Exposure to inhaled particulate matter activates early markers of oxidative stress, inflammation and unfolded protein response in rat striatum

Abstract

To study central nervous system airborne PM related subchronic toxicity, SD male rats were exposed for eight weeks to either coarse (32 μg/m³), fine (178 μg/m³) or ultrafine (107 μg/m³) concentrated PM or filtered air. Different brain regions (olfactory bulb, frontal cortex, striatum and hippocampus), were harvested from the rats following exposure to airborne PM. Subsequently, prooxidant (HO-1 and SOD-2), and inflammatory markers (IL-1β and TNFα), apoptotic (caspase 3), and unfolded protein response (UPR) markers (XBP-1S and BiP), were also measured using real-time PCR. Activation of nuclear transcription factors Nrf-2 and NF-κB, associated with antioxidant and inflammation processes, respectively, were also analyzed by GSMA. Ultrafine PM increased HO-1 and SOD-2 mRNA levels in the striatum and hippocampus, in the presence of Nrf-2 activation. Also, ultrafine PM activated NF-κB and increased IL-1β and TNFα in the striatum. Activation of UPR was observed after exposure to coarse PM through the increment of XBP-1S and BiP in the striatum, accompanied by an increase in antioxidant response markers HO-1 and SOD-2. Our results indicate that exposure to different size fractions of PM may induce physiological changes (in a neuroanatomical manner) in the central nervous system (CNS), specifically within the striatum, where inflammation, oxidative stress and UPR signals were effectively activated.

Keywords: ATF6; BiP; Central nervous system; GSMA; HO-1; IL-1β; IRE1α; Inflammation; NF-κB; Nrf-2; Oxidative stress; PAHs; PERK; PM; Particulate matter; SOD; Striatum; TNFα; UPR; Unfolded protein response; VACES; X-box binding protein 1; XBP-1; XBP-1 spliced form; XBP-1 unspliced form; XBP-1S; XBP-1U; activating transcription factor 6; eukaryotic translation initiation factor 2-alpha kinase 3; gel shift mobility assay; heat shock 70kDa protein 5 (glucose-regulated protein, 78kDa); heme oxygenase 1; inositol-requiring protein 1; interleukin 1 beta; nuclear factor (erythroid-derived 2)-like 2; nuclear factor kappa-light-chain-enhancer of activated B cells; particulate matter; polycyclic aromatic hydrocarbons; superoxide dismutase; tumor necrosis factor-alpha; unfolded protein response; versatile aerosol concentrator system.

Fig. 1

Expression of mRNA levels of HO-1 in olfactory bulb, striatum, frontal cortex and hippocampus. Data represent mean of 6 samples of mRNA fold changes ± S.E. FA, filtered air; C, coarse; F, fine; UF, ultrafine. *Value is significantly different (p ≤ 0.05) from filtered air.

Fig. 2

Gel shift mobility analysis of levels of activated Nrf-2 in the striatum and hippocampus. Panel A: Gel shift mobility analysis of levels of activated Nrf-2 (SC, specific competitor containing sample and unlabeled Nrf-2 consensus oligonucleotide; NSC, non-specific competitor containing sample and unlabeled SP1 consensus oligonucleotide). Integrated density of the shifted band. *Value is significantly different (p ≤ 0.05) from filtered air. Bars represent mean of 3 samples ± S.E. (B).

Fig. 3

Expression of mRNA of SOD2 in striatum and hippocampus. Bars represent mean of 6 samples ± S.E. *Value is significantly different to filtered air.

Fig. 4

Expression of mRNA of IL-1β and TNFα and gel shift mobility assay of NF-κB. Panel A: Bars represent mean of 6 samples ± S.E. Panel B: Gel shift mobility analysis of levels of activated NF-κB (SC, specific competitor containing sample and unlabelled NF-κB consensus oligonucleotide; NSC, non-specific competitor containing sample and unlabelled SP1 consensus oligonucleotide). Integrated density of the shifted band. *Value is significantly different (p ≤ 0.05) from the control. Panel C: Bars represent mean of 3 individuals ± S.E.

Fig. 5

RNA expression of BiP and XBP-1S. Bars represent mean of 6 individuals ± S.E. *Value is significantly different (p ≤ 0.05) from filtered air.

Fig. 6

Schematic representation of the matter and blood vessels networks of brain regions evaluated. We propose that some components of PM like metals can reach the striatum and hippocampus from the olfactory bulb directly through the olfactory tract, and to the frontal cortex through the uncinate fasciculus by transneuronal transport, previously reported for nanoparticles of Mn, Al, Fe, Zn, Co, Ni. Fine and ultrafine PM, as well as cytokines produced secondarily for PM exposure, can also reach brain regions.