Critical Roles of the Circadian Transcription Factor BMAL1 in Reproductive Endocrinology and Fertility

Sleep disturbances and female infertility: a systematic review

BACKGROUND

Sleep disturbances are more prevalent among women with infertility. Current research increasingly highlights the significant relationship between sleep disturbances and female infertility, suggesting that sleep may be a key factor in reproductive health. In this review, we aim to delve into the complex interplay between sleep disturbances and female infertility, as well as to assess the underlying mechanisms involved, and seek to illuminate the causes of sleep-related fertility issues. The understanding of these contents may help clinicians enhance clinical strategies for managing sleep disturbances in women facing infertility challenges and provide timely support to those seeking fertility treatments.

METHODS

A comprehensive literature search was conducted in the PubMed and EMBASE databases. Studies that described sleep patterns or any type of sleep disturbance, sleep breathing disorders and their associations with female infertility or female fecundity, published between January 1, 2010, and November 1, 2023, were identified and extracted. The screening, data extraction, and quality assessment processes were independently performed by paired reviewers. The quality of the included studies was assessed using the Joanna Briggs Institute (JBI) Critical Appraisal tools for observational and cohort studies.

RESULTS

A total of 1,179 articles were initially identified from the search strategy (PubMed, n = 377; EMBASE, n = 802). After removing duplicates (n = 83) and screening for eligibility (n = 75), 19 studies were reviewed and determined to be eligible for inclusion. Infertile women generally report poorer sleep quality and exhibit more evening sleep chronotypes. Sleep disorders are significantly associated with infertility. Poor sleep quality, extreme sleep durations, and certain sleep chronotypes are associated with poorer fertility treatment outcomes, such as a reduced number of retrieved oocytes, decreased embryo quality, and lower fertilization rates. Obstructive sleep apnea (OSA) is also more prevalent in women with fertility issues, especially those with polycystic ovary syndrome (PCOS), and may negatively impact reproductive outcomes. The circadian rhythms of the Clock gene system, melatonin and hormone dysregulation, oxidative stress and immune response are considered to be potential mechanisms explaining how sleep disturbance impairs reproductive function, remain to be fully elucidated, and therefore, require further investigation.

CONCLUSIONS

Sleep disturbances are negatively associated with female infertility and poor fertility treatment outcomes. Longitudinal studies are expected to substantiate these findings and inform more nuanced approaches to prior sleep management and lifestyle advisement for infertile women, especially those undergoing fertility treatments.

TRIAL REGISTRATION

This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO, #CRD42024498443).

Uncovering the Penile Clock: Expression of Molecular Clock Proteins in Human Penile Cavernous Tissue

PURPOSE

To evaluate the expression of core molecular clock genes/proteins in penile cavernous tissue from healthy male subjects and to determine whether their expression has circadian variation.

MATERIALS AND METHODS

Corpus cavernosum biopsy samples were obtained from 10 healthy males with penile deviation or fracture who underwent surgical intervention during the day and night. The daytime group (n=5) underwent corpus cavernosum tissue sampling during zeitgeber time (ZT) 8-12, while the nighttime group (n=5) underwent sampling during ZT 20-24. The expression and localization of BMAL1, CLOCK, PER1, PER2, PER3, CRY1, and CRY2 proteins were analyzed using immunohistochemistry and quantified using H-score analysis. RT-qPCR analysis was performed to assess the expression of core molecular clock genes in the corpus cavernosum tissue of 5 additional daytime patients.

RESULTS

The expression of core molecular clock proteins was detected in vascular endothelial cells (VECs) and smooth muscle cells (SMCs) in corpus cavernosum during daytime and nighttime. BMAL1 exhibited the most significant nuclear expression during daytime in both cell types, whereas its expression decreased significantly at night. In VECs, a significant decrease in the nuclear expression of CRY1 was observed at night. In SMCs, a significant decrease in the cytoplasmic expression of PER3 was observed at night. The expression patterns of the core molecular clock genes were ascertained through a RT-qPCR analysis.

