Testicular Stem Cells Express Follicle-Stimulating Hormone Receptors and Are Directly Modulated by FSH

Engineering of gelatin scaffold by extracellular matrix of Sertoli cells for embryonic stem cell proliferation

Mimicking the microenvironment of seminiferous tubules plays an indispensable role in directing differentiation of stem cells toward germ cells in vitro. In this work, we fabricated electrospun gelatin (EG) mats (i.e., with diameter <500 nm) conditioned with Sertoli cells' extracellular matrix (ECM) to simulate both 3D structures and composition of normal testis tissue. Sertoli cells were isolated from mice testis and represented through immunocytochemistry (ICC) staining for expression of vimentin, a specific marker of Sertoli cells. The morphological characteristics of ECM-coated scaffold were investigated under scanning electron microscope (SEM). The efficient elimination of cells was confirmed by MTT assay. Furthermore, the cyto/biocompatibility of ECM-conditioned EG scaffold was determined for Sertoli cells and embryonic stem cells (ESCs), alone and as in co-culture. According to the results, the designed scaffold provided a mat for cell proliferation with negligible toxicity (almost 100% cell viability). SEM micrographs displayed cells with elongated shape and complete stretching morphology when compared with those cultured on scaffold without ECM. Moreover, an enhanced differentiation of ESCs toward sperm-generating cells was obtained through co-culturing of Sertoli cells and ESCs, where cell viability was found almost 100%. Our findings introduce the ECM-conditioned EG scaffold as a potentially influential engineered substrate for in vitro guidance of stem cells differentiation by mimicking the native microenvironment.

Initiation of Cancer: The Journey From Mutations in Somatic Cells to Epigenetic Changes in Tissue-resident VSELs

Multiple theories exist to explain cancer initiation, although a consensus on this is crucial for developing effective therapies. 'Somatic mutation theory' suggests that mutations in somatic cells during DNA repair initiates cancer but this concept has several attached paradoxes. Research efforts to identify quiescent cancer stem cells (CSCs) that survive therapy and result in metastasis and recurrence have remained futile. In solid cancers, CSCs are suggested to appear during epithelial-mesenchymal transition by the dedifferentiation and reprogramming of epithelial cells. Pluripotent and quiescent very small embryonic-like stem cells (VSELs) exist in multiple tissues but remain elusive owing to their small size and scarce nature. VSELs are developmentally connected to primordial germ cells, undergo rare, asymmetrical cell divisions and are responsible for the regular turnover of cells to maintain tissue homeostasis throughout life. VSELs are directly vulnerable to extrinsic endocrine insults because they express gonadal and gonadotropin hormone receptors. VSELs undergo epigenetic changes due to endocrine insults and transform into CSCs. CSCs exhibit genomic instability and develop mutations due to errors during DNA replication while undergoing excessive proliferation and clonal expansion to form spheroids. Thus tissue-resident VSELs offer a connection between extrinsic insults and variations in cancer incidence reported in various body tissues. To conclude, cancer is indeed a stem cell disease with mutations occurring as a consequence. In addition to immunotherapy, targeting mutations, and Lgr5 + organoids for developing new therapeutics, targeting CSCs (epigenetically altered VSELs) by improving their niche and epigenetic status could serve as a promising strategy to treat cancer.

Current Progress in Stem Cell Therapy for Male Infertility

Infertility has become one of the most common issues worldwide, which has negatively affected society and infertile couples. Meanwhile, male infertility is responsible for about 50% of infertility. Accordingly, a great number of researchers have focused on its treatment during the last few years; however, current therapies such as assisted reproductive technology (ART) are not effective enough in treating male infertility. Because of their self-renewal and differentiation capabilities and unlimited sources, stem cells have recently raised great hope in the treatment of reproductive system disorders. Stem cells are undifferentiated cells that can induce different numbers of specific cells, such as male and female gametes, demonstrating their potential application in the treatment of infertility. The present review aimed at identifying the causes and potential factors that influence male fertility. Besides, we highlighted the recent studies that investigated the efficiency of stem cells such as spermatogonial stem cells (SSCs), embryonic stem cells (ESCs), very small embryonic-like stem cells (VSELs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs) in the treatment of various types of male infertility.

Preventing/Reversing Adverse Effects of Endocrine Disruption on Mouse Testes by Normalizing Tissue Resident VSELs

Reproductive health of men is declining in today's world due to increased developmental exposure to endocrine-disrupting chemicals (EDCs). We earlier reported that neonatal exposure to endocrine disruption resulted in reduced numbers of seminiferous tubules in Stage VIII, decreased sperm count, and infertility along with testicular tumors in 65% of diethylstilbestrol (DES) treated mice. Epigenetic changes due to EDCs, pushed the VSELs out of a quiescent state to enter cell cycle and undergo excessive self-renewal while transition of c-KIT- stem cells into c-KIT + germ cells was blocked due to altered MMR axis (Np95, Pcna, Dnmts), global hypomethylation (reduced expression of 5-methylcytosine) and loss of imprinting at Igf2-H19 and Dlk1-Meg3 loci. The present study was undertaken to firstly show similar defects in FACS sorted VSELs from DES treated testis and to further explore the reversal of these testicular pathologies by (i) oral administration of XAR (a nano-formulation of resveratrol) or (ii) inter-tubular transplantation of mesenchymal stromal cells (MSCs). Similar defects as reported earlier in the testes were evident, based on RNAseq data, on FACS sorted VSELs from DES treated mice. Both strategies were found effective, improved spermatogenesis, increased number of tubules in Stage VIII, normalized numbers of VSELs and c-KIT + cells, improved epigenetic status of VSELs to restore quiescent state, and reduced cancer incidence from 65% after DES to 13.33% and 20% after XAR treatment or MSCs transplantation respectively. Results provide a basis for initiating clinical studies and the study falls under the umbrella of United Nations Sustainable Development Goal 3 to ensure healthy lives and well-being for all of all ages.

Inadequate detection of the FSHR complicates future research on extragonadal FSHR localization

INTRODUCTION

Recently, follicle stimulating hormone (FSH) through interaction with its receptor (FSHR) has been proposed to play a role in postmenopausal osteoporosis and cardiovascular disease, rather than the loss of estrogen. To explore this hypothesis, unravelling which cells express extragonadal FSHR on protein level is key.

METHODS

We used two commercial anti-FSHR antibodies and validated them by performing immunohistochemistry on positive (ovary, testis) and negative controls (skin).

RESULTS

The monoclonal anti-FSHR antibody could not identify the FSHR in ovary or testis. The polyclonal anti-FSHR antibody stained the granulosa cells (ovary) and Sertoli cells (testis), yet there was equally intense staining of other cells/extracellular matrix. Furthermore, the polyclonal anti-FSHR antibody also stained skin tissue extensively, suggesting that the antibody stains more than just FSHR.

DISCUSSION

The findings in this study may add accuracy to literature on extragonadal FSHR localization and warrants attention to the use of inadequate anti-FSHR antibodies to value the potential role of FSH/FSHR in postmenopausal disease.

Extremely Active Nano-formulation of Resveratrol (XAR™) attenuates and reverses chemotherapy-induced damage in mice ovaries and testes

BACKGROUND

Fertility preservation and restoration in cancer patients/survivors is the need of present times when increased numbers of patients get cured of cancer but face infertility as a serious side effect. Resveratrol has beneficial effects on chemoablated ovaries and testes in mice but has failed to enter the clinics because of extremely poor bioavailability. The present study was undertaken to evaluate the protective and curative effects of Extremely active Resveratrol (XAR™)- a nano-formulation of resveratrol with significantly improved bioavailability- on mouse ovary and testis after chemotherapy. Effects of XAR™ and FSH were compared on stimulation of follicle growth in adult mice ovaries. XAR™ (25 mg/kg) was administered for two days prior to chemotherapy to study the protective effects on the mouse gonads. XAR™ was also administered for 14 days post chemoablation to study the regenerative effects. Besides effect on numbers of primordial and growing follicles and spermatogenesis, the effect of XAR™ was also evaluated on the transcripts specific for ovarian/testicular stem/progenitor/germ cells, their proliferation, differentiation, meiosis, and the antioxidant indices.

