A Multi-Oscillatory Circadian System Times Female Reproduction

Crosstalk between circadian clocks and pathogen niche

Circadian rhythms are intrinsic 24-hour oscillations found in nearly all life forms. They orchestrate key physiological and behavioral processes, allowing anticipation and response to daily environmental changes. These rhythms manifest across entire organisms, in various organs, and through intricate molecular feedback loops that govern cellular oscillations. Recent studies describe circadian regulation of pathogens, including parasites, bacteria, viruses, and fungi, some of which have their own circadian rhythms while others are influenced by the rhythmic environment of hosts. Pathogens target specific tissues and organs within the host to optimize their replication. Diverse cellular compositions and the interplay among various cell types create unique microenvironments in different tissues, and distinctive organs have unique circadian biology. Hence, residing pathogens are exposed to cyclic conditions, which can profoundly impact host-pathogen interactions. This review explores the influence of circadian rhythms and mammalian tissue-specific interactions on the dynamics of pathogen-host relationships. Overall, this demonstrates the intricate interplay between the body's internal timekeeping system and its susceptibility to pathogens, which has implications for the future of infectious disease research and treatment.

Lunar Age-Dependent Oscillations in Expression of the Genes for Kisspeptin, GnIH, and Their Receptors in the Grass Puffer during the Spawning Season

Grass puffer is a semilunar-synchronized spawner: spawning occurs on beaches only for several days of spring tide around new moon (lunar age 0) and full moon (lunar age 15) every 2 weeks from spring to early summer. To investigate the role of kisspeptin and gonadotropin-inhibitory hormone (GnIH) in the semilunar-synchronized spawning, lunar age-dependent expression of the genes encoding kisspeptin (kiss2), kisspeptin receptor (kissr2), GnIH (gnih), GnIH receptor (gnihr), gonadotropin-releasing hormone 1 (GnRH1) (gnrh1), and three gonadotropin (GTH) subunits (gpa, fshb, lhb) was examined in the male grass puffer, which was kept in an aquarium under natural light condition in a lunar month during the spawning period. In the brain, both kiss2 and kissr2 showed lunar variations with a peak at lunar age 10, while both gnih and gnihr showed semilunar variations with two peaks at lunar age 0 and 20. On the other hand, gnrh1 showed semilunar variation with two peaks at lunar age 0 and 15. In the pituitary, kiss2, kissr2, gnih, and gnihr showed similar variations to those shown in the brain. The fshb and lhb mRNA levels showed semilunar variations with two peaks at lunar age 0 and 15. The present study shows lunar and semilunar oscillations of kiss2/kissr2 and gnih/gnihr expressions, respectively, with their peaks around spring tide in the brain and pituitary along with the semilunar expressions of gnrh1 and the pituitary GTH subunit genes. These results suggest that the lunar age-dependent expressions of the kisspeptin, GnIH, and their receptor genes may be primarily important in the control of the precisely timed semilunar spawning of the grass puffer.

Dim Light at Night Promotes Circadian Disruption in Female Rats, at the Metabolic, Reproductive, and Behavioral Level

Inhabitants of urban areas are constantly exposed to light at night, which is an important environmental factor leading to circadian disruption. Streetlights filtering light through the windows and night dim light lamps are common sources of dim light at night (DLAN). The female population is susceptible to circadian disruption. The present study is aimed to determine the impact of DLAN on female Wistar rats circadian rhythms, metabolism, reproductive physiology, and behavior. After 5 weeks of DLAN exposure daily, oscillations in activity and body temperature of female rats are abolished. DLAN also decreases nocturnal food ingestion, which results in a diminishment in total food consumption. These alterations in the temporal organization of the body are associated with a significant decrease in melatonin plasmatic levels, reproductive disruptions, decreased exploration times, and marked anhedonia. This study highlights the importance of avoiding exposure to light at night, even at low intensities, to maintain the circadian organization of physiology, and denotes the great necessity of increasing the studies in females since the sexual dimorphism within the effects of desynchronizing protocols has been poorly studied.

Circadian and kisspeptin regulation of the preovulatory surge

Fertility in mammals is ultimately controlled by a small population of neurons - the gonadotropin-releasing hormone (GnRH) neurons - located in the ventral forebrain. GnRH neurons control gonadal function through the release of GnRH, which in turn stimulates the secretion of the anterior pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In spontaneous ovulators, ovarian follicle maturation eventually stimulates, via sex steroid feedback, the mid-cycle surge in GnRH and LH secretion that causes ovulation. The GnRH/LH surge is initiated in many species just before the onset of activity through processes controlled by the central circadian clock, ensuring that the neuroendocrine control of ovulation and sex behavior are coordinated. This review aims to give an overview of anatomical and functional studies that collectively reveal some of the mechanisms through which the central circadian clock regulates GnRH neurons and their afferent circuits to drive the preovulatory surge.