CONCLUSIONS

Our research provides compelling evidence that core molecular clock genes are distinctly expressed in penile tissue in humans. Furthermore, we observed the expression of molecular clock proteins within the VECs and SMCs of the corpus cavernosum, with BMAL1 being the most prominently expressed. The discovery of core molecular clock genes in penile tissue, as well as proteins within the SMCs and VECs of the corpus cavernosum, introduces the potential significance of the molecular clock mechanism in the physiology of penile erection.

Bmal1 regulates female reproduction in mice via the hypothalamic-pituitary-ovarian axis

The hypothalamic-pituitary-gonadal axis (HPG) is the key neuroendocrine axis involved in reproductive regulation. Brain and muscle ARNT-like protein 1 (Bmal1) participates in regulating the metabolism of various endocrine hormones. However, the regulation of Bmal1 on HPG and female fertility is unclear. This study aims to explore the regulation of female reproduction by Bmal1 via the HPG axis in mice. Bmal1-knockout (Ko) mice were generated using the CRISPR/Cas9 technology. The structure, function, and estrous cycle of ovarian in Bmal1 Ko female mice were measured. The key genes and proteins of the HPG axis involved in regulating female reproduction were examined through transcriptome analysis and then verified by RT-PCR, immunohistochemistry, and western blot. Furthermore, the fertility of female mice was detected after intervening prolactin (PRL) and progesterone (Pg) in Bmal1 ko mice. The number of offspring and ovarian weight were significantly lower in Bmal1-Ko mice than in wild-type (Wt) mice. In Bmal1-Ko mice, ovarian cells were arranged loosely and irregularly, and the total number of follicles was significantly reduced. No corpus luteum was found in the ovaries. Vaginal smears revealed that Bmal1-Ko mice had an irregular estrus cycle. In Bmal1-Ko mice, Star expression was decreased, PRL and luteinizing hormone (LH) levels were increased, and dopamine (DA) and Pg levels were decreased. Inhibition of PRL partially recovered the estrous cycle, corpus luteum formation, and Star expression in the ovaries. Pg supplementation promoted embryo implantation in Bmal1-Ko female mice. Bmal1 Ko increases serum PRL levels in female mice likely by reducing DA levels, thus affecting luteal formation, resulting in decreased Star expression and Pg production, hindering female reproduction. Inhibition of PRL or restoration of Pg can partially restore reproductive capacity in female Bmal1-Ko mice. Thus, Bmal1 may regulate female reproduction via the HPG axis in mice, suggesting that Bmal1 is a potential target to treat female infertility.

Methylome analysis in girls with idiopathic central precocious puberty

BACKGROUND

Genetic and environmental factors are implicated in many developmental processes. Recent evidence, however, has suggested that epigenetic changes may also influence the onset of puberty or the susceptibility to a wide range of diseases later in life. The present study aims to investigate changes in genomic DNA methylation profiles associated with pubertal onset analyzing human peripheral blood leukocytes from three different groups of subjects: 19 girls with central precocious puberty (CPP), 14 healthy prepubertal girls matched by age and 13 healthy pubertal girls matched by pubertal stage. For this purpose, the comparisons were performed between pre- and pubertal controls to identify changes in normal pubertal transition and CPP versus pre- and pubertal controls.

RESULTS

Analysis of methylation changes associated with normal pubertal transition identified 1006 differentially methylated CpG sites, 86% of them were found to be hypermethylated in prepubertal controls. Some of these CpG sites reside in genes associated with the age of menarche or transcription factors involved in the process of pubertal development. Analysis of methylome profiles in CPP patients showed 65% and 55% hypomethylated CpG sites compared with prepubertal and pubertal controls, respectively. In addition, interestingly, our results revealed the presence of 43 differentially methylated genes coding for zinc finger (ZNF) proteins. Gene ontology and IPA analysis performed in the three groups studied revealed significant enrichment of them in some pathways related to neuronal communication (semaphorin and gustation pathways), estrogens action, some cancers (particularly breast and ovarian) or metabolism (particularly sirtuin).

