The functional significance of FSH in spermatogenesis and the control of its secretion in male primates

Insufficient androgen and FSH signaling may be responsible for the azoospermia of the infantile primate testes despite exposure to an adult-like hormonal milieu

BACKGROUND

In humans, as well as in other higher primates, the infantile testis is exposed to an adult-like hormonal milieu, but spermatogenesis is not initiated at this stage of primate development. In the present study, we examined the molecular basis of this intriguing infertile state of the primate testis.

METHODS

The integrity of androgen receptor (AR) and FSH receptor (FSHR) signaling pathways in primary cultures of Sertoli cells (Scs) harvested from azoospermic infant and spermatogenic pubertal monkey testes were investigated under identical in vitro hormonal conditions. In order to synchronously harvest Scs from early pubertal testis, the activation of testicular puberty was timed experimentally by prematurely initiating gonadotrophin secretion in juvenile animals with an intermittent infusion of gonadotrophin-releasing hormone.

RESULTS

While qRT-PCR demonstrated that AR and FSHR mRNA expression in Scs from infant and pubertal testes were comparable, androgen-binding and FSH-mediated cAMP production by infant Scs was extremely low. Compromised AR and FSHR signaling in infant Scs was further supported by the finding that testosterone (T) and FSH failed to augment the expression of the T responsive gene, claudin 11, and the FSH responsive genes, inhibin-βB, stem cell factor (SCF) and glial cell line-derived neurotrophic factor (GDNF) in Scs harvested at this stage of development.

CONCLUSION

These results indicate that compromised AR and FSHR signaling pathways in Scs underlie the inability of the infant primate testis to respond to an endogenous hormonal milieu that later in development, at the time puberty, stimulates the initiation of spermatogenesis. This finding may have relevance to some forms of idiopathic infertility in men.

Pharmacogenetics of follicle-stimulating hormone action

PURPOSE OF REVIEW

To review the current knowledge of genetic variants in the two genes affecting the individual responsiveness to follicle-stimulating hormone (FSH) action-the FSH beta-subunit (FSHB) and the FSH receptor (FSHR), as well as the pharmacogenetic ramifications of the findings.

RECENT FINDINGS

Four common variants in the FSHB and the FSHR genes were shown to exhibit significant effect on FSH action: linked FSHR variants Thr307Ala and Asn680Ser determining common receptor isoforms, and gene expression affecting polymorphisms FSHR -29G/A and FSHB -211G/T. In women, the FSHR Thr307Ala/Asn680Ser polymorphisms show consistent predictive value for estimating the most optimal recombinant FSH dosage in controlled ovarian hyperstimulation (COH). The same variants exhibit a potential for the pharmacogenetic assessment of the treatment of polycystic ovarian syndrome. The FSHR -29G/A variant was also shown to contribute to ovarian response to COH. Pilot studies have suggested the FSHB -211 TT homozygous oligozoospermic men with genetically determined low concentration of FSH, as potentially the best responders to FSH treatment; furthermore, modulation of this response by FSHR polymorphisms is possible.

SUMMARY

Genetic variants in FSHB and FSHR exhibit a potential for pharmacogenetic applications in selecting appropriate treatment options (timing and dosage) in male and female conditions requiring or benefiting from FSH therapy.

Assessment of circulating hormones in regulatory toxicity studies II. Male reproductive hormones

When test article-related testicular toxicity or Leydig cell tumors are identified in nonclinical studies, the measurement of circulating hormones such as luteinizing hormone, follicle-stimulating hormone, inhibin, testosterone, or prolactin is often considered in order to aid mechanistic investigations or to identify potential biomarkers in man. Although some hormone levels are relatively constant, others are subject to wide variability owing to pulsatility of secretion, diurnal rhythms, and stress. To avoid being misled, it is important that this variation is factored into any study design that includes hormone measurements. Since all these possibilities start from the pathologist's reading of the tissue sections, we begin with a review of the morphologic changes that are tied to underlying alterations in hormones. We then provide the reader with basic information and representative hormone data, including coefficients of variation, for the major male reproductive hormones in the three main nonclinical species (rats, dogs, and cynomolgus monkeys). Power and probability tables for rats and dogs allow estimates of the number of animals or samples needed to provide a given likelihood of detecting a hormonal change of a given size. More importantly, we highlight the variability of this process and the real value in readers developing this information at their own site.

The follicle-stimulating hormone receptor: a novel target in genitourinary malignancies

Follicle-stimulating hormone (FSH) is a central hormone in mammalian reproductive biology. The FSH receptor (FSHR), which was previously believed to be expressed primarily in the ovary and testis, was recently found to be expressed in the tumor blood vessels of many solid tumor types, including prostate adenocarcinoma, urothelial carcinoma, and renal cell carcinoma. While the biologic significance of FSHR in tumor blood vessels has yet to be elucidated, FSHR may contribute to neoangiogenesis. FSHR has been reported to be expressed by prostate cancer cells and, thus, targeting FSHR in prostate cancer may be of particular utility. In this report, we discuss the finding of FSHR in tumor blood vessels and review the literature concerning FSHR in genitourinary malignancy. We also discuss the features that make FSHR an appealing target for therapeutic and imaging purposes and the potential utility of FSHR as a prognostic and/or predictive biomarker in genitourinary cancers.

Possible therapeutic use of spermatogonial stem cells in the treatment of male infertility: a brief overview

Development of germ cells is a process starting in fetus and completed only in puberty. Spermatogonial stem cells maintain spermatogenesis throughout the reproductive life of mammals. They are undifferentiated cells defined by their ability to both self-renew and differentiate into mature spermatozoa. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression as well as the extrinsic gene signals from the local tissue microenvironment. The human testis is prone to damage, either for therapeutic reasons or because of toxic agents from the environment. For preservation of fertility, patients who will undergo radiotherapy and/or chemotherapy have an attractive possibility to keep in store and afterwards make a transfer of spermatogonial stem cells. Germ cell transplantation is not yet ready for the human fertility clinic, but it may be reasonable for young cancer patients, with no other options to preserve their fertility. Whereas this technique has become an important research tool in rodents, a clinical application must still be regarded as experimental, and many aspects of the procedure need to be optimized prior to a clinical application in men. In future, a range of options for the preservation of male fertility will get a new significance.

Neonatal gonadotropin therapy in male congenital hypogonadotropic hypogonadism

Congenital hypogonadotropic hypogonadism (CHH) causes pubertal failure and infertility in both women and men due to partial or total secretory failure of the two pituitary gonadotropins lutropin (LH) and follitropin (FSH) during periods of physiological activation of the gonadotropic axis. Men and women with CHH frequently seek treatment for infertility after hypogonadism therapy. Some etiologies, such as autosomal dominant or X-linked Kallmann syndrome, raise the question of hereditary transmission, leading to increasing demands for genetic counseling and monitoring of medically assisted pregnancies. Diagnosis and treatment of newborn boys is, therefore, becoming an increasingly important issue. In male individuals with complete forms of CHH, the antenatal and neonatal gonadotropin deficit leads to formation of a micropenis and cryptorchidism, which could undermine future sexual and reproductive functions. Standard treatments, usually started after the age of puberty, often only partially correct the genital abnormalities and spermatogenesis. The aim of this Review is to examine the possible additional benefits of neonatal gonadotropin therapy in male patients with CHH. Encouraging results of neonatal therapy, together with a few reports of prepubertal treatment, support the use of this novel therapeutic strategy aimed at improving sexual and reproductive functions in adulthood.

