Triiodothyronine decreases the activity of the proximal promoter (PII) of the aromatase gene in the mouse Sertoli cell line, TM4

Perinatal exposure to environmental chemicals that disrupt thyroid function can perturb testis development

Thyroid hormones (THs) are essential for normal growth and development. Their role in skeletal and brain development is well established, with congenital hypothyroidism causing stunted growth and severe intellectual disability. THs are also important for the development of other tissues and organs, including the testis. Developmental hypothyroidism can manifest as smaller testes in early postnatal life that later develop into macroorchidism in adulthood due to increased proliferation of Sertoli cells. Effects of hypothyroidism on the testes can be modelled in rodents by exposing developing animals to TH-suppressing pharmaceuticals such as propylthiouracil (PTU) and methimazole (MMI). These drugs act by inhibiting the thyroperoxidase (TPO) enzyme in the thyroid gland, inhibiting the synthesis of THs. It is possible that environmental chemicals that inhibit TPO activity can also cause TH-mediated effects on the developing testis, but the extent to which this occurs is not known. Herein, we characterized the effects of perinatal exposure to the herbicide amitrole together with the antithyroid drug MMI. Pregnant Sprague-Dawley rats were exposed by oral gavage to two doses of amitrole (25 or 50 mg/kg body weight/day) or MMI (8 or 16 mg/kg body weight/day) from gestational day 7 until birth. After birth, pup exposure was continued by dosing lactating dams from day of delivery until pup day 16. Both chemicals caused a significant reduction in TH levels on day 16. This perinatal hypothyroidism disrupted both germ and Sertoli cell development, resulting in smaller testes and reduced seminiferous tubule diameter in 16-day old pups. Notably, fetal male blood progesterone levels were increased after exposure to both amitrole and MMI, whereas the amitrole-exposed animals also displayed increased estradiol levels. Our study raises concerns that exposure to environmental chemicals that happen to disrupt TH production may disrupt TH-dependent testis development, with adverse consequences to human reproductive health.

Thyroid disorders and male sexual dysfunction

Though early research suggested that thyroid hormones were not involved with the testes, male spermatogenesis, or erectile function, investigations on this topic over the past few decades have increased and shed new light. A literature review of studies conducted between 1963 and 2022 regarding male sexual dysfunction (SD) and thyroid disorders was performed to define the diagnostic consideration, pathophysiology, and management of SD secondary to thyroid dysregulation. This article provides evidence and interpretation of prior clinical and preclinical studies and contextualizes these studies for clinical practice. Clinical manifestations of SDs included erectile and ejaculatory dysfunction, impaired spermatogenesis, and disruption of the hypothalamic-pituitary-gonadal axis. Our aim of this communication was to perform a literature review detailing the impact of thyroid disorders on male SD. We hope to provide a framework for practicing urologists, endocrinologists, or general practitioners when evaluating patients with concurrent thyroid and male SD. It is important to recognize that thyroid disorders can be an important part of the pathophysiology of male SD in patients. Future research studies are needed to further elucidate the mechanisms involved.

TNF-α/ENO1 signaling facilitates testicular phagocytosis by directly activating Elmo1 gene expression in mouse Sertoli cells

Phagocytic clearance of apoptotic germ cells (GCs), as well as residual bodies (RBs) released from developing spermatids, is critical for Sertoli cells (SCs) to maintain inner environment homeostasis within testis. However, the molecular mechanisms controlling the phagocytosis are ill defined. Here, we identify a new role for alpha-enolase (ENO1), a key enzyme during glycolysis, as a molecule that facilitates testicular phagocytosis via transactivation of the engulfment and cell motility 1 (Elmo1) gene. Using immunohistochesmitry and double-labeling immunofluorescence, ENO1 was observed to be expressed exclusively in the nuclei of SCs and its expression correlated with the completion of Sertoli cell differentiation. By incubating TM4 cells with different pharmacological inhibitors and establishing TM4^Tnfr1-/- cells, we demonstrated that Sertoli cell-specific expression of ENO1 was under a delicate paracrine control from apoptotic GCs. In turn, persistent blockade of ENO1 expression by a validated siRNA protocol resulted in the disturbance of spermatogenesis and impairment of male fertility. Furthermore, using chromatin immunoprecipitation, electrophoretic mobility shift assay and luciferase reporter assay, we showed that in the presence of apoptotic GCs, ENO1 binds to the distal region of the Elmo1 promoter and facilitates transactivation of the Elmo1 gene. In agreement, overexpression of ELMO1 ameliorated ENO1 deficiency-induced impairment of phagocytosis in TM4 cells. These data reveal a novel role for Sertoli cell-specific expression of ENO1 in regulating phagocytosis in testis, identify TNF-α and ELMO1 as critical upstream and downstream factors in mediating ENO1 action, and have important implications for understanding paracrine control of Sertoli cell function by adjacent GCs.

Lower TSH and higher free thyroxine predict incidence of prostate but not breast, colorectal or lung cancer

CONTEXT

Thyroid hormones modulate proliferative, metabolic and angiogenic pathways. However few studies have examined associations of thyroid hormones with cancer risk.

OBJECTIVES

To explore associations of thyrotropin (TSH), free thyroxine (FT4) and anti-thyroperoxidase antibodies (TPOAb) with the incidence of all (non-skin) cancers and specific common cancers.

DESIGN AND SETTING

A prospective cohort study of a community-dwelling population aged 25-84 years in Western Australia.

MAIN OUTCOME MEASURES

Archived sera from 3649 participants in the 1994/1995 Busselton Health Survey were assayed for TSH, FT4 and TPOAb. Cancer outcomes until 30 June 2014 were ascertained using data linkage. Longitudinal analyses were performed using Cox proportional hazards regression.

