Signaling pathways in spermatogonial stem cells and their disruption by toxicants

Application of testicular organ culture system for the evaluation of spermatogenesis impairment

Recently, it was reported that a testicular organ culture system (TOCS) using polydimethylsiloxane (PDMS) chips with excellent oxygen permeability and biocompatibility, called the PDMS-chip ceiling (PC) method, enables improved spermatogenesis efficiency. We investigated whether this PC method is useful for detecting impaired spermatogenesis caused by busulfan (Bu), a typical testicular toxicant. In this study, testicular tissue fragments from Acro3-EGFP mice, which express the green fluorescent protein (GFP) and reflect the progression of spermatogenesis, were subjected to the PC method. When treated with Bu, cultured tissues shrank in volume, and their GFP-expressing area decreased or disappeared. Histological examination confirmed the regression of spermatogenesis. In addition, immunohistochemical examination revealed that spermatogonia, including spermatogonial stem cells (SSCs), were the primary targets of Bu toxicity. Time-course analysis demonstrated that the recovery of spermatogenesis, dependent on Bu concentration, correlated closely with the severity of damage to these target cells. These results suggest that the PC method is a useful approach for detecting spermatogenesis impairment accurately through faithful recapitulation of spermatogenesis in vivo.

Synthetic human gonadal tissues for toxicology

The process of mammalian reproduction involves the development of fertile germ cells in the testis and ovary, supported by the surrounders. Fertilization leads to embryo development and ultimately the birth of offspring inheriting parental genome information. Any disruption in this process can result in disorders such as infertility and cancer. Chemical toxicity affecting the reproductive system and embryogenesis can impact birth rates, overall health, and fertility, highlighting the need for animal toxicity studies during drug development. However, the translation of animal data to human health remains challenging due to interspecies differences. In vitro culture systems offer a promising solution to bridge this gap, allowing the study of mammalian cells in an environment that mimics the physiology of the human body. Current advances on in vitro culture systems, such as organoids, enable the development of biomaterials that recapitulate the physiological state of reproductive organs. Application of these technologies to human gonadal cells would provide effective tools for drug screening and toxicity testing, and these models would be a powerful tool to study reproductive biology and pathology. This review focuses on the 2D/3D culture systems of human primary testicular and ovarian cells, highlighting the novel approaches for in vitro study of human reproductive toxicology, specifically in the context of testis and ovary.

Effects of bisphenol A on cardiovascular disease: An epidemiological study using National Health and Nutrition Examination Survey 2003-2016 and meta-analysis

As the most widely consumed endocrine-disrupting chemical, bisphenol A (BPA) has been linked to reproductive dysfunction, diabetes mellitus, and obesity. However, the evidence for an association between BPA and cardiovascular disease (CVD) remains insufficient. In the present study, we aimed to identify the association between BPA and CVD, using data from the 2003-2016 National Health and Nutrition Examination Surveys (NHANES). We estimated urine BPA concentration after adjustments for creatinine (ng/mg) and normalized the asymmetrical distribution using natural logarithmic transformation (ln-BPA/Cr). A multivariate logistic regression was performed to evaluate the odds ratio (OR) and 95% confidence interval (CI) for CVD, with ln-BPA/Cr concentration as predictor. We then performed a Mantel-Haenszel meta-analysis with five eligible studies and NHANES 2003-2016 data. Our subjects were 11,857 adults from the NHANES data. After adjusting for age, sex, race/ethnicity, body mass index (BMI), cigarette smoking, diabetes status, hypertension, and dyslipidemia, OR between ln-BPA/Cr and CVD was 1.13 (95% CI: 1.02-1.24). After propensity-score-matching with age, sex, race/ethnicity, BMI, cigarette smoking, diabetes, hypertension, and dyslipidemia, OR continued to be significant for the association between ln-BPA/Cr and CVD (OR: 1.18, 95% CI: 1.04-1.33). A restricted cubic spline plot of this relationship revealed a dose-dependent increase in OR. However, untransformed BPA had a linear relationship with CVD only at low concentrations, whereas the OR of BPA plateaued at high concentrations. In a meta-analysis with 22,878 subjects, after adjusting for age, sex, and various cardiometabolic risk factors, OR was 1.13 (95% CI, 1.03-1.23). In conclusion, our study provides additional epidemiological evidence supporting an association between BPA and CVD.

