Yashiro Motooka

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.

Tumor suppressor BRCA2 executes homologous recombination to repair DNA double-strand breaks in collaboration with RAD51, involving exon 11 and 27. Exon 11 constitutes a region where pathogenic variants (PVs) accumulate, and mutations in this region are known to contribute to carcinogenesis. However, the impact of the heterozygous PVs of BRCA2 exon 11 on the life quality beyond cancer risk, including male fertility, remains unclear. Here, we established a rat model with a frameshift on the seventh BRC repeat in Brca2 exon 11 (Brca2+/p.T1942fs), which is homologous to human BRCA2+/p.T1974fs, using CRISPR/Cas9 system. Our analyses revealed that the heterozygous rats with the PV in the BRCA2 exon 11 showed increased DNA double-strand breaks and apoptosis in spermatogonia and spermatocytes, accelerated testicular germ cell loss, and deterioration in sperm quality according with aging, ultimately resulting in early male reproductive dysfunction. Of note, these alterations in testes and sperm, including DNA fragmentation in spermatozoa, were observed from completion of sexual maturation. The present findings suggest that it is crucial to consider not only cancer risk but also potential declines in reproductive capacity in men carrying BRCA2 exon 11 PVs. Further investigation is warranted to determine whether similar traits appear in humans.