Insulin-like peptide 3 (INSL3) as an indicator of leydig cell insufficiency (LCI) in Middle-aged and older men with hypogonadism: reference range and threshold

Insulin-like peptide 3 (INSL3) is a circulating biomarker for Leydig cell functional capacity in men, also indicating Leydig Cell Insufficiency (LCI) and potential primary hypogonadism. Using results from large cohort studies we explore sources of biological and technical variance, and establish a reference range for adult men. It is constitutively secreted with little within-individual variation and reflects testicular capacity to produce testosterone. The main INSL3 assays available indicate good concordance with low technical variance; there is no effect of ethnicity. INSL3 declines with age from 35 years at about 15% per decade. Like low calculated free testosterone, and to a lesser extent low total testosterone, reduced INSL3 is significantly associated with increasing age-related morbidity, including lower overall sexual function, reflecting LCI. Consequently, low INSL3 (≤0.4 ng/ml; ca. <2 SD from the population mean) might serve as an additional biochemical marker in the assessment of functional hypogonadism (late-onset hypogonadism, LOH) where testosterone is in the borderline low range. Excluding individuals with low LCI (INSL3 ≤ 0.4 ng/ml) leads to an age-independent (> 35 years) reference range (serum) for INSL3 in the eugonadal population of 0.4 - 2.3 ng/ml, with low INSL3 prospectively identifying individuals at risk of increased future morbidity.

Perspectives on biomarkers of reproductive aging for fertility and beyond

Reproductive aging, spanning an age-related functional decline in the female and male reproductive systems, compromises fertility and leads to a range of health complications. In this Perspective, we first introduce a comprehensive framework for biomarkers applicable in clinical settings and discuss the existing repertoire of biomarkers used in practice. These encompass functional, imaging-based and biofluid-based biomarkers, all of which reflect the physiological characteristics of reproductive aging and help to determine the reproductive biological age. Next, we delve into the molecular alterations associated with aging in the reproductive system, highlighting the gap between these changes and their potential as biomarkers. Finally, to enhance the precision and practicality of assessing reproductive aging, we suggest adopting cutting-edge technologies for identifying new biomarkers and conducting thorough validations in population studies before clinical applications. These advancements will foster improved comprehension, prognosis and treatment of subfertility, thereby increasing chances of preserving reproductive health and resilience in populations of advanced age.

Seasonal piRNA Expression Profile Changes in the Testes of Plateau Zokor (Eospalax baileyi)

Seasonal reproduction is a mammalian behavior that has developed over an extended evolutionary period and requires animals to respond to external environmental changes to facilitate reproduction. In this study, we investigated the role of PIWI-interacting RNA (piRNA) in the seasonal reproduction of plateau zokors (Eospalax baileyi). piRNA expression profiles in plateau zokor testes during both breeding and non-breeding seasons were examined. The piRNAs had a distinctive ping-pong signature and ranged from 27 to 32 nt with a peak at 30 nt. Testicular piRNAs predominantly aligned to specific genomic regions, including repeat and gene regions. Analysis of the piRNA-mRNA interaction network and functional enrichment of differentially expressed piRNAs targeting mRNAs revealed their association with testicular development and spermatogenesis. Significantly, PIWIL4 is an mRNA gene that interacts with piRNA and exhibits high expression levels within the testes during the non-breeding phase. This study provides a foundation to improve our understanding of piRNA regulatory mechanisms during testicular development and spermatogenesis in seasonally reproducing animals and, specifically, in the plateau zokor.

INSL3 Variation in Dogs Following Suppression and Recovery of the HPG Axis

Insulin-like peptide 3 (INSL3) is a constitutive product of mature, adult-type Leydig cells of the testes and consequently in most mammals is an ideal biomarker with which to monitor pubertal development. A new heterologous time-resolved fluorescence immunoassay was developed and validated to measure circulating INSL3 in the blood of adult male dogs. Compared to other species, INSL3 concentration is low with marked variation between individuals, which appears to be independent of breed, age, or weight. A model system was then used in which a cohort of beagle dogs was subject to a GnRH-agonist implant to suppress the HPG axis and spermatogenesis, followed by implant removal and recovery. Unlike testosterone, INSL3 levels were not fully suppressed in all animals by the GnRH agonist, nor was the recovery of Leydig cell function following implant removal uniform or complete, even after several weeks. In dogs, and dissimilar from other species (including humans), Leydig-cell INSL3 appears to be quite variable between individual dogs and only weakly connected to the physiology of the HPG axis after its suppression by a GnRH-agonist implant and recovery. Consequently, INSL3 may be less useful in this species for the assessment of testis function.

The male reproductive toxicity after nanoplastics and microplastics exposure: Sperm quality and changes of different cells in testis

Nanoplastics (NPs) and Microplastics (MPs) pollution has become a severe threat to the planet and is a growing concern. However, their effects on male reproductive toxicity remain poorly understood. In this study, a series of morphological analyses were completed to explore the influence of NPs and MPs exposure on the testis in mice. After 12-weeks exposure, although both NPs and MPs exposure can lead to reproductive toxicity, compared with NPs exposure, exposure to MPs leads to a more significant increase in reproductive toxicity dependent on some particle size. Moreover, increased reproductive toxicities, including increased spermatogenesis disorders, and sperm physiological abnormality, oxidative stress, testis inflammation was more associated with MPs group than NPs group. Ultra-pathological structure observed by transmission electron microscopy indicated that both NPs and MPs have different effects on spermatogonia, spermatocytes and Sertoli cells. Exposure to MPs resulted in decreased Sertoli cell numbers and reduced Leydig cell area, and showed no effects on differentiation of Leydig cells by the expression level of the Insulin-Like factor 3 (INSL3) in Leydig cells. Transcriptomic sequencing analysis provided valuable insights into the differential effects of NPs and MPs on cellular processes. Specifically, our findings demonstrated that NPs were predominantly involved in the regulation of steroid biosynthesis, whereas MPs primarily influenced amino acid metabolism. This study demonstrates the effect of adult-stage reproductive toxicity in mice after exposure to NPs and MPs, which will deep the understanding of the NPs and MPs induced toxicity.

Age-related changes in circulating INSL3 concentrations and their associations with ovarian conditions in Japanese Black beef cattle

Information on circulating levels of insulin-like peptide 3 (INSL3) in female domesticated animals is limited, as their concentrations are significantly lower than in males. The objectives of the present study were to 1) develop a sandwich time-resolved fluorescence immunoassay (TRFIA) with higher detectability to measure blood INSL3 concentrations in female cattle, 2) determine INSL3 concentrations in female cattle among age groups and reproductive conditions, and 3) explore associations between INSL3 levels and ultrasonographic ovarian measurements. Blood was collected repeatedly from Japanese Black beef female calves (n = 12; 0－8 mo), heifers (n = 10; 10－26 mo), and cows (n = 20; 27－200 mo). Blood was taken from the cows (n = 13) at follicular, post-ovulatory, and luteal phases, and from cows with follicular cysts (n = 12). Ultrasonography of ovaries was conducted in the calves (n = 12) and the cows without ovarian diseases (n = 9). The ovarian area, as well as the number and diameters of antral follicles ≥ 2 mm, were determined in each ovary. The proposed method detected a difference in plasma INSL3 between calves (0.01 ng/mL) and heifers (0.18 ng/mL). However, the conventional assay showed similar levels for calves and heifers (1.82 vs 2.07 ng/mL). Plasma INSL3 and testosterone concentrations increased from calves to heifers (P < 0.0001), but only INSL3 rose from heifers to cows (P < 0.0001). INSL3 and testosterone concentrations did not change across the estrus cycle in cows, and the levels of both hormones in follicular cystic cows did not differ from those in the follicular phase. Ovarian area, maximal and average follicular diameters, and total volume of all follicles per animal were higher in cows than calves (P < 0.001). Plasma INSL3 concentrations correlated positively with the total volumes of all follicles in calves (P < 0.05) and cows (P < 0.05), whereas testosterone concentrations did not correlate with ovarian follicular measurements. In conclusion, plasma INSL3 concentrations measured by the proposed sandwich TRFIA showed a clear increase from female calves to cows in beef cattle. These results suggest that circulating levels of INSL3, but not of testosterone, are associated with the total volume of all antral follicles in both ovaries per animal in female cattle.

