Effect of vascular endothelial growth factor and testis tissue culture on spermatogenesis in bovine ectopic testis tissue xenografts

Using a testis regeneration model, FGF9, LIF, and SCF improve testis cord formation while RA enhances gonocyte survival

Implantation of testis cell aggregates from various donors under the back skin of recipient mice results in de novo formation of testis tissue. We used this implantation model to study the putative in vivo effects of six different growth factors on testis cord development. Recipient mice (n = 7/group) were implanted with eight neonatal porcine testis cell aggregates that were first exposed to a designated growth factor: FGF2 at 1 µg/mL, FGF9 at 5 µg/mL, VEGF at 3.5 µg/mL, LIF at 5 µg/mL, SCF at 3.5 µg/mL, retinoic acid (RA) at 3.5 × 10^-5 M, or no growth factors (control). The newly developed seminiferous cords (SC) were classified based on their morphology into regular, irregular, enlarged, or aberrant. Certain treatments enhanced implant weight (LIF), implant cross-sectional area (SCF) or the relative cross-sectional area covered by SC within implants (FGF2). RA promoted the formation of enlarged SC and FGF2 led to the highest ratio of regular SC and the lowest ratio of aberrant SC. Rete testis-like structures appeared earlier in implants treated with FGF2, FGF9, or LIF. These results show that even brief pre-implantation exposure of testis cells to these growth factors can have profound effects on morphogenesis of testis cords using this implantation model.

Application of Tissue-Specific Extracellular Matrix in Tissue Engineering: Focus on Male Fertility Preservation

In vitro spermatogenesis and xenotransplantation of the immature testicular tissues (ITT) are the experimental approaches that have been developed for creating seminiferous tubules-like functional structures in vitro and keeping the integrity of the ITTs in vivo, respectively. These strategies are rapidly developing in response to the growing prevalence of infertility in adolescent boys undergoing cancer treatment, by the logic that there is no sperm cryopreservation option for them. Recently, with the advances made in the field of tissue engineering and biomaterials, these methods have achieved promising results for fertility preservation. Due to the importance of extracellular matrix for the formation of vascular bed around the grafted ITTs and also the creation of spatial arrangements between Sertoli cells and germ cells, today it is clear that the scaffold plays a very important role in the success of these methods. Decellularized extracellular matrix (dECM) as a biocompatible, functionally graded, and biodegradable scaffold with having tissue-specific components and growth factors can support reorganization and physiologic processes of originated cells. This review discusses the common protocols for the tissue decellularization, sterilization, and hydrogel formation of the decellularized and lyophilized tissues as well as in vitro and in vivo studies on the use of the testis-derived dECM for testicular organoids.

Fertility Preservation and Restoration Options for Pre-Pubertal Male Cancer Patients: Current Approaches

Fertility preservation for prepubertal male patients undergoing gonadotoxic therapies, potentially depleting spermatogonial cells, is an expanding necessity, yet most of the feasible options are still in the experimental phase. We present our experience and a summary of current and novel possibilities regarding the different strategies to protect or restore fertility in young male patients, before proceeding with chemotherapy or radiotherapy for malignances or other diseases. Adult oncological patients should always be counselled to cryopreserve the semen before starting treatment, however this approach is not suitable for prepubertal boys, who aren't capable to produce sperm yet. Fortunately, since the survival rate of pediatric cancer patients has skyrocketed in the last decade and it's over 84%, safeguarding their future fertility is becoming a major concern for reproductive medicine. Surgical and medical approaches to personalize treatment or protect the gonads could be a valid first step to take. Testicular tissue autologous grafting or xenografting, and spermatogonial stem cells (SSCs) transplantation, are the main experimental options available, but spermatogenesis in vitro is becoming an intriguing alternative. All of these methods feature both strong and weak prospects. There is also relevant controversy regarding the type of testicular material to preserve and the cryopreservation methods. Since transplanted cells are bound to survive based on SSCs number, many ways to enrich their population in cultures have been proposed, as well as different sites of injection inside the testis. Testicular tissue graft has been experimented on mice, rabbits, rhesus macaques and porcine, allowing the birth of live offspring after performing intracytoplasmic sperm injection (ICSI), however it has never been performed on human males yet. In vitro spermatogenesis remains a mirage, although many steps in the right direction have been performed. The manufacturing of 3D scaffolds and artificial spermatogenetic niche, providing support to stem cells in cultures, seems like the best way to further advance in this field.

Accelerated and Improved Vascular Maturity after Transplantation of Testicular Tissue in Hydrogels Supplemented with VEGF- and PDGF-Loaded Nanoparticles

Avascular transplantation of frozen-thawed testicular tissue fragments represents a potential future technique for fertility restoration in boys with cancer. A significant loss of spermatogonia was observed in xeno-transplants of human tissue most likely due to the hypoxic period before revascularization. To reduce the effect of hypoxia-reoxygenation injuries, several options have already been explored, like encapsulation in alginate hydrogel and supplementation with nanoparticles delivering a necrosis inhibitor (NECINH) or VEGF. While these approaches improved short-term (5 days) vascular surfaces in grafts, neovessels were not maintained up to 21 days; i.e., the time needed for achieving vessel stabilization. To better support tissue grafts, nanoparticles loaded with VEGF, PDGF and NECINH were developed. Testicular tissue fragments from 4-5-week-old mice were encapsulated in calcium-alginate hydrogels, either non-supplemented (control) or supplemented with drug-loaded nanoparticles (VEGF-nanoparticles; VEGF-nanoparticles + PDGF-nanoparticles; NECINH-nanoparticles; VEGF-nanoparticles + NECINH-nanoparticles; and VEGF-nanoparticles + PDGF-nanoparticles + NECINH-nanoparticles) before auto-transplantation. Grafts were recovered after 5 or 21 days for analyses of tissue integrity (hematoxylin-eosin staining), spermatogonial survival (immuno-histo-chemistry for promyelocytic leukemia zinc finger) and vascularization (immuno-histo-chemistry for α-smooth muscle actin and CD-31). Our results showed that a combination of VEGF and PDGF nanoparticles increased vascular maturity and induced a faster maturation of vascular structures in grafts.

