Urban traffic-derived nanoparticulate matter reduces neurite outgrowth via TNFα in vitro
© Cheng et al. 2016
Received: 2 September 2015
Accepted: 11 January 2016
Published: 26 January 2016
The basis for air pollution-associated neurodegenerative changes in humans is being studied in rodent models. We and others find that the ultrafine particulate matter (PM) derived from vehicular exhaust can induce synaptic dysfunction and inflammatory responses in vivo and in vitro. In particular, a nano-sized subfraction of particulate matter (nPM, PM0.2) from a local urban traffic corridor can induce glial TNFα production in mixed glia (astrocytes and microglia) derived from neonatal rat cerebral cortex.
Here, we examine the role of TNFα in neurite dysfunctions induced by nPM in aqueous suspensions at 12 μg/ml. First, we show that the proximal brain gateway to nPM, the olfactory neuroepithelium (OE), rapidly responds to nPM ex vivo, with induction of TNFα, activation of macrophages, and dendritic shrinkage. Cell interactions were further analyzed with mixed glia and neurons from neonatal rat cerebral cortex.
Microglia contributed more than astrocytes to TNFα induction by nPM. We then showed that the threefold higher TNFα in conditioned media (nPM-CM) from mixed glia was responsible for the inhibition of neurite outgrowth by small interfering RNA (siRNA) TNFα knockdown and by TNFα immunoneutralization. Despite lack of TNFR1 induction by nPM in the OE, experimental blocking of TNFR1 by TNFα receptor blockers restored total neurite length.
These findings implicate microglia-derived TNFα as a mediator of nPM in air pollution-associated neurodegenerative changes which alter synaptic functions and neuronal growth.
KeywordsAir pollution Nanoparticulate matter Olfactory neuroepithelium TNFα Neurite outgrowth Cell culture Microglia
Air pollution epidemiology has traditionally focused on cardiovascular and respiratory outcomes. These adverse associations have been extended to show the acceleration of cognitive decline of elderly community-based populations [1–5] and neurodevelopmental impairments of children [6, 7]. The causes of cognitive impairment are being analyzed in rodent and cell models, which implicate neuroinflammatory responses to urban air pollutants [8–11]. Specifically, we and others observed that the ultrafine size class of air pollution PM0.2 (<0.2 μm diameter) activated microglia and induced TNFα and IL-1, among other inflammatory responses [10, 12–14]. This evidence supports findings of increased microglial activation and white matter hyperintensities in small postmortem samples of children from a highly polluted Mexican city [7, 15] and in the association of white matter loss in older human adults in an MRI analysis of the WHIMS cohort of US women .
Composition of nPM
Ambient nPM (%)
Eluted nPM (%)
% ambient in eluted nPM
Organic carbon, water soluble
Organic carbon, water insoluble
Metals (Cu, Fe, Ni, V)
nPM collection and transfer into aqueous suspension
Nano-sized particulate matter (nPM; <0.2 μm in diameter) was collected on Teflon filters by a High-Volume Ultrafine Particle (HVUP) Sampler  at 400 l/min flow in urban Los Angeles, downwind from the local I-110 Freeway . These samples are a mix of fresh ambient PM, mostly from vehicular traffic emissions and secondary aerosols [29, 30]. The nPM samples were collected continuously during July–Sept. 2010 and Nov. 2011–Feb. 2012; these pooled samples approximate the annual average composition of nPM near the I-110 corridor . The filter-trapped dried nPM were eluted by sonication into deionized water. The nPM comprise 20 % by mass of ambient PM2.5. Water-soluble metals and organic compounds were efficiently transferred (Table 1). Relative to the total filter-trapped ultrafines (PM0.2), the nPM subfraction eluted into aqueous phases is depleted in black carbon and water-insoluble organic compounds. nPM suspensions (350 μg/ml) were stored at −20 °C. For controls of nPM extracts, fresh sterile filters were sham-extracted.
C57BL/6J mice were purchased from The Jackson Laboratory (Sacramento, CA, USA) for breeding and pregnant Sprague Dawley rats from Harlan Labs (Livermore, CA, USA). Animals were maintained following NIH guidelines, approved by the USC Institutional Animal Care and Use Committee (IACUC). Animals were euthanized by cervical dislocation after anesthesia by isoflurane or CO2.
