Selective ablation of the androgen receptor in mouse sertoli cells affects sertoli cell maturation, barrier formation and cytoskeletal development

Chronic depletion of gonadal testosterone leads to blood-brain barrier dysfunction and inflammation in male mice

A dysfunction in the blood-brain barrier (BBB) is associated with many neurological and metabolic disorders. Although sex steroid hormones have been shown to impact vascular tone, endothelial function, oxidative stress, and inflammatory responses, there are still no data on the role of testosterone in the regulation of BBB structure and function. In this context, we investigated the effects of gonadal testosterone depletion on the integrity of capillary BBB and the surrounding parenchyma in male mice. Our results show increased BBB permeability for different tracers and endogenous immunoglobulins in chronically testosterone-depleted male mice. These results were associated with disorganization of tight junction structures shown by electron tomography and a lower amount of tight junction proteins such as claudin-5 and ZO-1. BBB leakage was also accompanied by activation of astrocytes and microglia, and up-regulation of inflammatory molecules such as inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), interleukin 1 beta (IL-1β), and tumor necrosis factor (TNF). Supplementation of castrated male mice with testosterone restored BBB selective permeability, tight junction integrity, and almost completely abrogated the inflammatory features. The present demonstration that testosterone transiently impacts cerebrovascular physiology in adult male mice should help gain new insights into neurological and metabolic diseases linked to hypogonadism in men of all ages.

Transcriptional mechanisms coordinating tight junction assembly during epithelial differentiation

Epithelial tissues form a selective barrier via direct cell-cell interactions to separate and establish concentration gradients between the different compartments of the body. Proper function and formation of this barrier rely on the establishment of distinct intercellular junction complexes. These complexes include tight junctions, adherens junctions, desmosomes, and gap junctions. The tight junction is by far the most diverse junctional complex in the epithelial barrier. Its composition varies greatly across different epithelial tissues to confer various barrier properties. Thus, epithelial cells rely on tightly regulated transcriptional mechanisms to ensure proper formation of the epithelial barrier and to achieve tight junction diversity. Here, we review different transcriptional mechanisms utilized during embryogenesis and disease development to promote tight junction assembly and maintenance of intercellular barrier integrity. We focus particularly on the Grainyhead-like transcription factors and ligand-activated nuclear hormone receptors, two central families of proteins in epithelialization.

Co-Administration of Vitamin E and Testosterone Attenuates The Atrazine-Induced Toxic Effects on Sperm Quality and Testes in Rats

OBJECTIVE

Atrazine (ATZ) as a widely used herbicide is considered as a potent endocrine disrupter which adversely affects reproductive systems in both genders. This study aimed to assess the effects of testosterone (T)- and vitamin E (VitE)- alone and their coadministration on testicular function and sperm parameters after exposure to ATZ in rats.

MATERIALS AND METHODS

In this experimental study, the rats (n=30) are assigned into the following 5 groups: control-sham group (n=6) receiving corn oil, ATZ group (n=6) receiving 200 mg/kg ATZ alone, ATZ+VitE group (n=6) receiving 150 mg/kg ATZ+VitE, ATZ+T group (n=6) receiving 400 µg/kg ATZ+T, and ATZ+VitE+T group (n=6) receiving ATZ+VitE+T for 48 consecutive days. Total antioxidant capacity (TAC), total thiol molecules (TTM), and malondialdehyde (MDA) were analyzed. Serum levels of T, luteinizing hormone (LH), and inhibin-B (IN-B) were also determined. Histological examination and sperm analysis were performed. The data were analyzed using Graph-Pad Prism software version 2.01.

RESULTS

Co-administration of VitE and T significantly (P<0.05) increased ATZ-decreased TAC and TTM levels and reduced ATZ-increased MDA content. T and VitE significantly (P<0.05) increased serum levels of ATZ-reduced T (1.94 ± 0.96), IN-B (122.10 ± 24.33) and LH (0.40 ± 0.10). The T+VitE animals showed a reduction in apoptotic cells and an increase in Leydig cells steroidogenesis. Co-administration of T and VitE significantly (P<0.05) reduced the ATZ-induced DNA disintegrity and chromatin de-condensation. VitE and T protected germinal cells RNA and protein contents against ATZ-induced damages.

CONCLUSION

T and VitE in simultaneous form of administration were able to normalize the ATZ-induced derangements through promoting antioxidant capacity and endocrine function.

BMP6 Regulates Proliferation and Apoptosis of Human Sertoli Cells Via Smad2/3 and Cyclin D1 Pathway and DACH1 and TFAP2A Activation

Sertoli cells are essential for regulating normal spermatogenesis. However, the mechanisms underlying human Sertoli cell development remain largely elusive. Here we examined the function and signaling pathways of BMP6 in regulating human Sertoli cells. RT-PCR, immunocytochemistry and Western blots revealed that BMP6 and its multiple receptors were expressed in human Sertoli cells. CCK-8 and EDU assays showed that BMP6 promoted the proliferation of Sertoli cells. Conversely, BMP6 siRNAs inhibited the division of these cells. Annexin V/PI assay indicated that BMP6 reduced the apoptosis in human Sertoli cells, whereas BMP6 knockdown assumed reverse effects. BMP6 enhanced the expression levels of ZO1, SCF, GDNF and AR in human Sertoli cells, and ELISA assay showed an increase of SCF by BMP6 and a reduction by BMP6 siRNAs. Notably, Smad2/3 phosphorylation and cyclin D1 were enhanced by BMP6 and decreased by BMP6 siRNAs in human Sertoli cells. The levels of DACH1 and TFAP2A were increased by BMP6 and reduced by BMP6 siRNAs, and the growth of human Sertoli cells was inhibited by these siRNAs. Collectively, these results suggest that BMP6 regulates the proliferation and apoptosis of human Sertoli cells via activating the Smad2/3/cyclin D1 and DACH1 and TFAP2A pathway.

Effect of extracellular matrix on testosterone production during in vitro culture of bovine testicular cells

Testosterone is believed to play a significant role in spermatogenesis, but its contribution to the process of spermatogenesis is not completely understood. Given that extracellular matrix (ECM) facilitates differentiation of spermatogonial stem cells (SSCs) during culture, the present study was conducted to elucidate whether testosterone contribute to the permissive effect of ECM on SSCs differentiation. In experiment 1, testosterone production was measured in testicular cells cultured for 12 days on ECM or plastic (control). In experiment 2, testosterone production was assessed in testicular cells cultured on ECM or plastic (control) and exposed to different concentrations of hCG. In experiment 3, the gene expression of factors involved in testosterone production was analyzed. Testosterone concentration was lower in ECM than in the control group in experiment 1 (p < 0.05). In experiment 2, testosterone concentration was increased in response to hCG in both groups but cells cultured on ECM were more responsive to hCG than those cultured on plastic (p < 0.05). In the experiment 3, qRT-PCR revealed the inhibitory effect of ECM on the gene expression of steroidogenic acute regulatory protein (StAR) (p < 0.05). Nevertheless, the expression of LH receptor was greater in ECM-exposed than in unexposed cells (p < 0.05). In conclusion, the present study showed that inhibiting the expression of StAR, ECM could lower testosterone production by Leydig cells during in vitro culture. In addition, the results indicated that ECM could augment the responsiveness of Leydig cells to hCG through stimulating the expression of LH receptor.