Timed restricted feeding cycles drive daily rhythms in female rats maintained in constant light but only partially restore the estrous cycle

Light at night is an emergent problem for modern society. Rodents exposed to light at night develop a loss of circadian rhythms, which leads to increased adiposity, altered immune response, and increased growth of tumors. In female rats, constant light (LL) eliminates the estrous cycle leading to a state of persistent estrus. The suprachiasmatic nucleus (SCN) drives circadian rhythms, and it interacts with the neuroendocrine network necessary for reproductive function. Timed restricted feeding (RF) exerts a powerful entraining influence on the circadian system, and it can influence the SCN activity and can restore rhythmicity or accelerate re-entrainment in experimental conditions of shift work or jet lag. The present study explored RF in female rats exposed to LL, with the hypothesis that this cyclic condition can rescue or prevent the loss of daily rhythms and benefit the expression of the estrous cycle. Two different feeding schedules were explored: 1. A 12-h food/12-h fasting schedule applied to arrhythmic rats after 3 weeks in LL, visualized as a rescue strategy (LL + RFR, 3 weeks), or applied simultaneously with the first day of LL as a preventive strategy (LL + RFP, 6 weeks). 2. A 12-h window of food intake with food given in four distributed pulses (every 3 h), applied after 3 weeks in LL, as a rescue strategy (LL + PR, 3 weeks) or applied simultaneously with the first day of LL as a preventive strategy (LL + PP, 6 weeks). Here, we present evidence that scheduled feeding can drive daily rhythms of activity and temperature in rats exposed to LL. However, the protocol of distributed feeding pulses was more efficient to restore the day–night activity and core temperature as well as the c-Fos day–night change in the SCN. Likewise, the distributed feeding partially restored the estrous cycle and the ovary morphology under LL condition. Data here provided indicate that the 12-h feeding/12-h fasting window determines the rest-activity cycle and can benefit directly the circadian and reproductive function. Moreover, this effect is stronger when food is distributed along the 12 h of subjective night.

Mistimed restricted feeding disrupts circadian rhythms of male mating behavior and female preovulatory LH surges in mice

In rodents, eating at atypical circadian times, such as during the biological rest phase when feeding is normally minimal, reduces fertility. Prior findings suggest this fertility impairment is due, at least in part, to reduced mating success. However, the physiological and behavioral mechanisms underlying this reproductive suppression are not known. In the present study, we tested the hypothesis that mistimed feeding-induced infertility is due to a disruption in the normal circadian timing of mating behavior and/or the generation of pre-ovulatory luteinizing hormone (LH) surges (estrogen positive feedback). In the first experiment, male+female mouse pairs, acclimated to be food restricted to either the light (mistimed feeding) or dark (control feeding) phase, were scored for mounting frequency and ejaculations over 96 h. Male mounting behavior and ejaculations were distributed much more widely across the day in light-fed mice than in dark-fed controls and fewer light-fed males ejaculated. In the second experiment, the timing of the LH surge, a well characterized circadian event driven by estradiol (E2) and the SCN, was analyzed from serial blood samples taken from ovariectomized and E2-primed female mice that were light-, dark-, or ad-lib-fed. LH concentrations peaked 2 h after lights-off in both dark-fed and ad-lib control females, as expected, but not in light-fed females. Instead, the normally clustered LH surges were distributed widely with high inter-mouse variability in the light-fed group. These data indicate that mistimed feeding disrupts the temporal control of the neural processes underlying both ovulation and mating behavior, contributing to infertility.

Mutual Effects of Orexin and Bone Morphogenetic Proteins on Gonadotropin Expression by Mouse Gonadotrope Cells

Orexin plays a key role in the regulation of sleep and wakefulness and in feeding behavior in the central nervous system, but its receptors are expressed in various peripheral tissues including endocrine tissues. In the present study, we elucidated the effects of orexin on pituitary gonadotropin regulation by focusing on the functional involvement of bone morphogenetic proteins (BMPs) and clock genes using mouse gonadotrope LβT2 cells that express orexin type 1 (OX1R) and type 2 (OX2R) receptors. Treatments with orexin A enhanced LHβ and FSHβ mRNA expression in a dose-dependent manner in the absence of GnRH, whereas orexin A in turn suppressed GnRH-induced gonadotropin expression in LβT2 cells. Orexin A downregulated GnRH receptor expression, while GnRH enhanced OX1R and OX2R mRNA expression. Treatments with orexin A as well as GnRH increased the mRNA levels of Bmal1 and Clock, which are oscillational regulators for gonadotropin expression. Of note, treatments with BMP-6 and -15 enhanced OX1R and OX2R mRNA expression with upregulation of clock gene expression. On the other hand, orexin A enhanced BMP receptor signaling of Smad1/5/9 phosphorylation through upregulation of ALK-2/BMPRII among the BMP receptors expressed in LβT2 cells. Collectively, the results indicate that orexin regulates gonadotropin expression via clock gene expression by mutually interacting with GnRH action and the pituitary BMP system in gonadotrope cells.

Environmental disruption of reproductive rhythms

Reproduction is a key biological function requiring a precise synchronization with annual and daily cues to cope with environmental fluctuations. Therefore, humans and animals have developed well-conserved photoneuroendocrine pathways to integrate and process daily and seasonal light signals within the hypothalamic-pituitary-gonadal axis. However, in the past century, industrialization and the modern 24/7 human lifestyle have imposed detrimental changes in natural habitats and rhythms of life. Indeed, exposure to an excessive amount of artificial light at inappropriate timing because of shift work and nocturnal urban lighting, as well as the ubiquitous environmental contamination by endocrine-disrupting chemicals, threaten the integrity of the daily and seasonal timing of biological functions. Here, we review recent epidemiological, field and experimental studies to discuss how light and chemical pollution of the environment can disrupt reproductive rhythms by interfering with the photoneuroendocrine timing system.

