FSH induces the development of circadian clockwork in rat granulosa cells via a gap junction protein Cx43-dependent pathway

Gap junctions in polycystic ovary syndrome: Implications for follicular arrest

Gap junctions are specialized intercellular conduits that provide a direct pathway between neighboring cells, which are involved in numerous physiological processes, such as cellular differentiation, cell growth, and metabolic coordination. The effect of gap junctional hemichannels in folliculogenesis is particularly obvious, and the down-regulation of connexins is related to abnormal follicle growth. Polycystic ovary syndrome (PCOS) is a ubiquitous endocrine disorder of the reproductive system, affecting the fertility of adult women due to anovulation. Exciting evidence shows that gap junction is involved in the pathological process related to PCOS and affects the development of follicles in women with PCOS. In this review, we examine the expression of connexins in follicular cells of PCOS and figure out whether such communication could have consequences for PCOS women. While along with results from clinical and related animal studies, we summarize the mechanism of connexins involved in the pathogenesis of PCOS.

The molecular characteristic analysis of TRIB2 gene and its expressional patterns in Bos grunniens tissue and granulosa cells

Tribbles homolog 2 (TRIB2) plays an important role in the follicular development of female mammals. However, its expression and function in the yak (Bos grunniens) are still unclear. In this study, we predicted the molecular characteristics of TRIB2, and revealed its expression pattern in yak (Bos grunniens) tissues and ovarian granulosa cells. We cloned the full length of the yak TRIB2 gene obtained by RT-PCR was 1368 bp and the coding sequence (CDS) was 624 bp, encoding 207 amino acids (AA). Homology analysis showed that the yak TRIB2 is highly conserved among species. TRIB2 was detected to be extensively expressed in seven tissues of the yak liver, spleen, lung, kidney, ovary, oviduct and uterus by qPCR. The expression of TRIB2 mRNA in the ovary during gestation was significantly lower than that in the non-pregnant (p < 0.05). At each stage of follicle development, the TRIB2 mRNA in granulosa cells showed a significant upward trend with the development of follicles. The expression of TRIB2 gradually decreased with the increase of the culture time of the granulosa cells in vitro. In conclusion, these results suggest that TRIB2 may play an important role in the follicular development of yaks.

Advances in circadian clock regulation of reproduction

The mammalian circadian clock is an endogenously regulated oscillator that is synchronized with solar time and cycle within a 24-h period. The circadian clock exists not only in the suprachiasmatic nucleus (SCN) of the hypothalamus, a central pacemaker of the circadian clock system, but also in numerous peripheral tissues known as peripheral circadian oscillators. The SCN and peripheral circadian oscillators mutually orchestrate the diurnal rhythms of various physiological and behavioral processes in a hierarchical manner. In the past two decades, peripheral circadian oscillators have been identified and their function has been determined in the mammalian reproductive system and its related endocrine glands, including the hypothalamus, pituitary gland, ovaries, testes, uterus, mammary glands, and prostate gland. Increasing evidence indicates that both the SCN and peripheral circadian oscillators play discrete roles in coordinating reproductive processes and optimizing fertility in mammals. The present study reviews recent evidence on circadian clock regulation of reproductive function in the hypothalamic-pituitary-gonadal axis and reproductive system. Additionally, we elucidate the effects of chronodisruption (as a result of, for example, shift work, jet lag, disrupted eating patterns, and sleep disorders) on mammalian reproductive performance from multiple aspects. Finally, we propose potential behavioral changes or pharmaceutical strategies for the prevention and treatment of reproductive disorders from the perspective of chronomedicine. Conclusively, this review will outline recent evidence on circadian clock regulation of reproduction, providing novel perspectives on the role of the circadian clock in maintaining normal reproductive functions and in diseases that negatively affect fertility.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

Integrative analysis of transcriptome complexity in pig granulosa cells by long-read isoform sequencing

Background

In intensive and large-scale farms, abnormal estradiol levels in sows can cause reproductive disorders. The high incidence rate of reproductive disturbance will induce the elimination of productive sows in large quantities, and the poor management will bring great losses to the pig farms. The change in estradiol level has an important effect on follicular development and estrus of sows. To solve this practical problem and improve the productive capacity of sows, it is significant to further clarify the regulatory mechanism of estradiol synthesis in porcine granulosa cells (GCs). The most important function of granulosa cells is to synthesize estradiol. Thus, the studies about the complex transcriptome in porcine GCs are significant. As for precursor-messenger RNAs (pre-mRNAs), their post-transcriptional modification, such as alternative polyadenylation (APA) and alternative splicing (AS), together with long non-coding RNAs (lncRNAs), may regulate the functions of granulosa cells. However, the above modification events and their function are unclear within pig granulosa cells.

Methods

Combined PacBio long-read isoform sequencing (Iso-Seq) was conducted in this work for generating porcine granulosa cells' transcriptomic data. We discovered new transcripts and possible gene loci via comparison against reference genome. Later, combined Iso-Seq data were adopted to uncover those post-transcriptional modifications such as APA or AS, together with lncRNA within porcine granulosa cells. For confirming that the Iso-Seq data were reliable, we chose four AS genes and analyzed them through RT-PCR.

Results

The present article illustrated that pig GCs had a complex transcriptome, which gave rise to 8,793 APA, 3,465 AS events, 703 candidate new gene loci, as well as 92 lncRNAs. The results of this study revealed the complex transcriptome in pig GCs. It provided a basis for the interpretation of the molecular mechanism in GCs.

