Evaluation of mitochondria in mouse oocytes following cisplatin exposure

An overview of different methods to establish a murine premature ovarian failure model

Premature ovarian failure (POF)is defined as the loss of normal ovarian function before the age of 40 and is characterized by increased gonadotropin levels and decreased estradiol levels and ovarian reserve, often leading to infertility. The incomplete understanding of the pathogenesis of POF is a major impediment to the development of effective treatments for this disease, so the use of animal models is a promising option for investigating and identifying the molecular mechanisms involved in POF patients and developing therapeutic agents. As mice and rats are the most commonly used models in animal research, this review article considers studies that used murine POF models. In this review based on the most recent studies, first, we introduce 10 different methods for inducing murine POF models, then we demonstrate the advantages and disadvantages of each one, and finally, we suggest the most practical method for inducing a POF model in these animals. This may help researchers find the method of creating a POF model that is most appropriate for their type of study and suits the purpose of their research.

Chronic psychosocial stress affects insulin-like growth factor 1 and its receptors in mouse ovaries

Context Chronic psychosocial stress negatively affects folliculogenesis and oogenesis. Intraovarian mechanisms mediating these effects are poorly understood. Aims This work aimed to find out how chronic psychosocial stress affects ovarian IGF1 and its receptor (IGF1R), as well as Igf1 and Igf1r gene expression in cumulus-oocyte complexes (COCs). It also aimed to address possible protective effects of gonadotropin stimulation on IGF1 ovarian signalling. Methods Female CD1 mice experienced chronic psychosocial stress of 11-day isolation followed by overcrowding for 10days. To verify the model, blood corticosterone levels and the quality of oocytes were evaluated in stressed females. The levels of IGF1/IGF1R, blood IGF1 concentration, and expression of Igf1 /Igf1r in the ovaries were compared in stressed and unstressed females. Key results Psychosocial stress caused an elevation of corticosterone level, which was alleviated by gonadotropin treatment. The stressed mice showed a decreased IGF1 level in the ovaries and a decreased expression of Igf1 and Igf1r in COCs. In the unstressed females, gonadotropin injection decreased the expression of Igf1 and Igf1r ; in the stressed females, the same treatment increased Igf1r expression. Neither stress nor ovarian stimulation with gonadotropins affected the serum IGF1 level. Conclusions Psychosocial stress suppresses IGF1 signalling in the ovaries. Gonadotropin treatment modulates these effects differently in stressed and unstressed animals. Implications The results may have translational value for human reproduction. Ovarian IGF1 can be considered a candidate for further improvement of IVF results in women under conditions of chronic stress.

Gynotoxic Effects of Chemotherapy and Potential Protective Mechanisms

Chemotherapy is one of the leading cancer treatments. Unfortunately, its use can contribute to several side effects, including gynotoxic effects in women. Ovarian reserve suppression and estrogen deficiency result in reduced quality of life for cancer patients and are frequently the cause of infertility and early menopause. Classic alkylating cytostatics are among the most toxic chemotherapeutics in this regard. They cause DNA damage in ovarian follicles and the cells they contain, and they can also induce oxidative stress or affect numerous signaling pathways. In vitro tests, animal models, and a few studies among women have investigated the effects of various agents on the protection of the ovarian reserve during classic chemotherapy. In this review article, we focused on the possible beneficial effects of selected hormones (anti-Müllerian hormone, ghrelin, luteinizing hormone, melatonin), agents affecting the activity of apoptotic pathways and modulating gene expression (C1P, S1P, microRNA), and several natural (quercetin, rapamycin, resveratrol) and synthetic compounds (bortezomib, dexrazoxane, goserelin, gonadoliberin analogs, imatinib, metformin, tamoxifen) in preventing gynotoxic effects induced by commonly used cytostatics. The presented line of research appears to provide a promising strategy for protecting and/or improving the ovarian reserve in the studied group of cancer patients. However, well-designed clinical trials are needed to unequivocally assess the effects of these agents on improving hormonal function and fertility in women treated with ovotoxic anticancer drugs.