Improvement of in vitro proliferation of cockerel spermatogonial stem cells using different combinations of growth factors

1. This study examined whether in vitro proliferation and maintenance of cockerel spermatogonial stem cells (SSCs) could be improved by adding different combinations of growth factors (GFs), including glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF) or leukaemia inhibitory factor (LIF) into the culture medium. 2. The SSCs were isolated from the testes of immature cockerels. For short-term cultures, a medium supplemented with different combinations of GFs for 7 d in 5 replicates was used. The groups were classified as follows: without GF (control group); with GDNF (G group); with GDNF and bFGF (GF group); and with GDNF, bFGF and LIF (GFL group). The number of colonies and cells per colony, as well as the transcript abundance of STRA8 and OCT4 genes, was determined 7 d after the initial culturing. Immunofluorescence staining of SSEA-1, SSEA-3 and VASA protein markers, besides periodic acid-Schiff (PAS) staining, was carried out. 3. The number of colonies and cells per colony increased in the G, GF and GFL groups, compared to the control group (P < 0.01); however, the highest proliferation and colony formation were observed in the GFL group. The positive immunofluorescence staining of SSEA-1, SSEA-3 and VASA protein markers, as well as PAS staining, confirmed the self-renewal and colonisation of cockerel SSCs. The proliferation results were supported by the increased STRA8 and OCT4 transcript abundance in the treated groups (G, GF and GLF), compared to the control group. The SSC proliferation was associated with the higher transcript abundance of STAR8 and OCT4 genes in the GFL group, compared to the G and GF groups (P < 0.01). 4. The results showed that proliferation and colony-forming capacity of cockerel SSCs were positively improved by GDNF, bFGF and LIF. However, the most significant effect was observed when the medium was supplemented with LIF in combination with GDNF and bFGF.

Bisphenols Threaten Male Reproductive Health via Testicular Cells

Male reproductive function and health are largely dependent on the testes, which are strictly regulated by their major cell components, i. e., Sertoli, Leydig, and germ cells. Sertoli cells perform a crucial phagocytic function in addition to supporting the development of germ cells. Leydig cells produce hormones essential for male reproductive function, and germ cell quality is a key parameter for male fertility assessment. However, these cells have been identified as primary targets of endocrine disruptors, including bisphenols. Bisphenols are a category of man-made organic chemicals used to manufacture plastics, epoxy resins, and personal care products such as lipsticks, face makeup, and nail lacquers. Despite long-term uncertainty regarding their safety, bisphenols are still being used worldwide, especially bisphenol A. While considerable attention has been paid to the effects of bisphenols on health, current bisphenol-related reproductive health cases indicate that greater attention should be given to these chemicals. Bisphenols, especially bisphenol A, F, and S, have been reported to elicit various effects on testicular cells, including apoptosis, DNA damage, disruption of intercommunication among cells, mitochondrial damage, disruption of tight junctions, and arrest of proliferation, which threaten male reproductive health. In addition, bisphenols are xenoestrogens, which alter organs and cells functions via agonistic or antagonistic interplay with hormone receptors. In this review, we provide in utero, in vivo, and in vitro evidence that currently available brands of bisphenols impair male reproductive health through their action on testicular cells.