Transcriptional Feedback Loops in the Caprine Circadian Clock System

The circadian clock system is based on interlocked positive and negative transcriptional and translational feedback loops of core clock genes and their encoded proteins. The mammalian circadian clock system has been extensively investigated using mouse models, but has been poorly investigated in diurnal ruminants. In this study, goat embryonic fibroblasts (GEFs) were isolated and used as a cell model to elucidate the caprine circadian clock system. Real-time quantitative PCR analysis showed that several clock genes and clock-controlled genes were rhythmically expressed in GEFs over a 24 h period after dexamethasone stimulation. Immunofluorescence revealed that gBMAL1 and gNR1D1 proteins were expressed in GEFs, and western blotting analysis further verified that the proteins were expressed with circadian rhythmic changes. Diurnal changes in clock and clock-controlled gene expression at the mRNA and protein levels were also observed in goat liver and kidney tissues at two representative time points in vivo. Amino acid sequences and tertiary structures of goat BMAL1 and CLOCK proteins were found to be highly homologous to those in mice and humans. In addition, a set of goat representative clock gene orthologs and the promoter regions of two clock genes of goats and mice were cloned. Dual-luciferase reporter assays showed that gRORα could activate the promoter activity of the goat BMAL1, while gNR1D1 repressed it. The elevated pGL4.10-gNR1D1-Promoter-driven luciferase activity induced by mBMAL1/mCLOCK was much higher than that induced by gBMAL1/gCLOCK, and the addition of gCRY2 or mPER2 repressed it. Real-time bioluminescence assays revealed that the transcriptional activity of BMAL1 and NR1D1 in goats and mice exhibited rhythmic changes over a period of approximately 24 h in NIH3T3 cells or GEFs. Notably, the amplitudes of gBMAL1 and gNR1D1 promoter-driven luciferase oscillations in NIH3T3 cells were higher than those in GEFs, while mBMAL1 and mNR1D1 promoter-driven luciferase oscillations in NIH3T3 cells had the highest amplitude. In sum, transcriptional and translational loops of the mammalian circadian clock system were found to be broadly conserved in goats and not as robust as those found in mice, at least in the current experimental models. Further studies are warranted to elucidate the specific molecular mechanisms involved.

Circadian clock regulates granulosa cell autophagy through NR1D1-mediated inhibition of ATG5

Autophagy of granulosa cells (GCs) is involved in follicular atresia, which occurs repeatedly during the ovarian development cycle. Several circadian clock genes are rhythmically expressed in both rodent ovarian tissues and GCs. Nuclear receptor subfamily 1 group D member 1 (NR1D1), an important component of the circadian clock system, is involved in the autophagy process through the regulation of autophagy-related genes. However, there are no reports illustrating the role of the circadian clock system in mouse GC autophagy. In the present study, we found that core circadian clock genes (Bmal1, Per2, Nr1d1, and Dbp) and an autophagy-related gene (Atg5) exhibited rhythmic expression patterns across 24 h in mouse ovaries and primary GCs. Treatment with SR9009, an agonist of NR1D1, significantly reduced the expression of Bmal1, Per2, and Dbp in mouse GCs. ATG5 expression was significantly attenuated by SR9009 treatment in mouse GCs. Conversely, Nr1d1 knockdown increased ATG5 expression in mouse GCs. Decreased NR1D1 expression at both the mRNA and protein levels was detected in the ovaries of Bmal1^-/- mice, along with elevated expression of ATG5. Dual-luciferase reporter assay and electrophoretic mobility shift assay showed that NR1D1 inhibited Atg5 transcription by binding to two putative retinoic acid-related orphan receptor response elements within the promoter. In addition, rapamycin-induced autophagy and ATG5 expression were partially reversed by SR9009 treatment in mouse GCs. Taken together, our current data demonstrated that the circadian clock regulates GC autophagy through NR1D1-mediated inhibition of ATG5 expression, and thus, plays a role in maintaining autophagy homeostasis in GCs.

Bmal1 promotes prostaglandin E2 synthesis by upregulating Ptgs2 transcription in response to increasing estradiol levels in day 4 pregnant mice

Prostaglandin G/H synthase 2 (PTGS2) is a rate-limiting enzyme in prostaglandin synthesis. The present study assessed the role of the uterine circadian clock on Ptgs2 transcription in response to steroid hormones during early pregnancy. We demonstrated that the core clock genes (Bmal1, Per2, Nr1d1, and Dbp), Vegf, and Ptgs2, and their encoded proteins, have rhythmic expression in the mouse uterus from days 3.5 to 4.5 (D3.5-4.5) of pregnancy. Progesterone (P4) treatment of cultured uterus endometrial stromal cells (UESCs) isolated from mPer2Luciferase reporter gene knock-in mice on D4 induced a phase shift in PER2::LUCIFERASE oscillations. This P4-induced phase shift of PER2::LUCIFERASE oscillations was significantly attenuated by the P4 antagonist RU486. Additionally, the amplitude of PER2::LUCIFERASE oscillations was increased by estradiol (E2) treatment in the presence of P4. Consistently, the mRNA levels of clock genes (Bmal1 and Per2), Vegf, and Ptgs2 were markedly increased by E2 treatment of UESCs in the presence of P4. Treatment with E2 also promoted prostaglandin E2 (PGE2) synthesis by UESCs. Depletion of Bmal1 in UESCs by small-interfering RNA (siRNA) decreased the transcript levels of clock genes (Nr1d1 and Dbp), Vegf, and Ptgs2 compared with nonsilencing siRNA treatment. Bmal1 knockdown also inhibited PGE2 synthesis. Moreover, the mRNA expression levels of clock genes (Nr1d1 and Dbp), Vegf, and Ptgs2, and their respective proteins were significantly decreased in the uterus of Bmal1-/- mice. Thus, these data suggest that Bmal1 in mice promotes PGE2 synthesis by upregulating Ptgs2 in response to increases in E2 on D4 of pregnancy.NEW & NOTEWORTHY Rhythmic expression of Bmal1 and Ptgs2 was observed in the uterus isolated from D3.5-4.5 of pregnant mice. E2 increased the expression of Bmal1 and Ptg2 in UESCs isolated from mice on D4. The expression of Ptgs2 was significantly decreased in Bmal1-siRNA treated UESCs. Bmal1 knockdown also inhibited PGE2 synthesis. Thus, these data suggest that Bmal1 in mice promotes PGE2 synthesis by upregulating Ptgs2 in response to increases in E2 on D4 of pregnancy.

