Pancreatic β-cell tRNA hypomethylation and fragmentation link TRMT10A deficiency with diabetes

Transfer RNAs (tRNAs) are non-coding RNA molecules essential for protein synthesis. Post-transcriptionally they are heavily modified to improve their function, folding and stability. Intronic polymorphisms in CDKAL1, a tRNA methylthiotransferase, are associated with increased type 2 diabetes risk. Loss-of-function mutations in TRMT10A, a tRNA methyltransferase, are a monogenic cause of early onset diabetes and microcephaly. Here we confirm the role of TRMT10A as a guanosine 9 tRNA methyltransferase, and identify tRNA(Gln) and tRNA(iMeth) as two of its targets. Using RNA interference and induced pluripotent stem cell-derived pancreatic beta-like cells from healthy controls and TRMT10A-deficient patients we demonstrate that TRMT10A deficiency induces oxidative stress and triggers the intrinsic pathway of apoptosis in beta-cells. We show that tRNA guanosine 9 hypomethylation leads to tRNA(Gln) fragmentation and that 5'-tRNA(Gln) fragments mediate TRMT10A deficiency-induced beta-cell death. This study unmasks tRNA hypomethylation and fragmentation as a hitherto unknown mechanism of pancre-atic beta-cell demise relevant to monogenic and polygenic forms of diabetes.