TOLL-LIKE 4 RECEPTOR CONTROLS ASTROGLIAL CONVERSION TO THE PROINFLAMMATORY PHENOTYPE

ROSCISZEWSKI G; CADENA V; VILLARREAL A ; ROGER T; RAMOS AJ

Mar del Plata

Congreso; LXI meeting de la Sociedad Argentina de Investigacion Clínica (SAIC); 2016

Sociedad Argentina de Investigacion Clinica - Sociedad Argentina de Inmunología

Astrocytes are starting to be recognized as a facultative immunocompetentcell type able to participate in innate immunityresponse in the Central Nervous System (CNS). Astrocytes reactto brain injury with a generic response known as reactive gliosis,which involves activation of multiple intracellular pathways includingseveral that may be beneficial for neuronal survival. However,by unknown mechanisms reactive astrocytes can polarize into aproinflammatory phenotype that induces neurodegeneration. Wehypothesized that astroglial polarization to the proinflammatoryphenotype involves excessive activation of TLR4 and downstreamNFkB. Using in vitro primary astroglial cell cultures exposed tooxygen-glucose deprivation (OGD) and rat brains exposed toischemia by cortical devascularization, we observed that bothparadigms induce TLR4 expression in astrocytes. In vivo, confocalimages showed an early increase in TLR4 expression in theischemic core and penumbra. Then, we exposed enriched astrocyticculture to OGD for 6 h, and 16 h later we treated them withlipopolysaccharide (LPS). OGD-exposed astrocytes responded toLPS with a significantly increased response of stellation comparedwith astrocytes exposed to control conditions. Conversely, primaryastrocytes obtained from TLR4 KO, but not those obtained fromTLR2 KO animals, showed reduced NFkB activation when exposedto LPS. Gain of function studies using plasmidmediated TLR4 overexpressionexacerbated astroglial response to LPS by producing asustained NFkB activation and increased levels of proinflammatoryIL1B and TNF-a; while mock-transfected astrocytes showed a peakof NFkB activation and lesser proinflammatory cytokines level byqPCR. We conclude that reactive astrocytes exposed to ischemiain vitro and in vivo express higher TLR4 levels and its activationby TLR4 ligands such as LPS induces astroglial polarization to the proinflammatory-neurodegenerative profile probably facilitatingneuronal death.