Efforts to create an artificial testis: culture systems of male germ cells under biochemical conditions resembling the seminiferous tubular biochemical environment

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.

Use of alginate hydrogel to improve long-term 3D culture of spermatogonial stem cells: stemness gene expression and structural features

The quality and quantity of a spermatogonial stem-cell (SSC) culture can be measured in less time using a 3D culture in a scaffold. The present study investigated stemness gene expression and the morphological and structural characterization of SSCs encapsulated in alginate. SSCs were harvested from BALB/c neonatal mice testes through two-step mechanical and enzymatic digestion. The spermatogonial populations were separated using magnetic-activated cell sorting (MACS) using an anti-Thy1 antibody and c-Kit. The SSCs then were encapsulated in alginate hydrogel. After 2 months of SSC culturing, the alginate microbeads were extracted and stained to evaluate their histological properties. Real-time polymerase chain reaction (PCR) was performed to determine the stemness gene expression. Scanning electron microscopy (SEM) was performed to evaluate the SSC morphology, density and scaffold structure. The results showed that encapsulated SSCs had decreased expression of Oct4, Sox2 and Nanos2 genes, but the expression of Nanog, Bcl6b and Plzf genes was not significantly altered. Histological examination showed that SSCs with pale nuclei and numerous nucleolus formed colonies. SEM evaluation revealed that the alginate scaffold structure preserved the SSC morphology and density for more than 60 days. Cultivation of SSCs on alginate hydrogel can affect Oct4, Sox2 and Nanos2 expression.

Evaluation of co-cultured spermatogonial stem cells encapsulated in alginate hydrogel with Sertoli cells and their transplantation into azoospermic mice

An in vitro spermatogonial stem cell (SSC) culture can serve as an effective technique to study spermatogenesis and treatment for male infertility. In this research, we compared the effect of a three-dimensional alginate hydrogel with Sertoli cells in a 3D culture and co-cultured Sertoli cells. After harvest of SSCs from neonatal mice testes, the SSCs were divided into two groups: SSCs on a 3D alginate hydrogel with Sertoli cells and a co-culture of SSCs with Sertoli cells for 1 month. The samples were evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays and bromodeoxyuridine (BrdU) tracing, haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) staining after transplantation into an azoospermic testis mouse. The 3D group showed rapid cell proliferation and numerous colonies compared with the co-culture group. Molecular assessment showed significantly increased integrin alpha-6, integrin beta-1, Nanog, Plzf, Thy-1, Oct4 and Bcl2 expression levels in the 3D group and decreased expression levels of P53, Fas, and Bax. BrdU tracing, and H&E and PAS staining results indicated that the hydrogel alginate improved spermatogenesis after transplantation in vivo. This finding suggested that cultivation of SSCs on alginate hydrogel with Sertoli cells in a 3D culture can lead to efficient proliferation and maintenance of SSC stemness and enhance the efficiency of SSC transplantation.

Progress and challenges in developing organoids in farm animal species for the study of reproduction and their applications to reproductive biotechnologies

Within the past decades, major progress has been accomplished in isolating germ/stem/pluripotent cells, in refining culture medium and conditions and in establishing 3-dimensional culture systems, towards developing organoids for organs involved in reproduction in mice and to some extent in humans. Haploid male germ cells were generated in vitro from primordial germ cells. So were oocytes, with additional support from ovarian cells and subsequent follicle culture. Going on with the female reproductive tract, spherical oviduct organoids were obtained from adult stem/progenitor cells. Multicellular endometrial structures mimicking functional uterine glands were derived from endometrial cells. Trophoblastic stem cells were induced to form 3-dimensional syncytial-like structures and exhibited invasive properties, a crucial point for placentation. Finally, considering the embryo itself, pluripotent embryonic cells together with additional extra-embryonic cells, could self-organize into a blastoid, and eventually into a post-implantation-like embryo. Most of these accomplishments have yet to be reached in farm animals, but much effort is devoted towards this goal. Here, we review the progress and discuss the specific challenges of developing organoids for the study of reproductive biology in these species. We consider the use of such organoids in basic research to delineate the physiological mechanisms involved at each step of the reproductive process, or to understand how they are altered by environmental factors relevant to animal breeding. We evaluate their potential in reproduction of animals with a high genetic value, from a breeding point of view or in the context of preserving local breeds with limited headcounts.

