Exogenous α-synuclein induces toll-like receptor 4 dependent inflammatory responses in astrocytes.
BACKGROUND
The pathological hallmarks of Parkinson's disease are intracellular inclusions composed mainly of misfolded α-synuclein (αSYN). Under physiological conditions αSYN is mostly localized in synapses. In addition, a portion of αSYN is secreted to the extracellular space, where it may be sequestered by neighboring cells and could induce inflammatory responses. The mechanisms of αSYN internalization and signal transduction are not unequivocally clarified. In this work we investigated in primary mouse astrocytes the involvement of toll-like receptor 4 (TLR4) in the induction of inflammatory responses upon exposure to purified human αSYN produced in bacteria.


RESULTS
The mRNA induction of pro-inflammatory cytokines, inducible nitric oxide synthase and cyclooxygenase-2 was significantly reduced in TLR4 knockout astrocytes. The αSYN-mediated activation of c-Jun N-terminal kinases and p38 mitogen-activated protein kinase tended to be diminished, and nuclear translocation of the p65 subunit of nuclear factor κB was abolished in TLR4 knockout astrocytes. In contrast, the uptake of exogenous αSYN was unaffected by TLR4 knockout.


CONCLUSIONS
Extracellular αSYN can activate pro-inflammatory TLR4 pathways in astrocytes, whereas αSYN uptake is independent of TLR4.
Laboratory of Functional Neurogenetics, Department of Neurodegeneration, Faculty of Medicine, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried Müller Str. 27, 72076, Tübingen, Germany. emmy.rannikko@ki.se.|Division of Translational Alzheimer Neurobiology, Department of Neurobiology, Care Sciences and Society, Karolinska Institute, Stockholm, Sweden. emmy.rannikko@ki.se.
Emmy H
EH
Rannikko
Laboratory of Functional Neurogenetics, Department of Neurodegeneration, Faculty of Medicine, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried Müller Str. 27, 72076, Tübingen, Germany. stephanie.sara.weber@googlemail.com.
Stephanie S
SS
Weber
Laboratory of Functional Neurogenetics, Department of Neurodegeneration, Faculty of Medicine, Hertie Institute for Clinical Brain Research, University of Tübingen, Otfried Müller Str. 27, 72076, Tübingen, Germany. philipp.kahle@uni-tuebingen.de.|German Center for Neurodegenerative Diseases, Tübingen, Germany. philipp.kahle@uni-tuebingen.de.
Philipp J
PJ
Kahle
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D001253:Astrocytes / Q000276:immunology*; D001921:Brain / Q000276:immunology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000378:metabolism; D004926:Escherichia coli; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D018345:Mice, Knockout; D008822:Mice, Transgenic; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000378:metabolism; D051844:alpha-Synuclein / Q000235:genetics / Q000633:toxicity*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D012333:RNA, Messenger; D011994:Recombinant Proteins; C498144:Rela protein, mouse; C497604:SNCA protein, human; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D051996:Transcription Factor RelA; D051844:alpha-Synuclein; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases