Testicular phenotype in luteinizing hormone receptor knockout animals and the effect of testosterone replacement therapy

Deoxynivalenol exposure-related male reproductive toxicity in mammals: Molecular mechanisms, detoxification and future directions

An increasing body of evidence indicates that exposure to widespread, environmental and food contaminants such as mycotoxins may cause endocrine disorders and infertility. Deoxynivalenol (DON), which is a toxic secondary metabolite produced by Fusarium fungi, can lead to multiple harmful effects in humans and animals, such as hepatotoxicity, nephrotoxicity, immunotoxicity, gastrointestinal toxicity, neurotoxicity, genetic toxicity and carcinogenicity. Recently, there has been growing concern about DON-induced male infertility. Exposure to DON and its metabolites can damage the structure and function of male reproductive organs, resulting in impairment of gametogenesis and thus impaired fertility. Potential molecular mechanisms involve oxidative stress, inflammatory response, mitochondrial dysfunction, apoptosis, cell cycle arrest, pyroptosis, and ferroptosis. Moreover, several signaling pathways, including nuclear factor-kappa B, mitogen-activated protein kinase, NLR family pyrin domain containing 3, nuclear factor erythroid 2-related factor 2, AMP-activated protein kinase, mitochondrial apoptotic pathways, and microRNAs are involved in these detrimental biological processes. Research has shown that several antioxidants, small-molecule inhibitors, or proteins (such as lactoferrin) supplementation can potentially offer protective effects by targeting these signaling pathways. This review comprehensively summarizes the harmful effects of DON exposure on male reproductive function in mammals, the underlying molecular mechanisms and emphasizes the potential of several small molecules as protective therapeutics. In the further, the systematic risk assessment when DON at environmental exposure doses to human reproductive health, the in-depth and precise molecular mechanism investigation using emerging technologies, and the development of more effective intervention strategies warrant urgent investigation.

The SPARC-related modular calcium binding 1 ( Smoc1 ) regulated by androgen is required for mouse gubernaculum development and testicular descent

ABSTRACT

Testicular descent occurs in two consecutive stages: the transabdominal stage and the inguinoscrotal stage. Androgens play a crucial role in the second stage by influencing the development of the gubernaculum, a structure that pulls the testis into the scrotum. However, the mechanisms of androgen actions underlying many of the processes associated with gubernaculum development have not been fully elucidated. To identify the androgen-regulated genes, we conducted large-scale gene expression analyses on the gubernaculum harvested from luteinizing hormone/choriogonadotropin receptor knockout ( Lhcgr KO) mice, an animal model of inguinoscrotal testis maldescent resulting from androgen deficiency. We found that the expression of secreted protein acidic and rich in cysteine (SPARC)-related modular calcium binding 1 ( Smoc1 ) was the most severely suppressed at both the transcript and protein levels, while its expression was the most dramatically induced by testosterone administration in the gubernacula of Lhcgr KO mice. The upregulation of Smoc1 expression by testosterone was curtailed by the addition of an androgen receptor antagonist, flutamide. In addition, in vitro studies demonstrated that SMOC1 modestly but significantly promoted the proliferation of gubernacular cells. In the cultures of myogenic differentiation medium, both testosterone and SMOC1 enhanced the expression of myogenic regulatory factors such as paired box 7 ( Pax7 ) and myogenic factor 5 ( Myf5 ). After short-interfering RNA-mediated knocking down of Smoc1 , the expression of Pax7 and Myf5 diminished, and testosterone alone did not recover, but additional SMOC1 did. These observations indicate that SMOC1 is pivotal in mediating androgen action to regulate gubernaculum development during inguinoscrotal testicular descent.

Developmental exposures to common environmental pollutants result in long-term Reprogramming of hypothalamic-pituitary axis in mice

Humans are exposed to a range of endocrine disrupting chemicals (EDCs). Many studies demonstrate that exposures to EDCs during critical windows of development can permanently affect endocrine health outcomes. Most experimental studies address changes in secretion of hormones produced by gonads, thyroid gland and adrenals, and little is known about the ability of EDCs to produce long-term changes in the hypothalamic-pituitary (HP) control axes. Here, we examined the long-term effects of three common EDCs on male mouse HP gene expression, following developmental exposures. Pregnant mice were exposed to 0.2 mg/ml solutions of bisphenol S (BPS), 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), or 3,3',5,5'-tetrabromobisphenol A (TBBPA) from pregnancy day 8 through lactation day 21 (weaning day). Male offspring were left untreated until postnatal day 140, where pituitaries and hypothalami were collected. Pituitaries were assed for gene expression via RNA sequencing, while specific genes were assessed for expression in hypothalami via RT-qPCR. Differential expression, as well as gene enrichment and pathway analysis, indicated that all three chemicals induced long-term changes, (mostly suppression) in pituitary genes involved in its endocrine function. BPS and BDE-47 produced effects overlapping significantly at the level of effected genes and pathways. All three chemicals altered pathways of gonad and liver HP axes, while BPS altered HP-adrenal and BDE-47 altered HP-thyroid pathways specifically. All three chemicals reduced expression of immune genes in the pituitaries. Targeted gene expression in the hypothalamus indicates down regulation of hypothalamic endocrine control genes by BPS and BDE-47 groups, concordant with changes in the pituitary, suggesting that these chemicals suppress overall HP endocrine function. Interestingly, all three chemicals altered pituitary genes of GPCR-mediated intracellular signaling molecules, key signalers common to many pituitary responses to hormones. The results of this study show that developmental exposures to common EDCs have long-term impacts on hormonal feedback control at the hypothalamic-pituitary level.