CONCLUSIONS

The different methylation profiles of girls with normal and precocious puberty indicate that regulation of the pubertal process in humans is associated with specific epigenetic changes. Differentially methylated genes include ZNF genes that may play a role in developmental control. In addition, our data highlight changes in the methylation status of genes involved in signaling pathways that determine the migration and function of GnRH neurons and the onset of metabolic and neoplastic diseases that may be associated with CPP in later life.

Evaluating the Adaptive Fitness of Circadian Clocks and their Evolution

Surely most chronobiologists believe circadian clocks are an adaptation of organisms that enhances fitness, but are we certain that this focus of our research effort really confers a fitness advantage? What is the evidence, and how do we evaluate it? What are the best criteria? These questions are the topic of this review. In addition, we will discuss selective pressures that might have led to the historical evolution of circadian systems while considering the intriguing question of whether the ongoing climate change is modulating these selective pressures so that the clock is still evolving.

Neuroendocrine effects of the duper mutation in Syrian hamsters: a role for Cryptochrome 1

Molecular and physiological determinants of the timing of reproductive events, including the pre-ovulatory LH surge and seasonal fluctuations in fertility, are incompletely understood. We used the Cryptochrome 1-deficient duper mutant to examine the role of this core circadian clock gene in Syrian hamsters. We find that the phase of the LH surge and its stability upon shifts of the light: dark cycle are altered in duper mutants. The intensity of immunoreactive PER1 in GnRH cells of the preoptic area peaks earlier in the day in duper than wild type hamsters. We note that GnRH fibers coursing through the suprachiasmatic nucleus (SCN) contact vasopressin- and VIP-immunoreactive cells, suggesting a possible locus of circadian control of the LH surge. Unlike wild types, duper hamsters do not regress their gonads within 8 weeks of constant darkness, despite evidence of melatonin secretion during the subjective night. In light of the finding that the duper allele is a stop codon in Cryptochrome 1, our results suggest important neuroendocrine functions of this core circadian clock gene.

The rhythms of histones in regeneration: The epigenetic modifications determined by clock genes

The evolutionary establishment of an internal biological clock is a primordial event tightly associated with a 24-h period. Changes in the circadian rhythm can affect cellular functions, including proliferation, DNA repair and redox state. Even isolated organs, tissues and cells can maintain an autonomous circadian rhythm. These cell-autonomous molecular mechanisms are driven by intracellular clock genes, such as BMAL1. Little is known about the role of core clock genes and epigenetic modifications in the skin. Our focus was to identify BMAL1-driven epigenetic modifications associated with gene transcription by mapping the acetylation landscape of histones in epithelial cells responding to injury. We explored the role of BMAL1 in epidermal wound and tissue regeneration using a loss-of-function approach in vivo. We worked with BMAL1 knockout mice and a contraction-resistance wound healing protocol, determining the histone modifications using specific antibodies to detect the acetylation levels of histones H3 and H4. We found significant differences in the acetylation levels of histones in both homeostatic and injured skin with deregulated BMAL1. The intact skin displayed varied acetylation levels of histones H3 and H4, including hyperacetylation of H3 Lys 9 (H3K9). The most pronounced changes were observed at the repair site, with notable alterations in the acetylation pattern of histone H4. These findings reveal the importance of histone modifications in response to injury and indicate that modulation of BMAL1 and its associated epigenetic events could be therapeutically harnessed to improve skin regeneration.

