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Toll-like receptor 4 in glial inflammatory responses to air pollution in vitro and in vivo

View Article: PubMed Central - PubMed

ABSTRACT

Background: Exposure to traffic-related air pollution (TRAP) is associated with accelerated cognitive aging and higher dementia risk in human populations. Rodent brains respond to TRAP with activation of astrocytes and microglia, increased inflammatory cytokines, and neurite atrophy. A role for Toll-like receptor 4 (TLR4) was suggested in mouse TLR4-knockouts, which had attenuated lung macrophage responses to air pollution.

Methods: To further analyze these mechanisms, we examined mixed glial cultures (astrocytes and microglia) for RNA responses to nanoscale particulate matter (nPM; diameter <0.2 μm), a well-characterized nanoscale particulate matter subfraction of TRAP collected from a local freeway (Morgan et al. Environ Health Perspect 2011; 119,1003–1009, 2011). The nPM was compared with responses to the endotoxin lipopolysaccharide (LPS), a classic TLR4 ligand, using Affymetrix whole genome microarray in rats. Expression patterns were analyzed by significance analysis of microarrays (SAM) for fold change and by weighted gene co-expression network analysis (WGCNA) to identify modules of shared responses between nPM and LPS. Finally, we examined TLR4 activation in hippocampal tissue from mice chronically exposed to nPM.

Results: SAM and WGCNA analyses showed strong activation of TLR4 and NF-κB by both nPM and LPS. TLR4 siRNA attenuated TNFα and other inflammatory responses to nPM in vitro, via the MyD88-dependent pathway. In vivo, mice chronically exposed to nPM showed increased TLR4, MyD88, TNFα, and TNFR2 RNA, and decreased NF-κB and TRAF6 RNA TLR4 and NF-κB responses in the hippocampus.

Conclusions: These results show TLR4 activation is integral in brain inflammatory responses to air pollution, and warrant further study of TLR4 in accelerated cognitive aging by air pollution.

Electronic supplementary material: The online version of this article (doi:10.1186/s12974-017-0858-x) contains supplementary material, which is available to authorized users.

No MeSH data available.


Flowchart of analysis. RNA responses of mixed glial cultures to nPM or LPS were analyzed by whole genome microarray for fold change by significance analysis of microarrays (SAM), and for shared RNA responses by weighted gene co-expression network analysis (WGCNA), given as correlation modules. Correlation modules are the clusters of correlated genes. The results from SAM and WGCNA were then analyzed for biological processes using the Gene Ontology (GO) database, and transcription factor targets (TFTs). GO output is given as nodes, which are enriched biological processes, and as networks, which are groups of connected nodes. Responding RNAs that met the criteria for fold change were analyzed for GO and TFT enrichment. For WGCNA, only modules of shared responses between nPM and LPS were examined
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Fig1: Flowchart of analysis. RNA responses of mixed glial cultures to nPM or LPS were analyzed by whole genome microarray for fold change by significance analysis of microarrays (SAM), and for shared RNA responses by weighted gene co-expression network analysis (WGCNA), given as correlation modules. Correlation modules are the clusters of correlated genes. The results from SAM and WGCNA were then analyzed for biological processes using the Gene Ontology (GO) database, and transcription factor targets (TFTs). GO output is given as nodes, which are enriched biological processes, and as networks, which are groups of connected nodes. Responding RNAs that met the criteria for fold change were analyzed for GO and TFT enrichment. For WGCNA, only modules of shared responses between nPM and LPS were examined

Mentions: Mixed glial acute responses to nPM and LPS were analyzed by whole genome microarray and processed in tandem by significance analysis of microarrays (SAM), and by weighted gene co-expression network analysis (WGCNA) (Fig. 1). SAM identified responses in individual RNAs, by fold change, to nPM or LPS. WGCNA determined shared RNA responses between nPM and LPS treatments, defined as modules for groups of RNAs with correlated expression. The results from SAM and WGCNA were then analyzed for enriched biological processes, by Gene Ontology (GO), and for transcription factor targets (TFTs).Fig. 1


