Increased Oral Detection, but Decreased Intestinal Signaling for Fats in Mice Lacking Gut Microbiota

Abstract

Germ-free (GF) mice lacking intestinal microbiota are significantly leaner than normal (NORM) control mice despite consuming more calories. The contribution of microbiota on the recognition and intake of fats is not known. Thus, we investigated the preference for, and acceptance of, fat emulsions in GF and NORM mice, and associated changes in lingual and intestinal fatty acid receptors, intestinal peptide content, and plasma levels of gut peptides. GF and NORM C57Bl/6J mice were given 48-h two-bottle access to water and increasing concentrations of intralipid emulsions. Gene expression of the lingual fatty acid translocase CD36 and protein expression of intestinal satiety peptides and fatty-acid receptors from isolated intestinal epithelial cells were determined. Differences in intestinal enteroendocrine cells along the length of the GI tract were quantified. Circulating plasma satiety peptides reflecting adiposity and biochemical parameters of fat metabolism were also examined. GF mice had an increased preference and intake of intralipid relative to NORM mice. This was associated with increased lingual CD36 (P<0.05) and decreased intestinal expression of fatty acid receptors GPR40 (P<0.0001), GPR41 (P<0.0001), GPR43 (P<0.05), and GPR120 (P<0.0001) and satiety peptides CCK (P<0.0001), PYY (P<0.001), and GLP-1 (P<0.001). GF mice had fewer enteroendocrine cells in the ileum (P<0.05), and more in the colon (P<0.05), relative to NORM controls. Finally, GF mice had lower levels of circulating leptin and ghrelin (P<0.001), and altered plasma lipid metabolic markers indicative of energy deficits. Increased preference and caloric intake from fats in GF mice are associated with increased oral receptors for fats coupled with broad and marked decreases in expression of intestinal satiety peptides and fatty-acid receptors.

Replication of Obesity and Associated Signaling Pathways Through Transfer of Microbiota From Obese-Prone Rats

“…Gut microbiota modulate expression of intestinal nutrient receptors (7,11), and here we demonstrate that obesityassociated differences in GPRs were replicated in GF recipient mice, affecting the ability of enteroendocrine cells to sense and respond to intestinal nutrients. In line with this, intestinal and circulating satiety peptide levels were both reduced in OP and CVOP animals in addition to reduced L-cell number.…”

“…Animals were housed individually in a temperaturecontrolled vivarium with 12:12-h light/dark cycle (lights on at 0700). Starting at 8 weeks of age, rats were fed a HF diet (4.2 kcal/g; D12334B; Research Diets, New Brunswick, NJ) for 12 weeks, until sacrifice (11). Additional OP (n = 5) and OR (n = 4) rats, kept in the same housing conditions, were maintained on chow throughout and used for microbiota analysis.…”

“…For all experiments, protein and RNA extraction, and subsequent Western blotting and quantitative (q)PCR were performed as previously described (11). Briefly, RNA was extracted by using TRiZol, quantified, 10 mg RNA was reverse transcribed, and cDNA was diluted fivefold for qRT-PCR using TaqMan gene expression assays (Applied Biosystems).…”

The Microbiota, the Gut and the Brain in Eating and Alcohol Use Disorders: A ‘Ménage à Trois’?

“…Gut bacteria perform host metabolic functions, facilitate energy extraction from food, increase nutrient availability (Backhed et al, 2005) and alter taste receptors (Duca et al, 2012).…”

Neuropeptides and the Microbiota-Gut-Brain Axis

“…Emerging evidence indicates that this applies to ghrelin [55,56], cholecystokinin [56] as well as leptin [56]. In addition, germfree mice have a smaller number of enteroendocrine cells than conventionally colonized animals [56].…”