Effects of tamoxifen on the sex determination gene and the activation of sex reversal in the developing gonad of mice

Sex blind: bridging the gap between drug exposure and sex-related gene expression in Danio rerio using next-generation sequencing (NGS) data and a literature review to find the missing links in pharmaceutical and environmental toxicology studies

The sex of both humans and Danio rerio has previously been shown to affect the way individuals respond to drug exposure. Genes which allow identification of sex in juvenile zebrafish show potential to reveal these confounding variables between sex in toxicological and preclinical trials but the link between these is so far missing. These sex-specific, early expressed genes where expression is not altered by drug exposure must be carefully selected for this purpose. We aimed to discover genes which can be used in pharmaceutical trials and environmental toxicology studies to uncover sex-related variations in gene expression with drug application using the model organism Danio rerio. Previously published early sex determining genes from King et al. were evaluated as well as additional genes selected from our zebrafish Next-generation sequencing (NGS) data which are known from previously published works not to be susceptible to changes in expression with drug exposure. NGS revealed a further ten female-specific genes (vtg1, cyp17a1, cyp19a1a, igf3, ftz-f1, gdf9, foxl2a, Nr0b1, ipo4, lhcgr) and five male related candidate genes (FKBP5, apobb1, hbaa1, dmrt1, spata6) which are also expressed in juvenile zebrafish, 28 days post fertilisation (dpf). Following this, a literature review was performed to classify which of these early-expressed sex specific genes are already known to be affected by drug exposure in order to determine candidate genes to be used in pharmaceutical trials or environmental toxicology testing studies. Discovery of these early sex-determining genes in Danio rerio will allow identification of sex-related responses to drug testing to improve sex-specific healthcare and the medical treatment of human patients.

Ovarian Reserve Disorders, Can We Prevent Them? A Review

The ovarian reserve is finite and begins declining from its peak at mid-gestation until only residual follicles remain as women approach menopause. Reduced ovarian reserve, or its extreme form, premature ovarian insufficiency, stems from multiple factors, including developmental, genetic, environmental exposures, autoimmune disease, or medical/surgical treatment. In many cases, the cause remains unknown and resulting infertility is not ultimately addressed by assisted reproductive technologies. Deciphering the mechanisms that underlie disorders of ovarian reserve could improve the outcomes for patients struggling with infertility, but these disorders are diverse and can be categorized in multiple ways. In this review, we will explore the topic from a perspective that emphasizes the prevention or mitigation of ovarian damage. The most desirable mode of fertoprotection is primary prevention (intervening before ablative influence occurs), as identifying toxic influences and deciphering the mechanisms by which they exert their effect can reduce or eliminate exposure and damage. Secondary prevention in the form of screening is not recommended broadly. Nevertheless, in some instances where a known genetic background exists in discrete families, screening is advised. As part of prenatal care, screening panels include some genetic diseases that can lead to infertility or subfertility. In these patients, early diagnosis could enable fertility preservation or changes in family-building plans. Finally, Tertiary Prevention (managing disease post-diagnosis) is critical. Reduced ovarian reserve has a major influence on physiology beyond fertility, including delayed/absent puberty or premature menopause. In these instances, proper diagnosis and medical therapy can reduce adverse effects. Here, we elaborate on these modes of prevention as well as proposed mechanisms that underlie ovarian reserve disorders.

Systematic review of prenatal exposure to endocrine disrupting chemicals and autism spectrum disorder in offspring