RESULTS

Similar to FSH, XAR™ increased the numbers of primordial follicles (PF) as well as growing follicles. It protected the gonads from the adverse effects of chemotherapy and showed the ability to regenerate non-functional, chemoablated gonads. Besides stimulating follicle growth in adult ovaries similar to FSH, XAR™ also protected the testes from the adverse effects of chemotherapy and improved spermatogenesis. This was accompanied by improved anti-oxidant indices.

CONCLUSIONS

The results of the present study potentiate the use of XAR™ in pilot clinical studies to protect gonadal function during oncotherapy and also regenerate non-functional gonads in cancer survivors by improving antioxidant indices and stem cell-based tissue regeneration.

A novel role of follicle-stimulating hormone (FSH) in various regeneration-related functions of endometrial stem cells

Follicle-stimulating hormone (FSH) promotes the production and secretion of estrogen, which in turn stimulates the growth and maturation of ovarian follicles. Therefore, consecutive FSH treatment to induce ovarian hyperstimulation (superovulation) is still considered the most cost-effective option for the majority of assisted reproductive technologies (ARTs). However, a relatively high cancellation rate and subsequent low pregnancy outcomes (approximately 15%) are the most challenging aspects of this FSH-based ART. Currently, the main cause for this low implantation rate of FSH-based ART has not yet been revealed. Therefore, we hypothesized that these high cancellation rates with FSH-based superovulation protocols might be associated with the harmful effects of consecutive FSH treatment. Importantly, several recent studies have revealed that tissue-resident stem cell deficiency can significantly reduce cyclic endometrial regeneration and subsequently decrease the pregnancy outcome. In this context, we investigated whether FSH treatment could directly inhibit endometrial stem cell functions and consequently suppress endometrial regeneration. Consistent with our hypothesis, our results revealed for the first time that FSH could inhibit various regeneration-associated functions of endometrial stem cells, such as self-renewal, migration, and multilineage differentiation capacities, via the PI3K/Akt and ERK1/2 signaling pathways both in vitro and in vivo.

Follicle-stimulating hormone (FSH) is commonly administered to treat female infertility by stimulating the ovaries, but FSH treatment can also inhibit key cellular and physiological processes required for successful pregnancy. In the light of pregnancy outcomes as low as 15 percent after FSH-based assisted reproduction technologies, In-Sun Hong at Gachon University, Incheon, South Korea, and colleagues investigated the effects of FSH. Working with cultured human stem cells from the lining of the uterus, they found that FSH could inhibit multiple cellular regenerative functions that normally maintain this lining. They also identified a specific molecular signaling pathway involved in mediating these inhibitory effects. Studies in mice supported the cell culture results. The findings could help improve infertility treatment strategies by guiding research into methods to alleviate the unwanted effects of FSH.

Testicular cancer in mice: interplay between stem cells and endocrine insults

BACKGROUND

Incidence of type II germ cell tumors (T2GCT) has increased in young men possibly due to fetal/perinatal exposure to estrogenic compounds. Three-fold increased incidence of T2GCT was reported in men exposed in utero to diethylstilbestrol (DES). T2GCT is a development-related disease arising due to blocked differentiation of gonocytes into spermatogonia in fetal testes which survive as germ cell neoplasia in situ (GCNIS) and initiate T2GCT. In our earlier study, T2GCT-like features were observed in 9 out of 10 adult, 100-day-old mice testes upon neonatal exposure to DES (2 μg/pup/day on days 1-5). Neonatal DES exposure affected testicular very small embryonic-like stem cells (VSELs) and spermatogonial stem cells and resulted in infertility, reduced sperm counts and tumor-like changes leading to our postulate that testicular dysgenesis syndrome possibly has a stem cell basis. The present study was undertaken to further characterize testicular tumor in mice testes.

METHODS

DES-exposed mice pups (n = 70) were studied on D100 and after 12 months to understand how T2GCT progresses. Besides histological studies, a carefully selected panel of markers were studied by immuno-fluorescence and qRT-PCR.

RESULTS

DES resulted in either atrophied or highly vascularized, big-sized testes and extra-testicular growth was also observed. GCNIS-like cells with big, vacuolated cytoplasm and increased expression of OCT-4, SSEA-1, SCA-1 and CD166 (cancer stem cells marker) along with reduced c-KIT, MVH and PTEN were evident. Global hypomethylation was found associated with altered expression of Dnmts, Igf2-H19 and Dlk-Meg3 imprinted genes along with reduced expression of Ezh2, cell cycle regulator p57KIP2 and Meg3; however, Pten remained unaltered. Increased expression of PCNA and Ki67 was observed in concert with complete lack of SOX-9 suggesting Sertoli cells independent proliferation.

CONCLUSIONS

Mouse model for T2GCT is described which will have immense potential to understand cancer initiation, cancer stem cells and also to develop effective therapies in future. T2GCT initiates from tissue-resident, pluripotent VSELs due to their altered epigenome. Neonatal exposure to DES blocks differentiation (spermatogenesis) and VSELs get transformed into CD166 positive cancer stem cells that undergo excessive self-renewal and initiate cancer in adult life challenging existing concept of fetal origin of T2GCT.

GFP Tagged VSELs Help Delineate Novel Stem Cells Biology in Multiple Adult Tissues

Various types of stem cells are being researched upon to exploit their potential for regenerative medicine including pluripotent human embryonic stem (hES) cells derived from spare human embryos, induced pluripotent stem (iPS) cells by reprogramming somatic cells to a pluripotent state and multipotent mesenchymal stem/stromal cells (MSCs) obtained in vitro from multiple tissues. More than 50 independent groups have reported another novel population of pluripotent stem cells in adult tissues termed very small embryonic-like stem cells (VSELs). VSELs are developmentally linked to primordial germ cells, which rather than giving rise to the germ cells and later ceasing to exist, survive throughout life in multiple organs along with tissue-specific adult stem cells better described as lineage-restricted, tissue-committed progenitors with limited plasticity. VSELs survive total body irradiation in bone marrow, oncotherapy in the gonads, bilateral ovariectomy in the uterus and partial pancreatectomy in the pancreas of mice and participate in the regeneration of multiple organs under normal physiological conditions. VSELs and tissue-specific progenitor cells work together in a subtle manner, maintain life-long tissue homeostasis and their dysfunction leads to various pathologies including cancer. However, due to their quiescent state, VSELs have invariably eluded lineage-tracing studies reported so far. Present article reviews novel insights into VSELs biology and how VSELs enriched from GFP (green fluorescent protein) mice have enabled to delineate their role in various biological processes in vivo. VSELs biology needs to be understood in-depth as this alone will help evolve the field of regenerative medicine and win the war against cancer.

Additional evidence to support OCT-4 positive VSELs and EnSCs as the elusive tissue-resident stem/progenitor cells in adult mice uterus

OBJECTIVE

True identity and specific set of markers to enrich endometrial stem cells still remains elusive. Present study was undertaken to further substantiate that very small embryonic-like stem cells (VSELs) are the true and elusive stem cells in adult mice endometrium.

METHODS

This was achieved by undertaking three sets of experiments. Firstly, SSEA-1+ and Oct-4 + positive VSELs, sorted from GFP mice, were transplanted into the uterine horns of wild-type Swiss mice and GFP uptake was studied within the same estrus cycle. Secondly, uterine lumen was scratched surgically and OCT-4 expressing stem/progenitor cells were studied at the site of injury after 24-72 h. Thirdly, OCT-4  expression was studied in the endometrium and myometrium of adult mice after neonatal exposure to estradiol (20 µg/pup/day on days 5-7 after birth).

RESULTS

GFP + ve VSELs expressing SSEA-1 and Oct-4 engrafted and differentiated into the epithelial cells lining the lumen as well as the glands during the estrus stage when maximum remodeling occurs. Mechanical scratching activated tissue-resident, nuclear OCT-4 positive VSELs and slightly bigger 'progenitors' endometrial stem cells (EnSCs, cytoplasmic OCT-4) which underwent clonal expansion and further differentiated into luminal and glandular epithelial cells. Neonatal exposure to endocrine disruption resulted in increased numbers of OCT-4 positive VSELs/EnSCs in adult endometrium.

