Loss of PUMA protects the ovarian reserve during DNA-damaging chemotherapy and preserves fertility

Granulosa cell death is a significant contributor to DNA-damaging chemotherapy-induced ovarian insufficiency†

Typically, DNA-damaging chemotherapy (CTx) regimens have a gonadotoxic effect and cause premature ovarian insufficiency (POI), characterized by infertility and estrogen deficiency. However, whether loss of granulosa cells killed directly by CTx contributes significantly to POI has not been determined. To address this issue, we used a previously established mouse model of CTx-induced POI. The alkylating drugs Busulfan (8.75 mg/kg) and Cyclophosphamide (100 mg/kg) were administered to 8-week-old FVB female mice by intraperitoneal (IP) injection three times at 48-h intervals, after which ovarian tissues were harvested and examined by immunofluorescence. The number of primordial follicles was significantly reduced at day (d)6, whereas the number of growing follicles was relatively unchanged. CTx led to DNA double strand breaks in both oocytes and granulosa cells based on the presence of γH2AX foci. However, markers of apoptosis predominantly labeled granulosa cells in growing follicles. We next examined the effect of inhibiting apoptosis in growing granulosa cells by generating Bak-/-Baxfx/fx; Cyp19a1Cre transgenic mice. On d10 after the first CTx, Bak-/-Baxfx/fx; Cyp19a1Cre ovaries had fewer apoptotic granulosa cells and more surviving follicles than controls. Furthermore, Bak-/-Baxfx/fx; Cyp19a1Cre mice showed better fertility than controls after CTx. Our data suggest that granulosa cell death is a significant contributor to follicle depletion and fertility loss after Cyclophosphamide and Busulfan.

Developments in pharmacotherapy for the preservation of ovarian function during cancer treatment

INTRODUCTION

Cancer is one of the major causes of human death, and anti-cancer therapy often results in premature ovarian failure and infertility, depending on factors such as age, initial ovarian reserve, and chemotherapy type and dose. Fertility preservation procedures, such as oocyte, embryo, and ovarian cortex cryopreservation, can help women achieve pregnancy after cancer treatment. However, the development of pharmacological therapies to protect ovarian function during chemotherapy would represent a significant advancement.

AREAS COVERED

We searched the published articles in PubMed up to December 2024, containing key words '"chemotherapy",' 'cancer,' '"ovarian protection",' '"pharmacological therapy",' '"ovarian reserve"' and '"fertility".' Chemotherapeutic agents act via various mechanisms in the human ovary, including direct DNA damage leading to oocyte apoptosis, as well as damage to ovarian stroma and microvascular architecture. In recent years, numerous protective agents have emerged, showing promise in protecting ovaries from chemotherapy-induced damage. However, most studies have relied on animal models, and only a limited number have directly tested these agents in human ovarian tissue. At present, no pharmacological treatment has been conclusively proven effective for preserving fertility.

EXPERT OPINION

A comprehensive understanding of the mechanisms underlying chemotherapy-induced ovarian damage is critical for the development of efficient and targeted pharmacological therapies.

Susceptibility of Brca1(L63X/+) rat to ovarian reserve dissipation by chemotherapeutic agents to breast cancer

BRCA1 is one of the causative genes for hereditary breast and ovarian cancer syndrome with a high risk of early-onset breast cancer. Whereas olaparib (OLA), an inhibitor of poly-ADP-ribose polymerase, has been applied as adjuvant therapy to those cancer patients, its effect on ovarian reproductive function remains unelucidated. Recently, a rat model (MUT; Brca1(L63X/+) mutation) mimicking a human BRCA1 pathogenic variant has been established. Using this model, we evaluated the effects of OLA on ovarian reproductive function in comparison with the wild-type (WT) rats. MUT showed a significantly reduced number of primordial follicles and subfertility in accordance with aging. Oxidative stress was significantly elevated in the young MUT granulosa cells (GCs) accompanied by increased mTOR but decreased PTEN signals. OLA administration in MUT further decreased primordial follicles, with gene set enrichment analysis, indicating upregulated DNA repair pathways. Furthermore, a combination of OLA and cyclophosphamide (CPA) induced empty primordial follicles, recognized as CPA-induced severe ovarian toxicity. Whereas OLA + CPA caused greater reduction in primordial follicles both in MUT and WT in comparison with CPA alone, MUT ovaries were more susceptible to oxidative stress, potentially depleting primordial follicles via activation of GCs and inducing oocyte death due to accumulated DNA damage by OLA treatment. Our findings in this preclinical model underscore the importance of evaluating ovarian reserve prior to chemotherapy by performing reproductive consultation with female patients with BRCA1 pathogenic variants.

Can we really protect the ovary from chemotherapy damage?

Future alternatives to current fertility preservation methods such as pharmacological strategies to prevent chemotherapy-induced ovarian damage in female cancer patients are of growing interest. Chemotherapeutic agents, especially alkylating agents, cause DNA damage and apoptosis in ovarian follicles, significantly reducing ovarian reserve. To mitigate this gonadotoxicity, various emerging strategies are being explored, including kinase inhibitors, PI3K/Akt/mTOR pathway inhibitors, antioxidants, miRNAs and GnRH agonists. These treatments work by preventing follicular apoptosis or excessive activation of primordial follicles. Although promising results have been observed in vitro and in vivo in rodent models, further investigations to bypass their limitations are needed to confirm their efficacy and safety. These challenges include the non-interference with anti-tumoral effect of chemotherapy and the specificity of fertoprotective agents to ovaries.

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.

Cyclophosphamide-Induced Infertility and the Impact of Antioxidants

An important drawback of anticancer chemotherapy is the harm it causes to healthy cells. Cyclophosphamide (CP) is a widely used chemotherapeutic alkylating agent that is regularly used in cancer treatment. However, it can cause severe side effects, including genotoxicity, due to its ability to damage DNA. This toxicity is thought to be associated with oxidative stress induced by an excessive amount of reactive oxygen species (ROS). Therefore, there is a specific focus on the potential effects of anticancer treatments on fertility. Due to the increasing life expectancy of cancer patients, those desiring parenthood may face the negative impacts of therapies. Utilizing substances with antioxidant and cytoprotective characteristics to protect the reproductive system from harmful consequences during chemotherapy would be highly beneficial. This review introduces the physiological and pathological roles of ROS in the reproductive systems of both males and females, then we address the adverse effects of CP administration on infertility and discuss how antioxidants can reverse these effects.