SOX9 and SF1 are involved in cyclic AMP-mediated upregulation of anti-Mullerian gene expression in the testicular prepubertal Sertoli cell line SMAT1

In Sertoli cells, anti-Müllerian hormone (AMH) expression is upregulated by FSH via cyclic AMP (cAMP), although no classical cAMP response elements exist in the AMH promoter. The response to cAMP involves NF-κB and AP2; however, targeted mutagenesis of their binding sites in the AMH promoter do not completely abolish the response. In this work we assessed whether SOX9, SF1, GATA4, and AP1 might represent alternative pathways involved in cAMP-mediated AMH upregulation, using real-time RT-PCR (qPCR), targeted mutagenesis, luciferase assays, and immunocytochemistry in the Sertoli cell line SMAT1. We also explored the signaling cascades potentially involved. In qPCR experiments, Amh, Sox9, Sf1, and Gata4 mRNA levels increased after SMAT1 cells were incubated with cAMP. Blocking PKA abolished the effect of cAMP on Sox9, Sf1, and Gata4 expression, inhibiting PI3K/PKB impaired the effect on Sf1 and Gata4, and reducing MEK1/2 and p38 MAPK activities curtailed Gata4 increase. SOX9 and SF1 translocated to the nucleus after incubation with cAMP. Mutations of the SOX9 or SF1 sites, but not of GAT4 or AP1 sites, precluded the response of a 3,063-bp AMH promoter to cAMP. In conclusion, in the Sertoli cell line SMAT1 cAMP upregulates SOX9, SF1, and GATA4 expression and induces SOX9 and SF1 nuclear translocation mainly through PKA, although other kinases may also participate. SOX9 and SF1 binding to the AMH promoter is essential to increase the activity of the AMH promoter in response to cAMP.

Genetically determined dosage of follicle-stimulating hormone (FSH) affects male reproductive parameters

CONTEXT

The detailed role of FSH in contributing to male testicular function and fertility has been debated. We have previously identified the association between the T-allele of the FSHB promoter polymorphism (rs10835638; G/T, -211 bp from the mRNA start) and significantly reduced male serum FSH.

OBJECTIVE

In the current study, the T-allele carriers of the FSHB -211 G/T single nucleotide polymorphism represented a natural model for documenting downstream phenotypic consequences of insufficient FSH action.

DESIGN AND SUBJECTS

We genotyped rs10835638 in the population-based Baltic cohort of young men (n = 1054; GG carriers, n = 796; GT carriers, n = 244; TT carriers, n = 14) recruited by Andrology Centres in Tartu, Estonia; Riga, Latvia; and Kaunas, Lithuania. Marker-trait association testing was performed using linear regression (additive, recessive models) adjusted by age, body mass index, smoking, and recruitment center.

RESULTS

Serum hormones directly correlated with the T-allele dosage of rs10835638 included FSH (additive model, P = 1.11 × 10(-6); T-allele effect, -0.41 IU/liter), inhibin-B (P = 2.16 × 10(-3); T-allele effect, -14.67 pg/ml), and total testosterone (P = 9.30 × 10(-3); T-allele effect, -1.46 nmol/liter). Parameters altered only among TT homozygotes were reduced testicular volume (recessive model, P = 1.19 × 10(-4); TT genotype effect, -9.47 ml) and increased serum LH (P = 2.25 × 10(-2); TT genotype effect, 1.07 IU/liter). The carrier status of rs10835638 alternative genotypes did not affect sperm motility and morphology, calculated free testosterone, serum SHBG, and estradiol concentrations.

CONCLUSION

We showed for the first time that genetically determined low FSH may have wider downstream effects on the male reproductive system, including impaired testes development, altered testicular hormone levels (inhibin-B, total testosterone, LH), and affected male reproductive potential.

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

The observation that mice with a selective ablation of the androgen receptor (AR) in Sertoli cells (SC) (SCARKO mice) display a complete block in meiosis supports the contention that SC play a pivotal role in the control of germ cell development by androgens. To delineate the physiological and molecular mechanism responsible for this control, we compared tubular development in pubertal SCARKO mice and littermate controls. Particular attention was paid to differences in SC maturation, SC barrier formation and cytoskeletal organization and to the molecular mediators potentially involved. Functional analysis of SC barrier development by hypertonic perfusion and lanthanum permeation techniques and immunohistochemical analysis of junction formation showed that SCARKO mice still attempt to produce a barrier separating basal and adluminal compartment but that barrier formation is delayed and defective. Defective barrier formation was accompanied by disturbances in SC nuclear maturation (immature shape, absence of prominent, tripartite nucleoli) and SC polarization (aberrant positioning of SC nuclei and cytoskeletal elements such as vimentin). Quantitative RT-PCR was used to study the transcript levels of genes potentially related to the described phenomena between day 8 and 35. Differences in the expression of SC genes known to play a role in junction formation could be shown from day 8 for Cldn11, from day 15 for Cldn3 and Espn, from day 20 for Cdh2 and Jam3 and from day 35 for ZO-1. Marked differences were also noted in the transcript levels of several genes that are also related to cell adhesion and cytoskeletal dynamics but that have not yet been studied in SC (Actn3, Ank3, Anxa9, Scin, Emb, Mpzl2). It is concluded that absence of a functional AR in SC impedes the remodeling of testicular tubules expected at the onset of spermatogenesis and interferes with the creation of the specific environment needed for germ cell development.

Genomics and genetics of gonadotropin beta-subunit genes: Unique FSHB and duplicated LHB/CGB loci

The follicle stimulating hormone (FSH), luteinizing hormone (LH) and chorionic gonadotropin (HCG) play a critical role in human reproduction. Despite the common evolutionary ancestry and functional relatedness of the gonadotropin hormone beta (GtHB) genes, the single-copy FSHB (at 11p13) and the multi-copy LHB/CGB genes (at 19q13.32) exhibit locus-specific differences regarding their genomic context, evolution, genetic variation and expressional profile. FSHB represents a conservative vertebrate gene with a unique function and it is located in a structurally stable gene-poor region. In contrast, the primate-specific LHB/CGB gene cluster is located in a gene-rich genomic context and demonstrates an example of evolutionary young and unstable genomic region. The gene cluster is shaped by a constant balance between selection that acts on specific functions of the loci and frequent gene conversion events among duplicons. As the transcription of the GtHB genes is rate-limiting in the assembly of respective hormones, the genomic and genetic context of the FSHB and the LHB/CGB genes largely affects the profile of the hormone production.

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.

Appropriate cut-off value for follicle-stimulating hormone in azoospermia to predict spermatogenesis

BACKGROUND

This study was undertaken to determine the optimal cut-off value for FSH to predict the presence of spermatogenesis in patients with non-obstructive azoospermia.

METHODS

A total of 206 non-obstructive azoospermic men were enrolled in this prospective study. By using receiver operating characteristic (ROC) curves, we determined the optimal cut-off value for FSH and evaluated whether the test could adequately predict successful sperm retrieval.

RESULTS

There were 108 non-obstructive azoospermic patients who had evidence of spermatogenesis (group A) and achieved success in sperm retrieval. Another 98 non-obstructive azoospermic patients (group B) failed in sperm retrieval. The mean value of serum FSH in group B was significantly higher than in group A (28.03 +/- 14.56 mIU/mL vs 7.94 +/- 4.95 mIU/mL, p < 0.01; respectively). The area under the receiver operating characteristic curves were 0.939 +/- 0.02 and a cut-off value of 19.4 mIU/mL discriminated between group A and B with a sensitivity of 70%. The positive predictive value for failed sperm retrieval (group B) can reach 100%.

CONCLUSIONS

Elevated plasma levels of FSH of more than 19.4 mIU/mL could be used as a reliable criterion for a trial of sperm retrieval from testes in artificial reproductive techniques.

Undifferentiated primate spermatogonia and their endocrine control

The biology of spermatogonial stem cells is currently an area of intensive research and contemporary studies in primates are emerging. Quantitative regulation of sperm output by the primate testis seems to be exerted primarily on the transition from undifferentiated to differentiating spermatogonia. This review examines recent advances in our understanding of the mechanisms governing spermatogonial renewal and early differentiation in male primates, with a focus on the monkey. Emerging revisions to the classic view of dark and pale type A spermatogonia as reserve and renewing spermatogonial stem cells, respectively, are critically evaluated and essential features of endocrine control of undifferentiated spermatogonia throughout postnatal primate development are discussed. Obstacles in gaining a more complete understanding of primate spermatogonia are also identified.

Spermatogonial stem cells in higher primates: are there differences from those in rodents?

