METTL3 aggravates lung injury in neonatal mice with <i>Streptococcus pneumoniae</i> -induced pneumonia via the circ_0001239/KLF10 axis

As a leading causative agent of pneumonia infection worldwide, <i>Streptococcus pneumoniae</i> (<i>Spn</i>) induces lung injury and presents substantial therapeutic challenges. To elucidate the role of methyltransferase-like 3 (METTL3) in modulating circular RNA_0001239 (circ_0001239), YTH domain containing protein 2 (YTHDC2), and Krüppel-like factor 10 (KLF10) through m6A modification, we established <i>Spn</i>-induced neonatal mouse models. The survival rates, bacterial load in bronchoalveolar lavage fluid, and METTL3 expression in pulmonary tissue were evaluated. After METTL3 downregulation, lung wet-to-dry ratio, myeloperoxidase activity, and inflammatory markers were assessed. Methylated RNA immunoprecipitation detected enriched m6A modification on circ_0001239, while RNA immunoprecipitation validated the bindings of circ_0001239 to YTHDC2 and YTHDC2 to KLF10. The KLF10 mRNA stability was analyzed via actinomycin D treatment. METTL3 and circ_0001239 were upregulated in pneumonic lungs, while KLF10 was downregulated. METTL3 knockdown improved survival, alleviated lung injury, increased superoxide dismutase levels, and suppressed interleukin (IL)-6, IL-1β, and malondialdehyde levels. METTL3 promoted the binding of circ_0001239 to YTHDC2 via m6A modification, destabilizing KLF10 mRNA. Circ_0001239 overexpression or KLF10 knockdown reversed the protective effects of low expression of METTL3 on lung damage in neonatal mice with pneumonia. In conclusion, METTL3 aggravates <i>Spn</i>-induced lung injury via m6A-dependent circ_0001239/YTHDC2/KLF10 axis, thereby providing potential therapeutic targets for severe pneumonia.