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Research Question: What is the underlying mechanism of IVF and embryo transfer (IVF-ET) failure in patients with elevated peripheral blood natural killer cell (pNK) counts?, Design: Patients undergoing IVF-ET cycles for tubal obstruction or pelvic adhesion (n = 486) were assigned to three groups: high (CD56 + CD16 + pNK >30% [n = 49]); medium (15< CD56 + CD16 + pNK ≤30% [n = 211]); and normal pNK groups (5≤ CD56 + CD16 + pNK ≤15% [n = 226]). Their general condition, previous pregnancy history and IVF outcomes were compared. Uterine fluid and endometrial tissue from patients in the high and normal pNK groups were collected during the mid-secretory phase and studied to elucidate the molecular mechanism underlying impaired endometrial receptivity., Results: The highest incidence of IVF-ET cycles (P < 0.0001) and biochemical pregnancy losses (P < 0.0001), and lowest implantation and clinical pregnancy rates (both P < 0.0001), were observed in patients with pNK over 30%. No significant difference was found in the number of previous miscarriages and rate of spontaneous miscarriage in IVF outcomes. Lower Septin11 (SEPT11) expression in the uterine fluid and endometrial epithelial cells (EEC), and higher endometrial IFN-γ, was observed in patients with high pNK. Ishikawa cell and human endometrial epithelial cell (HEEC) adhesion was inhibited after SEPT11 knock-down. Elevated IFN-γ decreased the SEPT11 protein levels in Ishikawa cells and HEECs., Conclusions: CD56 + CD16 + pNK above 30% may be a threshold for adverse IVF-ET outcomes. Low SEPT11 expression in EEC inhibits cell adhesion, which may cause impaired endometrial receptivity in patients with elevated pNK. The level of SEPT11 in mid-secretory uterine fluid could serve as a non-invasive marker to assess endometrial receptivity in these patients., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Introduction: Recurrent implantation failure (RIF) is a challenging problem of assisted reproductive technology that arises mainly due to inadequate endometrial receptivity and its pathogenesis is still unclear., Objectives: In this study, we conducted the first investigation of the effect of decreased PIBF1 expression in mid-secretory phase on endometrial receptivity in patients with RIF., Methods: Microarray assay, reverse transcriptase-quantitative polymerase chain reaction, western blot, and in-vitro experiments were conducted., Results: The results showed that progesterone-induced blocking factor 1 (PIBF1) expression was highest in the mid-secretory endometrium in control subjects, but was significantly lower in RIF patients. In Ishikawa and human endometrial stromal cells (HESCs), rather than human endometrial epithelial cells, PIBF1 knockdown significantly downregulated cell proliferation and the levels of interleukin 6 (IL6) and phosphorylated signal transducer and activator of transcription-3 (p-STAT3). Besides, in HESCs, the levels of IL6, p-STAT3, prolactin and insulin-like growth factor binding-protein-1 (IGFBP1) decreased after PIBF1 knockdown during in-vitro decidualization. All these cellular changes could be notably restored by PIBF1 or IL6 overexpression. Consistent with our findings with PIBF1, the levels of IL6, p-STAT3, ki-67, prolactin, and IGFBP1 in the mid-secretory endometrium were notably lower in patients with RIF compared with controls., Conclusion: In summary, in the mid-secretory phase, decreased expression of PIBF1, IL6, and p-STAT3 inhibited HESC proliferation and decidualization, which is of theoretical and clinical importance for future research and clinical-treatment strategies., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2020 The Authors. Published by Elsevier B.V. on behalf of Cairo University.)

