Modulation of the gastrointestinal microbiota normalizes the systemic inflammation and islet immunocyte recruitment capacity associated with autoimmune diabetes (in Biobreeding rats) [RatIslet_Longitudinal]. Rattus norvegicus

The incidence of Type 1 diabetes (T1D), a T-cell mediated autoimmunity that targets the insulin secreting β-cells, has significantly increased, suggesting greater environmental pressure. In studies of T1D families and the BioBreeding rat model, we have identified a peripheral innate inflammatory state that is associated with diabetes susceptibility, consistent with pattern recognition receptor (PRR) ligation, but independent of disease progression. Here, compared to control strains, islets of spontaneously diabetic BB DRlyp/lyp and nondiatetic BB DR+/+ weanlings provided a standard cereal diet were found to temporally express a proinflammatory transcriptional program consistent with microbial antigen exposure that included numerous cytokines/chemokines. Dependence of this proinflammatory phenotype on the diet and gastrointestinal microbiota was investigated by transitioning DR+/+ weanlings to a hydrolyzed casein diet (HCD) or treating them with antibiotics to respectively alter or reduce PRR ligand exposure. Sequencing of the bacterial 16S rRNA gene revealed that these treatments significantly altered the ileal and cecal microbiota, resulting in increases in the Firmicutes:Bacteriodetes ratio, and abundances of lactobacilli and butyrate producing genera. Both treatments partially normalized the peripheral inflammatory state, reducing plasma cytokine, chemokine and TLR-4 activity levels. The proinflammatory islet transcriptome was more extensively normalized by HCD and immune-fluorescent staining revealed reductions in β-cell chemokine expression. HCD and antibiotic treatment did not normalize BB rat PBMC hyper-responsiveness to ex vivo mitogen stimulation. Combined, these studies link islet-level T1D susceptibility in BB rats to a genetically controlled innate inflammatory state that is influenced by environmental determinants encompassing the diet and the intestinal microbiota. Overall design: In order to investigate T1D susceptibility at the target tissue level, we longitudinally examined the islet transcriptomes of using RNA pools of DRlyp/lyp, DR+/+, Flyp/lyp, and F+/+ rats provided normal cereal chow (n=6-8 rats per pool, technical triplicates were conducted at experimental condition). The study design encompassed day 20 (weaning), day 30 (prior to histological detection of Ccl11 expression by BB rat β-cells), day 40 (prior to insulitis in DRlyp/lyp rats), and day 50 (after insulitis but prior to diabetes onset in DRlyp/lyp rats). Unsupervised PCA found the islet transcriptomes of young and old rats were highly distinct, and the longitudinal data set for each stain was analyzed with STEM (Short Time Series Expression Miner).