Publications by authors named "Michelle I Smith"

21 Publications

  • Page 1 of 1

Anti-Microbial Antibody Response is Associated With Future Onset of Crohn's Disease Independent of Biomarkers of Altered Gut Barrier Function, Subclinical Inflammation, and Genetic Risk.

Gastroenterology 2021 Jul 20. Epub 2021 Jul 20.

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, Ontario, Canada; Division of Gastroenterology & Hepatology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. Electronic address:

Background And Aims: Altered host immune reactivity to microbial antigens is hypothesized to trigger the onset of Crohn's disease (CD). We aimed to assess whether increased serum anti-microbial antibody response in asymptomatic first-degree relatives (FDRs) of CD patients is an independent risk factor for future CD development.

Methods: We measured host serum antibody response to 6 microbial antigens at enrollment (Prometheus enzyme-linked immunosorbent assay test: anti-Saccharomyces cerevisiae antibodies immunoglobulin A/immunoglobulin G, anti-OmpC, anti-A4-Fla2, anti-FlaX, anti-CBir1) and derived the sum of positive antibodies (AS). We used samples at enrollment of prospectively followed healthy FDRs from a nested case-control cohort of the Crohn's and Colitis Canada Genetics Environment Microbial Project. Those who later developed CD (n = 77) were matched 1:4 by age, sex, follow-up duration, and geographic location with control FDRs remaining healthy (n = 307). To address our research aims, we fitted a multivariable conditional logistic regression model and performed causal mediation analysis.

Results: High baseline AS (≥2) (43% of cases, 11% of controls) was associated with higher risk of developing CD (adjusted odds ratio, 6.5; 95% confidence interval, 3.4-12.7; P < .001). Importantly, this association remained significant when adjusted for markers of gut barrier function, fecal calprotectin, C-reactive protein, and CD-polygenic risk score, and in subjects recruited more than 3 years before diagnosis. Causal mediation analysis showed that the effect of high AS on future CD development is partially mediated (42%) via preclinical gut inflammation.

Conclusions: Our results suggest that increased anti-microbial antibody responses are associated with risk of future development of CD, independent of biomarkers of abnormal gut barrier function, subclinical inflammation, and CD-related genetic risks. This suggests that anti-microbial antibody responses are an early predisease event in the development of CD.
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http://dx.doi.org/10.1053/j.gastro.2021.07.009DOI Listing
July 2021

Serum Zonulin Measured by Commercial Kit Fails to Correlate With Physiologic Measures of Altered Gut Permeability in First Degree Relatives of Crohn's Disease Patients.

Front Physiol 2021 25;12:645303. Epub 2021 Mar 25.

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, ON, Canada.

Intestinal epithelial cell tight junctions (TJs) contribute to the integrity of the intestinal barrier allowing for control of the physical barrier between external antigens or bacterial products and the internal environment. Zonula occludens-1 (ZO-1) is a protein that modulates intestinal TJs, and serum levels of ZO-1 has been suggested as a biomarker of disrupted barrier function in humans. Previous studies suggested that increased intestinal permeability was associated with evidence of TJ abnormalities. However, there is limited information on the serological measurement of ZO-1 and its relation to other tests of barrier function in healthy subjects. We investigated the correlation of serum ZO-1, with physiologic measures of intestinal permeability (as the ratio of the fractional excretion of lactulose-mannitol or LMR) in a cohort of 39 healthy FDRs of Crohn's disease (CD) patients. No significant correlation was found between LMR and ZO-1 levels (2 = 0.004, < 0.71), or intestinal fatty acid binding proteins (I-FABP) (2 = 0.004, < 0.71). In conclusion, our data show that ZO-1 and I-FABP are not a marker of gut permeability as defined by LMR.
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http://dx.doi.org/10.3389/fphys.2021.645303DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8027468PMC
March 2021

Novel Fecal Biomarkers That Precede Clinical Diagnosis of Ulcerative Colitis.

Gastroenterology 2021 04 10;160(5):1532-1545. Epub 2020 Dec 10.

Farncombe Family Digestive Health Research Institute, Department of Medicine, McMaster University, Hamilton, Canada. Electronic address:

Background & Aims: Altered gut microbiota composition and function have been associated with inflammatory bowel diseases, including ulcerative colitis (UC), but the causality and mechanisms remain unknown.