Fertility preservation in boys: recent developments and new insights †

BACKGROUND

Infertility is an important side effect of treatments used for cancer and other non-malignant conditions in males. This may be due to the loss of spermatogonial stem cells (SSCs) and/or altered functionality of testicular somatic cells (e.g. Sertoli cells, Leydig cells). Whereas sperm cryopreservation is the first-line procedure to preserve fertility in post-pubertal males, this option does not exist for prepubertal boys. For patients unable to produce sperm and at high risk of losing their fertility, testicular tissue freezing is now proposed as an alternative experimental option to safeguard their fertility.

OBJECTIVE AND RATIONALE

With this review, we aim to provide an update on clinical practices and experimental methods, as well as to describe patient management inclusion strategies used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss.

SEARCH METHODS

Based on the expertise of the participating centres and a literature search of the progress in clinical practices, patient management strategies and experimental methods used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss were identified. In addition, a survey was conducted amongst European and North American centres/networks that have published papers on their testicular tissue banking activity.

OUTCOMES

Since the first publication on murine SSC transplantation in 1994, remarkable progress has been made towards clinical application: cryopreservation protocols for testicular tissue have been developed in animal models and are now offered to patients in clinics as a still experimental procedure. Transplantation methods have been adapted for human testis, and the efficiency and safety of the technique are being evaluated in mouse and primate models. However, important practical, medical and ethical issues must be resolved before fertility restoration can be applied in the clinic.Since the previous survey conducted in 2012, the implementation of testicular tissue cryopreservation as a means to preserve the fertility of prepubertal boys has increased. Data have been collected from 24 co-ordinating centres worldwide, which are actively offering testis tissue cryobanking to safeguard the future fertility of boys. More than 1033 young patients (age range 3 months to 18 years) have already undergone testicular tissue retrieval and storage for fertility preservation.

LIMITATIONS REASONS FOR CAUTION

The review does not include the data of all reproductive centres worldwide. Other centres might be offering testicular tissue cryopreservation. Therefore, the numbers might be not representative for the entire field in reproductive medicine and biology worldwide. The key ethical issue regarding fertility preservation in prepubertal boys remains the experimental nature of the intervention.

WIDER IMPLICATIONS

The revised procedures can be implemented by the multi-disciplinary teams offering and/or developing treatment strategies to preserve the fertility of prepubertal boys who have a high risk of fertility loss.

STUDY FUNDING/COMPETING INTERESTS

The work was funded by ESHRE. None of the authors has a conflict of interest.

The air-liquid interface culture of the mechanically isolated seminiferous tubules embedded in agarose or alginate improves in vitro spermatogenesis at the expense of attenuating their integrity

Optimization of tissue culture systems able to complete male germ cell maturation to post-meiotic stages is considered as an important matter in reproductive biology. Considering that hypoxia is one of the factors limiting the efficiency of organ culture, the aim of this study was to use isolated seminiferous tubules (STs), having more surface and less thickness, in an organotypic culture system in order to improve oxygen diffusion and reduce hypoxia. The mechanically separated STs embedded in agarose or alginate and 1-3-mm³ testicular tissue fragments of 3 adult mice were separately placed on the flat surface of agarose gel that was half-soaked in the medium. Survival and differentiation of germ cells using PLZF and SCP3 markers, identity of Sertoli cell using GATA4, cell proliferation with the Ki67 marker, and ST integrity using a ST scoring were evaluated up to 36 d at different culture times, each corresponding to the duration of one spermatogenic cycle. We observed a significantly reduced ST integrity in STs embedded in agarose or alginate on day 9 (versus tissue fragments p ≤ 0.05). There was no difference in the number of PLZF-positive cells between groups, but the number of SCP3 (in all-time points) and GATA4-positive cells was significantly higher in the culture of embedded STs. Although embedding STs can be useful for the progress of in vitro spermatogenesis, it makes them sensitive to degeneration. Further improvements are required to modify the air-liquid interface method to maintain ST integrity.

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.

Organ culture of seminiferous tubules using a modified soft agar culture system

BACKGROUND

In-vitro spermatogenesis in mammalian species is considered an important topic in reproductive biology. New strategies for achieving a complete version of spermatogenesis ex vivo have been conducted using an organ culture method or culture of testicular cells in a three-dimensional soft agar culture system (SACS). The aim of this study was to develop a new method that supports spermatogenesis to the meiotic phase and morphologically mature spermatozoa through the culture of testicular cells and seminiferous tubules (STs) in a modified SACS, respectively.

METHODS

First, enzymatically dissociated testicular cells and mechanically dissociated STs of neonatal mice were separately embedded in agarose and then placed on the flat surface of agarose gel half-soaked in the medium to continue culture with a gas-liquid interphase method.

RESULTS

Following 40 days of culture, the meiotic (Scp3) and post-meiotic (Acr) gene expression in aggregates and STs was confirmed by real-time polymerase chain reaction. These results were complemented by immunohistochemistry. The presence of morphologically mature spermatozoa in the frozen sections of STs was demonstrated with hematoxylin and eosin staining. We observed Plzf- or Integrin α6-positive spermatogonia in both cultures after 40 days, indicating the potency of the culture system for both self-renewal and differentiation.

CONCLUSIONS

This technique can be used as a valuable approach for performing research on spermatogenesis and translating it into the human clinical setting.

