Elsevier

Physiology & Behavior

Volume 173, 1 May 2017, Pages 305-317
Physiology & Behavior

Diet-driven microbiota dysbiosis is associated with vagal remodeling and obesity

https://doi.org/10.1016/j.physbeh.2017.02.027Get rights and content

Highlights

  • High sugar diets induce gut microbiota dysbiosis.

  • High sugar diets induce gut inflammation.

  • High sugar diets trigger remodeling of gut-brain axis.

  • High sugar diets lead to an increase in body fat mass.

Abstract

Obesity is one of the major health issues in the United States. Consumption of diets rich in energy, notably from fats and sugars (high-fat/high-sugar diet: HF/HSD) is linked to the development of obesity and a popular dietary approach for weight loss is to reduce fat intake. Obesity research traditionally uses low and high fat diets and there has been limited investigation of the potential detrimental effects of a low-fat/high-sugar diet (LF/HSD) on body fat accumulation and health. Therefore, in the present study, we investigated the effects of HF/HSD and LF/HSD on microbiota composition, gut inflammation, gut-brain vagal communication and body fat accumulation. Specifically, we tested the hypothesis that LF/HSD changes the gut microbiota, induces gut inflammation and alters vagal gut-brain communication, associated with increased body fat accumulation.

Sprague-Dawley rats were fed an HF/HSD, LF/HSD or control low-fat/low-sugar diet (LF/LSD) for 4 weeks. Body weight, caloric intake, and body composition were monitored daily and fecal samples were collected at baseline, 1, 6 and 27 days after the dietary switch. After four weeks, blood and tissues (gut, brain, liver and nodose ganglia) were sampled. Both HF/HSD and LF/HSD-fed rats displayed significant increases in body weight and body fat compared to LF/LSD-fed rats. 16S rRNA sequencing showed that both HF/HSD and LF/HSD-fed animals exhibited gut microbiota dysbiosis characterized by an overall decrease in bacterial diversity and an increase in Firmicutes/Bacteriodetes ratio. Dysbiosis was typified by a bloom in Clostridia and Bacilli and a marked decrease in Lactobacillus spp. LF/HSD-fed animals showed a specific increase in Sutterella and Bilophila, both Proteobacteria, abundances of which have been associated with liver damage. Expression of pro-inflammatory cytokines, such as IL-6, IL-1β and TNFα, was upregulated in the cecum while levels of tight junction protein occludin were downregulated in both HF/HSD and LF/HSD fed rats. HF/HSD and LF/HSD-fed rats also exhibited an increase in cecum and serum levels of lipopolysaccharide (LPS), a pro-inflammatory bacterial product. Immunofluorescence revealed the withdrawal of vagal afferents from the gut and at their site of termination the nucleus of the solitary tract (NTS) in both the HF/HSD and LF/HSD rats. Moreover, there was significant microglia activation in the nodose ganglia, which contain the vagal afferent neuron cell bodies, of HF/HSD and LF/HSD rats. Taken together, these data indicate that, similar to HF/HSD, consumption of an LF/HSD induces dysbiosis of gut microbiota, increases gut inflammation and alters vagal gut-brain communication. These changes are associated with an increase in body fat accumulation.

Introduction

Obesity has reached epidemic proportion in Western countries, including the United States [1]. Evidence suggests that consumption of an energy-dense high-fat/high-sugar diet (HF/HSD) promotes excessive weight gain and that there is a direct relationship between the amount of dietary fat and the degree of obesity [2]. Consequently, lowering dietary fat intake has been considered one of the best approaches for weight management. However, a growing body of evidence has been pointing to its inadequacy for weight loss or disease prevention [3], [4]. Interestingly, many commercial low-fat foods are high in sugar and refined carbohydrates [5] and increased intake of sugars, especially fructose has been linked to increased body fat accumulation and obesity [6].

