Isolation and characterization of string-forming female germline stem cells from ovaries of neonatal mice

Shanyao regulates the PI3K/AKT/P21 pathway to promote oogonial stem cell proliferation and stemness restoration to alleviate premature ovarian insufficiency

ETHNOPHARMACOLOGICAL RELEVANCE

Shanyao (SY, yam, Rhizoma Dioscoreae, the dried rhizome of Dioscorea oppositifolia L.) was recorded in the Chinese pharmacopoeia and was often used in the treatment of premature ovarian insufficiency (POI).

AIM OF STUDY

To evaluate the efficacy of shanyao in cyclophosphamide (CTX)-induced POI and explore its potential mechanism of action.

MATERIAL AND METHODS

We employed network pharmacology, Liquid Chromatograph Mass Spectrometer (LC-MS), and molecular docking methods to identify active compounds and core targets, and predict the mechanism of shanyao for treating POI. The mechanism was subsequently validated through a series of experiments. Female Sprague-Dawley (SD) rats were randomly divided into five groups: control (CON), model, estradiol valerate (EV), low-dose shanyao, and high-dose shanyao. An experimental rat model of POI was established using cyclophosphamide and treated with either shanyao or EV for a duration of two months. We assessed the efficacy of shanyao in vivo through methods such as weighing, Enzyme-linked Immunosorbent Assay (ELISA), and Hematoxylin and Eosin (H&E) staining. Oogonial stem cells (OSCs) were isolated, after modeling, treated them with a serum containing either shanyao or EV. Using methods such as CCK8 assay, immunofluorescence staining, flow cytometry (FCM) analysis, and Western blot analysis to verify the mechanism of shanyao in treating POI.

RESULTS

In this study, we found that after treatment with shanyao, the general condition of POI rats was improved, body weight and the ratio of ovarian weight to body weight were increased, FSH, E2 and AMH levels were improved, primary follicles and preantral follicles were significantly increased, atretic follicles were decreased. However, the number of antral follicles and fresh corpus luteum was no statistical difference. We identified 10 active compounds of shanyao that act on 220 target genes, 176 of which are associated with POI. Denudatin B and Kadsurenone were finally identified as core components. Through topological analysis, 18 key targets were selected, and ultimately PI3K, CCND1, and CDK4 were identified as core targets. Molecular docking results showed that core components had good binding energy with core targets. The results of GO and KEGG enrichment analysis mainly focus on cell cycle regulation and PI3K/AKT signaling pathway. A series of molecular biology experiments confirmed that after shanyao treatment, the phosphorylation level of PI3K and AKT in POI rats were increased, P21 was inhibited, PI3K/AKT/P21 signaling pathway was activated, and the expression levels of CCND1 and CDK4 were increased. At the same time, the expression of Oct4, fragilis and Mvh of ovarian stem cells was up-regulated.

CONCLUSION

The active compounds of shanyao can regulate the PI3K/AKT/P21 signaling pathway, promote the proliferation of oogonial stem cells, stemness restoration, and delay ovarian aging. This study provides valuable insights into shanyao treatment for POI.

Which Side of the Coin Are You on Regarding Possible Postnatal Oogenesis?

It is well known that oocytes are produced during fetal development and that the total number of primary follicles is determined at birth. In humans, there is a constant loss of follicles after birth until about two years of age. The number of follicles is preserved until the resumption of meiosis at puberty and there is no renewal of the oocytes; this dogma was maintained in the last century because there were no suitable techniques to detect and obtain stem cells. However, following stem cell markers, several scientists have detected them in developing and adult human ovarian tissues, especially in the ovarian surface epithelial cells. Furthermore, many authors using different methodological strategies have indicated this possibility. This evidence has led many scientists to explore this hypothesis; there is no definitive consensus to accept this idea. Interestingly, oocyte retrieval from mature ovaries and other tissue sources of stem cells has contributed to the development of strategies for the retrieval of mature oocytes, useful for assisted reproductive technology. Here, we review the evidence and controversies on oocyte neooogenesis in adult women; in addition, we agree with the idea that this process may occur in adulthood and that its alteration may be related to various pathologies in women, such as polycystic ovary syndrome, premature ovarian insufficiency, diminished ovarian reserve and several infertility and genetic disorders.