Experimental models of testicular development and function using human tissue and cells

The mammalian testis has two main roles, production of gametes for reproduction and synthesis of steroid- and peptide hormones for masculinization. These processes are tightly regulated and involve complex interactions between a number of germ and somatic cell-types that comprise a unique microenvironment known as the germ stem cell niche. In humans, failure of normal testicular development or function is associated with susceptibility to a variety of male reproductive disorders including disorders of sex development, infertility and testicular cancer. Whilst studies in rodent models have provided detailed insight into the signaling pathways and molecular mechanisms that regulate the testis, there are important species differences in testicular development, function and reproductive disorders that highlight the need for suitable experimental models utilising human testicular tissues or cells. In this review, we outline experimental approaches used to sustain cells and tissue from human testis at different developmental time-points and discuss relevant end-points. These include survival, proliferation and differentiation of cell lineages within the testis as well as autocrine, paracrine and endocrine function. We also highlight the utility of these experimental approaches for modelling the effects of environmental exposures on testicular development and function.

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.

Hyperglycemia induced testicular damage in type 2 diabetes mellitus rats exhibiting microcirculation impairments associated with vascular endothelial growth factor decreased via PI3K/Akt pathway

As an endocrine disease, type 2 diabetes mellitus (T2DM) can cause testicular damage which induces male infertility. However, the underlying mechanism is still not clear. We prove that T2DM induced testicular microcirculation impairment involves the decrease of VEGF and these actions are regulated by PI3K/Akt pathway. In our study, rats were divided into three groups (n=8): control group, diabetes group and diabetes + VEGF group. Intraperitoneal injection of streptozotocin (STZ, 65mg/Kg, at 9^th week) and daily high-fat diet were used to establish T2DM rat model. Serum glucose in diabetes group and diabetes + VEGF group obviously exceeded 13mmol/L after STZ injection. Immunohistochemical studies indicated that VEGF level in diabetes group significantly decreased. In diabetes group, testicular blood velocity and vascular area reduced evaluated by Doppler and FITC. Furthermore, atrophic testicular morphology and increasing apoptosis cells were evaluated by haematoxylin and eosin staining and TUNEL assay. In diabetes + VEGF group, the administration of VEGF (intraperitoneally, 10mg/kg) can significantly alleviated hyperglycemia-induced impairment of testes in above aspects. Finally, we used Western blot to analyze the mechanism of hyperglycemia-induced testicular VEGF decrease. The results indicated that hyperglycemia-induced VEGF decreased is regulated by PI3K/Akt pathway in Rats testicular sertoli cells (RTSCs). Together, we demonstrate that T2DM can reduce testicular VEGF expression, which results in testicular microcirculation impairment, and then induces testicular morphological disarrangement and functional disorder. These actions are triggered by PI3K/Akt pathway. Our findings provide solid evidence for VEGF becoming a therapeutic target in T2DM related male infertility.

Dysregulation of angiogenesis-specific signalling in adult testis results in xenograft degeneration

Ectopic xenografting of testis is a feasible option for preservation of male fertility and angiogenesis plays a pivotal role in xenograft survival and functionality. When compared to immature testis, the adult testis is unable to establish functional xenografts due to potentially lower efficiency to induce angiogenesis. The precise molecular mechanism, however, remains elusive. In the present study, we compared adult and immature testis xenografts for survival, maturation and germ cell differentiation. Further, we evaluated differential expression of angiogenesis signalling-specific proteins in adult and immature testis and their xenografts. Results showed that adult testis xenografts degenerated whereas immature testis xenografts survived and established spermatogenesis with the production of haploid germ cells. Protein expression analysis demonstrated that immature testis xenografts were able to establish angiogenesis either through eNOS activation via VEGF and PI3K/AKT or through EGFR-mediated STAT3 pathway. The role of ERK/MAPK pathway in xenograft angiogenesis was ruled out. The absence or reduced expression of angiogenesis-specific proteins in adult testis and its xenografts possibly resulted in poor angiogenesis and in their subsequent degeneration. This study provides insight into angiogenesis mechanism that can be utilized to augment testis xenografting efficiency.

Restoring Fertility with Cryopreserved Prepubertal Testicular Tissue: Perspectives with Hydrogel Encapsulation, Nanotechnology, and Bioengineered Scaffolds

New and improved oncological therapies are now able to cure more than 80% of cancer-affected children in Europe. However, such treatments are gonadotoxic and result in fertility issues, especially in boys who are not able to provide a sperm sample before starting chemo/radiotherapy because of their prepubertal state. For these boys, cryopreservation of immature testicular tissue (ITT) is the only available option, aiming to preserve spermatogonial stem cells (SSCs). Both slow-freezing and vitrification have been investigated to this end and are now applied in a clinical setting for SSC cryopreservation. Research now has to focus on methods that will allow fertility restoration. This review discusses different studies that have been conducted on ITT transplantation, including those using growth factor supplementation like free molecules, or tissue encapsulation with or without nanoparticles, as well as the possibility of developing a bioartificial testis that can be used for in vitro gamete production or in vivo transplantation.

