Light-driven repair: Photobiomodulation restores blood–brain barrier function following hypoxic injury

Abstract A functional blood-brain barrier (BBB) is essential for the central nervous system (CNS) homeostasis and its disruption is an early event in acute brain injury and chronic neurodegeneration. Hypoxia triggers BBB breakdown, promoting endothelial dysfunction, oxidative stress, metabolic dysregulation and thrombo-inflammatory responses that compromise barrier integrity. However, strategies that directly restore BBB function remain limited. Here, we investigated whether photobiomodulation (PBM), a non-invasive light therapy, can rescue BBB dysfunction following acute hypoxic stress. Using a multicellular in vitro BBB model comprising immortalised human brain microvascular endothelial cells, pericytes and astrocytes, we induced hypoxic injury (6 h, 1% O₂) and applied three PBM treatments during recovery. Hypoxia significantly reduced transendothelial electrical resistance (TEER), whereas PBM restored barrier function in endothelial monocultures and tri-cultures. Endothelial cells showed the strongest hypoxic response, with increased hypoxia-inducible factor-1α, plasminogen activator inhibitor-1 and von Willebrand factor (vWF), all attenuated by PBM. Importantly, siRNA-mediated knockdown of vWF partially recapitulated PBM-induced barrier rescue, identifying endothelial vWF as a mediator of recovery. PBM also reduced reactive oxygen species in hypoxic astrocytes and pericytes, indicating coordinated multicellular modulation. These findings demonstrate that PBM restores BBB integrity after hypoxic insult by modulating endothelial thrombo-inflammatory signalling while reducing oxidative stress in glial cells. Rather than acting as a general cytoprotective stimulus, PBM engages defined molecular pathways linked to endothelial activation. This work establishes a mechanistically informed platform for studying BBB repair and supports PBM as a targeted strategy to protect vascular integrity in hypoxia-associated neurological disorders. Key points summary Hypoxia is a major driver of blood-brain barrier (BBB) dysfunction, yet there are currently no targeted therapies that directly restore barrier integrity. Photobiomodulation (PBM) is a non-invasive low-level light intervention known to facilitate mitochondrial function and cellular stress responses. In a human in vitro BBB model, repeated PBM treatment restored transendothelial electrical resistance (TEER) 24 and 48 hours after hypoxic injury, with endothelial rescue linked to downregulation of von Willebrand factor (vWF). PBM modulated oxidative stress, hypoxia signalling, and thrombo-inflammatory pathways across endothelial cells, astrocytes, and pericytes. These findings support light-driven modulation of endothelial signalling as a potential strategy to restore BBB integrity in hypoxia-associated neurological conditions. Graphical abstract