A. In response to doxorubicin-induced stress conditions, the cell responds by activating the adaptive defense system, thereby triggering the phosphorylation of GSK-3β at serine 9, resulting in an increase in the inhibition of GSK-3. The inhibited GSK-3 rescues Nrf2 from proteasomal degradation by suppressing the ubiquitination of Nrf2. The rescued Nrf2 is then translocated into the nucleus to activate the transcription of antioxidant genes, which prevents the generation of reactive oxygen species, leading to an increase in cell survival, a decrease in ovarian tissue damage and the maintenance of ovarian function.

B. When the doxorubicin-induced toxicity is not reversed or is prolonged, the cellular adaptive defense mechanism against oxidative stress becomes decompensated by the exhaustion of the serine 9 phosphorylation of GSK-3β, resulting in a decrease in inactive GSK-3, followed by the ubiquitination and proteasomal degradation of Nrf2, a reduction in the Nrf2 that is translocated into the nucleus, a decrease in the transcription of antioxidant genes, an increase in the accumulation of reactive oxygen species, eventually leading to oxidative ovarian tissue damage and to a subsequent decrease in ovarian function

Chemotherapy induces ovarian failure in female children and young female cancer survivors. It has been shown that doxorubicin (DOX), an antitumor drug of the anthracycline group, causes gonadotoxicity via the stimulation of oxidative stress. The inhibition of glycogen synthase kinase-3 (GSK-3) was reported to be able to regulate oxidative stress. The present study assessed whether GSK-3 inhibition confers protection to the ovary against DOX-induced oxidative stress damage. An intraperitoneal injection of DOX was used to induce oxidative damage in the mouse ovary, while the inhibition of GSK-3 was achieved by the administration of SB216763, a small and potent GSK-3 inhibitor. DOX increased the mRNA expression levels of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and the antioxidant genes heme-oxygenase-1 (HO-1) and catalase (CAT), while reducing the levels of glutathione peroxidase (GSH-Px) and superoxide dismutase-1 (SOD-1) compared with those of the control. When the GSK-3 inhibitor was combined with DOX increased more expression levels of Nrf2 mRNA and restored levels of GSH-Px and SOD-1 mRNA similar to those in the control group. DOX remarkably decreased the Nrf2 protein expression compared to that in the control, which was significantly associated with increased MDA levels. Interestingly, the SB216763 and DOX coadministration restored the Nrf2 protein expression and MDA levels to levels that were similar to those in the control. DOX significantly decreased the number of primordial, primary, preantral and antral follicles while increasing the number of atretic follicles compared to those in the control. SB216763 caused the drastic recovery of these follicles from the DOX effects. SB216763 and DOX coadministration significantly reduced the apoptotic index compared with that with DOX treatment. DOX decreased the serum AMH and E2 levels and increased the FSH levels compared to those in the controls. However, SB216763 and DOX coadministration restored AMH and E2 while decreasing the FSH levels compared to those in the DOX-treated group. In addition, SB216763 and DOX coadministration reduced the mature oocyte abnormalities that resulted from DOX-induced ovarian damage. Given these results, we suggest that GSK-3/Nrf2 is a promising protective pathway against doxorubicin-induced oxidative damage to the ovaries of females at reproductive ages. Thus, GSK-3 could be an attractive target for the research and development of new drugs for preserving ovarian function during chemotherapy.