Experimental diabetes negatively affects the spermatogonial stem cells' self-renewal by suppressing GDNF network interactions

The present study was done to analyse the time-dependent effects of diabetes on Sertoli cells-spermatogonial stem cells' (SSCs) network interaction by focusing on glial cell line-derived neurotrophic factor (GDNF) and its special receptors, gfrα1 and c-RET as well as the Bcl-6b. In total, 40 Wistar rats were considered in; control, 20, 45 and 60 days diabetes-induced groups. An experimental diabetes was induced by STZ. The GDNF, gfrα1, c-RET and Bcl-6b expressions were evaluated. The serum level of testosterone, tubular repopulation (RI) and spermiogenesis (SPI) indices, general histological alterations, germ cells, mRNA damage, sperm count and viability were assessed. The diabetes, in a time-dependent manner, diminished mRNA and protein levels of GDNF, gfrα1, c-RET and Bcl-6b versus control group (p < .05), enhanced percentage of seminiferous tubules with negative RI, SPI, and diminished Leydig and Sertoli cells distribution, serum levels of testosterone, sperm count and viability. Finally, the number, percentage of cells and seminiferous tubules with normal mRNA content were significantly (p < .05) diminished. In conclusion, as a new data, we showed that the diabetes by inducing severe mRNA damage and suppressing GDNF, gfrα1, c-RET and Bcl-6b expressions, potentially affects the Sertoli-SSCs' network and consequently inhibits the SSCs' self-renewal process.

Proposed Key Characteristics of Male Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Evidence in Human Health Hazard Assessments

BACKGROUND

Assessing chemicals for their potential to cause male reproductive toxicity involves the evaluation of evidence obtained from experimental, epidemiological, and mechanistic studies. Although mechanistic evidence plays an important role in hazard identification and evidence integration, the process of identifying, screening and analyzing mechanistic studies and outcomes is a challenging exercise due to the diversity of research models and methods and the variety of known and proposed pathways for chemical-induced toxicity. Ten key characteristics of carcinogens provide a valuable tool for organizing and assessing chemical-specific data by potential mechanisms for cancer-causing agents. However, such an approach has not yet been developed for noncancer adverse outcomes.

OBJECTIVES

The objective in this study was to identify a set of key characteristics that are frequently exhibited by exogenous agents that cause male reproductive toxicity and that could be applied for identifying, organizing, and summarizing mechanistic evidence related to this outcome.

DISCUSSION

The identification of eight key characteristics of male reproductive toxicants was based on a survey of known male reproductive toxicants and established mechanisms and pathways of toxicity. The eight key characteristics can provide a basis for the systematic, transparent, and objective organization of mechanistic evidence relevant to chemical-induced effects on the male reproductive system. https://doi.org/10.1289/EHP5045.

The Impact of Bisphenol A on Fertility, Reproductive System, and Development: A Review of the Literature

Bisphenol A (BPA) has been used since the 1950s, in food packaging, industrial materials, dental sealants, and personal hygiene products. Everyone is exposed to BPA through skin, inhalation, and digestive system. BPA disrupts endocrine pathways, because it has weak estrogenic, antiandrogenic, and antithyroid activities. Despite the rapid metabolism, BPA can accumulate in different tissues. Many researchers proved the impact of BPA on human development, metabolism, and finally reproductive system. There is increasing evidence that BPA has impact on human fertility and is responsible for the reproductive pathologies, e.g., testicular dysgenesis syndrome, cryptorchidism, cancers, and decreased fertility in male and follicle loss in female.

The hypothalamic-pituitary-testicular axis and the testicular function are modulated after silver nanoparticle exposure

Silver nanoparticles (AgNPs) are widely used in industrial and medical applications and humans may be exposed through different routes, increasing the risk of toxicity. We investigated the transcript expression of genes involved in the regulation of the hypothalamic-pituitary-testicular (HPT) axis and the parameters associated with sperm functionality after prepubertal exposure. AgNPs modulated the transcript expression of genes involved in the control of the HPT axis and spermatogenesis in the groups treated with lower doses, while the functional parameters related to sperm and puberty were affected in the groups administered higher doses. These results suggest that the HPT axis is disrupted by AgNPs during the prepubertal and pubertal periods, which are highly susceptible windows for the endocrine-disrupting chemical activity.

