Dynamic chromatin remodeling in cycling human endometrium at single-cell level.

Estrogen-dependent proliferation followed by progesterone-dependent differentiation of the endometrium culminates in a short implantation window. We performed single-cell assay for transposase-accessible chromatin with sequencing on endometrial samples obtained across the menstrual cycle to investigate the regulation of temporal gene networks that control embryo implantation. We identify uniquely accessible chromatin regions in all major cellular constituents of the endometrium, delineate temporal patterns of coordinated chromatin remodeling in epithelial and stromal cells, and gain mechanistic insights into the emergence of a receptive state through integrated analysis of enriched transcription factor (TF) binding sites in dynamic chromatin regions, chromatin immunoprecipitation sequencing analyses, and gene expression data. We demonstrate that the implantation window coincides with pervasive cooption of transposable elements (TEs) into the regulatory chromatin landscape of decidualizing cells and expression of TE-derived transcripts in a spatially defined manner. Our data constitute a comprehensive map of the chromatin changes that control TF activities in a cycling endometrium at cellular resolution.

A molecular staging model for accurately dating the endometrial biopsy.

Natural variability in menstrual cycle length, coupled with rapid changes in endometrial gene expression, makes it difficult to accurately define and compare different stages of the endometrial cycle. Here we develop and validate a method for precisely determining endometrial cycle stage based on global gene expression. Our 'molecular staging model' reveals significant and remarkably synchronised daily changes in expression for over 3400 endometrial genes throughout the cycle, with the most dramatic changes occurring during the secretory phase. Our study significantly extends existing data on the endometrial transcriptome, and for the first time enables identification of differentially expressed endometrial genes with increasing age and different ethnicities. It also allows reinterpretation of all endometrial RNA-seq and array data that has been published to date. Our molecular staging model will significantly advance understanding of endometrial-related disorders that affect nearly all women at some stage of their lives, such as heavy menstrual bleeding, endometriosis, adenomyosis, and recurrent implantation failure.

Progesterone and its derivatives for the treatment of catamenial epilepsy: A systematic review.

OBJECTIVE: Catamenial epilepsy (CE) is defined as an increase in seizure frequency during specific phases of the menstrual cycle in women with epilepsy. The treatment usually includes a combination of non-hormonal and hormonal therapies. This systematic review summarizes the available data on the efficacy of progesterone and its derivates to treat CE. METHODS: We performed a systematic search of the literature to identify studies reporting data on the use of progesterone and its derivatives (any type and dose) for the treatment of CE. The main outcome included the efficacy of progesterone and its derivatives on seizure frequency. RESULTS: Nineteen articles (457 patients) were included; four were randomized controlled trials (two comparing progesterone vs placebo and two comparing norethisterone vs placebo). Progesterone was generally administered during the luteal phase (from day 15 to 25) or during perimenstrual exacerbations (from day 23 to 25), with an average dose of 10-30 mg/day to a maximum of 300 mg/day. The therapy, usually well tolerated, was ineffective in the randomized controlled trials; conversely, it was associated with an overall reduction in seizure frequency in case reports and uncontrolled studies. CONCLUSIONS: Although data from uncontrolled studies suggest that hormone therapy with progesterone may be useful in the treatment of CE, its efficacy has not been demonstrated in controlled trials. The possible antiseizure effect of progesterone could be mediated by its active metabolite allopregnanolone, making the plasmatic measurement of these hormones mandatory to evaluate efficacy. Further randomized controlled trials should investigate the efficacy of progesterone and its derivatives, addressing these pharmacological issues.

MSX1-expression during the different phases in healthy human endometrium.