RESULTS

During 20-year follow-up, 600 participants were diagnosed with non-skin cancer, including 126, 100, 103 and 41 prostate, breast, colorectal and lung cancers respectively. Higher TSH was associated with a lower risk of prostate cancer after adjusting for potential confounders, with a 30% lower risk for every 1 IU/L increase in TSH (adjusted hazard ratio (HR): 0.70, 95% confidence interval (CI): 0.55-0.90, P = 0.005). Similarly, higher FT4 was associated with an increased risk of prostate cancer (adjusted HR: 1.11 per 1 pmol/L increase, 95% CI: 1.03-1.19, P = 0.009). There were no associations of TSH, FT4 or TPOAb with all non-skin cancer events combined, or with breast, colorectal or lung cancer.

CONCLUSION

In a community-dwelling population, lower TSH and higher FT4 were associated with an increased risk of prostate cancer. Further studies are required to assess if thyroid function is a biomarker or risk factor for prostate cancer.

Estrogens in Male Physiology

Estrogens have historically been associated with female reproduction, but work over the last two decades established that estrogens and their main nuclear receptors (ESR1 and ESR2) and G protein-coupled estrogen receptor (GPER) also regulate male reproductive and nonreproductive organs. 17β-Estradiol (E2) is measureable in blood of men and males of other species, but in rete testis fluids, E2 reaches concentrations normally found only in females and in some species nanomolar concentrations of estrone sulfate are found in semen. Aromatase, which converts androgens to estrogens, is expressed in Leydig cells, seminiferous epithelium, and other male organs. Early studies showed E2 binding in numerous male tissues, and ESR1 and ESR2 each show unique distributions and actions in males. Exogenous estrogen treatment produced male reproductive pathologies in laboratory animals and men, especially during development, and studies with transgenic mice with compromised estrogen signaling demonstrated an E2 role in normal male physiology. Efferent ductules and epididymal functions are dependent on estrogen signaling through ESR1, whose loss impaired ion transport and water reabsorption, resulting in abnormal sperm. Loss of ESR1 or aromatase also produces effects on nonreproductive targets such as brain, adipose, skeletal muscle, bone, cardiovascular, and immune tissues. Expression of GPER is extensive in male tracts, suggesting a possible role for E2 signaling through this receptor in male reproduction. Recent evidence also indicates that membrane ESR1 has critical roles in male reproduction. Thus estrogens are important physiological regulators in males, and future studies may reveal additional roles for estrogen signaling in various target tissues.

A link between hypothyroidism, obesity and male reproduction

Hypothyroidism is a condition in which the serum levels of thyroid hormones are below that necessary to carry out physiological functions in the body. Hypothyroidism is related to obesity as an increase in body weight gain is seen in hypothyroid patients. Moreover, an inverse correlation between free thyroxine values and body mass index has been reported. Leptin, a polypeptide hormone produced by adipocytes, was originally thought to be an antiobesity hormone due its anorexic effects on hypothalamic appetite regulation. However, nowadays it is known that leptin conveys information about the nutritional status to the brain being considered a crucial endocrine factor for regulating several physiological processes including reproduction. Since the identification of thyroid hormone and leptin receptors on the testes, these hormones are being recognized as having important roles in male reproductive functions. A clear link exists among thyroid hormones, leptin and reproduction. Both hormones can negatively affect spermatogenesis and consequently may cause male infertility. The World Health Organization (WHO) estimates the overall prevalence of primary infertility ranging from 8 to 15%. The fact that 30% of couples' inability to conceive is related to a male factor and that the longer hypothyroidism persisted, the greater the damage to the testes, strongly suggest that more studies attempting to clarify both hormones actions directly in the testes need to be conducted specially in cases of congenital hypothyroidism. Therefore, the goal of this review is to highlight the relationship of such hormones in the reproductive system.

Igf Binding Proteins Protect Undifferentiated Spermatogonia in the Zebrafish Testis Against Excessive Differentiation

IGF binding proteins (IGFBPs) modulate the availability of IGFs for their cognate receptors. In zebrafish testes, IGF3 promotes the proliferation and differentiation of type A undifferentiated (A_und) spermatogonia, and igf3 expression is strongly elevated by FSH but also responds to T₃. Here we report the effects of FSH and T₃ on igfbp transcript levels in adult zebrafish testis. We then examined T₃ and FSH effects on zebrafish spermatogenesis and explored the relevance of IGFBPs in modulating these T₃ or FSH effects, using a primary tissue culture system for adult zebrafish testis. T₃ up-regulated igfbp1a and igfbp3 expression, whereas FSH reduced igfbp1a transcript levels. To quantify effects on spermatogenesis, we determined the mitotic index and relative section areas occupied by A_und, type A differentiating, or type B spermatogonia. In general, T₃ and FSH stimulated spermatogonial proliferation and increased the areas occupied by spermatogonia, suggesting that both self-renewal and differentiating divisions were stimulated. Preventing IGF/IGFBP interaction by NBI-31772 further increased T₃- or FSH-induced spermatogonial proliferation. However, under these conditions the more differentiated type A differentiating and B spermatogonia occupied larger surface areas at the expense of the area held by A_und spermatogonia. Clearly decreased nanos2 transcript levels are in agreement with this finding, and reduced amh expression may have facilitated spermatogonial differentiation. We conclude that elevating IGF3 bioactivity by blocking IGFBPs shifted T₃- or FSH-induced signaling from stimulating spermatogonial self-renewal as well as differentiation toward predominantly stimulating spermatogonial differentiation, which leads to a depletion of type A_und spermatogonia.

Effect of neonatal or adult heat acclimation on plasma fT3 level, testicular thyroid receptors expression in male rats and testicular steroidogenesis in vitro in response to triiodothyronine treatment

This study aimed to evaluate the effect of heat acclimation of neonatal and adult rats on their testes response to in vitro treatment with triiodothyronine (T3). Four groups of rats were housed from birth as: 1) control (CR) at 20°C for 90 days, 2) neonatal heat-acclimated (NHA) at 34°C for 90 days, 3) adult heat-acclimated (AHA) at 20°C for 45 days followed by 45 days at 34°C and 4) de-acclimated (DA) at 34°C for 45 days followed by 45 days at 20°C. Blood plasma and both testes were harvested from 90-day old rats. Testicular slices were then submitted to in vitro treatment with T3 (100 ng/ml) for 8 h. Plasma fT3 level was lower in AHA, NHA and DA groups than in CR group. Basal thyroid hormone receptor α1 (Thra1) expression was higher in testes of NHA and DA and β1 receptor (Thrb1) in DA rats vs. other groups. In the in vitro experiment, T3: 1) decreased Thra1 expression in all groups and Thrb1 in DA group, 2) increased Star expression in CR, NHA and DA groups, and Hsd17b3 expression in NHA group, 3) decreased the expression of Cyp11a1 in NHA and DA groups, and Cyp19a1 in all the groups, 4) did not affect the activity of steroidogenic enzymes and steroid secretion (A4, T, E2) in all the groups. These results indicate, that heat acclimation of rats, depending on their age, mainly affects the testicular expression of steroidogenic enzymes in response to short-lasting treatment with T3.

Glucocorticoid Receptor as a Potential Target to Decrease Aromatase Expression and Inhibit Leydig Tumor Growth

Leydig cell tumors are the most frequent interstitial neoplasms of the testis with increased incidence in recent years. They are hormonally active and are considered one of the steroid-secreting tumors. Although usually benign, the malignant phenotype responds poorly to conventional chemotherapy or radiation, highlighting the need to identify new therapeutic targets for treatment. Here, we identified a novel glucocorticoid-mediated mechanism that controls cell growth in Leydig cell tumors. We found that a synthetic glucocorticoid receptor agonist, dexamethasone, reduces cell proliferation in rat Leydig tumor cells by decreasing the expression and the enzymatic activity of the estrogen-producing enzyme aromatase. This inhibitory effect relies on the ability of activated glucocorticoid receptor to regulate the aromatase gene transcriptional activity through the recruitment of nuclear receptor corepressor protein and silencing mediator of retinoid and thyroid hormone receptors to a newly identified putative glucocorticoid responsive element within the aromatase promoter II. Our in vivo studies reveal a reduction of tumor growth, after dexamethasone treatment, in animal xenografts. Tumors from dexamethasone-treated mice exhibit a decrease in the expression of the proliferation marker Ki-67 and the aromatase enzyme. Our data demonstrate that activated glucocorticoid receptor, decreasing aromatase expression, induces Leydig tumor regression both in vitro and in vivo, suggesting that glucocorticoid receptor might be a potential target for the therapy of Leydig cell tumors.

Localization of the aromatase enzyme expression in the human pituitary gland and its effect on growth hormone, prolactin, and thyroid stimulating hormone axis

The aim of this study is to evaluate aromatase expression in prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) secreting cells. Nontumoral human pituitary specimens were obtained from autopsy samples. Aromatase co-expression was determined by double immunohistochemical staining and assessed using H scores. H scores for GH-aromatase co-expression (GH-aromatase), TSH-aromatase co-expression (TSH-aromatase), and PRL-aromatase co-expression (PRL-aromatase) were 83.1 ± 13.1, 95.6 ± 16.1, and 83.7 ± 14.5, respectively. TSH producing cells exhibited the highest H score for co-expression of aromatase (p < 0.001). There was no gender difference in terms of H scores for aromatase expression and double immunohistochemical staining results (p > 0.05 for all). There was a negative correlation between the H scores for aromatase and PRL-aromatase, GH-aromatase and TSH-aromatase, respectively (r = -0.592, p < 0.001; r = -0.593, p < 0.001; r = -0.650, p < 0.001, respectively). Also, H scores for aromatase co-expression of each hormone were negatively correlated with the H scores for the corresponding hormone (r = -0.503, p < 0.001 for PRL-aromatase and PRL; r = -0.470, p < 0.001 for GH-aromatase, and GH; r = -0.641, p < 0.001 for TSH-aromatase and TSH). H scores for mean aromatase, GH-aromatase, TSH-aromatase were invariant of age (p > 0.05 for all). Age was negatively correlated with PRL-aromatase H score (r = -0.373, p = 0.008). Our study demonstrated significant aromatase co-expression in PRL, GH, and TSH secreting cells of the human anterior pituitary gland. The mutual paracrinal regulation between aromatase and three adenohypophyseal hormones indicates that aromatase may have a regulatory role on the synthesis and secretion of these hormones.

Transcriptional control of local estrogen formation by aromatase in the breast

Aromatase is the critical enzyme that converts androgens to estrogens. It is frequently highly expressed in the tumour bearing breast of women diagnosed with estrogen receptor positive tumours, resulting in dramatically increased local estrogen production to drive tumour progression. Expression of aromatase is regulated primarily at the transcriptional level of its encoding gene CYP19A1, located on chromosome 15 of the human genome. A characteristic feature of CYP19A1 expression is its use of alternative promoters to regulate transcription in a tissue-specific manner. In breast cancer, the increase in aromatase expression is mediated via higher expression of the distal adipose-specific promoter I.4 and a switch to the preferential use of proximal promoters I.3 and II. This results in a net increase of CYP19A1 transcripts in tumour-bearing breast up to 3-4-fold higher than normal breast. Current aromatase inhibitors - whilst efficacious - exhibit significant side effects that reduce patient compliance. Understanding the transcription factors and signalling pathways that control aromatase expression will lead to opportunities to develop breast-specific inhibitors with an improved side-effects profile. This article is part of a Special Issue entitled 'Essential role of DHEA'.

Crossover of the hypothalamic pituitary-adrenal/interrenal, -thyroid, and -gonadal axes in testicular development

Besides the well-known function of thyroid hormones (THs) for regulating metabolism, it has recently been discovered that THs are also involved in testicular development in mammalian and non-mammalian species. THs, in combination with follicle stimulating hormone, lead to androgen synthesis in Danio rerio, which results in the onset of spermatogenesis in the testis, potentially relating the hypothalamic-pituitary-thyroid (HPT) gland to the hypothalamic-pituitary-gonadal (HPG) axes. Furthermore, studies in non-mammalian species have suggested that by stimulating the thyroid-stimulating hormone (TSH), THs can be induced by corticotropin-releasing hormone. This suggests that the hypothalamic-pituitary-adrenal/interrenal gland (HPA) axis might influence the HPT axis. Additionally, it was shown that hormones pertaining to both HPT and HPA could also influence the HPG endocrine axis. For example, high levels of androgens were observed in the testis in Odonthestes bonariensis during a period of stress-induced sex-determination, which suggests that stress hormones influence the gonadal fate toward masculinization. Thus, this review highlights the hormonal interactions observed between the HPT, HPA, and HPG axes using a comparative approach in order to better understand how these endocrine systems could interact with each other to influence the development of testes.

Mechanisms of crosstalk between endocrine systems: regulation of sex steroid hormone synthesis and action by thyroid hormones

Thyroid hormones (THs) are well-known regulators of development and metabolism in vertebrates. There is increasing evidence that THs are also involved in gonadal differentiation and reproductive function. Changes in TH status affect sex ratios in developing fish and frogs and reproduction (e.g., fertility), hormone levels, and gonad morphology in adults of species of different vertebrates. In this review, we have summarized and compared the evidence for cross-talk between the steroid hormone and thyroid axes and present a comparative model. We gave special attention to TH regulation of sex steroid synthesis and action in both the brain and gonad, since these are important for gonad development and brain sexual differentiation and have been studied in many species. We also reviewed research showing that there is a TH system, including receptors and enzymes, in the brains and gonads in developing and adult vertebrates. Our analysis shows that THs influences sex steroid hormone synthesis in vertebrates, ranging from fish to pigs. This concept of crosstalk and conserved hormone interaction has implications for our understanding of the role of THs in reproduction, and how these processes may be dysregulated by environmental endocrine disruptors.

Distinct nuclear receptor expression in stroma adjacent to breast tumors

The interaction between breast tumor epithelial and stromal cells is vital for initial and recurrent tumor growth. While breast cancer-associated stromal cells provide a favorable environment for proliferation and metastasis, the molecular mechanisms contributing to this process are not fully understood. Nuclear receptors (NRs) are intracellular transcription factors that directly regulate gene expression. Little is known about the status of NRs in cancer-associated stroma. Nuclear Receptor Low-Density Taqman Arrays were used to compare the gene expression profiles of all 48 NR family members in a collection of primary cultured cancer-associated fibroblasts (CAFs) obtained from estrogen receptor (ER)α positive breast cancers (n = 9) and normal breast adipose fibroblasts (NAFs) (n = 7). Thirty-three of 48 NRs were expressed in both the groups, while 11 NRs were not detected in either. Three NRs (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX-1); estrogen-related receptor beta (ERR-β); and RAR-related orphan receptor beta (ROR-β)) were only detected in NAFs, while one NR (liver receptor homolog-1 (LRH-1)) was unique to CAFs. Of the NRs co-expressed, four were significantly down-regulated in CAFs compared with NAFs (RAR-related orphan receptor-α (ROR-α); Thyroid hormone receptor-β (TR-β); vitamin D receptor (VDR); and peroxisome proliferator-activated receptor-γ (PPAR-γ)). Quantitative immunohistochemistry for LRH-1, TR-β, and PPAR-γ proteins in stromal fibroblasts from an independent panel of breast cancers (ER-positive (n = 15), ER-negative (n = 15), normal (n = 14)) positively correlated with mRNA expression profiles. The differentially expressed NRs identified in tumor stroma are key mediators in aromatase regulation and subsequent estrogen production. Our findings reveal a distinct pattern of NR expression that therefore fits with a sustained and increased local estrogen microenvironment in ER-positive tumors. NRs in CAFs may provide a new avenue for the development of intratumoral-targeted therapies in breast cancer.

Thyroid hormone and leptin in the testis

Leptin is primarily expressed in white adipose tissue; however, it is expressed in the hypothalamus and reproductive tissues as well. Leptin acts by activating the leptin receptors (Ob-Rs). Additionally, the regulation of several neuroendocrine and reproductive functions, including the inhibition of glucocorticoids and enhancement of thyroxine and sex hormone concentrations in human beings and mice are leptin functions. It has been suggested that thyroid hormones (TH) could directly regulate leptin expression. Additionally, hypothyroidism compromises the intracellular integration of leptin signaling specifically in the arcuate nucleus. Two TH receptor isoforms are expressed in the testis, TRa and TRb, with TRa being the predominant one that is present in all stages of development. The effects of TH involve the proliferation and differentiation of Sertoli and Leydig cells during development, spermatogenesis, and steroidogenesis. In this context, TH disorders are associated with sexual dysfunction. An endocrine and/or direct paracrine effect of leptin on the gonads inhibits testosterone production in Leydig cells. Further studies are necessary to clarify the effects of both hormones in the testis during hypothyroidism. The goal of this review is to highlight the current knowledge regarding leptin and TH in the testis.

GPER Signaling in Spermatogenesis and Testicular Tumors

Estrogens play important roles in the regulation of testis development and spermatogenesis. Moreover, several evidences suggest that estrogen signaling can be involved in testicular tumorigenesis. The physiological effects of estrogen are mediated by the classical nuclear estrogen receptors ESR1 and 2, which regulate both genomic and rapid signaling events. In the recent years, a member of the seven-transmembrane G protein-coupled receptor family, GPR30 (GPER), has been identified to promote estrogen action in target cells including testicular cells. Ours and other studies reported that GPER is expressed in normal germ cells (spermatogonia, spermatocytes, spermatids), somatic cells (Sertoli and Leydig cells), and it is also involved in mediating estrogen action during spermatogenesis and testis development. In addition, GPER seems to be involved in modulating estrogen-dependent testicular cancer cell growth. However, in this context, the effects of GPER stimulation on cell survival and proliferation appear to be cell type specific. This review summarizes the current knowledge on the functions regulated by estrogens and mediated by GPER in normal and tumor testicular cells.