Nasal cavity ex vivo incubation
P3 mice (both sexes) were anesthetized and decapitated; the nasal bone was removed to reveal the nasal cavity. The entire nasal cavity including the snout intact was removed in the gross. Nasal cavities were incubated with 12 μg/ml nPM in artificial cerebral spinal fluid (CSF) for 2 h/37 °C. After incubation, the OE was peeled from the nasal cavity for quantitative polymerase chain reaction (qPCR) or immunohistochemistry. Mice were chosen for these experiments because their smaller size facilitates slide preparation and obviates decalcification.
Mixed glia were originated from the cerebral cortex of postnatal day 3 (P3) rats (both sexes). Primary glia were grown in Dulbecco’s modified Eagle’s medium/Ham’s F12 50/50 Mix (DMEM F12 50/50) supplemented with 10 % fetal bovine serum (FBS) and 1 % l-glutamine in a humidified incubator (37 °C/5 % CO2) . After culture for 2.5 weeks, their composition was 3:1 astrocytes:microglia. Microglia were isolated by shaking for 4 h/37 °C. Embryonic day 18 (E18) rat cortical neurons were originated at 15,000 neurons/cm2 on poly-d-lysine-coated coverslips in DMEM supplemented with B27 (Invitrogen, Grand Island, NY).
For in vitro exposure, mixed glia were trypsinized and replated in six-well plates at 1 × 106 cells/well and grown overnight. Secondary cultures of mixed glia were treated with nPM aqueous suspensions (12 μg/ml) diluted in neuronal media for 24 h before assay. This dose consistently induced glial TNFα and IL-1α messenger RNA (mRNA) . The resulting conditioned media (CM) was collected and centrifuged (10,000g/10 min) to remove residual cells. For small interfering RNA (siRNA) experiments, mixed glia were treated with siRNA (Silencer Negative Control No. 1 siRNA, AM4611; Ambion, Austin, TX) or TNFα siRNA (AM16708, Ambion). Scrambled and TNFα siRNAs were mixed with a siPORT NeoFX transfection agent (Ambion) to 50 nM. Mixed glia were grown for 24 h post transfection and then treated with nPM or vehicle before plating onto E18 neurons. Immunoneutralization of TNFα used 20 μg/ml antibody (MAB510; R&D Systems, Minneapolis, MN); TNF receptor activity was inhibited by TNFR1/2 blocking peptide (E-20, L-20; SCBT, Dallas, TX) at 5 μg/ml before CM application. Rats were used for in vitro experiments, following our prior studies  and the better yields of microglia than from mice.
Quantitative polymerase chain reaction
Total cellular RNA was extracted using TRI reagent (Sigma, St. Louis, MO). cDNA was prepared from 1 μg of RNA by Superscript III RT kit (Invitrogen, Carlsbad, CA) and analyzed by qPCR with appropriate primers for both mouse and rat for Ct (threshold cycle) values. Genes examined by qPCR include TNFα (forward: 5′ CGTCAGCCGATTTGCTATCT 3′; reverse: 5′ CGGACTCCGCAAAGTCTAAG 3′) (CT range 26–30), Iba1 (forward: 5′ CCTGATTGGAGGTGGATGTCAC 3′; reverse: 5′ GGCTCACGACTGTTTCTTTTTTCC 3′) (CT range 25–26), IL-1α (forward: 5′ TCGGGAGGAGACGACTCTAA 3′; reverse: 5′ GTGCACCCGACTTTGTTCTT 3′) (CT range 29–31), GFAP (forward: 5′ CCAAGCCAAACACGAAGCTAA 3′; reverse: 5′ AGGAATGGTGATGCGGTTTTC 3′) (CT range 30–31), iNOS (forward: 5′ CATTGGAAGTGAAGCGTTTCG 3′; reverse: 5′ CAGCTGGGCTGTACAAACCTT 3′) (CT range 27–29), TNFR1 (forward: 5′ GGGCACCTTTACGGCTTCC 3′; reverse: 5′ GGTTCTCCTTACAGCCACACA 3′) (CT range 22–23), TNFR2 (forward: 5′ CAGGTTGTCTTGACACCCTAC 3′ reverse: 5′ GCACAGCACATCTGAGCCT 3′) (CT range 25–26), βIII-tubulin (forward: 5′ CGCACGACATCTAGGACTGA 3′; reverse: 5′ TGAGGCCTCCTCTCACAAGT 3′) (CT range 19–20), and rGAPDH (forward: 5′ AGACAGCCGCATCTTCTTGT 3′; reverse: 5′ CTTGCCGTGGGTAGAGTCAT 3′) (CT range 16–17). Data were normalized to GAPDH and quantified as ΔΔCt.