Oocyte death is triggered by the stabilization of TAp63α dimers in response to cisplatin

The TAp63α protein is highly expressed in primordial follicle oocytes, where it typically exists in an inactive dimeric form. Upon DNA damage, TAp63α undergoes hyperphosphorylation, transitioning from a dimeric to a tetrameric structure, which initiates oocyte apoptosis by upregulating pro-apoptotic gene. Our results demonstrate that cisplatin, an alkylating anti-cancer agent, predominantly produced the TAp63α dimer rather than the tetramer. We further observed that TAp63α protein accumulation occurred in primordial follicle oocytes following cisplatin treatment, and this accumulation was significantly reduced by cycloheximide, a protein synthesis inhibitor. These findings suggest that TAp63α accumulation is driven primarily by de novo protein synthesis in response to DNA damage. Notably, cycloheximide protected oocytes from cisplatin-induced apoptosis, as evidenced by reduced levels of both PUMA, a known pro-apoptotic target gene of TAp63α, and TAp63α itself. Additionally, TAp63α turnover appears to be regulated by ubiquitination and proteasome degradation, as evidenced by TAp63α accumulation without oocyte death when treated with PYR-41, a pharmacological inhibitor. However, when TAp63α was stabilized by PYR-41 and subsequently activated by cisplatin, oocyte death occurred, marked by increased γH2AX and Cleaved PARP. Moreover, the Casein kinase 1 inhibitor PF-670462 effectively blocked cisplatin-induced oocyte death, indicating that CK1-mediated phosphorylation is essential for TAp63α activation, even in the absence of tetramer formation. The ATR inhibitor BEZ235 prevented cisplatin-induced TAp63α accumulation, suggesting that TAp63α accumulation precedes its phosphorylation-driven activation. Collectively, our study reveals a novel mechanism of cisplatin-induced apoptosis in primordial follicle oocyte through TAp63α stabilization and accumulation, independent of tetramerization.

Evidence of apoptosis as an early event leading to cyclophosphamide-induced primordial follicle depletion in a prepubertal mouse model

Introduction

The mechanisms leading to ovarian primordial follicle depletion following gonadotoxic chemotherapy with cyclophosphamide and other cytotoxic drugs are currently understood through two main explanatory theories: apoptosis and over-activation. Discrepancies between the findings of different studies investigating these mechanisms do not allow to reach a firm conclusion. The heterogeneity of cell types in ovaries and their different degrees of sensitivity to damage, cell-cell interactions, periodical follicle profile differences, model age-dependent differences, and differences of exposure durations of tested drugs may partially explain the discrepancies among studies.

Methods

This study used intact prepubertal mice ovaries in culture as study model, in which most follicles are primordial follicles. Histological and transcriptional analyses of ovaries exposed to the active metabolite of cyclophosphamide 4-hydroperoxycyclophosphamide (4-HC) were carried out via a time-course experiment at 8, 24, 48, and 72 h.

Results

4-HC treated ovaries showed a significant decrease in primordial follicle density at 24 h, along with active DNA damage (TUNEL) and overexpressed apoptosis signals (cleaved-poly ADP ribose polymerase in immunohistochemistry and western blotting). Meanwhile 4-HC treatment significantly up-regulated H2ax, Casp 6, Casp 8, Noxa, and Bax in ovaries, and up-regulated Puma in primordial follicles (FISH).

Discussion

Our results indicated that cyclophosphamide-induced acute ovarian primordial follicle depletion was mainly related to apoptotic pathways. No evidence of follicle activation was found, neither through changes in the expression of related genes to follicle activation nor in the density of growing follicles. Further validation at protein level in 4-HC-treated prepubertal mice ovaries at 24 h confirmed these observations.

Chemotherapy drug combinations induced maternal ovarian damage and long-term effect on fetal reproductive system in mice

With the postponement of female reproductive age and the higher incidence of cancer in young people, fertility preservation has become increasingly important in childbearing age. Chemotherapy during pregnancy is crucial for maternal cancer treatments and fetal outcomes. It is a need to further study ovarian damage caused by chemotherapy drug combinations and long-term effects on offspring development, and a detailed understanding of side effects of chemotherapy drugs. In this study, chemotherapy drug combinations significantly impacted on ovarian function, especially epirubicin/cyclophosphamide (EC) combination led to an unbalance in the development of the left and right ovary. Exposure to EC and cisplatin/paclitaxel (TP) increased the number of progenitor follicles while decreased the count of antral follicles and corpora luteum. As to the estrus cycle, EC exposure resulted in a longer estrus period and diestrus period, while TP exposure only extended the diestrus period. EC and TP affected steroid biosynthesis by reducing the expression of SF1 and P450arom.γ-H2AX was detected in both EC and TP exposure groups. As to the impact on the offspring from 4T1 tumor-bearing pregnant mice injected with EC, no significant difference was observed in the physical and neurological development compared to the control, but the ovarian weights, estrus cycles of the offspring were significantly different. Chemotherapy drug combinations exhibit ovarian toxicity, not only causing direct damage on the follicle cells but also disrupting steroid biosynthesis. The reproductive system of offspring from maternal tumor-bearing mice exposed to chemotherapy drugs was observed disorder, but the concrete mechanism still needs further exploration.

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.

Oncofertility as an Essential Part of Comprehensive Cancer Treatment in Patients of Reproductive Age, Adolescents and Children

The number of children, adolescents and young adults diagnosed with cancer has been rising recently. Various oncological treatments have a detrimental effect on female fertility, and childbearing becomes a major issue during surveillance after recovery. This review discusses the impact of oncological treatments on the ovarian reserve with a thorough explanation of oncologic treatments' effects and modes of oncofertility procedures. The aim of this review is to help clinicians in making an informed decision about post-treatment fertility in their patients. Ultimately, it may lead to improved overall long-term outcomes among young populations suffering from cancer.

An update on oncofertility in prepubertal females

Cancer is a life-threatening event for pediatric patients. Treatment advancements in pediatric cancer have improved prognosis, but some of these treatments have gonadotoxic potential and may affect fertility in different ways. Due to the growing interest of the research community in the life prospects of young cancer survivors, there has been a demand to intersect reproductive medicine and oncology, which is referred to as "oncofertility". There are various fertility preservation options according to gender and pubertal status, and shared decisions must take place at the time of diagnosis. This study aims to provide a critical review of current and emerging strategies for preserving and restoring fertility in prepubertal females, ranging from established methods to experimental approaches that can be offered before, during, and after anticancer therapies. Additionally, the author aims to review how clinicians' awareness of oncofertility options and the latest advancements in this field, timely referral, and proper consultations with patients and their families are vital in addressing their concerns, providing emotional support, and guiding them through the decision-making process, as well as potential barriers that may hinder the fertility preservation process.

The Impacts of Periconceptional Alcohol on Neonatal Ovaries and Subsequent Adult Fertility in the Rat

Maternal exposures during pregnancy can impact the establishment of the ovarian reserve in offspring, the lifetime supply of germ cells that determine a woman's reproductive lifespan. However, despite alcohol consumption being common in women of reproductive age, the impact of prenatal alcohol on ovarian development is rarely investigated. This study used an established rat model of periconceptional ethanol exposure (PCEtOH; 12.5% v/v ethanol) for 4 days prior to 4 days post-conception. Ovaries were collected from neonates (day 3 and day 10), and genes with protein products involved in regulating the ovarian reserve analyzed by qPCR. Adult offspring had estrous cycles monitored and breeding performance assessed. PCEtOH resulted in subtle changes in expression of genes regulating apoptosis at postnatal day (PN) 3, whilst those involved in regulating growth and recruitment of primordial follicles were dysregulated at PN10 in neonatal ovaries. Despite these gene expression changes, there were no significant impacts on breeding performance in adulthood, nor on F2-generation growth or survival. This contributes additional evidence to suggest that a moderate level of alcohol consumption exclusively around conception, when a woman is often unaware of her pregnancy, does not substantially impact the fertility of her female offspring.

SIRT1 overexpression by melatonin and resveratrol combined treatment attenuates premature ovarian failure through activation of SIRT1/FOXO3a/BCL2 pathway

AIM

To evaluate the synergistic effect of combined treatment with melatonin (MEL) and resveratrol (RES) in cisplatin (CIS)-induced premature ovarian failure (POF) model in rats and to elucidate the molecular mechanism of this therapeutic effect.

