The role of Galectin-3 in α-synuclein-induced microglial activation.
BACKGROUND
Parkinson's disease (PD) is the most prevalent neurodegenerative motor disorder. The neuropathology is characterized by intraneuronal protein aggregates of α-synuclein and progressive degeneration of dopaminergic neurons within the substantia nigra. Previous studies have shown that extracellular α-synuclein aggregates can activate microglial cells, induce inflammation and contribute to the neurodegenerative process in PD. However, the signaling pathways involved in α-synuclein-mediated microglia activation are poorly understood. Galectin-3 is a member of a carbohydrate-binding protein family involved in cell activation and inflammation. Therefore, we investigated whether galectin-3 is involved in the microglia activation triggered by α-synuclein.


RESULTS
We cultured microglial (BV2) cells and induced cell activation by addition of exogenous α-synuclein monomers or aggregates to the cell culture medium. This treatment induced a significant increase in the levels of proinflammatory mediators including the inducible Nitric Oxide Synthase (iNOS), interleukin 1 Beta (IL-1β) and Interleukin-12 (IL-12). We then reduced the levels of galectin-3 expression using siRNA or pharmacologically targeting galectin-3 activity using bis-(3-deoxy-3-(3-fluorophenyl-1H-1,2,3-triazol-1-yl)-β-D-galactopyranosyl)-sulfane. Both approaches led to a significant reduction in the observed inflammatory response induced by α-synuclein. We confirmed these findings using primary microglial cells obtained from wild-type and galectin-3 null mutant mice. Finally, we performed injections of α-synuclein in the olfactory bulb of wild type mice and observed that some of the α-synuclein was taken up by activated microglia that were immunopositive for galectin-3.


CONCLUSIONS
We show that α-synuclein aggregates induce microglial activation and demonstrate for the first time that galectin-3 plays a significant role in microglia activation induced by α-synuclein. These results suggest that genetic down-regulation or pharmacological inhibition of galectin-3 might constitute a novel therapeutic target in PD and other synucleinopathies.
Experimental Neuroinflammation Laboratory, BMC, Lund University, 221 84, Lund, Sweden. antonio.boza_serrano@med.lu.se.
Antonio
A
Boza-Serrano
Neuronal Survival Unit, BMC, Lund University, 221 84, Lund, Sweden. juan.reyespalacios@epfl.ch.
Juan F
JF
Reyes
Neuronal Survival Unit, BMC, Lund University, 221 84, Lund, Sweden. nolwen.rey@vai.org.|Translational Parkinson's Disease Research, Center for Neurodegenerative Science, Van Andel Institute, Grand Rapids, MI, USA. nolwen.rey@vai.org.
Nolwen L
NL
Rey
Section MIG, Department of Laboratory Medicine, Solvegatan 23, Lund University, 223 62, Lund, Sweden. Hakon.Leffler@med.lu.se.
Hakon
H
Leffler
Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Bat 34, Avenue de la Terrasse, 91198, Gif-sur-Yvette, France. bousset@lebs.cnrs-gif.fr.
Luc
L
Bousset
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, PO Box 124, 221 00, Lund, Sweden. ulf.nilsson@chem.lu.se.
Ulf
U
Nilsson
Neuronal Survival Unit, BMC, Lund University, 221 84, Lund, Sweden. patrik.brundin@vai.org.|Translational Parkinson's Disease Research, Center for Neurodegenerative Science, Van Andel Institute, Grand Rapids, MI, USA. patrik.brundin@vai.org.
Patrik
P
Brundin
Departamento de Bioquímica y Biología Molecular, Universidad de Sevilla, Facultad de Farmacia, Sevilla, Spain. jlvenero@us.es.
Jose Luis
JL
Venero
Department of Oncology-Pathology, Cancer Centrum Karolinska, Karolinska Institutet, 171 76, Stockholm, Sweden. miguel.burguillos@ki.se.
Miguel Angel
MA
Burguillos
Experimental Neuroinflammation Laboratory, BMC, Lund University, 221 84, Lund, Sweden. tomas.deierborg@med.lu.se.
Tomas
T
Deierborg
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D037502:Galectin 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018664:Interleukin-12 / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects / Q000502:physiology*; D015213:Neuroimmunomodulation / Q000502:physiology; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D009830:Olfactory Bulb / Q000276:immunology; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology; D034741:RNA, Small Interfering; D011994:Recombinant Proteins / Q000008:administration & dosage; D051844:alpha-Synuclein / Q000008:administration & dosage / Q000378:metabolism*
D037502:Galectin 3; C587672:IL1B protein, mouse; D053583:Interleukin-1beta; C485095:Lgals3 protein, mouse; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C497605:Snca protein, mouse; D051844:alpha-Synuclein; D018664:Interleukin-12; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse