Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome

We have investigated the interrelationship between diet, gut microbial ecology, and energy balance using a mouse model of obesity produced by consumption of a prototypic Western diet. Diet-induced obesity (DIO) produced a bloom in a single uncultured clade within the Mollicutes class of the Firmicutes, which was diminished by subsequent dietary manipulations that limit weight gain. Microbiota transplantation from mice with DIO to lean germ-free recipients promoted greater fat deposition than transplants from lean donors. Metagenomic and biochemical analysis of the gut microbiome together with sequencing and metabolic reconstructions of a related human gut-associated Mollicute (Eubacterium dolichum) revealed features that may provide a competitive advantage to members of the bloom in the Western diet nutrient milieu, including import and processing of simple sugars. Our study illustrates how combining comparative metagenomics with gnotobiotic mouse models and specific dietary manipulations can disclose the niches of previously uncharacterized members of the gut microbiota.     

哺乳期过度喂养对幼鼠肥胖和肠道菌群结构的影响

目的 研究哺乳期过度喂养对幼鼠肠道细菌组成的影响以及肠道细菌与哺乳期过度喂养导致的幼年肥胖的相关性.方法 将正常出生体重的4日龄雄性ICR仔鼠分为正常喂养组(NF组,每8只由1只母鼠喂养)和哺乳期过度喂养组(OF组,每4只由1只母鼠喂养),哺乳至3周龄时,对仔鼠进行口服糖耐量试验(OGTT),称量体重、各种器官和脂肪组织的重量,用基于细菌16S rRNA基因的变性梯度凝胶电泳(DGGE)和实时定量PCR分析仔鼠的粪便细菌组成,对细菌类群数量与表型数据进行相关分析.结果 OF组仔鼠从10日龄起体重显著高于NF组,3周龄时附睾和肾周脂肪垫重量显著高于NF组,两组仔鼠的空腹血糖以及OGTT血糖曲线下面积比较差异无统计学意义.对DGGE图谱的主成分分析表明两组仔鼠的菌群结构比较差异有统计学意义.定量PCR显示,OF组仔鼠粪便中产生内毒素的肠杆菌科细菌和产生破坏肠屏障功能的H2S的硫酸盐还原菌的数量显著高于NF组,而双歧杆菌、乳杆菌和丁酸盐产生菌的数量在两组仔鼠之间差异无统计学意义.粪便硫酸盐还原菌的数量与内脏脂肪的重量显著正相关.结论 哺乳期过度喂养增加了肠道中肠杆菌科细菌和硫酸盐还原菌的数量,这些细菌的增加与仔鼠幼年期肥胖相关.     

Diet-induced obesity in rats leads to a decrease in sperm motility

Background  

Obesity is rapidly becoming a worldwide epidemic that affects children and adults. Some studies have shown a relationship between obesity and infertility, but until now it remains controversial. Thus, the aim of the present study was to investigate the effect of high-fat diet-induced obesity on male reproductive parameters.     

Diarrhea in young children from low-income countries leads to large-scale alterations in intestinal microbiota composition

Background

Diarrheal diseases continue to contribute significantly to morbidity and mortality in infants and young children in developing countries. There is an urgent need to better understand the contributions of novel, potentially uncultured, diarrheal pathogens to severe diarrheal disease, as well as distortions in normal gut microbiota composition that might facilitate severe disease.

Results

We use high throughput 16S rRNA gene sequencing to compare fecal microbiota composition in children under five years of age who have been diagnosed with moderate to severe diarrhea (MSD) with the microbiota from diarrhea-free controls. Our study includes 992 children from four low-income countries in West and East Africa, and Southeast Asia. Known pathogens, as well as bacteria currently not considered as important diarrhea-causing pathogens, are positively associated with MSD, and these include Escherichia/Shigella, and Granulicatella species, and Streptococcus mitis/pneumoniae groups. In both cases and controls, there tend to be distinct negative correlations between facultative anaerobic lineages and obligate anaerobic lineages. Overall genus-level microbiota composition exhibit a shift in controls from low to high levels of Prevotella and in MSD cases from high to low levels of Escherichia/Shigella in younger versus older children; however, there was significant variation among many genera by both site and age.