Spermatogonial stem cells (SSCs) maintain spermatogenesis throughout the reproductive life of mammals. While A(single) spermatogonia comprise the rodent SSC pool, the identity of the stem cell pool in the primate spermatogenic lineage is not well established. The prevailing model is that primate spermatogenesis arises from A(dark) and A(pale) spermatogonia, which are considered to represent reserve and active stem cells respectively. However, there is limited information about how the A(dark) and A(pale) descriptions of nuclear morphology correlate with the clonal (A(single), A(paired), and A(aligned)), molecular (e.g. GFRalpha1 (GFRA1) and PLZF), and functional (SSC transplantation) descriptions of rodent SSCs. Thus, there is a need to investigate primate SSCs using criteria, tools, and approaches that have been used to investigate rodent SSCs over the past two decades. SSCs have potential clinical application for treating some cases of male infertility, providing impetus for characterizing and learning to manipulate these adult tissue stem cells in primates (nonhuman and human). This review recounts the development of a xenotransplant assay for functional identification of primate SSCs and progress dissecting the molecular and clonal characteristics of the primate spermatogenic lineage. These observations highlight the similarities and potential differences between rodents and primates regarding the SSC pool and the kinetics of spermatogonial self-renewal and clonal expansion. With new tools and reagents for studying primate spermatogonia, the field is poised to develop and test new hypotheses about the biology and regenerative capacity of primate SSCs.

Increased Prevalance of the -211 T allele of follicle stimulating hormone (FSH) beta subunit promoter polymorphism and lower serum FSH in infertile men

CONTEXT

The human FSHB promoter polymorphism (rs10835638; -211 G/T) has been associated with serum FSH in a cohort of young Estonian men. The minor allele carriers had reduced serum FSH (15.7% in GT heterozygotes; 40% in TT homozygotes) compared with GG homozygotes.

OBJECTIVE

Because FSH is essential for normal spermatogenesis and fertility, we speculated that abnormalities in FSH action could contribute to male infertility. We sought to study whether genetically inherited constitutively reduced FSH levels may affect male reproduction and replicate the association between rs10835638 and serum FSH among infertile male patients.

DESIGN

Genotyping of rs10835638 in a cohort of infertile men (n = 1029; Andrology Center of the Tartu University Clinics, Estonia), including idiopathic infertility cases (IIFC; n = 750).

PATIENTS

Patients included male partners (sperm concentration <20 x 10(6)/ml) of infertile couples failing to conceive a child for 12 months or longer.

RESULTS

A significant excess of TT homozygotes (1.1 vs. 2.4%) as well as GT heterozygotes (22.4 vs. 25.1%) was detected among infertile men compared with the young male cohort (chi(2) test, P < 0.05). The T allele of rs10835638 was associated with reduced serum FSH (analysis of covariance; full cohort: P = 1.20 x 10(-6), F = 13.8; IIFC: P = 7.70 x 10(-7), F = 14.3) as well as with low FSH to LH ratio (full cohort: P = 1.52 x 10(-11), F = 25.6; IIFC: P = 3.25 x 10(-9), F = 20.4). The median serum FSH levels differed between the GG and TT carriers by 48.5%. All IIFC with TT genotype exhibited low (<1.8) FSH to LH ratio.

CONCLUSIONS

In perspective, this genetic marker may have clinical significance in molecular diagnostics of male reproductive success and a potential to identify positive responders to FSH treatment.

Effects of oestradiol on gonadotrophin levels in normal and castrated men

CONTEXT

Testosterone inhibits gonadotrophin release in men either directly or after aromatization to oestradiol. We hypothesized that in males the androgen receptor-mediated effect of testosterone on LH release is negligible relative to that of oestradiol.

OBJECTIVE

To compare the effect of experimentally induced variations of plasma oestradiol levels on LH levels in normal (physiological testosterone levels) and castrated men (very low testosterone levels).

DESIGN

Prospective, open label, intervention.

SUBJECTS AND INTERVENTIONS

We suppressed endogenous oestradiol in 10 young men with letrozole 2.5 mg once daily. In these men and in 10 young healthy castrated men, we restored plasma oestradiol levels with oestradiol patches (first week 100 mug/day, second week 50 mug/day, third week 25 mug/day and fourth week no oestradiol patch).

MEASUREMENTS

The effect of the intervention on plasma levels of LH were monitored and compared between the groups.

RESULTS

With the intervention, the mean plasma oestradiol level in the two groups varied from supraphysiological to below the lower reference range. Levels of LH mirrored plasma oestradiol levels in both the groups, as did testosterone in the intact group. Despite similar oestradiol levels, mean levels of LH were significantly higher in the castrated group compared to the intact group for all doses of oestradiol, and supraphysiological levels of oestradiol were unable to suppress LH into the physiological range in the castrated group.

CONCLUSIONS

Physiological plasma oestradiol levels have a substantial suppressive effect on LH in men. However, low-normal testosterone levels are a prerequisite for suppression of LH into the normal range.

Immature rat seminiferous tubules reconstructed in vitro express markers of Sertoli cell maturation after xenografting into nude mouse hosts

Sertoli cells undergo a maturation process during post-natal testicular development that leads to the adult-type Sertoli cell, which is required for spermatogenesis. Understanding Sertoli cell maturation is therefore necessary to gain insight into the underlying causes of impaired spermatogenesis and male infertility. The present study characterized the cellular and molecular differentiation of Sertoli cells in a xenograft model of mammalian testicular development. Immature rat Sertoli cells were cultured in a three-dimensional culture system to allow the formation of cord-like structures. The in vitro Sertoli cell cultures were then grafted into nude mice. Sertoli cell proliferation, morphological differentiation and mRNA expression of Sertoli cell maturation markers were evaluated in xenografts. Sertoli cell proliferation significantly decreased between 1 and 4 weeks (6.7 +/- 0.9 versus 1.2+/- 0.1%, P < 0.001), and was maintained at low levels thereafter. Sertoli cell cord-like structures significantly decreased between 1 and 4 weeks (59.6 versus 21%, P < 0.05), whereas Sertoli cell tubules were more frequently observed after 4 weeks (13.3 versus 73.1%, P < 0.05). Furthermore, expression of androgen binding protein, transferrin and follicle stimulating hormone receptor, markers for mature Sertoli cells, was detected after 1 week of grafting and increased significantly thereafter. We conclude from these results that rat Sertoli cells continue maturation after xenografting to the physiological environment of a host. This model of in vitro tubule formation will be helpful in future investigations addressing testicular maturation in the mammalian testis.

Normal testicular function and spermatogenesis

The testis performs two basic functions, sperm production and testosterone secretion. Formation of the testis is genetically controlled; expression of the SRY gene directs the embryonic gonads into the pathway leading to the development of testes. By the fourth week of gestation in humans, the primordial germ cells derived from pluripotent cells of the embryonic epiblast proliferate and migrate from the endoderm of the yolk sac into the undifferentiated gonad, which becomes morphologically distinct during the seventh week of gestation in humans. Histological development of the testis is largely completed by the end of the third month of gestation.

Lack of androgen receptor expression in Sertoli cells accounts for the absence of anti-Mullerian hormone repression during early human testis development

CONTEXT

Puberty is associated with increased testicular testosterone (TT) synthesis, which is required to trigger spermatogenesis and to repress anti-Mullerian hormone (AMH) production. However, testicular gonadotropin stimulation during fetal and newborn life neither initiates spermatogenesis nor represses AMH.

OBJECTIVE

We postulated that a lack of androgen receptor (AR) expression in Sertoli cells (SC) might explain why these processes do not occur during early human development.

METHODS AND PATIENTS

Using immunohistochemistry and quantitative PCR, we examined the relationship between AR, AMH, and FSH receptor expression in fetal, newborn, and adult human testis. The ability of testosterone to repress AMH secretion was evaluated in male newborns, neonates, and two adults with androgen insensitivity syndrome and also in vitro using SMAT1 SC.

RESULTS

FSH receptor was present in SC at all developmental stages. In fetal and newborn testis, AR was expressed in peritubular and Leydig cells but not in SC. This coincided with the absence of spermatogenesis and with strong SC AMH expression. In adult testis, spermatogenesis was associated with AR expression and with a decrease in SC AMH content. Accordingly, AR mRNA expression was lower and AMH mRNA expression higher in fetal testes than in adult testes. In androgen insensitivity syndrome patients, combined gonadotropin stimulation induced an increase in circulating testosterone and AMH, a finding consistent with a failure of TT to repress AMH in the absence of AR signalling. Finally, direct androgen repression of AMH only occurred in AR-expressing SMAT1 cells.

CONCLUSION

Functional ARs are essential for TT-mediated AMH repression in SC.