CM from nPM-treated glia was sampled after 24 h of exposure and analyzed for TNFα by solid phase sandwich ELISA (BD Biosciences, San Jose, CA).
The OE and olfactory bulb of P3 neonatal mice were fixed with 4 % paraformaldehyde in phosphate buffered saline (PBS) pH 7.4. Specimens were immersed in 10 % sucrose/PBS pH 7.4, then 30 % sucrose/PBS pH 7.4 at 4 °C, then embedded in optimal cutting temperature compound (OCT; Fisher Scientific, Waltham, MA) before transverse cryostat sectioning (18 μm). Antigen retrieval was performed by submerging slides in 10 mM sodium citrate buffer and microwaving for 3 min. Tissue was permeabilized with 1 % NP-40/PBS and blocked with 5 % BSA, then probed with antibodies specific for the Olfactory Marker Protein of olfactory sensory neurons (OMP 1:100; SCBT, Dallas, TX), βIII-tubulin (1:400; Sigma Chemical Co., St. Louis, MO), astrocytes (GFAP 1:400; Sigma), and microglia (Iba1 1:200, Wako). Immunofluorescence was visualized with Alexa Fluor 488 or 594 antibodies (1:400; Molecular Probes).
Fluorescent images were analyzed with a Nikon Eclipse TE300 microscope (Nikon, Melville, NY). One hundred neurons were selected from a distribution of nine images per coverslip for analysis.
Neurite outgrowth assays
After exposure to glial conditioned media, E18 neurons were fixed in 4 % paraformaldehyde and immunostained with anti-βIII-tubulin (1:400). Neurites were visualized by F-actin with Rhodamine phalloidin (1:50; Molecular Probes, Carlsbad, CA). Images were analyzed for neurite length, density, and number by NeuronJ of ImageJ software; soma size was determined by the Neurphology plugin of ImageJ. Only neurons with neurites fully visible were analyzed. Neurite density was assayed as total βIII-tubulin fluorescence after skeletonizing. Axons were identified as the longest neurite .
The olfactory sensory neuron (OSN) dendritic layer of the OE was assessed by NeuronJ plugin of ImageJ in 20 evenly spaced regions in the nasal septum and ethmoturbinates. The dendritic layer thickness was defined as the distance between the OSN cell body and the outer edge of the sensory dendrites in the nasal cavity.
GraphPad Prism Version 5 (Graph Pad, La Jolla, CA) was used. Single and multiple comparisons used Student’s t test (unpaired) and ANOVA/Tukey’s multiple comparison post-test, respectively. Level of significance alpha = 0.05.
nPM rapidly induced TNFα in olfactory neuroepithelium ex vivo
nPM-induced TNFα in both astrocytes and microglia
Conditioned media from nPM-treated astrocytes and microglia reduce neurite outgrowth
Inhibiting or reducing TNFα in the CM rescued neurite outgrowth
Blocking TNFR1 in neurons reduced the CM effect on neurite outgrowth
These studies further document the role of glial TNFα in neuroinflammatory responses to air pollution PM that modify neuronal function. In particular, we studied nPM, which are a subfraction of urban PM2.5 (“Methods” section) that epidemiological studies have associated with neurodevelopmental dysfunctions from pre- and early childhood exposure [37, 38]. Rodent models include exposure of pregnant rats to nPM, which altered neonatal neuronal maturation  and exposure of early postnatal mice to ultrafine PM, which caused ventriculomegaly and glial activation . For inflammatory responses, we focused on TNFα because of its consistent elevation in rodent models of air pollution [8, 10, 40–42] as well as in postmortem human brains from a highly polluted megacity . In vitro activities of nPM include induction of TNFα in mixed glia from cerebral cortex and reduced neurotrophic support by the CM of mixed glia exposed to nPM . We also document the stability of nPM activity to induce TNFα, in which the dose response was nearly identical, despite collection from the same site on different years.
