April 3, 2013
Obesity In Adult Mice Typical When Overfed As Infants
Michael Harper for redOrbit.com — Your Universe Online
A new study from the Baylor College of Medicine (BCM) in Houston, Texas finds that when female mice are overfed as babies, they´re more likely to become obese as adults. The doctors conducting this study believe that this overfeeding changes the female´s DNA in the brain, thus causing her to become obese. Without this outside influence of overfeeding, the DNA is not wired to allow the mouse to grow so large. This is shown in female mice that were not overfed and were much more physically active than those who had been overfed as infants.
The results of this study are published in the journal Diabetes.
Dr. Robert Waterland, an associate professor of pediatrics and nutrition at BCM and a scientist at the US Department of Agriculture (USDA) and Agricultural Research Service Center, is the lead researcher for this study. According to Dr. Waterland, this is the first time that researchers have been able to discover why overfed animals are destined to become overweight adults.
"We have known for decades that when mice are overfed during the newborn period they tend to stay fatter for their entire lives, but we did not know why," said Dr. Waterland in a press statement. "It was generally thought that animals that are over-nourished in infancy just maintain a higher food intake throughout life."
For the study, Dr. Waterland and his associates examined the suckling habits of baby mice. The researchers studied mice who suckled in small litters and compared these habits to mice who suckled in normal sized litters.
The baby mice in the smaller litters had easier access to their mothers milk and, according to Dr. Waterland, took advantage of the bounty. The mice who suckled in a normal sized litter had to fight a bit for their mother´s milk and therefore were not fed as well as the others.
Once the baby mice from both sets of litters had been weaned, they were fed the same amount of “mouse chow” to even out the results.
Even after they had been weaned, the female mice from the smaller litters were found to be larger and less active than their counterparts.
The researchers were surprised to discover that even though the female mice from the smaller litters had more access to their mother´s milk, they ate the same amount as their peers.
Dr. Waterland and his colleagues then studied the DNA of both sets of mice to understand, on a genetic level, why female mice which had an abundance of food in the early stages were becoming fatter as adults.
According to their studies, those mice who had free and open access to their mother´s milk had gone through a post-genetic or epigenetic change. The DNA in the hypothalamus portion of the brain (the area of the brain which regulates body weight) had been switched, thereby genetically ensuring that the mice would be larger as they grew up into adulthood.
"Infancy is [a] critical period for developmental epigenetics in the mouse hypothalamus," said Dr. Waterland. "Over nutrition in infancy is causing persistent changes that last into adulthood. These could mediate the persistent changes in physical activity."
Dr. Waterland concluded by saying that even though these changes may be subtle at infancy, the ramifications could have a “long-term impact on behavior and energy expenditure."
Dr. Waterland and his associates did not say if these findings are a sign that the same kind of genetic change can happen in humans.