Development of an LC-MS/MS assay for quantification of intact INSL3 in rat plasma

Background: Relatively large disulfide-linked polypeptides can serve as signaling molecules for a diverse array of biological processes and may be studied in animal models to investigate their function in vivo. The aim of this work was to develop an LC-MS/MS assay to measure a model peptide, INSL3, in rat plasma. Results: A dual enrichment strategy incorporating both protein precipitation and solid phase extraction was utilized to isolate INSL3 from rat plasma, followed by targeted LC-MS/MS detection. The method was able to measure full-length INSL3 (6.1 kDa) down to 0.2 ng/ml with acceptable accuracy and precision. Conclusion: The final assay was applied to support an exploratory pharmacokinetic study to evaluate steady-state concentrations of dosed INSL3 in rat plasma.

Influence on the adult male Leydig cell biomarker insulin‐like peptide 3 of maternal exposure to estrogenic and anti‐androgenic endocrine disrupting compound mixtures: A retrospective study

Insulin-like peptide 3 (INSL3) is a peptide biomarker secreted specifically by the mature Leydig cells of the testes. It is constitutive, has low within-individual variance, and effectively measures the functional capacity of Leydig cells to make testosterone. In young adult men there is a large 10-fold range of serum INSL3 concentration, persisting into old age, and implying that later hypogonadal status might be programmed in early life. To determine whether maternal exposure to environmental endocrine disrupting compounds (EDCs) influences adult serum INSL3 concentration, using a retrospective paradigm, INSL3 was measured in young adult male rats (80-90 days) from the F1 generation of females maternally exposed to varied doses of bisphenol A (BPA), butylparaben, epoxiconazole, and fludioxonil as single compounds, as well as estrogenic and anti-androgenic mixtures of BPA and butylparaben, and di(2-ethylhexyl) phthalate and procymidone respectively. A mixture of BPA and butylparaben significantly reduced circulating INSL3 concentration in adult male progeny. The remaining compounds or mixtures tested, though sufficient to induce other effects in the F1 generation were without significant effect. Maternal exposure to low concentrations of some EDCs may be a contributing factor to the variation in the Leydig cell biomarker INSL3 in young adulthood, though caution is warranted translating results from rats to humans.

Expression and Role of INSL3 in the Fetal Testis

Insulin-like peptide 3 (INSL3) is a small peptide hormone of the insulin-relaxin family which is produced and secreted by the fetal Leydig cells in the testes only. It appears to be undetectable in female fetuses. In the human fetus INSL3 synthesis begins immediately following gonadal sex determination at weeks 7 to 8 post coitum and the peptide can be detected in amniotic fluid 1 to 2 weeks later. INSL3 acts through a unique G-protein-coupled receptor, called RelaXin-like Family Peptide receptor 2 (RXFP2), which is expressed by the mesenchymal cells of the gubernacular ligament linking the testes to the inguinal wall. The role of INSL3 in the male fetus is to cause a thickening of the gubernaculum which then retains the testes in the inguinal region, while the remainder of the abdominal organs grow away in an antero-dorsal direction. This represents the first phase of testis descent and is followed later in pregnancy by the second inguino-scrotal phase whereby the testes pass into the scrotum through the inguinal canal. INSL3 acts as a significant biomarker for Leydig cell differentiation in the fetus and may be reduced by maternal exposure to endocrine disrupting chemicals, such as xenoestrogens or phthalates, leading to cryptorchidism. INSL3 may have other roles within the fetus, but as a Leydig cell biomarker its reduction acts also as a surrogate for anti-androgen action.

Intronic miR-140-5p contributes to beta-cypermethrin-mediated testosterone decline

Beta-cypermethrin (β-CYP), a widely-used pyrethroid pesticide, is considered to have anti-androgenic effects and could impair male reproduction. To ascertain whether MAPK pathways, DNA methyltransferases (DNMTs), and miRNAs played pleiotropic roles in β-CYP-mediated testicular dysfunction, Sprague-Dawley rats and Leydig cells were employed in this study. Results showed that plasma testosterone levels were declined, testicular histomorphology and ultrastructures were abnormally altered, and Leydig cell functions were damaged after β-CYP exposure. JNK and p38/MAPK pathways were inactivated, accompanied by the decrease in c-Jun and Sp1 expressions. Specific activators/inhibitors of MAPK pathways and Co-IP demonstrated that DNMT3α was synergistically regulated by JNK/p38 pathways. The activity, mRNA and protein expressions of DNMT3α were all reduced by β-CYP. β-CYP induced expressions of intronic miR-140-5p and its host gene Wwp2, and then overexpressed miR-140-5p suppressed steroidogenic StAR, P450scc, and 3β-HSD by directly targeting SF-1. SF-1 silencing/overexpression, ChIP, and qPCR indicated that SF-1 modulated positively StAR, P450scc, and 3β-HSD expressions by directly binding to their promoter regions. Intriguingly, 5α-reductase expressions were downregulated after β-CYP exposure. Collectively, β-CYP has the anti-androgenic feature and the DNMT3α/miR-140-5p/SF-1 cascade co-regulated by JNK/p38 functions critically in β-CYP-caused testosterone declines. The downregulation of 5α-reductases may be a potential compensatory mechanism of the organism.

Insulin-like peptide 3 in domestic animals with normal and abnormal reproductive functions, in comparison to rodents and humans

Background

Insulin-like peptide 3 (INSL3) is a circulating hormone secreted from only testis and ovaries in mammals. Findings on INSL3 have been gathered from subjects with normal and abnormal reproductive statuses, especially rodents and humans. However, little to no review articles focusing on INSL3 in domestic animals exist.

Methods

The author reviewed the past and recent literature regarding the structure, expression, roles of INSL3 in the reproductive organs, and its circulation under normal and aberrant reproductive conditions in domestic animals in comparison with rodents and humans.

Main findings

As with humans and rodents, blood INSL3 concentrations rise around puberty in normal male domestic animals and are associated with testicular size. INSL3 levels are acutely upregulated by luteinizing hormone (LH), and the increase is smaller than that of testosterone in male ruminants, whereas the acute regulation of INSL3 by LH does not occur in human men. Dogs with cryptorchidism and bulls with abnormal semen have lowered INSL3 levels.

Conclusion

The findings regarding INSL3 secretions in male domestic animals with normal and aberrant reproductive functions illustrate similar or dissimilar points to humans and rodents. Data on blood INSL3 levels in normal and abnormal female domestic species are still limited and require further investigation.

Bisphenol A decreases expression of Insulin-like factor 3 and induces histopathological changes in the Testes of Rats

Bisphenol A (BPA) is a chemical agent known to have detrimental reproductive and developmental effects. The tissue-specific impacts of BPA exposures and target tissues sensitiveness to BPA are still unclear. The aim of this study was to determine the short- and long-term dose-dependent toxic effects of BPA on rat testes. Forty-eight Wistar albino male rats were divided into four groups each containing 12 rats. To induce toxicity, BPA was administered orally at three different dosages (50, 100, and 200 mg/kg) for 14 and 28 days, respectively. Testis tissues were examined using light and electron microscopy, immunohistochemistry, and biochemical methods. Serum testosterone (T) and luteinizing hormone (LH) levels were measured. Additionally, insulin-like factor 3 (INSL3) as a marker of Leydig cell function was evaluated immunohistochemically. Groups administered high doses of BPA showed severe degenerations such as testicular atrophy, spermatogenic arrest, and interstitial edema in testis. Also, a significant decrease in INSL3 immunoreactivity and serum LH and T levels was found. The results indicated that both increased exposure time and dosage of BPA caused more serious detrimental effects on testes in the rat. Decreased INSL3 and T levels was evidence of Leydig cell function impairment due to BPA.

Age-related changes in human Leydig cell status

STUDY QUESTION

What are the consequences of ageing on human Leydig cell number and hormonal function?