DISCUSSION

Results support the presence of functionally active VSELs in adult endometrium. VSELs self-renew and give rise to EnSCs that further differentiate into epithelial cells under normal physiological conditions. Also, VSELs are vulnerable to endocrine insults. To conclude VSELs are true and elusive uterine stem cells that maintain life-long uterine homeostasis and their dysregulation may result in various pathologies.

Research Advances in Gametogenesis and Embryogenesis Using Pluripotent Stem Cells

The previous studies of human gametogenesis and embryogenesis have left many unanswered questions, which hinders the understanding of the physiology of these two vital processes and the development of diagnosis and treatment strategies for related diseases. Although many results have been obtained from animal studies, particularly mouse research, the results cannot be fully applied to humans due to species differences in physiology and pathology. However, due to ethical and material limitations, the direct study of human gametes and embryos is very difficult. The emergence and rapid development of organoids allow the construction of organoid systems that simulate gametogenesis and embryogenesis in vitro, and many studies have successfully established organoid systems for some parts of or even the entire processes of gametogenesis and embryogenesis. These studies typically start with the establishment of mouse models and then modify these models to obtain human organoid models. These organoid models can be used to obtain a better understanding of the signaling pathways, molecular mechanisms, genetics, and epigenetic changes involved in gametogenesis and embryogenesis and could also be applied to clinical applications, such as drug screening. Here, we discuss the formation of primordial stem cell-like cells (PGCLCs), and in vitro-induced gametes and embryoids using pluripotent stem cells (PSCs). We also analyze their applications and limitations.

Overview of follicle stimulating hormone and its receptors in reproduction and in stem cells and cancer stem cells

Follicle stimulating hormone (FSH) and its receptor (FSHR) have been reported to be responsible for several physiological functions and cancers. The responsiveness of stem cells and cancer stem cells towards the FSH-FSHR system make the function of FSH and its receptors more interesting in the context of cancer biology. This review is comprised of comprehensive information on FSH-FSHR signaling in normal physiology, gonadal stem cells, cancer cells, and potential options of utilizing FSH-FSHR system as an anti-cancer therapeutic target.

Gonadotropins as novel active partners in vascular diseases: Insight from angiogenic properties and thrombotic potential of endothelial colony-forming cells

BACKGROUND

The impact of estrogen and testosterone on atherosclerotic cardiovascular disease is well known, but the role of the gonadotropins follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) to some extent remain less studied.

OBJECTIVES

To explore the angiogenic potential of gonadotropins on endothelial colony-forming cells (ECFCs).

METHODS

We examined the effects of various doses of gonadotropins on ECFCs obtained from cord blood by assessing colony number, proliferation, migration, and sprouting ability. Moreover, we studied thrombin generation in ECFCs exposed to gonadotropins by performing a thrombin generation assay. Finally, we determined the levels of circulating gonadotropins in 30 men, to exclude the effect of estrogen, with lower extremity arterial disease (LEAD), in comparison with age- and sex-matched controls.

RESULTS

Exposure to FSH, LH, or PRL resulted in an increase in ECFC migration but showed no effect on proliferation or ECFC commitment from cord blood mononuclear cells. Using a three-dimensional fibrin gel assay, we showed that ECFC sprouting was significantly enhanced by gonadotropins. Exposure to FSH also increased the thrombin generation of ECFCs exposed to FSH. Finally, FSH and LH levels in men with LEAD were higher than those in controls.

CONCLUSION

Gonadotropins increase ECFC-related angiogenesis and may be involved in thrombin generation in cardiovascular disease. Gonadotropins may act as biomarkers; moreover, we hypothesize that gonadotropin-blocking strategies may be a novel interesting therapeutic approach in atherosclerotic cardiovascular disease.

An overview of FSH-FSHR biology and explaining the existing conundrums

FSH was first identified in 1930 and is central to mammalian reproduction. It is indeed intriguing that despite being researched upon for about 90 years, there is still so much more to learn about FSH-FSHR biology. The purpose of this review is to provide an overview of current understanding of FSH-FSHR biology, to review published data on biological and clinical relevance of reported mutations, polymorphisms and alternately spliced isoforms of FSHR. Tissue-resident stem/progenitor cells in multiple adult tissues including ovaries, testes and uterus express FSHR and this observation results in a paradigm shift in the field. The results suggest a direct action of FSH on the stem cells in addition to their well-studied action on Granulosa and Sertoli cells in the ovaries and testes respectively. Present review further addresses various concerns raised in recent times by the scientific community regarding extragonadal expression of FSHR, especially in cancers affecting multiple organs. Similar population of primitive and pluripotent tissue-resident stem cells expressing FSHR exist in multiple adult tissues including bone marrow and reproductive tissues and help maintain homeostasis throughout life. Any dysfunction of these stem cells results in various pathologies and they also most likely get transformed into cancer stem cells and initiate cancer. This explains why multiple solid as well as liquid tumors express OCT-4 and FSHR. More research efforts need to be focused on alternately spliced FSHR isoforms.

Endogenous, tissue-resident stem/progenitor cells in gonads and bone marrow express FSHR and respond to FSH via FSHR-3

Follicle stimulating hormone (FSH) is secreted by the anterior pituitary and acts on the germ cells indirectly through Granulosa cells in ovaries and Sertoli cells in the testes. Extragonadal action of FSH has been reported but is still debated. Adult tissues harbor two populations of stem cells including a reserve population of primitive, small-sized, pluripotent very small embryonic-like stem cells (VSELs) and slightly bigger, tissue-specific progenitors which include ovarian stem cells (OSCs) in ovaries, spermatogonial stem cells (SSCs) in testes, endometrial stem cells (EnSCs) in uterus and hematopoietic stem cells (HSCs) in the bone marrow. Data has accumulated in animal models showing FSHR expression on both VSELs and progenitors in ovaries, testes, uterus and bone marrow and eventually gets lost as the cells differentiate further. FSH exerts a direct action on the stem/progenitor cells via alternatively spliced FSHR-3 rather than the canonical FSHR-1. FSH stimulates VSELs to undergo asymmetrical cell divisions to self-renew and give rise to the progenitors that in turn undergo symmetrical cell divisions and clonal expansions followed by differentiation into specific cell types. Excessive self-renewal of VSELs results in cancer and this explains ubiquitous expression of embryonic markers including nuclear OCT-4 along with FSHR in cancerous tissues. Focus of this review is to compile published data to support this concept. FSHR expression in stem/progenitor cells was confirmed by immuno-fluorescence, Western blotting, in situ hybridization and by quantitative RT-PCR. Two different commercially available antibodies (Abcam, Santacruz) were used to confirm specificity of FSHR expression along with omission of primary antibody and pre-incubation of antibody with immunizing peptide as negative controls. Western blotting allowed detection of alternatively spliced FSHR isoforms. Oligoprobes and primers specific for Fshr-1 and Fshr-3 were used to study these alternately-sliced isoforms by in situ hybridization and their differential expression upon FSH treatment by qRT-PCR. To conclude, stem/progenitor cells in adult tissues express FSHR and directly respond to FSH via FSHR-3. These findings change the field of FSH-FSHR biology, call for paradigm shift, explain FSHR expression on cancer cells in multiple organs and provide straightforward explanations for various existing conundrums including extragonadal expression of FSHR.

Actions and Roles of FSH in Germinative Cells

Follicle stimulating hormone (FSH) is produced by the pituitary gland in a coordinated hypothalamic-pituitary-gonadal (HPG) axis event, plays important roles in reproduction and germ cell development during different phases of reproductive development (fetal, neonatal, puberty, and adult life), and is consequently essential for fertility. FSH is a heterodimeric glycoprotein hormone of two dissociable subunits, α and β. The FSH β-subunit (FSHβ) function starts upon coupling to its specific receptor: follicle-stimulating hormone receptor (FSHR). FSHRs are localized mainly on the surface of target cells on the testis and ovary (granulosa and Sertoli cells) and have recently been found in testicular stem cells and extra-gonadal tissue. Several reproduction disorders are associated with absent or low FSH secretion, with mutation of the FSH β-subunit or the FSH receptor, and/or its signaling pathways. However, the influence of FSH on germ cells is still poorly understood; some studies have suggested that this hormone also plays a determinant role in the self-renewal of germinative cells and acts to increase undifferentiated spermatogonia proliferation. In addition, in vitro, together with other factors, it assists the process of differentiation of primordial germ cells (PGCLCs) into gametes (oocyte-like and SSCLCs). In this review, we describe relevant research on the influence of FSH on spermatogenesis and folliculogenesis, mainly in the germ cell of humans and other species. The possible roles of FSH in germ cell generation in vitro are also presented.