Methods: We applied 16S ribosomal RNA gene sequencing, shotgun metagenomic sequencing, in vitro functional assays, and gnotobiotic colonizations to define the microbial composition and function in fecal samples obtained from a cohort of healthy individuals at risk for inflammatory bowel diseases (pre-UC) who later developed UC (post-UC) and matched healthy control individuals (HCs).

Results: Microbiota composition of post-UC samples was different from HC and pre-UC samples; however, functional analysis showed increased fecal proteolytic and elastase activity before UC onset. Metagenomics identified more than 22,000 gene families that were significantly different between HC, pre-UC, and post-UC samples. Of these, 237 related to proteases and peptidases, suggesting a bacterial component to the pre-UC proteolytic signature. Elastase activity inversely correlated with the relative abundance of Adlercreutzia and other potentially beneficial taxa and directly correlated with known proteolytic taxa, such as Bacteroides vulgatus. High elastase activity was confirmed in Bacteroides isolates from fecal samples. The bacterial contribution and functional significance of the proteolytic signature were investigated in germ-free adult mice and in dams colonized with HC, pre-UC, or post-UC microbiota. Mice colonized with or born from pre-UC-colonized dams developed higher fecal proteolytic activity and an inflammatory immune tone compared with HC-colonized mice.

Conclusions: We have identified increased fecal proteolytic activity that precedes the clinical diagnosis of UC and associates with gut microbiota changes. This proteolytic signature may constitute a noninvasive biomarker of inflammation to monitor at-risk populations that can be targeted therapeutically with antiproteases.
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http://dx.doi.org/10.1053/j.gastro.2020.12.004DOI Listing
April 2021

Associations of NOD2 polymorphisms with Erysipelotrichaceae in stool of in healthy first degree relatives of Crohn's disease subjects.

BMC Med Genet 2020 10 15;21(1):204. Epub 2020 Oct 15.

Department of Medicine, University of Toronto, Toronto, ON, Canada.

Background: Genetic analyses have identified many variants associated with the risk of inflammatory bowel disease (IBD) development. Among these variants, the ones located within the NOD2 gene have the highest odds ratio of all IBD genetic risk variants. Also, patients with Crohn's disease (CD) have been shown to have an altered gut microbiome, which might be a reflection of inflammation itself or an effect of other parameters that contribute to the risk of the disease. Since NOD2 is an intracellular pattern recognition receptor that senses bacterial peptidoglycan in the cytosol and stimulates the host immune response (Al Nabhani et al., PLoS Pathog 13:e1006177, 2017), it is hypothesized that NOD2 variants represent perfect candidates for influencing host-microbiome interactions. We hypothesized that NOD2 risk variants affect the microbiome composition of healthy first degree relative (FDR) of CD patients and thus potentially contribute to an altered microbiome state before disease onset.

Methods: Based on this, we studied a large cohort of 1546 healthy FDR of CD patients and performed a focused analysis of the association of three major CD SNPs in the coding region of the NOD2 gene, which are known to confer a 15-40-fold increased risk of developing CD in homozygous or compound heterozygous individuals.

Results: Our results show that carriers of the C allele at rs2066845 was significantly associated with an increase in relative abundance in the fecal bacterial family Erysipelotrichaceae.

Conclusions: This result suggests that NOD2 polymorphisms contribute to fecal microbiome composition in asymptomatic individuals. Whether this modulation of the microbiome influences the future development of CD remains to be assessed.
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http://dx.doi.org/10.1186/s12881-020-01115-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7566148PMC
October 2020

Increased Intestinal Permeability Is Associated With Later Development of Crohn's Disease.

Gastroenterology 2020 12 10;159(6):2092-2100.e5. Epub 2020 Aug 10.

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada. Electronic address:

Background & Aims: Increased intestinal permeability has been associated with Crohn's disease (CD), but it is not clear whether it is a cause or result of the disease. We performed a prospective study to determine whether increased intestinal permeability is associated with future development of CD.

Methods: We assessed the intestinal permeability, measured by the urinary fractional excretion of lactulose-to-mannitol ratio (LMR) at recruitment in 1420 asymptomatic first-degree relatives (6-35 years old) of patients with CD (collected from 2008 through 2015). Participants were then followed up for a diagnosis of CD from 2008 to 2017, with a median follow-up time of 7.8 years. We analyzed data from 50 participants who developed CD after a median of 2.7 years during the study period, along with 1370 individuals who remained asymptomatic until October 2017. We used the Cox proportional hazards model to evaluate time-related risk of CD based on the baseline LMR.

