Cold environment influences the composition of intestinal bacteria (Press Release)

Freezing increases the production of bile acids and thus changes the intestinal environment. Under these different metabolic conditions, some bacteria in the gut obviously thrive better than at warm temperatures, while other bacterial species multiply less well. This was discovered by a team from the Cluster of Excellence “Inflammation at Interfaces”, in conjunction with Hamburg scientists, using mice as model organisms. “Exposure to the cold changes the intestinal microbiome, irrespective of what is fed,” emphasised Malte Rühlemann, doctoral candidate at the Institute of Clinical Molecular Biology at Kiel University’s Faculty of Medicine, in the working group of Cluster board member Professor Andre Franke. In the study, now published in Nature Medicine, a mechanism in the liver was also demonstrated which enables the organism to efficiently convert excess cholesterol into bile acids, and thus render it harmless.

If the environment is cold, the body must produce more heat. This is ensured in particular by the so-called brown adipose tissue, whereas the normal white adipose tissue primarily stores excess energy in the form of fat. The activity of the brown adipose tissue depends – amongst other things – on the temperature. It is activated by cold, says co-author Rühlemann. For the study, mice were kept at normal and at cold temperatures. The scientists were able to demonstrate for the first time how the activation of the brown adipose tissue stimulates the liver, increasing conversion of cholesterol to bile acids. Rühlemann: “It was actually proven that exposure to the cold causes bile acid production in the liver to increase dramatically, sometimes up to 40 times the normal value. This change in the metabolism has an effect on the microbiome in the intestine, and conversely the intestinal bacteria can also convert bile acids.” It is still not clear what the results of changing the microbiome may be.

“The impact of bile acids on the microbiome is of great interest, since we know that intestinal bacteria can influence the progress of inflammatory liver diseases, for example. Through the discovery of the alternative metabolic pathway in the liver, and its regulation via the brown adipose tissue, we hope in future to be able to develop new therapeutic approaches, in particular for the treatment of chronic inflammatory liver diseases,” explained Professor Jörg Heeren, coordinating director of studies at the Department of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf (UKE).

UKE press release:

Original publication:
A. Worthmann et al. Cold-induced conversion of cholesterol to bile acids in mice shapes the gut microbiome and promotes adaptive tumorgenesis. Nature Medicine 2017, published online June 12 doi: 10.1038/nm.4357

Malte C. Rühlemann
Institute of Clinical Molecular Biology at Kiel University
Tel.: +49 (0)431 500 15132

Prof. Dr Andre Franke
Institute of Clinical Molecular Biology at Kiel University
Tel.: +49 (0)431 500 15110

Cluster of Excellence “Inflammation at Interfaces”
Scientific Office, Head: Dr habil. Susanne Holstein
Press and Communications, Dr Tebke Böschen, Text: Kerstin Nees
Postal address: Christian-Albrechts-Platz 4, 24118 Kiel, Germany
Tel.: +49 (0)431 880-4850, Fax: +49 (0)431 880-4894

The Cluster of Excellence “Inflammation at Interfaces” has been funded since 2007 by the Excellence Initiative of the German Government and the federal states with a total budget of 68 million Euros. It is currently in its second phase of funding. Around 300 cluster members are spread across the four locations: Kiel (Kiel University, University Medical Center Schleswig-Holstein (UKSH)), Lübeck (University of Lübeck, UKSH), Plön (Max Planck Institute for Evolutionary Biology) and Borstel (Research Center Borstel (FZB) – Center for Medicine and Biosciences) and are researching an innovative, systematic approach to the phenomenon of inflammation, which can affect all barrier organs such as the intestines, lungs and skin.