title: Activation of phagocytic activity in astrocytes by reduced expression of the inflammasome component ASC and its implication in a mouse model of Alzheimer disease.
abstract: BACKGROUND
  The proinflammatory cytokine interleukin-1β (IL-1β) is overexpressed in Alzheimer disease (AD) as a key regulator of neuroinflammation. Amyloid-β (Aβ) peptide triggers activation of inflammasomes, protein complexes responsible for IL-1β maturation in microglial cells. Downregulation of NALP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome has been shown to decrease amyloid load and rescue cognitive deficits in a mouse model of AD. Whereas activation of inflammasome in microglial cells has been described in AD, no data are currently available concerning activation of inflammasome in astrocytes, although they are involved in inflammatory response and phagocytosis. Here, by targeting the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD domain), we investigated the influence of activation of the inflammasome on the phagocytic activity of astrocytes.
  
  
  METHODS
  We used an ASC knockout mouse model, as ASC is a central protein in the inflammasome, acting as an adaptor and stabilizer of the complex and thus critical for its activation. Lipopolysaccharide (LPS)-primed primary cultures of astrocytes from newborn mice were utilized to evaluate Aβ-induced inflammasome activation by measuring IL-1β release by ECLIA (electro-chemiluminescence immunoassay). Phagocytosis efficiency was measured by incorporation of bioparticles, and the release of the chemokine CCL3 (C-C motif ligand 3) was measured by ECLIA. ASC mice were crossbred with 5xFAD (familial Alzheimer disease) mice and tested for spatial reference memory using the Morris water maze (MWM) at 7-8 months of age. Amyloid load and CCL3 were quantified by thioflavine S staining and quantitative real-time polymerase chain reaction (qRT-PCR), respectively.
  
  
  RESULTS
  Cultured astrocytes primed with LPS and treated with Aβ showed an ASC-dependent production of IL-1β resulting from inflammasome activation mediated by Aβ phagocytosis and cathepsin B enzymatic activity. ASC+/- astrocytes displayed a higher phagocytic activity as compared to ASC+/+ and ASC -/- cells, resulting from a higher release of the chemokine CCL3. A significant decrease in amyloid load was measured in the brain of 7-8-month-old 5xFAD mice carrying the ASC +/- genotype, correlated with an increase in CCL3 gene expression. In addition, the ASC +/- genotype rescued spatial reference memory deficits observed in 5xFAD mice.
  
  
  CONCLUSIONS
  Our results demonstrate that Aβ is able to activate astrocytic inflammasome. Downregulation of inflammasome activity increases phagocytosis in astrocytes due to the release of CCL3. This could explain why downregulation of inflammasome activity decreases amyloid load and rescues memory deficits in a mouse model of AD.
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. julien.couturier@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. julien.couturier@uclouvain.be.
authors.forename: Julien
authors.initials: J
authors.lastname: Couturier
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. ilie-cosmin.stancu@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. ilie-cosmin.stancu@uclouvain.be.
authors.forename: Ilie-Cosmin
authors.initials: IC
authors.lastname: Stancu
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. olivier.schakman@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. olivier.schakman@uclouvain.be.
authors.forename: Olivier
authors.initials: O
authors.lastname: Schakman
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. nathalie.pierrot@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. nathalie.pierrot@uclouvain.be.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Pierrot
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. francois.huaux@uclouvain.be.|Louvain Centre for Toxicology and Applied Pharmacology (LTAP), Université catholique de Louvain, Brussels, Belgium. francois.huaux@uclouvain.be.
authors.forename: François
authors.initials: F
authors.lastname: Huaux
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. pascal.kienlen-campard@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. pascal.kienlen-campard@uclouvain.be.
authors.forename: Pascal
authors.initials: P
authors.lastname: Kienlen-Campard
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. ilse.dewachter@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. ilse.dewachter@uclouvain.be.
authors.forename: Ilse
authors.initials: I
authors.lastname: Dewachter
authors.affiliation: Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. jean-noel.octave@uclouvain.be.|Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate 54, B1.5410, B-1200, Brussels, Belgium. jean-noel.octave@uclouvain.be.
authors.forename: Jean-Noël
authors.initials: JN
authors.lastname: Octave
mesh_terms: D000544:Alzheimer Disease / Q000150:complications / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D016229:Amyloid beta-Peptides / Q000494:pharmacology; D016564:Amyloid beta-Protein Precursor / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D053468:CARD Signaling Adaptor Proteins; D016022:Case-Control Studies; D002478:Cells, Cultured; D054405:Chemokine CCL3 / Q000378:metabolism / Q000494:pharmacology; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D008569:Memory Disorders / Q000209:etiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D009550:Nigericin / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010586:Phagocytes / Q000378:metabolism*; D053764:Presenilin-1 / Q000235:genetics
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D054405:Chemokine CCL3; D016207:Cytokines; D007476:Ionophores; C508853:PSEN1 protein, human; D010446:Peptide Fragments; D053764:Presenilin-1; C498534:Pycard protein, mouse; C075222:amyloid beta-protein (1-42); D009550:Nigericin
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