In-vitro spermatogenesis resumption in men with maturation arrest: relationship with in-vivo blocking stage and serum FSH

In vitro spermatogenesis in artificial testis: current knowledge and clinical implications for male infertility

Men's reproductive health exclusively depends on the appropriate maturation of certain germ cells known as sperm. Certain illnesses, such as Klinefelter syndrome, cryptorchidism, and syndrome of androgen insensitivity or absence of testis maturation in men, resulting in the loss of germ cells and the removal of essential genes on the Y chromosome, can cause non-obstructive azoospermia. According to laboratory research, preserving, proliferating, differentiating, and transplanting spermatogonial stem cells or testicular tissue could be future methods for preserving the fertility of children with cancer and men with azoospermia. Therefore, new advances in stem cell research may lead to promising therapies for treating male infertility. The rate of progression and breakthrough in the area of in vitro spermatogenesis is lower than that of SSC transplantation, but newer methods are also being developed. In this regard, tissue and cell culture, supplements, and 3D scaffolds have opened new horizons in the differentiation of stem cells in vitro, which could improve the outcomes of male infertility. Various 3D methods have been developed to produce cellular aggregates and mimic the organization and function of the testis. The production of an artificial reproductive organ that supports SSCs differentiation will certainly be a main step in male infertility treatment.

Advances of three-dimensional (3D) culture systems for in vitro spermatogenesis

The loss of germ cells and spermatogenic failure in non-obstructive azoospermia are believed to be the main causes of male infertility. Laboratory studies have used in vitro testicular models and different 3-dimensional (3D) culture systems for preservation, proliferation and differentiation of spermatogonial stem cells (SSCs) in recent decades. The establishment of testis-like structures would facilitate the study of drug and toxicity screening, pathological mechanisms and in vitro differentiation of SSCs which resulted in possible treatment of male infertility. The different culture systems using cellular aggregation with self-assembling capability, the use of different natural and synthetic biomaterials and various methods for scaffold fabrication provided a suitable 3D niche for testicular cells development. Recently, 3D culture models have noticeably used in research for their architectural and functional similarities to native microenvironment. In this review article, we briefly investigated the recent 3D culture systems that provided a suitable platform for male fertility preservation through organ culture of testis fragments, proliferation and differentiation of SSCs.

Human in vitro spermatogenesis as a regenerative therapy - where do we stand?

Spermatogenesis involves precise temporal and spatial gene expression and cell signalling to reach a coordinated balance between self-renewal and differentiation of spermatogonial stem cells through various germ cell states including mitosis, and meiosis I and II, which result in the generation of haploid cells with a unique genetic identity. Subsequently, these round spermatids undergo a series of morphological changes to shed excess cytoplast, develop a midpiece and tail, and undergo DNA repackaging to eventually form millions of spermatozoa. The goal of recreating this process in vitro has been pursued since the 1920s as a tool to treat male factor infertility in patients with azoospermia. Continued advances in reproductive bioengineering led to successful generation of mature, functional sperm in mice and, in the past 3 years, in humans. Multiple approaches to study human in vitro spermatogenesis have been proposed, but technical and ethical obstacles have limited the ability to complete spermiogenesis, and further work is needed to establish a robust culture system for clinical application.

Haploid Germ Cells Generated in Organotypic Culture of Testicular Tissue From Prepubertal Boys