Thyroid and male reproduction

Male reproduction is governed by the classical hypothalamo-hypophyseal testicular axis: Hypothalamic gonadotropin releasing hormone (GnRH), pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) and the gonadal steroid, principally, testosterone. Thyroid hormones have been shown to exert a modulatory influence on this axis and consequently the sexual and spermatogenic function of man. This review will examine the modulatory influence of thyroid hormones on male reproduction.

Thyroid hormone function in the rat testis

Thyroid hormones are emerging regulators of testicular function since Sertoli, germ, and Leydig cells are found to express thyroid hormone receptors (TRs). These testicular cells also express deiodinases, which are capable of converting the pro-hormone T4 to the active thyroid hormone T3, or inactivating T3 or T4 to a non-biologically active form. Furthermore, thyroid hormone transporters are also found in the testis. Thus, the testis is equipped with the transporters and the enzymes necessary to maintain the optimal level of thyroid hormone in the seminiferous epithelium, as well as the specific TRs to execute thyroid hormone action in response to different stages of the epithelial cycle of spermatogenesis. Studies using genetic models and/or goitrogens (e.g., propylthiouracil) have illustrated a tight physiological relationship between thyroid hormone and testicular function, in particular, Sertoli cell differentiation status, mitotic activity, gap junction function, and blood-testis barrier assembly. These findings are briefly summarized and discussed herein.

Thyroid hormone stimulates the proliferation of Sertoli cells and single type A spermatogonia in adult zebrafish (Danio rerio) testis

Thyroid hormones participate in regulating growth and homeostatic processes in vertebrates, including development and adult functioning of the reproductive system. Here we report a new stimulatory role of thyroid hormone on the proliferation of Sertoli cells (SCs) and single, type A undifferentiated spermatogonia (A(und)) in adult zebrafish testes. A role for T3 in zebrafish testis is suggested by in situ hybridization studies, which localized thyroid receptor α (thrα) in SCs and the β (thrβ) mRNA in Sertoli and Leydig cells. Using a primary zebrafish testis tissue culture system, the effect of T3 on steroid release, spermatogenesis, and the expression of selected genes was evaluated. Basal steroid release and Leydig cell gene expression did not change in response to T3. However, in the presence of FSH, T3 potentiated gonadotropin-stimulated androgen release as well as androgen receptor (ar) and 17α-hydroxylase/17,20 lyase (cyp17a1) gene expression. Moreover, T3 alone stimulated the proliferation of both SCs and A(und), potentially resulting in newly formed spermatogonial cysts. Additional tissue culture studies demonstrated that Igf3, a new, gonad-specific member of the IGF family, mediated the stimulatory effect of T3 on the proliferation of A(und) and SCs. Finally, T3 induced changes in connexin 43 mRNA levels in the testis, a known T3-responsive gene. Taken together, our studies suggest that T3 expands the population of SCs and A(und) involving Igf signaling and potentiates gonadotropin-stimulated testicular androgen production as well as androgen sensitivity.

Thyroid hormones in male reproductive development: evidence for direct crosstalk between the androgen and thyroid hormone axes

Thyroid hormones (THs) exert a broad range of effects on development in vertebrate species, demonstrating connections in nearly every biological endocrine system. In particular, studies have shown that THs play a role in sexual differentiation and gonadal development in mammalian and non-mammalian species. There is considerable evidence that the effects of THs on reproductive development are mediated through the female hormonal axis; however, recent findings suggest a more direct crosstalk between THs and the androgen axis. These findings demonstrate that THs have considerable influence in the sexual ontogeny of male vertebrates, through direct interactions with select sex-determining-genes and regulation of gonadotropin production in the hypothalamus-pituitary-gonad axis. THs also regulate androgen biosynthesis and signaling through direct and indirect regulation of steroidogenic enzyme expression and activity. Novel promoter analysis presented in this work demonstrates the potential for direct and vertebrate wide crosstalk at the transcriptional level in mice (Mus musculus), Western clawed frogs (Silurana tropicalis) and medaka (Oryzias latipes). Cumulative evidence from previous studies; coupled with novel promoter analysis suggests mechanisms for a more direct crosstalk between the TH and male reproductive axes across vertebrate species.

Epigenetic modifications during sex change repress gonadotropin stimulation of cyp19a1a in a teleost ricefield eel (Monopterus albus)

In vertebrates, cytochrome P450 aromatase, encoded by cyp19a1, converts androgens to estrogens and plays important roles in gonadal differentiation and development. The present study examines whether epigenetic mechanisms are involved in cyp19a1a expression and subsequent gonadal development in the hermaphroditic ricefield eel. The expression of the ricefield eel cyp19a1a was stimulated by gonadotropin via the cAMP pathway in the ovary but not the ovotestis or testis. The CpG within the cAMP response element (CRE) of the cyp19a1a promoter was hypermethylated in the ovotestis and testis compared with the ovary. The methylation levels of CpG sites around CRE in the distal region (region II) and around steroidogenic factor 1/adrenal 4 binding protein sites and TATA box in the proximal region (region I) were inversely correlated with cyp19a1a expression during the natural sex change from female to male. In vitro DNA methylation decreased the basal and forskolin-induced activities of cyp19a1a promoter. Chromatin immunoprecipitation assays indicated that histone 3 (Lys9) in both regions I and II of the cyp19a1a promoter were deacetylated and trimethylated in the testis, and in contrast to the ovary, phosphorylated CRE-binding protein failed to bind to these regions. Lastly, the DNA methylation inhibitor 5-aza-2'-deoxycytidine reversed the natural sex change of ricefield eels. These results suggested that epigenetic mechanisms involving DNA methylation and histone deacetylation and methylation may abrogate the stimulation of cyp19a1a by gonadotropins in a male-specific fashion. This may be a mechanism widely used to drive natural sex change in teleosts as well as gonadal differentiation in other vertebrates.

