The Niche for Spermatogonial Stem Cells in the Mammalian Testis

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

G3BP2, a stress granule assembly factor, is dispensable for spermatogenesis in mice

Background

Spermatogenesis is a complex process that includes mitosis, meiosis, and spermiogenesis. During spermatogenesis, genetic factors play a vital role inthe formation of properly functioning sperm. GTPase-activating protein (SH3 domain)-binding protein 2 (G3BP2) is known to take part in immune responses, mRNA transport, and stress-granule assembly. However, its role in male fertility is unclear. Here, we generated a G3bp2 conditional knockout (cKO) mouse model to explore the function of G3BP2 in male fertility.

Methods

Polymerase chain reaction (PCR) and western blotting (WB) were used to confirm testis-specific G3bp2 knockout. Hematoxylin-eosin (HE) staining to observe testicular morphology and epididymal structure. Computer-aided sperm analysis (CASA) to detect sperm concentration and motility. Terminal deoxynucleotidyl transferase-dUTP nick-end labeling (TUNEL) assay was used to detect apoptotic cells.

Results

We found that cKO male mice are fertile with the normal morphology of the testis and sperm. Additionally, CASA of the semen from cKO mice showed that they all had a similar sperm concentration and motility. In addition, sperm from these mice exhibited a similar morphology. But the tunnel assay revealed increased apoptosis in their testes relative to the level in the wild type (WT).

Conclusion

Together, our data demonstrate that G3BP2 is dispensable for spermatogenesis and male fertility in mice albeit with the increased germ-cell apoptosis.

Primary culture of germ cells that portray stem cell characteristics and recipient preparation for autologous transplantation in the rhesus monkey

Fertility preservation for prepubertal cancer patients prior to oncologic treatment is an emerging issue, and non‐human primates are considered to constitute suitable models due to the limited availability of human testicular tissues. However, the feasibility of spermatogonial stem cell (SSC) propagation in vitro and autologous testicular germ cell transplantation in vivo requires further exploration in monkeys. Herein, we characterized germ cells in macaque testes at 6 months (M), 18 M and 60 M of age, and effectively isolated the spermatogenic cells (including the spermatogonia) from macaque testes with high purity (over 80%) using combined approaches of STA‐PUT separation, Percoll gradients and differential plating. We also generated recipient monkey testes with ablated endogenous spermatogenesis using the alkylating agent busulfan in six macaques, and successfully mimicked autologous cell transplantation in the testes under ultrasonographic guidance. The use of trypan blue led to successful intratubular injection in 4 of 4 testes. Although SSCs in culture showed no significant propagation, we were able to maintain monkey testicular germ cells with stem cell characteristics for up to 3 weeks. Collectively, these data provided meaningful information for future fertility preservation and SSC studies on both non‐human primates and humans.

Roles of Spermatogonial Stem Cells in Spermatogenesis and Fertility Restoration

Spermatogonial stem cells (SSCs) are a group of adult stem cells in the testis that serve as the foundation of continuous spermatogenesis and male fertility. SSCs are capable of self-renewal to maintain the stability of the stem cell pool and differentiation to produce mature spermatozoa. Dysfunction of SSCs leads to male infertility. Therefore, dissection of the regulatory network of SSCs is of great significance in understanding the fundamental molecular mechanisms of spermatogonial stem cell function in spermatogenesis and the pathogenesis of male infertility. Furthermore, a better understanding of SSC biology will allow us to culture and differentiate SSCs in vitro, which may provide novel stem cell-based therapy for assisted reproduction. This review summarizes the latest research progress on the regulation of SSCs, and the potential application of SSCs for fertility restoration through in vivo and in vitro spermatogenesis. We anticipate that the knowledge gained will advance the application of SSCs to improve male fertility. Furthermore, in vitro spermatogenesis from SSCs sets the stage for the production of SSCs from induced pluripotent stem cells (iPSCs) and subsequent spermatogenesis.

Heterogeneity and Dynamics of Vasculature in the Endocrine System During Aging and Disease

The endocrine system consists of several highly vascularized glands that produce and secrete hormones to maintain body homeostasis and regulate a range of bodily functions and processes, including growth, metabolism and development. The dense and highly vascularized capillary network functions as the main transport system for hormones and regulatory factors to enable efficient endocrine function. The specialized capillary types provide the microenvironments to support stem and progenitor cells, by regulating their survival, maintenance and differentiation. Moreover, the vasculature interacts with endocrine cells supporting their endocrine function. However, the structure and niche function of vasculature in endocrine tissues remain poorly understood. Aging and endocrine disorders are associated with vascular perturbations. Understanding the cellular and molecular cues driving the disease, and age-related vascular perturbations hold potential to manage or even treat endocrine disorders and comorbidities associated with aging. This review aims to describe the structure and niche functions of the vasculature in various endocrine glands and define the vascular changes in aging and endocrine disorders.

