Role of tRNA-derived fragments in the cross-talk between immune cells and beta cells during type 1 diabetes pathogenesis (PD in vivo)
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 ß-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 ß-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 ß-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 ß-cells, upon T cell adoptive transfer in NOD scid mice. Morevoer, the up-regulation of selected tRFs associated with the autoimmune reaction triggers ß-cell apoptosis and gene expression changes that affect the immune regulatory capacity of ß-cells. Our data point to tRFs as novel players in type 1 diabetes and potentially in other autoimmune disorders. Overall design: Using NOD mice as a model of T1D, we detected a specific tRF signature in islet cells during the initial phases of the disease. We wanted to demonstrate that some tRFs are released by CD4+ /CD25- T lymphocytes and are transferred in vivo to islet cells during the initial phases of T1D. We used CD4+/CD25- T lymphocytes of NOD BDC2.5 mice that upon inoculation into NOD.SCID mice, promote the appearance of autoimmune diabetes within less than 10 days. CD4+/CD25- T-cells from NOD BDC2.5 were isolated and incubated with Ethynyl Uridine for 48h, together with T-cell activator factors. The cells were then washed and inoculated into NOD.SCID mice by intravenous injection (IV) into the tail vein. Control mice were injected with saline solution. Two days after IV injection, animals were sacrificed, islets isolated, and ß-cells FACS-sorted. The RNA isolated from FACS-sorted ß-cells was biotinylated and pulled-down with streptavidin beads, with the aim of isolating only the EU-tagged RNA coming from T-cell EVs. Pulled-down RNA was analysed by small RNAseq.