Claudin-11 Tight Junctions in Myelin Are a Barrier to Diffusion and Lack Strong Adhesive Properties

The radial component is a network of interlamellar tight junctions (TJs) unique to central nervous system myelin. Ablation of claudin-11, a TJ protein, results in the absence of the radial component and compromises the passive electrical properties of myelin. Although TJs are known to regulate paracellular diffusion, this barrier function has not been directly demonstrated for the radial component, and some evidence suggests that the radial component may also mediate adhesion between myelin membranes. To investigate the physical properties of claudin-11 TJs, we compared fresh, unfixed Claudin 11-null and control nerves using x-ray and neutron diffraction. In Claudin 11-null tissue, we detected no changes in myelin structure, stability, or membrane interactions, which argues against the notion that myelin TJs exhibit significant adhesive properties. Moreover, our osmotic stressing and D2O-H2O exchange experiments demonstrate that myelin lacking claudin-11 is more permeable to water and small osmolytes. Thus, our data indicate that the radial component serves primarily as a diffusion barrier and elucidate the mechanism by which TJs govern myelin function.

Sertoli cells are capable of proliferation into adulthood in the transition region between the seminiferous tubules and the rete testis in Wistar rats

Sertoli cells (SCs) play a crucial role in testis differentiation, development and function, determining the magnitude of sperm production in sexually mature animals. For over 40 years, it has been considered that these key testis somatic cells stop dividing during early pre-pubertal phase, between around 10 to 20 days after birth respectively in mice and rats, being after that under physiological conditions a stable and terminally differentiated population. However, evidences from the literature are challenging this dogma. In the present study, using several important functional markers (Ki-67, BrdU, p27, GATA-4, Androgen Receptor), we investigated the SC differentiation status in 36 days old and adult Wistar rats, focusing mainly in the transition region (TR) between the seminiferous tubules (ST) and the rete testis. Our results showed that SCs in TR remain undifferentiated for a longer period and, although at a lesser degree, even in adult rats proliferating SCs were observed in this region. Therefore, these findings suggest that, different from the other ST regions investigated, SCs residing in the TR exhibit a distinct functional phenotype. These undifferentiated SCs may compose a subpopulation of SC progenitors that reside in a specific microenvironment capable of growing the ST length if needed from this particular testis region. Moreover, our findings demonstrate an important aspect of testis function in mammals and opens new venues for other experimental approaches to the investigation of SC physiology, spermatogenesis progression and testis growth. Besides that, the TR may represent an important site for pathophysiological investigations and cellular interactions in the testis.

Regulation of the blood-testis barrier

The purpose of this review is to describe the endocrine and local testicular factors that contribute to the regulation of the blood-testis barrier (BTB), using information gained from in vivo and in vitro models of BTB formation during/after puberty, and from the maintenance of BTB function during adulthood. In vivo the BTB, in part comprised of tight junctions between adjacent somatic Sertoli cells, compartmentalizes meiotic spermatocytes and post-meiotic spermatids away from the vasculature, and therefore prevents autoantibody production by the immune system against these immunogenic germ cells. This adluminal compartment also features a unique biochemical milieu required for the completion of germ cell development. During the normal process of spermatogenesis, earlier germ cells continually cross into the adluminal compartment, but the regulatory mechanisms and changes in junctional proteins that allow this translocation step without causing a 'leak' remain poorly understood. Recent data describing the roles of FSH and androgen on the regulation of Sertoli cell tight junctions and tight junction proteins will be discussed, followed by an examination of the role of paracrine factors, including members of the TGFβ superfamily (TGFβ3, activin A) and retinoid signalling, as potential mediators of junction assembly and disassembly during the translocation process.

Flutamide induces alterations in the cell-cell junction ultrastructure and reduces the expression of Cx43 at the blood-testis barrier with no disturbance in the rat seminiferous tubule morphology

BACKGROUND

Present study was designed to establish a causal connection between changes in the cell-cell junction protein expression at the blood-testis barrier and alterations in the adult rat testis histology following an anti-androgen flutamide exposure. Particular emphasis was placed on the basal ectoplasmic specialization (ES) in the seminiferous epithelium and expression of gap junction protein, connexin 43 (Cx43).

METHODS

Flutamide (50 mg/kg body weight) was administered to male rats daily from 82 to 88 postnatal day. Testes from 90-day-old control and flutamide-exposed rats were used for all analyses. Testis morphology was analyzed using light and electron microscopy. Gene and protein expressions were analyzed by real-time RT-PCR and Western blotting, respectively, protein distribution by immunohistochemistry, and steroid hormone concentrations by radioimmunoassay.

RESULTS

Seminiferous epithelium of both groups of rats displayed normal histology without any loss of germ cells. In accord, no difference in the apoptosis and proliferation level was found between control and treated groups. As shown by examination of semi-thin and ultrathin sections, cell surface occupied by the basal ES connecting neighboring Sertoli cells and the number of gap and tight junctions coexisting with the basal ES were apparently reduced in flutamide-treated rats. Moreover, the appearance of unconventional circular ES suggests enhanced internalization and degradation of the basal ES. These changes were accompanied by decreased Cx43 and ZO-1 expression (p < 0.01) and a loss of linear distribution of these proteins at the region of the blood-testis barrier. On the other hand, Cx43 expression in the interstitial tissue of flutamide-treated rats increased (p < 0.01), which could be associated with Leydig cell hypertrophy. Concomitantly, both intratesticular testosterone and estradiol concentrations were elevated (p < 0.01), but testosterone to estradiol ratio decreased significantly (p < 0.05) in flutamide-treated rats compared to the controls.

CONCLUSIONS

Short-term treatment with flutamide applied to adult rats exerts its primary effect on the basal ES, coexisting junctional complexes and their constituent proteins Cx43 and ZO-1, without any apparent morphological alterations in the seminiferous epithelium. In the interstitial compartment, however, short-term exposure leads to both histological and functional changes of the Leydig cells.

Prenatal and lactation nicotine exposure affects Sertoli cell and gonadotropin levels in rats

Nicotine is largely consumed in the world as a component of cigarettes. It can cross the placenta and reach the milk of smoking mothers. This drug induces apoptosis, affects sex hormone secretion, and leads to male infertility. To investigate the exposure to nicotine during the whole intrauterine and lactation phases in Sertoli cells, pregnant rats received nicotine (2 mg/kg per day) through osmotic minipumps. Male offsprings (30, 60, and 90 days old) had blood collected for hormonal analysis (FSH and LH) and their testes submitted for histophatological study, analysis of the frequency of the stages of seminiferous epithelium cycle, immunolabeling of apoptotic epithelial cells (TUNEL and Fas/FasL), analysis of the function and structure of Sertoli cells (respectively using transferrin and vimentin immunolabeling), and analysis of Sertoli-germ cell junctional molecule (β-catenin immunolabeling). The exposure to nicotine increased the FSH and LH plasmatic levels in adult rats. Although nicotine had not changed the number of apoptotic cells, neither in Fas nor FasL expression, it provoked an intense sloughing of epithelial cells and also altered the frequency of some stages of the seminiferous epithelium cycle. Transferrin and β-catenin expressions were not changed, but vimentin was significantly reduced in the early stages of the seminiferous cycle of the nicotine-exposed adult rats. Thus, we concluded that nicotine exposure during all gestational and lactation periods affects the structure of Sertoli cells by events causing intense germ cell sloughing observed in the tubular lumen and can compromise the fertility of the offspring.