Advanced bioengineering of male germ stem cells to preserve fertility

In modern life, several factors such as genetics, exposure to toxins, and aging have resulted in significant levels of male infertility, estimated to be approximately 18% worldwide. In response, substantial progress has been made to improve in vitro fertilization treatments (e.g. microsurgical testicular sperm extraction (m-TESE), intra-cytoplasmic sperm injection (ICSI), and round spermatid injection (ROSI)). Mimicking the structure of testicular natural extracellular matrices (ECM) outside of the body is one clear route toward complete in vitro spermatogenesis and male fertility preservation. Here, a new wave of technological innovations is underway applying regenerative medicine strategies to cell-tissue culture on natural or synthetic scaffolds supplemented with bioactive factors. The emergence of advanced bioengineered systems suggests new hope for male fertility preservation through development of functional male germ cells. To date, few studies aimed at in vitro spermatogenesis have resulted in relevant numbers of mature gametes. However, a substantial body of knowledge on conditions that are required to maintain and mature male germ cells in vitro is now in place. This review focuses on advanced bioengineering methods such as microfluidic systems, bio-fabricated scaffolds, and 3D organ culture applied to the germline for fertility preservation through in vitro spermatogenesis.

Creation of a Model of Co-Culturing of Sertoli-Like Mouse Cells with Spermatogonial Cells

Sertoli-like cells is a cell population in the testes of adult mice capable of growth in culture and expressing many genes typical of Sertoli cells and supporting the development of germ cells in the gonad. A technique of co-culturing of Sertoli-like cells with spermatogonial cells was proposed that allows maintaining the growth and viability of germ cells and inducing their differentiation. This technique can provide the basis for obtaining fully differentiated germ cells in culture through using Sertoli-like cells as the supporting somatic cells.

Systemic LPS induces toll-like receptor 3 (TLR3) expression and apoptosis in testicular mouse tissue

It is well known that sepsis and inflammation reduce male fertility. Within the testis, toll-like receptor 3 (TLR3) is constitutively expressed and recognizes double-stranded RNA (dsRNA) from viruses, degraded bacteria, damaged tissues and necrotic cells. To characterize the potential role of TLR3 in response to testicular infections, its expression and downstream signaling were investigated upon challenge with lipopolysaccharides (LPS) in two mouse strains that differ in their immuno-competence regarding T cell-regulated immunity. Thereto, Balb/c and Foxn1nu mice were randomized into six interventional groups treated with either i.v. application of saline or LPS followed by 20 min, 5 h 30 min and 18 h of observation and two sham-treated control groups. LPS administration induced a significant stress response; the amplification was manifested for TLR3 and interleukin 6 (IL6) mRNA in the impaired testis 5 h 30 min after LPS injection. TLR3 immunostaining revealed that TLR3 was primarily localized in spermatocytes. The TLR3 expression displayed different temporal dynamics between both mouse strains. However, immunofluorescence staining indicated only punctual interferon regulatory factor 3 (IRF3) expression upon LPS treatment along with minor alterations in interferon β (IFNβ) mRNA expression. Induction of acute inflammation was closely followed by a significant shift of the Bax/Bcl2 ratio to pro-apoptotic signaling accompanied by augmented TUNEL-positive cells 18 h after LPS injection with again differing patterns in both mouse strains. In conclusion, this study shows the involvement of TLR3 in response to LPS-induced testicular inflammation in immuno-competent and -incompetent mice, yet lacking transmission into its signaling pathway.

Cellular and molecular characterization of gametogenic progression in ex vivo cultured prepuberal mouse testes

BACKGROUND

Recently, an effective testis culture method using a gas-liquid interphase, capable of differentiate male germ cells from neonatal spermatogonia to spermatozoa has been developed. Nevertheless, this methodology needs deep analyses that allow future experimental approaches in basic, pathologic and/or reprotoxicologic studies. Because of this, we characterized at cellular and molecular levels the entire in vitro spermatogenic progression, in order to understand and evaluate the characteristics that define the spermatogenic process in ex vivo cultured testes compared to the in vivo development.