SUMMARY ANSWER

Leydig cell number significantly decreases in parallel with INSL3 expression and Sertoli cell number in aged men, yet the in vitro Leydig cell androgenic potential does not appear to be compromised by advancing age.

WHAT IS KNOWN ALREADY

There is extensive evidence that ageing is accompanied by decline in serum testosterone levels, a general involution of testis morphology and reduced spermatogenic function. A few studies have previously addressed single features of the human aged testis phenotype one at a time, but mostly in tissue from patients with prostate cancer.

STUDY DESIGN, SIZE, DURATION

This comprehensive study examined testis morphology, Leydig cell and Sertoli cell number, steroidogenic enzyme expression, INSL3 expression and androgen secretion by testicular fragments in vitro. The majority of these endpoints were concomitantly evaluated in the same individuals that all displayed complete spermatogenesis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testis biopsies were obtained from 15 heart beating organ donors (age range: 19-85 years) and 24 patients (age range: 19-45 years) with complete spermatogenesis. Leydig cells and Sertoli cells were counted following identification by immunohistochemical staining of specific cell markers. Gene expression analysis of INSL3 and steroidogenic enzymes was carried out by qRT-PCR. Secretion of 17-OH-progesterone, dehydroepiandrosterone, androstenedione and testosterone by in vitro cultured testis fragments was measured by LC-MS/MS. All endpoints were analysed in relation to age.

MAIN RESULTS AND THE ROLE OF CHANCE

Increasing age was negatively associated with Leydig cell number (R = -0.49; P < 0.01) and concomitantly with the Sertoli cell population size (R= -0.55; P < 0.001). A positive correlation (R = 0.57; P < 0.001) between Sertoli cell and Leydig cell numbers was detected at all ages, indicating that somatic cell attrition is a relevant cellular manifestation of human testis status during ageing. INSL3 mRNA expression (R= -0.52; P < 0.05) changed in parallel with Leydig cell number and age. Importantly, steroidogenic capacity of Leydig cells in cultured testis tissue fragments from young and old donors did not differ. Consistently, age did not influence the mRNA expression of steroidogenic enzymes. The described changes in Leydig cell phenotype with ageing are strengthened by the fact that the different age-related effects were mostly evaluated in tissue from the same men.

LIMITATIONS, REASONS FOR CAUTION

In vitro androgen production analysis could not be correlated with in vivo hormone values of the organ donors. In addition, the number of samples was relatively small and there was scarce information about the concomitant presence of potential confounding variables.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides a novel insight into the effects of ageing on human Leydig cell status. The correlation between Leydig cell number and Sertoli cell number at any age implies a connection between these two cell types, which may be of particular relevance in understanding male reproductive disorders in the elderly. However aged Leydig cells do not lose their in vitro ability to produce androgens. Our data have implications in the understanding of the physiological role and regulation of intratesticular sex steroid levels during the complex process of ageing in humans.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from Prin 2010 and 2017. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Heat stress response of somatic cells in the testis

The testis is a temperature-sensitive organ that needs to be maintained 2-7 °C below core body temperature to ensure the production of normal sperm. Failure to maintain testicular temperature in mammals impairs spermatogenesis and leads to low sperm counts, poor sperm motility and abnormal sperm morphology in the ejaculate. This review discusses the recent knowledge on the response of testicular somatic cells to heat stress and, specifically, regarding the relevant contributions of heat, germ cell depletion and inflammatory reactions on the functions of Sertoli and Leydig cells. It also outlines mechanisms of testicular thermoregulation, as well as the thermogenic factors that impact testicular function.

The Production of Testosterone and Gene Expression in Neonatal Testes of Rats Exposed to Diisoheptyl Phthalate During Pregnancy is Inhibited

Background: Diisoheptyl phthalate (DIHP) is a phthalate plasticizer, which is a branched phthalate. Here, we reported the effects of gestational exposure to DIHP on testis development in male rats. Methods: Pregnant Sprague-Dawley rats were orally fed with vehicle (corn oil, control) or DIHP (10, 100, 500, and 1,000 mg/kg) from gestational day (GD) 12-21. At GD21, serum testosterone levels, the number and distribution of fetal Leydig cells, and testicular mRNA and protein levels, the incidence of multinucleated gonocytes, and focal testicular hypoplasia in the neonatal testis were measured. Results: DIHP increased the fetal Leydig cell cluster size and decreased the fetal Leydig cell size with LOAEL of 10 mg/kg. DIHP did not affect the fetal Leydig cell number. DIHP significantly lowered serum testosterone levels, down-regulated the expression of steroidogenesis-related genes (Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1, and Hsd17b3) and testis descent-related gene (Insl3) as well as protein levels of cholesterol side-chain cleavage enzyme (CYP11A1) and insulin-like 3 (INSL3). DIHP dose-dependently increased the percentage of multinucleated gonocytes with the low observed adverse-effect level (LOAEL) of 100 mg/kg. DIHP induced focal testicular hypoplasia. Conclusion: Gestational exposure to DIHP causes testis dysgenesis in rats.

Male seminal parameters are not associated with Leydig cell functional capacity in men

BACKGROUND

Insulin-like peptide 3 (INSL3) is a constitutive, secreted peptide produced in the male uniquely by the Leydig cells of the testes. It is a biomarker for Leydig cell functional capacity, which is a measure of the numbers and differentiation status of these steroidogenic cells and lacks the biological and technical variance of the steroid testosterone. This retrospective study was carried out to examine the relationship between seminal parameters and the Leydig cell compartment, and secondarily to assess other factors responsible for determining Leydig cell functional capacity.

METHODS

INSL3 was assessed together with seminal, anthropometric, and hormonal parameters in a Swedish cohort of 18-year-old men, representing the average population, and in a smaller, more heterogeneous cohort of men visiting an Australian infertility clinic.

RESULTS AND DISCUSSION

Average INSL3 concentration at 18 years is greater than that reported at younger or older ages and indicated a large 10-fold variation. In neither cohort was there a relationship between INSL3 concentration and any semen parameter. For the larger, more uniform Swedish cohort of young men, there was a significant negative relationship between INSL3 and BMI, supporting the idea that adult Leydig cell functional capacity may be established during puberty. In both cohorts, there was a significant relationship between INSL3 and FSH, but not LH concentration. No relationship was found between INSL3 and androgen receptor trinucleotide repeat polymorphisms, reinforcing the notion that Leydig cell functional capacity is unlikely to be determined by androgen influence alone. Nor did INSL3 correlate with the T/LH ratio, an alternative measure of Leydig cell functional capacity, supporting the view that these are independent measures of Leydig cell function.

Exposure to di-n-octyl phthalate during puberty induces hypergonadotropic hypogonadism caused by Leydig cell hyperplasia but reduced steroidogenic function in male rats

Humans are exposed to phthalates ubiquitously, which may threaten health. However, whether di-n-octyl phthalate can prevent pubertal sexual maturity is still elusive. In this study, male Sprague Dawley rats (age 35 days) were treated daily by gavage with 0, 10, 100, and 1000 mg/kg body weight of di-n-octyl phthalate from day 35 to day 49 after birth. Di-n-octyl phthalate significantly reduced serum testosterone levels at doses of 100 and 1000 mg/kg, but increased serum luteinizing hormone levels of 1000 mg/kg and decreased testosterone/luteinizing hormone ratio at ≥10 mg/kg, without affecting serum follicle-stimulating hormone levels. Di-n-octyl phthalate significantly induced Leydig cell hyperplasia (increased number of CYP11A1-positive Leydig cells) at 100 and 1000 mg/kg. Di-n-octyl phthalate down-regulates the gene expression of Cyp11a1, Hsd3b1 and Insl3 in individual Leydig cells. Di-n-octyl phthalate can also reduce the number of sperm in the epididymis. Di-n-octyl phthalate increased phosphorylated AKT1/AKT2 without affecting their total proteins, but increased the total protein and phosphorylated protein of ERK1/2 and GSK-3β. Primary immature Leydig cells isolated from 35-day-old rats were treated with 0-50 μM di-n-octyl phthalate for 3 h. This phthalate inhibited androgen production under basal, LH-stimulated, and cAMP-stimulated conditions by 5 and 50 μM in vitro via down-regulating Cyp11a1 expression but up-regulating Srd5a1 expression in vitro. In conclusion, di-n-octyl phthalate induces hypergonadotropic hypogonadism caused by Leydig cell hyperplasia but reduced steroidogenic function and prevents sperm production.