Transgenic Chickens Overexpressing Aromatase Have High Estrogen Levels but Maintain a Predominantly Male Phenotype

Estrogens play a key role in sexual differentiation of both the gonads and external traits in birds. The production of estrogen occurs via a well-characterized steroidogenic pathway, which is a multistep process involving several enzymes, including cytochrome P450 aromatase. In chicken embryos, the aromatase gene (CYP19A1) is expressed female-specifically from the time of gonadal sex differentiation. Ectopic overexpression of aromatase in male chicken embryos induces gonadal sex reversal, and male embryos treated with estradiol become feminized; however, this is not permanent. To test whether a continuous supply of estrogen in adult chickens could induce stable male to female sex reversal, 2 transgenic male chickens overexpressing aromatase were generated using the Tol2/transposase system. These birds had robust ectopic aromatase expression, which resulted in the production of high serum levels of estradiol. Transgenic males had female-like wattle and comb growth and feathering, but they retained male weights, displayed leg spurs, and developed testes. Despite the small sample size, this data strongly suggests that high levels of circulating estrogen are insufficient to maintain a female gonadal phenotype in adult birds. Previous observations of gynandromorph birds and embryos with mixed sex chimeric gonads have highlighted the role of cell autonomous sex identity in chickens. This might imply that in the study described here, direct genetic effects of the male chromosomes largely prevailed over the hormonal profile of the aromatase transgenic birds. This data therefore support the emerging view of at least partial cell autonomous sex development in birds. However, a larger study will confirm this intriguing observation.

Transfection of Sertoli cells with androgen receptor alters gene expression without androgen stimulation

Background

Androgens play an important role for the development of male fertility and gained interest as growth and survival factors for certain types of cancer. Androgens act via the androgen receptor (AR/Ar), which is involved in various cell biological processes such as sex differentiation. To study the functional mechanisms of androgen action, cell culture systems and AR-transfected cell lines are needed. Transfection of AR into cell lines and subsequent gene expression analysis after androgen treatment is well established to investigate the molecular biology of target cells. However, it remains unclear how the transfection with AR itself can modulate the gene expression even without androgen stimulation. Therefore, we transfected Ar-deficient rat Sertoli cells 93RS2 by electroporation using a full length human AR.

Results

Transfection success was confirmed by Western Blotting, immunofluorescence and RT-PCR. AR transfection-related gene expression alterations were detected with microarray-based genome-wide expression profiling of transfected and non-transfected 93RS2 cells without androgen stimulation. Microarray analysis revealed 672 differentially regulated genes with 200 up- and 472 down-regulated genes. These genes could be assigned to four major biological categories (development, hormone response, immune response and metabolism). Microarray results were confirmed by quantitative RT-PCR analysis for 22 candidate genes.

Conclusion

We conclude from our data, that the transfection of Ar-deficient Sertoli cells with AR has a measurable effect on gene expression even without androgen stimulation and cause Sertoli cell damage. Studies using AR-transfected cells, subsequently stimulated, should consider alterations in AR-dependent gene expression as off-target effects of the AR transfection itself.

Electronic supplementary material

The online version of this article (doi:10.1186/s12867-015-0051-7) contains supplementary material, which is available to authorized users.

Mouse Spermatogenesis Requires Classical and Nonclassical Testosterone Signaling

Testosterone acts though the androgen receptor in Sertoli cells to support germ cell development (spermatogenesis) and male fertility, but the molecular and cellular mechanisms by which testosterone acts are not well understood. Previously, we found that in addition to acting through androgen receptor to directly regulate gene expression (classical testosterone signaling pathway), testosterone acts through a nonclassical pathway via the androgen receptor to rapidly activate kinases that are known to regulate spermatogenesis. In this study, we provide the first evidence that nonclassical testosterone signaling occurs in vivo as the MAP kinase cascade is rapidly activated in Sertoli cells within the testis by increasing testosterone levels in the rat. We find that either classical or nonclassical signaling regulates testosterone-mediated Rhox5 gene expression in Sertoli cells within testis explants. The selective activation of classical or nonclassical signaling pathways in Sertoli cells within testis explants also resulted in the differential activation of the Zbtb16 and c-Kit genes in adjacent spermatogonia germ cells. Delivery of an inhibitor of either pathway to Sertoli cells of mouse testes disrupted the blood-testis barrier that is essential for spermatogenesis. Furthermore, an inhibitor of nonclassical testosterone signaling blocked meiosis in pubertal mice and caused the loss of meiotic and postmeiotic germ cells in adult mouse testes. An inhibitor of the classical pathway caused the premature release of immature germ cells. Collectively, these observations indicate that classical and nonclassical testosterone signaling regulate overlapping and distinct functions that are required for the maintenance of spermatogenesis and male fertility.

Blood-testis barrier and spermatogenesis: lessons from genetically-modified mice

The blood-testis barrier (BTB) is found between adjacent Sertoli cells in the testis where it creates a unique microenvironment for the development and maturation of meiotic and postmeiotic germ cells in seminiferous tubes. It is a compound proteinous structure, composed of several types of cell junctions including tight junctions (TJs), adhesion junctions and gap junctions (GJs). Some of the junctional proteins function as structural proteins of BTB and some have regulatory roles. The deletion or functional silencing of genes encoding these proteins may disrupt the BTB, which may cause immunological or other damages to meiotic and postmeiotic cells and ultimately lead to spermatogenic arrest and infertility. In this review, we will summarize the findings on the BTB structure and function from genetically-modified mouse models and discuss the future perspectives.

Androgen Receptor Coactivator ARID4B Is Required for the Function of Sertoli Cells in Spermatogenesis

Defects in spermatogenesis, a process that produces spermatozoa inside seminiferous tubules of the testis, result in male infertility. Spermatogenic progression is highly dependent on a microenvironment provided by Sertoli cells, the only somatic cells and epithelium of seminiferous tubules. However, genes that regulate such an important activity of Sertoli cells are poorly understood. Here, we found that AT-rich interactive domain 4B (ARID4B), is essential for the function of Sertoli cells to regulate spermatogenesis. Specifically, we generated Sertoli cell-specific Arid4b knockout (Arid4bSCKO) mice, and showed that the Arid4bSCKO male mice were completely infertile with impaired testis development and significantly reduced testis size. Importantly, severe structural defects accompanied by loss of germ cells and Sertoli cell-only phenotype were found in many seminiferous tubules of the Arid4bSCKO testes. In addition, maturation of Sertoli cells was significantly delayed in the Arid4bSCKO mice, associated with delayed onset of spermatogenesis. Spermatogenic progression was also defective, showing an arrest at the round spermatid stage in the Arid4bSCKO testes. Interestingly, we showed that ARID4B functions as a "coactivator" of androgen receptor and is required for optimal transcriptional activation of reproductive homeobox 5, an androgen receptor target gene specifically expressed in Sertoli cells and critical for spermatogenesis. Together, our study identified ARID4B to be a key regulator of Sertoli cell function important for male germ cell development.

Androgen receptor roles in spermatogenesis and infertility

Androgens such as testosterone are steroid hormones essential for normal male reproductive development and function. Mutations of androgen receptors (AR) are often found in patients with disorders of male reproductive development, and milder mutations may be responsible for some cases of male infertility. Androgens exert their action through AR and its signalling in the testis is essential for spermatogenesis. AR is not expressed in the developing germ cell lineage so is thought to exert its effects through testicular Sertoli and peri-tubular myoid (PTM) cells. AR signalling in spermatogenesis has been investigated in rodent models where testosterone levels are chemically supressed or models with transgenic disruption of AR. These models have pinpointed the steps of spermatogenesis that require AR signalling, specifically maintenance of spermatogonial numbers, blood-testis barrier integrity, completion of meiosis, adhesion of spermatids and spermiation, together these studies detail the essential nature of androgens in the promotion of male fertility.

