Abstract

Persistent inflammation impedes peripheral nerve regeneration, in which infiltrating macrophages play pivotal roles by regulating the M1/M2 phenotypic balance. M2 macrophages facilitate repair, yet factors driving M1-to-M2 transition remain unclear. Lactate, a key metabolic byproduct in injured tissue, dynamically regulates microenvironmental signaling. Here, we observed a correlation between M2 macrophage accumulation and lactate elevation within 5 days post-sciatic nerve injury. In vitro, both Schwann cells and macrophages were identified as important lactate producers. In vivo, low-dose lactate (10–20 mM) enhanced M2 polarization and accelerated regeneration, whereas high-dose lactate (50 mM) showed no benefit. Transcriptomic analysis revealed that 10 mM lactate upregulated M2 markers (arginase 1 (Arg1), vascular endothelial growth factor (VEGF), transforming growth factor-beta (TGF-β)) and oxidative phosphorylation (OXPHOS)-related genes in M1 macrophages. Seahorse analysis and adenosine triphosphate (ATP) quantification confirmed lactate-driven OXPHOS activation. Conversely, 50 mM lactate induced excessive reactive oxygen species (ROS) and reduced mitochondrial membrane potential which may explain its lack of regenerative efficacy. Furthermore, CCAAT/enhancer-binding protein beta (Cebpb), a transcription factor can promote Arg1 and VEGF expression in M1 cells under 20 mM lactate. Our findings demonstrate that low-dose lactate promotes M1-to-M2 transition via OXPHOS metabolic reprogramming and Cebpb upregulation, whereas excessive lactate disrupts mitochondrial function. This highlights lactate concentration-dependent modulation of macrophage polarization, a finding that provides insights into metabolic regulation of inflammatory responses during nerve repair. The current data, which focus on macrophage polarization outcomes, support further investigation into whether targeting metabolic rewiring could optimize regenerative microenvironments for functional nerv