Current Status and Future Prospects of Stem Cell Therapy for Infertile Patients with Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI), also known as premature menopause or premature ovarian failure, signifies the partial or complete loss of ovarian endocrine function and fertility before 40 years of age. This condition affects approximately 1% of women of childbearing age. Although 5-10% of patients may conceive naturally, conventional infertility treatments, including assisted reproductive technology, often prove ineffective for the majority. For infertile patients with POI, oocyte donation or adoption exist, although a prevalent desire persists among them to have biological children. Stem cells, which are characterized by their undifferentiated nature, self-renewal capability, and potential to differentiate into various cell types, have emerged as promising avenues for treating POI. Stem cell therapy can potentially reverse the diminished ovarian endocrine function and restore fertility. Beyond direct POI therapy, stem cells show promise in supplementary applications such as ovarian tissue cryopreservation and tissue engineering. However, technological and ethical challenges hinder the widespread clinical application of stem cells. This review examines the current landscape of stem cell therapy for POI, underscoring the importance of comprehensive assessments that acknowledge the diversity of cell types and functions. Additionally, this review scrutinizes the limitations and prospects associated with the clinical implementation of stem cell treatments for POI.

Application of Matrigel in the 3-dimension culture of female germline stem cells

Female germline stem cells (FGSCs) are a group of rare undifferentiated cells found in ovarian cortex, which have the unique ability to self-renew and differentiate. Stable maintenance and proliferation of FGSCs in culture are pivotal for clinic research. However, conventional 2-D (dimension) culture systems are limited in their ability to mimic the ovarian microenvironment during in vitro studies. To establish a suitable in vitro microenvironment for FGSCs, we conducted experiments using a Matrigel-based 3-D culture system. This involves testing different dilution ratios, medium compositions, and co-culture cells to find the optimal conditions for FGSCs maintenance and proliferation. Our results demonstrated the feasibility of using Matrigel as a FGSCs 3-D culture media. Moreover, co-culturing FGSCs with some types of cells in the Matrigel-based 3-D culture system had the potential to form ovarian organoids. Meanwhile, the safety of Matrigel was confirmed in vivo through transplantation experiment, which suggests the potential for clinic research.

Engineering Female Germline Stem Cells with Exocytotic Polymer Dots

Germline stem cells (GSCs) are the only cell population capable of passing genetic information to offspring, making them attractive targets in reproductive biology and fertility research. However, it is generally more difficult to introduce exogenous biomolecules into GSCs than other cell types, impeding the exploration and manipulation of these cells for biomedical purposes. Herein, semiconductor polymer dots (Pdots)-based nanocomplex Pdot-siRNA is developed and achieves effective knockdown of target genes in female germline stem cells (FGSCs). Advantage of high fluorescence brightness of Pdots is taken for comprehensive investigation of their cellular uptake, intracellular trafficking, and exocytosis in FGSCs. Importantly, Pdots show excellent biocompatibility and minimally disturb the differentiation of FGSCs. Intracellular Pdots escape from the lysosomes and undergo active exocytosis, which makes them ideal nanocarriers for bioactive cargos. Moreover, Pdot-siRNA can penetrate into 3D ovarian organoids derived from FGSCs and down-regulate the expression levels of target genes. This study investigates the interface between a type of theranostic nanoparticles and FGSCs for the first time and sheds light on the manipulation and medical application of FGSCs.

Inhibition of EED activity enhances cell survival of female germline stem cell and improves the oocytes production during oogenesis in vitro

Ovarian organoids, based on female germline stem cells (FGSCs), are nowadays widely applied for reproductive medicine screening and exploring the potential mechanisms during mammalian oogenesis. However, there are still key issues that urgently need to be resolved in ovarian organoid technology, one of which is to establish a culture system that effectively expands FGSCs in vitro, as well as maintaining the unipotentcy of FGSCs to differentiate into oocytes. Here, FGSCs were EED226 treated and processed for examination of proliferation and differentiation in vitro. According to the results, EED226 specifically increased FGSC survival by decreasing the enrichment of H3K27me3 on Oct4 promoter and exon, as well as enhancing OCT4 expression and inhibiting P53 and P63 expression. Notably, we also found that FGSCs with EED226 treatment differentiated into more oocytes during oogenesis in vitro, and the resultant oocytes maintained a low level of P63 versus control at early stage development. These results demonstrated that inhibition of EED activity appeared to promote the survival of FGSCs and markedly inhibited their apoptosis during in vitro differentiation. As a result of our study, we propose an effective culture strategy to culture FGSCs and obtain oocytes in vitro, which provides a new vision for oogenesis in vitro.