Transcriptome analysis revealed differences in the microenvironment of spermatogonial stem cells in seminiferous tubules between pre-pubertal and adult buffaloes

The microenvironment in the seminiferous tubules of buffalo changes with age, which affects the self-renewal and growth of spermatogonial stem cells (SSCs) and the process of spermatogenesis, but the mechanism remains to be elucidated. RNA-seq was performed to compare the transcript profiles of pre-pubertal buffalo (PUB) and adult buffalo (ADU) seminiferous tubules. In total, 17,299 genes from PUB and ADU seminiferous tubules identified through RNA-seq, among which 12,271 were expressed in PUB and ADU seminiferous tubules, 4,027 were expressed in only ADU seminiferous tubules, and 956 were expressed in only PUB seminiferous tubules. Of the 17,299 genes, we identified 13,714 genes that had significant differences in expression levels between PUB and ADU through GO enrichment analysis. Among these genes, 5,342 were significantly upregulated and possibly related to the formation or identity of the surface antigen on SSCs during self-renewal; 7,832 genes were significantly downregulated, indicating that genes in PUB seminiferous tubules do not participate in the biological processes of sperm differentiation or formation in this phase compared with those in ADU seminiferous tubules. Subsequently, through the combination with KEGG analysis, we detected enrichment in a number of genes related to the development of spermatogonial stem cells, providing a reference for study of the development mechanism of buffalo spermatogonial stem cells in the future. In conclusion, our data provide detailed information on the mRNA transcriptomes in PUB and ADU seminiferous tubules, revealing the crucial factors involved in maintaining the microenvironment and providing a reference for further in vitro cultivation of SSCs.

Fertility preservation for prepubertal boys: lessons learned from the past and update on remaining challenges towards clinical translation

BACKGROUND

Childhood cancer incidence and survivorship are both on the rise. However, many lifesaving treatments threaten the prepubertal testis. Cryopreservation of immature testicular tissue (ITT), containing spermatogonial stem cells (SSCs), as a fertility preservation (FP) option for this population is increasingly proposed worldwide. Recent achievements notably the birth of non-human primate (NHP) progeny using sperm developed in frozen-thawed ITT autografts has given proof of principle of the reproductive potential of banked ITT. Outlining the current state of the art on FP for prepubertal boys is crucial as some of the boys who have cryopreserved ITT since the early 2000s are now in their reproductive age and are already seeking answers with regards to their fertility.

OBJECTIVE AND RATIONALE

In the light of past decade achievements and observations, this review aims to provide insight into relevant questions for clinicians involved in FP programmes. Have the indications for FP for prepubertal boys changed over time? What is key for patient counselling and ITT sampling based on the latest achievements in animals and research performed with human ITT? How far are we from clinical application of methods to restore reproductive capacity with cryostored ITT?

SEARCH METHODS

An extensive search for articles published in English or French since January 2010 to June 2020 using keywords relevant to the topic of FP for prepubertal boys was made in the MEDLINE database through PubMed. Original articles on fertility preservation with emphasis on those involving prepubertal testicular tissue, as well as comprehensive and systematic reviews were included. Papers with redundancy of information or with an absence of a relevant link for future clinical application were excluded. Papers on alternative sources of stem cells besides SSCs were excluded.

OUTCOMES

Preliminary follow-up data indicate that around 27% of boys who have undergone testicular sampling as an FP measure have proved azoospermic and must therefore solely rely on their cryostored ITT to ensure biologic parenthood. Auto-transplantation of ITT appears to be the first technique that could enter pilot clinical trials but should be restricted to tissue free of malignant cells. While in vitro spermatogenesis circumvents the risk linked to cancer cell contamination and has led to offspring in mice, complete spermatogenesis has not been achieved with human ITT. However, generation of haploid germ cells paves the way to further studies aimed at completing the final maturation of germ cells and increasing the efficiency of the processes.

WIDER IMPLICATIONS

Despite all the research done to date, FP for prepubertal boys remains a relatively young field and is often challenging to healthcare providers, patients and parents. As cryopreservation of ITT is now likely to expand further, it is important not only to acknowledge some of the research questions raised on the topic, e.g. the epigenetic and genetic integrity of gametes derived from strategies to restore fertility with banked ITT but also to provide healthcare professionals worldwide with updated knowledge to launch proper multicollaborative care pathways in the field and address clinical issues that will come-up when aiming for the child's best interest.

Decreased abundance of GDNF mRNA transcript in the immature Sertoli cells of cattle in response to protein kinase inhibitor staurosporine

Sertoli cells (SC) have important functions in spermatogenesis by regulating development of spermatogenic cells. Glial cell line-derived neurotrophic factor (GDNF) are produced by SC. Although the effects of GDNF on spermatogenesis have been well studied, the understanding of how GDNF is synthesized is still limited, especially in food animal producing species. Because protein kinase (PK) has varied functions in multiple cellular processes and the PK pathway modulates SC functions, the objective of the present study was to determine whether PK modulates the abundance of GDNF protein in SC of cattle. To conduct this study, immature SC were enriched from cryopreserved testicular tissues of 1-day-old bulls. These cells had a marked proliferation capacity. Results from immunostaining analysis indicated that there was a sustained abundance of SC mRNA marker protein transcripts and marker proteins: androgen bind protein (ABP), GATA4 and VIMENTIN. There was subsequent characterization of SC treated with the PK inhibitor staurosporine for 0, 1 or 2 h. Results from real-time-PCR and Western blot analyses indicated the treatment (2 h) resulted in a decrease in Gdnf mRNA transcript and GDNF protein. Additionally, the staurosporine treatment resulted in an increase in the abundance of anti-apoptosis Bcl2 and decrease in pro-apoptosis Bax mRNA transcripts. Furthermore, results of the TUNEL assay indicated there was a decrease in apoptosis in the staurosprine-treated SC. Collectively, results indicate the PK signaling is involved in regulation of GDNF protein abundance in the immature SC and the survival of these cells in cattle.