Internalization of silver nanoparticles into mouse spermatozoa results in poor fertilization and compromised embryo development

Silver nanoparticles (AgNPs) have many features that make them attractive as medical devices, especially in therapeutic agents and drug delivery systems. Here we have introduced AgNPs into mouse spermatozoa and then determined the cytotoxic effects of AgNPs on sperm function and subsequent embryo development. Scanning electron microscopy and transmission electron microscopy analyses showed that AgNPs could be internalized into sperm cells. Furthermore, exposure to AgNPs inhibited sperm viability and the acrosome reaction in a dose-dependent manner, whereas sperm mitochondrial copy numbers, morphological abnormalities, and mortality due to reactive oxygen species were significantly increased. Likewise, sperm abnormalities due to AgNPs internalization significantly decreased the rate of oocyte fertilization and blastocyst formation. Blastocysts obtained from AgNPs-treated spermatozoa showed lower expression of trophectoderm-associated and pluripotent marker genes. Overall, we propose that AgNPs internalization into spermatozoa may alter sperm physiology, leading to poor fertilization and embryonic development. Such AgNPs-induced reprotoxicity may be a valuable tool as models for testing the safety and applicability of medical devices using AgNPs.

Adult exposure to bisphenol A (BPA) in Wistar rats reduces sperm quality with disruption of the hypothalamic-pituitary-testicular axis

Reproductive physiology involves complex biological processes that can be disrupted by exposure to environmental contaminants. The effects of bisphenol A (BPA) on spermatogenesis and sperm quality is still unclear. The objective of this study was to investigate the reproductive toxicity of BPA at dosages considered to be safe (5 or 25mg BPA/kg/day). We assessed multiple sperm parameters, the relative expression of genes involved in the central regulation of the hypothalamic-pituitary-testicular axis, and the serum concentrations of testosterone, estradiol, LH and FSH. BPA exposure reduced sperm production, reserves and transit time. Significant damage to the acrosomes and the plasma membrane with reduced mitochondrial activity and increased levels of defective spermatozoa may have compromised sperm function and caused faster movement through the epididymis. BPA exposure reduced the serum concentrations of testosterone, LH and FSH and increased the concentration of estradiol. The relative gene expression revealed an increase in gonadotropin releasing hormone receptor (Gnrhr), luteinizing hormone beta (Lhb), follicle stimulating hormone beta (Fshb), estrogen receptor beta (Esr2) and androgen receptor (Ar) transcripts in the pituitary and a reduction in estrogen receptor alpha (Esr1) transcripts in the hypothalamus. In this study, we demonstrated for the first time that adult male exposure to BPA caused a reduction in sperm production and specific functional parameters. The corresponding pattern of gene expression is indicative of an attempt by the pituitary to reestablish normal levels of LH, FSH and testosterone serum concentrations. In conclusion, these data suggest that at dosages previously considered nontoxic to reproductive function, BPA compromises the spermatozoa and disrupts the hypothalamic-pituitary-gonadal axis, causing a state of hypogonadotropic hypogonadism.

Engineered nanomaterials: an emerging class of novel endocrine disruptors

Over the past decade, engineered nanomaterials (ENMs) have garnered great attention for their potentially beneficial applications in medicine, industry, and consumer products due to their advantageous physicochemical properties and inherent size. However, studies have shown that these sophisticated molecules can initiate toxicity at the subcellular, cellular, and/or tissue/organ level in diverse experimental models. Investigators have also demonstrated that, upon exposure to ENMs, the physicochemical properties that are exploited for public benefit may mediate adverse endocrine-disrupting effects on several endpoints of mammalian reproductive physiology (e.g., steroidogenesis, spermatogenesis, pregnancy). Elucidating these complex interactions within reproductive cells and tissues will significantly advance our understanding of ENMs as an emerging class of novel endocrine disruptors and reproductive toxicants. Herein we reviewed the recent developments in reproductive nanotoxicology and identified the gaps in our knowledge that may serve as future research directions to foster continued advancement in this evolving field of study.

