Germline niche transplantation restores fertility in infertile mice

What should be done in terms of fertility preservation for patients with cancer? The French 2021 guidelines

AIM

To provide practice guidelines about fertility preservation (FP) in oncology.

METHODS

We selected 400 articles after a PubMed review of the literature (1987-2019).

RECOMMENDATIONS

Any child, adolescent and adult of reproductive age should be informed about the risk of treatment gonadotoxicity. In women, systematically proposed FP counselling between 15 and 38 years of age in case of treatment including bifunctional alkylating agents, above 6 g/m2 cyclophosphamide equivalent dose (CED), and for radiation doses on the ovaries ≥3 Gy. For postmenarchal patients, oocyte cryopreservation after ovarian stimulation is the first-line FP technique. Ovarian tissue cryopreservation should be discussed as a first-line approach in case of treatment with a high gonadotoxic risk, when chemotherapy has already started and in urgent cases. Ovarian transposition is to be discussed prior to pelvic radiotherapy involving a high risk of premature ovarian failure. For prepubertal girls, ovarian tissue cryopreservation should be proposed in the case of treatment with a high gonadotoxic risk. In pubertal males, sperm cryopreservation must be systematically offered to any male who is to undergo cancer treatment, regardless of toxicity. Testicular tissue cryopreservation must be proposed in males unable to cryopreserve sperm who are to undergo a treatment with intermediate or severe risk of gonadotoxicity. In prepubertal boys, testicular tissue preservation is: - recommended for chemotherapy with a CED ≥7500 mg/m2 or radiotherapy ≥3 Gy on both testicles. - proposed for chemotherapy with a CED ≥5.000 mg/m2 or radiotherapy ≥2 Gy. If several possible strategies, the ultimate choice is made by the patient.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

[Reconstruction of spermatogonial niche for male fertility preservation]

Infertility is one of the late side effects of cancer treatment. Expansion of anti-cancer treatment allow patients to have more life time, however infertility is becoming a matter damaging QOL during the young cancer survivors. The passive strategy such as avoiding the gonad-toxic drug or decreasing the total volume of them and shielding the gonads against cancer therapy has been conducted. To preserve the fertility of young female, ovary tissue cryopreservation is becoming a standard over the world after the success of offspring from cryopreserved ovary tissue autograft was reported. Sperm preservation method is established for the male fertility preservation method, however this is only applicable for sexually matured male patients. For the sake of preserving fertility of sexually immature male patients, many trials using cryopreserved testis tissues or testicular cells have been undergone. Recently, in vitro gametogenesis from stem cell of the human and the mouse to primordial germ cell like cell has been achieved. Here the previous challenges and the latest reports for obtaining functional sperm from immature testis and the reconstruction of spermatogonial niche as a potential approach for preserving fertility procedure are described.

Analysis of chromatin accessibility in p53 deficient spermatogonial stem cells for high frequency transformation into pluripotent state

OBJECTIVES

Spermatogonial stem cells (SSCs), the germline stem cells (GSCs) committed to spermatogenesis in niche, can transform into pluripotent state in long-term culture without introduction of exogenous factors, typically in p53 deficiency condition. As the guardian for genomic stability, p53 is associated with epigenetic alterations during SSCs transformation. However, the mechanism is still unknown, since complicated roles of p53 baffle our understanding of the regulating process.

MATERIALS AND METHODS

The chromatin accessibility and differentially expressed genes (DEGs) were analysed in p53+/+ and p53-/- SSCs using the Assay for Transposase-Accessible Chromatin with high-throughput Sequencing (ATAC-seq) and RNA-sequencing (RNA-seq), to explore the connection of p53 and cell fate at chromosomal level.

RESULTS

Several transcription factors (TFs), such as CTCF, SMAD3 and SOX2, were predicted as important factors mediating the transformation. Molecular evidence suggested that SMAD3 efficiently promoted pluripotency-associated gene expression both in fresh and long-term cultured SSCs. However, p53 knockout (KO) is insufficient to induce SMAD3 expression in SSCs.

CONCLUSIONS

These observations indicate that SMAD3 is a key factor for SSCs transformation, and an unknown event is required to activate SMAD3 as the prerequisite for SSCs reprogramming, which may occur in the long-term culture of SSCs. This study demonstrates the connection of p53 and pluripotency-associated factors, providing new insight for understanding the mechanisms of SSCs reprogramming and germline tumorigenesis.

Updates in Sertoli Cell-Mediated Signaling During Spermatogenesis and Advances in Restoring Sertoli Cell Function

Since their initial description by Enrico Sertoli in 1865, Sertoli cells have continued to enchant testis biologists. Testis size and germ cell carrying capacity are intimately tied to Sertoli cell number and function. One critical Sertoli cell function is signaling from Sertoli cells to germ cells as part of regulation of the spermatogenic cycle. Sertoli cell signals can be endocrine or paracrine in nature. Here we review recent advances in understanding the interplay of Sertoli cell endocrine and paracrine signals that regulate germ cell state. Although these findings have long-term implications for treating male infertility, recent breakthroughs in Sertoli cell transplantation have more immediate implications. We summarize the surge of advances in Sertoli cell ablation and transplantation, both of which are wedded to a growing understanding of the unique Sertoli cell niche in the transitional zone of the testis.

