[show abstract][hide abstract] ABSTRACT: Toll-like receptors (TLRs), which have been implicated in various neuroinflammatory responses, are thought to act in defense mechanisms by inhibiting neuronal cell death in Alzheimer's disease. In this study, we evaluated the effects of TLR2 on amyloid beta peptide 25-35 (Aβ25-35)-induced neuronal cell death, synaptic dysfunction, and microglial activation in organotypic hippocampal slice cultures (OHSCs) from wild-type (WT) C57BL/6 mice and TLR2-knockout (KO) mice. In WT mice, Aβ25-35 induced β-amyloid aggregation and surrounding TLR2 expression. And, propidium iodide (PI) uptake, which is a measure of cell death, increased in a dose-dependent manner in slices with Aβ25-35 treatment. In the Aβ25-35-treated TLR2-KO OHSCs, the PI uptake was significantly attenuated to the control level, indicating that the cells were less susceptible to Aβ25-35-induced neuronal toxicity. In the ultrastructural analysis, nuclear shrinkage, slightly swollen mitochondria, and degraded organelles were detected in the Aβ25-35-treated slices from WT mice but not in the Aβ25-35-treated slices from TLR2-KO, suggesting the resistance of TLR2-KO to Aβ25-35-induced neurotoxicity. In Aβ25-35-treated OHSCs of WT mice, the levels of phosphorylated tau were increased and the levels of synaptophysin were decreased in a dose-dependent manner, but they were not changed in OHSCs of TLR2-KO mice. In WT mice, Aβ25-35 increased total protein level and immunoreactivity of Iba-1, which was colocalized with TLR2. However, there were no significant changes in the slices of Aβ25-35-treated TLR2-KO mice. These results suggested that TLR2 may play a role in Aβ25-35-induced neuronal cell loss and synaptic dysfunction through the activation of microglia in OHSCs.
Neurochemistry International 10/2013; · 2.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Intracellular reactive oxygen species (ROS) are essential secondary messengers in many signaling cascades governing innate immunity and cellular functions. TLR3 signaling is crucially involved in antiviral innate and inflammatory responses; however, the roles of ROS in TLR3 signaling remain largely unknown. In this study, we show that TLR3-induced ROS generation is required for the activation of NF-κB, IFN-regulatory factor 3, and STAT1-mediated innate immune responses in macrophages. TLR3 induction led to a rapid increase in ROS generation and a physical association between components of the NADPH oxidase (NOX) enzyme complex (NOX2 and p47(phox)) and TLR3 via a Ca(2+)-c-Src tyrosine kinase-dependent pathway. TLR3-induced ROS generation, NOX2, and p47(phox) were required for the phosphorylation and nuclear translocation of STAT1 and STAT2. TLR3-induced activation of STAT1 contributed to the generation of inflammatory mediators, which was significantly attenuated in NOX2- and p47(phox)-deficient macrophages, suggesting a role for ROS-STAT1 in TLR3-mediated innate immune responses. Collectively, these results provide a novel insight into the crucial role that TLR3-ROS signaling plays in innate immune responses by activating STAT1.
The Journal of Immunology 05/2013; · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Abnormal aggregation of α-synuclein and sustained microglial activation are important contributors to the pathogenic processes of Parkinson's disease. However, the relationship between disease-associated protein aggregation and microglia-mediated neuroinflammation remains unknown. Here, using a combination of in silico, in vitro and in vivo approaches, we show that extracellular α-synuclein released from neuronal cells is an endogenous agonist for Toll-like receptor 2 (TLR2), which activates inflammatory responses in microglia. The TLR2 ligand activity of α-synuclein is conformation-sensitive; only specific types of oligomer can interact with and activate TLR2. This paracrine interaction between neuron-released oligomeric α-synuclein and TLR2 in microglia suggests that both of these proteins are novel therapeutic targets for modification of neuroinflammation in Parkinson's disease and related neurological diseases.
[show abstract][hide abstract] ABSTRACT: Toll-like receptors (TLRs) are type I transmembrane signaling molecules that are expressed in cells of the innate immune system. In these cells, TLRs function as pattern recognition receptors (PRR) that recognize specific molecular patterns derived from microorganisms. Upon activation, TLRs trigger a cascade of intracellular signaling pathways in innate immune cells, leading to the induction of inflammatory and innate immune responses, which in turn regulate adaptive immune responses. In the nervous system, different members of the TLR family are expressed on glial cells (astrocytes, microglia, oligodendrocytes, and Schwann cells) and neurons. Recently, increasing evidence has supported the idea that TLRs also recognize endogenous molecules that are released from damaged tissue, thereby regulating inflammatory responses and subsequent tissue repair. These findings imply that TLRs on glial cells may also be involved in the inflammatory response to tissue damage in the nervous system. In this review, we discuss recent studies on TLR expression in the cells of the nervous system and their roles in acute neurological disorders involving tissue damage such as strokes, traumatic spinal cord and brain injuries, and peripheral nerve injuries.
