Rapamycin maintains the primordial follicle pool and protects ovarian reserve against cyclophosphamide-induced damage

Abstract

Any abnormal activation of primordial follicles and subsequent depletion can irreversibly diminish the ovarian reserve, which is one of the major chemotherapy-induced adverse effects in young patients with cancer. Herein, we investigated the effects of rapamycin on the activation and development of ovarian follicles to evaluate its fertility-sparing therapeutic value in a cyclophosphamide (CTX)-treated mouse model. Based on ovarian histomorphological changes and follicle counting in 50 SPF female C57BL/6 mice, daily administration of 5 mg/kg rapamycin for 30 days was deemed an ideal dosage and duration for administration in subsequent experiments. Compared with the control group, rapamycin treatment inhibited the activation of quiescent primordial follicles, with no obvious side effects observed. Finally, 48 mice were randomly divided into four groups: control, rapamycin-treated, cyclophosphamide-treated, and rapamycin intervention. Body weight, ovarian histomorphological changes, number of primordial follicles, DDX4/MVH expression, apoptosis of follicular cells, and expression of apoptosis protease-activating factor (APAF)-1, cleaved caspase 3, and caspase 3 were monitored. Co-administration of rapamycin reduced primordial follicle loss and the development of follicular cell apoptosis, thereby rescuing the ovarian reserve after CTX treatment. On analyzing the mTOR signaling pathway, we observed that rapamycin significantly decreased CTX-mediated overactivation of mTOR and its downstream molecules. These findings suggest that rapamycin exhibits potential as an ovarian-protective agent that could maintain the ovarian primordial follicle pool and preserve fertility in young female patients with cancer undergoing chemotherapy.

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

“…Our data demonstrating the ability of rapamycin to attenuate 4-HC-induced upregulated PI3K signalling in the human ovary is perhaps expected, given the mechanism of action of this well-known inhibitor; this effect has also been reported in multiple rodent studies alongside the chemoprotective efficacy of mTOR inhibitors in general ( Goldman et al , 2017 ; Zhou et al , 2017 ; Tanaka et al , 2018 ; Chen et al , 2022 ). Although not significant in our data, possibly due to limited numbers of growing follicles, other work in rodents has demonstrated the effectiveness of rapamycin treatment in attenuating cyclophosphamide-induced growing follicle damage ( Zhou et al , 2017 ; Chen et al , 2022 ).…”

“…Our data demonstrating the ability of rapamycin to attenuate 4-HC-induced upregulated PI3K signalling in the human ovary is perhaps expected, given the mechanism of action of this well-known inhibitor; this effect has also been reported in multiple rodent studies alongside the chemoprotective efficacy of mTOR inhibitors in general ( Goldman et al , 2017 ; Zhou et al , 2017 ; Tanaka et al , 2018 ; Chen et al , 2022 ). Although not significant in our data, possibly due to limited numbers of growing follicles, other work in rodents has demonstrated the effectiveness of rapamycin treatment in attenuating cyclophosphamide-induced growing follicle damage ( Zhou et al , 2017 ; Chen et al , 2022 ). Although human ovary cortex cultured with rapamycin for 6 days had a high proportion of follicles with fragmented or shrunken oocytes ( McLaughlin et al , 2011 ), this adverse effect on oocyte health was not observed in rodent studies or human ovarian cortical xenotransplantation experiments ( Yorino and Kawamura, 2020 ) nor are there any reports describing adverse reproductive outcomes following rapamycin treatment.…”

“…Since then, numerous studies have demonstrated the effectiveness of rapamycin in protecting the rodent ovary from both chemotherapy-induced primordial follicle damage and excessive follicle activation. These data have been generated using in vitro and in vivo models of chemotherapy exposure, investigating the effects of both cyclophosphamide and cisplatin ( Zhou et al , 2017 ; Xie et al , 2020 ; Chen et al , 2022 ). Data collected following the use of the mTOR inhibitor everolimus to protect against cisplatin-induced ovarian toxicity further support inhibition of mTOR as a pathway to chemoprotection ( Goldman et al , 2017 ; Tanaka et al , 2018 ).…”

The mTOR Inhibitor Rapamycin Counteracts Follicle Activation Induced by Ovarian Cryopreservation in Murine Transplantation Models

“…This study showed that rapamycin was able to inhibit mTOR pathway activation in ovaries directly after the thawing process and in ovaries five days after grafting in mice [ 61 ]. In addition, Chen et al showed that the injection of rapamycin in mice resulted in lower levels of follicle proliferation [ 62 ].…”

Making a good egg: human oocyte health, aging, and in vitro development

“…Rapamycin treatment prevents PFA and preserves the ovarian reserve both in vivo and in vitro in mice ( 203 , 217 – 222 ) and rats ( 223 ). Rapamycin and everolimus have also been reported to protect the ovarian reserve against chemotherapy-induced early follicular exhaustion in mice by maintaining primordial follicles in a dormant state ( 224 – 227 ).…”