While in mice various studies have described the completion of spermatogenesis in vitro using either organotypic culture of prepubertal testicular tissue or 3D culture of isolated cells, in humans it has not been possible to achieve germ cell differentiation from immature testicular tissue (ITT). In our study, we evaluated the ability of human ITT to differentiate via a long-term organotypic culture of frozen–thawed 1 mm³ testicular fragments from five prepubertal boys in two different culture media. Tissue and supernatants were analyzed at regular intervals up to day 139. Sertoli cell (SC) viability and maturation was evaluated using immunohistochemistry (IHC) for SOX9, GDNF, anti-Mullerian hormone (AMH) and androgen receptor (AR), and AMH concentration in supernatants. Spermatogonia (SG) and proliferating cells were identified by MAGE-A4 (for SG) and Ki67 (for proliferating cells) via immunohistochemistry (IHC). Apoptotic cells were studied by active caspase 3. To evaluate Leydig cell (LC) functionality testosterone was measured in the supernatants and steroidogenic acute regulatory protein (STAR) IHC was performed. Germ cell differentiation was evaluated on Hematoxylin-Eosin histological sections, via IHC for synaptonemal complex 3 (SYCP3) for spermatocytes, Protein boule-like (BOLL) for spermatocytes and round spermatids, angiotensin-converting enzyme (ACE), protamine 2 and transition protein 1 (for elongated spermatids) and via chromogenic in situ hybridization (CISH). We reported the generation of meiotic and postmeiotic cells after 16 days of culture, as shown by the histological analyses, the presence of differentiation markers and the increase of haploid germ cells. We showed SC viability and maturation by a decrease of AMH secretion in the supernatants (p ≤ 0.001) while the number of SOX9 positive cells did not show any variation. A decrease of spermatogonia (p ≤ 0.001) was observed. The number of apoptotic cells did not vary. LC functionality was shown by the increase in STAR expression (p ≤ 0.007) and a peak in testosterone secretion, followed by a reduction (p ≤ 0.001) with stabilization. According to our knowledge, this is the first report of generation of haploid cells in human ITT. Differentiating germ cells have to be further evaluated for their ability to complete differentiation, their fecundability and epigenetic characteristics.

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.

Spermatogenesis in humans and its affecting factors

Spermatogenesis is an extraordinary complex process. The differentiation of spermatogonia into spermatozoa requires the participation of several cell types, hormones, paracrine factors, genes and epigenetic regulators. Recent researches in animals and humans have furthered our understanding of the male gamete differentiation, and led to clinical tools for the better management of male infertility. There is still much to be learned about this intricate process. In this review, the critical steps of human spermatogenesis are discussed together with its main affecting factors.

Models of in vitro spermatogenesis

Understanding the mechanisms that lead to the differentiation of male germ cells from their spermatogonial stem cells through meiosis to give rise to mature haploid spermatozoa has been a major quest for many decades. Unlike most other cell types this differentiation process is more or less completely dependent upon the cells being located within the strongly structured niche provided by mature Sertoli cells within an intact seminiferous epithelium. While much new information is currently being obtained through the application and description of relevant gene mutations, there is still a considerable need for in vitro models with which to explore the mechanisms involved. Not only are systems of in vitro spermatogenesis important for understanding the basic science, they have marked pragmatic value in offering ex vivo systems for the artificial maturation of immature germ cells from male infertility patients, as well as providing opportunities for the transgenic manipulation of male germ cells. In this review, we have summarized literature relating to simplistic culturing of germ cells, co-cultures of germ cells with other cell types, especially with Sertoli cells, cultures of seminiferous tubule fragments, and briefly mention the opportunities of xenografting larger testicular pieces. The majority of methods are successful in allowing the differentiation of small steps in the progress of spermatogonia to spermatozoa; few tolerate the chromosomal reduction division through meiosis, and even fewer seem able to complete the complex morphogenesis which results in freely swimming spermatozoa. However, recent progress with complex culture environments, such as 3-d matrices, suggest that possibly success is now not too far away.

Quantitative analysis of cellular proliferation and differentiation of the human seminiferous epithelium in vitro

The aim of the present work was to quantitate the temporal and stage-specific effects of follicle-stimulating hormone (FSH) and testosterone on the proliferation and differentiation capacities of the human seminiferous epithelium. Seminiferous tubule fragments were kept in culture for 28 days and 5-bromo-2'-deoxyuridine incorporation was used to determine cell proliferation. Data demonstrated a gradual loss of germ cells during the culture period, no decrease in Sertoli cell numbers, and maintenance of the general architecture of the seminiferous tubules. Both FSH and testosterone increased germ cell survival, spermatogonia proliferation, and germ cell differentiation, especially during the first week of culture. At the end of the first week, differentiation of spermatocytes was observed, especially when 50 IU/L FSH and 1 µmol/L testosterone were used. In conclusion, using this methodology, it was possible to quantify germ cell proliferation and differentiation, in a reproducible way, with results compatible with the timing of human spermatogenesis in vivo.