The Effect of Photoperiodic Conditions on GnRH/LH Secretion in Ewes

Simple Summary

During the course of evolution, animals have evolved biological rhythms that are associated with changes in the lighting and temperature of their environment. Females in most breeds of sheep are seasonal breeders, with ovulatory cycles occurring in the autumn and winter and anovulation in the spring and summer. Secretion of gonadotropin releasing hormone and luteinizing hormone, the main hormones regulating reproduction in females, displays a circadian pattern; however, data concerning the day/night differences in their secretion in ewes are incomplete. The aim of the undertaken study was to determine the day/night differences in the secretion of gonadotropin releasing hormone and luteinizing hormone in follicular phase and anestrous ewes. It was demonstrated that secretion of investigated hormones is subject to diurnal and seasonal changes. The observed reduction in luteinizing hormone release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase. It could be concluded that the nocturnal suppression of luteinizing hormone secretion in follicular phase ewes may be a mechanism moving this hormone surge to the early morning.

Abstract

Secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) displays a circadian pattern. Data concerning differences in daily GnRH/LH secretion during different seasons in sheep are fragmentary. The aim of the study was to determine day/night differences in GnRH/LH secretion in the follicular phase and in the anestrous ewes. The studies were performed on Blackhead ewes (n = 24). Ewes from each season were divided into two groups of six animals (day and night group). The animals were euthanized 5 h after sunset or 5 h after sunrise and blood was taken to determine LH and melatonin concentrations. In the hypothalamus, the expression of GnRH and gonadotropin releasing hormone receptor (GnRHR) was determined. In the anterior pituitary, the expression of mRNA encoding subunit β of LH (LHβ) and GnRHR was assayed. Our study showed that GnRH/LH secretion is subject to diurnal and seasonal changes. The observed reduction in LH release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase, when the processes occurring at the hypothalamus are more equivocal. It could be concluded that the nocturnal suppression of LH secretion in follicular phase ewes may be a mechanism moving the LH surge to the early morning.

Biphasic Roles of Clock Genes and Bone Morphogenetic Proteins in Gonadotropin Expression by Mouse Gonadotrope Cells

Roles of Clock genes and the bone morphogenetic protein (BMP) system in the regulation of gonadotropin secretion by gonadotropin-releasing hormone (GnRH) were investigated using mouse gonadotropin LβT2 cells. It was found that luteinizing hormone (LH)β mRNA expression level in LβT2 cells changed gradually over time, with LHβ expression being suppressed in the early phase up to 12 h and then elevated in the late phase 24 h after GnRH stimulation. In addition, the mRNA expression levels of Clock genes, including Bmal1, Clock, Per2, and Cry1, also showed temporal changes mimicking the pattern of LHβ expression in the presence and absence of GnRH. Notably, the expression levels of Bmal1 and Clock showed strong positive correlations with LHβ mRNA expression levels. Moreover, a functional link of the ERK signaling of mitogen-activated protein kinases (MAPKs) in the suppression of LHβ mRNA expression, as well as Bmal1 and Clock mRNA expression by GnRH at the early phase, was revealed. Inhibition of Bmal1 and Clock expression using siRNA was involved in the reduction in LHβ mRNA levels in the late phase 24 h after GnRH stimulation. Furthermore, in the presence of BMP-6 and -7, late-phase Bmal1 and LHβ mRNA expression after GnRH stimulation was significantly attenuated. Collectively, the results indicated that LH expression in gonadotrope cells exhibits Bmal1/Clock-dependent fluctuations under the influence of GnRH and that the fluctuations are regulated by ERK and BMPs in the early and late stages, respectively, in a phase-dependent manner after GnRH stimulation.

Development and validation of the self-rating of biological rhythm disorder for Chinese adolescents

Modern lifestyles, and the popularization of artificial light at night, have led to maladjusted social time and internal circadian rhythm, so developing an instrument on biological rhythms is critical. A 36-item self-rated questionnaire assessing biological rhythm disorder in adolescents was developed according to the literature and expert evaluations. Based on a literature review, four dimensions, digital media use, sleep, eating habits, and activity, were determined. After preliminary item analysis, seven unqualified items were eliminated. A total of 1,152 college students and 8,082 middle school students were selected. Two independent sample t-tests, the Pearson correlations, and confirmatory factor analysis, were used to evaluate the reliability and validity of the questionnaire. The final questionnaire consisted of 4 dimensions covering 29 items, and the variance cumulative contribution was 62.65%. Cronbach's α for the total questionnaire was 0.950 and ranged from 0.817 to 0.904 for each dimension. The Pearson correlation coefficients between each item and the total score ranged from 0.360 to 0.755, and the Pearson correlation coefficient between each item and its dimension was between 0.575 and 0.841. Confirmatory factor analysis showed that the indices of CFI, TLI and RMSEA were 0.911, 0.901 and 0.043, respectively, which is a good degree of fit. The self-rating scale is consistent with the evaluation standard of psychometrics and can be used to evaluate the degree of biological rhythm disorder in adolescents.

Association between the Effects of High Temperature on Fertility and Sleep in Female Intra-Specific Hybrids of Drosophila melanogaster

Humans and fruit flies demonstrate similarity in sleep-wake behavior, e.g., in the pattern of sleep disturbances caused by an exposure to high temperature. Although research has provided evidence for a clear connection between sleeping problems and infertility in women, very little is known regarding the mechanisms underlying this connection. Studies of dysgenic crosses of fruit flies revealed that an exposure to elevated temperature induces sterility in female intra-specific hybrids exclusively in one of two cross directions (progeny of Canton-S females crossed with Harwich males). Given the complexity and limitations of human studies, this fruit flies' model of temperature-sensitive sterility might be used for testing whether the effects of high temperature on fertility and on 24-h sleep pattern are inter-related. To document this pattern, 315 hybrids were kept for at least five days in constant darkness at 20 °C and 29 °C. No evidence was found for a causal link between sterility and sleep disturbance. However, a diminished thermal responsiveness of sleep was shown by females with temperature-induced sterility, while significant responses to high temperature were still observed in fertile females obtained by crossing in the opposite direction (i.e., Canton-S males with Harwich females) and in fertile males from either cross.