Results: An abnormal LMR (>0.03) was associated with a diagnosis of CD during the follow-up period (hazard ratio, 3.03; 95% CI, 1.64-5.63; P = 3.97 × 10). This association remained significant even when the test was performed more than 3 years before the diagnosis of CD (hazard ratio, 1.62; 95% CI, 1.051-2.50; P = .029).

Conclusions: Increased intestinal permeability is associated with later development of CD; these findings support a model in which altered intestinal barrier function contributes to pathogenesis. Abnormal gut barrier function might serve as a biomarker for risk of CD onset.
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http://dx.doi.org/10.1053/j.gastro.2020.08.005DOI Listing
December 2020

Persistent Diarrhea in Patients With Crohn's Disease After Mucosal Healing Is Associated With Lower Diversity of the Intestinal Microbiome and Increased Dysbiosis.

Clin Gastroenterol Hepatol 2021 02 24;19(2):296-304.e3. Epub 2020 Mar 24.

Division of Gastroenterology, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; Zane Cohen Centre for Digestive Diseases, Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, Canada.

Background & Aims: In patients with inflammatory bowel diseases (IBDs), symptoms do not always associate with the severity of endoscopic inflammation and can persist after mucosal healing. We investigated whether symptoms in patients with successfully treated IBD are related to the composition of the intestinal microbiome.

Methods: We analyzed 590 tissue biopsy specimens from 215 patients with IBD and 48 healthy individuals (controls). We obtained mucosal biopsy specimens from 2 colon sites (ascending and rectosigmoid) and from the terminal ileum along with clinical data. Bacterial DNA was extracted from the biopsy specimens and the V4 region of 16s ribosomal RNA sequenced by Miseq and processed using the QIIME v1.9 pipeline.

Results: Mucosal biopsy specimens from patients with Crohn's disease (CD) who achieved mucosal healing (Mayo scores of 0-1 or segmental endoscopic severity CD scores of 0-5) had lower Chao1 diversity than biopsy specimens from patients with ulcerative colitis (UC) or unclassified IBD (IBD-U), or controls. After endoscopic evidence of improvement in patients with UC or IBD-U, diversity of the tissue-associated microbiota did not differ significantly from that of controls. Colon biopsy specimens from patients with CD had lower microbial diversity, before and after healing (segmental endoscopic severity CD scores, 0-2), than colon biopsy specimens from controls (P < .002). In patients with CD who achieved mucosal healing, residual clinical activity (CD activity index scores >150; P = .03) and persistent diarrhea were associated with reduced microbial diversity (P = .01). Continued diarrhea was associated with a trend toward dysbiosis, based on the microbial dysbiosis index (P = .059). In patients with UC or IBD-U with moderate to severe inflammation, increasing severity of diarrhea was associated with reduced microbial diversity (P = .03).

Conclusions: In an analysis of biopsy specimens from patients with IBD and controls, we found that despite endoscopic evidence of improvement or remission, α-diversity of the tissue-associated intestinal microbiome remained lower in patients with CD than in controls. This observation, along with the reduced Chao1 diversity and greater dysbiosis in intestinal microbiota of patients with residual symptoms of IBD, indicates that microbiome composition could be associated with persistent diarrhea.
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http://dx.doi.org/10.1016/j.cgh.2020.03.044DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7511440PMC
February 2021

Analysis of Genetic Association of Intestinal Permeability in Healthy First-degree Relatives of Patients with Crohn's Disease.

Inflamm Bowel Dis 2019 10;25(11):1796-1804

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, Ontario, Canada.