LAY ABSTRACT

Autism spectrum disorders comprise a complex group with many subtypes of behaviorally defined neurodevelopmental abnormalities in two core areas: deficits in social communication and fixated, restricted, repetitive, or stereotyped behaviors and interests each with potential unique risk factors and characteristics. The underlying mechanisms and the possible causes of autism spectrum disorder remain elusive and while increased prevalence is undoubtable, it is unclear if it is a reflection of diagnostic improvement or emerging risk factors such as endocrine disrupting chemicals. Epidemiological studies, which are used to study the relation between endocrine disrupting chemicals and autism spectrum disorder, can have inherent methodological challenges that limit the quality and strength of their findings. The objective of this work is to systematically review the treatment of these challenges and assess the quality and strength of the findings in the currently available literature. The overall quality and strength were "moderate" and "limited," respectively. Risk of bias due to the exclusion of potential confounding factors and the lack of accuracy of exposure assessment methods were the most prevalent. The omnipresence of endocrine disrupting chemicals and the biological plausibility of the association between prenatal exposure and later development of autism spectrum disorder highlight the need to carry out well-designed epidemiological studies that overcome the methodological challenges observed in the currently available literature in order to be able to inform public policy to prevent exposure to these potentially harmful chemicals and aid in the establishment of predictor variables to facilitate early diagnosis of autism spectrum disorder and improve long-term outcomes.

Chlorogenic acid co-administration abates tamoxifen-mediated reproductive toxicities in male rats: An experimental approach

Reports over the years have demonstrated toxic side effect-including reproductive toxicity- of tamoxifen (TAM), a drug of choice in the management of primary breast cancer. Chlorogenic acid (CGA), a dietary polyphenol, reportedly elicits beneficial pharmacological effects. However, the impact of CGA on TAM-associated reproductive toxicity is absent in the literature. We, therefore, experimented on CGA's effect and TAM-mediated reproductive toxicity in rats. Cohorts of rats were treated with TAM (50 mg/kg) or co-treated with CGA (25 or 50 mg/kg) for 14 consecutive days. The result showed that treatment of CGA significantly increases testosterone, LH, and FSH levels compared to the TAM group. However, prolactin level was markedly decreased after pretreatment of CGA in TAM-treated rats. CGA abated TAM-induced decreases acid phosphatase, alkaline phosphatase, and antioxidant enzymes in the testis. CGA alleviated TAM-facilitated surges of reactive oxygen and nitrogen species, myeloperoxidase, nitric oxide, interleukin-1β, and tumor necrosis factor-alpha in rats epididymis and testes. Additionally, CGA increased anti-inflammatory cytokine -interleukin-10-, suppressed caspase-3 activity, and reduced pathological lesions in the examined organs of rats co-treated with CGA and TAM. CGA phytoprotective effect improved reproductive function occasioned by TAM-mediated toxicities in rats, by abating oxido-inflammatory damages and downregulating apoptotic responses. PRACTICAL APPLICATIONS: CGA protects against the damaging oxido-inflammatory responses incumbent on TAM metabolism. As an antioxidant abundant in plant-derived foods, CGA reportedly protects against inflammatory damage, hypertension, and neurodegenerative diseases. We present evidence that CGA ameliorates TAM-induced reproductive dysfunction by suppressing oxidative and inflammation stress downregulate apoptosis and improve reproductive function biomarker in rats.

Mast4 knockout shows the regulation of spermatogonial stem cell self-renewal via the FGF2/ERM pathway

Spermatogenesis is an important cellular differentiation process that produces the male gametes and remains active throughout the individual's lifespan. Sertoli cell-only syndrome (SCO) refers to the dysfunction of the male reproductive system, including infertility. Accurate self-renewal of spermatogonial stem cells (SSCs) is essential to prevent SCO syndrome. This study investigated the role of microtubule-associated serine/threonine kinase family member 4 (MAST4) in spermatogenesis in mice. MAST4 was localized in Sertoli cells before puberty, providing a somatic niche for spermatogenesis in mice and MAST4 expression shifted to Leydig cells and spermatids throughout puberty. Mast4 knockout (KO) testes were reduced in size compared to wild-type testes, and germ cell depletion associated with an increase in apoptosis and subsequent loss of tubular structure were similar to the SCO phenotype. In addition, MAST4 phosphorylated the Ets-related molecule (ERM), specifically the serine 367 residue. The phosphorylation of ERM ultimately controls the transcription of ERM target genes related to SSC self-renewal. The expression of spermatogenesis-associated proteins was significantly decreased whereas Sertoli cell markers were increased in Mast4 KO testes, which was well-founded by RNA-sequencing analysis. Therefore, MAST4 is associated with the fibroblast growth factor 2 (FGF2)/ERM pathway and this association helps us explore the capacity of SSCs to maintain a vertebrate stem cell niche.

