Endocrine disruptors impact physical activity and metabolism in mice
By Caleb O’Brien | MU Bond Life Sciences Center
Could your experiences in the womb make you lazy as an adult?
A recent study of California mice suggests that early exposure to environmental chemicals can later impact an animal’s metabolism and level of voluntary physical activity, according to new University of Missouri research.
“We found that if we developmentally exposed California mice to bisphenol A (BPA) or ethinyl estradiol (EE), the estrogen present in birth control pills, it caused later disruptions in voluntary physical activity,” said Cheryl Rosenfeld, a researcher in MU’s Bond Life Sciences Center and associate professor of biomedical sciences in the College of Veterinary Medicine. “What that means is they move around less in their home cage, they’re more likely to sleep, and they engage in less voluntary physical activity.”
Rosenfeld’s lab studies the ways that exposure to environmental chemicals such as BPA can affect other behaviors, including cognition and parenting. Endocrine-disrupting chemicals can accumulate in the environment and act like the hormones naturally produced by many organisms, including humans. To test the chemicals’ impact on metabolism and activity, the lab used California mice. This mouse model is a good model for metabolic diseases. And because these animals are initially derived from the wild, they may better replicate the genetic diversity of most human populations.
The researchers exposed the mice to BPA and EE in the womb and until weaning via the mom’s diet. A third group of mice whose mothers were placed on a phytoestrogen-free control diet was not exposed to either chemical. The scientists then placed all the mice on this same control diet and measured their energy expenditure, body composition and level of voluntary physical activity as adults.
To test those attributes, Rosenfeld’s lab relied on a variety of tools and techniques. They rigged bicycle computers to “hamster wheels” to track how far, fast and for how long the mice ran. Using a device called a “Promethion continuous measurement indirect calorimetry system” the researchers continuously monitored the mice’s energy expenditure by measuring oxygen consumption and carbon dioxide production and by using a three-beam system, tracked the rodents’ movements during the dark and light cycles.
Later, the researcher measured the animals’ body composition using an EchoMRI, a tiny MRI machine the size of a filing cabinet, and finally measured circulating concentrations of glucose and hormones that regulate metabolism.
Female mice exposed to BPA and EE were less active than control mice. They moved around their cages less at night (when the nocturnal California mouse is considered most active), moved more slowly, drank less water, and spent more time sleeping. In addition, BPA-exposed females burned more carbohydrates relative to fats, as compared to control mice. This is similar to the difference between obese and slender humans, and many researchers believe that burning more carbohydrates relative to fats can lead to fats gradually accumulating in the body.
“It’s worrisome that environmental chemicals we are exposed to in utero can override our genes and disrupt our neuro-circuitry,” said Sarah Johnson, a research specialist and graduate student in Rosenfeld’s lab and primary author on the study. “The net effect is that we can have behavioral disruptions into adulthood, including altered physical activity.”
The researchers are currently conducting follow-up studies to determine if the changes caused by exposure to BPA and EE predispose mice to obesity and other metabolic disorders. They also are interested in exploring if exposure could affect the children and grandchildren of these mice and examining the potential underlying neural mechanisms.
“Our findings are significant because decreased voluntary physical activity, or lack of exercise, can predispose animals or humans to cardiovascular diseases, metabolic disorders and even cancer,” Rosenfeld said.
Other authors on the study are Angela Javurek and Michele Painter (MU Biomedical Sciences), Mark Ellersieck (MU Agriculture Experimental Station- Statistics), Charles Wiedmeyer (MU Veterinary Medical Diagnostic Laboratory and Department of Veterinary Pathobiology) and John Thyfault (Kansas University Medical Center, Molecular and Integrative Physiology)
The study, “Sex-Dependent Effects of Developmental Exposure to Bisphenol A and Ethinyl Estradiol on Metabolic Parameters and Voluntary Physical Activity” was supported by NIH Grant 5R21ES023150 (to C.S.R.) and R01DK088940 (JPT) and was published in the Journal of Developmental Origins of Health and Disease.