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.

Pubertal mammary gland development is a key determinant of adult mammographic density

Mammographic density refers to the radiological appearance of fibroglandular and adipose tissue on a mammogram of the breast. Women with relatively high mammographic density for their age and body mass index are at significantly higher risk for breast cancer. The association between mammographic density and breast cancer risk is well-established, however the molecular and cellular events that lead to the development of high mammographic density are yet to be elucidated. Puberty is a critical time for breast development, where endocrine and paracrine signalling drive development of the mammary gland epithelium, stroma, and adipose tissue. As the relative abundance of these cell types determines the radiological appearance of the adult breast, puberty should be considered as a key developmental stage in the establishment of mammographic density. Epidemiological studies have pointed to the significance of pubertal adipose tissue deposition, as well as timing of menarche and thelarche, on adult mammographic density and breast cancer risk. Activation of hypothalamic-pituitary axes during puberty combined with genetic and epigenetic molecular determinants, together with stromal fibroblasts, extracellular matrix, and immune signalling factors in the mammary gland, act in concert to drive breast development and the relative abundance of different cell types in the adult breast. Here, we discuss the key cellular and molecular mechanisms through which pubertal mammary gland development may affect adult mammographic density and cancer risk.

Modeling circadian regulation of ovulation timing: age-related disruption of estrous cyclicity

The circadian clocks within the hypothalamic–pituitary–gonadal axis control estrous cycles in female rodents. The suprachiasmatic nucleus (SCN), where the central clock is located, generates daily signals to trigger surge release of luteinizing hormone (LH), which in turn induces ovulation. It has been observed in aged rodents that output from the SCN such as neuronal firing activity is declined, and estrous cycles become irregular and finally stop. Circadian clock mutants display accelerated reproductive aging, suggesting the complicated interplay between the circadian system and the endocrine system. To investigate such circadian regulation of estrous cycles, we construct a mathematical model that describes dynamics of key hormones such as LH and of circadian clocks in the SCN and in the ovary, and simulate estrous cycles for various parameter values. Our simulation results demonstrate that reduction of the amplitude of the SCN signal, which is a symptom of aging, makes estrous cycles irregular. We also show that variation in the phase of the SCN signal and changes in the period of ovarian circadian clocks exacerbates the aging effect on estrous cyclicity. Our study suggests that misalignment between the SCN and ovarian circadian oscillations is one of the primary causes of the irregular estrous cycles.

Adipokines: A gear shift in puberty

In this review, we discuss the role of adipokines in the onset of puberty in children with obesity during adrenarche and gonadarche and provide a clear and detailed overview of the biological processes of two major players, leptin and adiponectin. Adipokines, especially leptin and adiponectin, seem to induce an early onset of puberty in girls and boys with obesity by affecting the hypothalamic-pituitary-gonadal (HPG) axis. Moreover, adipokines and their receptors are expressed in the gonads, suggesting a role in sexual maturation and reproduction. All in all, adipokines may be a clue in understanding mechanisms underlying the onset of puberty in childhood obesity and puberty onset variability.

Adolescent Dietary Habit-induced Obstetric and Gynecologic Disease (ADHOGD) as a New Hypothesis-Possible Involvement of Clock System

There are growing concerns that poor dietary behaviors at young ages will increase the future risk of chronic diseases in adulthood. We found that female college students who skipped breakfast had higher incidences of dysmenorrhea and irregular menstruation, suggesting that meal skipping affects ovarian and uterine functions. Since dysmenorrhea is more prevalent in those with a past history of dieting, we proposed a novel concept that inadequate dietary habits in adolescence become a trigger for the subsequent development of organic gynecologic diseases. Since inadequate feeding that was limited during the non-active phase impaired reproductive functions in post-adolescent female rats, we hypothesize that circadian rhythm disorders due to breakfast skipping disrupts the hypothalamic–pituitary–ovarian axis, impairs the reproductive rhythm, and leads to ovarian and uterine dysfunction. To explain how reproductive dysfunction is memorized from adolescence to adulthood, we hypothesize that the peripheral clock system also plays a critical role in the latent progression of reproductive diseases together with the central system, and propose naming this concept “adolescent dietary habit-induced obstetric and gynecologic disease (ADHOGD)”. This theory will contribute to analyzing the etiologies of and developing prophylaxes for female reproductive diseases from novel aspects. In this article, we describe the precise outline of the above hypotheses with the supporting evidence in the literature.

Impact of Circadian Disruption on Female Mice Reproductive Function

In female mammals, cycles in reproductive function depend both on the biological clock synchronized to the light/dark cycle and on a balance between the negative and positive feedbacks of estradiol, whose concentration varies during oocyte maturation. In women, studies report that chronodisruptive environments such as shiftwork may impair fertility and gestational success. The objective of this study was to explore the effects of shifted light/dark cycles on both the robustness of the estrous cycles and the timing of the preovulatory luteinizing hormone (LH) surge in female mice. When mice were exposed to a single 10-hour phase advance or 10-hour phase delay, the occurrence and timing of the LH surge and estrous cyclicity were recovered at the third estrous cycle. By contrast, when mice were exposed to chronic shifts (successive rotations of 10-hoursour phase advances for 3 days followed by 10-hour phase delays for 4 days), they exhibited a severely impaired reproductive activity. Most mice had no preovulatory LH surge at the beginning of the chronic shifts. Furthermore, the gestational success of mice exposed to chronic shifts was reduced, because the number of pups was 2 times lower in shifted than in control mice. In conclusion, this study reports that exposure of female mice to a single phase shift has minor reproductive effects, whereas exposure to chronically disrupted light/dark cycles markedly impairs the occurrence of the preovulatory LH surge, leading to reduced fertility.

