Comparative analysis of the germ cell markers c-KIT, SSEA-1 and VASA in testicular biopsies from secretory and obstructive azoospermias

Conversion from spermatogonia to spermatocytes: Extracellular cues and downstream transcription network

Spermatocyte (spc) formation from spermatogonia (spg) differentiation is the first step of spermatogenesis which produces prodigious spermatozoa for a lifetime. After decades of studies, several factors involved in the functioning of a mouse were discovered both inside and outside spg. Considering the peculiar expression and working pattern of each factor, this review divides the whole conversion of spg to spc into four consecutive development processes with a focus on extracellular cues and downstream transcription network in each one. Potential coordination among Dmrt1, Sohlh1/2 and BMP families mediates Ngn3 upregulation, which marks progenitor spg, with other changes. After that, retinoic acid (RA), as a master regulator, promotes A1 spg formation with its helpers and Sall4. A1-to-B spg transition is under the control of Kitl and impulsive RA signaling together with early and late transcription factors Stra8 and Dmrt6. Finally, RA and its responsive effectors conduct the entry into meiosis. The systematic transcription network from outside to inside still needs research to supplement or settle the controversials in each process. As a step further ahead, this review provides possible drug targets for infertility therapy by cross-linking humans and mouse model.

N-Cadherin Is Critical for the Survival of Germ Cells, the Formation of Steroidogenic Cells, and the Architecture of Developing Mouse Gonads

Normal gonad development assures the fertility of the individual. The properly functioning gonads must contain a sufficient number of the viable germ cells, possess a correct architecture and tissue structure, and assure the proper hormonal regulation. This is achieved by the interplay between the germ cells and different types of somatic cells. N-cadherin coded by the Cdh2 gene plays a critical role in this interplay. To gain an insight into the role of N-cadherin in the development of mouse gonads, we used the Cre-loxP system to knock out N-cadherin separately in two cell lines: the SF1⁺ somatic cells and the OCT4⁺ germ cells. We observed that N-cadherin plays a key role in the survival of both female and male germ cells. However, the N-cadherin is not necessary for the differentiation of the Sertoli cells or the initiation of the formation of testis cords or ovigerous cords. In the later stages of gonad development, N-cadherin is important for the maintenance of testis cord structure and is required for the formation of steroidogenic cells. In the ovaries, N-cadherin is necessary for the formation of the ovarian follicles. These results indicate that N-cadherin plays a major role in gonad differentiation, structuralization, and function.

A truncated form of a transcription factor Mamo activates vasa in Drosophila embryos

Expression of the vasa gene is associated with germline establishment. Therefore, identification of vasa activator(s) should provide insights into germline development. However, the genes sufficient for vasa activation remain unknown. Previously, we showed that the BTB/POZ-Zn-finger protein Mamo is necessary for vasa expression in Drosophila. Here, we show that the truncated Mamo lacking the BTB/POZ domain (MamoAF) is a potent vasa activator. Overexpression of MamoAF was sufficient to induce vasa expression in both primordial germ cells and brain. Indeed, Mamo mRNA encoding a truncated Mamo isoform, which is similar to MamoAF, was predominantly expressed in primordial germ cells. The results of our genetic and biochemical studies showed that MamoAF, together with CBP, epigenetically activates vasa expression. Furthermore, MamoAF and the germline transcriptional activator OvoB exhibited synergy in activating vasa transcription. We propose that a Mamo-mediated network of epigenetic and transcriptional regulators activates vasa expression.

A clinical trial on the consistency of bilateral testicular tissue histopathology and Johnsen score: single side or bilateral side biopsy?