We hypothesized that glial TNFα was a mediator of these CM effects because TNFα in vitro inhibits neurite outgrowth [24, 34] with growth cone collapse  and inhibits astrocytic neurotrophic support . Before further analysis of cerebral cortex glia, we investigated if TNFα induction by air pollution PM extended to the OE which is the initial site of exposure of inhaled air pollutants from which olfactory neurons project into the brain. Importantly, besides the acute inflammatory responses of TNFα and macrophage activation, the OE expresses high levels of phase I and phase II detoxifying enzymes, e.g., cytochrome P450 (CYP) isoforms and glutathione S-transferases (GST) [45, 46], which may mediate detoxifying environmental pollutants.
We developed an ex vivo model for the initial impact of air pollution on olfactory neurons, in which the neonatal mouse nose is incubated with aqueous suspensions of nPM. During ex vivo incubation with nPM, the neonatal OE showed rapid shrinkage of the OSN dendritic layer concurrently with induction of TNFα and macrophage activation in the OE. We hypothesized that olfactory neuron dendritic regression was driven by TNFα from macrophages in the OE. This is supported by another model of olfactory damage, where TNFα was shown to inhibit OE regeneration . We further tested this hypothesis with primary glial cultures from the neonatal mouse cerebral cortex as discussed below.
In rodent models, nPM cross from the nose into the brain by undefined transport processes which are presumed to include the projections of OSN axons that synapse in the main olfactory bulb [19, 20]. Studies with different artificial ultrafine PM observed that inhaled  or nasally instilled  PM reached the forebrain and cerebellum as well as the OB within 24 h . The passage of nPM from the nares beyond the OB into the posterior brain structures gives a rationale for using cerebral cortex glia as an experimental model for direct nPM exposure. Although astrocyte cell bodies were not detected in the OE, there still may be a role of astrocytic TNFα in the OB which has deep neuronal projections caudally into the brain.
To develop our observations of OE dendritic shrinkage, we further analyzed mechanisms of neuronal responses to nPM with a model of primary cultures of mixed glia and neurons from the cerebral cortex. We extended our observation that CM from nPM-exposed mixed glia inhibited neurite outgrowth  by resolving cell type contributions. In subcultures from mixed glia, microglia contributed 60 % of the TNFα in CM, consistent with the greater inhibition of neurite outgrowth by CM from microglia. Similarly, the microglial CM caused more inhibition of neurite outgrowth and neurite density than the astrocyte CM. A primary role of microglia in nPM responses is also consistent with the low abundance of GFAP-immunopositive cells or processes in the OE, especially during development . The precise mechanism of nPM uptake in cells is not well defined but could include phagocytosis  as well as direct diffusion .
The role of TNFα in neurite outgrowth inhibition was further defined by suppressing TNFα expression with siRNA, by immunoblockade of TNFα, and by TNFR1 blockade, all of which restored neurite outgrowth to control levels. The restoration of axonal length by TNFα immunoblockade is also consistent with enhanced axonal regeneration by TNFα blockade after injury . Because these conditions did not consistently alter the total number of neurites or neuronal perikaryal size, they define an experimental model for effects of nPM on neuronal plasticity without major cell damage that could be useful for efficient screening of neuroprotective agents.
Several mechanisms may mediate the glial-derived TNFα influences on neurite outgrowth. Although TNFα has both cytosolic and transmembrane forms, we would not expect a significant role for transmembrane TNFα because the nPM-CM has negligible cell membrane content. Notably, of the two defined TNFRs, only blockade of TNFR1 rescued the nPM-CM effect. This specificity is consistent with the 20-fold higher affinity of TNFR1 (Ka) to soluble TNFα vs TNFR2 [52–54]. TNFR1 activation is associated with reduced neuronal differentiation, as well as apoptosis, whereas TNFR2 is associated with neuroprotection and survival . Blocking TNFR1 may have improved neurite outgrowth by diminishing growth cone collapse (Fig. 7c) through reduction of CM TNFα signaling. The small GTPase RhoA mediates the TNFα inhibition of neurite outgrowth , but mechanisms from receptor signaling to neurite outgrowth inhibition are less defined. RhoA activation by TNFα can cause growth cone collapse and attenuate neurite outgrowth [24, 34, 56], but this process has not been directly linked to TNFR1/2 signaling .
