Abstract 18: Toll-Like Receptor 4 Knockout Attenuates Microglia-Mediated Oxidative Stress and White Matter Toxicity

Abstract

Background: Exposure to ambient air pollution causes neuroinflammation and white matter (WM) damage. In patients with preexisting cerebrovascular disease, pollution exposure can compound underlying pathology and may accelerate functional decline. Major mechanisms of this toxicity are microglial reactivity and oxidative stress. We therefore hypothesized that attenuation of the Toll-like receptor 4 (TLR4)-dependent microglial response would significantly decrease oxidative WM damage in a joint experimental model of pollutant exposure and chronic cerebral hypoperfusion modeled by surgical bilateral carotid artery stenosis (BCAS). Methods: Inducible microglial/macrophage-specific TLR4 deletion was achieved using a Tamoxifen-induced Cx3cr1CreER+/- mouse model. Male and female Cx3cr1CreER+/- mice treated with tamoxifen (i-mTLR4-ko) or corn oil (control) were exposed to 120 hours of filtered air (FA) or aerosolized diesel exhaust particulate (DEP), and 30 days of BCAS or sham surgery using a factorial design. The 8 experimental groups were: 1) control/FA (n=10), 2) control/DEP (n=10), 3) control/FA + BCAS (n=9), 4) control/DEP+BCAS (n=10), 5) i-mTLR4-ko/FA (n=9), 6) i-mTLR4-ko/DEP (n=8), 7) i-mTLR4-ko/FA + BCAS (n=8), and 8) i-mTLR4-ko/DEP+BCAS (n=10). Immunofluorescence was used to identify 4-HNE and 8-OHdG expression in the corpus callosum (CC). Results: While control mice showed elevations of 4-HNE in the CC after DEP (p<0.01) and DEP+BCAS (p<0.0001), i-mTLR4-ko prevented this change (Figure 1). While control mice exhibited a rise in 8-OHdG in the CC after DEP+BCAS (p<0.05), i-mTLR4-ko prevented this rise. Conclusions: We demonstrate that i-mTLR4-ko is sufficient to abate major elevations in oxidative stress markers in WM after DEP and BCAS exposures. This suggests a potential role for therapies targeting TLR4 signaling to minimize pollution-associated neurotoxicity, particularly in the setting of cerebral hypoperfusion.