Myeloid-specific Ythdf2 deletion alleviates acute lung injury by attenuating macrophage inflammation

Acute lung injury (ALI) is characterized by dysregulated pulmonary inflammation, in which alveolar macrophages (AMs) play a crucial role. The m⁶A reader protein YTHDF2, known to facilitate mRNA degradation, is implicated in inflammation; however, its specific function in ALI pathogenesis remains unclear. Using myeloid-specific Ythdf2 knockout mice subjected to cecal ligation and puncture (CLP)-induced ALI, we demonstrate that Ythdf2 deficiency significantly attenuates lung injury, as evidenced by reduced histopathological damage, pulmonary edema, and inflammatory cell infiltration, along with lower levels of pro-inflammatory cytokines (IL-6, TNF-α) in both bronchoalveolar lavage fluid and serum. Moreover, Ythdf2 deletion was accompanied by a substantial upregulation of Hmox1 protein expression in both lung tissues and AMs, an observation consistent with the known role of Ythdf2 in pulmonary hypertension. Furthermore, global m⁶A methylation levels and the expression of key methyltransferases (Mettl3, Mettl14) were elevated during ALI, coinciding with increased Ythdf2 expression. This upregulation of m⁶A regulators (YTHDF2, METTL3, METTL14) was also confirmed in pulmonary macrophages from human septic lungs. In conclusion, our findings support the concept that the myeloid-specific deletion of Ythdf2 ameliorates lung injury, an effect closely associated with the upregulation of Hmox1, highlighting Ythdf2 as a potential therapeutic target for ALI.