These experimental findings suggest a role for TNFα induction by the nPM subfraction of PM2.5. We propose that TNFα from microglia-macrophage activation by nPM in inhaled air pollutants is a main mediator of neuroinflammation and neurodevelopmental impairments from airborne particulate pollution. Studies are needed to evaluate other TNF superfamily receptors and their relation to the glutamatergic changes observed in rodent models of air pollution [10, 11, 42]. Further fractionation of the nPM may resolve the role of the persistent free radicals in nPM  and specific chemical components in the heterogeneous nPM. Although these nPM fractions do not include ozone and other gases with cognitive epidemiological associations [2, 21], gaseous pollutants could still contribute to nPM neurotoxicity in the real world. Identifying the neurotoxic components in air pollution could prioritize environmental policy targets to minimize neurodegenerative activities in the urban air we must breathe.
glial fibrillary acidic protein
ionized calcium-binding adaptor molecule 1 and monocytic marker
nano-sized particulate matter
olfactory sensory neuron
tumor necrosis factor alpha
tumor necrosis factor receptor
This work was supported by grants from grants to CEF from the NIA (R21AG040753, R21AG040683); the Ellison Medical Foundation; and the USC Zumberge Research and Innovation Fund; SCEHSC Center grant P30ES007048.
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- Ailshire JA, Crimmins EM. Fine particulate matter air pollution and cognitive function among older US adults. Am J Epidemiol. 2014;180:359–66.PubMed CentralView ArticlePubMedGoogle Scholar
- Chen JC, Schwartz J. Neurobehavioral effects of ambient air pollution on cognitive performance in US adults. Neurotoxicol. 2009;30:231–9.View ArticleGoogle Scholar
- Gatto NM, Henderson VW, Hodis HN, St. John JA, Lurmann F, Chen JC, et al. Components of air pollution and cognitive function in middle-aged and older adults in Los Angeles. Neurotoxicol. 2014;40:1–7.View ArticleGoogle Scholar
- Jung CR, Lin YT, Hwang BF. Ozone, particulate matter, and newly diagnosed Alzheimer’s disease: a population-based cohort study in Taiwan. J Alzheimer’s Dis. 2015;44:573–84.Google Scholar
- Weuve J, Puett RC, Schwartz J, Yanosky JD, Laden F, Grodstein F. Exposure to particulate air pollution and cognitive decline in older women. Arch Intern Med. 2012;172:219–27.PubMed CentralView ArticlePubMedGoogle Scholar
- Volk HE, Lurmann F, Penfold B, Hertz-Picciotto I, McConnell R. Traffic-related air pollution, particulate matter, and autism. JAMA Psychiatry. 2013;70:71–7.PubMed CentralView ArticlePubMedGoogle Scholar
- Calderón-Garcidueñas L, Torres-Jardon R, Kulesza RJ, Park SB, D’Angiulli A. Air pollution and detrimental effects on children’s brain. The need for a multidisciplinary approach to the issue complexity and challenges. Front Hum Neurosci. 2014;8:613.PubMed CentralPubMedGoogle Scholar
- Levesque S, Taetzsch T, Lull ME, Kodavanti U, Stadler K, Wagner A, et al. Diesel exhaust activates and primes microglia: air pollution, neuroinflammation, and regulation of dopaminergic neurotoxicity. Environ Health Perspect. 2011;1198:1149–55.View ArticleGoogle Scholar
- Genc S, Zadeoglulari Z, Fuss SH, Genc K. The adverse effects of air pollution on the nervous system. J Toxicol. 2012;2012:1–23.View ArticleGoogle Scholar
- Morgan TE, Davis DD, Iwata N, Tanner JM, Snyder D, Ning Z, et al. Glutamatergic neurons in rodent models respond to nanoscale particulate urban air pollutants in vivo and in vitro. Env Health Perspect. 2011;119:1003–9.View ArticleGoogle Scholar
