Clocks underneath: the role of peripheral clocks in the timing of female reproductive physiology

The Circadian Clock, Nutritional Signals and Reproduction: A Close Relationship

The circadian rhythm, which is necessary for reproduction, is controlled by clock genes. In the mouse uterus, the oscillation of the circadian clock gene has been observed. The transcription of the core clock gene period (Per) and cryptochrome (Cry) is activated by the heterodimer of the transcription factor circadian locomotor output cycles kaput (Clock) and brain and muscle Arnt-like protein-1 (Bmal1). By binding to E-box sequences in the promoters of Per1/2 and Cry1/2 genes, the CLOCK-BMAL1 heterodimer promotes the transcription of these genes. Per1/2 and Cry1/2 form a complex with the Clock/Bmal1 heterodimer and inactivate its transcriptional activities. Endometrial BMAL1 expression levels are lower in human recurrent-miscarriage sufferers. Additionally, it was shown that the presence of BMAL1-depleted decidual cells prevents trophoblast invasion, highlighting the importance of the endometrial clock throughout pregnancy. It is widely known that hormone synthesis is disturbed and sterility develops in Bmal1-deficient mice. Recently, we discovered that animals with uterus-specific Bmal1 loss also had poor placental development, and these mice also had intrauterine fetal death. Furthermore, it was shown that time-restricted feeding controlled the uterine clock's circadian rhythm. The uterine clock system may be a possibility for pregnancy complications, according to these results. We summarize the most recent research on the close connection between the circadian clock and reproduction in this review.

Derailed peripheral circadian genes in polycystic ovary syndrome patients alters peripheral conversion of androgens synthesis

STUDY QUESTION

Do circadian genes exhibit an altered profile in peripheral blood mononuclear cells (PBMCs) of polycystic ovary syndrome (PCOS) patients and do they have a potential role in androgen excess?

SUMMARY ANSWER

Our findings revealed that an impaired circadian clock could hamper the regulation of peripheral steroid metabolism in PCOS women.

WHAT IS KNOWN ALREADY

PCOS patients exhibit features of metabolic syndrome. Circadian rhythm disruption is involved in the development of metabolic diseases and subfertility. An association between shift work and the incidence of PCOS in females was recently reported.

STUDY DESIGN, SIZE, DURATION

This is a retrospective case-referent study in which peripheral blood samples were obtained from 101 control and 101 PCOS subjects. PCOS diagnoses were based on Rotterdam Consensus criteria.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study comprised 101 women with PCOS and 101 control volunteers, as well as Swiss albino mice treated with dehydroepiandrosterone (DHEA) to induce PCOS development. Gene expression analyses of circadian and steroidogenesis genes in human PBMC and mice ovaries and blood were executed by quantitative real-time PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed aberrant expression of peripheral circadian clock genes in PCOS, with a significant reduction in the core clock genes, circadian locomotor output cycles kaput (CLOCK) (P ≤ 0.00001), brain and muscle ARNT-like 1 (BMAL1) (P ≤ 0.00001) and NPAS2 (P ≤ 0.001), and upregulation of their negative feedback loop genes, CRY1 (P ≤ 0.00003), CRY2 (P ≤ 0.00006), PER1 (P ≤ 0.003), PER2 (P ≤ 0.002), DEC1 (P ≤ 0.0001) and DEC2 (P ≤ 0.00005). Transcript levels of an additional feedback loop regulating BMAL1 showed varied expression, with reduced RORA (P ≤ 0.008) and increased NR1D1 (P ≤ 0.02) in PCOS patients in comparison with the control group. We also demonstrated the expression pattern of clock genes in PBMCs of PCOS women at three different time points. PCOS patients also exhibited increased mRNA levels of steroidogenic enzymes like StAR (P ≤ 0.0005), CYP17A1 (P ≤ 0.005), SRD5A1 (P ≤ 0.00006) and SRD5A2 (P ≤ 0.009). Knockdown of CLOCK/BMAL1 in PBMCs resulted in a significant reduction in estradiol production, by reducing CYP19A1 and a significant increase in dihydrotestosterone production, by upregulating SRD5A1 and SRD5A2 in PBMCs. Our data also showed that CYP17A1 as a direct CLOCK-BMAL1 target in PBMCs. Phenotypic classification of PCOS subgroups showed a higher variation in expression of clock genes and steroidogenesis genes with phenotype A of PCOS. In alignment with the above results, altered expression of ovarian core clock genes (Clock, Bmal1 and Per2) was found in DHEA-treated PCOS mice. The expression of peripheral blood core clock genes in DHEA-induced PCOS mice was less robust and showed a loss of periodicity in comparison with that of control mice.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

We could not evaluate the circadian oscillation of clock genes and clock-controlled genes over a 24-h period in the peripheral blood of control versus PCOS subjects. Additionally, circadian genes in the ovaries of PCOS women could not be evaluated due to limitations in sample availability, hence we employed the androgen excess mouse model of PCOS for ovarian circadian assessment. Clock genes were assessed in the whole ovary of the androgen excess mouse model of PCOS rather than in granulosa cells, which is another limitation of the present work.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations suggest that the biological clock is one of the contributing factors in androgen excess in PCOS, owing to its potential role in modulating peripheral androgen metabolism. Considering the increasing prevalence of PCOS and the rising frequency of delayed circadian rhythms and insufficient sleep among women, our study emphasizes the potential in modulating circadian rhythm as an important strategy in PCOS management, and further research on this aspect is highly warranted.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the RGCB-DBT Core Funds and a grant (#BT/PR29996/MED/97/472/2020) from the Department of Biotechnology (DBT), India, to M.L. B.S.J. was supported by a DST/INSPIRE Fellowship/2015/IF150361 and M.B.K. was supported by the Research Fellowship from Council of Scientific & Industrial Research (CSIR) (10.2(5)/2007(ii).E.U.II). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Physiological effects of food availability times in higher vertebrates

