Endometrium

The human endometrium, previously considered a sterile environment, is now recognized as a low-biomass but biologically active microbial niche critical to reproductive health. Advances in sequencing technologies, particularly shotgun metagenomics, have provided unprecedented insights into the taxonomic and functional complexity of the endometrial microbiome. While 16S rRNA sequencing has delineated the distinction between Lactobacillus-dominant and non-dominant microbial communities, shotgun metagenomics has revealed additional diversity at the species and strain level, uncovering microbial signatures that remain undetected by amplicon-based approaches. Current evidence supports the association of Lactobacillus dominance with endometrial homeostasis and favorable reproductive outcomes. Dysbiosis, characterized by increased microbial diversity and enrichment of anaerobic taxa such as Gardnerella, Atopobium, Prevotella, and Streptococcus, is linked to chronic endometritis, implantation failure, and adverse IVF results. Beyond compositional differences, the endometrial microbiome interacts with the host through immunological, metabolic, and epigenetic mechanisms. These interactions modulate cytokine signaling, epithelial barrier integrity, and receptivity-associated gene expression, ultimately influencing embryo implantation. However, discrepancies between published studies reflect the lack of standardized protocols for sampling, DNA extraction, and bioinformatic analysis, as well as the inherent challenges of studying low-biomass environments. Factors such as geography, ethnicity, hormonal status, and antibiotic exposure further contribute to interindividual variability. Culturomics approaches complement sequencing by enabling the isolation of viable bacterial strains, offering perspectives for microbiome-based biotherapeutics. Emerging 3D endometrial models provide additional tools to dissect microbiome-host interactions under controlled conditions. Taken together, the growing body of data highlights the potential of endometrial microbiome profiling as a biomarker for reproductive success and as a target for personalized interventions. Future research should focus on integrating multi-omics approaches and functional analyses to establish causal relationships and translate findings into clinical practice. This review gives a new insight into current knowledge on the uterine microbiome and its impact on implantation success, analyzed through the lenses of microbiology, immunology, and oxidative stress.

Polycystic ovary syndrome (PCOS) is a systemic metabolic and endocrine disorder that significantly disrupts reproductive physiology and endometrial function. In this narrative review, we examine the molecular impact of metabolic and hormonal imbalances on the endometrium of women with PCOS. We investigate the specific mechanisms that delineate how hyperinsulinemia and insulin resistance, chronic low-grade inflammation, and estrogen/progesterone/androgen imbalance contribute to altered epigenetic, transcriptomic, metabolomic, and signaling profiles in a wide array of different cell types within endometrial tissues. The synergistic interplay between upregulated inflammatory cytokines (e.g., IL-1,2,6,8,17,18, and TNF-α), along with key changes in critical molecular pathways associated with hyperinsulinemia and insulin resistance (e.g., PI3K/AKT/MAPK, and Wnt/β-catenin), in addition to aberrant sex steroid hormone signaling (e.g., CYP19A1, COX-2, PGE2, HOXA10, 11βHSD2), promotes deleterious changes within the endometrial microenvironment. These anomalies underpin a spectrum of clinical manifestations observed in women with PCOS at each stage of the life course, including abnormal uterine bleeding in reproductive-age women, impaired decidualization in pregnancy, and altered postmenopausal endometrial physiology. Clinically, these alterations are associated with abnormal uterine bleeding, subfertility, implantation failure, miscarriage, pregnancy complications, and postmenopausal endometrial hyperplasia and cancer. Overall, our review provides novel insights into the molecular mechanisms linking systemic metabolic and endocrine dysfunction with endometrial pathology in PCOS and has broader implications that apply to all women.

Endometriosis is a chronic disease characterized by the ectopic presence of endometrial cells that evade apoptosis and survive and proliferate under harsh environmental conditions. It is closely associated with infertility and pregnancy-related complications. This review focuses on the molecular pathophysiology of endometriosis, particularly the disruption of the p53-AMPK-mTOR signaling axis, and highlights the dysregulation of decidualization and cellular senescence, incorporating recent findings in reproductive physiology. A comprehensive literature search was conducted using PubMed and Google Scholar without temporal restrictions. Endometriotic cells adapt to the hostile peritoneal environment through resistance to apoptosis and alterations in autophagy. In the early stages, autophagy activation may promote cell survival; however, as the disease progresses, autophagic activity tends to decline. Aberrant activation of mTOR signaling is implicated in this process, contributing to the suppression of autophagy, impaired decidualization, and promotion of cellular senescence, ultimately facilitating lesion progression and infertility. Indeed, in the eutopic endometrium of patients with endometriosis, progesterone resistance, elevated inflammatory cytokines, and epigenetic abnormalities are known to reduce endometrial receptivity. Moreover, suppression of autophagy leads to excessive cellular senescence and secretion of the senescence-associated secretory phenotype (SASP), thereby interfering with proper decidualization. Maintaining an appropriate balance between decidualization and cellular senescence is essential for reproductive function. Future development of therapeutic strategies targeting these processes is expected to help overcome infertility associated with endometriosis.

Endometrial regeneration remains a significant clinical challenge for women with intrauterine adhesions (IUAs), thin endometrium, or uterine factor infertility, conditions that severely impair fertility and reproductive outcomes. Traditional hormonal and surgical interventions often fail to restore the structural and functional integrity of damaged endometrial tissue. This review comprehensively examines integrative bioengineering strategies for endometrial regeneration, focusing on the synergistic applications of biomaterials, stem cells, organoids, and organ-on-a-chip technologies. Natural polymers such as collagen, gelatin, alginate, hyaluronic acid, and synthetic polymers including PCL, PLA, PGA, and PLGA have been comprehensively evaluated for their ability to mimic extracellular matrix, support cell proliferation, angiogenesis, and modulate immune responses. The incorporation of mesenchymal stem cells, extracellular vesicles, and growth factors into bioengineered scaffolds, such as hydrogels and nanofiber membranes, enhances regenerative efficacy. Furthermore, emerging platforms, such as endometrial organoids, 3D bioprinting, and organ-on-a-chip systems, offer physiologically relevant models for precision regenerative medicine. Innovations such as AI-assisted monitoring, 4D printing, and advanced drug delivery systems represent transformative approaches to overcome current therapeutic limitations. This review highlights the convergence of materials science, stem cell biology, and microengineering as a foundation for next-generation, personalized therapies aimed at restoring endometrial function and fertility. In addition, the review highlights biomaterial-based strategies as the foundation of endometrial regeneration, by detailing how natural polymers (e.g., collagen, gelatin, alginate, hyaluronic acid) and synthetic polymers (e.g., PCL, PLA, PLGA) support tissue repair structurally and by mediating biological functions. The integration of advanced technologies, such as 4D printing, AI-assisted monitoring, and stem cell-derived extracellular vesicle delivery has emerged as a transformative direction for overcoming current clinical challenges. Collectively, these approaches offer a next-generation therapeutic paradigm for restoring endometrial function and fertility.