Local control systems within the testis

Spermatogenesis and cryptorchidism

Cryptorchidism represents the most common endocrine disease in boys, with infertility more frequently observed in bilateral forms. It is also known that undescended testes, if untreated, lead to an increased risk of testicular tumors, usually seminomas, arising from mutant germ cells. In normal testes, germ cell development is an active process starting in the first months of life when the neonatal gonocytes transform into adult dark (AD) spermatogonia. These cells are now thought to be the stem cells useful to support spermatogenesis. Several researches suggest that AD spermatogonia form between 3 and 9 months of age. Not all the neonatal gonocytes transform into AD spermatogonia; indeed, the residual gonocytes undergo involution by apoptosis. In the undescended testes, these transformations are inhibited leading to a deficient pool of stem cells for post pubertal spermatogenesis. Early surgical intervention in infancy may allow the normal development of stem cells for spermatogenesis. Moreover, it is very interesting to note that intra-tubular carcinoma in situ in the second and third decades have enzymatic markers similar to neonatal gonocytes suggesting that these cells fail transformation into AD spermatogonia and likely generate testicular cancer (TC) in cryptorchid men. Orchidopexy between 6 and 12 months of age is recommended to maximize the future fertility potential and decrease the TC risk in adulthood.

Tzfp represses the androgen receptor in mouse testis

The testis zinc finger protein (Tzfp), also known as Repressor of GATA, belongs to the BTB/POZ zinc finger family of transcription factors and is thought to play a role in spermatogenesis due to its remarkably high expression in testis. Despite many attempts to find the in vivo role of the protein, the molecular function is still largely unknown. Here, we address this issue using a novel mouse model with a disrupted Tzfp gene. Homozygous Tzfp null mice are born at reduced frequency but appear viable and fertile. Sertoli cells in testes lacking Tzfp display an increase in Androgen Receptor (AR) signaling, and several genes in the testis, including Gata1, Aie1 and Fanc, show increased expression. Our results indicate that Tzfp function as a transcriptional regulator and that loss of the protein leads to alterations in AR signaling and reduced number of apoptotic cells in the testicular tubules.

Cholesterol and male fertility: what about orphans and adopted?

The link between cholesterol homeostasis and male fertility has been clearly suggested in patients who suffer from hyperlipidemia and metabolic syndrome. This has been confirmed by the generation of several transgenic mouse models or in animals fed with high cholesterol diet. Next to the alteration of the endocrine signaling pathways through steroid receptors (androgen and estrogen receptors); "orphan" and "adopted" nuclear receptors, such as the Liver X Receptors (LXRs), the Proliferating Peroxisomal Activated Receptors (PPARs) or the Liver Receptor Homolog-1 (LRH-1), have been involved in this cross-talk. These transcription factors show distinct expression patterns in the male genital tract, explaining the large panel of phenotypes observed in transgenic male mice and highlighting the importance of lipid homesostasis and the complexity of the molecular pathways involved. Increasing our knowledge of the roles of these nuclear receptors in male germ cell differentiation could help in proposing new approaches to either treat infertile men or define new strategies for contraception.

Epigenetic: a molecular link between testicular cancer and environmental exposures

In the last decades, studies in rodents have highlighted links between in utero and/or neonatal exposures to molecules that alter endocrine functions and the development of genital tract abnormalities, such as cryptorchidism, hypospadias, and impaired spermatogenesis. Most of these molecules, called endocrine disrupters exert estrogenic and/or antiandrogenic activities. These data led to the hypothesis of the testicular dysgenesis syndrome which postulates that these disorders are one clinical entity and are linked by epidemiological and pathophysiological relations. Furthermore, infertility has been stated as a risk factor for testicular cancer (TC). The incidence of TC has been increasing over the past decade. Most of testicular germ cell cancers develop through a pre-invasive carcinoma in situ from fetal germ cells (primordial germ cell or gonocyte). During their development, fetal germ cells undergo epigenetic modifications. Interestingly, several lines of evidence have shown that gene regulation through epigenetic mechanisms (DNA and histone modifications) plays an important role in normal development as well as in various diseases, including TC. Here we will review chromatin modifications which can affect testicular physiology leading to the development of TC; and highlight potential molecular pathways involved in these alterations in the context of environmental exposures.

