285-OR: m⁶A carRNA Methylation Regulates Chromatin State and Transcription in Islets from Humans with Type 2 Diabetes

RNA N⁶-methyladenosine (m⁶A) is among the most abundant mRNA modifications in mammals. Seminal work from our lab has reported that the “writers” of m⁶A (e.g. methyltransferase-like [METTL3] and METTL14) are significantly downregulated in islets of humans with type 2 diabetes (T2D). Consequently, the global m⁶A landscape in the islets segregates the T2D from the control group significantly better than the transcriptome (n=7 for Control and n=8 for T2D islets). Hypomethylation of key transcripts in the insulin/IGF-1-AKT-PDX1 pathway impaired insulin secretion and decreased β-cell proliferation. We now show this decreased m⁶A on RNA is not limited to the mRNA but also affects chromatin-associated regulatory RNAs (carRNA). carRNAs, which include promoter- and enhancer-associated RNAs as well as several non-coding repeat elements have been previously shown to regulate gene expression in an m6A-dependent manner. Intriguingly, downregulation of METTL3 and METTL14 in human β-cell line EndoC-βH1 differentially regulates these regulatory versus protein-coding transcripts. We observe that while METTL14 KD causes global downregulation of transcripts belonging to pathways important for β-cell identity and function (including calcium signaling, PI3K-AKT/MAPK signaling pathway, pancreatic secretion etc.), it leads to an upregulation of pathways involved in RNA processing and global gene transcription (Transcription by RNA Pol II, metabolism and splicing of mRNA, chromatin organization and modification etc.) {false discovery rate (FDR) < 0.05}. Considering carRNAs have been previously reported to regulate global chromatin accessibility and transcription, our observations on their ability to get differentially regulated m⁶A writer proteins provide novel insights into the epigenetic regulation of human islet cells. These findings provide opportunities to develop therapeutic approaches to regulate β-cell identity and/or insulin secretion in T2D.