Circadian clock gene BMAL1 controls testosterone production by regulating steroidogenesis-related gene transcription in goat Leydig cells

Testosterone is produced by Leydig cells (LCs) and undergoes diurnal changes in serum levels in rats, mice, and humans, but little is known in goats. The present study revealed that goat serum testosterone levels displayed diurnal rhythmic changes (peak time at ZT11.2). Immunohistochemical staining showed that BMAL1, a circadian clock protein, is highly expressed in goat LCs. ELISA revealed that both hCG (0-5 IU/ml) and 22R-OH-cholesterol (0-30 μM) addition stimulated testosterone synthesis in primary goat LCs in a dose-dependent manner. Treating goat LCs with hCG (5 IU/ml) significantly increased intracellular cAMP levels. Additionally, real-time quantitative polymerase chain reaction (PCR) analysis revealed that the circadian clock (BMAL1, PER1, PER2, DBP, and NR1D1) and steroidogenesis-related genes (SF1, NUR77, StAR, HSD3B2, CYP17A1, CYP11A1, and HSD17B3) showed rhythmic expression patterns in goat LCs following dexamethasone synchronization. Several Bmal1-Luc circadian oscillations were clearly observed in dexamethasone-treated goat LCs transfected with the pLV6-Bmal1-Luc plasmid. BMAL1 knockdown significantly downregulated mRNA levels of PER2, NR1D1, DBP, StAR, HSD3B2, SF1, NUR77, and GATA4, and dramatically decreased StAR and HSD3B2 protein levels and testosterone production. In contrast, BMAL1 overexpression significantly increased the mRNA and protein expression levels of StAR and HSD17B3 and enhanced testosterone production. Reporter assays revealed that goat BMAL1, or in combination with mouse CLOCK, activated goat HSD17B3 transcription in vitro. These data indicate that BMAL1 contributes to testosterone production by regulating transcription of steroidogenesis-related genes in goat LCs, providing a basis for further exploring the underlying mechanism by which the circadian clock regulates ruminant reproductive capability.

Zearalenone perturbs the circadian clock and inhibits testosterone synthesis in mouse Leydig cells

Zearalenone (ZEA), a mycotoxin, is known to impair reproductive capability by disrupting the synthesis and secretion of testosterone by Leydig cells (LCs), although the mechanism is unknown. Robust rhythmicity of circadian clock and steroidogenic genes were identified in LCs. The aim of this study was to examine whether ZEA significantly attenuated the transcription of core clock genes (Bmal1, Dbp, Per2, and Nr1d1) as well as steroidogenic genes (StAR, Hsd3b2, and Cyp11a1) in mouse testis Leydig cell line (TM3). Western blotting confirmed declines in BMAL1, NR1D1, and StAR protein levels. ZEA also suppressed secreted testosterone levels. In primary LCs, isolated from PER2::LUCIFERASE reporter gene knock in mice, ZEA diminished the amplitude of PER2::LUC expression, and induced a phase shift and period extension. In primary LCs, ZEA also suppressed the expression levels of core clock and steroidogenic genes, reduced protein levels of BMAL1, and decreased testosterone secretion. In vivo expression of core clock and steroidogenic genes were reduced in testes of mice exposed to ZEA for 1 week leading to decreased serum testosterone levels. In summary, data suggest that ZEA may impair testosterone synthesis through attenuation of the circadian clock in LCs culminating in reproductive dysfunction in male mammals .

HIF-1α Protects Granulosa Cells From Hypoxia-Induced Apoptosis During Follicular Development by Inducing Autophagy

Owing to the avascular structure of the ovarian follicle, proliferation of granulosa cells (GCs) and development of follicles occur under hypoxia, which is obviously different from the cell survival requirements of most mammalian cells. We hypothesized that autophagy may exert an inhibitory effect on GC apoptosis. To decipher the underlying mechanism, we constructed a rat follicular development model using pregnant mare serum gonadotropin and a cell culture experiment in hypoxic conditions (3% O₂). The present results showed that the autophagy level was obviously increased and was accompanied by the concomitant elevation of hypoxia inducible factor (HIF)-1α and BNIP3 (Bcl-2/adenovirus E1B 19kDa-interacting protein 3) in GCs during follicular development. The levels of Bax (Bcl2-associated X) and Bcl-2 (B-cell lymphoma-2) were increased, while the activation of caspase-3 exhibited no obvious changes during follicular development. However, inhibition of HIF-1α attenuated the increase in Bcl-2 and promoted the increase in Bax and cleaved caspase-3. Furthermore, we observed the downregulation of BNIP3 and the decrease in autophagy after treatment with a specific HIF-1α activity inhibitor (echinomycin), indicating that HIF-1α/BNIP3 was involved in autophagy regulation in GCs in vivo. In an in vitro study, we also found that hypoxia did not obviously promote GC apoptosis, while it significantly enhanced the activation of HIF-1α/BNIP3 and the induction of autophagy. Expectedly, this effect could be reversed by 3-methyladenine (3-MA) treatment. Taken together, these findings demonstrated that hypoxia drives the activation of HIF-1α/BNIP3 signaling, which induces an increase in autophagy, protecting GC from apoptosis during follicular development.