Androgens and spermatogenesis: lessons from transgenic mouse models

Transgenic mouse models have contributed considerably to our understanding of the cellular and molecular mechanisms by which androgens control spermatogenesis. Cell-selective ablation of the androgen receptor (AR) in Sertoli cells (SC) results in a complete block in meiosis and unambiguously identifies the SC as the main cellular mediator of the effects of androgens on spermatogenesis. This conclusion is corroborated by similar knockouts in other potential testicular target cells. Mutations resulting in diminished expression of the AR or in alleles with increased length of the CAG repeat mimick specific human forms of disturbed fertility that are not accompanied by defects in male sexual development. Transcriptional profiling studies in mice with cell-selective and general knockouts of the AR, searching for androgen-regulated genes relevant to the control of spermatogenesis, have identified many candidate target genes. However, with the exception of Rhox5, the identified subsets of genes show little overlap. Genes related to tubular restructuring, cell junction dynamics, the cytoskeleton, solute transportation and vitamin A metabolism are prominently present. Further research will be needed to decide which of these genes are physiologically relevant and to identify genes that can be used as diagnostic tools or targets to modulate the effects of androgens in spermatogenesis.

d-Aspartic acid and nitric oxide as regulators of androgen production in boar testis

D-Aspartic acid (D-Asp) and nitric oxide (NO) are two biologically active molecules playing important functions as neurotransmitters and neuromodulators of nerve impulse and as regulators of hormone production by endocrine organs. We studied the occurrence of D-Asp and NO as well as their effects on testosterone synthesis in the testis of boar. This model was chosen for our investigations because it contains more Leydig cells than other mammals. Indirect immunofluorescence applied to cryostat sections was used to evaluate the co-localization of D-Asp and of the enzyme nitric oxide synthase (NOS) in the same Leydig cells. D-Asp and NOS often co-existed in the same Leydig cells and were found, separately, in many other testicular cytotypes. D-Asp level was dosed by an enzymatic method performed on boar testis extracts and was 40+/-3.6 nmol/g of fresh tissue. NO measurement was carried out using a biochemical method by NOS activity determination and expressed as quantity of nitrites produced: it was 155.25+/-21.9 nmol/mg of tissue. The effects of the two molecules on steroid hormone production were evaluated by incubating testis homogenates, respectively with or without D-Asp and/or the NO-donor L-arginine (L-Arg). After incubation, the testosterone presence was measured by immunoenzymatic assay (EIA). These in vitro experiments showed that the addition of D-Asp to incubated testicular homogenates significantly increased testosterone concentration, whereas the addition of L-Arg decreased the hormone production. Moreover, the inclusion of L-Arg to an incubation medium of testicular homogenates with added D-Asp, completely inhibited the stimulating effects of this enantiomer. Our results suggest an autocrine action of both D-Asp and NO on the steroidogenetic activity of the Leydig cell.

Protection from Radiation-Induced Male Germ Cell Loss by Sphingosine-1-Phosphate1

Male germ cells are susceptible to radiation-induced injury, and infertility is a common problem after total-body irradiation. Here we investigated, first, the effects of irradiation on germ cells in mouse testis and, second, the role of sphingosine-1-phosphate (S1P) treatment in radiation-induced male germ cell loss. Irradiation of mouse testes mainly damaged the early developmental stages of spermatogonia. The damage was seen by means of DNA flow cytometry 21 days after irradiation as decreasing numbers of spermatocytes and spermatids with increasing amounts of ionizing radiation (0.1-2.0 Gy). Intratesticular injections of S1P given 1-2 h before irradiation (0.5 Gy) did not protect against short-term germ cell loss as measured by in situ end labeling of DNA fragmentation 16 h after irradiation. However, after 21 days, in the S1P-treated testes, the numbers of primary spermatocytes and spermatogonia at G2 (4C peak as measured by flow cytometry) were higher at all stages of spermatogenesis compared with vehicle-treated testes, indicating protection of early spermatogonia by S1P, whereas the spermatid (1C) populations were similar. In conclusion, S1P appears to protect partially (16%-47%) testicular germ cells against radiation-induced cell death. This warrants further studies aimed at development of therapeutic agents capable of blocking sphingomyelin-induced pathways of germ cell loss.