Busulfan Suppresses Autophagy in Mouse Spermatogonial Progenitor Cells via mTOR of AKT and p53 Signaling Pathways

In testis, a rare undifferentiated germ cell population with the capacity to regenerate robustly and support spermatogenesis, is defined as spermatogonial progenitor cells (SPCs) population. As a widely used drug for tumor therapy or bone marrow transplantation, busulfan has a severe side effect on SPCs population and causes a consequent infertility. Recently, accumulating evidence revealed the protective role of autophagy in stem cell maintenance under exogenous stress. To better understand the role of autophagy in SPCs fates, we investigated the potential function of autophagy in SPCs under busulfan stress, and found that treatment of busulfan induced the formation of autophagic vesicles and autophagosomes in mouse SPCs. Subsequently, a connection of autophagy and SPCs maintenance and survival was demonstrated in a dose-dependent manner. Moreover, mTOR was identified as an essential factor for autophagy in SPCs with a complicated mechanism: (1) mTOR is phosphorylated by AKT to activate its target genes, p70s6 kinase, resulting in the inhibition of autophagy during short-term busulfan treatment. (2) mTOR mediates autophagy with p53 together, to regulate the fate of SPCs. Collectively, observations from this study indicate that moderate autophagy effectively protects SPCs from the stress of chemotherapy, which may provide an important hint for fertility protection in clinic.

Very small embryonic-like stem cells (VSELs) regenerate whereas mesenchymal stromal cells (MSCs) rejuvenate diseased reproductive tissues

Compared to embryonic and induced pluripotent stem cells, mesenchymal stem/stromal cells (MSCs) have made their presence felt with good therapeutic promise and safety profile. Transplanting MSCs has successfully helped to reverse infertility and resulted in live births in animal models and also in humans. But the underlying mechanism for their therapeutic potential is not yet clear. MSCs are not pluripotent and hence lack plasticity to differentiate into multiple adult cell types. They rather act as 'paracrine providers' to the tissue-resident stem cells since similar beneficial effects are also observed when their secretome (microvesicles or exosomes) is transplanted. Cytokines, growth factors, signaling lipids, mRNAs, and miRNAs secreted by MSCs enables tissue-resident stem cells to undergo differentiation into specific cell types. Tissue-resident stem cells include pluripotent, very small embryonic-like stem cells (VSELs) and progenitors [spermatogonial (SSCs), ovarian (OSCs) and endometrial (EnSCs) stem cells in testes, ovary and uterus respectively] which function in a subtle manner to maintain life-long tissue homeostasis and regenerate damaged (non-functional) reproductive tissues by differentiating into sperm, oocytes and endometrial epithelial cells respectively. Similar to restoring spermatogenesis, primordial follicles numbers are increased upon transplanting MSCs. Published literature suggests that MSCs do not differentiate into epithelial cells in the endometrium. Nuclear OCT-4 positive VSELs and cytoplasmic OCT-4, AXIN2 and KERATIN-19 positive epithelial progenitors have a greater role during endometrial regeneration. We propose, transplantation of MSCs simply provides growth factors/cytokines essential for the tissue-resident stem/progenitor cells to undergo differentiation into sperm, eggs and endometrial epithelial cells in the reproductive tissues.

Additional Evidence to Establish Existence of Two Stem Cell Populations Including VSELs and SSCs in Adult Mouse Testes

Present study aims to describe a simple and robust protocol to delineate the presence of pluripotent, very small embryonic-like stem cells (VSELs) in addition to spermatogonial stem cells (SSCs) in adult mouse testes. Testicular seminiferous tubules were subjected to enzymatic dissociation to obtain single cells suspension. Stem cells were enriched by spinning at different speeds wherein majority of somatic cells were pelleted at 1000 rpm (250 g, Pellet A) and putative stem cells by spinning the supernatant (obtained after separating Pellet A) at 3000 rpm (1000 g, Pellet B). Viable (7AAD-ve), 2-6 μm, LIN-CD45-SCA-1+ VSELs were studied after doublets exclusion by flow cytometry in both Pellets A & B. Almost ten-fold enrichment of VSELs was obtained in Pellet B (0.27 + 0.05%) compared to Pellet A (0.03 + 0.003%). SCA-1 expressing SSCs (>6 μm, 0.18 + 0.06%) were clearly distinguished from VSELs (2-6 μm, 0.07 + 0.003%) by flow cytometry studies on total testicular cells suspension collected by spinning at 3000 rpm. Enriched stem cells from Pellet B were used to study expression of OCT-4, NANOG, SCA-1, SSEA-1, LIFR, GFRa, c-KIT, ERα and ERβ. Cells in Pellet B were also subjected to RT-PCR to study pluripotent (Oct-4a, Sox2, Nanog), primordial germ cells (Stella, Fragilis), SSCs (Oct-4) and estrogen receptors (ERα and ERβ) specific transcripts. qRT-PCR analysis showed >2 folds up-regulation of stem cell markers in Pellet B (Oct-4A, Oct-4, Sox2, Nanog) compared to Pellet A. To conclude, spinning at higher speed led to successful enrichment of pluripotent VSELs from testes which have remained ignored till now. Expression of ERα & β on VSELs/SSCs makes them vulnerable to endocrine disruption.

Altered Biology of Testicular VSELs and SSCs by Neonatal Endocrine Disruption Results in Defective Spermatogenesis, Reduced Fertility and Tumor Initiation in Adult Mice

Reproductive health of men has declined in recent past with reduced sperm count and increased incidence of infertility and testicular cancers mainly attributed to endocrine disruption in early life. Present study aims to evaluate whether testicular stem cells including very small embryonic-like stem cells (VSELs) and spermatogonial stem cells (SSCs) get affected by endocrine disruption and result in pathologies in adult life. Effect of treatment on mice pups with estradiol (20 μg on days 5-7) and diethylstilbestrol (DES, 2 μg on days 1-5) was studied on VSELs, SSCs and spermatogonial cells in adult life. Treatment affected spermatogenesis, tubules in Stage VIII & sperm count were reduced along with reduction of meiotic (4n) cells and markers (Prohibitin, Scp3, Protamine). Enumeration of VSELs by flow cytometry (2-6 μm, 7AAD-, LIN-CD45-SCA-1+) and qRT-PCR using specific transcripts for VSELs (Oct-4a, Sox-2, Nanog, Stella, Fragilis), SSCs (tOct-4, Gfra-1, Gpr-125) and early germ cells (Mvh, Dazl) showed several-fold increase but transition from c-Kit negative to c-Kit positive spermatogonial cells was blocked on D100 after treatment. Transcripts specific for apoptosis (Bcl2, Bax) remained unaffected but tumor suppressor (p53) and epigenetic regulator (NP95) transcripts showed marked disruption. 9 of 10 mice exposed to DES showed tumor-like changes. To conclude, endocrine disruption resulted in a tilt towards excessive self-renewal of VSELs (leading to testicular cancer after DES treatment) and blocked differentiation (reduced numbers of c-Kit positive cells, meiosis, sperm count and fertility). Understanding the underlying basis for infertility and cancer initiation from endogenous stem cells through murine modelling will hopefully improve human therapies in future.

Advances in the Regulation of Mammalian Follicle-Stimulating Hormone Secretion

Simple Summary

The reproduction of mammals is regulated by the hypothalamic-pituitary-gonadal axis. Follicle stimulating hormone, as one of the gonadotropins secreted by the pituitary gland, plays an immeasurable role. This article mainly reviews the molecular basis and classical signaling pathways that regulate the synthesis and secretion of follicle stimulating hormone, and summarizes its internal molecular mechanism, which provides a certain theoretical basis for the research of mammalian reproduction regulation and the application of follicle stimulating hormone in production practice.