MATERIAL & METHODS

Female Sprague Dawley rats were divided into 7 experimental groups as follows; CONT (Control), CIS, MEL, RES, POF + MEL, POF + RES, and POF + MEL + RES. H&E staining was performed to evaluate follicular cell vacuolization/degeneration, vascular congestion/hemorrhage, and inflammation, by using an ordinal scale from 0 to 4 to grade the severity of observed changes (0 = normal, 1 = mild, 2 = moderate, 3 = severe, 4 = very severe). Zona pellucida integrity and connective tissue amount in the ovarian tissue were detected using PAS & Masson Trichrome staining. The immunofluorescence method was used to determine the immune localizations of pH2Ax, SIRT1, FOXO3a, and BCL2. The connective tissue amounts and immunoreactivity staining intensities were measured using ImageJ. The gene expression of SIRT1, FOXO3a, and BCL2 was determined using RT-PCR. Serum estrogen hormone levels were measured by ELISA. Statistically, Bonferroni correction was performed, and p < 0.002 were considered significant.

RESULTS

A significant difference was observed in the POF group compared to the CONT group in all parameters except tertiary follicle count and hemorrhage. The decrease in the number of atretic follicles in the POF + MEL + RES group was found significant compared to both POF + MEL and POF + RES groups. The expression of pH2Ax, SIRT1, FOXO3a, and BCL2 at the protein level and SIRT1 and BCL2 at the mRNA level were significant in the POF + MEL + RES group compared to the POF group. Between the single and combination treatment groups, the difference in protein level was found in pH2Ax, SIRT1, FOXO3a, and BCL2 expression. The POF + MEL + RES group exhibited significantly higher SIRT1 mRNA expression compared to the groups receiving single treatments.

CONCLUSION

The present study provides evidence that MEL and RES have synergistic effects in preventing the decrease in follicle reserve and increase in DNA break (pH2Ax) and follicle atresia in POF ovaries. This therapeutic effect is mediated by SIRT1 overexpression and activation of the SIRT1/FOXO3a/BCL2 pathway.

Anti-Mullerian hormone attenuates both cyclophosphamide-induced damage and PI3K signalling activation, while rapamycin attenuates only PI3K signalling activation, in human ovarian cortex in vitro

STUDY QUESTION

What are the effects of cyclophosphamide exposure on the human ovary and can anti-Mullerian hormone (AMH) and rapamycin protect against these?

SUMMARY ANSWER

Exposure to cyclophosphamide compromises the health of primordial and transitional follicles in the human ovarian cortex and upregulates PI3K signalling, indicating both direct damage and increased follicular activation; AMH attenuates both of these chemotherapy-induced effects, while rapamycin attenuates only PI3K signalling upregulation.

WHAT IS KNOWN ALREADY

Studies primarily in rodents demonstrate that cyclophosphamide causes direct damage to primordial follicles or that the primordial follicle pool is depleted primarily through excessive initiation of follicle growth. This increased follicular activation is mediated via upregulated PI3K signalling and/or reduced local levels of AMH production due to lost growing follicles. Furthermore, while rodent data show promise regarding the potential benefits of inhibitors/protectants alongside chemotherapy treatment to preserve female fertility, there is no information about the potential for this in humans.

STUDY DESIGN, SIZE, DURATION

Fresh ovarian cortical biopsies were obtained from 17 healthy women aged 21-41 years (mean ± SD: 31.8 ± 4.9 years) at elective caesarean section. Biopsies were cut into small fragments and cultured for 24 h with either vehicle alone (DMSO), the active cyclophosphamide metabolite 4-hydroperoxycyclophosphamide (4-HC) alone, 4-HC + rapamycin or 4-HC+AMH. Two doses of 4-HC were investigated, 0.2 and 2 μM in separate experiments, using biopsies from seven women (aged 27-41) and six women (aged 21-34), respectively. Biopsies from four women (aged 28-38) were used to investigate the effect of rapamycin or AMH only.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Histological analysis of ovarian tissue was undertaken for follicle staging and health assessment. Western blotting and immunostaining were used to assess activation of PI3K signalling by measuring phosphorylation of AKT and phosphorylated FOXO3A staining intensity, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

Exposure to either dose of 4-HC caused an increase in the proportion of unhealthy primordial (P < 0.0001, both doses) and transitional follicles (P < 0.01 for low dose and P < 0.01 for high dose) compared to vehicle. AMH significantly reduced follicle damage by approximately half in both of the investigated doses of 4-HC (P < 0.0001), while rapamycin had no protective effect on the health of the follicles. Culture with AMH or rapamycin alone had no effect on follicle health. Activation of PI3K signalling following 4-HC exposure was demonstrated by both Western blotting data showing that 4-HC increased in AKT phosphorylation and immunostaining showing increased phosphorylated FOXO3A staining of non-growing oocytes. Treatment with rapamycin reduced the activation of PI3K signalling in experiments with low doses of 4-HC while culture with AMH reduced PI3K activation (both AKT phosphorylation and phosphorylated FOXO3A staining intensity) across both doses investigated.

LIMITATIONS, REASONS FOR CAUTION

These in vitro studies may not replicate in vivo exposures. Furthermore, longer experiment durations are needed to determine whether the effects observed translate into irreparable deficits of ovarian follicles.

WIDER IMPLICATIONS OF THE FINDINGS

These data provide a solid foundation on which to explore the efficacy of AMH in protecting non-growing ovarian follicles from gonadotoxic chemotherapies. Future work will require consideration of the sustained effects of chemotherapy treatment and potential protectants to ensure these agents do not impair the developmental competence of oocytes or lead to the survival of oocytes with accumulated DNA damage, which could have adverse consequences for potential offspring.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from TENOVUS Scotland, the Academy of Medical Sciences (to R.R.), the Medical Research Council (G1100357 to R.A.A., MR/N022556/1 to the MRC Centre for Reproductive Health), and Merck Serono UK (to R.A.A.). R.R., H.L.S., N.S., and E.E.T. declare no conflicts of interest. R.A.A. reports grants and personal fees from Roche Diagnostics and Ferring Pharmaceuticals, and personal fees from IBSA and Merck outside the submitted work.

TRIAL REGISTRATION NUMBER

N/A.

Genome Instability and DNA Repair in Somatic and Reproductive Aging

Genetic material is constantly subjected to genotoxic insults and is critically dependent on DNA repair. Genome maintenance mechanisms differ in somatic and germ cells as the soma only requires maintenance during an individual's lifespan, while the germline indefinitely perpetuates its genetic information. DNA lesions are recognized and repaired by mechanistically highly diverse repair machineries. The DNA damage response impinges on a vast array of homeostatic processes and can ultimately result in cell fate changes such as apoptosis or cellular senescence. DNA damage causally contributes to the aging process and aging-associated diseases, most prominently cancer. By causing mutations, DNA damage in germ cells can lead to genetic diseases and impact the evolutionary trajectory of a species. The mechanisms ensuring tight control of germline DNA repair could be highly instructive in defining strategies for improved somatic DNA repair. They may provide future interventions to maintain health and prevent disease during aging.

The Dominant Mechanism of Cyclophosphamide-Induced Damage to Ovarian Reserve: Premature Activation or Apoptosis of Primordial Follicles?

