11-OR: Transcriptome Heterogeneity in Insulin-Positive Insulitic vs. Noninsulitic Human Islets in Type 1 Diabetes (T1D)

Insulitis involves the infiltration of predominantly CD3+ T cells in islets in a patchy distribution between lobes in a pancreas. We hypothesized that gene expression profiling of insulin containing islets (INS⁺CD3^-) vs. insulin containing insulitic islets (INS⁺CD3⁺) would show heterogeneity in autoimmune and ßcell dysfunction pathways within the same donor. Pancreatic islets were obtained by laser-capture microdissection from nPOD donors (5 autoantibody positive nondiabetic (AAb+) and 6 T1D) . Transcriptome data was collected and compared in 83 individual islets. INS⁺CD3⁺ islets were compared to the average of all INS⁺CD3^- islets in each donor. For each INS⁺CD3⁺ islet we created two registries of genes >2-fold up or >2-fold downregulated that were analyzed to detect differences in pathways and ontologies. Islets were analyzed based on five categories: immunity, mitochondrial, metabolism, secretion, and cell signaling. A majority of donors (64%) had all 5 categories represented in either up or downregulated pathways. The most upregulated category in T1D donor islets was immunity (39%) and most downregulated was secretion (33%) . These islets were distinguished by extreme heterogeneity in signaling pathways. In AAb+ donor islets, the most upregulated category was immunity (32%) , with the most downregulated noted as metabolism (21%) . Similarly, AAb+ donor islets had heterogeneity in signaling pathways. In contrast, we observed great intra-donor heterogeneity; each individual islet had 65% unique genes upregulated and 58% downregulated compared to other INS⁺CD3⁺ islets within the same donor.

In summary, similar themes of up or downregulated categories were noted in INS⁺CD3⁺ compared to averaged INS⁺CD3^- islets. Most strikingly, significant heterogeneity between INS⁺CD3⁺ islets within donors at the individual gene levels was observed. These findings indicate substantial complexity of pancreatic islet destruction leading to T1D.