Multiple omics integration analysis reveals the regulatory effect of chitosan oligosaccharide on testicular development

Infertility is a global health problem affecting millions of people of reproductive age worldwide, with approximately half caused by males. Chitosan oligosaccharide (COS) has strong antioxidant capacity, but its impact on the male reproductive system has not been effectively evaluated. To address this, we integrated RNA-seq, serum metabolomics and intestinal 16 S rDNA analysis to conduct a comprehensive investigation on the male reproductive system. The results showed that COS has potential targets for the treatment of oligospermia, which can promote the expression of meiotic proteins DDX4, DAZL and SYCP1, benefit germ cell proliferation and testicular development, enhance antioxidant capacity, and increase the expression of testicular steroid proteins STAR and CYP11A1. At the same time, COS can activate PI3K-Akt signaling pathway in testis and TM3 cells. Microbiome and metabolomics analysis suggested that COS alters gut microbial community composition and cooperates with serum metabolites to regulate spermatogenesis. Therefore, COS promotes male reproduction by regulating intestinal microorganisms and serum metabolism, activating PI3K-Akt signaling pathway, improving testicular antioxidant capacity and steroid regulation.

Trace and essential elements as vital components to improve the performance of the male reproductive system: Implications in cell signaling pathways

Successful male fertilization requires the main processes such as normal spermatogenesis, sperm capacitation, hyperactivation, and acrosome reaction. The progress of these processes depends on some endogenous and exogenous factors. So, the optimal level of ions and essential and rare elements such as selenium, zinc, copper, iron, manganese, calcium, and so on in various types of cells of the reproductive system could affect conception and male fertility rates. The function of trace elements in the male reproductive system could be exerted through some cellular and molecular processes, such as the management of active oxygen species, involvement in the action of membrane channels, regulation of enzyme activity, regulation of gene expression and hormone levels, and modulation of signaling cascades. In this review, we aim to summarize the available evidence on the role of trace elements in improving male reproductive performance. Also, special attention is paid to the cellular aspects and the involved molecular signaling cascades.

The effects of inhaled pollutants on reproduction in marginalized communities: a contemporary review

Important differences in health that are closely linked with social disadvantage exist within and between countries. According to the World Health Organization, life expectancy and good health continue to increase in many parts of the world, but fail to improve in other parts of the world, indicating that differences in life expectancy and health arise due to the circumstances in which people grow, live, work, and age, and the systems put in place to deal with illness. Marginalized communities experience higher rates of certain diseases and more deaths compared to the general population, indicating a profound disparity in health status. Although several factors place marginalized communities at high risk for poor health outcomes, one important factor is exposure to air pollutants. Marginalized communities and minorities are exposed to higher levels of air pollutants than the majority population. Interestingly, a link exists between air pollutant exposure and adverse reproductive outcomes, suggesting that marginalized communities may have increased reproductive disorders due to increased exposure to air pollutants compared to the general population. This review summarizes different studies showing that marginalized communities have higher exposure to air pollutants, the types of air pollutants present in our environment, and the associations between air pollution and adverse reproductive outcomes, focusing on marginalized communities.

Withaferin-A attenuates diabetes mellitus induced male reproductive dysfunction mediated by ERα in brain and testes of Swiss albino mice

Diabetes mellitus (DM) is a chronic metabolic disease, characterized by persistent hyperglycemia resulting from diminished insulin secretion or insulin resistance. The present study evaluated the ameliorative effects of Withaferin-A (WA) on DM-induced reproductive dysfunction in mice. For the same, mice were intraperitoneally injected with Streptozotocin (STZ), (40 mg/kg/day) for 5 consecutive days to induce DM. Mice were then treated with WA (8 mg/kg/day) in normal and diabetic conditions (STZ + WA). Next, blood glucose levels, oral glucose tolerance, intraperitoneal insulin tolerance, oxidative stress and reproductive parameters were estimated. For reproductive performance, immunofluorescent localization of gonadotropin-releasing hormone (GnRH-I) and estrogen receptor alpha (ERα) in the preoptic area and paraventricular nucleus region of hypothalamus and ERα in testes was performed. STZ-induced diabetes triggered reproductive dysfunctions as mediated by low GnRH-I and ERα in the brain and ERα in the testes along with declined testosterone and estradiol levels. Treatment with WA significantly reduced the blood glucose levels and enhanced glucose clearance accompanied by reduced oxidative stress in the brain, pancreas and testes as indicated by the low levels of H2O2 and MDA in diabetic mice treated with WA (STZ + WA). This study reports, for the first time, that WA can efficiently ameliorate DM-induced reproductive dysfunctions by enhancing endogenous testosterone, estrogen and increased GnRH-I and ERα in the brain and ERα in the testes of DM-induced male mice.

Oral administration of VDAC1-derived small molecule peptides increases circulating testosterone levels in male rats

Cholesterol is the precursor of all steroid hormones, and the entry of cholesterol into the mitochondria is the rate-limiting step of steroidogenesis. Voltage-dependent anion channel (VDAC1) is an outer mitochondrial protein part of a multiprotein complex that imports cholesterol. We previously reported that intratesticular administration of a 25 amino acid peptide blocking the interaction between 14-3-3ϵ with VDAC1 increased circulating levels of testosterone. This fusion peptide was composed of a HIV-1 transactivator of transcription (TAT) protein transduction domain cell-penetrating peptide, a glycine linker, and amino acids 159-172 of VDAC1 (TV159-172). Here, we describe the development of a family of small molecules that increase circulating testosterone levels after an oral administration. We first characterized an animal model where TV159-172 was delivered subcutaneously. This subcutaneous model allowed us to study the interactions between TV159-172 and the hypothalamus-pituitary-gonadal axis (HPG) and identify the biologically active core of TV159-172. The core consisted of the tetrapeptide RVTQ, which we used as a platform to design synthetic peptide derivatives that can be administered orally. We developed a second animal model to test various derivatives of RVTQ and found 11 active compounds. Dose-response experiments identified 4 synthetic peptides that robustly increased androgen levels in a specific manner. We selected RdVTQ as the leading VDAC1-core derivative and profiled the response across the lifespan of Brown-Norway rats. In summary, we present the development of a new class of therapeutics that act within the HPG axis to increase testosterone levels specifically. This new class of small molecules self-regulates, preventing abuse.