Integrin participates in the effect of thyroxine on plasma membrane in immature rat testis

BACKGROUND

The secretory activity of Sertoli cells (SC) is dependent on ion channel functions and protein synthesis and is critical to ongoing spermatogenesis. The aim of this study was to investigate the mechanism of action associated with a non-metabolizable amino acid [14C]-MeAIB (alpha-(methyl-amino)isobutyric acid) accumulation stimulated by T4 and the role of the integrin receptor in this event, and also to clarify whether the T4 effect on MeAIB accumulation and on Ca2+ influx culminates in cell secretion.

METHODS

We have studied the rapid and plasma membrane initiated effects of T4 by using 45Ca2+ uptake and [45C]-MeAIB accumulation assays, respectively. Thymidine incorporation into DNA was used to monitor nuclear activity and quinacrine to analyze the secretory activity on SC.

RESULTS

The stimulation of MeAIB accumulation byT4 appears to be mediated by the integrin receptor in the plasma membrane since tetrac and RGD peptide were able to nullify the effect of this hormone. In addition, T4 increases extracellular Ca2+ uptake and Ca2+ from intracellular stocks to enhance nuclear activity, but this genomic action seems not to influence SC secretion mediated by T4. Also, the cytoskeleton and CIC-3 chloride channel contribute to the membrane-associated responses of SC.

CONCLUSIONS

T4 integrin receptor activation ultimately determines the plasma membrane responses on amino acid transport in SC, but it is not involved in calcium influx, cell secretion or the nuclear effect of the hormone.

GENERAL SIGNIFICANCE

The integrin receptor activation by T4 may take a role in plasma membrane processes involved in the male reproductive system.

Leptin increases HER2 protein levels through a STAT3-mediated up-regulation of Hsp90 in breast cancer cells

Obesity condition confers risks to breast cancer development and progression, and several reports indicate that the adipokine leptin, whose synthesis and plasma levels increase with obesity, might play an important role in modulating breast cancer cell phenotype. Functional crosstalk occurring between leptin and different signaling molecules contribute to breast carcinogenesis. In this study, we show, in different human breast cancer cell lines, that leptin enhanced the expression of a chaperone protein Hsp90 resulting in increased HER2 protein levels. Silencing of Hsp90 gene expression by RNA interference abrogated leptin-mediated HER2 up-regulation. Leptin effects were dependent on JAK2/STAT3 activation, since inhibition of this signaling cascade by AG490 or ectopic expression of a STAT3 dominant negative abrogated leptin-induced HER2 and Hsp90 expressions. Functional experiments showed that leptin treatment significantly up-regulated human Hsp90 promoter activity. This occurred through an enhanced STAT3 transcription factor binding to its specific responsive element located in the Hsp90 promoter region as revealed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Analysis of HER2, Akt and MAPK phosphorylation levels revealed that leptin treatment amplified the responsiveness of breast cancer cells to growth factor stimulation. Furthermore, we found that long-term leptin exposure reduced sensitivity of breast cancer cells to the antiestrogen tamoxifen. In the same experimental conditions, the combined treatment of tamoxifen with the Hsp90 inhibitor 17-AAG completely abrogated leptin-induced anchorage-independent breast cancer cell growth. In conclusion, our results highlight, for the first time, the ability of the adipocyte-secreted factor leptin to modulate Hsp90/HER2 expressions in breast cancer cells providing novel insights into the molecular mechanism linking obesity to breast cancer growth and progression.

Inhibition of Leydig tumor growth by farnesoid X receptor activation: the in vitro and in vivo basis for a novel therapeutic strategy

Leydig cell tumors (LCTs) are the most common tumors of the gonadal stroma and represent about 3% of all testicular neoplasms. In most cases, LCTs are benign; however, if the tumor is malignant, no effective treatments are currently available. We have recently reported that farnesoid X receptor (FXR) is expressed in R2C Leydig tumor cells, and it reduces the estrogen-dependent cell proliferation by negatively regulating aromatase expression. Here, we demonstrated that treatment with GW4064, a specific FXR agonist, markedly reduced Leydig tumor growth in vivo by inhibiting proliferation and inducing apoptosis. Indeed, the tumors from GW4064-treated mice exhibited a decrease in the expression of the proliferation marker Ki-67 and aromatase along with an increase in the apoptotic nuclei. FXR activation induced an enhanced poly(ADP-ribose) polymerase cleavage, a marked DNA fragmentation and a strong increase in TUNEL-positive R2C cells also in vitro. Moreover, in both in vivo and in vitro models, FXR ligands upregulated mRNA and protein levels of p53 and of its downstream effector p21(WAF1/Cip1) . Functional experiments showed that FXR ligands upregulated p53 promoter activity and this occurred through an increased binding of FXR/nuclear factor-kB (NF-kB) complex to the NF-kB site located within p53 promoter region as revealed by electrophoretic mobility shift assay and chromatin immunoprecipitation analysis. Taken together, results from our study show, for the first time, that treatment with FXR ligands induces Leydig tumor regression in vivo, suggesting that activation of FXR may represent a promising therapeutic strategy for LCTs.

Estrogen receptor beta (ERβ) produces autophagy and necroptosis in human seminoma cell line through the binding of the Sp1 on the phosphatase and tensin homolog deleted from chromosome 10 (PTEN) promoter gene

Testicular germ cell tumors are the most common tumor in male and the least studied. We focused on human seminoma using the TCAM2 cell line. Through ERβ, 10 nM estradiol (E2) was able to induce PTEN gene expression and promoter transactivation. Transient transfections, ChIP and EMSA assays evidenced the 5'-flanking region of PTEN gene promoter E2-responsive. The ERβ binding to the Sp1 on PTEN promoter decreased cell survival. The presence of ERβ or PTEN is necessary to induce the loss of cell survival upon E2, addressing their cooperation in this action. pAKT and AKT expression decreased under E2 and DPN, while known apoptotic markers appeared to be unchanged. The PI3K/AKT pathway inhibition also leads to autophagy: E2 and DPN enhanced the expression of autophagy-related markers such as PI3III, Beclin 1, AMBRA and UVRAG. MDC and TEM assays confirmed E2-induced autophagy. The absence of DNA fragmentation, caspase 9 and PARP1 cleavages suggested that necroptosis and/or parthanatos may occur. FACS analysis, LDH assay and RIP1 expression attested this hypothesis. Our study reveals a unique mechanism through which ERβ/PTEN signaling induces cell death in TCAM2 by autophagy and necroptosis. These data, supporting estrogen-dependency of human seminoma, propose ERβ ligands for therapeutic use in the treatment of this pathological condition.