Role of stem cells in fertility preservation: current insights

While improvements made in the field of cancer therapy allow high survival rates, gonadotoxicity of chemo- and radiotherapy can lead to infertility in male and female pre- and postpubertal patients. Clinical options to preserve fertility before starting gonadotoxic therapies by cryopreserving sperm or oocytes for future use with assisted reproductive technology (ART) are now applied worldwide. Cryopreservation of pre- and postpubertal ovarian tissue containing primordial follicles, though still considered experimental, has already led to the birth of healthy babies after autotransplantation and is performed in an increasing number of centers. For prepubertal boys who do not produce gametes ready for fertilization, cryopreservation of immature testicular tissue (ITT) containing spermatogonial stem cells may be proposed as an experimental strategy with the aim of restoring fertility. Based on achievements in nonhuman primates, autotransplantation of ITT or testicular cell suspensions appears promising to restore fertility of young cancer survivors. So far, whether in two- or three-dimensional culture systems, in vitro maturation of immature male and female gonadal cells or tissue has not demonstrated a capacity to produce safe gametes for ART. Recently, primordial germ cells have been generated from embryonic and induced pluripotent stem cells, but further investigations regarding efficiency and safety are needed. Transplantation of mesenchymal stem cells to improve the vascularization of gonadal tissue grafts, increase the colonization of transplanted cells, and restore the damaged somatic compartment could overcome the current limitations encountered with transplantation.

Male fertility preservation in DSD, XXY, pre-gonadotoxic treatments - Update, methods, ethical issues, current outcomes, future directions

This paper aims at reviewing the fertility preservation strategies that could be considered in several conditions at risk of spermatogonial depletion such as 46,XY disorders of sexual development, Klinefelter syndrome and after gonadotoxic treatment in males highlighting current knowledge on diseases and processes involved in infertility as well as future directions along with their specific ethical issues. While sperm cryopreservation after puberty is the only validated technique for fertility preservation, for prepubertal boys facing gonadotoxic therapies or at risk of testicular tissue degeneration where testicular sperm is not present, cryopreservation of spermatogonial cells may be an option to ensure future parenthood. Promising results with transplantation and in vitro maturation of spermatogonial cells were achieved in animals but so far none of the techniques was applied in humans.

Postnatal testis development in the collared peccary (Tayassu tajacu), with emphasis on spermatogonial stem cells markers and niche

Collared peccaries (Tayassu tajacu) present a unique testis cytoarchitecture, where Leydig cells (LC) are mainly located in cords around the seminiferous tubules (ST) lobes. This peculiar arrangement is very useful to better investigate and understand the role of LC in spermatogonial stem cells (SSCs) biology and niche. Recent studies from our laboratory using adult peccaries have shown that the undifferentiated type A spermatogonia (A_und or SSCs) are preferentially located in ST regions adjacent to the intertubular compartment without LC. Following these studies, our aims were to investigate the collared peccary postnatal testis development, from birth to adulthood, with emphasis on the establishment of LC cytoarchitecture and the SSCs niche. Our findings demonstrated that the unique LC cytoarchitecture is already present in the neonate peccary's testis, indicating that this arrangement is established during fetal development. Based on the most advanced germ cell type present at each time period evaluated, puberty (the first sperm release in the ST lumen) in this species was reached at around one year of age, being preceded by high levels of estradiol and testosterone and the end of Sertoli cell proliferation. Almost all gonocytes and SSCs expressed Nanos1, Nanos2 and GFRA1. The analysis of SSCs preferential location indicated that the establishment of SSCs niche is coincident with the occurrence of puberty. Taken together, our findings reinforced and extended the importance of the collared peccary as an animal model to investigate testis function in mammals, particularly the aspects related to testis organogenesis and the SSCs biology and niche.

Cryostorage of testicular tissue and retransplantation of spermatogonial stem cells in the infertile male

Transplantation of own cryostored spermatogonial stem cells (SSCs) is a promising technique for fertility restoration when the SSC pool has been depleted. In this regard, cryopreservation of pre-pubertal testicular tissue or SSCs suspensions before gonadotoxic therapies is ethically accepted and increasingly proposed. SSC transplantation has also been considered to treat other causes of infertility relying on the possibility of propagating SSCs retrieved in the testes of infertile men before autologous re-transplantation. Although encouraging results were achieved in animals and in preclinical experiments, clinical perspectives are still limited by a number of unresolved technical and safety issues, such as the risk of cancer cell contamination of cells intended for transplantation and the genetic and epigenetic stability of SCCs when cultured before re-transplantation. Moreover, while genome editing techniques raise the hope of modifying the SSCs genome before re-transplantation, their application for reproductive purposes might be a step too far for the moment.

Testicular injection of busulfan for recipient preparation in transplantation of spermatogonial stem cells in mice

Intraperitoneal busulfan injections are used to prepare recipients for spermatogonial stem cell (SSC) transplantation but they are associated with haematopoietic toxicity. Testicular injections of busulfan have been proposed to overcome this limitation. To date, testicular injections have not been studied in the mouse model. Therefore, in the present study we used ICR mice as recipients for SSC transplantation and prepared these mice by testicular injection of busulfan on both sides (2, 3, 4 or 6mgkg^-1 per side). Following this, donor germ cells expressing red fluorescent protein (RFP) from transgenic C57BL/6J male mice were transplanted into recipients via the efferent duct on Days 16-17 after busulfan treatment. Positive control mice were prepared by intraperitoneal injection of 40mgkg^-1 busulfan and negative control mice were treated with bilateral testicular injection of 50% dimethyl sulfoxide. On Day 49 after transplantation, recipient mice that were RFP-positive by in vivo imaging were mated with ICR female mice. Donor-derived germ cell colonies with red fluorescence were observed on Day 60 after transplantation, and donor-derived offspring were obtained. The results demonstrated that endogenous germ cells were successfully eliminated in the seminiferous tubules via testicular busulfan administration, and that exogenous SSCs successfully undergo spermatogenesis in the testes of recipient mice prepared by testicular injections of busulfan. In addition to its effects on recipient preparation, this method was safe in rodents and could possibly be adapted for use in other species.