Cyclophosphamide (CPM), a part of most cancer treatment regimens, has demonstrated high gonadal toxicity in females. Initially, CPM is believed to damage the ovarian reserve by premature activation of primordial follicles, for the fact that facing CPM damage, primordial oocytes show the activation of PTEN/PI3K/AKT pathways, accompanied by accelerated activation of follicle developmental waves. Meanwhile, primordial follicles are dormant and not considered the target of CPM. However, many researchers have found DNA DSBs and apoptosis within primordial oocytes under CPM-induced ovarian damage instead of premature accelerated activation. A stricter surveillance system of DNA damage is also thought to be in primordial oocytes. So far, the apoptotic death mechanism is considered well-proved, but the premature activation theory is controversial and unacceptable. The connection between the upregulation of PTEN/PI3K/AKT pathways and DNA DSBs and apoptosis within primordial oocytes is also unclear. This review aims to highlight the flaw and/or support of the disputed premature activation theory and the apoptosis mechanism to identify the underlying mechanism of CPM's injury on ovarian reserve, which is crucial to facilitate the discovery and development of effective ovarian protectants. Ultimately, this review finds no good evidence for follicle activation and strong consistent evidence for apoptosis.

Potential Therapeutic Options for Premature Ovarian Insufficiency: Experimental and Clinical Evidence

Premature ovarian insufficiency (POI) is a condition in which a woman experiences premature decline in ovarian function before the age of 40 years, manifested by menstrual disorders, decreased fertility, and possibly postmenopausal symptoms such as insomnia, hot flashes, and osteoporosis, and is one of the predominant clinical syndromes leading to female infertility. Genetic, immunologic, iatrogenic and other factors, alone or in combination, have been reported to trigger POI, yet the etiology remains unknown in most cases. The main methods currently used clinically to ameliorate menopausal symptoms due to hypoestrogenemia in POI patients are hormone replacement therapy, while the primary methods available to address infertility in POI patients are oocyte donation and cryopreservation techniques, both of which have limitations to some degree. In recent years, researchers have continued to explore more efficient and safe therapies, and have achieved impressive results in preclinical trials. In this article, we will mainly review the three most popular therapies and their related signaling pathways published in the past ten years, with the aim of providing ideas for clinical applications.

Overactivation or Apoptosis: Which Mechanisms Affect Chemotherapy-Induced Ovarian Reserve Depletion?

Dormant primordial follicles (PMF), which constitute the ovarian reserve, are recruited continuously into the cohort of growing follicles in the ovary throughout female reproductive life. Gonadotoxic chemotherapy was shown to diminish the ovarian reserve pool, to destroy growing follicle population, and to cause premature ovarian insufficiency (POI). Three primary mechanisms have been proposed to account for this chemotherapy-induced PMF depletion: either indirectly via over-recruitment of PMF, by stromal damage, or through direct toxicity effects on PMF. Preventative pharmacological agents intervening in these ovotoxic mechanisms may be ideal candidates for fertility preservation (FP). This manuscript reviews the mechanisms that disrupt follicle dormancy causing depletion of the ovarian reserve. It describes the most widely studied experimental inhibitors that have been deployed in attempts to counteract these affects and prevent follicle depletion.

CHEK2 signaling is the key regulator of oocyte survival after chemotherapy

Cancer treatments can damage the ovarian follicle reserve, leading to primary ovarian insufficiency and infertility among survivors. Checkpoint kinase 2 (CHEK2) deficiency prevents elimination of oocytes in primordial follicles in female mice exposed to radiation and preserves their ovarian function and fertility. Here, we demonstrate that CHEK2 also coordinates the elimination of oocytes after exposure to standard-of-care chemotherapy drugs. CHEK2 activates two downstream targets-TAp63 and p53-which direct oocyte elimination. CHEK2 knockout or pharmacological inhibition preserved ovarian follicle reserve after radiation and chemotherapy. However, the lack of specificity for CHEK2 among available inhibitors limits their potential for clinical development. These findings demonstrate that CHEK2 is a master regulator of the ovarian cellular response to damage caused by radiation and chemotherapy and warrant the development of selective inhibitors specific to CHEK2 as a potential avenue for ovario-protective treatments.

Chemotherapy-induced ovarian damage and protective strategies

More than 9.2 million women worldwide suffer from cancer, and about 5% of them are at reproductive age. Chemotherapy-induced impairment of fertility affects the quality of life of these women. Several chemotherapeutic agents have been proven to cause apoptosis and autophagy by inducing DNA damage and cellular stress. Injuries to the ovarian stroma and micro-vessel network are also considered as pivotal factors resulting in ovarian dysfunction induced by chemotherapeutic agents. Primordial follicle pool over-activation may also be the mechanism inducing damage to the ovarian reserve. Although many studies have explored the mechanisms involved in chemotherapy-induced reproductive toxicity, the exact molecular mechanisms have not been elucidated. It is essential to understand the mechanisms involved in ovarian damage, in order to develop potential protective treatments to preserve fertility. In this article, we reviewed the current knowledge on the mechanism of chemotherapy-induced ovarian damage and possible protective strategies that prevent the ovary from such damages.

Inhibition of checkpoint kinase prevents human oocyte apoptosis induced by chemotherapy and allows enhanced tumour chemotherapeutic efficacy

STUDY QUESTION

Could inhibition of the checkpoint kinase (CHEK) pathway protect human oocytes and even enhance the anti-tumour effects, during chemotherapy?

SUMMARY ANSWER

CHEK inhibitors prevented apoptosis of human oocytes induced by chemotherapy and even enhanced the anti-tumour effects.

WHAT IS KNOWN ALREADY

CHEK inhibitors showed ovarian protective effects in mice during chemotherapy, while their role in human oocytes is unclear.

STUDY DESIGN, SIZE, DURATION

This experimental study evaluated the ovarian reserve of young patients (120 patients) with cancer, exposed or not exposed to taxane and platinum (TP)-combined chemotherapy. Single RNA-sequencing analysis of human primordial oocytes from 10 patients was performed to explore the mechanism of oocyte apoptosis induced by TP chemotherapy. The damaging effects of paclitaxel (PTX) and cisplatin on human oocytes were also evaluated by culturing human ovaries in vitro. A new mouse model that combines human ovarian xenotransplantation and patient-derived tumour xenografts was developed to explore adjuvant therapies for ovarian protection. The mice were randomly allocated to four groups (10 mice for each group): control, cisplatin, cisplatin + CK1 (CHEK1 inhibitor, SCH 900776), and cisplatin + CK2 (CHEK2 inhibitor, BML277).

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the prospective cohort study, human ovarian follicles were counted and serum AMH levels were evaluated. RNA-sequencing analysis was conducted, and staining for follicular damage (phosphorylated H2AX histone; γH2AX), terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) assays and assessments of apoptotic biomarkers (western blot and immunofluorescence) were conducted in human ovaries. After the treatments, histological analysis was performed on human ovarian samples to investigate follicular populations, and oocyte damage was measured by γH2AX staining, BAX staining, and TUNEL assays. At the same time, the tumours were evaluated for volume, weight, and apoptosis levels.