Physiology and evolution of the INSL3/RXFP2 hormone/receptor system in higher vertebrates

Although the insulin-like peptide hormone INSL3 and its cognate receptor RXFP2 (relaxin-family peptide receptor 2) have existed throughout chordate evolution, their physiological diversification appears to be linked closely with mammalian emergence and radiation. In contrast, they have been lost in birds and reptiles. Both hormone and receptor are expressed from autosomal genes which have maintained their synteny across vertebrate evolution. Whereas the INSL3 gene comprises only two exons closely linked to the JAK3 gene, RXFP2 is normally encoded by 18 exons. Both genes, however, are subject to alternative splicing to yield a variety of possibly inactive or antagonistic molecules. In mammals, the INSL3-RXFP2 dyad has maintained a probably primitive association with gametogenesis, seen also in fish, whereby INSL3 promotes the survival, growth and differentiation of male germ cells in the testis and follicle development in the ovary. In addition, however, the INSL3/RXFP2 system has adopted a typical 'neohormone' profile, essential for the promotion of internal fertilisation and viviparity; fetal INSL3 is essential for the first phase of testicular descent into a scrotum, and also appears to be associated with male phenotype, in particular horn and skeletal growth. Circulating INSL3 is produced exclusively by the mature testicular Leydig cells in male mammals and acts as a potent biomarker for testis development during fetal and pubertal development as well as in ageing. As such it can be used also to monitor seasonally breeding animals as well as to investigate environmental or lifestyle conditions affecting development. Nevertheless, most information about INSL3 and RXFP2 comes from a very limited selection of species; it will be especially useful to gain further information from a more diverse range of animals, especially those whose evolution has led them to express unusual reproductive phenotypes.

Diverse functions of insulin-like 3 peptide

Insulin-like 3 peptide (INSL3) is a member of the insulin-like peptide superfamily and is the only known physiological ligand of relaxin family peptide receptor 2 (RXFP2), a G protein-coupled receptor (GPCR). In mammals, INSL3 is primarily produced both in testicular Leydig cells and in ovarian theca cells, but circulating levels of the hormone are much higher in males than in females. The INSL3/RXFP2 system has an essential role in the development of the gubernaculum for the initial transabdominal descent of the testis and in maintaining proper reproductive health in men. Although its function in female physiology has been less well-characterized, it was reported that INSL3 deletion affects antral follicle development during the follicular phase of the menstrual cycle and uterus function. Since the discovery of its role in the reproductive system, the study of INSL3/RXFP2 has expanded to others organs, such as skeletal muscle, bone, kidney, thyroid, brain, and eye. This review aims to summarize the various advances in understanding the physiological function of this ligand-receptor pair since its first discovery and elucidate its future therapeutic potential in the management of various diseases.

Expression of RXFP2 receptor on human spermatozoa and the anti-apoptotic and antioxidant effects of insulin-like factor 3

Insulin-like factor 3 (INSL3) has an important role in the human reproductive system; however, its detailed function is still mysterious. We aimed to investigate the possibility of expression of RXFP2 receptor on human spermatozoa and to determine the anti-apoptotic and antioxidant mechanism derived the binding of INSL3 and RXFP2. In this experimental study, the expression/location of the RXFP2 receptor was determined on the spermatozoa of fertile and infertile men. Twenty samples from 20 fertile men were collected and divided into 6 parts (control group, and five groups treated with INSL3 10, 100, 250, 500, 1,000 ng/ml). DNA damage, active caspase, reactive oxygen species (ROS) and sperm parameters were evaluated by TUNEL, flow cytometry, optical microscope and computer-assisted sperm analysis. The expression of RXFP2 was confirmed by Western blot. Immunocytochemistry illustrated that this receptor is expressed in the posterior half of the spermatozoa's head. The INSL3 at concentrations of 500 and 1,000 ng/ml reduced the active caspase and mitochondrial ROS, and also reduced DNA fragmentation at 1,000 ng/ml. Besides, INSL3 500 and 1,000 ng/ml significantly increased the sperm motility. This study confirmed the presence of RXFP2 receptor in fertile and infertile men's spermatozoa, indicating the highly dose-dependent efficacy of the INSL3, which may have promising impacts on the in-vitro fertilisation outcomes.

Effects of in utero exposure to diisodecyl phthalate on fetal testicular cells in rats

Diisodecyl phthalate (DIDP) is one of synthetic phthalate plasticizers. It is widely used in plastic products and is a potential endocrine disruptor. However, the effects of DIDP on fetal testicular cell development remain unclear. The objective of the present study was to determine the effects of DIDP on fetal testis development in rats after in utero exposure. Sprague Dawley dams were randomly divided into 5 groups and were daily gavaged with DIDP (0, 10, 100, 500, and 1000 mg/kg body weight) from gestational day 14-21. Serum testosterone levels, fetal Leydig cell number and distribution, testicular gene and protein expression in male pups were examined. DIDP decreased serum testosterone levels at 1000 mg/kg (1.37 ± 0.40 ng/mL, mean ± SE) when compared to the control level (3.14 ± 0.60 ng/mL). DIDP did not affect numbers of Leydig and Sertoli cells. DIDP significantly induced abnormal aggregation of fetal Leydig cells and increased the incidence of multinucleated gonocytes at 1000 mg/kg. Furthermore, DIDP down-regulated expression of Star, Cyp11a1, Hsd17b3, and Insl3 in fetal Leydig cells at 1000 mg/kg and Sox9 in Sertoli cells at 1000 mg/kg. In conclusion, the current study indicates that in utero exposure to high-dose DIDP disrupts the development of fetal testicular cells, thus affecting the male reproductive system.

Prepubertal nutrition alters Leydig cell functional capacity and timing of puberty

Leydig cell functional capacity reflects the numbers and differentiation status of the steroidogenic Leydig cells in the testes and becomes more or less fixed in early adulthood with the final establishment of the hypothalamo-pituitary-gonadal (HPG) axis after puberty. Factors influencing Leydig cell functional capacity and its role in puberty are poorly understood. Using a bovine model of dairy bulls fed four different nutritional regimes from 1 month to 12 months, and applying circulating Insulin-like peptide 3 (INSL3) as an accurate biomarker of Leydig cell functional capacity, showed that a high plane of nutrition in the first 6 months of life, but not later, significantly increased INSL3 in young adulthood. Moreover, INSL3 concentration at 4 months indicated a marked differential in early feeding regime and correlated well (negatively) with the timing of puberty, as reflected by the age in days for the first production of an ejaculate with >50 million sperm and >10% forward motility, as well as with testis size at 18 months. Reversing the diet at 6 months was unable to rectify the trend in either parameter, unlike for other parameters such as testosterone, body weight, and scrotal circumference. This study has shown that early prepubertal nutrition is a key factor in the development of Leydig cell functional capacity in early adulthood and appears to be a key driver in the dynamic progression of puberty.

Fibroblast growth factor homologous factor 1 stimulates Leydig cell regeneration from stem cells in male rats

Fibroblast growth factor homologous factor 1 (FHF1) is an intracellular protein that does not bind to cell surface fibroblast growth factor receptor. Here, we report that FHF1 is abundantly present in Leydig cells with up‐regulation during its development. Adult male Sprague Dawley rats were intraperitoneally injected with 75 mg/kg ethane dimethane sulphonate (EDS) to ablate Leydig cells to initiate their regeneration. Then, rats daily received intratesticular injection of FHF1 (0, 10 and 100 ng/testis) from post‐EDS day 14 for 14 days. FHF1 increased serum testosterone levels without affecting the levels of luteinizing hormone and follicle‐stimulating hormone. FHF1 increased the cell number staining with HSD11B1, a biomarker for Leydig cells at the advanced stage, without affecting the cell number staining with CYP11A1, a biomarker for all Leydig cells. FHF1 did not affect PCNA‐labelling index in Leydig cells. FHF1 increased Leydig cell mRNA (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Insl3, Nr5a1 and Hsd11b1) and their protein levels in vivo. FHF1 increased preadipocyte biomarker Dlk1 mRNA level and decreased fully differentiated adipocyte biomarker (Fabp4 and Lpl) mRNA and their protein levels. In conclusion, FHF1 promotes Leydig cell regeneration from stem cells while inhibiting the differentiation of preadipocyte/stem cells into adipocytes in EDS‐treated testis.

