Multi 'Omics Analysis of Intestinal Tissue in Ankylosing Spondylitis Identifies Alterations in the Tryptophan Metabolism Pathway.

Adam J Berlinberg,Blair P Fennimore,Julie A Reisz,Mark E Gerich,Ana Brar,Emilie H Regner,Frank I Scott,Alison E Freeman,Andrew Stahly,Kristine A Kuhn

doi:10.3389/fimmu.2021.587119

Abstract

Intestinal microbial dysbiosis, intestinal inflammation, and Th17 immunity are all linked to the pathophysiology of spondyloarthritis (SpA); however, the mechanisms linking them remain unknown. One potential hypothesis suggests that the dysbiotic gut microbiome as a whole produces metabolites that influence human immune cells. To identify potential disease-relevant, microbiome-produced metabolites, we performed metabolomics screening and shotgun metagenomics on paired colon biopsies and fecal samples, respectively, from subjects with axial SpA (axSpA, N=21), Crohn’s disease (CD, N=27), and Crohn’s-axSpA overlap (CD-axSpA, N=12), as well as controls (HC, N=24). Using LC-MS based metabolomics of 4 non-inflamed pinch biopsies of the distal colon from subjects, we identified significant alterations in tryptophan pathway metabolites, including an expansion of indole-3-acetate (IAA) in axSpA and CD-axSpA compared to HC and CD and indole-3-acetaldehyde (I3Ald) in axSpA and CD-axSpA but not CD compared to HC, suggesting possible specificity to the development of axSpA. We then performed shotgun metagenomics of fecal samples to characterize gut microbial dysbiosis across these disease states. In spite of no significant differences in alpha-diversity among the 4 groups, our results confirmed differences in gene abundances of numerous enzymes involved in tryptophan metabolism. Specifically, gene abundance of indolepyruvate decarboxylase, which generates IAA and I3Ald, was significantly elevated in individuals with axSpA while gene abundances in HC demonstrated a propensity towards tryptophan synthesis. Such genetic changes were not observed in CD, again suggesting disease specificity for axSpA. Given the emerging role of tryptophan and its metabolites in immune function, altogether these data indicate that tryptophan metabolism into I3Ald and then IAA is one mechanism by which the gut microbiome potentially influences the development of axSpA.

Highlights

Ankylosing spondylitis is a form of axial spondyloarthritis resulting in inflammation of the axial spine, peripheral joints, and entheses [1]
Using Venn diagrams to demonstrate the similarities and differences from pairwise comparisons of the most significantly changed metabolites, we discovered that indole-containing compounds from tryptophan metabolism associated with the presence of axial spondyloarthritis (axSpA) when compared to HC; when compared to CD, the presence of axSpA seemed to associate with omega 3 fatty acids (Supplemental Figure 3)
Because prior microbiome studies compared axSpA and CD-axSpA combined versus HC as stated above, we performed this analysis with our data set and found significantly increased abundances of Porphyromonas bennonis (p

Summary

Introduction

Ankylosing spondylitis is a form of axial spondyloarthritis (axSpA) resulting in inflammation of the axial spine, peripheral joints, and entheses [1]. In the HLA-B27/b2m transgenic rat model that develops spontaneous SpA and bowel inflammation, transcriptional changes in IL-17, IL-23, and TNF, key cytokines in the pathophysiology of SpA [8], in the intestinal tissues are associated with metabolic changes as well as microbial changes that are found in human SpA [9]. This finding suggests that dysbiosis can influence pathogenic immunity of SpA. Community function leading to metabolic alterations that affect mucosal immunity may be more relevant than specific taxa in influencing pathophysiology

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