MAIN RESULTS AND THE ROLE OF CHANCE

Patients who received TP chemotherapy showed decreased ovarian reserves. Single RNA-sequencing analysis of human primordial oocytes indicated that TP chemotherapy induced apoptosis of human primordial oocytes by causing CHEK-mediated TAp63α phosphorylation. In vitro culture of human ovaries showed greater damaging effects on oocytes after cisplatin treatment compared with that after PTX treatment. Using the new animal model, CHEK1/2 inhibitors prevented the apoptosis of human oocytes induced by cisplatin and even enhanced its anti-tumour effects. This protective effect appeared to be mediated by inhibiting DNA damage via the CHEK-TAp63α pathway and by generation of anti-apoptotic signals in the oocytes.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This was a preclinical study performed with human ovarian samples, and clinical research is required for validation.

WIDER IMPLICATIONS OF THE FINDINGS

These findings highlight the therapeutic potential of CHEK1/2 inhibitors as a complementary strategy for preserving fertility in female cancer patients.

STUDY FUNDING/COMPETING INTEREST(S)

This work was financially supported by the National Natural Science Foundation of China (nos. 82001514 and 81902669) and the Fundamental Research Funds for the Central Universities (2021yjsCXCY087). The authors declare no conflict of interest.

Adolescent exposure to low-dose Δ9-tetrahydrocannabinol depletes the ovarian reserve in female mice

Cannabis use by adolescents is widespread, but its effects on the ovaries remain largely unknown. Δ9-tetrahydrocannabinol (THC) exerts its pharmacological effects by activating, and in some conditions hijacking, cannabinoid receptors (CBRs). We hypothesized that adolescent exposure to THC affects ovarian function in adulthood. Peripubertal female C57BL/6N mice were given THC (5 mg/kg) or its vehicle, once daily by intraperitoneal injection. Some mice received THC from postnatal day (PND) 30-33 and their ovaries were harvested PND34; other mice received THC from PND30-43, and their ovaries were harvested PND70. Adolescent treatment with THC depleted ovarian primordial follicle numbers by 50% at PND70, 4 weeks after the last dose. The treatment produced primordial follicle activation, which persisted until PND70. THC administration also caused DNA damage in primary follicles and increased PUMA protein expression in oocytes of primordial and primary follicles. Both CB1R and CB2R were expressed in oocytes and theca cells of ovarian follicles. Enzymes involved in the formation (N-acylphosphatidylethanolamine phospholipase D) or deactivation (fatty acid amide hydrolase) of the endocannabinoid anandamide were expressed in granulosa cells of ovarian follicles and interstitial cells. Levels of mRNA for CBR1 were significantly increased in ovaries after adolescent THC exposure, and upregulation persisted for at least 4 weeks. Our results support that adolescent exposure to THC may cause aberrant activation of the ovarian endocannabinoid system in female mice, resulting in substantial loss of ovarian reserve in adulthood. Relevance of these findings to women who frequently used cannabis during adolescence warrants investigation.

Ovarian scaffolds promoted mouse ovary recovery from cyclophosphamide damage

There is growing evidence to suggest that scaffold of tissue can promote the tissue reparation. In this study, we investigate the effects of ovarian scaffolds on the reparation of cyclophosphamide (CPA) damaged mice ovaries. The mice were first administered with CPA, was then either transplanted an ovarian scaffold into each ovarian bursa for the experimental group (EG) or underwent sham surgery as the control (CG). To evaluate the extent of ovarian damage caused by CPA, a third group which did not undergo any treatment was included for the normal control (NG). Their ovaries were harvested for examination at day 30, 60, and 90 post CPA injection. We found that in EG, the number of all types of follicles in the ovaries remained almost the same throughout. The numbers of follicles were not significantly different from CG, except at day 60, where in CG the numbers of each type of follicle decreased to basal levels. The decrease in the number of ovarian follicles at day 60 in CG was mirrored by the significant increase in the number of apoptotic granulosa cells in the follicles, and was corroborated further by the basal levels of serum estradiol. Furthermore, we observed a significant decrease in collagen composition preceded by macrophage polarization, and elevation of inflammatory cytokine expression in the ovaries of the EG compared to the CG at day 60. We concluded that ovarian scaffolds can effectively protect primordial follicles from CPA-damage and promote the reparation of CPA-damaged ovaries. This research establishes a proof of concept for the future treatment of chemo-damaged ovaries.

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.

Radiotherapy exposure directly damages the uterus and causes pregnancy loss

Female cancer survivors are significantly more likely to experience infertility than the general population. It is well established that chemotherapy and radiotherapy can damage the ovary and compromise fertility, yet the ability of cancer treatments to induce uterine damage, and the underlying mechanisms, have been understudied. Here, we show that in mice total-body γ-irradiation (TBI) induced extensive DNA damage and apoptosis in uterine cells. We then transferred healthy donor embryos into ovariectomized adolescent female mice that were previously exposed to TBI to study the impacts of radiotherapy on the uterus independent from effects to ovarian endocrine function. Following TBI, embryo attachment and implantation were unaffected, but fetal resorption was evident at midgestation in 100% of dams, suggesting failed placental development. Consistent with this hypothesis, TBI impaired the decidual response in mice and primary human endometrial stromal cells. TBI also caused uterine artery endothelial dysfunction, likely preventing adequate blood vessel remodeling in early pregnancy. Notably, when pro-apoptotic protein Puma-deficient (Puma-/-) mice were exposed to TBI, apoptosis within the uterus was prevented, and decidualization, vascular function, and pregnancy were restored, identifying PUMA-mediated apoptosis as a key mechanism. Collectively, these data show that TBI damages the uterus and compromises pregnancy success, suggesting that optimal fertility preservation during radiotherapy may require protection of both the ovaries and uterus. In this regard, inhibition of PUMA may represent a potential fertility preservation strategy.

TP63 gain-of-function mutations cause premature ovarian insufficiency by inducing oocyte apoptosis

The transcription factor p63 guards genome integrity in the female germline, and its mutations have been reported in patients with premature ovarian insufficiency (POI). However, the precise contribution of the TP63 gene to the pathogenesis of POI needs to be further determined. Here, in 1,030 Chinese patients with POI, we identified 6 heterozygous mutations of the TP63 gene that impaired the C-terminal transactivation-inhibitory domain (TID) of the TAp63α protein and resulted in tetramer formation and constitutive activation of the mutant proteins. The mutant proteins induced cell apoptosis by increasing the expression of apoptosis-inducing factors in vitro. We next introduced a premature stop codon and selectively deleted the TID of TAp63α in mice and observed rapid depletion of the p63+/ΔTID mouse oocytes through apoptosis after birth. Finally, to further verify the pathogenicity of the mutation p.R647C in the TID that was present in 3 patients, we generated p63+/R647C mice and also found accelerated oocyte loss, but to a lesser degree than in the p63+/ΔTID mice. Together, these findings show that TID-related variants causing constitutive activation of TAp63α lead to POI by inducing oocyte apoptosis, which will facilitate the genetic diagnosis of POI in patients and provide a potential therapeutic target for extending female fertility.

Chemotherapy: how to reduce its adverse effects while maintaining the potency?