Current Protein and Peptide Science 02/2013; · 2.33 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have previously reported that NADPH oxidase 2 (Nox2) is upregulated in spinal cord microglia after spinal nerve injury, demonstrating that it is critical for microglia activation and subsequent pain hypersensitivity. However, the mechanisms and molecules involved in Nox2 induction have not been elucidated. Previous studies have shown that Toll-like receptors (TLRs) are involved in nerve injury-induced spinal cord microglia activation. In this study, we investigated the role of TLR in Nox2 expression in spinal cord microglia after peripheral nerve injury. Studies using TLR knock-out mice have shown that nerve injury-induced microglial Nox2 upregulation is abrogated in TLR2, but not in TLR3 or 4 knock-out mice. Intrathecal injection of lipoteichoic acid (LTA), a TLR2 agonist, induced Nox2 expression in spinal cord microglia both at the mRNA and protein levels. Similarly, LTA stimulation induced Nox2 expression and reactive oxygen species production in primary spinal cord glial cells in vitro. Studies on intracellular signaling pathways indicate that p38 MAP kinase activation is required for TLR2-induced Nox2 expression in spinal cord glial cells. Conclusively, our data show that TLR2 mediates nerve injury-induced Nox2 gene expression in spinal cord microglia via p38 activation, and thereby may contribute to spinal cord microglia activation.
Journal of Biological Chemistry 02/2013; · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: c-Jun N-terminal kinase (JNK), a member of the MAPK family, is an important regulatory factor of synaptic plasticity as well as neuronal differentiation and cell death. Recently, JNK has been reported to modulate synaptic plasticity by the direct phosphorylation of synaptic proteins. The specific role of c-Jun phosphorylation in JNK mediated synaptic plasticity, however, remains unclear. In this study, we investigated the effects of c-Jun phosphorylation on synaptic structure and function by using c-Jun mutant mice, c-JunAA, in which the active phosphorylation sites at serines 63 and 73 were replaced by alanines. The gross hippocampal anatomy and number of spines on hippocampal pyramidal neurons were normal in c-JunAA mice. Basal synaptic transmission, input-output ratios, and paired-pulse facilitation (PPF) were also no different in c-JunAA compared with wild-type mice. Notably, however, the induction of long-term potentiation (LTP) at hippocampal CA3-CA1 synapses in c-JunAA mice was impaired, whereas induction of long-term depression (LTD) was normal. These data suggest that phosphorylation of the c-Jun N-terminus is required for LTP formation in the hippocampus, and may help to better characterize JNK-mediated modulation of synaptic plasticity.
[show abstract][hide abstract] ABSTRACT: Recent studies show that necrotic neuronal cells (NNC) activate microglia, thereby leading to neuronal cell death. This suggests that chemicals that inhibit microglia activation may be used as neuroprotective drugs. In this context, we screened a chemical library for inhibitors of microglia activation. Using a screening system based on a nitrite assay, we isolated two chemicals that inhibit nitric oxide (NO) release from activated microglia: triamcinolone acetonide (TA) and amcinonide. The half-maximal inhibitory concentrations (IC50) of TA and amcinonide for NO release inhibition were 1.78 nM and 3.38 nM, respectively. These chemicals also inhibited NNC-induced expression of the proinflammatory genes iNOS, TNF-α, and IL-1β in glial cells. A study based on a luciferase assay revealed that TA attenuated NNC-induced microglia activation by blocking the NF-κB signaling pathway. In addition, TA protected cortical neurons in coculture with microglia from LPS/IFN-γ-induced neuronal cell death. In conclusion, TA may inhibit microglia activation and may protect neuronal cells from death induced by microglial activation.