VEGF/VEGFR2 Signaling Regulates Germ Cell Proliferation in vitro and Promotes Mouse Testicular Regeneration in vivo

Vascular endothelial growth factor (VEGF) plays fundamental roles in testicular development; however, its function on testicular regeneration remains unknown. The objective of this study was to explore the roles VEGF/VEGFR2 signaling plays in mouse germ cells and in mouse testicular regeneration. VEGF and the VEGFR2 antagonist SU5416 were added to culture medium to evaluate their effects on spermatogonial stem cell line (C18-4 cells) proliferation. Testicular cells obtained from newborn male ICR mice were grafted into the dorsal region of male BALB/c nude mice. VEGF and SU5416 were injected into the graft sites to assess the effects of the VEGF and VEGFR2 signaling pathways on testicular reconstitution. The grafts were analyzed after 8 weeks. We found that VEGF promoted C18-4 proliferation in vitro, indicating its role in germ cell survival. HE staining revealed that seminiferous tubules were reconstituted and male germ cells from spermatogonia to spermatids could be observed in testis-like tissues 8 weeks after grafting. A few advantaged male germ cells, including spermatocytes and spermatids, were found in SU5416-treated grafts. Moreover, VEGF enhanced the expression of genes specific for male germ cells and vascularization in 8-week grafts, whereas SU5416 decreased the expression of these genes. SU5416-treated grafts had a lower expression of MVH and CD31, indicating that blockade of VEGF/VEGFR2 signaling reduces the efficiency of seminiferous tubule reconstitution. Collectively, these data suggest that VEGF/VEGFR2 signaling regulates germ cell proliferation and promotes testicular regeneration via direct action on germ cells and the enhancement of vascularization.

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.

Xenografting of testicular tissue pieces: 12 years of an in vivo spermatogenesis system

Spermatogenesis is a dynamic and complex process that involves endocrine and testicular factors. During xenotransplantation of testicular tissue fragments into immunodecifient mice, a functional communication between host brain and donor testis is established. This interaction allows for the progression of spermatogenesis and recovery of fertilisation-competent spermatozoa from a broad range of mammalian species. In the last few years, significant progress has been achieved in testis tissue xenografting that improves our knowledge about the factors determining the success of grafting. The goal of this review is to provide up to date information about the role of factors such as donor age, donor species, testis tissue preservation or type of recipient mouse on the efficiency of this technique. Applications are described and compared with other techniques with similar purposes. Recent work has demonstrated that testicular tissue xenografting is used as a model to study gonadotoxicity of drugs and to obtain sperm from valuable young males.

De novo morphogenesis of testis tissue: an improved bioassay to investigate the role of VEGF165 during testis formation

De novo formation of testis tissue from single-cell suspensions allows manipulation of different testicular compartments before grafting to study testicular development and the spermatogonial stem cell niche. However, the low percentages of newly formed seminiferous tubules supporting complete spermatogenesis and lack of a defined protocol have limited the use of this bioassay. Low spermatogenic efficiency in de novo formed tissue could result from the scarcity of germ cells in the donor cell suspension, cell damage caused by handling or from hypoxia during tissue formation in the host environment. In this study, we compared different proportions of spermatogonia in the donor cell suspension and the use of Matrigel as a scaffold to support de novo tissue formation and spermatogenesis. Then, we used the system to investigate the role of vascular endothelial growth factor 165 (VEGF165) during testicular morphogenesis on blood vessel and seminiferous tubule formation, and on presence of germ cells in the de novo developed tubules. Our results show that donor cell pellets with 10×10(6) porcine neonatal testicular cells in Matrigel efficiently formed testis tissue de novo. Contrary to what was expected, the enrichment of the cell suspension with germ cells did not result in higher numbers of tubules supporting spermatogenesis. The addition of VEGF165 did not improve blood vessel or tubule formation, but it enhanced the number of tubules containing spermatogonia. These results indicate that spermatogenic efficiency was improved by the addition of Matrigel, and that VEGF165 may have a protective role supporting germ cell establishment in their niche.

Generation of live piglets for the first time using sperm retrieved from immature testicular tissue cryopreserved and grafted into nude mice

Cryopreservation of immature testicular tissues is essential for increasing the possibilities of offspring generation by testicular xenografting for agricultural or medical purposes. However, successful production of offspring from the sperm involved has never been reported previously. In the present study, therefore, using intracytoplasmic sperm injection (ICSI), we examined whether xenogeneic sperm obtained from immature pig testicular tissue after cryopreservation would have the capacity to produce live piglets. Testicular fragments from 9- to 11-day-old piglets were vitrified after 10- or 20-min immersion in vitrification solution containing ethylene glycol (EG), polyvinyl pyrrolidone (PVP) and trehalose as cryoprotectants, and then stored in liquid nitrogen for more than 140 days. Thirty nude mice were assigned to each immersion-time group. Testicular fragments were transplanted under the back skin of castrated mice immediately after warming and removal of the cryoprotectants. Blood and testicular grafts were then recovered from the recipient mice on days 60, 120, 180 and 230−350 (day 0 =  grafting). Histological assessment of the testicular grafts and analyses of inhibin and testosterone production revealed no significant differences between the two immersion-time groups, indicating equal growth activity of the cryopreserved tissues. A single sperm obtained from a mouse in each group on day 230−350 was injected into an in vitro-matured porcine oocyte, and then the ICSI oocytes were transferred to the oviducts of estrus-synchronized recipient gilts. One out of 4 gilts that had received oocytes fertilized using sperm from the 10-min immersion group delivered 2 live piglets, and one of another 4 gilts from the 20-min group delivered 4 live piglets. Thus, we have successfully generated porcine offspring utilizing sperm from immature testicular tissues after cryopreservation and transplantation into nude mice. The present model using pigs will be applicable to many large animals, since pigs are phylogenetically distant from the murine recipients.

Spermatogonial stem cell preservation and transplantation: from research to clinic

STUDY QUESTION

What issues remain to be solved before fertility preservation and transplantation can be offered to prepubertal boys?

SUMMARY ANSWER

The main issues that need further investigation are malignant cell decontamination, improvement of in vivo fertility restoration and in vitro maturation.

WHAT IS KNOWN ALREADY

Prepubertal boys who need gonadotoxic treatment might render sterile for the rest of their life. As these boys do not yet produce sperm cells, they cannot benefit from sperm banking. Spermatogonial stem cell (SSC) banking followed by autologous transplantation has been proposed as a fertility preservation strategy. But before this technique can be applied in the clinic, some important issues have to be resolved.