The Concept of Coupling in the Mammalian Circadian Clock Network

The circadian clock network regulates daily rhythms in mammalian physiology and behavior to optimally adapt the organism to the 24-h day/night cycle. A central pacemaker, the hypothalamic suprachiasmatic nucleus (SCN), coordinates subordinate cellular oscillators in the brain, as well as in peripheral organs to align with each other and external time. Stability and coordination of this vast network of cellular oscillators is achieved through different levels of coupling. Although coupling at the molecular level and across the SCN is well established and believed to define its function as pacemaker structure, the notion of coupling in other tissues and across the whole system is less well understood. In this review, we describe the different levels of coupling in the mammalian circadian clock system - from molecules to the whole organism. We highlight recent advances in gaining knowledge of the complex organization and function of circadian network regulation and its significance for the generation of stable but plastic intrinsic 24-h rhythms.

Individual evaluation of luteinizing hormone in aged C57BL/6 J female mice

In female mammals, reproductive senescence is a complex process involving progressive ovarian dysfunction associated with an altered central control of the hypothalamic-pituitary axis. The objective of this study was to compare the longitudinal change in preovulatory luteinizing hormone (LH) secretion as well as estrous cycle in individual C57BL/6 J female mice at 3, 6, 9 and 12 months. Amplitude and timing of LH secretion at the surge were similar from 3 to 9 months but were altered in 12-month old mice with a significant decrease of more than 50% of peak LH value and a 2 h delay in the occurrence of the LH surge as compared to younger mice. The analysis of two to three successive LH surges at 3, 6, 9 and 12 months showed low and similar intra-individual variability at all ages. The estrous cycle length and intra/inter variability were stable over the age. This study shows that female mice in regular environmental conditions display stable LH surge timing and amplitude up to 9 months, but at 12 months, the LH surge is delayed with a reduced amplitude, however without overt modification in the estrous cycles. Analysis of individual preovulatory LH secretion and estrous cycle indicates that mice can be followed up to 9 months to investigate the detrimental effects of various parameters on mouse reproductive activity.

Impaired decidualization caused by downregulation of circadian clock gene BMAL1 contributes to human recurrent miscarriage†

Recurrent miscarriage (RM) is characterized by two or more consecutive losses of a clinically established intrauterine pregnancy at early gestation. To date, the etiology of RM remains poorly understood. Impaired decidualization is thought to predispose women to subsequent pregnancy failure. The transcriptional factor brain and muscle aryl hydrocarbon receptor nuclear translocator-like (BMAL1) controls circadian rhythms and regulates a very large diversity of physiological processes. BMAL1 is essential for fertility. Here, we investigated the expression and function of BMAL1 in human decidualization and its relation with RM. A total of 39 decidua samples were collected. We also examined human endometrial stromal cells (HESCs) and primary endometrial stromal cells (ESCs), and primary decidual stromal cells (DSCs) isolated from decidua of first-trimester pregnancies. Compared to normal pregnant women, the expression of BMAL1 was reduced in the decidual tissues from individuals with RM. After in vitro induction of decidualization, the transcription of BMAL1 in both HESCs and primary ESCs was increased. This is in line with the relatively higher expression of BMAL1 in DSCs than in ESCs. Silencing of BMAL1 resulted in impaired decidualization. Moreover, levels of tissue inhibitors of metalloproteinases (TIMPs) increased significantly upon decidualization. Further experiments demonstrated that BMAL1 silencing curtails the ability of DSCs to restrict excessive trophoblast invasion via downregulation of TIMP3. Our study demonstrates a functional role for BMAL1 during decidualization: the downregulation of BMAL1 in RM leads to impaired decidualization and aberrant trophoblast invasion by regulating TIMP3 and consequently predisposing individuals for RM.

The estrogen-macrophage interplay in the homeostasis of the female reproductive tract

BACKGROUND

Estrogens are known to orchestrate reproductive events and to regulate the immune system during infections and following tissue damage. Recent findings suggest that, in the absence of any danger signal, estrogens trigger the physiological expansion and functional specialization of macrophages, which are immune cells that populate the female reproductive tract (FRT) and are increasingly being recognized to participate in tissue homeostasis beyond their immune activity against infections. Although estrogens are the only female gonadal hormones that directly target macrophages, a comprehensive view of this endocrine-immune communication and its involvement in the FRT is still missing.

OBJECTIVE AND RATIONALE

Recent accomplishments encourage a revision of the literature on the ability of macrophages to respond to estrogens and induce tissue-specific functions required for reproductive events, with the aim to envision macrophages as key players in FRT homeostasis and mediators of the regenerative and trophic actions of estrogens.

SEARCH METHODS

We conducted a systematic search using PubMed and Ovid for human, animal (rodents) and cellular studies published until 2018 on estrogen action in macrophages and the activity of these cells in the FRT.

OUTCOMES

Our search identified the remarkable ability of macrophages to activate biochemical processes in response to estrogens in cell culture experiments. The distribution at specific locations, interaction with selected cells and acquisition of distinct phenotypes of macrophages in the FRT, as well as the cyclic renewal of these properties at each ovarian cycle, demonstrate the involvement of these cells in the homeostasis of reproductive events. Moreover, current evidence suggests an association between estrogen-macrophage signaling and the generation of a tolerant and regenerative environment in the FRT, although a causative link is still missing.

