Air pollution is implicated in neurodegenerative disease risk and progression and in microglial activation, but the mechanisms are unknown. In this study, microglia remained activated 24 h after ozone (O3) exposure in rats, suggesting a persistent signal from lung to brain. Ex vivo analysis of serum from O3‐treated rats revealed an augmented microglial proinflammatory response and β‐amyloid 42 (Aβ42) neurotoxicity independent of traditional circulating cytokines, where macrophage‐1 antigen‐mediated microglia proinflammatory priming. Aged mice exhibited reduced pulmonary immune profiles and the most pronounced neuroinflammation and microglial activation in response to mixed vehicle emissions. Consistent with this premise, cluster of differentiation 36 (CD36) ^–/– mice exhibited impaired pulmonary immune responses concurrent with augmented neuroinflammation and microglial activation in response to O ₃ . Further, aging glia were more sensitive to the proinflammatory effects of O ₃ serum. Together, these findings outline the lung‐brain axis, where air pollutant exposures result in circulating, cytokine‐independent signals present in serum that elevate the brain proinflammatory milieu, which is linked to the pulmonary response and is further augmented with age.—Mumaw, C. L., Levesque, S., McGraw, C., Robertson, S., Lucas, S., Stafflinger, J. E., Campen, M. J., Hall, P., Norenberg, J. P., Anderson, T., Lund, A. K., McDonald, J. D., Ottens, A. K., Block, M. L. Microglial priming through the lung‐brain axis: the role of air pollution‐induced circulating factors. FASEB J. 30, 1880–1891 (2016). www.fasebj.org

Background: Traffic-generated air pollution-exposure is associated with adverse effects in the central nervous system (CNS) in both human exposures and animal models, including neuroinflammation and neurodegeneration. While alterations in the blood brain barrier (BBB) have been implicated as a potential mechanism of air pollution-induced CNS pathologies, pathways involved have not been elucidated.Objectives: To determine whether inhalation exposure to mixed vehicle exhaust (MVE) mediates alterations in BBB permeability, activation of matrix metalloproteinases (MMP) -2 and −9, and altered tight junction (TJ) protein expression.Methods: Apolipoprotein (Apo)E^−/−and C57Bl6 mice were exposed to either MVE (100 μg/m³ PM) or filtered air (FA) for 6 hr/day for 30 days and resulting BBB permeability, expression of ROS, TJ proteins, markers of neuroinflammation, and MMP activity were assessed. Serum from study mice was applied to anin vitroBBB co-culture model and resulting alterations in transport and permeability were quantified.Results: MVE-exposedApo E^−/−mice showed increased BBB permeability, elevated ROS and increased MMP-2 and −9 activity, compared to FA controls. Additionally, cerebral vessels from MVE-exposed mice expressed decreased levels of TJ proteins, occludin and claudin-5, and increased levels of inducible nitric oxide synthase (iNOS) and interleukin (IL)-1β in the parenchyma. Serum from MVE-exposed animals also resulted in increasedin vitroBBB permeability and altered P-glycoprotein transport activity.Conclusions: These data indicate that inhalation exposure to traffic-generated air pollutants promotes increased MMP activity and degradation of TJ proteins in the cerebral vasculature, resulting in altered BBB permeability and expression of neuroinflammatory markers.

Objective— Mechanisms of air pollution–induced exacerbation of cardiovascular disease are currently unknown, thus we examined the roles of vascular endothelin-1 (ET-1) and reactive oxygen species (ROS) in regulating mediators of vascular remodeling, namely matrix metalloproteinases (MMPs), after exposure to vehicle engine emissions. Methods and Results— ApoE ^−/− mice were exposed by inhalation to filtered air or gasoline engine exhaust (GEE, 1:12 dilution) 6 hours per day for 1 or 7 days. Concurrently, mice were treated with either ET _A receptor antagonist BQ-123 (100 ng/kg/d) via osmotic minipumps, Tempol (≈41 mg/kg/d, orally), or vehicle. GEE-exposure increased vascular MMP-2 and -9, endothelin-1 (ET-1), tissue inhibitor of metalloproteinases (TIMP)-2 mRNA and ROS levels. Aortic MMP protein and plasma MMP-9 were similarly upregulated. GEE-mediated increases in vascular ROS were attenuated by Tempol-treatment, as were MMP-2 and TIMP-2; whereas BQ-123 ameliorated GEE-induced vascular expression of MMP-9, MMP-2, ROS, and ET-1. In a parallel study, diesel exhaust exposure in volunteer human subjects induced significant increases in plasma ET-1 and MMP-9 expression and activity. Conclusions— These findings demonstrate that acute exposure to vehicular source air pollutants results in upregulation of circulating and vascular factors associated with progression of atherosclerosis, mediated in part through activation of ET-1–ET _A receptor pathways.

A peer-reviewed open access journal published by the National Institute of Environmental Health Sciences

Rationale: To determine vascular signaling pathways involved in inhaled air pollution (vehicular engine emission) exposure–induced exacerbation of atherosclerosis that are associated with onset of clinical cardiovascular events. Objectives: To elucidate the role of oxidized low-density lipoprotein (oxLDL) and its primary receptor on endothelial cells, the lectin-like oxLDL receptor (LOX-1), in regulation of endothelin-1 expression and matrix metalloproteinase activity associated with inhalational exposure to vehicular engine emissions. Methods: Atherosclerotic apolipoprotein E knockout mice were exposed by inhalation to filtered air or mixed whole engine emissions (250 μg particulate matter [PM]/m3 diesel + 50 μg PM/m3 gasoline exhausts) 6 h/d for 7 days. Concurrently, mice were treated with either mouse IgG or neutralizing antibodies to LOX-1 every other day. Vascular and plasma markers of oxidative stress and expression proatherogenic factors were assessed. In a parallel study, healthy human subjects were exposed to either 100 μg PM/m3 diesel whole exhaust or high-efficiency particulate air and charcoal-filtered “clean” air (control subjects) for 2 hours, on separate occasions. Measurements and Main Results: Mixed emissions exposure increased oxLDL and vascular reactive oxygen species, as well as LOX-1, matrix metalloproteinase-9, and endothelin-1 mRNA expression and also monocyte/macrophage infiltration, each of which was attenuated with LOX-1 antibody treatment. In a parallel study, diesel exhaust exposure in volunteer human subjects induced significant increases in plasma-soluble LOX-1. Conclusions: These findings demonstrate that acute exposure to vehicular source pollutants results in up-regulation of vascular factors associated with progression of atherosclerosis, endothelin-1, and matrix metalloproteinase-9, mediated through oxLDL–LOX-1 receptor signaling, which may serve as a novel target for future therapy.