Stem Cell-Based Therapeutic Strategies for Premature Ovarian Insufficiency and Infertility: A Focus on Aging

Reproductive aging is on the rise globally and inseparable from the entire aging process. An extreme form of reproductive aging is premature ovarian insufficiency (POI), which to date has mostly been of idiopathic etiology, thus hampering further clinical applications and associated with enormous socioeconomic and personal costs. In the field of reproduction, the important functional role of inflammation-induced ovarian deterioration and therapeutic strategies to prevent ovarian aging and increase its function are current research hotspots. This review discusses the general pathophysiology and relative causes of POI and comprehensively describes the association between the aging features of POI and infertility. Next, various preclinical studies of stem cell therapies with potential for POI treatment and their molecular mechanisms are described, with particular emphasis on the use of human induced pluripotent stem cell (hiPSC) technology in the current scenario. Finally, the progress made in the development of hiPSC technology as a POI research tool for engineering more mature and functional organoids suitable as an alternative therapy to restore infertility provides new insights into therapeutic vulnerability, and perspectives on this exciting research on stem cells and the derived exosomes towards more effective POI diagnosis and treatment are also discussed.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.

Identification of Stem Cell-Like Cells in the Ovary

Understanding the function of stem cells and cellular microenvironments in in vitro oogenesis, including ovarian folliculogenesis, is crucial for reproductive biology. Because mammalian females cannot generate oocytes after birth, the number of oocyte decreases with the progression of reproductive age. Meanwhile, there is an emerging need for the neogenesis of female germ cells to treat the increasing infertility-related issues in cancer survivors. The concept of oocytes neogenesis came from the promising results of stem cells in reproductive medicine. The stem cells that generate oocytes are defined as stem cell-like cells in the ovary (OSCs). Several recent studies have focused on the origin, isolation, and characteristic of OSCs and the differentiation of OSCs into oocytes, ovarian follicles and granulosa cells. Hence, in this review, we focus on the experimental trends in OSC research and discuss the methods of OSC isolation. We further summarized the characteristics of OSCs and discuss the markers used to identify OSCs differentiated from various cell sources. We believe that this review will be beneficial for advancing the research and clinical applications of OSCs.

Zuogui pills maintain the stemness of oogonial stem cells and alleviate cyclophosphamide-induced ovarian aging through Notch signaling pathway

BACKGROUND

Zuogui pills (ZGP), a classical prescription of traditional Chinese medicine, have been widely used in the treatment of ovarian aging. Previous studies have demonstrated its efficacy on protecting ovarian aging, and the mechanisms were mostly relevant to inhibiting the apoptosis of follicles and activating the primordial follicles. However, whether ZGP could stimulate the oogonial stem cells (OSCs) to refresh the follicle pool remains poorly understood.

PURPOSE

To investigate the effects of ZGP on the stemness of OSCs in cyclophosphamide (Cy)-induced ovarian aging.

STUDY DESIGN AND METHODS

Female Sprague-Dawley (SD) rats were randomly divided into 8 groups: control group, model group, ZGP groups (low / high dose groups), estradiol valerate (EV) groups (low / high dose groups), DAPT group and DAPT+ZGP-L group. After modeling with Cy, the ZGP groups and EV groups were treated with ZGP and EV for 8 weeks respectively. Meanwhile, the DAPT groups were treated with DAPT twice a week. Additionally, OSCs were also isolated after modeling, and then treated with drug serum containing ZGP or EV. Ovarian volume and the ratio of weight of total ovaries to the body weight were measured. The serum hormones were measured by ELISA. Quantities and location of OSCs in ovaries were detected by flow cytometry and immunofluorescence. Cell viability was measured by CCK8. And OSCs were identified by immunofluorescence. Biomarkers of germ cells, stem cells and associated to differentiation and meiosis were detected by qPCR and western blot. Proteins in Notch signaling pathway were detected by western blot and immunofluorescence.

RESULTS

After treating with ZGP, ovarian volume and the ratio of weight of total ovaries to the body weight increased. ZGP could increase serum AMH and E2 level and decrease serum FSH level. Quantities and cell viability of OSCs increased after ZGP treatment in vivo and in vitro. In addition, treatment with ZGP could increase not only the expression of MVH, Oct4 and DAZL, but also the expression of ZP1 and ZP2. Furthermore, ZGP could up-regulate the expression of Notch intracellular domain (NICD), HES1 and HES5. After blocking the Notch signaling pathway, ZGP could increase not only the expression of NICD, HES1 and HES5, but also the expression of MVH, Oct4, DAZL, ZP1 and ZP3.

CONCLUSION

In conclusion, the mechanism of ZGP on treating ovarian aging may be relevant to maintain the stemness of OSCs by up-regulating Notch signaling pathway, which added the mechanism of ZGP on the perspective of OSCs at first time.

