Cervical mucus: its physiological role and clinical significance

Neuronal control of the vagina in vertebrates: A review

BACKGROUND

At present, there is an increased interest in the vaginal microbiome. It is believed that microbes play equally important roles in the vagina, including the modulation of neuronal pathways, as in the gut. However, in man as well as in animals, the vagina is the least well-studied part of the female reproductive system. The vagina, a fibromuscular tract, having two main functions, i.e., childbirth and sexual intercourse, is mainly innervated by the pudendal nerve and the pelvic splanchnic nerves (the uterovaginal nerve plexus) containing sympathetic, parasympathetic and nociceptive nerve fibers. Innervation density in the vaginal wall undergoes significant remodeling due to hormonally mediated physiological activity. Knowledge about expression and function of neuropeptides and neurotransmitters in the vaginal fibers is incomplete or not established. Most research concerning the neuroregulation of the vagina and the function and expression of neuropeptides and neurotransmitters, is performed in several vertebrate species, including large farm animals, rodents, domestic fowl and lizards.

METHODS

This review summarizes, on a bibliographic basis, the current knowledge on vaginal innervation and function of neuropeptides and neurotransmitters expressed in vaginal nerve fibers in several vertebrate species, including humans. The presence and role played by the local microbioma is also explored.

CONCLUSION

A thorough knowledge of the vaginal innervation is necessary to unravel the putative communication of the vaginal microbiome and vaginal nerve fibers, but also to understand the effects of vaginal pathologies and of administered drugs on the neuroregulation of the vagina.

Light Microscopy and Proteomic Patterns of Ovulation in Cervical Mucus

There is an increasing number of couples interested in identifying the fertile window for the purpose of conceiving. From what has been published so far, it can be concluded that there are no reliable methods to predict ovulation, and, therefore, to predict the fertile window. Proteins of the cervical mucus (CM) could behave as biomarkers to allow the early and precise identification of ovulation. CM samples were collected from the lumen of the cervical canal from women of reproductive age, on three different days of the same menstrual cycle. Samples were first analyzed and classified by light microscopy. High-resolution mass spectrometry and bioinformatic analysis were performed afterwards to determine the in vivo changes of CM protein composition. CM underwent cyclical changes in its biophysical composition, which were evidenced by changes in the crystallographic patterns observed under the light microscope. The proteomic analysis revealed changes in the protein composition of CM along the cycle. Twenty-five out of the forty-eight total proteins identified could become potential biomarkers of ovulation. The coordinated changes in the composition of the CM around the time of ovulation could be happening to specifically grant access to a foreign body, such as the sperm might be.

Insight into the ecology of vaginal bacteria through integrative analyses of metagenomic and metatranscriptomic data

Background

Vaginal bacterial communities dominated by Lactobacillus species are associated with a reduced risk of various adverse health outcomes. However, somewhat unexpectedly, many healthy women have microbiota that are not dominated by lactobacilli. To determine the factors that drive vaginal community composition we characterized the genetic composition and transcriptional activities of vaginal microbiota in healthy women.

Results

We demonstrate that the abundance of a species is not always indicative of its transcriptional activity and that impending changes in community composition can be predicted from metatranscriptomic data. Functional comparisons highlight differences in the metabolic activities of these communities, notably in their degradation of host produced mucin but not glycogen. Degradation of mucin by communities not dominated by Lactobacillus may play a role in their association with adverse health outcomes. Finally, we show that the transcriptional activities of L. crispatus, L. iners, and Gardnerella vaginalis vary with the taxonomic composition of the communities in which they reside. Notably, L. iners and G. vaginalis both demonstrate lower expression of their cholesterol-dependent cytolysins when co-resident with Lactobacillus spp. and higher expression when co-resident with other facultative and obligate anaerobes. The pathogenic potential of these species may depend on the communities in which they reside and thus could be modulated by interventional strategies.

Conclusions

Our results provide insight to the functional ecology of the vaginal microbiota, demonstrate the diagnostic potential of metatranscriptomic data, and reveal strategies for the management of these ecosystems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02635-9.