Abstract

Mammalian reproduction is mainly driven and regulated by the hypothalamic-pituitary-gonadal (HPG) axis. Follicle-stimulating hormone (FSH), which is synthesized and secreted by the anterior pituitary gland, is a key regulator that ultimately affects animal fertility. As a dimeric glycoprotein hormone, the biological specificity of FSH is mainly determined by the β subunit. As research techniques are being continuously innovated, studies are exploring the underlying molecular mechanism regulating the secretion of mammalian FSH. This article will review the current knowledge on the molecular mechanisms and signaling pathways systematically regulating FSH synthesis and will present the latest hypothesis about the nuclear cross-talk among the various endocrine-induced pathways for transcriptional regulation of the FSH β subunit. This article will provide novel ideas and potential targets for the improved use of FSH in livestock breeding and therapeutic development.

Adult tissue-resident stem cells-fact or fiction?

Life-long tissue homeostasis of adult tissues is supposedly maintained by the resident stem cells. These stem cells are quiescent in nature and rarely divide to self-renew and give rise to tissue-specific “progenitors” (lineage-restricted and tissue-committed) which divide rapidly and differentiate into tissue-specific cell types. However, it has proved difficult to isolate these quiescent stem cells as a physical entity. Recent single-cell RNAseq studies on several adult tissues including ovary, prostate, and cardiac tissues have not been able to detect stem cells. Thus, it has been postulated that adult cells dedifferentiate to stem-like state to ensure regeneration and can be defined as cells capable to replace lost cells through mitosis. This idea challenges basic paradigm of development biology regarding plasticity that a cell enters point of no return once it initiates differentiation. The underlying reason for this dilemma is that we are putting stem cells and somatic cells together while processing for various studies. Stem cells and adult mature cell types are distinct entities; stem cells are quiescent, small in size, and with minimal organelles whereas the mature cells are metabolically active and have multiple organelles lying in abundant cytoplasm. As a result, they do not pellet down together when centrifuged at 100–350g. At this speed, mature cells get collected but stem cells remain buoyant and can be pelleted by centrifuging at 1000g. Thus, inability to detect stem cells in recently published single-cell RNAseq studies is because the stem cells were unknowingly discarded while processing and were never subjected to RNAseq. This needs to be kept in mind before proposing to redefine adult stem cells.

Testicular Stem Cell Dysfunction Due to Environmental Insults Could Be Responsible for Deteriorating Reproductive Health of Men

Reproductive health of men has declined over time including reduced semen quality specifically sperm count, increased incidence of infertility, and testicular cancers. Our recent findings suggest that these disease states possibly arise as a result of disruption of testicular stem cells biology by perinatal insults including exposure to endocrine disrupting chemicals. Testicular stem cells include relatively quiescent, very small embryonic-like stem cells (VSELs), and actively dividing spermatogonial stem cells (SSCs). Both VSELs and SSCs express estrogen receptors and are directly vulnerable to endocrine disruption. Exposing mice pups to estradiol (20 μg/pup/day on days 5-7) or diethylstilbestrol (2 μg/pup/day on days 1-5) affected spermatogenesis during adult life with reduced numbers of tubules in stage VIII, tetraploid cells and sperm. These mice were infertile and majority of diethylstilbestrol treated mice revealed testicular cancer-like changes. An increase in VSEL numbers, observed by both flow cytometry and qRT-PCR, was associated with marked reduction of c-KIT positive spermatogonial cells. VSELs undergo epigenetic changes due to endocrine disruption that results in blocked differentiation (impaired spermatogenesis) leading to reduced sperm count and infertility, and their excessive self-renewal initiates cancer-like changes in adult life. Thus, testicular dysgenesis syndrome (TDS) has a stem cell rather than a genetic basis.

An Overview on the Complexity of OCT4: at the Level of DNA, RNA and Protein

OCT4 plays critical roles in self-renewal and pluripotency maintenance of embryonic stem cells, and is considered as one of the main stemness markers. It also has pivotal roles in early stages of embryonic development. Most studies on OCT4 have focused on the expression and function of OCT4A, which is the biggest isoform of OCT4 known so far. Recently, many studies have shown that OCT4 has various transcript variants, protein isoforms, as well as pseudogenes. Distinguishing the expression and function of these variants and isoforms is a big challenge in expression profiling studies of OCT4. Understanding how OCT4 is functioning in different contexts, depends on knowing of where and when each of OCT4 transcripts, isoforms and pseudogenes are expressed. Here, we review OCT4 known transcripts, isoforms and pseudogenes, as well as its interactions with other proteins, and emphasize the importance of discriminating each of them in order to understand the exact function of OCT4 in stem cells, normal development and development of diseases.

Bisphenol A and 17α-ethinylestradiol-induced transgenerational gene expression differences in the brain-pituitary-testis axis of medaka, Oryzias latipes†

Endocrine disrupting chemicals (EDCs), such as bisphenol A (BPA) and 17α-ethinylestradiol (EE2), can have far reaching health effects, including transgenerational abnormalities in offspring that never directly contacted either chemical. We previously reported reduced fertilization rates and embryo survival at F2 and F3 generations caused by 7-day embryonic exposure (F0) to 100 μg/L BPA or 0.05 μg/L EE2 in medaka. Crossbreeding of fish in F2 generation indicated subfertility in males. To further understand the mechanisms underlying BPA or EE2-induced adult onset and transgenerational reproductive defects in males, the present study examined the expression of genes regulating the brain-pituitary-testis (BPT) axis in the same F0 and F2 generation male medaka. Embryonic exposure to BPA or EE2 led to hyperactivation of brain and pituitary genes, which are actively involved in reproduction in adulthood of the F0 generation male fish, and some of these F0 effects continued to the F2 generation (transgenerational effects). Particularly, the F2 generation inherited the hyperactivated state of expression for kisspeptin (kiss1 and kiss2) and their receptors (kiss1r and kiss2r), and gnrh and gnrh receptors. At F2 generation, expression of DNA methyltransferase 1 (dnmt1) decreased in brain of the BPA treatment lineage, while EE2 treatment lineage showed increased dnmt3bb expression. Global hypomethylation pattern was observed in the testis of both F0 and F2 generation fish. Taken together, these results demonstrated that BPA or EE2-induced transgenerational reproductive impairment in the F2 generation was associated with alterations of reproductive gene expression in brain and testis and global DNA methylation in testis.

Pluripotent Stem (VSELs) and Progenitor (EnSCs) Cells Exist in Adult Mouse Uterus and Show Cyclic Changes Across Estrus Cycle

We have earlier reported pluripotent, very small embryonic-like stem cells (VSELs) and slightly bigger endometrial stem cells (EnSCs) in adult mouse uterus and their regulation by gonadotropin and steroid hormones. VSELs can differentiate into cells of all three lineages in vitro; however, they neither expand readily in vitro nor compliment a developing embryo. In the present study, a robust protocol is described to enrich uterine stem/progenitor cells along with their characterization and variation across estrus cycle. After enzymatic digestion of adult mouse uterus, single-cell suspension obtained was spun at 1000 rpm (250 g) to pellet majority of cells. Stem cells remain buoyant at this speed and were pelleted by spinning supernatant at 3000 rpm (1000 g). Spherical, darkly stained VSELs (2-6 μm) with high nucleo-cytoplasmic ratio and EnSCs (> 6 μm) expressed OCT-4, NANOG, SSEA-1, SCA-1, and c-KIT. OCT-4-positive cells co-expressed SSEA-1, ERα, ERβ, PR, and FSHR. Transcripts specific for pluripotent state (Oct-4, Oct-4a, Sox-2, Nanog), primordial germ cells (Stella, Fragilis), and receptors for pituitary and steroid hormones (ERα, ERβ, PR, FSHR 1 and 3) were studied by RT-PCR in 3000 rpm pellet. Cell pellet collected at 3000 rpm showed 10-fold enrichment of VSELs (2-6 μm, viable cells with surface phenotype of LIN-CD45-SCA-1+) by flow cytometry and upregulation of pluripotent transcripts by qRT-PCR compared with 1000 rpm pellet. VSELs were maximal during estrus and metestrus phases of estrus cycle. To conclude, VSELs/EnSCs can be enriched from adult uterus using the strategy described here, vary in numbers across estrus cycle, and are vulnerable to endocrine disruption as they express steroid receptors.