STUDY DESIGN, SIZE DURATION

Original articles as well as review articles published in English were included in a search of the literature.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Relevant studies were selected by an extensive Medline search. Search terms were fertility preservation, cryopreservation, prepubertal, SSC, testis tissue, transplantation, grafting and in vitro spermatogenesis. The final number of studies selected for this review was 102.

MAIN RESULTS AND THE ROLE OF CHANCE

Cryopreservation protocols for testicular tissue have been developed and are already being used in the clinic. Since the efficiency and safety of SSC transplantation have been reported in mice, transplantation methods are now being adapted to the human testes. Very recently, a few publications reported on in vitro spermatogenesis in mice, but this technique is still far from being applied in a clinical setting.

LIMITATIONS, REASONS FOR CAUTION

Using tissue from cancer patients holds a potential risk for contamination of the collected testicular tissue. Therefore, it is of immense importance to separate malignant cells from the cell suspension before transplantation. Because biopsies obtained from young boys are small and contain only few SSCs, propagation of these cells in vitro will be necessary.

WIDER IMPLICATIONS OF THE FINDINGS

The ultimate use of the banked tissue will depend on the patient's disease. If the patient was suffering from a non-malignant disease, tissue grafting might be offered. In cancer patients, decontaminated cell suspensions will be injected in the testis. For patients with Klinefelter syndrome, the only option would be in vitro spermatogenesis. However, at present, restoring fertility in cancer and Klinefelter patients is not yet possible.

STUDY FUNDING/COMPETING INTEREST(S)

Research Foundation, Flanders (G.0385.08 to H.T.), the Institute for the Agency for Innovation, Belgium (IWT/SB/111245 to E.G.), the Flemish League against Cancer (to E.G.), Kom op tegen kanker (G.0547.11 to H.T.) and the Fund Willy Gepts (to HT). E.G. is a Postdoctoral Fellow of the FWO, Research Foundation, Flanders. There are no conflicts of interest.

Does early cell death cause germ cell loss after intratesticular tissue grafting?

OBJECTIVE

To assess cell death in intratesticular grafts.

DESIGN

Experimental animal study.

SETTING

University.

ANIMAL(S)

F1-hybrids from SV129 X C57BL.

INTERVENTION(S)

Intratesticular tissue transplantation was performed and cell death in the grafts was evaluated at different time points after transplantation.

MAIN OUTCOME MEASURE(S)

Apoptotic cell death in spermatogonia was evaluated by flow cytometry with the use of the annexin V assay. Immunohistochemistry was used to evaluate graft development and the global occurrence of cell death.

RESULT(S)

The highest level of spermatogonia-specific cell death was found on days 4 and 10, although no statistical difference was observed compared with control tissue. Statistically significant reductions in tubule integrity were observed 1 day and 2 months after transplantation. More degenerated tubules were observed in the center of the grafts 1 and 4 days after transplantation, and higher numbers of apoptotic tubules were found 1 day after transplantation. No difference in overall cell death was observed between grafts and controls for any time point except for the frozen grafts 1 day after transplantation.

CONCLUSION(S)

Spermatogonia-specific apoptosis does not explain the stem cell loss observed after intratesticular tissue grafting; it probably results from degeneration of tubules in the center of the graft owing to hypoxia during the first days after transplantation.

VEGFA family isoforms regulate spermatogonial stem cell homeostasis in vivo

The objective of the present study was to investigate vascular endothelial growth factor A (VEGFA) isoform regulation of cell fate decisions of spermatogonial stem cells (SSC) in vivo. The expression pattern and cell-specific distribution of VEGF isoforms, receptors, and coreceptors during testis development postnatal d 1-180 suggest a nonvascular function for VEGF regulation of early germ cell homeostasis. Populations of undifferentiated spermatogonia present shortly after birth were positive for VEGF receptor activation as demonstrated by immunohistochemical analysis. Thus, we hypothesized that proangiogenic isoforms of VEGF (VEGFA(164)) stimulate SSC self-renewal, whereas antiangiogenic isoforms of VEGF (VEGFA(165)b) induce differentiation of SSC. To test this hypothesis, we used transplantation to assay the stem cell activity of SSC obtained from neonatal mice treated daily from postnatal d 3-5 with 1) vehicle, 2) VEGFA(164), 3) VEGFA(165)b, 4) IgG control, 5) anti-VEGFA(164), and 6) anti-VEGFA(165)b. SSC transplantation analysis demonstrated that VEGFA(164) supports self-renewal, whereas VEGFA(165)b stimulates differentiation of mouse SSC in vivo. Gene expression analysis of SSC-associated factors and morphometric analysis of germ cell populations confirmed the effects of treatment on modulating the biological activity of SSC. These findings indicate a nonvascular role for VEGF in testis development and suggest that a delicate balance between VEGFA(164) and VEGFA(165)b isoforms orchestrates the cell fate decisions of SSC. Future in vivo and in vitro experimentation will focus on elucidating the mechanisms by which VEGFA isoforms regulate SSC homeostasis.

Expression of vascular endothelial growth factor (VEGF) transcript and protein in the testis of several vertebrates, including endangered species

Vascular endothelial growth factor (VEGF) is known to influence the testis function. To establish the role of VEGF in the testis of a variety of species, we analyzed the expression of VEGF transcript using human gene-specific primers by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis in the testes of 18 vertebrates, including a few endangered species. An amplicon of 566 bp representing VEGF(165) was identified in testis of all species in this study. Sequence analysis of these amplicons revealed 84 to 96% homology to available human VEGF sequence and to the VEGF sequences of other species in GenBank. Immunohistochemical analysis revealed expression of VEGF protein, primarily in Sertoli and Leydig cells and occasionally in the germ cells of the testis sections. It can be concluded from this study that expression of VEGF transcript is conserved in the testis of several vertebrates and may have a role in the process of spermatogenesis.

