The effect that obesity has on the quality of a woman's eggs is being studied as scientists search for ways to improve the ability of obese women to conceive and also have healthier offspring.
"Many obese women have a hard time getting pregnant," according to an article on the daily news site for the journal Science. "When they do, often with the help of infertility treatments, they tend to have children who are prone to obesity themselves."
Now, working with mice, researchers have identified a process in egg cells that explains why an obese person's lifestyle can alter the way their cells function. Eating lots of fat and cholesterol is like throwing a wrench in your cells' machinery. As explained in Science, "obesity stresses the endoplasmic reticulum (ER), where proteins are made and shuttled throughout the cell. This process, known as ER stress, can cause the cell to self-destruct and can occur in cells throughout the body, including the liver, pancreas and brain."
The next step was discovering if this same type of stress response happens in egg cells. To do this, researchers led by cell biologist Rebecca Robker at the University of Adelaide in Australia used mice with a genetic mutation that causes them to overeat. The aptly named "Blobby" mice, when compared to their regular-size counterparts, had much higher levels of genetic markers for ER stress. Also, they showed a reduction in the activity of their mitochondria, which are essentially a cell's power plant.
"When we saw that the mitochondria in the eggs were damaged, we knew that that was a very important and critical problem," Robker told Science. That's because mitochondria from a mother's egg are where all mitochondria in each cell in an offspring's body comes from.
According to the article, "The researchers found that the damaged mitochondria in the eggs of obese mice couldn’t replicate properly in the embryos. The fetuses that developed from the eggs of Blobby mice were heavier than those from skinny mice, and they had less mitochondrial DNA in their livers, kidneys and hearts."
By treating the obese mice with drugs, Robker and her team hoped to reverse the cellular stress response and the mitochondrial damage. They found that by giving the obese mice an ER stress inhibitor, which is already in early clinical trials for diabetes research, proved to lower the levels of stress in the cellular stress in the obese mice, as well as promote higher mitochondrial activity. The team also reported online in Development that when these healthier eggs were fertilized and transferred into surrogate embryos, the mice fetuses did not grow to be overweight.
The effect of this drug is promising for obese women having trouble conceiving, or who are worried about the weight of their offspring. Researchers also point out that exercise and lifestyle changes are effective means for overweight women to improve their natural fertility without having to take any drugs.