PURPOSE: The human endometrium consists of different layers (basalis and functionalis) and undergoes different phases throughout the menstrual cycle. In a former paper, our research group was able to describe MSX1 as a positive prognosticator in endometrial carcinomas. The aim of this study was to examine the MSX1 expression in healthy endometrial tissue throughout the different phases to gain more insight on the mechanics of MSX-regulation in the female reproductive system. MATERIALS AND METHODS: In this retrospective study, we investigated a total of 17 normal endometrial tissues (six during proliferative phase and five during early and six during late secretory phase). We used immunohistochemical staining and an immunoreactive score (IRS) to evaluate MSX1 expression. We also investigated correlations with other proteins, that have already been examined in our research group using the same patient collective. RESULTS: MSX1 is expressed in glandular cells during the proliferative phase and downregulated at early and late secretory phase (p = 0.011). Also, a positive correlation between MSX1 and the progesterone-receptor A (PR-A) (correlation coefficient (cc) = 0.0671; p = 0.024), and the progesterone receptor B (PR-B) (cc = 0.0691; p = 0.018) was found. A trend towards negative correlation was recognized between MSX1 and Inhibin Beta-C-expression in glandular cells (cc = - 0.583; p-value = 0.060). CONCLUSION: MSX1 is known as a member of the muscle segment homeobox gene family. MSX1 is a p53-interacting protein and overexpression of homeobox MSX1 induced apoptosis of cancer cells. Here we show that MSX1 is expressed especially in the proliferative phase of glandular epithelial tissue of the normal endometrium. The found positive correlation between MSX1 and progesterone receptors A and B confirms the results of a previous study on cancer tissue by our research group. Because MSX1 is known to be downregulated by progesterone, the found correlation of MSX1 and both PR-A and -B may represent a direct regulation of the MSX1 gene by a PR-response element. Here further investigation would be of interest.

Delta and kappa opioid receptors in human endometrium during the menstrual cycle: Expression and localization.

OBJECTIVE: Endogenous opioid peptides were reported to be involved in the regulation of reproductive physiology and their precursors and receptors were described in many of the male and female reproductive tissues. Mu opioid receptor (MOR) was described in human endometrial cells and its expression and localization changed during the menstrual cycle. However, there is no data from the distribution of the other opioid receptors: Delta (DOR) and Kappa (KOR). The objective of the present work was to analyze the dynamics of expression and localization of DOR and KOR in human endometrium throughout the menstrual cycle. STUDY DESIGN: Human endometrial samples from different menstrual cycle phases were analyzed by immunohistochemistry. RESULTS: DOR and KOR were present in all samples analyzed and the protein expression and localization changed throughout the menstrual cycle. Both receptor expression increased during the late proliferative phase and decreased during the late secretory-one, especially in the luminal epithelium. DOR expression was generally higher than KOR expression in all cell compartments. CONCLUSIONS: The presence of DOR and KOR in human endometrium and their dynamic changes during the menstrual cycle join the results previously obtained in MOR suggesting a possible role of opioids in reproduction events related to the human endometrium.

miR-23b-3p regulates human endometrial epithelial cell adhesion implying a role in implantation.

In brief: miR-23b-3p expression is increased in fertile endometrium during receptivity. This study investigates the function of miR-23b-3p on endometrial adhesion and its downstream targets. Abstract: The human endometrium undergoes dramatic remodeling throughout the menstrual cycle that is essential for successful blastocyst attachment and implantation in the mid-secretory (receptive) phase. microRNA (miR) plays a role in the preparation of endometrial receptivity. miR-23b-3p expression is increased in fertile endometrium during receptivity. Here, we aimed to investigate miR-23b-3p function during receptivity. qPCR and in situ hybridization were used to investigate the expression and localization of miR-23b-3p in human endometrium, respectively. Ishikawa cells (endometrial epithelial cell line) and endometrial organoid-derived epithelial cells were transfected with miR-23b-3p mimic, and trophoblast progenitor spheroid (blastocyst surrogate) adhesion assay was used to determine effects on blastocyst adhesion to endometrial cells. We demonstrated that miR-23b-3p was significantly upregulated in the fertile endometrium of the receptive phase compared to the non-receptive, proliferative phase. No difference was identified for the expression of miR-23b-3p between fertile and infertile mid-secretory phase endometrium. miR-23b-3p localized to the epithelium and stroma in the mid-secretory phase but was undetectable in the proliferative phase of fertile endometrium. Functionally, miR-23-3p overexpression in Ishikawa cells and fertile endometrial organoid-derived epithelial cells significantly improved their adhesive capacity to trophoblast progenitor spheroids. miR-23b-3p overexpression in infertile endometrial organoid-derived epithelial cells did not improve adhesion. Among 10 miR-predicted gene targets examined, miR-23b-3p overexpression in Ishikawa cells significantly reduced the expression of MET, secreted frizzled-related protein 4 (SFRP4) and acyl-CoA dehydrogenase short/branched chain (ACADSB) compared to control. The reduction of SFRP4 after miR23b-3p overexpression was confirmed by immunoblotting in fertile organoid-derived epithelial cells. SFRP4 expression in fertile endometrium exhibited an inverse expression pattern compared to miR-23b-3p and was higher in the proliferative phase compared to the mid-secretory phase. Overall, miR-23b-3p is likely a critical regulator of endometrial epithelial adhesion and receptivity.