A Sertoli cell-selective knockout of the androgen receptor causes spermatogenic arrest in meiosis

Androgens control spermatogenesis, but germ cells themselves do not express a functional androgen receptor (AR). Androgen regulation is thought to be mediated by Sertoli and peritubular myoid cells, but their relative roles and the mechanisms involved remain largely unknown. Using Cre/loxP technology, we have generated mice with a ubiquitous knockout of the AR as well as mice with a selective AR knockout in Sertoli cells (SC) only. Mice with a floxed exon 2 of the AR gene were crossed with mice expressing Cre recombinase ubiquitously or selectively in SC (under control of the anti-Müllerian hormone gene promoter). AR knockout males displayed a complete androgen insensitivity phenotype. Testes were located abdominally, and germ cell development was severely disrupted. In contrast, SC AR knockout males showed normal testis descent and development of the male urogenital tract. Expression of the homeobox gene Pem, which is androgen-regulated in SC, was severely decreased. Testis weight was reduced to 28% of that in WT littermates. Stereological analysis indicated that the number of SC was unchanged, whereas numbers of spermatocytes, round spermatids, and elongated spermatids were reduced to 64%, 3%, and 0% respectively of WT. These changes were associated with increased germ cell apoptosis and grossly reduced expression of genes specific for late spermatocyte or spermatid development. It is concluded that cell-autonomous action of the AR in SC is an absolute requirement for androgen maintenance of complete spermatogenesis, and that spermatocyte/spermatid development/survival critically depends on androgens.

Antifertility effect of chronically administered Martynia annua root extract on male rats

The effects of 50% ethanol extract of Martynia annua L. root on reproduction was studied on male rats. The study was divided into four groups of five animals each. The first group (I) received vehicle alone to serve as control. The second, third and fourth groups (II, III and IV) of animals were administered the root extract daily at 50 mg/kg body weight, po, 100 mg/kg body weight, po, and 200 mg/kg body weight, po, respectively, for a period of 60 days. Significant decreases in the weights of testes, epididymides, seminal vesicle and ventral prostate were observed. A dose related reduction in the testicular sperm count, epididymal sperm count and motility, number of fertile males, ratio between delivered and inseminated females and number of pups were observed. The testis showed a clear correlation between the dose and severity of lesions of seminiferous epithelium. In general, the seminiferous tubules appear reduced in size with a frequently filled eosinophilic material. Spermatogenesis arrested at the secondary spermatocyte stage. Pachytene spermatocytes were undergoing degeneration. Disorganisation and sloughing of immature germ cells were visible. Leydig cells were atrophied. No morphological changes were observed in Sertoli cells. Significant reduction in serum concentration of luteinising hormone and testosterone were observed. No distinct change in serum FSII concentration was recorded. The final body weights of all groups were elevated markedly. No alterations were recorded in any hematological parameters. It is concluded that the 50% ethanol extract of M. annua root produced dose related effects on male reproduction without altering general body metabolism.

Computer-assisted sperm motion analysis of bovine sperm treated with insulin-like growth factor I and II: implications as motility regulators and chemokinetic factors

The effects of insulin-like growth factors (IGFs) I and II on motility of bovine sperm were examined using a computer-assisted sperm motion analyzer (CASA). The following kinematic parameters were examined: percentage of rapidly moving cells, straight-line velocity , curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency. Sperm were treated with IGF-I (100 ng/mL) or IGF-II (250 ng/mL) and compared to sperm in modified Tyrodes' medium only (control) at 90, 180, and 360 min using CASA. Insulin-like growth factor I and II increased the percentage of rapidly moving cells, straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency compared to the control treatment. These results indicate that IGFs may be involved in initiation and maintenance of bovine sperm motility.

