Chronic predator stress in female mice reduces primordial follicle numbers: implications for the role of ghrelin

Chronic stress causes ovarian fibrosis to impair female fertility in mice

OBJECTIVE

Chronic psychological stress is associated with impaired follicular development and ovarian dysfunction. Many aspects of this dysfunction and the underlying mechanisms remain unclear. Using a chronic unpredictable mild stress (CUMS) mouse model, we investigate the influence of chronic stress on ovarian function and explore potential mechanisms.

METHODS

A CUMS mouse model was constructed over eight months, covering the period from sexual maturity to the onset of declining fertility in mice. At the end of the 2nd, 4th, 6th, and 8th months of exposure to CUMS, behavioral and physiological assays, including the sucrose preference test, tail suspension test, and serum corticosterone levels, were conducted to validate the effectiveness of the stress model. Fertility and ovarian function were assessed by analyzing the estrous cycle, number of offspring, sex hormone levels, follicle counts, granulosa cell proliferation and apoptosis, and the expression levels of fibrosis markers. Furthermore, proteomic analyses were performed on the ovaries to investigate the molecular mechanisms of ovarian fibrosis induced by CUMS.

RESULTS

With continued CUMS exposure, there was a gradual decline in both the ovary-to-body weight ratio and the number of offspring. Moreover, the percentage of atretic follicles was notably higher in the CUMS-exposed groups compared to the control groups. It is noticeable that CUMS triggered granulosa cell apoptosis and halted proliferation. Additionally, increased expression of α-SMA and Collagen I in the ovaries of CUMS-exposed mice indicated that CUMS could induce ovarian fibrosis. Proteomic analysis provided insights into the activation of specific biological processes and molecules associated with fibrosis induced by chronic stress.

CONCLUSIONS

Our results strongly suggest that exposure to CUMS induces ovarian fibrosis, which influences follicular development and ultimately contributes to fertility decline. These findings offer novel perspectives on the impact of chronic stress on ovarian dysfunction.

A terrified-sound stress causes cognitive impairment in female mice by impairing neuronal plasticity

Stress is an important environmental factor affecting mental health that cannot be ignored. Moreover, due to the great physiological differences between males and females, the effects of stress may vary by sex. Previous studies have shown that terrified-sound stress, meaning exposed mice to the recorded vocalizations in response to the electric shock by their kind to induce psychological stress, can cause cognitive impairment in male. In the study, we investigated the effects of the terrified-sound stress on adult female mice.

METHODS

32 adults female C57BL/6 mice were randomly divided into control (n = 16) and stress group (n = 16). Sucrose preference test (SPT)was carried out to evaluate the depressive-like behavior. Using Open field test (OFT) to evaluate locomotor and exploratory alterations in mice. Spatial learning and memory ability were measured in Morris Water maze test (MWM), Golgi staining and western blotting showed dendritic remodeling after stress. In addition, serum hormone quantifications were performed by ELISA.

RESULTS

we found the sucrose preference of stress group was significantly decreased (p < 0.05) compared with control group; the escape latency of the stress group was significantly prolonged (p < 0.05), the total swimming distance and the number of target crossings(p < 0.05) were significantly increased (p < 0.05) in MWM; Endocrine hormone, Testosterone (T) (p < 0.05), GnRH (p < 0.05), FSH and LH levels was decreased; Golgi staining and western blotting showed a significant decrease in dendritic arborization, spine density and synaptic plasticity related proteins PSD95 and BDNF in the stress group.

CONCLUSION

Terrified-sound stress induced depressive-like behaviors, locomotor and exploratory alterations. And impaired cognitive by altering dendritic remodeling and the expression of synaptic plasticity-related proteins. However, females are resilient to terrified-sound stress from a hormonal point of view.

The power of effective study design in animal Experimentation: Exploring the statistical and ethical implications of asking multiple questions of a data set

One of the chief advantages of using highly standardised biological models including model organisms is that multiple variables can be precisely controlled so that the variable of interest is more easily studied. However, such an approach often obscures effects in sub-populations resulting from natural population heterogeneity. Efforts to expand our fundamental understanding of multiple sub-populations are in progress. However, such stratified or personalised approaches require fundamental modifications of our usual study designs that should be implemented in Brain, Behavior and Immunity (BBI) research going forward. Here we explore the statistical feasibility of asking multiple questions (including incorporating sex) within the same experimental cohort using statistical simulations of real data. We illustrate and discuss the large explosion in sample numbers necessary to detect effects with appropriate power for every additional question posed using the same data set. This exploration highlights the strong likelihood of type II errors (false negatives) for standard data and type I errors when dealing with complex genomic data, where studies are too under-powered to appropriately test these interactions. We show this power may differ for males and females in high throughput data sets such as RNA sequencing. We offer a rationale for the use of alternative experimental and statistical strategies based on interdisciplinary insights and discuss the real-world implications of increasing the complexities of our experimental designs, and the implications of not attempting to alter our experimental designs going forward.