Excessive intestinal permeability or intestinal barrier dysfunction as measured by various assays has been observed in various diseases. However, little is known about the factors contributing to altered gut permeability in these diseases. Our objective was to determine the genetic determinants of altered gut permeability as measured by the lactulose mannitol fractional excretion ratio (LacMan ratio) in 1075 healthy first-degree relatives of patients with Crohn's disease (CD). In a targeted analysis of single nucleotide polymorphisms (SNPs) located in genes associated with intestinal barrier function related or not to inflammatory bowel disease, we did not find a significant association with intestinal permeability. In an untargeted genome-wide association analysis, the top 100 associations were located in 22 genomic loci, although they were not statistically significant after correction for multiple testing (raw P values [1.8 × 10-7 - 1.4 × 10-5]. The lowest P value was obtained for rs9616637 (22q13.33, C22orf34), for which the minor allele A was associated with a decreased LacMan ratio. These results suggest that host genetic background has limited contribution toward intestinal permeability. Despite this, our study is currently the largest of its kind assessing gut permeability in vivo. It remains possible that smaller genetic effect sizes on LacMan ratio are not detectable in this sized cohort. Larger studies are warranted to identify the potential genetic contribution to intestinal permeability.
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http://dx.doi.org/10.1093/ibd/izz116DOI Listing
October 2019

Differential miRNA Expression in Ileal and Colonic Tissues Reveals an Altered Immunoregulatory Molecular Profile in Individuals With Crohn's Disease versus Healthy Subjects.

J Crohns Colitis 2019 Oct;13(11):1459-1469

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, ON, Canada.

Background: MicroRNAs [miRNAs] are key modulators of gene expression in Crohn's disease [CD] and may drive tissue-specific molecular alterations underlying CD susceptibility. In this study, we analysed differential miRNA expression between CD and healthy subjects across ileal and colonic tissues.

Methods: A cohort of CD and healthy control [HC] subjects was recruited and clinical data collected. Endoscopically quiescent CD [CDq] was defined as inactive or mild by the Simple Endoscopic Score for CD. Total RNA was extracted from endoscopic biopsies taken from the terminal ileum and sigmoid colon. miRNA expression was quantified using NanoString Technologies. Statistical significance was assessed across biopsy site and diagnosis per miRNA, and corrected for multiple testing.

Results: In total, 23 CDq and 38 HC subjects were enrolled; 112 samples were included in the analysis, 51 from the ileum and 61 from the colon. We found 47 miRNAs differentially expressed by biopsy site in healthy tissue. Nine miRNAs were differentially expressed across HC and CDq, accounting for biopsy location. One of these, miR-223-3p, showed age and sex effects. We identified miRNA expression driven by diagnosis targeting genes involved in chemokine and cytokine signalling. miR-31-5p expression was driven by location and may be a biomarker for location subtypes in CD.

Conclusions: We identified differentially expressed miRNAs in healthy ileal and colonic tissues. We discovered spatial miRNA expression patterns in CD and HC, suggesting site-specific regulation in subjects with no or minimal intestinal inflammation. These miRNAs target genes involved in immunoregulatory processes, suggesting a functional, tissue-specific role in CD.
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http://dx.doi.org/10.1093/ecco-jcc/jjz076DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6821350PMC
October 2019

FUT2 genotype and secretory status are not associated with fecal microbial composition and inferred function in healthy subjects.

Gut Microbes 2018 07 27;9(4):357-368. Epub 2018 Apr 27.

a Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital , Toronto , ON , Canada.

Heritability analysis of the microbiota has demonstrated the importance of host genotype in defining the human microbiota. The alpha (1,2)-fucosyltransferase 2 encoded by FUT2 is involved in the formation of the H antigen and the SNP, rs601338 is associated with ABO histo-blood group antigen secretion in the intestinal mucosa. Previous studies have provided non replicated results for the association of this polymorphism with the composition and inferred function of intestinal microbiota. We aimed to assess this relationship in a large cohort of 1,190 healthy individuals. Genotyping was performed using the HumanCoreEXOME chip, microbial composition was addressed by 16S rRNA gene sequencing. Firmicutes, Bacteroidetes, and Actinobacteria were the dominant phyla in this cohort. Although we have sufficient power to detect significant associations of FUT2 genotype/ inferred phenotype with the microbiota, our data demonstrate that FUT2 genotype and secretor status is not associated with microbial alpha diversity, microbial composition or inferred microbial function after correction for multiple testing. Thus, FUT2 genotype and inferred phenotype are not associated with human fecal microbial composition and imputed function.
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http://dx.doi.org/10.1080/19490976.2018.1445956DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219652PMC
July 2018

Differential Expression of microRNAs in Peripheral Blood Mononuclear Cells Identifies Autophagy and TGF-Beta-Related Signatures Aberrantly Expressed in Inflammatory Bowel Disease.