Integrative analysis of the 3D genome structure reveals that CTCF maintains the properties of mouse female germline stem cells

The three-dimensional configuration of the genome ensures cell type-specific gene expression profiles by placing genes and regulatory elements in close spatial proximity. Here, we used in situ high-throughput chromosome conformation (in situ Hi-C), RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) to characterize the high-order chromatin structure signature of female germline stem cells (FGSCs) and identify its regulating key factor based on the data-driven of multiple omics data. By comparison with pluripotent stem cells (PSCs), adult stem cells (ASCs), and somatic cells at three major levels of chromatin architecture, A/B compartments, topologically associating domains, and chromatin loops, the chromatin architecture of FGSCs was most similar to that of other ASCs and largely different from that of PSCs and somatic cells. After integrative analysis of the three-dimensional chromatin structure, active compartment-associating loops (aCALs) were identified as a signature of high-order chromatin organization in FGSCs, which revealed that CCCTC-binding factor was a major factor to maintain the properties of FGSCs through regulation of aCALs. We found FGSCs belong to ASCs at chromatin structure level and characterized aCALs as the high-order chromatin structure signature of FGSCs. Furthermore, CTCF was identified to play a key role in regulating aCALS to maintain the biological functions of FGSCs. These data provide a valuable resource for future studies of the features of chromatin organization in mammalian stem cells and further understanding of the fundamental characteristics of FGSCs.

Germ cells of the mammalian female: A limited or renewable resource?

In many non-mammalian organisms, a population of germ-line stem cells supports continuing production of gametes during most or all the life of the individual, and germ-line stem cells are also present and functional in male mammals. Traditionally, however, they have been thought not to exist in female mammals, who instead generate all their germ cells during fetal life. Over the last several years, this dogma has been challenged by several reports, while supported by others. We describe and compare these conflicting studies with the aim of understanding how they came to opposing conclusions. We first consider studies that, by examining marker-gene expression, the fate of genetically marked cells, and consequences of depleting the oocyte population, addressed whether ovaries of post-natal females contain oogonial stem cells (OSC) that give rise to new oocytes. We next discuss whether ovaries contain cells that, even if inactive under physiological conditions, nonetheless possess OSC properties that can be revealed through cell-culture. We then examine studies of whether cells harvested after long-term culture of cells obtained from ovaries can, following transplantation into ovaries of recipient females, give rise to oocytes and offspring. Finally, we note studies where somatic cells have been re-programmed to acquire a female germ-cell fate. We conclude that the weight of evidence strongly supports the traditional interpretation that germ-line stem cells do not exist post-natally in female mammals. However, the ability to generate germ cells from somatic cells in vitro establishes a method to generate new gametes from cells of post-natal mammalian females.

Novel circGFRα1 Promotes Self-Renewal of Female Germline Stem Cells Mediated by m6A Writer METTL14

Circular RNAs (circRNAs) play important roles in the self-renewal of stem cells. However, their significance and regulatory mechanisms in female germline stem cells (FGSCs) are largely unknown. Here, we identified an N ⁶-methyladenosine (m⁶A)-modified circRNA, circGFRα1, which is highly abundant in mouse ovary and stage-specifically expressed in mouse FGSC development. Knockdown of circGFRα1 in FGSCs significantly reduced their self-renewal. In contrast, overexpression of circGFRα1 enhanced FGSC self-renewal. Mechanistically, circGFRα1 promotes FGSC self-renewal by acting as a competing endogenous RNA (ceRNA) that sponges miR-449, leading to enhanced GFRα1 expression and activation of the glial cell derived neurotrophic factor (GDNF) signaling pathway. Furthermore, circGFRα1 acts as a ceRNA based on METTL14-mediated cytoplasmic export through the GGACU motif. Our study should help to understand the mechanisms regulating germ cell development, add new evidence on the mechanism of action of circRNA, and deepen our understanding of the development of FGSCs.