Psycho-emotional stress, folliculogenesis, and reproductive technologies: clinical and experimental data

Modern life, especially in large cities, exposes people to a high level of noise, high density of population, disrupted sleeping, large amount of excessive and controversial information as well as to other negative factors; all this may cause chronic psycho-emotional stress. The latest publications often use the term “Syndrome of megalopolis”, which means disruption of sleeping, high anxiety, and altered reproductive function. Medical treatment of infertility may also be considered as a stress factor, especially when infertility lasts for years and is aggravated with emotional frustration. Long-lasting distress may worsen health in general and suppress reproductive function, in particular. The review presents the data on the effects of maternal stress on folliculogenesis, especially when assisted reproductive technologies (ARTs) are used. Clinical data are presented alongside data from laboratory animal experiments. Different maternal stress models are taken into account in respect of their inf luence on oocyte maturation and embryo development. The interfering of psycho-emotional stress and reproductive function is the focus of the review. In these situations, exogenous hormones compensate for the stress-related disruption of the hypothalamic-pituitary-gonadal axis. When ARTs are implemented, stress-induced disruption of oogenesis is realized not via a decrease in hypothalamic and pituitary hormones, but by other ways, which involve paracrine mechanisms described in this review. Based on the literature analysis, one may conclude that stress negatively affects oocyte maturation in the ovary and suppresses subsequent embryo development. The role of some ovarian paracrine factors, such as BDNF, GDF-9, HB-EGF, TNF-α, and some others has been elucidated

Long-term role of neonatal microglia and monocytes in ovarian health

Early life microglia are essential for brain development, and developmental disruption in microglial activity may have long-term implications for the neuroendocrine control of reproduction. We and others have previously shown that early life immune activation compromises the long-term potential for reproductive function in females. However, the supportive role of microglia in female reproductive development is still unknown. Here, we examined the long-term programming effects of transient neonatal microglial and monocyte ablation on hypothalamic-pituitary-gonadal (HPG) axis function in female rats. We employed a Cx3cr1-Dtr transgenic Wistar rat model to acutely ablate microglia and monocytes, commencing on either postnatal day (P) 7 or 14, since the development of the HPG axis in female rodents primarily occurs during the first two to three postnatal weeks. After an acutely diminished expression of microglia and monocyte genes in the brain and ovaries, respectively, microglia had repopulated the brain by P21, albeit that cellular complexity was still reduced in both groups at this time. Removal of microglia and monocytes on P7, but not P14 reduced circulating luteinising hormone levels in adulthood and ovarian gonadotropin receptors mRNA. These changes were notably associated with fewer primary and antral follicles in these rats. These data suggest that transient ablation of microglia and monocytes at the start of the second but not the third postnatal week has long-term effects on ovarian health. The findings highlight the important developmental role of a healthy immune system for female potential reproductive capacity and the importance of critical developmental periods to adult ovarian health.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus–pituitary–gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus-pituitary-gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

The Role of the Gastric Hormones Ghrelin and Nesfatin-1 in Reproduction

Ghrelin and nesfatin-1 are enteroendocrine peptide hormones expressed in rat X/A-like and human P/D1cells of the gastric mucosa. Besides their effect on food intake, both peptides are also implicated in various other physiological systems. One of these is the reproductive system. This present review illustrates the distribution of ghrelin and nesfatin-1 along the hypothalamus–pituitary–gonadal (HPG) axis, their modulation by reproductive hormones, and effects on reproductive functions as well as highlighting gaps in current knowledge to foster further research.