Food availability is a crucial ecological determinant of population size and community structure, and controls various life-history traits in most, if not all, species. Food availability is not constant; there are daily and seasonal differences in food abundance. When coupled to appetite (urge to eat), this is expressed as the eating schedule of a species. Food availability times affect daily and seasonal physiology and behaviour of organisms both directly (by affecting metabolic homeostasis) and indirectly (by altering synchronization of endogenous rhythms). Restricted food availability times may, for example, constrain reproductive output by limiting the number or quality of offspring or the number of reproductive attempts, as has been observed for nesting frequency in birds. Consuming food at the wrong time of day reduces the reproductive ability of a seasonal breeder, and can result in quality-quantity trade-offs of offspring. The food availability pattern serves as a conditioning environment, and can shape the activity of the genome by influencing chromatin activation/silencing; however, the functional linkage of food availability times with epigenetic control of physiology is only beginning to emerge. This Review gives insights into how food availability times, affected by changes in eating schedules and/or by alterations in feeding environment or lifestyle, could have hitherto unknown consequences on the physiology and reproductive fitness of seasonally breeding vertebrates and those that reproduce year round.

Roles of NR5A1 and NR5A2 in the regulation of steroidogenesis by Clock gene and bone morphogenetic proteins by human granulosa cells

The functional role of the transcription factors NR5A1 and NR5A2 and their interaction with Clock gene and bone morphogenetic proteins (BMPs) were investigated in human granulosa KGN cells. Treatment with BMP-15 and GDF-9 suppressed forskolin (FSK)-induced steroidogenesis as shown by the mRNA expression levels of StAR and P450scc but not the mRNA expression level of P450arom. Of interest, treatment with BMP-15 and GDF-9 also suppressed FSK-induced NR5A2 mRNA expression. Treatment with BMP-15 suppressed NR5A2 mRNA and protein expression but increased Clock mRNA and protein expression levels by granulosa cells. The mRNA expression levels of NR5A1, but not those of NR5A2, were positively correlated with the levels of Clock mRNA, while the mRNA levels of Id-1, the target gene of BMP signaling, were positively correlated with those of NR5A1 but not with those of NR5A2. It was also demonstrated that the mRNA expression levels of NR5A1 were positively correlated with those of P450arom and 3βHSD, whereas the mRNA expression level of NR5A2 was correlated with those of StAR and P450scc. Furthermore, inhibition of Clock gene expression by siRNA attenuated the expression of NR5A1, and the mRNA levels of Clock gene were significantly correlated with those of NR5A1. Collectively, the results suggested a novel mechanism by which Clock gene expression induced by BMP-15 is functionally linked to the expression of NR5A1, whereas NR5A2 expression is suppressed by BMP-15 in granulosa cells. The interaction between Clock NR5A1/NR5A2 and BMP-15 is likely to be involved in the fine-tuning of steroidogenesis by ovarian granulosa cells.

Effect of a health education program on puberty knowledge among visually impaired female adolescent students

Background: One of the most important aspects of life is reproductive health, which receives less attention in public policy considerations because of its sociopolitical sensitivities. The aim of this study was to evaluate the effect of a designed health education program on knowledge about puberty health among visually impaired female adolescent students during 2011 and 2015.

Methods: This quasi-experimental study was conducted on 100 visually impaired female students aged 10 to 19 years. Data collection tool was a researcher-made questionnaire. Participants were recruited using convenience sampling method from Narjes educational center in Tehran. The educational needs assessments survey was used to learn about important issues and problems faced by this group to design effective educational programs. The effectiveness of the designed program was assessed by comparing the students' knowledge at the baseline and at 1-month follow-up. Data were analyzed in SPSS V.21 by using parametric descriptive statistics. The significant level was set as p<0.05

Results: The results showed that the puberty knowledge of participants was increased in all educational domains after intervention compared to the baseline (p<0.05). The knowledge about the onset of puberty changes showed the highest increase (from 2.02 at baseline to 7.51 at follow-up) and the knowledge about personal hygiene had the least change after the intervention (from 6.67 to 8.23). The majority of students did not have any information resources regarding puberty health, and about one quarter of them reported their mother as the main resource of puberty information.

Conclusion: Providing educational programs during puberty has a crucial role in young girls’ knowledge increase. Providing a continuous health educational program that is tailored to the needs of this group of students using suitable strategies is recommended.

Vasopressinergic Activity of the Suprachiasmatic Nucleus and mRNA Expression of Clock Genes in the Hypothalamus-Pituitary-Gonadal Axis in Female Aging

The important involvement of the suprachiasmatic nucleus (SCN) and the activity of vasopressinergic neurons in maintaining the rhythmicity of the female reproductive system depends on the mRNA transcription-translation feedback loops. Therefore, circadian clock function, like most physiological processes, is involved in the events that determine reproductive aging. This study describes the change of mRNA expression of clock genes, Per2, Bmal1, and Rev-erbα, in the hypothalamus-pituitary-gonadal axis (HPG) of female rats with regular cycle (RC) and irregular cycle (IC), and the vasopressinergic neurons activity in the SCN and kisspeptin neurons in the arcuate nucleus (ARC) of these animals. Results for gonadotropins and the cFos/AVP-ir neurons in the SCN of IC were higher, but kisspeptin-ir was minor. Change in the temporal synchrony of the clock system in the HPG axis, during the period prior to the cessation of ovulatory cycles, was identified. The analysis of mRNA for Per2, Bmal1, and Rev-erbα in the reproductive axis of adult female rodents shows that the regularity of the estrous cycle is guaranteed by alternation in the amount of expression of Bmal1 and Per2, and Rev-erbα and Bmal1 between light and dark phases, which ceases to occur and contributes to determining reproductive senescence. These results showed that the desynchronization between the central and peripheral circadian clocks contributes to the irregularity of reproductive events. We suggest that the feedback loops of clock genes on the HPG axis modulate the spontaneous transition from regular to irregular cycle and to acyclicity in female rodents.

Aging attenuates the ovarian circadian rhythm

Objective

To study the effect of aging on ovarian circadian rhythm.

Design

Human and animal study.

Setting

University hospital and research laboratory.

