MEG3-4 is a miRNA decoy that regulates IL-1β abundance to initiate and then limit inflammation to prevent sepsis during lung infection

Long noncoding RNAs (lncRNAs) regulate gene expression. We investigated the role of lncRNAs in the inflammatory response to bacterial infection in the lungs. We identified the lncRNA MEG3 as a tissue-specific modulator of inflammatory responses during bacterial infection. Among the 10 transcript isoforms of MEG3, transcript 4 (referred to as MEG3-4) encodes the isoform with the lowest abundance in mouse lungs. Nonetheless, we found that MEG3-4 bound to the microRNA miR-138 in a competitive manner with mRNA encoding the proinflammatory cytokine interleukin-1 beta (IL-1 beta), thereby increasing IL-1 beta abundance and intensifying inflammatory responses to bacterial infection in alveolar macrophages and lung epithelial cells in culture and in lung tissue in mice. MEG3-4-mediated sponging of miR-138 in the cytoplasm increased the autocrine activity of IL-1 beta that subsequently induced a negative feedback mechanism mediated by nuclear factor kappa B that decreased MEG3-4 abundance and inflammatory cytokine production. This timely reduction in MEG3-4 abundance tempered proinflammatory responses in mice with pulmonary bacterial infection, preventing the progression to sepsis. Together, these findings reveal that MEG3-4 dynamically modulates pulmonary inflammatory responses through transcriptional regulation of immune response genes, extending the decoy and sponge mechanism associated with lncRNAs to antibacterial immunity, which affects both response and disease progression.