Sub-acute intravenous administration of silver nanoparticles in male mice alters Leydig cell function and testosterone levels

The aim of this study was to determine whether short-term, in vivo exposure to silver nanoparticles (AgNPs) could be toxic to male reproduction. Low dose (1mg/kg/dose) AgNPs were intravenously injected into male CD1 mice over 12 days. Treatment resulted in no changes in body and testis weights, sperm concentration and motility, fertility indices, or follicle-stimulating hormone and luteinizing hormone serum concentrations; however, serum and intratesticular testosterone concentrations were significantly increased 15 days after initial treatment. Histologic evaluation revealed significant changes in epithelium morphology, germ cell apoptosis, and Leydig cell size. Additionally, gene expression analysis revealed Cyp11a1 and Hsd3b1 mRNA significantly upregulated in treated animals. These data suggest that AgNPs do not impair spermatogonial stem cells in vivo since treatment did not result in significant decreases in testis weight and sperm concentrations. However, AgNPs appear to affect Leydig cell function, yielding increasing testicular and serum testosterone levels.

Daily exposure to silver nanoparticles during prepubertal development decreases adult sperm and reproductive parameters

As silver nanoparticles (AgNPs) have antimicrobial properties and potentiate the activity of some antibiotics, they are broadly used in both medical and nonmedical applications. In this study, prepubertal male Wistar rats were orally treated with 15 or 30 µg/kg/day AgNPs from postnatal day 23 (PND23) to PND58 and sacrificed at PND102. The acrosome integrity, plasma membrane integrity, mitochondrial activity and morphological alterations of the sperm were analyzed. Sexual partner preference, sexual behavior and the serum concentrations of FSH, LH, testosterone and estradiol were also recorded. The results were evaluated following the appropriate statistical analyses, and differences among the groups were considered significant when p < 0.05. AgNPs reduced the acrosome and plasma membrane integrities, reduced the mitochondrial activity and increased the abnormalities of the sperm in both treatment groups. AgNP exposure also delayed the onset of puberty, although no changes in body growth were observed in either treatment group. The animals did not show changes in sexual behavior or serum hormone concentrations. This study shows for the first time that prepubertal exposure to AgNPs causes alterations in adult sperm parameters. Importantly, the sperm appeared to be more sensitive to the toxic effects of AgNPs and demonstrated adverse effects following exposure to lower doses. Consequently, the effects of AgNPs on sperm should be considered in order to establish safety limits for the use of these particles.

Testicular biodistribution of 450 nm fluorescent latex particles after intramuscular injection in mice

The significant expansion in the use of nanoparticles and submicron particles during the last 20 years has led to increasing concern about their potential toxicity to humans and particularly their impact on male fertility. Currently, an insufficient number of studies have focused on the testicular biodistribution of particles. The aim of our study was to assess the distribution of 450 nm fluorescent particles in mouse testes after intramuscular injection. To this end, testes were removed from 5 groups of 3 mice each at 1 h (H1), 4 days (D4), 21 days (D21), 45 days (D45) and 90 days (D90) after the injection of 7.28 × 10⁹ particles in the tibialis anterior muscles of each mouse. We examined histological sections from these samples by epifluorescence microscopy and confocal microscopy and identified testicular biodistribution of a small number of particles in groups H1, D4, D21, D45 and D90. Using CD11b immunostaining, we showed that particles were not carried into the testis by macrophages. The intratesticular repartition of particles mainly followed testicular vascularization. Finally, we found some particles in seminiferous tubules but could not determine if the blood-testis barrier was crossed.

Transgenerational effects of di-(2-ethylhexyl) phthalate on testicular germ cell associations and spermatogonial stem cells in mice

Recent evidence has linked human phthalate exposure to abnormal reproductive and hormonal effects. Phthalates are plasticizers that confer flexibility and transparency to plastics, but they readily contaminate the body and the environment. In this study, timed pregnant CD1 outbred mice were treated with di-(2-ethylhexyl) phthalate (DEHP) from Embryonic Day 7 (E7) to E14. The subsequent generation (F1) offspring were then bred to produce the F2, F3, and F4 offspring, without any further DEHP treatment. This exposure scheme disrupted testicular germ cell association and decreased sperm count and motility in F1 to F4 offspring. By spermatogonial transplantation techniques, the exposure scheme also disrupted spermatogonial stem cell (SSC) function of F3 offspring. The W/W(V) recipient testes transplanted with F3 offspring germ cells from the DEHP-treated group had a dramatically lower percentage of donor germ cell-derived spermatogenic recovery in seminiferous tubules when compared to the recipient testes transplanted with CD1 control germ cells. Further characterization showed that the major block of donor germ cell-derived spermatogenesis was before the appearance of undifferentiated spermatogonia. Interestingly, the testes transplanted with the F3 offspring germ cells from the DEHP-treated group, when regenerated, replicated testis morphology similar to that observed in the testes from the F1 to F3 offspring of the DEHP-treated group, suggesting that the germ cell disorganization phenotype originates from the stem cells of F3 offspring. In conclusion, embryonic exposure to DEHP was found to disrupt testicular germ cell organization and SSC function in a transgenerational manner.

