Methods
This study included 1,131 cognitively intact individuals from the Chinese Alzheimer's Biomarker and LifestylE database with data provided on cerebrospinal fluid (CSF) AD biomarkers (amyloid beta-peptide 42 [Aβ42], total tau [t-tau], and phosphorylated tau [p-tau]), neuroinflammatory (CSF sTREM2), and systemic inflammatory markers (high sensitivity C-reactive protein and peripheral immune cells). The 2-year averaged levels of ambient fine particulate matter with diameter <2.5 μm (PM2.5 ), nitrogen dioxide (NO2 ), and ozone (O3 ) were estimated at each participant's residence. Multiple-adjusted models were approached to detect associations of air pollution with inflammatory markers and AD-related proteins.
Results
Ambient 2-year averaged exposure of PM2.5 was associated with changes of neuroinflammatory markers, that is, CSF sTREM2 (β = -0.116, p = 0.0002). Similar results were found for O3 exposure among the elderly (β = -0.111, p = 0.0280) or urban population (β = -0.090, p = 0.0144). No significant evidence supported NO2 related to CSF sTREM2. For potentially causal associations with accumulated AD pathologies, the total effects of PM2.5 on CSF amyloid-related protein (CSF Aβ42 and p-tau/Aβ42) were partly mediated by CSF sTREM2, with proportions of 14.22% and 47.15%, respectively. Additional analyses found inverse associations between peripheral inflammatory markers with PM2.5 and NO2 , but a positive correlation with O3 . Interpretation: These findings demonstrated a strong link between PM2.5 exposure and microglial dysfunction. Furthermore, CSF sTREM2 as a key mediator modulated the influences of PM2.5 exposure on AD amyloid pathologies.