Research ArticleFertility

Impairment of BRCA1-Related DNA Double-Strand Break Repair Leads to Ovarian Aging in Mice and Humans

Science Translational Medicine  13 Feb 2013:
Vol. 5, Issue 172, pp. 172ra21
DOI: 10.1126/scitranslmed.3004925

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Preserving Fertility Breeds Flexibility

Last month, the U.K. Office for National Statistics reported that, in 2010, ~48% of infants were born to mothers 30 years and older, a level not seen since 1946—just after the end of World War II. Delaying childbearing can allow women flexibility with respect to career options. But unlike many somatic tissues, the female germline ages early, with reproductive capacity beginning to diminish after young adulthood. Attempts to stem oocyte aging and preserve fertility will depend on finely characterizing the molecular mechanisms behind the aging process in the female reproductive system. Now, Titus et al. provide evidence for a new mechanism to explain age-related oocyte dysfunction.

The authors showed that double-stranded breaks (DSBs) in DNA—which are essential for normal development—accumulate with age and contribute to reproductive aging in mice and women. In single mouse and human oocytes, the expression of DSB repair genes BRCA1, MRE11, RAD51, and ATM declined with age. Thus DSBs likely collect in the oocyte genome because of age-related missteps in DSB repair, which stimulate apoptosis and diminishes ovarian reserve. Indeed, in Brca1-deficient mice, numbers of primordial follicles—immature primary oocytes—were decreased, DSBs were increased, and reproductive capacity was impaired relative to wild-type mice. Using RNA interference in mouse oocytes, the authors showed that inhibition of Brca1, MRE11, RAD51, and, in turn, ATM expression increased DSBs and reduced oocyte survival. The authors then measured serum concentrations of anti-Müllerian hormone—a measure of fertility—in young women with germline BRCA1 mutations versus controls and showed that ovarian reserve was compromised in the latter group. Together, these findings show that the efficiency of DNA DSB repair is a crucial determinant of oocyte loss. The discovery of therapies that target this pathway might help to enhance the duration of ovarian function.