Shiftwork and Light at Night Negatively Impact Molecular and Endocrine Timekeeping in the Female Reproductive Axis in Humans and Rodents

Shiftwork, including work that takes place at night (nightshift) and/or rotates between day and nightshifts, plays an important role in our society, but is associated with decreased health, including reproductive dysfunction. One key factor in shiftwork, exposure to light at night, has been identified as a likely contributor to the underlying health risks associated with shiftwork. Light at night disrupts the behavioral and molecular circadian timekeeping system, which is important for coordinated timing of physiological processes, causing mistimed hormone release and impaired physiological functions. This review focuses on the impact of shiftwork on reproductive function and pregnancy in women and laboratory rodents and potential underlying molecular mechanisms. We summarize the negative impact of shiftwork on female fertility and compare these findings to studies in rodent models of light shifts. Light-shift rodent models recapitulate several aspects of reproductive dysfunction found in shift workers, and their comparison with human studies can enable a deeper understanding of physiological and hormonal responses to light shifts and the underlying molecular mechanisms that may lead to reproductive disruption in human shift workers. The contributions of human and rodent studies are essential to identify the origins of impaired fertility in women employed in shiftwork.

Downregulation of gap junctional intercellular communication and connexin 43 expression by bisphenol A in human granulosa cells

Gap junctional intercellular communication (GJIC) is the transfer of ions, metabolites, and second messengers between neighboring cells through intercellular junctions. Connexin 43 (Cx43) was found to be the type of gap junction protein responsible for human granulosa cells (GCs) and oocyte communication, which is required for folliculogenesis and oocyte maturation. Bisphenol A (BPA), an estrogenic-like endocrine-disrupting chemical, is one of the most widely produced chemicals around the world. There are reports that the chemical might cause endometrial tumorigenesis and several female reproductive disorders. This study demonstrated that cell culture medium, containing antioxidants (N-acetyl-l-cysteine and l-ascorbic acid-2-phosphate), was able to enhance the survival and self-renewal of GCs. In addition, we found that BPA at environmentally relevant concentration (10^-7  M) reduced Cx43 expression and GJIC in GCs through estrogen receptor and mitogen-activated protein kinase pathways. The results of this study not only reveal the reproductive toxicity of BPA but also provide possible mechanisms by which BPA inhibited GJIC in GCs.

Connexins: Key Players in the Control of Vascular Plasticity and Function

Of the 21 members of the connexin family, 4 (Cx37, Cx40, Cx43, and Cx45) are expressed in the endothelium and/or smooth muscle of intact blood vessels to a variable and dynamically regulated degree. Full-length connexins oligomerize and form channel structures connecting the cytosol of adjacent cells (gap junctions) or the cytosol with the extracellular space (hemichannels). The different connexins vary mainly with regard to length and sequence of their cytosolic COOH-terminal tails. These COOH-terminal parts, which in the case of Cx43 are also translated as independent short isoforms, are involved in various cellular signaling cascades and regulate cell functions. This review focuses on channel-dependent and -independent effects of connexins in vascular cells. Channels play an essential role in coordinating and synchronizing endothelial and smooth muscle activity and in their interplay, in the control of vasomotor actions of blood vessels including endothelial cell reactivity to agonist stimulation, nitric oxide-dependent dilation, and endothelial-derived hyperpolarizing factor-type responses. Further channel-dependent and -independent roles of connexins in blood vessel function range from basic processes of vascular remodeling and angiogenesis to vascular permeability and interactions with leukocytes with the vessel wall. Together, these connexin functions constitute an often underestimated basis for the enormous plasticity of vascular morphology and function enabling the required dynamic adaptation of the vascular system to varying tissue demands.

Role of core circadian clock genes in hormone release and target tissue sensitivity in the reproductive axis

Precise timing in hormone release from the hypothalamus, the pituitary and ovary is critical for fertility. Hormonal release patterns of the reproductive axis are regulated by a feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. The timing and rhythmicity of hormone release and tissue sensitivity in the HPG axis is regulated by circadian clocks located in the hypothalamus (suprachiasmatic nucleus, kisspeptin and GnRH neurons), the pituitary (gonadotrophs), the ovary (theca and granulosa cells), the testis (Leydig cells), as well as the uterus (endometrium and myometrium). The circadian clocks integrate environmental and physiological signals to produce cell endogenous rhythms generated by a transcriptional-translational feedback loop of transcription factors that are collectively called the "molecular clock". This review specifically focuses on the contribution of molecular clock transcription factors in regulating hormone release patterns in the reproductive axis, with an emphasis on the female reproductive system. Specifically, we discuss the contributions of circadian rhythms in distinct neuronal populations of the female hypothalamus, the molecular clock in the pituitary and its overall impact on female and male fertility.

High-fat diet-induced dysregulation of ovarian gene expression is restored with chronic omega-3 fatty acid supplementation

Chronic high-fat diet (HFD) consumption causes ovarian dysfunction in rodents. Acute dietary treatment with docosahexaenoic acid (DHA) increases oocyte quality and ovarian reserve at advanced reproductive age. We hypothesized that DHA supplementation after HFD exposure reverses HFD-induced ovarian defects. We conducted a dietary intervention with reversal to chow, DHA-supplemented chow, or DHA-supplemented HFD after HFD consumption. After 10 weeks, HFD-fed mice had impaired estrous cyclicity, decreased primordial follicles, and altered ovarian expression of 24 genes compared to chow controls. Diet reversal to either chow or chow + DHA restored estrous cyclicity, however only chow + DHA appeared to mitigated the impact of HFD on ovarian reserve. All dietary interventions restored HFD-dysregulated gene expression to chow levels. We found no association between follicular fluid DHA levels and ovarian reserve. In conclusion our data suggest some benefit of DHA supplementation after HFD, particularly in regards to ovarian gene expression, however complete restoration of ovarian function was not achieved.

Leptin Receptor Mediates Bmal1 Regulation of Estrogen Synthesis in Granulosa Cells

Simple Summary

There is increased interest in determining the effect of the biological clock system on reproduction, but how this biological system affects mammalian fertility and the regulation by clock genes on key genes of reproduction is poorly understood. This study examined the function of Leptin on reproduction through interaction with the Leptin receptor (Lepr) and the regulation of the key clock gene brain and muscle ARNT-like 1 (Bmal1) on Lepr. The results suggested that estrogen (E₂) synthesis is regulated by Bmal1 through the Leptin–Lepr pathway as part of the regulatory mechanism of the circadian system on the fertility of female mammals.