- Davis DA, Akopian G, Walsh JP, Sioutas C, Morgan TE, Finch CE. Urban air pollutants reduce synaptic function of CA1 neurons via an NMDA/NȮ pathway in vitro. J Neurochem. 2013;127:509–19.View ArticlePubMedGoogle Scholar
- Zhang H, Liu H, Davies KJ, Sioutas C, Finch CE, Morgan TE, et al. Nrf2-regulated phase II enzymes are induced by chronic ambient nanoparticle exposure in young mice with age-related impairments. Free Radic Biol Med. 2012;52:2038–46.PubMed CentralView ArticlePubMedGoogle Scholar
- Kleinman MT, Araujo JA, Nel A, Sioutas C, Campbell A, Cong PQ, et al. Inhaled ultrafine particulate matter affects CNS inflammatory processes and may act via MAP kinase signaling pathways. Toxicol Lett. 2008;178:127–30.PubMed CentralView ArticlePubMedGoogle Scholar
- Block ML, Calderón-Garcidueñas L. Air pollution: mechanisms of neuroinflammation and CNS disease. Trends Neurosci. 2009;32:506–16.PubMed CentralView ArticlePubMedGoogle Scholar
- Calderón-Garcidueñas L, Engle R, Mora-Tiscareño A, Styner M, Gómez-Garza G, Zhu H, et al. Exposure to severe urban air pollution influences cognitive outcomes, brain volume and systemic inflammation in clinically healthy children. Brain Cogn. 2011;77:345–55.View ArticlePubMedGoogle Scholar
- Chen JC, Wang X, Wellenius G, Serre M, Driscoll I, Casanova R, et al. Ambient air pollution and neurotoxicity on brain structure: evidence from Women's Health Initiative Memory study. Ann Neurol. 2015;78:466–76.View ArticlePubMedGoogle Scholar
- Li N, Sioutas C, Cho A, Schmitz D, Misra C, Sempf J, et al. Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environ Health Perspect. 2003;111:455–60.PubMed CentralView ArticlePubMedGoogle Scholar
- Gillespie P, Tajuba J, Lippmann M, Chen LC, Veronesi B. Particulate matter neurotoxicity in culture is size-dependent. Neurotoxicol. 2013;36:112–7.View ArticleGoogle Scholar
- Oberdörster G, Sharp Z, Atudorei V, Elder A, Gelein R, Kreyling W, et al. Translocation of inhaled ultrafine particles to the brain. Inhal Toxicol. 2004;16:437–45.View ArticlePubMedGoogle Scholar
- Elder A, Gelein R, Silva V, Feikert T, Opanashuk L, Carter J, et al. Translocation of inhaled ultrafine manganese oxide particles to the central nervous system. Environ Health Perspect. 2006;114:1172–8.PubMed CentralView ArticlePubMedGoogle Scholar
- Wu YC, Lin YC, Yu HL, Chen JH, Chen TF, Sun Y, et al. Association between air pollutants and dementia risk in the elderly. DADM. 2015;1:220–28.Google Scholar
- Allen JL, Liu X, Pelkowski S, Palmer B, Conrad K, Oberdörster G, et al. Early postnatal exposure to ultrafine particulate matter air pollution: persistent ventriculomegaly, neurochemical disruption, and glial activation preferentially in male mice. Environ Health Perspect. 2014;122:939–45.PubMed CentralPubMedGoogle Scholar
- Mathew SJ, Haubert D, Kronke M, Leptin M. Looking beyond death: a morphogenetic role for the TNF signalling pathway. J Cell Sci. 2009;122:1939–946.View ArticlePubMedGoogle Scholar
- Neumann H, Schweigreiter R, Yamashita T, Rosenkranz K, Wekerle H, Barde YA. Tumor necrosis factor inhibits neurite outgrowth and branching of hippocampal neurons by a Rho-dependent mechanism. J Neurosci. 2002;22:854–62.PubMedGoogle Scholar
- Wójciak-Stothard B, Entwistle A, Garg R, Ridley AJ. Regulation of TNF-α-induced reorganization of the actin cytoskeleton and cell-cell junctions by Rho, Rac, and Cdc42 in human endothelial cells. J Cell Physiol. 1998;176:150–65.View ArticlePubMedGoogle Scholar