The Cervicovaginal Mucus Barrier

Preterm births are a global health priority that affects 15 million babies every year worldwide. There are no effective prognostic and therapeutic strategies relating to preterm delivery, but uterine infections appear to be a major cause. The vaginal epithelium is covered by the cervicovaginal mucus, which is essential to health because of its direct involvement in reproduction and functions as a selective barrier by sheltering the beneficial lactobacilli while helping to clear pathogens. During pregnancy, the cervical canal is sealed with a cervical mucus plug that prevents the vaginal flora from ascending toward the uterine compartment, which protects the fetus from pathogens. Abnormalities of the cervical mucus plug and bacterial vaginosis are associated with a higher risk of preterm delivery. This review addresses the current understanding of the cervicovaginal mucus and the cervical mucus plug and their interactions with the microbial communities in both the physiological state and bacterial vaginosis, with a focus on gel-forming mucins. We also review the current state of knowledge of gel-forming mucins contained in mouse cervicovaginal mucus and the mouse models used to study bacterial vaginosis.

Ultrastructural and physico-chemical characterization of saliva during menstrual cycle in perspective of ovulation in human

Human saliva is a potential diagnostic fluid and any alteration in body might be reflected in saliva so that saliva is considered as "mirror of the body". Variations in salivary hormone level, ultra structure, pH, flow rate, buffering capacity and electrolytes level are found during menstrual cycle in regard to ovulation. Thirty healthy volunteers were used for the assessment of physico-chemical changes in saliva. Reproductive cycle was categorized as pre-ovulation phase (5 to 12 days), ovulation phase (13 or 14 days) and post-ovulation phase (15 to 25 days) according to salivary arborization test and hormonal analysis. Estradiol and luteinizing hormone was gradually increased and attained peak at the level of 2.28 ± 0.20 pg/mL and 1.35 ± 0.41 mIU/mL respectively during the ovulation phase. The electrolytes result clearly indicates that the influx of common electrolytes is important for crystallization and help to induce clear ferning pattern in ovulation phase. Sodium (Na) and chloride (Cl) were found to be high during ovulation phase only. Average salivary pH was 7.5, 7.1, and 7.3 during ovulation, pre- and post-ovulation phases respectively. Buffering capacity of saliva was normal during pre- and post- ovulation phases. In contrast, in ovulation phase the buffer capacity was slightly higher. At the first time, the scanning electron microscopy (SEM) studies revealed the ultra structure difference of saliva during menstrual cycle. During ovulation phase a compact network-shaped mesh was appeared; such structure was not appeared in pre- and post ovulation phases. Additionally, we observed the saliva is arrayed as a fine mosaic-like structure during ovulation. Based on physico-chemical properties and hormonal levels may lead to develop a detection kit/sensor for detecting the ovulation phase in human.

Biopolymeric Mucin and Synthetic Polymer Analogs: Their Structure, Function and Role in Biomedical Applications

Mucin networks are viscoelastic fibrillar aggregates formed through the complex self-association of biopolymeric glycoprotein chains. The networks form a lubricious, hydrated protective shield along epithelial regions within the human body. The critical role played by mucin networks in impacting the transport properties of biofunctional molecules (e.g., biogenic molecules, probes, nanoparticles), and its effect on bioavailability are well described in the literature. An alternate perspective is provided in this paper, presenting mucin’s complex network structure, and its interdependent functional characteristics in human physiology. We highlight the recent advances that were achieved through the use of mucin in diverse areas of bioengineering applications (e.g., drug delivery, biomedical devices and tissue engineering). Mucin network formation is a highly complex process, driven by wide variety of molecular interactions, and the network possess structural and chemical variations, posing a great challenge to understand mucin’s bulk behavior. Through this review, the prospective potential of polymer based analogs to serve as mucin mimic is suggested. These analog systems, apart from functioning as an artificial model, reducing the current dependency on animal models, can aid in furthering our fundamental understanding of such complex structures.