Gene expression during testis development in Duroc boars

Androstenone is a steroid pheromone occurring in the pubertal Leydig cells. Breeding against androstenone can decrease pheromone odour in swine meat but appears to cause unwanted side effects such as delayed onset of puberty. To study causality, global gene expression in developing boar testes at 12, 16, 20 and 27 weeks was investigated using a porcine cDNA microarray. The morphological status and androgenic levels of the same individuals have been described in a previous publication. In the present paper, expression of genes and pathways has been analysed with reference to these findings. Nine clusters of genes with significant differential expression over time and 49 functional charts were found in the analysed testis samples. Prominent pathways in the prepubertal testis were associated with tissue renewal, cell respiration and increased endocytocis. E-cadherines may be associated with the onset of pubertal development. With elevated steroidogenesis (weeks 16 to 27), there was an increase in the expression of genes in the MAPK pathway, STAR and its analogue STARD6. A pubertal shift in genes coding for cellular cholesterol transport was observed. Increased expression of meiotic pathways coincided with the morphological onset of puberty. Puberty-related change in Ca(2+) pathway transcripts, neurosteroids, neuronal changes and signalling in redox pathways suggested a developmental-specific period of neuromorphogenesis. Several growth factors were found to increase differentially over time as the testis matured. There may be interactions between MAPK, STAR and growth factors during specific periods. In conclusion, pathways for neurogenesis, morphological pathways and several transcripts for growth factors, which have known modulating effects on steroidogenesis and gonadotropins in humans and rodents, act at specific ages and developmental stages in the boar testis. The age dependency and complexity shown for development-specific testis transcripts must be considered when selecting phenotypic parameters for genetic selection for low androstenone. The results of selection based on measurement of phenotypic maturation and androstenone (or other steroid) levels at one specific age may differ depending on the age used. More research is necessary to find the optimal phenotype to use in order to reduce the unwanted side effects.

Impact of low molecular weight phthalates in inducing reproductive malfunctions in male mice: Special emphasis on Sertoli cell functions

Phthalates are commonly used as plasticizers in a variety of products. Since they have been identified as endocrine-disrupting chemicals (EDCs), effect of phthalates on human health is a major concern. In this study, we evaluated individual as well as combined mixture effects of three low molecular weight phthalates on the reproductive system of male mice, specifically on the Sertoli cell structure and function. In order to analyze the blood testes barrier (BTB) dynamics, primary culture of Sertoli cells from 3-weeks old male mice was used for mimicking typical tight junction structures. Male mice were exposed to long-term (45 days) and combined mixture of three phthalates, diethyl phthalate (DEP), diphenyl phthalate (DPP), and dimethyl isophthalate (DMIP) between pre-pubertal to adult stage. Our data showed significant decrease (p < 0.05) in the rates of transcription of certain prominent Sertoli cell specific genes like transferrin, testin and occludin. Moreover, we also observed significant decreases in the expression of proteins like 3β-HSD, connexin-43 and occludin in testicular lysates of treated animals (p < 0.05). The transmission electron microscopic analysis revealed that the test compounds significantly altered the structural integrity of Sertoli cells. The significant changes of Sertoli cell tight junction structure by test compounds were associated with phosphorylation of ERK. Taken together, our study suggests that low molecular weight phthalates may affect male fertility by altering both structural and functional integrity of Sertoli cells in testes.

Diet-induced obesity in male C57BL/6 mice decreases fertility as a consequence of disrupted blood-testis barrier

Obesity is a complex metabolic disease that is a serious detriment to both children and adult health, which induces a variety of diseases, such as cardiovascular disease, type II diabetes, hypertension and cancer. Although adverse effects of obesity on female reproduction or oocyte development have been well recognized, its harmfulness to male fertility is still unclear because of reported conflicting results. The aim of this study was to determine whether diet-induced obesity impairs male fertility and furthermore to uncover its underlying mechanisms. Thus, male C57BL/6 mice fed a high-fat diet (HFD) for 10 weeks served as a model of diet-induced obesity. The results clearly show that the percentage of sperm motility and progressive motility significantly decreased, whereas the proportion of teratozoospermia dramatically increased in HFD mice compared to those in normal diet fed controls. Besides, the sperm acrosome reaction fell accompanied by a decline in testosterone level and an increase in estradiol level in the HFD group. This alteration of sperm function parameters strongly indicated that the fertility of HFD mice was indeed impaired, which was also validated by a low pregnancy rate in their mated normal female. Moreover, testicular morphological analyses revealed that seminiferous epithelia were severely atrophic, and cell adhesions between spermatogenic cells and Sertoli cells were loosely arranged in HFD mice. Meanwhile, the integrity of the blood-testis barrier was severely interrupted consistent with declines in the tight junction related proteins, occludin, ZO-1 and androgen receptor, but instead endocytic vesicle-associated protein, clathrin rose. Taken together, obesity can impair male fertility through declines in the sperm function parameters, sex hormone level, whereas during spermatogenesis damage to the blood-testis barrier (BTB) integrity may be one of the crucial underlying factors accounting for this change.

Restoration of spermatogenesis and male fertility using an androgen receptor transgene

Androgens signal through the androgen receptor (AR) to regulate male secondary sexual characteristics, reproductive tract development, prostate function, sperm production, bone and muscle mass as well as body hair growth among other functions. We developed a transgenic mouse model in which endogenous AR expression was replaced by a functionally modified AR transgene. A bacterial artificial chromosome (BAC) was constructed containing all AR exons and introns plus 40 kb each of 5' and 3' regulatory sequence. Insertion of an internal ribosome entry site and the EGFP gene 3’ to AR allowed co-expression of AR and EGFP. Pronuclear injection of the BAC resulted in six founder mice that displayed EGFP production in appropriate AR expressing tissues. The six founder mice were mated into a Sertoli cell specific AR knockout (SCARKO) background in which spermatogenesis is blocked at the meiosis stage of germ cell development. The AR-EGFP transgene was expressed in a cyclical manner similar to that of endogenous AR in Sertoli cells and fertility was restored as offspring were produced in the absence of Sertoli cell AR. Thus, the AR-EGFP transgene under the control of AR regulatory elements is capable of rescuing AR function in a cell selective, AR-null background. These initial studies provide proof of principle that a strategy employing the AR-EGFP transgene can be used to understand AR functions. Transgenic mice expressing selective modifications of the AR-EGFP transgene may provide crucial information needed to elicit the molecular mechanisms by which AR acts in the testis and other androgen responsive tissues.

Testosterone signaling and the regulation of spermatogenesis

Spermatogenesis and male fertility are dependent upon the presence of testosterone in the testis. In the absence of testosterone or the androgen receptor, spermatogenesis does not proceed beyond the meiosis stage. The major cellular target and translator of testosterone signals to developing germ cells is the Sertoli cell. In the Sertoli cell, testosterone signals can be translated directly to changes in gene expression (the classical pathway) or testosterone can activate kinases that may regulate processes required to maintain spermatogenesis (the non-classical pathway). Contributions of the classical and non-classical testosterone signaling pathways to the maintenance of spermatogenesis are discussed. Studies that may further elaborate the mechanisms by with the pathways support spermatogenesis are proposed.

Reconstruction of a seminiferous tubule-like structure in a 3 dimensional culture system of re-aggregated mouse neonatal testicular cells within a collagen matrix

Male gonad development is initiated by the aggregation of pre-Sertoli cells (SCs), which surround germ cells to form cords. Several attempts to reconstruct testes from dissociated testicular cells have been made; however, only very limited morphogenesis beyond seminiferous cord formation has been achieved. Therefore, we aimed to reconstruct seminiferous tubules using a 3-dimensional (D) re-aggregate culture of testicular cells, which were dissociated from 6-dpp neonatal mice, inside a collagen matrix. We performed a short-term culture (for 3 days) and a long-term culture (up to 3 wks). The addition of KnockOut Serum Replacement (KSR) promoted (1) the enlargement of SC re-aggregates; (2) the attachment of peritubular myoid (PTM) cells around the SC re-aggregates; (3) the sorting of germ cells inside, and Leydig cells outside, seminiferous cord-like structures; (4) the alignment of SC polarity inside a seminiferous cord-like structure relative to the basement membrane; (5) the differentiation of SCs (the expression of the androgen receptor); (6) the formation of a blood-testis-barrier between the SCs; (7) SC elongation and lumen formation; and (8) the proliferation of SCs and spermatogonia, as well as the differentiation of spermatogonia into primary spermatocytes. Eventually, KSR promoted the formation of seminiferous tubule-like structures, which accompanied germ cell differentiation. However, these morphogenetic events did not occur in the absence of KSR. This in vitro system presents an excellent model with which to identify the possible factors that induce these events and to analyze the mechanisms that underlie cellular interactions during testicular morphogenesis and germ cell differentiation.