There is evidence that the gut microbiota plays a role in obesity [7]. In humans and animal models, changes in diet composition can rapidly trigger changes in gut microbiota composition [8], [9]. Interestingly, colonization of germ-free (GF) animals with either a “lean” or an “obese” microbiota leads to a recapitulation of the donor phenotype, identifying the gut microbiota as a potential driver of obesity [10]. The gut microbiota impacts the host metabolism and notably affects energy harvest and fat storage [8], [10] as well as inflammatory status [10], [11]. Consumption of HF/HSD has been associated with increased production of bacterial pro-inflammatory factors, such a lipopolysaccharide (LPS, a breakdown product of the outer membrane of Gram-negative bacteria) [7], [11]. Moreover, diet-driven gut inflammation results in impairment in the gut epithelial barrier leading to enhanced LPS uptake into the plasma [7], [12]. An increase in circulating LPS, also called metabolic endotoxemia, can trigger systemic inflammation, impair liver function, alter food intake [12] and promote body fat accumulation [11], [12]. Interestingly, LPS has been shown in culture to activate vagal afferent neurons [13] and chronic treatment with low doses of LPS results in NG inflammation and impairs vagal satiety signaling [12].

Gut-originating peptides signal via the vagus nerve to control meal initiation and termination [14], [15]. Disruption of vagal afferent signaling is sufficient to drive obesity in a diet-induced rat obesity model [13]. Therefore, microbiota-mediated dysregulation of gut-brain vagal communication might contribute to the pathogenesis of obesity and its related diseases.

In the present study, we investigated the influence of diets rich in sugars, with different fat contents, on microbiota composition and gut-brain axis inflammation. Results show that regardless of fat contents, diets rich in sugars promote gut microbiota dysbiosis, induce gut inflammation, increase gut permeability, and alter vagal gut-brain communication when compared to control chow diet.

Section snippets

Animals and diet

Male Sprague-Dawley rats (6 weeks old; Envigo, Indianapolis, IN) were housed in individual plastic cages in a temperature-controlled vivarium with ad libitum access to food and water. Rats were maintained on a 12-h light/dark schedule and habituated to laboratory conditions for one week before their diet was changed. All animal procedures were approved by the University of Georgia Institutional Animal Care and Use Committee and conformed to National Institutes of Health guidelines for the care

Consumption of diets rich in sugars can promote obesity

We determined the animals' body weight, body fat mass, and lean mass at baseline and throughout the four-week feeding study. As expected, there were no significant differences in body weight and body composition between groups at baseline (Fig. 1A). However, body weights of the LF/HSD and HF/HSD fed rats were significantly increased after 4 weeks on their respective diets when compared to the LF/LSD control rats (Fig. 1A). The HF/HSD fed animals weighed significantly more than the LF/LSD after

Conclusion

Summarizing the present data and considering our previous observations, we propose that ingestion of an HSD leads to changes in gut microbiota, which, possibly via an increase in LPS and inflammatory cytokines leads to withdrawal of vagal innervation in the gut and hindbrain. Dysbiosis-driven gastrointestinal inflammation could lead to an increase in gut permeability allowing passage of LPS and other pro-inflammatory signals from the lumen to the lamina propria. These pro-inflammatory products

Conflict of interest statement

All authors declare that there are no conflicts of interest.

The following are the supplementary data related to this article.

. Rarefaction curve by diet group and experimental time point. Data are shown as means for each group/time and indicate > 120,000 sequences and > 1000 OTUs per sample on average.

. Heatmap with dendrogram, prepared using Pearson distance measure and Ward clustering algorithm, shows all LF/LSD grouped with baseline LF/HSD (blue) and baseline HF/HSD (red) at

Acknowledgments

This research is supported by grant 5R01DC013904 from the National Institute of Health. The authors thank Brent Joseph Gawey, Mariam Ahmed, Jeremy Alan Long, and Rebecca Kirkland for their valuable time and useful contribution to complete this manuscript.

References (79)

  • H. Li et al.

    Binding of the isolectin I-B4 from Griffonia simplicifolia to the general visceral afferents in the vagus nerve: a light- and electron-microscope study in the rat

    Neurosci. Lett.

    (1997)
  • H. Wang et al.

    Transganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons

    Neuroscience

    (1994)
  • M. Covasa et al.

    Rats maintained on high-fat diets exhibit reduced satiety in response to CCK and bombesin

    Peptides

    (1998)
  • T.J. Little et al.