The structure-activity relationship (SAR) for phthalate-mediated developmental and reproductive toxicity in males

Testicular dysgenesis syndrome includes the hypospadias, cryptorchidism and abnormal fetal testis in male neonate. This is possibly caused by the environmental phthalates, which down-regulate the expression of androgen synthetic genes and Insl3 or directly inhibits steroidogenic enzymes. There are distinct structure-activity relationships (SARs) for phthalate-mediated developmental and reproductive toxicity. Here, we review the SAR for phthalate-mediated testicular dysgenesis syndrome. Of phthalates of straight side chains, C5-C6 ones are the most potent, C4 or C7 are moderate, C3 is weakest, and C1-2 or C8-13 are ineffective. The branching and unsaturation of side chains increases the toxicity. The cycling of side chains does not increase the toxicity.

Age related and seasonal changes of plasma concentrations of insulin-like peptide 3 and testosterone from birth to early-puberty in Thoroughbred male horses

The peripheral blood concentrations of insulin-like peptide 3 (INSL3) have been detected in many mammalian species, but the level of INSL3 in horse remains unknown. The objectives were to develop a time-resolved fluorescence immunoassay (TRFIA) to detect INSL3 concentrations from horse blood as well as to determine the age-related and seasonal changes of plasma concentrations of INSL3 and testosterone from birth to early-puberty in Thoroughbred male horse (n = 11). Monthly blood sample and measurement of body weight, height, chest and cannon bone size were done from birth until 16 mo. The TRFIA and EIA were used to measure plasma concentrations of INSL3 and testosterone, respectively. An increase in mean body weight, height, chest and cannon bone size was observed throughout the study. The monthly blood sampling revealed an increase in mean plasma INSL3 concentrations up to 2 mo, followed by a decreasing and increasing pattern until the end of experiment at 16 mo. A high testosterone level was detected at birth followed by a sharp decrease to basal level within 1 mo, maintained low level up to10 mo before a gradual rise until 16 mo. In case of seasonality, there was no difference in mean plasma INSL3 concentrations between breeding (March to September) and non-breeding (October to February) seasons, whereas a higher (P < 0.001) mean plasma testosterone concentrations in the second breeding season compared to non-breeding season was observed. In age categorized group, an increase (P < 0.01) in mean plasma INSL3 concentrations was noticed at pre-puberty (1-12 mo) and early-puberty (13-16 mo) compared to birth, but a lower (P < 0.001) mean plasma testosterone concentrations was observed at pre-puberty compared to birth and early-puberty. In conclusion, a TRFIA was developed to measure INSL3 levels in horse. An increase in plasma concentrations of INSL3 and testosterone were observed with the advancement of age, whereas for testosterone a very lower level was detected at the non-breeding season than in the second breeding season after birth in Thoroughbred male horse. The INSL3 secretions seemed independent of seasonal influence, at least before puberty.

In utero exposure to bisphenol A disrupts fetal testis development in rats

Bisphenol A (BPA) is widely used in consumer products and is a potential endocrine disruptor linked with abnormal development of male reproductive tract. However, its action and its effects on the pathways in the development of male gonad are still unclear. Here we report that effects of BPA exposure during gestation on male gonad development. Sprague-Dawley rats were gavaged daily with BPA (0, 4, 40, and 400 mg/kg body weight) from gestational day 12 to day 21. BPA dose-dependently decreased serum testosterone levels (0.45 ± 0.08 ng/ml and 0.32 ± 0.08 ng/ml for 40 and 400 mg/kg BPA, respectively) versus the control level (1.11 ± 0.22 ng/ml, Mean ± SE). BPA lowered Leydig cell Insl3 and Hsd17b3 mRNA and their protein levels at doses of 40 and 400 mg/kg. BPA also lowered Leydig cell (Lhcgr, Cyp11a1, and Cyp17a1) and Sertoli cell (Amh) mRNA and their protein levels at 400 mg/kg. BPA decreased fetal Leydig cell number via inhibiting their proliferation, but it did not affect fetal Sertoli cell number. In conclusion, the current study shows that in utero exposure to BPA inhibits fetal Leydig and Sertoli cell differentiation, possibly disrupting the development of male reproductive tract.

In utero exposure to triphenyltin disrupts rat fetal testis development

Triphenyltin is an organotin that is widely used as an anti-fouling agent and may have endocrine-disrupting effects. The objective of the current study was to investigate effects of triphenyltin on the development of rat fetal testis. Female pregnant Sprague Dawley dams were gavaged daily with triphenyltin (0, 0.5, 1, and 2 mg/kg body weight/day) from gestational day 12 to day 21. Triphenyltin dose-dependently decreased serum testosterone levels (0.971 ± 0.072 and 0.972 ± 0.231 ng/ml at 1 and 2 mg/kg, respectively) from control level (2.099 ± 0.351 ng/ml). Triphenyltin at 1 and 2 mg/kg doses also induced fetal Leydig cell aggregation, decreased fetal Leydig cell size and cytoplasmic size. Triphenyltin decreased the expression levels of Lhcgr, Scarb1, Star, Cyp11a1, Cyp17a1, Insl3, Fshr, Pdgfa, and Sox9 by 0.5 mg/kg dose and above. However, triphenyltin did not affect Leydig and Sertoli cell numbers. In conclusion, the current study indicated that in utero exposure of triphenyltin disrupted fetal Leydig and Sertoli cell development.

Relationships of plasma insulin-like peptide 3, testosterone, inhibin, and insulin-like growth factor-I concentrations with scrotal circumference and testicular weight in Japanese Black beef bull calves

This study was conducted to clarify the relationships of plasma concentrations of insulin-like peptide 3 (INSL3), testosterone, inhibin, and insulin-like growth factor-I (IGF-I) with scrotal circumference and testicular weight in Japanese Black beef bull calves (n = 20), from birth to pre-puberty. Monthly blood sampling (0 to 7 months) and scrotal circumference measurements (0 to 7 months) were performed. Testicular weight was recorded immediately after castration at 7 months. Plasma INSL3, testosterone, inhibin, and IGF-I concentrations were measured either by enzyme immunoassay or time-resolved fluorescence immunoassay. The correlation coefficients of these hormonal concentrations with scrotal circumference were significant (P < 0.0001) and it was higher for INSL3 (r = 0.647) than for testosterone (r = 0.597), IGF-I (r = 0.400), and inhibin (r = –0.453). Calves with heavier testes (> 60 g) at castration (7 months) had higher (P < 0.05) plasma INSL3 (from 3 to 7 months) and inhibin (from 1 to 4 months) concentrations than those with lighter testes (< 60 g). The calves with heavier testes at castration had larger (P < 0.05) scrotal circumference than those with lighter testes from 3 to 7 months. In conclusion, blood INSL3 concentrations may be the best functional indicator among the hormones analyzed for determining total testicular volume during pre-puberty in bull calves. In addition, inhibin and INSL3 concentrations in early calfhood may be functional predictors for testicular weight at pre-puberty.