Impact of chronic variable stress on neuroendocrine hypothalamus and pituitary in male and female C57BL/6J mice

Chronic stress exerts multiple negative effects on the physiology and health of an individual. In the present study, we examined hypothalamic, pituitary and endocrine responses to 14 days of chronic variable stress (CVS) in male and female C57BL/6J mice. In both sexes, CVS induced a significant decrease in body weight and enhanced the acute corticosterone stress response, which was accompanied by a reduction in thymus weight only in females. However, single-point blood measurements of basal prolactin, thyroid-stimulating hormone, luteinising hormone, growth hormone and corticosterone levels taken at the end of the CVS were not different from those of controls. Similarly, pituitary mRNA expression of Fshb, Lhb, Prl and Gh was unchanged by CVS, although Pomc and Tsh were significantly elevated. Within the adrenal medulla, mRNA for Th, Vip and Gal were elevated following CVS. Avp transcript levels within the paraventricular nucleus of the hypothalamus were increased by CVS; however, levels of Gnrh1, Crh, Oxt, Sst, Trh, Ghrh, Th and Kiss1 remained unchanged. Oestrous cycles were lengthened slightly by CVS and ovarian histology revealed a reduction in the number of preovulatory follicles and corpora lutea. Taken together, these observations indicate that 14 days of CVS induces an up-regulation of the neuroendocrine stress axis and creates a mild disruption of female reproductive function. However, the lack of changes in other neuroendocrine axes controlling anterior and posterior pituitary secretion suggest that most neuroendocrine axes are relatively resilient to CVS.

Ovarian follicles are resistant to monocyte perturbations-implications for ovarian health with immune disruption†

Monocytes and macrophages are the most abundant immune cell populations in the adult ovary, with well-known roles in ovulation and corpus luteum formation and regression. They are activated and proliferate in response to immune challenge and are suppressed by anti-inflammatory treatments. It is also likely they have a functional role in the healthy ovary in supporting the maturing follicle from the primordial through to the later stages; however, this role has been unexplored until now. Here, we utilized a Cx3cr1-Dtr transgenic Wistar rat model that allows a conditional depletion of circulating monocytes, to investigate their role in ovarian follicle health. Our findings show that circulating monocyte depletion leads to a significant depletion of ovarian monocytes and monocyte-derived macrophages. Depletion of monocytes was associated with a transient reduction in circulating anti-Müllerian hormone (AMH) at 5 days postdepletion. However, the 50-60% ovarian monocyte/macrophage depletion had no effect on ovarian follicle numbers, follicle atresia, or apoptosis, within 5-21 days postdepletion. These data reveal that the healthy adult ovary is remarkably resistant to perturbations of circulating and ovarian monocytes despite acute changes in AMH. These data suggest that short-term anti-inflammatory therapies that transiently impact on circulating monocytes are unlikely to disrupt ovarian follicle health, findings that have significant implications for fertility planning relative to the experience of an immune challenge or immunosuppression.

High Maternal Omega-3 Supplementation Dysregulates Body Weight and Leptin in Newborn Male and Female Rats: Implications for Hypothalamic Developmental Programming

Maternal diet is critical for offspring development and long-term health. Here we investigated the effects of a poor maternal diet pre-conception and during pregnancy on metabolic outcomes and the developing hypothalamus in male and female offspring at birth. We hypothesised that offspring born to dams fed a diet high in fat and sugar (HFSD) peri-pregnancy will have disrupted metabolic outcomes. We also determined if these HFSD-related effects could be reversed by a shift to a healthier diet post-conception, in particular to a diet high in omega-3 polyunsaturated fatty acids (ω3 PUFAs), since ω3 PUFAs are considered essential for normal neurodevelopment. Unexpectedly, our data show that there are minimal negative effects of maternal HFSD on newborn pups. On the other hand, consumption of an ω3-replete diet during pregnancy altered several developmental parameters. As such, pups born to high-ω3-fed dams weighed less for their length, had reduced circulating leptin, and also displayed sex-specific disruption in the expression of hypothalamic neuropeptides. Collectively, our study shows that maternal intake of a diet rich in ω3 PUFAs during pregnancy may be detrimental for some metabolic developmental outcomes in the offspring. These data indicate the importance of a balanced dietary intake in pregnancy and highlight the need for further research into the impact of maternal ω3 intake on offspring development and long-term health.