The Fertile Window and Biomarkers: A Review and Analysis of Normal Ovulation Cycles

El objetivo de este artículo es revisar los principales conceptos en la literatura acerca de la ventana de la fertilidad en pacientes con ciclos menstruales normales. El énfasis principal del artículo se ha dirigido al análisis de la teoría de Brown de la ovulación, revisar conceptos básicos de la ovulación, secreción y metabolismo de la hormona folículo estimulante, y al estudio clínico, ecográfico y bioquímicos del desarrollo folicular de la ventana de la fertilidad. Este artículo también repasa los biomarcadores clínicos y los diferentes metabolitos endocrinos que delimitan en la fase fértil del ciclo. Se revisan diferentes estudios en los cuales las valoraciones en suero y orina de los esteroides sexuales, han corroborado tener una correlación directa para enmarcar el período fértil. Actualmente tienen relevancia estos conocimientos en diferentes grupos de interés, sobre todo en mujeres con un alto nivel de motivación interesadas en el reconocimiento de su fertilidad, las cuales pueden beneficiarse mediante la aplicación de conocimientos técnicos actuales que detectan la ventana fértil. También estos conocimientos suelen cobrar importancia en aquellas personas que pertenecen a programas de regulación de la fertilidad (PRF), con intención de distanciar un embarazo, o de reconocer el periodo fértil del ciclo para conseguir un embarazo espontáneamente, o mediante programas de NaProTecnología. Otros grupos de interés, son aquellos en los cuales no se tiene experiencia en cursos de PRF, pero desean mejorar sus conocimientos en el reconocimiento de la fertilidad por medio de una breve entrevista, o por medio de cursos de orientación familiar.

Characterization of the Human Cervical Mucous Proteome

Introduction

Cervical cancer is among the most common cancers in women worldwide. Discovery of biomarkers for the early detection of cervical cancer would improve current screening practices and reduce the burden of disease.

Objective

In this study, we report characterization of the human cervical mucous proteome as the first step towards protein biomarker discovery.

Methods

The protein composition was characterized using one- and two-dimensional gel electrophoresis, and liquid chromatography coupled with mass spectrometry. We chose to use this combination of traditional biochemical techniques and proteomics to allow a more comprehensive analysis.

Results and Conclusion

A total of 107 unique proteins were identified, with plasma proteins being most abundant. These proteins represented the major functional categories of metabolism, immune response, and cellular transport. Removal of high molecular weight abundant proteins by immunoaffinity purification did not significantly increase the number of protein spots resolved. We also analyzed phosphorylated and glycosylated proteins by fluorescent post-staining procedures. The profiling of cervical mucous proteins and their post-translational modifications can be used to further our understanding of the cervical mucous proteome.

Optimization of SELDI-TOF protein profiling for analysis of cervical mucous

Cervical mucous, produced in the region where cervical neoplasia occurs, is thought to be a good choice for discovery of biomarkers to improve cervical cancer screening. In this study, SELDI-TOF MS analysis was used to evaluate parameters for protein profiling of mucous. Proteins were extracted from mucous collected with Weck-Cel sponges. Several parameters like extraction reagent, loading protein concentration, matrix type, bind/wash conditions and sample fractionation, on different protein chip surfaces were evaluated. SELDI peak number and consistency in the resulting spectra were used to evaluate each condition. Analysis of spectra generated by different protein chips revealed an average of 30 peaks in the 2.5-30 kDa mass range using sinnapinic acid in the unfractionated sample. Sample concentration and buffer conditions evaluated did not lead to large alterations in the profiles. Quality control spectra were reproducible with intra- and inter-assay intensity CV for CM10, H50 and Q10 arrays being less than 20% and 30% respectively. IMAC30-Cu chips had higher intra- and inter-assay CV's at 25% and 35%. Current data showed that optimizing pre-analytical parameters can help in standardization and reproducibility of protein profiles produced by cervical mucous, and thus can be used for protein biomarker discovery with the SELDI platform.

Immunoglobulin levels and phagocytes in the cervical mucus plug at term of pregnancy

BACKGROUND

To characterize the potential for adaptive immune protection in cervical mucus plugs with respect to immunoglobulin isotypes and effector cells (phagocytes).