Gestational exposure to tetrabutyltin blocks rat fetal Leydig cell development

Tetrabutyltin is a stable organotin and may exhibit endocrine disrupting properties. Herein, we investigated effects of tetrabutyltin on the development of rat fetal Leydig cells, which support differentiation of the male reproductive tract in late gestation. Female pregnant Sprague Dawley rats were gavaged with tetrabutyltin (0, 100, 200, and 500 mg/kg) from gestational day (GD) 12 to GD 21. Tetrabutyltin dose-dependently decreased testicular testosterone levels (0.756 ± 0.208 and 0.813 ± 0.277 ng/testis at the 200 and 500 mg/kg doses, respectively) compared to control (1.692 ± 0.218 ng/testis) at GD 21. Furthermore, tetrabutyltin induced fetal Leydig cell aggregation, decreased fetal Leydig cell size and cytoplasmic size at the ≥100 mg/kg doses, and downregulated the expression levels of Scarb1, Cyp17a1, and Insl3 at doses ≥100 mg/kg and Star expression at 200 mg/kg. Taking together, the present results indicated that prenatal exposure of male rats to tetrabutyltin affected fetal Leydig cell development.

Expression and localization of relaxin family peptide receptor 4 in human spermatozoa and impact of insulin-like peptide 5 on sperm functions

Insulin-like peptide 5 (INSL5) is a member of the insulin superfamily peptide that interacts with the relaxin family peptide receptor 4 (RXFP4). Numerous recent studies have focused on the functional effects of INSL5 on fat and glucose metabolism. Although there is no evidence that the human sperm may be a candidate target of INSL5, it has been detected in mice testis and sperm. Therefore, the present study sought to analyze the localization and expression of RXFP4 on human sperm and determine the efficiency of INSL5 in human sperm. Normal semen samples were incubated in different doses and exposure time periods of INSL5. We analyzed sperm motility by computer-assisted sperm analysis (CASA) and ROS levels by flow cytometry using the MitoSOX™ Red probe. Localization and expression of RXFP4 were assayed by immunofluorescence and RT-PCR, respectively. The results confirmed the presence of RXFP4 in human spermatozoa, which localized in the neck and midpiece of sperm. Nested PCR showed the expression of RXFP4 in human sperm. INSL5 could attenuate generation of mitochondrial ROS at the 1, 10, 30, and 100nmol/L doses. This result was particularly noted in the 30nmol/L treated samples after 4h incubation. Total motility of sperm was significantly preserved in the 100nmol/L after 2h and in 30nmol/L after 4h incubation period. This study, for the first time, clarified the expression and localization of RXFP4 on human sperm and revealed the role of INSL5 in sperm motility and mitochondrial ROS generation in a dose-dependent manner.

Probing GATA factor function in mouse Leydig cells via testicular injection of adenoviral vectors

Testicular Leydig cells produce androgens essential for proper male reproductive development and fertility. Here, we describe a new Leydig cell ablation model based on Cre/Lox recombination of mouse Gata4 and Gata6, two genes implicated in the transcriptional regulation of steroidogenesis. The testicular interstitium of adult Gata4flox/flox ; Gata6flox/flox mice was injected with adenoviral vectors encoding Cre + GFP (Ad-Cre-IRES-GFP) or GFP alone (Ad-GFP). The vectors efficiently and selectively transduced Leydig cells, as evidenced by GFP reporter expression. Three days after Ad-Cre-IRES-GFP injection, expression of androgen biosynthetic genes (Hsd3b1, Cyp17a1 and Hsd17b3) was reduced, whereas expression of another Leydig cell marker, Insl3, was unchanged. Six days after Ad-Cre-IRES-GFP treatment, the testicular interstitium was devoid of Leydig cells, and there was a concomitant loss of all Leydig cell markers. Chromatin condensation, nuclear fragmentation, mitochondrial swelling, and other ultrastructural changes were evident in the degenerating Leydig cells. Liquid chromatography-tandem mass spectrometry demonstrated reduced levels of androstenedione and testosterone in testes from mice injected with Ad-Cre-IRES-GFP. Late effects of treatment included testicular atrophy, infertility and the accumulation of lymphoid cells in the testicular interstitium. We conclude that adenoviral-mediated gene delivery is an expeditious way to probe Leydig cell function in vivo Our findings reinforce the notion that GATA factors are key regulators of steroidogenesis and testicular somatic cell survival.Free Finnish abstract: A Finnish translation of this abstract is freely available at http://www.reproduction-online.org/content/154/4/455/suppl/DC2.

Hypoxia reduces testosterone synthesis in mouse Leydig cells by inhibiting NRF1-activated StAR expression

Male fertility disorders play a key role in half of all infertility cases. Reduction in testosterone induced by hypoxia might cause diseases in reproductive system and other organs. Hypoxic exposure caused a significant decrease of NRF1. Software analysis reported that the promoter region of steroidogenic acute regulatory protein (StAR) contained NRF1 binding sites, indicating NRF1 promoted testicular steroidogenesis. The purpose of this study is to determine NRF1 is involved in testosterone synthesis; and under hypoxia, the decrease of testosterone synthesis is caused by lower expression of NRF1. We designed both in vivo and in vitro experiments. Under hypoxia, the expressions of NRF1 in Leydig cells and testosterone level were significantly decreased both in vivo and in vitro. Overexpression and interference NRF1 could induced StAR and testosterone increased and decreased respectively. ChIP results confirmed the binding of NRF1 to StAR promoter region. In conclusion, decline of NRF1 expression downregulated the level of StAR, which ultimately resulted in a reduction in testosterone synthesis.

Neohormones in milk

Neohormone systems evolved specifically to regulate those mammalian traits, such as internal fertilization, pregnancy and lactation, which have proved to be central to the success, environmental independence, and adaptability of mammals as a vertebrate group. Neohormones such as oxytocin or relaxin are not only involved in the regulation of mammary gland development and function, but are also significant components of milk itself. Particularly for the latter hormone, it has been shown for the pig that relaxin in the first milk is taken up by the gastrointestinal tract of the offspring, enters the neonatal circulation and can have specific physiological and epigenetic effects on target organs such as the female reproductive system. Nevertheless, there are large gaps in our knowledge and understanding of such lactocrine systems especially in regard to other neohormones, species, and neonatal organ systems.

Relaxin-like peptides in male reproduction - a human perspective

The relaxin family of peptide hormones and their cognate GPCRs are becoming physiologically well-characterized in the cardiovascular system and particularly in female reproductive processes. Much less is known about the physiology and pharmacology of these peptides in male reproduction, particularly as regards humans. H2-relaxin is involved in prostate function and growth, while insulin-like peptide 3 (INSL3) is a major product of the testicular Leydig cells and, in the adult, appears to modulate steroidogenesis and germ cell survival. In the fetus, INSL3 is a key hormone expressed shortly after sex determination and is responsible for the first transabdominal phase of testicular descent. Importantly, INSL3 is becoming a very useful constitutive biomarker reflecting both fetal and post-natal development. Nothing is known about roles for INSL4 in male reproduction and only very little about relaxin-3, which is mostly considered as a brain peptide, or INSL5. The former is expressed at very low levels in the testes, but has no known physiology there, whereas the INSL5 knockout mouse does exhibit a testicular phenotype with mild effects on spermatogenesis, probably due to a disruption of glucose homeostasis. INSL6 is a major product of male germ cells, although it is relatively unexplored with regard to its physiology or pharmacology, except that in mice disruption of the INSL6 gene leads to a disruption of spermatogenesis. Clinically, relaxin analogues may be useful in the control of prostate cancer, and both relaxin and INSL3 have been considered as sperm adjuvants for in vitro fertilization.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Changes of plasma concentrations of insulin-like peptide 3 and testosterone, and their association with scrotal circumference during pubertal development in male goats

