Stem cell paracrine actions in tissue regeneration and potential therapeutic effect in human endometrium: a retrospective study

A self-forming bone membrane generated by periosteum-derived stem cell spheroids enhances the repair of bone defects

The periosteum, a highly specialized thin tissue, is instrumental in contributing to as much as 70 % of early bone formation. Recognizing the periosteum's vital physiological roles, the fabrication of a biomimetic periosteum has risen as an auspicious strategy for addressing extensive bone defects. In the study, we obtained such biomimetic periosteum by utilizing periosteum-derived stem cells (PDSCs) spheroids. These spheroids are induced to spontaneously generate a bioactive membrane on a delicate 3D-printed polycaprolactone (PCL) substrate. This process yields a biomimetic periosteum rich in the resources needed for bone repair. The in vitro evaluations demonstrated that this membrane can act as a repository for growth factors and stem cells. The release kinetics confirmed a sustained delivery of BMP-2 and VEGF, which promoted enhanced osteogenesis and angiogenesis in vitro, respectively. The in vivo results further highlighted robust bone regeneration from critical cranial defects upon the application of this biomimetic periosteum. The biomimetic periosteum, easily harvested and potent in bioactivity, presents substantial clinical potential, particularly for the treatment of critical-sized bone defects. STATEMENT OF SIGNIFICANCE: PDSC theoretically demonstrates substantial potential in membrane construction, a value we've harnessed in this pioneering application. By employing cell spheroids, we've successfully integrated a substantial number of cells into the membrane framework. PDSC spheroids exhibit the remarkable ability to self-assemble into functional membranes, endowing them with robust biological capabilities that enhance their performance in biological systems. The in vitro evaluations demonstrated that this membrane can act as a repository for growth factors and stem cells. The in vivo bone repair facilitated by this membrane is notably effective, characterized by superior bone quality and accelerated formation rates. This process mirrors the natural intramembrane ossification, offering a promising approach to bone integration and regeneration.

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/.

Advances in Nanomedicine and Biomaterials for Endometrial Regeneration: A Comprehensive Review

The endometrium is an extremely important component of the uterus and is crucial for individual health and human reproduction. However, traditional methods still struggle to ideally repair the structure and function of damaged endometrium and restore fertility. Therefore, seeking and developing innovative technologies and materials has the potential to repair and regenerate damaged or diseased endometrium. The emergence and functionalization of various nanomedicine and biomaterials, as well as the proposal and development of regenerative medicine and tissue engineering techniques, have brought great hope for solving these problems. In this review, we will summarize various nanomedicine, biomaterials, and innovative technologies that contribute to endometrial regeneration, including nanoscale exosomes, nanomaterials, stem cell-based materials, naturally sourced biomaterials, chemically synthesized biomaterials, approaches and methods for functionalizing biomaterials, as well as the application of revolutionary new technologies such as organoids, organ-on-chips, artificial intelligence, etc. The diverse design and modification of new biomaterials endow them with new functionalities, such as microstructure or nanostructure, mechanical properties, biological functions, and cellular microenvironment regulation. It will provide new options for the regeneration of endometrium, bring new hope for the reconstruction and recovery of patients' reproductive abilities.

The Endometrial Stem/Progenitor Cells and Their Niches

Endometrial stem/progenitor cells are a type of stem cells with the ability to self-renew and differentiate into multiple cell types. They exist in the endometrium and form niches with their neighbor cells and extracellular matrix. The interaction between endometrial stem/progenitor cells and niches plays an important role in maintaining, repairing, and regenerating the endometrial structure and function. This review will discuss the characteristics and functions of endometrial stem/progenitor cells and their niches, the mechanisms of their interaction, and their roles in endometrial regeneration and diseases. Finally, the prospects for their applications will also be explored.