AAV-mediated gene therapy produces fertile offspring in the Lhcgr-deficient mouse model of Leydig cell failure

Leydig cell failure (LCF) caused by gene mutation results in testosterone deficiency and infertility. Serum testosterone levels can be recovered via testosterone replacement; however, established therapies have shown limited success in restoring fertility. Here, we use a luteinizing hormone/choriogonadotrophin receptor (Lhcgr)-deficient mouse model of LCF to investigate the feasibility of gene therapy for restoring testosterone production and fertility. We screen several adeno-associated virus (AAV) serotypes and identify AAV8 as an efficient vector to drive exogenous Lhcgr expression in progenitor Leydig cells through interstitial injection. We observe considerable testosterone recovery and Leydig cell maturation after AAV8-Lhcgr treatment in pubertal Lhcgr^-/- mice. Of note, this gene therapy partially recovers sexual development, substantially restores spermatogenesis, and effectively produces fertile offspring. Furthermore, these favorable effects can be reproduced in adult Lhcgr^-/- mice. Our proof-of-concept experiments in the mouse model demonstrate that AAV-mediated gene therapy may represent a promising therapeutic approach for patients with LCF.

Seasonal Expression of Gonadotropin Genes in the Pituitary and Testes of Male Plateau Zokor (Eospalax baileyi)

The gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), are glycoprotein hormones in the hypothalamic-pituitary-gonadal (HPG) axis and regulate mammalian reproduction. The expression of these genes in the plateau zokor (Eospalax baileyi) is poorly understood. We characterized the immunolocalization of the luteinizing hormone receptor (LHR) and follicle stimulating hormone receptor (FSHR) in the testes and evaluated the positive immunohistochemical results and the relative mRNA expression of gonadotropin genes. During the non-breeding season (September), the relative testes weight and the seminiferous tubule diameter were significantly reduced. All germ cell types were observed during the breeding season (May), whereas only spermatogonia were observed during the non-breeding season. LHR was present in the Leydig cells whereas FSHR was present in the Sertoli cells. The mean optical density was higher during the breeding season. The mRNA expression of LHβ and FSHβ was lower in the pituitary but LHR and FSHR genes expression were higher in the testes during the breeding season. These data elucidate the expression of gonadotropin genes in the HPG axis of the male plateau zokor and suggest that gonadotropins play a vital role in the regulation of seasonal breeding.

The Roles of Luteinizing Hormone, Follicle-Stimulating Hormone and Testosterone in Spermatogenesis and Folliculogenesis Revisited

Spermatogenesis and folliculogenesis involve cell–cell interactions and gene expression orchestrated by luteinizing hormone (LH) and follicle-stimulating hormone (FSH). FSH regulates the proliferation and maturation of germ cells independently and in combination with LH. In humans, the requirement for high intratesticular testosterone (T) concentration in spermatogenesis remains both a dogma and an enigma, as it greatly exceeds the requirement for androgen receptor (AR) activation. Several data have challenged this dogma. Here we report our findings on a man with mutant LH beta subunit (LHβ) that markedly reduced T production to 1–2% of normal., but despite this minimal LH stimulation, T production by scarce mature Leydig cells was sufficient to initiate and maintain complete spermatogenesis. Also, in the LH receptor (LHR) knockout (LuRKO) mice, low-dose T supplementation was able to maintain spermatogenesis. In addition, in antiandrogen-treated LuRKO mice, devoid of T action, the transgenic expression of a constitutively activating follicle stimulating hormone receptor (FSHR) mutant was able to rescue spermatogenesis and fertility. Based on rodent models, it is believed that gonadotropin-dependent follicular growth begins at the antral stage, but models of FSHR inactivation in women contradict this claim. The complete loss of FSHR function results in the complete early blockage of folliculogenesis at the primary stage, with a high density of follicles of the prepubertal type. These results should prompt the reassessment of the role of gonadotropins in spermatogenesis, folliculogenesis and therapeutic applications in human hypogonadism and infertility.

Immunization with oral KISS1 DNA vaccine inhibits testicular Leydig cell proliferation mainly via the hypothalamic-pituitary-testicular axis and apoptosis-related genes in goats

This study aimed to analyze the effect and mechanism of immunization of oral KISS1 DNA vaccine on the proliferation of goat testicular Leydig cells. Ten 8-week-old male goats were randomly divided into KISS1 DNA vaccine and control groups for immunization (five goats each group). These goats were sacrificed at 8 weeks after primary immunization, and the tissue samples of hypothalamus, pituitary, and testis and Leydig cell samples were collected for RT-PCR and CCK8 assay. Immunization with the oral KISS1 DNA vaccine effectively inhibited the proliferation of Leydig cells, the expression of hypothalamus KISS1, GPR54, and GnRH mRNA, pituitary GnRHR and LH mRNA, testicular LHR mRNA, and apoptosis-inhibitory gene Bcl-2 mRNA in Leydig cells. By contrast, the immunization enhanced the mRNA expression of apoptosis-promoting gene Bax and Clusterin in Leydig cells. These findings indicate that immunization with the oral KISS1 DNA vaccine can inhibit the proliferation of goat testicular Leydig cells mainly via the hypothalamic-pituitary-testicular axis and apoptosis-related genes.

