Yassine Sakar

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

Aberrations in gut microbiota are associated with metabolic disorders, including obesity. However, whether shifts in the microbiota profile during obesity are a characteristic of the phenotype or a consequence of obesogenic feeding remains elusive. Therefore, we aimed to determine differences in the gut microbiota of obese-prone (OP) and obese-resistant (OR) rats and examined the contribution of this microbiota to the behavioral and metabolic characteristics during obesity. We found that OP rats display a gut microbiota distinct from OR rats fed the same high-fat diet, with a higher Firmicutes-to-Bacteroidetes ratio and significant genera differences. Transfer of OP but not OR microbiota to germ-free (GF) mice replicated the characteristics of the OP phenotype, including reduced intestinal and hypothalamic satiation signaling, hyperphagia, increased weight gain and adiposity, and enhanced lipogenesis and adipogenesis. Furthermore, increased gut permeability through conventionalization resulted in inflammation by proinflammatory nuclear factor (NF)-κB/inhibitor of NF-κB kinase subunit signaling in adipose tissue, liver, and hypothalamus. OP donor and GF recipient animals harbored specific species from Oscillibacter and Clostridium clusters XIVa and IV that were completely absent from OR animals. In conclusion, susceptibility to obesity is characterized by an unfavorable microbiome predisposing the host to peripheral and central inflammation and promoting weight gain and adiposity during obesogenic feeding.

Decreased intestinal nutrient response in diet-induced obese rats: role of gut peptides and nutrient receptors

Background and Aims:Diet-induced obesity (DIO) is an excellent model for examining human obesity comprising both genotypic and environmental (diet) factors. Decreased responsiveness to peripheral satiety signaling may be responsible for the hyperphagia in this model. In this study, we investigated responses to nutrient-induced satiation in outbred DIO and DIO-resistant (DR) rats fed a high-energy/high-fat (HE/HF) diet as well as intestinal satiety peptide content, intestinal nutrient-responsive receptor abundance and vagal anorectic receptor expression.Methods:Outbred DIO and DR rats fed a HE/HF diet were tested for short-term feeding responses following nutrient (glucose and intralipid (IL)) gastric loads. Gene and protein expressions of intestinal satiety peptides and fatty acid-responsive receptors were examined from isolated proximal intestinal epithelial cells and cholecystokinin-1 receptor (CCK-1R) and leptin receptor (LepR) mRNA from the nodose ganglia of DIO and DR animals.Results:DIO rats were less responsive to IL- (P<0.05) but not glucose-induced suppression of food intake compared with DR rats. DIO rats exhibited decreased CCK, peptide YY (PYY) and glucagon-like peptide-1 (GLP-1; P<0.05 for each) protein expression compared with DR rats. Also, DIO rats expressed more G-protein-coupled receptor 40 (GPR40; P<0.0001), GPR41 (P<0.001) and GPR120 (P<0.01) relative to DR rats. Finally, there were no differences in mRNA expression for CCK-1R and LepR in the nodose ganglia of DIO and DR rats.Conclusions:Development of DIO may be partly due to decreased fat-induced satiation through low levels of endogenous satiety peptides, and changes in intestinal nutrient receptors.

Increased oral detection, but decreased intestinal signaling for fats in mice lacking gut microbiota.

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.

The modulatory role of high fat feeding on gastrointestinal signals in obesity

The gastrointestinal (GI) tract is a specialized sensory system that detects and responds to constant changes in nutrient- and bacterial-derived intestinal signals, thus contributing to controls of food intake. Chronic exposure to dietary fat causes morphological, physiological and metabolic changes leading to disruptions in the regulatory feeding pathways promoting more efficient fat absorption and utilization, blunted satiation signals and excess adiposity. Accumulating evidence demonstrates that impaired gastrointestinal signals following long-term high fat consumption are, at least partially, responsible for increased caloric intake. This review focuses on the role of dietary fat in modulating oral and post-oral chemosensory signaling elements responsible for lipid detection and responses, including changes in sensitivity to satiation signals, such as GLP-1, PYY and CCK and their impact on food intake and weight gain. Furthermore, the influence of the gut microbiota on mechanisms controlling energy regulation in the face of excessive fat exposure will be explored. The profound influence of dietary fats on altering complex regulatory feeding pathways can result in dysregulation of body weight and development of obesity, while restoration or manipulation of satiation signaling may prove an effective tool in prevention and treatment of obesity.

Combination of obesity and high-fat feeding diminishes sensitivity to GLP-1R agonist, Exendin-4

Gastrointestinal mechanisms involved in the suppression of appetite are compromised in obesity. Glucagon-like peptide-1 (GLP-1) is released in response to nutrients, suppresses food intake, and has been shown to play a role in regulation of energy balance. It is not known whether obese-prone (OP) rats exhibit dysfunctional GLP-1 signaling that could contribute to decreased nutrient-induced satiation and hyperphagia. Therefore, we examined the effects of exogenous intraperitoneal administration of the GLP-1R agonist, exendin-4 (Ex-4), on food intake in OP and obese-resistant (OR) rats during chow or high-energy/high-fat (HE/HF) feeding. All doses of Ex-4 effectively suppressed intake in OP and OR rats fed chow; however, during HE/HF-feeding, OP rats suppressed intake significantly less than OR rats at all Ex-4 doses tested. This was associated with downregulation of GLP-1R mRNA expression in the vagal nodose ganglia of OP rats. Furthermore, HE/HF-fed OP rats had significantly lower plasma GLP-1 levels, decreased protein levels of GLP-1 in the intestinal epithelium, and reduced number of L cells in the distal ileum. These results demonstrate that HE/HF-feeding, coupled with OP phenotype, results in reduced endogenous GLP-1 and GLP-1R activation, indicating that impaired GLP-1 signaling during obesity may exacerbate hyperphagia and weight gain.

Impact of high-fat feeding on basic helix-loop-helix transcription factors controlling enteroendocrine cell differentiation.

Impact of high-fat feeding on basic helix–loop–helix transcription factors controlling enteroendocrine cell differentiation

Preserved adiposity in the Fischer 344 rat devoid of gut microbiota

The gut microbiota is implicated in host metabolism and energy regulation. Germ‐free (GF) C57BL/6 mice display decreased adiposity, an effect associated with increased intestinal fasting‐induced adipose factor (FIAF) and decreased hepatic lipogenesis. However, whether the altered metabolism observed in the absence of gut microbiota extends to other species, commonly used to examine energy metabolism, is unknown. Thus, we used the GF Fischer 344 rat to examine adiposity and associated alterations in intestinal nutrient chemoreceptors, gut peptide levels, and FIAF expression, as well as markers of hepatic and adipose lipogenesis and adipogenesis. We found that GF rats displayed similar body weights and adiposity relative to controls. GF state was associated with up‐regulation of intestinal and hepatic FIAF, decreased expression of hepatic FAS, ACC‐1, and SREBP, and increased pAMPK and pACC. However, GF rats displayed reduced adipocyte FIAF, increased lipogenic enzymes, and decreased pAMPK, accompanied by an increase in adipocyte size. These findings show that, despite increased intestinal FIAF and reduced hepatic lipogenesis, adiposity is preserved in the Fisher 344 GF rat, unlike the C57Bl/6J GF mouse, with a shift in increased adipocyte lipogenesis. This also demonstrates that adipose, rather than intestinal, FIAF may have a more prominent role in adiposity.—Swartz, T.D., Sakar, Y., Duca, F.A., Covasa, M. Preserved adiposity in the Fischer 344 rat devoid of gut microbiota. FASEB J. 27, 1701–1710 (2013). www.fasebj.org