Direct action of FSH on testicular stem cells

Recently published article by Pieri’s group suggested that follicle-stimulating hormone (FSH) activates canine testicular spermatogonial stem cells (SSCs) and results in increased expression of pluripotent markers and formation of germ cell clumps possibly via indirect paracrine effect of Sertoli cells. We disagree with their interpretations and herewith provide a better explanation to their findings. We have earlier reported the presence of pluripotent, very small embryonic-like stem cells (VSELs) as a sub-group among the SSCs in human and mouse testes and that both VSELs and SSCs express FSH receptors. Thus, FSH exerts a direct stimulatory action on the testicular stem/progenitor cells whereby VSELs undergo asymmetrical cell divisions to self-renew (result in upregulation of pluripotent markers) and give rise to slightly bigger SSCs which undergo symmetrical cell divisions and “clonal expansion” (rapid proliferation with incomplete cytokinesis) which was noted by the authors as “clump” formation. This action of FSH is mediated via alternately spliced FSHR3 rather than the canonical FSHR1 receptor isoform, and FSH exerts similar action on ovarian and uterine stem/progenitor cells also. Being quiescent by nature, VSELs survive chemotherapy. Transplanted germ cells colonize chemoablated tubules but do not differentiate into sperm since the testicular stem cell niche comprising Sertoli cells gets functionally compromised by chemotherapy. Transplanting healthy niche cells (Sertoli or bone marrow-derived mesenchymal cells) can restore spermatogenesis in chemoablated testes.

Stem cells survive oncotherapy & can regenerate non-functional gonads: A paradigm shift for oncofertility

A large proportion of patients who survive cancer are rendered infertile as an unwanted side effect of oncotherapy. Currently accepted approaches for fertility preservation involve banking eggs/sperm/embryos or ovarian/testicular tissue before oncotherapy for future use. Such approaches are invasive, expensive, technically challenging and depend on assisted reproductive technologies (ART). Establishing a gonadal tissue bank (for cancer patients) is also fraught with ethical, legal and safety issues. Most importantly, patients who find it difficult to meet expenses towards cancer treatment will find it difficult to meet expenses towards gonadal tissue banking and ART to achieve parenthood later on. In this review an alternative strategy to regenerate non-functional gonads in cancer survivors by targeting endogenous stem cells that survive oncotherapy is discussed. A novel population of pluripotent stem cells termed very small embryonic-like stem cells (VSELs), developmentally equivalent to late migratory primordial germ cells, exists in adult gonads and survives oncotherapy due to their quiescent nature. However, the stem-cell niche gets compromised by oncotherapy. Transplanting niche cells (Sertoli or mesenchymal cells) can regenerate the non-functional gonads. This approach is safe, has resulted in the birth of fertile offspring in mice and could restore gonadal function early in life to support proper growth and later serve as a source of gametes. This newly emerging understanding on stem cells biology can obviate the need to bank gonadal tissue and fertility may also be restored in existing cancer survivors who were earlier deprived of gonadal tissue banking before oncotherapy.

Pluripotent Very Small Embryonic-Like Stem Cells in Adult Testes - An Alternate Premise to Explain Testicular Germ Cell Tumors

Developmental exposure to endocrine disruptors has resulted in the increased incidence of infertility and testicular germ cell tumors (T2GCT) in young men residing in developed countries. Unlike T1GCT (infants and young children) and T3GCT (aged men), T2GCT arise from CIS/GCNIS that develops from pre-CIS. Pre-CIS represents undifferentiated, growth-arrested gonocytes that persist in fetal testes due to endocrine disruption. However, whether pre-CIS truly exist, do CIS develop into T2GCT, why no CIS in T1GCT/T3GCT, why germ cell tumors (GCT) also occur along midline at extra-gonadal sites, why T1GCT show partial erasure and T2GCT show complete erasure of genomic imprints are open questions that are awaiting answers. We propose that rather than pre-CIS, pluripotent, very small embryonic-like stem cells (VSELs) get affected by exposure to endocrine disruption. Since VSELs are developmentally equivalent to primordial germ cells (PGCs), T2GCT cells show complete erasure of genomic imprints and CIS represents growth-arrested clonally expanding stem/progenitor cells. PGCs/VSELs migrate along the midline to various organs and this explains why GCT occur along the midline, T1GCT show partial erasure of imprints as they develop from migrating PGCs. T3GCT possibly reflects effects of aging due to compromised differentiation and expansion of pre-meiotic spermatocytes. Absent spermatogenesis in pre-pubertal and aged testes explains absence of CIS in T1GCT and T3GCT. Endocrine disruptors possibly alter epigenetic state of VSELs and thus rather than maintaining normal tissue homeostasis, VSELs undergo increased proliferation and compromised differentiation resulting in reduced sperm count, infertility and TGCT. This newly emerging understanding offers alternate premise to explain TGCT and warrants further exploration.

Heterogeneity of Stem Cells in the Ovary

Every organ in the body is thought to harbor two populations of stem cells, including the quiescent and the actively dividing, that leads to heterogeneity among them. It is generally believed that the ovary harbors a fixed number of follicles at birth that differentiate during fetal development from the primordial germ cells. The numbers of follicles decrease by age, leading to menopause. However, in 2004, it was suggested that ovary may harbor stem cells that are possibly involved in the formation of new follicles throughout reproductive life. Research over little more than a decade shows that ovarian stem cells include a quiescent population of very small embryonic-like stem cells (VSELs) and slightly bigger, actively dividing ovarian stem cells (OSCs). This heterogeneity among ovarian stem cells is similar to the presence of VSELs along with spermatogonial stem cells (SSCs) in the testis or hematopoietic stem cells (HSCs) in the hematopoietic system. VSELs express embryonic markers, including nuclear OCT-4, and are lodged in the ovary surface epithelium (OSE). Ovarian VSELs undergo asymmetric cell division to self-renew and give rise to OSCs that in turn undergo symmetric cell divisions and clonal expansion (germ cell nest) followed by meiosis to form an oocyte that gets assembled as a primordial follicle. Both VSELs and OSCs also express receptors for follicle-stimulating hormone (FSHR) and are directly activated by FSH to undergo neo-oogenesis and primordial follicle assembly. Whether stimulation of ovaries by FSH in Infertility Clinics activates the stem cells leading to the formation of multiple follicles needs further investigation. Epithelial cells lining the surface of ovary provide a niche to the stem cells under normal circumstances and undergo epithelial-mesenchymal transition (EMT) to form granulosa cells for primordial follicle assembly. Compromised function of the epithelial cells with age possibly leads to inability of stem cells to form follicles, leading to menopause. More than 90% of ovarian cancers arise in the OSE, possibly due to excessive self-renewal of VSELs. Altered biology of the OSE cells results in the formation of myofibroblasts by EMT and may provide a cancerous niche that supports excessive expansion of the stem cells lodged in the OSE, leading to ovarian cancer. Ovarian cancer cells express markers like OCT-4 and FSHR, which are also expressed by the VSELs lodged in the OSE, whereas the epithelial cells are distinctly negative for the same. Lot more research is required in the field to gain further understanding of ovarian stem cell biology.