Research progress on mitochondrial damage and repairing in oocytes: A review

Oocytes are the female germ cells, which are susceptible to stress stimuli. The development of oocytes in the ovary is affected by many environmental and metabolic factors, food toxins, aging, and pathological factors. Mitochondria are the main target organelles of these factors, and the damage to mitochondrial structure and function can affect the production of ATP, the regulation of redox reactions, and apoptosis in oocytes. Mitochondrial damage is closely related to the decrease in oocyte quality and is the main factor leading to female infertility. Antioxidant foods or drugs have been used to prevent mitochondrial damage from some stressors or to repair damaged mitochondria, thereby improving oocyte development and female reproductive outcomes. In this paper, the damage of mitochondria during oocyte development by the above factors has been reviewed, and the relevant measures to alleviate the damage of mitochondria in oocytes have been discussed. Our findings may provide a theoretical basis and experimental basis for improving female fertility.

Xrcc5/KU80 is not required for the survival or activation of prophase-arrested oocytes in primordial follicles

Introduction

The non-growing, meiotically-arrested oocytes housed within primordial follicles are exquisitely sensitive to genotoxic insults from endogenous and exogenous sources. Even a single DNA double-strand break (DSB) can trigger oocyte apoptosis, which can lead to accelerated depletion of the ovarian reserve, early loss of fertility and menopause. Therefore, repair of DNA damage is important for preserving the quality of oocytes to sustain fertility across the reproductive lifespan. This study aimed to evaluate the role of KU80 (encoded by the XRCC5 gene) - an essential component of the non-homologous end joining (NHEJ) pathway - in the repair of oocyte DNA DSBs during reproductive ageing, and following insult caused by the DNA-damaging chemotherapies cyclophosphamide and cisplatin.

Methods

To investigate the importance of KU80 following endogenous and exogenous DNA damage, ovaries from conditional oocyte-specific Xrcc5 knockout (Xrcc5 cKO) and wildtype (WT) mice that were aged or exposed to DNA damage-inducing chemotherapy were compared. Ovarian follicles and oocytes were quantified, morphologically assessed and analysed via immunohistochemistry for markers of DNA damage and apoptosis. In addition, chemotherapy exposed mice were superovulated, and the numbers and quality of mature metaphase- II (MII) oocytes were assessed.

Results

The number of healthy follicles, atretic (dying) follicles, and corpora lutea were similar in Xrcc5 cKO and WT mice at PN50, PN200 and PN300. Additionally, primordial follicle number and ovulation rates were similar in young adult Xrcc5 cKO and WT mice following treatment with cyclophosphamide (75mg/kg), cisplatin (4mg/kg), or vehicle control (saline). Furthermore, KU80 was not essential for the repair of exogenously induced DNA damage in primordial follicle oocytes.

Discussion

These data indicate that KU80 is not required for maintenance of the ovarian reserve, follicle development, or ovulation during maternal ageing. Similarly, this study also indicates that KU80 is not required for the repair of exogenously induced DSBs in the prophase-arrested oocytes of primordial follicles.

SIRT1 reduction contributes to doxorubicin-induced oxidative stress and meiotic failure in mouse oocytes

Impaired fertility is the major side effect of chemotherapy for female cancer patients, accumulated evidence indicates this is associated with damage on oocyte quality, but the underlying mechanisms remain unclear. Previously we reported that doxorubicin (DXR) exposure, one of the most widely used chemotherapy drugs, disrupted mouse oocyte meiotic maturation in vitro. In the current study, we identified that SIRT1 expression was remarkably reduced in DXR exposure oocytes. Next, we found that increasing SIRT1 expression by resveratrol partially alleviated the effects of DXR exposure on oocyte maturation, which was counteracted by SIRT1 inhibition. Furthermore, we revealed that increasing SIRT1 expression mitigated DXR induced oocyte damage through reducing ROS levels, increasing antioxidant enzyme MnSOD expression, and preventing spindle and chromosome disorganization, lowering the incidence of aneuploidy. Importantly, by performing in vitro fertilization and embryo transfer assays, we demonstrated that increasing SIRT1 expression significantly improved the fertilization ability, developmental competence of oocytes and early embryos. In summary, our data uncover that SIRT1 reduction represents one mechanism that mediates the effects of DXR exposure on oocyte quality.

