GnRH pulse frequency differentially regulates steroidogenic factor 1 (SF1), dosage-sensitive sex reversal-AHC critical region on the X chromosome gene 1 (DAX1), and serum response factor (SRF): potential mechanism for GnRH pulse frequency regulation of LH beta transcription in the rat

Intermittent fasting ameliorates di-(2-ethylhexyl) phthalate-induced precocious puberty in female rats: A study of the hypothalamic-pituitary-gonadal axis

Di-(2-ethylhexyl) phthalate has been reported to interfere with the development and function of animal reproductive systems. However, hardly any studies provide methods to minimize or prevent the adverse effects of DEHP on reproduction. The energy balance state of mammals is closely related to reproductive activities, and the reproductive axis can regulate reproductive activities according to changes in the body's energy balance state. In this study, the effects of every other day fasting (EODF), as a way of intermittent fasting, on preventing the precocious puberty induced by DEHP in female rats was studied. EODF significantly improved the advancement of vaginal opening age (as the markers of puberty onset) and elevated serum levels of luteinizing hormone and estradiol (detected by ELISA) induced by 5 mg kg^-1 DEHP exposure (D5). The mRNA and western blot results showed that the EODF could minimized the increase of gonadotropin-releasing hormone expression induced by DEHP exposure. The administration of DEHP could elevate the levels of kisspeptin protein and the number of kisspeptin-immunoreactive neurons in anteroventral periventricular nucleu, and this increase was diminished considerably by EODF treatment. In contrast, the D5 and D0 groups showed no remarkable difference in the level of Kiss1 expression in arcuate nucleus, whereas the D5 + EODF group had a remarkable decrease in kisspeptin expression as compared with the other two groups. Our results indicated that EODF might inhibit the acceleration of puberty onset induced by DEHP exposure via HPG axis.

Opposite effects of high- and low-dose di-(2-ethylhexyl) phthalate (DEHP) exposure on puberty onset, oestrous cycle regularity and hypothalamic kisspeptin expression in female rats

Di-(2-ethylhexyl) phthalate (DEHP) is ubiquitous in the environment and has been proposed to lead to reproductive disruption. In this study, we systematically investigated the effects of different doses of DEHP exposure on female hypothalamic-pituitary-gonadal axis development. Female Sprague-Dawley rats were gavaged with vehicle (corn oil) or DEHP (5 or 500mgkg-1 day-1) during postnatal Days (PNDs) 22-28 or PNDs 22-70. Results demonstrated that the low and high doses of DEHP exerted opposite effects on puberty onset, circulating luteinising hormone, serum oestradiol and progesterone levels, with the low dose (5mgkg-1) promoting and the high dose (500mgkg-1) inhibiting these parameters. Significant dose-related differences were also found in the D500 group with longer oestrous cycle duration, lower ovarian/bodyweight ratio, fewer corpus lutea and more abnormal ovarian stromal tissue in comparison with the oil or D5 groups. Molecular data showed that the hypothalamic Kiss1 mRNA expression in the anteroventral periventricular but not in the arcuate nucleus significantly decreased in the D500 rats and increased in the D5 rats relative to the rats in the oil group. These findings suggested that the kisspeptin system is a potential target for DEHP to disrupt reproductive development and function.

Gestational chronodisruption leads to persistent changes in the rat fetal and adult adrenal clock and function

KEY POINTS

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Here we explored the developmental impact of gestational chronodisruption (chronic photoperiod shift, CPS) on adult and fetal adrenal biorhythms and function. We found that gestational chronodisruption altered fetal and adult adrenal function, at the molecular, morphological and physiological levels. The differences between control and CPS offspring suggest desynchronization of the adrenal circadian clock and steroidogenic pathway, leading to abnormal stress responses and metabolic adaptation, potentially increasing the risk of developing chronic diseases.