- Bourhis ML, Rimbaud S, Grebert D, Congar P, Meunier N. Endothelin uncouples gap junctions in sustentacular cells and olfactory ensheathing cells of the olfactory mucosa. Eur J Neurosci. 2014;40:2878–887.View ArticlePubMedGoogle Scholar
- Ronnett GV, Leopold D, Cai X, Hoffbuhr KC, Moses L, Hoffman EP, et al. Olfactory biopsies demonstrate a defect in neuronal development in Rett's Syndrome. Ann Neurol. 2003;54:206–18.View ArticlePubMedGoogle Scholar
- Misra C, Kim S, Shen S, Sioutas C. A high flow rate, very low pressure drop impactor for inertial separation of ultrafine from accumulation mode particles. J Aerosol Sci. 2002;33:735–52.View ArticleGoogle Scholar
- Saffari A, Daher N, Shafer MM, Schauer JJ, Sioutas C. Seasonal and spatial variation in reactive oxygen species activity of quasi-ultrafine particles (PM 0.25) in the Los Angeles metropolitan area and its association with chemical composition. Atmos Environ. 2013;79:566–75.View ArticleGoogle Scholar
- Ning Z, Geller MD, Moore KF, Sheesley R, Schauer JJ, Sioutas C. Daily variation in chemical characteristics of urban ultrafine aerosols and inference of their sources. Environ Sci Technol. 2007;41:6000–6.View ArticlePubMedGoogle Scholar
- Daher N, Hasheminassab S, Shafer MM, Schauer JJ, Sioutas C. Seasonal and spatial variability in chemical composition and mass closure of ambient ultrafine particles in the megacity of Los Angeles. Environ Sci Process Impacts. 2013;15:283–95.View ArticlePubMedGoogle Scholar
- Rozovsky I, Finch CE, Morgan TE. Age-related activation of microglia and astrocytes: in vitro studies show persistent phenotypes of aging, increased proliferation, and resistance to down-regulation. Neurobiol Aging. 1998;19:97–103.View ArticlePubMedGoogle Scholar
- Yamamoto H, Demura T, Morita M, Banker GA, Tanii T, Nakamura S. Differential neurite outgrowth is required for axon specification by cultured hippocampal neurons. J Neurochem. 2012;123:904–10.PubMed CentralView ArticlePubMedGoogle Scholar
- Kato K, Liu H, Kikuchi S, Myers RR, Shubayev VI. Immediate anti-tumor necrosis factor-alpha (etanercept) therapy enhances axonal regeneration after sciatic nerve crush. J Neurosci Res. 2010;88:360–68.PubMed CentralView ArticlePubMedGoogle Scholar
- Morgan TE, Laping NJ, Rozovsky I, Oda T, Hogan TH, Finch CE, et al. Clusterin expression by astrocytes is influenced by transforming growth factor beta 1 and heterotypic cell interactions. J Neuroimmunol. 1995;58:101–10.View ArticlePubMedGoogle Scholar
- Stone DJ, Rozovsky I, Morgan TE, Anderson CP, Hajian H, Finch CE. Astrocytes and microglia respond to estrogen with increased apoE mRNA in vivo and in vitro. Exp Neurol. 1997;143:313–8.View ArticlePubMedGoogle Scholar
- Sunyer J, Esnaola M, Alvarez-Pedrerol M, Forns J, Rivas I, López-Vicente M, et al. Association between traffic-related air pollution in schools and cognitive development in primary school children: a prospective cohort study. PLoS Med. 2015; doi:10.1371/journal.pmed.1001792
- Woodward N, Finch CE, Morgan TE. Traffic-related air pollution and brain development. AIMS Environ Sci. 2015;2:353–73.View ArticleGoogle Scholar
- Davis DA, Bortolato M, Godar SC, Sander TK, Iwata N, Pakbin P, et al. Prenatal exposure to urban air nanoparticles in mice causes altered neuronal differentiation and depression-like responses. PLoS One. 2013b; doi:10.1371/journal.pone.0064128
- Campbell A, Oldham M, Becaria A, Bondy SC, Meacher D, Sioutas C, et al. Particulate matter in polluted air may increase biomarkers of inflammation in mouse brain. Neurotoxicol. 2005;26:133–40.View ArticleGoogle Scholar