The guardians of germ cells; Sertoli-derived exosomes against electromagnetic field-induced oxidative stress in mouse spermatogonial stem cells

Nowadays, prolonged exposure to electromagnetic fields (EMF) has raised public concern about the detrimental potential of EMF on spermatogonial stem cells (SSCs) and spermatogenesis. Recent studies introduced the fundamental role of Sertoli cell paracrine signaling in the regulation of SSCs maintenance and differentiation in fertility preservation. Thus we investigated the therapeutic effect of Sertoli-derived exosomes (Sertoli-EXOs) as powerful paracrine mediators in SSCs subjected to EMF and its underlying mechanisms. SSCs and Sertoli cells were isolated from neonate mice testis, and identified by their specific markers. Then SSCs were exposed to 50 Hz EMF with intensity of 2.5 mT (1 h for 5 days) and supplemented with exosomes that were isolated from pre-pubertal Sertoli cells. Sertoli-EXOs were characterized and the uptake was observed by PKH26 labeling. The cell viability, colonization efficiency, reactive oxygen species (ROS) balance, cell cycle arrest and apoptosis induction were then analysed. SSCs were confirmed by immunocytochemistry (Oct4, Plzf) and Sertoli cells were identified through Sox9 and vimentin expression by immunocytochemistry and Real-time PCR (qRT-PCR), respectively. Our results demonstrated the detrimental effect of EMF via ROS accumulation that reduced the expression of catalase antioxidant, cell viability and colonization of SSCs. Also, AO/PI and flow cytometry analysis demonstrated the elevation of apoptosis in SSCs exposed to EMF in comparison with control. qRT-PCR data confirmed the up-regulation of apoptotic gene (Caspase-3) and down-regulation of SSCs specific gene (GFRα1). Consequently, the administration of Sertoli-EXOs exerted ameliorative effect on SSCs and significantly improved these changes through the regulation of oxidative stress. These findings suggest that Sertoli-EXOs have positive impact on SSCs exposed to EMF and can be useful in further investigation of Sertoli-EXOs as a novel therapeutic agent which may recover the deregulated SSCs microenvironment and spermatogenesis after exposure to EMF.

Cellular Therapy via Spermatogonial Stem Cells for Treating Impaired Spermatogenesis, Non-Obstructive Azoospermia

Male infertility is a major health problem affecting about 8–12% of couples worldwide. Spermatogenesis starts in the early fetus and completes after puberty, passing through different stages. Male infertility can result from primary or congenital, acquired, or idiopathic causes. The absence of sperm in semen, or azoospermia, results from non-obstructive causes (pretesticular and testicular), and post-testicular obstructive causes. Several medications such as antihypertensive drugs, antidepressants, chemotherapy, and radiotherapy could lead to impaired spermatogenesis and lead to a non-obstructive azoospermia. Spermatogonial stem cells (SSCs) are the basis for spermatogenesis and fertility in men. SSCs are characterized by their capacity to maintain the self-renewal process and differentiation into spermatozoa throughout the male reproductive life and transmit genetic information to the next generation. SSCs originate from gonocytes in the postnatal testis, which originate from long-lived primordial germ cells during embryonic development. The treatment of infertility in males has a poor prognosis. However, SSCs are viewed as a promising alternative for the regeneration of the impaired or damaged spermatogenesis. SSC transplantation is a promising technique for male infertility treatment and restoration of spermatogenesis in the case of degenerative diseases such as cancer, radiotherapy, and chemotherapy. The process involves isolation of SSCs and cryopreservation from a testicular biopsy before starting cancer treatment, followed by intra-testicular stem cell transplantation. In general, treatment for male infertility, even with SSC transplantation, still has several obstacles. The efficiency of cryopreservation, exclusion of malignant cells contamination in cancer patients, and socio-cultural attitudes remain major challenges to the wider application of SSCs as alternatives. Furthermore, there are limitations in experience and knowledge regarding cryopreservation of SSCs. However, the level of infrastructure or availability of regulatory approval to process and preserve testicular tissue makes them tangible and accurate therapy options for male infertility caused by non-obstructive azoospermia, though in their infancy, at least to date.

β-estradiol promotes the growth of primary human fetal spermatogonial stem cells via the induction of stem cell factor in Sertoli cells

BACKGROUND

Mammalian spermatogenesis is responsible for male fertility and is supported by the self-renewal and differentiation of spermatogonial stem cells (SSCs). Sertoli cells provide a supportive microenvironment for SSCs, in part by the production of stem cell factor (SCF), which is a potent regulator of spermatogonia proliferation and survival.