Stage-specific approaches promote in vitro induction for spermatogenesis

Spermatogenesis in vitro has been demonstrated using spermatogonial stem cells (SSCs) in monolayer culture or testis tissue fragments in agarose-constructed three-dimensional (3-D) conditions. However, the low efficiency of gamete maturation and the lack of a novel induction platform have limited the progress of its use in further research and clinical applications. Here, we provide modified stage-specific induction approaches for spermatogenesis in in vitro culture with cells possessing a totipotent status. With this stage-specific propagation in a monolayer condition and a changing cytokine combination, we obtained spermatogenic cells in the forward to late meiosis stages with haploid features. Based on this technical platform, we refined a novel serum-free culture system with various cytokines in 3-D Matrigel for spermatogenesis that promote totipotent embryonic stem cells to meiosis stage with distinct SCP3 expression. And we also explored the effects of coculture with fibroblasts, the mutual interactions in the induction conditions promote the mouse embryonic fibroblasts underwent stromal cells differentiation. In further overexpression of spermatogenic gene Dazl in mouse embryonic fibroblasts, we found early stage initiation for spermatogenesis, and that will enhanced if cocultured with embryonic stem cells in the induction condition. Our results provide alternative approaches for effective spermatogenesis and support the development of promising avenues for infertility therapies.

Tissue Engineering to Improve Immature Testicular Tissue and Cell Transplantation Outcomes: One Step Closer to Fertility Restoration for Prepubertal Boys Exposed to Gonadotoxic Treatments

Despite their important contribution to the cure of both oncological and benign diseases, gonadotoxic therapies present the risk of a severe impairment of fertility. Sperm cryopreservation is not an option to preserve prepubertal boys’ reproductive potential, as their seminiferous tubules only contain spermatogonial stem cells (as diploid precursors of spermatozoa). Cryobanking of human immature testicular tissue (ITT) prior to gonadotoxic therapies is an accepted practice. Evaluation of cryopreserved ITT using xenotransplantation in nude mice showed the survival of a limited proportion of spermatogonia and their ability to proliferate and initiate differentiation. However, complete spermatogenesis could not be achieved in the mouse model. Loss of germ cells after ITT grafting points to the need to optimize the transplantation technique. Tissue engineering, a new branch of science that aims at improving cellular environment using scaffolds and molecules administration, might be an approach for further progress. In this review, after summarizing the lessons learned from human prepubertal testicular germ cells or tissue xenotransplantation experiments, we will focus on the benefits that might be gathered using bioengineering techniques to enhance transplantation outcomes by optimizing early tissue graft revascularization, protecting cells from toxic insults linked to ischemic injury and exploring strategies to promote cellular differentiation.

Testicular organoids: a new model to study the testicular microenvironment in vitro?

BACKGROUND

In recent decades, a broad range of strategies have been applied to model the testicular microenvironment in vitro. These models have been utilized to study testicular physiology and development. However, a system that allows investigations into testicular organogenesis and its impact in the spermatogonial stem-cell (SSC) niche in vitro has not been developed yet. Recently, the creation of tissue-specific organ-like structures called organoids has resurged, helping researchers to answer scientific questions that previous in vitro models could not help to elucidate. So far, a small number of publications have concerned the generation of testicular organoids and their application in the field of reproductive medicine and biology.

OBJECTIVE AND RATIONALE

Here, we aim to elucidate whether testicular organoids might be useful in answering current scientific questions about the regulation and function of the SSC niche as well as germ cell proliferation and differentiation, and whether or not the existing in vitro models are already sufficient to address them. Moreover, we would like to discuss how an organoid system can be a better solution to address these prominent scientific problems in our field, by the creation of a rationale parallel to those in other areas where organoid systems have been successfully utilized.

SEARCH METHODS

We comprehensively reviewed publications regarding testicular organoids and the methods that most closely led to the formation of these organ-like structures in vitro by searching for the following terms in both PubMed and the Web of Science database: testicular organoid, seminiferous tubule 3D culture, Sertoli cell 3D culture, testicular cord formation in vitro, testicular morphogenesis in vitro, germ cell 3D culture, in vitro spermatogenesis, testicular de novo morphogenesis, seminiferous tubule de novo morphogenesis, seminiferous tubule-like structures, testicular in vitro model and male germ cell niche in vitro, with no restrictions to any publishing year. The inclusion criteria were based on the relation with the main topic (i.e. testicular organoids, testicular- and seminiferous-like structures as in vitro models), methodology applied (i.e. in vitro culture, culture dimensions (2D, 3D), testicular cell suspension or fragments) and outcome of interest (i.e. organization in vitro). Publications about grafting of testicular tissue, germ-cell transplantation and female germ-cell culture were excluded.

OUTCOMES

The application of organoid systems is making its first steps in the field of reproductive medicine and biology. A restricted number of publications have reported and characterized testicular organoids and even fewer have denominated such structures by this method. However, we detected that a clear improvement in testicular cell reorganization is recognized when 3D culture conditions are utilized instead of 2D conditions. Depending on the scientific question, testicular organoids might offer a more appropriate in vitro model to investigate testicular development and physiology because of the easy manipulation of cell suspensions (inclusion or exclusion of a specific cell population), the fast reorganization of these structures and the controlled in vitro conditions, to the same extent as with other organoid strategies reported in other fields.

WIDER IMPLICATIONS

By way of appropriate research questions, we might use testicular organoids to deepen our basic understanding of testicular development and the SSC niche, leading to new methodologies for male infertility treatment.

