Brainwork in the ovary: kisspeptin and BDNF signaling converge to ensure oocyte survival

Effects of indented zona pellucida on oocyte growth and development explored from changes of gene expression in cumulus cells

PURPOSE

Abnormal Zona Pellucida (ZP) of human oocytes is an extracellular oocyte abnormality leading to subfertility or infertility, among which indented ZP (iZP) is a common clinical case, and there is currently no effective clinical solution. The study aimed to find out the influence of this abnormal ZP on the growth and development of GC and further explore its influence on the growth and development of oocytes, hoping to provide new ideas for the etiology and treatment of such patients.

METHODS

In this study, we collected granulosa cells GC from oocytes with iZP(four cases) and GC from oocytes with a normal appearance of the ZP(eight cases) during ICSI treatment cycles, and submitted them to transcriptomic analysis using next-generation RNA sequencing (RNAseq).

RESULTS

177 Differentially Expressed Genes (DEG) were identified by RNAseq analysis of Granulosa Cells (GC) from oocytes with a normal ZP morphological appearance and those with iZP. Correlation analysis of these DEGs showed that the expression levels of the immune factor CD274 and the inflammatory factors IL4R and IL-7R, which are positively associated with ovulation, were significantly down-regulated in the GC of oocytes with iZP. Hippo, PI3K-AKT, Ras and calcium signaling pathways related to oocyte growth and development, NTRK2 and its ligands (BDNF and NT5E) from the neurotrophin family that are trophic to the oocyte were also significantly down-regulated in the GC of oocytes with iZP. In addition, the expression of cadherin family members CDH6, CDH12 and CDH19 were significantly down-regulated in DEGs, and the down-regulation of these proteins may affect the gap junction between Granulosa cells and oocytes.

CONCLUSION

IZP might cause obstacles to dialogue and material exchange between GC and oocytes and further affect the growth and development of oocytes.

Brain-Derived Neurotrophic Factor in Gestational Diabetes: Analysis of Maternal Serum and Cord Blood Pairs and Comparison of Dietary- and Insulin-Dependent GDM

The Objective of our study was to investigate the influence of dietary (dGDM) and insulin-dependent (iGDM) gestational diabetes (GDM) on BDNF blood levels of corresponding maternal-neonatal pairs and compare them to pregnancies unaffected by GDM. Blood samples from 293 maternal-neonatal pairs were analyzed. Statistical analysis was performed using multiple regression analysis for association of log-transformed maternal and neonatal BDNF levels in relation to GDM, gestational age, neonatal sex, and mode of delivery. This was followed by a 2:1 matching of healthy and diabetic pairs. Maternal and neonatal BDNF levels were lowest in the iGDM group, followed by the dGDM group and healthy controls (maternal: healthy 665 ± 562 (26–2343) pg/mL vs. dGDM 593 ± 446 (25–1522) pg/mL vs. iGDM 541 ± 446 (68–2184) pg/mL; neonate: healthy 541 ± 464 (9.5–2802) pg/mL vs. dGDM 375 ± 342 (1–1491) pg/mL vs. iGDM 330 ± 326 (47–1384) pg/mL). After multiple regression analysis and additional 2:1 matching neonatal log-BDNF was significantly lower (−152.05 pg/mL, p = 0.027) in neonates of mothers with GDM compared to healthy pairs; maternal log-BDNF was also lower (−79.6 pg/mL), but did not reach significance. Our study is the first to analyze BDNF in matched maternal-neonatal pairs of GDM patients compared to a metabolically unaffected control group.

Role of Mitochondria in Interplay between NGF/TRKA, miR-145 and Possible Therapeutic Strategies for Epithelial Ovarian Cancer

Ovarian cancer is the most lethal gynecological neoplasm, and epithelial ovarian cancer (EOC) accounts for 90% of ovarian malignancies. The 5-year survival is less than 45%, and, unlike other types of cancer, the proportion of women who die from this disease has not improved in recent decades. Nerve growth factor (NGF) and tropomyosin kinase A (TRKA), its high-affinity receptor, play a crucial role in pathogenesis through cell proliferation, angiogenesis, invasion, and migration. NGF/TRKA increase their expression during the progression of EOC by upregulation of oncogenic proteins as vascular endothelial growth factor (VEGF) and c-Myc. Otherwise, the expression of most oncoproteins is regulated by microRNAs (miRs). Our laboratory group reported that the tumoral effect of NGF/TRKA depends on the regulation of miR-145 levels in EOC. Currently, mitochondria have been proposed as new therapeutic targets to activate the apoptotic pathway in the cancer cell. The mitochondria are involved in a myriad of functions as energy production, redox control, homeostasis of Ca⁺², and cell death. We demonstrated that NGF stimulation produces an augment in the Bcl-2/BAX ratio, which supports the anti-apoptotic effects of NGF in EOC cells. The review aimed to discuss the role of mitochondria in the interplay between NGF/TRKA and miR-145 and possible therapeutic strategies that may decrease mortality due to EOC.

