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Vitamin D emerges from ‘gut flora’ murk

U. ROCHESTER (US)—The vitamin D receptor is a key player amid gut bacteria—what scientists refer to as the “gut flora”—helping to govern activity, responding to cues, and sometimes countering their presence.

Findings deliver a new lead to scientists investigating how bacteria might play a role in the development of inflammatory bowel diseases such as Crohn’s disease or ulceractive colitis.

The work appears online in the American Journal of Pathology.

The work complements studies suggesting that Salmonella infection can increase the risk of inflammatory bowel disease.

“Vitamin D deficiency is a known factor in the pathology of inflammatory bowel disease and colon cancer,” says Jun Sun, assistant professor of gastroenterology and hepatology at the University of Rochester Medical Center.

“But there have been very few reports about how bacteria might play a role by targeting the vitamin D receptor. Our work suggests one possible mechanism, by working through the vitamin D receptor, a sensor and regulator for the majority of functions of vitamin D.”

Sun has previously shown that bacteria often found in the human intestine affect molecular signals known to contribute to inflammatory response and cell growth.

Vitamin D and the receptor are associated with many types of cancer, as well as osteoporosis, heart disease, diabetes, inflammatory bowel disease, and infection.

Researchers took a close look at the vitamin D receptor in mice and its interactions with bacteria in the colon. The team studied normal mice; mice in which the vitamin D receptor had been knocked out; and mice that were completely free of any germs.

The mice responded to infection with either a harmless strain of E. coli or a pathogenic strain of Salmonella Typhimurium.

Salmonella is able to regulate the vitamin D receptor, increasing its activity and determining where in the colon the receptor is active. In the presence of Salmonella, the receptor was more prevalent than usual deep within folded intestinal structures known as crypts.

The researchers also discovered that the vitamin D receptor plays a key role in defending the body from assault by Salmonella and squelching inflammation. The receptor stops a molecule known as NF-Kappa B, a well-known master player in the world of inflammation, by binding to it and preventing it from activating other inflammatory molecules.

While scientists have known that the receptor interacts with NF-Kappa B, details of the interaction modulated by bacteria in the colon are new.

Salmonella is much more virulent and aggressive in mice in which the vitamin D receptor had been turned off. These mice showed higher levels of activity of inflammatory molecules, and they lost weight more quickly and were much more likely to die in response to infection.

“We live together in a mutually beneficial state with most of the bacteria in our gut,” explains Sun. “They help us digest foods like fruits and vegetables, and we provide them a place to live and thrive. We co-exist peacefully—most of the time.

“But we aren’t able to culture most of these bacteria in the laboratory, and we don’t know what most of them are doing. We need to understand our gut flora much more than we do. This is particularly important for understanding how we might manipulate the natural gut flora to stop an invader like Salmonella,” she adds.

Researchers from the University of Chicago and the University of North Carolina-Chapel Hill contributed to the research, funded by the National Institute of Diabetes and Digestive Kidney Diseases.

More health news from University of Rochester: www.urmc.rochester.edu/news/

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