It’s no secret that female fertility gradually changes over time. From the mid-30s onwards, the chances of conceiving generally start to decline, recalls New Scientist. However, in many countries, pregnancies are occurring later and later, as career paths, economic constraints and personal choices push back the age of motherhood. Today, in France, according to a study by Public Health France, more than a quarter of mothers are 35 years old or over.
Researchers have been interested for several years in the mechanisms that explain the decline in female fertility with age. Among the avenues studied is the aging of the ovaries themselves: over time, their tissues become progressively more rigid, which could disrupt the development of oocytes and contribute to the decline in their quality. So Shixuan Wang, of Huazhong University of Science and Technology in Wuhan, China, and colleagues wondered whether the fertile window could be extended by making the ovaries less rigid.
To understand the mechanisms behind this phenomenon, the team of scientists measured protein levels in the ovaries of women aged 18 to 28, 35 to 42 and 47 to 52 years. They found that the protein called interleukin-11 gradually increased with age and that it activated connective tissue cells called fibroblasts, which produce collagen (a contributing factor to ovarian rigidity). We therefore had to find a way to make the ovaries no longer respond to this protein.
A promising drug
Researchers have created an experimental drug that can block the production of interleukin-11 by deactivating the gene responsible for it. To test its potential, they injected the product into the tails of 36-week-old mice (30-40 years in human age), twice a week for four weeks. The results observed in rodents were particularly striking.
In treated females, ovarian rigidity decreased by 36% compared to untreated animals. This change was accompanied by a clear increase in fertility: their conception rate doubled, from 25% to 50%, while the average litter size increased from three to five young.
In older rats, the effect appears to have been even more pronounced. Their conception rate has also increased from 20% to 50%, and the average number of pups per litter has increased fivefold, from just one pup to five. For Francesca Duncan, a researcher at Northwestern University in Illinois, these results open an interesting avenue for human fertility. According to her, the approach could produce comparable effects in premenopausal women.
Beyond the sole issue of fertility, this approach could have broader consequences on women’s health. For Barbara Vanderhyden, researcher at the University of Ottawa in Canada, preserving ovarian function for longer could help delay certain effects associated with menopause.
These include an increased risk of osteoporosis or cardiovascular disease. “Prolonging the activity of the ovaries would therefore not only concern the ability to have children, but could also play a role in the healthy aging of women”she believes.