J Crohns Colitis 2018 Apr;12(5):568-581

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, ON, Canada.

Background And Aims: MicroRNAs [miRNAs] have emerged as important regulators in inflammatory bowel disease [IBD]. This study investigated differential expression of miRNAs across clinical phenotypes in a well-characterized cohort of IBD patients and healthy controls [HCs].

Methods: A cohort of Crohn's disease [CD] and ulcerative colitis [UC] patients and HCs was prospectively accrued. Total RNA was extracted from peripheral blood mononuclear cells for all subjects. miRNA expression was measured using NanoString technologies. The subjects were stratified according to disease activity and location. Statistical significance was assessed per miRNA across outcomes and corrected for multiple testing. miRNA regulation of transcription of important results was confirmed in vitro by a dual luciferase reporter assay and autophagy function was evaluated using immunofluorescence imaging of LC3 puncta in HeLa cells.

Results: In total, 120 subjects were enrolled. Seventy-four miRNAs were differentially expressed across CD, UC and HCs. Comparing quiescent CD [CDq] with HCs we found ten miRNAs upregulated in CDq. When comparing colonic CD [CCD] to UC, seven miRNAs were upregulated in CCD. The most differentially expressed miRNA in CCD vs UC was miR-874-3p, and we showed its possible utility as a biomarker of differential diagnosis. We showed miR-874-3p targets ATG16L1 and reduces its expression in vitro. An miR-874-3p mimic dysregulates autophagy by a reduction of LC3 in vitro.

Conclusions: We identified unique miRNA signatures expressed in distinct IBD phenotypes. These associations highlight pathways dysregulated by aberrant miRNA expression, revealing possible mechanisms underlying the pathophysiology of IBD, but also suggest a cluster of miRNAs as readily accessible biomarkers to aid in differential diagnosis.
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http://dx.doi.org/10.1093/ecco-jcc/jjy010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6018685PMC
April 2018

Centrally Determined Standardization of Flow Cytometry Methods Reduces Interlaboratory Variation in a Prospective Multicenter Study.

Clin Transl Gastroenterol 2017 Nov 2;8(11):e126. Epub 2017 Nov 2.

Division of Gastroenterology, School of Medicine, University of California San Diego, San Diego, CA, USA.

Objectives: Flow cytometry (FC) aids in characterization of cellular and molecular factors involved in pathologic immune responses. Although FC has potential to facilitate early drug development in inflammatory bowel disease, interlaboratory variability limits its use in multicenter trials. Standardization of methods may address this limitation. We compared variability in FC-aided quantitation of T-cell responses across international laboratories using three analytical strategies.

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from three healthy donors, stimulated with phorbol 12-myristate 13-acetate and ionomycin at a central laboratory, fixed, frozen, and shipped to seven international laboratories. Permeabilization and staining was performed in triplicate at each laboratory using a common protocol and centrally provided reagents. Gating was performed using local gating with a local strategy (LGLS), local gating with a central strategy (LGCS), and central gating (CG). Median cell percentages were calculated across triplicates and donors, and reported for each condition and strategy. The coefficient of variation (CV) was calculated across laboratories. Between-strategy comparisons were made using a two-way analysis of variance adjusting for donor.

Results: Mean interlaboratory CV ranged from 1.8 to 102.1% depending on cell population and gating strategy (LGLS, 4.4-102.1%; LGCS, 10.9-65.6%; CG, 1.8-20.9%). Mean interlaboratory CV differed significantly across strategies and was consistently lower with CG.

Conclusions: Central gating was the only strategy with mean CVs consistently lower than 25%, which is a proposed standard for pharmacodynamic and exploratory biomarker assays.
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http://dx.doi.org/10.1038/ctg.2017.52DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5717516PMC
November 2017

Association of host genome with intestinal microbial composition in a large healthy cohort.

Nat Genet 2016 11 3;48(11):1413-1417. Epub 2016 Oct 3.

Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital, Toronto, Ontario, Canada.