Insulin-like peptide 3 (INSL3) has been used as a testis-specific biomarker for puberty in several species, but the secretory profile of INSL3 during pubertal development in small ruminants is unknown. Here we sought to determine the age-related changes in the plasma concentrations of INSL3 and testosterone and their association with scrotal circumference during pubertal development in five male Shiba goats. Blood samples and scrotal circumference measurement were taken every 2 weeks from week 10 to week 52 of each goat's lifespan. Based on the changes in scrotal circumference, data were grouped into early pubertal (10-22 weeks), late pubertal (22-34 weeks) and post-pubertal (34-52 weeks) categories. The plasma concentrations of testosterone and luteinizing hormone (LH) were measured by enzyme-immunoassays (EIAs), and we used a time-resolved fluorescence immunoassay (TRFIA) to measure plasma INSL3. The biweekly sampling showed that the plasma INSL3 secretions maintained a moderate increase during and after puberty, whereas the plasma testosterone secretions fluctuated over the same period. The comparison of the three age categories revealed a significant increase (p < 0.01) in the mean plasma INSL3 concentrations during the late and post-pubertal periods compared to the early pubertal period. There was no difference in the mean plasma testosterone concentrations between the early and late pubertal periods, but a significant increase (p < 0.01) was observed during the post-pubertal period compared to early and late pubertal periods. The mean plasma LH concentrations increased significantly (p < 0.05) from the early pubertal to late pubertal and from the late pubertal to post-pubertal periods. A significant increase (p < 0.05) in the mean scrotal circumference from the early pubertal to late pubertal and from the late pubertal to post-pubertal periods was observed. The R² value of the best regression curves between scrotal circumference and INSL3 (0.513; p < 0.001) was higher than that between scrotal circumference and testosterone (0.162; p < 0.01) from 10 to 52 weeks of age. In conclusion, in male goats, plasma concentrations of INSL3 increased continuously during and after puberty, whereas testosterone secretions were fluctuated. The scrotal circumference was more highly correlated with the INSL3 concentrations than with testosterone, implying that INSL3 is superior as a biomarker of testicular total Leydig cell volume.

In utero methoxychlor exposure increases rat fetal Leydig cell number but inhibits its function

The objective of the present study is to determine whether in utero exposure to methoxychlor (MXC) affects rat fetal Leydig cell number, cell size, or functions. Pregnant Sprague Dawley dams were gavaged with corn oil (control, 0mg/kg/day MXC) or MXC at doses of 10, 50, or 100mg/kg/day from gestational day (GD) 12 to 21. The results show that MXC increased fetal Leydig cell numbers dose-dependently from 95±8×10³ cells/testis (control, mean±SEM) to 101±6, 148±22, and 168±21×10³ cells/testis, at the doses of 10, 50, and 100mg/kg, respectively. The increase of Leydig cell number by MXC was contributed by the increase of single cell population of Leydig cells, which increased from 21±2% of the control to 31±4%, 39±3%, or 40±4% at the doses of 10, 50 or 100mg/kg, respectively. Quantitative PCR results show that MXC increased Lhcgr expression at dose of 10mg/kg and Scarb1 and Cyp11a1 mRNA levels at doses of 50 and 100mg/kg. Immunohistochemical staining demonstrated the increase of CYP11A1 protein level from the dose of 10mg/kg. However, at the highest dose (100mg/kg) MXC reduced the testicular testosterone level and MXC (1μM) in vitro treatment also inhibited androgen production from isolated fetal Leydig cells. In conclusion, our findings indicate that at low dose MXC may increase fetal Leydig cell numbers and the expressions of some steroidogenic enzymes, but at high dose it reduces the testicular testosterone level leading to reproductive tract malformations in the male offspring.

Functional insulin-like factor 3 (INSL3) hormone-receptor system in the testes and spermatozoa of domestic ruminants and its potential as a predictor of sire fertility

Insulin-like factor 3 (INSL3) is essential for fetal testis descent, and has been implicated in the testicular and sperm functions in adult males; however, similar functions in domestic ruminants remain largely unknown. This study investigated the functional INSL3 hormone-receptor system in adult ruminant testes and spermatozoa, and explored its potential to diagnose the fertility of sires. Testes and spermatozoa were obtained from fertile bulls, rams and he-goats, whereas subfertile testes and spermatozoa were obtained only from bulls. As expected, INSL3 was visualized in Leydig cells, while we clearly demonstrated that the functional receptor, relaxin family peptide receptor 2 (RXFP2), enabling INSL3 to bind was identified in testicular germ cells and in the sperm equatorial segment of bulls, rams and he-goats. In comparison to fertile bulls, the percentage of INSL3- and RXFP2-expressing cells and their expression levels per cell were significantly reduced in the testes of subfertile bulls. In addition, the population of INSL3-binding spermatozoa was also significantly reduced in the semen of subfertile bulls. These results provide evidence for a functional INSL3 hormone-receptor system operating in ruminant testes and spermatozoa, and its potential to predict subfertility in sires.

The Male Fetal Biomarker INSL3 Reveals Substantial Hormone Exchange between Fetuses in Early Pig Gestation

The peptide hormone INSL3 is uniquely produced by the fetal testis to promote the transabdominal phase of testicular descent. Because it is fetal sex specific, and is present in only very low amounts in the maternal circulation, INSL3 acts as an ideal biomarker with which to monitor the movement of fetal hormones within the pregnant uterus of a polytocous species, the pig. INSL3 production by the fetal testis begins at around GD30. At GD45 of the ca. 114 day gestation, a time at which testicular descent is promoted, INSL3 evidently moves from male to female allantoic compartments, presumably impacting also on the female fetal circulation. At later time-points (GD63, GD92) there is less inter-fetal transfer, although there still appears to be significant INSL3, presumably of male origin, in the plasma of female fetuses. This study thus provides evidence for substantial transfer of a peptide hormone between fetuses, and probably also across the placenta, emphasizing the vulnerability of the fetus to extrinsic hormonal influences within the uterus.

Effects of in Utero Exposure to Dicyclohexyl Phthalate on Rat Fetal Leydig Cells

Dicyclohexyl phthalate (DCHP) is one of the phthalate plasticizers. The objective of the present study was to investigate the effects of DCHP on fetal Leydig cell distribution and function as well as testis development. Female pregnant Sprague Dawley dams orally received vehicle (corn oil, control) or DCHP (10, 100, and 500 mg/kg/day) from gestational day (GD) 12 to GD 21. At GD 21.5, testicular testosterone production, fetal Leydig cell number and distribution, testicular gene and protein expression levels were examined. DCHP administration produced a dose-dependent increase of the incidence of multinucleated gonocytes at ≥100 mg/kg. DCHP dose-dependently increased abnormal fetal Leydig cell aggregation and decreased fetal Leydig cell size, cytoplasmic size, and nuclear size at ≥10 mg/kg. DCHP reduced the expression levels of steroidogenesis-related genes (including Star, Hsd3b1, and Hsd17b3) and testis-descent related gene Insl3 as well as protein levels of 3β-hydroxysteroid dehydrogenase 1 (HSD3B1) and insulin-like 3 (INSL3) at ≥10 mg/kg. DCHP significantly inhibited testicular testosterone levels at ≥100 mg/kg. The results indicate that in utero exposure to DCHP affects the expression levels of fetal Leydig cell steroidogenic genes and results in the occurrence of multinucleated gonocytes and Leydig cell aggregation.

Alterations of gene profiles in Leydig-cell-regenerating adult rat testis after ethane dimethane sulfonate-treatment

Only occupying about 1%–5% of total testicular cells, the adult Leydig cell (ALC) is a unique endocrine cell that produces androgens. Rat Leydig cells regenerate after these cells in the testis are eliminated with ethane dimethane sulfonate (EDS). In this study, we have characterized Leydig cell regeneration and messenger ribonucleic acids (mRNA) profiles of EDS treated rat testes. Serum testosterone, testicular gene profiling and some steroidogenesis-related proteins were analyzed at 7, 21, 35 and 90 days after EDS treatment. Testicular testosterone levels declined to undetectable levels until 7 days after treatment and then started to recover. Seven days after treatment, 81 mRNAs were down-regulated greater than or equal to two-fold, with 48 becoming undetectable. These genes increased their expression 21 days and completely returned to normal levels 90 days after treatment. The undetectable genes include steroidogenic pathway proteins: steroidogenic acute regulatory protein, Scarb1, Cyp11a1, Cyp17a1, Hsd3b1, Cyp1b1 and Cyp2a1. Seven days after treatment, there were 89 mRNAs up-regulated two-fold or more including Pkib. These up-regulated mRNAs returned to normal 90 days after treatment. Cyp2a1 did not start to recover until 35 days after treatment, indicating that this gene is only expressed in ALCs not in the precursor cells. Quantitative polymerase chain reaction, western blotting and semi-quantitative immunohistochemical staining using tissue array confirmed the changes of several randomly picked genes and their proteins.