Androgen-dependent sertoli cell tight junction remodeling is mediated by multiple tight junction components

Sertoli cell tight junctions (SCTJs) of the seminiferous epithelium create a specialized microenvironment in the testis to aid differentiation of spermatocytes and spermatids from spermatogonial stem cells. SCTJs must be chronically broken and rebuilt with high fidelity to allow the transmigration of preleptotene spermatocytes from the basal to adluminal epithelial compartment. Impairment of androgen signaling in Sertoli cells perturbs SCTJ remodeling. Claudin (CLDN) 3, a tight junction component under androgen regulation, localizes to newly forming SCTJs and is absent in Sertoli cell androgen receptor knockout (SCARKO) mice. We show here that Cldn3-null mice do not phenocopy SCARKO mice: Cldn3(-/-) mice are fertile, show uninterrupted spermatogenesis, and exhibit fully functional SCTJs based on imaging and small molecule tracer analyses, suggesting that other androgen-regulated genes must contribute to the SCARKO phenotype. To further investigate the SCTJ phenotype observed in SCARKO mutants, we generated a new SCARKO model and extensively analyzed the expression of other tight junction components. In addition to Cldn3, we identified altered expression of several other SCTJ molecules, including down-regulation of Cldn13 and a noncanonical tight junction protein 2 isoform (Tjp2iso3). Chromatin immunoprecipitation was used to demonstrate direct androgen receptor binding to regions of these target genes. Furthermore, we demonstrated that CLDN13 is a constituent of SCTJs and that TJP2iso3 colocalizes with tricellulin, a constituent of tricellular junctions, underscoring the importance of androgen signaling in the regulation of both bicellular and tricellular Sertoli cell tight junctions.

Mice depleted of the coxsackievirus and adenovirus receptor display normal spermatogenesis and an intact blood-testis barrier

The coxsackievirus and adenovirus receptor (CXADR (CAR)) is a cell adhesion molecule expressed mainly in epithelial cells. Numerous evidence indicate that CXADR has an important role in testis development and function of the blood-testis barrier (BTB) in vitro. The role of CXADR in testis physiology in vivo has, however, not been addressed. We therefore constructed a conditional CXADR knockout (cKO) mouse model in which CXADR can be depleted at any chosen timepoint by the administration of tamoxifen. We report for the first time that testicular depletion of CXADR in adult and pubertal mice does not alter BTB permeability or germ cell migration across the BTB during spermatogenesis. Adult cKO mice display normal junctional ultra-structure and localization of the junctional proteins claudin-3, occludin, junction-associated molecule-A (JAM-A), and ZO1. The BTB was intact with no leakage of biotin and lanthanum tracers into the tubular lumen. Adult CXADR cKO mice were fertile with normal sperm parameters and litter size. Breeding experiments and genotyping of the pups demonstrated that CXADR-negative sperm could fertilize WT eggs. In addition, knocking down CXADR from postnatal day 9 (P9) does not affect testicular development and BTB formation. These cKO mice were analyzed at P49 and P90 and display an intact barrier and uncompromised fertility. We conclude that CXADR possesses no direct role in testicular physiology in vivo.

The regulation of spermatogenesis by androgens

Testosterone is essential for maintaining spermatogenesis and male fertility. However, the molecular mechanisms by which testosterone acts have not begun to be revealed until recently. With the advances obtained from the use of transgenic mice lacking or overexpressing the androgen receptor, the cell specific targets of testosterone action as well as the genes and signaling pathways that are regulated by testosterone are being identified. In this review, the critical steps of spermatogenesis that are regulated by testosterone are discussed as well as the intracellular signaling pathways by which testosterone acts. We also review the functional information that has been obtained from the knock out of the androgen receptor from specific cell types in the testis and the genes found to be regulated after altering testosterone levels or androgen receptor expression.

Genome-wide identification of AR-regulated genes translated in Sertoli cells in vivo using the RiboTag approach

An understanding of the molecular mechanisms by which androgens drive spermatogenesis has been thwarted by the fact that few consistent androgen receptor (AR) target genes have been identified. Here, we addressed this issue using next-generation sequencing coupled with the RiboTag approach, which purifies translated mRNAs expressed in cells that express cyclic recombinase (CRE). Using RiboTag mice expressing CRE in Sertoli cells (SCs), we identified genes expressed specifically in SCs in both prepubertal and adult mice. Unexpectedly, this analysis revealed that the SC-specific gene program is already largely defined at the initiation of spermatogenesis despite the subsequent dramatic maturational changes known to occur in SCs. To identify AR-regulated genes, we generated triple-mutant mice in which the SCs express the RiboTag but lack ARs. RNA sequencing analysis revealed hundreds of SC-expressed AR-regulated genes that had previously gone unnoticed, including suppressed genes involved in ovarian development. Comparison of the SC-enriched dataset with that from the whole testes allowed us to classify genes in terms of their degree of expression in SCs. This revealed that a greater fraction of AR-up-regulated genes than AR-down-regulated genes were expressed predominantly in SCs. Our results also revealed that AR signaling in SCs causes a large number of genes not detectably expressed in SCs to undergo altered expression, thereby providing genome-wide evidence for wide-scale communication between SCs and other cells. Taken together, our results identified novel classes of genes expressed in a hormone-dependent manner in different testicular cell subsets and highlight a new approach to analyze cell type-specific gene regulation.

Receptors and signaling pathways involved in proliferation and differentiation of Sertoli cells

The identification of the hormones and other factors regulating Sertoli cell survival, proliferation, and maturation in neonatal, peripubertal, and pubertal life remains one of the most critical questions in testicular biology. The regulation of Sertoli cell proliferation and differentiation is thought to be controlled by cell-cell junctions and a set of circulating and local hormones and growth factors. In this review, we will focus on receptors and intracellular signaling pathways activated by androgen, follicle-stimulating hormone, thyroid hormone, activin, retinoids, insulin, insulin-like growth factor, relaxin, and estrogen, with special emphasis on estrogen receptors. Estrogen receptors activate intracellular signaling pathways that converge on cell cycle and transcription factors and play a role in the regulation of Sertoli cell proliferation and differentiation.

Differential role of the estrogen receptors ESR1 and ESR2 on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats

The aim of the present study was to investigate the role of each estrogen receptors on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats. Activation of ESR1 by 17β-estradiol (E2) and ESR1-selective agonist PPT increased CCND1 expression, and this effect was dependent on NF-kB activation. E2 and the ESR2-selective agonist DPN, but not PPT, increased, in a PI3K and CREB-dependent manner, the expression of CDKN1B and the transcription factors GATA-1 and DMRT1. Analyzing the expression of ESR1 and ESR2 in different stages of development of Sertoli cells, we observed that the ESR1/ESR2 ratio decreased with age, and this ratio seems to be important to determine the end of cell proliferation and the start of cell differentiation. In Sertoli cells from 15-day-old rats, the ESR1/ESR2 ratio favors the effect of ESR1 and the activation of this receptor increased [Methyl-(3)H]thymidine incorporation. We propose that in Sertoli cells from 15-day-old rats E2 modulates Sertoli cell proliferation through ESR1/NF-kB-mediated increase of CCND1, and cell cycle exit and differentiation through ESR2/CREB-mediated increase of CDKN1B, GATA-1 and DMRT1. The present study reinforces the important role of estrogen for normal testis development.