Characteristics and sex dimorphism of 17β-hydroxysteroid dehydrogenase family genes in the olive flounder Paralichthys olivaceus

Sex steroid hormones play important roles in fish sex differentiation, gonadal development and secondary sexual characteristics. Olive flounder Paralichthys olivaceus is a valuable commercial marine fish species and has marked sexual dimorphism. However, the mechanisms of action of sex hormones in flounder sex are still unclear. In this study, a total of ten Hsd17b family genes, including Hsd17b3, -4, -7, -8, -9, -10, -12a, -12b, -14 and -15, were identified in the flounder, which encoded critical enzymes acting on sex steroid synthesis and metabolism. Hsd17b genes were distributed on eight chromosomes. Hsd17b12a and -12b were located on chromosomes 19 and 7, respectively. It was speculated that these two genes were just highly similar rather than different transcripts derived from the same gene. According to the results of domain and motif analyses, they all belonged to the SDR superfamily and contained conserved Hsd17b motifs TGxxxGxG, PGxxxT, NNAG and YxxxK. Analysis of amino acid sequences predicted that Hsd17b1, -4, -7, -12a and -14 were hydrophilic proteins. The stability of Hsd17b1, -3 and -12b proteins was predicted to be low. The various Hsd17b family genes differed in tissue expression pattern, and Hsd17b10, -12a and -12b were highly expressed in the flounder ovary. Moreover, throughout gonadal development, Hsd17b3 was highly expressed in the testis, and Hsd17b1, -12a and -12b were highly expressed in the ovary, suggesting that they might play an important role in testosterone synthesis in the testis or estrogen synthesis in the ovary. Activities of Hsd17b3 at stages I-V were all significantly higher in the testis than in the ovary (P < 0.05, P < 0.01). Transfection analysis in HEK293T cells showed that Hsd17b1 and -3 were located in both the cytoplasm and nucleus. Additionally, after challenging fish with tamoxifen, Hsd17b3 expression level in the testis decreased significantly (P < 0.01), and in the ovary no significant change was observed. Moreover, the expression of Hsd17b1 in the ovary was significantly upregulated after injection with flutamide (P < 0.05). These findings introduce the characteristics of the flounder Hsd17b in subfamily, which contribute to our understanding of the regulation of sex steroid hormone synthesis in fish gonadal development.

Effects of estrogens and antiestrogens on gonadal sex differentiation and embryonic development in the domestic fowl (Gallus gallus domesticus)

Since it is known that environmental contaminants have the potential to cause endocrine disorders in humans and animals, there is an urgent need for in vivo tests to assess possible effects of these endocrine disrupting chemicals (EDCs). Although there is no standardized guideline, the avian embryo has proven to be particularly promising as it responds sensitively to a number of EDCs preferentially impacting the reproductive axis. In the present study we examined the effects of in ovo exposure to fulvestrant and tamoxifen as antiestrogenic model compounds and co-exposure to both substances and the potent estrogen 17α-ethinylestradiol (EE₂) regarding sex differentiation and embryonic development of the domestic fowl (Gallus gallus domesticus). The substances were injected into the yolk of fertilized eggs on embryonic day 1. On embryonic day 19 sex genotype and phenotype were determined, followed by gross morphological and histological examination of the gonads. Sole EE₂-treatment (20 ng/g egg) particularly affected male gonads and resulted in an increased formation of female-like gonadal cortex tissue and a reduction of seminiferous tubules. In ovo exposure to tamoxifen (0.1/1/10 µg/g egg) strongly impaired the differentiation of female gonads, led to a significant size reduction of the left ovary and induced malformations of the ovarian cortex, while fulvestrant (0.1/1/10 µg/g egg) did not affect sexual differentiation. However, both antiestrogens were able to antagonize the feminizing effects of EE₂in genetic males when administered simultaneously. Since both estrogens and antiestrogens induce concentration-dependent morphological alterations of the sex organs, the chick embryo can be regarded as a promising model for the identification of chemicals with estrogenic and antiestrogenic activity.

