N⁶-Adenosine Methylation of Socs1 mRNA Is Required to Sustain the Negative Feedback Control of Macrophage Activation.

Bacterial infection triggers a cytokine storm that needs to be resolved to maintain the host's wellbeing. Here, we report that ablation of m⁶A methyltransferase subunit METTL14 in myeloid cells exacerbates macrophage responses to acute bacterial infection in mice, leading to high mortality due to sustained production of pro-inflammatory cytokines. METTL14 depletion blunts Socs1 m⁶A methylation and reduces YTHDF1 binding to the m⁶A sites, which diminishes SOCS1 induction leading to the overactivation of TLR4/NF-κB signaling. Forced expression of SOCS1 in macrophages depleted of METTL14 or YTHDF1 rescues the hyper-responsive phenotype of these macrophages in vitro and in vivo. We further show that LPS treatment induces Socs1 m⁶A methylation and sustains SOCS1 induction by promoting Fto mRNA degradation, and forced FTO expression in macrophages mimics the phenotype of METTL14-depleted macrophages. We conclude that m⁶A methylation-mediated SOCS1 induction is required to maintain the negative feedback control of macrophage activation in response to bacterial infection.

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