Abstract

Chronobiology affects female fertility in mammals. Lepr is required for leptin regulation of female reproduction. The presence of E-box elements in the Lepr promoter that are recognized and bound by clock genes to initiate gene transcription suggested that circadian systems might regulate fertility through Lepr. However, it is unclear whether Bmal1, a key oscillator controlling other clock genes, is involved in leptin regulation in hormone synthesis through Lepr. In this study, serum estradiol (E₂) concentration and the expressions of Bmal1, Lepr, Cyp19a1, and Cyp11a1 genes were found to display well-synchronized circadian rhythms. Knockdown of Bmal1 significantly reduced expression levels of Lepr, Fshr, and Cyp19a1 genes; protein production of Bmal1, Lepr, and Cyp19a1; and the E₂ concentration in granulosa cells. Knockdown of Lepr reduced the expression levels of Cyp19a1 and Cyp11a1 genes and Cyp19a1 protein, and also reduced E₂ concentration. Addition of leptin affected the expression of Cyp19a1, Cyp11a1, and Fshr genes. Bmal1 deficiency counteracted leptin-stimulated upregulation of the genes encoding E₂ synthesis in granulosa cells. These results demonstrated that Bmal1 participates in the process by which leptin acts on Lepr to regulate E₂ synthesis.

ER stress activation impairs the expression of circadian clock and clock-controlled genes in NIH3T3 cells via an ATF4-dependent mechanism

Endoplasmic reticulum (ER) stress and circadian clockwork signaling pathways mutually regulate various cellular functions, but the details regarding the cross-talk between these pathways in mammalian cells are unclear. In this study, whether perturbation of ER stress signaling affects the cellular circadian clockwork and transcription of clock-controlled genes was investigated in NIH3T3 mouse fibroblasts. An NIH3T3 cell model stably expressing luciferase (Luc) under the control of the Bmal1 clock gene promoter was established using a lentiviral system. Then, Luc activity was monitored in real-time to detect Bmal1-Luc oscillations. The ER stress activators thapsigargin (Tg) and tunicamycin (Tm) markedly reduced Bmal1-Luc oscillation amplitudes and induced phase delay shifts in NIH3T3 cells. Treatment with Tg/Tm activated ER stress signaling by upregulating GRP78, CHOP, ATF6, and ATF4 and simultaneously significantly decreased BMAL1 protein levels and inhibited the transcription of circadian clock (Bmal1, Per2, Nr1d1, and Dbp) and clock-controlled (Scad1, Fgf7, and Arnt) genes. 4-Phenylbutyric acid, an ER stress inhibitor, alleviated the transcriptional repression of the circadian clock genes and partially restored Bmal1-Luc oscillation amplitudes in Tg- or Tm-treated NIH3T3 cells. More importantly, knock-down of ATF4, but not ATF6, in Tg-treated NIH3T3 cells partially rescued Bmal1-Luc oscillation amplitudes and mRNA expression of the four circadian clock genes. Taken together, our study demonstrates that ER stress activation inhibits the transcription of circadian clock and clock-controlled genes via an ATF4-dependent mechanism.

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.

Rhythmic expression of circadian clock genes in the preovulatory ovarian follicles of the laying hen

The circadian clock is reported to play a role in the ovaries in a variety of vertebrate species, including the domestic hen. However, the ovary is an organ that changes daily, and the laying hen maintains a strict follicular hierarchy. The aim of this study was to examine the spatial-temporal expression of several known canonical clock genes in the granulosa and theca layers of six hierarchy follicles. We demonstrated that the granulosa cells (GCs) of the F1-F3 follicles harbored intrinsic oscillatory mechanisms in vivo. In addition, cultured granulosa cells (GCs) from F1 follicles exposed to luteinizing hormone (LH) synchronization displayed Per2 mRNA oscillations, whereas, the less mature GCs (F5 plus F6) displayed no circadian change in Per2 mRNA levels. Cultures containing follicle-stimulating hormone (FSH) combined with LH expressed levels of Per2 mRNA that were 2.5-fold higher than those in cultures with LH or FSH alone. These results show that there is spatial specificity in the localization of clock cells in hen preovulatory follicles. In addition, our results support the hypothesis that gonadotropins provide a cue for the development of the functional cellular clock in immature GCs.

The Functional and Clinical Significance of the 24-Hour Rhythm of Circulating Glucocorticoids

Adrenal glucocorticoids are major modulators of multiple functions, including energy metabolism, stress responses, immunity, and cognition. The endogenous secretion of glucocorticoids is normally characterized by a prominent and robust circadian (around 24 hours) oscillation, with a daily peak around the time of the habitual sleep-wake transition and minimal levels in the evening and early part of the night. It has long been recognized that this 24-hour rhythm partly reflects the activity of a master circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus. In the past decade, secondary circadian clocks based on the same molecular machinery as the central master pacemaker were found in other brain areas as well as in most peripheral tissues, including the adrenal glands. Evidence is rapidly accumulating to indicate that misalignment between central and peripheral clocks has a host of adverse effects. The robust rhythm in circulating glucocorticoid levels has been recognized as a major internal synchronizer of the circadian system. The present review examines the scientific foundation of these novel advances and their implications for health and disease prevention and treatment.