Circulating CD200 is increased in the secretory phase of women with endometriosis as is endometrial mRNA, and endometrial stromal cell CD200R1 is increased in spite of reduced mRNA.

PROBLEM: Estrogen-dependent extrauterine implantation and growth of menstrual endometrial tissue affects roughly 10% of reproductive age women and depends on suppression of local innate immune defenses to prevent ectopic tissue rejection. Immunohistochemistry has shown the immune check-point inhibitor CD200 which can suppress rejection is expressed in eutopic endometrium and in ectopic deposits. Soluble CD200 accumulated in venules draining eutopic and ectopic endometrium of endometriosis cases in the secretory phase but not proliferative phase of the menstrual cycle, and should be increased in the circulation. METHOD OF STUDY: Sera from endometriosis and non-endometriosis controls were tested by ELISA for CD200. Endometrial CD200, CD200R1 and CD200R2 mRNA in eutopic was quantified by RT-PCR and localized by in situ hybridization. CD200R1 protein was quantified by immunohistochemistry. RESULTS: Secretory phase serum CD200 was elevated in women with endometriosis compared to controls. Serum CD200 correlated with matched endometrial CD200 mRNA levels. Expression of mRNA for CD200R1 which signals immune suppression was decreased whereas mRNA for the CD200R2 activating receptor was increased. In situ staining of CD200R1 and CD200R2 mRNA showed both receptors were expressed and the fraction of CD200R that is CD200R1 was reduced in secretory and menstrual phase endometriosis endometrium consistent with the RT-PCR result. By contrast, CD200R1 protein and CD200R1 fraction of total CD200R protein were increased in endometriosis. CONCLUSIONS: Failure to suppress circulating CD200 levels in the secretory phase had an 87% specificity and 90% sensitivity for endometriosis. CD200 and increased CD200R1 expression may facilitate development of ectopic deposits by suppressing rejection mechanisms.

Luteinizing Hormone Dynamics in Menstruation.

Menstruation is a finely-controlled cycle that responds to the prevailing endocrine and paracrine environment. However, social stigma has led to inadequate menstrual literacy, both among academics and the larger public. The poorly understood mechanisms of menstruation ultimately lead to suboptimal healthcare treatment and services for biological females, culminating in a physical, financial, and emotional burden. Various hormones signal the beginning and end of each stage of menstruation. In particular, luteinizing hormone (LH) is a major player in ovulation, corpus luteum function, and the stimulation of other key hormones. A LH model could be used to understand the larger control system of menstruation if analyzed in conjunction with models for other major hormones (e.g., FSH, progesterone, and GnRH). Thus, exploring a smaller subsection of LH dynamics within the larger control system of menstruation can lead to a greater understanding of menstruation, contributing towards therapeutics and research for women's health. Using parameters and kinetic equations in the existing body of literature, a transfer function was derived to model LH dynamics. Analysis of system stability reveals overdamped dynamics in LH sensitization at baseline, and underdamped mildly resonant dynamics at the peak of the menstrual cycle, the strength of which depends on the values of the rate constants of LH receptor formation, binding, and desensitization.