WIDER IMPLICATIONS

Dysregulation of the functions and estrogen responsiveness of FRT macrophages may be involved in infertility and estrogen- and macrophage-dependent gynecological diseases, such as ovarian cancer and endometriosis. Thus, more research is needed on the physiology and pharmacological control of this endocrine-immune interplay.

Rotating night shift work and menopausal age

STUDY QUESTION

How are rotating night shift schedules associated with age at menopause among a large, national cohort of shift working nurses?

SUMMARY ANSWER

Our findings suggest that working rotating night shifts with sufficient frequency may modestly accelerate reproductive senescence among women who may already be predisposed to earlier menopause.

WHAT IS KNOWN ALREADY

Younger age at menopause has been associated with increased risk of adverse health outcomes, particularly those linked to reproduction. Night work has been associated with reproductive dysfunction, including disruption of menstrual cycle patterns.

STUDY DESIGN, SIZE, DURATION

This cohort study was conducted among 80 840 women of the Nurses' Health Study 2 (NHS2), with prospective follow-up from 1991 through 2013. Loss-to-follow-up of the NHS2 is estimated to be <10%.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We assessed the association between cumulative and current rotating night shift work and age at natural menopause over 22 years of follow-up (1991-2013). Cox proportional hazards models were used to estimate hazard ratios (HR) for menopause, adjusted for age, smoking status, body mass index, physical activity, alcohol consumption, reproductive factors and exogenous hormone use.

MAIN RESULTS AND THE ROLE OF CHANCE

Over follow-up, 27 456 women (34%) reached natural menopause. Women who worked 20 or more months of rotating night shifts in the prior 2-year had an increased risk of earlier menopause (multivariable-adjusted (MV)-HR = 1.09, 95% CI: 1.02-1.16) compared to women without rotating night shift work. This risk was stronger among women undergoing menopause or otherwise censored under age 45 years (MV-HR = 1.25, 95% CI: 1.08-1.46), than it was for those continuing in the study when >45 years old (MV-HR = 1.05, 95% CI: 0.99-1.13). Working 10 or more years of cumulative rotating night work was also associated with higher risk of menopause among women reaching menopause under age 45 (MV-HR10-19 years = 1.22, 95% CI: 1.03-1.44; MV-HR≥20 years = 1.73, 95% CI: 0.90-3.35), though not over the age of 45 years (MV-HR10-19 years = 1.04, 95% CI: 0.99-1.10; MV-HR≥20 years = 1.01, 95% CI: 0.89-1.15).

LIMITATIONS, REASONS FOR CAUTION

The degree to which observed effects of rotating night shifts on age at natural menopause are due to circadian disruption, rather than fatigue and stress associated with working more demanding schedules, is uncertain due to potential residual confounding by these factors.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to assess the effects of night work on menopausal timing among a larger national cohort of shift working women. Women already prone to earlier menopause may further truncate their reproductive lifetime by working schedules comprising day as well as night shifts.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by Center for Disease Control and Prevention/The National Institute for Occupational Safety and Health Grant 5R01OH009803 (PI: Schernhammer E), as well as UM1 CA176726 from the National Institute of Health. The funding sources had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review or approval of the article; and decision to submit the article for publication. The authors have no conflicts of interest.

Functional Implications of RFRP-3 in the Central Control of Daily and Seasonal Rhythms in Reproduction

Adaptation of reproductive activity to environmental changes is essential for breeding success and offspring survival. In mammals, the reproductive system displays regular cycles of activation and inactivation which are synchronized with seasonal and/or daily rhythms in environmental factors, notably light intensity and duration. Thus, most species adapt their breeding activity along the year to ensure that birth and weaning of the offspring occur at a time when resources are optimal. Additionally, female reproductive activity is highest at the beginning of the active phase during the period of full oocyte maturation, in order to improve breeding success. In reproductive physiology, it is therefore fundamental to delineate how geophysical signals are integrated in the hypothalamo-pituitary-gonadal axis, notably by the neurons expressing gonadotropin releasing hormone (GnRH). Several neurochemicals have been reported to regulate GnRH neuronal activity, but recently two hypothalamic neuropeptides belonging to the superfamily of (Arg)(Phe)-amide peptides, RFRP-3 and kisspeptin, have emerged as critical for the integration of environmental cues within the reproductive axis. The goal of this review is to survey the current understanding of the role played by RFRP-3 in the temporal regulation of reproduction, and consider how its effect might combine with that of kisspeptin to improve the synchronization of reproduction to environmental challenges.

