1 reduces spheroids attachment in vitro. Clinical study found that intrauterine injection of hCG could enhance implantation rate in IVF/ICSI. Our preliminary result showed that Olfm1 was also expressed in epithelial cells of Fallopian tube. Interestingly, results from our laboratory demonstrated that decreased epithelial Olfm1 expressions were found in Fallopian tubes from women with TEP. Furthermore, our unpublished data suggested that human chorionic gonadotropin (hCG), a heterodimeric peptide hormone secreted by human pre-implantation embryo, down-regulated Olfm1 expression in Fallopian tube epithelial cells (OE-E6/E7). Therefore, we hypothesize that embryonic hCG and possibly sex steroid hormone down-regulates Oflm1 in the Fallopian tube leading to tubal implantation and hence causing TEP. This study aimed to find out the role of hCG in establishment of TEP. Immunohistochemistry of estrogen receptor alpha (ER alpha), progesterone receptor (PR), glucocorticoid receptor (GR), hCG receptor and Olfm1 was compared in sections of Fallopian tubes taken from women in the follicular (n=6) and luteal (n=5) phases . JAR spheroid-Fallopian epithelial cell (OE-E6/E7) coculture model was used to evaluate the attachment rate. No significant difference (p>0.05) was observed in ER alpha, PR and GR expressions in both follicular and luteal phase samples; while hCG receptor and Olfm1 were up- and down-regulated respectively in luteal phase Fallopian tubes compared to those in follicular phase. In the co-culture model, hCG (25IU/ml) down-regulated Olfm1 expression but stimulates JAR spheroids attachment onto OE-E6/E7 cells when the OE-E6/E7 cells but not the JAR cells were treated with hCG. Moreover, only hCG and its beta-subunit could enhance attachment in vitro. Knockdown of hCG receptor in the OE-E6/E7 cells by siRNA reduced; while knockdown of Olfm1 increased spheroids attachment in vitro. Taken together, Olfm1 showed a cyclic expression pattern in Fallopian epithelial cells, which is the same as endometrium epithelial cells. hCG down-regulated Olfm1 and enhanced spheroids attachment onto Fallopian epithelial cells. The molecular mechanism by which hCG down-regulates Olfm1 warrants further investigation. (The work is partly supported by CRCG grant to KFL)