    Modulation by high-fat diets of gastrointestinal function and hormones associated with the regulation of energy intake: implications for the pathophysiology of obesity

    Am. J. Clin. Nutr.

    (2007)
  • C.J. Henry et al.

    Peripheral lipopolysaccharide (LPS) challenge promotes microglial hyperactivity in aged mice that is associated with exaggerated induction of both pro-inflammatory IL-1beta and anti-inflammatory IL-10 cytokines

    Brain Behav. Immun.

    (2009)
  • G. Paulino et al.

    Adaptation of lipid-induced satiation is not dependent on caloric density in rats

    Physiol. Behav.

    (2008)
  • J.E. Beilharz et al.

    The effect of short-term exposure to energy-matched diets enriched in fat or sugar on memory, gut microbiota and markers of brain inflammation and plasticity

    Brain Behav. Immun.

    (2016)
  • C. Erridge et al.

    A high-fat meal induces low-grade endotoxemia: evidence of a novel mechanism of postprandial inflammation

    Am. J. Clin. Nutr.

    (2007)
  • P.C. Kashyap et al.

    Complex interactions among diet, gastrointestinal transit, and gut microbiota in humanized mice

    Gastroenterology

    (2013)
  • C.C. Horn et al.

    Role of vagal afferent innervation in feeding and brain Fos expression produced by metabolic inhibitors

    Brain Res.

    (2001)
  • Y. Konishi et al.

    L-Ornithine intake affects sympathetic nerve outflows and reduces body weight and food intake in rats

    Brain Res. Bull.

    (2015)
  • C. Liu et al.

    PPARgamma in vagal neurons regulates high-fat diet induced thermogenesis

    Cell Metab.

    (2014)
  • E.A. Finkelstein et al.

    Annual medical spending attributable to obesity: payer-and service-specific estimates

    Health Aff. (Millwood)

    (2009)
  • A. Golay et al.

    The role of dietary fat in obesity

    Int. J. Obes. Relat. Metab. Disord.

    (1997)
  • E.L. Melanson et al.

    The relationship between dietary fat and fatty acid intake and body weight, diabetes, and the metabolic syndrome

    Ann. Nutr. Metab.

    (2009)
  • B.V. Howard et al.

    Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification trial

    JAMA

    (2006)
  • B.J. Rolls et al.

    Is the low-fat message giving people a license to eat more?

    J. Am. Coll. Nutr.

    (1997)
  • J.J. DiNicolantonio et al.

    Added sugars drive nutrient and energy deficit in obesity: a new paradigm

    Open Heart

    (2016)
  • P.D. Cani et al.

    Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice

    Diabetes

    (2008)
  • P.J. Turnbaugh et al.

    An obesity-associated gut microbiome with increased capacity for energy harvest

    Nature

    (2006)
  • L.A. David et al.

    Diet rapidly and reproducibly alters the human gut microbiome

    Nature

    (2014)
  • F. Backhed et al.

    The gut microbiota as an environmental factor that regulates fat storage

    Proc. Natl. Acad. Sci. U. S. A.

    (2004)
  • P.D. Cani et al.

    Metabolic endotoxemia initiates obesity and insulin resistance

    Diabetes

    (2007)
  • G. de Lartigue et al.

    Leptin resistance in vagal afferent neurons inhibits cholecystokinin signaling and satiation in diet induced obese rats

    PLoS ONE

    (2012)
  • C.A. Campos et al.

    CCK-induced reduction of food intake and hindbrain MAPK signaling are mediated by NMDA receptor activation

    Endocrinology

    (2012)
  • B. Kunnecke et al.

    Quantitative body composition analysis in awake mice and rats by magnetic resonance relaxometry

    Obes. Res.

    (2004)
  • D. Arndt et al.

    METAGENassist: a comprehensive web server for comparative metagenomics

    Nucleic Acids Res.

    (2012)
  • N. Segata et al.

    Toward an efficient method of identifying core genes for evolutionary and functional microbial phylogenies

    PLoS ONE

    (2011)
  • N. Segata et al.

    Metagenomic biomarker discovery and explanation

    Genome Biol.

    (2011)
  • Cited by (173)

    View all citing articles on Scopus
    View full text