Diabetes mellitus and the impairment of male reproductive function: Possible signaling pathways

BACKGROUND AND AIMS

Today, it has been shown that diabetes mellitus (DM) can affect male fertility. Glucose metabolism is a vital process in spermatogenesis that is impacted by diabetes condition. But the mechanisms by which DM causes male infertility are not wholly clarified. The aim of this review is to provide brief information about the influence of hyperglycemia on male fertility and specific emphasis on the molecular signaling pathway that is involved.

METHODS

Broad literature search in the electronic database "Pubmed", "Google Scholar", the website of "World Health Organization" (WHO) and Control Disease and Prevention (CDC) took place. There was no time restriction. A key criterion for the selection of articles was English and language. Finally, one hundred thirty seven articles were included in the review.

RESULTS

Diabetes mellitus affects many signaling pathways that involved in the spermatogenesis. It seems that increased ROS and oxidative stress in the diabetes is the beginning of all fertility problems and affects all of involved signaling pathways in the spermatogenesis.

CONCLUSIONS

It seems that there was strong interconnected between oxidative stress and all of involved signaling pathways in the reproductive problems in diabetes. So, approaches that diminish oxidative stress in the testis can be effective in improving diabetes related infertility complications.

Testosterone Supplementation Rescues Spermatogenesis and In Vitro Fertilizing Ability of Sperm in Kiss1 Knockout Mice

Restoration of spermatogenesis and fertility is a major issue to be solved in male mammals with hypogonadotropic hypogonadism. Kiss1 knockout (KO) male mice are postulated to be a suitable animal model to investigate if hormonal replacement rescues spermatogenesis in mammals with this severe reproductive hormone deficiency, because KO mice replicate the hypothalamic disorder causing hypogonadism. The present study investigated whether testosterone supplementation was able to restore spermatogenesis and in vitro fertilization ability in Kiss1 KO mice. To this end, spermatogenesis, in vitro fertilization ability of Kiss1 KO sperm, and preimplantation development of wild-type embryos inseminated with Kiss1 KO sperm, were examined. The newly generated Kiss1 KO male mice showed infertility with cryptorchidism. Subcutaneous testosterone supplementation for 6 weeks restored plasma and intratesticular testosterone levels, elicited testicular descent, and induced complete spermatogenesis from spermatocytes to elongated spermatids in the testis, resulting in an increase in epididymal sperm number in testosterone-supplemented Kiss1 KO male mice. Epididymal sperm derived from the testosterone-supplemented Kiss1 KO mice showed normal in vitro fertilization ability, and the fertilized eggs showed normal preimplantation development, while the males failed to impregnate females. These results suggest that the failure of spermatogenesis in Kiss1 KO mice is mainly due to a lack of testosterone production, and that Kiss1 KO sperm are capable of fertilizing eggs if the animals receive the appropriate testosterone supplementation without local kisspeptin signaling in the testis and epididymis. Thus, testosterone supplementation would restore spermatogenesis of male mammals showing hypogonadotropic hypogonadism with genetic inactivation of the KISS1/Kiss1 gene.

Entry into puberty is reflected in changes in hormone production but not in testicular receptor expression in Atlantic salmon (Salmo salar)

BACKGROUND

Puberty in male Atlantic salmon in aquaculture can start as early as after the first winter in seawater, stunts growth and entails welfare problems due to the maturation-associated loss of osmoregulation capacity in seawater. A better understanding of the regulation of puberty is the basis for developing improved cultivation approaches that avoid these problems. Our aim here was to identify morphological and molecular markers signaling the initiation of, and potential involvement in, testis maturation.

METHODS

In the first experiment, we monitored for the first time in large Atlantic salmon males several reproductive parameters during 17 months including the first reproductive cycle. Since testicular growth accelerated after the Winter solstice, we focused in the second experiment on the 5 months following the winter solstice, exposing fish from February 1 onwards to the natural photoperiod (NL) or to continuous additional light (LL).

RESULTS

In the first experiment, testis weight, plasma androgens and pituitary gonadotropin transcript levels increased with the appearance of type B spermatogonia in the testis, but testicular transcript levels for gonadotropin or androgen receptors did not change while being clearly detectable. In the second experiment, all males kept under NL had been recruited into puberty until June. However, recruitment into puberty was blocked in ~ 40% of the males exposed to LL. The first morphological sign of recruitment was an increased proliferation activity of single spermatogonia and Sertoli cells. Irrespective of the photoperiod, this early sign of testis maturation was accompanied by elevated pituitary gnrhr4 and fshb and testicular igf3 transcript levels as well as increased plasma androgen levels. The transition into puberty occurred again with stable testicular gonadotropin and androgen receptor transcript levels.

CONCLUSIONS

The sensitivity to reproductive hormones is already established before puberty starts and up-regulation of testicular hormone receptor expression is not required to facilitate entry into puberty. The increased availability of receptor ligands, on the other hand, may result from an up-regulation of pituitary Gnrh receptor expression, eventually activating testicular growth factor and sex steroid release and driving germ and Sertoli cell proliferation and differentiation.

A novel role for zinc transporter 8 in the facilitation of zinc accumulation and regulation of testosterone synthesis in Leydig cells of human and mouse testicles

OBJECTIVE

Zinc is intimately involved in testosterone production. Zinc transporter 8 (ZnT8) is found to be localized in insulin secretory granules as a β-cell specific Zn transporter. The effect of ZnT8 and related zinc accumulation in steroidogenesis, however, is still unknown. The present study aimed to explore whether ZnT8 plays a role in the facilitation of zinc accumulation and regulation of testosterone synthesis in testicles.

