With the advancement of in vitro fertilization-embryo transfer (IVF-ET), various aspects from controlled ovarian stimulation to embryo transfer have improved significantly. Nevertheless, approximately 5 %–10 % of patients undergoing assisted reproductive technology (ART) are diagnosed as recurrent implantation failure (RIF) during the treatment [1,2]. RIF has become a bottleneck issue affecting the success rate of IVF-ET. Although clinicians have recognized the existence of RIF, its exact pathogenesis remains unclear and requires further in-depth research [3]. Currently, the etiology of RIF remains unclear. Exploring the molecular mechanisms underlying RIF and identifying breakthroughs to improve embryo implantation success are crucial for infertile couples affected by this condition.

Embryo implantation consists of three stages: apposition, adhesion, and invasion. This process relies on the coordinated interaction between embryo development and changes in endometrium, with decidualization playing a crucial role [4]. Decidualization involves the transformation of endometrial stromal cells into secretory decidual stromal cells under the influence of estrogen and progesterone [[5], [6], [7], [8]]. These decidual stromal cells secrete specific biomarkers, such as prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1), which regulate steroid metabolism and other pathways crucial for embryo implantation [9,10].

Impaired decidualization is increasingly recognized as a factor in implantation-related disorders, including embryo implantation failure and early miscarriage [[11], [12], [13], [14], [15]]. During decidualization, the endometrium undergoes rapid growth and differentiation, along with the degradation and remodeling of the extracellular matrix (ECM) [16]. The ECM responds to trophoblast invasion during embryo implantation, participating in the remodeling of the maternal-fetal interface [17]. Fibronectin interacts with various small molecules, growth factors, proteoglycans, and cell surface receptors, playing significant role in this process. These interactions provide essential signals that induce specific cellular behaviors, such as differentiation and epithelial-mesenchymal transition [18]. Both processes are vital during endometrial decidualization, underscoring the importance of a well-coordinated decidualization process for successful embryo implantation [19].

Members of the transforming growth factor-β (TGF-β) family have multiple binding sites in fibronectin [20]. They interact with each other and influence various biological activities mutually, collectively regulating cellular functions. TGF-β proteins can co-localize with fibronectin and induce epithelial-mesenchymal transition through fibronectin [21]. Studies have shown that inhibition of TGF-β1 can decrease the mRNA level of extracellular matrix-related genes collagen I and fibronectin 1 (FN1) in hypertrophic scar fibroblasts, inhibiting extracellular matrix deposition [22]. In bone marrow mesenchymal stem cells, TGF-β1 can enhance the expression levels of FN1 and further accelerate the self-transformation of bone marrow mesenchymal stem cells [23]. In rat glomerular mesangial cells, TGF-β1 can induce the expression of extracellular matrix proteins such as FN1, participating in the regulation of anti-fibrosis processes in the kidney mediated by all-trans retinoic acid [24].

FN1 is a high-molecular-weight glycoprotein that plays a crucial role in cell adhesion, proliferation, migration, and differentiation. It has been implicated in various biological, including fibrosis and epithelial-mesenchymal transition [25,26]. FN1 interacts with collagen, and fibrinogen to regulate its structural conformation and biological activity [27]. Notably, FN1 knockdown significantly inhibits the proliferation and adhesion capacity of normal endometrial fibroblasts [26]. The expression of FN1 is also closely associated endometrial pathology. It is downregulated in the endometrium of patients with endometriosis [28], whereas it is upregulated in uterine fibroids and is associated with the proliferation and adhesion functions of fibroid cells [29]. These studies suggest that FN1 plays a critical role in extracellular matrix remodeling, cell proliferation, and adhesion. However, its precise function in embryo implantation and its involvement in the pathogenesis of RIF warrant further investigation.

With advancements in mass spectrometry, proteomics has increasingly transitioned from basic medical research to clinical applications. Scheliga et al. employed proteomic techniques to analyze protein expression changes before and after endometrial scratching, revealing endometrial scratching may influence endometrial receptivity by modulating extracellular matrix remodeling. This finding provides a theoretical foundation for clinical procedures [30]. Similarly, Pérez-Debén et al. utilized isobaric tags for relative and absolute quantitation (iTRAQ) to compare the endometrial proteomes of fertile women, intrauterine device users, and RIF patients. Their study demonstrated significant alterations in the endometrial proteome induced by intrauterine devices and identified key proteins involved in regulating endometrial receptivity [31]. iTRAQ facilitates a better understanding of endometrial protein function by allowing accurate comparison of protein expression between multiple samples [32]. In this study, we employed iTRAQ-based mass spectrometry analysis to identify differentially expressed proteins in the endometrium of RIF patients compared to healthy women. Furthermore, we explored the molecular mechanisms by which these proteins contribute to the pathophysiology of RIF.