Isolation and characterization of cyp19a1a and cyp19a1b promoters in the protogynous hermaphrodite orange-spotted grouper (Epinephelus coioides)

Aromatase (CYP19A1) catalyzes the conversion of androgens to estrogens. In teleosts, duplicated copies of cyp19a1 genes, namely cyp19a1a and cyp19a1b, were identified, however, the transcriptional regulation of these two genes remains poorly understood. In the present study, the 5'-flanking regions of the orange-spotted grouper cyp19a1a (gcyp19a1a) and cyp19a1b (gcyp19a1b) genes were isolated and characterized. The proximal promoter regions of both genes were relatively conserved when compared to those of the other teleosts. Notably, a conserved FOXO transcriptional factor binding site was firstly reported in the proximal promoter of gcyp19a1a, and deletion of the region (-112 to -60) containing this site significantly decreased the promoter activities. The deletion of the region (-246 to -112) containing the two conserved FTZ-F1 sites also dramatically decreased the transcriptional activities of gcyp19a1a promoter, and both two FTZ-F1 sites were shown to be stimulatory cis-acting elements. A FTZ-F1 homologue isolated from ricefield eel (eFTZ-F1) up-regulated gcyp19a1a promoter activities possibly via the FTZ-F1 sites, however, a previously identified orange-spotted grouper FTZ-F1 homologue (gFTZ-F1) did not activate the transcription of gcyp19a1a promoter unexpectedly. As to gcyp19a1b promoter, all the deletion constructs did not show good promoter activities in either TM4 or U251-MG cells. Estradiol (100nM) up-regulated gcyp19a1b promoter activities by about 13- and 36-fold in TM4 and U251-MG cells, respectively, via the conserved ERE motif, but did not stimulate gcyp19a1a promoter activities. These results are helpful to further elucidate the regulatory mechanisms of cyp19a1a and cyp19a1b expression in the orange-spotted grouper as well as other teleosts.

Teasing out the role of aromatase in the healthy and diseased testis

Scientific discoveries over the past decade have shifted the stereotypical view of androgens as male hormones and estrogens as female hormones. It is now recognized that a delicate balance of both androgens and estrogens, a process controlled by aromatase, is fundamental for normal testicular development and fertility. While the site-specific actions of these two classes of steroids within the testis are becoming better documented, the role and regulation of estrogen biosynthesis by aromatase within the testis remains unclear. The majority of data comes from a wide range of animal species, particularly genetically modified mouse models; aromatase knockout (ArKO) and overexpressing (AROM(+)), with limited information on humans, however the existence of congenital aromatase mutations has provided some insight into its effects on individual parameters of the testis. This review dissects out the localization and activity of aromatase in the healthy and diseased testis, addresses the cellular insult to the testis that occurs in its absence and over abundance and proposes potential molecular mechanisms of aromatase regulation in the testis.

The obesogen hypothesis: a shift of focus from the periphery to the hypothalamus

The obesogen concept proposes that environmental contaminants may be contributing to the epidemic of obesity and its related pathology, metabolic disorder. The first references to such a notion appeared at the beginning of the current decade, with the hypothesis that the correlation between increasing incidence of obesity and enhanced industrial chemical production was not simply coincidental, but potentially causally related. The next event was the introduction of the term "obesogen" as representing an environmental pollutant that adversely affects various aspects of adipose tissue functions. More recently, the concept was extended to include substances that may modify metabolic balance at the central, hypothalamic level. The actions of two prime candidate obesogens, tributyltin (TBT) and tetrabromobisphenol A (TBBPA), acting at the central level are the main focus of this review. Having discussed the evidence for contaminant accumulation in the environment and in human tissues and the potential mechanisms of action, data are provided showing that these two widespread pollutants modify hypothalamic gene regulations. Our studies are based on maternal exposure and measurement of effects in the progeny, mainly based on in vivo gene reporter assays. Such models are obviously pertinent to testing current hypotheses that propose that early exposure might exert effects on later development and physiological functions. The potential molecular mechanisms involved are discussed, as are the broader physiological consequences of these hypothalamic dysregulations.

The role of thyroid hormone in testicular development and function

Thyroid hormone is a critical regulator of growth, development, and metabolism in virtually all tissues, and altered thyroid status affects many organs and systems. Although for many years testis has been regarded as a thyroid hormone unresponsive organ, it is now evident that thyroid hormone plays an important role in testicular development and function. A considerable amount of data show that thyroid hormone influences steroidogenesis as well as spermatogenesis. The involvement of tri-iodothyronine (T(3)) in the control of Sertoli cell proliferation and functional maturation is widely accepted, as well as its role in postnatal Leydig cell differentiation and steroidogenesis. The presence of thyroid hormone receptors in testicular cells throughout development and in adulthood implies that T(3) may act directly on these cells to bring about its effects. Several recent studies have employed different methodologies and techniques in an attempt to understand the mechanisms underlying thyroid hormone effects on testicular cells. The current review aims at presenting an updated picture of the recent advances made regarding the role of thyroid hormones in male gonadal function.