To evaluate and compare left and right testicular tissue histopathology and Johnsen score, and to investigate the necessity for bilateral testicular biopsy. We recruited180 patients with non-obstructiveazoospermia (NOA) on testicular biopsy who had undergonetesticular sperm aspiration (TESA). Pathological sections of testicular tissue were diagnosed by specially-assigned doctors, who evaluated pathological findings, determined the Johnsen score and confirmed for the presence or absence of sperm. Sperm positive rates for left and right testicular histopathology were 55.0% and 51.7% respectively, and the proportion of Johnsen scores≥8 for left and right testes were 53.3% and 50.0%, respectively. Cohen kappa values revealed that the identification of sperm in bilateral testicular samples was not consistent and was related to random effects; Optimized cut-off value for bilateral testicular volume was 11ml (Johnsen score ≥8), and optimized cut-off values of E₂ on left and right testes were 144.5pmol/L and 133.5 pmol/L (Johnsen score≤7). However, age, serum prolactin (PRL), follicle stimulating hormone (FSH), luteinizing hormone (LH) and total testosterone (TT) levels were not accurate predictors for the existence of testicular sperm. There was nostatistical significance between left and right testicular histopathology in terms of sperm positive rates or Johnsen score; the Johnsen score were caused entirely by random effects and a score from one side could not represent the other side. Therefore, we recommend that both testes need to undergo surgery when NOA patients undergo testicular biopsy or sperm retrieval.

VASA mRNA (DDX4) detection is more specific than immunohistochemistry using poly- or monoclonal antibodies for germ cells in the male urogenital tract

VASA, also known as DDX4, is reported to be specifically expressed in cells belonging to the germ cell lineage, both in males and females. Therefore, it could be an informative protein biomarker to be applied on semen to differentiate between obstructive and nonobstructive azoospermia (OA and NOA, respectively). In addition, it could be of value to predict sperm retrieval based on testicular sperm extraction. Immunocytochemistry of proven OA semen using both polyclonal and monoclonal antibodies against VASA showed positive staining of both cells and cell sized particles. This is spite of being the absolute negative controls, completely lacking germ lineage derived cells and material. In order to identify the source of the VASA-positive material, a detailed screen of different anatomical parts of the whole male urogenital tract was performed of multiple cases using immunohistochemistry.The polyclonal antibody stained, besides the expected germ cells in the testis, epithelium of the bladder and the seminal vesicles. The monoclonal antibody only stained the latter. To investigate whether the immunohistochemical staining is associated with the presence of the corresponding VASA mRNA, samples of seminal vesicles, bladder, testis, and semen (with and without germ cells) were investigated using the specific quantitative reverse transcription-polymerase chain reaction (qRT-PCR) on 42 samples. A positive result was detected in testis and semen containing germ cells (n = 10 and 8), being negative in semen without germ cells (n = 11), bladder (n = 3), and seminal vesicles (n = 10).Two commercially available VASA antibodies (mono- and polyclonal) are not specific. In contrast, VASA-mRNA evaluation, using qRT-PCR, is specific for the presence of germ cells, therefore, is an interesting molecular biomarker for germ cell detection in semen.

Does detection of DDX4 mRNA in cell-free seminal plasma represents a reliable noninvasive germ cell marker in patients with nonobstructive azoospermia?

This study aimed to investigate the potential application of DDX4 gene expression in cell-free seminal mRNA as a noninvasive biomarker for the identification of the presence of germ cells in men with nonobstructive azoospermia and to correlate this factor with testicular biopsy. Male reproductive organ-specific genes were chosen: DDX4, which is a germ cell-specific gene and transglutaminase 4, which is a prostate-specific gene that was used as a control gene. Thirty-nine azoospermic males and twenty-eight normospermic fertile males (serving as a control group) participated in the study. Histopathological examination of testicular biopsies categorised azoospermic males into 20.5% with maturation arrest, 17.9% with incomplete Sertoli cell-only syndrome and 61.5% with complete Sertoli cell-only syndrome. Using real-time polymerase chain reaction, positivity for DDX4 gene was detected in 17 of 39 males with NOA which was due to maturation arrest in 35.3% (n = 6/17) of cases, due to incomplete Sertoli cell only in 23.5% (n = 4/17) and due to complete Sertoli cell only in 41.2% (n = 7/17). The study recommends joint utilisation of molecular transcripts as noninvasive biomarkers and histopathological examination of testicular biopsies in management of cases with azoospermia of the nonobstructive type.