A comparison between a new vitrification protocol and the slow freezing method in the cryopreservation of prepubertal testicular tissue

OBJECTIVE

This study aimed to compare a new vitrification protocol with reduced cryoprotectant exposure to the slow freezing method in the cryopreservation of prepubertal rat testicular tissue.

METHODS

Five sexually immature male Wistar rats were submitted to bilateral orchiectomy. Tissue samples from each testicle were fragmented into small pieces and randomly assigned to three groups: Group A, fresh tissue (control); Group B, slow programmable freezing (SPF); and Group C (vitrification). Frozen/thawed, vitrified/warmed, and fresh testicular tissue were histologically compared. A pathologist blinded to the procedures assessed the morphology (cell differentiation, nuclei, and epithelium) of 10 seminiferous tubules from each testicle (100 tubules per Group).

RESULTS

Sertoli and spermatogonial stem cells were easily differentiated, and the nucleoli were easily viewed in the tubules assessed in all three groups. Small alterations in tissue architecture were observed in the control group as a result of tissue handling. Moderate alterations of the epithelium with the formation of small gaps and cell detachment from the basement membrane were observed in 28% of the frozen and 9% of the vitrified tubules. Condensed nuclei involving a small proportion of cells were observed in six and three tubules of the frozen and vitrified group, respectively. Despite the alterations, 97% of the frozen and 99% of the vitrified tubules were considered well preserved.

CONCLUSIONS

The findings indicate that the vitrification protocol tested in this study adequately preserved the morphological integrity of prepubertal testicular tissue in a rat model. Further studies are required to confirm testicular tissue function after grafting.

Horse spermatogonial stem cell cryopreservation: feasible protocols and potential biotechnological applications

The establishment of proper conditions for spermatogonial stem cells (SSCs) cryopreservation and storage represents an important biotechnological approach for the preservation of the genetic stock of valuable animals. This study demonstrates the effects of different cryopreservation protocols on the survival rates and phenotypic expression of SSCs in horses. The cells were enzymatically isolated from testes of eight adult horses. After enrichment and characterization of germ cells in the suspension, the feasibility of several cryopreservation protocols were evaluated. Three different cryomedia compositions, associated with three different methods of freezing (vitrification, slow-freezing and fast-freezing) were evaluated. Based on the rates of viable SSCs found before and after thawing, as well as the number of recovered cells after cryopreservation, the best results were obtained utilizing the DMSO-based cryomedia associated with the slow-freezing method. In addition, when isolated cells were cultured in vitro, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and immunofluorescence analysis indicated that the cryopreserved cells were as metabolically active as the fresh cells and were also expressing typical SSCs proteins (VASA, NANOS2 and GFRA1). Therefore, our results indicate that equine SSCs can be cryopreserved without impairment of structure, function, or colony-forming abilities.

Is the protein expression window during testicular development affected in patients at risk for stem cell loss?

STUDY QUESTION

Is the protein expression window during testicular development affected in prepubertal patients at risk for stem cell loss?

SUMMARY ANSWER

Nuclear ubiquitin carboxyl-terminal esterase L1 (UCHL1) expression in Sertoli cells and interstitial expression of inhibin α (INHA), sex-determining region Y-box 9 (SOX9) and steroidogenic acute regulatory protein (STAR) was affected in patients with Klinefelter syndrome.

WHAT IS KNOWN ALREADY

Some patients undergoing testicular tissue banking have already been treated before the testis biopsy is taken. These treatments include chemotherapy or hydroxyurea, which can have an influence on the stem cell number and function. A germinal loss occurs in Klinefelter patients, but its cause is currently unknown.

STUDY DESIGN, SIZE, DURATION

Parrafin-embedded testicular tissue from 5 fetuses, 25 prepubertal patients and 5 adults was used to characterize the spatial and temporal distribution of different testicular marker proteins during testicular development. Expression of the markers was evaluated in germ cells, Sertoli cell and interstitial cells. The integrity of this time window was analyzed in patients at risk for germ cell loss: patients treated with hydroxyurea (n = 7), patients treated with chemotherapy (n = 6) and patients affected by Klinefelter syndrome (n = 5).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Immunohistochemistry was performed in normal fetal, prepubertal and adult testicular tissue to set up a timeline for the expression of melanoma antigen family A4 (MAGE-A4), ubiquitin carboxyl-terminal esterase L1 (UCHL1), octamer-binding transcription factor 4 (OCT4), stage-specific embryonic antigen-4 (SSEA4), homeobox protein NANOG, INHA, anti-Müllerian hormone, androgen receptor (AR), SOX9 and STAR. The established timeline was used to evaluate whether the expression of these markers was altered in patients at risk for germ cell loss (patients treated for sickle cell disease (hydroxyurea) or cancer (chemotherapy) and patients with Klinefelter syndrome).

MAIN RESULTS AND THE ROLE OF CHANCE

A protein expression timeline was created using different markers expressed in different testicular cell types. Less positive tubules and less positive cells per tubule were observed for MAGE-A4 and UCHL1 expression in the KS compared with the non-treated group (P < 0.01). Higher nuclear UCHL1 Sertoli cell expression was observed in the KS group compared with the non-treated group (P < 0.05). Higher interstitial expression of INHA (P < 0.05), SOX9 (P < 0.01) and STAR (P < 0.05) was observed in KS compared with the non-treated group.

LIMITATIONS, REASONS FOR CAUTION

Important age variations exist in the prepubertal groups. Therefore, data were represented in three age groups. However, owing to the limited access to prepubertal tissue, no statistical comparison was possible between these groups. For the Klinefelter group, tissue was only available from patients older than 12 years.