Patients/animals

Human granulosa cells were obtained by follicular aspiration from women undergoing in vitro fertilization (IVF), and ovarian and liver tissues were obtained from female C57BL/6 mice.

Intervention(s)

None.

Main outcome measure(s)

Expression of circadian genes in young and older human granulosa cells and circadian rhythm in ovaries and livers of young and older mice.

Result(s)

All examined circadian clock genes in human granulosa cells showed a downward trend in expression with aging, and their mRNA expression levels were negatively correlated with age (P < 0.05). Older patients (≥ 40 years of age) had significantly reduced serum anti-Müllerian hormone (AMH) levels. Except for Rev-erbα, all other examined circadian clock genes were positively correlated with the level of AMH (P < 0.05). The circadian rhythm in the ovaries of older mice (8 months) was changed significantly relative to that in ovaries of young mice (12 weeks), although the circadian rhythm in the livers of older mice was basically consistent with that of young mice.

Conclusion(s)

Lower ovarian reserve in older women is partially due to ovarian circadian dysrhythmia as a result of aging.

Electronic supplementary material

The online version of this article (10.1007/s10815-020-01943-y) contains supplementary material, which is available to authorized users.

Circadian rhythms in the mouse reproductive axis during the estrous cycle and pregnancy

Molecular and behavioral timekeeping is regulated by the circadian system which includes the brain's suprachiasmatic nucleus (SCN) that translates environmental light information into neuronal and endocrine signals aligning peripheral tissue rhythms to the time of day. Despite the critical role of circadian rhythms in fertility, it remains unexplored how circadian rhythms change within reproductive tissues during pregnancy. To determine how estrous cycle and pregnancy impact phase relationships of reproductive tissues, we used PER2::Luciferase (PER2::LUC) circadian reporter mice and determined the time of day of PER2::LUC peak (phase) in the SCN, pituitary, uterus, and ovary. The relationships between reproductive tissue PER2::LUC phases changed throughout the estrous cycle and late pregnancy and were accompanied by changes to PER2::LUC period in the SCN, uterus, and ovary. To determine if the phase relationship adaptations were driven by sex steroids, we asked if progesterone, a hormone involved in estrous cyclicity and pregnancy, could regulate Per2-luciferase expression. Using an in vitro transfection assay, we found that progesterone increased Per2-luciferase expression in immortalized SCN (SCN2.2) and arcuate nucleus (KTAR) cells. In addition, progesterone shortened PER2::LUC period in ex vivo uterine tissue recordings collected during pregnancy. As progesterone dramatically increases during pregnancy, we evaluated wheel-running patterns in PER2::LUC mice. We confirmed that activity levels decrease during pregnancy and found that activity onset was delayed. Although SCN, but not arcuate nucleus, PER2::LUC period changed during late pregnancy, onset of locomotor activity did not correlate with SCN or arcuate nucleus PER2::LUC period.

Pregnancy rest-activity patterns are related to salivary cortisol rhythms and maternal-fetal health indicators in women from a disadvantaged population

Irregular rest-activity patterns can disrupt metabolic and hormonal physiology and potentially lead to disease. Little is known regarding rest-activity patterns during gestation and their association with hormonal rhythms and health in pregnant women. We conducted a pilot study to determine if 24 h rest-activity was related to saliva cortisol rhythms and maternal-fetal health in an economically disadvantaged population. Primiparous women wore a wrist actigraphy device for a week to record activity during gestational weeks 22 (G22; n = 50) and 32 (G32; n = 46) and postpartum week one (PPW1; n = 39). Participants collected saliva samples every 4 hr over a 24 hr period during G22 (n = 22), G32 (n = 20) and 24–48 hr postnatal (n = 20), and cortisol concentrations were measured with ELISA. Circadian rhythmicity was assessed using autocorrelation coefficient (r24) and cosinor analysis. Blood glucose levels, body mass index (BMI), gestational disease data, and gestational age of infant at birth were abstracted from medical charts. Time of cortisol peak (acrophase) during G22 was related with acrophase of activity (r = 0.66; p = 0.001) and blood glucose levels (r = 0.58; p = 0.006). During G22, minutes of wake after sleep onset was positively related to cortisol mesor and AUC (p <0.05). Rest-activity r24, R², and mesor during G32 were positively (p<0.05) associated with gestational age of infant at birth. Across all three time points r24 of activity was related with cortisol amplitude (r = 0.33; p = 0.01). Findings support a relationship between rest-activity patterns and saliva cortisol rhythms during pregnancy. The association of less robust activity rhythms with earlier gestational age of infant at birth indicates a potential link between circadian system disruption and maternal-fetal health outcomes.

Circadian Clock, Time-Restricted Feeding and Reproduction

The goal of this review was to seek a better understanding of the function and differential expression of circadian clock genes during the reproductive process. Through a discussion of how the circadian clock is involved in these steps, the identification of new clinical targets for sleep disorder-related diseases, such as reproductive failure, will be elucidated. Here, we focus on recent research findings regarding circadian clock regulation within the reproductive system, shedding new light on circadian rhythm-related problems in women. Discussions on the roles that circadian clock plays in these reproductive processes will help identify new clinical targets for such sleep disorder-related diseases.