Sex- and sub region-dependent modulation of arcuate kisspeptin neurones by vasopressin and vasoactive intestinal peptide

A population of kisspeptin neurones located in the hypothalamic arcuate nucleus (ARN) very likely represent the gonadotrophin-releasing hormone pulse generator responsible for driving pulsatile luteinising hormone secretion in mammals. As such, it has become important to understand the neural inputs that modulate the activity of ARN kisspeptin (ARN^KISS ) neurones. Using a transgenic GCaMP6 mouse model allowing the intracellular calcium levels ([Ca²⁺ ]_i ) of individual ARN^KISS neurones to be assessed simultaneously, we examined whether the circadian neuropeptides vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) modulated the activity of ARN^KISS neurones directly. To validate this methodology, we initially evaluated the effects of neurokinin B (NKB) on [Ca²⁺ ]_i in kisspeptin neurones residing within the rostral, middle and caudal ARN subregions of adult male and female mice. All experiments were undertaken in the presence of tetrodotoxin and ionotropic amino acid antagonists. NKB was found to evoke an abrupt increase in [Ca²⁺ ]_i in 95%-100% of kisspeptin neurones throughout the ARN of both sexes. By contrast, both VIP and AVP were found to primarily activate kisspeptin neurones located in the caudal ARN of female mice. Although 58% and 59% of caudal ARN kisspeptin neurones responded to AVP and VIP, respectively, in female mice, only 0%-8% of kisspeptin neurones located in other ARN subregions responded in females and 0%-12% of cells in any subregion in males (P < 0.05). These observations demonstrate unexpected sex differences and marked heterogeneity in functional neuropeptide receptor expression amongst ARN^KISS neurones organised on a rostro-caudal basis. The functional significance of this unexpected influence of VIP and AVP on ARN^KISS neurones remains to be established.

Circadian Control of Neuroendocrine Function: Implications for Health and Disease

The circadian timing system orchestrates daily rhythms in physiology and behavior via the suprachiasmatic nucleus (SCN), the master brain clock. Because endocrine secretions have far-reaching influence on the brain and periphery, circadian regulation of hormones is essential for normal functioning and disruptions to circadian timing (e.g., irregular sleep patterns, limited exposure to sunlight, jet lag, nighttime light exposure) have detrimental health consequences. Herein, we provide an overview of circadian timing in three major endocrine axes, the hypothalamo-pituitary-gonadal (HPG), hypothalamo-pituitary-adrenal (HPA) and hypothalamo-pituitary-thyroid (HPT) axes, and then consider the negative health consequences of circadian disruptions in each of these systems. For example, disruptions to HPG axis circadian timing lead to a host of negative reproductive outcomes such as irregular menstrual cycles, low sperm density and increased rates of miscarriages and infertility. Dysregulation of HPA axis timing is associated with obesity and metabolic disease, whereas disruptions to the HPT axis are associated with dysregulated metabolic gene rhythms in the heart. Together, this overview underscores the significance of circadian endocrine rhythms in normal health and disease prevention.

Periodic regulation of expression of genes for kisspeptin, gonadotropin-inhibitory hormone and their receptors in the grass puffer: Implications in seasonal, daily and lunar rhythms of reproduction

The seasonal, daily and lunar control of reproduction involves photoperiodic, circadian and lunar changes in the activity of kisspeptin, gonadotropin-inhibitory hormone (GnIH) and gonadotropin-releasing hormone (GnRH) neurons. These changes are brought through complex networks of light-, time- and non-photic signal-dependent control mechanisms, which are mostly unknown at present. The grass puffer, Takifugu alboplumbeus, a semilunar spawner, provides a unique and excellent animal model to assess this question because its spawning is synchronized with seasonal, daily and lunar cycles. In the diencephalon, the genes for kisspeptin, GnIH and their receptors showed similar expression patterns with clear seasonal and daily oscillations, suggesting that they are regulated by common mechanisms involving melatonin, circadian clock and water temperature. For implications in semilunar-synchronized spawning rhythm, melatonin receptor genes showed ultradian oscillations in expression with the period of 14.0-15.4 h in the pineal gland. This unique ultradian rhythm might be driven by circatidal clock. The possible circatidal clock and circadian clock in the pineal gland may cooperate to drive circasemilunar rhythm to regulate the expression of the kisspeptin, GnIH and their receptor genes. On the other hand, high temperature (over 28 °C) conditions, under which the expression of the kisspeptin and its receptor genes is markedly suppressed, may provide an environmental signal that terminates reproduction at the end of breeding period. Taken together, the periodic regulation of the kisspeptin, GnIH and their receptor genes by melatonin, circadian clock and water temperature may be important in the precisely-timed spawning of the grass puffer.

Strong Circadian Rhythms in the Choroid Plexus: Implications for Sleep-Independent Brain Metabolite Clearance

Cerebrospinal fluid (CSF) is a fluidic part of the brain’s microenvironment that isolates the brain from the rest of the body. CSF dilutes metabolites from neuronal activities and removes them from the brain. Its production and resorption are regulated dynamically and are central to maintaining brain homeostasis. We discovered that the major CSF source, the choroid plexus (CP), harbors the brain’s strongest circadian clock. Here, we consider some implications of the CP circadian clock for metabolite clearance in the brain. If the circadian clock contributes to timed production of the CSF, its synchronization with sleep timing can maximize clearance efficiency and help prevent neurodegenerative diseases such as Alzheimer’s disease.

Molecular basis of androgen action on human sexual desire

Reproduction is a fundamental process for the species maintenance and the propagation of genetic information. The energy expenditure for mating is overtaken by motivational stimuli, such as orgasm, finely regulated by steroid hormones, gonadotropins, neurotransmitters and molecules acting in the brain and peripheral organs. These functions are often investigated using animal models and translated to humans, where the androgens action is mediated by nuclear and membrane receptors converging in the regulation of both long-term genomic and rapid non-genomic signals. In both sexes, testosterone is a central player of this game and is involved in the regulation of sexual desire and arousal, and, finally, in reproduction through cognitive and peripheral physiological mechanisms which may decline with aging and circadian disruption. Finally, genetic variations impact on reproductive behaviours, resulting in sex-specific effect and different reproductive strategies. In this review, androgen actions on sexual desire are evaluated, focusing on the molecular levels of interaction.

