Steroidogenic activities in MA-10 Leydig cells are differentially altered by cAMP and Müllerian inhibiting substance

A 35-bp Conserved Region Is Crucial for Insl3 Promoter Activity in Mouse MA-10 Leydig Cells

The peptide hormone insulin-like 3 (INSL3) is produced almost exclusively by Leydig cells of the male gonad. INSL3 has several functions such as fetal testis descent and bone metabolism in adults. Insl3 gene expression in Leydig cells is not hormonally regulated but rather is constitutively expressed. The regulatory region of the Insl3 gene has been described in various species; moreover, functional studies have revealed that the Insl3 promoter is regulated by various transcription factors that include the nuclear receptors AR, NUR77, COUP-TFII, LRH1, and SF1, as well as the Krüppel-like factor KLF6. However, these transcription factors are also found in several tissues that do not express Insl3, indicating that other, yet unidentified factors, must be involved to drive Insl3 expression specifically in Leydig cells. Through a fine functional promoter analysis, we have identified a 35-bp region that is responsible for conferring 70% of the activity of the mouse Insl3 promoter in Leydig cells. All tri- and dinucleotide mutations introduced dramatically reduced Insl3 promoter activity, indicating that the entire 35-bp sequence is required. Nuclear proteins from MA-10 Leydig cells bound specifically to the 35-bp region. The 35-bp sequence contains GC- and GA-rich motifs as well as potential binding elements for members of the CREB, C/EBP, AP1, AP2, and NF-κB families. The Insl3 promoter was indeed activated 2-fold by NF-κB p50 but not by other transcription factors tested. These results help to further define the regulation of Insl3 gene transcription in Leydig cells.

Mechanism of Action of an Environmentally Relevant Organochlorine Mixture in Repressing Steroid Hormone Biosynthesis in Leydig Cells

Within Leydig cells, steroidogenesis is induced by the pituitary luteinizing hormone (LH). The binding of LH to its receptor increases cAMP production, which then activates the expression of genes involved in testosterone biosynthesis. One of these genes codes for the steroidogenic acute regulatory (STAR) protein. STAR is part of a complex that shuttles cholesterol, the precursor of all steroid hormones, through the mitochondrial membrane where steroidogenesis is initiated. Organochlorine chemicals (OCs) are environmental persistent organic pollutants that are found at high concentrations in Arctic areas. OCs are known to affect male reproductive health by decreasing semen quality in different species, including humans. We previously showed that an environmentally relevant mixture of OCs found in Northern Quebec disrupts steroidogenesis by decreasing STAR protein levels without affecting the transcription of the gene. We hypothesized that OCs might affect STAR protein stability. To test this, MA-10 Leydig cell lines were incubated for 6 h with vehicle or the OCs mixture in the presence or absence of 8Br-cAMP with or without MG132, an inhibitor of protein degradation. We found that MG132 prevented the OC-mediated decrease in STAR protein levels following 8Br-cAMP stimulation. However, progesterone production was still decreased by the OC mixture, even in the presence of MG132. This suggested that proteins involved in steroid hormone production in addition to STAR are also affected by the OC mixture. To identify these proteins, a whole cell approach was used and total proteins from MA-10 Leydig cells exposed to the OC mixture with or without stimulation with 8Br-cAMP were analyzed by 2D SDS-PAGE and LC-MS/MS. Bioinformatics analyses revealed that several proteins involved in numerous biological processes are affected by the OC mixture, including proteins involved in mitochondrial transport, lipid metabolism, and steroidogenesis.

The Nuclear Receptor COUP-TFII Regulates Amhr2 Gene Transcription via a GC-Rich Promoter Element in Mouse Leydig Cells