Genome-wide DNA methylation analysis of pituitaries during the initiation of puberty in gilts

It has been widely recognized that the early or delayed puberty appears to display harmful effects on adult health outcomes. During the timing of puberty, pituitaries responds to the hypothalamus and then introduce the following response of ovaries in hypothalamic-pituitary-gonadal axis. DNA methylation has been recently suggested to regulate the onset of puberty in female mammals. However, to date, the changes of DNA methylation in pituitaries have not been investigated during pubertal transition. In this study, using gilts as the pubertal model, the genome-scale DNA methylation of pituitaries was profiled and compared across Pre-, In- and Post-puberty by using the reduced representation bisulfite sequencing. We found that average methylation levels of each genomic feature in Post- were lower than Pre- and In-pubertal stage in CpG context, but they were higher in In- than that in Pre- and Post-pubertal stage in CpH (where H = A, T, or C) context. The methylation patterns of CpHs were more dynamic than that of CpGs at the location of high CpG content, low CpG content promoter genes, and differently genomic CGIs. Furthermore, the differently genomic CGIs were likely to show in a similar manner in CpG context but display in a stage-specific manner in the CpH context across the Pre-, In- and Post-pubertal stage. Among these pubertal stages, 5 kb upstream regions of the transcription start sites were protected from both CpG and CpH methylation changes. 12.65% of detected CpGs were identified as the differentially methylated CpGs, regarding 4301 genes which were involved in the fundamental functions of pituitaries. 0.35% of detected CpHs were identified as differentially methylated CpHs, regarding 3691 genes which were involved in the biological functions of releasing gonadotropin hormones. These observations and analyses would provide valuable insights into epigenetic mechanism of the initiation of puberty in pituitary level.

Interaction of ovarian steroidogenesis and clock gene expression modulated by bone morphogenetic protein-7 in human granulosa cells

A functional link between clock gene expression and ovarian steroidogenesis was studied using human granulosa KGN cells. Similarities between changes in the mRNA and protein expression levels of Bmal1 and Clock and those of Per2 and Cry1 were found in KGN cells after treatment with forskolin. Among the interrelationships between the expression levels of clock and steroidogenic factors, Clock mRNA had a strongly positive correlation with P450arom and a negative correlation with 3βHSD. Knockdown of Clock gene by siRNA resulted in a significant reduction of estradiol production by inhibiting P450arom expression, while it induced a significant increase of progesterone production by upregulating 3βHSD in KGN cells treated with forskolin. Moreover, BMP-7 had an enhancing effect on the expression of Clock mRNA and protein in KGN cells. Thus, the expression levels of Clock, being upregulated by forskolin and BMP-7, were functionally linked to estradiol production and progesterone suppression by human granulosa cells.

Involvement of the luteinizing hormone surge in the regulation of ovary and oviduct clock gene expression in mice

Circadian dysfunction perturbs the female reproductive cycle. In particular, mice lacking the clock gene Bmal1 show severe infertility, implying that BMAL1 plays roles in ovulation and luteinization. Here, we examined temporal changes in clock gene expression in the ovary and oviduct before and during gonadotropin-induced follicular growth, ovulation, and luteinization in sexually immature mice. While the oviduct did not show a drastic change in clock gene expression, Bmal1 expression in the ovary was higher than that in control mice during the period from 4 to 16 hr after human chorionic gonadotropin (hCG) administration. Bmal1 expression reached a maximum at 16 hr after hCG administration, when follicle luteinization occurred. In an interesting manner, administration of hCG to ex vivo-cultured oviduct triggered a shorter circadian period and inevitably resulted in phase advance. Together, our present data suggest that LH surge induces continuous expression of BMAL1 in the mouse ovary and modulates circadian phase in the mouse oviduct.

Flexible clock systems: adjusting the temporal programme

Under natural conditions, many aspects of the abiotic and biotic environment vary with time of day, season or even era, while these conditions are typically kept constant in laboratory settings. The timing information contained within the environment serves as critical timing cues for the internal biological timing system, but how this system drives daily rhythms in behaviour and physiology may also depend on the internal state of the animal. The disparity between timing of these cues in natural and laboratory conditions can result in substantial differences in the scheduling of behaviour and physiology under these conditions. In nature, temporal coordination of biological processes is critical to maximize fitness because they optimize the balance between reproduction, foraging and predation risk. Here we focus on the role of peripheral circadian clocks, and the rhythms that they drive, in enabling adaptive phenotypes. We discuss how reproduction, endocrine activity and metabolism interact with peripheral clocks, and outline the complex phenotypes arising from changes in this system. We conclude that peripheral timing is critical to adaptive plasticity of circadian organization in the field, and that we must abandon standard laboratory conditions to understand the mechanisms that underlie this plasticity which maximizes fitness under natural conditions.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Fitness effects of interspecific competition between two species of desert rodents

Many factors affect individual fitness, but while some factors, such as resource availability, have received strong experimental support, others including interspecific competition have rarely been quantified. Nevertheless, interspecific competition is commonly mentioned in the context of reproductive success and fitness. In general, when reproduction is likely to fail, reproductive suppression may occur. We studied the golden spiny mouse (Acomys russatus) and the common spiny mouse (A. cahirinus; however, recent molecular analysis in spiny mice from Jordan and Sinai suggests this species is A. dimidiatus (Frynta et al., 2010), as a model for the effect of competition on reproduction in four field enclosures: two populated only by A. russatus individuals, and two populated by individuals of both species. In presence of A. cahirinus, fitness of A. russatus was lower: the number of A. rusatus offspring was significantly lower; more males had regressed testes (indicating reproductive depression); more A. russatus young had damaged tails. However, no clear effect was evident in A. russatus female vaginal smear cytology. We conclude that the presence of A. cahirinus impairs fitness and reproductive success of A. russatus. While various direct and/or indirect mechanisms may be responsible for the effect of competition on reproduction, a plausible mechanism is increased use of torpor induced by the presence of A. cahirinus previously documented in A. russatus.

Circadian Rhythms and Clock Genes in Reproduction: Insights From Behavior and the Female Rabbit's Brain

Clock gene oscillations are necessary for a successful pregnancy and parturition, but little is known about their function during lactation, a period demanding from the mother multiple physiological and behavioral adaptations to fulfill the requirements of the offspring. First, we will focus on circadian rhythms and clock genes in reproductive tissues mainly in rodents. Disruption of circadian rhythms or proper rhythmic oscillations of clock genes provoke reproductive problems, as found in clock gene knockout mice. Then, we will focus mainly on the rabbit doe as this mammal nurses the young just once a day with circadian periodicity. This daily event synchronizes the behavior and the activity of specific brain regions critical for reproductive neuroendocrinology and maternal behavior, like the preoptic area. This region shows strong rhythms of the PER1 protein (product of the Per1 clock gene) associated with circadian nursing. Additionally, neuroendocrine cells related to milk production and ejections are also synchronized to daily nursing. A threshold of suckling is necessary to entrain once a day nursing; this process is independent of milk output as even virgin does (behaving maternally following anosmia) can display circadian nursing behavior. A timing motivational mechanism may regulate such behavior as mesolimbic dopaminergic cells are entrained by daily nursing. Finally, we will explore about the clinical importance of circadian rhythms. Indeed, women in chronic shift-work schedules show problems in their menstrual cycles and pregnancies and also have a high risk of preterm delivery, making this an important field of translational research.