METHODS

We investigated the novel role of β-estradiol in modulating the proliferation and apoptosis of fetal SSCs via the regulation of SCF secretion in Sertoli cells isolated from human fetal testes. The proliferation of SSCs in the co-culture system was determined by colony formation and BrdU incorporation assays. TUNEL assay was used to measure SSC apoptosis in co-culture in response to treatment with control, β-estradiol, or the combination of β-estradiol and the estrogen receptor inhibitor ICI 182780.

RESULTS

In the system with purified human fetal Sertoli cells (MIS+/c-Kit-/AP-), β-estradiol upregulated the production of SCF in a dose- and time-dependent manner. In the co-culture system of primary human fetal SSCs (c-Kit+/SSEA-4+/Oct-4+/AP+) and Sertoli cells (MIS+), β-estradiol markedly increased the proliferation of SSCs. Moreover, SSC apoptosis was significantly inhibited by β-estradiol and was completely reversed by the combination of β-estradiol and ICI 182780.

CONCLUSION

Here we report, for the first time, that β-estradiol can induce the increase of SCF expression in human fetal Sertoli cells and regulates the growth and survival of human fetal SSCs. These novel findings provide new perspectives on the current understanding of the role of estrogen in human spermatogenesis.

Therapeutic application of Sertoli cells for treatment of various diseases

Sertoli cells (SCs) are immune privileged cells found in the testis that function to immunologically protect maturing germ cells from immune destruction. This immune protection is due to the blood-testis-barrier, which prevents infiltration of cytotoxic immune cells and antibodies, and SC production of immunomodulatory factors, that favor a tolerogenic environment. The ability of SCs to create an immune privileged environment has led to the exploration of their potential use in the treatment of various diseases. SCs have been utilized to create a tolerogenic ectopic microenvironment, to protect co-grafted cells, and to deliver therapeutic proteins through gene therapy. To date, numerous studies have reported the potential use of SCs for the treatment of diabetes, neurodegenerative disorders, and restoration of spermatogenesis. Additionally, SCs have been investigated as a delivery vehicle for therapeutic products to treat other diseases like Laron syndrome, muscular dystrophy, and infections. This review will provide an overview of these therapeutic applications.

Sertoli cell ablation and replacement of the spermatogonial niche in mouse

Spermatogonia, which produce sperm throughout the male lifetime, are regulated inside a niche composed of Sertoli cells, and other testis cell types. Defects in Sertoli cells often lead to infertility, but replacement of defective cells has been limited by the inability to deplete the existing population. Here, we use an FDA-approved non-toxic drug, benzalkonium chloride (BC), to deplete testis cell types in vivo. Four days after BC administration, Sertoli cells are preferentially depleted, and can be replaced to promote spermatogenesis from surviving (host) spermatogonia. Seven days after BC treatment, multiple cell types can be engrafted from fresh or cryopreserved testicular cells, leading to complete spermatogenesis from donor cells. These methods will be valuable for investigation of niche-supporting cell interactions, have the potential to lead to a therapy for idiopathic male infertility in the clinic, and could open the door to production of sperm from other species in the mouse.

Sertoli cells and other somatic cells of the testis comprise the germ cell niche and are critical to regulate spermatogenesis. Here the authors present a method in which Sertoli cells are selectively targeted for ablation by the compound benzalkonium chloride (BC) in mice, and the spermatogenic niche is subsequently repopulated in regions that have been affected by BC treatment.

Retinoid-related orphan nuclear receptor alpha (RORα)-deficient mice display morphological testicular defects

The role of retinoid-related orphan receptor, one of the transcription factors reported in testis, in testicular function is unclear, so this study was performed to evaluate the qualitative and quantitative changes in the testicular structure of RORα-deficient mice using light-, electron-microscopy, and immunohistochemistry. Among the most striking alterations observed in the testis of the mutant mice were hypospermatogenesis, marked reduction in volume proportions of interstitial tissues and number of Leydig cells, significant decrease in the diameter of seminiferous tubules and height of their epithelium, vacuolation in the epithelium of the seminiferous tubules with occurrence of mast cells, appearance of delay spermiation signs, and changes in sperm morphology. Moreover, the testis of mutant mice showed symplasts, in addition to appearance of multinucleated giant bromophenol-positive cells. ATPase activity was limited to spermatogonia and some primary spermatocytes, with higher alkaline phosphatase expression. Stronger vimentin reaction was immunolocalized to spermatogonia, spermatids, Leydig cells, and Sertoli cells. The expression of CD117 (C-kit, stem cell growth factor receptor) was limited to spermatogonia, primary spermatocytes, and Leydig cells. Seminiferous tubules showed overexpression of vascular endothelial growth factor (VEGF). Transmission electron microscopy examination of the mutant mice revealed abnormal Sertoli cells, hypertrophied spermatogonia, spermatocytes with degenerated mitochondria, and incompletely developed sperms. In conclusion, RORα is one of the essential proteins that regulate testicular structure.

