Intestinal Bacteria Drive Obesity and Metabolic Disease in Immune-Altered Mice
Posted Jul 22 2010 9:44am
The finding strengthens the case that intestinal bacteria can contribute to human obesity and metabolic disease, since previous research has shown that intestinal bacterial populations differ between obese and lean humans.
“It has been assumed that the obesity epidemic in the developed world is driven by an increasingly sedentary lifestyle and the abundance of low-cost high-calorie foods,” says senior author Andrew Gewirtz, PhD, associate professor of pathology and laboratory medicine at Emory University School of Medicine. “However, our results suggest that excess caloric consumption is not only a result of undisciplined eating but that intestinal bacteria contribute to changes in appetite and metabolism.”
The first author of the paper is Emory faculty member Matam Vijay-Kumar, PhD, who has been studying a mouse strain with an altered immune system. These mice were engineered to lack a gene, Toll-like receptor 5 (TLR5), which helps cells sense the presence of bacteria. TLR5 recognizes flagellin, the main component of the apparatus (flagella) that many bacteria use to propel themselves.
The study began with Emory researcher Jesse Aitken’s unexpected observation that TLR5-deficient mice are about 20 percent heavier than regular mice and have elevated triglycerides, cholesterol and blood pressure. They also have mildly elevated blood sugar and increased production of insulin, Vijay-Kumar and Gewirtz found. TLR5-deficient mice tended to consume about 10 percent more food than their regular relatives. When their food was restricted they lost weight but still had a decreased response to insulin (i.e. insulin resistance). When fed a high-fat diet, TLR5-deficient mice gained more weight than regular mice and, moreover, developed full-blown diabetes and fatty liver disease. In short, TLR5-deficient mice exhibit “metabolic syndrome,” a cluster of disorders that in humans increases the risk of developing heart disease and diabetes.