Role of tRNA-derived fragments in the cross-talk between immune cells and beta cells during type 1 diabetes pathogenesis (NOD islets)

Transfer RNAs (tRNAs) play a central and well recognized role in protein synthesis. Recent studies revealed that these molecules can be cleaved to generate tRNA fragments (tRFs) with regulatory functions. Here, we studied the contribution of tRFs to pancreatic β-cell loss during the initial phases of type 1 diabetes (T1D), an autoimmune disorder characterized by the invation of immune cells in the pancreas and progressive loss of insulin-secreting cells. Small RNA-profiling showed that the pool of tRFs present in pancreatic β-cells is altered in non-obese diabetic (NOD) mice, a mouse model used to study T1D. We found that part of these changes is triggered by the exposure of β-cells to proinflammatory cytokines released during the autoimmune reaction while others result from the direct transfer of tRFs from autoreactive T lymphocytes to insulin-secreting cells via extracellular vesicles. Indeed, using an RNA-tagging approach, we could demonstrate that a group of tRFs are transferred in vivo in from CD4+CD25- T lymphocytes to pancreatic β-cells, upon T cell adoptive transfer in NOD scid mice. Morevoer, the up-regulation of selected tRFs associated with the autoimmune reaction triggers β-cell apoptosis and gene expression changes that affect the immune regulatory capacity of β-cells. Our data point to tRFs as novel players in type 1 diabetes and potentially in other autoimmune disorders. NOD mice constitute the best characterized and most widely used animal model of T1D. At four weeks of age, the islets of NOD mice display a normal morphology and function but starting from the age of 6 weeks they are progressively invaded by immune cells, resulting in β-cell dysfunction and death and, starting from weeks 12-14, in the appearance of diabetes. To assess the potential contribution of tRFs to the initial phases of T1D, we isolated the RNA of pancreatic islets of NOD mice and pretreated the samples for end repair and modifications removal. We then compared by small RNA-sequencing (RNA-seq) the level of tRFs in the islets of control (4 weeks old) and prediabetic (8 weeks old) NOD mice.