Spermatogonial stem cells

Spermatogonial stem cells (SSCs) are the most primitive spermatogonia in the testis and have an essential role to maintain highly productive spermatogenesis by self-renewal and continuous generation of daughter spermatogonia that differentiate into spermatozoa, transmitting genetic information to the next generation. Since the 1950s, many experimental methods, including histology, immunostaining, whole-mount analyses, and pulse-chase labeling, had been used in attempts to identify SSCs, but without success. In 1994, a spermatogonial transplantation method was reported that established a quantitative functional assay to identify SSCs by evaluating their ability to both self-renew and differentiate to spermatozoa. The system was originally developed using mice and subsequently extended to nonrodents, including domestic animals and humans. Availability of the functional assay for SSCs has made it possible to develop culture systems for their ex vivo expansion, which dramatically advanced germ cell biology and allowed medical and agricultural applications. In coming years, SSCs will be increasingly used to understand their regulation, as well as in germline modification, including gene correction, enhancement of male fertility, and conversion of somatic cells to biologically competent male germline cells.

Manipulation of spermatogonial stem cells in livestock species

We are entering an exciting epoch in livestock biotechnology during which the fundamental approaches (such as transgenesis, spermatozoa cryopreservation and artificial insemination) will be enhanced based on the modern understanding of the biology of spermatogonial stem cells (SSCs) combined with the outstanding recent advances in genomic editing technologies and in vitro cell culture systems. The general aim of this review is to outline comprehensively the promising applications of SSC manipulation that could in the nearest future find practical application in livestock breeding. Here, we will focus on 1) the basics of mammalian SSC biology; 2) the approaches for SSC isolation and purification; 3) the available in vitro systems for the stable expansion of isolated SSCs; 4) a discussion of how the manipulation of SSCs can accelerate livestock transgenesis; 5) a thorough overview of the techniques of SSC transplantation in livestock species (including the preparation of recipients for SSC transplantation, the ultrasonographic-guided SSC transplantation technique in large farm animals, and the perspectives to improve further the SSC transplantation efficiency), and finally, 6) why SSC transplantation is valuable to extend the techniques of spermatozoa cryopreservation and/or artificial insemination. For situations where no reliable data have yet been obtained for a particular livestock species, we will rely on the data obtained from studies conducted in rodents because the knowledge gained from rodent research is translatable to livestock species to a great extent. On the other hand, we will draw special attention to situations where such translation is not possible.

Androgen promotes differentiation of PLZF+ spermatogonia pool via indirect regulatory pattern

Background

Androgen plays a pivotal role in spermatogenesis, accompanying a question how androgen acts on germ cells in testis since germ cells lack of androgen receptors (AR). Promyelocytic leukemia zinc-finger (PLZF) is essential for maintenance of undifferentiated spermatogonia population which is terminologically called spermatogonia progenitor cells (SPCs).

Aims

We aim to figure out the molecular connections between androgen and fates of PLZF⁺ SPCs population.

Method

Immunohistochemistry was conducted to confirm that postnatal testicular germ cells lacked endogenous AR. Subsequently, total cells were isolated from 5 dpp (day post partum) mouse testes, and dihydrotestosterone (DHT) and/or bicalutamide treatment manifested that Plzf was indirectly regulated by androgen. Then, Sertoli cells were purified to screen downstream targets of AR using ChIP-seq, and gene silence and overexpression were used to attest these interactions in Sertoli cells or SPCs-Sertoli cells co-culture system. Finally, these connections were further verified in vivo using androgen pharmacological deprivation mouse model.

Results

Gata2 is identified as a target of AR, and β1-integrin is a target of Wilms’ tumor 1 (WT1) in Sertoli cells. Androgen signal negatively regulate β1-integrin on Sertoli cells via Gata2 and WT1, and β1-integrin on Sertoli cells interacts with E-cadherin on SPCs to regulate SPCs fates.

Conclusion

Androgen promotes differentiation of PLZF⁺ spermatogonia pool via indirect regulatory pattern.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0369-8) contains supplementary material, which is available to authorized users.

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.

Neonatal testicular cell transplantation restores murine spermatogenesis damaged in the course of herpes simplex virus-induced orchitis

Genital tract infection and inflammation may affect male fertility, causing germ and Sertoli cell loss. We determined if testicular cell transplantation is effective at repairing testicular injury induced by herpes simplex virus (HSV) orchitis. ROSA26 mice were used as donors and the recipients were C57BL/6 mice after HSV testicular inoculation; some of the recipients were treated with the antiviral drug acyclovir (ACV). ACV reduced the amount of HSV antigen in testes on Day 3 after transplantation and enhanced the efficacy of transplantation at Day 30. In recipient testes, donor Sertoli cells formed new seminiferous tubules; significantly more new tubules were observed in the testes of ACV-treated mice compared with mice not treated with ACV (17.8% vs 3.6%). Over half (50.4%) of new tubules in ACV-treated testes contained germ cells and round spermatids were detected in 14.2% of new tubules compared with 15.9% and 5.3% in testes not treated with ACV, respectively. At Day 150 the seminiferous epithelium was completely recovered in some donor tubules and elongated spermatids were observed inside it. Thus, our findings reveal the effectiveness of the combination of antiviral therapy with neonatal testis-cell transplantation for the restoration of spermatogenesis damaged by viral infection.