Dynamics of Bone Marrow VSELs and HSCs in Response to Treatment with Gonadotropin and Steroid Hormones, during Pregnancy and Evidence to Support Their Asymmetric/Symmetric Cell Divisions

Gender plays an important role in the incidence of hematological malignancies and recently hematopoietic stem cells (HSCs) were found to proliferate more in females that gets further augmented during pregnancy. It was suggested that since basal numbers of HSCs remain the same in both sexes, possibly HSCs in females undergo increased self-renewal and apoptosis. Then how is self-renewal of stem cells regulated in males? More important, do HSCs undergo asymmetric cell divisions (ACD) or a more primitive population of pluripotent, very small embryonic-like stem cells (VSELs) undergo ACD to self-renew and specify into HSCs? Lot more clarity is required on the bone marrow stem cells biology. Present study was undertaken to evaluate whether similar dimorphism reported for HSCs also exists among VSELs. Bone marrow VSELs and HSCs were studied in bilaterally ovariectomized and castrated mice by flow cytometry after treating with gonadotropin (FSH) and sex steroid (estrogen & progesterone) hormones and during pregnancy. Differential expression of pluripotent (Oct-4A, Sox2, Nanog) and differentiation (Oct-4, Sca1, c-Kit, Ikaros) specific transcripts was studied. Basal BrdU uptake was more in both VSELs (p < 0.01) and HSCs (p < 0.05) in female bone marrow. FSH exerted a more profound effect compared to estradiol in both the sexes. Flow cytometry results showed ten-fold increase in spleen VSELs by mid-gestation associated with approximately two-fold increase in HSCs. These results point to a novel yet unreported role of spleen VSELs during pregnancy. Furthermore, VSELs underwent ACD to self-renew and give rise to slightly bigger HSCs based on unequal expression of NUMB, CD45 and OCT-4.

Gonadotropin and steroid hormones regulate pluripotent very small embryonic-like stem cells in adult mouse uterine endometrium

Background

Very small embryonic-like stem cells (VSELs) exist in adult organs, express pluripotent markers and have the ability to differentiate into three germ layers in vitro. Testicular, ovarian and hematopoietic stem/progenitor cells express receptors for follicle stimulating (FSH) and ovarian hormones and are activated by them to undergo proliferation/differentiation. VSELs exist in mouse uterus and are regulated by physiological dose of estradiol (E) & progesterone (P) during endometrial growth, differentiation and regeneration/remodeling. In the present study, effects of daily administration of E (2 μg/day), P (1 mg/Kg/day) or FSH (5 IU/day) for 7 days on the endometrium and stem/progenitor cells was studied in bilaterally ovariectomized mice.

Results

E treatment resulted in hypertrophy whereas P resulted in hyperplasia and overcrowding of epithelial cells. FSH also directly stimulated the endometrial cells. Nuclear OCT-4A positive VSELs were visualized in ovariectomized (atrophied) endometrium and cytoplasmic OCT-4B positive epithelial, stromal and endothelial cells were observed after treatment. FSH treated uterine tissue showed presence of 4 alternately spliced FSHR isoforms by Western blotting. 3–5 μm VSELs with a surface phenotype of LIN-/CD45-/SCA-1+ were enumerated by flow cytometry and were found to express ER, PR, FSHR1 and FSHR3 by RT-PCR analysis. Differential effects of treatment were observed on pluripotent (Oct4A, Sox2, Nanog), progenitors (Oct-4, Sca-1), primordial germ cells (Stella, Fragilis) and proliferation (Pcna) specific transcripts by qRT-PCR analysis. FSH and P (rather than E) exerted profound, direct stimulatory effects on uterine VSELs. Asymmetric, symmetric divisions and clonal expansion of stem/progenitor cells was confirmed by co-expression of OCT-4 and NUMB.

Conclusions

Results confirm presence of VSELs and their regulation by circulatory hormones in mouse uterus. Stem cell activation was more prominent after P and FSH compared to E treatment. The results question whether epithelial cells proliferation is regulated by paracrine influence of stromal cells or due to direct action of hormones on stem cells. VSELs expressing nuclear OCT-4A are the most primitive and pluripotent stem cells, undergo asymmetric cell division to self-renew and differentiate into epithelial, stromal and endothelial cells with cytoplasmic OCT-4B. Role of follicle stimulating and steroid hormones on the stem cells needs to be studied in various uterine pathologies.

Novel Insights into Adult and Cancer Stem Cell Biology

Adult tissues are thought to harbor two populations of "dormant" and "actively dividing" stem cells. Quiescent stem cells undergo rare asymmetric cell divisions (ACDs) through which they self-renew and give rise to tissue-committed "progenitors" of distinct fate and "progenitors" in turn undergo symmetric cell divisions (SCDs) and clonal expansion. However, quiescent stem cells have not been demonstrated in adult tissues such as skin, testis, liver, and brain. After surgical removal of part of liver and pancreas-adult differentiated cells divide and regenerate and a possible role of stem cells remains doubtful. Long-term repopulating hematopoietic stem cells are quiescent in nature but ACD has not been convincingly demonstrated even among them. Attempts by various groups to identify a common stemness program that ensures self-renewal among different kinds of stem cells have also remained futile. Uncontrolled self-renewal and compromised differentiation of stem cells possibly initiate leukemia/cancer, but the identity of leukemic stem cells and whether cancer stem cells arise by epithelial-mesenchymal transition (EMT) in solid tumors are all open-ended questions that need greater clarity. Acceptance of the presence of very small embryonic-like stem cells (VSELs) in adult tissues could clarify several of these existing dilemmas in the field. Data are compiled showing that VSELs undergo ACD in the hematopoietic system, testis, ovary, uterus, and pancreas, whereas tissue-committed progenitors undergo SCD and clonal expansion. VSELs possess similar overlapping stemness program as in embryonic stem cells, embryonic carcinoma cells, embryonic germ cells, induced pluripotent stem cells, and primordial germ cells. VSELs and leukemic and cancer cells express overlapping embryonic markers. Uncontrolled proliferation of VSELs and compromised differentiation possibly initiate leukemia. Process of EMT and initiation of solid tumor from VSELs (located among the epithelial cells) are indeed two distinct and parallel events. To conclude, VSELs provide explanation to several confounding aspects of adult stem cell biology.

The need to revisit the definition of mesenchymal and adult stem cells based on their functional attributes

A debate is ongoing about the ‘stem cell’ status of mesenchymal stem cells (MSCs). This can easily be resolved based on the definition of a stem cell. ‘True’ stem cells are expected to undergo asymmetric cell divisions (ACD) whereby they divide to self-renew and give rise to a slightly bigger, differentiated cell. However, MSCs like any other adult tissue-specific stem cells, including hematopoietic (HSCs), spermatogonial (SSCs) and ovarian (OSCs) stem cells, do not undergo ACD; rather they undergo rapid symmetrical cell divisions. The true stem cells in adult tissues are possibly the pluripotent stem cells termed very small embryonic-like stem cells (VSELs), which were recently shown to undergo ACD to give rise to tissue-specific stem cells ‘progenitors’ (currently termed ‘adult stem cells’) that in turn undergo rapid symmetric cell divisions and clonal expansion (sphere formation with incomplete cytokinesis) followed by differentiation into tissue-specific cell types. MSCs can be cultured from any tissue source and are an excellent source of growth factors/cytokines and thus could provide a niche for proper functioning of the stem/progenitor cells.

Further characterization of adult sheep ovarian stem cells and their involvement in neo-oogenesis and follicle assembly

BACKGROUND

Stem cells in the ovary comprise of two distinct populations including very small embryonic-like stem cells (VSELs) and slightly bigger progenitors termed ovarian stem cells (OSCs). They are lodged in ovary surface epithelium (OSE) and are expected to undergo neo-oogenesis and primordial follicle (PF) assembly in adult ovaries. The ovarian stem cells express follicle stimulating hormone (FSH) receptors and are directly activated by FSH resulting in formation of germ cell nests (GCN) in vitro. Present study was undertaken to further characterize adult sheep OSCs and to understand their role during neo-oogenesis and PF assembly.

METHODS

Stem cells were collected by gently scraping the OSE cells and were characterized by H&E staining, immuno-localization, immuno-phenotyping and RT-PCR studies. Expression of FSH receptors and markers specific for stem cells (OCT-4, SSEA-4) and proliferation (PCNA) were studied on stem/progenitor cells in OSE culture and on adult sheep ovarian cortical tissue sections. Effect of FSH on stem cells was also studied in vitro. Asymmetric cell division (ACD) was monitored by studying expression of OCT-4 and NUMB.