Rabconnectin-3α is required for the morphological maturation of GnRH neurons and kisspeptin responsiveness

A few hundred hypothalamic neurons form a complex network that controls reproduction in mammals by secreting gonadotropin-releasing hormone (GnRH). Timely postnatal changes in GnRH secretion are essential for pubertal onset. During the juvenile period, GnRH neurons undergo morphological remodeling, concomitantly achieving an increased responsiveness to kisspeptin, the main secretagogue of GnRH. However, the link between GnRH neuron activity and their morphology remains unknown. Here, we show that brain expression levels of Dmxl2, which encodes the vesicular protein rabconnectin-3α, determine the capacity of GnRH neurons to be activated by kisspeptin and estradiol. We also demonstrate that Dmxl2 expression levels control the pruning of GnRH dendrites, highlighting an unexpected role for a vesicular protein in the maturation of GnRH neuronal network. This effect is mediated by rabconnectin-3α in neurons or glial cells afferent to GnRH neurons. The widespread expression of Dmxl2 in several brain areas raises the intriguing hypothesis that rabconnectin-3α could be involved in the maturation of other neuronal populations.

Both the Suprachiasmatic Nucleus and the Superior Ovarian Nerve Contribute to the Processes of Ovulation and Steroid Hormone Secretion on Proestrus

The aims of the present study were to analyze if the superior ovarian nerve (SON) plays a role in the neural signals from suprachiasmatic nucleus (SCN) that lead to ovulation and ovarian steroids secretion on proestrus day. Rats on proestrus day were treated at 11.00 to 11.30 or 17.00 to 17.30 hours with 1 of the 3 experimental procedures (1) unilateral or bilateral SON sectioning, (2) unilateral or bilateral injury to the SCN, or (3) unilateral injury to the SCN followed by unilateral sectioning of the SON ipsilateral to the treated SCN. Treatments were evaluated 24 hours after surgical procedures. Compared to laparotomized animals, right or bilateral SON sectioning treatment at 17.00 hours resulted in lower ovulation rates and number of ova shed by the right ovary. The ovaries of nonovulating animals showed early follicular luteinization signs and trapped ova. Bilateral SCN injury treatment at 11.00 hours resulted in anovulation; whereas right SCN injury treatment, with or without right SON sectioning, resulted in a lower number of ova shed. Injecting luteinizing hormone-releasing hormone to animals with bilateral SCN injury restored ovulation. In rats with unilateral or bilateral SON sectioning, or with injury to the SCN with or without unilateral sectioning of the SON, the effects on hormone levels depended of the hormone studied and the time of day treatment was performed. The present results suggest that on proestrus day, the role of the right or both SON in ovulation and steroid hormone secretion regulation takes place through different neuroendocrine mechanisms from SCN.

Neurons and Glial Cells Are Added to the Female Rat Anteroventral Periventricular Nucleus During Puberty

The anteroventral periventricular nucleus (AVPV) orchestrates the neuroendocrine-positive feedback response that triggers ovulation in female rodents. The AVPV is larger and more cell-dense in females than in males, and during puberty, only females develop the capacity to show a positive feedback response. We previously reported a potential new mechanism to explain this female-specific gain of function during puberty, namely a female-biased sex difference in the pubertal addition of new cells to the rat AVPV. Here we first asked whether this sex difference is due to greater cell proliferation and/or survival in females. Female and male rats received the cell birthdate marker 5-bromo-2'-deoxyuridine (BrdU; 200 mg/kg, ip) on postnatal day (P) 30; brains were collected at short and long intervals after BrdU administration to assess cell proliferation and survival, respectively. Overall, females had more BrdU-immunoreactive cells in the AVPV than did males, with no sex differences in the rate of cell attrition over time. Thus, the sex difference in pubertal addition of AVPV cells appears to be due to greater cell proliferation in females. Next, to determine the phenotype of pubertally born AVPV cells, daily BrdU injections were given to female rats on P28-56, and tissue was collected on P77 to assess colocalization of BrdU and markers for mature neurons or glia. Of the pubertally born AVPV cells, approximately 15% differentiated into neurons, approximately 19% into astrocytes, and approximately 23% into microglia. Thus, both neuro- and gliogenesis occur in the pubertal female rat AVPV and potentially contribute to maturation of female reproductive function.

RFRP Neurons - The Doorway to Understanding Seasonal Reproduction in Mammals

Seasonal control of reproduction is critical for the perpetuation of species living in temperate zones that display major changes in climatic environment and availability of food resources. In mammals, seasonal cues are mainly provided by the annual change in the 24-h light/dark ratio (i.e., photoperiod), which is translated into the nocturnal production of the pineal hormone melatonin. The annual rhythm in this melatonin signal acts as a synchronizer ensuring that breeding occurs when environmental conditions favor survival of the offspring. Although specific mechanisms might vary among seasonal species, the hypothalamic RF (Arg-Phe) amide-related peptides (RFRP-1 and -3) are believed to play a critical role in the central control of seasonal reproduction and in all seasonal species investigated, the RFRP system is persistently inhibited in short photoperiod. Central chronic administration of RFRP-3 in short day-adapted male Syrian hamsters fully reactivates the reproductive axis despite photoinhibitory conditions, which highlights the importance of the seasonal changes in RFRP expression for proper regulation of the reproductive axis. The acute effects of RFRP peptides, however, depend on species and photoperiod, and recent studies point toward a different role of RFRP in regulating female reproductive activity. In this review, we summarize the recent advances made to understand the role and underlying mechanisms of RFRP in the seasonal control of reproduction, primarily focusing on mammalian species.