METHODS

Testicular explants of CD1 mice aged 6 and 10 days post-partum were respectively cultured during 55 and 89 days. Cytological and molecular approaches were performed, analyzing germ cell proportion at different time culture points, meiotic markers immunodetecting synaptonemal complex protein SYCP3 by immunocytochemistry and the relative expression of different marker genes along the differentiation process by Reverse Transcription - quantitative Polymerase Chain Reaction. In addition, microRNA and piwi-interactingRNA profiles were also evaluated by Next Generation Sequencing and bioinformatic approaches.

RESULTS

The method promoted and maintained the spermatogenic process during 89 days. At a cytological level we detected spermatogenic development delays of cultured explants compared to the natural in vivo process. The expression of different spermatogenic stages gene markers correlated with the proportion of different cell types detected in the cytological preparations.

CONCLUSIONS

In vitro progression analysis of the different spermatogenic cell types, from both 6.5 dpp and 10.5 dpp testes explants, has revealed a relative delay in relation to in vivo process. The expression of the genes studied as biomarkers correlates with the cytologically and functional detected progression and differential expression identified in vivo. After a first analysis of deep sequencing data it has been observed that as long as cultures progress, the proportion of microRNAs declined respect to piwi-interactingRNAs levels that increased, showing a similar propensity than which happens in in vivo spermatogenesis. Our study allows to improve and potentially to control the ex vivo spermatogenesis development, opening new perspectives in the reproductive biology fields including male fertility.

Does Fluoride Affect Serum Testosterone and Androgen Binding Protein with Age-Specificity? A Population-Based Cross-Sectional Study in Chinese Male Farmers

Many studies have demonstrated that exposure to excess fluoride was associated with a variety of diseases. Little is known about the variation of testosterone (T) levels caused by fluoride exposure. The aim of this study is to explore the association of fluoride exposure and age with serum T and androgen-binding protein (ABP) levels in male farmers. A cross-sectional study was conducted in a county of Henan Province, China, including high fluoride exposure from drinking water villages and control villages. Male farmers aged 18-55 years old who lived in these villages were recruited by cluster sampling and divided into a higher fluoride exposure group (HFG) and a lower fluoride exposure group (LFG) according to the level of urinary fluoride. Levels of T and ABP in serum were measured using chemiluminescence immunoassay (CLIA) and enzyme-linked immunosorbent assay (ELISA) respectively. Markedly lower T levels were observed in male farmers from the HFG than in those from the LFG (t = 2.496, P < 0.05). Furthermore, younger farmers, 18-29 and 30-39 years old, may be the most likely to have lower T levels when exposed to fluoride (P < 0.05). No significant differences were observed in serum ABP levels in all male farmers between the two groups with different fluoride exposure. These results supported that excess fluoride exposure decreased serum T levels of male farmers with age-specificity.

Beyond the mouse monopoly: studying the male germ line in domestic animal models

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and essential to maintain the continuous production of spermatozoa after the onset of puberty in the male. The study of the male germ line is important for understanding the process of spermatogenesis, unravelling mechanisms of stemness maintenance, cell differentiation, and cell-to-cell interactions. The transplantation of SSCs can contribute to the preservation of the genome of valuable individuals in assisted reproduction programs. In addition to the importance of SSCs for male fertility, their study has recently stimulated interest in the generation of genetically modified animals because manipulations of the male germ line at the SSC stage will be maintained in the long term and transmitted to the offspring. Studies performed mainly in the mouse model have laid the groundwork for facilitating advancements in the field of male germ line biology, but more progress is needed in nonrodent species in order to translate the technology to the agricultural and biomedical fields. The lack of reliable markers for isolating germ cells from testicular somatic cells and the lack of knowledge of the requirements for germ cell maintenance have precluded their long-term maintenance in domestic animals. Nevertheless, some progress has been made. In this review, we will focus on the state of the art in the isolation, characterization, culture, and manipulation of SSCs and the use of germ cell transplantation in domestic animals.