Role of Kisspeptin on Hypothalamic-Pituitary-Gonadal Pathology and Its Effect on Reproduction

Kisspeptin is a neuropeptide that plays a significant role in human reproduction by its action on the hypothalamic-pituitary-gonadal (HPG) axis and functions through a G-protein-coupled receptor called G-protein-coupled receptor 54/kisspeptin 1 receptor (GPR54/KISS1R). It is encoded by the kisspeptin 1 (KISS1) gene that is mainly expressed in the hypothalamus. Kisspeptins are also recognized as vital aspects of maturation and proper function of the reproductive system in both males and females. It also plays its role in the onset of puberty, sexual patterns, desires, ovum development in women, sperm quality in men, feedback mechanisms, pregnancy, and lactation. Studies proved the pathological role of kisspeptin dysregulation in disorders like polycystic ovarian syndrome (PCOS) and infertility. Mutations in the KISS1 gene also contribute to precocious puberty or hypogonadotropic hypogonadism, depending upon the nature of mutations. Levels of kisspeptin also aid in the identification of a few pregnancy-related complications like preeclampsia, intrauterine growth restriction, and act as a marker of miscarriage. Due to the wide range of effects that kisspeptin has on the reproductive axis, investigations are being carried out to develop it as a diagnostic marker, treat diseases like hypogonadism and PCOS, and solve infertility issues.

Brain-derived neurotrophic factor (BDNF) expression and function in the mammalian reproductive Tract

BACKGROUND

Neurotrophins of the nerve growth factor family are soluble polypeptides that are best known for their role in nerve growth, survival and differentiation in the central nervous system. A growing body of literature shows that neurotrophins and their receptors are also expressed throughout the reproductive tract.

OBJECTIVE AND RATIONALE

Neurotrophins are key regulatory proteins in reproductive physiology during development and throughout adult life. Of the neurotrophins, the literature describing the expression and function of brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, neurotrophin receptor kinase-2 (NTRK2), has been expanding rapidly. We therefore conducted a systematic inductive qualitative review of the literature to better define the role of the BDNF in the reproductive tract. We postulate that BDNF and NTRK2 are central regulatory proteins throughout the reproductive system.

SEARCH METHODS

An electronic search of Medline (PubMed) and Web of Science for articles relating to BDNF and the reproductive system was carried out between January 2018 and February 2019.

OUTCOMES

In the ovary, BDNF expression and levels have been linked with follicle organisation during ovarian development, follicle recruitment and growth and oocyte maturation. In the endometrium, BDNF is involved in cell proliferation and neurogenesis. In contrast, literature describing the role of BDNF in other reproductive tissues is sparse and BDNF-NTRK2 signalling in the male reproductive tract has been largely overlooked. Whilst estradiol appears to be the primary regulator of BDNF expression, we also identified reports describing binding sites for glucocorticoid and myocyte enhancer factor-2, a calcium-response element through activation of an N-methyl-D-aspartate (NMDA) receptor, and aryl hydrocarbon receptor nuclear transporter protein-4 (ARNT) response elements in promoter regions of the BDNF gene. Expression is also regulated by multiple microRNAs and post-translational processing of precursor proteins and intracellular shuttling. BDNF-NTRK2 signalling is modulated through tissue specific receptor expression of either the full-length or truncated NTRK2 receptor; however, the functional importance remains to be elucidated. Dysregulation of BDNF expression and circulating concentrations have been implicated in several reproductive disorders including premature ovarian failure, endometriosis, pre-eclampsia, intra-uterine growth restriction (IUGR) and several reproductive cancers.

WIDER IMPLICATIONS

We conclude that BDNF and its receptors are key regulatory proteins central to gonadal development, ovarian regulation and uterine physiology, as well as embryo and placenta development. Furthermore, dysregulation of BDNF-NTRK2 in reproductive diseases suggests their potential role as candidate clinical markers of disease and potential therapeutic targets.