The nuclear receptor chicken ovalbumin upstream promoter–transcription factor type II (COUP-TFII)/NR2F2 is expressed in adult Leydig cells, and conditional deletion of the Coup-tfii/Nr2f2 gene impedes their differentiation. Steroid production is also reduced in COUP-TFII–depleted Leydig cells, supporting an additional role in steroidogenesis for this transcription factor. COUP-TFII action in Leydig cells remains to be fully characterized. In the present work, we report that COUP-TFII is an essential regulator of the gene encoding the anti-Müllerian hormone receptor type 2 (Amhr2), which participates in Leydig cell differentiation and steroidogenesis. We found that Amhr2 mRNA levels are reduced in COUP-TFII–depleted MA-10 Leydig cells. Consistent with this, COUP-TFII directly activates a −1486 bp fragment of the mouse Amhr2 promoter in transient transfection assays. The COUP-TFII responsive region was localized between −67 and −34 bp. Chromatin immunoprecipitation assay confirmed COUP-TFII recruitment to the proximal Amhr2 promoter whereas DNA precipitation assay revealed that COUP-TFII associates with the −67/−34 bp region in vitro. Even though the −67/−34 bp region contains an imperfect nuclear receptor element, COUP-TFII–mediated activation of the Amhr2 promoter requires a GC-rich sequence at −39 bp known to bind the specificity protein (SP)1 transcription factor. COUP-TFII transcriptionally cooperates with SP1 on the Amhr2 promoter. Mutations that altered the GCGGGGCGG sequence at −39 bp abolished COUP-TFII–mediated activation, COUP-TFII/SP1 cooperation, and reduced COUP-TFII binding to the proximal Amhr2 promoter. Our data provide a better understanding of the mechanism of COUP-TFII action in Leydig cells through the identification and regulation of the Amhr2 promoter as a novel target.

Functional Genetic Variation in the Anti-Müllerian Hormone Pathway in Women With Polycystic Ovary Syndrome

CONTEXT

Polycystic ovary syndrome (PCOS) is a highly heritable, common endocrine disorder characterized by hyperandrogenism, irregular menses, and polycystic ovaries. PCOS is often accompanied by elevated levels of anti-Müllerian hormone (AMH). AMH inhibits follicle maturation. AMH also inhibits steroidogenesis through transcriptional repression of CYP17A1. We recently identified 16 rare PCOS-specific pathogenic variants in AMH.

OBJECTIVE

To test whether additional members of the AMH signaling pathway also contribute to the etiology of PCOS.

PARTICIPANTS/DESIGN

Targeted resequencing of coding and regulatory regions of AMH and its specific type 2 receptor, AMHR2, was performed on 608 women affected with PCOS and 142 reproductively normal control women. Prediction tools of deleteriousness and in silico evidence of epigenetic modification were used to prioritize variants for functional evaluation. Dual-luciferase reporter assays and splicing assays were used to measure the impact of genetic variants on function.

RESULTS

We identified 20 additional variants in/near AMH and AMHR2 with significantly reduced signaling activity in in vitro assays. Collectively, from our previous study and as reported herein, we have identified a total of 37 variants with impaired activity in/near AMH and AMHR2 in 41 women affected with PCOS, or 6.7% of our PCOS cohort. Furthermore, no functional variants were observed in the 142 phenotyped controls. The functional variants were significantly associated with PCOS in our cohort of 608 women with PCOS and 142 controls (P = 2.3 × 10-5) and very strongly associated with PCOS relative to a larger non-Finnish European (gnomAD) population-based control cohort (P < 1 × 10-9).

CONCLUSION

The AMH signaling cascade plays an important role in PCOS etiology.

Insights into the Development of the Adult Leydig Cell Lineage from Stem Leydig Cells

Adult Leydig cells (ALCs) are the steroidogenic cells in the testes that produce testosterone. ALCs develop postnatally from a pool of stem cells, referred to as stem Leydig cells (SLCs). SLCs are spindle-shaped cells that lack steroidogenic cell markers, including luteinizing hormone (LH) receptor and 3β-hydroxysteroid dehydrogenase. The commitment of SLCs into the progenitor Leydig cells (PLCs), the first stage in the lineage, requires growth factors, including Dessert Hedgehog (DHH) and platelet-derived growth factor-AA. PLCs are still spindle-shaped, but become steroidogenic and produce mainly androsterone. The next transition in the lineage is from PLC to the immature Leydig cell (ILC). This transition requires LH, DHH, and androgen. ILCs are ovoid cells that are competent for producing a different form of androgen, androstanediol. The final stage in the developmental lineage is ALC. The transition to ALC involves the reduced expression of 5α-reductase 1, a step that is necessary to make the cells to produce testosterone as the final product. The transitions along the Leydig cell lineage are associated with the progressive down-regulation of the proliferative activity, and the up-regulation of steroidogenic capacity, with each step requiring unique regulatory signaling.