Amniotic membrane mesenchymal stem cells can differentiate into germ cells in vitro

This is the first report on differentiation of mouse amniotic membrane mesenchymal stem cells (AM-MSCs) into male germ cells (GCs). AM-MSCs have the multipotent differentiation capacity and can be differentiated into various cell types. In the present study, AM-MSCs were induced for differentiation into GCs. AM-MSCs were isolated from mouse embryonic membrane by enzymatic digestion. AM-MSCs were characterized with osteogenic and adipogenic differentiation test and flow cytometric analysis of some CD-markers. AM-MSCs were induced to differentiate into GCs using a creative two-step method. Passage-3 AM-MSCs were firstly treated with 25 ng/ml bone morphogenetic protein 4 (BMP4) for 5 d and in continuing with 1 μM retinoic acid (RA) for 12 d (total treatment time was 17 d). At the end of the treatment period, real-time reverse transcription (RT)-PCR was performed to evaluate the expression of GC-specific markers-Itgb1, Dazl, Stra8, Piwil2, Mvh, Oct4, and c-Kit- in the cells. Moreover, flow cytometry and immunofluorescence staining were performed to evaluate the expression of Mvh and Dazl at protein level. Real-time RT-PCR showed that most of the tested markers were upregulated in the treated AM-MSCs. Furthermore, flow cytometric and immunofluorescence analyses both revealed that a considerable part of the treated cells expressed GC-specific markers. The percentage of positive cells for Mvh and Dazl was about 23 and 46%, respectively. Our results indicated that a number of AM-MSCs successfully differentiated into the GCs. Finally, it seems that AM-MSCs would be a potential source of adult pluripotent stem cells for in vitro generation of GCs and cell-based therapies for treatment of infertility.

Human spermatogonial stem cells display limited proliferation in vitro under mouse spermatogonial stem cell culture conditions

OBJECTIVE

To study the ability of human spermatogonial stem cells (hSSCs) to proliferate in vitro under mouse spermatogonial stem cell (mSSC) culture conditions.

DESIGN

Experimental basic science study.

SETTING

Reproductive biology laboratory.

PATIENT(S)

Cryopreserved testicular tissue with normal spermatogenesis obtained from three donors subjected to orchiectomy due to a prostate cancer treatment.

INTERVENTION(S)

Testicular cells used to create in vitro cell cultures corresponding to the following groups: [1] unsorted human testicular cells, [2] differentially plated human testicular cells, and [3] cells enriched with major histocompatibility complex class 1 (HLA^-)/epithelial cell surface antigen (EPCAM⁺) in coculture with inactivated testicular feeders from the same patient.

MAIN OUTCOME MEASURE(S)

Analyses and characterization including immunocytochemistry and quantitative reverse-transcription polymerase chain reaction for somatic and germ cell markers, testosterone and inhibin B quantification, and TUNEL assay.

RESULT(S)

Putative hSSCs appeared in singlets, doublets, or small groups of up to four cells in vitro only when testicular cells were cultured in StemPro-34 medium supplemented with glial cell line-derived neurotrophic factor (GDNF), leukemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF). Fluorescence-activated cell sorting with HLA^-/EPCAM⁺ resulted in an enrichment of 27% VASA⁺/UTF1⁺ hSSCs, compared to 13% in unsorted controls. Coculture of sorted cells with inactivated testicular feeders gave rise to an average density of 112 hSSCs/cm² after 2 weeks in vitro compared with unsorted cells (61 hSSCs/cm²) and differentially plated cells (49 hSSCS/cm²). However, putative hSSCs rarely stained positive for the proliferation marker Ki67, and their presence was reduced to the point of almost disappearing after 4 weeks in vitro.

CONCLUSION(S)

We found that hSSCs show limited proliferation in vitro under mSSC culture conditions. Coculture of HLA^-/EPCAM⁺ sorted cells with testicular feeders improved the germ cell/somatic cell ratio.

Recent insights on the significance of transcriptomic and metabolomic analysis of male factor infertility

Infertility is a worldwide reproductive health problem which affects approximately 15% of couples, with male factor infertility dominating nearly 50% of the affected population. The nature of the phenomenon is underscored by a complex array of transcriptomic, proteomic and metabolic differences which interact in unknown ways. Many causes of male factor infertility are still defined as idiopathic, and most diagnosis tends to be more descriptive rather than specific. As such, the emergence of novel transcriptomic and metabolomic studies may hold the key to more accurately diagnose and treat male factor infertility. This paper provides the most recent evidence underlying the role of transcriptomic and metabolomic analysis in the management of male infertility. A summary of the current knowledge and new discovery of noninvasive, highly sensitive and specific biomarkers which allow the expansion of this area is outlined.