Exosomes from preconditioned mesenchymal stem cells: Tissue repair and regeneration

As a prominent research area in tissue repair and regeneration, mesenchymal stem cells (MSCs) have garnered substantial attention for their potential in the treatment of various diseases. It is now widely recognized that the therapeutic effects of MSCs primarily occur through paracrine mechanisms. Among these mechanisms, exosomes play a crucial role by exerting a series of regulatory effects on surrounding cells and tissues. While exosomes have shown promise in treating various diseases, they do have some limitations, such as limited secretion, poor targeting, and single functionality. However, MSC preconditioning can enhance the production of exosomes, lead to more stable functionality and improve therapeutic effects. Moreover, exosomes could also serve as carriers for specific drugs or genes, enabling more precise treatments of diseases. This review summarizes the most recent literatures on how preconditioning of MSCs influences the regenerative potential of their exosomes in tissue repair and provides new insights into the therapeutic application of exosomes derived from MSCs.

Long-term maintenance of human endometrial epithelial organoids and their stem cell properties

The endometrium undergoes dynamic changes throughout the menstrual cycle and pregnancy, which is unique to primates. Endometrium remodeling is essential for the implantation and nutritional support of the conceptus. Despite this, the role of uterine glands in driving endometrial tissue remodeling is still poorly understood. To address this, a 3-dimensional culture system was used to generate endometrial epithelial organoids from human endometrium biopsies. These organoids are genetically stable, long-term expandability. They reproduce some functions of uterine glands in vivo. The epithelial organoids exhibit characteristics of stem cells, with the proportion of stem cells increasing with culture time and passage number. Long-term maintenance of organoids strongly expressed stemness related genes accompanied by a decrease expression in mature epithelial gene, which suggests the organoids had switched from a mature stage to a progenitor stage. Thus we proposed the possible markers for epithelial progenitors. Meanwhile, long-term cultured organoids exhibit an increase in the proportion of luminal epithelial stem cells, accompanied by a decrease of glandular epithelial stem cells. Organoids also show hormone responsiveness, reflecting the various stages of the menstrual cycle and early pregnancy.

Exosomes Highlight Future Directions in the Treatment of Acute Kidney Injury

Acute kidney injury (AKI) is a severe health problem associated with high morbidity and mortality rates. It currently lacks specific therapeutic strategies. This review focuses on the mechanisms underlying the actions of exosomes derived from different cell sources, including red blood cells, macrophages, monocytes, mesenchymal stem cells, and renal tubular cells, in AKI. We also investigate the effects of various exosome contents (such as miRNA, lncRNA, circRNA, mRNA, and proteins) in promoting renal tubular cell regeneration and angiogenesis, regulating autophagy, suppressing inflammatory responses and oxidative stress, and preventing fibrosis to facilitate AKI repair. Moreover, we highlight the interactions between macrophages and renal tubular cells through exosomes, which contribute to the progression of AKI. Additionally, exosomes and their contents show promise as potential biomarkers for diagnosing AKI. The engineering of exosomes has improved their clinical potential by enhancing isolation and enrichment, target delivery to injured renal tissues, and incorporating small molecular modifications for clinical use. However, further research is needed to better understand the specific mechanisms underlying exosome actions, their delivery pathways to renal tubular cells, and the application of multi-omics research in studying AKI.

Development of cell-laden multimodular Lego-like customizable endometrial tissue assembly for successful tissue regeneration

BACKGROUND

The endometrium, the inner lining of the uterine cavity, plays essential roles in embryo implantation and its subsequent development. Although some positive results were preliminarily archived, the regeneration of damaged endometrial tissues by administrating stem cells only is very challenging due to the lack of specific microenvironments and their low attachment rates at the sites of injury. In this context, various biomaterial-based scaffolds have been used to overcome these limitations by providing simple structural support for cell attachment. However, these scaffold-based strategies also cannot properly reflect patient tissue-specific structural complexity and thus show only limited therapeutic effects.

METHOD

Therefore, in the present study, we developed a customizable Lego-like multimodular endometrial tissue architecture by assembling individually fabricated tissue blocks.

RESULTS

Each tissue block was fabricated by incorporating biodegradable biomaterials and certain endometrial constituent cells. Each small tissue block was effectively fabricated by integrating conventional mold casting and 3D printing techniques. The fabricated individual tissue blocks were properly assembled into a larger customized tissue architecture. This structure not only properly mimics the patient-specific multicellular microenvironment of the endometrial tissue but also properly responds to key reproductive hormones in a manner similar to the physiological functions.

CONCLUSION

This customizable modular tissue assembly allows easy and scalable configuration of a complex patient-specific tissue microenvironment, thus accelerating various tissue regeneration procedures.