The expression pattern of endometrial receptivity genes is desynchronized between endometrium and matched endometriomas.

RESEARCH QUESTION: Are paired samples of endometrium and ovarian endometriomas synchronous with each other throughout the menstrual cycle? DESIGN: The expression levels of 57 endometrial receptivity-associated genes were determined from matched endometrial and endometrioma samples (n=31) collected from women with endometriosis throughout the menstrual cycle. RESULTS: The expression profile of endometrial receptivity genes divided endometrial samples according to their menstrual cycle phase. Endometrioma samples grouped together irrespective of the menstrual cycle phase and formed a cluster distinct from endometrial samples. Pairwise comparison showed 21, 16, 33 and 23 differentially expressed genes (adjusted P < 0.001-0.05) between the lesions and endometria collected in the proliferative, early-secretory, mid-secretory and late-secretory menstrual cycle phases, respectively, confirming the distinct expression profiles of endometrium and endometrioma. CONCLUSIONS: No menstrual cycle synchronicity was found between matched eutopic and ectopic endometrium, suggesting that the concept of cycling endometrial tissue inside the endometrioma should be revised.

Spatiotemporal expression pattern of Progesterone Receptor Component (PGRMC) 1 in endometrium from patients with or without endometriosis or adenomyosis.

The endometrium plays a crucial role in reproduction and, in humans, is cyclically remodeled under hormonal control. Estradiol favors tissue proliferation whereas progesterone inhibits tissue growth and induces morphological changes. Endometriosis is often associated with fertility issues and with exacerbated estrogen and reduced progesterone concentration or response in the eutopic endometrium. However, underlying mechanisms remain unclear. Progesterone Receptor Membrane Component (PGRMC) 1 is a protein able to modulate progesterone response and its murine knockout reduced fertility. However, the precise spatiotemporal pattern of PGRMC1 expression in the human endometrium is still poorly characterized. We investigated variations of eutopic endometrial PGRMC1 expression by combining RT-qPCR, immunofluorescence and in situ hybridization. We found that PGRMC1 expression progressively increases during the proliferative phase and decreases during the secretory phase. However, immunolabeling and identification of mRNA-containing cells were regularly heterogeneous in samples, according to tissue depth, with a gradient extending from the surface epithelium towards the basalis. There was no significant difference in PGRMC1 mRNA amounts between patients with or without endometriosis or adenomyosis, for any phase of the menstrual cycle, but cells with strong or moderate PGRMC1 immunolabeling were reduced during the proliferative phase in endometriotic patients. In conclusion, although the cyclical variation of PGRMC1 expression globally follows fluctuation of ovarian steroids, further work is required to precisely characterize hormonal control and identify the additional levels of regulation responsible for local adjustment of PGRMC1 concentration. This is particularly important in the light of recent studies emphasizing the correlation between adequate PGRMC1 amounts and fertility.

Does Anti-Müllerian hormone vary during a menstrual cycle? A systematic review and meta-analysis.

OBJECTIVE: Numerous studies have indicated that the level of the Anti-Müllerian hormone (AMH), one of the main markers for the ovarian reserve, does not fluctuate throughout a menstrual cycle, while some studies have rejected this finding. The purpose of this systematic and meta-analysis study is to consensus on all contradictory studies that have measured AMH levels throughout the menstrual cycle and to investigate the exact extent of AMH variation in a cycle. METHODS: The protocol for this meta-analysis was registered at PROSPERO before data extraction. Relevant studies were identified by systematic search in PubMed, ScienceDirect, Embase, Cochrane Library, and Google Scholar with no limitation on publication date. Longitudinal studies which have evaluated AMH levels in the follicular and luteal phases of an unstimulated (natural) menstrual cycle in healthy women without endocrinology or ovarian disorders were included. We used the JBI Critical Appraisal Checklist for assessing the quality of studies found eligible for meta-analysis. RESULTS: A total of 11 studies involving 733 women with regular menstrual cycles were included. The results showed that the AMH level in the follicular phase was significantly higher than in the luteal phase (95% Cl = 0.11 [0.01 to 0.21]; p < 0.05) and it varies about 11.5% from the luteal phase. The analysis of studies which had also examined the ovulatory phase (n = 380) showed that the serum levels of AMH in the ovulatory phase (about 2.02 ng/ml) did not significantly vary compared to follicular (95% Cl = 0.11 [-0.10 to 0.33]; p = 0.30) and luteal (95% Cl = 0.06 [-0.08 to 0.20]; p = 0.43) phases. CONCLUSIONS: According to the results of this study, AMH levels differ between follicular and luteal phases which might be due to ovarian response to the gonadotropins. It seems the phase of AMH measurement needs to be considered for interpretation of the serum AMH test.

