Xenotransplantation of canine spermatogonial stem cells (cSSCs) regulated by FSH promotes spermatogenesis in infertile mice

Spermatogonial stem cell technologies: applications from human medicine to wildlife conservation†

Spermatogonial stem cell (SSC) technologies that are currently under clinical development to reverse human infertility hold the potential to be adapted and applied for the conservation of endangered and vulnerable wildlife species. The biobanking of testis tissue containing SSCs from wildlife species, aligned with that occurring in pediatric human patients, could facilitate strategies to improve the genetic diversity and fitness of endangered populations. Approaches to utilize these SSCs could include spermatogonial transplantation or testis tissue grafting into a donor animal of the same or a closely related species, or in vitro spermatogenesis paired with assisted reproduction approaches. The primary roadblock to progress in this field is a lack of fundamental knowledge of SSC biology in non-model species. Herein, we review the current understanding of molecular mechanisms controlling SSC function in laboratory rodents and humans, and given our particular interest in the conservation of Australian marsupials, use a subset of these species as a case-study to demonstrate gaps-in-knowledge that are common to wildlife. Additionally, we review progress in the development and application of SSC technologies in fertility clinics and consider the translation potential of these techniques for species conservation pipelines.

Detection of spermatogonial stem cells in testicular tissue of dogs with chronic asymptomatic orchitis

Chronic asymptomatic idiopathic orchitis (CAO) is an important but neglected cause of acquired infertility due to non-obstructive azoospermia (NOA) in male dogs. The similarity of the pathophysiology in infertile dogs and men supports the dog's suitability as a possible animal model for studying human diseases causing disruption of spermatogenesis and evaluating the role of spermatogonial stem cells (SSCs) as a new therapeutic approach to restore or recover fertility in cases of CAO. To investigate the survival of resilient stem cells, the expression of the protein gene product (PGP9.5), deleted in azoospermia like (DAZL), foxo transcription factor 1 (FOXO1) and tyrosine-kinase receptor (C-Kit) were evaluated in healthy and CAO-affected canine testes. Our data confirmed the presence of all investigated germ cell markers at mRNA and protein levels. In addition, we postulate a specific expression pattern of FOXO1 and C-Kit in undifferentiated and differentiating spermatogonia, respectively, whereas DAZL and PGP9.5 expressions were confirmed in the entire spermatogonial population. Furthermore, this is the first study revealing a significant reduction of PGP9.5, DAZL, and FOXO1 in CAO at protein and/or gene expression level indicating a severe disruption of spermatogenesis. This means that chronic asymptomatic inflammatory changes in CAO testis are accompanied by a significant loss of SSCs. Notwithstanding, our data confirm the survival of putative stem cells with the potential of self-renewal and differentiation and lay the groundwork for further research into stem cell-based therapeutic options to reinitialize spermatogenesis in canine CAO-affected patients.

Co-Culture of Cryopreserved Healthy Sertoli Cells with Testicular Tissue of Non-Obstructive Azoospermia (NOA) Patients in Culture Media Containing Follicle-Stimulating Hormone (FSH)/Testosterone Has No Advantage in Germ Cell Maturation

Different cell culture conditions and techniques have been used to mature spermatogenic cells to increase the success of in vitro fertilization. Sertoli cells (SCs) are essential in maintaining spermatogenesis and FSH stimulation exerts its effect through direct or indirect actions on SCs. The effectiveness of FSH and testosterone added to the co-culture has been demonstrated in other studies to provide microenvironment conditions of the testicular niche and to contribute to the maturation and meiotic progression of spermatogonial stem cells (SSCs). In the present study, we investigated whether co-culture of healthy SCs with the patient's testicular tissue in the medium supplemented with FSH/testosterone provides an advantage in the differentiation and maturation of germ cells in NOA cases (N = 34). In men with obstructive azoospermia (N = 12), healthy SCs from testicular biopsies were identified and purified, then cryopreserved. The characterization of healthy SCs was done by flow cytometry (FC) and immunohistochemistry using antibodies specific for GATA4 and vimentin. FITC-conjugated annexin V/PI staining and the MTT assay were performed to compare the viability and proliferation of SCs before and after freezing. In annexin V staining, no difference was found in percentages of live and apoptotic SCs, and MTT showed that cryopreservation did not inhibit SC proliferation compared to the pre-freezing state. Then, tissue samples from NOA patients were processed in two separate environments containing FSH/testosterone and FSH/testosterone plus co-culture with thawed healthy SCs for 7 days. FC was used to measure 7th-day levels of specific markers expressed in spermatogonia (VASA), meiotic cells (CREM), and post-meiotic cells (protamine-2 and acrosin). VASA and acrosin basal levels were found to be lower in infertile patients compared to the OA group (8.2% vs. 30.6% and 12.8% vs. 30.5%, respectively; p < 0.05). Compared to pre-treatment measurements, on the 7th day in the FSH/testosterone environment, CREM levels increased by 58.8% and acrosin levels increased by 195.5% (p < 0.05). Similarly, in medium co-culture with healthy SCs, by day 7, CREM and acrosin levels increased to 92.2% and 204.8%, respectively (p < 0.05). Although VASA and protamine levels increased in both groups, they did not reach a significant level. No significant difference was found between the day 7 increase rates of CREM, VASA, acrosin and protamine-2 in either FSH/testosterone-containing medium or in medium additionally co-cultured with healthy SCs (58.8% vs. 92.2%, 120.6% vs. 79.4%, 195.5% vs. 204.8%, and 232.3% vs. 198.4%, respectively; p > 0.05). Our results suggest that the presence of the patient's own SCs for maturation of germ cells in the culture medium supplemented with FSH and testosterone is sufficient, and co-culture with healthy SCs does not have an additional advantage. In addition, the freezing-thawing process would not impair the viability and proliferation of SCs.