METHODS

Leydig cells were isolated from the testicles of human, CD-1 suckling and ZnT8-KO mice. Zn accumulation in mitochondria was induced by hCG stimulation. Transfection of hZnT8-EGFP and RNA interfere of mZnT8 were done in MLTC-1 cells. ZnT8 expression and its co-localization with steroidogenic acute regulatory (StAR) protein were analyzed with RT-PCR, Western blot and dual-fluorescent staining protocols. Serum testosterone levels in mice were determined with chemiluminescent enzyme immunoassay.

RESULTS

ZnT8 was found to be presented in Leydig cells and up-regulated in suckling mouse Leydig cells and MLTC-1 cells after hCG administration, by which zinc accumulation occurred in mitochondria. ZnT8 gene silencing or knockout inhibited stimulated progesterone and testosterone production, reduced stimulated zinc accumulation and down-regulated phosphorylated steroidogenic acute regulatory (StAR) expression in Leydig cells. Furthermore, an inhibitor (H89) of PKA blocked hCG-stimulated progesterone caused by ZnT8 over-expression and zinc treatment.

CONCLUSION

The present study provided the first evidence that ZnT8 transports Zn into Leydig cell mitochondria with gonadotropin stimulation and suggests that ZnT8 may play a role in testosterone production via the PKA signaling pathway.

Testosterone Retention Mechanism in Sertoli Cells: A Biochemical Perspective

Mechanism(s) involved in regulating Intratesticular Testosterone levels (iT) have assumed importance in recent years, from the point of view of hormonal contraception. Contraceptives using Testosterone (T) in combination with Progestins (P), for more effective suppression of pituitary gonadotropins thereby iT, are not 100% effective in suppressing spermatogenesis in human males, likely due to pesrsistence of Intratesticular Dihydrotestosterone (iD) in poor-responders. Several lacunae pertaining to the mechanism of action of principal male hormone T during spermatogenesis remain to be resolved. Notably, the mechanism through which T brings about the stage-specific differentiation of germ cells lacking Androgen Receptors (AR). Testosterone is a highly anabolic steroid with a rapid tissue clearance rate. T is intratesticular substrate for synthesis of Dihydrotestosterone (DHT) and Estradiol (E2) involved in spermtaogenesis. Therefore, it is important to delineate the mechanism(s) for retention of iT, in order to understand regulation of its bioavailability in testis. In depth studies, pertaining to the role of androgen-binding protein(s) in sequestration, retention and bioavailability of T/DHT are required to understand male fertility regulation. The appropriate approach to overcome this lacuna would be development of mice lacking functional testicular Androgen-Binding Protein (ABPKO), but not deficient T/DHT, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), in order to understand its physiological functions. Insights gained about androgen retention mechanism(s) from the ABPKO murine model will be of immense help in improving the efficacy of male hormonal contraceptives and infertility management.

Mouse models for the analysis of gonadotropin secretion and action

Gonadotropins are pituitary gonadotrope-derived glycoprotein hormones. They act by binding to G-protein coupled receptors on gonads. Gonadotropins play critical roles in reproduction by regulating both gametogenesis and steroidogenesis. Although biochemical and physiological studies provided a wealth of knowledge, gene manipulation techniques using novel mouse models gave new insights into gonadotropin synthesis, secretion and action. Both gain of function and loss of function mouse models for understanding gonadotropin action in a whole animal context have already been generated. Moreover, recent studies on gonadotropin actions in non-gonadal tissues challenged the central dogma of classical gonadotropin actions in gonads and revealed new signaling pathways in these non-gonadal tissues. In this Chapter, we have discussed our current understanding of gonadotropin synthesis, secretion and action using a variety of genetically engineered mouse models.

The Luteinizing Hormone-Testosterone Pathway Regulates Mouse Spermatogonial Stem Cell Self-Renewal by Suppressing WNT5A Expression in Sertoli Cells

Spermatogenesis originates from self-renewal of spermatogonial stem cells (SSCs). Previous studies have reported conflicting roles of gonadotropic pituitary hormones in SSC self-renewal. Here, we explored the role of hormonal regulation of SSCs using Fshb and Lhcgr knockout (KO) mice. Although follicle-stimulating hormone (FSH) is thought to promote self-renewal by glial cell line-derived neurotrophic factor (GDNF), no abnormalities were found in SSCs and their microenvironment. In contrast, SSCs were enriched in Lhcgr-deficient mice. Moreover, wild-type SSCs transplanted into Lhcgr-deficient mice showed enhanced self-renewal. Microarray analysis revealed that Lhcgr-deficient testes have enhanced WNT5A expression in Sertoli cells, which showed an immature phenotype. Since WNT5A was upregulated by anti-androgen treatment, testosterone produced by luteinizing hormone (LH) is required for Sertoli cell maturation. WNT5A promoted SSC activity both in vitro and in vivo. Therefore, FSH is not responsible for GDNF regulation, while LH negatively regulates SSC self-renewal by suppressing WNT5A via testosterone.

Seasonal expression of luteinizing hormone receptor and follicle stimulating hormone receptor in testes of the wild ground squirrels (Citellus dauricus Brandt)

The objective of this study was to evaluate whether luteinizing hormone (LH), follicle stimulating hormone (FSH) and their receptors luteinizing hormone receptor (LHR) and follicle stimulating hormone receptor (FSHR) play roles in the seasonal spermatogenesis of the wild ground squirrels. To that end, we characterized the testicular immunolocalization of LHR and FSHR, their expression on both mRNA and protein levels, as well as serum concentrations of LH and FSH in male wild ground squirrels throughout the annual reproductive cycle. Histologically, all types of spermatogenic cells including mature spermatozoa were identified in the breeding season (April), while spermatogonia and primary spermatocytes were observed in the non-breeding season (June), and spermatogonia, primary spermatocytes and secondary spermatocytes were found in pre-hibernation (September). LHR was present in Leydig cells during the whole periods with more intense staining in the breeding season; Stronger immunostaining of FSHR was observed in Sertoli cells during the breeding season compared to the non-breeding season and pre-hibernation. Consistently, the mRNA and protein levels of LHR and FSHR were higher in testes of the breeding season, and then decreased to a relatively lower level in the non-breeding season and pre-hibernation. Meanwhile, serum LH and FSH concentrations were significantly higher in the breeding season than those in the non-breeding season and pre-hibernation. These results suggested that gonadotropins and its receptors, LHR and FSHR may be involved in the regulation of seasonal changes in testicular functions of the wild ground squirrels.