Circadian clock and steroidogenic-related gene expression profiles in mouse Leydig cells following dexamethasone stimulation

Previous studies have shown that circadian clock genes are expressed in mammalian testes; however, it remains unclear if the expression patterns of these genes are cyclic. Furthermore, it is unknown whether Leydig cells, the primary androgen secreting cells in the testis, play a role in the rhythmicity of circadian clock and steroidogenic-related gene transcription. Here, we examine the circadian clock of mouse Leydig cells, and the link to steroidogenic-related gene transcription. We confirm, via sampling over a full circadian time (CT) period, a lack of circadian rhythmicity in mouse testes in comparison with the robust gene expression cycling of circadian clock genes in mouse livers. Immunofluorescence imaging of mouse testes collected at CT0 and CT12 show that the BMAL1 protein is exclusively expressed in mouse Leydig cells, and clearly linked to the circadian oscillation. Furthermore, dexamethasone treatment synchronized the expression of several of these canonical circadian clock and steroidogenic-related genes. Bioinformatic analyses revealed the presence of several circadian clock-related sequence motifs in the promoters of these steroidogenic-related genes. Our results suggest mouse Leydig cells may contain a functional circadian oscillator and the circadian clockwork in mouse Leydig cells regulates steroidogenic-related gene transcription by binding to the E-box, RORE, and D-box motifs in their promoters. However, additional research is required to determine the specific molecular mechanisms involved.

ATF6 knockdown decreases apoptosis, arrests the S phase of the cell cycle, and increases steroid hormone production in mouse granulosa cells

Activating transcription factor 6 (ATF6), a sensor protein located in the endoplasmic reticulum (ER) membrane, is an important factor in the ER stress signaling pathway. ER stress is known to be involved in folliculogenesis, follicular growth, and ovulation; however, the physiological function of ATF6 in mouse granulosa cells remains largely unknown. The aim of this study was to assess the role of ATF6 in mouse granulosa cells with respect to apoptosis, the cell cycle, and steroid hormone production, as well as several key genes related to follicular development, via RNA interference, immunohistochemical staining, real-time quantitative PCR, Western blotting, flow cytometry, terminal deoxynucleotidyltransferase-mediated deoxy-UTP nick end labeling (TUNEL) assay, and ELISA. Immunohistochemical staining revealed that ATF6 was extensively distributed in the granulosa cells of various ovarian follicles and oocytes in adult female mice. FSH or LH treatment significantly increased ATF6 protein levels in mouse granulosa cells. In the meantime, a recombinant plasmid was used to deplete ATF6 successfully using short hairpin RNA-mediated interference technology, which was verified at both the mRNA and protein levels. Flow cytometry and TUNEL assay analysis indicated that ATF6 depletion decreased apoptosis and arrested the S phase of the cell cycle in mouse granulosa cells. Consistent with these results, p53, caspase-3, B cell lymphoma 2 (Bcl-2)-associated X protein, CCAAT-enhancer-binding protein homologous protein, cyclin A1, cyclin B1, and cyclin D2 mRNA expression decreased, whereas Bcl-2 and glucose-regulated protein 78 kDa mRNA expression increased. Interestingly, ATF6 knockdown obviously increased progesterone and estradiol production in mouse granulosa cells. Cytochrome P450 1b1 (Cyp1b1) mRNA levels were downregulated, whereas Cyp11a1, steroidogenic acute regulatory, and Cyp19a1 mRNA levels were upregulated, in keeping with the changes in steroid hormones. Furthermore, ATF6 disruption remarkably increased insulin-like growth factor binding protein4 (Igfbp4) expression and decreased hyaluronan synthase 2 (Has2), prostaglandin-endoperoxide synthase 2 (Ptgs2), and prostaglandin F receptor (Ptgfr) expression in mouse granulosa cells, which are proteins crucial for follicular development. But, after treating with tunicamycin, the levels of Has2, Ptgs2, and Ptgfr increased relatively, whereas Igfbp4 expression decreased. Collectively, these results imply that ATF6, as a key player in ER stress signaling, may regulate apoptosis, the cell cycle, steroid hormone synthesis, and other modulators related to folliculogenesis in mouse granulosa cells, which may indirectly be involved in the development, ovulation, and atresia of ovarian follicles by affecting the physiological function of granulosa cells. The present study extends our understanding and provides new insights into the physiological significance of ATF6, a key signal transducer of ER stress, in ovarian granulosa cells.

Observation of the dynamics of follicular development in the ovary

The number of ovulated oocytes is different among mammals but does not vary much within the same species. In order to sustain periodic ovulation, follicular development must be coordinated at the tissue level. Elucidating the regulatory mechanisms of follicular development is difficult because the ovary has a complicated structure and it takes a long time for primordial follicles to develop into Graafian follicles. Therefore, it is not possible to observe follicular development by conventional experiments. The authors previously developed a new ovarian tissue culture method that enabled the observation of follicular development from the early follicle stage. These findings indicated that follicular interactions are important in regulating follicular development and ovulation. This review describes the current methods of observing follicular development in the ovary and the regulatory mechanisms of follicular development.

The nuclear receptor REV-ERBα represses the transcription of growth/differentiation factor 10 and 15 genes in rat endometrium stromal cells

Cellular oscillators in the uterus play critical roles in the gestation processes of mammals through entraining of the clock proteins to numerous downstream genes, including growth/differentiation factor (Gdf)10 and Gdf15. The expression of Gdf10 and Gdf15 is significantly increased in the uterus during decidualization, but the mechanism underlying the regulation of Gdf gene expression in the uterus is poorly understood. Here, we focused on the function of the cellular oscillators in the expression of Gdf family by using uterine endometrial stromal cells (UESCs) isolated from pregnant Per2‐dLuc transgenic rats. A significant decline of Per2‐dLuc bioluminescence activity was induced in in vitro decidualized UESCs, and concomitantly the expression of canonical clock genes was downregulated. Conversely, the expression of Gdf10 and Gdf15 of the Gdf was upregulated. In UESCs transfected with Bmal1‐specific siRNA, in which Rev‐erbα expression was downregulated, Gdf10 and Gdf15 were upregulated. However, Gdf5, Gdf7, and Gdf11 were not significantly affected by Bmal1 silencing. The expression of Gdf10 and Gdf15 was enhanced after treatment with a REV‐ERBα antagonist in the presence or absence of progesterone. Chromatin immunoprecipitation‐PCR analysis revealed the inhibitory effect of REV‐ERBα on the expression of Gdf10 and Gdf15 in UESCs by recognizing their gene promoters. Collectively, our findings indicate that the attenuation of REV‐ERBα leads to an upregulation of Gdf10 and Gdf15 in decidual cells, in which cellular oscillators are impaired. Our results provide novel evidence regarding the functions of cellular oscillators regulating the expression of downstream genes during the differentiation of UESCs.

