Background/Purpose: HLA-B27 and human beta 2-microglobulin expression in rats (transgenic; TG) induces a spontaneous inflammatory disease resembling human spondyloarthritis (SpA) with associated gastrointestinal inflammation. While aspects of rat SpA have been studied in detail, our understanding of gut inflammation remains limited. We recently showed that HLA-B27 affects the gut microbiota in TG rats. Therefore, the aim for our current project was to determine the association between intestinal microbiota and host gut transcriptome among TG rats developing SpA-like disease. Lewis (LEW), Fischer (F344), and Dark Agouti (DA) rats with same transgene locus (33-3) at 2, 3 and 6 months of age along with strain-specific controls were studied. TG LEW and F344 rats develop SpA beginning with colitis at about 8 weeks of age, while TG DA rats are disease resistant. Arthritis develops later in LEW and F344 TG animals, and is more variable.

Methods: To determine gut inflammation, tissue samples from cecum and colon were stained with H&E and scored for histology. Gut transcriptome differences were analyzed using Illumina HiSeq 2000 and differential gene expression was assessed. To characterize microbial profiles, 16SrRNA gene from gut microbiota was amplified and sequenced using Illumina MiSeq. Data were quality-filtered using Quantitative Insights Into Microbial Ecology (QIIME) and relative frequency was calculated.

Results: Inflammation in the cecum and colon occurred earlier and was more severe in F344 TG rats compared to LEW based on histology scores. Differential gene expression in LEW and F344 TG animals revealed marked up-regulation of IL-17 (A, F) as well as upregulation of Il23a. Interferon (IFNg) and IFN response genes were upregulated in TG rats, as were apoptotic signaling and oxidative stress pathways (upregulation of Gpx2, Nox1, Duox2 and downregulation of Apoa1). Although there was no significant gut inflammation in DA TG rats, we observed upregulation of many of these genes at 2-3 months, followed by return to normal at 6 months of age. Microbial profiling revealed increased relative frequency of Akkermansia in F344 TG and LEW TG rats. Increased abundance of Candidatus Arthromitus, a segmented filamentous bacteria (SFB) implicated in inducing Th17 responses, was detected in the F344 and LEW animals. Interestingly we were unable to detect SFB in DA, which could account for the lack of Th17 cytokines and absence of SpA including gut inflammation.

Conclusion: Transcriptome analysis of the HLA-B27 TG reveals upregulation of interferon and Il23/Il17 mediated pathways suggesting a proinflammatory shift in the immune microenvironment of the gut. In TG rats, microbial dysbiosis is associated with a decrease in Firmicutes, and an expansion of Proteobacteria, Prevotella spp. and Akkermansia muciniphila. Protective effects of DA background may be linked to the absence of SFB in the gut. Ongoing analyses underway correlating microbial communities with activation of the IL-23/IL-17 axis, IFN signaling, and oxidative stress pathways will establish links with disease severity. This should increase our understanding of SpA associated IBD and generate mechanistic hypotheses as well as potential biomarkers for diagnosis and treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/analysis-of-hla-b27-transgenic-rats-reveals-specific-gut-transcriptome-and-microbiome-signatures-associated-with-inflammation/