Subfertility and Risk of Testicular Cancer in the EPSAM Case-Control Study

Background/objectives

It has been suggested that subfertility and testicular cancer share genetic and environmental risk factors. We studied both subfertility and the strongest known testicular cancer susceptibility gene, the c-KIT ligand (KITLG), whose pathway is involved in spermatogenesis.

Methods

The EPSAM case-control study is comprised of testicular cancer patients from the Province of Turin, Italy, diagnosed between 1997 and 2008. The present analysis included 245 cases and 436 controls from EPSAM, who were aged 20 years or older at diagnosis/recruitment. The EPSAM questionnaire collected information on factors such as number of children, age at first attempt to conceive, duration of attempt to conceive, use of assisted reproduction techniques, physician-assigned diagnosis of infertility, number of siblings, and self-reported cryptorchidism. Genotyping of the KITLG single nucleotide polymorphism (SNP) rs995030 was performed on the saliva samples of 202 cases and 329 controls.

Results

Testicular cancer was associated with the number of children fathered 5 years before diagnosis (odds ratio (OR) per additional child: 0.78, 95% confidence interval (CI): 0.58–1.04) and sibship size (OR per additional sibling: 0.76, 95% CI: 0.66–0.88). When considering the reproductive history until 1 year before diagnosis, attempting to conceive for at least 12 months or fathering a child using assisted reproduction techniques was not associated with the risk of testicular cancer, nor was age at first attempt to conceive or physician-assigned diagnosis of infertility. The SNP rs995030 was strongly associated with risk of testicular cancer (per allele OR: 1.83; 95%CI: 1.26–2.64), but it did not modify the association between number of children and the risk of testicular cancer.

Conclusion

This study supports the repeatedly reported inverse association between number of children and risk of testicular cancer, but it does not find evidence of an association for other indicators of subfertility.

Review Article: Stem Cells in Human Reproduction

The derivation of human embryonic stem (hES) cells heralds a new era in stem cell research, generating excitement for their therapeutic potential in regenerative medicine. Pioneering work of embryologists, developmental biologists, and reproductive medicine practitioners in in vitro fertilization clinics has facilitated hES cell research. This review summarizes current research focused on optimizing hES cell culture conditions for good manufacturing practice, directing hES cell differentiation toward trophectoderm and germ cells, and approaches used to reprogram cells for pluripotent cell derivation. The identification of germ stem cells in the testis and the recent controversy over their existence in the ovary raise the possibility of harnessing them for treating young cancer survivors. There is also the potential to harvest fetal stem cells with pluripotent cell-like properties from discarded placental tissues. The recent identification of adult stem/progenitor cell activity in the human endometrium offers a new understanding of common gynecological diseases. Discoveries resulting from research into embryonic, germ, fetal, and adult stem cells are highly relevant to human reproduction.

Testis tissue explantation cures spermatogenic failure in c-Kit ligand mutant mice

Male infertility is most commonly caused by spermatogenic defects or insufficiencies, the majority of which are as yet cureless. Recently, we succeeded in cultivating mouse testicular tissues for producing fertile sperm from spermatogonial stem cells. Here, we show that one of the most severe types of spermatogenic defect mutant can be treated by the culture method without any genetic manipulations. The Sl/Sl(d) mouse is used as a model of such male infertility. The testis of the Sl/Sl(d) mouse has only primitive spermatogonia as germ cells, lacking any sign of spermatogenesis owing to mutations of the c-kit ligand (KITL) gene that cause the loss of membrane-bound-type KITL from the surface of Sertoli cells. To compensate for the deficit, we cultured testis tissues of Sl/Sl(d) mice with a medium containing recombinant KITL and found that it induced the differentiation of spermatogonia up to the end of meiosis. We further discovered that colony stimulating factor-1 (CSF-1) enhances the effect of KITL and promotes spermatogenesis up to the production of sperm. Microinsemination of haploid cells resulted in delivery of healthy offspring. This study demonstrated that spermatogenic impairments can be treated in vitro with the supplementation of certain factors or substances that are insufficient in the original testes.

In vitro production of haploid cells after coculture of CD49f+ with Sertoli cells from testicular sperm extraction in nonobstructive azoospermic patients

OBJECTIVE

To isolate CD49f+ cells from testicular sperm extraction (TESE) samples of azoospermic patients and induce meiosis by coculturing these cells with Sertoli cells.

DESIGN

Prospective analysis.

SETTING

Research center.

PATIENT(S)

Obstructive azoospermic (OA) and nonobstructive azoospermic (NOA) patients.