Purification and identification of 25-hydroxycholesterol in a reptile: Seasonal variation and hormonal regulation

The present in vitro study, for the first time, demonstrates the production of 25-hydroxycholestrol (25-HC) by testicular macrophages of a non-mammalian vertebrate. The ether extracts of testicular macrophage-conditioned medium (TMCM) were fractionated on a C18 reversed phase high-performance liquid chromatography (HPLC) column using methanol as the mobile phase. The mass spectrometry (MS) fragmentation pattern of HPLC-purified 25-HC was found to be identical to that of authentic 25-HC. Further, a significant seasonal variation in 25-HC concentration was observed with maximal level in regressed and minimal during breeding phase. To understand the hormonal control of 25-HC production, testicular macrophages from regressed phase testes were incubated with 0.5μg/ml of ovine follicle stimulating hormone (FSH) and 0.1, 1 and 10μg/ml of testosterone (T). FSH considerably enhanced 25-HC production by testicular macrophages. In contrast, T markedly inhibited 25-HC production in a dose-dependent manner. In addition, T significantly inhibited FSH-induced 25-HC production, though pre-treatment with T was more effective as compared to post-treatment with T to FSH. Our findings on production, seasonal variation and hormonal control of 25-HC suggest the functional significance of 25-HC in the testis of reptiles.

Low temperature-induced circulating triiodothyronine accelerates seasonal testicular regression

In temperate zones, animals restrict breeding to specific seasons to maximize the survival of their offspring. Birds have evolved highly sophisticated mechanisms of seasonal regulation, and their testicular mass can change 100-fold within a few weeks. Recent studies on Japanese quail revealed that seasonal gonadal development is regulated by central thyroid hormone activation within the hypothalamus, depending on the photoperiodic changes. By contrast, the mechanisms underlying seasonal testicular regression remain unclear. Here we show the effects of short day and low temperature on testicular regression in quail. Low temperature stimulus accelerated short day-induced testicular regression by shutting down the hypothalamus-pituitary-gonadal axis and inducing meiotic arrest and germ cell apoptosis. Induction of T3 coincided with the climax of testicular regression. Temporal gene expression analysis over the course of apoptosis revealed the suppression of LH response genes and activation of T3 response genes involved in amphibian metamorphosis within the testis. Daily ip administration of T3 mimicked the effects of low temperature stimulus on germ cell apoptosis and testicular mass. Although type 2 deiodinase, a thyroid hormone-activating enzyme, in the brown adipose tissue generates circulating T3 under low-temperature conditions in mammals, there is no distinct brown adipose tissue in birds. In birds, type 2 deiodinase is induced by low temperature exclusively in the liver, which appears to be caused by increased food consumption. We conclude that birds use low temperature-induced circulating T3 not only for adaptive thermoregulation but also to trigger apoptosis to accelerate seasonal testicular regression.

Genetic Models for the Study of Luteinizing Hormone Receptor Function

The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is essential for fertility in men and women. LHCGR binds luteinizing hormone (LH) as well as the highly homologous chorionic gonadotropin. Signaling from LHCGR is required for steroidogenesis and gametogenesis in males and females and for sexual differentiation in the male. The importance of LHCGR in reproductive physiology is underscored by the large number of naturally occurring inactivating and activating mutations in the receptor that result in reproductive disorders. Consequently, several genetically modified mouse models have been developed for the study of LHCGR function. They include targeted deletion of LH and LHCGR that mimic inactivating mutations in hormone and receptor, expression of a constitutively active mutant in LHCGR that mimics activating mutations associated with familial male-limited precocious puberty and transgenic models of LH and hCG overexpression. This review summarizes the salient findings from these models and their utility in understanding the physiological and pathological consequences of loss and gain of function in LHCGR signaling.

Endocrine control of spermatogenesis: Role of FSH and LH/ testosterone

Evaluation of testicular functions (production of sperm and androgens) is an important aspect of preclinical safety assessment and testicular toxicity is comparatively far more common than ovarian toxicity. This chapter focuses (1) on the histological sequelae of disturbed reproductive endocrinology in rat, dog and nonhuman primates and (2) provides a review of our current understanding of the roles of gonadotropins and androgens. The response of the rodent testis to endocrine disturbances is clearly different from that of dog and primates with different germ cell types and spermatogenic stages being affected initially and also that the end-stage spermatogenic involution is more pronounced in dog and primates compared to rodents. Luteinizing hormone (LH)/testosterone and follicle-stimulating hormone (FSH) are the pivotal endocrine factors controlling testicular functions. The relative importance of either hormone is somewhat different between rodents and primates. Generally, however, both LH/testosterone and FSH are necessary for quantitatively normal spermatogenesis, at least in non-seasonal species.