Application of three-dimensional culture systems to study mammalian spermatogenesis, with an emphasis on the rhesus monkey (Macaca mulatta)

In vitro culture of spermatogonial stem cells (SSCs) has generally been performed using two-dimensional (2D) culture systems; however, such cultures have not led to the development of complete spermatogenesis. It seems that 2D systems do not replicate optimal conditions of the seminiferous tubules (including those generated by the SSC niche) and necessary for spermatogenesis. Recently, one of our laboratories has been able to induce proliferation and differentiation of mouse testicular germ cells to meiotic and postmeiotic stages including generation of sperm in a 3D soft agar culture system (SACS) and a 3D methylcellulose culture system (MCS). It was suggested that SACS and MCS form a special 3D microenvironment that mimics germ cell niche formation in the seminiferous tubules, and thus permits mouse spermatogenesis in vitro. In this review, we (1) provide a brief overview of the differences in spermatogenesis in rodents and primates, (2) summarize data related to attempts to generate sperm in vitro, (3) report for the first time formation of colonies/clusters of cells and differentiation of meiotic (expression of CREM-1) and postmeiotic (expression of acrosin) germ cells from undifferentiated spermatogonia isolated from the testis of prepubertal rhesus monkeys and cultured in SACS and MCS, and (4) indicate research needed to optimize 3D systems for in vitro primate spermatogenesis and for possible future application to man.

More attention should be paid to the treatment of male infertility with drugs--testosterone: to use it or not?

Testosterone replacement is strictly contraindicated for the treatment of male infertility’ was the advanced view from the ‘2013 European Association of Urology (EAU) guidelines on male infertility’, and this view brings extensive concern and questions. Although sufficient numbers of well-performed and controlled clinical trials that provide evidence supporting drug treatment of male infertility are not available at present, the opportunity to prove that these drugs are effective should not be prevented, and rigorous examination of drug therapy should be encouraged and strengthened. Therefore, I believe the above conclusion in the EAU guidelines is poorly conceived.

Hanging drop cultures of human testis and testis cancer samples: a model used to investigate activin treatment effects in a preserved niche

Background:

Testicular germ cell tumours of young adults, seminoma or non-seminomas, are preceded by a pre-invasive precursor, carcinoma in situ (CIS), understood to arise through differentiation arrest of embryonic germ cells. Knowledge about the malignant transformation of germ cells is currently limited by the lack of experimental models. The aim of this study was to establish an experimental tissue culture model to maintain normal and malignant germ cells within their niche and allow investigation of treatment effects.

Methods:

Human testis and testis cancer specimens from orchidectomies were cultured in ‘hanging drops' and effects of activin A and follistatin treatment were investigated in seminoma cultures.

Results:

Testis fragments with normal spermatogenesis or CIS cells were cultured for 14 days with sustained proliferation of germ cells and CIS cells and without increased apoptosis. Seminoma cultures survived 7 days, with proliferating cells detectable during the first 5 days. Activin A treatment significantly reduced KIT transcript and protein levels in seminoma cultures, thereby demonstrating a specific treatment response.

Conclusions:

Hanging drop cultures of human testis and testis cancer samples can be employed to delineate mechanisms governing growth of normal, CIS and tumorigenic germ cells retained within their niche.

Disturbances of sperm maturation and minipuberty: is there a connection?

Male reproductive function in the general population raises an increased attention due to reports indicating declining sperm counts, increased occurrence of testicular cancer, cryptorchidism, and hypospadias. It is also hypothesized that prolonged exposure of the developing male, during both fetal and postnatal life, to exogenous estrogens could reduce Sertoli cell number and thus reduce sperm output (and sperm counts) in adult life. Fact is that infertility, which is defined as the inability to conceive after 1 year of unprotected intercourse, has a global prevalence of 9%. A male contributory factor is involved in approximately half of these cases, but most of the causes of reduced semen quality and other disturbances of male reproductive function are unknown. In the most affected men (azoospermic men) 15-20% had a prior history of cryptorchidism. The association between the cryptorchidism and infertility is one of the most studied potential causes of infertility. There are numerous studies that accentuate the importance of minipuberty for future fertility. Is it possible that a normal minipuberty ensures normal fertility despite malpositioned testes? And to move away from cryptorchidism, could impaired minipuberty be responsible for fertility problems in men who were born with both testes in their scrotal sacs?