INTERVENTION(S)

TESE, with enzymatic dissociation of samples to obtain a cell suspension, which was cultured for 4 days with 4 ng/mL GDNF. The CD49f+ cells were sorted using fluorescence-activated cell sorting (FACS) as a marker to identify spermatogonial stem cells (SSCs), which were cocultured with Sertoli cells expressing red fluorescent protein (RFP) in knockout serum replacement (KSR) media with addition of 1,000 IU/mL of follicle-stimulating hormone (FSH), 1 μM testosterone, 40 ng/mL of GDNF, and 2 μM retinoic acid (RA) for 15 days in culture at 37°C and 5% CO(2) to induce meiotic progression. Cells were collected and analyzed by immunofluorescence for meiosis progression with specific markers SCP3 and CREST, and they were confirmed by fluorescence in situ hybridization (FISH).

MAIN OUTCOME MEASURE(S)

Isolation of CD49f+ cells and coculture with Sertoli cells, meiosis progression in vitro, assessment of SSCs and meiotic markers real-time polymerase chain reaction (RT-PCR), immunohistochemical analysis, and FISH.

RESULT(S)

The CD49f+ isolated from the of total cell count in the TESE samples of azoospermic patients varied from 5.45% in OA to 2.36% in NOA. Sertoli cells were obtained from the same TESE samples, and established protocols were used to characterize them as positive for SCF, rGDNF, WT1, GATA-4, and vimentin, with the presence of tight junctions and lipid droplets shown by oil red staining. After isolation, the CD49f+ cells were cocultured with RFP Sertoli cells in a 15-day time-course experiment. Positive immunostaining for meiosis markers SCP3 and CREST on days 3 to 5 was noted in the samples obtained from one NOA patient. A FISH analysis for chromosomes 13, 18, 21, X, and Y confirmed the presence of haploid cells on day 5 of the coculture.

CONCLUSION(S)

In vitro coculture of SSCs from TESE samples of NOA patients along with Sertoli cells promoted meiosis induction and resulted in haploid cell generation. These results improve the existing protocols to generate spermatogenesis in vitro and open new avenues for clinical translation in azoospermic patients.

Effects of multiple doses of cyclophosphamide on mouse testes: accessing the germ cells lost, and the functional damage of stem cells

Spermatogenesis is sensitive to the chemotherapeutic drug cyclophosphamide, which decreases the patients' sperm count. Since the recovery of fertility is dependent on regeneration from stem cells, in the present study we evaluated the ability of cyclophosphamide-exposed stem spermatogonia from mice to regenerate spermatogenesis in situ and after transplantation. When seven doses of cyclophosphamide were given at 4-day intervals, the differentiating germ cells were largely eliminated but ~50% of the undifferentiated type A spermatogonia remained. We monitored the recovery and found that sperm production recovered to 64% of control within the time expected. When the cyclophosphamide-surviving spermatogonia were transplanted into recipient mice, recovery of spermatogenesis from the cyclophosphamide-exposed donor cells was observed, but was reduced when compared to cells from cryptorchid donors. Thus, multidose regimens of cyclophosphamide did not eliminate the stem spermatogonia, but resulted in cell loss and residual damage.

New advances on the expansion and storage of human spermatogonial stem cells

PURPOSE OF REVIEW

Fertility in adult life can be severely impaired by gonadotoxic therapies and with remarkable advancements in the treatment of childhood cancers there is a growing population of adult survivors of childhood malignancies. The aim of the study is to review the developments that have been made in spermatogonial stem cell research and potential future utility in fertility preservation.

RECENT FINDINGS

Whereas intense interest and subsequent research surrounds the regenerative potential of spermatogonial stem cells, a recent article highlights the in-vitro propagation of human spermatogonial stem cells from testicular biopsies for future transplantation and restoration of fertility. Whereas in-vitro propagation of spermatogonial stem cells has been established in animal models this is the first study in humans.

SUMMARY

Spermatogonial stem cell transplantation began as a theoretical approach that currently is studied ardently by several research groups to make this a valid clinical option. Restoration of fertility following spermatogonial stem cell transplantation in animals suggests therapeutic potential for the technique in humans, and further research is proceeding to address the safety and efficacy of this technique.

Spermatogonial stem cell regulation and spermatogenesis

This article will provide an updated review of spermatogonial stem cells and their role in maintaining the spermatogenic lineage. Experimental tools used to study spermatogonial stem cells (SSCs) will be described, along with research using these tools to enhance our understanding of stem cell biology and spermatogenesis. Increased knowledge about the biology of SSCs improves our capacity to manipulate these cells for practical application. The chapter concludes with a discussion of future directions for fundamental investigation and practical applications of SSCs.