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

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

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

Progress in germline stem cell transplantation in mammals and the potential usage

Germline stem cells (GSCs) are germ cells with the capacities of self-renewal and differentiation into functional gametes, and are able to migrate to their niche and reconstitute the fertility of recipients after transplantation. Therefore, GSCs transplantation is a promising technique for fertility recovery in the clinic, protection of rare animals and livestock breeding. Though this novel technique faces tremendous challenges, numerous achievements have been made after several decades' endeavor. This review summarizes the current knowledge of GSCs transplantation and its utilization in mammals, and discusses the application prospect in reproductive medicine and animal science.

Recellularized rat testis scaffolds with embryoid bodies cells: a promising approach for tissue engineering

Tissue engineering is gaining use to investigate the application of its techniques for infertility treatment. The use of pluripotent embryonic cells for in vitro production of viable spermatozoa in testicular scaffolds is a promising strategy that could solve male infertility. Due to cell-extracellular matrix (ECM) interactions, here we aim to investigate the differentiation of embryoid bodies (EBs) in cultured into decellularized rat testis scaffolds. Decellularized testis (P = 0.019) with a low concentration of gDNA (30.58 mg/ng tissue) was obtained by sodium dodecyl sulfate perfusion. The structural proteins (collagens type I and III) and the adhesive glycoproteins of ECM (laminin and fibronectin) were preserved according to histological and scanning electron microscopy (SEM) analyses. Then, decellularized rat testis were cultured for 7 days with EB, and EB mixed with retinoic acid (RA) in non-adherent plates. By SEM, we observe that embryonic stem cells adhered in the decellularized testis ECM. By immunofluorescence, we verified the positive expression of HSD17B3, GDNF, ACRV-1, and TRIM-36, indicating their differentiation using RA in vitro, reinforcing the possibility of EB in male germ cell differentiation. Finally, recellularized testis ECM may be a promising tool for future new approaches for testicular cell differentiation applied to assisted reproduction techniques and infertility treatment.Abbreviations: ACRV-1: Acrosomal vesicle protein 1; ATB: Penicillin-streptomycin; DAPI: 4,6-Diamidino-2-phenylindole; EB: Embryoid bodies; ECM: Extracellular matrix; ESCs: Pluripotent embryonic stem cells; GAGs: Glycosaminoglycans; gDNA: Genomic DNA; GDNF: Glial cell line-derived neurotrophic factor; H&E: Hematoxylin and eosin; HSD17B3: 17-beta-Hydroxysteroid dehydrogenase type 3; PBS: Phosphate-buffered saline; PGCLCs: Primordial germ-cell-like cells; RA: Retinoic acid; SDS: Sodium dodecyl sulfate; SEM: Scanning electron microscopy; SSCs: Spermatogonial stem cells; TRIM-36: Tripartite Motif Containing 36.

Actions and Roles of FSH in Germinative Cells

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

Cryopreservation and Culture of Testicular Tissues: An Essential Tool for Biodiversity Preservation

Systematic cryo-banking of reproductive tissues could enhance reproductive management and ensure sustainability of rare mammalian genotypes. Testicular tissues contain a vast number of germ cells, including at early stages (spermatogonia and spermatocytes), that can potentially develop into viable spermatozoa after grafting or culture in vitro, and the resulting sperm cells then can be used for assisted reproductive techniques. The objective of this review was to describe current advances, limitations, and perspectives related to the use of testicular tissue preservation as a strategy for the conservation of male fertility. Testes can be obtained from mature or prepubertal individuals, immediately postmortem or by orchiectomy, but testicular biopsies could also be an alternative to collect samples from living individuals. Testicular fragments can be then cryopreserved by using slow or ultra-rapid freezing, or even vitrification methods. The composition of cryopreservation media can vary according to species-specific characteristics, especially regarding the cryoprotectant type and concentration. Finally, spermatozoa have been usually obtained after xenografting of testicular fragments into severely immunodeficient mice, while this method still has to be optimized after in vitro culture conditions.

Direct action of FSH on testicular stem cells

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