Urban airborne PM2.5-activated microglia mediate neurotoxicity through glutaminase-containing extracellular vesicles in olfactory bulb.

Emerging evidence has showed that exposure to airborne particulate matter (PM) with an aerodynamic diameter less than 2.5 µm (PM2.5) is associated with neurodegeneration. Our previous studies in vitro found that PM2.5 exposure causes primary neurons damage through activating microglia. However, the molecular mechanism of microglia-mediated neurotoxicity remains to elucidate. In this study, five groups (N = 13 or 10) of six-week-old male C57BL/6 mice were daily exposed to PM2.5 (0.1 or 1 mg/kg/day body weight), Chelex-treated PM2.5 (1 mg/kg/day body weight), PM2.5 (1 mg/kg/day body weight) plus CB-839 (glutaminase inhibitor), or deionized water by intranasal instillation for 28 days, respectively. Compared with the control groups, We found that PM2.5 triggered reactive oxygen species (ROS) generation and microglia activation evidenced by significant increase of ionized calcium binding adaptor molecule-1 (IBa-1) staining in the mouse olfactory bulbs (OB). Data from transmission electron microscope (TEM) images and Western blot analysis showed that PM2.5 significantly increased extracellular vesicles (EVs) release from OB or murine microglial line BV2 cells, and glutaminase C (GAC) expression and glutamate generation in isolated OB and BV2 cells. However, treatment with N-acetylcysteine (NAC) or CB-839 significantly diminished the number of EVs and the expression of GAC and abolished PM2.5-induced neurotoxicity. These findings provide new insights that PM2.5 induces oxidative stress and microglia activation through its metal contents and glutaminase-containing EVs in OBs, which may serve as a potential pathway/mechanism of excessive glutamate generation in PM2.5-induced neurotoxicity.