Up-regulation of SOX9 in sertoli cells from testiculopathic patients accounts for increasing anti-mullerian hormone expression via impaired androgen receptor signaling

Background

Testosterone provokes Sertoli cell maturation and represses AMH production. In adult patients with Sertoli-cells-only syndrome (SCOS) and androgen insensitivity syndrome (AIS), high level of AMH expression is detected in Sertoli cells due to defect of androgen/AR signaling.

Objective

We postulated that up-regulation of SOX9 due to impairment of androgen/AR signaling in Sertoli cells might explain why high level of anti-Mullerian hormone (AMH) expression occur in these testiculopathic patients.

Methods

Biological research of testicular specimens from men with azoospermia or mouse. The serum hormone levels were studied in 23 men with obstructive azoospermia, 33 men with SCOS azoospermia and 21 volunteers with normal seminograms during a period of 4 years.

Immunohistochemical staining and reverse-transcription PCR were used to examine the relationships among AR, SOX9 and AMH expression in adult human and mouse testes. The ability of AR to repress the expression of SOX9 and AMH was evaluated in vitro in TM4 Sertoli cells and C3H10T1/2 cells.

Results

SCOS specimens showed up-regulation of SOX9 and AMH proteins but down-regulation of AR proteins in Sertoli cells. The mRNA levels of AR were significantly lower and the SOX9, AMH mRNA levels higher in all SCOS patients compared to controls (P< 0.05). The testosterone levels in the SCOS patients were within the normal range, but most were below the median of the controls. Furthermore, our invitro cell line experiments demonstrated that androgen/AR signaling suppressed the gene and protein levels of AMH via repression of SOX9.

Conclusions

Our data show that the functional androgen/AR signaling to repress SOX9 and AMH expression is essential for Sertoli cell maturation. Impairment of androgen/AR signaling promotes SOX9-mediated AMH production, accounts for impairments of Sertoli cells in SCOS azoospermic patients.

Vitamin A deprivation affects the progression of the spermatogenic wave and initial formation of the blood-testis barrier, resulting in irreversible testicular degeneration in mice

The blood testis-barrier (BTB) is essential for maintaining homeostasis in the seminiferous epithelium. Although many studies have reported that vitamin A (VA) is required for the maintenance of spermatogenesis, the relationships between the BTB, spermatogenesis and VA have not been elucidated. In this study, we analyzed BTB assembly and spermatogenesis in the testes of mice fed the VA-deficient (VAD) diet from the prepubertal period to adulthood. During the prepubertal period, no changes were observed in the initiation and progression of the first spermatogenic wave in mice fed the VAD diet. However, the numbers of preleptotene/leptotene spermatocytes derived from the second spermatogenic wave onwards were decreased, and initial BTB formation was also delayed, as evidenced by the decreased expression of mRNAs encoding BTB components and VA signaling molecules. From 60 days postpartum, mice fed the VAD diet exhibited apoptosis of germ cells, arrest of meiosis, disruption of the BTB, and dramatically decreased testis size. Furthermore, vacuolization and calcification were observed in the seminiferous epithelium of adult mice fed the VAD diet. Re-initiation of spermatogenesis by VA replenishment in adult mice fed the VAD diet rescued BTB assembly after when the second spermatogenic wave initiated from the arrested spermatogonia reached the preleptotene/leptotene spermatocytes. These results suggested that BTB integrity was regulated by VA metabolism with meiotic progression and that the impermeable BTB was required for persistent spermatogenesis rather than meiotic initiation. In conclusion, consumption of the VAD diet led to critical defects in spermatogenesis progression and altered the dynamics of BTB assembly.

Androgen receptor (AR) physiological roles in male and female reproductive systems: lessons learned from AR-knockout mice lacking AR in selective cells

Androgens/androgen receptor (AR) signaling is involved primarily in the development of male-specific phenotypes during embryogenesis, spermatogenesis, sexual behavior, and fertility during adult life. However, this signaling has also been shown to play an important role in development of female reproductive organs and their functions, such as ovarian folliculogenesis, embryonic implantation, and uterine and breast development. The establishment of the testicular feminization (Tfm) mouse model exploiting the X-linked Tfm mutation in mice has been a good in vivo tool for studying the human complete androgen insensitivity syndrome, but this mouse may not be the perfect in vivo model. Mouse models with various cell-specific AR knockout (ARKO) might allow us to study AR roles in individual types of cells in these male and female reproductive systems, although discrepancies are found in results between labs, probably due to using various Cre mice and/or knocking out AR in different AR domains. Nevertheless, no doubt exists that the continuous development of these ARKO mouse models and careful studies will provide information useful for understanding AR roles in reproductive systems of humans and may help us to develop more effective and more specific therapeutic approaches for reproductive system-related diseases.

Experimental varicocoele in rats affects mechanisms that control expression and function of the androgen receptor

Varicocoele is an important cause of male infertility. Normal male reproductive function and fertility depends on a delicate balance between androgen receptor (AR) and the classic oestrogen receptors ESR1 (ERα) and ESR2 (ERβ). Using a model of surgically induced varicocoele in rats, this study aimed to investigate the effects of varicocoele on the expression of AR, ESR1, ESR2 and G-protein coupled oestrogen receptor (GPER). Varicocoele did not affect the mRNA and protein expression of ESR1 and ESR2 in both testes. Varicocoele did not affect the mRNA and protein expression of GPER in the right testis, but slightly reduced the mRNA and increased the protein levels in the left testis. Varicocoele did not affect the mRNA for AR, but reduced the protein levels in both testes. A proteomic approach was used in an attempt to find differentially expressed targets with possible correlation with AR downregulation. Varicocoele caused the differential expression of 29 proteins. Six proteins were upregulated, including the receptor for activated C kinase 1 (RACK1), and 23 were downregulated, including dihydrolipoamide dehydrogenase, alpha-enolase and pyrophosphatase 1. Western blot analysis confirmed that varicocoele upregulated the expression of RACK1, a protein involved with tyrosine phosphorylation and regulation of AR transcriptional activity, AR metabolism and dynamics of the blood-testis barrier. In conclusion, this study suggests that varicocoele affects mechanisms that control AR expression and function. This regulation of AR may play an important role in the varicocoele-induced testicular dysfunction. Furthermore, varicocoele downregulates several other proteins in the testis that may be useful markers of spermatozoa function and male infertility.

The prepubertal testis: biomarkers and functions

PURPOSE OF REVIEW

Biomarkers of prepubertal testicular function have become widely available only in recent years. The aim of this review is to update the knowledge on key biomarkers used to assess hypogonadism in boys.

RECENT FINDINGS

Sertoli cells are the most representative cells of the prepubertal testis. Anti-Müllerian hormone and inhibin B are essential biomarkers of Sertoli cell function. Also, INSL3 arises as an additional marker of Leydig cell dysfunction.