Long-term proliferation and characterization of human spermatogonial stem cells obtained from obstructive and non-obstructive azoospermia under exogenous feeder-free culture conditions

OBJECTIVES

The aim of the present study was to improve efficiency of isolation and to optimize proliferative potential of human spermatogonial stem cells (SSCs) obtained from obstructive azoospermic (OA) and non-obstructive azoospermic (NOA) patients, and further, to characterize these cells for potential use in infertility treatment or study of reproductive biology.

MATERIALS AND METHODS

We have applied a cell-sorting method, using collagen and magnetic activated cell separation to overcome obstacles, developing a collection system, and simple long-term proliferation system, that yields large numbers of high-purity SSCs from obstructive OA and NOA patients.

RESULTS

SSCs derived from OA and NOA patients proliferated and maintained their characteristics for more than 12 passages (>6 months) in vitro. Moreover, the population of cells positive for the SSC-specific markers GFRalpha-1 and integrin alpha6, increased to more than 80% at passage 8.

CONCLUSION

These finding may support the idea that in vitro propagation of SSCs could be a useful tool for infertility treatment and study of reproductive biology.

Differentiation of human round spermatids into motile spermatozoa through in vitro coculture with Vero cells

Purpose

This study was undertaken to examine whether human early round spermatids will differentiate in an in vitro coculture with Vero cells.

Methods

A total of 1450 and 400 isolated early round spermatids mechanically collected from two non-obstructive and three obstructive azoospermic men with a normal karyotype were cocultured on Vero cell monolayers in minimum essential medium plus 10% fetal bovine serum, with or without 50 or 100 IU/L FSH and 1 or 10 μmol/L testosterone, at 32.5°C, in an environment of 5% CO₂ in air. Morphological changes of the spermatids were observed microscopically.

Results

After 7 days of coculture, almost half (40-50%) of the round spermatids from both non-obstructive and obstructive azoospermic men resumed spermiogenesis in vitro. Only cells from the latter patients gave rise to spermatozoa, a few of which had a motile flagellum. Low concentrations of FSH and testosterone increased the percentage of in vitro spermiogenesis.

Conclusions

Isolated round spermatids can resume spermiogenesis in vitro when cocultured on a Vero cell monolayer.

Isolated spermatogonia protrude active pseudopodia in vitro

When dispersed spermatogenic cells obtained by enzymatic digestion from prepuberal mice, adult male mice, nonazoospermic men and normospermic men were observed live using Normarski optics, it was found that, respectively, 47.4%, 1.4%, 5.1%, and 2.4% of them protruded active pseudopodia. These cells were 8 to 10 mum in diameter, had a high N/C ratio, and had one to two prominent nucleoli that were close to a distinct nuclear membrane. They showed low alkaline phosphatase activities and homogeneous nuclear immunoreactive patterns using gamma-H2AX, which suggests that they were spermatogonia.

Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Intracytoplasmic sperm injection (ICSI) has become the method of choice to overcome male infertility when all other forms of assisted fertilization have failed. Animals in which ICSI has produced normal offspring include many species. Success rate with normal spermatozoa is well above 50% in the mouse but ICSI success rates in other animals have been low, ranging from 0.3 to 16.5%. Mouse ICSI revealed that spermatozoa that cannot participate in normal fertilization can produce normal offspring by ICSI, provided their nuclei are genomically intact. Human ICSI using infertile spermatozoa has been highly successful perhaps because of the intrinsic instability of human sperm plasma membrane. The health of children born after ICSI and other assisted fertilization techniques is of major concern. Careful analyses suggest that higher incidences of congenital malformations and/or low birth weights after assisted fertilization are largely attributable to parental genetic background and increased incidence of multiple births, rather than to the techniques of assisted fertilization. Since the physiological and nutritional environments of developing embryos may cause persisting alteration in DNA methylation, extreme caution must be exercised in handling gametes and embryos in vitro. In the mouse, round spermatid injection (ROSI) has been routinely successful but its use in humans is controversial. Whether human ROSI and assisted fertilization involving younger spermatogenic cells are medically safe must be the subject of further investigations.

