Differential regulation of osteopontin and CD44 correlates with infertility status in PCOS patients

R Paravati,E K Onyido,K Brüsehafer,D Gonzalez,Lavinia Margarit,S Spencer-Harty,R S Conlan,K Younas,L W Francis,N De Mello

doi:10.1007/s00109-020-01985-w

Abstract

Endometrial receptivity is mediated by adhesion molecules at the endometrium-trophoblast interface where osteopontin (OPN) and CD44 form a protein complex that plays an important role in embryo recognition. Here, we undertook a prospective study investigating the expression and regulation of OPN and CD44 in 50 fertile and 31 infertile ovulatory polycystic ovarian syndrome (PCOS) patients in the proliferative and secretory phases of the natural menstrual cycle and in 12 infertile anovulatory PCOS patients. Endometrial biopsies and blood samples were evaluated for expression of OPN and CD44 using RT-PCR, immunohistochemistry and ELISA analysis to determine circulating levels of OPN, CD44, TNF-α, IFN-γ and OPN and CD44 levels in biopsy media. Our findings highlighted an increased level of circulating OPN and CD44 in serum from infertile patients that inversely correlated with expression levels in endometrial tissue and positively correlated with levels secreted into biopsy media. OPN and CD44 levels positively correlated to each other in serum and media from fertile and PCOS patients, as well as to circulating TNF-α and IFN-γ. In vitro analysis revealed that hormone treatment induced recruitment of ERα to the OPN and CD44 promoters with a concomitant increase in the expression of these genes. In infertile patients, inflammatory cytokines led to recruitment of NF-κB and STAT1 proteins to the OPN and CD44 promoters, resulting in their overexpression. These observations suggest that the endometrial epithelial OPN-CD44 adhesion complex is deficient in ovulatory PCOS patients and displays an altered stoichiometry in anovulatory patients, which in both cases may perturb apposition. This, together with elevated circulating and local secreted levels of these proteins, may hinder endometrium-trophoblast interactions by saturating OPN and CD44 receptors on the surface of the blastocyst, thereby contributing to the infertility associated with ovulating PCOS patients.Key messages• Endometrial epithelial OPN-CD44 adhesion complex levels are deficient in ovulatory PCOS patients contributing to the endometrial infertility associated with ovulating PCOS patients.• Circulating levels of OPN, CD44 and inflammatory cytokines TNF-α and IFN-γ are altered in infertile PCOS patients.• Increased levels of both OPN and CD44 in biopsy media and serum inversely correlate with endometrial expression of these markers in endometrial tissue.• In infertile PCOS patients, high levels of oestrogens and inflammatory cytokines stimulate the recruitment of transcription factors to the OPN and CD44 promoters to enhance gene transcription.• Our study identifies a novel crosstalk between the CD44-OPN adhesion complex, ERα, STAT1 and NF-κB pathways modulating endometrial receptivity.

Highlights

Endometrial receptivity depends on synchronous biochemical, structural and molecular events for successful embryo implantation to occur during the window of implantation at day 20 to 24 in the menstrual cycle
Significant increases in STAT1 recruitment to STAT1B binding sites in the CD44 (−780/−682, p = 0.041; Fig. 5e) and OPN (−1855/−1681, p = 0.0306; Fig. 5f) promoters were observed following 24 h of IFN-γ stimulation. These results demonstrate that CD44 and OPN regulation by inflammatory cytokines TNF-α and IFN-γ is mediated by the recruitment of NF-κB and STAT1 transcription factors to the promoters of these genes, and is likely to occur in the endometrial tissue of polycystic ovary syndrome (PCOS) patients where the levels of these two cytokines increase
OPN and CD44 are adhesion molecules involved in the trophoblast-endometrial interaction, facilitating apposition of the embryo [8, 31]

Summary

Introduction

Endometrial receptivity depends on synchronous biochemical, structural and molecular events for successful embryo implantation to occur during the window of implantation at day 20 to 24 in the menstrual cycle. This is characterised by optimal hormone levels, cytokine signalling and the presence of luminal endometrial adhesion proteins, including osteopontin (OPN) and CD44, to support the embryo attachment [1, 2]. In infertile PCOS patients, expression of ERα and PR is elevated, leading to altered expression of ERα- and PR-regulated proteins involved in implantation [4]. In the normal secretory phase, endometrium CD44 expression is increased [7], mirroring the expression of OPN, supporting a role for CD44 in facilitating attachment of the blastocyst [8]

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