FGF15/FGFR4 signaling suppresses M1 macrophage polarization and multi-organ inflammation in septic mice by inhibiting H3K18 lactylation-driven Irf7 expression through NF2-Hippo activation.

M1 macrophage polarization plays a key role in the onset and progression of sepsis. Fibroblast growth factor 15 (FGF15) suppresses septic inflammation through its FGF receptor 4 (FGFR4); however, the underlying mechanisms are largely unclear. In this study, we evaluated the anti-inflammatory effects of recombinant FGF15 (rFGF15) in cecal ligation and puncture (CLP)-induced septic mice in vivo, as well as lipopolysaccharide (LPS)-stimulated mouse bone marrow-derived macrophages (BMDMs) and RAW264.7 macrophages in vitro. We observed that rFGF15 suppressed M1 macrophage polarization and associated inflammatory responses in both CLP-induced septic mice and LPS-stimulated BMDMs and RAW264.7 macrophages. Additionally, macrophage-depleted CLP mice transplanted with LPS-stimulated BMDMs pre-treated with rFGF15 exhibited reduced multi-organ inflammation and enhanced survival compared to those receiving LPS-stimulated BMDMs without rFGF15 treatment. Mechanistically, FGF15 activated the neurofibromin 2 (NF2)-Hippo pathway through FGFR4, leading to the inhibition of glycolysis, lactate production, and histone H3K18 lactylation. This led to reduced expression of interferon regulatory factor 7 (Irf7), a key regulator of type I interferon responses. In conclusion, FGF15 suppresses M1 macrophage polarization and associated inflammatory responses in sepsis by activating the NF2-Hippo pathway, thereby inhibiting H3K18 lactylation-driven Irf7 expression. FGF15 holds promise as a potential innovative therapy for sepsis.