Chemotherapy is one of the widely used anticancer treatments that involves the use of powerful cytotoxic drugs to stop tumor growth by targeting rapidly dividing cells through various mechanisms, which will be elucidated in this review. Introduced during the early twentieth century, chemotherapy has since lengthened the longevity of innumerable cancer patients. However, the increase in lifespan is at the expense of quality of life as patients are at risk of developing short-term and long-term side effects following chemotherapy, such as alopecia (hair loss), chemotherapy-induced peripheral neuropathy, chemotherapy-induced nausea and vomiting, cardiotoxicity, diarrhea, infertility, and chemo brain. Currently, a number of these chemotherapy-induced adverse effects are managed through supportive care and approved treatments, while the rest of the side effects are unavoidable. Hence, chemotherapeutic drugs associated with inevitable side effects are only administered when their therapeutic role outweighs their chemotoxicity, thus severely limiting the potency of chemotherapy in treating malignancy. Therein, the potential approaches to alleviating side effects of chemotherapy ranging from pharmaceutical drugs to alternative therapies will be discussed in this review in hopes of increasing the tolerance and effectiveness of future chemotherapeutic treatments.

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.

DNA Damage Stress Response and Follicle Activation: Signaling Routes of Mammalian Ovarian Reserve

Chemotherapy regimens and radiotherapy are common strategies to fight cancer. In women, these therapies may cause side effects such as premature ovarian insufficiency (POI) and infertility. Clinical strategies to protect the ovarian reserve from the lethal effect of cancer therapies needs better understanding of the mechanisms underlying iatrogenic loss of follicle reserve. Recent reports demonstrate a critical role for p53 and CHK2 in the oocyte response to different DNA stressors, which are commonly used to treat cancer. Here we review the molecular mechanisms underlying the DNA damage stress response (DDR) and discuss crosstalk between DDR and signaling pathways implicated in primordial follicle activation.

hucMSC-derived exosomes protect ovarian reserve and restore ovarian function in cisplatin treated mice

Anti-cancer therapy often causes premature ovarian insufficiency and infertility as the ovarian follicle reserve is extremely sensitive to chemotherapy drugs, such as cisplatin. Various fertility preservation methods have been explored for women, especially prepubertal girls undergoing radiotherapy and chemotherapy due to cancer. In recent years, mesenchymal stem cell-derived exosomes (MSC-exos) have been reported to play an important role in tissue repair and the treatment of various diseases. In the current study, we observed that human umbilical cord-derived MSC-exos (hucMSC-exos) after short-term culture improved follicular survival and development while receiving cisplatin treatment. Moreover, intravenous injection of hucMSC-exos improved ovarian function and ameliorated inflammatory environment within the ovary. The underlying mechanism of hucMSC-exos on fertility preservation was associated with the down-regulation of p53-related apoptosis and their anti-inflammatory function. Based on these findings, we propose that hucMSC-exos may be a potential approach to improve fertility in women diagnosed with cancer.

Development of protective agents against ovarian injury caused by chemotherapeutic drugs

BACKGROUND

Chemotherapy is one of the causes of ovarian injury and infertility. Although assisted reproductive technology helps young female patients with cancer become pregnant, preventing chemotherapy-induced ovarian injury will often possess even more significant benefits.

OBJECTIVE

We aimed at demonstrating the hazardous effects and mechanisms of ovarian injury by chemotherapeutic agents, as well as demonstrating agents that protect the ovary from chemotherapy-induced injury.

RESULTS

Chemotherapeutic agents cause death or accelerate activation of follicles and damage to the blood vessels in the ovary, resulting in inflammation. These often require drug development to protect the ovaries from injury.

CONCLUSIONS

Our findings provide a basis for the development of drugs to protect the ovaries from injury. Although there are many preclinical studies on potential protective drugs, there is still an urgent need for a large number of clinical experiments to verify their potential use.

Oocyte CTR1 is not essential for cisplatin-induced oocyte death of primordial follicle

Accumulated evidence indicates that cisplatin, a platinum-based alkylating agent, causes preferential DNA damage to oocytes of primordial follicles (PFs) in the ovary, suggesting oocyte-favored accumulation of cisplatin. Copper transporter 1 (CTR1; Slc31a1 ) is implicated in facilitating cisplatin uptake in cells. Here we found that oocytes of PFs had constitutively higher expression of CTR1 than other cell types in mouse ovary. However, oocyte-specific Slc31a1 knockout was not sufficient to prevent cisplatin-induced depletion of PFs in vitro . Our data indicate that CTR1 would not be the only route for cisplatin to be transported inside the oocytes of PFs in the ovary.

A synopsis of global frontiers in fertility preservation

Since 2007, the Oncofertility Consortium Annual Conference has brought together a diverse network of individuals from a wide range of backgrounds and professional levels to disseminate emerging basic and clinical research findings in fertility preservation. This network also developed enduring educational materials to accelerate the pace and quality of field-wide scientific communication. Between 2007 and 2019, the Oncofertility Consortium Annual Conference was held as an in-person event in Chicago, IL. The conference attracted approximately 250 attendees each year representing 20 countries around the world. In 2020, however, the COVID-19 pandemic disrupted this paradigm and precluded an in-person meeting. Nevertheless, there remained an undeniable demand for the oncofertility community to convene. To maintain the momentum of the field, the Oncofertility Consortium hosted a day-long virtual meeting on March 5, 2021, with the theme of "Oncofertility Around the Globe" to highlight the diversity of clinical care and translational research that is ongoing around the world in this discipline. This virtual meeting was hosted using the vFairs ® conference platform and allowed over 700 people to participate, many of whom were first-time conference attendees. The agenda featured concurrent sessions from presenters in six continents which provided attendees a complete overview of the field and furthered our mission to create a global community of oncofertility practice. This paper provides a synopsis of talks delivered at this event and highlights the new advances and frontiers in the fields of oncofertility and fertility preservation around the globe from clinical practice and patient-centered efforts to translational research.

Comparison of CD146 +/- mesenchymal stem cells in improving premature ovarian failure

BACKGROUND

Mesenchymal stem cells (MSCs) are a heterogeneous group of subpopulations with differentially expressed surface markers. CD146 + MSCs correlate with high therapeutic and secretory potency. However, their therapeutic efficacy and mechanisms in premature ovarian failure (POF) have not been explored.

METHODS

The umbilical cord (UC)-derived CD146 +/- MSCs were sorted using magnetic beads. The proliferation of MSCs was assayed by dye670 staining and flow cytometry. A mouse POF model was established by injection of cyclophosphamide and busulfan, followed by treatment with CD146 +/- MSCs. The therapeutic effect of CD146 +/- MSCs was evaluated based on body weight, hormone levels, follicle count and reproductive ability. Differential gene expression was identified by mRNA sequencing and validated by RT-PCR. The lymphocyte percentage was detected by flow cytometry.

RESULTS

CD146 +/- MSCs had similar morphology and surface marker expression. However, CD146 + MSCs exhibited a significantly stronger proliferation ability. Gene profiles revealed that CD146 + MSCs had a lower levels of immunoregulatory factor expression. CD146 + MSCs exhibited a stronger ability to inhibit T cell proliferation. CD146 +/- MSCs treatment markedly restored FSH and E2 hormone secretion level, reduced follicular atresia, and increased sinus follicle numbers in a mouse POF model. The recovery function of CD146 + MSCs in a reproductive assay was slightly improved than that of CD146 - MSCs. Ovary mRNA sequencing data indicated that UC-MSCs therapy improved ovarian endocrine locally, which was through PPAR and cholesterol metabolism pathways. The percentages of CD3, CD4, and CD8 lymphocytes were significantly reduced in the POF group compared to the control group. CD146 + MSCs treatment significantly reversed the changes in lymphocyte percentages. Meanwhile, CD146 - MSCs could not improve the decrease in CD4/8 ratio induced by chemotherapy.

