It is well established that
DNA-damaging
chemotherapies can cause
infertility and ovarian endocrine failure by depleting the ovarian reserve of primordial follicles. Currently, no effective pharmacological
therapies exist for the preservation of long-term fertility and ovarian function in female
cancer patients, due to a limited understanding of the mechanisms of
chemotherapy-induced follicle depletion. This study investigated the cellular targets, molecular mechanisms, and temporal course of ovarian reserve depletion following treatment with commonly used chemotherapeutic drugs. Adult female C57BL/6 mice were injected i.p. with saline,
cisplatin (5mg/kg), or
cyclophosphamide (300mg/kg); ovaries were harvested after 8 or 24 hours. Follicle counts showed depletion of all follicular stages 24 hours after administration of
cisplatin or
cyclophosphamide. Eight hours post-treatment, H2A
histone family member X (γH2AX) immunofluorescence showed
DNA double-stranded breaks at all follicular stages, including within primordial follicle oocytes. This staining was resolving by 24 hours, indicating that primordial follicle oocytes begin to undergo either apoptosis or repair in this timeframe. γH2AX-positive follicles were further examined to identify the specific cell types damaged. In primordial, transitional, and primary follicles, only oocytes sustained DNA damage, whereas in secondary and
antral follicles, only somatic cells were affected. TUNEL staining confirmed that apoptosis occurs in these targeted cell types. Whilst multi-drug and multi-dose regimens were not examined, this study conclusively shows that
cyclophosphamide and
cisplatin cause direct damage to primordial follicle oocytes, which then undergo apoptosis. Therefore, future pharmacological strategies to prevent
chemotherapy-induced
infertility in females must specifically prevent primordial follicle oocyte death.