Gene expression of the endocannabinoid system in endometrium through menstrual cycle.

Endocannabinoids mediate cellular functions and their activity is controlled by a complex system of enzymes, membrane receptors and transport molecules. Endocannabinoids are present in endometrium, a cyclical regenerative tissue requiring tightly regulated cellular mechanisms for maturation. The objective of this study was to investigate the gene expression of key elements involved in the endocannabinoid system across the menstrual cycle. RNA was isolated from endometrial tissue and genome-wide gene expression datasets were generated using RNA-sequencing. An a priori set of 70 genes associated with endocannabinoid system were selected from published literature. Gene expression across the menstrual cycle was analyzed using a moderated t test, corrected for multiple testing with Bonferroni's method. A total of 40 of the 70 genes were present in > 90% of the samples, and significant differential gene expression identified for 29 genes. We identified 4 distinct regulation patterns for synthesizing enzymes, as well as a distinct regulation pattern for degradations and transporting enzymes. This study charts the expression of endometrial endocannabinoid system genes across the menstrual cycle. Altered expression of genes that control endocannabinoid may allow fine control over endocannabinoid concentrations and their influence on cellular function, maturation and differentiation as the endometrium matures through the menstrual cycle.

[Epilepsy with catamenial pattern]. / Epilepsia con patrón catamenial.

Catamenial pattern epilepsy is defined as an increase in the frequency of seizures during a specific stage of the menstrual cycle compared to baseline. It has been described that around a third of women with epilepsy have a catamenial pattern. The changes in the seizure pattern would be explained by the influence of catamenial fluctuations, of female gonadal hormones on neuronal excitability. Progesterone through its metabolite allopregnanolone plays a protective role by increasing GABAergic transmission; however, its effect on brain progesterone receptors can increase neuronal excitability. The effects of estrogens are complex, they tend to increase neuronal excitability, although their effects depend on their concentration and exposure time. Three catamenial patterns of seizure exacerbation have been proposed: the perimenstrual pattern, the periovulatory pattern, and the luteal pattern. The diagnostic approach is carried out through a systematic process of 4 steps: a) clinical history of the pattern of the menstrual cycle and epileptic seizures; b) diagnostic methods to characterize the menstrual cycle and the pattern of seizures; c) check diagnostic criteria; and d) categorize the catamenial pattern. The treatment options studied require a higher level of evidence, and there is no specific treatment. Optimization of conventional antiseizure treatment is recommended as the first therapeutic option. Other therapeutic options, such as non-hormonal and hormonal treatments, could be useful in case the first therapeutic option proves to be ineffective.