Constitutive WNT/beta-catenin signaling in murine Sertoli cells disrupts their differentiation and ability to support spermatogenesis

Sertoli and germ cell interactions are essential for spermatogenesis and, thus, male fertility. Sertoli cells provide a specialized microenvironment for spermatogonial stem cells to divide, allowing both self-renewal and spermatogenesis. In the present study, we used mice with a conditional activated allele of the beta-catenin gene (Ctnnb1(tm1Mmt)(/+)) in Sertoli cells expressing Cre recombinase driven by the anti-Müllerian hormone (AMH; also known as Müllerian-inhibiting substance) type II receptor promoter (Amhr2(tm3(cre)Bhr)(/+)) to show that constitutively activated beta-catenin leads to their continuous proliferation and compromised differentiation. Compared to controls, Sertoli cells in mature mutant mice continue to express high levels of both AMH and glial cell-derived neurotrophic factor (GDNF), which normally are expressed only in immature Sertoli cells. We also show evidence that LiCl treatment, which activates endogenous nuclear beta-catenin activity, regulates both AMH and GDNF expression at the transcriptional level. The epididymides were devoid of sperm in the Amhr2(tm3(cre)Bhr)(/+);Ctnnb1(tm1Mmt)(/+) mice at all ages examined. We show that the mutant mice are infertile because of defective differentiation of germ cells and increased apoptosis, both of which are characteristic of GDNF overexpression in Sertoli cells. Constitutive activation of beta-catenin in Amhr2-null mice showed the same histology, suggesting that the phenotype was the result of persistent overexpression of GDNF. These results show that dysregulated wingless-related MMTV integration site/beta-catenin signaling in Sertoli cells inhibits their postnatal differentiation, resulting in increased germ cell apoptosis and infertility.

NEW HOPE FOR INFERTILITY THERAPY: FABRICATING GAMETES FROM STEM CELLS

The field of reproductive and developmental biology has been revolutionized by recent advanced studies. These studies indicate that stem cells are capable of forming gametes in vivo and in vitro in both mouse and human. This has provided powerful tools for undertaking new types of reproductive studies, and particularly might provide new technology and novel approaches in assisted reproductive medicine.

Donor Sertoli cells transplanted into irradiated rat testes stimulate partial recovery of endogenous spermatogenesis

Irradiation of rat testes leads to the failure to support differentiation of the surviving spermatogonia due to damage of the somatic environment. To determine the involvement of Sertoli cells in this somatic damage, we transplanted seminiferous tubule cells from normal immature GFP-transgenic rats into the testes of irradiated rats. The donor Sertoli cells colonized and developed in the host testes. In many seminiferous tubules, the donor Sertoli cells formed abnormal spherical structures in the lumen, but in some tubules they formed a normal-appearing epithelium, but with only isolated spermatogonia, on the basement membrane. When the donor cells were injected into the interstitial region of the testis, they formed tubule-like structures containing Sertoli cells and occasional isolated spermatogonia, both of donor origin. Surprisingly, in host tubules adjacent to these newly formed donor-cell tubules or adjacent to the endogenous tubules with abnormal donor Sertoli-cell structures, endogenous spermatogonia differentiated to the spermatocyte or even to spermatid stages. Around these newly donor cell-formed tubules and the host tubules with abnormal donor Sertoli-cell structures, many cells including macrophages, which perhaps represented chronic inflammation, accumulated in the interstitium. We conclude that the donor Sertoli cells that colonized the seminiferous tubules did not directly support recovery of spermatogenesis. Instead, the colonizing Sertoli cells acted indirectly on the interstitium to stimulate localized differentiation of endogenous spermatogonia.

Seminal discoveries in regenerative medicine: contributions of the male germ line to understanding pluripotency

Germ cells are highly specialized cells that form gametes (sperm and eggs), and they are the only cells within an organism that contribute genes to offspring. Due to the fact that the genetic information contained within germ cells is passed from generation to generation, the germ line is often thought of as immortal. Studies have revealed that germ cells are remarkably similar to pluripotent embryonic stem cells (ESCs). For example, there is a significant overlap in the gene expression profile between ESCs and primordial germ cells (PGCs), the founders of the germ cell lineage. In addition, pluripotent embryonic germ (EG) cell lines have been derived from mammalian PGCs. Secondly, a subset of testicular germ cell tumors, known as non-seminomas, often contain differentiated cells representative of all three germ layers, a definitive test of pluripotency. Lastly, recent results have demonstrated the ability of spermatogonial stem cells (SSCs) to de-differentiate into pluripotent ES-like cells, underscoring a unique relationship between the germ line and pluripotent cells that are present during the earliest stages of embryonic development. Here, we will review the factors that regulate the self-renewal and maintenance of male germline stem cells (GSCs) and discuss how these factors may allow us to manipulate the germ line to create pluripotent cells that could serve as a critical tool in cell replacement therapies and regenerative medicine.

No place like home: anatomy and function of the stem cell niche

Stem cells are rare cells that are uniquely capable of both reproducing themselves (self-renewing) and generating the differentiated cell types that are needed to carry out specialized functions in the body. Stem cell behaviour, in particular the balance between self-renewal and differentiation, is ultimately controlled by the integration of intrinsic factors with extrinsic cues supplied by the surrounding microenvironment, known as the stem cell niche. The identification and characterization of niches within tissues has revealed an intriguing conservation of many components, although the mechanisms that regulate how niches are established, maintained and modified to support specific tissue stem cell functions are just beginning to be uncovered.