Environmental influences on ovarian dysgenesis - developmental windows sensitive to chemical exposures

A woman's reproductive health and ability to have children directly affect numerous aspects of her life, from personal well-being and socioeconomic standing, to morbidity and lifespan. In turn, reproductive health depends on the development of correctly functioning ovaries, a process that starts early during fetal life. Early disruption to ovarian programming can have long-lasting consequences, potentially manifesting as disease much later in adulthood. A growing body of evidence suggests that exposure to chemicals early in life, including endocrine-disrupting chemicals, can cause a range of disorders later in life, such as those described in the ovarian dysgenesis syndrome hypothesis. In this Review, we discuss four specific time windows during which the ovary is particularly sensitive to disruption by exogenous insults: gonadal sex determination, meiotic division, follicle assembly and the first wave of follicle recruitment. To date, most evidence points towards the germ cell lineage being the most vulnerable to chemical exposure, particularly meiotic division and follicle assembly. Environmental chemicals and pharmaceuticals, such as bisphenols or mild analgesics (including paracetamol), can also affect the somatic cell lineages. This Review summarizes our current knowledge pertaining to environmental chemicals and pharmaceuticals, and their potential contributions to the development of ovarian dysgenesis syndrome. We also highlight knowledge gaps that need addressing to safeguard female reproductive health.

A network-based method for the identification of putative genes related to infertility

BACKGROUND

Infertility has become one of the major health problems worldwide, with its incidence having risen markedly in recent decades. There is an urgent need to investigate the pathological mechanisms behind infertility and to design effective treatments. However, this is made difficult by the fact that various biological factors have been identified to be related to infertility, including genetic factors.

METHODS

A network-based method was established to identify new genes potentially related to infertility. A network constructed using human protein-protein interactions based on previously validated infertility-related genes enabled the identification of some novel candidate genes. These genes were then filtered by a permutation test and their functional and structural associations with infertility-related genes.

RESULTS

Our method identified 23 novel genes, which have strong functional and structural associations with previously validated infertility-related genes.

CONCLUSIONS

Substantial evidence indicates that the identified genes are strongly related to dysfunction of the four main biological processes of fertility: reproductive development and physiology, gametogenesis, meiosis and recombination, and hormone regulation.

GENERAL SIGNIFICANCE

The newly discovered genes may provide new directions for investigating infertility. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Di(2-Ethylhexyl) Phthalate Exposure In Utero Damages Sertoli Cell Differentiation Via Disturbance of Sex Determination Pathway in Fetal and Postnatal Mice

Mice may share similar mechanism with human underlying reproductive toxicity induced by di(2-ethylhexyl) phthalate (DEHP), which is not supposed to be associated with decreased testicular testosterone. Pregnant mice were exposed to DEHP by gavage, with the dosage regime beginning at human relevant exposure level. After in utero DEHP exposure, loss of Sertoli cells and germ cells were observed in the male pups at postnatal days 21. And SRY-related HMG box 9 (SOX9), Fibroblast growth factor-9 (FGF9), and Double-sex and Mab-3 related transcripttion factor 1 (DMRT1) proteins were significantly downregulated by DEHP at 2 mg/kg/d and above, suggesting the depression of Sertoli cell differentiation. The repression of Sox9 genes expression was supported by whole-mount in situ hybridization and real-time real-time-quantitative PCR. The expressions of Cyp11α1 and Star were not significantly affected by in utero DEHP exposure, indicating the absence of effects on testosterone biosynthesis. Furthermore, the testosterone-independent pathway regulating Sertoli cells differentiation was disturbed in fetus by DEHP at 2 mg/kg/d and above during the critical time window of sex determination, involving Gadd45g → Gata4/Fog2 → Sry → Sox9 → Fgf9 The results suggest that in utero DEHP exposure damaged Sertoli cells in the postnatal life of mice offspring via disturbance of the differentiation regulating pathway, potentially inducing declines in spermatogenesis.