Fas ligand expression in TM4 Sertoli cells is enhanced by estradiol "in situ" production

The testis is an immunologically privileged site of the body where Sertoli cells work on to favor local immune tolerance by testicular autoantigens segregation and immunosuppressive factors secretion. Fas/Fas Ligand (FasL) system, expressed prevalently in Sertoli cells, has been considered to be one of the central mechanisms in testis immunological homeostasis. In different cell lines it has been reported that the proapoptotic protein FasL is regulated by 17-beta estradiol (E2). Thus, using as experimental model mouse Sertoli cells TM4, which conserve a large spectrum of functional features present in native Sertoli cells, like aromatase activity, we investigated if estradiol "in situ" production may influence FasL expression. Our results demonstrate that an aromatizable androgen like androst-4-ene-3,17-dione (Delta4) enhanced FasL mRNA, protein content and promoter activity in TM4 cells. The treatment with N(6),2'-O-dibutyryladenosine-3'-5'-cyclic monophosphate [(Bu)(2)cAMP] (simulating FSH action), that is well known to stimulate aromatase activity in Sertoli cells, amplified Delta4 induced FasL expression. Functional studies of mutagenesis, electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays revealed that the Sp-1 motif on FasL promoter was required for E2 enhanced FasL expression in TM4 cells. These data let us to recruit FasL among those genes whose expression is up-regulated by E2 through a direct interaction of ERalpha with Sp-1 protein. Finally, evidence that an aromatizable androgen is able to increase FasL expression suggests that E2 production by aromatase activity may contribute to maintain the immunoprivilege status of Sertoli cells.

The Effects of Triiodothyronine on Rat Testis: A Morphometric and Immunohistochemical Study

The aim of present study was to investigate the effects of 3,3',5-triiodothyronine (T(3)) on rat testis both morphometrically and immunohistochemically with determining of insulin-like growth factor I (IGF-I) expression. Adult male Wistar-albino rats used in the study were divided into two groups; control and T(3)-treated groups. After T(3) treatment there was observed to be a decrease in testicular weights, diameters of seminiferous tubules and the number of sertoli cells, and an increase in the number of leydig cells (P<0.05). Some of the seminiferous tubule lumens of T(3) administrated rats had cellular debris. IGF-I was localized in sertoli cells, late spermatids and leydig cells of all groups. IGF-I immunoreactivity in T(3) treated rats was higher than in controls in all stages of the cycle of rat seminiferous epithelium, but the staining intensity of leydig cells were similar in both groups. In conclusion, the present results suggest that T(3) may modulate the testicular function by affecting IGF-I activity at the gonadal level.

Interactions between Prostaglandin E2, Liver Receptor Homologue-1, and Aromatase in Breast Cancer

Local synthesis of estrogens within breast adipose tissue by cytochrome P450 aromatase contributes to the growth of postmenopausal breast cancers. One of the major stimulators of aromatase expression in breast is prostaglandin E2 (PGE2) derived from tumorous epithelium and/or infiltrating macrophages. Recently, the orphan nuclear receptor, liver receptor homologue-1 (LRH-1), has also been shown to regulate aromatase expression in breast adipose tissue. We therefore examined the expression of, and correlations between, aromatase and LRH-1 mRNA in a panel of breast carcinoma tissues and adjacent adipose tissue. LRH-1 mRNA expression was low in normal breast tissue but markedly elevated in both breast carcinoma tissue and adipose tissue surrounding the tumor invasion (thereby paralleling aromatase expression). Laser capture microdissection localized the site of LRH-1 expression to tumor epithelial cells but not to intratumoral stromal cells. A strong correlation between LRH-1 and aromatase mRNA levels was observed in tumor-containing adipose tissue but not in tumor tissue. Ectopic expression of LRH-1 in primary human adipose stromal cells strongly activated endogenous aromatase mRNA expression and enzyme activity. Finally, treatment of adipose stromal cells with PGE2 induced expression of both LRH-1 and aromatase. We suggest that PGE2 derived from breast tumor tissue may increase aromatase expression in the surrounding adipose stroma in part by inducing LRH-1 in these cells. The roles of LRH-1 in breast cancer proliferation merit further study.

Differential expression of steroidogenic factor-1/adrenal 4 binding protein and liver receptor homolog-1 (LRH-1)/fetoprotein transcription factor in the rat testis: LRH-1 as a potential regulator of testicular aromatase expression

Aromatase converts testicular androgens to estrogens, which are essential for male fertility. Aromatase expression in testis occurs via transcription from promoter II, and requires the presence of a nuclear receptor half-site that binds the orphan receptor steroidogenic factor-1 [SF-1 (nuclear receptor 5A1)] to mediate basal and (in part) cAMP-induced transcription. We hypothesized that liver receptor homolog-1 (LRH-1) (nuclear receptor 5A2), a receptor closely related to SF-1, could also play a role in regulating aromatase expression in the testis. We demonstrate expression of LRH-1 in adult rat and immature mouse Leydig cells (LHR-1 > SF-1) as well as in pachytene spermatocytes and round spermatids but not in Sertoli cells, which in contrast, express high levels of SF-1. In transient transfection assays using TM3 Leydig cells and TM4 Sertoli cells, a rat promoter II luciferase reporter construct was stimulated by cotransfection of LRH-1 expression vector. Mutation analysis showed that induction by LRH-1 in TM3 and TM4 cells requires an AGGTCA motif at position -90, to which LRH-1 bound in gel shift analysis. We therefore provide evidence that LRH-1 plays an important role in the regulation of aromatase expression in Leydig cells. The colocalization of LRH-1 and aromatase to multiple testis cell types suggests that LRH-1 may have important effects on estrogen production, testis development, spermatogenesis, and testicular carcinogenesis.

Thyroid hormone, glucocorticoids, and prolactin at the nexus of physiology, reproduction, and toxicology

A symposium at the 2003 Annual Meeting of the Society of Toxicology brought together an expert group of endocrinologists to review how non-reproductive hormones can affect the endocrine system. This publication captures the essence of those presentations. Paul Cooke and Denise Holsberger recapitulate the evidence of how thyroid hormones affect male and female reproduction, and reproductive development. Ray Witorsch summarizes the many effects of glucocorticoids on the reproductive system. Finally, Paul Sylvester reviews the mechanism of action of prolactin, and reminds us that this ancient hormone has many functions beyond lactation.