Exogenous Nucleotides Ameliorate Age-Related Decline in Testosterone in Male Senescence-Accelerated Mouse Prone-8 (SAMP8) Mice by Modulating the Local Renin-Angiotensin System Antioxidant Pathway

In older men, an age-related decline in testosterone is closely associated with various adverse health outcomes. With the progression of aging, hyperactivation of the local renin-angiotensin system (RAS) and oxidative stress increase in the testis. The regulation of RAS antioxidants may be a target to delay testicular aging and maintain testosterone levels. Exogenous nucleotides (NTs) have anti-aging potential in several systems, but there are no studies of their effects on the reproductive system. In our study, we examined the effects of exogenous NTs on testosterone synthesis and explored possible mechanisms of action. Therefore, senescence-accelerated mouse prone-8 (SAMP8) mice and senescence-accelerated mouse resistant 1 (SAMR1) were used in the experiment, and they were randomly divided into an NTs free group (NTs-F), a normal control group (control), a low-dose NTs group (NTs-L), a middle-dose NTs (NTs-M), a high-dose NTs group (NTs-H) and SAMR1 groups, and the testis of the mice were collected for testing after 9 months of intervention. The results showed that exogenous NTs could increase the testicular organ index in mice during aging, and delayed the age-associated decline in testosterone levels in SAMP8 male mice, possibly by modulating the local RAS antioxidant pathway and reducing oxidative stress to protect the testis. The present study provides new research clues for the development of preventive and therapeutic strategies for related diseases.

Core clock gene, Bmal1, is required for optimal second-level interval production

Perception and production of second-level temporal intervals are critical in several behavioral and cognitive processes, including adaptive anticipation, motor control, and social communication. These processes are impaired in several neurological and psychological disorders, such as Parkinson's disease and attention-deficit hyperactivity disorder. Although evidence indicates that second-level interval timing exhibit circadian patterns, it remains unclear whether the core clock machinery controls the circadian pattern of interval timing. To investigate the role of core clock molecules in interval timing capacity, we devised a behavioral assay called the interval timing task to examine prospective motor interval timing ability. In this task, the mouse produces two separate nose pokes in a pretrained second-level interval to obtain a sucrose solution as a reward. We discovered that interval perception in wild-type mice displayed a circadian pattern, with the best performance observed during the late active phase. To investigate whether the core molecular clock is involved in the circadian control of interval timing, we employed Bmal1 knockout mice (BKO) in the interval timing task. The interval production of BKO did not display any difference between early and late active phase, without reaching the optimal interval production level observed in wild-type. In summary, we report that the core clock gene Bmal1 is required for the optimal performance of prospective motor timing typically observed during the late part of the active period.

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

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

Integrating sperm cell transcriptome and seminal plasma metabolome to analyze the molecular regulatory mechanism of sperm motility in Holstein stud bulls

Considering that artificial insemination is the most widely used assisted reproductive technique in the dairy industry, the semen quality of bulls is very important for selecting excellent stud bulls. Sperm motility is one of the important traits of semen quality, and related genes may be regulated by environmental factors. Seminal plasma can affect sperm cell transcriptome and further affect sperm motility through exosome or other processes. However, the molecular regulation mechanism of bull sperm motility has not been studied by combining the sperm cell transcriptome with seminal plasma metabolome. The number of motile sperm per ejaculate (NMSPE) is an integrated indicator for assessing sperm motility in stud bulls. In the present study, we selected 7 bulls with higher NMSPE (5,698.55 million +/- 945.40 million) as group H and 7 bulls with lower NMSPE (2,279.76 million +/- 1,305.69 million) as group L from 53 Holstein stud bulls. The differentially expressed genes (DEGs) in sperm cells were evaluated between the two groups (H vs. L). We conducted gene co-expression network analysis (WGCNA) on H and L groups of bulls, as well as two monozygotic twin Holstein bulls with different NMSPE values, to screen candidate genes for NMSPE. The regulatory effect of seminal plasma metabolome on the candidate genes of NMSPE was also investigated. A total of 1,099 DEGs were identified in the sperm cells of H and L groups. These DEGs were primarily concentrated in energy metabolism and sperm cell transcription. The significantly enriched Kyoto encyclopedia of genes and genomes (KEGG) pathways of the 57 differential metabolites were the aminoacyl-tRNA biosynthesis pathway and vitamin B6 metabolism pathway. Our study discovered 14 genes as the potential candidate markers for sperm motility, including FBXO39. We observed a broad correlation between transcriptome of sperm cells and seminal plasma metabolome, such as three metabolites, namely, mesaconic acid, 2-coumaric acid, and 4-formylaminoantipyrine, might regulate FBXO39 expression through potential pathways. The genes related to seminal plasma metabolites expressed in sperm cells are not only located near the quantitative trait loci of reproductive traits, but also enriched in the genome-wide association study signal of sire conception rate. Collectively, this study was the first to investigate the interplays among transcriptome of sperm cells and seminal plasma metabolome from Holstein stud bulls with different sperm motility.

