Lactate Accelerates Early Angiogenesis and Bone Regeneration Through Macrophage <scp>M1</scp> Polarisation

Failure of timely bone regeneration compromises structural integrity and delays functional recovery; therefore immune regulation of the early repair microenvironment is crucial for successful healing. M1 (pro-inflammatory) phenotype macrophages play pivotal roles in vascularisation during the early phase of bone regeneration and are typically activated by interferon-gamma (IFN-γ) or lipopolysaccharide (LPS) as well as by metabolite-derived signals. Lactate, a metabolite known to regulate a series of pathophysiological processes, has not yet been fully investigated for its specific immunomodulatory role in the microenvironment of bone injury healing. Our in vitro experiments demonstrated that lactate induced macrophage polarisation to the M1 phenotype and accelerated angiogenesis, with the HIF1α-NOD1-calcium influx axis identified as a key mediator. In vivo validation further confirmed the positive effects of lactate intervention in promoting vascularised bone regeneration at the early stage of injury. Thus, this study uncovers how lactate modulates immune response in association with M1 macrophages and indicates its potential as a therapeutic strategy for promoting vascularised bone healing.