The impaired endometrial receptivity is a major factor contributing to infertility in patients with endometriosis (EM), but the underlying mechanism remains unclear. Our study aimed to investigate the role of Kruppel-like factor 15 (KLF15) in endometrial receptivity and its regulation in EM. We observed a significant decrease in KLF15 expression in the mid-secretory epithelial endometrial cells of EM patients compared to normal females without EM. To confirm the role of KLF15 in endometrial receptivity, we found a significantly reduced KLF15 expression and a significant decrease in embryo implantation number in the rat model via uterine horn infection with siRNA. This highlights the importance of KLF15 as a regulator receptivity. Furthermore, through ChIP-qPCR, we discovered that the progesterone receptor (PR) directly binds to KLF15 promoter regions, indicating that progesterone resistance may mediate the decrease in KLF15 expression in EM patients. Additionally, we found that the mid-secretory endometrium of EM patients exhibited impaired epithelial–mesenchymal transition (EMT). Knockdown of KLF15 upregulated E-cadherin and downregulated vimentin expression, leading to inhibited invasiveness and migration of Ishikawa cells. Overexpression KLF15 promotes EMT, invasiveness, and migration ability, and increases the attachment rate of JAR cells to Ishikawa cells. Through RNA-seq analysis, we identified TWIST2 as a downstream gene of KLF15. We confirmed that KLF15 directly binds to the promoter region of TWIST2 via ChIP-qPCR, promoting epithelial cell EMT during the establishment of endometrial receptivity. Our study reveals the involvement of KLF15 in the regulation of endometrial receptivity and its downstream effects on EMT. These findings provide valuable insights into potential therapeutic approaches for treating non-receptive endometrium in patients with EM.

Current endometrial receptivity analysis is invasive, preventing embryo transfer during the biopsy cycle. This study aims to screen serum sncRNAs as non-invasive biomarkers for ERA tests. The study included 12 infertile patients undergoing IVF-ET and ERA, whose serum samples were collected for high-energy sequencing technology to detect sncRNA expression profiles. We overexpressed and knocked down tsRNA-35:73-Asp-GTC-1 in the decidualized Immortalized Human Eutopic Endometrial Stromal Cells (HESC) model cultured in vitro to further investigate the its effect on decidualization. The predicted tsRNA-35:73-Asp-GTC-1 target gene was verified by PCR analysis. We screened 286 differentially expressed tsRNAs, 46 miRNAs, and 106 piRNAs. KEGG analysis indicated that differentially expressed tsRNAs were associated with pathways such as 'Calcium signaling pathway,' 'Sphingolipid signaling pathway,' etc. The results of RT-qPCR validation showed that the trends of four significantly differentially expressed tsRNAs in serum and endometrium were consistent with sequencing results. ROC curves demonstrated that these four tsRNAs have good predictive value for endometrial receptivity. Overexpression of tsRNA-35:73-Asp-GTC-1 affected the morphology of decidualized cells, and the decidualization indicators also showed a decreasing trend. While knocking down tsRNA-35:73-Asp-GTC-1 had the opposite effect. The RT-qPCR results showed that tsRNA-35:73-Asp-GTC-1 was associated with the Wnt3 target gene. Serum sncRNA analysis shows potential for studying the molecular mechanisms of endometrial receptivity. Four serum tsRNAs can serve as novel biomarkers for non-invasive endometrial receptivity detection. TsRNA-35:73-Asp-GTC-1 may further regulate endometrial receptivity by targeting Wnt3.

Studies have reported that non-receptive endometrium or abnormal decidualization was closely related to recurrent implantation failure (RIF). MLL1 is a histone H3 lysine 4 trimethylation (H3K4me3) transferase that regulates the transcriptional activation of target genes. The role of MLL1 has been underexplored during decidualization. In our research, we found the expression of MLL1 was closely related to endometrial receptivity, and it was responsible to hormone stimulation. Inhibiting the function of MLL1 by MM102 reduced the transformation of HESCs. Furthermore, down-regulation of MLL1 by siRNA transfection significantly decreased PGR and its target genes expression. MLL1 act as a co-activator of ER alpha, and both of them were recruited to PGR regulatory regions, thus promote PGR transcription. Our study showed that MLL1 plays a key role in promoting progesterone signalling transmission.