Chronic neuroinflammation is an integral pathological feature of major neurodegenerative diseases. The recruitment of microglia to affected brain regions and the activation of these cells are the major events leading to disease-associated neuroinflammation. In a previous study, we showed that neuron-released alpha-synuclein can activate microglia through activating the Toll-like receptor 2 (TLR2) pathway, resulting in proinflammatory responses. However, it is not clear whether other signaling pathways are involved in the migration and activation of microglia in response to neuron-released alpha-synuclein. In the current study, we demonstrated that TLR2 activation is not sufficient for all of the changes manifested by microglia in response to neuron-released alpha-synuclein. Specifically, the migration of and morphological changes in microglia, triggered by neuron-released alpha-synuclein, did not require the activation of TLR2, whereas increased proliferation and production of cytokines were strictly under the control of TLR2. Construction of a hypothetical signaling network using computational tools and experimental validation with various peptide inhibitors showed that beta1-integrin was necessary for both the morphological changes and the migration. However, neither proliferation nor cytokine production by microglia was dependent on the activation of beta1-integrin. These results suggest that beta1-integrin signaling is specifically responsible for the recruitment of microglia to the disease-affected brain regions, where neurons most likely release relatively high levels of alpha-synuclein.
Animals ; Antigens, CD29/genetics/*metabolism ; Cell Line, Tumor ; *Cell Movement ; Cells, Cultured ; Culture Media, Conditioned/*pharmacology ; Gene Regulatory Networks ; Humans ; Mice ; Mice, Inbred C57BL ; Microglia/drug effects/metabolism/*physiology ; Neurons/*metabolism ; Rats ; Rats, Sprague-Dawley ; Signal Transduction ; Toll-Like Receptor 2/metabolism ; alpha-Synuclein/*pharmacology

Synucleinopathies are a collection of neurological diseases that are characterized by deposition of α-synuclein aggregates in neurons and glia. These diseases include Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy. Although it has been increasingly clear that α-synuclein is implicated in the pathogenesis of PD and other synucleinopathies, the precise mechanism underlying the disease process remains to be unraveled. The past studies on how α-synuclein exerts pathogenic actions have focused on its direct, cell-autonomous neurotoxic effects. However, recent findings suggested that there might be indirect, non-cell-autonomous pathways, perhaps through the changes in glial cells, for the pathogenic actions of this protein. Here, we present evidence that α-synuclein can cause neurodegeneration through a non-cell-autonomous manner. We show that α-synuclein can be secreted from neurons and induces inflammatory responses in microglia, which in turn secreted neurotoxic agents into the media causing neurodegeneration. The neurotoxic response of microglia was mediated by activation of toll-like receptor 2 (TLR2), a receptor for neuron-derived α-synuclein. This work suggests that TLR2 is the key molecule that mediates non-cell-autonomous neurotoxic effects of α-synuclein, hence a candidate for the therapeutic target.
Dementia ; Lewy Bodies ; Microglia ; Multiple System Atrophy ; Neuroglia ; Neurons ; Parkinson Disease ; Toll-Like Receptor 2* ; Toll-Like Receptors*

Synucleinopathies are neurodegenerative disorders characterized by the progressive accumulation of α-synuclein (α-syn) in neurons and glia and include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). In this review, we consolidate our key findings and recent studies concerning the role of Toll-like receptor 2 (TLR2), a pattern recognition innate immune receptor, in the pathogenesis of synucleinopathies. First, we address the pathological interaction of α-syn with microglial TLR2 and its neurotoxic inflammatory effects. Then, we show that neuronal TLR2 activation not only induces abnormal α-syn accumulation by impairing autophagy, but also modulates α-syn transmission. Finally, we demonstrate that administration of a TLR2 functional inhibitor improves the neuropathology and behavioral deficits of a synucleinopathy mouse model. Altogether, we present TLR2 modulation as a promising immunotherapy for synucleinopathies.
Animals ; Autophagy ; Dementia ; Immunotherapy ; Lewy Bodies ; Mice ; Neurodegenerative Diseases ; Neuroglia ; Neurons ; Neuropathology ; Parkinson Disease ; Toll-Like Receptor 2 ; Toll-Like Receptors

Compared to other organs, the brain has limited antioxidant defenses. In particular, the hippocampus is the central region for learning and memory and is highly susceptible to oxidative stress. Glial cells are the most abundant cells in the brain, and sustained glial cell activation is critical to the neuroinflammation that aggravates neuropathology and neurotoxicity. Therefore, regulating glial cell activation is a promising neurotherapeutic treatment. Quinic acid (QA) and its derivatives possess anti-oxidant and anti-inflammatory properties. Although previous studies have evidenced QA’s benefit on the brain, in vivo and in vitro analyses of its anti-oxidant and anti-inflammatory properties in glial cells have yet to be established. This study investigated QA’s rescue effect in lipopolysaccharide (LPS)-induced behavior impairment. Orally administering QA restored social impairment and LPS-induced spatial and fear memory. In addition, QA inhibited proinflammatory mediator, oxidative stress marker, and mitogen-activated protein kinase (MAPK) activation in the LPS-injected hippocampus. QA inhibited nitrite release and extracellular signal-regulated kinase (ERK) phosphorylation in LPS-stimulated astrocytes. Collectively, QA restored impaired neuroinflammation-induced behavior by regulating proinflammatory mediator and ERK activation in astrocytes, demonstrating its potential as a therapeutic agent for neuroinflammation-induced brain disease treatments.

Microglial cells are the resident innate immune cells that sense pathogens and tissue injury in the central nervous system (CNS). Microglial activation is critical for neuroinflammatory responses. The synthetic compound 2-hydroxy-3',5,5'-trimethoxychalcone (DK-139) is a novel chalcone-derived compound. In this study, we investigated the effects of DK-139 on Toll-like receptor 4 (TLR4)-mediated inflammatory responses in BV2 microglial cells. DK-139 inhibited lipopolysaccharide (LPS)-induced TLR4 activity, as determined using a cell-based assay. DK-139 blocked LPS-induced phosphorylation of IkappaB and p65/RelA NF-kappaB, resulting in inhibition of the nuclear translocation and trans-acting activity of NF-kappaB in BV2 microglial cells. We also found that DK-139 reduced the expression of NF-kappaB target genes, such as those for COX-2, iNOS, and IL-1beta, in LPS-stimulated BV2 microglial cells. Interestingly, DK-139 blocked LPS-induced Akt phosphorylation. Inhibition of Akt abrogated LPS-induced phosphorylation of p65/RelA, while overexpression of dominant-active p110CAAX enhanced p65/RelA phosphorylation as well as iNOS and COX2 expression. These results suggest that DK-139 exerts an anti-inflammatory effect on microglial cells by inhibiting the Akt/IkappaB kinase (IKK)/NF-kappaB signaling pathway.
Animals ; Binding Sites ; Cell Line ; Chalcones/chemistry/*pharmacology ; Cyclooxygenase 2/metabolism ; I-kappa B Kinase/metabolism ; Inflammation/*drug therapy ; Interleukin-1beta/metabolism ; Lipopolysaccharides/immunology ; Microglia/*drug effects/immunology/metabolism ; Molecular Dynamics Simulation ; NF-kappa B/*antagonists & inhibitors ; Nitric Oxide Synthase Type II/metabolism ; Phosphorylation/drug effects ; Protein Binding ; Proto-Oncogene Proteins c-akt/*antagonists & inhibitors ; Rats ; Signal Transduction ; Toll-Like Receptor 4/*antagonists & inhibitors/metabolism ; Transcription Factor RelA/metabolism