Conclusions

Our findings expand the current understanding of microbiota-associated diarrhea pathogenicity in young children from developing countries. Our findings are necessarily based on correlative analyses and must be further validated through epidemiological and molecular techniques.     

Responses of gut microbiota to diet composition and weight loss in lean and obese mice

Maintenance of a reduced body weight is accompanied by a decrease in energy expenditure beyond that accounted for by reduced body mass and composition, as well as by an increased drive to eat. These effects appear to be due--in part--to reductions in circulating leptin concentrations due to loss of body fat. Gut microbiota have been implicated in the regulation of body weight. The effects of weight loss on qualitative aspects of gut microbiota have been studied in humans and mice, but these studies have been confounded by concurrent changes in diet composition, which influence microbial community composition. We studied the impact of 20% weight loss on the microbiota of diet-induced obese (DIO: 60% calories fat) mice on a high-fat diet (HFD). Weight-reduced DIO (DIO-WR) mice had the same body weight and composition as control (CON) ad-libitum (AL) fed mice being fed a control diet (10% calories fat), allowing a direct comparison of diet and weight-perturbation effects. Microbial community composition was assessed by pyrosequencing 16S rRNA genes derived from the ceca of sacrificed animals. There was a strong effect of diet composition on the diversity and composition of the microbiota. The relative abundance of specific members of the microbiota was correlated with circulating leptin concentrations and gene expression levels of inflammation markers in subcutaneous white adipose tissue in all mice. Together, these results suggest that both host adiposity and diet composition impact microbiota composition, possibly through leptin-mediated regulation of mucus production and/or inflammatory processes that alter the gut habitat.     

Diet-induced obesity leads to the development of leptin resistance in vagal afferent neurons

Ingestion of high-fat, high-calorie diets is associated with hyperphagia, increased body fat, and obesity. The mechanisms responsible are currently unclear; however, altered leptin signaling may be an important factor. Vagal afferent neurons (VAN) integrate signals from the gut in response to ingestion of nutrients and express leptin receptors. Therefore, we tested the hypothesis that leptin resistance occurs in VAN in response to a high-fat diet. Sprague-Dawley rats, which exhibit a bimodal distribution of body weight gain, were used after ingestion of a high-fat diet for 8 wk. Body weight, food intake, and plasma leptin levels were measured. Leptin signaling was determined by immunohistochemical localization of phosphorylated STAT3 (pSTAT3) in cultured VAN and by quantifaction of pSTAT3 protein levels by Western blot analysis in nodose ganglia and arcuate nucleus in vivo. To determine the mechanism of leptin resistance in nodose ganglia, cultured VAN were stimulated with leptin alone or with lipopolysaccharide (LPS) and SOCS-3 expression measured. SOCS-3 protein levels in VAN were measured by Western blot following leptin administration in vivo. Leptin resulted in appearance of pSTAT3 in VAN of low-fat-fed rats and rats resistant to diet-induced obesity but not diet-induced obese (DIO) rats. However, leptin signaling was normal in arcuate neurons. SOCS-3 expression was increased in VAN of DIO rats. In cultured VAN, LPS increased SOCS-3 expression and inhibited leptin-induced pSTAT3 in vivo. We conclude that VAN of diet-induced obese rats become leptin resistant; LPS and SOCS-3 may play a role in the development of leptin resistance.     

肥胖孕妇肠道菌群与子代肥胖的相关性

妊娠期肥胖发生率在世界范围内呈上升趋势,成为影响人类健康的公共卫生问题。肥胖母亲肠道菌群失调导致婴儿早期定植菌群异常,而婴儿早期菌群定植情况与其日后生长发育密切相关,容易导致成年后出现肥胖、胰岛素抵抗、代谢综合征等疾病。因此针对肥胖孕妇肠道菌群分析,以及婴儿肠道菌群及生长发育的分析,对于孕妇孕期管理、健康宣教提高国民整体身体素质具有重要意义。     

Alterations in the diversity and composition of mice gut microbiota by lytic or temperate gut phage treatment