Effect of lipopolysaccharide on circadian clock genes Per2 and Bmal1 in mouse ovary

In mammals, circadian rhythms are associated with multiple physiological events. The aim of the present study was to examine the effect of lipopolysaccharide (LPS) on circadian systems in the ovary. Immature female mice were received an intra-peritoneal injection of equine chorionic gonadotropin (eCG) and LPS. Total RNA was collected from the ovary at 6-h intervals throughout a 48 h of experimental period. The expression of the circadian genes period 2 (Per2) and brain and muscle ARNT-like 1 (Bmal1) such as circadian genes was measured by quantitative PCR. Although expression of Per2 and Bmal1 in the ovary did not display clear diurnal oscillation, LPS suppressed the amplitude of Per2 expression. Additionally, LPS inhibited the expression of cytochrome P450 aromatase (CYP19) and luteinizing hormone receptor (LHr) genes in the ovary of eCG-treated mice. Our data suggest that Per2 may be associated with the inhibition of CYP19 and LHr expression by LPS in the ovaries of immature mice.

The Circadian Timing System and Environmental Circadian Disruption: From Follicles to Fertility

The internal or circadian timing system is deeply integrated in female reproductive physiology. Considerable details of rheostatic timing function in the neuroendocrine control of pituitary hormone secretion, adenohypophyseal hormone gene expression and secretion, gonadal steroid hormone biosynthesis and secretion, ovulation, implantation, and parturition have been reported. The molecular clock, an autonomous feedback loop oscillator of interacting transcriptional regulators, dictates the timing and amplitude of gene expression in each tissue of the female hypothalamic-pituitary-gonadal (HPG) axis. Although multiple targets of the molecular clock have been identified, many associated with critical physiological functions in the HPG axis, the full extent of clock-driven gene expression and physiology in this critical system remains unknown. Environmental circadian disruption (ECD), the disturbance of temporal relationships within and between internal clocks (brain and periphery), and external timing cues (eg, light, nutrients, social cues) due to rotating/night shift work or transmeridian travel have been linked to reproductive dysfunction and subfertility. Moreover, ECD resulting from exposure to endocrine disrupting chemicals, environmental toxins, and/or irregular hormone levels during sexual development can also reduce fertility. Thus, perturbations that disturb clock function at the molecular, cellular or systemic level correlate with significant declines in female reproductive function. Here we briefly review the evidence for molecular clock function in each tissue of the female HPG axis (GnRH neuron, pituitary, uterus, oviduct, and ovary), describe the human epidemiological and animal data supporting the negative effects of ECD on fertility, and explore the potential for novel chronotherapeutics in women's health and fertility.

Conditional Deletion of Bmal1 in Ovarian Theca Cells Disrupts Ovulation in Female Mice

Rhythmic events in female reproductive physiology, including ovulation, are tightly controlled by the circadian timing system. The molecular clock, a feedback loop oscillator of clock gene transcription factors, dictates rhythms of gene expression in the hypothalamo-pituitary-ovarian axis. Circadian disruption due to environmental factors (eg, shift work) or genetic manipulation of the clock has negative impacts on fertility. Although the central pacemaker in the suprachiasmatic nucleus classically regulates the timing of ovulation, we have shown that this rhythm also depends on phasic sensitivity to LH. We hypothesized that this rhythm relies on clock function in a specific cellular compartment of the ovarian follicle. To test this hypothesis we generated mice with deletion of the Bmal1 locus in ovarian granulosa cells (GCs) (Granulosa Cell Bmal1 KO; GCKO) or theca cells (TCs) (Theca Cell Bmal1 KO; TCKO). Reproductive cycles, preovulatory LH secretion, ovarian morphology and behavior were not grossly altered in GCKO or TCKO mice. We detected phasic sensitivity to LH in wild-type littermate control (LC) and GCKO mice but not TCKO mice. This decline in sensitivity to LH is coincident with impaired fertility and altered patterns of LH receptor (Lhcgr) mRNA abundance in the ovary of TCKO mice. These data suggest that the TC is a pacemaker that contributes to the timing and amplitude of ovulation by modulating phasic sensitivity to LH. The TC clock may play a critical role in circadian disruption-mediated reproductive pathology and could be a target for chronobiotic management of infertility due to environmental circadian disruption and/or hormone-dependent reprogramming in women.

Evidence for a Putative Circadian Kiss-Clock in the Hypothalamic AVPV in Female Mice

The kisspeptin (Kp) neurons in the anteroventral periventricular nucleus (AVPV) are essential for the preovulatory LH surge, which is gated by circulating estradiol (E2) and the time of day. We investigated whether AVPV Kp neurons in intact female mice may be the site in which both E2 and daily signals are integrated and whether these neurons may host a circadian oscillator involved in the timed LH surge. In the afternoon of proestrous day, Kp immunoreactivity displayed a marked and transient decrease 2 hours before the LH surge. In contrast, Kp content was stable throughout the day of diestrus, when LH levels are constantly low. AVPV Kp neurons expressed the clock protein period 1 (PER1) with a daily rhythm that is phase delayed compared with the PER1 rhythm measured in the main clock of the suprachiasmatic nuclei (SCN). PER1 rhythm in the AVPV, but not in the SCN, exhibited a significant phase delay of 2.8 hours in diestrus as compared with proestrus. Isolated Kp-expressing AVPV explants from PER2::LUCIFERASE mice displayed sustained circadian oscillations of bioluminescence with a circadian period (23.2 h) significantly shorter than that of SCN explants (24.5 h). Furthermore, in AVPV explants incubated with E2 (10 nM to 1 μM), the circadian period was lengthened by 1 hour, whereas the SCN clock remained unaltered. In conclusion, these findings indicate that AVPV Kp neurons display an E2-dependent daily rhythm, which may possibly be driven by an intrinsic circadian clock acting in combination with the SCN timing signal.

