Ozone and PM2.5 co-exposure induced neurodegenerative alterations in mice: Implication of mitochondrial dysfunction in glial cells

Co-occurrence of ground-level ozone (O₃) and fine particulate matter (PM_2.5, ≤2.5 μm in aerodynamic diameter) has been a common air pollution scenario in urban areas worldwide. Existing evidence indicates exposure to O₃ or PM_2.5 is associated with neurodegenerative alterations. However, the association of co-exposure to O₃ and PM_2.5 with neurodegenerative disorders has been scarcely reported. This study examined neurodegenerative alterations following O₃ and PM_2.5 co-exposure and potential mechanisms. Ten-month-old male C57BL/6 mice were randomly divided into four groups: control, O₃, PM_2.5, and co-exposure (O₃ + PM_2.5). The conditions of co-exposure were established based on a real environmental exposure in the Central Plains Urban Agglomeration in Central China. Specifically, O₃ exposure was set at 0.6 ppm for 4 h/day over 30 consecutive days, while PM_2.5 exposure was performed through oropharyngeal aspiration of PM_2.5 suspension (5.6 mg/kg bw) every other day, 4 h prior to O₃ exposure. The results demonstrated that co-exposure significantly worsened memory impairment, neuroinflammation, blood-brain barrier (BBB) damage, and activation of glial cells, indicative of neurodegeneration. Omics approaches further revealed oxidative stress, mitochondrial injury, and endoplasmic reticulum stress in glial clusters following co-exposure. Moreover, strong associations between memory impairment, neuroinflammation, glial cell activation, and brain tissue damage with mitochondrial complex dysfunction in glial cells were uncovered. Taken together, O₃ and PM_2.5 co-exposure exacerbates neurodegenerative disorders, which involves mitochondrial complex dysfunction in glial cells, especially astrocytes. This study provides insights into the mechanisms underlying air pollution-induced neurodegenerative diseases.