Levels of liver X receptors in testicular biopsies of patients with azoospermia

OBJECTIVE

To determine whether the transcription factors liver X receptors (LXRs) and their downstream genes, which are involved in the regulation of several testicular functions in mouse models, are differentially expressed in testes of men with nonobstructive azoospermia (NOA) or obstructive azoospermia (OA).

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

Patients with various types of NOA (n=22) and with OA (n=5).

INTERVENTION(S)

Human testicular biopsies.

MAIN OUTCOME MEASURE(S)

Transcript levels were measured in testicular biopsies with the use of quantitative polymerase chain reaction. Correlations of LXR mRNA levels with the number of germ cells, the expression of proliferation and apoptosis markers, and the amount of intratesticular lipids and testosterone were evaluated. The localization of LXRα was analyzed by immunofluorescence.

RESULT(S)

LXR mRNA levels were decreased by 49%-98% in NOA specimens and positively correlated with germ cell number. Accumulations of IDOL and SREBP1c (LXR targets involved in lipid homeostasis) were 1.8-2.1 times lower in NOA samples and mRNA levels of the SREBP1c target gene ELOVL6 were increased 1.9-2.4-fold. Interestingly, the amount of triglycerides and free fatty acids were higher in NOA testes (3.4-12.2-fold). LXRα was present in Leydig cells. Accumulations of LXR downstream genes encoding the steroidogenic proteins StAR and 3βHSD2 were higher in NOA testes (5.9-12.8-fold).

CONCLUSION(S)

Knowledge of changes in the transcript levels of LXRs and some of their downstream genes during altered spermatogenesis may help us to better understand the physiopathology of testicular failure in azoospermic patients.

A combined approach facilitates the reliable detection of human spermatogonia in vitro

STUDY QUESTION

Does a combined approach allow for the unequivocal detection of human germ cells and particularly of spermatogonia in vitro?

SUMMARY ANSWER

Based on our findings, we conclude that an approach comprising: (i) the detailed characterization of patients and tissue samples prior to the selection of biopsies, (ii) the use of unambiguous markers for the characterization of cultures and (iii) the use of biopsies lacking the germ cell population as a negative control is the prerequisite for the establishment of human germ cell cultures.

WHAT IS KNOWN ALREADY

The use of non-specific marker genes and the failure to assess the presence of testicular somatic cell types in germ cell cultures may have led to a misinterpretation of results and the erroneous description of germ cells in previous studies.

STUDY DESIGN, SIZE, DURATION

Testicular biopsies were selected from a pool of 264 consecutively obtained biopsies. Based on the histological diagnosis, biopsies with distinct histological phenotypes were selected (n = 35) to analyze the expression of germ cell and somatic cell markers. For germ cell culture experiments, gonadotrophin levels and clinical data were used as selection criteria resulting in the following two groups: (i) biopsies with qualitatively intact spermatogenesis (n = 4) and (ii) biopsies from Klinefelter syndrome Klinefelter patients lacking the germ cell population (n = 3).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative real-time PCR analyses were performed to evaluate the specificity of 18 selected germ cell and 3 somatic marker genes. Cell specificity of individual markers was subsequently validated using immunohistochemistry. Finally, testicular cell cultures were established and were analyzed after 10 days for the expression of germ cell- (UTF1, FGFR3, MAGE A4, DDX4) and somatic cell-specific markers (SMA, VIM, LHCGR) at the RNA and the protein levels.

MAIN RESULTS AND THE ROLE OF CHANCE

Interestingly, only 9 out of 18 marker genes reflected the presence of germ cells and cell specificity could be validated using immunohistochemistry. Furthermore, VIM, SMA and LHCGR were found to reflect the presence of testicular somatic cells at the RNA and the protein levels. Using this validated marker panel and biopsies lacking the germ cell population (n = 3) as a negative control, we demonstrated that germ cell cultures containing spermatogonia can be established from biopsies with normal spermatogenesis (n = 4) and that these cultures can be maintained for the period of 10 days. However, marker profiling has to be performed at regular time points as the composition of testicular cell types may continuously change under longer term culture conditions.