RESULTS

Additional evidence was generated on the presence of two populations of stem cells in the OSE including VSELs and OSCs. FSHR expression was observed on both VSELs and OSCs by immuno-localization and immuno-phenotyping studies. FSH treatment in vitro stimulated VSELs that underwent ACD to self-renew and give rise to OSCs which divided rapidly by symmetric cell divisions (SCD) and clonal expansion with incomplete cytokinesis to form GCN. ACD was further confirmed by differential expression of OCT-4 in VSELs and NUMB in the OSCs. Immuno-histochemical expression of OCT-4, PCNA and FSHR was noted on stem cells located in the OSE in sheep ovarian sections. GCN and cohort of PF were observed in the ovarian cortex and provided evidence in support of neo-oogenesis from the stem cells.

CONCLUSION

Results of present study provide further evidence in support of two stem cells populations in adult sheep ovary. Both VSELs, OSCs and GCN express FSH receptors and FSH possibly regulates their function to undergo neo-oogenesis and primordial follicle assembly.

Novel evidence that pituitary sex hormones regulate migration, adhesion, and proliferation of embryonic stem cells and teratocarcinoma cells

The pituitary sex hormones (SexHs): follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) regulate several functions crucial for reproduction, including oogenesis, spermatogenesis, and lactation. An important source of prolactin-like hormones, known as lactogens, is the placenta, and lactogens bind to the PRL receptor (PRLR) with high affinity and thereby mimic the actions of PRL. Recently, it has been demonstrated that pituitary SexHs were involved in metastatic lung cancer, certain sarcomas, and leukemia. In the present study we aimed to investigate whether FSH, LH, and PRL were able to stimulate stem cells involved in early development. To address this issue we employed a murine embryonic stem cell line (ES-D3) as well as two teratocarcinoma cell lines, P19 (murine) and NTera2 (human). We determined that all these cells expressed SexH receptors at the mRNA and protein levels and that stimulation of these receptors induced phosphorylation of p42/44 MAPK, p38 MAPK, and AKT. Moreover, ES-D3, P19, and NTera2 cells responded with increased migration and adhesion to physiological concentrations of pituitary SexHs. In view of these findings we proposed that maternal-derived pituitary SexHs regulate the biology of stem cells involved in early development.

Making gametes from alternate sources of stem cells: past, present and future

Infertile couples including cancer survivors stand to benefit from gametes differentiated from embryonic or induced pluripotent stem (ES/iPS) cells. It remains challenging to convert human ES/iPS cells into primordial germ-like cells (PGCLCs) en route to obtaining gametes. Considerable success was achieved in 2016 to obtain fertile offspring starting with mouse ES/iPS cells, however the specification of human ES/iPS cells into PGCLCs in vitro is still not achieved. Human ES cells will not yield patient-specific gametes unless and until hES cells are derived by somatic cell nuclear transfer (therapeutic cloning) whereas iPS cells retain the residual epigenetic memory of the somatic cells from which they are derived and also harbor genomic and mitochondrial DNA mutations. Thus, they may not be ideal starting material to produce autologus gametes, especially for aged couples. Pluripotent, very small embryonic-like stem cells (VSELs) have been reported in adult tissues including gonads, are relatively quiescent in nature, survive oncotherapy and can be detected in aged, non-functional gonads. Being developmentally equivalent to PGCs (natural precursors to gametes), VSELs spontaneously differentiate into gametes in vitro. It is also being understood that gonadal stem cells niche is compromised by oncotherapy and with age. Improving the gonadal somatic niche could regenerate non-functional gonads from endogenous VSELs to restore fertility. Niche cells (Sertoli/mesenchymal cells) can be directly transplanted and restore gonadal function by providing paracrine support to endogenous VSELs. This strategy has been successful in several mice studies already and resulted in live birth in a woman with pre-mature ovarian failure.

Ovarian stem cells-resolving controversies

A recent review on ovarian stem cells by Horan and Williams entitled "Oocyte Stem Cells: Fact or Fantasy?" suggests that the debate on ovarian stem cells (OSCs) is still not over. They did not even discuss the presence of two distinct populations of stem cells in the ovary in their review. OSCs are located in the ovary surface epithelium and Tilly's group reported them in the size range of 5-8 μm whereas Virant-Klun's group has reported pluripotent, 2-4 μm OSCs. Our group reported OSCs of two distinct sizes including pluripotent very small embryonic-like stem cells (VSELs) which are smaller in size than RBCs (similar to those reported by Virant-Klun's group) and slightly bigger (similar to those reported by Tilly's group) tissue committed progenitors (OSCs) that presumably differentiate from VSELs. These stem/progenitor cells express receptors for follicle stimulating hormone (FSH) and are activated by FSH. Our opinion article provides explanation to several open-ended questions raised in the review on OSCs by Horan and Williams. VSELs survive chemotherapy; maintain life-long homeostasis; loss of their function due to a compromised niche results in age-related senescence and presence of overlapping pluripotent markers suggest that they may also be implicated in epithelial ovarian cancers.

Mouse Bone Marrow VSELs Exhibit Differentiation into Three Embryonic Germ Lineages and Germ & Hematopoietic Cells in Culture

Very small embryonic-like stem cells (VSELs) have been reported in various adult tissues, express pluripotent and primordial germ cells (PGCs) specific markers, are mobilized under stress/disease conditions, give rise to tissue committed progenitors and thus help regenerate and maintain homeostasis. The aim of the present study was to evaluate in vitro differentiation potential of VSELs using a quantitative approach. VSELs were collected from mouse bone marrow after 4 days of 5-fluorouracil (5-FU, 150 mg/Kg) treatment, further enriched by size based filtration and cultured on a feeder support in the presence of specific differentiation media. Cultured VSELs were found to differentiate into all three embryonic germ cell lineages, germ and hematopoietic cells after 14 days in culture. This was confirmed by studying Nestin, PDX-1, NKX2.5, DAZL, CD45 and other markers expression by various approaches. Very small, CD45 negative cells collected and enriched from GFP positive 5-FU treated mice bone marrow transitioned into CD45 positive cells in vitro thus demonstrating that VSELs can give rise to hematopoietic stem cells (HSCs). We envision that VSELs may be responsible for plasticity and ability of bone marrow cells to give rise to non-hematopoietic tissue progenitors of all 3 germ layers. Moreover the ability of VSELs to differentiate into germ cells as well as all the three lineages provides further evidence to support their pluripotent state and confirms developmental link between bone marrow VSELs and PGCs. The property of quiescence, no risk of teratoma formation and autologus source, make pluripotent VSELs a potential candidate to facilitate endogenous regeneration compared to cell replacement strategy envisioned using embryonic and induced pluripotent stem cells.

Underlying Mechanisms that Restore Spermatogenesis on Transplanting Healthy Niche Cells in Busulphan Treated Mouse Testis

Very small embryonic-like stem cells (VSELs) exist among spermatogonial stem cells and survive chemotherapy in both mice and human testes because of their relatively quiescent nature. Our earlier study revealed that inter-tubular transplantation of niche (Sertoli or bone marrow derived mesenchymal) cells can restore spermatogenesis from endogenous surviving VSELs. Present study was undertaken to delineate the effect of busulphan on testicular stem/germ/Sertoli cells and to comprehend the underlying mechanisms of how transplanted niche cells restore spermatogenesis. Ploidy analysis showed an increase in diploid cells on D7 and VSELs (2-6 μm; LIN-/CD45-/SCA-1+) were detected at all time-points studied and were maximum on D15 after busulphan treatment. They were visualized in cell smears, expressed nuclear NANOG and SOX2 and BrdU uptake on D15 suggested they were proliferating in response to stress induced by busulphan. Verapamil-sensitive side population detected comprised SCA-1 positive stem cells (5 ± 0.02 % in normal and 8.6 ± 2.02 % in chemoablated testis). Adverse effects of busulphan on Sertoli cells by transcriptome analysis included altered expression of Gdnf, Scf, Fgf, Bmp4, androgen binding protein, components of blood-testis-barrier and also stem cells related signaling pathways including Wnt. GFP positive transplanted cells aligned themselves as 'neo-tubules' and were visualized adjacent to 'native' germ cells depleted tubules. 'Neo-tubules' provide paracrine support to endogenous VSELs to undergo spermatogenesis. Quantitative analysis was done to track proliferation (PCNA) and differentiation (MVH) of stem cells by immuno-localization studies at different time intervals. Results provide an alternative strategy to restore spermatogenesis in cancer survivors from endogenous stem cells which needs to be further researched.