Intestinal microbiota is known to be important in health and disease. Its composition is influenced by both environmental and host factors. Few large-scale studies have evaluated the association between host genetic variation and the composition of microbiota. We recruited a cohort of 1,561 healthy individuals, of whom 270 belong in 123 families, and found that almost one-third of fecal bacterial taxa were heritable. In addition, we identified 58 SNPs associated with the relative abundance of 33 taxa in 1,098 discovery subjects. Among these, four loci were replicated in a second cohort of 463 subjects: rs62171178 (nearest gene UBR3) associated with Rikenellaceae, rs1394174 (CNTN6) associated with Faecalibacterium, rs59846192 (DMRTB1) associated with Lachnospira, and rs28473221 (SALL3) associated with Eubacterium. After correction for multiple testing, 6 of the 58 associations remained significant, one of which replicated. These results identify associations between specific genetic variants and the gut microbiome.
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http://dx.doi.org/10.1038/ng.3693DOI Listing
November 2016

Gut DNA viromes of Malawian twins discordant for severe acute malnutrition.

Proc Natl Acad Sci U S A 2015 Sep 8;112(38):11941-6. Epub 2015 Sep 8.

Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St. Louis, MO 63108; Center for Gut Microbiome and Nutrition Research, Washington University School of Medicine, St. Louis, MO 63108; Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110;

The bacterial component of the human gut microbiota undergoes a definable program of postnatal development. Evidence is accumulating that this program is disrupted in children with severe acute malnutrition (SAM) and that their persistent gut microbiota immaturity, which is not durably repaired with current ready-to-use therapeutic food (RUTF) interventions, is causally related to disease pathogenesis. To further characterize gut microbial community development in healthy versus malnourished infants/children, we performed a time-series metagenomic study of DNA isolated from virus-like particles (VLPs) recovered from fecal samples collected during the first 30 mo of postnatal life from eight pairs of mono- and dizygotic Malawian twins concordant for healthy growth and 12 twin pairs discordant for SAM. Both members of discordant pairs were sampled just before, during, and after treatment with a peanut-based RUTF. Using Random Forests and a dataset of 17,676 viral contigs assembled from shotgun sequencing reads of VLP DNAs, we identified viruses that distinguish different stages in the assembly of the gut microbiota in the concordant healthy twin pairs. This developmental program is impaired in both members of SAM discordant pairs and not repaired with RUTF. Phage plus members of the Anelloviridae and Circoviridae families of eukaryotic viruses discriminate discordant from concordant healthy pairs. These results disclose that apparently healthy cotwins in discordant pairs have viromes associated with, although not necessarily mediators, of SAM; as such, they provide a human model for delineating normal versus perturbed postnatal acquisition and retention of the gut microbiota's viral component in populations at risk for malnutrition.
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http://dx.doi.org/10.1073/pnas.1514285112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586842PMC
September 2015

Bacteria from diverse habitats colonize and compete in the mouse gut.

Cell 2014 Oct 2;159(2):253-66. Epub 2014 Oct 2.

Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St. Louis, MO 63108, USA. Electronic address:

To study how microbes establish themselves in a mammalian gut environment, we colonized germ-free mice with microbial communities from human, zebrafish, and termite guts, human skin and tongue, soil, and estuarine microbial mats. Bacteria from these foreign environments colonized and persisted in the mouse gut; their capacity to metabolize dietary and host carbohydrates and bile acids correlated with colonization success. Cohousing mice harboring these xenomicrobiota or a mouse cecal microbiota, along with germ-free "bystanders," revealed the success of particular bacterial taxa in invading guts with established communities and empty gut habitats. Unanticipated patterns of ecological succession were observed; for example, a soil-derived bacterium dominated even in the presence of bacteria from other gut communities (zebrafish and termite), and human-derived bacteria colonized germ-free bystander mice before mouse-derived organisms. This approach can be generalized to address a variety of mechanistic questions about succession, including succession in the context of microbiota-directed therapeutics.
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http://dx.doi.org/10.1016/j.cell.2014.09.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4194163PMC
October 2014

Microbiome analysis - from technical advances to biological relevance.

F1000Prime Rep 2014 8;6:51. Epub 2014 Jul 8.

Zane Cohen Centre for Digestive Diseases, Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital 600 University Avenue, Room 437, Toronto, ON Canada, M5G 1X5 ; Institute of Medical Science, Department of Medicine University of Toronto, Toronto, ON Canada, M5S 1A8.

