Effects of HLA–B27 on Gut Microbiota in Experimental Spondyloarthritis Implicate an Ecological Model of Dysbiosis

• Published in: Arthritis & rheumatology (Hoboken, N.J.) Vol. 70; no. 4; pp. 555 - 565
• Main Authors: Gill, Tejpal, Asquith, Mark, Brooks, Stephen R., Rosenbaum, James T., Colbert, Robert A.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.04.2018
• Subjects: Agouti Signaling Protein; Animals; Arthritis; CD4 antigen; Cecum; Cecum - metabolism; Cecum - microbiology; Colon; Colon - metabolism; Colon - microbiology; Cytokines; Disease Models, Animal; Disease resistance; Dysbacteriosis; Dysbiosis - genetics; Ecological effects; Ecological models; Ecological monitoring; Filamentous bacteria; Gastrointestinal Microbiome - genetics; Gene expression; Gene sequencing; Helper cells; Histocompatibility antigen HLA; HLA-B27 Antigen - metabolism; Identification methods; Immune response; Immune system; Inflammation; Inflammatory diseases; Interferon; Interleukins; Intestinal microflora; Lymphocytes T; Microbiota; Microorganisms; Pathogenesis; Rats; Rats, Inbred F344; Rats, Inbred Lew; Rats, Transgenic; Rheumatic diseases; Ribonucleic acid; RNA; RNA, Ribosomal, 16S - metabolism; Rodents; rRNA 16S; Spondylarthropathies - genetics; Spondylarthropathies - microbiology
• ISSN: 2326-5191; 2326-5205
• DOI: 10.1002/art.40405

Objective To investigate whether HLA–B27–mediated experimental spondyloarthritis (SpA) is associated with a common gut microbial signature, in order to identify potential drivers of pathogenesis. Methods The effects of HLA–B27 on 3 genetic backgrounds, dark agouti (DA), Lewis, and Fischer, were compared, using wild‐type littermates and HLA–B7–transgenic Lewis rats as controls. Cecum and colon tissue specimens or contents were collected from the rats at 2, 3–4, and 6–8 months of age, and histologic analysis was performed to assess inflammation, RNA sequencing was used to determine gene expression differences, and 16S ribosomal RNA gene sequencing was used to determine microbiota differences. Results Both HLA–B27–transgenic Lewis rats and HLA–B27–transgenic Fischer rats developed gut inflammation, while DA rats were resistant to the effects of HLA–B27, and HLA–B7–transgenic rats were not affected. Immune dysregulation was similar in affected Lewis and Fischer rats and was dominated by activation of interleukin‐23 (IL‐23)/IL‐17, interferon, tumor necrosis factor, and IL‐1 cytokines and pathways in the colon and cecum, while DA rats exhibited low‐level cytokine dysregulation without inflammation. Gut microbial changes in HLA–B27–transgenic rats were strikingly divergent on the 3 different host genetic backgrounds, including different patterns of dysbiosis in HLA–B27–transgenic Lewis and HLA–B27–transgenic Fischer rat strains, with some overlap. Interestingly, DA rats lacked segmented filamentous bacteria that promote CD4+ Th17 cell development, which may explain their resistance to disease. Conclusion The effects of HLA–B27 on gut microbiota and dysbiosis in SpA are highly dependent on the host genetic background and/or environment, despite convergence of dysregulated immune pathways. These results implicate an ecological model of dysbiosis, with the effects of multiple microbes contributing to the aberrant immune response, rather than a single or small number of microbes driving pathogenesis.