L-Theanine-Treated Adipose-Derived Mesenchymal Stem Cells Alleviate the Cytotoxicity Induced by N-Nitrosodiethylamine in Liver

BACKGROUND

Liver inflammation is the main cause of severe liver diseases, including liver fibrosis, steatohepatitis, cirrhosis and hepatocellular carcinoma. Cell therapy topics are receiving increasingly more attention. The therapeutic applications of mesenchymal stem cells (MSC) have become one of the most discussed issues. While other stem cells have therapeutic effects, they have only one or two clinical applications. MSCs are responsible for repairing a variety of tissue injuries. Moreover, MSCs could be derived from several sources, including adipose tissue. MSCs are usually more abundant and easier to obtain compared to other stem cells.

METHODS

To prove the concept that MSCs have homing ability to the injured tissue and assist in tissue repair, we examined the effects of intravenous injected adipose-derived mesenchymal stem cells (ADSCs) in a N-nitrosodiethylamine (DEN)-induced liver injury rat model.

RESULTS

The significant repairing ability of ADSCs was observed. The levels of fibrosis, apoptosis, and tumorigenesis in the DEN-injured liver tissues all decreased after ADSC treatment. Furthermore, to enhance the therapeutic effects of ADSCs, we pretreated them with L-theanine, which promotes the hepatocyte growth factor secretion of ADSC, and therefore improved the healing effects on injured liver tissue.

CONCLUSION

ADSCs, especially L-theanine-pretreated ADSCs, have anti-inflammation, anti-apoptosis, and anti-tumorigenesis effects on the N-nitrosodiethylamine-induced liver injury rat model.

Human umbilical cord platelet-rich plasma to treat endometrial pathologies: methodology, composition and pre-clinical models

STUDY QUESTION

Can human umbilical cord platelet-rich plasma (hUC-PRP) efficiently treat endometrial damage and restore fertility in a preclinical murine model?

SUMMARY ANSWER

Local application of hUC-PRP promotes tissue regeneration and fertility restoration in a murine model of Asherman syndrome and endometrial atrophy (AS/EA).

WHAT IS KNOWN ALREADY

AS/EA are well-described endometrial pathologies that cause infertility; however, there are currently no gold-standard treatments available. Recent reports have described the successful use of human platelet-rich plasma in reproductive medicine, and its regenerative potential is further enhanced using hUC-PRP, due to the ample growth factors and reduced pro-inflammatory cytokines in the latter.

STUDY DESIGN SIZE DURATION

hUC-PRP (n = 3) was processed, characterized and delivered locally to endometrial damage in a murine model (n = 50). The hUC-PRP was either used alone or loaded into a decellularized porcine endometrium-derived extracellular matrix (EndoECM) hydrogel; endometrial regeneration, fertility outcomes and immunocompatibility were evaluated 2 weeks following treatment administration.

PARTICIPANTS/MATERIALS SETTING METHODS

Umbilical cord blood was obtained from women in childbirth. Endometrial damage (mimicking AS/EA) was induced using ethanol in 8-week-old C57BL/6 mice, and treated with the most concentrated hUC-PRP sample 4 days later. Characterization of hUC-PRP and immunotolerance was carried out with multiplex technology, while uterine samples were analyzed by immunohistochemistry and quantitative PCR. The number of embryos and their morphology was determined visually.

MAIN RESULTS AND THE ROLE OF CHANCE

Platelet density was enhanced 3-fold in hUC-PRP compared to that in hUC blood (P < 0.05). hUC-PRP was enriched with growth factors related to tissue regeneration (i.e. hepatocyte growth factor, platelet-derived growth factor-BB and epidermal growth factor), which were released constantly (in vitro) when hUC-PRP was loaded into EndoECM. Both treatments (hUC-PRP alone and hUC-PRP with EndoECM) were immunotolerated and caused significantly regeneration of the damaged endometrium, evidenced by increased endometrial area, neoangiogenesis, cell proliferation and gland density and lower collagen deposition with respect to non-treated uterine horns (P < 0.05). Additionally, we detected augmented gene expression of Akt1, VEGF and Ang, which are involved in regenerative and proliferation pathways. Finally, hUC-PRP treatment restored pregnancy rates in the mouse model.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

This proof-of-concept pilot study was based on a murine model of endometrial damage and the use of EndoECM requires further validation prior to clinical implementation for women affected by AS/EA.

