Underlying Mechanism of Ovarian Reserve Preservation from Gonadotoxicity

Cancer therapies often lead to premature ovarian insufficiency by ovarian damage and follicle depletion. However, the oocyte death pathway induced by chemotherapies has been debated. Here we clarified the precise mechanism of ovarian depletion induced by cyclophosphamide and doxorubicin. Cyclophosphamide induced direct apoptosis in oocytes rather than overactivation of primordial follicles. Dormant oocytes instead of activated oocytes with high PI3K activity were more sensitive to cyclophosphamide. Although the ABL inhibitor, GNF2, has been proposed to ameliorate the apoptosis of primordial follicles against cyclophosphamide, GNF2 did not prevent the loss of primordial follicles induced by cyclophosphamide in the systems tested. Oocyte-specific deletion of Abl1 also failed to protect primordial follicles from cyclophosphamide, confirming the dispensability of ABL for the regulation of oocyte death by DNA damage. In contrast to previous reports, this study identified TAp63 as pivotal for cyclophosphamide and doxorubicin-induced oocyte death. Oocyte-specific knockout of Trp63 prevented primordial follicle loss in response to cyclophosphamide and doxorubicin. Consistently, the deletion of Trp63 from oocytes provided protection from cyclophosphamide- and doxorubicin-triggered apoptosis, as evidenced by undetectable levels of BAX and cleaved PARP, as well as increased OPA1 expression, compared to wildtype oocytes. Additionally, reproductive function was maintained in cyclophosphamide-exposed Trp63 knockout mice, confirmed by the delivery of healthy offspring with comparable numbers of pups and litters to the wildtype/solvent-treated mice. Therefore, we demonstrated that TAp63 is fundamental in determining the signaling of oocyte death induced by 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