25-hydroxysterol mitigates microgravity-induced retinal damage by suppressing microglial inflammation through...

Spaceflight-associated neuro-ocular syndrome (SANS) poses a significant risk to astronaut vision during long-duration missions, yet its immunological underpinnings remain poorly defined. Here, we identify retinal microglia as key mediators of ocular degeneration under simulated microgravity (SMG). Using a 3D clinostat model, we show that SMG induces early activation of retinal pigment epithelium (RPE), which in turn promotes microglial activation and triggers a feedforward cascade of RPE damage and neuronal loss. We further demonstrate that 25-hydroxycholesterol (25-HC), an oxysterol capable of penetrating the blood-retinal barrier, attenuates this inflammatory cascade by disrupting lipid raft formation in microglia. Low-dose 25-HC suppresses the recruitment of cytokine receptors to lipid rafts, mitigating microglia-driven retinal injury. These findings uncover a critical immunopathological axis underlying SANS and propose 25-HC as a non-invasive, immunomodulatory countermeasure to preserve retinal integrity during spaceflight.