Abstract
Introduction
Odontoblasts are involved in innate immunity against invading microorganisms. However,
the mechanisms of host inflammatory responses to bacterial DNA in odontoblasts are
not fully understood. The purpose of this study was to investigate whether microbial
cytidine-phosphate-guanosine (CpG) DNA influences interleukin-8 (IL-8) expression
in odontoblasts and the signaling pathways involved.
Methods
The effect of CpG oligonucleotide (CpG ODN) on IL-8 mRNA and protein expression levels
in the mouse odontoblast-like cell line MDPC-23 was investigated by real-time polymerase
chain reaction (PCR) analysis and enzyme-linked immunosorbent assay (ELISA). Whether
Toll-like receptor 9 (TLR9), myeloid differentiation marker 88 (MyD88), nuclear factor
kappa B (NF-κB), or mitogen-activated protein kinase (MAPK) pathways were involved
in the CpG ODN–induced IL-8 expression was determined by examined real-time PCR, ELISA,
and luciferase activity assay. Extracellular signal-regulated kinase (ERK) activation
and TLR9 protein expression were measured by Western blot analysis.
Results
Exposure to CpG ODN induced significant up-regulation of IL-8 mRNA and protein in
MDPC-23 cells. CpG ODN–induced IL-8 up-regulation was attenuated by TLR9 inhibitor
(chloroquine) and MyD88 inhibitory peptide. CpG ODN also increased the expression
of TLR9 mRNA and protein in MDPC-23 cells. Treatment of MDPC-23 cells with NF-κB inhibitors
(pyrrolidine dithiocarbamate), IκBα phosphorylation inhibitors (Bay 117082), or IκB
protease inhibitor (L-1-tosylamido-2-phenylethyl chloromethyl ketone) decreased CpG
ODN–induced IL-8 expression. Furthermore, stimulation of cells with CpG ODN enhanced
κB-luciferase activity, and the activity was diminished by the overexpression of dominant
negative mutants of MyD88 and IκBα. In addition, CpG ODN–induced IL-8 expression was
markedly suppressed by U0126, but not by SB203580 and SP600125. Moreover, CpG ODN
activated ERK phosphorylation in a time-dependent manner.
Conclusions
These data demonstrate that CpG ODN–induced IL-8 expression was mediated through TLR9,
MyD88, NF-κB, and ERK pathways in MDPC-23 cells and suggest a possible role for the
CpG DNA–mediated immune response in odontoblasts with involvement of TLR9, MyD88,
and ERK pathways in this process.
Key Words
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Article info
Publication history
Published online: April 06, 2012
Footnotes
Wenxi He and Yaqing Zhang contributed equally to this work.
Supported by grant 30872869 and grant 81070831 from the Chinese National Natural Science Foundation.
Identification
Copyright
© 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.