Inhibitory effect of central ghrelin on steroid synthesis affecting reproductive health in female mice

Ghrelin is a 28-amino acid peptide hormone that regulates ovarian steroid hormone synthesis; however, there is limited evidence regarding the regulation of this pathway by ghrelin in mice ovary. Thus, we aimed to investigate whether central ghrelin action plays a role in murine reproductive health by inhibiting steroid synthesis. Further, we sought to examine the mechanism of central ghrelin action in ovarian steroid hormone synthesis. After the administration of intracerebroventricular ghrelin (1 nmol), we found reduced serum concentrations of oestradiol and progesterone and reduced secretion of follicle-stimulating hormone and luteinising hormone. Although ghrelin reduced 3β-hydroxysteroid dehydrogenase mRNA and protein levels in the hypothalamus, it did not affect the expression of steroidogenic acute regulatory protein and cytochrome P450 17A1. In the ovary, central ghrelin regulation indirectly inhibited the mRNA and protein levels of steroidogenic acute regulatory protein, cytochrome P450 17A1, and 3β-hydroxysteroid dehydrogenase. Moreover, no changes were observed in the expression of proliferating cell nuclear antigen and phosphorylation of extracellular signal-regulated kinase. We hypothesised that central ghrelin regulation suppressed serum oestradiol and progesterone levels by indirectly inhibiting the expression of steroidogenic acute regulatory protein, cytochrome P450 17A1, and 3β-hydroxysteroid dehydrogenase in the ovary. In this regulation, the suppressed secretion of the follicle-stimulating hormone and luteinising hormone in the pituitary by ghrelin could be involved. Furthermore, hypothalamic 3β-hydroxysteroid dehydrogenase expression is reduced by ghrelin injection.

A distinctive epigenetic ageing profile in human granulosa cells

STUDY QUESTION

Does women’s age affect the DNA methylation (DNAm) profile differently in mural granulosa cells (MGCs) from other somatic cells?

SUMMARY ANSWER

Accumulation of epimutations by age and a higher number of age-related differentially methylated regions (DMR) in MGCs were found compared to leukocytes from the same woman, suggesting that the MGCs have a distinctive epigenetic profile.

WHAT IS KNOWN ALREADY

The mechanisms underlying the decline in women’s fertility from the mid-30s remain to be fully elucidated. The DNAm age of many healthy tissues changes predictably with and follows chronological age, but DNAm age in some reproductive tissues has been shown to depart from chronological age (older: endometrium; younger: cumulus cells, spermatozoa).

STUDY DESIGN, SIZE, DURATION

This study is a multicenter cohort study based on retrospective analysis of prospectively collected data and material derived from healthy women undergoing IVF or ICSI treatment following ovarian stimulation with antagonist protocol. One hundred and nineteen women were included from September 2016 to June 2018 from four clinics in Denmark and Sweden.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blood samples were obtained from 118 healthy women with varying ovarian reserve status. MGCs were collected from 63 of the 119 women by isolation from pooled follicles immediately after oocyte retrieval. DNA from leukocytes and MGCs was extracted and analysed with a genome-wide methylation array. Data from the methylation array were processed using the ENmix package. Subsequently, DNAm age was calculated using established and tailored age predictors and DMRs were analysed with the DMRcate package.

MAIN RESULTS AND ROLE OF CHANCE

Using established age predictors, DNAm age in MGCs was found to be considerable younger and constant (average: 2.7 years) compared to chronological age (average: 33.9 years). A Granulosa Cell clock able to predict the age of both MGCs (average: 32.4 years) and leukocytes (average: 38.8 years) was successfully developed. MGCs differed from leukocytes in having a higher number of epimutations (P = 0.003) but predicted telomere lengths unaffected by age (Pearson’s correlation coefficient = −0.1, P = 0.47). DMRs associated with age (age-DMRs) were identified in MGCs (n = 335) and in leukocytes (n = 1) with a significant enrichment in MGCs for genes involved in RNA processing (45 genes, P = 3.96 × 10−08) and gene expression (152 genes, P = 2.3 × 10−06). The top age-DMRs included the metastable epiallele VTRNA2-1, the DNAm regulator ZFP57 and the anti-Müllerian hormone (AMH) gene. The apparent discordance between different epigenetic measures of age in MGCs suggests that they reflect difference stages in the MGC life cycle.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

No gene expression data were available to associate with the epigenetic findings. The MGCs are collected during ovarian stimulation, which may influence DNAm; however, no correlation between FSH dose and number of epimutations was found.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings underline that the somatic compartment of the follicle follows a different methylation trajectory with age than other somatic cells. The higher number of epimutations and age-DMRs in MGCs suggest that their function is affected by age.

STUDY FUNDING/COMPETING INTEREST(S)

This project is part of ReproUnion collaborative study, co-financed by the European Union, Interreg V ÖKS, the Danish National Research Foundation and the European Research Council. The authors declare no conflict of interest.