Estrogen promotes germ cell and seminiferous tubule development in the baboon fetal testis

The foundation for development of the male reproduction system occurs in utero, but relatively little is known about the regulation of primate fetal testis maturation. Our laboratories have shown that estrogen regulates key aspects of the physiology of pregnancy and fetal development. Therefore, in the present study, we characterized and quantified germ cells and Sertoli cells in the fetal baboon testis in late normal gestation (i.e., Day 165; term is 184 days) and in baboons administered the aromatase inhibitor letrozole throughout the second half of gestation to assess the impact of endogenous estrogen on fetal testis development. In untreated baboons, the seminiferous cords were comprised of undifferentiated (i.e., type A) spermatogonia classified by their morphology as dark (Ad) or pale (Ap), gonocytes (precursors of type A spermatogonia), unidentified cells (UI), and Sertoli cells. In letrozole-treated baboons, serum estradiol levels were decreased by 95%. The number per milligram of fetal testis (x10(4)) of Ad spermatogonia (0.42 +/- 0.11) was 45% lower (P = 0.03), and that of gonocytes (0.58 +/- 0.06) and UI (0.45 +/- 0.12) was twofold greater (P < 0.01 and P = 0.06, respectively), than in untreated baboons. Moreover, in the seminiferous cords of estrogen-deprived baboons, the basement membrane appeared fragmented, the germ cells and Sertoli cells appeared disorganized, and vacuoles were present. We conclude that endogenous estrogen promotes fetal testis development and that the changes in the germ cell population in the estrogen-deprived baboon fetus may impair spermatogenesis and fertility in adulthood.

Molecular dissection of the male germ cell lineage identifies putative spermatogonial stem cells in rhesus macaques

BACKGROUND

The spermatogonial stem cell (SSC) pool in the testes of non-human primates is poorly defined.

METHODS

To begin characterizing SSCs in rhesus macaque testes, we employed fluorescence-activated cell sorting (FACS), a xenotransplant bioassay and immunohistochemical methods and correlated our findings with classical descriptions of germ cell nuclear morphology (i.e. A_dark and A_pale spermatogonia).

RESULTS

FACS analysis identified a THY-1⁺ fraction of rhesus testis cells that was enriched for consensus SSC markers (i.e. PLZF, GFRα1) and exhibited enhanced colonizing activity upon transplantation to nude mouse testes. We observed a substantial conservation of spermatogonial markers from mice to monkeys [PLZF, GFRα1, Neurogenin 3 (NGN3), cKIT]. Assuming that molecular characteristics correlate with function, the pool of putative SSCs (THY-1⁺, PLZF⁺, GFRα1⁺, NGN3^+/−, cKIT⁻) comprises most A_dark and A_pale and is considerably larger in primates than in rodents. It is noteworthy that the majority of A_dark and A_pale share a common molecular phenotype, considering their distinct functional classifications as reserve and renewing stem cells, respectively. NGN3 is absent from A_dark, but is expressed by some A_pale and may mark the transition from undifferentiated (cKIT⁻) to differentiating (cKIT⁺) spermatogonia. Finally, the pool of transit-amplifying progenitor spermatogonia (PLZF⁺, GFRα1⁺, NGN3⁺, cKIT^+/−) is smaller in primates than in rodents.

CONCLUSIONS

These results provide an in-depth analysis of molecular characteristics of primate spermatogonia, including SSCs, and lay a foundation for future studies investigating the kinetics of spermatogonial renewal, clonal expansion and differentiation during primate spermatogenesis.

Adverse effects of a clinically relevant dose of hydroxyurea used for the treatment of sickle cell disease on male fertility endpoints

Two experiments were conducted to determine: 1) whether the adult male transgenic sickle cell mouse (Tg58 x Tg98; TSCM), exhibits the patterns of reproductive endpoints (hypogonadism) characteristic of men with sickle cell disease (SCD) and 2) whether hydroxyurea (HU) exacerbates this condition. In Experiment 1, blood samples were collected from adult age-matched TSCM and ICR mice (ICRM) (N = 10/group) for plasma testosterone measurements. Subsequently, mice were sacrificed, testes excised and weighed and stored spermatozoa recovered for the determination of sperm density, progressive motility and percentage of spermatozoa with normal morphology. In experiment 2, adult male TSCM were orally treated with 25 mg HU/kg body weight/day for 28 or 56 days. Control mice received the vehicle for HU (saline) as described above. At the end of the treatment periods, blood samples were collected for quantification of circulating testosterone. Subsequently, mice were sacrificed, testes and epididymides were recovered and weighed and one testis per mouse was subjected to histopathology. Stored spermatozoa were recovered for the determination of indices of sperm quality mentioned in Experiment 1. Testis weight, stored sperm density, progressive motility, percentage of spermatozoa with normal morphology and plasma testosterone concentrations of TSCM were significantly lower by 40, 65, 40, 69 and 66%, respectively than those of ICRM. These data indicate that adult TSCM used in this study suffered from hypogonadism, characteristically observed among adult male SCD patients. In Experiment 2, HU treatment significantly decreased testis weight on day 28, (0.09 +/- 0.004 g) that was further decreased on day 56 (0.06 +/- 0.003 g; treatment x time interaction) compared with controls (day 28, 0.15 +/- 0.01 g; day 56, 2, 0.16 +/- 0.01 g). Concomitant with a 52% shrinkage (P<0.001) in area of testes in 56 days of HU treatment, testes from HU-treated TSCM exhibited significant atrophic degeneration in the seminiferous tubules compared with controls. Furthermore, treated TSCM had only Sertoli cells and cell debris remaining in most of the seminiferous tubules in comparison with controls. Leydig cell prominence and hyperplasia were more evident (P<0.05) in the steroidogenic compartments of testes of HU-treated TSCM compared with controls. However, plasma testosterone concentrations were reduced by HU treatment (P<0.05; treatment x time interaction) compared with controls on the two time periods studied. Epididymides from HU-treated TSCM sustained a 25% shrinkage (P<0.05), along with 69 (P<0.005) and 95% reduction (P<0.005), in stored sperm density and sperm progressive motility (treatment x time interaction P<0.05), respectively on day 56 of treatment compared with controls. These data demonstrate that TSCM used in this study exhibited SCD-induced hypogonadism, thus authenticating their use for studying the effect of HU on male reproductive endpoints observed in SCD patients. Secondarily, our data show that HU treatment exacerbated the already SCD-induced hypogonadism to gonadal failure.

A re-examination of proliferation and differentiation of type A spermatogonia in the adult rhesus monkey (Macaca mulatta)

BACKGROUND

Companion studies using an experimental non-human primate paradigm known as a testicular clamp indicated that the behavior of undifferentiated type A spermatogonia did not conform fully to earlier classical models. This issue was therefore re-examined in normal monkeys.

METHODS

Adult male rhesus monkeys (n = 4) received an i.v. bolus of 5-bromo-2'-deoxyuridine (BrdU): one testis (first) was removed 3 h later and the remaining testis (second) was removed after 11 days and 3 h. Tissue was fixed in Bouin's solution, and numbers of A dark (Ad), small A pale (Aps) and large A pale spermatogonia, differentiating B spermatogonia, S-phase-labeled and degenerating cells were enumerated. Data are given as mean +/- SEM.

RESULTS

During the early stages of the seminiferous epithelial cycle in the first testis, Ap spermatogonia (1.3 cells/cross section) were predominantly Aps (nuclear dia., 7.1 +/- 0.1 microm). Aps were never S-phase labeled. Apl (nuclear dia., 8.8 +/- 0.5 microm) appeared in Stages IV-VI and were maximal in Stages VII-X when S-phase labeling of this phenotype at 3 h was greatest. The first generation of B spermatogonia appeared in Stages XI-XII (0.84 cells/cross section). Using cells/cross section, the ratio of Ap (Stages I-V):B1:B2:B3:B4:preleptotene spermatocyte was 1:0.7:1.4:2.8:5.6:11.2. In the second testis, labeled Aps (and Apl) were observed. Ad were not BrdU labeled, and degenerating cells were rarely observed.

CONCLUSIONS

The results are not entirely consistent with earlier models of spermatogonial proliferation and differentiation in the monkey. Most notably, our findings suggest that in any one cycle of the seminiferous epithelium only a fraction of Ap spermatogonia is mitotically active.