Effects of different storage protocols on cat testis tissue potential for xenografting and recovery of spermatogenesis

The loss of genetic diversity due to premature death of valuable individuals is a significant problem in animal conservation programs, including endangered felids. Testis tissue xenografting has emerged as a system to obtain spermatozoa from dead immature animals, however protocols to store this tissue before xenografting are still lacking. This study focused on testis tissue cryopreservation and storage from the domestic cat (Felis catus) classified as "pre-pubertal" and "pubertal" according to spermatogenesis development. Grafts from testis tissue cryopreserved with DMSO 1.4M, recovered after 10 weeks xenografting, presented seminiferous tubules with no germ cells. On the contrary, testis tissue from pre-pubertal animals preserved in ice-cold medium for 2 to 5 days presented no loss of viability or spermatogenic potential, while the number of grafts of pubertal cat testis tissue with germ cells after 10 weeks of xenografting decreased with increasing storage time. Nevertheless, even grafts from pre-pubertal cat testis tissue presented lower anti-DDX4 and anti-BOULE staining (proteins necessary for the meiosis completion), when compared with adult cat testis. Finally, a strong correlation found between testis weight and xenograft outcome may help choose good candidates for xenografting.

Effects of recipient mouse strain, sex and gonadal status on the outcome of testis tissue xenografting

The aim of the present study was to examine factors that may affect the outcome of testis tissue xenografting. Recipient factors were examined by grafting small fragments of testis tissue from newborn piglets under the back skin of immunodeficient mice of different strains (severe combined immunodeficiency (SCID) v. nude), sex (male v. female) and gonadal status (intact v. gonadectomised) using a factorial design (eight groups; n = 7 mice per group). Recipient mice were killed after 8 months to compare the gross and histological attributes of the recovered grafts. Overall, approximately 94% of grafts were recovered. Gonadectomy of male or female recipients did not affect any of the measured outcomes of testis tissue xenografting, therefore data were pooled. Overall, in terms of sex, male mice and, in terms of strain, SCID mice tended to show higher gross and histological development of grafts. The group of female nude mice had the lowest graft recovery rate (75%) compared with the other groups (95-100%; P < 0.05). The grafts from male SCID mice were, on average the largest and had the highest percentage of spermatozoa-containing seminiferous tubules among all the groups (P < 0.05). These results suggest that male SCID mice provide a suitable recipient model for testis tissue xenografting and that the mice do not need to be castrated for optimal results.

Meiotic activity in orthotopic xenografts derived from human postpubertal testicular tissue

BACKGROUND

Grafting of frozen-thawed testicular tissue has been suggested as a novel fertility preservation method for patients undergoing gonadotoxic treatments. However, this technique still needs further optimization before any clinical application. So far, grafting of human testicular tissue has only been performed to the back skin of nude mice and has shown spermatogonial stem-cell survival and occasionally differentiation up to primary spermatocytes. In this study, orthotopic grafting to mouse testes was evaluated as an alternative, and the effect of freezing and the donor's age was studied.

METHODS

Human testicular tissue was obtained from two prepubertal (aged 3 and 5) and two postpubertal (aged 12 and 13) boys. Both fresh and frozen-thawed testicular tissue was grafted to the testis of immuno-deficient nude mice. Four and nine months after transplantation, testes were analyzed by histology and immunohistochemistry.

RESULTS

Four and nine months after transplantation, spermatogonial stem cells were observed in all tissue grafts. Germ cell survival was found to be higher in xenografts from the older boys when compared with that from younger donors. Furthermore, no differentiation was observed in the xenografts from younger patients, but the grafts of two older donors showed differentiation up to the primary spermatocyte level, with the presence of secondary spermatocytes in the oldest donor 9 months after transplantation.

CONCLUSIONS

This xenografting study shows that intratesticular grafting results in high germ cell survival. In grafts derived from the older boys, meiotic activity was maintained in the xenografts for at least 9 months. Although difficult to conduct due to the scarcity of the tissue, more comparative research is needed to elucidate an optimal grafting strategy.

Xenografting as a tool to preserve endangered species: outcomes and challenges in model systems

The use of testis tissue xenografting as a valuable tool to rescue endangered and genetically valuable individuals that die young or otherwise fail to produce sperm has been the subject of much interest. Although the technique has been successfully applied to a wide variety of species, little is known about what determines the outcome. Furthermore, to improve the applicability of xenografting, new methods to preserve and transport testis tissue from valuable animals are emerging. However, one major issue remains: the application of xenografting implies the development of subsequent ART techniques to produce offspring from the recovered material. This paper focuses on these three aspects of testis tissue xenografting as a tool for rescuing endangered and valuable genetic pools.

The number of grafted fragments affects the outcome of testis tissue xenografting from piglets into recipient mice

To optimize the procedure for testis tissue xenografting, we grafted 2, 4, 8, or 16 small fragments of immature porcine testis tissue under the back skin of immunodeficient castrated mice (n = 10 mice/group). At 8 months post grafting, the graft recovery rate did not differ between groups; however, not only the total but also the average graft weights were higher (by ∼12-fold and ∼2.5-fold, resp.) in mice receiving 16 fragments than those receiving 2 fragments (P < .05). The recipient mice with 16 fragments had the largest vesicular glands (indicators of testosterone release by the grafts) compared with those with 2 fragments (P = .007). The grafts in the group of 16 fragments also had more (P < .05) percentage of tubules with round spermatids than those of the group of mice receiving 2 fragments. Therefore, recipient mice can be grafted with at least 16 testis tissue fragments for optimal results.