TITLE: Epilepsia con patrón catamenial.La epilepsia con patrón catamenial se define como el aumento en la frecuencia de crisis epilépticas durante una etapa específica del ciclo menstrual respecto al basal. Se ha descrito que alrededor de un tercio de las mujeres con epilepsia presenta patrón catamenial. Los cambios en el patrón de crisis epilépticas se explicarían por la influencia de las fluctuaciones catameniales de las hormonas gonadales femeninas sobre la excitabilidad neuronal. La progesterona, a través de su metabolito alopregnanolona, desempeña un papel protector incrementando la transmisión gabérgica; sin embargo, su efecto en los receptores de progesterona cerebral puede incrementar la excitabilidad neuronal. Los efectos de los estrógenos son complejos y tienden a incrementar la excitabilidad neuronal, aunque dependen de su concentración y tiempo de exposición. Se han propuesto tres patrones catameniales de exacerbación de crisis epilépticas: el patrón perimenstrual, el patrón periovulatorio y el patrón lúteo. El abordaje diagnóstico se realiza mediante un proceso sistemático de cuatro pasos: a) historia clínica del patrón del ciclo menstrual y de las crisis epilépticas; b) métodos diagnósticos para caracterizar el ciclo menstrual y el patrón de las crisis epilépticas; c) comprobar los criterios diagnósticos, y d) categorizar el patrón catamenial. Las opciones de tratamiento estudiadas requieren mayor nivel de evidencia, y no existe ningún tratamiento específico aprobado por la Food and Drug Administration. Se recomienda la optimización del tratamiento anti crisis epilépticas convencional como primera opción terapéutica. Otras opciones terapéuticas, como tratamientos no hormonales y hormonales, podrían ser de utilidad en caso de que la primera opción terapéutica resulte ineficaz.

Endometrial macrophages in health and disease.

Macrophages are present in the endometrium throughout the menstrual cycle and are most abundant during menstruation. Endometrial macrophages contribute to tissue remodeling during establishment of pregnancy and are thought to play key roles in mediating tissue breakdown and repair during menstruation. Despite these important roles, the phenotype and function of endometrial macrophages remains poorly understood. In this review, we summarize approaches used to characterize endometrial macrophage phenotype, current understanding of the functional role of macrophages in normal endometrial physiology as well as the putative contribution of macrophage dysfunction to women's reproductive health disorders.

Podocalyxin molecular characteristics and endometrial expression: high conservation between humans and macaques but divergence in mice†.

Podocalyxin (PODXL) is a newly identified key negative regulator of human endometrial receptivity, specifically down-regulated in the luminal epithelium at receptivity to permit embryo implantation. Here, we bioinformatically compared the molecular characteristics of PODXL among the human, rhesus macaque, and mouse, determined by immunohistochemistry and in situ hybridization (mouse tissues) whether endometrial PODXL expression is conserved across the three species and examined if PODXL inhibits mouse embryo attachment in vitro. The PODXL gene, mRNA, and protein sequences showed greater similarities between humans and macaques than with mice. In all species, PODXL was expressed in endometrial luminal/glandular epithelia and endothelia. In macaques (n = 9), luminal PODXL was significantly down-regulated when receptivity is developed, consistent with the pattern found in women. At receptivity, PODXL was also reduced in shallow glands, whereas endothelial expression was unchanged across the menstrual cycle. In mice, endometrial PODXL did not vary considerably across the estrous cycle (n = 16); however, around embryo attachment on d4.5 of pregnancy (n = 4), luminal PODXL was greatly reduced especially near the site of embryo attachment. Mouse embryos failed to attach or thrive when co-cultured on a monolayer of Ishikawa cells overexpressing PODXL. Thus, endometrial luminal PODXL expression is down-regulated for embryo implantation in all species examined, and PODXL inhibits mouse embryo implantation. Rhesus macaques share greater conservations with humans than mice in PODXL molecular characteristics and regulation, thus represent a better animal model for functional studies of endometrial PODXL for treatment of human fertility.

Modelling female physiology from head to Toe: Impact of sex hormones, menstrual cycle, and pregnancy.

Men and women exhibit notable differences not only in the reproductive system and reproductive behaviors, but in many other organ and physiological systems as well. Notable examples include; the stress and immune systems, the anatomy of the brain, and the metabolic and cardiovascular functions. Furthermore, female physiology is affected by the menstrual cycle and by pregnancy and lactation. If we are to successfully develop effective sex-based therapies, we must attain a comprehensive understanding of the effects of sex hormones, the menstrual cycle, and pregnancy on physiological function. By analyzing experimental findings, mathematical modelling can play a major role in facilitating and contributing to advancing the understanding of sex differences in physiology and pathophysiology. In this review, we present a survey of existing sex-specific modelling studies of physiological systems, describe the impact of the menstrual cycle and pregnancy, and discuss future modelling opportunities.