A selective monotropic elevation of FSH, but not that of LH, amplifies the proliferation and differentiation of spermatogonia in the adult rhesus monkey (Macaca mulatta)

BACKGROUND

Unilateral orchidectomy in monkeys increases spermatogenesis in the remaining testis in association with elevated follicle-stimulating hormone (FSH) secretion and testicular testosterone. The present study examined the relative importance of FSH and testosterone in driving the primate testis toward its spermatogenic ceiling.

METHODS

Adult male rhesus monkeys were treated with a gonadotropin-releasing hormone receptor antagonist to inhibit endogenous FSH and luteinizing hormone (LH) secretion. The gonadotrophin drive to the testis was replaced with a pulsatile recombinant human FSH and LH infusion to maintain testicular volume and circulating testosterone and inhibin B at physiological levels. A selective monotropic elevation of FSH or LH that doubled the concentrations of inhibin B or testosterone, respectively, was then imposed for 4 weeks, each in a group of four monkeys. In a third group (n = 4), the gonadotrophin drive remained clamped at physiological levels. Bromo-deoxyuridine was administered 3 h prior to castration, and the effects of the monotropic hormone increments on germ cell number, S-phase labeling and degeneration were determined.

RESULTS

Increased FSH, but not LH, produced increases in testicular volume (P < 0.05), the proportion of A pale spermatogonia entering the cell cycle and the numbers of differentiated spermatogonia and more advanced germ cells (P < 0.05). Indexes for spermatogonia labeling and germ cell degeneration were not affected.

CONCLUSIONS

Under physiological conditions, circulating concentrations of FSH directly dictate sperm output of the primate testis by regulating the proportion of Ap spermatogonia in the growth fraction. An effect of FSH on survival of the first generation of differentiated B spermatogonia is not excluded.

The expression and localization of inhibin isotypes in mouse testis during postnatal development

Inhibin, which is important for normal gonadal function, acts on the pituitary gonadotropins to suppress follicle-stimulating hormone (FSH) secretion. The level and cellular localization of the inhibin isotypes, α, β_A and β_B, in the testis of mice were examined during postnatal development in order to determine if inhibin expression is related to testicular maturation. Mouse testes were sampled on postnatal days (PNDs) 1, 3, 6, 18, 48 and 120, and analyzed by Western blotting and immunofluorescence. Western blot analysis showed very low levels of inhibin α, β_A and β_B expression in the testes at days 1 to 6 after birth. The levels then increased gradually from PND 18 to 48-120, and there were significant peaks at PND 48. Inhibin α, β_A and β_B were detected in testicular cells during postnatal development using immunohistochemistry. The immunoreactivity of inhibin α was rarely observed in testicular cells during PND 1 to 6, or in the cytoplasmic process of Sertoli cells surrounding the germ cells and interstitial cells during PND 18 to 120. Inhibin β_A and β_B immunoreactivity was rarely observed in the testis from PND 1 to 6. On the other hand, it was observed in some spermatogonial cells, as well as in the interstitial space between PND 48 and PND 120. We conclude that the expression of inhibin isotypes increases progressively in the testis of mice with increasing postnatal age, suggesting that inhibin is associated with a negative feedback signal for FSH in testicular maturation.

Endocrine regulation of the establishment of spermatogenesis in pigs

Somatic and germ cell maturation precedes the start of spermatogenesis and is coordinated, so efficient spermatogenesis will occur in the adults. The present study was conducted to evaluate endocrine regulation of germ and somatic cell homeostasis in the neonatal boar testis associated with the establishment of spermatogenesis. Testis tissue obtained from 3-, 5-, 7- and 14-day-old piglets were ectopically xenografted onto castrated, immunodeficient nude mice. Grafts were removed 22 weeks later and evaluated for growth and the establishment of spermatogenesis. Recipient mouse testosterone biosynthesis and follicle-stimulating hormone (FSH) concentrations were also assayed. Testis tissue graft growth was significantly greater in testis grafts from 3-day donor tissue when compared to all other ages; 5-, 7- and 14-day-old donor tissue weights were not significantly different at removal. Follicle-stimulating hormone concentrations in recipient mice supporting testis grafts from 5-, 7- and 14-day-old donor tissues did not differ and were similar to normal physiological levels in age-matched, intact nude mice. Serum FSH levels were significantly lower in recipient mice supporting testis grafts from 3-day-old donor tissue. Radioimmunoassay and biological assay indicated no differences in testosterone production by testis tissue grafts of varying donor age. Porcine testis tissue obtained from 3-, 5-, 7- and 14-day-old neonatal boars were all capable of producing round and elongate spermatids after 22 weeks of grafting, but testis grafts from 14-day-old donors had a significantly greater (eightfold) percentage of seminiferous tubules with spermatids compared to all other donor ages (p < 0.05). Cryopreservation did not affect the ability of testis tissue grafts to grow, produce testosterone or establish spermatogenesis when compared to controls (p < 0.05). Collectively, these data demonstrate intrinsic differences in the biological activity of germ and somatic cell populations during neonatal boar testis development associated with the establishment of spermatogenesis.

Alteration of testicular steroidogenesis and histopathology of reproductive system in male rats treated with triclosan

Triclosan (TCS), a chlorophenol, is widely used as a preservative in different types of commercial preparations. The reports on TCS-mediated endocrine disruption are controversial and the present study aimed to elucidate the probable mode of action of TCS as an antiandrogenic compound using a robust study design. Male albino rats, Rattus norvegicus, were treated with three doses of triclosan for a period of 60 days followed by the analysis of various biochemical parameters. RT-PCR analysis demonstrated a significant decrease in mRNA levels for testicular steroidogenic acute regulatory (StAR) protein, cytochrome P450(SCC), cytochrome P450(C17), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and androgen receptor (AR) in TCS treated rats (p<0.05). TCS also induced a perturbed translation of testicular StAR, and AR proteins as shown by Western blot analysis in treated groups of rats. A reduced level of StAR was further indicated by immunohistochemistry in testicular Leydig cells. Further, there was a significant decrease (p<0.05) in the level of serum lutenizing hormone (LH), follicle stimulating hormone (FSH), cholesterol, pregnenolone, and testosterone. In vitro assays demonstrated more than 30% decrease in testicular 3beta-HSD and 17beta-HSD enzyme activities in treated group of animals. Extensive histopathological malformations were observed in the testis and sex accessory tissues of the treated rats. Overall this study showed that TCS decreased the synthesis of androgens followed by reduced sperm production in treated male rats which could be mediated by a decreased synthesis of LH and FSH thus involving hypothalamo-pituitary-gonadal axis.

Alteration of fertility endpoints in adult male F-344 rats by subchronic exposure to inhaled benzo(a)pyrene

The objective of this study was to evaluate the reproductive risk associated with exposure of adult male Fisher-344 rats to inhaled benzo(a)pyrene (BaP). Rats were assigned randomly to a treatment or control group. Treatment consisted of sub-chronic exposure of rats via inhalation to 75microgBaP/m(3), 4h daily for 60 days, while control animals were unexposed (UNC). Blood samples were collected immediately after the cessation of exposures (time 0) and subsequently at 24, 48, and 72h, to assess the effect of bioavailable BaP on plasma testosterone and luteinizing hormone (LH) concentrations. Rats were sacrificed after the last blood collection. Testes were harvested, weighed and prepared for histology and morphometric analysis, and cauda epididymides were isolated for the determination of progressive motility and density of stored spermatozoa. BaP exposure reduced testis weight compared with UNC (mean+/-SE; 2.01+/-0.11 versus 3.04+/-0.16g; P<0.025), and caused significant reductions in the components of the steroidogenic and spermatogenic compartments of the testis. Progressive motility and mean density of stored spermatozoa were reduced (P<0.05). Plasma testosterone concentrations were decreased by two-thirds in BaP-exposed rats throughout the time periods studied compared with those of their UNC counterparts (P<0.05), concomitant with increased concentrations of LH in BaP-exposed rats (P<0.05). These data suggest that sub-chronic exposure to inhaled BaP contribute to reduced testicular and epididymal function in exposed rats.

The relative role of gonadal sex steroids and gonadotropin-releasing hormone pulse frequency in the regulation of follicle-stimulating hormone secretion in men

OBJECTIVE

Our objective was to determine the importance of testosterone (T), estradiol (E(2)), and GnRH pulse frequency to FSH regulation in men.