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.

Effects of BMAL1-SIRT1-positive cycle on estrogen synthesis in human ovarian granulosa cells: an implicative role of BMAL1 in PCOS

Brain and muscle ARNT-like protein 1 (BMAL1) is necessary for fertility and has been found to be essential to follicle growth and steroidogenesis. Sirtuin1 (SIRT1) has been reported to interact with BMAL1 and function in a circadian manner. Evidence has shown that SIRT1 regulates aromatase expression in estrogen-producing cells. We aimed to ascertain if there is a relationship between polycystic ovary syndrome (PCOS) and BMAL1, and whether and how BMAL1 takes part in estrogen synthesis in human granulosa cells (hGCs). Twenty-four women diagnosed with PCOS and 24 healthy individuals undergoing assisted reproduction were studied. BMAL1 expression in their granulosa cells (GCs) was observed by quantitative real-time polymerase chain reaction (qRT-PCR). The level of expression in the PCOS group was lower than that of the group without PCOS (p < 0.05). We also analyzed estrogen synthesis and aromatase expression in KGN cell lines. Both were downregulated after BMAL1 and SIRT1 knock-down and, conversely, upregulated after overexpression treatments of these two genes in KGN cells. Both BMAL1 and SIRT1 had a mutually positive regulation, as did the phosphorylation of JNK. Furthermore, JNK overexpression increased estrogen synthesis activity and the expression levels of aromatase, BMAL1, and SIRT1. In KGN and hGCs, estrogen synthesis and aromatase expression were downregulated after treatment with JNK and SIRT1 inhibitors. In addition, BMAL1, SIRT1, and JNK expression levels were all downregulated. Our results demonstrate the effects of BMAL1 on estrogen synthesis in hGCs and suggest a BMAL1-SIRT1-JNK positive feedback cycle in this process, which points out an important role of BMAL1 in the development of PCOS.

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.

Timing in the Testis

The testis provides not just one but several models of temporal organization. The complexity of its rhythmic function arises in part from its compartmentalization and diversity of cell types: not only does the testis produce gametes, but it also serves as the major source of circulating androgens. Within the seminiferous tubules, the germ cells divide and differentiate while in intimate contact with Sertoli cells. The tubule is highly periodic: a spermatogenic wave travels along its length to determine the timing of the commitment of spermatogonia to differentiate, the phases of meiotic division, and the rate of differentiation of the postmeiotic germ cells. Recent evidence indicates that oscillations of retinoic acid play a major role in determining periodicity of the seminiferous epithelium. In the interstitial space, Leydig cells produce the steroid hormones required both for the completion of spermatogenesis and the development and maintenance of male sexual characteristics throughout the body. This endocrine output also oscillates; although the pulse generator lies outside the gonad, the steroidogenic function of Leydig cells is tuned to a regular episodic input. While the oscillations of the intratubular and interstitial cells have multihour (ultradian) and multiday (infradian) periodicities, respectively, the functions of both compartments also display dramatic seasonal rhythms. Furthermore, circadian rhythms are evident in some of the cell types, although their amplitude and pervasiveness are not as great as in many other tissues of the same organism, and their detection may require methods that recognize the heterogeneity of the testis. This review examines the periodicity of testicular function along multiple time scales.

CRTC2 and Nedd4 ligase involvement in FSH and TGFβ1 upregulation of connexin43 gap junction

The major mission of the ovarian follicle is the timely production of the mature fertilizable oocyte, and this is achieved by gonadotropin-regulated, gap junction-mediated cell-cell communication between the oocyte and surrounding nurturing granulosa cells. We have demonstrated that FSH and transforming growth factor beta 1 (TGFβ1) stimulate Gja1 gene-encoded connexin43 (Cx43) gap junction formation/function in rat ovarian granulosa cells is important for their induction of steroidogenesis; additionally, cAMP-protein kinase A (PKA)- and calcium-calcineurin-sensitive cAMP response element-binding (CREB) coactivator CRTC2 plays a crucial role during steroidogenesis. This study was to explore the potential molecular mechanism whereby FSH and TGFβ1 regulate Cx43 synthesis and degradation, particularly the involvement of CRTC2 and ubiquitin ligase Nedd4. Primary culture of granulosa cells from ovarian antral follicles of gonadotropin-primed immature rats was used. At 48 h post-treatment, FSH plus TGFβ1 increased Cx43 level and gap junction function in a PKA- and calcineurin-dependent manner, and TGFβ1 acting through its type I receptor modulated FSH action. Chromatin-immunoprecipitation analysis reveals FSH induced an early-phase (45 min) and FSH+TGFβ1 further elicited a late-phase (24 h) increase in CRTC2, CREB and CBP binding to the Gja1 promoter. Additionally, FSH+TGFβ1 increased the half-life of hyper-phosphorylated Cx43 (Cx43-P2). Also, the proteasome inhibitor MG132 prevented the brefeldin A (blocker of protein transport through Golgi)-reduced Cx43-P2 level and membrane Cx43 gap junction plaque. This is associated with FSH+TGFβ1-attenuated Cx43 interaction with Nedd4 and Cx43 ubiquitination. In all, this study uncovers that FSH and TGFβ1 upregulation of Cx43 gap junctions in ovarian granulosa cells critically involves enhancing CRTC2/CREB/CBP-mediated Cx43 expression and attenuating ubiquitin ligase Nedd4-mediated proteosomal degradation of Cx43 protein.