The future of fertility preservation for women treated with chemotherapy

Cytotoxic chemotherapies have been a mainstay of cancer treatment, but are associated with numerous systemic adverse effects, including impacts to fertility and endocrine health. Irreversible ovarian damage and follicle depletion are side-effects of chemotherapy that can lead to infertility and premature menopause, both being major concerns of young cancer patients. Notably, many women will proceed with fertility preservation, but unfortunately existing strategies don't entirely solve the problem. Most significantly, oocyte and embryo freezing do not prevent cancer treatment-induced ovarian damage from occurring, which may result in the impairment of long-term hormone production. Unfortunately, loss of endogenous endocrine function is not fully restored by hormone replacement therapy. Additionally, while GnRH agonists are standard care for patients receiving alkylating chemotherapy to lessen the risk of premature menopause, their efficacy is incomplete. The lack of more broadly effective options stems, in part, from our poor understanding of how different treatments damage the ovary. Here, we summarise the impacts of two commonly utilised chemotherapies - cyclophosphamide and cisplatin - on ovarian function and fertility, and discuss the mechanisms underpinning this damage. Additionally, we critically analyse current research avenues in the development of novel fertility preservation strategies, with a focus on fertoprotective agents.

TAp63 determines the fate of oocytes against DNA damage

Cyclophosphamide and doxorubicin lead to premature ovarian insufficiency as an off-target effect. However, their oocyte death pathway has been debated. Here, we clarified the precise mechanism of ovarian depletion induced by cyclophosphamide and doxorubicin. Dormant oocytes instead of activated oocytes with high PI3K activity were more sensitive to cyclophosphamide. Checkpoint kinase 2 (CHK2) inhibitor rather than GNF2 protected oocytes from cyclophosphamide and doxorubicin, as cyclophosphamide up-regulated p-CHK2 and depleted primordial follicles in Abl1 knockout mice. Contrary to previous reports, TAp63 is pivotal in cyclophosphamide and doxorubicin-induced oocyte death. Oocyte-specific Trp63 knockout mice prevented primordial follicle loss and maintained reproductive function from cyclophosphamide and doxorubicin, indicated by undetectable levels of BAX and cPARP. Here, we demonstrated that TAp63 is fundamental in determining the signaling of oocyte death against DNA damage. This study establishes the role of TAp63 as a target molecule of adjuvant therapies to protect the ovarian reserve from different classes of chemotherapy.

Anti-Müllerian hormone treatment enhances oocyte quality, embryonic development and live birth rate†

The anti-Müllerian hormone (AMH) produced by the granulosa cells of growing follicles is critical for folliculogenesis and is clinically used as a diagnostic and prognostic marker of female fertility. Previous studies report that AMH-pretreatment in mice creates a pool of quiescent follicles that are released following superovulation, resulting in an increased number of ovulated oocytes. However, the quality and developmental competency of oocytes derived from AMH-induced accumulated follicles as well as the effect of AMH treatment on live birth are not known. This study reports that AMH priming positively affects oocyte maturation and early embryonic development culminating in higher number of live births. Our results show that AMH treatment results in good-quality oocytes with greater developmental competence that enhances embryonic development resulting in blastocysts with higher gene expression. The transcriptomic analysis of oocytes from AMH-primed mice compared with those of control mice reveal that AMH upregulates a large number of genes and pathways associated with oocyte quality and embryonic development. Mitochondrial function is the most affected pathway by AMH priming, which is supported by more abundant active mitochondria, mitochondrial DNA content and adenosine triphosphate levels in oocytes and embryos isolated from AMH-primed animals compared with control animals. These studies for the first time provide an insight into the overall impact of AMH on female fertility and highlight the critical knowledge necessary to develop AMH as a therapeutic option to improve female fertility.