- Campbell A, Daher N, Solaimani P, Mendoza K, Sioutas C. Human brain derived cells respond in a type-specific manner after exposure to urban particulate matter. Toxicol In Vitro. 2014;28:1290–295.View ArticlePubMedGoogle Scholar
- Wen-Shwe TT, Mitsushima D, Yamamoto S, Fukushima A, Funabashi T, Kobayashi T, et al. Changes in neurotransmitter levels and proinflammatory cytokine mRNA expressions in the mice olfactory bulb following nanoparticle exposure. Toxicol Appl Pharm. 2008;226:192–98.View ArticleGoogle Scholar
- Gelbard HA, Dzenko KA, Wang L, Talley A, James H, Epstein L. HIV-1-derived neurotoxic factors: effects on human neuronal cultures. In: Major EO, Levy JA, Schoenberg D, editors. Technical advances in AIDS research in the human nervous system. New York: Plenum Press; 1995. p. 61–72.View ArticleGoogle Scholar
- Abd-El-Basse EM. Pro-inflammatory cytokine; tumor necrosis factor alpha (TNF-α) inhibits astrocytic support of neuronal survival and neurites outgrowth. Adv Biosci Biotechnol. 2013;4:73–80.View ArticleGoogle Scholar
- Bond JA, Harkema JR, Russell VI. Regional distribution of xenobiotic metabolizing enzymes in respiratory airways of dogs. Drug Metab Dispos. 1988;16:116–24.PubMedGoogle Scholar
- Longo V, Ingelman-Sundberg M, Amato G, Salvetti A, Gervasi PG. Effect of starvation and chlormethiazole on cytochrome P450s of rat nasal mucosa. Biochem Pharmacol. 2000;59:1425–32.View ArticlePubMedGoogle Scholar
- Turner JH, Liang KL, May L, Lane AP. Tumor necrosis factor alpha inhibits olfactory regeneration in a transgenic model of chronic rhinosinusitis-associated olfactory loss. Am J Rhinol Allergy. 2010;24:336–40.PubMed CentralView ArticlePubMedGoogle Scholar
- Oberdörster G, Elder A, Rinderknecht A. Nanoparticles and the brain: cause for concern? J Nanosci Nanotechno. 2009;9:4996–5007.View ArticleGoogle Scholar
- Vincent AJ, West AK, Chuah MI. Morphological and functional plasticity of olfactory ensheathing cells. J Neurocytol. 2005;34:65–80.View ArticlePubMedGoogle Scholar
- Xia T, Kovochich M, Brant J, Hotze M, Sempf J, Oberley T, et al. Comparison of the abilities of ambient and manufactured nanoparticles to induce cellular toxicity according to an oxidative stress paradigm. Nano Lett. 2006;6:1794–807.View ArticlePubMedGoogle Scholar
- Geiser M, Rothen-Rutishauser B, Kapp N, Schürch S, Kreyling W, Schulz H, et al. Ultrafine particles cross cellular membranes by nonphagocytic mechanisms in lungs and in cultured cells. Environ Health Perspect. 2005;113:1555–60.PubMed CentralView ArticlePubMedGoogle Scholar
- Ksontini R. Revisiting the role of tumor necrosis factor alpha and the response to surgical injury and inflammation. Arch Surg. 1998;133:558–67.View ArticlePubMedGoogle Scholar
- Cabal-Hierro L, Lazo PS. Signal transduction by tumor necrosis factor receptors. Cell Signal. 2012;24:1297–305.View ArticlePubMedGoogle Scholar
- Grell M, Wajant H, Zimmermann G, Scheurich P. The type 1 receptor (CD120a) is the high-affinity receptor for soluble tumor necrosis factor. Proc Natl Acad Sci. 1998;95:570–5.PubMed CentralView ArticlePubMedGoogle Scholar
- Chen Z, Palmer TD. Differential roles of TNFR1 and TNFR2 signaling in adult hippocampal neurogenesis. Brain Behav Immun. 2013;30:45–53.PubMed CentralView ArticlePubMedGoogle Scholar
- Wu KY, Hengst U, Cox LJ, Macosko EZ, Jeromin A, Urquhart ER, et al. Local translation of RhoA regulates growth cone collapse. Nature. 2005;436:1020–024.PubMed CentralView ArticlePubMedGoogle Scholar