Concise review: Spermatogenesis in an artificial three-dimensional system

Culture of spermatogonial stem cells has been performed under a variety of conditions. Most featured two-dimensional systems, with different types of sera, conditioned media, feeder layers, and growth factors. Some have used three-dimensional (3D) matrices produced from gelatin, collagen, or other material. In spite of their increasingly sophisticated composition, however, complete spermatogenesis in vitro has not yet been achieved. In the seminiferous tubules, spermatogenesis occurs in an environment where cells are embedded in a 3D structure with specific niches regulating each stage of germ cell maturation mediated by hormones and paracrine/autocrine factors. We have recently reported achievement of complete in vitro spermatogenesis of mouse testicular germ cells in a 3D culture system featuring a soft agar matrix. This review discusses the advantages of the 3D culture system for studying the spermatogenic process in its entirety. Also discussed are the steps necessary to expand the applicability of the 3D culture system to human germ cell development and determine the functionality of culture-produced spermatozoa for generating offspring.

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.

Differentiation of murine male germ cells to spermatozoa in a soft agar culture system

Establishment of an in vitro system that allows the development of testicular germ cells to sperm will be valuable for studies of spermatogenesis and future treatments for male infertility. In the present study, we developed in vitro culture conditions using three-dimensional agar culture system (SACS), which has the capacity to induce testicular germ cells to reach the final stages of spermatogenesis, including spermatozoa generation. Seminiferous tubules from testes of 7-day-old mice were enzymatically dissociated, and intratubular cells were cultured in the upper layer of the SACS in RPMI medium supplemented with fetal calf serum (FCS). The lower layer of the SACS contained only RPMI medium supplemented with FCS. Colonies in the upper layer were isolated after 14 and 28 days of culture and were classified according to their size. Immunofluorescence and real-time PCR were used to analyse specific markers expressed in undifferentiated and differentiated spermatogonia (Vasa, Dazl, OCT-4, C-Kit, GFR-α-1, CD9 and α-6-integrin), meiotic cells (LDH, Crem-1 and Boule) and post-meiotic cells (Protamine-1, Acrosin and SP-10). Our results reveal that it is possible to induce mouse testicular pre-meiotic germ cell expansion and induce their differentiation to spermatozoa in SACS. The spermatozoa showed normal morphology and contained acrosomes. Thus, our results demonstrate that SACS could be used as a novel in vitro system for the maturation of pre-meiotic mouse germ cells to post-meiotic stages and morphologically-normal spermatozoa.

An in vitro, short-term culture method for mammalian haploid round spermatids amenable for molecular manipulation

Extensive chromatin remodeling is a characteristic feature of mammalian spermiogenesis. To date, methods for the molecular manipulation of haploid spermatids are not available as there is a lack of a well-established culture system. Biochemical experiments and knockout studies reveal only the final outcome; studying the incremental details of the intricate mechanisms involved is still a challenge. We have established an in vitro culture system for pure haploid round spermatids isolated from rat testes that can be maintained with good viability for up to 72 hr. Changes in cell morphology and flagellar growth were also studied in the cultured spermatids. Further, we have demonstrated that upon treatment of cells with specific histone deacetylase inhibitors, sodium butyrate and trichostatin A, there is an increase in the hyperacetylation status of histone H4, mimicking an important event characteristic of histone replacement process that occurs during later stages of spermiogenesis. We have also tried various methods for introducing DNA and protein into these round spermatids in culture, and report that while DNA transfection is still a challenging task, protein transfection could be achieved using Chariot™ peptide as a transfection reagent. Thus, the method described here sets a stage to study the molecular roles of spermatid-specific proteins and chromatin remodelers in the cellular context.

High-purity flow sorting of early meiocytes based on DNA analysis of guinea pig spermatogenic cells