DESIGN

This was a prospective study with four arms.

SETTING

The study was performed at the General Clinical Research Center.

PATIENTS OR OTHER PARTICIPANTS

There were 20 normal (NL) men and 15 men with idiopathic hypogonadotropic hypogonadism (IHH) who completed the study.

INTERVENTION

Medical castration and inhibition of aromatase were achieved using ketoconazole x 7 d with: 1) no sex steroid addback, 2) T addback starting on d 4, and 3) E(2) addback starting on d 4. IHH men in these arms received GnRH every 120 min. In a further six IHH men receiving ketoconazole with no addback, GnRH frequency was increased to 35 min for d 4-7. Blood was drawn every 10 min x 12 h at baseline, overnight on d 3-4 and 6-7.

MAIN OUTCOME MEASURES

Mean FSH was calculated from the pool of each frequent sampling study.

RESULTS

In NL men FSH levels increased from 5.1 +/- 0.7 to 8.7 +/- 1.3 and 9.7 +/- 1.5 IU/liter (P < 0.0001). T caused no suppression of FSH. E(2) reduced FSH from 12.4 +/- 1.8 to 9.3 +/- 1.3 IU/liter (P < 0.05). In IHH men on GnRH every 120 min, FSH levels went from 6.0 +/- 1.6 to 9.0 +/- 3.0 and 11.9 +/- 4.3 (P = 0.07). T caused no suppression of FSH. E(2) decreased FSH such that levels on d 6-7 were similar to baseline. Increasing GnRH frequency to 35 min had no impact on FSH.

CONCLUSIONS

The sex steroid component of FSH negative feedback in men is mediated by E(2). Increasing GnRH frequency to castrate levels has no impact on FSH in the absence of sex steroids. When inhibin B levels are NL, sex steroids exert a modest effect on FSH.

FSHB promoter polymorphism within evolutionary conserved element is associated with serum FSH level in men

BACKGROUND

No polymorphisms affecting serum FSH levels have been described in the human FSHB gene. We have identified a potential regulatory single nucleotide polymorphism (SNP, rs10835638; G/T) 211 bp upstream from the FSHB mRNA transcription start-site, located within a highly conserved region among placental mammals. We aimed to determine the correlation of carrier status of rs10835638 alternative alleles with serum FSH level in men, and testicular and hormonal parameters.

METHODS

A quantitative genetic association study using a cohort of healthy men (n = 554; age 19.2 ± 1.7 years) visiting the Centre of Andrology, Tartu University Hospital, Estonia.

RESULTS

Rs10835638 (allele frequencies: G 87.6%, T 12.4%) was significantly associated with serum FSH level (analysis of variance: F = 13.0, P = 0.0016, df = 1; regression testing for a linear trend: P = 0.0003). Subjects with the GG genotype exhibited higher FSH levels (3.37 ± 1.79 IU/l, n = 423) compared with heterozygotes (2.84 ± 1.54 IU/l, n = 125) (P = 0.0005), the group of T-allele carriers (GT+TT, 2.78 ± 1.51 IU/l, n = 131) (P = 0.0005) and TT-homozygotes (2.02 ± 0.81 IU/L, n = 6) (P = 0.031). Rs10835638 was also associated with significant (P < 0.05) reduction in free testosterone index and testes volume, but increased semen volume, sex hormone-binding globulin, serum testosterone and estradiol. LH and inhibin-B levels did not differ significantly between groups.

CONCLUSIONS

The identification of a regulatory SNP in FSHB promoter paves the way to study the effect of constitutively low FSH on male health and fertility. As FSH contributes to follicular development and sex steroid production in women, the role of this FSHB variant in female reproductive success is still to be addressed.

Relative roles of inhibin B and sex steroids in the negative feedback regulation of follicle-stimulating hormone in men across the full spectrum of seminiferous epithelium function

CONTEXT AND OBJECTIVE

Our aim was to explore the relative roles of gonadal sex steroids and inhibin B in the regulation of FSH across a spectrum of seminiferous epithelium function.

SUBJECTS

The study included three groups: group I, healthy men (n = 31); group II, men with idiopathic hypogonadotropic hypogonadism receiving pulsatile GnRH (n = 12) selected to represent a spectrum of seminiferous tubular development, testicular size, and baseline inhibin B levels; and group III, men with functional anorchia (n = 3) receiving testosterone replacement.

DESIGN

Subjects were studied before and after 3 d of acute sex steroid withdrawal.

SETTING

The study was conducted at the Mallinckrodt General Clinical Research Center of Massachusetts General Hospital.

INTERVENTIONS

Acute biochemical castration was achieved using high-dose ketoconazole (groups I and II) or withdrawal of androgen therapy (group III).

MAIN OUTCOME MEASURES

The relationship between FSH and inhibin B in both normal and castrate sex steroid milieu was measured.

RESULTS

In both normal and castrate sex steroid milieus, there was a negative relationship between inhibin B and FSH, best described by a logarithmic model. Acute biochemical castration resulted in the most dramatic increases in FSH in men with the lowest baseline inhibin B levels.

CONCLUSIONS

We came to the following conclusions: 1) in the human male, inhibin B is the principal gonadal feedback regulator of FSH secretion unless seminiferous tubular function is severely compromised, and a logarithmic model best describes this relationship; and 2) sex steroid inhibition of FSH secretion is most apparent when serum inhibin B levels fall well below the normal range.

Age-related changes in diurnal rhythms and levels of gonadotropins, testosterone, and inhibin B in male rhesus monkeys (Macaca mulatta)

Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns. In elderly men, the diurnal rhythm of testosterone is blunted and inhibin levels fall. Here we explore whether aging exerts similar effects in the rhesus monkey. We collected blood samples from groups of young (6-9 yr) and old (12-16 yr) male rhesus monkeys at 20-min intervals for a period of 24 h under remote sampling via a venous catheter. We determined moment-to-moment changes in plasma levels of testosterone, FSH, and LH by RIA, and of inhibin B by ELISA. We found significant diurnal patterns of testosterone in both groups. The circadian rhythm in testosterone was enhanced in older monkeys. Testosterone levels and pulse frequencies dropped significantly below those of young monkeys during midday hours. Diminished pulse frequency of LH appeared to be responsible for the midday testosterone decrease in old monkeys, while LH and testosterone pulse frequency did not change in young monkeys at corresponding time points. Old monkeys showed extended periods of LH-pulse quiescence in the morning and midday hours. Inhibin B and FSH levels were generally lower in old monkeys compared with the young group, but neither inhibin B nor FSH showed circadian rhythms. We conclude from these data that old rhesus monkeys have a more prominent circadian rhythm of LH and testosterone resulting from an extended midday period of quiescence in the hypothalamus-pituitary-gonadal axis.

Effects of benzo(a)pyrene on intra-testicular function in F-344 rats

The objective of this study was to evaluate the reproductive risk associated with exposure of adult male Fisher-344 (F-344) rats to inhaled benzo(a)pyrene (BaP), a ubiquitous environmental toxicant present in cigarette smoke, automobile exhaust fumes and industrial emissions. Rats were assigned randomly to a treatment or control group. Treatment consisted of exposure of rats via nose-only inhalation to 75 microg BaP/m3, 4 hours daily for 60 days, while control animals were unexposed (UNC). Blood samples were collected immediately on day 60 of exposures (time 0) and subsequently at 24, 48, and 72 hours, to assess the effect of exposures to BaP on plasma testosterone and luteinizing hormone (LH) concentrations. Mean testis weight, total weight of tubules and total tubular length per paired testes were reduced 33% (P < 0.025), 27% (P < 0.01) and 39%, respectively in exposed rats (P < 0.01) compared with UNC rats. The number of homogenization -resistant spermatids was significantly reduced in BaP-exposed versus UNC rats. Plasma testosterone and intra-testicular testosterone (ITT) concentrations were significantly decreased by BaP compared with those of UNC rats. The decreases in circulating plasma testosterone were accompanied by concomitant increases in plasma LH concentrations in BaP-exposed versus control rats (P < 0.05). These data suggest that 60 days exposure to inhaled BaP contribute to reduced testicular endocrine and spermatogenic functions in exposed rats.