Identification of IL-6 as one of the important cytokines responsible for the ability of mononuclear cells to stimulate Sertoli cell functions

There is increasing evidence that locally produced cytokines may play an important role in the control of testicular function. In a previous report we demonstrated that medium conditioned by activated human peripheral blood mononuclear cells (PBMC-CM), which is a rich source of cytokines, has extremely potent effects on Sertoli cell transferrin and cGMP secretion. Part of this activity could be explained by interleukin-1beta (IL-1beta) but additional cytokines were evidently involved. In the present study we tried to characterize and purify additional components active on Sertoli cells from PBMC-CM. To this end PBMC-CM was subjected to a purification procedure involving successively: adsorption to silicic acid, affinity chromatography with an antiserum recognizing a mixture of cytokines except IL-1beta, gel-filtration, reversed-phase HPLC and cation-exchange FPLC. Throughout this protocol a Sertoli cell bioassay was used to monitor the effects on transferrin and cGMP production. After cation-exchange FPLC, SDS-PAGE using silver staining showed a single protein band in the bioactive fractions. NH2-terminal amino-acid sequencing revealed that the active principle(s) in this band corresponded to four truncated forms of IL-6 missing the first 13, 14, 17 and 18 N-terminal amino-acids, respectively. The truncated IL-6 molecules were as active as intact IL-6 in the Sertoli cell bioassay. Since neither IL-1beta nor IL-6 alone or in combination could account for the extremely potent effect of PBMC-CM, we tested a series of additional cytokines (IL-1alpha, INF-alpha, IL-4, TGF-beta, IFN-gamma) alone and in combination with IL-1beta and IL-6. These data suggest that IL-1beta, IL-6 and TNF-alpha display more than additive effects on Sertoli cell transferrin and cGMP secretion and that the combination of these cytokines may explain the major part of the effects observed with crude PBMC-CM. The observation that the latter effects could be observed with murine as well as human IL-1beta, IL-6 and TNF-alpha further supports the potential physiological relevance of these findings.

Vitamin A and beta carotene levels in constitutional delay of growth and puberty

The objective of this study was to investigate the vitamin A (vit A) status and beta carotene levels of children with constitutional delay of growth and puberty (CDGP). Serum vit A and beta-carotene levels of 26 children with CDGP were measured. 20 age-matched healthy children with normal pubertal development served as controls. Except for the height SDS, which was significantly lower in the CDGP group (p < 0.05), no significant differences were found between chronological ages, weight for height indices and beta-carotene levels of the two groups (p > 0.05). Although serum vit A levels of children in both groups were within normal limits according to WHO criteria, serum vit A levels were significantly lower in the CDGP group than in controls (44.13 +/- 12.25 and 59.60 +/- 19.75 micrograms/dl respectively, p < 0.05). It was concluded that vit A deficiency may play a role in CDGP in developing countries.

Sertoli cell conditioned media modulate the androgen biosynthetic pathways in rat Leydig cell primary cultures

Increasing evidence suggests the presence of local modulators that contribute to testicular function regulation in rats. The seminiferous tubules and Sertoli cell factors influence the steroidogenic activity of Leydig cells. Addition of Sertoli cell conditioned media to primary cultures of adult rat Leydig cells produces in a dose-dependent manner an inhibition of testosterone production with a concomitant decrease in the C21 delta 4-intermediates of the steroidogenic pathway, modifying the C21/C19 ratios in normal cells. The nature and mechanisms of action of this putative modulating activity are currently under study.