CONCLUSION

UC-MSCs therapy improved premature ovarian failure significantly. CD146 +/- MSCs both had similar therapeutic effects in repairing reproductive ability. CD146 + MSCs had advantages in modulating immunology and cell proliferation characteristics.

Protective Effects of Antioxidants on Cyclophosphamide-Induced Ovarian Toxicity

The most common limitation of anticancer chemotherapy is the injury to normal cells. Cyclophosphamide, which is one of the most widely used alkylating agents, can cause premature ovarian insufficiency and infertility since the ovarian follicles are extremely sensitive to their effects. Although little information is available about the pathogenic mechanism of cyclophosphamide-induced ovarian damage, its toxicity is attributed to oxidative stress, inflammation, and apoptosis. The use of compounds with antioxidant and cytoprotective properties to protect ovarian function from deleterious effects during chemotherapy would be a significant advantage. Thus, this article reviews the mechanism by which cyclophosphamide exerts its toxic effects on the different cellular components of the ovary, and describes 24 cytoprotective compounds used to ameliorate cyclophosphamide-induced ovarian injury and their possible mechanisms of action. Understanding these mechanisms is essential for the development of efficient and targeted pharmacological complementary therapies that could protect and prolong female fertility.

Senotherapy Protects against Cisplatin-Induced Ovarian Injury by Removing Senescent Cells and Alleviating DNA Damage

Ovarian damage induced by platinum-based chemotherapy seriously affects young women with cancer, manifesting as infertility, early menopause, and premature ovarian insufficiency. However, effective prevention strategies for such damage are lacking. Senescent cells may be induced by chemotherapeutic agents. We hypothesized that cisplatin can lead to senescence in ovarian cells during the therapeutic process, and senolytic drugs can protect animals against cisplatin-induced ovarian injury. Here, we demonstrated the existence of senescent cells in cisplatin-treated ovaries, identified the senescence-associated secretory phenotype, and observed significant improvement of ovarian function by treatment with metformin or dasatinib and quercetin (DQ) independently or in combination. These senotherapies improved both oocyte quality and fertility, increased the ovarian reserve, and enhanced hormone secretion in cisplatin-exposed mice. Additionally, attenuated fibrosis, reorganized subcellular structure, and mitigated DNA damage were observed in the ovaries of senotherapeutic mice. Moreover, RNA sequencing analysis revealed upregulation of the proliferation-related genes Ki, Prrx2, Sfrp4, and Megfl0; and the antioxidative gene H2-Q10 after metformin plus DQ treatment. Gene ontology analysis further revealed that combining senotherapies enhanced ovarian cell differentiation, development, and communication. In this study, we demonstrated that metformin plus DQ recovered ovarian function to a greater extent compared to metformin or DQ independently, with more follicular reserve, increased pups per litter, and reduced DNA damage. Collectively, our work indicates that senotherapies might prevent cisplatin-induced ovarian injury by removing senescent cells and reducing DNA damage, which represent a promising therapeutic avenue to prevent chemotherapy-induced ovarian damage.

Unlaid Eggs: Ovarian Damage after Low-Dose Radiation

The total body irradiation of lymphomas and co-irradiation in the treatment of adjacent solid tumors can lead to a reduced ovarian function, premature ovarian insufficiency, and menopause. A small number of studies has assessed the radiation-induced damage of primordial follicles in animal models and humans. Studies are emerging that evaluate radiation-induced damage to the surrounding ovarian tissue including stromal and immune cells. We reviewed basic laboratory work to assess the current state of knowledge and to establish an experimental setting for further studies in animals and humans. The experimental approaches were mostly performed using mouse models. Most studies relied on single doses as high as 1 Gy, which is considered to cause severe damage to the ovary. Changes in the ovarian reserve were related to the primordial follicle count, providing reproducible evidence that radiation with 1 Gy leads to a significant depletion. Radiation with 0.1 Gy mostly did not show an effect on the primordial follicles. Fewer data exist on the effects of radiation on the ovarian microenvironment including theca-interstitial, immune, endothelial, and smooth muscle cells. We concluded that a mouse model would provide the most reliable model to study the effects of low-dose radiation. Furthermore, both immunohistochemistry and fluorescence-activated cell sorting (FACS) analyses were valuable to analyze not only the germ cells but also the ovarian microenvironment.

Inhibition of Sirtuin-1 hyperacetylates p53 and abrogates Sirtuin-1-p53 interaction in Cr(VI)-induced apoptosis in the ovary

Environmental contamination with hexavalent chromium, Cr(VI), has been increasing in the United States as well as in developing countries. Exposure to Cr(VI) predisposes the human population to various diseases, including cancer, infertility, and developmental problems in children. Previous findings from our laboratory reported that prenatal exposure to Cr(VI) caused premature ovarian failure through p53-mediated mechanisms. Sirtuin 1 (SIRT1) is an NAD+ -dependent histone deacetylase class III. SIRT1 deacetylates several histones and non-histone proteins such as p53 and NFkB. The current study determines a role for the SIRT1-p53 network in apoptosis induced by Cr(VI) in the ovary and establishes physical interaction between SIRT1 and p53. Adult pregnant dams were given regular drinking water or Cr(VI) (10 ppm potassium dichromate in drinking water, ad libitum), and treated with SIRT1 inhibitor, EX-527 (50 mg/kg body weight, i.p.,), during 9.5 - 14.5 days post-coitum. On postnatal day-1, ovaries from F1 offspring were collected for various analyses. Results indicated that Cr(VI) increased germ cell and somatic cell apoptosis, upregulated acetyl-p53, activated the apoptotic pathway, and inhibited cell survival pathways. Cr(VI) decreased acetyl-p53-SIRT1 co-localization in the ovary. In an immortalized rat granulosa cell line SIGC, Cr(VI) inhibited the physical interaction between SIRT1 and acetyl-p53 by altering the p53:SIRT1 ratio. EX-527 exacerbated Cr(VI)-induced mechanisms. The current study shows a novel mechanism for Cr(VI)-induced apoptosis in the ovary, mediated through the p53-SIRT1 network, suggesting that targeting the p53 pathway may be an ideal approach to rescue ovaries from Cr(VI)-induced apoptosis.

Protective effects of a SIRT1 inhibitor on primordial follicle activation and growth induced by cyclophosphamide: insights from a bovine in vitro folliculogenesis system

Purpose

Although oncological advances have improved survival rates of female cancer patients, they often suffer a reduced fertility due to treatment side effects. In the present study, we evaluated the potential fertoprotective effects of the specific inhibitor of SIRT1, EX-527, on the gonadotoxic action exerted by cyclophosphamide (CPM) on loss of primordial follicles (PFs).

Methods

The effects of the CPM metabolite phosphoramide mustard (PM) on follicle activation, growth and viability and the protective action of EX-527 against PM effects were evaluated on bovine ovarian cortical strips in vitro cultured for 1 or 6 days. To understand whether PFs exposed to PM plus EX-527 were able to activate and grow to the secondary stage after suspension of the treatment, strips cultured for 3 days in PM plus EX-527 for 3 days were transferred to plain medium until day 6. Follicle growth and health were evaluated through histology and viability assay at a confocal microscope. In order to investigate the molecular pathways underlying the ovarian response to PM in the presence of EX-527, we analysed the protein level of SIRT1, HuR, PARP1 and SOD2 after 1 day of in vitro culture.