A novel potent indazole carboxylic acid derivative blocks spermatogenesis and is contraceptive in rats after a single oral dose

Women have historically been the focus for development of new contraceptive methods. The National Institutes of Health, World Health Organization, and Institute of Medicine have stressed the need to develop nonhormonal, nonsteroidal male contraceptive agents. We report results from initial dose-ranging studies of a new indazole carboxylic acid analogue, gamendazole. An infertility rate of 100% was achieved in seven out of seven proven-fertile male rats 3 wk after a single oral dose of 6 mg/kg of gamendazole. Fertility returned by 9 wk in four of seven animals, with typical numbers of normal-appearing conceptuses. A fertility rate of 100% returned in four of six animals that became infertile at a single oral dose of 3 mg/kg of gamendazole. No differences in mating behavior were observed in either of the gamendazole-treated groups versus the control (vehicle-only) group. In the animals that showed reversible infertility, a transient increase in circulating FSH levels coincided with an initial decline in inhibin B levels after administration of gamendazole, but no other significant changes in circulating reproductive hormones were observed. Gamendazole inhibited production of inhibin B by primary Sertoli cells in vitro with a median inhibitory concentration of 6.8 thorn+/- 3.0 (SEM) (3/4)x 10(-10) M, suggesting that Sertoli cells are a primary target. A biotinylated gamendazole analogue revealed cytoplasmic and perinuclear binding of gamendazole in primary Sertoli cells. Gamendazole represents the most potent new oral antispermatogenic indazole carboxylic acid to date. Our results, however, demonstrate that additional dose-finding studies are required to improve reversibility and widen the therapeutic window before more detailed drug development of this potential nonhormonal male contraceptive agent can occur.

Characterization, cryopreservation, and ablation of spermatogonial stem cells in adult rhesus macaques

Spermatogonial stem cells (SSCs) are at the foundation of mammalian spermatogenesis. Whereas rare A(single) spermatogonia comprise the rodent SSC pool, primate spermatogenesis arises from more abundant A(dark) and A(pale) spermatogonia, and the identity of the stem cell is subject to debate. The fundamental differences between these models highlight the need to investigate the biology of primate SSCs, which have greater relevance to human physiology. The alkylating chemotherapeutic agent, busulfan, ablates spermatogenesis in rodents and causes infertility in humans. We treated adult rhesus macaques with busulfan to gain insights about its effects on SSCs and spermatogenesis. Busulfan treatment caused acute declines in testis volume and sperm counts, indicating a disruption of spermatogenesis. One year following high-dose busulfan treatment, sperm counts remained undetectable, and testes were depleted of germ cells. Similar to rodents, rhesus spermatogonia expressed markers of germ cells (VASA, DAZL) and stem/progenitor spermatogonia (PLZF and GFRalpha1), and cells expressing these markers were depleted following high-dose busulfan treatment. Furthermore, fresh or cryopreserved germ cells from normal rhesus testes produced colonies of spermatogonia, which persisted as chains on the basement membrane of mouse seminiferous tubules in the primate to nude mouse xenotransplant assay. In contrast, testis cells from animals that received high-dose busulfan produced no colonies. These studies provide basic information about rhesus SSC activity and the impact of busulfan on the stem cell pool. In addition, the germ cell-depleted testis model will enable autologous/homologous transplantation to study stem cell/niche interactions in nonhuman primate testes.

Haplotype structure of FSHB, the beta-subunit gene for fertility-associated follicle-stimulating hormone: possible influence of balancing selection

Follicle-stimulating hormone (FSH) is essential for human reproduction. The unique functions of this hormone are provided by the FSH receptor-binding beta-subunit encoded by the FSHB gene. Resequencing and genotyping of FSHB in three European, two Asian and one African population, as well as in the great apes (chimpanzee, gorilla, orangutan), revealed low diversity and significant excess of polymorphisms with intermediate frequency alleles. Statistical tests for FSHB showed deviations from neutrality in all populations suggesting a possible effect of balancing selection. Two core haplotypes were identified (carried by 76-96.6% of each population's sample), the sequences of which are clearly separated from each other. As fertility most directly affects an organism's fitness, the carriers of these haplotypes have apparently had more success in human history to contribute to the next generation. There is a preliminary observation suggesting that the second most frequent FSHB haplotype may be associated with rapid conception success in females. Interestingly, the same haplotype is related to an ancestral FSHB variant shared with the ancestor of the great apes. The determination of the functional consequence of the two core FSHB variants may have implications for understanding and regulating human fertility, as well as in assisting infertility treatments.

Phenotypic characterisation of mice with exaggerated and missing LH/hCG action

In order to study the physiology and pathophysiology of gonadotrophin action, we have produced transgenic (TG) mice overexpressing human chorionic gonadotrophin (hCG) alpha and beta subunits (hCG+ mice) and knockout (KO) mice for the luteinising hormone receptor (LHR; LuRKO mice). The two extremes in LH function, i.e. strong LH/hCG stimulation and total blockade of this action, confirm numerous earlier concepts about LH function, but they also reveal new aspects about gonadal function during excessive LH production and in the absence of this trophic stimulus. The purpose of this review is to summarise the key findings on these two genetically modified mouse models.

Decreased serum free testosterone in workers exposed to high levels of di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP): a cross-sectional study in China

BACKGROUND

Observations of adverse developmental and reproductive effects in laboratory animals and wildlife have fueled increasing public concern regarding the potential for various chemicals to impair human fertility.

OBJECTIVE

Our objective in this study was to assess the effect of occupational exposure to high levels of phthalate esters on the balance of gonadotropin and gonadal hormones including luteinizing hormone, follicle-stimulating hormone, free testosterone (fT), and estradiol.

METHODS

We examined urine and blood samples of 74 male workers at a factory producing unfoamed polyvinyl chloride flooring exposed to di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) and compared them with samples from 63 male workers from a construction company, group matched for age and smoking status.

RESULTS

Compared to the unexposed workers, the exposed workers had substantially and significantly elevated concentrations of mono-n-butyl phthalate (MBP; 644.3 vs. 129.6 microg/g creatinine, p < 0.001) and mono-2-ethylhexyl phthalate (MEHP; 565.7 vs. 5.7 microg/g creatinine, p < 0.001). fT was significantly lower (8.4 vs. 9.7 microg/g creatinine, p = 0.019) in exposed workers than in unexposed workers. fT was negatively correlated to MBP (r = -0.25, p = 0.03) and MEHP (r = -0.19, p = 0.095) in the exposed worker group. Regression analyses revealed that fT decreases significantly with increasing total phthalate ester score (the sum of quartiles of MBP and MEHP; r = -0.26, p = 0.002).

CONCLUSION

We observed a modest and significant reduction of serum fT in workers with higher levels of urinary MBP and MEHP compared with unexposed workers.

Effects of high doses of recombinant human follicle-stimulating hormone in the treatment of male factor infertility: results of a pilot study

We performed a randomized double-blind placebo-controlled study on seminal parameters and endocrine profile of 30 normogonadotropic patients with male factor infertility to assess the efficacy of treatment with recombinant human FSH (rhFSH) at high doses (300 IU on alternate days) for a period of >or=4 months. The treatment induced a marked increase in sperm count, a slight increase in sperm motility, no change in sperm morphology, and an evident increase only in FSH serum levels, showing that a prolonged treatment with rhFSH at high doses led to an evident improvement of sperm count in normogonadotropic infertile patients with idiopathic oligoasthenozoospermia.

Rescue of spermatogenesis arrest in azoospermic men after long-term gonadotropin treatment

Several studies have shown that FSH treatment can improve sperm production quantitatively and increase the spermatogonial population in oligozoospermic men with normal hormonal profiles. In this study, we describe the results of long-term gonadotropin therapy of normogonadotropic patients with nonobstructive azoospermia.

