NFAT5 in alveolar macrophages exacerbates seawater-induced acute lung injury via PFKP-driven glycolysis

Seawater-induced acute lung injury (ALI) shares pathological features with other forms of ALI, characterised by high mortality; however, it presents unique traits, particularly persistent hypoxemia. Nuclear Factor of Activated T cells 5 (NFAT5), initially recognised as a tonicity-responsive enhancer-binding protein, has emerged as acritical regulator of inflammation. Nonetheless, its specific function in alveolar macrophages (AMs) during hyperosmolar seawater-induced ALI remains unclear. This study establishes a murine model of seawater-induced ALI, revealing significantly elevated NFAT5 expression in lung macrophages. Siglec1-specific NFAT5 knockout effectively mitigated seawater-induced lung injury. Mechanistically, NFAT5 was found to directly bind the promoter region of Phosphofructokinase, Platelet type (PFKP) in AMs, enhancing its transcriptional activity. NFAT5 knockdown resulted in downregulation of PFKP expression and suppression of glycolysis, which inhibited M1 macrophage polarisation while promoting M2 macrophage polarisation, thereby reducing the release of inflammatory cytokines. Additional in vitro and in vivo experiments demonstrated that PFKP overexpression counteracts the protective effects of Siglec1-specific NFAT5 knockout in seawater-induced ALI by restoring glycolytic activity. Collectively, these findings illustrate that the NFAT5-PFKP signaling axis in AMs regulates macrophage polarisation and inflammatory responses through glycolytic reprogramming, playing a critical pathogenic role in seawater-induced ALI. These insights enhance understanding of the energy metabolism in AMs, previously regarded as less relevant in inflammation, and identify the NFAT5-PFKP axis as a promising therapeutic target for seawater-induced ALI.