ABSTRACT

Light at night is essential to a 24/7 society, but it has negative consequences on health. Basically, light at night induces an alteration of our biological clocks, known as chronodisruption, with effects even when this occurs during pregnancy. Indeed, an abnormal photoperiod during gestation alters fetal development, inducing long-term effects on the offspring. Accordingly, we carried out a longitudinal study in rats, exploring the impact of gestational chronodisruption on the adrenal biorhythms and function of the offspring. Adult rats (90 days old) gestated under chronic photoperiod shift (CPS) decrease the time spent in the open arm zone of an elevated plus maze to 62% and increase the rearing time to 170%. CPS adults maintained individual daily changes in corticosterone, but their acrophases were distributed from 12.00 h to 06.00 h. CPS offspring maintained clock gene expression and oscillation, nevertheless no daily rhythm was observed in genes involved in the regulation and synthesis of steroids. Consistent with adult adrenal gland being programmed during fetal life, blunted daily rhythms of corticosterone, core clock gene machinery, and steroidogenic genes were observed in CPS fetal adrenal glands. Comparisons of the global transcriptome of CPS versus control fetal adrenal gland revealed that 1078 genes were differentially expressed (641 down-regulated and 437 up-regulated). In silico analysis revealed significant changes in Lipid Metabolism, Small Molecule Biochemistry, Cellular Development and the Inflammatory Response pathway (z score: 48-20). Altogether, the present results demonstrate that gestational chronodisruption changed fetal and adult adrenal function. This could translate to long-term abnormal stress responses and metabolic adaptation, increasing the risk of developing chronic diseases.

Regulation of reproduction via tight control of gonadotropin hormone levels

Mammalian reproduction is controlled by the hypothalamic-pituitary-gonadal axis. GnRH from the hypothalamus regulates synthesis and secretion of gonadotropins, LH and FSH, which then control steroidogenesis and gametogenesis. In females, serum LH and FSH levels exhibit rhythmic changes throughout the menstrual or estrous cycle that are correlated with pulse frequency of GnRH. Lack of gonadotropins leads to infertility or amenorrhea. Dysfunctions in the tightly controlled ratio due to levels slightly outside the normal range occur in a larger number of women and are correlated with polycystic ovaries and premature ovarian failure. Since the etiology of these disorders is largely unknown, studies in cell and mouse models may provide novel candidates for investigations in human population. Hence, understanding the mechanisms whereby GnRH regulates gonadotropin hormone levels will provide insight into the physiology and pathophysiology of the reproductive system. This review discusses recent advances in our understanding of GnRH regulation of gonadotropin synthesis.

Maternal Vitamin D Deficiency Programs Reproductive Dysfunction in Female Mice Offspring Through Adverse Effects on the Neuroendocrine Axis

Vitamin D (VitD) deficiency affects more than 1 billion people worldwide with a higher prevalence in reproductive-aged women and children. The physiological effects of maternal VitD deficiency on the reproductive health of the offspring has not been studied. To determine whether maternal VitD deficiency affects reproductive physiology in female offspring, we monitored the reproductive physiology of C57BL/6J female offspring exposed to diet-induced maternal VitD deficiency at three specific developmental stages: 1) in utero, 2) preweaning, or 3) in utero and preweaning. We hypothesized that exposure to maternal VitD deficiency disrupts reproductive function in exposed female offspring. To test this hypothesis, we assessed vaginal opening and cytology and ovary and pituitary function as well as gonadotropin and gonadal steroid levels in female offspring. The in utero, preweaning, and in utero and preweaning VitD deficiency did not affect puberty. However, all female mice exposed to maternal VitD deficiency developed prolonged and irregular estrous cycles characterized by oligoovulation and extended periods of diestrus. Despite similar gonadal steroid levels and GnRH neuron density, females exposed to maternal VitD deficiency released less LH on the evening of proestrus. When compared with control female offspring, there was no significant difference in the ability of females exposed to maternal VitD deficiency to respond robustly to exogenous GnRH peptide or controlled ovarian hyperstimulation. These findings suggest that maternal VitD deficiency programs reproductive dysfunction in adult female offspring through adverse effects on hypothalamic function.