Male patients with terminal renal failure exhibit low serum levels of antimüllerian hormone

Male reproductive function is impaired during end-stage renal disease (ESRD). Disturbance of the hypothalamic-pituitary-gonadal axis, and therefore the regulation of sex hormones, is one of the major causes. Our focus was to include antimüllerian hormone (AMH) and inhibin B concentrations. Twenty male patients on hemodialysis, median age 40 (26–48) years, were analyzed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, sex hormone-binding globulin (SHBG), testosterone, estradiol, AMH and inhibin B levels. We used 144 proven fertile men, median age 32 (19–44) years as a control group and analyzed differences using multiple linear regression. Males with ESRD demonstrated higher mean values for prolactin, 742 versus normal 210 mIE l⁻¹ (95% confidence interval (CI): 60.3, 729), LH, 8.87 versus normal 4.5 IE l⁻¹ (95% CI: 2.75, 6.14), and estradiol 89.7 versus normal 79.0 pmol l⁻¹ (95% CI: −1.31, −0.15). Mean value for AMH was lower, 19.5 versus normal 47.3 pmol l⁻¹ (95% CI: −37.6, −11.6). There were no differences found for FSH, SHBG, inhibin B and testosterone. The most important difference was found for AMH, a marker of Sertoli cell function in the testes, which decreased by close to 60% when compared with controls. Combined with an increase in LH, these findings may indicate a dysfunction of Sertoli cells and an effect on Leydig cells contributing to a potential mechanism of reproductive dysfunction in men with ESRD.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Notch signaling represses GATA4-induced expression of genes involved in steroid biosynthesis

Notch2 and Notch3 and genes of the Notch signaling network are dynamically expressed in developing follicles, where they are essential for granulosa cell proliferation and meiotic maturation. Notch receptors, ligands, and downstream effector genes are also expressed in testicular Leydig cells, predicting a potential role in regulating steroidogenesis. In this study, we sought to determine if Notch signaling in small follicles regulates the proliferation response of granulosa cells to FSH and represses the up-regulation steroidogenic gene expression that occurs in response to FSH as the follicle grows. Inhibition of Notch signaling in small preantral follicles led to the up-regulation of the expression of genes in the steroid biosynthetic pathway. Similarly, progesterone secretion by MA-10 Leydig cells was significantly inhibited by constitutively active Notch. Together, these data indicated that Notch signaling inhibits steroidogenesis. GATA4 has been shown to be a positive regulator of steroidogenic genes, including STAR protein, P450 aromatase, and 3B-hydroxysteroid dehydrogenase. We observed that Notch downstream effectors HEY1, HEY2, and HEYL are able to differentially regulate these GATA4-dependent promoters. These data are supported by the presence of HEY/HES binding sites in these promoters. These studies indicate that Notch signaling has a role in the complex regulation of the steroidogenic pathway.

Crucial genes and pathways in chicken germ stem cell differentiation

Male germ cell differentiation is a subtle and complex regulatory process. Currently, its regulatory mechanism is still not fully understood. In our experiment, we performed the first comprehensive genome and transcriptome-wide analyses of the crucial genes and signaling pathways in three kinds of crucial cells (embryonic stem cells, primordial germ cell, and spermatogonial stem cells) that are associated with the male germ cell differentiation. We identified thousands of differentially expressed genes in this process, and from these we chose 173 candidate genes, of which 98 genes were involved in cell differentiation, 19 were involved in the metabolic process, and 56 were involved in the differentiation and metabolic processes, like GAL9, AMH, PLK1, and PSMD7 and so on. In addition, we found that 18 key signaling pathways were involved mainly in cell proliferation, differentiation, and signal transduction processes like TGF-β, Notch, and Jak-STAT. Further exploration found that the candidate gene expression patterns were the same between in vitro induction experiments and transcriptome results. Our results yield clues to the mechanistic basis of male germ cell differentiation and provide an important reference for further studies.

Sex differences in neurosteroid and hormonal responses to metyrapone in posttraumatic stress disorder

RATIONALE

Mechanisms contributing to sex differences in the regulation of acute stress responsivity and their effect on the increased incidence of posttraumatic stress disorder (PTSD) in women are poorly understood. The reproductive hormone, progesterone, through conversion to allopregnanolone (ALLO), suppresses the hypothalamic pituitary adrenal (HPA) axis and has potent anxiolytic effects. The potential that progesterone and allopregnanolone reactivity modulate HPA axis responses and account for sex differences in PTSD has not been previously examined.