Development of strips of ovine testes after xenografting under the skin of mice and co-transplantation of exogenous spermatogonia with grafts

Xenografting of testicular tissue is an attractive new strategy for studying postnatal development of spermatogenesis and to preserve male genetics in large mammals. Typically, small cubes of immature testis (1 mm(3)) are grafted under the dorsal skin of immune-deficient mice. We attempted to increase the total number of seminiferous tubules in each xenograft with spermatogenesis by grafting flat strips of testis (approximately 9 x 5 x 1 mm) from ram lambs in immune-deficient mice. The percentage of grafts that survived and percentage of seminiferous tubules that developed spermatogenesis were the same as those reported after xenografting small cubes of lamb testis. Partially purified sheep spermatogonia were labeled with the fluorescent dye carboxy fluorescein diacetate succinyl diester and transplanted into the seminiferous tubules of one of the donor testis just before engraftment. The temporary label in the donor cells was detected for 4 weeks after xenografting, suggesting that co-engraftment of spermatogonia with testicular tissue may be a way to rapidly determine the effect of a specific gene on spermatogenesis. Finally, Sertoli cell lesions in xenografts of lamb testes were quantified, and their number and severity were found to increase, especially after grafts had been in place for 4 weeks. Although this coincided with the development of spermatogenesis, the extent of germ cell differentiation negatively correlated with severity of the lesions.

Recent developments in testis tissue xenografting

Development of the mammalian testis and spermatogenesis involve complex processes of cell migration, proliferation, differentiation, and cell–cell interactions. Although our knowledge of these processes has increased in the last few decades, many aspects still remain unclear. The lack of suitable systems that allow to recapitulate and manipulate both testis development and spermatogenesisex situhas limited our ability to study these processes. In the last few years, two observations suggested novel strategies that will improve our ability to study and manipulate mammalian spermatogenesis: i) testis tissue from immature animals transplanted ectopically into immunodeficient mice is able to respond to mouse gonadotropins and to initiate and complete differentiation to the level where fertilization-competent sperm are obtained, and ii) isolated testis cells are able to organize and rearrange into seminiferous cords that subsequently undergo complete development, including production of viable sperm. The current paper reviews recent advances that have been obtained with both techniques that represent novel opportunities to explore testis development and spermatogenesis in diverse mammalian species.

Vascular endothelial growth factor regulates germ cell survival during establishment of spermatogenesis in the bovine testis

Vascular endothelial growth factor-A (VEGFA) is a hypoxia-inducible peptide essential for angiogenesis and targets nonvascular cells in a variety of tissues and cell types. The objective of the current study was to determine the function of VEGF during testis development in bulls. We used an explant tissue culture and treatment approach to test the hypothesis that VEGFA-164 could regulate the biological activity of bovine germ cells. We demonstrate that VEGFA, KDR, and FLT1 proteins are expressed in germ and somatic cells in the bovine testis. Treatment of bovine testis tissue with VEGFA in vitro resulted in significantly more germ cells following 5 days of culture when compared with controls. Quantitative real-time RT-PCR analysis determined that VEGF treatment stimulated an intracellular response that prevents germ cell death in bovine testis tissue explants, as indicated by increased expression of BCL2 relative to BAX and decreased expression of BNIP3 at 3, 6, and 24 h during culture. Blocking VEGF activity in vitro using antisera against KDR and VEGF significantly reduced the number of germ cells in VEGF-treated testis tissue to control levels at 120 h. Testis grafting provided in vivo evidence that bovine testis tissue treated with VEGFA for 5 days in culture contained significantly more differentiating germ cells compared with controls. These findings support the conclusion that VEGF supports germ cell survival and sperm production in bulls.

Testicular angiogenic activity in response to food restriction in rabbits

The objective of this study was to evaluate the effects of two different levels of food restriction on testicular angiogenic activity, microvascularization, tissue growth, and regression, using the rabbit as a study model. The rabbits (Oryctolagus cuniculus cuniculus) were randomly assigned to a control group (A, n=5), fed ad libitum, and to groups B (n=5) and C (n=5), with two different levels of food restriction. Food restriction was responsible for a 21.2% decrease in body weight in group B and 34.7% in group C. Testis explants were cultured for 24 h and conditioned media were tested for their ability to stimulate mitogenesis of bovine aortic endothelial cells (BAEC). There was an increase in testicular microvascular area and mitogenesis of BAEC in group C rabbits. Despite no change in testicular DNA concentration among groups, food restriction decreased both RNA and protein compared with control. No treatment differences in the percentage of seminiferous tubules filled with all stages of spermatogenesis (spermatogonia, spermatocytes, and spermatids) and spermatozoa, as well as the area occupied by seminiferous tubules, were observed. Nevertheless, serum testosterone was markedly less in group C compared with groups A and B. These results suggest that angiogenesis may play a role in overcoming testicular nutritional impairment in rabbits subjected to food restriction.

Xenografting of sheep testis tissue and isolated cells as a model for preservation of genetic material from endangered ungulates

Recovery of germ cells could be an option for preservation of the genetic pool of endangered animals. In immature males, xenografting of testis tissue provides the opportunity to recover sperm from these animals. In adult animals, xenografting has been less successful, but de novo morphogenesis of functional testis tissue from dissociated testis cells could be an alternative. To assess the potential use of these techniques in endangered bovid species, the domestic sheep was used as a model. Testes from 2-week-old lambs were grafted as tissue fragments or cell suspensions into nude mice. Grafts were recovered at 4, 8, 12 and 16 weeks post grafting. For isolated cells, two additional time points at 35 and 40 weeks after grafting were added. In addition, to analyse the possible effect of social stress among mice within a group on the development of the grafts, testis tissue grafts were recovered 13 weeks post grafting from mice housed individually and in groups. Complete spermatogenesis occurred in sheep testis xenografts at 12 weeks, similar to the situation in situ. Isolated sheep testis cells were able to reorganize and form functional testicular tissue de novo. Housing mice individually or in groups did not have any effect on the development of xenografts. Xenografting of testis tissue might be useful to obtain sperm from immature endangered ungulates that die prematurely. Testis tissue de novo morphogenesis from isolated cells could open interesting options to recover germ cells from mature males with impaired spermatogenesis.