Mammalian spermatogenesis is still nowadays poorly understood at the molecular level. Testis cellular heterogeneity is a major drawback for spermatogenic gene expression studies, especially when research is focused on stages that are usually very short and poorly represented at the cellular level such as initial meiotic prophase I (i.e., leptotene [L] and zygotene [Z]). Presumably, genes whose products are involved in critical meiotic events such as alignment, pairing and recombination of homologous chromosomes are expressed during the short stages of early meiotic prophase. Aiming to characterize mammalian early meiotic gene expression, we have found the guinea pig (Cavia porcellus) as an especially attractive model. A detailed analysis of its first spermatogenic wave by flow cytometry (FCM) and optical microscopy showed that guinea pig testes exhibit a higher representation of early meiotic stages compared to other studied rodents, partly because of their longer span, and also as a result of the increased number of cells entering meiosis. Moreover, we have found that adult guinea pig testes exhibit a peculiar 4C DNA content profile, with a bimodal peak for L/Z and P spermatocytes that is absent in other rodents. Besides, we show that this unusual 4C peak allows the separation by FCM of highly pure L/Z spermatocyte populations aside from pachytene ones, even from adult individuals. To our knowledge, this is the first report on an accurate and suitable method for highly pure early meiotic prophase cell isolation from adult mammals, and thus sets an interesting approach for gene expression studies aiming at a deeper understanding of the molecular groundwork underlying male gamete production.

Immunohistochemical and hybridocytochemical study on ghrelin signalling in the rat seminiferous epithelium

The results of presented study demonstrate expression of ghrelin, its functional receptor GHSR-1a and their genes in spermatogenic cells of rat testis suggesting their functioning within seminiferous epithelium. The immunohistochemical and hybrydocytochemical expression, of proteins and transcripts, was estimated taking into account the cycle of seminiferous epithelium and phases of spermatogenesis. Both transcripts and ghrelin was found to show nuclear expression and scarcely cytoplasmic. Expression of genes for ghrelin and GHSR-1a was shown in early spermatocytes and round spermatids representing transcriptional phases of meiosis and spermiogenesis. Ghrelin was evidenced to show nuclear expression in two stage-specific windows, in late spermatogonia, in spermatocytes up to early pachytenes, and again in spermatids of acrosome and early maturation phase of spermiogenesis. In late pachytenes, secondary spermatocytes, round spermatids, maturing spermatids and spermatozoa the reaction is lacking. With two types of antibodies against the GHSR-1a used the two different patterns of immunostaining was evidenced suggesting two isoforms of GHSR-1a. The first evidenced GHSR-1a in cytoplasm of spermatocytes, cell membrane and acrosomes of spermatids, Sertoli cell processes and heads of spermatozoa. With second type of antibodies the immunostaining marks all steps of evolution of acrosome in spermatids. It is believed that site of ghrelin expression in seminiferous epithelium may indicate its role in local regulations, not excepting the intracellular signalling. Immunostaining pattern for GHSR-1a seems to suggest both its participation in the cross-talk among the cells and also process of furnishing gametes with GHSR-1a for its response to ghrelin in seminal plasma or female reproductive tract.

New horizons for in vitro spermatogenesis? An update on novel three-dimensional culture systems as tools for meiotic and post-meiotic differentiation of testicular germ cells

Culture and differentiation of male germ cells has been performed for various purposes in the past. To date, none of the studies aimed at in vitro spermatogenesis has resulted in a sufficient number of mature gametes. Numerous studies have revealed worthy pieces of information, building up a body of information on conditions that are required to maintain and mature male germ cells in vitro. In this review, we report on previously published and unpublished experiments addressing murine germ cell differentiation in three-dimensional (3D) in vitro culture systems. In a systematic set of experiments, we examined the influence of two different matrices (soft agar and methylcellulose) as well as the need for gonadotrophin support. For the first time, we demonstrate that pre-meiotic male germ cells [revealed by the absence of meiotic marker expression (e.g. Boule)] obtained from immature mice pass through meiosis in vitro. After several weeks of culture, we obtained morphologically normal spermatozoa embedded in the matrix substance. Complete maturation relied on support from somatic testicular cells and the presence of gonadotrophins but appeared independent from the matrix in a 3D culture environment. Further research efforts are required to reveal the applicability of this culture technique for human germ cells and the functionality of the spermatozoa for generating offspring.

