| The public health burden of obesity and metabolic disorders increases rapidly worldwide.The prevalence of these diseases is considered mainly due to the change of environmental factors,such as diet and lifestyles.Growing evidences have indicated that the gut microbiota is an important contributor to the development of these diseases.Clinical trials and animal models have demonstrated that gut microbiota targeted diet intervention can alleviate obesity and related metabolic disorders.In our previous clinical intervention trial,we found that a diet consisting of whole grains,traditional Chinese medicinal foods and prebiotics significantly reduced body weights and improved clinical parameters of volunteers with obesity.Particularly,a volunteer(weight 174.8 kg,body mass index 58.8 kg m-2)had lost 51.4 kg and recovered from hyperglycemia and hypertension at the end of 23-week trial.Meanwhile,Enterobacter,a genus of opportunistic pathogens,decreased from 35% relative abundance of gut bacteria to non-detectable level.Enterobacter cloacae B29,an Enterobacter strain from this volunteer,was then isolated and transplanted to germfree mice.It was found that B29 combined with high fat diet(HFD)resulted in obesity and insulin resistance in germfree mice whereas B29 or high fat diet alone did not,confirming the causative role of B29 in metabolic deteriorations of the germfree mice.As a LPS(lipopolysaccharide)-producing bacterium,B29 provided endotoxin load to the germfree mice that the B29+HFD group displayed the highest increase in systemic inflammation with the greatest increase in the serum amyloid A protein levels and the greatest decrease in adiponectin secretion.However,analysis with qRT-PCR(Reverse transcription-quantitative polymerase chain reaction)and microarray techniques found that the liver and the epididymal fat pad had significantly increased genes involved in inflammation while the ileum had not,suggesting the inflammation was local.The previous study did not investigate colon,which is an important immune organ,the main site of microbial fermentation with the highest bacterial concentrations and an active site of metabolism.Many studies have tried to understand the underlying mechanism of how diet affects gut microbiota and the interactions between microbiota and the host through 16 S rRNA based platform or metagenomic technology.The former is usually used to trace the change of the microbiota structure and the latter is to explore the function of the microbiome.In addition,some studies also have used microarray or/and qRT-PCR to investigate the gene expression of the host.However,both methods were restricted with the number and the sequencing depth of the genes detectable.A high throughput cDNA sequencing technology,mRNA-Seq,which is more powerful in characterizing transcript sequences and gene expressions,hence becomes an alternative candidate to provide more comprehensive information.Using deep mRNA sequencing technology,we compared different gene expression profiles in the colon samples of the germfree mice treated with/without B29 and/or high fat diet(HFD)for 16 weeks and identified 279 differential expressed genes in total,including up-regulated genes Apoa4(fold change,2.77),Ido1(2.66),Cyp4a10(7.01),and down-regulated genes Cyp2e1(0.11),Cyp26b1(0.34),Akr1b7(0.42),Adipoq(0.36),Cyp1a1(0.11),Apoa1(0.44),Npc1l1(0.37),Tff2(0.13),Apoc1(0.30),Ctla2a(0.34),Mttp(0.49),Lpl(0.48).Fifty-nine GO biological processes and five KEGG pathways,particularly the peroxisome proliferator-activated receptors(PPARs)signaling pathway,were significantly enriched in response to HFD+B29,which were mainly relevant to inflammation and the metabolism of lipid,lipoprotein and sterols.These functional changes were consistent with the developed obesity,insulin-resistance,and aggravated inflammatory conditions of the HFD+B29 mice.This work provides insight into the gene expression changes in response to HFD+B29,helping to understand the mechanism of the interactions among HFD,B29 and the germfree mice. |
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