Paroxetine exposure skews litter sex ratios in mice suggesting a Trivers-Willard process

While conducting a toxicity assessment of the antidepressant paroxetine (Paxil®), in wild-derived mice (Mus musculus), we observed that exposed dams (P₀) produced female biased litters (32:68 M:F). Though numerous experimental manipulations have induced sex ratio bias in mice, none have assessed the fitness of the offspring from these litters relative to controls. Here, we retrospectively analyze experimentally derived fitness data gathered for the purpose of toxicological assessment in light of 2 leading hypothesis (Trivers-Willard hypothesis [TWH] and cost of reproduction hypothesis [CRH]), seeking to test if this facultative sex ratio adjustment fits into an adaptive framework. Control F₁ males were heavier than F₁ females, but no differences in mass were detected between exposed F₁ males and females, suggesting that exposed dams did not save energy by producing fewer males, despite producing 29.2% lighter litters relative to controls. F₁ offspring of both treatments were released into seminatural enclosures where fitness was quantified. In enclosures, the relative reproductive success of F₁-exposed males (compared with controls) was reduced by ~20% compared with the relative reproductive success of F₁-exposed females. Thus, exposed dams increased their fitness by adjusting litters toward females who were less negatively affected by the exposure than males. Collectively, these data provide less support that the observed sex ratio bias results in energetic savings (CRH), and more support for the TWH because fitness was increased by biasing litters toward female offspring. These mammalian data are unique in their ability to support the TWH through the use of relevant fitness data.

Effects of tamoxifen on autosomal genes regulating ovary maintenance in adult mice

Environmental endocrine-disrupting chemicals (EDCs), known to bind to estrogen/androgen receptors and mimic native estrogens, have been implicated as a main source for increasing human reproductive and developmental deficiencies and diseases. Tamoxifen (TAM) is one of the most well-known antiestrogens with defined adverse effects on the female reproductive tract, but the mechanisms related to autosomal gene regulation governing ovary maintenance in mammals remain unclear. The expression pattern and levels of key genes and proteins involved in maintaining the ovarian phenotype in mice were analyzed. The results showed that TAM induced significant upregulation of Sox9, which is the testis-determining factor gene. The results showed that TAM induced significant upregulation of Sox9, the testis-determining factor gene, and the expression level of Sox9 mRNA in the ovaries of mice exposed to 75 or 225 mg/kg bw TAM was 2- and 10-fold that in the control group, respectively (p < 0.001). Furthermore, the testicular fibroblast growth factor gene, Fgf9, was also elevated in TAM-treated ovaries. Accordingly, expression of the ovary development marker, forkhead transcription factor (FOXL2), and WNT4/FST signaling, were depressed. The levels of protein expression changed consistently with the target genes. Moreover, the detection of platelet/endothelial cell adhesion molecule 1 (PECAM-1) in TAM-treated ovaries suggested the formation of vascular endothelial cells, which is a further evidence for the differentiation of the ovaries to a testis-like phenotype. During this period, the level of 17β-estradiol, progesterone, and luteinizing hormone decreased, while that of testosterone increased by 3.3-fold (p = 0.013). The activation of a testis-specific molecular signaling cascade was a potentially important mechanism contributing to the gender disorder induced by TAM, which resulted in the differentiation of the ovaries to a testis-like phenotype in adult mice. Limited with a relatively higher exposure, the present study provided preliminary molecular insights into the sexual disorder induced by antiestrogens and compounds that interrupted estrogen signaling by other modes of action.