WIDER IMPLICATIONS OF THE FINDINGS

The local administration of hUC-PRP has high impact and is immunotolerated in a murine model of AS/EA, as has been reported in other tissues, making it a promising candidate for heterologous treatment of these endometrial pathologies.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by the Ministerio de Ciencia, Innovación y Universidades; Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital, Generalitat Valenciana; and Instituto de Salud Carlos III. The authors do not have any conflicts of interest to declare.

The therapeutic effect of stem cells from human exfoliated deciduous teeth on a rat model of tracheal fistula

Background

Tracheal fistulas (TF) can be dangerous and even fatal in patients. The current treatment is really challenging. Previous studies reported that mesenchymal stem cells (MSCs) could be used to treat respiratory tract fistulas. Stem cells from human exfoliated deciduous teeth (SHED) are considered to be MSC-like cells that may also have the potential to treat the tracheal fistulas. In this study, we investigated the therapeutic effects of SHED in rat tracheal fistula models.

Methods

A total of 80 SD rats were randomly divided into five groups: a sham-operated group, a local PBS group (L-PBS), an intravenous PBS group (I-PBS), a local SHED treatment group (L-SHED), and an intravenous SHED treatment group (I-SHED). The L-SHED and I-SHED groups were given a topical application around the fistula or an intravenous injection of 1*10⁷ SHED via the tail vein, respectively, while the L-PBS and I-PBS groups were given an equivalent volume of PBS through local or intravenous administration. A stereomicroscope was used to observe fistula healing on the 2nd, 3rd, and 5th days following transplantation. On the 7th day, the survival of SHED was observed by immunofluorescence. The pathology of the lungs and fistulas was observed by hematoxylin and eosin (H&E) and Masson staining. The expression levels of the Toll-like receptor 4 (TLR4), interleukin (IL)-1β, IL-33, and IL-4 were measured using immunohistochemistry. The expression levels of TLR4, high mobility group box 1 (HMGB1), and myeloid differentiation factor 88 (MYD88) were studied using western blotting. On day 14, airway responsiveness of rats was detected and analyzed.

Results

Fistula healing in the L-SHED and I-SHED groups was faster than that in their respective PBS groups after transplantation. The fistula diameters in the L-SHED and I-SHED groups were significantly smaller than those in the L-PBS and I-PBS groups on the 3rd day. Moreover, the phenomenon of fibroblast proliferation and new blood vessel growth around the fistula seemed more pronounced in the L-SHED and I-SHED groups. Although no discernible difference was found in airway responsiveness after SHED treatment, the degree of inflammation in the lungs was reduced by intravenous SHED treatment. However, there was no significant reduction in lung inflammation by local SHED treatment. The expression levels of IL-1β and IL-33 were decreased in the I-SHED group, while IL-4 was elevated compared with the I-PBS group. Interestingly, intravenous SHED treatment inhibited the activation of HMGB1/TLR4/MYD88 in the lung tissues of TF rats.

Conclusions

SHED transplantation accelerated the rate of fistula healing in rats. Intravenous SHED treatment reduced lung inflammation. Thus, SHED may have potential in the treatment of tracheal fistula, providing hope for future therapeutic development for TF.

Therapeutic Potential of Pretreatment with Exosomes Derived from Stem Cells from the Apical Papilla against Cisplatin-Induced Acute Kidney Injury