The role of mitochondria in the establishment of oocyte functional competence

Mitochondria are maternally inherited, semi-autonomous organelles with their own genomes (mtDNA), largely responsible for the generation of energy in the form of cellular ATP. However, mitochondrial replication and transcription of mtDNA do not commence until well into embryonic differentiation. This means that the oocyte needs to contain sufficient stocks of functioning mitochondria to fuel the first few days of embryonic development. In this review, I examine how qualitative and quantitative aspects of mitochondria help us define the notion of functional competence.

Overcoming maturation arrest by in vitro spermatogenesis: search for the optimal culture system

In some men with nonobstructive azoospermia caused by germ cell maturation arrest, spermatogenesis can be reactivated in vitro, either by culturing segments of explanted seminiferous tubules or by coculturing isolated germ cells on monolayers of somatic cell lines. Further studies are needed to compare the efficacy of these two culture systems in terms of restoration of fertilizing ability of in vitro-formed gametes and to evaluate the safety of the clinical use of these cells in assisted reproduction treatment.

Assessment of Sertoli cell functional reserve and its relationship to sperm parameters

Sertoli cell functional reserve was assessed in normozoospermic men and oligozoospermic patients and its prognostic potential was evaluated for patient selection and treatment. For the first objective, three groups of normo-follicle-stimulating hormone (FSH)/normozoospermic fertile men (n:12), normo-FSH/oligozoospermic (n:21) and hyper-FSH/oligozoospermic subfertile men participated in the study whereas for the second objective 24 normo-FSH oligozoospermic patients volunteered for a pilot therapeutic trial. For the first part, high purity (hp) FSH (225 i.u., i.m.), human chorionic gonadotropin (hCG) (1500 i.u., i.m.) or their combination was given separately at weekly intervals, with samplings at 0, 3, 24 and 48 h. For the pilot trial, rec-FSH (150 i.u./48 h, i.m.) or placebo were prescribed for 6 months. The main outcome measures for the study were inhibin-B (inh-B), insulin-like growth factor (IGF)-I, testosterone and oestradiol concentrations and the main sperm parameters. Bolus administration of hp-FSH or hp-FSH/hCG combination in normozoospermic men resulted in a significant rise of inh-B in normozoospermic men (mean +/- SD, basal: 183.8+/-24.2 pg/mL in hp-FSH and 175.2+/-23.5 in hp-FSH/hCG treatment; 48 h: 256.1+/-34.2 and 246.3+/-19.0, respectively, p<0.001 for both). In oligozoospermic groups basal inh-B concentration was lower than in normozoospermic men (normo-FSH: 117.4+/-16.5, hyper-FSH: 81.2+/-19.8, p<0.001 for both) with a post-stimulation increase noted only in normo-FSH patients (hp-FSH 24-h: 132.8+/-19.7, p<0.01; hp-FSH/hCG 0 min: 105.7+/-20.1, 24-h: 119.5+/-20.6, p<0.05). Total sperm number and progressive motility showed significant improvements (p<0.05 for both) after 6 months of rec-FSH treatment in the group of patients with a satisfactory response to hp-FSH stimulation. In conclusion, the basal and reserve activity of Sertoli cells, as judged by inh-B secretion, was higher in normozoospermic than in dyspermic men, with a better therapeutic outcome noted in those patients with an adequate response to hp-FSH stimulation.

Pharmacological concentrations of follicle-stimulating hormone and testosterone improve the efficacy of in vitro germ cell differentiation in men with maturation arrest

OBJECTIVE

To examine whether in vitro differentiation of germ cells from men with maturation arrest is improved by augmenting FSH and T concentrations above the values effective in samples from men with normal spermatogenesis.

DESIGN

Prospective, controlled in vitro study.

SETTING

Private assisted reproduction centers and a university department.

PATIENT(S)

Men with meiotic or postmeiotic maturation arrest.

INTERVENTION(S)

Testicular spermatid extraction, in vitro culture of testicular biopsy samples, intraoocyte injection of elongated spermatids, embryo culture and transfer.

MAIN OUTCOME MEASURE(S)

Progression of in vitro germ cell differentiation, fertilization, and pregnancy outcomes with in vitro cultured germ cells.

RESULT(S)

In some cases of meiotic and postmeiotic maturation arrest, more advanced germ cell stages were achieved by in vitro culture in the presence of 500 IU/L FSH as compared with 50 IU/L FSH. The beneficial effect of 500 IU/L FSH was further potentiated by a simultaneous increase of T concentration from 1 to 10 microM. Fertilizations with germ cells recovered after incubation with these pharmacological hormone concentrations gave rise to viable embryos and the births of five healthy babies.

