Serpina3k lactylation protects from cardiac ischemia reperfusion injury

Lactate produced during ischemia-reperfusion injury is known to promote lactylation of proteins, which play controversial roles. By analyzing the lactylomes and proteomes of mouse myocardium during ischemia-reperfusion injury using mass spectrometry, we show that both Serpina3k protein expression and its lactylation at lysine 351 are increased upon reperfusion. Both Serpina3k and its human homolog, SERPINA3, are abundantly expressed in cardiac fibroblasts, but not  in cardiomyocytes. Biochemically, lactylation of Serpina3k enhances protein stability. Using Serpina3k knockout mice and mice overexpressing its lactylation-deficient mutant, we find that Serpina3k protects from cardiac injury in a lysine 351 lactylation-dependent manner. Mechanistically, ischemia-reperfusion-stimulated fibroblasts secrete Serpina3k/SERPINA3, and protect cardiomyocytes from reperfusion-induced apoptosis in a paracrine fashion, partially through the activation of cardioprotective reperfusion injury salvage kinase and survivor activating factor enhancement pathways. Our results demonstrate the pivotal role of protein lactylation in cardiac ischemia-reperfusion injury, which may hold therapeutic value.