LIMITATIONS, REASONS FOR CAUTION

There are significant differences regarding the spermatogonial stem cell (SSC) system and spermatogenesis between rodents and primates. It is therefore possible that marker genes that do not reflect the presence of spermatogonia in the human are specific for spermatogonia in other animal models.

WIDER IMPLICATIONS OF THE FINDINGS

While some studies have reported that human SSCs can be maintained in vitro and show characteristics of pluripotency, the germ cell origin and the differentiation potential of these cells were subsequently called into question. This study provides critical insights into possible sources for the misinterpretation of results regarding the presence of germ cells in human testicular cell cultures and our findings can therefore help to avoid conflicting reports in the future.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by the Stem Cell Network North Rhine-Westphalia and the Innovative Medical Research of the University of Münster Medical School (Grant KO111014). In addition, it was funded by the DFG-Research Unit FOR 1041 Germ Cell Potential (GR 1547/11-1 and SCHL 394/11-2), the BMBF (01GN0809/10) and the IZKF (CRA 03/09). The authors declare that there is no conflict of interest.

TRIAL REGISTRATION NUMBER

Not applicable.

Very small embryonic-like stem cells: implications in reproductive biology

The most primitive germ cells in adult mammalian testis are the spermatogonial stem cells (SSCs) whereas primordial follicles (PFs) are considered the fundamental functional unit in ovary. However, this central dogma has recently been modified with the identification of a novel population of very small embryonic-like stem cells (VSELs) in the adult mammalian gonads. These stem cells are more primitive to SSCs and are also implicated during postnatal ovarian neo-oogenesis and primordial follicle assembly. VSELs are pluripotent in nature and characterized by nuclear Oct-4A, cell surface SSEA-4, and other pluripotent markers like Nanog, Sox2, and TERT. VSELs are considered to be the descendants of epiblast stem cells and possibly the primordial germ cells that persist into adulthood and undergo asymmetric cell division to replenish the gonadal germ cells throughout life. Elucidation of their role during infertility, endometrial repair, superovulation, and pathogenesis of various reproductive diseases like PCOS, endometriosis, cancer, and so on needs to be addressed. Hence, a detailed review of current understanding of VSEL biology is pertinent, which will hopefully open up new avenues for research to better understand various reproductive processes and cancers. It will also be relevant for future regenerative medicine, translational research, and clinical applications in human reproduction.

A comprehensive review of genetics and genetic testing in azoospermia

Azoospermia due to obstructive and non-obstructive mechanisms is a common manifestation of male infertility accounting for 10-15% of such cases. Known genetic factors are responsible for approximately 1/3 of cases of azoospermia. Nonetheless, at least 40% of cases are currently categorized as idiopathic and may be linked to unknown genetic abnormalities. It is recommended that various genetic screening tests are performed in azoospermic men, given that their results may play vital role in not only identifying the etiology but also in preventing the iatrogenic transmission of genetic defects to offspring via advanced assisted conception techniques. In the present review, we examine the current genetic information associated with azoospermia based on results from search engines, such as PUBMED, OVID, SCIENCE DIRECT and SCOPUS. We also present a critical appraisal of use of genetic testing in this subset of infertile patients.

Divergent RNA-binding proteins, DAZL and VASA, induce meiotic progression in human germ cells derived in vitro

Our understanding of human germ cell development is limited in large part due to inaccessibility of early human development to molecular genetic analysis. Pluripotent human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have been shown to differentiate to cells of all three embryonic germ layers, as well as germ cells in vitro, and thus may provide a model for the study of the genetics and epigenetics of human germline. Here, we examined whether intrinsic germ cell translational, rather than transcriptional, factors might drive germline formation and/or differentiation from human pluripotent stem cells in vitro. We observed that, with overexpression of VASA (DDX4) and/or DAZL (Deleted in Azoospermia Like), both hESCs and iPSCs differentiated to primordial germ cells, and maturation and progression through meiosis was enhanced. These results demonstrate that evolutionarily unrelated and divergent RNA-binding proteins can promote meiotic progression of human-derived germ cells in vitro. These studies describe an in vitro model for exploring specifics of human meiosis, a process that is remarkably susceptible to errors that lead to different infertility-related diseases.