WIDER IMPLICATIONS OF THE FINDINGS

The expression timeline can add knowledge to the process of spermatogenesis and be used to evaluate altered protein patterns in patients undergoing potentially gonadotoxic treatments, to monitor spermatogenesis established in vitro and to unravel causes of germ cell loss in Klinefelter patients.

Peritubular myoid cells participate in male mouse spermatogonial stem cell maintenance

Peritubular myoid (PM) cells surround the seminiferous tubule and together with Sertoli cells form the cellular boundary of the spermatogonial stem cell (SSC) niche. However, it remains unclear what role PM cells have in determining the microenvironment in the niche required for maintenance of the ability of SSCs to undergo self-renewal and differentiation into spermatogonia. Mice with a targeted disruption of the androgen receptor gene (Ar) in PM cells experienced a progressive loss of spermatogonia, suggesting that PM cells require testosterone (T) action to produce factors influencing SSC maintenance in the niche. Other studies showed that glial cell line-derived neurotrophic factor (GDNF) is required for SSC self-renewal and differentiation of SSCs in vitro and in vivo. This led us to hypothesize that T-regulated GDNF expression by PM cells contributes to the maintenance of SSCs. This hypothesis was tested using an adult mouse PM cell primary culture system and germ cell transplantation. We found that T induced GDNF expression at the mRNA and protein levels in PM cells. Furthermore, when thymus cell antigen 1-positive spermatogonia isolated from neonatal mice were cocultured with PM cells with or without T and transplanted to the testes of germ cell-depleted mice, the number and length of transplant-derived colonies was increased considerably by in vitro T treatment. These results support the novel hypothesis that T-dependent regulation of GDNF expression in PM cells has a significant influence on the microenvironment of the niche and SSC maintenance.

Lipopolysaccharide inhibits the self-renewal of spermatogonial stem cells in vitro via downregulation of GDNF expression in Sertoli cells. Reprod Toxicol. 2014;45:87-93. [PMID: 24503145 DOI: 10.1016/j.reprotox.2014.01.009]

Lipopolysaccharide (LPS) can reduce sperm count and sperm quality. The molecular mechanisms underlying this process are not fully understood. In this report, we investigated the effects of LPS-treated Sertoli cells on self-renewal and differentiation of spermatogoinial stem cells (SSCs). Sertoli cell cultures were established and incubated with LPS (10μg/ml) for 1, 2 or 3 days, respectively. The culture media were collected and used as conditioned media (CM) to culture SSCs. The expression of glial cell-derived neurotrophic factor (GDNF), stem cell factor (SCF) and bone morphogenetic protein 4 (BMP4) in Sertoli cells treated with LPS was analyzed by RT-PCR and Western blotting. The results showed that the expression of SSC differentiation markers, c-kit and Sohlh2, was increased, while the expression of SSC self-renewal markers, plzf, oct4, and PCNA, was repressed when cultured in CM from LPS-treated Sertoli cells. GDNF levels in Sertoli cells and CM reduced dramatically after LPS treatments, while SCF and BMP4 levels did not show any significant changes. Moreover, correlated with the GDNF levels in CM, GDNF target genes, Bcl6b and Etv5, were reduced markedly in SSCs. Our results suggest that LPS inhibits the expression of GDNF in Sertoli cells, and might prevent the SSC self-renewal via down-regulation of GDNF target genes.

Influence of Exposure to Benzo[a]pyrene on Mice Testicular Germ Cells during Spermatogenesis

The objective of this study was to assess the toxicological effect of exposure to benzo(a)pyrene, B[a]P, on germ cells during spermatogenesis. Mice were exposed to B[a]P at 1, 10, 50, and 100 mg/kg/day for 30 days via oral ingestion. Germ cells, including spermatogonia, spermatocytes, pachytene spermatocytes, and round spermatids, were recovered from testes of mice exposed to B[a]P, while mature spermatozoa were isolated from vas deferens. Reproductive organs were collected and weighed. Apoptotic response of germ cells and mature spermatozoa were qualified using the terminal deoxynucleotidyl transferase mediated deoxy-UTP nick end labeling (TUNEL) assay. B[a]P exposure at ≤10 mg/kg/day for 30 days did not significantly alter concentrations of germ cells and mature spermatozoa and apoptotic response in germ cells and mature spermatozoa. Exposure to B[a]P at 50 and 100 mg/kg/day induced testicular atrophy and yielded a significant reduction in the concentrations of spermatogonia, spermatocytes, pachytene spermatocytes, and round spermatid cells as compared with the control. Also, mature spermatozoa experienced decreased concentrations and viability. B[a]P-exposed mice experienced a significant increase in apoptotic germ cells as compared to the control mice. However, the mice dose concentrations were not relevant for comparison to human exposure.