Phages, the most abundant species in the mammalian gut, have numerous advantages as biocontrol agent over antibiotics. In this study, mice were orally treated with the lytic gut phage PA13076 (group B), the temperate phage BP96115 (group C), no phage (group A), or streptomycin (group D) over 31 days. At the end of the experiment, fecal microbiota diversity and composition was determined and compared using high-throughput sequencing of the V3–V4 hyper-variable region of the 16S rRNA gene and virus-like particles (VLPs) were quantified in feces. There was high diversity and richness of microbiota in the lytic and temperate gut phage-treated mice, with the lytic gut phage causing an increased alpha diversity based on the Chao1 index (p < 0.01). However, the streptomycin treatment reduced the microbiota diversity and richness (p = 0.0299). Both phage and streptomycin treatments reduced the abundance of Bacteroidetes at the phylum level (p < 0.01) and increased the abundance of the phylum Firmicutes. Interestingly, two beneficial genera, Lactobacillus and Bifidobacterium, were enhanced by treatment with the lytic and temperate gut phage. The abundance of the genus Escherichia/Shigella was higher in mice after temperate phage administration than in the control group (p < 0.01), but lower than in the streptomycin group. Moreover, streptomycin treatment increased the abundance of the genera Klebsiella and Escherichia/Shigella (p < 0.01). In terms of the gut virome, fecal VLPs did not change significantly after phage treatment. This study showed that lytic and temperate gut phage treatment modulated the composition and diversity of gut microbiota and the lytic gut phage promoted a beneficial gut ecosystem, while the temperate phage may promote conditions enabling diseases to occur.

     

肠道微生物对肥胖影响

肠道微生物是哺乳动物最密集的微生物群落,也是最多样化的微生物群落之一。随着宏基因组学的不断发展,肠道微生物成为热门的研究领域。肠道微生物具有保护和代谢等功能,在胰岛素抵抗和肥胖等疾病中发挥重要作用。本文介绍了肠道微生物及其代谢物通过调节食欲、神经递质合成分泌、炎性反应进而调节肥胖,探讨了肠道微生物的影响因素,展望了肠道微生物对治疗人类肥胖的应用前景。     

Human gut microbiota and bifidobacteria: from composition to functionality

The human gut is the home of an estimated 10(18) bacterial cells, many of which are uncharacterized or unculturable. Novel culture-independent approaches have revealed that the majority of the human gut microbiota consists of members of the phyla Bacteroidetes and Firmicutes. Nevertheless the role of bifidobacteria in gut ecology illustrates the importance of Actinomycetes and other Actinobacteria that may be underestimated. The human gut microbiota represents an extremely complex microbial community the collective genome of which, the microbiome, encodes functions that are believed to have a significant impact on human physiology. The microbiome is assumed to significantly enhance the metabolism of amino and glycan acids, the turnover of xenobiotics, methanogenesis and the biosynthesis of vitamins. Co-colonisation of the gut commensals Bifidobacterium longum and Bacteroides thetaiotaomicron in a murine model system revealed that the presence of bifidobacteria induced an expansion in the diversity of polysaccharides targeted for degradation by Bacteroides and also induced host genes involved in innate immunity. In addition, comparative analysis of individual human gut microbiomes has revealed various strategies that the microbiota use to adapt to the intestinal environment while also pointing to the existence of a distinct infant and adult-type microbiota.     

Diet-induced obesity and hepatic gene expression alterations in C57BL/6J and ICAM-1-deficient mice

The effects of high-fat feeding on the development of obesity were evaluated in intercellular adhesion molecule-1 (ICAM-1) knockout and C57BL/6J (B6) male mice fed a high-fat diet for < or =50 days. Serum and tissues were collected at baseline and after 1, 11, and 50 days on the diet. After 11 days on the diet, ICAM-1-deficient, but not B6, mice developed fatty livers and showed a significant increase in inguinal fat pad weight. At day 50, ICAM-1-deficient mice weighed less, and their adiposity index and circulating leptin levels were significantly lower than those of B6 controls. To better understand the early differential response to the diet, liver gene expression was analyzed at three time points by use of Affymetrix GeneChips. In both strains, a similar pattern of gene expression was detected in response to the high-fat diet. However, sterol regulatory element-binding protein-1, apolipoprotein A4, and adipsin mRNAs were significantly induced in ICAM-1-deficient livers, suggesting that these genes and their associated pathways may be involved in the acute diet response observed in the knockout mice.     