Acute kidney injury (AKI) is the most serious side effect of treatment with cisplatin in clinical practice. The aim of this study was to investigate the therapeutic effect of exosomes derived from stem cells from the apical papilla (SCAPs) on AKI. The medium from a SCAP culture was collected after 2 d of culture. From this, SCAP-derived exosomes (SCAP-ex), which were round (diameter: 30-150 nm) and expressed the characteristic proteins CD63 and CD81, were collected via differential ultracentrifugation. Rat renal epithelial cells (NRK-52E) were pretreated with SCAP-ex for 30 min and subsequently treated with cisplatin to induce acute injury. The extent of oxidative stress, inflammation, and apoptosis were used to evaluate the therapeutic effect of SCAP-ex against cisplatin-induced nephrotoxicity. The viability assay showed that the survival of damaged cells increased from 65% to 89%. The levels of reactive oxygen species decreased from 176% to 123%. The glutathione content increased by 78%, whereas the levels of malondialdehyde and tumor necrosis factor alpha (TNF-α) decreased by 35% and 9%, respectively. These results showed that SCAP-ex can retard oxidative stimulation in damaged kidney cells. Quantitative reverse transcription-polymerase chain-reaction gene analysis showed that they can also reduce the expression of nuclear factor-κβ (NF-κβ), interleukin-1β (IL-1β), and p53 in AKI. Further, they increased the gene expression of antiapoptotic factor B-cell lymphoma-2 (Bcl-2), whereas they reduced that of proapoptotic factors Bcl-2-associated X (Bax) and caspase-8 (CASP8), CASP9, and CASP3, thereby reducing the risk of cell apoptosis.

The Role of Endometrial Stem/Progenitor Cells in Recurrent Reproductive Failure

Recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL), collectively referred to as recurrent reproductive failure (RRF), are both challenging conditions with many unanswered questions relating to causes and management options. Both conditions are proposed to be related to an aberrant endometrial microenvironment, with different proposed aetiologies related to a restrictive or permissive endometrium for an invading embryo. The impressive regenerative capacity of the human endometrium has been well-established and has led to the isolation and characterisation of several subtypes of endometrial stem/progenitor cells (eSPCs). eSPCs are known to be involved in the pathogenesis of endometrium-related disorders (such as endometriosis) and have been proposed to be implicated in the pathogenesis of RRF. This review appraises the current knowledge of eSPCs, and their involvement in RRF, highlighting the considerable unknown aspects in this field, and providing avenues for future research to facilitate much-needed advances in the diagnosis and management of millions of women suffering with RRF.

Development of a Bone-Mimetic 3D Printed Ti6Al4V Scaffold to Enhance Osteoblast-Derived Extracellular Vesicles' Therapeutic Efficacy for Bone Regeneration

Extracellular Vesicles (EVs) are considered promising nanoscale therapeutics for bone regeneration. To date, EVs are typically procured from cells on 2D tissue culture plastic, an artificial environment that limits cell growth and does not replicate in situ biochemical or biophysical conditions. This study investigated the potential of 3D printed titanium scaffolds coated with hydroxyapatite to promote the therapeutic efficacy of osteoblast-derived EVs. Ti6Al4V titanium scaffolds with different pore sizes (500 and 1000 µm) and shapes (square and triangle) were fabricated by selective laser melting. A bone-mimetic nano-needle hydroxyapatite (nnHA) coating was then applied. EVs were procured from scaffold-cultured osteoblasts over 2 weeks and vesicle concentration was determined using the CD63 ELISA. Osteogenic differentiation of human bone marrow stromal cells (hBMSCs) following treatment with primed EVs was evaluated by assessing alkaline phosphatase activity, collagen production and calcium deposition. Triangle pore scaffolds significantly increased osteoblast mineralisation (1.5-fold) when compared to square architectures (P ≤ 0.001). Interestingly, EV yield was also significantly enhanced on these higher permeability structures (P ≤ 0.001), in particular (2.2-fold) for the larger pore structures (1000 µm). Furthermore osteoblast-derived EVs isolated from triangular pore scaffolds significantly increased hBMSCs mineralisation when compared to EVs acquired from square pore scaffolds (1.7-fold) and 2D culture (2.2-fold) (P ≤ 0.001). Coating with nnHA significantly improved osteoblast mineralisation (>2.6-fold) and EV production (4.5-fold) when compared to uncoated scaffolds (P ≤ 0.001). Together, these findings demonstrate the potential of harnessing bone-mimetic culture platforms to enhance the production of pro-regenerative EVs as an acellular tool for bone repair.