Testicular xenografts: a novel approach to study cytotoxic damage in juvenile primate testis

The underlying primary damage to the testis caused by chemotherapeutic regimens during childhood is largely unknown. Xenografting of monkey testes was successfully applied in maturation of juvenile testis to the point of complete spermatogenesis. This allows us to manipulate developing primate testis without direct treatment of patients. This new model is validated establishing the effects of cytotoxic treatment in the immature primate testis. Male castrated nude mice received eight s.c. grafts of juvenile monkey testicular tissue and, 28 weeks later, were injected with busulfan (38 mg/kg, i.p.) or vehicle. Graft numbers, size, and histology were examined. Grafts showed pubertal induction of spermatogenesis to the level of pachytene spermatocytes at point of busulfan treatment and further progressed to the level of round spermatids in control samples at 4 weeks. Busulfan treatment caused a statistically significant decrease in the number of seminiferous tubules containing germ cells. Type B spermatogonia and more advanced stages of spermatogenesis were depleted. A statistically significant decrease to pretreatment level was observed in the number of type A pale and centrally located spermatogonia. Busulfan did not affect type A dark spermatogonia. Occasionally, elongating spermatids were detected in busulfan-treated grafts. Observations show that busulfan selectively destroys differentiating spermatogonia whereas some of the spermatocytes present at the moment of cytotoxic insult are able to continue differentiation. Data indicate that xenografting of testicular monkey tissue is a valid approach to detect the busulfan-induced germ cell damage and serves as a powerful experimental tool to study cytotoxic effects in developing primate testis.

Atm-deficient mice: an osteoporosis model with defective osteoblast differentiation and increased osteoclastogenesis

Atm is a Ser/Thr kinase involved in DNA damage response and is required for genome integrity and stem cell renewal. Here, we report an additional role for Atm in bone remodeling. Atm-/- mice showed reduced bone mass, especially at the trabecular bones, accompanied by a decrease in bone formation rate and defective differentiation of osteoblasts, but normal numbers of osteoprogenitor cells and osteoblasts. Atm might affect osteoblast differentiation by modulating the expression of osterix, a lineage-specific transcription factor essential for osteoblast maturation, likely via the bone morphogenetic proteins pathway. Atm-/- mice also displayed a marked increase in osteoclastogenesis and bone resorption, although Atm had no cell-autonomous effect on osteoclast differentiation and resorption. Increased osteoclastogenesis could be caused by a substantial reduction in testosterone and estradiol levels in male and female mice, respectively. The steroid hormone deficiency is a result of gonad developmental defects, which led to an increase in serum gonadotrophic hormone, FSH via a feedback regulation. Overall, these results indicate that Atm deficiency leads to osteoporosis mainly as a result of hypogonadism-induced bone resorption together with compromised osteoblast differentiation, and that Atm plays a positive role in regulating expression of osteoblast-specific transcription factor, osterix.

Characterization of testis-specific serine-threonine kinase 3 and its activation by phosphoinositide-dependent kinase-1-dependent signalling

The family of testis-specific serine-threonine kinases (TSSKs) consists of four members whose expression is confined almost exclusively to testis. Very little is known about their physiological role and mechanisms of action. We cloned human and mouse TSSK3 and analysed the biochemical properties, substrate specificity and in vitro activation. In vitro TSSK3 exhibited the ability to autophosphorylate and to phosphorylate test substrates such as histones, myelin basic protein and casein. Interestingly, TSSK3 showed maximal in vitro kinase activity at 30 degrees C, in keeping with it being testis specific. Sequence comparison indicated the existence of a so-called 'T-loop' within the TSSK3 catalytic domain, a structure present in the AGC family of protein kinases. To test if this T-loop is engaged in TSSK3 regulation, we mutated the critical threonine residue within the T-loop to alanine (T168A) which resulted in inactivation of TSSK3 kinase. Furthermore, Thr168 is phosphorylated in vitro by the T-loop kinase phosphoinositide-dependent protein kinase-1 (PDK1). PDK1-induced phosphorylation increased in vitro TSSK3 kinase activity, suggesting that TSSK3 can be regulated in the same way as AGC kinase family members. Analysis of peptide sequences identifies the peptide sequence RRSSSY containing Ser5 that is a target for TSSK3 phosphorylation, as an efficient and specific substrate for TSSK3.

Changes in Circulating and Testicular Levels of Inhibin A and B During Postnatal Development in Bulls

We investigated testicular and circulating levels of dimeric inhibins in Holstein bulls from the infantile to postpubertal periods (5 to 50 weeks of age) and examined the relationship between the profiles of circulating dimeric inhibins and FSH. Concentrations of total inhibin and inhibin B in the testis were highest at 4 to 5 weeks of age but decreased gradually as the bulls aged. Testicular inhibin A levels showed a gradual decline to a nadir at 15 to 26 weeks of age, but by 39 weeks, they were high again. The contents of total inhibin, inhibin A, and inhibin B per testis generally increased with age. Fractionation of testicular homogenates obtained from 15-week-old bulls by a combination of immunoaffinity chromatography and SDS-PAGE confirmed the presence of two major molecular weight forms (32 and 45 kDa) of dimeric inhibins in the testes. Circulating levels of total inhibin and inhibin A showed a significant increase in bulls at around 10 to 14 weeks of age compared to the levels between 5 and 7 weeks of age but decreased thereafter. However, immunoreactivity for inhibin B was not detected in the peripheral circulation, probably because of low sensitivity of the inhibin B assays. The concentrations of plasma FSH were high at 5 weeks of age but declined to lower levels between 11 and 40 weeks, and then increased from 41 weeks onward. There was no significant correlation between the plasma levels of FSH and inhibin A or total inhibin. The results clearly indicate that the bull testis produces inhibin A and B and secretes at least inhibin A into the circulation during postnatal development. However, the profile of circulating FSH in bulls shows no reciprocal relationship with the inhibin A or total inhibin profile during the postnatal period.

Prepubertal expansion of dark and pale type A spermatogonia in the rhesus monkey (Macaca mulatta) results from proliferation during infantile and juvenile development in a relatively gonadotropin independent manner

The purpose of the present study was to determine whether dark and pale type A spermatogonia (Ad and Ap, respectively) are mitotically active during prepubertal development and whether proliferation of these germ cells during this protracted phase of primate development occurs predominantly during infancy before gonadotropin secretion is arrested. Four neonate (1-2 days of age), four infant (4-5 mo of age), and four juvenile (14-17 mo of age) rhesus monkeys (Macaca mulatta) were castrated 2 h after receiving an i.v. bolus of 5-bromo2'-deoxy-uridine (BrdU, 33 mg/kg body weight). Tissue was fixed in Bouin solution, and 5-microm paraffin sections were cut. Using periodic acid-Schiff reagent/Gill hematoxylin staining, the number per testis of Ad and Ap spermatogonia were determined. BrdU S-phase-labeled nuclei were identified using immunofluorescence. Conservative criteria were employed for classifying cell types, and this resulted in a fraction of A spermatogonia remaining unclassified. Ad, Ap, and the unclassified A spermatogonia each showed an approximately 4-fold increase over the 5-mo period from birth to infancy, and a similar increase was observed over the 10-mo period between infancy and the juvenile stage of development. Both Ad and Ap (and unclassified A spermatogonia) exhibited robust and similar S-phase labeling at the three stages of development. We conclude that the prepubertal expansion of Ad and Ap spermatogonia is achieved by mitotic proliferation that is relatively gonadotropin independent. This conclusion raises the question of the nature of the signal that arrests the cell cycle of Ad in adult testis.

Control of spermatogenesis in primate and prospect of male contraception

The present review is a summary of mechanisms of spermatogenesis in primates with emphasis on anti-spermatogenesis of testosterone (T), gossypol, and "testicular heat stress" for development of male contraception, Both FSH and testosterone stimulate all phases of spermatogenesis. FSH is capable of amplifying the population of the differential spermatogonia (B1, B2, B3 and B4) and controls the spermatogonia production rate, and, in synergy with testosterone, regulating spermatogenesis in adult monkeys. Pituitary FSH beta gene expression is governed by a feedback of Beta inhibin, which is a major component of the testicular negative feedback signals. Beta inhibin secreted by Sertoli cells is in turn inhibited by testosterone from Leydig cells under the control of LH. Disturbance of the normal interaction of pituitary FSH with Sertoli cell Beta inhibin is responsible for azoospermia or oligozoospermia induced by exogenous T. Three possible regimens of T, gossypol and "heat stress" have been suggested for male contraception. They act on different sites and stages of spermatogenesis in testis or sperm activity in epididymis. Apoptosis induced by testosterone occurs mainly at staged VII-VIII of spermatogenesis while that by testicular "heat stress" mostly occurs at stages I-IV and X-XII. Low dose of gossypol mainly influences the sperm activity in the epididymis although it also acts on testicular spermatids.