肥胖相关的肠道微生物群落结构动力学与功能解析研究

肥胖及相关的慢性代谢性疾病近年来已经成为威胁全球的公共健康问题。越来越多的证据表明,在宿主的营养、免疫和代谢中有不可替代的作用的肠道菌群不仅可以通过调节宿主脂肪吸收存储相关的基因,影响后者的能量平衡,更重要的是其结构失调导致宿主循环系统中内毒素增加,诱发慢性、低水平炎症,导致肥胖和胰岛素抵抗。运用微生物分子生态学、元基因组学和代谢组学的方法,揭示与代谢性疾病相关的菌群结构失调,并鉴定出相关的特定细菌类群及其功能,使得通过以菌群为靶点的营养干预手段防止慢性代谢性疾病成为可能,将带来代谢性疾病预防和控制策略的革命性的变化。     

肠道微生物菌群对脑及行为的影响

肠道微生物菌群组成的变化对正常生理的影响及其在疾病中的作用逐渐成为研究热点。肠道微生物菌群通过脑肠轴影响宿主生理学的各个方面,包括脑-肠交流、脑功能甚至行为。对无菌动物、被致病细菌感染的、使用益生菌或用抗生素药物的动物研究表明,肠道微生物菌群可以调节宿主焦虑样症状及行为。研究表明对肠道微生物菌群的调节可能是治疗复杂中枢神经系统失调症的新策略。     

Diet-induced obesity increases NF-κB signaling in reporter mice

The nuclear factor (NF)-κB is a primary regulator of inflammatory responses and may be linked to pathology associated with obesity. We investigated the progression of NF-κB activity during a 12-week feeding period on a high-fat diet (HFD) or a low-fat diet (LFD) using NF-κB luciferase reporter mice. In vivo imaging of luciferase activity showed that NF-κB activity was higher in the HFD mice compared with LFD-fed mice. Thorax region of HFD females displayed fourfold higher activity compared with LFD females, while no such increase was evident in males. In male HFD mice, abdominal NF-κB activity was increased twofold compared with the LFD males, while females had unchanged NF-κB activity in the abdomen by HFD. HFD males, but not females, exhibited evident glucose intolerance during the study. In conclusion, HFD increased NF-κB activity in both female and male mice. However, HFD differentially increased activity in males and females. The moderate increase in abdomen of male mice may be linked to glucose intolerance.     

Molecular analysis of gut microbiota in obesity among Indian individuals

Obesity is a consequence of a complex interplay between the host genome and the prevalent obesogenic factors among the modern communities. The role of gut microbiota in the pathogenesis of the disorder was recently discovered; however, 16S-rRNA-based surveys revealed compelling but community-specific data. Considering this, despite unique diets, dietary habits and an uprising trend in obesity, the Indian counterparts are poorly studied. Here, we report a comparative analysis and quantification of dominant gut microbiota of lean, normal, obese and surgically treated obese individuals of Indian origin. Representative gut microbial diversity was assessed by sequencing fecal 16S rRNA libraries for each group (n=5) with a total of over 3000 sequences. We detected no evident trend in the distribution of the predominant bacterial phyla, Bacteroidetes and Firmicutes. At the genus level, the bacteria of genus Bacteroides were prominent among the obese individuals, which was further confirmed by qPCR (P less than 0.05). In addition, a remarkably high archaeal density with elevated fecal SCFA levels was also noted in the obese group. On the contrary, the treated-obese individuals exhibited comparatively reduced Bacteroides and archaeal counts along with reduced fecal SCFAs. In conclusion, the study successfully identified a representative microbial diversity in the Indian subjects and demonstrated the prominence of certain bacterial groups in obese individuals; nevertheless, further studies are essential to understand their role in obesity.     