Immunopharmacology and Immunotoxicology 05/2012; · 1.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: Immunosuppression is a characteristic feature of Toxoplasma gondii-infected murine hosts. The present study aimed to determine the effect of the immunosuppression induced by T. gondii infection on the pathogenesis and progression of Alzheimer’s disease (AD) in Tg2576 AD mice. Mice were infected with a cyst-forming strain (ME49) of T. gondii, and levels of inflammatory mediators (IFN-c and nitric oxide), anti-inflammatory cytokines (IL-10 and TGF-b), neuronal damage, and b- amyloid plaque deposition were examined in brain tissues and/or in BV-2 microglial cells. In addition, behavioral tests, including the water maze and Y-maze tests, were performed on T. gondii-infected and uninfected Tg2576 mice. Results revealed that whereas the level of IFN-c was unchanged, the levels of anti-inflammatory cytokines were significantly higher in T. gondii-infected mice than in uninfected mice, and in BV-2 cells treated with T. gondii lysate antigen. Furthermore, nitrite production from primary cultured brain microglial cells and BV-2 cells was reduced by the addition of T. gondii lysate antigen (TLA), and b-amyloid plaque deposition in the cortex and hippocampus of Tg2576 mouse brains was remarkably lower in T. gondii-infected AD mice than in uninfected controls. In addition, water maze and Y-maze test results revealed retarded cognitive capacities in uninfected mice as compared with infected mice. These findings demonstrate the favorable effects of the immunosuppression induced by T. gondii infection on the pathogenesis and progression of AD in Tg2576 mice.
PLoS ONE 03/2012; 7(3):e33312. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Imiquimod (IQ) is known as an agonist of Toll-like receptor 7 (TLR7) and is widely used to treat various infectious skin diseases. However, it causes severe itching sensation as its side effect. The precise mechanism of how IQ causes itching sensation is unknown. A recent report suggested a molecular target of IQ as TLR7 expressed in dorsal root ganglion (DRG) neurons. However, we recently proposed a TLR7-independent mechanism, in which the activation of TLR7 is not required for the action of IQ in DRG neurons. To resolve this controversy regarding the involvement of TLR7 and to address the exact molecular identity of itching sensation by IQ, we investigated the possible molecular target of IQ in DRG neurons.
When IQ was applied to DRG neurons, we observed an increase in action potential (AP) duration and membrane resistance both in wild type and TLR7-deficient mice. Based on these results, we tested whether the treatment of IQ has an effect on the activity of K(+) channels, K(v)1.1 and K(v)1.2 (voltage-gated K(+) channels) and TREK1 and TRAAK (K(2P) channels). IQ effectively reduced the currents mediated by both K(+) channels in a dose-dependent manner, acting as an antagonist at TREK1 and TRAAK and as a partial antagonist at K(v)1.1 and K(v)1.2.
Our results demonstrate that IQ blocks the voltage-gated K(+) channels to increase AP duration and K(2P) channels to increase membrane resistance, which are critical for the membrane excitability of DRG neurons. Therefore, we propose that IQ enhances the excitability of DRG neurons by blocking multiple potassium channels and causing pruritus.
[show abstract][hide abstract] ABSTRACT: NADPH oxidase 1 (Nox1) is essential for reactive oxygen species production in the innate immune responses mediated by toll-like receptor (TLR), but the mechanism regulating its expression remains uncertain. Here, we find that Nox1 induction is TLR2-dependent, but independent of myeloid differentiation primary response gene 88 (MyD88). We demonstrate the capacity of signal transducer and activator of transcription 3 (STAT3) to activate Nox1's transcription, as well as cooperative regulation by janus kinase 1 and 3 (JAK1 and JAK3). We find that regulator of G-protein signaling 2 (RGS2) inhibits STAT3-mediated Nox1 transcription, and can itself be repressed by TLR2; Nox1 induction upon RGS2 down-regulation is controlled by protein kinase C-η (PKC-η) and phospholipase D2 (PLD2). A GFP-tagged version of RGS2 concentrates in the nucleus; RGS2 additionally directly binds STAT3 to regulate its transcriptional activity through TLR2 stimulation. Cumulatively, these results suggest that TLR2 signaling enhances Nox1 expression through the JAK1/3-STAT3 pathway, and that RGS2, through its regulation by the PKC-η/PLD2 pathway, represses STAT3's transcriptional activation of Nox1.
[show abstract][hide abstract] ABSTRACT: We have previously reported that nerve injury-induced neuropathic pain is attenuated in toll-like receptor 2 (TLR2) knock-out mice. In these mice, inflammatory gene expression and spinal cord microglia actvation is compromised, whereas the effects in the dorsal root ganglia (DRG) have not been tested. In this study, we investigated the role of TLR2 in inflammatory responses in the DRG after peripheral nerve injury.
