Redox regulation of m⁶A methyltransferase METTL3 in -cells controls the innate immune response in type 1 diabetes

Type 1 diabetes (T1D) is characterized by the destruction of pancreatic beta-cells. Several observations have renewed the interest in beta-cell RNA sensors and editors. Here, we report that N-6-methyladenosine (m(6)A) is an adaptive beta-cell safeguard mechanism that controls the amplitude and duration of the antiviral innate immune response at T1D onset. m(6)A writer methyltransferase 3 (METTL3) levels increase drastically in beta-cells at T1D onset but rapidly decline with disease progression. m(6)A sequencing revealed the m(6)A hypermethylation of several key innate immune mediators, including OAS1, OAS2, OAS3 and ADAR1 in human islets and EndoC-beta H1 cells at T1D onset. METTL3 silencing enhanced 2'-5'-oligoadenylate synthetase levels by increasing its mRNA stability. Consistently, in vivo gene therapy to prolong Mettl3 overexpression specifically in beta-cells delayed diabetes progression in the non-obese diabetic mouse model of T1D. Mechanistically, the accumulation of reactive oxygen species blocked upregulation of METTL3 in response to cytokines, while physiological levels of nitric oxide enhanced METTL3 levels and activity. Furthermore, we report that the cysteines in position C276 and C326 in the zinc finger domains of the METTL3 protein are sensitive to S-nitrosylation and are important to the METTL3-mediated regulation of oligoadenylate synthase mRNA stability in human beta-cells. Collectively, we report that m(6)A regulates the innate immune response at the beta-cell level during the onset of T1D in humans.