Recent studies showed that germ-free (GF) mice are resistant to obesity when consuming a high-fat, high-carbohydrate Western diet. However, it remains unclear what mechanisms are involved in the antiobesity phenotype and whether GF mice develop insulin resistance and dyslipidemia with high-fat (HF) feeding. In the present study, we compared the metabolic consequences of HF feeding on GF and conventional (conv) C57BL/6J mice. GF mice consumed fewer calories, excreted more fecal lipids, and weighed significantly less than conv mice. GF/HF animals also showed enhanced insulin sensitivity with improved glucose tolerance, reduced fasting and nonfasting insulinemia, and increased phospho-Akt((Ser-473)) in adipose tissue. In association with enhanced insulin sensitivity, GF/HF mice had reduced plasma TNF-α and total serum amyloid A concentrations. Reduced hypercholesterolemia, a moderate accretion of hepatic cholesterol, and an increase in fecal cholesterol excretion suggest an altered cholesterol metabolism in GF/HF mice. Pronounced nucleus SREBP2 proteins and up-regulation of cholesterol biosynthesis genes indicate that enhanced cholesterol biosynthesis contributed to the cholesterol homeostasis in GF/HF mice. Our results demonstrate that fewer calorie consumption and increased lipid excretion contributed to the obesity-resistant phenotype of GF/HF mice and reveal that insulin sensitivity and cholesterol metabolism are metabolic targets influenced by the gut microbiota.

To determine the role in chemosensation of intestinal solitary cells that express taste receptors and Trpm5, we carried out a microarray study of the transcriptome of FACS-sorted transgenic mouse intestinal cells expressing enhanced green fluorescent protein (eGFP) under the control of the Trpm5 promoter and compared it with that of intestinal cells that do not express eGFP. The findings of the study are: 1) Morphology and expression of markers show that most eGFP+ cells are brush cells. 2) The majority of proteins known to be involved in taste signal transduction are expressed in the eGFP+ cells, although the isoforms are not always the same. 3) eGFP+ cells express pre- and postsynaptic markers and nerves are often found in close proximity. 4) Several genes that play a role in inflammation are expressed specifically in eGFP+ cells. Furthermore, these cells express the entire biosynthesis pathway of leucotriene C4, an eicosanoid involved in modulation of intestinal smooth muscle contraction. 5) Angiotensinogen, renin, and succinate receptor genes are expressed in the eGFP+ cells, suggesting a role in the regulation of water and sodium transport, vasomotricity, and blood pressure. These data suggest that the Trpm5-expressing cells integrate many signals, including chemical signals from ingested food, and that they may regulate several physiological functions of the gastrointestinal tract.

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Recent studies showed that germ‐free (GF) mice are resistant to obesity when consuming a high‐fat, high‐carbohydrate Western diet. However, it remains unclear what mechanisms are involved in the antiobesity phenotype and whether GF mice develop insulin resistance and dyslipidemia with high‐fat (HF) feeding. In the present study, we compared the metabolic consequences of HF feeding on GF and conventional (conv) C57BL/6J mice. GFmice consumed fewer calories, excreted more fecal lipids, and weighed significantly less than conv mice. GF/HF animals also showed enhanced insulin sensitivity with improved glucose tolerance, reduced fasting and nonfasting insuline‐mia, and increased phospho‐Akt(Ser‐473) in adipose tissue. In association with enhanced insulin sensitivity, GF/HF mice had reduced plasma TNF‐α and total serum amyloid A concentrations. Reduced hypercholes‐terolemia, a moderate accretion of hepatic cholesterol, and an increase in fecal cholesterol excretion suggest an altered cholesterol metabolism in GF/HF mice. Pronounced nucleus SREBP2 proteins and up‐regulation of cholesterol biosynthesis genes indicate that enhanced cholesterol biosynthesis contributed to the cholesterol homeostasis in GF/HF mice. Our results demonstrate that fewer calorie consumption and increased lipid excretion contributed to the obesity‐resistant phenotype of GF/HF mice and reveal that insulin sensitivity and cholesterol metabolism are metabolic targets influenced by the gut microbiota.— Rabot, S., Membrez, M., Bruneau, A., Gerard, P., Harach, T., Moser, M., Raymond, F., Mansourian, R., Chou. C. J. Germ‐free C57BL/6J mice are resistant to high‐fat‐diet‐induced insulin resistance and have altered cholesterol metabolism. FASEB J. 24, 4948–4959 (2010). http://www.fasebj.org