Analysis of Gene Expression in Bovine Testis Tissue Prior to Ectopic Testis Tissue Xenografting and During the Grafting Period1

The purpose of this study was to identify factors that contribute to bovine testis development and donor age-dependent differences in the abilities of bovine ectopic testis tissue grafts to produce elongated spermatids. We used real-time RT-PCR and microarrays to evaluate and to identify the expression of genes that are involved in Sertoli and germ cell development in bovine testis tissues. Testis tissues were obtained from 2-, 4-, and 8-wk-old bull calves and were grafted immediately. Grafted bovine testis tissue was removed from mice, RNA was isolated from the grafts, and real-time RT-PCR was used to evaluate gene expression during the grafting period. In addition, the gene expression in the donor tissue was analyzed using Affymetrix Bovine GeneChips, to identify differentially expressed genes. Examination of the testis tissue grafts indicated that Sertoli cell-specific gene expression was lower in 8-wk donor tissue grafts compared to the donors of other ages. Furthermore, the expression of KIT, which is a germ cell-specific gene, was low in testis tissue grafts. Microarray analysis of the donor tissue showed that several genes that are involved in angiogenesis or tissue growth were differentially expressed in 2-, 4-, and 8-wk-old bovine testes. The levels of expression of the genes for angiogenin, transgelin, thrombomodulin, early growth response 1, insulin-like growth factor 2, and insulin-like growth factor-binding protein 3 were lower in testis tissues from older animals. Using these data, it will be possible in the future to manipulate the testis xenograft microenvironment so as to improve the efficiency of sperm production within the graft.

Xenografting of adult mammalian testis tissue

Xenografting of testis tissue from immature males from several mammalian species to immunodeficient mouse hosts results in production of fertilization-competent sperm. However, the efficiency of testis tissue xenografting from adult donors has not been critically evaluated. Testis tissue xenografting from sexually mature animals could provide an option to preserve the genetic material from valuable males when semen for cryopreservation cannot be collected. To assess the potential use of this technique for adult individuals, testes from adult animals of six species (pig, goat, cattle, donkey, horse and rhesus monkey) were ectopically grafted to host mice. Grafts were recovered and analyzed at three time points: less than 12 weeks, between 12 and 24 weeks and more than 24 weeks after grafting. Histological analysis of the grafts revealed effects of species and donor tissue maturity: all grafts from species with greater daily sperm production (pig and goat) were found to have degenerated tubules or grafts were completely degenerated. None of the xenografts from mature adult bull and monkeys contained differentiated spermatogenic cells when examined more than 12 weeks post-grafting but tubules with Sertoli cells only remained. In grafts from a young adult bull, Sertoli cells persisted much longer than with the mature adult grafts. In grafts from a young adult horse, spermatogenesis proceeded to meiosis. In grafts from a young adult donkey and monkey, however, complete spermatogenesis was found in the grafts. These results show that testis tissue grafts from mature adult donors did not support germ cell differentiation but seminiferous tubules with Sertoli cells only survived in some species. The timing and progression of tubular degeneration after grafting of adult testis tissue appear to be related to the intensity of spermatogenesis at the time of grafting. Testis tissue from sub-adult donors survives better as xenograft than tissue from mature adult donors, and complete spermatogenesis can occur albeit with species-specific differences.

Spermatogenesis in testis xenografts grafted from pre-pubertal Holstein bulls is re-established by stem cell or early spermatogonia

Xenografting of testis explants into recipient mice has resulted in successful restoration of spermatogenesis in several species. Most studies have utilized neonatal donor tissue, although a few have used prepubertal testes. In Holstein bulls, prepubertal development of the testis occurs between 16 and 32 weeks of age. The purpose of the present study was to determine the optimal age during prepubertal development of Holstein bulls for testis grafting. Explants of testis tissue from Holstein bulls between 12 and 32 weeks of age (2 bulls/age; 6 ages) were subcutaneously grafted into castrated or intact immunocompromised mice (n=8/age), then recovered after 75 and 173 days (n=4 mice/grafting period) and evaluated histologically for spermatogenic progression. Seminiferous tubules were assigned a score based on the most advanced type of germ cell present within the tubule and the average for all tubules scored (n=25) within an explant was calculated. Scores for all explants per mouse (n=6) were averaged to give a single spermatogenic progression score per mouse. No difference in spermatogenic progression of grafts between intact and castrated recipients was observed. Spermatocytes were observed in testis grafts from bulls of all ages 75 days post-grafting. At 173 days, the spermatogenic progression score for explants derived from 20 weeks bulls was greater than all ages except 12 weeks donors (p<0.05), with 8% of tubules containing spermatids. Donor material from bulls older than 20 weeks had lesser spermatogenic progression scores largely attributed to the greater number of atrophic tubules in grafts from older donors. Grafts from 28 and 32 weeks donors showed signs of degeneration by 75 days post-grafting, with 30 and 55% atrophic tubules, respectively, and lesser spermatogenic efficiency scores. By 173 days post-grafting, 72% of tubules in explants from 32 weeks donors were atrophic. The results of the present study suggest that the early stages of prepubertal development are optimal for testis grafting while advanced spermatogenesis in the donor tissue prior to grafting had a negative effect on graft development. Spermatogenesis within the grafts apparently needs to be re-established by spermatogonial stem cells or early spermatogonia.