The effects of type 1 diabetes on the hypothalamic, pituitary and testes axis

Type 1 diabetes is an autoimmune disorder characterized by a lack of insulin production by the beta cells of the pancreas. This lack of insulin causes a variety of systemic effects on whole-body metabolism. Poorly managed type 1 diabetes can lead to cardiovascular disease, diabetic neuropathy, and diabetic retinopathy. Increasingly, even well-managed type 1 diabetic patients show damage to peripheral organs related to complications from the disease. The central role of insulin in energy homeostasis also renders it an important signaling factor in the reproductive tract. type 1 diabetes has now been demonstrated to cause defects in sperm and testes. The aim of this review is to present the known effects of insulin's role in the function of the male reproductive tract. These effects might be mediated through hormonal alterations in the hypothalamic pituitary gonadal axis or through the direct interaction of insulin on the testes and sperm cells. Although fertility complications also occur in type 2 diabetic males, this review will focus on the defects specifically linked with the lack of insulin seen in type 1 diabetes.

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.

The role of RXFP2 in mediating androgen-induced inguinoscrotal testis descent in LH receptor knockout mice

LH receptor knockout (LhrKO) male mice exhibit a bilateral cryptorchidism resulting from a developmental defect in the gubernaculum during the inguinoscrotal phase of testis descent, which is corrected by testosterone replacement therapy (TRT). In vivo and in vitro experiments were conducted to investigate the roles of the androgen receptor (AR) and RXFP2 signals in regulation of gubernacular development in LhrKO animals. This study demonstrated that AR and RXFP2 proteins were expressed in the gubernaculum during the entire postnatal period. TRT normalized gubernacular RXFP2 protein levels inLhrKO mice. Organ and primary cell cultures of gubernacula showed that 5alpha-dihydrotestosterone (DHT) upregulated the expression of Rxfp2 which was abolished by the addition of an AR antagonist, flutamide. A single s.c. testosterone injection also led to a significant increase in Rxfp2 mRNA levels in a time-dependent fashion in LhrKO animals. DHT, natural and synthetic insulin-like peptide 3 (INSL3), or relaxin alone did not affect proliferation of gubernacular mesenchymal cells, while co-treatments of DHT with either INSL3 or relaxin resulted in an increase in cell proliferation, and they also enhanced the mesenchymal cell differentiation toward the myogenic pathway, which included a decrease in a mesenchymal cell marker, CD44 and the expression of troponin. These effects were attenuated by the addition of flutamide, siRNA-mediated Rxfp2 knockdown, or by an INSL3 antagonist. Co-administration of an INSL3 antagonist curtailed TRT-induced inguinoscrotal testis descent in LhrKO mice. Our findings indicate that the RXFP2 signaling pathway plays an important role in mediating androgen action to stimulate gubernaculum development during inguinoscrotal testis descent.

Impact of a constitutively active luteinizing hormone receptor on testicular gene expression and postnatal Leydig cell development

The actions of luteinizing hormone (LH) mediated through its receptor (LHR) are critical for testicular steroidogenesis and Leydig cell differentiation. We have previously characterized transgenic mice expressing a genetically engineered, constitutively active yoked hormone-receptor complex (YHR), in which a fusion protein of human chorionic gonadotropin (hCG) was covalently linked to LHR. Elevated testosterone levels were detected in male mice expressing YHR (YHR(+)) at 3 and 5 weeks of age, accompanied by decreases in testicular weight and serum levels of LH and follicle stimulating hormone (FSH). Here we report a temporal study to identify testicular genes whose expression is altered in YHR(+) mice during postnatal development. The mRNA expression levels for the steroidogenic enzymes, P450 17alpha-hydroxylase, 17beta-hydroxysteroid dehydrogenase3 and 5alpha-reductase1 were down-regulated in 3- and 5-week-old YHR(+) testis. This result coupled with an immunohistochemical analysis of Leydig cell specific proteins and quantification of Leydig cell numbers identified a decrease in adult Leydig cells in YHR(+) mice. Surprisingly, no change was detected for cytochrome P450 side-chain cleavage or steroidogenic acute regulatory protein RNA levels between WT and YHR(+) mice. In contrast, mRNA levels for insulin-like growth factor binding protein 3 were up-regulated in 3- and 5-week-old YHR(+) mice. The mRNA levels for several germ cell-specific proteins were up-regulated at 5 weeks of age in both WT and YHR(+) mice. We conclude that premature high levels of testosterone alter the expression of a select number of testicular genes and impair the differentiation of adult Leydig cells in mice.

The steroidogenic acute regulatory protein as a target of endocrine disruption in male reproduction

Development of the adult male reproductive tract requires proper spatial-temporal expression of the sex hormones testosterone and estrogen during fetal developmental stages and at puberty. Exogenous agents that disrupt the production and/or actions of the testosterone and estrogen and cause aberrant reproductive tract development can be thought of as endocrine disruptors (ED). This review will focus on the impact of ED on testosterone production by Leydig cells during fetal development and in the adult. In particular, the genes encoding the steroidogenic acute regulatory protein (StAR) and cytochrome P450 17 alpha hydroxylase/17,20 lyase (CYP17A1) within the steroid hormone biosynthetic pathway are highlighted as ED targets. We begin with an overview of steroidogenesis and regulation of StAR then summarize the published literature on the effects of diethylstibesterol, phthalate esters, and arsenite on male reproduction with a focus on the expression and function of StAR.

