GSE131320
Human Islet Response to Selected Type 1 Diabetes Associated Bacteria
Type 1 diabetes (T1D) is a chronic autoimmune disease that results from destruction of pancreatic ß-cells. T1D subjects were recently shown to harbor distinct intestinal microbiome profiles. Based on these findings, the role of gut bacteria in T1D is being intensively investigated. The mechanism connecting intestinal microbial homeostasis with the development of T1D is unknown.  Specific gut bacteria such as Bacteroides dorei (BD) and Ruminococcus gnavus (RG) show markedly increased abundance prior to the development of autoimmunity. One hypothesis is that these bacteria might traverse the damaged gut barrier, and their constituents elicit a response from human islets that causes metabolic abnormalities and inflammation. We have tested this hypothesis by exposing human islets to BD and RG in vitro, after which RNA-Seq analysis was performed. The bacteria altered expression of many islet genes. The commonly upregulated genes by these bacteria were cytokines, chemokines and enzymes, suggesting a significant effect of gut bacteria on islet antimicrobial and biosynthetic pathways. Additionally, each bacteria displayed a unique set of differentially expressed genes (DEGs). Ingenuity pathway analysis of DEGs revealed that top activated pathways and diseases included TREM1 Signaling and Inflammatory Response, illustrating the ability of bacteria to induce islet inflammation. The increased levels of selected factors were confirmed using immunoblotting and ELISA methods. Our data demonstrate that islets produce a complex anti-bacterial response. The response includes both symbiotic and pathogenic aspects. Both oxidative damage and leukocyte recruitment factors were prominent, which could induce beta cell damage and subsequent autoimmunity. Overall design: In the present study, we experimentally tested the hypothesis that intestinal dysbiosis and leakage of bacteria into the human pancreas could trigger an islet anti-bacterial immune response. This response could lead to subsequent recruitment of immune cells to islets, initiating autoimmunity. To achieve that aim, isolated human islets were exposed to Bacteroides dorei and Ruminococcus gnavus, two bacteria overrepresented in the gut just before/at incidence of autoimmunity and Escherichia coli, a ubiquitous bacterium associated with accelerated maturation of the gut microbiome for 6h or 24h. Islets exposed to the potent cytokine IL-1ß for the same time periods were used as positive controls. Islets exposed to serum-free medium were additionally used as negative controls.