Effects of vitamin A on in vitro maturation of pre-pubertal mouse spermatogonial stem cells

Testicular tissue cryopreservation is the only potential option for fertility preservation in pre-pubertal boys exposed to gonadotoxic treatment. Completion of spermatogenesis after in vitro maturation is one of the future uses of harvested testicular tissue. The purpose of the current study was to evaluate the effects of vitamin A on in vitro maturation of fresh and frozen-thawed mouse pre-pubertal spermatogonial stem cells in an organ culture system. Pre-pubertal CD1 mouse fresh testes were cultured for 7 (D7), 9 (D9) and 11 (D11) days using an organ culture system. Basal medium was supplemented with different concentrations of retinol (Re) or retinoic acid (RA) alone or in combination. Seminiferous tubule morphology (tubule diameter, intra-tubular cell type), intra-tubular cell death and proliferation (PCNA antibody) and testosterone level were assessed at D7, D9 and D11. Pre-pubertal mouse testicular tissue were frozen after a soaking temperature performed at -7°C, -8°C or -9°C and after thawing, were cultured for 9 days, using the culture medium preserving the best fresh tissue functionality. Retinoic acid at 10^-6M and retinol at 3.3.10^-7M, as well as retinol 10^-6M are favourable for seminiferous tubule growth, maintenance of intra-tubular cell proliferation and germ cell differentiation of fresh pre-pubertal mouse spermatogonia. Structural and functional integrity of frozen-thawed testicular tissue appeared to be well-preserved after soaking temperature at -8°C, after 9 days of organotypic culture using 10^-6M retinol. RA and Re can control in vitro germ cell proliferation and differentiation. Re at a concentration of 10^-6M maintains intra-tubular cell proliferation and the ability of spermatogonia to initiate spermatogenesis in fresh and frozen pre-pubertal mouse testicular tissue using a soaking temperature at -8°C. Our data suggested a possible human application for in vitro maturation of cryopreserved pre-pubertal testicular tissue.

An improved protocol for isolation and culturing of mouse spermatogonial stem cells

Spermatogonial stem cells (SSCs) represent a unique testicular cell type that has the capacity for proliferating, differentiating, and transmitting genetic information. This particular cell type is a strong focus of stem cell research, with isolation and maintenance of SSCs as an important issue. Therefore, we attempted to optimize SSCs handling and to analyze different media and feeder layers, such as adult and embryonic Sertoli cells. The expression patterns of SSC-specific proteins (α6 and β1 integrins, Stra8, and DAZL) and restoration of spermatogenesis were chosen as parameters to demonstrate the efficacy of the protocol. SSCs were isolated from testes of 3- to 6-day-old mice using a magnetic activated cell-sorting system and Thy-1 antibody. After enrichment, SSCs were cultured for 7 days with different media and feeder layers. Then, SSCs were transplanted to recipient mice. Culturing on adult and embryonic Sertoli cells and in the presence of different growth factors [glial cell line-derived neurotrophic factor (GDNF), GDNF family receptor α1 (GFR-α1), and basic fibroblast growth factor (bFGF) resulted in an undifferentiated SSC phenotype with typical stem cell characteristics observed in vivo. The established co-culture model could help to improve the recovery and quality of stem cell preparation of mammalian testis.

Fertility preservation: current prospects and future challenges

Due to remarkable advances in cancer therapies, we have seen great improvements in survival rates of pediatric and reproductive-age male patients. Unfortunately, fertility in adult life might be severely impaired by these treatments. Gonadotoxic therapy is also used to cure a variety of non-malignant disorders. Providing young people undergoing gonadotoxic treatment with adequate fertility preservation options is a challenging area of reproductive medicine and merits broader diffusion in clinical practice. This paper, therefore, aims to review current concepts and perspectives to restore fertility from germ cells or gonadal tissue cryostored prior to gonadotoxic therapies in pre- and post-pubertal patients. For patients rendered sterile after treatment, who did not benefit from fertility preservation measures before therapy, the reproductive potential of alternative sources of stem cells is also examined, although this is at the research stage.

Gene expression profiling revealed specific spermatogonial stem cell genes in mouse

Mammalian spermatogenesis originates from spermatogonial stem cells (SSCs), which undergo mitosis, meiosis and spermiogenesis in order to generate mature spermatozoa. SSCs are adult stem cells that can both self-renew and differentiate. To maintain pluripotency, SSCs are regulated by both extrinsic factors secreted from surrounding somatic cells and intrinsic factors including specific gene expression programs. Using fluorescent labeled germ line stem cells, mouse gonocytes and SSCs were purified up to 97% by improved FACS method. Through microarray analyses, global gene expression profiles of gonocytes, SSCs, and differentiated cells were compared. A large number of distinctive genes were found to be enriched in respective cell populations, indicating different functional requirements of each cell type. Functional clustering analyses revealed that while gonocytes and SSCs preferentially express genes implicated in gene expression regulation and epigenetic modifications, differentiated cells including somatic cells are enriched with genes encoding proteins involved in various cellular activities. Further in situ hybridization and RT-PCR experiments confirmed SSC specific expression of several genes of which functions have not been characterized in SSCs. The comparative gene expression profiling provides a useful resource for gene discovery in relation to SSC regulation and opens new avenues for the study of molecular mechanisms underlying SSC self-renewal and differentiation.

Cryopreservation of human testicular diploid germ cell suspensions

For patients with threatened fertility, preservation of it is a major concern. Although promising results have been obtained in animal models using testicular germ cell suspensions, in humans, it is crucial to first develop an efficient method of cryopreservation to be able to apply to transplantation. Thus, four reliable and available cryopreservation techniques in any fertility centre were tested to cryopreserve an enriched fraction of diploid germ cells isolated from human testicular biopsies. The protocols were evaluated based on cell viability, and the results showed significant differences between the four methods. The semen and tissue cryopreservation methods appeared to be inadequate for diploid germ cell suspensions, and programmed slow freezing gave significantly lower results than open pulled straw vitrification; the latter was found to be the protocol that best preserved cell viability. The vitrification of isolated human diploid germ cells is innovative and constitutes valuable information for cryopreservation in cases of transplants or in vitro maturation.