The development of culture-independent techniques and next-generation sequencing has led to a staggering rise in the number of microbiome studies over the last decade. Although it remains important to identify the taxa of microbes present in a variety of environmental samples, including the gut microbiomes of healthy and diseased individuals, the next stage of microbiome research will need to focus on uncovering the role of the microbiome rather than its mere composition. Here, we introduce techniques that go beyond identifying the taxa present within a sample and examine the biological function of the microbiome or the host-microbiome interaction.
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http://dx.doi.org/10.12703/P6-51DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4108955PMC
September 2014

Analyzing the human microbiome: a "how to" guide for physicians.

Am J Gastroenterol 2014 Jul 22;109(7):983-93. Epub 2014 Apr 22.

1] Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada [2] Zane Cohen Centre for Digestive Diseases, Mount Sinai Hospital Inflammatory Bowel Disease Group, Toronto, Ontario, Canada.

The application of high-throughput next-generation sequencing to the analysis of the human microbiome has led to a shift in our understanding of the etiology of complex diseases. In consequence, a great deal of literature can now be found exploring this complex system, and reviewing recent findings. Observations of alterations in the intestinal microbiome associating with inflammatory bowel disease and other chronic conditions are well supported and have been widely accepted by the research community. Yet, it can be difficult to objectively evaluate the importance of these results, given the wide variety of methodologies applied by different groups in the field. The aim of this review is to focus attention on the basic principles involved in microbiome analyses, and to describe factors that may have an impact on the accurate interpretation of results.
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http://dx.doi.org/10.1038/ajg.2014.73DOI Listing
July 2014

Gut microbiomes of Malawian twin pairs discordant for kwashiorkor.

Science 2013 Feb 30;339(6119):548-54. Epub 2013 Jan 30.

Center for Genome Sciences and Systems Biology, Washington University in St. Louis, St. Louis, MO 63110, USA.

Kwashiorkor, an enigmatic form of severe acute malnutrition, is the consequence of inadequate nutrient intake plus additional environmental insults. To investigate the role of the gut microbiome, we studied 317 Malawian twin pairs during the first 3 years of life. During this time, half of the twin pairs remained well nourished, whereas 43% became discordant, and 7% manifested concordance for acute malnutrition. Both children in twin pairs discordant for kwashiorkor were treated with a peanut-based, ready-to-use therapeutic food (RUTF). Time-series metagenomic studies revealed that RUTF produced a transient maturation of metabolic functions in kwashiorkor gut microbiomes that regressed when administration of RUTF was stopped. Previously frozen fecal communities from several discordant pairs were each transplanted into gnotobiotic mice. The combination of Malawian diet and kwashiorkor microbiome produced marked weight loss in recipient mice, accompanied by perturbations in amino acid, carbohydrate, and intermediary metabolism that were only transiently ameliorated with RUTF. These findings implicate the gut microbiome as a causal factor in kwashiorkor.
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http://dx.doi.org/10.1126/science.1229000DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3667500PMC
February 2013

Minimum information about a marker gene sequence (MIMARKS) and minimum information about any (x) sequence (MIxS) specifications.

Nat Biotechnol 2011 May;29(5):415-20

Microbial Genomics and Bioinformatics Group, Max Planck Institute for Marine Microbiology, Bremen, Germany.

Here we present a standard developed by the Genomic Standards Consortium (GSC) for reporting marker gene sequences--the minimum information about a marker gene sequence (MIMARKS). We also introduce a system for describing the environment from which a biological sample originates. The 'environmental packages' apply to any genome sequence of known origin and can be used in combination with MIMARKS and other GSC checklists. Finally, to establish a unified standard for describing sequence data and to provide a single point of entry for the scientific community to access and learn about GSC checklists, we present the minimum information about any (x) sequence (MIxS). Adoption of MIxS will enhance our ability to analyze natural genetic diversity documented by massive DNA sequencing efforts from myriad ecosystems in our ever-changing biosphere.
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http://dx.doi.org/10.1038/nbt.1823DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367316PMC
May 2011

Skeletal muscle differentiation evokes endogenous XIAP to restrict the apoptotic pathway.

PLoS One 2009 31;4(3):e5097. Epub 2009 Mar 31.

Department of Cell and Developmental Biology and Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA.