Expression of insulin-like factor 3 hormone-receptor system in the reproductive organs of male goats

Relaxin-like factor (RLF), generally known as insulin-like factor 3 (INSL3), is essential for testis descent during fetal development. However, its role in adult males is not fully understood. We investigate the function of INSL3 in male Saanen goats by identifying cell types expressing its receptor, relaxin/insulin-like family peptide receptor (RXFP)2 and by characterizing the developmental expression pattern of INSL3 and RXFP2 and the binding of INSL3 to target cells in the male reproductive system. A highly specific RXFP2 antibody that co-localizes with an anti-FLAG antibody in HEK-293 cells recognizes RXFP2-transcript-expressing cells in the testis. INSL3 and RXFP2 mRNA expression is upregulated in the testis, starting from puberty. INSL3 mRNA and protein expression has been detected in Leydig cells, whereas RXFP2 mRNA and protein localize to Leydig cells, to meiotic and post-meiotic germ cells and to the epithelium and smooth muscle of the cauda epididymis and vas deferens. INSL3 binds to all of these tissues and cell types, with the exception of Leydig cells, in a hormone-specific and saturable manner. These results provide evidence for a functional intra- and extra-testicular INSL3 ligand-receptor system in adult male goats.

GATA4 is a key regulator of steroidogenesis and glycolysis in mouse Leydig cells

Transcription factor GATA4 is expressed in somatic cells of the mammalian testis. Gene targeting studies in mice have shown that GATA4 is essential for proper differentiation and function of Sertoli cells. The role of GATA4 in Leydig cell development, however, remains controversial, because targeted mutagenesis experiments in mice have not shown a consistent phenotype, possibly due to context-dependent effects or compensatory responses. We therefore undertook a reductionist approach to study the function of GATA4 in Leydig cells. Using microarray analysis and quantitative RT-PCR, we identified a set of genes that are down-regulated or up-regulated after small interfering RNA (siRNA)-mediated silencing of Gata4 in the murine Leydig tumor cell line mLTC-1. These same genes were dysregulated when primary cultures of Gata4(flox/flox) adult Leydig cells were subjected to adenovirus-mediated cre-lox recombination in vitro. Among the down-regulated genes were enzymes of the androgen biosynthetic pathway (Cyp11a1, Hsd3b1, Cyp17a1, and Srd5a). Silencing of Gata4 expression in mLTC-1 cells was accompanied by reduced production of sex steroid precursors, as documented by mass spectrometric analysis. Comprehensive metabolomic analysis of GATA4-deficient mLTC-1 cells showed alteration of other metabolic pathways, notably glycolysis. GATA4-depleted mLTC-1 cells had reduced expression of glycolytic genes (Hk1, Gpi1, Pfkp, and Pgam1), lower intracellular levels of ATP, and increased extracellular levels of glucose. Our findings suggest that GATA4 plays a pivotal role in Leydig cell function and provide novel insights into metabolic regulation in this cell type.

Novel markers of gonadectomy-induced adrenocortical neoplasia in the mouse and ferret

Gonadectomy (GDX) induces sex steroid-producing adrenocortical tumors in certain mouse strains and in the domestic ferret. Transcriptome analysis and DNA methylation mapping were used to identify novel genetic and epigenetic markers of GDX-induced adrenocortical neoplasia in female DBA/2J mice. Markers were validated using a combination of laser capture microdissection, quantitative RT-PCR, in situ hybridization, and immunohistochemistry. Microarray expression profiling of whole adrenal mRNA from ovariectomized vs. intact mice demonstrated selective upregulation of gonadal-like genes including Spinlw1 and Insl3 in GDX-induced adrenocortical tumors of the mouse. A complementary candidate gene approach identified Foxl2 as another gonadal-like marker expressed in GDX-induced neoplasms of the mouse and ferret. That both "male-specific" (Spinlw1) and "female-specific" (Foxl2) markers were identified is noteworthy and implies that the neoplasms exhibit mixed characteristics of male and female gonadal somatic cells. Genome-wide methylation analysis showed that two genes with hypomethylated promoters, Igfbp6 and Foxs1, are upregulated in GDX-induced adrenocortical neoplasms. These new genetic and epigenetic markers may prove useful for studies of steroidogenic cell development and for diagnostic testing.

Age related changes of cAMP and MAPK signaling in Leydig cells of Wistar rats

Here, we chronologically analyzed age-associated changes of cAMP- and MAPK-signaling in Leydig cells (LCs) in relation with decreased testosterone (T) production. In Wistar rats, decreased serum T observed in 12 to 24-month-old rats was not related to decreased serum LH concentration but to reduced luteinizing hormone receptor (Lhr/LHR) and time-coordinated reduction of steroidogenic gene expression (decreased Cyp11a1, Cyp17a1 in 12-month-old rats followed by decreased Star/StAR, Hsd3b/HSD3B, Hsd17b4, and increased Cyp19a1 later in life). The predecessors of age-related changes noted in LCs from 6 to 12-month-old rats were increased level of soluble adenylate cyclase (Adcy/AC) 10, increased JNK phosphorylation but suppressed P38 MAPK. At approximately the same time changed mRNA abundance for transcription factors important for steroidogenesis was detected (increased Nur77 and decreased Sf1, Dax1). Aging caused biphasic expression pattern of ERK1/2 and Nur77: increased in 12-month but decreased in LCs from 24-month-old rats. Further, decreased basal cAMP level observed from 12 to 24th month coincidence with increased expression of cAMP-specific phosphodiesterase (Pde)4a, Pde4b and regulatory subunit of protein kinase A (Prkar/PKAR). Exposing of senescent LCs to permeable cAMP-analog improved transcription of Sf1, Nur77, Star, Cyp11a1,Cyp17a1, but without effect on aging pattern of Dax1, Pde4a/b, Prkar2a, Lhr and MAPK genes. Collectively, results indicated that age-related LC dysfunction is accompanied with changes in MAPK and cAMP signaling and coordinated reduction in the expression of many of the genes that participate in T synthesis. The predecessors of aged-related changes are increased ratio of pJNK/JNK, AC10 and decreased P38 level in LCs from 6-month-old rats.

Cryptorchidism in the orl rat is associated with muscle patterning defects in the fetal gubernaculum and altered hormonal signaling

Cryptorchidism, or undescended testis, is a common male genital anomaly of unclear etiology. Hormonal stimulation of the developing fetal gubernaculum by testicular androgens and insulin-like 3 (INSL3) is required for testicular descent. In studies of the orl fetal rat, one of several reported strains with inherited cryptorchidism, we studied hormone levels, gene expression in intact and hormone-stimulated gubernaculum, and imaging of the developing cremaster muscle facilitated by a tissue clearing protocol to further characterize development of the orl gubernaculum. Abnormal localization of the inverted gubernaculum was visible soon after birth. In the orl fetus, testicular testosterone, gubernacular androgen-responsive transcript levels, and muscle-specific gene expression were reduced. However, the in vitro transcriptional response of the orl gubernaculum to androgen was largely comparable to wild type (wt). In contrast, increases in serum INSL3, gubernacular INSL3-responsive transcript levels, expression of the INSL3 receptor, Rxfp2, and the response of the orl gubernaculum to INSL3 in vitro all suggest enhanced activation of INSL3/RXFP2 signaling in the orl rat. However, DNA sequence analysis did not identify functional variants in orl Insl3. Finally, combined analysis of the present and previous studies of the orl transcriptome confirmed altered expression of muscle and cellular motility genes, and whole mount imaging revealed aberrant muscle pattern formation in the orl fetal gubernaculum. The nature and prevalence of developmental muscle defects in the orl gubernaculum are consistent with the cryptorchid phenotype in this strain. These data suggest impaired androgen and enhanced INSL3 signaling in the orl fetus accompanied by defective cremaster muscle development.