High-fat diet alters gut microbiota physiology in mice

The intestinal microbiota is known to regulate host energy homeostasis and can be influenced by high-calorie diets. However, changes affecting the ecosystem at the functional level are still not well characterized. We measured shifts in cecal bacterial communities in mice fed a carbohydrate or high-fat (HF) diet for 12 weeks at the level of the following: (i) diversity and taxa distribution by high-throughput 16S ribosomal RNA gene sequencing; (ii) bulk and single-cell chemical composition by Fourier-transform infrared- (FT-IR) and Raman micro-spectroscopy and (iii) metaproteome and metabolome via high-resolution mass spectrometry. High-fat diet caused shifts in the diversity of dominant gut bacteria and altered the proportion of Ruminococcaceae (decrease) and Rikenellaceae (increase). FT-IR spectroscopy revealed that the impact of the diet on cecal chemical fingerprints is greater than the impact of microbiota composition. Diet-driven changes in biochemical fingerprints of members of the Bacteroidales and Lachnospiraceae were also observed at the level of single cells, indicating that there were distinct differences in cellular composition of dominant phylotypes under different diets. Metaproteome and metabolome analyses based on the occurrence of 1760 bacterial proteins and 86 annotated metabolites revealed distinct HF diet-specific profiles. Alteration of hormonal and anti-microbial networks, bile acid and bilirubin metabolism and shifts towards amino acid and simple sugars metabolism were observed. We conclude that a HF diet markedly affects the gut bacterial ecosystem at the functional level.     

Impact of the factors shaping gut microbiota on obesity

Obesity is considered as a risk factor for chronic health diseases such as heart diseases, cancer and diabetes 2. Reduced physical activities, lifestyle, poor nutritional diet and genetics are among the risk factors associated with the development of obesity. In recent years, several studies have explored the link between the gut microbiome and the progression of diseases including obesity, with the shift in microbiome abundance and composition being the main focus. The alteration of gut microbiome composition affects both nutrients metabolism and specific gene expressions, thereby disturbing body physiology. Specifically, the abundance of fibre-metabolizing microbes is associated with weight loss and that of protein and fat-metabolizing bacteria with weight gain. Various internal and external factors such as genetics, maternal obesity, mode of delivery, breastfeeding, nutrition, antibiotic use and the chemical compounds present in the environment are known to interfere with the richness of the gut microbiota (GM), thus influencing weight gain/loss and ultimately the development of obesity. However, the effectiveness of each factor in potentiating the shift in microbes’ abundance to result in significant changes that can lead to obesity is not yet clear. In this review, we will highlight the factors involved in shaping GM, their influence on obesity and possible interventions. Understanding the influence of these factors on the diversity of the GM and how to improve their effectiveness on disease conditions could be keys in the treatment of metabolic diseases.     

Fatty acid overproduction by gut commensal microbiota exacerbates obesity

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Liraglutide modulates gut microbiota and reduces NAFLD in obese mice

Metabolic disorders such as insulin resistance and diabetes are associated with obesity and nonalcoholic fatty liver disease (NAFLD). The aggressive form of a fatty liver disease may progress to cirrhosis and hepatocellular carcinoma. Furthermore, recent studies demonstrated that there is a dysbiosis in the gut microbiota associated with early stages of metabolic disease. Therefore, the identification and repurposing of drugs already used to treat insulin resistance may be an excellent option for other disorders. We evaluated the effect of liraglutide on obesity, NAFLD and gut microbiota modulation in two different animal models of obesity: the ob/ob mice and the high-fat diet (HFD)-fed mice. Liraglutide treatment induced significant weight loss in both obesity models, showed improvements in glycemic parameters and reduced inflammatory cell infiltration in the cecum and the liver. In ob/ob mice, the liraglutide treatment was able to reduce the accumulation of liver fat by 78% and reversed steatosis in the HFD mice. The gut microbiota analysis showed that liraglutide changed the overall composition as well as the relative abundance of weight-relevant phylotypes such as a reduction of Proteobacteria and an increase of Akkermansia muciniphila in the treated HFD group. We show that liraglutide can lead to weight loss and gut microbiota modulations, and is associated with an improvement of NAFLD. Furthermore, by generating a profile of the intestinal microbiota, we compiled a list of potential bacterial targets that may modulate metabolism and induce a metabolic profile that is considered normal or clinically controlled.