Strategies for managing asherman's syndrome and endometrial atrophy: Since the classical experimental models to the new bioengineering approach

Endometrial function is essential for embryo implantation and pregnancy, but managing endometrial thickness that is too thin to support pregnancy or an endometrium of compromised functionality due to intrauterine adhesions is an ongoing challenge in reproductive medicine. Here, we review current and emerging therapeutic and experimental options for endometrial regeneration with a focus on animal models used to study solutions for Asherman's syndrome and endometrial atrophy, which both involve a damaged endometrium. A review of existing literature was performed that confirmed the lack of consensus on endometrial therapeutic options, though promising new alternatives have emerged in recent years (platelet-rich plasma, exosomes derived from stem cells, bioengineering-based techniques, endometrial organoids, among others). In the future, basic research using established experimental models of endometrial pathologies (combined with new high-tech solutions) and human clinical trials with large population sizes are needed to evaluate these emerging and new endometrial therapies.

Adult stem cells in endometrial regeneration: Molecular insights and clinical applications

Endometrial damage is an important cause of female reproductive problems, manifested as menstrual abnormalities, infertility, recurrent pregnancy loss, and other complications. These conditions are collectively termed "Asherman syndrome" (AS) and are typically associated with recurrent induced pregnancy terminations, repeated diagnostic curettage and intrauterine infections. Cancer treatment also has unexpected detrimental side effects on endometrial function in survivors independently of ovarian effects. Endometrial stem cells act in the regeneration of the endometrium and in repair through direct differentiation or paracrine effects. Nonendometrial adult stem cells, such as bone marrow-derived mesenchymal stem cells and umbilical cord-derived mesenchymal stem cells, with autologous and allogenic applications, can also repair injured endometrial tissue in animal models of AS and in human studies. However, there remains a lack of research on the repair of the damaged endometrium after the reversal of tumors, especially endometrial cancers. Here, we review the biological mechanisms of endometrial regeneration, and research progress and challenges for adult stem cell therapy for damaged endometrium, and discuss the potential applications of their use for endometrial repair after cancer remission, especially in endometrial cancers. Successful application of such cells will improve reproductive parameters in patients with AS or cancer. Significance: The endometrium is the fertile ground for embryos, but damage to the endometrium will greatly impair female fertility. Adult stem cells combined with tissue engineering scaffold materials or not have made great progress in repairing the injured endometrium due to benign lesions. However, due to the lack of research on the repair of the damaged endometrium caused by malignant tumors or tumor therapies, the safety and effectiveness of such stem cell-based therapies need to be further explored. This review focuses on the molecular insights and clinical application potential of adult stem cells in endometrial regeneration and discusses the possible challenges or difficulties that need to be overcome in stem cell-based therapies for tumor survivors. The development of adult stem cell-related new programs will help repair damaged endometrium safely and effectively and meet fertility needs in tumor survivors.

Concentrated small extracellular vesicles from menstrual blood-derived stromal cells improve intrauterine adhesion, a pre-clinical study in a rat model

We previously reported that transplantation of menstrual blood-derived stromal cells (MenSCs) significantly improved fertility restoration in intrauterine adhesion (IUA). However, it is difficult to obtain menstrual blood samples in some severe IUA patients who have amenorrhea or oligomenorrhea. Thus, a safe and effective stem cell replacement therapy is necessary to promote endometrial regeneration. Recent studies demonstrated that the effects of MenSCs are partly mediated in a paracrine manner via small extracellular vesicles (sEVs). To explore this possibility, we performed a pre-clinical study to investigate whether concentrated MenSC-derived sEVs (MenSCs-sEVs) are sufficient to repair IUA and the mechanisms underlying their action. Rat IUA models were established by mechanical injury, followed by the administration of MenSCs or MenSCs-sEVs through intrauterine transplantation. Consistent with the efficacy of MenSCs, MenSCs-sEVs effectively recovered the morphology, promoted regeneration of the glands and angiogenesis, and reversed endometrial fibrosis in the IUA uterus. The endometrial receptivity and pregnancy outcome significantly improved after repeated MenSCs-sEVs transplantations. In addition, all rats in the MenSCs-sEVs group had no hematological or biochemical abnormalities. Three-dimensional fluorescence imaging suggested that MenSCs tended to migrate through the bloodstream, whereas MenSCs-sEVs had a better localized therapeutic effect. Moreover, MenSCs and MenSCs-sEVs inhibited the TGFβ1/SMAD3 pathway in the IUA endometrium, while promoting the phosphorylation of SMAD1/5/8 and ERK 1/2 and upregulating the expression of BMP7. Thus, MenSCs-sEVs safely and effectively enhanced endometrial restoration, suggesting a promising non-cellular therapy for endometrial regeneration and a key role in MenSC-mediated IUA treatment.