Toll-like receptor 4 in glial inflammatory responses to air pollution in vitro and in vivo
Flowchart of analysis. RNA responses of mixed glial cultures to nPM or LPS were analyzed by whole genome microarray for fold change by significance analysis of microarrays (SAM), and for shared RNA responses by weighted gene co-expression network analysis (WGCNA), given as correlation modules. Correlation modules are the clusters of correlated genes. The results from SAM and WGCNA were then analyzed for biological processes using the Gene Ontology (GO) database, and transcription factor targets (TFTs). GO output is given as nodes, which are enriched biological processes, and as networks, which are groups of connected nodes. Responding RNAs that met the criteria for fold change were analyzed for GO and TFT enrichment. For WGCNA, only modules of shared responses between nPM and LPS were examined
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5391610&req=5

Fig1: Flowchart of analysis. RNA responses of mixed glial cultures to nPM or LPS were analyzed by whole genome microarray for fold change by significance analysis of microarrays (SAM), and for shared RNA responses by weighted gene co-expression network analysis (WGCNA), given as correlation modules. Correlation modules are the clusters of correlated genes. The results from SAM and WGCNA were then analyzed for biological processes using the Gene Ontology (GO) database, and transcription factor targets (TFTs). GO output is given as nodes, which are enriched biological processes, and as networks, which are groups of connected nodes. Responding RNAs that met the criteria for fold change were analyzed for GO and TFT enrichment. For WGCNA, only modules of shared responses between nPM and LPS were examined
Mentions: Mixed glial acute responses to nPM and LPS were analyzed by whole genome microarray and processed in tandem by significance analysis of microarrays (SAM), and by weighted gene co-expression network analysis (WGCNA) (Fig. 1). SAM identified responses in individual RNAs, by fold change, to nPM or LPS. WGCNA determined shared RNA responses between nPM and LPS treatments, defined as modules for groups of RNAs with correlated expression. The results from SAM and WGCNA were then analyzed for enriched biological processes, by Gene Ontology (GO), and for transcription factor targets (TFTs).Fig. 1

View Article: PubMed Central - PubMed

ABSTRACT

Background: Exposure to traffic-related air pollution (TRAP) is associated with accelerated cognitive aging and higher dementia risk in human populations. Rodent brains respond to TRAP with activation of astrocytes and microglia, increased inflammatory cytokines, and neurite atrophy. A role for Toll-like receptor 4 (TLR4) was suggested in mouse TLR4-knockouts, which had attenuated lung macrophage responses to air pollution.

Methods: To further analyze these mechanisms, we examined mixed glial cultures (astrocytes and microglia) for RNA responses to nanoscale particulate matter (nPM; diameter <0.2 μm), a well-characterized nanoscale particulate matter subfraction of TRAP collected from a local freeway (Morgan et al. Environ Health Perspect 2011; 119,1003–1009, 2011). The nPM was compared with responses to the endotoxin lipopolysaccharide (LPS), a classic TLR4 ligand, using Affymetrix whole genome microarray in rats. Expression patterns were analyzed by significance analysis of microarrays (SAM) for fold change and by weighted gene co-expression network analysis (WGCNA) to identify modules of shared responses between nPM and LPS. Finally, we examined TLR4 activation in hippocampal tissue from mice chronically exposed to nPM.

Results: SAM and WGCNA analyses showed strong activation of TLR4 and NF-κB by both nPM and LPS. TLR4 siRNA attenuated TNFα and other inflammatory responses to nPM in vitro, via the MyD88-dependent pathway. In vivo, mice chronically exposed to nPM showed increased TLR4, MyD88, TNFα, and TNFR2 RNA, and decreased NF-κB and TRAF6 RNA TLR4 and NF-κB responses in the hippocampus.

Conclusions: These results show TLR4 activation is integral in brain inflammatory responses to air pollution, and warrant further study of TLR4 in accelerated cognitive aging by air pollution.

Electronic supplementary material: The online version of this article (doi:10.1186/s12974-017-0858-x) contains supplementary material, which is available to authorized users.

No MeSH data available.