The apical ES-BTB-BM functional axis is an emerging target for toxicant-induced infertility

Testes are sensitive to toxicants, such as cadmium and phthalates, which disrupt a local functional axis in the seminiferous epithelium known as the 'apical ectoplasmic specialization (apical ES)-blood-testis barrier (BTB)-basement membrane (BM)'. Following exposure, toxicants contact the basement membrane and activate the Sertoli cell, which perturbs its signaling function. Thus, toxicants can modulate signaling and/or cellular events at the apical ES-BTB-BM axis, perturbing spermatogenesis without entering the epithelium. Toxicants also enter the epithelium via drug transporters to potentiate their damaging effects, and downregulation of efflux transporters by toxicants impedes BTB function such that toxicants remain in the epithelium and efficiently disrupt spermatogenesis. These findings support a novel model of toxicant-induced disruption of spermatogenesis that could be interfered with using small molecules.

Effects of prepubertal exposure to silver nanoparticles on reproductive parameters in adult male Wistar rats

The incidence of male reproductive pathologies, such as hypospadias, cryptorchidism, testicular cancer, and low sperm production in adulthood, is increasing and may be related to exposure to environmental contaminants. The silver nanoparticles (AgNP) are a new class of chemical compounds commonly used in both medical and nonmedical settings, and they affect development of spermatogonial stem cells in vitro. The aim of this study was to examine the adverse productive toxic effects of AgNPs in male Wistar rats exposed during the prepubertal period and sacrificed at postnatal day (PND) 53 and PND90. Growth was assessed by daily weighing. The progress of puberty in the rats was measured by preputial separation, while spermatogenesis was assayed by (1) measuring the sperm count in testes and epididymis and (2) examining the morphology and morphometry of seminiferous epithelium using stereological analysis. In addition, testosterone and estradiol levels were assayed by radioimmunoassay. The weight of the animals at PND90 did not change markedly, but growth was less in the group treated with AgNP at 50 μg/kg from PND34 to PND53. AgNP exposure produced a delay in puberty in both treated groups. Decreased sperm reserves in the epididymis and diminished sperm transit time were observed at PND53, while a reduction in sperm production occurred at PND90. The morphology of the seminiferous epithelium was markedly altered. Data demonstrated that prepubertal exposure to AgNP altered reproductive development in prepubertal male Wistar rats, as evidenced by impairment in spermatogenesis and a lower sperm count in adulthood.

Use of human amniotic epithelial cells as a feeder layer to support undifferentiated growth of mouse spermatogonial stem cells via epigenetic regulation of the Nanog and Oct-4 promoters

Spermatogonial stem cells (SSCs) are defined by unique properties like other stem cells. However, there are two major challenges: long-term cultivation of normal SSCs into stable cell lines and maintaining the SSCs as undifferentiated and capable of self-renewal. Here, we compared different culture methods for mouse SSCs isolated and cultured from testicular tissue. We found that human amniotic epithelial cells (hAECs) can behave as feeder cells, allowing mouse SSCs to maintain a high level of alkaline phosphatase (AP) activity when cultured long-term. Also, we observed that expression of Nanog, Oct-4 and other important stem cells markers were higher in mouse SSCs cultured on hAECs compared to those cultured on MEF or without any feeder cells. Furthermore, we demonstrated that the CpG islands of the Nanog and Oct-4 promoters were hypomethylated in cells cultured on hAECs. In addition, mouse SSCs cultured on hAECs exhibited higher levels of H3AC and H3K4Me3 in the Nanog and Oct-4 promoters than those cultured on MEF or without feeder cells. Taken together, these results suggest that the hAEC-induced epigenetic modifications at the Nanog and Oct-4 locus could be a key mechanism for maintaining mouse SSCs in an undifferentiated state capable of self-renewal.