Transcriptome profiling analysis of underlying regulation of growing follicle development in the chicken

Large ovarian follicles are primary characteristics of oviparous species. The development of such follicles is crucially governed by strict intrinsic complex regulation. Many aspects of the genetic basis of this regulation remain obscure. To identify the dominant genes controlling follicular development in the chicken, growing follicles (400–1,600 μm in diameter) were selected for RNA sequencing and bioinformatics analysis. Comparing the 400-μm follicles with 800-μm follicles identified a total of 3,627 differentially expressed genes (1,792 upregulated and 1,835 downregulated genes). Comparing the 400-μm follicles with 1,600-μm follicles revealed 9,650 differentially expressed genes (including 4,848 upregulated and 4,802 downregulated genes). Comparing 800-μm with 1,600-μm follicles revealed a total of 6,779 differentially expressed genes (3,427 upregulated and 3,352 downregulated genes). Transcriptome analysis revealed that genes related to the extracellular matrix–receptor interactions, steroid biosynthesis, cell adhesion, and phagosomes displayed remarkable differential expressions. Relative to 400-μm follicles, collagen content, production of steroid hormones, cell adhesion, and phagocytic factors were significantly increased in the 1,600-μm follicles. This study identifies the dominant genes involved in the promotion of follicular development in oviparous vertebrates and represents the extraordinary gene regulation pattern related to development of the growing follicles in poultry.

In Vitro Generation of Oocyte Like Cells and Their In Vivo Efficacy: How Far We have been Succeeded

In the last few decades, stem cell therapy has grown as a boon for many pathological complications including female reproductive disorders. In this review, a brief description of available strategies that are related to stem cell-based in vitro oocyte-like cell (OLC) development are given. We have tried to cover all the aspects and latest updates of the in vitro OLC developmental methodologies, marker profiling, available disease models, and in vivo efficacies, with a special focus on mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs) usage. The differentiation abilities of both the ovarian and non-ovarian stem cell sources under various induction conditions have shown different effects on morphological alterations, proliferation- and size-associated developments, hormonal secretions under gonadotropic stimulations, and their neo-oogenesis or folliculogenesis abilities after in vivo transplantations. The attainment of characters like oocyte-like morphology, size expansion, and meiosis initiation have been found to be major obstacles during in vitro oogenesis. A number of reports have either lacked in vivo studies or have shown their functional incapability to produce viable and healthy offspring. Though researchers have gained many valuable insights regarding in vitro gametogenesis, still there are many things to do to make stem cell-derived OLCs fully functional.

AKT3 Is a Pivotal Molecule of Cadherin-22 and GDNF Family Receptor-α1 Signal Pathways Regulating Self-Renewal in Female Germline Stem Cells

Female germline stem cells (FGSCs) are rare population residing in cortex of ovary, with the potential to rescue female infertility caused by ovary failure. Recently, we reported that cadherin-22 (CDH22), a member of cadherin family, regulates self-renewal of mouse FGSCs via interaction with JAK-STAT signal pathway and β-catenin. In this study, the expression profiles of FGSCs and spermatogonial stem cells (SSCs) were analyzed to further reveal their similarity and difference, and AKT3 was predicted as a pivotal molecule for FGSCs self-renewal. Then, we demonstrated that CDH22 interacted with PI3K to phosphorylate AKT3 and subsequently enhanced the expression levels of N-myc and cyclin family in FGSCs to promote self-renewal. Moreover, glial cell line-derived neurotrophic factor (GDNF) was identified as an essential factor for FGSCs self-renewal with a more complicated mechanism: GDNF-GFRA1 activates AKT3 via PI3K or Src family kinase (SFK), and SFK upregulates its target genes, Bcl6b, Etv5, and Lhx1, to promote self-renewal of FGSCs. However, Src, the key intermediate factor for SSCs, was not the functional molecule of SFK family in the GDNF signal network of FGSCs. Based on the observations of bioinformatics analysis and molecular evidence, we demonstrate the underlying links of potential factors which are critical to the self-renewal in FGSC and imply the therapeutic potentials of FGSCs in cure of female infertility. Stem Cells 2019;37:1095-1107.

Molecular characteristics of early-stage female germ cells revealed by RNA sequencing of low-input cells and analysis of genome-wide DNA methylation

High-throughput stage-specific transcriptomics provides an unbiased approach for understanding the process of cell development. Here, we report transcriptome analysis of primordial germ cell, female germline stem cell (FGSC), germinal vesicle and mature oocyte by performing RNA sequencing of freshly isolated cells in mice. As expected, these stages and gene-expression profiles are consistent with developmental timing. Analysis of genome-wide DNA methylation during female germline development was used for confirmation. By pathway analysis and blocking experiments, we demonstrate PI3K-AKT pathway is critical for FGSC maintenance. We also identify functional modules with hub genes and lncRNAs, which represent candidates for regulating FGSC self-renewal and differentiation. Remarkably, we note alternative splicing patterns change dramatically during female germline development, with the highest occurring in FGSCs. These findings are invaluable resource for dissecting the molecular pathways and processes into oogenesis and will be wider applications for other types of stem cell research.