Localization and quantitative analysis of Cx43 in porcine oocytes during in vitro maturation

Many studies of the main gap junction protein, Cx43, have been conducted in porcine oocyte research, but they have been limited to investigations of cumulus–oocyte complexes (COCs). In this study, we verified Cx43 not in COCs, but in porcine oocytes during maturation, and conducted a quantitative time course analysis. The location and dynamics of Cx43 were examined by immunocytochemistry and western blotting, respectively. COCs were cultured in NCSU23 medium and processed for immunocytochemistry and western blotting at 0, 14, 28, and 42 h after denuding. A Cx43 signal was detected on oolemmas, transzonal projections and the surface of zona pellucidae. Western blotting showed that Cx43 band density increased from 0 to 14 h, and gradually decreased thereafter. Our results clarified that Cx43 is localized in the ooplasmic membrane through zona pellucidae and its level changes over time during culture in porcine oocytes.

Inhibitory role of REV-ERBα in the expression of bone morphogenetic protein gene family in rat uterus endometrium stromal cells

Uterus circadian rhythms have been implicated in the gestation processes of mammals through entraining of the clock proteins to numerous downstream genes. Bone morphogenetic proteins (BMPs), having clock-controlled regulatory sites in their gene promoters, are expressed in the uterus during decidualization, but the regulation of the Bmp gene expression is poorly understood. The present study was designed to dissect the physiological roles of the uterus oscillators in the Bmp expression using the uterus endometrial stromal cells (UESCs) isolated from Per2-dLuc transgenic rats on day 4.5 of gestation. The in vitro decidualization of UESCs was induced by medroxyprogesterone acetate and 2-O-dibutyryl cAMP. A significant decline of Per2-dLuc bioluminescence activity was induced in decidual cells, and concomitantly, the expression of canonical clock genes was downregulated. Conversely, the expression of the core Bmp genes Bmp2, Bmp4, Bmp6, and Bmp7 was upregulated. In UESCs transfected with Bmal1-specific siRNA, in which Rev-erbα expression was downregulated, Bmp genes, such as Bmp2, Bmp4, and Bmp6 were upregulated. However, Bmp1, Bmp7, and Bmp8a were not significantly affected by Bmal1 silencing. The expression of all Bmp genes was enhanced after treatment with the REV-ERBα antagonist (SR8278), although their rhythmic profiles were differed from each other. The binding of REV-ERBα to the proximal regions of the Bmp2 and Bmp4 promoters was revealed by chromatin immunoprecipitation-PCR analysis. Collectively, these results indicate that the Bmp genes are upregulated by the attenuation of the cellular circadian clock; in particular, its core component REV-ERBα functions as a transcriptional silencer in the Bmp gene family.

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.

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.

Downregulation of core clock gene Bmal1 attenuates expression of progesterone and prostaglandin biosynthesis-related genes in rat luteinizing granulosa cells

Ovarian circadian oscillators have been implicated in the reproductive processes of mammals. However, there are few reports regarding the detection of ovarian clock-controlled genes (CCGs). The present study was designed to unravel the mechanisms through which CCG ovarian circadian oscillators regulate fertility, primarily using quantitative RT-PCR and RNA interference against Bmal1 in rat granulosa cells. Mature granulosa cells were prepared from mouse Per2-destabilized luciferase ( dLuc) reporter gene transgenic rats. A real-time monitoring system of Per2 promoter activity was employed to detect Per2-dLuc oscillations. The cells exposed to luteinizing hormone (LH) displayed clear Per2-dLuc oscillations and a rhythmic expression of clock genes ( Bmal1, Per1, Per2, Rev-erbα, and Dbp). Meanwhile, the examined ovarian genes ( Star, Cyp19a1, Cyp11a1, Ptgs2, Lhcgr, and p53) showed rhythmic transcript profiles except for Hsd3b2, indicating that these rhythmic expression genes may be CCGs. Notably, Bmal1 small interfering (si)RNA treatment significantly decreased both the amplitude of Per2-dLuc oscillations and Bmal1 mRNA levels compared with nonsilencing RNA treatment in luteinizing granulosa cells. Depletion of Bmal1 by siRNA decreased the transcript levels of clock genes ( Per1, Per2, Rev-erbα, and Dbp) and examined ovarian genes ( Star, Cyp19a1, Cyp11a1, Ptgs2, Hsd3b2, and Lhcgr). Accordingly, knockdown of Bmal1 also inhibited the synthesis of progesterone and prostaglandin E2, which are associated with crucial reproductive processes. Collectively, these data suggest that ovarian circadian oscillators regulate the synthesis of steroid hormones and prostaglandins through ovarian-specific CCGs in response to LH stimuli. The present study provides new insights into the physiologic significance of Bmal1 related to fertility in ovarian circadian oscillators.

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

The central circadian pacemaker in the suprachiasmatic nucleus (SCN) is a critical component of the neuroendocrine circuit controlling gonadotropin secretion from the pituitary gland. The SCN conveys photic information to hypothalamic targets including the gonadotropin releasing hormone neurons. Many of these target cells are also cell autonomous clocks. It has been suggested that, rather then being singularly driven by the SCN, the timing of gonadotropin secretion depends on the activity of multiple hypothalamic oscillators. While this view provides a novel twist to an old story, it does little to diminish the central role of rhythmic hypothalamic output in this system. It is now clear that the pituitary, ovary, uterus, and oviduct have functional molecular clocks. Evidence supports the notion that the clocks in these tissues contribute to the timing of events in reproductive physiology. The aim of this review is to highlight the current evidence for molecular clock function in the peripheral components of the female hypothalamo-pituitary-gonadal axis as it relates to the timing of gonadotropin secretion, ovulation, and parturition.