High-Throughput Sequencing Reveals Hypothalamic MicroRNAs as Novel Partners Involved in Timing the Rapid Development of Chicken (Gallus gallus) Gonads

Onset of the rapid gonad growth is a milestone in sexual development that comprises many genes and regulatory factors. The observations in model organisms and mammals including humans have shown a potential link between miRNAs and development timing. To determine whether miRNAs play roles in this process in the chicken (Gallus gallus), the Solexa deep sequencing was performed to analyze the profiles of miRNA expression in the hypothalamus of hens from two different pubertal stages, before onset of the rapid gonad development (BO) and after onset of the rapid gonad development (AO). 374 conserved and 46 novel miRNAs were identified as hypothalamus-expressed miRNAs in the chicken. 144 conserved miRNAs were showed to be differentially expressed (reads > 10, P < 0.05) during the transition from BO to AO. Five differentially expressed miRNAs were validated by real-time quantitative RT-PCR (qRT-PCR) method. 2013 putative genes were predicted as the targets of the 15 most differentially expressed miRNAs (fold-change > 4.0, P < 0.01). Of these genes, 7 putative circadian clock genes, Per2, Bmal1/2, Clock, Cry1/2, and Star were found to be targeted multiple times by the miRNAs. qRT-PCR revealed the basic transcription levels of these clock genes were much higher (P < 0.01) in AO than in BO. Further functional analysis suggested that these 15 miRNAs play important roles in transcriptional regulation and signal transduction pathways. The results provide new insights into miRNAs functions in timing the rapid development of chicken gonads. Considering the characteristics of miRNA functional conservation, the results will contribute to the research on puberty onset in humans.

Melatonin: an inhibitor of breast cancer

The present review discusses recent work on melatonin-mediated circadian regulation, the metabolic and molecular signaling mechanisms that are involved in human breast cancer growth, and the associated consequences of circadian disruption by exposure to light at night (LEN). The anti-cancer actions of the circadian melatonin signal in human breast cancer cell lines and xenografts heavily involve MT1 receptor-mediated mechanisms. In estrogen receptor alpha (ERα)-positive human breast cancer, melatonin suppresses ERα mRNA expression and ERα transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of other members of the nuclear receptor superfamily, estrogen-metabolizing enzymes, and the expression of core clock and clock-related genes. Furthermore, melatonin also suppresses tumor aerobic metabolism (the Warburg effect) and, subsequently, cell-signaling pathways critical to cell proliferation, cell survival, metastasis, and drug resistance. Melatonin demonstrates both cytostatic and cytotoxic activity in breast cancer cells that appears to be cell type-specific. Melatonin also possesses anti-invasive/anti-metastatic actions that involve multiple pathways, including inhibition of p38 MAPK and repression of epithelial-mesenchymal transition (EMT). Studies have demonstrated that melatonin promotes genomic stability by inhibiting the expression of LINE-1 retrotransposons. Finally, research in animal and human models has indicated that LEN-induced disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer and drives breast tumors to endocrine and chemotherapeutic resistance. These data provide the strongest understanding and support of the mechanisms that underpin the epidemiologic demonstration of elevated breast cancer risk in night-shift workers and other individuals who are increasingly exposed to LEN.

Melatonin: an inhibitor of breast cancer

The present review discusses recent work on melatonin-mediated circadian regulation, the metabolic and molecular signaling mechanisms that are involved in human breast cancer growth, and the associated consequences of circadian disruption by exposure to light at night (LEN). The anti-cancer actions of the circadian melatonin signal in human breast cancer cell lines and xenografts heavily involve MT1 receptor-mediated mechanisms. In estrogen receptor alpha (ERα)-positive human breast cancer, melatonin suppresses ERα mRNA expression and ERα transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of other members of the nuclear receptor superfamily, estrogen-metabolizing enzymes, and the expression of core clock and clock-related genes. Furthermore, melatonin also suppresses tumor aerobic metabolism (the Warburg effect) and, subsequently, cell-signaling pathways critical to cell proliferation, cell survival, metastasis, and drug resistance. Melatonin demonstrates both cytostatic and cytotoxic activity in breast cancer cells that appears to be cell type-specific. Melatonin also possesses anti-invasive/anti-metastatic actions that involve multiple pathways, including inhibition of p38 MAPK and repression of epithelial-mesenchymal transition (EMT). Studies have demonstrated that melatonin promotes genomic stability by inhibiting the expression of LINE-1 retrotransposons. Finally, research in animal and human models has indicated that LEN-induced disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer and drives breast tumors to endocrine and chemotherapeutic resistance. These data provide the strongest understanding and support of the mechanisms that underpin the epidemiologic demonstration of elevated breast cancer risk in night-shift workers and other individuals who are increasingly exposed to LEN.

Does Circadian Disruption Play a Role in the Metabolic-Hormonal Link to Delayed Lactogenesis II?

Breastfeeding improves maternal and child health. The American Academy of Pediatrics recommends exclusive breastfeeding for 6 months, with continued breastfeeding for at least 1 year. However, in the US, only 18.8% of infants are exclusively breastfed until 6 months of age. For mothers who initiate breastfeeding, the early post-partum period sets the stage for sustained breastfeeding. Mothers who experience breastfeeding problems in the early post-partum period are more likely to discontinue breastfeeding within 2 weeks. A major risk factor for shorter breastfeeding duration is delayed lactogenesis II (DLII; i.e., onset of milk "coming in" more than 72 h post-partum). Recent studies report a metabolic-hormonal link to DLII. This is not surprising because around the time of birth the mother's entire metabolism changes to direct nutrients to mammary glands. Circadian and metabolic systems are closely linked, and our rodent studies suggest circadian clocks coordinate hormonal and metabolic changes to support lactation. Molecular and environmental disruption of the circadian system decreases a dam's ability to initiate lactation and negatively impacts milk production. Circadian and metabolic systems evolved to be functional and adaptive when lifestyles and environmental exposures were quite different from modern times. We now have artificial lights, longer work days, and increases in shift work. Disruption in the circadian system due to shift work, jet-lag, sleep disorders, and other modern life style choices are associated with metabolic disorders, obesity, and impaired reproduction. We hypothesize that DLII is related to disruption of the mother's circadian system. Here, we review literature that supports this hypothesis, and describe interventions that may help to increase breastfeeding success.