CONCLUSION(S)

Pharmacological concentrations of FSH and T are beneficial for in vitro maturation of germ cells from some men with in vivo maturation arrest.

Assisted reproduction with in-vitro-cultured testicular spermatozoa in cases of severe germ cell apoptosis: a pilot study

BACKGROUND

Apoptosis-related cell damage is known to compromise success rates of assisted reproduction with ejaculated spermatozoa. This study was undertaken to determine whether the frequency of apoptosis-related cell damage and reproductive performance of testicular spermatozoa from men with non-obstructive azoospermia can be improved by in-vitro culture.

METHODS

Testicular tissue samples were cultured for 2 days in the presence of 50 IU/l FSH and 1 micromol/l testosterone. The frequency of spermatozoa showing DNA strand breakage and plasma membrane phosphatidylserine externalization was compared in before-culture and after-culture samples. The after-culture samples were used in assisted reproduction attempts.

RESULTS

In a group of 11 azoospermic patients with at least two previous intracytoplasmic sperm injection (ICSI) failures, the incidence of DNA strand breakage was high in living testicular spermatozoa from before-culture samples, but significantly lower in after-culture samples (96 versus 30%, P < 0.001). The same applied to the incidence of phosphatidylserine externalization in the motile sperm subpopulation from the before-culture and after-culture samples (83 versus 6%, P < 0.001). Seven ongoing clinical pregnancies (six with fresh embryos and one with cryopreserved embryos) were established.

CONCLUSIONS

Severe testicular sperm apoptosis may become a new indication for testicular tissue in-vitro culture before ICSI.

Present and future therapeutic strategies for idiopathic oligozoospermia

The effectiveness of medical treatment for idiopathic oligozoospermia (IO) has been at best doubtful until now and a logical consequence of this unsatisfactory situation has been the partial displacement of this approach by assisted reproduction techniques. This state of affairs has resulted from insufficient investigation, inappropriately designed clinical trials and consistent disregard for the principles of evidence-based medicine. Protocol-related shortcomings and wrong interpretation of the data available have also been some of the all too frequent problems encountered in this therapeutic approach. In this rather misty situation, it appears that, of the therapeutic agents used so far, follicle stimulating hormone (FSH) (mainly FSH-secretagogues) may exert some beneficial effects on a number of biological endpoints related to spermatogenesis and sperm maturation. The short and medium term prospects of medical treatment for IO rest mainly with improvement of investigative procedures to a higher degree of sophistication, with emphasis placed on identifying the causes rather than the results of dysfunction so that a better selection of candidates can be made. Moreover, the introduction of prognostic indices for evaluation of the beneficial effects of a therapeutic agent may be of paramount importance. Finally, a better assessment of the preparations available and, possibly, the introduction of new more specific agents may also be an important step forward in this field. This type of large-scale effort should not be left to individual investigators or special centres working independently, but it may come under the auspices of a central regulating agency so that undisputed results from large, multicentre and uniform studies might be obtained, if medical treatment is to remain a good option. In this context, it may also be emphasized that andrology's main task should always be to treat the male with the problem rather than his healthy female partner, whenever this is possible.

Immature germ cell conception-in vitro germ cell manipulation

Experimental studies in laboratory animals have shown that successful conception can be achieved by fertilizing oocytes with immature male germ cells. This gave rise to the concept that immature germ cells recovered from the testes of azoospermic men with maturation arrest may be used for assisted reproduction. However, in contrast to using germ cells recovered from healthy animals, clinical application to the treatment of male sterility is burdened by inherent defects in germ cells attributable to underlying testicular pathology. The recent introduction of in vitro germ cell culture/manipulation techniques makes it possible, in some cases, to overcome the in vivo maturation arrest by allowing an additional meiotic and post-meiotic differentiation and the selective harvesting of cells devoid of apoptosis-related nuclear and cytoplasmic damage. These techniques enabled the first births of normal infants fathered by azoospermic men with maturation arrest at the primary spermatocyte stage and improved the efficacy of assisted reproduction in men with maturation arrest at the round spermatid stage.