METHODS

Thirty-one cervical mucus plugs were collected from healthy women in labor at term. The cervical mucus plugs were allocated either to analysis of immunoglobulins by enzyme-linked immunosorbent assay (ELISA), gel chromatography and Western blotting (n = 20) or to microscopical, including immunocytochemical, analyses. The levels of immunoglobulin in the plugs were compared to the levels in 10 samples of ovulatory cervical mucus from nonpregnant women.

RESULTS

In the cervical mucus plugs, levels of immunoglobulin G (IgG) [median 3270 microg/mL (100-14 500)] and IgA [540 (22-2820)], but not IgM [30.5 (1.0-160)], were significantly elevated compared to cervical mucus from nonpregnant women (p < 0.02 for IgG and IgA). The IgG : IgA ratio in the plugs was also elevated (p < 0.02). The proportion of secretory immunoglobulin A (SIgA) relative to total IgA in the plugs ranged from 16 to 65% (n = 5). IgA and IgG were largely intact. Microscopically, the vagina-proximal part of the cervical mucus plugs contained bacteria and was rich in cells, mainly phagocytes. Conversely, the uterine part contained few cells.

CONCLUSION

The high immunoglobulin levels in combination with the presence of phagocytes suggest a potential for adaptive immune defense in the cervical mucus plug, which, together with innate immune factors, may act as an immunological gatekeeper protecting the fetomaternal unit against infection from the vagina.

Alterations in protein, sialic acid and some enzymes in cervical mucus of female rats during NET-EN treatment

The effect of norethisterone enanthate (NET-EN) on cervical mucus protein, sialic acid and some enzymes (e.g. peroxidase, alkaline phosphatase and alpha-amylase) were studied in adult female rats. One mg NET-EN every 12 days was found to be an effective contraceptive dose of this drug in this species, acting primarily through the cervical mucus. NET-EN produced a highly significant increase in protein content and peroxidase and alkaline phosphatase activities. However, sialic acid content and amylase activity did not exhibit any definite pattern after NET-EN therapy. The increased protein content together with persistent elevated levels of peroxidase and alkaline phosphatase corroborates the hypothesis that NET-EN creates a progestogenic phase which prevents sperm penetration and thus conception.

Variances in mucus architecture as a cause of cervical factor infertility

A cervical factor accounts for 5% to 10% of infertility among women. In the absence of an immunologic or endocrine-related basis for incompetent sperm/mucus interaction, an idiopathic cause is usually ascribed. This study describes quantitative analyses of the microstructure of mucin strands, observed under scanning electron microscopy, from infertile women displaying incompetent sperm/mucus interaction unrelated to any apparent immunologic or endocrine-associated cause. The results revealed a highly significant reduction in the spacing of mucin fibers incompatible to sperm penetrability and migration. Additional quantitative measurements of mucin strand diameter and number and geometry of strand crosslinks suggest inadequate hydration of the mucin gel as a causative basis for the structural inadequacies observed in some cases of cervical-factor infertility.

Comparative studies of mucus and mucin physicochemistry

The transport of mucus on a ciliated epithelium, and the penetration of sperm through cervical mucus, have been shown to be functions of the rheological, principally viscoelastic, properties of the secretion. These physicochemical properties, in turn, are largely determined by the composition and concentration of mucin glycoproteins, which are the principal macromolecular components of the secretion. These functions and properties of various types of mucous secretions are discussed, emphasizing both similarities and differences. Background and data are presented supporting these concepts, based on studies of human cervical and middle ear mucus, as well as bovine cervical and canine tracheal mucus. A major determinant of differences in function between mucus samples appears to be the carbohydrate composition of the mucin, after corrections are made for environmental factors such as pH, ionic strength and mucin concentration Mucin behaviour also depends on specific solutes in the secretion, such as Ca2+. Although significant differences in mucus properties and function exist, it is hypothesized that these developed as variations of the major function common to all mucous secretions, which is to maintain and control the water balance of epithelial mucosa.