Intrauterine Injection of Umbilical Cord Mesenchymal Stem Cell Exosome Gel Significantly Improves the Pregnancy Rate in Thin Endometrium Rats

Strategies and Challenges of Mesenchymal Stem Cells-Derived Extracellular Vesicles in Infertility

Having genetically related offspring remains an unattainable dream for couples with reproductive failure. Mesenchymal stem cells (MSCs) are multipotent stromal cells derived from various human tissues and organs. As critical paracrine effectors of MSCs, extracellular vesicles (EVs) can carry and deliver bioactive content, thereby participating in intercellular communication and determining cell fate. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have shown promising therapeutic effects, including repairing injured endometria, restoration of ovarian functions, and improving sperm quantity, morphology, and motility, owing to their regenerative potential, abundant sources, high proliferation rates, low immunogenicity, and lack of ethical issues. However, limited knowledge on purification and isolation of MSC-EVs, therapeutic effects, and unpredictable safety have caused challenges in overcoming female and male infertility. To overcome them, future studies should focus on modification/engineering of MSC-EVs with therapeutic biomolecules and combining attractive biomaterials and MSC-EVs. This review highlights the latest studies on MSC-EVs therapies in infertility and the major challenges that must be overcome before clinical translation.

Understanding molecular characteristics of extracellular vesicles derived from different types of mesenchymal stem cells for therapeutic translation

Mesenchymal stem cells (MSCs) have been studied for decades as candidates for cellular therapy, and their secretome, including secreted extracellular vesicles (EVs), has been identified to contribute significantly to regenerative and reparative functions. Emerging evidence has suggested that MSC-EVs alone, could be used as therapeutics that emulate the biological function of MSCs. However, just as with MSCs, MSC-EVs have been shown to vary in composition, depending on the tissue source of the MSCs as well as the protocols employed in culturing the MSCs and obtaining the EVs. Therefore, the importance of careful choice of cell sources and culture environments is receiving increasing attention. Many factors contribute to the therapeutic potential of MSC-EVs, including the source tissue, isolation technique, and culturing conditions. This review illustrates the molecular landscape of EVs derived from different types of MSC cells along with culture strategies. A thorough analysis of publicly available omic datasets was performed to advance the precision understanding of MSC-EVs with unique tissue source-dependent molecular characteristics. The tissue-specific protein and miRNA-driven Reactome ontology analysis was used to reveal distinct patterns of top Reactome ontology pathways across adipose, bone marrow, and umbilical MSC-EVs. Moreover, a meta-analysis assisted by an AI technique was used to analyze the published literature, providing insights into the therapeutic translation of MSC-EVs based on their source tissues.

Bioengineering approaches for the endometrial research and application

The endometrium undergoes a series of precise monthly changes under the regulation of dynamic levels of ovarian hormones that are characterized by repeated shedding and subsequent regeneration without scarring. This provides the potential for wound healing during endometrial injuries. Bioengineering materials highlight the faithful replication of constitutive cells and the extracellular matrix that simulates the physical and biomechanical properties of the endometrium to a larger extent. Significant progress has been made in this field, and functional endometrial tissue bioengineering allows an in-depth investigation of regulatory factors for endometrial and myometrial defects in vitro and provides highly therapeutic methods to alleviate obstetric and gynecological complications. However, much remains to be learned about the latest progress in the application of bioengineering technologies to the human endometrium. Here, we summarize the existing developments in biomaterials and bioengineering models for endometrial regeneration and improving the female reproductive potential.

Evolution of biotechnological advances and regenerative therapies for endometrial disorders: a systematic review

BACKGROUND

The establishment and maintenance of pregnancy depend on endometrial competence. Asherman syndrome (AS) and intrauterine adhesions (IUA), or endometrial atrophy (EA) and thin endometrium (TE), can either originate autonomously or arise as a result from conditions (i.e. endometritis or congenital hypoplasia), or medical interventions (e.g. surgeries, hormonal therapies, uterine curettage or radiotherapy). Affected patients may present an altered or inadequate endometrial lining that hinders embryo implantation and increases the risk of poor pregnancy outcomes and miscarriage. In humans, AS/IUA and EA/TE are mainly treated with surgeries or pharmacotherapy, however the reported efficacy of these therapeutic approaches remains unclear. Thus, novel regenerative techniques utilizing stem cells, growth factors, or tissue engineering have emerged to improve reproductive outcomes.