L5 spinal nerve transection injury induced the expression of macrophage-attracting chemokines such as CCL2/MCP-1 and CCL3/MIP-1 and subsequent macrophage infiltration in the DRG of wild-type mice. In TLR2 knock-out mice, however, the induction of chemokine expression and macrophage infiltration following nerve injury were markedly reduced. Similarly, the induction of IL-1β and TNF-α expression in the DRG by spinal nerve injury was ameliorated in TLR2 knock-out mice. The reduced inflammatory response in the DRG was accompanied by attenuation of nerve injury-induced spontaneous pain hypersensitivity in TLR2 knock-out mice.
Our data show that TLR2 contributes to nerve injury-induced proinflammatory chemokine/cytokine gene expression and macrophage infiltration in the DRG, which may have relevance in the reduced pain hypersensitivity in TLR2 knock-out mice after spinal nerve injury.
[show abstract][hide abstract] ABSTRACT: Traumatic spinal cord injury (SCI) is followed by massive infiltration and activation of myeloid cells such as neutrophils and macrophages, but the functions of these cells are controversial. In this study, our objective was to elucidate the in vivo role of a signaling pathway involved in activation of these innate immune cells in SCI using myeloid cell-specific IκB kinase (IKK)-β conditional knockout (ikkβΔmye) mice. In these mice, the ikkβ gene has been specifically deleted from myeloid cells, compromising their in vivo IKK/NF-κB-dependent activation. We found that ikkβΔmye mice had significantly reduced neutrophil and macrophage infiltrations after SCI compared to ikkβ(+/+) controls. SCI-induced proinflammatory gene expression was also reduced in ikkβΔmye mice. Reduced neuroinflammation in ikkβΔmye mice was accompanied by attenuated neuronal loss and behavioral deficits in motor activity. In addition, the SCI-induced expression of CXC ligand 1 was reduced in ikkβΔmye mice, which may be responsible for the reduced neutrophil infiltration in these mice. Our data demonstrate that IKK-β-dependent myeloid cell activation potentiates neuroinflammation and neuronal damage after SCI.
European Journal of Immunology 03/2011; 41(5):1266-77. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: Despite its clinical importance, the mechanisms that mediate or generate itch are poorly defined. The identification of pruritic compounds offers insight into understanding the molecular and cellular basis of itch. Imiquimod (IQ) is an agonist of Toll-like receptor 7 (TLR7) used to treat various infectious skin diseases such as genital warts, keratosis, and basal cell carcinoma. Itch is reportedly one of the major side effects developed during IQ treatments. We found that IQ acts as a potent itch-evoking compound (pruritogen) in mice via direct excitation of sensory neurons. Combined studies of scratching behavior, patch-clamp recording, and Ca(2+) response revealed the existence of a unique intracellular mechanism, which is independent of TLR7 as well as different from the mechanisms exploited by other well-characterized pruritogens. Nevertheless, as for other pruritogens, IQ requires the presence of transient receptor potential vanilloid 1 (TRPV1)-expressing neurons for itch-associated responses. Our data provide evidence supporting the hypothesis that there is a specific subset of TRPV1-expressing neurons that is equipped with diverse intracellular mechanisms that respond to histamine, chloroquine, and IQ.
Proceedings of the National Academy of Sciences 02/2011; 108(8):3371-6. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Endothelin (ET)-1 and its receptors (ETA and ETB receptor) are present in the central nervous system. ET exerts biological effects on gliogenesis and glial cell functions. In order to define a possible mechanism of ETA receptor signaling, the distribution of the ETA receptor in developing oligodendrocytes and the effects of ET-1 on the myelination of oligodendrocytes were examined. ETA receptor immunoreactivity was confined to the perivascular elements of the blood vessels during early postnatal development. However later in development, ETA receptor immunoreactivity was no longer observed in the vessels but became localized to the myelinating oligodendrocytes of the primitive corpus callosum of the white matter, apart from the vessels. ET-1 induced myelin basic protein (MBP) in primary oligodendrocyte precursor cell culture though the ETA receptor and was blocked by an ETA receptor antagonist. In addition, ET-1 evoked the release of Ca(2+) which is a central regulator of oligodendrocyte differentiation. Our results provide a link between ET-1 and its ETA receptor and myelination during oligodendrocyte differentiation.