Study Question: Is recurrent implantation failure (RIF) associated with decreased expression of platelet and endothelial cell adhesion molecule 1 (PECAM1) and transforming growth factor β1 (TGF-β1) in the endometrium during the implantation window?, Summary Answer: The present study demonstrates that the expression of PECAM1 and TGF-β1 is significantly decreased in the mid-secretory endometrium in women with RIF, which may account for embryo implantation failure., What Is Known Already: RIF has become a bottleneck issue that hampers the improvement of pregnancy rates in IVF-embryo transfer (IVF-ET). The causes of RIF are complex and may involve the dysregulation of various growth factors, metabolites, and inflammatory cytokines. At present, the precise pathogenesis of RIF has not been elucidated., Study Design, Size, Duration: This was a prospective case-control study. Endometrial tissue samples were obtained from January 2014 to December 2016 from two groups of women who had undergone IVF (RIF group, 22 women who underwent ≥3 ETs including a total of ≥4 good-quality embryos without pregnancy, control group, 18 women who conceived in their first treatment cycle). At the same time, samples were obtained from 18 women with infertility secondary to tubal factor in the early proliferative, late proliferative and mid-secretory phases of the menstrual cycle (n = 6 per group). Samples used for isolation of primary human endometrial epithelial cells and stromal cells (HEECs and HESCs) were collected in December 2017 from six women with infertility secondary to tubal factor., Participants/materials, Setting, Methods: We investigated gene expression using integrative whole genome expression microarray analysis, including differentially expressed gene screening, principal component analysis, and functional enrichment analysis. RT-qPCR, western blotting, immunohistochemistry, immunofluorescence co-localization analysis and short hairpin RNA (shRNA) plasmid transfection in Ishikawa cell line, HEECs and HESCs were used to investigate the expression of PECAM1 and TGF-β1., Main Results and the Role of Chance: Integrative data mining of whole-genome expression profiles identified cell adhesion as a key regulator in RIF. Database retrieval and literature review screened several novel cell adhesion-related genes that might participate in embryo implantation, which include PECAM1, intercellular adhesion molecule 2 (ICAM2), integrin subunit β2 (ITGB2), selectin P (SELP) and TEK receptor tyrosine kinase (TEK). Among these targets, the mRNA and protein levels of PECAM1 were significantly lower in the RIF group than those in the control group. During the menstrual cycles of women with secondary infertility, the protein expression level of PECAM1 was the lowest in early proliferative phase, slightly increased in late proliferative phase and was the highest in mid-secretory phase. While the expression level of HOXA10, an endometrial receptivity marker, kept at a low level in early proliferative phase and increased in late proliferative phase, then maintained at a high level in the mid-secretory phase. Furthermore, TGF-β1, mediated by PECAM1, was also decreased significantly in the RIF group. Using shRNA-based approach, we demonstrated that the depletion of PECAM1 significantly decreased the expression of TGF-β1 in Ishikawa cells, as well as in primary HEECs and HESCs. These results indicated that PECAM1 and TGF-β1 might play a pivotal role in modulating endometrial receptivity., Limitations Reasons for Caution: Although we have shown that PECAM1 and TGF-β1 were down-regulated in the women with RIF, the molecular mechanism of the effect of the factors on the endometrial receptivity remain unclear., Wider Implications of the Findings: Our findings provide insight into the contribution of PECAM1 and TGF-β1 in regulating implantation, which could be used to develop potential therapeutic methods for RIF., Study Funding/competing Interest(s): This work was supported by grants from the National Natural Science Foundation of China (Nos. 81771656 and 81370763), Special fund for clinical research of the Chinese Medical Association (No. 16020480664), and the Merck Serono China Research Fund for Fertility Agreement. The authors have no competing interests.

Background: The precise pathogenesis of poor endometrial receptivity in recurrent implantation failure (RIF) remains unclear. This study was aimed at exploring the effects of different CD44 isoforms in the mid-secretory phase endometrium on endometrial receptivity in women with RIF. Methods: Mid-secretory phase endometrial tissue samples were obtained from the following two groups of women who had undergone IVF: (a) 24 patients with RIF and (b) 18 patients with infertility due to tubal obstruction, who had achieved a successful clinical pregnancy after the first embryo transfer in IVF (control group). Identification of differentially expressed CD44 isoforms in endometrial tissues was assessed using immunohistochemistry, qPCR, and western blotting. Effects of overexpression and knockdown of CD44v3 on proliferation and decidualization of immortalized human endometrial stromal cells (T-HESCs) and primary HESCs were investigated by qPCR and western blot analysis. A heterologous coculture system of embryo implantation was constructed to mimic the process of trophoblast invasion during implantation. Results: The expression of CD44v3 was significantly higher in the mid-secretory phase of endometrial stromal cells than in the proliferation phase, but was notably lower in RIF patients. Knockdown of CD44v3 significantly downregulated cell proliferation both in T-HESCs and HESCs. The expression of decidualization markers, prolactin (PRL) and insulin like growth factor binding protein-1 (IGFBP1), was notably decreased following the knockdown of CD44v3, whereas the expression of both PRL and IGFBP1 increased after its overexpression in HESCs. Furthermore, the CD44v3-knockdown HESCs displayed significant deficiency in supporting trophoblast outgrowth in a coculture system of embryo implantation; however, overexpression of CD44v3 in HESCs promoted trophoblast outgrowth. Conclusion: The reduced expression of CD44v3 suppresses the proliferation and decidualization of HESCs, which might play a pivotal role in poor endometrial receptivity in women with RIF. [ABSTRACT FROM AUTHOR]