In vivo oestrogenic modulation of Egr1 and Pitx1 gene expression in female rat pituitary gland

EGR1 and PITX1 are transcription factors required for gonadotroph cell Lhb promoter activation. To determine changes in Egr1 and Pitx1 mRNA levels in central and peripheral pituitary stimulations, an in vivo model based on i.c.v. pulsatile (1 pulse/0.5 h over 2 h) GnRH agonist (1.5 nM buserelin) or antagonist (2 nM antide) microinjections was used. The microinjections were given to ovariectomised and 17β-oestradiol (E2) (3×20 μg), ERA (ESR1) agonist propyl pyrazole triol (PPT) (3×0.5 mg), ERB (ESR2) agonist diarylpropionitrile (DPN) (3×0.5 mg) s.c. pre-treated rats 30 min after last pulse anterior pituitaries were excised. Relative mRNA expression was determined by quantitative RT-PCR (qRT-PCR). Results revealed a gene-specific response for GnRH and/or oestrogenic stimulations in vivo. Buserelin pulses enhanced Egr1 expression by 66% in ovariectomised rats, whereas the oestradiol-supplemented+i.c.v. NaCl-microinjected group showed a 50% increase in Egr1 mRNA expression. The oestrogenic signal was transmitted via ERA (ESR1) and ERB (ESR2) activation as administration of PPT and DPN resulted in 97 and 62%, respectively, elevation in Egr1 mRNA expression. A synergistic action of GnRH agonist and 17β-oestradiol (E2) stimulation of the Egr1 gene transcription in vivo were found. GnRHR activity did not affect Pitx1 mRNA expression; regardless of NaCl, buserelin or antide i.c.v. pulses, s.c. oestrogenic supplementation (with E2, PPT or DPN) consistently decreased (by -46, -48 and -41% respectively) the Pitx1 mRNA in the anterior pituitary gland. Orchestrated Egr1 and Pitx1 activities depending on specific central and peripheral regulatory inputs could be responsible for physiologically variable Lhb gene promoter activation in vivo.

Polyribosome and ribonucleoprotein complex redistribution of mRNA induced by GnRH involves both EIF2AK3 and MAPK signaling

The neuropeptide gonadotropin-releasing hormone stimulates synthesis and secretion of the glycoprotein gonadotropic hormones and activates the unfolded protein response, which causes a transient reduction of endoplasmic reticulum-associated mRNA translation. Hormone-treated cell extracts were fractionated to resolve mRNA in active polyribosomes from mRNA in inactive complexes. Quantitative real-time PCR and expression array analysis were used to determine hormone-induced redistribution of mRNAs between fractions and individual mRNAs were found to be redistributed differentially. Among the affected mRNAs relevant to gonadotropin synthesis, the luteinizing hormone subunit genes Lhb and Cga were enriched in the ribonucleoprotein pool. The MAP kinase phosphatase Dusp1 was enriched in the polyribosome pool. Enrichment of Dusp1 mRNA in the polyribosome pool was independent of the unfolded protein response, sensitive to ERK inhibition, and dependent on the 3'untranslated region. The results show that GnRH exerts translational control to modulate physiologically relevant gene expression through two distinct signaling pathways.

Constant light disrupts the circadian rhythm of steroidogenic proteins in the rat adrenal gland

The circadian rhythm of corticosterone (CORT) secretion from the adrenal cortex is regulated by the suprachiasmatic nucleus (SCN), which is entrained to the light-dark cycle. Since the circadian CORT rhythm is associated with circadian expression of the steroidogenic acute regulatory (StAR) protein, we investigated the 24h pattern of hormonal secretion (ACTH and CORT), steroidogenic gene expression (StAR, SF-1, DAX1 and Nurr77) and the expression of genes involved in ACTH signalling (MC2R and MRAP) in rats entrained to a normal light-dark cycle. We found that circadian changes in ACTH and CORT were associated with the circadian expression of all gene targets; with SF-1, Nurr77 and MRAP peaking in the evening, and DAX1 and MC2R peaking in the morning. Since disruption of normal SCN activity by exposure to constant light abolishes the circadian rhythm of CORT in the rat, we also investigated whether the AM-PM variation of our target genes was also disrupted in rats exposed to constant light conditions for 5weeks. We found that the disruption of the AM-PM variation of ACTH and CORT secretion in rats exposed to constant light was accompanied by a loss of AM-PM variation in StAR, SF-1 and DAX1, and a reversed AM-PM variation in Nurr77, MC2R and MRAP. Our data suggest that circadian expression of StAR is regulated by the circadian expression of nuclear receptors and proteins involved in both ACTH signalling and StAR transcription. We propose that ACTH regulates the secretion of CORT via the circadian control of steroidogenic gene pathways that become dysregulated under the influence of constant light.