Radiation-induced brain injury is a severe complication of cranial radiotherapy, but the redox-dependent mechanisms linking neuronal damage to microglial neuroinflammation remain incompletely understood. Here, we investigated whether radiation-induced reactive oxygen species (ROS) are associated with neuronal mitochondrial dysfunction, lipid accumulation, and subsequent microglial inflammatory activation. Using an irradiated mouse brain injury model and neuron-microglia conditioned-medium systems, we found that ionizing radiation increased neuronal ROS production and impaired mitochondrial homeostasis, accompanied by enhanced autophagic turnover and mitophagy-related changes. These changes were accompanied by lipid droplet formation and free fatty acid accumulation in neurons. Pharmacological modulation of ROS and mitophagy-related processes supported an association among ROS, mitophagy and neuronal lipid accumulation after irradiation. Lipid accumulation was associated with reduced SIRT1 expression and increased HMGB1 acetylation, redistribution, and release from irradiated neurons. Manipulation of fatty acid uptake and SIRT1 activity further supported the involvement of lipid accumulation and reduced SIRT1 activity in HMGB1 acetylation, redistribution and release from irradiated neurons. Conditioned medium from irradiated neurons promoted microglial inflammatory activation, whereas HMGB1 neutralization attenuated inflammatory cytokine production. Pharmacological inhibition of TLR4, NF-κB, and inflammasome-related signaling reduced downstream inflammatory responses in these pretreated microglia. These findings support a working model linking radiation-induced neuronal oxidative and mitochondrial stress, lipid accumulation, HMGB1 signaling, and microglial inflammatory activation. This metabolic-inflammatory coupling may represent a potential intervention point for radiation-induced brain injury, although further genetic and in vivo validation is required.
