Mettl14-Mediated m(6)A Modification Facilitates Liver Regeneration by Maintaining Endoplasmic Reticulum Homeostasis

BACKGROUND & AIMS: N(6)-methyladenosine (m(6)A), the most prevalent and dynamic posttranscriptional methylation modification of mammalian mRNA, is involved in various biological processes, but its role in liver regeneration has not been characterized. METHODS: We first conducted transcriptome-wide m(6)A mRNA sequencing and characterized the expression pattern of m(6)A in regenerating mouse liver. Next, we generated hepatocyte-specific Mettl3- or Mettl14-deficient mice and investigated their role in liver regeneration. A series of biochemical experiments in vitro and in vivo was further performed to investigate potential mechanisms. RESULTS: We identified an overwhelming proportion of m(6)A-modified genes with initially up-regulated and subsequently down-regulated m(6)A levels as liver regeneration progressed. Loss of Mettl14 but not of Mettl3 resulted in markedly disrupted liver regeneration, and Mettl14-ablated hepatocytes were arrested in the G1 phase of the cell cycle. Most strikingly, the Mettl14-ablated regenerating liver exhibited extensive parenchymal necrosis. mRNA transcripts, such as Hsp90b1, Erp29, Stt3a, P4hb, and Lman1, encoding proteins involved in polypeptide processing and the endoplasmic reticulum (ER) stress response, were m(6)A-hypomethylated, and their mRNA and protein levels were subsequently decreased, resulting in unresolved ER stress, hepatocyte death, and inhibited proliferation. CONCLUSIONS: We demonstrate the essential role of Mettl14 in facilitating liver regeneration by modulating polypeptide-processing proteins in the ER in an m(6)A-dependent manner.