Spermatogonial stem cells, infertility and testicular cancer

The spermatogonial stem cells (SSCs) are responsible for the transmission of genetic information from an individual to the next generation. SSCs play critical roles in understanding the basic reproductive biology of gametes and treatments of human infertility. SSCs not only maintain normal spermatogenesis, but also sustain fertility by critically balancing both SSC self-renewal and differentiation. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression within the SSC as well as the extrinsic gene signals from the niche. Increased SSCs self-renewal at the expense of differentiation result in germ cell tumours, on the other hand, higher differentiation at the expense of self-renewal can result in male sterility. Testicular germ cell cancers are the most frequent cancers among young men in industrialized countries. However, understanding the pathogenesis of testis cancer has been difficult because it is formed during foetal development. Recent studies suggest that SSCs can be reprogrammed to become embryonic stem (ES)-like cells to acquire pluripotency. In the present review, we summarize the recent developments in SSCs biology and role of SSC in testicular cancer. We believe that studying the biology of SSCs will not only provide better understanding of stem cell regulation in the testis, but eventually will also be a novel target for male infertility and testicular cancers.

Assessment of freezing procedures for rat immature testicular tissue

Fertility preservation has been included in the management of childhood cancer treatment. Cryopreservation of immature testicular tissue is the only available solution for pre-pubertal boys. Different freezing protocols have been developed in several species but without a clearly identified procedure. We tried to evaluate several protocols for cryopreservation of rat immature testicular tissue. Twelve different freezing protocols using different (i) cryoprotectant (dimethylsulphoxide [DMSO] or 1,2-propanediol [PROH]), (ii) cryoprotectant concentration (1.5M or 3M), (iii) equilibration time (30 or 60 min), (iv) equilibration temperature (4 °C or room temperature), (v) size of testicular fragment (7.5mg or 15 mg), (vi) package (straws or cryovials), were compared using cord morphological damage evaluation. A testicular tissue piece of 7.5mg cryopreserved in cryovial using 1.5M DMSO, an equilibration time of 30 min at 4 °C showed fewer morphological alterations than the other protocols tested. The selected freezing protocol was able to maintain rat immature testicular tissue architecture, functionality after testicular pieces organotypic culture, and could be proposed in a human application.

Efficient and safe recipient preparation for transplantation of mouse spermatogonial stem cells: pretreating testes with heat shock

Recipient preparation is of prime importance for the successful transplantation of spermatogonial stem cells (SSCs). Busulfan destroys endogenous germs cells and is commonly used for recipient preparation. However, busulfan produces significant side effects, including systemic toxicity, and it is lethal in certain species. The side effects associated with busulfan compromise the efficiency of SSC transplantation and threaten the safety of recipients. Here, we show that heat shock treatment of testes can be used as an alternative to busulfan treatment. Fourteen days after heat shock treatment, mice received a testicular injection of donor germ cells expressing enhanced green fluorescent protein (EGFP). Busulfan-treated mice were used as controls. Two months after transplantation, the number (12 ± 1 mm) and length (30.46 ± 5.23 mm) of EGFP-expressing testicular colonies in heat shock-treated recipients were not significantly different from those in busulfan-treated recipients. Furthermore, healthy EGFP-expressing offspring were obtained after intracytoplasmic injection of round spermatids recovered from heat shock-treated recipients. This result indicates that donor SSCs undergo complete spermatogenesis in the heat shock-treated testes of recipients. Our findings demonstrate the feasibility of using heat shock for the preparation of recipients before SSC transplantation in mice. Heat shock may prove to be useful for recipient preparation in mammalian species in which busulfan produces significant toxicity.

Spermatogonial stem cells and in vitro spermatogenesis

Spermatogonial stem cells (SSCs) provide the basis for the life-long production of enormous numbers of sperm. The nature of these mysterious cells is being clarified. Although they were regarded to be mostly dormant, dividing rarely and remaining static in a niche, their rather dynamic behavior in the seminiferous tubules has been disclosed. The territories of each colony of SSCs can also quickly change in size. The development of a culture method for SSCs also shed light on their stable, but at the same time, fragile characteristics. In addition, an in vitro system for spermatogenesis was developed which can produce functional sperm from SSCs. These new developments will contribute to reproductive medicine.

Zebrafish models of germ cell tumor

Germ cell tumors are neoplasms arising from pluripotent germ cells. In humans, these tumors occur in infants, children and young adults. The tumors display a wide range of histologic differentiation states which exhibit different clinical behaviors. Information about the molecular basis of germ cell tumors, and representative animal models of these neoplasms, are lacking. Germline development in zebrafish and humans is broadly conserved, making the fish a useful model to probe the connections between germ cell development and tumorigenesis. Here, we provide an overview of germline development and a brief review of germ cell tumor biology in humans and zebrafish. We also outline some methods for studying the zebrafish germline.

Evolution and spermatogenesis

Sexual reproduction depends on the production of haploid gametes, and their fusion to form diploid zygotes. Here, we discuss sperm production and function in a molecular and functional evolutionary context, drawing predominantly from studies in model organisms (mice, Drosophila, Caenorhabditis elegans). We consider the mechanisms involved in establishing and maintaining a germline stem cell population in testes, as well as the factors that regulate their contribution to the pool of differentiating cells. These processes involve considerable interaction between the germline and the soma, and we focus on regulatory signalling events in a variety of organisms. The male germline has a unique transcriptional profile, including expression of many testis-specific genes. The evolutionary pressures associated with gene duplication and acquisition of testis function are discussed in the context of genome organization and transcriptional regulation. Post-meiotic differentiation of spermatids involves very dramatic changes in cell shape and acquisition of highly specialized features. We discuss the variety of sperm motility mechanisms and how various reproductive strategies are associated with the diversity of sperm forms found in animals.