Regenerative Potential of DPSCs and Revascularization: Direct, Paracrine or Autocrine Effect?

A new source of mesenchymal stem cells has recently been discovered, the so-called dental pulp derived stem cells (DPSCs) which therefore could represent potentially tools for regenerative medicine. DPSC originate from the neural crest and are physiologically involved in dentin homeostasis; moreover, they contribute to bone remodeling and differentiation into several tissues including cartilage, bone, adipose and nervous tissues. DPSCs have also been shown to influence the angiogenesis process, for example through the release of secretory factors or by differentiating into vascular and/or perivascular cells. Angiogenesis, that has a pivotal role in tissue regeneration and repair, is defined as the formation of new vessels from preexisting vessels and is mediated by mutual and reciprocal interactions between endothelial cells and perivascular cells. It is also known that co-cultures of perivascular and endothelial cells (ECs) can form a vascular network in vitro and also in vivo. Since DPSCs seem to have characteristics similar to pericytes, understanding the possible mechanism of interaction between DPSCs and ECs during neo-angiogenesis is dramatically important for the development of advanced clinical application in the field of regeneration.

Stem Cells and the Endometrium: From the Discovery of Adult Stem Cells to Pre-Clinical Models

Adult stem cells (ASCs) were long suspected to exist in the endometrium. Indeed, several types of endometrial ASCs were identified in rodents and humans through diverse isolation and characterization techniques. Putative stromal and epithelial stem cell niches were identified in murine models using label-retention techniques. In humans, functional methods (clonogenicity, long-term culture, and multi-lineage differentiation assays) and stem cell markers (CD146, SUSD2/W5C5, LGR5, NTPDase2, SSEA-1, or N-cadherin) facilitated the identification of three main types of endogenous endometrial ASCs: stromal, epithelial progenitor, and endothelial stem cells. Further, exogenous populations of stem cells derived from bone marrow may act as key effectors of the endometrial ASC niche. These findings are promoting the development of stem cell therapies for endometrial pathologies, with an evolution towards paracrine approaches. At the same time, promising therapeutic alternatives based on bioengineering have been proposed.

Mesenchymal stem cell spheroids incorporated with collagen and black phosphorus promote osteogenesis of biodegradable hydrogels

Mesenchymal stem cell (MSC)-spheroids have sparked significant interest in bone tissue engineering due to their resemblance to natural bone tissue, especially in terms of cell-cell and cell-extracellular matrix interactions. Many biomaterials or biomolecules have been incorporated into MSC-spheroids to enhance their osteogenic abilities. In this respect, we assessed the osteogenic responses of MSC spheroids leveraged through the unique combination of collagen and black phosphorus (BP). The MSC spheroids were successfully constructed with 6 μg/mL collagen and/or a concentration gradient (0 μg/mL, 4 μg/mL, 8 μg/mL, and 16 μg/mL) of BP and were evaluated for MSC viability and their osteogenic differentiation over a time period of 14 days. Improved MSC viability and osteogenic ability were observed for the spheroids with collagen and BP at the concentration of 4 μg/mL and 8 μg/mL. Next, blank spheroids (Control) or the optimized MSC spheroids with 6 μg/mL collagen and 4 μg/mL BP (Col+BP4) were further encapsulated into two types of hydrogel scaffolds: porous oligo[poly(ethylene glycol) fumarate] (OPF) hydrogel and hydroxyapatite-collagen I scaffold (HE-COL). The osteogenic abilities of these four groups were evaluated after 14 and 21 days of osteogenic induction. The MSC spheroids incorporated with collagen and BP implanted into OPF porous hydrogel (Col+BP/OPF) elicited a higher expression of Runx2, osteopontin, and alkaline phosphatase than blank spheroids implanted into OPF porous hydrogel (Control/OPF). Enhanced osteogenesis was also observed in the Col+BP/HE-COL group as compared to Control/HE-COL. Taken together, the results from this study showed the perspectives of collagen and BP incorporated MSC spheroids for the development of injectable cellular therapies for bone regeneration.