A novel application of cell-free seminal mRNA: non-invasive identification of the presence of germ cells or complete obstruction in men with azoospermia

BACKGROUND

Cell-free seminal mRNA (cfs-mRNA) exists in human ejaculate at high concentrations and with high stability, and contains many tissue-specific transcripts secreted from the male reproductive system. Owing to the sensitivity of RNA technology, cfs-mRNAs are ideal candidates for non-invasive biomarkers of physiopathological conditions. This study applied cfs-mRNA in identifying the presence of either germ cells or complete obstruction in men with azoospermia.

METHODS

RT-PCR was performed to amplify the germ cell-specific (DDX4), seminal vesicle-specific (SEMG1) and prostate-specific (TGM4) mRNAs from cfs-mRNAs, which were isolated from the seminal plasma of men with non-obstructive azoospermia (NOA) or obstructive azoospermia (OA). The 39 patients with NOA, diagnosed by testicular biopsy, included 8 men with maturation arrest (MA), 3 men with incomplete sertoli cell only (iSCO) syndrome and 28 men with complete SCO (cSCO). The 29 patients with OA, confirmed by the presence of sperm in the testis or epididymis, included 8 men with congenital bilateral absence of the vas deferens (CBAVD) and 21 men with non-CBAVD. Healthy individuals and vasectomized men were enrolled as controls.

RESULTS

TGM4 was detected in all participants. Consistent with their diagnosis, DDX4 was detected in all patients with MA or iSCO but was absent in most cases of cSCO (n = 21, 75.0%) or non-CBAVD (n = 18, 85.7%), and in all men with vasectomy or CBAVD. The presence of DDX4 in the other seven men with cSCO and three patients with non-CBAVD suggests the presence of germ cells in the testis, and incomplete obstruction, respectively. SEMG1 was undetectable in three patients with CBAVD with bilateral absence of the seminal vesicles, and in two non-CBAVD cases with low ejaculate volume.

CONCLUSIONS

These results suggest that, with high sensitivity and representativity, cfs-mRNA could be non-invasive biomarkers for identifying the presence of germ cells or complete obstruction in azoospermia.

Transient protection from heat-stress induced apoptotic stimulation by metastasis-associated protein 1 in pachytene spermatocytes

BACKGROUND

Deregulated thermal factors have been frequently implicated in the pathogenesis of male infertility, but the molecular basis through which certain responses are directed remain largely unknown. We previously reported that overexpression of exogenous Metastasis-associated protein 1 (MTA1) protects spermatogenic tumor cells GC-2spd (ts) against heat-induced apoptosis. To further dissect the underlying mechanism, we addressed here the fine coordination between MTA1 and p53 in pachytene spermatocytes upon hyperthermal stimulation.

METHODOLOGY/PRINCIPAL FINDINGS

High level of MTA1 expression sustained for 1.5 h in primary spermatocytes after heat stress before a notable decrease was detected conversely correlated to the gradual increase of acetylation status of p53 and of p21 level. Knockdown of the endogenous MTA1 in GC-2spd (ts) elevated the acetylation of p53 by diminishing the recruitment of HDAC2 and thereafter led to a dramatic increase of apoptosis after heat treatment. Consistent with this, in vivo interference of MTA1 expression in the testes of C57BL/6 mice also urged an impairment of the differentiation of spermatocytes and a disruption of Sertoli cell function due to the elevated apoptotic rate after heat stress. Finally, attenuated expression of MTA1 of pachytene spermatocytes was observed in arrested testes (at the round spermatid level) of human varicocele patients.

CONCLUSIONS

These data underscore a transient protective effect of this histone modifier in primary spermatocytes against heat-stress, which may operate as a negative coregulator of p53 in maintenance of apoptotic balance during early phase after hyperthermal stress.