Transforming growth factor-beta1 null mutation causes infertility in male mice associated with testosterone deficiency and sexual dysfunction

TGFbeta1 is a multifunctional cytokine implicated in gonad and secondary sex organ development, steroidogenesis, and spermatogenesis. To determine the physiological requirement for TGFbeta1 in male reproduction, Tgfb1 null mutant mice on a Prkdc(scid) immunodeficient background were studied. TGFbeta1-deficient males did not deposit sperm or induce pseudopregnancy in females, despite an intact reproductive tract with morphologically normal penis, seminal vesicles, and testes. Serum and intratesticular testosterone and serum androstenedione were severely diminished in TGFbeta1-deficient males. Testosterone deficiency was secondary to disrupted pituitary gonadotropin secretion because serum LH and to a lesser extent serum FSH were reduced, and exogenous LH replacement with human chorionic gonadotropin (hCG) induced serum testosterone to control levels. In the majority of TGFbeta1-deficient males, spermatogenesis was normal and sperm were developmentally competent as assessed by in vitro fertilization. Analysis of sexual behavior revealed that although TGFbeta1 null males showed avid interest in females and engaged in mounting activity, intromission was infrequent and brief, and ejaculation was not attained. Administration of testosterone to adult males, even after neonatal androgenization, was ineffective in restoring sexual function; however, erectile reflexes and ejaculation could be induced by electrical stimulation. These studies demonstrate the profound effect of genetic deficiency in TGFbeta1 on male fertility, implicating this cytokine in essential roles in the hypothalamic-pituitary-gonadal axis and in testosterone-independent regulation of mating competence.

Cryptorchidism in LhrKO animals and the effect of testosterone-replacement therapy

BACKGROUND

The objective of the current study was to characterize the morphological and genetic basis of cryptorchidism.

METHODS AND RESULTS

We investigated cryptorchidism in LH receptor (Lhr) knockout (LhrKO) mice and how testosterone-replacement therapy (TRT) worked to correct the phenotype. The results revealed that while gubernacular development was indistinguishable between Lhr-null and wild-type animals until 7 days of age, it was subsequently severely impaired in null animals. This was due to a reduction in mesenchymal cell division, differentiation into cremaster muscle cells and their delayed maturation. While transcript levels of Hoxa10, Hoxa11, Desrt and Dll1 were indistinguishable, the levels of Notch1, Numb and Lgr8 in the gubernaculum and Insl3 in the testes were lower in Lhr-null than in wild-type siblings. The TRT, which completed testicular descent into the scrotum, corrected the morphological changes and the expression of Lgr8, Numb and Notch, but not Insl3, to wild-type levels. Transection of the genitofemoral nerve did not prevent the TRT effect.

CONCLUSION

In summary, cryptorchidism in Lhr-null animals was caused by defects in the gubernacular development due to testosterone deficiency. TRT reversed all the morphological and gene expression changes except Insl3, suggesting that testosterone, not INSL3, secreted by Leydig cells, facilitates the completion of testicular descent.

Effect of high intratesticular estrogen on the seminiferous epithelium in adult male rats

The presence of estrogen receptor beta and aromatase in the germ cell has highlighted the physiological role of the traditionally female hormone, estrogen, in spermatogenesis. Estrogen receptor alpha knockouts and aromatase knockouts have further accentuated the role of estrogen in germ cell maturation. To delineate the direct action of estrogen in the seminiferous epithelium, we studied the effects of high intratesticular estradiol. The study was based on the fact that administration of exogenous estradiol suppresses the hypothalamus pituitary gonadal axis (HPG) with a dose-dependant concomitant increase in intratesticular estrogen levels. Three doses of 17-beta estradiol, namely 20, 100 and 200 microg/kg/day were administered subcutaneously to different batches of adult male rats for 10 days. The effect of the three doses on serum hormonal profile, intratesticular testosterone (T) and estradiol (E) levels were studied. Twenty micrograms per kilograms per day of 17-beta estradiol affected the hypothalamus-pituitary axis, reducing serum gonadotropins and intratesticular testosterone; however, 100 microg/kg/day of 17-beta estradiol decreased serum FSH and intratesticular testosterone, increased intratesticular estradiol, but had no effect on serum LH. Interestingly, 200 microg/kg/day of 17-beta estradiol decreased serum and intratesticular T without any effect on serum gonadotropins. This could be attributed to the positive feedback effect of estrogens on gonadotropins. In the testis, morphologically two visible effects were seen, namely 'spermiation failure' in all three doses attributed to the suppression of T and FSH and a 'maintenance effect' in the 100 microg/kg/day attributed to E and/or 10% of available intratesticular T. The direct effect of an increase in intratesticular estradiol levels was observed in terms of a decrease in apoptosis in germ cell. The study, therefore, suggests that 100 microg/kg/day of 17-beta estradiol could be used to study the effects of high intratesticular estradiol with a concomitant decrease in intratesticular T and serum FSH levels on spermatogenesis.

Targeted disruption of LH receptor gene revealed the importance of uterine LH signaling

Numerous previous studies have demonstrated that LH and hCG can directly regulate several uterine functions. We investigated in the present study, whether uterine phenotype in LH receptor knockout animals resulted also from the absence of direct actions of LH in the uterus. The phenotype consisted of marked growth reduction of uterus, decreased thickness of endometrial and myometrial layers, number of endometrial glands, height of luminal epithelium and vascular space. Analysis of uterine gene expression by mouse genome U74Av2 Affymetrix genechips revealed a differential expression of 155 genes by more than 3-fold (range 3-53-fold) between null and wild-type animals. Of these, 89 genes decreased and 66 increased in uterus of null animals. Semi-quantitative RT-PCR confirmed the differential expression of several selected genes. The decreased genes can be clustered into 18 functional families and the increased into 15 functional families. Semi-quantitative RT-PCR, Western blotting and immunocytochemistry demonstrated a decreased expression of ERbeta, PR-A, PR-B and AR in uterus of null animals as compared with wild-type siblings. Twenty-one-day estradiol and progesterone replacement therapy did not normalize the decrease in the number of endometrial glands and several genes that either decreased or increased in expression. The partial success of therapy suggests that direct LH actions could be required to completely normalize the uterus. In summary, findings on the knockout model reaffirm that LH and hCG control uterine functions directly as well as indirectly through increasing ovarian synthesis of steroid hormones and both actions are required for normal uterine biology.