Peripheral action of kisspeptin at reproductive tissues-role in ovarian function and embryo implantation and relevance to assisted reproductive technology in livestock: a review

Kisspeptin (KISS1) is encoded by the KISS1 gene and was initially found to be a repressor of metastasis. Natural mutations in the KISS1 receptor gene (KISS1R) were subsequently shown to be associated with idiopathic hypothalamic hypogonadism and impaired puberty. This led to interest in the role of KISS1 in reproduction. It was established that KISS1 had a fundamental role in the control of gonadotropin releasing hormone (GnRH) secretion. KISS1 neurons have receptors for leptin and estrogen receptor α (ERα), which places KISS1 at the gateway of metabolic (leptin) and gonadal (ERα) regulation of GnRH secretion. More recently, KISS1 has been shown to act at peripheral reproductive tissues. KISS1 and KISS1R genes are expressed in follicles (granulosa, theca, oocyte), trophoblast, and uterus. KISS1 and KISS1R proteins are found in the same tissues. KISS1 appears to have autocrine and paracrine actions in follicle and oocyte maturation, trophoblast development, and implantation and placentation. In some studies, KISS1 was beneficial to in vitro oocyte maturation and blastocyst development. The next phase of KISS1 research will explore potential benefits on embryo survival and pregnancy. This will likely involve longer-term KISS1 treatments during proestrus, early embryo development, trophoblast attachment, and implantation and pregnancy. A deeper understanding of the direct action of KISS1 at reproductive tissues could help to achieve the next step change in embryo survival and improvement in the efficiency of assisted reproductive technology.

Serum and follicular fluid levels of serotonin, kisspeptin, and brain-derived neurotrophic factor in patients undergoing in vitro fertilization: an observational study : Neurohormones in patients receiving IVF

OBJECTIVE

This study aimed to examine the effect of interactions between serotonin (5-HT), brain-derived neurotrophic factor (BDNF), and kisspeptin on the reproductive potential in women receiving in vitro fertilization (IVF).

METHODS

Paired serum and follicular fluid (FF) samples were obtained from 30 consecutive patients receiving IVF. Primary and secondary outcome measures were the rate of chemical/clinical pregnancy and the number of mature oocytes and embryos, respectively. Serum and FF 5-HT, BDNF, kisspeptin, and platelet-activating factor (PAF) levels were measured by enzyme-linked immunosorbent assay.

RESULTS

In response to ovarian hyperstimulation, serum 5-HT and kisspeptin levels significantly increased, whereas serum BDNF and PAF levels remained unchanged. These factors were detected in FF, but they were unrelated to serum levels. FF 5-HT and BDNF levels were positively correlated. Serum kisspeptin levels were negatively correlated with FF BDNF and serum and FF PAF levels. Women who were pregnant had significantly lower FF BDNF levels compared with women who were not pregnant (21.96±12.75 vs 47.63±52.90 µg/mL). Multivariate stepwise linear regression and logistic regression analyses showed that only 5-HT and kisspeptin improved IVF outcome.

CONCLUSIONS

This study indicates a role of serotoninergic mechanisms in success of IVF, but the contribution of interacting neuropeptides requires additional investigation.

The Role of Kisspeptin in Female Reproduction

CONTEXT

Kisspeptin (KISS1), a recently discovered neuropeptide that acts upstream of gonadotropin-releasing hormone (GnRH) neurons, is critical for maturation and function of the reproductive axis. This review aimed at providing comprehensive and up-to-date information on Kisspeptin and its role in female reproduction.

EVIDENCE ACQUISITION

A literature review was performed using PubMed for all English language articles published between 1999 and 2016.

RESULTS

The kisspeptin system (KISS1/G protein-coupled receptor-54,GPR54) has recently been addressed as an essential gatekeeper of puberty onset and gonadotropin secretion. Compelling evidence has documented that hypothalamic Kisspeptin mediates steroid feedback and metabolic cues at different developmental stages throughout lifespan. Furthermore, in pre/postnatally androgenized animal models, which exhibit many of the characteristics of Polycystic Ovarian Syndrome (PCOS), the hypothalamic expression of KISS1 and GnRH is abnormal, which might lead to multiple tissue abnormalities observed in this disorder.

CONCLUSIONS

Kisspeptin, a principal activator of GnRH neurons and the target of endocrine and metabolic cues, is a prerequisite for the onset of puberty and maintenance of normal reproductive function, as abnormal KISS1/GPR54 system has been reported in both animal models and patients with certain forms of infertility, e.g. Idiopathic Hypogonadotropic hypogonadism (IHH) and PCOS. The information suggests that kisspeptin or its receptor represents a potential therapeutic target in the treatment of patients with fertility disorders.