Developmental programming by androgen affects the circadian timing system in female mice

Circadian clocks play essential roles in the timing of events in the mammalian hypothalamo-pituitary-ovarian (HPO) axis. The molecular oscillator driving these rhythms has been localized to tissues of the HPO axis. It has been suggested that synchrony among these oscillators is a feature of normal reproductive function. The impact of fertility disorders on clock function and the role of the clock in the etiology of endocrine pathology remain unknown. Polycystic ovarian syndrome (PCOS) is a particularly devastating fertility disorder, affecting 5%-10% of women at childbearing age with features including a polycystic ovary, anovulation, and elevated serum androgen. Approximately 40% of these women have metabolic syndrome, marked by hyperinsulinemia, dyslipidemia, and insulin resistance. It has been suggested that developmental exposure to excess androgen contributes to the etiology of fertility disorders, including PCOS. To better define the role of the timing system in these disorders, we determined the effects of androgen-dependent developmental programming on clock gene expression in tissues of the metabolic and HPO axes. Female PERIOD2::luciferase (PER2::LUC) mice were exposed to androgen (dihydrotestosterone [DHT]) in utero (Days 16-18 of gestation) or for 9-10 wk (DHT pellet) beginning at weaning (pubertal androgen excess [PAE]). As expected, both groups of androgen-treated mice had disrupted estrous cycles. Analysis of PER2::LUC expression in tissue explants revealed that excess androgen produced circadian misalignment via tissue-dependent effects on phase distribution. In vitro treatment with DHT differentially affected the period of PER2::LUC expression in tissue explants and granulosa cells, indicating that androgen has direct and tissue-specific effects on clock gene expression that may account for the effects of developmental programming on the timing system.

A Multi-Oscillatory Circadian System Times Female Reproduction

Rhythms in female reproduction are critical to insure that timing of ovulation coincides with oocyte maturation and optimal sexual arousal. This fine tuning of female reproduction involves both the estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei (SCN) as an indicator of the time of the day. Herein, we are providing an overview of the state of knowledge regarding the differential inhibitory and stimulatory effects of estradiol at different stages of the reproductive axis, and the mechanisms through which the two main neurotransmitters of the SCN, arginine vasopressin, and vasoactive intestinal peptide, convey daily time cues to the reproductive axis. In addition, we will report the most recent findings on the putative functions of peripheral clocks located throughout the reproductive axis [kisspeptin (Kp) neurons, gonadotropin-releasing hormone neurons, gonadotropic cells, the ovary, and the uterus]. This review will point to the critical position of the Kp neurons of the anteroventral periventricular nucleus, which integrate both the stimulatory estradiol signal, and the daily arginine vasopressinergic signal, while displaying a circadian clock. Finally, given the critical role of the light/dark cycle in the synchronization of female reproduction, we will discuss the impact of circadian disruptions observed during shift-work conditions on female reproductive performance and fertility in both animal model and humans.

Circadian Clock Function in the Mammalian Ovary

Rhythmic events in the female reproductive system depend on the coordinated and synchronized activity of multiple neuroendocrine and endocrine tissues. This coordination is facilitated by the timing of gene expression and cellular physiology at each level of the hypothalamo-pituitary-ovarian (HPO) axis, including the basal hypothalamus and forebrain, the pituitary gland, and the ovary. Central to this pathway is the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) that, through its myriad outputs, provides a temporal framework for gonadotropin release and ovulation. The heart of the timing system, a transcription-based oscillator, imparts SCN pacemaker cells and a company of peripheral tissues with the capacity for daily oscillations of gene expression and cellular physiology. Although the SCN sits comfortably at the helm, peripheral oscillators (such as the ovary) have undefined but potentially critical roles. Each cell type of the ovary, including theca cells, granulosa cells, and oocytes, harbor a molecular clock implicated in the processes of follicular growth, steroid hormone synthesis, and ovulation. The ovarian clock is influenced by the reproductive cycle and diseases that perturb the cycle and/or follicular growth can disrupt the timing of clock gene expression in the ovary. Chronodisruption is known to negatively affect reproductive function and fertility in both rodent models and women exposed to shiftwork schedules. Thus, influencing clock function in the HPO axis with chronobiotics may represent a novel avenue for the treatment of common fertility disorders, particularly those resulting from chronic circadian disruption.

Loss of BMAL1 in ovarian steroidogenic cells results in implantation failure in female mice

The circadian clock plays a significant role in many aspects of female reproductive biology, including estrous cycling, ovulation, embryonic implantation, onset of puberty, and parturition. In an effort to link cell-specific circadian clocks to their specific roles in female reproduction, we used the promoter that controls expression of Steroidogenic Factor-1 (SF1) to drive Cre-recombinase-mediated deletion of the brain muscle arnt-like 1 (Bmal1) gene, known to encode an essential component of the circadian clock (SF1-Bmal1(-/-)). The resultant SF1-Bmal1(-/-) females display embryonic implantation failure, which is rescued by progesterone supplementation, or bilateral or unilateral transplantation of wild-type ovaries into SF1-Bmal1(-/-) dams. The observation that the central clock, and many other peripheral clocks, are fully functional in this model allows the assignment of the implantation phenotype to the clock in ovarian steroidogenic cells and distinguishes it from more general circadian related systemic pathology (e.g., early onset arthropathy, premature aging, ovulation, late onset of puberty, and abnormal estrous cycle). Our ovarian transcriptome analysis reveals that deletion of ovarian Bmal1 disrupts expression of transcripts associated with the circadian machinery and also genes critical for regulation of progesterone production, such as steroidogenic acute regulatory factor (Star). Overall, these data provide a powerful model to probe the interlocking and synergistic network of the circadian clock and reproductive systems.