Effects of inhibin on rat gonadal differentiation and development in vitro

Previously we examined that inhibin-alpha subunit, transforming growth factor-beta 1 (TGF-beta 1) and epidermal growth factor (EGF) were expressed in sex-, cell- and stage-specific manners in perinatal rat gonads. To clarify effects of these growth factors on the rat gonadal differentiation and development, indifferent gonadal primordia with mesonephric tubules on gestational day 13 were cultured in vitro for 4 days in serum-free CMRL-1066 medium with inhibin, TGF-beta 1, EGF, anti-sera against these growth factors, testosterone or estradiol-17 beta, and then morphologically examined with reference to seminiferous tubule formation, germ cell division, Wolffian and Müllerian duct development. In male gonads, anti-inhibin-alpha serum suppressed the seminiferous tubule formation but inhibin, TGF-beta 1, EGF or steroid hormones did not affect on the tubule formation, germ cell proliferation nor gonoduct development. Seminiferous tubules in male gonads cultured in the medium containing anti-inhibin-alpha serum were incomplete and irregular in shape. On the other hand, in female gonads, inhibin suppressed the germ cell division and anti-inhibin-alpha serum led to the necrosis of germ cells, but other factors affected to neither sex cord formation nor germ cell division. Testosterone and estradiol-17 beta stimulated female Wolffian and Müllerian duct development, respectively. These results indicate that inhibin induces the seminiferous tubule formation and suppresses the female germ cell division in developing rat gonads in vitro.

Insulin-like growth factor (IGF-I) mRNA and IGF-I receptor in trout testis and in isolated spermatogenic and Sertoli cells

Few data exist concerning the occurrence and potential role of an insulin-like growth factor (IGF) system in fish gonads. Using Northern and slot blot hybridization with a specific salmon IGF-I cDNA, we confirmed that IGF-I transcription occurs in trout testis. Testicular IGF-I mRNA abundance may be increased by long-term GH treatment in juvenile fish, while shorter treatment with growth hormone (GH) or a gonadotropin (GTH-II) in maturing males had no statistically significant effect. Radiolabelled recombinant human IGF-I binds with high affinity to crude trout testis preparation, to cultured isolated testicular cells, and to a membrane fraction of these cells (Ka = 0.2 to 0.7 x 10(10) M-1; Bmax = 10 to 20 fmol/10(7) cells, and 68 fmol/mg protein of membrane). The binding site was identified as type 1 IGF receptor by its binding specificity (IGF-I > IGF-II >>> insulin) and the molecular size of its alpha-subunit labelled with 125I-IGF-I (M(r)125-140 kDa). 125I-IGF-II also bound to the type 1 receptor whereas IGF-II/ mannose 6 phosphate receptors could not be detected. Separation of isolated testicular cells by Percoll gradient and centrifugal elutriation provided populations enriched in different types of intratubular cells. IGF-I mRNA (detected by reverse transcription + polymerase chain reaction [PCR]) and IGF-I receptors (measured by competitive binding) were observed to a greater extent in Sertoli cell-enriched populations and in spermatogonia with primary spermatocytes. Therefore, IGF-I is a potential paracrine/autocrine regulator inside the spermatogenic compartment and appears as a possible mediator of GH action at the gonadal level in fish.

Male contraception

With the powerful tools of molecular investigation, the last decade has witnessed the most remarkable scientific advance in our history, yet no new leads for male contraception have been forthcoming. All the likely methods of male contraception discussed above were derived from relatively 'old' physiological principles or serendipitous observations. The increasing gap between fundamental research (in the control of mammalian spermatogenesis) and the lack of clinical application are a testament to the low public funding priority afforded to male reproduction and the unwillingness of the pharmaceutical industry to invest in male reproductive research and development. Yet amidst such an unfavourable setting and with very limited support, it is heartening to note that the prospects of introducing a new systemic method for male contraception into the market by the end of this millenium has been greatly enhanced. Thus the results of recent studies have confirmed the contraceptive efficacy of sex steroid-induced oligozoospermia and unexpectedly revealed an ethnically distinct pattern of susceptibility to the hormonal suppression of spermatogenesis. Thus, Asian men are more responsive than are caucasian, and long-acting testosterone esters now being tested in that most densely populated part of the world may well hasten the large-scale application of this method. This is probably the most effective way to correct the misconceptions that men are unwilling or disinterested in sharing in family planning options with their partners. Together with the increased acceptance of novel non-surgical and reversible methods of vas deferens occlusion and the availability of improved non-latex condoms, the currently unfulfilled contraceptive needs of millions of men can be increasingly met in future years. The consequent increase in overall contraceptive prevalence could well make the telling difference between demographic catastrophe and maintaining good quality existence. Politicians, scientists and industrialists need to wake up to their responsibilities and the opportunities offered by this untapped resource and market potential.