Amniotic fluid stem cell-based models to study the effects of gene mutations and toxicants on male germ cell formation

Male infertility is a major public health issue predominantly caused by defects in germ cell development. In the past, studies on the genetic regulation of spermatogenesis as well as on negative environmental impacts have been hampered by the fact that human germ cell development is intractable to direct analysis in vivo. Compared with model organisms including mice, there are fundamental differences in the molecular processes of human germ cell development. Therefore, an in vitro model mimicking human sperm formation would be an extremely valuable research tool. In the recent past, both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have been reported to harbour the potential to differentiate into primordial germ cells and gametes. We here discuss the possibility to use human amniotic fluid stem (AFS) cells as a biological model. Since their discovery in 2003, AFS cells have been characterized to differentiate into cells of all three germ layers, to be genomically stable, to have a high proliferative potential and to be non-tumourigenic. In addition, AFS cells are not subject of ethical concerns. In contrast to iPS cells, AFSs cells do not need ectopic induction of pluripotency, which is often associated with only imperfectly cleared epigenetic memory of the source cells. Since AFS cells can be derived from amniocentesis with disease-causing mutations and can be transfected with high efficiency, they could be used in probing gene functions for spermatogenesis and in screening for male reproductive toxicity.

The blood-testis barrier and its implications for male contraception

The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium into the basal and the apical (adluminal) compartments. Meiosis I and II, spermiogenesis, and spermiation all take place in a specialized microenvironment behind the BTB in the apical compartment, but spermatogonial renewal and differentiation and cell cycle progression up to the preleptotene spermatocyte stage take place outside of the BTB in the basal compartment of the epithelium. However, the BTB is not a static ultrastructure. Instead, it undergoes extensive restructuring during the seminiferous epithelial cycle of spermatogenesis at stage VIII to allow the transit of preleptotene spermatocytes at the BTB. Yet the immunological barrier conferred by the BTB cannot be compromised, even transiently, during the epithelial cycle to avoid the production of antibodies against meiotic and postmeiotic germ cells. Studies have demonstrated that some unlikely partners, namely adhesion protein complexes (e.g., occludin-ZO-1, N-cadherin-β-catenin, claudin-5-ZO-1), steroids (e.g., testosterone, estradiol-17β), nonreceptor protein kinases (e.g., focal adhesion kinase, c-Src, c-Yes), polarity proteins (e.g., PAR6, Cdc42, 14-3-3), endocytic vesicle proteins (e.g., clathrin, caveolin, dynamin 2), and actin regulatory proteins (e.g., Eps8, Arp2/3 complex), are working together, apparently under the overall influence of cytokines (e.g., transforming growth factor-β3, tumor necrosis factor-α, interleukin-1α). In short, a "new" BTB is created behind spermatocytes in transit while the "old" BTB above transiting cells undergoes timely degeneration, so that the immunological barrier can be maintained while spermatocytes are traversing the BTB. We also discuss recent findings regarding the molecular mechanisms by which environmental toxicants (e.g., cadmium, bisphenol A) induce testicular injury via their initial actions at the BTB to elicit subsequent damage to germ-cell adhesion, thereby leading to germ-cell loss, reduced sperm count, and male infertility or subfertility. Moreover, we also critically evaluate findings in the field regarding studies on drug transporters in the testis and discuss how these influx and efflux pumps regulate the entry of potential nonhormonal male contraceptives to the apical compartment to exert their effects. Collectively, these findings illustrate multiple potential targets are present at the BTB for innovative contraceptive development and for better delivery of drugs to alleviate toxicant-induced reproductive dysfunction in men.