OBJECTIVE

The present study examined the effects of sex and PTSD on adrenocorticotropic hormone (ACTH), progesterone, and allopregnanolone responses to metyrapone and whether progesterone and allopregnanolone reactivity could affect the ACTH response in PTSD.

METHODS

Healthy medication-free male and premenopausal follicular phase female participants with chronic PTSD (n = 43; 49 % female) and controls (n = 42; 50 % female) completed an overnight metyrapone challenge and ACTH, progesterone, and allopregnanolone were obtained by repeated blood sampling.

RESULTS

The increase in ACTH response to metyrapone was higher in PTSD subjects compared to controls and in women compared to men. Contrary to our initial prediction of an inverse relationship, progesterone and allopregnanolone were positively associated with ACTH. Progesterone and allopregnanolone partially mediated the relationship between PTSD and ACTH.

CONCLUSIONS

Our findings of increased ACTH to metyrapone in PTSD and in women may reflect heightened hypothalamic CRF hypersecretion. Progesterone and allopregnanolone partially mediated the ACTH response in PTSD. Further characterizing sex differences in these processes will advance our understanding of the pathophysiology of PTSD, and may ultimately lead to better-targeted, more effective treatment.

Sex-specific expression of CTNNB1 in the gonadal morphogenesis of the chicken

BACKGROUND

Beta-catenin (CTNNB1), as a key transcriptional regulator in the WNT signal transduction cascade, plays a pivotal role in multiple biological functions such as embryonic development and homeostasis in adults. Although it has been suggested that CTNNB1 is required for gonad development and maintenance of ovarian function in mice, little is known about the expression and functional role of CTNNB1 in gonadal development and differentiation in the chicken reproductive system.

METHODS

To examine sex-specific, cell-specific and temporal expression of CTNNB1 mRNA and protein during gonadal development to maturation of reproductive organs, we collected left and right gonads apart from mesonephric kidney of chicken embryos on embryonic day (E) 6, E9, E14, E18, as well as testes, oviduct and ovaries from 12-week-old and adult chickens and performed quantitative PCR, in situ hybridization, and immunohistochemical analyses. In addition, localization of Sertoli cell markers such as anti-Müllerian hormone (AMH), estrogen receptor alpha (ESR1), cyclin D1 (CCND1) and N-cadherin (CDH2) during testicular development was evaluated.

RESULTS

Results of the present study showed that CTNNB1 mRNA and protein are expressed predominantly in the seminiferous cords on E6 to E14 in the male embryonic gonad, and are mainly localized to the medullary region of female embryonic gonads from E6 to E9. In addition, CTNNB1 mRNA and protein are abundant in the Sertoli cells in the testes and expressed predominantly in luminal epithelial cells of the oviduct, but not in the ovaries from 12-week-old and adult chickens. Concomitant with CTNNB1, AMH, ESR1, CCND1 and CDH2 were detected predominantly in the seminiferous cord of the medullary region of male gonads at E9 (after sex determination) and then maintained or decreased until hatching. Interestingly, AMH, ESR1, CCND1 and CDH2 were located in seminiferous tubules of the testes from 12-weeks-old chickens and ESR1, CCND1 and CDH2 were expressed predominantly in the Sertoli cells within seminiferous tubules of adult testes.

CONCLUSIONS

Collectively, these results revealed that CTNNB1 is present in gonads of both sexes during embryonic development and it may play essential roles in differentiation of Sertoli cells during formation of seminiferous tubules during development of the testes.

Dihydrolipoamide dehydrogenase and cAMP are associated with cadmium-mediated Leydig cell damage

Cadmium (Cd) directly inhibits testosterone production in Leydig cells, but its mechanism is still unclear. To further explore the signaling pathway of Cd-mediated toxicity to Leydig cells, various concentrations of Cd were cultured with R2C cells for 24h, and two-dimensional gel electrophoresis (2DE)-based proteomics profiling was used to analyze the change of protein expressions. Cd caused a concentration-dependent inhibition of cell viability with IC(25), IC(50) and IC(75) of 2.42×10(-5)M, 4.83×10(-5)M and 7.39×10(-5)M, respectively. Cd significantly reduced progesterone production and mitochondrial membrane potential (ΔΨ(m)) in a concentration-dependent manner. 2DE-based proteomics showed 34 protein spots with altered expression by 2-folds or more, and dihydrolipoamide dehydrogenase (DLD) was the hub in the network of these altered proteins. Real-time polymerase chain reaction (PCR) and Western blotting showed that Cd downregulated the expression of DLD. Cd also decreased intracellular levels of cyclic adenosine monophosphate (cAMP). The results suggest that DLD and cAMP may be key elements related to Cd toxicity to Leydig cells.