Spatiotemporal dynamics of clonal selection and diversification in normal endometrial epithelium.

It has become evident that somatic mutations in cancer-associated genes accumulate in the normal endometrium, but spatiotemporal understanding of the evolution and expansion of mutant clones is limited. To elucidate the timing and mechanism of the clonal expansion of somatic mutations in cancer-associated genes in the normal endometrium, we sequence 1311 endometrial glands from 37 women. By collecting endometrial glands from different parts of the endometrium, we show that multiple glands with the same somatic mutations occupy substantial areas of the endometrium. We demonstrate that "rhizome structures", in which the basal glands run horizontally along the muscular layer and multiple vertical glands rise from the basal gland, originate from the same ancestral clone. Moreover, mutant clones detected in the vertical glands diversify by acquiring additional mutations. These results suggest that clonal expansions through the rhizome structures are involved in the mechanism by which mutant clones extend their territories. Furthermore, we show clonal expansions and copy neutral loss-of-heterozygosity events occur early in life, suggesting such events can be tolerated many years in the normal endometrium. Our results of the evolutionary dynamics of mutant clones in the human endometrium will lead to a better understanding of the mechanisms of endometrial regeneration during the menstrual cycle and the development of therapies for the prevention and treatment of endometrium-related diseases.

Moving beyond inclusion: Methodological considerations for the menstrual cycle and menopause in research evaluating effects of dietary nitrate on vascular function.

Recent reports have acknowledged the underrepresentation of women in the field of dietary nitrate (NO3-) research. Undoubtedly, greater participation from women is warranted to clarify potential sex differences in the responses to dietary NO3- interventions. However, careful consideration for the effects of sex hormones - principally 17ß-estradiol - on endogenous nitric oxide (NO) synthesis and dietary NO3- reductase capacity is necessary for improved interpretation and reproducibility of such investigations. From available literature, we present a narrative review describing how hormonal variations across the menstrual cycle, as well as with menopause, may impact NO biosynthesis catalyzed by NO synthase enzymes and NO3- reduction via the enterosalivary pathway. In doing so, we address methodological considerations related to the menstrual cycle and hormonal contraceptive use relevant for the inclusion of premenopausal women along with factors to consider when testing postmenopausal women. Adherence to such methodological practices may explicate the utility of dietary NO3- supplementation as a means to improve vascular function among women across the lifespan.

One-carbon metabolism during the menstrual cycle and pregnancy.

Many enzymes in one-carbon metabolism (OCM) are up- or down-regulated by the sex hormones which vary diurnally and throughout the menstrual cycle. During pregnancy, estradiol and progesterone levels increase tremendously to modulate physiological changes in the reproductive system. In this work, we extend and improve an existing mathematical model of hepatic OCM to understand the dynamic metabolic changes that happen during the menstrual cycle and pregnancy due to estradiol variation. In particular, we add the polyamine drain on S-adenosyl methionine and the direct effects of estradiol on the enzymes cystathionine ß-synthase (CBS), thymidylate synthase (TS), and dihydrofolate reductase (DHFR). We show that the homocysteine concentration varies inversely with estradiol concentration, discuss the fluctuations in 14 other one-carbon metabolites and velocities throughout the menstrual cycle, and draw comparisons with the literature. We then use the model to study the effects of vitamin B12, vitamin B6, and folate deficiencies and explain why homocysteine is not a good biomarker for vitamin deficiencies. Additionally, we compute homocysteine throughout pregnancy, and compare the results with experimental data. Our mathematical model explains how numerous homeostatic mechanisms in OCM function and provides new insights into how homocysteine and its deleterious effects are influenced by estradiol. The mathematical model can be used by others for further in silico experiments on changes in one-carbon metabolism during the menstrual cycle and pregnancy.