Neural function of Bmal1: an overview

Bmal1 (Brain and muscle arnt-like, or Arntl) is a bHLH/PAS domain transcription factor central to the transcription/translation feedback loop of the biologic clock. Although Bmal1 is well-established as a major regulator of circadian rhythm, a growing number of studies in recent years have shown that dysfunction of Bmal1 underlies a variety of psychiatric, neurodegenerative-like, and endocrine metabolism-related disorders, as well as potential oncogenic roles. In this review, we systematically summarized Bmal1 expression in different brain regions, its neurological functions related or not to circadian rhythm and biological clock, and pathological phenotypes arising from Bmal1 knockout. This review also discusses oscillation and rhythmicity, especially in the suprachiasmatic nucleus, and provides perspective on future progress in Bmal1 research.

Bmal1 Regulates Prostate Growth via Cell-Cycle Modulation

The circadian clock system exists in most organs and regulates diverse physiological processes, including growth. Here, we used a prostate-specific Bmal1-knockout mouse model (pBmal1 KO: PbsnCre+; Bmal1^fx/fx) and immortalized human prostate cells (RWPE-1 and WPMY-1) to elucidate the role of the peripheral prostate clock on prostate growth. Bmal1 KO resulted in significantly decreased ventral and dorsolateral lobes with less Ki-67-positive epithelial cells than the controls. Next, the cap analysis of gene expression revealed that genes associated with cell cycles were differentially expressed in the pBmal1 KO prostate. Cdkn1a (coding p21) was diurnally expressed in the control mouse prostate, a rhythm which was disturbed in pBmal1 KO. Meanwhile, the knockdown of BMAL1 in epithelial RWPE-1 and stromal WPMY-1 cell lines decreased proliferation. Furthermore, RWPE-1 BMAL1 knockdown increased G0/G1-phase cell numbers but reduced S-phase numbers. These findings indicate that core clock gene Bmal1 is involved in prostate growth via the modulation of the cell cycle and provide a rationale for further research to link the pathogenesis of benign prostatic hyperplasia or cancer with the circadian clock.

Uterine Deletion of Bmal1 Impairs Placental Vascularization and Induces Intrauterine Fetal Death in Mice

Recently, it was demonstrated that the expression of BMAL1 was decreased in the endometrium of women suffering from recurrent spontaneous abortion. To investigate the pathological roles of uterine clock genes during pregnancy, we produced conditional deletion of uterine Bmal1 (cKO) mice and found that cKO mice could receive embryo implantation but not sustain pregnancy. Gene ontology analysis of microarray suggested that uterine NK (uNK) cell function was suppressed in cKO mice. Histological examination revealed the poor formation of maternal vascular spaces in the placenta. In contrast to WT mice, uNK cells in the spongiotrophoblast layer, where maternal uNK cells are directly in contact with fetal trophoblast, hardly expressed an immunosuppressive NK marker, CD161, in cKO mice. By progesterone supplementation, pregnancy could be sustained until the end of pregnancy in some cKO mice. Although this treatment did not improve the structural abnormalities of the placenta, it recruited CD161-positive NK cells into the spongiotrophoblast layer in cKO mice. These findings indicate that the uterine clock system may be critical for pregnancy maintenance after embryo implantation.