Global gene expression and Ingenuity biological functions analysis on PCBs 153 and 138 induced human PBMC in vitro reveals differential mode(s) of action in developing toxicities

Several reports have indicated that low level of polychlorinated biphenyl (PCB) exposure can adversely affect a multitude of physiological disorders and diseases in in vitro, in vivo, and as reported in epidemiological studies. This investigation is focused on the possible contribution of two most prevalent PCB congeners in vitro in developing toxicities. We used PCBs 138 and 153 at the human equivalence level as model agents to test their specificity in developing toxicities. We chose a global approach using oligonucleotide microarray technology to investigate modulated gene expression for biological effects, upon exposure of PCBs, followed by Ingenuity Pathway Analysis (IPA), to understand the underlying consequence in developing disease and disorders. We performed in vitro studies with human peripheral blood mononuclear cells (PBMC), where PBMC cells were exposed to respective PCBs for 48 h. Overall, our observation on gene expression indicated that PCB produces a unique signature affecting different pathways, specific for each congener. While analyzing these data through IPA, the prominent and interesting disease and disorders were neurological disease, cancer, cardiovascular disease, respiratory disease, as well as endocrine system disorders, genetic disorders, and reproductive system disease. They showed strong resemblances with in vitro, in vivo, and in the epidemiological studies. A distinct difference was observed in renal and urological diseases, organisimal injury and abnormalities, dental disease, ophthalmic disease, and psychological disorders, which are only revealed by PCB 138 exposure, but not in PCB 153. The present study emphasizes the challenges of global gene expression in vitro and was correlated with the results of exposed human population. The microarray results give a molecular mechanistic insight and functional effects, following PCB exposure. The extent of changes in genes related to several possible mode(s) of action highlights the changes in cellular functions and signaling pathways that play major roles. In addition to understanding the pathways related to mode of action for chemicals, these data could lead to the identification of genomic signatures that could be used for screening of chemicals for their potential to cause disease and developmental disorders.

Human amniotic epithelial cells maintain mouse spermatogonial stem cells in an undifferentiated state due to high leukemia inhibitor factor (LIF) expression

Spermatogonial stem cells (SSCs), like other stem cells, have unique properties: prolonged proliferation, self-renewal, generation of differentiated progeny, and maintenance of developmental potential. Long-term cultivation of normal SSCs into stable cell lines, and maintaining SSCs in an undifferentiated state capable of self-renewal, is a major challenge. Here, we compare the effect of leukemia inhibitory factor (LIF) expression on mouse SSCs isolated from testicular tissue cultured under different conditions. We found that human amniotic epithelial cells (hAECs) with high LIF expression (LIF(high)) feeder cells allowed mouse SSCs to maintain a high level of AP activity when cultured long term. Expression of some important stem cell markers was higher in mouse SSCs cultured on hAECs (LIF(high)) compared to those cultured on hAECs (LIF(low)). Taken together, these results suggest that LIF expression could be a crucial component for feeder cells to maintain mouse SSCs in an undifferentiated, proliferative state capable of self-renewal.

Morphology of spermatogenic and accessory cells in the mussel Modiolus kurilensis under environmental pollution

A comparative light- and electron microscopic study of the male gonads of the bivalve mollusk Modiolus kurilensis from the reference and polluted sites in Amursky Bay (Sea of Japan) was conducted. Testicular acini in the mussels from the reference site had well-ordered structure (vertical spermatogenic columns located among the accessory cells bodies) whereas in the testes of the mollusks from the polluted site, the accessory and spermatogenic cell populations were disarranged. Mussels from the polluted station had about 26% of spermatogenic cells with marginal localization of nuclear chromatin, swollen outer nuclear membrane and heavily vacuolated cytoplasm and about 8% of spermatozoa with transformed or destructed acrosome; in mussels from the reference station, these values were close to zero. The accessory cells in the mussels from the polluted site were underdeveloped, and their phagocytic activity was inhibited. Our ultrastructural observations provide evidence that both spermatogenic and accessory cells are targets of environmental pollution in marine mussels.