OBJECTIVE AND RATIONALE

This review comprehensively summarizes the methodologies and outcomes of emerging biotechnologies (cellular, acellular, and bioengineering approaches) to treat human endometrial pathologies. Regenerative therapies derived from human tissues or blood which were studied in preclinical models (in vitro and in vivo) and clinical trials are discussed.

SEARCH METHODS

A systematic search of full-text articles available in PubMed and Embase was conducted to identify original peer-reviewed studies published in English between January 2000 and September 2023. The search terms included: human, uterus, endometrium, Asherman syndrome, intrauterine adhesions, endometrial atrophy, thin endometrium, endometritis, congenital hypoplasia, curettage, radiotherapy, regenerative therapy, bioengineering, stem cells, vesicles, platelet-rich plasma, biomaterials, microfluidic, bioprinting, organoids, hydrogel, scaffold, sheet, miRNA, sildenafil, nitroglycerine, aspirin, growth hormone, progesterone, and estrogen. Preclinical and clinical studies on cellular, acellular, and bioengineering strategies to repair or regenerate the human endometrium were included. Additional studies were identified through manual searches.

OUTCOMES

From a total of 4366 records identified, 164 studies (3.8%) were included for systematic review. Due to heterogeneity in the study design and measured outcome parameters in both preclinical and clinical studies, the findings were evaluated qualitatively and quantitatively without meta-analysis. Groups using stem cell-based treatments for endometrial pathologies commonly employed mesenchymal stem cells (MSCs) derived from the human bone marrow or umbilical cord. Alternatively, acellular therapies based on platelet-rich plasma (PRP) or extracellular vesicles are gaining popularity. These are accompanied by the emergence of bioengineering strategies based on extracellular matrix (ECM)-derived hydrogels or synthetic biosimilars that sustain local delivery of cells and growth factors, reporting promising results. Combined therapies that target multiple aspects of tissue repair and regeneration remain in preclinical testing but have shown translational value. This review highlights the myriad of therapeutic material sources, administration methods, and carriers that have been tested.

WIDER IMPLICATIONS

Therapies that promote endometrial proliferation, vascular development, and tissue repair may help restore endometrial function and, ultimately, fertility. Based on the existing evidence, cost, accessibility, and availability of the therapies, we propose the development of triple-hit regenerative strategies, potentially combining high-yield MSCs (e.g. from bone marrow or umbilical cord) with acellular treatments (PRP), possibly integrated in ECM hydrogels. Advances in biotechnologies together with insights from preclinical models will pave the way for developing personalized treatment regimens for patients with infertility-causing endometrial disorders such as AS/IUA, EA/TE, and endometritis.

REGISTRATION NUMBER

https://osf.io/th8yf/.

Impaired receptivity of thin endometrium: therapeutic potential of mesenchymal stem cells

The endometrium is a resilient and highly dynamic tissue, undergoing cyclic renewal in preparation for embryo implantation. Cyclic endometrial regeneration depends on the intact function of several cell types, including parenchymal, endothelial, and immune cells, as well as adult stem cells that can arise from endometrial or extrauterine sources. The ability of the endometrium to undergo rapid, repeated regeneration without scarring is unique to this tissue. However, if this tissue renewal process is disrupted or dysfunctional, women may present clinically with infertility due to endometrial scarring or persistent atrophic/thin endometrium. Such disorders are rate-limiting in the treatment of female infertility and in the success of in vitro fertilization because of a dearth of treatment options specifically targeting the endometrium. A growing number of studies have explored the potential of adult stem cells, including mesenchymal stem cells (MSCs), to treat women with disorders of endometrial regeneration. MSCs are multipotent adult stem cells with capacity to differentiate into cells such as adipocytes, chondrocytes, and osteoblasts. In addition to their differentiation capacity, MSCs migrate toward injured sites where they secrete bioactive factors (e.g. cytokines, chemokines, growth factors, proteins and extracellular vesicles) to aid in tissue repair. These factors modulate biological processes critical for tissue regeneration, such as angiogenesis, cell migration and immunomodulation. The MSC secretome has therefore attracted significant attention for its therapeutic potential. In the uterus, studies utilizing rodent models and limited human trials have shown a potential benefit of MSCs and the MSC secretome in treatment of endometrial infertility. This review will explore the potential of MSCs to treat women with impaired endometrial receptivity due to a thin endometrium or endometrial scarring. We will provide context supporting leveraging MSCs for this purpose by including a review of mechanisms by which the MSC secretome promotes regeneration and repair of nonreproductive tissues.

