Transcription profiling of mouse small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J strain

Obesity and insulin resistance are two major risk factors underlying the metabolic syndrome. To gain more insight in the role of the small intestine in the etiology of these metabolic disorders, a microarray study was performed on small intestines (SI) of C57BL/6J mice that were fed a high fat diet mimicking the fatty acid composition of a Western-style human diet. The mice became obese and developed dietary fat-induced glucose intolerance. For gene expression profiling, the small intestines were subdivided in three equal parts along the longitudinal axis. The most pronounced effects of dietary fat were detected in part 2 of the small intestine. The biological processes that were most extensively modulated on a high fat diet were related to lipid metabolism, especially β- and ω-fatty acid oxidation seemed to play an important role, cell cycle and inflammation/immune response. An additional secretome analysis revealed differentially expressed secreted proteins, such as Il18, Ffgf15, Mif, Igfbp3 and Angptl4, which might provoke systemic effects in peripheral organs by influencing their metabolic homeostasis. Furthermore, many of the dietary fat-modulated genes and biological processes in small intestine were previously already associated with obesity and/or insulin resistance. Together, the data of this exploratory study provided various leads for an essential role of the small intestine in development of obesity and/or insulin resistance. Experiment Overall Design: After a run-in period of 3 weeks on a low-fat diet, 9 weeks old mice were fed a high- (HF) or a low-fat (LF) purified diet for 2, 4, and 8 weeks (n=6 per diet, per time point). Body weight was recorded weekly and after 7 weeks of diet intervention an oral glucose tolerance test was performed. At the end of the experiment, mice were anaesthetized with a mixture of isofluorane (1.5%), nitrous oxide (70%) and oxygen (30%). The small intestines were excised and the adhering fat and pancreatic tissue were carefully removed. The small intestines were divided in three equal parts along the proximal to distal axis (SI 1, SI 2 and SI 3).