SUMMARY

The widespread use of these biomarkers has enhanced our knowledge on the pathophysiology and diagnosis of prepubertal male hypogonadism. Beyond their well known germ-cell toxicity, oncologic treatments may also affect Sertoli cell function. Pathophysiology is not the same in all aneuploidies leading to infertility: while hypogonadism is not evident until mid-puberty in Klinefelter syndrome, it is established in early infancy in Down syndrome. In Noonan syndrome, the occurrence of primary hypogonadism depends on the existence of cryptorchidism, and Prader-Willi syndrome may present with either primary or combined forms of hypogonadism. Prepubertal testicular markers have also provided insights into the effects of environmental disruptors on gonadal function from early life, and helped dissipate concerns about testicular function in boys born preterm or small for gestational age or conceived by assisted reproductive technique procedures.

Evidence for multiple roles for grainyhead-like 2 in the establishment and maintenance of human mucociliary airway epithelium.[corrected]

Most of the airways of the human lung are lined by an epithelium made up of ciliated and secretory luminal cells and undifferentiated basal progenitor cells. The integrity of this epithelium and its ability to act as a selective barrier are critical for normal lung function. In other epithelia, there is evidence that transcription factors of the evolutionarily conserved grainyheadlike (GRHL) family play key roles in coordinating multiple cellular processes required for epithelial morphogenesis, differentiation, remodeling, and repair. However, only a few target genes have been identified, and little is known about GRHL function in the adult lung. Here we focus on the role of GRHL2 in primary human bronchial epithelial cells, both as undifferentiated progenitors and as they differentiate in air-liquid interface culture into an organized mucociliary epithelium with transepithelial resistance. Using a dominant-negative protein or shRNA to inhibit GRHL2, we follow changes in epithelial phenotype and gene transcription using RNA sequencing or microarray analysis. We identify several hundreds of genes that are directly or indirectly regulated by GRHL2 in both undifferentiated cells and air-liquid interface cultures. Using ChIP sequencing to map sites of GRHL2 binding in the basal cells, we identify 7,687 potential primary targets and confirm that GRHL2 binding is strongly enriched near GRHL2-regulated genes. Taken together, the results support the hypothesis that GRHL2 plays a key role in regulating many physiological functions of human airway epithelium, including those involving cell morphogenesis, adhesion, and motility.

ARID4A and ARID4B regulate male fertility, a functional link to the AR and RB pathways

ARID4A and ARID4B are homologous members of the ARID (AT-rich interaction domain) gene family. ARID4A and ARID4B physically interact with each other. ARID4A is a retinoblastoma (RB)-binding protein. Biological function of these interactions is still unknown. Here, we report that mice with complete deficiency of Arid4a, combined with haploinsufficiency of Arid4b (Arid4a(-/-)Arid4b(+/-)), showed progressive loss of male fertility, accompanied by hypogonadism and seminal vesicle agenesis/hypodysplasia. Arid4a and Arid4b are expressed mainly in Sertoli cells of testes, which implies that their roles in Sertoli cell function are to support spermatogenesis and create the impermeable blood-testis barrier. In fact, evaluation of germ cell development in the Arid4a(-/-)Arid4b(+/-) mice showed spermatogenic arrest at the stages of meiotic spermatocytes and postmeiotic haploid spermatids. Analysis of the integrity of the blood-testis barrier showed increased permeability of seminiferous tubules in the Arid4a(-/-)Arid4b(+/-) testes. Interestingly, phenotypic Sertoli cell dysfunction in the Arid4a(-/-)Arid4b(+/-) mice, including spermatogenic failures and the impaired blood-testis barrier, recapitulated the defects found in the Sertoli cell-specific androgen receptor (AR) knockout mice and the Sertoli cell-specific RB knockout mice. Investigation of the molecular mechanism identified several AR- and RB-responsive genes as downstream targets of ARID4A and ARID4B. Our results thus indicate that ARID4A and ARID4B function as transcriptional coactivators for AR and RB and play an integral part in the AR and RB regulatory pathways involved in the regulation of Sertoli cell function and male fertility.

Entamoeba histolytica exacerbates epithelial tight junction permeability and proinflammatory responses in Muc2(-/-) mice

Human mucin-2 (MUC-2) is the first line of innate host defense in preventing pathogen-induced epithelial injury. Entamoeba histolytica (Eh) colonizes the mucus layer by binding of the parasite's surface galactose lectin to galactose and N-acetyl-d-galactosamine residues on colonic MUC-2, preventing parasite contact-dependent cytolysis of epithelial cells. We quantified early innate responses to Eh in wild-type and MUC-2-deficient mice (Muc2(-/-)) using closed colonic loops. Eh infection in wild-type but not Muc2(-/-) mice induced a time-dependent increase in (3)H-labeled mucin and nonmucin glycoprotein secretions. Immunohistochemical staining revealed intense MUC-2 secretion, which formed a thick, protective mucus plug overlying the surface epithelium, entrapping Eh. In Muc2(-/-) mice, Eh induced a pronounced time-dependent secretory exudate with increased gross pathology scores and serum albumin leakage. Colonic pathology, secretory responses, and increased proinflammatory cytokine secretions of TNF-α, IFN-γ, and IL-13 correlated with altered expression of the tight junction proteins claudin-2, occludin, and ZO-1. We identified the putative Eh virulence factor that elicits the proinflammatory responses and alters tight junction permeability as Eh cysteine protease A5 (EhCP-A5). The present findings demonstrate that colonic mucins confer both luminal and epithelial barrier functions and that, in the absence of MUC-2, mice are more susceptible to Eh-induced secretory and proinflammatory responses mediated by EhCP-A5.

The androgen receptor in health and disease

Androgens play pivotal roles in the regulation of male development and physiological processes, particularly in the male reproductive system. Most biological effects of androgens are mediated by the action of nuclear androgen receptor (AR). AR acts as a master regulator of downstream androgen-dependent signaling pathway networks. This ligand-dependent transcriptional factor modulates gene expression through the recruitment of various coregulator complexes, the induction of chromatin reorganization, and epigenetic histone modifications at target genomic loci. Dysregulation of androgen/AR signaling perturbs normal reproductive development and accounts for a wide range of pathological conditions such as androgen-insensitive syndrome, prostate cancer, and spinal bulbar muscular atrophy. In this review we summarize recent advances in understanding of the epigenetic mechanisms of AR action as well as newly recognized aspects of AR-mediated androgen signaling in both men and women. In addition, we offer a perspective on the use of animal genetic model systems aimed at eventually developing novel therapeutic AR ligands.

A switch in Sertoli cell responsiveness to FSH may be responsible for robust onset of germ cell differentiation during prepubartal testicular maturation in rats

FSH and Testosterone (T) regulate spermatogenesis via testicular Sertoli cells (Sc), which bear receptors for these hormones. Despite sufficient circulating levels of FSH and T postnatally, predominant appearance of spermatogonia B and spermatocytes is not discernible until 11 and 18 days of postnatal age, respectively, in rat testes. In an attempt to explore the underlying causes, we cultured Sc from neonatal (5- and 9-day-old) and prepubertal (12- and 19-day-old) rat testes and compared the status of FSH receptor (FSH-R) and androgen receptor (AR) signaling. Protein and mRNA levels of FSH-R and AR remained uniform in cultured Sc from all age groups. Androgen binding ability of AR was similar, and T-induced nuclear localization of AR was discernible in Sc from all age groups. Binding of FSH to FSH-R, subsequent production of cAMP, and mRNA of stem cell factor (SCF) and glial cell line-derived neurotrophic factor (GDNF), known to be essential for the robust differentiation of repopulating spermatogonia, were significantly augmented in prepubertal Sc compared with those in neonatal Sc. However, treatment of neonatal Sc with cholera toxin or forskolin, which stimulate cAMP production bypassing FSH-R, demonstrated a concomitant rise in SCF and GDNF mRNA expression, which was similar to the FSH-mediated rise observed in prepubertal Sc. These observations suggested that, during prepubertal Sc maturation, the ability of FSH-R to respond to FSH is significantly augmented and is associated with the robust differentiation of repopulating spermatogonia, and such a switch in Sc from FSH-resistant to FSH-responsive mode during prepubertal development may underlie the initiation of robust spermatogenesis.