Myotube apoptosis occurs normally during muscle development and aging but it can lead to destruction of skeletal muscle in neuromuscular diseases. Therefore, understanding how myotube apoptosis is regulated is important for developing novel strategies for treatment of muscle loss. We investigated the regulation of apoptosis in skeletal muscle and report a striking increase in resistance to apoptosis following differentiation. We find mitotic C2C12 cells (myoblast-like cells) are sensitive to cytosolic cytochrome c microinjection. However, differentiated C2C12 cells (myotube-like cells) and primary myotubes are markedly resistant. This resistance is due to endogenous X-linked inhibitor of apoptotic protein (XIAP). Importantly, the selective difference in the ability of XIAP to block myotube but not myoblast apoptosis is not due to a change in XIAP but rather a decrease in Apaf-1 expression. This decrease in Apaf-1 links XIAP to caspase activation and death. Our findings suggest that in order for myotubes to die, they may degrade XIAP, functionally inactivate XIAP or upregulate Apaf-1. Importantly, we identify a role for endogenous Smac in overcoming XIAP to allow myotube death. However, in postmitotic cardiomyocytes, where XIAP also restricts apoptosis, endogenous Smac was not capable of overcoming XIAP to cause death. These results show that as skeletal muscle differentiate, they become resistant to apoptosis because of the ability of XIAP to regulate caspase activation. The increased restriction of apoptosis in myotubes is presumably important to ensure the long term survival of these postmitotic cells as they play a vital role in the physiology of organisms.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0005097PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658743PMC
May 2009

Differential Apaf-1 levels allow cytochrome c to induce apoptosis in brain tumors but not in normal neural tissues.

Proc Natl Acad Sci U S A 2007 Dec 18;104(52):20820-5. Epub 2007 Dec 18.

Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27708, USA.

Brain tumors are typically resistant to conventional chemotherapeutics, most of which initiate apoptosis upstream of mitochondrial cytochrome c release. In this study, we demonstrate that directly activating apoptosis downstream of the mitochondria, with cytosolic cytochrome c, kills brain tumor cells but not normal brain tissue. Specifically, cytosolic cytochrome c is sufficient to induce apoptosis in glioblastoma and medulloblastoma cell lines. In contrast, primary neurons from the cerebellum and cortex are remarkably resistant to cytosolic cytochrome c. Importantly, tumor tissue from mouse models of both high-grade astrocytoma and medulloblastoma display hypersensitivity to cytochrome c when compared with surrounding brain tissue. This differential sensitivity to cytochrome c is attributed to high Apaf-1 levels in the tumor tissue compared with low Apaf-1 levels in the adjacent brain tissue. These differences in Apaf-1 abundance correlate with differences in the levels of E2F1, a previously identified activator of Apaf-1 transcription. ChIP assays reveal that E2F1 binds the Apaf-1 promoter specifically in tumor tissue, suggesting that E2F1 contributes to the expression of Apaf-1 in brain tumors. Together, these results demonstrate an unexpected sensitivity of brain tumors to postmitochondrial induction of apoptosis. Moreover, they raise the possibility that this phenomenon could be exploited therapeutically to selectively kill brain cancer cells while sparing the surrounding brain parenchyma.
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http://dx.doi.org/10.1073/pnas.0709101105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409225PMC
December 2007

Chromatin modification of Apaf-1 restricts the apoptotic pathway in mature neurons.

J Cell Biol 2007 Dec;179(5):825-32

Neuroscience Center and 2Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Although apoptosis has been extensively studied in developing neurons, the dynamic changes in this pathway after neuronal maturation remain largely unexplored. We show that as neurons mature, cytochrome c- mediated apoptosis progresses from inhibitor of apoptosis protein-dependent to -independent regulation because of a complete loss of Apaf-1 expression. However, after DNA damage, mature neurons resynthesize Apaf-1 through the cell cycle-related E2F1 pathway and restore their apoptotic potential. Surprisingly, we find that E2F1 is sufficient to induce Apaf-1 expression in developing but not mature neurons. Rather, Apaf-1 up-regulation in mature neurons requires both chromatin derepression and E2F1 transcriptional activity. This differential capacity of E2F1 to induce Apaf-1 transcription is because of the association of the Apaf-1 promoter with active chromatin in developing neurons and repressed chromatin in mature neurons. These data specifically illustrate how the apoptotic pathway in mature neurons becomes increasingly restricted by a novel mechanism involving the regulation of chromatin structure.
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http://dx.doi.org/10.1083/jcb.200708086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2099178PMC
December 2007
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