Results

We found that (1) PM, the main CPM active metabolite, promotes PF activation; (2) the ovarian stress response induced by PM includes a SIRT1-dependent pathway; and (3) EX-527 reduces PF activation and growth induced by PM.

Conclusion

SIRT1 can represent a candidate molecule to be targeted to protect ovarian follicles from alkylating agents and EX-527 could represent a potential fertoprotective agent for cancer patients.

Preserving Oocytes in Oncofertility†

The prodigious rise of cancer survival rates enables many cancer survivors to live long lives. Therefore, the side effects of cancer treatments as well as the long-term quality of life after cancer have become more relevant. Ovarian toxicity is a major off-target effect of anticancer agents for childhood and young adult female cancer patients. Both chemotherapy and irradiation have been demonstrated to damage the ovary and increase the risks of premature ovarian failure (POF), early menopause, ovarian endocrine disorders, and sub- or infertility. Oncofertility is an emerging and multidisciplinary research and medical field that focuses on providing cancer patients with fertility preservation options. Oocyte quality and quantity are one of the most important factors to determine women's fertility success; therefore, preserving oocytes is paramount for maintaining the ability of young female cancer patients' reproduction after their recovery. This review summarizes peer-reviewed literature on current oocyte preservation options in oncofertility. We describe in-depth oocyte and embryo cryopreservation, ovarian suppression, ovarian tissue cryopreservation, in vitro maturation, ovarian transposition, and adjuvant therapy. Further, we discuss current guidelines and practices of female fertility preservation that cover preserving oocytes.

The impact of oocyte death on mouse primordial follicle formation and ovarian reserve

Background

Ovaries, the source of oocytes, maintain the numbers of primordial follicles, develop oocytes for fertilization and embryonic development. Although it is well known that about two-thirds of oocytes are lost during the formation of primordial follicles through cyst fragmentation and the aggregation of oocytes within the cyst, the mechanism responsible for this remains unclear.

Methods

We provide an overview of cell death that is associated with the oocyte cyst breakdown and primordial follicle assembly along with our recent findings for mice that had been treated with a TNFα ligand inhibitor.

Main Findings

It is generally accepted that apoptosis is the major mechanism responsible for the depletion of germ cells. In fact, a gene deficiency or the overexpression of apoptosis regulators can have a great effect on follicle numbers and/or fertility. Apoptosis, however, may not be the only cause of the large-scale oocyte attrition during oocyte cyst breakdown, and other mechanisms, such as aggregation, may also be involved in this process.

Conclusion

The continued study of oocyte death during primordial follicle formation could lead to the development of novel strategies for manipulating the primordial follicle pool, leading to improved fertility by enhancing the ovarian reserve.

Female Oncofertility: Current Understandings, Therapeutic Approaches, Controversies, and Future Perspectives

Recent advances in early detection and oncological therapies have ameliorated the survival rate of young cancer patients. Yet, ovarian impairment induced by chemotherapy and radiotherapy is still a challenging issue. This review, based on clinical and lab-based studies, summarizes the evidence of gonadotoxicity of chemoradiotherapy, the recent approaches, ongoing controversies, and future perspectives of fertility preservation (FP) in female patients who have experienced chemo- or radio-therapy. Existing data indicate that chemotherapeutic agents induce DNA alterations and massive follicle activation via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Meanwhile, the radiation causes ionizing damage, leading to germ cell loss. In addition to the well-established methods, numerous therapeutic approaches have been suggested, including minimizing the follicle loss in cryopreserved ovarian grafts after transplantation, in vitro activation or in vitro growing of follicles, artificial ovarian development, or fertoprotective adjuvant to prevent ovarian damage from chemotherapy. Some reports have revealed positive outcomes from these therapies, whereas others have demonstrated conflictions. Future perspectives are improving the live birth rate of FP, especially in patients with adverse ovarian reserve, eliminating the risk of malignancy reintroducing, and increasing society’s awareness of FP importance.

Ovarian tissue and oocyte cryopreservation prior to iatrogenic premature ovarian insufficiency

Gonadotoxic treatments like chemotherapy or radiotherapy and ovarian surgery may result in an accelerated depletion of the ovarian reserve and subsequent premature ovarian insufficiency. Important determinants of this severe risk that require fertility preservation strategies are patient age, ovarian reserve, type of treatment, and administered dose. Oocytes and ovarian tissue can both be cryopreserved, with encouraging results in terms of pregnancy and live birth rates according to recent publications. Moreover, since ovarian tissue transplantation also results in long-term endocrine resumption, it represents a potential future therapeutic option for complete ovarian function restoration in patients with premature ovarian insufficiency.

PI3K/PTEN/AKT Signaling Pathways in Germ Cell Development and Their Involvement in Germ Cell Tumors and Ovarian Dysfunctions

Several studies indicate that the PI3K/PTEN/AKT signaling pathways are critical regulators of ovarian function including the formation of the germ cell precursors, termed primordial germ cells, and the follicular pool maintenance. This article reviews the current state of knowledge of the functional role of the PI3K/PTEN/AKT pathways during primordial germ cell development and the dynamics of the ovarian primordial follicle reserve and how dysregulation of these signaling pathways may contribute to the development of some types of germ cell tumors and ovarian dysfunctions.

The Role of Mutant p63 in Female Fertility

The transcription factor p63, one of the p53 family members, plays an essential role in regulating maternal reproduction and genomic integrity as well as epidermal development. TP63 (human)/Trp63 (mouse) produces multiple isoforms: TAp63 and ΔNp63, which possess a different N-terminus depending on two different promoters, and p63a, p63b, p63g, p63δ, and p63ε as products of alternative splicing at the C-terminus. TAp63 expression turns on in the nuclei of primordial germ cells in females and is maintained mainly in the oocyte nuclei of immature follicles. It has been established that TAp63 is the genomic guardian in oocytes of the female ovaries and plays a central role in determining the oocyte fate upon oocyte damage. Lately, there is increasing evidence that TP63 mutations are connected with female infertility, including isolated premature ovarian insufficiency (POI) and syndromic POI. Here, we review the biological functions of p63 in females and discuss the consequences of p63 mutations, which result in infertility in human patients.

Unraveling the mechanisms of chemotherapy-induced damage to human primordial follicle reserve: road to developing therapeutics for fertility preservation and reversing ovarian aging

Among the investigated mechanisms of chemotherapy-induced damage to human primordial follicle reserve are induction of DNA double-strand breaks (DSBs) and resultant apoptotic death, stromal-microvascular damage and follicle activation. Accumulating basic and translational evidence suggests that acute exposure to gonadotoxic chemotherapeutics, such as cyclophosphamide or doxorubicin, induces DNA DSBs and triggers apoptotic death of primordial follicle oocytes within 12-24 h, resulting in the massive loss of ovarian reserve. Evidence also indicates that chemotherapeutic agents can cause microvascular and stromal damage, induce hypoxia and indirectly affect ovarian reserve. While it is possible that the acute reduction of the primordial follicle reserve by massive apoptotic losses may result in delayed activation of some primordial follicles, this is unlikely to be a predominant mechanism of loss in humans. Here, we review these mechanisms of chemotherapy-induced ovarian reserve depletion and the potential reasons for the discrepancies among the studies. Based on the current literature, we propose an integrated hypothesis that explains both the acute and delayed chemotherapy-induced loss of primordial follicle reserve in the human ovary.