Semen quality is influenced by androgen receptor and aromatase gene synergism

STUDY QUESTION

Does synergism between AR(CAG)(n) and CYP19(TTTA)(n) polymorphisms influence the quality of sperm?

SUMMARY ANSWER

AR(CAG)(n) and CYP19(TTTA)(n) polymorphisms had a synergistic effect on sperm concentration and motility.

WHAT IS KNOWN ALREADY

Androgens exert their action in the testicular tissue by binding to androgen receptor (AR), while their action is mediated by the aromatase P450 enzyme (CYP19). AR(CAG)(n) alleles are associated with sperm motility and CYP19(TTTA)(n) allelic variants have implications for sperm concentration and motility.

STUDY DESIGN, SIZE, DURATION

Two hundred oligozoospermic and 250 normozoospermic men who presented for infertility investigation were examined during a period of 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Conventional semen analysis was performed. DNA was extracted from spermatozoa and both polymorphisms were genotyped by polymerase chain reaction. Serum hormone levels were determined.

MAIN RESULTS AND THE ROLE OF CHANCE

Six combined genotypes were identified between the 18 AR(CAG)(n) alleles with 12-32 repeats and the 6 CYP19(TTTA)(n) alleles with 7-12 repeats. A gradual reduction in the sperm concentration (10(6)/ml) and motility (%) from long AR allele-non-CYP19(TTTA)(7) allele carriers to long AR allele-CYP19(TTTA)(7) homozygotes and from short AR allele-non-CYP19(TTTA)(7) carriers to short AR allele-CYP19(TTTA)(7) homozygotes was observed in normozoospermic men (means ± SD; concentration: 93 ± 53.1 versus 65 ± 48.6 and 85 ± 60.1 versus 37 ± 17.2l, P < 0.002; motility: 63 ± 10.3 versus 55 ± 14.5 and 52 ± 19.6 versus 41 ± 13.7, P < 0.001, respectively). Similar associations were observed in oligozoospermic men (concentration: 10 ± 4.2 versus 9 ± 5.9 and 10 ± 6.3 versus 6 ± 3.1, P < 0.03; motility: 47 ± 17.1 versus 39 ± 6.2 and 39 ± 22 versus 27 ± 18.3, P < 0.003, respectively). The above associations of the combined genotypes with sperm concentration and motility were confirmed in the total study population (P < 0.006 and P < 0.001, respectively).

LIMITATIONS, REASONS FOR CAUTION

Our study population was limited to Greek Caucasian adult males, residents of Northwest Greece.

WIDER IMPLICATIONS OF THE FINDINGS

The confirmation of our findings in other populations would verify the significance of AR and CYP19 genes for spermatogenesis.

STUDY FUNDING/COMPETING INTERESTS

This study did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector. The authors declare no conflicts of interest.

Proteomic changes in rat spermatogenesis in response to in vivo androgen manipulation; impact on meiotic cells

The production of mature sperm is reliant on androgen action within the testis, and it is well established that androgens act on receptors within the somatic Sertoli cells to stimulate male germ cell development. Mice lacking Sertoli cell androgen receptors (AR) show late meiotic germ cell arrest, suggesting Sertoli cells transduce the androgenic stimulus co-ordinating this essential step in spermatogenesis. This study aimed to identify germ cell proteins responsive to changes in testicular androgen levels and thereby elucidate mechanisms by which androgens regulate meiosis. Testicular androgen levels were suppressed for 9 weeks using testosterone and estradiol-filled silastic implants, followed by a short period of either further androgen suppression (via an AR antagonist) or the restoration of intratesticular testosterone levels. Comparative proteomics were performed on protein extracts from enriched meiotic cell preparations from adult rats undergoing androgen deprivation and replacement in vivo. Loss of androgenic stimulus caused changes in proteins with known roles in meiosis (including Nasp and Hsp70–2), apoptosis (including Diablo), cell signalling (including 14-3-3 isoforms), oxidative stress, DNA repair, and RNA processing. Immunostaining for oxidised DNA adducts confirmed spermatocytes undergo oxidative stress-induced DNA damage during androgen suppression. An increase in PCNA and an associated ubiquitin-conjugating enzyme (Ubc13) suggested a role for PCNA-mediated regulation of DNA repair pathways in spermatocytes. Changes in cytoplasmic SUMO1 localisation in spermatocytes were paralleled by changes in the levels of free SUMO1 and of a subunit of its activating complex, suggesting sumoylation in spermatocytes is modified by androgen action on Sertoli cells. We conclude that Sertoli cells, in response to androgens, modulate protein translation and post-translational events in spermatocytes that impact on their metabolism, survival, and completion of meiosis.

Tissue- and cell-specific functions of the androgen receptor revealed through conditional knockout models in mice

This review aims to evaluate the contribution of individual cell-selective knockout models to our current understanding of androgen action. Cre/loxP technology has allowed the generation of cell-selective knockout models targeting the androgen receptor (AR) in distinct putative target cells in a wide variety of organs and tissues including: testis, ovary, accessory sex tissues, muscle, bone, fat, liver, skin and myeloid tissue. In some androgen-regulated processes such as spermatogenesis and folliculogenesis this approach has lead to the identification of a key cellular mediator of androgen action (Sertoli and granulosa cells, respectively). In many target tissues, however, the final response to androgens appears to be more complex. Here, cell-selective knockout technology offers a platform upon which we can begin to unravel the more complex interplay and signaling pathways of androgens. A prototypic example is the analysis of mesenchymal-epithelial interactions in many accessory sex glands. Furthermore, for some actions of testosterone, in which part of the effect is mediated by the active metabolite 17β-estradiol, conditional knockout technology offers a novel strategy to study the relative contribution of AR and estrogen receptor-mediated signaling. The latter approach has already resulted in a better understanding of androgen action in brain and bone. Finally, cell-selective knockout technology has generated valuable models to search for AR-controlled molecular mediators of androgen action, a strategy that has successfully been applied to the study of androgen action in the testis and in the epididymis. Although some conditional knockout models have provided clear answers to physiologic questions, it should be noted that others have pointed to unexpected complexities or technical limitations confounding interpretation of the results.

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.

Sertoli cell-specific deletion of the androgen receptor compromises testicular immune privilege in mice

In the mammalian testis, meiotic and postmeiotic germ cell antigens are granted immune privilege. Both local immune suppression and specialized intercellular junctions between somatic Sertoli cells have been proposed to contribute to a highly restricted and effective blood-testis barrier (BTB) that helps maintain tolerance to germ cell antigens. Several studies have suggested that androgens play a role in immune suppression, although direct evidence for this is lacking. We previously reported that Sertoli cell-specific ablation of the androgen receptor (Ar) decreases expression of Cldn3, an androgen-regulated gene and component of Sertoli cell tight junctions, and increases the permeability of the BTB to biotin, a small-molecular-weight tracer. The physiological consequences of Sertoli cell-specific Ar (S-Ar) ablation on immune privilege are unknown. Here we show that in the testes of S-Ar mutant mice, the ultrastructure of Sertoli cell tight junctions is defective and testicular IgG levels are elevated. The interstitium of S-Ar mutant testes becomes populated with macrophages, neutrophils, plasma cells, and eosinophils, and serum samples of mutant mice contain antibodies against germ cell antigens. Together, these results suggest that Sertoli cell-specific deletion of the androgen receptor results in loss of testicular immune privilege. Suppressed levels of androgen signaling may be a contributing factor in idiopathic male infertility.