ETV5 is required for continuous spermatogenesis in adult mice and may mediate blood testes barrier function and testicular immune privilege

The transcription factor Ets-variant gene 5 (ETV5) is essential for spermatogonial stem cell (SSC) self-renewal, as the targeted deletion of the Etv5 gene in mice (Etv5(-/-)) results in only the first wave of spermatogenesis. Reciprocal transplants of neonatal germ cells from wild-type (WT) and Etv5(-/-) testes were performed to determine the role of ETV5 in Sertoli cells and germ cells. ETV5 appears to be needed in both cell types for normal spermatogenesis. In addition, Etv5(-/-) recipients displayed increased interstitial inflammation and tubular involution after transplantation. Preliminary studies suggest that the blood-testis barrier (Sertoli-Sertoli tight junctional complex) is abnormal in the Etv5(-/-) mouse.

In vitro culture of testicular germ cells: regulatory factors and limitations

Spermatogenesis is regulated mainly by endocrine factors and also by testicular paracrine/autocrine growth factors. These factors are produced by Sertoli cells, germ cells, peritubular cells and interstitial cells, mainly Leydig cells and macrophages. The interactions and the ratio between Sertoli and germ cells in the seminiferous tubules ensure successful spermatogenesis. In order to culture spermatogonial stem cells (SSCs) in vitro, researchers tried to overcome some of the obstacles -- such as the low number of stem cells in the testis, absence of specific markers to identify SSCs -- in addition to difficulties in keeping the SSCs alive in culture. Recently, some growth factors important for the proliferation and differentiation of SSCs were identified, such as glial cell line derived neurotrophic factor (GDNF), stem cell factor (SCF) and leukemia inhibitory factor (LIF); also, markers for SSCs at different stages were reported. Therefore, some groups succeeded in culturing SSCs (under limitations), or more differentiated cells and even were able to produce in vitro germ cells from embryonic stem cells. Thus, success in culturing SSCs is dependent on understanding the molecular mechanisms behind self-renewal and differentiation. Culture of SSCs should be a good tool for discovering new therapeutic avenue for some infertile men or for patients undergoing chemotherapy/radiotherapy (pre-puberty or post-puberty).

Fate of bone marrow stem cells transplanted into the testis: potential implication for men with testicular failure

To assess adult stem cell differentiation in the testis, we injected bone marrow cells from adult green fluorescent protein (GFP) transgenic mice into the seminiferous tubules and the testicular interstitium of busulfan-treated wild-type or c-kit mutant (W/W(v)) mice. Ten to 12 weeks after transplantation, we examined the fate of the transplanted bone marrow cells and found that they survived in recipient testes. In both the busulfan-treated and W/W(v) mice, some of the GFP-positive donor cells had a Sertoli cell appearance and expressed follicle-stimulating hormone receptor within the seminiferous tubules. In addition, GFP-positive donor cells were found in the interstitium of recipient testes, and they expressed the cytochrome P450 side chain cleavage enzyme (P450scc). In the seminiferous tubules of busulfan-treated mice, GFP-positive donor cells had the appearance of spermatogonia or spermatocytes and expressed VASA. However, this was not found in the seminiferous tubules of W/W(v) mice. We conclude that adult bone marrow cells, in a favorable testicular environment, differentiate into somatic and germ cell lineages. The resident neighboring cells in the recipient testis may control site-appropriate stem cell differentiation. This clinically relevant finding raises the possibility for treatment of male infertility and testosterone deficiency through the therapeutic use of stem cells.

The radiation-induced block in spermatogonial differentiation is due to damage to the somatic environment, not the germ cells

Radiation and chemotherapeutic drugs cause permanent sterility in male rats, not by killing most of the spermatogonial stem cells, but by blocking their differentiation in a testosterone-dependent manner. However, it is not known whether radiation induces this block by altering the germ or the somatic cells. To address this question, we transplanted populations of rat testicular cells containing stem spermatogonia and expressing the green fluorescent protein (GFP) transgene into various hosts. Transplantation of the stem spermatogonia from irradiated adult rats into the testes of irradiated nude mice, which do not show the differentiation block of their own spermatogonia, permitted differentiation of the rat spermatogonia into spermatozoa. Conversely transplantation of spermatogonial stem cells from untreated prepubertal rats into irradiated rat testes showed that the donor spermatogonia were able to colonize along the basement membrane of the seminiferous tubules but could not differentiate. Finally, suppression of testosterone in the recipient irradiated rats allowed the differentiation of the transplanted spermatogonia. These results conclusively show that the defect caused by radiation in the rat testes that results in the block of spermatogonial differentiation is due to injury to the somatic compartment. We also observed colonization of tubules by transplanted Sertoli cells from immature rats. The present results suggest that transplantation of spermatogonia, harvested from prepubertal testes to adult testes that have been exposed to cytotoxic therapy might be limited by the somatic damage and may require hormonal treatments or transplantation of somatic elements to restore the ability of the tissue to support spermatogenesis.