Estrogen receptor beta gene mutations in Indian infertile men

Recent studies suggest that estrogens play an important role in male fertility. Estrogen signaling is mediated by Estrogen Receptors (ERalpha and ERbeta). Association of ERbeta with male infertility has not been analyzed to date except for genotyping of known polymorphisms in two different studies, which yielded controversial interpretation. Hence, we performed sequencing of all the exons and untranslated regions of ERbeta gene in 300 infertile and 255 fertile control Indian men. We identified eight novel mutations and four known single nucleotide polymorphisms (SNPs). Of the eight novel mutations, four were non-synonymous, of which one was detected only in infertile men, whereas the other three mutations were detected only in fertile men. Using different bioinformatics tools, we predicted that non-synonymous mutations were benign and they neither altered the structure nor the function of the protein. Among synonymous novel mutations, one was detected in both fertile and infertile men, two were exclusive to infertile men and one was exclusive to fertile men. None of the known SNPs or novel mutations showed statistically significant difference between infertile and fertile men. Moreover, infertile men having ERbeta mutations had normal reproductive tract and serum hormone levels. Our results suggest that the SNPs and mutations in ERbeta gene are not a common cause of spermatogenesis failure in Indian men, although mutations specifically found in infertile men can affect transcription, translation or have synergic effect with other variants in causing infertility.

Negative influence of paternal age on clinical intracytoplasmic sperm injection cycle outcomes in oligozoospermic patients

OBJECTIVE

To evaluate the effect of male age on clinical outcomes of intracytoplasmic sperm injection (ICSI) cycles, according to sperm concentration.

DESIGN

Retrospective, observational study.

SETTING

Assisted reproduction center.

PATIENT(S)

The study included 1,024 couples undergoing ICSI cycles with fresh spermatozoa.

INTERVENTION(S)

The influence of paternal age on ICSI outcomes of oligozoospermic and normozoospermic patients was evaluated.

MAIN OUTCOME MEASURE(S)

Rates of high-quality embryos, pregnancy, implantation, and miscarriage were evaluated through linear logistic regression analyses.

RESULT(S)

When the sperm concentration was abnormal, paternal age influenced implantation (regression coefficient value = -0.7009) and pregnancy rates (odds ratio = 0.95, 95% confidence interval 0.91-0.99). However, in normozoospermic patients, no influence of paternal age was observed on implantation (regression coefficient value = 0.0566) or pregnancy rates (odds ratio = 1.00, 95% confidence interval 0.97-1.03).

CONCLUSION(S)

For couples in which the men are oligozoospermic, the implantation rate could be impaired by increased paternal age. In these couples, the chance of pregnancy decreased 5% for each year of paternal age. When men are normozoospermic, this effect is not observed.

Autonomous differentiation of Drosophila spermatogonia in vitro

Spermatogenesis is a complex process that produces functional sperm by establishing male germline stem cells (mGSCs) in adult testes. To study Drosophila spermatogenesis in vitro, we examined various culture conditions of spermatogonia. Spermatogonia from larval testes began to differentiate soon after culture, whereas mGSCs did not undergo self-renewal division. Strikingly, 16-cell spermatogonia from early and late larval testes differentiated into motile spermatids autonomously. Furthermore, individual spermatogonia developed into motile spermatids even after mechanical dissociation from encapsulating cyst cells. This is the first study to report that spermatogonia in larval testes retain the ability to differentiate into spermatids in the absence of gonadal tissue. Our in vitro system should provide an excellent opportunity to study spermatogenesis in detail and apply genetic manipulation.

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

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

In vitro differentiation of germ cells from nonobstructive azoospermic patients using three-dimensional culture in a collagen gel matrix

OBJECTIVE

To assess the effectiveness of the three-dimensional culture of spermatogenic cells in a collagen gel matrix from nonobstructive azoospermic patients and examine the relation between the success rate of in vitro spermatogenesis and serum FSH level as a diagnostic prediction.

DESIGN

Prospective study using radioimmunoassay, immunocytochemistry, and flow cytometry with primary cultured cells.

SETTING

Gynecologic clinics and human reproduction research laboratory.

PATIENT(S)

Primary culture of spermatogenic cells established from 18 nonobstructive azoospermic patients who underwent histologic diagnoses.

INTERVENTION(S)

Primary culture of spermatogenic cells in a collagen-based gel matrix, subjected to immunological and flow cytometric analyses.

MAIN OUTCOME MEASURE(S)

In vitro culture of spermatogenic cells was established in an extracellular milieu that more closely resembled the in vivo condition. The number of chromosomes in newly generated cells during culture was determined by fluorescence-activated cell sorter (FACS) and immunocytochemical analysis. Effects of FSH on the differentiation of the spermatogenic cells were measured.