Journal of Korean medical science 01/2011; 26(1):92-9. · 0.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recent studies indicate that Toll-like receptors (TLRs), originally identified as infectious agent receptors, also mediate
sterile inflammatory responses during tissue damage. In this study, we investigated the role of TLR2 in excitotoxic hippocampal
cell death using TLR2 knock-out (KO) mice. TLR2 expression was up-regulated in microglia in the ipsilateral hippocampus of
kainic acid (KA)-injected mice. KA-mediated hippocampal cell death was significantly reduced in TLR2 KO mice compared with
wild-type (WT) mice. Similarly, KA-induced glial activation and proinflammatory gene expression in the hippocampus were compromised
in TLR2 KO mice. In addition, neurons in organotypic hippocampal slice cultures (OHSCs) from TLR2 KO mouse brains were less
susceptible to KA excitotoxicity than WT OHSCs. This protection is partly attributed to decreased expression of proinflammatory
genes, such as TNF-α and IL-1β in TLR2 KO mice OHSCs. These data demonstrate conclusively that TLR2 signaling in microglia
contributes to KA-mediated innate immune responses and hippocampal excitotoxicity.
Journal of Biological Chemistry 12/2010; 285(50):39447-39457. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recent studies indicate that Toll-like receptors (TLRs), originally identified as infectious agent receptors, also mediate sterile inflammatory responses during tissue damage. In this study, we investigated the role of TLR2 in excitotoxic hippocampal cell death using TLR2 knock-out (KO) mice. TLR2 expression was up-regulated in microglia in the ipsilateral hippocampus of kainic acid (KA)-injected mice. KA-mediated hippocampal cell death was significantly reduced in TLR2 KO mice compared with wild-type (WT) mice. Similarly, KA-induced glial activation and proinflammatory gene expression in the hippocampus were compromised in TLR2 KO mice. In addition, neurons in organotypic hippocampal slice cultures (OHSCs) from TLR2 KO mouse brains were less susceptible to KA excitotoxicity than WT OHSCs. This protection is partly attributed to decreased expression of proinflammatory genes, such as TNF-α and IL-1β in TLR2 KO mice OHSCs. These data demonstrate conclusively that TLR2 signaling in microglia contributes to KA-mediated innate immune responses and hippocampal excitotoxicity.
Journal of Biological Chemistry 10/2010; 285(50):39447-57. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Increasing evidence supports the notion that spinal cord microglia activation plays a causal role in the development of neuropathic pain after peripheral nerve injury; yet the mechanisms for microglia activation remain elusive. Here, we provide evidence that NADPH oxidase 2 (Nox2)-derived ROS production plays a critical role in nerve injury-induced spinal cord microglia activation and subsequent pain hypersensitivity. Nox2 expression was induced in dorsal horn microglia immediately after L5 spinal nerve transection (SNT). Studies using Nox2-deficient mice show that Nox2 is required for SNT-induced ROS generation, microglia activation, and proinflammatory cytokine expression in the spinal cord. SNT-induced mechanical allodynia and thermal hyperalgesia were similarly attenuated in Nox2-deficient mice. In addition, reducing microglial ROS level via intrathecal sulforaphane administration attenuated mechanical allodynia and thermal hyperalgesia in SNT-injured mice. Sulforaphane also inhibited SNT-induced proinflammatory gene expression in microglia, and studies using primary microglia indicate that ROS generation is required for proinflammatory gene expression in microglia. These studies delineate a pathway involving nerve damage leading to microglial Nox2-generated ROS, resulting in the expression of proinflammatory cytokines that are involved in the initiation of neuropathic pain.
Proceedings of the National Academy of Sciences 08/2010; 107(33):14851-6. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Toll-like receptors (TLRs) functionally expressed in salivary epithelial cells, but their roles remain elusive. Among TLRs family, TLR3 is activated by dsRNA, a byproduct of viral infection. The aim of this study was to investigate the role of TLR3 in the inflammatory immune responses using HSG cells. Reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR and ELISA were performed to identify expression of TLRs and TLR3-mediated chemokine inductions. The chemotaxis assay of activated T lymphocytes was also performed. Treatment of HSG cells with polyinosinic: polycytidylic acid (poly(I:C)) significantly increased interferon-γ-inducible protein 10 (IP-10), interferoninducible T-cell α chemoattractant (I-TAC), and regulated on activation, normal T-cells expressed and secreted (RANTES) gene expressions in a concentration-dependent manner. Anti-TLR3 antibody blocked the increases of IP-10 and I-TAC genes. Poly(I:C)-induced increases of IP-10 and I-TAC were also confirmed at protein levels from cell lysates, but their release into extracellular medium was detected only in IP-10. We found that the culture media from HSG cells stimulated with poly(I:C) significantly increases T lymphocyte migration. Our results suggest that TLR3 plays an important role in chemokine induction, particularly IP-10, in salivary epithelial cells.
Korean Journal of Physiology and Pharmacology 08/2010; 14(4):235-40. · 1.00 Impact Factor