Mullerian Inhibiting Substance is an ovarian growth factor of emerging clinical significance

OBJECTIVE

To examine Mullerian Inhibiting Substance (MIS) as an emerging diagnostic marker of ovarian function.

DESIGN

Medline review of published studies pertaining to the role of MIS in assessing ovarian aging, predicting response to ovulation induction in preparation for in vitro fertilization, assessing risk of developing ovarian hyperstimulation (OHSS) before ovulation induction, and diagnosis of polycystic ovarian disease (PCOS).

RESULT(S)

The majority of published studies to date support a role for MIS as a marker of ovarian reserve. Specific cut-off values are dependent upon the particular assay used. Mullerian Inhibiting Substance may offer value in assessing risk of OHSS and diagnosis of PCOS.

CONCLUSION(S)

Potential advantages of MIS compared with other conventional markers of ovarian reserve include: 1) MIS is the earliest marker to change with age; 2) it has the least intercycle variability; 3) it has the least intracycle variability; and 4) it may be informative if randomly obtained during the cycle. Widespread clinical use of MIS may await the availability of an international standard for MIS so that results using different assays may be reliably compared.

The chick embryo: an animal model for detection of the effects of hormonal compounds

Hormonal compounds are a class of pharmaceutical product that disrupt the endocrine system of animals and humans. Exposure to these molecules, even at low concentrations, can have severely damaging effects on the environment, to organisms, and to humans. The cumulative presence of these compounds is also characterized by synergistic effects which are difficult to estimate. They are an underestimated danger to the environment and to the human population. This paper presents an in-vivo model enabling to assessment of the real impact of exposure to hormonal compounds and the synergistic effect which can be involved. The anatomical effects of in-ovo exposure to two natural estrogen compounds (estrone and estriol, at 600 ng g(-1)) and a synthetic estrogen (ethynylestradiol, at 20 ng g(-1)) have been investigated. Estrone and estriol lead to morphological defects, mainly in the urogenital system of the developing chick embryo, whereas ethynylestradiol has fewer effects. Estriol caused persistence of Müllerian ducts in 50% of male embryos and hypertrophic oviducts in 71% of females. Estrone had the same effects but at the percentages were lower. Kidney dysfunction was also observed, but only with estrone, in both males and females. We also tested estrogenic compounds in two types of cell line which are estrogen sensitive (BG1 and MCF7) then completed and confirmed our previous in-vivo results. Seven pharmaceutical-like compounds--estrone (E1), estradiol (E2), estriol (E3), ethynylestradiol (EE(2)), carbamazepine (C), genistein (G), and bisphenol-A (BPA)--were tested alone or in mixtures. Different effects on the two cell lines were observed, indicating that endocrine compounds can act differently on this organism. Experiments also showed that these molecules have synergistic action and induce more severe effects when they are in mixtures.

Diagnosis of 5alpha-reductase type 2 deficiency: contribution of anti-Müllerian hormone evaluation

AIM

To evaluate anti-Müllerian hormone (AMH) levels in patients with clinical and molecular diagnosis of 5alpha-reductase 2 deficiency.

PATIENTS AND METHODS

Data from 14 patients whose age ranged from 21 days to 29 years were analyzed according to age and pubertal stage. Sexual ambiguity was rated as Prader III in 11 patients. LH, FSH, testosterone (T), dihydrotestosterone (DHT) and AMH serum levels were measured in all but two patients, who had been previously submitted to gonadectomy; T and DHT were also measured in 20 age-matched controls.

RESULTS

Gonadotropin levels were normal in all but one patient who retained gonads (six of whom had reached puberty) and T/DHT ratio was elevated in all patients when compared to controls. All prepubertal patients had AMH levels < -1 SD for age, while most pubertal patients had AMH levels compatible with pubertal stage.

CONCLUSIONS

Prepubertal patients with 5alpha-reductase 2 deficiency have AMH values in the lower part of the normal range. These data indicate that T does not need to be converted to DHT to inhibit AMH secretion by Sertoli cells.