Exosomal miR-205-5p Improves Endometrial Receptivity by Upregulating E-Cadherin Expression through ZEB1 Inhibition

Endometrial receptivity is a complex process that prepares the uterine endometrium for embryo implantation; insufficient endometrial receptivity is one of the causes of implantation failure. Here, we analyzed the microRNA expression profiles of exosomes derived from both receptive (RL95-2) and non-receptive (AN3-CA) endometrial epithelial cell (EEC) lines to identify exosomal miRNAs closely linked to endometrial receptivity. Among the 466 differentially expressed miRNAs, miR-205-5p was the most highly expressed in exosomes secreted from receptive RL95-2 cells. miR-205-5p, enriched at the adhesive junction, was closely related to endometrial receptivity. ZEB1, a transcriptional repressor of E-cadherin associated with endometrial receptivity, was identified as a direct target of miR-205-5p. miR-205-5p expression was significantly lower in the endometrial tissues of infertile women than in that of non-infertile women. In vivo, miR-205-5p expression was upregulated in the post-ovulatory phase, and its inhibitor reduced embryo implantation. Furthermore, administration of genetically modified exosomes overexpressing miR-205-5p mimics upregulated E-cadherin expression by targeting ZEB1 and improved spheroid attachment of non-receptive AN3-CA cells. These results suggest that the miR-205-5p/ZEB1/E-cadherin axis plays an important role in regulating endometrial receptivity. Thus, the use of exosomes harboring miR-205-5p mimics can be considered a potential therapeutic approach for improving embryo implantation.

Fibroblast growth factor 1 ameliorates thin endometrium in rats through activation of the autophagic pathway

Background: Thin endometrium is a reproductive disorder that affects embryo implantation. There are several therapies available for this disease, however they are not so effective. Fibroblast growth factor 1 (FGF1) is a member of fibroblast growth factor superfamily (FGFs), and it has been demonstrated that FGF1 expression was altered in samples collected from patients with thin endometrium. However, it is unclear if FGF1 could improve thin endometrium. The aim of this study was to investigate whether FGF1 have a therapeutic effect on thin endometrium. Methods: A model of thin endometrium induced by ethanol was constructed to investigate the effect and mechanism of action of FGF1 in thin endometrium. In the characterization experiments, 6-8 weeks female rats (n = 40) were divided into four groups: i) Control group; ii) Sham group; iii) Injured group; (iv) FGF1 therapy group. Endometrial tissues would be removed after three sexuel cycles after molding. Morphology and histology of the endometrium were evaluated by visual and hematoxylin and eosin staining. Masson staining and expression of α-SMA in endometrium showed the degree of endometrial fibrosis. Western blotting (PCNA、vWF and Vim) and immunohistochemistry (CK19 and MUC-1) demonstrated the effect of FGF1 on cell proliferation and angiogenesis. Moreover, immunohistochemistry (ER and PR) was used to explore the function of endometrium. The remaining rats (n = 36) were divided into three groups: i) Injured group; ii) FGF1 therapy group; and iii) 3-methyladenine. Western blotting (p38、p-p38、PI3K 、SQSTM1/p62、beclin-1 and LC3) was used to explore the mechanisms of FGF1. Results: In FGF1 therapy group, the morphology and histology of endometrium improved compared with the model group. Masson staining and the expression level of α-SMA showed that FGF1 could decrease the fibrotic area of endometrium. Besides, changes in ER and PR expression in the endometrium suggested that FGF1 could restore endometrium-related functions. Western blotting and immunohistochemistry revealed that PCNA, vWF, Vim, CK19 and MUC-1 were significantly increased after FGF1 treatment compared with the thin endometrium. In addition, Western blotting showed that p38, p-p38, PI3K, SQSTM1/p62, beclin-1 and LC3 levels were higher in FGF1 group than in the injured group. Conclusion: FGF1 application cured the thin endometrium caused by ethanol through autophagy mechanism.