RESULT(S)

Results of histologic studies indicated that 8 of 18 patients showed the spermatocyte arrest. Immunocytochemical and FACS analysis indicated that after 12 days in culture, haploid cells comprised 11%-37% of the cultured cell population with a characteristic expression of a cellular marker for spermatids. The serum level of FSH appeared to be closely correlated with an increase in the number of haploid cells in culture.

CONCLUSION(S)

The present three-dimensional culture in a collagen gel matrix provides a suitable means by which spermatocytes could be induced to differentiate into presumptive spermatids in vitro. In addition, the plasma FSH level could be a good indicator for the success of differentiation of cultured spermatogenic cells obtained from patients with spermatogenic arrest.

Genetic and epigenetic risks of intracytoplasmic sperm injection method

Pregnancies achieved by assisted reproduction technologies, particularly by intracytoplasmic sperm injection (ICSI) procedures, are susceptible to genetic risks inherent to the male population treated with ICSI and additional risks inherent to this innovative procedure. The documented, as well as the theoretical, risks are discussed in the present review study. These risks mainly represent that consequences of the genetic abnormalities underlying male subfertility (or infertility) and might become stimulators for the development of novel approaches and applications in the treatment of infertility. In addition, risks with a polygenic background appearing at birth as congenital anomalies and other theoretical or stochastic risks are discussed. Recent data suggest that assisted reproductive technology might also affect epigenetic characteristics of the male gamete, the female gamete, or might have an impact on early embryogenesis. It might be also associated with an increased risk for genomic imprinting abnormalities.

Successful long term culture of immature porcine sertoli cells in the reconstructed testicular cell cord

The ultimate goal of this study was to establish an in vitro system to produce sperms. To pursue this goal, immature porcine testicular cells were cultured in stereostructural form and cultured testicular cord was investigated morphologically. At 4 weeks of age, the seminiferous tubules of the porcine testes consisted of undifferentiated germ cells (gonocytes and undifferentiated spermatogonia) and immature Sertoli cells. The interstitial tissue was largely occupied by Leydig cells. The testes were enzymatically digested, and the dispersed cells were encapsulated with alginate either immediately or after freeze-thawing. The resulting testicular cell cords were cultured for up to 10 weeks. After 2 weeks of culture, Sertoli cells, which were identified by their inhibin-positive reaction in immunohistochemistry, and Leydig cells, which were identified by their morphological characteristics, were observed in the cords. Neither undifferentiated nor differentiated types of germ cells were detected. The number of cells in the cords progressively decreased during the culture period. In order to discover the fate of the Sertoli cells, the level of inhibin in the spent media was determined. Inhibin in the media was at a detectable level after 2 days of culture. The levels increased and peaked at 2 weeks. When frozen-thawed testicular cells were applied to the culture, the peak level was maintained for over 8 weeks, in contrast to the gradual decrease of inhibin level when fresh cells were cultured. These results indicate that the culture conditions can sustain the survival of Sertoli cells. Further improvement is required for proliferation and differentiation of germ cells.

Human testis in organotypic culture: application for basic or clinical research

BACKGROUND

Over recent decades, recurring efforts have been devoted to developing testicular cell or tissue cultures for basic and clinical research. However, there remains much confusion, particularly concerning the fate of human germ cells in culture.

OBJECTIVE

To reassess the status of human testicular cell types as well as the ability of germ cells to divide and differentiate in organotypic culture.

METHODS

Human testicular fragments were maintained for 2 weeks in culture. The viability and functionality of testicular cells were assessed using light and electronic microscopy, apoptotic cell labelling, 5-bromo-2'-deoxyuridine (BrdU) incorporation, immunohistochemistry and quantitative PCR against specific cell markers.

RESULTS

A gradual loss of meiotic and post-meiotic germ cells occurred throughout the culture period, irrespective of the presence of gonadotrophins. However, all germ cell types remained traceable for up to 16 days, some still dividing and differentiating at a rate compatible with the in vivo situation. Good maintenance of the general architecture of the explants associated with clearly quantifiable levels of several somatic cell markers was observed.

CONCLUSION

Although this culture model is clearly unsuitable for preparing germ cells for therapeutic purposes, it does represent a most valuable tool for testing the effects of biological and chemical agents on testicular tissue.