Disrupted reproduction, estrous cycle, and circadian rhythms in female mice deficient in vasoactive intestinal peptide

The female reproductive cycle is gated by the circadian timing system and may be vulnerable to disruptions in the circadian system. Prior work suggests that vasoactive intestinal peptide (VIP)-expressing neurons in the suprachiasmatic nucleus (SCN) are one pathway by which the circadian clock can influence the estrous cycle, but the impact of the loss of this peptide on reproduction has not been assessed. In the present study, we first examine the impact of the genetic loss of the neuropeptide VIP on the reproductive success of female mice. Significantly, mutant females produce about half the offspring of their wild-type sisters even when mated to the same males. We also find that VIP-deficient females exhibit a disrupted estrous cycle; that is, ovulation occurs less frequently and results in the release of fewer oocytes compared with controls. Circadian rhythms of wheel-running activity are disrupted in the female mutant mice, as is the spontaneous electrical activity of dorsal SCN neurons. On a molecular level, the VIP-deficient SCN tissue exhibits lower amplitude oscillations with altered phase relationships between the SCN and peripheral oscillators as measured by PER2-driven bioluminescence. The simplest explanation of our data is that the loss of VIP results in a weakened SCN oscillator, which reduces the synchronization of the female circadian system. These results clarify one of the mechanisms by which disruption of the circadian system reduces female reproductive success.

Environmental control of biological rhythms: effects on development, fertility and metabolism

Internal temporal organisation properly synchronised to the environment is crucial for health maintenance. This organisation is provided at the cellular level by the molecular clock, a macromolecular transcription-based oscillator formed by the clock and the clock-controlled genes that is present in both central and peripheral tissues. In mammals, melanopsin in light-sensitive retinal ganglion cells plays a considerable role in the synchronisation of the circadian timing system to the daily light/dark cycle. Melatonin, a hormone synthesised in the pineal gland exclusively at night and an output of the central clock, has a fundamental role in regulating/timing several physiological functions, including glucose homeostasis, insulin secretion and energy metabolism. As such, metabolism is severely impaired after a reduction in melatonin production. Furthermore, light pollution during the night and shift work schedules can abrogate melatonin synthesis and impair homeostasis. Chronodisruption during pregnancy has deleterious effects on the health of progeny, including metabolic, cardiovascular and cognitive dysfunction. Developmental programming by steroids or steroid-mimetic compounds also produces internal circadian disorganisation that may be a significant factor in the aetiology of fertility disorders such as polycystic ovary syndrome. Thus, both early and late in life, pernicious alterations of the endogenous temporal order by environmental factors can disrupt the homeostatic function of the circadian timing system, leading to pathophysiology and/or disease.

Melatonin and the circadian system: contributions to successful female reproduction

OBJECTIVE

To summarize the role of melatonin and circadian rhythms in determining optimal female reproductive physiology, especially at the peripheral level.

DESIGN

Databases were searched for the related English-language literature published up to March 1, 2014. Only papers in peer-reviewed journals are cited.

SETTING

Not applicable.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Melatonin treatment, alterations of the normal light:dark cycle and light exposure at night.

MAIN OUTCOME MEASURE(S)

Melatonin levels in the blood and in the ovarian follicular fluid and melatonin synthesis, oxidative damage and circadian rhythm disturbances in peripheral reproductive organs.

RESULT(S)

The central circadian regulatory system is located in the suprachiasmatic nucleus (SCN). The output of this master clock is synchronized to 24 hours by the prevailing light-dark cycle. The SCN regulates rhythms in peripheral cells via the autonomic nervous system and it sends a neural message to the pineal gland where it controls the cyclic production of melatonin; after its release, the melatonin rhythm strengthens peripheral oscillators. Melatonin is also produced in the peripheral reproductive organs, including granulosa cells, the cumulus oophorus, and the oocyte. These cells, along with the blood, may contribute melatonin to the follicular fluid, which has melatonin levels higher than those in the blood. Melatonin is a powerful free radical scavenger and protects the oocyte from oxidative stress, especially at the time of ovulation. The cyclic levels of melatonin in the blood pass through the placenta and aid in the organization of the fetal SCN. In the absence of this synchronizing effect, the offspring may exhibit neurobehavioral deficits. Also, melatonin protects the developing fetus from oxidative stress. Melatonin produced in the placenta likewise may preserve the optimal function of this organ.

CONCLUSION(S)

Both stable circadian rhythms and cyclic melatonin availability are critical for optimal ovarian physiology and placental function. Because light exposure after darkness onset at night disrupts the master circadian clock and suppresses elevated nocturnal melatonin levels, light at night should be avoided.

Opposite influence of light and blindness on pituitary-gonadal function

Some environmental factors may influence the pituitary-gonadal function. Among these, light plays an important role in animals and in humans. The effect of light on the endocrine system is mediated by the pineal gland, through the modulation of melatonin secretion. In fact, melatonin secretion is stimulated by darkness and suppressed by light, thus its circadian rhythm peaks at night. Light plays a favorable action on the hypothalamic-pituitary axis likely inhibiting melatonin secretion, while the exogenous melatonin administration does not seem to impair the hormonal secretions of this axis. The basal and rhythmic pituitary-gonadal hormone secretions are regulated by a central clock gene and some independent clock genes in the peripheral tissues. Light is able to induce the expression of some of these genes, thus playing an important role in regulating the hormonal secretions of pituitary-gonadal axis and the sexual and reproductive function in animals and humans. The lack of light stimulus in blind subjects induces increase in plasma melatonin concentrations with a free-running rhythm of secretion, which impairs the hormonal secretions of pituitary-gonadal axis, causing disorders of reproductive processes in both sexes.